Tuesday, September 6, 2011

Increasing Height by Manipulating the Cell Cycle

Stem Cells and Chondrocytes like all cells engage in a cell cycle.  A cell that has left the cycle is senescent and has stopped dividing.  Once all the cells stop dividing the left over extracellular matrix like collagen type II is degraded.  Thus, forcing us to try to induce chondrogenic differentiation with no cartilagenous template.  The longer cells spend in the cell cycle, the more time before senescence and the taller you will grow.

Cell cycle analysis of proliferative zone chondrocytes in growth plates elongating at different rates.

"Regulation of postnatal growth of long bones occurs in multiple levels of chondrocytic activity, including stem cell proliferation, proliferative zone cycling, and regulation of changes in chondrocytic shape during hypertrophy[thus altering all those things can help us grow taller during ordinary development and when trying to induce chondrogenesis once more with LSJL]. The differentiation sequence of chondrocytes is the same in all growth plates, but rates of elongation at a single point in time and over a period of time differ widely among individual growth plates, which suggests that the rates of sequential gene activation and suppression in this phenotypic pattern can vary. The purpose of this study was to investigate, directly and in vivo, parameters of the cell cycle of proliferative chondrocytes in growth plates growing at widely different rates at a single point in time in order to analyze the relationship between cell cycle time, including the duration of each phase of the cell cycle (G1, S, G2, and M), and the rate of growth[In G1 cells grow but there is no DNA replication, in stage S DNA replication begins, in G2 cells resume growing and continue DNA replication, in stage M growth and DNA replication ceases and division occurs]. The experimental design used repeated pulse labeling with bromodeoxyuridine and was analyzed using a regression model of time of pulse label with increasing labeling index. Total cell cycle time was calculated as the inverse of the slope of the relationship of the labeling index and the time between labels. The y intercept was the calculated labeling index at time zero. Multiple comparison contrasts were used to test for individual differences among four growth plates with growth rates ranging from approximately 50 to 400 microns per 24 hours from 28-day-old rats. The estimate of total cell cycle time for the proximal tibial growth plate was 30.9 hours[So if we were to induce one stem cell to differentiate into a chondrocyte with LSJL we would have about 31 hours to try to induce more stem cell chondrogenesis before mitosis occurs followed by senescence]. Cell cycle times for the other three growth plates were 34.0, 48.7, and 76.3 hours for the distal radius, distal tibia and proximal radius, respectively[the proximal radius is by the elbow, it's the bump on the side.  It may be worthwhile to target that region if it does spend so much time in the cell cycle]. Although the times for the proximal tibia and distal radius did not differ significantly, all other times were significantly different (p < 0.05). Almost all differences in total cell cycle time were attributable to significant differences in the length of the G1 phase[thus we likely(but not necessarily) want to stimulate the G1 phase of the cell cycle, note that the distal radius has a long cell cycle and most people have relatively longer arms than their height this could be correlated to G1 cell cycle length]. The S phase was estimated at 3.4-6.1 hours; the G2 phase, at 3.0 hours; and the M phase, at 0.5-0.6 hours. The current study suggests that regulation through cell cycle parameters, specifically in the G1 phase, may be involved in overall regulation of differential postnatal long bone growth. It has previously been established that increase and shape change of cellular volume during hypertrophy may be regulated at the level of individual growth plates and that both are significant in understanding differential growth of long bone at this level. By demonstrating that chondrocytes in the proliferating zone have different cell cycle times that are regulated primarily through differences in the duration of G1, this study suggests that, in addition to systemic controls of chondrocyte proliferation, local controls may modulate rates of proliferation of individual growth plates and thus may be another locally mediated regulator of differential growth."

"The increase in length of a bone achieved by a specific growth plate in any one 24-hour period is determined by a complex interplay of proliferative kinetics, matrix synthesis throughout the growth plate with controlled matrix degradation, and chondrocytic enlargement during hypertrophy that is accompanied by a disproportionate increase in height (in the direction of growth) compared with width as the volume of the cell expands"

According to the chart in the study, growth rate is actually inverse to the time spent in G1.  Of course growth rate does not correlate to final adult height.  But this indicates that it may be worthwhile to actually diminish time spent in G1.  Though by definition of having a longer cell cycle it makes sense to have a slower growth rate because everything takes a longer time to do.

"Circadian rhythms associated with mitosis of growth plate chondrocytes also have been reported"<-thus light, absence of light, and melatonin may be able to manipulate mitosis and the bodies height increasing ability.

"when chondrocytic performance has been studied in mammalian growth plates growing at different rates, it has been demonstrated repeatedly that the growth plates elongating at the fastest rate have the largest hypertrophic chondrocytes with respect to final volume"<-thus it may be worthwhile to try to increase growth rate.

