Spinal toll-like receptor 4-mediated signalling pathway contributes to visceral hypersensitivity induced by neonatal colonic irritation in rats.

Abstract

Although visceral hypersensitivity is a major pathophysiological feature of irritable bowel syndrome (IBS), its underlying mechanisms remain elusive. Toll-like receptor 4 (TLR4) is a critical pattern recognition molecule of the innate immune system. In this study, we investigated whether the TLR4/myeloid differentiation factor 88 (MyD88)/nuclear factor-kappa B (NF-κB) signalling pathway in the spinal cord contributed to the visceral hypersensitivity induced by neonatal colonic irritation (CI) in rats. The Sprague-Dawley rat model of IBS was induced by colon irritation on post-natal day (PND) 8, PND10 and PND12. Experiments were conducted in adult rats. TLR4 mRNA and protein, and its downstream signalling molecules, MyD88, inhibitory nuclear factor-kappa B (IκB) and NF-κB protein expressions in L2-S4 spinal segments were detected by quantitative real-time reverse transcription-polymerase chain reaction as well as Western blotting. TLR4 co-localization was determined by immunohistochemistry. Levels of tumour necrosis factor-alpha (TNF-α) and interleukin 1β (IL-1β) were measured with enzyme-linked immunosorbent assay. We found that neonatal CI treatment induced long-lasting visceral hypersensitivity without identifiable structural abnormalities in descending colons of adult rats. Neonatal CI treatment evoked a significant up-regulation of the expressions of TLR4 in glia, MyD88, p-IκB-α and NF-κB in adult rats. Neonatal CI treatment also increased the levels of its downstream inflammatory agents TNF-α and IL-1β in the L2-S4 regions of the spinal cord of adult rats. These results suggest that neonatal CI stimulates the production of IL-1β and TNF-α through the TLR4/MyD88/NF-κB signalling pathway in the spinal cord, which contributed to visceral hypersensitivity induced by neonatal CI in rats.