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Sirtuins are NAD(+)-dependent protein deacetylases. They mediate adaptive responses to a variety of stresses, including calorie restriction and metabolic stress. Sirtuin 3 (SIRT3) is localized in the mitochondrial matrix, where it regulates the acetylation levels of metabolic enzymes, including acetyl coenzyme A synthetase 2 (refs 1, 2). Mice lacking both Sirt3 alleles appear phenotypically normal under basal conditions, but show marked hyperacetylation of several mitochondrial proteins. Here we report that SIRT3 expression is upregulated during fasting in liver and brown adipose tissues. During fasting, livers from mice lacking SIRT3 had higher levels of fatty-acid oxidation intermediate products and triglycerides, associated with decreased levels of fatty-acid oxidation, compared to livers from wild-type mice. Mass spectrometry of mitochondrial proteins shows that long-chain acyl coenzyme A dehydrogenase (LCAD) is hyperacetylated at lysine 42 in the absence of SIRT3. LCAD is deacetylated in wild-type mice under fasted conditions and by SIRT3 in vitro and in vivo; and hyperacetylation of LCAD reduces its enzymatic activity. Mice lacking SIRT3 exhibit hallmarks of fatty-acid oxidation disorders during fasting, including reduced ATP levels and intolerance to cold exposure. These findings identify acetylation as a novel regulatory mechanism for mitochondrial fatty-acid oxidation and demonstrate that SIRT3 modulates mitochondrial intermediary metabolism and fatty-acid use during fasting.

Cells remodel glycerophospholipid acyl chains via the Lands cycle to adjust membrane properties. Membrane-bound O-acyltransferase (MBOAT) 7 acylates lyso-phosphatidylinositol (lyso-PI) with arachidonyl-CoA. MBOAT7 mutations cause brain developmental disorders, and reduced expression is linked to fatty liver disease. In contrast, increased MBOAT7 expression is linked to hepatocellular and renal cancers. The mechanistic basis of MBOAT7 catalysis and substrate selectivity are unknown. Here, we report the structure and a model for the catalytic mechanism of human MBOAT7. Arachidonyl-CoA and lyso-PI access the catalytic center through a twisted tunnel from the cytosol and lumenal sides, respectively. N-terminal residues on the ER lumenal side determine phospholipid headgroup selectivity: swapping them between MBOATs 1, 5, and 7 converts enzyme specificity for different lyso-phospholipids. Finally, the MBOAT7 structure and virtual screening enabled identification of small-molecule inhibitors that may serve as lead compounds for pharmacologic development. Wang et al. report a structure for human MBOAT7, the enzyme responsible for remodeling acyl chains of phosphatidylinositol. The structure enabled the identification of MBOAT7 inhibitors and provides insights into substrate specificity among MBOATs. [ABSTRACT FROM AUTHOR]

Inhibitors of triacylglycerol (TG) synthesis have been developed to treat metabolism-related diseases, but we know little about their mechanisms of action. Here, we report cryo-EM structures of the TG-synthesis enzyme acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), a membrane bound O-acyltransferase (MBOAT), in complex with two different inhibitors, T863 and DGAT1IN1. Each inhibitor binds DGAT1's fatty acyl-CoA substrate binding tunnel that opens to the cytoplasmic side of the ER. T863 blocks access to the tunnel entrance, whereas DGAT1IN1 extends further into the enzyme, with an amide group interacting with more deeply buried catalytic residues. A survey of DGAT1 inhibitors revealed that this amide group may serve as a common pharmacophore for inhibition of MBOATs. The inhibitors were minimally active against the related MBOAT acyl-CoA:cholesterol acyltransferase 1 (ACAT1), yet a single-residue mutation sensitized ACAT1 for inhibition. Collectively, our studies provide a structural foundation for developing DGAT1 and other MBOAT inhibitors. Sui et al. elucidate the mechanisms of action for small molecule inhibitors of human triacylglycerol synthesis enzyme DGAT1 and provide insights into how these inhibitors achieve selectivity for DGAT1 rather than other closely related MBOAT enzymes. [ABSTRACT FROM AUTHOR]

