Wednesday, December 8, 2010

Grow your Height with Dexamethasone?

Dexamethasone is a bit of a paradox.  As it has the ability to increase chondrogenic differentiation of stem cells yet it also inhibited the growth of bones in rats(however it seemed to reduce growth rate only as chondrocyte proliferation increased after dexamethasone withdrawl).  Dexamethasone also reduced levels of GHR and GHBP in the growth plate(this would explain why it affected growth rate and not growing to your final height).  GHR receptors go down following Dexamethasone treatment and then are upregulated after dexamethasone levels diminish.  Dexamethasone may decrease proliferation rate but it also slows down numerical depletion of growth plate cells.  What can you apply from Dexamethasone in your quest to grow your height? 

Short bouts of mechanical loading are as effective as dexamethasone at inducing matrix production by human bone marrow mesenchymal stem cell.

"Dexamethasone (Dex) is used widely to induce differentiation in human mesenchymal stem cells (hMSCs). The goal of the present study was to investigate the effects of dynamic compressive loading on differentiation and mineralized matrix production of hMSCs in 3D polyurethane scaffolds, using a loading regimen previously shown to stimulate mineralised matrix production of mature bone cells (MLO-A5). hMSCs were seeded in polyurethane scaffolds and cultured in standard culture media with or without Dex. Cell-seeded scaffolds were compressed at 5% global strain for 2 h on day 9 and then every 5 days in a media-filled sterile chamber. Samples were tested for mRNA expression of alkaline phosphatase (ALP), osteopontin (OPN), collagen type 1 (col 1) and runt-related transcription factor-2 (RUNX-212 h) after the first loading, cell viability by MTS assay and alkaline phosphatase activity at day 12 of culture and cell viability, collagen content by Sirius red and calcium content by alizarin red at day 24 of culture. Neither Dex nor loading had significant effects on cell viability. Collagen content was significantly higher (p<0.01) in the loaded group compared with the non-loaded group in all conditions. There was no difference in ALP activity or the amount of collagen and calcium produced between the non-loaded group supplemented with Dex and the loaded group without Dex. We conclude that dynamic loading has the ability to stimulate osteogenic differentiation of hMSC in the absence of glucocorticoids."

Note that the stem cells were loaded in polyurethane.  The stem cells that differentiated into chondrocytes were induced by hydrostatic pressure and a chondrogenic medium.  When you think about it the cells most likely to be compressed are those in the periosteum which need to deposit bone beneath the periosteum to grow wider bones.  And, the cells most likely to be affected by hydrostatic pressure are those in the epiphysis which need to differentiate into chondrocytes to undergo endochondral ossification.  The most important aspect of LSJL is inducing hydrostatic pressure(can also be induced by LIPUS).  This is why vertical compression doesn't help you grow taller as it doesn't generate hydrostatic pressure.  It only compresses the stem cells which causes them to differentiate into osteoblasts not chondrocytes.  Dexamethasone enhanced chondrogenic differentiation in the rabbit study which indicates that environment is an important factor in ensuring chondrogenic differentiation of stem cells. 

IGF-I and not IGF-II expression is regulated by glucocorticoids in human fetal epiphyseal chondrocytes.

"We studied the regulation by dexamethasone (Dx) and IGF-I of proliferation and IGF axis components and matrix protein gene expression in human fetal epiphyseal chondrocytes.
High Dx concentration (10(-7)-10(-6)M) inhibited (3)H-thymidine incorporation, mifepristone (MF) 10(-6)M limited inhibition by Dx, and IGF-I (100 ng/ml) significantly stimulated proliferation and completely opposed inhibition by Dx. Dx dose-dependently (10(-9)-10(-6)M) inhibited IGF-I, IGFBP3 and SOX9 gene expression and expression of GHR, COL2A1 and aggrecan from 10(-7)M to 10(-6)M whereas it stimulated IGF-IR expression. By contrast, Dx had no significant effect on IGF-II expression. IGF-I stimulated IGF-I, IGFBP3, SOX9, COL2A1 and aggrecan expression whereas it inhibited IGF-IR expression. IGF-I could oppose COL2A1 and aggrecan gene expression inhibition by Dx.
We demonstrated for the first time by real-time quantitative PCR that human fetal epiphyseal chondrocytes expressed IGF axis components, such as IGF-I, IGF-II, IGFBP3, IGF-IR and GHR and SOX9, COL2A1 and aggrecan, and that their expression was regulated by Dx and IGF-I. Among IGFs, IGF-I and not IGF-II expression was demonstrated to be down-regulated by GCs whereas IGF-I expression was up-regulated by itself."

