Renal cell apoptosis in chronic obstructive uropathy: the roles of caspases

Can urinary caspase-3 and cytochrome c levels be used as predictive biomarkers in the management of unilateral antenatal hydronephrosis?

PURPOSE

We aimed to investigate the urinary caspase-3 and cytochrome c levels in patients with unilateral antenatal hydronephrosis and to determine whether changes in urinary biomarker levels could be useful for both predicting the need for surgical intervention due to ureteropelvic junction obstruction (UPJO) and postoperative surgical success.

METHODS

Sixty-five children with a history of unilateral antenatal hydronephrosis and postnatal anteroposterior diameter ≥ 10 mm were included in this prospective case-control study between January 2013 and December 2021. The obstruction group consisted of 33 patients (28 boys, 84.8%) who underwent open dismembered pyeloplasty due to UPJO. The non-obstructive dilatation (NOD) group consisted of 32 patients (27 boys, 84.4%) with stable or improving hydronephrosis and no significant reduction in ipsilateral split renal function during follow-up, whereas 34 healthy children were enrolled in the study as a control group. Urinary urinary caspase-3 and cytochrome c levels using ELISA were measured.

RESULTS

The median preoperative urinary caspase-3 level was significantly higher in the obstruction group when compared to the NOD group (4.82 ng/mgCr vs. 2.61 ng/mgCr, p = 0.013) as well as the control group (4.82 ng/mgCr vs. 1.72 ng/mgCr, p = 0.002). In the postoperative period, urinary caspase-3 levels significantly decreased compared to preoperative measurements (4.82 ng/mgCr vs. 2.51 ng/mgCr, p = 0.006) and became similar to the control group (2.51 ng/mgCr vs. 1.72 ng/mgCr, p = 0.422). On the other hand, no significant differences were observed in urinary cytochrome c levels between the groups. All patients who underwent pyeloplasty achieved postoperative resolution in hydronephrosis and improved drainage on MAG-3, so none of the patients required re-do pyeloplasty. Postoperative decrease in caspase-3 level was found to be compatible with adequate urine drainage on MAG-3 scan. The cut-off value of urinary caspase-3 to predict patients requiring pyeloplasty was found to be 3.31 ng/mg creatinine with 63.6% sensitivity, 62.5% specificity (AUC = 0.679). In the multivariable analysis, urinary caspase-3 level (OR: 1.653, p = 0.019), anteroposterior pelvic diameter (OR: 1.401, p = 0.001), and split renal function on MAG-3 (OR: 1.277, p = 0.011) were found to be independent factors in determining patients who require surgery.

CONCLUSION

Based on our preliminary findings, urinary caspase-3 levels could be a useful biomarker not only for predicting the need for surgical intervention but also for determining the postoperative surgical success in children with UPJO.

Antioxidant, Anti-Apoptotic, and Anti-Inflammatory Effects of Farrerol in a Mouse Model of Obstructive Uropathy

Obstructive uropathy is a clinical condition that can lead to chronic kidney disease. However, treatments that can prevent the progression of renal injury and fibrosis are limited. Farrerol (FA) is a natural flavone with potent antioxidant and anti-inflammatory properties. Here, we investigated the effect of FA on renal injury and fibrosis in a mouse model of unilateral ureteral obstruction (UUO). Mice underwent a sham or UUO operation and received intraperitoneal injections of FA (20 mg/kg) daily for 8 consecutive days. Histochemistry, immunohistochemistry and immunofluorescence staining, TdT-mediated dUTP nick end labeling assay, Western blotting, gene expression analysis, and biochemical tests were performed. FA attenuated renal dysfunction (p < 0.05) and ameliorated renal tubular injury (p < 0.01) and interstitial fibrosis (p < 0.001) in UUO mice. FA alleviated 4-hydroxynonenal expression (p < 0.001) and malondialdehyde levels (p < 0.01) by regulating pro-oxidant and antioxidant enzymes. Apoptosis in the kidneys of UUO mice was inhibited by FA (p < 0.001), and this action was accompanied by decreased expression of cleaved caspase-3 (p < 0.01). Moreover, FA alleviated pro-inflammatory cytokine production (p < 0.001) and macrophage infiltration (p < 0.01) in the kidneys of UUO mice. These results suggest that FA ameliorates renal injury and fibrosis in the UUO model by inhibiting oxidative stress, apoptosis, and inflammation.

Dissecting the Involvement of Ras GTPases in Kidney Fibrosis

Many different regulatory mechanisms of renal fibrosis are known to date, and those related to transforming growth factor-β1 (TGF-β1)-induced signaling have been studied in greater depth. However, in recent years, other signaling pathways have been identified, which contribute to the regulation of these pathological processes. Several studies by our team and others have revealed the involvement of small Ras GTPases in the regulation of the cellular processes that occur in renal fibrosis, such as the activation and proliferation of myofibroblasts or the accumulation of extracellular matrix (ECM) proteins. Intracellular signaling mediated by TGF-β1 and Ras GTPases are closely related, and this interaction also occurs during the development of renal fibrosis. In this review, we update the available in vitro and in vivo knowledge on the role of Ras and its main effectors, such as Erk and Akt, in the cellular mechanisms that occur during the regulation of kidney fibrosis (ECM synthesis, accumulation and activation of myofibroblasts, apoptosis and survival of tubular epithelial cells), as well as the therapeutic strategies for targeting the Ras pathway to intervene on the development of renal fibrosis.

Deletion of Akt1 Promotes Kidney Fibrosis in a Murine Model of Unilateral Ureteral Obstruction

We investigated the role of Akt1, one of the three isoforms of Akt, in renal fibrosis using the murine model of unilateral ureteral obstruction (UUO). We subjected wild type and Akt1^−/− mice to UUO. The Akt1 gene was silenced in vitro using short hairpin RNA delivered via a lentiviral vector in human proximal tubular cells (HK2 cells) and kidney fibroblasts (NRK-49F cells). The obstructive kidneys of Akt1^−/− mice showed more severe tubulointerstitial fibrosis than those of wild type mice. The expression of fibronectin and type I collagen was significantly increased in obstructed kidneys of Akt1^−/− mice compared to those of wild type mice. The important finding was that the expression of transforming growth factor β1 (TGFβ1) was significantly increased in the Akt1^−/− mice compared to the wild type mice. The knockdown of Akt1 enhanced the expression of TGFβ1 in HK2 cells. Interestingly, the upregulation of TGFβ1 due to genetic knockdown of Akt1 was associated with activation of signal transducer and activator of transcript 3 (STAT3) independently of the Smad pathway in NRK-49F and HK2 cells. Immunohistochemical staining also showed that expression of phosphorylated STAT3 was more increased in Akt1^−/− mice than in wild type mice after UUO. Additionally, the deletion of Akt1 led to apoptosis of the renal tubular cells in both in vivo and in vitro studies. Conclusively, these results suggest that the deletion of Akt1 may contribute to renal fibrosis via induction of the TGFβ1/STAT3 pathway in a murine model of UUO.