Haploinsufficiency of the progranulin (PGRN) gene (GRN) causes familial frontotemporal lobar degeneration (FTLD) and modulates an innate immune response in humans and in mouse models. GRN polymorphism may be linked to late-onset Alzheimer's disease (AD). However, the role of PGRN in AD pathogenesis is unknown. Here we show that PGRN inhibits amyloid β (Aβ) deposition. Selectively reducing microglial expression of PGRN in AD mouse models impaired phagocytosis, increased plaque load threefold and exacerbated cognitive deficits. Lentivirus-mediated PGRN overexpression lowered plaque load in AD mice with aggressive amyloid plaque pathology. Aβ plaque load correlated negatively with levels of hippocampal PGRN, showing the dose-dependent inhibitory effects of PGRN on plaque deposition. PGRN also protected against Aβ toxicity. Lentivirus-mediated PGRN overexpression prevented spatial memory deficits and hippocampal neuronal loss in AD mice. The protective effects of PGRN against Aβ deposition and toxicity have important therapeutic implications. We propose enhancing PGRN as a potential treatment for PGRN-deficient FTLD and AD., PGRN is a secreted pleiotropic growth factor expressed in peripheral organs and the central nervous system. In the brain, PGRN is expressed in neurons and microglia (1-3). Loss-of-function mutations in [...]

Congenital diarrheal disorders (CDDs) are a collection of rare, heterogeneous enteropathies with early onset and often severe outcomes. Here, we report a family of Ashkenazi Jewish descent, with 2 out of 3 children affected by CDD. Both affected children presented 3 days after birth with severe, intractable diarrhea. One child died from complications at age 17 months. The second child showed marked improvement, with resolution of most symptoms at 10 to 12 months of age. Using exome sequencing, we identified a rare splice site mutation in the DGAT1 gene and found that both affected children were homozygous carriers. Molecular analysis of the mutant allele indicated a total loss of function, with no detectable DGAT1 protein or activity produced. The precise cause of diarrhea is unknown, but we speculate that it relates to abnormal fat absorption and buildup of DGAT substrates in the intestinal mucosa. Our results identify DGAT1 loss-of-function mutations as a rare cause of CDDs. These findings prompt concern for DGAT1 inhibition in humans, which is being assessed for treating metabolic and other diseases., Introduction Congenital diarrheal disorders (CDDs) are rare and heterogeneous enteropathies, often with severe clinical manifestations (1), (2). Those whose cause has been identified typically result from autosomal recessive mutations. Affected [...]

Progranulin (PGRN) is a widely expressed secreted protein that is linked to inflammation. In humans, PGRN haploinsufficiency is a major inherited cause of frontotemporal dementia (FTD), but how PGRN deficiency causes neurodegeneration is unknown. Here we show that loss of PGRN results in increased neuron loss in response to injury in the CNS. When exposed acutely to 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydrophine (MPTP), mice lacking PGRN ([Grn.sup.-/-]) showed more neuron loss and increased microgliosis compared with wild-type mice. The exacerbated neuron loss was due not to selective vulnerability of [Grn.sup.-/-] neurons to MPTP, but rather to an increased microglial inflammatory response. Consistent with this, conditional mutants lacking PGRN in microglia exhibited MPTP-induced phenotypes similar to [Grn.sup.-/-] mice. Selective depletion of PGRN from microglia in mixed cortical cultures resulted in increased death of wild-type neurons in the absence of injury. Furthermore, [Grn.sup.-/-] microglia treated with LPS/IFN-γ exhibited an amplified inflammatory response, and conditioned media from these microglia promoted death of cultured neurons. Our results indicate that PGRN deficiency leads to dysregulated microglial activation and thereby contributes to increased neuron loss with injury. These findings suggest that PGRN deficiency may cause increased neuron loss in other forms of CNS injury accompanied by neuroinflammation., Introduction Progranulin (PGRN) is an approximately 70-kDa secreted protein involved in cellular processes such as wound healing and inflammation (1), (2). PGRN has been implicated as a regulator of TNF-α-mediated [...]

