Cytochrome c mediates apoptosis in hypertensive nephrosclerosis in Dahl/Rapp rats

Transcriptomic changes in glomeruli in response to a high salt challenge in the Dahl SS rat

Salt sensitivity impacts a significant portion of the population and is an important contributor to the development of chronic kidney disease. One of the significant early predictors of salt-induced damage is albuminuria, which reflects the deterioration of the renal filtration barrier: the glomerulus. Despite significant research efforts, there is still a gap in knowledge regarding the molecular mechanisms and signaling networks contributing to instigating and/or perpetuating salt-induced glomerular injury. To address this gap, we used 8-wk-old male Dahl salt-sensitive rats fed a normal-salt diet (0.4% NaCl) or challenged with a high-salt diet (4% NaCl) for 3 wk. At the end of the protocol, a pure fraction of renal glomeruli obtained by differential sieving was used for next-generation RNA sequencing and comprehensive semi-automatic transcriptomic data analyses, which revealed 149 differentially expressed genes (107 and 42 genes were downregulated and upregulated, respectively). Furthermore, a combination of predictive gene correlation networks and computational bioinformatic analyses revealed pathways impacted by a high salt dietary challenge, including renal metabolism, mitochondrial function, apoptotic signaling and fibrosis, cell cycle, inflammatory and immune responses, circadian clock, cytoskeletal organization, G protein-coupled receptor signaling, and calcium transport. In conclusion, we report here novel transcriptomic interactions and corresponding predicted pathways affecting glomeruli under salt-induced stress.NEW & NOTEWORTHY Our study demonstrated novel pathways affecting glomeruli under stress induced by dietary salt. Predictive gene correlation networks and bioinformatic semi-automatic analysis revealed changes in the pathways relevant to mitochondrial function, inflammatory, apoptotic/fibrotic processes, and cell calcium transport.

MnO2 nanoparticles and MnSO4 differentially affected hepatic lipid metabolism through miR-92a/acsl3-dependent de novo lipogenesis in yellow catfish Pelteobagrusfulvidraco

With the increasing production and use of MnO2 NPs and MnSO4 in various fields, their discharge into the aquatic environment is inevitable, which poses potential threats to aquatic organisms and humans. However, to date, few studies have been conducted to investigate the potential mechanism of the toxicity of MnO2 NPs, and a comprehensive understanding of the differences between this mechanism and the toxicity mechanism of inorganic Mn (MnSO4) is still lacking. Since lipid metabolism-relevant parameters have been widely recognized as novel biomarkers for risk assessment of environmental contaminants, the present study investigated the differential mechanisms of how MnO2 NPs and MnSO4 affect hepatic lipid metabolism in a freshwater fish yellow catfish. Compared to MnSO4, dietary MnO2 NPs caused liver injury, increased hepatic lipid accumulation and induced lipotoxicity, and up-regulated mRNA expression of de novo lipogenic genes. Moreover, MnO2 NPs downregulated the expression of miR-92a and miR-92b-3p, microRNAs involved in regulation of lipid metabolism, in the liver. Mechanistically, we found that acls3, an acetyl-coenzyme A synthetase, is target gene of miR-92a, and miR-92a-acsl3-dependent de novo lipogenesis contributes to lipid accumulation and lipotoxicity induced by MnO2 NPs. Collectively, these findings provided novel insights into mechanism whereby miRNAs mediate nanoparticles- and inorganic Mn-induced hepatic lipotoxicity and changes of lipid metabolism in vertebrates. Our findings also shed new perspective for ecotoxicity and ecological risk of MnO2 NPs and MnSO4 in aquatic environment.

