Identification of human ccn2 (connective tissue growth factor) promoter polymorphisms

ERK and p38 MAPK inhibition controls NF-E2 degradation and profibrotic signaling in renal proximal tubule cells

Aims:

Transforming growth factor-β (TGF-β) mediates fibrotic manifestations of diabetic nephropathy. We demonstrated proteasomal degradation of anti-fibrotic protein, nuclear factor-erythroid derived 2 (NF-E2), in TGF-β treated human renal proximal tubule (HK-11) cells and in diabetic mouse kidneys. The current study examined the role of mitogen-activated protein kinase (MAPK) pathways in mediating NF-E2 proteasomal degradation and stimulating profibrotic signaling in HK-11 cells.

Main methods:

HK-11 cells were pretreated with vehicle or appropriate proteasome and MAPK inhibitors, MG132 (0.5 μM), SB203580 (1 μM), PD98059 (25 μM) and SP600125 (10 μM), respectively, followed by treatment with/without TGF-β (10 ng/ml, 24 h). Cell lysates and kidney homogenates from FVB and OVE26 mice treated with/without MG132 were immunoblotted with appropriate antibodies. pUse vector and pUse-NF-E2 cDNA were transfected in HK-11 cells and effects of TGF-β on JNK MAPK phosphorylation (pJNK) was examined.

Key findings:

We demonstrated activation of p38, ERK, and JNK MAPK pathways in TGF-β treated HK-11 cells. Dual p38 and ERK MAPK blockade prevented TGF-β-induced pSer⁸²Hsp27, fibronectin and connective tissue growth factor (CTGF) expression while preserving NF-E2 expression. Blockade of JNK MAPK inhibited TGF-β-induced CTGF expression without preserving NF-E2 expression. MG132 treatment prevented TGF-β-induced pJNK in HK-11 cells and in type 1 diabetic OVE26 mouse kidneys, demonstrating that TGF-β- and diabetes-induced pJNK occurs downstream of proteasome activation. A direct role for NF-E2 in modulating pJNK activation was demonstrated by NF-E2 over-expression.

Significance:

ERK and p38 MAPK promotes NF-E2 proteasomal degradation while proteasome activation promotes pJNK and profibrotic signaling in renal proximal tubule cells.

Pref-1 induced lung fibroblast differentiation by hypoxia through integrin α5β1/ERK/AP-1 cascade

Chronic obstructive asthma is characterized by airway fibrosis. Hypoxia and connective tissue growth factor (CTGF) play important roles in airway fibrosis. Preadipocyte factor-1 (Pref-1) participates in adipocyte differentiation and liver fibrosis. Herein, we investigated the role of Pref-1 in airway fibrosis in chronic obstructive asthma. We found that Pref-1 was overexpressed in lung tissues from chronic obstructive asthma patients compared to normal subjects. Extracellular matrix proteins were inhibited by Pref-1 small interfering (si)RNA in airway fibroblasts from chronic obstructive asthma patients. Furthermore, ovalbumin induced prominent Pref-1 expression and fibronectin coexpression. Hypoxia induced Pref-1 upregulation and its release into medium of WI-38 cells. Hypoxia-induced CTGF expression was inhibited by Pref-1 siRNA. We also found that Pref-1-stimulated fibrotic protein expressions were reduced by ATN-161, curcumin, U0126, and c-Jun siRNA in WI-38. Furthermore, ATN161 inhibited Pref-1-induced ERK phosphorylation, and ITGA5 siRNA inhibited c-Jun phosphorylation. Moreover, expression of CTGF, Fibronectin, α-SMA, and ERK and c-Jun phosphorylation were all increased in fibroblasts from patients with chronic obstructive asthma. Taken together, these results suggest that Pref-1 participates in airway fibrosis and hypoxia-induced CTGF expression via the integrin receptor α5β1/ERK/AP-1 pathway.

Mycobacterium tuberculosis induces connective tissue growth factor expression through the TLR2-JNK-AP-1 pathway in human lung fibroblasts

Mycobacterium tuberculosis (M.tb) infection in lung causes pulmonary fibrosis, which leads to the irreversible reduction of pulmonary function. Fibrotic protein connective tissue growth factor (CTGF) expression has been confirmed to play a crucial role in lung fibrosis. However, the underlying signal pathway and effect of M.tb on CTGF expression in human lung fibroblasts are unclear. Our results revaled that M.tb caused time- and concentration-dependent increases in CTGF expression in human lung fibroblasts. A mechanistic investigation revealed that M.tb induced CTGF expression through TLR2 but not TLR4. The promoter activity assay indicated that M.tb-induced CTGF activity was mainly controlled by the promoter region at -747 to -184 bp, which contained signal transducer and activator of transcription 3 and activator protein 1 (AP-1) binding sites. Moreover, curcumin (AP-1 inhibitor) restrained M.tb-induced CTGF expression. M.tb also induced increases in AP-1 luciferase activity and DNA binding activity of c-Jun and c-Fos on the CTGF promoter. Furthermore, the knockdown of c-Jun by small interfering RNA attenuated M.tb-induced CTGF expression and AP-1 luciferase activity. A JNK inhibitor (SP600125) and a JNK dominant-negative mutant suppressed M.tb-induced CTGF expression. We also discovered that M.tb could induce the phosphorylation of JNK and c-Jun. Furthermore, SP600125 inhibited M.tb-induced c-Jun phosphorylation and AP-1- luciferase activity. M.tb-induced fibronectin expression was inhibited by anti-CTGF antibody. These results demonstrate that M.tb is activated through TLR2 to induce JNK activation, further increasing the DNA binding activity of c-Jun and c-Fos and finally inducing CTGF expression and extracellular matrix production.-Lee, H.-S., Hua, H.-S., Wang, C.-H., Yu, M.-C., Chen, B.-C., Lin, C.-H. Mycobacterium tuberculosis induces connective tissue growth factor expression through the TLR2-JNK-AP-1 pathway in human lung fibroblasts.

MEKK1, JNK, and SMAD3 mediate CXCL12-stimulated connective tissue growth factor expression in human lung fibroblasts

Background

In idiopathic pulmonary fibrosis, the interaction of CXCL12 and CXC receptor 4 (CXCR4) plays a critical role in lung fibrosis. Connective tissue growth factor (CTGF) overexpression underlies the development of pulmonary fibrosis. Our previous report showed that the Rac1-dependent extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and activator protein (AP)-1 pathways are involved in CXCL12-generated CTGF expression in human lung fibroblasts (WI-38). In present study, we additionally inspected the involvement of mitogen-activated protein kinase kinase kinase 1 (MEKK1)/JNK-dependent SMAD3 in CXCL12-triggered CTGF expression in WI-38 cells.

Methods

WI-38 cells were stimulated with CXCL12 in the absence or presence of specific inhibitors or small interfering RNAs (siRNAs). CTGF expression and signaling transduction molecules were assessed by Western blot, luciferase activity assay, or ChIP assay.

Results

CXCL-12-induced CTGF expression was attenuated by SIS3 (a SMAD3 inhibitor) and SMAD3 siRNA, but not by SB431542 (an activin receptor-like kinase 5, ALK5, inhibitor). CXCL12-stimulated CTGF expression was also attenuated by MEKK1 siRNA. Treatment of cells with CXCL12 caused an increase in SMAD3 phosphorylation at Ser208, translocation to nuclei, SMAD3-luciferase activity, and recruitment of SMAD3 to the CTGF promoter. Stimulation of cells with CXCL12 resulted in increase in JNK phosphorylation at Thr183/Tyr185 and MEKK1 phosphorylation at Thr261. Moreover, CXCL12-mediated SMAD3 phosphorylation or SMAD3-luciferase activity was inhibited by MEKK1 siRNA or SP600125. Finally, CXCL12-mediated JNK phosphorylation was attenuated by MEKK1 siRNA.

