Contributions of angiotensin II and tumor necrosis factor-alpha to the development of renal fibrosis

A2B adenosine receptor-mediated induction of IL-6 promotes CKD

Chronic elevation of adenosine, which occurs in the setting of repeated or prolonged tissue injury, can exacerbate cellular dysfunction, suggesting that it may contribute to the pathogenesis of CKD. Here, mice with chronically elevated levels of adenosine, resulting from a deficiency in adenosine deaminase (ADA), developed renal dysfunction and fibrosis. Both the administration of polyethylene glycol-modified ADA to reduce adenosine levels and the inhibition of the A(2B) adenosine receptor (A(2B)R) attenuated renal fibrosis and dysfunction. Furthermore, activation of A(2B)R promoted renal fibrosis in both mice infused with angiotensin II (Ang II) and mice subjected to unilateral ureteral obstruction (UUO). These three mouse models shared a similar profile of profibrotic gene expression in kidney tissue, suggesting that they share similar signaling pathways that lead to renal fibrosis. Finally, both genetic and pharmacologic approaches showed that the inflammatory cytokine IL-6 mediates adenosine-induced renal fibrosis downstream of A(2B)R. Taken together, these data suggest that A(2B)R-mediated induction of IL-6 contributes to renal fibrogenesis and shows potential therapeutic targets for CKD.

TGF-β1-activated kinase-1 regulates inflammation and fibrosis in the obstructed kidney

Activation of c-Jun amino kinase (JNK), p38 mitogen-activated protein kinase (MAPK), and the transcription factor nuclear factor-κB (NF-κB) drives renal inflammation and fibrosis. However, the upstream MAP kinase kinase kinase (MAP3K) enzyme(s) that activate these pathways in kidney disease are unknown. We determined the role of one candidate MAP3K enzyme, transforming growth factor-β1-activated kinase-1 (TAK1/ MAP3K7), in activation of JNK, p38, and NF-κB in the obstructed kidney using conditional gene deletion in adult mice, and assessed the potential protective effect of TAK1 deletion on renal pathology. TAK1 deletion in cultured tubular epithelial cells substantially inhibited IL-1 and TNF-α-induced JNK, p38, and NF-κB signaling and the proinflammatory response. Map3k7(f/f)Cre-ER(TM) mice (in which tamoxifen induces global TAK1 deletion) and control Map3k7(f/f) mice were given tamoxifen at the time of unilateral ureteric obstruction (UUO) and then killed 2, 4, or 5 days later. Tamoxifen-treated control Map3k7(f/f) mice showed the expected activation of JNK, p38, and NF-κB signaling on days 2, 4, and 5, with macrophage infiltration and upregulation of mRNA levels of proinflammatory molecules (IL-1α, TNF-α, NOS2, and CCL2). Control Map3k7(f/f) mice also showed interstitial myofibroblast accumulation and collagen deposition in the obstructed kidney. Tamoxifen treatment of Map3k7(f/f)Cre-ER(TM) mice caused a 60% reduction in renal TAK1 expression on day 4 and >80% on day 5 UUO. Coincident with TAK1 deletion, activation of JNK, p38, and NF-κB signaling was markedly suppressed on days 4 to 5 UUO, which halted renal macrophage accumulation and expression of proinflammatory molecules. TAK1 deletion also halted the development of renal fibrosis in terms of myofibroblast accumulation, collagen deposition, and expression of profibrotic molecules. In conclusion, these studies establish TAK1 as a major upstream activator of JNK, p38, and NF-κB signaling in the obstructed kidney, and they define a pathologic role for TAK1 in renal inflammation and fibrosis.

Etiopathology of chronic tubular, glomerular and renovascular nephropathies: clinical implications

Chronic kidney disease (CKD) comprises a group of pathologies in which the renal excretory function is chronically compromised. Most, but not all, forms of CKD are progressive and irreversible, pathological syndromes that start silently (i.e. no functional alterations are evident), continue through renal dysfunction and ends up in renal failure. At this point, kidney transplant or dialysis (renal replacement therapy, RRT) becomes necessary to prevent death derived from the inability of the kidneys to cleanse the blood and achieve hydroelectrolytic balance. Worldwide, nearly 1.5 million people need RRT, and the incidence of CKD has increased significantly over the last decades. Diabetes and hypertension are among the leading causes of end stage renal disease, although autoimmunity, renal atherosclerosis, certain infections, drugs and toxins, obstruction of the urinary tract, genetic alterations, and other insults may initiate the disease by damaging the glomerular, tubular, vascular or interstitial compartments of the kidneys. In all cases, CKD eventually compromises all these structures and gives rise to a similar phenotype regardless of etiology. This review describes with an integrative approach the pathophysiological process of tubulointerstitial, glomerular and renovascular diseases, and makes emphasis on the key cellular and molecular events involved. It further analyses the key mechanisms leading to a merging phenotype and pathophysiological scenario as etiologically distinct diseases progress. Finally clinical implications and future experimental and therapeutic perspectives are discussed.

Renal fibrosis in murine obstructive nephropathy is attenuated by depletion of monocyte lineage, not dendritic cells

The role of renal dendritic cells (DCs) in renal fibrosis is unknown. The present study was conducted to examine the relative role of renal DCs and macrophages in the development of renal fibrosis in murine obstructive nephropathy. CD11c-diphtheria toxin receptor (DTR) transgenic mice and CD11b-DTR transgenic mice were subjected to unilateral ureteral obstruction. To conditionally and selectively deplete DCs or macrophages, DT was given to these mice and kidneys were harvested on day 5. Ureteral obstruction elicited renal fibrosis characterized by tubulointerstitial collagen III deposition and accumulation of α-smooth muscle actin-positive cells. Flow cytometric analysis revealed a marked increase in cell counts of F4/80(+) macrophages, F4/80(+) DCs, as well as neutrophils and T cells in the obstructed kidney. DT administration to CD11c-DTR mice led to selective depletion of renal CD11c(+) DCs, but did not affect renal fibrosis. In contrast, administration of DT to CD11b-DTR mice resulted in ablation of all monocyte lineages including macrophages and DCs and attenuated renal fibrosis. Our results do not support the role of renal DCs, but confirm the importance of monocyte lineage cells other than DCs in the development of the early phase of renal fibrosis following ureteral obstruction in mice.

A conceptual framework for the molecular pathogenesis of progressive kidney disease

The data regarding the pathogenesis of progressive kidney disease implicate cytokine effects, physiological factors, and myriad examples of relatively nonspecific cellular dysfunction. The sheer volume of information being generated on this topic threatens to overwhelm our efforts to understand progression in chronic kidney disease or to derive rational strategies to treat it. Here, a conceptual framework is offered for organizing and considering these data. Disease is initiated by an injury that evokes a tissue-specific cellular response. Subsequent structural repair may be effective, or the new structure may be sufficiently changed that it requires an adaptive physiological response. If this adaptation is not successful, subsequent cycles of misdirected repair or maladaptation may lead to progressive nephron loss. To illustrate how this framework can be used to organize our approach to disease pathogenesis, the role of cytokines in proteinuria and progressive glomerular disease is discussed. Finally, this theoretical framework is reconsidered to examine its implications for the diagnosis and treatment of clinical conditions. Application of this schema could have significant relevance to both research inquiry and clinical practice.

Proinflammatory gene expression and renal lipogenesis are modulated by dietary protein content in obese Zucker fa/fa rats

Obesity is a risk factor for the development of chronic kidney disease (CKD) and end-stage renal disease. It is not clear whether the adoption of a high-protein diet in obese patients affects renal lipid metabolism or kidney function. Thus the aims of this study were to assess in obese Zuckerfa/fa rats the effects of different types and amounts of dietary protein on the expression of lipogenic and inflammatory genes, as well as renal lipid concentration and biochemical parameters of kidney function. Rats were fed different concentrations of soy protein or casein (20, 30, 45%) for 2 mo. Independent of the type of protein ingested, higher dietary protein intake led to higher serum triglycerides (TG) than rats fed adequate concentrations of protein. Additionally, the soy protein diet significantly increased serum TG compared with the casein diet. However, rats fed soy protein had significantly decreased serum cholesterol concentrations compared with those fed a casein diet. No significant differences in renal TG and cholesterol concentrations were observed between rats fed with either protein diets. Renal expression of sterol-regulatory element binding protein 2 (SREBP-2) and its target gene HMG-CoA reductase was significantly increased as the concentration of dietary protein increased. The highest protein diets were associated with greater expression of proinflammatory cytokines in the kidney, independent of the type of dietary protein. These results indicate that high soy or casein protein diets upregulate the expression of lipogenic and proinflammatory genes in the kidney.

