Wednesday, October 13, 2010

Elongating Height Increase by inhibiting VEGF?

Recently, we discovered that inhibiting F-spondin increased height by 30% in some cases.  VEGF was one of the factors stimulated by F-Spondin and Plasmin.  Optimal levels of FGF were essential for growth.  SMUF1(Sulfatase-Modifying Factor) was found to increase height by inhibiting FGF signaling.    Since we need some FGF or else we won't grow at all, it's clear that enhancing inhibitating factors like SMUF1 is key to maximizing growth.  Even though reducing Fibroblast growth factors to the optimal levels will increase growth, it is still possible that several of the factors modified by F-spondin inhibit growth.  Thus, we should look at all of them and see if we can modify them to elongate individual's height increase period.

Effects of bone morphogenetic proteins on osteoblast cells: vascular endothelial growth factor, calcium, inorganic phosphate, and nitric oxide levels.

"Bone morphogenetic proteins (BMPs) play an important role in the initiation of bone formation by affecting cell growth and differentiation in a variety of cell types including osteoblasts. Vascular endothelial growth factor (VEGF) is an important regulator of angiogenesis[angiogensis is the growth of new blood vessals from pre-existing ones] and vasculogenesis[the organic growth of blood vessals], and also, VEGF signaling is important for skeletal development. Nitric oxide (NO), calcium (Ca), and inorganic Phosphate (Pi) are important molecules for cell functions.  The effects of BMP on VEGF, Ca, NO, and Pi levels were investigated in an osteoblast cell culture.
Fifty thousand cells per milliliter were seeded and cultured on graft materials for 24 and 48 hours. Different concentrations of BMPs (combination of BMPs numbered from 1 to 14) were supplemented to the medium.
BMP [increases] VEGF, Ca, and Pi especially in the first 24 hours. The increase in the NO in the experimental groups were found to be statistically insignificant."

BMP increases VEGF levels.

Intravenous administration of anti-vascular endothelial growth factor humanized monoclonal antibody bevacizumab improves articular cartilage repair.

"We investigate the efficacy of repairing an osteochondral defect in rabbit knee joints by administering bevacizumab, a humanized monoclonal anti-vascular endothelial growth factor (VEGF) antibody.
An osteochondral defect was created on the patellar groove of 20 Japanese white rabbits that were classified into two recipient groups: group B, administration of bevacizumab (100-mg intravenous injection on the day of surgery and two weeks later); and control group (defect only). Rabbits were sacrificed 1 and 3 months postoperatively. Sections were stained with safranin O. Repair sites were evaluated using the modified O'Driscoll international cartilage repair society grading system. The expression of chondromodulin (ChM)-I and VEGF was evaluated using immunohistochemical analyses.
At 1 month postoperatively, the repair site in group B was filled with cartilaginous tissue. At 3 months, the repair site retained this cartilage phenotype. At 1 month in the controls, the defects were mainly filled with fibrous tissue. At 3 months, the defect was replaced by fibrous tissue and bone. Over the 3-month period, histological scores were significantly higher in group B than in the controls. At 1 month, group B showed intense positive results for ChM-I in the bottom of the repair tissue. VEGF was also identified in the same area. In the controls, no ChM-I was observed in the repair tissue. Conversely, the remodeling hypertrophic chondrocyte layer stained intensely for VEGF.
Intravenous administration of bevacizumab contributes to better repair of articular cartilage in an osteochondral defect model."

"Bevacizumab binds to VEGF secreted by angiogenic tumors and thereby inhibits VEGF binding to the VEGF receptor in vascular endothelial cells"

Anti-VEGF inhibitors like Bevacizumab keep cartilage and inhibits fibrous tissue and bone.  VEGF inhibitors may or may not increase height as ossification is an important stage in height increase.  But it seems that initial inhibition of VEGF may help with chondroinduction.

"articular cartilage is a naturally avascular tissue, except during skeletal development, when endochondral bone formation occurs."

