Friday, April 30, 2010

Osteoclasts Increase Height?

Intuitively, one would think that osteoclasts(bone breakers) would be bad for height increase.  Osteoblasts build up bone and osteoclasts tear down bone.  But, do osteoclasts play a vital role in the height increase process and if so how can we use this in our own grow taller methodology? 

Alendronate affects long bone length and growth plate morphology in the oim mouse model for Osteogenesis Imperfecta. 

"Alendronate, a bisphosphonate drug, has shown promise in reducing remodeling and bone loss in postmenopausal osteoporosis. Alendronate acts directly on the osteoclast, inhibiting its resorption capability. This inhibition of osteoclast activity has led to the use of bisphosphonates in the treatment of the osteogenesis imperfecta condition. Treatment of osteogenesis imperfecta[Osteogenesis imperfecta is a disease where there are brittle bones that fracture easily] with bisphosphonates[which inhibit osteoclasts] enhances bone strength, but the consequences on linear bone growth are not well defined. Using the oim mouse model for type III osteogenesis imperfecta, two doses of alendronate, low (0.125 mg/kg/wk) and high (2.5 mg/kg/wk) were administered weekly via intraperitoneal injection starting at 4 weeks of age and ending at 12 weeks of age to assess the effects of alendronate on humerus and ulna length. The higher dose of alendronate reduced humerus and ulna length in the oim/wt and wt/wt genotypes for both sexes (P < 0.05). The oim/oim humerus and ulna were not significantly affected by the higher dose of alendronate in females, but reduced bone length in males (P < 0.0085). Proximal humerus growth plate area was affected by both genotype and alendronate dose and growth plate diameter was increased at the chondro-osseous junction by both alendronate doses (P < 0.011). Genotype and alendronate dose affected growth plate height. The oim/oim genotype displayed taller growth plates. The high dosage of alendronate increased overall growth plate height, particularly within the hypertrophic zone, which suggests a failure of vascular invasion-induced apoptosis in the hypertrophic cells. In conclusion, these results indicate that high doses of alendronate (>2.5 mg/kg/wk) inhibit long bone length in mice through alteration of the growth plate and possibly reduced resorption at the chondro-osseous junction." 

"Although the mechanism of long bone growth relies upon clonal expansion and subsequent hypertrophy of chondrocytes, endochondral bone growth absolutely requires that chondroclasts resorb the septa of calcified cartilage at the chondro-osseous junction of the growth plate, permitting vascular invasion of the hypertrophic cell lacunae. Inhibition of the resorption impedes the elongation process. In addition, osteoclasts must participate in the ultimate replacement of calcified cartilage by remodeling the metaphyseal primary spongiosa to create a mechanically sound metaphyseal architecture. If a bisphosphonate used to treat OI in children inhibits the function of osteoclasts and chondroclasts, the result could significantly exacerbate the tendency of OI to interfere with the patient’s normal growth and bone development."

"The low dose of alendronate did have a significant effect on the length of the humerus in males"

So it's not a matter of that total inhibition of osteoclasts is bad for height growth.  An incomplete inhibition of osteoclasts can be bad for height growth.  

"Alendronate interferes with osteoclast action by interrupting the prenylation of small guanidine triphosphate-associated proteins involved in the intracellular signaling pathway that modulates osteoclast structural proteins. The osteoclast then becomes unable to attach to bone matrix and loses its resorbing ability. The septoclast (chondroclast) operates in the same manner as the osteoclast, and only differs in the types of hydrolytic enzymes secreted and its location within the growing bone. Thus, it is reasonable to believe that alendronate acts via a similar antiprenylation pathway in this cell. Inhibition of septoclastic resorption would obstruct vascular invasion and reduce chondrocyte apoptosis at the base of the growth plate, leading to an increase in growth plate area and height and diminished bone length. This mechanism would be consistent with the qualitative observation in this study that alendronate treatment diminished removal of cartilagenous cores in the primary spongiosa; persistent calcified cartilage within primary spongiosa as a consequence of alendronate treatment."

Alternatively, Alendronate may inhibit height by a non-osteoclast related mechanism...
"Furthermore, prenylation of guanidine triphosphate-associated proteins (such as Ras, Rac, and Rho) is involved in the intracellular regulation of growth factors controlling growth plate function and alendronate may affect growth via this pathway. For example, inhibition of prenylation may disrupt cell progression within the growth plate by disrupting the ability of terminal hypertrophic chondrocytes to respond to hormones and signaling molecules. This too would be consistent with the experimental observations of reduced bone length, increased overall growth plate height, increased height of the hypertrophic zone, and obvious derangement of the growth plate and adjacent metaphyseal bone."

The apoptosis of hypertrophic cells is a critical part of endochondral ossification(long bone growth).  In the zone of calcification in the growth plate dead cartilage cells are consumed by bone-forming cells.  Alendronate, a biophosphate actually increased the growth plate height, but did not result in an increase in the length of the bone.  Osteoclasts are a critical part of growth plate remodeling which is vital for height growth.  Epiphyseal distraction was a method tried by scientists to increase height and reduce limb length discrepancies which although increased growth rate ultimately failed to improve final adult stature.  Showing that longer growth plates does not necessarily lead to increased final adult height.

A single nucleotide polymorphism on exon-4 of the gene encoding PPARdelta is associated with reduced height in adults and children. 

"CONTEXT: Peroxisome proliferator-activated receptor (PPAR)-delta is a nuclear transcription factor that plays a key role in many metabolic processes, including energy metabolism, and lipid and glucose metabolism. Candidate gene studies have identified a putative functional variant, rs2016520, in the gene encoding PPARdelta (PPARD), which is associated in some studies with metabolic traits. In addition, this single-nucleotide polymorphism was associated with adult height in several whole-genome scans, but this association did not achieve whole genome significance. OBJECTIVE: This study sought to determine whether PPARD variation influenced height. DESIGN: Haplotype tagging analysis across PPARD was performed in about 11,000 individuals from the Wellcome Trust U.K. Type 2 Diabetes Case Control Collection (Go-DARTS2). RESULTS: There was an association between rs2016520 and height in both patients with type 2 diabetes and controls without diabetes (combined P = 5 x 10(-5)). In a metaanalysis using published data from Caucasian cohorts totaling more than 38,000 participants, compelling evidence was found for this locus and its association with height (P = 10(-8)) with an overall effect size of about 0.5 cm per allele. A similar analysis in a group of 2700 prepubescent children also displayed a similar effect size to that seen in the adults. CONCLUSION: PPARD variation is clearly associated with a phenotype of reduced stature in both adults and children. Because height is an important indicator of metabolic and nutritional status, this provides additional support for a key role for PPARdelta in critical metabolic functions. PPARdelta may affect height through a variety of mechanisms including altered metabolic efficiency or effects on osteoclast function." 

Proper osteoclast function seems to be necessary for achieving maximum adult stature but it doesn't seem like improving osteoclast function would take you past that stature. 

"With this in mind, it has been shown that PPAR{delta} activation modulates cholesterol uptake from the gut[cholesterol is important for height growth so lack of cholesterol uptake may stunt growth]. Other evidence suggests that PPARdelta may exert a direct effect on the control of bone growth in the early rapid growth phase shown by young children because it has been demonstrated that activation of PPARdelta by agonists promotes bone remodeling by osteoclasts" 

PPAR delta stimulates osteoclasts without that stimulation height growth is reduced.

"height is inversely associated with glucose intolerance and type 2 diabetes"

Deficiency of insulin receptor substrate-1 impairs skeletal growth through early closure of epiphyseal cartilage. 

"Morphological analyses in and around the epiphyseal cartilage of mice deficient in insulin receptor substrate-1 (IRS-1) showed IRS-1 signaling to be important for skeletal growth by preventing early closure of the epiphyseal cartilage and maintaining the subsequent bone turnover at the primary spongiosa[Bone Turnover including osteoclasts is important]. Introduction: IRS-1 is an essential molecule for intracellular signaling by IGF-I and insulin, both of which are potent anabolic regulators of cartilage and bone metabolism. To clarify the role of IRS-1 signaling in the skeletal growth, morphological analyses were performed in and around the epiphyseal cartilage of mice deficient in IRS-1 (IRS-1(-/-)), whose limbs and trunk were 20-30% shorter than wildtype (WT) mice. MATERIALS AND METHODS: The epiphyseal cartilage and the primary spongiosa at proximal tibias of homozygous IRS-1(-/-) and WT male littermates were compared using histological, immunohistochemical, enzyme cytohistochemical, ultrastructural, and bone histomorphometrical analyses. RESULTS: In and around the WT epiphyseal cartilage, IRS-1 and insulin-like growth factor (IGF)-1 receptors were widely expressed, whereas IRS-2 was weakly localized in bone cells. Chronological observation revealed that height of the proliferative zone and the size of hypertrophic chondrocytes were decreased in WT mice as a function of age, and these decreases were accelerated in the IRS-1 (-/-) cartilage, whose findings at 12 weeks were similar to those of WT at 24 weeks. In the IRS-1(-/-) cartilage, proliferating chondrocytes with positive proliferating cell nuclear antigen (PCNA) or parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor immunostaining had almost disappeared by 12 weeks. Contrarily, TUNEL+ apoptotic cells were increased in the hypertrophic zone, at the bottom of which most of the chondrocytes were surrounded by the calcified matrix, suggesting the closure of the cartilage. In the primary spongiosa, bone volume, alkaline phosphatase (ALP)+ osteoblasts, TRACP+ osteoclasts[IRS-1 interacts with osteoclasts], and the osteopontin-positive cement line were markedly decreased. Bone histomorphometrical parameters for both bone formation and resorption were significantly lower in IRS-1(-/-) mice, indicating the suppression of bone turnover. CONCLUSION: The IRS-1(-/-) epiphyseal cartilage exhibited insufficient proliferation of chondrocytes, calcification of hypertrophic chondrocytes, acceleration of apoptosis, and early closure of the growth plate. Thus, the data strongly suggest that IRS-1 signaling is important for the skeletal growth by preventing early closure of the epiphyseal cartilage and by maintaining the subsequent bone turnover at the primary spongiosa." 

