Mechanisms of cell death in hypoxia/reoxygenation injury

Cyclosporine A regulate oxidative stress-induced apoptosis in cardiomyocytes: mechanisms via ROS generation, iNOS and Hsp70

1. Previous study suggested that cyclosporine A (CsA) could partially reduce ischaemia/reperfusion-induced injury in isolated heart, but the mechanism was still unclear. In this study, the possible mechanisms of cyclosporine A in regulating oxidative stress-induced cardiomyocyte apoptosis were examined. 2. Morphological (cell shrinkage, apoptotic body formation, and DNA fragmentation) and biochemical (annexin-V staining for exposed phosphatidylserine residues) evidences showed that both hydrogen peroxide (H(2)O(2)) and hypoxia/reoxygenation could induce apoptotic change in the embryonal rat heart myoblast-derived cells (H9c2). These effects were inhibited by pre-treatment with CsA at concentration of 0.01-1.0 micro M for 24 h, but were increased with 10.0 micro M CsA. 3. While examining the mechanisms of CsA in protecting cardiomyocyte apoptosis, we found that the collapse of mitochondria membrane potential (DeltaPsim) induced by oxidative stress was partially reversed by CsA (0.01-1.0 micro M). 4. Compared to the control, CSA at the concentration of 0.1 and 10.0 micro M significantly increased the level of intracellular reactive oxygen species (ROS) to 117.2+/-12.4% and 234.4+/-9.3%, respectively. Co-incubating with the antioxidant, ascorbic acid (10.0 micro M), could partially reduce the protective effect of CsA (0.01-1.0 micro M) and the toxic effect of 10.0 micro M CsA. 5. Pre-treatment with CsA at concentration of 0.01-1.0 micro M for 24 h produced up-regulation of heat shock protein 70 (Hsp 70), inducible nitric oxide synthase (iNOS) and also induced NO production, indicating that these factors might be associated with the cell protective effects of CsA. 6. These results suggest that CsA could protect the oxidative stress-induced cardiomyocyte apoptosis not only by preventing the loss of DeltaPsim in mitochondria, but also through ROS generation, Hsp70, and iNOS up-regulation.

Hypoxia induces nitric oxide production in mouse microglia via p38 mitogen-activated protein kinase pathway

In vitro exposure of microglial cells to hypoxia induces cellular activation. Also, in vivo studies of glial activation following ischemic hypoxia have shown that neuronal cell death is followed by microglial activation. Thus, it is likely that toxic inflammatory mediators produced by activated microglial cells under hypoxic conditions may exacerbate neuronal injury following cerebral ischemia. Nitric oxide (NO), which is known to be produced by activated microglia, may participate in this process. In the current work, we sought to determine whether and how the production of NO and the expression of inducible NO synthase (iNOS) are triggered by hypoxia in microglial cells. Exposure of established microglial cell lines as well as primary mouse microglial cultures to mild hypoxia (8 h) followed by reoxygenation (24 h) induced the production of NO and TNFalpha, indicating that hypoxia could lead to the inflammatory activation of microglia. Hypoxic induction of NO was accompanied by iNOS induction. Moreover, hypoxia induced the activation of p38 MAPK, but not ERK or JNK/SAPK, in BV-2 mouse microglial cells. SB203580, a specific inhibitor of p38 MAPK, blocked the hypoxic induction of NO and iNOS. Taken together, our results indicated that hypoxia could induce inflammatory activation of microglia, and the hypoxic induction of NO production in microglia is mediated through p38 MAPK pathway. Thus, during cerebral ischemia, hypoxia may not only directly damage neurons, but may also promote neuronal injury indirectly via microglial activation.

Positive inotropic stimulation

Adrenergic receptors transduce signals through the G proteins to regulate cardiac function. The catecholamines, via alpha- and beta-adrenergic receptor (beta-AR) stimulation, may play a role in the development of heart failure. Norepinephrine and isoproterenol can induce cardiac myocyte apoptosis. Studies suggest that alpha-, beta1-, and beta2-adrenergic pathways differentially regulate cardiac myocyte apoptosis. The stimulation of beta1-AR leads to cyclic AMP-dependent apoptosis, whereas that of the beta2-AR elicits concurrent apoptosis and survival signals in cardiac myocytes coupled to Gs protein. Overexpression of alpha1-adrenergic receptors does not induce apoptosis in wild-type mice. In contrast, the heart failure observed in some murine models has to be related to an enhanced beta-AR kinase expression. These recent advances make it possible to understand the beneficial effects of beta-blockers in the treatment of chronic heart failure and provide novel therapeutic modalities through the stimulation of beta2-ARs or the inhibition of beta-AR kinase expression.

Protective effects of oral creatine supplementation on spinal cord injury in rats

STUDY DESIGN

To evaluate a potential protective effect of increased creatine levels in spinal cord injury (SCI) in an animal model.

OBJECTIVES

Acute SCI initiates a series of cellular and molecular events in the injured tissue leading to further damage in the surrounding area. This secondary damage is partly due to ischemia and a fatal intracellular loss of energy. Phospho-creatine in conjunction with the creatine kinase isoenzyme system acts as a potent intracellular energy buffer. Oral creatine supplementation has been shown to elevate the phospho-creatine content in brain and muscle tissue, leading to neuroprotective effects and increased muscle performance.

SETTING

Zurich, Switzerland.

METHODS

Twenty adult rats were fed for 4 weeks with or without creatine supplemented nutrition before undergoing a moderate spinal cord contusion.

RESULTS

Following an initial complete hindlimb paralysis, rats of both groups substantially recovered within 1 week. However, creatine fed animals scored 2.8 points better than the controls in the BBB open field locomotor score (11.9 and 9.1 points respectively after 1 week; P=0.035, and 13 points compared to 11.4 after 2 weeks). The histological examination 2 weeks after SCI revealed that in all rats a cavity had developed which was comparable in size between the groups. In creatine fed rats, however, a significantly smaller amount of scar tissue surrounding the cavity was found.

CONCLUSIONS

Thus creatine treatment seems to reduce the spread of secondary injury. Our results favour a pretreatment of patients with creatine for neuroprotection in cases of elective intramedullary spinal surgery. Further studies are needed to evaluate the benefit of immediate creatine administration in case of acute spinal cord or brain injury.

