Abstract

Foam cell formation and monocytes adhesion are key events in pathogenesis of atherosclerosis. Vascular smooth muscle cells (VSMCs) are an important origin of foam cells besides macrophages. Fibronectin type III domain containing protein 5 (FNDC5) is a protein, which induces browning of fat and attenuates glucose/lipid metabolic derangements in obese mice. The present study was designed to determine the roles of FNDC5 in inhibiting foam cell formation and monocyte adhesion in VSMCs and its underlying mechanisms. Oxidized low-density lipoprotein (oxLDL) was used to induce foam cell formation and monocyte adhesion in human aortic VSMCs. Foam cell formation was evaluated by intracellular lipid droplets, cholesterol contents, and mRNA levels of acyl-coenzyme A: cholesterol acyltransferase 1 (ACAT-1) and ATP binding cassette transporter A-1 (ABCA-1). Monocyte adhesion was evaluated by the number of monocytes adhered to VSMCs and mRNA levels of monocyte chemotactic protein-1 (MCP-1) and vascular cell adhesion molecule-1 (VCAM-1). FNDC5 inhibited oxLDL-induced foam cell formation, monocyte adhesion, ABCA-1 mRNA downregulation, and ACAT-1, MCP-1 and VCAM-1 mRNA upregulation in VSMCs. It inhibited oxLDL-induced p65-NFκB nuclear translocation, NLRP3 upregulation, caspase-1 and IL-1β production. Inhibition of NFκB with BMS-345541 or inhibition of NLRP3 inflammasome with MCC950 showed similar effects to FNDC5 in attenuating the oxLDL-induced foam cell formation, monocyte adhesion, and caspase-1 and IL-1β production. The oxLDL-induced NLRP3 upregulation was prevented by BMS-345541 rather than MCC950. These results indicate that FNDC5 inhibits oxLDL-induced foam cell formation and monocyte adhesion in VSMCs via suppressing NFκB-mediated NLRP3 upregulation and IL-1β production.