Tofacitinib improves mitochondrial function in psoriatic arthritis fibroblast-like synoviocytes via autophagy modulation

Psoriatic arthritis (PsA) is a chronic inflammatory systemic disease, and peripheral joints involvement is responsible of significant morbidity for patients, leading to damage accrual. Different drugs are available for the systemic management of this condition, with different mechanisms of action. Nevertheless, the rules driving the correct therapeutical choice in each individual patient are not completely defined. Janus kinases (JAK) inhibitors are a class of drugs able to reduce synovial inflammation in patients, and tofacitinib, a JAK1/3 inhibitor, is the most studied. Preliminary evidence suggest an effect of tofacitinib on fibroblast-like synoviocytes (FLS), reducing pro-invasive and pro-inflammatory properties, as well as improving mitochondrial function. The link between JAK inhibition and mitochondrial function improvement at synovial level is not completely understood. Materials and Methods: This is an in vitro study. Patients with active PsA underwent ultrasound-guided synovial biopsy in the context of a tertiary-referral outpatient clinic. Histological evaluation was performed according to Krenn’s synovitis score. FLS, peripheral blood mononuclear cells (PBMCs), and synovial explants cultures were set up, and cells were treated in vitro with tofacitinib 1 µM or vehicle control for 24h. For some experiments, the autophagy-inducer rapamycin was utilized, as well. Protein levels in cellular homogenates were analysed by western blot for relevant autophagy markers, and chemokines/cytokines into culture supernatants were quantified by ELISA. Migration assays were used to investigate the effect of tofacitinib on invasive properties of FLS, while specific mitochondrial probes were used to measure intracellular reactive oxygen species (ROS), mitochondrial potential, and mitophagy. Oxygen consumption rate (OCR), reflecting oxidative phosphorylation, was quantified using the Seahorse technology. Differences were determined adopting the non-parametric Wilcoxon signed rank test. Results: 16 patients with moderately active PsA were enrolled. Mean (SD) Krenn’s synovitis score was 4.4. (1.9). Tofacitinib significantly increased LC3-II (p=0.0002) and ATG7 (p=0.0001) levels in PsA FLS compared to vehicle control, suggesting an increase in spontaneous autophagy activity. No effect was highlighted in PBMCs and synovial explants cultures. Tofacitinib reduced migration properties of PsA FLS (p=0.0024), and a similar trend was documented using rapamycin. Moreover, tofacitinib reduced MCP-1 and IL-6 release into FLS supernatants (p=0.0007 and p=0.0022, respectively), reduced intracellular ROS production (p=0.0180), increased basal OCR (p=0.02809), ATP production (p=0.0280) and maximal respiratory capacity (p=0.0180), and enhanced mitophagy (p=0.0156). Conclusion: The JAK inhibitor tofacitinib reduces pro-invasive and pro-inflammatory properties of PsA FLS and improves mitochondrial function. The induction of autophagy/mitophagy by tofacitinib might permit the removal of damaged mitochondria and a better functioning of the remaining ones.