Heat Shock Protein 90 (Hsp90) as a Molecular Target for the Development of Novel Drugs Against the Dermatophyte Trichophyton rubrum

Fungal heat shock proteins: molecular phylogenetic insights into the host takeover

Heat shock proteins are constitutively expressed chaperones induced by cellular stress, such as changes in temperature, pH, and osmolarity. These proteins, present in all organisms, are highly conserved and are recruited for the assembly of protein complexes, transport, and compartmentalization of molecules. In fungi, these proteins are related to their adaptation to the environment, their evolutionary success in acquiring new hosts, and regulation of virulence and resistance factors. These characteristics are interesting for assessment of the host adaptability and ecological transitions, given the emergence of infections by these microorganisms. Based on phylogenetic inferences, we compared the sequences of HSP9, HSP12, HSP30, HSP40, HSP70, HSP90, and HSP110 to elucidate the evolutionary relationships of different fungal organisms to suggest evolutionary patterns employing the maximum likelihood method. By the different reconstructions, our inference supports the hypothesis that these classes of proteins are associated with pathogenic gains against endothermic hosts, as well as adaptations for phytopathogenic fungi.

Accelerating the understanding of Aspergillus terreus: Epidemiology, physiology, immunology and advances

Aspergillus species encompass a variety of infections, ranging from invasive aspergillosis to allergic conditions, contingent upon the immune status of the host. In this spectrum, Aspergillus terreus stands out due to its emergence as a notable pathogen and its intrinsic resistance to amphotericin-B. The significance of Aspergillus-associated infections has witnessed a marked increase in the past few decades, particularly with the increasing number of immunocompromised individuals. The exploration of epidemiology, morphological transitions, immunopathology, and novel treatment approaches such as new antifungal drugs (PC945, olorofim) and combinational therapy using antifungal drugs and phytochemicals (Phytochemicals: quercetin, shikonin, artemisinin), also using immunotherapies to modulate immune response has resulted in better outcomes. Furthermore, in the context COVID-19 era and its aftermath, fungal infections have emerged as a substantial challenge for both immunocompromised and immunocompetent individuals. This is attributed to the use of immune-suppressing therapies during COVID-19 infections and the increase in transplant cases. Consequently, this review aims to provide an updated overview encompassing the epidemiology, germination events, immunopathology, and novel drug treatment strategies against Aspergillus terreus-associated infections.

The Transcriptome Response to Azole Compounds in Aspergillus fumigatus Shows Differential Gene Expression across Pathways Essential for Azole Resistance and Cell Survival

The opportunistic pathogen Aspergillus fumigatus is found on all continents and thrives in soil and agricultural environments. Its ability to readily adapt to novel environments and to produce billions of spores led to the spread of azole-resistant A. fumigatus across the globe, posing a threat to many immunocompromised patients, including critically ill patients with severe influenza or COVID-19. In our study, we sought to compare the adaptational response to azoles from A. fumigatus isolates that differ in azole susceptibility and genetic background. To gain more insight into how short-term adaptation to stressful azole compounds is managed through gene expression, we conducted an RNA-sequencing study on the response of A. fumigatus to itraconazole and the newest clinically approved azole, isavuconazole. We observed many similarities in ergosterol biosynthesis up-regulation across isolates, with the exception of the pan-azole-resistant isolate, which showed very little differential regulation in comparison to other isolates. Additionally, we found differential regulation of membrane efflux transporters, secondary metabolites, iron metabolism, and various stress response and cell signaling mechanisms.

Insights and Perspectives on the Role of Proteostasis and Heat Shock Proteins in Fungal Infections

Fungi are a diverse group of eukaryotic organisms that infect humans, animals, and plants. To successfully colonize their hosts, pathogenic fungi must continuously adapt to the host's unique environment, e.g., changes in temperature, pH, and nutrient availability. Appropriate protein folding, assembly, and degradation are essential for maintaining cellular homeostasis and survival under stressful conditions. Therefore, the regulation of proteostasis is crucial for fungal pathogenesis. The heat shock response (HSR) is one of the most important cellular mechanisms for maintaining proteostasis. It is activated by various stresses and regulates the activity of heat shock proteins (HSPs). As molecular chaperones, HSPs participate in the proteostatic network to control cellular protein levels by affecting their conformation, location, and degradation. In recent years, a growing body of evidence has highlighted the crucial yet understudied role of stress response circuits in fungal infections. This review explores the role of protein homeostasis and HSPs in fungal pathogenicity, including their contributions to virulence and host-pathogen interactions, as well as the concerted effects between HSPs and the main proteostasis circuits in the cell. Furthermore, we discuss perspectives in the field and the potential for targeting the components of these circuits to develop novel antifungal therapies.

An update on the myriad antifungal resistance mechanisms in dermatophytes and the place of experimental and existential therapeutic agents for Trichophyton complex implicated in tinea corporis and cruris

INTRODUCTION

There is an epidemic emergence of increased resistance in dermatophytes with to antifungal drugs with ergosterol1 (Erg1) and Erg11 mutations to terbinafine and azoles. Apart from mutations, mechanisms that predict clinical failure include efflux pumps, cellular kinases, heat shock proteins (Hsp), and biofilms. Apart from itraconazole and SUBATM (Super-Bioavailable) itraconazole, measures that can be used in terbinafine failure include efflux-pump inhibitors, Hsp inhibitors and judicious use of antifungal drugs (topical + systemic) combinations.

