Fasting-Refeeding Impacts Immune Cell Dynamics and Mucosal Immune Responses.

Nutritional status potentially influences immune responses; however, how nutritional signals regulate cellular dynamics and functionality remains obscure. Herein, we report that temporary fasting drastically reduces the number of lymphocytes by ∼50% in Peyer's patches (PPs), the inductive site of the gut immune response. Subsequent refeeding seemingly restored the number of lymphocytes, but whose cellular composition was conspicuously altered. A large portion of germinal center and IgA+ B cells were lost via apoptosis during fasting. Meanwhile, naive B cells migrated from PPs to the bone marrow during fasting and then back to PPs during refeeding when stromal cells sensed nutritional signals and upregulated CXCL13 expression to recruit naive B cells. Furthermore, temporal fasting before oral immunization with ovalbumin abolished the induction of antigen-specific IgA, failed to induce oral tolerance, and eventually exacerbated food antigen-induced diarrhea. Thus, nutritional signals are critical in maintaining gut immune homeostasis.

AP-1B regulates interactions of epithelial cells and intraepithelial lymphocytes in the intestine.

Intraepithelial lymphocytes (IELs) reside in the epithelial layer and protect against foreign pathogens, maintaining the epithelial barrier function in the intestine. Interactions between IEL and epithelial cells are required for IELs to function effectively; however, the underlying molecular machinery remains to be elucidated. In this study, we found that intestinal epithelium-specific deficiency of the clathrin adaptor protein (AP)-1B, which regulates basolateral protein sorting, led to a massive reduction in IELs. Quantitative proteomics demonstrated that dozens of proteins, including known IEL-interacting proteins (E-cadherin, butyrophilin-like 2, and plexin B2), were decreased in the basolateral membrane of AP-1B-deficient epithelial cells. Among these proteins, CD166 interacted with CD6 on the surface of induced IEL. CD166 knockdown, using shRNA in intestinal organoid cultures, significantly inhibited IEL recruitment to the epithelial layer. These findings highlight the essential role of AP-1B-mediated basolateral sorting in IEL maintenance and survival within the epithelial layer. This study reveals a novel function of AP-1B in the intestinal immune system.

Nicotinamide phosphoribosyl transferase in mammary gland epithelial cells is required for nicotinamide mononucleotide production in mouse milk.

Tissue-specific deficiency of nicotinamide phosphoribosyl transferase (NAMPT), the rate-limiting enzyme of the nicotinamide adenine dinucleotide (NAD+)-salvage pathway, causes a decrease of NAD+ in the tissue, resulting in functional abnormalities. The NAD+-salvage pathway is drastically activated in the mammary gland during lactation, but the significance of this has not been established. To investigate the impact of NAD+ perturbation in the mammary gland, we generated two new lines of mammary gland epithelial-cell-specific Nampt-knockout mice (MGKO). LC-MS/MS analyses confirmed that the levels of NAD+ and its precursor nicotinamide mononucleotide (NMN) were significantly increased in lactating mammary glands. We found that murine milk contained a remarkably high level of NMN. MGKO exhibited a significant decrease in tissue NAD+ and milk NMN levels in the mammary gland during lactation periods. Despite the decline in NAD+ levels, the mammary glands of MGKO appeared to develop normally. Transcriptome analysis revealed that the gene profiles of MGKO were indistinguishable from those of their wild-type counterparts, except for Nampt. Although the NMN levels in milk from MGKO were decreased, the metabolomic profile of milk was otherwise unaltered. The mammary gland also contains adipocytes, but adipocyte-specific deficiency of Nampt did not affect mammary gland NAD+ metabolism or mammary gland development. These results demonstrate that the NAD+ -salvage pathway is activated in mammary epithelial cells during lactation and suggest that this activation is required for production of milk NMN rather than mammary gland development. Our MGKO mice could be a suitable model for exploring the potential roles of NMN in milk.

Butyricimonas is a key gut microbiome component for predicting postoperative recurrence of esophageal cancer.

BACKGROUND: Recently, intestinal bacteria have attracted attention as factors affecting the prognosis of patients with cancer. However, the intestinal microbiome is composed of several hundred types of bacteria, necessitating the development of an analytical method that can allow the use of this information as a highly accurate biomarker. In this study, we investigated whether the preoperative intestinal bacterial profile in patients with esophageal cancer who underwent surgery after preoperative chemotherapy could be used as a biomarker of postoperative recurrence of esophageal cancer. METHODS: We determined the gut microbiome of the patients using 16S rRNA metagenome sequencing, followed by statistical analysis. Simultaneously, we performed a machine learning analysis using a random forest model with hyperparameter tuning and compared the data obtained. RESULTS: Statistical and machine learning analyses revealed two common bacterial genera, Butyricimonas and Actinomyces, which were abundant in cases with recurrent esophageal cancer. Butyricimonas primarily produces butyrate, whereas Actinomyces are oral bacteria whose function in the gut is unknown. CONCLUSION: Our results indicate that Butyricimonas spp. may be a biomarker of postoperative recurrence of esophageal cancer. Although the extent of the involvement of these bacteria in immune regulation remains unknown, future research should investigate their presence in other pathological conditions. Such research could potentially lead to a better understanding of the immunological impact of these bacteria on patients with cancer and their application as biomarkers.

