Angiotensin II increases connective tissue growth factor in the kidney

Interactions between aldosterone and connective tissue growth factor in vascular and renal damage in spontaneously hypertensive rats

OBJECTIVE

The aim of the present study was to investigate possible inter-relationships between connective tissue growth factor (CTGF) and aldosterone in vascular and renal damage associated with hypertension.

METHOD

Spontaneously hypertensive rats (SHR) were treated with two doses (100 and 30 mg/kg per day) of the mineralocorticoid receptor antagonist eplerenone, or with antihypertensive therapy (HHR) (20 mg/kg per day hydralazine + 7 mg/kg per day hydrochlorothiazide + 0.15 mg/kg per day reserpine).

RESULTS

CTGF mRNA expression and protein levels in the aorta of SHR were upregulated (P < 0.05) compared with Wistar-Kyoto rats. Both doses of eplerenone similarly and significantly diminished CTGF upregulation, correlated with amelioration of aortic remodelling and endothelium-dependent relaxations. Only high-dose eplerenone and HHR significantly reduced arterial blood pressure. HHR treatment also diminished CTGF overexpression, suggesting a blood-pressure-mediated effect in CTGF regulation. This reduction, however, was lower (P < 0.05) than that produced by eplerenone (100 mg/kg per day). The direct effect of aldosterone on vascular smooth muscle cells was also studied. Incubation of cultured vascular smooth muscle cells with aldosterone increased CTGF production in a dose-related manner, but was reduced (P < 0.05) by the mineralocorticoid receptor antagonist spironolactone. Renal CTGF mRNA and protein levels were higher in SHR than in Wistar-Kyoto rats (P < 0.05), and were similarly diminished by all treatments (P < 0.05).

CONCLUSIONS

These data show that aldosterone and haemodynamic stress from elevated blood pressure levels regulate vascular and renal CTGF in SHR. The results suggest that aldosterone, through CTGF stimulation, could participate in vascular and renal structural alterations associated with hypertension, describing a novel mechanism of aldosterone in hypertensive target organ damage.

Glomerular localization and expression of Angiotensin-converting enzyme 2 and Angiotensin-converting enzyme: implications for albuminuria in diabetes

Angiotensin-converting enzyme 2 (ACE2) expression has been shown to be altered in renal tubules from diabetic mice. This study examined the localization of ACE and ACE2 within the glomerulus of kidneys from control (db/m) and diabetic (db/db) mice and the effect of chronic pharmacologic ACE2 inhibition. ACE2 co-localized with glomerular epithelial cell (podocyte) markers, and its localization within the podocyte was confirmed by immunogold labeling. ACE, by contrast, was seen only in glomerular endothelial cells. By immunohistochemistry, in glomeruli from db/db mice, strong ACE staining was found more frequently than in control mice (db/db 64.6 +/- 6.3 versus db/m 17.8 +/- 3.4%; P < 0.005). By contrast, strong ACE2 staining in glomeruli from diabetic mice was less frequently seen than in controls (db/db 4.3 +/- 2.4 versus db/m 30.6 +/- 13.6%; P < 0.05). For investigation of the significance of reduced glomerular ACE2 expression, db/db mice were treated for 16 wk with a specific ACE2 inhibitor (MLN-4760) alone or combined with telmisartan, a specific angiotensin II type 1 receptor blocker. At the end of the study, glomerular staining for fibronectin, an extracellular matrix protein, was increased in both db/db and db/m mice that were treated with MLN-4760. Urinary albumin excretion (UAE) increased significantly in MLN-4760-treated as compared with vehicle-treated db/db mice (743 +/- 200 versus 247 +/- 53.9 microg albumin/mg creatinine, respectively; P < 0.05), and the concomitant administration of telmisartan completely prevented the increase in UAE associated with the ACE2 inhibitor (161 +/- 56; P < 0.05). It is concluded that ACE2 is localized in the podocyte and that in db/db mice glomerular expression of ACE2 is reduced whereas glomerular ACE expression is increased. The finding that chronic ACE2 inhibition increases UAE suggests that ACE2, likely by modulating the levels of glomerular angiotensin II via its degradation, may be a target for therapeutic interventions that aim to reduce albuminuria and glomerular injury.

