ABSTRACTMuch remains unknown about how the intestinal microbiome interfaces with the protective intestinal mucus layer.Bifidobacteriumspecies colonize the intestinal mucus layer and can modulate mucus production by goblet cells. However, selectBifidobacteriumstrains can also degrade protective glycans on mucin proteins. We hypothesized that the human-derived speciesBifidobacterium dentiumwould increase intestinal mucus synthesis and expulsion, without extensive degradation of mucin glycans.In silicodata revealed thatB. dentiumlacked the enzymes necessary to extensively degrade mucin glycans. This finding was confirmed by demonstrating thatB. dentiumcould not use naive mucin glycans as primary carbon sourcesin vitro. To examineB. dentiummucus modulationin vivo, Swiss Webster germfree mice were monoassociated with live or heat-killedB. dentium. LiveB. dentium-monoassociated mice exhibited increased colonic expression of goblet cell markersKrüppel-like factor 4(Klf4),Trefoil factor 3(Tff3),Relm-β,Muc2, and several glycosyltransferases compared to both heat-killedB. dentiumand germfree counterparts. Likewise, liveB. dentium-monoassociated colon had increased acidic mucin-filled goblet cells, as denoted by Periodic Acid-Schiff-Alcian Blue (PAS-AB) staining and MUC2 immunostaining.In vitro,B. dentium-secreted products, including acetate, were able to increase MUC2 levels in T84 cells. We also identified thatB. dentium-secreted products, such as γ-aminobutyric acid (GABA), stimulated autophagy-mediated calcium signaling and MUC2 release. This work illustrates thatB. dentiumis capable of enhancing the intestinal mucus layer and goblet cell function via upregulation of gene expression and autophagy signaling pathways, with a net increase in mucin production.IMPORTANCEMicrobe-host interactions in the intestine occur along the mucus-covered epithelium. In the gastrointestinal tract, mucus is composed of glycan-covered proteins, or mucins, which are secreted by goblet cells to form a protective gel-like structure above the epithelium. Low levels of mucin or alterations in mucin glycans are associated with inflammation and colitis in mice and humans. Although current literature links microbes to the modulation of goblet cells and mucins, the molecular pathways involved are not yet fully understood. Using a combination of gnotobiotic mice and mucus-secreting cell lines, we have identified a human-derived microbe,Bifidobacterium dentium, which adheres to intestinal mucus and secretes metabolites that upregulate the major mucin MUC2 and modulate goblet cell function. Unlike otherBifidobacteriumspecies,B. dentiumdoes not extensively degrade mucin glycans and cannot grow on mucin alone. This work points to the potential of usingB. dentiumand similar mucin-friendly microbes as therapeutic agents for intestinal disorders with disruptions in the mucus barrier.
Impact of Mucin on Drug Diffusion: Development of a Straightforward In Vitro Method for the Determination of Drug Diffusivity in the Presence of Mucin
