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Journal of Lipid Research, Vol. 44, 280-295, February 2003 PPARß regulates vitamin A metabolism-related gene expression in hepatic stellate cells undergoing activation
* Laboratory of Molecular Liver Cell Biology, Vrije Universiteit Brussel, 1090 Brussels Belgium
1 To whom correspondence should be addressed. e-mail: khellem{at}minf.vub.ac.be Activation of cultured hepatic stellate cells correlated with an enhanced expression of proteins involved in uptake and storage of fatty acids (FA translocase CD36, Acyl-CoA synthetase 2) and retinol (cellular retinol binding protein type I, CRBP-I; lecithin:retinol acyltransferases, LRAT). The increased expression of CRBP-I and LRAT during hepatic stellate cells activation, both involved in retinol esterification, was in contrast with the simultaneous depletion of their typical lipid-vitamin A (vitA) reserves. Since hepatic stellate cells express high levels of peroxisome proliferator activated receptor ß (PPARß), which become further induced during transition into the activated phenotype, we investigated the potential role of PPARß in the regulation of these changes. Administration of L165041, a PPARß-specific agonist, further induced the expression of CD36, B-FABP, CRBP-I, and LRAT, whereas their expression was inhibited by antisense PPARß mRNA. PPARß-RXR dimers bound to CRBP-I promoter sequences. Our observations suggest that PPARß regulates the expression of these genes, and thus could play an important role in vitA storage. In vivo, we observed a striking association between the enhanced expression of PPARß and CRBP-I in activated myofibroblast-like hepatic stellate cells and the manifestation of vitA autofluorescent droplets in the fibrotic septa after injury with CCl4 or CCl4 in combination with retinol.
Abbreviations: ACS, acyl-CoA synthetase; ARAT, acyl-CoA:retinol acyltransferase; FAT/CD36, FA translocase; CRABP, cellular retinoic acid binding protein; CRBP, cellular retinol binding protein; FABP, fatty acid binding protein; LCFA, long chain fatty acid; LRAT, lecithin:retinol acyltransferase; PPAR, peroxisome proliferator-activated receptor; PPRE, PPAR-responsive element; RAR, retinoic acid receptor; RARE, RAR-responsive element; RBP, retinol-binding protein; RE, retinyl ester; RXR, retinoid X receptor; vitA, vitamin A Supplementary key words liver fibrosis peroxisome proliferator-activated receptor ß fatty acid binding protein CD36 ACS2 cellular retinol binding protein lecithin:retinol acyltransferases
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