Hepatitis C virus (HCV) infection is closely tied to the lipid metabolism of liver cells. Here we identify the triglyceride-synthesizing enzyme diacylglycerol acyltransferase-1 (DGAT1) as a key host factor for HCV infection. DGAT1 interacts with the viral nucleocapsid core and is required for the trafficking of core to lipid droplets. Inhibition of DGAT1 activity or RNAi-mediated knockdown of DGAT1 severely impairs infectious virion production, implicating DGAT1 as a new target for antiviral therapy., Over 160 million individuals are infected with HCV, and, in ~80% of cases, infection persists and can lead to severe liver disease. No vaccine is available, and current treatments are [...]

Diet-induced obesity (DIO) leads to inflammatory activation of macrophages in white adipose tissue (WAT) and subsequently to insulin resistance. PPARγ agonists are antidiabetic agents known to suppress inflammatory macrophage activation and to induce expression of the triacylglycerol (TG) synthesis enzyme acyl CoA: diacylglycerol acyltransferase 1 (DGAT1) in WAT and in adipocytes. Here, we investigated in mice the relationship between macrophage lipid storage capacity and DIO-associated inflammatory macrophage activation. Mice overexpressing DGAT1 in both macrophages and adipocytes (referred to herein as aP2-Dgat1 mice) were more prone to DIO but were protected against inflammatory macrophage activation, macrophage accumulation in WAT, systemic inflammation, and insulin resistance. To assess the contribution of macrophage DGAT1 expression to this phenotype, we transplanted wild-type mice with aP2-Dgat1 BM. These mice developed DIO similar to that of control mice but retained the protection from WAT inflammation and insulin resistance seen in aP2-Dgat1 mice. In isolated macrophages, Dgat1 mRNA levels correlated directly with TG storage capacity and inversely with inflammatory activation by saturated fatty acids (FAs). Moreover, PPARγ agonists increased macrophage Dgat1 mRNA levels, and the protective effects of these agonists against FA-induced inflammatory macrophage activation were absent in macrophages isolated from Dgat1-null mice. Thus, increasing DGAT1 expression in murine macrophages increases their capacity for TG storage, protects against FA-induced inflammatory activation, and is sufficient to reduce the inflammatory and metabolic consequences of DIO., Introduction Chronic diet-induced obesity (DIO) promotes infiltration of the white adipose tissue (WAT) by monocyte-derived phagocytic and antigen-presenting cells that include macrophages and dendritic cells. These macrophages accumulate in crown-like [...]

Eukaryotic cells store neutral lipids in cytoplasmic lipid droplets (1,2) enclosed in a monolayer of phospholipids and associated proteins (3,4). These dynamic organelles (5) serve as the principal reservoirs for [...]

Numerous mutations that impair retrograde membrane trafficking between endosomes and the Golgi apparatus lead to neurodegenerative diseases. For example, mutations in the endosomal retromer complex are implicated in Alzheimer’s and Parkinson’s diseases, and mutations of the Golgi-associated retrograde protein (GARP) complex cause progressive cerebello-cerebral atrophy type 2 (PCCA2). However, how these mutations cause neurodegeneration is unknown. GARP mutations in yeast, including one causing PCCA2, result in sphingolipid abnormalities and impaired cell growth that are corrected by treatment with myriocin, a sphingolipid synthesis inhibitor, suggesting that alterations in sphingolipid metabolism contribute to cell dysfunction and death. Here we tested this hypothesis in wobbler mice, a murine model with a homozygous partial loss-of-function mutation in Vps54 (GARP protein) that causes motor neuron disease. Cytotoxic sphingoid longchain bases accumulated in embryonic fibroblasts and spinal cords from wobbler mice. Remarkably, chronic treatment of wobbler mice with myriocin markedly improved their wellness scores, grip strength, neuropathology, and survival. Proteomic analyses of wobbler fibroblasts revealed extensive missorting of lysosomal proteins, including sphingolipid catabolism enzymes, to the Golgi compartment, which may contribute to the sphingolipid abnormalities. Our findings establish that altered sphingolipid metabolism due to GARP mutations contributes to neurodegeneration and suggest that inhibiting sphingolipid synthesis might provide a useful strategy for treating these disorders. [ABSTRACT FROM AUTHOR]

