Abstract
Background
Changes in serotonin (5-HT) levels, anomalies in serotonergic and cholinergic machinery and altered Toll-like receptor 4 (TLR4) expression have been shown in IBD in patients and related animal models. Thus, we aimed to assess the crosstalk of enteric serotonergic system and TLR4 signalling in a mouse model of dinitrobenzene sulfonic acid (DNBS)-induced colitis.
Methods
Male C57/Bl6 (WT) and TLR4−/− mice (9 ± 2 weeks old; N = 10 mice) were presensitised with 1% dinitrobenzene sulfonic acid (DNBS), and after 1 week was intrarectally instilled with 2.5% DNBS. Small intestine inflammation was measured by disease activity index and histological analysis. Changes in ileal muscle tension were isometrically recorded following: (1) cumulative addition of carbachol (CCh; 0.1–100 µM); (2) electric field stimulation (EFS, 0–40 Hz); (3) 60 mM KCl; (4) 30 μM 5-HT addition with or without 0.1 μM ondansetron (5-HT3R antagonist). Immunofluorescence distribution of the neuronal HuC/D and nNOS and glial GFAP markers were determined in longitudinal-muscle-myenteric plexus whole mounts (LMMPs) by confocal microscopy.
Results
In WT mice, DNBS treatment altered receptor and not-receptor mediated responses (+120% of Emax to CCh and +103% of contraction to KCl, respectively; p < 0.001, N = 5 mice/group) together with an altered cholinergic neurotransmission (−50% at 10 Hz; p < 0.01, N = 5 mice/group) and 2-fold increase to 30 μM 5-HT-mediated response (p < 0.001, N = 5 mice/group). After DNBS treatment TLR4−/− mice showed a significant increase in excitatory-mediated response (+98% of Emax to CCh; +80% of contraction to KCl; +120% at 10 Hz; p < 0.001, N = 5 mice/group) together with a significant reduction of 30 μM 5-HT-mediated response (−50%, p < 0.001, N = 5 mice/group). These changes were associated to a significant decrease of the total number of HuC/D+ neurons (−44% and −19% for WT DNBS and TLR4 DNBS mice, respectively) together with a 1.3-fold increase in S100b immunofluorescence in WT mice after DNBS treatment.
Conclusion
These findings not only suggest an important role of TLR4 in small intestine neuromuscular dysfunction during colitis but also provide novel information on the potential benefits of targeting TLR4 in various gut disorders that exhibit aberrant cholinergic and 5-HT signalling.
CD4+CD25+Foxp3+ regulatory T cells regulate immune balance in unexplained recurrent spontaneous abortion via the Toll-like receptor 4/nuclear factor-κB pathway
