To examine the effects of tofacitinib on metabolic activity, mitochondrial function, and proinflammatory mechanisms in rheumatoid arthritis (RA).
Ex vivo RA synovial explants and primary RA synovial fibroblasts (RASFs) were cultured with 1 μM tofacitinib. RASF bioenergetics were assessed using an XF24 analyzer, and key metabolic genes were assessed by reverse transcription-polymerase chain reaction (RT-PCR) analysis. Mitochondrial function was assessed using specific cell fluorescent probes and by mitochondrial gene arrays. Mitochondrial mutagenesis was quantified using a mitochondrial random mutation capture assay, and lipid peroxidation was quantified by enzyme-linked immunosorbent assay (ELISA). The effect of tofacitinib on spontaneous release of proinflammatory mediators from RA whole tissue synovial explants was quantified by ELISAs/MSD multiplex assays, and metabolic markers were quantified by RT-PCR. Finally, RASF invasion, matrix degradation, and synovial outgrowths were assessed by transwell invasion/Matrigel outgrowth assays and ELISA.
Tofacitinib significantly decreased mitochondrial membrane potential, mitochondrial mass, and reactive oxygen species production by RASFs and differentially regulated key mitochondrial genes. Tofacitinib significantly increased oxidative phosphorylation, ATP production, and the maximal respiratory capacity and the respiratory reserve in RASFs, an effect paralleled by a decrease in glycolysis and the genes for the key glycolytic enzymes hexokinase 2 (HK2), glycogen synthase kinase 3α (GSK-3α), lactate dehydrogenase A, and hypoxia-inducible factor 1α. Tofacitinib inhibited the effect of oncostatin M (OSM) on interleukin-6 (IL-6) and monocyte chemotactic protein 1 and reversed the effects of OSM on RASF cellular metabolism. Using RA whole tissue synovial explants, we found that tofacitinib inhibited the key metabolic genes for glucose transporter 1, 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3, 3'-phosphoinositide-dependent protein kinase 1, HK2, and GSK-3α, the proinflammatory mediators IL-6, IL-8, IL-1β, intercellular adhesion molecule 1, vascular endothelial growth factor, and TIE-2, and RASF outgrowth from synovial explants, RASF invasion, and matrix metalloproteinase 1 activity.
This study demonstrates that JAK/STAT signaling mediates the complex interplay between inflammation and cellular metabolism in RA pathogenesis.