Salidroside Ameliorates Renal Interstitial Fibrosis by Inhibiting the TLR4/NF-κB and MAPK Signaling Pathways

Salidroside (Sal) is an active ingredient that is isolated from Rhodiola rosea, which has been reported to have anti-inflammatory activities and a renal protective effect. However, the role of Sal on renal fibrosis has not yet been elucidated. Here, the purpose of the current study is to test the protective effects of Sal against renal interstitial fibrosis (RIF), and to explore the underlying mechanisms using both in vivo and in vitro models. In this study, we establish the unilateral ureteric obstruction (UUO) or folic acid (FA)-induced mice renal interstitial fibrosis in vivo and the transforming growth factor (TGF)-β1-stimulated human proximal tubular epithelial cell (HK-2) model in vitro. The levels of kidney functional parameters and inflammatory cytokines in serum are examined. The degree of renal damage and fibrosis is determined by histological assessment. Immunohistochemistry and western blotting are used to determine the mechanisms of Sal against RIF. Our results show that treatment with Sal can ameliorate tubular injury and deposition of the extracellular matrix (ECM) components (including collagen Ш and collagen I). Furthermore, Sal administration significantly suppresses epithelial-mesenchymal transition (EMT), as evidenced by a decreased expression of α-SMA, vimentin, TGF-β1, snail, slug, and a largely restored expression of E-cadherin. Additionally, Sal also reduces the levels of serum biochemical markers (serum creatinine, Scr; blood urea nitrogen, BUN; and uric acid, UA) and decreases the release of inflammatory cytokines (IL-1β, IL-6, TNF-α). Further study revealed that the effect of Sal on renal interstitial fibrosis is associated with the lower expression of TLR4, p-IκBα, p-NF-κB and mitogen-activated protein kinases (MAPK), both in vivo and in vitro. In conclusion, Sal treatment improves kidney function, ameliorates the deposition of the ECM components and relieves the protein levels of EMT markers in mouse kidneys and HK-2 cells. Furthermore, Sal treatment significantly decreases the release of inflammatory cytokines and inhibits the TLR4/NF-κB and MAPK signaling pathways. Collectively, these results suggest that the administration of Sal could be a novel therapeutic strategy in treating renal fibrosis.

The Protective Effect of Fluorofenidone against Cyclosporine A-Induced Nephrotoxicity

BACKGROUND/AIMS

Cyclosporine A (CsA) is an immunosuppressant drug that is used during organ transplants. However, its utility is limited by its nephrotoxic potential. This study aimed to investigate whether fluorofenidone (AKF-PD) could provide protection against CsA-induced nephrotoxicity.

METHODS

Eighty-five male Sprague-Dawley rats were divided into 5 groups: drug solvent, CsA, CsA with AKF-PD (250, 500 mg/kg/day), and CsA with pirfenidone (PFD, 250 mg/kg/day). Tubulointerstitial injury index, extracellular matrix (ECM) deposition, expression of type I and IV collagen, transforming growth factor (TGF)-β1, platelet-derived growth factor (PDGF), Fas ligand (FASL), cleaved-caspase-3, cleaved-poly(ADP-ribose) polymerase (PARP)-1, and the number of transferase-mediated nick end-labeling (TUNEL)-positive renal tubule cells were determined. In addition, levels of TGF-β1, FASL, cleaved-caspase-3, cleaved-PARP-1, and number of annexin V-positive cells were determined in rat proximal tubular epithelial cells (NRK-52E) treated with CsA (20 μmol/L), AKF-PD (400 μg/mL), PFD (400 μg/mL), and GW788388 (5 μmol/L).

RESULTS

AKF-PD (250, 500 mg/kg/day) significantly reduced tubulointerstitial injury, ECM deposition, expression of type I and IV collagen, TGF-β1, PDGF, FASL, cleaved-caspase-3, cleaved-PARP-1, and number of TUNEL-positive renal tubule cells in the CsA-treated kidneys. In addition, AKF-PD (400 μg/mL) significantly decreased TGF-β1, FASL, cleaved-caspase-3, and PARP-1 expression in NRK-52E cells and further reduced the number of annexin V-positive cells.

CONCLUSION

AKF-PD protect kidney from fibrosis and apoptosis in CsA-induced kidney injury.

Effects of colchicine on renal fibrosis and apoptosis in obstructed kidneys

BACKGROUND/AIMS

Colchicine is an established drug for microtubule stabilization that may reduce tissue injury. No data were available that its effects may depend on the dosage of colchicine. We investigated the anti-fibrotic and apoptotic effects of various dose of colchicine in a unilateral ureteral obstruction (UUO) model.

METHODS

Thirty-six Sprague-Dawley rats were randomly assigned into six groups. Two sham groups were divided into a vehicle-treated or colchicine-treated group (100 μg/kg/day). Four UUO groups were treated with either vehicle or three different doses of colchicine for 7 days (30, 60, and 100 μg/kg/day, intraperitoneally). All of the animals were sacrificed on day 7.

RESULTS

Colchicine treatment diminished acetylated α-tubulin and tumor growth factor-β immunoreactivities in the cortical area of the 7-day obstructed kidneys, which was in dose dependent manner. Colchicine attenuated tubulointerstitial damage and apoptosis in both cortical and medullary area, and beneficial effects of colchicine therapy were dramatically shown at the higher dosage of colchicine. The expression levels of cleaved caspase-3, ED-1, and fibronectin were decreased in UUO animals.

CONCLUSIONS

We found that the proper dosage of colchicine may have anti-fibrotic and anti-apoptotic effects in obstructed kidneys. For clinical applications, an optimal dose of colchicine should be evaluated to maximize the prevention of renal disease progression.

Cell death-based approaches in treatment of the urinary tract-associated diseases: a fight for survival in the killing fields

Urinary tract-associated diseases comprise a complex set of disorders with a variety of etiologic agents and therapeutic approaches and a huge global burden of disease, estimated at around 1 million deaths per year. These diseases include cancer (mainly prostate, renal, and bladder), urinary tract infections, and urolithiasis. Cell death plays a key role in the pathogenesis and therapy of these conditions. During urinary tract infections, invading bacteria may either promote or prevent host cell death by interfering with cell death pathways. This has been studied in detail for uropathogenic E. coli (UPEC). Inhibition of host cell death may allow intracellular persistence of live bacteria, while promoting host cell death causes tissue damage and releases the microbes. Both crystals and urinary tract obstruction lead to tubular cell death and kidney injury. Among the pathomechanisms, apoptosis, necroptosis, and autophagy represent key processes. With respect to malignant disorders, traditional therapeutic efforts have focused on directly promoting cancer cell death. This may exploit tumor-specific characteristics, such as targeting Vascular Endothelial Growth Factor (VEGF) signaling and mammalian Target of Rapamycin (mTOR) activity in renal cancer and inducing survival factor deprivation by targeting androgen signaling in prostate cancer. An area of intense research is the use of immune checkpoint inhibitors, aiming at unleashing the full potential of immune cells to kill cancer cells. In the future, this may be combined with additional approaches exploiting intrinsic sensitivities to specific modes of cell death such as necroptosis and ferroptosis. Here, we review the contribution of diverse cell death mechanisms to the pathogenesis of urinary tract-associated diseases as well as the potential for novel therapeutic approaches based on an improved molecular understanding of these mechanisms.

Posterior urethral valve in fetuses: evidence for the role of inflammatory molecules

BACKGROUND

The aim of this cross-sectional study was to investigate inflammatory biomarkers in urine samples of 24 fetuses with posterior urethral valve (PUV) collected at 22 ± 4 weeks of gestation and to compare the findings with measurements in urine samples of 22 male healthy preterm neonates at 23 ± 4 weeks (control group).

