Showing papers by "Robert V. Farese published in 2002"

Increased insulin and leptin sensitivity in mice lacking acyl CoA:diacylglycerol acyltransferase 1

Abstract: Acyl coenzyme A:diacylglycerol acyltransferase 1 (DGAT1) is one of two known DGAT enzymes that catalyze the final step in mammalian triglyceride synthesis. DGAT1-deficient mice are resistant to diet-induced obesity through a mechanism involving increased energy expenditure. Here we show that these mice have decreased levels of tissue triglycerides, as well as increased sensitivity to insulin and to leptin. Importantly, DGAT1 deficiency protects against insulin resistance and obesity in agouti yellow mice, a model of severe leptin resistance. In contrast, DGAT1 deficiency did not affect energy and glucose metabolism in leptin-deficient (ob/ob) mice, possibly due in part to a compensatory upregulation of DGAT2 expression in the absence of leptin. Our results suggest that inhibition of DGAT1 may be useful in treating insulin resistance and leptin resistance in human obesity.

Identification of a gene encoding MGAT1, a monoacylglycerol acyltransferase.

Abstract: Acyl-CoA:monoacylglycerol acyltransferase (MGAT) catalyzes the synthesis of diacylglycerol, the precursor of physiologically important lipids such as triacylglycerol and phospholipids. In the intestine, MGAT plays a major role in the absorption of dietary fat because resynthesis of triacylglycerol is required for the assembly of lipoproteins that transport absorbed fat to other tissues. MGAT activity has also been reported in mammalian liver and white adipose tissue. However, MGAT has never been purified to homogeneity from mammalian tissues, and its gene has not been cloned. We identified a gene that encodes an MGAT (MGAT1) in mice. This gene has sequence homology with members of a recently identified diacylglycerol acyltransferase gene family. Expression of the MGAT1 cDNA in insect cells markedly increased MGAT activity in cell membranes. In addition, MGAT activity was proportional to the level of MGAT1 protein expressed, and the amount of diacylglycerol produced depended on the concentration of either of its substrates, oleoyl-CoA or monooleoylglycerol. In mice, MGAT1 expression and MGAT activity were detected in the stomach, kidney, white and brown adipose tissue, and liver. However, MGAT1 was not expressed in the small intestine, implying the existence of a second MGAT gene. The identification of the MGAT1 gene should greatly facilitate research on the identification of the intestinal MGAT gene and on the function of MGAT enzymes in mammalian glycerolipid metabolism.

Function and dysfunction of aPKC isoforms for glucose transport in insulin-sensitive and insulin-resistant states.

Abstract: Considerable evidence suggests that atypical protein kinase C isoforms (aPKCs), serving downstream of insulin receptor substrates and phosphatidylinositol (PI) 3-kinase, are required for insulin-st...

Knockout of PKCα enhances insulin signaling through PI3K

Abstract: Insulin stimulates glucose transport and certain other metabolic processes by activating atypical PKC isoforms (lambda, zeta, iota) and protein kinase B (PKB) through increases in D3-polyphosphoinositides derived from the action of PI3K. The role of diacylglycerol-sensitive PKC isoforms is less clear as they have been suggested to be both activated by insulin and yet inhibit insulin signaling to PI3K. Presently, we found that insulin signaling to insulin receptor substrate 1-dependent PI3K, PKB, and PKC lambda, and downstream processes, glucose transport and activation of ERK, were enhanced in skeletal muscles and adipocytes of mice in which the ubiquitous conventional diacylglycerol-sensitive PKC isoform, PKC alpha, was knocked out by homologous recombination. On the other hand, insulin provoked wortmannin-insensitive increases in immunoprecipitable PKC alpha activity in adipocytes and skeletal muscles of wild-type mice and rats. We conclude that 1) PKC alpha is not required for insulin-stimulated glucose transport, and 2) PKC alpha is activated by insulin at least partly independently of PI3K, and largely serves as a physiological feedback inhibitor of insulin signaling to the insulin receptor substrate 1/PI3K/PKB/PKC lambda/zeta/iota complex and dependent metabolic processes.