Functional activation of heat shock factor and hypoxia-inducible factor in the kidney

Renal ischemia is the result of a complex series of events, including decreases in oxygen supply (hypoxia) and the availability of cellular energy (ATP depletion). In this study, the functional activation of two stress-responsive transcription factors, i.e., heat shock factor-1 (HSF-1) and hypoxia-inducible factor-1 (HIF-1), in the kidney was assessed. When rats were subjected to 45 min of renal ischemia, electrophoretic mobility shift assays of kidney nuclear extracts revealed rapid activation of both HIF-1 and HSF. Western blot analyses further demonstrated that this activation resulted in increased expression of the HSF and HIF-1 target genes heat shock protein-72 and heme oxygenase-1, respectively. Whether hypoxia or ATP depletion alone could produce similar activation patterns in vitro was then investigated. Renal epithelial LLC-PK(1) cells were subjected to either ATP depletion (0.1 microM antimycin A and glucose deprivation) or hypoxia (1% O(2)). After ATP depletion, HSF was rapidly activated (within 30 min), whereas HIF-1 was unaffected. In contrast, hypoxia led to the activation of HIF-1 but not HSF. Hypoxic activation of HIF-1 was observed within 30 min and persisted for 4 h, whereas no HSF activation was detected even with prolonged periods of hypoxia. HIF-1 was transcriptionally active in LLC-PK(1) cells, as demonstrated by luciferase reporter gene assays using the vascular endothelial growth factor promoter or a synthetic promoter construct containing three hypoxia-inducible elements. Interestingly, intracellular ATP levels were not affected by hypoxia but were significantly reduced by ATP depletion. These findings suggest that HIF-1 is activated specifically by decreased O(2) concentrations and not by reduced ATP levels alone. In contrast, HSF is activated primarily by metabolic stresses associated with ATP depletion and not by isolated O(2) deprivation. In vivo, the two transcription factors are simultaneously activated during renal ischemia, which might account for observed differences between in vivo and in vitro epithelial cell injury and repair. Selective modulation of either pathway might therefore be of potential interest for modification of the response of the kidney to ischemia, as well as the processes involved in recovery from ischemia.

Hypoxia-induced cell death and changes in hypoxia-inducible factor-1 activity in PC12 cells upon exposure to nerve growth factor

The transcription factor hypoxia-inducible factor-1 (HIF-1) strongly contributes to the expression of adaptive genes under hypoxic conditions. In addition, HIF-1 has been implicated in the regulation of delayed neuronal cell death. Suspension-grown and adherent PC12 cells treated with NGF were used as an experimental model for studying the relationship between hypoxia-induced cell death and activation of HIF-1. Cell damage was assessed by flow cytometry of double-stained (Annexin V and propidiumiodide) cells, and by analysis of the overall death parameters LDH and mitochondrial dehydrogenase. In parallel, cells were transfected with a control and a three-hypoxia-responsive-elements (HRE)-containing vector and HIF-1-driven luciferase activity was determined. Exposure of NGF-treated PC12 cells to hypoxia resulted in a higher cell death rate when compared to untreated controls. PC12 cells exposed for 2 days to NGF exhibited a decrease of HIF-1 activity up to a factor of ten. This decrease may contribute to the enhanced hypoxia-induced cell death via reduced expression of HIF-1alpha-regulated genes responsible for adaptation to hypoxia, like those for glucose transport proteins and enzymes of the glycolytic chain. The decrease in HIF-1 activity and the increase in hypoxia sensitivity may suggest that NGF act as an hierarchically organized signaling molecule.

Enhanced development of caspase-independent cortical cell death during cold storage in kidneys of non-heart-beating donors

BACKGROUND

Understanding the mechanisms of injury associated with cardiac arrest is essential for defining strategies aimed at improving preservation and function of kidneys harvested in non-heart-beating (NHB) donors.

METHODS

We standardized a model of NHB donors in rats and studied the kinetics and types (apoptosis vs. necrosis) of renal cell death developing during cold storage. Using quantitative polymerase chain reaction, immunoblotting, and caspase inhibition, we also studied the molecular pathways regulating renal cell death in this model.

RESULTS

The kinetics and extent of cell death developing in cortical tubules during cold storage were found to be increased in non-heart-beating (NHB) kidneys. Apoptosis of cortical tubules predominated in NHB kidneys exposed to 10 hr of cold storage, whereas necrosis increased after longer periods of cold ischemia. Shortly after cardiac arrest, a rapid up-regulation of Bax and Hsp 70 was found at the protein level in NHB kidneys. After 24 hr of cold storage, induction of Bax was maintained, whereas protein levels of Hsp70 returned to levels comparable to heart-beating (HB) controls. Also, mRNA levels of Bax were found to increase during cold storage in NHB kidneys. Cortical cell death was found to be largely caspase-independent but responsive to hydroxyl-radical scavenging with dimethyl sulfoxide (DMSO).

CONCLUSIONS

Cardiac arrest promotes activation of death-inducing molecules such as Bax and is associated with increased development of caspase-independent renal cell death during cold storage. Developing strategies, such as free radical scavenging, aimed at inhibiting cell death during cold storage, could prove useful for improving preservation of NHB kidneys.

Oxygen metabolites and hypoxic renal injury: effect of mitochondrial electron transport blockade

Isolated perfusion of the rat kidney causes hypoxic damage in the cells of the thick ascending limb of the loop of Henle. The cell damage is driven by active solute transport, which generates an imbalance of oxygen supply and demand. This injury is paradoxically prevented by adding the mitochondrial electron transport inhibitors rotenone or antimycin to the perfusion media. The present study shows that rotenone and antimycin decrease production of hydrogen peroxide in the thick ascending limb during perfusion. The findings support the hypothesis that the injury in this model is dependent on mitochondrial electron flow and suggest that mitochondrial electron flow, driven by the work of active solute transport in the presence of limited oxygen availability, may result in the generation of toxic oxygen metabolites.

Anoxia-induced apoptosis occurs through a mitochondria-dependent pathway in lung epithelial cells

The intracellular signaling pathways that control O(2) deprivation (anoxia)-induced apoptosis have not been fully defined in lung epithelial cells. We show here that the lung epithelial cell line A549 releases cytochrome c and activates caspase-9 followed by DNA fragmentation and plasma membrane breakage in response to anoxia. The antiapoptotic protein Bcl-X(L) prevented the anoxia-induced cell death by inhibiting the release of cytochrome c and caspase-9 activation. A549 cells devoid of mitochondrial DNA (rho(o)-cells) and lacking a functional electron transport chain were resistant to anoxia-induced apoptosis. A549 cells preconditioned with either hypoxia (1.5% O(2)) or tumor necrosis factor-alpha, which activated the transcription factors hypoxia-inducible factor-1 or nuclear factor-kappaB, respectively, did not provide protection from anoxia-induced cell death. These results indicate that A549 cells require a functional electron transport chain and the release of cytochrome c for anoxia-induced apoptosis.

