Association of mitochondrial RNA expression levels in saliva and plasma with interferon signature gene expression and disease activity in patients with Sjögren disease.

Objective: To unveil the clinical implications of mitochondrial RNAs (mt-RNAs) in Sjögren disease (SjD), this study evaluated mt-RNA expression levels in the plasma and saliva of patients with SS and their association with SjD-related features.

Methods: Plasma, saliva and/or peripheral blood mononuclear cells (PBMCs) were collected from 111 patients with SjD and 35 healthy controls (HCs), with 40 rheumatoid arthritis (RA) and 40 systemic lupus erythematosus (SLE) disease controls. The expression levels of mt-RNAs and interferon-stimulated genes (ISGs) were quantified by real-time PCR. Composite mt-RNA and ISG scores were calculated using logistic regression models. Their discriminative power was evaluated using receiver operating characteristic curve analyses, and correlations with clinical data were explored.

Results: Altered mt-RNA expression in saliva or plasma and ISG expression in PBMCs were detected in patients with SjD, compared with HCs. Saliva and plasma mt-RNA scores showed better discriminative ability (area under the curve values=0.847 and 0.789, respectively) than ISG scores in distinguishing SjD from HCs. Plasma mt-RNA scores were significantly higher in patients with SjD than in those with RA and SLE (p<0.05). Saliva mt-RNA scores were positively associated with objective disease activity measures and Raynaud phenomenon in patients with SjD, whereas plasma mt-RNA scores did not show this association. RA and SLE disease activity correlated with plasma mt-RNA scores.

Conclusions: Extracellular mt-RNA burden is elevated in SjD, and mt-RNA scores effectively discriminated patients with SjD from HCs. Saliva mt-RNA levels were associated with SjD disease activity, suggesting their potential utility in disease monitoring and stratification of SjD.