Effect of the inosine 5'-monophosphate dehydrogenase inhibitor BMS-566419 on renal fibrosis in unilateral ureteral obstruction in rats

Chronic allograft nephropathy (CAN) is a major cause of late allograft loss. One morphological characteristic of CAN is renal interstitial fibrosis. Mycophenolate mofetil (MMF), the inosine 5'-monophosphate dehydrogenase (IMPDH) inhibitor, has been reported to attenuate the progression of renal interstitial fibrosis. However, the question of whether the newly synthesized IMPDH inhibitors with structures different from MMF have an antifibrotic effect remains unanswered. We evaluated the antifibrotic effects of BMS-566419, a chemically synthesized IMPDH inhibitor, using an experimental rat model, unilateral ureteral obstruction (UUO), in comparison with those of MMF. Expression levels of monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor-beta1 (TGF-β1), which play important roles in UUO-induced renal fibrosis, were also investigated to determine the mechanism by which BMS-566419 affects the progression of renal fibrosis. After 14 days of UUO, interstitial fibrosis was frequently observed in the renal cortex of rats administered vehicle control. BMS-566419 by oral administration showed a significant and dose-dependent suppressive effect on UUO-induced renal fibrosis in histopathological experiments. BMS-566419 treatment also decreased collagen content, as indicated by hydroxyproline concentration, and the expression of collagen type 1 mRNA. BMS-566419 also decreased the expression of mRNA for both MCP-1 and TGF-β1. The antifibrotic effects of treatment with BMS-566419 at 60 mg/kg seemed comparable to those with MMF at 40 mg/kg. These results suggest that BMS-566419 and other chemically synthesized IMPDH inhibitors have beneficial pharmacological effects similar to those of MMF, and are potential pharmaceutical candidates in the treatment of fibrotic renal disease, including CAN.

A reduction of unilateral ureteral obstruction-induced renal fibrosis by a therapy combining valsartan with aliskiren

The protective effect of combination therapy with valsartan and aliskiren against renal fibrosis remains to be defined. This study was undertaken to examine the protective effects of the combination of valsartan and aliskiren against renal fibrosis induced by unilateral ureteral obstruction (UUO). Combination therapy with valsartan (15 mg·kg(-1)·day(-1)) and aliskiren (10 mg·kg(-1)·day(-1)), valsartan monotherapy (30 mg·kg(-1)·day(-1)), and aliskiren monotherapy (20 mg·kg(-1)·day(-1)) all significantly ameliorated the increase in blood urea nitrogen and the degree of hydronephrosis determined by the increase in weight and length of the obstructed kidney. The dose titration study and blood pressure measurement confirmed that the combination therapy provided a greater benefit independent of the vasodilatory effect. There were no significant changes in serum levels of creatinine, sodium, and potassium in UUO rats and any treatment groups. Combination therapy also attenuated UUO-related increases in the scores of tubular dilatation, interstitial volume, interstitial collagen deposition, α-smooth muscle actin, the activation of ERK 1/2, the infiltration of monocytes/macrophages, the mRNA expression of snail-1, and transforming growth factor-β1 to a greater extent compared with aliskiren or valsartan used alone. The mRNA expression of renin and the (pro)renin receptor significantly increased after UUO. Combination therapy and monotherapy of valsartan and aliskiren had a comparable enhancing effect on the mRNA expression of renin, whereas all these treatments did not affect the expression of the (pro)renin receptor. In conclusion, a direct renin inhibitor in conjunction with an angiotensin II receptor blocker exerts increased renal protection against renal fibrosis and inflammation during obstruction over either agent alone.

Effect of Astragalus membranaceus and Angelica sinensis combined with Enalapril in rats with obstructive uropathy

ACE inhibitors (ACEi) reduce renal tubulointerstitial fibrosis but are not completely effective. Combined extract of Astragalus membranaceus and Angelica sinensis (A&A) is a traditional antifibrotic agent in China. The present investigation aimed to determine whether an ACEi (Enalapril) and A&A together have a better antifibrotic effect in unilateral ureteral obstruction (UUO) than monotherapy with either agent. Male Sprague-Dawley rats (N = 4 per group) had either sham operation or UUO alone, with A&A (combined aqueous and ethanol extract equivalent to 2.1 g dried herbs), with Enalapril (in drinking water at 200 mg/mL) or with both treatments. Kidney and liver were collected for protein extraction or fixed for histologic stains, immunohistochemistry (IHC), microscopy. Enalapril or A&A individually were antifibrotic. Transforming growth factor-beta1, fibroblast activation, collagen deposition, macrophage accumulation and tubular cell apoptosis were all decreased. The combination of the two drugs was significantly more effective than Enalapril alone in reducing tumor necrosis factor-alpha, collagen accumulation, activation of fibroblasts, and tubular cell apoptosis. In conclusion, Enalapril with A&A significantly decreased tubulointerstitial fibrosis to a greater extent than treatment with Enalapril alone. Further studies focusing on the isolation of the active constituents of A&A and the clinical application of the combination of ACEi plus A&A are warranted to determine the value of this treatment in humans.

LSKL, a peptide antagonist of thrombospondin-1, attenuates renal interstitial fibrosis in rats with unilateral ureteral obstruction

The effects of LSKL, the peptide antagonist of thrombospondin-1 (TSP-1), on renal interstitial fibrosis in rats subjected to unilateral ureteral obstruction (UUO) were investigated. Rats were divided randomly into three groups (n = 20 each): UUO group, sham-operation group and UUO plus LSKL treatment group. Collagen deposition was studied using histopathology and reverse transcription polymerase chain reaction analysis (RT-PCR). TSP-1, transforming growth factor beta 1 (TGF-beta1), phosphorylated Smad2 (pSsmad2) and alpha-smooth muscle actin (alpha-SMA) in the kidney were measured using immunocytochemistry, western blotting analysis, RT-PCR and enzyme-linked immunosorbent assay. Biochemical analyses in the serum and urine were made. Histopathology showed severe tubular dilatation and atrophy, interstitial inflammation and collagen accumulation after surgery and LSKL significantly inhibited interstitial fibrosis including tubular injury as well as collagen deposition. The protein and mRNA levels of TSP-1 increased notably at different time point and significantly decreased in the presence of LSKL. The expression of TGF-beta1 and pSmad2 were upregulated in the obstructed kidney and substantially suppressed by LSKL treatment. Myofibroblast accumulation could be alleviated after administration of LSKL. Biochemical parameters did not show differences among the three groups. As TSP-1 is the major activator of TGF-beta1, we demonstrate that LSKL can attenuate renal interstitial fibrosis in vivo by preventing TSP-1-mediated TGF-beta1 activation.

Toll-like receptor 4: a novel signaling pathway during renal fibrogenesis

BACKGROUND

The toll-like receptor (TLR) family serves an important regulatory role in the innate immune system, and recent evidence has implicated TLR signaling in the pro-inflammatory response of a variety of endogenous and exogenous stimuli within the kidney. The role of TLR signaling in fibrotic renal injury, however, remains unknown.

MATERIALS AND METHODS

C3H/HeJ TLR4 hyporesponsive mice (TLR4(Lps-d)) or WT controls (C3H/HeOu/J) underwent either sham operation or 1 wk of unilateral ureteral obstruction (UUO). The kidneys were harvested and tissues were analyzed for TLR4 expression (Western blot; RTPCR), E-cadherin and alpha smooth muscle actin (α-SMA) expression (Western blot), fibroblast accumulation (fibroblast specific protein (FSP-1+) staining), renal fibrosis (collagen I RTPCR, total collagen assay, Masson's trichrome staining), cytokine gene expression (tumor necrosis factor-alpha (TNF-α) and transforming growth factor-beta1 (TGF-β1) RTPCR), and pSMAD2 and integrin α1 expression (Western blot).

