Tissue-specific activation of insulin signaling as a potential target for obesity-related metabolic disorders.

The incidence of obesity is rapidly increasing worldwide. Obesity-associated insulin resistance has long been established as a significant risk factor for obesity-related disorders such as type 2 diabetes and atherosclerosis. Insulin plays a key role in systemic glucose metabolism, with the liver, skeletal muscle, and adipose tissue as the major acting tissues. Insulin receptors and the downstream insulin signaling-related molecules are expressed in various tissues, including vascular endothelial cells, vascular smooth muscle cells, and monocytes/macrophages. In obesity, decreased insulin action is considered a driver for associated disorders. However, whether insulin action has a positive or negative effect on obesity-related disorders depends on the tissue in which it acts. While an enhancement of insulin signaling in the liver increases hepatic fat accumulation and exacerbates dyslipidemia, enhancement of insulin signaling in adipose tissue protects against obesity-related dysfunction of various organs by increasing the capacity for fat accumulation in the adipose tissue and inhibiting ectopic fat accumulation. Thus, this "healthy adipose tissue expansion" by enhancing insulin sensitivity in adipose tissue, but not in the liver, may be an effective therapeutic strategy for obesity-related disorders. To effectively address obesity-related metabolic disorders, the mechanisms of insulin resistance in various tissues of obese patients must be understood and drugs that enhance insulin action must be developed. In this article, we review the potential of interventions that enhance insulin signaling as a therapeutic strategy for obesity-related disorders, focusing on the molecular mechanisms of insulin action in each tissue.

Okuma H ，Tsuchiya K 《-》

Ugonin J improves metabolic disorder and ameliorates nonalcoholic fatty liver disease by regulating the AMPK/AKT signaling pathway.

Closely associated with visceral obesity, hepatic steatosis resulting from non-alcoholic fatty liver disease (NAFLD) exacerbates insulin resistance. Developing effective drugs to treat NAFLD is imperative. Here, we investigated the pharmacological mechanism of ugonin J (UJ) in controlling metabolic disorder and ameliorating NAFLD pathophysiology in diet-induced obese mice. The effects of UJ were assessed in 5-week-old C57BL/6 J mice fed a high-fat diet (HFD) for 12 weeks. UJ treatment averted HFD-induced body weight gain by reducing fat deposition in adipose tissues and reduced HFD-induced hyperlipidemia and hepatic inflammation. UJ also improved HFD-induced glucose tolerance and insulin resistance. Moreover, the mode of action of UJ was analyzed in palmitate (PA)-induced steatotic human HuS-E/2 hepatocytes and in hyperglycemia-simulating rat BRIN-BD11 pancreatic β cells. In PA-induced steatotic human hepatocytes, UJ treatment promoted lipid clearance via pAMPK, pACC and CPT-1 upregulation and SREBP-1c downregulation. Interestingly, UJ upregulated Akt activity in hepatocytes and increased insulin secretion from β cells in acute insulin secretion tests. Taken together, UJ improved adipocyte hypertrophy, hyperinsulinemia, hyperglycemia, hyperlipidemia and fat deposition in livers. UJ also reduced fatty acid accumulation by modulating key metabolic regulators. Our findings demonstrated the therapeutic potential of UJ for the treatment of NAFLD and diet-induced metabolic disorders.

Chang TC ，Chiou WC ，Lai WH ，Huang HC ，Huang YL ，Liu HK ，Liang YC ，Huang C ... -  《-》

Deficiency of oncostatin M receptor β (OSMRβ) exacerbates high-fat diet-induced obesity and related metabolic disorders in mice.

Oncostatin M (OSM) belongs to the IL-6 family of cytokines and has diverse biological effects, including the modulation of inflammatory responses. In the present study we analyzed the roles of OSM signaling in obesity and related metabolic disorders. Under a high-fat diet condition, OSM receptor β subunit-deficient (OSMRβ(-/-)) mice exhibited increases in body weight and food intake compared with those observed in WT mice. In addition, adipose tissue inflammation, insulin resistance, and hepatic steatosis were more severe in OSMRβ(-/-) mice than in wild-type (WT) mice. These metabolic phenotypes did not improve when OSMRβ(-/-) mice were pair-fed with WT mice, suggesting that the effects of OSM signaling on these phenotypes are independent of the increases in the body weight and food intake. In the liver of OSMRβ(-/-) mice, the insulin-induced phosphorylation of p70 S6 kinase remained intact, whereas insulin-induced FOXO1 phosphorylation was impaired. In addition, OSMRβ(-/-) mice displayed a higher expression of genes related to de novo lipogenesis in the liver than WT mice. Furthermore, treatment of genetically obese ob/ob mice with OSM improved insulin resistance, adipose tissue inflammation, and hepatic steatosis. Intraportal administration of OSM into ob/ob mice activated STAT3 and increased the expression of long-chain acyl-CoA synthetase (ACSL) 3 and ACSL5 with decreased expression of fatty acid synthase in the liver, suggesting that OSM directly induces lipolysis and suppresses lipogenesis in the liver of obese mice. These findings suggest that defects in OSM signaling promote the deterioration of high-fat diet-induced obesity and related metabolic disorders.

Komori T ，Tanaka M ，Senba E ，Miyajima A ，Morikawa Y ... -  《-》

Dietary capsaicin reduces obesity-induced insulin resistance and hepatic steatosis in obese mice fed a high-fat diet.

Kang JH ，Goto T ，Han IS ，Kawada T ，Kim YM ，Yu R ... -  《-》

Aryl hydrocarbon receptor deficiency protects mice from diet-induced adiposity and metabolic disorders through increased energy expenditure.

Xu CX ，Wang C ，Zhang ZM ，Jaeger CD ，Krager SL ，Bottum KM ，Liu J ，Liao DF ，Tischkau SA ... -  《-》