"expression of high levels of VEGF during the terminal stages of chondrogenesis leads to endochondral ossification through angiogenesis"

"ChM-I was expressed in the early stage of tissue repair after bevacizumab administration. ChM-I stimulates chondrocyte proliferation and proteoglycan synthesis in vitro"

"ChM-I acts to inhibit vascular invasion in the immature state of articular cartilage, and levels of ChM-I gradually decrease with age thereafter. ChM-I is expressed in the avascular zone of cartilage in developing bone, but is not present in calcifying cartilage."

"ChM-I is thought to form a barrier to inhibit vascular invasion from subchondral bone, indicating that it facilitates the acquisition of articular cartilage through the process of MSC differentiation in endochondral ossification."

Fluid flow-induced soluble vascular endothelial growth factor isoforms regulate actin adaptation in osteoblasts[Fluid flow is induced by Lateral Synovial Joint Loading]

"Although load-induced mechanical signals play a key role in bone formation and maintenance of bone mass and structure, the cellular mechanisms involved in the translation of these signals are still not well understood. Recent identification of a novel flow-induced mechanosignaling pathway involving VEGF in osteoblasts and the known VEGF regulation of actin reorganization in various cell types has led us to hypothesize that fluid shear stress-induced Vegf up-regulation underlies the actin cytoskeleton adaptation observed in osteoblasts during mechanotransduction. Our results show that MC3T3-E1 cells secrete significant VEGF in response to 5 h of pulsatile fluid shear stress (PFSS; 5 dynes/cm(2) at 1 Hz), whereas expression of VEGF receptors (VEGFR-1, VEGFR-2, or NRP1) is unaffected. These receptors, in particular VEGFR-2, participate in PFSS-induced VEGF release. Exposure to flow-conditioned medium or exogenous VEGF significantly induces stress fiber formation in osteoblasts that is comparable with PFSS-induced stress fiber formation, whereas VEGF knockdown abrogates this response to PFSS, thereby providing evidence that flow-induced VEGF release plays a role in actin polymerization. Using neutralizing antibodies against the receptors and VEGF isoforms, we found that soluble VEGFs, in particular VEGF(164), play a crucial role in transient stress fiber formation during osteoblast mechanotransduction, most likely through VEGFR-2 and NRP1. Based on these data we conclude that flow-induced VEGF release from osteoblasts regulates osteoblast actin adaptation during mechanotransduction and that VEGF paracrine signaling may provide potent cross-talk among bone cells and endothelial cells that is essential for fracture healing, bone remodeling, and osteogenesis[growth of new bone]."

Actin is essentially a way for cells to better communicate.  This is good and shouldn't inhibit growth.  And VEGF may affect stem cells:

Anti-vascular endothelial growth factor treatment in combination with chemotherapy delays hematopoietic recovery due to decreased proliferation of bone marrow hematopoietic progenitor cells.

"Mouse model and in vitro studies were undertaken to determine the effect of interference with VEGF signaling by VEGF-specific agents or a multitargeted VEGF receptor (VEGFR) tyrosine kinase inhibitor on proliferation of hematopoietic progenitor cell (HPC) and repopulation of the hematopoietic compartment after myeloablation.
The studies demonstrated that blockage of VEGFR1 or VEGFR2 signaling decreased HPC proliferation and impaired repopulation of the hematopoietic compartment after myelosuppression by slowing the progression of HPC through the cell cycle. The combination of cytotoxic drugs and VEGFR tyrosine kinase inhibitor had an additive inhibitory effect and decreased proliferation of HPC significantly stronger than either agent alone."

Proper VEGF signaling increases stem cell proliferation.

TGF-beta1 induces mouse dendritic cells to express VEGF and its receptor (Flt-1) under hypoxic conditions.

