Cardiomyocyte-specific knockout of endothelin receptor a attenuates obesity cardiomyopathy

Endothelin (ET)-1 is implicated in the pathophysiology of cardiovascular diseases although its role in obesity anomalies has not been fully elucidated. This study was designed to examine the impact of ET-1 receptor A (ET_A) ablation on obesity-induced changes in cardiac geometry and contractile function, as well as the mechanisms involved with a focus on autophagy. Cardiomyocyte-specific ET_A receptor knockout (ETAKO) and WT mice were fed either low-fat (10% calorie from fat) or high-fat (45% calorie from fat) diet for 24 weeks. Glucose tolerance test was examined to confirm insulin resistance. High-fat diet intake compromised myocardial geometry (enlarged left ventricular diameters in systole and diastole), morphology (cardiac hypertrophy, increased wall thickness and interstitial fibrosis), contractile function (reduced fractional shortening, ejection fraction and cardiomyocyte shortening) and intracellular Ca²⁺ handling, the effect of which was significantly attenuated by ETAKO. TUNEL staining revealed overt apoptosis in high-fat-fed group, the effect was reverted by ETAKO. Western blot analysis noted that high-fat intake downregulated leptin receptor and PPARγ, insulin signaling (elevated basal/dampened insulin-stimulated phosphorylation of Akt and IRS1), phosphorylation of AMPK, ACC, upregulated GATA-4, ANP, NFATc3, PPARα, m-TOR/p70s6k signaling, which were attenuated by ETAKO with the exception of AMPK/ACC. Furthermore, high-fat intake suppressed cardiac autophagy, which was abrogated by ETAKO. In cultured murine cardiomyocytes, palmitic acid challenged mimicked high-fat diet-induced hypertrophic and autophagic responses, the effect of which were abolished by the ET_A receptor antagonist BQ123 or mTOR inhibitor rapamycin. These results suggest that inhibition of ET_A rescues high-fat intake-induced cardiac anomalies possibly through autophagy regulation.