The diagnosis of hemochromatosis, or 'bronze diabetes,' should be considered in adult patients, especially men with non-insulin-dependent diabetes mellitus (NIDDM). Idiopathic hemochromatosis (IH) results from an inherited disorder of increased [...]

In the article, the authors discuss the benefits of scientific partnership or collaboration in modern science, particularly in working in research laboratories. Also cited are some successful partnerships like Mike Brown and Joe Goldstein, Carl and Gerty Cori, and Mike Bishop and Harold Varmus, tips in finding a partner, and pointers in managing a joint laboratory.

Vertical sleeve gastrectomy (VSG) is currently one of the most effective treatments for obesity. Despite recent developments, the underlying mechanisms that contribute to the metabolic improvements following bariatric surgery remain unresolved. VSG reduces postprandial intestinal triglyceride (TG) production, but whether the effects of VSG on intestinal metabolism are related to metabolic outcomes has yet to be established. The lipid synthesis enzyme acyl CoA:monoacylglycerol acyltransferase-2 (Mogat2; MGAT2) plays a crucial role in the assimilation of dietary fat in the intestine and in regulation of adiposity stores as well. Given the phenotypic similarities between VSG-operated and MGAT2-deficient animals, we reasoned that this enzyme could also have a key role in mediating the metabolic benefits of VSG. However, VSG reduced body weight and fat mass and improved glucose metabolism similarly in whole body MGAT2-deficient (Mogat2-/-) mice and wild-type littermates. Furthermore, along with an increase in energy expenditure, surgically naive Mogat2-/- mice had altered macronutrient preference, shifting preference away from fat and toward carbohydrates, and increased locomotor activity. Collectively, these data suggest that the beneficial effects of VSG on body weight and glucose metabolism are independent of MGAT2 activity and rather that they are separate from the effects of MGAT2 deficiency. Because MGAT2 inhibitors are proposed as a pharmacotherapeutic option for obesity, our data suggest that, in addition to increasing energy expenditure, shifting macronutrient preference away from fat could be another important mechanism by which these compounds could contribute to weight loss. [ABSTRACT FROM AUTHOR]

Transactive response DNA-binding protein 43 (TDP-43) is a major pathological protein in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). There are many disease-associated mutations in TDP-43, and several cellular and animal models with ectopic overexpression of mutant TDP-43 have been established. Here we sought to study altered molecular events in FTD and ALS by using induced pluripotent stem cell (iPSC) derived patient neurons. We generated multiple iPSC lines from an FTD/ALS patient with the TARDBP A90V mutation and from an unaffected family member who lacked the mutation. After extensive characterization, two to three iPSC lines from each subject were selected, differentiated into postmitotic neurons, and screened for relevant cell-autonomous phenotypes. Patient-derived neurons were more sensitive than control neurons to 100 nM straurosporine but not to other inducers of cellular stress. Three disease-relevant cellular phenotypes were revealed under staurosporine-induced stress. First, TDP-43 was localized in the cytoplasm of a higher percentage of patient neurons than control neurons. Second, the total TDP-43 level was lower in patient neurons with the A90V mutation. Third, the levels of microRNA-9 (miR-9) and its precursor pri-miR-9-2 decreased in patient neurons but not in control neurons. The latter is likely because of reduced TDP-43, as shRNA-mediated TDP-43 knockdown in rodent primary neurons also decreased the pri-miR-9-2 level. The reduction in miR-9 expression was confirmed in human neurons derived from iPSC lines containing the more pathogenic TARDBP M337V mutation, suggesting miR-9 downregulation might be a common pathogenic event in FTD/ALS. These results show that iPSC models of FTD/ALS are useful for revealing stress-dependent cellular defects of human patient neurons containing rare TDP-43 mutations in their native genetic contexts. [ABSTRACT FROM AUTHOR]

