Increased expression of TGF-beta1 but not of its receptors contributes to human obstructive nephropathy

CDH12 as a Candidate Gene for Kidney Injury in Posterior Urethral Valve Cases: A Genome-wide Association Study Among Patients with Obstructive Uropathies

Background

Posterior urethral valves (PUVs) and ureteropelvic junction obstruction (UPJO) are congenital obstructive uropathies that may impair kidney development.

Objective

To identify genetic variants associated with kidney injury in patients with obstructive uropathy.

Design, setting, and participants

We included 487 patients born in 1981 or later who underwent pyeloplasty or valve resection before 18 yr of age in the discovery phase, 102 PUV patients in a first replication phase, and 102 in a second replication phase.

Outcome measurements and statistical analysis

Signs of kidney injury were defined as dialysis, nephrectomy, kidney transplantation, estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m², high blood pressure, antihypertensive medication use, proteinuria, and/or one kidney functioning at <45%. We used χ² tests to calculate p values and odds ratios for >600 000 single-nucleotide polymorphisms (SNPs) in the discovery sample comparing patients with and without signs of kidney injury within 5 yr after surgery. We performed stratified analyses for PUV and UPJO and Kaplan-Meier and Cox regression analyses in the discovery and two replication samples for the associated SNPs, and RNA and protein expression analyses for the associated gene in fetal tissues.

Results and limitations

Despite the small and nonhomogeneous sample, we observed suggestive associations for six SNPs in three loci, of which rs6874819 in the CDH12 gene was the most clear (p = 7.5 × 10^–7). This SNP also seemed to be associated with time to kidney injury in the PUV discovery and replication samples. RNA expression analyses showed clear CDH12 expression in fetal kidneys, which was confirmed by protein immunolocalization.

Conclusions

This study identified CDH12 as a candidate gene for kidney injury in PUV.

Patient summary

We found that variants of the CDH12 gene increase the risk of kidney injury in patients with extra flaps of tissue in the urethra (posterior urethral valves). This is the first report on this gene in this context. Our study provides interesting new information about the pathways involved and important leads for further research for this condition.

Selective Detection of Nano-Sized Diagnostic Markers Using Au-ZnO Nanorod-Based Surface-Enhanced Raman Spectroscopy (SERS) in Ureteral Obstruction Models

Background

This study investigated the diagnosis of renal diseases using a biochip capable of detecting nano-sized biomarkers. Raman measurements from a kidney injury model were taken, and the feasibility of early diagnosis was assessed.

Materials and Methods

Rat models with mild and severe unilateral ureteral obstructions were created, with the injury to the kidney varying according to the tightness of the stricture. After generating the animal ureteral obstruction models, urine was collected from the kidney and bladder.

Results and Discussion

After confirming the presence of renal injury, urine drops were placed onto a Raman chip whose surface had been enhanced with Au-ZnO nanorods, allowing nano-sized biomarkers that diffused into the nanogaps to be selectively amplified. The Raman signals varied according to the severity of the renal damage, and these differences were statistically confirmed.

Conclusion

These results confirm that ureteral stricture causes kidney injury and that signals in the urine from the release of nano-biomarkers can be monitored using surface-enhanced Raman spectroscopy.

Urinary excretion of EGF and MCP-1 in children with vesicoureteral reflux

Purpose

The aim of this study was to investigate the urinary concentration of epidermal growth factor (EGF) and monocyte chemotactic protein-1 (MCP-1) as reflux nephropathy (RN) biomarkers before and after endoscopic treatment of moderate to severe vesico-ureteral reflux (VUR).

Materials and methods

A prospective study was carried out on 72 children with moderate to severe VUR. All patients underwent endoscopic treatment using Macroplastique® or Deflux®. Vesico-ureteral reflux resolution was tested by post-operative voiding cystourethrography after 3 months and 2 years. Follow-up urinary samples were collected at that time. Control samples were taken from healthy children with no clinical evidence of renal and bladder disease and no history of UTI.

Results

In VUR patients, pre-operative urinary EGF levels had a down-regulation when compared to controls. Following successful VUR repair, urinary EGF levels of VUR children progressively increased only at long term follow-up but without returning to normal levels. Urinary MCP-1 levels were highly expressed in pre-operative samples and decreased markedly during early post-operative measurements. Urinary MCP-1 levels did not further decreased in late post-operative follow-up. In fact, these levels remained significantly higher when compared to controls.

Conclusions

Urinary levels of EGF and MCP-1 may become useful markers for monitoring the response to surgical treatment in VUR patients. Although endoscopic VUR treatment is effective in reducing the inflammatory response, the persistence of significant abnormal levels of inflammatory cytokines (such as urinary MCP-1) at long term follow-up suggests that surgery alone may not completely treat the chronic renal inflammation evidenced in these children.