"Angiogenesis is a multi-step process that involves the activation, proliferation, and migration of endothelial cells. TGF-beta1 can induce mouse macrophages to produce VEGF{LSJL stimulates parts of the TGF-Beta pathway and may increase the amount of active TGF-Beta}, a potent angiogenic factor. In the present study, we explored whether TGF-beta1 has a similar effect on mouse dendritic cells. First, we show that under hypoxic conditions, TGF-beta1 induced the expression of VEGF transcripts in bone marrow-derived dendritic cells. Overexpression of Smad3/4 further augmented TGF-beta1-induced VEGF transcription, while overexpression of DN-Smad3 decreased VEGF transcription in DC2.4 cells, a mouse dendritic cell line. TGF-beta1 and Smads are involved in the induction of VEGF protein secretion. Under the same conditions, the expression of VEGF receptor 1 (Flt-1) was also elevated at both the transcriptional and protein levels. TGF-beta1-induced VEGF secretion in activated DC2.4 cells has wound-healing properties. Finally, Smad7 and Smurf1 negatively regulated the TGF-beta1-induced and Smad3/4-mediated VEGF expression. TGF-beta1 can enhance the expression of VEGF and Flt-1 through the typical Smad pathway in mouse dendritic cells."

LSJL may upregulate VEGF through fluid flow and by it's upregulation of TGF-Beta.

Transcriptional regulation of endochondral ossification by HIF-2alpha during skeletal growth and osteoarthritis development.

"Chondrocyte hypertrophy followed by cartilage matrix degradation[the loss of the hyaline cartilage growth plate line] and vascular invasion, characterized by expression of type X collagen (COL10A1), matrix metalloproteinase-13 (MMP-13) and vascular endothelial growth factor (VEGF), respectively, are central steps of endochondral ossification during normal skeletal growth and osteoarthritis development. A COL10A1 promoter assay identified hypoxia-inducible factor-2alpha (HIF-2alpha, encoded by EPAS1) as the most potent transactivator of COL10A1. HIF-2alpha enhanced promoter activities of COL10A1, MMP13 and VEGFA through specific binding to the respective hypoxia-responsive elements. HIF-2alpha, independently of oxygen-dependent hydroxylation, was essential for endochondral ossification of cultured chondrocytes and embryonic skeletal growth in mice. HIF-2alpha expression was higher in osteoarthritic cartilages versus nondiseased cartilages of mice and humans. Epas1-heterozygous deficient mice showed resistance to osteoarthritis development, and a functional single nucleotide polymorphism (SNP) in the human EPAS1 gene was associated with knee osteoarthritis in a Japanese population. RELA, a nuclear factor-kappaB (NF-kappaB) family member, [is] a potent inducer of HIF-2alpha expression. HIF-2alpha is a central transactivator that targets several crucial genes for endochondral ossification."

"vascular invasion [of growth plate cartilage] depends on an angiogenic switch by VEGF"

"Under normoxic conditions, the α-subunit members HIF-1α, HIF-2α and HIF-3α undergo oxygen-dependent hydroxylation, resulting in ubiquitination and degradation by the proteasome. In contrast, under hypoxic conditions, they are neither hydroxylated nor degraded, and they heterodimerize with the constitutive β-subunit members known as aryl hydrocarbon receptor nuclear translocator (ARNT), ARNT2, ARNT-like (ARNTL) and ARNTL2. The heterodimers activate transcription of the target genes by binding the consensus sequence called hypoxia-responsive element (HRE) in the promoters"

"During differentiation of ATDC5 cells, Epas1 expression increased in accordance with the three representative factors for central steps of endochondral ossification: Col10a1, Mmp13 and Vegfa, whereas Hif1a expression was strong at the early stage and decreased thereafter. Hif3a expression was very low, and the β-subunit members were extensively expressed in all differentiation stages"

"The homozygous deficient mutants (Epas1−/−) were extraordinarily small and died at the early embryonic stage"

"heterozygous deficient mutants (Epas1+/−) developed and grew without abnormalities of major organs, [but] they showed mild but proportional dwarfism compared to wild-type littermates from embryonic stages up to 1 week after birth"

"Hif-2α insufficiency impaired not only chondrocyte hypertrophy but also subsequent steps such as matrix degradation and vascularization"

"mRNA levels of the chondrocyte hypertrophy markers Mmp3 and Mmp9 were decreased after overexpression of a dominant-negative mutant form of HIF-2α and siRNA specific for Epas1 mRNA in ATDC5 cells"

VEGF plays a role in the vascular invasion of the cartilage cells but that doesn't happen until after MMP13 degrades the cartiliginous matrix.

