Introduction Accumulating evidence suggests that adverse early-life events interfere with the perinatal programming and maturation of the immune system, predisposing the host to complex diseases including inflammatory bowel diseases (IBD). We hypothesise that neonatal inflammation (NI) induces susceptibility to aggravated and prolonged immune response in the colon when subjected to a 2nd inflammatory insult in adult-life.
Method We used a two-hit model: NI was induced in 10 day old rat pups by intrarectal administration of trinitrobenzene sulfonic acid (TNBS, 130 mg/kg), and the 2nd dose of TNBS (80 mg/kg) was applied to induce adult inflammation (AI) 8 weeks later. All 4 groups (Veh+Veh, NI+Veh, Veh+AI, and NI+AI) of rats were euthanized 7 days later.
Results In NI+AI rats, we observed an aggravated immune response, evidenced by a greater loss of body weight, a drastic increase of myeloperoxidase activity, and a greater overexpression of IL-1β in colonic mucosa and submucosa (MSM) when compared with the other 3 groups. We found that norepinephrine and epinephrine levels in plasma were significantly elevated only in NI+AI rats, suggesting an involvement of adrenoceptors in IL-1β activation. In vivo treatment with propranolol (2 mg/kg, daily IP), a β blocker, markedly ameliorated TNBS-induced swelling and tissue damage and the overexpression of IL-1β. To elucidate the molecular mechanisms underlying IL-1β activation, we assessed NF-kB status and its interaction with the IL-1β promoter in the colonic MSM. Our data revealed an aggravated decrease of IκBα and a greater increase of p65 in NI+AI rats. In addition, acetylation of histone H4 lysine 12 (H4K12Ac) increased significantly at both the NF-κB binding region and the core promoter of IL-1β gene in NI+AI (vs Veh+AI) rats, causing greater chromatin relaxation. H4K12Ac at the IL-1β promoter was slightly elevated in NI+Veh (vs Veh+Veh) rats. Accordingly, p65 binding to the IL-1β promoter was markedly enhanced in NI+AI vs Veh+AI rats (14.3±3.1 vs 2.7±0.6). Aa a result, RNA polymerase II association with the IL-1β promoter was augmented in NI+AI vs Veh+AI (5.9±0.9 vs 2.5±0.5, p<0.05) rats, leading to an aberrant IL-1β overexpression. In vivo treatment of NI+AI rats with sodium butyrate (20 mM, 1 ml, daily IP after AI) markedly repressed the exacerbated increase of p65 binding at the IL-1β promoter and significantly ameliorated the IL-1β overexpression, suggesting a therapeutic potential of sodium butyrate for IBD patients.
Conclusion Severe NI renders the host susceptible to aggravated immune response by epigenetically sensitising the colonic epithelium, in which IL-1β activation is exacerbated through stress hormone/NF-κB/IL-1β signalling axis, when subjected to a 2nd insult in adult-life.
Disclosure of Interest None Declared
- histone acetylation
- neonatal inflammation
- sodium butyrate
- trinitrobenzene sulfonic acid