Abstract
Vulvovaginal candidiasis (VVC), caused primarily by the human fungal pathogen Candida albicans, results in significant quality-of-life issues for women worldwide. Candidalysin, a toxin derived from a polypeptide (Ece1p) encoded by the ECE1 gene, plays a crucial role in driving immunopathology at the vaginal mucosa. This study aimed to determine if expression and/or processing of Ece1p differs across C. albicans isolates and whether this partly underlies differential pathogenicity observed clinically. Using a targeted sequencing approach, we determined that isolate 529L harbors a similarly expressed, yet distinct Ece1p isoform variant that encodes for a predicted functional candidalysin; this isoform was conserved amongst a collection of clinical isolates. Expression of the ECE1 open reading frame (ORF) from 529L in an SC5314-derived ece1Δ/Δ strain resulted in significantly reduced vaginopathogenicity as compared to an isogenic control expressing a wild-type (WT) ECE1 allele. However, in vitro challenge of vaginal epithelial cells with synthetic candidalysin demonstrated similar toxigenic activity amongst SC5314 and 529L isoforms. Creation of an isogenic panel of chimeric strains harboring swapped Ece1p peptides or HiBiT tags revealed reduced secretion with the ORF from 529L that was associated with reduced virulence. A genetic survey of 78 clinical isolates demonstrated a conserved pattern between Ece1p P2 and P3 sequences, suggesting that substrate specificity around Kex2p-mediated KR cleavage sites involved in protein processing may contribute to differential pathogenicity amongst clinical isolates. Therefore, we present a new mechanism for attenuation of C. albicans virulence at the ECE1 locus.
Highlights
Vulvovaginal candidiasis (VVC), caused primarily by the human fungal pathogen Candida albicans, results in significant quality-of-life issues for women worldwide [1]
We aimed to determine if genetic variation of ECE1 existed across a collection of C. albicans clinical isolates
We constructed isogenic chimeric strains harboring swapped Ece1p peptides or HiBiT tags between representative isoforms and showed impaired secretion with the variant that was associated with reduced virulence in vitro and in vivo
Summary
Vulvovaginal candidiasis (VVC), caused primarily by the human fungal pathogen Candida albicans, results in significant quality-of-life issues for women worldwide [1]. VVC has recently been described as an immunopathology, in which robust innate host defense mechanisms (e.g. neutrophil migration and pro-inflammatory cytokines) drive disease symptoms, including itching, burning, and soreness of the vaginal mucosa [3]. Using hypha-deficient mutant strains, we demonstrated that the yeast-to-hypha switch is crucial for eliciting mucosal damage and concomitant neutrophil recruitment and pro-inflammatory signaling at the vaginal interface [10]. These results largely recapitulated observations made using similar hypha-deficient mutants in the context of in vitro infection of vaginal epithelial cells. Similar to a model of oropharyngeal candidiasis (OPC), expression of candidalysin is critical for robust induction of immunopathology during murine VVC, as strains lacking
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