Extracellular Vesicles From Sporothrix brasiliensis Are an Important Virulence Factor That Induce an Increase in Fungal Burden in Experimental Sporotrichosis

In Vitro Interaction Between Yeast Extracellular Vesicles and Human Monocyte-Derived Dendritic Cells

Extracellular vesicles (EVs) are lipid-bound particles produced by a wide variety of cells from different biological species. EVs can carry molecules, such as nucleic acids and metabolites, and are involved in cell functioning, communication, and signaling. Recent literature reported that pathogenic or commensal yeast strains can produce EVs targeting the host's immune system and exerting immunomodulatory actions. In humans, yeast EVs can be endocytosed by dendritic cells (DCs), characterized by phagocyting and migrating capabilities with the role of capturing antigens to present to T lymphocytes, triggering the immune response. Physiological or disease-associated immunosenescence impairs both DC functionality and gut microbiota; thus investigating the interaction between commensal microorganisms and the host's immune system would help elucidate the impact of aging on the immune system-microbiota interplay. We hereby present a protocol for the incubation of in vitro-generated human monocyte-derived DCs with EVs purified from different yeast strains isolated from fermented milk. The protocol includes flow cytometry analysis on DC activation markers and endocytosis assay.

Extracellular vesicles from virulent P. brasiliensis induce TLR4 and dectin-1 expression in innate cells and promote enhanced Th1/Th17 response

Extracellular vesicles (EVs) are membrane-enclosed nanoparticles that transport several biomolecules and are involved in important mechanisms and functions related to the pathophysiology of fungal diseases. EVs from Paracoccidioides brasiliensis, the main causative agent of Paracoccidioidomycosis (PCM), modulate the immune response of macrophages. In this study, we assessed the EVs proteome from a virulent P. brasiliensis isolated from granulomatous lesions and compared their immunomodulatory ability with EVs isolated from the fungus before the animal passage (control EVs) when challenging macrophages and dendritic cells (DCs). Proteome showed that virulent EVs have a higher abundance of virulence factors such as GP43, protein 14-3-3, GAPDH, as well as virulence factors never described in PCM, such as aspartyl aminopeptidase and a SidJ analogue compared with control EVs. Virulent extracellular vesicles induced higher expression of TLR4 and Dectin-1 than control EVs in macrophages and dendritic cells (DCs). In opposition, a lower TLR2 expression was induced by virulent EVs. Additionally, virulent EVs induced lower expression of CD80, CD86 and TNF-α, but promoted a higher expression of IL-6 and IL-10, suggesting that EVs isolated from virulent P. brasiliensis-yeast promote a milder DCs and macrophage maturation. Herein, we showed that EVs from virulent fungi stimulated a higher frequency of Th1/Tc1, Th17, and Treg cells, which gives new insights into fungal extracellular vesicles. Taken together, our results suggest that P. brasiliensis utilizes its EVs as virulence bags that manipulate the immune system in its favour, creating a milder immune response and helping with fungal evasion from the immune system.

Overview of extracellular vesicles in pathogens with special focus on human extracellular protozoan parasites

Extracellular vesicles (EVs) are lipid-bilayered membrane-delimited particles secreted by almost any cell type, involved in different functions according to the cell of origin and its state. From these, cell to cell communication, pathogen-host interactions and modulation of the immune response have been widely studied. Moreover, these vesicles could be employed for diagnostic and therapeutic purposes, including infections produced by pathogens of diverse types; regarding parasites, the secretion, characterisation, and roles of EVs have been studied in particular cases. Moreover, the heterogeneity of EVs presents challenges at every stage of studies, which motivates research in this area. In this review, we summarise some aspects related to the secretion and roles of EVs from several groups of pathogens, with special focus on the most recent research regarding EVs secreted by extracellular protozoan parasites.

Fungal Extracellular Vesicle Proteins with Potential in Biological Interaction

Extracellular vesicles (EVs) are vesicle-like structures composed of lipid bilayers, which can be divided into apoptotic bodies, microbubbles and exosomes. They are nanoparticles used for the exchange of information between cells. EVs contains many substances, including protein. With the development of proteomics, we know more about the types and functions of protein in vesicles. The potential functions of proteins in the envelope are mainly discussed, including cell wall construction, fungal virulence transmission, signal transmission and redox reactions, which provides a new perspective for studying the interaction mechanism between fungi and other organisms. The fungal protein markers of EVs are also summarized, which provided an exploration tool for studying the mechanism of vesicles. In addition, the possible role of immune protein in the EVs in the treatment of human diseases is also discussed, which provides new ideas for vaccine development.

Extracellular Vesicles from Scedosporium apiospermum Mycelial Cells: Implication for Fungal-Host Interplays

The release of extracellular vesicles (EVs) has been implicated as an alternative transport mechanism for the passage of macromolecules through the fungal cell wall, a phenomenon widely reported in yeasts but poorly explored in mycelial cells. In the present work, we have purified and characterized the EVs released by mycelia of the emerging, opportunistic, widespread and multidrug-resistant filamentous fungus Scedosporium apiospermum. Transmission electron microscopy images and light scattering measurements revealed the fungal EVs, which were observed individually or grouped with heterogeneous morphology, size and electron density. The mean diameter of the EVs, evaluated by the light scattering technique, was 179.7 nm. Overall, the structural stability of S. apiospermum EVs was preserved during incubation under various storage conditions. The lipid, carbohydrate and protein contents were quantified, and the EVs' protein profile was evidenced by SDS-PAGE, revealing proteins with molecular masses ranging from 20 to 118 kDa. Through immunoblotting, ELISA and immunocytochemistry assays, antigenic molecules were evidenced in EVs using a polyclonal serum (called anti-secreted molecules) from a rabbit inoculated with conditioned cell-free supernatant obtained from S. apiospermum mycelial cells. By Western blotting, several antigenic proteins were identified. The ELISA assay confirmed that the anti-secreted molecules exhibited a positive reaction up to a serum dilution of 1:3200. Despite transporting immunogenic molecules, S. apiospermum EVs slightly induced an in vitro cytotoxicity effect after 48 h of contact with either macrophages or lung epithelial cells. Interestingly, the pretreatment of both mammalian cells with purified EVs significantly increased the association index with S. apiospermum conidia. Furthermore, EVs were highly toxic to Galleria mellonella, leading to larval death in a typically dose- and time-dependent manner. Collectively, the results represent the first report of detecting EVs in the S. apiospermum filamentous form, highlighting a possible implication in fungal pathogenesis.

The multiple frontiers in the study of extracellular vesicles produced by fungi

The production of extracellular vesicles (EVs) by fungi has been recognized for about a decade. Here we discuss the roles played by fungal EVs in biofilm formation, antifungal resistance, and release of immunogens with vaccine potential. We also explore their significance in promoting international collaboration and understanding of fungal biology.

Traversing the Cell Wall: The Chitinolytic Activity of Histoplasma capsulatum Extracellular Vesicles Facilitates Their Release

Histoplasma capsulatum is the causative agent of histoplasmosis. Treating this fungal infection conventionally has significant limitations, prompting the search for alternative therapies. In this context, fungal extracellular vesicles (EVs) hold relevant potential as both therapeutic agents and targets for the treatment of fungal infections. To explore this further, we conducted a study using pharmacological inhibitors of chitinase (methylxanthines) to investigate their potential to reduce EV release and its subsequent impact on fungal virulence in an in vivo invertebrate model. Our findings revealed that a subinhibitory concentration of the methylxanthine, caffeine, effectively reduces EV release, leading to a modulation of H. capsulatum virulence. To the best of our knowledge, this is the first reported instance of a pharmacological inhibitor that reduces fungal EV release without any observed fungicidal effects.

