Changes in heparan sulfate correlate with increased glomerular permeability

Loss of anionic sites from the glomerular basement membrane in human glomerulonephritides

Changes in glomerular anionic sites were analyzed in 31 patients with various types of glomerulonephritis using the high-iron diamine-thiocarbohydrazide-silver proteinate method. On the basis of the degree of proteinuria at the time of biopsy, the patients were divided into 3 groups as follows: Group 1, less than 10 mg/kg/24 h; Group 2, 10-50 mg/kg/24 h; Group 3, more than 50 mg/kg/24 h. The number of glomerular anionic sites per 300 nm length of the lamina rare externa was 16.20 +/- 3.37 in Group 1, 12.19 +/- 3.42 in Group 2 and 9.97 +/- 2.51 in Group 3. Moreover, smaller and irregularly distributed anionic sites, and a greater loss of anionic sites in the paramesangial region were observed in Groups 2 and 3. On the other hand, there was no significant correlation between the mesangial sclerosis index and the number of anionic sites (r = -0.40) in patients with IgA nephropathy (9 cases) and nephritis of Henoch-Schönlein purpura (6 cases). These results suggest that the proteinuria seen in various types of glomerulonephritis is related to the loss of glomerular anionic sites, i.e., dysfunction of the charge-selective barrier.

Albuminuria reflects widespread vascular damage. The Steno hypothesis

Albuminuria in Type 1 (insulin-dependent) diabetes is not only an indication of renal disease, but a new, independent risk-marker of proliferative retinopathy and macroangiopathy. The coincidence of generalised vascular dysfunction and albuminuria, advanced mesangial expansion, proliferative retinopathy, and severe macroangiopathy suggests a common cause of albuminuria and the severe renal and extrarenal complications associated with it. Enzymes involved in the metabolism of anionic components of the extracellular matrix (e.g. heparan sulphate proteoglycan) vulnerable to hyperglycaemia, seem to constitute the primary cause of albuminuria and the associated complications. Genetic polymorphism of such enzymes is possibly the main reason for variation in susceptibility.

Alterations in the extracellular matrix components in human glomerular diseases

We investigated the distribution of extracellular matrix components such as fibronectin, laminin, type III, IV, V, and VI collagens and heparan sulfate proteoglycan (HSPG) in normal and diseased glomeruli using the indirect immunofluorescence method. This study included 96 renal biopsies: 7 controls, 3 minimal change nephrotic syndrome (MCNS), 47 mesangial proliferative glomerulonephritis (PGN), 25 membranous nephropathy (MN) and 14 membranoproliferative glomerulonephritis (MPGN) including 3 lupus nephritis. Fibronectin was detected predominantly in the mesangium and less prominently in the glomerular basement membrane (GBM) of normal glomeruli. Laminin and type IV collagen were present in the mesangium and GBM, type III collagen in the interstitium, and type V collagen in the mesangium, interstitium and a part of GBM. Type VI collagen was observed in the mesangium, interstitium and slightly in GBM. Anti-HSPG antibody reacted with the mesangium and GBM. MCNS showed a distribution of these antigens similar to that in normal controls. The finding that staining for HSPG was not decreased in the GBM and mesangium indicated that there was no change in the core protein of HSPG. Fibronectin, laminin, type IV collagen and HSPG were increased in the thickened GBM of MN and in the expanded mesangium of PGN. In MPGN, these matrix components were increased in the mesangium and GBM with remarkable increase of type V and VI collagens. While type III collagen was not found in normal glomeruli, it became detectable in the mesangium and a part of GBM in MPGN. No significant decrease in the intensity of fluorescence for HSPG was observed in the glomeruli from nephrotic patients. These findings suggest that proteinuria might be caused by the structural alteration in the glycosaminoglycan portion of HSPG, changes in any anionic material other than HSPG, or both, and also indicate that the glomerular mesangial sclerosis is closely related to the increase of type V and VI collagens.