Abstract 10230: Sestrin2 Plays an Essential Role in Regulating the Unfolded Protein Response During Cardiac Ischemia/Reperfusion and Preventing Excessive Myocardial Apoptosis

Abstract

Introduction: Cardiac ischemia/reperfusion (I/R) alters cellular redox and calcium homeostasis, causing protein-folding errors in the endoplasmic reticulum (ER) which activates the unfolded protein response (UPR). Although appropriate UPR is an adaptive response of the cell, excessive and prolonged UPR can cause cellular apoptosis and aggravate I/R injury. We showed that Sestrin2 (Sesn2) regulates AMP-activated protein kinase (AMPK) activity and acts as an endogenous inhibitor of the mammalian target of rapamycin complex 1 (mTORC1) to modulate protein synthesis and autophagy in the heart. Hypothesis: We hypothesized that Sesn2 regulates activation of UPR and maintains ER homeostasis as a protective response during myocardial I/R. Methods: Ligation and release of the left anterior descending coronary artery (LAD) was performed in wild-type (WT) C57BL/6J and cardiac specific Sesn2 knock out (KO) mice to induce myocardial I/R injury (45’ ischemia with different time of reperfusion). Results: I/R induced UPR in a time-dependent manner, reaching its peak 6 hours post reperfusion, and returning to normal values after 24 hours of reperfusion in WT mice. Pharmacological inhibition of the UPR by 4-phenylbutyrate (100mg/kg, i.p.) after reperfusion attenuated myocardial infarction size and restored systolic function. Conversely, genetic ablation of cardiac-specific Sesn2 was associated with increased myocardial infarction of 49.4%, and decreased systolic function of 22.9%, compared to WT mice. Molecular analysis showed that cardiac Sesn2 deficiency resulted in greater and prolonged activation of the UPR, and increased myocardial apoptosis compared to WT mice. Furthermore, activation of mTORC1 pathway after I/R was more pronounced and prolonged in cardiac-specific Sesn2 KO hearts, whereas AMPK activity post reperfusion was similar in both groups. Inhibiting mTORC1 with rapamycin (3mg/kg, i.p.) after I/R reduced myocardial apoptosis in a similar fashion in WT and cardiac-specific Sesn2 KO mice. Conclusions: During I/R, regulation of mTORC1 signaling pathway by Sesn2 may be a key factor for maintaining ER homeostasis and reducing I/R-induced apoptosis and cardiac injury.