Psoriasis : from transcriptome to miRNA function and biomarkers

Abstract

Psoriasis is a chronic inflammatory, immune-mediated skin condition that affects in average 2 to 3% of the world population, phenotypically characterized by red and scaly plaques on the skin of affected patients. It is a multifactorial disorder, in which both genetic predisposition and environment play key roles. Psoriasis lesional skin is characterized by abnormal keratinocyte differentiation and proliferation, as well as dermal immune cell infiltration. Psoriasis is associated with several comorbidities, e.g. arthritis, however, currently no biomarkers exist that could be used to predict or identify these at an early stage. Many studies aimed to characterize the psoriasis transcriptome, but few studies have been focusing on elucidating the gene alterations in keratinocytes in this disease. In this thesis, we explored the transcriptomic landscape of epidermal cells from lesional and non-lesional skin of patients with psoriasis, as well as from healthy volunteers’ skin and investigated the biomarker-potential of circulating microRNAs.

In our first study, we investigated the alterations of the protein-coding transcriptome in the psoriasis epidermal compartment. The separation of the epidermis from the dermis and sorting for CD45-neg cells allowed us to exclude dermal signatures including those from fibroblasts, endothelial cells, dendritic cells and T cells, but also from immune cells infiltrating the epidermis, known to populate at increased ratio the psoriasis lesional skin. We have identified biological pathways related to immune responses, cell cycle and keratinization involved in the epidermal alterations, as well as the enrichment and dominance of psoriasis-associated cytokine signatures. Moreover, we established that genetic variations associated with psoriasis may contribute to the keratinocyte transcriptomic changes in the disease.

In our second study, we investigated the alterations of the non-protein-coding transcriptome in psoriasis and identified a set of long non-coding RNAs differentially expressed in psoriasis epidermal cells. Several had genomic localization overlapping psoriasis-associated SNPs, suggesting their potential implication in the genetic susceptibility to psoriasis. We validated the over-expression of the lncRNA LINC00958 in CD45-neg cells from psoriasis lesions compared to non-lesional and healthy skin and determined its expression in different skin cell types and subcellular localization.

In our third study, we focused on psoriatic arthritis, the major psoriasis comorbidity, affecting about 1/3 of the patients with cutaneous psoriasis. In particular, we investigated the potential of circulating microRNAs as biomarkers for early diagnosis of psoriatic arthritis symptoms in patients with cutaneous psoriasis. We have identified two circulating microRNAs, let-7b-5p and miR-30e-5p, with significantly reduced levels in plasma-derived extracellular vesicles of patients with confirmed psoriatic arthritis, compared to cutaneous-only psoriasis patients.

Finally, in our fourth study, we investigated the role and functions of miR-378a, previously found overexpressed in psoriasis lesional keratinocytes compared to non-lesional and healthy skin. In vivo, in a mouse model of psoriasis-like skin inflammation, the injection of miR-378a resulted in increased clinical signs of inflammation, increased skin thickness and number of proliferating cells in the epidermis. In vitro, in cultured primary human keratinocytes, miR-378a overexpression enhanced the expression of pro-inflammatory chemokines CXCL8/IL8 and CCL20, as well as reduction of NFKBIA proteins levels.