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ABSTRACT: Transcription factor FoxO1 promotes hepatic glucose production. Genetic inhibition of FoxO1 function prevents diabetes in experimental animal models, providing impetus to identify pharmacological approaches to modulate this function. Altered Notch signaling is evident in tumorigenesis, and Notch antagonists are in clinical testing for application in cancer. Here we report that FoxO1 and Notch coordinately regulate hepatic glucose metabolism. Combined haploinsufficiency of FoxO1 and Notch1 markedly raises insulin sensitivity in diet-induced insulin resistance, as does liver-specific knockout of the Notch transcriptional effector Rbp-Jκ. Conversely, Notch1 gain-of-function promotes insulin resistance in a FoxO1-dependent manner and induces glucose-6-phosphatase expression. Pharmacological blockade of Notch signaling with γ-secretase inhibitors raises insulin sensitivity after in vivo administration in lean mice and in obese, insulin-resistant mice. The data identify a heretofore unknown metabolic function of Notch and suggest that Notch inhibition is beneficial in diabetes treatment, in part by helping to offset excessive FoxO1-driven hepatic glucose production.
Nature medicine 01/2011; 17(8):961-7. · 27.14 Impact Factor
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ABSTRACT: Adiponectin is an adipocyte-specific secretory protein found in circulation in several different forms and is present at significantly lower levels in the plasma of diabetic patients compared with that of insulin-sensitive individuals. We wanted to test whether insulin per se is a contributing factor toward lower plasma adiponectin concentrations and, if so, whether the splanchnic bed contributes to this phenomenon.
We sampled femoral artery and hepatic venous samples and measured the high-molecular weight (HMW) and low-molecular weight (LMW) fractions of adiponectin in 11 type 2 diabetic and 7 nondiabetic subjects matched for age, sex, and BMI during basal conditions and during a hyperglycemic (approximately 9.5 mmol/l) hyperinsulinemic (approximately 700 pmol/l) clamp.
Under these conditions, total arterial adiponectin, HMW, and the ratio of HMW to total adiponectin all were lower (P < 0.01) in the diabetic versus nondiabetic subjects, whereas the LMW form did not significantly differ. Under hyperinsulinemic conditions, total adiponectin levels dropped, primarily due to a reduction of the HMW form, whereas LMW forms were not significantly affected.
HMW adiponectin and the ratio of HMW to total adiponectin are lower in individuals with diabetes than in nondiabetic subjects. We conclude that HMW adiponectin is downregulated in hyperinsulinemia and type 2 diabetes.
Diabetes 08/2007; 56(8):2174-7. · 8.29 Impact Factor
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Andrea R Nawrocki,
Michael W Rajala,
Eva Tomas, Utpal B Pajvani,
Asish K Saha,
Myrna E Trumbauer,
Zhen Pang,
Airu S Chen,
Neil B Ruderman,
Howard Chen,
Luciano Rossetti,
Philipp E Scherer
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ABSTRACT: The adipose tissue-derived hormone adiponectin improves insulin sensitivity and its circulating levels are decreased in obesity-induced insulin resistance. Here, we report the generation of a mouse line with a genomic disruption of the adiponectin locus. We aimed to identify whether these mice develop insulin resistance and which are the primary target tissues affected in this model. Using euglycemic/insulin clamp studies, we demonstrate that these mice display severe hepatic but not peripheral insulin resistance. Furthermore, we wanted to test whether the lack of adiponectin magnifies the impairments of glucose homeostasis in the context of a dietary challenge. When exposed to high fat diet, adiponectin null mice rapidly develop glucose intolerance. Specific PPARgamma agonists such as thiazolidinediones (TZDs) improve insulin sensitivity by mechanisms largely unknown. Circulating adiponectin levels are significantly up-regulated in vivo upon activation of PPARgamma. Both TZDs and adiponectin have been shown to activate AMP-activated protein kinase (AMPK) in the same target tissues. We wanted to address whether the ability of TZDs to improve glucose tolerance is dependent on adiponectin and whether this improvement involved AMPK activation. We demonstrate that the ability of PPARgamma agonists to improve glucose tolerance in ob/ob mice lacking adiponectin is diminished. Adiponectin is required for the activation of AMPK upon TZD administration in both liver and muscle. In summary, adiponectin is an important contributor to PPARgamma-mediated improvements in glucose tolerance through mechanisms that involve the activation of the AMPK pathway.
