Search

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

Radiotherapy is an effective tool in the treatment of malignant brain tumors. However, damage to brain stem and progenitor cells constitutes a major problem and is associated with long-term side effects. Autophagy has been shown to be involved in cell death, and the purpose of this study was to evaluate the effect of autophagy inhibition on neural stem and progenitor cell death in the juvenile brain. Ten-day-old selective Atg7 knockout (KO) mice and wild-type (WT) littermates were subjected to a single 6Gy dose of whole-brain irradiation. Cell death and proliferation as well as microglia activation and inflammation were evaluated in the dentate gyrus of the hippocampus and in the cerebellum at 6 h after irradiation. We found that cell death was reduced in Atg7 KO compared with WT mice at 6 h after irradiation. The number of activated microglia increased significantly in both the dentate gyrus and the cerebellum of WT mice after irradiation, but the increase was lower in the Atg7 KO mice. The levels of proinflammatory cytokines and chemokines decreased, especially in the cerebellum, in the Atg7 KO group. These results suggest that autophagy might be a potential target for preventing radiotherapy-induced neural stem and progenitor cell death and its associated long-term side effects.

Neuronal programmed cell death (PCD) contributes to delayed tissue damage after traumatic brain injury (TBI). Both caspase-dependent and caspase-independent mechanisms have been implicated, with the latter including apoptosis inducing factor (AIF). The peptidyl-proplyl isomerase Cyclophilin A (CypA) transports AIF from the cytosol to the nucleus, a key step for AIF-dependent cell death. We compared the effects of single versus combined inhibition of caspase and AIF pathways in a mouse controlled cortical impact (CCI) model, by examining the effects of CypA gene knockout (CypA(-/-)), caspase inhibition with a pan-caspase inhibitor (boc-aspartyl(OMe)-fluoromethylketone, BAF), or combined modulation. TBI caused caspase activation as well as translocation of AIF to the nucleus. Markers of caspase activation including caspase-specific fodrin cleavage fragments and number of FLIVO-positive cells were reduced in BAF-treated CypA(+/+) mice, whereas markers of AIF activation including AIF/H2AX interaction and AIF translocation to the nucleus were attenuated in CypA(-/-) mice. Each single intervention, (CypA(-/-) or BAF-treated CypA(+/+)) reduced the number of apoptotic cells (TUNEL-positive) in the cortex and improved long-term sensorimotor function; CypA(-/-) also attenuated microglial activation after injury. Importantly, BAF-treated CypA(-/-) mice, showed greater effects than either intervention alone on multiple outcomes including: reduction in TUNEL-positive cells, decrease in neuroinflammation, improved motor and cognitive recovery, and attenuation of lesion volume and neuronal loss in the hippocampus. Using two in vitro neuronal cell death models known to induce AIF-mediated PCD, we also showed that neurons from CypA(-/-) animals were protected and that effects were unrelated to caspase activation. These data indicate that AIF-mediated and caspase-dependent pathways contribute independently and in parallel to secondary injury after TBI, and suggest that combined therapeutic strategies directed at multiple PCD pathways may provide superior neuroprotection than those directed at single mechanisms., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Traumatic brain injury (TBI) consists of two phases: an immediate phase in which damage is caused as a direct result of the mechanical impact; and a late phase of altered biochemical events that results in delayed tissue damage and is therefore amenable to therapeutic treatment. Because the molecular mechanisms of delayed post-traumatic neuronal cell death are still poorly understood, we investigated whether apoptosis-inducing factor (AIF), a pro-apoptotic mitochondrial molecule and the key factor in the caspase-independent, cell death signaling pathway, plays a causal role in neuronal death following TBI. Using an in vitro model of neuronal stretch injury, we demonstrated that AIF translocated from mitochondria to the nucleus of neurons displaying axonal disruption, chromatin condensation, and nuclear pyknosis in a caspase-independent manner, whereas astrocytes remained unaffected. Similar findings were observed following experimental TBI in mice, where AIF translocation to the nucleus coincided with delayed neuronal cell death in both cortical and hippocampal neurons. Down-regulation of AIF in vitro by siRNA significantly reduced stretch-induced neuronal cell death by 67%, a finding corroborated in vivo using AIF-deficient harlequin mutant mice, where secondary contusion expansion was significantly reduced by 44%. Hence, our current findings demonstrate that caspase-independent, AIF-mediated signaling pathways significantly contribute to post-traumatic neuronal cell death and may therefore represent novel therapeutic targets for the treatment of TBI.

