The apoptosis/necrosis transition in cerebellar granule cells depends on the mutual relationship of the antioxidant and the proteolytic systems which regulate ROS production and cytochrome c release en route to death

Ibogaine Induces Cardiotoxic Necrosis in Rats-The Role of Redox Processes

Ibogaine is an organic indole alkaloid that is used in alternative medicine to combat addiction. Numerous cases of life-threatening complications and sudden deaths associated with ibogaine use have been reported, and it has been hypothesized that the adverse effects are related to ibogaine's tendency to induce cardiac arrhythmias. Considering that the bioavailability of ibogaine and its primary metabolite noribogaine is two to three times higher in female rats than in male rats, we here investigated the effect of a single oral dose (1 or 20 mg/kg) of ibogaine on cardiac histopathology and oxidative/antioxidant balance. Our results show that ibogaine induced dose-dependent cardiotoxic necrosis 6 and 24 h after treatment and that this necrosis was not a consequence of inflammation. In addition, no consistent dose- and time-dependent changes in antioxidant defense or indicators of oxidative damage were observed. The results of this study may contribute to a better understanding of ibogaine-induced cardiotoxicity, which is one of the main side effects of ibogaine use in humans and is often fatal. Nevertheless, based on this experiment, it is not possible to draw a definitive conclusion regarding the role of redox processes or oxidative stress in the occurrence of cardiotoxic necrosis after ibogaine administration.

Dysfunction of Mitochondria in Alzheimer’s Disease: ANT and VDAC Interact with Toxic Proteins and Aid to Determine the Fate of Brain Cells

Alzheimer’s disease (AD), certainly the most widespread proteinopathy, has as classical neuropathological hallmarks, two groups of protein aggregates: senile plaques and neurofibrillary tangles. However, the research interest is rapidly gaining ground in a better understanding of other pathological features, first, of all the mitochondrial dysfunctions. Several pieces of evidence support the hypothesis that abnormal mitochondrial function may trigger aberrant processing of amyloid progenitor protein or tau and thus neurodegeneration. Here, our aim is to emphasize the role played by two ‘bioenergetic’ proteins inserted in the mitochondrial membranes, inner and outer, respectively, that is, the adenine nucleotide translocator (ANT) and the voltage-dependent anion channel (VDAC), in the progression of AD. To perform this, we will magnify the ANT and VDAC defects, which are measurable hallmarks of mitochondrial dysfunction, and collect all the existing information on their interaction with toxic Alzheimer’s proteins. The pathological convergence of tau and amyloid β-peptide (Aβ) on mitochondria may finally explain why the therapeutic strategies used against the toxic forms of Aβ or tau have not given promising results separately. Furthermore, the crucial role of ANT-1 and VDAC impairment in the onset/progression of AD opens a window for new therapeutic strategies aimed at preserving/improving mitochondrial function, which is suspected to be the driving force leading to plaque and tangle deposition in AD.

Personalized Medicine in Mitochondrial Health and Disease: Molecular Basis of Therapeutic Approaches Based on Nutritional Supplements and Their Analogs

Mitochondrial diseases (MDs) may result from mutations affecting nuclear or mitochondrial genes, encoding mitochondrial proteins, or non-protein-coding mitochondrial RNA. Despite the great variability of affected genes, in the most severe cases, a neuromuscular and neurodegenerative phenotype is observed, and no specific therapy exists for a complete recovery from the disease. The most used treatments are symptomatic and based on the administration of antioxidant cocktails combined with antiepileptic/antipsychotic drugs and supportive therapy for multiorgan involvement. Nevertheless, the real utility of antioxidant cocktail treatments for patients affected by MDs still needs to be scientifically demonstrated. Unfortunately, clinical trials for antioxidant therapies using α-tocopherol, ascorbate, glutathione, riboflavin, niacin, acetyl-carnitine and coenzyme Q have met a limited success. Indeed, it would be expected that the employed antioxidants can only be effective if they are able to target the specific mechanism, i.e., involving the central and peripheral nervous system, responsible for the clinical manifestations of the disease. Noteworthily, very often the phenotypes characterizing MD patients are associated with mutations in proteins whose function does not depend on specific cofactors. Conversely, the administration of the antioxidant cocktails might determine the suppression of endogenous oxidants resulting in deleterious effects on cell viability and/or toxicity for patients. In order to avoid toxicity effects and before administering the antioxidant therapy, it might be useful to ascertain the blood serum levels of antioxidants and cofactors to be administered in MD patients. It would be also worthwhile to check the localization of mutations affecting proteins whose function should depend (less or more directly) on the cofactors to be administered, for estimating the real need and predicting the success of the proposed cofactor/antioxidant-based therapy.

AMPK is activated early in cerebellar granule cells undergoing apoptosis and influences VADC1 phosphorylation status and activity

The neurodegeneration of cerebellar granule cells, after low potassium induced apoptosis, is known to be temporally divided into an early and a late phase. Voltage-dependent anion channel-1 (VDAC1) protein, changing from the closed inactive state to the active open state, is central to the switch between the early and late phase. It is also known that: (i) VDAC1 can undergo phosphorylation events and (ii) AMP-activated protein kinase (AMPK), the sensor of cellular stress, may have a role in neuronal homeostasis. In the view of this, the involvement of AMPK activation and its correlation with VDAC1 status and activity has been investigated in the course of cerebellar granule cells apoptosis. The results reported in this study show that an increased level of the phosphorylated, active, isoform of AMPK occurs in the early phase, peaks at 3 h and guarantees an increase in the phosphorylation status of VDCA1, resulting in a reduced activity of this latter. However this situation is transient in nature, since, in the late phase, AMPK activation decreases as well as the level of phosphorylated VDAC1. In a less phosphorylated status, VDAC1 fully recovers its gating activity and drives cells along the death route.

Aberrant GSH reductase and NOX activities concur with defective CFTR to pro-oxidative imbalance in cystic fibrosis airways

Cystic fibrosis (CF) is associated to impaired Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) channel also causing decreased glutathione (GSH) secretion, defective airway bacterial clearance and inflammation. Here we checked the main ROS-producing and ROS-scavenging enzymes as potential additional factors involved in CF pathogenesis. We found that CFBE41o-cells, expressing F508del CFTR, have increased NADPH oxidase (NOX) activity and expression level, mainly responsible of the increased ROS production, and decreased glutathione reductase (GR) activity, not dependent on GR protein level decrease. Furthermore, defective CFTR proved to cause both extracellular and intracellular GSH level decrease, probably by reducing the amount of extracellular GSH-derived cysteine required for cytosolic GSH synthesis. Importantly, we provide evidence that defective CFTR and NOX/GR activity imbalance both contribute to NADPH and GSH level decrease and ROS overproduction in CF cells.