METHODS

Inflammatory biomarkers in urine were measured using a cytometric bead array [interleukin (IL)-2, IL-4, IL-6, IL-10, interferon (IFN)-γ, soluable tumor necrosis factor receptor (TNFR) 1, sTNFR2, monocyte chemoattractant protein-1/chemokine ligand 2 (MCP-1/CCL2), eotaxin/CCL11 and interferon gamma-induced protein/10/C-X-C motif chemokine 10 (IP-10/CXCL10)] and ELISA assays [TNF, IL-8/CXCL8 and transforming growth factor-beta (TGF-β)]. The Mann-Whitney test was used to compare medians. Markers of glomerular (creatinine) and tubular [beta 2 (β₂)-microglobulin, uromodulin, osmolality] functions were correlated with inflammatory biomarkers (Spearman test).

RESULTS

An intense inflammatory profile was identified, with significantly increased concentrations of urinary IL-2, IL-4, IL-6, TNF, sTNFRI, sTNFRII, IFN-γ, MCP-1/CCL2, eotaxin/CCL11 and IL-8/CXCL8 in the PUV group compared to the controls. The same was observed for the anti-inflammatory cytokine IL-10 and for the fibrogenic mediator TGF-β. In the correlation analysis, β₂-microglobulin positively correlated with the presence of MCP-1/CCL2, sTNFRI and eotaxin/CCL11 and negatively correlated with the presence of creatinine.

CONCLUSIONS

This study shows that inflammatory molecules are already increased in fetuses with PUV at the mean gestational age of 22 weeks, suggesting a physiopathological role for inflammation just after the embryological formation of the urethral membrane.

Regulation of the Ku70 and apoptosis-related proteins in experimental diabetic nephropathy

BACKGROUND

Apoptosis contributes nephropathy pathogenesis in diabetes. However, its mechanisms still remain unclear. We examined the extent to which the angiotensin-II type 1 receptor blocker (AT1RB) irbesartan and the angiotensin converting enzyme inhibitor (ACEI) perindopril affected the apoptosis-related proteins Bcl-2, Bax, caspase-3, cytochrome-c and Ku70 in streptozotocin (STZ)-diabetic rats.

MATERIALS AND METHODS

Animals were divided into five groups of eight each, four of which received STZ (60mg/kg in a single dose, i.p.) to induce diabetes. The groups were performed as untreated diabetic; non-diabetic control; daily irbesartan (15mg/kg/day) or perindopril (6mg/kg/day) and also combined irbesartan and perindopril (respectively, 5mg/kg/day, 3mg/kg/day) were applied by gavage for 30days to STZ-diabetic rats. The kidney tissue analysis was performed by using immunohistochemical staining with Bcl-2, Bax, caspase-3, cytochrome-c and Ku70 antibodies and by using Western blot analysis with caspase-3 and cytochrome-c antibodies.

RESULTS

Immunoreactivity of Bax, caspase-3, cytochrome-c and Ku70 was increased in the tubuli and glomeruli of the untreated diabetic group, but decreased in all treated diabetic groups. In the irbesartan and perindopril treated diabetic groups Bcl-2 immunoreactivity was higher than that of the untreated diabetic group. Caspase-3 and cytoplasmic cytochrome-c protein levels increased in the untreated diabetic group.

CONCLUSIONS

We conclude that the increased expression of Bax and caspase-3, and the increased level of cytoplasmic cytochrome-c relate to renal tissue injury. This case is also seen in the early stages of diabetes as a result of the damage caused by local increased expression of renin angiotensin system (RAS) in the renal tissue, which is induced by hyperglycemia. The increase of the cytosolic cytochrome-c, caspase-3 and Ku70 expression in the tubuli is suggestive of apoptosis. Overall, our results show that treatments of irbesartan and perindopril are effective and efficient in preventing renal tissue injury and apoptosis by blocking the RAS in experimental diabetic nephropathy and reducing the expression of proteins associated with apoptosis.

The Green Tea Polyphenol(-)-epigallocatechin-3-gallate and its beneficial roles in chronic kidney disease

Chronic kidney disease (CKD), a condition that affects around 10% of the population, has become a significant public health concern. Current therapeutic strategies to slow down the progression of CKD remain limited. Thus, it is urgent to develop new strategies to manage the patients with CKD. Work within the past decade has improved our understanding of the mechanisms contributing to CKD. In particular, oxidative stress as well as inflammation appears to play a pivotal role in CKD progression. ()-Epigallocatechin-3-gallate (EGCG), the major catechin of green tea extract, is known as a powerful antioxidant and reactive oxygen species scavenger. Various studies have shown EGCG has a potential role in chronic kidney disease models. It is suggested that EGCG modulates cellular and molecular mechanisms via inflammation-related NF-кB and Nrf2 signaling pathway, as well as apoptosis-related ER stress pathway and mitochondrial pathway. Therefore, based on these studies, this review attempts to present a recent state of our knowledge and understanding of mechanisms of its role on the process of CKD, with the aim of providing some clues for the future optimization of EGCG in renal diseases.

Ureteral obstruction promotes proliferation and differentiation of the renal urothelium into a bladder-like phenotype

The renal urothelium, the monolayered epithelium that covers the papilla, is the direct target of increased pressure during obstruction, yet most studies have mainly focused on tubules, fibroblasts, and inflammatory cells. We studied this epithelium in a unilateral ureteral obstruction mouse mode land found that it was disrupted and had broken tight junctions, enlarged intercellular space, with loss of apicaluroplakins, and marginal lumen desquamation. Shortly after obstruction these urothelial cells proliferated, peaking at day 2. By day 14, the renal urothelium was transformed into a multilayered barrier with newly synthesized uroplakins including the de novo induction of uroplakin II. This proliferation was found to be fibroblast growth factor (FGF)dependent. Renal urothelial cells constitutively express the FGF receptor 2, and obstruction activated the receptor by phosphorylation. Treatment with FGF receptor 2-antisense or vitamin A (an inhibitor of the MAP kinase in the FGFR2 pathway) decreased renal urothelial cell proliferation. Among known FGF receptor 2 ligands, only FGF7 was upregulated.Infusion of FGF7 into control mice caused the formation of a multilayered structure at 7 days, resembling the urothelium 14 days following obstruction. Thus, the pressure/stretching of renal monolayered urothelial cells is a very efficient trigger for proliferation, causing the formation of a bladder-like multistratified barrier with enhanced apical uroplakin plaques. Presumably, this ensures efficient barrier protection and repair.

Interactions between cytokines, congenital anomalies of kidney and urinary tract and chronic kidney disease

Fetal hydronephrosis is the most common anomaly detected on antenatal ultrasound, affecting 1-5% of pregnancies. Postnatal investigation has the major aim in detecting infants with severe urinary tract obstruction and clinically significant urinary tract anomalies among the heterogeneous universe of patients. Congenital uropathies are frequent causes of pediatric chronic kidney disease (CKD). Imaging techniques clearly contribute to this purpose; however, sometimes, these exams are invasive, very expensive, and not sufficient to precisely define the best approach as well as the prognosis. Recently, biomarkers have become a focus of clinical research as potentially useful diagnostic tools in pediatric urological diseases. In this regard, recent studies suggest a role for cytokines and chemokines in the pathophysiology of CAKUT and for the progression to CKD. Some authors proposed that the evaluation of these inflammatory mediators might help the management of postnatal uropathies and the detection of patients with high risk to developed chronic kidney disease. Therefore, the aim of this paper is to revise general aspects of cytokines and the link between cytokines, CAKUT, and CKD by including experimental and clinical evidence.

Immunohistochemical and electron microscopic examination of Cajal cells in ureteropelvic junction obstruction

OBJECTIVE

We examine the ultrastructural configurations of Cajal cells by electron microscopy, as well as the quantitative changes occurring in Cajal cells by light microscopy.

