Apoptosis in the kidney

Cascading renal injury after brain death: Unveiling glycocalyx alteration and the potential protective role of tacrolimus

Brain death (BD) is a complex medical state that triggers systemic disturbances and a cascade of pathophysiological processes. This condition significantly impairs both kidney function and structural integrity, thereby presenting considerable challenges to graft viability and the long-term success of transplantation endeavors. Tacrolimus (FK506), an immunosuppressive drug, was used in this study to assess its impact as a pretreatment on brain death-induced renal injury. This study aimed to investigate changes associated with brain death-induced renal injury in a 4-month-old female porcine model. The experimental groups included brain death placebo-pretreated (BD; n = 9), brain death tacrolimus-pretreated using the clinical dose of 0.25 mg/kg the day before surgery, followed by 0.05 mg/kg/day 1 hour before the procedure (BD + FK506; n = 8), and control (ctrl, n = 7) piglets, which did not undergo brain death induction. Furthermore, we aimed to assess the effect of FK506 on these renal alterations through graft preconditioning. We hypothesized that immunosuppressive properties of FK506 reduce tissue inflammation and preserve the glycocalyx. Our findings revealed a series of interconnected events triggered by BD, leading to a deterioration of renal function and increased proteinuria, increased apoptosis in the vessels, glomeruli and tubules, significant leukocyte infiltration into renal tissue, and degradation of the glycocalyx in comparison with ctrl group. Importantly, treatment with FK506 demonstrated significant efficacy in attenuating these adverse effects. FK506 helped reduce apoptosis, maintain glycocalyx integrity, regulate neutrophil infiltration, and mitigate renal injury following BD. This study offers new insights into the pathophysiology of BD-induced renal injury, emphasizing the potential of FK506 pretreatment as a promising therapeutic intervention for organ preservation, through maintaining endothelial function with the additional benefit of limiting the risk of rejection.

Bicyclol alleviates obesity-induced renal injury by inhibiting JNK and NF-κB-mediated inflammation

Obesity is recognized as a major risk factor for chronic kidney disease (CKD), which is accompanied by increased renal lipid build-up, fibrosis, inflammation, apoptosis and pyroptosis. Bicyclol (BIC), a Chinese marketed hepatoprotective drug, has shown excellent anti-inflammatory, anti-fibrosis, anti-apoptotic, and lipid regulation effects in different animal models. In this study, we explored the role and mechanism of BIC in high-fat diet (HFD)-induced obesity-related nephropathy. Mice were fed with HFD for 24 weeks to develop obesity-related nephropathy, while mice in the BIC administration group were treated with BIC (50 mg/kg or 100 mg/kg, once every two days) at the last 12 weeks. We found that BIC treatment relieved the impairment of kidney structure and renal dysfunction caused by HFD. In addition, we found that BIC mitigated HFD-induced renal fibrosis, inflammation, apoptosis and pyroptosis by inhibiting JNK and NF-κB pathways. SV40-MES-13 cells treated with palmitate (PA) were used as the in vitro model. Our data show that BIC pre-administration relieved cellular damage caused by PA through suppressing JNK and NF-κB signaling pathways. In conclusion, we demonstrated that BIC attenuated obesity-induced renal injury by inhibiting chronic inflammation, fibrosis, apoptosis and pyroptosis via targeting JNK and NF-κB pathways. Our data suggested that BIC could be potentially used to prevent obesity-associated nephropathy, which warrants future investigation.

Cross Talk Between TGF-β and JAK Expressions and Nepherotoxicity Induced by Tetrachloromethane: Role of Phytotherapy

The aim of the current study is to assess the effectiveness of milk thistle seeds (Mth) in combination with Taraxacum officinale (Tof) and/or Camellia sinensis (Csin) against tetrachloromethane (Tcm) renotoxicity in rats. Tetrachloromethane was injected in a single dose, followed by 1-month treatments with Mth, Tof, and Csin alone or in combination. Serum urea, uric acid, and creatinine levels were significantly increased matched with the control group. Masson trichrome stain revealed increase in the deposition of fibrous tissue in the interstitium between the tubules and the renal corpuscles. Immunohistochemical analysis of kidney tissues revealed that Tcm induced an increase in the immune response of tumor growth factor β (TGF-β) and Janus kinase (JAK) protein expressions and cysteine–aspartic acid protease 3 (caspase 3), while B-cell lymphoma 2 (Bcl2) was downregulated. Treatment with the antioxidants in question either alone or in combination ameliorated all kidney function parameters and showed mild immune reactivity toward TGF-β and JAK protein expressions in blood vessels and glomeruli in the kidney tissues and downregulated caspase 3 and activated Bcl2 protein expression. The combination regimen of the 3 antioxidants showed the most significant renoprotective effect. This was also confirmed histopathologically. It was concluded that the antioxidant mixture is considered as a promising candidate toward renal dysfunction and immune reactivity induced by Tcm and other toxicants.

