DGAT enzymes are required for triacylglycerol synthesis and lipid droplets in adipocytes

Abstract

Lipid droplets (LDs) are found in nearly all eukaryotic cells, and each consists of a neutral lipid core enveloped by a phospholipid monolayer and surface proteins ( 1 ). The main lipids found in the cores of LDs are triacylglycerols (TGs) and sterol esters (SEs). Whether TGs are required for the formation of LDs is unknown. The major known enzymes that catalyze TG synthesis in mammals are the acyl CoA:diacylglycerol acyltransferases (DGAT; Fig. 1A ) ( 2 ), which catalyze the covalent addition of a fatty acyl chain to diacylglycerol. Genetic deletion of DGAT1 in mice revealed that this enzyme is not essential and that DGAT1 knockout (DGAT1 KO) mice have reductions in TG levels in many tissues, including adipose tissue, when fed a high-fat diet ( 3 ). Deletion of DGAT2 revealed that this enzyme is essential: mice lacking DGAT2 have severe reductions in TG levels and die shortly after birth ( 4 ). Nevertheless, newborn DGAT2 KO mice do have some TG, which may be due to DGAT1 activity. Given that enzymes in both the DGAT1 (MBOAT, 16 family members) and DGAT2 (7 members) families possess many different lipid acyltransferase activities ( 5, 6 ), and that several of these Abstract The total contribution of the acyl CoA:diacylglycerol acyltransferase (DGAT) enzymes, DGAT1 and DGAT2, to mammalian triacylglycerol (TG) synthesis has not been determined. Similarly, whether DGAT enzymes are required for lipid droplet (LD) formation is unknown. In this study, we examined the requirement for DGAT enzymes in TG synthesis and LDs in differentiated adipocytes with genetic deletions of DGAT1 and DGAT2. Adipocytes with a single deletion of either enzyme were capable of TG synthesis and LD formation. In contrast, adipocytes with deletions of both DGATs were severely lacking in TG and did not have LDs, indicating that DGAT1 and DGAT2 account for nearly all TG synthesis in adipocytes and appear to be required for LD formation during adipogenesis. DGAT enzymes were not absolutely required for LD formation in mammalian cells, however; macrophages defi cient in both DGAT enzymes were able to form LDs when incubated with cholesterolrich lipoproteins. Although adipocytes lacking both DGATs had no TG or LDs, they were fully differentiated by multiple criteria.Our fi ndings show that DGAT1 and DGAT2 account for the vast majority of TG synthesis in mice, and DGAT function is required for LDs in adipocytes, but not in all cell

Hepatitis C Virus Core Protein Decreases Lipid Droplet Turnover

“…Calcium phosphatemediated transfection of HEK293T cells was used for the production of lentiviral particles. Mouse embryonic fibroblasts were established from DGAT1 Ϫ/Ϫ or DGAT2 Ϫ/Ϫ embryos or their control littermates as described previously (29).…”

“…-dependent Manner-To examine whether core-induced lipid accumulation involves a specific DGAT enzyme, we introduced core into mouse embryonic fibroblasts from DGAT1-or DGAT2-deficient mice (29) and examined LD accumulation by ORO staining and fluorescent microscopy. Core expression caused an ϳ60-fold increase in cellular LD content in wild-type (WT) and DGAT2…”

“…We showed recently that core specifically interacts with DGAT1 (27), one of the two host diacylglycerol acyltransferase (DGAT) enzymes that produce TGs in the ER (28). DGAT1 and DGAT2 account for nearly all TG synthesis in mammalian cells (29), and both enzymes reside in the ER, although they are found in distinct ER microdomains (30). Both DGATs have been implicated in the development of diet-induced hepatic steatosis (31)(32)(33).…”

Murine Diacylglycerol Acyltransferase-2 (DGAT2) Can Catalyze Triacylglycerol Synthesis and Promote Lipid Droplet Formation Independent of Its Localization to the Endoplasmic Reticulum

“…Two different DGAT enzymes, DGAT1 and DGAT2, are responsible for the acyl-CoA-dependent synthesis of TG in mammalian tissues (2)(3)(4). The genes encoding these two enzymes have no sequence homology and they each belong to distinct gene families.…”

2-(3-Benzoylthioureido)-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylic acid ameliorates metabolic disorders in high-fat diet-fed mice

“…Currently, most drugs for the treatment of lipid-related metabolic disorders target rate-limiting enzymes involved in lipogenesis, such as FAS, which is a key enzyme in fatty acid synthesis; DGAT (acyl CoA: diacylgycerol acyltransferase), which catalyzes the final step, is the only key and ratelimiting enzyme in triglyceride synthesis [47] . However, the total or partial inhibition of rate-limiting enzymes may result in two adverse issues: the accumulation of substrate may cause lysosomal storage disease [48] and the reduction of product will cause compensatory action.…”