ToxSci Advance Access originally published online on January 18, 2006
Toxicological Sciences 2006 90(2):392-399; doi:10.1093/toxsci/kfj106
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Single and Combination Toxic Metal Exposures Induce Apoptosis in Cultured Murine Podocytes Exclusively via the Extrinsic Caspase 8 Pathway
* Pediatric Nephrology Division, C. S. Mott Children's Hospital, University of Michigan, Ann Arbor, Michigan 48109, and Division of Nephrology & Hypertension, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, Ohio 45229-3039
1 To whom correspondence should be addressed at Pediatric Nephrology Division, University of Michigan, 8220 MSRB III, Box 0646, 1150 W. Medical Center Drive, Ann Arbor, MI 48109. Fax: (734) 615-6595. E-mail: wsmoyer{at}med.umich.edu.
Received November 16, 2005; accepted January 10, 2006
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Arsenite, cadmium, and mercury are among the most abundant toxic metals (TM) in the environment. Although the most common renal manifestation of TM toxicity is proximal tubular dysfunction, significant glomerular injury can also occur. We hypothesized that glomerular injury following TM exposure results from TM-induced apoptosis of podocytes. To test this hypothesis we examined the extent of apoptosis and the apoptotic pathways induced in cultured murine podocytes incubated for three days with arsenite, cadmium, or mercury, and with equimolar combinations of all three metals. Apoptosis was detected by DNA laddering, and the number of apoptotic nuclei determined by Tunel assay. Treatment for three days with each TM resulted in DNA laddering and induced a dose-dependent increase in apoptotic nuclei. In contrast, treatment with equimolar combinations of TM induced significantly fewer apoptotic nuclei than individual TM treatments. Apoptosis induced by each TM was associated with a significant (
400%) increase in caspase 8 activity, but no change in caspase 9 activity, and Western analyses revealed a marked up-regulation of Fas (500%) and FADD (300%) with no change in expression of Bax, Bcl-2, or Bcl-xL. Similar to the apoptotic response, combinations of TM induced less caspase 8 activity and Fas/FADD expression than individual TM treatments. Collectively, these results demonstrate that (1) TM induced apoptosis in cultured murine podocytes via the extrinsic Fas-FADD caspase 8 pathway, rather than the mitochondrial apoptotic pathway, and (2) combination TM exposure induced less apoptosis than individual TM, indicating an antagonistic rather than an additive or synergistic toxicity. Key Words: apoptotic pathway; cadmium; mercury; arsenite.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The most common toxic metals (TM) known to induce renal disease through prolonged occupational or environmental exposure include cadmium (Cd), mercury (Hg), and the metalloid arsenite (As) (Madden and Fowler, 2000
). Environmental TM accumulate primarily in the liver and kidneys (Kim et al., 2003), with their toxic effects dependent on exposure levels. Acute exposures to large amounts of TM are generally characterized by renal tubular necrosis, while lower exposures have demonstrated that TM exposure induces programmed cell death (apoptosis) in renal tubular cells (Erfurt et al., 2003). Although less widely appreciated than renal tubular injury, chronic TM exposure has been found to cause high molecular weight proteinuria (Hoedemaeker et al., 1988), a hallmark of injury to the glomerular filtration barrier. In addition, a recent assessment of the nephrotoxic effects of low environmental cadmium exposure found significant adverse effects on glomerular as well as tubular function (Akesson et al., 2005). The filtration barrier is comprised of an inner glomerular endothelial cell layer surrounded by a glomerular basement membrane upon which the distal foot processes of visceral epithelial cells (podocytes) interdigitate and are connected to processes on adjacent podocytes via a slit membrane.
The characteristic features of apoptosis include membrane blebbing, cell shrinkage, nuclear condensation, and internucleosomal DNA fragmentation, and have been observed in many renal diseases in which the severity of renal injury was below the threshold for the development of necrosis (Ueda et al., 1996). Two primary apoptotic pathways exist within the cell, the extrinsic and intrinsic pathways. Extrinsic apoptosis is mediated by plasma membrane receptors (Fas or TNF), while intrinsic apoptosis is associated with organelles (primarily the mitochondria) and initiated intracellularly (Pulido and Parrish, 2003). The activation of these pathways has been shown to depend on both the cell type and the type of initiating factor, with TM-induced apoptosis assumed to by initiated primarily through the mitochondria (intrinsic pathway) by the formation of reactive oxygen species (Chen et al., 2001).
