Exhaustive exercise increases the TNF-α production in response to flagellin via the upregulation of toll-like receptor 5 in the large intestine in mice

Although intense exercise may induce temporary immune depression, it is unclear whether exercise stimulates tumor necrosis factor-alpha (TNF-alpha) production in response to flagella protein flagellin (FG), which binds to toll-like receptor 5 (TLR5) and induces the production of pro-inflammatory cytokines. Male C3H/HeN mice were administered FG (1 mg/kg, i.v.) after exhaustive exercise (EX), and the plasma TNF-alpha concentrations were examined. The production of TNF-alpha and the TLR5 expression in both RAW264 and Caco2 cells were measured under FG conditions in vitro. Although the plasma TNF-alpha concentrations were observed to significantly increase in both the EX and non-EX (N-EX) mice (p < 0.01, respectively) following PG injection, the TNF-alpha levels in the EX mice were significantly higher than those observed in the N-EX mice (p < 0.01). Epinephrine (Ep) treatment accelerated the PG-induced TNF-alpha production and TLR5 expression on the Caco2, but not RAW264 cells. Interestingly, a high Ep-induced TLR5 expression was observed on the Caco2 cell surface, which was inhibited by an inhibitor of phosphoinositide-3-kinase (PI3K), Ly294002, as well as a beta-adrenergic blocker, propranolol. In addition, the EX-induced TNF-alpha production observed in response to PG was also attenuated by pretreatment with propranolol. Our findings suggest that exhaustive exercise upregulates the production of TNF-alpha in response to FG via a high expression of TLR5 on the intestinal cell surface following the stimulation of beta-adrenergic receptors with exercise. (C) 2014 Elsevier B.V. All rights reserved.