Conclusion

In conclusion, results of this study suggest that CXCL12 activates the MEKK1/JNK signaling pathway, which in turn initiates SMAD3 phosphorylation, its translocation to nuclei, and recruitment of SMAD3 to the CTGF promoter, which ultimately induces CTGF expression in human lung fibroblasts.

Induction of Connective Tissue Growth Factor Expression by Hypoxia in Human Lung Fibroblasts via the MEKK1/MEK1/ERK1/GLI-1/GLI-2 and AP-1 Pathways

Several reports have indicated that hypoxia, GLI, and connective tissue growth factor (CTGF) contribute to pulmonary fibrosis in idiopathic pulmonary fibrosis. We investigated the participation of mitogen-activated protein kinase kinase (MEK) kinase 1 (MEKK1)/MEK1/ERK1/GLI-1/2 and activator protein-1 (AP-1) signaling in hypoxia-induced CTGF expression in human lung fibroblasts. Hypoxia time-dependently increased CTGF expression, which was attenuated by the small interfering RNA (siRNA) of GLI-1 (GLI-1 siRNA) and GLI-2 (GLI-2 siRNA) in both human lung fibroblast cell line (WI-38) and primary human lung fibroblasts (NHLFs). Moreover, GLI-1 siRNA and GLI-2 siRNA attenuated hypoxia-induced CTGF-luciferase activity, and the treatment of cells with hypoxia induced GLI-1 and GLI-2 translocation. Furthermore, hypoxia-induced CTGF expression was reduced by an MEK inhibitor (PD98059), MEK1 siRNA, ERK inhibitor (U0126), ERK1 siRNA, and MEKK1 siRNA. Both PD98059 and U0126 significantly attenuated hypoxia-induced CTGF-luciferase activity. Hypoxia time-dependently increased MEKK1, ERK, and p38 MAPK phosphorylation. Moreover, SB203580 (a p38 MAPK inhibitor) also apparently inhibited hypoxia-induced CTGF expression. The treatment of cells with hypoxia induced ERK, GLI-1, or GLI-2 complex formation. Hypoxia-induced GLI-1 and GLI-2 translocation into the nucleus was significantly attenuated by U0126. In addition, hypoxia-induced ERK Tyr204 phosphorylation was impeded by MEKK1 siRNA. Moreover, hypoxia-induced CTGF-luciferase activity was attenuated by cells transfected with AP-1 site mutation in a CTGF construct. Exposure to hypoxia caused a time-dependent phosphorylation of c-Jun, but not of c-Fos. Chromatin immunoprecipitation (ChIP) revealed that hypoxia induced the recruitment of c-Jun, GLI-1, and GLI-2 to the AP-1 promoter region of CTGF. Hypoxia-treated cells exhibited an increase in α-smooth muscle actin (α-SMA) and collagen production, which was blocked by GLI-1 siRNA and GLI-2 siRNA. Overall, these data implied that the MEKK1/MEK1/ERK1/GLI-1/GLI-2, and AP-1 pathways mediated hypoxia-induced CTGF expression in human lung fibroblasts. Furthermore, GLI-1 and GLI-2 found to be involved in hypoxia-induced α-SMA and collagen expression.

Suppressive effect of SATB1 on hepatic stellate cell activation and liver fibrosis in rats

Liver fibrosis is a worldwide clinical issue. Activation of hepatic stellate cells (HSCs) is the central event during liver fibrosis. We investigated the role of SATB1 in HSC activation and liver fibrogenesis. The results show that SATB1 expression is reduced during HSC activation. Additionally, SATB1 inhibits HSC activation, proliferation, migration, and collagen synthesis. Furthermore, CTGF, a pro-fibrotic agent, is also significantly inhibited by SATB1 through the Ras/Raf-1/MEK/ERK/Ets-1 pathway. In vivo, SATB1 deactivates HSCs and attenuates fibrosis in TAA-induced fibrotic rat livers. These data indicate that SATB1 plays an important role in HSC activation and liver fibrosis.

Probucol attenuates ethanol-induced liver fibrosis in rats by inhibiting oxidative stress, extracellular matrix protein accumulation and cytokine production

1. Liver fibrosis is characterized by excessive accumulation of extracellular matrix (ECM) proteins in the liver. Probucol, a lipid-lowering drug, was found to prevent liver injury in rats treated with carbon tetrachloride (CCl4 ). In the present study, we investigated whether probucol has protective effect against liver fibrosis in rats treated with ethanol and CCl4 . 2. Thirty rats were randomly divided into five groups. Groups I and II served as the normal control and the model of liver fibrosis, respectively. Groups III-V were treated with probucol at a doses of 250, 500 and 1000 mg/kg, respectively. Rats in Group II were fed a complex diet that includes alcohol, corn oil and pyrazole, and were injected intraperitoneally with CCl4 to induce hepatic fibrosis. Blood was obtained to assess markers of liver function. Liver samples were collected to evaluate mRNA and protein expression, histological changes and oxidative stress. 3. Probucol significantly attenuated the histological changes induced by ethanol + CCl4 and improved liver function. Expression levels of α-smooth muscle actin and collagen I was decreased in the probucol-treated groups. Moreover, probucol markedly suppressed increases in oxidative stress, ECM protein accumulation and cytokine production induced by ethanol + CCl4 . Finally, probucol inhibited activation of the extracellular signal-regulated kinase signalling pathway induced by ethanol + CCl4 . 4. Our findings reveal that probucol attenuates ethanol + CCl4 -induced liver fibrosis by inhibiting oxidative stress, ECM protein accumulation and cytokine production. These data suggest that probucol may be useful for the prevention and treatment of hepatic fibrosis.

CXCL12 induces connective tissue growth factor expression in human lung fibroblasts through the Rac1/ERK, JNK, and AP-1 pathways

CXCL12 (stromal cell-derived factor-1, SDF-1) is a potent chemokine for homing of CXCR4+ fibrocytes to injury sites of lung tissue, which contributes to pulmonary fibrosis. Overexpression of connective tissue growth factor (CTGF) plays a critical role in pulmonary fibrosis. In this study, we investigated the roles of Rac1, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and activator protein-1 (AP-1) in CXCL12-induced CTGF expression in human lung fibroblasts. CXCL12 caused concentration- and time-dependent increases in CTGF expression and CTGF-luciferase activity. CXCL12-induced CTGF expression was inhibited by a CXCR4 antagonist (AMD3100), small interfering RNA of CXCR4 (CXCR4 siRNA), a dominant negative mutant of Rac1 (RacN17), a mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor (PD98059), a JNK inhibitor (SP600125), a p21-activated kinase inhibitor (PAK18), c-Jun siRNA, and an AP-1 inhibitor (curcumin). Treatment of cells with CXCL12 caused activations of Rac1, Rho, ERK, and c-Jun. The CXCL12-induced increase in ERK phosphorylation was inhibited by RacN17. Treatment of cells with PD98059 and SP600125 both inhibited CXCL12-induced c-Jun phosphorylation. CXCL12 caused the recruitment of c-Jun and c-Fos binding to the CTGF promoter. Furthermore, CXCL12 induced an increase in α-smooth muscle actin (α-SMA) expression, a myofibroblastic phenotype, and actin stress fiber formation. CXCL12-induced actin stress fiber formation and α-SMA expression were respectively inhibited by AMD3100 and CTGF siRNA. Taken together, our results suggest that CXCL12, acting through CXCR4, activates the Rac/ERK and JNK signaling pathways, which in turn initiates c-Jun phosphorylation, and recruits c-Jun and c-Fos to the CTGF promoter and ultimately induces CTGF expression in human lung fibroblasts. Moreover, overexpression of CTGF mediates CXCL12-induced α-SMA expression.

