The role of microRNAs in allergic contact dermatitis and skin responses to ultraviolet radiation

Abstract

MicroRNAs are small non-protein coding RNA transcripts that control gene expression in a posttranscriptional manner, affecting several cellular processes including development, differentiation, apoptosis and disease. MicroRNAs are crucially important in the immune system and their deregulation leads to inflammatory diseases or cancer. In particular miR-155 is critical in antigen presentation by dendritic cells; miR-146a is transcribed by NF-κB and miR-125b silences TNF-α. Thus, these microRNAs are implicated in processes that take place in the sensitization process of allergic contact dermatitis (ACD), when the Langerhans cells (LC) migrate from the epidermis to present the hapten to T-cells. In this project, these microRNAs’ expression profiles were investigated using an ACD model which involved the application of the allergen 2,4- dinitrochlorobenzene (DNCB) onto skin tissue ex vivo, human primary keratinocytes (HPK) and monocyte derived dendritic cells (MoDCs) in vitro, in order to elucidate their role in ACD initiation. Migration experiments showed consistent LC depletion after DNCB application (N=8). However, qPCR data from DNCB treated skin explants showed variable or no modulation of miR-155, -125b and -146a. HPK expressed the aforementioned microRNAs but failed to show any significant modulation in their expression. In DNCB stimulated MoDCs, the miR-146a expression was found significantly suppressed (p<0.5) in N=8 individuals. This suppression was absent in MoDCs treated with supernatants from DNCB treated HPK but miR-125b was found significantly upregulated (p<0.05). These findings reveal that the DNCB has a distinct impact on miR-138 and miR-146a expression in MoDCs that could be used a microRNA signature for antigenicity of potential contact allergens. Exposure of cells to DNA damaging stimuli, including ionising radiation (IR), adriamycin and ultraviolet radiation (UVR), leads to DNA damage and subsequent upregulation of the p53 protein. p53 activation plays a determinant role in cell cycle arrest/survival or programmed cell death. Post IR or adriamycin insult, p53 triggers transcriptional activation of microRNA-34a (miR-34a) which regulates cell cycle and DNA damage response genes, and represses silent information regulator 1 (SIRT1) thus promoting apoptosis. However, SIRT1 levels remain unaffected by UVR treatment. In this study, it is investigated whether UVR causes transcriptional activation of miR-34a and silencing of SIRT1 translation. HCT116 cells and primary human keratinocytes were exposed separately to UV, ionising radiation and adriamycin. Ex vivo human skin was irradiated with ionising radiation and UVR. HCT116 cells and HPK were exposed to IR and adriamycin that led to significant increases in p53 and miR-34a. Even though, UVR caused similar increases in p53, miR-34a expression was significantly suppressed. p53 protein levels were increased by UVR and IR but miR-34a was only induced in the case of IR. In addition, IR and adriamycin reduced SIRT1 protein levels, whereas UVR did not modulate SIRT1 levels. This unique modulation of miR-34a post DNA damage may have important implications for skin carcinogenesis.

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Identifiers

ORCID for Tilman Sanchez-Elsner: orcid.org/0000-0003-1915-2410

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