Using Salmonella enterica serotype typhimurium to model intestinal fibrosis

Salmonella Infection in Chronic Inflammation and Gastrointestinal Cancer

Salmonella not only causes acute infections, but can also cause patients to become chronic "asymptomatic" carriers. Salmonella has been verified as a pathogenic factor that contributes to chronic inflammation and carcinogenesis. This review summarizes the acute and chronic Salmonella infection and describes the current research progress of Salmonella infection contributing to inflammatory bowel disease and cancer. Furthermore, this review explores the underlying biological mechanism of the host signaling pathways manipulated by Salmonella effector molecules. Using experimental animal models, researchers have shown that Salmonella infection is related to host biological processes, such as host cell transformation, stem cell maintenance, and changes of the gut microbiota (dysbiosis). Finally, this review discusses the current challenges and future directions in studying Salmonella infection and its association with human diseases.

Parathyroid Hormone-Like Hormone Induces Epithelial-to-Mesenchymal Transition of Intestinal Epithelial Cells by Activating the Runt-Related Transcription Factor 2

Epithelial-to-mesenchymal transition (EMT) is a key contributor to fibroblast activation in fibrosis of multiple organs, including the intestine. Parathyroid hormone-like hormone (PTHLH) is an important factor in renal fibrosis and regulates several processes, including EMT. Herein, we investigated the role of PTHLH-induced EMT in intestinal fibrosis associated with Crohn disease. The expression levels of the EMT-related proteins, PTHLH, and parathyroid hormone receptor 1 (PTH1R) in intestinal tissues were determined by immunohistochemistry, and our results revealed that PTHLH and PTH1R were significantly elevated and associated with EMT marker expression. Moreover, neutralizing PTH1R and antagonizing PTHLH bioactivity prevented transforming growth factor-β1-induced EMT. PTH1R can propagate the protein kinase A (PKA) signal and activate downstream nuclear transcription factors, including runt-related transcription factor 2 (Runx2). In addition, lentiviral vector-PTHLH-treated mice were highly sensitive to 2,4,6-trinitrobenzene sulfonic acid, and analysis of the PTHLH-PTH1R axis revealed the involvement of PKA-Runx2 in PTHLH-induced EMT. Our results indicate that PTHLH triggered EMT in intestinal epithelial cells through the PKA-Runx2 pathway, which might serve as a therapeutic target for intestinal fibrosis in Crohn disease.

Effect of TGF-β1 neutralizing antibody on intestinal fibrosis in a mouse model of chronic colitis induced with trinitrobenzene sulfonic acid

AIM

To evaluate the effect of transforming growth factor-β₁ (TGF-β₁) neutralizing antibody on intestinal fibrosis in a mouse model of chronic colitisinduced with trinitrobenzene sulfonic acid (TNBS).

METHODS

Forty-eight Balb/c mice were randomly divided into a normal control group, a model control group, a treatment control group, and a TGF-β₁ antibody group. Chronic colitis and intestinal fibrosis were induced with TNBS/ethanol enema for 6 wk. Mice in the TGF-β₁ antibody group and treatment control group were administered with TGF-β₁ neutralizing antibody and physiological saline, respectively, at 24 h after the administration of TNBS/ethanol enema. The pathological changes in intestine tissue were detected by HE and VG collage staining. Expression of TGF-β₁ and collagen types Ⅰ, Ⅲ, and Ⅴ mRNAs in the colon was detected.

RESULTS

HE and VG collage staining showed that pathologic histology was improved in the TGF-β₁ antibody group. The expression of collagen types Ⅰ, Ⅲ, and Ⅴ and TGF-β₁ mRNAs decreased significantly in the TGF-β₁ antibody group compared with the model control group and the treatment control group (P < 0.05). The protein expression of TGF-β₁ also decreased significantly in the TGF-β₁ antibody group compared with the model control group and the treatment control group (P < 0.05).

CONCLUSION

TGF-β₁ neutralizing antibody can effectively down-regulate the expression of TGF-β₁ and collagen in mice with chronic colitis, and intestinal fibrosis can be abrogated by targeting TGF-β₁.

NOD-Like Receptors: Guardians of Intestinal Mucosal Barriers

The NOD-like receptors (NLRs) are cytosolic pattern-recognition receptors, which are critically involved in mucosal immune defense. The association of the NLR, NOD2, with inflammatory bowel disease first pointed to the NLRs potential function as guardians of the intestinal barrier. Since then, several studies have emphasized the importance of NLRs in maintaining gut homeostasis and intestinal infections, and in shaping the microbiota. In this review, we will highlight the function of NLRs in intestinal inflammation.

Irsogladine maleate ameliorates inflammation and fibrosis in mice with chronic colitis induced by dextran sulfate sodium

Intestinal fibrosis is a common and severe complication of inflammatory bowel disease (IBD), especially Crohn's disease (CD). To investigate the therapeutic approach to intestinal fibrosis, we have developed a mouse model of intestinal fibrosis by administering dextran sulfate sodium (DSS) and examining the effects of irsogladine maleate (IM) [2,4-diamino-6-(2,5-dichlorophenyl)-s-triazine maleate], which has been widely used as an antiulcer drug for gastric mucosa in Japan, on DDS-induced chronic colitis. In this experimental colitis lesion, several pathognomonic changes were found: increased deposition of collagen, increased number of profibrogenic mesenchymal cells such as fibroblasts (vimentin(+), α-SMA(-)) and myofibroblasts (vimentin(+), α-SMA(+)) in both mucosa and submucosa of the colon with infiltrating inflammatory cells, and increased mRNA expressions of collagen type I, transforming growth factor (TGF)-β, matrix metalloproteinase (MMP)-2, and tissue inhibitor of matrix metalloproteinase (TIMP)-1. When IM was administered intrarectally to this colitis, all these pathological changes were significantly decreased or suppressed, suggesting a potential adjunctive therapy for intestinal fibrosis. IM could consequently reduce fibrosis in DSS colitis by direct or indirect effect on profibrogenic factors or fibroblasts. Therefore, the precise effect of IM on intestinal fibrosis should be investigated further.

Analysis of intestinal fibrosis in chronic colitis in mice induced by dextran sulfate sodium

Fibrogenic mesenchymal cells including fibroblasts and myofibroblasts play a key role in intestinal fibrosis, however, their precise role is largely unknown. To investigate their role in intestinal fibrosis, we analyzed the lesions of chronic colitis in C57BL/6 (B6) mice induced by dextran sulfate sodium (DSS). B6 mice exposed to single cycle administration of DSS for 5 days developed acute colitis that progressed to severe chronic inflammation with dense infiltrates of mononuclear cells, irregular epithelial structure, thickening of colonic wall, and persistent deposits of collagen. Increased mRNA expressions of proinflammatory cytokines are correlated with extensive cellular infiltration, and the mRNA expressions of collagen 1, transforming growth factor (TGF)-β, and matrix metalloproteinases were also enhanced in the colon. In the colon of chronic DSS colitis, fibroblasts (vimentin(+), α-smooth muscle actin (α-SMA)(-)) were increased in both mucosal and submucosal layers, while myofibroblasts (vimentin(+), α-SMA(+)) were increased in mucosal but not in submucosal layers. Primary mouse subcutaneous fibroblast cultures experiments revealed that exogenously added TGF-β 1 substantially augmented the expressions of both vimentin and α-SMA proteins with increased production of collagen. In conclusion, profibrogenic mesenchymal cells play an important role in the development of intestinal fibrosis in this chronic DSS-induced colitis model.