Cisplatin induces apoptosis in LLC-PK1 cells via activation of mitochondrial pathways

Cisplatin, a commonly used chemotherapeutic agent, has a major limitation because of its nephrotoxicity. Recent studies have shown that cisplatin causes apoptotic cell death in renal tubule cells, but the underlying molecular mechanisms remain to be elucidated. In this study, cisplatin was found to induce apoptosis in a dose- and duration-dependent manner in cultured proximal tubule (LLC-PK1) cells, as evidenced by DNA laddering and TdT-mediated dUTP nick end-labeling assay. Pretreatment with the specific caspase 9 inhibitor LEHD-CHO completely prevented the apoptosis, whereas the caspase 8 inhibitor IETD-fmk had no effect. Furthermore, the activity of caspase 9 was upregulated about sixfold by cisplatin in a dose-dependent manner. These results implicated the caspase 9-dependent mitochondrial apoptotic pathways. Indeed, cisplatin triggered a duration-dependent translocation of cytochrome c from the mitochondria to the cytosol, by immunofluorescence and Western blots. Cisplatin treatment also resulted in the duration-dependent activation and mitochondrial translocation of the pro-apoptotic molecule Bax, by immunofluorescence. Finally, cisplatin induced a duration-dependent onset of the mitochondrial permeability transition. Our results indicate that cisplatin induces apoptosis in LLC-PK1 cells via activation of mitochondrial signaling pathways. The sequence of events may be summarized as follows: activation of Bax induces mitochondrial permeability transition, leading to release of cytochrome c, activation of caspase 9, and entry into the execution phase of apoptosis. Inhibition of this specific pathway may provide a strategy to minimize cisplatin-induced nephrotoxicity.

Activation of c-Jun N-terminal kinase promotes survival of cardiac myocytes after oxidative stress

Reperfusion injury occurs when ischaemic tissue is reperfused. It involves the generation and release of reactive oxygen that activates numerous signalling pathways and initiates cell death. Exposure of isolated cardiac myocytes to chronic hypoxia followed by reoxygenation results in the early activation of c-Jun N-terminal kinase (JNK) and death by apoptosis of approx. 30% of the myocytes. Although JNK activation has been described in a number of models of ischaemia/reperfusion, the contribution of JNK activation to cell fate has not been established. Here we report that the activation of JNK by reoxygenation correlates with myocyte survival. Transfection of myocytes with JNK pathway interfering plasmid vectors or infection with adenoviral vectors support the hypothesis that JNK is protective. Transfection or infection with JNK inhibitory mutants increased the rates of apoptosis by almost 2-fold compared with control cultures grown aerobically or subjected to hypoxia and reoxygenation. Caspase 9 activity, measured by LEHD cleavage, increased >3-fold during reoxygenation and this activity was enhanced significantly at all times in cultures infected with dominant negative JNK adenovirus. Hypoxia-reoxygenation mediated a biphasic (2.6- and 2.9-fold) activation of p38 mitogen-activated protein kinase, as well as a small increase of tumour necrosis factor alpha (TNFalpha) secretion, but treatments with the p38 MAPK-specific inhibitor SB203580 or saturating levels of a TNFalpha-1 blocking antibody provided only partial protection against apoptosis. The results suggest that JNK activation is protective and that the pathway is largely independent of p38 MAPK or secreted TNFalpha.

Leukocyte mitochondria alterations after aerobic exercise in trained human subjects

Exercise is associated with intensity-dependent immune disturbances. Leukocyte mitochondrial alterations and apoptosis may contribute to this phenomenon.

PURPOSE

To investigate the effects of different intensities of aerobic exercise (AE) on leukocyte mitochondrial transmembrane potential (MTP) and the propensity of apoptosis.

METHODS

Blood samples were collected from 12 subjects who performed AE for 3 consecutive days (35% maximal oxygen consumption (VO2max)). Leukocyte MTP and apoptosis were measured by flow cytometry. The subjects performed two additional sessions of AE of higher intensities (60% and 85% VO2max) with an intervening 4-wk washout period. The measurements were repeated during each session.

RESULTS

Leukocyte MTP declined during daily, repetitive AE at an intensity of 60% and 85% VO2max. Similar changes were not found during a more moderate AE (35% VO2max). Leukocytes increased their propensity of apoptosis a period (3-5 d) after the start of the AE.

CONCLUSION

High-intensity AE has accumulative effects on the mitochondrial energization status and vitality of peripheral blood leukocytes. Leukocyte MTP is a potentially applicable indicator for monitoring immune distress due to overtraining.

Transgenic mice overexpressing human Bcl-2 are resistant to hepatic ischemia and reperfusion

BACKGROUND/AIMS

Apoptosis is a key mechanism of reperfusion injury in the ischemic liver. The apoptotic pathway is highly regulated by anti-apoptotic factors, such as Bcl-2. We evaluated the effect of Bcl-2 overexpression on apoptosis and the activation of the apoptotic cascade after hepatic ischemia and reperfusion.

METHODS

Ninety minutes of ischemia and reperfusion was performed in Bcl-2 transgenic and non-transgenic mice. Bcl-2 overexpression was determined by immunohistochemistry and Western blot. Liver injury was determined by aspartate aminotransferase (AST), Tunel test and the activation of the apoptotic cascade and animal survival.

RESULTS

Bcl-2 overexpression was present in all hepatocytes and non-parenchymal liver cells in transgenic mice. Bcl-2 overexpression resulted in significant decreased AST levels after ischemic injury, and complete inhibition of apoptosis. After 90 min of total hepatic ischemia all control mice died, while four transgenic mice survived permanently. Bcl-2 overexpression was associated with inhibition of caspase 3 activation after reperfusion and increased baseline levels of cytoplasmic cytochrome c, caspase 3, and a reduction of Bcl-x(L) production.

CONCLUSIONS

Bcl-2 overexpression protects against ischemic injury by inhibiting apoptosis. Extensive overproduction of Bcl-2 is associated with a compensatory increase of baseline levels of cytoplasmic cytochrome c and caspase 3, and a deletion of Bcl-x(L).

Reactive species mechanisms of cellular hypoxia-reoxygenation injury

Exacerbation of hypoxic injury after restoration of oxygenation (reoxygenation) is an important mechanism of cellular injury in transplantation and in myocardial, hepatic, intestinal, cerebral, renal, and other ischemic syndromes. Cellular hypoxia and reoxygenation are two essential elements of ischemia-reperfusion injury. Activated neutrophils contribute to vascular reperfusion injury, yet posthypoxic cellular injury occurs in the absence of inflammatory cells through mechanisms involving reactive oxygen (ROS) or nitrogen species (RNS). Xanthine oxidase (XO) produces ROS in some reoxygenated cells, but other intracellular sources of ROS are abundant, and XO is not required for reoxygenation injury. Hypoxic or reoxygenated mitochondria may produce excess superoxide (O) and release H(2)O(2), a diffusible long-lived oxidant that can activate signaling pathways or react vicinally with proteins and lipid membranes. This review focuses on the specific roles of ROS and RNS in the cellular response to hypoxia and subsequent cytolytic injury during reoxygenation.

