The Aspergillus fumigatus Mismatch Repair MSH2 Homolog Is Important for Virulence and Azole Resistance

Abstract

The genetic stability of every living organism depends on accurate DNA replication and repair systems. Here, we investigated the Aspergillus fumigatus MSH2 mismatch repair (MMR) gene MshA and how it impacts virulence and the evolution of azole resistance. We examined mshA gene variation in 62 environmental and clinical A. fumigatus strains. We have observed 12 strains with variants (18.2%), and 8 strains among them showed missense variants. We demonstrated that A. fumigatus mshA null mutants are haploid and have conserved karyotypes with discrete gross chromosomal rearrangements. The ΔmshA strains are not sensitive to several DNA-damaging agents. The lack of mshA caused a significant reduction of virulence of A. fumigatus in a neutropenic murine model of invasive pulmonary aspergillosis and in the invertebrate alternative model Galleria mellonella. Wild-type and ΔmshA populations did not show any significant changes in drug resistance acquisition after they were transferred 10 times in minimal medium in the absence of any stress. However, these populations rapidly acquired virulence in the ΔmshA background and high levels of resistance to posaconazole in the presence of this drug (at least 200-fold-higher levels of resistance than those derived from the wild-type strain). Taken together, these results suggest that genetic instability caused by ΔmshA mutations can confer an adaptive advantage, mainly increasing posaconazole resistance and virulence acquisition. IMPORTANCE Invasive aspergillosis (IA) has emerged as one of the most common life-threatening fungal diseases in immunocompromised patients, with mortality rates as high as 90%. Systemic fungal infections such as IA are usually treated with triazoles; however, epidemiological research has shown that the prevalence of azole-resistant Aspergillus fumigatus isolates has increased significantly over the last decade. There is very little information about the importance of genomic stability for A. fumigatus population structure, azole resistance, and virulence. Here, we decided to investigate whether the mismatch repair system could influence A. fumigatus azole resistance and virulence, focusing on one of the components of this system, MSH2. Although the mutation frequency of mshA (the A. fumigatus MSH2 homologue) is low in environmental and clinical isolates, our results indicate that loss of mshA function can provide increased azole resistance and virulence when selected for. These results demonstrate the importance of genetic instability in A. fumigatus as a possible mechanism of evolving azole resistance and establishing fitness in the host.

Drug-Resistant Fungi: An Emerging Challenge Threatening Our Limited Antifungal Armamentarium

“…New studies implicating various cellular components and pathways involved in azole resistance resulted in significant advances on the topic of azole resistance in A . fumigatus [ 148 , 149 , 150 , 151 ].…”

Antifungal Agents in Agriculture: Friends and Foes of Public Health

“…They showed that exposing Aspergillus flavus to azoles changed the sensitivity of the fungus to the antifungals itraconazole, voriconazole, and posaconazole, evidencing the development of resistant phenotypes, and constituting the first case report of antifungal resistance induced by azole exposure. Dos Reis et al [101] investigated the Aspergillus fumigatus MSH2 mismatch repair (MMR) gene mshA and its impact on virulence and evolution of azole resistance [101]. The mshA mutant A. fumigatus strain showed significantly reduced virulence in a neutropenic murine model of invasive pulmonary aspergillosis.…”

The Quiet and Underappreciated Rise of Drug-Resistant Invasive Fungal Pathogens

“…These compensatory mechanisms orchestrate a rapid and appropriate response to stress, allowing the cell to "buy time" to acquire mutations in critical genes and/or undertake gross chromosomal changes, consequently leading to permanent resistance [31,32]. The acquisition of such mutations in genes associated with resistance may occur in the presence of specific mutations/absence of DNA repair mechanisms, such as mismatch repair (MSH2), resulting in increased antifungal tolerance and virulence [32,33]. Of note, the link between MSH2, in vitro tolerance, and clinical tolerance is uncertain [34,35].…”