A large proportion of cells that proliferate in the adult dentate gyrus under normal conditions or in response to brain insults exhibit only short-term survival. Here, we sought to determine which cell death pathways are involved in the degeneration of newly formed neurons in the rat dentate gyrus following 2 h of electrically induced status epilepticus. We investigated the role of three families of cysteine proteases, caspases, calpains, and cathepsins, which can all participate in apoptotic cell death. Status epilepticus increased the number of bromodeoxyuridine (BrdU)-positive proliferated cells in the subgranular zone of the dentate gyrus. At the time of maximum cell proliferation, immunohistochemical analyses revealed protein expression of active caspase-cleaved poly (ADP-ribose) polymerase (PARP) in approximately 66% of the BrdU-positive cells, while none of them expressed cathepsin B or the 150-kDa calpain-produced fodrin breakdown product. To evaluate the importance of cysteine proteases in regulating survival of the newly formed neurons, we administered intracerebroventricular infusions of a caspase inhibitor cocktail (zVAD-fmk, zDEVD-fmk and zLEHD-fmk) over a 2-week period, sufficient to allow for neuronal differentiation, starting 1 week after the epileptic insult. Increased numbers of cells double-labelled with BrdU and neuron-specific nuclear protein (NeuN) marker were detected in the subgranular zone and granule cell layer of the caspase inhibitor-treated rats. Our data indicate that caspase-mediated cell death pathways are active in progenitor cell progeny generated by status epilepticus and compromise survival during neuronal differentiation.

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Acute neurological conditions such as cerebrovascular diseases and trauma are associated with irreversible loss of neurons and glial cells. Severe or prolonged injury results in uncontrollable cell death within the core of lesions. Conversely, cells that are less severely damaged succumb in a relatively slow fashion, frequently via the intrinsic pathway of cell death, through the deterioration of mitochondrial functions. The permeabilization of mitochondrial membranes determines whether cells will succumb to or survive the injury, and represents a 'point of no return' in mitochondrial cell death. It is therefore an attractive target for the development of new neuroprotective interventions. [ABSTRACT FROM AUTHOR]

Cyclophilin D (CypD), a regulator of the mitochondrial membrane permeability transition pore (PTP), enhances Ca2+-induced mitochondrial permeabilization and cell death in the brain. However, the role of CypD in hypoxic-ischemic (HI) brain injury at different developmental ages is unknown. At postnatal day (P) 9 or P60, littermates of CypD-deficient [knock-out (KO)], wild-type (WT), and heterozygous mice were subjected to HI, and brain injury was evaluated 7 d after HI. CypD deficiency resulted in a significant reduction of HI brain injury at P60 but worsened injury at P9. After HI, caspase-dependent and -independent cell death pathways were more induced in P9 CypD KO mice than in WT controls, and apoptotic activation was minimal at P60. The PTP had a considerably higher induction threshold and lower sensitivity to cyclosporin A in neonatal versus adult mice. On the contrary, Bax inhibition markedly reduced caspase activation and brain injury in immature mice but was ineffective in the adult brain. Our findings suggest that CypD/PTP is critical for the development of brain injury in the adult, whereas Bax-dependent mechanisms prevail in the immature brain. The role of CypD in HI shifts from a predominantly prosurvival protein in the immature to a cell death mediator in the adult brain. [ABSTRACT FROM AUTHOR]

Cyclophilin D (CypD), a regulator of the mitochondrial membrane permeability transition pore (PTP), enhances Ca2+-induced mitochondrial permeabilization and cell death in the brain. However, the role of CypD in hypoxic-ischemic (HI) brain injury at different developmental ages is unknown. At postnatal day (P) 9 or P60, littermates of CypD-deficient [knock-out (KO)], wild-type (WT), and heterozygous mice were subjected to HI, and brain injury was evaluated 7 d after HI. CypD deficiency resulted in a significant reduction of HI brain injury at P60 but worsened injury at P9. After HI, caspase-dependent and -independent cell death pathways were more induced in P9 CypD KO mice than in WT controls, and apoptotic activation was minimal at P60. The PTP had a considerably higher induction threshold and lower sensitivity to cyclosporin A in neonatal versus adult mice. On the contrary, Bax inhibition markedly reduced caspase activation and brain injury in immature mice but was ineffective in the adult brain. Our findings suggest that CypD/PTP is critical for the development of brain injury in the adult, whereas Bax-dependent mechanisms prevail in the immature brain. The role of CypD in HI shifts from a predominantly prosurvival protein in the immature to a cell death mediator in the adult brain. [ABSTRACT FROM AUTHOR]

