2007年4月14日−4月15日
代表・世話人：児島 将康（久留米大学分子生命科学研究所）
所内対応者：箕越 靖彦（自然科学研究機構・生理学研究所）
- （１）
- Appetite control by gastrointestinal hormones and therapeutic potential of
ghrelin for cachexia
Masamitsu Nakazato (Miyazaki Univ)
- （２）
- Young-adult specific hyperphagia due to NPY neuron hyperactivity is coupled with
visceral obesity and leptin resistance in type 2 diabetic GK rats
Toshihiko Yada (Jichi Medical Univ)
- （３）
- A new anorexigenic molecule, nesfatin-1
Hiroyuki Shimizu (Gunma Univ)
- （４）
- Role of clusterin (apoprotein J) in the regulation of food intake and body weight
Minseon Kim (Ulsan Univ)
- （５）
- Pathophysiological roles of adiponectin and adipoRs
Toshimasa Yamauchi (Tokyo Univ)
- （６）
- Activation of the central melanocortin system mediates the restoration of
skeletal muscle AMP-activated protein kinase in mice fed high fat diet
Hiroaki Masuzaki (Kyoto Univ)
- （７）
- Angiopoietin-like factors (Angptls): potential new targets for therapy of obesity
and related insulin resistance
Yuichi Oike (Kumamoto Univ)
- （８）
- Chemical shift of redox state of pyridine nucleotides reverses obesity and
metabolic syndrome
Minho Shong (Chungnam National Univ)
- （９）
- Role of the peroxisome proliferator-activated receptor-gamma
co-activator-1 alpha (PGC-1 alpha) in diabetes ; Friend and foe
In-Kyu Lee (Kyungpook Univ)
- （10）
- Genipin inhibits UCP2-mediated proton leak and acutely reverses obesity- and
high glucose-inducedbcell dysfunction in isolated pancreatic islets
Chen-Yu Zhang (Nanjing Univ)
- （11）
- LXR-mediated lipotoxicity in pancreatic beta-cells
Jae Bum Kim (Seoul National Univ)
- （12）
- Adipo-vascular crosstalk in obesity and cardiovascular disease
Ichiro Manabe (Tokyo Univ)
- （13）
- Molecular basis for obesity-related adipose tissue inflammation
Yoshihiro Ogawa (Tokyo Med Dent Univ)
- （14）
- Stresses on adipose tissue in obesity; ROS and Hypoxia,
and their impact on adipocytokine dysregulation
Morihiro Matsuda (Osaka Univ)
- （15）
- Clinical implication of adipocytokines in pre-diabetes and high-risk patients of
type 2 diabetes mellitus
Sung-Hee Choi (Seoul National Univ)
- （16）
- The role of forkhead transcription factor Foxo1 in pancreaticbcells and
brain hypothalamus
Tadahiro Kitamura (Gunma Univ)
- （17）
- Activation of AMP-kinase in the paraventricular hypothalamus increases
the preference for high carbohydrate diet in mice
Yasuhiko Minokoshi (NIPS)
- （18）
- Autonomic nerve circuits modulate energy and glucose metabolism
Tetsuya Yamada (Tohoku Univ)
- （19）
- Identification of neuromedin S and its possible role in the mammalian circadian
oscillator system and feeding behavior
Takanori Ida (Kurume Univ)
【参加者名】
Inkyu Lee (Kyungpook National University)，Kyong Soo Park (Seoul National University College of Medicine)，Young-Bum Kim (Harvard Medical School)，Jae Bum Kim，Sung Hee Choi (Seoul National University)，Min-Seon Kim (University of Ulsan College of Medicine)，Minho Shong (Chungnam National University School of Medicine)，Chen-Yu Zhang (Nanjing University)，中里雅光（宮崎大学），尾池雄一（熊本大学），児島将康，佐藤貴弘，井田隆得（久留米大学），松田守弘（大阪大学），益崎裕章，村松成暢，宮木貴志（京都大学），山内敏正，真鍋一郎，大石由美子，窪田哲也（東京大学），小川佳宏（東京医科歯科大学），北村忠弘，清水弘行（群馬大学），黄虎（筑波大学），矢田俊彦，前島裕子，鳥谷真佐子，須山成朝，吉田なつ，山本早和子（自治医科大学），山田哲也（東北大学），富永真琴，福見-富永知子，兼子佳子（岡崎統合バイオサイエンスセンター），箕越靖彦，岡本士毅，志内哲也，鈴木敦，李順姫，戸田知得，大和麻耶（生理学研究所）
【概要】
肥満，糖尿病などいわゆる生活習慣病は，今や先進諸国のみならず一部の発展途上国における大きな社会問題であり，その克服は急務である。本研究会は，当該分野における主として基礎的研究に携わる日韓研究者が集まり，最新研究成果を発表することによって肥満・糖尿病の発症機構を理解するとともに，今後の研究に役立てる事を目的とする。
近年，肥満・糖尿病の発症，増悪機構に関する研究は，大きく進歩しつつある。中でも，肥大した脂肪細胞を主因とするインスリン抵抗性の発現機構，及び摂食行動の調節機構に関する個体・分子レベルの研究は大きく進展した。そこで本研究会では，1) 摂食・エネルギー消費の調節機構，2) インスリン・シグナルとインスリン抵抗性発症機構，3) 肥満・糖尿病の発症にかかわる新規調節因子の3つのテーマに関して発表を行う。
Masamitsu Nakazato (Miyazaki Medical College, University of Miyazaki)
The gastrointestinal tract produces a large array of substances to regulate feeding. Energy balance is controlled by the complicated and minute interactions of substances to stimulate or suppress food intake and energy expenditure. The molecular mechanisms of energy balance are coming to light by the recent robust progresses in the molecular biology and neuroscience.Hypothalamus,thecenterofenergyhomeostasis, receives information related to satiety and fast from the body and other brain regions, integrate them, and mediate interactions with efferent pathways. We have identified peptide ligands for orphan G-protein coupled receptors and studied their physiological and clinical implications in the regulation of energy homeostasis. We have clarified that the vagal afferent is the major pathway conveying signals of gut hormones to the brain. I will talk about a feeding-stimulating (orexigenic) peptide, ghrelin and its therapeutic potential in cachexia. These findings will provide a clue to our better understanding of the molecular etiology of body weight control and the pathogenesis of obesity and anorexia in humans.
