Peroxisome proliferator-activated receptor alpha (PPARA) is a nuclear transcription factor and key mediator of systemic lipid metabolism. Prolonged activation in rodents causes hepatocyte proliferation and hepatocellular carcinoma. Little is known about the contribution of non-parenchymal cells (NPCs) to PPARA-mediated cell proliferation. NPC contribution to PPARA agonist-induced hepatomegaly was assessed in hepatocyte (Ppara∆Hep)- and macrophage (Ppara∆Mac)-specific Ppara null mice. Mice were treated with the agonist Wy-14643 for 14 days and response of conditional null mice was compared to conventional knockout mice (Ppara-/-). Wy-14643 treatment caused weight loss and severe hepatomegaly in wild-type and Ppara∆Mac mice and histological analysis revealed characteristic hepatocyte swelling; Ppara∆Hep and Ppara-/- mice were protected from these effects. Ppara∆Mac serum chemistries, as well as AST and ALT levels, matched wild-type mice. Agonist treated Ppara∆Hep mice had elevated serum cholesterol, phospholipids, and triglycerides when compared to Ppara-/- mice indicating a possible role for extrahepatic PPARA in regulating circulating lipid levels. BrdU labeling confirmed increased cell proliferation only in wild-type and Ppara∆Mac mice. Macrophage PPARA disruption did not impact agonist-induced upregulation of lipid metabolism, cell proliferation, or DNA damage and repair-related gene expression, while gene expression was repressed in Ppara∆Hep mice. Interestingly, downregulation of inflammatory cytokines IL15 and IL18 were dependent on macrophage PPARA. Cell type-specific regulation of target genes was confirmed in primary hepatocytes and Kupffer cells. These studies conclusively show that cell proliferation is mediated exclusively by PPARA activation in hepatocytes and that Kupffer cell PPARA has an important role in mediating the anti-inflammatory effects of PPARA agonists.
- Kupffer cell
- cell proliferation
- Copyright © 2016, American Journal of Physiology-Gastrointestinal and Liver Physiology