A disease with a sweet tooth: exploring the Warburg effect in Alzheimer's disease

After more than 80 years from the revolutionary discoveries of Otto Warburg, who observed high glucose dependency, with increased glycolysis and lactate production regardless of oxygen availability in most cancer cells, the 'Warburg effect' returns to the fore in neuronal cells affected by Alzheimer's disease (AD). Indeed, it seems that, in the mild phase of AD, neuronal cells "prefer" to use the energetically inefficient method of burning glucose by glycolysis, as in cancer, proving to become resistant to β-amyloid (Aβ)-dependent apoptosis. However, in the late phase, while most AD brain cells die in response to Aβ toxicity, only small populations of neurons, exhibiting increased glucose uptake and glycolytic flux, are able to survive as they are resistant to Aβ. Here we draw an overview on the metabolic shift for glucose utilization from oxidative phosphorylation to glycolysis, focusing on the hypothesis that, as extreme attempt to oppose the impending death, mitochondria-whose dysfunction and central role in Aβ toxicity is an AD hallmark-are sent into quiescence, this likely contributing to activate mechanisms of resistance to Aβ-dependent apoptosis. Finally, the attempt turns out fruitless since the loss of the adaptive advantage afforded by elevated aerobic glycolysis exacerbates the pathophysiological processes associated with AD, making the brain susceptible to Aβ-induced neurotoxicity and leading to cell death and dementia. The understanding of how certain nerve cells become resistant to Aβ toxicity, while the majority dies, is an attractive challenge toward the identification of novel possible targets for AD therapy.

PEP-1-GSTpi protein enhanced hippocampal neuronal cell survival after oxidative damage

Reactive oxygen species generated under oxidative stress are involved in neuronal diseases, including ischemia. Glutathione S-transferase pi (GSTpi) is a member of the GST family and is known to play important roles in cell survival. We investigated the effect of GSTpi against oxidative stress-induced hippocampal HT-22 cell death, and its effects in an animal model of ischemic injury, using a cell-permeable PEP-1-GSTpi protein. PEP-1-GSTpi was transduced into HT-22 cells and significantly protected against H2O2-treated cell death by reducing the intracellular toxicity and regulating the signal pathways, including MAPK, Akt, Bax, and Bcl-2. PEP-1-GSTpi transduced into the hippocampus in animal brains, and markedly protected against neuronal cell death in an ischemic injury animal model. These results indicate that PEP-1-GSTpi acts as a regulator or an antioxidant to protect against oxidative stress-induced cell death. Our study suggests that PEP-1-GSTpi may have potential as a therapeutic agent for the treatment of ischemia and a variety of oxidative stress-related neuronal diseases. [BMB Reports 2016; 49(7): 382-387]

Metabolic reprogramming by the pyruvate dehydrogenase kinase-lactic acid axis: Linking metabolism and diverse neuropathophysiologies

Emerging evidence indicates that there is a complex interplay between metabolism and chronic disorders in the nervous system. In particular, the pyruvate dehydrogenase (PDH) kinase (PDK)-lactic acid axis is a critical link that connects metabolic reprogramming and the pathophysiology of neurological disorders. PDKs, via regulation of PDH complex activity, orchestrate the conversion of pyruvate either aerobically to acetyl-CoA, or anaerobically to lactate. The kinases are also involved in neurometabolic dysregulation under pathological conditions. Lactate, an energy substrate for neurons, is also a recently acknowledged signaling molecule involved in neuronal plasticity, neuron-glia interactions, neuroimmune communication, and nociception. More recently, the PDK-lactic acid axis has been recognized to modulate neuronal and glial phenotypes and activities, contributing to the pathophysiologies of diverse neurological disorders. This review covers the recent advances that implicate the PDK-lactic acid axis as a novel linker of metabolism and diverse neuropathophysiologies. We finally explore the possibilities of employing the PDK-lactic acid axis and its downstream mediators as putative future therapeutic strategies aimed at prevention or treatment of neurological disorders.

Glycolytic enzyme upregulation and numbness of mitochondrial activity characterize the early phase of apoptosis in cerebellar granule cells

Alzheimer's disease (AD) and cancer proceed via one or more common molecular mechanisms: a metabolic shift from oxidative phosphorylation to glycolysis-corresponding to the activation of the Warburg effect-occurs in both diseases. The findings reported in this paper demonstrate that, in the early phase of apoptosis, glucose metabolism is enhanced, i.e. key proteins which internalize and metabolize glucose-glucose transporter, hexokinase and phosphofructokinase-are up-regulated, in concomitance with a parallel decrease in oxygen consumption by mitochondria and increase of L-lactate accumulation. Reversal of the glycolytic phenotype occurs in the presence of dichloroacetate, inhibitor of the pyruvate dehydrogenase kinase enzyme, which speeds up apoptosis of cerebellar granule cells, reawakening mitochondria and then modulating glycolytic enzymes. Loss of the adaptive advantage afforded by aerobic glycolysis, which occurs in the late phase of apoptosis, exacerbates the pathological processes underlying neurodegeneration, leading inevitably the cell to death. In conclusion, the data propose that both aerobic, i.e. Warburg effect, essentially due to the protective numbness of mitochondria, and anaerobic glycolysis, rather due to the mitochondrial impairment, characterize the entire time frame of apoptosis, from the early to the late phase, which mimics the development of AD.

Resveratrol relieves ischemia-induced oxidative stress in the hippocampus by activating SIRT1

Resveratrol, a naturally occurring phytoalexin, acts as an activator of sirtuin 1 (SIRT1) and has been shown to have a neuroprotective role in various models. Healthy adult male Sprague-Dawley rats were subjected to cerebral ischemia in order to study the protective effect of resveratrol on the brain following ischemia, and to investigate the effects of SIRT1 activation on the hippocampus. Untreated and resveratrol-treated rats were anesthetized prior to undergoing surgery to induce middle cerebral artery occlusion followed by reperfusion. SIRT1 expression was evaluated by immunohistochemistry, western blotting and reverse transcription-quantitative polymerase chain reaction, and SIRT1 activity was also evaluated. In addition, terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) and Nissl staining assays were conducted and the levels of reactive oxygen species were determined. It was observed that resveratrol significantly decreased the number of TUNEL-positive cells and increased the expression of SIRT1 mRNA in a dose-dependent manner. This was accompanied by increases in SIRT1 protein expression levels and SIRT1 activity. The results demonstrate the neuroprotective and antioxidant effects of resveratrol against ischemia-induced apoptosis in the rat hippocampus.

