Apoptosis in polycystic kidney disease: involvement of caspases

Molecular Mechanisms of Epigenetic Regulation, Inflammation, and Cell Death in ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder, which is caused by mutations in the PKD1 and PKD2 genes, characterizing by progressive growth of multiple cysts in the kidneys, eventually leading to end-stage kidney disease (ESKD) and requiring renal replacement therapy. In addition, studies indicate that disease progression is as a result of a combination of factors. Understanding the molecular mechanisms, therefore, should facilitate the development of precise therapeutic strategies for ADPKD treatment. The roles of epigenetic modulation, interstitial inflammation, and regulated cell death have recently become the focuses in ADPKD. Different epigenetic regulators, and the presence of inflammatory markers detectable even before cyst growth, have been linked to cyst progression. Moreover, the infiltration of inflammatory cells, such as macrophages and T cells, have been associated with cyst growth and deteriorating renal function in humans and PKD animal models. There is evidence supporting a direct role of the PKD gene mutations to the regulation of epigenetic mechanisms and inflammatory response in ADPKD. In addition, the role of regulated cell death, including apoptosis, autophagy and ferroptosis, have been investigated in ADPKD. However, there is no consensus whether cell death promotes or delays cyst growth in ADPKD. It is therefore necessary to develop an interactive picture between PKD gene mutations, the epigenome, inflammation, and cell death to understand why inherited PKD gene mutations in patients may result in the dysregulation of these processes that increase the progression of renal cyst formation.

The effects of intrinsic apoptosis on cystogenesis in PKD1-deficient ADPKD pig model

BACKGROUND

Apoptosis is a form of cell death that plays a critical role in the maintenance of tissue homeostasis involving the development and elimination of unwanted cells. Dysregulation of apoptosis appears to be associated in the pathogenesis of many human diseases. Autosomal dominant polycystic kidney disease (ADPKD) is a common monogenetic disease and is mainly caused by mutations in PKD1. Previous studies proved that increased cell death occurred in ADPKD patients and animal models. However, the role of apoptosis in kidney cystogenesis is not clear.

METHODS

In current study, due to the high similarities between human and pig, PKD1-deficient (PKD1^+/-) pigs and PKD1-knockdown (PKD1^KD) pig kidney epithelial cells were used to investigate the mechanisms of apoptosis in driving cystogenesis.

RESULTS

In PKD1^+/- pigs, increased intrinsic and extrinsic apoptosis were found at ages of 1 month and 3 months, whereas the autophagy and pyroptosis were not altered. Meanwhile, the intrinsic apoptosis was activated along with untouched extrinsic apoptosis in PKD1^KD pig kidney cells. Thus, the intrinsic apoptosis played important roles in cystogenesis.

CONCLUSIONS

This work provides detail analysis of the roles of different cell death types during cystogenesis in ADPKD pig model. The results suggested a potential new strategy for the diagnosis and treatment of ADPKD by targeting intrinsic apoptosis.

Apoptosis and autophagy in polycystic kidney disease (PKD)

Apoptosis in the cystic epithelium is observed in most rodent models of polycystic kidney disease (PKD) and in human autosomal dominant PKD (ADPKD). Apoptosis inhibition decreases cyst growth, whereas induction of apoptosis in the kidney of Bcl-2 deficient mice increases proliferation of the tubular epithelium and subsequent cyst formation. However, alternative evidence indicates that both induction of apoptosis as well as increased overall rates of apoptosis are associated with decreased cyst growth. Autophagic flux is suppressed in cell, zebra fish and mouse models of PKD and suppressed autophagy is known to be associated with increased apoptosis. There may be a link between apoptosis and autophagy in PKD. The mammalian target of rapamycin (mTOR), B-cell lymphoma 2 (Bcl-2) and caspase pathways that are known to be dysregulated in PKD, are also known to regulate both autophagy and apoptosis. Induction of autophagy in cell and zebrafish models of PKD results in suppression of apoptosis and reduced cyst growth supporting the hypothesis autophagy induction may have a therapeutic role in decreasing cyst growth, perhaps by decreasing apoptosis and proliferation in PKD. Future research is needed to evaluate the effects of direct autophagy inducers on apoptosis in rodent PKD models, as well as the cause and effect relationship between autophagy, apoptosis and cyst growth in PKD.

