Activation of ERK in renal fibrosis after unilateral ureteral obstruction: modulation by antioxidants

Ureic clearance granule, alleviates renal dysfunction and tubulointerstitial fibrosis by promoting extracellular matrix degradation in renal failure rats, compared with enalapril

ETHNOPHARMACOLOGICAL RELEVANCE

Chinese herbal compound prescription has a unique therapeutic action on chronic kidney disease (CKD) in China. In clinics, Uremic Clearance Granules (UCG), a compounded Chinese patent medicine, has been frequently used to treat chronic renal failure (CRF) patients for nearly 30 years, however, the deep therapeutic mechanisms involved in vivo remain a challenge. This study aims to demonstrate the effects and mechanisms of UCG on renal dysfunction and tubulointerstitial fibrosis by regulating extracellular matrix (ECM) degradation and transforming growth factor (TGF)-beta1/Smad signaling activity in vivo, compared with enalapril.

MATERIALS AND METHODS

Twenty-six rats were randomly divided into 4 groups, a sham-operated group (Sham group), a vehicle-intervened group (Vehicle group), a UCG-treated group (UCG group) (5g/kg/day) and an enalapril-treated group (Enalapril group) (20mg/kg/day). The rats with renal failure were induced by adenine (150 mg/kg/day) and unilateral ureteral obstruction (UUO), and killed on day 35 after the administration. Proteinuria, urinary N-acetyl-beta-D-glucosaminidase (UNAG), blood biochemical parameters, renal morphological changes, collagen type IV (CIV), matrix metalloproteinase (MMP)-2, MMP-9 and tissue inhibitors of metalloproteinase (TIMP)-1, as well as the key molecular protein expressions in TGF-beta1/Smad signaling pathway were observed, respectively.

RESULTS

Adenine administration and UUO induced severe renal damages, as indicated by renal dysfunction, proteinuria and the marked histopathological injuries in the tubules and interstitium, which were associated with MMP-2/TIMP-1 imbalance and TGF-beta1/Smad signaling activity, as shown by up-regulation of the protein expressions of TGF-beta1, TGF-beta receptor type I (RI), TGF-beta receptor type II (RII), Smad2/3, phosphorylated-Smad2/3 (p-Smad2/3) and Smad4, as well as down-regulation of the protein expression of Smad7 in the kidney. UCG treatment, however, significantly not only attenuated renal dysfunction and tubulointerstitial fibrosis, but also improved the protein expressions of MMP-2, TIMP-1, TGF-beta1, TGF-beta RI, p-Smad2/3, Smad4 and Smad7 in the kidney. Besides, the effects of UCG were stronger than those of enalapril partly.

CONCLUSION

UCG similar to enalapril, is renoprotective via ameliorating renal dysfunction and tubulointerstitial fibrosis in the renal failure model. The potential mechanisms by which UCG exerts its therapeutical effects in vivo are through promoting ECM degradation and regulating MMP-2/TIMP-1 balance or signaling molecular activity in TGF-beta1/Smad pathway in the kidney. These findings suggest that UCG treatment is undoubtedly useful in preventing the progression of CRF.

Longitudinal assessment of mouse renal injury using high-resolution anatomic and magnetization transfer MR imaging

The purpose of this study is to evaluate the utility of high-resolution non-invasive endogenous high-field MRI methods for the longitudinal structural and quantitative assessments of mouse kidney disease using the model of unilateral ureter obstruction (UUO). T1-weighted, T2-weighted and magnetization transfer (MT) imaging protocols were optimized to improve the regional contrast in mouse kidney. Conventional T1 and T2 weighted images were collected in UUO mice on day 0 (~3h), day 1, day 3 and day 6 after injury, on a 7 T small animal MRI system. Cortical and medullary thickness, corticomedullary contrast and Magnetization Transfer Ratio (MTR) were assessed longitudinally. Masson trichrome staining was used to histologically assess changes in tissue microstructure. Over the course of UUO progression there were significant (p<0.05) changes in thickness of cortex and outer medulla, and regional changes in T2 signal intensity and MTR values. Histological changes included tubular cell death, tubular dilation, urine retention, and interstitial fibrosis, assessed by histology. The MRI measures of renal cortical and medullary atrophy, cortical-medullary differentiation and MTR changes provide an endogenous, non-invasive and quantitative evaluation of renal morphology and tissue composition during UUO progression.

Effect of angiotensin II and small GTPase Ras signaling pathway inhibition on early renal changes in a murine model of obstructive nephropathy

Tubulointerstitial fibrosis is a major feature of chronic kidney disease. Unilateral ureteral obstruction (UUO) in rodents leads to the development of renal tubulointerstitial fibrosis consistent with histopathological changes observed in advanced chronic kidney disease in humans. The purpose of this study was to assess the effect of inhibiting angiotensin II receptors or Ras activation on early renal fibrotic changes induced by UUO. Animals either received angiotensin II or underwent UUO. UUO animals received either losartan, atorvastatin, and farnesyl transferase inhibitor (FTI) L-744,832, or chaetomellic acid A (ChA). Levels of activated Ras, phospho-ERK1/2, phospho-Akt, fibronectin, and α-smooth muscle actin were subsequently quantified in renal tissue by ELISA, Western blot, and/or immunohistochemistry. Our results demonstrate that administration of angiotensin II induces activation of the small GTPase Ras/Erk/Akt signaling system, suggesting an involvement of angiotensin II in the early obstruction-induced activation of renal Ras. Furthermore, upstream inhibition of Ras signalling by blocking either angiotensin AT1 type receptor or by inhibiting Ras prenylation (atorvastatin, FTI o ChA) reduced the activation of the Ras/Erk/Akt signaling system and decreased the early fibrotic response in the obstructed kidney. This study points out that pharmacological inhibition of Ras activation may hold promise as a future strategy in the prevention of renal fibrosis.

Involvement of Nrf2-GSH signaling in TGFβ1-stimulated epithelial-to-mesenchymal transition changes in rat renal tubular cells

Transforming growth factor-β1 (TGFβ1) induces epithelial-to-mesenchymal transition (EMT) in cultured renal tubular epithelial cells. This phenotypic transition has been known to be involved in the development of chronic kidney diseases by activating profibrotic gene expression. Since oxidative stress has been recognized as one of the contributors to this TGFβ1-mediated pathology, we investigated the potential involvement of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), which is a key transcription factor for the regulation of multiple antioxidant genes, in TGFβ1-stimulated EMT gene changes using the rat proximal tubular epithelial cell line NRK52E. The treatment of NRK52E with TGFβ1 led to changes in EMT gene expression, including increased α-Sma and decreased E-cadherin expression. In these cells, the TGFβ1 treatment decreased the transcript level of the catalytic subunit of γ-glutamate cysteine ligase (Gclc), a glutathione (GSH) biosynthetic enzyme, and reduced the total GSH content with a concomitant decrease in Nrf2 transcription activity. Accordantly, pre-incubation with the GSH precursor N-acetylcysteine attenuated TGFβ1-stimulated EMT gene changes. The involvement of Nrf2 in EMT gene changes has been demonstrated using NRK52E cells with nrf2 knockdown or pharmacological activation. When the expression of Nrf2 was stably silenced in NRK52E cells using interfering RNA administration, Gclc expression was significantly reduced and the increase in the levels of α-Sma and fibronectin-1 by TGFβ1 was greater than those in the nonspecific RNA control group. Conversely, Nrf2 activation and subsequent Gclc increase by Nrf2-activating sulforaphane alleviated the TGFβ1-stimulated α-Sma increase and E-cadherin decrease. Collectively, these results indicate that Nrf2-GSH signaling can modulate TGFβ1-stimulated EMT gene changes and further suggest a beneficial role of Nrf2 inducers in renal pathogenesis.

