Expression of platelet-derived growth factor receptors in normal and diseased human kidney. An immunohistochemistry and in situ hybridization study

Effects of the indolocarbazole 3744W on the tyrosine kinase activity of the cytoplasmic domain of the platelet-derived growth factor beta-receptor

The cytoplasmic domain of the platelet-derived growth factor (PDGF) beta-receptor was expressed in insect cells by using a baculovirus system. The resulting protein was a constitutively active tyrosine kinase that could phosphorylate both protein and peptide substrates. A recently identified potent and selective inhibitor of intact PDGF receptor autophosphorylation, 3744W, inhibited the autophosphorylation of the cytoplasmic domain both in vitro (IC50 1.8+/-0.12 microM) and within intact insect cells (IC50 2.0 microM). However, under identical assay conditions, 3744W did not inhibit the phosphorylation of the synthetic polymeric peptide poly(Glu4Tyr1) even at concentrations as high as 100 microM. These results suggest that, although 3744W inhibits PDGF receptor autophosphorylation directly, it can discriminate between phosphate acceptor substrates.

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.

Fibronectin stimulates transcription of the platelet-derived growth factor beta-receptor in cultured rat aortic smooth muscle cells

Fibronectin seems to play an important role in promoting the characteristic changes of vascular smooth muscle cells in diabetes mellitus including overexpression of the platelet-derived growth factor beta-receptor. To determine the regulatory mechanism of the beta-receptor by fibronectin, we have analyzed the effect of fibronectin on the expression of the beta-receptor in cultured rat aortic smooth muscle cells using the beta-receptor promoter/luciferase expression vector system. Fibronectin was found to stimulate the expression of the beta-receptor at the transcriptional level. Both a MEK1 inhibitor PD98059 and a tyrosine kinase inhibitor herbimycin A significantly inhibited the fibronectin-stimulated receptor transcription. Herbimycin A also completely inhibited the fibronectin-stimulated increase in tyrosine phosphorylation of focal adhesion kinase. These data suggest the involvement of the integrin-mediated mitogen-activated protein kinase pathway downstream of fibronectin stimulation in the activation process of the beta-receptor promoter.

Paracrine stimulation of human renal fibroblasts by proximal tubule cells

Paracrine stimulation of human renal fibroblasts by proximal tubule cells.

BACKGROUND

Interstitial fibrosis strongly predicts the degree and progression of renal failure in human renal disorders. Since active fibrosis tends to initially occur in a peritubular distribution, the possibility that human proximal tubule cells (PTC) relay fibrogenic signals to neighboring cortical fibroblasts was examined in vitro.

METHODS

Cell proliferation (cell counts and thymidine incorporation), total collagen synthesis (proline incorporation), matrix metalloproteinase (MMP) activity (gelatin zymography), and autocrine secretion of insulin-like growth factor-I (IGF-I) were measured in primary cultures of human cortical fibroblasts cocultured with PTC or exposed to PTC-conditioned media (PTCCM).

RESULTS

Cell numbers and thymidine incorporation rates were increased in cortical fibroblasts cocultured with PTC (136.4+/-7.3% and 119.3+/-8.2% of control values, respectively, P < 0.05) or incubated in PTC-CM (114.0+/-5.9%, P < 0.05 and 146.7+/-13.3%, P < 0.05, respectively). PTC-CM stimulated cortical fibroblast collagen synthesis (13.5+/-1.0% vs. 10.8+/-0.7%, respectively, N = 24, P < 0.05) and MMP-2 and MMP-9 secretion. Cortical fibroblast secretion of IGF-I binding protein-3 (IGFBP-3), which in turn modulates the autocrine and paracrine actions of IGF-I, was enhanced in the presence of PTC-CM compared with control (1162.2+/-94.2 vs. 969.1+/-58.9 ng/mg protein/day, P < 0.05), but no change was observed in cortical fibroblast secretion of IGFBP-2 (260.9+/-38.8 vs. 290.9+/-36.6 ng/mg protein/day, P = NS) or IGF-I (56.7+/-6.6 vs. 57.0+/-6.8 ng/mg protein/day, P = NS). Human PTC secreted transforming growth factor-beta1 (TGF-beta1) and the AB heterodimer of platelet-derived growth factor (PDGF-AB) in a time-dependent fashion and the augmentation of cortical fibroblasts mitogenesis, collagen synthesis and IGFBP-3 secretion induced by PTC-CM was replicated by exogenous TGF-beta1 and PDGF. Furthermore, the stimulatory effects of PTC on cortical fibroblasts were potentiated in transiently acidified PTC-CM (which activated latent TGF-beta1), and were abrogated by neutralizing antibodies specifically directed against TGF-beta1 and PDGF-AB. Cortical fibroblasts in turn released a soluble factor(s) into cortical fibroblast-conditioned media that reciprocally stimulated PDGF-AB production by PTC (4.79+/-1.55 vs. 0.78+/-.06 ng/mg protein/day, P < 0.05).