Renal injury due to renin-angiotensin-aldosterone system activation of the transforming growth factor-beta pathway

Glomerulosclerosis, interstitial fibrosis, and tubular atrophy occur with end-stage kidney failure, irrespective of the primary etiology. The transforming growth factor-beta (TGF-beta) is a key factor in these alterations either directly, by stimulating synthesis of extracellular matrix components and reducing collagenase production, or indirectly through other profibrogenic factors such as connective tissue growth factor (CTGF). TGF-beta is important for the proliferation of intrarenal fibroblasts and the epithelial-mesenchymal transition through which tubular cells become fibroblasts. Although several factors induce TGF-beta expression in the kidney, one very interesting aspect is the link between the renin-angiotensin-aldosterone (Aldo) system (RAAS) and TGF-beta. Angiotensin II (ANG II) stimulates TGF-beta expression in the kidney by various mechanisms and upregulates receptors for TGF-beta. ANG II can directly phosphorylate Smads without inducing TGF-beta. Recent data provide compelling evidence that other components of the RAAS including ANG III, renin, and Aldo also activate the TGF-beta system. As direct modulation of the TGF-beta system is not yet feasible in humans, angiotensin-converting enzyme (ACE) inhibitors and angiotensin type 1 (AT1)-receptor blockers are currently the most potential drugs to interfere with this ANG II-mediated TGF-beta expression. This review highlights some current aspects of the interaction between the RAAS and the TGF-beta axis.

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.

Effect of cyclosporine and sirolimus on the expression of connective tissue growth factor in rat experimental chronic nephrotoxicity

BACKGROUND/AIMS

Connective tissue growth factor (CTGF) is a pro-fibrotic growth factor that acts downstream of transforming growth factor (TGF)-beta. However, CTGF regulation remains unknown. We tried to determine the effect of two commonly used immunosuppressants, cyclosporine (CsA) and sirolimus (SRL), on CTGF expression in a model of chronic nephrotoxicity.

METHODS

Adult Sprague-Dawley rats kept on a low-salt diet were treated daily for 4 weeks with vehicle (VH), SRL (0.3 mg/kg), CsA5 (5 mg/kg), CsA10 (10 mg/kg) or both CsA5 and SRL. CTGF and TGF-beta1 expressions were evaluated by Northern blot. Functional and histologic parameters in addition to number of apoptotic cells were determined.

RESULTS

At 28 days, both CsA doses were capable of inhibiting CTGF mRNA expression to levels similar to control. On the other hand, SRL increased CTGF expression by 3.5-fold. However, addition of CsA to SRL completely reversed that trend and returned levels to control. The results were different for TGF-beta1, which was increased by both CsA and SRL and to a greater extent by the drug combination.

CONCLUSION

Unlike TGF-beta, CTGF does not seem to play an important role in CsA-induced chronic nephrotoxicity. In addition, calcineurin-dependent pathways are likely involved in CTGF regulation.

Influence of connective tissue growth factor antisense oligonucleotide on angiotensin II-induced epithelial mesenchymal transition in HK2 cells

AIM

The present study was designed to further investigate the effect of connective tissue growth factor antisense oligonucleotide (CTGF-AS) on angiotensin II (Ang II)-induced tubular cell epithelial mesenchymal transition (EMT) in vitro.

METHODS

The human proximal tubular cell line (HK2) was grown in Dulbecco's modified Eagle's medium containing 10% heat inactivated fetal calf serum. After being rested in serum-free medium for 24 h, the influence of CTGF-AS (20 mug/mL) on Ang II-induced (0.1 micromol/L) CTGF mRNA and the protein expression were examined by using reverse transcription-polymerase chain reaction and indirect-immunofluorescence. The effect of CTGF-AS on Ang II-induced cellular ultrastructure was observed using a transmissive electronic microscope. The expression of alpha-smooth action (alpha-SMA) was assayed by immunocytochemistry. In all experiments, the control group was treated with scrambled oligonucleotide.

RESULTS

It was shown that Ang II significantly induced the increasing expression of CTGF mRNA and protein (P<0.01, respectively), which were significantly abolished by treatment with CTGF-AS. After stimulating cells with Ang II, the cellular ultrastructure showed mesenchymal features. These effects were partially inhibited by CTGF-AS. Ang II significantly resulted in the expression of alpha-SMA in time dependent manner, which was markedly attenuated by the treatment with CTGF-AS (P<0.01, respectively). In contrast, no similar effects were observed in the control group treated with scrambled oligonucleotide.

