Membrane‐bound stem cell factor is the major but not only driver of fibroblast‐induced murine skin mast cell differentiation

The maintenance and modulation of cutaneous mast cell (MC) numbers is held to be important for skin immune responses to allergens and pathogens. The increase in MC numbers in the skin is achieved by proliferation and the differentiation of precursor to mature MCs. Fibroblast‐derived SCF is thought to be the major skin MC growth factor and it potently induces MC proliferation. The mechanisms of fibroblast‐induced skin MC differentiation, including the role of SCF, however, remain insufficiently characterized and understood. Using cocultures of immature murine MCs and fibroblasts, we found that the adhesion of immature MCs to fibroblasts via VCAM‐1 and α₄β₇ integrin is very important for subsequent differentiation, which is driven by fibroblast membrane‐bound SCF and additional fibroblast‐derived membrane‐bound signals. Thus, our results show that fibroblast‐induced MC differentiation is induced by direct cell–cell contact and involves both Kit‐dependent and Kit‐independent pathways. Our findings add to the understanding of how immature mast cells mature in murine skin and encourage further analyses of the underlying mechanisms, which may result in novel targets for the modulation of skin mast cell driven diseases.     

Integrin αE(CD103) is induced but plays no pathogenic role in psoriasiform skin lesions of TGFβ1 transgenic mice

T‐cells expressing α_E(CD103), an integrin induced by TGFβ on T‐cells in vitro, accumulate within epithelia in inflammatory disorders, including psoriasis. However, it is unclear, if and how α_E(CD103) contributes to skin inflammation. Using two complementary approaches, we have investigated α_E(CD103) in psoriasis‐like skin inflammation of mice with transgenic epidermal expression of human TGFβ1: α_E(CD103) was inhibited by function‐blocking antibodies in vivo, and double‐mutants with additional α_E(CD103)‐depletion were generated in two different genetic backgrounds. Epidermal hTGFβ1 expression was associated with prominent expression of α_E(CD103) on infiltrating cells. However, neither treatment with α_E(CD103)‐blocking antibodies nor deficiency of α_E(CD103) in double‐mutant mice altered the psoriasis‐like phenotype. In addition, histopathological and flow cytometric analyses revealed similar pathological skin alterations and lymphocyte subgroups in the different mouse strains. Thus, while α_E(CD103) expression is indeed associated with hTGFβ1 in vivo, it has little, if any, influence on the course of the psoriasis‐like phenotype in K5.hTGFβ1 transgenic mice.     

Functional redundancy of extracellular matrix protein 1 in epidermal differentiation

BACKGROUND: Extracellular matrix protein 1 (ECM1) is a secreted protein expressed in skin. Its dermatological relevance has been highlighted by the discovery of loss-of-function mutations in ECM1 in patients with lipoid proteinosis (LiP). OBJECTIVES: To determine the role of ECM1 in epidermal differentiation by examining gene and protein expression of epidermal differentiation markers in individuals with LiP and histological assessment of transgenic mouse skin that overexpresses Ecm1a in basal or suprabasal epidermis. METHODS: Subconfluent, confluent and postconfluent LiP and control keratinocyte cultures were analysed by Northern and Western blotting for differences in expression of differentiation markers. Expression of these markers was analysed in skin of patients with LiP by immunohistochemistry. To study effects of Ecm1 overexpression on epidermal differentiation, transgenic mice were generated under control of either a keratin 14 or an involucrin promoter. RESULTS: No differential expression of the different markers analysed was observed in LiP keratinocytes compared with controls. No histological differences were found in Ecm1-overexpressing mouse skin compared with wild-type. CONCLUSIONS: Absence of ECM1 does not lead to differences in epidermal differentiation. Moreover, overexpression of Ecm1a in vivo does not exert dramatic effects on epidermal structure. Collectively, these findings suggest no role of ECM1 in epidermal differentiation.     

Role of epidermal γδ T‐cell‐derived interleukin 13 in the skin‐whitening effect of Ginsenoside F1

Ginsenoside F1 (GF1) is a metabolite of ginsenoside Rg1. Although GF1 has several benefits for skin physiology, the effect of GF1 on skin pigmentation has not been reported. We found that a cream containing 0.1% GF1 showed a significant whitening effect on artificially tanned human skin after 8 weeks of application. However, GF1 did not inhibit mRNA expression of tyrosinase or dopachrome tautomerase (DCT) in normal human epidermal melanocytes (NHEMs) or cocultured NHEMs/normal human epidermal keratinocytes. Interestingly, GF1 enhanced production of interleukin 13 (IL‐13) from human epidermal γδ T cells. IL‐13 significantly reduced the mRNA expression and protein amount of both tyrosinase and DCT and reduced melanin synthesis activities in NHEMs, resulting in visible brightening of NHEM pellet. These results suggest that enhancement of IL‐13 production by GF1 from epidermal γδ T cells might play a role in the skin‐whitening effect of GF1 via the suppression of tyrosinase and DCT.     

