Connective tissue growth factor: a potential stimulus for glomerulosclerosis and tubulointerstitial fibrosis in progressive renal disease

(Pro)renin Receptor-Dependent Induction of Profibrotic Factors Is Mediated by COX-2/EP4/NOX-4/Smad Pathway in Collecting Duct Cells

The binding of prorenin to the (pro)renin receptor (PRR) triggers the activation of MAPK/ERK1/2 pathway, induction of cyclooxygenase-2 (COX-2), NOX-4-dependent production of reactive oxygen species (ROS), and the induction of transforming growth factor β (TGF-β) and profibrotic factors connecting tissue growth factor (CTGF) and plasminogen activator inhibitor (PAI-I) in collecting duct (CD) cells. However, the role of COX-2 and the intracellular pathways involved are not clear. We hypothesized that the PRR activation increases profibrotic factors through COX-2-mediated PGE2 activation of E prostanoid receptor 4 (EP4), upregulation of NOX-4/ROS production, and activation of Smad pathway in mouse CD cells. Recombinant prorenin increased ROS production and protein levels of CTGF, PAI-I, and TGF-β in M-1 CD cell line. Inhibition of MAPK, NOX-4, and COX-2 prevented this effect. Inhibition of MEK, COX-2, and EP4 also prevented the upregulation of NOX-4. Because TGF-β activates Smad pathway, we evaluate the phosphorylation of Smad2 and 3. COX-2 inhibition or EP4 antagonism significantly prevented phosphorylation of Smad 2/3. Mice that were infused with recombinant prorenin showed an induction in the expression of CTGF, PAI-I, TGF-β, fibronectin, and collagen I in isolated collecting ducts as well as the expression of alpha smooth muscle actin (α-SMA) in renal tissues. COX-2 inhibition prevented this induction. These results indicate that the induction of TGF-β, CTGF, PAI-I, and ROS occurs through PRR-dependent activation of MAPK and NOX-4; however, this mechanism depends on COX-2-derived PGE2 production and the activation of EP4 and Smad pathway.

Left ventricular mass in dialysis patients, determinants and relation with outcome. Results from the COnvective TRansport STudy (CONTRAST)

BACKGROUND AND OBJECTIVES

Left ventricular mass (LVM) is known to be related to overall and cardiovascular mortality in end stage kidney disease (ESKD) patients. The aims of the present study are 1) to determine whether LVM is associated with mortality and various cardiovascular events and 2) to identify determinants of LVM including biomarkers of inflammation and fibrosis.

DESIGN SETTING PARTICIPANTS & MEASUREMENTS

Analysis was performed with data of 327 ESKD patients, a subset from the CONvective TRAnsport STudy (CONTRAST). Echocardiography was performed at baseline. Cox regression analysis was used to assess the relation of LVM tertiles with clinical events. Multivariable linear regression models were used to identify factors associated with LVM.

RESULTS

Median age was 65 (IQR: 54-73) years, 203 (61%) were male and median LVM was 227 (IQR: 183-279) grams. The risk of all-cause mortality (hazard ratio (HR) = 1.73, 95% CI: 1.11-2.99), cardiovascular death (HR = 3.66, 95% CI: 1.35-10.05) and sudden death (HR = 13.06; 95% CI: 6.60-107) was increased in the highest tertile (>260 grams) of LVM. In the multivariable analysis positive relations with LVM were found for male gender (B = 38.8±10.3), residual renal function (B = 17.9±8.0), phosphate binder therapy (B = 16.9±8.5), and an inverse relation for a previous kidney transplantation (B = -41.1±7.6) and albumin (B = -2.9±1.1). Interleukin-6 (Il-6), high-sensitivity C-reactive protein (hsCRP), hepcidin-25 and connective tissue growth factor (CTGF) were not related to LVM.

CONCLUSION

We confirm the relation between a high LVM and outcome and expand the evidence for increased risk of sudden death. No relationship was found between LVM and markers of inflammation and fibrosis.

TRIAL REGISTRATION

Controlled-Trials.com ISRCTN38365125.