CONCLUSIONS

PTC modulate the biological behavior of neighboring cortical fibroblasts in the human kidney through paracrine mechanisms, which include the production and release of PDGF-AB and TGF-beta1. Renal insults that result in proximal tubule injury may perturb this paracrine interaction, thereby culminating in excessive fibroblast proliferation and interstitial fibrosis.

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.

Interleukin-6, interleukin-8 and monocyte chemotactic peptide-1 gene expression and protein synthesis are independently modulated by hemodialysis membranes

BACKGROUND

Uremia produces a wide range of abnormalities of the immune system. Blood-membrane interaction in hemodialysis results in activation and severe dysfunction of peripheral blood mononuclear cells (PBMC). However, the question of whether the use of different dialytic membranes may improve PBMC dysfunctions remains unanswered.

METHODS

To address this issue, the spontaneous interleukin (IL)-6, IL-8 and monocyte chemotactic peptide-1 (MCP-1) gene expression and protein release were studied in PBMC isolated from 7 healthy subjects, 8 uremic patients on conservative therapy and 8 uremic patients undergoing subsequent one month periods of hemodialysis with cuprophan (CU) and high-flux noncomplement activating membranes, polymethylmethacrylate (PMMA) and polyamide (PA). At the end of each period of treatment, PBMC were harvested at the beginning (T0) and after 180 minutes of dialysis (T180), and then were cultured in complete medium. IL-6, IL-8 and MCP-1 mRNA expression were studied by RT-PCR. In addition, MCP-1 gene expression was evaluated also by in situ hybridization. Cytokines released in the supernatant were measured by ELISA.

RESULTS

Compared to the control group, PBMC from uremic patients on conservative therapy and treated by CU showed a clear reduction in the cytokine release, while PMMA and PA membranes were able to normalize IL-6, IL-8 and MCP-1 protein concentration, which had been reduced by CU treatment. Interestingly, at T0, mRNA expression for all three cytokines was increased in the patients treated by CU, when compared to the control group and the uremic patients on conservative therapy. A further up-regulation was observed at T180. PMMA and PA treatment, despite increasing the cytokine secretion, significantly reduced the dialysis-induced cytokine gene expression.

CONCLUSION

PBMC exposure to CU membranes results in cytokine mRNA overexpression associated with a paradoxically reduced protein release. In contrast, long-term hemodialysis with synthetic high-flux membranes reduces IL-6, IL-8 and MCP-1 gene expression and improves the ability of PBMC to secrete these cytokines. The reduced cytokine secretion during bioincompatible dialysis may reflect a PBMC adaptation that protects uremic patients against the inflammatory effects of persistent cytokine release.

Indolocarbazoles: potent and selective inhibitors of platelet-derived growth factor receptor autophosphorylation

A quantitative assay for measuring the autophosphorylation of platelet-derived growth factor (PDGF) receptors in intact vascular smooth muscle cells has been developed and used to screen for novel tyrosine kinase (TK) inhibitors. Several novel inhibitors of PDGF receptor autophosphorylation have been identified from the indolocarbazole series, including the 3,9 dimethoxy derivative, 3744W (IC50 = 14.5+/-2 nM). Tested against a panel of tyrosine and serine/threonine kinases, 3744W is at least 1,000 fold selective for the PDGF receptor tyrosine kinase and was found to inhibit autophosphorylation of both the alpha and beta isoforms of the PDGF receptor in human smooth muscle cells. PDGF-BB-stimulated DNA synthesis in quiescent cultures of human smooth muscle cells was blocked in a concentration-dependent manner by 3744W, IC50 = 10 nM. Binding studies showed that 3744W did not block the binding of PDGF-BB to cell surface receptors on human airway smooth muscle cells. Furthermore, inhibition of bone marrow stem cell proliferation by 3744W was only observed at concentrations 100-1,000 times greater than those needed to block PDGF-driven DNA synthesis in human smooth muscle cells. 3744W represents a novel, potent and selective inhibitor of PDGF receptor autophosphorylation and a powerful biochemical probe for investigating PDGF-dependent responses in vitro.

