CDLD Pilot Project 2: Impact of Anaphylatoxin C3aR on Immune Responses and Gut Microbiota in IBD

Silvia Guglietta – Department of Microbiology

Guglietta Lab Webpage

Inflammatory bowel diseases (IBD) affect more than ten million people worldwide with the highest prevalence in North America and increased trend in newly industrialized countries and in pediatric patients. Ulcerative colitis (UC) and Crohn’s disease (CD) are the two clinical manifestations of IBD and are characterized by chronic diarrhea and abdominal pain, which predispose to severe complications such as fibrosis and colon cancer. Despite the identification of several therapeutic targets, all treatments, including the most promising anti-TNF-alpha, fail to demonstrate long lasting efficacy. Defective innate immune responses with consequent failure to control microbial flora are regarded as a key factor in triggering IBD but the mechanisms are largely unknown. The complement system is a central component of the innate immunity and recent population-based studies identified mutations in the complement pathway among the most significant common variants associated with IBD. Complement anaphylatoxin 3a (C3a) is released upon cleavage of the central complement component C3 and signals through its receptor (C3aR) to regulate immune responses, intestinal stem cell regeneration and bacterial infections. We recently found that sub-groups of CRC patients down-regulate C3aR. Despite these evidences, the role of C3a/C3aR axis in modulating gut microbiota and intestinal inflammation is largely understudied.

We hypothesize that loss of C3aR affects immune and epithelial cell functions resulting in the emergency of a pro-inflammatory microbiota that confers enhanced susceptibility to IBD.

To investigate how loss of C3aR affects intestinal inflammation, we will evaluate disease severity and outcome and will perform an immune profiling of intestinal tissues using by cytometry and RNASeq in clinically relevant models of CD and UC using WT and C3aR-/- mice. Experiments of bone marrow chimera will clarify the contribution of C3aR on immune and non-immune cells. To assess the impact of C3aR on microbiome composition, we will perform 16S sequencing of fecal microbiota. Taking advantage of our unique gnotobiotic facility, we will investigate how fecal microbiota from C3aR-/- mice into germ free mice affects immune responses and intestinal inflammation and whether microbial dysbiosis can contribute to C3aR loss or down-regulation via epigenetic modifications.

By elucidating the mechanistic impact of C3a/C3aR axis on gut microbiota and intestinal inflammatory responses, our study will shed light on novel pathways involved in IBD pathogenesis with the long-term goal to develop patient-centered therapeutic strategies with long-lasting efficacy.