Quercetin provides greater cardioprotective effect than its glycoside derivative rutin on isoproterenol-induced cardiac fibrosis in the rat

Quercetin exhibits numerous pharmacological effects, including the capacity for cardioprotection. This study aimed to investigate whether quercetin or its glycoside derivative rutin has any protective action against isoproterenol (ISO) induced cardiac fibrosis, and investigate the structure-activity relationship. Male Wistar rats were injected subcutaneously with ISO (15 mg·(kg body mass)(-1)) to induce experimental cardiac fibrosis. The cardioprotective effect of co-treatment with quercetin (25 or 50 mg·kg(-1)) or rutin (25 or 50 mg·kg(-1)) was investigated in ISO-induced cardiac fibrosis in rats. The administration of quercetin and rutin signifcantly decreased the cardiac weight index and myocardial enzyme activity, increased the activity of superoxide dismutase in the serum, and inhibited the ISO-induced increase in angiotensin II and aldosterone in the plasma. Furthermore, overexpression of transforming growth factor β1 (TGF-β1), connective tissue growth factor (CTGF), and excessive deposition of extracellular matrix (ECM) in isoproterenol-treated myocardial tissues were normalized by quercetin and rutin. Our results suggest that both quercetin and rutin exhibited cardioprotective effects in cardiac fibrosis induced by ISO in the rat heart. Moreover, the effects of rutin are weaker than quercetin at the same dose. The mechanism of these effects may be related to antioxidative stress, inhibition of the renin-angiotensin-aldosterone system, decrease in the expression of TGF-β1 and CTGF, and the subsequent reduction in the deposition of the ECM.

Regulation of connective tissue growth factor gene expression and fibrosis in human heart failure

BACKGROUND

Heart failure (HF) is associated with excessive extracellular matrix (ECM) deposition and abnormal ECM degradation leading to cardiac fibrosis. Connective tissue growth factor (CTGF) modulates ECM production during inflammatory tissue injury, but available data on CTGF gene expression in failing human heart and its response to mechanical unloading are limited.

METHODS AND RESULTS

Left ventricle (LV) tissue from patients undergoing cardiac transplantation for ischemic (ICM; n = 20) and dilated (DCM; n = 20) cardiomyopathies and from nonfailing (NF; n = 20) donor hearts were examined. Paired samples (n = 15) from patients undergoing LV assist device (LVAD) implantation as "bridge to transplant" (34-1,145 days) also were analyzed. There was more interstitial fibrosis in both ICM and DCM compared with NF hearts. Hydroxyproline concentration was also significantly increased in DCM compared with NF samples. The expression of CTGF, transforming growth factor (TGF) β1, collagen (COL) 1-α1, COL3-α1, matrix metalloproteinase (MMP) 2, and MMP9 mRNA in ICM and DCM were also significantly elevated compared with NF samples. Although TGF-β1, CTGF, COL1-α1, and COL3-α1 mRNA levels were reduced by unloading, there was only a modest reduction in tissue fibrosis and no difference in protein-bound hydroxyproline concentration between pre- and post-LVAD tissue samples. The persistent fibrosis may be related to a concomitant reduction in MMP9 mRNA and protein levels following unloading.

CONCLUSIONS

CTGF may be a key regulator of fibrosis during maladaptive remodeling and progression to HF. Although mechanical unloading normalizes most genotypic and functional abnormalities, its effect on ECM remodeling during HF is incomplete.

Inhibitory effects of glycosaminoglycans on basal and stimulated transforming growth factor-β1 expression in mesangial cells: biochemical and structural considerations

A number of glycosaminoglycan (GAG) species related to heparin, dermatan sulfate (DeS) and chondroitin sulfate were tested for their ability to interfere with the physiological expression and/or pathological overexpression of the TGF-β1 gene. The influence of the molecular weight, molecular weight distribution, degree of sulfation and location of the sulfate groups was examined in an attempt to unveil fine relationships between structure and activity. The nature of the polysaccharide plays a major part, heparins proving able to inhibit both basal and stimulated TGF-β1 gene expression, DeSs being essentially inactive and chondroitin sulfates only inhibiting stimulated TGF-β1 gene expression. Within this frame, the particular physical and chemical properties of some GAGs appear to further modulate TGF-β1 gene response. Judging from our investigation, chondroitin sulfates seem the most promising for potential pharmacological applications in disorders characterized by fibrogenic TGF-β1 overexpression.