Leptin modulates the effects of acyl CoA:diacylglycerol acyltransferase deficiency on murine fur and sebaceous glands

Abstract: Acyl CoA:diacylglycerol acyltransferase (DGAT) is a ubiquitously expressed enzyme that catalyzes the final reaction in the major pathways of triglyceride synthesis. Mice lacking DGAT1 (Dgat–/–) demonstrate significant changes in lipid metabolism in several tissues, including the skin. Here we report the effects of DGAT1 deficiency on fur and sebaceous glands. Adult Dgat–/– mice had dry fur and hair loss, which were associated with atrophic sebaceous glands and fur lipid abnormalities. As a result, Dgat–/– mice had impaired water repulsion and defective thermoregulation after water immersion. These phenotypes were mostly absent in Dgat–/– mice with leptin deficiency, indicating an unexpected role for leptin in modulating the skin phenotype. Our findings indicate that DGAT1 plays an important role in normal fur and sebaceous gland physiology and provide evidence that leptin modulates these processes in the skin.

Dissociation of obesity and impaired glucose disposal in mice overexpressing acyl coenzyme a:diacylglycerol acyltransferase 1 in white adipose tissue.

Abstract: Acyl coenzyme A:diacylglycerol acyltransferase 1 (DGAT1) is one of two DGAT enzymes known to catalyze the final step in mammalian triglyceride synthesis. Mice deficient in DGAT1 are resistant to obesity and have enhanced insulin sensitivity. To understand better the relationship between triglyceride synthesis and energy and glucose metabolism, we generated transgenic (aP2- Dgat1 ) mice in which expression of murine DGAT1 in the white adipose tissue (WAT) was twofold higher than normal. aP2- Dgat1 mice that were fed a regular diet had larger adipocytes and greater total fat pad weight than wild-type (WT) mice. In response to a high-fat diet, aP2- Dgat1 mice became more obese (∼20% greater body weight after 15 weeks) than WT mice. However, the increase in adiposity in aP2- Dgat1 mice was not associated with impaired glucose disposal, as demonstrated by glucose and insulin tolerance tests. Correlating with this finding, triglyceride deposition in the liver and skeletal muscle, two major target tissues of insulin, was similar in aP2- Dgat1 and WT mice. Thus, DGAT1 overexpression in murine WAT provides a model in which obesity does not impair glucose disposal. Our findings support the lipotoxicity hypothesis that the deposition of triglycerides in insulin-sensitive tissues other than adipocytes causes insulin resistance.

PKC-ζ Mediates Insulin Effects on Glucose Transport in Cultured Preadipocyte-Derived Human Adipocytes

Abstract: Insulin-stimulated glucose transport is impaired in the early phases of type 2 diabetes mellitus. Studies in rodent cells suggest that atypical PKC (aPKC) isoforms (zeta, lamda, and iota) and PKB, and their upstream activators, PI3K and 3-phosphoinositide-dependent protein kinase-1 (PDK-1), play important roles in insulin-stimulated glucose transport. However, there is no information on requirements for aPKCs, PKB, or PDK-1 during insulin action in human cell types. Presently, by using preadipocyte-derived adipocytes, we were able to employ adenoviral gene transfer methods to critically examine these requirements in a human cell type. These adipocytes were found to contain PKC-zeta, rather than PKC-lamda/iota, as their major aPKC. Expression of kinase-inactive forms of PDK-1, PKC-zeta, and PKC-lamda (which functions interchangeably with PKC-zeta) as well as chemical inhibitors of PI 3-kinase and PKC-zeta/lamda, wortmannin and the cell-permeable myristoylated PKC-zeta pseudosubstrate, respectively, effectively inhibited insulin-stimulated glucose transport. In contrast, expression of a kinase-inactive, activation-resistant, triple alanine mutant form of PKB-alpha had little or no effect, and expression of wild-type and constitutively active PKC-zeta or PKC-lamda increased glucose transport. Our findings provide convincing evidence that aPKCs and upstream activators, PI 3-kinase and PDK-1, play important roles in insulin-stimulated glucose transport in preadipocyte-derived human adipocytes.

