Shizuya Yamashita

Bio: Shizuya Yamashita is an academic researcher from Osaka University. The author has contributed to research in topics: Cholesterol & Lipoprotein. The author has an hindex of 70, co-authored 355 publications receiving 28033 citations.

Plasma Concentrations of a Novel, Adipose-Specific Protein, Adiponectin, in Type 2 Diabetic Patients

Abstract: —Adiponectin is a novel, adipose-specific protein abundantly present in the circulation, and it has antiatherogenic properties. We analyzed the plasma adiponectin concentrations in age- and body mass index (BMI)–matched nondiabetic and type 2 diabetic subjects with and without coronary artery disease (CAD). Plasma levels of adiponectin in the diabetic subjects without CAD were lower than those in nondiabetic subjects (6.6±0.4 versus 7.9±0.5 μg/mL in men, 7.6±0.7 versus 11.7±1.0 μg/mL in women; P<0.001). The plasma adiponectin concentrations of diabetic patients with CAD were lower than those of diabetic patients without CAD (4.0±0.4 versus 6.6±0.4 μg/mL, P<0.001 in men; 6.3±0.8 versus 7.6±0.7 μg/mL in women). In contrast, plasma levels of leptin did not differ between diabetic patients with and without CAD. The presence of microangiopathy did not affect the plasma adiponectin levels in diabetic patients. Significant, univariate, inverse correlations were observed between adiponectin levels and fas...

Novel Modulator for Endothelial Adhesion Molecules: Adipocyte-Derived Plasma Protein Adiponectin

Abstract: Background—Among the many adipocyte-derived endocrine factors, we recently found an adipocyte-specific secretory protein, adiponectin, which was decreased in obesity. Although obesity is associated with increased cardiovascular mortality and morbidity, the molecular basis for the link between obesity and vascular disease has not been fully clarified. The present study investigated whether adiponectin could modulate endothelial function and relate to coronary disease. Methods and Results—For the in vitro study, human aortic endothelial cells (HAECs) were preincubated for 18 hours with the indicated amount of adiponectin, then exposed to tumor necrosis factor-α (TNF-α) (10 U/mL) or vehicle for the times indicated. The adhesion of human monocytic cell line THP-1 cells to HAECs was determined by adhesion assay. The surface expression of vascular cell adhesion molecule-1 (VCAM-1), endothelial-leukocyte adhesion molecule-1 (E-selectin), and intracellular adhesion molecule-1 (ICAM-1) was measured by cell ELISA. ...

Visfatin: a protein secreted by visceral fat that mimics the effects of insulin.

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.

Visfatin : A protein secreted by visceral fat that mimics the effects of insulin

Abstract: Recent studies of obesity show that fat tissue fulfills an endocrine function by producing a variety of secreted proteins, called adipocytokines, that may play key metabolic roles. The present investigators have isolateda newly identified adipocytokine, visfatin, from visceral fat of both mice and humans. Expression of visfatin in the plasma increases as obesity develops. This substance corresponds to a protein identified as preB cell colony-enhancing factor (PBEF), a cytokine expressed in lymphocytes. In a study of 101 human males and females, plasma levels of PBEF correlated closely with the amount of visceral fat as estimated by computed tomography. Correlation with the amount of subcutaneous fat was weak. Significant elevations of PBEF mRNA were also found in KKAy mice, which serve as a model for obesity-related type 2 diabetes. These mice become obese at age 6 to 12 weeks and, at the same time, plasma PBEF levels increase significantly, as do levels of PBEF mRNA in visceral fat. Levels in subcutaneous fat change very little. Mice fed a high-fat diet had higher plasma PBEF concentrations than those fed normal chow. When recombinant visfatin was administered intravenously to c57BL/6J mice, plasma glucose decreased within 30 minutes in a dose-dependent manner. The same effect was noted in insulin-resistant obese KKAy mice, mimicking the effect of insulin injection. Visfatin also had insulin-like effects on cultured cells. In both strains of mice, chronic exposure to visfatin, using adenovirus, significantly lowered plasma levels of both glucose and insulin. Visfatin was found to bind to-and activate-the insulin receptor but in a way different from insulin. These studies indicate that visfatin shares properties of insulin both in vitro and in vivo. In addition to helping to understand glucose and lipid homeostasis and adipocyte proliferation, visfatin may prove to be a useful target when developing drug treatments for diabetes.

