Biology subjects

Ross, B. S.

Publications and source records attributed to Ross, B. S..

7 recordsLinked to original sources

bioRxiv2026

Trans-Kingdom dsRNA Sensing: Aspergillus fumigatus Mycovirus Activates MDA5/MAVS Immunity and Limits Allergic Bronchopulmonary Aspergillosis

MDA5 is a cytosolic pattern-recognition receptor (PRR) that binds to double-stranded RNA (dsRNA) and subsequently interacts with the signaling adaptor protein MAVS to initiate the antiviral interferon (IFN) response. Our group previously demonstrated that MDA5 is essential for host resistance against the fungal pathogen, Aspergillus fumigatus. Although fungal dsRNA was sufficient to activate MDA5 signaling, the precise source of A. fumigatus dsRNA responsible for this MDA5-stimulating function remains unknown. Here, we demonstrate that the magnitude of the IFN-dependent antifungal response is A. fumigatus strain dependent. Unexpectedly, we found that A. fumigatus isolates infected with dsRNA mycoviruses triggered a more robust MAVS-dependent inflammatory response within alveolar macrophages. Furthermore, dsRNA mycovirus infection increased fungal susceptibility to antifungal killing without altering other A. fumigatus growth characteristics. Although dsRNA mycovirus infection did not alter virulence in an acute bronchopneumonia model of A. fumigatus infection, it significantly impaired virulence and improved disease parameters in a chronic model of allergic bronchopulmonary aspergillosis (ABPA). Collectively, these findings reveal a novel role for trans-kingdom interactions in driving the host antifungal IFN response and modulating virulence in chronic aspergillosis models.

immunology↗

bioRxiv2023

The Cystic Fibrosis treatment, Trikafta, affects growth, viability, and cell wall of Aspergillus fumigatus biofilms

People with Cystic Fibrosis (pwCF) commonly test positive for the pathogenic fungus, Aspergillus fumigatus, which is associated with a decline in lung function. Trikafta is a recently approved therapy for pwCF that improves quantity and function of the CFTR protein, however, it is not known how Trikafta affects microbial communities in the lung. Therefore, the aim of this study was to determine whether Trikafta directly affects A. fumigatus growth and biology. While Trikafta did not impact the viability of A. fumigatus conidia, treatment of A. fumigatus biofilms with Trikafta reduced overall biofilm biomass. This finding was associated with increased membrane permeability, decreased viability, and reduced metabolic activity following long-term treatment of biofilms. Trikafta-induced membrane permeability and biomass reduction was partially blocked with the calcium channel inhibitor Verapamil and fully blocked by the mammalian CFTR inhibitor GlyH-101. Trikafta-induced biomass reduction and metabolic activity was shown to be regulated by the High Osmolarity Glycerol (HOG) pathway gene sakA. Trikafta treatment also induced resistance to the cell wall stressor calcofluor white, susceptibility to the antifungal caspofungin, and decreased inflammatory responses from murine bone marrow cells. Collectively, these results reveal that Trikafta affects infection-relevant A. fumigatus biology and host-microbial interactions. IMPORTANCEPeople with Cystic Fibrosis (pwCF) commonly test positive for the pathogenic fungus, Aspergillus fumigatus, which is associated with a decline in lung function. Trikafta is a recently approved therapy for pwCF that improves quantity and function of the CFTR protein, however, it is not known how Trikafta affects microbial communities in the CF lung. Here we report that Trikafta has anti-fungal activity against the infection relevant form of A. fumigatus, termed biofilms. When exposed to Trikafta A. fumigatus biofilms lose their viability. In addition, exposure to Trikafta enhances the susceptibility of A. fumigatus biofilms to the clinically utilized anti-fungal drug caspofungin. These data suggest Trikafta impacts the cell wall of A. fumigatus and suggests the potential for using Trikafta to augment existing anti-fungal therapy.

microbiology↗

bioRxiv2021

Combined Pan-, Population-, and Phylo-Genomic Analysis of Aspergillus fumigatus Reveals Population Structure and Lineage-Specific Diversity