Mitochondrial Damage and Hypertension: Another Dark Side of Sodium Excess

PURPOSE OF REVIEW

Essential or primary hypertension (HT) is a worldwide health problem with no definitive cure. Although the exact pathogenesis of HT is not known, genetic factors, increased renin-angiotensin and sympathetic system activity, endothelial dysfunction, oxidative stress, and inflammation play a role in its development. Environmental factors such as sodium intake are also important for BP regulation, and excess sodium intake in the form of salt (NaCl, sodium chloride) increases blood pressure in salt-sensitive people. Excess salt intake increases extracellular volume, oxidative stress, inflammation, and endothelial dysfunction. Recent evidence suggests that increased salt intake also disturbs mitochondrial function both structurally and functionally which is important as mitochondrial dysfunction is associated with HT. In the current review, we have summarized the experimental and clinical data regarding the impact of salt intake on mitochondrial structure and function.

RECENT FINDINGS

Excess salt intake damage mitochondrial structure (e.g., shorter mitochondria with less cristae, increased mitochondrial fission, increased mitochondrial vacuolization). Functionally, high salt intake impairs mitochondrial oxidative phosphorylation and electron transport chain, ATP production, mitochondrial calcium homeostasis, mitochondrial membrane potential, and mitochondrial uncoupling protein function. Excess salt intake also increases mitochondrial oxidative stress and modifies Krebs cycle protein expressions. Studies have shown that high salt intake impairs mitochondrial structure and function. These maladaptive mitochondrial changes facilitate the development of HT especially in salt-sensitive individuals. High salt intake impairs many functional and structural components of mitochondria. These mitochondrial alterations along with increased salt intake promote the development of hypertension.

A transcriptomics and network pharmacology approach to elucidate the mechanism of action of geniposide on carbon tetrachloride-induced liver injury in rats

Geniposide, the main active component of Fructus Gardeniae (FG), is known to confer protection against liver diseases. Herein we explored the hepatoprotective effects of geniposide and elucidated its molecular mechanism by transcriptome RNA-seq and network pharmacology. Liver injury was modeled by intraperitoneally injecting CCl₄ (0.15% prepared with refined peanut oil) at a dose of 1.5 mL/kg thrice a week; from the second week, rats were administered geniposide (20 mg/kg or 40 mg/kg) by gavage for 6 weeks. Serum and liver samples were then collected to assess liver function indicators and inflammatory factors and to observe pathological changes in the liver. The Illumina HiSeq 4000 platform was used to obtain transcriptome data from the liver tissue of rats after geniposide administration. Core targets and pathways related to the liver protection mechanism of geniposide were further analyzed by integrating transcriptomics and network pharmacology. Differentially expressed genes (DEGs), core targets, and signaling pathways were identified by methods such as q-PCR, molecular docking, and Western blotting. We found that after geniposide administration, the levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and inflammatory factors decreased in the model group, and liver injury cells be effectively repaired. RNA-seq data analysis showed that compared to control group, the model group reversed 1,451 DEGs; further, compared to model group, geniposide reversed 511 DEGs. Eight key targets, including PIK3R1, ACOX3, and EGF, were found through further analyses. Geniposide was determined to mainly regulate the PPAR signaling pathway, apoptosis signaling pathway, and MAPK signaling pathway in liver tissues. To summarize, the protective and restorative effects of geniposide on rat liver may seem to be related to its efficacy in inhibiting the activation of inflammatory pathways, thereby reducing cell apoptosis. Our findings should serve as the basis for the development of functional foods or drugs to prevent and treat liver diseases.

FPR-1 (Formyl Peptide Receptor-1) Activation Promotes Spontaneous, Premature Hypertension in Dahl Salt-Sensitive Rats

[Figure: see text].