DAP kinase activity is critical for C(2)-ceramide-induced apoptosis in PC12 cells

Exposure of PC12 cells to C(2)-ceramide results in dose- dependent apoptosis. Here, we investigate the involvement of death-associated protein (DAP) kinase, initially identified as a positive mediator of the interferon-gamma-induced apoptosis of HeLa cells, in the C(2)-ceramide-induced apoptosis of PC12 cells. DAP kinase is endogenously expressed in these cells. On exposure of PC12 cells to 30 microm C(2)-ceramide, both the total (assayed in the presence of Ca(2+)/calmodulin) and Ca(2+)/calmodulin-independent (assayed in the presence of EGTA) DAP kinase activities were transiently increased 5.0- and 12.2-fold, respectively, at 10 min, and then decreased to 1.7- and 3.4-fold at 90 min. After 10 min exposure to 30 microm C(2)-ceramide, the Ca(2+)/calmodulin independent activity/ total activity ratio increased from 0.22 to 0.60. These effects were dependent on the C(2)-ceramide concentration. C(8)-ceramide, another active ceramide analog, also induced apoptosis and activated DAP kinase, while C(2)-dihydroceramide, an inactive ceramide analog, failed to induce apoptosis and increase DAP kinase activity. Furthermore, transfection studies revealed that overexpression of wild-type DAP kinase enhanced the sensitivity to C(2)- and C(8)-ceramide, while a catalytically inactive DAP kinase mutant and a construct containing the death domain and C-terminal tail of DAP kinase, which act in a dominant-negative manner, rescued cells from C(2)-, and C(8)-ceramide-induced apoptosis. These findings demonstrate that DAP kinase is an important component of the apoptotic machinery involved in ceramide-induced apoptosis, and that the intrinsic DAP kinase activity is critical for ceramide-induced apoptosis.

Bcl-2 family members and functional electron transport chain regulate oxygen deprivation-induced cell death

The mechanisms underlying cell death during oxygen deprivation are unknown. We report here a model for oxygen deprivation-induced apoptosis. The death observed during oxygen deprivation involves a decrease in the mitochondrial membrane potential, followed by the release of cytochrome c and the activation of caspase-9. Bcl-X(L) prevented oxygen deprivation-induced cell death by inhibiting the release of cytochrome c and caspase-9 activation. The ability of Bcl-X(L) to prevent cell death was dependent on allowing the import of glycolytic ATP into the mitochondria to generate an inner mitochondrial membrane potential through the F(1)F(0)-ATP synthase. In contrast, although activated Akt has been shown to inhibit apoptosis induced by a variety of apoptotic stimuli, it did not prevent cell death during oxygen deprivation. In addition to Bcl-X(L), cells devoid of mitochondrial DNA (rho degrees cells) that lack a functional electron transport chain were resistant to oxygen deprivation. Further, murine embryonic fibroblasts from bax(-/-) bak(-/-) mice did not die in response to oxygen deprivation. These data suggest that when subjected to oxygen deprivation, cells die as a result of an inability to maintain a mitochondrial membrane potential through the import of glycolytic ATP. Proapoptotic Bcl-2 family members and a functional electron transport chain are required to initiate cell death in response to oxygen deprivation.

Immunoreactivity for Bcl-2 and C-Jun/AP1 in hippocampal corpora amylacea after ischaemia in humans

Corpora amylacea (CAm) are regarded as a hallmark of brain ageing, but little is known about their role in normal and pathological circumstances. CAm contain, in addition to glucose polymers, ageing-, stress- and proinflammatory proteins. In view of their almost universal occurrence and their cumulation with time, formation of CAm may represent a basic mechanism for the management of metabolic degradation products. In this context, we studied samples from post-mortem cases with repetitive brain hypoxic episodes in the past history. We investigated, by immunohistochemistry, the presence of Bcl-2, c-jun and bax in CAm. CAm showed immunoreactivity for the mitochondrial membrane associated protein Bcl-2, and for the major component of activator protein 1 transcriptional factor c-Jun. We found higher numbers of CAm in the hippocampus and the dentate gyrus in cases with repetitive cerebral hypoxia than in controls. We conclude that: (1) the presence of C-Jun and Bcl-2 within the glucose polymer mass of CAm may be related to mitochondrial damage and/or a transient overload of proteolytic systems during cellular injury; and (2) repetitive cellular stress during life may cause the age-related increase of CAm in elderly subjects.

The von Hippel-Lindau gene product inhibits renal cell apoptosis via Bcl-2-dependent pathways

Previous studies have reported a protective role for the von Hippel-Lindau (VHL) gene products against pro-apoptotic cellular stresses, but the mechanisms remain unclear. In this study, we examined the role of VHL in renal cells subjected to chemical hypoxia, using four VHL-negative and two VHL-positive cell lines. VHL-negative renal carcinoma cells underwent apoptosis following chemical hypoxia (short-term glucose deprivation and antimycin treatment), as evidenced by morphologic changes and internucleosomal DNA cleavage. Reintroduction of VHL expression prevented this apoptosis. VHL-negative cells displayed a significant (greater than 5-fold) activation of caspase 9 and release of cytochrome c into the cytosol following chemical hypoxia. In contrast, VHL-positive cells showed minimal caspase 9 activation, and absence of cytochrome c release under the same conditions. Caspase 8 was only minimally activated in both VHL-negative and -positive cells. In addition, VHL-positive cells displayed a striking up-regulation of Bcl-2 expression (5-fold) following chemical hypoxia. Antisense oligonucleotides to Bcl-2 significantly down-regulated Bcl-2 protein expression in VHL-positive cells and rendered them sensitive to apoptosis. Overexpression of Bcl-2 in VHL-negative cells conferred resistance to apoptosis. Our results suggest that VHL protects renal cells from apoptosis via Bcl-2-dependent pathways.

Ovulation-induced DNA damage in ovarian surface epithelial cells of ewes: prospective regulatory mechanisms of repair/survival and apoptosis

Oxidative base (8-oxoguanine) damage, DNA fragmentation, and apoptosis occurred among ovarian surface epithelial cells within the formative site of ovulation in sheep. The incidence of 8-oxoguanine adducts in surviving antiapoptotic Bcl-2/base excision repair polymerase beta-positive cells at the margins of ruptured follicles (which avoid the focal point of the ovulatory assault) was intermediate between apoptotic and outlying healthy epithelium. Cells containing perturbations to DNA expressed the tumor suppressor p53. Localized reactions of DNA injury and programmed cellular death were averted by ovulation blockade with indomethacin. Progesterone enhanced the biosynthesis of polymerase beta in ovarian surface epithelial cells exposed in vitro to a sublethal concentration of H(2)O(2). Ovulation is a putative etiological factor in common epithelial ovarian cancer. A genetically altered progenitor cell, with unrepaired DNA, but not committed to death, could give rise to a transformed phenotype that is hence propagated upon healing of the ovulatory wound; it appears that this incongruity is normally reconciled by up-regulation of the base excision repair pathway during the ensuing luteal phase.

