Monoacylglycerol Acyltransferase Activity Research Articles

Transmembrane Protein 68 Functions as an MGAT and DGAT Enzyme for Triacylglycerol Biosynthesis.

Triacylglycerol (TG) biosynthesis is an important metabolic process for intracellular storage of surplus energy, intestinal dietary fat absorption, attenuation of lipotoxicity, lipid transportation, lactation and signal transduction in mammals. Transmembrane protein 68 (TMEM68) is an endoplasmic reticulum (ER)-anchored acyltransferase family member of unknown function. In the current study we show that overexpression of TMEM68 promotes TG accumulation and lipid droplet (LD) formation in a conserved active sites-dependent manner. Quantitative targeted lipidomic analysis showed that diacylglycerol (DG), free fatty acid (FFA) and TG levels were increased by TMEM68 expression. In addition, TMEM68 overexpression affected the levels of several glycerophospholipids, such as phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, as well as sterol ester contents. TMEM68 exhibited monoacylglycerol acyltransferase (MGAT) and diacylglycerol acyltransferase (DGAT) activities dependent on the conserved active sites in an in vitro assay. The expression of lipogenesis genes, including DGATs, fatty acid synthesis-related genes and peroxisome proliferator-activated receptor γ was upregulated in TMEM68-overexpressing cells. These results together demonstrate for the first time that TMEM68 functions as an acyltransferase and affects lipogenic gene expression, glycerolipid metabolism and TG storage in mammalian cells.

The monoacylglycerol acyltransferase pathway contributes to triacylglycerol synthesis in HepG2 cells

The monoacylglycerol acyltransferase (MGAT) pathway has a well-established role in the small intestine where it facilitates the absorption of dietary fat. In enterocytes, MGAT participates in the resynthesis of triacylglycerol using substrates (monoacylglycerol and fatty acids) generated in the gut lumen from the breakdown of triacylglycerol consumed in the diet. MGAT activity is also present in the liver, but its role in triacylglycerol metabolism in this tissue remains unclear. The predominant MGAT isoforms present in human liver appear to be MGAT2 and MGAT3. The objective of this study was to use selective small molecule inhibitors of MGAT2 and MGAT3 to determine the contributions of these enzymes to triacylglycerol production in liver cells. We found that pharmacological inhibition of either enzyme had no effect on TG mass in HepG2 cells but did alter lipid droplet size and number. Inhibition of MGAT2 did result in decreased DG and TG synthesis and TG secretion. Interestingly, MGAT2 preferentially utilized 2-monoacylglycerol derived from free glycerol and not from exogenously added 2-monoacylglycerol. In contrast, inhibition of MGAT3 had very little effect on TG metabolism in HepG2 cells. Additionally, we demonstrated that the MGAT activity of DGAT1 only makes a minor contribution to TG synthesis in intact HepG2 cells. Our data demonstrated that the MGAT pathway has a role in hepatic lipid metabolism with MGAT2, more so than MGAT3, contributing to TG synthesis and secretion.

Hepatic monoacylglycerol acyltransferase 1 is induced by prolonged food deprivation to modulate the hepatic fasting response

During prolonged fasting, the liver plays a central role in maintaining systemic energy homeostasis by producing glucose and ketones in processes fueled by oxidation of fatty acids liberated from adipose tissue. In mice, this is accompanied by transient hepatic accumulation of glycerolipids. We found that the hepatic expression of monoacylglycerol acyltransferase 1 (Mogat1), an enzyme with monoacylglycerol acyltransferase (MGAT) activity that produces diacyl-glycerol from monoacylglycerol, was significantly increased in the liver of fasted mice compared with mice given ad libitum access to food. Basal and fasting-induced expression of Mogat1 was markedly diminished in the liver of mice lacking the transcription factor PPARα. Suppressing Mogat1 expression in liver and adipose tissue with antisense oligonucleotides (ASOs) reduced hepatic MGAT activity and triglyceride content compared with fasted controls. Surprisingly, the expression of many other PPARα target genes and PPARα activity was also decreased in mice given Mogat1 ASOs. When mice treated with control or Mogat1 ASOs were gavaged with the PPARα ligand, WY-14643, and then fasted for 18 h, WY-14643 administration reversed the effects of Mogat1 ASOs on PPARα target gene expression and liver triglyceride content. In conclusion, Mogat1 is a fasting-induced PPARα target gene that may feed forward to regulate liver PPARα activity during food deprivation.

