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Query: UMLS:C0033687 (proteinuria)
 24,015 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Passive Heymann nephritis is an experimental rat model of human membranous nephropathy induced by injection of antisera against crude renal cortical fractions such as Fx1A or rat tubular microvilli. This results in the formation of subepithelial immune deposits, the activation of the C5b-9 membrane attack complex of complement, and severe proteinuria. While the formation of immune deposits is attributed to in situ immune complex formation with antibodies specific for the gp330-Heymann nephritis antigenic complex (HNAC), activation of complement and proteinuria appear to be caused by at least one additional antibody species present in anti-Fx1A sera. We have separated by affinity absorption polyspecific antisera against Fx1A and rat microvilli into one IgG fraction directed specifically against microvillar proteins (anti-Fx1A-prot) and another IgG fraction specific for glycolipids (ant-Fx1A-lip) of tubular microvilli. When injected into rats, the anti-Fx1A-prot fraction induced immune deposits but failed to activate complement or produce proteinuria, similar to results obtained with affinity-purified anti-gp330 IgG. When the antibodies of the anti-Fx1A-lip fraction were injected alone they did not bind to glomeruli. By contrast, when the IgGs specific for the Fx1A-prot fraction (or for gp330-HNAC) were combined with those directed against the Fx1A-lip glycolipid preparation, immune deposits were formed, in situ complement activation was observed, and also proteinuria was induced. It is concluded that within anti-Fx1A and anti-microvillar sera there are at least two IgG fractions of relevance for the development of PHN: one directed against the gp330-HNAC complex which is responsible for the development of immune deposits, and a second specific for glycolipid antigen(s) which activate(s) the complement cascade.
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PMID:Antibodies to glycolipids activate complement and promote proteinuria in passive Heymann nephritis. 816 Jul 66

Heymann nephritis of the rat has several similarities to human idiopathic membranous glomerulo-nephropathy, and therefore serves as an animal model for study of the human disease. The disease process in the rat is initiated by autoantibodies forming in situ immune deposits on the surface of the glomerular epithelial cell in the lamina rara externa region of the glomerular basement membrane. It is now understood that multispecific antibodies (like anti-gp600) form the nephritogenic deposits which cause proteinuria, while MoAb (like anti-gp330, anti-90 kD and anti-gp70) form only transient deposits which do not give rise to proteinuria. The reasons for differences between pathologic effects of mono- and multispecific antibodies are not known. Following characterization of putative antigens of Heymann nephritis by immunofluorescence, immunogold and immunoblot techniques, we have investigated the metabolic handling of a multispecific (anti-600), monospecific antibody (anti-gp70) and a MoAb (anti-gp330) by the cultured glomerular epithelial cell to gain an insight into the mechanism of nephritogenicity of multispecific antibody. Anti-gp600 reacted to multiple antigens in the 330-kD and 70-kD regions; anti-gp70 reacted to only the 70-kD region. Ultrastructurally, all three types of antigens were present on the plasma membrane, concentrated in the microvillar region. The cells were incubated with the antibodies, and clearance of the antibodies from the cells was evaluated. Following binding, all three antibodies were internalized by the cells. However, it was found that monoclonal anti-gp330 MoAb was cleared most rapidly from the cell (t1/2 5 min), followed by anti-gp70 (t1/2 30 min). Anti-gp600 was cleared at four times slower rate than anti-gp70 (t1/2 2h) by the cell. While anti-gp330 MoAb and monospecific anti-gp70 antibody were expelled from the cell in 25-32% digested form, the multispecific anti-gp600 was digested to the extent of only 5-8%. No immune complexes were detected in the medium with any of the three antibodies. The shed label was in intact IgG form. It is concluded that multispecific antibodies of Heymann nephritis are nephritogenic because of their slower clearance and digestion and therefore, higher accretion rate on the surface of the glomerular epithelial cell. The differential handling of the antibodies by the glomerular epithelial cell offers an explanation for the in vivo differences in the nephritogenicity of these antibodies observed earlier.
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PMID:Metabolic fate of monovalent and multivalent antibodies of Heymann nephritis following formation of surface immune complexes on glomerular epithelial cells. 825 99