Inhibitory role of the KEAP1-NRF2 pathway in TGFβ1-stimulated renal epithelial transition to fibroblastic cells: a modulatory effect on SMAD signaling

Transforming growth factor β1 (TGFβ1) is a potent stimulator of epithelial-to-mesenchymal transition (EMT) and has been associated with chronic kidney diseases by activating profibrotic gene expression. In this study, we investigated the role of the KEAP1-NRF2 pathway, which is a master regulator of the cellular antioxidant system, in TGFβ1-stimulated EMT gene changes using human renal tubular epithelial HK2. Treatment with TGFβ1 enhanced the levels of reactive oxygen species (ROS) and TGFβ1-stimulated EMT gene changes, including an increase in profibrotic fibronectin-1 and collagen 1A1, were diminished by the antioxidant N-acetylcysteine. In HK2, TGFβ1 suppressed NRF2 activity and thereby reduced the expression of GSH synthesizing enzyme through the elevation of ATF3 level. Therefore, the activation of NRF2 signaling with sulforaphane effectively attenuated the TGFβ1-stimulated increase in fibronectin-1 and collagen 1A1. Conversely, the TGFβ1-EMT gene changes were further enhanced by NRF2 knockdown compared to the control cells. The relationship of NRF2 signaling and TGFβ1-EMT changes was further confirmed in a stable KEAP1-knockdown HK2, which is a model of pure activation of NRF2. The TGFβ1-mediated increase of collagen 1A1 and fibronectin-1 in KEAP1 knockdown HK2 was suppressed. In particular, TGFβ1-SMAD signaling was modulated in KEAP1 knockdown HK2: the TGFβ1-stimulated SMAD2/3 phosphorylation and SMAD transcriptional activity were repressed. Additionally, the protein level of SMAD7, an inhibitor of SMAD signaling, was elevated and the level of SMURF1, an E3 ubiquitin ligase for SMAD7 protein, was diminished in KEAP1 knockdown HK2. Finally, the inhibition of SMAD7 expression in KEAP1 knockdown HK2 restored TGFβ1 response, indicating that SMURF1-SMAD7 may be a molecular signaling linking the NRF2-GSH pathway to TGFβ1-EMT changes. Collectively, these results indicate that the KEAP1-NRF2 antioxidant system can be an effective modulator of TGFβ1-stimulated renal epithelial transition to fibroblastic cells through the SMUR1-SMAD7 signaling, and further implies the beneficial role of NRF2 in chronic renal diseases.

ROS dependence of cyclooxygenase-2 induction in rats subjected to unilateral ureteral obstruction

Oxidative stress resulting from unilateral ureteral obstruction (UUO) may be aggravated by increased production of ROS. Previous studies have demonstrated increased cyclooxygenase (COX)-2 expression in renal medullary interstitial cells (RMICs) in response to UUO. We investigated, both in vivo and in vitro, the role of ROS in the induction of COX-2 in rats subjected to UUO and in RMICs exposed to oxidative and mechanical stress. Rats subjected to 3-day UUO were treated with two mechanistically distinct antioxidants, the NADPH oxidase inhibitor diphenyleneiodonium (DPI) and the complex I inhibitor rotenone (ROT), to interfere with ROS production. We found that UUO-mediated induction of COX-2 in the inner medulla was attenuated by both antioxidants. In addition, DPI and ROT reduced tubular damage and oxidative stress after UUO. Moreover, mechanical stretch induced COX-2 and oxidative stress in RMICs. Likewise, RMICs exposed to H2O2 as an inducer of oxidative stress showed increased COX-2 expression and activity, both of which were reduced by DPI and ROT. Similarly, ROS production, which was increased after exposure of RMICs to H2O2, was also reduced by DPI and ROT. Furthermore, oxidative stress-induced phosphorylation of ERK1/2 and p38 was blocked by both antioxidants, and inhibition of ERK1/2 and p38 attenuated the induction of COX-2 in RMICs. Notably, COX-2 inhibitors further exacerbated the oxidative stress level in H2O2-exposed RMICs. We conclude that oxidative stress as a consequence of UUO stimulates COX-2 expression through the activation of multiple MAPKs and that the induction of COX-2 may exert a cytoprotective function in RMICs.

Increased progression to kidney fibrosis after erythropoietin is used as a treatment for acute kidney injury

Treatment of renal ischemia-reperfusion (IR) injury with recombinant human erythropoietin (rhEPO) reduces acute kidney injury and improves function. We aimed to investigate whether progression to chronic kidney disease associated with acute injury was also reduced by rhEPO treatment, using in vivo and in vitro models. Rats were subjected to bilateral 40-min renal ischemia, and kidneys were studied at 4, 7, and 28 days postreperfusion for renal function, tubular injury and repair, inflammation, and fibrosis. Acute injury was modulated using rhEPO (1,000 or 5,000 IU/kg, intraperitoneally) at the time of reperfusion. Renal tubular epithelial cells or fibroblasts in culture were subjected to hypoxia or oxidative stress, with or without rhEPO (200 IU/ml), and fibrogenesis was studied. The results of the in vivo model confirmed functional and structural improvement with rhEPO at 4 days post-IR (P < 0.05). At 7 days post-IR, fibrosis and myofibroblast stimulation were increased with IR with and without rhEPO (P < 0.01). However, at 28 days post-IR, renal fibrosis and myofibroblast numbers were significantly greater with IR plus rhEPO (P < 0.01) compared with IR only. Mechanistically, rhEPO stimulated profibrotic transforming growth factor-β, oxidative stress (marker 8-hydroxy-deoxyguanosine), and phosphorylation of the signal transduction protein extracellular signal-regulated kinase. In vitro, rhEPO protected tubular epithelium from apoptosis but stimulated epithelial-to-mesenchymal transition and also protected and activated fibroblasts, particularly with oxidative stress. In summary, although rhEPO was protective of renal function and structure in acute kidney injury, the supraphysiological dose needed for renoprotection contributed to fibrogenesis and stimulated chronic kidney disease in the long term.

Kindlin-2 regulates renal tubular cell plasticity by activation of Ras and its downstream signaling

Kindlin-2 is an adaptor protein that contributes to renal tubulointerstitial fibrosis (TIF). Epithelial-to-mesenchymal transition (EMT) in tubular epithelial cells was regarded as one of the key events in TIF. To determine whether kindlin-2 is involved in the EMT process, we investigated its regulation of EMT in human kidney tubular epithelial cells (TECs) and explored the underlying mechanism. In this study, we found that overexpression of kindlin-2 suppressed epithelial marker E-cadherin and increased the expression of fibronectin and the myofibroblast marker α-smooth muscle actin (SMA). Kindlin-2 significantly activated ERK1/2 and Akt, and inhibition of ERK1/2 or Akt reversed kindlin-2-induced EMT in human kidney TECs. Mechanistically, kindlin-2 interacted with Ras and son of sevenless (Sos)-1. Furthermore, overexpression of kindlin-2 increased Ras activation through recruiting Sos-1. Treatment with a Ras inhibitor markedly repressed kindlin-2-induced ERK1/2 and Akt activation, leading to restraint of EMT. We further demonstrated that knockdown of kindlin-2 inhibited EGF-induced Ras-Sos-1 interaction, resulting in reduction of Ras activation and suppression of EMT stimulated by EGF. Importantly, we found that depletion of kindlin-2 significantly inhibited activation of ERK1/2 and Akt signaling in mice with unilateral ureteral obstruction. We conclude that kindlin-2, through activating Ras and the downstream ERK1/2 and Akt signaling pathways, plays an important role in regulating renal tubular EMT and could be a potential therapeutic target for the treatment of fibrotic kidney diseases.

