Demonstration of PDGF B-chain mRNA in glomeruli in mesangial proliferative nephritis by in situ hybridization

Characterization of binding mode of action of a blocking anti-platelet-derived growth factor (PDGF)-B monoclonal antibody, MOR8457, reveals conformational flexibility and avidity needed for PDGF-BB to bind PDGF receptor-β

Platelet derived growth factor-BB (PDGF-BB) is an important mitogen and cell survival factor during development. PDGF-BB binds PDGF receptor-β (PDGFRβ) to trigger receptor dimerization and tyrosine kinase activation. We present the pharmacological and biophysical characterization of a blocking PDGF-BB monoclonal antibody, MOR8457, and contrast this to PDGFRβ. MOR8457 binds to PDGF-BB with high affinity and selectivity, and prevents PDGF-BB induced cell proliferation competitively and with high potency. The structural characterization of the MOR8457-PDGF-BB complex indicates that MOR8457 binds with a 2:1 stoichiometry, but that binding of a single MOR8457 moiety is sufficient to prevent binding to PDGFRβ. Comparison of the MOR8457-PDGF-BB structure with that of the PDGFRβ-PDGF-BB complex suggested the potential reason for this was a substantial bending and twisting of PDGF-BB in the MOR8457 structure, relative to the structures of PDGF-BB alone, bound to a PDGF-BB aptamer or PDGFRβ, which makes it nonpermissive for PDGFRβ binding. These biochemical and structural data offer insights into the permissive structure of PDGF-BB needed for agonism as well as strategies for developing specific PDGF ligand antagonists.

The platelet-derived growth factor system in renal disease: an emerging role of endogenous inhibitors

The platelet-derived growth factor (PDGF) family consists of four isoforms which are secreted as homodimers (PDGF-AA, PDGF-BB, PDGF-CC and PDGF-DD) or heterodimers (PDGF-AB), and two receptor chains (PDGFR-α and -β). All members of the PDGF system are constitutively or inducibly expressed in renal cells and are involved in the regulation of cell proliferation and migration, the accumulation of extracellular matrix proteins and the secretion of pro- and anti-inflammatory mediators. Particular roles have been identified in mediating mesangioproliferative changes, renal interstitial fibrosis and glomerular angiogenesis. Different endogenous inhibitors of PDGF-induced biological responses exist which affect the activation/deactivation of PDGF isoforms, the activity of the PDGFRs, or which block downstream signaling pathways of the autophosphorylated PDGFRs. The novel endogenous inhibitor nephroblastoma overexpressed gene (NOV, CCN3) reduces PDGF-induced cell proliferation and is downregulated by PDGF isoforms itself. Among all identified inhibitors only few "true" PDGF antagonists have been identified. A better understanding of these inhibitors may aid in the design of novel therapeutic approaches to PDGF-mediated diseases.

TGFbeta intercepts nuclear glycogen synthase kinase 3beta to inhibit PDGF-induced DNA synthesis in mesangial cells

Here, we demonstrate a mechanism of TGFbeta-mediated inhibition of PDGF-induced DNA synthesis in mesangial cells. TGFbeta significantly inhibited nuclear Akt phosphorylation without any effect on PDGF-stimulated phosphorylation of PDGFR at PI 3 kinase binding site (Tyr-751). Remarkably, TGFbeta inhibited cyclin D1 and cyclin E expression with concomitant decrease in CDK2 activity induced by PDGF. More importantly, we demonstrate that TGFbeta significantly abolished Akt-mediated serine-9 phosphorylation of glycogen synthase kinase 3beta (GSK3beta), thus prevented its inactivation. Expression of inactive GSK3betaK85R mutant increased cyclin D1 expression and DNA synthesis similar to PDGF. These results provide the first evidence that TGFbeta intercepts Akt kinase activity in the nucleus to block inactivation of GSK3beta, leading to attenuation of PDGF-induced CDK2 activity and DNA synthesis.

Uncoupling of the VEGF-endothelial nitric oxide axis in diabetic nephropathy: an explanation for the paradoxical effects of VEGF in renal disease

In many forms of experimental kidney diseases, renal VEGF is low, and administering VEGF can be shown to be protective. A paradox occurs in diabetes, in which renal VEGF levels are high and a deleterious effect of VEGF on kidney disease has been shown. We have hypothesized that endothelial dysfunction induced by hyperglycemia or other factors may underlie the pathogenic mechanisms of a high VEGF state. VEGF normally stimulates endothelial nitric oxide (NO) release and acts in concert with elevated NO levels as a trophic factor for vascular endothelium. The increased NO derived from the endothelial cell acts as an inhibitory factor that prevents excess endothelial cell proliferation, vascular smooth muscle cell proliferation, and macrophage infiltration. In the setting where NO bioavailability is reduced in diabetes, high levels of VEGF lead to excessive endothelial cell proliferation, stimulation of macrophage chemotaxis, and vascular smooth muscle cell activation. Consistent with this hypothesis is our recent observation that diabetes induced in endothelial NO-deficient mice results in clinical and histological features identical to human diabetic nephropathy. The discovery of the key role for impaired endothelial NO bioavailability in the stimulation of VEGF and VEGF-dependent disease may provide key insights into not only the pathogenesis of diabetic nephropathy but also the utility and hazard of administering VEGF as a treatment for kidney disease.

Mesenchymal stem cells prevent progressive experimental renal failure but maldifferentiate into glomerular adipocytes

Glomerulonephritis (GN) is a major cause of renal failure. This study sought to determine whether intrarenal injection of rat mesenchymal stem cells (MSC) can preserve renal function in a progressive rat model of GN. Early in GN (day 10), fluorescently labeled rat MSC localized to more than 70% of glomeruli, ameliorated acute renal failure, and reduced glomerular adhesions. Fifty days later, proteinuria had progressed in controls to 40 +/- 25 mg/d but stayed low in MSC-treated rats (13 +/- 4 mg/d; P < 0.01). Renal function on day 60 in the MSC group was better than in medium controls. Kidneys of the MSC group as compared with controls on day 60 contained 11% more glomeruli per 1-mm(2) section of cortex but also significantly more collagen types I, III, and IV and alpha-smooth muscle actin. Approximately 20% of the glomeruli of MSC-treated rats contained single or clusters of large adipocytes with pronounced surrounding fibrosis. Adipocytes exhibited fluorescence in their cytoplasm and/or intracellular lipid droplets. Lipid composition in these adipocytes in vivo mirrored that of MSC that underwent adipogenic differentiation in vitro. Thus, in this GN model, the early beneficial effect of MSC of preserving damaged glomeruli and maintaining renal function was offset by a long-term partial maldifferentiation of intraglomerular MSC into adipocytes accompanied by glomerular sclerosis. These data suggest that MSC treatment can be a valuable therapeutic approach only if adipogenic maldifferentiation is prevented.