Oligo-fucoidan prevents renal tubulointerstitial fibrosis by inhibiting the CD44 signal pathway

Tubulointerstitial fibrosis is recognized as a key determinant of progressive chronic kidney disease (CKD). Fucoidan, a sulphated polysaccharide extracted from brown seaweed, exerts beneficial effects in some nephropathy models. The present study evaluated the inhibitory effect of oligo-fucoidan (800 Da) on renal tubulointerstitial fibrosis. We established a mouse CKD model by right nephrectomy with transient ischemic injury to the left kidney. Six weeks after the surgery, we fed the CKD mice oligo-fucoidan at 10, 20, and 100 mg/kg/d for 6 weeks and found that the oligo-fucoidan doses less than 100 mg/kg/d improved renal function and reduced renal tubulointerstitial fibrosis in CKD mice. Oligo-fucoidan also inhibited pressure-induced fibrotic responses and the expression of CD44, β-catenin, and TGF-β in rat renal tubular cells (NRK-52E). CD44 knockdown downregulated the expression of β-catenin and TGF-β in pressure-treated cells. Additional ligands for CD44 reduced the anti-fibrotic effect of oligo-fucoidan in NRK-52E cells. These data suggest that oligo-fucoidan at the particular dose prevents renal tubulointerstitial fibrosis in a CKD model. The anti-fibrotic effect of oligo-fucoidan may result from interfering with the interaction between CD44 and its extracellular ligands.

Deficiency of fibroblast activation protein alpha ameliorates cartilage destruction in inflammatory destructive arthritis

Introduction

Inflammatory destructive arthritis, like rheumatoid arthritis (RA), is characterized by invasion of synovial fibroblasts (SF) into the articular cartilage and erosion of the underlying bone, leading to progressive joint destruction. Because fibroblast activation protein alpha (FAP) has been associated with cell migration and cell invasiveness, we studied the function of FAP in joint destruction in RA.

Methods

Expression of FAP in synovial tissues and fibroblasts from patients with osteoarthritis (OA) and RA as well as from wild-type and arthritic mice was evaluated by immunohistochemistry, fluorescence microscopy and polymerase chain reaction (PCR). Fibroblast adhesion and migration capacity was assessed using cartilage attachment assays and wound-healing assays, respectively. For in vivo studies, FAP-deficient mice were crossed into the human tumor necrosis factor transgenic mice (hTNFtg), which develop a chronic inflammatory arthritis. Beside clinical assessment, inflammation, cartilage damage, and bone erosion were evaluated by histomorphometric analyses.

Results

RA synovial tissues demonstrated high expression of FAP whereas in OA samples only marginal expression was detectable. Consistently, a higher expression was detected in arthritis SF compared to non-arthritis OA SF in vitro. FAP-deficiency in hTNFtg mice led to less cartilage degradation despite unaltered inflammation and bone erosion. Accordingly, FAP^−/− hTNFtg SF demonstrated a lower cartilage adhesion capacity compared to hTNFtg SF in vitro.

Conclusions

These data point to a so far unknown role of FAP in the attachment of SF to cartilage, promoting proteoglycan loss and subsequently cartilage degradation in chronic inflammatory arthritis.

MicroRNA-328 inhibits renal tubular cell epithelial-to-mesenchymal transition by targeting the CD44 in pressure-induced renal fibrosis

Epithelial-mesenchymal transition (EMT) occurs in stressed tubular epithelial cells, contributing to renal fibrosis. Initial mechanisms promoting EMT are unknown. Pressure force is an important mechanism contributing to the induction and progression of renal fibrogenesis in ureteric obstruction. In our study of cultured rat renal tubular cells (NRK-52E) under 60 mmHg of pressure, we found that the epithelial marker E-cadherin decreased and mesenchymal markers, e.g., α-smooth muscle actin, fibronectin and Snail, increased. Pressure also induced the expression of connective tissue growth factor and transforming growth factor-β. MicroRNA array assays showed that pressure reduced miR-328 at the initial stage of pressurization. We identified a potential target sequence of miR-328 in rat CD44 3′-untranslated regions. In contrast with the miR-328 expression, CD44 expression was up-regulated at the initial pressurization stage. We also found that miR-328 expression decreased and CD44 increased in ureteric obstruction kidneys in the animal study. CD44 siRNA transfection significantly increased E-cadherin expression and inhibited pressure-induced EMT. Both hyaluronan binding peptide pep-1 and osteopontin neutralizing antibody inhibited pressure-induced EMT. Our results suggest that miR-328-mediated CD44 transient upregulation is an important trigger of the pressure-induced EMT in renal fibrosis.