Anticystogenic activity of a small molecule PAK4 inhibitor may be a novel treatment for autosomal dominant polycystic kidney disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a common hereditary renal disease with no currently available targeted therapies. Based on the established connection between β-catenin signaling and renal ciliopathies, and on data from our and other laboratories showing striking similarities of this disease and cancer, we evaluated the use of an orally bioavailable small molecule, KPT-9274 (a dual inhibitor of the protein kinase PAK4 and nicotinamide phosphoribosyl transferase), for treatment of ADPKD. Treatment of PKD-derived cells with this compound not only reduces PAK4 steady-state protein levels and regulates β-catenin signaling, but also inhibits nicotinamide phosphoribosyl transferase, the rate-limiting enzyme in a key NAD salvage pathway. KPT-9274 can attenuate cellular proliferation and induce apoptosis associated with a decrease in active (phosphorylated) PAK4 and β-catenin in several Pkd1-null murine cell lines, with a less pronounced effect on the corresponding phenotypically normal cells. Additionally, KPT-9274 shows inhibition of cystogenesis in an ex vivo model of cyclic AMP-induced cystogenesis as well as in the early stage Pkd1^flox/flox:Pkhd1-Cre mouse model, the latter showing confirmation of specific anti-proliferative, apoptotic, and on-target effects. NAD biosynthetic attenuation by KPT-9274, while critical for highly proliferative cancer cells, does not appear to be important in the slower growing cystic epithelial cells during cystogenesis. KPT-9274 was not toxic in our ADPKD animal model or in other cancer models. Thus, this small molecule inhibitor could be evaluated in a clinical trial as a viable therapy of ADPKD.

Proliferation, apoptosis and expression of matrix metalloproteinase-9 in human fetal lung

Expression pattern of the Ki-67, caspase-3 and matrix metalloproteinases-9 (MMP-9) factors were immunohistochemically analyzed in 48 human fetal lungs from 12 to 40 weeks of gestation. The number of Ki-67 positive cells in the epithelium of canaliculare (88cells/mm(2)) and sacculare stage (93cells/mm(2)) were significantly higher than in the epithelium of pseudoglandular stage (12cells/mm(2)) (p=0.0008 vs. p=0.003). The number of Ki-67 positive cells in the mesenchyme of canaliculare stage (132cells/mm(2)) was significantly higher than in the mesenchyme of pseudoglandular stage (37cells/mm(2)) (p=0.001). The proliferation of mesenchymal cells was higher than the epithelial cells in all developmental stages, especially in the canaliculare stage (p=0.007). Similarly, the number of caspase-3 positive cells in the epithelium of canalicular stage (13cells/mm(2)) was significantly higher than in the epithelium of pseudoglandular stage (6cells/mm(2)) (p=0.002) with peaks in the conductive epithelium of canalicular stage. The number of caspase-3 positive cells in the mesenchyme of canaliculare stage (3cells/mm(2)) was significantly higher than in the mesenchyme of saccular stage (0cells/mm(2)) (p=0.05). There were no caspase-3 positive cells in the mesenchyme of pseudoglandular stage. However, unlike the Ki-67 expression, mesenchymal cells in comparison to epithelial cells express substantially less caspase-3 in all developmental stages. Up to the saccular stage, the expression of MMP-9 in mesenchymal cells showed a linear increase with most pronounced expression in that stage. The number of MMP-9 positive cells in the mesenchyme of canaliculare (20cells/mm(2)) and sacculare (39cells/mm(2)) stage were significantly higher than in the mesenchyme of pseudoglandular stage (12cells/mm(2)) (p=0.04 vs. p=0.004). The first epithelial cells that express MMP-9 were present only at the alveolar stage. Increased proliferation and apoptosis of the mesenchymal cells of canalicular stage is important for formation of definite structures within the stroma of the lung parenchyma. Although apoptosis in the epithelium is not pronounced as proliferation, it is important for thinning of the epithelium and consequent spread of respiratory tract. However in the saccular stage when mesenchyme disappears, MMP-9 expression is more important for primitive alveoli differentiation.

Decreased levels of proapoptotic factors and increased key regulators of mitochondrial biogenesis constitute new potential beneficial features of long-lived growth hormone receptor gene-disrupted mice

Decreased somatotrophic signaling is among the most important mechanisms associated with extended longevity. Mice homozygous for the targeted disruption of the growth hormone (GH) receptor gene (GH receptor knockout; GHRKO) are obese and dwarf, are characterized by a reduced weight and body size, undetectable levels of GH receptor, high concentration of serum GH, and greatly reduced plasma levels of insulin and insulin-like growth factor-I, and are remarkably long lived. Recent results suggest new features of GHRKO mice that may positively affect longevity-decreased levels of proapoptotic factors and increased levels of key regulators of mitochondrial biogenesis. The alterations in levels of the proapoptotic factors and key regulators of mitochondrial biogenesis were not further improved by two other potential life-extending interventions-calorie restriction and visceral fat removal. This may attribute the primary role to GH resistance in the regulation of apoptosis and mitochondrial biogenesis in GHRKO mice in terms of increased life span.