IRS-1 deficiency decreases height growth.  IRS-1 interacts with Osteoclasts.

"Regarding osteoclastic cells, because we previously reported that IRS-1 is not expressed in these cells, the downregulation of bone resorption markers is likely to be caused by the decrease in the supporting ability of osteoclastogenesis by osteoblasts through RANKL induction"

Role of tartrate-resistant acid phosphatase (TRAP) in long bone development.

"Tartrate resistant acid phosphatase (TRAP)[TRAP expression is connected to osteoclasts] was shown to be critical for skeleton development, and TRAP deficiency leads to a reduced resorptive activity during endochondral ossification resulting in an osteopetrotic phenotype and shortened long bones in adult mice. A proper longitudinal growth depends on a timely, well-coordinated vascularization and formation of the secondary ossification centre (SOC) of the long bones epiphysis. Our results demonstrate that TRAP is not essential for the formation of the epiphyseal vascular network. Therefore, in wild type (Wt) controls as well as TRAP deficient (TRAP-/-) mutants vascularised cartilage canals are present from postnatal day (P) five[so perhaps osteoclasts are not necessary for the formation of cartilage canals]. However, in the epiphysis of the TRAP-/- mice cartilage mineralization, formation of the marrow cavity and the SOC occur prematurely compared with the controls[so osteoclasts keep "growth plates" open longer]. In the mutant mice the entire growth plate is widened due to an expansion of the hypertrophic zone. This is not seen in younger animals but first detected at week (W) three and during further development. Moreover, an enhanced number of thickened trabeculae, indicative of the osteopetrotic phenotype, are observed in the metaphysis beginning with W three. Epiphyseal excavation was proposed as an important function of TRAP, and we examined whether TRAP deficiency affects this process. We therefore evaluated the marrow cavity volume (MCV) and the epiphyseal volume (EV) and computed the MCV to EV ratio (MCV/EV). We investigated developmental stages until W 12. Our results indicate that both epiphyseal excavation and establishment of the SOC are hardly impaired in the knockouts. Furthermore, no differences in the morphology of the epiphyseal bone trabeculae and remodelling of the articular cartilage layers are noted between Wt and TRAP-/- mice. We conclude that in long bones, TRAP is critical for the development of the growth plate and the metaphysis but apparently not for the epiphyseal vascularization, excavation, and establishment of the SOC. "

So osteoclasts may play a role in height growth other than cartilage canal formation.

"The canals erode the non-mineralized cartilage matrix and thus give blood vessels and bone-forming cells access to the epiphysis for the subsequent development of the SOC. Canal formation is governed by several matrix metalloproteinases (MMPs) and, most notably, membrane-bound type-1 matrix metalloproteinase (MT1-MMP = MMP 14) is critical for this process. As a result, MT1-MMP−/−mice reveal a vascular defect accompanied by delayed ossification"<-so MT1-MMP may help you grow taller.

"In mice lacking both MMP 9 and MMP 13 epiphyseal development is affected"<-So MMP9 and 13 help with height as well.

As does VEGF...

"the establishment of the epiphyseal vascular network is triggered by the vascular endothelial growth factor (VEGF), and VEGF deficiency causes a delayed vascularization and formation of the SOC"

"Tartrate-resistant acid phosphatase activity type 5 (TRAP or Acp5) is an iron-containing enzyme that is found in humans and murine species. It occurs in diverse tissues including bone and cartilage . TRAP is, at first, synthesized as a latent proenzyme with low activity, and proteolytic processing generates two subunits of about 16 and 20–23 kDa with enhanced enzymatic activity. The cysteine proteinase cathepsin K has been suggested to be responsible for the proteolytic activation of TRAP. TRAP is highly expressed in chondroclasts as well as osteoclasts"

"chondroclasts attack the mineralized cartilage matrix whereas osteoclasts participate in the resorption of the mineralized bone matrix. TRAP prompts the dephosphorylation of bone matrix phosphoproteins like osteopontin and bone sialoprotein and was originally shown to be important for a normal endochondral bone formation"

"In long bones, the excavation of the epiphysis is mainly achieved by chondro/osteoclasts that bind to the substrate via their ruffled border. They create a highly acidic milieu, enabling disintegration and finally resorption of the mineralized cartilage and bone matrix. We could show that in Wt controls and TRAP−/− mice chondro/osteoclasts were formed to the same extent throughout development, hence the absence of TRAP did not impair their genesis. Moreover, their differentiation is normal, even though several ultrastructural subdomains are altered, resulting in a moderately reduced lysosomal degradation of the mineral crystallites compared to Wt littermates. Apart from TRAP, chondro/osteoclasts secrete tartrate-sensitive lysosomal acid phosphatase (LAP) during the resorptive process[so osteoclasts secrete LAP to compensate for the loss of TRAP but LAP is less effective at increasing height]. LAP mutants show almost no bone abnormalities but in LAP/TRAP doubly deficient mice, bone malformations are severe, and long bones are distinctly shorter compared to the TRAP knockouts. Furthermore, in the double knockout mice a distinct enlargement of the liver and spleen has been observed whereas hepatosplenomegaly has never been noted in LAP- and TRAP single knockout mice. This suggests that in distinct tissues the two phosphatases are capable to complement for each other thereby maintaining lysosomal function. We could demonstrate that after examination of a long postnatal period, epiphyseal excavation and bone formation was hardly impaired in the femur of mice lacking TRAP. Furthermore, trabeculation and reorganization of the articular cartilage layers was not altered in the knockouts. Thus, our data collectively indicate that the absence of TRAP does not affect marrow cavity formation, bone morphology and formation of the articular cartilage, and we suggest that LAP largely compensates for the loss of TRAP."

So if there are instances where LAP is being used over TRAP it may cause a loss of height.

So, it's likely that the proper paired activity of osteoblasts and osteoclasts are needed for proper height growth.  Things like Alendronate disrupt that homeostasis reduce height growth.  Similar disruption of that homeostasis with excessive osteoclasts is not likely to increase height either.  An increase in both osteoblasts/osteoclasts simultaneously may increase height.

Osteoclasts promote the formation of hematopoietic stem cell niches in the bone marrow.

"Formation of the hematopoietic stem cell (HSC) niche in bone marrow (BM) is tightly associated with endochondral ossification[endochondral ossification is required to form stem cell niches within the bone marrow]. We used the oc/oc mouse, a mouse model with impaired endochondral ossification caused by a loss of osteoclast (OCL) activity, to investigate the role of osteoblasts (OBLs) and OCLs in the HSC niche formation. The absence of OCL activity resulted in a defective HSC niche associated with an increased proportion of mesenchymal progenitors but reduced osteoblastic differentiation, leading to impaired HSC homing to the BM[so without osteoclasts there are more MSCs but they don't go to bone marrow]. Restoration of OCL activity reversed the defect in HSC niche formation. Our data demonstrate that OBLs are required for establishing HSC niches and that osteoblastic development is induced by OCLs."

"Signaling through Jagged 1 (Jag-1) on OBLs and its receptor Notch on HSCs is involved in the expansion of the HSC pool, and signaling through stromal Angiopoietin 1 (Ang-1) and its receptor Tie-2 on HSCs is involved in maintaining HSC quiescence in the niche"

"OBLs and mesenchymal cells also express osteopontin (OPN), which is a negative regulator of HSC pool size that inhibits HSC proliferation, promotes HSC apoptosis, and affects the expression of Jag-1 and Ang-1 by stromal cells"<-Maybe inhibiting osteopontin will help you grow taller?

"Stromal-derived factor-1 (SDF-1), which is produced by mesenchymal cells and OBLs, is the major chemoattractant for many hematopoietic progenitors, including HSCs"<-maybe we can induce expression of SDF-1 to where we want the growth plate to be to grow taller in that specific area?

"Coupling factors such as insulin-like growth factor, basic fibroblast growth factor, TGF-β, bone morphogenetic proteins, and platelet-derived growth factor are released from the bone matrix during bone resorption and are known to induce bone formation, thereby coupling bone resorption and formation "<-Many of these factors are pro-chondrogenic.
Therapeutic implications of suppressing osteoclast formation versus function

"osteoclasts recruit osteoblasts to sites of bone remodelling by mobilizing chemotactic proteins from matrix and direct secretion of such proteins that attract osteoblast precursors. Thus, anti-resorptive agents, such as the cathepsin K inhibitor odanacatib, that dampen osteoclast function but not number may also preserve osteoblast recruitment by preserving the bone resorptive cell."

"Evidence exists that osteoclasts recruit osteoblasts to sites of bone remodelling by two distinct mechanisms. The first is mobilization and activation of bone-residing growth factors such as TGFβ and IGF-I. These proteins, in turn, target mesenchymal stem cells that are osteoblast precursors and recruit them to sites of remodelling where they undergo differentiation into mature bone-forming cells. The other mechanism whereby osteoclasts recruit osteoblasts is by direct secretion of chemotactic molecules independent of bone degradation. CTHRC1 has recently been identified as one such molecule. Thus osteoclasts promote bone formation by mobilizing matrix-residing growth factors and by direct secretion of molecules such as CTHCR1, both of which recruit osteoblast precursors."

