IgA1-secreting cell lines from patients with IgA nephropathy produce aberrantly glycosylated IgA1

Abstract

Aberrant glycosylation of IgA1 plays an essential role in the pathogenesis of IgA nephropathy. This abnormality is manifested by a deficiency of galactose in the hinge-region O-linked glycans of IgA1. Biosynthesis of these glycans occurs in a stepwise fashion beginning with the addition of N-acetylgalactosamine by the enzyme N-acetylgalactosaminyltransferase 2 and continuing with the addition of either galactose by β1,3-galactosyltransferase or a terminal sialic acid by a N-acetylgalactosamine-specific α2,6-sialyltransferase. To identify the molecular basis for the aberrant IgA glycosylation, we established EBV-immortalized IgA1-producing cells from peripheral blood cells of patients with IgA nephropathy. The secreted IgA1 was mostly polymeric and had galactose-deficient O-linked glycans, characterized by a terminal or sialylated N-acetylgalactosamine. As controls, we showed that EBV-immortalized cells from patients with lupus nephritis and healthy individuals did not produce IgA with the defective galactosylation pattern. Analysis of the biosynthetic pathways in cloned EBV-immortalized cells from patients with IgA nephropathy indicated a decrease in β1,3-galactosyltransferase activity and an increase in N-acetylgalactosamine-specific α2,6-sialyltransferase activity. Also, expression of β1,3-galactosyltransferase was significantly lower, and that of N-acetylgalactosamine-specific α2,6-sialyltransferase was significantly higher than the expression of these genes in the control cells. Thus, our data suggest that premature sialylation likely contributes to the aberrant IgA1 glycosylation in IgA nephropathy and may represent a new therapeutic target.

Expression and glycoengineering of functionally active heteromultimeric IgM in plants

“…Although it is well demonstrated that correct assembly of the 21 (or 24, depending on the oligomerization status) polypeptides is a prerequisite for the functionality of IgMs (7), the impact of glycosylation is largely unknown. However, results from clinical studies, particularly on IgGs, indicate that carbohydrates play a structural and functional role for all immunoglobulins (8)(9)(10).…”

Clustered O-Glycans of IgA1

“…The polymeric form of IgA1 myeloma protein (Ale) was previously isolated from plasma of a patient with multiple myeloma (14). Briefly, the plasma sample was precipitated with ammonium sulfate (50% saturation) and dissolved in phosphate buffer, and IgG and IgM were removed by affinity chromatography with protein G and anti-human IgM antibodies, respectively (32).…”

“…Carbohydratespecific lectin analysis of O-glycoproteins can provide information on glycan composition and comparative differences between samples, such as those from healthy controls and patients with various disease states. We have successfully demonstrated this in the analysis of IgA1 O-glycans from patients with IgAN versus healthy controls and disease controls (13)(14)(15). This included proximal assessment of sites with galactose (Gal)-deficient O-glycans after digests with IgAspecific proteases (8).…”

A SPRY2 mutation leading to MAPK/ERK pathway inhibition is associated with an autosomal dominant form of IgA nephropathy

“…Three clinical reports 25 provide support to this hypothesis: these concerned two patients treated with EGFR inhibitors (cetuximab and gefitinib) and one patient treated with sorafenib, who showed a marked worsening of their kidney function because of IgA deposits. This very rare complication for cetuximab, gefitinib and sorafenib has never been reported during clinical trials and it is probably related to the fact that the drug triggered or exacerbated a latent IgAN, already present in those patients, by blocking the MAPK/ERK pathway.…”