Inhibition of COX 1 and 2 prior to renal ischemia/reperfusion injury decreases the development of fibrosis

Ischemia and reperfusion injury (IRI) contributes to the development of chronic interstitial fibrosis/tubular atrophy in renal allograft patients. Cyclooxygenase (COX) 1 and 2 actively participate in acute ischemic injury by activating endothelial cells and inducing oxidative stress. Furthermore, blockade of COX 1 and 2 has been associated with organ improvement after ischemic damage. The aim of this study was to evaluate the role of COX 1 and 2 in the development of fibrosis by performing a COX 1 and 2 blockade immediately before IRI. We subjected C57Bl/6 male mice to 60 min of unilateral renal pedicle occlusion. Prior to surgery mice were either treated with indomethacin (IMT) at days -1 and 0 or were untreated. Blood and kidney samples were collected 6 wks after IRI. Kidney samples were analyzed by real-time reverse transcription-polymerase chain reaction for expression of transforming growth factor beta (TGF-beta), monocyte chemoattractant protein 1 (MCP-1), osteopontin (OPN), tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-1 beta, IL-10, heme oxygenase 1 (HO-1), vimentin, connective-tissue growth factor (CTGF), collagen I, and bone morphogenic protein 7 (BMP-7). To assess tissue fibrosis we performed morphometric analyses and Sirius red staining. We also performed immunohistochemical analysis of anti-actin smooth muscle. Renal function did not significantly differ between groups. Animals pretreated with IMT showed significantly less interstitial fibrosis than nontreated animals. Gene transcript analyses showed decreased expression of TGF-beta, MCP-1, TNF-alpha, IL-1-beta, vimentin, collagen I, CTGF, and IL-10 mRNA (all P < 0.05). Moreover, HO-1 mRNA was increased in animals pretreated with IMT (P < 0.05). Conversely, IMT treatment decreased osteopontin expression and enhanced BMP-7 expression, although these levels did not reach statistical significance when compared with control expression levels. The blockade of COX 1 and 2 resulted in less tissue fibrosis, which was associated with a decrease in proinflammatory cytokines and enhancement of the protective cellular response.

Connective tissue growth factor as a mediator of intraocular fibrosis

PURPOSE

To investigate the role of connective tissue growth factor (CTGF) in the pathogenesis of proliferative vitreoretinopathy (PVR).

METHODS

Expression of CTGF was evaluated immunohistochemically in human PVR membranes, and the accumulation of CTGF in the vitreous was evaluated by ELISA. The effects of CTGF on type I collagen mRNA and protein expression in RPE were assayed by real-time PCR and ELISA, and migration was assayed with a Boyden chamber assay. Experimental PVR was induced in rabbits with vitreous injection of RPE cells plus rhCTGF; injection of RPE cells plus platelet derived-growth factor, with or without rhCTGF, or by injection of RPE cells infected with an adenoviral vector that expressed CTGF.

RESULTS

CTGF was highly expressed in human PVR membranes and partially colocalized with cytokeratin-positive RPE cells. Treatment of RPE with rhCTGF stimulated migration with a peak response at 50 ng/mL (P < 0.05) and increased expression of type I collagen (P < 0.05). There was a prominent accumulation of the N-terminal half of CTGF in the vitreous of patients with PVR. Intravitreous injection of rhCTGF alone did not produce PVR, whereas such injections into rabbits with mild, nonfibrotic PVR promoted the development of dense, fibrotic epiretinal membranes. Similarly, intravitreous injection of RPE cells infected with adenoviral vectors that overexpress CTGF induced fibrotic PVR. Experimental PVR was associated with increased CTGF mRNA in PVR membranes and accumulation of CTGF half fragments in the vitreous.

CONCLUSIONS

The results identify CTGF as a major mediator of retinal fibrosis and potentially an effective therapeutic target for PVR.

Connective tissue growth factor: a role in airway remodelling in asthma?

1. Severe persistent asthma is accompanied by structural changes in the airway, referred to as remodelling. The mechanisms driving airway remodelling are poorly understood. 2. Transforming growth factor (TGF)-beta is increased in the airways of patients with asthma. Many of the effects of TGF-beta are mediated by connective tissue growth factor (CTGF). 3. Overexpression of CTGF is linked to many fibrotic diseases, but its exact role in airway remodelling is unknown. 4. Connective tissue growth factor mediates cell adhesion, migration, proliferation, survival, extracellular matrix synthesis and has a role in angiogenesis. 5. Current asthma therapies do not inhibit CTGF induction. 6. Understanding the mechanisms underlying the role of CTGF in airway remodelling may lead to new therapeutic strategies for asthma.

