Browsing by Subject "inflammatory bowel disease"

Dendritic cells (DCs) are potent antigen presenting cells (APC) that sense microbes and induce T cell activation and functional differentiation. The APC function of DCs is upregulated by the signaling pathway downstream of the microbial sensing receptor, a process well studied during pathogen infection and immunization. Multiple lines of evidence suggested that DCs in the intestine lamina propria (LP-DCs) frequently interact with the innocuous microbiota, and through these interactions LP-DCs support intestinal immune homeostasis. However, DC responses to microbiota, if not regulated, can give rise to inflammatory T cells and trigger inflammatory bowel disease (IBD). The DC subsets, DC functions and signaling pathways that induce inflammatory T cells remain incompletely characterized. Here, we demonstrated that mice lacking signaling attenuator A20 (A20cko mice) in DCs develop spontaneous small intestine inflammation that is dependent of microbiota, DCs and T cells. LP-DCs induce inflammatory T cells and that the signals perceived and APC functions are unique for three distinct LP-DC subsets. Thus, while CD103+CD11b- DCs exclusively upregulate their ability to instruct IFNγ+ T cells, CD103+CD11b+ DCs exclusively upregulate their ability to instruct IL-17+ T cells. Of note, APC functions of both DC subsets are upregulated in a MyD88-independent fashion. In contrast, CD103-CD11b+ DCs instruct both IFNγ+ and IL-17+ T cells, and only the IL-17-inducing APC functions require MyD88. In disease pathogenesis, both CD103-CD11b+ and CD103+CD11b+ DCs expand pathologic Th17 cells.

Although MyD88 pathways are potent inducer of intestinal inflammation in the colitis of IL-10 knockout mice and upon transferring of naïve T cells into Rag-deficient hosts, MyD88 pathways are not required for the inflammation of small intestine in A20cko mice. Among the MyD88-independent signaling pathways that could mediate host interaction with microbiota, Dectin-1 pathway is of particular interest because both the receptor Dectin-1 and the downstream signaling molecule CARD9 are IBD-associated genes. Additionally, the defect in either molecule influences the severity of the intestinal inflammation in mouse. We established that the production of inflammatory cytokines downstream of the Dectin-1 pathway is restricted by A20. Mechanistically, A20 inhibits TRAF6 ubiquitination downstream of the Dectin-1 pathway, thereby controlling NFκB and Jnk activation. Although we showed that CD103-CD11b+ and CD103+CD11b+ DCs express Dectin-1 and CARD9, the Dectin-1 pathway is not required for the upregulation of DC function and expansion of inflammatory T cells in the intestine of A20cko mice. Thus, our studies have unveiled a critical role of MyD88-independent pathways in mediating the interaction of the microbiota and LP-DCs. MyD88-independent pathway is capable of driving functional maturation of LP-DCs, pathological expansion of CD4 T cells, and the inflammatory disease in the small intestine.

The inflammatory bowel diseases (IBD) occur in genetically susceptible individuals that mount inappropriate immune responses to their microbiota leading to chronic intestinal inflammation. The natural history of IBD progression includes early subclinical stages of disease occurring before disease is diagnosed in the clinic. There is evidence in first degree relatives of IBD patients and members of the general population who go on to develop IBD, that these stages are characterized by increased gut barrier permeability, increased levels of inflammation biomarkers, detection of microbiota-specific antibodies in sera, and changes in microbiota composition. Mouse models can be a useful tool in studying disease dynamics during these early stages. The transcription factor Hepatocyte nuclear factor 4 alpha (HNF4A) has been associated with human IBD, and deletion of Hnf4a in intestinal epithelial cells (IEC) in mice (Hnf4aΔIEC) leads to spontaneous colonic inflammation by 6-12 months of age. However, early stages of disease in this mouse model were not well defined, and the role of microbiota in promoting disease was also unclear. Here I tested if pathology in Hnf4aΔIEC mice begins earlier in life and if microbiota contribute to that process, as well as later inflammatory stages of disease. Longitudinal analysis revealed that Hnf4aΔIEC mice reared in specific pathogen-free (SPF) conditions develop episodically elevated fecal lipocalin 2 (Lcn2) and episodic loose stools beginning by 4-5 weeks of age. Lifetime cumulative Lcn2 levels correlated with histopathological features of colitis at 12 months of age. Antibiotic and gnotobiotic tests showed that these phenotypes in Hnf4aΔIEC mice were dependent on microbiota. Fecal 16S rRNA gene sequencing in SPF Hnf4aΔIEC and control mice disclosed that genotype significantly contributed to differences in microbiota composition by 12 months, and longitudinal analysis of the Hnf4aΔIEC mice with the highest lifetime cumulative Lcn2 revealed that microbial community differences emerged early in life when elevated fecal Lcn2 was first detected. These microbiota differences included enrichment of a novel phylogroup of Akkermansia muciniphila in Hnf4aΔIEC mice. I conclude that HNF4A functions in IEC to shape composition of the gut microbiota, and protect against episodic inflammation induced by microbiota throughout the lifespan. Lastly, I discuss future directions for this work, including using single cell RNA sequencing of the colonic epithelium to identify genes regulated by HNF4A in distinct colonic epithelial cell types, gnotobiotic studies using the strain of Akkermansia muciniphila we isolated to test the hypothesis that it can promote disease in Hnf4aΔIEC mice, testing clinically relevant disease triggers using this mouse IBD model, and further immune cell profiling.