Progranulin (PGRN) is a secreted glycoprotein expressed in neurons and glia that is implicated in neuronal survival on the basis that mutations in the GRN gene causing haploinsufficiency result in a familial form of frontotemporal dementia (FTD). Recently, a direct interaction between PGRN and tumor necrosis factor receptors (TNFR I/II) was reported and proposed to be a mechanism by which PGRN exerts anti-inflammatory activity, raising the possibility that aberrant PGRN-TNFR interactions underlie the molecular basis for neuroinflammation in frontotemporal lobar degeneration pathogenesis. Here, we report that we find no evidence for a direct physical or functional interaction between PGRN and TNFRs. Using coimmunoprecipitation and surface plasmon resonance (SPR) we replicated the interaction between PGRN and sortilin and that between TNF and TNFR1/II, but not the interaction between PGRN and TNFRs. Recom-binant PGRN or transfection of a cDNA encoding PGRN did not antagonize TNF-dependent NFKB, Akt, and Erk1/2 pathway activation; inflammatory gene expression; or secretion of inflammatory factors in BV2 microglia and bone marrow-derived macrophages (BMDMs). Moreover, PGRN did not antagonize TNF-induced cytotoxicity on dopaminergic neuroblastoma cells. Last, co-addition or pre-incubation with various N- or C-terminal-tagged recombinant PGRNs did not alter lipopolysaccharide-induced inflammatory gene expression or cytokine secretion in any cell type examined, including BMDMs from Grn+/-- or Grn--/-- mice. Therefore, the neuroinflammatory phenotype associated with PGRN deficiency in the CNS is not a direct consequence of the loss of TNF antagonism by PGRN, but may be a secondary response by glia to disrupted interactions between PGRN and Sortilin and/or other binding partners yet to be identified. [ABSTRACT FROM AUTHOR]

Frontotemporal dementia (FTD) is a neurodegenerative disease with hallmark deficits in social and emotional function. Heterozygous loss-of-function mutations in GRN, the progranulin gene, are a common genetic cause of the disorder, but the mechanisms by which progranulin haploinsufficiency causes neuronal dysfunction in FTD are unclear. Homozygous progranulin knock-out (Grn-/-) mice have been studied as a model of this disorder and show behavioral deficits and a neuroinflammatory phenotype with robust microglial activation. However, homozygous GRN mutations causing complete progranulin deficiency were recently shown to cause a different neurological disorder, neuronal ceroid lipofuscinosis, suggesting that the total absence of progranulin may have effects distinct from those of haploinsufficiency. Here, we studied progranulin heterozygous (Grn+/-) mice, which model progranulin haploinsufficiency. We found that Grn-/- mice developed age-dependent social and emotional deficits potentially relevant to FTD. However, unlike Grn-/- mice, behavioral deficits in Grn mice occurred in the absence of gliosis or increased expression of tumor necrosis factor-ɑ. Instead, we found neuronal abnormalities in the amygdala, an area of selective vulnerability in FTD, in Grn-/- mice. Our findings indicate that FTD-related deficits resulting from progranulin haploinsufficiency can develop in the absence of detectable gliosis and neuroinflammation, thereby dissociating microglial activation from functional deficits and suggesting an important effect of progranulin deficiency on neurons. [ABSTRACT FROM AUTHOR]

