GRK2-mediated phosphorylation and de-succinylation of PKM2 reduce macrophage glycolysis in rheumatoid arthritis

Abstract

Glucose metabolism disorder is an important hallmark of rheumatoid arthritis (RA). Inhibiting key glycolysis enzymes is the primary approach, but effective treatments targeting glycolytic metabolism have not yet reached clinical practice. G protein-coupled receptor kinase 2 (GRK2) as a multi-signals regulatory hub has attracted wide attention. In this study, we investigated the role of GRK2 inhibitor on glycolysis of monocyte-derived macrophages (MDMs), the primary source of inflammatory mediators in RA synovium. Human peripheral mononuclear cells were obtained from RA patients and differentiated into MDMs with M-CSF (100 ng/ml) for 5 days. By analyzing the metabolic status of RA MDMs in normoxia and hypoxia, we found that glycolysis was increased in RA MDMs, and inhibiting glycolysis could suppress the macrophage inflammatory phenotype. The antiglycolytic role of GRK2 deletion was tested in MDMs in vitro and in vivo. We conducted proteomics and mass spectrometric analysis and confirmed the inhibitory role of GRK2 on several key glycolytic enzymes. GRK2 maintained PKM2 tetramer stability through two synergistic modifications-phosphorylation at S406 and de-succinylation at K433. In RA, decreased cytoplasmic GRK2 protein levels impaired its regulation toward PKM2, leading to enhanced glycolysis and accelerating RA progression. Administration of GRK2 inhibitors paroxetine, CP-25, or the glycolysis inhibitor 2-DG for 21 days in the CIA mouse model all restored cytoplasmic GRK2 levels and homeostatic regulation, offering a potential therapeutic approach for RA glycolysis.

Keywords: GRK2; PKM2; glycolysis; rheumatoid arthritis; synovial macrophages.