Immunomodulatory Potential of Fungal Extracellular Vesicles: Insights for Therapeutic Applications

Extracellular vesicles (EVs) are membranous vesicular organelles that perform a variety of biological functions including cell communication across different biological kingdoms. EVs of mammals and, to a lesser extent, bacteria have been deeply studied over the years, whereas investigations of fungal EVs are still in their infancy. Fungi, encompassing both yeast and filamentous forms, are increasingly recognized for their production of extracellular vesicles (EVs) containing a wealth of proteins, lipids, and nucleic acids. These EVs play pivotal roles in orchestrating fungal communities, bolstering pathogenicity, and mediating interactions with the environment. Fungal EVs have emerged as promising candidates for innovative applications, not only in the management of mycoses but also as carriers for therapeutic molecules. Yet, numerous questions persist regarding fungal EVs, including their mechanisms of generation, release, cargo regulation, and discharge. This comprehensive review delves into the present state of knowledge regarding fungal EVs and provides fresh insights into the most recent hypotheses on the mechanisms driving their immunomodulatory properties. Furthermore, we explore the considerable potential of fungal EVs in the realms of medicine and biotechnology. In the foreseeable future, engineered fungal cells may serve as vehicles for tailoring cargo- and antigen-specific EVs, positioning them as invaluable biotechnological tools for diverse medical applications, such as vaccines and drug delivery.

Fungal extracellular vesicle-mediated regulation: from virulence factor to clinical application

Invasive fungal disease (IFD) poses a significant threat to immunocompromised patients and remains a global challenge due to limited treatment options, high mortality and morbidity rates, and the emergence of drug-resistant strains. Despite advancements in antifungal agents and diagnostic techniques, the lack of effective vaccines, standardized diagnostic tools, and efficient antifungal drugs contributes to the ongoing impact of invasive fungal infections (IFI). Recent studies have highlighted the presence of extracellular vesicles (EVs) released by fungi carrying various components such as enzymes, lipids, nucleic acids, and virulence proteins, which play roles in both physiological and pathological processes. These fungal EVs have been shown to interact with the host immune system during the development of fungal infections whereas their functional role and potential application in patients are not yet fully understood. This review summarizes the current understanding of the biologically relevant findings regarding EV in host-pathogen interaction, and aim to describe our knowledge of the roles of EV as diagnostic tools and vaccine vehicles, offering promising prospects for the treatment of IFI patients.

The characterization of RNA-binding proteins and RNA metabolism-related proteins in fungal extracellular vesicles

RNA-binding proteins (RBPs) are essential for regulating RNA metabolism, stability, and translation within cells. Recent studies have shown that RBPs are not restricted to intracellular functions and can be found in extracellular vesicles (EVs) in different mammalian cells. EVs released by fungi contain a variety of proteins involved in RNA metabolism. These include RNA helicases, which play essential roles in RNA synthesis, folding, and degradation. Aminoacyl-tRNA synthetases, responsible for acetylating tRNA molecules, are also enriched in EVs, suggesting a possible link between these enzymes and tRNA fragments detected in EVs. Proteins with canonical RNA-binding domains interact with proteins and RNA, such as the RNA Recognition Motif (RRM), Zinc finger, and hnRNP K-homology (KH) domains. Polyadenylate-binding protein (PABP) plays a critical role in the regulation of gene expression by binding the poly(A) tail of messenger RNA (mRNA) and facilitating its translation, stability, and localization, making it a key factor in post-transcriptional control of gene expression. The presence of proteins related to the RNA life cycle in EVs from different fungal species suggests a conserved mechanism of EV cargo packing. Various models have been proposed for selecting RNA molecules for release into EVs. Still, the actual loading processes are unknown, and further molecular characterization of these proteins may provide insight into the mechanism of RNA sorting into EVs. This work reviews the current knowledge of RBPs and proteins related to RNA metabolism in EVs derived from distinct fungi species, and presents an analysis of proteomic datasets through GO term and orthology analysis, Our investigation identified orthologous proteins in fungal EVs on different fungal species.

The State of the Art in Transcriptomics and Proteomics of Clinically Relevant Sporothrix Species

Proteomics provide a robust approach to profile and quantify proteins within cells, organs, or tissues, providing comprehensive insights about the dynamics of cellular processes, modifications, and interactions. Similarly, understanding the transcriptome is essential to decipher functional elements of the genome, unraveling the mechanisms of disease development and the molecular constituents of cells and tissues. Some thermodimorphic fungi of the genus Sporothrix cause sporotrichosis, a subcutaneous mycosis of worldwide relevance. The transcriptome and proteome of the main Sporothrix species of clinical interest can elucidate the mechanisms underlying pathogenesis and host interactions. Studies of these techniques can contribute to the advancement of novel diagnostic and therapeutic strategies. A literature review was carried out, addressing all articles based on proteomics using mass spectrometry and transcriptomics of Sporothrix spp. Twenty-one studies were eligible for this review. The main findings include proteins and genes involved in dimorphism, cell differentiation, thermotolerance, virulence, immune evasion, metabolism, cell adhesion, cell transport, and biosynthesis. With the spread and emergence of sporotrichosis in different countries, ongoing research efforts and new discoveries are welcome to advance knowledge about this mycosis and its agents.

The emerging role of extracellular vesicles in fungi: a double-edged sword

Fungi are eukaryotic microorganisms found in nature, which can invade the human body and cause tissue damage, inflammatory reactions, organ dysfunctions, and diseases. These diseases can severely damage the patient's body systems and functions, leading to a range of clinical symptoms that can be life-threatening. As the incidence of invasive fungal infections has progressively increased in the recent years, a wealth of evidence has confirmed the "double-edged sword" role of fungal extracellular vesicles (EVs) in intercellular communication and pathogen-host interactions. Fungal EVs act as mediators of cellular communication, affecting fungal-host cell interactions, delivering virulence factors, and promoting infection. Fungal EVs can also have an induced protective effect, affecting fungal growth and stimulating adaptive immune responses. By integrating recent studies, we discuss the role of EVs in fungi, providing strong theoretical support for the early prevention and treatment of invasive fungal infections. Finally, we highlight the feasibility of using fungal EVs as drug carriers and in vaccine development.

Extracellular vesicles derived from Talaromyces marneffei contain immunogenic compounds and modulate THP-1 macrophage responses

Pathogenic eukaryotes including fungi release extracellular vesicles (EVs) which are composed of a variety of bioactive components, including peptides, nucleic acids, polysaccharides, and membrane lipids. EVs contain virulence-associated molecules suggesting a crucial role of these structures in disease pathogenesis. EVs derived from the pathogenic yeast phase of Talaromyces (Penicillium) marneffei, a causative agent of systemic opportunistic mycoses "talaromycosis," were studied for their immunogenic components and immunomodulatory properties. Some important virulence factors in EVs including fungal melanin and yeast phase specific mannoprotein were determined by immunoblotting. Furthermore, fluorescence microscopy revealed that T. marneffei EVs were internalized by THP-1 human macrophages. Co-incubation of T. marneffei EVs with THP-1 human macrophages resulted in increased levels of supernatant interleukin (IL)-1β, IL-6 and IL-10. The expression of THP-1 macrophage surface CD86 was significantly increased after exposed to T. marneffei EVs. These findings support the hypothesis that fungal EVs play an important role in macrophage "classical" M1 polarization. T. marneffei EVs preparations also increased phagocytosis, suggesting that EV components stimulate THP-1 macrophages to produce effective antimicrobial compounds. In addition, T. marneffei EVs stimulated THP-1 macrophages were more effective at killing T. marneffei conidia. These results indicate that T. marneffei EVs can potently modulate macrophage functions, resulting in the activation of these innate immune cells to enhance their antimicrobial activity.

