miR-146a inhibits inflammatory responses in human keratinocytes and in different mouse models of skin inflammation. Little is known about the role of miR-146b in the skin. In the present study, we confirmed the increased expression of miR-146a and miR-146b (miR-146a/b) in lesional skin of psoriasis patients. The expression of miR-146a was about 2-fold higher than that of miR-146b in healthy human skin and it was more strongly induced by stimulation of pro-inflammatory cytokines in keratinocytes and fibroblasts. miR-146a/b target genes regulating inflammatory responses or proliferation were altered in the skin of psoriasis patients, among which FERMT1 was verified as direct target of miR-146a. In silico analysis of genome-wide data from >4,000 psoriasis cases and >8,000 controls confirmed a moderate association between psoriasis and genetic variants in miR-146a gene. Transfection of miR-146a/b suppressed and inhibition enhanced keratinocyte proliferation and the expression of psoriasis-related target genes. Enhanced expression of miR-146a/b-influenced genes was detected in cultured keratinocytes from miR-146a−/− and skin fibroblasts from miR-146a−/− and miR-146b−/− mice stimulated with psoriasis-associated cytokines as compared to wild type mice. Our results indicate that besides miR-146a, miR-146b is expressed and might be capable of modulation of inflammatory responses and keratinocyte proliferation in psoriatic skin.

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Materials and Methods ethics approval. This study was approved by the Research Ethics Committee of the University of Tartu. Permission number 245/M-18. The Declaration of Helsinki protocols were followed and patients gave their informed, written consent.

Little is known about the functions of microRNAs (miRNAs) in skin pigmentation disorders. The aim of this study was to investigate the expression and potential role of miRNAs in vitiligo. Of 12 studied miRNAs with proven functions in cell proliferation, differentiation, immune responses and melanogenesis, miR-99b, miR-125b, miR-155 and miR-199a-3p were found to be increased and miR-145 was found to be decreased in the skin of patients with vitiligo. Combined pathway and target analysis revealed melanogenesis-associated targets for miR-99b, miR-125b, miR-155 and miR-199a-3p. In situ hybridization analysis demonstrated increased expression of miR-155 in the epidermis of patients with vitiligo. Correspondingly, miR-155 was induced by vitiligo-associated cytokines in human primary melanocytes and keratinocytes. When overexpressed, miR-155 inhibited the expression of melanogenesis-associated genes and altered interferon-regulated genes in melanocytes and keratinocytes. In conclusion, this study demonstrates that the expression of miRNAs is dysregulated in the skin of patients with vitiligo and suggests that miR-155 contributes to the pathogenesis of vitiligo.

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Melanocytes possess several functions besides a role in pigment synthesis, but detailed characteristics of the cells are still unclear. We used whole transcriptome sequencing (RNA-Seq) to assess differential gene expression of cultivated normal human melanocytes with respect to keratinocytes, fibroblasts and whole skin. The present results reveal cultivated melanocytes as highly proliferative cells with possible stem cell-like properties. The enhanced readiness to regenerate makes melanocytes the most vulnerable cells in the skin and explains their high risk of developing into malignant melanoma.

The corticotrophin-releasing hormone-proopiomelanocortin (CRH-POMC) system in the skin coordinates pigmentation and the immune response. The aim of this study was to evaluate the regulatory role of the neuroendocrine system in the pathogenesis of psoriasis. Using quantitative real-time-PCR, mRNA expression levels of 15 genes related to the CRH-POMC system were measured in punch biopsies from lesional and non-lesional skin of patients with psoriasis and from skin of healthy control subjects. Statistically significant up-regulation of POMC, CRH receptor type 1, melanin-concentrating hormone receptor (MCHR1) and melanocortin receptors 2, 3 and 4 mRNA expression in lesional and in non-lesional skin compared with healthy control samples were established. Tyrosinase (TYR), T(Y)RP-1 and ASIP genes were statistically significantly down-regulated in lesional and non-lesional skin of psoriasis samples compared with healthy subjects. The up-regulation of POMC, melanocortin receptors, CRH receptor type 1 and MCHR1 in the lesional and non-lesional skin of psoriasis patients supports the importance of the local CRH-POMC system in the pathogenesis of psoriasis.

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