Previous studies have shown that caspases and Apaf-1 are required for the normal programmed cell death (PCD) in vivo of immature postmitotic neurons and mitotically active neuronal precursor cells. In contrast, caspase activity is not necessary for the normal PCD of more mature postmitotic neurons that are establishing synaptic connections. Although normally these cells use caspases for PCD, in the absence of caspase activity these neurons undergo a distinct nonapoptotic type of degeneration. We examined the survival of these more mature postmitotic neuronal populations in mice in which Apaf-1 has been genetically deleted and find that they exhibit quantitatively normal PCD of developing postmitotic neurons. We next characterized the morphological mode of PCD in these mice and show that the neurons degenerate by a caspase-independent, nonapoptotic pathway that involves autophagy. However, autophagy does not appear to be involved in the normal PCD of postmitotic neurons in which caspases and Apaf-1 are present and functional because quantitatively normal neuronal PCD occurred in the absence of a key gene required for autophagy (ATG7). Finally, we examined the possible role of another caspase-independent type of neuronal PCD involving the apoptosis-inducing factor (AIF). Mice deficient in AIF also exhibit quantitatively normal PCD of postmitotic neurons after caspase inhibition. Together, these data indicate that, when key components of the type 1 apoptotic pathway (i.e., caspases and Apaf-1) are perturbed in vivo, developing postmitotic neurons nonetheless undergo quantitatively normal PCD by a caspase-independent pathway involving autophagy and not requiring AIF. [ABSTRACT FROM AUTHOR]

Perinatal hypoxia/ischemia (H/I) is the leading cause of neurological injury resulting from birth complications and pre-maturity. Our studies have demonstrated that this injury depletes the subventricular zone (SVZ) of progenitors. In this study, we sought to reveal which cell death pathways are activated within these progenitors after H/I. We found that calpain activity is detected as early as 4 h of reperfusion and is sustained for 48 h, while caspase 3 activation does not occur until 8 h and peaks at 24 h post-insult. Activated calpains and caspase 3 co-localized within precursors situated in the lateral aspects of the SVZ (which coincides with progenitor cell death), whereas neither enzyme was activated in the medial SVZ (which harbors the neural stem cells that are resilient to this insult). These studies reveal targets for neuroprotective agents to protect precursors from cell death towards the goal of restoring normal brain development after H/I. [ABSTRACT FROM AUTHOR]

Sex-related brain injury was evaluated after unilateral hypoxia–ischaemia (HI) in C57/BL6 mice on postnatal day (P) 5, 9, 21 or 60, corresponding developmentally to premature, term, juvenile and adult human brains. There was no sex difference in brain injury when the insult was severe, as evaluated by pathological scoring or tissue loss, but when the insult was moderate, adult (P60) females displayed less injury. In the immature (P9) male brains, neurones displayed a more pronounced translocation of apoptosis-inducing factor (AIF) (loss of AIF from the mitochondrial fraction and increase in nuclear AIF) after HI, whereas the female brain neurones displayed a stronger activation of caspase 3 (more pronounced loss of pro-caspase 3, increase in cleaved caspase 3 and increase in caspase 3 enzymatic activity). Two other mechanisms of injury, peroxynitrite-induced formation of nitrotyrosine and autophagy, were no different between males and females at P9. These data show that the CNS is more resistant to HI in adult females compared with males, whereas no sex differences were found in the extent of injury in neonatal mice. However, critical sex-dependent differences were demonstrated in vivo with regard to cellular, apoptosis-related mechanisms. [ABSTRACT FROM AUTHOR]

The effectiveness of hypothermia in preventing ischemic brain damage depends on when it is started. The purpose of this study was to investigate the effects of temperature reduction during a hypoxic–ischemic (HI) insult on brain injury and signalling pathways of neuronal cell death and survival. Seven-day-old mice were subjected to left common carotid artery ligation and hypoxia (10% oxygen) at different temperatures (37, 36 or 34 °C) for 50 min. Brain injury at 7 days post-HI was significantly reduced from 67.4% at 37 °C to 31.6% at 36 °C and 10% at 34 °C, with no observable injury in the cortex of the 34 °C group. Cytochrome c release, caspase-3 activation and apoptosis-inducing factor translocation from mitochondria to nuclei were all significantly inhibited after intraischemic temperature reduction. Concurrently, the cell survival signalling pathway involving Akt was significantly sustained (the phosphorylated form of Akt was maintained) when the hypoxia temperature was decreased. These results indicate that intraischemic hypothermia diminished apoptosis through inhibition of both caspase-dependent and caspase-independent neuronal cell death pathways and promoted cell survival by inhibition of phosphorylated Akt dephosphorylation in the neonatal brain, thereby preventing neuronal cell death. [ABSTRACT FROM AUTHOR]