AREAS COVERED

A PubMed search was done for the relevant studies and reviews published in the last 22 years using keywords dermatophytes OR Trichophyton, anti-fungal, resistance, mechanism and fungal AND resistance mechanisms. Our aim was to look for literature on prevalent species and we specifically researched studies on Trichophyton genus. We have analyzed varied antifungal drug mechanisms and detailed varied experimental and approved drugs to treat recalcitrant dermatophytosis.

EXPERT OPINION

Apart from administering drugs with low minimum inhibitory concentration, combinations of oral and topical antifungals (based on synergy data) and new formulations of existing drugs are useful in recalcitrant cases. There is a need for research into resistance mechanism of the existent Trichophyton strains in therapeutic failures in tinea corporis & cruris instead of data derived from laboratory strains which may not mirror clinical failures.

Target- and prodrug-based design for fungal diseases and cancer-associated fungal infections

Invasive fungal infections (IFIs) are emerging as a serious threat to public health and are associated with high incidence and mortality. IFIs also represent a frequent complication in patients with cancer who are undergoing chemotherapy. However, effective and safe antifungal agents remain limited, and the development of severe drug resistance further undermines the efficacy of antifungal therapy. Therefore, there is an urgent need for novel antifungal agents to treat life-threatening fungal diseases, especially those with new mode of action, favorable pharmacokinetic profiles, and anti-resistance activity. In this review, we summarize new antifungal targets and target-based inhibitor design, with a focus on their antifungal activity, selectivity, and mechanism. We also illustrate the prodrug design strategy used to improve the physicochemical and pharmacokinetic profiles of antifungal agents. Dual-targeting antifungal agents offer a new strategy for the treatment of resistant infections and cancer-associated fungal infections.

Antifungal Activity, Antibiofilm and Association Studies with O-Alkylamidoximes against Cryptococcus spp

This is the first study that describes the antifungal and anti-biofilm potential of O-alkylamidoximes against strains of Cryptococcus neoformans and Cryptococcus gattii. In vitro tests have shown that O-alkylamidoximes are capable of inhibiting fungal growth and biofilm formation of the C. neoformans and C. gattii strains, suggesting, from molecular docking, the potential for interaction with the Hsp90. The associations between O-alkylamidoximes and amphotericin B were beneficial. Therefore, O-alkylamidoximes can be a useful alternative to contribute to the limited arsenal of drugs, since they showed a powerful action against the primary agents of Cryptococcosis.

A Preliminary in vitro and in vivo Evaluation of the Effect and Action Mechanism of 17-AAG Combined With Azoles Against Azole-Resistant Candida spp

Invasive candidiasis is the primary reason for the increased cases of mortality in a medical environment. The resistance spectra of Candida species to antifungal drugs have gradually expanded. Particularly, the resistance spectra of Candida auris are the most prominent. Hsp90 plays a protective role in the stress response of fungi and facilitates their virulence. In contrast, Hsp90 inhibitors can improve the resistance of fungi to antifungal drugs by regulating the heat resistance of Hsp90, which destroys the integrity of the fungal cell walls. Hsp90 inhibitors thus offer a great potential to reduce or address fungal drug resistance. The drugs tested for the resistance include itraconazole, voriconazole, posaconazole, fluconazole, and 17-AAG. A total of 20 clinical strains of Candida were investigated. The broth microdilution checkerboard technique, as adapted from the CLSI M27-A4 method, was applied in this study. We found that 17-AAG alone exerted limited antifungal activity against all tested strains. The MIC range of 17-AAG was 8 to >32 μg/ml. A synergy was observed among 17-AAG and itraconazole, voriconazole, and posaconazole against 10 (50%), 7 (35%), and 13 (65%) of all isolates, respectively. Moreover, the synergy between 17-AAG and fluconazole was observed against 5 (50%) strains of azole-resistant Candida. However, no antagonism was recorded overall. Our result adequately verifies the influence of 17-AAG on the formation of Candida spp. biofilm. Moreover, we determined that with the use of rhodamine 6G to detect drug efflux and that of dihydrorhodamine-123 to detect intracellular reactive oxygen species (ROS), treatment with 17-AAG combined with azole drugs could inhibit the efflux pump of fungi and promote the accumulation of ROS in the fungal cells, thereby inducing fungal cell apoptosis. Thus, the mechanism of 17-AAG combined with azoles can kill fungi. Our results thus provide a new idea to further explore drugs against drug-resistant Candida spp.

Anti-dermatophytic activity of cold atmospheric plasma against Trichophyton rubrum via affecting fungal growth, morphology, drug susceptibility and HSP90 gene expression

Trichophyton rubrum, a major human pathogenic dermatophyte, is responsible for the most recurrent dermatophytoses as globally important superficial fungal infections. Typical chemotherapy is used to handle such infections; however, emerging drug resistance and side effects necessitate the new remedial method development. Cold atmospheric plasma (CAP) is an emerging technology, consisted of neutral and charged particles and photons newly developed as a potent and safe antimicrobial technique to combat drug-resistant microbial pathogens. In the present study, the vast effects of CAP irradiation containing oxygen (2%) and helium (98%) on T. rubrum growth and pathogenicity were explored. After exposure of T. rubrum to CAP jet for 90, 120, 150, 180, and 210 s in 96-well microtiter plates, cell morphology and viability, ergosterol content of fungal hyphae, HSP90 gene expression, and the pattern of drug susceptibility were studied by using electron microscopy, RT-qPCR, spectrophotometry, disk diffusion and CLSI microbroth dilution methods. CAP irradiation significantly inhibited the fungal growth by 25.83 to 89.10%, reduced fungal cell viability by 11.68 to 87.71%, disrupted cellular membranous organelles and structures of the fungal hyphae, and suppressed efficiently the expression of HSP90 gene by 2 folds in 210 s exposure. Taken together, our results demonstrated that CAP is an efficient tool with potential in-vivo therapeutic applications against chronic dermatophytosis caused by T. rubrum due to its effectiveness, harmless, and ease of access.