Osteoclasts: more than ‘bone eaters’

"Osteoclasts (OC) differentiate from OC precursors (OCP) under the influence of MCSF and RANKL produced by osteoblast (OB) lineage cells including osteocytes. As OCs create a resorption pit, growth factors, including TGFβ and IGF1, are released from the bone matrix. These growth factors may recruit mesenchymal osteoblast progenitors and promote their differentiation into mature cells that secrete osteoid to fill the area of resorbed bone. Some OBs differentiate further into matrix embedded osteocytes."

"Osteoclasts degrade bone by the polarized secretion of proteolytic enzymes (e.g. cathepsin K) and acid, which hydrolyze and solubilize the organic and inorganic components of bone, respectively. Proton and enzyme secretion is directed into a resorption lacunae, which is partitioned from rest of the bone microenvironment by a sealing zone of densely packed podosomes that surrounds the apical membrane of the osteoclast"

"Transforming growth factor β 1 (TGFβ1) released during osteoclast culture on bone induces the migration of mesenchymal stem cells (MSC) in vitro and MSC migration to bone surfaces is reduced in Tgfb1−/− mice"

The application of nanogenerators and piezoelectricity in osteogenesis

"Piezoelectricity is one of several mechanical responses of the bone matrix that allows osteocytes, osteoblasts, osteoclasts, and osteoprogenitors to react to changes in their environment."

"Mechanical force can push some atoms closer together or further apart in piezoelectric materials, upsetting the balance of positive and negative forces, and causing net electrical charges to appear outside."

"The extracellular matrix consists of 65% mineral matrix and 35% organic matrix. Type I collagen makes up about 90% of the organic matrix and possesses a triple helical structure that contributes tensile strength to the extracellular matrix. Inorganic minerals, which are responsible for the compressive strength of bone, are incorporated with the collagen fibrils in the form of calcium hydroxyapatite. Osteoblasts arise from mesenchymal stem cells and are responsible for bone formation. On the other hand, osteoclasts are multinucleated cells deriving from hematopoietic progenitors in the bone marrow and are responsible for bone resorption. Osteocytes are thought to be mechanosensor cells that control the activity of osteoblasts and osteoclasts. They are embedded in lacunae with long processes located in small channels called canaliculi. Canaliculi are considered the lifelines that permit nutrients, oxygen, and waste products to be exchanged with the blood vessels within the Haversian canal, Volkmann canal, and osteocytes. When a bone is loaded, the interstitial fluid within the lacuna and canaliculi is squeezed through a thin layer of non-mineralized matrix surrounding the cell bodies and cell processes toward the Haversian or Volkmann channels. This flow of fluid mobilizes the cell surface glycocalyx and initiates biochemical processes promoting osteogenesis"

"here are two major effects of calcium hydroxyapatite that contribute to collagen piezoelectricity. One is that the mineral crystal structure of calcium hydroxyapatite displays a high elastic modulus compared to other biological molecules and bone. This allows the collagen fibers to respond mechanically to loads onto the bone locally and bear the greatest strain of all the molecules within the solid matrix, thus generating the needed deformation required for a piezoelectric effect. The other is water resistance and restriction of hydroxyapatite to collagen. A number of physical observations support the dehydrating effect of calcium hydroxyapatite, including the result that collagen in calcified bone does not shrink and there exists a higher rate of water resorption in decalcified bone than that measured in calcified bone"

"The re-organization of a dipole moment is triggered by the compressive force on collagen, thus generating negative charges on the surface. The negative charges can open the voltage-gated calcium channels on osteocytes. After the opening of voltage-gated calcium channels, cascades of signaling pathways are triggered. The active channels promote the influx of extracellular calcium and further activate calmodulin, which subsequently stimulates the activation of calcineurin. This could ultimately lead to the activation of Ras and the extracellular signal-related protein kinase (ERK) signaling pathway that is critical for Runx2 activation and induction of several growth factors, including transforming growth factor β and bone morphogenetic protein. Growth factors can promote osteoblast activation, proliferation, differentiation, extracellular matrix deposition, and subsequent bone formation. However, the deformation of bone tissue during normal locomotion does not exceed 0.1%, and in vitro studies have shown that at least 1 to 10% deformation of bone tissue is necessary for osteocytes to respond to a mechanical strain. Mechanical strains resulting in such deformations would cause the bone to fracture"

"Primary bone healing involves a direct attempt by the cortex to reestablish itself in circumstances of strains less than 5% with compressive or tensile pressures of 0.15 MPa or less. Primary bone healing is driven by remodeling osteoclasts and osteoblasts bridging the fracture gap and rejoining the fractured fragments"

"Without grossly visible callus formation, osteoclasts cut across the fracture line, and osteoblasts then follow the osteoclasts to deposit new bone, and this occurs along with angiogenesis. If the fracture gaps prevent direct extension of osteons across the fracture site, osteoblasts fill the defects with woven bone. New lamellar bone is thus formed, and the fracture is bridged. Haversian remodeling starts reestablishing a normal cortical bone structure after the gaps are filled with woven bone."

"primary bone healing is rare, and the majority of fracture healing proceeds via secondary bone healing, or endochondral ossification, which occurs via a cartilage callus. There are four major phases of secondary bone healing, which include the inflammatory phase, early callus phase, mature callus phase, and remodeling phase. The inflammatory phase is characterized by an acute bone marrow response, post-damaged inflammation, and hematoma formation immediately following the fracture and up to 3–4 days after. The damaged tissue releases proinflammatory mediators, such as interleukin 1 (IL-1), IL-6, and tumor necrosis factor alpha (TNF-α), to initiate the repair process. The second stage is the early callus phase. This phase is predominated by soft cartilage callus formation, angiogenesis, and chondrogenesis at the fracture gap. Subsequently, the cartilaginous matrix is mineralized to begin the third phase, the mature callus phase. At this point, the chondrocytes undergo apoptosis and osteoblasts infiltrate the callus. The primary bone is laid down on these surfaces. In the last phase or remodeling phase, the newly formed woven bone is progressively replaced by mature lamellar bone, ultimately restoring the original cortical structure"

"The piezoelectricity induced by mechanical deformation of bone generates a negative electrical charge in areas of bone compression and a positive charge in the areas of traction"

Conclusion:  Height Increase Methods that involve suppressing osteoclast activity will not increase height.  Osteoclasts are an important part of the process of growing taller.  Ensuring proper function of insulin receptor substrate-1 and peroxisome profilerator-activated receptor in children can increase final adult stature.

Thursday, April 29, 2010

I increased my height by another 1/4" thanks to LSJL

Here's my previous progress: Bone Length|One Month + One Week In

My fibular measurement was about 15 1/2" and my tibial measurement was about 13 3/4".  I measured myself on the wall and sure enough I was 5'9".  I'm getting better and better at performing Lateral Synovial Joint Loading.  I'm much better now at maximizing the load on the epiphysis of my long bones.  Those of you who are trying the routine keep with it and you will get better.  Performing LSJL is a neurological task, you need to practice to get better at the targeting laterally the epiphysis of your long bones.

I'm doing 30 seconds adductor, abductor, 30 seconds both side of knee + 30 seconds both side of ankle.  I'm also tapping all the epiphysis of long bones I can for 30 taps each.  I'm not sure exactly what out of those is causing the height gain.  Increasing height is a field where if you miss by an inch you miss by a mile, the gap between 5'8 1/2" and 5'9" seems like a long place.  Basically, I'm saying it's very hard to increase height by posture unless your head is tilted forward.

Time to keep going until I gain enough height where it's proof.

Wednesday, April 28, 2010

Growing Taller with Hypnosis?

What's the power of positive thinking?  Very little.  Visualization is effective when you visualize the process not the result. You don't visualize winning in a sport, you visualize practicing the sport.  You don't visualize winning the race, the visualize going through the movements of the race.  Without the process, you can't get to the result.

If you're in a hypnotic state and a hypnotherapist suggests to you "grow taller, grow taller, grow taller."  Your body isn't going to know what to do.  Your endocrine system and your growth plates don't know what the words grow and taller mean.  Your body knows the language of chemicals and stimulus, not the artificial language of men.

Hypnosis could be effective if a hypnotherapist could put in a hypnotic suggestion to inhibit myostatin or block myostatin receptors, enhance the proliferation and differentiation of the cartilage cells in the growth plate, manipulate your natruiretic peptide signaling pathway, stimulate your endocrine system to produce more IGF-1, or induce your periosteum to increase in size.

But someone who was able to do that wouldn't be a hypnotherapist, they would be telekinetic.  The brain is a powerful thing, however we don't have control over most of it.  If we did we could change our fat storage distribution patterns or control our muscular development.  The actions of our brains however are predictable.  We control our brains by providing it with the stimulus that we want to use to achieve the desired result.

The body adapts specifically to a stimulus.  Does it adapt optimally to the stimulus?  No.  Does playing basketball make you taller?  No.  Does being a boxer increase your arm length?  No.  But basketball and boxing induce predictable adaptations in our body.  To manipulate our brains we need to pick a specific stimulus that gives us the desired adaptation(increase our height), hypnosis is not that stimulus.

