MicroRNA‐17‐3p protects against excessive posthypoxic autophagy in H9C2 cardiomyocytes via PTEN–Akt–mTOR signaling pathway

The activity of phosphatase and tensin homolog (PTEN) can be inhibited by miR‐17‐3p, which results in attenuating myocardial ischemia/reperfusion injury (IRI), however, the mechanism behind this phenomenon is still elusive. Suppression of PTEN leads to augmented protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling strength and constrained autophagy activation, which might be the one mechanism for the ameliorated myocardial IRI. Thus, we tested the hypothesis that miR‐17‐3p attenuated hypoxia/reoxygenation (H/R)‐mediated damage in cardiomyocytes by downregulating excessive autophagy via the PTEN–Akt–mTOR axis. The expression of miR‐17‐3p was remarkably increased after H/R treatment (6‐h hypoxia followed by 6‐h reoxygenation; H6/R6), which was concomitant with the increase of the release of lactic acid dehydrogenase (cell injury marker) and the enhancement LC3II/I ratio (autophagy markers) in H9C2 cardiomyocytes. Ectoexpression of miR‐17‐3p agomir led to remarkable augmentation of miR‐17‐3p expression and evidently attenuated H/R‐mediated cell damage and excessive autophagy. Furthermore, an increase in miR‐17‐3p expression elicited constrained phosphorylation of PTEN (Ser380) while enhanced the phosphorylation of Akt (Thr308, Ser473) and mTOR (Ser536) after H/R stimulation. In addition, pretreatment with LY‐294002 (an Akt selective inhibitor) and rapamycin (an mTOR selective inhibitor) significantly abrogated the protective function of miR‐17‐3p on H/R‐mediated cell damage and autophagy in H9C2 cardiomyocytes. Taken together, these observations indicated that the enhancement of the PTEN/Akt/mTOR axis and the consequent suppression of autophagy overactivation might represent an underlying mechanism by which miR‐17‐3p attenuated H/R‐mediated damage in H9C2 cells.