Mass Spectrometry Analysis Reveals Lipids Induced by Oxidative Stress in Candida albicans Extracellular Vesicles

Candida albicans is a commensal fungus in healthy humans that causes infection in immunocompromised individuals through the secretion of several virulence factors. The successful establishment of infection is owing to elaborate strategies to cope with defensive molecules secreted by the host, including responses toward oxidative stress. Extracellular vesicle (EV) release is considered an alternative to the biomolecule secretory mechanism that favors fungal interactions with the host cells. During candidiasis establishment, the host environment becomes oxidative, and it impacts EV release and cargo. To simulate the host oxidative environment, we added menadione (an oxidative stress inducer) to the culture medium, and we explored C. albicans EV metabolites by metabolomics analysis. This study characterized lipidic molecules transported to an extracellular milieu by C. albicans after menadione exposure. Through Liquid Chromatography coupled with Mass Spectrometry (LC-MS) analyses, we identified biomolecules transported by EVs and supernatant. The identified molecules are related to several biological processes, such as glycerophospholipid and sphingolipid pathways, which may act at different levels by tuning compound production in accordance with cell requirements that favor a myriad of adaptive responses. Taken together, our results provide new insights into the role of EVs in fungal biology and host-pathogen interactions.

Isolation and characterization of extracellular vesicles from Fusarium oxysporum f. sp. cubense, a banana wilt pathogen

Fusarium wilt of banana is a destructive widespread disease caused by Fusarium oxysporum f. sp. cubense (Foc) that ravaged banana plantations globally, incurring huge economic losses. Current knowledge demonstrates the involvement of several transcription factors, effector proteins, and small RNAs in the Foc-banana interaction. However, the precise mode of communication at the interface remains elusive. Cutting-edge research has emphasized the significance of extracellular vesicles (EVs) in trafficking the virulent factors modulating the host physiology and defence system. EVs are ubiquitous inter- and intra-cellular communicators across kingdoms. This study focuses on the isolation and characterization of Foc EVs from methods that make use of sodium acetate, polyethylene glycol, ethyl acetate, and high-speed centrifugation. Isolated EVs were microscopically visualized using Nile red staining. Further, the EVs were characterized using transmission electron microscopy, which revealed the presence of spherical, double-membrane, vesicular structures ranging in size from 50 to 200 nm (diameter). The size was also determined using the principle based on Dynamic Light Scattering. The Foc EVs contained proteins that were separated using SDS-PAGE and ranged between 10 and 315 kDa. Mass spectrometry analysis revealed the presence of EV-specific marker proteins, toxic peptides, and effectors. The Foc EVs were found to be cytotoxic, whose toxicity increased with EVs isolated from the co-culture preparation. Taken together, a better understanding of Foc EVs and their cargo will aid in deciphering the molecular crosstalk between banana and Foc.

Extracellular Vesicles from Candida haemulonii var. vulnera Modulate Macrophage Oxidative Burst

Members of the Candida haemulonii species complex are multidrug-resistant emergent yeast pathogens able to cause superficial and invasive infections in risk populations. Fungal extracellular vesicles (EVs) play a critical role in the pathogenicity and virulence of several species and may perform essential functions during infections, such as carrying virulence factors that behave in two-way communications with the host, affecting survival and fungal resistance. Our study aimed to describe EV production from Candida haemulonii var. vulnera and evaluate whether murine macrophage RAW 264.7 cells respond to their stimuli by generating an oxidative response after 24 h. For this purpose, reactive oxygen species detection assays demonstrated that high concentrations of yeast and EVs (10¹⁰ particles/mL) of Candida haemulonii did not change macrophage viability. However, the macrophages recognized these EVs and triggered an oxidative response through the classical NOX-2 pathway, increasing O₂^•- and H₂O₂ levels. However, this stress did not cause lipid peroxidation in the RAW 264.7 cells and neither lead to the activation of the COX-2-PGE₂ pathway. Thus, our data suggest that low concentrations of C. haemulonii EVs are not recognized by the classical pathway of the oxidative burst generated by macrophages, which might be an advantage allowing the transport of virulence factors via EVs, not identified by the host immune system that could work as fine tube regulators during infections caused by C. haemulonii. In contrast, C. haemulonii var. vulnera and high EV concentrations activated microbicidal actions in macrophages. Therefore, we propose that EVs could participate in the virulence of the species and that these particles could be a source of antigens to be exploited as new therapeutic targets.

Aspergillus fumigatus Extracellular Vesicles Display Increased Galleria mellonella Survival but Partial Pro-Inflammatory Response by Macrophages

Fungal extracellular vesicles (EVs) mediate intra- and interspecies communication and are critical in host-fungus interaction, modulating inflammation and immune responses. In this study, we evaluated the in vitro pro- and anti-inflammatory properties of Aspergillus fumigatus EVs over innate leukocytes. A. fumigatus EVs induced a partial proinflammatory response by macrophages, characterized by increased tumor necrosis factor-alpha production, and increased gene expression of induced nitric oxide synthase and adhesion molecules. EVs induce neither NETosis in human neutrophils nor cytokine secretion by peripheral mononuclear cells. However, prior inoculation of A. fumigatus EVs in Galleria mellonella larvae resulted in increased survival after the fungal challenge. Taken together, these findings show that A. fumigatus EVs play a role in protection against fungal infection, although they induce a partial pro-inflammatory response.

SUR7 deletion in Candida albicans impacts extracellular vesicle features and delivery of virulence factors

Extracellular vesicles (EVs) from human fungal pathogens have been implicated in fungal virulence, yet little is known about their role in the host-pathogen interaction. Progress has been hampered by the lack of a specific marker for fungal EVs that can be used to monitor EV isolation and tracking in biological systems. Here we report the effect of a SUR7 gene knockout on the production, properties, and role of EVs in the virulence of Candida albicans. Sur7 is a component of the membrane compartment of Can1 (MCC) complex and is enriched in the EVs from C. albicans and other fungal species. MCC is a plasma membrane complex which together with the eisosome, a cytoplasmic protein complex, is a key regulator in plasma membrane organisation and plasma membrane associated processes. The SUR7 knockout strain produces smaller EVs than the wild-type (WT) with different protein and carbohydrate cargos. Furthermore, proteins with known roles in Candida pathogenesis were present in WT EVs and absent or diminished in the sur7Δ EVs. We demonstrate that the reduced virulence of the sur7Δ cells can be partially restored with EVs from a WT strain. These findings demonstrate the importance of Sur7-like proteins in the biogenesis of EVs in fungi and enhance our understanding of the role of fungal EVs in human pathogenesis.

