Role of AMPK in Determining the Mediator of Flow Induced Dilation in the Human Microvasculature

Abstract

An important measure of microvascular endothelial function is flow-induced dilation (FID), the ability of an arteriole to dilate in response to increased flow. In healthy adults, FID is predominantly mediated by endothelial-derived nitric oxide (NO), a vasoactive compound with anti-inflammatory properties. In microvessels from patients with coronary artery disease (CAD), FID occurs via formation and release of hydrogen peroxide (H2O2), a pro-inflammatory vasoactive mediator. We have previously shown that exogenous adiponectin restores NO-mediated FID in CAD arterioles, however the mechanism remains unknown. Because AMP kinase (AMPK), a downstream target of adiponectin receptors, increases cellular NO, we hypothesized that inhibition of AMPK would promote H2O2 as the mediator of FID in arterioles from healthy, nonCAD subjects. Human microvessels (80-200µm) were dissected from discarded surgical adipose specimens, cannulated onto micropipettes and pressurized. Arterioles were pre-constricted with endothelin-1 and changes in vessel wall diameter were measured during graded increases in flow using videomicroscopy. FID was observed in healthy arterioles treated with the AMPK inhibitor, Compound C (1µM, 16hrs) in the presence of the NO scavenger c-PTIO (100µM) (77.9 % max dilation ± 6, n=3), as well as with the H2O2 degradation enzyme PEG-Catalase (500U), (62.4% max dilation ±15, n=3). Interestingly, FID was suppressed only in the presence of both c-PTIO and PEG-Catalase (42.1% max dilation ±16, n=3) compared to controls (69.4% max dilation ±6, n=3). Together, these data may suggest that NO and H2O2 compensate for loss of one another during inhibition of AMPK. Future studies will investigate whether adiponectin-induced restoration of NO requires activation of AMPK as thorough understanding of this pathway during FID is critical for understanding the mechanism by which adiponectin improves microvascular endothelial function during disease.