Identification and Phenotypic Characterization of Hsp90 Phosphorylation Sites That Modulate Virulence Traits in the Major Human Fungal Pathogen Candida albicans

The highly conserved, ubiquitous molecular chaperone Hsp90 is a key regulator of cellular proteostasis and environmental stress responses. In human pathogenic fungi, which kill more than 1.6 million patients each year worldwide, Hsp90 governs cellular morphogenesis, drug resistance, and virulence. Yet, our understanding of the regulatory mechanisms governing fungal Hsp90 function remains sparse. Post-translational modifications are powerful components of nature’s toolbox to regulate protein abundance and function. Phosphorylation in particular is critical in many cellular signaling pathways and errant phosphorylation can have dire consequences for the cell. In the case of Hsp90, phosphorylation affects its stability and governs its interactions with co-chaperones and clients. Thereby modulating the cell’s ability to cope with environmental stress. Candida albicans, one of the leading human fungal pathogens, causes ~750,000 life-threatening invasive infections worldwide with unacceptably high mortality rates. Yet, it remains unknown if and how Hsp90 phosphorylation affects C. albicans virulence traits. Here, we show that phosphorylation of Hsp90 is critical for expression of virulence traits. We combined proteomics, molecular evolution analyses and structural modeling with molecular biology to characterize the role of Hsp90 phosphorylation in this non-model pathogen. We demonstrated that phosphorylation negatively affects key virulence traits, such as the thermal stress response, morphogenesis, and drug susceptibility. Our results provide the first record of a specific Hsp90 phosphorylation site acting as modulator of fungal virulence. Post-translational modifications of Hsp90 could prove valuable in future exploitations as antifungal drug targets.

The effect of biosynthesized selenium nanoparticles on the expression of CYP51A and HSP90 antifungal resistance genes in Aspergillus fumigatus and Aspergillus flavus

The application of biological nanoparticles (NPs) can be considered as a way to overcome the problem of antifungal resistance in pathogenic fungi. This study takes a new approach to biosynthesized NPs influence on the expression of CYP51A and HSP90 antifungal resistance genes in Aspergillus fumigatus and A. flavus, and comparison with antifungal agents. Selenium NPs (Se-NPs) were biosynthesized using Aspergillus strains and their production was proved by several methods including, UV-Vis, XRD, FTIR, FESEM, and EDX techniques. The minimum inhibitory concentrations (MICs) of Aspergillus strains were determined using the CLSI M38-A2 broth microdilution method. The differences in expression levels of CYP51A and HSP90 genes were examined between untreated and treated of A. fumigatus and A. flavus using itraconazole and amphotericin B and biosynthesized Se-NPs through real-time PCR. After confirming the results of NPs synthesis, the MIC of itraconazole and amphotericin B against A. fumigatus and A. flavus was 4 μg/ml. Based on the real-time PCR results, the obtained ∆∆CTs for these strains were -0.18, -1.46, and -1.14. Whereas the MIC values for treated samples with Se-NPs have decreased to 0.5 μg/ml, and the ∆∆CTs for these were -0.25, -1.76, and -1.68. The expression of CYP51A and HSP90 genes was significantly down-regulated through the use of Se-NPs against A. fumigatus and A. flavus.

State-of-the-Art Dermatophyte Infections: Epidemiology Aspects, Pathophysiology, and Resistance Mechanisms

The burden of fungal infections is not widely appreciated. Although these infections are responsible for over one million deaths annually, it is estimated that one billion people are affected by severe fungal diseases. Mycoses of nails and skin, primarily caused by fungi known as dermatophytes, are the most common fungal infections. Trichophyton rubrum appears to be the most common causative agent of dermatophytosis, followed by Trichophyton interdigitale. An estimated 25% of the world’s population suffers from dermatomycosis. Although these infections are not lethal, they compromise the quality of life of infected patients. The outcome of antidermatophytic treatments is impaired by various conditions, such as resistance and tolerance of certain dermatophyte strains. The adage “know your enemy” must be the focus of fungal research. There is an urgent need to increase awareness about the significance of these infections with precise epidemiological data and to improve knowledge regarding fungal biology and pathogenesis, with an emphasis on adaptive mechanisms to tackle adverse conditions from host counteractions. This review outlines the current knowledge about dermatophyte infections, with a focus on signaling pathways required for fungal infection establishment and a broad perspective on cellular and molecular factors involved in antifungal resistance and tolerance.