Maybe Dexamethasone encourages stem cells to stop proliferation and start differentiating into chondrocytes(or osteoblasts) which is ultimately bad for maximizing height growth.  Like how you want to avoid Alkaline Phosphatase secretion for as long as possible. 

Functional characterization of hypertrophy in chondrogenesis of human mesenchymal stem cells.

"Mesenchymal stem cells (MSCs) are promising candidate cells for cartilage tissue engineering. Expression of cartilage hypertrophy markers (e.g., type X collagen) by MSCs undergoing chondrogenesis raises concern for a tissue engineering application for MSCs, because hypertrophy would result in apoptosis and ossification. To analyze the biologic basis of MSC hypertrophy, we examined the response of chondrifying MSCs to culture conditions known to influence chondrocyte hypertrophy, using an array of hypertrophy-associated markers.
Human MSC pellet cultures were predifferentiated for 2 weeks in a chondrogenic medium, and hypertrophy was induced by withdrawing transforming growth factor beta (TGFbeta), reducing the concentration of dexamethasone, and adding thyroid hormone (T3)[So TGFBeta may be good for elongating the proliferative phase before the hypertrophic phase]. Cultures were characterized by histologic, immunohistochemical, and biochemical methods, and gene expression was assessed using quantitative reverse transcription-polymerase chain reaction.
The combination of TGFbeta withdrawal, a reduction in the level of dexamethasone, and the addition of T3[You need all three of these things to induce chondrogenic hypertrophy] was essential for hypertrophy induction. Cytomorphologic changes were accompanied by increased alkaline phosphatase activity, matrix mineralization, and changes in various markers of hypertrophy, including type X collagen, fibroblast growth factor receptors 1-3, parathyroid hormone-related protein receptor, retinoic acid receptor gamma, matrix metalloproteinase 13, Indian hedgehog, osteocalcin, and the proapoptotic gene p53. However, hypertrophy was not induced uniformly throughout the pellet culture, and distinct regions of dedifferentiation were observed.
Chondrogenically differentiating MSCs behave in a manner functionally similar to that of growth plate chondrocytes, expressing a very similar hypertrophic phenotype. Under the in vitro culture conditions used here, MSC-derived chondrocytes underwent a differentiation program analogous to that observed during endochondral embryonic skeletal development, with the potential for terminal differentiation. This culture system is applicable for the screening of hypertrophy-inhibitory conditions and agents that may be useful to enhance MSC performance in cartilage tissue engineering."

Since Dexamethasone has potential negative effects it would seem that increasing TGF-Beta levels would be the best way to inhibit premature chondrocyte hypertrophy.  Exogenous Melatonin increased TGF-Beta levels in chondrocytes.

Dexamethasone stimulates expression of C-type Natriuretic Peptide in chondrocytes.

