Increase in proteinuria and reduction in number of anionic sites on the glomerular basement membrane in rabbits by infusion of human nephrotic plasma in vivo

National Unified Renal Translational Research Enterprise: Idiopathic Nephrotic Syndrome (NURTuRE-INS) study

Background

Idiopathic nephrotic syndrome (INS) is a heterogenous disease and current classification is based on observational responses to therapies or kidney histology. The National Unified Renal Translational Research Enterprise (NURTuRE)-INS cohort aims to facilitate novel ways of stratifying INS patients to improve disease understanding, therapeutics and design of clinical trials.

Methods

NURTuRE-INS is a prospective cohort study of children and adults with INS in a linked biorepository. All recruits had at least one sampling visit collecting serum, plasma, urine and blood for RNA and DNA extraction, frozen within 2 hours of collection. Clinical histology slides and biopsy tissue blocks were also collected.

Results

A total of 739 participants were recruited from 23 centres to NURTuRE-INS, half of whom were diagnosed in childhood [n = 365 (49%)]. The majority were white [n = 525 (71%)] and the median age at recruitment was 32 years (interquartile range 12-54). Steroid-sensitive nephrotic syndrome (SSNS) was the most common clinical diagnosis [n = 518 (70%)]. Of patients diagnosed in childhood who underwent a kidney biopsy, for SSNS (n =103), 76 demonstrated minimal change disease (MCD), whereas for steroid-resistant nephrotic syndrome (n =80), 21 had MCD. Almost all patients diagnosed in adulthood had a kidney biopsy [n = 352 (94%)]; 187 had MCD and 162 had focal segmental glomerulosclerosis.

Conclusions

NURTuRE-INS is a prospective cohort study with high-quality biosamples and longitudinal data that will assist research into the mechanistic stratification of INS. Samples and data will be available through a Strategic Access and Oversight Committee.

"Idiopathic" minimal change nephrotic syndrome: a podocyte mystery nears the end

The discovery of zinc fingers and homeoboxes (ZHX) transcriptional factors and the upregulation of hyposialylated angiopoietin-like 4 (ANGPTL4) in podocytes have been crucial in explaining the cardinal manifestations of human minimal change nephrotic syndrome (MCNS). Recently, uncovered genomic defects upstream of ZHX2 induce a ZHX2 hypomorph state that makes podocytes inherently susceptible to mild cytokine storms resulting from a common cold. In ZHX2 hypomorph podocytes, ZHX proteins are redistributed away from normal transmembrane partners like aminopeptidase A (APA) toward alternative binding partners like IL-4Rα. During disease relapse, high plasma soluble IL-4Rα (sIL-4Rα) associated with chronic atopy complements the cytokine milieu of a common cold to displace ZHX1 from podocyte transmembrane IL-4Rα toward the podocyte nucleus. Nuclear ZHX1 induces severe upregulation of ANGPTL4, resulting in incomplete sialylation of part of the ANGPTL4 protein, secretion of hyposialylated ANGPTL4, and hyposialylation-related injury in the glomerulus. This pattern of injury induces many of the classic manifestations of human minimal change disease (MCD), including massive and selective proteinuria, podocyte foot process effacement, and loss of glomerular basement membrane charge. Administration of glucocorticoids reduces ANGPTL4 upregulation, which reduces hyposialylation injury to improve the clinical phenotype. Improving sialylation of podocyte-secreted ANGPTL4 also reduces proteinuria and improves experimental MCD. Neutralizing circulating TNF-α, IL-6, or sIL-4Rα after the induction of the cytokine storm in Zhx2 hypomorph mice reduces albuminuria, suggesting potential new therapeutic targets for clinical trials to prevent MCD relapse. These studies collectively lay to rest prior suggestions of a role of single cytokines or soluble proteins in triggering MCD relapse.

What is circulating factor disease and how is it currently explained?