Metabolic importance of adipose tissue monoacylglycerol acyltransferase 1 in mice and humans

Adipocyte triglyceride storage provides a reservoir of energy that allows the organism to survive times of nutrient scarcity, but excessive adiposity has emerged as a health problem in many areas of the world. Monoacylglycerol acyltransferase (MGAT) acylates monoacylglycerol to produce diacylglycerol; the penultimate step in triglyceride synthesis. However, little is known about MGAT activity in adipocytes, which are believed to rely primarily on another pathway for triglyceride synthesis. We show that expression of the gene that encodes MGAT1 is robustly induced during adipocyte differentiation and that its expression is suppressed in fat of genetically-obese mice and metabolically-abnormal obese human subjects. Interestingly, MGAT1 expression is also reduced in physiologic contexts where lipolysis is high. Moreover, knockdown or knockout of MGAT1 in adipocytes leads to higher rates of basal adipocyte lipolysis. Collectively, these data suggest that MGAT1 activity may play a role in regulating basal adipocyte FFA retention.

Epigenetic programming at the Mogat1 locus may link neonatal overnutrition with long-term hepatic steatosis and insulin resistance.

Postnatal overfeeding increases the risk of chronic diseases later in life, including obesity, insulin resistance, hepatic steatosis, and type 2 diabetes. Epigenetic mechanisms might underlie the long-lasting effects associated with early nutrition. Here we aimed to explore the molecular pathways involved in early development of insulin resistance and hepatic steatosis, and we examined the potential contribution of DNA methylation and histone modifications to long-term programming of metabolic disease. We used a well-characterized mouse model of neonatal overfeeding and early adiposity by litter size reduction. Neonatal overfeeding led to hepatic insulin resistance very early in life that persisted throughout adulthood despite normalizing food intake. Up-regulation of monoacylglycerol O-acyltransferase ( Mogat) 1 conceivably mediates hepatic steatosis and insulin resistance through increasing intracellular diacylglycerol content. Early and sustained deregulation of Mogat1 was associated with a combination of histone modifications that might favor Mogat1 expression. In sum, postnatal overfeeding causes extremely rapid derangements of hepatic insulin sensitivity that remain relatively stable until adulthood. Epigenetic mechanisms, particularly histone modifications, could contribute to such long-lasting effects. Our data suggest that targeting hepatic monoacylglycerol acyltransferase activity during early life might provide a novel strategy to improve hepatic insulin sensitivity and prevent late-onset insulin resistance and fatty liver disease.-Ramon-Krauel, M., Pentinat, T., Bloks, V. W., Cebrià, J., Ribo, S., Pérez-Wienese, R., Vilà, M., Palacios-Marin, I., Fernández-Pérez, A., Vallejo, M., Téllez, N., Rodríguez, M. À., Yanes, O., Lerin, C., Díaz, R., Plosch, T., Tietge, U. J. F., Jimenez-Chillaron, J. C. Epigenetic programming at the Mogat1 locus may link neonatal overnutrition with long-term hepatic steatosis and insulin resistance.

