Background/Purpose:  Rheumatoid arthritis (RA) is a chronic joint disease, characterised by synovial inflammation and destruction of articular cartilage/bone. The Janus-Kinase and Signal Transducer and Activator of Transcription (JAK-STAT) signalling pathway is implicated in the pathogenesis of RA. The objective of our research was to examine the effect of tofacitinib, a selective JAK inhibitor, on metabolic activity, mitochondrial function and pro-inflammatory mechanisms in RA.

Methods:  Primary RA synovial fibroblasts and ex-vivo RA synovial explants were cultured with tofacitinib (1µM). Expression of active phosphoSTAT3 (pSTAT3) was quantified by Western blot. The effect of tofacitinib on RA pro-inflammatory mediators, including cytokines, growth factors and matrix metalloproteinases (MMP) was quantified by ELISA and MSD multiplex assays and on RASFC invasion by Biocoat^TM assays. RASFC metabolism was assessed by the XF24-Flux-analyser and RASFC mitochondrial mutagenesis was quantified using a mitochondrial random mutation capture assay (RMCA). Mitochondrial function was assessed for reactive oxygen species (ROS), mitochondrial membrane potential (MMpot) and mitochondrial mass (MM) using the specific cell fluorescent probes and differential gene expression by mitochondrial gene arrays. Mitochondrial morphological structure was assessed by TEM. Lipid peroxidation (4HNE) and serum amyloid A were quantified by ELISA.

Results: IL-6, OSM and IL-17 induce pSTAT3 expression in RASFC. Tofacitinib inhibited basal, OSM- and IL-17-induced secretion of IL-6 and MCP-1 from RASFC (p<0.05) with no effect observed for basal and IL-17-induced IL-8 and Rantes. OSM inhibited Rantes secretion from RASFC, an effect that was reversed by Tofacitinib. In RASFC, tofacitinib significantly inhibited ROS (p<0.05), MM (p<0.05), MMpot (p<0.05) and induced glycolytic activity with concomitant attenuation of mitochondrial respiration. This was coupled with altered mitochondrial structural morphology in RASFC and differential regulation of mitochondrial genes, specifically inhibiting BCL2L1, TOMM24, PMAIP1, and inducing UCP-1 and SCS25A (p<0.05). This was also associated with changes in hypoxia response genes including HIF1a and PHD2. In RA whole tissue synovial explants, which maintain the architecture and cell-cell contact of the joint thus closely reflecting the in-vivo environment, tofacitinib significantly inhibited spontaneous secretion of IL-6, IL-8, IL-1b, ICAM-1, VEGF, Tie2 and MMP1 (all p<0.05). While tofacitinib also inhibited TNFa, IFNg and IL-12, this did not reach significance, with no effect on VCAM-1, PIGF, bFGF, 4HNE or A-SAA. Finally conditioned media from tofacitinib treated RA synovial explants inhibited RASFC invasion.

Conclusion:  This study further supports JAK-STAT inhibition as a therapeutic target for the treatment of RA

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/altered-bioenergetics-mitochondrial-function-and-pro-inflammatory-pathways-in-ra-synovium-in-response-to-tofacitinib/