Adipophilin Enhances Lipid Accumulation and Prevents Lipid Efflux From THP-1 Macrophages

Abstract

Objective-Uptake of modified low-density lipoprotein (LDL) by macrophages through scavenger receptors results in lipid droplets accumulation and foam cell formation. Excess lipid deposition in macrophages has been reported to modulate expression of several genes including adipophilin. In this study, we investigated the function of adipophilin in lipid accumulation and cholesterol efflux in THP-1 macrophages. Methods and Results-Adipophilin mRNA expression was 3.5-fold higher in human atherosclerotic plaques compared with healthy areas of the same arteries. Moreover, in the presence of acetylated LDL (AcLDL), triglycerides and cholesteryl esters were increased in macrophages overexpressing adipophilin by 40% and 67%, respectively, whereas their accumulation was reduced when endogenous cellular adipophilin was depleted using siRNA approach. In addition, neither overexpression nor downregulation of adipophilin altered expression of genes involved in lipid efflux. However, the affinity and the number of AcLDL receptors were not affected. After 24-hour incubation of lipid-loaded macrophages with apolipoprotein A-I, cholesterol efflux was reduced by 47% in adipophilin transfected cells versus control cells. Key Words: adipophilin Ⅲ macrophage Ⅲ acetylated LDL Ⅲ cholesterol efflux Ⅲ atherosclerosis A therosclerosis, a complex disease process, is initiated by an infiltration of low-density lipoproteins (LDL) into the subendothelial space where they accumulate and become modified mainly by oxidation. In parallel, chemokines elaborated by endothelial cells attract circulating monocytes into the intima, where they differentiate into macrophages. 1 Intimal macrophages contribute to the formation of arterial lesions by accumulating large amounts of cholesteryl ester (CE) through the uptake of modified lipoproteins such as oxidized LDL (oxLDL) by a variety of mechanisms, including the scavenger pathway. 2,3 Several studies indicated that oxLDL has a number of diverse effects on macrophage function including growth stimulation 4 proinflammatory effects such as expression of inflammatory cytokines, 5 increase in cytotoxicity and expression of metalloproteinases, 6 inhibition of expression of inducible nitric oxide synthase, 7 and effects on lipid metabolism and accumulation. 8,9 Using either a DNA array approach 10 or a subtractive approach, 11 numerous genes have been shown to be regulated on exposure of THP-1 cells to modified LDL. Adipophilin, or adipose differentiation-related protein (ADRP), a 50-kDa protein initially described in adipocytes, 12 which is considered a marker of lipid accumulation, is among those genes upregulated by modified LDL. Conclusion-OurAdipophilin is found associated with intracellular lipid droplets in a variety of cells and tissues that store or synthesize lipids. 13,14 In addition to oxLDL, 15 acetylated LDL (AcLDL) 11 or enzymatically modified LDL, 16 the nuclear receptor PPAR␦, is involved in lipid accumulation in human macrophages and THP-1-derived macrophages, and also increases adipophilin e...

Lipid homeostasis and the formation of macrophage-derived foam cells in atherosclerosis

“…ADRP is the most abundant and best characterized PAT protein in human and mouse macrophage-derived foam cells (Buechler et al, 2001;Larigauderie et al, 2004;Paul et al, 2008b). Interestingly, the expression of ADRP in the atherosclerosis-studded arteries of ApoE-deficient mice was approximately 3.5-fold higher than in the atherosclerosis-free arteries of wild-type mice (Paul et al, 2008b).…”

“…Inactivation of the Adrp gene in ApoE-deficient mice significantly reduced the number of lipid droplets in the foam cells in atherosclerotic lesions and protected mice against atherosclerosis (Paul et al, 2008b). Moreover, overexpression of ADRP resulted in increased lipid droplet accumulation due to reduced cholesterol efflux from THP-1 macrophages (Larigauderie et al, 2004). In contrast, peritoneal macrophages isolated from © Higher Education Press and Springer-Verlag Berlin Heidelberg 2012…”

Leptin and mTOR: Partners in metabolism and inflammation

“…[60][61][62] ADRP is a member of the PAT family (Perilipin, ADRP, TIP47) of proteins and plays an important role in adipocyte differentiation, lipolysis modulation, lipid body assembly and biogenesis (reviewed in ref. 63).…”

“…Increased ADRP expression by itself has been shown to be directly related to the enhanced capacity of neutral lipid storage, as ADRP promotes triglycerides and cholesterol storage and reduces cholesterol efflux. 60 ADRP may act also as a nucleation center for the assembly of lipids to form nascent lipid bodies and to enhance droplet stability upon lipolytic conditions. 64,65 In accordance, Kjerrulf et al, showed reduced cholesterol accumulation in ob/ob mouse macrophages.…”

Identification of High and Low Responders to Lipopolysaccharide in Normal Subjects: An Unbiased Approach to Identify Modulators of Innate Immunity

“…ADFP is an intracellular protein that associates with intracellular lipid droplets in adipocytes, monocytes, and macrophages and is thought to facilitate the accumulation of cholesterol esters from acetylated low-density lipoprotein (26,27). Gene expression profiling showed that ADFP is expressed in higher quantities at baseline in lps high than lps low individuals (Table VI), suggesting that increased ADFP expression marks a cell that is predisposed to produce higher amounts of LPS-induced cytokines and that ADFP may have a functional effect on LPS-induced cellular responses.…”