Obesity: Mizunoya W

Naitoh R, Miyawaki K, Harada N, Mizunoya W, Toyoda K, Fushiki T, Yamada Y, Seino Y, Inagaki N. · Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan. · Biochem Biophys Res Commun. · Pubmed #18723001 No free full text.

Abstract: Gastric inhibitory polypeptide (GIP) is an incretin and directly promotes fat accumulation in adipocytes. Inhibition of GIP signaling prevents onset of obesity and increases fat oxidation in peripheral tissues under high-fat diet (HFD), but the mechanism is unknown. In the present study, we investigated the effects of inhibition of GIP signaling on adiponectin levels after 3 weeks of HFD by comparing wild-type (WT) mice and GIP receptor-deficient (Gipr(-/-)) mice. In HFD-fed Gipr(-/-) mice, fat oxidation was significantly increased and adiponectin mRNA levels in white adipose tissue and plasma adiponectin levels were significantly increased compared to those in HFD-fed WT mice. In addition, the PPARalpha mRNA level was increased and the ACC mRNA level was decreased in skeletal muscle of HFD-fed Gipr(-/-) mice compared with those in HFD-fed WT mice. These results indicate that inhibition of GIP signaling increases adiponectin levels, resulting in increased fat oxidation in peripheral tissues under HFD.

Nishino N, Tamori Y, Tateya S, Kawaguchi T, Shibakusa T, Mizunoya W, Inoue K, Kitazawa R, Kitazawa S, Matsuki Y, Hiramatsu R, Masubuchi S, Omachi A, Kimura K, Saito M, Amo T, Ohta S, Yamaguchi T, Osumi T, Cheng J, Fujimoto T, Nakao H, Nakao K, Aiba A, Okamura H, Fushiki T, Kasuga M. · Department of Internal Medicine, Kobe University Graduate School of Medicine, Kobe, Japan. · J Clin Invest. · Pubmed #18654663 links to  free full text

Abstract: White adipocytes are unique in that they contain large unilocular lipid droplets that occupy most of the cytoplasm. To identify genes involved in the maintenance of mature adipocytes, we expressed dominant-negative PPARgamma in 3T3-L1 cells and performed a microarray screen. The fat-specific protein of 27 kDa (FSP27) was strongly downregulated in this context. FSP27 expression correlated with induction of differentiation in cultured preadipocytes, and the protein localized to lipid droplets in murine white adipocytes in vivo. Ablation of FSP27 in mice resulted in the formation of multilocular lipid droplets in these cells. Furthermore, FSP27-deficient mice were protected from diet-induced obesity and insulin resistance and displayed an increased metabolic rate due to increased mitochondrial biogenesis in white adipose tissue (WAT). Depletion of FSP27 by siRNA in murine cultured white adipocytes resulted in the formation of numerous small lipid droplets, increased lipolysis, and decreased triacylglycerol storage, while expression of FSP27 in COS cells promoted the formation of large lipid droplets. Our results suggest that FSP27 contributes to efficient energy storage in WAT by promoting the formation of unilocular lipid droplets, thereby restricting lipolysis. In addition, we found that the nature of lipid accumulation in WAT appears to be associated with maintenance of energy balance and insulin sensitivity.

Zhou H, Yamada Y, Tsukiyama K, Miyawaki K, Hosokawa M, Nagashima K, Toyoda K, Naitoh R, Mizunoya W, Fushiki T, Kadowaki T, Seino Y. · Department of Diabetes and Clinical Nutrition, Kyoto University Graduate School of Medicine, Kyoto, Japan. · Biochem Biophys Res Commun. · Pubmed #16105663 No free full text.

Abstract: Gut hormone gastric inhibitory polypeptide (GIP) stimulates insulin secretion from pancreatic beta-cells upon ingestion of nutrients. Inhibition of GIP signaling prevents the onset of obesity and consequent insulin resistance induced by high-fat diet. In this study, we investigated the role of GIP in accumulation of triglycerides into adipocytes and in fat oxidation peripherally using insulin receptor substrate (IRS)-1-deficient mice and revealed that IRS-1(-/-)GIPR(-/-) mice exhibited both reduced adiposity and ameliorated insulin resistance. Furthermore, increased gene expression of CD36 and UCP2 in liver, and increased expression and enzyme activity of 3-hydroxyacyl-CoA dehydrogenase in skeletal muscle of IRS-1(-/-)GIPR(-/-) mice might contribute to the lower respiratory quotient and the higher fat oxidation in light phase. These results suggest that GIP plays a crucial role in switching from fat oxidation to fat accumulation under the diminished insulin action as a potential target for secondary prevention of insulin resistance.

