Changes in heparan sulfate correlate with increased glomerular permeability

Association between circulatory complement activation and hypertensive renal damage: a case-control study

OBJECTIVE

The aim of this study was to investigate the potential importance of complement system activation, with particular emphasis on the complement alternative pathway (AP), in the pathogenesis of hypertensive renal damage.

METHODS

Serum complement C3, complement Factor H (CFH) and AP activation were assessed in 66 participants with established essential hypertension with renal damage (RD). Fifty-nine patients with age- and sex-matched essential hypertension without renal damage (NRD) and 58 healthy participants (normal) were selected.

RESULTS

Our study revealed that C3 and AP50 continuously increased from normal to NRD to RD (p < 0.05, respectively), while CFH was significantly lower than that in NRD and healthy participants (p < 0.05, respectively). After multifactorial logistic regression analysis corrected for confounders, elevated serum C3 (p = 0.001) and decreased CFH (p < 0.001) were found to be independent risk factors for hypertension in healthy participants; elevated serum C3 (p = 0.034), elevated AP50 (p < 0.001), decreased CFH (p < 0.001), increased age (p = 0.011) and increased BMI (p = 0.013) were found to be independent risk factors for the progression of hypertension to hypertensive renal damage; elevated serum C3 (p = 0.017), elevated AP50 (p = 0.023), decreased CFH (p = 0.005) and increased age (p = 0.041) were found to be independent risk factors for the development of hypertensive renal damage in healthy participants.

CONCLUSION

Abnormal activation of complement, particularly complement AP, may be a risk factor for the development and progression of hypertensive renal damage.

AMPK differentially alters sulphated glycosaminoglycans under normal and high glucose milieu in proximal tubular cells

Glycosaminoglycans (GAGs) and AMP-activated protein kinase (AMPK) are two critical molecular players involved in cellular homeostasis. Both of them are altered due to hyperglycaemia in the kidney, leading to the pathogenesis of diabetic nephropathy. Here, we have looked into the effect of AMPK modulation on sulphated GAG (sGAG) levels of tubular cells of proximal and distal origin to understand the mechanism of hyperglycaemia-mediated pathogenesis of the diabetic nephropathy. In MDCK cells (distal tubular cell) and NRK-52E (proximal tubular cell), AMPK inhibition resulted in increased sGAG levels under normal glucose conditions characteristically of heparan sulphate class, whereas AMPK activation did not have any effect. High glucose (HG) condition did not alter sGAG levels in MDCK cell despite a decrease in AMPK phosphorylation. Subjecting NRK-52E cells to HG milieu significantly decreased sGAG levels more so of chondroitin/dermatan sulphate, which is significantly prevented when HG is co-treated with AMPK activator. Interestingly, knockdown of AMPK by AMPKα1/α2 siRNA showed increased sGAG levels in NRK-52E. Our results suggest that changes in sGAG level, in particular, as a result of AMPK modulation is differentially regulated and is dependent on cell type as well as its physiological status. Furthermore, activation of AMPK is beneficial in preventing the HG-mediated decrease in sGAGs in proximal tubular cells.

Retinal capillary basement membrane thickening: Role in the pathogenesis of diabetic retinopathy

Vascular basement membrane (BM) thickening has been hailed over half a century as the most prominent histological lesion in diabetic microangiopathy, and represents an early ultrastructural change in diabetic retinopathy (DR). Although vascular complications of DR have been clinically well established, specific cellular and molecular mechanisms underlying dysfunction of small vessels are not well understood. In DR, small vessels develop insidiously as BM thickening occurs. Studies examining high resolution imaging data have established BM thickening as one of the foremost structural abnormalities of retinal capillaries. This fundamental structural change develops, at least in part, from excess accumulation of BM components. Although BM thickening is closely associated with the development of DR, its contributory role in the pathogenesis of DR is coming to light recently. DR develops over several years before clinical manifestations appear, and it is during this clinically silent period that hyperglycemia induces excess synthesis of BM components, contributes to vascular BM thickening, and promotes structural and functional lesions including cell death and vascular leakage in the diabetic retina. Studies using animal models show promising results in preventing BM thickening with subsequent beneficial effects. Several gene regulatory approaches are being developed to prevent excess synthesis of vascular BM components in an effort to reduce BM thickening. This review highlights current understanding of capillary BM thickening development, role of BM thickening in retinal vascular lesions, and strategies for preventing vascular BM thickening as a potential therapeutic strategy in alleviating characteristic lesions associated with DR.

Renal Tubular- and Vascular Basement Membranes and their Mimicry in Engineering Vascularized Kidney Tubules

The high prevalence of chronic kidney disease leads to an increased need for renal replacement therapies. While there are simply not enough donor organs available for transplantation, there is a need to seek other therapeutic avenues as current dialysis modalities are insufficient. The field of regenerative medicine and whole organ engineering is emerging, and researchers are looking for innovative ways to create (part of) a functional new organ. To biofabricate a kidney or its functional units, it is necessary to understand and learn from physiology to be able to mimic the specific tissue properties. Herein is provided an overview of the knowledge on tubular and vascular basement membranes' biochemical components and biophysical properties, and the major differences between the two basement membranes are highlighted. Furthermore, an overview of current trends in membrane technology for developing renal replacement therapies and to stimulate kidney regeneration is provided.

Are filtered plasma proteins processed in the same way by the kidney?

In order to understand the mechanism of albuminuria we have explored how other plasma proteins are processed by the kidney as compared to inert molecules like Ficolls. When fractional clearances are plotted versus protein radius there is a remarkable parallelism between protein (molecular weight range 30-150kDa) clearance in healthy controls, in Dent's disease, in nephrotic states and the clearance of Ficolls. Although there are significant differences in the levels of fractional clearances in these states. Dent's disease results in a 2-fold increase in the fractional clearance of proteins as compared to healthy controls whereas in nephrotic states there is a further 3-fold increase in fractional clearance. Previous thinking that albumin uptake was controlled primarily by the megalin/cubilin receptor does not explain the albumin urinary excretion data and is therefore an incorrect concept. Protein clearance in nephrotic states approach the fractional clearance of inert Ficolls for a given radius. It therefore appears that there are two pathways processing these proteins. A low capacity pathway associated with megalin/cubilin that degrades filtered protein (that is inhibited in Dent's disease) and a high capacity pathway that retrieves the filtered protein and returns it to the blood supply (without retrieval nephrotic protein excretion will occur and this will account for hypoproteinemia). On the other hand low molecular weight proteins (<20kDa) are processed entirely differently by the kidney. They are not retrieved but are comprehensively degraded in the kidney with the degradation products predominantly returned to the blood supply.