Transplanted mesenchymal stem cells accelerate glomerular healing in experimental glomerulonephritis

Bone marrow-derived cells contribute to glomerular cell turnover and repair, but the cell types involved are unknown. Whether rat mesenchymal stem cells (MSC) can accelerate recovery from damage in rat mesangioproliferative anti-Thy1.1 glomerulonephritis was studied. After injection into the left renal artery on day 2 after disease induction, fluorescently labeled MSC were detected in 20 to 50% of glomeruli and rare intrarenal vessels but not in the tubulointerstitium, in contralateral kidneys, or in medium controls. In control experiments, injected mesangial cells were detected less frequently in glomeruli in comparison with injected MSC. In nephritic outbred Wistar rats, MSC injection led to an approximately 50% reduction of mesangiolysis on days 4 and 6 after disease induction, accompanied by three- to four-fold higher intraglomerular cell proliferation on day 4 and more rapid mesangial reconstitution as detected by alpha-smooth muscle actin expression. Injection of MSC into tail veins or intra-arterial injection of mesangial cells instead of MSC failed to reproduce any of these findings. In inbred Lewis rats, anti-Thy1.1 nephritis followed an aggravated course with transient acute renal failure. Acute renal failure was ameliorated by MSC injection into the left renal artery on day 2 after disease induction. Again, MSC led to more rapid recovery from mesangiolysis, increased glomerular cell proliferation, and reduction of proteinuria by 28%. Double immunostaining of 5-bromo-2'-deoxyuridine-labeled MSC for endothelial, mesangial, or monocyte/macrophage antigens showed that 85 to 95% of MSC that localized in glomeruli on day 6 failed to express these markers. In vitro, MSC secreted high amounts of vascular endothelial growth factor and TGF-beta1 but not PDGF-BB. In conclusion, even low numbers of MSC can markedly accelerate glomerular recovery from mesangiolytic damage possibly related to paracrine growth factor release and not to differentiation into resident glomerular cell types or monocytes/macrophages.

Antagonism of PDGF-D by human antibody CR002 prevents renal scarring in experimental glomerulonephritis

Glomerular mesangial cell proliferation and/or matrix accumulation characterizes many progressive renal diseases. PDGF-D was identified recently as a novel mediator of mesangial cell proliferation in vitro and in vivo. This study investigated the long-term consequences of PDGF-D inhibition in vivo. Rats with progressive mesangioproliferative glomerulonephritis (uninephrectomy plus anti-Thy-1.1 antibody) received the PDGF-D-neutralizing, fully human mAb CR002 on days 3, 10, and 17 after disease induction. Glomerular mesangioproliferative changes on day 10 were significantly reduced by anti-PDGF-D treatment as compared with control antibody. Eight weeks after disease induction, anti-PDGF-D therapy significantly ameliorated focal segmental glomerulosclerosis, podocyte damage (de novo desmin expression), tubulointerstitial damage, and fibrosis as well as the accumulation of renal interstitial matrix including type III collagen and fibronectin. Treatment with anti-PDGF-D also reduced the cortical infiltration of monocytes/macrophages on day 56, possibly related to lower renal cortical complement activation (C5b-9 deposition) and/or reduced epithelial-to-mesenchymal transition (preserved cortical expression of E-cadherin and reduced expression of vimentin and alpha-smooth muscle actin). In conclusion, these data provide evidence for a causal role of PDGF-D in the pathogenesis of renal scarring and point to a new therapeutic approach to progressive mesangioproliferative renal disease.

Hypoxia regulates PDGF-B interactions between glomerular capillary endothelial and mesangial cells

BACKGROUND

Platelet-derived growth factor (PDGF)-B regulates mesangial cell and vessel development during embryogenesis, and contributes to the pathogenesis of adult renal and vascular diseases. Endothelial cell PDGF-B exerts paracrine effects on mesangial cells, but its regulation is not well defined. We examined the impact of hypoxia on PDGF-B-mediated interactions between glomerular endothelial and mesangial cells, a condition of potential relevance in developing, and diseased adult, kidneys.

METHODS

Glomerular endothelial or mesangial cells were subjected to hypoxia and responses compared to normoxic cells. Endothelial PDGF-B was studied by Northern and Western analysis. Mesangial proliferative responses to PDGF-B were assessed by (3)H-thymidine incorporation, and migration by a modified Boyden chamber assay. Hypoxia-induced changes in receptor specific binding capacity were studied by saturation binding assays.

RESULTS

Hypoxia stimulated increases in endothelial PDGF-B mRNA and protein. In normoxic mesangial cells, PDGF-B stimulated dose-dependent proliferation, but the proliferative response of hypoxic cells was two to three times greater. Exogenous PDGF-B also caused prompter migration in hypoxic mesangial cells. Mesangial cells were treated with endothelial cell-conditioned medium. More cells migrated when hypoxic cells were stimulated with hypoxic conditioned medium, than when normoxic cells were stimulated with normoxic conditioned medium. Preincubating conditioned medium with PDGF-B neutralizing antibody greatly decreased the chemoattractant activity. Binding studies demonstrated increased specific binding capacity in hypoxic cells.

CONCLUSION

Hypoxia enhances PDGF-B paracrine interactions between glomerular endothelial and mesangial cells. These hypoxia-regulated interactions may be important during glomerulogenesis in fetal life and during the pathogenesis of adult glomerular disease.

Regulation of PDGF and its receptors in fibrotic diseases

Platelet-derived growth factor (PDGF) isoforms play a major role in stimulating the replication, survival, and migration of myofibroblasts during the pathogenesis of fibrotic diseases. During fibrogenesis, PDGF is secreted by a variety of cell types as a response to injury, and many pro-inflammatory cytokines mediate their mitogenic effects via the autocrine release of PDGF. PDGF action is determined by the relative expression of PDGF alpha-receptors (PDGFRalpha) and beta-receptors (PDGFRbeta) on the surface of myofibroblasts. These receptors are induced during fibrogenesis, thereby amplifying biological responses to PDGF isoforms. PDGF action is also modulated by extracellular binding proteins and matrix molecules. This review summarizes the literature on the role of PDGF and its receptors in the development of fibrosis in a variety of organ systems, including lung, liver, kidney, and skin.

Expression of platelet-derived growth factor-BB in liver tissues of patients with chronic hepatitis B

AIM: To study the relationship between expression of platelet-derived growth factor-BB (PDGF-BB) and fibrogenesis in chronic hepatitis B.

METHODS: Hepatic tissues from 43 patients with chronic hepatitis B were embedded in paraffin. The sections were stained with HE and picric acid-sirius red to determine inflammatory activity and fibrosis stages. PDGF-BB expression was detected by immunohistochemistry and assessed semiquantatively. Levels of serum hyaluronic acid (HA), pro-collagen III (PCIII), collagen IV (IV-C) and laminin (LN) were examined by radioimmunoassay (RIA).

RESULTS: The expression level of PDGF-BB was found to be positively correlated with inflammatory activity, fibrosis stage and grade of histological findings (τ = 0.58, 0.55, 0.55, P < 0.01). The positive correlation was also observed between tissue level of PDGF-BB expression and contents of HA, PCIII, IV-C and LN in the circulation (r = 0.52, 0.32, 0.40, 0.33, P < 0.05).

CONCLUSION: PDGF-BB may play some role in the development and progression of liver fibrosis.

A fully human monoclonal antibody (CR002) identifies PDGF-D as a novel mediator of mesangioproliferative glomerulonephritis

PDGF-B is of central importance in mesangioproliferative diseases. PDGF-D, a new PDGF isoform, like PDGF-B, signals through the PDGF betabeta-receptor. The present study first determined that PDGF-D is mitogenic for rat mesangial cells and is not inhibited by a PDGF-B antagonist. Low levels of PDGF-D mRNA were detected in normal rat glomeruli. After induction of mesangioproliferative nephritis in rats by anti-Thy 1.1 mAb, glomerular PDGF-D mRNA and protein expression increased significantly from days 4 to 9 in comparison with nonnephritic rats. Peak expression of PDGF-D mRNA occurred 2 d later than peak PDGF-B mRNA expression. In addition, PDGF-D serum levels increased significantly in the nephritic animals on day 7. For investigating the functional role of PDGF-D, neutralizing fully human mAb were generated using the XenoMouse technology. Rats with anti-Thy 1.1-induced nephritis were treated on days 3 and 5 with different amounts of a fully human PDGF-DD-specific neutralizing mAb (CR002), equal amounts of irrelevant control mAb, or PBS by intraperitoneal injection. Specific antagonism of PDGF-D led to a dose-dependent (up to 67%) reduction of glomerular cell proliferation. As judged by double immunostaining for 5-bromo-2'-deoxyuridine and alpha-smooth muscle actin, glomerular mesangial cell proliferation was reduced by up to 57%. Reduction of glomerular cell proliferation in the rats that received CR002 was not associated with reduced glomerular expression of PDGF-B mRNA. PDGF-D antagonism also led to reduced glomerular infiltration of monocytes/macrophages (day 5) and reduced accumulation of fibronectin (day 8). In contrast, no effect was noted in normal rats that received an injection of CR002. These data show that PDGF-D is overexpressed in mesangioproliferative states and can act as an auto-, para-, or even endocrine glomerular cell mitogen, indicating that antagonism of PDGF-D may represent a novel therapeutic approach to mesangioproliferative glomerulonephritides.

