Quantitative studies of monoclonal antibody 5-1-6-induced proteinuric state in rats

SV2B is essential for the integrity of the glomerular filtration barrier

The glomerular visceral epithelial cell (podocyte) is characterized as a specialized structure of the interdigitating foot processes, covering the outer side of the glomerular basement membrane (GBM). The neighboring foot processes are connected by a slit diaphragm, which is a key structure regulating the barrier function of the glomerular capillary wall to prevent proteinuria. We have previously reported that synaptic vesicle protein 2 B (SV2B) is expressed in the podocyte and that the expression is clearly decreased in nephrotic models. However, the precise function of SV2B in the podocyte is unclear. To investigate the role of SV2B in maintaining the podocyte function and to better understand the function of the neuron-like vesicle expressing SV2B in the podocyte, we analyzed them with SV2B knockout (KO) mice. An increase in the amount of proteinuria, effacement of the foot process of the podocyte, and alterations of the GBM were detected in SV2B KO mice. It was also found that the expression of CD2AP, nephrin, and NEPH1, the functional molecules of the slit diaphragm, and laminin, a critical component of the GBM, is clearly altered in SV2B KO mice. Synaptotagmin and neurexin, which have a role in the synaptic vesicle docking in neurons, are downregulated in the kidney cortex of SV2B KO mice. We have previously reported that neurexin interacts with CD2AP, and the present study shows that SV2B interacts with CD2AP. These findings suggest that the SV2B-neurexin complex is involved in the formation and maintenance of the slit diaphragm. In addition, SV2B is densely expressed close to the cell surface in the presumptive podocyte in the early stage of glomerulogenesis. These results suggest that SV2B has an essential role in the formation and maintenance of the glomerular capillary wall.

Dissociation of NEPH1 from nephrin is involved in development of a rat model of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a disease showing severe proteinuria, and the disease progresses to end-stage kidney failure in many cases. However, the pathogenic mechanism of FSGS is not well understood. The slit diaphragm (SD), which bridges the neighboring foot processes of glomerular epithelial cells, is understood to function as a barrier of the glomerular capillary wall. To investigate the role of SD dysfunction in the development of FSGS, we analyzed the expression of SD-associated molecules in rat adriamycin-induced nephropathy, a mimic of FSGS. The staining of the SD molecules nephrin, podocin, and NEPH1 had already shifted to a discontinuous dotlike pattern at the initiation phase of the disease, when neither proteinuria nor any morphological alterations were detected yet. The alteration of NEPH1 expression was the most evident among the molecules examined, and NEPH1 was dissociated from nephrin at the initiation phase. On day 28, when severe proteinuria was detected and sclerotic changes were already observed, alteration of the expressions of nephrin, podocin, and NEPH1 worsened, but no alteration in the expression of other SD-associated molecules or other podocyte molecules was detected. It is postulated that the dissociation of NEPH1 from nephrin initiates proteinuria and that the SD alteration restricted in these molecules plays a critical role in the development of sclerotic changes in FSGS.

Plasma exchange and retransplantation in recurrent nephrosis of patients with congenital nephrotic syndrome of the Finnish type (NPHS1)

BACKGROUND

Recurrent nephrotic syndrome (NS) is a severe problem after renal transplantation in patients with congenital nephrotic syndrome of the Finnish type (NPHS1). The NPHS1 kidneys do not express nephrin, and antibodies against this major glomerular filter protein have been observed in NPHS1 children with recurrent NS. We evaluated here the use of plasma exchange (PE) therapy and kidney retransplantation in NPHS1 patients with recurrent NS and extended our studies on the pathogenesis of the recurrence.

METHODS

Clinical data on 65 NPHS1 patients who received 77 kidney transplants between the years 1986 and 2006 was collected. Serum anti-nephrin antibodies were assayed with an enzyme-linked immunosorbent assay method, and the kidney biopsy samples were evaluated by light microscopy and immunohistochemistry.

