Renal tubular apoptosis after partial ureteral obstruction

Bone morphogenetic protein-7 attenuates pancreatic damage under diabetic conditions and prevents progression to diabetic nephropathy via inhibition of ferroptosis

Background

Approximately 30% of diabetic patients develop diabetic nephropathy, a representative microvascular complication. Although the etiological mechanism has not yet been fully elucidated, renal tubular damage by hyperglycemia-induced expression of transforming growth factor-β (TGF-β) is known to be involved. Recently, a new type of cell death by iron metabolism called ferroptosis was reported to be involved in kidney damage in animal models of diabetic nephropathy, which could be induced by TGF-β. Bone morphogenetic protein-7 (BMP7) is a well-known antagonist of TGF-β inhibiting TGF-β-induced fibrosis in many organs. Further, BMP7 has been reported to play a role in the regeneration of pancreatic beta cells in diabetic animal models.

Methods

We used protein transduction domain (PTD)-fused BMP7 in micelles (mPTD-BMP7) for long-lasting in vivo effects and effective in vitro transduction and secretion.

Results

mPTD-BMP7 successfully accelerated the regeneration of diabetic pancreas and impeded progression to diabetic nephropathy. With the administration of mPTD-BMP7, clinical parameters and representative markers of pancreatic damage were alleviated in a mouse model of streptozotocin-induced diabetes. It not only inhibited the downstream genes of TGF-β but also attenuated ferroptosis in the kidney of the diabetic mouse and TGF-β-stimulated rat kidney tubular cells.

Conclusion

BMP7 impedes the progression of diabetic nephropathy by inhibiting the canonical TGF-β pathway, attenuating ferroptosis, and helping regenerate diabetic pancreas.

Cell Death in the Kidney

Apoptotic cell death is usually a response to the cell’s microenvironment. In the kidney, apoptosis contributes to parenchymal cell loss in the course of acute and chronic renal injury, but does not trigger an inflammatory response. What distinguishes necrosis from apoptosis is the rupture of the plasma membrane, so necrotic cell death is accompanied by the release of unprocessed intracellular content, including cellular organelles, which are highly immunogenic proteins. The relative contribution of apoptosis and necrosis to injury varies, depending on the severity of the insult. Regulated cell death may result from immunologically silent apoptosis or from immunogenic necrosis. Recent advances have enhanced the most revolutionary concept of regulated necrosis. Several modalities of regulated necrosis have been described, such as necroptosis, ferroptosis, pyroptosis, and mitochondrial permeability transition-dependent regulated necrosis. We review the different modalities of apoptosis, necrosis, and regulated necrosis in kidney injury, focusing particularly on evidence implicating cell death in ectopic renal calcification. We also review the evidence for the role of cell death in kidney injury, which may pave the way for new therapeutic opportunities.

Exosomal proteomic analysis reveals changes in the urinary proteome of rats with unilateral ureteral obstruction

Congenital urinary tract obstruction (UTO) is a commonly noted disorder with the potential to cause permanent loss of renal function. Due to the possibility of spontaneous resolution, postnatal management strategies require lengthy and invasive surveillance methods to monitor the status of renal function and severity of obstruction. Here, a quantitative proteome analysis of urinary exosomes from weanling rats with surgically introduced UTO identifies a number of candidate biomarkers with the potential to improve diagnostic and prognostic methods for this disease. Using gel-assisted digestion coupled to liquid chromatography/tandem mass spectrometry (LC–MS/MS), 318 proteins were identified. Relative protein quantitation by spectral counting showed 190 proteins with significant changes in abundance due to either partial or complete obstruction. Numerous proteins identified here have been shown to be similarly altered in abundance in other renal diseases that cause tubule apoptosis and interstitial fibrosis. Extrapolating the role of the proteins showing quantifiable changes in abundance here from other forms of renal disease suggests they have potential for clinical applicability as biomarkers of congenital UTO. Included in the list of identified proteins are markers of apoptosis, oxidative stress, fibrosis, inflammation, and tubular cell damage, which are commonly associated with UTO. This study therefore provides a number of candidate biomarkers that, following validation in children experiencing UTO, have the potential to improve postnatal management of this disease.

Current radiological techniques used to evaluate unilateral partial ureteral obstruction: an experimental rabbit study

AIM

The aim of this study was to evaluate functional and prognostic benefits of Doppler ultrasonography (DU), diuretic renal scintigraphy (DRS), and magnetic resonance urography (MRU) during diagnosis and follow-up of ureteropelvic junction obstruction (UPJO) and to examine apoptosis rates caused by UPJO in an experimental rabbit model.

METHOD

Twenty-four rabbits were divided randomly into two groups. The left kidneys of 15 rabbits from the first group underwent Ulm-Miller surgery to create UPJO, whereas the left kidneys of nine rabbits from the second group underwent sham surgery. A pressure flow study (Whitaker's test) was done during postoperative week 6. Based on the Whitaker test, the DU, DRS, and MRU findings were compared. The number of apoptotic renal cells was counted after death.

RESULT

The Whitaker test run during postoperative week 6 revealed obstructions in 15 rabbits from group 1; the nine rabbits of the sham group had no obstructions. Sensitivity and specificity of DRS were 93.3 and 88.8 %, respectively, and those of MRU were 93.3 and 88.8 %, respectively. The postoperative mean RI values were significantly higher than the preoperative values, associated with sensitivity of 86.6 % and specificity of 77.5 % for detecting UPJO. DRS, MRU, and RI could not predict UPJO in one (8 %), one (8 %), and two (16 %) kidneys, respectively. Likelihood ratio (LR) was 8.4 for MRU and scintigraphy, while for RI, LR was 3.9. Pathology specimens revealed that all kidneys with UPJO underwent apoptosis, and the number of apoptotic cells was significantly higher on the UPJO-created side than on the contralateral and in the sham group (p < 0.05). No test predicted all apoptosis related to UPJO.

