Sox9 determines whether BMP2 is chondrogenic or osteogenic

Many of the supplements to encourage chondrogenic differentiation also encourage osteogenic differentiation.  Since growth plates are made of chondrocytes, it is much more advantageous to encourage chondrogenic over osteogenic differentiation.  Some of these factors include BMP2, TGFBeta1, etc.

This study suggests that Sox9 levels may be one factor affecting whether BMP2 encourages osteogenic or chondrogenic differentiation of mesenchymal stem cells:

Sox9 Potentiates BMP2-Induced Chondrogenic Differentiation and Inhibits BMP2-Induced Osteogenic Differentiation.

“Bone morphogenetic protein 2 (BMP2) is one of the key chondrogenic growth factors involved in the cartilage regeneration. However, it also exhibits osteogenic abilities and triggers endochondral ossification{but enchondral ossification is good for height growth, however without the growth base chondrocytes for the growth plate the stimuli for endochondral ossification is pointless}. Effective chondrogenesis and inhibition of BMP2-induced osteogenesis and endochondral ossification can be achieved by directing the mesenchymal stem cells (MSCs) towards chondrocyte lineage with chodrogenic factors, such as Sox9. Here we investigated the effects of Sox9 on BMP2-induced chondrogenic and osteogenic differentiation of MSCs. Exogenous overexpression of Sox9 enhanced the BMP2-induced chondrogenic differentiation of MSCs in vitro. Also, it inhibited early and late osteogenic differentiation of MSCs in vitro. Subcutaneous stem cell implantation demonstrated Sox9 potentiated BMP2-induced cartilage formation and inhibited endochondral ossification. Mouse limb cultures indicated that BMP2 and Sox9 acted synergistically to stimulate chondrocytes proliferation, and Sox9 inhibited BMP2-induced chondrocytes hypertrophy and ossification. This study strongly suggests that Sox9 potentiates BMP2-induced MSCs chondrogenic differentiation and cartilage formation, and inhibits BMP2-induced MSCs osteogenic differentiation and endochondral ossification.”

You’re not going to be able to genetically engineer your mesenchymal stem cells to be transgenic for Sox9 but with supplements and mechanical stimuli you could upregulate the MSC expression of Sox9.  Icariin increased Sox9 but only in cells that were already chondrocytesElectroacupencture increased Sox9 expression.  LSJL also upregulates Sox9.  Lactoferrin upregulated Sox9 in pluripotent stem cellsVitamin C increased Sox9 in pre-chondrogenic ATDC5 stem cellsQuercetin increases Sox9 levelsKaempferol increases Sox9 also in ATDC5 cells.

Quercetin had the most prominent effect on increasing Sox9 in normal stem cells.

“BMP2 induced Sox9 expression was transient and relatively at a lower level during the early stages of MSCs differentiation.”

“Sox9 and BMP2 synergistically promoted chondrocytes condensation and proliferation. However, Sox9 inhibited BMP2 induced chondrocytes hypertrophy, and ossification.”<-So we want optimal levels of Sox9 to form neo growth plates as chondrocyte hypertrophy and ossification are vital stages in the growth plates mechanisms of increasing height.

“Sox9 inhibits BMP2-induced early osteogenic differentiation.”<-So stem cells need to have high Sox9 expression to become chondrocytes but then levels of Sox9 need to increase to undergo endochondral ossification.

“we also explored the effect of Sox9 on skeletal development using the fetal limb culture assay. The skinned fetal limbs were isolated from mouse E18.5 perinatal embryos and cultured in the organ culture medium in presence of AdGFP, AdBMP2, and/or AdSox9 for 14 days. The limbs were infected with indicated recombinant adenoviruses effectively at day 5. On histological examination, both BMP2 and Sox9 induced chondrocytes proliferation and condensation. However, only BMP2 induced chondrocyte hypertrophy and ossification. When the limbs were co-infected with AdBMP2 and AdSox9, the proliferating chondrocyte zone was expanded with no obvious expansion of hypertrophic chondrocyte zone

“combined treatment of BMP2 and Sox9 had the largest length of proliferating chondrocyte zone, while BMP2 alone exhibited the largest length of hypertrophic chondrocyte zone”<-So you’d be taller if you just had BMP2 and not Sox9.  This link is supported by genes such as Twist1 which supress Sox9 but which overexpression increases height.

” Sox9 alone was insufficient to induce MSCs chondrogenic differentiation, but required other growth factors, such as Sox5, Sox6, IGF1, FGF or TGF-β”

“transient overexpression of Sox9 using adenovirus vector was insufficient to induce chondrogenic differentiation of MSCs.”<-So you need sustained expression of Sox9 to induce the initial chondrogenesis.

“exogenous overexpression of Sox9 in BMP2-induced osteogenic differentiation of MSCs showed a significant decrease in the levels of Runx2 expression, sequentially with delayed osteogenic differentiation, and endochondral ossification. Apart from overexpression of Sox9, silencing or removing Runx2 might achieve a similar outcome in BMP2-induced MSCs differentiation.”<-Alternatively inducing Runx2 after chondrogenesis has been inducted by Sox9 might be the right way to get the chondrocytes back on track to endochondral ossification.

Given that you start with an initial pool of progenitor cells  to form a growth plate(although the idea with LSJL is to create new progenitors), to maximize height growth you want to maximize the growth per progenitor cell via increasing expression of genes like CNP and Twist1.  After this pool is exhausted how much growth you get per cell is less important as any growth is better than zero so it’s more important to induce this initial expression of Sox9 to get the right kind of cells in the first place.

Here’s a study about Notch inhibiting Twist1 which inhibits Sox9:

Notch inhibits chondrogenic differentiation of mesenchymal progenitor cells by targeting Twist1.

“Notch inhibition of chondrogenesis acts via up-regulation of the transcription factor Twist1. Upon Notch activation, murine limb bud mesenchymal progenitor cells in micromass culture displayed an inhibition of chondrogenesis. Twist1 was found to be exclusively expressed in mesenchymal progenitor cells at the onset stage of chondrogenesis during Notch activation. Inhibition of Notch signaling in these cells significantly reduced protein expression of Twist1. Furthermore, the inhibition effect of NICD1 on MPC chondrogenesis was markedly reduced by knocking down of Twist1. Constitutively active Notch signaling significantly enhanced Twist1 promoter activity; whereas mutation studies indicated that a putative NICD/RBPjK binding element in the promoter region is required for the Notch-responsiveness of the Twist1 promoter. Finally, chromatin immunoprecipitation assays further confirmed that the Notch intracellular domain influences Twist1 by directly binding to the Twist1 promoter.”

“Twist1 is developmentally expressed in mesoderm-derived embryonic tissues and postnatally in adult mesoderm-derived mesenchymal stem cells, where it functions as a major regulator of mesenchymal cell differentiation”

“mRNA expression of both Col2a1 and Agc1 in NICD1-expressing cells was down-regulated at time points 3–7 days, in which NICD1 protein expression was highly expressed, suggest an inhibition of cartilage matrix synthesis at that stage.”

Leave a Reply

Your email address will not be published. Required fields are marked *