RESULTS

Twenty-three episodes of recurrent NS occurred in 19 grafts of 13 NPSH1 patients homozygous for Fin-major mutation. Six retransplantations were performed to four NPHS1 patients, who lost their graft because of recurrent NS, and heavy proteinuria developed immediately in all cases. Although 73% of the patients had detectable serum anti-nephrin antibodies, the kidney biopsy findings were minimal. Introduction of PE alongside cyclophosphamide proved effective in the treatment of the proteinuric episodes (one graft loss out of nine). If remission was achieved, recurrent NS did not significantly deteriorate the long term graft function.

CONCLUSIONS

The clinical and pathological data suggest that anti-nephrin antibodies effectively impair the glomerular function in kidney grafts of NPHS1 patients homozygous for Fin-major mutation. Plasma exchange is a useful adjunct to the treatment of the recurrent NS.

Role of podocyte slit diaphragm as a filtration barrier (Review Article)

Although the role of glomerular basement membrane has been emphasised as the barrier for retaining plasma proteins in the past three decades, some recent studies have demonstrated that the slit diaphragm of the glomerular epithelial cell (podocyte) is the structure likely to be the barrier in the glomerular capillary wall. Nephrin and podocin were identified as gene products mutated in Finnish-type congenital nephrotic syndrome and autosomal recessive steroid-resistant nephrotic syndrome, respectively. Nephrin s located at the outer leaflet of plasma membranes of the slit diaphragm. Podocin is reported to have an interaction with nephrin. The anti-nephrin antibody is capable of inducing massive proteinuria, which indicates that nephrin is a key functional molecule in the slit diaphragm. The expression of nephrin and podocin was reduced in glomeruli of minimal change nephrotic syndrome, which suggested that the altered expression of these molecules contributes to the development of proteinuria also in acquired diseases. Some recent studies demonstrated that CD2-associated protein (CD2AP) is also a functional molecule in the slit diaphragm, and its expression is altered in membranous nephropathy. These observations suggested that alteration of the molecular arrangement in the slit diaphragm is involved in the development of proteinuria in several kinds of glomerular diseases.

Heparanase inhibition reduces proteinuria in a model of accelerated anti-glomerular basement membrane antibody disease

BACKGROUND

The beta-d-endoglycosidase, heparanase, is emerging as an important contributor to the pathogenesis of proteinuria. The purpose of the present study therefore was to examine the role of heparanase in a model of accelerated anti-glomerular basement disease (anti-GBM).

METHODS

Accelerated anti-GBM disease was induced and animals sacrificed at day 10 to establish heparanase expression using immunohistochemistry and western blot analysis. In addition, cortex was isolated from normal and diseased glomeruli to determine if mRNA levels altered with disease. A previously validated anti-heparanase antibody associated with proteinuria reduction, in a model of membranous nephropathy, was administered prior to disease induction to establish its impact on protein excretion in this model.

RESULTS

At day 10 of anti-GBM disease, an increase in glomerular heparanase was shown using immunohistochemistry. Sequential staining studies revealed that this increase was associated with glomerular endothelial, epithelial cells and invading ED-1-positive inflammatory cells. RT-PCR revealed an insignificant 1.2-fold induction of mRNA at day 10 of disease. Western blot analysis of kidney cortex confirmed that the active 58-kDa heparanase species was restricted to diseased kidney at day 10. The inactive 65-kDa precursor, however, was found only in cortex derived from normal kidney. Proteinuria at day 10 of disease was significantly reduced, in the absence of altered rat anti-sheep antibody titres, after administration of a validated polyclonal anti-heparanase antibody (P < 0.05). Furthermore, sheep IgG deposition was not altered by administration of the anti-heparanase antibody.

CONCLUSION

These data suggest that heparanase contributes to the pathogenesis of proteinuria in a model of anti-GBM disease.