Comparative proteomic analysis suggests that mitochondria are involved in autosomal recessive polycystic kidney disease

Autosomal recessive polycystic kidney disease (ARPKD), characterized by ectatic collecting duct, is an infantile form of PKD occurring in 1 in 20 000 births. Despite having been studied for many years, little is known about the underlying mechanisms. In the current study, we employed, for the first time, a MS-based comparative proteomics approach to investigate the differently expressed proteins between kidney tissue samples of four ARPKD and five control individuals. Thirty two differently expressed proteins were identified and six of the identified protein encoding genes performed on an independent group (three ARPKD subjects, four control subjects) were verified by semi-quantitative RT-PCR, and part of them were further validated by Western blot and immunohistochemistry. Moreover, similar alteration tendency was detected after downregulation of PKHD1 by small interfering RNA in HEK293T cell. Interestingly, most of the identified proteins are associated with mitochondria. This implies that mitochondria may be implicated in ARPKD. Furthermore, the String software was utilized to investigate the biological association network, which is based on known and predicted protein interactions. In conclusion, our findings depicted a global understanding of ARPKD progression and provided a promising resource of targeting protein, and shed some light further investigation of ARPKD.

Cell proliferation and apoptosis in the fusion of human primary and secondary palates

The markers of cell proliferation (Ki-67) and apoptosis [caspase-3, TdT-mediated biotin-dUTP nick-end labelling (TUNEL)] and the expression of syndecan-1 and heat shock protein 70 (Hsp70) were analyzed immunohistochemically in 11 developing human palates, from developmental weeks 6 to 10. During fusion of the primary palate, the proportion of proliferating cells decreased from 42 to 32% and the proportion of apoptotic cells decreased from 11 to 7% in the medial-edge epithelium. At later stages, the proportions of both types of cells decreased in the ectomesenchyme, except for proliferating cells in its non-condensing part. At developmental weeks 9-10, the epithelial seam in the secondary palate comprised 28% proliferative cells and 5% apoptotic cells. While condensing ectomesenchyme contained more apoptotic cells than proliferating cells, the opposite was observed for the non-condensing ectomesenchyme. Co-expression of syndecan-1 and Hsp70 was detected in cells budding from the epithelial seam. Our study indicates similar principles for human primary palate and secondary palate fusion, and parallel persistence of proliferation and apoptotic activity. While proliferation enables growth and fusion of different palatal primordia, apoptosis results in the removal of of large numbers epithelial cells at the fusion point. The disintegration of seam remnants seems to be executed through the processes of change in protein content and cell migration, probably leading to cell death as their final outcome.

Deletion of growth hormone receptor gene but not visceral fat removal decreases expression of apoptosis-related genes in the kidney-potential mechanism of lifespan extension

Mice homozygous for the targeted disruption of the growth hormone (GH) receptor (Ghr) gene (GH receptor knockout; GHRKO; KO) are hypoinsulinemic, highly insulin sensitive, normoglycemic, and long-lived. Visceral fat removal (VFR) is a surgical intervention which improves insulin signaling in normal (N) mice and rats and extends longevity in rats. We have previously demonstrated decreased expression level of certain pro-apoptotic genes in skeletal muscles and suggested that this may contribute to the regulation of longevity in GHRKO mice. Alterations in apoptosis-related genes expression in the kidneys also may potentially lead to lifespan extension. In this context, we decided to examine the renal expression of the following genes: caspase-3, caspase-9, caspase-8, bax, bad, bcl-2, Smac/DIABLO, Apaf-1, p53, and cytochrome c1 (cyc1) in male GHRKO and N mice subjected to VFR or sham surgery, at approximately 6 months of age. The kidneys were collected 2 months after VFR. As a result, caspase-3, caspase-9, and bax expressions were decreased in KO mice as compared to N animals. Expressions of Smac/DIABLO, caspase-8, bcl-2, bad, and p53 did not differ between KOs and N mice. VFR did not change the expression of the examined genes in KO or N mice. In conclusion, endocrine abnormalities in GHRKO mice result in decreased expression of pro-apoptotic genes and VFR did not alter the examined genes expression in N and KO mice. These data are consistent with a model in which alterations of GH signaling and/or insulin sensitivity lead to increased lifespan mediated by decreased renal expression of pro-apoptotic genes.

Renal pro-apoptotic proteins are reduced by growth hormone resistance but not by visceral fat removal

Growth hormone (GH) receptor knockout (GHRKO) mice are highly insulin sensitive and long-lived. Surgical visceral fat removal (VFR) improves insulin signaling in normal mice and rats and extends longevity in rats. We have previously demonstrated decreased expression of certain pro-apoptotic genes in kidneys of GHRKO mice and suggested that this could contribute to the increased longevity of these animals. The aim of the present study was to examine the level of the following proteins: caspase-3, caspase-9, caspase-8, bax, bad, phospho-bad, bcl-2, Smac/DIABLO, Apaf-1, phospho-p53 (pp53) and cytochrome c in male GHRKO and normal (N) mice subjected to VFR or sham surgery, at approximately six months of age. The kidneys were collected two months after VFR. Caspase-3, caspase-8, bax, bad, Smac/DIABLO, Apaf-1 and pp53 levels were decreased in GHRKO mice as compared to N animals. VFR did not change the level of any of the examined proteins. The decreased renal levels of pro-apoptotic proteins could contribute to the extended life-span caused by targeted disruption of the GH receptor gene but are apparently not involved in mediating the effects of VFR.