Current Promising Therapeutic Targets for Aspergillosis Treatment

Aspergillosis is a fungal disease caused by different species of Aspergillus. They live in soil,dust and decomposed material. Number of Aspergillus species found till now is about 300 and more are still to be identified. Only few Aspergillus species can cause human disease and the most common species for human infection is Aspergillus fumigatus, which is a ubiquitous airborne saprophytic fungus. Severity of the disease ranges from an allergic response to life-threatening generalized infection. They grow optimally at 37°C and can grow upto 50°C. The fungal conidia are being constantly inhaled by humans and animals everyday normally gets eliminated by innate immune mechanism. Due to increasing number of immunocompromised patients, severe and fatal Aspergillosis cases have augmented. Currently, available antifungal drug for the treatment of Aspergillosis act on these three molecular target are 14 alpha demethylase for Azoles, ergosterol for Polyene and β-1,3-glucan synthase for Echinocandin. These antifungal drug show high resistance problem and toxicity. So, it is high time to develop new drugs for treatment with reduced toxicity and drug resistant problem. Synthesis of essential amino acid is absent in human as they obtain it from their diet but fungi synthesis these amino acid. Thus, enzymes in this pathway acts as novel drug target. This article summarizes promising drug targets presents in different metabolic pathway of Aspergillus genome and discusses their molecular functions in detail. This review also list down the inhibitors of these novel target. We present a comprehensive review that will pave way for discovery and development of novel antifungals against these drug targets for Aspergillosis treatment.

Immunopathogenesis of Dermatophytoses and Factors Leading to Recalcitrant Infections

The pathogenesis of dermatophytic infections involves the interplay of three major factors: the dermatophyte, the inherent host defense, and the adaptive host immune response. The fungal virulence factors determine the adhesion and invasion of the skin while the immune response depends on an interaction of the pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMP) with pattern recognition receptors (PRRs) of the host, which lead to a differential Th (T helper) 1, Th2, Th17, and Treg response. While anthropophilic dermatophytes Trichophyton rubrum and now increasingly by T. interdigitale subvert the immune response via mannans, zoophilic species are eliminated due to a brisk immune response. Notably, delayed-type hypersensitivity (Th1) response of T lymphocytes causes the elimination of fungal infection, while chronic disease caused by anthropophilic species corresponds to toll-like receptor 2 mediated IL (interleukin)-10 release and generation of T-regulatory cells with immunosuppressive potential. Major steps that determine the ultimate clinical course and chronicity include genetic susceptibility factors, impaired epidermal and immunological barriers, variations in the composition of sebum and sweat, carbon dioxide tension, skin pH, and topical steroid abuse. It is important to understand these multifarious aspects to surmount the problem of recalcitrant dermatophytosis when the disorder fails conventional therapeutic agents.

Myco-Fabrication of Copper Nanoparticles and Its Effect on Crop Pathogenic Fungi

Phytopathogens are responsible for huge losses in the agriculture sector. Amongst them, fungal phytopathogen is quite difficult to control. Many chemicals are available in the market, claiming the high activity against them. However, the development of resistance by the fungal pathogen is the main concern to overcome their menace. Nanotechnology-based products can be a potential alternative to conventional fungicides. Amongst various nanoparticles, Copper nanoparticles (CuNPs) are appearing to be a promising antifungal candidate. It can be synthesized by various methods, but the myco-fabrication appears to be an environmental-friendly approach. Hence, the present study is an attempt to synthesize CuNPs using Aspergillus flavus. The myco-fabricated CuNPs were characterized by UV spectrophotometer, Fourier transform infrared spectroscopy (FTIR), Nanoparticles tracking and analysis system (NTA), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD) and Zeta potential measurement. Myco-fabricated CuNPs showed maximum absorbance at 602 nm and particle size ranging 5-12 nm with the least average size of 8 nm with spherical shape and moderate stability. Myco-fabricated CuNPs tested against selected fungal crop pathogens viz. Aspergillus niger, Fusariumoxysporum, and Alternaria alternata reveal a significant effect. Besides these we have given the hypothetical mechanism depicting the antifungal action of myco-fabricated CuNPs.

Reduced expression levels of heat shock protein 90 in a diminazene aceturate-resistant Babesia gibsoni isolate

Heat shock protein 90 (HSP90) is a molecular chaperon and an essential component for stage differentiation and intracellular growth inside the host cells of many protozoans. HSP90 of Babesia gibsoni (BgHSP90) was suggested to function in the development of diminazene aceturate (DA)-resistance. Therefore, we examined the expression level of BgHSP90 in a DA-resistant B. gibsoni isolate. Transcription of the BgHSP90 gene in the DA-resistant isolate and wild-type B. gibsoni was assessed by quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR). As a result, the copy number and relative amount of BgHSP90 transcripts in the DA-resistant isolate were significantly lower than those in the wild-type. Moreover, a rabbit anti-recombinant BgHSP90 antibody was developed, and the protein synthesis of BgHSP90 in the DA-resistant isolate was compared with that in the wild-type by Western blot analysis and indirect fluorescence assay. There was significantly less BgHSP90 protein than in the wild-type. Additionally, the relative intensity of BgHSP70 in DA-resistant isolate was also lower than that in the wild-type. This suggested that the expression of BgHSP90 and BgHSP70 in the DA-resistant B. gibsoni isolate was suppressed and that the reduced amount of BgHSP90 and BgHSP70 might cause the weak proliferation of the DA-resistant isolate. Further studies are necessary to elucidate the function of BgHSP90.

