Mechanical forces play a critical role in regulating cellular function. Cells sense and transduce mechanical signals through cell-cell adhesions and cell-extracellular matrix (ECM) adhesions. Shortly after birth, muscle cells of the mammalian heart lose their ability to divide. Thus, they are unable to effectively replace dying cells in the injured heart. Loss of regenerative potential within the first week of postnatal life coincides with downregulation of the ECM protein fibronectin and its receptor alpha5 integrin, while the N-cadherin/catenin adhesion complex re-distributes to the bipolar ends of the myocyte, creating a specialized cell-cell contact called the intercalated disc (ICD). N-cadherin junctions are stabilized at the ICD by the dynamic binding of the intracellular cadherin domain to the actin cytoskeleton via beta- and alpha-catenins. In recent work our laboratory demonstrated that the simultaneous depletion of both alpha-catenins (aE-/aT-catenin double knockout (DKO)) in the heart resulted in aberrant formation of ICDs and sustained myocyte proliferation beyond the first week of life. Importantly, our preclinical studies showed that temporal inactivation of alpha-catenins in adult hearts following myocardial infarction increases Yap activity, cardiomyocyte proliferation, and improves cardiac function. Yap has been identified as a nuclear relay of mechanical signals, but the molecular mechanisms that lead to Yap activation are poorly understood. We hypothesize that alpha-catenin-regulated cytoskeleton organization couples signals from N-cadherin to integrin in an integrated mechanochemical signaling system to ultimately control cardiomyocyte proliferation. It is proposed that this novel proliferative signal requires Rho-driven changes in cytoskeletal tension, and increased focal adhesion signaling. The following interrelated aims are proposed: (1) To determine the molecular mechanisms by which alpha-catenin regulates tension-driven cardiomyocyte proliferation. (2) To determine whether alpha5 integrin and fibronectin matrix assembly are required to transduce the proliferative signal in alpha-catenin-deficient cardiomyocytes. (3) To determine whether actomyosin-mediated tension via ROCK activation is sufficient to induce ECM assembly, tissue stiffening, and proliferation in the heart. This project will lead to an integrated molecular understanding of how cardiomyocytes coordinate signals from cadherins, integrins, and cytoskeletal network into a proliferative response, and may suggest new therapeutic strategies to stimulate cardiac regeneration in heart failure patients.
Successful completion of this project will enhance our understanding of the molecular mechanisms controlling cardiac regeneration, and potentially identify novel targets to exploit for stimulating cardiac proliferation following myocardial infarction.