Long non-coding RNA H19X as a regulator of mononuclear cell adhesion to the endothelium in systemic sclerosis.

OBJECTIVE: To define the functional relevance of H19 X-linked (H19X) co-expressed long non-coding RNA (lncRNA) in endothelial cell (EC) activation as a key process in SSc vasculopathy. METHODS: H19X expression in SSc skin biopsies was analysed from single-cell RNA sequencing (scRNA-seq) data. Differential expression and pathway enrichment analysis between cells expressing (H19Xpos) and non-expressing H19X (H19Xneg) cells was performed. H19X function was investigated in human dermal microvascular ECs (HDMECs) by silencing. H19X and EC adhesion molecule levels were analysed by real-time quantitative PCR and western blot after stimulation with pro-inflammatory cytokines. Cytoskeletal rearrangements were analysed by fluorescent staining. Endothelial adhesion was evaluated by co-culture of HDMECs and fluorescent-labelled peripheral blood mononuclear cells (PBMCs). Shedding vascular cell adhesion protein 1 (VCAM1) was evaluated by ELISA on HDMEC supernatant. RESULTS: The scRNA-seq data showed significant upregulation of H19X in SSc compared with healthy ECs. In HDMECs, H19X was consistently induced by IFN type I and II. H19X knockdown lead to a significant decrease in the mRNA of several adhesion molecules. In particular, VCAM1 was significantly reduced at the protein and mRNA levels. Co-expression analysis of the scRNA-seq data confirmed higher expression of VCAM1 in H19Xpos ECs. ECs were also strongly associated with the 'cell adhesion molecule' pathway. Moreover, the VCAM1 downstream pathway displayed less activation following H19X knockdown. Contractility of HDMECs, PBMC adhesion to HDMECs and VCAM1 shedding were also reduced following H19X knockdown. CONCLUSIONS: lncRNA H19X may contribute to EC activation in SSc vasculopathy, acting as a regulator of expression of adhesion molecules in ECs.