17 November 2004
Background: The proteinuria resulting from IgA nephropathy is secondary to altered charge-selective and/or size-selective properties of the glomerular capillary walls. However, the functional changes occurring within the glomerular capillary network which lead to proteinuria are still poorly understood. In this study, we analyzed the participation of charged components in the glomerular capillary and their role with respect to proteinuria in childhood IgA nephropathy. Methods: We examined glomerular anionic charge in renal biopsy specimens with confocal laser scanning microscopy using FITC-conjugated poly- L-lysine as a cationic tracer. The renal specimens investigated were from 9 children with IgA nephropathy (IgAN(+)) associated with detectable proteinuria in a morning urine specimen, 8 children with IgA nephropathy (IgAN(–)) and 11 children with thin basement membrane disease (TBMD) with no detectable proteinuria. Results: The labeling intensity of glomerular fixed anionic sites from IgAN(+) was significantly lower than that of IgAN(–) and TBMD. Staining the serial sections following methylation treatment revealed that the labeling intensity for fixed anionic sites in TBMD was significantly higher than that of both IgAN(+) and IgAN(–). On the other hand, saponification treatment resulted in significantly more intensive fluorescence in TBMD and IgAN(–) than in IgAN(+). Furthermore, statistical analysis demonstrated a significant correlation between 24-hour protein excretion and the intensity of fixed anionic sites in all patients with IgA nephropathy at pH 7.0 and following staining with saponification treatment. Conclusions: These findings suggest that a reduction of glomerular anionic charge might be causally associated with the development of proteinuria in childhood IgA nephropathy. Furthermore, sulfate components such as heparan sulfate proteoglycan might be involved initially followed by carboxyl components such as sialoglycoproteins in the glomeruli of patients with IgA nephropathy contributing to the occurrence of proteinuria. We suggest that this method represents a straightforward approach to dissect the participation of charged components in the pathogenesis of childhood IgA nephropathy and their relationship to the development of glomerular proteinuria.