Hepatocyte retinoid X receptor alpha-dependent regulation of lipid homeostasis and inflammatory cytokine expression contributes to alcohol-induced liver injury.
Hepatocyte retinoid X receptor alpha (RXRalpha)-deficient mice are more sensitive to ethanol toxicity than wild-type mice. Because RXRalpha-mediated pathways are implicated in lipid homeostasis and the inflammatory response, we hypothesized that a compromise in lipid metabolism and associated production of proinflammatory mediators are responsible for the hepatotoxicity observed in ethanol-treated hepatocyte RXRalpha-deficient mice. Wild-type and hepatocyte RXRalpha-deficient mice were fed ethanol-containing diets or pair-fed control diets for 6 weeks. After ethanol treatment, serum ALT levels increased significantly (4-fold) in hepatocyte RXRalpha-deficient mice, but not in the wild-type mice. Hepatic liver fatty acid binding protein (L-FABP) mRNA and protein levels were reduced due to RXRalpha deficiency. Ethanol induced L-FABP mRNA and protein in wild-type mice and provided protection against nonesterified fatty acid toxicity; however, this effect was absent in the mutant mice. Accordingly, hepatic nonesterified fatty acid level was increased in ethanol-fed mutant mice. Ethanol increased nuclear factor (NF)-kappaB binding activity in hepatocyte RXRalpha-deficient mice, but not in wild-type mice. In agreement, hepatic mRNA levels of proinflammatory cytokines and chemokines were increased to a greater extent in the mutant than in wild-type mice. Furthermore, signal transducer and activator of transcription factor (STAT) 3 and associated Bcl-xL induction was observed in ethanol-fed wild-type mice but not in ethanol-fed hepatocyte RXRalpha-deficient mice. Taken together, after ethanol treatment, hepatocyte RXRalpha deficiency results in lack of L-FABP induction, increased hepatic free fatty acids, NF-kappaB activation, and proinflammatory cytokines production and a lack of STAT3 activation, which in part may contribute to alcohol-induced liver damage.
Gyamfi
Maxwell Afari
MA
Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160-7417, USA.
He
Lin
L
French
Samuel William
SW
Damjanov
Ivan
I
Wan
Yu-Jui Yvonne
YJ
D000818:Animals; D016207:Cytokines / Q000096:biosynthesis* / Q000235:genetics; D000431:Ethanol / Q000008:administration & dosage*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D007249:Inflammation / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008055:Lipids / Q000502:physiology*; D008108:Liver Diseases, Alcoholic / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D047490:Retinoid X Receptor alpha / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
D016207:Cytokines; D008055:Lipids; D047490:Retinoid X Receptor alpha; D000431:Ethanol