Altered mitochondrial ultrastructure in salivary epithelial cells of patients with Sjögren's disease is associated with mitochondrial DNA release and increased activation of pattern recognition receptors: potential use of tofacitinib as therapy.

Abstract

This study aimed to analyse structural and functional mitochondrial alterations, the release of mitochondrial DNA (mtDNA), and the activation of inflammatory signalling pathways that can be reversed by tofacitinib in the salivary glands (SG) of patients with Sjögren's disease (SjD). SG from patients with SjD and controls, as well as from mice with SjD treated with or without tofacitinib, were analysed. We determined the mitochondrial ultrastructure, the presence of mtDNA in the cytosol, and the levels and localisation of pattern recognition receptors (PRRs) that recognise mtDNA. The adenosine triphosphate (ATP) levels and oxygen consumption rate (OCR) were measured to evaluate mitochondrial respiration in frozen SG. We also evaluated the OCR in human submandibular gland cells incubated with interferon-gamma (IFN-γ), tofacitinib, or both. Increased mtDNA release into the cytosol was observed in SG epithelial cells of patients with SjD. This change was linked with increased PRR activation (cyclic GMP-AMP synthase, Z-DNA-binding protein 1, and nucleotide-binding oligomerisation domain-like receptor protein 3) and decreased mitochondrial transcription factor A (TFAM). Similar mitochondrial ultrastructural alterations and increased PRR activation were observed in the SG of the SjD mouse model. These changes were reversed by tofacitinib. Interestingly, increased activity of electron transport chain complexes was observed in SG of patients with SjD, which could be modulated by IFN-γ, as observed in vitro. We also found that tofacitinib stabilised mitochondrial function at basal conditions in vitro, counteracting the mitochondrial adaptations induced by IFN-γ. Taken together, these results suggest that mitochondrial alterations are linked with inflammation and support the potential use of tofacitinib in patients with SjD.