CONCLUSION

The RI, DRS, and DMRU results correlated with the pressure flow results for detecting UPJO. No single radiological technique predicted all initial UPJO-created kidneys that concluded with apoptosis. Further studies are required to seek with better methods for diagnosing an obstruction or to define a combination of radiological techniques aiding in the management decision.

[Experimental study with Doppler ultrasound in partial chronic obstructive uropathy]

INTRODUCTION

This study has aimed to assess the hemodynamic parameters, Renal Resistive Index (RI), Peak Systolic Velocity (PSV), End-Diastolic Velocity (EDV) and Blood Flow of the Renal Artery (FR) by Doppler Ultrasound for diagnosis and monitoring postsurgical partial chronic obstructive uropathy.

MATERIAL AND METHODS

Fifty pigs were used. The experiment was divided into three phases. Phase I consisted of a duplex-Doppler evaluation of the both kidneys to determine the parameters under study. The ratio of each index is calculated as the difference between the value of study kidney and the contralateral. After, a fluoroscopic examination was performed by compressive cystography, excretory urography and retrograde ureteropyelography. Finally, a model of partial right ureteral obstruction was created. After six weeks of the obstructive model, Phase II was begun with the diagnosis of the uropathy, by means of the aforementioned diagnostic methods and the endourological treatment was completed. Phase III is a follow-up performed at 6 months of treatment using the same methods as in the previous phases.

RESULTS

Of the parameters studied, the EDV and its ratio showed greater sensitivity and specificity as a diagnostic marker of obstructive uropathy. In the postoperative monitoring, it was observed that the RI and the EDV returned to baseline levels, with the baseline values.

CONCLUSIONS

The ΔEDV and its ratio is the parameter that shows the greater efficacy for the diagnosis of chronic partial obstructive uropathy, however, it is insufficient to avoid conventional diagnostic techniques. All the parameters, mainly the EDV, have proven useful as complementary tests for monitoring after endourologic resolution of obstructive uropathy.

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.

Upper urinary tract dilatation: prenatal diagnosis, management and outcome

Upper urinary tract dilatation is one of the most common abnormalities detected on prenatal ultrasound scanning. It is commonly due to transient urine flow impairment (UFI) at the level of the pelvi-ureteric and vesico-ureteric junctions, which improves with time in most cases. It is usually in the neonatal period that the diagnosis is confirmed and during the first 18 months of life that the prognosis of the dilatation is defined.

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.

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

BACKGROUND

A recent in vitro model of oxidative stress-induced renal fibrosis demonstrated that activated or phosphorylated extracellular signal-regulated protein kinase (pERK) played a role in apoptosis of renal fibroblasts, but not tubular epithelium where it promoted cell growth and survival. The present study utilized an in vivo model of renal fibrosis after unilateral ureteral obstruction (UUO) to examine the relationship between pERK, apoptosis, proliferation, and differentiation in renal fibroblast and tubular epithelial cells, in comparison with the in vitro results.

METHODS

UUO was induced in rats for 0 (controls, untreated), 6, and 24 hours, 2, 4, and 7 days (N= 4), and tissue analyzed for fibrotic characteristics using microscopy and special stains, Western immunoblots and reverse transcription-polymerase chain reaction (RT-PCR). Controls and UUO animals were also treated with vitamin E, N-acetylcysteine (NAC), or fluvastatin to assess any antioxidant effect on attenuation of fibrosis and pERK expression.

RESULTS

Azan stain and alpha-smooth muscle actin (alpha-SMA), collagen III, and fibronectin expression confirmed development of UUO-induced fibrosis. Oxidative stress markers heme oxygenase-1 (HO-1) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) confirmed oxidative stress at all UUO time points. Tubular epithelial and interstitial mitosis and apoptosis were significantly increased over controls at 2 to 7 days after UUO (P < 0.01). The pERK/ERK ratio increased significantly at 1 to 7 days of UUO in comparison with controls (three- to fivefold, P < 0.05). There was a significant spatiotemporal correlation between pERK and tubular epithelial proliferation (P < 0.001). pERK occasionally colocalized with apoptotic cells (dual labeling) in the interstitium but not in the tubular epithelium. Fluvastatin was the only treatment that attenuated fibrosis (decreased alpha-SMA, fibronectin, tubular epithelial apoptosis) and it also significantly decreased expression of 8-OHdG at 2 and 7 days (P < 0.05). It was associated with decreased pERK at 7 days, compared with UUO alone (P < 0.05).

CONCLUSION

Promotion of tubular epithelial proliferation and survival, and interstitial cell apoptosis, may minimize renal fibrosis after UUO. In the present study, both were linked spatially and temporally with increased pERK expression. Fluvastatin treatment attenuated UUO-induced fibrosis via an antioxidant and pERK-related mechanism.

Altered expression of immune modulator and structural genes in neonatal unilateral ureteral obstruction

BACKGROUND

Congenital obstructive nephropathy is a condition characterized by hydronephrosis, tubular dilatation, apoptosis, and atrophy, as well as interstitial cellular infiltration and progressive interstitial fibrosis. The renal consequences of chronic unilateral ureteral obstruction (UUO) in the neonatal rat are similar to those of clinical congenital obstructive nephropathy.