Frontotemporal lobar degeneration is a progressive neurodegenerative syndrome that is the second most common cause of early-onset dementia. Mutations in the progranulin gene are a major cause of familial frontotemporal lobar degeneration [Baker M, et al. (2006) Nature 442:916-919 and Cruts M, et al. (2006) Nature 442:920-924]. Although progranulin is involved in wound healing, inflammation, and tumor growth, its role in the nervous system and the mechanism by which insufficient levels result in neurodegeneration are poorly understood [Eriksen and Mackenzie (2008) J Neurochem 104:287-297]. We have characterized the normal function of progranulin in the nematode Caenorhabditis elegans. We found that mutants lacking pgrn-1 appear grossly normal, but exhibit fewer apoptotic cell corpses during development. This reduction in corpse number is not caused by reduced apoptosis, but instead by more rapid clearance of dying cells. Likewise, we found that macrophages cultured from progranulin KO mice displayed enhanced rates of apoptotic-cell phagocytosis. Although most neurodegenerative diseases are thought to be caused by the toxic effects of aggregated proteins, our findings suggest that susceptibility to neurodegeneration may be increased by a change in the kinetics of programmed cell death. We propose that cells that might otherwise recover from damage or injury are destroyed in progranulin mutants, which in turn facilitates disease progression. [ABSTRACT FROM AUTHOR]

Progranulin deficiency is thought to cause some forms of frontotemporal dementia (FTD), a major early-onset agedependent neurodegenerative disease. How progranulin (PGRN) expression is regulated is largely unknown. We identified an evolutionarily conserved binding site for microRNA-29b (miR-29b) in the 39 untranslated region (39UTR) of the human PGRN (hPGRN) mRNA. miR-29b downregulates the expression of luciferase through hPGRN or mouse PGRN (mPGRN) 39UTRs, and the regulation was abolished by mutations in the miR-29b binding site. To examine the direct effect of manipulating endogenous miR-29b on hPGRN expression, we established a stable NIH3T3 cell line that expresses hPGRN under the control of the cytomegalovirus promoter. Ectopic expression of miR-29b decreased hPGRN expression at the both mRNA and protein levels. Conversely, knockdown of endogenous miR-29b with locked nucleic acid increased the production and secretion of hPGRN in NIH3T3 cells. Endogenous hPGRN in HEK 293 cells was also regulated by miR-29b. These findings identify miR-29b as a novel posttranscriptional regulator of PGRN expression, raising the possibility that miR- 29b or other miRNAs might be targeted therapeutically to increase hPGRN levels in some FTD patients. [ABSTRACT FROM AUTHOR]

Insulin resistance and type 2 diabetes are frequently accompanied by lipid accumulation in skeletal muscle. However, it is unknown whether primary lipid deposition in skeletal muscle is sufficient to cause insulin resistance or whether the type of muscle fiber, oxidative or glycolytic fiber, is an important determinant of lipid-mediated insulin resistance. Here we utilized transgenic mice to test the hypothesis that lipid accumulation specifically in glycolytic muscle promotes insulin resistance. Overexpression of DGAT2, which encodes an acyl-CoA:diacylglycerol acyltransferase that catalyzes triacylglycerol (TG) synthesis, in glycolytic muscle of mice increased the content of TG, ceramides, and unsaturated long-chain fatty acyl-CoAs in young adult mice. This lipid accumulation was accompanied by impaired insulin signaling and insulin-mediated glucose uptake in glycolytic muscle and impaired whole body glucose and insulin tolerance. We conclude that DGAT2-mediated lipid deposition specifically in glycolytic muscle promotes insulin resistance in this tissue and may contribute to the development of diabetes. [ABSTRACT FROM AUTHOR]

A pluripotent cell line, C3H10T1/2, is induced to undergo adipogenesis by a mixture of factors that includes a glucocorticoid such as dexamethasone. We found that expression of myostatin (MSTN), a TGF-β family member extensively studied in muscle, was induced by dexamethasone under those differentiation conditions. Moreover, MSTN could substitute for dexamethasone in the adipogenesis mixture. However, the adipocytes induced by MSTN in both cell culture and transgenic mice were small and expressed markers characteristic of immature adipocytes. These adipocytes exhibited cell-autonomous increases in insulin sensitivity and glucose oxidation. In mice, these effects produced elevated systemic insulin sensitivity and resistance to diet-induced obesity. Modulation of the final stages of adipogenesis may provide a novel approach to understanding and treating metabolic disease. [ABSTRACT FROM AUTHOR]