Effects of leukocytosis and macrophage activation on anti-Thy 1.1 glomerulonephritis in the rat

OBJECTIVE

In anti-Thy 1.1 proliferative glomerulonephritis (GN), glomerular infiltration of polymorphonuclear leukocytes (PMNs) reaches a peak level after 1 h and that of macrophages does so 24 h after induction. However, the roles of PMNs and macrophages in the pathogenesis of anti-Thy 1.1 GN remain unclear. We examined the effects on this model of leukocytosis induced by granulocyte colony-stimulating factor (G-CSF) and of macrophages stimulated by macrophage colony-stimulating factor (M-CSF).

MATERIAL AND METHODS

Anti-Thy 1.1 GN was induced in male Wistar rats by intravenous injection of OX-7, a monoclonal antibody to the Thy 1 antigen. G-CSF (10 microg/kg/day), M-CSF (20 microg/kg/day) or vehicle was administered intraperitoneally for 7 days starting 24 h before the injection of OX-7. Histological examination of renal biopsy specimens was performed on Days 1, 5 and 14 after induction.

RESULTS

Circulating and glomerular-infiltrating PMNs (RP-3-positive cells) were increased at Day 5 in G-CSF-treated rats compared with controls receiving vehicle, and glomerular mesangiolysis continued at Day 5. The number of proliferating cells positive for proliferating cell nuclear antigen at Day 5 and matrix scores at Day 14 were smaller in G-CSF-treated rats than in control rats. The mesangiolysis score was significantly higher in the G-CSF group than in the control group at Days 5 and 14, but not at Day 1. ED-1-positive cells were increased in number at Day 5 and matrix accumulation decreased at Day 14 in M-CSF-treated rats compared with controls. Serum creatinine level at Day 14 was lower in the M-CSF group, but not in the G-CSF group, compared with the control group.

CONCLUSIONS

Activated macrophages may inhibit excess matrix accumulation and ameliorate the recovery of renal function, whereas leukocytosis inhibits the repair of mesangial cell injury in this model.

Transforming growth factor-beta receptors in self-limited vs. chronic progressive nephritis in rats

Increases in transforming growth factor-beta (TGF-beta) expression and extracellular matrix accumulation are transient in acute self-limited mesangial proliferative glomerulonephritis induced by a single injection of anti-thymocyte serum (ATS), while these increases persist following repeated injections that produce chronic progressive sclerosing glomerulonephritis with tubulointerstitial lesions. However, little is known about the expression of TGF-beta receptors (TbetaRs) in cells involved in the proliferative and sclerosing renal lesions. A study of protein and mRNA expression for type I (TbetaRI), type II (TbetaRII), and type III (TbetaRIII) TbetaR in both forms of nephritis was therefore carried out by immunohistochemistry and in situ hybridization. Inhibition of cell proliferation and stimulation of matrix production by TGF-beta1 were assessed in isolated glomeruli using [(3)H]thymidine incorporation and [(3)H]proline metabolic labelling, respectively. In acute self-limited nephritis, expression of TbetaRI, TbetaRII, and TbetaRIII increased in the glomerular and Bowman's capsular epithelial cells comprising the glomerular tuft adhesions to Bowman's capsules. However, TbetaRII expression was not prominent in proliferating mesangial cells. Glomeruli isolated from rats with acute self-limited nephritis at day 7, when mesangial cell proliferation was maximal, were partially resistant to the mitoinhibitory effects of TGF-beta1. In contrast, expression of all three TbetaRs was elevated in glomerular and tubulointerstitial lesions in chronic progressive nephritis, and glomeruli isolated from rats with chronic progressive nephritis 7 days after the second ATS injection were sensitive to TGF-beta1. These data suggest that distinct cellular responses to TGF-beta1 resulting from differential expression of TbetaR underlie the difference between acute self-limited mesangial proliferative and chronic progressive sclerosing ATS nephritis in the development of proliferative and sclerotic renal lesions.

Preventive effect of sulphated colominic acid on P-selectin-dependent infiltration of macrophages in experimentally induced crescentic glomerulonephritis

Leucocytes infiltrate into renal tissue and are involved in the pathogenesis of crescentic glomerulonephritis. The initial event in the process of leucocyte infiltration is characterized by selectin-mediated leucocyte rolling on endothelial surface. Role of selectins in pathogenesis of glomerulonephritis has still been controversial. Sulphated glycolipids and sulphated polysaccharides interfere with the binding of P- and L-selectin with carbohydrate ligands on endothelial cells or on leucocytes. Here we evaluated the role of selectins and the preventive effects of sulphated colominic acid (SCA), a synthetic sulphated polysaccharide, on experimental crescentic glomerulonephritis in Wistar-Kyoto (WKY) rats. Crescentic glomerulonephritis was induced by injection of nephrotoxic serum (NTS) in WKY rats. Rats subsequently received intraperitoneal injection of saline, neutralizing or non-neutralizing monoclonal antibody (mAb) to rat P-selectin and L-selectin, SCA (5 or 10mg/kg/day) or nonsulphated colominic acid (CA) (10mg/kg/day) for 2 weeks. Localization of P-, E-selectin, ligands for L-selectin and intraglomerular leucocytes was examined by immunohistochemistry. Gene expression of platelet-derived growth factor (PDGF) B chain in glomeruli was quantified using real-time RT-PCR. P-selectin was highly expressed on glomerular endothelial cells after injection of NTS, whereas E-selectin and L-selectin ligands were not detected. Anti-P-selectin mAb, but not anti-L-selectin mAb, significantly reduced glomerular infiltration of macrophages, crescent formation, and proteinuria. SCA also reduced proteinuria, macrophage infiltration, and crescent formation in a dose-dependent manner. Furthermore, SCA suppressed gene expression of PDGF B chain in glomeruli. Our results indicate that P-selectin partially mediates glomerular infiltration of macrophage in experimental crescentic glomerulonephritis. Moreover, SCA may inhibit intraglomerular infiltration of macrophages by interfering with P-selectin-dependent adhesion pathway, and progression of experimental crescentic glomerulonephritis.