METHODS

To define alterations in renal gene expression induced by chronic neonatal UUO, Sprague-Dawley rats were subjected to UUO or sham operation within the first 2 days of life, and kidneys were harvested after 12 days.

RESULTS

Microarray analysis revealed that the mRNA expression of multiple immune modulators, including krox24, interferon-gamma regulating factor-1 (IRF-1), monocyte chemoattractant protein-1 (MCP-1), interleukin-1beta (IL-1beta), CCAAT/enhancer binding protein (C/EBP), p21, c-fos, c-jun, and pJunB, was significantly increased in obstructed compared to sham-operated kidneys (all P < 0.05). Western blot analysis revealed significant changes in immune modulator protein abundance in the obstructed versus sham-operated kidney for krox24 (P = 0.0004), IRF-1 (P = 0.005), MCP-1 (P = 0.01), and JunD (P = 0.0008). Alternatively, the abundance of all of the immune modulator proteins was similar in sham-operated and obstructed kidneys in rats subjected to acute (4 days) neonatal UUO. Microarray analysis studies also reveal that structural genes that comprise the cytoskeleton and cell matrix are significantly up-regulated by chronic neonatal UUO, including calponin, desmin, dynamin, and lumican (all P < 0.05).

CONCLUSION

Multiple genes are aberrantly expressed in the kidney of rats subjected to chronic neonatal UUO. Elucidation of these genes involved in neonatal UUO may lead to new insight about congenital obstructive nephropathy.

Bone Morphogenetic Protein-7 Improves Renal Fibrosis and Accelerates the Return of Renal Function

ABSTRACT. A prevention protocol has demonstrated that bone morphogenetic protein-7 (BMP-7) blunted the development of fibrosis in a rat model of unilateral ureteral obstruction. This prevention protocol also preserved, to an extent, renal function. The prevention protocol was extended and a treatment protocol used to examine if BMP-7 was beneficial at limiting fibrosis of the kidney when the BMP-7 was administered during the progression of fibrotic disease. Animals were distributed into four groups. Group 1 received vehicle, group 2 received enalapril (12.5 mg/kg body wt per d), group 3 received BMP-7 (50 or 300 μg/kg), and group 4 received both the enalapril and the high dose of BMP-7. Rats underwent reversible unilateral ureteral obstruction for 3 d, after which the obstruction was relieved. In the treatment protocol, 300 μg/kg BMP-7 was given after the release of obstruction. Seven days after release of the obstruction and the onset of treatment glomerular filtration rate (GFR), renal blood flow, and various histologic indexes of fibrosis were determined. On a consistent basis, BMP-7 treatment alone was found to be slightly but significantly (P < 0.04 to 0.007) better than enalapril alone or in combination with enalapril at decreasing interstitial volume or tubule atrophy. BMP-7 treatment was slightly but not significantly better (P < 0.09) than enalapril at restoring GFR in the prevention protocol. Treatment with BMP-7 significantly boosted GFR (P < 0.01) above that seen with vehicle treatment. These results suggest that BMP-7 treatment is capable of blunting the progression of fibrotic disease and of decreasing interstitial volume. Importantly, a return of renal function is accelerated by BMP-7 treatment. These results suggest that administration of BMP-7 may be an effective treatment to restore or preserve renal histology and renal function in this experimental model of renal disease.

Salutary role for angiotensin in partial urinary tract obstruction

BACKGROUND

In the neonatal period, angiotensin II (Ang II) is up-regulated and induces a timely development of the renal pelvis and ureteral peristalsis, thereby protecting the kidney from hydronephrosis. We tested the possibility that in adulthood, Ang II may act salutarily on the kidney structure during partial urinary tract obstruction by inducing adaptive changes in the peristaltic machinery.

METHODS

Adult male Sprague-Dawley rats were subjected to partial unilateral ureteral obstruction (UUO) and divided into two groups, that is, those treated with (group L, N = 21) and those without (group C, N = 21) an angiotensin type 1 (AT1) receptor antagonist (losartan). Control animals were sham operated (N = 10). Rats were sacrificed either at day 7 or day 14.

RESULTS

The degree of hydronephrosis determined morphometrically was significantly more severe in group L than group C at both day 7 and day 14, indicating that Ang II inhibition accentuated hydronephrosis. The measurement of upstream pressure within the partially ligated ureter in vivo revealed that losartan significantly attenuates the frequency of ureteral peristaltic activities. In in vitro studies using ureteral strips harvested from normal adult Sprague-Dawley rats (N = 10), Ang II (10(-8) mol/L) was shown to augment contraction, which was completely inhibited by losartan (10(-6) mol/L).

CONCLUSIONS

Ang II has a salutary effect of protecting kidneys from hydronephrosis during partial ureteral obstruction through its ability to augment ureteral peristalsis.