Thioredoxin/thioredoxin reductase system involvement in cerebellar granule cell apoptosis

The involvement of thioredoxin/thioredoxin reductase system has been investigated in cerebellar granule cells (CGCs), a cellular system in which neurons are induced in apoptosis by the physiological stimulus of lowering extracellular potassium. Clarifying the sequence of events that occur during apoptosis is a critical issue as it can lead to the identification of those key events that, if blocked, can slow down or reverse the death process. The results reported in this work show that TrxR is involved in the early phase of CGC apoptosis with an increase in activity that coincides with the increased expression of the TrxR1 isoform and guarantees the maintenance of adequate level of Trx in its reduced, active form. However, in late apoptosis, when about 50 % of cells are dead, partial proteolysis of TrxR1 by calpain occurs and the reduction of TrxR1 mRNA, together with the overall decrease in TrxR activity, contribute to increase the levels of the oxidized form of Trx. When the reduced form of Trx is externally added to apoptotic cultures, a significant reduction in cell death is achieved confirming that a well-functioning thioredoxin/thioredoxin reductase system is required for survival of CGCs.

Glucose-6-phosphate tips the balance in modulating apoptosis in cerebellar granule cells

A metabolic shift from oxidative phosphorylation to glycolysis (i.e. the Warburg effect) occurs in Alzheimer's disease accompanied by an increase of both activity and level of HK-I. The findings reported here demonstrate that in the early phase of apoptosis VDAC1 activity, but not its protein level, progressively decreases, in concomitance with the physical interaction of HK-I with VDAC1. In the late phase of apoptosis, glucose-6-phosphate accumulation in the cell causes the dissociation of the two proteins, the re-opening of the channel and the recovery of VDAC1 function, resulting in a reawakening of the mitochondrial function, thus inevitably leading to cell death.

Extracellular ADP prevents neuronal apoptosis via activation of cell antioxidant enzymes and protection of mitochondrial ANT-1

Apoptosis in neuronal tissue is an efficient mechanism which contributes to both normal cell development and pathological cell death. The present study explores the effects of extracellular ADP on low [K(+)]-induced apoptosis in rat cerebellar granule cells. ADP, released into the extracellular space in brain by multiple mechanisms, can interact with its receptor or be converted, through the actions of ectoenzymes, to adenosine. The findings reported in this paper demonstrate that ADP inhibits the proapoptotic stimulus supposedly via: i) inhibition of ROS production during early stages of apoptosis, an effect mediated by its interaction with cell receptor/s. This conclusion is validated by the increase in SOD and catalase activities as well as by the GSSG/GSH ratio value decrease, in conjunction with the drop of ROS level and the prevention of the ADP protective effect by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), a novel functionally selective antagonist of purine receptor; ii) safeguard of the functionality of the mitochondrial adenine nucleotide-1 translocator (ANT-1), which is early impaired during apoptosis. This effect is mediated by its plausible internalization into cell occurring as such or after its hydrolysis, by means of plasma membrane nucleotide metabolizing enzymes, and resynthesis into the cell. Moreover, the findings that ADP also protects ANT-1 from the toxic action of the two Alzheimer's disease peptides, i.e. Aβ1-42 and NH2htau, which are known to be produced in apoptotic cerebellar neurons, further corroborate the molecular mechanism of neuroprotection by ADP, herein proposed.

Induction of cell death by graphene in Arabidopsis thaliana (Columbia ecotype) T87 cell suspensions

The toxicity of graphene on suspensions of Arabidopsis thaliana (Columbia ecotype) T87 cells was investigated by examining the morphology, mitochondrial dysfunction, reactive oxygen species generation (ROS), and translocation of graphene as the toxicological endpoints. The cells were grown in Jouanneau and Péaud-Lenoel (JPL) media and exposed to graphene at concentrations 0-80 mg/L. Morphological changes were observed by scanning electron microscope and the adverse effects such as fragmented nuclei, membrane damage, mitochondrial dysfunction was observed with fluorescence microscopy by staining with Hoechst 33342/propidium iodide and succinate dehydrogenase (mitochondrial bioenergetic enzyme). Analysis of intracellular ROS by 2',7'-dichlorofluorescein diacetate demonstrated that graphene induced a 3.3-fold increase in ROS, suggesting that ROS are key mediators in the cell death signaling pathway. Transmission electron microscopy verified the translocation of graphene into cells and an endocytosis-like structure was observed which suggested graphene entering into the cells by endocytosis. In conclusion, our results show that graphene induced cell death in T87 cells through mitochondrial damage mediated by ROS.

Dissecting the molecular mechanism by which NH2htau and Aβ1-42 peptides impair mitochondrial ANT-1 in Alzheimer disease

To find out whether and how the adenine nucleotide translocator-1 (ANT-1) inhibition due to NH2htau and Aβ1-42 is due to an interplay between these two Alzheimer's peptides, ROS and ANT-1 thiols, use was made of mersalyl, a reversible alkylating agent of thiol groups that are oriented toward the external hydrophilic phase, to selectively block and protect, in a reversible manner, the -SH groups of ANT-1. The rate of ATP appearance outside mitochondria was measured as the increase in NADPH absorbance which occurs, following external addition of ADP, when ATP is produced by oxidative phosphorylation and exported from mitochondria in the presence of glucose, hexokinase and glucose-6-phosphate dehydrogenase. We found that the mitochondrial superoxide anions, whose production is induced at the level of Complex I by externally added Aβ1-42 and whose release from mitochondria is significantly reduced by the addition of the VDAC inhibitor DIDS, modify the thiol group/s present at the active site of mitochondrial ANT-1, impair ANT-1 in a mersalyl-prevented manner and abrogate the toxic effect of NH2htau on ANT-1 when Aβ1-42 is already present. A molecular mechanism is proposed in which the pathological Aβ-NH2htau interplay on ANT-1 in Alzheimer's neurons involves the thiol redox state of ANT-1 and the Aβ1-42-induced ROS increase. This result represents an important innovation because it suggests the possibility of using various strategies to protect cells at the mitochondrial level, by stabilizing or restoring mitochondrial function or by interfering with the energy metabolism providing a promising tool for treating or preventing AD.