Apoptosis in polycystic kidney disease

Apoptosis is the process of programmed cell death. It is a ubiquitous, controlled process consuming cellular energy and designed to avoid cytokine release despite activation of local immune cells, which clear the cell fragments. The process occurs during organ development and in maintenance of homeostasis. Abnormalities in any step of the apoptotic process are associated with autoimmune diseases and malignancies. Polycystic kidney disease (PKD) is the most common inherited kidney disease leading to end-stage renal disease (ESRD). Cyst formation requires multiple mechanisms and apoptosis is considered one of them. Abnormalities in apoptotic processes have been described in various murine and rodent models of PKD as well as in human PKD kidneys. The purpose of this review is to outline the role of apoptosis in progression of PKD as well as to describe the mechanisms involved. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Mammalian target of rapamycin and caspase inhibitors in polycystic kidney disease

One of the most important abnormalities of the tubular epithelial cells lining the cysts as well as noncystic tubular epithelium is a disturbance in the balance between tubular cell proliferation and apoptosis. Activation of the mammalian target of rapamycin signaling pathway results in increased cell proliferation. Recent studies suggested abnormalities of the mammalian target of rapamycin signaling pathway in polycystic kidney disease. Mammalian target of rapamycin inhibition with sirolimus or everolimus results in attenuation of cyst formation in rat and mouse models of polycystic kidney disease. Apoptosis is a pathologic feature of most models of polycystic kidney disease, including human polycystic kidneys. Caspases, the major mediators of apoptosis, are increased in polycystic kidney disease kidneys. Both in vitro and in vivo studies suggest that caspase or apoptosis inhibition attenuates cyst formation. This review focuses on mammalian target of rapamycin and apoptosis signaling pathways in polycystic kidney disease and the role of mammalian target of rapamycin inhibitors and apoptosis inhibitors as potential therapies to reduce cyst formation.

Role of mitotic, pro-apoptotic and anti-apoptotic factors in human kidney development

The expression pattern of mitotic Ki-67 and anti-apoptotic bcl-2 proteins, as well as apoptotic caspase-3 and p53 proteins, were investigated in the human mesonephros and metanephros of 5-9 week-old human conceptuses. Apoptotic cells were additionally detected using the terminal deoxynucleotidyl transferase (TdT) nick-end labelling (TUNEL) method. Between the 5th and 7th developmental weeks Ki-67, caspase-3 and TUNEL-positive cells characterized all mesonephric structures, indicating importance of cell proliferation in the growth of the mesonephros and role of apoptosis in nephrogenesis. From the 7th week on, p53 and bcl-2 positive cells appeared in the mesonephros as well. Regressive changes in the mesonephros could be regulated by activation of p53, while bcl-2 could contribute to selective survival of some tubules giving rise to adult structures. In the early human metanephros (5-7 weeks), Ki-67 positive cells characterized all metanephric structures, indicating a role of cell proliferation in branching of the ureteric bud and in nephron formation. During the same period bcl-2, caspase-3 and TUNEL-positive cells were found only in the metanephric mesenchyme and nephrons. Bcl-2 protein probably protected nephrons from apoptosis, while caspase-3 protein controlled cell death in the mesenchyme. At later stages (7-9-weeks), appearance of p53-expressing cells could participate in further morphogenesis of the metanephric collecting system. The factors investigated had a spatially and temporally restricted pattern of appearance in developing kidneys. Changes in that pattern might lead to serious disturbances of kidney formation and function in early childhood.

Peripheral CD4 T-Cell Depletion Is Not Sufficient to Prevent Ischemic Acute Renal Failure

BACKGROUND

Ischemia reperfusion injury leading to acute renal failure (ARF) and delayed graft function is an important problem in organ transplantation. CD4+ T cells, essential for transplant rejection, may mediate ischemic ARF. We have demonstrated that the caspase-1 mediated production of IL-18 is pathogenic in ischemic ARF in mice. A potential source of IL-18 in ischemic ARF is the CD4+ T cell. We therefore examined the effect CD4+ T cell depletion on the development of ischemic ARF and the activation of IL-18.

METHODS

Functional and histological correlates were examined in two groups of mice with ischemic ARF: 1) CD4 T-cell depleted with the antibody GK1.5, and 2) T-cell receptor alpha-chain deficient (TCRalpha -/-) mice. TCRalpha -/- mice lack the alpha chain of the T-cell receptor and therefore lack functional CD4+ and CD8+ T cells.

