Peroxisome proliferator-activated receptors and hepatic stellate cell activation

The present study examined the roles of peroxisome proliferator-activated r eceptors (PPAR) in activation of hepatic stellate cells (HSC), a pivotal ev ent in liver fibrogenesis. RNase protection assay detected mRNA for PPAR ga mma1 but not that for the adipocyte-specific gamma (2) isoform in HSC isola ted from sham-operated rats, whereas the transcripts for neither isoforms w ere detectable in HSC from cholestatic liver fibrosis induced by bile duct ligation (BDL), Semi-quantitative reverse transcriptase-polymerase chain re action confirmed a 70% reduction in PPAR gamma mRNA level in HSC from BDL, Nuclear extracts from BDL cells showed an expected diminution of binding to PPAR-responsive element, whereas NF-kappaB and AP-I binding were increased . Treatment of cultured-activated HSC with ligands for PPAR gamma (10 muM 1 5-deoxy-Delta (12,14)-PGJ(2) (15dPGJ(2)); 0.1 similar to 10 muM BRL49653) i nhibited DNA and collagen synthesis without affecting the cell viability. S uppression of HSC collagen by 15dPGJ(2), was abrogated 70% by the concomita nt treatment with a PPAR gamma antagonist (GW9662). HSC DNA and collagen sy nthesis were inhibited by WY14643 at the concentrations known to activate b oth PPAR alpha and gamma (>100 muM) but not at those that only activate PPA Ra (<10 <mu>M) Or by a synthetic PPAR alpha -selective agonist (GW9578). 15 dPGJ(2), reduced Phi1(I) procollagen, smooth muscle alpha -actin, and monoc yte chemotactic protein-1 mRNA levels while inducing matrix metalloproteina se-3 and CD36, 15dPGJ(2), and BRL49653 inhibited alpha1(I) procollagen prom oter activity. Tumor necrosis factor or (10 ng/ml) reduced PPAR gamma mRNA, and this effect was prevented by the treatment with 15dPGJ(2),, These resu lts demonstrate that HSC activation is associated with the reductions in PP AR gamma expression and PPAR-responsive element binding in vivo and is reve rsed by the treatment with PPAR gamma ligands in vitro. These findings impl icate diminished PPAR gamma signaling in molecular mechanisms underlying ac tivation of HSC in liver fibrogenesis and the potential therapeutic value o f PPAR gamma ligands for liver fibrosis.