Regulation of osteopontin expression in rat mesangial cells

Hypercellularity and accumulation of extracellular matrix are common responses of renal glomeruli to inflammatory stimuli. Using the differential display approach, we compared the gene expression patterns of proliferating and differentiating rat mesangial cells in two- and three-dimensional cultures. Osteopontin, an extracellular matrix protein, was found to be transcribed, synthesized, and secreted by rat mesangial cells. Osteopontin transcription was not associated with cell proliferation and was found to be FCS-inducible in proliferating cells. Osteopontin expression was independent of exogenously supplied FCS in differentiating cells. The presented data indicate that osteopontin is differentially regulated in proliferating and differentiating mesangial cells.

In situ hybridization in the study of remodeling in proliferative glomerulonephritis

In situ hybridization combined with immunohistochemistry provides a powerful tool to study the temporal and spatial relationships between cellular sources of mRNA and localization of translated protein in normal biologic and pathologic processes. In this symposium, techniques in probe selection for the detection of mRNA in normal kidney and renal disease were discussed. Examples of the application of in situ hybridization in the study of renal disease were demonstrated using a model of proliferative glomerulonephritis induced by habu snake venom. This model follows an accelerated course of remodeling involving mesangial cell migration, proliferation, and extracellular matrix synthesis. The cellular sources and temporal expression of 2 adhesive proteins, fibronectin and thrombospondin, known to have a role in cell remodeling during embryogenesis and wound healing, were examined and compared to mesangial cell behaviors during the course of habu venom-induced glomerulonephritis. Mesangial cell migration in early lesions was associated with thrombospondin and fibronectin derived from platelets or macrophages. Thrombospondin mRNA and protein peaked at 48 hr after habu venom and were associated with mesangial cell proliferation; but thrombospondin mRNA and protein declined at 72 hr when expression of collagen type IV and laminin mRNA and protein peaked. Mesangial cell expression of fibronectin first appeared at 48 hr, and peaked at 72 hr after habu venom. Thus, mesangial cell migration was associated with exogenous fibronectin and thrombospondin derived from platelets or macrophages. Mesangial cell expression of thrombospondin was associated with migration and proliferation, whereas, expression of fibronectin was associated with proliferation and matrix synthesis. These results suggest distinctive temporal and spatial roles for thrombospondin and fibronectin in remodeling during glomerulonephritis and illustrate the utility of in situ hybridization and immunohistochemistry in the detection of cellular sources of translated proteins.

Normal ultrastructure of the kidney and lower urinary tract

The mammalian urinary tract includes the kidneys, ureters, urinary bladder, and urethra. The renal parenchyma is composed of the glomeruli and a heterogeneous array of tubule segments that are specialized in both function and structure and are arranged in a specific spatial distribution. The ultrastructure of the glomeruli and renal tubule epithelia have been well characterized and the relationship between the cellular structure and the function of the various components of the kidney have been the subject of intense study by many investigators. The lower urinary tract, the ureters, urinary bladder, and urethra, which are histologically similar throughout, are composed of a mucosal layer lined by transitional epithelium, a tunica muscularis, and a tunica serosa or adventitia. The present manuscript reviews the normal ultrastructural morphology of the kidney and the lower urinary tract. The normal ultrastructure is illustrated using transmission electron microscopy of normal rat kidney and urinary bladder preserved by in vivo perfusion with glutaraldehyde fixative and processed in epoxy resin.

Selective inhibition of platelet-derived growth factor (PDGF) receptor autophosphorylation and PDGF-mediated cellular events by a quinoline derivative

This report describes the biological effects of our original compound, Ki6783 ((3,4-dimethoxy)-4-phenoxy-6,7-dimethoxyquinoline), a potent and selective inhibitor of platelet-derived growth factor (PDGF) receptor autophosphorylation. This compound strongly inhibited autophosphorylation of the PDGF beta-receptor in cultured rat glomerular mesangial cells (MC) bearing this receptor (IC50 0.1 microM), although it did not inhibit autophosphorylation of other growth factor receptors even at 100 microM. In a cell-free kinase experiment, it showed selective inhibition of PDGF beta-receptor tyrosine kinase. A kinetic study of the compound to this tyrosine kinase revealed a competitive mode of action to ATP. [3H]Thymidine incorporation and cell proliferation of MC were inhibited by Ki6783 in a dose-dependent manner after Ki6783 and PDGF-BB were added to the culture medium. Furthermore, this compound normalized the fibrotic cell shape of v-sis-transformed NIH3T3 cells, which grow in an autocrine manner via the PDGF receptor. These effects could be explained by the inhibition of intracellular signal transduction triggered by PDGF receptor autophosphorylation, in which activation of mitogen-activated protein kinase occurs. These results suggest that Ki6783 is one of the more potent and selective inhibitors of PDGF receptor autophosphorylation and that it may be useful in ameliorating cell abnormalities due to excess action of PDGF and its receptor systems in several diseases.