Monday, April 26, 2010

Acupuncture to Grow Taller

Previously I've dismissed acupuncture as only a way to get postural height increase.  However, their are more complex forms of acupuncture.  I've recently been made aware of something called aqua acupuncture where microscopic quantities of sterile water are injected just below the skin on specific points on the ear and body(knee, top of head, neck).  The procedure is based on a book by Anton Jayasuriya called Clinical Acupuncture.

Acupuncture causes your muscles to relax so there is a confounding variable for the height increase.  Is the height increase due to an improvement in alignment or is it due to something else?  But the thing is that acupuncture is associated with Kimi/Yoko height increase which is a known scam.

Here's an interesting quote I found related to Aquapressure: "Right after one treatment, (40mins after) you can see the difference, averagely people can increase 1-1.5cm (it is not permanent for the first time, just prove people can grow)"  The height gain not being permanent indicates that it's a postural improvement.

It is theoretically possible to manipulate the endocrine system to make you taller if you increase the levels of IGF-1 which results in the proliferation of mesenchymal stem cells.  Maybe there's a way to push a button in your ear and neck(prick your ear and neck with a needle) to reprogram someone's endocrine system.  Maybe there's a way to do it with reflexology as well.

The thing is there needs to be studies.  Acupuncturists and Refloxologists don't have to show an increase in height, they just have to show a long term increase in IGF-1 level's following treatment.  Their have been a couple of studies that associate acupuncture with an increase in IGF-1 but only in conjunction with exercise and only in the presence of a pre-existing condition.  The increase in IGF-1 has to be completely systemic as well.  The increase can't be localized to certain muscles as you want the IGF-1 to either alter the bodies homeostatic mechanisms(like an enlarged anterior pituitary gland) or increase the amount of mesenchymal stem cells in the growth plate.

Here's a  traditional Chinese medicine school that explains the possible benefits of acupuncture.  The blood theory seems the most promising in terms of height increase.  If you increase blood flow to the top of the skull then you will be taller(only temporary height though).  Also, if you increase blood flow to the intervertebral discs then it will be easier for those intervertebral discs to repair thus increasing height in that way.  A nerve theory is also listed but that would only have a benefit if you changed the nervous system to say inhibit myostatin or produce more IGF-1.

So, reflexologists and acupuncturalists, I have a challenge for you.  Prove that the various forms of Chinese Traditional Medicine increase the level of Insulin like Growth Factor One at a systemic level or at least in a location that could possibly increase height.

Sunday, April 25, 2010

Kojima's limb lengthening clinic review

There's a clinic in Japan run by a Ginza Kojima company.  It's a form of non-surgical limb lengthening.  According to a biology text book that I own soaking a bone in an acid for a period of time destroys the mineral content of the bone leaving only the collagen fibers.  These collagen fibers are incredibly flexible and the bone can be lengthened in this de-mineralized state.

Now there's something to be said about dangerous versus worthless(like so-called height increase pills that are merely vitamin supplements).  The Kojima procedure involves bathing the bone in green light(which I believe de-mineralizes the bone enabling it to be stretched) and then stretching the bone.   The Kojima website discourages use of heavy weights after undergoing the procedure which is evidence that the Kojima method does in fact de-mineralize the bone.

The procedure works and the site has x-rays to prove it.  The site claims that it works by enhancing your growth hormone levels but that makes no sense at all especially since the gains in height are almost instantaneous.  The clinic must have found that the bone gains its mineral content back rather quickly.  It only takes one four hour session to grow 2 cm.  The bone must gain it's mineral back or after that four hours your bones would be like Gumby.

Now I can't speak as to the long term affects of radiation on your bones but we all know the horror stories of radiation poisoning(and Godzilla).  Really Kojima's clinic is violating the patient's bill of rights by not giving people informed consent.  At least with regular Limb Lengthening Surgery, you know the risks but with Kojima's method you don't know exactly what radiation you are being exposed to and how much.

Thursday, April 22, 2010

Grew Taller by 1/4" with Lateral Synovial Joint Loading

Here's the pictures from only six days ago: Bone Length | One Month In.  My fibular measurement was about 15.  My tibial measurement was about 13 1/4.  Here's the latest pictures:

Fibular measurement was about 15 1/4" and Tibial measurement was about 13 1/2".  I measured my height on the wall and I was 5'8 3/4".  You can click on the pictures to enlarge and you can see the numbers on the ruler to evaluate my measuring abilities.

Wednesday, April 21, 2010

Growing Taller by inhibiting the myostatin gene?

It is well known in the bodybuilding community that Myostatin is a gene that inhibits muscle mass.  Turns out it has properties on height gain as well.  A mutation in the myostatin receptor and a mutation in Myostatin will have positive effects as well.  There have been a couple of people born without the presence of Myostatin.

Myostatin (GDF-8) as a key factor linking muscle mass and bone structure. 

"Myostatin (GDF-8) is a member of the transforming growth factor-beta (TGF-beta) superfamily that is highly expressed in skeletal muscle, and myostatin loss-of-function leads to doubling of skeletal muscle mass. Myostatin-deficient mice have been used as a model for studying muscle-bone interactions, and here we review the skeletal phenotype associated with altered myostatin signaling. It is now known that myostatin is a key regulator of mesenchymal stem cell proliferation and differentiation[More proof that LSJL works by causing the differentiation of mesenchymal stem cells into chondrocytes], and mice lacking the myostatin gene show decreased body fat and a generalized increase in bone density and strength. The increase in bone density is observed in most anatomical regions, including the limbs, spine, and jaw, and myostatin inhibitors have been observed to significantly increase bone formation. Myostatin is also expressed in the early phases of fracture healing, and myostatin deficiency leads to increased fracture callus size and strength. Together, these data suggest that myostatin has direct effects on the proliferation and differentiation of osteoprogenitor cells, and that myostatin antagonists and inhibitors are likely to enhance both muscle mass and bone strength." 

It doesn't mention that myostatin has an impact on cartilage and chondrocytes but if it has impacts on mesenchymal stem cell proliferation than at the bare minimum it increases the number of MSCs available for chondrogenic differentiation.

"Myostatin circulates in the blood in a latent form bound to a propeptide, which gets cleaved by BMP1/Tolloid matrix metalloproteinase releasing the active form. Follistatin and follistatin–related gene (FLRG) are other proteins that can bind and inhibit the activity of myostatin by maintaining its latency2,5. Active myostatin binds to its receptor, the type IIB activin receptor (ActRIIB), with high affinity and regulates the expression of its target genes through a TGF-β signaling pathway. Recent studies also show that myostatin can activate the p38 MAPK, Erk1/2, and Wnt pathways[possible pathways that can indirectly affect myostatin's inhibition of height growth]" 

So you can also inhibit myostatin by inhibiting BMP1, increasing the levels of follistatin, inhibiting type IIB activin, and by preventing the effects of Myostatin in the pathways it triggers like the MAPK or Wnt signaling pathways.

The scientists speculate that the effect on bone may be due to an indirect effect based on muscle mass but the degree of adaption is just too great for it to be an effect of muscle mass alone.

SNPs in the myostatin gene of the mollusk Chlamys farreri: association with growth traits. 

"Myostatin (MSTN) is a member of the transforming growth factor-beta superfamily which negatively regulates growth of muscle tissue. In this study, 103 cultivated Chlamys farreri individuals were screened for polymorphisms in the MSTN gene using PCR-single strand conformation polymorphism (PCR-SSCP) and DNA sequencing methods. Two mutations were found: A/G at position 327 in exon 2, which caused an amino acid change from Thr to Ala (Thr305Ala), and C/T at position 289 in exon 3, which caused an amino acid change from Cys to Arg (Cys422Arg). One way ANOVA of the SNPs and growth traits showed that genotype GG of primer M5 had significantly higher body mass, soft-tissue mass, adductor muscle mass, shell length, shell height, absolute growth rate of shell height and body mass than those of genotype AG and AA (P<0.05). Genotype frequencies of genotype AA, AG and GG were 68.94%, 27.18% and 3.88%, respectively. The results present evidence that the C. farreri MSTN gene may be selected as a candidate gene for these growth traits." 

Essentially the mollusks that had Myostatin inhibition(or specific polymorphisms within the Myostatin gene) were taller than those who were able to express Myostatin. 

Myostatin (GDF-8) deficiency increases fracture callus size, Sox-5 expression, and callus bone volume. 

"Myostatin (GDF-8) is a negative regulator of skeletal muscle growth and mice lacking myostatin show increased muscle mass. We have previously shown that myostatin deficiency increases bone strength and biomineralization throughout the skeleton, and others have demonstrated that myostatin is expressed during the earliest phase of fracture repair. In order to determine the role of myostatin in fracture callus morphogenesis, we studied fracture healing in mice lacking myostatin. Adult wild-type mice (+/+), mice heterozygous for the myostatin mutation (+/-), and mice homozygous for the disrupted myostatin sequence (-/-) were included for study at two and four weeks following osteotomy of the fibula. Expression of Sox-5 and BMP-2 were significantly upregulated in the fracture callus of myostatin-deficient (-/-) mice compared to wild-type (+/+) mice at two weeks following osteotomy. Fracture callus size was significantly increased in mice lacking myostatin at both two and four weeks following osteotomy, and total osseous tissue area and callus strength in three-point bending were significantly greater in myostatin -/- mice compared to myostatin +/+ mice at four weeks post-osteotomy. Our data suggest that myostatin functions to regulate fracture callus size by inhibiting the recruitment and proliferation of progenitor cells in the fracture blastema. Myostatin deficiency increases blastema size during the early inflammatory phase of fracture repair, ultimately producing an ossified callus having greater bone volume[bone volume includes height] and greater callus strength. While myostatin is most well known for its effects on muscle development, it is also clear that myostatin plays a significant, direct role in bone formation and regeneration." 

