Abstract 340: Cardiomyocyte-Derived Mechanical Signals Function in a Paracrine Manner to Regulate Tissue Stiffness and Myocardial Proliferation

Abstract

Cells sense and transduce mechanical signals through cell-cell adhesions and cell-extracellular matrix adhesions. After birth, contractile force generation and tissue stiffness increase as cardiac output increases to support the needs of the newborn organism. During this postnatal period, the N-cadherin adhesion complex assembles at the intercalated disc (ID) as integrin-fibronectin (FN) adhesions decrease, accompanying the switch from hyperplastic to hypertrophic growth. However, little is known regarding the reciprocity between integrin and N-cadherin adhesions in the regulation of cell cycle withdrawal that occurs in cardiomyocytes after birth. α-catenins function as mechanosensors and transduce the intercellular force from N-cadherin to the actin cytoskeleton. Cardiac-specific αE- and αT-catenins double knockout (DKO) mice exhibit sustained cardiomyocyte proliferation beyond the first week of life. To investigate the role of cell-matrix interactions in DKO hearts, the spatial distribution of integrin-FN complexes was examined at postnatal day (P) 4, P7, P14, and P60. DKO hearts exhibited aberrant N-cadherin localization accompanied by altered distribution of α5/β1 integrin, the primary FN receptor. Normally found at the lateral membrane, α5 and β1 accumulated at the ID while N-cadherin was reduced at the termini. FN matrix assembly, as monitored by immunofluorescent staining and its insolubility in the detergent deoxycholate, was increased in DKO hearts. Meanwhile, focal adhesion kinase (FAK) was activated in early postnatal DKO hearts. Complementary experiments performed with deformable substrata demonstrated that stiffness-mediated proliferation was dependent on FAK activity. Finally, treatment of DKO pups with the lysyl oxidase inhibitor, β-aminopropionitrile (BAPN), was sufficient to reduce cardiomyocyte proliferation to wild-type levels suggesting that matrix assembly and tissue stiffness feedback to promote cardiomyocyte proliferation in DKO hearts. This data demonstrates that α-catenins regulate the balance between cell-cell and cell-matrix adhesions, which, in turn, controls cardiomyocyte proliferation, thus providing a molecular explanation for loss of regenerative potential shortly after birth.