Gürol Tuncman

A central role for JNK in obesity and insulin resistance

Obesity is closely associated with insulin resistance and establishes the leading risk factor for type 2 diabetes mellitus, yet the molecular mechanisms of this association are poorly understood. The c-Jun amino-terminal kinases (JNKs) can interfere with insulin action in cultured cells and are activated by inflammatory cytokines and free fatty acids, molecules that have been implicated in the development of type 2 diabetes. Here we show that JNK activity is abnormally elevated in obesity. Furthermore, an absence of JNK1 results in decreased adiposity, significantly improved insulin sensitivity and enhanced insulin receptor signalling capacity in two different models of mouse obesity. Thus, JNK is a crucial mediator of obesity and insulin resistance and a potential target for therapeutics.

Treatment of diabetes and atherosclerosis by inhibiting fatty-acid-binding protein aP2

Adipocyte fatty-acid-binding protein, aP2 (FABP4) is expressed in adipocytes and macrophages, and integrates inflammatory and metabolic responses. Studies in aP2-deficient mice have shown that this lipid chaperone has a significant role in several aspects of metabolic syndrome, including type 2 diabetes and atherosclerosis. Here we demonstrate that an orally active small-molecule inhibitor of aP2 is an effective therapeutic agent against severe atherosclerosis and type 2 diabetes in mouse models. In macrophage and adipocyte cell lines with or without aP2, we also show the target specificity of this chemical intervention and its mechanisms of action on metabolic and inflammatory pathways. Our findings demonstrate that targeting aP2 with small-molecule inhibitors is possible and can lead to a new class of powerful therapeutic agents to prevent and treat metabolic diseases such as type 2 diabetes and atherosclerosis.

Double-stranded RNA-dependent Protein Kinase Links Pathogen Sensing with Stress and Metabolic Homeostasis

As chronic inflammation is a hallmark of obesity, pathways that integrate nutrient- and pathogen sensing pathways are of great interest in understanding the mechanisms of insulin resistance, type 2 diabetes, and other chronic metabolic pathologies. Here, we provide evidence that double-stranded RNA-dependent protein kinase (PKR) can respond to nutrient signals as well as endoplasmic reticulum (ER) stress and coordinate the activity of other critical inflammatory kinases such as the c-Jun N-terminal kinase (JNK) to regulate insulin action and metabolism. PKR also directly targets and modifies insulin receptor substrate and hence integrates nutrients and insulin action with a defined pathogen response system. Dietary and genetic obesity features marked activation of PKR in adipose and liver tissues and absence of PKR alleviates metabolic deterioration due to nutrient or energy excess in mice. These findings demonstrate PKR as a critical component of an inflammatory complex that responds to nutrients and organelle dysfunction.

Adipocyte/macrophage fatty acid–binding proteins contribute to metabolic deterioration through actions in both macrophages and adipocytes in mice

Adipose tissue inflammation is a characteristic of obesity. However, the mechanisms that regulate this inflammatory response and link adipose inflammation to systemic metabolic consequences are not fully understood. In this study, we have taken advantage of the highly restricted coexpression of adipocyte/macrophage fatty acid-binding proteins (FABPs) aP2 (FABP4) and mal1 (FABP5) to examine the contribution of these lipid chaperones in macrophages and adipocytes to local and systemic inflammation and metabolic homeostasis in mice. Deletion of FABPs in adipocytes resulted in reduced expression of inflammatory cytokines in macrophages, whereas the same deletion in macrophages led to enhanced insulin signaling and glucose uptake in adipocytes. Using radiation chimerism through bone marrow transplantation, we generated mice with FABP deficiency in bone marrow and stroma-derived elements in vivo and studied the impact of each cellular target on local and systemic insulin action and glucose metabolism in dietary obesity. The results of these experiments indicated that neither macrophages nor adipocytes individually could account for the total impact of FABPs on systemic metabolism and suggest that interactions between these 2 cell types, particularly in adipose tissue, are critical for the inflammatory basis of metabolic deterioration.

Adipocyte Lipid Chaperone aP2 Is a Secreted Adipokine Regulating Hepatic Glucose Production

Proper control of hepatic glucose production is central to whole-body glucose homeostasis, and its disruption plays a major role in diabetes. Here, we demonstrate that although established as an intracellular lipid chaperone, aP2 is in fact actively secreted from adipocytes to control liver glucose metabolism. Secretion of aP2 from adipocytes is regulated by fasting- and lipolysis-related signals, and circulating aP2 levels are markedly elevated in mouse and human obesity. Recombinant aP2 stimulates glucose production and gluconeogenic activity in primary hepatocytes in vitro and in lean mice in vivo. In contrast, neutralization of secreted aP2 reduces glucose production and corrects the diabetic phenotype of obese mice. Hyperinsulinemic-euglycemic and pancreatic clamp studies upon aP2 administration or neutralization demonstrated actions of aP2 in liver. We conclude that aP2 is an adipokine linking adipocytes to hepatic glucose production and that neutralizing secreted aP2 may represent an effective therapeutic strategy against diabetes.