Although the toxicity of these metals has been examined individually, environmental exposure is typically long-term and involves simultaneous or sequential exposure to multiple toxins, with unknown interactions occurring among them and their cellular mechanisms (Fowler and Mahaffey, 1978; Madden and Fowler, 2000; Mahaffey and Fowler, 1977). In addition to the paucity of information about TM-induced glomerular injury, even less is understood about the toxic effects of the arguably more clinically relevant scenario of exposure to combinations of TM. We therefore hypothesized that prolonged TM exposure would induce glomerular injury via induction of apoptosis in glomerular podocytes. We further hypothesized that prolonged exposure to combinations of TM would induce toxic effects on podocytes that were not simply additive, but either synergistic or antagonistic. To begin to test these hypotheses, we designed a series of experiments to examine both the extent of induction of apoptosis and the apoptotic pathways activated in cultured murine podocytes following prolonged exposure to several common environmental TM.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Cell culture and TM treatment.
A conditionally immortalized mouse podocyte clonal cell line (MPC-5) isolated from the ‘Immortomouse’ (Mundel et al., 1997
) was used for all experiments, and cells were cultured and induced to differentiate as previously described (Smoyer and Ransom, 2002). Toxic metal treatments were performed by addition of 3 µl of 10, 20, or 40 mM aqueous solutions of HgCl2, CdCl2, or NaAsO2 (Sigma-Aldrich, St. Louis, MO) to fresh culture medium, which were then added to podocyte cultures and incubated for three days under normal culture conditions. Combination TM treatments consisted of equimolar mixtures of all three TM (e.g., 20 µM combination treatment contained 6.7 µM of each TM salt).
DNA laddering assays.
DNA laddering assays were performed for the detection of apoptosis, as previously described (Erkan et al., 2001; Park et al., 2002). Briefly, cells were resuspended in lysis buffer (1% SDS, 25 mM EDTA, 1 mg/ml proteinase K, pH 8) at 50°C overnight, digested with ribonuclease A (10 mg/ml), and the chromosomal DNA extracted and separated by agarose gel electrophoresis.
Tunel assays.
Terminal deoxynucleotidedyl transferase (Tunel) assays (ApoAlert Assay Kit; BD Biosciences Clontech, San Jose, CA) were performed as previously described (Erkan et al., 2001; Park et al., 2002). Briefly, cells grown on cover slips were fixed with 4% formaldehyde for 30 min at 4°C, permeabilized with 0.2% Triton X-100 for 15 min at 4°C, incubated with a mixture of nucleotides and TdT enzyme for 60 min at 37°C in a dark humidified chamber, the reaction terminated with 2X SSC, and the cover slips mounted on glass slides. Apoptotic nuclei were detected by fluorescence microscopy, and only cells that displayed the characteristic morphology of apoptosis, including nuclear fragmentation, nuclear condensation, and intensely fluorescent nuclei were counted as apoptotic. Cells that were merely Tunel-positive, in the absence of these morphologic criteria, were not considered apoptotic. A total of 100 cells were counted for each sample. Results were expressed as Tunel positive nuclei as a percentage of all nuclei visualized by phase contrast microscopy.
Caspase assays.
Caspase 8 and caspase 9 activity assays were performed as previously described (Erkan et al., 2001; Park et al., 2002) using the ApoAlert Caspase 8 Colorimetric Assay and the Caspase 9 Fluorescent assay kits (both from Clontech), respectively. Equal numbers of control or treated cells were incubated in cell lysis buffer for 10 min, centrifuged, the supernatants incubated in reaction buffer containing IETD-AFC (a specific substrate for caspase 8) or LEHD-AMC (a specific substrate for caspase 9) at 37°C for 1 h. The activities were assayed by absorption measurements at 405 nm for caspase 8 or by measuring fluorescence at 460 nm after excitation at 380 nm for caspase 9 according to the manufacturer's protocols.
