miR-146b Probably Assists miRNA-146a in the Suppression of Keratinocyte Proliferation and Inflammatory Responses in Psoriasis

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 this study, we confirmed the increased expression of miR-146a and miR-146b (miR-146a/b) in the lesional skin of patients with psoriasis. The expression of miR-146a was approximately twofold higher than that of miR-146b in healthy human skin, and it was more strongly induced by stimulation of proinflammatory cytokines in keratinocytes and fibroblasts. miR-146a/b target genes regulating inflammatory responses or proliferation were altered in the skin of patients with psoriasis, among which FERMT1 was verified as a 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 the miR-146a encoding 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 with 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.

Signs of innate immune activation and premature immunosenescence in psoriasis patients

Psoriasis is a chronic inflammatory disease that affects skin and is associated with systemic inflammation and many serious comorbidities ranging from metabolic syndrome to cancer. Important discoveries about psoriasis pathogenesis have enabled the development of effective biological treatments blocking the T helper 17 pathway. However, it has not been settled whether psoriasis is a T cell-mediated autoimmune disease or an autoinflammatory disorder that is driven by exaggerated innate immune signalling. Our comparative gene expression and hierarchical cluster analysis reveal important gene circuits involving innate receptors. Innate immune activation is indicated by increased absent in melanoma 2 (AIM2) inflammasome gene expression and active caspase 1 staining in psoriatic lesional skin. Increased eomesodermin (EOMES) expression in lesional and non-lesional skin is suggestive of innate-like virtual memory CD8+ T cell infiltration. We found that signs of systemic inflammation were present in most of the patients, correlated with the severity of the disease, and pointed to IL-6 involvement in the pathogenesis of psoriatic arthritis. Among the circulating T cell subpopulations, we identified a higher proportion of terminally differentiated or senescent CD8+ T cells, especially in patients with long disease duration, suggesting premature immunosenescence and its possible implications for psoriasis co-morbidities.

MicroRNA-155 is Dysregulated in the Skin of Patients with Vitiligo and Inhibits Melanogenesis-associated Genes in Melanocytes and Keratinocytes

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.