Somatostatin receptor 5 is critical for protecting intestinal barrier function in vivo and in vitro

Somatostatin alleviates diversion colitis after fecal-stream bypass colostomy surgeries in rats

BACKGROUND

Diversion colitis (DC) is a prevalent complication of colostomy characterized by intestinal inflammation. This study aimed to investigate the therapeutic potential of somatostatin (SST) in managing DC.

METHODS

After establishing a rat DC model, SST was administered via Mini Osmotic Pumps 2001W at a pumping rate of 1.0 μL/h. Various techniques, including hematoxylin and eosin staining, periodic acid-Schiff staining, immunofluorescence staining, and electron microscopy were employed to assess the effects of SST. Intestinal barrier functions were evaluated using Evans blue, enzyme-linked immunosorbent assay, and MacConkey agar.

RESULTS

After SST treatment, the significant weight loss and associated high mortality in the DC group were successfully mitigated. Upregulation of claudin-3 and claudin-4 restored mechanical barriers in colon epithelial tissue, whereas protection of goblet cells and stimulation of mucus secretion enhanced mucus barriers. SST effectively reduced leaky gut and alleviated systemic inflammation.

CONCLUSION

This study provides initial evidence supporting the efficacy of SST in the treatment of DC. It offers insights into the role of SST in DC by elucidating its ability to restore damaged intestinal barriers.

Compromised NHE8 Expression Is Responsible for Vitamin D-Deficiency Induced Intestinal Barrier Dysfunction

Objectives: Vitamin D (VitD) and Vitamin D receptor (VDR) are suggested to play protective roles in the intestinal barrier in ulcerative colitis (UC). However, the underlying mechanisms remain elusive. Evidence demonstrates that Na+/H+ exchanger isoform 8 (NHE8, SLC9A8) is essential in maintaining intestinal homeostasis, regarded as a promising target for UC therapy. Thus, this study aims to investigate the effects of VitD/VDR on NHE8 in intestinal protection. Methods: VitD-deficient mice, VDR-/- mice and NHE8-/- mice were employed in this study. Colitis mice were established by supplementing DSS-containing water. Caco-2 cells and 3D-enteroids were used for in vitro studies. VDR siRNA (siVDR), VDR over-expression plasmid (pVDR), TNF-α and NF-κb p65 inhibitor QNZ were used for mechanical studies. The expression of interested proteins was detected by multiple techniques. Results: In colitis mice, paricalcitol upregulated NHE8 expression was accompanied by restoring colonic mucosal injury. In VitD-deficient and VDR-/- colitis mice, NHE8 expression was compromised with more serious mucosal damage. Noteworthily, paricalcitol could not prevent intestinal barrier dysfunction and histological destruction in NHE8-/- mice. In Caco-2 cells and enteroids, siVDR downregulated NHE8 expression, further promoted TNF-α-induced NHE8 downregulation and stimulated TNF-α-induced NF-κb p65 phosphorylation. Conversely, QNZ blocked TNF-α-induced NHE8 downregulation in the absence or presence of siVDR. Conclusions: Our study indicates depressed NHE8 expression is responsible for VitD-deficient-induced colitis aggravation. These findings provide novel insights into the molecular mechanisms of VitD/VDR in intestine protection in UC.

Artemisinin analog SM934 alleviates epithelial barrier dysfunction via inhibiting apoptosis and caspase-1-mediated pyroptosis in experimental colitis

