Nuclear curvature determines Yes-Associated Protein nuclear localization and differentiation of mesenchymal stem cells.

Controlling mesenchymal stem cells (MSCs) differentiation remains a critical challenge in their therapeutic application. Numerous biophysical and mechanical stimuli influence stem cell fate, however, their relative efficacy and specificity in mechanically directed differentiation remain unclear. Yes-associated protein (YAP) is one key mechanosensitive protein that controls MSC differentiation. Previous studies have related nuclear mechanics with YAP activity, but we still lack an understanding of what nuclear deformation specifically regulates YAP, and its relationship with mechanical stimuli. Here we report that maximum nuclear curvature is the most precise biophysical determinant for YAP mechanotransduction mediated MSC differentiation, and is a relevant parameter for stem cell-based therapies. We employed traction force microscopy and confocal microscopy to characterize the causal relationships between contractility and nuclear deformation in regulating YAP activity in MSCs. We observed that an increase in contractility compresses nuclei anisotropically, where the degree of asymmetric compression increased the bending curvature of the nuclear membrane. We then examined membrane curvature and tension using thin micropatterned adhesive substrate lines and a FRET-based tension sensor, revealing the direct role of curvature in YAP activity driven by both active and passive nuclear import. Finally, we employed micropatterned lines to control nuclear curvature and precisely direct MSC differentiation. This work illustrates that nuclear curvature subsumes other biophysical aspects to control YAP-mediated differentiation in MSCs and may provide a deterministic solution to some of the challenges in mesenchymal stem cell therapies.