Antimicrobial Peptides Human Beta-Defensin-2 and -3 Protect the Gut During Candida albicans Infections Enhancing the Intestinal Barrier Integrity: In Vitro Study.

Alessandra Fusco,Giovanna Donnarumma,Brunella Perfetto,Vittoria Savio,Maria Donniacuo

doi:10.3389/fcimb.2021.666900

Abstract

The intestinal mucosa is composed of a monolayer of epithelial cells, which is highly polarized and firmly united to each other thanks to the presence of proteins complexes, called Tight junctions (TJs). Alteration of the mucus layer and TJs causes an increase in intestinal permeability, which can lead to a microbial translocation and systemic disorders. Candida albicans, in addition to its role of commensal, is an opportunistic pathogen responsible for disseminated candidiasis, especially in immunocompromised subjects where the dysbiosis leads to damage of the intestinal mucosal barrier . In this work, we used a line of intestinal epithelial cells able to stably express the genes that encodes human beta defensin-2 (HBD-2) and -3 (HBD-3) to monitor the invasion of C. albicans in vitro. Defensins are a group of antimicrobial peptides (AMPs) found in different living organisms, and are involved in the first line of defense in the innate immune response against pathogens. The results obtained show that the presence of antimicrobial peptides improves the expression of TJs and increases the Trans Epithelial Electrical Resistence value. In addition, the invasive ability of C. albicans in transfected cells is significantly reduced, as well as the expression levels of genes involved in the apoptotic pathway. Through the study of interaction between antimicrobial peptides and microbiota we will be able in the future to better understand the mechanisms by which they exert the host defense function against intestinal pathogens.

Highlights

The human intestinal microbiota is a complex ecosystem composed mainly of bacterial cells and archaea, viruses and eukariota such as parasites and fungi
The results obtained (Figure 1) show that overexpression of defensin genes is preserved during the 3 weeks of differentiation, and that both antimicrobial peptides strengthen the integrity of the barrier, but in two different ways: human beta defensin-2 (HBD-2) significantly upregulates the expression of MUC-2 and strongly of Occludin but has no effect on the expression of the other Tight junctions (TJs)
Due to the similarity between Caco-2 monolayers and human intestinal epithelial cell barrier in morphology with the same cell polarity and TJs structure (Sambuy et al, 2005), we created a clone of Caco-2 cells stably transfected with antimicrobial peptides HBD-2 and HBD-3 to determine if their protective role in the intestinal barrier is associated with the expression of TJ proteins

Summary

Introduction

The human intestinal microbiota is a complex ecosystem composed mainly of bacterial cells and archaea, viruses and eukariota such as parasites and fungi. Its composition is unique and peculiar to each individual and differs along the digestive tract, according to the environmental influences and lifestyle stimuli. It sustains gut integrity and prevents gut colonization by pathogens. It is an opportunist pathogen belong to the family of Saccharomycetaceae, which can grow in a variety of morphological forms such as yeast, pseudohyphae and hyphae (Sudbery et al, 2004; Nadeem et al, 2013), present on the mucosal surfaces of most healthy individuals and which can cause superficial to severe systemic infections mostly originating from the gastrointestinal tract (Paoletti et al, 2013; Höfs et al, 2016; Bertolini et al, 2019), especially in immune-compromised patients. The major risk factor for disseminated candidiasis includes damage to the mucosal intestinal barrier and dysbiosis with alteration of the resident microbiota (Allert et al, 2018)

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Conclusion