CONCLUSION

Ang II-induced EMT in human proximal tubular epithelial cells (PTC) can be attenuated by treatment with CTGF-AS. Our data provides further evidence that CTGF might be involved in Ang II-induced EMT in PTC.

SGK1-dependent cardiac CTGF formation and fibrosis following DOCA treatment

The mineralocorticoids aldosterone and deoxycorticosterone acetate (DOCA) stimulate renal tubular salt reabsorption, increase salt appetite, induce extracellular volume expansion, and elevate blood pressure. Cardiac effects of mineralocorticoids include stimulation of matrix protein deposition leading to cardiac fibrosis, which is at least partially due to the direct action of the hormones on cardiac cells. The signaling mechanisms mediating mineralocorticoid-induced cardiac fibrosis have so far remained elusive. Mineralocorticoids have been shown to upregulate the serum- and glucocorticoid-inducible kinase 1 (SGK1), which participates in the effects of mineralocorticoids on renal tubular Na+ reabsorption and salt appetite. To explore the involvement of SGK1 in the pathogenesis of mineralocorticoid-induced cardiac fibrosis, SGK1 knockout mice (sgk1-/-) and wild-type littermates (sgk1+/+) were implanted a 21-day-release 50-mg DOCA pellet and supplied with 1% NaCl in drinking water for 18 days. This DOCA/high-salt treatment increased blood pressure in both genotypes but led to significant cardiac fibrosis only in sgk1+/+ but not in sgk1-/- mice. According to real-time polymerase chain reaction and Western blotting, DOCA/high-salt treatment enhanced transcript levels and protein expression of cardiac connective tissue growth factor (CTGF) only in sgk1+/+ but not in sgk1-/- mice. Furthermore, DOCA (10 microM) upregulated CTGF expression and enhanced CTGF promoter activity in lung fibroblasts isolated from sgk1+/+ but not from sgk1-/- mice, an effect involving spironolactone-sensitive mineralocorticoid receptors and activation of nuclear factor-kappaB (NFkappaB). Our results suggest that SGK1 plays a decisive role in mineralocorticoid-induced CTGF expression and cardiac fibrosis.

Connective Tissue Growth Factor-Mediated Angiotensin II-Induced Hypertrophy of Proximal Tubular Cells

BACKGROUND

Cellular hypertrophy is an early, important pathological feature of renal diseases such as diabetic nephropathy and remnant kidney. Recent studies have demonstrated that angiotensin II (AngII) plays a key role in mediating cell hypertrophy. The aim of our work was to explore the role of connective tissue growth factor (CTGF) in mediating AngII-induced tubular cell hypertrophy in vivoandin vitro.

METHODS

In an in vivo study, male Sprague-Dawley rats were randomly divided into three groups: control rats, diabetic rats and diabetic rats treated with irbesartan (IRB). The index of kidney hypertrophy (kidney weight/body weight, KW/BW), glomerular tuft area (AG), glomerular tuft volume (VG) and proximal tubular area (AT) were determined. Renal expression for CTGF was detected by immunohistochemical staining. In an in vitro study, the influence of CTGF antisense oligonucleotide (CTGF AS) on AngII-induced CTGF expression and cell hypertrophy was also investigated.

RESULTS

In an in vivo study, diabetic rats showed a significant increase of KW/BW, AG, VG, and AT from week 1 onwards compared to normal control, which could be significantly inhibited by using IRB. Furthermore, there was a significantly increasing expression of CTGF in both glomeruli and tubuli in diabetic rats compared to control, and the extent of CTGF expression closely correlated with the severity of renal hypertrophy. Treatment with IRB could markedly inhibit the renal expression of CTGF. In an in vitro study, AngII stimulated the expression of CTGF mRNA and CTGF protein. AngII significantly increased the total protein content in HK2 cells, which was markedly inhibited by co-treatment with CTGF AS. The average cellular diameter determined by scanning electronic microscope showed that the increase of cell size induced by AngII could be significantly inhibited by CTGF AS. Furthermore, flow cytometer study showed that AngII arrested the cell cycle in the G0-G1 phase, which was significantly reversed by treatment with CTGF AS.

