Abstract 17001: Nebulette Knock-Out in Mice Leads to Dilated Cardiomyopathy

Abstract

Introduction: Cardiomyopathy is a serious heart condition that can lead to heart failure. Nebulette is a cardiac-specific Z-disk protein which plays a crucial role in mechanosensing and force generation in the heart. Previous studies have shown that nebulette mutations are associated with various cardiomyopathies including hypertrophic, left ventricular noncompaction and dilated cardiomyopathy. However, the molecular mechanisms by which nebulette affects the cardiac structure and function are not well-understood. Hypothesis: In this study, we tested whether decrease in nebulette causes cardiac remodeling, dysfunction and dilated cardiomyopathy in vivo. Methods: We generated a novel nebulette knockout (KO, excision of exon 3) mice using the Cre/loxP technique. Mice were characterized prior to being subjected to serial echocardiography and electrocardiogram (ECG) at 6 weeks, 3 months, 6 months and one year of age. A separate cohort of mice were used for histopathological and molecular studies. Results: KO mice were born following Mendelian laws. Western blot and qPCR data revealed significant decrease in nebulette expression in KO mouse hearts compared to heterozygous (Het) and WT mice. Confocal microscopy further elicited diminished nebulette expression and perturbed distribution in myocardial sections as well as isolated cardiomyocytes from KO mice. Echocardiography showed a deterioration of cardiac function in KO mice starting from 6 weeks of age to one year of age, which were characterized by reduced fractional shortening and MV E/A, increased LV diastolic dimension as compared with age-matched WT mice. KO mice showed tachycardia and lower QRS voltage at one year of age compared to WT and Het mice. KO hearts revealed increased fibrosis, sarcomere disorganization, enlarged t-tubules and less apparent M-lines. Western blot demonstrated reduced cardiac TnT and increased TnI levels in the KO mice whereas desmin, actin and cardiac ankyrin repeat protein (CARP) remained comparable between the genotypes. Conclusions: Taken together, these data provide evidence for the critical role of nebulette in maintaining cardiac structure and function. Further data that provides mechanistic insight will be presented.