Thermogenesis in diabetes-obesity syndromes in mutant mice

Summary The two mouse mutants, obese (ob) and diabetes (db), cause similar diabetes-obesity syndromes that are characterized by a marked increase in apparent metabolic efficiency with regard to utilization of energy. A failure to thermoregulate in a normal fashion would save energy which could then be diverted to other functions and be reflected as increased metabolic efficiency. This study assesses the contribution of a defect in thermogenesis to the increased metabolic efficiency. Thermogenesis in obese (ob) and diabetes (db) mutant mice was quantified at various environmental temperatures. Both mutants maintained body temperatures near normal when maintained at ambient temperatures (23 °C), and if exposed to cold at 10 °C for a brief period, became cold-adapted and would survive indefinitely at 4°C. Rectal temperatures of mutants maintained at 4 °C were only 1 °–2 °C less than those seen in normal mice. This maintenance of nearly normal body temperature at temperatures less than thermoneutral was reflected by increased food consumption in all mice maintained in the cold. The data presented suggest that the defect in thermogenesis in both mutants is not a major cause of the increased metabolic efficiency. Hyperinsulinaemia, a consistent feature of both mutants, might by increasing anabolic processes (synthesis) and decreasing degradation spare energy normally used for tissue turnover and account for some of this increased metabolic efficiency.     

Intracerebroventricular administration of neuropeptide Y to normal rats increases obese gene expression in white adipose tissue

Summary The aim of this work was to determine the possible inter-relationship between neuropeptide Y (NPY, a hypothalamic stimulator of feeding) and adipose tissue expression of the ob protein (a novel potent inhibitor of feeding). Such a relationship could be of importance in the maintenance of normal body weight. To this end, normal rats were intracerebro-ventricularly (i.c.v.) infused for 6 days with NPY. NPY infusion resulted in hyperphagia and a marked increase in adipose tissue ob mRNA levels. The effect of NPY on ob expression persisted when hyperphagia was prevented by pair-feeding, and was reversed following cessation of NPY infusion. Basal and glucose-stimulated insulinaemia were increased by i. c. v. NPY infusion compared to control values, regardless of whether animals were ad libitum-fed or pair-fed. Cessation of NPY infusion was accompanied by normalisation of insulinaemia. These changes in insulinaemia produced by i. c. v. NPY infusion paralleled the observed changes in ob expression. When normal rats were made hyperinsulinaemic-euglycaemic for 24 h, such hyperinsulinaemia also resulted in increased ob mRNA levels in white adipose tissue. This suggested that NPY-induced hyperinsulinaemia could be responsible for the upregulation of ob mRNA levels of NPY-infused rats. It is concluded that central (i. c. v.) NPY infusion increases adipose tissue ob expression, a functional relationship that is linked, at least in part, via NPY-induced hyperinsulinaemia.Abbreviations NPY Neuropeptide Y - i. c. v. intracerebroventricular     

Abnormal plasma glucose and insulin responses in heterozygous lean (ob/+) mice

Summary To investigate the effect of the ob gene in the heterozygous condition, plasma glucose and insulin responses of adult heterozygous lean (ob/+) mice were compared with mice of the homozygous lean (+/+) and homozygous obese (ob/ob) genotypes. The ob/+ mice consumed 24% more food than +/+ mice although body weights were similar. Plasma glucose and insulin concentrations were respectively 16% and 176% higher in ob/+ mice than +/+ mice in the freely fed state, and 44% and 88% higher during glucose tolerance tests. In 24 hour fasted ob/+ mice, plasma glucose concentrations were 23% higher than +/+ mice but plasma insulin concentrations were not significantly different. Arginine produced a greater insulin response (172%) and a greater fall in glycaemia (200%) in ob/ + mice. A significant difference in the hypoglycaemic effect of insulin in ob/+ and +/+ mice was not observed. These results demonstrate an effect of the ob gene on glucose homeostasis in heterozygous lean (ob/+) mice. The abnormalities were qualitatively similar but considerably less severe than those in ob/ob mice, suggesting that ob/+ mice might prove useful to study factors predisposing to inappropriate hyperglycaemia.     

