The nuclear receptors peroxisome proliferator-activated receptor α and Rev-erbα mediate the species-specific regulation of apolipoprotein A-I expression by fibrates

Fibrates are widely used hypolipidemic drugs which activate the nuclear peroxisome proliferator-activated receptor (PPAR) alpha and thereby alter the transcription of genes controlling lipoprotein metabolism. Fibrates influence plasma high density lipoprotein and its major protein, apolipoprotein (apo) A-I, in an opposite manner in man (increase) versus rodents (decrease), In the present study we studied the molecular mechanisms of this species-specific regulation of apoA-I expression by fibrates, In primary rat and human hepatocytes fenofibric acid, respectively, decreased and increased apoA-I mRNA levels. The absence of induction of rat apoA-I gene expression by fibrates is due to 3 nucleotide differences between the rat and the human apoA-I promoter A site, rendering a positive PPAR-response element in the human apoA-I promoter nonfunctional in rats. In contrast, rat, but not human, apoA-I transcription is repressed by the nuclear receptor Rev-erb alpha, which binds to a negative response element adjacent to the TATA box of the rat apoA-I promoter. In rats fibrates increase liver Rev-erb alpha mRNA levels >10-fold. In conclusion, the opposite regulation of rat and human apoA-I gene expression by fibrates is linked to differences in cis-elements in their respective promoters leading to repression by Rev-erb alpha of rat apoA-I and activation by PPAR alpha of human apoA-I, Finally, Rev-erb alpha is identified as a novel fibrate target gene, suggesting a role for this nuclear receptor in lipid and lipoprotein metabolism.