Perhaps if Myostatin was inhibited pre-limb lengthening surgery.  The bone could be stretched by more than one mm a day. 

"The [fracture healing] process can be separated into three general phases: an initial inflammatory phase, a chondrogenic phase, and an osteogenic phase. The inflammatory phase is characterized by increased expression of GDF8[GDF8 is Myostatin], BMP2[BMP-2 helps initial chondrogenic differentiation, however BMP-2 is not enough to induce chondrogenic differentiation], and Wnt-5A, the chondrogenic phase by elevated expression of GDF5[GDF5 enhances extracellular matrix production], TGFβ2,3[TGF-Beta3 Is capable of inducing chondrogenic differentiation], and beta-catenin[Beta-Catenin can be induced by BMP-2 so this is expected], and the osteogenic phase by expression of BMP3,4,7,8, and Frizzled. The role of early GDF8 (myostatin) expression in the callus during the inflammatory phase of fracture healing has, however, been difficult to interpret since this factor is most well known for its effects on myogenesis. It is now known that the receptor for myostatin is expressed in bone-marrow derived stromal cell, and that myostatin can stimulate adipogenic differentiation in mesenchymal stem cells whereas its absence increases osteogenic differentiation. Myostatin regulates myogenic differentiation in part by suppressing the expression of myogenic factors such as MyoD, but it also inhibits myoblast proliferation by increasing levels of p21"

So Myostatin seems to be involved in the stem cell phase rather than at later stages.  So inhibiting myostatin will increase height mainly as a result of increasing stem cell proliferation.  So the earlier myostatin can be inhibited the better.  Probably why Testosterone and Creatine and other Myostatin inhibitors don't increase height that much as much of the stem cells are already differentiated into chondrocytes.

So, inhibiting Myostatin may augment height gain if used in conjunction with methods involving stem cells but after early development Myostatin increases effectiveness as a lot of the stem cells have already differentiated into chondrocytes.

Myostatin may have a direct inhibitory effect on Sox9.  Remember though that you want more Beta-Catenin than Sox9 to maximize height growth.

Myostatin (GDF-8) inhibits chondrogenesis and chondrocyte proliferation in vitro by suppressing Sox-9 expression.

"Here, we investigate a possible direct role for myostatin in chondrogenesis. First, we examined the effects of myostatin on the proliferation of bone marrow stromal cells (BMSCs) and epiphyseal growth plate (EGP) chondrocytes (EGPCs) isolated from myostatin-deficient mice. Results show that myostatin deficiency is associated with a significant (P < 0.001) increase in proliferation of both BMSCs (+25%) and EGPCs (+35%) compared with wild-type cells. Next, we examined the effects of myostatin treatment on chondrogenic differentiation of BMSCs. These experiments show that myostatin treatment starting at either 0 or 48 h induces a significant decrease in collagen type II protein synthesis by 31% (P < 0.001) and 25% (P < 0.05), respectively. Real-time PCR reveals significant (P < 0.01) down regulation of Sox9 mRNA expression with 10 and 100 ng/ml treatments. Together, these findings suggest that myostatin has direct effects on chondrogenesis, and may, therefore, represent a potential therapeutic target for improving bone repair."

So Myostatin directly affects the cells involved in height.

Tuesday, April 20, 2010

LimbCenter.Org Review

I've been covering the latest easy height info back in this past and updating at as Sky develops his clinic.  Since Sky moved his new website to I thought I'd make a new post.  Here's Sky's impressions questionnaire, I thought I'd answer:

1. Do you have a false impression that growing taller is quick and easy?
I didn't until you posted a website called easy height dot com.  LSJL looks promising and might be the easiest method yet but is still untested.

2. Do you have a false impression that taking growth hormone pills can magically reshape your bones?
This is Googles fault for allowing faulty advertisements in their adwords for search results.  But, anyways this comes from bodybuilding mostly which has always tried to exploit growth hormone.  The problem is that most of these supplements don't contain growth hormone but rather amino acids that are supposed to help release growth hormone. 

3. Do you have a false impression that somewhere in the world an ancient herbal medicine exists to help you grow taller? 
Alfalfa was your idea Sky.  Is this survey for you?  But it still might be possible for a herbal medicine to exist and it might be possible for America to try to cover it up.  However, other nations would have results about it.

4. Do you have a false impression that scientists have discovered the secret fountain of youth in anti-aging pills that could mysteriously unfuse your growth plates?
Well, I believe that the growth plates are not technically fused as their is still a growth plate line.  If this growth plate line were distracted and mesenchymal stem cells were inserted then growth plate function could be restored.

5. Do you have a false impression that 21st century medicine is so far advanced technologically and scientifically and is able to produce a “growth” pill for mankind?
Hardly, I know how long science takes.  I know that there's not enough money to study everything that needs to be studied and there's a huge bias against height increase.

6. Do you have a false impression that Yoga and stretching exercises result in permanent growth?
I don't think even Grow Taller 4 Idiots ever said that.  They always said it was temporary disc height.

7. Do you have a false impression that inversion exercises and back stretching machines give you permanent growth?
I don't think anybody ever said that with inversion exercises.  I've never heard of a back stretching machine to determine if it was effective.

8. Do you have a false impression that the force of spinal decompression will triumph over the force of gravity?
You can certainly minimize the effects of gravity.  Better posture when sitting.  Strong back muscles help maintain proper posture when standing.

9. Do you have a false impression that swimming and bar hanging are effective for height increase in adults?
Swimming can increase in periosteal width so technically it is "effective."  Bar hanging is good for spinal decompression.

10. Do you have a false impression that kicking or jumping with 15 pounds (6.8 kg) of ankle weights (each leg) can trigger a vertical bone transformation?
You gave us that idea Sky.

11. Do you have a false impression that electrical bone growth stimulators can safely and proportionately influence vertical bone growth (but not horizontal)?
Never heard of an electrical bone growth stimulator.  There's pizeoelectric current but that occurs in response to any load.

12. Do you have a false impression that sitting or sleeping with 35 pounds (16 kg) of ankle weights (each leg) is sufficient for bone remodeling?'s bone modeling.  Bone remodeling is regular maintenance of bone.  And sitting and sleeping with ankle weights is another one of Sky's ideas.

13. Do you have a false impression that inverting with 30 pounds (13.6 kg) of dumbbells (each hand) is enough to overcome the earth’s gravitational pull?
Well the discs decompress as a result of fluid loss.  Can't prevent that but you can slow it down.  Inversion helps get nutrients like chondroitin and glucosamine get to the discs, it's not an overnight thing.

14. Do you have a false impression that inverting with 100 pounds (45.4 kg) of weight vest is enough to influence the thickening of the lumbar fibrocartilage discs?
We can't know for sure as the thickening would be pretty small. 

Wolf's Law is retro Sky, we have to go far beyond that.  Bone's lengthening at the point of maximum strain is more microstrain(Utah paradigm) theory.

Sunday, April 18, 2010

Height Increase Stretches

I've read a lot of natural height increase programs that detail a lot of grow taller stretching routines.  Stretching is not a highly effective height increase method but it is still useful as a complement to more effective routines.  Getting nutrients to your intervertebral discs is important as is proper spinal alignment both of which stretching can help.  The grow taller 4 idiots height increase program/scam details several stretches as part of its routine.  All of which you can find on you tube or frankly any stretching routine.  We are looking for the biggest, best deal in terms of stretches.

The best stretches are those that we can increase the load(load is usually the most important factor in how effective an exercise is) and those that can be performed easily.

Best Stretches:

Inversion on a decline bench(hold dumbells instead of plates for better leverage).  You get better leverage on a decline bench versus when you are hanging upside down.

I also like hanging with a dip belt(Harbinger 28800 Leather Weight Dip Belt).  I rotate 180 degrees when I do this to also get some shearing and twisting forces to try to build up my vertebral bones periosteal width.

Height increase stretching is a common theme on a lot of height increase sites.  I think these two stretches with additional weight are the two best exercises you can do to minimize the amount of time you spend stretching so you can spend more time on more effective exercises(like LSJL).

Does stretching the intervertebral discs do anything to increase the size or height of the discs?

Effects of Torsion on Intervertebral Disc Gene Expression and Biomechanics, Using a Rat Tail Model

"In vitro biomechanical tests were performed in torsion on rat tail motion segments subjected to 4 treatments: elastase, collagenase, genipin, control. In vivo tests were performed on rats with Ilizarov-type fixators implanted to caudal motion segments with five 90-minute loading groups: 1 Hz cyclic torsion to ±5°, ±15°, and ±30°, static torsion to +30°, and sham. Anulus and nucleus tissues were separately analyzed for gene expression of anabolic, catabolic, and proinflammatory cytokine markers.
In vitro tests showed decreased torsional stiffness following elastase treatment and no changes in stiffness with frequency. In vivo tests showed no significant changes in dynamic stiffness with time. Cyclic torsion upregulated elastin expression in the anulus fibrosus. Upregulation of TNF-α and IL-1β was measured at ±30°.
Strong differences in the disc response to cyclic torsion and compression are apparent with torsion increasing elastin expression and compression resulting in a more substantial increase in disc metabolism in the nucleus pulposus. Results highlight the importance of elastin in torsional loading and suggest that elastin remodels in response to shearing. Torsional loading can cause injury to the disc at excessive amplitudes that are detectable biologically before they are biomechanically."

