miRNA miR‐17‐92 cluster is differentially regulated in the imiqumod‐treated skin but is not required for imiqumod‐induced psoriasis‐like dermatitis in mice

MicroRNAs (miRNAs) play very important roles in the control of immune cell and keratinocyte development and function and are implicated in skin inflammatory diseases, including psoriasis. miRNA miR‐17‐92 was reported to promote the differentiation of Th1 and Th1 cells and to regulate cell proliferation and apoptosis. Here we showed that imiquimod (IMQ) differentially regulates the expression of miR‐17‐92 cluster in the mouse skin, upregulating miR‐17 and miR‐19 families and downregulating miR‐92. To investigate whether miR‐17‐92 cluster is functionally involved in the psoriasis, we have generated three mutant mice with specific deletion or overexpression of miR‐17‐92 cluster in keratinocytes, or with deletion of miR‐17‐92 cluster in T cells. Interestingly, deletion or overexpression of miR‐17‐92 cluster in keratinocytes, or deletion of miR‐17‐92 in T cells did not significantly affect IMQ‐induced psoriasis‐like dermatitis development in the mutant mice compared with wild‐type littermates. Thus, miRNA miR‐17‐92 cluster may not be a key factor regulating imiqumod‐induced psoriasis‐like dermatitis.     

Interleukin‐21 receptor signalling is not critically required for imiquimod‐induced psoriasiform dermatitis in mice

Psoriasis is largely mediated by interleukin (IL)‐23/T helper (Th) 17 axis, and IL‐21 is a pleiotropic cytokine expressed by Th17 cells. Despite previously reported possible pathogenic roles of IL‐21 in human psoriasis, we found that IL‐21 receptor (IL‐21R) signalling was not crucial for imiquimod‐induced psoriatic inflammation, using IL‐21R^?/? mice. The severity of imiquimod‐induced psoriatic manifestation and pro‐inflammatory Th17 cytokine levels, IL‐17A‐producing γδ T cells and CD4+ T cells, and in vitro IL‐17A production by γδ T cells after IL‐23 stimulation was comparable between wild‐type and IL‐21R^?/? mice. Collectively, IL‐21R signalling was not critically involved in IMQ‐induced psoriatic inflammation despite an increased IL‐21 expression in the IMQ‐treated mouse skin. Our data may represent the significant differences between human psoriasis and murine psoriasis model, and further studies using other models will be required to elucidate the role of IL‐21 in psoriasis pathogenesis.     

Hair miR‐29a levels are decreased in patients with scleroderma

In the present study, we evaluated the possibility that we can utilize hair shaft miR‐29a levels as disease marker of scleroderma. Hair samples were obtained from 20 scleroderma patients, five dermatomyositis patients and 13 controls. microRNAs were purified from hairs as well as skins or sera, and miR‐29a levels were measured with quantitative real‐time polymerase chain reaction. Mean hair miR‐29a levels in scleroderma patients were significantly lower than those in control subjects or dermatomyositis, while expression levels of hair shaft marker keratin 34 were similar among them. There was no strong correlation among the miR‐29a levels in the hair, skin and serum of each patient, suggesting that hair microRNAs can be independent biomarkers. We found scleroderma patients with decreased miR‐29a levels had contracture of the phalanges at a significantly higher prevalence than those without. To confirm the clinical usefulness of hair microRNAs, large‐scale researches are needed in the future.     

miR‐424 levels in hair shaft are increased in psoriatic patients

Objective diagnostic markers have not been in clinical use for psoriasis. In this study, we investigated the levels of miR‐424 in hair roots and hair shafts in psoriatic patients, and evaluated the possibility that miR‐424 can be a biomarker of the disease. A single hair root and five pieces of hair shafts (~5 cm in length) were obtained from the non‐lesional occiput of each individual of 26 psoriatic patients. Control hair samples were collected from nine normal subjects. Samples from 10 atopic dermatitis patients were also included as the disease control. miR‐424 levels were determined by quantitative real‐time polymerase chain reaction. Hair shaft miR‐424 levels were significantly upregulated only in patients with psoriasis compared with normal controls and those with atopic dermatitis. By receiver–operator curve analysis of hair shaft miR‐424 to distinguish psoriatic patients from normal subjects, the area under the curve was 0.77. However, relative miR‐424 levels were not correlated with disease activity markers including disease duration, body surface area and Psoriasis Area and Severity Index. Hair root miR‐424 was not useful for evaluating both diagnosis and severity of the disease. Our results indicated hair shaft miR‐424 levels may be useful as a diagnostic marker of psoriasis.     

