Glycosylation of Vitamin D binding protein reduced in Juvenile Arthritis patients at risk of disease extension

Introduction: Juvenile idiopathic arthritis (JIA) comprises a poorly
understood group of chronic autoimmune diseases with variable
clinical outcomes.
Aims/background: We investigated whether profiling of the synovial
fluid (SF) proteome could distinguish the subset of patients in whom
inflammation extends to affect a large number of joints, early in the
disease process.
Method: SF samples from n = 57 newly diagnosed JIA patients were
labelled with Cy dyes and separated by two-dimensional electrophoresis.
Multivariate analyses were used to isolate a panel of
proteins which distinguish patient subgroups. Proteins were identified
using MALDI-TOF mass spectrometry with vitamin D binding protein
(VDBP) expression and sialylation further verified by
immunohistochemistry and ELISA test. Sialic acid residues were
enzymatically cleaved from immunopurified SF VDBP, enriched by
hydrophilic interaction liquid chromatography (HILIC) and analysed
by mass spectrometry.
Results: A cleaved isoform of VDBP, spot 873, is present at significantly
reduced levels in the SF of oligoarticular patients at risk of
disease extension, relative to other subgroups (p\0.05). Conversely
total levels of vitamin D binding protein are elevated in plasma and
ROC curves indicate an improved diagnostic sensitivity to detect
patients at risk of disease extension, over both spot 873 and CRP
levels. Sialysed forms of intact immunopurified VDBP were more
prevalent in persistent oligoarticular patient synovial fluids.
Conclusions: Reduced conversion of VDBP to a macrophage activation
factor may represent a novel pathway contributing to increased
risk of disease extension in JIA patients.