Renal Glomerular Mitochondria Function in Salt-Sensitive Hypertension

Salt-sensitive (SS) hypertension is accompanied with an early onset of proteinuria, which results from the loss of glomerular podocytes. Here, we hypothesized that glomerular damage in the SS hypertension occurs in part due to mitochondria dysfunction, and we used a unique model of freshly isolated glomeruli to test this hypothesis. In order to mimic SS hypertension, we used Dahl SS rats, an established animal model. Animals were fed a 0.4% NaCl (normal salt, NS) diet or challenged with a high salt (HS) 4% NaCl diet for 21 days to induce an increase in blood pressure (BP). Similar to previous studies, we found that HS diet caused renal hypertrophy, increased BP, glomerulosclerosis, and renal lesions such as fibrosis and protein casts. We did not observe changes in mitochondrial biogenesis in the renal cortex or isolated glomeruli fractions. However, Seahorse assay performed on freshly isolated glomeruli revealed that basal mitochondrial respiration, maximal respiration, and spare respiratory capacity were lower in the HS compared to the NS group. Using confocal imaging and staining for mitochondrial H₂O₂ using mitoPY1, we detected an intensified response to an acute H₂O₂ application in the podocytes of the glomeruli isolated from the HS diet fed group. TEM analysis showed that glomerular mitochondria from the HS diet fed group have structural abnormalities (swelling, enlargement, less defined cristae). Therefore, we report that glomerular mitochondria in SS hypertension are functionally and structurally defective, and this impairment could eventually lead to loss of podocytes and proteinuria. Thus, the glomerular–mitochondria axis can be targeted in novel treatment strategies for hypertensive glomerulosclerosis.

Histopathological Changes in the Kidney following Congestive Heart Failure by Volume Overload in Rats

BACKGROUND

This study investigated histopathological changes and apoptotic factors that may be involved in the renal damage caused by congestive heart failure in a rat model of infrarenal aortocaval fistula (ACF).

METHODS

Heart failure was induced using a modified approach of ACF in male Wistar rats. Sham-operated controls and ACF rats were characterized by their morphometric and hemodynamic parameters and investigated for their histopathological, ultrastructural, and apoptotic factor changes in the kidney.

RESULTS

ACF-induced heart failure is associated with histopathological signs of congestion and glomerular and tubular atrophy, as well as nuclear and cellular degeneration in the kidney. In parallel, overexpression of proapoptotic Bax protein, release of cytochrome C from the outer mitochondrial membrane into cell cytoplasm, and nuclear transfer of activated caspase 3 indicate apoptotic events. This was confirmed by electron microscopic findings of apoptotic signs in the kidney such as swollen mitochondria and degenerated nuclei in renal tubular cells.

CONCLUSIONS

This study provides morphological evidence of renal injury during heart failure which may be due to caspase-mediated apoptosis via overexpression of proapoptotic Bax protein, subsequent mitochondrial cytochrome C release, and final nuclear transfer of activated caspase 3, supporting the notion of a cardiorenal syndrome.

Pathogenesis of target organ damage in hypertension: role of mitochondrial oxidative stress

Hypertension causes target organ damage (TOD) that involves vasculature, heart, brain and kidneys. Complex biochemical, hormonal and hemodynamic mechanisms are involved in the pathogenesis of TOD. Common to all these processes is an increased bioavailability of reactive oxygen species (ROS). Both in vitro and in vivo studies explored the role of mitochondrial oxidative stress as a mechanism involved in the pathogenesis of TOD in hypertension, especially focusing on atherosclerosis, heart disease, renal failure, cerebrovascular disease. Both dysfunction of mitochondrial proteins, such as uncoupling protein-2 (UCP2), superoxide dismutase (SOD) 2, peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α), calcium channels, and the interaction between mitochondria and other sources of ROS, such as NADPH oxidase, play an important role in the development of endothelial dysfunction, cardiac hypertrophy, renal and cerebral damage in hypertension. Commonly used anti-hypertensive drugs have shown protective effects against mitochondrial-dependent oxidative stress. Notably, few mitochondrial proteins can be considered therapeutic targets on their own. In fact, antioxidant therapies specifically targeted at mitochondria represent promising strategies to reduce mitochondrial dysfunction and related hypertensive TOD. In the present article, we discuss the role of mitochondrial oxidative stress as a contributing factor to hypertensive TOD development. We also provide an overview of mitochondria-based treatment strategies that may reveal useful to prevent TOD and reduce its progression.

