Abstract 141: Class I Histone Deacetylases Localize to Cardiac Myocyte Mitochondria and Contribute to Ischemia Reperfusion Injury

Abstract

Approximately half of the damage done to the heart by a myocardial infarction occurs during reperfusion of the ischemic region while the patient is in the care of the treatment team. While many different adjuvant treatments have been explored in an attempt to attenuate this ischemia-reperfusion (I/R) injury, little progress has been made in translating novel therapies to the clinic. Recently, it was discovered that epigenetic enzymes contribute to reperfusion-induced damage, but little is known about the exact mechanism by which they exacerbate I/R injury. Previously, we have shown that class I histone deacetylase (HDACs) activity acutely exacerbates I/R injury, and that inhibition of class I HDACs with MS-275 (entinostat) preserves left-ventricular (LV) function and substantially reduces the area of infarcted tissue in isolated rat hearts subjected to ischemia-reperfusion (IR) injury. Notably, this protective effect occurs whether MS-275 is given as a pretreatment or during the reperfusion phase alone. Given the acute nature of this protective effect, we hypothesized that class I HDACs mediate reperfusion injury by modulating the acetylation state of non-histone proteins in signaling cascades that are essential to cell survival. To examine this, hearts from male Sprague-Dawley rats were subjected to ex vivo I/R injury +/- class I HDAC inhibition during reperfusion. We then performed mass spectrometry to analyze the changes in the acetylome between sham and I/R groups with and without class I HDAC inhibition. Unexpectedly, mass spectrometry analysis revealed significant changes in the acetylation state of multiple mitochondrial enzymes. Further biochemical studies show that class I HDACs localize to cardiac mitochondria and may directly modulate mitochondrial acetylation. Interestingly, these effects are correlated with a reduction in the mitochondrial respiratory capacity and mitochondrial oxidative stress during reperfusion. This study is the first to identify a class I HDAC that localizes to the mitochondria and emphasizes the importance of exploring class I HDAC inhibitors for protection against ischemia-reperfusion injury.