Downregulation of integrin‐αvβ6 on keratinocytes in the scar of lichen planopilaris and folliculitis decalvans: Relevance for the disappearance of epidermal Langerhans cells

Primary cicatricial alopecia (PCA) is a group of poorly understood mechanisms in which the destruction of hair follicles leads to permanent hair loss. Lichen planopilaris (LPP) is a type of lymphocytic PCA and it has been known for epidermal Langerhans cells (LC) to disappear in the scar of LPP. We also found that epidermal LC also disappeared in the scar of folliculitis decalvans (FD), a type of neutrophilic PCA. Of note was that epidermal LC did not disappear in the scar of discoid lupus erythematosus, another type of lymphocytic PCA, suggesting that LC disappearance in the scar was not always a common feature of PCA. We found that the expression of integrin (ITG)‐αvβ6 in scar epidermis was significantly diminished in LPP and FD, but not in other PCA and disorders accompanied with scar formation. We also found that exogenous interleukin‐1β and α‐interferon downregulated ITG‐αvβ6 expression in normal human epidermal keratinocytes. These data suggest that downregulation of ITG‐αvβ6 may be one of the causes of LC disappearance in the scar of LPP and FD.     

Chronic ultraviolet radiation modulates epidermal differentiation as it up-regulates transglutaminase 1 and its substrates

BACKGROUND: Ultraviolet radiation (UVR) stimulates cellular mitosis, which leads to epidermal hyperplasia. On the basis of hypothesis that chronic UVR may modulate differentiation as well as epidermal hyperplasia, we evaluated the modulation of markers of epidermal differentiation, such as transglutaminase 1 (TGase 1), filaggrin and loricrin, by chronic UVR in vivo. METHODS: Total TGase activities assay or in situ TGase activities were measured in human and mouse skin. TGase 1 expression was identified by immunohistochemical staining in human skin. In the human, the pre-auricular skin of face was used for samples of chronic UVR, and the post-auricular skin was selected as non-UVR control. The changes of filaggrin and loricrin were identified by western immunoblots. RESULTS: In human and mouse epidermis, chronic UVR induced the increase of in situ TGase activities or total TGase activities as it up-regulated TGase 1 expression in the epidermis. As the substrates of TGase 1, chronic UVR induced the up-regulation of filaggrin and loricrin in mouse epidermis as well. At the same time, chronic UVR induced the marked epidermal hyperplasia in human and mouse skin. CONCLUSION: Chronic UVR stimulates epidermal differentiation as it up-regulates TGase 1 and its substrates. The modified epidermal differentiation is balanced with epidermal hyperplasia, leading to the maintenance of epidermal homeostasis in the UV-irradiated epidermis.     

Cannabinoid receptors 1 and 2 oppositely regulate epidermal permeability barrier status and differentiation

Cannabinoid receptors (CBR) 1 and 2 have been implicated in keratinocyte differentiation/proliferation. How CB receptors affect epidermal permeability barrier and stratum corneum structure and function remains unclear. Permeability barrier abrogation was induced by sequential tape-stripping of the SC and assessed in both CB1R and CB2R knockout (-/-) mice in comparison with wild-type (+/+) littermates. Absence of CB1R delays permeability barrier recovery, while the latter was found to be accelerated in CB2R -/- mice. While increased lamellar body (LB) secretion is observed in CB2R -/- mice accounting for the enhanced recovery, CB1R -/- animals display strong alterations in lipid bilayer structures. Markers for epidermal differentiation (i.e. filaggrin, loricrin and involucrin) and terminal differentiation (i.e. TUNEL assay and caspase-14 activation) were respectively decreased and increased in CB1R and CB2R -/- mice. Surprisingly, CB1R agonist treatment of human cultured keratinocytes increases mRNA of p21 and cytokeratin 1 and 10 and decreases cyclin D1 but protein levels remained unchanged. Such paradox could partially be explained by the increase in non-phosphorylated-4E-BP1, an inhibitor of mRNA translation, following CB1R agonist treatment. Altogether, these observations put forward the importance and the complexity of cannabinoid signalling for the regulation of permeability barrier and epidermal differentiation.     