Heparanase Is Essential for the Development of Acute Experimental Glomerulonephritis

Heparanase, a heparan sulfate (HS)--specific endoglucuronidase, mediates the onset of proteinuria and renal damage during experimental diabetic nephropathy. Glomerular heparanase expression is increased in most proteinuric diseases. Herein, we evaluated the role of heparanase in two models of experimental glomerulonephritis, being anti-glomerular basement membrane and lipopolysaccharide-induced glomerulonephritis, in wild-type and heparanase-deficient mice. Induction of experimental glomerulonephritis led to an increased heparanase expression in wild-type mice, which was associated with a decreased glomerular expression of a highly sulfated HS domain, and albuminuria. Albuminuria was reduced in the heparanase-deficient mice in both models of experimental glomerulonephritis, which was accompanied by a better renal function and less renal damage. Notably, glomerular HS expression was preserved in the heparanase-deficient mice. Glomerular leukocyte and macrophage influx was reduced in the heparanase-deficient mice, which was accompanied by a reduced expression of both types 1 and 2 helper T-cell cytokines. In vitro, tumor necrosis factor-α and lipopolysaccharide directly induced heparanase expression and increased transendothelial albumin passage. Our study shows that heparanase contributes to proteinuria and renal damage in experimental glomerulonephritis by decreasing glomerular HS expression, enhancing renal leukocyte and macrophage influx, and affecting the local cytokine milieu.

[Renal physiology]

The kidneys are responsible for the urinary excretion of uremic toxins and the regulation of several body systems such as intra and extracellular volume status, acid-base status, calcium and phosphate metabolism or erythropoiesis. They adapt quantitative and qualitative composition of the urine to keep these systems in balance. The flow of plasma is filtered in the range of 120 mL/min, and depends on the systemic and renal hemodynamics which is subject to self-regulation. The original urine will then be modified in successive segments of the nephron. The proximal nephron is to lead the massive reabsorption of water and essential elements such as sodium, bicarbonates, amino-acids and glucose. The distal nephron includes the distal convoluted tubule, the connector tube and the collecting duct. Its role is to adapt the quality composition of urine to the needs of the body.

Basement membranes: cell scaffoldings and signaling platforms

Basement membranes are widely distributed extracellular matrices that coat the basal aspect of epithelial and endothelial cells and surround muscle, fat, and Schwann cells. These extracellular matrices, first expressed in early embryogenesis, are self-assembled on competent cell surfaces through binding interactions among laminins, type IV collagens, nidogens, and proteoglycans. They form stabilizing extensions of the plasma membrane that provide cell adhesion and that act as solid-phase agonists. Basement membranes play a role in tissue and organ morphogenesis and help maintain function in the adult. Mutations adversely affecting expression of the different structural components are associated with developmental arrest at different stages as well as postnatal diseases of muscle, nerve, brain, eye, skin, vasculature, and kidney.

Disease-dependent mechanisms of albuminuria

The mechanism of albuminuria is perhaps one of the most complex yet important questions in renal physiology today. Recent studies have directly demonstrated that the normal glomerulus filters substantial amounts of albumin and that charge selectivity plays little or no role in preventing this process. This filtered albumin is then processed by proximal tubular cells by two distinct pathways; dysfunction in either one of these pathways gives rise to discrete forms of albuminuria. Most of the filtered albumin is returned to the peritubular blood supply by a retrieval pathway. Albuminuria in the nephrotic range would arise from retrieval pathway dysfunction. The small quantities of filtered albumin that are not retrieved undergo obligatory lysosomal degradation before urinary excretion as small peptide fragments. This degradation pathway is sensitive to metabolic factors responsible for hypertrophy and fibrosis, particularly molecules such as angiotensin II and transforming growth factor-beta1, whose production is stimulated by hyperglycemic and hypertensive environments. Dysfunction in this degradation pathway leads to albuminuria below the nephrotic range. These new insights into albumin filtration and processing argue for a reassessment of the role of podocytes and the slit diaphragm as major direct determinants governing albuminuria, provide information on how glomerular morphology and "tubular" albuminuria may be interrelated, and offer a new rationale for drug development.

Properties of the Glomerular Barrier and Mechanisms of Proteinuria

This review focuses on the intricate properties of the glomerular barrier. Other reviews have focused on podocyte biology, mesangial cells, and the glomerular basement membrane (GBM). However, since all components of the glomerular membrane are important for its function, proteinuria will occur regardless of which layer is affected by disease. We review the properties of endothelial cells and their surface layer, the GBM, and podocytes, discuss various methods of studying glomerular permeability, and analyze data concerning the restriction of solutes by size, charge, and shape. We also review the physical principles of transport across biological or artificial membranes and various theoretical models used to predict the fluxes of solutes and water. The glomerular barrier is highly size and charge selective, in qualitative agreement with the classical studies performed 30 years ago. The small amounts of albumin filtered will be reabsorbed by the megalin-cubulin complex and degraded by the proximal tubular cells. At present, there is no unequivocal evidence for reuptake of intact albumin from urine. The cellular components are the key players in restricting solute transport, while the GBM is responsible for most of the resistance to water flow across the glomerular barrier.

Tissue factor pathway inhibitor (TFPI) release after heparin stimulation is increased in Type 1 diabetic patients with albuminuria

AIMS

To study heparin-stimulated TFPI release in relation to complications in Type 1 diabetic patients.