Ghrelin, an endogenous peptide ligand for the growth hormone secretagogue receptor, is produced mainly by stomach cells and stimulates hunger centers in the hypothalamus which controls food intake and body mass. Ghrelin secretion is stimulated upon energy deficits and induces food intake. The plasma ghrelin concentration is upregulated before meal and decreases after feeding. At present ghrelin is the only peptide to transmit hunger information from the periphery to the brain. Gastric ghrelin functions to maintain energy homeostasis. Plasma ghrelin levels in cachexic patients suffered from cancer, chronic heart failure and respiratory failure are upregulated compared with non-cachexic patients, but its anabolic effect is insufficient to maintain body weight. Peripherally administered ghrelin stimulates appetite in normal volunteers. Some clinical trials to investigate therapeutic potentials of ghrelin in cachexia have started for patients with anorexia nervosa, cancer, chronic heart failure, and chronic obstructive pulmonary disease in Japan, USA, and European countries. Ghrelin suppresses proinflammatory cytokines expression in leukocytes and this anti-inflammatory activity has a potency to inhibit the development of cachexia induced by cancer progression. The effects of ghrelin on energy balance have implications in its potential use as a therapeutic target associated with cachexic and/or inflammatory diseases.
Toshihiko Yada1, Fumihiko Maekawa1, Daisuke Kohno1,
Yuko Maejima1, Hideharu Kurita1,2 and Masako Toriya1
(1Division of Integrative Physiology, Department of Physiology,
2Department of Neurosurgery, Jichi Medical University School of Medicine)
GK rats, a model of type-2 diabetes with impaired insulin release and action, exhibited hyperphagia selectively at 6-13 weeks of age, while body weight was not changed, as compared to control Wistar rats. In 11 weeks-old hyperphagic GK rats, visceral fat was accumulated and plasma leptin was elevated. Leptin-induced suppression of food intake and phosphorylation of STAT3 in the hypothalamic arcuate nucleus (ARC) were markedly reduced, and NPY mRNA level in ARC was elevated. Intracerebroventricular (icv) injection of NPY Y1 receptor antagonist corrected the hyperphagia. The results indicate that the young-adult hyperphagia in GK rats is caused by hyperactivity of ARC NPY neurons, which may result from and/or lead to visceral fat accumulation and leptin resistance. Young-adult GK rats exhibit hyperphagia, visceral obesity and diabetes, providing a unique model of metabolic syndrome.
Here, an important question is“How leptin regulates NPY neurons?”, NPY neurons were isolated from young-adult (6 week) rats, and cytosolic Ca2+ concentration ([Ca2+]i) was measured by fura-2 fluorescence imaging. Ghrelin increased [Ca2+]i in NPY neurons, and leptin counteracted the ghrelin-induced [Ca2+]i increases. The leptin effect was blocked by inhibitors of PI3 kinase and phosphodiesterase 3 (PDE3), but not STAT3 and ATP-sensitive K+ channels. Furthermore, stimulation of feeding by icv ghrelin in rats was counteracted by leptin in a PDE3-dependent manner.
Thus, the PI3 kinase- and PDE3-dependent leptin signaling plays a central role in suppressing the activity of ARC NPY neurons and thereby feeding. Dysfunction of this pathway may be involved in hyperphagia and visceral obesity in GK rats and possibly other models of diabetes and metabolic syndrome.
