A Secreted Phospholipase A(2) Induces Formation of Smooth Muscle Foam Cells Which Transdifferentiate to Macrophage-Like State

Abstract

Vascular smooth muscle cells (VSMCs) loaded with lipid droplets (LDs) are markers of atherosclerosis. In this disease, inflammatory Group IIA-secreted phospholipase A(2)s (GIIA sPLA(2)s) are highly expressed in VSMCs, but their actions in these cells are unknown. Here, we investigated the ability of myotoxin III (MT-III), an ophidian GIIA sPLA(2) sharing structural and functional features with mammalian GIIA sPLA(2)s, to induce LD formation and lipid metabolism factors involved in this effect. Modulation of VSMC phenotypes by this sPLA(2) was also evaluated. Incubation of VSMCs with MT-III significantly increased the number of LDs. MT-III upregulated scavenger receptor type 1 (SR-A1) and lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) protein expression and enhanced acetylated-low density lipoprotein (acLDL) uptake by VSMCs, revealing the ability of a GIIA PLA(2) to modulate scavenger receptor activities. MT-III induced translocation and protein expression of PPAR-gamma and -beta/delta. Inhibition of peroxisome proliferator-activated receptors (PPARs) and diacylglycerol O-acyltransferase (DGAT) and acyl-CoA:cholesterolacyltransferase (ACAT) enzymes abrogated MT-III-induced LD formation. Moreover, in response to MT-III, VSMCs acquired phagocytic activity and expressed macrophage markers CD68 and MAC-2. In conclusion, MT-III is able to stimulate VSMCs and recruit factors involved in lipid uptake and metabolism, leading to the formation of VSMC-derived foam cells with acquisition of macrophage-like markers and functions.