Differential Effects of Fenofibrate or Simvastatin Treatment of Rats on Hepatic Microsomal Overt and Latent Diacylglycerol Acyltransferase Activities

Waterman, Ian J.; Zammit, Victor A.

doi:10.2337/diabetes.51.6.1708

Cited by 58 publications

(48 citation statements)

References 49 publications

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“…The subsequent use of a second membrane-permeabilizing agent, namely alamethacin, a poreforming peptide that acts through an entirely different membrane permeabilization mechanism, allowed the discrete quantification of overt and latent DGAT activities in situ in cells without disruption of the native ER structure. Importantly, the similarity of the ratios of latent to overt DGAT activities as quantified in whole (rat-derived) McA-RH7777 cells and in rat isolated liver microsomes suggests that our original observations (9,11,12,26) are unlikely to have been due to artifacts arising during the preparation of liver microsomal fractions.…”

Section: Discussionmentioning

confidence: 67%

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Evidence That Diacylglycerol Acyltransferase 1 (DGAT1) Has Dual Membrane Topology in the Endoplasmic Reticulum of HepG2 Cells

Wurie

Buckett

Zammit

2011

Journal of Biological Chemistry

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Triacylglycerol (TAG) synthesis and secretion are important functions of the liver that have major impacts on health, as overaccumulation of TAG within the liver (steatosis) or hypersecretion of TAG within very low density lipoproteins (VLDL) both have deleterious metabolic consequences. Two diacylglycerol acyltransferases (DGATs 1 and 2) can catalyze the final step in the synthesis of TAG from diacylglycerol, which has been suggested to play an important role in the transfer of the glyceride moiety across the endoplasmic reticular membrane for (re)synthesis of TAG on the lumenal aspect of the endoplasmic reticular (ER) membrane (Owen, M., Corstorphine, C. C., and Zammit, V. A. (1997) Biochem. J. 323, 17-21). Recent topographical studies suggested that the oligomeric enzyme DGAT1 is exclusively lumen facing (latent) in the ER membrane. By contrast, in the present study, using two specific inhibitors of human DGAT1, we present evidence that DGAT1 has a dual topology within the ER of HepG2 cells, with approximately equal DGAT1 activities exposed on the cytosolic and lumenal aspects of the ER membrane. This was confirmed by the observation of the loss of both overt (partial) and latent (total) DGAT activity in microsomes prepared from livers of Dgat1 ؊/؊ mice. Conformational differences between DGAT1 molecules having the different topologies were indicated by the markedly disparate sensitivities of the overt DGAT1 to one of the inhibitors. These data suggest that DGAT1 belongs to the family of oligomeric membrane proteins that adopt a dual membrane topology.Hypertriglyceridemia is a key biomarker for the metabolic/ insulin resistance syndrome and for associated morbidities, including type-2 diabetes and cardiovascular disease (1). Similarly, excessive accumulation of triglycerides in cytoplasmic lipid droplets results in hepatic steatosis, now recognized as being associated, possibly causatively, with whole body insulin resistance, and which may progress to nonalcoholic fatty liver or steatohepatitis (2, 3). Fasting hypertriglyceridemia is primarily due to the hypersecretion of triglyceride (TAG) 3 by the liver, within very low density lipoproteins (VLDL). Therefore, an understanding of the enzymology involved in triglyceride synthesis, remodeling, storage, and assembly into secreted VLDL is essential for the design of pharmacological strategies aimed at managing dyslipidaemia without the exacerbation of hepatic steatosis, and vice versa.Diacylglycerol acyltransferases (DGATs) catalyze the final reaction of TAG synthesis. Two distinct gene products, DGAT1 and DGAT2, that catalyze most of tissue TAG synthesis have been described (4, 5) but remain relatively poorly characterized, and their respective, nonredundant functions are still to be elucidated. In the present study, we have used two specific inhibitors (which belong to different chemical classes of compounds) of human DGAT1, in combination with the selective permeabilization of the plasma membrane and the ER membrane of whole hepatocytes, to study the sidednes...

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Section: Discussionmentioning

confidence: 67%

“…We also described how the relative expression of the two activities varies with physiological (11) and nutritional state 4 and responds to treatment of rats with different types of hypolipidemic agent (12). This pathway may also account for the remodeling of TAG that occurs par-ticularly in the sn-3 position before it is secreted (9).…”

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confidence: 99%

Evidence That Diacylglycerol Acyltransferase 1 (DGAT1) Has Dual Membrane Topology in the Endoplasmic Reticulum of HepG2 Cells

Wurie

Buckett

Zammit

2011

Journal of Biological Chemistry

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“…Quantitative RT-PCR analysis of the mRNAs from the liver of KK-A y mice indicated that the expression of ACO and MCAD, which are known to be regulated by PPARa and to be involved in b-oxidation in liver, 20 was increased by IHE supplementation. In contrast, the expression of the DGAT2 gene, which plays a vital role in the production of triacylglycerol, 21,22 was reduced by IHE.…”