"An increase in expression of proteases and their inhibitors, including MMP-3, ADAMTS-4, and TIMP-1 as well as cytokines IL-1β and TNF-α have also been associated with degeneration"

"Torsion results in interlaminar shears and tension of anulus fibrosus (AF) fibers while axial compression leads to substantially greater nucleus pulposus (NP) pressurization and tensile hoop stresses in the AF."

"In the AF, elastin mRNA expression was significantly upregulated in response to cyclic torsion at all amplitudes, while ADAMTS4 was the only catabolic gene significantly upregulated (±30°) with respect to sham. Changes in MMP12 expression in the AF were also detected, but accompanied with changes in sham with respect to the internal control. In the NP, there was a significant upregulation of aggrecan (2-fold) at ±30° as well as a small significant increase (1.3-fold) of TIMP3 also for ±30°. ADAMTS4 was upregulated (3-fold) for the ±15° group but downregulated in the sham compared to internal control. The static condition showed trends of upregulation for similar genes as cyclic ±30° but this was not significant. Proinflammatory cytokines IL-1β and TNF-α showed a significant increase in the AF for ±30°, although for IL-1β this was accompanied by an increase in sham with respect to internal control."

Compression significantly upregulated the chondrogenic gene col2a1 plus aggrecan and the endochondral ossification gene MMP13.  Torsion increased these genes at a far less significant level and in the nucleus pulposus MMP13 expression was decreased.

"Cyclic torsion stimulates elastin expression with small effects on other genes while cyclic compression results in a more general increase in metabolic response."


Short-term effects of zoledronate on the histomorphology of osteoclast in young albino rats.

"Zoledronate, a third generation bisphosphonate, [was appliead] on the metaphysis of the proximal end of tibia in twenty day old male albino rats. Zoledronate (2.8 μg/kg body weight), was daily given subcutaneously for eleven days. The animals were sacrificed; tibiae were dissected out and decalcified in EDTA. Seven micron thick, serial longitudinal paraffin sections were stained with haematoxylin and eosin and examined under a Zeiss light microscope and Image Pro-Express Analyzer. In zoledronate treated rats, a significant increase in the number of osteoclasts was observed both in the regions of primary spongiosa (zoledronate treated: 6.41 ± 0.30/mm(2), control: 2.90 ± 0.28/mm(2)) and secondary spongiosa (zoledronate treated: 49.58 ± 0.84/mm(2), control: 31.81 ± 2.02/mm(2)) along with a significant increase in the length of the metaphyseal region as compared to the control group. The number of nuclei per osteoclast and area of the osteoclast also showed a significant increase following the uptake of zoledronate."

Length of Tibia of Saline treated rats in mm: 25.37 ± 0.56
Length of Tibia of Zoledronate treated rats in mm: 25.35 ± 1.03

The higher standard deviation means that it's possible that zoledronate could possibly increase bone length but not above measurement.

Full-size image (187 K)"Photomicrograph of a longitudinal section of proximal tibia showing the extent of metaphysis in control and zoledronate treated group. In the experimental rat, trabeculae are seen to extend deeper into the medullary cavity of the diaphyseal region as compared to the control. "  The growth plate looks to be of higher quality in the control group.

"Abbreviations: GP: growth plate; GCMJ: growth cartilage metaphyseal junction; PS: primary spongiosa; SS: secondary spongiosa; trab: trabeculae; mc: medullary cavity."

" in rats, long-term administration of bisphosphonates APD[also known as pamidronic acid] caused a significant shortening of radius"

It's likely that zoledronate has some effect on height but we don't know whether that effect is positive or negative.

Saturday, April 17, 2010

Growing Taller with IGF-1?

IGF-1 promotes growth in every cell in the body and encourages cell growth and development. My hypothesis is that IGF-1 will promote growth in the periosteum of irregular, short, and flat bones resulting in the Tito Ortiz or Kurtwood Smith head but not in the long bones as the limiting factor is mesenchymal(red bone marrow) stem cells and if they are not already in the growth plate they will cannot replicate(multiplying 0 by 100 is still zero). If you are pre-puberty, then injecting your mesenchymal stem cells with IGF-1 may result in a greater "final" adult height.  IGF-1 has systematic affects as well so if you manage to increase your system IGF-1 levels while getting around the negative feedback induced reduction of insulin sensitivity you will be taller.  The best place for the IGF-1 is probably the somotrophic portion of the anterior pituitary which regulates growth and has been linked with gigantism.

High serum levels of IGF-I contribute to promotion of endochondral ossification in mandibular condyle and cause its specific elongation in acromegaly-like rats.

"Mandibular protrusion accompanies acromegaly or acrogigantism. To clarify the detailed mechanisms, we used an acromegaly-like rat model recently developed by exogenous administration of insulin-like growth factor I (IGF-I). Human recombinant IGF-I (640 microg/day) continuously was infused subcutaneously to 10-week-old male rats (n=12) for four weeks[Ten week old rates are not very old]. Control, sham-operated animals (n=12) were injected with saline alone. Twelve rats (six from each group) were killed immediately after ending administration at age 14 weeks. Another 12 rats (six from each group) were housed for an additional four weeks after treatment ended. Mandibular condylar length increased significantly in the IGF-I rats compared with the control rats, but no significant intergroup difference was found in the lengths of the coronoid and angular processes. Cartilaginous layer width, bone matrix volume, and the number of osteoblasts in the mandibular condyle increased significantly in the IGF-I group. These histopathological changes in the condyle disappeared after IGF-I administration was discontinued; however, the morphological change in condylar length remained. These findings suggest that mandibular protrusion in patients with acromegaly or acrogigantism may be evoked by superfluous elongation of the mandibular condyle and that such elongation can be induced by endochondral ossification caused by high IGF-I serum levels."

Endochondral ossification is the process involved in long bone growth. Since the IGF-1 was applied systemically thus suggests that increasing IGF-1 levels may increase final height. Here's a picture of the mandible:

One explanation for why only the mandibular condyle grew is that the mandibular condyle is the part of the jaw bone that is most like a long bone. It states that there was no significant increase in length in the other areas perhaps there was an insignificant increase in periosteal width.

Growth Hormone, Insulin-Like Growth Factors, and the Skeleton

According to the article, IGF-1 operates independently of GH in embryonic development. Both IGF-1 and GH have an effect on periosteal width post puberty, to see the power of periosteal width in action just look at Andre the Giant... IGF-1 has both systematic and local effects.

"GH affects the fate of mesenchymal precursors favoring osteoblastogenesis and chondrogenesis and opposing adipogenesis. Mesenchymal precursor cells can differentiate into adipocytes, osteoblasts, and chondrocytes in a tightly controlled process."

GH encourages mesenchynal stem cells to turn into osteoblasts or cartilage rather than adipose tissue.

The less bold of a line, the less of an effect one factor has on another. Of course, mesenchymal stem cells should also be pointing to the growth plate as well.

"Transgenic mice overexpressing IGF-I under the control of the osteoblast-specific osteocalcin promoter exhibit transient increases in trabecular bone secondary to an increase in osteoblast function and bone formation. Changes in osteoblast number were not observed, confirming the predominant effect of IGF-I on osteoblastic function, and not on mitogenesis."

Mitogenesis of course being the money maker, cell proliferation and within the grown plate: height gain.

Combination therapy with acipimox enhances the effect of growth hormone treatment on linear body growth in the normal and small-for-gestational-age rat

"GH treatment of children with idiopathic short stature or SGA(low birth weight?) does not lead to achievement of genetic height potential"

"The present trial utilized acipimox acts as an antilipolytic agent. Acipimox can lower plasma insulin concentrations and has been shown to enhance spontaneous GH secretion in obese humans and to considerably enhance GH secretion in response to various secretagogues. Acipimox has also been shown to restore the GH response to GH-releasing hormone in elderly subjects."

"GH increased tibial length in all treated groups relative to saline-treated controls."  Including the normal sized rat group.

"GH plus acipimox treatment further significantly enhanced the GH-induced effects on tibial growth."

"Plasma IGF-I concentrations were increased in GH and GH-plus-acipimox-treated control."

So the increase in tibial bone length could be a result in an increase in IGF-1 levels.

"Acipimox may have altered GH output through neural pathways via altered activation of dopaminergic neural circuits."

To those who want to induce gigantism but don't know how to get around the negative feedback mechanisms:

"Pharmacological antilipolysis can restore insulin sensitivity during growth hormone exposure."

IGF-1 has been shown to enhance somatic tissue growth(somatic being any body cell). This also means that you can grow taller by increasing your skin thickness or your cartilage thickness.

We know that exercise increases insulin sensitivity. Therefore, any form of exercise can make you taller by enhancing the effects of IGF-1 on your cells(but not significantly).  IGF-1 does seem to promote chondrogenic differentiation of stem cells.

Differential regulation of immature articular cartilage compressive moduli and Poisson's ratios by in vitro stimulation with IGF-1 and TGF-beta1.

