Detyrosinated microtubules (MTs) provide mechanical resistance that can impede the motion of contracting cardiomyocytes. However, the functional effects of MT detyrosination in heart failure or in human hearts have not previously been studied. Here we utilize mass spectrometry and single-myocyte mechanical assays to characterize changes to the cardiomyocyte cytoskeleton and their functional consequences in human heart failure. Proteomic analysis of left ventricle tissue reveals a consistent upregulation and stabilization of intermediate filaments and MTs in failing human hearts. As revealed by super-resolution imaging, failing cardiomyocytes are characterized by a dense, heavily detyrosinated MT network, which is associated with increased myocyte stiffness and impaired contractility. Pharmacological suppression of detyrosinated MTs lowers the viscoelasticity of failing myocytes and restores 40–50% of lost contractile function; reduction of MT detyrosination using a genetic approach also softens cardiomyocytes and improves contractile kinetics. Together, these data demonstrate that a modified cytoskeletal network impedes contractile function in cardiomyocytes from failing human hearts and that targeting detyrosinated MTs could represent a new inotropic strategy for improving cardiac function.

Rationale 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. The recent discovery that the transcriptional co-activator Yap is necessary and sufficient for cardiomyocyte proliferation has gained considerable attention. However, the upstream regulators and signaling pathways that control Yap activity in the heart are poorly understood. Objective To investigate the role of α-catenins in the heart using cardiac-specific αE- and αT-catenin double knockout (α-cat DKO) mice. Methods and Results We used two cardiac-specific Cre transgenes to delete both αE-catenin (Ctnna1) and αT-catenin (Ctnna3) genes either in the perinatal or in the adult heart. Perinatal depletion of α-catenins increased cardiomyocyte number in the postnatal heart. Increased nuclear Yap and the cell cycle regulator cyclin D1 accompanied cardiomyocyte proliferation in the α-cat DKO hearts. Fetal genes were increased in the α-cat DKO hearts indicating a less mature cardiac gene expression profile. Knockdown (KD) of α-catenins in neonatal rat cardiomyocytes also resulted in increased proliferation, which could be blocked by KD of Yap. Finally, inactivation of α-catenins in the adult heart using an inducible Cre led to increased nuclear Yap and cardiomyocyte proliferation and improved contractility following myocardial infarction. Conclusions These studies demonstrate that α-catenins are critical regulators of Yap, a transcriptional co-activator essential for cardiomyocyte proliferation. Furthermore, we provide proof-of-concept that inhibiting α-catenins might be a useful strategy to promote myocardial regeneration following injury.