CONCLUSION

Our data provide both in vivo and in vitroevidence that CTGF is involved in mediating AngII-induced renal hypertrophy.

The Rho-kinase pathway regulates angiotensin II-induced renal damage

BACKGROUND

Angiotensin II (AngII) is a key factor in the pathogenesis of renal damage. AngII via AngII type 1 receptors activates several intracellular signaling systems, including the small guanosine triphosphatase Rho and its downstream effector Rho-dependent serine-threonine kinase (Rho-kinase). The Rho/Rho-kinase pathway contributes to inflammatory and proliferative changes observed in cardiovascular diseases. However, the data on renal diseases are scarce. The aim of this study was to investigate the effect of Rho-kinase inhibition in AngII-induced renal damage.

METHODS

We used the model of systemic AngII infusion into normal rats (100 ng/kg per minute; subcutaneous osmotic minipumps), and some animals were treated with the Rho-kinase inhibitor Y-27632 (30 mg/kg per day). In the kidneys of these animals, we evaluated renal lesions, transcription factor activity (by electrophoretic mobility shift assay), and messenger RNA (by polymerase chain reaction) and protein expression levels (by Western blot and/or immunohistochemistry) of proinflammatory and profibrotic factors.

RESULTS

Rats infused with AngII for three days present renal inflammatory cell infiltration and slight tubular damage, which were diminished by treatment with the Rho-kinase inhibitor Y-27632. AngII activates nuclear factor-kappaB and causes overexpression of proinflammatory factors, including cytokines (tumor necrosis factor alpha) and chemokines (monocyte chemotactic protein-1), and of profibrotic factors (connective tissue growth factor). Treatment of AngII-infused rats with Y-27632 decreases the upregulation of these proinflammatory and profibrotic mediators.

CONCLUSION

These data demonstrate that the Rho-kinase pathway is involved in renal damage caused by AngII through the regulation of proinflammatory and profibrotic mediators. These results suggest that inhibition of the Rho-kinase pathway represents a novel therapy for renal diseases associated with local AngII generation.

Angiotensin II: a key factor in the inflammatory and fibrotic response in kidney diseases

Angiotensin II (AngII) participates in the pathogenesis of renal diseases, through the regulation of two key processes inflammation and fibrosis. AT1 and AT2 are the main receptors of AngII. AT1 mediates most of the actions of AngII. This receptor regulates the expression of profibrotic factors, such as connective tissue growth factor (CTGF). The Smad signalling pathway and the Rho/Rho kinase system are two novel mechanisms involved in AngII-induced matrix regulation recently described. The role of AT2 receptors in renal pathophysiological processes is not fully elucidated. Experimental data suggest that AT2 receptors through activation of nuclear factor-kappaB participate in renal inflammatory cell recruitment. Studies in animal models of kidney injury have shown that the combined blockade of both AT1 and AT2 receptors, as well as the inhibition of the NF-kappaB pathway are necessary to stop the inflammatory process fully. On the whole, these data highlight the complex signalling systems activated by AngII and suggest novel potential targets to block fibrosis and inflammation in renal diseases.

Angiotensin and diabetic retinopathy

Diabetic retinopathy develops in patients with both type 1 and type 2 diabetes and is the major cause of vision loss and blindness in the working population. In diabetes, damage to the retina occurs in the vasculature, neurons and glia resulting in pathological angiogenesis, vascular leakage and a loss in retinal function. The renin-angiotensin system is a causative factor in diabetic microvascular complications inducing a variety of tissue responses including vasoconstriction, inflammation, oxidative stress, cell hypertrophy and proliferation, angiogenesis and fibrosis. All components of the renin-angiotensin system including the angiotensin type 1 and angiotensin type 2 receptors have been identified in the retina of humans and rodents. There is evidence from both clinical and experimental models of diabetic retinopathy and hypoxic-induced retinal angiogenesis that the renin-angiotensin system is up-regulated. In these situations, retinal dysfunction has been linked to angiotensin-mediated induction of growth factors including vascular endothelial growth factor, platelet-derived growth factor and connective tissue growth factor. Evidence to date indicates that blockade of the renin-angiotensin system can confer retinoprotection in experimental models of diabetic retinopathy and ischemic retinopathy. This review examines the role of the renin-angiotensin system in diabetic retinopathy and the potential of its blockade as a treatment strategy for this vision-threatening disease.

