Hypertrophy-Reduced Autophagy Causes Cardiac Dysfunction by Directly Impacting Cardiomyocyte Contractility.

Cardiac remodeling and contractile dysfunction are leading causes in hypertrophy-associated heart failure (HF), increasing with a population's rising age. A hallmark of aged and diseased hearts is the accumulation of modified proteins caused by an impaired autophagy-lysosomal-pathway. Although, autophagy inducer rapamycin has been described to exert cardioprotective effects, it remains to be shown whether these effects can be attributed to improved cardiomyocyte autophagy and contractility. In vivo hypertrophy was induced by transverse aortic constriction (TAC), with mice receiving daily rapamycin injections beginning six weeks after surgery for four weeks. Echocardiographic analysis demonstrated TAC-induced HF and protein analyses showed abundance of modified proteins in TAC-hearts after 10 weeks, both reduced by rapamycin. In vitro, cardiomyocyte hypertrophy was mimicked by endothelin 1 (ET-1) and autophagy manipulated by silencing Atg5 in neonatal cardiomyocytes. ET-1 and siAtg5 decreased Atg5-Atg12 and LC3-II, increased natriuretic peptides, and decreased amplitude and early phase of contraction in cardiomyocytes, the latter two evaluated using ImageJ macro Myocyter recently developed by us. ET-1 further decreased cell contractility in control but not in siAtg5 cells. In conclusion, ET-1 decreased autophagy and cardiomyocyte contractility, in line with siAtg5-treated cells and the results of TAC-mice demonstrating a crucial role for autophagy in cardiomyocyte contractility and cardiac performance.

Selective Mineralocorticoid Receptor Cofactor Modulation as Molecular Basis for Finerenone's Antifibrotic Activity.

Mineralocorticoid receptor antagonists (MRAs) reduce morbidity and mortality in chronic heart failure. Novel nonsteroidal MRAs are currently developed and need to be pharmacologically characterized in comparison to classical steroidal MRAs. A mouse model of cardiac fibrosis induced by short-term isoproterenol injection was used to compare the nonsteroidal MRA finerenone and the steroidal MRA eplerenone in equi-efficient systemic MR blocking dosages. Molecular mechanisms were studied in MR-expressing H9C2/MR+ cardiomyocytes and in MR transcriptional cofactor binding assays. Both MRAs significantly inhibited an isoproterenol-mediated increase of left ventricular mass. Isoproterenol-induced cardiac fibrosis and macrophage invasion were potently blocked by finerenone, whereas eplerenone had no significant effect. Speckle tracking echocardiography revealed a significant improvement of global longitudinal peak strain by finerenone, an effect less prominent with eplerenone. Antifibrotic actions of finerenone were accompanied by a significant inhibition of profibrotic cardiac TNX (tenascin-X) expression, a regulation absent with eplerenone. Finally, we show a higher potency/efficacy and inverse agonism of finerenone versus eplerenone in MR transcriptional cofactor binding assays indicating differential MR cofactor modulation by steroidal and nonsteroidal MRAs. This study demonstrates that the nonsteroidal MRA finerenone potently prevents cardiac fibrosis and improves strain parameters in mice. Cardiac antifibrotic actions of finerenone may result from the inhibition of profibrotic TNX gene expression mediated by differential MR cofactor binding. Selective MR cofactor modulation provides a molecular basis for distinct (pre)-clinical actions of nonsteroidal and steroidal MRAs.

Application of Speckle-Tracking Echocardiography in an Experimental Model of Isolated Subendocardial Damage.

BACKGROUND: The subendocardium is highly vulnerable to damage and is thus affected even in subclinical disease stages. Therefore, methods reflecting subendocardial status are of great clinical relevance for the early detection of cardiac damage and the prevention of functional impairment. The aim of this study was to investigate the potential ability of myocardial strain parameters to evaluate changes within the subendocardium. METHODS: Male 129/Sv mice were injected with isoproterenol (ISO; n = 32) to induce isolated subendocardial fibrotic lesions or saline as appropriate control (n = 15). Transthoracic echocardiography was performed using a 30-MHz linear-frequency transducer coupled to a high-resolution imaging system, and acquired images were analyzed for conventional and strain parameters. The degree of collagen content within the different cardiac layers was quantified by histologic analysis and serum levels of tissue inhibitor of metalloproteinase-1, a biomarker for fibrosis, were assessed. RESULTS: ISO treatment induced a marked increase in subendocardial collagen content in response to cell loss (control vs ISO, 0.6 ± 0.3% vs 5.8 ± 0.9%; P < .001) and resulted in a moderate increase in left ventricular wall thickness with preserved systolic function. Global longitudinal peak strain (LS) and longitudinal strain rate were significantly decreased in ISO-treated animals (LS, -15.49% vs -11.49% [P = .001]; longitudinal strain rate, -4.81 vs -3.88 sec-1 [P < .05]), whereas radial and circumferential strain values remained unchanged. Global LS was associated with subendocardial collagen content (r = 0.46, P = .01) and tissue inhibitor of metalloproteinase-1 serum level (r = 0.52, P < .05). Further statistical analyses identified global LS as a superior predictor for the presence of subendocardial fibrosis (sensitivity, 84%; specificity, 80%; cutoff value, -14.4%). CONCLUSION: Assessment of LS may provide a noninvasive method for the detection of subendocardial damage and may consequently improve early diagnosis of cardiac diseases.