Effects of folic acid on rat kidney exposed to 900 MHz electromagnetic radiation

Because of increased use of cell phones, the purpose of this study was to investigation of the oxidative damage caused by electromagnetic radiation (EMR) emitted by cell phones and histological and morphometrical determination of the possible protective role of folic acid (FA) in preventing the detrimental effects of EMR on the kidney. Twenty-four adult male Wistar albino rats were divided into control (Cont), EMR, EMR + FA and FA groups, each containing six rats. The EMR and EMR + FA groups were exposed to EMR for 60 min a day over a period of 21 days, while no EMR exposure was applied to the Cont and FA groups. The source of the EMR was an EMR device which emits a digital signal producing 900-MHz frequency radiation. The generator connected to a one-monopole antenna was used in this study and the rats were placed in the plexiglass restrainer at an equal distance from the monopole antenna. Following the experimental period, and after tissue processing, a physical disector-Cavalieri method combination was applied to the sections. The mean volume of the cortex, medulla, proximal and distal tubules increased significantly in the EMR groups compared to the Cont group (p < 0.01). Contrarily, the total number of glomeruli in the EMR group decreased compared to the Cont group (p < 0.01). The protective effects of FA was observed in the kidney (p < 0.05).

In conclusion, the 900-MHz EMR leads to kidney damage. FA may exhibit a protective effect against the adverse effects of EMR exposure in terms of the total number of glomeruli.

Rhizoma smilacis glabrae protects rats with gentamicin-induced kidney injury from oxidative stress-induced apoptosis by inhibiting caspase-3 activation

ETHNOPHARMACOLOGICAL RELEVANCE

Rhizoma smilacis glabrae (RSG), which is mild-natured and tastes sweet or bland, has pharmacological action of eliminating dampness, detoxifying, and ensuring that joints were healthy and supple in traditional Chinese medicine.

AIM OF THE STUDY

To discuss the protective effect of RSG on gentamicin (GM)-induced kidney injury in rats and its regulatory mechanisms of oxidative stress-induced apoptosis by inhibiting caspase-3 activation.

MATERIALS AND METHODS

A total of 40 Sprague-Dawley (SD) rats were randomly divided into 5 groups: control group, model group, and RSG low, middle, and high dose groups (0.75，1.5，3gkg^-1). Six hours after intramuscular GM injections, rats in the model group were given distilled water by intragastric administration, and rats in the 3 RSG intervention groups were given different dosages of RSG water-extracts. Twenty-four hours after the last administration, blood and kidney samples were collected to test for biochemical indexes of kidney injury, oxidative stress, histopathological defects, apoptosis rate, and caspase-3 protein expression to assess the protective effect of RSG water-extracts against GM-induced kidney injury.

RESULTS

Compared with the model group, serum TP and ALB levels were significantly higher (P<0.05), and BUN, CRE, and UA levels were significantly lower (P<0.05) in the 3 RSG intervention groups. In kidney tissues, SOD, CAT, and GSH levels increased significantly (P<0.05), while MDA level decreased significantly (P<0.05). Total apoptosis rate dropped markedly (P<0.01), and the protein expressions of caspase-3 increased, while expressions of activated caspase-3 decreased. Histopathological analysis showed shrinkage of kidney cells reduced with appearance of complete kidney structure and decrease in activated caspase-3 expressions in impaired renal tubules decreased. Among the 3 RSG intervention groups, the middle dose group (1.5gkg^-1) showed the best protective effect.

CONCLUSIONS

RSG water-extracts had protective effects against GM-induced kidney injury in rats, and its mechanism of action was related to oxidative stress-induced apoptosis by inhibiting caspase-3 activation.