Unilateral ureteral obstruction: beyond obstruction

Unilateral ureteral obstruction is a popular experimental model of renal injury. However, the study of the kidney response to urinary tract obstruction is only one of several advantages of this model. Unilateral ureteral obstruction causes subacute renal injury characterized by tubular cell injury, interstitial inflammation and fibrosis. For this reason, it serves as a model both of irreversible acute kidney injury and of events taking place during human chronic kidney disease. Being a unilateral disease, it is not useful to study changes in global kidney function, but has the advantage of a low mortality and the availability of an internal control (the non-obstructed kidney). Experimental unilateral ureteral obstruction has illustrated the molecular mechanisms of apoptosis, inflammation and fibrosis, all three key processes in kidney injury of any cause, thus providing information beyond obstruction. Recently this model has supported key concepts on the role in kidney fibrosis of epithelial-mesenchymal transition, tubular epithelial cell G2/M arrest, the anti-aging hormone Klotho and renal innervation. We now review the experimental model and its contribution to identifying novel therapeutic targets in kidney injury and fibrosis, independently of the noxa.

The antifibrotic effect of a serine protease inhibitor in the kidney

Interstitial fibrosis is a final common pathway for the progression of chronic kidney diseases. Activated fibroblasts have an extremely important role in the progression of renal fibrosis, and transforming growth factor (TGF)-β₁ is a major activator of fibroblasts. Since previous reports have indicated that serine protease inhibitors have a potential to inhibit TGF-β₁ signaling in vitro, we hypothesized that a synthetic serine protease inhibitor, camostat mesilate (CM), could slow the progression of renal fibrosis. TGF-β₁ markedly increased the phosphorylation of TGF-β type I receptor, ERK 1/2, and Smad2/3 and the levels of profibrotic markers, such as α-smooth muscle actin (α-SMA), connective tissue growth factor (CTGF), and plasminogen activator inhibitor-1, in renal fibroblasts (NRK-49F cells), and they were all significantly reduced by CM. In protocol 1, 8-wk-old male Sprague-Dawley rats were subjected to unilateral ureteral obstruction (UUO) and were concurrently treated with a slow-release pellet of CM or vehicle for 14 days. Protocol 2 was similar to protocol 1 except that CM was administered 7 days after UUO. CM substantially improved renal fibrosis as determined by sirius red staining, collagen expression, and hydroxyproline levels. The phosphorylation of ERK1/2 and Smad2/3 and the levels of α-SMA, CTGF, promatrix metalloproteinase-2, and matrix metalloproteinase-2 were substantially increased by UUO, and they were all significantly attenuated by CM. These antifibrotic effects of CM were also observed in protocol 2. Our present results suggest the possibility that CM might represent a new class of therapeutic drugs for the treatment of renal fibrosis through the suppression of TGF-β₁ signaling.

Rosuvastatin inhibits pressure-induced fibrotic responses via the expression regulation of prostacyclin and prostaglandin E2 in rat renal tubular cells

Statins are reported to alleviate renal fibrosis in animal models with ureteral obstruction. However, the molecular mechanism of this antifibrotic effect is still unclear. Pressure force is an important mechanism contributing to induction and progression of tubulointerstitial fibrogenesis in ureteric obstruction. In this study, we investigated the influence of rosuvastatin on pressure-induced fibrotic responses in rat renal tubular cells (NRK-52E). We established an in vitro pressure culture system to study pressure-induced fibrotic responses in NRK-52E cells. When NRK-52E cells were cultured in the pressure culture system, 60 mm Hg of pressure induced the expression of connective tissue growth factor (CTGF), transforming growth factor (TGF)-β, fibronectin, Smad3, and phospho-Smad3. Rosuvastatin significantly reduced these pressure-induced fibrotic responses at concentrations above 10 μM. Rosuvastatin also reduced the TGF-β-induced expression of fibronectin and CTGF in NRK-52E cells. Pretreatment with rosuvastatin significantly induced prostacyclin (PGI(2)) generation, but reduced pressure-induced prostaglandin E(2) (PGE(2)). PGI(2) synthase small interfering RNA (siRNA) transfection significantly inhibited rosuvastatin-induced peroxisome proliferator-activated receptor α activation. The blockage of peroxisome proliferator-activated receptor α by siRNA transfection reduced the inhibitory effect of rosuvastatin on pressure-induced fibrotic responses. N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide (NS398), a specific inhibitor of cyclooxygenase-2, diminished pressure-induced PGE(2) generation, and also reduced pressure-induced fibrotic responses. Additionally, PGE(2) decreased the antifibrotic effect of rosuvastatin. In conclusion, rosuvastatin reduces pressure-induced fibrotic responses in renal tubular cells by enhancing the PGI(2)-peroxisome proliferator-activated receptor α pathway and reducing PGE(2) generation.

