Key Takeaways & Executive Findings
- •• Identified a sub-cluster of Cryptococcus gattii VGI strains with distinct virulence profiles, highlighting the role of CAT2 in pathogenicity. • Demonstrated that CAT2 knockout increases susceptibility to oxidative stress and antifungal drugs, and reduces virulence in a mouse model. • Comparative transcriptomics revealed CAT2's involvement in oxidative stress response, metabolism, and sugar transport, providing mechanistic insights. • Findings suggest potential for genotype-specific targeted therapies against cryptococcosis caused by C. gattii VGI.
Abstract
Cryptococcus gattii causes cryptococcosis and life-threatening cryptococcal meningitis. Currently, the pathogenic virulence mechanisms of C. gattii remain a significant area of ongoing research with considerable unexplored aspects. On the basis of our established research, a sub-cluster of strains with independent evolutionary relationships from WM276 in the phylogenetic analysis of VGI-type strains is identified. In vivo infection experiments on this sub-branch of strains reveal that there are hypervirulent strains and hypovirulent strains among these strains, and the virulence differences are significant (P < 0.001). Bioinformatic interrogation of differentially expressed genes reveals that the catalase-encoding gene CGB_J0620W, CAT2, is a pivotal virulence-associated gene. The hypervirulent clinical isolate G4 (G4-WT) is selected as the parental strain, from which an isogenic CAT2-knockout mutant (cat2Δ) is constructed via homologous recombination, which shows increased sensitivity to oxidative stress, as well as growth defects in response to hyperosmosis, 5-fluorocytosine, fluconazole and amphotericin B. The cat2Δ::CAT2 strain exhibits phenotypic restoration to wild type (WT). In the mouse experiments, significant differences in survival (P < 0.001), pulmonary fungal burden (P < 0.01), and alveolar structural damage are observed between the WT and cat2Δ strains, which are completely different from C. neoformans. Moreover, comparative transcriptome analysis is performed on the WT and cat2Δ strains, which reveals that enzymes encoded by CAT2 may be involved in oxidative stress, metabolism and sugar transport. In conclusion, this study may explain the differences in virulence among different genetic evolutionary processes of a sub-cluster of the VGI geneotype of C. gattii and provide a theoretical basis for targeted therapy in a specific genotype population in the future.
1. Introduction
Cryptococcus gattii mainly infects immunocompetent populations, and its degree of harm is greater than that of C. neoformans. It is divided into four gene types: VGI, VGII, VGIII and VGIV. Among them, VGI-type strains are the main epidemic genotypes in China and even in Asia [1–3]. In the past, research on VGI-type strains has focused mainly on the standard strain WM276. However, in our previous studies [4], we found a sub-cluster of strains with independent evolutionary relationships from WM276 (eight strains in total) in the phylogenetic analysis of VGI-type strains.
To understand the key genes that cause virulence differences in these strains and the impact of these genes on strain cell function, pathogenesis in vivo, and transcription differences, we established an in vivo mouse model and conducted transcriptomic analysis on these strains to identify candidate virulence genes.
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Yemei Huang, Hengyu Deng, Xuelei Zang, Enqi Zhao, Yan Zhuo, Wencong He, Chen Wang, Yangyu Zhou, Jiahui Huang, Rui Liu, Tingyue Tian, Chen Yang, Jing Liu, Ping Zhang, Liye Zhang, Xinying Xue (2026). The catalase gene CAT2 and its role in the virulence of one sub-cluster of Cryptococcus gattii VGI clinical isolates. Acta Biochimica et Biophysica Sinica. https://doi.org/10.3724/abbs.2025170
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Frequently Asked Questions
What is the main finding of this study?
The study identifies the catalase gene CAT2 as a key virulence factor in a sub-cluster of Cryptococcus gattii VGI clinical isolates, showing that its deletion reduces virulence and increases susceptibility to oxidative stress and antifungal drugs.
How was the CAT2 gene studied?
The researchers constructed a CAT2 knockout mutant in a hypervirulent clinical isolate (G4) via homologous recombination and compared its phenotype, virulence in mice, and transcriptome with the wild-type strain.
What are the implications of this research?
The findings may explain virulence differences among C. gattii strains and provide a basis for developing targeted therapies for infections caused by specific genotypes.
What methods were used in the study?
The study used phylogenetic analysis, in vivo mouse infection models, gene knockout, phenotypic assays (oxidative stress, drug susceptibility), and comparative transcriptomics.
What is the significance of the CAT2 gene?
CAT2 encodes a catalase that helps the fungus combat oxidative stress, and its absence leads to reduced virulence and increased sensitivity to antifungal drugs, highlighting its potential as a therapeutic target.
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