Endothelin-1 induces connective tissue growth factor expression in human lung fibroblasts by ETAR-dependent JNK/AP-1 pathway

Endothelin-1 (ET-1) acts as a key mediator of vasoconstriction and tissue repair. Overproduction of connective tissue growth factor (CTGF) underlies the development of lung fibrosis. ET-1 induces expression of matrix-associated genes in lung fibroblasts, however, little is known about the signaling pathway of CTGF expression caused by ET-1. In this study, we found that ET-1 caused concentration- and time-dependently increases in CTGF expression in human embryonic lung fibroblast cell line (WI-38). ET-1-induced CTGF expression was inhibited by BQ123 (ETAR antagonist), but not BQ788 (ETBR antagonist). Moreover, ET-1-induced CTGF expression was significantly reduced by JNK inhibitor (SP600125), the dominant-negative mutants of JNK1/2 (JNK1/2 DN), and AP-1 inhibitor (curcumin). ET-1 induced phosphorylations of JNK and c-Jun in time-dependent manners. AP-1 luciferase activity was concentration-dependently increased by ET-1, and this effect was attenuated by SP600125. We also found that ET-1-induced CTGF expression was most controlled by the AP-1 binding region of CTGF promoter. ET-1-indiced CTGF luciferase activity was predominately controlled by the sequence -747 to -408 bp upstream of the transcription start site on the human CTGF promoter. Furthermore, ET-1 caused the formation of AP-1-specific DNA-protein complex and the recruitment of c-Jun to the CTGF promoter. Moreover, we found that ET-1 induced α-smooth muscle actin (α-SMA) expression, which was inhibited by BQ123, SP600125, curcumin, and anti-CTGF antibody. These results suggest that ET-1 stimulates expressions of CTGF and α-SMA through ETAR/JNK/AP-1 signaling pathway, and CTGF is required for ET-1-induced α-SMA expression in human lung fibroblasts.

Protective effect of statin therapy on connective tissue growth factor induction by diabetes in vivo and high glucose in vitro

Transcriptional activity of connective tissue growth factor (CTGF) promoter in transfected HEK293 cells was determined by luciferase assays. Secreted CTGF in cultured human mesangial cells was measured by enzyme-linked immunosorbent assay (ELISA). CTGF in urine and plasma was also measured in 405 subjects with/without type 2 diabetes. Our results showed that high glucose significantly increased transcription of the promoter in the transfected cells by more than 2.5-folds (p < 0.0005). CTGF secretion was induced by high glucose in the cells (p < 0.0005). These increases were inhibited by simvastatin. Urine CTGF was positively associated with plasma CTGF in both type 2 diabetes (p = 0.0005) and controls (p = 0.01). Urine CTGF levels in patients with macroalbuminuria were significantly higher than patients without macroalbuminuria (p < 0.05). In conclusion, our in vitro study suggests that statin may have a renal-protective effect through the inhibition of CTGF expression. Urine CTGF may be a good marker for the prediction of diabetic nephropathy.

Transcriptional network analysis for the regulation of left ventricular hypertrophy and microvascular remodeling

Hypertension and cardiomyopathies share maladaptive changes of cardiac morphology, eventually leading to heart failure. These include left ventricular hypertrophy (LVH), myocardial fibrosis, and structural remodeling of coronary microcirculation, which is the morphologic hallmark of coronary microvascular dysfunction. To pinpoint the complex molecular mechanisms and pathways underlying LVH-associated cardiac remodeling independent of blood pressure effects, we employed gene network approaches to the rat heart. We used the Spontaneously Hypertensive Rat model showing many features of human hypertensive cardiomyopathy, for which we collected histological and histomorphometric data of the heart and coronary vasculature, and genome-wide cardiac gene expression. Here, we provide a large catalogue of gene co-expression networks in the heart that are significantly associated with quantitative variation in LVH, microvascular remodeling, and fibrosis-related traits. Many of these networks were significantly conserved to human idiopathic and/or ischemic cardiomyopathy patients, suggesting a potential role for these co-expressed genes in human heart disease.

Thrombin-induced CCN2 expression in human lung fibroblasts requires the c-Src/JAK2/STAT3 pathway

Thrombin might activate c-Src to induce JAK2 activation, which causes STAT3 activation, inducing CCN2 expression in human lung fibroblasts.

Thrombin is a multifunctional serine protease and an important fibrotic mediator that induces CCN2 expression. We previously showed that thrombin induces CCN2 expression via an ASK1-dependent JNK/AP-1 pathway in human lung fibroblasts. In this study, we further investigated the roles of c-Src, JAK2, and STAT3 in thrombin-induced CCN2 expression. Thrombin-induced CCN2 expression and CCN2-Luc activity were attenuated by a JAK inhibitor (AG490) and JAK2DN, STAT3DN, and the STAT decoy ODN. Moreover, transfection of cells with a CCN2-mtSTAT-Luc construct inhibited thrombin-induced CCN2-Luc activity. Treatment of cells with thrombin caused JAK2 phosphorylation at Tyr1007/1008 and STAT3 phosphorylation at Tyr705 in time-dependent manners. Thrombin-induced STAT3 phosphorylation was inhibited by AG490 and JAK2DN. Thrombin-induced STAT3 binding to the CCN2 promoter was analyzed by a DNA-binding affinity pull-down assay. In addition, thrombin-induced CCN2 expression and CCN2-Luc activity were inhibited by c-SrcDN and PP2 (an Src inhibitor). Transfection of cells with c-SrcDN also inhibited thrombin-induced JAK2 and STAT3 phosphorylation. Taken together, these results indicate that thrombin might activate c-Src to induce JAK2 activation, which in turn, causes STAT3 activation, and finally induces CCN2 expression in human lung fibroblasts.

The CTGF gene -945 G/C polymorphism is not associated with cardiac or kidney complications in subjects with type 2 diabetes

Background

Connective tissue growth factor (CTGF) has been implicated in the cardiac and kidney complications of type 2 diabetes, and the CTGF −945 G/C polymorphism is associated with susceptibility to systemic sclerosis, a disease characterised by tissue fibrosis. This study investigated the association of the CTGF −945 G/C promoter variant with cardiac complications (left ventricular (LV) hypertrophy (LVH), diastolic and systolic dysfunction) and chronic kidney disease (CKD) in type 2 diabetes.

Methods

The CTGF −945 G/C polymorphism (rs6918698) was examined in 495 Caucasian subjects with type 2 diabetes. Cardiac structure and function were assessed by transthoracic echocardiography. Kidney function was assessed using estimated glomerular filtration rate (eGFR) and albuminuria, and CKD defined as the presence of kidney damage (decreased kidney function (eGFR <60 ml/min/1.73 m²) or albuminuria).

Results

The mean age ± SD of the cohort was 62 ± 14 years, with a body mass index (BMI) of 31 ± 6 kg/m² and median diabetes duration of 11 years [25^th, 75^th interquartile range; 5, 18]. An abnormal echocardiogram was present in 73% of subjects; of these, 8% had LVH alone, 74% had diastolic dysfunction and 18% had systolic ± diastolic dysfunction. CKD was present in 42% of subjects. There were no significant associations between the CTGF −945 G/C polymorphism and echocardiographic parameters of LV mass or cardiac function, or kidney function both before and after adjustment for covariates of age, gender, BMI, blood pressure and hypertension. CTGF −945 genotypes were not associated with the cardiac complications of LVH, diastolic or systolic dysfunction, nor with CKD.

Conclusions

In Caucasians with type 2 diabetes, genetic variation in the CTGF −945 G/C polymorphism is not associated with cardiac or kidney complications.

