Thursday, February 10, 2011

Grow Taller with Hypoxia

Our goal with Lateral Synovial Joint Loading, is to induce chondrogenic differentiation of stem cells in the epiphysis of long bones by way of hydrostatic pressure.  Previously, we have discovered that Hypoxia Inducible Factor-1 is expressed during long bone development.  Hypoxic environments[low oxygen environments] were found to upregulate chondrogenic genes like Sox9LIPUS can increase levels of HIF-1 as well.

Either performing LIPUS immediately before LSJL or by performing intense cardiovascular activity to induce an oxygen debt before LSJL may help to induce the chondrogenic differentiation of stem cells we're after.  There are other ways to lower the oxygen content of the bone and that is by inhibiting vascularity related genes like VEGF.

Hypoxia, HIFs and bone development.

"Oxygen is not only an obviously important substrate, but it is also a regulatory signal that controls expression of a specific genetic program. Crucial mediator of the adaptive response of cells to hypoxia is the family of Hypoxia-Inducible Transcription Factors (HIFs). The fetal growth plate, which is an avascular structure of mesenchymal origin, has a unique out-in gradient of oxygenation. HIF-1alpha is necessary for chondrogenesis in vivo by controlling a complex homeostatic response that allows chondrocytes to survive and differentiate in a hypoxic environment.  [HIFs have a critical role in] endochondral bone development."

"HIF-1 is a heterodimer of two proteins, HIF-1α and HIF-1β; HIF-1β is constitutively expressed, whereas HIF-1α is the hypoxic-responsive component of the complex. When oxygen drops below 5%, HIF-1α translocates to the nucleus, heterodimerizes with the β subunit, and initiates its transcriptional program"
You can also see how the cells for endochondral ossification are located in the epiphysis.  Also, vascularization of the growth plate may inhibit growth.  Since estrogen is involved in vascularization this may be how estrogen can inhibit growth despite evidence that cellular senescence is intrinsic to the cells itself.


"Conditional knockout of VEGF-A in chondrocytes causes cell death in the center of mutant growth plates, indicating that VEGF-A is critical for chondrocyte survival"

How do we increase levels of HIF-1alpha other than by LIPUS or exercise?  The Nitric Oxide Pathway may be involved.  Nitric Oxide is involved in the stabilization of HIF-1alpha.  This is a knock against Icariin which reduces HIF-1alpha synthesis.  Reactive Oxygen Species that are reduced by Anti-Oxidants may also stimulate HIF-1alpha.  Living in a higher altitude can also simulate hypoxia.  However, there is evidence that high altitude may reduce height...

Tradeoffs between oxygen and energy in tibial growth at high altitude.

"Some studies of high altitude populations argue that stature reduction results from caloric, rather than hypoxic, stress. However, tradeoff models of oxygen and glucose metabolism predict that in hypoxemia, glucose metabolism will be downregulated. We used tradeoff assumptions in two hypotheses: First, that hypoxia targets leg segment growth differentially, and second, that proportions of leg segments partition the impact of high altitude into hypoxemic and energetic components. A group of 113 Han and Tibetan middle school children at 3100 m aged 8 to 11 were measured for segment anthropometries, skinfolds, vital capacity, blood oxygen saturation, and percent body fat. MANOVA showed that Tibetan children were significantly larger and fatter than Han children. Independent of ethnicity or caloric status, absolute and relative tibia length was significantly reduced in children with lower blood oxygen saturation. Height, chest circumference, sitting height, tibia length, and ankle diameter were greatest in fatter children, independent of ethnicity or blood oxygen. For children of either ethnicity with the lowest blood oxygen, size as well as proportion was impacted. These results support the tradeoff model. Caloric reserves and ethnicity independently affect total skeletal size. Oxygen saturation and ethnicity affect leg proportions. In hypoxemia, body fat has less impact on growth than when ample oxygen is present."

Of course, final leg height may be greater in the hypoxic children and only a decrease in growth velocity may observed in low oxygen saturation.

Molecular mechanism of hypoxia-induced chondrogenesis and its application in in vivo cartilage tissue engineering.

