Obesity: Segawa K

Nozaki M, Fukuhara A, Segawa K, Okuno Y, Abe M, Hosogai N, Matsuda M, Komuro R, Shimomura I. · Department of Metabolic Medicine, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. · Biochem Biophys Res Commun. · Pubmed #17931601 No free full text.

Abstract: Obesity is associated with infiltration of macrophages into adipose tissue, and macrophages are an important source of nitric oxide (NO). Dysregulated production of fat-derived secretory factor, adipocytokine, leads to obesity-linked metabolic disorders. However, it has not been fully determined whether NO might have direct effects on adipocytokine expressions. Here, we show that NO donor treatment downregulated gene expression and secretion of adiponectin, and upregulated mRNA levels of PAI-1 and IL-6. NO donor reduced promoter activity of adiponectin through PPARgamma responsive element. Moreover, NO donor activated JNK and NF-kappaB pathways, and inhibitors of these pathways rescued NO-mediated upregulation of PAI-1 and IL-6. Analysis of adipose tissue of high-fat-fed obese mice showed upregulation of PAI-1 and IL-6 expression, increased synthesis of NO, and downregulation of adiponectin. Our results suggest that increased NO synthesis might be partly responsible for dysregulation of adipocytokines in adipose tissue.

Hosogai N, Fukuhara A, Oshima K, Miyata Y, Tanaka S, Segawa K, Furukawa S, Tochino Y, Komuro R, Matsuda M, Shimomura I. · Department of Metabolic Medicine, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. · Diabetes. · Pubmed #17395738 links to  free full text

Abstract: Obesity is linked to a variety of metabolic disorders, such as insulin resistance and atherosclerosis. 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. Here, we show that adipose tissue of obese mice is hypoxic and that local adipose tissue hypoxia dysregulates the production of adipocytokines. Tissue hypoxia was confirmed by an exogenous marker, pimonidazole, and by an 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 endoplasmic reticulum (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 plasminogen activator inhibitor type-1, and increased the mRNAs of ER stress marker genes, CHOP and GRP78 (glucose-regulated protein, 78 kD). Expression of CHOP attenuated adiponectin promoter activity, and RNA interference of CHOP partly reversed hypoxia-induced suppression of adiponectin mRNA expression in adipocytes. Hypoxia also increased instability of adiponectin mRNA. Our results suggest that hypoperfusion and hypoxia in adipose tissues underlie the dysregulated production of adipocytokines and metabolic syndrome in obesity.

Segawa K, Fukuhara A, Hosogai N, Morita K, Okuno Y, Tanaka M, Nakagawa Y, Kihara S, Funahashi T, Komuro R, Matsuda M, Shimomura I. · Department of Medicine and Pathophysiology, Graduate School of Medicine, Osaka University, Osaka, Japan. · Biochem Biophys Res Commun. · Pubmed #16970912 No free full text.

Abstract: Obesity is associated with metabolic disorders, such as insulin resistance. Visfatin is an adipose-derived secretory factor to exert insulin-mimetic effects. Plasma visfatin levels and mRNA levels of visfatin in adipose tissues are increased in obesity. However, the mechanism that mediates induction of visfatin mRNA in adipose tissue of obesity remains unknown. Recent studies have reported that fat tissue is hypoxia in obesity. In this study, we investigated the effects of hypoxia on mRNA expression of visfatin in adipocytes. Hypoxia increased visfatin mRNA expression. Desferoxamine and Cobaltous chloride, two hypoxia mimetic compounds, also increased visfatin mRNA levels. Dimethyloxallyl glycine, a stabilizer of hypoxia-inducible factor 1alpha (HIF1alpha), mimicked the hypoxia-mediated upregulation of visfatin, and YC1, an inhibitor of HIF1 cancelled the hypoxia-induced upregulation of visfatin mRNA. We identified two functional hypoxia responsive elements (HRE) in mouse visfatin promoter. Hypoxic treatment and overexpression of HIF1alpha increased the promoter activity, and mutation of the HRE blunted hypoxia-induced activation of visfatin promoter. Our results suggest that visfatin mRNA expression is upregulated in the fat tissue of obesity through the activation of HIF1alpha pathway due to hypoxia.

Fukuhara A, Matsuda M, Nishizawa M, Segawa K, Tanaka M, Kishimoto K, Matsuki Y, Murakami M, Ichisaka T, Murakami H, Watanabe E, Takagi T, Akiyoshi M, Ohtsubo T, Kihara S, Yamashita S, Makishima M, Funahashi T, Yamanaka S, Hiramatsu R, Matsuzawa Y, Shimomura I. · Department of Medicine and Pathophysiology, Graduate School of Medicine, and Department of Organismal Biosystems, Graduate School of Frontier Biosciences, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. · Science. · Pubmed #15604363 links to  free full text

Abstract: Fat tissue produces a variety of secreted proteins (adipocytokines) with important roles in metabolism. We isolated a newly identified adipocytokine, visfatin, that is highly enriched in the visceral fat of both humans and mice and whose expression level in plasma increases during the development of obesity. Visfatin corresponds to a protein identified previously as pre-B cell colony-enhancing factor (PBEF), a 52-kilodalton cytokine expressed in lymphocytes. Visfatin exerted insulin-mimetic effects in cultured cells and lowered plasma glucose levels in mice. Mice heterozygous for a targeted mutation in the visfatin gene had modestly higher levels of plasma glucose relative to wild-type littermates. Surprisingly, visfatin binds to and activates the insulin receptor. Further study of visfatin's physiological role may lead to new insights into glucose homeostasis and/or new therapies for metabolic disorders such as diabetes.