Expression of glomerular ecto-ATPase in idiopathic nephrotic syndrome

The pathogenesis of glomerular alterations leading to increased glomerular permeability in disorders like Minimal Change Disease (MCD) is obscure. One of the preliminary observed glomerular alterations in MCD involves diminished expression of glomerular ecto-ATP-diphosphohydrolase (denoted as ecto-ATPase) detectable by immunoflorescence in kidney biopsies from these patients. This glomerular alteration can also be induced by perfusion of a MCD-associated circulating plasma factor (called 100KF) into the rat kidney ex vivo. To further investigate the expression of glomerular ecto-ATPase in human kidney tissue, the stainability for this enzyme using anti-ATPase antibody was examined in kidney biopsies from subjects with biopsy proven MCD (n=16), focal glomerular sclerosis (FGS; n=9) and other forms of glomerulonephritis (GN; n=8), using standard indirect immunofluorescence techniques. Kidney sections from subjects without glomerular disease served as control tissue. All patients within the various groups, including the GN group (consisting of subjects with IgA nephropathy (n=5) and membranous glomerulo-nephritis (n=3), showed proteinuria at the time of biopsy. The results show that the antibody (the specificity of which was confirmed by dot-blot analysis) stains glomerular capillary walls of normal kidney in a bright granular pattern. A similar staining pattern was observed in glomeruli of subjects with GN. In contrast, significant reduction of stainability occurred in MCD and FGS. Scoring of the glomerular stainability of the patient groups studied showed a decreased expression of ecto-ATPase in 68.8+/-28.2% of the evaluated glomeruli in MCD (P less than or equal to 0.01), 93.7+/-18.0% in FGS (P less than or equal to 0.01) and 25.8+/-31.1 in the GN group (not significant) as compared to the control group (4.0+/-7.8%). In view of the sensitivity of this glomerular ecto-ATPase for reactive oxygen species (ROS), in association with the observation that the circulating factors 100KF is able to generate radicals in inflammatory cells, it is concluded that local release of ROS may contribute to the pathogenesis of MCD and related glomerular disorders.