Gut commensal microbes shape the mucosal immune system by regulating the differentiation and expansion of several types of T cell. Clostridia, a dominant class of commensal microbe, can induce colonic regulatory T (Treg) cells, which have a central role in the suppression of inflammatory and allergic responses. However, the molecular mechanisms by which commensal microbes induce colonic Treg cells have been unclear. Here we show that a large bowel microbial fermentation product, butyrate, induces the differentiation of colonic Treg cells in mice. A comparative NMR-based metabolome analysis suggests that the luminal concentrations of short-chain fatty acids positively correlates with the number of Treg cells in the colon. Among short-chain fatty acids, butyrate induced the differentiation of Treg cells in vitro and in vivo, and ameliorated the development of colitis induced by adoptive transfer of CD4(+) CD45RB(hi) T cells in Rag1(-/-) mice. Treatment of naive T cells under the Treg-cell-polarizing conditions with butyrate enhanced histone H3 acetylation in the promoter and conserved non-coding sequence regions of the Foxp3 locus, suggesting a possible mechanism for how microbial-derived butyrate regulates the differentiation of Treg cells. Our findings provide new insight into the mechanisms by which host-microbe interactions establish immunological homeostasis in the gut.

Heterogeneity of ribosome structure, due to variations in ribosomal protein composition, has been shown to be of physiological significance in plants and yeast. Mammalian genomics have demonstrated numerous genes that are paralogous to genes encoding ribosomal proteins. Although the vast majority are considered to be pseudogenes, mRNA expression of a few paralogues, such as human ribosomal protein L39-like/L39-2, has been reported. In the present study, ribosomes from the liver, mammary gland, and testis of rodents were analyzed using a combination of two-dimensional gel electrophoresis under radical-free and highly reducing conditions, and mass spectrometry. This system allowed identification of 78 ribosomal proteins and Rack1 from a single gel. The degree of heterogeneity was far less than that reported for plant and yeast ribosomes, and was in accord with published biochemical and genetic data for mammalian ribosomes. Nevertheless, an uncharacterized paralogue of ribosomal protein L22, ribosomal protein L22-like 1, was identified as a minor ribosomal component. Ribosomal proteins L10-like and L39-like, paralogues of ribosomal proteins L10 and L39, respectively, were found in ribosomes only from the testis. Reverse transcription-polymerase chain reaction yielded supportive evidence for specific expression of L10-like and L39-like in the testis. Newly synthesized L39-like is likely to be transported to the nucleolus, where ribosome biosynthesis occurs, and then incorporated into translating ribosomes in the cytoplasm. Heterogeneity of mammalian testicular ribosomes is structurally non-negligible, and may offer valuable insights into the function of the customized ribosome.

BackgroundThe dysbiosis of gut microbiota has been implicated in the pathogenesis of inflammatory bowel diseases; however, the underlying mechanisms have not yet been elucidated. Heavily glycosylated mucin establishes a first-line barrier against pathogens and serves as a niche for microbial growth.MethodsTo elucidate relationships among dysbiosis, abnormal mucin utilisation, and microbial metabolic dysfunction, we analysed short-chain fatty acids (SCFAs) and mucin components in stool samples of 40 healthy subjects, 49 ulcerative colitis (UC) patients, and 44 Crohn's disease (CD) patients from Japan.FindingsLevels of n-butyrate were significantly lower in stools of both CD and UC patients than in stools of healthy subjects. Correlation analysis identified seven bacterial species positively correlated with n-butyrate levels; the major n-butyrate producer, Faecalibacterium prausnitzii, was particularly underrepresented in CD patients, but not in UC patients. In UC patients, there were inverse correlations between mucin O-glycan levels and the production of SCFAs, such as n-butyrate, suggesting that mucin O-glycans serve as an endogenous fermentation substrate for n-butyrate production. Indeed, mucin-fed rodents exhibited enhanced n-butyrate production, leading to the expansion of RORgt+Treg cells and IgA-producing cells in colonic lamina propria. Microbial utilisation of mucin-associated O-glycans was significantly reduced in n-butyrate-deficient UC patients.InterpretationMucin O-glycans facilitate symbiosynthesis of n-butyrate by gut microbiota. Abnormal mucin utilisation may lead to reduced n-butyrate production in UC patients.FundJapan Society for the Promotion of Science, Health Labour Sciences Research Grant, AMED-Crest, AMED, Yakult Foundation, Keio Gijuku Academic Development Funds, The Aashi Grass Foundation, and The Canon Foundation.

Generally, soluble fibers increase small intestinal mucin secretion by increasing the number of goblet cells in a viscosity-dependent manner. The present study aimed to examine the mechanism by which low-methoxyl pectin (LPC) affects mucin secretion in the small intestine. First, diets containing 50 g/kg of low-viscosity fiber (LPC, gum arabic, guar gum, low-molecular konjac mannan, arabinogalactan, sodium alginate) or high-molecular konjac mannan (KMH) were fed to Wistar rats for 10 d. Luminal mucin was greater in the LPC and KMH groups than in the fiber-free control group, but only the KMH group had more goblet cells in the ileum compared with the other groups. Next, Sprague-Dawley rats were fed LPC, KMH, or high-methoxyl pectin (HPC) diets (50 g/kg) for 10 d. The KMH and LPC groups, but not the HPC group, had greater luminal mucin than the control group, whereas jejunum Muc2 expression was higher only in the LPC group. Sprague-Dawley rats fed the LPC diet for 1 or 3 d had greater luminal mucin and jejunum Muc2 expression than those fed the control diet. In vitro studies using HT-29MTX cells showed that, of the various fibers studied, only LPC and HPC affected mucin secretion. Finally, Wistar rats were fed the LPC diet with or without neomycin in drinking water for 10 d; neomycin treatment did not compromise the effect of LPC on mucin secretion. We conclude that LPC does not affect the number of goblet cells but can interact directly with the epithelium and stimulate small intestinal mucin secretion.

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