AMP‐Activated Protein Kinase (AMPK) Modulates Myoendothelial Junctions (MEJ) in Murine Microvessels

Abstract

Myoendothelial junctions (MEJ) in microvessels are not only the site of direct cell communication via gap junctions but also represent a signaling microdomain critical for regulating vascular processes such as endothelium dependent hyperpolarization (EDH). The 5′‐adenosine monophosphate‐activated protein kinase (AMPK) has been shown to influence vascular tone. It has not yet been studied, however, whether AMPK could also affect MEJ. Thus, the aim of this project was to elucidate the impact of AMPK on MEJ dynamics and its potential mechanism of action.We studied isolated small mesenteric and skeletal muscle resistance arteries of mice using a pressure myograph system developed in our laboratory. Using confocal and two photon excitation fluorescence microscopy we identified the internal elastic lamina, which in these vessels exhibits small holes that allow direct contact between endothelial and smooth muscle cells. On average, we found that in about 35% of the holes, structures with a bright actin core as assessed by using F‐actin fluorescence in LifeAct mice or by staining with phalloidin which we could define as sites of MEJ. These structures showed expression of Cx37 and Cx43 suggesting that gap junctions (MEGJs) were also localized in these structures. Over observation times of up to 2 hours, we found that the number and localization of these MEJ varied, while they always positioned in the area of holes of IEL only. Thus, for the first time we could investigate MEJ dynamics. AMPK negatively regulates MEJ formation, since in AMPK α1, but not α2 knockout (KO) mice, the number of MEJ was significantly increased. In accordance, in wild type mice, incubation with the AMPK inhibitory compound C (CC) significantly augmented the number of MEJ. Furthermore, KO of AMPK α1, in intact mice as well as in cultured human and porcine smooth muscle cells, went along with an increase in PAI‐1 expression. Accordingly, incubation of arteries with exogenous PAI‐1 also increased the number of MEJ. The negative effect of AMPK on PAI‐1 could be explained by enhanced expression of the silencer of the PAI‐1 gene, small heterodimer partner (SHP). Since MEJ are also involved in EDH, we studied whether an enhanced formation of MEJ correlated with the magnitude of EDH induced vasodilation. Indeed, a higher amount of MEJs in α1 KO mice went along with a left shift of acetylcholine (ACh) ‐induced dilation dose effect curve.This work describes for the first time a role of the α1 subunit of AMPK as a potent modulator of MEJ dynamics which is probably mediated by controlling PAI‐1 expression. Our data also for the first time demonstrate a dynamic regulation of MEJ expression in intact blood vessels.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.