Retinoic acid receptor alpha and retinoid X receptor specific agonists reduce renal injury in established chronic glomerulonephritis of the rat

Retinoids, derivatives of vitamin A, inhibit mesangial cell proliferation, glomerular inflammation, and extracellular matrix deposition in acute anti-Thy1.1 glomerulonephritis (Thy-GN) of the rat. We examined a model, chronic mesangioproliferative Thy-GN (MoAb 1-22-3), which is more akin to human disease. Treatment started on day 23 when Thy-GN had already been established. Nonnephritic control and Thy-GN rats were treated orally for 67 days with vehicle or with two doses of either the retinoic acid receptor alpha-specific agonist AGN 195183 (RARalpha agonist) or the retinoid X receptor specific agonist AGN 194204 (RXR agonist). Doses of either the RARalpha or the RXR agonist significantly reduced albuminuria and normalized blood pressure during the course of treatment. The glomerulosclerosis index, glomerular cell and interstitial cell counts, and area of the interstitial space were significantly lower in nephritic rats treated with the RARalpha agonist or RXR agonist than with vehicle. The RARalpha and RXR agonist significantly reduced the infiltration of the glomerulus by macrophages. The increase in glomerular TGFbeta1 and prepro-ET(1) gene expression in vehicle-treated nephritic rats was significantly attenuated by RARalpha or RXR agonists. Glomerular expression of RXRalpha and RARalpha receptor mRNA was significantly greater in vehicle-treated nephritic rats than in nonnephritic controls. Treatment with RARalpha or RXR agonists tended to normalize retinoid-receptor gene expression. Our data indicate that both RARalpha agonists and RXR agonists reduce renal damage in rats with established chronic glomerulonephritis. Receptor-specific retinoids may provide a novel therapeutic approach for the treatment of chronic glomerulonephritis.

mAb 5-1-6 nephropathy and nephrin

It is well established that the glomerular capillary wall consists of three layers: endothelial cell, glomerular basement membrane, and the slit diaphragm bridging foot processes of glomerular epithelial cell. Which structure in the glomerular capillary wall represents the primary filter for retaining plasma proteins is not clearly elucidated. An anti-slit diaphragm monoclonal antibody (mAb) 5-1-6 causes massive proteinuria in rats by single intravenous injection, which clearly indicates that the slit diaphragm plays a critical role for maintaining the barrier function of the glomerular capillary wall. Recently, we concluded that mAb 5-1-6 recognized a rat homolog of nephrin, a gene product of NPHS1. The expression of nephrin decreased in puromycin aminonucleoside nephropathy and adriamycin nephropathy as well as mAb 5-1-6-induced nephropathy, which suggested that nephrin was involved in the development of proteinuria in these proteinuric states. In mAb 5-1-6 nephropathy, the slit diaphragm was maintained morphologically normal, although nephrin expression dramatically decreased. The finding suggested that nephrin was not a sole component of the slit diaphragm. To better understand the structure of the slit diaphragm, it is particularly important to identify other components that build up the structure of the slit diaphragm together with nephrin.

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.

Alternatively spliced nephrin in experimental glomerular disease of the rat

Nephrin is a novel transmembrane protein of kidney glomerular podocytes, which appears crucially important for the maintenance of the glomerular filtration barrier. According to its predicted structure, nephrin has additional roles in cell-cell adhesion and/or signal transduction. We have previously cloned the rat homologue of nephrin and described its alternatively spliced transcripts alpha and beta. In this study we examined the alterations in expression and regulation of particularly the major alternatively spliced nephrin-alpha giving rise to a variant lacking the membrane spanning domain in the puromycin nephrosis of the rat. A down-regulation of up to 78% was observed of the full length mRNA after 10 d of PAN treatment. The expression changes of nephrin-alpha followed closely the expression of the full length mRNA. Interestingly, we also found nephrin protein in urine at the peak proteinuria samples of this model. These results suggest that soluble nephrin variants may be important markers for proteinuric diseases.

Cloning of rat nephrin: expression in developing glomeruli and in proteinuric states

BACKGROUND

Nephrin is identified as a product of the gene mutated in a patient with congenital nephrotic syndrome of the Finnish type. However, its precise localization and function are not yet fully clarified.

METHODS

To clone the rat homologue of nephrin, polymerase chain reaction (PCR) was employed. To elucidate the localization and expression of nephrin, immunohistological analysis with a specific antirat nephrin antibody, reverse transcription-PCR, and RNase protection assay were performed.