METHODS

In total, 35 patients with ureteropelvic junction (UPJ) obstruction and 7 patients without obstruction were compared immunohistochemically with c-kit (CD117) to quantify the number of cells. On electron microscopic examination, 7 patients with UPJ obstruction and 3 patients without obstruction were compared to evaluate the changes which occurred in the ultrastructural configuration of the Cajal cells.

RESULTS

On light microscopic examination, it was determined that the Cajal cells, which demonstrate c-kit (CD117) immunoreactive character, were located near the circular muscle layer and parallel to the muscle cells. The number of Cajal cells in the control group was significantly increased compared to the number of cells in patients with UPJ obstruction (p < 0.001). On electron microscopic examination, the number of interstitial cells was also higher in the control group. A decrease in the number of the caveolae in these cells was seen in the group with UPJ obstruction compared to the control group.

CONCLUSION

In UPJ obstruction, a decrease in the number of Cajal cells, as well as the changes in the morphologic structure of the Cajal cells, indicates that these cells have a role in the pacemaker system and are associated with ureteral peristalsis.

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.

Fluorofenidone inhibits Ang II-induced apoptosis of renal tubular cells through blockage of the Fas/FasL pathway

OBJECTIVES

The present study was designed to investigate the inhibitory effects of fluorofenidone on Ang II-induced apoptosis in renal tubular cells and the related signaling pathway.

METHODS

Rat proximal tubular epithelial cells (NRK-52E) were used to examine the anti-apoptosis effects of fluorofenidone. Cell proliferation was assessed by methyl thiazolyl tetrazolium assay. Apoptosis was examined by AO/EB staining and TUNEL assay. The expression of Fas/FasL pathway members, including Fas, FasL, Bax, Bcl-2, Caspase-8, and Caspase-3 was detected by real-time RT-PCR and/or Western blot, respectively. The activity of Caspase-8 and Caspase-3 was detected by spectrophotometry.

RESULTS

Fluorofenidone didn't affect the proliferation of NRK-52E cells, but significantly inhibited the apoptosis of NRK-52E cells induced by Ang II. Fluorofenidone significantly reduced Ang II-induced increases in Fas, FasL, Bax, Caspase-8 and Caspase-3 at the mRNA level. Consistent with these observations, fluorofenidone also prevented Ang II-mediated up-regulation of FasL and Bax at the protein level. Additionally, Ang II-induced activation of Caspase-8 and Caspase-3 as well as Ang II-initiated downregulation of Bcl-2 at both mRNA and protein levels was all prevented by fluorofenidone.

CONCLUSIONS

Fluorofenidone can inhibit Ang II-induced apoptosis of renal tubular cells through blockage of the Fas/FasL pathway.

28S-ribosomal RNA is superior to glyceraldehyde-3-phosphate dehydrogenase as a RNA reference gene in p53-deficient mice with unilateral ureteral obstruction

Although there are many kinds of reference genes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been commonly used by many researchers to assess the amount and integrity of RNA transcripts in RNA studies including Northern blot and reverse transcription real time-PCR. Although some data suggest that GAPDH could be inconstant in their situations or experiments, there is limited evidence that GAPDH expression is influenced by conditions of experiment, especially in mouse kidney model with unilateral ureteral obstruction (UUO). Therefore, the establishment of excellent reference gene according to the tissue types or conditions of experiment is a bottom line for the RNA study. Here we compared the expression of GAPDH with 28S rRNA gene by Northern blot analysis in the p53-deficient mice with UUO. We observed that GAPDH mRNA levels in ligated kidneys were significantly lower than those in contralateral kidneys, especially after postoperative day 15. In contrast, 28S rRNA levels were constant among control, ligated and contralateral kidneys. We also demonstrated that 28S rRNA signal was proportional to the amount of RNA loaded. In conclusion, these data indicate that much caution should be taken when using GAPDH as a RNA reference gene and 28S rRNA is an excellent gene for the RNA study in p53-deficient mice with UUO.

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.

Inhibition of histone deacetylase activity attenuates renal fibroblast activation and interstitial fibrosis in obstructive nephropathy

Activation of renal interstitial fibroblasts is critically involved in the development of tubulointerstitial fibrosis in chronic kidney diseases. In this study, we investigated the effect of trichostatin A (TSA), a specific histone deacetylase (HDAC) inhibitor, on the activation of renal interstitial fibroblasts in a rat renal interstitial fibroblast line (NRK-49F) and the development of renal fibrosis in a murine model of unilateral ureteral obstruction (UUO). alpha-Smooth muscle actin (alpha-SMA) and fibronectin, two hallmarks of fibroblast activation, were highly expressed in cultured NRK-49F cells, and their expression was inhibited in the presence of TSA. Similarly, administration of TSA suppressed the expression of alpha-SMA and fibronectin and attenuated the accumulation of renal interstitial fibroblasts in the kidney after the obstructive injury. Activation of renal interstitial fibroblasts was accompanied by phosphorylation of signal transducer and activator of transcription 3 (STAT3), and TSA treatment also abolished these responses. Furthermore, inhibition of the STAT3 pathway with AG490 inhibited expression of alpha-SMA and fibronectin in NRK-49F cells. Finally, TSA treatment inhibited tubular cell apoptosis and caspase-3 activation in the obstructive kidney. Collectively, we suggest that pharmacological HDAC inhibition may induce antifibrotic activity by inactivation of renal interstitial fibroblasts and inhibition of renal tubular cell death. STAT3 may mediate those actions of HDACs.

Effect of unilateral ureteral obstruction and anti-angiotensin II treatment on renal tubule and interstitial cell apoptosis in rats

AIM

To investigate the effects of angiotensin-converting enzyme inhibitor (cilazapril) and angiotensin II type I receptor antagonist (losartan) on tubular and interstitial cell apoptosis and caspase-3 activity in rats with obstructive nephropathy after unilateral ureteral obstruction.

METHODS

Rats with unilateral obstructive nephropathy and sham-operated rats were treated with cilazapril, losartan, or the vehicle (water). Tubular and interstitial cell apoptosis was detected morphologically on hematoxylin and eosin-stained renal specimens and by the terminal deoxynucleotidyl transferase-mediated nick end-labeling. Caspase-3 activity in whole-kidney tissue homogenates was measured colorimetrically.

RESULTS

After unilateral ureter ligation, there was a significant increase in the number of apoptotic tubular and interstitial cells in the obstructed kidney (P=0.049 and P=0.036, respectively, vs sham-operated rats, 10 days after ligation). In rats with unilateral obstructive nephropathy, neither cilazapril nor losartan had an effect on tubular cell apoptosis. However, cilazapril caused a significant increase in the number of renal apoptotic interstitial cells (P=0.019). Caspase-3 activity was not significantly different in rats with unilateral obstructive nephropathy than in sham-operated rats.

CONCLUSION

Rats with unilateral obstructive nephropathy had increased apoptosis of tubular and interstitial cells in comparison with sham-operated rats. Neither cilazapril nor losartan had an effect on tubular cell apoptosis, and cilazapril even increased interstitial cell apoptosis.

Erythropoietin attenuates renal injury in an experimental model of rat unilateral ureteral obstruction via anti-inflammatory and anti-apoptotic effects

PURPOSE

Erythropoietin was recently shown to exert important cytoprotective and anti-apoptotic effects in injury models of the brain, heart and kidney. We examined whether erythropoietin also attenuates renal injury in a rat model of unilateral ureteral obstruction via anti-apoptotic and anti-inflammatory actions.