Expression of a novel PDGF isoform, PDGF-C, in normal and diseased rat kidney

Platelet-derived growth factor-C (PDGF-C) is a new member of the PDGF family. Its expression in normal and diseased kidney is unknown. Rabbit antisera were generated against human full-length, core domain, and mouse PDGF-C, and their specificity was confirmed by Western blot analyses. Renal PDGF-C expression was analyzed by immunohistochemistry in normal rats (n = 8), mesangioproliferative anti-Thy 1.1 nephritis (n = 4 each at days 1, 4, 6, and 85), passive Heymann nephritis (PHN, n = 4), puromycin nephrosis (PAN, n = 2), Milan normotensive rats (MN, n = 2), and obese Zucker rats (n = 3). PDGF-C expression was also studied in anti-Thy 1.1 rats treated with PDGF-B aptamer antagonists (n = 5) or irrelevant control aptamers (n = 5). PDGF-C was constitutively expressed in arterial smooth muscle cells and collecting duct epithelial cells. Mesangial PDGF-C was markedly upregulated in anti-Thy 1.1 nephritis in parallel with the peak mesangial cell proliferation. Furthermore, PDGF-CC acted as a potent growth factor for mesangial cells in vitro. Inhibition of PDGF-B via specific aptamers reduced the injury in anti-Thy 1.1 nephritis but did not affect the glomerular PDGF-C overexpression or the mitogenicity of PDGF-CC in vitro. In PHN, PAN, and obese Zucker rats, glomeruli remained negative for PDGF-C despite severe glomerular injury. PDGF-C localized to podocytes at sites of focal and segmental sclerosis in MN. Interstitial PDGF-C expression was increased at sites of fibrosing injury in obese Zucker rats. The use of the different antisera resulted in virtually identical findings. It is concluded that PDGF-C is a novel mesangial cell mitogen that is constitutively expressed in the kidney and specifically upregulated in mesangial, visceral epithelial, and interstitial cells after predominant injury to these cells. PDGF-C may therefore be involved in the pathogenesis of renal scarring.

Nitric oxide inhibition enhances platelet aggregation in experimental anti-Thy-1 nephritis

In the present paper we studied the role of nitric oxide radicals (NO) on platelet aggregation, fibrinogen deposition, superoxide formation, peroxynitrite formation, hemodynamics, and leukocyte migration in the Thy-1 model of glomerulonephritis. To first study the baseline kinetics of these parameters, groups of anti-Thy-1-treated rats were sacrificed at 1 h, 4 h, 24 h, 3 days, 7 days, and 14 days and compared to controls. Urinary protein excretion was significantly elevated in Thy-1 nephritis at 3 and 7 days. Glomerular macrophages, PMNs, and superoxide anion-positive cells were significantly increased in Thy-1 nephritis. Nitrotyrosine immunoreactivity was absent during the entire study period. Glomerular platelet aggregation was significantly increased in anti-Thy-1 injected rats at 1 h, 4 h, 24 h, and 3 days. Glomerular fibrinogen deposition was significantly elevated at all time points. To elucidate the role of NO in this process, additional groups of anti-Thy-1-injected rats were treated with the NOS inhibitor l-NAME and studied at 24 h. Urinary protein excretion was significantly higher in l-NAME treated Thy-1 rats compared to nontreated Thy-1 rats. Plasma and urine nitrite/nitrate levels were significantly lower in l-NAME-treated Thy-1 rats compared to nontreated Thy-1 rats. Compared to nontreated Thy-1 rats, there were no differences in intraglomerular leukocyte accumulation after treatment with l-NAME. In contrast, we observed a marked increase in platelet aggregation following l-NAME treatment. From these data we conclude that the inflammatory infiltrate in Thy-1 nephritis develops independent of NO radical production, whereas NO radicals prevent the accumulation of platelet aggregates.

Early induction of platelet-derived growth factor ligands and receptors in acute rat renal allograft rejection

BACKGROUND

Acute rejection is the single most important risk factor for the development of subsequent chronic rejection. Platelet-derived growth factor (PDGF) is a major mitogen that mediates mesenchymal cell proliferation in chronic rejection. Therefore, we investigated whether PDGF ligands and receptors are induced during acute renal allograft rejection in rat.

METHODS

Kidney transplantations were performed from Dark Agouti (DA) to Wistar-Furth (WF) rats, and syngenic controls were performed from DA to DA rats. Allografts were immunosuppressed with cyclosporine (CsA) 1.5 mg/kg/d subcutaneously or left untreated. Grafts were harvested at 1, 3, 5, and 7 days for histology and immunohistochemistry.

RESULTS

In syngenic grafts, no histological signs of acute rejection were seen and the expression of PDGF ligands and receptors remained almost nonexistent. In nontreated allografts, intense rejection resulted in graft necrosis in 7 days. Acute rejection was associated with the induction of all PDGF ligands and receptors (P<0.05 compared to syngenic controls). The expression of PDGF ligands and receptors was located mainly to graft-infiltrating macrophages but also to capillary endothelium and arteriolar smooth muscle cells. CsA significantly ameliorated acute rejection but failed to inhibit the induction of PDGF and its receptors in CsA-treated allografts.

CONCLUSIONS

Our results demonstrate that PDGF ligands and receptors are induced during acute rejection. PDGF may be induced directly as a reparative response to graft injury in acute rejection or indirectly by various inflammatory mediators released by graft-infiltrating inflammatory cells. This study indicates that PDGF ligands and receptors are already induced in acute rejection, which suggests a link between acute rejection and the subsequent development of chronic rejection.

Electroporation-mediated PDGF receptor-IgG chimera gene transfer ameliorates experimental glomerulonephritis

BACKGROUND

Mesangial cell proliferation and phenotypic alteration occur in an early phase of glomerular injury and precede increased extracellular matrix accumulation. A critical growth factor responsible for mesangial proliferation is platelet-derived growth factor (PDGF), which has proved to be a potent mitogen.

METHODS

We generated a chimeric cDNA encoding an extracellular domain of the beta-PDGF receptor fused with IgG-Fc, termed PDGFR/Fc, and examined the feasibility of gene therapy targeting PDGF using PDGFR/Fc.

RESULTS

Chimeric PDGFR/Fc molecule completely inhibited the tyrosine phosphorylation of beta-PDGF receptors and cellular proliferation induced by PDGF in vitro. We then introduced the PDGFR/Fc expression vector into the muscle of anti-Thy-1 model of glomerulonephritic rats by electroporation. The plasma concentration of chimeric PDGFR/Fc levels was 244.4 +/- 89.8 ng/mL four days after transfection. On day 5, PDGFR/Fc gene transfer significantly reduced the number of PCNA-positive cells and glomerular cell numbers by 59.6 and 23.2%, respectively. Northern blot analysis demonstrated that glomerular mRNA levels of alpha-smooth muscle action, transforming growth factor-beta 1, and type I collagen were also suppressed on days 5 and 7 by the PDGFR/Fc transfection. There was a significant reduction in the matrix score of the transfected nephritic rats (2.91 +/- 0.75 and 2.06 +/- 0.95; disease control group vs. treated group, P < 0.001).

CONCLUSION

These results suggest that gene therapy by the manipulation of PDGF action using electroporation-mediated PDGFR/Fc gene transfer to the skeletal muscle might be a useful treatment for mesangioproliferative glomerulonephritis.

PDGF signal transduction inhibition ameliorates experimental mesangial proliferative glomerulonephritis

BACKGROUND

Platelet-derived growth factor (PDGF) has been consistently implicated in the cell proliferation and extracellular matrix accumulation, which characterize progressive glomerular disease. In the present study, the effects of a potent and selective inhibitor of PDGF receptor tyrosine kinase, STI 571, were examined in vitro and in vivo.

METHODS

Cultured mesangial cells were incubated with PDGF (50 ng/mL) and fibroblast growth factor-2 (FGF-2; 50 ng/mL) and treated with STI 571 (0.13 to 2.0 micromol/L). Experimental mesangial proliferative glomerulonephritis was induced in male Wistar rats with monoclonal OX-7, anti-rat Thy-1.1 antibody with rats randomized to receive either STI 571 (50 mg/kg intraperitoneally daily) or vehicle. Animals were examined six days later.