New insights in mitochondrial calcium handling by sodium/calcium exchanger

Mitochondria are now recognized as one of the main intracellular calcium-storing organelles which play a key role in the intracellular calcium signalling. Indeed, besides performing oxidative phosphorylation, mitochondria are able to sense and shape calcium (Ca(2+)) transients, thus controlling cytosolic Ca(2+) signals and Ca(2+)-dependent protein activity. It has been well established for many years that mitochondria have a huge capacity to accumulate calcium. While the physiological significance of this pathway was hotly debated until relatively recently, it is now clear that the ability of mitochondria in calcium handling is a ubiquitous phenomenon described in every cell system in which the issue has been addressed.In this chapter, we will review the molecular mechanisms involved in the regulation of mitochondrial calcium cycling in physiological conditions with particular regard to the role played by the mitochondrial Na(+)/Ca(2+) exchanger.

Apoptosis and in vitro Alzheimer disease neuronal models

Alzheimer disease (AD) is a human neurodegenerative disease characterized by co-existence of extracellular senile plaques (SP) and neurofibrillary tangles (NFT) associated with an extensive neuronal loss, primarily in the cerebral cortex and hippocampus. Several studies suggest that caspase(s)-mediated neuronal death occurs in cellular and animal AD models as well as in human brains of affected patients, although an etiologic role of apoptosis in such neurodegenerative disorder is still debated. This review summarizes the experimental evidences corroborating the possible involvement of apoptosis in AD pathogenesis and discusses the usefulness of ad hoc devised in vitro approaches to study how caspase(s), amyloidogenic processing and tau metabolism might reciprocally interact leading to neuronal death.

Alzheimer's proteins, oxidative stress, and mitochondrial dysfunction interplay in a neuronal model of Alzheimer's disease

In this paper, we discuss the interplay between beta-amyloid (Aβ) peptide, Tau fragments, oxidative stress, and mitochondria in the neuronal model of cerebellar granule neurons (CGNs) in which the molecular events reminiscent of AD are activated. The identification of the death route and the cause/effect relationships between the events leading to death could be helpful to manage the progression of apoptosis in neurodegeneration and to define antiapoptotic treatments acting on precocious steps of the death process. Mitochondrial dysfunction is among the earliest events linked to AD and might play a causative role in disease onset and progression. Recent studies on CGNs have shown that adenine nucleotide translocator (ANT) impairment, due to interaction with toxic N-ter Tau fragment, contributes in a significant manner to bioenergetic failure and mitochondrial dysfunction. These findings open a window for new therapeutic strategies aimed at preserving and/or improving mitochondrial function.

Genistein and daidzein prevent low potassium-dependent apoptosis of cerebellar granule cells

We have investigated the ability of certain dietary flavonoids, known to exert beneficial effects on the central nervous system, to affect neuronal apoptosis. We used cerebellar granule cells undergoing apoptosis due to potassium deprivation in a serum-free medium in either the absence or presence of the flavonoids genistein and daidzein, which are present in soy, and of catechin and epicatechin, which are present in cocoa. These compounds were used in a blood dietary concentration range. We found that genistein and daidzein, but not catechin and epicatechin, prevented apoptosis, with cell survival measured 24h after the induction of apoptosis being higher than that of the same cells incubated in flavonoid free medium (80% and 40%, respectively); there was no effect in control cells. A detailed investigation of the effect of these compounds on certain mitochondrial events that occur in cells en route to apoptosis showed that genistein and daidzein prevented the impairment of glucose oxidation and mitochondrial coupling, reduced cytochrome c release, and prevented both impairment of the adenine nucleotide translocator and opening of the mitochondrial permeability transition pore. Interestingly, genistein and daidzein were found to reduce the levels of reactive oxygen species, which are elevated in cerebellar granule cell apoptosis. These findings strongly suggest that the prevention of apoptosis depends mainly on the antioxidant properties of genistein and daidzein. This could lead to the development of a flavonoid-based therapy in neuropathies.

Effects of strontium fructose 1,6-diphosphate on expression of apoptosis-related genes and oxidative stress in testes of diabetic rats

OBJECTIVE

To investigate the effects of strontium fructose 1,6-diphosphate (FDP-Sr) on testicular dysfunction induced by diabetes.

METHODS

Diabetes was induced by a single injection of streptozotocin (65 mg/kg, i.p.). After 28 days, therapy with three doses (50, 100, and 200 mg/kg per day, p.o.) of FDP-Sr was carried out for another 4 weeks.

RESULTS

The rats exhibited morphological lesions of testes and significant decreases in serum testosterone levels after 2 months of diabetes. Testicular tissues of diabetic rats showed significantly increased malondialdehyde levels and declined glutathione peroxidase activity. Meanwhile, augmented DNA fragmentation was observed, along with downregulated Bcl-2 and upregulated Bax expressions at both mRNA and protein levels. FDP-Sr showed significant antioxidant effects in both in vitro and in vivo experiments, and significantly relieved apoptosis and the decline of serum testosterone caused by diabetes.

CONCLUSIONS

Testicular injury and apoptosis induced by diabetes are partially attributed to the augmented oxidative stress in testicular tissue. FDP-Sr indirectly alleviates these pathologic alterations by suppressing the generation of reactive oxygen species.

A transient proteasome activation is needed for acetic acid-induced programmed cell death to occur in Saccharomyces cerevisiae

To gain further insight into the mechanism by which yeast programmed cell death (PCD) occurs, we investigated whether and how proteasome activity changes in Saccharomyces cerevisiae cells undergoing PCD as a result of treatment with acetic acid (AA-PCD). We show that proteasome activation starts 60 min after AA-PCD induction, with a maximum at 90 min, and decreases at 150 min. Moreover, cell survival measurements carried out in the absence or presence of MG132, which inhibits proteasome function, show that the inhibition of proteasome activity partially prevents AA-PCD, thus indicating that a transient proteasome activation is needed for AA-PCD to occur.

Catalase T and Cu,Zn-superoxide dismutase in the acetic acid-induced programmed cell death in Saccharomyces cerevisiae

To investigate the role of catalase and superoxide dismutase (SOD) in the acetic acid (AA) induced yeast programmed cell death (AA-PCD), we compared Saccharomyces cerevisiae cells (C-Y) and cells individually over-expressing catalase T (CTT1-Y) and Cu,Zn-SOD (SOD1-Y) with respect to cell survival, hydrogen peroxide (H2O2) levels and enzyme activity as measured up to 200 min after AA treatment. AA-PCD does not occur in CTT1-Y, where H2O2 levels were lower than in C-Y and the over-expressed catalase activity decreased with time. In SOD1-Y, AA-PCD was exacerbated; high H2O2 levels were found, SOD activity increased early, remaining constant en route to AA-PCD, but catalase activity was strongly reduced.