Obstructive renal injury: from fluid mechanics to molecular cell biology

Urinary tract obstruction is a frequent cause of renal impairment. The physiopathology of obstructive nephropathy has long been viewed as a mere mechanical problem. However, recent advances in cell and systems biology have disclosed a complex physiopathology involving a high number of molecular mediators of injury that lead to cellular processes of apoptotic cell death, cell injury leading to inflammation and resultant fibrosis. Functional studies in animal models of ureteral obstruction using a variety of techniques that include genetically modified animals have disclosed an important role for the renin-angiotensin system, transforming growth factor-β1 (TGF-β1) and other mediators of inflammation in this process. In addition, high throughput techniques such as proteomics and transcriptomics have identified potential biomarkers that may guide clinical decision-making.

Noncanonical TGF-beta pathways, mTORC1 and Abl, in renal interstitial fibrogenesis

Renal interstitial fibrosis is a major determinant of renal failure in the majority of chronic renal diseases. Transforming growth factor-beta (TGF-beta) is the single most important cytokine promoting renal fibrogenesis. Recent in vitro studies identified novel non-smad TGF-beta targets including p21-activated kinase-2 (PAK2), the abelson nonreceptor tyrosine kinase (c-Abl), and the mammalian target of rapamycin (mTOR) that are activated by TGF-beta in mesenchymal cells, specifically in fibroblasts but less in epithelial cells. In the present studies, we show that non-smad effectors of TGF-beta including PAK2, c-Abl, Akt, tuberin (TSC2), and mTOR are activated in experimental unilateral obstructive nephropathy in rats. Treatment with c-Abl or mTOR inhibitors, imatinib mesylate and rapamycin, respectively, each blocks noncanonical (non-smad) TGF-beta pathways in the kidney in vivo and diminishes the number of interstitial fibroblasts and myofibroblasts as well as the interstitial accumulation of extracellular matrix proteins. These findings indicate that noncanonical TGF-beta pathways are activated during the early and rapid renal fibrogenesis of obstructive nephropathy. Moreover, the current findings suggest that combined inhibition of key regulators of these non-smad TGF-beta pathways even in dose-sparing protocols are effective treatments in renal fibrogenesis.

A case report suggesting the occurrence of epithelial-mesenchymal transition in obstructive nephropathy

Epithelial-mesenchymal transition (EMT) has been well investigated using cultured kidney epithelial cell lines and the mouse obstructive nephropathy model. The role of EMT in the genesis or progression of human renal fibrosis remains controversial. We report a case of obstructive nephropathy that occurred in a pregnant woman. Renal tissue obtained by percutaneous renal biopsy after the delivery showed marked interstitial fibrosis and obstructive tubuli. Immunofluorescence images clearly demonstrated S100A4-positive tubular epithelial cells in these specimens. With regard to human obstructive nephropathy, this is the first report which proves that tubular epithelial cells become positive for the fibroblast-specific marker. EMT is probably a common event not only in mouse but also in human.

Deletion of bradykinin B1 receptor reduces renal fibrosis

The Kallikrein-kinin system works through activation of two receptors. One constitutive, named B2 receptor (B2R) and another inducible, denominated B1 receptor (B1R). In renal fibrosis, B2R receptor activation appears to be protective, however B1R participation is unveiled. The aim of this study was to analyze how the deletion of the B1R would modify tissue responses after unilateral ureteral obstruction (UUO). For that, B1R knockout (B1KO) and wild-type mice (B1B2WT) were subjected to UUO and sacrificed at days 1, 5 and 14. Renal dysfunction was assayed by urine proteinuria/creatinine ratio and percentage of tubulointerstitial fibrosis. Kidneys were harvested at day 5 to analyze anti and pro-inflammatory molecules expression by real-time PCR. We demonstrated that at all time points, B1KO mice presented lower proteinuria/creatinine ratio from bladder urine. B1KO protection was reinforced by its lower tubular interstitial fibrosis percentage at day 14 (B1B2WT: 12.16+/-1.53% vs. B1KO: 6.73+/-1.07%, p<0.02). UUO was able to induce B1R expression and its highest transcription was achieved at day 5. At this day, B1KO had significant lower expression of pro-inflammatory molecules such as TGF-beta, MCP-1, OPN and IL-6 and higher anti-inflammatory components, as IL-10 and HO-1. Herein, we observed that B1R deletion may be an important component in renal fibrosis prevention.