RESULTS

In vitro, both PDGF and FGF-2 induced a threefold increase in mesangial cell 3H-thymidine incorporation. STI 571 reduced PDGF but not FGF-2-stimulated mesangial cell proliferation in a dose-dependent manner, with complete abolition at 0.4 micromol/L. In animals with Thy-1.1 glomerulonephritis, PDGF receptor tyrosine kinase blockade was associated with significant reductions in mesangial cell proliferation (P < 0.001), the number of activated (alpha-smooth muscle positive) mesangial cells, and glomerular type IV collagen deposition (P < 0.001).

CONCLUSION

The amelioration of the pathological findings of experimental mesangial proliferative glomerulonephritis by blockade of PDGF receptor activity suggests the potential clinical utility of this approach as a therapeutic strategy in glomerular disease.

Involvement of platelet-derived growth factor in disease: development of specific antagonists

Platelet-derived growth factor (PDGF) is a family of dimeric isoforms that stimulates, e.g., growth, chemotaxis and cell shape changes of various connective tissue cell types and certain other cells. The cellular effects of PDGF isoforms are exerted through binding to two structurally related tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation. This enables a number of SH2 domain containing signal transduction molecules to bind to the receptors, thereby initiating various signaling pathways. PDGF isoforms have important roles during the embryonic development, particularly in the formation of connective tissue in various organs. In the adult, PDGF stimulates wound healing. Overactivity of PDGF has been implicated in certain disorders, including fibrotic conditions, atherosclerosis, and malignancies. Different kinds of PDGF antagonists are currently being developed and evaluated in different animal disease models, as well as in clinical trials.

Pathogenesis of the glomerular abnormality in cyanotic congenital heart disease

We present evidence of 2 distinct glomerular abnormalities in cyanotic congenital heart disease--vascular and nonvascular--each believed to reflect a distinct pathogenesis. Glomeruli from both kidneys were studied with light microscopy in 13 necropsied cyanotic patients and in 8 controls. The vascular study characterized hilar arteriolar dilatation, capillary diameter, glomerular diameter, and capillary engorgement with red blood cells. The nonvascular study characterized juxtaglomerular cellularity, mesangeal cellularity, mesangeal matrix, focal interstitial fibrosis, and megakaryocytic nuclei per cm2 of renal cortex. There was a significant increase in each of the above vascular and nonvascular items of interest relative to controls. Electron microscopy identified whole megakaryocytes with their cytoplasm in glomeruli. The vascular abnormality is believed to result from intraglomerular release of nitric oxide. The nonvascular abnormality is believed to result from platelet-derived growth factor and transforming growth factor-beta.

Platelet-derived growth factor, basic fibroblast growth factor, and interferon gamma increase type IV collagen production in human fetal mesangial cells via a transforming growth factor-beta-dependent mechanism

BACKGROUND

Glomerulosclerosis is characterized by glomerular accumulation of extracellular matrix following mesangial cell proliferation. The precise pathomechanism of glomerulosclerosis is still undetermined. Platelet-derived growth factor (PDGF) and basic fibroblast growth factor (b-FGF) are known to be mitogenic for mesangial cells, and interferon gamma (IFN-gamma) is known to have an inhibitory effect on mesangial cell proliferation. We attempted to clarify the role of these cytokines on mesangial matrix production using cultured human fetal mesangial cells (HMC).

METHODS

HMC were incubated with these cytokines for 24-72 h and the levels of type IV collagen and TGF-beta in the cell supernatants were measured by enzyme immunoassay.

RESULTS

PDGF, b-FGF, and IFN-gamma stimulated type IV collagen production by HMC in a dose- and time-dependent manner. The anti-TGF-beta neutralizing antibody clearly inhibited their stimulatory effect on type IV collagen production. PDGF and b-FGF also stimulated TGF-beta production by HMC in a dose-dependent manner, although IFN-gamma did not.

CONCLUSION

PDGF, b-FGF, and IFN-gamma stimulate type IV collagen production in cultured HMC via a TGF-beta-dependent mechanism.

Immunohistochemical characterization of glomerular PDGF B-chain and PDGF beta-receptor expression in diabetic rats

Platelet-derived growth factor (PDGF) was found to contribute to the pathophysiological process in the development and progression of glomerulosclerosis characterized by mesangial cell proliferation and accumulation of extracellular matrix. To examine the role of PDGF in the development of diabetic nephropathy, we conducted immunohistochemical analysis for PDGF B-chain (PDGF-B) and PDGF beta-receptor (PDGFR-beta) in the glomeruli of streptozotocin-induced diabetic rats. At 2, 4, and 12 weeks after the onset of diabetes, the expression of PDGF-B in glomeruli of diabetic rats was increased significantly as compared to control or diabetic rats treated with insulin. Similar changes were observed on PDGFR-beta immunostaining. The immunostaining of mirror sections revealed the existence of PDGF-B or PDGFR-beta not only in mesangial cells but also in visceral epithelial cells. Glomerular volume was significantly increased in diabetes. This early glomerular abnormality was prevented by an inhibition of PDGF system with trapidil as well as by the treatment of insulin. Our results suggest that the activation of the PDGF system in glomerular cells might play an important role in the development of early glomerular lesion in diabetes.

Amelioration of accelerated diabetic mesangial expansion by treatment with a PKC beta inhibitor in diabetic db/db mice, a rodent model for type 2 diabetes

Activation of protein kinase C (PKC) is implicated as an important mechanism by which diabetes causes vascular complications. We have recently shown that a PKC beta inhibitor ameliorates not only early diabetes-induced glomerular dysfunction such as glomerular hyperfiltration and albuminuria, but also overexpression of glomerular mRNA for transforming growth factor beta1 (TGF-beta1) and extracellular matrix (ECM) proteins in streptozotocin-induced diabetic rats, a model for type 1 diabetes. In this study, we examined the long-term effects of a PKC beta inhibitor on glomerular histology as well as on biochemical and functional abnormalities in glomeruli of db/db mice, a model for type 2 diabetes. Administration of a PKC beta inhibitor reduced urinary albumin excretion rates and inhibited glomerular PKC activation in diabetic db/db mice. Administration of a PKC beta inhibitor also prevented the mesangial expansion observed in diabetic db/db mice, possibly through attenuation of glomerular expression of TGF-beta and ECM proteins such as fibronectin and type IV collagen. These findings provide the first in vivo evidence that the long-term inhibition of PKC activation in the renal glomeruli can ameliorate glomerular pathologies in diabetic state, and thus suggest that a PKC beta inhibitor might be an useful therapeutic strategy for the treatment of diabetic nephropathy.

Mechanism of action and in vivo role of platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

VEGF(165) mediates glomerular endothelial repair

VEGF(165), the most abundant isoform in man, is an angiogenic cytokine that also regulates vascular permeability. Its function in the renal glomerulus, where it is expressed in visceral epithelial and mesangial cells, is unknown. To assess the role of VEGF(165) in glomerular disease, we administered a novel antagonist - a high-affinity, nuclease-resistant RNA aptamer coupled to 40-kDa polyethylene glycol (PEG) - to normal rats and to rats with mesangioproliferative nephritis, passive Heymann nephritis (PHN), or puromycin aminonucleoside nephrosis (PAN). In normal rats, antagonism of VEGF(165) for 21 days failed to induce glomerular pathology or proteinuria. In rats with mesangioproliferative nephritis, the VEGF(165) aptamer (but not a sequence-scrambled control RNA or PEG alone) led to a reduction of glomerular endothelial regeneration and an increase in endothelial cell death, provoking an 8-fold increase in the frequency of glomerular microaneurysms by day 6. In contrast, early leukocyte influx and the proliferation, activation, and matrix accumulation of mesangial cells were not affected in these rats. In rats with PHN or PAN, administration of the VEGF(165) aptamer did not influence the course of proteinuria using various dosages and administration routes. These data identify VEGF(165) as a factor of central importance for endothelial cell survival and repair in glomerular disease, and point to a potentially novel way to influence the course of glomerular diseases characterized by endothelial cell damage, such as various glomerulonephritides, thrombotic microangiopathies, or renal transplant rejection.