Chronic hypoxia induces apoptosis in cardiac myocytes: a possible role for Bcl-2-like proteins

The effect of prolonged hypoxia as well as the molecular mechanisms on cardiac cell death is not well established. A possible role of Bcl-2 and Bax in hypoxia-induced apoptosis in different cell types has been proposed. Here we demonstrate the effect of hypoxia on the induction of apoptosis and the expression of Bcl-2-like proteins in vivo and in vitro. Hearts from rats exposed to chronic hypoxia (n = 4) showed an increased rate of apoptosis compared to normoxic hearts (n = 4). The induction of apoptosis in hypoxic hearts correlated with a significant decrease of Bcl-2 protein level, whereas Bax protein expression was increased. Exposure of isolated neonatal rat cardiac myocytes to hypoxia also resulted in a significant increase in apoptosis. However, Bcl-2 and Bax protein levels essentially remained unchanged. Our results may suggest a different molecular mechanism of hypoxia-induced apoptosis in vivo and in vitro.

Effect of poly(ADP-ribose) polymerase inhibitors on the ischemia-reperfusion-induced oxidative cell damage and mitochondrial metabolism in Langendorff heart perfusion system

Ischemia-reperfusion induces reactive oxygen species (ROS) formation, and ROS lead to cardiac dysfunction, in part, via the activation of the nuclear poly(ADP-ribose) polymerase (PARP, called also PARS and ADP-RT). ROS and peroxynitrite induce single-strand DNA break formation and PARP activation, resulting in NAD(+) and ATP depletion, which can lead to cell death. Although protection of cardiac muscle by PARP inhibitors can be explained by their attenuating effect on NAD(+) and ATP depletion, there are data indicating that PARP inhibitors also protect mitochondria from oxidant-induced injury. Studying cardiac energy metabolism in Langendorff heart perfusion system by (31)P NMR, we found that PARP inhibitors (3-aminobenzamide, nicotinamide, BGP-15, and 4-hydroxyquinazoline) improved the recovery of high-energy phosphates (ATP, creatine phosphate) and accelerated the reutilization of inorganic phosphate formed during the ischemic period, showing that PARP inhibitors facilitate the faster and more complete recovery of the energy production. Furthermore, PARP inhibitors significantly decrease the ischemia-reperfusion-induced increase of lipid peroxidation, protein oxidation, single-strand DNA breaks, and the inactivation of respiratory complexes, which indicate a decreased mitochondrial ROS production in the reperfusion period. Surprisingly, PARP inhibitors, but not the chemically similar 3-aminobenzoic acid, prevented the H(2)O(2)-induced inactivation of cytochrome oxidase in isolated heart mitochondria, suggesting the presence of an additional mitochondrial target for PARP inhibitors. Therefore, PARP inhibitors, in addition to their important primary effect of decreasing the activity of nuclear PARP and decreasing NAD(+) and ATP consumption, reduce ischemia-reperfusion-induced endogenous ROS production and protect the respiratory complexes from ROS induced inactivation, providing an additional mechanism by which they can protect heart from oxidative damages.

Transcriptional regulation of the BCL-X gene by NF-kappaB is an element of hypoxic responses in the rat brain

Signal transduction pathways that mediate neuronal commitment to apoptosis involve the nuclear factor kappa B (NF-kappaB) transcription factor. The bcl-x gene is a member of the bcl-2 family of genes that regulate apoptosis, and gives rise to two proteins, Bcl-XL and Bcl-XS, via alternative mRNA splicing. BCl-XL protein, like Bcl-2, is a dominant inhibitor of apoptotic cell death, whereas Bcl-XS promotes apoptosis. While there is high expression of Bcl-XL in the developing and adult brain, few transcriptional control elements have been identified in the bcl-x promoter. There are two functional nuclear factor-kappa B (NF-kappaB) DNA binding sites clustered upstream of the brain-specific transcription start site in the upstream promoter region of murine bcl-x. Recombinant NF-kappaB proteins bind to these sites. Also NF-kappaB overexpression, coupled with bcl-x promoter/reporter assays using a series of murine bcl-x promoter and deletion mutants, has identified the downstream 1.1kb of the bcl-x promoter as necessary for basal promoter activity and induction by NF-kappaB in support of the hypothesis that NF-kappaB can act to enhance BCl-XL expression via highly selective interactions with the bcl-x promoter, where NF-kappaB binding and promoter activation are dependent on specific DNA binding site sequences and NF-kappaB protein dimer composition. Hypoxia induces apoptosis in the hippocampus where the NF-kappaB dimers c-Rel/p50 and p50/pS0 bind to the bcl-x promoter NF-kappaB site.

Up-regulation of apoptosis inhibitory protein IAP-2 by hypoxia. Hif-1-independent mechanisms

Hypoxia is a key determinant of tissue pathology during tumor development and organ ischemia. However, little is known regarding hypoxic regulation of genes that are directly involved in cell death or death resistance. Here we report the striking induction by severe hypoxia of the anti-apoptotic protein IAP-2. Hypoxic cells with IAP-2 up-regulation became resistant to apoptosis. IAP-2 was induced by hypoxia per se rather than by the secondary effects of hypoxia, including ATP depletion and cell injury. The inductive response did not relate to alterations of cellular redox status or arrest of mitochondrial respiration. On the other hand, IAP-2 induction was attenuated by actinomycin D, suggesting a role for gene transcription. In vitro nuclear run-on assays demonstrated specific increases in IAP-2 transcriptional activity after hypoxia exposure. HIF-1, the primary transcription factor that is responsible for multiple gene activation under hypoxia, does not have a role in IAP-2 expression. HIF-1 and IAP-2 were induced by different degrees of hypoxia; severe hypoxia or anoxia was required for IAP-2 induction. Moreover, cobalt chloride and desferrioxamine activated HIF-1 but not IAP-2. Finally, IAP-2 was induced by severe hypoxia in mouse embryonic stem cells that were deficient of HIF-1. Thus, this study not only provides the first demonstration of hypoxic regulation of an anti-apoptotic gene but also suggests the participation of novel hypoxia-responsive transcription mechanisms.