SUBJECTS AND METHODS

Nineteen uncomplicated Type 1 diabetic patients (group I) were compared with 18 patients with retinopathy (group II), and nine patients with retinopathy and albuminuria (group III). Blood samples were taken before (basal) and till 30 min after 5000 IU of heparin i.v. (post-heparin). TFPI activity was measured chromogenically. Von Willebrand factor, tissue plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1) and thrombomodulin were also measured.

RESULTS

Basal TFPI activity was higher in group III (121 +/- 10%) compared with group II (111 +/- 8%) or group I (110 +/- 13%) (P < 0.05), and strongly correlated with albuminuria (r = 0.66, P < 0.05). At all time points after heparin administration, TFPI activity in group III was significantly higher than in group I. TFPI activity was also higher in group III than in group II 5-30 min post-heparin. The increase in post-heparin TFPI activity, measured as the incremental area under the curve, was higher in group III compared with group I (65 +/- 7 vs. 59 +/- 4; P < 0.05). Of the other parameters, only thrombomodulin was higher in group III (44 +/- 24 vs. 26 +/- 7 (group II) and 28 +/- 9 ng/ml (group I); P < 0.01).

CONCLUSIONS

We conclude that basal and post-heparin TFPI activity is increased in albuminuric patients. The increase in heparin-stimulated TFPI release in patients with albuminuria is higher than in patients with retinopathy or without complications. This could be the result of altered endothelial glycosaminoglycan characteristics.

Renal handling of albumin: a critical review of basic concepts and perspective

Biochemical and physiological processes that underlie the mechanism of albuminuria are completely reassessed in this article in view of recent discoveries that filtered proteins undergo rapid degradation during renal passage and the resulting excreted peptide fragments are not detected by conventional urine protein assays. This means that filtered protein and/or albumin levels in urine have been seriously underestimated. The concept that albuminuria is a result of changes in glomerular permeability is questioned in light of these findings and also in terms of a critical examination of charge selectivity, shunts, or large-pore formation and hemodynamic effects. The glomerulus appears to function merely in terms of size selectivity alone, and for albumin, this does not change significantly in disease states. Intensive albumin processing by a living kidney occurs through cellular processes distal to the glomerular basement membrane. Failure of this cellular processing primarily leads to albuminuria. This review brings together recent data about urinary albumin clearance and current knowledge of receptors known to process albumin in both health and disease states. We conclude with a discussion of topical and controversial issues associated with the proposed new understanding of renal handling of albumin.

Glomerular heparan sulfate alterations: mechanisms and relevance for proteinuria

Heparan sulfate (HS) is the anionic polysaccharide side chain of HS proteoglycans (HSPGs) present in basement membranes, in extracellular matrix, and on cell surfaces. Recently, agrin was identified as a major HSPG present in the glomerular basement membrane (GBM). An increased permeability of the GBM for proteins after digestion of HS by heparitinase or after antibody binding to HS demonstrated the importance of HS for the permselective properties of the GBM. With recently developed antibodies directed against the GBM HSPG (agrin) core protein and the HS side chain, we demonstrated a decrease in HS staining in the GBM in different human proteinuric glomerulopathies, such as systemic lupus erythematosus (SLE), minimal change disease, membranous glomerulonephritis, and diabetic nephropathy, whereas the staining of the agrin core protein remained unaltered. This suggested changes in the HS side chains of HSPG in proteinuric glomerular diseases. To gain more insight into the mechanisms responsible for this observation, we studied GBM HS(PG) expression in experimental models of proteinuria. Similar HS changes were found in murine lupus nephritis, adriamycin nephropathy, and active Heymann nephritis. In these models, an inverse correlation was found between HS staining in the GBM and proteinuria. From these investigations, four new and different mechanisms have emerged. First, in lupus nephritis, HS was found to be masked by nucleosomes complexed to antinuclear autoantibodies. This masking was due to the binding of cationic moieties on the N-terminal parts of the core histones to anionic determinants in HS. Second, in adriamycin nephropathy, glomerular HS was depolymerized by reactive oxygen species (ROS), mainly hydroxyl radicals, which could be prevented by scavengers both in vitro (exposure of HS to ROS) and in vivo. Third, in vivo renal perfusion of purified elastase led to a decrease of HS in the GBM caused by proteolytic cleavage of the agrin core protein near the attachment sites of HS by the HS-bound enzyme. Fourth, in streptozotocin-induced diabetic nephropathy and during culture of glomerular cells under high glucose conditions, evidence was obtained that hyperglycemia led to a down-regulation of HS synthesis, accompanied by a reduction in the degree of HS sulfation.

Effect of plasma from patients with idiopathic nephrotic syndrome on proteoglycan synthesis by human and rat glomerular cells

In vivo and in vitro findings have shown that plasma of patients with idiopathic nephrotic syndrome (INS) contain factors that increase glomerular permeability to proteins. The effects of these factors on proteoglycan synthesis by glomerular cells are unknown. To investigate the effect of plasma from patients with INS (n = 23) and other glomerulopathies (n = 12) on the amount of proteoglycans synthesized by cultured rat mesangial cells and human glomerular epithelial cells, glomerular cells were cultured for 24 h with plasma from patients or control subjects, and incorporation of Na2(35)SO4 in chondroitin dermatan sulfate and heparan sulfate was assessed using a cationic nylon membrane. The mean ratio of glycosaminoglycan produced by rat mesangial cells when in contact with plasma (5%) from INS patients to the amount produced when in contact with control plasma was 0.70+/-0.06. The mean ratio of heparan sulfate was 0.58+/-0.08. The decrease of heparan sulfate production was present in the cellular and in the extracellular fraction. It was observed when the cells were in contact with plasma from patients in relapse but not when in remission. No decrease of heparan sulfate production was observed with four of the five patients with membranous glomerulonephritis (ratio of 1.27+/-0.03), IgA nephropathy (n = 5, ratio of 1.27+/-0.03), and membranoproliferative glomerulonephritis (n = 2, ratio of 1.39+/-0.34). When human glomerular epithelial cells were exposed to 5% plasma from INS patients in relapse (n = 9), the mean ratio of heparan sulfate was 0.62+/-0.06 in the cellular fraction and 0.72+/-0.08 in the medium. When in contact with plasma from patients in remission, no difference of glycosaminoglycan production was observed. A factor present in plasma from patients with INS during initial episodes or relapses is able to decrease the proteoglycan production of glomerular cells.

