Exercise normalises overexpression of TNF-a in knockout mice Charlotte Keller a, * , Pernille Keller a , Merce ´ Giralt b , Juan Hidalgo b , Bente Klarlund Pedersen a a Copenhagen Muscle Research Centre, Rigshospitalet, Denmark b Animal Physiology unit, Universidad Auto ´ noma de Barcelona, Spain Received 15 June 2004 Abstract TNF-a is linked with insulin resistance, as greater amounts of TNF are detected in muscle and adipose tissue in glycemically challenged people and TNF-a inhibits insulin receptor signalling. However, what modulates this overexpression of TNF-a is cur- rently unknown. We examined the effect of 1 h exercise on overexpression of the TNF-a gene in TNF receptor 1 and 2 knockout mice. IL-6 knockout mice were included to elucidate the importance of IL-6 in regulating TNF-a in response to exercise. TNF-a gene expression was over-expressed in muscle in both TNFR knockout models. TNF-a overexpression returned to normal levels after exercise in the TNF-a receptor knockout models. In IL-6 knockout mice, a modest decrease in TNF-a was also observed. These data suggest that TNF-a-induced insulin resistance can be regulated by a single exercise bout by normalising TNF-a expres- sion. This exercise effect can be mediated via IL-6, but also an IL-6 independent mechanism seems to exist. Ó 2004 Published by Elsevier Inc. Keywords: TNF-a; IL-6; Exercise; Type II diabetes Exercise increases insulin sensitivity and decreases the risk of developing type II diabetes [1–3], however, the mechanisms whereby this happens are not fully under- stood. The role of cytokines in metabolism has gained interest in the last few years and may be regarded as ex- ercise-mediated regulators of insulin sensitivity. Espe- cially TNF-a, an abundantly expressed cytokine, seems to play a major role in metabolism and in relation to obesity and type II diabetes. TNF-a is linked with obes- ity and insulin resistance as increased levels of TNF-a mRNA are found in both muscle [4] and adipose tissue [5] as well as plasma protein [6] of patients with type II diabetes. Also several animal models of obesity and in- sulin resistance investigated so far demonstrate high TNF-a mRNA levels compared with controls [7–11]. A polymorphism in the TNF-a promoter region at posi- tion À308, which results in increased transcription of the TNF-a gene, is linked with decreased insulin sensitivity and increased percent body fat [12]. Furthermore, mice lacking TNF-a function are protected from obesity-in- duced insulin resistance [13], and TNF-a levels can be reduced by weight loss or treatment with the insulin-sen- sitiser pioglitazone [9], indicating an important role of TNF-a in insulin signalling. TNF-a signals via two transmembrane receptors, TNF-a receptor 1 (p55) and TNF-a receptor 2 (p75), which contain different intracellular domains and subse- quent signalling pathways [14]. Both receptors seem to be involved in glucose homeostasis regulation, as TNF-a can impair insulin-mediated glucose uptake pre- dominantly via the receptor 1 (R1) [15], whereas the TNF-a receptor 2 (R2) is linked with obesity, insulin re- sistance, and type II diabetes [16,17]. Lack of both re- ceptors or knockout of the TNF-a gene has been shown to lead to incomplete, but improved, insulin sen- sitivity, further indicating a major role of TNF-a as an inducer of insulin resistance [18]. TNF-a induces insulin 0006-291X/$ - see front matter Ó 2004 Published by Elsevier Inc. doi:10.1016/j.bbrc.2004.06.129 * Corresponding author. Fax: +45-35-45-76-44. E-mail address: charlotte_keller@yahoo.com (C. Keller). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 321 (2004) 179–182 BBRC