Strategies of Candida albicans and Candida glabrata to exit from macrophages

• Applicants: Dr. Sascha Brunke; Professor Dr. Bernhard Hube
• Subject Area: Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 446404928

Infections by the two medically most important Candida species, C. albicans and C. glabrata, are normally controlled by phagocytes. However, both species have convergently evolved strategies to exit host cells: C. albicans escapes from macrophages via hypha formation and kills host cells within hours after phagocytosis. In contrast, C. glabrata cannot form hyphae, but proliferates as yeast cells and escapes macrophages after a days-long intracellular existence. Furthermore, while C. albicans triggers a significant inflammatory response, C. glabrata does not cause any obvious immune activation. Data from the first funding period led us to develop a model with two distinct, critical phases for the exit of C. albicans from macrophages: Exit is initiated in an early, short phagosomal stage, which is characterized by a specific trigger that leads to hypha formation as the exclusive intracellular growth mode. A late cytosolic stage, which follows phagosomal damage (and escape), is characterized by access to cytosolic nutrients and pyroptotic and non-pyroptotic host cell death. In contrast, the phagosomal stage of yeast-locked C. albicans cells and of C. glabrata is much longer. Fungal fitness and persistence factors as well as intracellular storages of biotin and other nutrients allow intraphagosomal survival and proliferation of C. glabrata. This replication employs a persistence stage, supporting the view that C. glabrata can use macrophages as "Trojan Horses" to avoid immune surveillance. While the actual exit mechanisms still eludes us, we have now identified protein kinases to be central for escape after the late intracellular proliferation. These refined models and our additional data from the first funding period are the basis for our work programme for the next funding period. We will continue our project with (a) an investigation into the precise and still unknown triggers for C. albicans hypha formation inside macrophages, (b) an examination on how intracellular C. albicans and C. glabrata cells mobilize or acquire nutrients, and (c) the identification and characterization of fungal and host factors associated with intraphagosomal growth, phagosomal and host cell damage, and finally host cell killing and exit. We will use a range of well-established methods, including in vitro infection of primary human macrophages and cell lines, microscopic imaging, transcriptional profiling as well as molecular biology approaches to generate Candida mutants and to screen available large-scale mutant libraries. We will perform phenotypic screenings and follow additional cell biology approaches in collaboration with national and international partners. In continuation of our successful collaborations with partners of SPP 2225, we will analyse programmed cell death pathways in depth. Results will be compared to other organisms investigated within SPP 2225 to identify conserved and fungal-specific mechanism which allow the escape from macrophages.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2225: Exit strategies of intracellular pathogens