Thymidine phosphorylase participates in platelet activation and promotes inflammation in rheumatoid arthritis

The elevated risk of cardiovascular disease (CVD) associated with inflammatory rheumatic diseases has long been recognized. Patients with established rheumatoid arthritis (RA) have a higher mortality rate compared to the general population due to abnormal platelet activation. Thymidine phosphorylase (TYMP) plays a crucial role in platelet activation and thrombosis, following bridging the link between RA and CVD. Data from Gene Expression Omnibus (GEO) database exhibited that TYMP levels were highly expressed in synovial tissues, immune cells, and whole blood of RA patients especially those with high levels of inflammation. Platelet count (PLT) and plateletcrit (PCT) were positively correlated with the severity of inflammation in rheumatoid arthritis while platelet distribution width (PDW) and mean platelet volume (MPV) were adverse. Levels of CD62P and TYMP in platelets of patients with active RA were significantly elevated compared to patients in the inactive phase. In vivo exepriments showed that reducing TYMP expression levels of platelets could relieve inflammation in Adjuvant-Induced Arthritis (AIA) mice. Platelet activation was significantly elevated in AIA model mice, along with increased levels of intracellular calcium (Ca²⁺), reactive oxygen species (ROS), and decreased Mitochondrial Membrane Potential (ΔΨm). However, treatment with Tipiracil hydrochloride (TPI) or the utilization of Tymp^-/- mice reversed these effects. In vitro stimulation of wild type (WT) mouse platelets with tumor necrosis factor-alpha (TNF-α) promoted platelet activation, elevated levels of intracellular Ca²⁺as well as ROS while decreased ΔΨm. Platelets of WT mice treated with TPI or platelets of Tymp^-/- mice exhibited the adverse results. Our study illustrates the vital role of TYMP in promoting RA inflammation and platelet activation, suggesting that TYMP may be a potential therapeutic target for RA.