The IBD interactome: an integrated view of aetiology, pathogenesis and therapy

Intestinal Epithelial Cell Autophagy Is Required to Protect against TNF-Induced Apoptosis during Chronic Colitis in Mice

Genome-wide association studies have linked polymorphisms in the autophagy gene ATG16L1 with susceptibility to inflammatory bowel disease (IBD). However, the cell-type-specific effects of autophagy on the regulation of chronic intestinal inflammation have not been investigated. Here, we assessed the effect of myeloid-specific or intestinal epithelial cell (IEC)-specific deletion of Atg16l1 on chronic colitis triggered by the intestinal opportunistic pathogen Helicobacter hepaticus in mice. Although Atg16l1 deficiency in myeloid cells had little effect on disease, mice selectively lacking Atg16l1 in IECs (Atg16l1^VC) developed severely exacerbated pathology, accompanied by elevated pro-inflammatory cytokine secretion and increased IEC apoptosis. Using ex vivo IEC organoids, we demonstrate that autophagy intrinsically controls TNF-induced apoptosis and in vivo blockade of TNF attenuated the exacerbated pathology in Atg16l1^VC mice. These findings suggest that the IBD susceptibility gene ATG16L1 and the process of autophagy within the epithelium control inflammation-induced apoptosis and barrier integrity to limit chronic intestinal inflammation.

Pro-inflammatory adjuvant properties of pigment-grade titanium dioxide particles are augmented by a genotype that potentiates interleukin 1β processing

Background

Pigment-grade titanium dioxide (TiO₂) particles are an additive to some foods (E171 on ingredients lists), toothpastes, and pharma−/nutraceuticals and are absorbed, to some extent, in the human intestinal tract. TiO₂ can act as a modest adjuvant in the secretion of the pro-inflammatory cytokine interleukin 1β (IL-1β) when triggered by common intestinal bacterial fragments, such as lipopolysaccharide (LPS) and/or peptidoglycan.

Given the variance in human genotypes, which includes variance in genes related to IL-1β secretion, we investigated whether TiO₂ particles might, in fact, be more potent pro-inflammatory adjuvants in cells that are genetically susceptible to IL-1β-related inflammation.

Methods

We studied bone marrow-derived macrophages from mice with a mutation in the nucleotide-binding oligomerisation domain-containing 2 gene (Nod2^m/m), which exhibit heightened secretion of IL-1β in response to the peptidoglycan fragment muramyl dipeptide (MDP). To ensure relevance to human exposure, TiO₂ was food-grade anatase (119 ± 45 nm mean diameter ± standard deviation). We used a short ‘pulse and chase’ format: pulsing with LPS and chasing with TiO₂ +/− MDP or peptidoglycan.

Results

IL-1β secretion was not stimulated in LPS-pulsed bone marrow-derived macrophages, or by chasing with MDP, and only very modestly so by chasing with peptidoglycan. In all cases, however, IL-1β secretion was augmented by chasing with TiO₂ in a dose-dependent fashion (5–100 μg/mL). When co-administered with MDP or peptidoglycan, IL-1β secretion was further enhanced for the Nod2^m/m genotype. Tumour necrosis factor α was triggered by LPS priming, and more so for the Nod2^m/m genotype. This was enhanced by chasing with TiO₂, MDP, or peptidoglycan, but there was no additive effect between the bacterial fragments and TiO₂.

Conclusion

Here, the doses of TiO₂ that augmented bacterial fragment-induced IL-1β secretion were relatively high. In vivo, however, selected intestinal cells appear to be loaded with TiO₂, so such high concentrations may be ‘exposure-relevant’ for localised regions of the intestine where both TiO₂ and bacterial fragment uptake occurs. Moreover, this effect is enhanced in cells from Nod2^m/m mice indicating that genotype can dictate inflammatory signalling in response to (nano)particle exposure. In vivo studies are now merited.

Electronic supplementary material

The online version of this article (10.1186/s12989-017-0232-2) contains supplementary material, which is available to authorized users.

Protective Effect of Pogostone on 2,4,6-Trinitrobenzenesulfonic Acid-Induced Experimental Colitis via Inhibition of T Helper Cell

Inflammatory bowel disease (IBD) is a chronic immune-related disease mainly caused by the disequilibrium of T helper (Th) cell paradigm? Pogostone (PO) is one of the major chemical constituents of Pogostemon cablin (Blanco) Benth. The present study aims to investigate the potential benefit of PO against IBD in a 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced experimental colitis model. PO treatment by enema significantly brought down the disease activity index (DAI) of the TNBS-challenged rats, which was manifested by the ameliorated inflammatory features including ulceration, adhesion, and edema. Hematoxylin-eosin (HE) staining and immunohistochemistry analysis showed that PO effectively relived colon damage by restoring epithelium, and more importantly, by inhibiting the infiltration of pro-inflammatory Th1 and Th17 cells in the colon. Additionally, PO inhibited the activity of myeloperoxidase and secretion of inflammatory cytokines including IFN-γ, IL-12p70, IL-17A, and IL-10. Together with our previous findings, the present data indicated that the anti-IBD effect of PO probably related to its direct inhibition on Th cell proliferation and suppression of the cytokines secretion. These results highlighted the potential of PO as a promising candidate to relieve IBD.