Tranilast attenuates connective tissue growth factor-induced extracellular matrix accumulation in renal cells

Tranilast (N-[3,4-dimethoxycinnamoyl]anthranilic acid) is a synthetic compound that we have recently reported to inhibit transforming growth factor-beta1 (TGF-beta1)-induced tubulointerstitial fibrosis in the kidney. Connective tissue growth factor (CTGF) is recognized as a potent downstream mediator of TGF-beta1. Both proximal tubule cells (PTCs) and cortical fibroblasts (CFs) are considered to be responsible for the production of tubulointerstitial extracellular matrix (ECM). These studies were undertaken to assess the profibrotic effects of CTGF in an in vitro model of the human PTCs and CFs, and to determine whether tranilast is effective in limiting the in vitro matrix responses induced by CTGF. Primary cultures of PTCs and CFs were exposed to CTGF (20 ng/ml)+/-tranilast (100 microM). Cell hypertrophy and the secretion of the ECM proteins fibronectin and collagen IV were determined. The effects of tranilast on TGF-beta1-induced CTGF mRNA expression and on phosphorylation of Smad2 were determined. CTGF significantly induced cell hypertrophy, increased fibronectin, and collagen IV secretion in PTCs and CFs. In all cases, the CTGF-induced increase in ECM protein was inhibited in the presence of tranilast. Tranilast reduced CTGF mRNA and phosphorylation of Smad2, which were induced by TGF-beta1 in PTCs and CFs. These results suggest that tranilast is a potential effective antifibrotic compound in the kidney, exerting its effects via inhibition of TGF-beta1-induced CTGF expression and downstream activation of the Smad2 pathway in both PTCs and CFs.

TGF-beta1 induces IL-8 and MCP-1 through a connective tissue growth factor-independent pathway

Transforming growth factor-beta(1) (TGF-beta(1)) functions as an important immunomodulatory cytokine in human kidney. Evidence suggests that connective tissue growth factor (CTGF) is an important downstream mediator of the profibrotic effects of TGF-beta(1). However, the role of CTGF in TGF-beta(1)-induced chemokine production remains unknown. This study was undertaken to determine whether CTGF is involved in mediating TGF-beta(1)-induced chemokine production in renal proximal tubular (HK-2) cells. Interleukin-8 (IL-8) and macrophage chemoattractant protein-1 (MCP-1) were measured. TGF-beta(1) induced an increase in IL-8 and MCP-1 (both P < 0.05) compared with control levels. CTGF was effectively silenced using small interference RNA (siRNA) in HK-2 cells. RT-PCR and real-time PCR confirmed a 94% reduction in CTGF mRNA. In the CTGF-silenced cells, TGF-beta(1)-stimulated IL-8 and MCP-1 secretion was not altered compared with control cells. Similarly, basal secretion of IL-8 and MCP-1 was not changed in CTGF-silenced cells. The direct effect of CTGF (20, 200, and 400 ng/ml) on IL-8 and MCP-1 was assessed at 24-, 48-, and 72-h time points and no stimulation was observed. Our studies further demonstrate that in the CTGF gene-silenced cells, CTGF partially mediates TGF-beta(1)-induced fibronectin and collagen IV secretion. These data suggest that TGF-beta(1) induced IL-8 and MCP-1 via CTGF-independent pathway. TGF-beta mediates both fibrosis and chemokine production in the proximal tubule of the kidney. However, CTGF plays a more specific role as a downstream mediator of TGF-beta(1)-induced fibrosis.

Structural and functional properties of CCN proteins

The CCN family currently comprises six members (CCN1-6) that regulate diverse cell functions, including mitogenesis, adhesion, apoptosis, extracellular matrix (ECM) production, growth arrest, and migration. These properties can result in a multiplicity of effects during development, differentiation, wound healing, and disease states, such as tumorigenesis and fibrosis. CCN proteins have emerged as major regulators of chondrogenesis, angiogenesis, and fibrogenesis. CCN proteins are mosaic in nature and consist of up to four structurally conserved modules, at least two of which are involved in binding to cell surfaces via molecules that include integrins, heparan sulfate proteoglycans, and low-density lipoprotein receptor-related protein. CCN proteins use integrins as signal transducing receptors to regulate context-dependent responses in individual cell types. The involvement of integrins in mediating CCN signaling allows for considerable plasticity in response because some effects are specific for certain integrin subtypes and integrin signaling is coordinated with other signaling pathways in the cell. In addition to their own biological properties, CCN proteins regulate the functions of other bioactive molecules (e.g., growth factors) via direct binding interactions. CCN molecules demonstrate complex multifaceted modes of action and regulation and have emerged as important matricellular regulators of cell function.