Bufalin induces G0/G1 phase arrest through inhibiting the levels of cyclin D, cyclin E, CDK2 and CDK4, and triggers apoptosis via mitochondrial signaling pathway in T24 human bladder cancer cells

Most of the chemotherapy treatments for bladder cancer aim to kill the cancer cells, but a high recurrence rate after medical treatments is still occurred. Bufalin from the skin and parotid venom glands of toad has been shown to induce apoptotic cell death in many types of cancer cell lines. However, there is no report addressing that bufalin induced cell death in human bladder cancer cells. The purpose of this study was investigated the mechanisms of bufalin-induced apoptosis in a human bladder cancer cell line (T24). We demonstrated the effects of bufalin on the cell growth and apoptosis in T24 cells by using DAPI/TUNEL double staining, a PI exclusion and flow cytometric analysis. The effects of bufalin on the production of reactive oxygen species (ROS), the level of mitochondrial membrane potential (ΔΨ(m)), and DNA content including sub-G1 (apoptosis) in T24 cells were also determined by flow cytometry. Western blot analysis was used to examine the expression of G(0)/G(1) phase-regulated and apoptosis-associated protein levels in bufalin-treated T24 cells. The results indicated that bufalin significantly decreased the percentage of viability, induced the G(0)/G(1) phase arrest and triggered apoptosis in T24 cells. The down-regulation of the protein levels for cyclin D, CDK4, cyclin E, CDK2, phospho-Rb, phospho-AKT and Bcl-2 with the simultaneous up-regulation of the cytochrome c, Apaf-1, AIF, caspase-3, -7 and -9 and Bax protein expressions and caspase activities were observed in T24 cells after bufalin treatment. Based on our results, bufalin induces apoptotic cell death in T24 cells through suppressing AKT activity and anti-apoptotic Bcl-2 protein as well as inducing pro-apoptotic Bax protein. The levels of caspase-3, -7 and -9 are also mediated apoptosis in bufalin-treated T24 cells. Therefore, bufalin might be used as a therapeutic agent for the treatment of human bladder cancer in the future.

Quercetin-mediated cell cycle arrest and apoptosis involving activation of a caspase cascade through the mitochondrial pathway in human breast cancer MCF-7 cells

Dietary polyphenols have been correlated with a reduced risk of developing cancer. Quercetin (a natural polyphenolic compound) induced apoptosis in many human cancer cell lines, including breast cancer MCF-7 cells. However, the involvement of possible signaling pathways and the roles of quercetin in apoptosis are still undefined. The purpose of this study was to investigate the effects of quercetin on the induction of the apoptotic pathway in human breast cancer MCF-7 cells. When MCF-7 cells were treated with quercetin for 24 and 48 h and at various doses (10-175 microM), cell viability decreased significantly in time- and dose-dependent manners. Exposure of MCF-7 cells to 10-175 microM quercetin resulted in an approximate 90.25% decrease in viable cells. To explicate the mechanism underlying the antiproliferative effect of quercetin, cell cycle distribution and apoptosis in MCF-7 cells was investigated after exposure to 150 microM quercetin for 6-48 h. Quercetin caused a remarkable increase in the number of S phase (14.56% to 61.35%) and sub-G1 phase cells (0.1% to 8.32%) in a dose- and time-dependent manner. Quercetin caused S phase arrest by decreasing the protein expression of CDK2, cyclins A and B while increasing the p53 and p57 proteins. Following incubation with quercetin for 48 h, MCF-7 cells showed apoptotic cell death by the decreased levels of Bcl-2 protein and DeltaPsi(m) and increased activations of caspase-6, -8 and -9. Moreover, quercetin increased the AIF protein released from mitochondria to nuclei and the GADD153 protein translocation from endoplasmic reticulum to the nuclei. These data suggested that quercetin may induce apoptosis by direct activation of the caspase cascade through the mitochondrial pathway in MCF-7 cells.

