Biology subjects

Ruchti, F.

Publications and source records attributed to Ruchti, F..

5 recordsLinked to original sources

bioRxiv2024

Card9 and MyD88 differentially regulate Th17 immunity to the commensal yeast Malassezia in the murine skin

The fungal community of the skin microbiome is dominated by a single genus, Malassezia. Besides its symbiotic lifestyle at the host interface, this commensal yeast has also been associated with diverse inflammatory skin diseases in humans and pet animals. Stable colonization is maintained by antifungal type 17 immunity. The mechanisms driving Th17 responses to Malassezia remain, however, unclear. Here, we show that the C-type lectin receptors Mincle, Dectin-1, and Dectin-2 recognize conserved patterns in the cell wall of Malassezia and induce dendritic cell activation in vitro, while only Dectin-2 is required for Th17 activation during experimental skin colonization in vivo. In contrast, Toll-like receptor recognition was redundant in this context. Instead, inflammatory IL-1 family cytokines signaling via MyD88 were also implicated in Th17 activation in a T cell-intrinsic manner. Taken together, we characterized the pathways contributing to protective immunity against the most abundant member of the skin mycobiome. This knowledge contributes to the understanding of barrier immunity and its regulation by commensals and is relevant considering how aberrant immune responses are associated with severe skin pathologies.

immunology↗

bioRxiv2023

γδ T cells respond directly and selectively to the skin commensal yeast Malassezia for IL-17-dependent fungal control.

Stable microbial colonization of the skin depends on tight control by the host immune system. The lipid-dependent yeast Malassezia typically colonizes skin as a harmless commensal and is subject to host type 17 immunosurveillance, but this fungus has also been associated with diverse skin pathologies in both humans and animals. Using a murine model of Malassezia exposure, we show that V{gamma}4+ dermal {gamma}{delta} T cells expand rapidly and are the major source of IL-17A mediating fungal control in colonized skin. A pool of memory-like Malassezia-responsive V{gamma}4+ T cells persisted in the skin, were enriched in draining lymph nodes even after fungal clearance, and were protective upon fungal re-exposure up to several weeks later. Induction of {gamma}{delta}T17 immunity depended on IL-23 and IL-1 family cytokine signalling, whereas Toll-like and C-type lectin receptors were dispensable. Furthermore, V{gamma}4+ T cells from Malassezia-exposed hosts were able to respond directly and selectively to Malassezia-derived ligands, independently of antigen-presenting host cells. Reactivity of human {gamma}{delta} T cells against Malassezia spp. confirmed the relevance of this fungus-specific response across different host species. The fungal moieties detected were shared across diverse species of the Malassezia genus, but not conserved in other Basidiomycota or Ascomycota. These data provide novel mechanistic insight into the induction and maintenance of type 17 immunosurveillance of skin commensal colonization that has significant implications for cutaneous health. AUTHOR SUMMARYMalassezia is the most abundant fungus living on our skin and is usually harmless, but this microbe has also been shown to play a role in pathological conditions such as eczema and dermatitis. Here, we investigated how a population of V{gamma}4+ {gamma}{delta} T cells protect mouse skin against fungal overgrowth. While generally considered part of the innate immune system, we found that {gamma}{delta} T cells were maintained long after Malassezia was cleared from the skin of experimentally-infected animals. These cells displayed memory-like features and were highly efficient at fighting the fungus after a secondary challenge. We observed that classic fungal pattern recognition receptors were not involved, and that antigen-presenting cells were not required to generate Malassezia-protective {gamma}{delta} T cells. Finally, we confirmed that {gamma}{delta} T cells can recognise Malassezia, both in mice and human hosts. The fungal structure that triggers these responses was highly specific to Malassezia and was not conserved among other fungi. Our results highlight for the first time an important role for {gamma}{delta} T cells in preventing uncontrolled growth of the most abundant skin fungus. These findings have implications for several Malassezia-associated pathologies including eczema, dermatitis, and potentially even cancer.

immunology↗

bioRxiv2023

Epidermal barrier dysregulation in atopic skin predisposes for excessive growth of the allergy-associated yeast Malassezia

The skin barrier is vital for protection against environmental threats including insults caused by skin-resident microbes. Dysregulation of the barrier is a hallmark of atopic dermatitis (AD) and ichthyosis, with variable consequences for host immune control of colonizing commensals and opportunistic pathogens. While sensitisation to Malassezia, the most abundant commensal fungus of the skin, is common in AD, its relevance for pathogenesis remains unclear. Here we show that in barrier-disrupted skin, Malassezia acquires enhanced fitness. This is not a consequence of the dysregulated allergic immune status characteristic for AD but is rather explained by structural and metabolic changes in the cutaneous niche that provide increased accessibility and a favourable lipid profile, to which the lipid-dependent yeast adapts for enhanced nutrient assimilation. These findings reveal fundamental insights into the role of the mycobiota in the pathogenesis of common skin barrier disorders.