Nephrotic syndrome (NS) consists of the clinical triad of hypoalbuminaemia, high levels of proteinuria and oedema, and describes a heterogeneous group of disease processes with different underlying drivers. The existence of circulating factor disease (CFD) as a driver of NS has been epitomised by a subset of patients who exhibit disease recurrence after transplantation, alongside laboratory work. Several circulating factors have been proposed and studied, broadly grouped into protease components such as soluble urokinase-type plasminogen activator (suPAR), hemopexin (Hx) and calcium/calmodulin-serine protease kinase (CASK), and other circulating proteases, and immune components such as TNF-α, CD40 and cardiotrophin-like cytokine-1 (CLC-1). While currently there is no definitive way of assessing risk of CFD pre-transplantation, promising work is emerging through the study of 'multi-omic' bioinformatic data from large national cohorts and biobanks.

Novel mouse strains to study circulating permeability factor(s) in primary focal segmental glomerulosclerosis

Recurrence of proteinuria after kidney transplantation in primary focal segmental glomerulosclerosis (FSGS) is unpredictable. Several putative circulating permeability factors (CPFs) have been suggested, but none have been validated. A clinically relevant experimental model is required that demonstrates the presence of CPF(s) in patient material, to study CPF(s) and possibly predict recurrence in patients. We aimed to develop a FSGS-prone Thy-1.1 transgenic mouse model with accelerated proteinuria after injection of samples from patients with FSGS. The Thy-1.1 transgene was backcrossed into 5 mouse strains. The age of onset and severity of spontaneous proteinuria varied between the different genetic backgrounds. 129X1/Sv^Thy-1.1 and 129S2/SvPas^Thy-1.1 mice displayed proteinuria at 4 weeks, whereas Balb/c^Thy-1.1 and C57BL/6J^Thy-1.1 mice developed proteinuria from 6 weeks, and were used further. We determined the maximum protein dose that could be injected without causing protein overload in each background. Balb/c^Thy-1.1 and C57BL/6J^Thy-1.1 males and females were injected with presumably CPF-containing plasmapheresis effluent from 6 FSGS patients, which induced albuminuria particularly in Balb/c^Thy-1.1 males. Unfortunately, no response could be detected when using sera instead of plasmapheresis effluent, serum being more clinically relevant in the context of predicting FSGS recurrence. Considering the differences between responses elicited by serum and plasmapheresis effluent, simultaneously collected serum, plasma, and plasmapheresis effluent were tested. Whereas we could detect responses using a validated in vitro model, none of these presumably CPF-containing samples induced proteinuria in Balb/c^Thy-1.1 males. Thus, we have extensively tested the Thy-1.1 mouse model on different genetic backgrounds with proteinuria after injection of FSGS patient material as clinically relevant readout. The Balb/c^Thy-1.1 male mouse strain demonstrated the most promising results, but to detect CPF activity in FSGS serum e.g. prior to kidney transplantation, this strain clearly lacks sensitivity and is therefore not yet clinically applicable. It could, however, still be used as research tool to study CPFs in patient samples that did induce proteinuria.

Focal Segmental Glomerulosclerosis and Renal Transplantation

Primary focal segmental glomerulosclerosis (FSGS) is a major cause of nephrotic syndrome and eventual end-stage renal disease. It is known to be due to an abnormality of the visceral epithelial cells (podocytes) of the glomerulus. The morphological hallmark of primary FSGS is diffuse effacement of podocyte foot processes. The etiology of the podocyte damage is not been clearly established. FSGS can also be a secondary process due to underlying conditions including obesity and heroin use. In the secondary processes, the mechanism appears to be a decreased ratio of podocytes to the glomerular filtration surface area. Familial forms of FSGS also exist due to alterations of several different podocyte proteins. Primary FSGS is an increasing cause of end-stage renal disease. Recurrence of severe FSGS in renal allograft recipients presents a major challenge to transplant physicians. The incidence of recurrence is generally accepted to be between 20% and 30%. Risk factors for and characteristics of recurrence include a rapid progression of the primary disease to end-stage renal failure, early onset of nephrotic range proteinuria after allografting, frequent loss of the allograft, a high frequency of recurrence in subsequent allografts, and children less than 15 years of age. Some investigators have identified a circulating factor called the FSGS factor that appears to be associated with recurrence after transplantation. This factor has been shown to be a protein between 30 and 50 kd molecular weight. Logically, the possibility of a circulating factor associated with recurrence of FSGS led investigators to treat patients with plasmapheresis. Several studies have been reported with varying success. The response of patients to plasmapheresis seems to be completely individual. Other studies have added cyclophosphamide and/or mycophenolate mofetil to the plasmapheresis protocol. Again success in these studies has been variable. However, because some patients show complete recovery with plasmapheresis, individuals who develop recurrent FSGS after transplantation usually are given a trial of plasmapheresis therapy.