Coordinated Muc2 and Muc3 mucin gene expression in Trichinella spiralis infection in wild-type and cytokine-deficient mice

Mucin hypersecretion is an important component of the immune response to gastrointestinal nematode infection. Two discrete types of mucin proteins exist in the mouse intestine, secretory Muc2 and membrane-bound Muc3. We examined Muc2 and Muc3 expression in wild-type mice and mice lacking gamma interferon receptor (IFNR–/–), tumor necrosis factor receptor 1 (TNFR1–/–) and interleukin 4 (IL4–/–) infected with Trichinella spiralis. Infected wild-type mice demonstrated significant goblet cell hyperplasia and increased mucin glycoprotein. In situ hybridization showed this was accompanied by increases in Muc2 and Muc3 mRNA. Total intestinal mucin protein and Muc2 and Muc3 mRNA levels were also significantly increased in cytokine-deficient mice. These data demonstrate the coordinated up-regulation of two types of mucin genes in response to T. spiralis infection and may form the basis of an innate mucosal response independent of IFN-, TNF, and IL-4.     

代谢相关性脂肪性肝病小鼠不同高脂饮食时期血糖水平和肠道菌群变化动态分析

目的 探讨在不同高脂饮食喂养时期代谢相关性脂肪性肝病(MAFLD)小鼠血糖水平和肠道菌群的动态变化.方法 采用高脂食物饲喂12只C57BL/6小鼠24周,分别在喂养0周、8周、16周和24周行葡萄糖耐量试验(GTT)和胰岛素耐受试验(ITT).采集小鼠粪便进行16sRNA检测,分析肠道细菌结构和肠道菌群多样性的变化.结...     

Somatostatin in the pancreas and hypothalamus of obese mice

Summary The pancreatic content of somatostatin, insulin, and glucagon and the hypothalamic content of somatostatin were examined inob/ob mice at various ages and in goldthioglucose-obese mice. The total pancreatic content of somatostatin was increased inob/ob mice compared to controls: 92 ng vs 75 ng (a 22% increase) at 2 months of age; 208 ng vs 131 ng (a 60% increase) at 6 months of age; and 184 ng vs 118 ng (a 60% increase) at 8 months of age. The total pancreatic content of glucagon inob/ ob mice was already enhanced by 70% over controls at 2 months of age (301 ng vs 173 ng) and did not increase further at later stages, whereas that of insulin progressively rose with age. In goldthioglucoseobese mice the pancreatic content of insulin was also increased but to a lesser extent than inob/ob mice; the pancreatic levels of somatostatin and glucagon were unaltered. In bothob/ob mice (regardless of age) and goldthioglucose-obese mice, there was no significant change in the hypothalamic content of somatostatin compared with that of lean controls.     

Global gene expression analysis in liver of obese diabetic db/db mice treated with metformin

Aims/hypothesis Metformin is widely used as a hypoglycaemic reagent for type 2 diabetes. While the reduction of hepatic gluconeogenesis is thought to be a key effect, the detailed molecular mechanism of action of metformin remains to be elucidated. To gain insight into this, we performed a global gene expression profiling study.Materials and methods We performed DNA microarray analysis to study global gene expression in the livers of obese diabetic db/db mice 2 h after a single administration of metformin (400 mg/kg).Results This analysis identified 14 genes that showed at least a 1.5-fold difference in expression following metformin treatment, including a reduction of glucose-6-phosphatase gene expression. The mRNA levels of glucose-6-phosphatase showed one of the best correlations with blood glucose levels among 12,000 genes. Enzymatic activity of glucose-6-phosphatase was also reduced in metformin-treated liver. Moreover, intensive analysis of the expression profile revealed that metformin effected significant alterations in gene expression across at least ten metabolic pathways, including those involved in glycolysis-gluconeogenesis, fatty acid metabolism and amino acid metabolism.Conclusions/interpretation These results suggest that reduction of glucose-6-phosphatase activity, as well as suppression of mRNA expression levels of this gene, in liver is of prime importance for controlling blood glucose levels in vivo, at least at early time points after metformin treatment. Our results also suggest that metformin not only affects expression of specific genes, but also alters the expression level of multiple genes linked to the metabolic pathways involved in glucose and lipid metabolism in the liver.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

