Hepatocyte-specific PPARA Expression Exclusively Promotes Agonist-induced Cell Proliferation Without Influence from Nonparenchymal Cells

Peroxisome proliferator-activated receptor-α (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 nonparenchymal cells (NPCs) to PPARA-mediated cell proliferation. NPC contribution to PPARA agonist-induced hepatomegaly was assessed in hepatocyte ()- and macrophage ()-specific null mice. Mice were treated with the agonist Wy-14643 for 14 days, and response of conditional null mice was compared with conventional knockout mice ( ). Wy-14643 treatment caused weight loss and severe hepatomegaly in wild-type and mice, and histological analysis revealed characteristic hepatocyte swelling; and mice were protected from these effects. serum chemistries, as well as aspartate aminotransferase and alanine aminotransferase levels, matched wild-type mice. Agonist-treated mice had elevated serum cholesterol, phospholipids, and triglycerides when compared with mice, indicating a possible role for extrahepatic PPARA in regulating circulating lipid levels. BrdU labeling confirmed increased cell proliferation only in wild-type and mice. Macrophage PPARA disruption did not impact agonist-induced upregulation of lipid metabolism, cell proliferation, or DNA damage and repair-related gene expression, whereas gene expression was repressed in mice. Interestingly, downregulation of inflammatory cytokines IL-15 and IL-18 was 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.