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Biomedical subjects

W G Couser

Publications and source records attributed to W G Couser.

At least 73 records · Page 4Linked to original sources
PubMed1995

Thrombospondin 1 is expressed by proliferating mesangial cells and is up-regulated by PDGF and bFGF in vivo.

Thrombospondin 1 has been shown to be linked to PDGF-mediated mesangial cell proliferation and migration in vitro, but little is known regarding its expression or regulation in glomerular disease. Experimental mesangial proliferative nephritis was induced in rats by injection of anti-Thy1 antibody. Mesangial cell proliferation was associated with de novo expression of thrombospondin 1 mRNA (detected by Northern blot and in situ hybridization) and protein (by Western blot and immunostaining). Although some thrombospondin 1 was expressed by platelets and macrophages, double labeling showed that most thrombospondin 1 mRNA and protein were expressed by proliferating alpha-actin-positive mesangial cells. Thrombospondin 1 expression in anti-Thy1 nephritis was complement-dependent and could be reduced by treatment with anti-PDGF or anti-bFGF antibodies. Thrombospondin 1 could also be induced in normal rats by infusion of PDGF and in rats which were primed with low dose anti-Thy1 antibody by infusion of PDGF of bFGF. Thus, this study demonstrates that proliferating mesangial cells express thrombospondin 1 de novo in disease and that thrombospondin 1 expression in vivo is regulated by PDGF and bFGF.

Animals↗
PubMed1995

Modulation of experimental mesangial proliferative nephritis by interferon-gamma.

The observation that interferon-gamma (IFN-gamma) inhibits cell proliferation and collagen synthesis of a variety of cell types in culture has suggested that IFN-gamma may be useful in the treatment of fibroproliferative diseases. We administered recombinant IFN-gamma subcutaneously (10(5) U/kg/day for 3 days) to rats, beginning one day after the induction of mesangial proliferative nephritis with anti-Thy 1 antibody. IFN-gamma reduced glomerular (primarily mesangial) cell proliferation by 44% at days 2 and 4 compared to vehicle injected control rats with anti-Thy 1 nephritis (that is, proliferating cells that excluded the macrophage marker, ED-1, P < 0.001). Despite the inhibition of mesangial cell proliferation, IFN-gamma did not reduce the overall extracellular matrix deposition (by silver stain) or deposition of type IV collagen or laminin (by immunostaining) at 4 or 7 days, and glomerular type IV collagen and laminin mRNA levels were increased (1.4 and 1.7-fold) at 4 days relative to controls. The inability of IFN-gamma treatment to reduce mesangial matrix expansion may relate to the fact that IFN-gamma treated rats had a twofold increase in glomerular macrophages (that is, ED-1 positive cells, P < 0.001 at 2 and 4 days) with an increase in oxidant producing cells (day 2, P < 0.05) and a 1.6-fold increase in glomerular TGF-beta mRNA expression (4 days). This suggests that the effect of IFN-gamma to inhibit mesangial cell proliferation in glomerulonephritis may be offset by the ability of IFN-gamma to increase glomerular macrophages and TGF-beta expression. These data also show that IFN-gamma can partly dissociate the mesangial proliferative response from the extracellular matrix expansion in glomerulonephritis.

Animals↗
PubMed1995

IL-1 beta increases laminin B2 chain mRNA levels and activates NF-kappa B in rat glomerular epithelial cells.

The amount and distribution of laminin in the glomerular basement membrane (GBM) change in the course of many types of glomerular disease. Because interleukin-1 (IL-1) is thought to play a role in the pathogenesis of glomerulonephritis, it raises the possibility that this and other cytokines might regulate laminin gene expression. To determine whether laminin B2 chain mRNA levels change in response to cytokines, total mRNA from rat glomerular epithelial cells (GEC) grown in culture was analyzed by Northern blots. These studies showed an increase in laminin B2 chain mRNA levels in GEC treated with IL-1 beta. Nuclear factor kappa B (NF-kappa B) is a cytokine-responsive factor that regulates transcription of many genes from the cognate kappa B enhancer element. The mouse laminin B2 chain promoter contains several kappa B-like motifs, suggesting that NF-kappa B might be involved in IL-1-induced laminin B2 chain gene expression. Nuclear extracts from IL-1 beta-treated GEC showed increased binding to the immunoglobulin kappa B enhancer element and to a kappa B consensus sequence from the murine laminin B2 chain promoter in an electrophoretic mobility-shift assay (EMSA). The immunoglobulin kappa B and the laminin B2 chain kappa B-like motifs competed for the same DNA binding activity in nuclear extracts from IL-1 beta-treated GEC. Pretreatment of these nuclear extracts with antibodies to either the p50 or p65 subunits of NF-kappa B abrogated the DNA binding activity recognized by either of the two DNA motifs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Basic fibroblast growth factor augments podocyte injury and induces glomerulosclerosis in rats with experimental membranous nephropathy.

