Packing-driven mechanotransduction: local crowding overrides adhesion and stiffness cues for YAP activation in cellular collectives

The regulation of mechanotransduction is crucial for various cellular processes, including stem cell differentiation, wound healing and cancer progression. While the activation of mechanotransduction has been extensively studied in single cells, it remains unclear whether similar mechanisms extend to mechanotransduction in multicellular collectives. Here, by focusing on Yes-associated protein (YAP), known as the master regulator of mechanotransduction, we reveal that the local packing fraction of cells acts as the primary determinant of YAP activation in cell collectives. We further show that local packing fraction modulates the isotropic stress landscape, with sparse regions experiencing large stress fluctuations and dense regions displaying stress equilibration. Remarkably, this packing fraction-dependent regulation persists even under conditions of disrupted force transmission through cell-cell and cell-substrate adhesion, suggesting a robust and conserved relation between YAP activation and local packing fraction in cell collectives. In particular, we show that local packing fraction-dependent activation of YAP in cell collectives is independent of substrate stiffness, E-cadherin expression and myosin contractility, in stark contrast to YAP activation in single cells. Our results thus offer a new perspective on mechanotransduction, highlighting the critical role of the local packing fraction of cells in dictating YAP dynamics within multicellular contexts. These insights have significant implications for tissue engineering and understanding tumour microenvironments, where cellular heterogeneity often drives functional outcomes.