Understanding the Invasion Dynamics of Mycobacterium avium subspecies Paratuberculosis (MAP)

Abstract

Paratuberculosis is a global infectious disease caused by the bacterium, Mycobacterium avium subspecies Paratuberculosis (MAP). Infection of ruminants with MAP can trigger progressive wasting disease characterized by granulomatous lymphadenitis, enteritis, and severe intestinal pathology potentially leading to death of the animal. The role of MAP infection within innate immune cells, including macrophages, in the small intestine has been extensively examined; however, the mechanisms of MAP entrance into the mucosal barrier of the small intestine are poorly defined. Additionally, there is a potential zoonotic risk of MAP linked to Crohn’s Disease (CD), but these claims have yet to be substantiated. Due to this and the economic burden and welfare impact on the livestock industry, a deeper understanding of the initial mechanisms of MAP uptake within the host is crucial to revealing novel treatment strategies. While the current paradigm suggests MAP travels to the small intestine, where it gains entry through the epithelium, the exact cellular tropism/-mechanism(s) of entry are not well defined. Therefore, we developed an enteroid system to visualize entrance of MAP into distinct cells of the intestinal epithelium using a GFP-expressing MAP strain. We sought to test the hypothesis that MAP uptake occurs via M cells through receptor mediated transcytosis.To evaluate this hypothesis, we generated a novel mouse enteroid-derived monolayer with functional M cells capable of transcytosis. MAP was detected mainly within M cells, more notably with the fibronectin pre-incubation. Integrin-blocking peptides decreased this M cell tropism. With this novel model system developed, we were able to examine MAP-host pathogen interactions, which will provide insight into blocking MAP entry at its initial point. Beyond this, our model will add valuable information to the field of mouse enteroid-derived monolayer techniques and can be used in the future to study alternate intestinal pathogens. In the process of characterizing a mouse enteroid-derived monolayer with M cells for use in establishing a model for MAP invasion dynamics, we discovered unique roles for RANKL/RANK signalling regarding M cell differentiation and the intestinal epithelium.