Thrombin induced connective tissue growth factor expression in rat vascular smooth muscle cells via the PAR-1/JNK/AP-1 pathway

AIM

To investigate the signaling pathways involved in thrombin-induced connective tissue growth factor (CTGF) expression in rat vascular smooth muscle cells (VSMCs).

METHODS

Experiments were preformed on primary rat aortic smooth muscle cells (RASMCs) and a rat VSMC line (A10). CTGF protein levels were measured using Western blotting. Luciferase reporter genes and dominant negative mutants (DNs) were used to investigate the signaling pathways mediating the induction of CTGF expression by thrombin.

RESULTS

Thrombin (0.3-3.0 U/mL) caused a concentration- and time-dependent increase in CTGF expression in both RASMCs and A10 cells. Pretreating A10 cells with the protease-activated receptor 1 (PAR-1) antagonist SCH79797 (0.1 μmol/L) significantly blocked thrombin-induced CTGF expression, while the PAR-4 antagonist tcY-NH(2) (30 μmol/L) had no effect. The PAR-1 agonist SFLLRN-NH(2) (300 μmol/L) induced CTGF expression, while the PAR-4 agonist GYPGQV-NH(2) (300 μmol/L) had no effect. Thrombin (1 U/mL) caused time-dependent phosphorylation of c-Jun N-terminal kinase (JNK). Pretreating with the JNK inhibitor SP600125 (3-30 μmol/L) or transfection with DNs of JNK1/2 significantly attenuated thrombin-induced CTGF expression. Thrombin (0.3-3.0 U/mL) increased activator protein-1 (AP-1)-luciferase activity, which was inhibited by the JNK inhibitor SP600125. The AP-1 inhibitor curcumin (1-10 μmol/L) concentration-dependently attenuated thrombin-induced CTGF expression.

CONCLUSION

Thrombin acts on PAR-1 to activate the JNK signaling pathway, which in turn initiates AP-1 activation and ultimately induces CTGF expression in VSMCs.

Rad GTPase inhibits cardiac fibrosis through connective tissue growth factor

AIMS

Our previous studies documented that Rad (Ras associated with diabetes), a member of the RGK (Rad, Gem, and Kir) family of Ras-related small G protein, is significantly decreased in human failing hearts and plays an important role in attenuating cardiac hypertrophy. The goal of this study is to identify the effect of Rad on cardiac fibrosis and the underlying mechanisms.

METHODS AND RESULTS

Rad knockout (KO) mice showed more severe cardiac fibrosis compared with wild-type littermate controls as detected by Sirius Red staining. Western blot analyses demonstrated that the expression of connective tissue growth factor (CTGF), a key mediator of fibrosis, increased dramatically in Rad KO mice. Overexpression of Rad in cultured neonatal cardiomyocytes suppressed both basal and transforming growth factor-β1-induced CTGF expression. Elevated CTGF expression was observed in cardiomyocytes when Rad was reduced by RNA interference. Moreover, cardiac fibroblasts produced greater extracellular matrix (ECM) when stimulated with conditioned medium from Rad-knockdown cardiomyocytes. ECM production was completely abolished by adding a CTGF-neutralizing antibody into the medium. CCAAT/enhancer-binding protein δ (C/EBP-δ) was demonstrated to activate CTGF in cardiomyocytes. Chromatin immunoprecipitation assay and co-immunoprecipitation further demonstrated that Rad inhibited the binding of C/EBP-δ to the CTGF promoter via direct interaction with C/EBP-δ.

CONCLUSION

Our data reveal that Rad deficiency can lead to cardiac fibrosis. Rad inhibits CTGF expression through binding with C/EBP-δ, thus regulating ECM production in the heart. This study suggests a potential link between decreased Rad levels and increased cardiac fibrosis in human failing hearts.

Connective tissue growth factor reacts as an IL-6/STAT3-regulated hepatic negative acute phase protein

AIM

To investigate the mechanisms involved in a possible modulator role of interleukin (IL)-6 signalling on CYR61-CTGF-NOV (CCN) 2/connective tissue growth factor (CTGF) expression in hepatocytes (PC) and to look for a relation between serum concentrations of these two parameters in patients with acute inflammation.

METHODS

Expression of CCN2/CTGF, p-STAT3, p-Smad3/1 and p-Smad2 was examined in primary freshly isolated rat or cryo-preserved human PC exposed to various stimuli by Western blotting, electrophoretic mobility shift assay (EMSA), reporter-gene-assays and reverse-transcriptase polymerase chain reaction.

RESULTS

IL-6 strongly down-regulated CCN2/CTGF protein and mRNA expression in PC, enhanceable by extracellular presence of the soluble IL-6 receptor gp80, and supported by an inverse relation between IL-6 and CCN2/CTGF concentrations in patients' sera. The inhibition of TGFβ1 driven CCN2/CTGF expression by IL-6 did not involve a modulation of Smad2 (and Smad1/3) signalling. However, the STAT3 SH2 domain binding peptide, a selective inhibitor of STAT3 DNA binding activity, counteracted the inhibitory effect of IL-6 on CCN2/CTGF expression much more pronounced than pyrrolidine-dithiocarbamate, an inhibitor primarily of STAT3 phosphorylation. An EMSA confirmed STAT3 binding to the proposed proximal STAT binding site in the CCN2/CTGF promoter.

CONCLUSION

CCN2/CTGF is identified as a hepatocellular negative acute phase protein which is down-regulated by IL-6 via the STAT3 pathway through interaction on the DNA binding level.

Janus kinase 2/signal transducers and activators of transcription signal inhibition regulates protective effects of probucol on mesangial cells treated with high glucose

Probucol is a cholesterol-lowering drug with an anti-proliferative effect. Excessive growth of glomerular mesangial cells and overexpression of transforming growth factor-beta1 (TGF-beta1) and connective tissue growth factor (CTGF) are the pathological features of diabetic nephropathy. In this study, human mesangial cells (HMCs) treated with high glucose showed the above-mentioned features through the activation of Janus kinase 2 (JAK2)/signal transducers and activators of transcription (STAT) pathway. Probucol can suppress cell proliferation, down-regulate mRNA and protein levels of TGF-beta1 and CTGF in HMCs treated with high glucose. Phosphorylation of JAK2, STAT1 and STAT3 caused by high glucose was obviously prevented in HMCs pretreated with probucol, indicating that the protective effect of probucol on HMCs might be through the inhibition of JAK2/STAT pathway. Therefore, probucol could be a potential therapeutic agent for diabetic nephropathy, and this paper provides new insights into the molecular mechanisms underlying probucol's effects.

Genetic variant in the promoter of connective tissue growth factor gene confers susceptibility to nephropathy in type 1 diabetes

BACKGROUND The evidence for genetic susceptibility in the pathogenesis of diabetic nephropathy is well recognised, but the genes involved remain to be identified. It is hypothesised that mutations within the gene encoding connective tissue growth factor (CTGF/CCN2) will increase the propensity of diabetic subjects to develop nephropathy. METHODS AND RESULTS Genomic screening was performed for single nucleotide polymorphisms (SNPs) within the CTGF gene in 862 subjects from the DCCT/EDIC cohort of type 1 diabetes. A novel SNP was identified in the promoter region that changes a C-G at the position -20. The frequency of GG genotype in microalbuminuric patients (albumin excretion rate (AER) >40 mg/24 h) is significantly greater than diabetics with AER <40 mg/24 h, p<0.0001. The relative risk (RR) to develop microalbuminuria in diabetic subjects with the polymorphism is 3X higher than diabetic subjects without the polymorphism (RR 3.142, 95% CI 1.9238 to 5.1249; p<0.05). Kaplan-Meier survival curves demonstrated that the GG genotype group developed microalbuminuria and macroalbuminuria at a more rapid rate than the GC or CC genotypes. Functional studies demonstrated that the basal activity of the substituted allele/promoter (-20 GG allele) was significantly greater than that of the wild type promoter (-20 CC genotype). This higher level of basal activity of substituted allele CTGF/CCN2 promoter was abrogated upon suppression of Smad1 levels, indicating that SNP region in the CTGF/CCN2 promoter plays a vital role in the gene expression. CONCLUSIONS These findings provide the first evidence that variants within the promoter region of the CTGF/CCN2 gene predisposes diabetic subjects to develop albuminuria and demonstrate that Smad1 [corrected] controls the expression of CTGF/CCN2 promoter through this region.