Proteinuria and Fusion of Podocyte Foot Processes in Rats after Infusion of Cytokine from Patients with Idiopathic Minimal Lesion Nephrotic Syndrome

BACKGROUND/AIMS

We report on the isolation of a factor secreted by peripheral blood mononuclear cells from patients with idiopathic minimal lesion nephrotic syndrome (IMLNS) in relapse and its effect on proteinuria and podocyte morphology in the rat.

METHODS

Peripheral blood mononuclear cells from patients with IMLNS (in relapse and in remission) and patients with focal segmental glomerulosclerosis were cultured for 72 h. Supernatants from 20 x 10(6) cultured cells were separated by liquid chromatography into three fractions according to markers (bovine serum albumin, beta-amylase, and apoferritin). Each supernatant fraction was infused into rats for 5 days using an osmotic pump. Proteinuria, 24-hour albumin excretion or albumin/creatinine ratio in a 24-hour urine collection, was measured daily starting 3 days prior to fraction infusion. Renal tissue was obtained for electron microscopy studies. The beta-amylase fraction underwent electrophoresis using isoelectric focusing gel.

RESULTS

When protein excretion was compared prior to and during supernatant fraction infusion, a significant increase in proteinuria was observed only when beta-amylase fraction from IMLNS patients in relapse was infused (p < 0.05). Protein electrophoresis of the beta-amylase fraction showed a single band at pH 6.0 only in samples from IMLNS patients in relapse. The band was composed of two proteins, beta-amylase and a 100-kDa glycoprotein. Fusion of foot processes was observed only when the beta-amylase fraction from IMLNS patients in relapse was infused.

CONCLUSIONS

The infusion of the beta-amylase fraction containing a 100-kDa glycoprotein from IMLNS patients in relapse induced proteinuria and effacement of foot processes in the rat. This protein may play a role in the pathogenesis of IMLNS.

Proteinuria after injection of human focal segmental glomerulosclerosis factor

BACKGROUND

Recurrent focal segmental glomerulosclerosis (FSGS) is heralded by proteinuria that may remit after treatment with plasmapheresis or immunoadsorption. Study of recurrent FSGS has been hampered by lack of an animal model that exhibits a pattern of proteinuria that mimics human disease. We have obtained a component of FSGS patient plasma (FSGS factor) that increases glomerular albumin permeability (P(alb)) in vitro and causes transient proteinuria in vivo.

METHODS

Plasma fractions containing FSGS factor and comparable plasma fractions from normal donors were injected into normal male Sprague-Dawley rats. Urinary protein, albumin, and creatinine were measured at various time points. Additionally, plasma samples from test animals were collected after injection and tested for FS activity defined by increased P(alb). Finally, glomeruli were isolated from animals after injection and P(alb) of these glomeruli tested.

RESULTS

Proteinuria and albuminuria were increased by 24 hr after injection with FSGS factor, and returned to baseline by 48 hr after injection. Injection with the same fraction of normal plasma had no effect on urinary protein. FSGS factor increased urinary protein in a dose-dependent manner. Serum collected from rats 15 or 60 min after injection with FSGS factor increased P(alb) of glomeruli in vitro, whereas serum collected 3 or more hours after injection had no effect. Glomeruli isolated from rats receiving injections with FSGS factor had increased in vitro P(alb) compared with glomeruli from rats injected with a fraction from normal plasma.