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.

Influence of chronic kanamycin administration on basement membrane anionic sites in the labyrinth

We studied the effect of chronic treatment with kanamycin on the basement membrane (BM) anionic sites in the cochlea and endolymphatic sac using polyethyleneimine (PEI) as a cationic tracer. Albino guinea pigs weighing 250-300 g received kanamycin (400 mg/kg/day, i.m.) for 10 or 17 consecutive days. The number of BM anionic sites as derived from the PEI area was not affected in Reissner's membrane, spiral prominence, basilar membrane or endolymphatic sac, whereas it was significantly decreased in the stria vascularis and spiral limbus, being more marked in the guinea pigs treated for 17 days than in those treated for 10 days. The number of BM anionic sites in these regions did not recover until 6 weeks after kanamycin treatment. These findings suggest that chronically administered kanamycin may selectively and progressively affect the BM anionic sites in the stria vascularis and spiral limbus, resulting in disruption of a barrier function in the cochlea, and that severely impaired BM anionic sites in the cochlea may not recover.

Proteinuria and albumin homeostasis in the nephrotic syndrome: effect of dietary protein intake

Nephrotic syndrome is analyzed in the light of interventions designed to decrease proteinuria and renal injury. The effect of dietary protein intake on urinary protein losses and albumin homeostasis are discussed on the basis of the pathophysiologic mechanisms known to account for changes in renal function of nephrotic patients. In addition, the effect of angiotensin-converting enzyme inhibitors for reduction of proteinuria is discussed in terms of the modulation of glomerular permselectivity and hemodynamics.

Serum albumin is a specific inhibitor of apoptosis in human endothelial cells

Excess blood vessels are removed by apoptosis of endothelial cells, however, the signals responsible for this have not been defined. Apoptosis of cultured human umbilical vein endothelial cells is induced by deprivation of serum or adhesion. In this paper, apoptosis in human umbilical vein and microvascular endothelium was induced by deprivation of serum and or adhesion. Apoptosis was confirmed on the basis of morphology, ultrastructure and internucleosomal cleavage of DNA. Loss of endothelial adhesion was found to be an early event in cultured endothelial cell apoptosis and was exploited to quantitate apoptosis. The effect of: bovine serum albumin; human serum albumin; recombinant human albumin; dithiothreitol reduced human and bovine albumin; CNBr treated human and bovine albumin as well as ovalbumin upon endothelial apoptosis was determined. Native bovine and human albumin as well as recombinant human material inhibited apoptosis at physiological concentrations with identical dose response curves in both umbilical vein and microvascular cells. Dithiothreitol treatment destroyed all protective activity while bovine but not human albumin was partially inactivated by CNBr treatment. The unrelated protein ovalbumin was not protective. Albumin did not inhibit apoptosis if cells were also deprived of adhesion. The data suggest that albumin is a specific inhibitor of human endothelial apoptosis but does not protect cells also deprived of adhesion. Reduced supply of albumin to endothelium in poorly perfused blood vessels may provide a mechanism for the removal of excess blood vessels in remodelling tissues. Also, the failure of albumin to protect endothelial cells deprived of adhesion from apoptosis may reflect the need to remove potentially micro-embolic cells detached due to trauma.

Antihypertensive drugs and endothelial cell function

Arterial hypertension is associated with increased capillary permeability, a possible contributor to the vascular remodeling process which could be involved in certain pathological conditions arising from elevated blood pressure. This study evaluated the effects of various antihypertensive drugs on capillary permeability in the normal rat, using Evan's blue dye (EB) as a marker of albumin extravasation. The results reveal that acute injection of certain diuretics (furosemide, indapamide, hydrochlorothiazide) increase while others (amiloride, cicletanine) decrease capillary permeability via stimulation of the cyclooxygenase pathway. 10 day gavage with indapamide, amiloride and cicletanine, as well as angiotensin-converting enzyme (ACE) inhibitor perindopril and calcium channel blockers nifedipine and verapamil decreases capillary permeability, whereas furosemide, hydrochlorothiazide, ACE inhibitor captopril and calcium channel blocker clentiazem do not modify or increase EB extravasation. Hence, selected antihypertensive agents reduce capillary permeability and could therefore have a supplemental protective vascular effect, in addition to their lowering arterial pressure.

Proteoglycan production by human glomerular visceral epithelial cells and mesangial cells in vitro

Proteoglycans metabolically labelled with [35S]sulphate and [3H]glucosamine or [3H]leucine were isolated from the incubation medium and cell layer of human adult mesangial cells and glomerular visceral epithelial cells using sequential DEAE chromatography purification steps followed by gel-filtration chromatography. The proteoglycan composition of each peak was analysed by treatment with HNO2, chondroitinase ABC or chondroitinase AC followed by chromatography on Sephadex G-50 columns. Heparan sulphate proteoglycan (HSPG) and dermatan sulphate proteoglycan were detected in both the culture medium and cell layer of mesangial cells. Culture medium of glomerular visceral epithelial cells contained HSPG and a second proteoglycan with the properties of a hybrid molecule containing HS and chondroitin sulphate (CS). The cell layer contained HSPG and CSPG. Detailed analysis of the hybrid molecule revealed that it had an apparent molecular mass of 400 kDa. SDS/PAGE of hybrid molecules, after treatment with heparitinase and chondroitinase ABC, revealed a core protein of 80 kDa. Using 1.8% polyacrylamide/0.6% agarose-gel electrophoresis, we deduced that the HS and CS were independently attached to one core protein. Because glomerular-basement-membrane HSPG is thought to be derived from mesangial cells and glomerular visceral epithelial cells and this molecule is involved in several kidney diseases, we investigated its synthesis in more detail. Anti-(rat glomerular-basement-membrane HSPG) monoclonal antibodies (JM403) and anti-(human glomerular-basement-membrane HSPG) polyclonal antibodies (both antibodies known to react with the large basement-membrane HSPG, perlecan) reacted strongly with HSPG obtained from both mesangial cells and glomerular visceral epithelial cells. However, the hybrid molecule did not react with these antibodies, suggesting that the HS side chain and the core protein were different from glomerular-basement-membrane HSPG. To quantify HS we performed an inhibition ELISA using mouse antibodies specific for glomerular-basement-membrane HS glycosaminoglycan side chains. Glomerular visceral epithelial cells produced significantly higher levels of HS (between 197.56 and 269.40 micrograms/72 h per 10(6) cells) than mesangial cells (between 29.8 and 45.5 micrograms/72 h per 10(6) cells) (three different cell lines; n = 3; P < 0.001). HS production by these cells was inhibited by cycloheximide, revealing that it was synthesized de novo. Expression of perlecan mRNA, demonstrated using reverse transcriptase PCR, was different in the two cell types. We conclude that glomerular visceral epithelial cells and mesangial cells have characteristic patterns of proteoglycan production. Glomerular visceral epithelial cells produced a hybrid proteoglycan containing CS and HS independently attached to its core protein.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Evidence for direct anti-heparin-sulphate reactivity in sera of SLE patients