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 selective A3AR antagonist LJ-1888 ameliorates UUO-induced tubulointerstitial fibrosis

Adenosine in the normal kidney significantly elevates in response to cellular damage. The renal A3 adenosine receptor (A3AR) is up-regulated under stress, but the therapeutic effects of A3AR antagonists on chronic kidney disease are not fully understood. The present study examined the effect of LJ-1888 [(2R,3R,4S)-2-[2-chloro-6-(3-iodobenzylamino)-9H-purine-9-yl]-tetrahydrothiophene-3,4-diol], a newly developed potent, selective, species-independent, and orally active A3AR antagonist, on unilateral ureteral obstruction (UUO)-induced renal fibrosis. Pretreatment with LJ-1888 inhibited UUO-induced fibronectin and collagen I up-regulation in a dose-dependent manner. Masson's trichrome staining confirmed that LJ-1888 treatment effectively reduced UUO-induced interstitial collagen accumulation. Furthermore, delayed administration of LJ-1888 showed an equivalent therapeutic effect on tubulointerstitial fibrosis to that of losartan. Small-interfering A3AR transfection effectively inhibited transforming growth factor-β1 (TGF-β1)-induced fibronectin and collagen I up-regulation in proximal tubular cells similar to LJ-1888, confirming that the renoprotective effect of LJ-1888 resulted from A3AR blockade. UUO- or TGF-β1-induced c-Jun N-terminal kinase and extracellular signal-regulated kinase phosphorylation decreased significantly after LJ-1888 administration. A3AR blockade reduced UUO- or TGF-β1-induced up-regulation of lysyl oxidase, which induces cross-linking of extracellular matrix, suggesting that LJ-1888 may also regulate extracellular matrix accumulation via post-translational regulation. In conclusion, the present data demonstrate that the A3AR antagonist, LJ-1888, blocked the development and attenuated the progression of renal fibrosis, and they suggest that LJ-1888 may become a new therapeutic modality for renal interstitial fibrosis.

Pharmacological modulation of the bradykinin-induced differentiation of human lung fibroblasts: effects of budesonide and formoterol

OBJECTIVE

Bradykinin (BK) induces differentiation of lung fibroblasts into myofibroblasts, which play an important role in extracellular matrix remodeling in the airways of asthmatic patients. It is unclear whether this process is affected by antiasthma therapies. Here, we evaluated whether a glucocorticoid, budesonide (BUD), and a long-acting β2-agonist, formoterol (FM), either alone or in combination, modified BK-induced lung fibroblast differentiation, and affected the BK-activated intracellular signaling pathways.

METHODS

Human fetal lung fibroblasts were incubated with BUD (0.001-0.1 μM) and/or FM (0.0001-0.1 μM) before exposure to BK (0.1 or 1 μM). Fibroblast differentiation into α-smooth-muscle-actin-positive (α-SMA⁺) myofibroblasts, BK2 receptor (B2R) expression, extracellular signal-regulated kinase 1/2 (ERK 1/2) phosphorylation (p-ERK1/2), intracellular Ca²⁺ concentration ([Ca²⁺]i), and p65 nuclear factor kappa B translocation were evaluated.

RESULTS

BUD (0.1 μM) and FM (0.1 μM), either alone or in combination, completely inhibited BK-induced α-SMA protein expression and decreased the numbers of α-SMA⁺ fibroblasts, with a clear reduction in α-SMA stress fibers organization. BUD also completely inhibited the increase of B2R, whereas FM with or without BUD had no effect. BK-induced increases of [Ca²⁺]i and p-ERK1/2 were significantly reduced to similar levels by BUD and FM, either alone or in combination, whereas p65 translocation was completely inhibited by all treatments.

CONCLUSION

Both BUD and FM, either alone or in combination, effectively inhibited the BK-induced differentiation of fibroblasts into α-SMA⁺ myofibroblasts and the intracellular signaling pathways involved in fibroblast activation. These results suggest that BUD and FM combination therapy has potential to inhibit fibroblast-dependent matrix remodeling in the airways of asthmatic patients.

Induction of oxidative stress in kidney

Oxidative stress has a critical role in the pathophysiology of several kidney diseases, and many complications of these diseases are mediated by oxidative stress, oxidative stress-related mediators, and inflammation. Several systemic diseases such as hypertension, diabetes mellitus, and hypercholesterolemia; infection; antibiotics, chemotherapeutics, and radiocontrast agents; and environmental toxins, occupational chemicals, radiation, smoking, as well as alcohol consumption induce oxidative stress in kidney. We searched the literature using PubMed, MEDLINE, and Google scholar with “oxidative stress, reactive oxygen species, oxygen free radicals, kidney, renal injury, nephropathy, nephrotoxicity, and induction”. The literature search included only articles written in English language. Letters or case reports were excluded. Scientific relevance, for clinical studies target populations, and study design, for basic science studies full coverage of main topics, are eligibility criteria for articles used in this paper.

Diverse roles of TGF-β receptor II in renal fibrosis and inflammation in vivo and in vitro

TGF-β1 binds receptor II (TβRII) to exert its biological activities but its functional importance in kidney diseases remains largely unclear. In the present study, we hypothesized that TβRII may function to initiate the downstream TGF-β signalling and determine the diverse role of TGF-β1 in kidney injury. The hypothesis was examined in a model of unilateral ureteral obstructive (UUO) nephropathy and in kidney fibroblasts and tubular epithelial cells in which the TβRII was deleted conditionally. We found that disruption of TβRII inhibited severe tubulointerstitial fibrosis in the UUO kidney, which was associated with the impairment of TGF-β/Smad3 signalling, but not with the ERK/p38 MAP kinase pathway. In contrast, deletion of TβRII enhanced NF-κB signalling and renal inflammation including up-regulation of Il-1β and Tnfα in the UUO kidney. Similarly, in vitro disruption of TβRII from kidney fibroblasts or tubular epithelial cells inhibited TGF-β1-induced Smad signalling and fibrosis but impaired the anti-inflammatory effect of TGF-β1 on IL-1β-stimulated NF-κB activation and pro-inflammatory cytokine expression. In conclusion, TβRII plays an important but diverse role in regulating renal fibrosis and inflammation. Impaired TGF-β/Smad3, but not the non-canonical TGF-β signalling pathway, may be a key mechanism by which disruption of TβRII protects against renal fibrosis. In addition, deletion of TβRII also enhances NF-κB signalling along with up-regulation of renal pro-inflammatory cytokines, which may be associated with the impairment of anti-inflammatory properties of TGF-β1.

Cytoprotection behind heme oxygenase-1 in renal diseases

Renal insults are considered a public health problem and are linked to increased rates of morbidity and mortality worldwide. The heme oxygenase (HO) system consists of evolutionary specialized machinery that degrades free heme and produces carbon monoxide, biliverdin and free iron. In this sense, the inducible isoform HO-1 seems to develop an important role and is widely studied. The reaction involved with the HO-1 molecule provides protection to injured tissue, directly by reducing the toxic heme molecule and indirectly by the release of its byproducts. The up regulation of HO-1 enzyme has largely been described as providing antioxidant, antiapoptotic, anti-inflammatory and immunomodulatory properties. Several works have explored the importance of HO-1 in renal diseases and they have provided consistent evidence that its overexpression has beneficial effects in such injuries. So, in this review we will focus on the role of HO-1 in kidney insults, exploring the protective effects of its up regulation and the enhanced deleterious effects of its inhibition or gene deletion.