Dickkopf‐1 is involved in dexamethasone‐mediated hair follicle regression

The stress‐related neurohormones including glucocorticoids (GCs) are secreted by hair follicles (HFs), and GCs suppress murine hair growth in vivo. In this study, we found that dexamethasone (Dex), a synthetic GC, increased the expression of dickkopf‐1 (DKK1), a known catagen inducer, in dermal papilla (DP) cells, but not in follicular keratinocytes. The neutralizing DKK1 antibody significantly attenuated the Dex‐induced inhibition of human hair shaft elongation. In addition, the neutralizing Dkk1 antibody delayed Dex‐induced catagen in mice. Collectively, our data strongly suggest that stress‐related neurohormones cause DP cells to secrete DKK1, thereby leading to stress‐associated disturbances in hair growth.     

miR‐137 inhibits proliferation of melanoma cells by targeting PAK2

MicroRNAs (miRNA) are key players in a variety of cancers including malignant melanoma. miR‐137 has been reported to be a tumor suppressor in melanoma and several targets have been identified for this miRNA. We previously developed a novel proteomics technology, ³⁵S in vivo/vitro labelling analysis for dynamic proteomics (SiLAD). Because of its high sensitivity in analysing protein expression rates, SiLAD has the potential to unravel miRNA effects on mRNAs coding for proteins with long half‐lives or high abundance. Using SiLAD, we discovered that miR‐137 significantly downregulated the expression rate of p21‐activated kinase 2 (PAK2) in melanoma cells. Bioinformatics analysis predicted PAK2 as a direct target of miR‐137, which was confirmed by luciferase reporter assay and Western blot analysis. We found that overexpression of miR‐137 inhibited the proliferation of melanoma cells, which could be phenocopied by knockdown of PAK2 using siRNAs. Furthermore, overexpression of PAK2 restored miR‐137‐mediated suppression of cell proliferation. These findings indicate that miR‐137 could inhibit proliferation through targeting PAK2 in melanoma cells.     

Genetic 3′UTR variation is associated with human pigmentation characteristics and sensitivity to sunlight

Sunlight exposure induces signalling pathways leading to the activation of melanin synthesis and tanning response. MicroRNAs (miRNAs) can regulate the expression of genes involved in pigmentation pathways by binding to the complementary sequence in their 3′untranslated regions (3′UTRs). Therefore, 3′UTR SNPs are predicted to modify the ability of miRNAs to target genes, resulting in differential gene expression. In this study, we investigated the role in pigmentation and sun‐sensitivity traits, as well as in melanoma susceptibility, of 38 different 3′UTR SNPs from 38 pigmentation‐related genes. A total of 869 individuals of Spanish origin (526 melanoma cases and 343 controls) were analysed. The association of genotypic data with pigmentation traits was analysed via logistic regression. Web‐based tools for predicting the effect of genetic variants in microRNA‐binding sites in 3′UTR gene regions were also used. Seven 3′UTR SNPs showed a potential implication in melanoma risk phenotypes. This association is especially noticeable for two of them, rs2325813 in the MLPH gene and rs752107 in the WNT3A gene. These two SNPs were predicted to disrupt a miRNA‐binding site and to impact on miRNA‐mRNA interaction. To our knowledge, this is the first time that these two 3′UTR SNPs have been associated with sun‐sensitivity traits. We state the potential implication of these SNPs in human pigmentation and sensitivity to sunlight, possibly as a result of changes in the level of gene expression through the disruption of putative miRNA‐binding sites.     

2‐deoxy D‐glucose treatment does not elicit a hair growth response in alopecia areata

2‐deoxy D‐glucose (2DG) was tested for efficacy in treating alopecia areata using the C3H/HeJ skin graft model. 2DG has proven to be efficacious in treatment of various mouse models of autoimmunity with minimal serious side effects noted. This agent has been shown to normalize abnormally activated T‐cell populations while also preventing cell surface expression of NKG2D; key factors defining alopecia areata disease progression. Daily oral ingestion of 2DG via drinking water to mice with patchy or diffuse alopecia areata for 16 weeks failed to prevent expansion of alopecia or cause regrowth of hair in treated mice. Histologically, there were no differences between treated and control groups. These results indicate that, while 2DG is effective for some autoimmune diseases, it was not efficacious for the cell‐mediated autoimmune mouse disease, alopecia areata.     

