Abstract 12177: Important Roles of Endothelial Caveolin-1/eNOS Complex in Maintaining Microvascular Homeostasis Through Endothelium-dependent Hyperpolarization Mediated Mechanism

Abstract

Background: The endothelium plays important roles in maintaining cardiovascular homeostasis by synthesizing and releasing several vasodilators, including prostacyclin (PGI2), nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) factor. It is widely accepted that EDH plays important roles especially in microcirculation. We have previously demonstrated that endothelial NO synthase (eNOS) plays diverse roles depending on vessel size, as a NO generating system in conduit arteries and an EDH-mediated system in resistance arteries. Recently, we also have reported that caveolin-1 is involved in enhanced EDH-mediated mechanisms in resistance arteries through functional inhibition of eNOS. However, the detailed functions of caveolin-1 in the endothelium remain to be elucidated. Material and Results: We newly generated endothelium-specific caveolin-1-knockout mice (eCav-1-KO) under the control of Tie2 promoter. We confirmed that caveolae is absent in endothelial cells of those mice. Co-immunoprecipitation experiments showed the eNOS/Cav-1 complex formation in control mice, but not in eCav-1-KO mice. Western blot experiments demonstrated that the extent of eNOS phosphorylation at Ser1177 (stimulatory site) was comparable, whereas that at Thr495 (inhibitory site) was significantly reduced in mesenteric arteries from eCav-1-KO mice as compared with control mice, demonstrating hyperactivation of eNOS. Isometric tension experiments and Langendorff experiments showed that NO-mediated responses were significantly enhanced, whereas EDH-mediated responses were significantly reduced in microcirculations in eCav-1-KO mice. Importantly, eCav-1-KO mice showed altered endothelial functions and cardiac hypertrophy despite normal blood pressure level. Furthermore, the hearts from eCav-1-KO mice showed enhanced staining for nitrotyrosine, a marker of nitrosative stress in microvessels and epicardial arteries, whereas those from control mice only showed mild staining in epicardial arteries alone. Conclusions: These results indicate that endothelial Cav-1/eNOS complex plays important roles in maintaining microvascular homeostasis through EDH-mediated mechanisms in mice in vivo.