Hiroyuki Shimizu, Shinsuke Oh-I, Masatomo Mori
(Department of Medicine and Molecular Science,
Gunma University Graduate School of Medicine)
We identified a new anorexigenic molecule, nesfatin-1 by subtraction cloning assay. Nesfatin/NUCB2 is expressed in hypothamic nuclei that are involved in the regulation of feeding behavior. The i.c.v. injection of nesfatin/NUCB2 inhibited food intake in rats, while i.c.v. injection of the antibody against nesfatin/NUCB2 increased food intake. Prohormone convertase-1, 3 and -2 co-localized with nesfatin/NUCB2, indicating that this molecule can be processed by PC-1, 3 or -2. Nesfatin-1 existed in rat cerebrospinal fluid. The i.c.v. injection of nesfatin-1 decreased food intake in a dose-dependent manner, whereas injection of an antibody neutralizing nesfatin-1 stimulated appetite. In contrast, i.c.v. injection of other possible fragments processed from nesfatin/NUCB2 (nesfatin-2, nesfatin-3) did not promote satiety, and the mutant form of nesfatin (A83A84) failed to show any inhibition of food intake. These data indicated that conversion of nesfatin /NUCB2 to nesfatin-1 is necessary to induce feeding suppression. Chronic i.c.v. injection of nesfatin-1 reduced body weight, whereas rats gain body weight after chronic icv injection of an antisense morpholino-oligonucleotide against the nesfatin gene. The i.c.v. injection of nesfatin-1 reduced food intake in Zucker fatty rats with a leptin receptor mutation, and an anti-nesfatin-1 antibody did not block the leptin-induced anorexia. Treatment with i.c.v. injection of SHU9119, an antagonist specific for the melanocortin 3/4 receptor, completely abolished the anorexia by i.c.v. nesfatin-1 injection. However, i.c.v. injection of nesfatin-1 did not affect the expression of the genes encoding proopiomelanocortin in the paraventricular nucleus of the hypothalamus. Intraperitoneal injection of nesfatin-1 dose-dependently inhibited food consumption in mice. Nesfatin-1 may be involved in the physiological regulation of appetite, and it inhibits food intake, independent of leptin pathway. Nesfatin-1 may be one of possible candidates for the treatment of human obesity.
Minseon Kim
(Department of Internal Medicine University of Ulsan College of Medicine)
Clusterin (apoprotein J) is the 80 kDa disulfide-linked glycoprotein that is abundantly present in plasma, cerebrospinal fluid and seminal fluid. Clusterin has been implicated in lipoprotein transport, complement-mediated cell lysis, sperm maturation, cell migration and apoptosis. However, its major physiologic role is not still unclear.
Clusterin (apoprotein J) is expressed in the hypothalamus, a key organ regulating food intake and body weight. We have found that hypothalamic clusterin expression was increased by food intake but this change was blunted in obese ob/ob mouse, suggesting that clusterin may have a role in the control of food intake and body weight. To investigate the role of clusterin in the hypothalamus, we administered synthetic full length secretary form of clusterin into the 3rd cerebroventricle, adjacent to the hypothalamus, of C57BL/6J mice and monitored food intake and body weight. ICV administration of clusterin significantly decreased fasting- induced feeding and reduced body weight at 24 h post injection. Consistent with these findings, bilateral injection of clusterin-adenovirus in mediabasal hypothalamus decreased food intake but increased energy expenditure, resulting in decreased body weight. Similarly to leptin, a representative anorexigenic hormone, ICV administration of clusterin increased Signal Transducer Activated Transcript (STAT)-3 phosphorylation in the hypothalamic neurons. Co- administration of sub-clinical dose of clusterin potentiates the anorexigenic effect of leptin. Our data identify clusterin as a novel anorexigenic molecule.
Toshimasa Yamauchi1, Takashi Kadowaki2
(1Department of Integrated Molecular Science on Metabolic Diseases,
22nd Century Medical and Research Center
2Department of Metabolic Diseases, Graduate School of Medicine,
University of Tokyo)
We identified adiponectin as therapeutic target for metabolic syndrome by using the combination of genome-wide scanning and the use of DNA chips. Genetic studies on SNPs of adiponectin gene as well as functional analyses including generation of adiponectin transgenic or knockout mice suggest that reduced adiponectin levels play a causal role in the development of metabolic syndrome. Moreover, the human adiponectin mutations analyses led to identification of high molecular weight (HMW) adiponectin as most active form. We then developed a novel ELISA system and showed that measurement of HMW is useful for the prediction of metabolic syndrome.
We also identified adiponectin receptors (AdipoR1 and R2) by expression cloning and found that AdipoRs were also decreased in obesity. Functional analyses including generation of AdipoRs knockout mice or overexpression by adenoviruses suggest that AdipoRs are required for adiponectin binding and effects thus the major adiponectin receptors, and that not only agonism of AdipoRs but also strategies to increase AdipoRs should serve as versatile treatment strategies for metabolic syndrome. Moreover, network analyses revealed that AdipoR1 may be tightly linked to activation of AMP kinase pathway, whereas AdipoR2 may be tightly linked to activation of PPAR alpha pathway.
Finally, we showed that PPARgamma agonist up- regulated total and HMW adiponectin, whereas PPARalpha agonist up-regulated adiponectin receptors. Moreover, we showed osmotin, present in fruits and vegetables, activated AMPK via AdipoRs in myocytes.
Hiroaki Masuzaki1, Tomohiro Tanaka1, Shintaro Yasue1, Takako Ishii1, Naoki Arai1,
Toru Kusakabe1, Fumiko Miyanaga1, Ken Ebihara1, Masakazu Hirata1, Kiminori Hosoda1,
Tetsuya Shiuchi2, Yasuhiko Minokoshi2, Kazuwa Nakao1
(1Division of Endocrinology and Metabolism, Department of Medicine and Clinical Science,
Kyoto University Graduate School of Medicine
2Department of Developmental Physiology, National Institute for Physiological Sciences)
Little is known about a role of central melanocortin system in the control of fuel metabolism in the peripheral tissues. Skeletal muscle AMP-activated protein kinase (AMPK) is activated by leptin and serves as a master regulator of fatty acidb-oxidation. To elucidate an unidentified role of central melanocortin in muscle AMPK regulation, we treated conscious, unrestrained mice intracerebroventricularly with melanocortin agonist: MT-II or antagonist: SHU9119. MT-II augmented phosphorylation of AMPK and its target acetyl-CoA carboxylase (ACC) independent of caloric intake. Conversely, AMPK/ACC phosphorylation by leptin was abrogated by the co-administration of SHU9119, or in KKAy mice, which centrally express endogenous melanocortin antagonist. Importantly, high-fat diet-induced attenuation in AMPK/ACC phosphorylation in leptin-overexpressing transgenic mice was not reversed by central leptin, but markedly recovered by MT-II. Our data provide the first evidence of a critical role of central melanocortin in leptin-skeletal muscle AMPK axis, and highlight the system as a therapeutic target in leptin-resistance.
