Inhibition of PD-1 Protects against TNBS-Induced Colitis via Alteration of Enteric Microbiota

A guide to germ-free and gnotobiotic mouse technology to study health and disease

The intestinal microbiota has major influence on human physiology and modulates health and disease. Complex host-microbe interactions regulate various homeostatic processes, including metabolism and immune function, while disturbances in microbiota composition (dysbiosis) are associated with a plethora of human diseases and are believed to modulate disease initiation, progression and therapy response. The vast complexity of the human microbiota and its metabolic output represents a great challenge in unraveling the molecular basis of host-microbe interactions in specific physiological contexts. To increase our understanding of these interactions, functional microbiota research using animal models in a reductionistic setting are essential. In the dynamic landscape of gut microbiota research, the use of germ-free and gnotobiotic mouse technology, in which causal disease-driving mechanisms can be dissected, represents a pivotal investigative tool for functional microbiota research in health and disease, in which causal disease-driving mechanisms can be dissected. A better understanding of the health-modulating functions of the microbiota opens perspectives for improved therapies in many diseases. In this review, we discuss practical considerations for the design and execution of germ-free and gnotobiotic experiments, including considerations around germ-free rederivation and housing conditions, route and timing of microbial administration, and dosing protocols. This comprehensive overview aims to provide researchers with valuable insights for improved experimental design in the field of functional microbiota research.

The gut microbiota improves reproductive dysfunction in obese mice by suppressing the NLRP3/ASC/caspase-1 axis

Aim: To explore the complex relationship between gut microbiota, obesity-related male reproductive impairments, and the NLRP3 inflammasome.Methods: A high-fat diet was administered to induce obesity in a mouse model, fecal microbiota transplantation or a high-dietary fiber diet (HDFD) was administered for 5 weeks to evaluate changes in parameters related to reproductive capacity, NLRP3, gut microbiota composition and metabolites in mice.Results: A high-fat diet induces obesity and decreases reproductive capacity in male mice. Fecal microbiota transplantation and HDFD can improve reproductive capacity in obese mice by adjusting the gut microbiota population to suppress the NLRP3/ASC/caspase-1 axis, thereby reducing IL-1β levels.Conclusion: This study offers a potential treatment for obesity-induced reproductive dysfunction by targeting the gut microbiota and the NLRP3 inflammasome pathway.

The Gut Microbiota Metabolite Urolithin B Prevents Colorectal Carcinogenesis by Remodeling Microbiota and PD-L1/HLA-B

Colorectal cancer has risen to the third occurring cancer in the world. Fluorouracil (5-Fu), oxaliplatin, and cisplatin are the most effective chemotherapeutic agents for clinical chemotherapy. Nevertheless, due to chemotherapeutic drug resistance, the survival rate of patients with CRC remains very low. In this study, we used the inflammation-induced or mutation-family-inherited murine CRC models to study the anticancer and immunotherapy effects of urolithin B (UB), the final metabolite of polyphenols in the gastrointestinal tract. The label-free proteomics analysis and the gene ontology (GO) classifications were used to test and analyze the proteins affected by UB. And 16S rDNA sequencing and flow cytometry were utilized to uncover gut microbiome composition and immune defense improved by UB administration. The results indicated that urolithin B prevents colorectal carcinogenesis by remodeling gut microbial and tumor immune microenvironments, such as HLA-B, NK cells, regulatory T cells, and γδ TCR cells, and decreasing the PD-L1. The combination of urolithin B with first-line therapeutic drugs improved the colorectal intestinal hematochezia by shaping gut microbiota, providing a strategy for the treatment of immunotherapy treatment for CRC treatments. UB combined with anti-PD-1 antibody could inhibit the growth of colon cancer. Urolithin B may thus contribute to anticancer treatments and provide a high immune response microenvironment for CRC patients' further immunotherapy.