RESULTS

Flow cytometry of lymph nodes and immunohistochemistry of kidneys demonstrated complete depletion of CD4+ T cells in mice with ischemic ARF treated with GK 1.5. CD4+ T-cell depletion did not confer functional (serum creatinine, BUN and FITC-labeled inulin clearance) or histological protection against ischemic ARF. Likewise, TCRalpha -/- mice were not protected against ischemic ARF. Renal caspase-1 activity and IL-18 protein were similar in CD4+ T-cell depleted and wild-type postischemic reperfusion.

CONCLUSIONS

Ischemic ARF can occur in the absence of classical T-cell function. The evaluation of other inflammatory mediators (e.g., macrophages or NK cells) as a source of IL-18 and mediator of ischemic ARF warrants further investigation.

Altered ATP-sensitive P2 receptor subtype expression in the Han:SPRD cy/+ rat, a model of autosomal dominant polycystic kidney disease

The effects of extracellular ATP on fluid secretion and reabsorption by renal epithelial cells, as well as its known effects on cell proliferation and death, are potentially important contributory factors in the development and growth of renal cysts. In this study, we have investigated the protein and mRNA expression of several P2Y receptor subtypes (P2Y(1,2,4,6)), as well as the P2X(5) and P2X(7) receptors, in kidney tissue from the Han:SPRD (cy/+) rat model of polycystic kidney disease. All of the P2Y receptors tested for, and the P2X(5) and P2X(7) subtypes, were located on the cyst-lining cells of Han:SPRD (cy/+) rat polycystic kidneys; most immunostaining was cytosolic and we could not confidently localize it to one or other membrane. However, the staining pattern for P2Y(6) was uniquely granular when compared with the other P2 receptors. P2Y(2) and P2Y(6) receptor mRNA was increased in both homozygote (cy/cy) and heterozygote (cy/+) rat kidneys when compared with unaffected littermates. The protein levels of P2Y(2) and P2Y(6) receptors were also increased, being undetectable or at a low level, respectively, in control tissue. Finally, P2X(7) receptor mRNA was increased in cy/+, but not in cy/cy rat kidneys. Our results show that a number of P2Y receptor subtypes, as well as the P2X(5) and P2X(7) receptors, are clearly expressed in cyst-lining cells in the Han:SPRD (cy/+) rat model of renal cystic disease. Furthermore, P2Y(2) and P2Y(6) receptor mRNA and protein levels are markedly increased in cystic rat kidneys compared with normal rats of the same genetic background. Thus, the most consistent findings were an increase in the expression of P2Y(2), P2Y(6) and P2X(7) receptors in cystic tissue. Given the widely reported effects of stimulating these P2 receptor subtypes in epithelial and other renal cells, they could contribute to the development and growth of renal cysts: extracellular ATP and its products 'trapped' in cyst fluid may activate P2 receptors expressed by cyst-lining cells, causing cyst expansion from increased fluid secretion and/or reduced reabsorption, as well as an increase in cell turnover (re-modeling).

Caspase-1-deficient mice are protected against cisplatin-induced apoptosis and acute tubular necrosis

BACKGROUND

Cisplatin is a commonly used chemotherapeutic agent which causes apoptosis or necrosis of renal tubular epithelial cells in vitro. Caspases are a family of cysteine proteases that mediate apoptosis (caspase-3) and inflammation (caspase-1). Although well studied in vitro, caspases have not been previously studied in cisplatin-induced acute renal failure (ARF) in vivo.

METHODS

Cisplatin (30 mg/kg) was injected intraperitoneally into wild-type and caspase-1-deficient (-/-) C57BL/6 mice. Serum creatinine and blood urea nitrogen (BUN), and renal caspase-1, -3, -8 and -9 activity were measured on days 1, 2, and 3 after cisplatin injection. Kidneys were examined for acute tubular necrosis (ATN), neutrophils, and apoptosis on days 1, 2, and 3.

RESULTS

After cisplatin injection, serum creatinine and BUN were normal on day 1, began to increase on day 2, and peaked on day 3. Similarly, ATN scores and neutrophil counts peaked on day 3. In contrast, renal apoptosis significantly increased on day 2. Renal dysfunction, apoptosis, ATN scores and neutrophil infiltration were all reduced in the caspase-1(-/-) mice. In wild-type mice, caspase-1 and -3 activity increased on days 2 and 3. Caspase-3 activity was reduced by approximately 50% in caspase-1(-/-) mice; active caspase-3 detected by immunoblot was also reduced in caspase-1(-/-) mice. In vitro, addition of recombinant caspases to kidney cytosolic extracts determined that caspase-1 activates caspase-3 in renal tissue.

CONCLUSION

These results indicate that caspase-1 contributes to cisplatin-induced ARF and ATN (day 3). Furthermore, caspase-1 affects caspase-3 activation and apoptosis in cisplatin-induced ARF (day 2).