RESULTS

Mice with intact TLR4 signaling demonstrate a significant increase in TLR4 expression, α-SMA expression, fibroblast accumulation, collagen deposition, and interstitial fibrosis, and a significant decrease in E-cadherin expression in response to UUO. TLR4 deficient mice, however, exhibit a significant reduction in obstruction-induced α-SMA expression, fibroblast accumulation, and renal fibrosis, with preservation of E-cadherin expression. TLR4's influence on fibroblast accumulation and renal fibrosis occurred independent of any alterations in TNF-α, TGF-β1, or pSMAD2 expression, but did involve alterations integrin α1 expression.

CONCLUSION

TLR4 appears to be a significant mediator of fibrotic renal injury. While TLR4 signaling is recognized as a critical component of the innate immune response, this is the first study to demonstrate a novel role for TLR4 in renal fibroblast accumulation and tubulointerstitial fibrosis.

Loss of renal microvascular integrity in postnatal Crim1 hypomorphic transgenic mice

Crim1 is a cell-surface, transmembrane protein that binds to a variety of cystine knot-containing growth factors, including vascular endothelial growth factor A. In the developing renal glomerulus, Crim1 acts to tether vascular endothelial growth factor A to the podocyte cell surface, thus regulating its release to glomerular endothelial cells. The hypomorphic transgenic mouse (Crim1(KST264/KST264)) has glomerular cysts and severe glomerular vascular defects because of the lack of functional Crim1 in the glomerulus. Adult transgenic mice have a reduced glomerular filtration rate and glomerular capillary defects. We now show that, in these adult transgenic mice, renal vascular defects are not confined to the glomerulus but also extend to the peritubular microvasculature, as live imaging revealed leakiness of both glomerular and peritubular capillaries. An ultrastructural analysis of the microvasculature showed an abnormal endothelium and collagen deposition between the endothelium and the tubular basement membrane, present even in juvenile mice. Overt renal disease, including fibrosis and renin recruitment, was not evident until adulthood. Our study suggests that Crim1 is involved in endothelial maintenance and integrity and its loss contributes to a primary defect in the extraglomerular vasculature.

Loss of TIMP3 enhances interstitial nephritis and fibrosis

The balance of matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) determines the integrity of the extracellular matrix. TIMP3 is the most highly expressed tissue inhibitor of metalloproteinase (TIMP) in the kidney, but its function in renal disease is incompletely understood. In this study, TIMP3-/- mice demonstrated an age-dependent chronic tubulointerstitial fibrosis. After unilateral ureteral obstruction (UUO), young TIMP3-/- mice exhibited increased renal injury (tubular atrophy, cortical and medullary thinning, and vascular damage) compared with wild-type mice. In addition, TIMP3-/- mice had greater interstitial fibrosis; increased synthesis and deposition of type I collagen; increased activation of fibroblasts; enhanced apoptosis; and greater activation of MMP2, but not MMP9, after UUO. TIMP3 deficiency also led to accelerated processing of TNFalpha, demonstrated by significantly higher TACE activity and greater soluble TNFalpha levels by 3 d after UUO. The additional deletion of TNFalpha markedly reduced inflammation, apoptosis, and induction of a number of MMPs. Moreover, inhibition of MMPs in TIMP3-/-/TNFalpha-/- mice further abrogated postobstructive injury and prevented tubulointerestitial fibrosis. In humans, TIMP3 expression increased in the renal arteries and proximal tubules of subjects with diabetic nephropathy or chronic allograft nephropathy. Taken together, these results provide evidence that TIMP3 is an important mediator of kidney injury, and regulating its activity may have therapeutic benefit for patients with kidney disease.

Ginsenoside Rb1, a panoxadiol saponin against oxidative damage and renal interstitial fibrosis in rats with unilateral ureteral obstruction

OBJECTIVE

To investigate the possible protective effect and mechanism of ginsenoside Rb1 against oxidative damage and renal interstitial fibrosis on rats with unilateral ureteral obstruction (UUO).

METHODS

In total, 80 male rats were randomly divided into 4 groups, 20 in each group: the sham operated group (SOR), UUO group, UUO with ginsenoside Rb1 treatment group (treated with intraperitoneal injection of 50 mg/ kg daily) and UUO with Losartan treatment group (as the positive control, treated with 20 mg/kg by gastrogavage per day). The rats were randomly sacrificed on day 3, 7 and 14 after surgery, respectively. The histopathologic changes of renal interstitial tissues were observed with Masson staining. The mRNA of transforming growth factor beta 1 (TGF-beta 1), collagen I and fibronectin were reversed transcribed and quantified by Real-time PCR. Enzyme-linked immunosorbent assay was used to quantitatively detect TGF-beta 1 and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels. P47phox protein expression was assessed by immunohistochemistry and Western blot analysis.

RESULTS

In the UUO model, the obstructed kidney showed typical features of progressive renal tubulointerstitial fibrosis, and the levels of TGF-beta1, collagen I and fibronectin increased (P<0.05). As compared with the UUO group, ginsennoside Rb1 significantly inhibited the interstitial fibrosis including tubular injury and collagen deposition, and decreased the levels of TGF-beta1 (P<0.05). Ginsenoside Rb1 also inhibited the heme oxygenase (HO-1) and 8-OHdG, two markers of oxidative stress (P<0.05). Moreover, ginsenoside Rb1 suppressed the expression of p47phox, a subunit of nicotinamide adeninedinucleotide phosphate (NADPH) oxidase (P<0.05).

CONCLUSION

Ginsenoside Rb1 can obviously inhibit renal interstitial fibrosis in rats with UUO, its mechanism possibly via against the oxidative damage and suppressing TGF-beta1 expression.

Influence of ginsenoside Rg1, a panaxatriol saponin from Panax notoginseng, on renal fibrosis in rats with unilateral ureteral obstruction

Total saponins of Panax notoginseng (PNS) have been shown to ameliorate renal interstitial fibrosis. Ginsenoside Rg1, a panaxatriol saponin, is one of the major active molecules from PNS. The present study was undertaken to investigate the effect of ginsenoside Rg1 on renal fibrosis in rats with unilateral ureteral obstruction (UUO). The rats were randomly divided into 3 groups: sham-operation (n=15), UUO (n=15) and UUO with ginsenoside Rg1 treatment (n=15, 50 mg per kg body weight, intraperitoneally (i.p.) injected). The rats were sacrificed on Days 7 and 14 after the surgery. Histological examination demonstrated that ginsenoside Rg1 significantly inhibited interstitial fibrosis including tubular injury as well as collagen deposition. alpha-smooth muscle actin (alpha-SMA) and E-cadherin are two markers of tubular epithelial-myofibroblast transition (TEMT). Interestingly, ginsenoside Rg1 notably decreased alpha-SMA expression and simultaneously enhanced E-cadherin expression. The messenger RNA (mRNA) of transforming growth factor-beta1 (TGF-beta1), a key mediator to regulate TEMT, in the obstructed kidney increased dramatically, but was found to decrease significantly after administration of ginsenoside Rg1. Further study showed that ginsenoside Rg1 considerably decreased the levels of both active TGF-beta1 and phosphorylated Smad2 (pSmad2). Moreover, ginsenoside Rg1 substantially suppressed the expression of thrombospondin-1 (TSP-1), a cytokine which can promote the transcription of TGF-beta1 mRNA and the activation of latent TGF-beta1. These results suggest that ginsenoside Rg1 inhibits renal interstitial fibrosis in rats with UUO. The mechanism might be partly related to the blocking of TEMT via suppressing the expression of TSP-1.

