Uncoupling Caveolae From Intracellular Signaling In Vivo Short Communication

C aveolae organelles are flask-shaped invaginations of the plasma membrane implicated in a variety of biological processes, including endocytosis, transcytosis, mechanosens-ing, and signaling. Caveolin-1 (Cav-1) is the main coat protein of caveolae in endothelial cells (EC) and is essential for the formation of caveolae. 4 Despite the critical role of Cav-1 in caveolae assembly, Cav-1 knockout (KO) mice are viable and fertile, but show several cardiovascular and pulmonary phenotypes. Cav-1 KO mice exhibit impaired mechanosignaling and remodeling, myocardial hypertrophy, metabolic imbalances with elevated plasma lipids, pulmonary fibrosis, and hyper-tension and are protected from atherosclerosis. 5–10 The precise mechanisms of how Cav-1 regulates these diverse phenotypes are unknown, and most data are rationalized based on the critical role of Cav-1 in caveolae formation and mechanosignaling or via Cav-1 serving as a scaffolding protein integrating ex-tracellular signaling pathways to intracellular effectors, such as protein kinase A, 11 G protein–coupled receptors, 2,12 Rab5, 13 and endothelial nitric oxide synthase (eNOS). 14 eNOS-derived nitric oxide (NO) in the vascular system is a major regulator of vascular tone and, therefore, blood pressure. eNOS is post-translationally palmitoylated and trafficked to caveolae, 15 where its activity is decreased because of the binding to Cav-1. Domain mapping studies revealed that the aa 82–101 of Cav-1 are critical for Cav-1 interacting with eNOS, 14,16 whereas the aa T90, T91, and in particular F92 play a crucial role in the inhibitory action of this binding. After activation, eNOS is thought to be released from the in-hibitory clamp of Cav-1 and phosphorylated by kinases, including protein kinase B (Akt). 17 HSP90 (heat shock protein 90) and calmodulin binding leads to a fully activated eNOS, 18 resulting in increased NO release. A hallmark of many vascular and pulmonary diseases is a decrease in the NO biogenesis or bioavailability via uncoupling. Therefore, understanding how to selectively activate eNOS could be beneficial. Here, we report that inducible expression of a single point mutant of Cav-1 (Cav-1-F92A) in endothelium decreases sys-tolic blood pressure. The reduction in blood pressure occurs contemporaneously with enhanced levels of NO bioactivity. Moreover, Cav-1-F92A does not interfere with the formation of caveolae or promote pulmonary fibrosis, myocardial dys-function, or hypertrophy, as seen in global Cav-1 KO mice. Objective: This study was designed to separate caveolae formation from its downstream signaling effects. Conclusions: This study shows that mutant Cav-1-F92A forms caveolae structures similar to WT but leads to increases in NO bioavailability …