Yuichi Oike 1,2,3
(1Department of Molecular Genetics,
Graduate School of Medical Sciences, Kumamoto University,
2Laboratory of Vascular Biology & Metabolism,
Center for Integrated Medical Research,School of Medicine, Keio University,
3PRESTO, Japan Science Technology Agency (JST))
Obesity is an increasingly prevalent medical and social problem with potentially devastating consequences because it clusters with type 2 diabetes, hypertension and hyperlipidemia in the metabolic syndrome, which is an important risk factor for cardiovascular disease incidence and mortality. The molecular mechanisms underlying obesity have not been fully clarified, and effective therapeutic approaches are currently of general interest. We identified angiopoietin-related growth factor (AGF, also known as Angptl6 and encoded by the gene Angptl6) as a member of the Angptl family and showed that it is a circulating orphan protein that induces angiogenesis. Furthermore, AGF has been shown to counteract obesity and related insulin resistance, suggesting a possible role of AGF in the reduction of the cardiovascular disease. More recently, we analyzed the associations between serum AGF concentrations and several clinical parameters using our newly developed ELISA system in human. In this presentation, as a first topics, I will discuss recent findings regarding the role of AGF in obesity and insulin resistance in mice and human. And then, as a second subject, I would like to show the new role of Angptl2, which is a member of the Angptl family, in obesity and insulin resistance in mice.
Minho Shong
(Laboratory of Endocrine Cell Biology, National Research Laboratory Program,
Department of Internal Medicine, Chungnam National University School of Medicine)
Due to increasing worldwide incidence of metabolic syndrome, there is urgent need for effective novel therapeutic modalities to treat this disease. Currently, the most reliable therapeutic approach to metabolic syndrome is to restrict caloric intake and to increase energy expenditure through exercise, thus creating a negative energy balance and subsequent weight loss.The pyridine nucleotides, NAD(P) + and NAD(P)H play important roles in cellular energy metabolism and metabolic homeostasis by regulating mitochondrial oxidative phosphorylation and numerous enzymatic functions such as Sirt family proteins. When the cytoplasmic NAD(P)+to NAD(P)H ratio is high, the rates of glycolysis, fatty acid oxidation and mitochondrial oxidative phosphorylation increase. This observation suggests that a pharmacologically-induced increase in the cytoplasmic NAD(P)+/NAD(P)H ratio might stimulate mitochondrial oxidative phosphorylation and adaptive mitochondrial biogenesis. Furthermore, this might be a useful therapeutic approach for patients with metabolic syndrome. When cytoplasmic NAD(P)H:quinone oxidoreductase 1 (NQO1) is activated by exogenous compounds, the cytoplasmic NAD(P)+/NAD(P)H equilibrium is shifted towards oxidized NAD(P)+. Under these conditions, the high NAD(P)+ /NAD(P)H ratio stimulates mitochondrial oxidative phosphorylation and glycolysis and activates sirtuins. Here we show that the mechanism by which NQO1-mediated oxidation of NAD(P)H leads to enhanced mitochondrial fatty acid oxidation involves activation of AMP-activated protein kinase (AMPK). Furthermore, NQO1-mediated oxidation of NAD(P)H ameliorates most of phenotypes of metabolic syndrome, including obesity, glucose intolerance, dyslipidemia, and fatty liver disease in ob/ob mice and in mice on a high-calorie diet with diet-induced obesity. These phenotypic changes are associated with increased mitochondrial biogenesis and higher energy expenditure. These observations demonstrate that an NQO1-mediated shift in the NAD(P)+/NAD(P)H ratio may provide a novel pharmacological approach for treating the symptoms of metabolic syndrome including obesity. Due to increasing worldwide incidence of metabolic syndrome, there is urgent need for effective novel therapeutic modalities to treat this disease. Currently, the most reliable therapeutic approach to metabolic syndrome is to restrict caloric intake and to increase energy expenditure through exercise, thus creating a negative energy balance and subsequent weight loss.The pyridine nucleotides, NAD(P)+and NAD (P)H play important roles in cellular energy metabolism and metabolic homeostasis by regulating mitochondrial oxidative phosphorylation and numerous enzymatic functions such as Sirt family proteins. When the cytoplasmic NAD(P)+to NAD(P)H ratio is high, the rates of glycolysis, fatty acid oxidation and mitochondrial oxidative phosphorylation increase. This observation suggests that a pharmacologically- induced increase in the cytoplasmic NAD(P)+/NAD(P)H ratio might stimulate mitochondrial oxidative phosphorylation and adaptive mitochondrial biogenesis. Furthermore, this might be a useful therapeutic approach for patients with metabolic syndrome. When cytoplasmic NAD(P)H:quinone oxidoreductase 1 (NQO1) is activated by exogenous compounds, the cytoplasmic NAD(P)+/NAD(P)H equilibrium is shifted towards oxidized NAD(P)+. Under these conditions, the high NAD(P)+/NAD(P)H ratio stimulates mitochondrial oxidative phosphorylation and glycolysis and activates sirtuins. Here we show that the mechanism by which NQO1-mediated oxidation of NAD(P)H leads to enhanced mitochondrial fatty acid oxidation involves activation of AMP-activated protein kinase (AMPK). Furthermore, NQO1-mediated oxidation of NAD(P)H ameliorates most of phenotypes of metabolic syndrome, including obesity, glucose intolerance, dyslipidemia, and fatty liver disease in ob/ob mice and in mice on a high-calorie diet with diet-induced obesity. These phenotypic changes are associated with increased mitochondrial biogenesis and higher energy expenditure. These observations demonstrate that an NQO1-mediated shift in the NAD(P)+/NAD(P)H ratio may provide a novel pharmacological approach for treating the symptoms of metabolic syndrome including obesity.