Section: Discussionmentioning

confidence: 87%

Prevention of diet-induced obesity by dietary isomerized hop extract containing isohumulones, in rodents

et al. 2005

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OBJECTIVE: Isomerized hop extract (IHE), which consists mainly of isohumulones and is required in the beer brewing process, was investigated for its effects on diet-induced obesity in two strains of mice. DESIGN: C57BL/6N and KK-A y mice were fed a standard or high-fat diet containing IHE and their body and tissue weights were measured at various time points. Oral glucose tolerance tests (OGTT) and insulin tolerance tests (ITT) were carried out in high-fat diet-fed C57BL/6N mice. The effects of IHE on intestinal lipid absorption were examined in Wistar rats using a plasma triacylglycerol assay after oral administration of a lipid emulsion. Fecal lipid levels were also measured in these animals after they were fed a high-fat diet containing IHE for 15 days. The effects of IHE on pancreatic lipase activity and the expression of genes involved in hepatic lipid metabolism were also examined using an in vitro assay and quantitative RT-PCR, respectively. RESULTS: Supplementation of high-fat-containing chow with IHE reduced body weight gain and improved glucose tolerance in our experimental mice. A reduction in body weight gain was also observed in C57BL/6N mice fed a standard diet containing IHE. Wistar rats fed a high-fat diet containing IHE showed reduced plasma triacylglycerol levels and an increase in their fecal lipid excretion. Similarly, their pancreatic lipase activity was inhibited and their elevation in plasma triacylglycerol levels seen after the oral administration of lipid emulsion was significantly suppressed. IHE-fed mice showed an increased expression in their lipid oxidation genes and a decreased expression in genes involved in triacylglycerol biosynthesis. CONCLUSION: The inhibition of intestinal dietary fat absorption may be the mechanism by which IHE induces its weightlowering effects in high-fat diet-fed mice. The modulatory effect of IHE on lipid metabolism may also, at least partly, be responsible for its beneficial effects on body weight gain. These results suggest that IHE may be helpful in humans in preventing diet-induced obesity and perhaps even metabolic syndrome, the latter of which is known to be associated with obesity.

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“…DGAT, a ratelimited enzyme of TG synthesis, is a microsomal enzyme expressed abundantly in liver and adipose tissue. It catalyzes the final step in TG synthesis by converting diacylglycerol and fatty acyl-coenzyme A into TG (Yen et al 2008), and its expression is close to PPARa (Waterman & Zammit 2002). In the present study, our results showed that after administration of osthole 5-10 mg/kg for 4 weeks, the hepatic SREBP-1c, DGAT, and FAS mRNA expression were reduced, especially in the osthole 10 mg/kg group (p50.01, Figure 2), suggesting that reduced effects of osthole on FFA and TG were partly related to downregulation of these lipogenic gene expressions via activation of PPARa/g.…”

Section: Resultsmentioning

confidence: 99%

Osthole improves glucose and lipid metabolism via modulation of PPARα/γ-mediated target gene expression in liver, adipose tissue, and skeletal muscle in fatty liver rats

Zhao

Zhong

et al. 2015

Pharmaceutical Biology

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Context: Osthole may be a dual agonist of peroxisome proliferator-activated receptors (PPAR) a/g and ameliorate the insulin resistance (IR), but its mechanisms are not yet understood completely. Objective: We investigated the effects of osthole on PPARa/g-mediated target genes involved in glucose and lipid metabolism in liver, adipose tissue, and skeletal muscle in fatty liver and IR rats. Materials and methods: The rat model was established by orally feeding high-fat and high-sucrose emulsion for 9 weeks. The experimental rats were treated with osthole 5-10 mg/kg by gavage after feeding the emulsion for 6 weeks, and were sacrificed 4 weeks after administration. Results: After treatment with osthole 5-10 mg/kg for 4 weeks, the lipid levels in serum and liver were decreased by 37.9-67.2% and 31.4-38.5% for triglyceride, 33.1-47.5% and 28.5-31.2% for free fatty acid, respectively, the fasting blood glucose, fasting serum insulin, and homeostasis model assessment of IR were also decreased by 17.2-22.7%, 25.9-26.7%, and 37.5-42.8%, respectively. Osthole treatment might simultaneously decrease the sterol regulatory element binding protein1c, diacylglycerol acyltransferase, and fatty acid synthase mRNA expressions in liver and adipose tissue, and increase the carnitine palmitoyltransferase-1A mRNA expression in liver and glucose transporter-4 mRNA expression in skeletal muscle, especially in the osthole 10 mg/kg group (p50.01). Discussion and conclusion: Osthole can improve glucose and lipid metabolism in fatty liver and IR rats, and its mechanisms may be associated with synergic modulation of PPARa/g-mediated target genes involved in glucose and lipid metabolism in liver, adipose tissue, and skeletal muscle. ARTICLE HISTORY

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Differential Effects of Fenofibrate or Simvastatin Treatment of Rats on Hepatic Microsomal Overt and Latent Diacylglycerol Acyltransferase Activities

Cited by 58 publications

References 49 publications

Evidence That Diacylglycerol Acyltransferase 1 (DGAT1) Has Dual Membrane Topology in the Endoplasmic Reticulum of HepG2 Cells

Evidence That Diacylglycerol Acyltransferase 1 (DGAT1) Has Dual Membrane Topology in the Endoplasmic Reticulum of HepG2 Cells

Prevention of diet-induced obesity by dietary isomerized hop extract containing isohumulones, in rodents

Osthole improves glucose and lipid metabolism via modulation of PPARα/γ-mediated target gene expression in liver, adipose tissue, and skeletal muscle in fatty liver rats

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