Mice lacking acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), an enzyme that catalyzes the terminal step in triacylglycerol synthesis, have enhanced insulin sensitivity and are protected from obesity, a result of increased energy expenditure. In these mice, factors derived from white adipose tissue (WAT) contribute to the systemic changes in metabolism. One such factor, adiponectin, increases fatty acid oxidation and enhances insulin sensitivity. To test the hypothesis that adiponectin is required for the altered energy and glucose metabolism in DGAT1-deficient mice, we generated adiponectin-deficient mice and introduced adiponectin deficiency into DGAT1-deficient mice by genetic crosses. Although adiponectin-deficient mice fed a high-fat diet were heavier, exhibited worse glucose tolerance, and had more hepatic triacylglycerol accumulation than wild-type controls, mice lacking both DGAT1 and adiponectin, like DGAT1-deficient mice, were protected from diet-induced obesity, glucose intolerance, and hepatic steatosis. These findings indicate that adiponectin is required for normal energy, glucose, and lipid metabolism but that the metabolic changes induced by DGAT1-deficient WAT are independent of adiponectin and are likely due to other WAT-derived factors. Our findings also suggest that the pharmacological inhibition of DGAT1 may be useful for treating human obesity and insulin resistance associated with low circulating adiponectin levels. [ABSTRACT FROM AUTHOR]

Mammary gland development is a complex process that is dependent on interactions between the developing mammary epithelium and the surrounding stromal tissues. We show that mice lacking the triglyceride synthesis enzyme acyl CoA:diacylglycerol transferase 1 (DGAT1) have impaired mammary gland development, characterized by decreased epithelial proliferation and alveolar development, and reduced expression of markers of functional differentiation. Transplantation studies demonstrate that the impaired development results from a deficiency of DGAT1 in both the stromal and epithelial tissues. Our findings are the first to link defects in stromal lipid metabolism to impaired mammary gland development. [ABSTRACT FROM AUTHOR]

Discusses a study on the composition of MGAT2, a monoacylglycerol acyltransferase expressed in the small intestine. Role in the synthesis of diacylglycerol, a precursor of triacylglycerol; Significance to the absorption of dietary fat by catalyzing the resynthesis of triacylglycerol in enterocytes; Resynthesis required for the assembly of lipoproteins that transport absorbed fat to other tissues.

Excess lipid accumulation in non-adipose tissues is associated with insulin resistance, pancreatic β-cell apoptosis and heart failure. Here, we demonstrate in cultured cells that the relative toxicity of two common dietary long chain fatty acids is related to channeling of these lipids to distinct cellular metabolic fates. Oleic acid supplementation leads to triglyceride accumulation and is well tolerated, whereas excess palmitic acid is poorly incorporated into triglyceride and causes apoptosis. Unsaturated fatty acids rescue palmitate-induced apoptosis by channeling palmitate into triglyceride pools and away from pathways leading to apoptosis. Moreover, in the setting of impaired triglyceride synthesis, oleate induces lipotoxicity. Our findings support a model of cellular lipid metabolism in which unsaturated fatty acids serve a protective function against lipotoxicity though promotion of triglyceride accumulation. [ABSTRACT FROM AUTHOR]

