microRNA 33 Regulates Macrophage Autophagy in Atherosclerosis
Objective Defective autophagy in macrophages leads to pathological processes that contribute to atherosclerosis, including impaired cholesterol metabolism and defective efferocytosis. Autophagy promotes the degradation of cytoplasmic components in lysosomes and plays a key role in the catabolism of stored lipids to maintain cellular homeostasis. microRNA 33 (miR 33) is a post transcriptional regulator of genes involved in cholesterol homeostasis, yet the complete mechanisms by which miR 33 controls lipid metabolism are unknown. We investigated whether miR 33 targeting of autophagy contributes to its regulation of cholesterol homeostasis and atherogenesis. Approach and Results Using coherent anti Stokes Raman scattering microscopy, we show that miR 33 drives lipid droplet accumulation in macrophages, suggesting decreased lipolysis. Inhibition of neutral and lysosomal hydrolysis pathways revealed that miR 33 reduced cholesterol mobilization by a lysosomal dependent mechanism, implicating repression of autophagy. Indeed, we show that miR 33 targets key autophagy regulators and effectors in macrophages to reduce lipid droplet catabolism, an essential process to generate free cholesterol for efflux. Notably, miR 33 regulation of autophagy lies upstream of its known effects on ABCA1 (ATP binding cassette transporter A1) dependent cholesterol efflux, as miR 33 inhibitors fail to increase efflux upon genetic or chemical inhibition of autophagy. Furthermore, we find that miR 33 inhibits apoptotic cell clearance via an autophagy dependent mechanism. Macrophages treated with anti miR 33 show increased efferocytosis, lysosomal biogenesis, and degradation of apoptotic material. Finally, we show that treating atherosclerotic Ldlr mice with anti miR 33 restores defective autophagy in macrophage foam cells and plaques and promotes apoptotic cell clearance to reduce plaque necrosis. Conclusions Collectively, these data provide insight into the mechanisms by which miR 33 regulates cellular cholesterol homeostasis and atherosclerosis.
Arteriosclerosis, thrombosis, and vascular biology