Aspergillus fumigatus is a deadly agent of human fungal disease, where virulence heterogeneity is thought to be at least partially structured by genetic variation between strains. While population genomic analyses based on reference genome alignments offer valuable insights into how gene variants are distributed across populations, these approaches fail to capture intraspecific variation in genes absent from the reference genome. Pan-genomic analyses based on de novo assemblies offer a promising alternative to reference-based genomics, with the potential to address the full genetic repertoire of a species. Here, we use a combination of population genomics, phylogenomics, and pan-genomics to assess population structure and recombination frequency, phylogenetically structured gene presence-absence variation, evidence for metabolic specificity, and the distribution of putative antifungal resistance genes in A. fumigatus. We provide evidence for three primary populations of A. fumigatus, structured by both gene variation (SNPs and indels) and distinct gene presence-absence variation with unique suites of accessory genes present exclusively in each clade. Accessory genes displayed functional enrichment for nitrogen and carbohydrate metabolism, suggesting that populations may be stratified by environmental niche specialization. Similarly, the distribution of antifungal resistance genes and resistance alleles were often structured by phylogeny. A. fumigatus demonstrated exceptionally high levels of recombination and one of the largest fungal pan-genomes reported to date including many genes unrepresented in the Af293 reference genome. These results highlight the inadequacy of relying on a single-reference genome-based approach for evaluating intraspecific variation, and the power of combined genomic approaches to elucidate population structure, genetic diversity, and putative ecological drivers of clinically relevant fungi.

genomics↗

bioRxiv2021

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

Aspergillus fumigatus isolates display significant heterogeneity in growth, virulence, pathology, and inflammatory potential in multiple murine models of invasive aspergillosis. Previous studies have linked the initial germination of a fungal isolate in the airways to the inflammatory and pathological potential; but the mechanism(s) regulating A. fumigatus germination in the airways are unresolved. To explore the genetic basis for divergent germination phenotypes, we utilized a serial passaging strategy in which we cultured a slow germinating strain (AF293) in a murine lung based medium for multiple generations. Through this serial passaging approach, a strain emerged with an increased germination rate that induces more inflammation than the parental strain (herein named Lung Homogenate Evolved (LH-EVOL)). We identified a potential loss of function allele of Afu5g08390 (sskA) in the LH-EVOL strain. The LH-EVOL strain had a decreased ability to induce the SakA-dependent stress pathway, similar to AF293 {Delta}sskA and CEA10. In support of the whole genome variant analyses, sskA, sakA, or mpkC loss of function strains in the AF293 parental strain increased germination both in vitro and in vivo. Since the airway surface liquid of the lungs contains low glucose levels, the relationship of low glucose concentration on germination of these mutant AF293 strains was examined; interestingly, in low glucose conditions the sakA pathway mutants exhibited an enhanced germination rate. In conclusion, A. fumigatus germination in the airways is regulated by SskA through the SakA MAPK pathway and drives enhanced disease initiation and inflammation in the lungs. IMPORTANCEAspergillus fumigatus is an important human fungal pathogen particularly in immunocompromised individuals. Initiation of growth by A. fumigatus in the lung is important for its pathogenicity in murine models. However, our understanding of what regulates fungal germination in the lung environment is lacking. Through a serial passage experiment using lung-based medium, we identified a new strain of A. fumigatus which has increased germination potential and inflammation in the lungs. Using this serially passaged strain we found it had a decreased ability to mediate signaling through the osmotic stress response pathway. This finding was confirmed using genetic null mutants demonstrating that the osmotic stress response pathway is critical for regulating growth in the murine lungs. Our results contribute to the understanding of A. fumigatus adaptation and growth in the host lung environment.

microbiology↗

bioRxiv2021

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

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 pbs2C2 allele 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. ImportanceAspergillus fumigatus infection causes a spectrum of clinical manifestations. For individuals with Cystic Fibrosis (CF), Allergic Bronchopulmonary Aspergillosis (ABPA) is an established complication, but there is a growing appreciation for A. fumigatus airway persistence in CF disease progression. There currently is little consensus for clinical management of A. fumigatus long-term culture positivity in CF. A better understanding of A. fumigatus pathogenesis mechanisms in CF is expected to yield insights into when antifungal therapies are warranted. Here, a 4.5-year longitudinal collection of A. fumigatus isolates identified a persistent lineage that harbors a unique allele of the Pbs2 MAPKK necessary for unique CF-relevant stress phenotypes. Importantly for A. fumigatus CF patient diagnostics, this allele provides increased CF lung fitness at a cost of reduced in vitro growth in standard laboratory conditions. These data illustrate a molecular mechanism for A. fumigatus CF lung persistence with implications for diagnostics and antifungal therapy.

microbiology↗

bioRxiv2021

Antifungal activity of Propranolol against Fusarium keratitis isolates from the Mycotic Ulcer Treatment Trial (MUTT) and the United States.

