Fungal Extracellular Vesicles in Pathophysiology

Extracellular vesicle production: A bidirectional effect in the interplay between host and Candida fungi

Candida fungi exploit various virulence strategies to invade the human host, while host cells employ diverse mechanisms to maintain homeostasis and respond to infection. Extracellular vesicles (EVs) are integral components of the multifaceted landscape of host-pathogen interactions, with their abundant production by all contributors involved in these complex and dynamic relations. Herein, we present the current state of knowledge regarding the host response by releasing EVs in reaction to Candida, as well as the influence of fungal EVs on the functionality of the confronted host cells. Fungal vesicles contribute to enhanced adhesion of pathogens to human cells as evidenced for C. auris, and may modulate the production of several cytokines, including IL-6, IL-8, IL-10, IL-12p40, TGF-β and TNF-α, thereby exerting pro-infective and pro-inflammatory effects, as described for C. albicans and other Candida species. Whereas the biosynthesis of EVs by host cells can dynamically modulate the proliferation and viability of fungal cells and affect the candidacidal functionality of other effector cells. The reciprocal influence of EVs from host cells and Candida pathogens is a key focus, explaining their significant role in cell signaling and interkingdom communication.

Review of exosomes and their potential for veterinary medicine

Small extracellular vesicles called exosomes are released by almost all cell types and play a crucial role in both healthy and pathological circumstances. Exosomes, found in biological fluids (including plasma, urine, milk, semen, saliva, abdominal fluid and cervical vaginal fluid) and ranging in size from 50 to 150 nm, are critical for intercellular communication. Analysis of exosomal cargos, including micro RNAs (miRNAs), proteins and lipids, has been proposed as valuable diagnostic and prognostic biomarkers of disease. Exosomes can also be used as novel, cell-free, treatment strategies. In this review, we discuss the role, significance and application of exosomes and their cargos in diseases of animals.

Candida albicans Biofilm-Derived Extracellular Vesicles Are Involved in the Tolerance to Caspofungin, Biofilm Detachment, and Fungal Proteolytic Activity

It has been repeatedly reported that the cells of organisms in all kingdoms of life produce nanometer-sized lipid membrane-enveloped extracellular vesicles (EVs), transporting and protecting various substances of cellular origin. While the composition of EVs produced by human pathogenic fungi has been studied in recent decades, another important challenge is the analysis of their functionality. Thus far, fungal EVs have been shown to play significant roles in intercellular communication, biofilm production, and modulation of host immune cell responses. In this study, we verified the involvement of biofilm-derived EVs produced by two different strains of Candida albicans-C. albicans SC5314 and 3147 (ATCC 10231)-in various aspects of biofilm function by examining its thickness, stability, metabolic activity, and cell viability in the presence of EVs and the antifungal drug caspofungin. Furthermore, the proteolytic activity against the kininogen-derived antimicrobial peptide NAT26 was confirmed by HPLC analysis for C. albicans EVs that are known to carry, among others, particular members of the secreted aspartic proteinases (Saps) family. In conclusion, EVs derived from C. albicans biofilms were shown to be involved in biofilm tolerance to caspofungin, biofilm detachment, and fungal proteolytic activity.

First genome-scale insights into the virulence of the snow mold causal fungus Microdochium nivale

Pink snow mold, caused by a phytopathogenic and psychrotolerant fungus, Microdochium nivale, is a severe disease of winter cereals and grasses that predominantly occurs under snow cover or shortly after its melt. Snow mold has significantly progressed during the past decade, often reaching epiphytotic levels in northern countries and resulting in dramatic yield losses. In addition, M. nivale gradually adapts to a warmer climate, spreading to less snowy territories and causing different types of plant diseases throughout the growing period. Despite its great economic importance, M. nivale is poorly investigated; its genome has not been sequenced and its crucial virulence determinants have not been identified or even predicted. In our study, we applied a hybrid assembly based on Oxford Nanopore and Illumina reads to obtain the first genome sequence of M. nivale. 11,973 genes (including 11,789 protein-encoding genes) have been revealed in the genome assembly. To better understand the genetic potential of M. nivale and to obtain a convenient reference for transcriptomic studies on this species, the identified genes were annotated and split into hierarchical three-level functional categories. A file with functionally classified M. nivale genes is presented in our study for general use. M. nivale gene products that best meet the criteria for virulence factors have been identified. The genetic potential to synthesize human-dangerous mycotoxins (fumonisin, ochratoxin B, aflatoxin, and gliotoxin) has been revealed for M. nivale. The transcriptome analysis combined with the assays for extracellular enzymatic activities (conventional virulence factors of many phytopathogens) was carried out to assess the effect of host plant (rye) metabolites on the M. nivale phenotype. In addition to disclosing plant-metabolite-upregulated M. nivale functional gene groups (including those related to host plant protein destruction and amino acid metabolism, xenobiotic detoxication (including phytoalexins benzoxazinoids), cellulose destruction (cellulose monooxygenases), iron transport, etc.), the performed analysis pointed to a crucial role of host plant lipid destruction and fungal lipid metabolism modulation in plant-M. nivale interactions.

Translating extracellular vesicle packaging into therapeutic applications

Extracellular vesicles (EVs) are membrane-bound particles released by cells in various (patho)physiological conditions. EVs can transfer effector molecules and elicit potent responses in recipient cells, making them attractive therapeutic agents and drug delivery platforms. In contrast to their tremendous potential, only a few EV-based therapies and drug delivery have been approved for clinical use, which is largely attributed to limited therapeutic loading technologies and efficiency. As EV cargo has major influence on their functionality, understanding and translating the biology underlying the packaging and transferring of biomolecule cargos (e.g. miRNAs, pathogen antigens, small molecule drugs) into EVs is key in harnessing their therapeutic potential. In this review, through recent insights into EVs’ content packaging, we discuss different mechanisms utilized by EVs during cargo packaging, and how one might therapeutically exploit this process. Apart from the well-characterized EVs like exosomes and microvesicles, we also cover the less-studied and other EV subtypes like apoptotic bodies, large oncosomes, bacterial outer membrane vesicles, and migrasomes to highlight therapeutically-diverse opportunities of EV armoury.

Insight Into the Properties and Immunoregulatory Effect of Extracellular Vesicles Produced by Candida glabrata, Candida parapsilosis, and Candida tropicalis Biofilms

Currently, non-albicans Candida species, including C. tropicalis, C. glabrata, and C. parapsilosis, are becoming an increasing epidemiological threat, predominantly due to the distinct collection of virulence mechanisms, as well as emerging resistance to antifungal drugs typically used in the treatment of candidiasis. They can produce biofilms that release extracellular vesicles (EVs), which are nanometric spherical structures surrounded by a lipid bilayer, transporting diversified biologically active cargo, that may be involved in intercellular communication, biofilm matrix production, and interaction with the host. In this work, we characterize the size and protein composition of these structures for three species of non-albicans Candida fungi forming biofilm, indicating considerable heterogeneity of the investigated population of fungal EVs. Examination of the influence of EVs on cytokine production by the human monocytic cell line THP-1 differentiated into macrophage-like cells revealed that the tested vesicles have a stimulating effect on the secretion of tumor necrosis factor α and interleukin 8, while they reduce the production of interleukin 10. This may indicate the proinflammatory nature of the effect of EVs produced by these species on the host immune cells. Moreover, it has been indicated that vesicles may be involved in C. tropicalis biofilm resistance to fluconazole and caspofungin. This reveals the important role of EVs not only in the physiology of C. tropicalis, C. glabrata, and C. parapsilosis fungi but also in the pathogenesis of infections associated with the production of fungal biofilm.