Mogat1 is a fasting‐induced PPARα target gene that plays a role in coordinating the hepatic response to food deprivation

During prolonged fasting, the liver plays a central role in maintaining systemic energy homeostasis by producing glucose and ketones in processes fueled by oxidation of fatty acids liberated from adipose tissue. In mice, this is also accompanied by transient hepatic accumulation of complex lipids in the form of triglycerides. In mice fasted for 24 hours, the hepatic expression of Mogat1 was significantly increased compared to mice given ad libitum access to food. Mogat1 encodes an enzyme with monoacylglycerol (MAG) acyltransferase (MGAT) activity, which is an understudied step in glycerolipid synthesis. Basal and fasting‐induced expression of Mogat1 was markedly diminished in liver of mice lacking the transcription factor peroxisome proliferator‐activated receptor α (PPARα). Suppressing Mogat1 expression with antisense‐oligonucleotides (ASO) reduced hepatic MGAT activity and hepatic triglyceride content compared to fasted ASO control treated mice. Surprisingly, the expression of many other known PPARα target genes (Dgat1, Mgll, Cpt1α, Acadm, and Acadl) was also decreased in mice treated with Mogat1 ASO. We postulated that inhibiting Mogat1 suppressed PPARα activity, potentially by loss of a ligand for PPARα. Fasted mice treated with control or Mogat1 ASO were gavaged with the synthetic PPARα ligand WY‐14643, which reversed the effects of Mogat1 ASO on liver triglyceride content as well as PPARα target gene expression. In conclusion, Mogat1 is a fasting‐induced PPARα target gene and MGAT and may feed forward to regulate liver PPARα activity during fasting.Support or Funding InformationA.J.L. was supported by funds from NIH training grant T32 DK07120. K.S.M is supported by K99 HL136658 and A.M.H. is supported by 17‐IBS‐109 from the American Diabetes Association and R56 DK111735. This work was also funded by R01 DK078187 to B.N.F. The Core services of the Diabetes Research Center (P30 DK020579) and the Nutrition Obesity Research Center (P30 DK56341) at the Washington University School of Medicine also supported this work.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Discovery of Human Intestinal MGAT Inhibitors Using High-Throughput Mass Spectrometry

Monoacylglycerol acyltransferase (MGAT) activity catalyzes the synthesis of diacylglycerol (DAG) from fatty acyl-CoA and monoacylglycerol as substrates. It is important for the resynthesis of triacylglycerol (TAG) in the intestine. In the present study, we developed a MGAT enzymatic assay of human intestinal microsomes using a high-throughput mass spectrometry (MS)–based detection system. After screening with small-molecular-weight libraries for compounds exhibiting inhibitions against DAG and the consequent TAG syntheses, we identified multiple compounds that specifically inhibit intestinal MGAT activity. The inhibitory activities of these compounds were correlated to those determined using a recombinant human MGAT2 enzyme. An aryl-sulfonamide compound T1 showed potent inhibitory activity toward human intestinal MGAT and recombinant human MGAT2, with selectivity over MGAT3. This high-throughput MS-based assay provides a novel platform for the discovery of DAG or TAG synthesis inhibitors. The identified aryl-sulfonamide compound T1 is a promising starting compound for optimization studies of inhibitors with selectivity toward MGAT2.

Pharmacological characterization of a series of aryl-sulfonamide derivatives that potently and selectively inhibit monoacylglycerol acyltransferase 2

Monoacylglycerol acyltransferase (MGAT) 2 is an endoplasmic reticulum membrane enzyme that catalyzes the synthesis of diacylglycerol (DAG) from fatty acyl-CoA and monoacylglycerol as substrates. It is important for the resynthesis of triacylglycerol in the intestine. We have identified a series of aryl-sulfonamide MGAT2 inhibitors and demonstrated pharmacological inhibition of MGAT2 improved hyperlipidemia, obesity, and diabetes in animal models. However, its mechanism of action has not been elucidated in molecular and cellular levels. In the present study, we have characterized a series of aryl-sulfonamide derivatives that potently and selectively inhibit human MGAT2 and determined their pharmacological profiles. Analyses on the molecular mechanism of a representative aryl-sulfonamide MGAT2 inhibitor revealed a reversible inhibitory activity and a binding activity to MGAT2. The aryl-sulfonamide derivatives exhibited potent inhibitory activities against both human and mouse intestinal MGAT activities, which were correlated to those determined using recombinant human and mouse MGAT enzymes. We have developed a cellular assay using Liquid Chromatography-Mass Spectrometry and confirmed that the aryl-sulfonamide derivatives suppressed DAG synthesis in the cellular context. We have thus elucidated their pharmacological profiles and provided the fundamental clues for understanding the molecular and cellular actions of the aryl-sulfonamide MGAT2 inhibitors.