Journal of Biological Chemistry 03/2006; 281(5):2654-60. · 4.77 Impact Factor
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Andrea R. Nawrocki,
Michael W. Rajala,
Eva Tomas, Utpal B. Pajvani,
Asish K. Saha,
Myrna E. Trumbauer,
Zhen Pang,
Airu S. Chen,
Neil B. Ruderman,
Howard Chen,
Luciano Rossetti,
Philipp E. Scherer
[show abstract]
[hide abstract]
ABSTRACT: The adipose tissue-derived hormone adiponectin improves insulin sensitivity and its circulating levels are decreased in obesity-induced
insulin resistance. Here, we report the generation of a mouse line with a genomic disruption of the adiponectin locus. We
aimed to identify whether these mice develop insulin resistance and which are the primary target tissues affected in this
model. Using euglycemic/insulin clamp studies, we demonstrate that these mice display severe hepatic but not peripheral insulin
resistance. Furthermore, we wanted to test whether the lack of adiponectin magnifies the impairments of glucose homeostasis
in the context of a dietary challenge. When exposed to high fat diet, adiponectin null mice rapidly develop glucose intolerance.
Specific PPARγ agonists such as thiazolidinediones (TZDs) improve insulin sensitivity by mechanisms largely unknown. Circulating
adiponectin levels are significantly up-regulated in vivo upon activation of PPARγ. Both TZDs and adiponectin have been shown to activate AMP-activated protein kinase (AMPK) in the
same target tissues. We wanted to address whether the ability of TZDs to improve glucose tolerance is dependent on adiponectin
and whether this improvement involved AMPK activation. We demonstrate that the ability of PPARγ agonists to improve glucose
tolerance in ob/ob mice lacking adiponectin is diminished. Adiponectin is required for the activation of AMPK upon TZD administration in both
liver and muscle. In summary, adiponectin is an important contributor to PPARγ-mediated improvements in glucose tolerance
through mechanisms that involve the activation of the AMPK pathway.
Journal of Biological Chemistry 02/2006; 281(5):2654-2660. · 4.77 Impact Factor
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ABSTRACT: Recent studies identifying obesity as a significant and increasingly more common cause of morbidity and mortality have intensified research efforts aimed at increasing our understanding of adipose tissue biology. These efforts have culminated in the discovery of several adipokines, or adipose tissue-derived hormones, that have been implicated in the regulation of multiple physiological functions, as well as the realization that adipose tissue dysfunction plays an important role in the pathogenesis of diseases such as obesity and diabetes. To better understand the role of adipose tissue in these physiological/pathological events, several studies have employed transgenic strategies to eliminate adipose tissue. However, these mouse models of congenital lipoatrophy/lipodystrophy exhibit severe metabolic and somatic cell dysfunction. To circumvent this limitation, we have designed and characterized the first inducible fatless mouse. The FAT-ATTAC mouse is a transgenic model whereby expression of a myristoylated caspase 8-FKBP fusion protein enables selective ablation of adipocytes via induction of apoptosis that occurs upon treatment with a chemical dimerizer. The FAT-ATTAC mouse model not only has the advantage that adipocyte ablation be induced at any time during development, but it is also fully reversible, as adipose tissue regenerates after cessation of dimerizer treatment. The inducibility of this fatless mouse model holds potential for revealing novel physiological roles for adipose tissue as well as its contribution to the etiology and pathogenesis of various disease states. Here we describe several ongoing areas of research employing the FAT-ATTAC mouse; in addition we describe potential uses of the targeted transgenic apoptotic approach to study other cell types of interest.
Cell cycle (Georgetown, Tex.) 10/2005; 4(9):1141-5. · 5.36 Impact Factor
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ABSTRACT: We describe the generation and characterization of the first inducible 'fatless' model system, the FAT-ATTAC mouse (fat apoptosis through targeted activation of caspase 8). This transgenic mouse develops identically to wild-type littermates. Apoptosis of adipocytes can be induced at any developmental stage by administration of a FK1012 analog leading to the dimerization of a membrane-bound, adipocyte-specific caspase 8-FKBP fusion protein. Within 2 weeks of dimerizer administration, FAT-ATTAC mice show near-knockout levels of circulating adipokines and markedly reduced levels of adipose tissue. FAT-ATTAC mice are glucose intolerant, have diminished basal and endotoxin-stimulated systemic inflammation, are less responsive to glucose-stimulated insulin secretion and show increased food intake independent of the effects of leptin. Most importantly, we show that functional adipocytes can be recovered upon cessation of treatment, allowing the study of adipogenesis in vivo, as well as a detailed examination of the importance of the adipocyte in the regulation of multiple physiological functions and pathological states.