Exosomes: from biology to immunotherapy in infectious diseases

Exosomes are extracellular vesicles derived from the endosomal compartment, which are released by all kinds of eukaryotic and prokaryotic organisms. These vesicles contain a variety of biomolecules that differ both in quantity and type depending on the origin and cellular state. Exosomes are internalized by recipient cells, delivering their content and thus contributing to cell-cell communication in health and disease. During infections exosomes may exert a dual role, on one hand, they can transmit pathogen-related molecules mediating further infection and damage, and on the other hand, they can protect the host by activating the immune response and reducing pathogen spread. Selective packaging of pathogenic components may mediate these effects. Recently, quantitative analysis of samples by omics technologies has allowed a deep characterization of the proteins, lipids, RNA, and metabolite cargoes of exosomes. Knowledge about the content of these vesicles may facilitate their therapeutic application. Furthermore, as exosomes have been detected in almost all biological fluids, pathogenic or host-derived components can be identified in liquid biopsies, making them suitable for diagnosis and prognosis. This review attempts to organize the recent findings on exosome composition and function during viral, bacterial, fungal, and protozoan infections, and their contribution to host defense or to pathogen spread. Moreover, we summarize the current perspectives and future directions regarding the potential application of exosomes for prophylactic and therapeutic purposes.

The RNA Content of Fungal Extracellular Vesicles: At the “Cutting-Edge” of Pathophysiology Regulation

The role of extracellular vesicles (EVs) in interkingdom communication is widely accepted, and their role in intraspecies communication has been strengthened by recent research. Based on the regulation promoted by EV-associated molecules, the interactions between host and pathogens can reveal different pathways that ultimately affect infection outcomes. As a great part of the regulation is ascribable to RNA contained in EVs, many studies have focused on profiling RNAs in fungal and host EVs, tracking their accumulation during infection, and identifying potential target genes. Herein, we overview the main classes of RNA contained in fungal EVs and the biological processes regulated by these molecules, portraying a state-of-the-art picture of RNAs loaded in fungal EVs, while also raising several questions to drive future investigations. Our compiled data show unambiguously that EVs act as key elements in signaling pathways, and play a crucial role in pathosystems. A complete understanding of the processes that govern RNA content loading and trafficking, and its effect on recipient cells, will lead to improved technologies to ward off infectious agents that threaten human health.

Bioinformatics strategies for studying the molecular mechanisms of fungal extracellular vesicles with a focus on infection and immune responses

Fungal extracellular vesicles (EVs) are released during pathogenesis and are found to be an opportunistic infection in most cases. EVs are immunocompetent with their host and have paved the way for new biomedical approaches to drug delivery and the treatment of complex diseases including cancer. With computing and processing advancements, the rise of bioinformatics tools for the evaluation of various parameters involved in fungal EVs has blossomed. In this review, we have complied and explored the bioinformatics tools to analyze the host-pathogen interaction, toxicity, omics and pathogenesis with an array of specific tools that have depicted the ability of EVs as vector/carrier for therapeutic agents and as a potential theme for immunotherapy. We have also discussed the generation and pathways involved in the production, transport, pathogenic action and immunological interactions of EVs in the host system. The incorporation of network pharmacology approaches has been discussed regarding fungal pathogens and their significance in drug discovery. To represent the overview, we have presented and demonstrated an in silico study model to portray the human Cryptococcal interactions.

Candida albicans Hyphal Extracellular Vesicles Are Different from Yeast Ones, Carrying an Active Proteasome Complex and Showing a Different Role in Host Immune Response

Candida albicans is the principal causative agent of lethal fungal infections, predominantly in immunocompromised hosts. Extracellular vesicles (EVs) have been described as crucial in the interaction of microorganisms with their host. Since the yeast-to-hypha transition is an important virulence trait with great impact in invasive candidiasis (IC), we have addressed the characterization of EVs secreted by hyphal cells (HEVs) from C. albicans, comparing them to yeast EVs (YEVs). YEVs comprised a larger population of bigger EVs with mainly cell wall proteins, while HEVs were smaller, in general, and had a much higher protein diversity. YEVs were able to rescue the sensitivity of a cell wall mutant against calcofluor white, presumably due to the larger amount of cell wall proteins they contained. On the other hand, HEVs also contained many cytoplasmic proteins related to protein metabolism and intracellular protein transport and the endosomal sorting complexes required for transport (ESCRT) pathway related to exosome biogenesis, pointing to an intracellular origin of HEVs. Interestingly, an active 20S proteasome complex was secreted exclusively in HEVs. Moreover, HEVs contained a greater number of virulence-related proteins. As for their immunogenic role, both types of EV presented immune reactivity with human sera from patients suffering invasive candidiasis; however, under our conditions, only HEVs showed a cytotoxic effect on human macrophages and could elicit the release of tumor necrosis factor alpha (TNF-α) by these macrophages. IMPORTANCE This first analysis of HEVs of C. albicans has shown clear differences between them and the YEVs of C. albicans, showing their relevance and possible use in the discovery of new diagnostic markers and treatment targets against C. albicans infections. The data obtained point to different mechanisms of biogenesis of YEVs and HEVs, as well as different involvements in cell biology and host interaction. YEVs played a more relevant role in cell wall maintenance, while HEVs were more closely related to virulence, as they had greater effects on human immune cells. Importantly, an active 20S proteosome complex was described as a fungal-EV cargo. A deeper study of its role and those of many other proteins exclusively detected in HEVs and involved in different relevant biological processes of this fungus could open up interesting new areas of research in the battle against C. albicans.

Pathogenicity and Growth Conditions Modulate Fonsecaea Extracellular Vesicles' Ability to Interact With Macrophages

Chromoblastomycosis (CBM) is a chronic cutaneous and subcutaneous mycosis caused by black, dimorphic, and filamentous fungi of the Herpothrichiellaceae family, such as species of the genus Fonsecaea. These fungi can switch between the saprophytic forms (conidia and hyphae) and the pathogenic form, the muriform cells (MCs), which is considered an essential mechanism for fungal virulence. Nearly all types of cells can produce membranous structures formed by a lipid bilayer that communicate extracellularly with other cells, known as "extracellular vesicles" (EVs), which may act as virulence factors, as observed for several species of pathogenic fungi. Our findings demonstrated for the first time that F. pedrosoi, F. nubica, and F. erecta produce EVs in response to nutritional conditions. The EVs varied in sterol and protein contents, size, and morphology. Moreover, the EVs induced different cytokine and nitric oxide release patterns by bone marrow-derived macrophages (BMDMs). The EVs activated IL-1β production, possibly acting as the first signal in inflammasome activation. Unlike the pathogenic species, the EVs isolated from F. erecta did not significantly stimulate TNF and IL-10 production in general. Overall, these results demonstrated that different species of Fonsecaea produce EVs capable of modulating pro- and anti-inflammatory cytokine and nitric oxide production by BMDMs and that growth conditions affected the immunomodulatory capacities of the EVs as well as their size, content, and morphology.