Podocyte injury is believed to contribute to glomerulosclerosis in membranous nephropathy. To identify the factors involved, we investigated the effects of basic fibroblast growth factor (bFGF), a cytokine produced by podocytes, on rats with membranous nephropathy (passive Heymann nephritis [PHN]). All rats received a daily i.v. bolus of 10 microg bFGF or vehicle from days 3-8 after PHN induction. In proteinuric PHN rats on day 8, bFGF injections further increased proteinuria. Podocytes of bFGF-injected PHN rats showed dramatic increases in mitoses, pseudocyst formation, foot process retraction, focal detachment from the glomerular basement membrane, and desmin expression. bFGF injections in PHN rats did not alter antibody or complement deposition or glomerular leukocyte influx. bFGF-injected PHN rats developed increased glomerulosclerosis when compared with control PHN rats. Also, bFGF induced proteinuria and podocyte damage in rats injected with 10% of the regular PHN-serum dose. None of these changes occurred in bFGF-injected normal rats, complement-depleted PHN rats or rats injected with 5% of the regular PHN serum dose. These divergent bFGF effects were explained in part by upregulated glomerular bFGF receptor expression, induced by PHN serum. Thus, bFGF can augment podocyte damage, resulting in increased glomerular protein permeability and accelerated glomerulosclerosis. This bFGF action is confined to previously injured podocytes. Release of bFGF from glomerular sources (including podocytes themselves) during injury may represent an important mechanism by which podocyte damage is enhanced or becomes self sustained.

Animals↗
PubMed1995

The effects of soluble recombinant complement receptor 1 on complement-mediated experimental glomerulonephritis.

Complement is a major mediator of tissue injury in several types of glomerulonephritis. However, no therapeutic agents that inhibit complement activation are available for human use. sCR1 (TP10, BRL 55736) is a recombinant, soluble human complement receptor 1 (CR1) molecule lacking transmembrane and cytoplasmic domains that inhibits C3 and C5 convertase activity by preferentially binding C4b and C3b. To test the efficacy of sCR1 on complement-mediated glomerulonephritis, rats were pretreated with sCR1 (60 mg/kg per day) before and during the induction of three models of complement-dependent glomerulonephritis (concanavalin A and antithymocyte serum models of proliferative glomerulonephritis, passive Heyman nephritis). Daily sCR1 and complement hemolytic activity levels were measured, and renal histology and urine protein excretion were examined. Mean serum sCR1 levels of 100 to 200 micrograms/mL were maintained with a reduction in complement hemolytic activity to less than 15% in most animals. In the antithymocyte serum model, sCR1-treated animals had significant reductions in mesangiolysis, glomerular platelet and macrophage infiltrates, and proteinuria at 48 h. In the concanavalin A model, sCR1 significantly reduced glomerular C3 and fibrin deposits, platelet infiltrates, and proteinuria at 48 h. In passive Heymann nephritis, proteinuria was also significantly reduced (199 +/- 8.5 versus 125 +/- 16 mg/day, P < 0.002) at 5 days. It was concluded that sCR1 significantly reduces both morphologic and functional consequences of several different types of complement-mediated glomerulonephritis and deserves evaluation as a potential therapeutic agent in complement-mediated immune glomerular disease in humans.

Animals↗
PubMed1995

Pathogenesis of cyclosporine nephropathy: roles of angiotensin II and osteopontin.

