Vinculin-Mediated Cytoskeletal Remodeling Modulates Cardiac Morphology and Contractile Function During Ageing

Abstract

Heart failure associated with chronic aging is underscored by altered expression of actin-binding cytoskeletal molecules. How cytoarchitectural remodeling impacts cardiac structure and contractile function remains unclear. We have developed novel biophysical techniques to interrogate subcellular mechanics and cellular function in the genetically tractable, rapidly aging Drosophila, a useful model for mammalian cardiac development. Genotype-dependent, age-related remodeling was a conserved hallmark in wildtype flies signified by decreased systolic and diastolic dimensions between 1 and 5 weeks of age. Remodeling correlated with increased cortical stiffness, particularly at the intercalated disc (ID). Inhibition of actin polymerization reversed the stiffening phenotype at the ID while inhibition of actomyosin crosslinking did not. Age-related remodeling also correlated with preserved contractile function. In contrast, non-remodeled hearts experienced impaired shortening velocities. Cardiac-specific genetic perturbations were employed to determine how altered expression of vinculin (Vcl) affected structure and function independent of aging. Vcl overexpression resulted in increased localization to the ID, decreased diastolic diameter, and increased cortical stiffness at 1 wk of age preferentially at the ID. However, fractional shortening and shortening velocity increased as compared to controls, suggesting that muscle performance was not hindered by Vcl-overexpression despite altered physiology. Vcl-overexpressing hearts treated with cytochalasin D exhibited significant softening at the ID while blebbistatin-treated flies did not, suggesting that Vcl induces stiffening through actin recruitment. In contrast to current models that suggest that intercalated disc remodeling may be maladaptive for age-related cardiac decline, no reduction in systolic function was observed in hearts with Vcl-overexpression. Therefore, Vcl may play a key regulatory role in maintenance of cardiomyocyte structure and function with age. Further studies will investigate the biophysical mechanisms of increased shortening function due to Vcl-mediated remodeling and identify upstream activators of Vcl-upregulation.