CONCLUSIONS

We have demonstrated that a single injection of FSGS factor increases P(alb) and, causes transient albuminuria and proteinuria in rats. FS activity in the plasma of recipient rats is also transient. This is the first detailed description of the time course and dose-dependence of proteinuria caused by FSGS factor in an animal model.

Effect of plasma fractions from patients with focal and segmental glomerulosclerosis on rat proteinuria

BACKGROUND

Patients suffering from focal and segmental glomerulosclerosis (FSGS) and in whom this disease recurs after transplantation are likely to have an active form of the disease and to have a factor(s) (such as, albuminuric factor) present in their blood that alters glomerular permeability for albumin.

METHODS

We used a sequential 50 and 70% ammonium sulfate (AS) precipitation of plasma from patients with relapsing FSGS and non-FSGS nephrotic syndrome (NS), in addition to plasma from healthy individuals, to obtain both an immunoglobulin (Ig)-rich fraction (50% AS precipitate) and a non-Ig fraction (70% AS supernatant). These fractions were injected intra-arterially or intravenously/intraperitoneally into Sprague-Dawley rats, and proteinuria (g protein/mmol creatinine) was measured for 24 hours. Ig fractions eluted from immunoadsorption onto protein A were also tested. A biochemical characterization was then carried out on the 70% AS supernatants by ultrafiltration on 30 and 50 kD cut-off membranes and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Differentially stained bands were sequenced.

RESULTS

The 70% AS supernatants from FSGS patients induced proteinuria when injected intra-arterially into normal rats. This effect was significantly different (P < 0.05) from that observed when similar fractions were prepared from the plasma of patients suffering from non-FSGS NS, but was not different from that observed with fractions from healthy individuals and even with an injection of saline solution. Injections of other plasma fractions did not induce a significant proteinuria in the FSGS group versus the non-FSGS NS group. SDS-PAGE of 70% AS supernatants revealed a protein of 23 kD that was more concentrated in AS supernatants from FSGS plasma than the other plasma samples and that was identified by microsequencing as apolipoprotein A1. After sequential ultrafiltration of 70% AS supernatants on 30 and 50 kD cut-off membranes, a second band of 43 kD was found at a much higher concentration in the FSGS samples than in non-FSGS NS and healthy individuals samples. This band is likely to correspond to a candidate albuminuric factor recently reported by another group [1], and was identified by microsequencing as alpha1 acid glycoprotein or orosomucoid. Consequently, purified orosomucoid from the plasma of FSGS, non-FSGS NS patients, or healthy individuals was injected intra-arterially into rats. No differences were found between the proteinuria induced in each group.

CONCLUSIONS

These data strongly suggest that in vivo injection of material into the rat is not a reliable model for testing plasma fraction activity and that the 43 kD orosomucoid is not likely to be the albuminuric factor.

Induction of experimental proteinuria in vivo following infusion of human plasma hemopexin

BACKGROUND

The human plasma constituent hemopexin (Hx), following incubation with renal tissue, is able to induce glomerular alterations in vitro that are similar to those seen in minimal change disease (MCD). Whether this acute phase reactant is also able to induce proteinuria and minimal change-like alterations in vivo is questioned.

METHODS

In the first set of experiments, Hx (4.0 mg in 5.0 mL saline) or equal amounts of control fraction, that is, heat-inactivated Hx (HI-Hx), were infused into conscious rats (N = 6) that had been surgically equipped with a cannula inserted into the suprarenal artery (SRA), enabling direct contact of the infusate and the renal microvasculature. Each animal received HI-Hx at day 1 for 15 minutes (flow rate 20.0 mL/h), subsequently followed by saline for seven hours (Flow rate 5.0 mL/h), after which the cannula was disconnected. At day 2, identical infusions in the same rat were carried out, using native Hx. Urine samples collected every 30 minutes during the experiments were monitored for protein content using standard methods. In the second set of experiments, unilateral perfusion was done ex vivo in anesthetized rats with Hx (N = 5) or HI-Hx (N = 3; 1.5 mg/mL; 4.0 mL during 6 min). After reconnection of the circulation, urine samples of both kidneys were collected every 30 minutes during five hours via ureter cannulation. Urinary protein (expressed as the difference in excretion between perfused and nonperfused kidney) was calculated in mg/24 h. In additional experiments, rats were sacrificed two hours after perfusion of Hx or heat-inactivated (control) Hx (first set of experiments) or after five hours (second set of experiments), and kidneys were processed for immunohistochemical and ultrastructural examination.