On the role of the epidermal differentiation complex in ichthyosis vulgaris, atopic dermatitis and psoriasis

Undisturbed epidermal differentiation is crucial for an intact skin barrier function. The epidermal differentiation complex (EDC) is a cluster of genes on chromosome 1q21 encoding proteins that fulfil important functions in terminal differentiation in the human epidermis, including filaggrin, loricrin, S100 proteins and others. Recently, evidence emerged that variation within EDC genes plays an important role in the pathogenesis of three common skin disorders, ichthyosis vulgaris, atopic dermatitis (AD) and psoriasis. Two loss-of-function mutations in the filaggrin (FLG) gene, R501X and 2282del4, were identified as causative for ichthyosis vulgaris in 15 affected European families, and the mode of inheritance was found to be semidominant. As ichthyosis vulgaris and AD often occur concomitantly in affected individuals, these two mutations were subsequently investigated in AD patients and found to be strongly associated with the disease. Following this first report, seven replication studies have been performed that all confirm an association of these two mutations with AD (or AD subtypes) in several European cohorts. Additionally, two unique loss-of-function mutations in the FLG gene were identified in Japanese ichthyosis vulgaris families and found to be associated with AD in a Japanese cohort. Thus, the FLG mutations are among the most consistently replicated associations for AD. Additionally, linkage analysis has suggested that variation within the EDC might also predispose for psoriasis but the exact susceptibility variation(s) have not yet been elucidated. Taken together, these findings convincingly demonstrate the important role of barrier dysfunction in various common skin disorders.     

Expression profiles of cortisol‐inactivating enzyme, 11β‐hydroxysteroid dehydrogenase‐2, in human epidermal tumors and its role in keratinocyte proliferation

The enzyme 11β‐hydroxysteroid dehydrogenase (11β‐HSD) catalyzes the interconversion between hormonally active cortisol and inactive cortisone within cells. There are two isozymes: 11β‐HSD1 activates cortisol from cortisone and 11β‐HSD2 inactivates cortisol to cortisone. 11β‐HSD1 was recently discovered in skin, and we subsequently found that the enzyme negatively regulates keratinocyte proliferation. We verified 11β‐HSD1 and 11β‐HSD2 expression in benign and malignant skin tumors and investigated the role of 11β‐HSD in skin tumor pathogenesis. Randomly selected formalin‐fixed sections of skin lesions of seborrheic keratosis (SK), squamous cell carcinoma (SCC), and basal cell carcinoma (BCC) were stained with 11β‐HSD1 and 11β‐HSD2 antibodies, and 11β‐HSD expression was also evaluated in murine epidermis in which hyperproliferation was induced by 12‐O‐tetradecanoylphorbol‐13 acetate (TPA). We observed that 11β‐HSD1 expression was decreased in all SK, SCC, and BCC lesions compared with unaffected skin. Conversely, 11β‐HSD2 expression was increased in SK and BCC but not in SCC. Overexpression of 11β‐HSD2 in keratinocytes increased cell proliferation. In the murine model, 11β‐HSD1 expression was decreased in TPA‐treated hyperproliferative skin. Our findings suggest that 11β‐HSD1 expression is decreased in keratinocyte proliferative conditions, and 11β‐HSD2 expression is increased in basal cell proliferating conditions, such as BCC and SK. Assessing 11β‐HSD1 and 11β‐HSD2 expression could be a useful tool for diagnosing and characterizing skin tumors.     

Deranged epidermal differentiation in kl/kl mouse and the effects of βKlotho siRNA on the differentiation of HaCaT cells

Mice deficient in the klotho gene (kl/kl mice) display the phenotypes of human ageing. We found that the expression of epidermal differentiation‐associated factors (keratin 1, keratin 10, filaggrin and loricrin) was lower in the skin of kl/kl mice than that of wild‐type mice. In vitro experiments showed that the expression of βKlotho, a family of klotho gene‐encoded protein, was induced concomitantly with the differentiation of an immortalized human epidermal keratinocyte cell line (HaCaT cells) when they were cultured in an air–liquid interface. βKlotho knockdown by small interfering ribonucleic acid suppressed the expression of the above differentiation‐associated factors in HaCaT cells. βKlotho small interfering ribonucleic acid increased the expression of keratin 14, which is expressed in mitotically active basal layer cells, and activated p44/p42 mitogen‐activated protein kinase in the HaCaT cells grown in the air–liquid interface. These findings suggest that the epidermal differentiation is deranged in kl/kl mice, and βKlotho is required for the differentiation of human epidermal keratinocytes.     