Complementary interplay between matrix metalloproteinase-9, vascular endothelial growth factor and osteoclast function drives endochondral bone formation

"Long bone development depends on endochondral bone formation, a complex process requiring exquisite balance between hypertrophic cartilage (HC) formation and its ossification. Dysregulation of this process may result in skeletal dysplasias and heterotopic ossification. Endochondral ossification requires the precise orchestration of HC vascularization, extracellular matrix remodeling, and the recruitment of osteoclasts and osteoblasts. Matrix metalloproteinase-9 (MMP-9), vascular endothelial growth factor (VEGF) and osteoclasts have all been shown to regulate endochondral ossification. MMP-9, VEGF and osteoclast deficiency all cause impaired growth plate ossification resulting in the accumulation of HC. VEGF mRNA and protein expression are increased at the MMP-9-/- growth plate, and VEGF activity contributes to endochondral ossification since sequestration of VEGF by soluble receptors results in further inhibition of growth plate vascularization and ossification. However, VEGF bioavailability is still limited in MMP-9 deficiency, as exogenous VEGF is able to rescue the MMP-9-/- phenotype, demonstrating that MMP-9 may partially, but not fully, regulate VEGF bioavailability. The organization of the HC extracellular matrix at the MMP-9-/- growth plate is altered, supporting a role for MMP-9 in HC remodeling. Inhibition of VEGF impairs osteoclast recruitment, whereas MMP-9 deficiency leads to an accumulation of osteoclasts at the chondro-osseous junction. Growth plate ossification in osteoclast-deficient mice is impaired in the presence of normal MMP-9 expression, indicating that other osteoclastic functions are also necessary."

"We administered recombinant human VEGF165 systemically to 1-week-old MMP-9 null mice by daily intraperitoneal injection. After 1 week of treatment, there was a 35% reduction in the length of the HC zone in the treated mice"

"MMP-9 and MMP-13 co-operate in the degradation of cartilage type II collagen"

"c-Fos null growth plates showed decreased MMP-9 expression"

"mice lacking osteoclasts showed MMP-9 expression in non-osteoclastic cells and display milder defects in growth plate ossification than those seen in MMP-9 deficiency. These non-osteoclastic MMP-9-expressing cells may function as the TRAP-negative ‘chondroclasts’."

"administration of exogenous VEGF did not recruit more osteoclasts, but rather resulted in a reduction in their numbers, at the MMP-9−/− chondro-osseous junction. "

VEGFA is necessary for chondrocyte survival during bone development.

Wwe conditionally knocked out Vegfa in chondrocytes, using the Col2a1 promoter to drive expression of Cre recombinase. VEGFA plays a significant role in both early and late stages of cartilage vascularization, since Vegfa CKO mice showed delayed invasion of blood vessels into primary ossification centers and delayed removal of terminal hypertrophic chondrocytes. VEGFA is crucial for chondrocyte survival, since massive cell death was seen in joint and epiphyseal regions of Vegfa CKO endochondral bones. Chondrocytes in these regions were found to upregulate expression of Vegfa in wild-type mice at the time when massive cell death occurred in the Vegfa CKO mice. The expression of the VEGFA receptors Npr1 and Npr2 in epiphyseal chondrocytes and lack of blood vessel reduction in the vicinity of the cartilaginous elements in the Vegfa CKO mice raise the possibility that the observed cell death is the result of a direct involvement of VEGFA in chondrocyte survival. Interestingly, the extensive cell death seen in Vegfa CKO null bones had a striking similarity to the cell death phenotype observed when hypoxia-inducible factor 1 alpha (Hif1a) expression was abolished in developing cartilage. HIF1 alpha and VEGFA are components of a key pathway to support chondrocyte survival during embryonic bone development."