Neuronal apoptosis revealed by genomic analysis: integrating gene expression profiles with functional information

Apoptosis is a key physiological response that occurs during development of the nervous system, resulting in the death of nearly half of the embryonic neuronal population. Aberrant apoptotic mechanisms are thought to contribute significantly to many neurological disorders including Alzheimer's disease. Although many experiments in the past have demonstrated the requirement of de novo gene expression during neuronal apoptosis, the complete spectrum of genes involved in distinct temporal domains is mostly unknown. To begin a comprehensive survey of the gene-based molecular mechanisms that underlie neuronal apoptosis, we have used the unprecedented experimental opportunities that genome sequences and the development of DNA microarray technology now provide to perform genome-wide expression analysis in different paradigms of neuronal apoptosis. In order to extract knowledge from gene expression information we have developed new informatics applications that enable clustering methods based on semantic characteristics, such as gene ontologies. This review will highlight the use of a genomic approach to identify the molecular program underlying neuronal apoptosis and illustrate how a semantic clustering method can be useful to extract more knowledge from microarray data.

Transport and metabolism of L-lactate occur in mitochondria from cerebellar granule cells and are modified in cells undergoing low potassium dependent apoptosis

Having confirmed that externally added L-lactate can enter cerebellar granule cells, we investigated whether and how L-lactate is metabolized by mitochondria from these cells under normal or apoptotic conditions. (1) L-lactate enters mitochondria, perhaps via an L-lactate/H+ symporter, and is oxidized in a manner stimulated by ADP. The existence of an L-lactate dehydrogenase, located in the inner mitochondrial compartment, was shown by immunological analysis. Neither the protein level nor the Km and Vmax values changed en route to apoptosis. (2) In both normal and apoptotic cell homogenates, externally added L-lactate caused reduction of the intramitochondrial pyridine cofactors, inhibited by phenylsuccinate. This process mirrored L-lactate uptake by mitochondria and occurred with a hyperbolic dependence on L-lactate concentrations. Pyruvate appeared outside mitochondria as a result of external addition of L-lactate. The rate of the process depended on L-lactate concentration and showed saturation characteristics. This shows the occurrence of an intracellular L-lactate/pyruvate shuttle, whose activity was limited by the putative L-lactate/pyruvate antiporter. Both the carriers were different from the monocarboxylate carrier. (3) L-lactate transport changed en route to apoptosis. Uptake increased in the early phase of apoptosis, but decreased in the late phase with characteristics of a non-competitive like inhibition. In contrast, the putative L-lactate/pyruvate antiport decreased en route to apoptosis with characteristics of a competitive like inhibition in early apoptosis, and a mixed non-competitive like inhibition in late apoptosis.

Nitric oxide has dual opposite roles during early and late phases of apoptosis in cerebellar granule neurons

The involvement and the role of nitric oxide (NO) as a signaling molecule in the course of neuronal apoptosis, whether unique or modulated during the progression of the apoptotic program, has been investigated in a cellular system consisting of cerebellar granule cells (CGCs) where apoptosis can be induced by lowering extracellular potassium. Several parameters involved in NO signaling pathway, such as NO production, neuronal nitric oxide synthase (nNOS) expression, and cyclic GMP (cGMP) production were examined in the presence or absence of different inhibitors. We provide evidence that nitric oxide has dual and opposite effects depending on time after induction of apoptosis. In an early phase, up to 3 h of apoptosis, nitric oxide supports survival of CGCs through a cGMP-dependent mechanism. After 3 h, nNOS expression and activity decreased resulting in shut down of NO and cGMP production. Residual NO then contributes to the apoptotic process by reacting with rising superoxide anions leading to peroxynitrite production and protein inactivation. We conclude that whilst NO over-production protects neurons from death in the early phase of neuronal damage, its subsequent reduction may contribute to neuronal degeneration and ultimate cell death.

Substance P provides neuroprotection in cerebellar granule cells through Akt and MAPK/Erk activation: Evidence for the involvement of the delayed rectifier potassium current

In the current study, we have evaluated the ability of substance P (SP) and other neurokinin 1 receptor (NK1) agonists to protect, in a dose- and time-dependent manner, primary cultures of rat cerebellar granule cells (CGCs) from serum and potassium deprivation-induced cell death (S-K5). We also established the presence of SP high affinity NK1 transcripts and the NK1 protein localization in the membrane of a sub-population of CGCs. Moreover, SP significantly and dose-dependently reduced the Akt 1/2 and Erk1/2 dephosphorylation induced by S-K5 conditions, as demonstrated by Western blot analysis. Surprisingly, in SP-treated CGCs caspase-3 activity was not inhibited, while the calpain-1 activity was moderately reduced. Corroborating this result, SP blocked calpain-mediated cleavage of tau protein, as demonstrated by the reduced appearance of a diagnostic fragment of 17 kDa by Western blot analysis. In addition, SP induced a significant reduction of the delayed rectifier K+ currents (Ik) in about 42% of the patched neurons, when these were evoked with depolarizing potential steps. Taken together, the present results demonstrate that the activation of NK1 receptors expressed in CGCs promote the neuronal survival via pathways involving Akt and Erk activation and by inhibition of Ik which can contribute to the neuroprotective effect of the peptide.

YCA1 participates in the acetic acid induced yeast programmed cell death also in a manner unrelated to its caspase-like activity

Yeast cells lacking the metacaspase-encoding gene YCA1 (Deltayca1) were compared with wild-type (WT) cells with respect to the occurrence, nature and time course of acetic-acid triggered death. We show that Deltayca1 cells undergo programmed cell death (PCD) with a rate lower than that of the WT and that PCD in WT cells is caused at least in part by the caspase activity of Yca1p. Since in Deltayca1 cells this effect is lost, but z-VAD-fmk does not prevent both WT and Deltayca1 cell death, PCD in WT cells occurs via a Yca1p caspase and a non-caspase route with similar characteristics.

Evolving therapeutic approaches to treating acute ischemic stroke

Stroke contributes significantly to death, disability, and healthcare costs; however, recombinant tissue plasminogen activator (rt-PA) is the only approved thrombolytic therapy for acute ischemic stroke. One area of development for new ischemic stroke treatment options is focused on neuroprotection of viable tissue in the ischemic vascular bed. The ischemic penumbra is recognizable on MRI by decreased perfusion, in contrast to the core area of ischemia, which includes diffusion and perfusion abnormalities. Understanding the mechanisms of neuronal death, including the role of excitotoxic neurotransmitters, free radical production, and apoptotic pathways, is important in developing new therapies for stroke. This article reviews these causes and results of stroke, as well as current and future neuroprotective treatment options. Several compounds have shown neuroprotective effects in animal studies, but have failed to be effective in human clinical trials. Several promising therapeutic areas include targeting of free radicals, modulation of glutamatergic transmission, and membrane stabilization via ion channels.

