Abstract 306: Endothelial Arnt Mediates Cardiac Remodeling After Ischemia Reperfusion Injury Through an MMP Pathway

Abstract

Background: Prevention of myocardial injury following heart attack is a challenge due to lack of effective treatments and the potential to develop chronic heart failure (HF). Impaired endothelial function is thought to contribute to the progression of HF after cardiac ischemia-reperfusion injury (IR). However, the underlying mechanisms are unknown. Aryl Hydrocarbon Receptor Nuclear Translocator (ARNT), also known as hypoxia-inducible factor 1-beta (HIF1-β), plays a major role in vascular endothelial function and is implicated in ischemic diseases. We hypothesize that endothelial ARNT mediates cardiac remodeling following IR. Methods and Results: We generated inducible endothelial specific ARNT knockout mice (ecARNT -/- ) by crossing mice with loxP sequences flanking exon 6 of ARNT with Cre ERT2 mice under the VE-cadherin promoter. A 90% deletion of ecARNT was achieved following two weeks of oral tamoxifen administration. ecARNT -/- mice exhibit severe cardiac blood vessel leakage and impaired cardiac function after IR. Following 1 month of IR, ecARNT -/- mice had a 50% mortality rate, while no mortality was observed in the control group (ARNTf/f mice treated with tamoxifen). To determine the underlying mechanisms by which ARNT regulates endothelial function, we performed DNA sequencing on cardiac microvascular endothelial cells (CMECs) isolated from control and ecARNT -/- hearts. Data suggest a significant increase in the matrix metalloproteinases (MMP) family of proteins following ARNT knockdown. An increase in MMP activity in the serum of ecARNT -/- CMECs after IR was also detected. Moreover, use of an MMP inhibitor in vivo rescues heart failure induced by IR in ecARNT -/- mice. Taken together, these results suggest that ecARNT may mediate heart failure during IR through an MMP pathway. Conclusion: Endothelial ARNT is a critical regulator of endothelial function and could potentially serve as a therapeutic target for HF in response to IR injury.