SYNOPSISO_ST_ABSBackgroundC_ST_ABSFusarium keratitis is an infection of the cornea that often results in corneal perforation requiring corneal transplantation even with topical ocular antifungal therapy. The polyene natamycin remains the current antifungal of choice for Fusarium keratitis, but prompt sterilization of the cornea is often not achieved with contemporary therapy. Recently, natamycin synergy with the beta-adrenergic antagonist timolol against Fusarium species was reported. ObjectiveOur objective in this study was to characterize the in vitro antifungal effects of additional beta-adrenergic antagonists alone or in combination with natamycin on Fusarium keratitis isolates from the Mycotic Ulcer Treatment Trial (MUTT) and USA. MethodsMicrobroth dilution assays were used to determine the minimal inhibitory concentration (MIC) of beta-adrenergic antagonists against 18 Fusarium spp. keratitis (10 from MUTT, 8 from USA) and 3 Aspergillus fumigatus isolates. The fractional inhibitory concentration index (FICI) was calculated to assess interactions with natamycin. ResultsMost beta-blockers did not show antifungal activity or synergy with natamycin with the exception of propranolol. A racemic mix of propranolol had fungicidal activity with MIC between 31 and 83 g/mL for the Fusarium isolates. The MIC of the less cardioactive R enantiomer was lower (27-83 g/mL) than the MIC of the S enantiomer (42-104 g/mL). The MICs of both propranolol and natamycin were lower in combination but were not synergistic. The MIC of propranolol was 156 g/mL for the A. fumigatus isolates. ConclusionsPropranolol has intrinsic in vitro fungicidal activity and lowers the MIC of natamycin. Both the R and S enantiomers of propranolol had antifungal activity with the MIC modestly but significantly lower for R-propranolol. These findings have relevance both for the treatment of fungal keratitis and of glaucoma in the setting of fungal keratitis. Further study of propranolols antifungal activity may lead to a novel treatment for fungal keratitis and possibly other fungal infections. Trial RegistrationClinicalTrials.gov Identifier: NCT00997035 (MUTT Trial)

microbiology↗

bioRxiv2020

Strain specific persistence in the murine lung of Aspergillus fumigatus conidia causes an Allergic Broncho-Pulmonary Aspergillosis-like disease phenotype

Aspergillus fumigatus is a filamentous fungus which can cause multiple diseases in humans. Allergic Broncho-pulmonary Aspergillosis (ABPA) is a disease diagnosed primarily in Cystic Fibrosis patients caused by a severe allergic response often to long-term A. fumigatus colonization in the lungs. Mice develop an allergic response to repeated inhalation of A. fumigatus spores; however, no strains have been identified that can survive long-term in the mouse lung and cause ABPA-like disease. We characterized A. fumigatus strain W72310 by whole genome sequencing and in vitro and in vivo viability assays in comparison to a common reference strain, CEA10. W72310 was resistant to leukocyte-mediated killing and persisted in the mouse lung longer than CEA10, a phenotype that correlated with greater resistance to oxidative stressors, hydrogen peroxide and menadione, in vitro. In animals both sensitized and challenged with W72310, conidia, but not hyphae, were viable in the lungs for up to 21 days in association with eosinophilic airway inflammation, airway leakage, serum IgE, and mucus production. W72310-sensitized mice that were recall-challenged with conidia had increased inflammation, Th1 and Th2 cytokines, and airway leakage compared to controls. Collectively, our studies demonstrate that a unique strain of A. fumigatus resistant to leukocyte killing can persist in the mouse lung in conidial form and elicit features of ABPA-like disease. IMPORTANCEAllergic Broncho-pulmonary Aspergillosis (ABPA) patients often present with long-term colonization of Aspergillus fumigatus. Current understanding of ABPA pathogenesis has been complicated by a lack of long-term in vivo fungal persistence models. We have identified a clinical isolate of A. fumigatus, W72310, which persists in the murine lung and causes an ABPA-like disease phenotype. Surprisingly, while viable, W72310 showed little to no growth beyond the conidial stage in the lung. This indicates that it is possible that A. fumigatus can cause allergic disease in the lung without any significant hyphal growth. The identification of this strain of A. fumigatus can not only be used to better understand disease pathogenesis of ABPA and potential anti-fungal treatments, but also to identify features of fungal strains that drive long-term fungal persistence in the lung. Consequently, these observations are a step toward helping resolve the long-standing question when to utilize antifungal therapies in patients with ABPA and fungal allergic type diseases.

microbiology↗