Hypercholesterolemia decreases nitric oxide production by promoting the interaction of caveolin and endothelial nitric oxide synthase

Hypercholesterolemia is a central pathogenic factor of endothelial dysfunct ion caused in part by an impairment of endothelial nitric oxide (NO) produc tion through mechanisms that remain poorly characterized. The activity of t he endothelial isoform of NO synthase (eNOS) was recently shown to be modul ated by its reciprocal interactions with the stimulatory Ca2+-calmodulin co mplex and the inhibitory protein caveolin. We examined whether hypercholest erolemia may reduce NO production through alteration of this regulatory equ ilibrium. Bovine aortic endothelial cells were cultured in the presence of serum obtained from normocholesterolemic (NC) or hypercholesterolemic (HC) human volunteers. Exposure of endothelial cells to the HC serum upregulated caveolin abundance without any measurable effect on eNOS protein levels. T his effect of HC serum was associated with an impairment of basal NO releas e paralleled by an increase in inhibitory caveolin-eNOS complex formation. Similar treatment with HC serum significantly attenuated the NO production stimulated by the calcium ionophore A23187. Accordingly, higher calmodulin levels were required to disrupt the enhanced caveolin-eNOS heterocomplex fr om HC serum-treated cells. Finally, cell exposure to the low-density lipopr otein (LDL) fraction alone dose-dependently reproduced the inhibition of ba sal and stimulated NO release, as well as the upregulation of caveolin expr ession and its heterocomplex formation with eNOS, which were unaffected by cotreatment with antioxidants. Together, our data establish a new mechanism for the cholesterol-induced impairment of NO production through the modula tion of caveolin abundance in endothelial cells, a mechanism that may parti cipate in the pathogenesis of endothelial dysfunction and the proatherogeni c effects of hypercholesterolemia.