Relationship between oxidative stress and inflammatory cytokines in diabetic nephropathy

The prevalence of diabetes has dramatically increased worldwide due to the vast increase in the obesity rate. Diabetic nephropathy is one of the major complications of type 1 and type 2 diabetes and it is currently the leading cause of end-stage renal disease. Hyperglycemia is the driving force for the development of diabetic nephropathy. It is well known that hyperglycemia increases the production of free radicals resulting in oxidative stress. While increases in oxidative stress have been shown to contribute to the development and progression of diabetic nephropathy, the mechanisms by which this occurs are still being investigated. Historically, diabetes was not thought to be an immune disease; however, there is increasing evidence supporting a role for inflammation in type 1 and type 2 diabetes. Inflammatory cells, cytokines, and profibrotic growth factors including transforming growth factor-β (TGF-β), monocyte chemoattractant protein-1 (MCP-1), connective tissue growth factor (CTGF), tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1), interleukin-6 (IL-6), interleukin-18 (IL-18), and cell adhesion molecules (CAMs) have all been implicated in the pathogenesis of diabetic nephropathy via increased vascular inflammation and fibrosis. The stimulus for the increase in inflammation in diabetes is still under investigation; however, reactive oxygen species are a primary candidate. Thus, targeting oxidative stress-inflammatory cytokine signaling could improve therapeutic options for diabetic nephropathy. The current review will focus on understanding the relationship between oxidative stress and inflammatory cytokines in diabetic nephropathy to help elucidate the question of which comes first in the progression of diabetic nephropathy, oxidative stress, or inflammation.

Inflammatory cytokines as predictive markers for early detection and progression of diabetic nephropathy

Diabetic nephropathy is a major complication of diabetes mellitus and the leading cause of end-stage renal disease. Both hyperglycemia and hypertension (systemic and/or intraglomerular) are established causal factors for diabetic nephropathy. Nonetheless, there is growing evidence that activated innate immunity and inflammation are also contributing factors to the pathogenesis of diabetic nephropathy. This notion is based on increasing evidence indicating that both cytokines-chemokines and pro-fibrotic growth factors are important players in the progression of diabetic nephropathy, effectively accelerating and exacerbating inflammatory and fibrotic processes leading to end-stage renal disease. In this review, we focus on several predominant cytokines-chemokines as potential predictive markers for diabetic nephropathy. These cytokines-chemokines may also be helpful as biomarkers to monitor the progression of the disease and the impact of interventional modalities aimed at halting eventual manifestation of end-stage renal disease in diabetic patients.

Validation of connective tissue growth factor (CTGF/CCN2) and its gene polymorphisms as noninvasive biomarkers for the assessment of liver fibrosis

Clinical and experimental studies have demonstrated that connective-tissue growth factor (CTGF) expression is increased in fibrotic human liver and experimental animal models of liver fibrogenesis. CTGF has been linked to transforming growth factor-beta (TGF-beta) pathways in fibroproliferative diseases and specific polymorphisms within the CTGF gene may predispose for fibrosis in systemic sclerosis. As CTGF is detectable in various human fluids (serum, plasma and urine), it may provide information about fibrotic remodelling processes and reflect hepatic TGF-beta bioactivity. We established a novel ELISA for the measurement of serum CTGF and tested its clinical value in patients with chronic hepatitis C virus (HCV) infection and chronic liver disease (CLD). HCV infected patients (n = 138) had significantly higher serum CTGF levels than healthy controls. CTGF was linked to the histological degree of liver fibrosis. To expand the results to other aetiologies, a separate cohort of CLD patients (n = 129) was evaluated, showing higher serum CTGF than healthy controls and again an association with advanced stages of liver cirrhosis (Child B and C). Although independent of the underlying aetiology, serum CTGF was most powerful in indicating fibrosis/advanced disease states in HCV-related disorders. The genotyping of six polymorphisms (rs6917644, rs9399005, rs6918698, rs9493150, rs2151532 and rs11966728) covering the CTGF locus in 365 patients suffering from chronic hepatitis C revealed that none of these polymorphisms showed a genotypic or allelic association with the severity of hepatic fibrosis. Taken together, serum CTGF is suitable for determination of hepatic fibrosis and most powerful in patients with chronic HCV infection.

Hypoxia interferes with connective tissue growth factor (CTGF) gene expression in human proximal tubular cell lines

BACKGROUND

Hypoxia plays an important role in kidney injury. By the stabilization of the transcription factor HIF-1, hypoxia affects gene expression also in tubular epithelial cells. Increased expression of connective tissue growth factor (CTGF) is observed in different kidney diseases and is associated with deteriorating renal function. Therefore, we hypothesized that the expression of CTGF might be modulated under hypoxic conditions.

METHODS

The human proximal tubular epithelial cell lines HK-2 and HKC-8 were treated with reduced oxygen tension (1% O(2)) or the hypoxia mimetic dimethyloxalyl glycine (DMOG). CTGF was analysed by Western blotting, real-time RT-PCR and luciferase gene expression assays.

RESULTS

Exposure of HK-2 or HKC-8 cells to hypoxia or treatment with DMOG for up to 24 h reduced cellular as well as secreted CTGF protein synthesis. Downregulation was also detectable at the mRNA level and was confirmed by reporter gene assays. Hypoxic repression of CTGF synthesis was dependent on HIF-1, as shown by HIF-1alpha knockdown by siRNA. Furthermore, exposure to hypoxia reduced CTGF synthesis in response to TGF-beta. A negative correlation between HIF-1alpha accumulation and CTGF synthesis was also observed in renal cell carcinoma cells (RCC4 and RCC10). Reexpression of von Hippel-Lindau protein reduced HIF-1alpha and increased CTGF synthesis.

CONCLUSIONS

We provide evidence that hypoxia inhibits CTGF synthesis in human proximal tubular epithelial cells, involving HIF-1alpha. Under hypoxic conditions, induction of CTGF by TGF-beta was repressed. The reduced synthesis of the profibrotic factor CTGF may contribute to a potential protective effect of hypoxic preconditioning in acute renal injury.

Connective tissue growth factor: a fibrogenic master switch in fibrotic liver diseases

Connective tissue growth factor (CTGF=CCN2), one of six members of cysteine-rich, secreted, heparin-binding proteins with a modular structure, is recognized as an important player in fibrogenic pathways as deduced from findings in non-hepatic tissues and emerging results from liver fibrosis. Collectively, the data show strongly increased expression in fibrosing tissues and transforming growth factor (TGF-beta)-stimulated expression in hepatocytes, biliary epithelial cells and stellate cells. Functional activity as a mediator of fibre-fibre, fibre-matrix and matrix-matrix interactions, as an enhancer of profibrogenic TGF-beta and several secondary effects owing to TGF-beta enhancement, and as a down-modulator of the bioactivity of bone morphogenetic protein-7 has been proposed. By changing the activity ratio of TGF-beta to its antagonist bone-morphogenetic protein-7, CTGF is proposed as a fibrogenic master switch for epithelial-mesenchymal transition. Consequently, knockdown of CTGF considerably attenuates experimental liver fibrosis. The spill-over of CTGF from the liver into the blood stream proposes this protein as a non-invasive reporter of TGF-beta bioactivity in this organ. Indeed, CTGF-levels in sera correlate significantly with fibrogenic activity. The data suggest CTGF as a multifaceted regulatory protein in fibrosis, which offers important translational aspects for diagnosis and follow-up of hepatic fibrogenesis and as a target for therapeutic interventions. In addition, CTGF-promoter polymorphism might be of importance as a prognostic genetic marker to predict the progression of fibrosis.