Deficiency of acyl CoA:cholesterol acyitransferase 2 (ACAT2) in mice results in a reduction in cholesterol ester synthesis in the small intestine and liver, which in turn limits intestinal cholesterol absorption, hepatic cholesterol gallstone formation, and the accumulation of cholesterol esters in the plasma lipoproteins. Here we examined the contribution of ACAT2-derived cholesterol esters to atherosclerosis by crossing ACAT2-deficient (ACAT2[sup -/-]) mice with apolipoprotein (apo) E-deficient (ApoE[sup -/-]) mice, an atherosclerosissusceptible strain that has impaired apoE-mediated clearance of apoB-containing lipoproteins. ACAT2[sup -/-] ApoE[sup -/-] mice and ACAT2[sup +/+] ApoE[sup -/-] (control) mice had similar elevations of plasma apoB and total plasma lipids; however, the lipid cores of the apoB-containing lipoproteins in ACAT2[sup -/-] ApoE[sup -/-] mice contained primarily triglycerides rather than cholesterol esters. At 30 wk of age, only the control mice had significant atherosclerosis, which was nearly absent in ACAT2[sup -/-] ApoE[sup -/-] mice. ACAT2 deficiency in the apoE-deficient background also led to a compensatory increase in the activity of lecithin?cholesterol acyltransferase, the major plasma cholesterol esterification enzyme, which increased highdensity iipoprotein cholesterol esters. Our results demonstrate the crucial role of ACAT2-derived cholesterol esters in the development of atherosclerosis in mice and suggest that triglyceride-rich apoBcontaining lipoproteins are not as atherogenic as those containing cholesterol esters. Our results also support the rationale of pharmacological inhibition of ACAT2 as a therapy for atherosclerosis. [ABSTRACT FROM AUTHOR]

Mice lacking acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), a key enzyme in triglyceride synthesis, have increased energy expenditure and therefore are resistant to obesity. Because ambient temperature can significantly affect energy expenditure in mice, we undertook these studies to determine the effects of different ambient temperatures on energy expenditure, food intake, and thermoregulation in DGAT1-deficient [Dgat1(-/-)] mice. Dgat1(-/-) mice had increased energy expenditure irrespective of changes in the ambient temperature. Although core temperature was normal, surface temperature was increased in Dgat1(-/-) mice, most likely reflecting an active mechanism to dissipate heat from increased thermogenesis. Dgat1(-/-) mice had increased food intake at baseline, and this hyperphagia became more pronounced upon exposure to cold. When fasted in a cold environment, Dgat1(-/-) mice developed hypothermia, which was associated with hypoglycemia. These results suggest that the hyperphagia in Dgat1(-/-) mice is a secondary mechanism that compensates for the increased utilization of fuel substrates. Our findings offer insights into the mechanisms of hyperphagia and increased energy expenditure in a murine model of obesity resistance. [ABSTRACT FROM AUTHOR]

Examines the identification of a gene encoding an Acyl-CoA:monoacylglycerol acyltransferase (MGAT1) in mice. Role of MGAT1 in the absorption of dietary fat; Catalysis of diacylglycerol synthesis by MGAT1; Function of MGAT1 enzymes in mammalian glycerolipid metabolism.

Studies the introduction of huma apolipoprotein E4 'domain interaction' into mouse apolipoprotein E (ApoE). Distribution of Arg-61 and wild type in plasma lipoproteins; Generation and characterization of an Arg-61 Apoe allele; Plasma lipid levels.

NAT1/p97/DAP5 is a newly identified protein that shares homology with the translation initiation factor eIF4G. Studies in vitro and in transfected cells indicated that NAT1 might suppress global translation, thereby repressing cellular proliferation. Here we studied the functions of NAT1 in vivo by disrupting its gene in mice. NAT1-/- embryos died during gostrulation, indicating a crucial role for NAT1 in embryo-genesis. Undifferentiated NAT1-/- embryonic stem cells were normal in morphology, proliferation, global translation and gene expression profile. However, NAT1-/- cells exhibited an impaired ability to differentiate: they were resistant to differentiation induced by retinoic acid, and teratomas derived from them consisted of undifferentiated and poorly differentiated tissues. The expression of retinoie acid-responsive genes, such as the cell-cycle inhibitor p21WAF1, was selectively impaired in NAT1-/- cells. Transcription from synthetic retinoic acid-responsive elements was also impaired. These data demonstrated that this translation initiation factor homolog controls specific gene expression pathways required for cellular differentiation. [ABSTRACT FROM AUTHOR]

Presents research which studied the role of protease-activated receptors in platelet activation by thrombin. Health effects of platelet-dependent arterial thrombosis; Role of thrombin in platelet activation; Role of protease-activated receptor-1 (PAR1); Effects of PAR3; Identification of PAR4; PAR-activating peptides; Two-receptor system for platelet activation by thrombin.