RESULTS

Amino acid sequences of rat and human nephrin are highly homologous (82.2% identity). The domain structure of nephrin is also highly conserved between rats and humans. The rat nephrin was detected only in kidney glomeruli along glomerular capillary walls, and its localization was always identical to that of the anti-slit diaphragm monoclonal antibody (mAb) 5-1-6-recognized antigen in normal matured and fetal rat glomeruli and in the glomeruli of proteinuric states. The nephrin staining pattern was clearly distinguished from that of zonula occludens-1 (ZO-1), alpha3-integrin, or podocalyxin. mRNA expression for nephrin was first detected in the fetal rat kidneys at 18.5 embryonic days. Nephrin mRNA expression decreased just after injection of mAb 5-1-6 (47.4%) or puromycin aminonucleoside (51.2%), and the staining pattern of nephrin shifted from a linear to a granular pattern in both proteinuric states.

CONCLUSIONS

Nephrin is localized in slit diaphragm in the matured glomeruli and is identical with mAb 5-1-6 antigen. Nephrin is involved in the development of proteinuria not only in mAb 5-1-6 nephropathy, but also in puromycin aminonucleoside nephropathy.

Expression of agrin, dystroglycan, and utrophin in normal renal tissue and in experimental glomerulopathies

The dystrophin-glycoprotein complex, which comprises alpha- and beta-dystroglycan, sarcoglycans, and utrophin/dystrophin, links the cytoskeleton to agrin and laminin in the basal lamina in muscle and epithelial cells. Recently, agrin was identified as a major heparan sulfate proteoglycan in the glomerular basement membrane. In the present study, we found mRNA expression for agrin, dystroglycan, and utrophin in kidney cortex, isolated glomeruli, and cultured podocytes and mesangial cells. In immunofluorescence, agrin was found in the glomerular basement membrane. The antibodies against alpha- and beta-dystroglycan and utrophin revealed a granular podocyte-like staining pattern along the glomerular capillary wall. With immunoelectron microscopy, agrin was found in the glomerular basement membrane, dystroglycan was diffusely found over the entire cell surface of the podocytes, and utrophin was localized in the cytoplasm of the podocyte foot processes. In adriamycin nephropathy, a decrease in the glomerular capillary wall staining for dystroglycan was observed probably secondary to the extensive fusion of foot processes. Immunoelectron microscopy showed a different distribution pattern as compared to the normal kidney, with segmentally enhanced expression of dystroglycan at the basal side of the extensively fused podocyte foot processes. In passive Heymann nephritis we observed no changes in the staining intensity and distribution of the dystrophin-glycoprotein complex by immunofluorescence and immunoelectron microscopy. From these data, we conclude that agrin, dystroglycan, and utrophin are present in the glomerular capillary wall and their ultrastructural localization supports the concept that these molecules are involved in linking the podocyte cytoskeleton to the glomerular basement membrane.

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.

Blocking angiotensin II ameliorates proteinuria and glomerular lesions in progressive mesangioproliferative glomerulonephritis

BACKGROUND

The renin-angiotensin system is thought to be involved in the progression of glomerulonephritis (GN) into end-stage renal failure (ESRF) because of the observed renoprotective effects of angiotensin-converting enzyme inhibitors (ACEIs). However, ACEIs have pharmacological effects other than ACE inhibition that may help lower blood pressure and preserve glomerular structure. We previously reported a new animal model of progressive glomerulosclerosis induced by a single intravenous injection of an anti-Thy-1 monoclonal antibody, MoAb 1-22-3, in uninephrectomized rats. Using this new model of progressive GN, we examined the hypothesis that ACEIs prevent the progression to ESRF by modulating the effects of angiotensin II (Ang II) on the production of transforming growth factor-beta (TGF-beta) and extracellular matrix components.

