Hypoxia leads to abnormal epidermal differentiation via HIF-independent pathways.

Atmospheric oxygen is important for the epidermis, as the skin epidermis is not greatly affected by blood circulation. Therefore, it is necessary to understand the effect of hypoxic signals on the epidermis as some environmental stimuli can induce skin hypoxia. Here, we investigated how hypoxia (1% O2) affected skin equivalents (SEs) and normal human epidermal keratinocytes. We found that hypoxia specifically decreased the protein levels of keratin 1 (K1)/keratin 10 (K10), a representative marker of the epidermal spinous layer in the epidermis. However, hypoxia-inducible factors, the major regulators of hypoxia, did not affect hypoxia-induced down-regulation of K1/K10. We also found that N-acetyl-l-cysteine (NAC), a reactive oxygen species scavenger, antagonized the hypoxia-induced reduction of K1/K10 in keratinocytes and SEs. In contrast to the findings for NAC, inhibitors that blocked reactive oxygen species generation did not cause recovery of K1/K10 protein levels under hypoxic conditions. Taken together, these results indicate that hypoxia leads to abnormal keratinocyte differentiation by down-regulating K1/K10 and that this phenomenon can be ameliorated by NAC.

Dual oxidase 2 is essential for house dust mite-induced pro-inflammatory cytokine production in human keratinocytes.

House dust mites (HDMs) are known to trigger chronic inflammation through Toll-like receptors (TLRs) and their signalling cascades. In this study, we found that TLR2 ligation by HDMs induced the activation of dual oxidase 2 (Duox2) and nuclear factor-κB (NF-κB), leading to the production of pro-inflammatory cytokines in human keratinocytes. Stimulation of human keratinocytes with HDMs resulted in increases in interleukin-8 (IL-8) and chemokine (C-C motif) ligand 20 (CCL20) levels. However, pro-inflammatory cytokine production was abolished in keratinocytes transfected with TLR2 siRNA, indicating that HDM-induced cytokine production was mediated via TLR2 signalling. We also examined the function of Duox1/2 isozymes, which are primarily expressed in keratinocytes, in HDM-mediated pro-inflammatory cytokine production. Human keratinocytes transfected with control siRNA or Duox1 siRNA showed no inhibition of IL-8 or CCL20 production in response to HDMs, whereas the silencing of Duox2 expression resulted in a failure to induce cytokine production. Moreover, the phosphorylation and nuclear localization of RelA/p65, a component of NF-κB, were induced by HDMs in human keratinocytes. Transfection of human keratinocytes with TLR2 siRNA or Duox2 siRNA resulted in the complete abolishment of RelA/p65 nuclear localization in response to HDMs. Taken together, these results indicate that the HDM-dependent TLR2-Duox2 signalling axis indeed promotes NF-κB activation, which induces IL-8 and CCL20 production and mediates epidermal keratinocyte inflammation.

Fructose 1, 6-diphosphate regulates desmosomal proteins and collagen fibres in human skin equivalents.

We previously reported that fructose 1,6-diphosphate (FDP), a glycolytic metabolite, alleviates ultraviolet B-induced oxidative skin damage. Here, we further examined the effects of FDP on skin. FDP decreased the number of desmosomes, whereas it increased collagen fibres in skin equivalents (SEs). FDP significantly decreased the expression of corneodesmosomal components such as desmoglein 1 (DSG1), desmocollin 1 (DSC1) and corneodesmosin (CDSN), and desquamation-related proteases, kallikrein 5 (KLK 5) and kallikrein 7 (KLK7) in normal human epidermal keratinocytes (NHEKs). In addition, FDP treatment increased the phosphorylation of p38 MAPK, but the decreased expression of corneodesmosomal components is not recovered by the treatment of p38 MAPK inhibitors. Interestingly, FDP diminished the amplitude of Ca(2+) fluxes through down-regulation of SERCA2. Taken together, these results suggested that FDP induced a decrease in desmosomes and an increase in collagen fibres similar to the process of chemical peeling, the most common treatments for ageing skin.

Hydrogen peroxide generated by DUOX1 regulates the expression levels of specific differentiation markers in normal human keratinocytes.