Protein Acetylation/Deacetylation: A Potential Strategy for Fungal Infection Control

Protein acetylation is a universal post-translational modification that fine-tunes the major cellular processes of many life forms. Although the mechanisms regulating protein acetylation have not been fully elucidated, this modification is finely tuned by both enzymatic and non-enzymatic mechanisms. Protein deacetylation is the reverse process of acetylation and is mediated by deacetylases. Together, protein acetylation and deacetylation constitute a reversible regulatory protein acetylation network. The recent application of mass spectrometry-based proteomics has led to accumulating evidence indicating that reversible protein acetylation may be related to fungal virulence because a substantial amount of virulence factors are acetylated. Additionally, the relationship between protein acetylation/deacetylation and fungal drug resistance has also been proven and the potential of deacetylase inhibitors as an anti-infective treatment has attracted attention. This review aimed to summarize the research progress in understanding fungal protein acetylation/deacetylation and discuss the mechanism of its mediation in fungal virulence, providing novel targets for the treatment of fungal infection.

A Two-Way Road: Antagonistic Interaction Between Dual-Species Biofilms Formed by Candida albicans/Candida parapsilosis and Trichophyton rubrum

Dermatomycoses include superficial fungal infections of the skin and its appendages. Trichophyton rubrum, Candida albicans, and Candida parapsilosis are some of the most prevalent species that cause dermatomycoses. Several studies show a variable predominance of Candida spp. in relation to dermatophytes, especially in onychomycosis and the possibility of isolating both from the same site. The ability of dermatophytes to form biofilms recently been explored and there is currently no evidence on the involvement of these filamentous fungi in multi-species biofilms. Thus, this study aims to investigate the probable dual-species interaction between T. rubrum and C. albicans and T. rubrum and C. parapsilosis biofilms, considering variable formation conditions, as well as the susceptibility of these dual-species biofilms against terbinafine and efinaconazole. Three conditions of formation of dual-species biofilms were tested: (a) the suspensions of T. rubrum and Candida albicans or C. parapsilosis placed together; (b) suspensions of C. albicans and C. parapsilosis added the pre-adhesion of T. rubrum biofilms; (c) after the maturation of T. rubrum sessile cells. In the first and second conditions, the quantification of metabolic activities, biomass, and polysaccharide materials of mixed biofilms tended to resemble Candida monospecies biofilms. In the third condition, the profiles were modified after the addition of Candida, suggesting that T. rubrum biofilms served as substrate for the development of Candida biofilms. Scanning electron microscopy showed Candida predominance, however, numerous blastoconidia were noted, most evident in the conditions under which Candida was added after the pre-adhesion and maturation of T. rubrum biofilms. Despite the predominance of Candida, the presence of T. rubrum appears to inhibit C. albicans filamentation and C. parapsilosis development, confirming an antagonistic interaction. Fungal burden assays performed when the biofilms were formed together confirmed Candida predominance, as well as susceptibility to antifungals. Further studies will be needed to identify the components of the Candida and T. rubrum biofilm supernatants responsible for inhibiting dermatophyte growth and C. albicans filamentation.

Major challenges and perspectives in the diagnostics and treatment of dermatophyte infections

Dermatophytes are the aetiological factors of a majority of superficial fungal infections. What distinguishes them from other pathogenic filamentous fungi is their unique ability to degrade keratin. The remarkable ability of this group of fungi to survive in different ecosystems results from their morphological and ecological diversity as well as high adaptability to changing environmental conditions. Paradoxically, despite the progress in medicine, the prevalence of dermatophyte infections is increasing from year to year. At the beginning of the third millennium, practical diagnostic and therapeutic options are still very limited. This review focuses on understanding the major problems in this aspect of dermatophyte infections and indicates future strategies and perspectives for novel approaches to identification and drugs for elimination of dermatophytes. Particular importance is placed on development of a strategy for a diagnostic pathway and implementation of rapid and reliable diagnostics methods designed by international teams. Furthermore, among compounds that currently arouse great interest, representatives of terpenoids, alkaloids, saponins, flavonoids and essential oils deserve attention. Many of these compounds are undergoing clinical trials as potential antifungal agents, and future research should focus on attempts at determination of the applicability of tested substances. Finally, the advantages and disadvantages in implementation of new diagnostic paths and medicinal substances for routine use are indicated.

HacA Governs Virulence Traits and Adaptive Stress Responses in Trichophyton rubrum

The ability of fungi to sense environmental stressors and appropriately respond is linked to secretory system functions. The dermatophyte infection process depends on an orchestrated signaling regulation that triggers the transcription of genes responsible for adherence and penetration of the pathogen into host-tissue. A high secretion system is activated to support the host-pathogen interaction and assures maintenance of the dermatophyte infection. The gateway of secretion machinery is the endoplasmic reticulum (ER), which is the primary site for protein folding and transport. Current studies have shown that ER stress that affects adaptive responses is primarily regulated by UPR and supports fungal pathogenicity; this has been assessed for yeasts and Aspergillus fumigatus, in regard to how these fungi cope with host environmental stressors. Fungal UPR consists of a transmembrane kinase sensor (Ire1/IreA) and a downstream target Hac1/HacA. The active form of Hac is achieved via non-spliceosomal intron removal promoted by endonuclease activity of Ire1/IreA. Here, we assessed features of HacA and its involvement in virulence and susceptibility in Trichophyton rubrum. Our results showed that exposure to antifungals and ER-stressing agents initiated the activation of HacA from T. rubrum. Interestingly, the activation occurs when a 20 nt fragment is removed from part of the exon-2 and part of intron-2, which in turn promotes the arisen of the DNA binding site motif and a dimer interface domain. Further, we found changes in the cell wall and cellular membrane composition in the ΔhacA mutant as well as an increase in susceptibility toward azole and cell wall disturbing agents. Moreover, the ΔhacA mutant presented significant defects in important virulence traits like thermotolerance and growth on keratin substrates. For instance, the development of the ΔhacA mutant was impaired in co-culture with keratinocytes or human nail fragments. Changes in the pro-inflammatory cytokine release were verified for the ΔhacA mutant during the co-culture assay, which might be related to differences in pathogen-associated molecular patterns (PAMPs) in the cell wall. Together, these results suggested that HacA is an integral part of T. rubrum physiology and virulence, implying that it is an important molecular target for antidermatophytic therapy.