Conditioned media from lung cancer cell line A549 and PC9 inactivate pulmonary fibroblasts by regulating protein phosphorylation

Pulmonary fibrosis is a devastating condition resulting from excess extracellular matrix deposition that leads to progressive lung destruction and scarring. In the pathogenesis of fibrotic diseases, activation of myofibroblasts by transforming growth factor-β (TGF-β) plays a crucial role. Since no effective therapy for pulmonary fibrosis is currently recognized, finding an effective antifibrotic agent is an important objective. One approach might be through identification of agents that inactivate myofibroblasts. In the current study we examined the potential of conditioned medium obtained from several types of cells to exhibit myofibroblast inactivating activity. Conditioned media from lung cancer cell lines A549 and PC9 were found to have this action, as shown by its ability to decrease α-smooth muscle actin expression in MRC-5 cells. Subsequently the inhibitory factor was purified from the medium and identified as 5'-deoxy-5'-methylthioadenosine (MTA), and its mechanism of action elucidated. Activation of protein kinase A and cAMP responsive element binding protein (CREB) were detected. MTA inhibited TGF-β-induced mitogen-activated protein kinase activation. Furthermore, the gain-of-function mutant CREB caused inactivation of myofibroblasts. These results show that A549 and PC9 conditioned media have the ability to inactivate myofibroblasts, and that CREB-phosphorylation plays a central role in this process.

Disruption of Smad4 impairs TGF-β/Smad3 and Smad7 transcriptional regulation during renal inflammation and fibrosis in vivo and in vitro

The mechanism by which TGF-β regulates renal inflammation and fibrosis is largely unclear; however, it is well accepted that its biological effects are mediated through Smad2 and Smad3 phosphorylation. Following activation, these Smads form heteromeric complex with Smad4 and translocate into the nucleus to bind and regulate the expression of target genes. Here we studied the roles of Smad4 to regulate TGF-β signaling in a mouse model of unilateral ureteral obstruction using conditional Smad4 knockout mice and in isolated Smad4 mutant macrophages and fibroblasts. Disruption of Smad4 significantly enhanced renal inflammation as evidenced by a greater CD45(+) leukocyte and F4/80(+) macrophage infiltration and upregulation of IL-1β, TNF-α, MCP-1, and ICAM-1 in the obstructed kidney and in IL-1β-stimulated macrophages. In contrast, deletion of Smad4 inhibited renal fibrosis and TGF-β1-induced collagen I expression by fibroblasts. Further studies showed that the loss of Smad4 repressed Smad7 transcription, leading to a loss of functional protein. This, in turn, inhibited IκBα expression but enhanced NF-κB activation, thereby promoting renal inflammation. Interestingly, deletion of Smad4 influenced Smad3-mediated promoter activities and the binding of Smad3 to the COL1A2 promoter, but not Smad3 phosphorylation and nuclear translocation, thereby inhibiting the fibrotic response. Thus, Smad4 may be a key regulator for the diverse roles of TGF-β1 in inflammation and fibrogenesis by interacting with Smad7 and Smad3 to influence their transcriptional activities in renal inflammation and fibrosis.

Targeted genomic disruption of H-ras and N-ras has no effect on early renal changes after unilateral ureteral ligation

PURPOSE

To assess the contribution of two different Ras monomeric GTPases isoforms H- and N-Ras in the early changes associated to obstructive nephropathy induced by unilateral ureteral obstruction (UUO).

METHODS

UUO was performed in N-ras (N-ras−/−) and H-ras (H-ras−/−) knock-out mice and control (H-ras+/+/N-ras+/+) mice of C57Bl/6 background. Fibronectin, α-smooth muscle actin, cleaved caspase-3, ki-67, Ras-GTP, pERK, and pAkt expression was analyzed by western blot and/or immunohistochemistry. Ras isoforms activation and caspase activity were determined by both western blot and ELISA.

RESULTS

Three days after UUO, obstructed (O) kidneys of H-ras−/−, N-ras−/−and H-ras+/+/N-ras+/+mice showed no significant differences in activated total ras, pERK1/2, pAkt, total Akt levels, fibronectin, α-SMA expression, cell proliferation, and activated caspase-3. The morphological alterations in the O kidneys, revealed by histological and immunohistochemical studies, were also similar in H-ras−/−, N-ras−/−, and H-ras+/+/N-ras+/+mice.

CONCLUSIONS

These data suggest that the activation of H-ras and N-ras isoforms does not play a major role in the early renal damage induced by UUO.

Suramin inhibits renal fibrosis in chronic kidney disease

The activation of cytokine and growth factor receptors associates with the development and progression of renal fibrosis. Suramin is a compound that inhibits the interaction of several cytokines and growth factors with their receptors, but whether suramin inhibits the progression of renal fibrosis is unknown. Here, treatment of cultured renal interstitial fibroblasts with suramin inhibited their activation induced by TGF-β1 and serum. In a mouse model of obstructive nephropathy, administration of a single dose of suramin immediately after ureteral obstruction abolished the expression of fibronectin, largely suppressed expression of α-SMA and type I collagen, and reduced the deposition of extracellular matrix proteins. Suramin also decreased the expression of multiple cytokines including TGF-β1 and reduced the interstitial infiltration of leukocytes. Moreover, suramin decreased expression of the type II TGF-β receptor, blocked phosphorylation of the EGF and PDGF receptors, and inactivated several signaling pathways associated with the progression of renal fibrosis. In a rat model of CKD, suramin abrogated proteinuria, limited the decline of renal function, and prevented glomerular and tubulointerstitial damage. Collectively, these findings indicate that suramin is a potent antifibrotic agent that may have therapeutic potential for patients with fibrotic kidney diseases.

Erk in kidney diseases

Acute or chronic kidney injury results from various insults and pathological conditions, and is accompanied by activation of compensatory repair mechanisms. Both insults and repair mechanisms are initiated by circulating factors, whose cellular effects are mediated by activation selective signal transduction pathways. Two main signal transduction pathways are activated during these processes, the phosphatidylinositol 3' kinase (PI-3K)/mammalian target of rapamycin (mTOR) and the mitogen-activated protein kinase (MAPK) cascades. This review will focus on the latter, and more specifically on the role of extracellular signal-regulated kinase (ERK) cascade in kidney injury and repair.

Proximal tubular injury and rapid formation of atubular glomeruli in mice with unilateral ureteral obstruction: a new look at an old model

Unilateral ureteral obstruction (UUO), employed extensively as a model of progressive renal interstitial fibrosis, results in rapid parenchymal deterioration. Atubular glomeruli are formed in many renal disorders, but their identification has been limited by labor-intensive available techniques. The formation of atubular glomeruli was therefore investigated in adult male mice subjected to complete UUO under general anesthesia. In this species, the urinary pole of Bowman's capsule is normally lined by tall parietal epithelial cells similar to those of the proximal tubule, and both avidly bind Lotus tetragonolobus lectin. Following UUO, these cells became flattened, lost their affinity for Lotus lectin, and no longer generated superoxide (revealed by nitroblue tetrazolium infusion). Based on Lotus lectin staining, stereological measurements, and serial section analysis, over 80% of glomeruli underwent marked transformation after 14 days of UUO. The glomerulotubular junction became stenotic and atrophic due to cell death by apoptosis and autophagy, with concomitant remodeling of Bowman's capsule to form atubular glomeruli. In this degenerative process, transformed epithelial cells sealing the urinary pole expressed α-smooth muscle actin, vimentin, and nestin. Although atubular glomeruli remained perfused, renin immunostaining was markedly increased along afferent arterioles, and associated maculae densae disappeared. Numerous progressive kidney disorders, including diabetic nephropathy, are characterized by the formation of atubular glomeruli. The rapidity with which glomerulotubular junctions degenerate, coupled with Lotus lectin as a marker of glomerular integrity, points to new investigative uses for the model of murine UUO focusing on mechanisms of epithelial cell injury and remodeling in addition to fibrogenesis.