Nuclear factor Y controls the basal transcription activity of the mouse platelet-derived-growth-factor beta-receptor gene

To determine the regulatory mechanism of the expression of the mouse platelet-derived growth factor (PDGF) beta-receptor gene, a 1.9-kb 5' flanking genomic fragment was cloned and analyzed. Site-directed mutagenesis of a CCAAT motif, located 60 bp upstream of the transcriptional-start site, completely abolished the promoter activity [Ballagi, A. E., Ishisaki, A., Nelin, J.-O. & Funa, K. (1995) Biochem. Biophys. Res. Commun. 210, 165-1751. The sequence around the intact CCAAT motif was protected by in vitro DNase-I-footprinting analysis. Electrophoresis-mobility-shift assays with anti-[nuclear factor Y(NF-Y)]Ig revealed binding of the NF-Y complex to the CCAAT box. Furthermore, the double-stranded oligonucleotides corresponding to the sequence around the CCAAT motif were conjugated with DNA-affinity magnetic beads. The binding proteins were affinity purified and identified as the NF-Y transcription factor by western blotting. Our results indicate that NF-Y controls the basal transcription activity of the mouse PDGF beta-receptor gene.

Localization of PDGF alpha-receptor in the developing and mature human kidney

Using in situ hybridization and immunocytochemistry we describe the renal localization of the PDGF alpha-receptor. PDGF alpha-receptor mRNA was uniformly present in human metanephric kidney in interstitial cells and vascular arcades that course through the blastema. PDGF alpha-receptor mRNA was present in some mesangial structures in early glomeruli, but was largely lost as glomeruli matured. It was present in adventitial fibroblasts, but usually not in vascular smooth muscle cells or endothelial cells of the fetal vasculature. This pattern persisted in adult kidneys, with extensive expression of mRNA by interstitial cells and only occasional expression by mesangial cells. All in situ hybridization findings were corroborated by immunocytochemistry. Double immunolabeling confirmed the rare expression of the PDGF alpha-receptor protein by vascular smooth muscle cells and the absence of its expression by endothelial cells. Given that both PDGF A- and B-chain can promote smooth muscle cell and fibroblast migration and proliferation and that both signal through the PDGF alpha-receptor, these data suggest that PDGF alpha-receptor may play important roles in the early vasculogenesis of the fetal kidney as well as in the pathogenesis of renal interstitial fibrosis.

Monocyte chemotactic peptide-1 expression and monocyte infiltration in acute renal transplant rejection

Mononuclear cell infiltration is a common histopathological feature of acute renal transplant rejection, in which it seems to play a key role in the pathogenesis of tubulointerstitial lesions. Monocyte chemotactic peptide-1 (MCP-1) is a specific chemotactic and activating factor for monocytes. Thus, the present study was aimed at evaluating MCP-1 gene and protein expression in renal biopsies of kidney transplant recipients with acute deterioration of graft function, and to correlate it with the extent of monocyte infiltration. We studied 20 kidney transplant recipients with acute graft dysfunction (13 with acute rejection, seven with acute tubular damage). MCP-1 gene and protein expression were analyzed by in situ hybridization and immunohistochemistry, respectively. CD68-positive cells were identified as monocytes. CD68-positive cell number and MCP-1 expression were quantified by a computerized image analysis system. MCP-1 gene expression, undetectable in normal human kidneys, was strikingly increased in patients with acute rejection. The chemokine localized mainly to the proximal tubular cells and to mononuclear-infiltrating cells. In patients with acute tubular damage, the MCP-1 expression, even if higher than in controls, was significantly lower than in acute rejection. The expression of the chemokine strictly correlated with the number of infiltrating monocytes (r=0.87, P<0.05). Moreover, we measured MCP-1 urinary excretion by ELISA, in eight normal subjects (36+/-16 pg/mg urine creatinine), in 13 clinically stable transplant recipients (33+/-9 pg/mg, ns vs. normal patients), in 12 transplant recipients with acute rejection (250+/-46 pg/mg, P<0.01 vs. normal patients), and in five transplant recipients with acute tubular damage (97+/-33 pg/mg, P<0.05 vs. controls and patients with acute rejection). Urinary MCP-1 excretion directly correlated with renal MCP-1 gene expression (r=0.65, P=0.05). Finally, we observed a significant reduction in MCP-1 urine levels in patients with acute rejection, who responded to the antirejection treatment. In conclusion, our data suggest that MCP-1 may play a critical role in modulating monocyte influx and consequent tubulointerstitial damage in acute rejection. Therefore, an increase in urinary MCP-1 excretion may represent an early signal of ongoing acute graft rejection.