Pre-Exposure With Extracellular Vesicles From Aspergillus fumigatus Attenuates Inflammatory Response and Enhances Fungal Clearance in a Murine Model Pulmonary Aspergillosis

Aspergillus fumigatus is a ubiquitous and saprophytic filamentous fungus and the main etiologic agent of aspergillosis. Infections caused by A. fumigatus culminate in a strong inflammatory response that can evolve into respiratory failure and may be lethal in immunocompromised individuals. In the last decades, it has been demonstrated that extracellular vesicles (EVs) elicit a notable biological response in immune cells. EVs carry a variety of biomolecules, therefore are considered potential antigen delivery vehicles. The role of EVs as a strategy for modulating an effective response against infections caused by A. fumigatus remains unexplored. Here we investigate the use of EVs derived from A. fumigatus as an immunization tool to induce a more robust immune response to A. fumigatus pulmonary infection. In order to investigate that, male C57BL/6 mice were immunized with two doses of EVs and infected with A. fumigatus. Pre-exposure of mice to EVs was able to induce the production of specific IgG serum for fungal antigens. Besides that, the immunization with EVs reduced the neutrophilic infiltrate into the alveoli, as well as the extravasation of total proteins and the production of proinflammatory mediators IL-1β, IL-6, and CXCL-1. In addition, immunization prevented extensive lung tissue damage and also improved phagocytosis and fungus clearance. Noteworthy, immunization with EVs, associated with subclinical doses of Amphotericin B (AmB) treatment, rescued 50% of mice infected with A. fumigatus from lethal fungal pneumonia. Therefore, the present study shows a new role for A. fumigatus EVs as host inflammatory response modulators, suggesting their use as immunizing agents.

The development of extracellular vesicle markers for the fungal phytopathogen Colletotrichum higginsianum

Fungal phytopathogens secrete extracellular vesicles (EVs) associated with enzymes and phytotoxic metabolites. While these vesicles are thought to promote infection, defining the true contents and functions of fungal EVs, as well as suitable protein markers, is an ongoing process. To expand our understanding of fungal EVs and their possible roles during infection, we purified EVs from the hemibiotrophic phytopathogen Colletotrichum higginsianum, the causative agent of anthracnose disease in multiple plant species, including Arabidopsis thaliana. EVs were purified in large numbers from the supernatant of protoplasts but not the supernatant of intact mycelial cultures. We purified two separate populations of EVs, each associated with over 700 detected proteins, including proteins involved in vesicle transport, cell wall biogenesis and the synthesis of secondary metabolites. We selected two SNARE proteins (Snc1 and Sso2) and one 14-3-3 protein (Bmh1) as potential EV markers and generated transgenic strains expressing fluorescent fusions. Each marker was confirmed to be protected inside EVs. Fluorescence microscopy was used to examine the localization of each marker during infection on Arabidopsis leaves. These findings further our understanding of EVs in fungal phytopathogens and will help build an experimental system to study EV interkingdom communication between plants and fungi.

Extracellular Vesicles Regulate Biofilm Formation and Yeast-to-Hypha Differentiation in Candida albicans

In this study, we investigated the influence of fungal extracellular vesicles (EVs) during biofilm formation and morphogenesis in Candida albicans. Using crystal violet staining and scanning electron microscopy (SEM), we demonstrated that C. albicans EVs inhibited biofilm formation in vitro. By time-lapse microscopy and SEM, we showed that C. albicans EV treatment stopped filamentation and promoted pseudohyphae formation with multiple budding sites. The ability of C. albicans EVs to regulate dimorphism was further compared to EVs isolated from different C. albicans strains, Saccharomyces cerevisiae, and Histoplasma capsulatum. C. albicans EVs from distinct strains inhibited yeast-to-hyphae differentiation with morphological changes occurring in less than 4 h. EVs from S. cerevisiae and H. capsulatum modestly reduced morphogenesis, and the effect was evident after 24 h of incubation. The inhibitory activity of C. albicans EVs on phase transition was promoted by a combination of lipid compounds, which were identified by gas chromatography-tandem mass spectrometry analysis as sesquiterpenes, diterpenes, and fatty acids. Remarkably, C. albicans EVs were also able to reverse filamentation. Finally, C. albicans cells treated with C. albicans EVs for 24 h lost their capacity to penetrate agar and were avirulent when inoculated into Galleria mellonella. Our results indicate that fungal EVs can regulate yeast-to-hypha differentiation, thereby inhibiting biofilm formation and attenuating virulence.

Virulence Factors of Sporothrix schenckii

Sporothrix schenckii is one of the etiological agents of sporotrichosis. In this review, we discuss the virulence factors that have been proven to participate in the S. schenckii-host interaction. Among these known factors, we can find cell wall glycoproteins, adhesins, melanin, extracellular vesicles, and dimorphism. Furthermore, the morphological transition of S. schenckii in response to environmental conditions such as pH and temperature represents a means by which the fungus is able to establish mycosis in mammals. One of the key features in the development of sporotrichosis is the adhesion of the fungus to the host extracellular matrix. This event represents the first step to developing the mycosis, which involves adhesins such as the glycoproteins Gp70, Hsp60, and Pap1, which play a key role during the infection. The production of melanin helps the fungus to survive longer in the tissues and to neutralize or diminish many of the host’s attacks, which is why it is also considered a key factor in pathogenesis. Today, the study of human fungal pathogens’ virulence factors is a thriving area of research. Although we know some of the virulence factors in S. schenckii, much remains to be understood about the complex process of sporotrichosis development and the factors involved during the infection.

Extracellular Vesicles From Paracoccidioides brasiliensis Can Induce the Expression of Fungal Virulence Traits In Vitro and Enhance Infection in Mice

Extracellular vesicles (EVs) are cellular components involved in cargo delivery to the extracellular environment, including the fungal cell wall. Their importance in cell–cell communication, cell wall remodeling, and fungal virulence is starting to be better explored. In the human pathogenic Paracoccidioides spp., our group has pioneered the description of the EV secretome, carbohydrate cargo, surface oligosaccharide ligands, lipid, and RNA content. Presently, we studied the role of fungal EVs in the context of the virulent/attenuated model of the P. brasiliensis Pb18 isolate, which consists of variants transiently displaying higher (vPb18) or attenuated (aPb18) virulence capacity. In this model, the virulence traits can be recovered through passages of aPb18 in mice. Here, we have been able to revert the aPb18 sensitivity to growth under oxidative and nitrosative stress upon previous co-incubation with vEVs from virulent vPb18. That was probably due to the expression of antioxidant molecules, considering that we observed increased gene expression of the alternative oxidase AOX and peroxiredoxins HYR1 and PRX1, in addition to higher catalase activity. We showed that aEVs from aPb18 stimulated macrophages of the RAW 264.7 and bone marrow-derived types to express high levels of inflammatory mediators, specifically, TNF-α, IL-6, MCP-1, and NO. In our experimental conditions, subcutaneous treatment with EVs (three doses, 7-day intervals) before vPb18 challenge exacerbated murine PCM, as concluded by higher colony-forming units in the lungs after 30 days of infection and histopathology analysis. That effect was largely pronounced after treatment with aEVs, probably because the lung TNF-α, IFN-γ, IL-6, and MCP-1 concentrations were specially increased in aEV-treated when compared with vEV-treated mice. Our present studies were performed with EVs isolated from yeast cell washes of confluent cultures in Ham’s F-12 defined medium. Under these conditions, vEVs and aEVs have similar sizes but probably distinct cargo, considering that vEVs tended to aggregate upon storage at 4°C and −20°C. Additionally, aEVs have decreased amounts of carbohydrate and protein. Our work brings important contribution to the understanding of the role of fungal EVs in cell–cell communication and on the effect of EVs in fungal infection, which clearly depends on the experimental conditions because EVs are complex and dynamic structures.

