ERG2 and ERG24 Are Required for Normal Vacuolar Physiology as Well as Candida albicans Pathogenicity in a Murine Model of Disseminated but Not Vaginal Candidiasis

Abstract

Several important classes of antifungal agents, including the azoles, act by blocking ergosterol biosynthesis. It was recently reported that the azoles cause massive disruption of the fungal vacuole in the prevalent human pathogen Candida albicans. This is significant because normal vacuolar function is required to support C. albicans pathogenicity. This study examined the impact of the morpholine antifungals, which inhibit later steps of ergosterol biosynthesis, on C. albicans vacuolar integrity. It was found that overexpression of either the ERG2 or ERG24 gene, encoding C-8 sterol isomerase or C-14 sterol reductase, respectively, suppressed C. albicans sensitivity to the morpholines. In addition, both erg2⌬/⌬ and erg24⌬/⌬ mutants were hypersensitive to the morpholines. These data are consistent with the antifungal activity of the morpholines depending upon the simultaneous inhibition of both Erg2p and Erg24p. The vacuoles within both erg2⌬/⌬ and erg24⌬/⌬ C. albicans strains exhibited an aberrant morphology and accumulated large quantities of the weak base quinacrine, indicating enhanced vacuolar acidification compared with that of control strains. Both erg mutants exhibited significant defects in polarized hyphal growth and were avirulent in a mouse model of disseminated candidiasis. Surprisingly, in a mouse model of vaginal candidiasis, both mutants colonized mice at high levels and induced a pathogenic response similar to that with the controls. Thus, while targeting Erg2p or Erg24p alone could provide a potentially efficacious therapy for disseminated candidiasis, it may not be an effective strategy to treat vaginal infections. The potential value of drugs targeting these enzymes as adjunctive therapies is discussed.A variety of antifungal therapies act by blocking the biosynthesis of the membrane lipid ergosterol (1). This includes the most important and widely used class of antifungal treatments, the azoles, which inhibit lanosterol demethylase (Erg11p) (2). The resulting depletion of cellular ergosterol and accumulation of intermediate sterol species are both thought to cause plasma membrane dysfunction and ultimately lead to growth arrest. However, we recently reported that inhibition of Erg11p also causes massive disruption of the fungal vacuole in the human pathogen Candida albicans (3). Furthermore, vacuolar fragmentation can be observed before significant growth inhibition and is thus an early consequence of azole treatment. Previous studies with the nonpathogenic yeast Saccharomyces cerevisiae also indicated that ergosterol is important for endocytic trafficking from the plasma membrane to the fungal vacuole (4) and to support homotypic vacuole-vacuole fusion in an in vitro biochemical assay (5). Several S. cerevisiae ergosterol biosynthetic mutants are known to have an aberrant vacuole morphology (5, 6), and it has been reported that the activity of the proton pump responsible for vacuolar acidification is also ergosterol dependent and therefore diminished in the presence of an azole antifungal (7...

Endosomal Trafficking Defects Can Induce Calcium-Dependent Azole Tolerance in Candida albicans

“…We previously reported that the vps21⌬/⌬ mutant exhibits enhanced growth in the presence of the azole antifungals versus wild-type (WT) controls, despite ergosterol depletion (9). We therefore examined plasma membrane integrity following azole treatment using a luciferasebased assay (15) to determine if the vps21⌬/⌬ mutant exhibited signs of membrane damage. A cytoplasmic version of nanoluciferase (Nluc; Promega Corp.) (23) was expressed in mutant and control strains (see Fig.…”

The vaginal mycobiome: A contemporary perspective on fungi in women's health and diseases

“…12,62 Mechanisms of immunoprotection are still debated, and the factors that trigger the transition from commensal to pathogenic yeast are still obscure. However, it is generally accepted that predispositions for Candida growth/invasion are niche specific 63,64 , though immune defects, breaches in epithelial integrity and microbial dysbiosis are common themes. 55 While many similarities exist between the mucosal environments of the mouth and vagina, the immunology of Candida vaginitis is undoubtedly distinct.…”

Phenotypic and genotypic characteristics of Candida albicans isolates from bloodstream and mucosal infections

“…In the context of differences between mucosal and invasive Candida infections, it is of interest to mention a recent study by Luna‐Tapia et al. , which indicated that ERG2 and ERG24 are required for pathogenicity of C. albicans in experimental mouse systemic infection but not vaginal. Another recent study by Moyes et al.…”

“…It is of interest that Price 25 reported that blood isolates produced much higher levels than isolates from wounds or urine. In the context of differences between mucosal and invasive Candida infections, it is of interest to mention a recent study by Luna-Tapia et al [49], which indicated that ERG2 and ERG24 are required for pathogenicity of C. albicans in experimental mouse systemic infection but not vaginal. Another recent study by Moyes et al [50] described a toxin, candidalysin, which is critical for mucosal infection and elucidates mucosal pathogenesis.…”