Candidalysin triggers epithelial cellular stresses that induce necrotic death

Mariana Blagojevic,David L Moyes,Jonathan P Richardson,Michelle Maxson,Bernhard Hube,Giorgio Camilli,Julian R Naglik

doi:10.1111/cmi.13371

Abstract

Candida albicans is a common opportunistic fungal pathogen that causes a wide range of infections from superficial mucosal to hematogenously disseminated candidiasis. The hyphal form plays an important role in the pathogenic process by invading epithelial cells and causing tissue damage. Notably, the secretion of the hyphal toxin candidalysin is essential for both epithelial cell damage and activation of mucosal immune responses. However, the mechanism of candidalysin-induced cell death remains unclear. Here, we examined the induction of cell death by candidalysin in oral epithelial cells. Fluorescent imaging using healthy/apoptotic/necrotic cell markers revealed that candidalysin causes a rapid and marked increase in the population of necrotic rather than apoptotic cells in a concentration dependent manner. Activation of a necrosis-like pathway was confirmed since C. albicans and candidalysin failed to activate caspase-8 and -3, or the cleavage of poly (ADP-ribose) polymerase. Furthermore, oral epithelial cells treated with candidalysin showed rapid production of reactive oxygen species, disruption of mitochondria activity and mitochondrial membrane potential, ATP depletion and cytochrome c release. Collectively, these data demonstrate that oral epithelial cells respond to the secreted fungal toxin candidalysin by triggering numerous cellular stress responses that induce necrotic death. TAKE AWAYS: Candidalysin secreted from Candida albicans causes epithelial cell stress. Candidalysin induces calcium influx and oxidative stress in host cells. Candidalysin induces mitochondrial dysfunction, ATP depletion and epithelial necrosis. The toxicity of candidalysin is mediated from the epithelial cell surface.

Highlights

Candida albicans is a human fungal pathogen that causes morbidity and mortality in millions of individuals worldwide each year (Brown et al, 2012)
Toxin-induced host cell death can be driven by several biological processes including apoptosis and necrosis, which can influence the outcome of a microbial infection (Camilli et al, 2020; Jorgensen et al, 2017)
Candidalysin is the first, and currently only, peptide toxin identified in any human fungal pathogen (Moyes et al, 2016)

Summary

| INTRODUCTION

Candida albicans is a human fungal pathogen that causes morbidity and mortality in millions of individuals worldwide each year (Brown et al, 2012). Cell damage often results in cell stress and death, which can play a key role in host defence to microbial infections (Camilli, Blagojevic, Naglik, & Richardson, 2020; Jorgensen, Rayamajhi, & Miao, 2017). Pro- and anti-apoptotic signalling events have been reported following in vitro stimulation of myeloid and epithelial cells with C. albicans or fungal components, apoptosis is a non-lytic form of cell death and cannot account for C. albicans–induced lysis. Live C. albicans induced early apoptotic signalling events in oral epithelial cells and macrophages followed by necrotic death (Panagio, Felipe, Vidotto, & Gaziri, 2002; Villar & Zhao, 2010). It is hypothesised that candidalysin is secreted into the invasion pocket, where it intercalates into host membranes to induce pore formation, which results in cell damage and cell death (Naglik, Gaffen, & Hube, 2019). We provide evidence that candidalysin induces oxidative stress, mitochondrial dysfunction and epithelial cell death, which occurs predominantly via a necrotic pathway

| RESULTS

| DISCUSSION

Findings

| EXPERIMENTAL PROCEDURES