RESULTS

The results of experiment 1 show a significant increase of proteinuria after Hx infusion versus HI-Hx (means +/- SD, 41.91 +/- 16.01 mg/24 h vs. control, 21.22 +/- 5.69 mg/24 h; P </= 0.03). Histochemical and electron microscopical examination of kidney tissue fragments taken at the time of proteinuria showed diminished expression of glomerular ecto-ATPase and enhanced effacement of epithelial foot processes at the ultrastructural level. In the second set of experiments, the results show significant urinary protein excretion peaking one hour after perfusion (6.63 +/- 7.06 mg/24 h), exclusively in Hx-perfused animals (analysis of variance, P < or = 0.001).

CONCLUSION

It is concluded that Hx is able to induce proteinuria associated with MCD-like alterations in rat kidney in vivo.

Effect of protein A immunoadsorption in nephrotic syndrome of various etiologies

Protein A immunoadsorption (IA) has proved effective in reducing proteinuria in patients with nephrotic syndrome after recurrence of focal and segmental glomerulosclerosis (FSGS) in kidney transplants. The effect of IA in nephrotic syndrome of other etiologies remains unknown. Nine patients with nephrotic syndrome secondary to membranous nephropathy (four cases), diabetes mellitus (one case), IgA nephropathy (two cases), and amyloidosis (two cases) had three to five IA of 2.5 plasma volumes over 4 to 8 d. Patients received no concomitant immunosuppressive treatment, and antihypertensive drugs were left unchanged. Proteinuria decreased from 12.64 +/- 5.49 to 3.35 +/- 2.2 g/24 h (mean +/- SD) in all patients after three to five IA. Hematocrit decreased from 37.32 to 32.64% (12.5% hemodilution) and serum albumin from 25.43 to 18.6 g/L (26.4% decrease). Proteinuria returned to baseline levels within 1 mo, as described in recurrent FSGS following transplantation. When serum albumin balance was controlled by albumin infusion after IA in two patients, comparable decreases in proteinuria were observed. Therefore, IA is effective in producing short-term reduction of proteinuria in nephrotic syndromes related not only to FSGS but also to membranous and IgA nephropathies, diabetes mellitus, and amyloidosis, which suggests that IA removes a nonspecific circulating hemodynamic-altering or permeability-increasing factor.

"The FSGS factor:" enrichment and in vivo effect of activity from focal segmental glomerulosclerosis plasma

A circulating causative factor has been postulated in focal segmental glomerulosclerosis (FSGS). It has been shown that serum or plasma from some FSGS increases glomerular albumin permeability (Palb) in vitro. Palb greater than 0.5 (i.e., FS activity) is associated with recurrence after transplantation. Specimens from 15 FSGS patients were studied to document the presence of a permeability factor, to isolate this factor, to characterize its biochemical properties, and to show its effect in vivo. Total lipids were extracted by chloroform/methanol (2: 1); FS activity was absent from total lipid extract. Chylomicrons and lipoproteins were removed from the plasma with dextran sulfate, followed by sequential precipitation of proteins at 50 and 70% ammonium sulfate saturation. FS activity was retained in the 70% ammonium sulfate supernatant and exhibited a 100-fold purification. FS activity was lost after heating at 100 degrees C for 10 min or after protease digestion. Under nondenaturing conditions, electrophoresis of the FSGS 70% supernatant showed a prominent low molecular weight band that was not evident in the 70% supernatant from normal plasma. Dialysis and centrifugation-based membrane ultrafiltration of the FSGS factor indicated a molecular size between 30 and 50 kD. Injection of the 70% FSGS supernatant into rats caused a threefold increase in urine protein in collections from 6 to 24 h after injection. No increase in proteinuria occurred in rats injected with 70% supernatant from normal individuals. It is concluded that the FSGS factor is a low molecular weight protein with the potential to increase Palb in vitro and to cause proteinuria in vivo.

