Ultrastructural immunogold studies of heparan sulphate proteoglycan in normal human glomeruli and glomerulonephritis

Nucleosomes possess a high affinity for glomerular laminin and collagen IV and bind nephritogenic antibodies in murine lupus-like nephritis

AIM

Lupus nephritis is closely associated with in vivo autoantibody-binding to glomerular membrane-associated electron-dense structures (EDS). The biochemical nature and cellular origin of EDS are controversial, and definitive characterisation needs to be performed.

METHODS

By using the terminal transferase biotin-dUTP nick end-labelling (TUNEL) assay at the electron microscopic level, we have traced extracellular chromatin within the glomerular basement membranes of nephritic (NZBxNZW)F1 mice. The TUNEL assay was subsequently used in combination with standard immune electron microscopy (IEM). To analyse why chromatin particles associate with membranes, we determined the affinity of nucleosomes and DNA for glomerular laminin, collagen IV and the mesangial matrix proteoglycan perlecan by surface plasmon resonance.

RESULTS

This intra-assay colocalisation TUNEL IEM demonstrated that autoantibodies fully colocalised with extracellular TUNEL-positive chromatin observed as EDS in glomerular membranes, similar to results obtained by the same technique applied to human lupus nephritis. Most importantly, these data validate the murine variant of lupus nephritis as a model to study origin of extracellular chromatin as a key element in human lupus nephritis. Kinetic analyses demonstrated that nucleosomes had a high affinity for collagen IV and laminin, but not for perlecan.

CONCLUSION

Collectively, these results provide firm evidence that dominant target structures for nephritogenic autoantibodies are constituted by TUNEL-positive chromatin associated with glomerular capillary and mesangial matrix membranes at high affinity.

Alteration of anionic sites in renal glomerular basement membrane of pigs

Ultrastructural alteration of anionic sites (ASs) in the glomerular basement membrane (GBM) was studied in 10 cases of swine mesangial proliferative glomerulonephritis using a cationic ultrastructural tracer, 0.5% polyethyleneimine (M.W. = 1,800). Glomerular ASs were seen as discrete electron-dense particles in the GBM, mesangial matrix and epithelial cell surfaces by electron microscopy. In the lamina rara externa (LRE) of the normal GBM, ASs were distributed regularly in a single layer. In those areas of the LRE that contained electron dense deposits or clusters of spherical microparticles (SMPs), however, a distinct reduction or loss of ASs was observed in all the pigs. Quantitative assessment of ASs in the LRE over 1,000 nm of the GBM revealed a significant reduction in ASs in one case with diffuse global thickening of the GBM as compared with the remaining nine pigs without GBM thickening (P < 0.001, Mann-Whitney's U-test). There were no ASs in the lamina densa (LD) of the normal GBM, but an irregular distribution of ASs was seen within the LD of the pig showing diffuse global thickening of the GBM. These results suggest that a disturbance of the charge-selective barrier in the GBM may be induced by electron-dense deposits or SMPs, in the LRE as well as thickening of the GBM in swine glomerulonephritis.

Development of an enzyme immunoassay specific for a core protein epitope of a novel small basement membrane associated heparan sulphate proteoglycan from human kidney

Heparan sulphate proteoglycans are major components of the glomerular basement membrane and play a key role in their molecular organization and function. Moreover, their presence is essential for the maintenance of the selective permeability of the glomerular basement membrane. Recently, we have isolated and characterized a novel, small basement membrane associated heparan sulphate proteoglycan from human aorta and kidney. Using specific monoclonal antibodies we have shown that the novel heparan sulphate proteoglycan is predominantly located in the glomerular basement membrane, to a lesser extent in the basement membrane of tubuli, and also in the mesangium. Turnover or, in the course of kidney diseases, degradation of heparan sulphate proteoglycan from glomerular basement membranes may lead to urinary excretion of heparan sulphate proteoglycan. Therefore, changes in the structure and function of glomerular basement membranes may be directly detected by measuring the excretion of a component of this basement menbrane, e. g. heparan sulphate proteoglycan into urine. Here we describe the establishment of an enzyme immunoassay for the sensitive detection of the novel, small heparan sulphate proteoglycan in urine. In this assay the specific monoclonal antibody 1F10/B8, which recognizes a core protein epitope, was used to detect the polyanionic heparan sulphate proteoglycan bound to the surface of a cationic charge modified microtitre plate. This assay allows the sensitive and specific detection of the small heparan sulphate proteoglycan, which is released from the glomerular basement membrane into urine during normal turnover and also in the course of kidney diseases.