Low-salt-diet, cyclosporine (CsA; 15 mg/kg per day)-treated rats develop striped interstitial fibrosis, arteriolar hyalinosis, and azotemia similar to the chronic nephropathy observed in humans. To examine the role of angiotensin II in this model, rats on a low-salt diet were given CsA, CsA and the angiotensin II receptor Type I antagonist Losartan (10 mg/kg per day), CsA and hydralazine/furosemide, or vehicle. At Day 35, CsA-treated rats had tubular injury, arteriolopathy of the afferent arteriole, increased expression of the monocyte-macrophage adhesive protein osteopontin, interstitial macrophage infiltration, increased interstitial transforming growth factor-beta expression, and interstitial fibrosis. This study provides new insight in both pathogenic and therapeutic aspects of CsA nephropathy. The pathogenesis of CsA nephropathy involves the expression of osteopontin by tubular epithelial cells, the level of which closely correlates with the degree of macrophage infiltration and interstitial fibrosis in all groups (r = 0.79 and 0.74, respectively; P < 0.001). Therapeutic conclusions can be drawn from the observation that both losartan and hydralazine/furosemide reduced osteopontin expression, macrophage infiltration, transforming growth factor-beta expression, and interstitial fibrosis, but did not prevent the decrease in GFR. Treatment with losartan, but not with hydralazine and furosemide, markedly reduced arteriolopathy. It was concluded that angiotensin II contributes to the vasculopathy (hyalinosis) induced by CsA. In contrast, the interstitial fibrosis mediated by CsA can be partially prevented by both an angiotensin II Type I receptor antagonist or by hydralazine and furosemide. This suggests that the interstitial fibrosis can be dissociated from the vascular effects of CsA. The beneficial effects of lowering blood pressure or vasodilation per se may be difficult to distinguish from the specific effects of angiotensin II receptor blockade.

Angiotensin II↗
PubMed1995

Glomerular hemodynamic effects of late pregnancy in rats with experimental membranous glomerulonephropathy.

In these studies, the Fx1A model of accelerated, passive Heymann nephritis was used to produce membranous glomerulonephropathy. Female rats were studied at 7 wk after the administration of the Fx1A antibody either in the virgin state or in late pregnancy. The goals of these experiments were to determine whether preexisting membranous glomerulonephropathy compromises the pregnancy and whether the pregnancy acutely worsens the renal function. Virgin rats with membranous glomerulonephropathy developed massive proteinuria and exhibited glomerular capillary hypertension but without declines in GFR. In late pregnancy, there was no worsening of the proteinuria and glomerular blood pressure fell to normal values. Both afferent and efferent arteriolar resistances increased in pregnant rats with membranous glomerulonephropathy compared with virgins, leading to falls in glomerular plasma flow and single-nephron GFR. There were no histologic abnormalities in the glomeruli of either virgin or late pregnant rats with membranous glomerulonephropathy, and both groups exhibited similar immunoglobulin G and complement deposits. Up to Day 19 (term is 22 days), the pregnancy in rats with membranous glomerulonephropathy appeared uneventful. Thus, this study indicates that the Fx1A model of membranous glomerulonephropathy does not compromise the course of the pregnancy, at least until close to term. Pregnancy lowers glomerular blood pressure in rats with membranous glomerulonephropathy because of both a fall in systemic blood pressure and the atypical renal vasoconstriction, which leads to declines in single-nephron GFR.

Animals↗
PubMed1995

Participation of glomerular endothelial cells in the capillary repair of glomerulonephritis.

In many glomerular diseases severe injury to the mesangium may occur, leading to matrix dissolution and damage to the glomerular capillaries. Although the destruction of glomerular architecture may lead to permanent injury, in some cases spontaneous recovery occurs. The mechanisms that mediate this recovery are unknown. In this study we provide evidence for glomerular capillary repair (angiogenesis) in the adult injured glomerulus. Injection of anti-Thy 1 antibody into rats results in severe mesangiolysis with capillary ballooning, microaneurysm formation, and loss of endothelial cells in addition to mesangial cells. Although mesangial proliferation is a major response to injury, proliferation of endothelial cells also can be documented from days 2 to 14 in association with repair of the capillaries. The endothelial cell proliferation peaks on days 2 and 7, when it is seven- to ninefold greater than normal. Many of the endothelial cells display morphological features of angiogenesis. The initial wave of endothelial cell proliferation can be reduced by 40% with neutralizing anti-basic fibroblast growth factor antibodies (P < 0.001). The later glomerular endothelial cell proliferation is associated with upregulated expression of vascular permeability factor/endothelial cell growth factor (VPF/VEGF) and an increase of flk, a VPF/VEGF receptor. Although PDGF is expressed in this model, anti-PDGF antibody treatment did not affect the endothelial cell proliferative response. In summary, glomerular endothelial cells have an active role in the glomerular response to injury. Glomeruli are capable of healing microaneurysms, and the mechanism involves basic fibroblast growth factor- and VPF/VEGF-mediated endothelial proliferative responses.