Molecular requirements for induction of CTGF expression by TGF-beta1 in primary osteoblasts

Connective tissue growth factor (CTGF/CCN2) is a cysteine rich, extracellular matrix protein that acts as an anabolic growth factor to regulate osteoblast differentiation and function. In osteoblasts, CTGF is induced by TGF-beta1 where it acts as a downstream mediator of TGF-beta1 induced matrix production. The molecular mechanisms that control CTGF induction by TGF-beta1 in osteoblasts are not known. To assess the role of individual Smads in mediating the induction of CTGF by TGF-beta1, we used specific Smad siRNAs to block Smad expression. These studies demonstrated that Smads 3 and 4, but not Smad 2, are required for TGF-beta1 induced CTGF promoter activity and expression in osteoblasts. Since the activation of MAPKs (Erk, Jnk and p38) by TGF-beta1 is cell type specific, we were interested in determining the role of individual MAPKs in TGF-beta1 induction of CTGF promoter activity and expression. Using dominant negative (DN) mutants for Erk, Jnk and p38, we demonstrated that the expression of DN-Erk caused a significant inhibition of TGF-beta1 induced CTGF promoter activity. In contrast, the expression of DN-p38 or DN-Jnk failed to inhibit activation of CTGF promoter activity. To confirm the vital role of Erk, we used the Erk inhibitor (PD98059) to block its activation, demonstrating that it prevented TGF-beta1 activation of the CTGF promoter and up-regulation of CTGF expression in osteoblasts. Since Src can also act as a downstream signaling effector for TGF-beta in some cell types, we determined its role in TGF-beta1 induction of CTGF in osteoblasts. Treatment of osteoblasts with a Src family kinase inhibitor, PP2, or the expression of two independent kinase-dead Src mutant constructs caused significant inhibition of TGF-beta1 induced CTGF promoter activity and expression. Additionally, blocking Src activation prevented Erk activation by TGF-beta1 demonstrating a role for Src as an upstream mediator of Erk in regulating CTGF expression in osteoblasts. To investigate the involvement of the TGF-beta1 response element (TRE) and the SMAD binding element (SBE) in CTGF induction, we cloned the rat CTGF proximal promoter (-787 to +1) containing the TRE and SBE motifs into a pGL3-Luciferase reporter construct. Using a combination of CTGF promoter deletion constructs and site-directed mutants, we demonstrated the unique requirement of both the TRE and SBE for CTGF induction by TGF-beta1 in osteoblasts. Electro-mobility shift assays using specific probes containing the TRE, SBE or both showed TGF-beta1 inducible complexes that can be ablated by mutation of the respective motif, confirming their requirement for TGF-beta1 induced CTGF promoter activity. In conclusion, these studies demonstrate that CTGF induction by TGF-beta1 in osteoblasts involves Smads 3 and 4, the Erk and Src signaling pathways, and requires both the TRE and SBE motifs in the CTGF proximal promoter.

Transforming growth factor-beta1 (TGFbeta1) stimulates connective tissue growth factor (CCN2/CTGF) expression in human gingival fibroblasts through a RhoA-independent, Rac1/Cdc42-dependent mechanism: statins with forskolin block TGFbeta1-induced CCN2/CTGF expression

Regulation of connective tissue growth factor (CCN2/CTGF) in gingival fibroblasts is unique and may provide therapeutic opportunities to treat oral fibrotic diseases. RhoA was previously implicated in mediating the expression of CCN2/CTGF. We now present evidence that Rho family GTPases Rac1 and Cdc42 are the principal mediators of the transforming growth factor-beta1 (TGFbeta1)-stimulated expression of CCN2/CTGF in primary human gingival fibroblasts. TGFbeta1 does not stimulate RhoA activation in gingival fibroblasts, and the overexpression of dominant-negative RhoA does not reduce CCN2/CTGF expression in response to TGFbeta1. In contrast, the overexpression of dominant-negative forms of Cdc42 or Rac1 results in a dramatic reduction of CCN2/CTGF protein levels. Lovastatin and a geranylgeranyltransferase inhibitor reduce the TGFbeta1-stimulated levels of CCN2/CTGF protein by approximately 75 and 100%, respectively. We previously demonstrated that JNK1 phosphorylation by TGFbeta1 is also critical for TGFbeta1-induced CCN2/CTGF expression, and forskolin partially reduces levels of phosphorylated JNK1. Inhibition of geranylgeranyltransferase has no effect on levels of JNK phosphorylation in response to TGFbeta1 suggesting Rho-GTPases act independently of JNK1. The combination of lovastatin and forskolin results in a greater inhibitory effect than each agent alone and reduces CCN2/CTGF mRNA and protein expression by greater than 90%. This novel combination has additive inhibitory effects on the TGFbeta1-stimulated expression of CCN2/CTGF in human gingival fibroblasts through the simultaneous disruption of Rho- and JNK1-mediated pathways, respectively. This combination of available therapeutic compounds may therefore be useful in designing treatment strategies for oral fibrotic conditions in which gingival CCN2/CTGF is elevated.

Actin-dependent regulation of connective tissue growth factor

Expression of connective tissue growth factor (CTGF) in endothelial cells is modulated by shear stress affecting the organization of the cytoskeleton. The molecular connection between alterations of actin and CTGF expression was investigated in human umbilical vein endothelial cells (HUVEC) and a microvascular endothelial cell line. Overexpression of nonpolymerizable monomeric actin R62D interfered with stress fiber formation in HUVEC and concomitantly reduced immunoreactive CTGF. In microvascular endothelial cells, flow-dependent upregulation of CTGF was prevented by this actin mutant. In contrast, overexpression of actin S14C strengthened filamentous actin and increased CTGF expression. These data indicated an inverse relationship between CTGF expression and monomeric actin. Coexpression of the mutant actins and different CTGF promoter constructs revealed an actin-sensitive site between 3 and 4.5 kb of the CTGF promoter. A CArG-like box at −3791 bp was responsible for actin-dependent CTGF induction as shown by mutagenesis. Overexpression of actin S14C activated the nonmutated promoter significantly more strongly than the mutated promoter. Actin polymerization is regulated by the small GTPase RhoA and activation of serum response factor (SRF). Overexpression of constitutively active RhoA or SRF significantly increased CTGF protein synthesis. The 4.5-kb promoter construct, but not the construct with a mutation in the CArG box, was activated by SRF or RhoA, providing evidence for a functional role of this site in CTGF induction. These findings provide novel evidence that monomeric actin is the connecting link between alterations in the cytoskeleton and CTGF gene expression and demonstrate the importance of SRF in regulating CTGF transcription.

