Research leading to new insights into the pathogenesis of inflammatory bowel disease (IBD) highlighted the roles of: PTPN2 SNP in the pathogenesis of fibrosis in Crohn’s disease (CD); Proteus, Gram-negative facultative anaerobic bacilli in mediating inflammation in CD; and BUB1 (budding uninhibited by benzimidazoles-1) in the development of CD.
In patients with fibrostenotic CD, loss of PTPN2 function associated with rs7234029 in ileal subepithelial myofibroblasts (SEMF) leads to increased phosphorylation of pSTAT3 (Y705), and also results in the excess collagen I production and proliferation that occur in these patients’ strictures . These consequences of rs7234029 expression in fibrostenotic CD were found by studying primary SEMF cultures isolated from ileum of patients with Montreal B2 CD that were either naïve, transfected with wtPTPN2, or were used for CRISPR/Cas9-mediated PTPN2 gene deletion. Increased basal Y705, pErk1/2, collagen I production and proliferation in SEMF of strictured ileum were normalised by inhibition of STAT3 phosphorylation or expression of dominant negative STAT3 (Y705F). Despite a 3-fold increase in PTPN2 protein in strictured SEMF in these cells, levels of STAT3 phosphorylation were also increased, suggesting a loss of phosphatase function. This function was restored by wtPTPN2 expression, resulting in lowered levels of Y705.
The role of Proteus, Gram-negative facultative anaerobic bacilli, as a gut pathogen in mediating inflammation in CD was investigated. A urease producing organism in the gut called P. mirabilis was found to be associated with CD and can induce inflammation in cell lines and animal models of colitis . Dr Jiangwen Zhang (University of Hong Kong, Hong Kong) et al. suggest that P. mirabilis and related species may act as a pathobiont, and, thus, play a critical role in the pathogenesis of CD.
The prevalence of Proteus in faecal samples was higher in CD patients than in healthy controls (P<0.05). Proteus levels were significantly increased in CD biopsies compared with control tissue. The 24 Proteus-monoclones isolated from faeces and biopsy of CD patients all belonged to members of P. mirabilis lineages. Proteus gavaged mice had a shortened colon compared with mice treated with E. coli 1655 (P<0.05). Mice depleted of bacteria and exposed to Proteus and DSS showed significantly higher severity of inflammation. Of cells co-cultured with Proteus, 70-80% were unhealthy or dead. Increased necrotic cells were found in 4 cell lines co-cultured with Proteus due to bacterial invasion. Moreover, Proteus stimulated the production of pro-inflammatory cytokines including IL-18 (P<0.001) and IL-1α (P<0.01) and induced key pro-inflammatory pathways.
BUB1 (budding uninhibited by benzimidazoles-1) is a serine/threonine-protein kinase that was recently found to mediate TGFβ-dependent signalling. BUB1 was discovered to induce fibrosis in the gut. Thus, it might be a potential target for intestinal fibrosis associated with CD . Dr V. Garlatti (Humanitas University, Italy) explained that BUB1 expression levels were increased within the muscularis mucosa and muscularis propria of inflamed tissues, particularly when fibrosis was evident.
In vivo, intramural injection of AdBUB1 caused significant elevation of tissue BUB1 levels, transmural inflammatory cell infiltration, and transmural fibrosis in mice colorectum. Moreover, BUB1 inhibition remarkably reduced collagen deposition in colitic mice and significantly improved 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced chronic colitis. In vitro, BUB1 inhibition reduced collagen deposition and growth rate of CD-isolated myofibroblasts.
Keywords: Crohn’s disease
- Li C, et al. ECCO 2019, OP02.
- Zhang P, et al. ECCO 2019, P834.
- Garlatti V, et al. ECCO 2019, OP33.
Top image: © Pornpak Khunatorn
The content and interpretation of these conference highlights are the views and comments of the speakers/authors.