(52h) Cell-Cell Contact Regulates Myogenic Fate Differentiation of Mesenchymal Stem Cell Through OB-Cadherin

Mesenchymal stem cells (MSCs) are multipotent cells that can be differentiated into fat, bone, cartilage and muscle. Although TGFβ is a soluble factor that promotes myogenic differentiation, the role of cell-cell adhesion in this process is not well understood. In this study we examined how cell-cell communication determines the fate of MSC towards smooth muscle cells (SMC). In particular, we hypothesized that cadherin mediated cell-cell contact might promote MSC differentiation into contractile SMCs. To address this hypothesis, we examined the effect of cell-cell adhesion on myogenic differentiation of MSC, in the absence of soluble factors promoting MSC differentiation. First, we observed that increased cell density increased adherens junction (AJ) formation, as shown by translocation of b-catenin to the cell-cell contact sites. Simultaneously, high cell density increased expression of alpha smooth muscle actin (aSMA) as well as N-cadherin and OB-cadherin even in the presence of bFGF, which is known to suppress MSC differentiation. Gene knockdown studies revealed that N cadherin and OB-cadherin mediated myogenic differentiation of MSC. Specifically, knockdown of OB-cadherin diminished expression of all myogenic genes including aSMA, calponin, caldesmon and SM22. We also found that two pathways mediated cell-cell contact-induced differentiation: a TGF-b1-dependent and a TGF-b1 independent pathway. Interestingly, the TGF-b1 independent pathway was mediated by the activity of ROCK as the chemical inhibitor, Y27632 or shRNA diminished cell-cell contact induced differentiation. These results are novel as they identify cell-cell contact as an inducer of myogenic differentiation through cadherins and their intracellular mediators. Our data demonstrated that OB-cadherin mediated ROCK activation and was also necessary for the contractile SMC phenotype. Although activation of the TGF-b1-dependent pathway enhanced this process, it was not necessary. Our results demonstrated the mechanisms of MSC differentiation and may have implications for development of strategies to control stem cell fate.