Mass spectrometry-based approach for development of biomarkers in IgA nephropathy: a pilot trial

Abstract

IgA1 with galactose (Gal)-deficient hinge-region (HR) O-glycans (Gd-IgA1) plays a key role in IgA nephropathy (IgAN), and the serum level of Gd-IgA1 is elevated in the majority of IgAN patients. To characterize the involvement of IgA1 in the development and progression of IgAN, O-glycan micro-heterogeneity and attachment sites need to be analyzed, as each HR has nine potential sites for O-glycosylation.

We have developed an on-line liquid chromatography (LC) hybrid quadrupole mass filter/linear ion trap/orbitrap mass spectrometry (MS) protocol, which was used to analyze IgA1 from a patient with IgAN. LC-MS profiling provided the overall O-glycan micro-heterogeneity distribution of IgA1 HR O-glycoforms. The LC-extracted ion chromatogram (XIC) of HR O-glycoforms containing Gal-deficient O-glycans indicated that the Gal-deficient O-glycans attached at specific sites. Structural isomers based on changes in the amino acid position of the attached glycans were identified in relation to the IgA1 HR O-glycoforms containing Gal-deficient O-glycans. To identify the predominant O-glycoforms in the serum IgA1 from IgAN patients as candidate biomarkers, O-glycan micro-heterogeneity and attachment sites, including isomeric structures, need to be analyzed.

Our MS-based approach is useful in this respect and should prove a valuable tool for the development of biomarkers for IgA1 HR O-glycosylation in IgAN.