Myofibroblast differentiation during fibrosis: role of NAD(P)H oxidases

Progression of fibrosis involves interstitial hypercellularity, matrix accumulation, and atrophy of epithelial structures, resulting in loss of normal function and ultimately organ failure. There is common agreement that the fibroblast/myofibroblast is the cell type most responsible for interstitial matrix accumulation and consequent structural deformations associated with fibrosis. During wound healing and progressive fibrotic events, fibroblasts transform into myofibroblasts acquiring smooth muscle features, most notably the expression of alpha-smooth muscle actin and synthesis of mesenchymal cell-related matrix proteins. In renal disease, glomerular mesangial cells also acquire a myofibroblast phenotype and synthesize the same matrix proteins. The origin of interstitial myofibroblasts during fibrosis is a matter of debate, where the cells are proposed to derive from resident fibroblasts, pericytes, perivascular adventitial, epithelial, and/or endothelial sources. Regardless of the origin of the cells, transforming growth factor-beta1 (TGF-β1) is the principal growth factor responsible for myofibroblast differentiation to a profibrotic phenotype and exerts its effects via Smad signaling pathways involving mitogen-activated protein kinase and Akt/protein kinase B. Additionally, reactive oxygen species (ROS) have important roles in progression of fibrosis. ROS are derived from a variety of enzyme sources, of which the nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase family has been identified as a major source of superoxide and hydrogen peroxide generation in the cardiovasculature and kidney during health and disease. Recent evidence indicates that the NAD(P)H oxidase homolog Nox4 is most accountable for ROS-induced fibroblast and mesangial cell activation, where it has an essential role in TGF-β1 signaling of fibroblast activation and differentiation into a profibrotic myofibroblast phenotype and matrix production. Information on the role of ROS in mesangial cell and fibroblast signaling is incomplete, and further research on myofibroblast differentiation during fibrosis is warranted.

The Nrf2-Keap1 cellular defense pathway and heat shock protein 70 (Hsp70) response. Role in protection against oxidative stress in early neonatal unilateral ureteral obstruction (UUO)

Perturbation of renal tubular antioxidants and overproduction of reactive oxygen species may amplify the proinflammatory state of renal obstruction, culminating in oxidative stress and tubular loss. Here, we analyzed the heat shock protein 70 (Hsp70) response and the function and signal transduction of NF-E2-related protein 2 (Nrf2) transcription factor on oxidative stress modulation in obstruction. Rats were subjected to unilateral ureteral obstruction or sham operation and kidneys harvested at 5, 7, 10, and 14 days after obstruction. Hsp70 expression and Nrf2 activity and its downstream target gene products were assessed. After 10 and 14 days of obstruction, enhanced lipid peroxidation through higher thiobarbituric acid reactive substances levels and increased oxidative stress resulted in reduced total antioxidant activity and enhanced nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase activity were demonstrated. This was accompanied by decreased inducible Hsp70 expression and a progressive reduction of nuclear Nrf2 and its target gene products glutathione S-transferase A2 (GSTA2) and NADPH/quinone oxidoreductase 1 (NQO1), whereas the Nrf2 repressor Kelch-like ECH-associated protein-1 (Keap1) was upregulated. By contrast, on early obstruction for 7 days, lack of increased oxidative markers associated with higher inducible Hsp70 protein levels and a rapid nuclear accumulation of Nrf2, Keap1 downregulation, and mRNA induction of the identified Nrf2-dependent genes, NQO1 and GSTA2, were shown. For these results, we suggest that the magnitude of cytoprotection in early obstruction depends on the combined contribution of induced activation of Nrf2 upregulating its downstream gene products and Hsp70 response. Impaired ability to mount the biological response to the prevailing oxidative stress leading to renal injury was shown in prolonged obstruction.

Inhibitory effects of T/L-type calcium channel blockers on tubulointerstitial fibrosis in obstructed kidneys in rats

OBJECTIVES

To examine the effect of L- and T/L-type calcium channel blockers on interstitial fibrosis in chronic unilateral ureteral obstruction (UUO). Tubulointerstitial fibrosis is a common outcome of several progressive renal diseases. Calcium channel blockers are widely used for the treatment of hypertension with renal diseases; however, the direct effect of calcium channel blockers on renal diseases independent of lowering blood pressure has not been fully elucidated.

METHODS

Sprague-Dawley rats were divided into 3 treatment groups: (1) vehicle control; (2) nifedipine, an L-type calcium channel blockers; and (3) efonidipine, a T/L-type calcium channel blockers. Treatment was initiated 1 day before and continued until 6 days after creation of the UUO.

RESULTS

Tubulointerstitial fibrosis in the obstructed kidney was significantly increased compared with that in the contralateral unobstructed kidney. Furthermore, the increased fibrosis was accompanied by increased fibrogenic signaling expressed by transforming growth factor β1 and connective tissue growth factor mRNA levels, increased oxidative stress expressed by p22phox, p47phox and gp91phox mRNA level. Moreover, treatment with a nonhypotensive dose of efonidipine but not nifedipine in the obstructed kidney significantly suppressed the fibrogenic signaling and the oxidative stress, resulting in reduced tubulointerstitial fibrosis. The plasma aldosterone level in efonidipine-treated animals was increased compared with vehicle-treated animals, although not significantly. The increased plasma aldosterone level did not increase sgk-1 mRNA level in efonidipine but not in nifedipine treated animals.

CONCLUSIONS

Treatment with efonidipine improved tubulointerstitial fibrosis more effectively than treatment with nifedipine in UUO. The antifibrogenic effect by efonidipine was obtained through suppression of fibrogenic signaling.

Oxidative stress in obstructive nephropathy

Unilateral ureteric obstruction (UUO) is one of the most commonly applied rodent models to study the pathophysiology of renal fibrosis. This model reflects important aspects of inflammation and fibrosis that are prominent in human kidney diseases. In this review, we present an overview of the factors contributing to the pathophysiology of UUO, highlighting the role of oxidative stress.

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.

Mechanisms of renal injury and progression of renal disease in congenital obstructive nephropathy

Congenital obstructive nephropathy accounts for the greatest fraction of chronic kidney disease in children. Genetic and nongenetic factors responsible for the lesions are largely unidentified, and attention has been focused on minimizing obstructive renal injury and optimizing long-term outcomes. The cellular and molecular events responsible for obstructive injury to the developing kidney have been elucidated from animal models. These have revealed nephron loss through cellular phenotypic transition and cell death, leading to the formation of atubular glomeruli and tubular atrophy. Altered renal expression of growth factors and cytokines, including angiotensin, transforming growth factor-beta, and adhesion molecules, modulate cell death by apoptosis or phenotypic transition of glomerular, tubular, and vascular cells. Mediators of cellular injury include hypoxia, ischemia, and reactive oxygen species, while fibroblasts undergo myofibroblast transformation with increased deposition of extracellular matrix. Progression of the lesions involves interstitial inflammation and interstitial fibrosis, both of which impair growth of the obstructed kidney and result in compensatory growth of the contralateral kidney. The long-term outcome depends on timing and severity of the obstruction and its relief, minimizing ongoing injury, and enhancing remodeling. Advances will depend on new biomarkers to evaluate the severity of obstruction, to determine therapy, and to follow the evolution of lesions.

