Host Responses in an Ex Vivo Human Skin Model Challenged With Malassezia sympodialis

From Skin and Gut to the Brain: The Infectious Journey of the Human Commensal Fungus Malassezia and Its Neurological Consequences

The human mycobiome encompasses diverse communities of fungal organisms residing within the body and has emerged as a critical player in shaping health and disease. While extensive research has focused on the skin and gut mycobiome, recent investigations have pointed toward the potential role of fungal organisms in neurological disorders. Among those fungal organisms, the presence of the commensal fungus Malassezia in the brain has created curiosity because of its commensal nature and primary association with the human skin and gut. This budding yeast is responsible for several diseases, such as Seborrheic dermatitis, Atopic dermatitis, Pityriasis versicolor, Malassezia folliculitis, dandruff, and others. However recent findings surprisingly show the presence of Malassezia DNA in the brain and have been linked to diseases like Alzheimer's disease, Parkinson's disease, Multiple sclerosis, and Amyotrophic lateral sclerosis. The exact role of Malassezia in these disorders is unknown, but its ability to infect human cells, travel through the bloodstream, cross the blood-brain barrier, and reside along with the lipid-rich neuronal cells are potential mechanisms responsible for pathogenesis. This also includes the induction of pro-inflammatory cytokines, disruption of the blood-brain barrier, gut-microbe interaction, and accumulation of metabolic changes in the brain environment. In this review, we discuss these key findings from studies linking Malassezia to neurological disorders, emphasizing the complex and multifaceted nature of these cases. Furthermore, we discuss potential mechanisms through which Malassezia might contribute to the development of neurological conditions. Future investigations will open up new avenues for our understanding of the fungal gut-brain axis and how it influences human behavior. Collaborative research efforts among microbiologists, neuroscientists, immunologists, and clinicians hold promise for unraveling the enigmatic connections between human commensal Malassezia and neurological disorders.

Novel methodologies for host-microbe interactions and microbiome-targeted therapeutics in 3D organotypic skin models

BACKGROUND

Following descriptive studies on skin microbiota in health and disease, mechanistic studies on the interplay between skin and microbes are on the rise, for which experimental models are in great demand. Here, we present a novel methodology for microbial colonization of organotypic skin and analysis thereof.

RESULTS

An inoculation device ensured a standardized application area on the stratum corneum and a homogenous distribution of bacteria, while preventing infection of the basolateral culture medium even during prolonged culture periods for up to 2 weeks at a specific culture temperature and humidity. Hereby, host-microbe interactions and antibiotic interventions could be studied, revealing diverse host responses to various skin-related bacteria and pathogens.

CONCLUSIONS

Our methodology is easily transferable to a wide variety of organotypic skin or mucosal models and different microbes at every cell culture facility at low costs. We envision that this study will kick-start skin microbiome studies using human organotypic skin cultures, providing a powerful alternative to experimental animal models in pre-clinical research. Video Abstract.

Clinical characteristics and treatment outcomes of Pityrosporum folliculitis in immunocompetent patients

Pityrosporum folliculitis (PF) is a fungal acneiform disease of the hair follicles that often presents with pruritic papules and pustules on the upper body and face. This condition is commonly mistaken for acne vulgaris and can be distinguished from bacterial acne by the presence of fungal spores in the follicular lumen. Although studies have been performed to describe PF in cohorts, little work has been done to aggregate these data. Thus, the goal of this review is to describe the clinical characteristics and treatment outcomes of PF in immunocompetent patients. PubMed, Web of Science, and Embase were searched using the terms "Pityrosporum folliculitis" or "Malassezia folliculitis." All cohorts reporting PF characteristics in patients classified as immunocompetent were reviewed. A total of 15 studies were included. Majority of patients were male (64%) with the average age of presentation of 24.26 years. The most common locations of lesions were the chest (70%) and back/shoulders (69.2%). Pruritus was reported by the majority of patients (71.7%). Additionally, 40.5% of patients reported a history of unsuccessful treatment regimens. Treatment was most successful with an oral antifungal (92%), followed by a topical antifungal (81.6%). In conclusion, majority of patients with PF were younger males. Many patients were primarily treated incorrectly, suggesting the importance of proper diagnosis. PF may be distinguishable from acne vulgaris by the presence of pruritus or suggested when a new acneiform eruption develops following antibiotic therapy or immunosuppression. When properly diagnosed, majority of cases of PF achieve complete response with oral or topical antifungals.