Plumbing the depths of urinary tract obstruction by using murine models

Urinary tract obstruction leads to obstructive nephropathy, which in turn, frequently results in renal failure. Congenital urinary tract obstruction can be traced back to errors during the organogenesis of the urinary system. A fundamental understanding of the causes of urinary tract obstruction and the developmental processes involved are critical for improving the diagnostic and therapeutic strategies for this disease. A number of laboratories, including ours, have been using genetically engineered and spontaneously occurring mouse models to study the primary causes and the pathogenesis of urinary tract obstruction. These studies have shown that urinary tract obstruction is a very heterogeneous disease that can be caused by a diverse set of factors targeting multiple levels of the urinary system. Accumulating evidence also indicates that the development of the urinary tract requires the integration of progenitor cells of diverse embryonic origins, leading to the formation of multiple junctions prone to developmental errors. In addition, the high sensitivity of the pyeloureteral peristaltic machinery to disturbance affecting the structural or functional integrity of its components also contributes to the high incidence rate of urinary tract obstruction.

Turmeric-based diet can delay apoptosis without modulating NF-kappaB in unilateral ureteral obstruction in rats

The unilateral ureteral obstruction (UUO) model of renal injury in rat is characterized by nuclear factor kappaB (NF-kappaB) activation and tumour necrosis factor alpha (TNF-alpha) production, which induces apoptosis via activation of caspase 8 resulting in cell death. Curcumin, the major component found in turmeric spice, has been reported to provide protection against fibrosis and apoptosis elicited by UUO. This study examined the effects of a turmeric-based diet (5% w/w) on the apoptotic pathway induced by UUO in rats after 30 days of ligation. Administration of a turmeric-based diet demonstrated a significant decrease (P<0.05) in mRNA expression of TNF-alpha and caspase 8, but not NF-kappaB, expression, which may contribute to the protective role of the turmeric-based diet. We conclude that a turmeric-based diet can delay apoptosis without modulating NF-kappaB, so as not to sensitize the mesangial cells to the apoptotic stimuli.

Combination therapy with an angiotensin-converting enzyme inhibitor and a vitamin D analog suppresses the progression of renal insufficiency in uremic rats

Monotherapy with angiotensin-converting enzyme inhibitors has been shown to be beneficial in suppressing the progression of experimentally induced kidney diseases. Whether such therapy provides additional benefits when combined with vitamin D or an analog of vitamin D has not been established. Rats were made uremic by 5/6 nephrectomy and treated as follows: Uremic + vehicle (UC), uremic + enalapril (30 mg/L in drinking water; E), uremic + paricalcitol (19-nor; 0.8 microg/kg, three times a week), and uremic + enalapril + paricalcitol (E + 19-nor). A group of normal rats served as control (NC). BP was significantly elevated in the UC and 19-nor groups compared with the NC group but was indistinguishable from normal in the E and E + 19-nor groups. The decrease in creatinine clearance and the increase in the excretion of urinary protein that were observed in the UC group were ameliorated by the use of E alone or by E + 19-nor (P < 0.05 versus UC). The glomerulosclerotic index was significantly decreased in both the 19-nor (P < 0.01) and E + 19-nor groups (P < 0.01) compared with the UC group. Tubulointerstitial volume was significantly decreased in both the E (P < 0.05) and E + 19-nor groups (P < 0.01) compared with the UC group. Both macrophage infiltration (ED-1-positive cells) and production of the chemokine monocyte chemoattractant protein-1 were significantly blunted in E + 19-nor compared with E group. TGF-beta1 mRNA and protein expression were increased in the UC group (mRNA: 23.7-fold; protein: 29.1-fold versus NC). These increases were significantly blunted in the 19-nor group (mRNA: 7.1-fold; protein: 8.0-fold versus NC) and virtually normalized in the E + 19-nor group (protein: 0.8-fold versus NC). Phosphorylation of Smad2 was also elevated in the UC group (7.6-fold versus NC) but less so in the 19-nor-treated rats (5.5-fold versus NC). When rats were treated with E + 19-nor, the phosphorylation of Smad2 was normal (1.1-fold versus NC). Thus, 19-nor can suppress the progression of renal insufficiency via mediation of the TGF-beta signaling pathway, and this effect is amplified when BP is controlled via renin-angiotensin system blockade.

Reduced severity of a mouse colitis model with angiotensin converting enzyme inhibition

Ulcerative colitis is characterized by elevated rates of epithelial cell apoptosis, and an up-regulation of pro-apoptotic cytokines including tumor necrosis factor alpha (TNF-alpha). Recently, angiotensin converting enzyme (ACE) has been shown to promote apoptosis. In addition, pharmacologic ACE inhibition (ACE-I) both prevents apoptosis and reduces TNF-alpha expression in vitro. We hypothesized that ACE-I, using enalaprilat, would decrease colonic epithelial cell apoptosis and reduce colitis severity in the dextran sulfate sodium (DSS)-induced colitis model in mice. We assessed the severity of colitis, and colonic epithelial cell apoptosis, after administration of DSS. Mice were given either daily ACE-I treatment or daily placebo. ACE-I treatment markedly improved clinical outcomes. In addition, ACE-I treatment significantly reduced the maximum histopathologic colitis grade. ACE-I also dramatically reduced the epithelial apoptotic rate. To investigate the mechanism by which ACE-I reduced apoptosis; we measured TNF-alpha, Bcl-2, and Bax expression. TNF-alpha mRNA was significantly lower with ACE-I treatment compared to placebo at every time point, as was the ratio of Bax to Bcl-2. We conclude that ACE-I reduces the severity of DSS-induced colitis and reduces epithelial cell apoptosis.

Obesity and obesity-initiated metabolic syndrome: mechanistic links to chronic kidney disease

There is an epidemic of obesity and the metabolic syndrome in the United States and across the world. Both entities are associated with high mortality, mainly as a result of cardiovascular disease. The epidemic of obesity has been paralleled by an increase in the incidence of chronic kidney disease (CKD). Several recent epidemiologic studies have shown that obesity and the metabolic syndrome are independent predictors of CKD. In addition to diabetes and hypertension, several other mechanisms have been postulated to initiate and maintain kidney injury in patients with obesity and the metabolic syndrome. This article reviews the recent epidemiologic data linking obesity and the metabolic syndrome to CKD and summarizes the potential mechanisms of renal injury in this setting, with a focus on the role of inflammation, lipotoxicity, and hemodynamic factors. Potential preventive and therapeutic modalities based on the limited evidence available are discussed.

Legumain/asparaginyl endopeptidase controls extracellular matrix remodeling through the degradation of fibronectin in mouse renal proximal tubular cells

Legumain/asparaginyl endopeptidase (EC 3.4.22.34) is a novel cysteine protease that is abundantly expressed in the late endosomes and lysosomes of renal proximal tubular cells. Recently, emerging evidence has indicated that legumain might play an important role in control of extracellular matrix turnover in various pathological conditions such as tumor growth/metastasis and progression of atherosclerosis. We initially found that purified legumain can directly degrade fibronectin, one of the main components of the extracellular matrix, in vitro. Therefore, we examined the effect of legumain on fibronectin degradation in cultured mouse renal proximal tubular cells. Fibronectin processing can be inhibited by chloroquine, an inhibitor of lysosomal degradation, and can be enhanced by the overexpression of legumain, indicating that fibronectin degradation occurs in the presence of legumain in lysosomes from renal proximal tubular cells. Furthermore, in legumain-deficient mice, unilateral ureteral obstruction (UUO)-induced renal interstitial protein accumulation of fibronectin and renal interstitial fibrosis were markedly enhanced. These findings indicate that legumain might have an important role in extracellular matrix remodeling via the degradation of fibronectin in renal proximal tubular cells.

Cisplatin increases TNF-alpha mRNA stability in kidney proximal tubule cells

Cisplatin induces acute renal injury in part by increasing the production of TNF-alpha. However, the mechanism by which cisplatin increases renal TNF-alpha expression is not known. The transcription, translation, and stability of TNF-alpha mRNA are sites of regulation of TNF-alpha production. This study investigated the effects of cisplatin on TNF-alpha mRNA stability and the role of MAP kinases in this process in cultured renal proximal tubule cells. Cisplatin increased the expression of TNF-alpha mRNA by proximal tubule cells in a time- and dose-dependent manner, as well as activated p42/44 ERK kinase, p38 MAP kinase, and JNK in a dose-dependent manner. The inhibition of these pathways reduced TNF-alpha expression significantly. Cisplatin also increased the stability of TNF-alpha mRNA, but this effect was not mediated by MAP kinases and did not require the synthesis of a new protein. The treatment of cells with cisplatin induced the formation of complexes of cytosolic proteins and the AU-rich region of the TNF-alpha 3'UTR. These results are consistent with the view that cisplatin increases TNF-alpha mRNA stability in a MAP kinase-independent manner. The stabilization of TNF-alpha mRNA by cisplatin may involve the binding of certain proteins to AU-rich regions in the 3'UTR.