Alternative Splicing in Heat Shock Protein Transcripts as a Mechanism of Cell Adaptation in Trichophyton rubrum

Heat shock proteins (HSPs) are involved in critical processes like host tissue invasion, resistance, and pathogenicity in dermatophytes. RNA-Seq analysis of Trichophyton rubrum exposed to undecanoic acid (UDA) revealed intron retention events in HSP transcripts. Because HSPs are modulated in response to various stimuli and as alternative splicing (AS) can result in a broad diversity in the proteome of eukaryotic cells, our objective was to confirm the aforementioned retention events, investigating their consequences and extent. Furthermore, we aimed to determine: (1) the expression profile of HSP genes in an infection-like scenario and (2) the importance of Hsp90 for the keratinolytic potential of T. rubrum. RT and qPCR analyses comparing the exposure to UDA and terbinafine (TRB) confirmed the presence of two mRNA isoforms of the hsp7-like gene, with distinct expression patterns in response to UDA and TRB. The HSP expression profile revealed two upregulated, three downregulated, and four unmodulated transcripts; Hsp90 inhibition by 17-AAG resulted in a significant decrease in keratinolytic potential at 37 °C. Altogether, these results broaden the current knowledge on the importance of HSP-mediated pathways for cell adaptation and other aspects of dermatophyte biology, indicating that HSP network proteins can be potential targets for antifungal therapy.

Assessment of temperature-dependent proteomes of Pythium insidiosum by using the SWISS-PROT database

Pythium insidiosum causes the life-threatening disease, called pythiosis. Information on microbial pathogenesis could lead to an effective method of infection control. This study aims at assessing temperature-dependent proteomes, and identifying putative virulence factors of P. insidiosum. Protein extracts from growths at 25°C and 37°C were analyzed by mass spectrometry and SWISS-PROT database. A total of 1052 proteins were identified. Upon exposure to increased temperature, 219 proteins were markedly expressed, eight of which were putative virulence factors of P. insidiosum. These temperature-dependent proteins should be further investigated for their roles in pathogenesis, and some of which could be potential therapeutic targets.

Keratin hydrolysis by dermatophytes

Dermatophytes are the most common cause of superficial fungal infections (tinea infections) and are a specialized group of filamentous fungi capable of infecting and degrading keratinised tissues, including skin, hair, and nail. Essential to their pathogenicity and virulence is the production of a broad spectrum of proteolytic enzymes and other key proteins involved in keratin biodegradation and utilization of its breakdown products. The initial stage of biodegradation of native keratin is considered to be sulfitolysis, in which the extensive disulfide bridges present in keratin are hydrolyzed, although some secreted subtilisins can degrade dye-impregnated keratin azure without prior reduction (Sub3 and Sub4). Sulfitolysis facilitates the extracellular biodegradation of keratin by the dermatophytes' extensive array of endo- and exoproteases. The importance of dermatophyte proteases in infection is widely recognized, and these enzymes have also been identified as important virulence determinants and allergens. Finally, the short peptide and amino acid breakdown products are taken up by the dermatophytes, using as yet poorly characterised transporters, and utilized for metabolism. In this review, we describe the process of keratin biodegradation by dermatophytes, with an especial focus on recent developments in cutting edge molecular biology and '-omic' studies that are helping to dissect the complex process of keratin breakdown and utilization.

Trans-chalcone activity against Trichophyton rubrum relies on an interplay between signaling pathways related to cell wall integrity and fatty acid metabolism

Background

Trichophyton rubrum is the main etiological agent of skin and nail infections worldwide. Because of its keratinolytic activity and anthropophilic nature, infection models based on the addition of protein substrates have been employed to assess transcriptional profiles and to elucidate aspects related to host-pathogen interactions. Chalcones are widespread compounds with pronounced activity against dermatophytes. The toxicity of trans-chalcone towards T. rubrum is not fully understood but seems to rely on diverse cellular targets. Within this context, a better understanding of the mode of action of trans-chalcone may help identify new strategies of antifungal therapy and reveal new chemotherapeutic targets. This work aimed to assess the transcriptional profile of T. rubrum grown on different protein sources (keratin or elastin) to mimic natural infection sites and exposed to trans-chalcone in order to elucidate the mechanisms underlying the antifungal activity of trans-chalcone.

Results

Overall, the use of different protein sources caused only slight differences in the transcriptional profile of T. rubrum. The main differences were the modulation of proteases and lipases in gene categories when T. rubrum was grown on keratin and elastin, respectively. In addition, some genes encoding heat shock proteins were up-regulated during the growth of T. rubrum on keratin. The transcriptional profile of T. rubrum exposed to trans-chalcone included four main categories: fatty acid and lipid metabolism, overall stress response, cell wall integrity pathway, and alternative energy metabolism. Consistently, T. rubrum Mapk was strongly activated during the first hours of trans-chalcone exposure. Noteworthy, trans-chalcone inhibited genes involved in keratin degradation. The results also showed effects of trans-chalcone on fatty acid synthesis and metabolic pathways involved in acetyl-CoA supply.