Focal segmental glomerulosclerosis in children with acute lymphocytic leukemia: case reports and review of literature

PURPOSE

To report the occurrence of focal segmental glomerulosclerosis (FSGS) in children with acute lymphocytic leukemia (ALL), discuss pathogenesis and problems in management.

PATIENTS AND METHODS

Progressive renal dysfunction developed in two adolescent black girls with high-risk ALL who underwent renal biopsies that were consistent with FSGS. In both patients, no known etiologic factors, such as systemic lupus erythematosus, poststreptococcal glomerulonephritis, sickle cell anemia, or acquired immunodeficiency syndrome, were evident. FSGS induced by Adriamycin (Pharmacia & Upjohn, Columbus, OH) has been observed experimentally in rats. The patients had received anthracyclines and methotrexate, a known nephrotoxic chemotherapeutic agent.

RESULTS

One patient progressed to chronic renal failure and required prolonged dialysis followed by renal transplantation, though the leukemia remained in remission. The other patient is also in remission and on maintenance treatment for leukemia. She has persistent proteinuria and is currently undergoing a trial of high-dose steroid therapy.

CONCLUSION

The combination of FSGS with leukemia poses a management challenge to the clinician in terms of further treatment with potentially nephrotoxic drugs, complications of nephrotic syndrome (including infections), and timing of renal transplantation. Future studies should address whether FSGS represents a glomerular response to anthracycline-induced injury in susceptible black persons.

Glomerular charge selectivity for proteins larger than serum albumin as revealed by lactate dehydrogenase isoforms

It is well known that macromolecules like albumin are markedly restricted in their passage across the glomerular capillary wall. However, the relative importance of solute size, charge and shape is currently debated since much of the previous work is based on dextran in neutral or charge-modified forms. These polymers have certain drawbacks that make them less suitable for analysis of capillary permeability and the notion of a glomerular charge barrier has therefore been questioned. Moreover, macromolecules larger than albumin (mol. wt. 69,000) have been suggested to pass through nonselective 'shunt' pathways. In order to study glomerular permeability, isolated rat kidneys were perfused with albumin solutions containing trace amounts of two differently radiolabelled isoenzymes of lactate dehydrogenase (LDH) at low temperature to inhibit tubular function. The isoenzymes have similar size (mol. wt. 140,000) and shape but differ in charge, one carrying a negative net surface charge (LDH1, -19) and the other being slightly cationic (LDH5, +2). The urine and perfusate samples were subjected to high pressure liquid chromatography (HPLC) gel-filtration to allow for measurements of intact LDH. The fractional clearance was 0.11% +/- 0.04% for the anionic LDH1 and 0.56% +/- 0.07% for LDH5, whereas that for albumin was 0.21% +/- 0.03% at a glomerular filtration rate of 0.11 +/- 0.01 mL min-1 g-1 kidney wet weight. The results were analysed using a homogenously charged membrane model and are compatible with a charge density of 35 mEq L-1, with 95% confidence interval of 26-41 mEq L-1. These findings suggest a significant glomerular charge selectivity for proteins substantially larger than albumin. The charge density is, however, far less than estimated from dextran studies.