Expression of Mediators of Renal Injury in the Remnant Kidney of ROP Mice Is Attenuated by Cyclooxygenase-2 Inhibition

To investigate the effects of cyclooxygenase-2 (COX-2) inhibition on renal injury of mice, ROP mice were subjected to subtotal ablation ('remnant'). A subset of the remnant group was treated with a selective COX-2 inhibitor, SC58236, in the drinking water. At 12 weeks the remnant group developed significant albuminuria (181.3 +/- 15.8 microg/24 h), which was blunted by SC58236 treatment (138.9 +/- 17.1; p < 0.05 compared to remnant). SC58236 did not alter systemic blood pressure or GFR significantly. Immunoreactive COX-2 was upregulated in remnant (1.88 +/- 0.35 fold sham, n = 8, p < 0.05), which was blunted by SC58236 (to 1.26 +/- 0.31 fold sham). Collagen IV mRNA increased significantly in remnant kidneys (2.69 +/- 0.34 fold sham, n = 8, p < 0.05), and this increase was inhibited by SC58236 treatment (to 1.84 +/- 0.32 fold control). Immunoreactive TGF-beta1, connective tissue growth factor, HGF receptor, c-Met, and fibronectin all increased in remnant (2.85 +/- 0.51, 3.83 +/- 0.55, 2.56 +/- 0.31, and 2.80 +/- 0.39 fold sham respectively, n = 4-8, p < 0.05), and SC58236 blunted the increases (to 1.45 +/- 0.34, 1.85 +/- 0.13, 1.75 +/- 0.30, and 1.60 +/- 0.32 fold sham). Immunohistochemistry indicated that the major localization for these progression factors was in the tubulointerstitium, especially in the scar area, which is in agreement with the expression of a macrophage marker, F4/80. Therefore, these results indicate that in a mouse model of subtotal renal ablation, COX-2 inhibition blocks expression of mediators of renal tubulointerstitial injury.

Differential effects of simvastatin on mesangial cells

BACKGROUND

Statins are increasingly recognized as mediators of direct cellular effects independent of their lipid lowering capacity. Therefore, the time and concentration dependence of various statin-mediated cellular alterations was compared in renal mesangial cells.

METHODS

The effects of statins on cell proliferation, gene expression, cytoskeletal alterations, apoptosis, and cytotoxicity were analyzed in cultured mesangial cells using standard techniques.

RESULTS

Simvastatin and lovastatin decreased proliferation and cell number of rat mesangial cells concentration-dependently. Concurrently, the expression of the fibrogenic protein connective tissue growth factor (CTGF) was impaired and actin stress fibers, which are typical of mesangial cells in culture, became disassembled by simvastatin. A decrease of the posttranslational modification of RhoA by geranylgeranyl moieties was detected, supporting a role for RhoA as mediator of statin effects. Induction of apoptosis, determined by activation of caspase-3 and DNA fragmentation, and necrosis only occurred at later time points, when the morphology of the cells was strongly altered and the cells detached from the surface due to changes in the actin cytoskeleton. Basically, the same results were obtained with a human mesangial cell line. Furthermore, statin effects were mimicked by inhibition of the geranylgeranyltransferase.

CONCLUSION

Most of the cellular effects of the lipophilic statins occurred within the same time and concentration range, suggesting a common molecular mechanism. Only apoptosis and necrosis were observed at later time points or with higher concentrations of simvastatin and thus seem to be secondary to the changes in gene expression and alterations of the actin cytoskeleton.

Intracellular cyclic nucleotide analogues inhibit in vitro mitogenesis and activation of fibroblasts derived from obstructed rat kidneys

As several studies indirectly suggest that inhibiting the intracellular breakdown of cyclic nucleotides may inhibit fibrogenesis, this study used membrane permeable cyclic nucleotide analogues to examine the role of cAMP and cGMP signaling pathways in the regulation of renal fibroblast function. Fibroblasts were isolated by explant outgrowth culture of rat kidneys post unilateral ureteric obstruction. Subcultured cells were exposed to 10- 1,000 microM of the cyclic nucleotide analogues 8-bromo-cAMP (8br-cAMP) and 8-bromo-cGMP (8br-cGMP). Functional parameters examined included mitogenesis (thymidine incorporation), collagen synthesis (proline incorporation), myofibroblast differentiation (Western blotting for alpha-smooth muscle actin; alpha-SMA) and expression of CTGF (Northern blotting), a TGF-beta(1)-driven immediate early response gene. Serum-stimulated mitogenesis was decreased 27 +/- 4% by 100 microM 8br-cAMP (p < 0.01), 49 +/- 6% by 1,000 microM 8br-cAMP (p < 0.001) and 43 +/- 7% by 1,000 microM 8br-cGMP (p < 0.01). 1,000 microM 8br-cAMP and 8br-cGMP reduced basal collagen synthesis by 80 +/- 5 and 60 +/- 21% respectively (both p < 0.05). Maximum dose of 8br-cAMP but not 8br-cGMP inhibited basal expression of the differentiation marker alpha-SMA by 43 +/- 33 (p < 0.05), resulted in a more rounded cell morphology and reduced expression of CTGF by 39 +/- 24% (p < 0.05). Measurement of mitochondrial activity confirmed that effects were independent of cell toxicity. In conclusion, cyclic nucleotides inhibit fibrogenesis in vitro. Strategies which elevate intracellular cyclic nucleotide concentrations may therefore be therapeutically valuable in preventing the proliferation and activation of fibroblasts in progressive renal disease.