Nature Medicine 08/2005; 11(7):797-803. · 22.46 Impact Factor
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ABSTRACT: Resistin was originally reported as an adipose tissue-specific hormone that provided a link between obesity and diabetes. Resistin protein level was elevated in obese mice and decreased by insulin-sensitizing thiazolidinediones. Immunoneutralization of resistin improved insulin sensitivity in diet-induced obese mice, while the administration of exogenous resistin induced insulin resistance. More recently, we have shown that ablation of the resistin gene in mice decreased fasting glucose through impairment of gluconeogenesis, while resistin treatment in these knockout mice increased hepatic glucose production. However, the link between resistin and glucose homeostasis has been questioned by studies demonstrating reduced, rather than increased, resistin mRNA expression in obese and diabetic mice. To better understand the regulation of resistin, we developed a sensitive and specific RIA resistin that could accurately measure serum resistin levels in several mouse models. We show that while resistin mRNA is indeed suppressed in obese mice, the circulating resistin level is significantly elevated and positively correlated with insulin, glucose, and lipids. Both resistin mRNA expression and protein levels in Lep(ob/ob) mice are suppressed by leptin treatment in parallel with reductions in glucose and insulin. In wild-type mice, serum resistin increases after nocturnal feeding, concordant with rising levels of insulin. Resistin mRNA and protein levels decline in parallel with glucose and insulin during fasting and are restored after refeeding. We performed clamp studies to determine whether resistin is causally related to insulin and glucose. Adipose resistin expression and serum resistin increased in response to hyperinsulinemia and further in response to hyperglycemia. Taken together, these findings suggest that the nutritional regulation of resistin and changes in resistin gene expression and circulating levels in obesity are mediated, at least in part, through insulin and glucose.
Diabetes 08/2004; 53(7):1671-9. · 8.29 Impact Factor
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ABSTRACT: Whereas thiazolidinediones (TZDs) are known to rapidly improve insulin action in animals, short durations of TZD therapy have never been studied in humans. Among the many known actions of TZDs, increased circulating levels of the high molecular weight (HMW) multimer of adiponectin may be an important insulin-sensitizing mechanism. We examined the effects of only 21 days of 45 mg of pioglitazone (P+) versus placebo (P-) in nine subjects with type 2 diabetes (HbA(1c), 10.9 +/- 0.6%; BMI, 31.9 +/- 1.5 kg/m(2)). Total adiponectin levels increased by approximately twofold in P+ in association with increased adipose tissue gene expression. However, plasma free fatty acid and glucose levels were unchanged, and there were only minimal changes in other "adipokines." Glucose fluxes ([3-(3)H]glucose infusion) were measured during 6-h euglycemic (5 mmol/l) "pancreatic clamp" studies (somatostatin/glucagon/growth hormone) with stepped insulin levels. Pioglitazone induced marked decreases in endogenous glucose production (P+ = 0.9 +/- 0.1 vs. P- = 1.7 +/- 0.3 mg. kg(-1). min(-1); P < 0.05) at physiologic hyperinsulinemia ( approximately 50 microU/ml), which was highly correlated with an increased ratio of HMW adiponectin/total levels (r(2) = 0.90). Maximal insulin stimulation ( approximately 400 microU/ml) revealed pioglitazone-associated increases in glucose uptake (P+ = 10.5 +/- 0.9 vs. P- = 8.9 +/- 0.8 mg. kg(-1). min(-1); P < 0.05), which did not correlate with HMW or total adiponectin levels. Thus, only 21 days of pioglitazone therapy improved insulin action in humans with type 2 diabetes. Increased abundance of the HMW adiponectin multimer may contribute to the hepatic insulin-sensitizing effects of these agents.