Altered expression of fibrogenic growth factors in IgA nephropathy and focal and segmental glomerulosclerosis

The profile of fibrogenic growth factor expression was assessed in biopsies from 27 patients with IgA nephropathy (IgAN), 14 focal and segmental glomerulsclerosis (FSGS) patients and 8 controls, by immunohistochemistry. Increased platelet-derived growth factor (PDGF)-A and PDGF-B expression was detected in glomeruli and in vascular structures and collapsed tubules in the interstitium. Computer assisted image analysis demonstrated increased glomerular PDGF-A in IgAN (P < 0.05), but not FSGS patients, compared to controls, suggesting an association with mesangial proliferation. PDGF receptors were prominent in areas of mesangial expansion and intertubular fibrosis. Significant increases in interstitial PDGF Receptor beta (PDGFR-beta) were detected for both IgAN (P < 0.01) and FSGS (P < 0.05) patients. Interstitial PDGFR-beta expression was significantly correlated to monocyte/macrophage infiltrate (P < 0.0001). Increased basic fibroblast growth factor (bFGF) expression was observed segmentally in glomeruli, and in areas of tubulointerstitial damage. Higher proportions of patients with FSGS than IgAN had elevated interstitial bFGF (P < 0.005) and PDGF, reflecting the more severe degree of vascular and tubulointerstitial injury in FSGS patients. This study demonstrates distinct patterns of fibrinogenic growth factors in IgAN and FSGS, strongly associated with the severity and type of injury.

Mixed cryoglobulinemia as a model of systemic vasculitis

Leukocytoclastic vasculitis is the dominant lesion of mixed cryoglobulinemia (MC). The high prevalence of antibodies to hepatitis C virus (HCV) in association with the higher concentration of HCV RNA genomic sequences in the cryoglobulins suggests a close relationship between MC and HCV infection and strongly supports the view that this virus plays a key role in causing vascular damage. Analysis of the composition of immune complexes (ICs) provides evidence that cryoglobulins include virions mostly bound to IgG that is specifically reactive with HCV-related proteins, which in turn are crosslinked by monoclonal IgM with rheumatoid factor (RF) activity, frequently bearing the WA crossidiotype (XId). This structure is similar (if not identical) to that of circulating ICs from HCV-infected patients without cryoglobulins, suggesting that the virus may be directly responsible for the production of WA RF. Evidence for the role of circulating cryoproteins in the pathogenesis of cutaneous and renal vasculitis stems from the demonstration of HCV-related proteins and/or HCV RNA genomic sequences in the vessel wall of patients with MC. Our data indicate that endothelial cells are fully susceptible to infection by and replication of HCV, and support the contention that they serve as sufficient targets for the binding of HCV proteins expressed on the cell surface to serum immunoglobulins. The in situ demonstration of IgM RF WA XId adds further evidence that RF of the WA group participates in the development of vasculitis and probably stabilizes the binding of IgG antibodies. Lymphocytes may be crucial in the infection of endothelial cells by acting as a circulating viral reservoir. After encouraging initial results, controlled trials have defined the substantive efficacy of IFN-alpha in the treatment of MC. A response of IFN can be achieved in more than 50% of patients and includes improvement of cutaneous vasculitis and renal function. This clinical response is accompanied by a reduction in hepatitis C viremia, serum cryoglobulin concentration, and IgM RF synthesis. However, almost 80% of responders eventually have a clinical and biochemical relapse. Additional studies are required to improve the outcome and extension of this therapy, define the best candidates, and indicate the situations in which it is needed.