Renal uptake of the antiapoptotic protein survivin is mediated by megalin at the apical membrane of the proximal tubule

The inhibitor of apoptosis protein survivin is a bifunctional molecule that regulates cellular division and survival. We have previously shown that survivin protein can be found at high concentrations in the adult kidney, particularly in the proximal tubules. Here, survivin is localized primarily at the apical membrane, a pattern that may indicate absorption of the protein. Several proteins in primary urine are internalized by megalin, an endocytosis receptor, which is in principle found in the same localization as survivin. Immunolabeling for survivin in different species confirmed survivin signal localizing to the apical membrane of the proximal tubule. Immunoelectron microscopy also showed apical localization of survivin in human kidneys. Furthermore, in polarized human primary tubular cells endogenous as well as external recombinant survivin is stored in the apical region of the cells. Costaining of survivin and megalin by immunohistochemistry and immunoelectron microscopy confirmed colocalization. Finally, by surface plasmon resonance we were able to demonstrate that survivin binds megalin and cubilin and that megalin knockout mice lose survivin through the urine. Survivin accumulates at the apical membrane of the renal tubule by reuptake, which is achieved by the endocytic receptor megalin, collaborating with cubilin. For this to occur, survivin will have to circulate in the blood and be filtered into the primary urine. It is not known at this stage what the functional role of tubular survivin is. However, a small number of experimental and clinical reports implicate that renal survivin is important for functional integrity of the kidney.

Proliferative and nonproliferative lesions of the rat and mouse urinary system

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in the urinary tract of rats and mice. The standardized nomenclature of urinary tract lesions presented in this document is also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as those induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for urinary tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Oxidative stress: a possible mechanism for lead-induced apoptosis and nephrotoxicity

Lead-induced nephrotoxicity is a human health hazard problem. In this study, Human mesangial cells (HMCs) were treated with different concentration of lead acetate (5, 10, 20 μmol/l) in order to investigate the oxidative stress and apoptotic changes. It was revealed that lead acetate could induce a progressive loss in HMCs viability together with a significant increase in the number of apoptotic cells using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium (MTT) assay and flow cytometry, respectively. The apoptotic morphological changes induced by lead exposure in HMCs were demonstrated by PI-Hochest33342 staining. A DNA laddering pattern in lead-treated cells was shown, which could indicate nuclear fragmentation. In addition, lead acetate significantly increased the levels of malondialehyde (MDA) content and lactate dehydrogenase (LDH) activity. Therefore, it might be concluded that lead could promote HMCs' oxidative stress and apoptosis, which may be the chief mechanisms of lead-induced nephrotoxicity.

The tumor gene survivin is highly expressed in adult renal tubular cells: implications for a pathophysiological role in the kidney

The inhibitor of apoptosis protein survivin is of critical importance for regulation of cellular division and survival. Published data point to a restricted function of survivin in embryonic development and cancer; thus survivin has been broadly proposed as an ideal molecular target for specific anti-cancer therapy. In contrast to this paradigm, we report here broad expression of survivin in adult differentiated tissues, as demonstrated at the mRNA and protein levels. Focusing on the kidney, survivin is strongly expressed in proximal tubuli, particularly at the apical membrane, which can be verified in rat, mouse, and human kidneys. In the latter, survivin expression seems to be even stronger in proximal tubuli than in adjacent cancerous tissue. Primary and immortalized human renal tubular cells also showed high levels of survivin protein expression, and RNA interference resulted in a partial G(2)/M arrest of the cell cycle and increased rate of apoptosis. In conclusion, survivin may be of importance for renal pathophysiology and pathology. The predominant apical expression of survivin may indicate a further, yet unknown, function. Interventional strategies to inhibit survivin's function in malignancy need to be carefully (re)evaluated for renal side effects, as well as for other possible organ dysfunctions.

Renal tubular epithelial cell self-injury through Fas/Fas ligand interaction promotes renal allograft injury

Tubular epithelial cells (TECs) coexpress Fas and Fas ligand (FasL), which could influence renal allograft injury. While TECs can resist apoptosis by Fas antibody, TEC apoptosis by contact with adjacent TECs has not been studied. Fas expression increased in TECs with cytokine treatment (IFN-gamma, TNF-alpha) while abundant FasL levels were not altered. Apoptosis (Annexin-V, DNA fragmentation) occurred in cytokine-treated TECs monolayers from C3H-HeJ mice by 24 h, but was absent in similarly treated TECs from Fas-deficient (lpr) or FasL-mutant (gld) mice, suggesting that 'self injury' occurred through Fas/FasL. Membrane labeling of TECs in cocultures confirmed that FasL-bearing TECs induced apoptosis when in contact with Fas-bearing TECs. Culturing TECs with allogeneic C57BL/6 (H-2b) splenocytes resulted in apoptosis and elimination of C3H-HeJ TECs by 48 h, with enhanced survival and reduced apoptosis using lpr or gld TECs. In a renal allograft model, survival of C57BL/6 recipients was greater (p < 0.05) and renal function improved (p < 0.001) using C3H-lpr or C3H-gld (H-2 k) donor kidneys compared with C3H-HeJ kidneys. These data demonstrate for the first time that cytokine-activated TECs can injure TECs through expression of functional FasL and Fas. We suggest that inhibition of TEC-TEC 'self injury' may be a novel strategy to augment renal allograft survival.