Angiotensin II increases connective tissue growth factor in the kidney

Connective tissue growth factor (CTGF) has been described as a novel fibrotic mediator. CTGF is overexpressed in several kidney diseases and is induced by different factors involved in renal injury. Angiotensin II (AngII) participates in the pathogenesis of kidney damage, contributing to fibrosis; however, whether AngII regulates CTGF in the kidney has not been explored. Systemic infusion of AngII into normal rats for 3 days increased renal CTGF mRNA and protein levels. At day 7, AngII-infused rats presented overexpression of CTGF in glomeruli, tubuli, and renal arteries, as well as tubular injury and elevated fibronectin deposition. Only treatment with an AT(1) receptor antagonist, but not an AT(2), diminished CTGF and fibronectin overexpression and ameliorated tubular damage. In rats with immune complex nephritis, renal overexpression of CTGF was diminished by the ACE inhibitor quinapril, correlated with a diminution in fibrosis. In cultured renal cells (mesangial and tubular epithelial cells) AngII, via AT(1), increased CTGF mRNA and protein production, and a CTGF antisense oligonucleotide decreased AngII-induced fibronectin synthesis. Our data show that AngII regulates CTGF in the kidney and cultured in mesangial and tubular cells. This novel finding suggests that CTGF could be a mediator of the profibrogenic effects of AngII in the kidney.

Glucose-induced fibronectin and collagen type III expression in renal fibroblasts can occur independent of TGF-beta1

BACKGROUND

Various renal cell types have been shown to contribute to the excessive matrix deposition observed in diabetic nephropathy. The present study examined the effect of high ambient glucose and transforming growth factor-beta1 (TGF-beta1) on matrix production by human renal fibroblasts.

METHODS

Human renal fibroblasts (TK173) were used to examine the effects of high glucose and TGF-beta1 on fibronectin and collagen type III expression. Stable transfectants were generated of TK173 cells expressing a dominant negative TGF-beta type II receptor. Matrix components were measured in enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Fibronectin secretion by renal fibroblasts was increased upon exposure to high glucose, but with delayed kinetics compared to TGF-beta1-induced fibronectin. Exposure to high glucose resulted in an increased secretion of latent TGF-beta1. However, treatment with neutralizing pan-specific anti-TGF-beta antibodies could not attenuate the effects of glucose. Furthermore, collagen type III was up-regulated by high glucose, but not by TGF-beta1. Importantly, fibroblasts expressing a dominant negative TGF-beta type II receptor were defective in TGF-beta1-induced fibronectin production, whereas glucose-induced fibronectin and collagen type III were unaffected.

CONCLUSIONS

These data show that in renal fibroblasts exposure to high glucose can increase matrix production independent of endogenous TGF-beta1. Although glucose activation is accompanied by an increased production of latent TGF-beta1, which can have an important role in vivo, the data suggest involvement of alternative growth factors in the mechanism by which hyperglycemic conditions can modulate matrix accumulation in diabetic nephropathy.

Nitric oxide down-regulates connective tissue growth factor in rat mesangial cells

BACKGROUND

Nitric oxide (NO) exerts complex regulatory actions on mesangial cell (MC) biology, such as inhibition of proliferation, adhesion or contractility and induction of apoptosis. In our previous studies the NO-donor S-nitroso-glutathione (GSNO) was found to be a potent inhibitor of MC growth. This effect was mediated at least in part by inhibitory effects of GSNO on the transcription factor early growth response gene-1 (Egr-1) [10]. We therefore were interested in the regulation of gene expression in MC after treatment with NO.