Bcl-2 prevents Bax oligomerization in the mitochondrial outer membrane

ATP depletion results in Bax translocation from cytosol to mitochondria and release of cytochrome c from mitochondria into cytosol in cultured kidney cells. Overexpression of Bcl-2 prevents cytochrome c release, without ameliorating ATP depletion or Bax translocation, with little or no association between Bcl-2 and Bax as demonstrated by immunoprecipitation (Saikumar, P., Dong, Z., Patel, Y., Hall, K., Hopfer, U., Weinberg, J. M., and Venkatachalam, M. A. (1998) Oncogene 17, 3401-3415). Now we show that translocated Bax forms homo-oligomeric structures, stabilized as chemical adducts by bifunctional cross-linkers in ATP-depleted wild type cells, but remains monomeric in Bcl-2-overexpressing cells. The protective effects of Bcl-2 did not require Bcl-2/Bax association, at least to a degree of proximity or affinity that was stable to conditions of immunoprecipitation or adduct formation by eight cross-linkers of diverse spacer lengths and chemical reactivities. On the other hand, nonionic detergents readily induced homodimers and heterodimers of Bax and Bcl-2. Moreover, associations between translocated Bax and the voltage-dependent anion channel protein or the adenine nucleotide translocator protein could not be demonstrated by immunoprecipitation of Bax, or by using bifunctional cross-linkers. Our data suggest that the in vivo actions of Bax are at least in part dependent on the formation of homo-oligomers without requiring associations with other molecules and that Bcl-2 cytoprotection involves mechanisms that prevent Bax oligomerization.

Hypoxia inhibits the peroxisome proliferator-activated receptor alpha/retinoid X receptor gene regulatory pathway in cardiac myocytes: a mechanism for O2-dependent modulation of mitochondrial fatty acid oxidation

Hypoxia triggers a cascade of cellular energy metabolic responses including a decrease in mitochondrial oxidative flux. To characterize gene regulatory mechanisms by which mitochondrial fatty acid oxidative capacity is diminished in response to hypoxia, cardiac myocytes in culture were exposed to long-chain fatty acids (LCFA) under normoxic or hypoxic conditions. Hypoxia prevented the known LCFA-induced accumulation of mRNA encoding muscle carnitine palmitoyltransferase I (M-CPT I), an enzyme that catalyzes the rate-limiting step in mitochondrial fatty acid oxidation (FAO). Under hypoxic conditions, myocytes exhibited significant accumulation of intracellular neutral lipid consistent with reduced CPT I activity and diminished FAO capacity. Transient transfection experiments demonstrated that the hypoxia-mediated blunting of M-CPT I gene expression occurs at the transcriptional level, is localized to an LCFA/peroxisome proliferator-activated receptor alpha (PPARalpha)/retinoid X receptor (RXR) response element within the M-CPT I gene promoter, and is PPARalpha-dependent. DNA-protein binding studies demonstrated that exposure to hypoxia reduces PPARalpha/RXR binding activity. Immunoblotting studies demonstrated that whereas hypoxia had no effect on nuclear levels of PPARalpha protein, nuclear and cellular RXRalpha levels were reduced. Hypoxia also diminished the 9-cis-retinoic acid-mediated activation of a reporter containing an RXR homodimer response element. These results demonstrate that hypoxia deactivates PPARalpha by reducing the availability of its obligate partner RXR.

Inhibition of hypoxia/reoxygenation-induced apoptosis in metallothionein-overexpressing cardiomyocytes

To study possible mechanisms for metallothionein (MT) inhibition of ischemia-reperfusion-induced myocardial injury, cardiomyocytes isolated from MT-overexpressing transgenic neonatal mouse hearts and nontransgenic controls were subjected to 4 h of hypoxia (5% CO2-95% N2, glucose-free modified Tyrode's solution) followed by 1 h of reoxygenation in MEM + 20% fetal bovine serum (FBS) (5% CO2-95% air), and cytochrome c-mediated caspase-3 activation apoptotic pathway was determined. Hypoxia/reoxygenation-induced apoptosis was significantly suppressed in MT-overexpressing cardiomyocytes, as measured by both terminal deoxynucleotidyl transferase-mediated deoxyuridine 5-triphosphate nick-end labeling and annexin V-FITC binding. In association with apoptosis, mitochondrial cytochrome c release, as determined by Western blot, was observed to occur in nontransgenic cardiomyocytes. Correspondingly, caspase-3 was activated as determined by laser confocal microscopic examination with the use of FITC-conjugated antibody against active caspase-3 and by enzymatic assay. The activation of this apoptotic pathway was significantly inhibited in MT-overexpressing cells, as evidenced by both suppression of cytochrome c release and inhibition of caspase-3 activation. The results demonstrate that MT suppresses hypoxia/reoxygenation-induced cardiomyocyte apoptosis through, at least in part, inhibition of cytochrome c-mediated caspase-3 activation.

Morphologic, biochemical and molecular mitochondrial changes during reperfusion phase following brief renal ischemia

Ischemia/reperfusion of organs and cells induces apoptosis through a complicated series of changes in mitochondria, mainly the generation of oxygen free radicals, permeability transitions, calcium translocations, and release of apoptogenic factors such as cytochrome c and Bcl-2 family members. The liberation of these factors occurs very early after reoxygenation and it has been assumed that it takes place without any structural alteration of the mitochondrial membranes. The aim of this study was to detect ultrastructural changes of mitochondria in the initial stages of reperfusion at the time when Bcl-2 and succinic dehydrogenase, located in the outer and inner membranes, respectively, were released. Ischemia/reperfusion was produced in adult rats by clamping one renal artery for 60 min and reoxygenating for 60, 120, 180, and 240 min. A model of chemical hypoxia with intra-arterial 50 mM sodium azide served as comparison, allowing free blood flow for 30, 60, 120 and 180 min. Light and electron microscopy, immunostaining for Bcl-2, and enzyme histochemistry for succinic dehydrogenase were performed. Our results showed mitochondrial swelling, rupture of inner and outer membranes, and leakage of mitochondrial matrix into the cytoplasm in ischemia after 120 min of reperfusion. Bcl-2 immunoreactivity and focal lowering of SDH reactivity were also noted and became more pronounced at the same time that the mitochondrial ultrastructure demonstrated more evident changes including rupture of the inner and outer membranes. Our studies seem to indicate that in early ischemia-reperfusion and in chemical hypoxia-induced apoptosis, the earliest ultrastructural changes take place in mitochondria and that swelling and rupture of mitochondrial membranes occur in parallel with the loss of Bcl-2 and SDH activity.