Agrin is a major heparan sulfate proteoglycan in the human glomerular basement membrane

Agrin is a heparan sulfate proteoglycan (HSPG) that is highly concentrated in the synaptic basal lamina at the neuromuscular junction (NMJ). Agrin-like immunoreactivity is also detected outside the NMJ. Here we show that agrin is a major HSPG component of the human glomerular basement membrane (GBM). This is in addition to perlecan, a previously characterized HSPG of basement membranes. Antibodies against agrin and against an unidentified GBM HSPG produced a strong staining of the GBM and the NMJ, different from that observed with anti-perlecan antibodies. In addition, anti-agrin antisera recognized purified GBM HSPG and competed with an anti-GBM HSPG monoclonal antibody in ELISA. Furthermore, both antibodies recognized a molecule that migrated in SDS-PAGE as a smear and had a molecular mass of approximately 200-210 kD after deglycosylation. In immunoelectron microscopy, agrin showed a linear distribution along the GBM and was present throughout the width of the GBM. This was again different from perlecan, which was exclusively present on the endothelial side of the GBM and was distributed in a nonlinear manner. Quantitative ELISA showed that, compared with perlecan, the agrin-like GBM HSPG showed a sixfold higher molarity in crude glomerular extract. These results show that agrin is a major component of the GBM, indicating that it may play a role in renal ultrafiltration and cell matrix interaction. (J Histochem Cytochem 46:19-27, 1998)

Evidence for the existence of multiple heparan sulfate proteoglycans in the human glomerular basement membrane and mesangial matrix

Heparan sulfate proteoglycans (HSPGs) are essential components of the glomerular basement membrane (GBM) carrying a strong anionic charge. A well-characterized extracellular HSPG is perlecan, ubiquitously expressed in basement membranes. A cDNA construct encoding domains I and II of human perlecan was expressed as a fusion protein with glutathione S-transferase. This fusion protein was used to generate monoclonal antibody 95J10. We compared the staining pattern of 95J10 with that of M215, a previously prepared mAb that recognizes HSPG isolated from human GBM. In kidney cortex, the anti-perlecan mAb 95J10 showed a strong staining of the mesangium, Bowman's capsule, the tubular basement membrane, and stained the GBM only slightly. In contrast, M215 predominantly stained the GBM in a linear fashion. Immunoelectron microscopy supported these results, showing concentrations of perlecan in some regions of the GBM, whereas the unidentified M215 antigen was homogenously distributed throughout the GBM. In other human tissues, both antibodies also produced a different staining pattern. Furthermore, a polyclonal antiserum recognizing HSPG isolated from the GBM did not recognize perlecan from EHS tumors. These results provide evidence for the presence of another HSPG in the GBM that is immunologically distinct from perlecan. The absence of perlecan splice variants in the kidney suggests that this component is encoded by a different gene than perlecan. Given its marked expression in the GBM, this component could be a determining factor in the maintenance of selective glomerular permeability.

Circulating factor associated with increased glomerular permeability to albumin in recurrent focal segmental glomerulosclerosis

BACKGROUND

Heavy proteinuria and progressive renal injury recur after transplantation in up to 40 percent of patients with renal failure caused by idiopathic focal segmental glomerulosclerosis. A circulating factor may be responsible for this recurrence.

METHODS

To determine whether patients with focal segmental glomerulosclerosis have a circulating factor capable of causing glomerular injury, we tested serum samples from 100 patients with the disorder in an in vitro assay of glomerular permeability to albumin. Of the 56 patients who had undergone renal transplantation, 33 had recurrences. Sixty-four patients, many of whom had undergone transplantation, were being treated with dialysis. Thirty-one patients with other renal diseases and nine normal subjects were also studied.

RESULTS

The 33 patients with recurrent focal segmental glomerulosclerosis after transplantation had a higher mean (+/-SE) value for permeability to albumin (0.47+/-0.06) than the normal subjects (0.06+/-0.07) or the patients who did not have recurrences (0.14+/-0.06). After plasmapheresis in six patients with recurrences, the permeability was reduced (from 0.79+/-0.06 to 0.10+/-0.05, P = 0.008), and proteinuria was significantly decreased. Patients with corticosteroid-sensitive nephrotic syndrome or with membranous nephropathy after transplantation had low levels of serum activity. The circulating factor bound to protein A and hydrophobic-interaction columns and had an apparent molecular mass of about 50 kd.

