LPS inhibits endothelin-1-induced endothelial NOS activation in hepatic sinusoidal cells through a negative feedback involving caveolin-1.
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.
Kamoun
Walid S
WS
Department of Biology, University of North Carolina, Charlotte, NC 28223, USA.
Karaa
Amel
A
Kresge
Nicole
N
Merkel
Sandra M
SM
Korneszczuk
Katarzyna
K
Clemens
Mark G
MG
D000818:Animals; D051242:Caveolin 1 / Q000032:analysis / Q000502:physiology*; D019332:Endothelin-1 / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005246:Feedback; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D008297:Male; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley
D051242:Caveolin 1; D019332:Endothelin-1; D008070:Lipopolysaccharides; D052250:Nitric Oxide Synthase Type III