Candidiasis Cell Models for Research

Candidiasis is a fungal infection caused by Candida species, with Candida albicans being the most common. According to the WHO fungal priority pathogens list (2022), Candida auris is classified as critical priority, while Candida albicans and Candida glabrata are high priority. Global estimates suggest that invasive candidiasis affects over 250,000 people annually, with mortality rates exceeding 40% in bloodstream infections. Risk factors include immunosuppression, prolonged antibiotic use, central venous catheters, and diabetes. The NCI does not provide 5-year survival for candidiasis as it is an infectious disease, but invasive candidiasis mortality can reach 30-60% in hospitalized patients. The WHO reports that Candida species are among the leading causes of healthcare-associated bloodstream infections.

Candidiasis is an ideal model for mechanistic studies due to its well-characterized virulence factors, genetic tractability, and the availability of public datasets. Key subtypes include mucosal and invasive candidiasis, with species-specific differences in drug resistance. Open questions include the mechanisms of biofilm formation, host-pathogen interactions, and antifungal resistance. Public datasets such as those from NCBI GEO and the Candida Genome Database (CGD) provide transcriptomic and genomic data. The disease is amenable to gene-editing approaches to study gene function and drug targets.

Candidiasis is not a carcinogenic disease, but its pathogenesis involves several key pathways:

1. Morphogenesis and biofilm formation:

• • Yeast-to-hypha transition regulated by EFG1, CPH1, and RAS1.
• • Biofilm development involves ALS genes and extracellular matrix production.

2. Host immune evasion:

• • Masking of beta-glucan by mannoproteins.
• • Secretion of aspartyl proteases (SAPs) and phospholipases.

3. Antifungal resistance:

• • Efflux pumps (CDR1, CDR2, MDR1) overexpression.
• • Ergosterol biosynthesis pathway mutations (ERG11).

4. Metabolic adaptation:

• • Glyoxylate cycle and gluconeogenesis for survival in macrophages.

Data from COSMIC and ClinVar are not applicable as candidiasis is not a cancer. Data synthesized from NCBI and WHO reports.

Key signaling networks in Candida albicans pathogenesis include:

• • cAMP-PKA pathway:
• • Regulates morphogenesis and biofilm formation.
• • Components: Cyr1, Tpk1, Tpk2, Efg1.
• • MAPK pathway:
• • Controls hyphal development and stress response.
• • Components: Cst20, Hst7, Cek1, Cek2.
• • Rim101 pathway:
• • Regulates pH adaptation and virulence.
• • Components: Rim101, Rim8, Rim13.
• • Tor pathway:
• • Controls growth and nitrogen metabolism.
• • Target of rapamycin, inhibited by rapamycin.
• • Efflux pump regulation:
• • Tac1 and Mrr1 transcription factors regulate CDR1/CDR2 and MDR1.

Organoid advantages: 3D tissue models mimic host environment, allow study of biofilm formation and host-pathogen interactions, and enable high-throughput screening.

Animal models for candidiasis include:

• • Murine models:
• • Intravenous infection for disseminated candidiasis.
• • Oropharyngeal candidiasis in immunosuppressed mice.
• • Vaginal candidiasis in estrogen-treated mice.
• • Zebrafish models:
• • Allows real-time imaging of fungal invasion.
• • Galleria mellonella (wax moth) larvae:
• • Simple model for virulence and drug efficacy.
• • PDX models:
• • Not applicable as candidiasis is not a cancer.
• • GEMM (genetically engineered mouse models):
• • Knockout mice for immune genes (e.g., MyD88, CARD9) to study susceptibility.

CRISPR-Cas9 gene editing has revolutionized the study of Candida species. Isogenic lines with precise knockouts or knock-ins allow functional validation of virulence genes and drug targets. Examples include:

• • EFG1 knockout line: Generated by CRISPR in Candida albicans, shows defective hyphal formation and reduced virulence.
• • ERG11 point mutation knock-in line: Introduces azole resistance mutations (e.g., Y132F) for resistance studies.
• • Reporter lines: Expressing GFP under a hypha-specific promoter for high-throughput screening.

Commercially available, sequence-verified gene-edited cell models accelerate research by providing reproducible and validated tools. These models are available from commercial sources without naming specific companies. They enable drug discovery, target validation, and functional genomics.

Knockout and knock-in lines are used to validate gene function. For example, EFG1 knockout lines confirm its role in morphogenesis. CPH1 knockout lines show reduced biofilm formation. These models enable systematic screens to identify essential genes for growth and virulence.

Isogenic pairs (wild-type vs. mutant) are used in high-throughput screens to identify compounds that selectively inhibit resistant strains. For example, ERG11 mutant lines are used to test novel azoles. Resistance modeling with efflux pump knockouts helps identify inhibitors of CDR1/CDR2.

CRISPR synthetic lethality screens in Candida identify gene pairs that are essential only in specific genetic backgrounds, revealing potential drug targets. For example, screens in ERG11 mutant lines can identify collateral sensitivities. These approaches accelerate biomarker discovery for diagnostics and therapeutics.