In vivo and in vitro measurement of apoptosis in breast cancer cells using 99mTc-EC-annexin V

OBJECTIVE

The purpose of this study was to develop an imaging technique to measure and monitor tumor cells undergoing programmed death caused by radiation and chemotherapy using 99mTc-EC-annexin V. Annexin V has been used to measure programmed cell death both in vitro and in vivo. Assessment of apoptosis would be useful to evaluate the efficacy and mechanisms of therapy and disease progression or regression.

METHODS

Ethylenedicysteine (EC) was conjugated to annexin V using sulfo-N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-HCl as coupling agents. The yield of EC-annexin V was 100%. In vitro cellular uptake, pre- and post-radiation (10-30 Gy) and paclitaxel treatment, was quantified using 99mTc-EC-annexin V. Tissue distribution and planar imaging of 99mTc-EC-annexin V were determined in breast tumor-bearing rats at 0.5, 2, and 4 hrs. To demonstrate in vivo cell apoptosis that occurred during chemotherapy, a group of rats was treated with paclitaxel and planar imaging studies were conducted at 0.5-4 hrs. Computer outlined region of interest (ROI) was used to quantify tumor uptake on day 3 and day 5 post-treatment.

RESULTS

In vitro cellular uptake showed that there was significantly increased uptake of 99mTc-EC-annexin V after irradiation (10-30 Gy) and paclitaxel treatment. In vivo biodistribution of 99mTc-EC-annexin in breast tumor-bearing rats showed increased tumor-to-blood, tumor-to-lung and tumor-to-muscle count density ratios as a function of time. Conversely, tumor-to-blood count density ratios showed a time-dependent decrease with 99mTc-EC in the same time period. Planar images confirmed that the tumors could be visualized clearly with 99mTc-EC-annexin. There was a significant difference of ROI ratios between pre- and post-paclitaxel treatment groups at 2 and 4 hrs post injection.

CONCLUSION

The results indicate that apoptosis can be quantified using 99mTc-EC-annexin and that it is feasible to use 99mTc-EC-annexin to image tumor apoptosis.

Molecular pathway of germ cell apoptosis following ischemia/reperfusion of the rat testis

The present study investigates the molecular apoptotic pathway in germ cells following acute ischemia of the rat testis. Rats were subjected to ischemia-inducing torsion and testes were harvested after reperfusion. Apoptotic cells were identified with an antibody to single-stranded DNA. Seminiferous tubule RNA was examined by RNase protection assay or by reverse transcriptase-polymerase chain reaction (RT-PCR) for the presence and regulation of apoptotic molecules. Proteins from seminiferous tubules were used for Western blot analysis of cytochrome c. Germ cell apoptosis was maximal at 24 h after repair of torsion. Germ cells in stages II-III of the seminiferous epithelium cycle were the predominant early responders. The RNase protection assays revealed that Bcl-X(L) was the prominent mRNA species. Caspases 1, 2, 3, and Bax mRNA were consistently upregulated; however, the time of upregulation after torsion was variable. The Bcl-X(L) and Bcl-X(S) mRNAs were less consistently upregulated and there was no evidence for upregulation of Fas or Bcl-2. Fas ligand (FasL) was not detected by RNase protection assay, but RT-PCR revealed a significant increase in FasL expression 4 h after the repair of torsion. Western blot analysis for cytochrome c release demonstrated a significant increase 4 h after the repair of torsion. Results suggest that germ cell apoptosis following ischemia/reperfusion of the rat testis is initiated through the mitochondria-associated molecule Bax as well as Fas-FasL interactions.

Anaerobic and aerobic pathways for salvage of proximal tubules from hypoxia-induced mitochondrial injury

We have further examined the mechanisms for a severe mitochondrial energetic deficit, deenergization, and impaired respiration in complex I that develop in kidney proximal tubules during hypoxia-reoxygenation, and their prevention and reversal by supplementation with alpha-ketoglutarate (alpha-KG) + aspartate. The abnormalities preceded the mitochondrial permeability transition and cytochrome c loss. Anaerobic metabolism of alpha-KG + aspartate generated ATP and maintained mitochondrial membrane potential. Other citric-acid cycle intermediates that can promote anaerobic metabolism (malate and fumarate) were also effective singly or in combination with alpha-KG. Succinate, the end product of these anaerobic pathways that can bypass complex I, was not protective when provided only during hypoxia. However, during reoxygenation, succinate also rescued the tubules, and its benefit, like that of alpha-KG + malate, persisted after the extra substrate was withdrawn. Thus proximal tubules can be salvaged from hypoxia-reoxygenation mitochondrial injury by both anaerobic metabolism of citric-acid cycle intermediates and aerobic metabolism of succinate. These results bear on the understanding of a fundamental mode of mitochondrial dysfunction during tubule injury and on strategies to prevent and reverse it.

Diazepam promotes ATP recovery and prevents cytochrome c release in hippocampal slices after in vitro ischemia

Benzodiazepines protect hippocampal neurons when administered within the first few hours after transient cerebral ischemia. Here, we examined the ability of diazepam to prevent early signals of cell injury (before cell death) after in vitro ischemia. Ischemia in vitro or in vivo causes a rapid depletion of ATP and the generation of cell death signals, such as the release of cytochrome c from mitochondria. Hippocampal slices from adult rats were subjected to 7 min of oxygen-glucose deprivation (OGD) and assessed histologically 3 h after reoxygenation. At this time, area CA1 neurons appeared viable, although slight abnormalities in structure were evident. Immediately following OGD, ATP levels in hippocampus were decreased by 70%, and they recovered partially over the next 3 h of reoxygenation. When diazepam was included in the reoxygenation buffer, ATP levels recovered completely by 3 h after OGD. The effects of diazepam were blocked by picrotoxin, indicating that the protection was mediated by an influx of Cl(-) through the GABA(A) receptor. It is interesting that the benzodiazepine antagonist flumazenil did not prevent the action of diazepam, as has been shown in other studies using the hippocampus. Two hours after OGD, the partial recovery of ATP levels occurred simultaneously with an increase of cytochrome c (approximately 400%) in the cytosol. When diazepam was included in the reoxygenation buffer, it completely prevented the increase in cytosolic cytochrome c. Thus, complete recovery of ATP and prevention of cytochrome c release from mitochondria can be achieved when diazepam is given after the loss of ATP induced by OGD.

Cardiac functional improvement by a human Bcl-2 transgene in a mouse model of ischemia/reperfusion injury

BACKGROUND

Apoptosis has been shown to contribute to myocardial reperfusion injury. It has been suggested that, in reducing the apoptotic component within the ischemic area at risk, Bcl-2 overexpression could lead to a ventricular function improvement.

