Aspergillus fumigatusIn-Host HOG pathway mutation for Cystic Fibrosis Lung Microenvironment Persistence

Abstract

The prevalence of Aspergillus fumigatus colonization in individuals with Cystic Fibrosis (CF) and subsequent fungal persistence in the lung is increasingly recognized. However, there is no consensus for clinical management of A. fumigatus in CF individuals, due largely to uncertainty surrounding A. fumigatus CF pathogenesis and virulence mechanisms. To address this gap in knowledge, a longitudinal series of A. fumigatus isolates from an individual with CF were collected over 4.5 years. Isolate genotypes were defined with whole genome sequencing that revealed both transitory and persistent A. fumigatus in the lung. Persistent lineage isolates grew most readily in a low oxygen culture environment and conidia were more sensitive to oxidative stress inducing conditions compared to non-persistent isolates. Closely related persistent isolates harbor a unique allele of the high osmolarity glycerol (HOG) pathway mitogen activated protein kinase kinase, Pbs2 (pbs2C2). Data suggest this novel pbs2C2allele arose in vivo and is necessary for the fungal response to osmotic stress in a low oxygen environment through hyperactivation of the HOG (SakA) signaling pathway. Hyperactivation of the HOG pathway through pbs2C2 comes at the cost of decreased conidia stress resistance in the presence of atmospheric oxygen levels. These novel findings shed light on pathoadaptive mechanisms of A. fumigatus in CF, lay the foundation for identifying persistent A. fumigatus isolates that may require antifungal therapy, and highlight considerations for successful culture of persistent fungal CF isolates.

Host lung environment limits Aspergillus fumigatus germination through a SskA-dependent signaling response

“…Each strain was grown in GMM media for 30 hours at 37°C before being transferred to either GMM or GMM supplemented with 1M NaCl for 30 minutes. We choose to examine sakA expression itself, as well as SakA-dependent transcripts ptpA, gpdA , and pbsB which are highly upregulated in AF293 but not in AF293 Δ sakA following osmotic stress with 1M NaCl 13,47 . Transcript levels of sakA, ptpA, gpdA , and pbsB were all increased to a significantly greater extent in parental strain AF293 as opposed to LH-EVOL and AF293 Δ sakA when exposed to 1M NaCl (Figure 4D).…”

“…Consequently, SakA could be particularly important for A. fumigatus to adapt to the cystic fibrosis (CF) lung environment where there is increased oxidative stress 57 and ASL glucose concentrations can be 10 times higher than healthy adults 16 . Ross et al (2021) demonstrated a distinct relationship between activation of the SakA pathway and adaptation by A. fumigatus to the lung environment in a CF patient 47 . In that study, PbsB, an intermediary kinase between SskA and SakA, was found to have a missense mutation that resulted in increased SakA activity in response to osmotic stress 47 .…”

“…Ross et al (2021) demonstrated a distinct relationship between activation of the SakA pathway and adaptation by A. fumigatus to the lung environment in a CF patient 47 . In that study, PbsB, an intermediary kinase between SskA and SakA, was found to have a missense mutation that resulted in increased SakA activity in response to osmotic stress 47 . These data suggest a potentially important and distinct relationship between SakA activity in A. fumigatus in response to nutritional and oxidative stressors in the pulmonary environment, which may be critical to understanding disease initiation and progression within both acute and chronic models of aspergillosis.…”