Reactive oxygen species as mediators of calcium signaling by angiotensin II: implications in vascular physiology and pathophysiology

Reactive oxygen species (ROS), including superoxide anion, hydrogen peroxide, and hydroxyl radical, and reactive nitrogen species, such as nitric oxide and peroxynitrite, are biologically relevant O2 derivatives increasingly being recognized as important in vascular biology through their oxidation/reduction (redox) potential. All vascular cell types produce ROS primarily via membrane-associated NAD(P)H oxidase. ROS influence vascular function by modulating contraction/dilation, cell growth, apoptosis/anoikis, migration, inflammation, and fibrosis. An imbalance in redox state where prooxidants overwhelm antioxidant capacity results in oxidative stress. Oxidative excess and associated oxidative damage are mediators of altered vascular tone and structural remodeling in many cardiovascular diseases. ROS elicit these effects by influencing intracellular signaling events. In addition to modulating protein tyrosine kinases, protein phosphatases, mitogen-activated protein kinases, and transcription factors, ROS are important regulators of intracellular Ca2+ homeostasis and RhoA/Rho kinase signaling. ROS increase vascular [Ca2+]i by stimulating inositol trisphosphate-mediated Ca2+ mobilization, by increasing cytosolic Ca2+ accumulation through sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibition, and by stimulating Ca2+ influx through Ca2+ channels. Increased ROS generation enhances Ca2+ signaling and up-regulates RhoA/Rho kinase, thereby altering vascular contractility and tone. The present review discusses the importance of ROS in angiotensin II signaling in vascular biology and focuses specifically on the role of oxidative stress in Ca2+ signaling in the vasculature.

Reduction of urinary connective tissue growth factor by Losartan in type 1 patients with diabetic nephropathy

BACKGROUND

Connective tissue growth factor (CTGF) is an important profibrotic cytokine implicated in development of diabetic glomerulosclerosis. Urinary CTGF is reported to be significantly increased in patients with diabetic nephropathy. The present study aimed to investigate the short- and long term effects of angiotensin II receptor blockade by Losartan on urinary CTGF levels in hypertensive type 1 diabetic patients with diabetic nephropathy.

METHODS

Seventy-one hypertensive type 1 diabetic patients with diabetic nephropathy were included in the study. After a washout period of 4 weeks, the patients received Losartan 50 mg, 100 mg, and 150 mg once daily in treatment periods each lasting 2 months. Thereafter, patients were followed prospectively during treatment with Losartan 100 mg o.d. with a total mean follow-up time of 36 months. At baseline, after 2, 4, and 6 months and then biannually, urinary and plasma CTGF levels [enzyme linked immunosorbent assay (ELISA) fibroGen], albuminuria (Turbidimetry), glomerular filtration rate (GFR) [51-creatinine ethylenediaminetetraacetic acid ((51)Cr-EDTA plasma clearance)] and 24 hours blood pressure (TM2420)) were determined.

RESULTS

Baseline levels of urinary and plasma CTGF were 7076 (5708 to 8770) ng/24 hours [geometric mean (95% CI)] and 12.7 (7.3) ng/mL [mean (SD)], respectively. Albuminuria, GFR, and arterial blood pressure at baseline were 1152 (937 to 1416) mg/24 hours, 88 (24) mL/min/1.73 m(2), and 153/80 (17/9) mm Hg, respectively. Losartan significantly reduced urinary CTGF by 21% (9 to 31) (95% CI) initially (P < 0.05 vs. baseline), with no further reduction after increasing dose. The sustained reduction in urinary CTGF was 22% (12 to 32) (P < 0.05 vs. baseline). Rate of decline in GFR during the study was 3.2 (-1.6 to 15.9) mL/min/year [median (range)]. Reduction in urinary CTGF was correlated with a lower rate of decline in GFR (r= 0.23, P= 0.05). Plasma CTGF remained unchanged throughout the study.

CONCLUSION

Our 3-year study demonstrates that Losartan persistently reduces urinary CTGF excretion, which is associated with a slower rate of decline in GFR.