Safflower extract: a novel renal fibrosis antagonist that functions by suppressing autocrine TGF-beta

Progressive renal disease is characterized by the accumulation of extracellular matrix proteins in the renal interstitium. Hence, developing agents that antagonize fibrogenic signals is a critical issue facing researchers. The present study investigated the blood-circulation-promoting Chinese herb, safflower, on fibrosis status in NRK-49F cells, a normal rat kidney interstitial fibroblast, to evaluate the underlying signal transduction mechanism of transforming growth factor-beta (TGF-beta), a potent fibrogenic growth factor. Safflower was characterized and extracted using water. Renal fibrosis model was established both in vitro with fibroblast cells treated with beta-hydroxybutyrate and in vivo using rats undergone unilateral ureteral obstruction (UUO). Western blotting was used to examine protein expression in TGF-beta-related signal proteins such as type I and type II TGF-beta receptor, Smads2/3, pSmad2/3, Smads4, and Smads7. ELISA was used to analyze bioactive TGF-beta1 and fibronectin levels in the culture media. Safflower extract (SE) significantly inhibited beta-HB-induced fibrosis in NRK cells concomitantly with dose-dependent inhibition of the type I TGF-beta1 receptor and its down-stream signals (i.e., Smad). Moreover, SE dose-dependently enhanced inhibitory Smad7. Thus, SE can suppress renal cellular fibrosis by inhibiting the TGF-beta autocrine loop. Moreover, remarkably lower levels of tissue collagen were noted in the nephron and serum TGF-beta1 of UUO rats receiving oral SE (0.15 g/3 ml/0.25 kg/day) compared with the untreated controls. Hence, SE is a potential inhibitor of renal fibrosis. We suggest that safflower is a novel renal fibrosis antagonist that functions by down-regulating TGF-beta signals.

Parathyroid hormone-related protein interacts with vascular endothelial growth factor to promote fibrogenesis in the obstructed mouse kidney

Parathyroid hormone-related protein (PTHrP) interacts with vascular endothelial growth factor (VEGF) in osteoblasts. Since both PTHrP and VEGF have both proinflammatory and profibrogenic features, we assessed here whether these factors might act in concert to promote fibrogenesis in the obstructed kidney. VEGF receptor (VEGFR)-1 was upregulated, while VEGFR-2 was downregulated (at both mRNA and protein levels) in the mouse kidney within 2-6 days after ureteral obstruction. VEGF protein levels also increased in the obstructed kidney at the latter time. Moreover, this VEGF and VEGFR-1 upregulation was higher in mice overexpressing PTHrP in the proximal tubule than in control littermates. These changes were associated with higher fibronectin mRNA expression and alpha-smooth muscle actin (alpha-SMA) and integrin-linked kinase (ILK) immunostaining and lower apoptotic tubulointerstitial cells in the mouse obstructed kidney than in control littermates. Pretreatment with a neutralizing anti-VEGF antibody reversed these responses in the obstructed kidney of both types of mice. In vitro, PTHrP-(1-36) increased (maximal 2-fold vs. basal, at 100 nM) alpha-SMA and ILK protein expression and decreased E-cadherin protein levels in renal tubuloepithelial mouse cortical tubule and normal rat kidney (NRK) 52E cells. PTHrP-(1-36) also decreased cyclosporine A- and/or osmotic stress-induced apoptosis in these cells and in renal fibroblastic NRK 49F cells. These effects elicited by PTHrP-(1-36) were associated with both VEGF and VEGFR-1 upregulation, and abolished by the anti-VEGF antibody. Collectively, these findings strongly suggest that VEGF acts as an important mediator of PTHrP to promote fibrogenesis in the obstructed kidney.

Hepatocyte growth factor induction of macrophage chemoattractant protein-1 and osteophyte-inducing factors in osteoarthritis

In osteoarthritis (OA), hepatocyte growth factor (HGF) is supposed to play a role in cartilage repair. Because the development of osteophytes is a major characteristic of OA and thought to be part of an attempted repair process, the purpose of this study was to determine whether HGF may be involved in osteophyte formation. HGF levels in synovial fluids from 41 patients assessed by enzyme immunosorbant assay were correlated with disease severity and osteophyte formation, evaluated by anteroposterior weight-bearing radiographs. Detection of HGF, c-Met, and CD68 in cartilage and synovial tissues was assessed by immunohistochemistry. Effects of HGF on the secretion of TGF-beta1 and BMP-2 by chondrocytes, fibroblast-like synovial cells (FLS), and macrophages as well as HGF-induced secretion of MCP-1 by FLS and chondrocytes were determined by ELISA. HGF was detected in all synovial fluids and concentrations correlated highly with disease severity and osteophyte formation (p < 0.001). Immunohistochemistry revealed weak synovial staining for HGF, whereas increasing numbers of HGF expressing chondrocytes were detected depending on disease severity. In addition, an increased number of macrophages in synovial specimens was observed, which was likewise severity dependent. In a series of subsequent in vitro studies, HGF remarkable induced MCP-1 secretion by FLS in a dose-dependent manner. No effect on TGF-beta1 and BMP-2 secretion by FLS and chondrocytes was evident upon HGF stimulation, whereas secretion of these growth factors by PMA-differentiated THP-1 cells was significantly increased by HGF. The results indicate that HGF may facilitate osteophyte development by promoting MCP-1-mediated entry of monocytes/macrophages into the OA-affected joint and/or by stimulating macrophage-derived growth factors.