Induction of CD14 in tubular epithelial cells during kidney disease

Analysis of gene expression in a mouse model of unilateral ureteral obstruction (UUO) revealed significant induction of CD14 mRNA in kidneys with obstructed ureters. Immunocytochemical analysis indicated that CD14 was upregulated in tubular epithelial cells and this upregulation was not attributable to infiltration of the kidneys by mononuclear cells. This induction of CD14 mRNA was found to occur in BALB/C, C57BL/6, C3H/HeN, and C3H/HeJ mice during UUO. Ischemia/reperfusion of kidneys also induced CD14 mRNA. Mice lacking either of the tumor necrosis factor-alpha receptor (TNFR) genes were also studied; the induction of CD14 was blunted in TNFR 1-knockout mice but not in TNFR2-knockout mice. Apoptosis of tubular cells in lipopolysaccharide-resistant CH3/HeJ mice was significantly (P: < 0. 05) less than that in lipopolysaccharide-responsive CH3/HeN mice during UUO. These results suggest that CD14 is acutely induced in tubular epithelial cells in two mouse models of renal injury. This induction is regulated by tumor necrosis factor-alpha, through TNFR1. CD14 may participate in the apoptosis of tubular epithelial cells on a more chronic basis by activating a pathway that is absent or deficient in C3H/HeJ mice.

Attenuation of cisplatin-induced acute renal failure is associated with less apoptotic cell death

To clarify the pathophysiologic role of apoptosis in acute renal failure (ARF), we examined whether the attenuation of cisplatin-induced ARF is associated with the change in the degree of apoptotic cell death. The administration of cisplatin (CDDP) (6 mg/kg body weight) in rats induced ARF at day 5, as manifested by a significant increase in serum creatinine (Scr) and tubular damage. CDDP-induced apoptotic cell death was confirmed by electron microscopic examination, agarose gel electrophoresis, and increased cells positive for TaT-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) in the outer medulla of the kidney. Treatment with dimethylthiourea (DMTU)--a scavenger of hydroxyl radicals--or glycine abrogated CDDP-induced increases in Scr, the tubular damage score, and the number of TUNEL-positive cells. Pretreatment with uranyl acetate (UA) induced a significant expression of Bcl-2 in the kidney and ameliorated CDDP-induced increases in Scr, the tubular damage score, and TUNEL-positive cells in the outer stripe of the outer medulla. Our findings indicate (1) that the attenuation of CDDP-induced ARF was associated with less apoptotic cell death and (2) that the induction of the anti-apoptotic protein Bcl-2 attenuated apoptosis and tubular damage. Our results suggest that apoptotic cell death may play an important role in the development of cisplatin-induced ARF.

Expression of apoptosis regulatory genes in chronic cyclosporine nephrotoxicity favors apoptosis

Expression of apoptosis regulatory genes in chronic cyclosporine nephrotoxicity favors apoptosis.

BACKGROUND

Chronic cyclosporine (CsA) nephrotoxicity is characterized by interstitial fibrosis, tubular dropout, and loss of cellularity in areas of fibrosis. Apoptosis was found to play a role in CsA-induced fibrosis. We evaluated the role of the death genes p53, Bax, and Fas-L (ligand), survival gene Bcl-2, interleukin-converting enzyme (ICE), and caspase-3.

METHODS

Salt-depleted rats were administered CsA 15 mg/kg/day or vehicle (VH) and were sacrificed at 7 or 28 days. Apoptosis was detected by TdT-mediated dUTP-biotin nick end labeling assay. p53 and Bax expressions were evaluated by Northern and Western blot analysis. Fas-L and Bcl-2 expressions were evaluated by immunofluorescence. In addition to ICE mRNA, caspase-3 enzymatic activity was assayed.

RESULTS

Although no differences were seen at one week, apoptosis-positive cells increased with CsA at four weeks (P < 0.05) and correlated with tubular atrophy and interstitial fibrosis (r = 0.8, P < 0.05). CsA induced the expression of p53 (P < 0.05) and Bax (P < 0.01) and decreased that of Bcl-2 (P < 0.05). CsA up-regulated Fas-L expression (P < 0.001). ICE mRNA and caspase-3 activity were also increased (P < 0.01). The changes occurred as early as one week and remained statistically significant at four weeks.

CONCLUSIONS

Specific apoptotic genes are increased in chronic CsA nephrotoxicity. The balance favors the induction of apoptosis. Increased apoptosis could explain the tubular dropout and loss of cellularity with fibrosis. This then may impair the ability of the tubulointerstitium to remodel. Apoptosis could also contribute to some of CsA immunosuppressive effects on activated lymphocytes.

Role of TNFR1 and TNFR2 receptors in tubulointerstitial fibrosis of obstructive nephropathy