Activation of the MEK5/ERK5 cascade is responsible for biliary dysgenesis in a rat model of Caroli's disease

Polycystic kidney (PCK) rats exhibit a multiorgan cyst pathology similar to human autosomal recessive polycystic kidney disease, and are proposed as an animal model of Caroli's disease with congenital hepatic fibrosis (CHF). This study investigated the expression and function of selected components of the mitogen activated protein kinase (MAPK) pathway in cultured intrahepatic biliary epithelial cells (BECs) of PCK rats. Compared to the proliferative activity of cultured BECs of control rats, those of the PCK rats were hyperresponsive to epidermal growth factor (EGF). The increase in BEC proliferation was accompanied by overexpression of MAPK/extracellular signal-regulated protein kinase (ERK) kinase 5 (MEK5), and subsequent phosphorylation of ERK5 in vitro. The increased proliferative activity was significantly inhibited by the transfection of short interfering RNA against MEK5 mRNA. An EGF receptor tyrosine kinase inhibitor, gefitinib ("Iressa", ZD1839), also significantly inhibited the abnormal growth of cultured BECs of PCK rats. By contrast, treatment with PD98059 and U0126, inhibitors for MEK1/2, was less effective. These results suggest that the activation of the MEK5-ERK5 cascade plays a pivotal role in the biliary dysgenesis of PCK rats, and also provide insights into the pathogenesis of Caroli's disease with CHF. As the MEK5-ERK5 interaction is highly specific, it may represent a potential target of therapy.

Pathways of caspase-mediated apoptosis in autosomal-dominant polycystic kidney disease (ADPKD)

BACKGROUND

We have recently demonstrated an increase in apoptosis in Han:SPRD rat kidneys with autosomal-dominant polycystic kidney disease (ADPKD). Caspase-3 and caspase-7 are major mediators of apoptosis. There are two pathways of caspase-3 and caspase-7-mediated apoptosis: (1) the "extrinsic" pathway involving the death receptor Fas, Fas ligand (FasL), and caspase-8 and (2) the "mitochondrial" or "intrinsic" pathway involving Bcl-2 proteins, caspase-2, cytochrome c release, and caspase-9. The aim of the present study was to investigate the pathways of apoptosis in 3-week-old Han:SPRD rats with ADPKD.

METHODS

Fluorescent substrates were used to measure caspase activity. mRNA and protein was determined by ribonuclease protection assays and immunoblotting, respectively. The effect of caspase inhibitors on caspase activity in polycystic kidneys was determined.

RESULTS

Caspase-3 and caspase-7 activity was more than 100% increased in homozygous (Cy/Cy) compared to heterozygous (Cy/+) and normal littermate control (+/+) kidneys. Ribonuclease protection assays demonstrated no difference in caspase-3 mRNA. On immunoblotting, there was an increase in the proform of caspase-3 and caspase-7 in Cy/Cy compared to +/+ and Cy/+ kidneys. Caspase-8 and caspase-9 activity was more than 100% increased in Cy/Cy compared to Cy/+ and +/+ kidneys. On immunoblotting, there was an increase of the proform of both caspase-8 and caspase-9 in Cy/Cy kidneys. There was also an increase in cytochrome c release into the cytosol and an increase in caspase-2 protein and activity in Cy/Cy kidneys. On ribonuclease protection assay there was no difference in FasL mRNA between +/+, Cy/+, and Cy/Cy kidneys. Short-term treatment of Cy/Cy rats with the caspase inhibitor IDN-8050 resulted in inhibition of caspase-3 and caspase-7 activity in the kidney.

CONCLUSION

In Cy/Cy kidneys with ADPKD, there was an increase of the proform of caspase-9, an increase in cytochrome c release into the cytosol, and an increase in caspase-2 protein and activity demonstrating involvement of the intrinsic pathway. There was an increase in the proform of caspase-8 demonstrating involvement of the extrinsic pathway. No differences in FasL mRNA were seen suggesting that the extrinsic pathway is independent of the death receptor ligand, FasL.

The P2X7 ATP receptor modulates renal cyst development in vitro

P2X(7), a purinergic receptor, is expressed in renal collecting ducts as they undergo fulminant cystogenesis in the cpk/cpk mouse model of autosomal recessive polycystic kidney disease (ARPKD). Dissociated cpk/cpk kidneys generate cysts from cell aggregates within 24h of suspension culture and we demonstrate that BzATP, a P2X(7) agonist, reduces cystogenesis. This effect is P2X(7)-specific, because: (i) equimolar concentrations of other purinergic agonists, ATP and UTP, had lesser effects and (ii) the P2X(7) inhibitor, oxidized ATP, abrogated the BzATP-mediated reduction in cystogenesis. BzATP did not significantly affect total cell number, proliferation, LDH release or caspase 3 activity, and zVAD-fmk, a caspase blocker, failed to modulate BzATP effects. In addition, this P2X(7) agonist did not significantly alter cyst size, probably excluding altered vectorial transport. In vivo, ATP was detected in cyst fluid from cpk/cpk kidneys; moreover, P2X(7) protein was also upregulated in human fetal ARPKD epithelia versus normal fetal collecting ducts. Thus, ATP may inhibit pathological renal cyst growth through P2X(7) signaling.

