The antimicrobial heterodimer S100A8/S100A9 (calprotectin) is upregulated by bacterial flagellin in human epidermal keratinocytes.
Antimicrobial peptides (AMPs) have a central role in the innate immune system of the skin. Epidermal keratinocytes (KCs) express numerous such peptides either constitutively or in response to exposure to microbial compounds. Here, we investigated the regulation of S100A8 (calgranulin A) and S100A9 (calgranulin B), which form an antimicrobial heterodimeric complex also known as calprotectin, in KCs. Culture supernatants of gram-negative bacteria, but not of gram-positive bacteria nor of the yeast Candida albicans, triggered the expression of S100A8 and S100A9. To identify pathogen-associated molecular patterns (PAMPs) responsible for the upregulation of S100A8 and S100A9, KCs were stimulated with ligands for Toll-like receptors (TLRs). Quantitative real-time PCR (qRT-PCR) analysis revealed that the TLR5 ligand flagellin increased the mRNA expression of both S100A8 and S100A9. Supernatant from wild-type (WT) Escherichia coli, but not from a flagellin-deficient E. coli strain (ΔFliC), induced S100A8 and S100A9 protein production in KCs. Moreover, small interfering RNA-mediated knockdown of TLR5 expression suppressed the ability of KCs to upregulate S100A8 and S100A9 mRNA expression in response to E. coli supernatant. Like in cell culture, stimulation of human skin explants with E. coli induced the expression of S100A8 and S100A9. Our data suggest that bacterial flagellin induces the upregulation of S100A8/S100A9 via a TLR5-dependent mechanism in epidermal KCs.
Abtin
Arby
A
Department of Dermatology, Medical University of Vienna, Vienna, Austria.
Eckhart
Leopold
L
Gläser
Regine
R
Gmeiner
Ramona
R
Mildner
Michael
M
Tschachler
Erwin
E
D040501:Calgranulin A / Q000235:genetics / Q000378:metabolism*; D040502:Calgranulin B / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D000078404:Epidermal Cells; D004817:Epidermis / Q000276:immunology / Q000378:metabolism; D004926:Escherichia coli / Q000276:immunology* / Q000378:metabolism; D004927:Escherichia coli Infections / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D029968:Escherichia coli Proteins / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D005408:Flagellin / Q000378:metabolism*; D052816:Foreskin / Q000166:cytology; D015870:Gene Expression / Q000276:immunology; D006801:Humans; D015603:Keratinocytes / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D008297:Male; D009924:Organ Culture Techniques; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051198:Toll-Like Receptor 5 / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000502:physiology; D014621:Vagina / Q000166:cytology; D014844:Vulva / Q000166:cytology
D040501:Calgranulin A; D040502:Calgranulin B; D029968:Escherichia coli Proteins; D034741:RNA, Small Interfering; C495346:TLR5 protein, human; D051198:Toll-Like Receptor 5; D005408:Flagellin