Mucosal Duox2-based assays for dysbiosis-associated irritable bowel syndrome

There is mounting evidence that gut microbiota plays an important role in health and disease. The gut microbiome consists of >1013 commensal microbes whose community structures are vastly different between individuals and influenced by environmental factors such as diet and stress. One of the major limitations of studying gut microbiome and its role in disease pathogenesis is the lack of defined microbial community structures to differentiate normal healthy microbiota vs abnormal disease-promoting microbiota (a.k.a., dysbiosis) due to the heterogeneity between individuals. Thus, our long-term objective is to develop a screening assay to identify individuals with altered gut microbiota that may promote disease symptomatology. 

We and others recently showed that increased expression of mucosal DUOX2 is an epithelial response to increased bacterial attachment to the host intestinal surface. However, whether induction of mucosal DUOX2 could serve as a host marker to identify abnormal gut microbe-host interaction that contributes to disease manifestation is currently unknown. The objective here is to develop a DUOX2-based assay to screen for dysbiosis in patients with irritable bowel syndrome (IBS). Our central hypothesis is that IBS patients with increased levels of DUOX2 in their colonic biopsies harbor gut mucosal dysbiosis.  

Our Specific Aims are: 1) Determine whether DUOX2 is a sensitive marker of IBS-associated gut mucosal dysbiosis. Reanalysis of published IBS gene expression data showed that a subset of IBS patients have increased mucosal DUOX2 levels (DUOX2HI) compared to healthy controls. We hypothesize that DUOX2HI IBS patients will have distinct microbiota clustering (mucosal > fecal samples) compared to DUOX2LOW IBS or healthy volunteers. We plan to enroll IBS patients and matched controls undergoing colonoscopy and obtain colonic biopsies and fecal samples to address whether DUOX2HI subjects have gut dysbiosis. 2) Demonstrate a direct link that IBS-associated dysbiosis induces DUOX2. 
We recently showed that mice with increased ileal DUOX2 were colonized with epithelial attaching commensal SFB and SFB monoassociated germ-free mice similarly induced intestinal DUOX2. Thus, we hypothesize that the microbiota of DUOX2HI IBS patients harbor DUOX2-inducing bacteria that are closely associated with the gut mucosa. We plan to test this hypothesis by transferring mucosal and fecal microbiota of DUOX2HI IBS patients into germ-free mice and assess for DUOX2 induction and increased mucosal bacterial association. 

With respect to expected outcomes, the work proposed in the above Aims is expected to demonstrate the usefulness of measuring DUOX2 expression as a marker of gut dysbiosis. Such results are expected to have an important positive impact, because no screening tool is currently available to identify subgroup of IBS patients with dysbiosis that may be more responsive to antibiotics or probiotics. Having such a test will not only allow better assessment of the benefit of microbiota-targeting therapies (e.g., probiotics and fecal transplantation) in IBS patients but also further our understanding of the role of gut dysbiosis in other disorders such as obesity, metabolic syndrome, and cancer.