"Here, we assessed engineering of cartilage tissue starting from human bone marrow (hBM) stem cells under hypoxic environment and delineated the mechanism whereby chondrogenesis could be conducted without addition of exogenous growth factors. hBM stem cells were cultured in alginate beads and chondrogenesis was monitored by chondrocyte phenotypic markers. Activities and roles of Sox and HIF-1α transcription factors were investigated with complementary approaches of gain and loss of function and provided evidences that HIF-1α is essential for hypoxic induction of chondrogenesis. Thereafter, hBM cells and human articular chondrocytes (HAC) underwent chondrogenesis by 3D and hypoxic culture for 7 days or by ectopic expression of HIF-1α. After subcutaneous implantation of 3 weeks into athymic mice, tissue analysis showed that hypoxia or HIF-1α overexpression is effective and sufficient to induce chondrocyte phenotype in hBM cells[so we can induce HIF-1alpha in bone marrow MSCs to grow taller], without use of exogenous growth factors."

"In mammalian cells, it has been established that hypoxia mediates lot of its effect through the transcriptional complex HIF-1, which contains HIF-1α and HIF-1β subunits. This complex binds to specific hypoxia responsive elements (HRE), thereby initiating the transcription of specific genes, such as Sox9 or aggrecan"<-So hypoxia can induce the transcription of chondrogenic genes like Sox9.

"hypoxia, as well as CoCl2 treatment and ectopic expression of HIF-1α, markedly increased the binding of protein complexes to the COL2A1 enhancer sequence"<-Phosgene(CoCl2) is highly toxic so we wouldn't be able to incorporate it.

Hypoxia inhibits hypertrophic differentiation and endochondral ossification in explanted tibiae.

"Fetal mouse tibiae (E17.5) explants were cultured up to 21 days under normoxic or hypoxic conditions (21% and 2.5% oxygen respectively). Tibiae were analyzed on growth kinetics, histology, gene expression and protein secretion.
The oxygen level had a strong influence on the development of explanted fetal tibiae. Compared to hypoxia, normoxia increased the length of the tibiae, length of the hypertrophic zone, calcification of the cartilage and mRNA levels of hypertrophic differentiation-related genes e.g. MMP9, MMP13, RUNX2, COL10A1{up} and ALPL. Compared to normoxia, hypoxia increased the size of the cartilaginous epiphysis, length of the resting zone, calcification of the bone and mRNA levels of hyaline cartilage-related genes e.g. ACAN, COL2A1 and SOX9.{so normoxia may increase growth rate whereas hypoxia may result in the end result of more longitudinal growth} Additionally, hypoxia enhanced the mRNA and protein expression of the secreted articular cartilage markers GREM1, FRZB and DKK1, which are able to inhibit hypertrophic differentiation.
Normoxia stimulates hypertrophic differentiation evidenced by the expression of hypertrophic differentiation related genes. In contrast, hypoxia suppresses hypertrophic differentiation of chondrocytes, which might be at least partially explained by the induction of GREM1, FRZB and DKK1 expression."

"hypertrophic chondrocytes produce large amounts of angiogenic factors, such as vascular endothelial growth factor (Vegf) that recruits invading blood vessels into the hypertrophic cartilage. This not only allows for the infiltration of amongst others bone forming cells, but also the alleviation of hypoxic stress (less than 5% oxygen) that occurs in most of the hyaline cartilage "

"hypoxia stimulates chondrogenic behavior in mesenchymal stromal cells (MSCs)"

"in hypoxia a marked increase in tissue growth was observed at the lateral sites of the osseous – cartilaginous interface. This suggested that the out-in gradient of oxygen was able to influence the shape of developing cartilage."

"normoxia down regulated Mmp3{up in LSJL} mRNA, it up regulated Mmp9 and tended to increase Mmp13 mRNA levels"

So which results in the greatest net increase of height, hypoxia or normoxia?

So Hypoxia is important for height growth, but how to induce it in the one region we want which is in the epiphysis?


  1. are you still growing after you grew 1.5"?

  2. interesting though that i read NAC stimulates hypoxa..

  3. The problem with NAC is that NADPH oxidases are important for chondrogenic differentiation and NAC inhibits these Reactive Oxygen Species.