MATERIALS AND METHODS

We divided Sprague-Dawley rats (Korea Research Institute of Bioscience and Biotechnology, Daejeon, Korea) into 4 groups, including 1-vehicle treated with sham operation, 2-vehicle treated with unilateral ureteral obstruction for 3 days, 3-erythropoietin treatment with sham operation and 4-erythropoietin treatment for unilateral ureteral obstruction for 3 days. The erythropoietin treatment dose was 3,000 IU/kg per day intraperitoneally, administered daily. We compared competitive reverse transcriptase-polymerase chain reaction data on transforming growth factor-beta, tumor necrosis factor-alpha, monocyte chemoattractant protein-1, osteopontin, Fas and Bcl-2. Furthermore, we examined Western blots for caspase-3 and light microscopy findings with hematoxylin and eosin staining. We applied immunohistochemistry for transforming growth factor-beta, ED-1 and caspase-3, and TUNEL in each group.

RESULTS

Transforming growth factor-beta, tumor necrosis factor-alpha, monocyte chemoattractant protein-1, osteopontin and Fas mRNA levels in the erythropoietin treated, unilateral ureteral obstruction group were significantly lower than in the obstruction only group. The Bcl-2 mRNA level in the erythropoietin treated obstruction group was significantly higher than in the obstruction only group. Caspase-3 activity in the erythropoietin treated obstruction group was significantly lower than in the obstruction only group. On light microscopy interstitially infiltrated inflammatory cells were significantly decreased in the erythropoietin treated obstruction group compared to the obstruction only group. On immunohistochemistry the erythropoietin treated obstruction group showed significantly fewer reactions for transforming growth factor-beta, ED-1 and caspase-3 compared to the obstruction only group. Erythropoietin treatment in rats with unilateral ureteral obstruction significantly decreased the number of TUNEL positive cells.

CONCLUSIONS

Erythropoietin exerts renoprotective effects in an experimental unilateral ureteral obstruction rat model via anti-apoptotic and anti-inflammatory actions.

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.

Verapamil prevents the apoptotic and hemodynamic changes in response to unilateral ureteral obstruction

INTRODUCTION

Obstruction of the urinary tract has marked effects on renal blood flow, glomerular filtration rate (GFR), and tubular function. Moreover, ureteral obstruction results in an injury response that can progress to irreversible renal fibrosis and tubular atrophy by apoptosis.

METHODS

We examined the effect of a calcium channel blocker (verapamil) on renal functions and the abundance of apoptotic (p53, Fas, proliferating cell nuclear antigen [PCNA]) markers 1 week after Unilateral Ureteral Obstruction (UUO).

RESULTS

Immunohistochemistry studies revealed that UUO was markedly associated with up-regulation in the expression of p53 (1550 +/- 82 vs 100 +/- 23%), Fas (657 +/- 48 vs 100 +/- 31%), and proliferating cell nuclear antigen (945 +/- 70 vs 100 +/- 17% of sham levels). Administration of verapamil normalized the up-regulation of apoptotic markers p53 (724 +/- 116 vs 1550 +/- 82%); Fas (162 +/- 38 vs 657 +/- 48%) and PCNA (353 +/- 54 vs 945 +/- 70%). Furthermore, tubular diameter, as an important marker for detecting tubular atrophy was significantly decreased compared to those in UUO rabbits. The percent area of interstitial fibrosis in UUO kidneys was significantly greater than that in Verapamil-treated kidneys. Importantly, Verapamil reduced the development of interstitial fibrosis in UUO rabbits. We measured the GFR and renal blood flow in UUO. Short-term Verapamil challenge partially prevented the decrease in GFR (non-treated UUO: 62 +/- 14; Verapamil + UUO: 119 +/- 7; Sham: 127 +/- 23 microL x min(-1) x kg body wt(-1), P < 0.05) and renal blood flow (non-treated UUO: 1.1 +/- 0.4; Verapamil + UUO: 5.0 +/- 0.2; sham: 6.3 +/- 0.2 mL x min(-1) x kg body wt(-1), P < 0.05).

CONCLUSION

Verapamil significantly prevents impairment in renal function and also prevents the up-regulation of p53, Fas, and PCNA during UUO, demonstrating a marked renoprotective effect of Verapamil treatment in conditions with 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.

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.

HSP72 attenuates renal tubular cell apoptosis and interstitial fibrosis in obstructive nephropathy

Although heat shock protein 72 kDa (HSP72) protects tubular epithelium from a variety of acute insults, its role in chronic renal injury and fibrosis is poorly characterized. In this study, we tested the hypothesis that HSP72 reduces apoptosis and epithelial-to-mesenchymal transition (EMT), important contributors to tubular cell injury in vitro and in vivo. In rats, orally administered geranylgeranylacetone (GGA), an agent that selectively induces HSP72, markedly reduced both apoptosis and cell proliferation in tubular epithelium and decreased both interstitial fibroblast accumulation and collagen I deposition after unilateral ureteric obstruction, a model of chronic renal tubulointerstitial fibrosis and dysfunction. In cultured renal NRK52E cells, exposure to TGF-beta1 induced EMT and apoptosis, major causes of renal fibrosis and tubular atrophy, respectively. Exposure to a pan-caspase inhibitor (ZVAD-FMK) prevented TGF-beta1-induced apoptosis but did not reduce EMT. In contrast, selective HSP72 expression in vitro inhibited EMT caused by TGF-beta1 as indicated by preserving the E-cadherin expression level and alpha-smooth muscle actin induction. Small interfering RNA directed against HSP72 blocked the cytoprotective effects of HSP72 overexpression on EMT in TGF-beta1-exposed cells. Taken together, our data indicate that HSP72 ameliorates renal tubulointerstitial fibrosis in obstructive nephropathy by inhibiting both renal tubular epithelial cell apoptosis and EMT.

Effects of ischemia-reperfusion injury on renal ammonia metabolism and the collecting duct

Acute renal injury induces metabolic acidosis, but its specific effects on the collecting duct, the primary site for urinary ammonia secretion, the primary component of net acid excretion, are incompletely understood. We induced ischemia-reperfusion (I/R) acute renal injury in Sprague-Dawley rats by clamping the renal pedicles bilaterally for 30 min followed by reperfusion for 6 h. Control rats underwent sham surgery without renal pedicle clamping. I/R injury decreased urinary ammonia excretion significantly but did not persistently alter urine volume, Na+, K+, or bicarbonate excretion. Histological examination demonstrated cellular damage in the outer and inner medullary collecting duct, as well as in the proximal tubule and the thick ascending limb of the loop of Henle. A subset of collecting duct cells were damaged and/or detached from the basement membrane; these cells were present predominantly in the outer medulla and were less frequent in the inner medulla. Immunohistochemistry identified that the damaged/detached cells were A-type intercalated cells, not principal cells. Both TdT-mediated dUTP nick-end labeling (TUNEL) staining and transmission electron microscopic examination demonstrated apoptosis but not necrosis. However, immunoreactivity for caspase-3 was observed in the proximal tubule, but not in collecting duct intercalated cells, suggesting that mechanism(s) of collecting duct intercalated cell apoptosis differ from those operative in the proximal tubule. We conclude that I/R injury decreases renal ammonia excretion and is associated with intercalated cell-specific detachment and apoptosis in the outer and inner medullary collecting duct. These effects likely contribute to the metabolic acidosis frequently observed in acute renal injury.