Unilateral ureteral obstruction (UUO) results in tubulointerstitial fibrosis of the obstructed kidney. In this study, we report the contribution of tumor necrosis factor-alpha (TNF-alpha) to the fibrosis that develops after ureteral obstruction. Mice in which individual TNF-alpha receptors TNFR1 or TNFR2 had been genetically knocked out were used, and results were compared with mice of C57Bl/6 background after 5 days UUO. Both kidneys were removed and examined histologically for changes in interstitial volume (Vv(int)), collagen IV deposition, alpha-smooth muscle actin (alpha-SMA) matrix score, nuclear factor-kappaB (NF-kappaB) activity, and TNF-alpha mRNA levels. We found that the Vv(int) of contralateral unobstructed kidneys averaged approximately 7% and was indistinguishable among the three genotypes of mice. Vv(int) of ureteral obstructed kidney of C57Bl/6 mice averaged 33 +/- 3.9% after 5 days of UUO. Vv(int) of obstructed kidneys of TNFR1 mice was significantly reduced to 19.4 +/- 3.1%, whereas that of TNFR2 mice was significantly decreased to 25.4% +/- 4.8%. There was a modest but significant difference between Vv(int) of TNFR1 and TNFR2 (P < 0. 047). Both collagen IV and alpha-SMA matrix scores were decreased significantly in obstructed kidney of TNFR1 mouse compared with that of C57Bl/6 and TNFR2 mice. Nuclear extracts prepared from kidney cortex were found to have a significant increase in NF-kappaB binding activity in obstructed kidney compared with contralateral kidney. Individual knockout of the TNFR1 or TNFR2 genes resulted in significantly less NF-kappaB activation compared with the wild type, with TNFR1 being less than TNFR2 knockout. There was a significant increase in TNF-alpha mRNA in the kidney with ureteral obstruction in all three genotypes. TNFR1 knockout displayed a significant reduction in amount of TNF-alpha mRNA induced compared with wild-type or TNFR2 knockout mice. Treatment of TNFR1 knockout mice with an angiotensin converting enzyme inhibitor further decreased Vv(int) and TNF-alpha mRNA induction, suggesting an interaction of ANG II and TNF-alpha systems. These results suggest that TNF-alpha contributes, in part, to changes in interstitial volume, myofibroblast differentiation, and NF-kappaB activation in the kidney during ureteral obstruction. These changes appear to be mediated through both TNFR1 and TNFR2 gene products with effects through the TNFR1 receptor predominating. Furthermore, ANG II appears to stimulate TNF-alpha pathophysiological events leading to renal fibrosis.

Apoptosis in the kidney

Apoptosis is a highly regulated mechanism of cell death. Although apoptosis has a functional role in normal development and tissue homeostasis, aberrant triggering of the process by toxicants may lead to abnormal function or disease. Low level exposures to toxicants that induce apoptosis in kidney may therefore create a critical disturbance in kidney homeostasis, contributing to renal neoplasia or renal disease. In this report, we review the involvement of apoptosis in normal kidney development and in renal disease and discuss some of the toxicants and molecular factors involved in regulation of the process in renal cells.

Effect of experimentally induced urethral obstruction and surgical decompression in utero on renal development and function in rabbits

To investigate the effect of urethral obstruction during late fetal life on renal development and function, we developed a rabbit fetal model of obstructive nephropathy to examine the pathological and biochemical consequences of urethral obstruction and beneficial effects of early surgical decompression. Animals were divided into four groups, i.e., obstructed, early decompressed, late decompressed, and control. Fetal renal development was evaluated by histological examination and counting the number of glomeruli in the four groups. The number of renal glomeruli correlated with gestational age in the normal fetus (r = 0.90, P < 0.0001). Urethral ligation on gestational day 25 (full-term, 31 days) resulted in thinning of the renal cortex and significantly decreased the number of renal glomeruli. The concentration of urinary microalbumin was higher when urethral obstruction was maintained for 3 days than 1 day after urethral obstruction, although urinary beta2- microglobulin, Na, Cl, and osmotic pressure did not change during this period. Decompression of urethral obstruction 1 day after induction of urethral obstruction resulted in improvement in the severity glomerular hypoplasia compared with late decompression (P < 0.01). Our results suggest that the rabbit fetal model simulates fetal urethral obstruction in humans, and indicates that early surgical decompression may be effective in restoration of normal renal function.

Renal tubular apoptosis after release of ureteral obstruction in the rat kidney

BACKGROUND

Information concerning the mechanisms underlying recovery from hydronephrosis is limited. The frequency of apoptosis during healing from hydronephrosis was studied using a rat kidney model.

METHODS

The presence of apoptosis was studied using an in situ DNA 3' end labeling method, electron microscopy, and agarose gel electrophoresis.

RESULTS

The degree of apoptosis in both the medulla and cortex gradually increased during ureteral obstruction as shown by in situ DNA 3' end labeling. Release of the ureteral obstruction resulted in a further increase in the degree of apoptosis in the medulla and cortex. The increase in apoptosis in the medulla was transient and lasted for only 4 days following release, while that in the cortex continued for at least 3 weeks. Apoptosis in the glomerulus was not observed. Electron microscopy revealed cells with aggregated chromatin in compact granular masses that abutted the nuclear membrane. Following release of ureteral obstruction, DNA fragmentation characteristic of apoptosis was visible on agarose gel electrophoresis.

CONCLUSION

These results suggest that apoptosis is involved in post-obstructive tubular damage in the rat kidney.

Accelerated fibrosis and collagen deposition develop in the renal interstitium of angiotensin type 2 receptor null mutant mice during ureteral obstruction

We examined the role of angiotensin in renal remodeling that is specifically channeled through the angiotensin type 2 receptor (AT2 receptor). Previously, we observed that in mouse embryonic kidneys the AT2 mRNA is predominantly expressed in the mesenchyme. We therefore chose a model of unilateral ureteral obstruction, characterized by activation of the renin-angiotensin system, while fibrosis develops prominently within the renal interstitium. Male wild-type mice (Agtr2 -/Y) and mice null mutant for the AT2 gene (Agtr2 -/Y) were subjected to a complete unilateral ureteral ligation for 5 or 14 days. Obstructed kidneys of Agtr2 -/Y mice showed more severe interstitial fibrosis than those of Agtr2 +/Y mice, confirmed by increased collagen by point-counting on Masson trichrome stained sections, and increased alpha 1(I) collagen mRNA expression by Northern blot. Immunohistochemistry staining for PCNA (a marker of cell proliferation), F4/80 (a marker of macrophages), vimentin (a marker of fibroblasts), and alpha SMA (a marker of myofibroblasts) revealed that, while the two groups were comparable in the degree of cell proliferation and macrophage infiltration, fibroblasts/ myofibroblasts were present in a greater abundance in obstructed kidneys of Agtr2 -/Y mice than in Agtr2 +/Y at both 5 and 14 days after obstruction. Moreover, cells undergoing apoptosis were significantly less in Agtr2 -/Y than in Agtr2 +/Y. Thus, the AT2 receptor significantly impacts the remodeling process within renal interstitium, potentially by regulating the population of collagen-producing cells.

