GLP-1 agonists inhibit ox-LDL uptake in macrophages by activating protein kinase A

Oxidized low-density lipoprotein (ox-LDL) uptake by monocytes/macrophages plays a pivotal role in atherogenesis. This study was designed to examine the effect of glucagon-like peptide-1 (GLP-1) agonists on ox-LDL uptake in macrophages. Human primary monocytes/macrophages were incubated with native GLP-1 (nGLP-1) or GLP-1 agonist liraglutide to evaluate their effect on ox-LDL uptake and the expression of scavenger receptors (SRs), such as SR-A, CD36, and lectin-like ox-LDL SR-1, in this process. Our study showed a decrease in ox-LDL uptake and CD36 expression in macrophages treated with nGLP-1 or liraglutide. However, nGLP-1 and liraglutide did not affect the expression of other SRs SR-A and lectin-like ox-LDL SR-1. Simultaneously, there was an increase in the expression of activated protein kinase A (PKA). To examine the role of PKA in the effects of nGLP-1 or liraglutide, we treated macrophages with PK inhibitor (6-22) amide, a PKA inhibitor, followed by treatment with nGLP-1 or liraglutide. Inhibition of PKA activation markedly reversed the effect of nGLP-1 or liraglutide on ox-LDL uptake and enhanced the expression of CD36. Our results suggest that GLP-1 agonism inhibits ox-LDL uptake through PKA/CD36 pathway in macrophages. This study provides a novel insight in the mechanism of foam cell formation and the role by GLP-1 agonists therein.