(b) Viability of Caco-2 cells after 1824h culture in regular 12-wells plates (Caco-2 control), HoxBan setup with PBS-buffered agar, HoxBan with YCFAG agar without (Caco-2+YCFAG) and withF. 37 C and 5% CO2, coverslip-attached Caco-2 cells promoted growth and metabolism ofF. prausnitzii, whileF. prausnitziisuppressed inflammation and oxidative stress in Caco-2 cells. F. prausnitziidid not compromise Caco-2 cell viability. Exogenously added porcine mucin also advertised growth ofF. prausnitzii, suggesting that it may be part of the mechanism of Caco-2-stimulated growth ofF. prausnitzii. This Human oxygen-Bacteria anaerobic (HoxBan) coculturing system uniquely establishes host-microbe mutualism of a beneficial anaerobic stomach microbein vitroand principally allows the analysis of host-microbe interactions of pure and mixed cultures of bacteria and human being cells. The human gut microbiome is progressively recognized as an essential determinant to get human wellness, affecting a number of gut, metabolic, neurological and psychological disorders1. Gut microbiota provide essential nutrients and anti-inflammatory compounds LEE011 (Ribociclib) to the host and confine growth of pathogens2, 3, 4. High-throughput sequencing techniques possess uncovered the high complexity of the stomach microbiome and the composition changes during ageing and disease5, 6. The healthy stomach microbiome consists of 5001, 000 different bacterial species and their collective genomes (metagenome) encode at least a 100-fold more genes compared with the human genome7, eight, 9. Only a small fraction of these bacterial varieties are culturedin vitroand much more challenging is to coculture stomach bacteria and human cells10, 11. The main obstacle in a host-microbiome coculture system is that many (> 90%) gut bacteria are obligate anaerobes that die quickly when exposed to atmospheric conditions (21% O2), while human being cells depend on oxygen. Faecalibacterium prausnitziiis an obligate anaerobe that may stand for up to 25% of all bacteria in the healthy gut12. F. prausnitzii-excreted products and cell extracts suppress inflammatory signaling in intestinal epithelial (Caco-2) cellsin vitro, as well as in 2, 4, 6-trinitrobenzenesulphonic acid solution (TNBS)-induced colitis in micein vivo13. Moreover, human intestinal inflammation is usually associated with decreased numbers ofF. prausnitziiand low numbers of this bacterium predispose for post-operative ileal recurrence of Crohns disease13, 16, 15, sixteen. Among anaerobes, F. prausnitziihas the unique ability to grow close to the intestinal epithelium in the oxic-anoxic interphase in the gut17, 18, 19. However , it continues to be elusive whether direct mutualism exists between this stomach microbe and intestinal epithelial cells. In this study, we set out to create a coculture system for oxygen-requiring Adamts1 human stomach epithelial (Caco-2) cells and an anaerobic gut bacterium (F. prausnitzii). == Results and Conversation == The Human oxygen-Bacteria anaerobic (HoxBan) system developed in this study establishes coculturing of glass-adherent human being cells in liquid medium and anaerobic bacteria in solid agar medium for over 24 h and allows the analysis of cell growth, transcriptome and exo-metabolome of cocultured cells. A detailed protocol is given in thesupplementary/online section. In a nutshell, hand warm (~40 C) agar medium was inoculated withF. prausnitziistarter cultures and aliquots of 40 mL were allowed to solidify in 50 mL Falcon centrifugation tubes. Caco-2 cells produced on coverslips were positioned up-side-down along with theF. prausnitzii-containing YCFAG agar and overlaid with DMEM medium. The HoxBan coculture tubes (schematically drawn inFig. 1a) were placed either with a loose (air-open) or tightly-closed cover (air-closed) in a standard humidified incubator at 37 C, LEE011 (Ribociclib) 5% CO2and LEE011 (Ribociclib) atmospheric O2. F. prausnitziicolony formation, transcriptional adaptations of Caco-2 cells and excreted metabolites in the liquid medium were examined after 1836 h of coculture. == Figure 1 . Human intestinal cells promote growth ofF. prausnitziiin the HoxBan system. == (a) Schematic sketching of the HoxBan coculture system withF. prausnitziigrowing in solid YCFAG agar overlaid with liquid DMEM medium and Caco-2 cells on coverslips facing the agar. (b) Pictures documentingF. prausnitziicolony formation in the absence and presence of Caco-2 cells after 18 h (top panel) and thirty LEE011 (Ribociclib) six h (bottom panel) in air-open and air-tight tradition tubes. (c)F. prausnitziicolony formation after 18 h coculture with Caco-2 (left), DLD-1 (middle) and HepG2 cells (right). Within 18 h, F. prausnitziiformed colonies throughout the 40 mL YCFAG-agar. In the absence of Caco-2 cells, noF. prausnitziicolonies created in the LEE011 (Ribociclib) best agar coating, most likely due to penetration of intolerable amounts of oxygen (Fig. 1b, left 2 panels). In contrast, obvious and biggerF. prausnitziicolonies appeared close to the coverslip-attached Caco-2 cells, both in air-closed and air-open tubes (Figs 1b, 2panels on the right). Notably, F. prausnitziicontinued to expand over a total coculture time of thirty six h (Fig. 1b, 2bottom panels around the right). In a similar way, human colonic DLD-1 cells promoted growth ofF. prausnitziiin the top agar layer close to the coverslip, although bacterial growth was fewer pronounced compared to the cocultures with Caco-2 cells (Fig. 1c). In contrast to both intestine-derived cell lines, HepG2 (human hepatoma) cells did not stimulateF. prausnitziigrowth (Fig. 1c), indicating that this effect is usually cell type-specific. == Number 2 . F. prausnitziisuppresses manifestation of inflammatory and oxidative stress markers in Caco-2 cells. == (a) Ki-67 staining in the Caco-2 cells after 24 h monoculture (top panel) or HoxBan.
