A Growth Hormone-Releasing Peptide that Binds Scavenger Receptor CD36 and Ghrelin Receptor Up-Regulates Sterol Transporters and Cholesterol Efflux in Macrophages through a Peroxisome Proliferator-Activated Receptor γ-Dependent Pathway

Macrophages play a central role in the pathogenesis of atherosclerosis by accumulating cholesterol through increased uptake of oxidized low-density lipoproteins by scavenger receptor CD36, leading to foam cell formation. Here we demonstrate the ability of hexarelin, a GH-releasing peptide, to enhance the expression of ATP-binding cassette A1 and G1 transporters and cholesterol efflux in macrophages. These effects were associated with a transcriptional activation of nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ in response to binding of hexarelin to CD36 and GH secretagogue-receptor 1a, the receptor for ghrelin. The hormone binding domain was not required to mediate PPARγ activation by hexarelin, and phosphorylation of PPARγ was increased in THP-1 macrophages treated with hexarelin, suggesting that the response to hexarelin may involve PPARγ activation function-1 activity. However, the activation of PPARγ by hexarelin did not lead to an increase in CD36 expression, as opposed to liver...