CD36-mediated cholesterol efflux is associated with PPARγ activation via a MAPK-dependent COX-2 pathway in macrophages

Growth hormone-releasing peptides (GHRPs) as CD36 selective ligands feature potent anti-atherosclerotic activity that is associated with an upregulation of the peroxisome proliferator-activated receptor gamma (PPAR gamma)-liver X receptor alpha (LXR alpha)-ATP-binding cassette (ABC) transporter pathway. However, the mechanism involved in PPAR gamma activation in response to CD36 signalling has yet to be determined. Therefore, the present study aims to elucidate the upstream molecular mechanisms through which EP 80317, a selective CD36 ligand, promotes lipid efflux from macrophages through PPAR gamma activation. [H-3]-Cholesterol- and [H-3]-methylcholine chloride-labelled murine macrophages treated with EP 80317 showed a significant increase in cholesterol and phospholipid efflux to both apolipoprotein A-I and high-density lipoprotein in a CD36-dependent manner. Lipid efflux was associated with enhanced activation of PPAR gamma. The signalling pathway by which this CD36 ligand promoted lipid efflux involved an increase in intracellular 15-deoxy-delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) levels induced by extracellular signal-regulated kinase 1/2 (ERK1/2)-dependent cyclooxygenase-2 (COX-2) expression, leading to PPAR gamma activation. In agreement, EP 80317-mediated cholesterol efflux was abrogated by inhibitors of PPAR gamma, ERK1/2, and COX-2 as well as ABC transporter inhibitors, whereas a p38 mitogen-activated protein kinase inhibitor had no effect. These findings suggest a central role for the prostanoid 15d-PGJ(2) in PPAR gamma activation and the upregulation of the ABC transporter pathway in response to CD36 activation by synthetic GHRPs analogues. The resulting enhanced cholesterol efflux might explain, at least in part, the atheroprotective effect of selective CD36 ligands.