METHODS

To identify the genes that are regulated by NO in MC, gene expression was analyzed by representational difference analysis. Expression of connective tissue growth factor (CTGF) was studied by Northern and Western blot analyses.

RESULTS

Cultured rat MCs treated with GSNO for 8 hours were compared with unstimulated MCs and the CTGF mRNA was found to be down-regulated. The down-regulation was dose-dependent and transient, with a maximum inhibition seen after 6 hours. In parallel, down-regulation of CTGF protein by GSNO was observed by Western blot analysis. Other NO-donors such as S-nitroso-N-acetyl-D,L-penicillamine and spermine-NO showed similar effects. The induction of the inducible NO-synthase by TNF-alpha, IL-1beta and LPS provoked a transient down-regulation of CTGF mRNA, an effect that could be partially overcome by pretreatment with the NOS-inhibitor Nomega-nitro-l-arginine methyl ester. The observed NO-effect could be simulated by treatment with the stable cGMP analog 8br-cGMP, and was abolished by blocking the guanylyl cyclase with the inhibitor NS2028.

CONCLUSION

NO acts as a strong repressor of CTGF expression in cultured rat MC. Thus, in addition to its antiproliferative effects, NO potentially exerts antifibrotic activity by down-regulation of CTGF.

Novel growth factors involved in the pathogenesis of proliferative vitreoretinopathy

AIMS

To determine whether hepatocyte growth factor (HGF) and connective tissue growth factor (CTGF) are expressed in human specimens of proliferative vitreoretinopathy (PVR) and to propose a model of PVR pathogenesis based upon the known activities of these growth factors. Methods Immunohistochemical methods (ABC Elite) were used to demonstrate the presence of HGF and CTGF in cryostat sections of five human PVR membranes.

RESULTS

In each of the five PVR membranes, stromal cells were immunohistochemically positive for both HGF and CTGF. Based upon this information and the known actions of these growth factors, a model of PVR pathogenesis was developed. In this model, injury of the retina induces an inflammatory response that upregulates HGF expression inducing the formation of multilayered groups of migratory retinal pigment epithelial cells (RPE). These RPE, present in a provisional extracellular matrix, come in contact with vitreous containing TGF-beta. The TGF-beta is activated, upregulating expression of CTGF. Under the influence of TGF-beta and CTGF, RPE become myofibroblastic and fibrosis ensues. Retinal traction induces further detachment continuing the cycle of retinal injury.

CONCLUSIONS

HGF and CTGF are expressed in PVR membranes and may play important roles in the pathogenesis of PVR. The expression and function of these growth factors should be critically examined in human PVR specimens, in in vitro cultures of RPE, and in animal models of PVR.

Connective tissue growth factor is secreted through the Golgi and is degraded in the endosome

Connective tissue growth factor (CTGF) is a cysteine-rich heparin-binding polypeptide that promotes proliferation, collagen synthesis, and chemotaxis in mesanchymal cells. When coinjected subcutaneously with transforming growth factor beta (TGFbeta), CTGF promotes sustained fibrosis in rats. However, little is known about the cell biology and structure/functional relationship of CTGF. In particular, no detailed characterization of the subcellular localization of CTGF has occurred, nor have sequences been identified within this protein required for this localization. In this report, using immunofluorescence and Western blot analysis, we show that CTGF is localized to the Golgi apparatus both in dermal fibroblasts and activated hepatic stellate cells. Using these methods, no CTGF was detected in endosomal, plasma membrane, cytosolic or nuclear fractions. Addition of brefeldin A, a drug that disrupts the Golgi, blocks the secretion of CTGF. We further show that the amino-terminal 37 amino acids of CTGF are sufficient to localize a heterologous protein (red fluorescent protein, RFP) to the Golgi. Although within this region of human CTGF is a N-glycosylation site, tunicamycin, which blocks N-linked glycosylation, has no significant effect on CTGF secretion. Surprisingly, mutation of a single amino acid residue, CYS-34, to alanine prevents localization of a CTGF-RFP fusion protein to the Golgi. These results are the first proof that endogenous CTGF is localized to the Golgi apparatus. Furthermore, using exogenously added (125)I-labeled CTGF, we show that CTGF is internalized and rapidly degraded in the endosome. That is, CTGF is quantitatively secreted through the golgi and is degraded in the endosome.