Diabetes 06/2004; 53(6):1621-9. · 8.29 Impact Factor
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ABSTRACT: Adiponectin (ADP) is an adipocyte hormone involved in glucose and lipid metabolism. We detected a rise in ADP in cerebrospinal fluid after intravenous (i.v.) injection, consistent with brain transport. In contrast to leptin, intracerebroventricular (i.c.v.) administration of ADP decreased body weight mainly by stimulating energy expenditure. Full-length ADP, mutant ADP with Cys39 replaced with serine, and globular ADP were effective, whereas the collagenous tail fragment was not. Lep(ob/ob) mice were especially sensitive to i.c.v. and systemic ADP, which resulted in increased thermogenesis, weight loss and reduction in serum glucose and lipid levels. ADP also potentiated the effect of leptin on thermogenesis and lipid levels. While both hormones increased expression of hypothalamic corticotropin-releasing hormone (CRH), ADP had no substantial effect on other neuropeptide targets of leptin. In addition, ADP induced distinct Fos immunoreactivity. Agouti (A(y)/a) mice did not respond to ADP or leptin, indicating the melanocortin pathway may be a common target. These results show that ADP has unique central effects on energy homeostasis.
Nature Medicine 06/2004; 10(5):524-9. · 22.46 Impact Factor
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Utpal B Pajvani,
Meredith Hawkins,
Terry P Combs,
Michael W Rajala,
Tom Doebber,
Joel P Berger,
John A Wagner,
Margaret Wu,
Annemie Knopps,
Anny H Xiang,
Kristina M Utzschneider,
Steven E Kahn,
Jerrold M Olefsky,
Thomas A Buchanan,
Philipp E Scherer
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ABSTRACT: Adiponectin is an adipocyte-specific secretory protein that circulates in serum as a hexamer of relatively low molecular weight (LMW) and a larger multimeric structure of high molecular weight (HMW). Serum levels of the protein correlate with systemic insulin sensitivity. The full-length protein affects hepatic gluconeogenesis through improved insulin sensitivity, and a proteolytic fragment of adiponectin stimulates beta oxidation in muscle. Here, we show that the ratio, and not the absolute amounts, between these two oligomeric forms (HMW to LMW) is critical in determining insulin sensitivity. We define a new index, S(A), that can be calculated as the ratio of HMW/(HMW + LMW). db/db mice, despite similar total adiponectin levels, display decreased S(A) values compared with wild type littermates, as do type II diabetic patients compared with insulin-sensitive individuals. Furthermore, S(A) improves with peroxisome proliferator-activated receptor-gamma agonist treatment (thiazolidinedione; TZD) in mice and humans. We demonstrate that changes in S(A) in a number of type 2 diabetic cohorts serve as a quantitative indicator of improvements in insulin sensitivity obtained during TZD treatment, whereas changes in total serum adiponectin levels do not correlate well at the individual level. Acute alterations in S(A) (DeltaS(A)) are strongly correlated with improvements in hepatic insulin sensitivity and are less relevant as an indicator of improved muscle insulin sensitivity in response to TZD treatment, further underscoring the conclusions from previous clamp studies that suggested that the liver is the primary site of action for the full-length protein. These observations suggest that the HMW adiponectin complex is the active form of this protein, which we directly demonstrate in vivo by its ability to depress serum glucose levels in a dose-dependent manner.
Journal of Biological Chemistry 04/2004; 279(13):12152-62. · 4.77 Impact Factor
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Terry P Combs, Utpal B Pajvani,
Anders H Berg,
Ying Lin,
Linda A Jelicks,
Mathieu Laplante,
Andrea R Nawrocki,
Michael W Rajala,
Albert F Parlow,
Laurelle Cheeseboro,
Yang-Yang Ding,
Robert G Russell,
Dirk Lindemann,
Adam Hartley,
Glynn R C Baker,
Silvana Obici,
Yves Deshaies,
Marian Ludgate,
Luciano Rossetti,
Philipp E Scherer
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ABSTRACT: Adiponectin is a plasma protein expressed exclusively in adipose tissue. Adiponectin levels are linked to insulin sensitivity, but a direct effect of chronically elevated adiponectin on improved insulin sensitivity has not yet been demonstrated. We identified a dominant mutation in the collagenous domain of adiponectin that elevated circulating adiponectin values in mice by 3-fold. Adiponectinemia raised lipid clearance and lipoprotein lipase activity, and suppressed insulin-mediated endogenous glucose production. The induction of adiponectin during puberty and the sexual dimorphism in adult adiponectin values were preserved in these transgenic animals. As a result of elevated adiponectin, serum PRL values and brown adipose mass both increased. The effects on carbohydrate and lipid metabolism were associated with elevated phosphorylation of 5'-AMP-activated protein kinase in liver and elevated expression of peroxisomal proliferator-activated receptor gamma2, caveolin-1, and mitochondrial markers in white adipose tissue. These studies strongly suggest that increasing endogenous adiponectin levels has direct effects on insulin sensitivity and may induce similar physiological responses as prolonged treatment with peroxisomal proliferator-activated receptor gamma agonists.
