Human IL6 enhances leptin action in mice

AIMS/HYPOTHESIS: Interleukin-6 is an inflammatory cytokine with pleiotropic effects upon nutrient homeostasis. Many reports show that circulating IL6 correlates with obesity and contributes to insulin resistance; however, IL6 can promote energy expenditure that improves glucose homeostasis. METHODS: We investigated nutrient homeostasis in C57BL/6J mice with sustained circulating human IL6 (hIL6) secreted predominantly from brain and lung (hIL6 (tg) mice). RESULTS: The hIL6 (tg) mice displayed no features of systemic inflammation and were more insulin-sensitive than wild-type mice. On a high-fat diet, hIL6 (tg) mice were lean, had low leptin concentrations, consumed less food and expended more energy than wild-type mice. Like ob/ob mice, the ob/ob (IL6) mice (generated by intercrossing ob/ob and hIL6 (tg) mice) were obese and glucose-intolerant. However, low-dose leptin injections increased physical activity and reduced both body weight and food intake in ob/ob (IL6) mice, but was ineffective in ob/ob mice. Leptin increased hypothalamic signal transducer and activator of transcription-3 phosphorylation in ob/ob (IL6) mice, whereas ob/ob mice barely responded. CONCLUSIONS/INTERPRETATION: Human IL6 enhanced central leptin action in mice, promoting nutrient homeostasis and preventing diet-induced obesity. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00125-009-1580-8) contains supplementary material, which is available to authorised users.