IL-12 plays a significant role in the apoptosis of human T cells in the absence of antigenic stimulation

Interleukin-12 (IL-12) is an immunoregulatory cytokine that plays an essential role in cell-mediated immunity. It is known to induce T cell apoptosis in in vivo systems such as graft-versus-host disease (GVHD) and experimental autoimmune uveitis (EAU). However, the role of IL-12 in T cell apoptosis in the absence of antigenic stimulation has not been clearly defined. This study was conducted to investigate whether IL-12, in the absence of an antigen, is able to induce T cell apoptosis, and also, which signalling pathways utilized by IL-12 are involved in this process. Our data clearly showed that IL-12 in the absence of an antigen induces apoptosis in T cells. Flow cytometry and ELISA showed FasL up-regulation and increased IFN-gamma synthesis in IL-12 treated T cells, while Fas and TNF-R1 showed little change. Semi-quantitative RT-PCR demonstrated that IL-12 was able to up-regulate TNF-alpha and FasL mRNA expression. Furthermore, IL-12 induced apoptosis was associated with caspase-3, caspase-2, caspase-7, DNA fragmentation factor 45 (DFF45) and Fas associated death domain (FADD) whereas TNF receptor associated death domain (TRADD) and receptor interacting protein (RIP) were not. Inhibition of Janus tyrosine kinase (JAK) was able to suppress IL-12 induced T cell apoptosis. Anti-FasL antibody was able to block IL-12 induced T cell apoptosis. In conclusion, our findings suggest that IL-12 is able to induce T cell apoptosis in the absence of an antigen. In addition, the present data suggest that this process is FasL mediated and caspase-3 dependent. Furthermore, JAK was shown to be involved in this process. These results may have significant implications in the understanding of IL-12 mediated T cell apoptosis.

Apoptosis in the cortex of the developing mouse kidney

Published levels of apoptosis in developing rat kidney (approximately 2.5%) seem large for a tissue with no obvious need for continual cell death. This paper examines the levels and patterns of apoptosis and mitosis in the cortical region of the developing metanephros of the mouse, the standard mammalian model embryo. Using confocal microscopy on specimens stained with propidium iodide to highlight nuclear morphology, optical sections of wholemount kidneys to a depth of approximately 50 microm were analysed and mitotic, apoptotic and interphase nuclei counted in the various compartments. Of the approximately 200 000 cells examined over E11.5-16.5, 2-3% were mitotic, confirming observations based on cryosections; the mitotic index peaked at E14.5, dropping to approximately 0.5% by P14. The mean apoptotic index during this period was 0.28%; this figure from wholemounts was approximately 10% of that earlier reported in cryosectioned rat kidneys. One possible explanation for the difference is that cryosectioning turns out to create small nuclear fragments that can stain strongly with propidium. Such fragments are not seen in wholemounts and do not stain with TUNEL. Wholemount mouse E11.5 tails and E16.5 lungs were also analysed and both their mitotic and their apoptotic indexes were similar to those in wholemount developing kidneys. These results show that the level of apoptosis in wholemount embryonic mouse kidney cortex is far less than previously reported in cryosectioned rat embryonic kidneys, and typical of that in other mouse embryonic tissues whose development seems not to require apoptosis.