Differences in the development of the obese-hyperglycemic syndrome in obob and NZO mice

Summary Marked differences were shown in the development of the obese-hyperglycemic syndrome in NZO andobob mice. — In NZO mice glucose tolerance decreases continuously with increasing age and body weight. — Inobob mice three phases in the development of the obese-hyperglycemic syndrome are differentiated. In the first, dynamic phase glucose tolerance decreases and insulin secretion increases as does body weight. The intermediary or transitional phase, when the animals weigh about 55 g, is characterised by rapidly changing glucose patterns, i. e. an extremely poor glucose tolerance and extremely high serum insulin level is followed by improving glucose tolerance and decreasing insulin levels. In the third, static phase blood sugar values and serum insulin levels have nearly returned to those of the lean littermates. Body weight slowly decreases. The changes in glucose tolerance and serum insulin are parallelled by changes in islet cell morphology. The gluconeogenic capacity is increased during the dynamic and transitional phases, it declines during the static phase.Supported by grants from the Deutsche Forschungs-gemeinschaft, Bad Godesberg, and Landesamt für Forschung des Landes Nordrhein-Westfalen, Germany.     

Effects of adrenalectomy on the obese-hyperglycemic syndrome in mice (gene symbolob)

Summary Mice with the inherited obese-hyperglycemic syndrome (gene symbolob) and their lean litter mates were adrenalectomized and then studied for up to 30–36 weeks with regard to their body weights and the serum glucose and immunoreactive insulin level. Sham operated obese and lean mice were used as controls.-Adrenalectomy did not prevent the excessive weight gain of the obese mice. However, during the first three weeks after adrenalectomy the mean weight increase was some-what smaller than in the sham operated controls. The increase in the body weights of the lean animals was, however, not affected. The most prominent finding after adrenalectomy was a decrease of the serum levels of glucose and insulin in both obese and lean animals.-The results indicate that in the obese mice adrenalectomy decreases the pronounced insulin resistance. It is also suggested that insulin resistance may be dissociated from the development of obesity in these animals.     

Mechanical and chemical properties of the skin and its collagen from lean and obese-hyperglycaemic (ob/ob) mice

Summary We have compared the mechanical and chemical properties of the skin and its collagen from 24-week-old obese-hyperglycaemic (ob/ob) and lean mice. The skin from obese mice was mechanically weaker and generated a lower hydrothermal isometric force. However, there were no significant differences from lean mice in the type of reducible cross-links in the collagen or in its solubility, although it contained more reducible cross-links and glycosylated lysine. The total amount of skin collagen was similar in obese and lean mice from 3 to 24 weeks of age but the skin surface area was 60% greater in 24-week-old obese mice. When corrected for collagen content the tensile strength of skin from obese mice was greater than that from lean mice and we suppose that the weakness of obese mouse skin is caused by a failure of collagen deposition to match the increase in skin surface area as the animals become obese.     

Altered gene expression with abnormal patterning of the telencephalon in embryos of diabetic Albino Swiss mice

