Abstract 144: Increased CaMKII Activity in Hypertensive Vascular Endothelium

Abstract

The Ca2+-calmodulin dependent protein kinase II (CaMKII) plays a prime role in the development of cardiovascular diseases including heart failure and diabetes-associated vasculopathies. The multifunctional kinase can promote the genesis or sustainment of cardiovascular pathological conditions. Although the role of cardiac CaMKII is well established, literature on endothelial CaMKII is only emerging. Recent studies showed that CaMKII activation could alter expression and activity of enzymes such as eNOS suggesting that CaMKII might be involved in endothelial dysfunction. A better understanding of CaMKII signalling will lead to the improvement of cardiovascular therapies. CaMKII act as a Ca2+ sensor by its ability to decode oscillatory Ca2+ signalling through complex autophosphorylation steps. Such oscillatory Ca2+ signalling has only recently been reported in endothelium, the Ca2+ pulsars. The Ca2+ pulsars might represent a novel and distinctive activation mechanism for endothelial CaMKII. This study is aimed to elucidate the correlation between endothelial Ca2+ dynamics and CaMKII activity in microvasculature. PCR experiments showed that all four mammalian CaMKII isoforms are expressed in small murine mesenteric arteries but only variant 1 of CaMKIIβ have been identified. However, confocal microscopy revealed that only CaMKIIα, β and δ can be found in endothelial cells and only δ and γ in vascular myocytes. Moreover, α and β specifically converged at Ca2+ pulsar sites and stimulation of Ca2+ pulsars increased CaMKII clustering. Activated CaMKII (T286) also showed similar distribution. These evidences suggest that Ca2+ pulsars activate CaMKII. Our results showed that spontaneous Ca2+ pulsars are increased (54%) in arterial hypertension (AH) and can stimulate basal CaMKII activity. Indeed, CaMKII clustering is increased in AH (2 fold). However, an inverse correlation between CaMKIIβ expression and blood pressure was established (r2=0.6760), suggesting that blood pressure significantly alters expression of the kinase. This study demonstrates that CaMKII activity and expression is significantly modulated in hypertension and provides evidences that CaMKII represent an interesting therapeutic approach for vascular pathologies.