miRNA Targeting of Oxysterol-Binding Protein-Like 6 Regulates Cholesterol Trafficking and Efflux

Abstract

Objective Cholesterol homeostasis is fundamental to human health, and is thus, tightly regulated. MicroRNAs exert potent effects on biological pathways, including cholesterol metabolism, by repressing genes with related functions. We reasoned that this mode of pathway regulation could be exploited to identify novel genes involved in cholesterol homeostasis. Approach and Results Here, we identify oxysterol binding protein-like 6 (OSBPL6) as a novel target of two miRNA hubs regulating cholesterol homeostasis: miR-33 and miR-27b. Characterization of OSBPL6 revealed that it is transcriptionally regulated in macrophages and hepatocytes by LXR and in response to cholesterol loading, and in mice and non-human primates by Western diet feeding. OSBPL6 encodes the OSBPL-related protein 6 (ORP6), which contains dual membrane- and ER-targeting motifs. Subcellular localization studies showed that ORP6 is associated with the endolysosomal network and ER, suggesting a role for ORP6 in cholesterol trafficking between these compartments. Accordingly, knockdown of OSBPL6 results in aberrant clustering of endosomes and promotes the accumulation of free cholesterol in these structures, resulting in reduced cholesterol esterification at the ER. Conversely, ORP6 overexpression enhances cholesterol trafficking and efflux in macrophages and hepatocytes. Moreover, we show that hepatic expression of OSBPL6 is positively correlated with plasma levels of HDL-cholesterol in a cohort of 200 healthy individuals, whereas its expression is reduced in human atherosclerotic plaques. Conclusions These studies identify ORP6 as a novel regulator of cholesterol trafficking that is part of the miR-33 and miR-27b target gene networks that contribute to the maintenance of cholesterol homeostasis.

microRNA-33 Regulates Macrophage Autophagy in Atherosclerosis

“…Previous studies by our group and others established miR-33 as a potent inhibitor of cholesterol efflux and reverse cholesterol transport 18, 27 through its targeting of key genes involved in cholesterol transport ( Abca1 and Abcg1 16–18 ), biliary excretion ( Atp8b1 and Abcb11 35 ) and intracellular trafficking ( Npc1 18 and Osbpl6 36 ). We now show that by targeting key autophagy regulators and effectors in macrophages, miR-33 reduces the catabolism of lipid droplets by lysosomes, a process that generates free cholesterol for efflux.…”

Oxysterol-Binding Protein-Related Protein 1L Regulates Cholesterol Egress from the Endo-Lysosomal System

“…ORP5 (OSBPL5) is an ER-localized tail-anchored protein that mediates cholesterol efflux to the ER (Du et al, 2011), and it exchanges phosphatidylinositol 4-phosphate (PI-4P) and phosphatidylserine at ER-plasma membrane (PM) contact sites and possibly at ER-mitochondrial contact sites (Chung et al, 2015;Galmes et al, 2016). ORP6 (OSBPL6) associates with the endo-lysosomal network in macrophages, and it is implicated in the organization of early endosomes and cholesterol trafficking to the ER (Ouimet et al, 2016). ORP1L (OSBPL1) is localized to LELs (Johansson et al, 2003), regulates endosome dynamics (Johansson et al, 2003;Rocha et al, 2009), and binds sterols (Vihervaara et al, 2011), making it a candidate transporter of LEL cholesterol.…”

Macrophages

“…[23][24][25] Additional work from the Moore laboratory shows that miR-33 targets the endolysosome and endoplasmic reticulum-associated oxysterolbinding protein-like 6 (OSBPL6), which leads to alteration of intracellular cholesterol trafficking through abnormal endosome clustering, accumulation of free cholesterol, and reduction of cholesterol esterification. 26 Interestingly, miR-33 targeting of OSBPL6 is conserved in mice and nonhuman primates, and hepatic expression of OSBPL6 is positively correlated with circulating high-density lipoprotein cholesterol levels in humans, 26 further supporting the potential benefit of miR-33-targeted therapies in patients with cardiometabolic disease. A major in vivo target of miR-33 is ABCA1.…”