Agents in development for the treatment of diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal disease, and accounts for significant morbidity and mortality in patients with diabetes. Diabetic nephropathy seems to occur as a result of an interaction between metabolic and haemodynamic factors, which activate common pathways that lead to renal damage. In the past, the treatment of diabetic nephropathy has focused on the control of hyperglycaemia. Newer targets, some of which are linked to glucose-dependent pathways, appear to be a major focus of new treatments directed against the development and progression of renal damage as a result of diabetes. It is anticipated that additional therapeutic approaches that inhibit both metabolic and haemodynamic pathways will include strategies that target growth factors, cytokines and intracellular second messengers. Such an approach is expected to lead to improved therapies for the treatment of diabetic nephropathy.

High calcium diet down-regulates kidney angiotensin-converting enzyme in experimental renal failure

BACKGROUND

Calcium salts are used as phosphate binders in renal failure, while high calcium diet also improves vasorelaxation and enhances natriuresis. The influences of calcium intake on renal renin-angiotensin system (RAS) are largely unknown.

METHODS

Four weeks after NTX, rats were put on 3.0% or 0.3% calcium diet for 8 weeks (12-week study). In additional experiments, 15 weeks after NTX, rats were put on similar diets for 12 weeks (27-week study). Appropriate blood, urine, and kidney samples were taken. Renal angiotensin-converting enzyme (ACE) and angiotensin II receptors (AT1, AT2) were examined using autoradiography, ACE also using Western blotting, and connective tissue growth factor (CTGF) using immunohistochemistry.

RESULTS

In the 12-week study, albuminuria increased 5-fold in NTX rats, but only 2-fold in calcium NTX rats on 3.0% calcium. In the 27-week study, high calcium intake decreased blood pressure, retarded progression of renal failure, reduced glomerulosclerosis, interstitial damage, and aortic calcifications, and improved survival from 50% to 92% in NTX rats. In both experiments plasma parathyroid hormone and phosphate were elevated after NTX, and suppressed by high calcium diet, while kidney ACE was down-regulated by 40% or more after increased calcium intake. In the 27-week study renal CTGF was decreased and cortical AT1 receptor density reduced after high calcium diet.

CONCLUSION

High calcium diet down-regulated kidney ACE, reduced albuminuria and blood pressure, and favorably influenced kidney morphology in experimental renal failure. These findings suggest a link between calcium metabolism and kidney ACE expression, which may play a role in the progression of renal damage.

Suppressors of Cytokine Signaling Regulate Angiotensin II-Activated Janus Kinase-Signal Transducers and Activators of Transcription Pathway in Renal Cells

Suppressors of cytokine signaling (SOCS) family is constituted by cytokine-inducible proteins that modulate receptor signal transduction via tyrosine kinases, mainly the Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathway. Differential SOCS expression was noted in renal cells that were incubated with inflammatory stimuli, but the role of SOCS in the pathogenesis of renal diseases is not yet well defined. Because angiotensin II (Ang II) plays a key role in renal disease, SOCS proteins were studied as a novel mechanism involved in the negative regulation of Ang II-mediated processes. Systemic Ang II infusion for 3 d increased the renal mRNA expression of SOCS-3 and SOCS-1. SOCS protein synthesis was found in glomerular mesangial area and tubules. In cultured mesangial cells and tubular epithelial cells, Ang II induced a rapid and transient SOCS-3 and SOCS-1 expression in parallel with JAK2 and STAT1 activation. In both cell types, overexpression of SOCS proteins prevented the STAT activation in response to Ang II. SOCS expression observed in Ang II-infused rats and in Ang II-stimulated cells was significantly inhibited by treatment with AT(1) but not AT(2) receptor antagonist and was attenuated in mesangial cells from AT(1a)-deficient mice, demonstrating the implication of AT(1) in those responses. In SOCS-3 knockdown studies, antisense oligonucleotides inhibited the expression of SOCS-3 and increased the Ang II-induced STAT activation and c-Fos/c-Jun expression, then resulting in a more severe renal damage. These results suggest that SOCS proteins may act as negative regulators of Ang II signaling in renal cells and implicate SOCS as important modulators of renal damage.