"it has been demonstrated that shape change accompanying volume increase during hypertrophy
also is significant, and that cumulative differential height increases in the direction of growth from
proliferative to hypertrophic chondrocytes correlate positively with rate of growth"<-So the size of hypertrophic chondrocytes plays a large role in bone growth.  Although the height growth could be caused be a secondary factor related to hypertrophy like osmotic pressure changes that occur with the degradation of proteoglycans.

Chondrocyte p21(WAF1/CIP1) expression is increased by dexamethasone but does not contribute to dexamethasone-induced growth retardation in vivo.

p21 is a regulator of the G1 stage of the cell cycle and can cause senescence.  However, just be the title you can see that this surprisingly does not induce growth retardation.

"It has been shown that cell cycle genes play an important role in the coordination of chondrocyte proliferation and differentiation. The inhibitory effects of glucocorticoids (GCs) on chondrocyte proliferation are consistent with GCs disrupting cell cycle progression and promoting cell cycle exit. Cyclin-dependent kinase inhibitors (CDKIs) force cells to exit the cell cycle and differentiate, and studies have shown that expression of the CDKI p21(CIP1/WAF1) is increased in terminally differentiated cells[thus to grow taller you may want to inhibit CDKIs]. In this study, p21 mRNA and protein expression was increased during chondrocyte differentiation and after exposure to dexamethasone (Dex, 10(-6 )M) in murine chondrogenic ATDC5 cells. In 4-week-old mice lacking a functional p21 gene, Dex caused a reduction in body weight compared to saline control null mice, but this was consistent with the reduction in body weight observed in Dex-treated wild-type littermates. In addition, p21 ablation had no effect on the reduction in width of the growth plate or reduced mineral apposition rate in Dex-treated mice[the reduction in growth plate width occur regardless of removal of the p21 gene in Dex-treated mice]. However, an alteration in growth rate and epiphyseal structure is evident when comparing p21(-/-) and wild-type mice[so removal of p21 in normal mice does affect the growth plate, maybe Dexamethasone and p21 work via similar inhibitors]. These findings suggest that p21 does not directly contribute to GC-induced growth retardation in vivo but is involved in the maintenance of the growth plate."

"Disruption of the p57 gene has been shown to cause delayed chondrocyte differentiation, resulting in skeletal deformations and shortened limbs"<-thus you may not want to delay chondrocyte differentiation

"mice deficient in p27 do not show any obvious skeletal phenotypes, though they are larger than wild-type mice"<-inhibiting p27 may be a way to increase height.  Both p21 and p27 play similar roles.  If you inhibit p27 but maintain fully functional p21 you should be able to maintain full functionality without uncontrolled cellular proliferation and result in being taller.  PI3K-Akt inactivates p27 but inhibiting p27 does increase risk of cancer(because now you have to rely solely on p21 to regulate the cell cycle).  PI3K is stimulated by Insulin, IGF-1, and exercise.  The PI3K pathway is also stimulated by Puerarin(which is contained in Ghenerate).

Here's a study that explains what happens to articular chondrocytes in relation to senescence and aging, we can use this information about apply it to growth plate chondrocytes:

Events in Articular Chondrocytes with Aging.

"One of the most pronounced age-related changes in chondrocytes is the exhibition of a senescent phenotype, which is the result of several factors including the accumulation of reactive oxygen species[so could anti-oxidants help stave off senescence?] and advanced glycation end products. Compared with a normal chondrocyte, senescent chondrocytes exhibit an impaired ability to respond to many mechanical and inflammatory insults to the articular cartilage[so could mechanical and inflammatory signals be key to growth in growth plate chondrocytes]. Furthermore, protein secretion is altered in aging chondrocytes, demonstrated by a decrease in anabolic activity and increased production of proinflammatory cytokines and matrix-degrading enzymes."

Phenotype of chondrocyte aging
Molecular events
Altered gene expression related to senescence
• ↑ GADD45β and C/EBPβ → ↑ p21 transcription
• ↓ SIRT1 → ↑ p53, ↑ p21
• ↑ Caveolin 1 → ↑ p53, ↑ p21
• ↑ β-Galactosidase
DNA and telomere dysfunction
• ↓ TRF → telomere shortening
• ↓ XRCC5 → ↑ DNA damage
• Mitochondrial DNA degradation
Altered protein secretion
• ↑ Proinflammatory cytokines (ie, IL-1β, TNF-α) and proinflammatory mediators (PGE2, NO)
• ↑ MMPs (−1, −3, −13) and ADAMTS (−4, −5)
Oxidative damage
• ↑ ROS production
• ↓ Antioxidant enzyme activity
• Mitochondrial dysfunction
↓ Growth factor response
• Impaired responsiveness to IGF-1 , OP-1/BMP-7 , TGF-β
Cell death
• ↓ IGF-1 and OP-1 → reduced cellularity
• ↓ CK2 → apoptosis
• ↓ HMGB2 → apoptosis

This could very well apply to growth plate chondrocytes as well as the final stage is apoptosis.  You can perhaps slow down this senescence somewhat with anti-oxidants and telomere lengtheners like astragalus.

