BACKGROUND: There is a pressing need to identify early biomarkers of lung involvement in systemic sclerosis (SSc) to start as soon as possible antifibrotic therapy. We aimed to identify extracellular vesicle-derived microRNAs (EV-miRNAs) that are differentially expressed between SSc patients with and without interstitial lung disease (ILD), explore their diagnostic value and investigate their functional properties. METHODS: Small EVs (sEVs) derived from plasma were isolated from 91 well-characterised SSc patients with ILD (SSc-ILD, n=45), without ILD (SSc-no ILD, n=46) and 43 matched healthy subjects (HS). Small RNA sequencing followed by quantitative RT-PCR were used to identify and validate sEV-miRNAs associated to SSc-ILD. Correlations between SSc-ILD-associated miRNAs and clinical parameters were assessed, as well as the impact of related miRNAs/sEVs on fibrosis. RESULTS: We identified a 4-miRNA signature associated with ILD in SSc context (miR-584-5p, miR-744-5p, miR-1307-3p and miR-10b-5p) (ROC AUC=0.85, 95% CI 0.76-0.94, p<
0.0001). Deeper analysis revealed a correlation of these candidates with pulmonary function tests (DLCO and FVC), highlighting their capacity to monitor lung fibrosis progression in SSc patients. Furthermore, SSc-ILD-associated sEV miRNAs are positively correlated and enriched in circulating lymphocytes, suggesting that these immune cells are their cellular source. Finally, functional studies highlighted an alteration of functional properties of sEVs in SSc-ILD context mainly due to the transfer of profibrotic miR-584-5p in lung fibroblasts. CONCLUSIONS: Our sEV-based biomarker approach enabled to identify a promising 4-miRNA signature characteristic of ILD in SSc patients. Furthermore, the profibrotic properties of SSc-ILD-associated sEVs suggest a prominent role of these vesicles on SSc severity.