In-Kyu Lee
(Department of Internal Medicine, Kyungpook National University Hospital,
School of Medicine,Kyungpook National University )
The peroxisome proliferators-activated receptor- g co- activator-1a (GC-1 a) is a transcriptional coactivator identified as an upstream regulator of mitochondrial number and function. PGC-1 a is expressed in human aortic smooth muscle cells (HASMCs) as well as endothelial cells (HAECs) and is up-regulated by AMPK activators including metformin, rosiglitazone and alpha-lipoic acid. Tumor necrosis factor- a (TNF- a), major proinflammatory factor in the development of vascular inflammation, stimulated intracellular ROS production through increases in both mitochondrial ROS and NAD(P)H oxidase activity.
Adenovirus-mediate overexpression of the PGC-1 a gene to HASMCs and HAECs profoundly reduced intracellular ROS production, mitochondrial ROS production and NAD(P)H oxidase activity. Consequently, it decreased NF-k activation and expression of MCP-1 and VCAM-1 that were induced by TNF- a. This study presents the possibility that the agents increasing PGC-1 a expression in the vasculature may help prevent the development of atherosclerosis.
Recent report showed that PGC-1 a is also expressed in pancreatic b cells and its expression level is markedly elevated in diabetic animal models, including partially pancreatectomized rats. Defective insulin secretion was found in PGC-1 a -overexpressed pancreatic islets through down-regulation of the expression of transcription factor including PDX-1 as well as ATP production.
Herein, we found new molecular mechanism by which PGC-1 a decreases insulin gene expression.
Chen-Yu Zhang
(State Key Laboratory of Pharmaceutial Biotechnology,
School of Life Sciences, Nanjing University )
Uncoupling protein (UCP) 2 negatively regulates insulin secretion. UCP2 deficiency (by means of gene knockout) improves obesity and hyperglycemia-induced b -cell dysfunction, and consequently improves type 2 diabetes. In the present study, we have identified a cell-permeable inhibitor of UCP2, genipin. In isolated mitochondria, genipin specifically inhibits UCP2- and UCP3-mediated proton leak, which is induced by exogenously added superoxide. In pancreatic islets, genipin increases mitochondrial membrane potential and stimulates insulin secretion in a UCP2- dependent manner. Importantly, acute addition of genipin to isolated islets reverses hyperglycemia-and obesity-induced b -cell dysfunction. Therefore, genipin (or derivatives) represent a new class of compounds that might be useful for the treatment of b -cell dysfunction and type 2 diabetes.
Sung Sik Choe, A Hyun Choi, Joo Won Lee, Jae Bum Kim
(Department of Biological Sciences, Research Center for Functional Cellulomics,
Seoul National University)
Type 2 diabetes mellitus is characterized by hyperglycemia, insulin resistance, and defective insulin secretion. During the early phase of type 2 diabetes, normal blood glucose levels are maintained by a compensatory response in which pancreatic b cells increase insulin secretion. However, these cells gradually lose their ability to keep up with the prolonged high demand and eventually undergo apoptosis. The accumulation of excess lipid in the pancreatic islets of obese subjects (with type 2 diabetes) has been implicated as being one of the main causes of b -cell dysregulation. It has also been observed that chronic hyperlipidemia contributes to b -cell dysfunction in an interdependent manner with hyperglycemia. Despite considerable effort to decipher the detailed mechanisms behind this phenomenon, it is still unclear how hyperlipidemia induces b -cell failure under hyperglycemic conditions of type 2 diabetes.
Liver X receptor (LXR) a and LXR b play important roles in fatty acid metabolism and cholesterol homeostasis. Although the functional roles of LXR in the liver, intestine, fat, and macrophage are well established, its role in pancreatic b -cells has not been clearly defined. In this study, we revealed that chronic activation of LXR contributes to lipotoxicity-induced b -cell dysfunction. We observed significantly elevated expression of LXR in the islets of diabetic rodent models, including fa/fa ZDF rats, OLETF rats, and db/db mice. In primary pancreatic islets and INS-1 insulinoma cells, activation of LXR with a synthetic ligand, T0901317, stimulated the expression the lipogenic genes ADD1/SREBP1c, FAS, and ACC, and resulted in increased intracellular lipid accumulation. Moreover, chronic LXR activation induced apoptosis in pancreatic islets and INS-1 cells, which was synergistically promoted by high glucose condition. Taken together, we suggest lipid accumulation due to chronic activation of LXR in b -cells as a possible cause of b -cell lipotoxicity, a key step in the development of type 2 diabetes mellitus.
