PPARalpha and dyslipidemia.

Dyslipidemia is defined by abnormal levels of plasma lipoproteins. Several different types of dyslipidemia can be distinguished. An important group of drugs used in the treatment of dyslipidemia are the fibrates. Fibrates serve as agonists for the peroxisome proliferator-activated receptor alpha (PPARalpha), a ligand-activated transcription factor that belongs to the superfamily of nuclear hormone receptors. By binding to response elements mostly present in the promoter of target genes, PPARalpha governs the expression of numerous genes involved in a variety of metabolic processes. Activation of PPARalpha results in a reduction of plasma TG levels, which is achieved by: (1) induction of genes that decrease the availability of TG for hepatic VLDL secretion, and (2) induction of genes that promote lipoprotein lipase-mediated lipolysis of TG-rich plasma lipoproteins. The stimulatory effect of PPARalpha on plasma HDL levels in humans, which is opposite to what is observed in mice, appears to be mainly mediated via increased production of APOA1 and APOA2, the apolipoprotein constituents of HDL. Apart from its major actions outlined above, PPARalpha modulates lipoprotein metabolism in several other ways, mostly via direct up-regulation of specific PPARalpha target genes. By taking into account novel insights into the metabolism of plasma lipoproteins and by considering the latest information on PPARalpha-dependent gene regulation, a fresh perspective on the molecular mechanisms underlying the plasma lipoprotein modulating effect of PPARalpha is presented.