Obstructive nephropathy: towards biomarker discovery and gene therapy

Obstructive nephropathy is a major cause of renal failure, particularly in infants and children. Cellular and molecular mechanisms responsible for the progression of the tubular atrophy and interstitial fibrosis-processes that lead to nephron loss-have been elucidated in the past 5 years. Following urinary tract obstruction and tubular dilatation, a cascade of events results in upregulation of the intrarenal renin-angiotensin system, tubular apoptosis and macrophage infiltration of the interstitium. This is followed by accumulation of interstitial fibroblasts through proliferation of resident fibroblasts and epithelial-mesenchymal transformation of renal tubular cells. Under the influence of cytokines, chemokines and other signaling molecules produced by tubular and interstitial cells, fibroblasts undergo transformation to myofibroblasts that induce expansion of the extracellular matrix. The cellular interactions that regulate development of interstitial inflammation, tubular apoptosis and interstitial fibrosis are complex. Changes in renal gene expression and protein production afford many potential biomarkers of disease progression and targets for therapeutic manipulation. These include signaling molecules and receptors involved in macrophage recruitment and proliferation, tubular death signals and survival factors, and modulators of epithelial-mesenchymal transformation. Targeted gene deletion and various forms of gene therapy have been used in experimental obstructive nephropathy, mostly rodent models of unilateral ureteral obstruction or cell culture techniques. Further refinement of these models is needed to develop a matrix of biomarkers with clinical predictive value, as well as molecular therapies that will prevent or reverse the renal structural and functional consequences of obstructive nephropathy.

Obstructive nephropathy: insights from genetically engineered animals

Congenital obstructive nephropathy is the primary cause for end-stage renal disease (ESRD) in children. An increasingly used animal model of obstructive nephropathy is unilateral ureteral obstruction (UUO). This model mimics, in an accelerated manner, the different stages of obstructive nephropathy leading to tubulointerstitial fibrosis: cellular infiltration, tubular proliferation and apoptosis, epithelial-mesenchymal transition (EMT), (myo)fibroblast accumulation, increased extracellular matrix (ECM) deposition, and tubular atrophy. During the last decade genetically modified animals are increasingly used to study the development of obstructive nephropathy. Although the use of these animals (mainly knockouts) has highlighted some pitfalls of this approach (compensation by closely related gene products, absence of temporal knockouts) it has brought important information about the role of specific gene-products in the pathogenesis of obstructive nephropathy. Besides confirming the important pathologic role for angiotensin II (Ang II) and transforming growth factor-beta (TGF-beta) in obstructive nephropathy, these animals have shown the complexity of the development of tubulointerstitial fibrosis involving a large number of closely functionally related molecules. More interestingly, the use of these animals has led to the discovery of unexpected and contradictory roles (both potentially pro- and antifibrotic) for Ang II, for ECM degrading enzymes matrix metalloproteinase 9 (MMP-9) and tissue plasminogen activators (PAs), for plasminogen activator inhibitor 1 (PAI-1), and for the adhesion molecule osteopontin (OPN) in obstructive nephropathy. Further use of these animals, especially in combination with pharmacologic tools, should help to better identify potential antifibrotic strategies in obstructive nephropathy.

Evidence that inhibition of tubular cell apoptosis protects against renal damage and development of fibrosis following ureteric obstruction

Ureteric obstruction is frequently encountered in primary care urology and can lead to damage to the ipsilateral kidney. Relief of all types of obstruction generally leads to the normalization of any deterioration in renal function noted at diagnosis. However, some evidence from animal models suggests that obstruction can cause progressive deleterious effects on renal function and blood pressure control, especially in the presence of preexisting pathologies such as essential hypertension. The last 10 years have seen a proliferation of studies in rodents wherein complete unilateral ureteric obstruction has been used as a model of renal fibrosis. However, the relevance of the findings to human obstructive uropathy has, in many cases, not been the primary aim. In this review, we outline the major events linking damage to the renal parenchyma and cell death to the evolution of fibrosis following obstruction. Special focus is given to the role of apoptosis as a major cause of cell death during and post-complete ureteric obstruction. Several interventions that reduce tubular apoptosis are discussed in terms of their ability to prevent subsequent progression to end-organ damage and fibrosis.