Endocrinology 02/2004; 145(1):367-83. · 4.46 Impact Factor
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ABSTRACT: Adipocyte-specific secreted molecules, termed adipokines, have dispelled the notion of adipose tissue as an inert storage depot for lipids, and highlighted its role as an active endocrine organ that monitors and alters whole-body metabolism and maintains energy homeostasis. One of these adipokines, adiponectin (also known as Acrp30, AdipoQ, and GBP28), has gained significant attention recently as a mediator of insulin sensitivity. Many clinical reports and genetic studies over the past few years demonstrate decreased circulating levels of this hormone in metabolic dysfunction, such as obesity and insulin resistance, in both humans and animal models. Pharmacologic adiponectin treatments in rodents increase insulin sensitivity, although the primary site and detailed mechanism of action is yet to be determined. The phenotypes of adiponectin-deficient and transgenic adiponectin-overproducing animal models underscore the role of adiponectin in the maintenance of glucose and lipid homeostasis.
Current Diabetes Reports 07/2003; 3(3):207-13. · 2.50 Impact Factor
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ABSTRACT: Acrp30/adiponectin is an adipocyte-specific secretory protein that has recently been implicated as a mediator of systemic insulin sensitivity with liver and muscle as target organs. Acrp30 is found as two forms in serum, as a lower molecular weight trimer-dimer and a high molecular weight complex. Little is know about the regulation and significance of these Acrp30 complexes in serum and about the events that lead to the generation of the bioactive ligand. Here, we show that there is a profound sexual dimorphism of Acrp30 levels and complex distribution in serum. Female mice display significantly higher levels of the high molecular weight complex in serum than males. In both females and males, levels of the high molecular weight complex are significantly reduced in response to a systemic increase of insulin. The ratio of the two complexes is restored upon normalization of glucose levels. Structurally, we show that oligomer formation of Acrp30 critically depends on disulfide bond formation mediated by Cys-39. Mutation of Cys-39 results in trimers that are subject to proteolytic cleavage in the collagenous domain. Surprisingly, Acrp30(C39S) or wild-type Acrp30 treated with dithiothreitol are significantly more bioactive than the higher order oligomeric forms of the protein with respect to reduction of serum glucose levels. Furthermore, treatment of primary hepatocytes with trimeric and higher order forms of Acrp30 confirms that the increased bioactivity seen in vivo is reflected in an augmented potency to reduce glucose output in the presence of gluconeogenic stimuli. Combined, these results shed new light on the regulation of this complex protein and suggest a new model for in vivo activation of the protein, implicating a serum reductase activity.
Journal of Biological Chemistry 04/2003; 278(11):9073-85. · 4.77 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Acrp30/adiponectin is an adipocyte-specific secretory protein that has recently been implicated as a mediator of systemic
insulin sensitivity with liver and muscle as target organs. Acrp30 is found as two forms in serum, as a lower molecular weight
trimer-dimer and a high molecular weight complex. Little is know about the regulation and significance of these Acrp30 complexes
in serum and about the events that lead to the generation of the bioactive ligand. Here, we show that there is a profound
sexual dimorphism of Acrp30 levels and complex distribution in serum. Female mice display significantly higher levels of the
high molecular weight complex in serum than males. In both females and males, levels of the high molecular weight complex
are significantly reduced in response to a systemic increase of insulin. The ratio of the two complexes is restored upon normalization
of glucose levels. Structurally, we show that oligomer formation of Acrp30 critically depends on disulfide bond formation
mediated by Cys-39. Mutation of Cys-39 results in trimers that are subject to proteolytic cleavage in the collagenous domain.
Surprisingly, Acrp30(C39S) or wild-type Acrp30 treated with dithiothreitol are significantly more bioactive than the higher
order oligomeric forms of the protein with respect to reduction of serum glucose levels. Furthermore, treatment of primary
hepatocytes with trimeric and higher order forms of Acrp30 confirms that the increased bioactivity seen in vivo is reflected in an augmented potency to reduce glucose output in the presence of gluconeogenic stimuli. Combined, these results
shed new light on the regulation of this complex protein and suggest a new model for in vivo activation of the protein, implicating a serum reductase activity.
Journal of Biological Chemistry 03/2003; 278(11):9073-9085. · 4.77 Impact Factor