CONCLUSIONS

A circulating factor found in some patients with focal segmental glomerulosclerosis is associated with recurrent disease after renal transplantation and may be responsible for initiating the renal injury.

Effect of lipoid nephrosis cytokine on glomerular sulfated compounds and albuminuria

Supernatants from peripheral blood mononuclear cells cultures of 30 idiopathic, minimal lesion, nephrotic syndrome (IMLNS) patients in relapse and the same patients in remission were fractionated by gel filtration chromatography. Fractions eluting with carbonic anhydrase (29 kilodaltons) were infused for 5 days at the rate of 10 microliters/h into the left renal artery of Wistar rats using an Alzet osmotic pump. On the last day of infusion, rats were injected with 35sulfate (1.0 mCi/200 g) intraperitoneally and killed after 8 h. Glomeruli were isolated and glomerular basement membrane (GBM) obtained. There was a significant increase in 35sulfate uptake by GBM of the infused kidney (302 +/- 92 cpm/mg dry glomerular weight, mean +/- SEM) compared with the uptake seen in the contralateral kidney (157 +/- 36, P < 0.01) when the fraction from IMLNS patients in relapse was infused. No significant differences in 35sulfate incorporation were seen between infused kidney (166 +/- 41) and contralateral kidney (172 +/- 64) when the same fraction from patients in remission was administered. A significant increase in albuminuria was seen on the last day of infusion (14.2 +/- 1.0 mg/24 h, mean +/- SEM) when supernatant factor from IMLNS patients in relapse was used. No significant differences in urinary albumin excretion prior to and after infusion were seen when the same fraction from IMLNS patients in remission was administered. The in vivo infusion of supernatant factor from IMLNS patients in relapse increased the 35sulfate uptake by GBM and augmented albuminuria, suggesting that the factor may have pathogenic significance in the proteinuria of IMLNS.

The effect of lymphocytes from renal transplant patients on glomerular basement membrane sulfate uptake

We have studied the effect of peripheral blood mononuclear cells (PBMC) from renal transplant patients on 35sulfate uptake by rat glomerular basement membrane (GBM). Nine patients were included in the study; six were studied during an episode of acute allograft rejection and seven while not undergoing acute rejection. The sulfate uptake index, calculated as the ratio between uptake by GBM from rat glomeruli cocultured with PBMC and 35sulfate incorporation by GBM from glomeruli cultured alone, was significantly higher when glomeruli were cocultured with PBMC from patients undergoing an acute rejection (3.26 +/- 1.18, mean +/- SEM) than it when glomeruli were cocultured with PBMC from nonrejecting transplant patients not showing proteinuria (0.81 +/- 0.11) (P = 0.0053). After reversing the acute allograft rejection with resolution of proteinuria, the sulfate uptake index returned to normal in four of five patients. The fifth patient had persistent nephrotic syndrome and his sulfate uptake index remained elevated. These findings are similar to those observed in idiopathic minimal lesion nephrotic syndrome patients in relapse. Because the GBM sulfated compounds may play a role in glomerular permeability to plasma proteins, by acting on these compounds PBMC may be a common mechanism for proteinuria.

The anionic charge barrier in the renal corpuscle of the pronephros in the lamprey, Petromyzon marinus L

The charge barrier within the renal corpuscle of the pronephric kidney of the lamprey, Petromyzon marinus, was investigated at two life cycle intervals using cationized ferritin and polyethyleneimine. In the larval renal corpuscle the endothelium of the glomerular capillaries and the laminae rarae externa and interna of the glomerular basement membrane show regularly-spaced deposits of the tracers. The lamina densa remains unstained. Concomitant with a loss of major processes of the visceral epithelial podocytes and development of an extensive mesangial matrix in late adult life are alterations in the distribution of the anionic sites. The lamina rara interna is no longer a distinct entity and the mesangium contains irregularly-distributed anionic sites surrounding electron-dense deposits. The results indicate that the distribution of the anionic sites during adult life most likely affects the ability of the renal corpuscle to act as an efficient filtration device. This charge distribution is consistent with that seen during some renal pathologies of higher vertebrates.