Monocyte recruitment in cryoglobulinemic membranoproliferative glomerulonephritis: a pathogenetic role for monocyte chemotactic peptide-1

Monocyte chemotactic peptide-1 (MCP-1) belongs to a large family of cytokines known as chemokines. It is a potent mediator of inflammatory response and is thought to play a major role in recruiting monocytes into the site of inflammation. Mixed cryoglobulinemia is a systemic vasculitis characterized in 10 to 30% of the cases by renal involvement. Monocyte infiltration into the glomerulus, and in the periglomerular and perivascular areas is a common histopathological feature of this form of glomerulonephritis. We sought to determine, by in situ hybridization and immunohistochemistry, the renal gene and protein expression of MCP-1 in cryoglobulinemic glomerulonephritis compared to normal kidney, and to correlate it with macrophage infiltration. Kidney biopsy specimens were obtained from 9 patients with cryoglobulinemic glomerulonephritis and 9 control kidneys. The distribution and intensity of MCP-1 gene and protein expression, and the macrophage infiltration (CD68 positive cells) were evaluated and quantitated by a computerized image analysis system. In normal kidneys, MCP-1 was weakly expressed, both at the gene as well as at the protein level. In diseased kidneys, a statistically significant (P < 0.001) up-regulation of MCP-1 gene and protein expression was found, particularly within the areas of tubulointerstitial damage and the glomeruli. By means of CD68 positive cells, a significant correlation (P < 0.001) was found between glomerular, tubulointerstitial macrophage infiltration and MCP-1 expression. Moreover, by combining immunohistochemistry and in situ hybridization, we observed the presence of CD68 positive cells mainly, if not exclusively, around the cells expressing MCP-1 mRNA. Interestingly, a striking increase in MCP-1 urinary concentration was found in cryoglobulinemic patients. In conclusion, our data suggest that MCP-1 may play a major role in modulating the inflammatory process observed in cryoglobulinemic glomerulonephritis.

Urinary IL-6/EGF ratio: a useful prognostic marker for the progression of renal damage in IgA nephropathy

Interleukin 6 (IL-6) is produced by human mesangial and tubular cells, and its urinary levels has been proposed as a marker of mesangial proliferation and tubulointerstitial damage. Epidermal growth factor (EGF) is expressed within the Henle's loop and the distal tubule and has been shown to accelerate recovery from renal injury. In the present study we have defined renal gene and protein expression of IL-6 and EGF in 10 normal, 10 nonproliferative glomerulonephritis (NPGN) and 30 IgA nephropathy (IgAN) human kidneys by RT-PCR, in situ hybridization and immunohistochemical techniques. Moreover, urinary IL-6 and EGF levels were measured in 41 patients with IgAN and in 20 normal subjects (N). In normal kidneys, EGF was localized in Henle's loop and distal convoluted tubule whereas IL-6 was mainly located in the proximal tubule and, less, within the glomerulus. In IgAN patients, EGF was decreased whereas IL-6 expression was upregulated. These modifications paralleled the degree of tubulointerstitial damage. Moreover, IgAN patients as a whole exhibited a reduction of EGF and an increase of IL-6 urinary concentration (EGF values: N, 12.96 +/- 1.15; IgAN Grades 1-2, 20.05 +/- 2.64; Grades 3-4 7.60 +/- 1.70: Grade 5, 3.14 +/- 0.71, ng/mg urinary creatinine. IL-6 values: N, 2.04 +/- 0.51; IgAN Grades 1-2, 3.26 +/- 0.38; Grades 3-4, 5.67 +/- 0.92; Grade 5, 27.20 +/- 9.70 pg/mg urinary creatinine), that correlated with the degree of histological lesions, the presence of hypertension and serum creatinine level. Interestingly, patients with the highest urinary IL-6/EGF ratio showed a worse evolution in a three year follow-up. In conclusion, our data show that: (1) renal IL-6 and EGF expression are strictly correlated to the degree of tubulointerstitial damage; and (2) urinary IL-6/EGF ratio might be a valuable prognostic marker for the progression of the renal damage in IgAN.

High glucose concentration induces the overexpression of transforming growth factor-beta through the activation of a platelet-derived growth factor loop in human mesangial cells

High glucose concentration has been shown to induce the overexpression of transforming growth factor (TGF)-beta 1 mRNA and protein in different cell types, including murine mesangial cells, thus possibly accounting for the expansion of mesangial extracellular matrix observed in diabetic glomerulopathy. In the present study, we evaluated platelet-derived growth factor (PDGF) B-chain and PDGF-beta receptor gene expression in human mesangial cells (HMCs) exposed to different concentrations of glucose and then sought a possible relationship between a PDGF loop and the modulation of TGF-beta 1 expression. HMC [3H]thymidine incorporation was upregulated by 30 mmol/L glucose (HG) up to 24 hours, whereas it was significantly inhibited at later time points. Neutralizing antibodies to PDGF BB abolished the biphasic response to HG, whereas anti-TGF-beta antibodies reversed only the late inhibitory effect of hyperglycemic medium. HG induced an early and persistent increase of PDGF B-chain gene expression, as evaluated by reverse transcriptase polymerase chain reaction, whereas PDGF-beta receptor mRNA increased by twofold after 6 hours, thereafter declining at levels 70% lower than in controls after 24 hours. 125I-Labeled PDGF BB binding studies in HMCs exposed to HG for 24 hours confirmed the decrease of PDGF-beta receptor expression. TGF-beta 1-specific transcripts showed 43 and 78% increases after 24 and 48 hours of incubation in HG, respectively, which was markedly diminished by anti-PDGF BB neutralizing antibodies or suramin. We conclude that HG induces an early activation of a PDGF loop that, in turn, causes an increase of TGF-beta 1 gene expression, thus modulating both HMC proliferation and mesangial matrix production.

