LPS inhibits endothelin‐1–induced endothelial NOS activation in hepatic sinusoidal cells through a negative feedback involving caveolin‐1†

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Abstract
During endotoxemia, liver microcirculation disruption is characterized by a hypersensitivity to the constrictor effects of endothelin 1 (ET-1). The shift of ET-1–mediated effects toward vasoconstriction may result from depressed ET-1–mediated vasodilation through decreased ET-1–induced nitric oxide (NO) production. We have previously shown that lipopolysaccharide (LPS) pretreatment abrogates ET-1–induced endothelial nitric oxide synthase (eNOS) translocation, but its effects on eNOS activation are yet to be determined. Our aim was to assess the effects of LPS on ET-1–mediated eNOS activation in hepatic sinusoidal endothelial cells (SECs) and to investigate the molecular mechanisms involved. SECs were treated with LPS (100 ng/mL) for 6 hours followed by 30 minutes ET-1 (10 nmol/L) stimulation. LPS significantly inhibited ET-1–mediated eNOS activation. This inhibition was associated with upregulation of Caveolin-1 (CAV-1) and a shift in ET-1–mediated eNOS phosphorylation from an activation (Ser1177) to an inhibition (Thr495). LPS treatment has been shown to induce ET-1 expression and secretion from endothelial cells. We therefore investigated the role of endogenous ET-1 in the inhibition of ET-1 activation of eNOS after LPS. Antagonizing ET-1 effects and blocking its activation in LPS pretreated SECs decreased the LPS-induced overexpression of CAV-1 as well as the inhibition of ET-1–induced NOS activity. Furthermore, 6 hours of ET-1 treatment exerted the same effects on eNOS activity, phosphorylation, and CAV-1 expression as LPS treatment. In conclusion, LPS-induced suppression of ET-1–mediated eNOS activation is ET-1 dependent and suggest a pivotal role of CAV-1 in eNOS induction inhibition under stress. (HEPATOLOGY 2006;43:182–190.)