microbiology↗

bioRxiv2020

Horizontal gene transfer in the human and skin commensal Malassezia: a bacterially-derived flavohemoglobin is required for NO resistance and host interaction

The skin of humans and animals is colonized by commensal and pathogenic fungi and bacteria that share this ecological niche and have established microbial interactions. Malassezia are the most abundant fungal skin inhabitant of warm-blooded animals, and have been implicated in skin diseases and systemic disorders, including Crohns disease and pancreatic cancer. Flavohemoglobin is a key enzyme involved in microbial nitrosative stress resistance and nitric oxide degradation. Comparative genomics and phylogenetic analyses within the Malassezia genus revealed that flavohemoglobin-encoding genes were acquired through independent horizontal gene transfer events from different donor bacteria that are part of the mammalian microbiome. Through targeted gene deletion and functional complementation in M. sympodialis, we demonstrated that bacterially-derived flavohemoglobins are cytoplasmic proteins required for nitric oxide detoxification and nitrosative stress resistance under aerobic conditions. RNAseq analysis revealed that endogenous accumulation of nitric oxide resulted in upregulation of genes involved in stress response, and downregulation of the MalaS7 allergen-encoding genes. Solution of the high-resolution X-ray crystal structure of Malassezia flavohemoglobin revealed features conserved with both bacterial and fungal flavohemoglobins. In vivo pathogenesis is independent of Malassezia flavohemoglobin. Lastly, we identified additional 30 genus- and species-specific horizontal gene transfer candidates that might have contributed to the evolution of this genus as the most common inhabitants of animal skin. Significance statementMalassezia species are the main fungal components of the mammalian skin microbiome and are associated with a number of skin disorders. Recently, Malassezia has also been found in association with Crohns Disease and with pancreatic cancer. The elucidation of the molecular bases of skin adaptation by Malassezia is critical to understand its role as commensal and pathogen. In this study we employed evolutionary, molecular, biochemical, and structural analyses to demonstrate that the bacterially-derived flavohemoglobins acquired by Malassezia through horizontal gene transfer resulted in a gain of function critical for nitric oxide detoxification and resistance to nitrosative stress. Our study underscores horizontal gene transfer as an important force modulating Malassezia evolution and niche adaptation.

microbiology↗

bioRxiv2019

A novel mycovirus evokes transcriptional rewiring in Malassezia and provokes host inflammation and an immunological response

Mycoviruses infect fungi, and while most persist asymptomatically, there are examples of mycoviruses having both beneficial and detrimental effects on their host. Virus-infected Saccharomyces and Ustilago strains exhibit a killer phenotype conferring a growth advantage over uninfected strains and other competing yeast species, whereas hypovirus-infected Cryphonectria parasitica displays defects in growth, sporulation, and virulence. In this study we identify a dsRNA mycovirus in five Malassezia species. Sequence analysis reveals it to be a totivirus with two dsRNA segments: a larger 4.5 kb segment with genes encoding components for viral replication and maintenance, and a smaller 1.4 kb segment encoding a novel protein. Furthermore, RNA-seq of virus-infected versus virus-cured Malassezia sympodialis revealed an upregulation of dozens of ribosomal components in the cell, suggesting the virus modifies the transcriptional and translational landscapes of the cell. Given that Malassezia is the most abundant fungus on human skin, we assessed the impact of the mycovirus in a murine epicutaneous infection model. Although infection with virus-infected strains was not associated with an increased inflammatory response, we did observe enhanced skin colonization in one of two virus-infected M. sympodialis strains. Noteworthy, interferon-{beta} expression was significantly upregulated in bone marrow-derived macrophages when challenged with virus-infected, compared to virus-cured M. sympodialis, suggesting that the presence of the virus can induce an immunological response. Although many recent studies have illuminated how widespread mycoviruses are, there are relatively few in-depth studies about their impact on disease caused by the host fungus. We describe here a novel mycovirus in Malassezia and its possible implications in pathogenicity. ImportanceMalassezia species represent the most common fungal inhabitant of the mammalian skin microbiome, and are natural skin commensal flora. However, these fungi are also associated with a variety of clinical skin disorders. Recent studies have reported associations of Malassezia with Crohns disease and pancreatic cancer, further implicating this fungal genus in inflammatory and neoplastic disease states. Because M. sympodialis has lost genes involved in RNAi, we hypothesized Malassezia could harbor dsRNA mycoviruses. Indeed, we identified a novel mycovirus of the totivirus family in several Malassezia species, and characterized the MsMV1 mycovirus of M. sympodialis. We found conditions that lead to curing of the virus, and analyzed isogenic virus-infected/virus-cured strains to determine MsMV1 genetic and pathogenic impacts. MsMV1 induces a strong overexpression of transcription factors and ribosomal genes, while downregulating cellular metabolism. Moreover, MsMV1 induced a significantly higher level of interferon-{beta} expression in cultured macrophages. This study sheds light on the mechanisms of pathogenicity of Malassezia, focusing on a previously unidentified novel mycovirus.

microbiology↗