NAD(P)H oxidase mediates TGF-beta1-induced activation of kidney myofibroblasts

TGF-beta1 expression closely associates with activation and conversion of fibroblasts to a myofibroblast phenotype and synthesis of an alternatively spliced cellular fibronectin variant, Fn-ED-A. Reactive oxygen species (ROS), such as superoxide, which is a product of NAD(P)H oxidase, also promote the transition of fibroblasts to myofibroblasts, but whether these two pathways are interrelated is unknown. Here, we examined a role for NAD(P)H oxidase-derived ROS in TGF-beta1-induced activation of rat kidney fibroblasts and expression of alpha-smooth muscle actin (alpha-SMA) and Fn-ED-A. In vitro, TGF-beta1 stimulated formation of abundant stress fibers and increased expression of both alpha-SMA and Fn-ED-A. In addition, TGF-beta1 increased both the activity of NADPH oxidase and expression of Nox2 and Nox4, homologs of the NAD(P)H oxidase family, indicating that this growth factor induces production of ROS. Small interfering RNA targeted against Nox4 markedly inhibited TGF-beta1-induced stimulation of NADPH oxidase activity and reduced alpha-SMA and Fn-ED-A expression. Inhibition of TGF-beta1 receptor 1 blocked Smad3 phosphorylation; reduced TGF-beta1-enhanced NADPH oxidase activity; and decreased expression of Nox4, alpha-SMA, and Fn-ED-A. Diphenyleneiodonium, an inhibitor of flavin-containing enzymes such as the Nox oxidases, had no effect on TGF-beta1-induced Smad3 but reduced both alpha-SMA and Fn-ED-A protein expression. The Smad3 inhibitor SIS3 reduced NADPH oxidase activity, Nox4 expression, and blocked alpha-SMA and Fn-ED-A, indicating that stimulation of myofibroblast activation by ROS is downstream of Smad3. In addition, TGF-beta1 stimulated phosphorylation of extracellular signal-regulated kinase (ERK1/2), and this was inhibited by blocking TGF-beta1 receptor 1, Smad3, or the Nox oxidases; ERK1/2 activation increased alpha-SMA and Fn-ED-A. Taken together, these results suggest that TGF-beta1-induced conversion of fibroblasts to a myofibroblast phenotype involves a signaling cascade through Smad3, NAD(P)H oxidase, and ERK1/2.

Dimethylarginine dimethylaminohydrolase regulation: a novel therapeutic target in cardiovascular disease

Asymmetric dimethylarginine (ADMA), an endogenous methylated form of the amino acid L-arginine, inhibits the activity of the enzyme endothelial nitric oxide synthase, with consequent reduced synthesis of nitric oxide. ADMA is metabolised to L-citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). The modulation of DDAH activity and expression plays a pivotal role in regulating intracellular ADMA concentrations, with important effects on vascular homeostasis. For example, impairment in DDAH activity, resulting in elevated ADMA concentrations and reduced nitric oxide synthesis, can promote the onset and progression of atherosclerosis in experimental models. This review discusses the current role of ADMA and DDAH in vascular health and disease, the techniques used to assess DDAH activity and expression, and the results of recent studies on pharmacological and biological agents modulating DDAH activity and expression. Suggestions for future basic and clinical research directions are also discussed.

SOD1 deficiency causes salt sensitivity and aggravates hypertension in hydronephrosis

Hydronephrosis causes renal dysfunction and salt-sensitive hypertension, which is associated with nitric oxide deficiency and abnormal tubuloglomerular feedback (TGF) response. We investigated the role of oxidative stress for salt sensitivity and for hypertension in hydronephrosis. Hydronephrosis was induced in superoxide dismutase 1-transgenic (SOD1-tg), SOD1-deficient (SOD1-ko), and wild-type mice and in rats. In mice, telemetric measurements were performed during normal (0.7% NaCl) and high-sodium (4% NaCl) diets and with chronic tempol supplementation. The 8-iso-prostaglandin-F(2alpha) (F2-IsoPs) and protein excretion profiles and renal histology were investigated. The acute effects of tempol on blood pressure and TGF were studied in rats. In hydronephrosis, wild-type mice developed salt-sensitive hypertension (114 +/- 1 to 120 +/- 2 mmHg), which was augmented in SOD1-ko (125 +/- 3 to 135 +/- 4 mmHg) but abolished in SOD1-tg (109 +/- 3 to 108 +/- 3 mmHg). SOD1-ko controls displayed salt-sensitive blood pressure (108 +/- 1 to 115 +/- 2 mmHg), which was not found in wild types or SOD1-tg. Chronic tempol treatment reduced blood pressure in SOD1-ko controls (-7 mmHg) and in hydronephrotic wild-type (-8 mmHg) and SOD1-ko mice (-16 mmHg), but had no effect on blood pressure in wild-type or SOD1-tg controls. SOD1-ko controls and hydronephrotic wild-type and SOD1-ko mice exhibited increased fluid excretion associated with increased F2-IsoPs and protein excretion. The renal histopathological changes found in hydronephrotic wild-type were augmented in SOD1-ko and diminished in SOD-tg mice. Tempol attenuated blood pressure and normalized TGF response in hydronephrosis [DeltaP(SF): 15.2 +/- 1.2 to 9.1 +/- 0.6 mmHg, turning point: 14.3 +/- 0.8 to 19.7 +/- 1.4 nl/min]. Oxidative stress due to SOD1 deficiency causes salt sensitivity and plays a pivotal role for the development of hypertension in hydronephrosis. Increased superoxide formation may enhance TGF response and thereby contribute to hypertension.

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.

C/EBP-beta modulates transcription of tubulointerstitial nephritis antigen in obstructive uropathy

Tubulointerstitial injury leading to fibrosis is a common pathway of many renal diseases. During this type of injury, modeled by unilateral ureteral obstruction (UUO), cells undergo epithelial-to-mesenchymal transition (EMT), a process that is mediated by various cytokines that modulate the biology of extracellular matrix proteins. Here, we studied the tubulointerstitial nephritis antigen (TINag), a tubular basement membrane protein, in the UUO model of tubulointerstitial injury. We observed upregulation of type IV collagen but downregulation of both laminin and TINag in obstructed kidneys. TINag downregulation was a result of oxidative stress; in the proximal tubular epithelial cell line HK-2, TINag expression and its promoter activity decreased after treatment with H2O2. We identified multiple CCAAT/enhancer binding protein beta (C/EBP-beta) motifs in the TINag promoter and observed that oxidant stress perturbed interactions between TINag DNA and C/EBP-beta protein. Oxidant stress reduced nuclear translocation of C/EBP-beta in HK-2 cells, which was restored by antioxidants. In addition, overexpression of C/EBP-beta restored the H2O2-induced reduction of TINag promoter activity and expression. Furthermore, in vivo, renal obstruction reduced nuclear expression of C/EBP-beta. Cells grown on a TINag substratum maintained their normal epithelial phenotype and cytoskeletal organization, similar to those grown on type IV collagen, and demonstrated reduced synthesis of fibronectin. Taken together, these findings suggest that altered interactions between C/EBP-beta and TINag play a critical role in the pathophysiology of renal injury after obstruction.

Ginsenoside Rg1, a major active component isolated from Panax notoginseng, restrains tubular epithelial to myofibroblast transition in vitro

The medicinal herb, Panax notoginseng, has been used for thousands of years in traditional Chinese medicine and possesses anti-fibrosis properties. Epithelial-myofibroblast transition (EMT) plays an important role in renal tubulointerstitial fibrosis. The present study was designed to examine whether ginsenoside Rg1, a major active component isolated from Panax notoginseng, has an ability to block this phenotypic transition in rat renal tubular epithelial cells (NRK-52E) induced by transforming growth factor-beta1 (TGF-beta1). The morphology of tubular epithelial-myofibroblast transition was observed through light microscope and transmission electron microscopy. alpha-SMA and E-cadherin are two markers of tubular epithelial-myofibroblast transition, their protein expressions were assessed by immunohistochemistry and western blot analysis. Gene expression of alpha-SMA as well as the two major extracellular matrix components collagen I and fibronectin was measured by real-time PCR analysis. Enzyme-linked immunosorbent assay was used to quantitatively detect collagen I and fibronectin in the supernatant. Our results revealed that ginsenoside Rg1 obviously blocked morphologic transformation in NRK-52E induced by TGF-beta1. Meanwhile, ginsenoside Rg1 inhibited the expression of alpha-SMA and the loss of E-cadherin, subsequently decreased the levels of collagen I and fibronectin in a dose-dependent manner. In addition, western blot analysis indicated that ginsenoside Rg1 inhibited the expression of P-ERK1/2 in NRK-52E induced by TGF-beta1. These results suggest that ginsenoside Rg1 can restrain the process of EMT maybe via suppressing the expression of P-ERK1/2 in vitro.

