ERβ (oestrogen receptor β) activation has been shown to be cardioprotective, but the cell types and mechanisms involved are not understood. To investigate whether ERβ restricted to cardiomyocytes contributes to the observed cardioprotection, we tested the effects of cardiomyocyte-specific ERβ-OE (ERβ overexpression) on survival, cardiac remodelling and function after MI (myocardial infarction) and studied the molecular pathways potentially involved. Female and male mice with cardiomyocyte-specific ERβ-OE and WT (wild-type) littermates were subjected to chronic anterior coronary artery ligation or sham surgery. Two weeks after MI, ERβ-OE mice showed improved survival (100% and 83% compared with 76% and 58% in WT females and males respectively). ERβ-OE was associated with attenuated LV (left ventricular) dilatation, smaller increase in heart weight, less lung congestion at similar MI size, and improved systolic and diastolic function in both sexes. We identified two potential pathways for ERβ-mediated myocardial protection. First, male and female ERβ-OE mice had a lower reduction of SERCA2a (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 2a) expression after MI, suggesting less reduction in diastolic Ca2+-reuptake into the sarcoplasmic reticulum post-MI. Secondly, male ERβ-OE revealed attenuated cardiac fibrosis in the remote LV tissue and expression of fibrosis markers collagen I and III, periostin and miR-21. Cardiomyocyte-specific ERβ-OE improved survival associated with reduced maladaptive remodelling, improved cardiac function and less heart failure development after MI in both sexes. These effects seem to be related, at least in part, to a better maintenance of Ca2+ cycling in both sexes and a lower induction of cardiac fibrosis in males after MI.

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