Cardiotrophin-1 (CT-1) is a member of the gp130 family of cytokines. We observed that ct-1(-/-) mice develop mature-onset obesity, insulin resistance, and hypercholesterolemia despite reduced calorie intake. Decreased energy expenditure preceded and accompanied the development of obesity. Acute treatment with rCT-1 decreased blood glucose in an insulin-independent manner and increased insulin-stimulated AKT phosphorylation in muscle. These changes were associated with stimulation of fatty acid oxidation, an effect that was absent in AMPKα2(-/-) mice. Chronic rCT-1 treatment reduced food intake, enhanced energy expenditure, and induced white adipose tissue remodeling characterized by upregulation of genes implicated in the control of lipolysis, fatty acid oxidation, and mitochondrial biogenesis and genes typifying brown fat phenotype. Moreover, rCT-1 reduced body weight and corrected insulin resistance in ob/ob and in high-fat-fed obese mice. We conclude that CT-1 is a master regulator of fat and glucose metabolism with potential applications for treatment of obesity and insulin resistance.

Previous studies have demonstrated that the n-3 fatty acid EPA improves insulin resistance induced by high-fat diets. The aim of the present study was to investigate the potential role of visfatin and apelin in the insulin-sensitising effects of EPA ethyl ester. The effects of EPA on muscle and adipose GLUT mRNA, as well as on liver glucokinase (GK) and glucose-6-phosphatase (G6Pase) activity, were investigated. Male Wistar rats fed on a standard diet or a high-fat cafeteria diet were daily treated by oral administration with EPA ethyl ester (1 g/kg) for 5 weeks. A significant decrease (P, 0·01) in white adipose tissue (WAT) visfatin mRNA levels was found in the cafeteria-fed rats, which was reversed by EPA administration (P,0·05). Moreover, a negative relationship was observed between homeostatic model assessment (HOMA) and the visfatin:total WAT ratio. In contrast, cafeteria-diet feeding caused a significant increase (P, 0·01) in apelin mRNA in visceral WAT. EPA increased (P,0·01) apelin gene expression, and a negative relationship between HOMA index with visceral apelin mRNA and serum apelin:total WAT ratio was also observed. EPA treatment did not induce changes in skeletal muscle GLUT1, GLUT4 or insulin receptor mRNA levels. Neither liver GK and G6Pase activity nor the GK:G6Pase ratio was modified by EPA. These data suggest that somehow the insulin-sensitising effects of EPA could be related to its stimulatory action on both visfatin and apelin gene expression in visceral fat, while changes in skeletal muscle GLUT, as well as in hepatic glucose production, are not likely to be the main contributing factors in the improvement in insulin resistance induced by EPA.

Our data suggest that obesity susceptibility or resistance may depend on the genetic make up related to inflammatory features, and support a role for omega-3 fatty acids in the prevention of obesity-associated inflammation in adipose tissue. In addition, our data do not support the hypothesis that serum haptoglobin is an acute phase protein expected to be positively related to increased adiposity in rats, at least in early and medium stages of DIO.

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Cardiotrophin-1 (CT-1) belongs to the IL-6 family of cytokines. Previous studies of our group revealed that CT-1 is a key regulator of glucose and lipid metabolism. The aim of the present study was to analyze the in vitro and in vivo effects of CT-1 on the production of several adipokines involved in body weight regulation, nutrient metabolism, and inflammation. For this purpose, 3T3-L1 adipocytes were incubated with recombinant protein CT-1 (rCT-1) (1-40 ng/ml) for 1 and 18 h. Moreover, the acute effects of rCT-1 administration (0.2 mg/kg, i.v.) for 30 min and 3 h on adipokines levels were also evaluated in high-fat fed obese mice. In 3T3-L1 adipocytes, rCT-1 treatment downregulated the expression and secretion of leptin, resistin, and visfatin. However, rCT-1 significantly stimulated apelin mRNA and secretion. rCT-1 (18 h) also promoted the activation by phosphorylation of AKT, ERK 1/2, and STAT3. Interestingly, pre-treatment with the PI3K inhibitor LY294002 reversed the stimulatory effects of rCT-1 on apelin expression, suggesting that this pathway could be mediating the effects of rCT-1 on apelin production. In contrast, acute administration of rCT-1 (30 min and 3 h) to diet-induced obese mice downregulated leptin and resistin, without significantly modifying apelin or visfatin mRNA in adipose tissue. Furthermore, CT-1 null mice exhibited altered expression of adipokines in adipose tissue. The present study demonstrates that rCT-1 modulates the production of adipokines in vitro and in vivo, suggesting that the regulation of the secretory function of adipocytes could be involved in the metabolic actions of this cytokine. J. Cell. Physiol. 232: 2469-2477, 2017. © 2016 Wiley Periodicals, Inc.