Expression of Mouse MGAT in Arabidopsis Results in Increased Lipid Accumulation in Seeds.

Worldwide demand for vegetable oil is projected to double within the next 30 years due to increasing food, fuel, and industrial requirements. There is therefore great interest in metabolic engineering strategies that boost oil accumulation in plant tissues, however, efforts to date have only achieved levels of storage lipid accumulation in plant tissues far below the benchmark to meet demand. Monoacylglycerol acyltransferase (MGAT) is predominantly associated with lipid absorption and resynthesis in the animal intestine where it catalyzes monoacylglycerol (MAG) to form diacylglycerol (DAG), and then triacylglycerol (TAG). In contrast plant lipid biosynthesis routes do not include MGAT. Rather, DAG and TAG are either synthesized from glycerol-3-phosphate by a series of three subsequent acylation reactions, or originated from phospholipids via an acyl editing pathway. Mouse MGATs 1 and 2 have been shown to increase oil content transiently in Nicotiana benthamiana leaf tissue by 2.6 fold. Here we explore the feasibility of this approach to increase TAG in Arabidopsis thaliana seed. The stable MGAT2 expression resulted in a significant increase in seed oil content by 1.32 fold. We also report evidence of the MGAT2 activity based on in vitro assays. Up to 3.9 fold increase of radiolabeled DAG were produced in seed lysate which suggest that the transgenic MGAT activity can result in DAG re-synthesis by salvaging the MAG product of lipid breakdown. The expression of MGAT2 therefore creates an independent and complementary TAG biosynthesis route to the endogenous Kennedy pathway and other glycerolipid synthesis routes.

Inhibiting Monoacylglycerol Acyltransferase 1 Ameliorates Hepatic Metabolic Abnormalities but Not Inflammation and Injury in Mice

Abnormalities in hepatic lipid metabolism and insulin action are believed to play a critical role in the etiology of nonalcoholic steatohepatitis. Monoacylglycerol acyltransferase (MGAT) enzymes convert monoacylglycerol to diacylglycerol, which is the penultimate step in one pathway for triacylglycerol synthesis. Hepatic expression of Mogat1, which encodes an MGAT enzyme, is increased in the livers of mice with hepatic steatosis, and knocking down Mogat1 improves glucose metabolism and hepatic insulin signaling, but whether increased MGAT activity plays a role in the etiology of nonalcoholic steatohepatitis is unclear. To examine this issue, mice were placed on a diet containing high levels of trans fatty acids, fructose, and cholesterol (HTF-C diet) or a low fat control diet for 4 weeks. Mice were injected with antisense oligonucleotides (ASOs) to knockdown Mogat1 or a scrambled ASO control for 12 weeks while remaining on diet. The HTF-C diet caused glucose intolerance, hepatic steatosis, and induced hepatic gene expression markers of inflammation, macrophage infiltration, and stellate cell activation. Mogat1 ASO treatment, which suppressed Mogat1 expression in liver and adipose tissue, attenuated weight gain, improved glucose tolerance, improved hepatic insulin signaling, and decreased hepatic triacylglycerol content compared with control ASO-treated mice on HTF-C chow. However, Mogat1 ASO treatment did not reduce hepatic diacylglycerol, cholesterol, or free fatty acid content; improve histologic measures of liver injury; or reduce expression of markers of stellate cell activation, liver inflammation, and injury. In conclusion, inhibition of hepatic Mogat1 in HTF-C diet-fed mice improves hepatic metabolic abnormalities without attenuating liver inflammation and injury.

