Responses of reconstructed human epidermis to Trichophyton rubrum infection and impairment of infection by the inhibitor PD169316.

Despite the threatening incidence of dermatophytosis, information is still lacking about the consequences of infection on epidermal barrier functions and about the keratinocyte responses that alert immune components. In order to identify the mechanisms involved, arthroconidia of the anthropophilic dermatophyte Trichophyton rubrum were prepared to infect reconstructed human epidermis (RHE) in vitro. Integrity of the barrier was monitored during infection by measurements of trans-epithelial electrical resistance and dye-permeation through the RHE. Expression and release of pro-inflammatory cytokines and antimicrobial peptides (AMP) by keratinocytes inserted into the RHE were assessed, respectively, by RT-qPCR (to analyze mRNA content in tissue extracts) and by ELISA (to detect proteins in culture media). Results reveal that infection by T. rubrum is responsible for disruption of the epidermal barrier, including loss of functional tight junctions. It additionally causes simultaneous expression and release of cytokines and AMP by keratinocytes. Potential involvement of the p38 mitogen-activated protein kinase (MAPK) signaling pathway was evaluated during infection by targeted inhibition of its activity. Intriguingly, among several p38 MAPK inhibitors, PD169316 alone was able to inhibit growth of T. rubrum on Sabouraud agar and to suppress the process of infection on RHE: this suggests that PD169316 acts on specific target in dermatophytes themselves.