Mechanical Skin Injury Induces TLR4/MyD88 Dependent IL-23 Expression In Epidermal Keratinocytes

Abstract

RationaleScratching and epidermal hyperplasia are hallmarks of atopic dermatitis. IL-23 is a cytokine that induces epidermal hyperplasia. We examined the hypothesis that mechanical skin injury by tape stripping, a surrogate of scratching, induces IL-23 expression in the skin.MethodsEar skin of mice was tape stripped then examined 6 hrs later for IL-23 expression by quantitative RT-PCR and immunohistochemistry. Low molecular weight hyaluronic acid (HA) was injected intradermally, and 3 hrs later, skin was harvested. Langerhans cells were depleted by i.p. injection of 1 μg diphtheria toxin (DT) into langerin-eGFP-DTR mice, and 24 hrs later ear skin was tape stripped then harvested. The keratinocyte cell line, PAM212 cells was treated with HA (50 μg/ml) for 3hResultsTape stripping induced epidermal IL-23 expression of WT, but not TLR4 and MyD88 deficient mice. IL-23 induction by tape stripping in germ free mice was comparable to that in specific pathogen free mice. Skin of LC-depleted mice showed the same level of IL-23 induction compared to intact mice. Intradermal injection of the endogenous danger signal molecule, HA induced IL-23 expression in the skin of WT, but not TLR4 deficient mice. HA treatment induced IL-23 expression by PAM212 cells in vitro.ConclusionScratching may contribute to epidermal hyperplasia in AD through the release of the endogenous danger signal molecule HA, which directly induces IL-23 expression from keratinocytes through TLR4/MyD88 signaling. RationaleScratching and epidermal hyperplasia are hallmarks of atopic dermatitis. IL-23 is a cytokine that induces epidermal hyperplasia. We examined the hypothesis that mechanical skin injury by tape stripping, a surrogate of scratching, induces IL-23 expression in the skin. Scratching and epidermal hyperplasia are hallmarks of atopic dermatitis. IL-23 is a cytokine that induces epidermal hyperplasia. We examined the hypothesis that mechanical skin injury by tape stripping, a surrogate of scratching, induces IL-23 expression in the skin. MethodsEar skin of mice was tape stripped then examined 6 hrs later for IL-23 expression by quantitative RT-PCR and immunohistochemistry. Low molecular weight hyaluronic acid (HA) was injected intradermally, and 3 hrs later, skin was harvested. Langerhans cells were depleted by i.p. injection of 1 μg diphtheria toxin (DT) into langerin-eGFP-DTR mice, and 24 hrs later ear skin was tape stripped then harvested. The keratinocyte cell line, PAM212 cells was treated with HA (50 μg/ml) for 3h Ear skin of mice was tape stripped then examined 6 hrs later for IL-23 expression by quantitative RT-PCR and immunohistochemistry. Low molecular weight hyaluronic acid (HA) was injected intradermally, and 3 hrs later, skin was harvested. Langerhans cells were depleted by i.p. injection of 1 μg diphtheria toxin (DT) into langerin-eGFP-DTR mice, and 24 hrs later ear skin was tape stripped then harvested. The keratinocyte cell line, PAM212 cells was treated with HA (50 μg/ml) for 3h ResultsTape stripping induced epidermal IL-23 expression of WT, but not TLR4 and MyD88 deficient mice. IL-23 induction by tape stripping in germ free mice was comparable to that in specific pathogen free mice. Skin of LC-depleted mice showed the same level of IL-23 induction compared to intact mice. Intradermal injection of the endogenous danger signal molecule, HA induced IL-23 expression in the skin of WT, but not TLR4 deficient mice. HA treatment induced IL-23 expression by PAM212 cells in vitro. Tape stripping induced epidermal IL-23 expression of WT, but not TLR4 and MyD88 deficient mice. IL-23 induction by tape stripping in germ free mice was comparable to that in specific pathogen free mice. Skin of LC-depleted mice showed the same level of IL-23 induction compared to intact mice. Intradermal injection of the endogenous danger signal molecule, HA induced IL-23 expression in the skin of WT, but not TLR4 deficient mice. HA treatment induced IL-23 expression by PAM212 cells in vitro. ConclusionScratching may contribute to epidermal hyperplasia in AD through the release of the endogenous danger signal molecule HA, which directly induces IL-23 expression from keratinocytes through TLR4/MyD88 signaling. Scratching may contribute to epidermal hyperplasia in AD through the release of the endogenous danger signal molecule HA, which directly induces IL-23 expression from keratinocytes through TLR4/MyD88 signaling.