Aims/hypothesis Several studies have shown that maternal diabetes increases the risk of congenital malformations in various organ systems including the neural tube. The present study analysed molecular and morphological changes in the forebrain of embryos from diabetic Albino Swiss mice.Methods Maternal diabetes-induced morphological changes in the forebrain were examined histologically. Cell proliferation index was assayed by BrdU labelling. In situ hybridisation and quantitative real-time PCR were used to analyse the expression of genes coding for sonic hedgehog (Shh), Nkx2.1, brain factor-1 (BF-1) and bone morphogenetic protein-4 (Bmp4) that control forebrain patterning.Results There were no distinguishable abnormalities in the forebrain of embryos from diabetic pregnancies on embryonic day 0.5. At embryonic day 11.5, embryos of diabetic pregnancies displayed a fusion and thickening of the ventral telencephalic neuroepithelium and a partial absence of the dorsal telencephalon, indicating a severe patterning defect in the dorsoventral axis of the telencephalon. The cell proliferation index was also higher in the ventral telencephalon of these embryos. Molecular analyses indicated that expression of Shh, Nkx2.1 and BF-1 was increased and their expression domains expanded dorsally in the ventral telencephalon in embryos of diabetic mice at embryonic day 11.5. The expression of Bmp4 was reduced in the dorsal forebrain of these embryos. At embryonic day 8.5, only Shh expression was increased.Conclusions/interpretation Altered expression of various genes involved in dorsoventral patterning of the forebrain is associated with forebrain malformations in embryos of diabetic mice.Abbreviations Shh sonic hedgehog - Bmp4 bone morphogenetic protein-4 - BF-1 brain factor-1 - BMPs bone morphogenetic proteins - E embryonic day     

An analysis of the lipolysis in vitro of obese-hyperglycaemic and diabetic mice

Summary Mice homozygous for either the obese gene in linkage group XI or the diabetes gene in linkage VIII exhibit syndromes similar to those of diabetes mellitus in man, including obesity and hyperglycaemia. A study of the lipolysis in vitro of the epididymal adipose tissue of 5 genotypes of mice, namely, ob/ob, ob/ob ⁺, ob ⁺/ob ⁺, db/db, and db ⁺/db ⁺, demonstrates that the mutant homozygotes respond differently from wild type homozygotes to various lipolytic agents. The agents tested were epinephrine, norepinephrine, isoproterenol, corticotropin 1–24, theophylline and N⁶, O²-dibutyryl-cyclic-adenosine3,5-monophosphate. The response of ob/ob ⁺ tissue was the same as that of ob ⁺/ob ⁺ tissue. The data indicate that there is a defect with respect to lipolysis in ob/ob and db/db mice. This is discussed in light of the involvement of cyclic AMP.

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Untersuchungen der Lipolyse in vitro bei der fettsüchtig-hyperglykämischen und der diabetischen Maus

Zusammenfassung Mäuse, die entweder für Fettsucht (ob) in der Verbindungskette XI oder für Diabetes (db) in der Verbindungskette VIII homozygot sind, weisen Syndrome auf, die denen des menschlichen Diabetes mellitus ähnlich sind. Das bezieht sich auch auf Fettsucht und Hyperglykämie. Eine Untersuchung der in vitro Lipolyse der epididymalen adipösen Gewebe von 5 Mausgenotypen, ob/ob, ob/ob ⁺, ob ⁺/ob ⁺, db/db und db ⁺/db ⁺, zeigte, daß mutante Homozygoten anders auf lipolytische Mittel reagieren als homozygote Typen der Wildform. Die geprüften Wirkstoffe waren Adrenalin, Noradrenalin, Isoproterenol, Corticotropin 1–24, Theophyllin und N⁶, O²-Dibutyrylzyklo-adenosin 3,5-monophosphat. Die Reaktionen des ob/ob ⁺ Gewebes und des ob ⁺/ob ⁺ Gewebes sind gleichartig. Die Ergebnisse deuten auf einen Defekt der Lipolyse bei ob/ob und db/db Mäusen hin. Die Bedeutung des cyclischen AMP in dieser Hinsicht wird diskutiert.