Obesity is associated with macrophage accumulation in adipose tissue

Abstract: Obesity alters adipose tissue metabolic and endocrine function and leads to an increased release of fatty acids, hormones, and proinflammatory molecules that contribute to obesity associated complications. To further characterize the changes that occur in adipose tissue with increasing adiposity, we profiled transcript expression in perigonadal adipose tissue from groups of mice in which adiposity varied due to sex, diet, and the obesity-related mutations agouti (Ay) and obese (Lepob). We found that the expression of 1,304 transcripts correlated significantly with body mass. Of the 100 most significantly correlated genes, 30% encoded proteins that are characteristic of macrophages and are positively correlated with body mass. Immunohistochemical analysis of perigonadal, perirenal, mesenteric, and subcutaneous adipose tissue revealed that the percentage of cells expressing the macrophage marker F4/80 (F4/80+) was significantly and positively correlated with both adipocyte size and body mass. Similar relationships were found in human subcutaneous adipose tissue stained for the macrophage antigen CD68. Bone marrow transplant studies and quantitation of macrophage number in adipose tissue from macrophage-deficient (Csf1op/op) mice suggest that these F4/80+ cells are CSF-1 dependent, bone marrow-derived adipose tissue macrophages. Expression analysis of macrophage and nonmacrophage cell populations isolated from adipose tissue demonstrates that adipose tissue macrophages are responsible for almost all adipose tissue TNF-alpha expression and significant amounts of iNOS and IL-6 expression. Adipose tissue macrophage numbers increase in obesity and participate in inflammatory pathways that are activated in adipose tissues of obese individuals.

Inflammation in atherosclerosis

Abstract: Abundant data link hypercholesterolaemia to atherogenesis. However, only recently have we appreciated that inflammatory mechanisms couple dyslipidaemia to atheroma formation. Leukocyte recruitment and expression of pro-inflammatory cytokines characterize early atherogenesis, and malfunction of inflammatory mediators mutes atheroma formation in mice. Moreover, inflammatory pathways promote thrombosis, a late and dreaded complication of atherosclerosis responsible for myocardial infarctions and most strokes. The new appreciation of the role of inflammation in atherosclerosis provides a mechanistic framework for understanding the clinical benefits of lipid-lowering therapies. Identifying the triggers for inflammation and unravelling the details of inflammatory pathways may eventually furnish new therapeutic targets.

Untangling the ErbB signalling network

Abstract: When epidermal growth factor and its relatives bind the ErbB family of receptors, they trigger a rich network of signalling pathways, culminating in responses ranging from cell division to death, motility to adhesion. The network is often dysregulated in cancer and lends credence to the mantra that molecular understanding yields clinical benefit: over 25,000 women with breast cancer have now been treated with trastuzumab (Herceptin), a recombinant antibody designed to block the receptor ErbB2. Likewise, small-molecule enzyme inhibitors and monoclonal antibodies to ErbB1 are in advanced phases of clinical testing. What can this pathway teach us about translating basic science into clinical use?

Serum Immunoreactive-Leptin Concentrations in Normal-Weight and Obese Humans

Abstract: Background Leptin, the product of the ob gene, is a hormone secreted by adipocytes. Animals with mutations in the ob gene are obese and lose weight when given leptin, but little is known about the physiologic actions of leptin in humans. Methods Using a newly developed radioimmunoassay, we measured serum concentrations of leptin in 136 normal-weight subjects and 139 obese subjects (body-mass index, >27.3 for men and >27.8 for women; the body-mass index was defined as the weight in kilograms divided by the square of the height in meters). The measurements were repeated in seven obese subjects after weight loss and during maintenance of the lower weight. The ob messenger RNA (mRNA) content of adipocytes was determined in 27 normal-weight and 27 obese subjects. Results The mean (±SD) serum leptin concentrations were 31.3±24.1 ng per milliliter in the obese subjects and 7.5±9.3 ng per milliliter in the normal-weight subjects (P<0.001). There was a strong positive correlation between serum leptin concentration...

Chronic inflammation in fat plays a crucial role in the development of obesity-related insulin resistance.

Abstract: Insulin resistance arises from the inability of insulin to act normally in regulating nutrient metabolism in peripheral tissues Increasing evidence from human population studies and animal research has established correlative as well as causative links between chronic inflammation and insulin resistance However, the underlying molecular pathways are largely unknown In this report, we show that many inflammation and macrophage-specific genes are dramatically upregulated in white adipose tissue (WAT) in mouse models of genetic and high-fat diet-induced obesity (DIO) The upregulation is progressively increased in WAT of mice with DIO and precedes a dramatic increase in circulating-insulin level Upon treatment with rosiglitazone, an insulin-sensitizing drug, these macrophage-originated genes are downregulated Histologically, there is evidence of significant infiltration of macrophages, but not neutrophils and lymphocytes, into WAT of obese mice, with signs of adipocyte lipolysis and formation of multinucleate giant cells These data suggest that macrophages in WAT play an active role in morbid obesity and that macrophage-related inflammatory activities may contribute to the pathogenesis of obesity-induced insulin resistance We propose that obesity-related insulin resistance is, at least in part, a chronic inflammatory disease initiated in adipose tissue