Apoptosis induction is associated with decreased NHE1 expression in neonatal unilateral ureteric obstruction

OBJECTIVE To examine the participation of NHE1 in the regulation of the apoptotic response in neonatal obstruction, as the ubiquitously expressed NHE1 isoform is an important component of regulatory volume increase. MATERIALS AND METHODS Rats had a unilateral ureteric obstruction (UUO) or a sham operation, and the kidneys were harvested 5 and 14 days afterward. Cellular apoptosis in proximal tubules (PT) and collecting ducts (CD) was assessed using a standard assay, and NHE1 expression in the renal cortex assessed using reverse transcription-polymerase chain reaction and Western blots. Mitochondrial apoptosis was evaluated by Bax/BcL2 expression, and caspase-3 expression and activity. In addition, we evaluated the in vivo administration of increasing doses of 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) on NHE1 inhibition associated with the induction of apoptosis. RESULTS After 14 days there were consistently more apoptotic cells in CD than in PT, associated with a lower expression of NHE1 at the mRNA and protein levels. There was increased expression of the Bax/BcL2 ratio, linked to decreased pro-caspase-3 protein levels and with increased caspase-3 activation. NHE1 inhibition by increasing doses of EIPA induced epithelial cell apoptosis and increased caspase-3 activity in a dose-dependent manner. After in vitro incubation with amiloride (100 mm) there was less NHE1 expression associated with reduced 32 kDa pro-caspase-3 protein levels. Kidneys obstructed for 5 days showed no changes in NHE1 expression or induction of apoptosis. CONCLUSION In neonatal obstruction, we suggest that the decreased NHE1 expression could be a signal-transduction event participating in the induction of epithelial tubular cell apoptosis, through the regulation of the BcL-2 gene family and activation of caspase-3.

AT1 receptor blockade prevents interstitial and glomerular apoptosis but not fibrosis in pigs with neonatal induced partial unilateral ureteral obstruction

Obstruction-induced fibrosis is a leading cause of end-stage renal failure in children. The pathophysiological mechanisms may involve apoptosis and the renin-angiotensin system. We studied apoptosis and fibrosis in a well-established neonatal pig model with unilateral partial ureteral obstruction (PUUO) induced during ongoing nephrogenesis in 2-day-old piglets. The role of angiotensin II (ANG II) was studied using the AT(1) receptor blocker CV-11974 (0.12 mg/h candesartan from age 23 to 30 days). At day 30 the kidneys were perfusion fixed and fibrosis, apoptosis, and tubular lengths were quantitated using stereological methods, picro Sirius red staining, and immunohistochemical techniques identifying activated caspase 3, aquaporin-2 (AQP2), and von Willebrand factor. The collagen content was assessed by hydroxyproline density. Neonatal induced PUUO increased interstitial and glomerular cell apoptosis and fibrosis. At this stage, PUUO did not increase tubular cell apoptosis or decrease tubular length and cell number. AT(1) receptor blockade prevented the PUUO-induced interstitial and glomerular cell apoptosis but did not attenuate fibrosis. In conclusion, AT(1) receptor blockade after the end of nephrogenesis may prevent interstitial and glomerular cell apoptosis but not fibrosis, suggesting that pathways not involving AT(1) receptor stimulation contribute to neonatal obstruction-induced fibrosis or that prevention of interstitial cell apoptosis counteracts a potential antifibrotic effect of AT(1) receptor blockade in this pig model of congenital obstructive nephropathy. Our results demonstrate that ANG II plays a role in PUUO-induced glomerular cell apoptosis.

PAX2 is reactivated in urinary tract obstruction and partially protects collecting duct cells from programmed cell death

Obstruction of the urinary tract activates apoptotic pathways in collecting duct cells and leads to loss of renal parenchyma before surgical intervention. It has been suggested that developmental pathways may be reactivated to offset acute organ damage. One such molecule, PAX2, is expressed throughout the fetal collecting duct and was recently shown to suppress apoptosis during kidney development. We hypothesized that acute unilateral urinary tract obstruction (UUO) reactivates PAX2 expression in the mature kidney and partially suppresses apoptosis. If so, animals with PAX2 mutations should have increased susceptibility to parenchymal damage. Wild-type and heterozygous Pax2 mutant (C3H/Pax2(1Neu)) mice underwent unilateral ureteric ligation or sham operation at 6 wk of age; kidneys were examined after 5, 10, and 15 days. Whereas PAX2 protein levels fell to low levels in the first weeks of life, it was sharply reactivated by day 10 in collecting duct cells of wild-type but not in Pax2(1Neu) mutant mice with UUO. Wild-type mice with UUO had marked TUNEL and cleaved spectrin staining in tubular cells and reduced kidney weight after 10-15 days. Mutant mice had exaggerated increases in markers of apoptosis and exaggerated loss of renal parenchymal loss in the obstructed kidney. These observations suggest that PAX2 is rapidly reactivated in UUO and that mice with genetically limited PAX2 expression have heightened susceptibility to apoptosis.

Serial Microscopic Changes in Cell Proliferation and Apoptosis in Obstructed Ureter of Rat

PURPOSE

We investigated the histologic findings and serial changes in cell proliferation and apoptosis in obstructed rat ureters.

MATERIALS AND METHODS

After unilateral ligation of the ureter, animals from each of five groups of Sprague- Dawley rats were sacrificed for examination at 1, 5, 10, 15, 20, 25, 30, or 35 days. Cell division was detected with proliferating cell nuclear antigen (PCNA) immunohistochemistry, and apoptosis was detected with terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) in-situ nick-end labeling (TUNEL) study.

RESULTS

The epithelial layer was thickened in 5-day-obstructed ureters (5 DOUs). The severity of thickening of the fibrous and smooth-muscle layers progressed consistently to 15 DOUs and were maintained in 35 DOUs. Expression of PCNA in the epithelial layer was present in every ureter, and a significant increase in the number of labeled cells was present in 1 and 5 DOUs. Expression of PCNA in the fibrous and smoothmuscle layers was detectable in 10 DOUs and was maintained in 20 DOUs, after which, it declined significantly in the 25 DOUs. TUNEL-positive cells in the epithelial layer were shown in 10, 15, 20, 25, 30, and 35 DOUs, with the peak being reached at 25 days. TUNEL-positive cells in the fibrous and smooth-muscle layers were found in 25, 30, and 35 DOUs.

CONCLUSIONS

Cell proliferation and apoptosis may play an important role in the pathogenesis of damage in obstructed ureters. Peak times of proliferation and apoptosis were different in the epithelial and fibrous and smooth-muscle layers.

Smooth Muscle Cell Apoptosis and Defective Neural Development in Congenital Ureteropelvic Junction Obstruction

PURPOSE

We assessed the smooth muscle cell apoptosis along with changes in cellular and extracellular components of the ureteropelvic junction in 23 patients with unilateral obstruction and compared them with 25 autopsies from ureteropelvic junction regions of age matched cadavers.

MATERIALS AND METHODS

Tissue specimens obtained from pyeloplasty were divided into 3 sections-renal pelvis above the obstruction, obstructed ureteropelvic junction and ureter below the obstructed region. For the control group the normal ureteropelvic junctions of age matched infants were autopsied. In paraffin embedded sections we determined myocyte apoptosis index (using TUNEL assay), and the amount of muscular components and nerve terminals (using image analysis techniques after immunohistochemical staining). The collagen and elastin fibers were specifically stained for evaluation of changes in extracellular matrix.