Abrogating Monoacylglycerol Acyltransferase Activity in Liver Improves Glucose Tolerance and Hepatic Insulin Signaling in Obese Mice

Monoacylglycerol acyltransferase (MGAT) enzymes convert monoacylglycerol to diacylglycerol (DAG), a lipid that has been linked to the development of hepatic insulin resistance through activation of protein kinase C (PKC). The expression of genes that encode MGAT enzymes is induced in the livers of insulin-resistant human subjects with nonalcoholic fatty liver disease, but whether MGAT activation is causal of hepatic steatosis or insulin resistance is unknown. We show that the expression of Mogat1, which encodes MGAT1, and MGAT activity are also increased in diet-induced obese (DIO) and ob/obmice. To probe the metabolic effects of MGAT1 in the livers of obese mice, we administered antisense oligonucleotides (ASOs) against Mogat1 to DIO and ob/ob mice for 3 weeks. Knockdown of Mogat1 in liver, which reduced hepatic MGAT activity, did not affect hepatic triacylglycerol content and unexpectedly increased total DAG content. Mogat1 inhibition also increased both membrane and cytosolic compartment DAG levels. However, Mogat1 ASO treatment significantly improved glucose tolerance and hepatic insulin signaling in obese mice. In summary, inactivation of hepatic MGAT activity, which is markedly increased in obese mice, improved glucose tolerance and hepatic insulin signaling independent of changes in body weight, intrahepatic DAG and TAG content, and PKC signaling.

Intestine-specific Deletion of Acyl-CoA:Monoacylglycerol Acyltransferase (MGAT) 2 Protects Mice from Diet-induced Obesity and Glucose Intolerance

The absorption of dietary fat involves the re-esterification of digested triacylglycerol in the enterocytes, a process catalyzed by acyl-CoA:monoacylglycerol acyltransferase (MGAT) 2. Mice without a functional gene encoding MGAT2 (Mogat2(-/-)) are protected from diet-induced obesity. Surprisingly, these mice absorb normal amounts of dietary fat but increase their energy expenditure. MGAT2 is expressed in tissues besides intestine, including adipose tissue in both mice and humans. To test the hypothesis that intestinal MGAT2 regulates systemic energy balance, we generated and characterized mice deficient in MGAT2 specifically in the small intestine (Mogat2(IKO)). We found that, like Mogat2(-/-) mice, Mogat2(IKO) mice also showed a delay in fat absorption, a decrease in food intake, and a propensity to use fatty acids as fuel when first exposed to a high fat diet. Mogat2(IKO) mice increased energy expenditure although to a lesser degree than Mogat2(-/-) mice and were protected against diet-induced weight gain and associated comorbidities, including hepatic steatosis, hypercholesterolemia, and glucose intolerance. These findings illustrate that intestinal lipid metabolism plays a crucial role in the regulation of systemic energy balance and may be a feasible intervention target. In addition, they suggest that MGAT activity in extraintestinal tissues may also modulate energy metabolism.

Intestine‐specific inactivation of acyl CoA: monoacylglycerol acyltransferase 2 protects mice from diet‐induced obesity (822.12)

Acyl: CoA: monoacylglycerol acyltransferase (MGAT)2 catalyzes the re‐esterification of triacylglycerol in the enterocytes, a step required for fat absorption. Mice without functional MGAT2 enzymes (Mogat2‐/‐) are protected from diet‐induced obesity but, surprisingly, absorb normal amount of dietary fat and exhibit increased energy expenditure. MGAT2 is expressed in tissues besides intestine, including the kidney and adipose tissues in both mice and humans. To test the hypothesis that intestinal MGAT2 regulates systemic energy balance, in this study, we generated and characterized mice deficient in MGAT2 exclusively in the small intestine (Mogat2IKO). We found that, like Mogat2‐/‐ mice, Mogat2IKO mice showed delayed in fat absorption, a transient decrease in food intake when first exposed to a high‐fat diet, and a propensity to use fatty acids as fuel. Though to a lesser extent than Mogat2‐/‐ mice, Mogat2IKO mice also exhibited a persistent increase in energy expenditure and are protected against diet‐induced weight gain, excessive expansion of body fat, and associated comorbidities, including hepatic steatosis, hypercholesterolemia, and glucose intolerance. These findings illustrate that intestinal lipid metabolism plays a crucial role in the regulation of systemic energy balance. In addition, they also suggest that MGAT activity in tissues beside intestine may also contribute to energy metabolism.Grant Funding Source: Supported by NIH DK088210