Ultrastructural change of the glomerular basement membrane in rats with Heymann nephritis revealed by ultrahigh resolution scanning electron microscopy

To assess the relationship between the glomerular injury induced by immune complex deposition and proteinuria, ultrastructural changes of the glomerular basement membrane (GBM) were investigated in Heymann nephritis. Active Heymann nephritis was induced in rats by injecting them with tubular brush border antigen, known as Fx1A, emulsified in complete Freund's adjuvant (CFA). Measurement of urinary protein excretion and histological examinations were carried out for up to 15 weeks after immunization. Proteinuria developed in rats within 10 weeks of immunization and coincided with the development of subepithelial deposits with minimal spike-like basement membrane protrusion. Acellular glomeruli were prepared by detergent treatment and were subjected to tannic acid-osmium conductive staining prior to examination with an ultrahigh resolution scanning electron microscope (HSEM). HSEM of the acellular GBM prepared from control rats injected with CFA alone revealed a meshwork structure, with pores of about 9 nm in diameter. Proteinuric rats immunized with Fx1A showed a loosened meshwork structure, with pores of about 15 nm in the acellular GBM adjacent to the deposits. The newly formed GBM overlying the deposit consisted of a meshwork structure associated with unorganized thin fibrils. Ultrastructural changes were never seen in GBM devoid of deposits. These findings indicate that subepithelial deposits are closely involved in the development of proteinuria by injuring the size selectivity of the GBM.

Decreased glomerular basement membrane heparan sulfate proteoglycan in essential hypertension

Heparan sulfate proteoglycans are major components of the glomerular basement membrane and play a key role in the molecular organization and function of the basement membrane. Moreover, their presence is essential for maintenance of the selective permeability of the glomerular basement membrane. Recently, we isolated and characterized a novel small basement membrane-associated heparan sulfate proteoglycan from human aorta and kidney. Partial amino acid sequence data clearly show that this heparan sulfate proteoglycan is distinct from the large basement membrane-associated heparan sulfate proteoglycan (perlecan). Using specific monoclonal antibodies, we have shown that the novel heparan sulfate proteoglycan is located predominantly in the glomerular basement membrane and, to a lesser extent, in the basement membrane of tubuli. Turnover or, in the course of kidney diseases, degradation of heparan sulfate proteoglycan from glomerular basement membranes may lead to urinary excretion of heparan sulfate proteoglycan, which can be measured by a sensitive enzyme immunoassay. The aim of the present study was to analyze whether changes in the structure and function of glomerular basement membranes can be directly detected by measurement of the excretion of a component of this basement membrane, eg, heparan sulfate proteoglycan into urine. The excretion of this small heparan sulfate proteoglycan was compared after physical exercise in normotensive and hypertensive subjects. Normotensive subjects and treated, essential hypertensive patients underwent a standardized workload on a bicycle ergometer. Biochemical characterization of the urinary proteins and heparan sulfate proteoglycan was performed before and 15 and 45 minutes after exercises.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of integrin subunits in normal human kidney

We evaluated on serial sections the distribution of a large number of integrin alpha and beta chains in normal adult human kidney: 1) the beta 1 chain and its corresponding alpha subunits (alpha 1, alpha 2, alpha 3, alpha 4, alpha 5, alpha 6), 2) alpha v and beta 3 chains, 3) the beta 2 chain and its corresponding alpha chains (alpha X, alpha M, alpha L), and 4) the beta 4 chain. We also evaluated ICAM-1, VCAM and ELAM and the major extracellular matrix components (ECM). A three step immunoperoxidase technique was used on frozen sections. Each cell of the kidney shows a specific distribution of these molecules. The relation with ECM and some of their ligands was evaluated. This immunohistochemical study shows that there is no strict colocalisation of a given ECM component with its specific receptor.