DGAT1 promoter polymorphism associated with alterations in body mass index, high density lipoprotein levels and blood pressure in Turkish women

Abstract: Triglyceride synthesis is catalyzed by acyl CoA:diacylglycerol acyltransferases (DGAT), microsomal enzymes that use diacylglycerol and fatty acyl CoAs as substrates. Because DGAT1 expression is up-regulated during adipocyte differentiation and DGAT1 deficiency is associated with leanness in mice, we hypothesized that alterations in DGAT1 expression may affect human body weight. We identified five polymorphisms in the human DGAT1 promoter and 5' non-coding sequence in a random Turkish population. Functional analysis of one common variant, C79T, revealed reduced promoter activity for the 79T allele in cultured cell lines. In 476 Turkish women, the 79T allele was associated with lower body mass index (BMI) (p = 0.004), conferring an odds ratio of 2.0 (95% CI = 1.30-3.07, p = 0.0001) for BMI

Skeletal Muscle Insulin Resistance in Obesity-Associated Type 2 Diabetes in Monkeys Is Linked to a Defect in Insulin Activation of Protein Kinase C-ζ/λ/ι

Abstract: Rhesus monkeys frequently develop obesity and insulin resistance followed by type 2 diabetes when allowed free access to chow. This insulin resistance is partly due to defective glucose transport into skeletal muscle. In this study, we examined signaling factors required for insulin-stimulated glucose transport in muscle biopsies taken during euglycemic-hyperinsulinemic clamps in nondiabetic, obese prediabetic, and diabetic monkeys. Insulin increased activities of insulin receptor substrate (IRS)-1-dependent phosphatidylinositol (PI) 3-kinase and its downstream effectors, atypical protein kinase Cs (aPKCs) (ζ/λ/ι) and protein kinase B (PKB) in muscles of nondiabetic monkeys. Insulin-induced increases in glucose disposal and aPKC activity diminished progressively in prediabetic and diabetic monkeys. Decreases in aPKC activation appeared to be at least partly due to diminished activation of IRS-1-dependent PI 3-kinase, but direct activation of aPKCs by the PI 3-kinase lipid product PI-3,4,5-(PO 4 ) 3 was also diminished. In conjunction with aPKCs, PKB activation was diminished in prediabetic muscle but, differently from aPKCs, seemed to partially improve in diabetic muscle. Interestingly, calorie restriction and avoidance of obesity largely prevented development of defects in glucose disposal and aPKC activation. Our findings suggest that defective activation of aPKCs contributes importantly to obesity-dependent development of skeletal muscle insulin resistance in prediabetic and type 2 diabetic monkeys.

Skeletal Muscle Insulin Resistance in Obesity-Associated Type 2 Diabetes in Monkeys Is Linked to a Defect in Insulin Activation of

Abstract: Rhesus monkeys frequently develop obesity and insulin resistance followed by type 2 diabetes when allowed free access to chow. This insulin resistance is partly due to defective glucose transport into skeletal muscle. In this study, we examined signaling factors required for insulin-stimulated glucose transport in muscle biopsies taken during euglycemic-hyperinsulinemic clamps in nondiabetic, obese prediabetic, and diabetic monkeys. Insulin increased activities of insulin receptor substrate (IRS)-1– dependent phosphatidylinositol (PI) 3-kinase and its downstream effectors, atypical protein kinase Cs (aPKCs) (//) and protein kinase B (PKB) in muscles of nondiabetic monkeys. Insulin-induced increases in glucose disposal and aPKC activity diminished progressively in prediabetic and diabetic monkeys. Decreases in aPKC activation appeared to be at least partly due to diminished activation of IRS-1– dependent PI 3-kinase, but direct activation of aPKCs by the PI 3-kinase lipid product PI-3,4,5-(PO4)3 was also diminished. In conjunction with aPKCs, PKB activation was diminished in prediabetic muscle but, differently from aPKCs, seemed to partially improve in diabetic muscle. Interestingly, calorie restriction and avoidance of obesity largely prevented development of defects in glucose disposal and aPKC activation. Our findings suggest that defective activation of aPKCs contributes importantly to obesity-dependent development of skeletal muscle insulin resistance in prediabetic and type 2 diabetic monkeys. Diabetes 51:2936 –2943, 2002

Sorbitol activates atypical protein kinase C and GLUT4 glucose transporter translocation/glucose transport through proline-rich tyrosine kinase-2, the extracellular signal-regulated kinase pathway and phospholipase D.

