Defining cooperative roles for colonic microbiota and Muc2 mucin in mediating innate host defense against Entamoeba histolytica

Abstract

Amebiasis is caused by the protozoan parasite Entamoeba histolytica (Eh), a potentially fatal disease occurring mainly in developing countries. How Eh interacts with innate host factors in the gut is poorly understood. Eh resides and feed in/on the outer colonic mucus layer and thus share an ecological niche with indigenous microbiota. As gut microbiota regulates innate immune responses, in this study we characterized the cooperative roles that microbiota and the mucus layer play in Eh-induced pro-inflammatory responses in the colon. To study this, we used antibiotics treated and non-treated specific pathogen free Muc2-/- and Muc2+/+ littermates and germ-free mice inoculated with Eh in colonic loops as a short infection model. In antibiotic treated Muc2-/- and Muc2+/+ littermates, Eh elicited robust mucus and water secretions, enhanced pro-inflammatory cytokines and chemokine expression with elevated MPO activity and higher pathology scores as compared to the modest response observed in non-antibiotic treated littermates. Host responses were microbiota specific as mucus secretion and pro-inflammatory responses were attenuated following homologous fecal microbial transplants in antibiotic-treated Muc2+/+ quantified by secretion of 3H-glucosamine newly synthesized mucin, Muc2 mucin immunostaining and immunohistochemistry. Eh-elicited pro-inflammatory responses and suppressed goblet cell transcription factor Math1 as revealed by in vivo imaging of Eh-colonic loops in Math1GFP mice, and in vitro using Eh-stimulated LS174T human colonic goblet cells. Eh in colonic loops increased bacterial translocation of bioluminescent E. coli and indigenous bacteria quantified by FISH and quantitative PCR. In germ-free animals, Eh-induced mucus/water secretory responses, but acute pro-inflammatory responses and MPO activity were severely impaired, allowing the parasite to bind to and disrupt mucosal epithelial cells. These findings have identified key roles for intestinal microbiota and mucus in regulating innate host defenses against Eh, and implicate dysbiosis as a risk factor for amebiasis that leads to exacerbated immune responses to cause life-threatening disease.

Increased intestinal permeability exacerbates sepsis through reduced hepatic SCD-1 activity and dysregulated iron recycling

“…An Olympus FV1000 scanning confocal inverted microscope was used to visualize and record fluorescence in tissues. ImageJ software was used to calculate distance of bacteria from the epithelium 62 . IgA-coated bacteria in fecal samples from Muc2 −/− littermates were quantified and fecal samples from Rag −/− animals were used as negative controls 29 .…”

Mucins in Intestinal Mucosal Defense and Inflammation: Learning From Clinical and Experimental Studies

“…E. histolytica has been found to bind to αvβ3 integrins on goblet cells and stimulate the hypersecretion of mucus by exocytosis (193). Contrasting data suggests, however, that E. histolytica impairs the regulation of Math1 transcription factor required for goblet cell differentiation and can actually lead to decreased mucus production (194). In addition, during E. histolytica infection, MUC2, possibly by acting either as a cAMP ligand or by activating TLRs, can promote elevated levels of antimicrobial peptides such as cathelicidins (195).…”

Parasite–bacteria interrelationship

“…Moreover, germfree mice were not able to generate an adequate innate immunity against E. histolytica due to the absence of microbiota, allowing the parasites to attach to and disrupt mucosal epithelial cells. This study thus points out a crucial role for indigenous gut bacteria in educating and training the innate mucosal defenses of the host, essential for protection against E. histolytica invasion (Leon-Coria et al 2018).…”