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Background: Psoriasis is a chronic inflammatory skin disease characterised by disrupted crosstalk between keratinocytes and immune cells, resulting in epidermal dysfunction. Long non-coding RNAs (lncRNAs) regulate gene expression in a cell-or tissue-specific manner, yet their role in psoriatic epidermal dysfunction remains poorly understood.

Objectives: To generate a single-cell atlas of lncRNA expression in healthy and psoriatic epidermis and identify cell state-specific lncRNAs associated with disease.

Methods: Data from Smart-seq2 single-cell RNA sequencing of sorted CD45⁺ and CD45^-epidermal cells from healthy controls and lesional/non-lesional psoriatic skin were analysed. Selected lncRNAs were validated by RT-qPCR, single-molecule in situ hybridisation (RNAscope), and immunofluorescence. The regulation of LINC01137 was studied in IL-17A-treated primary keratinocytes and 3D epidermal models, and its function assessed using siRNA-mediated knockdown in keratinocytes.

Results: We identified 1412 epidermal lncRNAs with robust expression across distinct keratinocyte and immune cell states. LncRNAs exhibited strong cell type-specific expression in both keratinocytes and immune cells, moreover, several lncRNAs showed selective expression in psoriasis-associated cell states. LINC01137 was enriched in activated keratinocytes, induced by IL-17A and correlated with TGF-β pathway activity; its knockdown in primary keratinocytes attenuated TGF-β-induced SERPINE1/PAI-1 expression. LINC00892 was enriched in lesional Th1, Th17 and proliferating CD8⁺T cells and showed increased expression as well as co-localisation with the T cell marker CD3 in psoriasis epidermis.

Conclusions: This study identifies the single-cell non-coding transcriptomic landscape of the psoriatic epidermis and highlights distinct lncRNA signatures in keratinocytes and immune cells, suggesting their involvement in pathogenic processes in psoriasis. 

Psoriasis is a common chronic inflammatory skin disease determined by genetic and environmental factors, resulting in the activation of IL-23/IL-17-mediated immune response, epidermal hyperproliferation, and keratinocyte activation. Long non-coding RNAs (lncRNAs) are non-protein-coding transcripts > 500 nucleotides with diverse regulatory functions; their role in epidermal dysfunction in psoriasis is poorly understood. To identify epidermal transcripts with potential roles in psoriasis, including lncRNAs, we performed RNA sequencing on keratinocytes from psoriasis and healthy skin. We identified 889 differentially expressed lncRNAs, many of which with yet unknown functions. RP11-295G20.2 was identified as a lncRNA significantly induced in psoriasis keratinocytes, and this was verified by qRT-PCR and by single-molecule in situ hybridisation. Analysis of subcellular fractions of epidermis revealed a cytoplasmic localisation in line with results of single molecule in situ hybridisation. We report that RP11-295G20.2 has a skin-enriched expression, and within skin it is mainly expressed in suprabasal epidermal layers. Moreover, RP11-295G20.2 is induced by the key psoriasis cytokine IL-17A and shows a dynamic regulation during keratinocyte differentiation with upregulation during early differentiation and downregulation in the late stage. Knockdown of RP11-295G20.2 in keratinocytes promotes terminal differentiation. Based on our findings, we named RP11-295G20.2 Cytoplasmic Differentiation-Associated Epidermal RNA, CYDAER. In summary, our study provides a comprehensive characterisation of the non-coding RNA landscape of psoriasis keratinocytes and identifies CYDAER as a skin-enriched lncRNA regulating keratinocyte differentiation. Our data suggest that overexpression of CYDAER may contribute to altered differentiation in psoriatic epidermis.

Psoriasis is a common, immune-mediated skin disease characterized by epidermal hyperproliferation and chronic skin inflammation. Long noncoding RNAs are >200 nucleotide-long transcripts that possess important regulatory functions. To date, little is known about the contribution of long noncoding RNAs to psoriasis. In this study, we identify LINC00958 as a long noncoding RNA overexpressed in keratinocytes (KCs) from psoriasis skin lesions, in a transcriptomic screen performed on KCs sorted from psoriasis and healthy skin. Increased levels of LINC00958 in psoriasis KCs were confirmed by RT-qPCR and single-molecule in situ hybridization. Confocal microscopy and analysis of subcellular fractions showed that LINC00958 is mainly localized in the cytoplasm of KCs. IL-17A, a key psoriasis cytokine, induced LINC00958 in KCs through C/EBP-β and the p38 pathway. The inhibition of LINC00958 led to decreased proliferation as measured by Ki-67 expression, live cell analysis imaging, and 5-ethynyl-2-deoxyuridine assays. Transcriptomic analysis of LINC00958-depleted KCs revealed enrichment of proliferation- and cell cycle‒related genes among differentially expressed transcripts. Moreover, LINC00958 depletion led to decreased basal and IL-17A‒induced phosphorylation of p38. Furthermore, IL-17A‒induced KC proliferation was counteracted by the inhibition of LINC00958. In summary, our data support a role for the IL-17A‒induced long noncoding RNA, LINC00958, in the pathological circuits of psoriasis by reinforcing IL-17A‒induced epidermal hyperproliferation.