Abstract: Sorbitol, "osmotic stress", stimulates GLUT4 glucose transporter translocation to the plasma membrane and glucose transport by a phosphatidylinositol (PI) 3-kinase-independent mechanism that reportedly involves non-receptor proline-rich tyrosine kinase-2 (PYK2) but subsequent events are obscure. In the present study, we found that extracellular signal-regulated kinase (ERK) pathway components, growth-factor-receptor-bound-2 protein, son of sevenless (SOS), RAS, RAF and mitogen-activated protein (MAP) kinase/ERK kinase, MEK(-1), operating downstream of PYK2, were required for sorbitol-stimulated GLUT4 translocation/glucose transport in rat adipocytes, L6 myotubes and 3T3/L1 adipocytes. Furthermore, sorbitol activated atypical protein kinase C (aPKC) through a similar mechanism depending on the PYK2/ERK pathway, independent of PI 3-kinase and its downstream effector, 3-phosphoinositide-dependent protein kinase-1 (PDK-1). Like PYK2/ERK pathway components, aPKCs were required for sorbitol-stimulated GLUT4 translocation/glucose transport. Interestingly, sorbitol stimulated increases in phospholipase D (PLD) activity and generation of phosphatidic acid (PA), which directly activated aPKCs. As with aPKCs and glucose transport, sorbitol-stimulated PLD activity was dependent on the ERK pathway. Moreover, PLD-generated PA was required for sorbitol-induced activation of aPKCs and GLUT4 translocation/glucose transport. Our findings suggest that sorbitol sequentially activates PYK2, the ERK pathway and PLD, thereby increasing PA, which activates aPKCs and GLUT4 translocation. This mechanism contrasts with that of insulin, which primarily uses PI 3-kinase, D3-PO(4) polyphosphoinositides and PDK-1 to activate aPKCs.

Cbl, IRS-1, and IRS-2 Mediate Effects of Rosiglitazone on PI3K, PKC-λ, and Glucose Transport in 3T3/L1 Adipocytes

Abstract: The thiazolidenedione, rosiglitazone, increases basal and/or insulin-stimulated glucose transport in various cell types by diverse but uncertain mechanisms that may involve insulin receptor substrate (IRS)-1-dependent PI3K. Presently, in 3T3/L1 adipocytes, rosiglitazone induced sizable increases in basal glucose transport that were: dependent on PI3K, 3-phosphoinositide-dependent protein kinase-1 (PDK-1), and PKC-lambda; accompanied by increases in tyrosine phosphorylation of Cbl and Cbl-dependent increases in PI3K and PKC-lambda activity; but not accompanied by increases in IRS-1/2-dependent PI3K or protein kinase B activity. Additionally, rosiglitazone increased IRS-1 and IRS-2 levels, thereby enhancing insulin effects on IRS-1- and IRS-2-dependent PI3K and downstream signaling factors PKC-lambda and protein kinase B. Our findings suggest that Cbl participates in mediating effects of rosiglitazone on PI3K, PDK-1, and PKC-lambda and the glucose transport system and that this Cbl-dependent pathway complements the IRS-1 and IRS-2 pathways for activating PI3K, PDK-1, and PKC-lambda during combined actions of rosiglitazone and insulin in 3T3/L1 cells.

Deficiency of acyl coenzyme a:diacylglycerol acyltransferase 1 increases leptin sensitivity in murine obesity models.