Platelet-derived growth factor-BB induces renal tubulointerstitial myofibroblast formation and tubulointerstitial fibrosis

Tubulointerstitial fibrosis correlates closely with renal function, although the mechanism regulating tubulointerstitial fibrogenesis remains poorly understood. Since platelet-derived growth factor (PDGF) is a growth factor for fibroblasts, we examined the effect of daily (for 7 days) PDGF-AA or PDGF-BB administration on renal tubulointerstitial architecture in rats. PDGF-AA administration at a dose of 5 mg/kg did not affect the renal tubulointerstitium. By comparison, PDGF-BB induced dose-dependent renal tubulointerstitial cell proliferation and fibrosis. At 5 mg/kg, PDGF-BB increased BrdU labeling in tubulointerstitial fibroblasts at 24 hours (19-fold), which peaked at 72 hours (23-fold) with bromodeoxyuridine uptake returning to control values by 7 days. Tubulointerstitial proliferation was associated with the differentiation of these cells into myofibroblasts as evidenced by alpha-smooth muscle actin expression beginning on day 3. The expression of alpha-smooth muscle actin peaked on day 5 and had markedly declined by day 21. In addition, apoptotic cells were identified within the tubulointerstitium on day 3 and progressively increased through day 7, suggesting that the disappearance of myofibroblasts may have occurred through apoptosis. These changes were accompanied by increased expression of alpha 1 (III) collagen mRNA and interstitial accumulation of type III collagen within the renal cortex. By morphometric analysis, an approximately twofold increase in collagen III immunolabeling within the interstitial compartment was evident at 24 hours and peaked on days 5 to 7 (approximately fourfold). These data suggest that PDGF-BB may be an important mediator of tubulointerstitial hyperplasia and fibrosis.

Expression of platelet-derived growth factor and its receptors in normal human liver and during active hepatic fibrogenesis

Expression of platelet-derived growth factor (PDGF) and its receptor (R) subunits was evaluated in normal human liver and in cirrhotic liver tissue by in situ hybridization and immunohistochemistry. In normal liver, PDGF and PDGF-R subunit expression was limited to a few mesenchymal cells of the portal tract stroma and vessels. In cirrhotic liver, PDGF-A and -B chain mRNA expression was markedly increased and was co-distributed with immunoreactivity for PDGF-AA and -BB in infiltrating inflammatory cells and along vascular structures within fibrous septa. These aspects were paralleled by a marked overexpression of PDGF-R alpha- and beta-subunit mRNAs and of the relative immunoreactivities in a wide range of mesenchymal cells in fibrous septa and in perisinusoidal alpha-smooth-muscle-actin-positive cells. In general expression and distribution of PDGF-R subunits appeared to be related to the activation of different mesenchymal cell types involved in the fibroproliferative process. Therefore, we evaluated the expression of PDGF-R subunits in liver tissue specimens with increasing degrees of necroinflammatory activity. The results of this additional study confirmed that expression of PDGF-R subunits is highly correlated with the severity of histological lesions and collagen deposition. Our results, providing evidence for a functional involvement of PDGF/PDGF-R in liver fibrogenesis, greatly support the results of previous in vitro studies and direct attention toward pharmacological strategies able to affect the series of signaling events arising from the autophosphorylation of PDGF-R subunits.

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.