Intestine-specific expression of MOGAT2 partially restores metabolic efficiency in Mogat2-deficient mice

Acyl CoA:monoacylglycerol acyltransferase (MGAT) catalyzes the resynthesis of triacylglycerol, a crucial step in the absorption of dietary fat. Mice lacking the gene Mogat2, which codes for an MGAT highly expressed in the small intestine, are resistant to obesity and other metabolic disorders induced by high-fat feeding. Interestingly, these Mogat2⁻/⁻ mice absorb normal amounts of dietary fat but exhibit a reduced rate of fat absorption, increased energy expenditure, decreased respiratory exchange ratio, and impaired metabolic efficiency. MGAT2 is expressed in tissues besides intestine. To test the hypothesis that intestinal MGAT2 enhances metabolic efficiency and promotes the storage of metabolic fuels, we introduced the human MOGAT2 gene driven by the intestine-specific villin promoter into Mogat2⁻/⁻ mice. We found that the expression of MOGAT2 in the intestine increased intestinal MGAT activity, restored fat absorption rate, partially corrected energy expenditure, and promoted weight gain upon high-fat feeding. However, the changes in respiratory exchange ratio were not reverted, and the recoveries in metabolic efficiency and weight gain were incomplete. These data indicate that MGAT2 in the intestine plays an indispensable role in enhancing metabolic efficiency but also raise the possibility that MGAT2 in other tissues may contribute to the regulation of energy metabolism.

A Bifunctional Enzyme That Has Both Monoacylglycerol Acyltransferase and Acyl Hydrolase Activities

Monoacylglycerol acyltransferase (MGAT) catalyzes the synthesis of diacylglycerol, the precursor of triacylglycerol biosynthesis and an important signaling molecule. Here, we describe the isolation and characterization of the peanut (Arachis hypogaea) MGAT gene. The soluble enzyme utilizes invariant histidine-62 and aspartate-67 residues of the acyltransferase motif for its MGAT activity. A sequence analysis revealed the presence of a hydrolase (GXSXG) motif, and enzyme assays revealed the presence of monoacylglycerol (MAG) and lysophosphatidylcholine (LPC) hydrolytic activities, indicating the bifunctional nature of the enzyme. The overexpression of the MGAT gene in yeast (Saccharomyces cerevisiae) caused an increase in triacylglycerol accumulation. Similar to the peanut MGAT, the Arabidopsis (Arabidopsis thaliana) homolog (At1g52760) also exhibited both acyltransferase and hydrolase activities. Interestingly, the yeast homolog lacks the conserved HX(4)D motif, and it is deficient in the acyltransferase function but exhibits MAG and LPC hydrolase activities. This study demonstrates the presence of a soluble MGAT/hydrolase in plants. The predicted three-dimensional homology modeling and substrate docking suggested the presence of two separate substrate (MAG and LPC)-binding sites in a single polypeptide. Our study describes a soluble bifunctional enzyme that has both MGAT and hydrolase functions.

