Mechanosensitive Vinculin Signaling Regulates Stem Cell Fate

Abstract

Human mesenchymal stem cell (hMSC) proliferation, migration, and differentiation have all been linked to extracellular matrix stiffness, but despite serious scientific inquiry, a consensus on the signaling pathways that are necessary and sufficient for this mechanosensitive ability has yet to be reached. An analysis of kinase binding site accessibility revealed MAPK1 to be both prevalent and inaccessible in many focal adhesion/mechanosensing candidate proteins. One binding partner for MAPK1, vinculin, is activated upon binding to talin in a force-sensitive manner. A Cysteine Shotgun/Western Blot was used to confirm the unfolding of talin in response to changes in substrate stiffness. RNA interference was used to knock down vinculin, resulting in an 80% decrease in stiffness-induced MyoD, a muscle transcription factor; control cultures that induce Runx2 expression, an osteoblast transcription factor, were insensitive to vinculin knockdown. Vinculin knockdown was not observed to interfere with focal adhesion assembly, alter adhesive properties, or diminish cell traction force generation, indicating that its deletion only adversely affected MAPK1 signaling. In addition, vinculin domains were also selectively deleted and added back into knocked-down cells to assess which domains of the protein were sufficient for stiffness-induced differentiation. Together, these data provide some of the first in situ evidence that force-sensitive focal adhesion proteins can activate stem cell differentiation signals.