Commensal-bacteria-derived butyrate promotes the T-cell-independent IgA response in the colon.

Secretory immunoglobulin A (SIgA), the most abundant antibody isotype in the body, maintains a mutual relationship with commensal bacteria and acts as a primary barrier at the mucosal surface. Colonization by commensal bacteria induces an IgA response, at least partly through a T-cell-independent process. However, the mechanism underlying the commensal-bacteria-induced T-cell-independent IgA response has yet to be fully clarified. Here, we show that commensal-bacteria-derived butyrate promotes T-cell-independent IgA class switching recombination (CSR) in the mouse colon. Notably, the butyrate concentration in human stools correlated positively with the amount of IgA. Butyrate up-regulated the production of transforming growth factor ß1 and all-trans retinoic acid by CD103+CD11b+ dendritic cells, both of which are critical for T-cell-independent IgA CSR. This effect was mediated by G-protein-coupled receptor 41 (GPR41/FFA3) and GPR109a/HCA2, and the inhibition of histone deacetylase. The butyrate-induced IgA response reinforced the colonic barrier function, preventing systemic bacterial dissemination under inflammatory conditions. These observations demonstrate that commensal-bacteria-derived butyrate contributes to the maintenance of the gut immune homeostasis by facilitating the T-cell-independent IgA response in the colon.

Turicibacter and Acidaminococcus predict immune-related adverse events and efficacy of immune checkpoint inhibitor.

Introduction: Immune checkpoint inhibitors have had a major impact on cancer treatment. Gut microbiota plays a major role in the cancer microenvironment, affecting treatment response. The gut microbiota is highly individual, and varies with factors, such as age and race. Gut microbiota composition in Japanese cancer patients and the efficacy of immunotherapy remain unknown. Methods: We investigated the gut microbiota of 26 patients with solid tumors prior to immune checkpoint inhibitor monotherapy to identify bacteria involved in the efficacy of these drugs and immune-related adverse events (irAEs). Results: The genera Prevotella and Parabacteroides were relatively common in the group showing efficacy towards the anti-PD-1 antibody treatment (effective group). The proportions of Catenibacterium (P = 0.022) and Turicibacter (P = 0.049) were significantly higher in the effective group than in the ineffective group. In addition, the proportion of Desulfovibrion (P = 0.033) was significantly higher in the ineffective group. Next, they were divided into irAE and non-irAE groups. The proportions of Turicibacter (P = 0.001) and Acidaminococcus (P = 0.001) were significantly higher in the group with irAEs than in those without, while the proportions of Blautia (P = 0.013) and the unclassified Clostridiales (P = 0.027) were significantly higher in the group without irAEs than those with. Furthermore, within the Effective group, Acidaminococcus and Turicibacter (both P = 0.001) were more abundant in the subgroup with irAEs than in those without them. In contrast, Blautia (P = 0.021) and Bilophila (P= 0.033) were statistically significantly more common in those without irAEs. Discussion: Our Study suggests that the analysis of the gut microbiota may provide future predictive markers for the efficacy of cancer immunotherapy or the selection of candidates for fecal transplantation for cancer immunotherapy.

Cooperative action of gut-microbiota-accessible carbohydrates improves host metabolic function.

Microbiota-accessible carbohydrates (MACs) exert health-promoting effects, but how each MAC impacts gut microbiota and regulates host physiology remains unclear. Here, we show that l-arabinose and sucrose cooperatively act on gut microbiota and exert anti-obesogenic effects. Specifically, l-arabinose, a monosaccharide that is poorly absorbed in the gut and inhibits intestinal sucrase, suppresses diet-induced obesity in mice in the presence of sucrose. Additionally, the suppressive effect of l-arabinose on adiposity is abrogated in mice lacking the short-chain fatty acid (SCFA) receptors GPR43 and GPR41. Mechanistically, l-arabinose increases the relative abundance of acetate and propionate producers (e.g., Bacteroides), while sucrose enhances SCFA production. Furthermore, l-arabinose and sucrose activate the glycolytic and pentose phosphate pathways of Bacteroides, respectively, indicating that they synergistically promote acetate production through distinct pathways. These findings suggest that each MAC has a unique property and thus may serve as a precision gut-microbiota modulator to promote host homeostasis.

Gut Microbiota Prevents Sugar Alcohol-Induced Diarrhea.

While poorly-absorbed sugar alcohols such as sorbitol are widely used as sweeteners, they may induce diarrhea in some individuals. However, the factors which determine an individual's susceptibility to sugar alcohol-induced diarrhea remain unknown. Here, we show that specific gut bacteria are involved in the suppression of sorbitol-induced diarrhea. Based on 16S rDNA analysis, the abundance of Enterobacteriaceae bacteria increased in response to sorbitol consumption. We found that Escherichia coli of the family Enterobacteriaceae degraded sorbitol and suppressed sorbitol-induced diarrhea. Finally, we showed that the metabolism of sorbitol by the E. coli sugar phosphotransferase system helped suppress sorbitol-induced diarrhea. Therefore, gut microbiota prevented sugar alcohol-induced diarrhea by degrading sorbitol in the gut. The identification of the gut bacteria which respond to and degrade sugar alcohols in the intestine has implications for microbiome science, processed food science, and public health.