METHODS

We studied the effect of an ACEI (cilazapril) and an Ang II type 1 receptor antagonist (candesartan) on the clinical features and morphological lesions in the rat model previously reported. After 10 weeks of treatment with equihypotensive doses of cilazapril, cilazapril plus Hoe 140 (a bradykinin receptor B2 antagonist), candesartan, and hydralazine, we examined systolic blood pressure, urinary protein excretion, creatinine clearance, the glomerulosclerosis index, and the tubulointerstitial lesion index. We performed a semiquantitative evaluation of glomerular immunostaining for TGF-beta and collagen types I and III by immunofluorescence study and of these cortical mRNA levels by Northern blot analysis.

RESULTS

Untreated rats developed massive proteinuria, renal dysfunction, and severe glomerular and tubulointerstitial injury, whereas uninephrectomized control rats did not. There was a significant increase in the levels of glomerular protein and cortical mRNA for TGF-beta and collagen types I and III in untreated rats. Cilazapril and candesartan prevented massive proteinuria, increased creatinine clearance, and ameliorated glomerular and tubulointerstitial injury. These drugs also reduced levels of glomerular protein and cortical mRNA for TGF-beta and collagen types I and III. Hoe 140 failed to blunt the renoprotective effect of cilazapril. Hydralazine did not exhibit a renoprotective effect.

CONCLUSION

These results indicate that ACEIs prevent the progression to ESRF by modulating the effects of Ang II via Ang II type 1 receptor on the production of TGF-beta and collagen types I and III, as well as on intrarenal hemodynamics, but not by either increasing bradykinin activity or reducing blood pressure in this rat model of mesangial proliferative GN.

Slit diaphragm-reactive nephritogenic MAb 5-1-6 alters expression of ZO-1 in rat podocytes

Monoclonal antibody (MAb) 5-1-6 identifies a 51-kDa protein (p51) on rat podocyte foot processes and causes severe complement- and leukocyte-independent proteinuria when injected into rats. In the studies reported here, we used various immunohistological techniques to define the precise location of p51 and its relationship to ZO-1, a known component of the podocyte slit diaphragm in adult rat glomeruli. Our results demonstrate that p51 and ZO-1 lie close to each other on opposite sides of the podocyte plasma membrane at the point of insertion of the slit diaphragm: ZO-1 on the cytoplasmic face and p51 on the slit diaphragm and adjoining outer leaflet of the plasma membrane bordering the filtration slits. In addition to their geographic proximity, there appears to be a relationship between p51 and ZO-1. After MAb 5-1-6 injection, there was a progressive decline in stainable ZO-1 in the podocytes of heavily proteinuric rats. In addition, Western blot analysis of glomerular lysates showed that the decline in staining was due to a loss of immunoreactive ZO-1 rather than redistribution or diffusion of the protein. Simultaneously, the distribution of glomerular-bound MAb 5-1-6 became more clumped, apparently because of partial endocytosis into a lysosomal compartment, while the slit diaphragms remained morphologically intact. These findings suggest that MAb 5-1-6 alters the molecular composition of the slit diaphragm and thereby affects the glomerular permeability barrier.

Structural continuity of filtration slit (slit diaphragm) to plasma membrane of podocyte

Murine monoclonal antibody 5-1-6 was reported to bind to the slit membrane and closely related structures in rat renal glomeruli; it induced heavy, reversible proteinuria and appeared to redistribute onto the plasma membrane of epithelial cells after binding at the original target sites. This phenomenon of antigenic movement has not been analyzed in detail to date. In addition to normal kidneys we also studied localization of the antigen recognized by monoclonal antibody 5-1-6 in protamine sulfate-perfused rat kidneys, in which slit diaphragms are known to be functionally modified. Isolated glomeruli as well as ultrathin kidney cryosections were labeled by the immunogold technique to clarify the relation between this antigen and the slit diaphragm. Sequential localization of injected monoclonal antibody was visualized using a post-embedding immunogold method in rats 2 hours to 12 days after injection of antibody. Ultrastructural immunogold labeling demonstrated that under normal conditions antigenic molecules were expressed mainly in the area beneath the slit diaphragms. Occasionally labeling was found at the base of the foot process, facing the glomerular basement membrane. After protamine sulfate treatment antigenic sites were dislocated due to the lifting and disruption of slit diaphragms, indicating that this antigen is associated with slit diaphragms. Injected antibody was localized at the filtration slits at 2 hours, and by 12 hours it had moved onto the apical plasma cell membrane of foot process. In addition, from 3 days onwards patch or cap-like formation on the plasma cell membrane of podocytes was seen. Possible shedding of antibody from podocyte cell surface membrane was occasionally encountered, but internalization of antibody was a minor event. Elution experiments in isolated glomeruli at day 3 indicated that antigen and antibody were both localized on the podocyte cell surface membrane, suggesting redistribution of immune complexes. In conclusion, filtration slits (slit diaphragms) and the apical membrane of foot process of podocytes demonstrate structural continuity, as revealed by the movement of the antigen recognized by monoclonal antibody 5-1-6 as antigen-antibody complexes.