BACKGROUND: Recent studies have demonstrated that the production of reactive oxygen species (ROS) itself plays an indispensable role in the process of differentiation in various tissues. However, it is unclear whether ROS have an effect on the differentiation of keratinocytes essential for the development of the epidermal permeability barrier. OBJECTIVE: The aim of the study is to determine a major H2O2-generating source by ionomycin in normal human keratinocytes (NHKs), and elucidate the physiological role of H2O2 generated by identified dual oxidase 1 (DUOX1) on differentiation markers of NHKs. METHODS: To detect H2O2 level generated by ionomycin in NHKs, luminal-HRP assays are performed. To examine the effects of DUOX1 on differentiation markers of NHKs, analysis of Q-RT-PCR, siRNA knockdown, and Western blot analysis were performed. RESULTS: We found that levels of H2O2 generated by ionomycin, a Ca(2+) signal inducer, showed Ca(2+) dependence manner. In addition, DPI, an inhibitor of NOXes, significantly reversed the ionomycin-induced H2O2 level, and inhibited the mRNA expression levels of keratin 1, keratin 10, and filaggrin compared with other ROS generating system inhibitors. Interestingly, we demonstrated that extracellular Ca(2+) markedly up-regulated mRNA expression levels of DUOX1 among NADPH oxidase (NOX) isoforms. Knockdown of DUOX1 by RNA interference (RNAi) in NHKs significantly antagonized an increase of ionomycin-induced H2O2 level, and specifically decreased the expressions of several keratinocyte differentiation markers such as keratin 1, transglutaminase 3, desmoglein 1, and aquaporin 9. In addition, we also found that formation of cornified envelope was significantly reduced in DUOX1-knockdown NHKs. CONCLUSION: These results suggest that DUOX1 is the major H2O2-producing source in NHKs stimulated with Ca(2+), and plays a significant role in regulating the expression of specific markers necessary for the normal differentiation of keratinocytes.

Human dermal stem/progenitor cell-derived conditioned medium ameliorates ultraviolet a-induced damage of normal human dermal fibroblasts.

Adult skin stem cells are considered an attractive cell resource for therapeutic potential in aged skin. We previously reported that multipotent human dermal stem/progenitor cells (hDSPCs) can be enriched from (normal human dermal fibroblasts (NHDFs) using collagen type IV. However, the beneficial effects of hDSPCs on aged skin remain to be elucidated. In the present study, we analyzed the growth factors secreted from hDSPCs in conditioned medium (CM) derived from hDSPCs (hDSPC-CM) and found that hDSPCs secreted higher levels of bFGF, IGFBP-1, IGFBP-2, HGF, VEGF and IGF-1 compared with non-hDSPCs. We then investigated whether hDSPC-CM has an effect on ultraviolet A (UVA)-irradiated NHDFs. Real-time RT-PCR analysis revealed that the treatment of UVA-irradiated NHDFs with hDSPC-CM significantly antagonized the UVA-induced up-regulation of the MMP1 and the UVA-induced down-regulation of the collagen types I, IV and V and TIMP1 mRNA expressions. Furthermore, a scratch wound healing assay showed that hDSPC-CM enhanced the migratory properties of UVA-irradiated NHDFs. hDSPC-CM also significantly reduced the number of the early and late apoptotic cell population in UVA-irradiated NHDFs. Taken together, these data suggest that hDSPC-CM can exert some beneficial effects on aged skin and may be used as a therapeutic agent to improve skin regeneration and wound healing.

IL-4 inhibits the melanogenesis of normal human melanocytes through the JAK2-STAT6 signaling pathway.

Skin diseases can be characterized by their predominant CD4-positive T-helper (Th) cell profiles. Chronic dermatological conditions often give rise to abnormal skin pigmentation. To understand the role of Th cells in pigmentation, the effects of the major Th cell cytokines, IFNγ, IL-4, and IL-17A, on melanogenesis were evaluated using cultured normal human melanocytes (NHMs) instead of relying on transformed melanoma cell lines. IL-4 directly inhibited melanogenesis in NHMs and downregulated both transcription and translation of melanogenesis-associated genes, such as microphthalmia-associated transcription factor (MITF) and dopachrome tautomerase. Despite the lack of a direct inhibition of melanin pigment synthesis, IFNγ and IL-17A increased the synthesis of an antimelanogenic cytokine IL-6 in NHMs. IFNγ activated signal transducers and activators of transcription 1 (STAT1) and STAT3 phosphorylation in NHMs, and IL-4 increased the STAT3 and STAT6 phosphorylation. The differential phosphorylation profile of STAT proteins between IFNγ and IL-4 may explain the difference in their effect on melanogenesis in NHMs. The IL-4-induced downregulation of melanogenesis was inhibited by treating NHMs with a JAK2 inhibitor AG490 or STAT6 siRNA. In conclusion, the involvement of the IL-4-induced JAK2-STAT6 signaling and the IFNγ- or IL-17A-dependent antimelanogenic IL-6 production should be considered as one of the mechanisms explaining the association with hypopigmention in skin diseases.