There is considerable evidence that glomerular deposits in Heymann nephritis, a rat model of membranous nephritis, result from shedding of immune complexes formed on podocytes and that the principal antigen is part of the extracellular domain of a cell surface glycoprotein receptor called gp330 or megalin. It has also been reported that the immunogen that induces Heymann nephritis is a complex formed between gp330 and the receptor-associated protein RAP. The recent elucidation of the primary structure of gp330 makes it possible to investigate the ability of defined portions of gp330, devoid of RAP, to induce Heymann nephritis. In the present study we show that a gp330-glutathione-S-transferase fusion protein, containing 137 amino acid residues (1114 to 1250) of the ectodomain, induces active Heymann nephritis and that heterologous antibodies against this fusion protein produce passive Heymann nephritis. By immunofluorescence, typical glomerular immunoglobulin deposits were found, but complement components were lacking and the rats did not develop proteinuria. In the active model, we obtained evidence indicating that the deposits contained portions of the ectodomain of gp330, including regions other than those of the fusion protein. Thus, the deposits were stained by polyclonal antibodies to gp330 and to the gp330 fusion protein, as well as by two monoclonal antibodies reactive with portions of the ectodomain of gp330, only one of which reacted with the fusion protein in vitro. Antibodies against the cytoplasmic domain of gp330 did not stain. Furthermore, we found that RAP was able to bind to gp330 in the glomerular deposits but not to the gp330 fusion protein in vitro. The results show that the region of gp330 spanning amino acid residues 1114 to 1250 contains peptides capable of inducing pathogenic antibodies of Heymann nephritis without a contributory role of RAP.
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PMID:Induction of Heymann nephritis with a gp330/megalin fusion protein. 862 3

Maleate treatment of rats induces transport defects similar to those seen in the Fanconi syndrome (glycosuria, aminoaciduria, phosphaturia, proteinuria, etc.) and causes an accumulation of apical vesicles in proximal tubule epithelial cells. Because the apical membrane glycoprotein, gp330, is a receptor associated with the apical endocytotic and recycling apparatus in these cells, we examined the effect of maleate on the distribution of this protein and other brush border markers. Rats received sodium maleate (400 mg/kg ip) and were killed at various times between 45 min and 3 h; kidneys were perfusion fixed with paraformaldehyde-lysine-periodate before processing for immunofluorescence and immunoelectron microscopy. In control rats, staining with a polyclonal or monoclonal gp330 antibody showed a uniform distribution on the brush border and in coated pits of all proximal tubule cells. In the S3 segments, the immunofluorescence labeling of the microvilli was generally uniform but at times showed spike labeling, suggesting that gp330 sheds easily from the apical membrane. After maleate treatment, the staining intensity of the brush border was decreased in all proximal tubule segments, and cytoplasmic streaks as well as an intense vacuolar staining were seen. In the S3 segment, a remarkable mosaic pattern of staining was observed, with the brush border of some cells being completely negative, while adjacent cells showed an apparently normal staining pattern. These results were confirmed at the electron microscope level, using the protein A-gold technique. Maleate had no effect on the distribution or staining intensity of four other brush border markers, dipeptidyl peptidase IV, and various lectins (Helix pomatia lectin, peanut lectin, elderberry bark lectin). The urinary excretion of gp330 occurs in normal rats and was already increased as early as 1 h after maleate injection and remained at a twofold increment between 6 and 24 h. These data suggest that the generalized membrane transport derangement seen in this experimental Fanconi syndrome could occur via a specific effect on gp330, which seems to block endocytosis and the recycling apparatus at the late endosome level and inhibits the formation of new dense apical tubules.
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PMID:Specific effect of maleate on an apical membrane glycoprotein (gp330) in proximal tubule of rat kidneys. 889 22

The analysis and reassembly of the single steps in the pathogenesis of Heymann nephritis is reasonable well advanced, but still far from being comprehensive. It is established that antibodies against certain epitopes of the megalin/gp330 molecule or RAP are responsible for the formation of glomerular immune deposits. Apparently a second antibody antigen system targeting lipid antigens causes the activation of C5b-9, which triggers the biosynthesis of oxygen-radical-producing enzymes within glomerular epithelial cells. The oxygen radicals cause lipid peroxidation which, by virtue of its toxic products, causes cross-linking of type IV collagen via its NC1 domains. It is possible that this is associated with a distortion and increase of permeability of the glomerular basement membrane, thus causing proteinuria.
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PMID:[Molecular pathogenesis of experimental membraneous glomerulonephritis (Heymann nephritis)]. 892 92

