Organoid-derived adult human colonic epithelium responds to co-culture with a probiotic strain of Bifidobacterium longum

Abstract

In germ-free animals the lack of microbes within the gut results in a propensity to mucosal inflammation among other immune deficits. This suggests microbes are essential for the healthy function of the human gut, but we have lacked a reproducible mechanistic model of interactions between human colonic epithelium and the anaerobic microbes within the gut. To establish the physiological effect of a common anaerobe in the human gut, we co-cultured a probiotic strain of Bifidobacterium longum (35624) with organoid-derived adult human colonic epithelium in asymmetric gas conditions (anoxic apically, 5% oxygen basolaterally) and compared to axenic ( germ-free) epithelium. Bacteria proliferated and retained their normal cellular morphology in the presence of the human colonic epithelium. The human colonic mucosa retained trans-epithelial electrical resistance (TEER) consistent with an intact epithelium but lower than in axenic conditions. Changes in TEER corresponded to changes in Claudin-family gene expression. Inflammation was repressed in co-culture as compared to axenic, with reduced expression of executor and pyroptosis caspases; reduced expression of activators and increased expression of inhibitors of NFKB; reduced expression of toll-like-receptors (TLRs) and increased expression of TOLLIP (a negative regulator of TLRs). Consistent with the presence of actively fermenting bacteria that produce lactate and acetate but do not produce butyrate, PPARA expression was increased while PPARG expression was reduced. As in germ-free animal experiments, axenic human colonic mucosa is poised for inflammation. Co-culture with Bifidobacterium longum resolved the pro-inflammatory state while modulating barrier function (via Claudin genes) and cellular energetics (via PPARA and PPARG genes). ImportanceExperiments in animals demonstrate the importance of microbes with the gut for the health of the gut. Many of the microbes within the healthy gut are strictly anaerobic and cannot grow in the presence of oxygen; human tissues require some oxygen to live. Here we observe the effect of growing an anaerobic bacterium - Bifidobacterium longum - typically found in the human gut with human colonic tissue. We observed that the human tissue responded favorably to being cultivated with the microbe as compared to being alone. This experiment confirms human colonic tissues reduce their inflammation in the presence of a bacteria typically found in the gut.