Western blotting analyses.
Protein concentrations for all samples were determined by the Bradford assay (Bio-Rad, Hercules, CA) and equal amounts of protein were loaded in each lane. A monoclonal antibody to 
-tubulin (Sigma) was used at 1:10,000 dilution for confirmation of equal protein loading among samples. Other primary antibodies used included murine antibodies against Fas, FADD, Bcl-2, Bcl-xL and Bax (BD-Transduction Laboratories, Lexington, KY) used at 1:1000 (anti-Fas), 1:100 (anti-FADD), or 1:500 (all others) dilutions. Goat anti-mouse IgG secondary antibodies conjugated to horseradish peroxidase (Jackson ImmunoResearch, West Grove, PA) were used at 1:10,000 dilution. Antibody binding was visualized by enhanced chemiluminescence (Amersham, Arlington Heights, IL). Densitometric analyses of the resulting Fas and Fadd bands from all samples were performed, and the results expressed as percentages of control values.
Statistics.
Results were analyzed for statistically significant differences using Statview v. 4.57 software (Abacus Concepts, Berkeley, CA) by unpaired, two-tailed t-tests. Comparisons with R values < 0.05 were considered significant, and R values < 0.01 were separately noted.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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TM Treatments Induce Podocyte DNA Fragmentation
DNA laddering caused by internucleosomal DNA fragmentation was observed in separations of DNA extracted from cultured podocytes treated for three days with 10 µM or 20 µM cadmium, mercury, or arsenite (Fig. 1). The characteristic 180-bp laddering pattern was observed in each of two separate experiments with TM-treated cells. In contrast, DNA laddering was undetectable in control cells (Fig. 1). The internucleosomal DNA fragmentation observed in TM-treated cells is known to be a specific morphological change that occurs during the induction of apoptosis. No significant smearing of chromosomal DNA (indicative of necrotic cell death) was observed in extracts of podocytes treated with toxic metals. These results demonstrate that prolonged exposure to several common environmental TM induced apoptosis in cultured podocytes.
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Individual and Combination TM Treatments Induce Disparate Degrees of Apoptosis Detected by Tunel Staining
To confirm the results of the DNA fragmentation studies, and to extend these findings to combination metal treatments, Tunel staining was measured in five separate experiments in podocytes treated for three days with cadmium, mercury, or arsenite or with equimolar combinations of all three TM. Fluorescence microscopic images representative of all treatments are shown in Figure 2, which revealed positive Tunel staining of podocyte nuclei in cells treated with 10 µM and 20 µM arsenite. Podocytes treated with 10 µM and 20 µM of cadmium or mercury also showed similar positive Tunel staining, while those treated with 20 µM and 40 µM of combination TM displayed Tunel staining similar to that observed after 10 µM As (data not shown). Tunel staining was absent in control cells, and morphologic changes characteristic of necrotic cell death were not observed in either control or treated podocytes. The arrows in Figure 2 demonstrate the nuclear condensation and fragmentation characteristic of apoptosis. These results confirm the above DNA laddering assays and provide further evidence that prolonged exposure to common environmental TM results in induction of podocyte apoptosis.
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To measure TM-induced podocyte apoptosis, we counted the number of Tunel-positive apoptotic podocytes following prolonged exposure to either individual or combinations of TM. These results shown in Figure 3 demonstrated that arsenite, cadmium, and mercury all induced podocyte apoptosis in a dose-dependent manner, and that each of these common environmental TM were approximately equivalent in their toxicity to podocytes. Interestingly, treatment with combinations of all three of these metals resulted in a dose-independent increase in apoptosis, with both 20 µM and 40 µM treatments inducing a significant increase in podocyte apoptosis vs. controls but not significantly different from each other. In addition, treatment with both the 20 and 40 µM TM combinations (containing 6.7 or 13.3 µM, respectively, of each of the three metals) did not induce an increase in podocyte apoptosis that was significantly different from treatment with any 10 µM single metal treatment, and the number of Tunel-positive nuclei was in fact significantly less than the apoptosis induced by any 20 µM single metal treatment. Together these findings demonstrate dose-dependent induction of apoptosis of individual environmental TM on podocytes, and suggest that combination TM exposure has neither additive nor synergistic toxicity to podocytes, but rather an antagonistic effect on apoptosis.