Evidence for regulated monoacylglycerol acyltransferase expression and activity in human liver

Intrahepatic lipid accumulation is extremely common in obese subjects and is associated with the development of insulin resistance and diabetes. Hepatic diacylglycerol and triacylglycerol synthesis predominantly occurs through acylation of glycerol-3-phosphate. However, an alternative pathway for synthesizing diacylglycerol from monoacylglycerol acyltransferases (MGAT) could also contribute to hepatic glyceride pools. MGAT activity and the expression of the three genes encoding MGAT enzymes (MOGAT1, MOGAT2, and MOGAT3) were determined in liver biopsies from obese human subjects before and after gastric bypass surgery. MOGAT expression was also assessed in liver of subjects with nonalcoholic fatty liver disease (NAFLD) or control livers. All MOGAT genes were expressed in liver, and hepatic MGAT activity was readily detectable in liver lysates. The hepatic expression of MOGAT3 was highly correlated with MGAT activity, whereas MOGAT1 and MOGAT2 expression was not, and knockdown of MOGAT3 expression attenuated MGAT activity in a liver-derived cell line. Marked weight loss following gastric bypass surgery was associated with a significant reduction in MOGAT2 and MOGAT3 expression, which were also overexpressed in NAFLD subjects. These data suggest that the MGAT pathway is active and dynamically regulated in human liver and could be an important target for pharmacologic intervention for the treatment of obesity-related insulin resistance and NAFLD.

Serine/Threonine/Tyrosine Protein Kinase Phosphorylates Oleosin, a Regulator of Lipid Metabolic Functions

Plant oils are stored in oleosomes or oil bodies, which are surrounded by a monolayer of phospholipids embedded with oleosin proteins that stabilize the structure. Recently, a structural protein, Oleosin3 (OLE3), was shown to exhibit both monoacylglycerol acyltransferase and phospholipase A(2) activities. The regulation of these distinct dual activities in a single protein is unclear. Here, we report that a serine/threonine/tyrosine protein kinase phosphorylates oleosin. Using bimolecular fluorescence complementation analysis, we demonstrate that this kinase interacts with OLE3 and that the fluorescence was associated with chloroplasts. Oleosin-green fluorescent protein fusion protein was exclusively associated with the chloroplasts. Phosphorylated OLE3 exhibited reduced monoacylglycerol acyltransferase and increased phospholipase A(2) activities. Moreover, phosphatidylcholine and diacylglycerol activated oleosin phosphorylation, whereas lysophosphatidylcholine, oleic acid, and Ca(2+) inhibited phosphorylation. In addition, recombinant peanut (Arachis hypogaea) kinase was determined to predominantly phosphorylate serine residues, specifically serine-18 in OLE3. Phosphorylation levels of OLE3 during seed germination were determined to be higher than in developing peanut seeds. These findings provide direct evidence for the in vivo substrate selectivity of the dual-specificity kinase and demonstrate that the bifunctional activities of oleosin are regulated by phosphorylation.

Corrigendum: Linkage and Genome‐wide Association Analysis of Obesity‐related Phenotypes: Association of Weight With the MGAT1 Gene

ObesityVolume 18, Issue 6 p. 1276-1276 Free Access Corrigendum: Linkage and Genome-wide Association Analysis of Obesity-related Phenotypes: Association of Weight With the MGAT1 Gene First published: 06 September 2012 https://doi.org/10.1038/oby.2010.41AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Åsa Johansson, Fabio Marroni, Caroline Hayward, Christopher S. Franklin, Anatoly V. Kirichenko, Inger Jonasson, Andrew A. Hicks, Veronique Vitart, Aaron Isaacs, Tatiana Axenovich, Susan Campbell, Jamie Floyd, Nick Hastie, Sara Knott, Gordan Lauc, Irene Pichler, Kresimir Rotim, Sarah H. Wild, Irina V. Zorkoltseva, James F. Wilson, Igor Rudan, Harry Campbell, Cristian Pattaro, Peter Pramstaller, Ben A. Oostra, Alan F. Wright, Cornelia M. van Duijn, Yurii S. Aulchenko, Ulf Gyllensten for the EUROSPAN Consortium Obesity (2009) doi:10.1038oby.2009.359 Following the online publication of this article, the authors noted that one of the citations was incorrect. The MGAT1 gene in the article by Yen et al. ((1)) refers to the monoacylglycerol O-acyltransferase 1 (MOGAT1, but denoted MGAT1 in their original article) not the mannosyl (α-1,3-)-glycoprotein β-1,2-N-acetylglucosaminyltransferase that is discussed in the article. The following statements in the article are not related to the MGAT1 gene: Abstract line 16–17: “The monoacylglycerol acyltransferase (MGAT) enzyme family is known to be involved in dietary fat absorption.” Discussion: 3rd section: “Acyl-CoA:monoacylglycerol acyltransferase (MGAT) genes are best known for their role in fat absorption in the intestine. MGAT1 has been shown to exhibit MGAT activity in mammalian cell lines, specific for catalyzing diacylglycerol synthesis by incorporating fatty acyl-CoA into diacylglycerol (38).” REFERENCES 1 Yen CL, Stone SJ, Cases S, Zhou P, Farese RV Jr. Identification of a gene encoding MGAT1, a monoacylglycerol acyltransferase. Proc Natl Acad Sci USA 2002; 99: 8512– 8517. CrossrefCASPubMedWeb of Science®Google Scholar Volume18, Issue6June 2010Pages 1276-1276 ReferencesRelatedInformation