Accelerated apoptosis characterizes cyclosporine-associated interstitial fibrosis

Recently we developed a model of cyclosporine nephropathy in rats characterized by tubulointerstitial (TI) injury, macrophage infiltration, and progressive interstitial fibrosis [1, 2]. To determine if the TI injury accompanying cyclosporine A (CsA) nephropathy was associated with accelerated apoptosis and ischemia, we treated rats for five weeks with CsA with or without losartan (to block angiotensin II type 1 receptor), or hydralazine/furosemide (H/F) (protocol #1). In protocol #2, rats received CsA with or without L-NAME (to block nitric oxide) or L-arginine (to provide a precursor to nitric oxide formation). Cyclosporine A treated rats had increased apoptosis of tubular and interstitial cells documented by PAS, propidium iodide staining, TUNEL assay, and electron microscopy compared to vehicle treated controls. Macrophages containing apoptotic cells could be confirmed by TUNEL/ED-1 doublestaining and colocalized in areas of TI injury. Animals treated with CsA + losartan had a statistically significant decrease in apoptosis (TUNEL + cells/mm2) when compared to CsA treated animals (6.0 vs. 19.9, P < or = 0.0001). The decrease in apoptosis in the CsA + H/F group was not statistically significant. Animals treated with CsA + L-NAME had a statistically significant increase in apoptosis compared to the CsA treated animals (12.3 vs. 6.4, P = 0.001). L-arginine administration with CsA resulted in a decrease in tubulointerstitial apoptosis versus CsA treated animals, however, this did not reach statistical significance. The addition of L-arginine did result in a significant reduction in interstitial fibrosis (P < 0.0001). Regression analysis revealed a significant correlation between apoptosis and interstitial fibrosis in both protocols. (CsA vs. CsA + losartan r = 0.63, P < 0.0001; CsA vs. CsA + L-NAME r = 0.83, P < 0.0001). We conclude that CsA nephropathy is associated with a marked increase in apoptosis of tubular and interstitial cells. Cyclosporine A induced apoptosis is partially mediated by angiotensin II and nitric oxide inhibition, suggesting a role for renal ischemia in this process, and CsA induced apoptosis correlates with interstitial fibrosis.

Induction of p21WAF1/CIP1/SDI1 in kidney tubule cells affects the course of cisplatin-induced acute renal failure

The p21 protein is found in the nucleus of most cells at low levels and is induced to elevated levels after DNA damage, causing cell-cycle arrest. We have reported that p21 mRNA is rapidly induced to high levels in murine kidney after acute renal failure. The function(s) in the kidney of p21 induction in cisplatin-induced acute renal failure was studied with mice that are homozygous for a p21 gene deletion. After drug administration, as compared with their wild-type littermates, p21(-/-) mice display a more rapid onset of the physiologic signs of acute renal failure, develop more severe morphologic damage, and have a higher mortality. Therefore, the induction of p21 after cisplatin administration is a protective event for kidney cells. Using both bromodeoxyuridine incorporation and nuclear proliferating cell nuclear antigen detection, we found that cisplatin administration caused kidney cells to start entering the cell-cycle. However, cell-cycle progression is inhibited in wild-type mice, whereas kidney cells in the p21(-/-) mice progress into S-phase. We propose that p21 protects kidneys damaged by cisplatin by preventing DNA-damaged cells from entering the cell-cycle, which would otherwise result in death from either apoptosis or necrosis.

Constant elevation in renal pelvic pressure induces an increase in urinary N-acetyl-beta-D-glucosaminidase in a nonobstructive porcine model

PURPOSE

To clarify the physiological significance of renal pelvic pressure elevations encountered in the evaluation of hydronephrotic kidney we examined the effects of different levels of renal pelvic pressure on the induction of renal injury.

MATERIALS AND METHODS

A nonobstructive porcine model was created in which the urine drained against a constant predetermined pressure gradient. Renal pelvic pressure of 10, 20 and 40 cm. was created in 2, 2 and 4 animals, respectively. During 18 to 23 hours serial urinary N-acetyl-beta-D-glucosaminidase levels were determined as an indicator of renal tubular injury. Tissue specimens were examined histologically and renal arterial blood flow was monitored.

RESULTS

Urinary N-acetyl-beta-D-glucosaminidase levels in the kidneys subjected to 10 cm. water remained essentially unchanged. However, at 20 and 40 cm. water statistically significant increases were observed. Similarly, renal arterial blood flow was unchanged at 10 cm. water but it became significantly lower than in controls at 20 and 40 cm. water. Histological evaluation revealed mild to moderate tubular dilatation in the kidneys subjected to 20 and 40 cm. water.

CONCLUSIONS

Excessively high collecting system pressure induced renal cellular injury, as reflected by an increase in urinary N-acetyl-beta-D-glucosaminidase levels. While renal pelvic pressure up to 10 cm. water appeared to be innocuous, renal cellular injury was evident within as little as 1 hour at renal pelvic pressures 20 cm. water or greater. The degree of N-acetyl-beta-D-glucosaminidase in the urine also correlated with a decrease in renal arterial blood flow.