Synthetic/secreting and apoptotic phenotypes in renal biopsy tissues from hypertensive nephrosclerosis patients

The major glomerular abnormalities in hypertensive nephrosclerosis are described as glomerular obsolescence (GO), glomerulosclerosis (GS), and glomerular collapse (GC). However, glomerular cellular changes caused by hypertensive insults have not been well analyzed. Using an immunoenzyme method, we examined eleven biopsy samples from patients with hypertensive nephrosclerosis for two synthetic and secreting phenotypes, a-smooth muscle actin (alpha-SMA) and collagen type III (Col. III), and two apoptotic phenotypes, pro-apoptotic molecule Bax and anti-apoptotic molecule BcI-2. Together with the glomerular and vascular changes and interstitial fibrosis (IF) area, the results were scored quantitatively and semi-quantitatively and compared to the clinical findings, which included systolic blood pressure (SBP), mean arterial pressure (MAP), serum creatinine levels (sCr) and creatinine clearance (Ccr), using univariate and multivariate analyses. As a result, GS was frequently observed in the mild-to-moderate hypertensive group (140 < or = SBP<180 mmHg), whereas GC was positively correlated with SBP. Furthermore, there was a positive correlation of GS with mesangial alpha-SMA and Col. III, suggesting that GS was the reflection of these synthetic and secreting phenotypic changes in mesangial cells. Endothelial Bax was positively correlated with Ccr (p<0.01); in contrast, podocytic Bax was positively correlated with sCr (p<0.05) and showed a tendency to correlate with MAP (p=0.054). In conclusion, these findings support the view that mesangial synthetic and secreting phenotypic changes may be a reflection of cellular activation caused by mild-to-moderate hypertension and that apoptotic phenotypic expression in podocytes, rather than endothelial cells, may be related to the development of a severe form of hypertensive nephrosclerosis.

EGF receptor activity modulates apoptosis induced by inhibition of the proteasome of vascular smooth muscle cells

The observation that intracellular protein turnover rates participate directly in cell viability led to the development and clinical use of potent proteasome inhibitors. This study determined that the mechanism of apoptosis that is induced by inhibition of the proteasome of vascular smooth muscle cells (VSMC) was related to the intracellular accumulation of Bad, a BH3-only member of the Bcl-2 family of apoptosis regulators. Experiments confirmed that the apoptotic process was mitochondria- and caspase-dependent. Ubiquitination and accumulation of Bad in VSMC followed inhibition of the proteasome, and depletion of Bad using RNA interference prevented apoptosis that was induced by proteasome inhibition with PS-341. EGF receptor (EGFR) activation produced posttranslational modifications of Bad, providing the pro-survival signals that prevented apoptosis of smooth muscle cells during proteasome inhibition. Antagonists of the EGFR potentiated the apoptotic rate. In summary, the activities of the EGFR and the proteasome focused on Bad and the intrinsic apoptotic pathway and were involved integrally in determining viability of VSMC. These findings might prove useful in the management of diseases in which proliferation of vascular smooth muscle cells plays a central role.

Enhanced expression of EGF receptor in a model of salt-sensitive hypertension

Chronic kidney disease in the Dahl/Rapp salt-sensitive (S) rat is related to an arteriolopathic process that occurs following the onset of hypertension and involves vascular smooth muscle cell (VSMC) hyperplasia and luminal constriction. Because previous studies have shown that activation of the epidermal growth factor receptor (EGFR) produces a mitogenic stimulus in VSMC and the EGFR participates integrally in the vasoconstrictor responses of renal arterioles, the present study analyzed the expression of EGFR in these animals. Compared with Sprague-Dawley (SD) rats, renal cortical expression of EGFR was increased in both prehypertensive and hypertensive S rats. Immunohistochemistry using a polyclonal antibody to EGFR demonstrated that EGFR expression was prominent in the renal vasculature, particularly in the media of afferent and efferent arterioles and the aorta of S rats. When examined, primary cultures of VSMC from S rats showed increased expression of EGFR, compared with VSMC from SD and Dahl/Rapp salt-resistant rats. Following addition of EGF, autophosphorylation of the EGFR was enhanced in cells from S rats, as was the downstream signaling events that included activation of p42/44 MAPK and Akt pathways. Thus in vivo and in vitro studies demonstrated augmented expression and functional activity of the EGFR in S rats.