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TM-Induced Podocyte Apoptosis Occurs Exclusively via the Caspase 8 Pathway
To elucidate the apoptotic pathway(s) involved in TM-induced podocyte apoptosis, the activities of caspases 8 and 9 were measured in extracts of podocytes following prolonged TM exposure. The results of these assays are shown in Figure 4, and demonstrated that prolonged exposure of podocytes to TM dramatically increased the activity of caspase 8 relative to control cells (375%, 420%, and 360% of control values for 20 µM arsenite, cadmium, and mercury treatments, respectively). In marked contrast, we found no significant differences between caspase 9 activities in control and TM-treated cells. In addition, consistent with the apoptosis results above, we found that both the 20 and 40 µM combination TM treatments induced less caspase 8 activation (255% and 275% of controls, respectively) than any 20 µM single metal treatment (p < 0.01), and that the increase in caspase 8 activation was not dose-dependent. These results demonstrate that prolonged exposure of podocytes to TM results in activation exclusively of the extrinsic, caspase 8-mediated apoptotic pathway, rather than the intrinsic, caspase 9-mediated pathway, and that combination TM exposure induces less caspase 8 activation than individual TM exposure.
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TM Induce Accumulation of Extrinsic Apoptotic Pathway Proteins in Podocytes
To further define the apoptotic pathway(s) activated during TM-induced podocyte apoptosis, Western blots of protein extracts of TM-treated podocytes were probed for several apoptotic signal transducers. As shown in Figure 5, we observed a dramatic accumulation of both Fas and FADD proteins (mediators of the extrinsic, caspase 8 apoptotic pathway) following all individual and combination TM treatments. In contrast, there were no significant changes in the accumulation of Bax, Bcl-2, or Bcl-xL (mediators of the intrinsic, caspase 9 pathway). The signal intensities in Western blots probed for Fas and FADD in three separate experiments were measured by densitometry, and the results are shown in Figure 6. These analyses revealed significant accumulation of Fas after all TM treatments, with the greatest inductions (475–525% of controls) after individual TM treatments. Although combination TM treatment also significantly induced Fas accumulation (375–400% of controls), these values were significantly less than those for any individual 20 µM TM treatment (p < 0.01 vs. any 20 µM individual TM). Significant accumulation of FADD protein was also seen after TM treatment, although the induced changes were similar between individual and combination TM treatments (320–360% of controls). These findings demonstrate a strong recruitment of Fas and FADD, known mediators of the extrinsic, caspase 8 apoptotic pathway, during the induction of apoptosis in podocytes exposed to TM, and are entirely consistent with our findings of activation of caspase 8, but not caspase 9, activity following TM exposures. Similar to the extent of apoptosis induction, these findings also show less induction of mediators of apoptosis after exposure to combination TM compared to equimolar concentrations of individual TM.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Although prolonged exposure to environmental TM is widely recognized as a cause of renal tubular injury, glomerular injury can also occur in this setting. However, the mechanisms by which this glomerular injury occurs remain poorly understood. In addition, the renal effects of exposure to TM in combination rather than individually, as likely occur during the majority of environmental exposures, are also very poorly understood. The current studies were therefore designed to determine whether apoptosis was induced in cultured murine podocytes by TM and to characterize the apoptotic pathways activated following prolonged exposure to several common environmental TM. We found that arsenite, cadmium, and mercury were almost equally effective at inducing dose-dependent increases in the number of apoptotic podocytes and the activation and accumulation of proteins involved in the extrinsic apoptotic pathway, with no apparent involvement of the intrinsic pathway. In addition, we found that prolonged exposure to combinations of TM induced significantly less podocyte apoptosis than individual metals, and that the effects of combination TM treatments were not dose dependent. These findings demonstrate that prolonged TM exposure induced apoptosis in cultured podocytes exclusively via the extrinsic, caspase 8 pathway, and that exposure to combinations of TM in this setting appeared to result in an antagonistic, rather than an additive or synergistic, effect on toxicity compared to equimolar exposure to individual TM.