Ichiro Manabe
(Nano-Bioengineering Education Program,
The University of Tokyo Graduate School of Medicine)
We identified KLF5, a member of the Krüppel-like zinc finger transcription factor family, as a factor that plays a critical role in cardiovascular disease. KLF5 heterozygous knockout (KLF5+/) mice exhibit much reduced neointima formation, adventitial reactivity, and angiogenesis following vascular injury. They also showed reduced cardiac hypertrophy and fibrosis. Interestingly, KLF5 also crucially involved in adipogensis. KLF5+/ exhibited impaired WAT development. KLF5 is induced by C/EBP b and d and activates PPAR g promoter, thus mediating the early and late differentiation programs of 3T3-L1 adipocytes. Moreover, when KLF5+/ were fed with high fat diet, they showed clear resistance to high-fat diet-induced obesity and were protected from hypercholesterolemia, glucose intolerance and hepatic steatosis. Thus KLF5 appears to play roles in both injurious stress response and metabolic stress response, suggesting that it may be a common stress response factor in the cardiovascular and metabolic systems. Given that other transcription factors including C/EBP and Foxo play roles in the both systems, there might be a number of common stress response mechanisms. Indeed, by developing a novel living tissue imaging method we found that obesity of adipose tissue involves structural changes similar to those observed in atherogenesis. Furthermore, adipogenesis in obesity was tightly coupled with angiogenesis. Taken together, there appear to be extensive crosstalk between blood vessels and adipocytes in obesity and there may be common molecular mechanisms that regulate cellular stress response and tissue remodeling in obesity and atherosclerosis.
Yoshihiro Ogawa1,2, Takayoshi Suganami1
(1Department of Molecular Medicine and Metabolism,
2Center of Excellence Program for Frontier Research on Molecular Destruction and
Reconstitution of Tooth and Bone, Medical Research Institute,
Tokyo Medical and Dental University)
Evidence has accumulated indicating that weight gain is associated with infiltration of fat by macrophages. Using an in vitro co-culture system composed of 3T3-L1 adipocytes and RAW264 macrophages, we demonstrated that a paracrine loop involving saturated fatty acids and TNFa derived from adipocytes and macrophages, respectively, establishes a vicious cycle that aggravates inflammatory changes in obese adipose tissue (Arterioscler. Thromb. Vasc. Biol. 25:2062-2068, 2005). Pharmacological inhibition of NF-kB suppressed the co-culture-induced production of pro-inflammatory cytokines and adipocyte lipolysis. Peritoneal macrophages obtained from C3H/HeJ mice carrying a TLR4 mutation exhibited marked attenuation of TNFa production in response to saturated fatty acids. Notably, co-culture of hypertrophied adipocytes and C3H/HeJ macrophages resulted in the marked inhibition of pro-inflammatory cytokine production and adipocyte lipolysis. We also observed that endogenous fatty acids, which are released from adipocytes via the b -adrenergic stimulation, result in the activation of the TLR4/NF-kB pathway. Collectively, we postulate that saturated fatty acids, which are released in large quantities from hypertrophied adipocytes via the macrophage-induced adipocyte lipolysis, serve as a naturally occurring ligand for TLR4, thereby inducing the inflammatory changes in obese adipose tissue (Arterioscler. Thromb. Vasc. Biol. 27:84-91, 2007). Very recently, we have demonstrated the attenuation of adipose tissue inflammation in C3H/HeJ mice relative to control C3H/HeN mice during a high-fat diet (Biochem. Biophys. Res. Commun. 354:45-49, 2007). Our data suggest that the saturated fatty acids/TLR4/NF-k pathway plays a critical role in obesity-related adipose tissue inflammation and thus help identify the therapeutic targets that may reduce obesity-induced inflammation and the metabolic syndrome.
Morihiro Matsuda, Iichiro Shimomura
(Department of Metabolic Medicine,
Graduate School of Medicine, Osaka University)
Obesity is linked to a variety of metabolic disorders, such as insulin resistance. Dysregulated production of fat-derived secretory factors, adipocytokines, is partly responsible for obesity-linked metabolic disorders. However, the mechanistic role of obesity per se to adipocytokine dysregulation has not been fully elucidated. In this regard, we have focused on two kinds of obesity-associated stresses in adipose tissue, ROS and hypoxia.
First, we investigated oxidative stress in adipose tissue. Fat accumulation correlated with systemic oxidative stress in humans and mice. Production of ROS increased selectively in adipose tissue of obese mice, accompanied by augmented expression of NADPH oxidase and decreased expression of antioxidative enzymes. In cultured adipocytes, elevated levels of fatty acids increased oxidative stress via NADPH oxidase activation, and oxidative stress caused dysregulated production of adipocytokines, including adiponectin, PAI-1, IL-6, and MCP-1. Finally, in obese mice, treatment with NADPH oxidase inhibitor reduced ROS production in adipose tissue, attenuated the dysregulation of adipocytokines, and improved diabetes.
