Sobha Rani Bodduluri

The aryl hydrocarbon receptor (AHR) plays a central role in orchestrating gut barrier and mucosal immune functions in the pathogenesis of inflammatory bowel disease (IBD). Nevertheless, activation of the AHR by diverse ligands yields varied outcomes, and the downstream pathways responsible for these effects remain unknown. Here, we report that selective activation of AHR in mouse intestinal epithelial cells (IEC) by the microbial metabolite, urolithin A (UroA), triggers the Nod-like receptor pyrin domain-containing protein 6 (NLRP6) inflammasome, resulting in the release of interleukin (IL)−18 but not IL-1β. Further, we show that UroA-induced IL-18 in IECs is critical for IL-22, mucin 2 and REG3γ production, as well as protection against colitis. Moreover, UroA significantly upregulates IL-18 and IL-22 levels in IECs and type-3 innate lymphoid cells, respectively, in intestinal biopsies from patients with IBD patients. These results demonstrate that activation of AHR by UroA modulates intestinal barrier function through an NLRP6-IL-18-IL-22 pathway in both healthy and IBD conditions.

Independent studies demonstrate the significance of gut microbiota on the pathogenesis of chronic lung diseases; yet little is known regarding the role of the gut microbiota in lung fibrosis progression. Here we show, using the bleomycin murine model to quantify lung fibrosis in C57BL/6 J mice housed in germ-free, animal biosafety level 1 (ABSL-1), or animal biosafety level 2 (ABSL-2) environments, that germ-free mice are protected from lung fibrosis, while ABSL-1 and ABSL-2 mice develop mild and severe lung fibrosis, respectively. Metagenomic analysis reveals no notable distinctions between ABSL-1 and ABSL-2 lung microbiota, whereas greater microbial diversity, with increased Bifidobacterium and Lactobacilli, is present in ABSL-1 compared to ABSL-2 gut microbiota. Flow cytometric analysis reveals enhanced IL-6/STAT3/IL-17A signaling in pulmonary CD4 + T cells of ABSL-2 mice. Fecal transplantation of ABSL-2 stool into germ-free mice recapitulated more severe fibrosis than transplantation of ABSL-1 stool. Lactobacilli supernatant reduces collagen 1 A production in IL-17A- and TGFβ1-stimulated human lung fibroblasts. These findings support a functional role of the gut microbiota in augmenting lung fibrosis severity.