Old and New Insights into Sporothrix schenckii Complex Biology and Identification

Sporothrix schenckii is a worldwide-distributed thermally dimorphic fungus, which usually causes a subacute to chronic infection through traumatic implantation or inoculation of its infectious propagules. The fungus encompasses a group of phylogenetically closely related species, thus named the S. schenckii complex, of which S. schenckii sensu stricto and S. brasiliensis are main causative species of sporotrichosis. Owing to a multifaceted molecular dynamic, the S. schenckii complex can switch between the mycelium and the yeast form. This characteristic along with a varying cell wall composition account for significant species-specific differences in the host range, virulence, and susceptibility to antifungal drugs. While culture remains the gold standard to diagnose sporotrichosis, polymerase chain reaction (PCR) or matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry-based methods have become an essential for accurate species identification in many clinical laboratories. If directly applied on tissue samples, molecular methods are helpful to improve both sensitivity of and time to the etiological diagnosis of sporotrichosis. This mini-review aims to put together the old and new knowledge on the S. schenckii complex biology and identification, with particular emphasis on the laboratory diagnosis-related aspects of disease.

Current Models to Study the Sporothrix-Host Interaction

Sporotrichosis is a worldwide distributed subcutaneous mycosis that affects mammals, including human beings. The infection is caused by members of the Sporothrix pathogenic clade, which includes Sporothrix schenckii, Sporothrix brasiliensis, and Sporothrix globosa. The fungus can be acquired through traumatic inoculation of conidia growing in vegetal debris or by zoonotic transmission from sick animals. Although is not considered a life-threatening disease, it is an emergent health problem that affects mostly immunocompromised patients. The sporotrichosis causative agents differ in their virulence, host range, and sensitivity to antifungal drugs; therefore, it is relevant to understand the molecular bases of their pathogenesis, interaction with immune effectors, and mechanisms to acquired resistance to antifungal compounds. Murine models are considered the gold standard to address these questions; however, some alternative hosts offer numerous advantages over mammalian models, such as invertebrates like Galleria mellonella and Tenebrio molitor, or ex vivo models, which are useful tools to approach questions beyond virulence, without the ethical or budgetary features associated with the use of animal models. In this review, we analyze the different models currently used to study the host-Sporothrix interaction.

Fungal Extracellular Vesicles Are Involved in Intraspecies Intracellular Communication

Fungal infections are associated with high mortality rates in humans. The risk of fungal diseases creates the urgent need to broaden the knowledge base regarding their pathophysiology. In this sense, the role of extracellular vesicles (EVs) has been described to convey biological information and participate in the fungus-host interaction process. We hypothesized that fungal EVs work as an additional element in the communication routes regulating fungal responses in intraspecies interaction systems. In this respect, the aim of this study was to address the gene regulation profiles prompted by fungal EVs in intraspecies recipient cells. Our data demonstrated the intraspecies uptake of EVs in pathogenic fungi, such as Candida albicans, Aspergillus fumigatus, and Paracoccidioides brasiliensis, and the effects triggered by EVs in fungal cells. In C. albicans, we evaluated the involvement of EVs in the yeast-to-hypha transition, while in P. brasiliensis and A. fumigatus the function of EVs as stress transducers was investigated. P. brasiliensis and A. fumigatus were exposed to an inhibitor of glycosylation or UV light, respectively. The results demonstrated the role of EVs in regulating the expression of target genes and triggering phenotypic changes. The EVs treatment induced cellular proliferation and boosted the yeast to hyphal transition in C. albicans, while they enhanced stress responsiveness in A. fumigatus and P. brasiliensis, establishing a role for EVs in fungal intraspecies communication. Thus, EVs regulate fungal behavior, acting as potent message effectors, and understanding their effects and mechanism(s) of action could be exploited in antifungal therapies. IMPORTANCE Here, we report a study about extracellular vesicles (EVs) as communication mediators in fungi. Our results demonstrated the role of EVs from Candida albicans, Aspergillus fumigatus, and Paracoccidioides brasiliensis regulating the expression of target genes and phenotypic features. We asked whether fungal EVs play a role as message effectors. We show that fungal EVs are involved in fungal interaction systems as potent message effectors, and understanding their effects and mechanisms of action could be exploited in antifungal therapies.

Biogenesis and Biological Functions of Extracellular Vesicles in Cellular and Organismal Communication With Microbes

Extracellular vesicles (EVs) represent a prominent mechanism of transport and interaction between cells, especially microbes. Increasing evidence indicates that EVs play a key role in the physiological and pathological processes of pathogens and other symbionts. Recent research has focused on the specific functions of these vesicles during pathogen-host interactions, including trans-kingdom delivery of small RNAs, proteins and metabolites. Much current research on the function of EVs is focused on immunity and the interactions of microbes with human cells, while the roles of EVs during plant-microbe interactions have recently emerged in importance. In this review, we summarize recent research on the biogenesis of these vesicles and their functions in biology and pathology. Many key questions remain unclear, including the full structural and functional diversity of EVs, the roles of EVs in communication among microbes within microbiomes, how specific cargoes are targeted to EVs, whether EVs are targeted to specific destinations, and the full scope of EVs' transport of virulence effectors and of RNA and DNA molecules.

Cellular and Extracellular Vesicle RNA Analysis in the Global Threat Fungus Candida auris

Emerging and reemerging pathogens are a worldwide concern, and it is predicted that these microbes will cause severe outbreaks. Candida auris affects people with weakened immune systems, particularly those who are hospitalized or are in health care facilities. Extracellular vesicles (EVs) are lipid bilayer structures released by organisms from all domains of life. EVs can deliver functional molecules to target cells, including proteins and nucleic acids, especially RNA molecules. EVs from several pathogenic fungi species play diverse biological roles related to cell-cell communication and pathogen-host interaction. In this study, we describe a data set which we produced by sequencing the RNA content of EVs from C. auris under normal growth conditions and in the presence of the antifungal caspofungin, a first-line drug to treat this fungus. To generate a more complete data set for future comparative studies, we also sequenced the RNA cellular content of EVs under the same conditions. This data set addresses a previously unexplored area of fungal biology regarding cellular small RNA and EV RNA. Our data will provide a molecular basis for the study of the aspects associated with antifungal treatment, gene expression response, and EV composition in C. auris. These data will also allow the exploration of small RNA content in the fungal kingdom and might serve as an informative basis for studies on the mechanisms by which molecules are directed to fungal EVs. IMPORTANCE Candida auris, a relevant emerging human-pathogenic yeast, is the first fungus to be called a global public health threat by the WHO. This is because of its rapid spread on all inhabited continents, together with its extremely high frequency of drug and multidrug resistance. In our study, we generated a large data set for 3 distinct strains of C. auris and obtained cellular small RNA fraction as well as extracellular vesicle RNA (EV-RNA) during normal growth conditions and after treatment with caspofungin, the first-line drug used to treat C. auris infection.