The molecular pathogenesis of human membranous nephropathy (MN) is unknown, despite the relatively high incidence and severity of this glomerular immune disease. Heymann nephritis (HN) in rats is considered an instructive experimental model of MN. This study summarizes current molecular aspects of two key events common to both MN and HN, i.e., formation of characteristic subepithelial immune deposits in the glomerular basement membrane (GBM), and development of glomerular capillary wall damage resulting in proteinuria. In HN, the antigenic targets of immune deposit-forming antibodies were identified in cell membranes of glomerular epithelial cells as a 515-kd glycoprotein (megalin, or gp330), which is a polyspecific receptor related to the low-density lipoprotein receptor family, and an associated 44-kd protein (receptor associated protein, RAP). One epitope was recently narrowed to 14 amino acids in RAP, and several others on megalin/gp330 are under investigation. Proteinuria requires formation of the complement C5b-9 membrane attack complex, which is presumably triggered by antibodies directed against lipid antigens that associate with immune deposit-forming megalin/gp330 immune complexes. Sublytic C5b-9 attack on glomerular epithelial cells causes upregulation of expression of the NADPH oxidoreductase enzyme complex by glomerular cells, which is translocated to their cell surfaces, similar to activated neutrophil granulocytes in the respiratory burst reaction. Subsequently, reactive oxygen species (ROS) are produced locally, which reach the GBM matrix. Here formation of lipid peroxidation (LPO) adducts is found, preferentially on monomeric and dimerized NCl domains of covalently crosslinked Type IV collagen. These structural changes within the GBM could be of functional relevance because treatment with the potent LPO-antagonist probucol reduces proteinuria by < 80%. Intact or fragmented apoprotein E-containing lipoproteins were identified as potential sources of the polyunsaturated lipids required for the production of LPO adducts. Lipoproteins accumulate within immune deposits and show signs of oxidative damage, similar to oxidized LDL within atherosclerotic lesions. Collectively, the results obtained so far in HN permit the compilation of a sequence of events, linking formation of immune deposits with proteinuria. However, despite this relatively detailed knowledge of pathogenic events in HN, the bridge to human NM remains to be built.
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PMID:Molecular mechanisms of glomerular injury in rat experimental membranous nephropathy (Heymann nephritis) 898 29

Passive Heymann nephritis (PHN), a model of human membranous nephropathy, is an immune-complex-mediated glomerulonephritis characterized by the presence of complement-dependent tissue injury. Recent studies have confirmed the synthesis of C3, involved in both the classical and alternative pathways of complement, in injured human and animal renal tissues. However, there is little clear information on the role of local C3 synthesis in the pathogenesis of nephritides such as PHN. In the present study, using nonradioactive in situ hybridization and semiquantitative reverse transcriptase polymerase chain reaction, we examined C3 synthesis in the kidney and its contribution to tissue injury in a rat model of PHN induced by the injection of polyclonal anti-gp330 antibody. C3 mRNA was localized in mesangial cells, glomerular epithelial cells, and cells of Bowman's capsule. During the early stages of PHN, C3 mRNA expression was detected in mesangial cells and glomerular epithelial cells, whereas such expression was limited to mesangial cells during the late stages of the disease. Focal, weak C3 mRNA expression was detected in tubular epithelial cells and occasionally in the interstitium. Semiquantitative polymerase chain reaction demonstrated that the level of C3 mRNA expression correlated with that of proteinuria. Our results suggest that renal cells synthesize C3 mRNA in PHN in a site-specific manner and that locally produced C3 is associated with the development of proteinuria in this model.
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PMID:Intraglomerular C3 synthesis in rats with passive Heymann nephritis. 935 50

