Interaction between Caveolin‐1 and eNOS preserves NO synthesis by maintaining the availability of the eNOS cofactor BH4

Caveolin‐1 (Cav‐1) interacts with endothelial NO synthase (eNOS) and may exert a negative modulatory effect on eNOS. However, Cav‐1 knockout (CavKO) mice exhibit reduced vascular synthesis of NO. We tested the hypothesis that Cav1‐eNOS interaction in the caveolae prevents oxidation of the eNOS cofactor BH 4 , and thereby preserves stimulated NO synthesis, even if vessels are exposed to metabolic/oxidative stress. Acetylcholine (ACh)‐induced relaxation of aortic rings were studied in wild type (WT) and CavKO mice. CavKO mice exhibited a reduced ACh‐induced relaxation (39±2% vs 70±5% of WT), which in contrast to WT responses were not affected by the NOS inhibitor, L‐NAME. Incubation with Tiron (superoxide scavenger) restored ACh‐induced aortic relaxation in CavKO mice (75±12%) but had no effect on WT vessels. Sepiapterin, a BH 4 precursor, also restored ACh‐induced relaxation in CavKO mice (75±10%). When mice were fed a high fat diet (60% fat for 15 weeks, HFD) ACh‐induced relaxation was preserved in WT mice (61±4%) but was markedly reduced in Cav‐KO mice (30±5%). In HFD animals Tiron or Sepiapterin enhanced relaxation to ACh in CavKO but not in WT mice. In normal conditions, and particularly during metabolic/oxidative stress, Cav‐1‐eNOS interaction seems important in preserving NO synthesis, likely via preventing oxidation of the eNOS cofactor BH 4 . (Supported by NIH HL104126, PO1HL43023 and BHF RE/08/004)