Candidalysin activates innate epithelial immune responses via epidermal growth factor receptor

Abstract

Candida albicans is a fungal pathobiont, able to cause epithelial cell damage and immune activation. These functions have been attributed to its secreted toxin, candidalysin, though the molecular mechanisms are poorly understood. Here, we identify epidermal growth factor receptor (EGFR) as a critical component of candidalysin-triggered immune responses. We find that both C. albicans and candidalysin activate human epithelial EGFR receptors and candidalysin-deficient fungal mutants poorly induce EGFR phosphorylation during murine oropharyngeal candidiasis. Furthermore, inhibition of EGFR impairs candidalysin-triggered MAPK signalling and release of neutrophil activating chemokines in vitro, and diminishes neutrophil recruitment, causing significant mortality in an EGFR-inhibited zebrafish swimbladder model of infection. Investigation into the mechanism of EGFR activation revealed the requirement of matrix metalloproteinases (MMPs), EGFR ligands and calcium. We thus identify a PAMP-independent mechanism of immune stimulation and highlight candidalysin and EGFR signalling components as potential targets for prophylactic and therapeutic intervention of mucosal candidiasis.

Vulvovaginal Candidiasis: A Current Understanding and Burning Questions

“…Cleary, candidalysin causes excessive damage at mucosal surfaces, further amplifying innate immune signaling. In vitro and in vivo work suggests that MAPK signaling, engaged via epithelial growth factor receptor (EGFR) phosphorylation, is important for candidalysin-triggered immune activation [85]. Candidalysin also plays a significant role in eliciting IL-17 responses at the oral epithelium, driving a feed-forward inflammatory loop characterized by IL-1α/IL-β responses [86].…”

Candidalysin Is a Potent Trigger of Alarmin and Antimicrobial Peptide Release in Epithelial Cells

“…In support of this, ATP-dependent transactivation of EGFR has been reported in airway epithelial cells, which is thought to occur via dual oxidase 1 (DUOX1) and disintegrin and metalloproteinase domain-containing protein (ADAM)-17 [40]. Given that activation of EGFR and downstream signalling are known to support protective anti-Candida immunity [5, 12,24], the data may demonstrate a key role for ATP in triggering epithelial immune responses against C. albicans.…”

“…The release of other known candidalysin-induced proteins, such as hBD2, hBD3, LL37, G-CSF, GM-CSF, IL-1α and IL-1β, do not appear to be affected by Apyrase during infection. Thus a combination of factors and underlying redundancy likely exist within the system, with events such as calcium influx, shown to have roles in ROS induction [46] and Candidalysin-induced immune responses [12], potentially playing a role.…”

“…We previously reported the ability of candidalysin to induce EGFR activation and downstream MAPK signalling [12]. Given that both ATP [40] and ROS [41][42][43] are each capable of triggering EGFR activation, we investigated whether either of these molecules were involved in our model of candidalysin-induced EGFR activation.…”

“…Oral epithelial cells respond directly to the presence of candidalysin by activating epidermal growth factor receptor (EGFR) [12], a key tyrosine kinase important in cell biology and infection [13]. Consequent MAPK signalling, via the AP-1 transcription factor c-Fos and MAPK phosphatase (MKP)-1 [14,15], as well as the release of inflammatory cytokines IL-1α, IL-1β, IL-36γ, IL-6, GM-CSF and G-CSF [12,[14][15][16][17][18][19][20], follows EGFR activation. Candidalysin-induced IL-1α/β and IL-36γ signalling 2 of 11 drives expansion of innate TCRαβ + T-cells and consequent IL-17A expression, required for robust antifungal immune responses at the oral mucosa [20,21].…”