The membrane-bound form of heparin-binding epidermal growth factor-like growth factor promotes survival of cultured renal epithelial cells

To understand whether expression of membrane-anchored heparin binding epidermal growth factor (proHB-EGF) is involved in renal epithelial cell survival, rat membrane-bound HB-EGF precursor was stably transfected into a renal epithelial cell line, NRK 52E cells (NRKproHB-EGF). When exposed to 10% fetal calf serum (FCS), there were no differences in growth rates among wild-type (WT), vector-transfected (NRKvector), and NRKproHB-EGF. However, when cells were grown in the presence of 1% FCS, the growth rate of NRKproHB-EGF was 65% faster. When confluent cell monolayers were exposed to H2O2 or etoposide, WT or NRKvector exhibited significant apoptotic bodies and DNA laddering; in contrast, NRKproHB-EGF were resistant to both stimuli, as indicated by increased cell viability and marked decrease of apoptotic bodies and DNA laddering. When plated at high density onto plastic dishes without FCS, WT and NRKvector formed few attachments, did not proliferate, and underwent apoptosis. By day 3, no cells survived. Addition of exogenous recombinant HB-EGF (10(-8) M) to WT or NRKvector increased cell survival by <10% and incubation with conditioned media of NRKproHB-EGF had no effect. In contrast, NRKproHB-EGF attached and formed epithelial colonies, although they did not proliferate. After 3 days, cell viability was 84% of the initial cell number plated, and no evidence of apoptosis was present. When plated in 10% FCS, NRKproHB-EGF attachment to plastic substratum at 1, 2, and 3 h was 250% greater than that of WT or NRKvector. Addition of exogenous recombinant human HB-EGF to WT or NRKvector increased attachment by <50%. When grown on poly(2-hydroxyethyl methacrylate) or in the presence of the integrin receptor-blocking peptide GRGDTP, neither WT nor NRKvector attached to the substratum or formed cell-cell attachments. Compared with WT or NRKvector, NRKproHB-EGF exhibited 300% greater cell viability on either poly(2-hydroxyethyl methacrylate)-coated dishes or in the presence of GRGDTP and formed cell clusters. When plated at low density (1 x 10(3) cells/1.5-cm dish) or at high density in the presence of an anti-HB-EGF blocking antibody, NRKproHB-EGF failed to form epithelial colonies. Addition of formalin fixed NRKproHB-EGF promoted EGF receptor tyrosine phosphorylation in quiescent A431 cells and stimulated DNA synthesis and prevented H2O2-induced apoptosis in renal epithelial cells. These results indicate that membrane-bound HB-EGF promotes renal epithelial cell survival, possibly by promoting cell-matrix and cell-cell interactions. The failure of either conditioned media or exogenous HB-EGF to reproduce these findings suggests that juxtacrine or tightly coupled paracrine interactions underlie this cytoprotection.

Epidermal growth factor suppresses renal tubular apoptosis following ureteral obstruction

OBJECTIVES

Acute unilateral ureteral obstruction (UUO) results in ipsilateral hydronephrosis characterized by a decrease in epidermal growth factor (EGF) mRNA expression and EGF protein levels in the distal renal tubules. UUO results in programmed cell death with increases in the characteristic markers of apoptosis. To suppress the apoptotic response during UUO, recombinant EGF was administered during renal obstruction and the ensuing molecular and histologic changes were studied.

METHODS

Mature Sprague-Dawley rats underwent left ureteral obstruction and the kidneys were harvested at 24, 48, and 72 hours. Markers of apoptosis included DNA laddering pattern on agarose gel electrophoresis, in situ gap labeling of fragmented DNA for quantitative apoptotic body determination, polyadenylated mRNA expression of SGP-2, and in situ hybridization for sulfated glycoprotein-2 (SGP-2) mRNA. Studies were repeated in rats following administration of 10, 20, and 40 micrograms of subcutaneous recombinant EGF on a daily basis after UUO.

RESULTS

Subcutaneous injection of EGF into unilaterally obstructed rats promotes renal tubular epithelial cell regeneration, as demonstrated by increased cortical mitotic activity. Systemic EGF supplementation in these unilaterally obstructed rats also resulted in a decrease in the intensity of the DNA laddering pattern associated with renal tubular apoptosis. An in situ labeling procedure to identify apoptotic nuclei in the ureterally obstructed kidneys revealed a 50% reduction in apoptosis after EGF administration. Northern blot analysis and in situ hybridization for SGP-2 mRNA or clustering gene product also revealed a decreased expression in the obstructed and EGF-treated renal parenchyma.

CONCLUSIONS

These data suggest that EGF, apart from its known role as a mitogenic substance for renal tubular epithelial cells, is also a critical in vivo renal cell survival factor for the developmentally mature kidney.