Developmental expression of the nephritogenic antigen of monoclonal antibody 5-1-6

The biogenesis of p51, the target of nephritogenic monoclonal antibody 5-1-6, was studied in the developing glomerulus by immunolocalization and metabolic labeling. The localization of p51 was compared with that of ZO-1, a component of the cytoplasmic face of the epithelial slit diaphragm, and with that of podocalyxin, and apical marker of the podocyte. p51 first became faintly, but clearly, detectable on the basal and lateral sides of the developing podocytes at the S-shaped body stage. Staining intensity increased with further maturation and was restricted to the visceral epithelial cells. On immunoelectron microscopy, the antigen was seen along the basal and lateral surfaces below occluding junction at the early capillary loop stage and later, with the interdigitation of foot processes, became concentrated in the slit pores. At no stage was p51 seen on the apical surface. p51 and ZO-1 were closely localized in the mature glomerulus but arrived at their final positions from opposite directions. p51 was on basal and podocalyxin was on apical sides of the glomerular epithelium from the S-shaped body stage onwards. Metabolic labeling studies showed that p51 is actively synthesized during initial glomerular development and that the rate of synthesis declines substantially with maturation. We conclude that p51 is primarily synthesized during the initial glomerular development, becomes concentrated in the slit pores of mature podocytes, and serves as a basal differentiation marker for podocytes.

Strain variation in susceptibility to the development of monoclonal antibody 5-1-6-induced proteinuria in rats

Susceptibility to the development of MoAb 5-1-6-induced proteinuria was investigated in four different rat strains, i.e. Brown-Norway (BN), Lewis (LEW), Sprague-Dawley (SD) and Wistar. An intravenous injection of 5 mg of MoAb 5-1-6 to female 7-week-old rats of a given strain induced massive proteinuria in BN, LEW and Wistar rats. However, SD rats developed almost no proteinuria. A similar tendency was observed in the second experiment, in which the injected dose of MoAb was adjusted according to the body weight of each rat (3 mg/100 g body weight). Immunofluorescence (IF) and immunoelectron microscopy (IEM) revealed no differences between the binding patterns of the MoAbs to normal rat kidneys derived from each strain. Quantitative study using 125I-labelled MoAb showed that there was no significant difference in the amount of antibody bound to the kidney 1 h and 5 days after injection between two rat strains, LEW and SD. Localization of 5-1-6 in vivo and its kinetics were investigated. In IF a linear-like pattern along capillary walls was observed 2 h after injection in both LEW and SD strains. This linear-like pattern was shifted to a granular pattern in proteinuric LEW rats 6 days after injection, whereas it remained linear-like in non-proteinuric SD rats. IEM confirmed this difference in the localization of injected MoAb 6 days after injection to LEW and SD rats also at the ultrastructural level. We conclude that there is a clear-cut strain difference in the development of proteinuria induced by MoAb 5-1-6. SD rats were less susceptible to MoAb-induced glomerular injury than BN, LEW and Wistar rats. Although the exact reason for strain variation in susceptibility to MoAb-induced proteinuria remains to be clarified, the movement of bound MoAb, presumably together with corresponding antigenic molecule along the glomerular epithelial cell surface followed by endocytosis into the epithelial cell, seems to be closely related to the induction of proteinuria.