Obstructive nephropathy and renal fibrosis: The role of bone morphogenic protein-7 and hepatocyte growth factor

BACKGROUND

The nephropathy induced by ureteral obstruction is associated with increased interstitial volume due to matrix deposition, fibroblast differentiation/proliferation, and monocyte infiltration. Recent studies indicate that transforming growth factor-beta (TGF-beta) is linked to renal fibrosis. Tumor necrosis factor (TNF-alpha) has a role in the recruitment of inflammatory cells. We found that infiltration of macrophages of the interstitium in unilateral ureteral obstruction (UUO) occurred as early as four hours after the onset of UUO.

METHODS

Recent studies indicate that a renal tubular development morphogen, bone morphogenetic protein-7 (BMP-7), is effective in preventing the tubulointerstitial nephritis in the setting of obstructive nephropathy. The mechanism of action appears to be preservation of epithelial cell phenotype, inhibition of epithelial-mesenchymal transdifferentiation, and inhibition of injury-induced epithelial cell apoptosis. Hepatocyte growth factor (HGF) also inhibited tubulointerstitial fibrosis.

RESULTS

In a treatment protocol in rats with ureteral ligation, BMP-7 restored renal function. The preservation of glomerular filtration rate (GFR) was accompanied by a significant decrease in cortical interstitial volume. In diabetic rats given BMP-7 proteinuria was normalized. In mice with ureteral obstruction, HGF suppressed the expression of TGF-beta and of platelet-derived growth factor. The onset of tubulointerstitial fibrosis was almost completely inhibited by HGF.

CONCLUSION

Both BMP-7 and HGF attenuate the tubulointerstitial fibrosis due to ureteral obstruction. They also increase GFR and renal plasma flow.

[Experimental ureteral obstruction and knockout animals]

Obstructive uropathies caused by congenital malformations of the urinary tract are relatively frequent in newborn. These obstructive lesions are the main cause for renal disease in infancy. Most of these uropathies are treated by surgical interventions restoring the drainage function of the urinary tract. Clinically these patients are cured but the question remains wether these patients will develop renal disease in adult life, since it has been recently shown in animal models that transient, neonatal and prenatal, ureteral obstruction induces significant renal deterioration later in life. Except for angiotensin converting enzyme inhibitors that slow down the progression of renal disease, no specific drugs reducing renal fibrosis exist. Animal models of ureteral obstruction have allowed to clearly identify the events leading to tubulointerstitial fibrosis. Furthermore, more recently, the use of ureteral obstruction in genetically engineered animals has shown pro- and anti-fibrotic properties of a large number of molecules. These studies using genetically engineered animals have suggested several new future promising therapeutic directions to treat renal fibrosis.

Obstructive nephropathy and renal fibrosis

Interstitial fibrosis has a major role in the progression of renal diseases. Several animal models are available for the study of renal fibrosis. The models of aminonucleoside-induced nephrotic syndrome, cyclosporin nephrotoxicity, and passive Heyman nephritis are characterized by molecular and cellular events similar to those that occur in obstructive nephropathy. Additionally, inhibition of angiotensin-converting enzyme exerts salutary effects on the progression of renal fibrosis in obstructive nephropathy. Unilateral ureteral obstruction (UUO) has emerged as an important model for the study of the mechanisms of renal fibrosis and also for the evaluation of the impact of potential therapeutic approaches to ameliorate renal disease. Many quantifiable pathophysiological events occur over the span of 1 wk of UUO, making this an attractive model for study. This paper reviews some of the ongoing studies that utilized a rodent model of UUO. Some of the findings of the animal model have been compared with observations made in patients with obstructive nephropathy. Most of the evidence suggests that the rodent model of UUO is reflective of human renal disease processes.

Current concepts in radiation enteritis and implications for future clinical trials

BACKGROUND

Radiation enteritis is one of the most feared complications of abdominal and pelvic radiation. Once its occurs, the process is relentless and may result in the patient's death. Available treatment is only supportive. Recent progress in molecular biology has shed some light on the pathogenesis of radiation enteritis and other diseases that are characterized by excessive fibrosis. New treatment modalities may be devised to improve the outcome of patients who are affected with this complication.

METHODS

A literature search was used to identify the common denominator between many radiation-induced fibrotic conditions and other sclerotic diseases. Factors that affect the disease process and possible therapeutic interventions were evaluated.

RESULTS

The hyperstimulation of transforming growth factor beta1 (TGF-beta1) leads to increased fibrosis and, ultimately, organ failure. Interferon gamma (IFN-gamma) inhibits the effects of TGF-beta1 in the nucleus. The fibrotic process may be reverted by IFN-gamma in various pathologic conditions.