Intestinal barrier disruption due to the intestinal epithelial cells’ (IECs) death is one of the critical pathological features of inflammatory bowel diseases (IBDs). SM934, an artemisinin analog, has previously been proven to ameliorate colitis induced by dextran sulfate sodium (DSS) in mice by suppressing inflammation response. In this study, we investigated the protective effects of SM934 on the epithelial barrier and the underlying mechanism in trinitrobenzene sulfonic acid (TNBS)-induced colitis mice. We demonstrated that SM934 restored the body weight and colon length, and improved the intestine pathology. Furthermore, SM934 treatment preserved the intestinal barrier function via decreasing the intestinal permeability, maintaining epithelial tight junction (TJ) protein expressions, and preventing apoptosis of epithelial cells, which were observed both in the colon tissue and the tumor necrosis factor-α (TNF-α)-induced human colonic epithelial cell line HT-29. Specifically, SM934 reduced the pyroptosis of IECs exposed to pathogenic signaling and inhibited pyroptosis-related factors such as NOD-like receptor family pyrin domain containing 3 (NLRP3), adapter apoptosis-associated speck-like protein (ASC), cysteine protease-1 (caspase-1), gasdermin (GSDMD), interleukin-18 (IL-18), and high-mobility group box 1 (HMGB1) both in colon tissue and lipopolysaccharide (LPS) and adenosine triphosphate (ATP) co-stimulated HT-29 cells in vitro. Moreover, SM934 interdicted pyroptosis via blocking the transduction of mitogen-activated protein kinase (MAPK) and nuclear factor-kB (NF-kB) signaling pathways. In conclusion, SM934 protected TNBS-induced colitis against intestinal barrier disruption by inhibiting the apoptosis and pyroptosis of epithelial cells via the NLRP3/NF-κB/MAPK signal axis, and intestinal barrier protection in company with an anti-inflammatory strategy might yield greater benefits in IBD treatment.

Discoidin domain receptor 1(DDR1) promote intestinal barrier disruption in Ulcerative Colitis through tight junction proteins degradation and epithelium apoptosis

BACKGROUND AND AIMS

Discoidin domain receptor 1 (DDR1) encodes a receptor tyrosine kinase involved in multiple physiological and pathological processes. DDR1 is expressed in the intestinal epithelium, but its role in Ulcerative Colitis (UC) is poorly understand. This study aimed to identify the function of DDR1 in maintaining the homeostasis of UC.

METHODS

The DDR1 expression level in non-inflamed and inflamed colon samples from IBD patients were assessed. DDR1 knock-out (DDR1^-/-) and wild-type (WT) mice were administered dextran sulfate sodium (DSS) to induce colitis and assessed based on colitis symptoms. In addition, intestinal epithelial barrier injury was induced by TNF-α and IFN-γ incubation to cell monolayers transfected with PCDH-DDR1 or pLKO.1-sh-DDR1-1 plasmids. The effect of DDR1 in regulating barrier integrity, tight junctions (TJ) protein status, and cell apoptosis was investigated in vivo and in vitro. Furthermore, the activation of the NF-κB p65-MLCK-p-MLC2 pathway was also investigated.

RESULTS

Decreased DDR1 expression levels were observed at the inflamed sites compared with the non-inflamed. DDR1^-/- mice had alleviated intestinal mucosal barrier injuries, upregulated TJ proteins, decreased epithelium apoptosis from DSS-induced colitis, and reduced proinflammatory cytokines production in the colon. These findings were further confirmed in vitro. DDR1 over-expression aggravated the TNF-α/IFN-γ-induced TJ disruption, while DDR1 shRNA prevented TJ damage even in the presence of JSH-23. DDR1 dependently destroyed the intestinal barrier via the NF-κB p65-MLCK-p-MLC2 pathway.

CONCLUSION

Our findings revealed that DDR1 regulated the intestinal barrier in colitis by modulating TJ proteins expression and epithelium apoptosis, making it a potential target of UC.

Roles of gastrointestinal polypeptides in intestinal barrier regulation

The intestinal barrier is a dynamic entity that is organized as a multilayer system and includes various intracellular and extracellular elements. The gut barrier functions in a coordinated manner to impede the passage of antigens, toxins, and microbiome components and simultaneously preserves the balanced development of the epithelial barrier and the immune system and the acquisition of tolerance to dietary antigens and intestinal pathogens.Numerous scientific studies have shown a significant association between gut barrier damage and gastrointestinal and extraintestinal diseases such as inflammatory bowel disease, celiac disease and hepatic fibrosis. Various internal and external factors regulate the intestinal barrier. Gastrointestinal peptides originate from enteroendocrine cells in the luminal digestive tract and are critical gut barrier regulators. Recent studies have demonstrated that gastrointestinal peptides have a therapeutic effect on digestive tract diseases, enhancing epithelial barrier activity and restoring the gut barrier. This review demonstrates the roles and mechanisms of gastrointestinal polypeptides, especially somatostatin (SST) and vasoactive intestinal peptide (VIP), in intestinal barrier regulation.