A novel cell-permeable antioxidant peptide decreases renal tubular apoptosis and damage in unilateral ureteral obstruction

Unilateral ureteral obstruction (UUO) is characterized by decreases in renal function, increased interstitial fibrosis, tubular apoptosis, and cellular infiltration. It has been suggested that inhibition of tubular apoptosis may protect against renal damage in obstruction. We have recently developed a series of peptides which are concentrated in the inner mitochondrial membrane and prevent cell death. These peptides are also active in vivo, in myocardial infraction, ischemic brain injury, and amyotrophic lateral sclerosis models. We therefore used SS-31, a prototype of these peptides, and assessed its effects on renal damage and oxidative stress in a 14-day obstruction model. SS-31 (1 or 3 mg/kg) or saline was given 1 day before and throughout the 14 days of obstruction. Kidneys were harvested and assessed for apoptosis (terminal transferase-dUTP-nick-end labeling, caspase 3 expression), fibrosis (trichrome staining), macrophage infiltration, fibroblast expression (immunoperoxidase), and oxidative damage (8-OH deoxyguanosine and heme oxygenase-1 expression), cytokines, and signaling pathways (transforming growth factor-beta, CCR-1, p38-MAPK, NF-kappaB). SS-31 significantly attenuated the effects of obstruction on all aspects of renal damage which were examined, with both the 1 and 3 mg/kg doses showing efficacy. We noted increased oxidative stress in obstruction, which was also attenuated by SS-31 treatment. Signaling via NF-kappaB and p38 MAPK pathways were both affected by SS-31 treatment. This study provides a proof of concept that peptides which protect mitochondria in vitro can provide protection from renal damage in a UUO model. The mechanism by which protection is afforded requires further studies both in vitro and in vivo.

Heme oxygenase-1 deficiency promotes epithelial-mesenchymal transition and renal fibrosis

Induction of heme oxygenase-1 (HO-1) is associated with potential antifibrogenic effects. The effects of HO-1 expression on epithelial-mesenchymal transition (EMT), which plays a critical role in the development of renal fibrosis, are unknown. In this study, HO-1(-/-) mice demonstrated significantly more fibrosis after 7 d of unilateral ureteral obstruction compared with wild-type mice, despite similar degrees of hydronephrosis. The obstructed kidneys of HO-1(-/-) mice also had greater macrophage infiltration and renal tubular TGF-beta1 expression than wild-type mice. In addition, the degree of EMT was more extensive in obstructed HO-1(-/-) kidneys, as assessed by alpha-smooth muscle actin and expression of S100A4 in proximal tubular epithelial cells. In vitro studies using proximal tubular cells isolated from HO-1(-/-) and wild-type kidneys confirmed these observations. In conclusion, HO-1 deficiency is associated with increased fibrosis, tubular TGF-beta1 expression, inflammation, and enhanced EMT in obstructive kidney disease. Modulation of the HO-1 pathway may provide a new therapeutic approach to progressive renal diseases.

Origin of renal myofibroblasts in the model of unilateral ureter obstruction in the rat

Tubulo-interstitial fibrosis is a constant feature of chronic renal failure and it is suspected to contribute importantly to the deterioration of renal function. In the fibrotic kidney there exists, besides normal fibroblasts, a large population of myofibroblasts, which are supposedly responsible for the increased production of intercellular matrix. It has been proposed that myofibroblasts in chronic renal failure originate from the transformation of tubular cells via epithelial–mesenchymal transition (EMT) or from infiltration by bone marrow-derived precursors. Little attention has been paid to the possibility of a transformation of resident fibroblasts into myofibroblasts in renal fibrosis. Therefore we examined the fate of resident fibroblasts in the initial phase of renal fibrosis in the classical model of unilateral ureter obstruction (UUO) in the rat. Rats were perfusion-fixed on days 1, 2, 3 and 4 after ligature of the right ureter. Starting from 1 day of UUO an increasing expression of alpha-smooth muscle actin (αSMA) in resident fibroblasts was revealed by immunofluorescence and confirmed by the observation of bundles of microfilaments and webs of intermediate filaments in the electron microscope. Inversely, there was a decreased expression of 5′-nucleotidase (5′NT), a marker of renal cortical fibroblasts. The RER became more voluminous, suggesting an increased synthesis of matrix. Intercellular junctions, a characteristic feature of myofibroblasts, became more frequent. The mitotic activity in fibroblasts was strongly increased. Renal tubules underwent severe regressive changes but the cells retained their epithelial characteristics and there was no sign of EMT. In conclusion, after ureter ligature, resident peritubular fibroblasts proliferated and they showed progressive alterations, suggesting a transformation in myofibroblasts. Thus the resident fibroblasts likely play a central role in fibrosis in that model.

Activation of Erk1/2 and Akt following unilateral ureteral obstruction

Chronic unilateral ureteral obstruction is a well characterized model of renal injury leading to tubulointerstitial fibrosis and distinct patterns of cell proliferation and apoptosis in the obstructed kidney. In this study we assessed the contribution of the mitogen activated protein kinase (MAPK)-ERK1/2 and the phosphatidylinositol 3 kinase (PI3K)-Akt pathways to early renal changes following unilateral obstruction. Increased activation of small Ras GTPase and its downstream effectors ERK1/2 and Akt was detected in ligated kidneys. The use of specific pharmacological inhibitors to either ERK1/2 or Akt activation led to decreased levels of fibroblast-myofibroblast markers in the interstitium while inhibition of PI3K reduced the number of proliferating cells and the amount of interstitial extracellular matrix deposition. Treatment with an ERK1/2 inhibitor diminished the number of apoptotic tubule and interstitial cells. Our results suggest a role for the MAPK-ERK1/2 and PI3K-Akt systems in early changes induced by ureteral obstruction and that inhibition of these signaling pathways may provide a novel approach to prevent progression of renal fibrosis.

Activated extracellular signal-regulated kinase correlates with cyst formation and transforming growth factor-beta expression in fetal obstructive uropathy

Human renal dysplasia is frequently associated with urinary tract obstruction and the abnormal expression of mitogen-activated protein kinase (MAPK). Here, we determined the renal responses and MAPK expression in developing kidneys that were obstructed in fetal lambs. Kidneys were harvested at various times after obstruction (gestation day 60) through normal term (day 145). Dilation of Bowman's capsule and proximal tubules was seen 2 days after obstruction and involved the whole cortex 18 days later, with numerous cysts present throughout the kidney at term. The proliferation marker Ki-67 and transforming growth factor-beta (TGF-beta) were detected 2 days after obstruction and progressively increased in tubules, cysts, and the interstitium. In control kidneys, p38 was expressed in tubules only during the fetal stage, whereas phosphorylated extracellular signal-regulated kinase (P-ERK) was limited to ureteric buds and collecting ducts at all stages examined. However, Jun-N-terminal kinase (JNK) was absent in the fetal kidney but present in tubules at term. In obstructed kidneys, cyst epithelia were positive for p38 and P-ERK but negative for JNK throughout all stages. These studies show that P-ERK correlated spatially and temporally with Ki-67 and TGF-beta expression, which suggests that ERK may contribute to cyst formation and fibrosis in the obstructed fetal kidney.