Next, we investigated hypoxia in obese adipose tissue. Tissue hypoxia was confirmed by an exogenous marker, pimonidazole, and by elevated concentration of lactate, an endogenous marker. Moreover, local tissue hypoperfusion (measured by colored microspheres) was confirmed in adipose tissue of obese mice. Adiponectin mRNA expression was decreased, and mRNA of C/EBP homologous protein (CHOP), an ER-stress mediated protein, was significantly increased in adipose tissue of obese mice. In 3T3-L1 adipocytes, hypoxia dysregulated the expression of adipocytokines, such as adiponectin and PAI-1, and increased the mRNAs of ER stress marker genes, CHOP and GRP78. Expression of CHOP attenuated adiponectin promoter activity, and RNA interference of CHOP partly reversed hypoxia-induced suppression of adiponectin mRNA expression in adipocytes.
Collectively, our results suggest that increased oxidative stress and hypoxia in adipose tissues underlie the dysregulated production of adipocytokines and metabolic syndrome in obesity.
Sung Hee Choi, Soo Heon Kwak, Soo Lim, Young Min Cho, Kyong Soo Park,
Hong Kyu Lee, Young Bum Kim, Hak Chul Jang
(Department of Internal Medicine, Seoul National University)
Dysregulation of adipokines is closely associated with glucose homeostatsis and affects insulin sensitivity in many tissues.
Studies suggest that alterations in circulating levels of RBP4 and adiponectin may regulate systemic glucose metabolism and represent a possible mechanism linking insulin resistance to type 2 diabetes mellitus (DM). We want to investigate the possible clinical role of these novel adipocyte-derived adipokines in prediabetes and gestational diabetes patients, who are at high risk for developing type 2 DM.
To determine whether circulating adipokines contribute to the development of abnormal glucose homeostasis in women with a history of GDM, we measured plasma retinol binding protein-4 (RBP4), adiponectin, and the metabolic parameters of insulin resistance. Here we show that plasma RBP4 levels were significantly higher in subjects with DM-pGDM and IGT-pGDM, than in subjects with NGT-pGDM and NP. RBP4 levels correlated positively with blood pressure, fasting plasma glucose levels, fasting insulin levels, triglyceride levels, abdominal fat area, and HOMA-IR. In contrast, circulating adiponectin levels were reduced in subjects who had type 2 diabetes after GDM compared to the other groups and correlated inversely with parameters of insulin resistance. Moreover, an inverse correlation between plasma RBP-4 and adiponectin levels was observed, suggesting reciprocal regulation of these adipokines.
In other study we measured endothelial dysfunction of metabolic syndorme patients compared to type 2 DM patients. For improvement of endothelial dysfunction after PPAR-gamma agonist treatment, the level of adiponectin icrement shows strongest correlation in both group. The amount of adiponectin increment was 2-fold higher in metabolic syndrome group. Our group measured plasma concentrations of human RBP4 and compared them with various parameters associated with insulin resistance in the subjects with normal glucose tolerance (NGT, n = 57), impaired glucose tolerance (IGT, n = 48), and type 2 diabetes mellitus (DM, n = 49). The plasma RBP4 concentrations were higher in IGT and DM groups compared to NGT group (median [range] was 18.9 [11.2-45.8], 20.9 [9.9-48.5], and 18.1 [9.3-30.5] m /ml, respectively). However, there was no difference in plasma RBP4 concentration between IGT and DM groups.
Tadahiro Kitamura
(Metabolic Signal Research Center,
Institute for Molecular and Cellular Regulation, Gunma University)
Type 2 diabetes is caused by the insulin resistance in peripheral tissues, such as liver, skeletal muscle and adipose tissue and the dysfunction of pancreatic b cells. It has been recently suggested that the failure of central regulation of energy homeostasis also accounts for the development of type 2 diabetes. Recent studies showed that PI3-kinase/Akt pathway is the most important pathway in the metabolic functions of insulin. We focused on forkhead transcription factor FoxO1, a downstream target of Akt. FoxO1 regulates glucose and lipid metabolism in liver, as well as preadipocyte, myoblast and vascular endothelial cell differentiation. In the symposium, I will talk about the roles of FoxO1 in pancreatic b cells and brain hypothalamus. FoxO1 inhibits b cell proliferation through competition with FoxA2 for binding to Pdx1 promoter. On the other hand, the expression pattern of FoxO1 during pancreas development is identical to the pattern of Pdx1, Nkx2.2 and Pax4, transcription factors known to be critical for b cell development, suggesting that FoxO1 may play an important role in b cell differentiation.
Insulin and leptin control energy homeostasis through regulation of orexigenic (Agrp) and anorexigenic (Pomc) neuropeptides in the hypothalamus. However, the molecular mechanism by which insulin and leptin regulate Agrp and Pomc expression is unclear. We performed microinjection of adenovirus expressing constitutively active FoxO1 directly into the hypothalamic arcuate nucleus of rats, and showed that food intake and body weight were increased in these rats compared to control rats. FoxO1 increases Agrp and decreases Pomc transcription through the competition with Stat3 for binding to Agrp and Pomc promoters, which results in the increase in food intake.
Shiki Okamoto, Tetsuya Shiuchi, Atsushi Suzuki, Suni Lee, Yasuhiko Minokoshi
(Division of Endocrinology and Metabolism, National Institute for Physiological Sciences)
The hypothalamic AMP-kinase regulates feeding behavior in response to hormonal and nutrient signals. Decrease of AMP-kinase activity in the paraventricular (PVH) and arcuate hypothalamus plays an important role in anorexic effect of leptin. However, the effect of AMP-kinase on long-term energy balance remains to be established. In the present study, we examined the effect of chronic expression of constitutively-active AMP-kinase (CA-AMPK) in the PVH on food intake and body weight in male C57BL/6J mice, using lenti-viral vector with neuron specific-synapsin 1 promotor.
