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The bZIP Ap1 transcription factor is a negative regulator of virulence attributes of the anthropophilic dermatophyte Trichophyton rubrum

ABSTRACT: Highlights • The ap1 gene negatively regulates virulence traits in Trichophyton rubrum.• Ap1 regulates T. rubrum growth in keratin, playing a vital role in nail infection.• Ap1 may contribute to the chronicity of onychomycosis. Trichophyton rubrum is a fungus that causes chronic skin and nail infections in healthy individuals and immunocompromised patients. During infection, T. rubrum invades host cutaneous tissues by adapting to the acidic pH and the innate immune response of the host. Several genes are upregulated during the growth of T. rubrum in substrates found in human tissue, including the ap1 gene, which codes for the transcription factor Ap1. Here, we generated a null mutant strain by deleting the T. rubrum ap1 gene and performed a functional analysis of this gene. Our results showed that the Δap1mutant increased its growth in nail fragments and co-cultures with keratinocytes compared to the wild type. Furthermore, the mutant displayed hyperpigmentation, thickening of the conidia cell wall, increased conidia susceptibility to calcofluor-white compared to the wild type, and loss of control of the keratinolytic activity. Although the ap1 gene was upregulated during exposure to the antifungal drugs amphotericin B, nystatin, and terbinafine, its deletion did not alter the fungal susceptibility to these drugs, revealing the role of the ap1 gene in the physiological response to the stress caused by these drugs, but not in their resistance. Moreover, ap1 was also involved in the oxidative stress response caused by menadione, but not paraquat or hydrogen peroxide. These findings indicate that the ap1 gene plays a role in the negative control of virulence-related attributes and may contribute to the chronicity of nail infection caused by T. rubrum. Graphical Abstract Image, graphical abstract

SUBMITTER: Peres N

PROVIDER: S-EPMC9325736 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Fungal infections represent a significant concern worldwide, contributing to human morbidity and mortality. Dermatophyte infections are among the most significant mycoses, and Trichophyton rubrum appears to be the principal causative agent. Thus, an understanding of its pathophysiology is urgently required. Several lines of evidence have demonstrated that the APSES family of transcription factors (Asm1p, Phd1p, Sok2p, Efg1p, and StuA) is an important point of vulnerability in fungal pathogens and a potential therapeutic target. These transcription factors are unique to fungi, contributing to cell differentiation and adaptation to environmental cues and virulence. It has recently been demonstrated that StuA plays a pleiotropic role in dermatophyte pathophysiology. It was suggested that it functions as a mediator of crosstalk between different pathways that ultimately contribute to adaptive responses and fungal-host interactions. The complex regulation of StuA and its interaction pathways are yet to be unveiled. Thus, this study aimed to gain a deeper understanding of StuA-regulated processes in T. rubrum by assessing global gene expression following growth on keratin or glucose sources. The data showed the involvement of StuA in biological processes related to central carbon metabolism and glycerol catabolism, reactive oxygen species metabolism, and cell wall construction. Changes in carbohydrate metabolism may be responsible for the significant alteration in cell wall pattern and consequently in cell-cell interaction and adhesion. Loss of StuA led to impaired biofilm production and promoted proinflammatory cytokine secretion in a human keratinocyte cell line. We also observed the StuA-dependent regulation of catalase genes. Altogether, these data demonstrate the multitude of regulatory targets of StuA with a critical role in central metabolism that may ultimately trigger a cascade of secondary effects with substantial impact on fungal physiology and virulence traits.

Project description:Purpose: We evaluated T. rubrum transcriptome using high-throughput RNA-sequencing (RNA-seq) technology aiming to identify metabolic pathways modulated the development in keratin. Methods: T. rubrum strain CBS118892 was inoculated into 100 mL Sabouraud dextrose broth, and incubated under agitation at 28 °C for 96 h. Mycelia were aseptically transferred into 100 mL minimal medium (MM) at pH 5.0 containing 70 mM nitrate and 50 mM glucose (control) or 0.5% (w/v) bovine keratin (treatment) as the carbon source. The cultures were incubated under agitation at 28 °C for 24 h, 48 h, or 96 h. Equal amounts of RNA from three independent biological replicates of keratin or glucose cultures were sequenced with a Hiseq 2000 sequencer. Paired-end reads 150 bp in size were generated. Raw read data obtained were filtered for quality control by FastQC tool and trimmed with Trimmomatic to remove adapters and Illumina-specific sequences. Trimmed paired-end reads from each sample were aligned to the T. rubrum reference genome. Gene-level read counts were quantified with STAR’s ‘-quantModeGeneCounts’ parameter. Differential expression was analyzed with the DESeq2 bioconductor package. A Benjamini-Hochberg correction adjusted the P threshold and was applied to reveal statistically significant changes in gene expression levels. It was set to 0.05, with a log2 fold change ± 1.5 and postulated as a significantly modulated transcript abundance level. Genes surpassing these thresholds are hereinafter referred to as differentially expressed genes (DEG). They were functionally categorized with the Gene Ontology (GO) terms assigned by the Blast2GO algorithm. Highly represented categories were determined by enrichment analysis with the BayGO algorithm. Results: Our results present adaptive strategies in response to culture media. The global modulation in response to keratin supports fungal virulence and proper adaptation to the environment, in comparison to the availability of glucose as a carbon source. Conclusions: Our results revealed a profile of the adaptive events to the host environment, crucial to the establishment and maintenance of the infection. The observed metabolic modulation is necessary for fungus survival and perpetuation in the initial steps of the infective process in their host.

Project description: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.

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The bZIP Ap1 transcription factor is a negative regulator of virulence attributes of the anthropophilic dermatophyte Trichophyton rubrum

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