Angiotensin II induces phosphorylation of glucose-regulated protein-75 in WB rat liver cells

Studies in vascular smooth muscle cells suggest that, angiotensin II (Ang II)-mediated cellular response requires transactivation of epidermal growth factor receptor (EGF-R), and involves tyrosine phosphorylation of caveolin-1. Here we demonstrate that, exposure of WB rat liver cells to Ang II does not cause transactivation of EGF-R, but did rapidly activate p42/p44 mitogen-activated protein (MAP) kinases suggesting that it activates MAP kinases independent of EGF-R transactivation. We observed that the phospho-specific anti-caveolin-1 antibody detected a tyrosine phosphorylated, 75kDa protein in Ang II-treated cells which we identified as glucose regulated protein-75 (GRP-75). Phosphoamino acid analysis showed that Ang II induced its phosphorylation at tyrosine, serine and threonine residues and was localized to the cytoplasm. The ability of Ang-II to induce GRP-75 phosphorylation suggests that it may play a role in the protection of cytoplasmic proteins from the damaging effect of oxidative stress known to be produced during Ang-II induced signaling.

Gender differences in the renin-angiotensin and nitric oxide systems: relevance in the normal and diseased kidney

Female gender is associated with better renal function and resistance to renal injury, suggesting that an oestrogen-based effect or increased androgenic effects are responsible. Studies in rodents have confirmed a biological basis for this, based on the differential effects of androgens and oestrogens on the normal and diseased kidney. Many researchers in the field believe that the pre-menopausal levels of oestrogen are key to the protection observed in females. The key pressor effects of the renin-angiotensin (RA) system are due to both direct vasoconstrictory properties and alterations in renal control of extracellular fluid volume. Additionally, the RA has been shown to promote diverse aspects of renal injury. RA activity is positively modulated by androgens and antagonized by oestrogens. Nitric oxide (NO) is a potent vasorelaxant with a key role in renal control of extracellular fluid homeostasis. NO can variously have both protective and deleterious effects on renal injury. Endogenous oestrogen has an anti-hypertensive effect as well as protective effects against cell and organ damage, many of which are mediated via increases in NO generation. We examine how the RA- and NO-generating systems may underpin key aspects of gender differences in normal renal function and renal disease.

Expression and localization of PDGF-B, PDGF-D, and PDGF receptor in the kidney of angiotensin II-infused rat

Lipid accumulation in the kidney is a marker of tissue damage and may play a role in the development of renal injury. We have previously shown that long-term administration of angiotensin II in rats causes increased expression of transforming growth factor-beta1, coupled with an accumulation of lipids in the tubular and vascular wall cells in the kidney. In this study, we examine the regulation of expression of platelet-derived growth factor (PDGF) and its receptor system and their co-localization with lipid deposits in the kidneys of angiotensin II-infused rats. Real-time RT-PCR showed that expression of PDGF-B, PDGF-D, and PDGF receptor-beta (PDGFR-beta) mRNA was increased by angiotensin II infusion, and in situ hybridization showed the co-localization of these mRNAs. Tubular cells that had increased PDGF-B mRNA expression were positive for lipid deposition and also for cellular proliferation, which was indicated by the presence of proliferating cell nuclear antigen. By contrast, in the kidneys of angiotensin II-infused rats, apoptosis occurred in tubular cells that contained deposits of iron but not lipids. The deposition of lipids and upregulation of PDGF-B, PDGF-D, and PDGFR-beta induced by administration of angiotensin II were all suppressed by the selective angiotensin II type 1 (AT(1)) receptor antagonist losartan, but not by the nonspecific vasodilator hydralazine. The findings that lipid accumulation, upregulation of PDGF-B, PDGF-D, and PDGFR-beta, and cellular proliferation were topologically associated and regulated in an AT(1) receptor-dependent manner in the kidney of angiotensin II-infused rats suggests that these phenomena are related.

Rapamycin attenuates unilateral ureteral obstruction-induced renal fibrosis

Unilateral ureteral obstruction (UUO) is a well-characterized hydronephrosis model exhibiting interstitial inflammatory-cell infiltration and tubular dilatation followed by tubulointerstitial fibrosis of the obstructed kidney. Our recent report indicates that rapamycin is effective for 50% of transplant recipients with chronic allograft nephropathy. In this study, we investigate the effect of rapamycin on UUO-induced renal fibrosis. UUO or sham-operated rats were randomly assigned to rapamycin or vehicle and were killed on days 7 and 14 after UUO or sham operation. Rapamycin decreased cross-sectional and gross-morphology changes in the obstructed kidney significantly. Rapamycin markedly blunted the increase in weight of the obstructed kidney, obstructed kidney length, and the obstructed/non-obstructed kidney weight ratio (by 74.6, 42.8, and 61.6% on day 14, respectively, all P<0.01). The scores for tubular dilatation, interstitial volume, interstitial collagen deposition, and alpha-smooth muscle actin (alpha-SMA) after UUO were significantly reduced by rapamycin. Rapamycin also decreased the number of infiltrative anti-ED1-positive cells and the gene expression of transforming growth factor (TGF)-beta1 (84.8 and 80.2% on day 7) after UUO (both P<0.01). By double immunostaining and Western analysis, rapamycin blocked the TGF-beta1-induced loss of E-cadherin expression and de novo increase of the expression of alpha-SMA in a dose-dependent manner. In conclusion, rapamycin significantly attenuated tubulointerstitial damage in a UUO-induced rat model of renal fibrosis, suggesting that rapamycin may have the potential to delay the progression of tubulointerstitial renal fibrosis.

Angiotensin receptor blockade decreases fibrosis and fibroblast expression in a rat model of unilateral ureteral obstruction

PURPOSE

Unilateral ureteral obstruction is characterized by histopathological changes including interstitial fibrosis, fibroblast specific protein expression, tubular atrophy and apoptosis, and macrophage infiltration. Angiotensin II has been implicated in some of these changes. We examined the effect of angiotensin blockade on markers of renal injury, including fibroblast specific protein expression, fibrosis, apoptosis and macrophage infiltration. We used losartan, an angiotensin II antagonist, in a unilateral ureteral obstruction model and studied animals 3 weeks after unilateral ureteral obstruction, a time at which renal damage is well established.

MATERIALS AND METHODS

Rats underwent unilateral ureteral obstruction and were given either drinking water or losartan for 21 days. Kidneys were harvested and examined for fibrosis (trichrome and the Sircol assay for collagen), apoptosis (TUNEL), and fibroblast specific protein expression and macrophage infiltration (immunohistochemistry).

RESULTS

Unilateral ureteral obstruction was found to induce fibrosis, apoptosis, fibroblast expression and macrophage in the obstructed kidney. Losartan significantly decreased apoptosis and macrophage infiltration in the obstructed kidney. It also decreased fibrosis, as measured by either trichrome staining assessed by a pathologist, the Sircol assay for collagen or fibroblast specific protein expression. However, approximately 50% of the changes were not affected by the current treatment, suggesting that other factors contribute to renal damage in unilateral ureteral obstruction.

CONCLUSIONS

We observed the direct contribution of angiotensin II to both apoptotic and cellular transition processes (epithelial mesenchymal transition) and fibrosis in unilateral ureteral obstruction. Because these processes are active not only in unilateral ureteral obstruction, but also in other renal diseases, the value of angiotensin II blockade as an important part of the antifibrotic armamentarium has been confirmed.

Sex differences and the role of sex steroids in renal injury

PURPOSE

There is growing evidence that significant sex differences exist in the response of the kidney to injury. In this review we explored the cumulative clinical knowledge and experimental evidence of this phenomenon.

MATERIALS AND METHODS

The current clinical evidence of increased male susceptibility to acute and chronic renal injury, and experimental data elucidating potential mechanisms of this phenomenon were reviewed.