Cytochrome c is released in a reactive oxygen species-dependent manner and is degraded via caspase-like proteases in tobacco Bright-Yellow 2 cells en route to heat shock-induced cell death

To gain some insight into the mechanism of plant programmed cell death, certain features of cytochrome c (cyt c) release were investigated in heat-shocked tobacco (Nicotiana tabacum) Bright-Yellow 2 cells in the 2- to 6-h time range. We found that 2 h after heat shock, cyt c is released from intact mitochondria into the cytoplasm as a functionally active protein. Such a release did not occur in the presence of superoxide anion dismutase and catalase, thus showing that it depends on reactive oxygen species (ROS). Interestingly, ROS production due to xanthine plus xanthine oxidase results in cyt c release in sister control cultures. Maximal cyt c release was found 2 h after heat shock; later, activation of caspase-3-like protease was found to increase with time. Activation of this protease did not occur in the presence of ROS scavenger enzymes. The released cyt c was found to be progressively degraded in a manner prevented by either the broad-range caspase inhibitor (zVAD-fmk) or the specific inhibitor of caspase-3 (AC-DEVD-CHO), which have no effect on cyt c release. In the presence of these inhibitors, a significant increase in survival of the cells undergoing programmed cell death was found. We conclude that ROS can trigger release of cyt c, but do not cause cell death, which requires caspase-like activation.

Caspase-dependent alteration of the ADP/ATP translocator triggers the mitochondrial permeability transition which is not required for the low-potassium-dependent apoptosis of cerebellar granule cells

We investigated ADP/ATP exchange mediated by the adenine nucleotide translocator and opening of the mitochondrial permeability transition pore in homogenates from cerebellar granule cells en route to apoptosis induced by low potassium. We showed that, in the first 3 h of apoptosis, when maximum cytochrome c release had already occurred, adenine nucleotide translocator function was impaired owing to the action of reactive oxygen species, but no permeability transition pore opening occurred. Over 3-8 h of apoptosis, the permeability transition pore progressively opened, owing to caspase action, and further ADP/ATP translocator impairment occurred. The kinetics of transport and permeability transition pore opening were inversely correlated, both in the absence and presence of inhibitors of antioxidant and proteolytic systems. We conclude that, en route to apoptosis, alteration of the adenine nucleotide translocator occurs, resulting in permeability transition pore opening. This process depends on the action of caspase on pore component(s) other than the ADP/ATP translocator, because no change in either amount or molecular weight of the latter protein was noted during apoptosis, as measured by western blotting. Cell death occurs via apoptosis in the presence of cyclosporin A, the permeability transition pore inhibitor, thus showing that permeability transition pore opening, not needed for cytochrome c release, is also unnecessary for apoptosis to occur.

Bioenergetic analysis of cerebellar granule neurons undergoing apoptosis by potassium/serum deprivation

Apoptosis induced by K+/serum deprivation (low K+) in cerebellar granule neurons has been extensively investigated. The mitochondria play a key role in apoptosis by releasing proapoptotic factors into the cytoplasm, and mitochondrial dysfunction has been proposed as an early or initiating event in this model. To directly test this hypothesis, cellular and mitochondrial bioenergetics were quantified by determining the respiratory parameters of coverslip-attached neurons. While oxidative phosphorylation rate decreased 39-49% in low K+, this was due to decreased cellular ATP demand rather than impaired ATP/ADP exchange or respiratory chain inhibition. From 3 to 5 h in low K+, apoptosis progressed from 13 to 40% despite no appreciable change in respiratory parameters. Changes in steady-state O2-, assessed with dihydroethidium, were seen in granule but not hippocampal neurons. The O2- change correlated with changes in [Ca2+]c, but not mitochondrial respiration. Thus, early mitochondrial dysfunction can be excluded in this common model of neuronal apoptosis.

Ubiquitin–proteasome system and Parkinson's disease

Increasing genetic, pathological, and experimental evidence suggest that neurodegeneration in both familial and sporadic forms of Parkinson's disease (PD) may be related to a defect in the capacity of the ubiquitin-proteasome system (UPS) to clear unwanted proteins, resulting in protein accumulation, aggregation, and cytotoxicity. This concept is supported by in vitro and in vivo laboratory experiments which show that inhibition of UPS function can cause neurodegeneration coupled with the formation of Lewy body-like inclusions. This hypothesis could account for the presence of protein aggregates and Lewy bodies in PD, the other biochemical features seen in the disorder, and the age-related vulnerability of the substantia nigra pars compacta. It also suggests novel targets for putative neuroprotective therapies for PD.

Proteasome inhibition elicits a biphasic effect on neuronal apoptosis via differential regulation of pro-survival and pro-apoptotic transcription factors

The role of the proteasome in neuronal apoptosis is poorly understood since both anti- and pro-apoptotic effects result from proteasome inhibition. We studied the effects of proteasome inhibition in cultured rat cerebellar granule neurons. Acute exposure to proteasome inhibitors MG-132 and lactacystin blocked caspase activation induced by removal of depolarizing medium. However, chronic treatment with MG-132 activated caspases in neurons maintained in depolarizing potassium. The biphasic effect of MG-132 was hypothesized to be due to differential degradation of anti- and pro-apoptotic proteins. Accordingly, acute exposure to MG-132 inhibited the hyperphosphorylation, loss of DNA binding, ubiquitination, and degradation of the pro-survival transcription factor MEF2D induced by removal of depolarizing medium. In contrast, chronic exposure to MG-132 increased the expression and phosphorylation of c-Jun, elevated levels of the pro-apoptotic protein Bim, and triggered neuronal apoptosis, even in the presence of depolarizing medium. Thus, proteasome inhibition exerts an acute pro-survival action by stabilizing MEF2 transcription factors. However, chronic proteasome inhibition causes a build-up of phosphorylated c-Jun and Bim, which eventually overwhelms the effects of MEF2 and triggers apoptosis.