Hibuse T, Maeda N, Funahashi T, Yamamoto K, Nagasawa A, Mizunoya W, Kishida K, Inoue K, Kuriyama H, Nakamura T, Fushiki T, Kihara S, Shimomura I. · Department of Internal Medicine and Molecular Science, Graduate School of Medicine, Osaka University, 2-2-B5 Yamada-oka, Suita, Osaka 565-0871, Japan. · Proc Natl Acad Sci U S A. · Pubmed #16009937 links to  free full text

Abstract: In adipocytes, hydrolysis of triglycerides results in the release of free fatty acids and glycerol. Aquaporin 7 (AQP7), a member of aquaglyceroporins, is known to permeabilize glycerol and water. We recently generated Aqp7-knockout (KO) mice and demonstrated that such mice have low plasma glycerol levels and impaired glycerol release in response to beta3-adrenergic agonist, suggesting that AQP7 acts as a glycerol gateway molecule in adipocytes for the efficient release of glycerol in vivo. Although there was no difference in body weight between WT and KO mice until 10 weeks of age, here we found that KO mice developed adult-onset obesity. The body weight and fat mass increased significantly in KO mice compared with WT mice after 12 weeks of age. Adipocytes of KO mice were large and exhibited accumulation of triglycerides compared with WT mice. The KO mice developed obesity and insulin resistance even at a young age after consumption of high-fat/high-sucrose diet. We demonstrated the enhanced glycerol kinase enzymatic activity in Aqp7-KO and -knockdown adipocytes. A series of our results indicate that AQP7 disruption elevates adipose glycerol kinase activity, accelerates triglycerides synthesis in adipocytes, and, finally, develops obesity.

Miyawaki K, Yamada Y, Ban N, Ihara Y, Tsukiyama K, Zhou H, Fujimoto S, Oku A, Tsuda K, Toyokuni S, Hiai H, Mizunoya W, Fushiki T, Holst JJ, Makino M, Tashita A, Kobara Y, Tsubamoto Y, Jinnouchi T, Jomori T, Seino Y. · Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan. · Nat Med. · Pubmed #12068290 No free full text.

Abstract: Secretion of gastric inhibitory polypeptide (GIP), a duodenal hormone, is primarily induced by absorption of ingested fat. Here we describe a novel pathway of obesity promotion via GIP. Wild-type mice fed a high-fat diet exhibited both hypersecretion of GIP and extreme visceral and subcutaneous fat deposition with insulin resistance. In contrast, mice lacking the GIP receptor (Gipr(-/-)) fed a high-fat diet were clearly protected from both the obesity and the insulin resistance. Moreover, double-homozygous mice (Gipr(-/-), Lep(ob)/Lep(ob)) generated by crossbreeding Gipr(-/-) and obese ob/ob (Lep(ob)/Lep(ob)) mice gained less weight and had lower adiposity than Lep(ob)/Lep(ob) mice. The Gipr(-/-) mice had a lower respiratory quotient and used fat as the preferred energy substrate, and were thus resistant to obesity. Therefore, GIP directly links overnutrition to obesity and it is a potential target for anti-obesity drugs.

Komazawa N, Matsuda M, Kondoh G, Mizunoya W, Iwaki M, Takagi T, Sumikawa Y, Inoue K, Suzuki A, Mak TW, Nakano T, Fushiki T, Takeda J, Shimomura I. · Department of Social and Environmental Medicine, Graduate School of Frontier Bioscience, Osaka University, 2-2 Yamadaoka, Suita, Osaka, Japan. · Nat Med. · Pubmed #15489860 No free full text.

Abstract: Pten is an important phosphatase, suppressing the phosphatidylinositol-3 kinase/Akt pathway. Here, we generated adipose-specific Pten-deficient (AdipoPten-KO) mice, using newly generated Acdc promoter-driven Cre transgenic mice. AdipoPten-KO mice showed lower body and adipose tissue weights despite hyperphagia and enhanced insulin sensitivity with induced phosphorylation of Akt in adipose tissue. AdipoPten-KO mice also showed marked hyperthermia and increased energy expenditure with induced mitochondriagenesis in adipose tissue, associated with marked reduction of p53, inactivation of Rb, phosphorylation of cyclic AMP response element binding protein (CREB) and increased expression of Ppargc1a, the gene that encodes peroxisome proliferative activated receptor gamma coactivator 1 alpha. Physiologically, adipose Pten mRNA decreased with exposure to cold and increased with obesity, which were linked to the mRNA alterations of mitochondriagenesis. Our results suggest that altered expression of adipose Pten could regulate insulin sensitivity and energy expenditure. Suppression of adipose Pten may become a beneficial strategy to treat type 2 diabetes and obesity.