GALNT1 drives aggressive phenotypes of rheumatoid synoviocytes via NEK9 O‑glycosylation

Fibroblast-like synoviocytes (FLSs) are crucial in driving synovial inflammation and joint damage in rheumatoid arthritis (RA). This study explored the functions and underlying mechanisms of GALNT1-mediated O-glycosylation, which is markedly upregulated in RA FLSs, in synovial aggression and subsequent experimental joint damage. Targeted suppression of GALNT1 effectively curtailed migration and invasion in RA FLSs and mitigated arthritis severity in a rat collagen-induced arthritis (CIA) model. Mechanistically, NEK9 was identified as a pivotal substrate and downstream effector of GALNT1, affecting the aggressive phenotype of RA FLSs. In vitro experiments further demonstrated that O-glycosylation of NEK9, mediated by GALNT1, promotes the pathogenic phenotype of RA FLSs by promoting cytoskeleton reorganization and restraining excessive endoplasmic reticulum (ER) stress activation. Our study provides mechanistic insights into the activation of RA FLSs and identifies GALNT1 as a potential therapeutic target for RA.