Expression of platelet-derived growth factor in newly formed cholangiocytes during experimental biliary fibrosis in rats

BACKGROUND/AIMS

Chronic cholestasis stimulates a fibroductular reaction which may progress to secondary biliary fibrosis and cirrhosis. Since platelet-derived growth factor has been indicated as a major fibrogenic factor in chronic liver disease, we analyzed its expression and that of its receptor beta subunit in a rat model of chronic cholestasis.

METHODS

Liver tissue samples collected at 7, 10, 21, and 28 days after induction of cholestasis obtained by bile duct ligation, were analyzed by immunohistochemistry, in situ hybridization and RNase protection assay for the expression of platelet-derived growth factor (PDGF)-B chain and receptor beta subunit. Furthermore, the expression of PDGF-B chain mRNA was analyzed in highly purified cholangiocytes from normal and cholestatic rat liver.

RESULTS

In cholestatic liver, platelet-derived growth factor-BB and B chain mRNA expression increased up to 4 weeks in epithelial cells of proliferating bile ducts, and periductular mesenchymal cells. The increased expression of PDGF-B chain mRNA was confirmed in highly purified cholangiocytes obtained from normal and cholestatic rat liver. The expression of the receptor beta subunit progressively increased after induction of cholestasis and was mainly localized to desmin-positive periductular hepatic stellate cells.

CONCLUSIONS

These data suggest that platelet-derived growth factor-B chain can be synthesized by cholangiocytes during chronic cholestasis. The presence of its receptor on periductular hepatic stellate cells raises the possibility that, in this experimental setting, this cytokine might contribute to fibrogenesis in vivo.

Novel approach to specific growth factor inhibition in vivo: antagonism of platelet-derived growth factor in glomerulonephritis by aptamers

Mesangial cell proliferation and matrix accumulation, driven by platelet-derived growth factor (PDGF), contribute to many progressive renal diseases. In a novel approach to antagonize PDGF, we investigated the effects of a nuclease-resistant high-affinity oligonucleotide aptamer in vitro and in vivo. In cultured mesangial cells, the aptamer markedly suppressed PDGF-BB but not epidermal- or fibroblast-growth-factor-2-induced proliferation. In vivo effects of the aptamer were evaluated in a rat mesangioproliferative glomerulonephritis model. Twice-daily intravenous (i.v.) injections from days 3 to 8 after disease induction of 2.2 mg/kg PDGF-B aptamer, coupled to 40-kd polyethylene glycol (PEG), led to 1) a reduction of glomerular mitoses by 64% on day 6 and by 78% on day 9, 2) a reduction of proliferating mesangial cells by 95% on day 9, 3) markedly reduced glomerular expression of endogenous PDGF B-chain, 4) reduced glomerular monocyte/macrophage influx on day 6 after disease induction, and 5) a marked reduction of glomerular extracellular matrix overproduction (as assessed by analysis of fibronectin and type IV collagen) both on the protein and mRNA level. The administration of equivalent amounts of a PEG-coupled aptamer with a scrambled sequence or PEG alone had no beneficial effect on the natural course of the disease. These data show that specific inhibition of growth factors using custom-designed, high-affinity aptamers is feasible and effective.

Beneficial effects of a novel inhibitor of platelet-derived growth factor receptor autophosphorylation in the rat with mesangial proliferative glomerulonephritis

1. Our original compound, Ki6896 ((4-t-butylphenyl)(4-[(6,7-dimethoxy-4-quinolyl) oxy]phenyl) methanone) strongly inhibited the autophosphorylation of platelet-derived growth factor (PDGF) beta-receptor (IC50=0.31 microM) and that of basic fibroblast growth factor receptor (IC50=3.1 microM), whereas it did not inhibit some other kinases. 2. The [3H]thymidine incorporation and the growth of mesangial cells under the stimulation of PDGF were inhibited by Ki6896 in a dose-dependent manner. 3. In the mesangial proliferative glomerulonephritis rats induced by anti-Thy-1 monoclonal antibody, glomerulosclerosis was ameliorated and the number of glomerular proliferating cells was decreased by the daily administration of Ki6896. However, the accumulation of type I collagen and fibronectin in the glomeruli was not suppressed by Ki6896.

Expression of platelet-derived growth factor and its receptors in the developing and adult mouse kidney

BACKGROUND

Experimental analysis of gene function is increasingly being accomplished using mouse models. Glomerular malformations occur in mice in which the platelet-derived growth factor (PDGF) B-chain gene or the PDGF receptor beta-subunit gene have been deleted. To understand potential PDGF signaling pathways in the kidney, we determined the expression pattern of PDGF ligand and receptor genes in mouse kidney during development and in the mature adult kidney.

METHODS

We used in situ hybridization to map the expression of transcripts encoding the PDGF ligands (A-chain and B-chain) and PDGF receptors (PDGFRalpha and PDGFRbeta) in the developing and mature kidney of the mouse.

RESULTS

PDGF A-chain transcripts are expressed by epithelial cells (especially in what appear to be the loop of Henle) and possibly in vascular smooth muscle cells. Its receptor, PDGFRalpha, is expressed by interstitial cells. PDGF B-chain transcripts are most highly expressed by vascular endothelial cells of developing and adult kidney and minimally by visceral epithelia of immature glomeruli. PDGFRbeta transcripts are expressed by fetal blastemal cells, interstitial cells, mesangial cells, and vascular smooth muscle cells and by adult mesangial and interstitial cells. PDGFRalpha and PDGFRbeta expression is especially prominent in lipid-laden interstitial cells in the adult kidney.

CONCLUSIONS

These patterns of expression are similar, but not identical, to those observed in rat and human and suggest that paracrine interactions mediated by the PDGF/PDGF receptor system may coordinate the development of the tubular, vascular, and interstitial components during kidney development and disease.

C-type natriuretic peptide inhibits mesangial cell proliferation and matrix accumulation in vivo

Local C-type natriuretic peptide (CNP) production and CNP receptor expression have been demonstrated in glomeruli. However, the glomerular (patho-)physiological functions of CNP are largely unknown. We therefore investigated the effects of CNP on mesangial cell proliferation and matrix accumulation in the rat mesangioproliferative anti-Thy 1.1 model. Over seven days rats received a continuous infusion (1 microgram/kg/min) of either CNP (N = 6), an irrelevant control peptide (N = 3) or buffer alone (N = 6). Kidney biopsies were performed on days 2, 4 and 8. Few significant differences between the groups were noted on days 2 and 4. Compared to buffer treated rats on day 8, those receiving CNP showed a 35% reduction of glomerular mitoses, a 62% reduction of glomerular uptake of the thymidine analogue BrdU and a significant reduction in glomerular expression of PDGF B-chain. Double immunoperoxidase staining also revealed blunting of proliferating, activated mesangial cells (515 reduction of alpha-smooth muscle actin-/BrdU-positive cells) and macrophage influx. Moreover, there was a marked reduction of mesangial collagen IV and fibronectin accumulation at the protein and mRNA level. Rats receiving the control peptide were indistinguishable from buffer treated rats. Systemic blood pressure was reduced by 10 to 20% in both CNP and control peptide treated rats on day 8, excluding that the findings were due to hemodynamic effects of CNP. Our findings demonstrate that CNP is involved in the regulation of mesangial cell proliferation and matrix production in vivo. The data suggest the existence of a glomerular natriuretic peptide system that may regulate tissue homeostasis and contribute to resolution of mesangioproliferative diseases.