Evidence for low-density lipoprotein–induced expression of connective tissue growth factor in mesangial cells

BACKGROUND

Although hyperlipidemia is a risk factor for the progression of renal damage, the relationship between increased plasma lipoproteins and glomerular injury is poorly defined. Connective tissue growth factor (CTGF) is emerging as a key determinant of progressive fibrotic diseases and its expression is up-regulated by diabetes. To define the mechanisms through which low-density lipoproteins (LDLs) promote glomerular injury, we evaluated whether LDL can modulate the expression of CTGF and collagen I.

METHODS

The effects of LDL on CTGF and collagen I expression were carried out in rat mesangial cells.

RESULTS

Treatment of mesangial cells with LDL for 24 hours produced a significant increase in the protein levels of CTGF and collagen I compared to unstimulated controls. To explore if CTGF and collagen I are downstream targets for regulation by transforming growth factor-beta (TGF-beta), mesangial cells were treated with various concentration of TGF-beta for 24 hours. TGF-beta produced a concentration-dependent increase in the protein levels of CTGF and collagen I. The increase in CTGF and collagen I induced by LDL was significantly inhibited by neutralizing anti-TGF-beta antibodies. Inhibition of p38(mapk) or p42/44(mapk) activities did not affect LDL-induced TGF-beta1, CTGF, and collagen I expression, whereas inhibition of c-Jun NH2-terminal kinase (JNK) suppressed LDL-induced TGF-beta, CTGF, and collagen I expression.

CONCLUSION

These findings implicate JNK pathway and TGF-beta1 as key players in LDL signaling leading to CTGF and collagen I expression in mesangial cells. The data also point to a potential mechanistic pathway through which lipoproteins may promote glomerular injury.

Advanced glycation end-products induce connective tissue growth factor-mediated renal fibrosis predominantly through transforming growth factor beta-independent pathway

Advanced glycation end-products (AGEs) play a critical role in diabetic nephropathy by stimulating extracellular matrix (ECM) synthesis. Connective tissue growth factor (CTGF) is a potent inducer of ECM synthesis and increases in the diabetic kidneys. To determine the critical role of CTGF in AGE-induced ECM accumulation leading to diabetic nephropathy, rats were given AGEs by intravenous injection for 6 weeks. AGE treatment induced a significant renal ECM accumulation, as shown by increases in periodic acid-Schiff-positive materials, fibronectin, and type IV collagen (Col IV) accumulation in glomeruli, and a mild renal dysfunction, as shown by increases in urinary volume and protein content. AGE treatment also caused significant increases in renal CTGF and transforming growth factor (TGF)-beta 1 mRNA and protein expression. Direct exposure of rat mesangial cells to AGEs in vitro significantly induced increases in fibronectin and Col IV production, which could be completely prevented by pretreatment with anti-CTGF antibody. AGE treatment also significantly increased both TGF-beta 1 and CTGF mRNA expression; however, inhibition of TGF-beta 1 mRNA expression by shRNA or neutralization of TGF-beta 1 protein by anti-TGF-beta 1 antibody did not significantly prevent AGE-increased expression of CTGF mRNA and protein. These results suggest that AGE-induced CTGF expression, predominantly through a TGF-beta 1-independent pathway, plays a critical role in renal ECM accumulation leading to diabetic nephropathy.

Lipid infusion decreases the expression of nuclear encoded mitochondrial genes and increases the expression of extracellular matrix genes in human skeletal muscle

The association between elevated plasma free fatty acid (FFA) concentrations and insulin resistance is well known. Although the cause and effect relationship between FFAs and insulin resistance is complex, plasma FFA is negatively correlated with the expression of peroxisome proliferator activated receptor-gamma cofactor-1 (PGC-1) and nuclear encoded mitochondrial genes. To test whether this association is causal, we infused a triglyceride emulsion (or saline as control) into healthy subjects to increase plasma FFA for 48 h followed by muscle biopsies, microarray analysis, quantitative real time PCR, and immunoblots. Lipid infusion increased plasma FFA concentration from 0.48 +/- 0.02 to 1.73 +/- 0.43 mm and decreased insulin-stimulated glucose disposal from 8.82 +/- 0.69 to 6.67 +/- 0.66 mg/kg.min, both with p < 0.05. PGC-1 mRNA, along with mRNAs for a number of nuclear encoded mitochondrial genes, were reduced by lipid infusion (p < 0.05). Microarray analysis also revealed that lipid infusion caused a significant overexpression of extracellular matrix genes and connective tissue growth factor. Quantitative reverse transcription PCR showed that the mRNA expression of collagens and multiple extracellular matrix genes was higher after the lipid infusion (p < 0.05). Immunoblot analysis revealed that lipid infusion also increased the expression of collagens and the connective tissue growth factor protein. These data suggest that an experimental increase in FFAs decreases the expression of PGC-1 and nuclear encoded mitochondrial genes and also increases the expression of extracellular matrix genes in a manner reminiscent of inflammation.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Antiproteinuric effect of RAS blockade: New mechanisms

