The regeneration of intestinal epithelial are maintained by continuous differentiation and proliferation of intestinal stem cells (ISCs) under physiological and pathological conditions. However, little is known about the regulatory effect of intestinal microbiota on its recovery ability to repair damaged mucosal barrier. In this study, we established intestinal organoids and lamina propria lymphocytes (LPLs) co-cultured system, plus mice experiments, to explore the protective effect of Lactobacillus reuteri D8 on integrity of intestinal mucosa. We found that only live L. reuteri D8 was effective in protecting the morphology of intestinal organoids and normal proliferation of epithelial stained with EdU under TNF-α treatment, which was also further verified in mice experiments. L. reuteri D8 colonized in the intestinal mucosa and ameliorated intestinal mucosa damage caused by DSS treatment, including improvement of body weight, colon length, pathological change, and proliferation level. The repair process stimulated by L. reuteri D8 was also accompanied with increased numbers of Lgr5 and lysozyme cells both in intestinal organoids and mice intestine. Furthermore, we demonstrated that D8 metabolite indole-3-aldehyde stimulated LPLs to secret IL-22 through aryl hydrocarbon receptor (AhR) and then induced phosphorylation of STAT3 to accelerate proliferation of intestinal epithelial, thus recovering damaged intestinal mucosa. Our findings indicate L. reuteri protects intestinal barrier and activates intestinal epithelial proliferation, which sheds light on treatment approaches for intestinal inflammation based on ISCs with probiotics Lactobacillus and daily probiotic consumption in heath foods.

Inflammatory bowel disease (IBD) is a chronic inflammatory disease of intestinal mucosa and submucosa, characterized by the disruption of the intestinal epithelial barrier, increased production of inflammatory mediators, and excessive tissue injury. Intestinal epithelial cells, as well as microvascular endothelial cells, play important roles in IBD. To study the potential effects of kaempferol in IBD progress, we established a novel epithelial−endothelial cells coculture model to investigate the intestinal inflammation and barrier function. Data demonstrated an obvious increased transepithelial electrical resistance (TEER) (1222 ± 60.40 Ω cm 2 vs 1371 ± 38.77 Ω cm 2 ), decreased flux of FITC (180.8 ± 20.06 μg/mL vs 136.7 ± 14.78 μg/mL), and up-regulated occludin and claudin-2 expression in Caco-2 that was specifically cocultured with endothelial cells. Meanwhile, 80 μM kaempferol alleviated the drop of TEER, the increase of FITC flux, and the overexpression of interleukin-8 (IL-8) induced by 1 μg/mL lipopolysaccharide (LPS). Additionally, kaempferol also ameliorated the LPS-induced decrease of protein expression of zonula occludens-1 (ZO-1), occludin, and claudin-2, together with the inhibited protein expressions of the phosphorylation level of NF-κB and I-κB induced by LPS. Our results suggest that kaempferol alleviates the IL-8 secretion and barrier dysfunction of the Caco-2 monolayer in the LPS-induced epithelial−endothelial coculture model via inhibiting the NF-κB signaling pathway activation.

The intestine is home to trillions of microorganisms, and the vast diversity within this gut microbiota exists in a balanced state to protect the intestinal mucosal barrier. Research into the association of the intestinal microbiota with health and disease (including diet, nutrition, obesity, inflammatory bowel disease, and cancer) continues to expand, with the field advancing at a rapid rate. Intestinal stem cells (ISCs) are the fundamental component of the mucosal barrier; they undergo continuous proliferation to replace the epithelium, which is also intimately involved in intestinal diseases. The intestinal microbiota, such as Lactobacillus, communicates with ISCs both directly and indirectly to regulate the proliferation and differentiation of ISCs. Moreover, Salmonella infection significantly decreased the expression of intestinal stem cell markers Lgr5 and Bmi1. However, the detailed interaction of intestinal microbiota and ISCs are still unclear. This review considers the progress of research on the model and niches of ISCs, as well as the complex interplay between the gut microbiota and ISCs, which will be crucial for explaining the mechanisms of intestinal diseases related to imbalances in the intestinal microbiota and ISCs.

The gastrointestinal tract is exposed to pro-oxidants from food, host immune factors, and microbial pathogens, which may induce oxidative damage. Oxidative stress has been shown to play an important role in the onset of inflammatory bowel disease. This study aimed to use a novel model to evaluate the effects of a screened natural component and explore its possible mechanism. An in vitro oxidative stress Caco2 cell model induced by H 2 O 2 was established using a realtime cellular analysis system and verified by addition of glutathione (GSH). A variety of plant components were chosen for the screening. Quercetin was the most effective phytochemical to alleviate the decreased cell index caused by H 2 O 2 among the tested plant components. Furthermore, quercetin ameliorated dextran sulfate sodium salt (DSS)-induced colitis and further increased the serum GSH. The mechanism of quercetin protection was explored in Caco2. Reversed H 2 O 2 -induced cell damage and decreased reactive oxygen species and apoptosis ratio were observed in quercetintreated cells. Also, quercetin increased expression of the glutamate-cysteine ligase catalytic subunit (GCLC), the first rate-limiting enzyme of glutathione synthesis, and increased intracellular GSH concentration under H 2 O 2 treatment. This effect was abolished by the GCLC inhibitor buthionine sulfoximine. These results indicated that quercetin can improve cell proliferation and increase intracellular GSH concentrations by upregulating transcription of GCLC to eliminate excessive reactive oxygen species (ROS). Increased extracellular H 2 O 2 concentration induced by quercetin under oxidative stress was related to the inhibition of AQP3 and upregulation of NOX1/2, which may contribute to the observed protective effects of quercetin. Moreover, the novel H 2 O 2 -induced oxidative stress cell model based on the real-time cellular analysis system was an effective model to screen natural products to deal with intestinal oxidative damage and help accelerate the discovery of new drugs for inflammatory bowel disease (IBD).

The mammalian intestine is the largest immune organ that contains the intestinal stem cells (ISC), differentiated epithelial cells (enterocytes, Paneth cells, goblet cells, tuft cells, etc.), and gut resident-immune cells (T cells, B cells, dendritic cells, innate lymphoid cell, etc.). Inflammatory bowel disease (IBD), a chronic inflammatory disease characterized by mucosa damage and inflammation, threatens the integrity of the intestine. The continuous renewal and repair of intestinal mucosal epithelium after injury depend on ISCs. Inflamed mucosa healing could be a new target for the improvement of clinical symptoms, disease recurrence, and resection-free survival in IBD treated patients. The knowledge about the connections between ISC and immune cells is expanding with the development of in vitro intestinal organoid culture and single-cell RNA sequencing technology. Recent findings implicate that immune cells such as T cells, ILCs, dendritic cells, and macrophages and cytokines secreted by these cells are critical in the regeneration of ISCs and intestinal epithelium. Transplantation of ISC to the inflamed mucosa may be a new therapeutic approach to reconstruct the epithelial barrier in IBD. Considering the links between ISC and immune cells, we predict that the integration of biological agents and ISC transplantation will revolutionize the future therapy of IBD patients.