Extracellular Vesicles From Sporothrix brasiliensis Yeast Cells Increases Fungicidal Activity in Macrophages

Sporotrichosis is a subcutaneous mycosis and is distributed throughout the world, although most cases belong to endemic regions with a warmer climate such as tropical and subtropical areas. The infection occurs mainly by traumatic inoculation of propagules. Similarly, to other organisms, Sporothrix brasiliensis display many biological features that aid in its ability to infect the host, such as extracellular vesicles, bilayered biological structures that provides communication between host cells and between fungi cells themselves. Recently, research on Sporothrix complex have been focused on finding new molecules and components with potential for therapeutic approaches. Here, we study the relationship among EVs and the host's macrophages as well as their role during infection to assess whether these vesicles are helping the fungi or inducing a protective effect on mice during the infection. We found that after cocultivation with different concentrations of purified yeasts EVs from Sb, J774 macrophages displayed an increased fungicidal activity (Phagocytic Index) resulting in lower colony-forming units the more EVs were added, without jeopardizing the viability of the macrophages. Interleukins IL-6, IL-10, and IL-12 were measured during the infection period, showing elevated levels of IL-12 and IL-6 in a dose-dependent manner, but no significant change for IL-10. We also assessed the expression of important molecules in the immune response, such as MHC class II and the immunoglobulin CD86. Both these molecules were overexpressed in Sb yeasts infected mice. Our results indicate that EVs play a protective role during Sporothrix brasiliensis infections.

Analysis of Cryptococcal Extracellular Vesicles: Experimental Approaches for Studying Their Diversity Among Multiple Isolates, Kinetics of Production, Methods of Separation, and Detection in Cultures of Titan Cells

Extracellular vesicles (EVs) produced by members of the Cryptococcus genus are associated with fundamental processes of fungal physiology and virulence. However, several questions about the properties of cryptococcal EVs remain unanswered, mostly because of technical limitations. We recently described a fast and efficient protocol of high-yield EV isolation from solid medium. In this study, we aimed at using the solid medium protocol to address some of the open questions about EVs, including the kinetics of EV production, the diversity of EVs produced by multiple isolates under different culture conditions, the separation of vesicles in a density gradient followed by the recovery of functional EVs, the direct detection of EVs in culture supernatants, and the production of vesicles in solid cultures of Titan cells. Our results indicate that the production of EVs is directly impacted by the culture medium and time of growth, resulting in variable detection of EVs per cell and a peak of EV detection at 24 h of growth. Nanoparticle tracking analysis (NTA) of EV samples revealed that multiple isolates produce vesicles with variable properties, including particles of diverging dimensions. EVs were produced in the solid medium in amounts that were separated on a centrifugation density gradient, resulting in the recovery of functional EVs containing the major cryptococcal capsular antigen. We also optimized the solid medium protocol for induction of the formation of Titan cells, and analyzed the production of EVs by NTA and transmission electron microscopy. This analysis confirmed that EVs were isolated from solid cultures of cryptococcal enlarged cells. With these approaches, we expect to implement simple methods that will facilitate the analysis of EVs produced by fungal cells. IMPORTANCE Fungal extracellular vesicles (EVs) are considered to be important players in the biology of fungal pathogens. However, the limitations in the methodological approaches to studying fungal EVs impair the expansion of knowledge in this field. In the present study, we used the Cryptococcus genus as a model for the study of EVs. We explored the simplification of protocols for EV analysis, which helped us to address some important, but still unanswered, questions about fungal EVs.

Comparative Molecular and Immunoregulatory Analysis of Extracellular Vesicles from Candida albicans and Candida auris

Candida auris is a recently described multidrug-resistant pathogenic fungus that is increasingly responsible for health care-associated outbreaks across the world. Bloodstream infections of this fungus cause death in up to 70% of cases. Aggravating this scenario, the disease-promoting mechanisms of C. auris are poorly understood. Fungi release extracellular vesicles (EVs) that carry a broad range of molecules, including proteins, lipids, carbohydrates, pigments, and RNA, many of which are virulence factors. Here, we carried out a comparative molecular characterization of C. auris and Candida albicans EVs and evaluated their capacity to modulate effector mechanisms of host immune defense. Using proteomics, lipidomics, and transcriptomics, we found that C. auris released EVs with payloads that were significantly different from those of EVs released by C. albicans. EVs released by C. auris potentiated the adhesion of this yeast to an epithelial cell monolayer, while EVs from C. albicans had no effect. C. albicans EVs primed macrophages for enhanced intracellular yeast killing, whereas C. auris EVs promoted survival of the fungal cells. Moreover, EVs from both C. auris and C. albicans induced the activation of bone marrow-derived dendritic cells. Together, our findings show distinct profiles and properties of EVs released by C. auris and by C. albicans and highlight the potential contribution of C. auris EVs to the pathogenesis of this emerging pathogen.

IMPORTANCECandida auris is a recently described multidrug-resistant pathogenic fungus that is responsible for outbreaks across the globe, particularly in the context of nosocomial infections. Its virulence factors and pathogenesis are poorly understood. Here, we tested the hypothesis that extracellular vesicles (EVs) released by C. auris are a disease-promoting factor. We describe the production of EVs by C. auris and compare their biological activities against those of the better-characterized EVs from C. albicans. C. auris EVs have immunoregulatory properties, of which some are opposite those of C. albicans EVs. We also explored the cargo and structural components of those vesicles and found that they are remarkably distinct compared to EVs from C. auris’s phylogenetic relative Candida albicans.

A new insight into the cellular mechanisms of envenomation: Elucidating the role of extracellular vesicles in Loxoscelism

Envenomation by the Loxosceles genus spiders is a recurring health issue worldwide and specially in the Americas. The physiopathology of the envenomation is tightly associated to the venom's rich toxin composition, able to produce a local dermonecrotic lesion that can evolve systemically and if worsened, might result in multiple organ failure and lethality. The cellular and molecular mechanisms involved with the physiopathology of Loxoscelism are not completely understood, however, the venom's Phospholipases D (PLDs) are known to trigger membrane injury in various cell types. Here, we report for the first time the Loxosceles venom's ability to stimulate the production of extracellular vesicles (EVs) in various human cell lineages. Components of the Loxosceles venom were also detectable in the cargo of these vesicles, suggesting that they may be implicated in the process of extracellular venom release. EVs from venom treated cells exhibited phospholipase D activity and were able to induce in vitro hemolysis in human red blood cells and alter the HEK cell membranes' permeability. Nonetheless, the PLD activity was inhibited when an anti-venom PLDs monoclonal antibody was co-administered with the whole venom. In summary, our findings shed new light on the mechanisms underlying cellular events in the context of loxoscelism and suggest a crucial role of EVs in the process of envenomation.

mRNA Inventory of Extracellular Vesicles from Ustilago maydis

Extracellular vesicles (EVs) can transfer diverse RNA cargo for intercellular communication. EV-associated RNAs have been found in diverse fungi and were proposed to be relevant for pathogenesis in animal hosts. In plant-pathogen interactions, small RNAs are exchanged in a cross-kingdom RNAi warfare and EVs were considered to be a delivery mechanism. To extend the search for EV-associated molecules involved in plant-pathogen communication, we have characterised the repertoire of EV-associated mRNAs secreted by the maize smut pathogen, Ustilago maydis. For this initial survey, we examined EV-enriched fractions from axenic filamentous cultures that mimic infectious hyphae. EV-associated RNAs were resistant to degradation by RNases and the presence of intact mRNAs was evident. The set of mRNAs enriched inside EVs relative to the fungal cells are functionally distinct from those that are depleted from EVs. mRNAs encoding metabolic enzymes are particularly enriched. Intriguingly, mRNAs of some known effectors and other proteins linked to virulence were also found in EVs. Furthermore, several mRNAs enriched in EVs are also upregulated during infection, suggesting that EV-associated mRNAs may participate in plant-pathogen interactions.