"This study tested the hypothesis that IGF-1 and TGF-beta1 regulate immature cartilage compressive moduli and Poisson's ratios in a manner consistent with known effects on tensile properties[changes in cartilage shape, which are measured by compressive moduli and Poisson's ratio, alter hydrostatic pressure therefore IGF-1 and TGF-Beta1 alter hydrostatic pressure because they alter the effects of compression and tension]. Bovine calf articular cartilage from superficial-articular (S) and middle-growth (M) regions were analyzed fresh or following culture in medium with IGF-1 or TGF-beta1. Mechanical properties in confined (CC) and unconfined (UCC) compression, cartilage matrix composition, and explant size were assessed. Culture with IGF-1 resulted in softening in CC and UCC, increased Poisson's ratios, substantially increased tissue volume, and accumulation of glycosaminoglycan (GAG) and collagen (COL)[the three latter benefits definitely are beneficial for height growth]. Culture with TGF-beta1 promoted maturational changes in the S layer, including stiffening in CC and UCC and increased concentrations of GAG, COL, and pyridinoline crosslinks (PYR), but little growth[note though that this is existing articular cartilage and that TGF-Beta1 may have a larger effect on stem cells that have yet to differentiate into chondrocytes]. Culture of M layer explants with TGF-beta1 was nearly homeostatic. Across treatment groups, compressive moduli in CC and UCC were positively related to GAG, COL, and PYR concentrations, while Poisson's ratios were negatively related to concentrations of these matrix components[compressive moduli is essentially the resistance to compression.  A higher compressive moduli means a substance is more resistance to compression.  It's likely that GAG, COL, and PYR concentrations are causing the compression resistance.  When a material is compressed it stretches the material in the directions not being compressed.  So LSJL stretches the rest of the bone.  Poisson's ratio measures how much a material expands relative to how much it is compressed.  As material stretches more than it compresses, poisson's ratio gets higher.  GAG, COL, and PYR concentrations lowered Poisson's ratio but it also lowered compression therefore GAG, COL, and PYR concentrations must also resist bone stretching in all directions]. Thus, IGF-1 and TGF-beta1 differentially regulate the compressive mechanical properties and size of immature articular cartilage in vitro."

" Culture with IGF-1 is distinguished by significant tissue expansion at the expense of reduced tensile stiffness and strength. In contrast, culture with TGF-β1 maintains size and tensile properties"<-So both IGF-1 and TGF-B1 are likely needed for optimal height growth.  BMP-2 likely belongs somewhere in there too.

"dimensional changes in the 1- and 2-directions were small, averaging <5% for IGF-1 samples and <2% for TGF-β1 samples (data not shown), indicating that IGF-1 induced expansion primarily in the 3-direction." 50ng/ml of recombinant IGF-1 was used and 10ng/ml of recombinant TGF-Beta1 was used. 1-direction refers to left and right expension so width.  Direction-2 refers to up and down expansion so both IGF-1 and TGF-Beta1 would increase height by less than 5% and 2% respectively.  3-direction refers to front and back which won't really help for height growth but it does indicate that if you are increasing IGF-1 and TGF-Beta1 you should be seeing a significant increase in front and back thickness.  If you are not increasing front and back thickness you may not be increasing IGF-1 and TGF-Beta1 in a significant way.

Effect of IGF-I in the chondrogenesis of bone marrow mesenchymal stem cells in the presence or absence of TGF-beta signaling.

"IGF-I modulated MSC chondrogenesis by stimulating proliferation, regulating cell apoptosis, and inducing expression of chondrocyte markers. IGF-I chondroinductive actions were equally potent to TGF-beta1, and the two growth factors had additive effects. Using RIIKO-MSCs, we showed that IGF-I chondrogenic actions are independent from the TGF-beta signaling.  Extracellular signal-related kinase 1/2 mitogen-activated protein kinase (Erk1/2 MAPK) pathway mediated the TGF-beta1 mitogenic response and in part the IGF-I proliferative action."

"it is possible that the lack of IGF biological activity was caused by the nonspecific stimulation of IGFIR by the high levels of insulin present in the ITS Premix. In our study, we evaluated the IGF effects in the absence of insulin."<-So maybe you need low levels of insulin and high levels of IGF-1 to grow taller?

"IGF-I determined an increase in the expression of type II collagen and Sox-9 that was comparable with TGF-β1. "

IGF-1 can inhibit Wnt3A via IGFBP-4 thus reducing Beta-Catening stabliization and allowing for chondrogenesis.

IGFBP-4 is an inhibitor of canonical Wnt signalling required for cardiogenesis.

"Insulin-like growth-factor-binding proteins (IGFBPs) bind to and modulate the actions of insulin-like growth factors (IGFs). Some of the actions of IGFBPs have been reported to be independent of IGFsIGFBP-4 physically interacted with a Wnt receptor, Frizzled 8 (Frz8), and a Wnt co-receptor, low-density lipoprotein receptor-related protein 6 (LRP6), and inhibited the binding of Wnt3A to Frz8 and LRP6. Although IGF-independent, the cardiogenic effect of IGFBP-4 was attenuated by IGFs through IGFBP-4 sequestration. IGFBP-4 is therefore an inhibitor of the canonical Wnt signalling required for cardiogenesis and provides a molecular link between IGF signalling and Wnt signalling."

IGF-1 regulation of type II collagen and MMP-13 expression in rat endplate chondrocytes via distinct signaling pathways.

"Cultured endplate chondrocytes harvested from rat cervical spines were treated with IGF-1 (100ng/ml). Cells were also treated with pharmacological agents that block PI3K and MAPK signaling pathways.
IGF-1 increased Col2a1 mRNA expression in rat endplate chondrocytes in a time- and dose-dependent manner. IGF-1 treatment resulted in a fourfold increase of Col2a1 mRNA with the effect maximizing at 24h. In contrast, IGF-1 treatment for 24h caused a roughly 50% reduction in MMP-13 mRNA. Similar effects were seen on the protein levels of type II collagen (col2) and MMP-13. Consistent with these results, IGF-1 also repressed MMP-13 activity. IGF-1 activated both the PI3K and the extracellular signal-regulated kinase (ERK) pathways as evidenced by phosphorylation of either Akt or ERK1/2 (respectively){LSJL phosphorylates Akt}. The PI3K inhibitor Wartmannin significantly inhibited the IGF-1 effect on Col2a1 mRNA expression but did not affect IGF-1-induced repression of MMP-13 expression{LSJL stimulates the PI3K pathway}. In contrast, the ERK/MAPK inhibitor PD98059 significantly inhibited the effect of IGF-1 on MMP-13 mRNA repression and enhanced IGF-1-induced Col2a1 mRNA expression.
In rat endplate chondrocytes the PI3K pathway mainly transduces IGF-1 effect on col2 expression while the ERK pathway mediates IGF-1 effect on MMP-13 expression."

"IGF-1 exerts its biological effect by binding to the transmembrane type 1 IGF receptor and activating insulin receptor substrate-1"

IGF-1 had a linear effect on chondrocyte anabolism until at least 100ng/ml.

Insulin-like growth factor-I signaling is modified during chondrocyte differentiation.

"IGF-I has been shown to be a potent chondrocyte mitogen in vitro. We chose to study the action of IGF-I on an accepted model of chondrocyte differentiation, the ATDC5 cell line. Insulin concentrations sufficiently high to interact with the IGF-I receptor are routinely used to induce ATDC5 cells to differentiate. Therefore, we first examined the ability of IGF-I to promote chondrocyte differentiation at physiological concentrations. IGF-I could induce differentiation of these cells at concentrations below 10 nM. However, increasing IGF-I concentrations were less potent at inducing differentiation. We hypothesized that mitogenic effects of IGF-I might inhibit its differentiating effects. Indeed, the extracellular-signal-regulated kinase (ERK)-pathway inhibitor PD98059 inhibited ATDC5 cell DNA synthesis while enhancing differentiation. This suggested that the ability of IGF-I to promote both proliferation and differentiation might require that its signaling be modulated through the differentiation process. We therefore compared IGF-I-mediated ERK activation in proliferating and hypertrophic chondrocytes. IGF-I potently induced ERK activation in proliferating cells, but minimal ERK response was seen in hypertrophic cells. In contrast, IGF-I-mediated Akt activation was unchanged by differentiation, indicating intact upstream IGF-I receptor signaling. Similar findings were observed in the RCJ3.1C5.18 chondrogenic cell line and in primary chick chondrocytes. We conclude that IGF-I promotes both proliferation and differentiation of chondrocytes and that the differentiation effects of IGF-I may require uncoupling of signaling to the ERK pathway."

"GH receptor-null mice show severe postnatal growth retardation and extremely low circulating IGF-I levels. The growth plate in these animals narrows relative to wild-type animals starting at 2 weeks of age"

"Studies on ATDC5 cells have routinely employed the addition of high concentrations of insulin (10 μg/ml) to induce chondrocyte differentiation. "

Cartilage disorders: potential therapeutic use of mesenchymal stem cells.

"Insulin-like growth factors (IGFs) play a central role in chondrogenesis as indicated by the severe growth failure observed in animals carrying null mutations of Igfs and Igf1R genes. We have found that IGF-I has potent chondrogenic effects in MSC. Effects are similar to transforming growth factor-Beta (TGF-Beta). Insulin-like growth factor binding protein-3 (IGFBP-3), well characterized as IGF carrier, has intrinsic bioactivities that are independent of IGF binding. IGFBP-3 levels are increased in degenerative cartilage diseases such as osteoarthritis. IGFBP-3 has IGF-independent growth inhibitory effects in chondroprogenitors. IGFBP-3 induces MSC apoptosis and antagonizes TGF-Beta chondroinductive effects in chondroprogenitors."

Disruption of the insulin-like growth factor-1 gene in osteocytes impairs developmental bone growth in mice

So osteocyte signaling can affect endochondral ossification so the diaphysis effects of LSJL may be relevant to the epiphyseal lengthening effects.