CA-AMPK in the PVH significantly increased body weight (CA-AMPK mice: 11.0 ± 1.5 g vs. the control mice: 3.5 ± 0.3 g, during 3 months after the infection). CA-AMPK mice also increased food intake before the increase in body weight (CA-AMPK mice: 14.8 ± 0.9 kcal vs. control mice: 12.9 ± 0.1 kcal/day, 1 month after the infection). Interestingly, CA-AMPK mice increased food intake only under high carbohydrate diet (lob chow or high sucrose diet) but not under high fat diet (68% lard), while the control mice increased the intake of high fat diet but not high carbohydrate diet (intake of high fat diet in CA-AMPK mice: 11.7 ± 0.9 kcal and in the control mice: 16.5 ± 0.9 kcal/day). When high sucrose and high fat diets are simultaneously available, CA-AMPK mice chose high sucrose diet, whereas the control mice chose high fat diet. CA-AMPK increased the mRNA expression of fatty acid oxidation-related genes in the PVH such as PPAR alpha, FATP1, acyl-CoA synthetase1 and CPT-1c. Direct administration of etomoxir, an inhibitor of CPT-1 and fatty acid oxidation in mitochondria, into the PVH in the CA-AMPK mice, reversed to the high preference for high fat diet.
Thus, these findings suggest that AMP-kinase in the PVH regulates not only calorie intake but also the preference for carbohydrate and fat diets. AMP-kinase in the PVH may control the food preference by changing fatty acid metabolism in the nucleus.
Tetsuya Yamada1, Hideki Katagiri2
(1Division of Molecular Metabolism and Diabetes
2Division of Advanced Therapeutics for Metabolic Diseases
Tohoku University School of Medicine)
Cross-talk between organs/tissues plays important roles in regulating energy metabolism and maintaining glucose homeostasis. However, it remains unclear whether and how the liver transmits metabolic signals to other tissues/organs. In this study, we have identified a neuronal pathway that participates in this cross-talk. Reportedly, hepatic PPAR g expression is functionally enhanced in obese models and plays a role in not only hepatic but also peripheral lipid accumulation. Herein, adenovirus-mediated PPAR g 2 expression in the liver acutely aggravated hepatic steatosis on high fat chow loading, but remarkably diminished adipose tissues. For example, epididymal fat weight was decreased by 46.6% in PPAR g -mice as compared to controls. In addition, resting oxygen consumption was markedly increased, by 29.4%, in PPAR g 2-mice. Glucose tolerance and insulin tolerance tests as well as hyperinsulinemic euglycemic clamp experiments showed that hepatic expression of PPAR g 2 markedly improved glucose tolerance and insulin sensitivity. Furthermore, improved insulin sensitivity in the periphery was confirmed by enhanced tyrosine phosphorylation of the insulin receptor and IRS-1 in response to insulin administration. In PPAR g 2-mice, hepatic vagotomy had no effect on the PPAR g 2-induced phenotypes in the liver, but, interestingly, blocked the remote effects, including the reduction in peripheral adiposity, the increments in resting oxygen consumption and the improvements of glucose tolerance as well as insulin sensitivity. Furthermore, perivagal capsaicin application blocked the reduction in peripheral adiposity, confirming involvement of the afferent vagus in the remote effects of hepatic PPAR g 2 expression. Thus, the liver is likely to transmit metabolic signals via the afferent vagus. This novel neuronal pathway originating in the liver may regulate energy expenditure, fat storage redistribution as well as systemic insulin sensitivity, and is a potential therapeutic target against the metabolic syndrome.
T. Ida1, K. Mori2, M. Miyazato2, N. Murakami3, K. Kangawa2, T. Sato1, M. Kojima1
(1Department of Molecular Genetics, Institute of Life Sciences, Kurume University
2Department of Biochemistry, National Cardiovascular Center Research Institute
3Department of Veterinary Physiology, Faculty of Agriculture, University of Miyazaki)
We identified a novel neuropeptide of 36 amino-acid residues in rat brain as an endogenous ligand for the orphan G protein-coupled receptor FM-4/TGR-1, which was identified to date as the neuromedin U (NMU) receptor, and designate this peptide 'neuromedin S (NMS)' because it is specifically expressed in the suprachiasmatic nuclei (SCN) of the hypothalamus. NMS shares a C-terminal core structure with NMU. In rat brain, NMS expression is restricted to the core of the SCN and has a diurnal peak under light/dark cycling. Intracerebroventricular (icv) administration of NMS in rats activates SCN neurons and induces nonphotic type phase shifts in the circadian rhythm of locomotor activity and decreased 12-h food intake during the dark period in rats. This anorexigenic effect was more potent and persistent than that observed with the same dose of NMU. Icv administration of NMS increased POMC mRNA expression in the arcuate nucleus (Arc) and CRH mRNA in the paraventricular nucleus (PVN). Pretreatment with SHU9119 (antagonist for a melanocyte-stimulating hormone) and a -helical CRF-(9-41) (antagonist for CRH) attenuated NMS-induced suppression of 24 h food intake. These findings suggest that NMS is implicated in the regulation of circadian rhythms and feeding behavior.
