Abstract 80: Interplay Between Cell-cell and Cell-extracellular Matrix Forces Regulate Myocardial Proliferation

Changes in expression and distribution of integrin, fibronectin (FN), and N-cadherin in the postnatal heart accompany the switch from hyperplastic to hypertrophic growth. As FN decreases after birth, N-cadherin/catenin complex accumulates at the cell termini creating a specialized type of cell-cell contact called the intercalated disc (ID). Integrin-FN interactions promote cardiomyocyte and cardiac progenitor cell proliferation. However, little is known regarding the reciprocity between integrin and N-cadherin adhesions in the regulation of myocardial proliferation. Alpha-catenins function as mechanosensors and transduce the intercellular force from N-cadherin to the actin cytoskeleton. To investigate mechanotransduction in the heart, we generated cardiac-specific αE- and αT-catenins double knockout (DKO) mice. The relationship between N-cadherin, integrin, and FN was examined at postnatal day (P) 4, P7, P14, and P60. DKO hearts exhibited aberrant N-cadherin expression accompanied by increased expression of α5/β1 integrin, the primary receptor for FN. Normally found at the lateral membrane, α5 and FN accumulated at the ID along with N-cadherin in DKO hearts. FN-integrin binding leads to the formation of FN fibrils that are initially soluble in the detergent deoxycholate (DOC) but are gradually converted into a stable, DOC-insoluble form that comprises the mature matrix. Both α5 and FN were increased in the DOC-insoluble fraction consistent with enhanced matrix assembly in DKO hearts. Activation of focal adhesion kinase (FAK) and p130CAS were observed in the DKO hearts consistent with increased cell-extracellular matrix interactions. Complementary experiments performed with deformable substrata demonstrated that stiffness-mediated Yap nuclear accumulation was dependent on FAK activity. These data demonstrate that α-catenins regulate the balance between cell-cell and cell-matrix adhesions, which, in turn, controls Yap subcellular localization, thus providing a molecular explanation for loss of regenerative potential in the adult heart.