Deciphering the complexity of psoriasis : non-coding RNAs and cellular interactions

Abstract: Psoriasis is a prevalent immune-mediated skin disorder marked by chronically relapsing inflammation and epidermal hyperproliferation. As researchers delve deeper into the molecular intricacies of psoriasis, emerging evidence hints at the roles of non-coding RNAs (ncRNAs). Among these, long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) are of particular interest. While lncRNAs have regulatory capabilities that are yet to be fully mapped in psoriasis, miRNAs are established as crucial regulators of gene expression, especially in immune responses and inflammation. They are believed to modulate cellular function and inflammatory circuits in psoriasis as well as bridge the communication between infiltrating immune cells and keratinocytes. Although the chronic skin inflammation in psoriasis arises from an intricate interplay between immune cells and keratinocytes, the specific cell subsets involved and the extent of their cellular interactions in the psoriatic epidermis remain to be fully delineated. Together, the potential roles of ncRNAs (paper I-III) and the delicate cell-to-cell interactions (Paper IV) in the psoriatic epidermis emerge as central themes in psoriasis studies. Paper I: In this study, we spotlight LINC00958, a lncRNA notably elevated in psoriasis keratinocytes, as revealed through our transcriptomic analysis comparing psoriatic and healthy skin samples. Validations using RT-qPCR and in situ hybridization affirmed its heightened expression. Subcellular localization studies found LINC00958 predominantly in the keratinocyte cytoplasm. Interestingly, the psoriasis-associated cytokine, IL-17A, upregulates LINC00958 through the C/EBP-β and p38 pathways. When LINC00958 was inhibited, there was a marked decline in keratinocyte proliferation, corroborated by multiple assays including EdU incorporation and IncuCyte. Our transcriptomic insights from LINC00958-depleted keratinocytes underscored a set of dysregulated genes enriched to proliferation and cell cycle. Notably, LINC00958 inhibition moderated both inherent and IL-17A-stimulated p38 phosphorylation, effectively tempering IL-17A-driven keratinocyte growth. Collectively, our findings position LINC00958 as a critical lncRNA accentuating the IL-17A-fueled hyperproliferation in psoriasis. Paper II: In this study, we unveil a miRNA-mediated mechanism in psoriasis, wherein sensitizes keratinocytes to inflammatory triggers. IFN-γ treatment leads to rapid and sustained reduction in miR-149 levels in keratinocytes. This reduction in miR-149 results in extensive transcriptomic alterations and the upregulation of inflammatory markers, including IL-6, accompanied by an enhancement of the TWEAK pathway. We've also found that miR-149 directly targets the TWEAK receptor (TWEAKR), a novel discovery with clinical relevance highlighted by reduced miR-149 expression in psoriasis keratinocytes and the positive effects of synthetic miR-149 in a psoriasis mouse model induced by imiquimod (IMQ). These findings elucidate a novel mechanism by which IFN-γ sensitizes keratinocytes for TWEAK/TWEAKR-triggered inflammation by downregulating miR-149. Paper III: To further elucidate the role of miR-149 in keratinocyte immune responses and skin homeostasis, we generated knockout mice with epidermisspecific deletion of miR-149 (Mir149EKO). Despite the genetic alteration, Mir149EKO mice presented normal skin phenotype unless provoked by inflammation. Intriguingly, Mir149EKO-derived keratinocytes displayed increased Tweakr expression and a stronger response to Tweak stimulation. Using IMQ to simulate psoriasis conditions, Mir149EKO mice manifested pronounced inflammation, observed through skin thickening, increased immune cells infiltration, and heightened psoriasis-associated inflammatory mediators. Genetic profiling further highlighted the escalated inflammation-associated genes in Mir149EKO skin after IMQ treatment. A similar exacerbated inflammatory response was observed upon IL-23 injection. Notably, neutralizing the effect of Tweak mitigated this amplified inflammation upon miR-149 deletion. Conclusively, miR-149 seems pivotal in moderating skin inflammation, with its absence potentially exacerbating Tweak/Tweakr-driven inflammatory conditions in psoriasis. Paper IV: In this study, we aimed to map cellular interactions in healthy and psoriatic epidermis. Using skin biopsies from healthy individuals and untreated psoriasis patients, we performed a partial dissociation of epidermal cells to preserve inherent cell-cell interactions. Subsequently, we categorized cells based on the presence of CD45 and analyzed them using single-cell RNA sequencing. Our results uncovered three distinct keratinocyte states with specific activation patterns and a dominant IFN-α signature. We also identified seven immune cell populations, including tissue-resident memory cells, increased to the psoriatic epidermis. Notably, we pinpointed and verified an exclusive population of pDCs in the psoriatic epidermis, emphasizing their potential role in the disease. Additionally, our analyses highlighted an amplified interaction between skin cells and immune components in psoriasis. Overall, our study offers profound insights into the psoriatic epidermal landscape, emphasizing the critical roles of activated pDCs and intensified cell interactions in the disease's progression.