The extrinsic apoptotic pathway is characterized by an extracellular signal binding to a "death receptor" such as Fas leading to receptor clustering, binding of the FADD adapter protein, and the activation of caspase 8. Our results show that murine podocytes exposed to TM accumulate both Fas and FADD (Fig. 6), and that caspase 8 activity increases in these cells (Fig. 4). However, we did not observe any increase in the quantity of the Bcl-2 proteins that either promote (Bax) or inhibit (Bcl-2, Bcl-xL) the release of cytochrome c from mitochondria (Fig. 5). We also did not observe any increase in the activity of caspase 9 (Fig. 4), changes that would be indicative of TM-induced activation of the intrinsic apoptotic pathway. Toxic metals have previously been shown to activate caspase 8, as well as the downstream effector caspase 3, in promyelocytic leukemia cells (Liu et al., 2003). However, apoptosis induced by TM was reported to occur via the intrinsic apoptotic pathway leading to activation of caspases 9 and 3 in neuroblastoma (Humphrey et al., 2005) and glioma cells (Watjen et al., 2002), while in lung epithelial fibroblasts both caspase 8 and 9 were activated by cadmium (Oh et al., 2004). However, little is known about the apoptotic pathways induced in the kidney by TM, though the intrinsic pathway was also presumably activated in rat kidney tubular cells after long-term exposure to Cd, where apoptosis was reported accompanied by mitochondrial membrane oxidation and DNA deletion (Takaki et al., 2004). Toxic metals have been reported to induce the generation of reactive oxygen species, which may target the mitochondrial membrane, triggering one or more of the intrinsic, mitochondrial apoptotic pathways leading to activation of pro-caspases 9 and 3 (Chen et al., 2001). However, reactive oxygen species are also thought to play a role in the Fas receptor-mediated, extrinsic apoptotic pathway via JNK-mediated induction of FasL or Fas expression (Bauer et al., 1998; Chen et al., 2001; Provinciali et al., 2002). Our observation of Fas accumulation in cultured podocytes in response to TM is consistent with this proposed mechanism. Since we observed no caspase 9 activation or accumulation of Bcl-2 family proteins, however, our findings suggest that TM may induce apoptosis in podocytes through generation of reactive oxygen species leading to the induction of Fas, rather than by the intrinsic pathway shown to be sensitive to oxidative stress in other cells. As a cautionary note, apoptosis has previously been observed in cells conditionally immortalized by SV40 T-antigen upon transfer of cells to the non-permissive temperature (Guenal and Mignotte, 1995; Vayssiere et al., 1994; Yanai and Obinata, 1994), but these observations were made soon after temperature shift to 39–39.5°C (vs. the 13–17 day after shift to 37°C used in this study). Cultured podocytes also show little evidence of apoptosis in the absence of TM injury (see Fig. 1).
