Deletion of core septin geneaspBinAspergillus fumigatusresults in fungicidal activity of caspofungin
Authors: Busch Rebecca Jean , Doty Carson , Mills C. Allie , Latifi Flutur , Herring Laura E. , Konjufca Vjollca , Vargas-Muñiz José M 
Published: February 2025

Septins are a family of GTP-binding proteins found in many eukaryotic lineages. Although highly conserved throughout many eukaryotes, their functions vary across species. InAspergillus fumigatus, the etiological agent of invasive aspergillosis, septins participate in a variety of processes such as cell wall organization of conidia, septation, and response to cell wall stress. Previous studies determined that the ΔaspBstrain had a greater sensitivity to anti-cell wall drugs, especially the echinocandin caspofungin, yet mechanisms behind this augmented sensitivity are unknown. We performed cell viability staining of the deletion strains post-caspofungin exposure and found that the ΔaspA, ΔaspB, and ΔaspCstrains have significantly lower cell viability. Concomitant with the reduced viability, deletion strains are more susceptible to caspofungin on solid media. These results indicate that the septin cytoskeleton is important forA. fumigatussurvival in the presence of caspofungin. Due to the potential of improved therapeutic outcome, we followed up using a neutropenic murine model of invasive aspergillosis. Animals infected with the ΔaspBstrain and treated with caspofungin showed improved survival compared to the animals infected withakuBKU80wild-type or complemented strains. Additionally, histological analysis showed reduced fungal burden and inflammation in the ΔaspBinfected, caspofungin-treated group. Affinity purification coupled with quantitative proteomics identified proteins involved in the septin-dependent response to caspofungin, includng four candidate interactors involved in cell wall stress response. Deletion of these candidate genes resulted in increased susceptibility to caspofungin and moderately reduced viability post-drug exposure. Taken together, these data suggest that septin AspB contributes to the fungistatic response to caspofungin.

Author Summary

Invasive aspergillosis is a pulmonary disease caused by the fungusAspergillus fumigatusthat primarily occurs in immunocompromised patients. Invasive aspergillosis has a high mortality rate, ranging from 50-90%. Therapy options are limited due to few available drugs with fungicidal activity and growing global drug resistance. Treatment typically starts with triazoles, which target the fungal cell membrane. If unsuccessful, an echinocandin, which targets the cell wall, is given as a salvage therapy. Echinocandins, including caspofungin, are fungistatic againstA. fumigatus, slowing growth of the fungus rather than killing it. Due to this, echinocandins have a high therapeutic failure rate. Previous work suggests that deletion of the cytoskeletal septin genes increases sensitivity to caspofungin. Here we describe our finding that the septin genesaspA, aspB, andaspCare involved in the fungal response to caspofungin. Additionally, the deletion ofaspBresults in fungicidal activity of this otherwise fungistatic drug. These findings show promise for novel therapy options that block the septin-mediated response to caspofungin.