Extracellular Vesicles in the Fungi Kingdom

Extracellular vesicles (EVs) are membranous, rounded vesicles released by prokaryotic and eukaryotic cells in their normal and pathophysiological states. These vesicles form a network of intercellular communication as they can transfer cell- and function-specific information (lipids, proteins and nucleic acids) to different cells and thus alter their function. Fungi are not an exception; they also release EVs to the extracellular space. The vesicles can also be retained in the periplasm as periplasmic vesicles (PVs) and the cell wall. Such fungal vesicles play various specific roles in the lives of these organisms. They are involved in creating wall architecture and maintaining its integrity, supporting cell isolation and defence against the environment. In the case of pathogenic strains, they might take part in the interactions with the host and affect the infection outcomes. The economic importance of fungi in manufacturing high-quality nutritional and pharmaceutical products and in remediation is considerable. The analysis of fungal EVs opens new horizons for diagnosing fungal infections and developing vaccines against mycoses and novel applications of nanotherapy and sensors in industrial processes.

Omics Approaches for Understanding Biogenesis, Composition and Functions of Fungal Extracellular Vesicles

Extracellular vesicles (EVs) are lipid bilayer structures released by organisms from all kingdoms of life. The diverse biogenesis pathways of EVs result in a wide variety of physical properties and functions across different organisms. Fungal EVs were first described in 2007 and different omics approaches have been fundamental to understand their composition, biogenesis, and function. In this review, we discuss the role of omics in elucidating fungal EVs biology. Transcriptomics, proteomics, metabolomics, and lipidomics have each enabled the molecular characterization of fungal EVs, providing evidence that these structures serve a wide array of functions, ranging from key carriers of cell wall biosynthetic machinery to virulence factors. Omics in combination with genetic approaches have been instrumental in determining both biogenesis and cargo loading into EVs. We also discuss how omics technologies are being employed to elucidate the role of EVs in antifungal resistance, disease biomarkers, and their potential use as vaccines. Finally, we review recent advances in analytical technology and multi-omic integration tools, which will help to address key knowledge gaps in EVs biology and translate basic research information into urgently needed clinical applications such as diagnostics, and immuno- and chemotherapies to fungal infections.

The paradoxical and still obscure properties of fungal extracellular vesicles

Early compositional studies of fungal EVs revealed a complex combination of biomolecules, including proteins, lipids, glycans, polysaccharides, nucleic acid and pigments, indicating that these compartments could be involved with multiple functions. Curiously, some of the activities attributed to fungal EVs were already attested experimentally and are implicated with contrasting effects in vitro and in vivo. For instance, the presence of virulence factors is correlated with increased pathogenic potential. Indeed, the administration to hosts of EVs along with some fungal pathogens seems to help the disease development. However, it has been clearly shown that immunization of insects and mice with fungal EVs can protect these animals against a subsequent infection. Fungal EVs not only influence the host response, as concluded from the observation that these compartments also work as messengers between fungal organisms. In this context, despite their size characterization, other physical properties of EVs are poorly known. For instance, their stability and half-life under physiological conditions can be a crucial parameter determining their long-distance effects. In this review, we will discuss the paradoxical and still unexploited functions and properties of fungal EVs that could be determinant for their biological functions.

ExVe: The knowledge base of orthologous proteins identified in fungal extracellular vesicles

Extracellular vesicles (EVs) are double-membrane particles associated with intercellular communication. Since the discovery of EV production in the fungus Cryptococcus neoformans, the importance of EV release in its physiology and pathogenicity has been investigated. To date, few studies have investigated the proteomic content of EVs from multiple fungal species. Our main objective was to use an orthology approach to compare proteins identified by EV shotgun proteomics in 8 pathogenic and 1 nonpathogenic species. Using protein information from the UniProt and FungiDB databases, we integrated data for 11,433 hits in fungal EVs with an orthology perspective, resulting in 3,834 different orthologous groups. OG6_100083 (Hsp70 Pfam domain) was the unique orthologous group that was identified for all fungal species. Proteins with this protein domain are associated with the stress response, survival and morphological changes in different fungal species. Although no pathogenic orthologous group was found, we identified 5 orthologous groups exclusive to S. cerevisiae. Using the criteria of at least 7 pathogenic fungi to define a cluster, we detected the 4 unique pathogenic orthologous groups. Taken together, our data suggest that Hsp70-related proteins might play a key role in fungal EVs, regardless of the pathogenic status. Using an orthology approach, we identified at least 4 protein domains that could be novel therapeutic targets against pathogenic fungi. Our results were compiled in the herein described ExVe database, which is publicly available at http://exve.icc.fiocruz.br.

Size-exclusion chromatography allows the isolation of EVs from the filamentous fungal plant pathogen Fusarium oxysporum f. sp. vasinfectum (Fov)

Extracellular vesicles (EVs) are nano-sized compartments involved in cell communication and macromolecule transport that are well characterized in mammalian organisms. Fungal EVs transport virulence-related cargo and modulate the host immune response, but most work has been focused on human yeast pathogens. Additionally, the study of EVs from filamentous fungi has been hindered by the lack of protein markers and efficient isolation methods. In this study we performed the isolation and proteomic characterization of EVs from the filamentous cotton pathogen Fusarium oxysporum f. sp. vasinfectum (Fov). EVs were recovered from two different growth media, Czapek Dox and Saboraud's dextrose broth, and purified by size-exclusion chromatography. Our results show that the EV proteome changes depending on the growth medium but EV production remains constant. EVs contained proteins involved in polyketide synthesis, cell wall modifications, proteases and potential effectors. These results support a role in modulation of host-pathogen interactions for Fov EVs.

Sporothrix Brasiliensis: A Review of an Emerging South American Fungal Pathogen, Its Related Disease, Presentation and Spread in Argentina

Sporotrichosis, caused by Sporothrix schenckii and related species, is the most frequent implantation mycosis in Latin America. In Argentina, over the last 8 years, there have been 0.16 new cases per month of feline sporotrichosis in 2011, increasing to 0.75 cases per month in 2019 and involving zoonotic transmission to humans. Molecular identification by polymerase chain reaction (PCR) detected Sporothrix brasiliensis in these feline and zoonotic outbreaks. This study will focus on different feline and human sporotrichosis outbreaks caused by S. brasiliensis in Argentina during 2011–2019. We will address the sources of infection and environmental hotspots, as well as the application of several treatment strategies for improving the pharmacotherapy of the different clinical forms of the disease. Finally, we will provide a detailed summary of the clinical aspects and new advances in host–pathogen interactions, virulence factors and immune response, focusing on state-of-the-art diagnostic tools and potential vaccine candidates.

Fungal Extracellular Vesicles in Pathophysiology

Fungal pathogens are a concern in medicine and agriculture that has been exacerbated by the emergence of antifungal-resistant varieties that severely threaten human and animal health, as well as food security. This had led to the search for new and sustainable treatments for fungal diseases. Innovative solutions require a deeper understanding of the interactions between fungal pathogens and their hosts, and the key determinants of fungal virulence. Recently, a link has emerged between the release of extracellular vesicles (EVs) and fungal virulence that may contribute to finding new methods for fungal control. Fungal EVs carry pigments, carbohydrates, protein, nucleic acids and other macromolecules with similar functions as those found in EVs from other organisms, however certain fungal features, such as the fungal cell wall, impact EV release and cargo. Fungal EVs modulate immune responses in the host, have a role in cell-cell communication and transport molecules that function in virulence. Understanding the function of fungal EVs will expand our knowledge of host-pathogen interactions and may provide new and specific targets for antifungal drugs and agrichemicals.