Animals↗
PubMed1995

The pathogenesis of tubulointerstitial disease associated with glomerulonephritis: the glomerular cytokine theory.

Numerous studies have suggested that tubulointerstitial disease has a major impact on the overall function and prognosis of glomerular disease. The mechanism by which tubulointerstitial disease develops in patients with glomerular and other diseases is unknown. In this review, we discuss the hypothesis that factors released from injured glomeruli act on tubules and interstitial cells to induce expression of chemotactic and adhesive factors that attract mononuclear cells into the interstitium. Evidence is provided that osteopontin is one candidate leukocyte adhesive factor involved in this process, but others are likely involved. The recruited leukocytes (primarily macrophages) then release inflammatory mediators that injure tubular cells and activate interstitial fibroblasts, resulting in tubulointerstitial injury with eventual fibrosis.

Animals↗
PubMed1995

Hepatitis C virus associated membranous glomerulonephritis.

Hepatitis C virus infection has been associated with a variety of extrahepatic disorders. We report four patients with membranous glomerulonephritis and hepatitis C virus infection. In contrast to patients previously reported with HCV infection and membranoproliferative glomerulonephritis, these patients have normal or minimally reduced complement levels and no evidence of rheumatoid factor or cryoglobulinemia. A liver biopsy in one patient was consistent with chronic active hepatitis although liver enzymes were only minimally elevated and coagulation studies normal. Three patients were treated with alpha-interferon with some success. Treatment with alpha-interferon may have a beneficial effect in reducing proteinuria and improving liver function and may be related to the ability of interferon to suppress viremia. Future studies need to focus on clarifying the role of the virus in causing glomerular disease and improving dosing strategies for alpha-interferon. Randomized, controlled studies need to be performed to determine whether the beneficial effect of alpha interferon is significant, and if so, if it is superior to conventional therapies.

Adult↗
PubMed1994

Mechanisms of progressive renal disease in glomerulonephritis.

Progressive renal disease in glomerulonephritis (GN) involves both glomerular and interstitial processes. In the glomerulus, sclerosis occurs with progressive accumulation of extracellular matrix components that reduce filtration surface area. In the interstitium, early inflammatory changes accompany GN with later development of fibrosis and tubular atrophy. Our studies have focused on the role of early cellular events in the development of glomerular and interstitial fibrosis. In the antithymocyte serum (ATS) model of mesangial proliferative GN, mesangial cell proliferation is initiated by processes involving complement and platelets and may involve basic fibroblast growth factor (bFGF). Mesangial cell proliferation is maintained by an autocrine mechanism involving upregulation of mesangial cell PDGF and PDGF receptors. Mesangial cells also change phenotype with expression of alpha-smooth muscle actin and production of type I collagen. These early changes precede upregulation of genes for the production of extracellular matrix components and the development of mesangial matrix expansion and sclerosis. Matrix expansion is reduced by factors that block cell proliferation, including platelet and complement depletion, heparin, and antibody to PDGF. A similar sequence of early platelet infiltration, increased expression of PDGF, and mesangial cell proliferation occurs early in the development of glomerulosclerosis in the remnant kidney model, and mesangial cell proliferation is a prominent early feature of experimental diabetic nephropathy. We believe these early glomerular cellular changes are linked to the later development of sclerosis. In the interstitium, acute GN is accompanied by upregulation of mRNA and protein for osteopontin, a macrophage chemotactic/adhesive factor expressed by cortical tubules following several types of glomerular injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

C5b-9 increases albumin permeability of isolated glomeruli in vitro.