RESULTS

Renal damage induced by nephron reduction, patient age and renal ischemia is tolerated differently by the sexes. Sex differences in disease susceptibility have historically been attributed to the protective effects of estrogen but recent evidence suggests that male hormones also have an important role in these differences. Vascular mediators, such as endothelin, nitric oxide and angiotensin II, appear to be influenced by sex and sex steroids. Additionally, inflammatory mediators, such as transforming growth factor-beta1, tumor necrosis factor-alpha and p38 mitogen activating protein kinase, similarly show differential expression and activity based on sex and the presence of sex steroids. These mediators have a significant impact on the kidney response to inflammation and injury.

CONCLUSIONS

Greater understanding of the specific role of sex steroids in renal injury may provide new therapeutic strategies to protect against inflammatory injury and renal damage in the future.

TNF-alpha neutralization decreases nuclear factor-kappaB activation and apoptosis during renal obstruction

BACKGROUND

Obstruction of the upper urinary tract is an important cause of progressive renal injury in children. While tumor necrosis factor-alpha (TNF-alpha) and nuclear factor kappaB (NFkappaB) have independently been implicated in the pathophysiology of this process, TNF-alpha's role in obstruction-induced NFkappaB activation has not previously been investigated.

MATERIALS AND METHODS

To study this, male Sprague Dawley rats were subjected to 3 days of unilateral ureteral obstruction (UUO) versus sham operation. Twenty-four hours prior to surgery and 2 days after, rats received either a vehicle or a pegylated form of soluble TNF receptor type 1 (PEG-sTNFR1). The kidneys were harvested 3 days postoperatively, and tissue samples were analyzed for TNF-alpha expression (ELISA), NFkappaB activation (EMSA, immunohistochemistry), IkappaB degradation (Western blot), angiotensinogen expression (Western blot), and apoptosis (TUNEL).

RESULTS

Renal cortical TNF-alpha levels, NFkappaB activation, IkappaB degradation, angiotensinogen expression, and apoptotic cell death were significantly increased in response to obstruction. In contrast, TNF-alpha neutralization significantly reduced obstruction-induced TNF-alpha production, NFkappaB activation, IkappaB degradation, angiotensinogen expression, and renal tubular cell apoptosis.

CONCLUSION

TNF-alpha's potent pro-inflammatory and cytotoxic effect during renal obstruction is directed through NFkappaB activation via increased IkappaB-alpha phosphorylation. As the role of TNF-alpha and NFkappaB in renal obstruction are further defined, the development of therapeutic strategies that limit or prevent obstruction-induced renal injury may be realized.

p27Kip1 knockout mice are protected from diabetic nephropathy: Evidence for p27Kip1 haplotype insufficiency11See editorial by Qi and Breyer, p. 1896

BACKGROUND

High glucose up-regulates the mesangial cell expression of p27(Kip1), an inhibitor of cyclin-dependent kinases/cyclin complexes. Previous in vitro studies using cultured mesangial cells from p27(Kip1-/-) mice demonstrated that these cells do not undergo high glucose-mediated cellular hypertrophy. Since glomerular hypertrophy is an early feature of diabetic nephropathy and may precede the development of glomerulosclerosis, interference with p27(Kip1) expression may attenuate diabetic nephropathy. However, it is unclear whether deletion of p27(Kip1) protects the kidneys of diabetic nephropathy in vivo.

METHODS

Type 1 diabetes mellitus was induced in p27(Kip1+/+), p27(Kip1+/-), and p27(Kip1-/-) mice by injection of streptozotocin (STZ). Mice were studied for 6 weeks. Animals injected with citrate buffer only served as controls. At the end of the experiments, urine was collected, albuminuria was determined with an enzyme-linked immunosorbent assay (ELISA), and blood glucose concentrations were measured. Kidneys were perfusion-fixed for quantitative morphologic analysis with glutaraldehyde and for immunohistochemical studies with formaldehyde. Glomerular cell number and volume were analyzed. Glomerulosclerosis, tubulointerstitial, and vascular damage indices were semiquantitatively assessed according to standard methodology. Quantitative glomerular parameters (cell numbers and volumes of endothelial, mesangial, and epithelial cells) were measured on semithin sections. Expression of transforming growth factor-beta1 (TGF-beta1), laminin, and collagen type IV were determined by immunohistochemical staining.

RESULTS

In contrast to animals only injected with citrate buffer, mice that received STZ developed hyperglycemia. There was no significant difference in the degree of hyperglycemia among p27(Kip1+/+), p27(Kip1+/-), and p27(Kip1-/-) mice. Diabetic p27(Kip1+/+), but not control p27(Kip1+/+) animals, developed albuminuria. Albuminuria was significantly reduced in diabetic p27(Kip1+/-) and more profoundly in p27(Kip1-/-) animals. Diabetic p27(Kip1+/+) mice revealed a significant increase in mean glomerular volume at 6 weeks. The volumes of mesangial and endothelial cells and podocytes all increased, whereas cell numbers were reduced, consistent with cell hypertrophy. Glomerular, endothelial, mesangial and podocyte hypertrophy were reduced in diabetic p27(Kip1+/-) and p27(Kip1-/-) animals. Diabetic p27(Kip1) (+/+) animals had significantly increased glomerulosclerosis, tubulointerstium, and vascular damage indices compared to nondiabetic p27(Kip1+/+) controls. Diabetic p27(Kip1-/-) mice exhibited significantly less structural damage than diabetic wild-type animals. Diabetic p27(Kip1+/-) animals revealed intermediate glomerulosclerosis, tubulointerstium, and vascular damage values. Immunohistological stainings demonstrated increases in TGF-beta1, collagen type IV, and laminin expression in kidneys of diabetic p27(Kip1+/+) animals compared to nondiabetic p27(Kip1+/+) controls. Staining intensity for type IV collagen and laminin, but not for TGF-beta1, was significantly lower in diabetic p27(Kip1-/-) mice.

CONCLUSION

Deletion of p27(Kip1) attenuates the functional and morphologic features of diabetic nephropathy. Although deletion of p27(Kip1) abolished some parameters of diabetic glomerular hypertrophy, the significant reduction of TGF-beta1 expression in the tubulointerstitium indicates that other protective mechanisms could be operative. The p27(Kip1) gene is haplo-insufficient because diabetic p27(Kip1)+/- mice exhibited an intermediate degree of functional and structural renal injury. Our data shows that p27(Kip1) plays an important role in diabetic nephropathy.

Antibody blockade of TNF-alpha reduces inflammation and scarring in experimental crescentic glomerulonephritis

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine produced by macrophages, and by renal mesangial and tubular epithelial cells. It stimulates the release of interleukin (IL)-1beta, monocyte chemoattractant protein-1 (MCP-1), and transforming growth factor-beta (TGF-beta). Blockade of TNF-alpha is currently used clinically in several autoimmune inflammatory diseases. We hypothesised that blocking TNF-alpha with a monoclonal antibody would prevent inflammation and renal fibrosis in crescentic glomerulonephritis.

METHODS

Nephrotoxic nephritis was induced in Wistar Kyoto (WKY) rats by intravenous injection of rabbit antirat glomerular basement membrane (GBM) nephrotoxic serum (NTS). Anti-TNF-alpha monoclonal antibody or saline was given intraperitoneally three times per week in four protocols: experiment 1, days 0 to 7; experiment 2, days 0 to 14 and days 4 to 14; experiment 3, days 4 to 28; and experiment 4, days 14 to 28.

RESULTS

In experiment 1, rats treated from disease induction had less glomerular fibrinoid necrosis and fewer glomerular macrophages at day 7. In experiment 2, rats treated from day 0 or day 4 showed improved renal function, as judged by serum creatinine, with a significant reduction in crescents. In experiment 3, anti-TNF-alpha treatment significantly reduced urine protein to creatinine ratio and urinary MCP-1 levels. Serum creatinine was preserved at both day 14 and day 28. Tubulointerstitial inflammation, glomerular and tubulointerstitial scarring, and markers of fibrosis [alpha-smooth muscle actin (alpha-SMA) and type IV collagen] were significantly less in treated rats at day 28. In experiment 4, serum creatinine was higher and tubulointerstitial scarring was less in delayed-treated animals.