Mechanism of hypertensive nephropathy in the Dahl/Rapp rat: a primary disorder of vascular smooth muscle

The Dahl/Rapp salt-sensitive (S) rat is a model of salt-sensitive hypertension and hypertensive renal disease. This study explored the role of vascular remodeling in the development of renal failure in S rats. Groups of S and Sprague-Dawley rats were given 0.3 and 8.0% NaCl diets for up to 21 days and evidence of smooth muscle proliferation identified using immunohistochemistry that showed nuclear accumulation of proliferating cell nuclear antigen and 5-bromo-2′-deoxy-uridine. Compared with the other three groups, S rats on 8.0% NaCl diet showed increased nuclear labeling of cells of the aorta and arteries and arterioles of the kidney by the end of the first week of study. Progressive luminal narrowing of the interlobular arteries and preglomerular arterioles occurred in S rats over the 3 wk on the 8.0% NaCl diet. Accumulation of pimonidazole adducts and nuclear accumulation of hypoxia-inducible factor-1α (HIF-1α) were used as markers of tissue hypoxia. By the end of the second week of study, pimonidazole levels increased in S rats on 8.0% NaCl diet and deposition was apparent in tubular cells in the cortex and medulla. At the completion of the experiment, HIF-1α levels were increased in nuclear extracts from the cortex and medulla of S rats on this diet, compared with the other three groups of rats. The data demonstrated a disorder of the vascular remodeling process with proliferation of vascular smooth muscle cells temporally followed by development of tissue hypoxia in the hypertensive nephropathy of S rats on 8.0% NaCl diet.

Mitochondrial DNA mutations in focal segmental glomerulosclerosis lesions

Glomerular epithelial cells are primary pathogenic sites in focal segmental glomerulosclerosis (FGS) lesions. Glomerular epithelial cells are regarded as terminally differentiated cells that do not proliferate. These characteristics are also noted for neurons and muscular cells, which are major sites of mitochondrial DNA (mtDNA) mutation accumulation. Screening for mtDNA mutations was performed with renal biopsy specimens from patients with primary FGS and patients with IgA nephropathy (as subjects with secondary FGS and as control subjects). mtDNA extracted from kidney biopsy specimens was amplified with appropriate primer pairs for study of the mtDNA point mutations 3243A-->G, 3271T-->C, 8344A-->G, and 8993T-->G/C, as well as the common deletion (a 4977-bp deletion spanning mtDNA nucleotide pairs 8469 to 13447). In situ amplification of both total mtDNA and the common deletion was also performed. Two patients with FGS demonstrated the 3243A-->G point mutation; 12 patients with FGS and seven patients with IgA nephropathy accompanied by glomerulosclerotic lesions exhibited the common deletion in their kidney tissue. No patient demonstrated the mtDNA mutations 3271T-->C, 8344A-->G, or 8993T-->G/C. The degree of heteroplasmy for the 3243A-->G point mutation was >85%; however, the heteroplasmy for the common deletion was <1%. As determined with in situ PCR, normal mtDNA was mainly distributed in the tubular epithelium and mtDNA with the common deletion was mainly distributed among glomerular epithelial cells. In conclusion, it is suggested that mtDNA mutations are distributed in glomerular epithelial cells among some patients with primary FGS or secondary FGS with IgA nephropathy. These mutations may be related to glomerular epithelial cell damage.

Activation of the Fas/Fas ligand pathway in hypertensive renal disease in Dahl/Rapp rats

BACKGROUND

Hypertensive nephrosclerosis is the second most common cause of end-stage renal failure in the United States. The mechanism by which hypertension produces renal failure is incompletely understood. Recent evidence demonstrated that an unscheduled and inappropriate increase in apoptosis occurred in the Dahl/Rapp rat, an inbred strain of rat that uniformly develops hypertension and hypertensive nephrosclerosis; early correction of the hypertension prevents the renal injury. The present study examined the role of the Fas/FasL pathway in this process.

METHODS

Young male Dahl/Rapp salt-sensitive (S) and Sprague-Dawley rats were fed diets that contained 0.3% or 8.0% NaCl diets. Kidneys were examined at days 7 and 21 of the study.