Recently it has been suggested that anti-ds-DNA antibodies (Abs) promote tissue damage in systemic lupus erythematosus (SLE) by cross-reactivity with highly negatively charged tissue components such as heparan sulphate (HS), the major glycosaminoglycan of the glomerular basement membrane (GBM). Other authors, however, support the theory of DNA-anti-dsDNA immune complex deposition in situ. To further elucidate the possible role of HS antibodies, we developed a new ELISA system with heparan sulphate bound to solid phase. SLE patients (n = 40) showed a higher reactivity against HS (mean = 28.4, SD = 34.3) as compared to normal donors (n = 28, mean = 15.2, SD = 6.3) and patients with rheumatoid arthritis (n = 35, mean = 14.3, SD = 6.4). The addition of native dsDNA or HS to SLE sera was followed by a dose-dependent reduction in anti-HS reactivity. In contrast, in an anti-dsDNA ELISA, no reduction was observed when HS was added to SLE sera. An increase in reactivity was observed when SLE sera with and without a prior incubation with dsDNA were digested with DNAse I or II. After the purification of serum samples by protein A sepharose under dissociative conditions, seven out of eight SLE patients showed an increase in anti-HS reactivity. No correlation of the anti-HS Abs was found with organ involvement or other serological parameters. We concluded, that there is evidence for a direct anti-HS Ab reactivity in SLE sera. A part of these antibodies seems to show low avidity anti-dsDNA cross-reactivity.

Inhibition of angiotensin-converting enzyme reduces urinary albumin excretion but not regional albumin clearance in experimental diabetes

Albuminuria and increased regional albumin clearance are known to develop concomitantly in diabetes. The anti-proteinuric effect of angiotensin-converting enzyme inhibitor therapy is well established. We studied whether angiotensin-converting enzyme inhibitor therapy with perindoprilat in comparison with conventional antihypertensive treatment could influence the development of increased regional albumin clearance as well as albuminuria in experimental diabetes. Rats with streptozotocin-induced diabetes were randomized into a saline group (n = 7), a perindoprilat (1 mg/kg per day) group (n = 8), and a hydralazine (3 mg/kg per day) group (n = 6); six rats served as non-diabetic controls. After 6-8 weeks, blood pressure was equally reduced in the perindoprilat- and hydralazine-treated groups (P < 0.01). Twenty-four-hour urinary protein and albumin excretion were increased in diabetic rats compared to control rats (P < 0.001). Hydralazine did not reduce 24 h protein or albumin excretion, whereas perindoprilat treatment reduced both (P < 0.001) to levels comparable to those of control rats. Regional albumin clearance, assessed in the eye, ileum, lung, skeletal muscle and skin, was clearly elevated in diabetic rats compared to control rats; however, neither drug therapy had an effect on albumin clearance.

Glucosaminyl N-deacetylase in cultured fibroblasts; comparison of patients with and without diabetic nephropathy, and identification of a possible mechanism for diabetes-induced N-deacetylase inhibition

Impaired heparan sulphate biosynthesis through diabetes-induced inhibition of glucosaminyl N-deacetylase may have a central role in the development of diabetic nephropathy, and genetic differences in the vulnerability of the N-deacetylase could influence the risk of developing nephropathy. We studied N-deacetylase activity in fibroblast cultures from Type 1 (insulin-dependent) diabetic patients with (n = 14) or without (n = 13) diabetic nephropathy, together with non-diabetic control subjects (n = 7). No difference in N-deacetylase activity was found (p = 0.13), and no inhibition of N-deacetylase was found in cultures grown at 25 mmol/l glucose. N-deacetylase activity was inversely correlated to growth rate (r = -0.59, p = 0.0008), and in patients with nephropathy a negative correlation between HbA1C and fibroblast N-deacetylase activity (r = -0.72, p = 0.012) was found. Cell-cycle analysis revealed an increased fraction of S-phase cells in patients with nephropathy (28%(21-52%)) compared to healthy control subjects (17% (9-24%)), p = 0.0008, but not between patients with and without nephropathy (latter group 26%(11-43%)), p = 0.43. Forskolin, an activator of protein kinase A, specifically decreased N-deacetylase activity, whereas activation of protein kinase C produced a combined reduction in N-deacetylase activity and total protein synthesis. In conclusion, no constitutive defects in N-deacetylase activity were found in fibroblasts from these patients. Further studies should consider possible associations between fibroblast characteristics and pre-biopsy environmental parameters related to cellular memory phenomena. Finally, activation of protein kinase A provides a potential general pathway for regulating N-deacetylase activity.

