Modulation of Immune Signaling and Metabolism Highlights Host and Fungal Transcriptional Responses in Mouse Models of Invasive Pulmonary Aspergillosis

Abstract

Incidences of invasive pulmonary aspergillosis, an infection caused predominantly by Aspergillus fumigatus, have increased due to the growing number of immunocompromised individuals. While A. fumigatus is reliant upon deficiencies in the host to facilitate invasive disease, the distinct mechanisms that govern the host-pathogen interaction remain enigmatic, particularly in the context of distinct immune modulating therapies. To gain insights into these mechanisms, RNA-Seq technology was utilized to sequence RNA derived from lungs of 2 clinically relevant, but immunologically distinct murine models of IPA on days 2 and 3 post inoculation when infection is established and active disease present. Our findings identify notable differences in host gene expression between the chemotherapeutic and steroid models at the interface of immunity and metabolism. RT-qPCR verified model specific and nonspecific expression of 23 immune-associated genes. Deep sequencing facilitated identification of highly expressed fungal genes. We utilized sequence similarity and gene expression to categorize the A. fumigatus putative in vivo secretome. RT-qPCR suggests model specific gene expression for nine putative fungal secreted proteins. Our analysis identifies contrasting responses by the host and fungus from day 2 to 3 between the two models. These differences may help tailor the identification, development, and deployment of host- and/or fungal-targeted therapeutics.

NLRX1 is a key regulator of immune signaling during invasive pulmonary aspergillosis

“…In our opinion this understanding is paramount to identifying viable host targeted therapeutics. We became interested in Nlrx1 due to it being amongst only a handful of Nlrs that we found to be differentially expressed during immuno-suppressive mouse models of IPA using the CEA10 isolate [28]. Nlrs, particularly those involved with the inflammasome, are important for a robust immune response to A. fumigatus [29][30][31].…”

“…The multiple mechanistic functionalities of Nlrx1 suggests it is a critical immuno-metabolic hub in controlling both immune signaling in response to pathogen and cellular dangers as well as reactive oxygen species production. Based on these findings and our prior RNA-Seq analysis [28], we became interested in Nlrx1 as a regulator of immune signaling in response to fungal infections, specifically invasive pulmonary aspergillosis.…”

Revealing virulence potential of clinical and environmental Aspergillus fumigatus isolates using Whole-genome sequencing

“…We show evidence that supports the observation that all fungi have the ability to cause disease and that members of the A. fumigatus species lack the sophisticated virulence factors, commonly used to describe differences in virulence in species of the bacterial kingdom, that could explain differences in their pathogenic traits (25,34). In order to define what makes a virulent A. fumigatus isolate many researchers have attempted characterizing different aspects of the fungus: differences in the colonial and spore color phenotype (25), the strain-dependent immunomodulatory properties induced in the host (25), the clinical or environmental source of the isolate (13, 25,26), the strains ability to adapt and grow in stressful conditions like low oxygen microenvironments where hypoxia fitness was strongly correlated with an increase in virulence (26), and the ability of the fungus to adjust its gene expression to survive in different immunosuppressive conditions inside the host (3). These are all aspects that influence how fit a strain will be to produce an infection and further research on the virulence of this microorganism should take all these aspects into consideration when characterizing an experimental and/or clinical strain.…”

“…Aspergillus fumigatus ( A. fumigatus ) is an opportunistic fungal pathogen that poses one of the major threats to immunocompromised individuals in the clinic. High risk patients include neutropenic patients, hematopoietic stem cell transplant recipients, patients receiving a prolonged steroid treatment and critically-ill patient in the intensive care unit (ICU) with chronic obstructive pulmonary disease (COPD), liver cirrhosis, viral infections or microbial sepsis (1–3). In the context of an impaired immune function, inhaled airborne spores of A. fumigatus will not be effectively eliminated and will remain in human airways to cause a range of infections that include allergic bronchopulmonary aspergillosis (ABPA), aspergilloma (chronic aspergillosis) and invasive aspergillosis (IA) (1,4).…”

Proteome analysis of bronchoalveolar lavage fluids reveals host and fungal proteins highly expressed during invasive pulmonary aspergillosis in mice and humans

“…Several of these proteins (M10, M13, M21) have previously been shown to be secreted in in vitro culture, and glutamate dehydrogenase (M9) was previously identified as antigenic protein. A signaling protein (M19) and pectate lyase E (M14) have not yet been identified in the fungal secretome but they both carry a signal peptide and were shown to be transcriptionally upregulated in vivo [9,33]. In contrast to murine samples, only few peptides matching fungal proteins were detectable in human BAL, possibly due to higher dilution.…”