RESULTS

Smooth muscle cell apoptosis index was significantly increased at the site of ureteropelvic junction obstruction (5.68 +/- 0.18) compared to normal autopsied ureteropelvic junctions (3.60 +/- 0.11) and 2 other sections of obstructed ureteropelvic junction complex (renal pelvis 4.73 +/- 0.16, and ureter 3.97 +/- 0.16). The number of nerve terminals and the percentage of muscular component were significantly lower at the obstructed segments of affected patients compared to normal ureteropelvic junctions. Meanwhile, collagen fibers formed a significantly higher proportion of ureteral wall at the site of obstruction. Interestingly, there was negative correlation between myocyte apoptosis indices and number of nerve endings as well as amount of muscular components at the site of ureteropelvic junction obstruction. However, positive correlations were found between smooth muscle cell apoptosis and the percentage of collagen and elastin fibers.

CONCLUSIONS

Our findings suggest an important role for myocyte apoptosis and defective neural development in the pathogenesis of congenital ureteropelvic junction obstruction that could pave the road for the emergence of new therapeutic modalities.

Progression in chronic kidney disease

The pathogenic mechanisms that lead to chronic kidney disease (CKD) converge on a common pathway that results in progressive interstitial fibrosis, peritubular capillary loss with hypoxia, and destruction of functioning nephrons because of tubular atrophy. Interstitial recruitment of inflammatory leukocytes and myofibroblasts occurs early in kidneys destined to develop fibrosis. Circulating monocytes are recruited by locally secreted chemoattractant molecules, facilitated by leukocyte adhesion molecules. Functionally heterogeneous macrophages secrete many fibrosis-promoting molecules, but under some circumstances they may also serve a protective scavenging role. Excessive extracellular matrix production occurs primarily within interstitial myofibroblasts, a population of cells that appears to have more than 1 origin, including the resident interstitial fibroblasts, trans-differentiated tubular epithelial cells, and bone marrow-derived cells. Impaired activity of the endogenous renal matrix-degrading proteases may enhance interstitial matrix accumulation, but the specific pathways that are involved remain unclear. Tubules, inflammatory cells, and myofibroblasts synthesize the molecules that activate the fibrogenic cascades, the most important of which is transforming growth factor beta (TGF-beta). TGF-beta may direct cells to assume a pro-fibrotic phenotype or it may do so indirectly after stimulating synthesis of other fibrogenic molecules such as connective tissue growth factor and plasminogen activator inhibitor-1. Reduced levels of antifibrotic factors that are normally produced in the kidney such as hepatocyte growth factor and bone morphogenic protein-7 may accelerate fibrosis and its destructive consequences. Development of new therapeutic agents for CKD looks promising, but several agents that target different components of the fibrogenic cascade will almost certainly be necessary.

JNK/SAPK and p38 SAPK-2 mediate mechanical stretch-induced apoptosis via caspase-3 and -9 in NRK-52E renal epithelial cells

BACKGROUND/AIMS

In renal epithelial cells, mechanical forces produced from urinary obstruction serve as potential mediators of apoptosis by activating specific intracellular signaling pathways. In this study, we sought to further define the role of JNK and p38 SAPK-2 pathway and caspase activation in stretch-induced apoptosis.

METHODS

Immortalized cell lines derived from the various components of the nephron were subjected to cyclical stretch and their differential apoptotic response was assessed. Pharmacologic inhibitors and Western blot analysis were used to assess the involvement of the MAPK pathways. Caspases' activity was assessed with ELISA and by Western blot analysis.

RESULTS

Stretch-induced apoptosis was dependent upon the cell phenotype and the degree of stretch. In NRK-52E cells, it was mediated through both JNK and p38 SAPK-2 pathways, and inhibition of either pathway reduced the degree of stretch-induced apoptosis. Stretched cells showed increased activity of caspase-3 and -9 but not -2 or -8. Stretch-induced apoptosis was modulated by inhibition of caspase-3 and to a lesser extent by caspase-9.

CONCLUSION

These findings suggest that stretch induces apoptosis in renal epithelial cells through the specific activation of JNK/SAPK and p38 SAPK-2 pathways and is dependent on the activation of caspase-3 and -9.

Multifunctionality of PAI-1 in fibrogenesis: evidence from obstructive nephropathy in PAI-1-overexpressing mice

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1) has been implicated in the pathogenesis of chronic kidney disease based on its up-regulated expression and on the beneficial effects of PAI-1 inhibition or depletion in experimental models. PAI-1 is a multifunctional protein and the mechanisms that account for its profibrotic effects have not been fully elucidated.

METHODS

The present study was designed to investigate PAI-1-dependent fibrogenic pathways by comparing the unilateral ureteral obstruction model (UUO) (days 3, 7, and 14) in PAI-1-overexpressing mice (PAI-1 tg) to wild-type mice, both on a C57BL6 background.

RESULTS

Following UUO, total kidney PAI-1 mRNA and/or protein levels were significantly higher in the PAI-1 tg mice (N= 6 to 8/group) and fibrosis severity was significantly worse (days 3, 7, and 14), measured both as Sirius red-positive interstitial area (e.g., 10 +/- 3.2% vs. 4.5 +/- 1.0%) (day 14) and total kidney collagen (e.g., 11.1 +/- 1.7 vs. 6.2 +/- 1.3 microg/mg) (day 14). By day 14, the expression of two normal tubular proteins, E-cadherin and Ksp-cadherin, were significantly lower in the PAI-1 tg mice (3.2 +/- 0.5% vs. 11.7 +/- 5.9% and 2.6 +/- 1.6) vs. 6.2 +/- 0.8%, respectively), implying more extensive tubular damage. At least four fibrogenic pathways were differentially expressed in the PAI-1 tg mice. First, interstitial macrophage recruitment was more intense (P < 0.05 days 3 and 14). Second, interstitial myofibroblast density was greater (P < 0.05 days 3 and 7) despite similar numbers of proliferating tubulointerstitial cells. Third, transforming growth factor-beta1 (TGF-beta1) and collagen I mRNA were significantly higher. Finally, urokinase activity was significantly lower (P < 0.05 days 7 and 14) despite similar mRNA levels. Gene microarray studies documented that that the deletion of this single profibrotic gene had far-reaching consequences on renal cellular responses to chronic injury.

CONCLUSION

These data provide further evidence that PAI-1 is directly involved in interstitial fibrosis and tubular damage via two primary overlapping mechanisms: early effects on interstitial cell recruitment and late effects associated with decreased urokinase activity.

Cyclooxygenase-2 Inhibitor Decreases Extracellular Matrix Synthesis in Stretched Renal Fibroblasts

BACKGROUND/AIMS

Both TGF-beta and cyclooxygenase-2 have been implicated in the pathogenesis of interstitial fibrosis in unilateral ureteral obstruction (UUO). Cyclic tensile stretch has been used in vitro to mimic the changes in intrarenal pressure in UUO. We sought to determine the effect of meloxicam (a selective cyclooxygenase-2 inhibitor) on extracellular matrix and TGF-beta synthesis in stretched renal fibroblasts (NRK-49F).

METHODS

NRK-49F cells were subject to cyclic stretch (6 cycles/min, 15% elongation) using a Flexcell apparatus. Cells were stretched in the absence or presence of meloxicam for 48 h, and then cells and supernatants were isolated. Collagen was quantified by the Sircol assay; fibronectin and laminin were visualized using immunofluorescence. TGF-beta was quantified by ELISA, and protease activity determined by a colorimetric assay.

RESULTS

Both collagen and TGF-beta synthesis were increased following a 48-hour stretch of NRK-49F. Meloxicam significantly decreased the collagen and TGF-beta response to stretch. Stretch-induced fibronectin and laminin synthesis was also decreased by meloxicam. NRK-49F protease activity was decreased by stretch; this was unaffected by meloxicam.

