Diet- and obesity-independent improvements in insulin sensitivity in mice genetically deficient in tumor necrosis factor- α (TNF- α KO).

Abstract

High-fat (HF) feeding and obesity lead to progressive reductions in insulin sensitivity and type 2 diabetes mellitus. The cytokine TNF-α has been shown to contribute to this pathology in overweight HF-fed mice. Here we examined whether genetic deficiency of TNF-α protects against the development of insulin resistance independent of HF-feeding or obesity. Eight-wk old TNF-α KO and wild-type (WT) mice were fed chow (CH) or HF (60% energy from fat) diet. One and 4 week later plasma glucose and insulin levels were measured after 12-h fasts and 3-h re-feeding. Plasma leptin and resistin levels and body adiposity were measured after 4 week. KO mice ate more CH, but not more HF diet, than WT mice. BW and adiposity increased more in HF than CH mice, and TNF-α deficiency had no effect on either, despite the CH intake difference. Fasting glucose was lower after 1 week in KO HF than WT HF mice. Fasting insulin was lower in KO CH than WT CH mice. Fed glucose tended to be increased in KO mice in all tests, but was significantly so only in 4-week CH. Fed insulin was markedly lower in KO mice in all tests. Fasting leptin and resistin were increased by HF, with no genotype effect. Fed leptin (CH and HF) and resistin (HF) were reduced in KO mice. These data suggest that TNF-α deficiency improves insulin sensitivity even in the absence of HF-feeding or obesity, and that the mechanism may involve reduced circulating leptin.