orpkmouse model of polycystic kidney disease reveals essential role of primary cilia in pancreatic tissue organization

Polycystic kidney disease (PKD) includes a group of disorders that are characterized by the presence of cysts in the kidney and other organs,including the pancreas. Here we show that in orpk mice, a model system for PKD that harbors a mutation in the gene that encodes the polaris protein, pancreatic defects start to occur at the end of gestation, with an initial expansion of the developing pancreatic ducts. Ductal dilation continues rapidly after birth and results in the formation of large,interconnected cysts. Expansion of pancreatic ducts is accompanied by apoptosis of neighboring acinar cells, whereas endocrine cell differentiation and islet formation appears to be unaffected. Polaris has been shown to co-localize with primary cilia, and these structures have been implicated in the formation of renal cysts. In the orpk pancreas, cilia numbers are reduced and cilia length is decreased. Expression of polycystin-2, a protein involved in PKD, is mislocalized in orpk mice. Furthermore, the cellular localization of β-catenin, a protein involved in cell adhesion and Wnt signaling, is altered. Thus, polaris and primary cilia function are required for the maturation and maintenance of proper tissue organization in the pancreas.

Organic solvent-induced proximal tubular cell apoptosis via caspase-9 activation

Long-term exposure to solvents is associated with apoptosis, which is implicated in the development and progression of tubulo-interstitial fibrosis and chronic renal failure. In our previous study, we demonstrated that toluene and p-xylene as the most commonly used organic solvents induced proximal tubular cells apoptosis. This study was conducted to assess the apoptotic pathway of toluene and p-xylene induced proximal tubular apoptosis. This was assessed by measuring the caspase-9 activity LLC-PK1 cells exposed to both compounds. A model of proximal tubular cell (LLC-PK1) cytotoxicity exposed to 1mM of either p-xylene or toluene was compared to untreated control for caspase-9 activity and Bax/Bcl-2 protein level. Furthermore, DNA fragmentation in the presence of caspase-9 inhibitor (Z-LEHD-FMK) in a dose-dependent manner was assessed. Both compounds induced caspase-9 activity, which was accompanied by up-regulation of Bax, whereas Bcl-2 level did not change. DNA fragmentation induced by both solvents was inhibited by caspase-9 inhibitor in dose-dependent manner. This data suggest that p-xylene or toluene induces nephrotoxicity via mitochondrial caspase-9 pathway. This mechanism involves up-regulation of the apoptotic protein, Bax.

Perinatal development of the rat kidney: apoptosis and epidermal growth factor

Localization of apoptotic cells in the kidney of perinatal rats was examined by the terminal deoxynucleotidyl transferase-mediated d-UTP-biotin nick end labeling (TUNEL) method and electron microscopy. Perinatal changes in the percentage of kidney cells with DNA fragmentation were determined by flow cytometric analysis. Through observation of two successive sections, the relationship between the localization of the epidermal growth factor receptor (EGFR) positive cells and TUNEL positive cells in the kidney was determined. From fetal day 18 to neonatal day 5, TUNEL positive cells were noted in immature glomeruli, collecting ducts and interstitium. Electron microscopically, chromatin condensed nuclei and apoptotic bodies were seen in the same tissue component as the TUNEL positive cells. The percentage of DNA fragmented cells significantly increased from fetal days 18 to 20 and significantly decreased from fetal days 20 to 22, while they still remained low in the neonatal period. The TUNEL positive cells in immature glomeruli and collecting ducts were not reactive to the EGFR antibody. The TUNEL positive cells were not observed in the proximal tubular cells, which were positive to EGFR antibody. These results indicate that apoptotic cells are present in the kidney throughout the perinatal period in the rat and that EGF plays an important role in perinatal development of the rat kidney.