Pathogenesis of diabetic nephropathy: focus on transforming growth factor-beta and connective tissue growth factor

Although considerable improvement in the prognosis of diabetic nephropathy has been achieved in recent years due to intensive insulin and angiotensin-converting enzyme inhibitor treatment, these approaches do not provide complete protection against progression of diabetic nephropathy. An urgent need for additional novel therapies to prevent or further slow the progression of diabetic nephropathy motivated us to provide an up-to-date review with particular emphasis on the potential role of two growth factors--transforming growth factor-beta and connective tissue growth factor--in the pathogenesis of diabetic nephropathy. The most intensively studied to date, transforming growth factor-beta appears to play a central role in the pathogenesis of diabetic nephropathy. Recently, attention has focused on connective tissue growth factor, which mimics the biological activity of transforming growth factor-beta in profibrotic tissue formation. Thus, acting as a downstream mediator of the profibrotic activity of transforming growth factor-beta, connective tissue growth factor may constitute a more specific target for future antifibrotic therapies.

CTGF expression is induced by TGF- beta in cardiac fibroblasts and cardiac myocytes: a potential role in heart fibrosis

Connective tissue growth factor (CTGF) is a cysteine-rich protein induced by transforming growth factor beta (TGF- beta) in connective tissue cells. CTGF can trigger many of the cellular processes underlying fibrosis, such as cell proliferation, adhesion, migration and the synthesis of extracellular matrix; however, its role in acute and chronic cardiac injury is not fully understood. Here, we show that TGF- beta is a specific inducer of CTGF expression in both cardiac fibroblasts and cardiac myocytes. The activity of a CTGF promoter-based reporter construct correlated with endogenous CTGF expression, suggesting that TGF- beta induces CTGF expression most likely by activating its promoter. Upregulation of CTGF coincided with an increase in fibronectin, collagen type I and plasminogen activator inhibitor-1 production. Forskolin, a stimulator of cyclic AMP, blocked TGF- beta induced CTGF expression and reduced the basal level of CTGF, whereas an inhibitor that blocks the MAP kinase signaling pathway (PD 98059) significantly enhanced TGF- beta induced CTGF expression. Furthermore, we found that both TGF- beta and CTGF mRNAs were significantly elevated in the left ventricles and septa of rat hearts 2-16 weeks following myocardial infarction. This correlated well with concomitant increases in fibronectin, and type I and type III collagen mRNA levels in these animal hearts. Significant upregulation of CTGF was also detected in human heart samples derived from patients diagnosed with cardiac ischemia. Based on these findings, we propose that CTGF is an important mediator of TGF- beta signaling in the heart and abnormal expression of this gene could be used as a diagnostic marker for cardiac fibrosis.

Connective tissue growth factor: what's in a name?

Connective tissue growth factor (CTGF) is a member of the recently described CCN gene family which contains CTGF itself, cyr61, nov, elm1, Cop1, and WISP-3. CTGF is transcriptionally activated by several factors although its stimulation by transforming growth factor beta (TGF-beta) has attracted considerable attention. CTGF acts to promote fibroblast proliferation, migration, adhesion, and extracellular matrix formation, and its overproduction is proposed to play a major role in pathways that lead to fibrosis, especially those that are TGF-beta-dependent. This includes fibrosis of major organs, fibroproliferative diseases, and scarring. CTGF also appears to play a role in the extracellular matrix remodeling that occurs in normal physiological processes such as embryogenesis, implantation, and wound healing. However, recent advances have shown that CTGF is involved in diverse autocrine or paracrine actions in several other cell types such as vascular endothelial cells, epithelial cells, neuronal cells, vascular smooth muscle cells, and cells of supportive skeletal tissues. Moreover, in some circumstances CTGF has negative effects on cell growth in that it can be antimitotic and apoptotic. In light of these discoveries, CTGF has been implicated in a diverse variety of processes that include neovascularization, transdifferentiation, neuronal scarring, atherosclerosis, cartilage differentiation, and endochondral ossification. CTGF has thus emerged as a potential important effector molecule in both physiological and pathological processes and has provided a new target for therapeutic intervention in fibrotic diseases.

Cellular and molecular mediators in common pathway mechanisms of chronic renal disease progression

Injury mechanisms activated by the hemodynamic adaptations to nephron loss are considered to represent a final common pathway that underlies the progressive nature of chronic renal disease. In this article, we review experimental evidence that the induction of cell adhesion molecule, cytokine and profibrotic growth factor gene expression and the resultant renal infiltration by inflammatory cells, especially macrophages, are important components of these common pathway mechanisms. Interventions aimed at inhibiting these mechanisms may offer new treatments for slowing or arresting the progression of chronic renal disease.