Application of cationic probes for the ultrastructural localization of proteoglycans in basement membranes

The application of cationic probes for the ultrastructural detection of proteoglycans in basement membranes is reviewed. Proteoglycans are highly negatively charged macromolecules due to their glycosaminoglycan side chains. The interaction of cationic probes with proteoglycans is of an electrostatic nature. Methods are discussed to increase the specificity of probes for proteoglycans. The use of phthalocyanin-like dyes such as Cuprolinic blue, according to the critical electrolyte concentration method, results in a selective staining of proteoglycans. Enzymatic or chemical digestions, however, should be done to validate the proteoglycan nature of the dye-positive granules/filaments, and to establish the class of proteoglycan. The value of cationic probes in basement membrane research on development and pathology is discussed. The potential for deducting molecular information from the ultrastructural appearance of stained proteoglycans is indicated.

Alterations in the glomerular charge barrier in human lupus nephritis

Renal tissue taken from ten patients with proteinuria and diagnosed as suffering from human lupus nephritis was examined by a post-embedding charge labelling method using cationic gold (CG). The method allows localization of the anionic charge in the glomerular epithelial cell coat and/or glomerular basement membrane (GBM). Our results demonstrate that in human lupus nephritis there are gaps in the charge barrier associated with immune deposits found in the lamina rara externa of the GBM. These data suggest that the loss of glomerular fixed anionic charges in the GBM may play an important role in the development of proteinuria in patients suffering from lupus nephritis.

AA glomerular amyloid. An ultrastructural immunogold study of the colocalization of heparan sulphate proteoglycan and P component with amyloid fibrils together with changes in distribution of type IV collagen and fibronectin

An ultrastructural investigation was undertaken on paraformaldehyde-fixed Lowicryl resin-embedded human kidneys of three patients with AA amyloidosis to investigate the association of various basement membrane components with amyloid fibrils. An immunogold technique was used and antibodies to serum amyloid A, heparan sulphate proteoglycan, type IV collagen, P component, and fibronectin were applied to human normal and amyloid glomeruli. The amyloid was identified as AA, and P component was shown to be intimately associated with the fibrils. In addition, heparan sulphate proteoglycan was associated with amyloid in all subendothelial, subepithelial and intramembranous glomerular basement membrane deposits, and those throughout the mesangial matrix. This contrasted with the distribution of the proteoglycan in the normal glomerulus where it was found predominantly on the epithelial aspect of the basement membrane and only in the more peripheral regions of the mesangium. The accumulation of heparan sulphate proteoglycan with amyloid resulted in a marked increase in its amount in the glomeruli. The amyloid deposits contained little or no type IV collagen or fibronectin. These findings demonstrate a strong association of heparan sulphate proteoglycan with amyloid and suggest different roles for the various glomerular basement membrane components in amyloidogenesis.

Cationic gold staining of glomerular anionic sites in archived tissue, reprocessed from paraffin wax into LR gold resin

Glomerular capillary wall anionic sites have been demonstrated by cationic gold staining of archived renal biopsy tissue (up to 10 years old), obtained from six patients, originally embedded in paraffin wax, and subsequently reprocessed into LR gold resin. The staining patterns at pH 2.5 and pH 7.0, demonstrating different glomerular basement membrane (GBM) anionic constituents, were compared in three patients from whom tissue directly processed into LR gold and reprocessed tissue was available. Ultrastructural preservation was poorer and shrinkage artefact greater in paraformaldehyde-lysine periodate (PLP) as opposed to formol saline-fixed reprocessed tissue. However, GBM anionic site expression was well preserved, or even enhanced (lamina rara externa, pH 7.0) in reprocessed tissue, using either fixative. Although it may not be possible to compare subtle changes in anionic site distribution in variously fixed and processed tissues, due to these artefacts, the technique enables retrospective study of charge status in archived material from disease groups in which there are distinct anionic site aberrations.

