Biology subjects

Brown Harding, H.

Publications and source records attributed to Brown Harding, H..

3 recordsLinked to original sources

bioRxiv2025

Extracellular vesicles from diverse fungal pathogens induce species-specific and endocytosis-dependent immunomodulation

Microbial pathogens generate extracellular vesicles (EVs) for intercellular communication and quorum sensing. Microbial EVs also induce inflammatory pathways within host innate immune cells. We previously demonstrated that EVs secreted by Candida albicans trigger type I interferon signaling in host cells specifically via the cGAS-STING innate immune signaling pathway. Here, we show that despite sharing similar properties of morphology and internal DNA content, the interactions between EVs and the innate immune system differ according to the parental fungal species. EVs secreted by C. albicans, Saccharomyces cerevisiae, Cryptococcus neoformans, and Aspergillus fumigatus are endocytosed at different rates by murine macrophages triggering varied cytokine responses, innate immune signaling, and subsequent immune cell recruitment. Notably, cell wall constituents that decorate C. neoformans and A. fumigatus EVs inhibit efficient internalization by macrophages and dampen innate immune activation. Our data uncover the transcriptional and functional consequences of the internalization of diverse fungal EVs by immune cells and reveal novel insights into the early innate immune response to distinct clinically significant fungal pathogens.

microbiology↗

bioRxiv2024

Single-cell analysis of human airway epithelium identifies cell type-specific responses to Aspergillus and Coccidioides

Respiratory fungal infections pose a significant threat to human health. Animal models do not fully recapitulate human disease, necessitating advanced models to study human-fungal pathogen interactions. In this study, we utilized primary human airway epithelial cells (hAECs) to recapitulate the lung environment in vitro and investigate cellular responses to two diverse, clinically significant fungal pathogens, Aspergillus fumigatus and Coccidioides posadasii. To understand the mechanisms of early pathogenesis for both fungi, we performed single-cell RNA sequencing of infected hAECs. Analysis revealed that both fungi induced cellular stress and cytokine production. However, the cell subtypes affected and specific pathways differed between fungi, with A. fumigatus and C. posadasii triggering protein-folding-related stress in ciliated cells and hypoxia responses in secretory cells, respectively. This study represents one of the first reports of single-cell transcriptional analysis of hAECs infected with either A. fumigatus or C. posadasii, providing a vital dataset to dissect the mechanism of disease and potentially identify targetable pathways. ImportanceFungal infections in the lungs are dreaded complications for those with compromised immune systems and have limited treatment strategies available. These options are restricted further by the increased prevalence of treatment-resistant fungi. Many studies focus on how our immune systems respond to these pathogens, yet airway epithelial cells remain an understudied component of fungal infections in the lungs. Here, the authors provide a transcriptional analysis of primary human airway epithelial cells stimulated by two distinct fungal pathogens, Aspergillus fumigatus and Coccidioides posadasii. These data will enable further mechanistic studies of the contribution of the airway epithelium to initial host responses and represent a powerful new resource for investigators.

immunology↗

bioRxiv2024

Malassezia responds to environmental pH signals through the conserved Rim/Pal pathway

During mammalian colonization and infection, microorganisms must be able to rapidly sense and adapt to changing environmental conditions including alterations in extracellular pH. The fungus-specific Rim/Pal signaling pathway is one process that supports microbial adaptation to alkaline pH. This cascading series of interacting proteins terminates in the proteolytic activation of the highly conserved Rim101/PacC protein, a transcription factor that mediates microbial responses that favor survival in neutral/alkaline pH growth conditions, including many mammalian tissues. We identified the putative Rim pathway proteins Rim101 and Rra1 in the human skin colonizing fungus Malassezia sympodialis. Gene deletion by transconjugation and homologous recombination revealed that Rim101 and Rra1 are required for M. sympodialis growth at higher pH. Additionally, comparative transcriptional analysis of the mutant strains compared to wild-type suggested mechanisms for fungal adaptation to alkaline conditions. These pH-sensing signaling proteins are required for optimal growth in a murine model of atopic dermatitis, a pathological condition associated with increased skin pH. Together these data elucidate both conserved and phylum-specific features of microbial adaptation to extracellular stresses. ImportanceThe ability to adapt to host pH has been previously associated with microbial virulence in several pathogenic fungal species. Here we demonstrate that a fungal-specific alkaline response pathway is conserved in the human skin commensal fungus Malassezia sympodialis (Ms). This pathway is characterized by the pH-dependent activation of the Rim101/PacC transcription factor that controls cell surface adaptations to changing environmental conditions. By disrupting genes encoding two predicted components of this pathway, we demonstrated that the Rim/Pal pathway is conserved in this fungal species as a facilitator of alkaline pH growth. Moreover, targeted gene mutation and comparative transcriptional analysis supports the role of the Ms Rra1 protein as a cell surface pH sensor conserved within the basidiomycete fungi, a group including plant and human pathogens. Using an animal model of atopic dermatitis, we demonstrate the importance of Ms Rim/Pal signaling in this common inflammatory condition characterized by increased skin pH.

microbiology↗