Effects of PAX2 expression in a human fetal kidney (HEK293) cell line

PAX2, a member of the "paired-box" family of homeotic genes, is a nuclear transcription factor expressed in the early stages of nephrogenesis by induced blastemal cells as they progress from mesenchymal condensates to the "S-shaped" stage and also by the ureteric bud. Spontaneous mutations in one copy of PAX2 in humans causes a syndrome of proteinuric renal failure and coloboma of the eye (P. Sanyanusin et al., Nat. Genet. 9 (1995) 358-363); transgenic mice with disruption of the PAX2 gene are anephric (M. Torres et al., Development 121 (1995) 4057-4067. Although PAX2 is clearly critical for normal kidney development, its direct effects on kidney cell phenotype are unknown. To address this issue, we developed stable transfectants of the HEK293 human fetal kidney epithelial cell line expressing human PAX2 protein under tetracycline-regulatable promoter. In these cells, PAX2 had no effect on the proliferative rate, but increased the expression of the Wilms' tumor gene (2-fold) and E-cadherin (7-fold). PAX2 had a strong inhibitory effect on vimentin; vimentin/GAPDH mRNA ratio was suppressed to 8% of control whereas cytokeratin-18/GAPDH mRNA ratio was unchanged. During nephrogenesis, loss of vimentin and onset of low-level WT1 and E-cadherin expression occur in mesenchymal condensates. Our observations suggest that these events may be, in part, regulated by PAX2.

Anti-angiogenic compound (TNP-470) inhibits mesangial cell proliferation in vitro and in vivo

Growth factors, especially basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), and transforming growth factor-beta (TGF-beta) are known to play key roles in the pathogenesis of mesangial proliferative glomerulonephritis. TNP-470 (AGM-1470), a potent anti-angiogenic compound, has anti-growth factor properties and inhibits the activation of cyclin-dependent kinase (cdk) 2 and phosphorylation of RB protein. We investigated whether TNP-470 could suppress growth factor induced mesangial cell proliferation in vitro and experimental model of mesangial proliferative glomerulonephritis in vivo. TNP-470 inhibited potently PDGF- and bFGF-stimulated proliferation of rat mesangial cells in vitro (IC50 = 50 pg/ml). In anti-Thy 1.1 glomerulonephritis, high dose use of TNP-470 (20 mg/kg/day) markedly suppressed mesangial cell proliferation and mesangial matrix expansion on day 6; however, mesangiolysis remained. Low dose use of TNP-470 (10 mg/kg/day) moderately inhibited mesangial cell proliferation and mesangial matrix synthesis, and induced appropriate glomerular healing on day 14 in anti-Thy 1.1 glomerulonephritis. Thus, TNP-470 potently inhibits growth factor-induced proliferation of mesangial cells in vitro, and mesangial cell proliferation and extracellular matrix expansion in anti-Thy 1.1 glomerulonephritis in vivo. These results suggest a novel therapeutic potential of TNP-470 in mesangial proliferative glomerulonephritis.

Growth factor transcripts in rat renal transplants

Locally produced cytokines and growth factors may mediate tissue remodelling processes, as observed in renal transplants exposed to ischemia or acute rejection episodes. The present study was designed to investigate mRNA transcript levels of platelet-derived growth factor (PDGF)-receptor beta, PDGF-A, PDGF-B, fibroblast growth factor-1, and transforming growth factor beta 1 in normal rat kidneys, in kidneys following contralateral nephrectomy and in renal transplants with acute or chronic rejection. Platelet-derived growth factor-receptor beta mRNA levels increased significantly in syngeneic and allogeneic transplants in the first week after transplantation and in allogeneic transplants with chronic rejection. Immunohistochemistry showed induction of PDGF-receptor beta protein expression on vascular wall cells in such grafts. Platelet-derived growth factor-A chain mRNA levels increased in day 3 allografts and in syngeneic LEW grafts, while PDGF-B chain mRNA levels showed no significant changes with transplantation. Fibroblast growth factor-1 mRNA levels were detectable in normal kidneys, tended to decrease with acute rejection, and increased significantly in chronic rejection. Transforming growth factor-beta 1 transcripts increased in acute and chronic rejection; immunohistochemistry showed predominantly glomerular localization of the transforming growth factor-beta 1 protein. We conclude that transplantation and rejection are associated with changes in the intragraft mRNA levels for several growth factors; chronic rejection is characterized by an increase in fibroblast growth factor-1 and transforming growth factor-beta 1 transcript levels.

Differential expression of transforming growth factor-beta isoforms and receptors in experimental membranous nephropathy

In membranous nephropathy (MN) overproduction of matrix by glomerular epithelial cells (GEC) is believed to be responsible for glomerular basement membrane thickening and spikes. We studied experimental MN in rats (passive Heymann nephritis, PHN) at 5, 10 and 30 days. PHN rats exhibited a marked increase in GEC immunostaining for TGF-beta 2 at all time points. TGF-beta 3 staining was increased at day 10 only, and TGF-beta 1 was unchanged. Glomerular mRNA for TGF-beta 2 and -beta 3 was increased by day 5 when urine protein increased, whereas TGF-beta 1 was not. TGF-beta 2 bioactivity was increased at day 5. There was also a marked increase in GEC immunostaining for TGF-beta receptor type I (T beta IR) and TGF-beta receptor type II (T beta IIR) at all time points in PHN. mRNA levels for both receptors increased at day 5. Increases in protein expression and mRNA levels for the TGF-beta 2 and -beta 3 isoforms, and T beta IR and T beta RII were prevented by complement depletion. We conclude that complement-mediated injury to the GEC in vivo is associated with the up-regulation of TGF-beta 2 and -beta 3 isoforms, an increase in TGF-beta 2 bioactivity, and an increase in T beta RI and T beta RII expression. This contrasts with changes in TGF-beta 1 reported in mesangial disease, suggesting that TGF-beta 2 and -beta 3 may be important in diseases of the GEC. The differential expression of TGF-beta isoforms and receptors may be important determinants of the GEC response to injury.

Mechanisms involved in the pathogenesis of tubulointerstitial fibrosis in 5/6-nephrectomized rats

The 5/6 nephrectomy model is used to study pathogenetic mechanisms underlying chronic renal failure. We previously demonstrated that increased mesangial cell proliferation and glomerular PDGF B-chain expression precede glomerulosclerosis in this model. In the present study we have assessed the concomitant changes in the cortical tubulointerstitium. A wave of tubular and interstitial cell proliferation (as determined by immunostaining for PCNA) occurred at week 1 after 5/6 nephrectomy. This wave preceded the peak glomerular cell proliferation by one week. Tubulointerstitial cell proliferation decreased thereafter and reached control values by week 10. In situ hybridization and immunostaining for PDGF B-chain and beta-receptor in sham-operated controls showed labeling of distal tubules and collecting ducts, while no signal was present in the interstitium. PDGF B-chain mRNA and protein expression was markedly increased in tubules at weeks 2 and 4 after 5/6 nephrectomy and in the interstitium (particularly in areas of inflammatory infiltrates) at weeks 2 to 10. Similar changes occurred with PDGF receptor beta-subunit immunostaining. Interstitial expression of desmin and alpha-smooth muscle actin (markers of myofibroblasts) progressively increased after week 1. Interstitial influx of monocytes/macrophages with focal accentuation started at week 2. Counts of lymphocytes, neutrophils and platelets showed only minor changes. In parallel to the monocyte/macrophage influx, progressive interstitial accumulation of collagens I and IV, laminin, and fibronectin occurred. All of these changes were correlated with the increase in serum creatinine, proteinuria and an index of tubulointerstitial damage. We conclude that tubulointerstitial changes after 5/6 nephrectomy show similarities with those observed in the glomeruli. Tubular and interstitial overexpression of PDGF B-chain and its receptor may play a role in mediating fibroblast migration and/or proliferation in areas of tubulointerstitial injury.