Identification, characterization and phylogenic analysis of conserved genes within the p74 gene region of Choristoneura fumiferana granulovirus genome

The genes located within the p74 gene region of the Choristoneura fumiferana granulovirus (ChfuGV) were identified by sequencing an 8.9 kb BamHI restriction fragment on the ChfuGV genome. The global guanine-cytosine (GC) content of this region of the genome was 33.02%. This paper presents the ORFs within the p74 gene region along with their transcriptional orientations. This region contains a total of 15 open reading frames (ORFs). Among those, 8 ORFs were found to be homologues to the baculoviral ORFs: Cf-i-p , Cf-vi, Cf-vii, Cf-viii (ubiquitin), Cf-xi (pp31), Cf-xii (lef-11), Cf-xiii (sod) and Cf-xv-p (p74). To date, no specific function has been assigned to the ORFs: Cf-i, Cf-ii, Cf-iii, Cf-iv, Cf-v, Cf-vi, Cf-vii, Cf-ix and Cf-x. The most noticeable ORFs located in this region of the ChfuGV genome were ubiquitin, lef-11, sod, fibrillin and p74. The phylogenetic trees (constructed using conceptual products of major conserved ORFs) and gene arrangement in this region were used to further examine the classification of the members of the granulovirus genus. Comparative studies demonstrated that ChfuGV along with the Cydia pomonella granulovirus (CpGV), Phthorimaea operculella granulovirus (PhopGV), Adoxophyes orana granulovirus (AoGV) and Cryptophlebia leucotreta granulovirus (ClGV) share a high degree of amino acids sequence and gene arrangement preservation within the studied region. These results support a previous report, which classified a granuloviruses into 2 distinct groups: Group I: ChfuGV, CpGV, PhopGV and AoGV and Group II: Xestia c-nigrum granulovirus (XcGV) and Plutella xylostella granulovirus (PxGV). The phylogenetic and gene arrangement studies also placed ClGV as a novel member of the Group I granuloviruses.

Role of the autophagic-lysosomal system on low potassium-induced apoptosis in cultured cerebellar granule cells

Apoptotic and autophagic cell death have been implicated, on the basis of morphological and biochemical criteria, in neuronal loss occurring in neurodegenerative diseases and it has been shown that they may overlap. We have studied the relationship between apoptosis and autophagic cell death in cerebellar granule cells (CGCs) undergoing apoptosis following serum and potassium deprivation. We found that apoptosis is accompanied by an early and marked proliferation of autophagosomal-lysosomal compartments as detected by electron microscopy and immunofluorescence analysis. Autophagy is blocked by hrIGF-1 and forskolin, two well-known inhibitors of CGC apoptosis, as well as by adenovirus-mediated overexpression of Bcl-2. 3-Methyladenine (3-MA) an inhibitor of autophagy, not only arrests this event but it also blocks apoptosis. The neuroprotective effect of 3-MA is accompanied by block of cytochrome c (cyt c) release in the cytosol and by inhibition of caspase-3 activation which, in turn, appears to be mediated by cathepsin B, as CA074-Me, a selective inhibitor of this enzyme, fully blocks the processing of pro-caspase-3. Immunofluorescence analysis demonstrated that cathepsin B, normally confined inside the lysosomal-endosomal compartment, is released during apoptosis into the cytosol where this enzyme may act as an execution protease. Collectively, these observations indicate that autophagy precedes and is causally connected with the subsequent onset of programmed death.

An increase in the ATP levels occurs in cerebellar granule cells en route to apoptosis in which ATP derives from both oxidative phosphorylation and anaerobic glycolysis

Although it is recognized that ATP plays a part in apoptosis, whether and how its level changes en route to apoptosis as well as how ATP is synthesized has not been fully investigated. We have addressed these questions using cultured cerebellar granule cells. In particular, we measured the content of ATP, ADP, AMP, IMP, inosine, adenosine and L-lactate in cells undergoing apoptosis during the commitment phase (0-8 h) in the absence or presence of oligomycin or/and of citrate, which can inhibit totally the mitochondrial oxidative phosphorylation and largely the substrate-level phosphorylation in glycolysis, respectively. In the absence of inhibitors, apoptosis was accompanied by an increase in ATP and a decrease in ADP with 1:1 stoichiometry, with maximum ATP level found at 3 h apoptosis, but with no change in levels of AMP and its breakdown products and with a relatively low level of L-lactate production. Consistently, there was an increase in the cell energy charge and in the ratio ([ATP][AMP])/[ADP](2). When the oxidative phosphorylation was completely blocked by oligomycin, a decrease of the ATP content was found both in control cells and in cells undergoing apoptosis, but nonetheless cells still died by apoptosis, as shown by checking DNA laddering and by death prevention due to actinomycin D. In this case, ATP was provided by anaerobic glycolysis, as suggested by the large increase of L-lactate production. On the other hand, citrate itself caused a small decrease in ATP level together with a huge decrease in L-lactate production, but it had no effect on cell survival. When ATP level was further decreased due to the presence of both oligomycin and citrate, death occurred via necrosis at 8 h, as shown by the lack of DNA laddering and by death prevention found due to the NMDA receptor antagonist MK801. However, at a longer time, when ATP level was further decreased, cells died neither via apoptosis nor via glutamate-dependent necrosis, in a manner similar to something like to energy catastrophe. Our results shows that cellular ATP content increases in cerebellar granule cell apoptosis, that the role of oxidative phosphorylation is facultative, i.e. ATP can also derive from anaerobic glycolysis, and that the type of cell death depends on the ATP availability.

Intermittent hypoxia damages cerebellar cortex and deep nuclei

Obstructive sleep apnea patients show cerebellar cortex and deep nuclei gray matter loss, a possible consequence of intermittent hypoxia (IH) accompanying the syndrome. We exposed Sprague-Dawley rats (n=24) to room air only or 10.3% O2, balance N2, alternating every 480 s (240 s duty cycle) with room air for 5, 10, 15, 20 or 30 h (7.5 h per day) during light periods. IH-exposed rats showed increased numbers of damaged Purkinje cells (31.1, 50.5, 54.7, 65.2, and 94.4% for 5, 10, 15, 20 and 30 h groups, respectively; p<0.001 for slopes of the total, swollen/autolysed, and shrunken/dark cell counts), as assessed by hematoxylin and eosin staining. Anti-caspase-3 antibody density increased in the fastigial nuclei subsequent to 5-h exposure. Short-term IH exposure elicits dose-dependent cerebellar Purkinje and fastigial neuron damage.