Heart valve tissue engineering: concepts, approaches, progress, and challenges

Potential applications of tissue engineering in regenerative medicine range from structural tissues to organs with complex function. This review focuses on the engineering of heart valve tissue, a goal which involves a unique combination of biological, engineering, and technological hurdles. We emphasize basic concepts, approaches and methods, progress made, and remaining challenges. To provide a framework for understanding the enabling scientific principles, we first examine the elements and features of normal heart valve functional structure, biomechanics, development, maturation, remodeling, and response to injury. Following a discussion of the fundamental principles of tissue engineering applicable to heart valves, we examine three approaches to achieving the goal of an engineered tissue heart valve: (1) cell seeding of biodegradable synthetic scaffolds, (2) cell seeding of processed tissue scaffolds, and (3) in-vivo repopulation by circulating endogenous cells of implanted substrates without prior in-vitro cell seeding. Lastly, we analyze challenges to the field and suggest future directions for both preclinical and translational (clinical) studies that will be needed to address key regulatory issues for safety and efficacy of the application of tissue engineering and regenerative approaches to heart valves. Although modest progress has been made toward the goal of a clinically useful tissue engineered heart valve, further success and ultimate human benefit will be dependent upon advances in biodegradable polymers and other scaffolds, cellular manipulation, strategies for rebuilding the extracellular matrix, and techniques to characterize and potentially non-invasively assess the speed and quality of tissue healing and remodeling.

Engineering complex tissues

This article summarizes the views expressed at the third session of the workshop "Tissue Engineering--The Next Generation," which was devoted to the engineering of complex tissue structures. Antonios Mikos described the engineering of complex oral and craniofacial tissues as a "guided interplay" between biomaterial scaffolds, growth factors, and local cell populations toward the restoration of the original architecture and function of complex tissues. Susan Herring, reviewing osteogenesis and vasculogenesis, explained that the vascular arrangement precedes and dictates the architecture of the new bone, and proposed that engineering of osseous tissues might benefit from preconstruction of an appropriate vasculature. Jennifer Elisseeff explored the formation of complex tissue structures based on the example of stratified cartilage engineered using stem cells and hydrogels. Helen Lu discussed engineering of tissue interfaces, a problem critical for biological fixation of tendons and ligaments, and the development of a new generation of fixation devices. Rita Kandel discussed the challenges related to the re-creation of the cartilage-bone interface, in the context of tissue engineered joint repair. Frederick Schoen emphasized, in the context of heart valve engineering, the need for including the requirements derived from "adult biology" of tissue remodeling and establishing reliable early predictors of success or failure of tissue engineered implants. Mehmet Toner presented a review of biopreservation techniques and stressed that a new breakthrough in this field may be necessary to meet all the needs of tissue engineering. David Mooney described systems providing temporal and spatial regulation of growth factor availability, which may find utility in virtually all tissue engineering and regeneration applications, including directed in vitro and in vivo vascularization of tissues. Anthony Atala offered a clinician's perspective for functional tissue regeneration, and discussed new biomaterials that can be used to develop new regenerative technologies.

Relationship of five inflammatory gene polymorphisms with morbidity and mortality in 533 patients admitted to an ICU

BACKGROUND

The aim of this study was to analyze the association of polymorphisms of five candidate genes with the outcome of consecutive patients admitted to a medical ICU.

MATERIALS AND METHODS

The study population was prospectively recruited. Inclusion criteria were admission to the ICU and written informed consent by the patients or their relatives. A total of 533 patients were recruited. The morbidity was assessed by SAPS II Score. Outcome data of in hospital mortality and length of ICU and hospital stay were obtained. Genotyping for genetic polymorphisms (CRP 1059, IL1B -511, CTGF -477, CCR2 64VI, IL6 -174) were performed by allele-specific fluorogenic oligonucleotide probes (TaqMan analysis).

RESULTS

All of the investigated polymorphisms were not associated with an altered outcome. There was no difference in morbidity and ICU or in-hospital mortality (neither in cross tabs analysis nor in Kaplan Meier or Cox regression analysis including age, gender and diagnosis as covariates) between the different genotypes.

CONCLUSIONS

Genotyping of the investigated polymorphism for risk stratification of patients admitted to ICU does not seem to be appropriated.

Fibrosis in heart disease: understanding the role of transforming growth factor-beta in cardiomyopathy, valvular disease and arrhythmia

The importance of fibrosis in organ pathology and dysfunction appears to be increasingly relevant to a variety of distinct diseases. In particular, a number of different cardiac pathologies seem to be caused by a common fibrotic process. Within the heart, this fibrosis is thought to be partially mediated by transforming growth factor-beta1 (TGF-beta1), a potent stimulator of collagen-producing cardiac fibroblasts. Previously, TGF-beta1 had been implicated solely as a modulator of the myocardial remodelling seen after infarction. However, recent studies indicate that dilated, ischaemic and hypertrophic cardiomyopathies are all associated with raised levels of TGF-beta1. In fact, the pathogenic effects of TGF-beta1 have now been suggested to play a major role in valvular disease and arrhythmia, particularly atrial fibrillation. Thus far, medical therapy targeting TGF-beta1 has shown promise in a multitude of heart diseases. These therapies provide great hope, not only for treatment of symptoms but also for prevention of cardiac pathology as well. As is stated in the introduction, most reviews have focused on the effects of cytokines in remodelling after myocardial infarction. This article attempts to underline the significance of TGF-beta1 not only in the post-ischaemic setting, but also in dilated and hypertrophic cardiomyopathies, valvular diseases and arrhythmias (focusing on atrial fibrillation). It also aims to show that TGF-beta1 is an appropriate target for therapy in a variety of cardiovascular diseases.

Resequencing of the characterised CTGF gene to identify novel or known variants, and analysis of their association with diabetic nephropathy

Connective tissue growth factor (CTGF) has been implicated in the pathogenesis of diabetic nephropathy; however, to date there have been no reports of genomic analysis on this gene. The CTGF gene was comprehensively screened using WAVE (dHPLC) technology and direct capillary sequencing. Single nucleotide polymorphisms (SNPs) with minor allele frequencies greater than 5% were further investigated in an Irish, type 1 diabetic population. The case-control collection consisted of 272 diabetics with nephropathy and 367 non-nephropathic diabetic controls who were genotyped using TaqMan and Pyrosequencing technologies. Ten SNPs were identified, of which seven were novel. Four SNPs are located in the promoter, one in exon 2, two in intron 2 and three in the 3' untranslated region. Based on in silico analysis, three SNPs, c.-650G>C, c.-484T>C and c.247G>C, are potentially functional. Subsequent statistical analysis for common SNPs, c.-650G>C, c.-420InsT, c.-220G>C, c.289+94T>C and c.289+98T>C, in the case-control study revealed no significant differences in genotype or allele frequencies. CTGF has emerged as a biological candidate gene for diabetic nephropathy; however, no significant association was detected between common CTGF SNPs and nephropathy in this population.

Systemic sclerosis: the susceptible host (genetics and environment)

It is becoming evident that several genetic factors participate in modulating susceptibility to SSc and its clinical manifestations. Some genes that specifically affect ECM metabolism and vascular function may be unique to SSc and scleroderma-related disorders; others, such as those genes involved in regulating immune tolerance, are likely shared with other autoimmune diseases. The effect of genetic variations (or polymorphisms) that are found in most of these genes taken individually will likely have only a small or modest effect on disease risk; only a few genetic variations are expected to be highly penetrant. Moreover, genetic studies in SSc have to deal with the additional issues of heterogeneous phenotypes, low disease prevalence in the general population, and an even greater paucity of multiplex families that makes traditional linkage studies difficult, if not impossible. Alternative approaches include allelic association studies, but conventional case-controls designs may be subject to selection bias and will require large sample sizes if the genes that are under investigation confer only modest (OR = 1.5-2.0) disease risk (Fig. 2). The simultaneous examination of several genes that are biologically relevant to a specific disease process to attain higher aggregate ORs, is one approach that was used in several reports that were cited in this review. The use of family-based controls, such as in the transmission-disequilibrium test (based on assessment of the transmitted or nontransmitted alleles that are associated with disease from heterozygous parents to affected offspring), would provide more robustness to spurious associations from population stratification, but is actually less powerful and efficient than case-control designs. Furthermore, for many late adult-onset diseases the effort required to obtain samples from living parents are for a variety of reasons not trivial. The success of these allelic association-based approaches depends on the identification of likely candidate disease genes (or at least markers in disequilibrium with disease genes), careful definition/ascertainment of disease phenotypes to minimize genetic heterogeneity, and for case-control designs, strategies to account for population stratification or admixture. The identification of candidate genes will be aided by rapid progress in the Human Genome Project and other genome efforts that will eventually identify all human genetic variations. Although this will lead to better understanding of the genes that might be involved in complex diseases, much work is required to understand the basic biology of how disease genotypes become clinical phenotypes. This is especially daunting in complex diseases, such as SSc, where the phenotype (including disease susceptibility and clinical presentation) is influenced by dynamic interactions between genetic variations and environment. Multi-center collaborative efforts with research paradigms that integrate genetic and environmental factors (including sociodemographic variables) will be required to elucidate the contribution of environment and genetics in the pathogenesis of SSc.