Apoptosis of cultured rat glomerular mesangial cells induced by IgG2a monoclonal anti-Thy-1 antibodies

Anti-Thy-1 nephritis is a model of mesangial proliferative glomerulonephritis. It has been suggested that apoptosis, which is a counteracting regulatory mechanism against undesired cell proliferation, is involved in sequential histological changes in this model. In the present study, we investigated whether IgG2a anti-Thy-1 monoclonal antibody (ER4) or its F(ab')2 fragments are able to induce apoptosis of rat glomerular mesangial cells (GMC) in vitro. After co-culture with ER4 or its F(ab')2 fragments, apoptosis was assessed by morphological studies with Hoechst 33258 stain and FITC-annexin V. The latter detects the dislocation of negatively charged phospholipid, phosphatidylserine, from the inner to the outer leaflet of the membrane during apoptosis. This is a sensitive method for the detection of apoptosis. Under fluorescent microscopy, distinct nuclear condensation and positive reactivity with FITC-annexin V were observed in cells co-cultured with ER4 or its F(ab')2 fragments. The results obtained by FACS analysis with annexin V showed a direct correlation with the detection of apoptosis with the terminal deoxynucleotidyl transferase reaction (TDT). Up to 19% and 23% of rat GMC, which were co-cultured for 24 hours with 1 microgram/ml (0.5 microgram/l x 10(5) cells) of ER4 or its F(ab')2 fragments, were labeled by TDT, respectively. With annexin V, up to 34% and 31% cells displaying apoptosis were seen. The degree of apoptosis as measured by the annexin V method was dependent on the concentration of ER4 and time of incubation in the presence of ER4. Finally, apoptosis was confirmed by gel electrophoresis of DNA isolated from the cells co-cultured with each monoclonal antibody (MAb). DNA extracts from cells co-cultured with ER4 or its F(ab')2 fragments demonstrated typical internucleosomal DNA fragmentation. Medium alone, controls of anti-human C3bi receptor MAb (IB4) and anti-rat MHC class I MAb (OX18) showed neither nuclear changes nor significant labeling of the cells with the TDT reaction or with the annexin V. Taken together, these results demonstrate for the first time that anti-Thy-1 MAb is able to induce apoptosis of rat GMC in vitro. The Thy-1 antigen on rat GMC, therefore, seems to function as one of the molecules regulating cell death and thereby may determine the degree of mesangial alteration in Thy-1 nephritis.

Signals controlling the expression of PDGF

PDGF is an important polypeptide growth factor that plays an essential role during early vertebrate development and is associated with tissue repair and wound healing in the adult vertebrate. Moreover, PDGF is thought to play a role in a variety of pathological phenomena, such as cancer, fibrosis and atherosclerosis. PDGF is expressed as a dimer of A and/or B chains, the precursors of which are encoded by two single copy genes. Although the PDGF genes are expressed coordinately in a number of cell types, they are independently expressed in a majority of cell types. The expression of either PDGF gene can be affected by very diverse extracellular stimuli and the type of response is dependent on the cell type that is exposed to the stimulus. Expression of the PDGF chains can be modulated at every imaginable level: by regulating accessibility of the transcription start site, by varying the transcription initiation rate, by using alternative transcription start sites, by alternative splicing, by using alternative polyadenylation signals, by varying mRNA decay rates, by regulating efficiency of translation, by protein modification, and by regulating secretion. Even upon secretion, the activity of PDGF can be modulated by non-specific or specific PDGF-binding proteins. This review provides an overview of the cell types in which the PDGF genes are expressed, of the factors that are known to affect the expression of PDGF, and of the various levels at which the expression of PDGF genes can be regulated.

Modulatory role of platelet-derived growth factor on cytokine-induced nerve growth factor synthesis in rat glomerular mesangial cells

Recent evidence indicates that cytokines are potent inducers of nerve growth factor (NGF) expression in peripheral tissues and in brain. Cultured rat glomerular mesangial cells respond to interleukin-1 beta (IL-1 beta) and tumour necrosis factor-alpha (TNF-alpha) by increased NGF synthesis. We found that co-stimulation of rat glomerular mesangial cells with platelet-derived growth factor (PGDF-BB) and IL-1 beta/TNF-alpha significantly augments the IL-1 beta/TNF-alpha-induced NGF mRNA levels and NGF synthesis. In contrast, preincubation with PDGF-BB drastically reduces NGF gene expression and NGF protein synthesis in response to IL-1 beta/TNF-alpha stimulation. Thus our results indicate that PDGF-BB is a potent modulator of cytokine-induced NGF expression; its precise action is critically depending on the time at which the PDGF receptor is activated.

Endothelin-1 and endothelin B type receptor are induced in mesangial proliferative nephritis in the rat

We studied whether endothelin-1 (ET-1) and its receptor subtypes (ETAR, endothelin A type receptor; and ETBR, B type receptor) were up-regulated in the glomerulus of a rat model of mesangial proliferative glomerulonephritis induced by anti-thymocyte serum (anti-Thy-1 GN). A marked increase in preproET-1 mRNA could be demonstrated in glomerular RNA 3 and six days after disease induction (4.1- and 4.9-fold vs. day 0, respectively), corresponding to the time of mesangial cell proliferation, to the time of macrophage infiltration into glomeruli, and also to the time of increase in glomerular PDGF B-chain mRNA expression. The localization of ET-1 protein in the mesangial area and along the inner aspect of the glomerular capillary wall was also demonstrated by immunohistochemistry from day 3 and maximal at day 6. The major source of the cells expressing ET-1 in glomeruli appeared to be mesangial cells, glomerular endothelial cells and monocyte/macrophages. Furthermore, both gene and protein expression of ET-1 were associated with increased urinary excretion of ET-1. There was no increase in the plasma ET-1 immunoreactivity. Glomerular expression of ETBR mRNA increased in anti-Thy-1 GN (1.5-fold vs. day 0 at day 3 after disease induction, 3.6-fold at day 6 and 2.7-fold at day 10), but there was minimal change in ETAR mRNA expression. These results suggest that preproET-1 mRNA, which is induced in anti-Thy-1 GN, is linked primarily with ETBR mRNA expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Progressive renal lesions induced by administration of monoclonal antibody 1-22-3 to unilaterally nephrectomized rats

A new animal model of progressive glomerulosclerosis was developed by administering a single i.v., injection of MoAb 1-22-3 to unilaterally nephrectomized rats. Renal morphological analysis revealed that glomerular lesions characterized by mesangial cell proliferation and mesangial matrix expansion were induced in about 95% of the glomeruli. Approximately 20% of the glomeruli of the unilaterally nephrectomized rats showed sclerosis or segmental sclerosis by week 6 after MoAb injection and crescent formation was observed in some glomeruli (ca 4%). Cellular infiltration was also noted in some parts of the interstitium. Increased expression of transforming growth factor-beta (TGF-beta) was observed in the unilaterally nephrectomized rats treated with MoAb 1-22-3, but we could not demonstrate pathological involvement of platelet-derived growth factor (PDGF), even though early-stage mesangial cell proliferation was observed. The mechanism of mesangial cell proliferation in this model remains to be elucidated. The relatively short period of time needed to induce the sclerotic changes in considered to be a great advantage of this model for clarifying the mechanisms involved in the chronic progression of mesangial proliferative glomerulonephritis.