CONCLUSIONS

Radiation enteritis and other radiation-induced, long-term complications are characterized by excessive stimulation of TGF-beta1. Preliminary studies suggest that IFN-gamma may be effective in the treatment of patients with radiation-induced cutaneous fibrosis. IFN-gamma should be considered in Phase I-II studies to assess its toxicity and efficacy in the treatment of patients with radiation enteritis.

Deregulation of renal transforming growth factor-beta1 after experimental short-term ureteric obstruction in fetal sheep

Renal malformations are the commonest cause of chronic renal failure in children and they are often associated with urinary tract abnormalities that impair fetal urine flow. Up-regulation of transforming growth factor-beta1 (TGF-beta1) occurs after experimental postnatal urinary tract obstruction and we recently reported increased levels of TGF-beta1 in human renal malformations (Yang SP et al, Am J Pathol 2000, 157:1633-1647). These findings led us to propose that obstruction-induced stretch of developing renal epithelia causes up-regulation of TGF-beta1, which then perturbs renal development. In this study, therefore, we examined expression of components of the TGF-beta1 signaling axis in a previously characterized ovine model of fetal short-term urine flow impairment in which complete unilateral ureteric obstruction was induced at 90 days when a few layers of glomeruli had formed. Up-regulation of TGF-beta1 mRNA and protein was observed in obstructed kidneys, compared to sham-operated control organs, after only 10 days. Increased levels of TGF-beta1 receptors I (TGF-betaR1) and II (TGF-betaR2) were also detected on Western blot, and the cytokine and TGF-betaR1 co-localized in disrupted epithelia on immunohistochemistry. De novo expression of alpha-smooth muscle actin, a structural protein up-regulated during TGF-beta1-induced phenotypic switching between human renal dysplastic epithelial and mesenchymal lineages in vitro, was also observed in these aberrant epithelia. These findings implicate increased TGF-beta1 signaling in the early biological changes generated by fetal urinary tract obstruction.

Transforming growth factor-beta 1 antisense oligodeoxynucleotides block interstitial fibrosis in unilateral ureteral obstruction

BACKGROUND

Interstitial expression of transforming growth factor-beta1 (TGF-beta1) is important in tubulointerstitial fibrosis, a common process in most progressive renal diseases. However, no effective therapy for progressive interstitial fibrosis is known. Recently, we developed an artificial viral envelope (AVE)-type hemagglutinating virus of Japan (HVJ) liposome-mediated retrograde ureteral gene transfer method, which allowed us to introduce the genetic material selectively into renal interstitial fibroblasts.

METHOD

We introduced antisense or scrambled oligodeoxynucleotides (ODNs) for TGF-beta 1 into interstitial fibroblasts in rats with unilateral ureteral obstruction, a model of interstitial fibrosis, to block interstitial fibrosis by retrograde ureteral injection of AVE-type HVJ liposomes.

RESULTS

TGF-beta 1 and type I collagen mRNA increased markedly in the interstitium of untreated obstructed kidneys, and those were not affected by scrambled ODN transfection. Northern analysis and in situ hybridization revealed that the levels of TGF-beta 1 and type I collagen mRNA were dramatically decreased in antisense ODN-transfected obstructed kidneys. Consequently, the interstitial fibrotic area of the obstructed kidneys treated with antisense ODN was significantly less than that of the obstructed kidneys untreated or treated with scrambled ODN.

CONCLUSION

The introduction of TGF-beta 1 antisense ODN into interstitial fibroblasts may be a potential therapeutic maneuver for interstitial fibrosis.

Potential biological role of transforming growth factor-beta1 in human congenital kidney malformations

Transformations between epithelial and mesenchymal cells are widespread during normal development and adult disease, and transforming growth factor-beta1 (TGF-beta1) has been implicated in some of these phenotypic switches. Dysplastic kidneys are a common cause of chronic kidney failure in young children and result from perturbed epithelial-mesenchymal interactions. In this study, we found that components of the TGF-beta1 axis were expressed in these malformations: TGF-beta1 mRNA and protein were up-regulated in dysplastic epithelia and surrounding mesenchymal cells, whereas TGF-beta receptors I and II were expressed in aberrant epithelia. We generated a dysplastic kidney epithelial-like cell line that expressed cytokeratin, ZO1, and MET, and found that exogenous TGF-beta1 inhibited proliferation and decreased expression of PAX2 and BCL2, molecules characterizing dysplastic tubules in vivo. Furthermore, addition of TGF-beta1 specifically induced morphological changes compatible with a shift to a mesenchymal phenotype, accompanied by loss of ZO1 at cell borders and up-regulation of the mesenchymal markers alpha-smooth muscle actin and fibronectin. The descriptive and functional data presented in this report potentially implicate TGF-beta1 in the pathobiology of dysplastic kidneys and our results provide preliminary evidence that an epithelial-to-mesenchymal phenotypic switch may be implicated in a clinically important developmental aberration.