"Primary mouse chondrocytes in monolayer where incubated with the synthetic glucocorticoid Dexamethasone (DEX) for 12 to 72 hours.
We show that DEX does influence expression of key genes in the CNP pathway. Most importantly, DEX significantly increases RNA expression of the gene encoding CNP itself (Nppc). In addition, DEX stimulates expression of Prkg2 {upregulated 2.894 by LSJL} (encoding cGMP-dependent protein kinase II) and Npr3 (natriuretic peptide decoy receptor) genes. Conversely, DEX was found to down-regulate the expression of the gene encoding its receptor, Nr3c1 (glucocorticoid receptor), as well as the Npr2 gene (encoding the CNP receptor).
Our data suggest that the growth-suppressive activities of DEX are not due to blockade of CNP signaling. "

"loss-of-function mutations in the human NPR2 gene cause reduced height and skeletal effects in acromesomelic dysplasia, type Maroteaux"

"DEX caused a significant increase in Nppc mRNA levels, starting at 12 hours and reaching 3.7-fold stimulation after 72 hours of treatment. Expression of the CNP receptor Npr2 increased almost three-fold over the time course under control conditions"

"DEX treatment increased Npr3 mRNA levels at 48 and 72 hours."

" up-regulation of transcript levels for the decoy receptor Npr3 by DEX might counteract increased CNP levels"

So Dexamethasone can't really help you grow your height.  Obtain similar results with TGF-Beta, dynamic compression(osteoblasts), and hydrostatic pressure(chondrocytes).

Differential effects of dexamethasone on the chondrogenesis of mesenchymal stromal cells: influence of microenvironment, tissue origin and growth factor.

"Dexamethasone (DEX)--a synthetic glucocorticoid--is almost invariably applied to potentiate the growth-factor-induced chondrogenesis of MSCs in vitro, albeit that this effect has been experimentally demonstrated only for transforming-growth-factor-beta (TGF-β)-stimulated bone-marrow-derived MSCs. Clinically, systemic glucocorticoid therapy is associated with untoward side effects (e.g., bone loss and increased susceptibility to infection). Hence, the use of these agents should be avoided or limited. We hypothesize that the influence of DEX on the chondrogenesis of MSCs depends upon their tissue origin and microenvironment [absence or presence of an extracellular matrix (ECM)], as well as upon the nature of the growth factor. We investigated its effects upon the TGF-β1- and bone-morphogenetic-protein 2 (BMP-2)-induced chondrogenesis of MSCs as a function of tissue source (bone marrow vs. synovium) and microenvironment [cell aggregates (no ECM) vs. explants (presence of a natural ECM)]. In aggregates of bone-marrow-derived MSCs, DEX enhanced TGF-β1-induced chondrogenesis by an up-regulation of cartilaginous genes, but had little influence on the BMP-2-induced response. In aggregates of synovial MSCs, DEX exerted no remarkable effect on either TGF-β1- or BMP-2-induced chondrogenesis. In synovial explants, DEX inhibited BMP-2-induced chondrogenesis almost completely, but had little impact on the TGF-β1-induced response. Our data reveal that steroids are not indispensable for the chondrogenesis of MSCs in vitro. Their influence is context dependent (tissue source of the MSCs, their microenvironment and the nature of the growth-factor). This finding has important implications for MSC based approaches to cartilage repair."

"After stimulation with TGF-β1 for 4 weeks [in synovial tissues] in the absence of DEX, the ECM of synovial explants manifested intense metachromasia[meaning more chondrogenic].  When DEX was included in the culture medium, TGF-β1 induced weak metachromasia"

Dex enhanced GAG production in mesenchymal tissues however.

"the effects of DEX on the chondrogenesis of MSCs were shown to depend upon their microenvironment, their tissue origin and the nature of the growth factor (TGF-β1 or BMP-2)."

"The physiological and pharmacological actions of glucocorticoids (including synthetic ones) are predominantly mediated via the ubiquitously-expressed glucocorticoid receptor (GR).  To date, two isotypes have been identifi ed: GRalpha and GRβ. GRß is a dominant inhibitor of GRalpha, and changes in the cellular GRalpha-to-GRβ ratio can influence sensitization and resistance to glucocorticoids. Human bone-marrow derived MSCs have been reported to express both GRalpha and GRβ. Furthermore, over expression of GRß has been shown to inhibit the DEX and TGF-ß- induced up-regulation of reporter activity for the type-II-collagen-gene promoter."  Differential GR isoform topography could influence different Dexamethasone effects.

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