Kindlin-2 Mediates Mechanical Activation of Cardiac Myofibroblasts.

We identify the focal adhesion protein kindlin-2 as player in a novel mechanotransduction pathway that controls profibrotic cardiac fibroblast to myofibroblast activation. Kindlin-2 is co-upregulated with the myofibroblast marker alpha-smooth muscle actin (alpha-SMA) in fibrotic rat hearts and in human cardiac fibroblasts exposed to fibrosis-stiff culture substrates and pro-fibrotic TGF-beta 1. Stressing fibroblasts using ferromagnetic microbeads, stretchable silicone membranes, and cell contraction agonists all result in kindlin-2 translocation to the nucleus. Overexpression of full-length kindlin-2 but not of kindlin-2 missing a putative nuclear localization sequence ( increment NLS kindlin-2) results in increased alpha-SMA promoter activity. Downregulating kindlin-2 with siRNA leads to decreased myofibroblast contraction and reduced alpha-SMA expression, which is dependent on CC(A/T)-rich GG(CArG) box elements in the alpha-SMA promoter. Lost myofibroblast features under kindlin-2 knockdown are rescued with wild-type but not increment NLS kindlin-2, indicating that myofibroblast control by kindlin-2 requires its nuclear translocation. Because kindlin-2 can act as a mechanotransducer regulating the transcription of alpha-SMA, it is a potential target to interfere with myofibroblast activation in tissue fibrosis.