Modulation of epidermal terminal differentiation in patients after long-term topical corticosteroids.

The expression of the various markers for terminal epidermal differentiation in atrophic skin of patients after long-term topical corticosteroids (TCS) was studied by electron microscopy, immunofluorescence using antibody to profilaggrin/filaggrin (PF/FG), immunoperoxidase staining using antibody to involucrin, and oil red O stain for neural lipids of the stratum corneum. Thirty-nine patients were subdivided into two groups: (A) 19 patients suffering from rebound phenomenon after stopping TCS and (B) 20 patients without rebound phenomenon. Biopsy specimens were taken before ending the use of TCS in both groups. In group A, both the morphological markers (including the different epidermal strata, keratohyalin granules, lamellar granules, and cornified cell envelopes) and the molecular markers (including involucrin, PF/FG, and neutral lipids) of terminal epidermal differentiation were significantly suppressed. On the other hand, the differentiational markers in the atrophic skin of patients without rebound phenomena were only slightly altered. These results suggest that potent TCS not only has antiproliferative actions but also inhibits the differentiation of epidermis, resulting in structural defects in the epidermis, especially the stratum corneum.     

Pathogenic role of palatine tonsils in palmoplantar pustulosis: A review

Palmoplantar pustulosis (PPP) is characterized by symmetrical, erythematous, scaly plaques, with numerous, sterile, non‐bacterial, pinpoint pustules, which are restricted to the palms and soles. Because several reports have described the efficacy of tonsillectomy for improvement in PPP skin lesions, we consider that PPP is tonsil‐induced autoimmune/inflammatory syndrome (TIAS) while other factors are also involved in the pathogenesis of PPP. Here, the association between PPP pathogenesis and TIAS was examined, with a focus on results of previous studies. PPP patients show a hyperimmune response to indigenous bacteria such as α‐streptococci, due to impaired immunological tolerance towards such organisms. Such a novel immune response leads to T‐cell activation through the abnormal expression of secondary stimulation molecules, including cytotoxic T‐lymphocyte‐associated antigen 4, inducible T‐cell co‐stimulator and Smad7, in the tonsils of PPP patients. Activated tonsillar T cells express cutaneous lymphocyte antigen (CLA), CCR6 and β1‐integrin, enter the blood circulation and are recruited to PPP skin lesions. Within lesions, T cells roll onto endothelial cells through the interaction between CLA and E‐selectin, migrate into the extravascular area through β1‐integrin–vascular cell adhesion molecule 1 binding, and assemble in the skin through CCL20–CCR6 binding. Hyperimmune responses to autoantigens such as keratin and heat shock proteins could also be involved in PPP pathogenesis, through the stimulation of the T‐helper 17 reaction.     

病原相关分子模式对人3D皮肤皮脂腺模型表皮细胞增殖与分化影响的研究

目的：明确病原相关分子模式(PAMPs)对人表皮细胞增殖与分化的影响。方法：在人皮肤和永生化SZ95皮脂腺细胞体外共培养的3D皮肤皮脂腺培养模型中加入不同浓度(2、20、200 μg/mL)的PAMPs,包括脂多糖（LPS）,磷壁酸（LTA）和肽聚糖（PGN）,培养7天后,使用PhotoShop软件计算表皮面积;免疫组化观察Ki67,cytokeratin 10（CK10）的表达,采用ImageJ软件计算染色面积,Image-Pro Plus软件计算每张图片的累积光密度（IOD）。 结果：在不同浓度的PAMPs(LPS, LTA, PGN)作用下,表皮厚度总体较对照组呈现剂量依赖性增加;此外,表皮基底层及角质层细胞Ki67及CK10的表达也呈现不同程度的增加。结论：PAMPs具有体外促进表皮细胞的增殖与分化的作用,皮肤正常微生物可能在维护皮肤屏障功能上具有重要的生物学作用。     

The role of transforming growth factor‐β1 and oxidative stress in podoconiosis pathogenesis

