Highly Sensitive and Potent Upregulation of Apolipoprotein A-IV/V by Novel PPARα Agonist, KRP-101, as Major PPARα-Regulated Genes in Human Hepatocytes.

Nagasawa, Michiaki; Akasaka, Yunike; Ide, Tomohiro; Hara, Tomoko; Kobayashi, Naoki; Murakami, Koji

PPARα is a key regulator in hepatic lipid metabolism and a potential therapeutic target for dyslipidemia. However, in humans, the hepatic PPARα-regulated gene remains unclear because subtype selective agonists for human PPARα as well as human cell lines highly responsive to PPARα agonists are lacking. To investigate the effect of PPARα agonism on expressions of lipid metabolic-related genes in human livers, a novel PPARα agonist, KRP-101 (KRP), was used to treat the human hepatoma cell line, HepaRG cells for 24 hr. Unlike the findings in rodent hepatocytes, KRP did not affect AOX or L-PBE mRNA, involved in peroxisomal β-oxidation in HepaRG cells. KRP increased L-FABP, CPT1A, VLCAD, and PDK4 mRNA, involved in lipid transport and oxidation. However, their EC50 values (114-2500 nM) showed > 10-fold lower response than the EC50 value for human PPARα (10.9 nM in a transactivation assay). To search for more sensitive genes, we determined the mRNA levels of apolipoproteins, apoA-I and apoA-II, major components of HDL, apoAIV and apoA-V, components of HDL that are capable of LPL activation, and apoC-III, a component of VLDL and a known LPL inhibitor. KRP did not affect mRNA levels of apoA-I or apoC-III in HepaRG cells. KRP increased apoA-II mRNA with weak potency (EC50, >22.5 µM). Interestingly, we found that KRP increased mRNA levels of apoA-IV (EC50, 0.99 nM) and apoA-V (EC50, 0.29 nM), suggesting that these genes are highly sensitive to PPARα activation. Upregulations of apoA-IV/V by KRP were abrogated by knock down of PPARα using siRNA. Moreover, in the media of HepaRG cells, KRP showed significantly higher potency in increasing protein levels of a newly identified PPARα-regulated gene, apoA-IV. These findings suggest that in humans, upregulation of apo A-IV/V rather than lipid oxidation genes may be key mechanisms underlying PPARα agonist-induced triglyceride decrease and HDL elevation. In addition, our data show that HepaRG might be a useful cell line to investigate and predict the effects of PPARα agonist in humans.

APOLIPOPROTEINS; NUCLEAR receptors (Biochemistry); GENES; LIVER cells; TRIGLYCERIDES; HIGH density lipoproteins

Diabetes, 2007, Vol 56, pA56

0012-1797

Academic Journal