Caspase inhibitors as anti-inflammatory and antiapoptotic agents

The striking efficacy of Z-VAD-fmk in the various animal models presented above may reflect its ability to inhibit multiple enzymes including caspases. In accord with this, more selective, reversible inhibitors usually show low efficacy in multifactorial models such as ischaemia, but may offer some protection against NMDA-induced excitotoxicity and hepatitis. Importantly, caspase inhibitors may exhibit significant activity in vivo even when they are applied post insult. As far as the CNS is concerned, the first systemically active inhibitors have emerged. Functional recovery could be achieved in some ischaemia models, but long-term protection by caspase inhibitors is still being questioned. Recent developments in drug design enabled the first caspase inhibitors to enter the clinic. Although initially directed towards peripheral indications such as rheumatoid arthritis, caspase inhibitors will no doubt eventually be used to target CNS disorders. For this purpose the peptidic character of current inhibitors will have to be further reduced. Small molecule, nonpeptidic caspase inhibitors, which have appeared recently, indicate that this goal can be accomplished. Unfortunately, many fundamental questions still remain to be addressed. In particular, the necessary spectrum of inhibitory activity required to achieve the desired effect needs to be determined. There is also a safety aspect associated with prolonged administration. Therefore, the next therapeutic areas for broader-range caspase inhibitors are likely to involve acute treatment. Recent results with synergistic effects between MK-801 and caspase inhibitors in ischaemia suggest that caspase inhibitors may need to be used in conjunction with other drugs. It can be expected that, in the near future, research on caspases and their inhibitors will remain a rapidly developing area of biology and medicinal chemistry. More time, however, may be needed for the first caspase inhibitors to appear on the market.

Multiorgan mRNA misexpression in murine autosomal recessive polycystic kidney disease

BACKGROUND

BALB/c mice homozygous for the cpk mutation develop a form of polycystic kidney disease (PKD) with multiorgan pathology similar to human autosomal recessive PKD. Messenger RNA expression in multiple affected organs was analyzed to determine if common gene cascades were misexpressed in the cystic kidney and extrarenal sites of disease. In cystic kidneys, misexpressed mRNAs were found in one of four general groups: proliferation/cell growth, apoptosis, differentiation or extracellular matrix.

METHODS

RNA was isolated from kidney, liver and pancreas of cystic and normal BALB/c-cpk mice. Using Northern blot hybridization and ribonuclease protection assays (RPA), the expression of several genes thought to be associated with PKD, namely c-myc, epidermal growth factor receptor (EGF-R) and PKD-1, were evaluated. RPAs were used to assess mRNA expression of cyclins and members of the bax/bcl-2 family. In addition, kidney, liver and pancreas were immunostained for c-Myc and PCNA.

RESULTS

Cystic kidney, liver and pancreas all exhibited similar patterns of mRNA misexpression of c-myc, EGF-R and PKD-1. In addition, a number of cell proliferation and apoptosis-related mRNAs also were elevated in cystic kidney and pancreas. Renal epithelial cells expressing proliferation-associated proteins [c-Myc and proliferating cell nuclear antigen (PCNA)] were nearly absent in normal kidney; however, cells of cystic and non-cystic renal tubules plus liver and pancreatic cyst exhibited an increased number of nuclei labeled with antibodies to these proteins.

CONCLUSIONS

These data suggest that similar pathologic mechanisms (including the expression of c-myc, EGF-R, PKD-1, cyclin, and bax/bcl-2 family mRNAs) may be responsible for the development of cystic changes in kidney, liver and pancreas in murine autosomal recessive PKD. Treatments targeting these similarly misexpressed mRNAs may be efficacious in ameliorating the cystic pathology in the kidney as well as the other affected organs in ARPKD.

Caspases, Bcl-2 proteins and apoptosis in autosomal-dominant polycystic kidney disease

BACKGROUND

Apoptosis is a characteristic feature of human autosomal-dominant polycystic kidney disease (ADPKD). The Han:Sprague-Dawley (SPRD) rat model closely resembles human ADPKD and presents an opportunity to investigate the apoptotic pathway in the pathogenesis of this disease.

METHODS

Han:SPRD rats were studied during the early stages of ADPKD (newborn, 2 and 6 weeks old). Apoptotic cells were detected by the TUNEL (Tdt-mediated dUTP nick end-labeling) assay. Caspase-3 activity was measured using the fluorescent substrate DEVD-AMC and cleavage of poly (ADP-ribose) polymerase [PARP]. Expression of pro- and anti-apoptotic B-cell lymphoma (Bcl-2) proteins was detected on Western blot analysis.

RESULTS

TUNEL (+) cells, caspase-3 activity and caspase-mediated PARP breakdown were significantly increased in 2-week-old heterozygous (Cy/+) and homozygous (Cy/Cy) rat kidneys compared to normal littermate controls. In Cy/+ rat kidneys, decreased expression of anti-apoptotic Bcl-XL coincided with increased caspase-3 activity at 2 weeks of age while expression of Bcl-2, another anti-apoptotic protein, increased at 6 weeks of age. In Cy/Cy rat kidneys, decreased expression of Bcl-XL and increased expression of Bcl-2 was present at 2 weeks of age. Pro-apoptotic Bax and Bad expression was unchanged at 2 weeks of age in both Cy/+ and Cy/Cy rat kidneys.

CONCLUSIONS

Activation of caspase-3 and dysregulation of the balance between pro- and anti-apoptotic Bcl-2 family members, specifically a down-regulation of anti-apoptotic Bcl-XL, correlates with increased apoptosis in polycystic Han:SPRD rat kidneys.