CTGF expression in mesangial cells: involvement of SMADs, MAP kinase, and PKC

BACKGROUND

The induction of excess matrix in renal fibrosis seems to be mediated, at least in part, by the transforming growth factor-beta (TGF-beta)-mediated induction of connective tissue growth factor (CTGF) in mesangial cells.

METHODS

By examining CTGF protein and mRNA expression and promoter activity in the presence or absence of TGF-beta or inhibitors, the signaling pathways controlling basal and TGF-beta-induced CTGF expression in mesangial cells were investigated.

RESULTS

TGF-beta enhances CTGF mRNA and protein expression in mesangial cells. Mutation of a consensus SMAD binding element in the CTGF promoter completely abolished TGF-beta-induced CTGF expression and reduced basal CTGF expression. The previously identified basal control element-1 (BCE-1) site, but not Sp1 contributes to basal CTGF promoter activity. Ras/MEK/ERK, protein kinase C (PKC) and tyrosine kinase activity also contribute to basal and TGF-beta-induced CTGF promoter activity in cultured mesangial cells.

CONCLUSIONS

The TGF-beta-induction of CTGF in mesangial cells requires SMADs and PKC/ras/MEK/ERK pathways. SMADs are involved in basal CTGF expression, which presumably reflects the fact that mesangial cells express TGF-beta endogenously. TGF-beta also induces CTGF through ras/MEK/ERK. Inhibiting ras/MEK/ERK seems not to reduce phosphorylation (that is, activation) of SMADs, suggesting that SMADs, although necessary, are insufficient for the TGF-beta-stimulation of the CTGF promoter through ras/MEK/ERK. Thus, maximal TGF-beta induction of CTGF requires synergy between SMAD and ras/MEK/ERK signaling.

Gene regulation of connective tissue growth factor: new targets for antifibrotic therapy?

Connective tissue growth factor (CTGF) has recently received much attention as a possible key determinant of progressive fibrosis and excessive scarring and also of wound repair, neoangiogenesis, bone formation and embryonic development. CTGF is also up regulated in numerous fibrotic diseases, including atherosclerosis and lung-, skin-, pancreas-, liver- and kidney-fibrosis. TGFbeta induces CTGF through different signaling pathways and a specific TGFbeta responsive element in the CTGF promoter. CTGF is thought to act both as a profibrotic marker and as a downstream effector of TGFbeta by mediating at least some of its profibrotic activities. CTGF is an interesting target for future antifibrotic therapies as it is conceivable that inhibition of CTGF might block the profibrotic effects of TGFbeta, without affecting TGFbeta's anti-proliferative and immunosuppressive effects. In addition to TGFbeta, a number of other regulators of CTGF expression have been identified, including vascular endothelial growth factor, tumor necrosis factor alpha, shear stress, cell stretch and static pressure, H(2)O(2), O(2) and NO. In addition to trans-regulatory mechanisms, specific transcription factor binding sites in the CTGF promoter, as well as 3'untranslated region (UTR) regulatory sequences have been identified that are important for basal and induced CTGF expression. Outlining the mechanisms that underlie CTGF gene regulation in normal and fibrotic cells, might help design of future intervention strategies aiming at targeted specific interference with CTGF expression at sites of progressive fibrosis. In addition, alternative therapies targeting CTGF effects are proposed which might lead to a favorable outcome of wound repair and fibrosis.

Connective tissue growth factor: a new and important player in the pathogenesis of fibrosis

Connective tissue fibrosis is the final common pathogenic process for almost all forms of chronic tissue injury. Whether caused by vascular dysfunction, inflammation, metabolic injury, trauma, or environmental agents, once initiated the fibrogenic process results in the progressive replacement of the normal tissue architecture with fibrotic lesions that eventually lead to organ compromise and failure. Fibrosis can be considered as a dysregulation in the normal tissue repair mechanism, resulting in severe tissue scarring. Fibrosis appears to be a consequence of linked processes, including the proliferation of resident fibroblast cell types, the increased production and deposition of extracellular matrix components, and the transition of fibroblasts into cells exhibiting a myofibroblast phenotype. Although transforming growth factor-beta (TGF beta) has long been regarded as a pivotal growth factor in the formation and maintenance of connective tissues and as a major driving influence in many progressive fibrotic diseases, attention has focused recently on the role of connective tissue growth factor (CTGF) in fibrosis. CTGF is selectively and rapidly induced in mesenchymally derived cells by the action of TGF beta. CTGF expression is increased in many fibrosing diseases. In addition, increasing evidence from in vivo and in vitro models of tissue remodeling and fibrosis suggest that CTGF may represent a downstream effector molecule of the profibrotic activities of TGF beta in the maintenance and repair of connective tissues and within fibrotic disease settings.

Growth factors in idiopathic pulmonary fibrosis: relative roles

Treatment of idiopathic pulmonary fibrosis patients has evolved very slowly; the fundamental approach of corticosteroids alone or in combination with other immunosuppressive agents has had little impact on long-term survival. The continued use of corticosteroids is justified because of the lack of a more effective alternative. Current research indicates that the mechanisms driving idiopathic pulmonary fibrosis reflect abnormal, dysregulated wound healing within the lung, involving increased activity and possibly exaggerated responses by a spectrum of profibrogenic growth factors. An understanding of the roles of these growth factors, and the way in which they modulate events at cellular level, could lead to more targeted therapeutic strategies, improving patients' quality of life and survival.

Connective tissue growth factor: an attractive therapeutic target in fibrotic renal disease

Despite diverse initiating insults, glomerulosclerosis and tubulointerstitial fibrosis are pathological features common to most forms of progressive renal disease. Control of systemic hypertension and blockade of the renin-angiotensin system ameliorate the rate of progression of chronic renal disease; however they generally fail to completely arrest the scarring process. While the chain of events leading to scarring are still being defined, TGF-beta is a cytokine that plays a pivotal role in the pathogenesis of glomerulosclerosis and tubulointerstitial fibrosis [1]. Given the pleiotropic effects of TGF-beta, significant attention has focused on the potential of its downstream mediators as therapeutic targets. Connective tissue growth factor (CTGF) is a member of the CCN gene family, which includes CyR61 (cysteine rich 61), Nov (Nephroblastoma overexpressed) and the WISP family (for review see [2,3,4]). These immediate-early genes coordinate complex biologic processes during differentiation and tissue repair [5]. Increased expression of CTGF has been detected in experimental and human renal fibrosis where it correlates with glomerulosclerosis and the degree of tubulointerstitial fibrosis [6]. In these settings CTGF expression is regulated at least in part by TGF-beta. This review details the biology of CTGF with specific reference to its potential as a therapeutic target in renal fibrosis.