Novel acyl-coenzyme A:monoacylglycerol acyltransferase plays an important role in hepatic triacylglycerol secretion

Acyl-CoA:monoacylglycerol acyltransferase (MGAT) plays a predominant role in the resynthesis of triacylglycerol in the small intestine, but its contribution to triacylglycerol synthesis in other tissues, such as the liver, is not clear. In this study, we identified a novel MGAT gene, which is identical with lysophosphatidylglycerol acyltransferase1 (LPGAT1). Mouse LPGAT1 is expressed in a number of tissues and most highly expressed in the liver. Hepatic LPGAT1 expression in diabetic db/db mice is higher than that in the control db/m mouse, which is consistent with increased hepatic MGAT activity in db/db mouse. To elucidate the role of LPGAT1 gene in lipid metabolism in db/db mice, we constructed an adenovirus of short hairpin RNA (shRNA) targeting LPGAT1 to selectively knockdown LPGAT1 gene expression in the liver. Hepatic MGAT activity and LPGAT1 expression in db/db mice infected with LPGAT1 shRNA adenovirus were significantly lower than those in mice infected with the control virus. Notably, treatment with LPGAT1 shRNA adenovirus caused a marked reduction in serum triacylglycerol and cholesterol levels and a significant increase in hepatic cholesterol level. These findings indicate that LPGAT1, a newly identified MGAT enzyme, plays a significant role in hepatic triacylglycerol synthesis and secretion in db/db mice.

Altered small intestinal absorptive enzyme activities in leptin-deficient obese mice: influence of bowel resection

Background Residual bowel increases absorption after massive small bowel resection. Leptin affects intestinal adaptation, carbohydrate, peptide, and lipid handling. Sucrase, peptidase, and acyl coenzyme A:monoacylglycerol acyltransferase (MGAT) are involved in carbohydrate, protein, and lipid absorption. We hypothesized that leptin-deficient obese mice would have altered absorptive enzymes compared with controls before and after small bowel resection. Methods Sucrase, peptidase (aminopeptidase N [ApN], dipeptidyl peptidase IV [DPPIV]), and MGAT activities were determined from lean control (C57BL/6J, n = 16) and leptin-deficient ( Lep ob , n = 16) mice small bowel before and after 50% resection. Results Ileal sucrase activity was greater in obese mice before and after resection. Jejunal ApN and DPPIV activities were lower for obese mice before resection; ileal ApN activity was unaltered after resection for both strains. Resection increased DPPIV activity in both strains. Jejunal MGAT in obese mice decreased postresection. In both strains, ileal MGAT activity decreased after resection, and obese mice had greater activity in remnant ileum. Conclusions After small bowel resection, leptin-deficient mice have increased sucrase activity and diminished ileal ApN, DPPIV, and MGAT activity compared with controls. Therefore, we conclude that leptin deficiency alters intestinal enzyme activity in unresected animals and after small bowel resection. Altered handling of carbohydrate, protein, and lipid may contribute to obesity and diabetes in leptin-deficient mice.