Effect of diltiazem on glomerular heparan sulfate and albuminuria in diabetic rats

Calcium entry blockers, particularly diltiazem, have been shown to lower not only systemic blood pressure but also improve proteinuria in non-insulin-dependent diabetic patients. The presence of proteinuria is attributed to the loss of glomerular heparan sulfate, which confers a negative charge on the basement membrane. In the present study, we evaluated the efficacy of diltiazem in lowering blood pressure and proteinuria in diabetic rats and also examined the possibility that diltiazem prevents proteinuria through glomerular preservation of heparan sulfate. Diabetes was induced in male Wistar rats by streptozotocin (60 mg/kg). One group of diabetic rats was treated with diltiazem (25 mg/L) in drinking water for 20 weeks. Another group of diabetic rats and a group of nondiabetic rats were given tap water only. Systolic blood pressure was measured at 4, 8, 12, and 20 weeks. Urinary excretion of albumin was done at 4, 8, 12, 16, and 20 weeks. At the end of 20 weeks, all rats were killed, kidneys were removed, and glomeruli were isolated. Total glycosaminoglycan and heparan sulfate synthesis were determined by incubating glomeruli in the presence of [35S]sulfate. Diltiazem lowered blood pressure significantly in diabetic rats at 8, 12, and 20 weeks. Diabetic glomeruli synthesized less total glycosaminoglycan and heparan sulfate than glomeruli from normal rats. Characterization of heparan sulfate by ion-exchange chromatography showed that the fraction eluted with 1 M NaCl was significantly lower and the fraction eluted with 1.25 M NaCl significantly higher in diabetic than in normal rats. Diltiazem therapy returned not only glomerular synthesis but also various fractions of heparan sulfate to normal.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Loss of glomerular polyanion correlated with albuminuria in experimental cadmium nephropathy

The relationship between proteinuria and glomerular polyanion (GPA) charge has been studied in a model of experimental cadmium (Cd) nephropathy. Female Sprague-Dawley rats were administered Cd in drinking water for up to 18 months. From month 2, the animals showed an elevation of albuminuria preceding by about 6 months the rise of urinary beta 2-microglobulin and IgG. The nephrotoxic action of Cd was not readily detectable on the basis of the urinary output of beta-N-acetylglucosaminidase, alanine aminopeptidase and lactate dehydrogenase. These enzymes showed either little variation or were affected late in the intoxication process. Administration of Cd for 12 or 18 months did not impair the GFR. The glomerular origin of the albuminuria induced by Cd was demonstrated by estimating the glomerular filtration of rat or human (injected intravenously) albumin in rats whose tubular reabsorption had been blocked by a saturating dose of cytochrome C. The GPA charge was assessed by measuring the binding of the cationic dye, Alcian blue (AB), to membranes of isolated glomeruli. The sialic and sulfate content of these membranes was also determined. The Cd induced-albuminuria was negatively correlated (r = -0.73; n = 37) with the AB binding to glomerular membranes, their sialic acid content (r = -0.39) but not with their sulfate content (r = -0.15). A negative correlation (r = -0.62; n = 37) was also observed between the albuminuria and red blood cell membrane negative charges largely contributed by sialic acid. All these observations can be interpreted as the evidence that Cd enhances the glomerular filtration of proteins through a GPA depletion involving mainly sialic acid.

A fibre matrix model for the restricting junction of the blood-brain barrier in a cephalopod mollusc: implications for capillary and epithelial permeability

A model is proposed for the novel restricting junction forming the blood-brain barrier in a cephalopod mollusc, the cuttlefish Sepia officinalis. The model is based on electron-microscopic findings, from both thin-section and freeze-fracture material, the distribution of electron-dense tracers, and radioisotopic measurements of permeability using small non-electrolytes. Biochemical properties of Sepia plasma proteins are also considered. It is proposed that an effective blood-brain barrier is achieved by a combination of mechanisms. As much as 90% of the Sepia brain microvessel wall is covered by a 'seamless' glial sheath, without intercellular clefts, limiting the number of potential leakage sites. The remaining clefts follow a tortuous course increasing the diffusion path to the neuropile. Entry into the clefts is reduced by a restricting junctional region at the luminal end, characterized by delicate striations spanning the cleft, and forming an effective barrier to both horseradish peroxidase and ionic lanthanum. This is a novel junctional type, different from previously-described vertebrate and invertebrate occluding junctions. It is proposed that the junction acts as a fine-mesh molecular filter, with condensed extracellular material in the cleft, cross-linked and consolidated by bound plasma protein. Cephalopod haemocyanin or its subcomponents are considered likely candidates for the bound protein. The model predicts that blood-brain barrier permeability should be sensitive to the charge structure of the extracellular matrix and the presence of protein, and is analogous to the 'fibre matrix' model of vertebrate capillary permeability. The Sepia blood-brain barrier also highlights the different strategies available for constructing a restricting cell layer, and suggests a possible evolutionary pattern underlying the present range of junctional mechanisms in vertebrate and invertebrate epithelia.

A monoclonal antibody against GBM heparan sulfate induces an acute selective proteinuria in rats

After immunization of mice with partially-purified heparan sulfate proteoglycan (HSPG) isolated from rat glomeruli, a monoclonal antibody (mAb JM-403) was obtained, which was directed against heparan sulfate (HS), the glycosaminoglycan side chain of HSPG. In ELISA it reacted with isolated human glomerular basement membrane (GBM) HSPG, HS and hyaluronic acid, but not with the core protein of human GBM HSPG, and not with chondroitin sulfate A and C, dermatan sulfate, keratan sulfate and heparin. Furthermore, it did not bind to laminin, collagen type IV or fibronectin. Specificity of JM-403 for HS was also suggested by results of inhibition studies, which found that intact HSPG and HS, but not the core protein, inhibited the binding of JM-403 to HS. In indirect immunofluorescence on cryostat sections of rat kidney, a fine granular to linear staining of the GBM was observed, along with a variable staining of the other renal basement membranes. Pretreatment of the sections with heparitinase completely prevented the binding of mAb JM-403, whereas pretreatment with chondroitinase ABC or hyaluronidase had no effect. The precise binding site of mAb JM-403 was investigated by indirect immunoelectron microscopy. It revealed a diffuse staining of the whole width of the GBM. One hour after intravenous injection of JM-403 into rats, the mAb was detected along the glomerular capillary wall in a fine granular pattern, which shifted towards a more mesangial localization after 24 hours. No binding was observed anymore by day 15. Intravenous injection induced a dose-dependent, transient and selective proteinuria that was maximal immediately after the injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Urine glycosaminoglycans in congenital and acquired nephrotic syndrome