Malassezia sympodialis Mala s 1 allergen is a potential KELCH protein that cross reacts with human skin

Malassezia are the dominant commensal yeast species of the human skin microbiota and are associated with inflammatory skin diseases, such as atopic eczema (AE). The Mala s 1 allergen of Malassezia sympodialis is a β-propeller protein, inducing both IgE and T-cell reactivity in AE patients. We demonstrate by immuno-electron microscopy that Mala s 1 is mainly located in the M. sympodialis yeast cell wall. An anti-Mala s 1 antibody did not inhibit M. sympodialis growth suggesting Mala s 1 may not be an antifungal target. In silico analysis of the predicted Mala s 1 protein sequence identified a motif indicative of a KELCH protein, a subgroup of β-propeller proteins. To test the hypothesis that antibodies against Mala s 1 cross-react with human skin (KELCH) proteins we examined the binding of the anti-Mala s 1 antibody to human skin explants and visualized binding in the epidermal skin layer. Putative human targets recognized by the anti-Mala s 1 antibody were identified by immunoblotting and proteomics. We propose that Mala s 1 is a KELCH-like β-propeller protein with similarity to human skin proteins. Mala s 1 recognition may trigger cross-reactive responses that contribute to skin diseases associated with M. sympodialis.

Malassezia: A Commensal, Pathogen, and Mutualist of Human and Animal Skin

Identified in the late nineteenth century as a single species residing on human skin, Malassezia is now recognized as a diverse genus comprising 18 species inhabiting not only skin but human gut, hospital environments, and even deep-sea sponges. All cultivated Malassezia species are lipid dependent, having lost genes for lipid synthesis and carbohydrate metabolism. The surging interest in Malassezia results from development of tools to improve sampling, culture, identification, and genetic engineering, which has led to findings implicating it in numerous skin diseases, Crohn disease, and pancreatic cancer. However, it has become clear that Malassezia plays a multifaceted role in human health, with mutualistic activity in atopic dermatitis and a preventive effect against other skin infections due to its potential to compete with skin pathogens such as Candida auris. Improved understanding of complex microbe-microbe and host-microbe interactions will be required to define Malassezia's role in human and animal health and disease so as to design targeted interventions.

Single Nucleotide Polymorphism of Dectin-1 Gene Associates with Atopic Dermatitis in Children

BACKGROUND: Atopic dermatitis (AD) is a chronic inflammatory skin disease with complex and multifactorial pathophysiology, involving elements of barrier dysfunction, alterations in cell-mediated immune responses, IgE sensitization, and environmental factors. This encourages the search for predictors of disease development among both genetic markers and environment. AIM: The aim of the study was to examine if genetic factors of Malassezia recognition, or Malassezia colonization may be related to IgE sensitization or to severity of AD. METHODS: The study included 106 patients with eczema and 103 healthy children. Specific IgE against Malassezia mix (m227) was analyzed in 51 patients using immunochemiluminescent method on the ImmunoCAP 100 (Thermo Fisher Scientific Inc., Phadia, Sweden). Genotyping for rs7309123 in Dectin-1 was performed using Real-time PCR. The level of colonization by Malassezia in the scale samples was determined by a real-time PCR assay. RESULTS: Increased IgE to Malassezia spp. was observed in 29,4% of children with eczema. Higher Malassezia spp. – specific IgE titer positively correlated with severity of AD, age of onset, head–neck type of AD, and a higher total IgE. GG genotype rs7309123 Dectin-1 is significantly more often found in the patients than in the control group, but no correlation with IgE sensitization to Malassezia was found. Malassezia restricta and M. globosa were predominant in patients and controls, with some predominance of M. globosa over M. restricta among patients. CONCLUSION: Sensitization to Malassezia, genetic markers in Dectin-1, and Malassezia colonization of the skin can be tools for studying the gene-environment interactions in the pathogenesis of AD.

The aryl hydrocarbon receptor at the forefront of host-microbe interactions in the skin: A perspective on current knowledge gaps and directions for future research and therapeutic applications

The skin is home to a community of skin microbiota including bacteria, viruses and fungi, which are widely accepted to be of importance for skin homeostasis but also associated with skin diseases. Detailed knowledge on the skin microbiota composition and its changes in a number of skin diseases is available. Yet, specific interactions between microbes and the host skin cells or how they communicate with each other are less well understood. To identify, understand and eventually therapeutically exploit causal relationships of microbial dysbiosis with disease, studies are required that address the receptors and mediators involved in host‐microbe interactions. In this perspective article, we provide an outlook on one of such receptors, namely the aryl hydrocarbon receptor (AHR). The AHR is well known for being a ligand‐activated transcription factor regulating the proliferation, differentiation and function of many cell types present in the skin. Its targeting by anti‐inflammatory therapeutics such as coal tar and Tapinarof is effective in atopic dermatitis and psoriasis. AHR signalling is activated upon binding of wide variety of small chemicals or ligands, including microbiota‐derived metabolites. New evidence has emerged pointing towards a key role for epidermal AHR signalling through skin microbiota‐derived metabolites. In response, AHR‐driven expression of antimicrobial peptides and stratum corneum formation may alter the skin microbiota composition. This a self‐perpetuating feedback loop calls for novel therapeutic intervention strategies for which we herein discuss the requirements in future mechanistic studies.