AbstractsBiology & Animal Science

Cadherins are cell-cell adhesion proteins that mediate cell recognition, segregation, and signaling in many tissues. Recent findings demonstrated that type I classical cadherin complexes are mechanosensitive. Mechanical forces in the tissue environment play a profound role in the growth, morphogenesis, and physiology of cadherin-expressing cells. In order to establish how force impinges on critical cell functions in healthy or diseased tissue, it is essential to determine the mechanisms by which mechanical force is transduced into biochemical signals. In this dissertation, I provide new mechanistic insights into how mechanics alters the organization and function of cadherin-dependent adhesions, which are essential intercellular adhesions in all tissues. First, studies examined the dependence of GTPase signaling, associated with mechanotransduction, on cadherin ligation. Dynamic fluorescence imaging examined Rac1 activation at nascent cell-cell junctions, and revealed qualitative correlations between measured cadherin binding affinities and the signal amplitude triggered by cadherin ligation. Second, I examined the role of the cytosolic protein ??-catenin in E-cadherin-based adhesion and mechanotransduction, using bead-twisting measurements in conjunction with confocal fluorescence imaging. These experiments revealed rapid, early molecular events in mechanotransduction and the rudiments of a mechanotransduction mechanism. I further investigated how internal contractile forces, regulated by the stiffness of the cell substrate, influence intercellular junction formation and signaling in endothelial monolayers. Finally, experiments focused on a more physiologically relevant problem: VE-cadherin-mediated mechanotransduction in human pulmonary endothelial cells. These studies established that VE-cadherin complexes are mechanosensitive, and provides direct evidence that the associated mechanotransduction regulates both local cytoskeletal remodeling and global cell mechanics. Moreover, studies revealed that cadherin adhesions across the cell monolayer form a mechanosensitive network that regulates endothelial integrity in response to mechanical stimuli. These results suggest that VE-cadherin mechanotransduction can significantly impact cell function not only at the single cell level, but also across the cell monolayer. These studies were followed by work examining a clinically relevant problem: how a disease-associated single nucleotide polymorphism (SNP) in cortactin, a cytoskeletal adaptor protein, affects the regulation of endothelial cell-cell junctions. Combined MTC and imaging experiments revealed insights into both the role of the cortactin SNP in VE-cadherin mechanotransduction, and the functional implications of VE-cadherin mechanotransduction. These findings have critical implications for endothelial homeostasis and disease.