Delayed neuronal cell death occurring hours after reperfusion is a hallmark of ischemic stroke and a primary target for neuroprotective strategies. In the present study, we investigated whether apoptosis-inducing factor (AIF), a caspase-independent proapoptotic protein, is responsible for neuronal cell death after glutamate toxicity and oxygen- glucose deprivation (OGD) in vitro and after experimental stroke in vivo. AIF translocated to the nucleus in which it colocalized with DNA fragmentation and nuclear apoptotic morphology after exposure to glutamate or OGD in cultured neurons or after transient middle cerebral artery occlusion (MCAo) in mice. Small inhibitory RNA-mediated downregulation of AIF reduced glutamate- and OGD-induced neuronal apoptosis by 37 and 60%, respectively (p < 0.01). Moreover, Harlequin mutant mice, which express AIF at low levels (∼20% of wild-type mice), displayed smaller infarct volumes ( -43%; p < 0.03) and showed dramatically reduced cell death in the ischemic penumbra after 45 min of MCAo compared with wild-type littermates. Inhibition of poly(ADP-ribose) polymerase and Bid reduced nuclear AIF translocation. These results provide the first evidence for a causal role of AIF in ischemic neuronal cell death. Therefore, caspase-independent cell death signaling may provide a promising novel target for therapeutic interventions in cerebrovascular diseases. [ABSTRACT FROM AUTHOR]

In a newly established model of unilateral, irradiation (IR)-induced injury we compared the outcome after IR to the immature and juvenile brain, using rats at postnatal days 9 or 23, respectively. We demonstrate that (i) the immature brains contained more progenitors in the subventricular zone (SVZ) and subgranular zone (SGZ) compared with the juvenile brains; (ii) cellular injury, as judged by activation of caspase 3 and p53, as well as nitrotyrosine formation, was more pronounced in the SVZ and SGZ in the immature brains 6 h after IR; (iii) the number of progenitor and immature cells in the SVZ and SGZ decreased 6 h and 7 days post-IR, corresponding to acute and subacute effects in humans, respectively, these effects were more pronounced in immature brains; (iv) myelination was impaired after IR at both ages, and much more pronounced after IR to immature brains; (v) the IR-induced changes remained significant for at least 10 weeks, corresponding to late effects in humans, and were most pronounced after IR to immature brains. It appears that IR induces both an acute loss of progenitors through apoptosis and a perturbed microenvironment incompatible with normal proliferation and differentiation, and that this is more pronounced in the immature brain. [ABSTRACT FROM AUTHOR]

PROBLEM: The distribution and activation of μ-calpain and possible cleavage of integrin in human endometrial cells under hypoxic condition were investigated. METHOD OF STUDY: Human endometrial epithelial and stromal cells were subjected to hypoxia, and subsequently used for immunostaining and western blot analysis. RESULTS: The proform of μ-calpain was detected in the cytoplasm of normal cells, and displayed a substantial decrease after hypoxia. Conversely, the active form of μ-calpain was not detected in normal cells, but was abundant after hypoxia. The cytoplasmic domain of integrin β3 was also detected in the cytoplasm of endometrial cells. Western blot analysis confirmed that both the proform of μ-calpain and the integrin β3 cytoplasmic domain decreased during hypoxia. CONCLUSIONS: μ-Calpain is activated in human endometrial cells during hypoxia and that subsequent cleavage of the integrin β3 cytoplasmic domain may give some adverse effects to the function of human endometrium. [ABSTRACT FROM AUTHOR]