Dysbiotic change in gastric microbiome and its functional implication in gastric carcinogenesis

Although there is a growing interest in the role of gastric microbiome on the development of gastric cancer, the exact mechanism is largely unknown. We aimed to investigate the changes of gastric microbiome during gastric carcinogenesis, and to predict the functional potentials of the microbiome involved in the cancer development. The gastric microbiome was analyzed using gastric juice samples from 88 prospectively enrolled patients, who were classified into gastritis, gastric adenoma, or early/advanced gastric cancer group. Differences in microbial diversity and composition were analyzed with 16S rRNA gene profiling, using next-generation sequencing method. Metagenomic biomarkers were selected using logistic regression models, based on relative abundances at genus level. We used Tax4Fun to predict possible functional pathways of gastric microbiome involved in the carcinogenesis. The microbial diversity continuously decreased in its sequential process of gastric carcinogenesis, from gastritis to gastric cancer. The microbial composition was significantly different among the four groups of each disease status, as well as between the cancer group and non-cancer group. Gastritis group was differently enriched with genera Akkermansia and Lachnospiraceae NK4A136 Group, whereas the cancer group was enriched with Lactobacillus and Veillonella. Predictive analysis of the functional capacity of the microbiome suggested enrichment or depletion of several functional pathways related to carcinogenesis in the cancer group. There are significant changes in the diversity and composition of gastric microbiome during the gastric carcinogenesis process. Gastric cancer was characterized with microbial dysbiosis, along with functional changes potentially favoring carcinogenesis.

Selection strategy of dextran sulfate sodium-induced acute or chronic colitis mouse models based on gut microbial profile

BACKGROUND

Dextran sulfate sodium (DSS) replicates ulcerative colitis (UC)-like colitis in murine models. However, the microbial characteristics of DSS-triggered colitis require further clarification. To analyze the changes in gut microbiota associated with DSS-induced acute and chronic colitis.

METHODS

Acute colitis was induced in mice by administering 3% DSS for 1 week in the drinking water, and chronic colitis was induced by supplementing drinking water with 2.5% DSS every other week for 5 weeks. Control groups received the same drinking water without DSS supplementation. The histopathological score and length of the colons, and disease activity index (DAI) were evaluated to confirm the presence of experimental colitis. Intestinal microbiota was profiled by 16S rDNA sequencing of cecal content.

RESULTS

Mice with both acute and chronic DSS-triggered colitis had significantly higher DAI and colon histopathological scores in contrast to the control groups (P < 0.0001, P < 0.0001), and the colon was remarkably shortened (P < 0.0001, P < 0.0001). The gut microbiota α-diversity was partly downregulated in both acute and chronic colitis groups in contrast to their respective control groups (Pielou index P = 0.0022, P = 0.0649; Shannon index P = 0.0022, P = 0.0931). The reduction in the Pielou and Shannon indices were more obvious in mice with acute colitis (P = 0.0022, P = 0.0043). The relative abundance of Bacteroides and Turicibacter was increased (all P < 0.05), while that of Lachnospiraceae, Ruminococcaceae, Ruminiclostridium, Rikenella, Alistipes, Alloprevotella, and Butyricicoccus was significantly decreased after acute DSS induction (all P < 0.05). The relative abundance of Bacteroides, Akkermansia, Helicobacter, Parabacteroides, Erysipelatoclostridium, Turicibacter and Romboutsia was also markedly increased (all P < 0.05), and that of Lachnospiraceae_NK4A136_group, Alistipes, Enterorhabdus, Prevotellaceae_UCG-001, Butyricicoccus, Ruminiclostridium_6, Muribaculum, Ruminococcaceae_NK4A214_group, Family_XIII_UCG-001 and Flavonifractor was significantly decreased after chronic DSS induction (all P < 0.05).

CONCLUSION

DSS-induced acute and chronic colitis demonstrated similar symptoms and histopathological changes. The changes in the gut microbiota of the acute colitis model were closer to that observed in UC. The acute colitis model had greater abundance of SCFAs-producing bacteria and lower α-diversity compared to the chronic colitis model.