Experimental and clinical studies have shown that blockade of the renin-angiotensin system (RAS) is effective in reducing proteinuria in conditions such as diabetes by reducing systemic and intraglomerular hydrostatic pressure. However, increasing evidence suggests that nonhemodynamic effects, such as preservation of the podocyte slit diaphragm structure and function, may also mediate the antiproteinuric effects of RAS blockade. In this review, we analyze in detail the evidence for known and novel mechanisms considered to play important roles in mediating the antiproteinuric effect of RAS blockers, with a particular focus on diabetic nephropathy.

Prevention of renal vascular and glomerular fibrosis by epidermal growth factor receptor inhibition

Hypertension is frequently associated with the development of renal vascular and glomerular fibrosis. The purpose of the present study was to investigate whether epidermal growth factor receptor (EGFR) activation participates in the development of renal fibrosis and to test if blockade of EGFR activation would have therapeutic effects. Experiments were performed during nitric oxide (NO) deficiency-induced hypertension in rats (L-NAME model). After 4 weeks of L-NAME treatment, animals developed hypertension associated to deterioration of renal structure and function. Over the same period, EGFR was activated twofold within glomeruli. This activation was accompanied by increased activity of the mitogen-activated protein kinase (MAPK) p42/p44 pathway and exaggerated collagen I expression. Gefitinib, an EGFR-tyrosine kinase inhibitor, given concomitantly with L-NAME, normalized MAPK activation and collagen I expression and prevented the decline of renal function and the development of fibrosis. Since endothelin mediates the L-NAME-induced fibrogenesis, the endothelin-EGFR interaction was tested in transgenic mice expressing luciferase under the control of collagen I-alpha2 promoter: In renal cortex of these animals, the endothelin-induced collagen I gene activity was inhibited by an EGFR-phosphorylation inhibitor. These results provide the first evidence that EGFR activation plays an important role in the progression of renal vascular and glomerular fibrosis.

K317, R319, and E320 within the proximal C-terminus of the bradykinin B2 receptor form a motif important for phospholipase C and phospholipase A2 but not connective tissue growth factor related signaling

We showed previously that large domain exchanges between the bradykinin B2 (BKB2) and angiotensin II type 1a (AT1a) receptors can result in functional hybrids. However, when we proceeded to exchange the entire bradykinin B2 receptor (BKB2R) C-terminal tail with the AT1aR C-terminus, the hybrid, while continuing to bind BK and be endocytosed as wild type (WT) BKB2R, lost much of its ability to activate phosphatidylinositol (PI) turnover or the release of arachidonic acid (ARA). In this study, we constructed chimeric receptors within the proximal C-terminus between the BKB2R and AT1aR or bradykinin B1 receptor (BKB1R). The mutant and WT receptor cDNAs were stably transfected into Rat-1 cells. Also, point mutations were generated to evaluate the role of the individual residues within this region. These chimeric studies revealed that the proximal portion of the BKB2R C-tail is crucial for G protein-linked BKB2R functions. This region could not be swapped with the AT1aR to obtain a BK activated PI turnover or ARA release. Further studies demonstrated that the distal portion (325-330) of this region is exchangeable; however, the middle portion (317-324) is not. Small motif exchanges within this section identified the KSR and EVY motifs as crucial for G(alphaq), G(alphai) related signaling of the BKB2R. Point mutations then showed that the charged amino acids K317, R319, and E320 are the residues critical for linking to PI turnover and ARA release. However, these proximal chimeras showed normal receptor uptake. Interestingly, while apparently not activating G protein-linked signaling, the proximal tail AT1aR exchange mutant and the entire C-terminus exchange hybrid continued to cause a substantial bradykinin effected increase in connective tissue growth factor (CTGF) mRNA level, as WT BKB2R.