Megalin/gp330 is an endocytic receptor that internalizes multiple ligands including apolipoproteins E (apo E) and B100 (apo B). Megalin is the main antigenic target in passive Heymann nephritis (pHN), where it binds circulating autoantibodies leading to the formation of subepithelial immune deposits (ID)-the hallmark of pHN. Apo E and apo B were found recently to accumulate within these IDs, and evidence was provided that their lipids may undergo peroxidation, causing glomerular basement membrane damage and proteinuria. Here we investigated if ID-forming antimegalin IgG can inhibit the binding and internalization of apo E-betaVLDL (very low density lipoprotein) by megalin, and lead to their accumulation within IDs. By immunoelectron microscopy, apo E and apo B were detected in clathrin-coated pits and multivesicular bodies of podocytes in control rats, suggesting that the uptake of lipoproteins is a constitutive function of the glomerular epithelium. When pHN was induced by intravenous injection of antimegalin IgG, apo E and apo B were found within IDs by immunofluorescence and immunoelectron microscopy. Bound antibodies eluted from glomeruli of rats with pHN were found to inhibit the binding and internalization of apo E-enriched betaVLDL by megalin. These results indicate that pHN-inducing antimegalin IgG is capable of interfering with the uptake of lipoproteins by megalin in vivo during the formation of IDs.
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PMID:Pathogenic antibodies inhibit the binding of apolipoproteins to megalin/gp330 in passive Heymann nephritis. 941 Sep 8

Crry (complement receptor 1-related protein/gene y) is a key cellular complement regulator in rodents. It is also present in Fx1A, the renal tubular preparation used to immunize rats to induce active Heymann nephritis (HN), a model of membranous nephropathy. We hypothesized that rats immunized with anti-Fx1A develop autoantibodies (auto-Abs) to Crry as well as to the megalin-containing HN antigenic complex, and that anti-Crry Abs promote the development of injury in HN by neutralizing the complement regulatory activity of Crry. Rats immunized with Fx1A lacking Crry remained free of proteinuria and glomerular deposits of C3 during a 10-wk follow-up despite typical granular immunoglobulin (Ig)G deposits in glomeruli. Anti-Fx1A auto-Abs were present in their sera at levels that were not different from sera pooled from proteinuric rats with HN induced with nephritogenic Fx1A. Passive administration of sheep anti-Crry Abs to rats immunized with Crry-deficient Fx1A led to proteinuria and glomerular C3 deposition, which were not seen in such rats injected with preimmune IgG, nor in rats with collagen-induced arthritis injected with anti-Crry IgG. To directly examine the role of Crry in HN, rats were immunized with Crry-deficient Fx1A reconstituted with rCrry. This led to typical HN, with 8 out of 15 rats developing proteinuria within 14 wk. Moreover, the extent of glomerular C3 deposition correlated with proteinuria, and anti-Crry Abs were present in glomerular eluates. Thus, Crry is a key nephritogenic immunogen in Fx1A. Formation of neutralizing auto-Abs to Crry impairs its function, leading to unrestricted complement activation by Abs reactive with the HN antigenic complex on the epithelial cell surface.
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PMID:Inhibition of complement regulation is key to the pathogenesis of active Heymann nephritis. 976 14

Megalin is an endocytic receptor expressed on the luminal surface of the renal proximal tubules. The receptor is believed to play an important role in the tubular uptake of macromolecules filtered through the glomerulus. To elucidate the role of megalin in vivo and to identify its endogenous ligands, we analyzed the proximal tubular function in mice genetically deficient for the receptor. We demonstrate that megalin-deficient mice exhibit a tubular resorption deficiency and excrete low molecular weight plasma proteins in the urine (low molecular weight proteinuria). Proteins excreted include small plasma proteins that carry lipophilic compounds including vitamin D-binding protein, retinol-binding protein, alpha(1)-microglobulin and odorant-binding protein. Megalin binds these proteins and mediates their cellular uptake. Urinary loss of carrier proteins in megalin-deficient mice results in concomitant loss of lipophilic vitamins bound to the carriers. Similar to megalin knockout mice, patients with low molecular weight proteinuria as in Fanconi syndrome are also shown to excrete vitamin/carrier complexes. Thus, these results identify a crucial role of the proximal tubule in retrieval of filtered vitamin/carrier complexes and the central role played by megalin in this process.
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PMID:Megalin knockout mice as an animal model of low molecular weight proteinuria. 1051 18


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