CONCLUSIONS

Stretch of NRK-49F results in extracellular matrix synthesis, a process which may be activated in UUO and contribute to interstitial fibrosis. Inhibition of cyclooxygenase-2 may reduce fibrosis through a TGF-beta-dependent process.

Molecular Mechanism of Apoptosis Induced by Mechanical Forces

In all biological systems, a balance between cell proliferation/growth and death is required for normal development as well as for adaptation to a changing environment. To affect their fate, it is essential for cells to integrate signals from the environment. Recently, it has been recognized that physical forces such as stretch, strain, and tension play a critical role in regulating this process. Despite intensive investigation, the pathways by which mechanical signals are converted to biochemical responses is yet to be completely understood. In this review, we will examine our current understanding of how mechanical forces induce apoptosis in a variety of biological systems. Rather than being a degenerative event, physical forces act through specific receptor-like molecules such as integrins, focal adhesion proteins, and the cytoskeleton. These molecules in turn activate a limited number of protein kinase pathways (p38 MAPK and JNK/SAPK), which amplify the signal and activate enzymes (caspases) that promote apoptosis. Physical forces concurrently activate other signaling pathways such as PIK-3 and Erk 1/2 MAPK, which modulate the apoptotic response. The cell phenotype and the character of the physical stimuli determine which pathways are activated and, consequently, allow for variability in response to a specific stimulus in different cell types.

TNF-alpha mediates obstruction-induced renal tubular cell apoptosis and proapoptotic signaling

Obstruction of the upper urinary tract induces a progressive loss in renal mass through apoptotic renal cell death. Although TNF-alpha has been implicated in ischemia-reperfusion-induced apoptotic renal cell death, its role in obstructive renal cell apoptosis remains unknown. To study this, male Sprague-Dawley rats were subjected to left unilateral ureteral obstruction vs. sham operation. Twenty-four hours before surgery and every 84 h thereafter, rats received either vehicle or a pegylated form of soluble TNF receptor type 1 (PEG-sTNFR1). The kidneys were harvested 1, 3, or 7 days postoperatively, and tissue samples were subsequently analyzed for TNF-alpha (ELISA, RT-PCR), Fas ligand (RT-PCR), apoptosis (TUNEL, ELISA), and caspase 8 and 3 activity (Western blot). Renal obstruction induced increased tissue TNF-alpha and Fas ligand mRNA levels, TNF-alpha protein production, apoptotic renal tubular cell death, and elevated caspase 8 and 3 activity, whereas treatment with PEG-sTNFR1 significantly reduced obstruction-induced TNF-alpha production, renal tubular cell apoptosis, and caspase activity. PEG-sTNFR1 did not significantly alter Fas ligand expression. These results demonstrate that TNF-alpha mediates obstruction-induced renal tubular cell apoptosis and proapoptotic signaling and identify TNF-alpha neutralization as a potential therapeutic option for the amelioration of obstruction-induced 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.

Acatalasemia sensitizes renal tubular epithelial cells to apoptosis and exacerbates renal fibrosis after unilateral ureteral obstruction

Tissue homeostasis is determined by the balance between oxidants and antioxidants. Catalase is an important antioxidant enzyme regulating the level of intracellular hydrogen peroxide and hydroxyl radicals. The effect of catalase deficiency on renal tubulointerstitial injury induced by unilateral ureteral obstruction (UUO) has been studied in homozygous acatalasemic mutant mice (C3H/AnLCsbCsb) compared with wild-type mice (C3H/AnLCsaCsa). Complete UUO caused interstitial cell infiltration, tubular dilation and atrophy, and interstitial fibrosis with accumulation of type IV collagen in obstructed kidneys (OBK) of both mouse groups. However, the degree of injury showed a significant increase in OBK of acatalasemic mice compared with that of wild-type mice until day 7. The deposition of lipid peroxidation products including 4-hydroxy-2-hexenal, malondialdehyde, and 4-hydroxy-2-nonenal was severer in dilated tubules of acatalasemic OBK. Apoptosis in tubular epithelial cells significantly increased in acatalasemic OBK at day 4. Expression of caspase-9, a marker of mitochondrial pathway-derived apoptosis, increased in dilated tubules of acatalasemic mice. The level of catalase activity remained low in acatalasemic OBK until day 7 without compensatory upregulation of glutathione peroxidase activity. The data indicate that acatalasemia exacerbated oxidation of renal tissue and sensitized tubular epithelial cells to apoptosis in OBK of UUO. This study demonstrates that catalase deficiency enhanced tubulointerstitial injury and fibrosis in a murine model of UUO and thus supports the protective role of catalase in this model.

Persistent proteinuria up-regulates angiotensin II type 2 receptor and induces apoptosis in proximal tubular cells

Apoptosis is implicated in the progressive cell loss and fibrosis both at glomerular and tubulointerstitial level. In this study, we examined the potential mechanisms by which persistent proteinuria (protein-overload model) could induce apoptosis. After uninephrectomy (UNX), Wistar rats received daily injections of 0.5 g of bovine serum albumin (BSA)/100 g body weight or saline. Both at day 8 and day 28, rats receiving BSA had proteinuria and renal lesions characterized by tubular atrophy and/or dilation and mononuclear cell infiltration. In relation to control-UNX rats, renal cortex of nephritic rats showed an increment in AT2 mRNA (reverse transcriptase-polymerase chain reaction) and protein (Western blot) expression. In both groups, AT2 receptor immunostaining was mainly localized in proximal tubular cells. Rats with persistent proteinuria showed a significantly increased number of terminal dUTP nick-end labeling positive apoptotic cells compared with UNX-controls, both in glomeruli and tubulointerstitium. Double staining for apoptosis and AT2 receptor showed that most terminal dUTP nick-end labeling positive cells were found in tubules expressing AT2 receptor. Using an antibody that recognizes the active form caspase-3, we observed an increment in caspase-3 activation in rats receiving BSA with respect to those receiving saline. Rats with persistent proteinuria showed a diminution in the phosphorylation of Bcl-2 with respect to UNX-controls both at day 8 and day 28. By contrast, no changes were observed either in the Bax or in the Bcl-2 protein levels. The administration of BSA to UNX rats induced a diminution in the phosphorylation of ERK with respect to UNX-control at all times studied. The changes observed in ERK activities took place without alterations of ERK1/2 protein levels. In summary, our data suggest that persistent proteinuria causes apoptosis in tubular cells through the activation of AT2 receptor, which can, in turn, inhibit MAP kinase (ERK1/2) activation and Bcl-2 phosphorylation.

Mechanical deformation induced apoptosis in human proximal renal tubular epithelial cells is caspase dependent

PURPOSE

Ureteral obstruction (UO) results in apoptosis of renal tubular epithelial cells. We postulated that mechanical deformation and inflammation contribute to the cellular loss that occurs as a result of UO and it is mediated through altered heat shock protein 70 (HSP-70) expression and the caspase cascade.

MATERIALS AND METHODS

Human HK-2 renal tubular cells were subjected to mechanical stretch. Cell viability and apoptosis were assessed by flow cytometry; HSP-70 and caspase 3 protein expression by Western blotting, and caspase 3 activity by fluorescence substrates.

RESULTS

Mechanical stretch caused direct apoptosis induction and it also primed for tumor necrosis factor-alpha induced apoptosis, which was caspase 3 dependent. Although HSP-70 protein expression was increased during mechanical stretch, the protective effects of HSP-70 were only seen after further induction by heat shocking.

CONCLUSIONS

Altering HSP-70 expression and manipulating the caspase cell death proteases represent a novel pathway to protect against renal tubular cell apoptosis and the potential for progression to renal failure in UO.