Cardiomyopathy is a common disease of cardiac muscle that negatively affects cardiac function. HDAC3 commonly functions as corepressor by removing acetyl moieties from histone tails. However, a deacetylase‐independent role of HDAC3 has also been described. Cardiac deletion of HDAC3 causes reduced cardiac contractility accompanied by lipid accumulation, but the molecular function of HDAC3 in cardiomyopathy remains unknown. We have used powerful genetic tools in Drosophila to investigate the enzymatic and nonenzymatic roles of HDAC3 in cardiomyopathy. Using the Drosophila heart model, we showed that cardiac‐specific HDAC3 knockdown (KD) leads to prolonged systoles and reduced cardiac contractility. Immunohistochemistry revealed structural abnormalities characterized by myofiber disruption in HDAC3 KD hearts. Cardiac‐specific HDAC3 KD showed increased levels of whole‐body triglycerides and increased fibrosis. The introduction of deacetylase‐dead HDAC3 mutant in HDAC3 KD background showed comparable results with wild‐type HDAC3 in aspects of contractility and Pericardin deposition. However, deacetylase‐dead HDAC3 mutants failed to improve triglyceride accumulation. Our data indicate that HDAC3 plays a deacetylase‐independent role in maintaining cardiac contractility and preventing Pericardin deposition as well as a deacetylase‐dependent role to maintain triglyceride homeostasis.

Background: Cardiomyopathy is a common disease of cardiac muscle that negatively affects cardiac function. HDAC3 commonly functions as co-repressor by removing acetyl moieties from histone tails. However, a deacetylase-independent role of HDAC3 has also been described. Cardiac deletion of HDAC3 causes reduced cardiac contractility accompanied by lipid accumulation. The molecular function of HDAC3 in cardiomyopathy remains unknown. We have used the powerful genetic tools in Drosophila to investigate the enzymatic and non-enzymatic roles of HDAC3 in cardiomyopathy. Methods and Results: Using the Drosophila heart model, we showed that cardiac-specific HDAC3 knockdown leads to prolonged systoles and reduced cardiac contractility. Immunohistochemistry revealed structural abnormalities characterized by myofiber disruption in HDAC3 knock down hearts. Cardiac-specific HDAC3 knockdown showed increased levels of whole body triglycerides and increased fibrosis. The introduction of deacetylase-dead HDAC3 mutant in HDAC3 KD background showed comparable results with wild type HDAC3 in aspects of contractility and Pericardin deposition. However, deacetylase-dead HDAC3 mutants failed to improve triglyceride accumulation. Conclusions: Our data indicate that HDAC3 plays a deacetylase-independent role in maintaining cardiac contractility and preventing Pericardin deposition as well as a deacetylase-dependent role to maintain triglyceride homestasis.