Effect of traditional Chinese medicine (sairei-to) on monoclonal antibody-induced proteinuria in rats

The effects of traditional Chinese medicine (Sairei-to) on monoclonal antibody (mAb) inducing proteinuria were examined. Four hundred, 200 and 100 mg/kg body weight (BW) of Sairei-to and phosphate-buffered saline (PBS) as a control were injected intraperitoneally into four groups of female Wistar rats every day from 5 days before intravenous injection of mAb to the end of the experimental period. The amount of urinary protein excretion was significantly suppressed in roughly a dose-dependent manner. For example, 116.6 +/- 89.7 mg/day of proteinuria was observed in control groups compared to 4.2 +/- 15.2 mg/day in the 400 mg/kg BW of Sairei-to treated group 2 days after mAb injection (P < 0.01). Statistically significant (P < 0.01) differences were again observed in a repeat experiment (122.1 +/- 53.7 vs 10.2 +/- 10.1 mg/day on the 2nd day) without affecting the glomerular filtration rate. No significant difference was recognized between the total amount of mAb bound to glomeruli 1 h after mAb injection in Sairei-to-treated and non-treated rats, indicating that Sairei-to pretreatment has no effects on the number or quality of antigenic molecules. The effect of Sairei-to on a non-immunological model of proteinuria was also examined. No significant reduction of proteinuria by similar Sairei-to treatment was observed in aminonucleoside of puromycin nephropathy. The authors conclude that mAb-induced proteinuria in rats is significantly suppressed by the traditional Chinese medicine, Sairei-to.

Divalency of the monoclonal antibody 5-1-6 is required for induction of proteinuria in rats

A single i.v. injection of 3 mg of the F(ab')2 fragment of MoAb 5-1-6 into rats induced immediate proteinuria (128.1 +/- 80.7 mg/24 h on day 1) which lasted 1-2 days. In contrast, rats administered 10 mg of the corresponding Fab fragment did not develop abnormal proteinuria even though an equivalent dose of the intact MoAb 5-1-6 far exceeded the nephritogenic dose. The total kidney binding of 125I-Fab fragment was 209.5 +/- 34.3 micrograms/2 kidneys. This exceeded that obtained by injection of 3 mg MoAb 5-1-6 IgG1 (58.9 +/- 12.5 micrograms/2 kidneys at 1 h) and was similar to that obtained following injection of 3 mg F(ab')2 fragment (235.3 +/- 16.9 micrograms/2 kidneys). Immunofluorescence (IF) showed a linear pattern along the glomerular capillary wall at 1 h after the administration of MoAb 5-1-6 IgG1, F(ab')2 or Fab fragment. On day 5, fine to coarse granules were observed scattered in F(ab')2-injected rat glomeruli, whereas granules were densely localized in Fab-injected rat glomeruli. Complement-depleted rats injected with 3 mg of MoAb 5-1-6 IgG1 developed proteinuria with the same time course as non-depleted rats. This observation, together with the ability of F(ab')2 to induce proteinuria, indicates that proteinuria induced by MoAb 5-1-6 is complement-independent. This study suggests that MoAb 5-1-6-induced proteinuria is initiated by cross-linking of the epitopes by divalent MoAb 5-1-6 and is independent of complement activity.

Quantitative study of mesangial injury with proteinuria induced by monoclonal antibody 1-22-3

Murine MoAb 1-22-3 has already been reported to bind to the mesangial cell surface and to cause transient proteinuria and mesangial morphological changes characterized by mesangiolysis, subsequent mesangial cell proliferation and mesangial matrix increase by a single i.v. injection. In this study, MoAb-induced glomerulopathy was quantitatively analysed. No correlation between the severity of mesangial morphological changes and the degree of proteinuria was detected (r = 0.190). The minimum dose injected to induce abnormal proteinuria was 25 micrograms. This dose corresponded to 1.79 micrograms/2 kidneys 30 min after MoAb injection. The highest average level of proteinuria was observed in rats injected with 500 micrograms of MoAb, and less proteinuria was observed in rats injected with 10.0, 5.0 and 2.0 mg. Although the amounts of kidney-fixing MoAb and the subsequent deposition of rat C3 in the high-dose-injected group were larger than in the 500 micrograms injected group, the numbers of infiltrating inflammatory cells were the same in both groups. No correlations between the degrees of such mediators and proteinuria were observed.