Divergent roles for p55 and p75 TNF-α receptors in the induction of plasminogen activator inhibitor-1

Tumor necrosis factor-alpha (TNF-alpha) is elevated in obesity and in acute inflammatory states, and contributes to the elevated plasminogen activator inhibitor-1 (PAI-1) levels associated with these conditions. Mice genetically deficient in the p55 and p75 TNF-alpha receptors were used to study the roles of these receptors in the expression of PAI-1 in obese (ob/ob) mice, and in lean mice following acute stimulation with TNF-alpha. In ob/ob mice, p55 and p75 tumor necrosis factor-alpha receptors (TNFRs) act cooperatively to induce PAI-1 mRNA in most tissues, including the adipose tissue, kidney, heart, and liver. However, in lean mice, TNF-alpha-induced PAI-1 expression is mediated primarily by the p55 TNFR. Interestingly, PAI-1 mRNA expression in all tissues of the TNF-alpha-treated p75-deficient lean mice was significantly higher than that observed in TNF-alpha-treated wild-type mice. These observations suggest that the p75 TNFR may play a role in attenuating TNF-alpha-induced PAI-1 mRNA expression in acute inflammatory conditions. Our observation that soluble p75 TNFR was elevated in the plasma of TNF-alpha-treated mice in comparison to untreated mice supports this hypothesis. These studies thus provide insights into the TNF-alpha receptors involved in mediating and modulating the expression of PAI-1 in acute and chronic (eg, obesity) inflammatory states associated with elevated TNF-alpha.

Development of a therapeutic monoclonal antibody that targets secreted fatty acid-binding protein aP2 to treat type 2 diabetes.

A monoclonal antibody to fatty acid–binding protein aP2 has antidiabetic effects on glucose output and utilization. Kill the messenger A variety of metabolic messengers—many from adipose tissue itself—controls the energy state of organs and organisms. Recently, researchers showed that the fatty acid binding protein aP2, once thought to live and work only in the cytoplasm, is also secreted by adipose tissue and spurs metabolic changes in other organs. Now, Burak and colleagues test whether secreted aP2 can serve as a therapeutic target for type 2 diabetes. In mice, the secreted form of aP2 regulates glucose production in liver, systemic glucose homeostasis, and insulin resistance. Serum levels of aP2 were shown to be elevated in obese mice and humans and to correlate with metabolic complications. The authors identified a monoclonal antibody to aP2 that lowered fasting blood glucose, increased insulin sensitivity, and lowered both fat mass and fatty liver (steatosis) in obese mouse models, relative to a control antibody, but not in aP2-deficient mice. The antidiabetic effects of the therapeutic antibody were linked to the regulation of hepatic glucose output and peripheral glucose utilization. Together, these findings suggest that an aP2-targeted antibody that kills the messenger is a viable approach for diabetes treatment. The lipid chaperone aP2/FABP4 has been implicated in the pathology of many immunometabolic diseases, including diabetes in humans, but aP2 has not yet been targeted for therapeutic applications. aP2 is not only an intracellular protein but also an active adipokine that contributes to hyperglycemia by promoting hepatic gluconeogenesis and interfering with peripheral insulin action. Serum aP2 levels are markedly elevated in mouse and human obesity and strongly correlate with metabolic complications. These observations raise the possibility of a new strategy to treat metabolic disease by targeting serum aP2 with a monoclonal antibody (mAb) to aP2. We evaluated mAbs to aP2 and identified one, CA33, that lowered fasting blood glucose, improved systemic glucose metabolism, increased systemic insulin sensitivity, and reduced fat mass and liver steatosis in obese mouse models. We examined the structure of the aP2-CA33 complex and resolved the target epitope by crystallographic studies in comparison to another mAb that lacked efficacy in vivo. In hyperinsulinemic-euglycemic clamp studies, we found that the antidiabetic effect of CA33 was predominantly linked to the regulation of hepatic glucose output and peripheral glucose utilization. The antibody had no effect in aP2-deficient mice, demonstrating its target specificity. We conclude that an aP2 mAb–mediated therapeutic constitutes a feasible approach for the treatment of diabetes.

Molecular alterations in the TP53 gene of peripheral blood cells of patients with chronic myeloid leukemia

The TP53 gene has been extensively studied in patients with chronic myeloid leukemia (CML), both in chronic phase and in blast crisis. Mutations in the gene were found in up to 30% of the patients, especially among those in blast crisis. We report the results of an analysis of 29 blood samples from CML patients: 8 samples from chronic phase patients, 8 from patients in the accelerated phase, and 13 from patients in blast crisis. By using genomic DNA, we sequenced PCR products of the coding exons and most introns of the TP53 gene, finding genetic changes in 30% of the blast crisis samples and 12% in chronic phase. All mutations were found in introns and were previously unreported. Immunocytochemical studies revealed accumulation of TP53 in blood cells of samples both from chronic phase and blast crisis patients. Since these samples had no TP53 mutations, we believe that wild type TP53 accumulates in blood cells of CML patients. Our results, therefore, indicate that molecular changes in coding regions of the TP53 gene are rare. The significance of the abundance of intronic changes should be investigated further. Accumulation of wild type TP53 in CML cells may indicate an additional mechanism involving this gene in the pathogenesis of this disease. Genes Chromosomes Cancer 21:2–7, 1998.