CONCLUSION

Neutralization of endogenous TNF-alpha reduces glomerular inflammation, crescent formation, and tubulointerstitial scarring, with preservation of renal function, in experimental crescentic glomerulonephritis. TNF-alpha blockade is effective even when introduced at the time of maximum glomerular inflammation.

Effects of suppressing intrarenal angiotensinogen on renal transforming growth factor-beta1 expression in acute ureteral obstruction

BACKGROUND

Angiotensin II (Ang II) mediates the up-regulation of fibrogenic factors such as transforming growth factor-beta1 (TGF-beta1) in chronic renal diseases. In addition, it has been proposed that the intrarenal renin-angiotensin system (RAS) is as important as the systemic RAS in kidney disease progression.

METHODS

We suppressed angiotensinogen (AGT) gene expression in the kidney by transferring recombinant adenoviral vectors carrying a transgene expressing AGT antisense mRNA, and determined the effect of the local inhibition of the RAS on TGF-beta1 synthesis in the kidneys of rats with unilateral ureteral obstruction (UUO). Immediately after UUO, recombinant adenovirus vectors were injected intraparenchymally into the cortex of obstructed kidneys.

RESULTS

beta-galactosidase (beta-gal)-stained kidney sections revealed the efficient transduction of the recombinant adenoviral vectors into tubular epithelial cells. Kidney cortex injected with AGT antisense showed significantly lower native AGT mRNA and protein expressions than control UUO kidneys at 24 hours and 5 days post-UUO. TGF-beta1 was significantly up-regulated in the renal cortex 24 hours and 5 days post-UUO, whereas AGT antisense-injected UUO rats showed significantly reduced TGF-beta1 expression compared to control UUO rats. Both fibronectin and collagen type I expressions were increased 24 hours and 5 days post-UUO, and these augmentations were considerably reduced by AGT antisense RNA treatment.

CONCLUSION

This study demonstrates that the suppression of intrarenal RAS prevents the formation of renal cortical TGF-beta1, and of related fibrogenic factors, in early UUO.

Mediators of fibrosis and apoptosis in obstructive uropathies

Upper urinary tract obstruction, regardless of its cause, often poses a significant clinical challenge to the urologist. Renal cellular and molecular events that occur in response to upper urinary tract obstruction result in a progressive and permanent loss in renal function when left untreated. These pathologic changes include the development of renal fibrosis, tubular atrophy, interstitial inflammation, and apoptotic renal cell death. Several cytokines and growth factors have been identified as major contributors to obstruction-induced renal fibrosis and apoptotic cell death, most notably transforming growth factor-b1 (TGF-b1), angiotensin II, nuclear factor-kB (NF-kB), and tumor necrosis factor-a (TNF-a). This review examines the challenges of upper urinary tract obstruction and the role of these mediators in obstruction-induced renal injury.

Tumor necrosis factor-alpha receptor ablation in a chronic MPTP mouse model of Parkinson's disease

Recently, we demonstrated that mice deficient of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) were partly protected against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity. Here we extended the study and investigated TNF-alpha receptor 1 (-/-) (TNFR1) and TNF-alpha receptor 2 (-/-) (TNFR2) mice using a chronic MPTP dosing regimen (15 mg/kg MPTP on 8 consecutive days). One week after the last MPTP treatment, HPLC determination of striatal dopamine (DA) and immunostaining for the dopamine transporter (DAT) in the substantia nigra pars compacta (SNpc) was performed. MPTP treatment reduced striatal DA levels significantly; nigral DAT immunoreactivity was reduced to a lower extent. However, there was no difference in DA levels and the number of DAT positive neurons between TNFR1 (-/-), TNFR2 (-/-) and wild type mice after MPTP treatment. In contrast to TNF-alpha deficiency neither TNFR1 nor TNFR2 gene ablation showed protection against MPTP neurotoxicity, which argues for a protective mechanism of TNF-alpha not mediated by TNFR1 and TNFR2 signaling.

The renin-angiotensin system blockade does not prevent renal interstitial fibrosis induced by aristolochic acids

BACKGROUND

Experimental aristolochic acid nephropathy (AAN), characterized by interstitial fibrosis, tubular atrophy, and chronic renal failure, was reported after 35-day injections of aristolochic acids (AA) to salt-depleted male Wistar rats. The link between renal fibrosis and the renin-angiotensin system (RAS) in this model remains unknown.

METHODS

We investigated the impact of sodium diets (low and normal), of RAS inhibition with enalapril (ENA) alone, or combined with candesartan (CSN) for 35 days, and ENA + CSN for 65 days on AAN development. At the end of each observation period, blood pressure and renal angiotensin-converting enzyme activity were measured, as well as renal functional impairment (plasma creatinine increase, proteinuria) and histologic lesions (interstitial fibrosis, monocytes/macrophages infiltration, myofibroblasts collagens type I and IV, proliferating cells).

RESULTS

Sodium intake did not modify renal functional and morphologic impairment induced by AA. The RAS blockade by ENA or ENA + CSN in rats receiving AA did not result in any statistical difference in terms of renal failure, proteinuria, and interstitial fibrosis on day 35 or 65. On day 35, the monocytes/macrophages infiltration was significantly decreased by two-fold when ENA (P < 0.01) or ENA + CSN (P < 0.01) was given from day 0.

CONCLUSION

Our data demonstrate that RAS modulation by salt depletion and pharmacologic blockade do not influence renal failure and interstitial fibrosis in the rat model of AAN. We suggest that pathways of interstitial renal fibrosis may be independent of RAS at least in some conditions.

UNILATERAL URETERAL OBSTRUCTION INDUCES RENAL TUBULAR CELL PRODUCTION OF TUMOR NECROSIS FACTOR-α INDEPENDENT OF INFLAMMATORY CELL INFILTRATION

PURPOSE

Obstructive uropathy is a significant clinical problem that results in apoptotic renal cell death and progressive renal fibrosis. A number of different inflammatory mediators have been implicated in the pathophysiology of obstruction induced renal injury including tumor necrosis factor-alpha (TNF)-alpha. The cellular source of obstruction induced renal TNF-alpha production and its relationship to renal inflammatory cell infiltration remain unknown.

MATERIALS AND METHODS

Male Sprague-Dawley rats were anesthetized and exposed to varying lengths of unilateral ureteral obstruction vs sham operation. The kidneys were harvested following renal injury and evaluated for TNF-alpha mRNA expression (reverse transcriptase polymerase chain reaction), TNF-alpha protein production (enzyme-linked immunosorbent assay), TNF-alpha cellular localization (immunohistochemistry) and leukocyte infiltration (leukocyte staining).

RESULTS

Renal TNF-alpha mRNA expression and protein production peaked following 3 days of ureteral obstruction (54 +/- 5% vs sham 22 +/- 9% of glyceraldehyde-3-phosphate dehydrogenase mRNA, p <0.05 and 204 +/- 13 vs sham 84 +/- 9 pg/ml, p <0.05, respectively). TNF-alpha production localized primarily to renal cortical tubular cells following obstruction and the time point of maximal TNF-alpha production (3 days of obstruction) were not associated with a significant renal inflammatory cell infiltrate.

CONCLUSIONS

TNF-alpha is produced by the renal cortical tubular cells in response to ureteral obstruction and independent of a significant inflammatory cell infiltrate. Identification of the cellular source of TNF-alpha expression during renal obstruction may have therapeutic implications for the targeted inhibition of TNF-alpha production and potential amelioration of obstructive renal injury.

Inflammatory mediators and growth factors in obstructive renal injury

Obstruction of the upper urinary tract poses a significant clinical challenge to the urologist, and the cascade of renal cellular and molecular events triggered by upper urinary tract obstruction result in a progressive, and eventually permanent, loss in renal function. These pathological changes include the development of renal fibrosis, tubular atrophy, interstitial inflammation, and apoptotic renal cell death. A myriad of cytokines and growth factors have been identified as major contributors to obstruction-induced renal fibrosis and apoptotic cell death, including transforming growth factor-beta1, angiotensin II, nuclear factor-kappaB, and tumor necrosis factor-alpha. This review examines the role of these mediators in obstruction-induced renal injury.