Apoptosis in the mammalian kidney: incidence, effectors, and molecular control in normal development and disease states

In the preceding sections we have emphasized the current status of our knowledge concerning the involvement of apoptosis in normal and abnormal renal developmental processes, in control of the adult kidney size and capacity, in the development of renal disease states and in renal oncogenesis. At several points, we noted that studies of apoptosis in the kidney and in renal cells lag behind those in other organ systems. Even with the rudimentary knowledge now available, however, it is apparent that apoptosis is an extremely important process in the kidney. Recent observations lend credence to the view that continued study of this unique cell death process might enable the generation of novel and more effective therapies to treat renal diseases and renal malignancies. We wish to highlight several areas that require particular attention. First, the relationship between blood supply and apoptosis in the kidney requires further investigation. Benign human renal diseases are common in our population; and we now know that most of these diseases are associated with abnormal rates of apoptosis. Although the initiating agents for the various renal diseases vary, there is good reason to believe that much of the apoptosis that occurs in these adult diseases is the end result of reduced renal blood flow initiated by the causative agent. Cytokines or other extrinsic agents that can reduce the apoptotic loss of renal cells under these conditions hold theoretical promise in treating these diseases. Second, there is an urgent need to define the endocrine, paracrine, or autocrine roles of cytokines in normal renal physiology and in the pathogenesis of various renal syndromes. As indicated above, elaboration of fibrous extracellular material by fibroblasts in the tubulointerstitial regions of the kidney appears to be part of the final common pathway leading to end-stage renal disease. It is important to understand how the function of these fibroblasts is controlled. Conversely, apoptosis of glomerular or renal tubular cells also appears to play a role in the development of many of these syndromes. There is already experimental and clinical evidence showing that IGF-1 and hepatocyte growth factor therapies can be useful in renal diseases [57, 58]. It remains to be determined how much of the usefulness of these cytokines is related to their ability to suppress apoptosis as opposed to their ability to promote true growth. Finally, the analysis of apoptotic regulation during renal oncogenesis is critical. Maligant renal cell cancers are difficult to detect in adults before their metastases cause symptoms; and by this late stage renal tumors are almost invariably fatal. The ability of these tumors to regress spontaneously indicates that most apoptotic pathways are retained in these cells, yet their disappointing response to chemotherapy indicates that we have much to learn about how to trigger these pathways. Hopefully a better understanding of the control of these pathways will lead to improved therapy for this devastating group of neoplasms.

Glucose loading induces DNA fragmentation in rat proximal tubular cells

A 10% glucose, 10% mannitol, or 0.9% saline solution was infused in male Wistar rats for 300 minutes via the left cervical vein. Glomerular filtration rates (GFRs) were not significantly altered in any of the three groups. DNA was extracted from isolated proximal tubular cells at the end of each infusion. Electrophoresis on agarose gels showed a distinct ladder pattern of DNA fragmentation in 10% glucose-loaded rats, but no such pattern in 10% mannitol- or 0.9% saline-loaded rats. After infusion for 300 minutes, the plasma glucose level of the 10% glucose-loaded group was higher than that of the other two groups (each P < .005). These results suggest that hyperglycemia led to DNA fragmentation in the DNA of proximal tubular cells, similar to the process of programmed cell death known as apoptosis. DNA fragmentation may be associated with renal proximal tubular damage in the early stages of diabetic nephropathy.

Apoptosis--molecular mechanisms and biomedical implications

Apoptosis is a distinct form of cell death of importance in tissue development and homeostasis and in several diseases. This review summarizes current knowledge about the regulation and molecular mechanisms of apoptosis and discusses the potential role of disregulated apoptosis in several major diseases. Finally, we speculate that modulation of apoptosis may be a target in future drug therapy.

Deregulation of cell survival in cystic and dysplastic renal development

Various aberrations of cell biology have been reported in polycystic kidney diseases and in cystic renal dysplasias. A common theme in these disorders is failure of maturation of renal cells which superficially resemble embryonic tissue. Apoptosis is a feature of normal murine nephrogenesis, where it has been implicated in morphogenesis, and fulminant apoptosis occurs in the small, cystic kidneys which develop in mice with null mutations of bcl-2. Therefore, we examined the location and extent of apoptosis in pre- and postnatal samples of human polycystic and dysplastic kidney diseases using propidium iodide staining, in situ end-labeling and electron microscopy. In dysplastic kidneys cell death was prominent in undifferentiated cells around dysplastic tubules and was occasionally found in cystic epithelia. The incidence of apoptosis was significantly greater than in normal controls of comparable age both pre- and postnatally. In the polycystic kidneys there was widespread apoptosis in the interstitium around undilated tubules distant from cysts, in undilated tubules between cysts and in cystic epithelia. The level of apoptosis compared to controls was significantly increased postnatally. A similar increase of cell death was also noted in the early and late stages of renal disease in the polycystic cpk/cpk mouse model. We speculate that deregulation of cell survival in these kidneys may reflect incomplete tissue maturation, and may contribute to the progressive destruction of functional kidney tissue in polycystic kidneys and the spontaneous involution reported in cystic dysplastic kidneys.

Management of prenatally detected fetal hydronephrosis

The increased frequency of prenatal ultrasonography has resulted in an increase in the detection of fetal genitourinary abnormalities, many of which are of minimal clinical significance. Severe fetal urinary tract obstruction with associated oligohydramnios results in a recognizable constellation of physical findings, including renal dysplasia, pulmonary hypoplasia, and perinatal death. In selected cases, prenatal intervention to decompress urinary tract obstruction may reestablish amniotic fluid volume, prevent renal damage, and allow normal pulmonary development. After severe renal injury has occurred, intervention is unlikely to improve the prognosis of the affected fetus. Renal function may be analyzed prenatally by ultrasound examination and determination of chemical composition of fetal urine in order to identify fetuses in whom kidney development has not yet been irrevocably damaged and those likely to benefit from prenatal intervention. Postnatal renal evaluation with ultrasonography, voiding cystourethrography, and radionuclide imaging facilitates further characterization of the abnormality detected on prenatal ultrasound examination.