Hyperbaric oxygen improves ultraviolet B irradiation‐induced melanin pigmentation and diminishes senile spot size

Background: The effects of exposure to hyperbaric oxygen on ultraviolet B (UVB) irradiation‐induced melanin pigmentations of skins and on senile spot sizes of faces were investigated. Methods: In the first experiment, male subjects were irradiated with UVB on their upper arms for inducing erythema and the subsequent melanin pigmentation. They were exposed to a hyperbaric environment at 1.25 atmospheres absolute (ATA) with 32% oxygen for 1 h/day, three times per week. In the second experiment, female subjects were exposed to a hyperbaric environment at 1.25 ATA with 32% oxygen for 1 h/day, two times per week. Results: In the first experiment, melanin pigmentations lightened after 4 weeks of exposure to hyperbaric oxygen. In the second experiment, senile spot sizes became small after 12 weeks of exposure to hyperbaric oxygen. Conclusion: We concluded that exposure to hyperbaric oxygen used in this study accelerates both the fading in melanin pigmentation and the decrease in senile spot size.     

miR‐155 is involved in tumor progression of mycosis fungoides

Biopsy specimens from 23 early stage and 19 tumor‐stage mycosis fungoides (MF) patients were evaluated for miR‐155 expression by real‐time qualitative PCR and compared with 15 biopsy specimens from patients with T‐cell‐rich inflammatory skin diseases. Significant upregulation of miR‐155 was found in MF tumors compared with both early‐stage MF lesions and controls. There was no difference in miR‐155 expression between early‐stage and inflammatory dermatoses. Using laser capture microdissection, it was found that miR‐155 was significantly higher in the lymphoma cells in tumor stage compared with the intraepidermal lymphocytes in early stage. In contrast, there was no difference in miR‐155 expression between the intraepidermal lymphocytes and the dermal lymphocytes in early‐stage MF. These findings suggest that although miR‐155 expression cannot serve to discriminate early‐stage MF from inflammatory dermatoses; however, it is involved in the switch from the indolent early stage into the aggressive tumor stage of the disease.     

Prostaglandin D2 production in FM55 melanoma cells is regulated by α‐melanocyte‐stimulating hormone and is not related to melanin production

Please cite this paper as: Prostaglandin D₂ production in FM55 melanoma cells is regulated by α‐melanocyte‐stimulating hormone and is not related to melanin production. Experimental Dermatology 2010; 19 : 751–753. Abstract: This study shows that prostaglandins in human FM55 melanoma cells and epidermal melanocytes are produced by COX‐1. Prostaglandin production in FM55 melanoma cells was unrelated to that of melanin suggesting that the two processes can occur independently. α‐Melanocyte‐stimulating hormone, which had no effect on melanin production in FM55 cells, stimulated PGD₂ production in these cells without affecting PGE₂. While cAMP pathways may be involved in regulating PGD₂ production, our results suggest that α‐MSH acts independently of cAMP, possibly by regulating the activity of lipocalin‐type PGD synthase. This α‐MSH‐mediated effect may be associated with its role as an immune modulator.     

Cxcr4 is transiently expressed in both epithelial and mesenchymal compartments of nascent hair follicles but is not required for follicle formation

Hair follicle (HF) morphogenesis relies on the coordinated exchange of signals between mesenchymal and epithelial compartments of embryonic skin. Chemokine receptor Cxcr4 expression was recently identified in dermal condensates (DCs) of nascent HFs, but its role in promoting HF morphogenesis remains unknown. Our analyses confirmed Cxcr4 expression in condensate cells, and additionally revealed transient Cxcr4 expression in incipient epithelial hair placodes. Placodal Cxcr4 appeared prior to detection in DCs, representing a switch of expression between epithelial and mesenchymal compartments. To explore the functional role of this receptor in both compartments for early HF formation, we conditionally ablated Cxcr4 with condensate‐targeting Tbx18^cre knock‐in and epidermis‐targeting Krt14‐cre transgenic mice. Conditional knockouts for both crosses were viable throughout embryogenesis and into adulthood. Morphological and biochemical marker analyses revealed comparable numbers of HFs forming in knockout embryos compared to wild‐type littermate controls in both cases, suggesting that neither dermal nor epithelial Cxcr4 expression is required for early HF morphogenesis. We conclude that Cxcr4 expression and chemokine signaling through this receptor in embryonic mouse skin is dispensable for HF formation.