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Une analyse de la lipolyse in vitro de souris obèses hyperglycémiques et diabétiques

Résumé Les souris homozygotes (que ce soit le gène obèse du groupe XI ou le gène diabétique du groupe VIII) présentent des syndromes semblables à ceux du diabète sucré chez l'homme, y compris obésité et hyperglycémie. Une étude de la lipolyse in vitro du tissu adipeux épididymaire de 5 génotypes de souris, soit, ob/ob, ob/ob ⁺, ob ⁺/ob ⁺, db/db, et db ⁺/db ⁺, démontre que la réaction des homozygotes mutants à divers agents lipolytiques diffère de celle des homozygotes normaux. Les substances étudiées ont été l'adrénaline, la noradrénaline, l'isoprotérénol, la corticotropine 1–24, la théophylline et le N⁶, O²-dibutyryl-cyclique-adénosine-3,5-monophosphate. La réponse des tissus ob/ob ⁺ est la même que celle des tissus ob ⁺/ob ⁺. Les données indiquent qu'il existe un trouble de la lipolyse chez les souris ob/ob et db/db. Ceci est examiné à la lumière du rôle joué par l' AMP cyclique.

     

Polyunsaturated fatty acids of marine origin induce adiponectin in mice fed a high-fat diet

Aims/hypothesis Diets rich in n-3 polyunsaturated fatty acids, namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), protect against insulin resistance and obesity in rodents and increase insulin sensitivity in healthy humans. We tested whether the anti-diabetic effects of EPA and DHA involve enhanced production of the endogenous insulin sensitiser, adiponectin. Methods We studied the effects, in an obesity-promoting high-fat diet, of partial replacement of vegetable oils by EPA/DHA concentrate (6% EPA, 51% DHA) over a 5-week period in adult male C57BL/6J mice that either had free access to food or had their food intake restricted by 30%. At the end of the treatment, systemic markers of lipid and glucose metabolism and full-length adiponectin and leptin were measured. Adiponectin (Adipoq) and leptin (Lep) gene expression in dorsolumbar and epididymal white adipose tissue (WAT) and isolated adipocytes was quantified and adipokine production from WAT explants evaluated. Results In mice with free access to food, plasma triacylglycerols, NEFA, and insulin levels were lower in the presence of EPA/DHA, while glucose and leptin levels were not significantly altered. Food restriction decreased plasma triacylglycerols, glucose, insulin and leptin, but not adiponectin. EPA/DHA increased plasma adiponectin levels, independent of food intake, reflecting the stimulation of Adipoq expression in adipocytes and the release of adiponectin from WAT, particularly from epididymal fat. Expression of Lep and the release of leptin from WAT, while being extremely sensitive to caloric restriction, was unaltered by EPA/DHA. Conclusions/interpretation Intake of diets rich in EPA and DHA leads to elevated systemic concentrations of adiponectin, largely independent of food intake or adiposity and explain, to some extent, their anti-diabetic effects.     

Some cellular characteristics of the epididymal adipose tissue in lean and obese-hyperglycaemic mice

Summary 1. The nitrogen content, total water content,in vivo ¹²⁵l-albumin space, the number and size of adipocytes per unit wet weight of epididymal fat pad and the plasma volume have been studied in lean and obese mice, and in obese mice on chronic restriction of their food intake. — 2. There were fewer, larger adipocytes per unit wet weight of tissue (in young obese mice) with a proportional decrease in the vascular space and water content, and the same nitrogen content as had epididymal adipose tissue from lean mice. — 3. There was a reduction in the nitrogen content of epididymal adipose tissue from obese mice on a restricted diet. — 4. These findings are discussed in relation to the reduced glucose metabolism and lipolysis that are apparent when metabolic data are expressed per unit wet weight.     

Osteocalcin differentially regulates beta cell and adipocyte gene expression and affects the development of metabolic diseases in wild-type mice

The osteoblast-specific secreted molecule osteocalcin behaves as a hormone regulating glucose metabolism and fat mass in two mutant mouse strains. Here, we ask two questions: is the action of osteocalcin on β cells and adipocytes elicited by the same concentrations of the molecule, and more importantly, does osteocalcin regulate energy metabolism in WT mice? Cell-based assays using isolated pancreatic islets, a β cell line, and primary adipocytes showed that picomolar amounts of osteocalcin are sufficient to regulate the expression of the insulin genes and β cell proliferation markers, whereas nanomolar amounts affect adiponectin and Pgc1α expression in white and brown adipocytes, respectively. In vivo the same difference exists in osteocalcin''s ability to regulate glucose metabolism on the one hand and affect insulin sensitivity and fat mass on the other hand. Furthermore, we show that long-term treatment of WT mice with osteocalcin can significantly weaken the deleterious effect on body mass and glucose metabolism of gold thioglucose-induced hyperphagia and high-fat diet. These results establish in WT mice the importance of this novel molecular player in the regulation of glucose metabolism and fat mass and suggest that osteocalcin may be of value in the treatment of metabolic diseases.     

