Different glycosylation profile of serum IgA1 in IgA nephropathy according to the glomerular basement membrane thickness: normal versus thin.
BACKGROUND
Abnormal glycosylation of immunoglobulin A1 (IgA1) has been implicated in the pathophysiological characteristics of IgA nephropathy, leading to failure of normal clearance mechanisms and mesangial deposition of serum IgA1. Furthermore, systematic measurement of glomerular basement membrane (GBM) thickness by electron microscopy evidenced two different subgroups: IgA nephropathy with normal GBM (N-GBM) and thin GBM (T-GBM). This finding prompted us to study comparatively the profile of N- and O-glycosylation of IgA1 in the two subgroups.


METHODS
Using lectin-binding properties, sialylation and galactosylation of serum IgA1, isolated on jacalin-conjugated agarose, were investigated in male and female patients with IgA nephropathy with T-GBM (n = 22) and N-GBM (n = 22) compared with matched (age and sex) healthy controls (n = 22). Sambacus nigra agglutinin (SNA) and Maackia amurensis agglutinin (MAA) were designed to examine the detection of Neu5Acalpha2,6- and Neu5Acalpha2,3-linked galactose, respectively. Helix aspersa agglutinin (HAA) was used to examine the expression of terminal N-acetylgalactosamine of the O-linked glycans in the hinge region of IgA1.


RESULTS
The following galactosylation abnormalities were confirmed in the common subgroup with N-GBM: a trend to an alpha2,6 oversialylation (SNA binding) of native IgA1 associated with a defect in its terminal galactose (HAA binding); these two findings were predominant in male patients (P < 0.05 and 0.01 for SNA and HAA, respectively). No change in MAA was observed. Conversely, no significant anomaly was found in the T-GBM variant, which could indicate the absence or low magnitude of galactosylation defects (not significant) or another yet unidentified defect.


CONCLUSIONS
The present study evidenced differences in glycosylation profiles of serum IgA1 according to GBM thickness (N-GBM versus T-GBM) in patients with IgA nephropathy. These data raised the possibility of different mechanisms for IgA1 glomerular deposition.
Linossier
Marie-Thérèse
MT
Research Group on Glomerulonephritides and Renal Transplantation, Faculté de Médecine J. Lisfranc; and the Department of Nephrology, Dialysis and Renal Transplantation, CHU de Saint-Etienne, Hôpital Nord, Saint-Etienne, France.
Palle
Sabine
S
Berthoux
François
F
D000293:Adolescent; D000328:Adult; D000918:Antibody Specificity; D001485:Basement Membrane / Q000737:chemistry / Q000473:pathology* / Q000648:ultrastructure; D005260:Female; D005922:Glomerulonephritis, IGA / Q000097:blood*; D006031:Glycosylation; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood*; D007678:Kidney Glomerulus / Q000737:chemistry / Q000473:pathology* / Q000648:ultrastructure; D037102:Lectins / Q000737:chemistry; D008297:Male; D008854:Microscopy, Electron; D008875:Middle Aged; D019158:N-Acetylneuraminic Acid / Q000737:chemistry; D019081:O Antigens / Q000737:chemistry / Q000378:metabolism
D007070:Immunoglobulin A; D037102:Lectins; D019081:O Antigens; D019158:N-Acetylneuraminic Acid