Gene expression profiles of apoptotic neurons

The multigenic program underlying neuronal apoptosis is mostly unknown. To study the program, we used genome-scale screening by oligonucleotide microarrays during serum and potassium deprivation-induced apoptosis of cerebellar granule neurons. From the 8740 genes interrogated by the arrays, 423 genes were found to be regulated at both the transcriptional and the posttranscriptional level and segregated into distinct clusters. Semantic clustering based on gene ontologies showed coordinated expression of genes with common biological functions and metabolic pathways. Among the genes implicated in apoptotic cerebellar granule neurons, 70 were in common with those differentially expressed in cortical neurons exposed to amyloid beta-protein, indicating the existence of common mechanisms responsible for neuronal cell death. Our results offer a genomic view of the changes that accompany neuronal apoptosis and yield new insights into the underlying molecular basis.

Kaempferol blocks oxidative stress in cerebellar granule cells and reveals a key role for reactive oxygen species production at the plasma membrane in the commitment to apoptosis

Micromolar concentrations of the flavonoid kaempferol were found to efficiently block cerebellar granule cell (CGC) death through low K+-induced apoptosis, as demonstrated by prevention of the activation of caspase-3, internucleosomal DNA fragmentation, and chromatin condensation, without a significant rise in intracellular free Ca2+ concentration. Half of the maximum protection against CGC apoptosis was attained with 8 +/- 2 microM kaempferol. Reactive oxygen species (ROS) were monitored with 2',7'-dichlorodihydrofluorescein diacetate. Quantitative analysis of intracellularly and extracellularly oriented ROS production up to 3 h from the onset of low K+-induced CGC apoptosis was carried out with acquired digital fluorescence microscopy images of CGC in culture plates using a CCD camera, and also with fluorescence measurements of resuspended CGCs. In both cases, nearly 90% of ROS production by CGCs during the early stages (up to 3 h) after induction of low-K+ apoptosis occurs at the plasma membrane. Kaempferol, at concentrations that blocked CGC apoptosis, has been found to be a particularly potent blocker of extracellularly oriented ROS production by CGCs, and to inhibit the ascorbate-dependent NADH oxidase and superoxide anion production activities of the neuronal plasma membrane redox chain.

Ubiquitin-proteasome system and proteasome inhibition: new strategies in stroke therapy

BACKGROUND AND PURPOSE

Proteasomes are large multicatalytic proteinase complexes that are found in the cytosol and in the nucleus of eukaryotic cells with a central role in cellular protein turnover. The ubiquitin-proteasome system (UPS) has a central role in the selective degradation of intracellular proteins. Among the key proteins whose levels are modulated by the proteasome are those involved in the control of inflammatory processes, cell cycle regulation, and gene expression. There are now overwhelming data suggesting that the UPS contributes to cerebral ischemic injury.

SUMMARY OF REVIEW

Proteasome inhibition is a potential treatment option for stroke. Thus far, proof of principle has been obtained from studies in several animal models of cerebral ischemia. Treatment with proteasome inhibitors reduces effectively neuronal and astrocytic degeneration, cortical infarct volume, infarct neutrophil infiltration, and NF-kappaB immunoreactivity with an extension of the neuroprotective effect at least 6 hours after ischemic insult. However, it is clear that the UPS represents a central pathway for the processing and metabolism of multiple proteins with critical roles in cellular function. To avoid eliciting significant side effects associated with complete inhibition of the proteasome and the possible immunosuppressive effects from persistent suppression of NF-kappaB activation, it is critical that we understand how to partially and temporally attenuate proteasome function to elicit the desired therapeutic effect before any large-scale use in humans.

CONCLUSIONS

This review highlights the most recent advances in our knowledge on UPS, as well as the early experience of using proteasome inhibition strategies to treat acute stroke.

Production of reactive oxygen species, alteration of cytosolic ascorbate peroxidase, and impairment of mitochondrial metabolism are early events in heat shock-induced programmed cell death in tobacco Bright-Yellow 2 cells

To gain some insight into the mechanisms by which plant cells die as a result of abiotic stress, we exposed tobacco (Nicotiana tabacum) Bright-Yellow 2 cells to heat shock and investigated cell survival as a function of time after heat shock induction. Heat treatment at 55 degrees C triggered processes leading to programmed cell death (PCD) that was complete after 72 h. In the early phase, cells undergoing PCD showed an immediate burst in hydrogen peroxide (H2O2) and superoxide (O2*-) anion production. Consistently, death was prevented by the antioxidants ascorbate (ASC) and superoxide dismutase (SOD). Actinomycin D and cycloheximide, inhibitors of transcription and translation, respectively, also prevented cell death, but with a lower efficiency. Induction of PCD resulted in gradual oxidation of endogenous ASC; this was accompanied by a decrease in both the amount and the specific activity of the cytosolic ASC peroxidase (cAPX). A reduction in cAPX gene expression was also found in the late PCD phase. Moreover, changes of cAPX kinetic properties were found in PCD cells. Production of ROS in PCD cells was accompanied by early inhibition of glucose (Glc) oxidation, with a strong impairment of mitochondrial function as shown by an increase in cellular NAD(P)H fluorescence, and by failure of mitochondria isolated from cells undergoing PCD to generate membrane potential and to oxidize succinate in a manner controlled by ADP. Thus, we propose that in the early phase of tobacco Bright-Yellow 2 cell PCD, ROS production occurs, perhaps because of damage of the cell antioxidant system, with impairment of the mitochondrial oxidative phosphorylation.

Cytochrome c, released from cerebellar granule cells undergoing apoptosis or excytotoxic death, can generate protonmotive force and drive ATP synthesis in isolated mitochondria

In rat cerebellar granule cells, cytochrome c release takes place during glutamate toxicity and apoptosis due to deprivation of depolarising levels of potassium. We show that, as in necrosis, the released cytochrome c present in the cytosolic fraction obtained from cerebellar granule cells undergoing apoptosis can operate as a reactive oxygen species (ROS) scavenger and as a respiratory substrate. The capability of the cytosolic fraction containing cytochrome c, obtained from cerebellar granule cells undergoing either necrosis or apoptosis, to energise coupled mitochondria isolated by the same cells is also investigated. We show that, in both cases, the cytosolic fraction containing cytochrome c, added to mitochondria, can cause proton ejection, and membrane potential generation and can drive ATP synthesis and export in the extramitochondrial phase, as photometrically measured via the ATP detecting system. Cytochrome c, separated immunologically from the cytosolic fraction of apoptotic cells when added to mitochondria, is found to cause proton ejection to generate membrane potential and to drive ATP synthesis and export in a manner not sensitive to the further addition of the cytosolic fraction depleted of cytochrome c, which failed to do this. In the light of these findings we propose that in apoptosis the released cytochrome c can contribute to provide ATP required for the cell programmed death to occur.