In addition, to telomere length and reactive oxygen species number being possible preventable ways of slowing down cellular senescence, so too is the amount of advanced glycogen end-products.

"AGEs are produced through a nonenzymatic reaction between reducing sugars and free amino groups of proteins, lipids, or nucleic acids. AGEs are formed within the body, and are also derived from cooking techniques that involve “browning” foods. Excessive levels of AGEs in the body are pathogenic, and its effects include increased production of oxidative stress and inflammation. In chondrocytes, AGEs increase production of inflammatory cytokine tumor necrosis factor-α (TNF-α) and inflammatory mediators prostaglandin E2 and nitric oxide, suppress collagen II production, and stimulate expression of degradative enzymes matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)"<-so AGE number can be reduced by avoiding cooking techniques that brown foods.

Remember that osteoarthritis is very similar to endochondral ossification except that osteoarthritis does not seem to increase height.  Thus insights into delaying senescence in osteoarthritis can help us delay senescence in the growth plate.

Cell-cycle control and the cartilage growth plate.

"Progression through the eukaryotic cell-cycle is controlled by cyclin-dependent kinases (CDKs)"

"The activity of CDKs is highly regulated by a number of mechanisms: (a) the level of their respective partner proteins, the cyclins, (b) the levels of inhibitory proteins of the Cip/Kip (p21, p27, p57) and Ink (p15, p16, p18, p19) families (CDK inhibitors or CKIs), and (c) inhibitory and stimulatory phosphorylation of various CDK residues "

"High levels of cyclins therefore generally stimulate cell-cycle progression and proliferation through activation of CDKs, whereas high levels of CKIs antagonize these processes. The most prominent targets of CDKs are the retinoblastoma protein (pRb) and the closely related p107 and p130 proteins. In their hypophosphorylated forms, these proteins (commonly referred to as pocket proteins) form complexes with transcription factors of the E2F family. These complexes, in association with histone deacetylases, repress transcription of E2F target genes. Upon stepwise phosphorylation of pocket proteins by CDKs the complexes dissociate, and free E2F factors can now activate the transcription of genes required for cell-cycle progression and DNA replication."

"Within the growth plate, cyclin D1 expression is specific for the proliferative zone at the mRNA"

"cyclin D1 gene [is] a target of the transcription factor ATF-2 in chondrocytes"

Both Wnt5a over- and under- expression reduce Cyclin D1 activity.

"intracellular signaling molecules such as integrin-linked kinase, the small GTPase RhoA and the transcription factor c-Fos also stimulate cyclin D1 expression in cartilage."<-LSJL upregulates c-Fos.  LSJL affects Cyclin D1 given the effects of LSJL on c-Fos it is likely to increase Cyclin D1 expression.

"p21 expression in chondrocytes is induced or enhanced by FGF signaling through the transcription factor STAT1 "<-increased p21 expression may be a part of FGFR3 dwarfism.

" overexpression of an activated FGFR3 gene in transgenic mice also induces expression of the p16, p18, and p19 genes, CDK inhibitors of the INK family. In addition, FGF1 induces expression of p27 and p57 in RCS cells"

"Expression of p21 and the related p27 protein in chondrocytes is also enhanced by thyroid hormone, a well-characterized inducer of chondrocyte hypertrophy, and by bone morphogenetic protein (BMP)-2. Finally, the chondrogenic transcription factor Sox9 and signaling through the c-Raf/MEK/ERK MAP kinase cascade have also been shown to be important positive regulators of p21 expression, whereas parathyroid hormone represses p21 expression in the chondrogenic cell line ATDC5. In addition, chondrocyte proliferation is enhanced and p57 expression decreased in mice with cartilage-specific inactivation of the gene encoding HIF-1α, a transcription factor involved in the cellular response to hypoxia"

"expression of p21 and p16 is increased in mice deficient for β1 integrin, suggesting that integrin signaling suppresses expression of these cell-cycle inhibitors"

" both β1 integrin deficiency and loss of integrin-linked kinase, a crucial mediator of integrin signaling, result in reduced chondrocyte proliferation through modulation of cell-cycle gene expression [through] different target genes (p16 and p21 vs. cyclinD1)"

"Disruption of the p27 gene results in generalized overgrowth, indicating effects on the growth plates"

"Overexpression of E2F1 in ATDC5 cells resulted in a [dwarfism] phenotype of delayed early and late differentiation. Interestingly, overexpression of the similar E2F2, E2F3, or E2F4 proteins caused much milder phenotypes and did not block late (hypertrophic) chondrocyte differentiation, although high levels of E2F4 in proliferating chondrocytes have been reported "

1 comment:

  1. get rid of VEGF and increase the chondrocyte replication capacity.