Renal cortical remodelling by NO-synthesis blockers in rats is prevented by angiotensin-converting enzyme inhibitor and calcium channel blocker

The cortical remodelling was studied when chronically nitric oxide synthesis (NOs) blockade (L-NAME-induced) hypertensive rats are simultaneously treated, or not, with angiotensin-converting enzyme inhibitor or calcium channel blocker. Four groups of eight rats each were studied as follows: Control (C), L-NAME (L), L-NAME+Enalapril (L+E) and L-NAME+Verapamil (L+V). The systolic blood pressure (SBP) was weekly recorded. The cortex of the left kidneys was analysed according to the vertical section design. The volume-weighted mean glomerular volume (VWGV) was made through the "point-sampled intercepts" method. Enalapril and verapamil were efficient in reducing the SBP in rats submitted to NOs blockade. Glomeruli had considerable alterations in L group rats (glomerular hypertrophy or sclerosis) and tubular atrophy. The VWGV was 100% greater in L group rats than in the C group rats, while it was 30% smaller in L+E and L+V groups than in L group. The tubular volume was 30-50% greater, while the tubular length was 20-30% smaller in the L group than in the other groups. The renal cortical region showed glomerular sclerosis/hypertrophy and tubular remodelling in rats with NOs blockade that was efficiently prevented with the simultaneous treatment with enalapril or verapamil.

Rat kidney pathology induced by chronic exposure to fumonisin B1 includes rare variants of renal tubule tumor

The carcinogenicity of fumonisin B1 (FB1), a worldwide contaminant of corn produced by Fusaria species of fungi, has been tested recently in 2-year feeding studies in Fischer F344 rats and B6C3F1 mice. Inclusion of FB1 at 50 and 80 ppm in the diet induced liver tumors in female mice, and at 50 and 150 ppm induced renal tumors in male rats (22). In the present study, the kidneys from the rat bioassay were examined to characterize the various histopathological changes associated with renal tumor induction. In all high-dose (150 ppm) and mid-dose (50 ppm) male rats, and to a lesser extent in high-dose (100 ppm) female rats, there was evidence of sustained nephrotoxicity manifested as basophilia, apoptosis, cell regeneration, and simple tubule hyperplasia, affecting proximal convoluted tubules in the deep cortex, extending into the outer region of the outer stripe of outer medulla. A further alteration consisted of sporadic areas of interstitial hyalinization in deep cortex, suggestive of expanded basement membrane, coupled with tubule atrophy. The continued presence of nephrotoxicity throughout chronic exposure to FB1 suggested that renal tumor development may have been an outcome of sustained cell loss and compensatory regeneration. In some cases, preneoplastic tubules or incipient renal tumors presented an immature or fetal form in association with interstitial hyalinization. The renal tubule tumors induced by FB1 were typified by a rare, highly malignant, anaplastic variant capable of growth by infiltration. Of the 10 renal tubule tumors diagnosed in the mid-dose males, and the 16 in the high-dose males, 8 and 10, respectively, were graded as carcinomas. Anaplastic variants represented 50% of the mid-dose carcinomas and 80% of the high-dose carcinomas. One of the anaplastic carcinomas in a mid-dose male was a true sarcomatoid phenotype not previously recorded in the rodent. Metastatic invasion of the lung occurred with 25% of the mid-dose carcinomas and 50% of the high-dose carcinomas. It was speculated that FB1 may have been influencing the growth characteristics of the induced renal tumors via its inhibitory action on the synthesis of sphingolipids, which in turn, participate in regulating cell contact, growth, and differentiation, or alternatively by affecting cell adhesion molecules.

Age-related cell proliferation and apoptosis in the kidney of male Fischer 344 rats with observations on a spontaneous tubular cell adenoma

Cell proliferation rate and apoptosis were examined in archival kidneys from young, middle-aged, and old male F344 rats. Immunohistochemical expression of proliferating cell nuclear antigen (PCNA) and apoptosis were quantified in the same cell populations of the proximal tubule epithelium. A total of 79 kidneys from 40 rats were examined. There was a progressive increase in cell proliferation rates in rats from 4 and 6-10 months of age. In 23-month-old rats, proliferative activity appeared to be reduced. No age-related variations in apoptotic indices were found. One of the 16 rats aged 23 months had a tubular cell adenoma. In the tumor-affected kidney, cell proliferation rate was dramatically higher than in the contralateral kidney as well as in all the other kidneys examined. This high proliferative activity was not balanced by variation in cell death.

