The Role of IgG Fc Region N-Glycosylation in the Pathomechanism of Rheumatoid Arthritis

Abstract

Anti-citrullinated protein antibodies (ACPAs) are involved in the pathogenesis of rheumatoid arthritis. N-glycosylation pattern of ACPA-IgG and healthy IgG Fc differs. The aim of this study is to determine the relative sialylation and galactosylation level of ACPAs and control IgG to assess their capability of inducing TNFα production, and furthermore, to analyze the correlations between the composition of Fc glycans and inflammatory markers in RA. We isolated IgG from sera of healthy volunteers and RA patients, and purified ACPAs on a citrulline-peptide column. Immunocomplexes (IC) were formed by adding an F(ab)2 fragment of anti-human IgG. U937 cells were used to monitor the binding of IC to FcγR and to trigger TNFα release determined by ELISA. To analyze glycan profiles, control IgG and ACPA-IgG were digested with trypsin and the glycosylation patterns of glycopeptides were analyzed by determining site-specific N-glycosylation using nano-UHPLC-MS/MS. We found that both sialylation and galactosylation levels of ACPA-IgG negatively correlate with inflammation-related parameters such as CRP, ESR, and RF. Functional assays show that dimerized ACPA-IgG significantly enhances TNFα release in an FcγRI-dependent manner, whereas healthy IgG does not. TNFα production inversely correlates with the relative intensities of the G0 glycoform, which lacks galactose and terminal sialic acid moieties.

Reduced serum IgG galactosylation is associated with increased inflammation during relapses of neuromyelitis optica spectrum disorders

“…These findings support previous research indicating a significant association between total IgG galactosylation and rheumatoid factor in the sera of rheumatoid arthritis patients ( 24 ). ACPA-IgG galactosylation levels were negatively correlated with inflammation-related measurements, including erythrocyte sedimentation rate, C-reactive protein, and rheumatoid factor ( 25 ). A cohort study on systemic lupus erythematosus conducted by Jing Han et al.…”

“…For instance, IFN-γ stimulation was found to increase IgG galactosylation and upregulate beta-1,4-galactosyltransferase 1 ( 33 ). In vitro intervention cell assays of serum from rheumatoid arthritis patients demonstrated a negative correlation between IgG of galactose-free glycoforms and TNF-α production ( 25 ). However, reports on cytokines and IgG glycosylation in NMOSD and CNS autoimmune diseases are scarce.…”

Association between immunoglobulin G N-glycosylation and lupus nephritis in female patients with systemic lupus erythematosus: a case-control study

“…Proinflammatory changes in the IgG N-glycome are associated with increased levels of bisecting N-acetylglucosamine (GlcNAc) ( 21 , 22 ). IgG N-glycosylation has been identified as a potential biomarker of a variety of diseases, including chronic diseases, inflammatory diseases, neurodegenerative diseases, autoimmune diseases, and cancer, offering great research potential ( 23 – 25 ). On the basis of our findings in the association between the IgG N-glycome and SLE patients ( 26 , 27 ), we hypothesize that IgG N-glycosylation has potential value in the early diagnosis of LN among SLE patients.…”

The Role of Autophagy as a Trigger of Post-Translational Modifications of Proteins and Extracellular Vesicles in the Pathogenesis of Rheumatoid Arthritis

“…Therefore, ACPA-positive patients need an aggressive initial approach to prevent radiographic progression [ 43 ]. Moreover, it has been discovered that post-translational modifications of ACPAs seem to contribute to the pathogenesis of RA, such as the extensive glycosylation of the IgG ACPA V domain, or a decrease in Fc galactosylation and an increase in the Fc fucosylation of serum ACPA IgG1, which predisposes one to RA development [ 37 , 44 , 45 ]. The recent identification of novel anti-carbamylated protein antibodies (anti-CarP) suggested the hypothesis that the diagnostic gap including seronegative patients could be closed [ 46 , 47 ].…”