Background Podoconiosis (endemic nonfilarial elephantiasis) occurs in susceptible individuals who go barefoot in regions of irritant volcanic soil. Silicate particles absorbed via the skin are thought to induce an inflammatory process and a consequent endolymphangitis of the lower leg lymphatics. Objectives To establish which oxidative stress biomarkers play a part in the inflammatory process, and to test whether transforming growth factor (TGF)‐β1 also has a pathogenetic role. Patients and methods We enrolled 50 patients with early clinical stage disease, 43 patients with advanced stage disease and 35 local healthy controls. Oxidative stress biomarkers included serum total peroxides (TP), total antioxidant capacity (TAC), total nitrate plus nitrite (TN), malondialdehyde (MDA) and total superoxide dismutase (SOD) activity. The oxidative stress index (OSI) was also determined. Serum total TGF‐β1 was assayed using sandwich enzyme‐linked immunosorbent assay. Results Compared with healthy controls, patients with early stage disease showed significantly higher mean levels of TP (P < 0·001), MDA (P < 0·05) and OSI (P < 0·01); and significantly lower mean concentrations of SOD (P < 0·001) and TGF‐β1 (P < 0·001). Mean levels of TGF‐β1 were even lower among patients with advanced stage disease (P < 0·001). Mean TAC levels were significantly lower among patients with advanced disease than either other group (P < 0·001). Conclusions This is the first study, to our knowledge, to attempt to elucidate the molecular pathogenetic events in podoconiosis. We conclude that TGF‐β1 may have a pathogenetic role, with oxidative stress playing a minor role in the early stages of disease.     

Mapping of the associated phenotype of an absent granular layer in ichthyosis vulgaris to the epidermal differentiation complex on chromosome 1

Ichthyosis vulgaris (IV) is a mild to severe scaling disorder of uncertain etiology estimated to affect as many as 1 : 250 in the population. Family studies have shown that in many cases IV follows an autosomal dominant inheritance pattern, but gene mapping studies have not been reported. To investigate the genetic basis for inherited IV, we have performed gene linkage studies in two multigenerational families where affected individuals have clinical features of IV but distinct histological features. The epidermis in this disorder characteristically displays non-specific orthohyperkeratosis. Notably, a subset of IV patients with a reduced or absent granular epidermal layer (AGL) have been reported, and decreased filaggrin levels have been described in others. The prominent role of profilaggrin in human keratohyalin suggests that defects in the gene for profilaggrin (FLG), its processing of profillagrin to filaggrin, or a gene involved in profilaggrin regulation may underlie or modify the pathology in IV. Family 1 had seven individuals with IV, severe heat intolerance and epidermis with 1-3 granular layers (consistent with normal epidermal histology). Ichthyosis vulgaris in this family did not segregate with FLG or other genes in the epidermal differentiation complex. In contrast, five of the six IV patients in Family 2, all siblings, had epidermis with no granular layer. Significant evidence was obtained for linkage of IV with the associated AGL phenotype to the epidermal differentiation complex (which includes FLG) assuming either a recessive (max Lod 3.4) or dominant (max Lod 3.6) inheritance model. Sequence analysis of FLG did not reveal a mutation in the amino or carboxyl terminal portions of the coding sequence adjacent to filaggrin repeats. The AGL may represent an endophenotype for IV, and the presence of a modifier of IV pathology at this locus is discussed.     

Modulators of the endocannabinoid system influence skin barrier repair,epidermal proliferation,differentiation and inflammation in a mouse model

Endocannabinoids (ECs) are important regulators of cell signalling. Cannabinoid receptors are involved in keratinocyte proliferation/differentiation. Elevation of the endogenous cannabinoid tone leads to strong anti‐inflammatory effects. Here, we explored the influence of endocannabinoid system (ECS) modulators on skin permeability barrier repair, epidermal proliferation, differentiation and inflammation in hairless mice. We used WOBE440, a selective fatty acid amide hydrolase (FAAH) inhibitor, WOL067‐531, an inhibitor of endocannabinoid reuptake with no relevant FAAH activity, which both signal via cannabinoid receptor‐1 and cannabinoid receptor‐2 (CB‐1R and CB‐2R) and compared them to WOBE15 which signals via CB‐2R. Barrier disruption and skin irritation were induced by tape stripping or by sodium dodecyl sulphate (SDS) patch testing. Immediately after barrier disruption, 30 μL of 0.5% WOBE440, WOL067‐531 and WOBE15 solutions or the vehicle was applied topically. Barrier repair was monitored by transepidermal water loss at 1.5, 3, 5 and 7 hours. We found that barrier repair was significantly delayed by WOL067‐531. A tendency for a delay was noticed for WOBE440, whereas for WOBE15, no effect was observed. Immunohistology showed that the tape‐stripping‐induced increase in epidermal proliferation and filaggrin expression was significantly reduced by topical applications of WOL067‐531 and WOBE440, but not by WOBE15. Also, the SDS‐induced inflammation, as determined by the number of inflammatory cells, was reduced by WOL067‐531 and WOBE440. In summary, we showed that WOL067‐531 exhibits a significant effect on skin barrier repair, epidermal proliferation/differentiation and inflammation.