Few data are available describing the renal effects of exposures to multiple TM, though in most cases environmental exposures to TM involve more than one metal species. While in this study we demonstrated that an equimolar combination of the TM cadmium, mercury, and arsenite induced the same apoptotic pathway (extrinsic) as the individual metals, we also observed that treatment with 20 µM of this combination of metals only induced as much podocyte apoptosis as a 10 µM treatment with any single metal (Fig. 3), and that the effects of treatment with 40 µM of the TM combination were indistinguishable from those induced by 20 µM of the TM combination (Figs. 3–6
). We have previously shown in cultured podocytes that this combination of TM induced greater accumulation of heat shock proteins and less toxicity than any of its single metal constituents (Eichler et al., 2005). These findings suggest that differential induction of heat shock proteins may account for the different effects of combination vs. individual TM we observed in the current study, though a variety of other factors may also contribute to these differential effects. For example, we also found that in cultured podocytes treated with a combination of cadmium, mercury, and arsenite the accumulation of cadmium was greater, while the accumulation of mercury was less, than that found in cells treated with equimolar concentrations of individual metals (Eichler et al., 2005). Differential accumulation of TM has also been observed in other studies, including a report that cadmium inhibited mercury uptake in the renal cortex of rats (Zalups and Barfuss, 2002), and a study in enterocytic-like Caco-2 cells which showed that mercury uptake was by non-specific passive diffusion that was insensitive to cadmium inhibition, while cadmium uptake probably involved a thiol-mediated reaction that was highly sensitive to mercury inhibition (Aduayom et al., 2003). In contrast, another study showed decreased renal toxicity but not decreased mercury uptake in rats exposed to cadmium and mercury (Peixoto et al., 2003). Other studies have shown disparate renal toxicities in animals exposed to multiple TM. In mice treated with arsenite and cadmium together, renal toxicity was greater than that observed with either metal alone (Liu et al., 2000), while sequential treatment with arsenite and cadmium (but not cadmium followed by arsenite) decreased renal toxicity (Hochadel and Waalkes, 1997). Despite the lack of consensus concerning the differential accumulation of TM in the kidneys of animals treated with combinations of TM, and the paucity of information concerning exposures to TM combinations containing arsenite, our previous findings that podocytes treated with TM combinations containing cadmium, mercury, and arsenite accumulated more cadmium and less mercury than cells treated with individual metals suggest that differential accumulation of metals may account for our observed differences in the induction of podocyte apoptosis in response to combination vs. individual TM treatments, though differential accumulation of protective heat shock proteins is also supported by our previous results (Eichler et al., 2005). Interestingly, however, a recent report demonstrated that 10 µM cadmium could reduce apoptosis occurring via either the intrinsic or extrinsic pathways in cultured glomerular mesangial cells, resulting in suppression of caspase-8 and -9 (Gunawardana et al.), and suggesting that our finding that combinations of TM induce less podocyte apoptosis than individual metals may be due to a direct action of cadmium.
In conclusion, we found that the TM cadmium, mercury, and arsenite induce apoptosis in cultured murine podocytes in a dose-dependent manner and exclusively via the caspase 8-mediated extrinsic apoptotic pathway. In addition, although equimolar combinations of these three TM also induced podocyte apoptosis via the extrinsic pathway, this induction was not dose dependent and combinations of TM induced less apoptosis than individual metals. These findings suggest that podocytes in vivo may also be sensitive to TM-induced apoptosis, and that environmental TM exposure may induce glomerular injury, at least in part, via induction of podocyte apoptosis. Loss of podocytes is clinically very important, since podocytes are generally unable to proliferate and podocyte loss with the resultant denudation of the glomerular basement membrane have been shown to be critical to the development of focal segmental glomerulosclerosis (FSGS) and potential progression of renal disease to end stage renal disease (review see Kriz, 2002). Podocyte apoptosis has also been suggested to play a significant role in human glomerular disease in a study which reported that downregulation of podocyte Bcl-2 was closely associated with the development of progressive glomerular injury and poor clinical outcome (Qiu et al., 2004). These results together with our findings suggest that environmental TM exposure may be an underappreciated contributor to the development of glomerular disease, and that such exposure may induce glomerular injury via induction of podocyte apoptosis. Our results also suggest that exposure to combinations of TM may actually induce protective responses, or result in differential TM uptake, that result in less podocyte toxicity than exposure to individual metals.
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ACKNOWLEDGMENTS |
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This work was supported in part by a Program Project grant (P01 ES11188-01) from the National Institute of Environmental Health Sciences to W.E.S. P.D. is supported by grants from the Nation Institute of Diabetes & Digestive & Kidney Diseases (RO1-DK53289, P50-DK52612, R21-DK070163) and support for R.F.R. is provided in part by an NIDDK grant (5 R21 DK064793-02).
