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M W Marino

Bio: M W Marino is an academic researcher from Memorial Sloan Kettering Cancer Center. The author has contributed to research in topics: Adipose tissue & Insulin receptor. The author has an hindex of 2, co-authored 2 publications receiving 2474 citations.

Papers
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Journal ArticleDOI
09 Oct 1997-Nature
TL;DR: Results indicate that TNF-α is an important mediator of insulin resistance in obesity through its effects on several important sites of insulin action.
Abstract: Obesity is highly associated with insulin resistance and is the biggest risk factor for non-insulin-dependent diabetes mellitus. The molecular basis of this common syndrome, however, is poorly understood. It has been suggested that tumour necrosis factor (TNF)-alpha is a candidate mediator of insulin resistance in obesity, as it is overexpressed in the adipose tissues of rodents and humans and it blocks the action of insulin in cultured cells and whole animals. To investigate the role of TNF-alpha in obesity and insulin resistance, we have generated obese mice with a targeted null mutation in the gene encoding TNF-alpha and those encoding the two receptors for TNF-alpha. The absence of TNF-alpha resulted in significantly improved insulin sensitivity in both diet-induced obesity and that resulting for the ob/ob model of obesity. The TNFalpha-deficient obese mice had lower levels of circulating free fatty acids, and were protected from the obesity-related reduction in the insulin receptor signalling in muscle and fat tissues. These results indicate that TNF-alpha is an important mediator of insulin resistance in obesity through its effects on several important sites of insulin action.

2,161 citations

Journal ArticleDOI
TL;DR: Evidence is provided that TNF-alpha can act directly on adipocytes to regulate the release of a preformed pool of leptin and that the elevated adipose tissue expression of T NF-alpha that occurs in obesity may contribute to obesity-related hyperleptinemia.
Abstract: Cytokines, in particular tumor necrosis factor-alpha (TNF-alpha), have significant effects on energy metabolism and appetite although their mechanisms of action are largely unknown. Here, we examined whether TNF-alpha modulates the production of leptin, the recently identified fat-specific energy balance hormone, in cultured adipocytes and in mice. TNF-alpha treatment of 3T3-L1 adipocytes resulted in rapid stimulation of leptin accumulation in the media, with a maximum effect at 6 h. This stimulation was insensitive to cycloheximide, a protein synthesis inhibitor, but was completely inhibited by the secretion inhibitor brefeldin A, indicating a posttranslational effect. Treatment of mice with TNF-alpha also caused a similar increase in plasma leptin levels. Finally, in obese TNF-alpha-deficient mice, circulating leptin levels were significantly lower, whereas adipose tissue leptin was higher compared with obese wild-type animals. These data provide evidence that TNF-alpha can act directly on adipocytes to regulate the release of a preformed pool of leptin. Furthermore, they suggest that the elevated adipose tissue expression of TNF-alpha that occurs in obesity may contribute to obesity-related hyperleptinemia.

407 citations


Cited by
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Journal ArticleDOI
TL;DR: 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) found that the expression of 1,304 transcripts correlated significantly with body mass.
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.

8,902 citations

Journal ArticleDOI
14 Dec 2006-Nature
TL;DR: Dysfunction of the immune response and metabolic regulation interface can be viewed as a central homeostatic mechanism, dysfunction of which can lead to a cluster of chronic metabolic disorders, particularly obesity, type 2 diabetes and cardiovascular disease.
Abstract: Metabolic and immune systems are among the most fundamental requirements for survival. Many metabolic and immune response pathways or nutrient- and pathogen-sensing systems have been evolutionarily conserved throughout species. As a result, immune response and metabolic regulation are highly integrated and the proper function of each is dependent on the other. This interface can be viewed as a central homeostatic mechanism, dysfunction of which can lead to a cluster of chronic metabolic disorders, particularly obesity, type 2 diabetes and cardiovascular disease. Collectively, these diseases constitute the greatest current threat to global human health and welfare.

7,536 citations

Journal ArticleDOI
TL;DR: It is proposed that obesity-related insulin resistance is, at least in part, a chronic inflammatory disease initiated in adipose tissue, and that macrophage-related inflammatory activities may contribute to the pathogenesis of obesity-induced 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

6,165 citations

Journal ArticleDOI
TL;DR: An overview of the endocrine functions of adipose tissue can be found in this paper, where the authors highlight the adverse metabolic consequences of both adipose excess and deficiency, and propose a more rational therapy for these increasingly prevalent disorders.
Abstract: Adipose tissue is a complex, essential, and highly active metabolic and endocrine organ. Besides adipocytes, adipose tissue contains connective tissue matrix, nerve tissue, stromovascular cells, and immune cells. Together these components function as an integrated unit. Adipose tissue not only responds to afferent signals from traditional hormone systems and the central nervous system but also expresses and secretes factors with important endocrine functions. These factors include leptin, other cytokines, adiponectin, complement components, plasminogen activator inhibitor-1, proteins of the renin-angiotensin system, and resistin. Adipose tissue is also a major site for metabolism of sex steroids and glucocorticoids. The important endocrine function of adipose tissue is emphasized by the adverse metabolic consequences of both adipose tissue excess and deficiency. A better understanding of the endocrine function of adipose tissue will likely lead to more rational therapy for these increasingly prevalent disorders. This review presents an overview of the endocrine functions of adipose tissue.

5,484 citations

Journal ArticleDOI
TL;DR: It is suggested that increased oxidative stress in accumulated fat is an early instigator of metabolic syndrome and that the redox state in adipose tissue is a potentially useful therapeutic target for obesity-associated metabolic syndrome.
Abstract: Obesity is a principal causative factor in the development of metabolic syndrome. Here we report that increased oxidative stress in accumulated fat is an important pathogenic mechanism of obesity-associated metabolic syndrome. 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 (fat-derived hormones), including adiponectin, plasminogen activator inhibitor-1, IL-6, and monocyte chemotactic protein-1. Finally, in obese mice, treatment with NADPH oxidase inhibitor reduced ROS production in adipose tissue, attenuated the dysregulation of adipocytokines, and improved diabetes, hyperlipidemia, and hepatic steatosis. Collectively, our results suggest that increased oxidative stress in accumulated fat is an early instigator of metabolic syndrome and that the redox state in adipose tissue is a potentially useful therapeutic target for obesity-associated metabolic syndrome.

4,752 citations