The multidrug-resistance-1 (MDR1) gene encodes an ATP-dependent efflux transporter that is highly expressed in the colon. In mice, loss of MDR1 function results in colitis with similarities to human inflammatory bowel diseases (IBD). Here, we show that MDR1 has an unexpected protective role for the mitochondria where MDR1-deficiency results in mitochondrial dysfunction with increased mitochondrial ROS (mROS) driving the development of colitis. Exogenous induction of mROS accelerates, whilst inhibition attenuates colitis in vivo; these effects are amplified in MDR1-deficiency. In human IBD, MDR1 is negatively correlated to SOD2 gene expression required for mROS detoxification. To provide direct evidential support, we deleted intestinal SOD2 gene in mice and showed an increased susceptibility to colitis. We exploited the GWA datasets and found many (~5%) of IBD susceptibility genes with direct roles in regulating mitochondria homeostasis. As MDR1 primarily protects against xenotoxins via its efflux function, our findings implicate a distinct mitochondrial toxin + genetic susceptibility interaction leading to mitochondrial dysfunction, a novel pathogenic mechanism that could offer many new therapeutic opportunities for IBD.

Background The mechanisms by which the intestinal microbiome drives inflammation and disease activity in IBD is not clear. Most of the current efforts in developing treatments targeting the intestinal microbiome in IBD are focused on microbial taxa and very few treatments are developed based on microbiome functions in this condition. Using high-resolution functional microbiome analysis we have designed a live bacterial consortium consisting of four bacterial strains with anti-inflammatory functions (BMC333); and demonstrated the significant anti-inflammatory effects of this consortium in a mouse model of DSS-induced colitis by improving disease activity index, colon length, histologic score and fecal lipocalin (presented at DDW 2022). Aim To validate the anti-inflammatory effects and mechanisms of action of BMC333 using IL10-reporter mouse model. Methods Germ free mice bearing the IL10-GFP reporter gene (B6. IL10-GFP) were orally gavaged with BMC333 at 109 CFU/strain or vehicle/placebo (n=6 in each group) at experimental days 1 and 4. The induction period was followed by 10 days without intervention and the animals were sacrificed at day 14. Immunologic effects was assessed in mouse splenocytes and lamina propria by I. quantitating lamina propria immune-suppressive cells using flow cytometry. II. Comparing the effect of stimulation with each of BMC333 bacterial strains’ lysates on IL10- and IFNγ production by splenocytes from BMC333 or vehicle-treated mice. Results Treatment with BMC333 resulted in: I. Higher levels of immune-suppressive cells (IL10-expressing CD4 T cells and B cells, and regulatory T-cells) in the lamina propria of mice treated with BMC333 compared with vehicle-treated mice. II. Higher numbers of IL10-expressing splenic immunocytes stimulated with lysates compared to non-stimulated cells. Additionally, splenocytes stimulated by each of the BMC333 bacterial strains secreted higher IL10 levels, whereas the strain lysates did not induce secretion of the pro-inflammatory cytokine IFNγ, as measured by ELISA. Conclusion These results validate the anti-inflammatory effects of BMC333 and indicate that this beneficial effect is, at least partially, mediated by increasing IL-10 anti-inflammatory activity as demonstrated by the increased numbers of IL-10-producing lamina propria T and B cells after in vivo colonization, and higher IL-10 producing cells and secretion by BMC333 lysate-stimulated splenocytes. BMC333 stimulates increased immuno-suppressive cell populations in the lamina propria, but no increased production of the pro-inflammatory cytokine IFNγ. These findings are consistent with our previously reported in vivo studies and provide a strong rationale for further development of BMC333 as an effective treatment for IBD.