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.

Angiotensin II in the lesional skin of systemic sclerosis patients contributes to tissue fibrosis via angiotensin II type 1 receptors

OBJECTIVE

Tissue fibrosis in systemic sclerosis (SSc) is attributed to excessive deposition of extracellular matrix components produced by fibroblasts in skin lesions. Angiotensin II (Ang II), a vasoconstrictive peptide, is reported to have profibrotic activity as a result of induction of the extracellular matrix. The aim of the present study was to examine the expression of Ang II and its type 1 (AT(1)) and type 2 (AT(2)) receptors in affected skin and dermal fibroblasts from patients with SSc and to study the role of Ang II in collagen production by SSc dermal fibroblasts.

METHODS

Levels of Ang II in sera from SSc patients and normal subjects were measured by a solid-phase immobilized-epitope immunoassay. Expression of angiotensinogen (Angt) in the skin was evaluated by immunohistochemistry. Expression of Angt, AT(1), and AT(2) in cultured dermal fibroblasts was analyzed by reverse transcription-polymerase chain reaction and immunohistochemistry. Levels of type I procollagen produced by cultured dermal fibroblasts were measured by enzyme-linked immunosorbent assay.

RESULTS

Serum Ang II levels in patients with diffuse cutaneous SSc were significantly higher than those in patients with limited cutaneous SSc and in healthy donors. Immunohistochemical and immunoblotting analyses showed that Angt was present in skin from SSc patients, but not in normal skin. Angt messenger RNA (mRNA) was expressed in fibroblasts from patients with diffuse cutaneous SSc who had high levels of serum Ang II, but not in normal fibroblasts. AT(1) mRNA expression was found in both SSc and normal fibroblasts, whereas AT(2) mRNA was found only in SSc fibroblasts. Exogenous Ang II augmented the production of type I procollagen and transforming growth factor beta1 by cultured fibroblasts via activation of AT(1).

CONCLUSION

Aberrant Ang II production may be involved in tissue fibrosis through excessive production of the extracellular matrix components in SSc dermal fibroblasts. This suggests that the use of AT(1) receptor antagonists may be a novel strategy for the treatment of tissue fibrosis in SSc patients.

Perturbed medullary tubulogenesis in neonatal rat exposed to renin-angiotensin system inhibition

BACKGROUND

Pharmacological interruption of the angiotensin II type-1 receptor (AT(1)) signalling during nephrogenesis in rats induces irreversible abnormalities in kidney morphology, comprising papillary atrophy and tubulointerstitial damage, which are characterized by tubular dilatation/atrophy and interstitial inflammation/fibrosis. This study determined the time course for development of tubular structural and inflammatory changes and possible cytokine production in the renal medulla of newborn rats exposed to angiotensin-converting enzyme (ACE) inhibition. Additionally, medullary expression of E-cadherin, a marker for tubular formation, was investigated in ACE-inhibited rats.

METHODS

Newborn rats were exposed (postnatal days 0-12) to ACE inhibitor enalapril and killed at days 1, 2, 4, 9 and 13. One kidney was used for morphological evaluation and the other for immunohistochemistry, using antibodies directed against monocytes/macrophages, T cells and E-cadherin on frozen sections. In a separate experiment, rats were treated for 9 days and had their kidneys processed for western immunoblot and immunohistochemistry, where antibodies directed against monocyte chemoattractant protein-1 (MCP-1) and tumour necrosis factor-alpha (TNF-alpha) were used on paraffin sections.

RESULTS

In renal medulla from enalapril-treated rats, volume fractions of tubular lumens and interstitium were increased from postnatal days 2 and 4, respectively, while that of tubular cells was decreased from 4 days of age. Concomitant loss and/or reduction in E-cadherin expression (from day 2) was observed in dilated medullary tubules of enalapril-treated rats. Furthermore, in the medulla of enalapril-treated rats, the increased number of ED2+ (resident macrophages) cells, followed by the increase in ED1+ (monocytes/macrophages) and CD4+ T cells, was observed at days 9 and 13, respectively. This was accompanied by increased medullary expression of TNF-alpha at day 9.

CONCLUSIONS

Neonatal ACE inhibition perturbs medullary tubulogenesis, as indicated by tubular dilatation and a lack of E-cadherin expression in these tubules. Macrophage/monocyte-mediated immune response is a secondary event, coincidentally associated with the up-regulation of TNF-alpha.

Transforming growth factor-beta-dependent and -independent pathways of induction of tubulointerstitial fibrosis in beta6(-/-) mice

Transforming growth factor-beta1 (TGF-beta1) and the renin-angiotensin-aldosterone system are key mediators in kidney fibrosis. Integrin alphavbeta6, a heterodimeric matrix receptor expressed in epithelia, binds and activates latent TGF-beta1. We used beta6 integrin-null mice (beta6(-/-)) to determine the role of local TGF-beta1 activation in renal fibrosis in the unilateral ureteral obstruction (UUO) model. Obstructed kidneys from beta6(-/-) mice showed less injury than obstructed kidneys from wild-type (WT) mice, associated with lower collagen I, collagen III, plasminogen activator inhibitor (PAI-1), and TGF-beta1 mRNA levels and lower collagen content. Infusion with either angiotensin II (Ang II) or aldosterone (Aldo) or combination in beta6(-/-) UUO mice significantly increased collagen contents to levels comparable to those in identically treated WT. Active TGF-beta protein expression in beta6(-/-) mice was less in UUO kidneys with or without Ang II infusion compared to matched WT mice. Activated Smad 2 levels in beta6(-/-) obstructed kidneys were lower than in WT UUO mice, and did not increase when fibrosis was induced in beta6(-/-) UUO mice by Ang II infusion. Anti-TGF-beta antibody only partially decreased this Ang II-stimulated fibrosis in beta6(-/-) UUO kidneys. In situ hybridization and immunostaining showed low expression of PAI-1 mRNA and protein in tubular epithelium in beta6(-/-) UUO kidneys, with increased PAI-1 expression in response to Ang II, Aldo, or both. Our results indicate that interruption of alphavbeta6-mediated activation of TGF-beta1 can protect against tubulointerstitial fibrosis. Further, the robust induction of tubulointerstitial fibrosis without increase in activated Smad 2 levels in obstructed beta6(-/-) mice by Ang II suggests the existence of a TGF-beta1-independent pathway of induction of fibrosis through angiotensin.

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.

Hepatocyte growth factor gene therapy and angiotensin II blockade synergistically attenuate renal interstitial fibrosis in mice

Tubulointerstitial fibrosis is considered to be common endpoint result of many forms of chronic renal diseases. Except for renal replacement, chronic renal fibrosis is presently incurable. This study demonstrates that the combination of hepatocyte growth factor (HGF) gene therapy with inhibition of the renin-angiotensin system produced synergistic beneficial effects leading to dramatic attenuation of renal tubulointerstitial fibrosis in obstructive nephropathy in mice. The combined treatment with human HGF gene and losartan, an angiotensin II (AngII) type I receptor blocker, preserved renal mass and gross morphology of the obstructed kidneys. Although HGF gene therapy alone inhibited the expression of alpha-smooth muscle actin (alpha SMA) by approximately 54% and 60% at day 7 and day 14 after surgery, respectively, its combination with losartan almost completely abolished alpha SMA induction in the obstructed kidneys. The combined therapy also synergistically inhibited the accumulation of interstitial matrix components, such as fibronectin and collagen I, and suppressed renal expression of transforming growth factor-beta1 (TGF-beta1) and its type I receptor. In vitro studies revealed that AngII by itself did not induce alpha SMA, but it drastically potentiated TGF-beta1-initiated alpha SMA expression in tubular epithelial cells. Furthermore, HGF abrogated de novo alpha SMA expression induced by TGF-beta1 plus AngII. These results suggest that many factors are implicated in the pathogenesis of renal interstitial fibrosis; therefore, a combined therapy aimed at simultaneously targeting multiple pathologic pathways may be necessary for halting the progression of chronic renal diseases. These findings may provide the basis for designing future therapeutic regimens for blocking progressive renal fibrosis in patients.