Conclusion

Our results suggest that the mode of action of trans-chalcone is related to pronounced changes in fungal metabolism, including an imbalance between fatty acid synthesis and degradation that interferes with cell membrane and cell wall integrity. In addition, this compound exerts activity against important virulence factors. Taken together, trans-chalcone acts on targets related to dermatophyte physiology and the infection process.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5792-0) contains supplementary material, which is available to authorized users.

Host- and pathogen-dependent susceptibility and predisposition to dermatophytosis

Dermatophytes are a highly specialized group of keratinophilic and keratinolytic filamentous fungi causing a ringworm disease called dermatophytosis or superficial mycoses. Although dermatophyte infections do not threaten the host's life, they lower its quality in humans by causing discomfort related to cosmetic problems and through their epidemiological significance, whereas in farm animals they are responsible for economic losses and constitute a source of the spread of spores. Evidence from countless observational studies that have been conducted over the last 90 years indicates that dermatophytes infect humans of every age, race, gender and socioeconomic status with strikingly high rates, as well as both farmed and wild animals in various health conditions and with various epidemiological statuses. However, the prevalence of superficial fungal infections is highly variable, since it depends on several parameters associated with the infected individual and the dermatophyte, their mutual interactions, and epidemiological and geographical factors. The curious disparity in dermatophyte infection patterns has prompted many investigators to search for a link between the host, the host's predispositions and susceptibility to the disease, and the dermatophyte species and virulence. Thus, the question arises as to whether, in addition to the generally recognized factors predisposing hosts to diseases, there are some other predispositions to dermatophyte infections in a species-specific host. In this review, we describe recent findings about the mechanism of dermatophyte infections, focusing on the adaptation of the fungi to the host and conditions predisposing each side to the disease.

Response of Paracoccidioides lutzii to the antifungal camphene thiosemicarbazide determined by proteomic analysis

Aim: To perform the proteomic profile of Paracoccidioides lutzii after treatment with the compound camphene thiosemicarbazide (TSC-C) in order to study its mode of action. Methods: Proteomic analysis was carried out after cells were incubated with TSC-C in a subinhibitory concentration. Validation of the proteomic results comprised the azocasein assay, western blot and determination of the susceptibility of a mutant to the compound. Results: Proteins related to metabolism, energy and protein fate were regulated after treatment. In addition, TSC-C reduces the proteolytic activity of the protein extract similarly to different types of protease inhibitors. Conclusion: TSC-C showed encouraging antifungal activity, working as a protease inhibitor and downregulating important pathways impairing the ability of the fungi cells to produce important precursors.

Identification of inhibitors of the E. coli chaperone SurA using in silico and in vitro techniques

SurA is a gram-negative, periplasmic chaperone protein involved in the proper folding of outer membrane porins (OMPs), which protect bacteria against toxins in the extracellular environment by selectively regulating the passage of nutrients into the cell. Previous studies demonstrated that deletion of SurA renders bacteria more sensitive to toxins that compromise the integrity of the outer membrane. Inhibitors of SurA will perturb the folding of OMPs, leading to disruption of the outer membrane barrier and making the cell more vulnerable to toxic insults. The discovery of novel SurA inhibitors is therefore of great importance for developing alternative strategies to overcome antibiotic resistance. Our laboratory has screened over 10,000,000 compoundsin silicoby computationally docking these compounds onto the crystal structure of SurA. Through this screen and a screen of fragment compounds (molecular weight less than 250 g/mol), we found twelve commercially readily available candidate compounds that bind to the putative client binding site of SurA. We confirmed binding to SurA by developing and employing a competitive fluorescence anisotropy-based binding assay. Our results show that one of these compounds, Fmoc-β-(2-quinolyl)-d-alanine, binds the client binding site with high micromolar affinity. Using this compound as a lead, we also discovered that Fmoc-l-tryptophan and Fmoc-l-phenylalanine, but not Fmoc-l-tyrosine, bind SurA with similar micromolar affinity. To our knowledge, this is the first report of a competitive fluorescence anisotropy assay developed for the identification of inhibitors of the chaperone SurA, and the identification of three small molecules that bind SurA at its client binding site.

Antifungal activity of Cardiospermum halicacabum L. (Sapindaceae) against Trichophyton rubrum occurs through molecular interaction with fungal Hsp90

Introduction

Dermatophytosis is a superficial fungal infection limited to the stratum corneum of the epidermis, or to the hair and nails, and constitutes an important public health problem because of its high prevalence and associated morbidity. Dermatophyte fungi, especially 2 species, Trichophyton rubrum and Trichophyton mentagrophytes, are the predominant pathogens. Topical antifungal drugs, mainly azoles or allyamines, are currently used for the treatment of dermatophytoses, although in some cases, such as in nail and hair involvement, systemic treatment is required. However, therapeutic efficacy of current antifungal agents can be limited by their side effects, costs, and the emergence of drug resistance among fungi. Plant extracts represent a potential source of active antimicrobial agents, due to the presence of a variety of chemical bioactive compounds. In the present work, we evaluated in silico and in vitro the antifungal activity of an extract of the medicinal plant Cardiospermum halicacabum against T. rubrum suggesting a potential interaction with Hsp90 as playing an important role in both pathogenicity and drug susceptibility of T. rubrum.