Abstract: Acyl coenzyme A:diacylglycerol acyltransferase 1 (DGAT1) is one of two known enzymes that catalyze the final step in mammalian triglyceride synthesis. We have reported that DGAT1-deficient mice have increased insulin and leptin sensitivity, likely accounting for their protection against diet-induced obesity and insulin resistance. Here we show that DGAT1 deficiency enhanced the response to peripheral leptin infusion in Agouti yellow and leptin-deficient (ob/ob) mice, two genetic models of obesity and insulin resistance. Interestingly, DGAT1 deficiency did not enhance the response to intracerebroventricular leptin infusion. Moreover, DGAT1 deficiency did not alter the expression of key hypothalamic genes involved in leptin signaling or in the regulation of food intake and energy expenditure. Thus, the leptin-sensitizing effect of DGAT1 deficiency is present in both leptin-resistant and leptin-deficient genetic models of obesity and may occur in part by enhancing the effects of leptin in peripheral tissues.

Mono-and diacylglycerol acyltransferases and methods of use thereof

Abstract: Nucleic acid compositions encoding polypeptide products with diglyceride acyltransferase and/or monoacylglycerol acyltransferase activity, as well as the polypeptide products encoded thereby, i.e., mammalian DGAT2α, MGAT1, or MGAT2 polypeptide products, and methods for producing the same, are provided. Also provided are: methods and compositions for modulating DGAT2α, MGAT1, or MGAT2 activity; DGAT2α, MGAT1, or MGAT2 transgenic cells, animals and plants, as well as methods for their preparation; and methods for making diglyceride, diglyceride compositions, triglycerides and triglyceride compositions, as well as the compositions produced by these methods. The subject methods and compositions find use in a variety of different applications, including research, medicine, agriculture and industry applications.

Fatty acids, triglycerides, and glucose metabolism: recent insights from knockout mice.

Abstract: Purpose of reviewCellular lipid metabolism plays an important role in modulating glucose metabolism. Recent models of mice with disruptions in genes involved in cellular fatty acid and triglyceride metabolism have provided insight into the long recognized but incompletely understood relationship bet

Plant diacylglycerol O-acyltransferase and uses thereof

Abstract: Plant nucleic acid compositions encoding polypeptide products with diacylglyceride acyltransferase (DGAT) activity, as well as the polypeptide products encoded thereby and methods for producing the same, are provided. Methods and compositions for modulating DGAT activity in a plant, particularly DGAT activity in plant seeds, and transgenic plants with altered DGAT activity are provided. Such plants and seeds are useful in the production of human food and animal feedstuff, and have several other industrial applications. Also provided are methods for making triglycerides and triglyceride compositions, as well as the compositions produced by these methods. The subject methods and compositions find use in a variety of different applications, including research, medicine, agriculture and industry.

Gene-targeted animal model of apolipoprotein E4 domain interaction and uses thereof

Abstract: The invention provides gene-targeted non-human animals comprising a genetically modified apoE gene encodes a recombinant apoE polypeptide displaying domain interaction. The invention further provides cells isolated from the gene-targeted animals, which cells produce a recombinant apoE polypeptide displaying domain interaction. The invention further provides methods of identifying agents that reduce apoE4 domain interaction, and which are useful to treat apoE4-related neurological and cardiovascular disorders.

Methods and compositions for modulating sebaceous glands

Abstract: Methods and compositions for modulating sebaceous gland activity in a host are provided. In the subject methods, DGAT1 activity is modified, e.g., reduced or enhanced, to achieve the desired sebaceous gland activity modulation, e.g., reduction in sebum production and/or sebaceous gland size. Also provided are pharmaceutical preparations for use in practicing the subject methods. The subject methods and compositions find use in a variety of applications, including the treatment of hosts suffering from sebaceous gland related conditions, e.g., acne and related conditions.

Methods and compositions for modulating carbohydrate metabolism

Abstract: Methods and compositions for modulating carbohydrate metabolism in a host are provided. In the subject methods, diacylglycerol acyltransferase (DGAT) activity (specifically DGAT1 activity) is modulated, e.g., reduced or enhanced, to achieve a desired insulin and/or leptin sensitivity, thereby modulating carbohydrate metabolism, e.g., increasing or decreasing blood glucose levels, glucose uptake into cells and assimilation into glycogen. Also provided are pharmaceutical compositions for practicing the subject methods. The subject methods and compositions find use in a variety of applications, including the treatment of hosts suffering conditions associated with abnormal carbohydrate metabolism, such as obesity or diabetes.