Abstract 101: Endothelial Arnt Regulates Microvascular Endothelial Barrier Function in Heart Failure Through a Novel Mmp3 Pathway

Abstract

Background: Increased microvascular permeability and cardiac interstitial edema formation are major contributors to progressive myocyte dysfunction during ischemia/reperfusion (IR) injury. Effective clinical therapies for IR injury are lacking, primarily because the mechanisms linking IR to cardiac microvascular permeability and edema are largely unknown. Results from my current studies indicate that vascular permeability is limited by the expression of Aryl Hydrocarbon Receptor Nuclear Translocator (ARNT), a transcription factor that regulates gene expression by homodimerizing or by heterodimerizing with hypoxia-inducible factor (HIF) 1α, HIF2α, or other cofactors. We hypothesize that endothelial ARNT mediates cardiac remodeling following IR. Methods and Results: We have recently generated inducible VE-cadherin-Cre ERT2 endothelial cell (EC)-specific ARNT knockout mice (ecARNT -/- ), which, after ecARNT -/- induction by oral tamoxifen administration, display increased cardiac endothelial permeability with preserved contractile function of the heart. However, after 24 hours of ischemia-reperfusion, ecARNT -/- mice exhibit severe cardiac blood vessel leakage and impaired cardiac function. Following one month of IR, ecARNT -/- mice have a 50% mortality rate, and impaired cardiac function, as determined by EF% and FS%. Only 10% mortality is observed in the control group (ARNTf/f mice treated with tamoxifen). Furthermore, data from microarray analysis show that matrix metalloproteinases (MMPs) are significantly upregulated in ARNT deficient mouse cardiac microvascular endothelial cells (CMVECs), with a particularly significant increase in MMP3. MMP3 can cleave most extracellular matrix constituents and its inhibition attenuates the increase in cell permeability observed in ecARNT -/- CMVECs. Finally, 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 MMP3 pathway. Conclusion: Endothelial ARNT is a critical regulator of endothelial function and could potentially serve as a therapeutic target for heart failure in response to IR injury.