Microbiomal Mediators of TL1A-induced-Fibrosis

ABSTRACT Inflammatory Bowel Disease (IBD) results from a series of complex interactions between susceptibility and severity genes, the environment and the mucosal immune system, presenting as clinical disease. The gut microbiome contributes to IBD; altered gut microbial composition has been demonstrated in intestinal

inflammation, but few studies have examined intestinal fibrosis. A vast number of potential genetic, epigenetic and microbiotic variables contribute to the severity of IBD phenotypes. Among these, relatively clear, clinically- identifiable phenotypes are those with a distinct, severe, fibrosing Crohn’s disease presentation. The

gene/protein combination of tumor necrosis factor superfamily (TNFSF) member 15 and tumor necrosis factor- like (TL) cytokine 1A (referred to as: TNFSF15/TL1A) influences the severity of inflammation and fibrosis in both animal models and human disease. My recently published findings have implicated the gut microbiome in

intestinal fibrosis, and on which TL1A depends to exert its pro-fibrotic effects. The precise mechanisms and specific microbial contributors to intestinal fibrosis have yet to be elucidated, however. As fibroblasts are a predominant cell type responsible for fibrosis, the mechanisms by which TL1A and microbiota drive intestinal

fibrosis likely involve direct induction of fibroblast activation, as my preliminary data demonstrates. I hypothesize that TNFSF15/TL1A plays a central role in the induction and amplification of fibrosis by altering the microbiome to enhance fibrosis-promoting microbial populations and through the direct activation of fibroblasts to express

fibrosis-related factors and/or to become more susceptible to microbial stimulation. In Aim 1, I will determine whether TL1A-induced fibrosis in mouse models or TNFSF15-genetic risk in Veterans with Crohn’s disease is associated with alterations in the microbiome. I will characterize the gut microbiome as assessed by 16S rRNA

sequencing of stool and tissue specimens from patients with and without TNFSF15-genetic risk. To confirm the causal efficacy of these correlated organisms, WT and TL1A-transgenic germ-free C57/BL6 mice will be colonized with the candidate bacterial consortia to evaluate for development of fibrosis in vivo. These microbiota

will also be characterized using metabolomic methods to allow more specific insight into their role in disease pathogenesis. In Aim 2, I will characterize the TL1A-responsive effects and molecular mechanisms of direct bacterial products and metabolites identified in Aim 1 on fibroblasts using primary isolated fibroblasts in vitro. In

Aim 3, I will determine if specific bacterial metabolites can causally mediate intestinal fibrosis in vivo using selective administration in engineered mouse models. The results of this proposed study will provide insight into the specific microbes, or their products, that drive intestinal fibrosis in concert with TL1A. If host-microbiome

interactions and resulting pro-fibrotic fibroblast phenotypes can be mitigated by manipulation of TL1A or the microbiome/metabolome, intestinal fibrosis may be pre-empted in genetically susceptible individuals. These investigations may thus reveal additional downstream pathways, molecules, and potential targets for therapy.