PDGF and TGF-beta contribute to the natural course of human IgA glomerulonephritis

PDGF and TGF-beta are known mediators of mesangial cell proliferation and matrix expansion. The presence of these regulatory factors was examined in 30 renal biopsies from patients with IgA glomerulonephritis (IgA-GN) at the mRNA and protein level. Normal renal tissue served as control. The mRNA expression of PDGF A/B chains, PDGF-beta R and TGF-beta 1 was evaluated by means of RT/PCR with subsequent Southern blot hybridization and/or non-radioactive in situ hybridization. In addition, PDGF-AB/BB, PDGF-beta R, TGF-beta isoforms (beta 1, beta 1 + 2, beta 2 + 3), the small TGF-beta 1 latency associated peptide (TGF-beta 1 LAP) and the extracellular matrix proteins tenascin and decorin were analyzed by immunocytochemistry. The expression of growth factors was correlated with light microscopic and clinical features. Compared to normal control kidneys, an increased expression of PDGF-BB/PDGF-beta R mRNAs and the corresponding proteins was observed in all biopsies with IgA-GN. Up-regulation was related to the degree of glomerular proliferation and the extent of fibrosing interstitial lesions. In contrast, there was a discordance between TGF-beta 1 mRNA and protein expression (evaluated by immunocytochemistry). In all biopsies, irrespective of the stage of the disease, abundant TGF-beta 1 transcripts were detected, whereas TGF-beta 1 immunoreactivity was expressed to a lesser degree and disclosed a more variable staining pattern. In patients with significant proliferative glomerular lesions and minor tubulointerstitial alterations, TGF-beta 1 positivity was confined to areas of glomerular proliferation, whereas in cases with more severe histology including sclerosing lesions TGF-beta 1 immunoreactivity was less prominent. The distribution and the intensity of TGF-beta 1 LAP staining commonly exceeded the positivity noted for TGF-beta 1, indicating only limited TGF-beta 1 activation. A decreased reactivity for tenascin accompanied the morphological features of glomerular sclerosis. The staining patterns and the fact that only very few inflammatory cells, particularly CD68 positive monocytes/macrophages, were detected in glomeruli confirm that predominantly resident glomerular cells (mesangial and endothelial cells) are the major source of up-regulated growth factor production in IgA-GN. Since the expression of PDGF-AB/BB paralleled the severity of proliferative glomerular changes, PDGF seems to represent a potential indicator of activity in this condition. It is suggested that an imbalance between PDGF and TGF-beta (by restricted translation and/or activation) production contribute to the progressive nature of IgA-GN.

Platelet-derived growth factor A-chain expression in developing and mature human kidneys and in Wilms' tumor

Regulated expression of PDGF A-chain may be important in kidney development. We employed two polyclonal antisera to detect expression of PDGF A-chain in fetal and normal adult kidneys by immunohistochemistry. Specificity of the antisera was demonstrated by Western blots of fetal and adult kidneys, demonstrating monospecific bands at 10 to 15 kD, and by absorption studies with PDGF-A peptide. PDGF A-chain is uniformly expressed by visceral glomerular epithelial cells and the epithelial cells of the distal nephron, including collecting ducts and contiguous urothelium lining the renal pelvis, in both fetal and adult kidneys. Fetal kidneys also demonstrate expression of PDGF A-chain at the earliest stages of vesicle formation from the metanephric blastema; this expression is then only intermittently detectable in developing glomeruli until differentiation of visceral epithelial cells occurs. Fetal and mature arterial smooth muscle cells, and some express PDGF A-chain. In situ hybridization with a riboprobe made from PDGF A-chain cDNA showed close correlation of mRNA expression with protein immunohistochemistry. PDGF A-chain expression was also identified in epithelial elements of 5/6 Wilms' tumors studied. These are the first studies to localize PDGF A-chain expression in human kidney and suggest sites of activity for PDGF A-chain in development, neoplasia, and in the renal arterial sclerosis of aging.

Biosynthesis of C3 by human mesangial cells. Modulation by proinflammatory cytokines

Deposits of complement (C) components are found in the glomeruli of patients with various glomerulonephritides without detectable immunoglobulins, thus suggesting a pathogenetic role of the locally produced proteins of this system. In the present study, we have examined human mesangial cells (HMC) for their ability to secrete C3. Three different cell lines were examined and all showed a basal production of C3, which was up-regulated following stimulation with IL-1 beta. IL-6 had no direct stimulatory effect on its own, but synergized with IL-1 to induce an increased production of C3 in the culture supernatant and its relative amount was confirmed by SDS-PAGE and immunoblot. Another agonist such as lipopolysaccharide was not able to induce any significant C3 synthesis. Analysis of C3 HMC gene expression, performed by both reverse transcription-polymerase chain reaction of isolated RNA and Northern blot, confirmed the parallel increase of the specific transcript under IL-1 beta and IL-1 beta + IL-6 stimulation. From these data we conclude that production of C3 in the mesangium could have a pathophysiologic relevance.