ApoA-1 mimetic restores adiponectin expression and insulin sensitivity independent of changes in body weight in female obese mice

Background:

We examined the ability of the apolipoprotein AI mimetic peptide L-4F to improve the metabolic state of female and male ob mice and the mechanisms involved.

Methods:

Female and male lean and obese (ob) mice were administered L-4F or vehicle for 6 weeks. Body weight was measured weekly. Fat distribution, serum cytokines and markers of cardiovascular dysfunction were determined at the end of treatment.

Results:

L-4F significantly decreased serum interleukin (IL)-6, tumor necrosis factor-α and IL-1β. L-4F improved vascular function, and increased serum adiponectin levels and insulin sensitivity compared with untreated mice. In addition, L-4F treatment increased heme oxygenase (HO)-1, pAKT and pAMPK levels in kidneys of ob animals. pAKT and pAMPK levels were significantly reduced in the presence of an HO inhibitor. Interestingly, L4F did not alter body weight in female mice, but caused a significant reduction in males.

Conclusions:

L-4F treatments reduced cardiovascular risk factors and improved insulin sensitivity in female ob mice independent of body fat changes. Reduced inflammatory cytokine levels accompanied by increased HO activity, serum adiponectin and improved insulin sensitivity suggest that L-4F may promote the conversion of visceral fat to a healthier phenotype. Therefore, L-4F appears to be a promising therapeutic strategy for treating both cardiovascular risk factors and insulin resistance in obese patients of either gender.     

Potential involvement of adipocyte insulin resistance in obesity-associated up-regulation of adipocyte lysophospholipase D/autotaxin expression

Aims/hypothesis Autotaxin is a lysophospholipase D that is secreted by adipocytes and whose expression is substantially up-regulated in obese, diabetic db/db mice. The aim of the present study was to depict the physiopathological and cellular mechanisms involved in regulation of adipocyte autotaxin expression.Methods Autotaxin mRNAs were quantified in adipose tissue from db/db mice (obese and highly diabetic type 2), gold-thioglucose-treated (GTG) mice (highly obese and moderately diabetic type 2), high-fat diet-fed (HFD) mice (obese and moderately diabetic type 2), streptozotocin-treated mice (thin and diabetic type 1), and massively obese humans with glucose intolerance.Results When compared to non-obese controls, autotaxin expression in db/db mice was significantly increased, but not in GTG, HFD, or streptozotocin-treated mice. During db/db mice development, up-regulation of autotaxin occurred only 3 weeks after the emergence of hyperinsulinaemia, and simultaneously with the emergence of hyperglycaaemia. Adipocytes from db/db mice exhibited a stronger impairment of insulin-stimulated glucose uptake than non-obese and HFD-induced obese mice. Autotaxin expression was up-regulated by treatment with TNF (insulin resistance-promoting cytokine), and down-regulated by rosiglitazone treatment (insulin-sensitising compound) in 3T3F442A adipocytes. Finally, adipose tissue autotaxin expression was significantly up-regulated in patients exhibiting both insulin resistance and impaired glucose tolerance.Conclusions/interpretation The present work demonstrates the existence of a db/db-specific up-regulation of adipocyte autotaxin expression, which could be related to the severe type 2 diabetes phenotype and adipocyte insulin resistance, rather than excess adiposity in itself. It also showed that type 2 diabetes in humans is also associated with up-regulation of adipocyte autotaxin expression.