To evaluate the specificity of a raised heparan sulphate (HS) excretion previously reported in four children with congenital nephrotic syndrome (CNS), we measured the urinary excretion of HS and chondroitin sulphate (CS) in seven children with Finnish-type congenital nephrotic syndrome (CNSF), seven with diffuse mesangial sclerosis (DMS), nine with focal segmental glomerulosclerosis (FSGS), 14 with steroid-sensitive nephrotic syndrome of whom eight had a biopsy confirming minimal change histology (SSNS), and 17 controls. The urine HS/CS ratio in normal children had a median of 0.36 (observed range 0.21 to 0.68) and was independent of age. HS/CS ratio was significantly greater than controls in CNSF (median 0.80, range 0.43 to 1.28), DMS (median 0.81, range 0.49 to 1.13) and FSGS children (median 0.66, range 0.38 to 1.6), but was not in SSNS (median 0.44, range 0.28 to 0.70). There was a positive correlation between the HS/CS ratio and urine albumin excretion. High HS/CS ratios are not diagnostic of a particular histological variety of CNS.

Proteoglycan and glycosaminoglycan synthesis by cultured rat mesangial cells

The synthesis of metabolically labeled proteoglycans and glycosaminoglycans from medium, cell layer and substrate attached material by rat glomerular mesangial cells in culture was characterized. The cellular localization of the labeled proteoglycans and glycosaminoglycans was determined by treating the cells with Flavobacterial heparinase. Of the total sulfated glycosaminoglycans, 33% were heparan sulfate; 55% of the cell layer material was heparan sulfate; 80% of sulfated proteins in the medium were chondroitin sulfate/dermatan sulfate. Putative glycosaminoglycan free chains of heparan sulfate and chondroitin sulfate were found in both the medium and cell layer; 95% of total proteoglycans and most (90%) of the putative heparan sulfate free chains were removed from the cell layer by the heparinase, whereas only 50% of the chondroitin sulfate and 25% of dermatan sulfate were removed. Large amounts of hyaluronic acid labeled with 3H glucosamine were found in the cell layer. In summary, approximately 60% of total sulfated glycoproteins was in the form of putative glycosaminoglycan free chains. Thus rat mesangial cells may synthesize large amounts of putative glycosaminoglycan free chains, which may have biological functions in the glomerulus independent of proteoglycans.

Enalapril improves albuminuria by preventing glomerular loss of heparan sulfate in diabetic rats

Angiotensin converting enzyme (ACE) inhibitors, particularly enalapril and captopril, have been shown to decrease proteinuria in diabetic animals and human subjects. Since heparan sulfate proteoglycan confers a negative charge on the glomerular basement membrane, and either decreased synthesis or loss of this charge causes albuminuria in diabetic animals, we examined the possibility that enalapril prevents albuminuria through glomerular preservation of heparan sulfate in long-term diabetic rats. A total of 22 male Wistar rats were used in the study. Diabetes was induced in 15 rats by a single intraperitoneal injection of streptozotocin (60 mg/kg). The remaining 7 rats received buffer. One week following induction of diabetes, 8 diabetic rats were allowed to drink tap water containing enalapril at a concentration of 50 mg/liter; the remaining 7 diabetic and 7 nondiabetic rats were given only tap water. The drug treatment was continued for 20 weeks. Systolic blood pressure and 24-hr urinary excretion of albumin were measured at 2, 8, 16, and 20 weeks. At the end of 20 weeks, all rats were killed, kidneys were removed, and glomeruli were isolated by differential sieving technique. Total glycosaminoglycan and heparan sulfate synthesis was determined by incubating glomeruli in the presence of [35S]sulfate. Characterization of heparan sulfate was performed by ion-exchange chromatography. Systolic blood pressures were significantly lower in enalapril-treated diabetic rats compared to untreated diabetic rats. Diabetic glomeruli synthesized less heparan sulfate than glomeruli from nondiabetic rats. Also, glomerular heparan sulfate content of diabetics was significantly lower than that of nondiabetics. Further characterization of heparan sulfate showed that the fraction eluted with 1 M NaCl was significantly lower and the fraction eluted with 1.25 M NaCl significantly higher in diabetic than in normal rats. Enalapril treatment normalized not only glomerular synthesis and content but also various fractions of heparan sulfate in diabetic rats. Diabetic rats excreted increased quantities of heparan sulfate and albumin than nondiabetic rats. Enalapril therapy prevented both these increases in diabetic rats. These data suggest that enalapril treatment improves albuminuria through preservation of glomerular heparan sulfate and prevention of its urinary loss in diabetic rats.

Proteinuria: changes and mechanisms in toxic nephropathies

During the last few decades, considerable progress has been made in the understanding of the pathophysiological mechanisms of proteinuria. A great variety of hemodynamic or biochemical mechanisms acting at different sites of the nephron have been shown to alter the renal handling and the urinary excretion of proteins. The finding which perhaps has had most practical implications is that the pattern of protein excretion quantitatively and qualitatively varies with the site and severity of renal damage. This has led to the development of a large array of methods for the identification and quantitation of specific urinary proteins. These methods have been most extensively used by toxicologists in experimental, epidemiological, or clinical studies on potentially nephrotoxic chemicals (e.g., drugs, heavy metals, solvents, etc.). The present review summarizes the current state of knowledge on the mechanisms of proteinuria and the use of urinary proteins as indicators of nephrotoxicity.