"VEGFA has a direct effect on the activity of osteoblasts"

"in the unaffected mice at E15.5, we observed initiation of blood vessel invasion into the hypertrophic cartilage of long distal limb bones (tibia and fibula), whereas in the Vegfa CKO distal limb bones there was an expansion of the hypertrophic zone, so that it occupied most of the diaphysis, and no evidence of blood vessel invasion and trabecular bone formation could be seen. In order to document the differences in the invasion of blood vessels into the hypertrophic zone between unaffected and Vegfa CKO mice we stained for PECAM (CD31), an endothelial cell marker. At E16.0, in unaffected tibia we observed abundant CD31 staining throughout the diaphysis and capillary network adjacent to the growth plate. In contrast, in tibia of Vegfa CKO mice there was clearly no vessel invasion into cartilage. At E16.5, a marrow cavity was established in the distal limb bones of unaffected and Vegfa CKO mice, but despite this evidence of a normal architecture, the zones of hypertrophic chondrocytes remained larger in Vegfa CKO than in unaffected growth plates. Not only limb bones were affected in the Vegfa CKO mice; expansion of the hypertrophic zone could also be observed at E18.5 in ribs"

"Vegfa CKO bones contained several rows of chondrocytes expressing Osp, whereas expression was restricted to only one row of chondrocytes in the unaffected bones. These results suggest that there is delayed removal of terminally differentiated hypertrophic chondrocytes in the Vegfa CKO growth plates."

Estrogen upregulates VEGF expression as well.  Both anabolic and catabolic factors like osteoclasts and VEGF are essential for optimal endochondral ossification.  Reducing VEGF expression to optimal levels may have the effect of elongating the height increase period.  Increasing VEGF expression to optimal levels may have the effect of enhancing cellular proliferation and triggering appropriate organization of the growth plate.

Vascular regression is required for mesenchymal condensation and chondrogenesis in the developing limb.

"Vascular regression occurs during limb mesenchymal cell condensation and chondrogenesis. Beads presoaked with the potent angiogenic factor vascular endothelial growth factor (VEGF) were implanted in the vicinity of the prospective digit 2 in early chick embryo wing buds. VEGF treatment caused a marked local increase in blood vessel number and density. This was accompanied by inhibition of digit 2 development as revealed by lack of expression of chondrogenic transcription factor Sox9 and absence of Alcian blue staining. Vascular distribution and skeletal development in adjacent areas remained largely unaffected. Inhibition of digit formation and excess vascularization were both reversible upon further embryonic growth and dissipation of VEGF activity. When supernumerary digits were induced at the anterior limb margin by retinoic acid treatment, their development was also preceded by vascular regression; interestingly, cotreatment with VEGF inhibited supernumerary digit development as well. Direct exposure of limb mesenchymal cells in micromass cultures to VEGF caused no obvious effects on condensation and chondrogenesis, indicating that VEGF effects are not due to direct action on skeletal cells."

"The act of condensation brings the mesenchymal cells in close proximity, maximizing cell–cell contacts and minimizing intercellular space and matrix."<-So the MMPs could play a role in condensation by degrading the matrix.

"There is an inverse relationship between mesenchymal condensations and blood vessel distribution in the developing limb"

"blood vessels are initially present throughout the limb mesenchyme before formation of prechondrogenic condensations" "blood vessels undergo local regression from sites where precartilaginous condensations will form shortly thereafter."<-could causing blood vessel regression induce chondrogenesis?

"lack of blood vessels is not only a feature of the cell condensation step, but continues after the cells differentiate into chondrocytes and assemble cartilaginous skeletal elements. This antiangiogenic trend is eventually reversed when hypertrophic chondrocytes form at the chondro-osseous border during endochondral ossification and produce factors and proteases favoring angiogenesis and blood vessel invasion of the hypertrophic cartilage matrix"

"exogenous VEGF was able to induce local increases in blood vessels"

" when [mesenchymal] cells are grown in the presence of fibroblastic or myogenic cells, chondrogenesis is inhibited"

"if blood vessels were to persist, they could represent a physical barrier to the condensation process and interfere with the establishment of close cell–cell contacts; or they could “dilute” the density and/or reduce the homogeneity of committed prechondrogenic cells."

"Vascular endothelial cells and vessel-associated cells could provide several growth factors that inhibit chondrogenesis, including Gdf11, PDGF-AA, Wnt-1, Wnt-7a"


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