"osteocyte Igf1 conditional knockout (KO) mice [were] generated by crossing the Dmp1-driven Cre-expressing transgenic mice with Igf1 floxed mice containing loxP sites that flank exon 4 of the Igf1 gene. The periosteal diameter of femurs of homozygous conditional KO mutants was 8–12% smaller than wild-type (WT) littermates. The conditional mutants had 14–20%, 10–21%, and 15–31% reduction in total, trabecular, and cortical bone mineral contents, respectively. However, there were no differences in the total, trabecular, or cortical bone mineral densities, or in trabecular bone volume, thickness, number, and separation at secondary spongiosa between the mutants and WT littermates. The conditional KO mutants showed reduction in dynamic bone formation parameters at both periosteal and endosteal surfaces at the mid-diaphysis and in trabecular bone formation rate and resorption parameters at secondary spongiosa. The lower plasma levels of PINP and CTx in conditional KO mice support a regulatory role of osteocyte-derived IGF-1 in the bone turnover. The femur length of conditional KO mutants was 4–7% shorter due to significant reduction in the length of growth plate and hypertropic zone. The effect on periosteal expansion appeared to be bigger than that on longitudinal bone growth. The conditional KO mice had 14% thinner calvaria than WT littermates, suggesting that deficient osteocyte IGF-1 production also impairs developmental growth of intramembraneous bone. Conditional disruption of Igf1 in osteocytes did not alter plasma levels of IGF-1, calcium, or phosphorus[so it must be a direct signaling effect by osteocytes affecting longitudinal growth and not just a general effect due to elevated plasma]."

"Osteocytes are derived from osteoblasts as they become terminally differentiated and fully entrapped by the bone matrix."

"osteocytes regulate bone homeostasis by releasing paracrine factors, such as sclerostin, RANKL (receptor activator of nuclear factor kappa-β ligand) and produce and secrete fibroblast growth factor 23 (FGF23)."

"osteoblasts and osteocytes synthesize and release into circulation of under-carboxylated osteocalcin"

"osteocytes express large quantities of IGF-1 [and is upregulated in response to mechanical loading]" Not observed in LSJL however.

"the disruption of hepatic[liver] IGF-1 showed no significant impact on bone growth at early life, despite the fact that it decreased circulating IGF-1 levels by more than 75%".  Disruption of the igf1 gene resulted in shorter bones.

"the body and bone growth in the mutants with Igf1 conditional deletion in type 1α2 collagen-expressing osteoblasts were blunted at as early as 2 weeks of age, whereas the conditional ablation of Igf1 from type 2α1 collagen-expressing chondrocytes did not significantly suppress growth until the animals were at 8 weeks of age"

"Despite the substantial reduction in the Igf1 mRNA expression in osteocytes, the plasma IGF-1 level of KO mutant mice was not different significantly from that of WT littermates. However, the mutant mice showed significantly elevated levels of IGFBP3 but reduced levels of IGFBP5 at both 4- and 16-weeks of age,"

Bone length in IGF-1 KO mice was decreased by about 10%.

"The bone of osteocyte Igf1 conditional KO mice appears to be insensitive to loading, it is possible that the blunted longitudinal bone growth was a consequence of the decreased bone mechanosensitivity in osteocyte Igf1 conditional KO mutants."

Treatment of growth plate injury using IGF-I-loaded PLGA scaffolds.

"[We] develop an in vivo tissue-engineering approach for the treatment of growth plate injury via localized delivery of insulin-like growth factor I (IGF-I) from cell-free poly(lactic-co-glycolic acid) (PLGA) scaffolds. Mass loss and drug release studies were conducted to study the scaffold degradation and IGF-I release patterns. Rat bone marrow stromal cells seeded on the porous scaffolds colonized the pores and deposited matrix within the scaffolds. Implantation of scaffolds in proximal tibial growth plate defects in New Zealand white rabbits showed regeneration of cartilage, albeit with disorganized structure, at the site of implantation of IGF-I-releasing scaffolds; in contrast, only bone was formed in empty defects and those treated with IGF-free scaffolds."

Treatment with insulin-like growth factor-1 increases chondrogenesis by periosteum in vitro.

"Gene expression by periosteal explants in vitro was measured. Expression of type II collagen and aggrecan mRNA was increased in response to treatment with IGF-I. IGF-I treatment caused an increase in type II collagen and aggrecan mRNA that was time and concentration dependent. The effect of short and long-term (continuous) incubations was compared to determine if a pretreatment could be used to condition a graft for subsequent surgical use. Short-term incubation in vitro with IGF-I followed by incubation without IGF-I was nearly as effective at increasing expression of type II collagen and aggrecan mRNA as incubation for the same length of time with IGF-I present continuously in the culture media {So there may be a negative feedback mechanism or conditioning effect}. Treatment with IGF-I also produced cell clustering and nodule formation which are indicative of chondrogenesis{Which is also indicative of new growth plate formation}."

"fibrocartilage [degenerates] upon mechanical loading"

"Periosteum consists of two distinct layers, an outer fibrous layer and a more cellular cambium layer. Cells from the cambium layer are osteochondral and participate in the cartilaginous phase of fracture healing. During this phase, cells express aggrecan, type II collagen and type X collagen"  IGF-1 did not upregulated type I collagen.

"it may be possible to elicit chondrogenesis in vivo by treating periosteal grafts for short periods immediately prior to implantation."

Anabolic effects of IGF-1 signaling on the skeleton.

"GH promotes the formation of a ternary IGF binding complex composed of the acid-labile subunit (ALS) and IGF binding protein 3 (IGFBP-3), which in turn act to stabilize serum IGF-1."

"insulin receptor substrate (IRS) family [associates] with IGF-1R via PTB and SH2 domains, growth receptor binding protein-2 (Grb2) binds to specific motifs in the IGF-1 receptor as well as in IRS, and the p85 subunit of phosphatidyl inositol-3 kinase (PI3K) binds to other specific motifs within IRS. Shc, when tyrosine phosphorylated in response to IGF-1, binds to the SH2 domain of Grb2, which in turn forms a complex with Sos, a guanine nucleotide exchange factor."

IGF-1/PI3K/AKT pathway can increase BLC2 reducing apoptosis and increase cyclin D1 increasing cell proliferation.

Osteocalcin specific Knockout of IGF-1R did not increase bone length.  Global IGF-1 knockout and DMP1(IGF-1KO), Col1a2(IGF-1KO), Col2a1(IGF-1&IGF-1R KO), and hepatic IGF-1 knockout all reduced bone length.

"Rasgrf1 null animals exhibit decreased postnatal skeletal growth, decreased serum IGF-1 levels and reduced IGF-1 transcripts in the liver."

A novel mutation in IGFALS, c.380T>C (p.L127P), associated with short stature, delayed puberty, osteopenia and hyperinsulinemia in two siblings: insights into the roles of insulin growth factor-1 (IGF1).

"The acid-labile subunit (ALS) protein is crucial for maintaining the circulating IGF/IGFBP system. Inactivating mutations of IGFALS result in IGF1 deficiency associated with growth retardation. Although the first IGFALS mutation in humans was described in 2004, only 16 mutations have been reported since. Moreover, the phenotype of affected patients as a consequence of ALS deficiency is still highly variable. We assessed whether children with idiopathic short stature (ISS) harbor mutations in IGFALS and characterized affected patients' phenotype.
Sixty-five children with ISS were enrolled in the study. Serum ALS levels were measured by ELISA and IGFALS was sequenced.
A novel homozygous mutation in IGFALS, c.380T>C (p.L127P), was identified in two siblings of a consanguineous family. The proband, a 17.75-year-old male, was -1.9 SDS in height and -4.5 SDS in weight. Exaggerated stimulated GH (38 ng/ml), and extremely low IGF1 and IGFBP3 (<25 ng/ml and <500 ng/ml, respectively) indicated GH insensitivity. Both affected siblings had low or no ALS (43 and 0 mU/ ml, respectively). They were also mildly small for gestational age, severely underweight, and showed osteopenia, insulin insensitivity and delayed and slow puberty progression.
ALS deficiency due to IGFALS mutations is a rare cause of growth retardation in children. The unique combination of features presented by the two affected siblings emphasizes the important role of IGF1 in bone formation, insulin regulation and the pubertal process, in addition to its crucial effect on growth."

"IGFALS, located on chromosome 16p13.3, encodes the protein acid-labile subunit (ALS) which forms a ternary complex with IGF1 and IGFBP3 and IGFBP5."

"The main role of ALS is to extend the half-life of IGF1 by protecting the ternary complex from degradation. Mutations in IGFALS result in low plasma ALS concentrations"

"Inactivation of IGFALS in mice results in a lack of ALS causing only modest growth failure."

Modeling the Insulin-Like Growth Factor System in Articular Cartilage.

"We estimate the degradation half-lives of free IGF-I and IGFBPs in normal cartilage to be 20 and 100 mins respectively, and conclude that regulation of the IGF half-life, either directly or indirectly via extracellular matrix IGF-BP protease concentrations, are two critical factors governing the IGF-IR complex formation in the cartilage. Further we find that cellular regulation of IGF-II production, the IGF-IIR concentration and its clearance rate, all significantly influence IGF signaling. It is likely that negative feedback processes via regulation of these factors tune IGF signaling within a tissue, which may help explain the recent failures of single target drug therapies aimed at modifying IGF signaling."

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This diagram shows that stimulating the brain, kidney, and muscles may be a way to stimulate IGF-II.

"There is a certain threshold of IGF-I/ IGF-IR concentration that needs to be exceeded before protein synthesis is activated"
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