Abstract 292: Mitochondrial CLIC4 and CLIC5B Mediate Cardio-protection From Ischemia/reperfusion Injury

Abstract

Mitochondria are important for regulating myocardial physiology, cardiac function and cardio-protection from ischemia/reperfusion injury (IR). Cation channels like BK Ca and K ATP present in the cardiac mitochondria are important in reducing myocardial infarction (MI) upon IR injury. Mitochondrial anion channels are equally important as they regulate cell volume, maintain ionic homeostasis during ischemia and are considered as potential therapeutics for cardiac diseases. However, molecular identity of cardiac mitochondrial chloride channels is not yet elucidated. In this study we focus on unique class of dimorphic ion channels known as chloride intracellular channels (CLICs). Amongst the six paralogs in mammals, we found that CLIC1, CLIC4 and CLIC5 are abundant in heart isolated from R. norvegicus . CLIC4 and CLIC5 localize to the mitochondria whereas CLIC1 in endoplasmic reticulum. CLIC4 and CLIC5 localized to the outer and inner mitochondrial membrane (IMM), respectively, and modulate mitochondrial calcium retention capacity and reactive oxygen species (ROS) production. Interestingly, a splice variant CLIC5B predominantly present in the heart of R. norvegicus was responsible for IMM localization and its function. We also observed that CLICs are cardioprotective as blocking them with its inhibitor IAA-94 increased MI both in in vitro and in vivo IR injury assays . In addition, we performed left main descending coronary artery (LCA) occlusion in clic -/- and wild type (Wt) mice to induce IR injury. LCA was occluded for 40 min prior to 24 h of reperfusion. MI was significantly higher in clic4 -/- mice as compared to Wt mice (58±6 vs 42±2, n≥4, p≤0.05). Only 75% (3 of 4) of clic4 -/- mice showed significant reduction in left ventricular ejection (LVEF) fraction and fractional shortening (LVFS) after in vivo IR injury. Interestingly, 50% (3 of 6) of clic5 -/- mice showed significant increased MI as well as decreased LVEF and LVFS after in vivo IR injury. Clic1 -/- mice showed similar MI and left ventricular function as Wt mice. In conclusion, we demonstrate that cardiac mitochondrial CLIC4 and CLIC5 are vital for cardioprotection from IR injury likely by maintaining the calcium homeostasis and ROS generation by the mitochondria, respectively.