Non-coding RNAs in psoriasis : insights into epidermal dysregulation and inflammation

<p dir="ltr">Plaque psoriasis is a common chronic inflammatory skin disorder characterised by pruritic and scaly focal skin lesions. Characteristic skin changes include abnormal keratinocyte proliferation, dysregulated epidermal differentiation, activation of inflammatory pathways, and infiltration of immune cells into the skin. The inflammatory axis of the cytokines interleukin-23 (IL-23) and IL-17A is recognised as a central signalling pathway in the development of psoriasis and serves as an effective therapeutic target.</p><p dir="ltr">Non-coding RNAs have received increased attention over the past three decades as essential regulators of gene expression and translation in development, homeostasis, and disease. While some previous research has characterised the roles of various non-coding RNAs in psoriasis, their functions remain poorly understood. Therefore, this thesis investigates long non-coding RNAs and microRNAs and their role in psoriasis inflammatory signalling and keratinocyte dysfunction. Our work utilised bulk and single-cell RNA sequencing to profile the non-coding transcriptome, and we validated our findings through in vitro keratinocyte culture in monolayer and 3D epidermal models, in vivo mouse models of psoriasis skin inflammation, RT-qPCR and RNA in situ hybridisation.</p><p dir="ltr">Study I characterised miR-378a, a miRNA upregulated in psoriasis and regulated by IL17A that activates NF-KB signalling by repressing NFKBIA. Delivery of miR-378a lead to exacerbated skin inflammation in the imiquimod mouse model and potentiated the inflammatory effects of IL-17A in cell culture through a positive feedback mechanism, emphasising its pathogenic role in psoriasis.</p><p dir="ltr">Study II investigated the evolutionarily conserved role of miR-149 as an intrinsic suppressor of skin inflammation by repressing the TWEAK receptor. In psoriasis, miR-149 is downregulated, and epidermal deletion of miR-149 in mice leads to increased production of inflammatory mediators by keratinocytes, even in the absence of inflammatory stimuli, with no apparent phenotype resulting from its deletion in mice. In the imiquimod and Il-23 models of skin inflammation, epidermal miR-149 deletion exacerbated skin inflammation, increased immune cell infiltration, and production of inflammatory mediators. Single-cell RNA sequencing of the Il-23 model of skin inflammation identified mast cell infiltration as a notable cellular change caused by miR-149 epidermal depletion; pharmaceutical induction of mast cell apoptosis reduced imiquimod-induced skin inflammation in mice. These findings emphasise the importance of miR-149 in suppressing TWEAK/TWEAKR signalling to prevent skin inflammation, suggesting that restoring epidermal miR-149 could be a potential future treatment option for psoriasis.</p><p dir="ltr">Study III systematically describes the landscape of long non-coding RNAs in epidermal keratinocytes within psoriasis lesions and healthy skin. The skin-enriched lncRNA RP11-295G20.2 is found to be upregulated in psoriasis, regulated by IL-17A and early epidermal differentiation, and is demonstrated to suppress late-stage keratinocyte differentiation. Based on our findings, we renamed it cytoplasmic differentiation-associated epidermal RNA CYDAER.</p><p dir="ltr">Study IV created a single cell atlas of long non-coding RNAs in keratinocytes and immune cells in psoriasis and healthy epidermis, identifying distinct non-coding signatures of psoriasis cell states. LINC01137 is identified as a long non-coding RNA specifically overexpressed in psoriasis activated keratinocyte subtypes and regulated by IL-17A. LINC00892 is specifically expressed in Th1 and Th17 helper T cell subsets and proliferative cytotoxic T cells, possibly indicating T cell activation in psoriasis.</p><p dir="ltr">Collectively, the four constituent studies of this thesis elucidate the critical roles of differentially expressed non-coding RNAs in the pathogenesis of psoriasis, including amplifying inflammatory signalling, disrupting keratinocyte differentiation, and modulating immune cells. The findings contribute to an improved understanding of psoriasis pathogenesis and provide potential therapeutic targets and disease biomarkers.</p><h3>List of scientific papers</h3><p dir="ltr">I. miR-378a regulates keratinocyte responsiveness to interleukin-17A in psoriasis. Ping Xia, Lorenzo Pasquali, Chenying Gao, Ankit Srivastava, Nupur Khera, <b>Jan Cedric Freisenhausen</b>, Longlong Luo, Einar Rosen, Anke van Lierop, Bernhard Homey, Andor Pivarcsi, Eniko Sonkoly. British Journal of Dermatology, 2022 Aug;187(2):211-222. <a href="https://doi.org/10.1111/bjd.21232" rel="noreferrer" target="_blank">https://doi.org/10.1111/bjd.21232</a></p><p dir="ltr">II. Loss of epidermal microRNA-149 sensitizes to skin inflammation. Longlong Luo, Hao Yuan, Ankit Srivastava, Karl Annusver, Nupur Khera, Piyal Saha, Roxane Prieux, Kunal Das Mahapatra, Evelyn Kelemen, Menil Dholakia, <b>Jan C Freisenhausen</b>, Milena Petkova, Taija Mäkinen, Gunnar Pejler, Maria Kasper, Andor Pivarcsi, Eniko Sonkoly. [Manuscript]</p><p dir="ltr">III. RNA Sequencing Reveals the Long Non-Coding RNA Signature in Psoriasis Keratinocytes and Identifies CYDAER as a Long Non-Coding RNA Regulating Epidermal Differentiation. <b>Jan Cedric Freisenhausen</b>*, Longlong Luo*, Evelyn Kelemen, Jonathan Elton, Viktor Skoog, Andor Pivarcsi, Eniko Sonkoly. Experimental Dermatology, 2025 Feb;34(2):e70054. <a href="https://doi.org/10.1111/exd.70054" rel="noreferrer" target="_blank">https://doi.org/10.1111/exd.70054</a></p><p dir="ltr">IV. Single-cell transcriptomic analysis uncovers keratinocyte- and immune-specific long non-coding RNAs in psoriasis epidermis. <b>Jan Cedric Freisenhausen</b>*, Longlong Luo*, Huaitao Cheng, Martin Enge, Andor Pivarcsi, Enikö Sonkoly. [Manuscript]</p><p dir="ltr">* equal contribution.</p>