Inhibition of PKM2 lactylation by geniposide ameliorates synovial hyperplasia in experimental arthritis

Glycolytic reprogramming-driven aberrant proliferation of FLSs is a major cause of synovial hyperplasia in rheumatoid arthritis (RA). Geniposide (GE), an iridoid glycoside extracted from the plant Gardenia jasminoides J. Ellis, has been confirmed to inhibit the proliferative activity of RA-FLSs. However, whether this effect involves the regulation of glycolytic metabolism remains unclear. In this study, collagen-induced arthritis (CIA) rat models and TNF-α-induced MH7A cell models were established to investigate the specific mechanism by which GE regulates glycolytic reprogramming. The results showed that GE not only ameliorated synovial hyperplasia and suppressed glycolysis in CIA rats, but reduced the abnormal proliferation and glycolytic levels of TNF-α-induced MH7A cells. Increased lactylation of PKM2 was observed in the synovium of CIA rats and in TNF-α-induced MH7A cells, accompanied by the transition of PKM2 from tetramer to dimer and enhanced nuclear translocation. GE was found to inhibit the lactylation of PKM2. The SphK1/p300 signaling axis was activated both in vivo and in vitro. Investigations revealed that PF543, an inhibitor of SphK1, and A-485, an inhibitor of p300, inhibited the lactylation of PKM2. Moreover, GE suppressed the SphK1/p300 axis and prevented the interaction between PKM2 and p300. The inhibitory effect of GE on glycolysis was attenuated by lactate and the p300 agonist Cholera Toxin B (CTB). It was also found the suppression of glycolysis by GE was counteracted by both lactate and CTB. These results suggested GE suppressed the abnormal proliferation of FLSs by inhibiting the SphK1/p300-mediated lactylation of PKM2, highlighting a novel treatment strategy for RA.