Distribution of GBM heparan sulfate proteoglycan core protein and side chains in human glomerular diseases

Using monoclonal antibodies (mAbs) recognizing either the core protein or the heparan sulfate (HS) side chain of human GBM heparan sulfate proteoglycan (HSPG), we investigated their glomerular distribution on cryostat sections of human kidney tissues. The study involved 95 biopsies comprising twelve different glomerulopathies. Four normal kidney specimens served as controls. A homogenous to linear staining of the GBM was observed in the normal kidney with anti-HSPG-core mAb (JM-72) and anti-HS mAb (JM-403). In human glomerulopathies the major alteration was a segmental or total absence of GBM staining with anti-HS mAb JM-403, which is most pronounced in lupus nephritis, membranous glomerulonephritis (GN), minimal change disease and diabetic nephropathy, whereas the HSPG-core staining by mAb JM-72 was unaltered. In addition we found HSPG-core protein in the mesangial matrix when this was increased in membranoproliferative GN Type I, Schönlein-Henoch GN, IgA nephropathy, lupus nephritis, diabetic nephropathy and in focal glomerulosclerosis. Also staining with the anti-HS mAb JM-403 became positive within the mesangium, although to a lesser extent. Furthermore, amyloid deposits in AL and AA amyloidosis clearly stained with anti-HSPG-core mAb JM-72, and to a lesser degree with anti-HS mAb JM-403. Finally, in membranous GN (stage II and III), the GBM staining with anti-HSPG-core mAb JM-72 became irregular or granular, probably related to the formation of spikes. In conclusion, major alterations were observed in the glomerular distribution of HS and HSPG-core in various human glomerulopathies. The mAbs can be useful to further delineate the significance of HSPG and HS for glomerular diseases.

Ultrastructural alteration of glomerular anionic sites in nephrotic patients

The relationship of glomerular anionic sites to proteinuria was examined ultrastructurally in human nephrotic syndrome. The anionic sites were analysed morphometrically in patients with minimal-change nephrotic syndrome (MCNS, 11 patients) and in other glomerulonephritides complicated with nephrotic syndrome (4 patients) by the high-iron diamine-thiocarbohydrazide-silver proteinate method. The anionic sites in MCNS patients in remission (7 patients) were normal. In contrast, the anionic sites in nephrotic patients with MCNS (4 patients) and the other glomerulonephritides were decreased in number. Moreover, smaller and irregularly distributed anionic sites or the greater loss of them from the paramesangial region were observed in the nephrotic patients. The loss of glomerular anionic sites may induce structural alteration of the glomerular basement membrane and mesangial matrix. The loss and structural abnormalities of glomerular anionic sites in nephrotic patients may be one of the mechanisms responsible for massive proteinuria.

Diabetic glomerulosclerosis--immunogold ultrastructural studies on the glomerular distribution of type IV collagen and heparan sulphate proteoglycan

We have undertaken an ultrastructural immunogold investigation of the distribution of type IV collagen and heparan sulphate proteoglycan (HSPG) in glomeruli from the kidneys of one normal control and three patients with diabetes mellitus and proteinuria. The sample included both diffuse and nodular diabetic glomerulosclerosis. In the control and diabetic kidneys, the type IV collagen was present predominantly on the endothelial aspect of the glomerular basement membrane (GBM), and by contrast the HSPG was found mainly on the epithelial side. In the mesangium in both control and diabetic glomeruli, type IV collagen was found predominantly in the central regions, while HSPG was mostly restricted to the region beneath the epithelial cells. Consequently, where there is a marked increase in mesangial matrix with nodule formation in diabetics there is a corresponding increase in the amount of type IV collagen but not of HSPG. Although the three diabetic patients were proteinuric, the HSPG was not decreased in the thickened GBMs.