[ 背景と目的 ] TLR3 は微生物由来の核酸を認識して自然免疫を活性化するシグナル伝達レセプターである。さらに微生物の 他にも、 UVB ダメージによって NHEK から放出された ncRNA が TLR3 を活性化され、続いて炎症がされることが分 かっている。また、最近の報告ではこうした免疫応答だけでなく、 TLR3 のアゴニストである Poly (I:C) が TLR3 の 活性化を介して創傷治癒を促進することが報告されている。そこで筆者達は、 UVB ダメージ後の、皮膚バリア 機能の回復には TLR3 の活性化が必要であることを確かめた。 ［略語］ ncRNA, noncoding RNA snRNA, small nuclear RNA NHEK, normal human epidermal keratinocyte TEER, transepithelial electrical resistance ゼ ミ M1 中山千華 Journal of Investigative Dermatology, 18 September 2014 Toll-Like Receptor 3 Activation Is Required for Normal Skin Barrier Repair Following UV Damage UV ダメージからの皮膚バリア機能回復には Toll-Like Receptor3 の活性化が必要であ る TLR3, Toll-like receptor 3 TJ, tight junction Fig1. UVB ダメージを受けたケラチノサイトは皮膚バリアに重要な 遺伝子を刺激する Normal human keratinocytes were treated with 1 μg ml −1 Poly (I:C), sonicated keratinocytes, or UVB-treated keratinocytes for 24 hours. Real-time PCR was used to quantify mRNA levels, and fold-change values are calculated relative and normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression for (a) lipid transport (ATP-binding cassette subfamily A member 12 (ABCA12)), lipid metabolism (glucocerebrosidase (GBA) and acid sphingomyelinase (SMPD1)), transglutaminase-1 (TGM1), and (b) desmosome (CDSN) and tight junction (occludin (OCLN), TJ protein 1 (TJP1), and claudin 1 (CLDN1)) transcripts. Data are mean±SEM, n=3 and are representative of at least three independent experiments. *P<0.05, **P<0.01, and ***P<0.001 compared with control. τ P<0.05, ττ P<0.01, and τττ P<0.001 comparing sonicated with UVB-treated normal human epidermal keratinocyte (NHEK) treatments. One-way analysis of variance (ANOVA) with the Bonferroni post-test.

Fig2. Poly(I:C) はタイトジャンクション機能を増強する Transepithelial electrical resistance (TEER) was measured in confluent differentiated primary human keratinocytes grown in transwell inserts that were treated with various concentrations of Poly (I:C) for 24 hours (a) and 48 hours (b). (c) Time-course data of TEER values. (d) Paracellular flux was measured 30 minutes after addition of fluorescein sodium to differentiated keratinocytes that were treated with various concentrations of Poly (I:C) for 48 hours. Data are mean±SEM, n=3–8, and are representative of at least three independent experiments. *P<0.05, **P<0.01, and ***P< One-tailed t-test. Fig3. TLR3 の活性化は U1 RNA 起因の皮膚バリア遺伝子の発現変化に必要である. TLR3 was silenced in normal human epidermal keratinocytes (NHEKs) for 48 hours before treatment with 1 μg ml −1 U1 RNA or 1 μg ml −1 Poly (I:C) for 24 hours. Real-time PCR was used to quantify (a) ATP-binding cassette subfamily A member 12 (ABCA12), (b) glucocerebrosidase (GBA), (c) acid sphingomyelinase (SMPD1), and (d) tumor necrosis factor-α (TNFα) mRNA levels, and fold-change values are calculated relative to and normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression. Data are mean±SEM, n=3, and are representative of at least three independent experiments. *P<0.05, **P<0.01, and ***P< Two-tailed t- test. Ctrl, control.

Fig5 Tlr3 -/- マウスでは UVB によって崩れたバリア機能からの回復が遅れる Tlr3 −/− mice exhibit delayed barrier repair following UV treatment. (a) Transepidermal water loss (TEWL) values were measured daily for 5 days in wild-type (WT) and Tlr3 −/− mice exposed to 5 kJ m −2 UVB. Data are mean±SEM, n=3 WT, n=5 Tlr3 −/−, and are representative of at least two independent experiments. *P<0.05, two-way analysis of variance (ANOVA). (b) Barrier recovery between days 3 and 4. One-tailed t-test. Skin was harvested from mice 24 hours after treatment with 5 kJ m −2 UVB. (c) Toluidine blue-stained ultrathin sections. Bar=20 μm. (d) Transmission electron microscopy images of UVB-treated skin of WT and Tlr3 −/− mice. Bar=1 μm. (e, f) Mice were lethally irradiated and subsequently reconstituted with bone marrow 7 weeks before UVB irradiation and TEWL measurements. Data are mean±SEM, n=6–8, and are representative of at least two independent experiments. *P<0.05 and **P<0.01. Two-way analysis of variance (ANOVA). TLR, Toll-like receptor 3. Fig4. バリア機能関連・炎症性サイトカイン遺伝子発現に与える様々な snRNA. (a) Structures of snRNA species generated using RNAfold and VARNA applet. (b) Normal human epidermal keratinocytes (NHEKs) were treated with 1 μg ml −1 in vitro transcribed snRNAs for 24 hours in the presence of Dharmafect 1. Real-time PCR was used to quantify mRNA levels, and fold-change values are calculated relative to and normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression and then to NHEKs that have been treated with a control in vitro transcribed RNA. Data are mean±SEM, n=3, and are representative of at least three independent experiments. *P<0.05, **P<0.01, and ***P< Two-tailed t- test. ABCA12, ATP-binding cassette subfamily A member 12; GBA, glucocerebrosidase; SMPD1, acid sphingomyelinase; TGM1, transglutaminase 1; TNF, tumor necrosis factor.

まとめ ●UVB ダメージによって、 NHEK はバリア機能関連遺伝子の発現を促進する ●UVB ダメージを受けた NHEK から放出される物質が TLR3 を介してバリア機能の回復の影響を与える ● snRNA と Poly(I:C) は NHEK において同様の応答をする ●TLR3 欠損マウスはバリア機能の回復が遅れる ➣紫外線によってダメージを受けた皮膚のバリア機能回復には TLR3 の活性化が必要である (e, f) Mice were lethally irradiated and subsequently reconstituted with bone marrow 7 weeks before UVB irradiation and TEWL measurements. Data are mean±SEM, n=6–8, and are representative of at least two independent experiments. *P<0.05 and **P<0.01. Two-way analysis of variance (ANOVA). TLR, Toll-like receptor 3.