Mechanisms of proteinuria in noninflammatory glomerular diseases

Neither the initiating factors nor the proximate causes of injury that produce proteinuria in nephrotic syndrome have been clearly defined. Immune mechanisms have been postulated in minimal-change nephrotic syndrome (MCNS), focal segmental glomerular sclerosis (FSGS), and glomerular sclerosis associated with human immunodeficiency virus (HIV) infection. Circulating factors have been proposed in MCNS and FSGS, although no specific mediator has been identified. Prompt remission of proteinuria following steroid treatment and the presence of altered immune responsiveness in patients with MCNS have been used to support the participation of an immune mechanism in the pathogenesis of MCNS. Both FSGS and HIV-related nephropathy are usually steroid-resistant. Immune mechanisms are postulated in FSGS because of early recurrence after transplantation, and in HIV-related nephropathy because of the numerous associated immune abnormalities. Experimental models of nephrotic syndrome based on neutralization of glomerular charge, toxic injury to podocytes, injection of antibodies to glomerular components, or abnormalities in transgenic mice have been used to define mechanisms of glomerular injury. This review summarizes physiologic and immunologic abnormalities in MCNS, FSGS, and HIV-associated nephropathy and in several experimental models of nephrotic syndrome, and outlines the immunologic mechanisms and cellular reactions that may be responsible for glomerular dysfunction in these entities.

Effect of chlorpromazine on kinetics of injected monoclonal antibody in MoAb-induced glomerular injury

The effect of chlorpromazine, one of several calmodulin antagonists that inhibit cytoskeletal movement, on the local kinetics of injected proteinuria-inducing MoAb 5-1-6 was examined to test the hypothesis that proteinuria is inhibited if the antigen recognized by MoAb 5-1-6 or injected MoAb remains on the surface of epithelial foot processes. MoAb 5-1-6 was injected into both chlorpromazine-treated (5 mg/100 g body weight) and untreated rats. As a positive control for the chlorpromazine treatment, anti-Fx1A serum was also injected into other chlorpromazine-treated and untreated rats. Chlorpromazine inhibited neither the change in localization of injected MoAb 5-1-6 nor proteinuria, although it showed an inhibitory effect on redistribution of immune complex and the fixation of complement in passive Heymann glomerulonephritis induced by injection of anti-Fx1A serum. We conclude that the kinetics of bound MoAb 5-1-6 are regulated by a system different from that operating in passive Heymann glomerulonephritis.

Mesangial sclerotic change with persistent proteinuria in rats after two consecutive injections of monoclonal antibody 1-22-3

Irreversible mesangial changes with persistent proteinuria were induced in rats given two consecutive injections 2 weeks apart of a MoAb 1-22-3 to rat mesangial cell. The characteristics of the resulting lesions were investigated and compared with those of the reversible change induced by a single injection. At 24 h after the second injection, mesangiolytic changes similar to those after a single injection were evident. The accumulation of macrophage-like cells in glomeruli observed at 1 week after the first injection was not evident during the experimental period after the second injection. Hypercellularity with the characteristics of intrinsic mesangial cell and increased mesangial matrix were already present 1 week after the second injection. And mesangial sclerotic change progressed up to 6 months. Deposition of collagen type I and type III and accumulation of collagen fibril at the ultrastructural level were evident in rats 6 months after the second injection. Proteinuria started immediately and continued for more than 6 months after the second injection. The mesangial sclerotic change with persistent proteinuria described here is considered to be a better model for investigating the mechanism of chronic progression of human mesangial proliferative glomerulonephritis.