Ca2+-regulated Lysosome Fusion Mediates Angiotensin II-induced Lipid Raft Clustering in Mesenteric Endothelial Cells

It has been reported that intracellular Ca 2+ is involved in lysosome fusion and membrane repair in skeletal cells. Given that angiotensin II (Ang II) elicits an increase in intracellular Ca 2+ and that lysosome fusion is a crucial mediator of lipid raft (LR) clustering, we hypothesized that Ang II induces lysosome fusion and activates LR formation in rat mesenteric endothelial cells (MECs). We found that Ang II acutely increased intracellular Ca 2+ content, an effect that was inhibited by the extracellular Ca 2+ chelator ethylene glycol tetraacetic acid (EGTA) and the inositol 1,4,5-trisphosphate (IP3)-induced Ca 2+ release inhibitor 2-aminoethoxydiphenyl borate (2-APB). Further study showed that EGTA almost completely blocked Ang II-induced lysosome fusion, the translocation of acid sphingomyelinase (ASMase) to LR clusters, ASMase activation and NADPH (nicotinamide adenine dinucleotide phosphate) oxidase activation. In contrast, 2-APB had a slight inhibitory effect. Functionally, both the lysosome inhibitor bafilomycin A1 and the ASMase inhibitor amitriptyline reversed Ang II-induced impairment of vasodilation. We conclude that Ca 2+ -regulated lysosome fusion mediates the Ang II-induced regulation of the LR-redox signaling pathway and mesenteric endothelial dysfunction.