Methods

We investigated in vitro the effect of different concentrations of C. halicacabum (from 500 to 31.25 µg) against a clinical isolate of T. rubrum. Furthermore, using a computational assessment, the interaction between different C. halicacabum active compounds and the fungal Hsp90 was also investigated.

Results

Our results indicate a clear-cut antifungal activity of the total plant extract at the highest concentrations (500 and 250 µg). Among all tested C. halicacabum compounds, the luteolin and rutin molecules have been identified in silico as the most important potential inhibitors of Hsp90. Based on these data, luteolin and rutin were also individually assessed for their antifungal activity. Results demonstrate that both substances display an antifungal effect, even if lower than that of the total plant extract.

Conclusion

Our data indicate a strong fungistatic effect of C. halicacabum against T. rubrum, suggesting its potential therapeutic efficacy in the treatment of dermatophytoses. Additionally, C. halicacabum compounds, and particularly luteolin and rutin, are all possible Hsp90 interactors, explaining their fungistatic activity.

Dermatophyte Resistance to Antifungal Drugs: Mechanisms and Prospectus

Dermatophytes comprise pathogenic fungi that have a high affinity for the keratinized structures present in nails, skin, and hair, causing superficial infections known as dermatophytosis. A reasonable number of antifungal drugs currently exist on the pharmaceutical market to control mycoses; however, their cellular targets are restricted, and fungi may exhibit tolerance or resistance to these agents. For example, the stress caused by antifungal and cytotoxic drugs in sub-inhibitory concentrations promotes compensatory stress responses, with the over-expression of genes involved in cellular detoxification, drug efflux, and signaling pathways being among the various mechanisms that may contribute to drug tolerance. In addition, the ATP-binding cassette transporters in dermatophytes that are responsible for cellular efflux can act synergistically, allowing one to compensate for the absence of the other, revealing the complexity of drug tolerance phenomena. Moreover, mutations in genes coding for target enzymes could lead to substitutions in amino acids involved in the binding of antifungal agents, hindering their performance and leading to treatment failure. The relevance of each one of these mechanisms of resistance to fungal survival is hard to define, mainly because they can act simultaneously in the cell. However, an understanding of the molecular mechanisms involved in the resistance/tolerance processes, the identification of new antifungal targets, as well as the prospective of new antifungal compounds among natural or synthetic products, are expected to bring advances and new insights that facilitate the improvement or development of novel strategies for antifungal therapy.

The First Whole-Cell Proteome- and Lysine-Acetylome-Based Comparison between Trichophyton rubrum Conidial and Mycelial Stages

Trichophyton rubrum is the most common fungal pathogen in the world, which has been studied as an important dermatophyte model organism. Despite the prevalence of T. rubrum, the available antifungal therapies are not sufficiently efficient. In this study, we performed the first comparison between the two major growth stages of T. rubrum: conidial and mycelial stages, based on their whole-cell proteomes and lysine acetylomes. In total, 4343 proteins were identified in both stages, and 1879 proteins were identified as differentially expressed between the two stages. The results showed that secretory proteases were more abundant in conidia, while aerobic metabolism and protein synthesis were significantly activated in the mycelial stage. In addition, 386 acetylated sites on 285 proteins and 5414 acetylated sites on 2335 proteins were identified in conidia and mycelia, respectively. The acetylation modifications were highly involved in metabolism and protein synthesis in both stages but differentially involved in Kyoto Encyclopedia of Genes and Genomes pathways and in epigenetic regulation between the two stages. Furthermore, inhibition of acetyltransferases or deacetylases significantly inhibited fungal growth and induced apoptosis. These results will enhance our understanding of the biological and physiological characteristics of T. rubrum and facilitate the development of improved therapies targeting these medically important pathogenic fungi.

Antifungal Therapy: New Advances in the Understanding and Treatment of Mycosis

The high rates of morbidity and mortality caused by fungal infections are associated with the current limited antifungal arsenal and the high toxicity of the compounds. Additionally, identifying novel drug targets is challenging because there are many similarities between fungal and human cells. The most common antifungal targets include fungal RNA synthesis and cell wall and membrane components, though new antifungal targets are being investigated. Nonetheless, fungi have developed resistance mechanisms, such as overexpression of efflux pump proteins and biofilm formation, emphasizing the importance of understanding these mechanisms. To address these problems, different approaches to preventing and treating fungal diseases are described in this review, with a focus on the resistance mechanisms of fungi, with the goal of developing efficient strategies to overcoming and preventing resistance as well as new advances in antifungal therapy. Due to the limited antifungal arsenal, researchers have sought to improve treatment via different approaches, and the synergistic effect obtained by the combination of antifungals contributes to reducing toxicity and could be an alternative for treatment. Another important issue is the development of new formulations for antifungal agents, and interest in nanoparticles as new types of carriers of antifungal drugs has increased. In addition, modifications to the chemical structures of traditional antifungals have improved their activity and pharmacokinetic parameters. Moreover, a different approach to preventing and treating fungal diseases is immunotherapy, which involves different mechanisms, such as vaccines, activation of the immune response and inducing the production of host antimicrobial molecules. Finally, the use of a mini-host has been encouraging for in vivo testing because these animal models demonstrate a good correlation with the mammalian model; they also increase the speediness of as well as facilitate the preliminary testing of new antifungal agents. In general, many years are required from discovery of a new antifungal to clinical use. However, the development of new antifungal strategies will reduce the therapeutic time and/or increase the quality of life of patients.