Project description:BACKGROUND: Cardiac hypertrophy compensates for increased biomechanical stress of the heart induced by prevalent cardiovascular pathologies, but can result in cardiac failure if left untreated. We hypothesized that the tail-anchored protein Dysferlin with multiple Ca2+-binding C2-domains is critical for the integrity of the transverse-axial tubule (TAT) network inside cardiomyocytes, and contributes to the proliferation of TAT endomembranes during pressure overload-induced cardiac hypertrophy. OBJECTIVE: To reveal the impact of the membrane fusion and repair protein Dysferlin on TAT network stabilization and proliferation necessary for the hypertrophic growth of cardiomyocytes. METHODS AND RESULTS: Super-resolution light and electron microscopy of mouse cardiomyocytes identified a specific localization of Dysferlin in a vesicular compartment in nanometric proximity to contact sites of the TAT network with the sarcoplasmic reticulum (SR), a.k.a. junctional complexes for Ca2+-induced Ca2+ release. Mass spectrometry was used to characterize the cardiac Dysferlin interactome, thereby identifying a novel protein interaction with the membrane-tethering SR protein Juncophilin-2, a known interactor of L-type Ca2+ channels and Ryanodine Receptor Ca2+ release channels in junctional complexes. While the Dysferlin knockout caused a mild progressive phenotype of dilated cardiomyopathy in the mouse heart, global proteome analysis revealed changes preceding systolic failure. Following transverse aortic constriction (TAC), Dysferlin protein expression was significantly increased in hypertrophied wild-type myocardium, while Dysferlin knockout animals presented markedly reduced left-ventricular hypertrophy. Live-cell membrane imaging demonstrated a profound reorganization of the TAT network in wild-type left-ventricular myocytes post-TAC with robust proliferation of axial tubules, which critically depended on the increased expression of Dysferlin within newly-emerging tubule components. CONCLUSIONS: Dysferlin represents a new molecular target in cardiac disease that protects the integrity of tubule-SR junctional complexes for regulated excitation-contraction coupling, and controls TAT network reorganization and tubular membrane proliferation in cardiomyocyte hypertrophy induced by pressure-overload.

Project description:Aims: Cardiomyocyte-specific nitric oxide synthase 3 (NOS3) overexpression reduces left ventricular (LV) remodelling after myocardial infarction in mice, but its effect on sustained LV pressure-overload remains incompletely understood. We investigated LV structural and functional adaptation to elevated afterload in mice with cardiomyocyte-restricted NOS3 overexpression (NOS3TG) and wild type littermates (WT). Methods and Results: Hemodynamic indices, cardiac hypertrophy and interstitial fibrosis were measured 10 weeks after transverse aortic constriction (TAC). After 10 weeks TAC, NOS3TG had better preserved systolic function (maximum rates of pressure development normalized to maximal pressure 77Â±6 versus 65Â±2 ms-1, P=0.05), reduced heart weight-body weight ratio (HW/BW, 5.0Â±0.3 versus 5.8Â±0.1, P<0.05), and cardiomyocyte width than WT (14.9Â±0.4 vs 16.7Â±0.2 ?m, P<0.05). After 10 weeks TAC, a 44k cDNA chip-based microarray analysis was validated using real time PCR and revealed significantly altered expression pattern of genes involved in cellular growth, matrix remodelling, and inflammation between genotypes. Conclusions: Cardiomyocyte-restricted NOS3 overexpression attenuates TAC-induced hypertrophy via autocrine inhibition of cardiomyocyte cell growth, but does not mitigate myocardial fibrosis. The subsequent diastolic dysfunction suggests that inhibition of matrix producing cells during hypertrophic stress is necessary to prevent functional and structural deterioration of the pressure-overloaded heart. Left ventricular mRNA expression profiles were compared between alpha-myosin heavy chain driven nitric oxide synthase 3 (alpha-MHC-NOS3) transgenic and wild type (WT) littermate mice at baseline and 10 weeks after transversal aortic constrcition-induced pressure-overload. Biological repeats: n=4, two males and two females, for each group and condition. Transgenic mice were backcrossed for seven generations (F7) to a C57Bl/6 N background and age and weight matched animals were used for microarray experiments.

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Disruption of Actin Dynamics Regulated by Rho Effector mDia1 Attenuates Pressure Overload-Induced Cardiac Hypertrophic Responses and Exacerbates Dysfunction

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