Markers for Host-Induced Gene Expression inTrichophytonDermatophytosis

Abstract

Dermatophytes are adapted to infect keratinized tissues by their ability to utilize keratin as a nutrient source. Although there have been numerous reports that dermatophytes like Trichophyton sp. secrete proteolytic enzymes, virtually nothing is known about the patterns of gene expression in the host or even when the organisms are cultured on protein substrates in the absence of a host. We characterized the expression of an aminopeptidase gene, the Trichophyton mentagrophytes homolog of the Trichophyton rubrum Tri r 4 gene. The T. rubrum gene was originally isolated based on the ability of the protein encoded by it to induce immediate and delayed-type hypersensitivity in skin tests. T. mentagrophytes Tri m 4 is closely related to Tri r 4 (almost 94% identity at the protein level). Tri m 4 resembles other protease-encoding genes thought to be virulence factors (for example, DPP V of Aspergillus fumigatus). The Tri m 4 protein was detected immunochemically both in fungal extracts and in the culture medium. Expression of the Tri m 4 gene was induced severalfold when T. mentagrophytes was grown on keratin and elastin. Ex vivo, strong induction was observed after culture on blood plasma, but the use of homogenized skin did not result in a significant increase in Tri m 4 transcript levels. In order to identify additional genes encoding putative virulence factors, differential cDNA screening was performed. By this method, a fungal thioredoxin and a cellulase homolog were identified, and both genes were found to be strongly induced by skin extracellular matrix proteins. Induction by superficial (keratin) and deep (elastin) skin elements suggests that the products of these genes may be important in both superficial and deep dermatophytosis, and models for their function are proposed. Upregulation of several newly identified T. mentagrophytes genes on protein substrates suggests that these genes encode proteins which are relevant to the dermatophyte-skin interaction.

Generating and Testing Molecular Hypotheses in the Dermatophytes

“…In recent years, human skin sections have been used as models for dermatophyte infection (9,30,31). One model used homogenized skin samples to provide a uniform growth medium (30).…”

“…One model used homogenized skin samples to provide a uniform growth medium (30). In a more representative ex vivo model, human skin explants were obtained following plastic surgery and infected at the surface with conidia.…”

Incidence and prevalence of dermatophytosis in and around Chennai, Tamilnadu, India

“…They are keratinophilic in nature and have the ability to colonise keratinized non-living tissues such as skin, hair and nail in human and animals. 2 The infection spreads easily by direct contact from infected humans and animals or through fomites. 3 Although the infection is not invasive and easy to cure, its widespread nature and cost of the treatment is a major public health problem and causes colossal damage to the economic status of the tropical countries like India.…”

Gene Expression Profiling in the Human Pathogenic Dermatophyte Trichophyton rubrum during Growth on Proteins

“…In dermatophytes, recent applications of such techniques revealed the transcriptional response of T. rubrum cells in distinct developmental growth phases and in the presence of novel fatty acid synthase inhibitors (16,33). Differential cDNA screening allowed first insights into the response of Trichophyton menta-grophytes and T. rubrum during growth on protein substrates (12,19); nevertheless, the basic mechanisms of adaptation during growth under such conditions need further investigations. The aim of the present study was to analyze a broad gene expression profile by cDNA microarray analysis in T. rubrum cells during keratin utilization.…”