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REFERENCES |
|---|
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Aduayom, I., Campbell, P. G., Denizeau, F., and Jumarie, C. (2003). Different transport mechanisms for cadmium and mercury in Caco-2 cells: Inhibition of Cd uptake by Hg without evidence for reciprocal effects. Toxicol. Appl. Pharmacol. 189, 56–67.[CrossRef][Web of Science][Medline]
Akesson, A., Lundh, T., Vahter, M., Bjellerup, P., Lidfeldt, J., Nerbrand, C., Samsioe, G., Stromberg, U., and Skerfving, S. (2005). Tubular and glomerular kidney effects in Swedish women with low environmental cadmium exposure. Environ. Health Perspect. 113, 1627–1631.[Medline]
Bauer, M. K. A., Vogt, M., Los, M., Siegel, J., Wesselborg, S., and Schulze-Osthoff, K. (1998). Role of reactive oxygen intermediates in activation-induced CD95 (APO-1/Fas) ligand expression. J. Biol. Chem. 273, 8048–8055.
Chen, F., Vallyathan, V., Castranova, V., and Shi, X. (2001). Cell apoptosis induced by carcinogenic metals. Mol. Cell. Biochem. 222, 183–188.[Medline]
Eichler, T. E., Ransom, R. F., and Smoyer, W. E. (2005). Differential induction of podocyte heat shock proteins by prolonged single and combination toxic metal exposure. Toxicol. Sci. 84, 120–128.
Erfurt, C., Roussa, E., and Thevenod, F. (2003). Apoptosis by Cd2+ or CdMT in proximal tubule cells: different uptake routes and permissive role of endo/lysosomal CdMT uptake. Am. J. Physiol. Cell Physiol. 285, C1367–C1376.
Erkan, E., De Leon, M., and Devarajan, P. (2001). Albumin overload induces apoptosis in LLC-PK(1) cells. Am. J. Physiol. Renal Physiol. 280, F1107–F1114.
Fowler, B. A., and Mahaffey, K. R. (1978). Interactions among lead, cadmium, and arsenic in relation to porphyrin excretion patterns. Environ. Health Perspect. 25, 87–90.[Medline]
Guenal, I., and Mignotte, B. (1995). Studies of specific gene induction during apoptosis of cell lines conditionally immortalized by SV40. FEBS Lett. 374, 384–386.[CrossRef][Medline]
Gunawardana, C. G., Martinez, R. E., Xiao, W., and Templeton, D. M. Cadmium inhibits both intrinsic and extrinsic apoptotic pathways in renal mesangial cells. Am. J. Physiol. Renal Physiol. Epub ahead of print.
Hochadel, J. F., and Waalkes, M. P. (1997). Sequence of exposure to cadmium and arsenic determines the extent of toxic effects in male Fischer rats. Toxicology 116, 89–98.[CrossRef][Web of Science][Medline]
Hoedemaeker, P. J., Fleuren, G. J., and Weening, J. J. (1988). Experimental models of the nephrotic syndrome. In The Nephrotic Syndrome (J. S. Cameron and R. J. Glassock, Eds.), pp. 89–162. Marcel Dekker, New York.
Humphrey, M. L., Cole, M. P., Pendergrass, J. C., and Kiningham, K. K. (2005). Mitochondrial mediated thimerosal-induced apoptosis in a human neuroblastoma cell line (SK-N-SH). Neurotoxicology 26, 407–416.[CrossRef][Web of Science][Medline]
Kim, S. C., Cho, M. K., and Kim, S. G. (2003). Cadmium-induced non-apoptotic cell death mediated by oxidative stress under the condition of sulfhydryl deficiency. Toxicol. Lett. 144, 325–336.[CrossRef][Web of Science][Medline]
Kriz, W. (2002). Podocyte is the major culprit accounting for the progression of chronic renal disease. Microsc. Res. Tech. 57, 189–195.[CrossRef][Web of Science][Medline]
Liu, J., Liu, Y., Habeebu, S. M., Waalkes, M. P., and Klaassen, C. D. (2000). Chronic combined exposure to cadmium and arsenic exacerbates nephrotoxicity, particularly in metallothionein-I/II null mice. Toxicology 147, 157–166.[CrossRef][Web of Science][Medline]
Liu, Q., Hilsenbeck, S., and Gazitt, Y. (2003). Arsenic trioxide-induced apoptosis in myeloma cells: p53-dependent G1 or G2/M cell cycle arrest, activation of caspase-8 or caspase-9, and synergy with APO2/TRAIL. Blood 101, 4078–4087.