METHODS

Transgenic mice overexpressing the anti-apoptotic human Bcl-2 cDNA in heart were subjected to a 1-h left coronary artery occlusion followed by a 24-h reperfusion. At the end of the experiment, left ventricular function was assessed by two-dimensional echocardiography. After sacrifice, the area at risk (AR) and the infarct area (IA) were determined by Evans blue and triphenyltetrazolium chloride staining, respectively. The extent of apoptosis was assessed by the TUNEL method. Non-transgenic littermates served as controls.

RESULTS

Baseline AR was not different between Bcl-2 transgenic mice and their wild-type littermates. In contrast, left ventricular ejection fraction was significantly improved in the transgenic mice line (61.25 +/- 4.0%) compared to non-transgenic littermates (43.2 +/- 5.0%, p < 0.01). This functional amelioration was correlated with a significant reduction of infarct size in transgenic animals (IA/AR 18.51 +/- 3.4% vs 50.83 +/- 8.4% in non-transgenic littermates). Finally, apoptotic nuclei were less numerous in transgenic mice than in controls as quantified by TUNEL analysis (8.1 +/- 2.2% vs 20.6 +/- 4.4%).

CONCLUSIONS

Bcl-2 overexpression is effective in reducing myocardial reperfusion injury and improving heart function. This benefit correlates with a reduction of cardiomyocyte apoptosis. The apoptotic component of ischemia/reperfusion injury could therefore constitute a new therapeutic target in the acute phase of myocardial infarction.

Anoxia pretreatment protects soybean cells against H(2)O(2)-induced cell death: possible involvement of peroxidases and of alternative oxidase

Anoxia followed by reoxygenation causes extensive damage to cellular components through generation of reactive oxygen intermediates. We examined cellular responses to oxidative stress after anoxia in cultured soybean or human fibroblast cells. Anoxia pretreatment protected soybean but not fibroblasts against H(2)O(2) concentrations that induced programmed cell death in normoxic cells. H(2)O(2) removal in anoxia-pretreated soybean cultures was faster. Protection was associated with increased action of alternative oxidase (AOX) and peroxidases. AOX inhibitors abolished the protective effect, while induction of AOX protected normoxic cells against H(2)O(2). We propose that during anoxia, plant cells can prepare for reoxygenation injury by up-regulating their antioxidant capacity, and that AOX is involved in this process.

P53 and IGFBP-3: apoptosis and cancer protection

p53, perhaps the single most important human tumor suppressor, is commonly mutated in human cancers. Normally genotoxic stress and hypoxia activate p53, which, through DNA-specific transcription activation, transcriptional repression, and protein-protein interactions, triggers cell cycle arrest and apoptosis. One of the genes induced by p53 was identified as that encoding the insulin-like growth factor binding protein (IGFBP)-3. IGFBP-3 was originally defined by the somatomedin hypothesis as the principal carrier of IGF-I in the circulation and the primary regulator of the amount of free IGF-I available to interact with the IGF-1 receptor. However, there is accumulating evidence that IGFBP-3 can also cause apoptosis in an IGF-independent manner. Thus, IGFBP-3 induction by p53 constitutes a new means of cross-talk between the p53 and IGF axes, and suggests that the ultimate function of IGFBP-3 may be to serve a protective role against the potentially carcinogenic effects of growth hormone and IGF-I.

Cytochrome c release and caspase activation in traumatic axonal injury

Axonal injury is a feature of traumatic brain injury (TBI) contributing to both morbidity and mortality. The traumatic axon injury (TAI) results from focal perturbations of the axolemma, allowing for calcium influx triggering local intraaxonal cytoskeletal and mitochondrial damage. This mitochondrial damage has been posited to cause local bioenergetic failure, leading to axonal failure and disconnection; however, this mitochondrial damage may also lead to the release of cytochrome c (cyto-c), which then activates caspases with significant adverse intraaxonal consequences. In the current communication, we examine this possibility. Rats were subjected to TBI, perfused with aldehydes at 15-360 min after injury, and processed for light microscopic (LM) and electron microscopic (EM) single-labeling immunohistochemistry to detect extramitochondrially localized cytochrome c (cyto-c) and the signature protein of caspase-3 activation (120 kDa breakdown product of alpha-spectrin) in TAI. Combinations of double-labeling fluorescent immunohistochemistry (D-FIHC) were also used to demonstrate colocalization of calpain activation with cyto-c release and caspase-3-induction. In foci of TAI qualitative-quantitative LM demonstrated a parallel, significant increase in cyto-c release and caspase-3 activation over time after injury. EM analysis demonstrated that cyto-c and caspase-3 immunoreactivity were associated with mitochondrial swelling-disruption in sites of TAI. Furthermore, D-IFHC revealed a colocalization of calpain activation, cyto-c release, and caspase-3 induction in these foci, which also revealed progressive TAI. The results demonstrate that cyto-c and caspase-3 participate in the terminal processes of TAI. This suggests that those factors that play a role in the apoptosis in the neuronal soma are also major contributors to the demise of the axonal appendage.

More than one way to die: apoptosis, necrosis and reactive oxygen damage

Cell death is an essential phenomenon in normal development and homeostasis, but also plays a crucial role in various pathologies. Our understanding of the molecular mechanisms involved has increased exponentially, although it is still far from complete. The morphological features of a cell dying either by apoptosis or by necrosis are remarkably conserved for quite different cell types derived from lower or higher organisms. At the molecular level, several gene products play a similar, crucial role in a major cell death pathway in a worm and in man. However, one should not oversimplify. It is now evident that there are multiple pathways leading to cell death, and some cells may have the required components for one pathway, but not for another, or contain endogenous inhibitors which preclude a particular pathway. Furthermore, different pathways can co-exist in the same cell and are switched on by specific stimuli. Apoptotic cell death, reported to be non-inflammatory, and necrotic cell death, which may be inflammatory, are two extremes, while the real situation is usually more complex. We here review the distinguishing features of the various cell death pathways: caspases (cysteine proteases cleaving after particular aspartate residues), mitochondria and/or reactive oxygen species are often, but not always, key components. As these various caspase-dependent and caspase-independent cell death pathways are becoming better characterized, we may learn to differentiate them, fill in the many gaps in our understanding, and perhaps exploit the knowledge acquired for clinical benefit.

Therapeutic targets for hypoxia-elicited pathways

Diminished oxygen supply to tissues (hypoxia) can stem from many sources, and is a contributing factor to diverse disease processes. Cell and tissue responses to hypoxia are diverse and include dramatic changes in metabolic demand, regulation of cellular gene products, and release of lipid and protein mediators. Surprisingly little attention has been paid to targeted development of therapeutics for hypoxia-related disease processes. This review will focus on recent advances in cellular and molecular biology pertaining to the hypoxia response, and will discuss paradigms used to study hypoxia and the potential targets for therapeutic intervention.