Apoptosis of proliferative cortical tubular epithelia in chronic progressive nephrosis of rats

To investigate the role of apoptosis in the pathogenesis of rat chronic progressive nephrosis (CPN), the kidney of male F344/DuCrj rats, 19, 59, and 111 weeks of age, was examined histologically. In situ analysis for DNA fragmentation and proliferating cell nuclear antigen (PCNA) was performed simultaneously by TdT-mediated dUTP-biotin nick end labeling (TUNEL) and immunohistochemistry, respectively. CPN was seen in all the kidneys of 59-week-old (n=6) and 111-week-old rats (n=16), correlating significantly (p<0.01) with age. There were apoptotic bodies (ABs) in the single-layered epithelia of dilated tubules (SLD) and the multilayered epithelia (ML) of the cortical tubules. There were no ABs in any of the kidneys of the 19-week-old (n=5) or 59-week-old rats (n=6). Proliferative activity might have been enhanced in the single-layered and flattened epithelia, SLD, and ML of the cortical tubules in the kidneys of the 59-week-old rats (n=6) compared with that in 111-week-old rats (n=8). The correlations between the TUNEL-positive ratio and number of PCNA-positive cells, and age and the CPN grade were significant (p<0.01) exclusively in the ML. Thus, the results suggest that apoptosis occurs in the proliferative ML of rat CPN, and the pathological significance might be the removal of abnormal or excess cells.

Apoptosis in renal proximal tubules of rats treated with low doses of aminoglycosides

Kidney cortex apoptosis was studied with female Wistar rats treated for 10 days with gentamicin and netilmicin at daily doses of 10 or 20 mg/kg of body weight and amikacin or isepamicin at daily doses of 40 mg/kg. Apoptosis was detected and quantitated using cytological (methyl green-pyronine) and immunohistochemical (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) staining, in parallel with a measurement of drug-induced phospholipidosis (cortical phospholipids and phospholipiduria), cortical proliferative response ((3)H incorporation in DNA and histoautoradiography after in vivo pulse-labeling with [(3)H]thymidine), and kidney dysfunction (blood urea nitrogen and creatinine). Gentamicin induced in proximal tubules a marked apoptotic reaction which (i) was detectable after 4 days of treatment but was most conspicuous after 10 days, (ii) was dose dependent, (iii) occurred in the absence of necrosis, and (iv) was nonlinearly correlated with the proliferative response (tubular and peritubular cells). Comparative studies revealed a parallelism among the extents of phospholipidosis, apoptosis, and proliferative response for three aminoglycosides (gentamicin >> amikacin congruent with isepamicin). By contrast, netilmicin induced a marked phospholipidosis but a moderate apoptosis and proliferative response. We conclude that rats treated with gentamicin develop an apoptotic process as part of the various cortical alterations induced by this antibiotic at low doses. Netilmicin, and still more amikacin and isepamicin, appears safer in this respect. Whereas a relation between aminoglycoside-induced tubular apoptosis and cortical proliferative response seems to be established, no simple correlation with phospholipidosis can be drawn.

Studies on the mechanisms and kinetics of apoptosis induced by microinjection of cytochrome c in rat kidney tubule epithelial cells (NRK-52E)

Recent reports substantiating the role of cytochrome c in the induction of apoptosis led us to examine the kinetics and mechanisms involved in this process as an extension of our ongoing studies of cell injury and cell death. Microinjection of cytochrome c into NRK-52E kidney cells produced rapid apoptosis, which usually began within 30 minutes and reached a maximum of 60-70% by 3 hours. The changes that occurred included four phases: an initial shrinkage phase, an active phase, a spherical phase, and a necrotic phase. For morphological purposes, the progressive changes were followed by phase-contrast and fluorescence microscopy, transmission and scanning electron microscopy, and time-lapse video microscopy. Cells first showed shrinkage, then displayed multiple pseudopods, which rapidly extended and retracted, giving the cells a bosselated appearance. During this active phase there was chromatin condensation, mitochondria were swollen but retained membrane potential, and the endoplasmic reticulum was dilated. Within 2-4 hours, active-phase cells became spherical and smooth-surfaced but were still alive, the nuclei showed chromatin clumping, the mitochondria underwent high-amplitude swelling but retained membrane potential, the endoplasmic reticulum was highly dilated, and many large apical vacuoles were present. Elevation of [Ca(2+)](i) was seen at the late spherical phase, shortly before cell death. Pretreatment with the caspase 3 inhibitor (Ac-DEVD-CHO) prevented apoptosis, whereas overexpression of Bcl-2 did not. Depletion of cellular ATP by cyanide inhibition of energy metabolism prevented cytochrome c from inducing the active and later phases of apoptosis. The results clearly indicate that cytochrome c-induced apoptosis is a dynamic and energy-requiring process that has a distinct active and spherical phase before cell death.