Inhibition of NADPH oxidase reduces myocardial oxidative stress and apoptosis and improves cardiac function in heart failure after myocardial infarction

Increases in NADPH oxidase activity, oxidative stress, and myocyte apoptosis coexist in failing hearts. In cardiac myocytes in vitro inhibition of NADPH oxidase reduces apoptosis. In this study, we tested the hypothesis that NADPH oxidase inhibition reduces myocyte apoptosis and improves cardiac function in heart failure after myocardial infarction (MI). Rabbits with heart failure induced by MI and sham-operated animals were randomized to orally receive apocynin, an inhibitor of NADPH oxidase (15 mg per day) or placebo for 4 weeks. Left ventricular (LV) dimension and function were assessed by echocardiography and hemodynamics. Myocardial NADPH oxidase activity was measured by superoxide dismutase-inhibitable cytochrome c reduction assay, NADPH oxidase subunit p47phox expression by Western blot and immunofluorescence analysis, myocardial oxidative stress evaluated by 8-hydroxydeoxyguanosine (8-OHdG) and 4-hydroxy-2-nonenal (4-HNE) using immunohistochemistry, and myocyte apoptosis by TUNEL assay. MI rabbits exhibited LV dilatation and systolic dysfunction measured by LV fractional shortening and the maximal rate of LV pressure rise (dP/dt). These changes were associated with increases in NADPH oxidase activity, p47phox protein expression, 8-OHdG expression, 4-HNE expression, myocyte apoptosis, and Bax protein and a decrease in Bcl-2 protein. Apocynin reduced NADPH oxidase activity, p47phox protein, oxidative stress, myocyte apoptosis, and Bax protein, increased Bcl-2 protein, and ameliorated LV dilatation and dysfunction after MI. The results suggest that inhibition of NADPH oxidase may represent an attractive therapeutic approach to treat heart failure.

Oxidative stress as a common pathway to chronic tubulointerstitial injury in kidney allografts

A major challenge for kidney transplantation is to dissect out the identifiable causes of chronic allograft tubulointerstitial fibrosis and to develop cause-specific treatment strategies. There has been a recent interest in the role of oxidative stress (OS) as a mediator of injury in chronic allograft tubular atrophy (TA) and interstitial fibrosis (IF). A review of the literature and data from my laboratory studying chronic allograft TA/IF in rat, rhesus monkey, and human kidneys suggests that OS is increased in graft-infiltrating macrophages, activated myofibroblasts, interstitium, and areas of tubular injury. Chronic allograft OS may be induced by inflammation, abnormal tissue oxygenation, immunosuppressant drugs, and comorbid clinical conditions including diabetes, hypertension, proteinuria, anemia, and dyslipidemia. Moreover, OS-induced chronic TA/IF is associated with signaling pathways including inflammation, apoptosis, hypoxia, and epithelial-to-mesenchymal transition. Most of these injury pathways participate in a self-perpetuating cycle with OS. In conclusion, evidence suggests that OS is a common mechanism of injury in chronic allograft TA/IF. However, most available data demonstrate a correlation and no causal relationship. Furthermore, the extent to which TA/IF is dependent on OS is unknown. These questions may be answered by prospective randomized placebo-control trials examining the role of select antioxidants in the prevention of chronic allograft TA/IF.

High glucose promotes the production of collagen types I and III by cardiac fibroblasts through a pathway dependent on extracellular-signal-regulated kinase 1/2

Hyperglycemia promotes fibrosis by increasing collagen synthesis, a process involving mitogen activated protein kinases (MAPKs). Several studies of diabetic cardiomyopathy have demonstrated an accumulation of collagen, including collagen types I and III, in the myocardium, leading to interstitial fibrosis, which is related to left-ventricular diastolic dysfunction. However, the mechanisms of hyperglycemia-induced collagen production in cardiac fibroblasts are poorly defined. In the present study, neonatal rat cardiac fibroblasts treated with high glucose (25 mM) were assessed by real time PCR and enzyme linked immunosorbent assay (ELISA) showed an increase in both the mRNA and protein level of collagen types I and III. These effects were not due to changes in osmotic pressure. Extracellular signal regulated kinase 1/2 (ERK1/2) was activated by high glucose level (25 mM), and treatment with PD98059 to block ERK phosphorylation significantly inhibited the mRNA and protein expression of collagen types I and III. These results suggest that high glucose accelerates the synthesis of collagen types I and III, and an ERK1/2 cascade in cardiac fibroblasts play an essential role in the control of collagen deposition by high glucose.

Liver-type fatty acid-binding protein attenuates renal injury induced by unilateral ureteral obstruction

Liver-type fatty-acid-binding protein (L-FABP), which has high affinity for long-chain fatty acid oxidation products, may be an effective endogenous antioxidant. To examine the role of L-FABP in tubulointerstitial damage, we used a unilateral ureteral obstruction (UUO) model. We established human L-FABP (hL-FABP) gene transgenic (Tg) mice and compared the tubulointerstitial pathology of the Tg mice (n = 23) with that of the wild-type (WT) mice (n = 23). Mice were sacrificed on days 2, 4, 5, or 7 after UUO. Although mouse L-FABP was not expressed in WT mice, hL-FABP was expressed in the proximal tubules of the Tg mice with UUO (UUO-Tg) and in sham-operated Tg mice. The expression of renal hL-FABP was significantly increased in UUO-Tg compared with sham-operated Tg mice. The number of macrophages (F4/80) infiltrating the interstitium and the level of expression of MCP-1 and MCP-3 were significantly lower in UUO-Tg kidneys compared with UUO-WT kidneys. In UUO-Tg kidneys, the degree of the tubulointerstitial injury and the deposition of type I collagen were significantly lower than that of UUO-WT kidneys. On day 7, lipid peroxidation product accumulated in the UUO-WT kidneys but not in that of UUO-Tg kidneys. In conclusion, renal L-FABP may reduce the oxidative stress in the UUO model, ameliorating tubulointerstitial damage.

Oxidative stress during peritoneal dialysis: implications in functional and structural changes in the membrane

Progressive peritoneal fibrosis, membrane hyperpermeability, and ultrafiltration failure have been observed in patients on long-term peritoneal dialysis (PD). The present study tested the hypothesis that reactive oxygen species (ROS) generated by conventional PD solution (PDS) mediate functional and structural alterations of peritoneal membrane in vivo. Sprague-Dawley rats were randomized to control, PDS, PDS with an antioxidant, and PDS with an angiotensin II (Ang II) receptor blocker. Commercial PDS containing 3.86% glucose (20-30 ml) with or without N-acetylcystein (NAC) 10 mM or losartan 5 mg/kg was administered intraperitoneally twice a day for 12 weeks. Control rats received sham injection. Rats treated with PDS had significantly lower drain volume and D(4)/D(0) glucose, but higher D(4)/P(4) creatinine and increased membrane thickness and endothelial NOS (eNOS) expression compared to control rats. Omental transforming growth factor (TGF)-beta1, vascular endothelial growth factor (VEGF), collagen I, and heat-shock protein (hsp) 47 expression and lipid peroxide levels and dialysate VEGF and Ang II concentrations were significantly increased in rats treated with PDS compared to control. All of these changes were prevented by both NAC and losartan. In conclusion, the present study demonstrates that ROS generated by conventional PDS are, in large part, responsible for peritoneal fibrosis and membrane hyperpermeability. We suggest that antioxidants or Ang II receptor blockers may allow better preservation of the structural and functional integrity of the peritoneal membrane during long-term PD.

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.