Native low-density lipoprotein induces endothelial nitric oxide synthase dysfunction: role of heat shock protein 90 and caveolin-1
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Although native LDL (n-LDL) is well recognized for inducing endothelial cell (EC) dysfunction, the mechanisms remain unclear. One hypothesis is n-LDL increases caveolin-1 (Cav-1), which decreases nitric oxide (*NO) production by binding endothelial nitric oxide synthase (eNOS) in an inactive state. Another is n-LDL increases superoxide anion (O(2)(*-)), which inactivates *NO. To test these hypotheses, EC were incubated with n-LDL and then analyzed for *NO, O(2)(*-), phospho-eNOS (S1179), eNOS, Cav-1, calmodulin (CaM), and heat shock protein 90 (hsp90). n-LDL increased NOx by more than 4-fold while having little effect on A23187-stimulated nitrite production. In contrast, n-LDL decreased cGMP under basal and A23187-stimulated conditions and increased O(2)(*-) by a mechanism that could be inhibited by L-nitroargininemethylester (L-NAME) and BAPTA/AM. n-LDL increased phospho-eNOS by 149%, eNOS by approximately 34%, and Cav-1 by 28%, and decreased the association of hsp90 with eNOS by 49%. n-LDL did not appear to alter eNOS distribution between membrane fractions (approximately 85%) and cytosol (approximately 15%). Only 3-6% of eNOS in membrane fractions was associated with Cav-1. These data support the hypothesis that n-LDL increases O(2)(*-), which scavenges *NO, and suggest that n-LDL uncouples eNOS activity by decreasing the association of hsp90 as an initial step in signaling eNOS to generate O(2)(*-).
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