RESULTS

An increase in Fas and FasL expression was observed in glomerular and tubular compartments of kidneys of hypertensive S rats, whereas dietary salt did not change expression of either of these molecules in normotensive Sprague-Dawley rats. Associated with this increase was cleavage of Bid and activation of caspase-8, the initiator caspase in this apoptotic pathway, by day 21 of the study.

CONCLUSIONS

Augmented expression of apoptotic signaling by the Fas/FasL pathway occurred during development of end-stage renal failure in this model of hypertensive nephrosclerosis.

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

BACKGROUND

Apoptosis of tubular and interstitial cells is well documented in kidneys with chronic obstructive uropathy (COU) and probably plays an important role in the pathogenesis of this condition. The molecular control of apoptosis in COU remains poorly understood. Apoptosis in general is known to proceed initially along distinct pathways, which later converge into a common arm characterized by orderly activation of caspases. Caspases are cytosolic enzymes that belong to a 12-member family and serve as effector molecules for apoptosis. The role of individual caspases in mediating renal cell apoptosis in kidneys with COU is studied.

METHODS

Kidneys were harvested from sham-operated mice and mice with COU created by left ureter ligation at days 4, 7, 15, 20, and 30. The following studies were performed: (1) determination of dried kidney weight; (2) in situ end labeling of fragmented DNA to detect apoptotic tubular and interstitial cells; (3) ribonuclease protection assay with specific anti-sense RNA probes for caspases 1, 2, 3, 6, 7, 8, 9, 11, and 12 to detect the expression of individual caspases; (4) immunostaining for caspases; and (5) assay for caspase 3. To assess the role of caspases in COU-associated renal cell apoptosis, the frequencies of apoptotic tubular and interstitial cells were separately quantitated for each experimental time point, and their patterns of variation were correlated with those of individual caspases.

RESULTS

The obstructed kidneys showed progressive tissue loss (60% of control at day 15). Apoptosis of both tubular and interstitial cells was seen in obstructed kidneys. Tubular cell apoptosis peaked at four days after ureter ligation (13-fold of control), remained high between days 4 to 15, and thereafter decreased rapidly. Apoptotic interstitial cells were scanty initially, but gradually increased throughout the entire experiment. Apoptosis was minimal throughout the experiment in control and contralateral kidneys. In control and contralateral kidneys, caspases 2, 3, 6, 7, 8, and 9 mRNAs were expressed at low levels, whereas those for caspases 1, 11, and 12 were not detected. The obstructed kidneys displayed increased expression of all tested caspases. Caspases 1, 11, and 12 mRNAs were detected in obstructed kidneys in a common pattern characterized by a sharp increase at day 4, followed by a decrease until day 20, and a subsequent sharp increase until the end of the study at day 30. A similar pattern was noted for other caspases (2, 3, 6, 7, 8, and 9), which maximally reached twofold to fourfold that of controls. Immunostaining for caspases 1, 2, 3, 6, 7, 8, and 9 showed the same pattern characterized by focal and weak expression in proximal tubules of control or contralateral kidney, contrasting with increased staining in atrophic or dilated tubules of obstructed kidneys. Interstitial cells also displayed staining for several caspases, which paralleled the increasing density of interstitial cells toward the end of the experiment. Caspase-3 assay showed a marked increased activity in obstructed kidneys that reached fourfold and sevenfold of control at days 4 and 30, respectively. The rise and fall of caspase mRNAs between days 4 and 30 paralleled a similar fluctuation in tubular cell apoptosis. The subsequent increase of mRNAs was correlated with a continuous rise of interstitial cell apoptosis.

CONCLUSIONS

Urinary obstruction in mice induces apoptosis of both tubular and interstitial cells in the affected kidney in a distinctive pattern that parallels an increased expression of caspases. This correlation suggests that these caspases mediate COU-associated renal cell apoptosis. Among the evaluated caspases, increased renal caspase 3 activity implies its central role in renal cell apoptosis associated with urinary obstruction.