Madden, E. F., and Fowler, B. A. (2000). Mechanisms of nephrotoxicity from metal combinations: A review. Drug Chem. Toxicol. 23, 1–12.[CrossRef][Web of Science][Medline]
Mahaffey, K. R., and Fowler, B. A. (1977). Effects of concurrent administration of lead, cadmium, and arsenic in the rat. Environ. Health Perspect. 19, 165–171.[Medline]
Mundel, P., Reiser, J., Zuniga Mejia Borja, A., Pavenstadt, H., Davidson, G. R., Kriz, W., and Zeller, R. (1997). Rearrangements of the cytoskeleton and cell contacts induce process formation during differentiation of conditionally immortalized mouse podocyte cell lines. Exp. Cell Res. 236, 248–258.[CrossRef][Web of Science][Medline]
Oh, S. H., Lee, B. H., and Lim, S. C. (2004). Cadmium induces apoptotic cell death in WI 38 cells via caspase-dependent Bid cleavage and calpain-mediated mitochondrial Bax cleavage by Bcl-2-independent pathway. Biochem. Pharmacol. 68, 1845–1855.[CrossRef][Web of Science][Medline]
Park, M. S., De Leon, M., and Devarajan, P. (2002). Cisplatin induces apoptosis in LLC-PK1 cells via activation of mitochondrial pathways. J. Am. Soc. Nephrol. 13, 858–865.
Peixoto, N. C., Roza, T., Flores, E. M., and Pereira, M. E. (2003). Effects of zinc and cadmium on HgCl2-delta-ALA-D inhibition and Hg levels in tissues of suckling rats. Toxicol. Lett. 146, 17–25.[Medline]
Provinciali, M., Donnini, A., Argentati, K., Di Stasio, G., Bartozzi, B., and Bernardini, G. (2002). Reactive oxygen species modulate Zn(2+)-induced apoptosis in cancer cells. Free Radic. Biol. Med. 32, 431–445.[Medline]
Pulido, M. D., and Parrish, A. R. (2003). Metal-induced apoptosis: Mechanisms. Mutat. Res. 533, 227–241.[Medline]
Qiu, L. Q., Sinniah, R., and I-Hong Hsu, S. (2004). Downregulation of Bcl-2 by podocytes is associated with progressive glomerular injury and clinical indices of poor renal prognosis in human IgA nephropathy. J. Am. Soc. Nephrol. 15, 79–90.
Smoyer, W. E., and Ransom, R. F. (2002). Hsp27 regulates podocyte cytoskeletal changes in an in vitro model of podocyte process retraction. FASEB J. 16, 315–326.
Takaki, A., Jimi, S., Segawa, M., Hisano, S., Takebayashi, S., and Iwasaki, H. (2004). Long-term cadmium exposure accelerates age-related mitochondrial changes in renal epithelial cells. Toxicology 203, 145–154.[Medline]
Ueda, N., Baliga, R., and Shah, S. V. (1996). Role of ‘catalytic’ iron in an animal model of minimal change nephrotic syndrome. Kidney Int. 49, 370–373.[Web of Science][Medline]
Vayssiere, J. L., Petit, P. X., Risler, Y., and Mignotte, B. (1994). Commitment to apoptosis is associated with changes in mitochondrial biogenesis and activity in cell lines conditionally immortalized with simian virus 40. Proc. Natl. Acad. Sci. U.S.A. 91, 11752–11756.
Watjen, W., Haase, H., Biagioli, M., and Beyersmann, D. (2002). Induction of apoptosis in mammalian cells by cadmium and zinc. Environ. Health Perspect. 110, 865–867.
Yanai, N., and Obinata, M. (1994). Apoptosis is induced at nonpermissive temperature by a transient increase in p53 in cell lines immortalized with temperature-sensitive SV40 large T-antigen gene. Exp. Cell Res. 211, 296–300.[CrossRef][Web of Science][Medline]
Zalups, R. K., and Barfuss, D. W. (2002). Simultaneous coexposure to inorganic mercury and cadmium: a study of the renal and hepatic disposition of mercury and cadmium. J. Toxicol. Environ. Health A 65, 1471–1490.[Medline]
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