Prevention of albuminuria by captopril in diabetic rats

1. Streptozotocin diabetic rats were treated with captopril (50 mg l), an angiotensin converting enzyme-inhibitor, in drinking water for 20 weeks. 2. Systolic blood pressure and 24-hr urinary excretions of heparan sulfate and albumin were done at 2, 8, 16 and 20 weeks. 3. At the end of 20 weeks, all rats were killed, kidneys removed and glomeruli isolated. 4. Total glycosaminoglycan and heparan sulfate synthesis were determined by incubating glomeruli in the presence of 35S-sulfate. 5. Captopril significantly lowered blood pressure in diabetic rats 8 weeks after treatment. 6. Diabetic glomeruli synthesized less total glycosaminoglycan and heparan sulfate than glomeruli from nondiabetic rats. 7. Further characterization of heparan sulfate by ion-exchange chromatography showed that the fraction eluted with 1 M NaCl was significantly lower and the fraction eluted with 1.25 M NaCl significantly higher in diabetic than in normal rats. 8. Therapy with captopril normalized not only glomerular synthesis and content but also various fractions of heparan sulfate in diabetic rats. 9. Excretions of heparan sulfate and albumin were significantly higher in diabetic than in nondiabetic rats. 10. Captopril therapy did significantly lower but not normalize both these excretions in diabetic rats. 11. The data suggest that catopril therapy improves albuminuria through preservation of glomerular heparan sulfate and prevention of its urinary loss in diabetic rats.

Anti-heparan sulphate reactivity in sera from patients with systemic lupus erythematosus with renal or non-renal manifestations

Previously, we have shown that anti-DNA can bind to heparan sulphate (HS), a constituent of the glomerular basement membrane (GBM). We hypothesized that binding of anti-DNA to HS in the GBM plays a role in the onset of systemic lupus erythematosus (SLE) nephritis. To test this hypothesis we measured the anti-HS reactivity in cross-sectional and longitudinal studies of SLE patients with or without nephritis. In the transverse serum study single serum samples from 26 SLE patients were studied. We found no correlation between anti-HS reactivity and previously development of nephritis (anti-HS positive: seven out of 16 with history of nephritis, two out of 10 without nephritis). However, six of the seven anti-HS positive sera in the nephritis group were obtained within 1 month of the onset of nephritis, suggesting a temporal relationship between anti-HS reactivity and onset of nephritis. In the longitudinal serum study between six and 16 serum samples were studied from each of 10 SLE-patients. In five out of five episodes of nephritis we found anti-HS reactivity before the onset or exacerbation of the nephritis. In four non-renal manifestations anti-HS reactivity was found in only one episode; in none of the three patients who remained clinically stable did serum samples show anti-HS reactivity. Anti-HS reactivity was only found in sera positive for anti-DNA by Farr assay but the anti-HS titre was not a mere reflection of the reactivity measured in the Farr assay. This indicates that only a subpopulation of anti-DNA can bind to HS. We found a high correlation (r = 0.99) between anti-HS reactivities in plasma and serum and we conclude that anti-HS reactivity in serum samples from SLE patients is not due to in vitro complex formation during clotting. Although further prospective analysis is necessary, our data suggest that measurement of anti-HS reactivity in SLE patients might identify patients at risk for the development of nephritis.

Cross-reactivity of monoclonal anti-DNA antibodies with heparan sulfate is mediated via bound DNA/histone complexes

To study in more detail the cross-reactive binding of anti-DNA antibodies to heparan sulfate (HS) and heparan sulfate proteoglycan (HSPG) purified from glomerular basement membranes (GBM), the binding pattern of 31 murine IgG anti-DNA MoAbs, derived from MRL/lpr, NZB/W and graft-versus-host diseased mice, was analysed. In ELISA we found binding of 10 anti-DNA MoAbs to HS. Seven of the 10 anti-HS positive clones bound to HSPG but not to the HSPG core protein in ELISA and/or on Western blots. However, DNase-I treatment partly reduced this binding, whereas after purification of MoAb by protein-A sepharose chromatography under dissociative conditions, all clones completely lost their binding capacity to HS and HSPG. Culturing of hybridoma cells in the presence of 3H-thymidine revealed DNA bound to the MoAb. Although the binding to HS and HSPG could be reconstituted by the addition of the protein-A column effluent, this was not possible by the addition of DNA alone. Therefore, we performed immunoprecipitation of the effluent with purified MoAb and subsequent SDS-PAGE which showed that the complex also contained histones. However, histones alone were also not able to reconstitute the binding to HS and HSPG. It is concluded that binding of anti-DNA MoAb to HS and GMB-HSPG is mediated via bound complexes containing both DNA and histones. A comparable reaction with polyclonal anti-DNA Ab might play a role in the pathogenesis of SLE nephritis, since histones have a very high affinity for HS, the major glycosaminoglycan of the GBM.

Heparan sulfate proteoglycan from human tubular basement membrane. Comparison with this component from the glomerular basement membrane

Heparan sulfate proteoglycan (HSPG) was extracted from human tubular basement membrane (TBM) with guanidine and purified by ion-exchange chromatography and gel filtration. The glycoconjugate was sensitive to heparitinase and resistant to chondroitinase ABC, had an apparent molecular mass of 200-400 kDa and consisted of 70% protein and 30% glycosaminoglycan. The amino acid composition was characterized by its high content of glycine, proline, alanine and glutamic acid. Hydrolysis with trifluoromethanesulfonic acid yielded core proteins of 160 and 110 kDa. The heparan sulfate (HS) chains obtained after alkaline NaBH4 treatment had a molecular mass of about 18 kDa. Results of heparitinase digestion and HNO2 treatment suggest a clustering of sulfate groups in the distal portion of the HS side chains. These chemical data are comparable to those obtained previously on glomerular basement membrane (GBM) HSPG (Van den Heuvel et al. (1989) Biochem. J. 264, 457-465). Peptide patterns obtained after trypsin, clostripain or V8 protease digestion of TBM and GBM HSPG preparations showed a large similarity. Polyclonal antisera and a panel of monoclonal antibodies raised against both HSPG preparations and directed against the core protein showed complete cross-reactivity in ELISA and on Western blots. They stained all basement membranes in an intense linear fashion in indirect immunofluorescence studies on human kidneys. Based on these biochemical and immunological data we conclude that HSPGs from human GBM and TBM are identical, or at least very closely related, proteins.