Deposition of antibody and activation of the complement cascade are important in both naturally occurring glomerulonephritis and in experimental models including passive Heymann nephritis. We studied the effect of antibody and complement on albumin permeability of isolated glomeruli to determine the role of the terminal complement components (C5-C9) in mediating the proteinuria in nephritis. Isolated glomeruli were treated with anti-Fx1a (Heymann antibody) and then incubated them with pooled human serum, serum in which complement had been inactivated by heat, or serum deficient in C6 or C7. The albumin reflection coefficient (sigma albumin) was calculated from the volumetric response of glomeruli to transcapillary oncotic gradients produced by albumin or high molecular weight neutral dextran (252 kD). Convectional permeability to albumin (Palbumin) was calculated as 1-sigma albumin. Albumin permeability of control glomeruli was not different from 0. Albumin permeability was not altered by antibody alone but was increased to 0.65 +/- 0.04 when antibody treated glomeruli were incubated for 10 minutes with pooled serum as a source of complement. Heat treatment of serum to inactivate complement prevented the increase in permeability. Incubation for 10 minutes with serum without antibody pretreatment caused a lesser increase in permeability of isolated glomeruli (0.18 +/- 0.06). Serum deficient in either C6 or C7 did not cause an increase in albumin permeability of antibody pre-treated glomeruli, but incubation with a combination of these sera (now containing the complete cascade) increased permeability to the same extent as did pooled normal serum (0.58 +/- 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Hepatitis C virus-associated glomerulonephritis. Effect of alpha-interferon therapy.

Hepatitis C virus (HCV) infection may present as a primary glomerular disease. We report 34 adult patients who presented with proteinuria and had circulating anti-HCV antibodies. Primary risk factors included a history of intravenous drug abuse (56%) or blood transfusion (18%). Patients presented with nephrotic syndrome (71%) or with non-nephrotic proteinuria (29%) and had membranoproliferative or acute proliferative glomerulonephritis on renal biopsy. Signs of clinical liver disease were infrequent (18%), though elevated liver function tests were common (66%) and liver biopsy in 16 of 18 patients showed chronic active hepatitis. Cryoglobulinemia was frequent (59%), but only 44% had extrarenal manifestations. In 100% of cases tested, HCV RNA could be found in the serum or cryoprecipitates. Fourteen patients received interferon alpha for 6 to 12 months with a significant reduction in proteinuria but no improvement in renal function. A good clinical response correlated with disappearance of HCV RNA from the serum during treatment; however, relapse of viremia and renal disease was common after completing therapy. Evidence for HCV infection should be sought in all patients with primary glomerular disease. The optimal treatment strategy, however, remains to be defined.

Adult↗
PubMed1994

New insights into mechanisms of immune glomerular injury.

Although glomerular disease remains the most common cause of end-stage renal disease worldwide, major advances have been made recently in understanding the cellular and molecular mechanisms that mediate these disorders. The nephrotic syndrome in noninflammatory lesions such as minimal change or focal sclerosis and membranous nephropathy results from disorders of the glomerular epithelial cell that can be simulated in animal models by antibodies to various epithelial cell membrane epitopes. Clarification of how these antibodies affect epithelial cells to induce a loss of glomerular barrier function should substantially improve understanding of the pathogenesis of minimal change or focal sclerosis. In membranous nephropathy, proteinuria is mediated primarily by the C5b-9 complex through similar mechanisms that also involve glomerular epithelial cells as targets. Inflammatory glomerular lesions are induced by circulating inflammatory cells or proliferating resident glomerular cells. Understanding of how these cells induce tissue injury has also evolved considerably over the past decade. Neutrophil-induced disease involves leukocyte adhesion molecules in regulating neutrophil localization; proteases, oxidants, and myeloperoxidase in mediating injury; and platelets in augmenting these processes. The activated mesangial cell exhibits altered phenotype and proliferation with the release of oxidants and proteases. Mesangial cell proliferation may be initiated by basic fibroblast growth factor and is maintained by an autocrine mechanism involving platelet-derived growth factor. Transforming growth factor beta is important in the subsequent development of sclerosis.

Animals↗