UC San Diego

Mechanical signals have been shown to have an essential role in regulating stem cell fate. Human mesenchymal stem cell (hMSC) differentiation can be regulated by the stiffness of the surrounding extracellular matrix (ECM), via the process of mechanotransduction, in which specific mechanosensors at focal adhesion (FA) convert mechanical cues into intracellular biochemical signaling pathways. However, the molecular mechanisms underlying mechanotransduction still remain elusive. Vinculin is reported to be capable of undergoing conformational changes exposing a cryptic mitogen-activated protein kinase 1 (MAPK1) binding site on the head domain of vinculin when subjected to physiological forces generated from myosin contraction, suggesting that vinculin, among other FA proteins, may be sensitive to physical ECM properties and thus able to relay information leading to regulation on stem cell differentiation by mechanotransduction. In this thesis, endogenous vinculin in hMSCs was knocked-down by small interfering RNA (siRNA), resulting in a 70% decrease in MyoD muscle differentiation marker expression after four days of growth on matrices with stiffness that mimics muscles (11kPa). Addition of full-length vinculin or just the head domain back into cells was shown to be able to restore MyoD expression; addition of the vinculin tail domain was not able to rescue myogenesis. Together the results suggest that the MAPK1 binding site on vinculin may be important for regulating myogenesis