Abstract Activation of extracellular signal-related kinases (ERK1/2), also known as p42/44 mitogen-activated protein kinase (MAPK), is considered important for neuronal survival, cell proliferation and apoptosis. In the present study, activation (phosphorylation) of ERK1/2 (P-ERK) was investigated in brains of 7-day-oldrats after hypoxia-ischaemia (HI). In damaged areas, P-ERK-positive neurons appeared immediately after HI and the staining remained for at least 8 h. At later time points, 24 and 72 h post-HI, P-ERK-positive neurons were found in the core of the infarct and in the border zone to undamaged tissue. These cells also showed signs of DNA damage and calpain-induced fodrin breakdown, indicative of injury. At 72 h post-HI, P-ERK was also observed in microglia in the border zone to the damaged area and in astrocytes and oligodendrocytes in white matter of both hemispheres. P-ERK was strongly expressed in the subventricular zone in both hemispheres after HI at most time points, although the staining in the ipsilateral (damaged hemisphere) was stronger than in the contralateral (non-damaged hemisphere). In summary, ERK1/2 activation occurred early in neurons after HI in the neonatal brain, and mainly in cells displaying signs of damage. [ABSTRACT FROM AUTHOR]

Caspase-3 has been identified as a key protease that, by targeting a limited number of proteins, can disrupt essential homeostatic processes and initiate an orderly disassembly of cells, including degradation of genomic DNA. We demonstrate the usefulness of an antibody specific for activated caspase-3 in a model of neonatal rat hypoxia-ischemia (Hl) and correlate the spatial and temporal activation of caspase-3 with three different markers of DNA damage and with the loss of a neuronal marker [microtubule-associated protein 2 (MAP 2)]. An oligonucleotide hairpin probe (HPP) with one base overhang in the 3′ end displayed a close colocalization with caspase-3 activation at 3 h post-Hl, whereas terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) appeared later (24 h post-Hl). A monoclonal antibody against single-stranded DNA appeared to stain an entirely different population of cells, not positive for active caspase-3, HPP, or TUNEL at this time point. After 24 h of reperfusion, however, when cellular injury is extensive, all markers stained a large number of cells with a high degree of colocalization, and all markers delineated regions with loss of MAP 2. We conclude that the HPP shows the best correlation with pathological caspase-3 activation in this model. [ABSTRACT FROM AUTHOR]

Many sporadic cases of Parkinsons disease have mutations in the PINK protein kinase, whose substrate is now revealed to be a protein that protects mitochondria from oxidative stress. [ABSTRACT FROM AUTHOR]

Abstract: Depressed energy metabolism and oxidative stress are common features in many pathological situations in the brain, including stroke. In order to investigate astrocytic responses to such stress, we induced metabolic depression in cultured rat astrocytes. Iodoacetate (IA), an inhibitor of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used and resulted in a rapid inhibition of GAPDH activity. After 1h of GAPDH inhibition the ATP levels started to decrease and were completely abolished at 4h. In parallel, the activity of reactive oxygen species (ROS) was significantly increased, followed by extensive cell death involving flipping of phosphatidylserine and translocation of apoptosis-inducing factor, but not caspase-3 activation. When IA was combined with azide, a respiratory chain complex IV inhibitor, the ATP levels decreased immediately. Interestingly, with azide present, the ROS activity remained low and the astrocytes remained viable even at very low ATP levels. Addition of exogenous ROS-scavengers prevented the IA-induced ROS activity, the ATP levels were maintained and cell death was prevented. Similar protection could be obtained when astrocytes, prior to addition of IA, were incubated with substances known to activate the nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated endogenous antioxidant system. When IA was washed out, after a relatively moderate ATP depression, massive cell death occurred. This was efficiently prevented by addition of azide or ROS scavengers during the IA treatment or by pre-activation of the Nrf2 system. Our results demonstrate that astrocytes in culture can endure and recover from glycolytic inhibition if the ROS activity remained at a low level and suggest that oxidative stress can be an important component for astrocytic cell death following metabolic stress. [Copyright &y& Elsevier]

Abstract: X chromosome-linked inhibitor of apoptosis protein is an endogenous inhibitor of caspases and is an important regulator of cell death. XIAP can also influence cell signaling, but downstream proteins affected are largely unknown. We show here using neuronal PC6.3 cells that XIAP increases the levels of antioxidants, particularly superoxide dismutase-2 that is localized to mitochondria. Studies using reporter constructs and NF-κB Rel-A deficient mouse embryonic fibroblasts showed that NF-κB signaling is required for the induction of Sod2 by XIAP. XIAP also reduced oxidative stress in the PC6.3 cells as shown by decreased production of reactive oxygen species. These findings disclose a novel role for XIAP in control of oxidative stress and mitochondrial antioxidants that may contribute to cell protection after various injuries. [Copyright &y& Elsevier]

Abstract: The effect of magnetic fields on the brain is a matter of debate. The objective of this study was to investigate whether repeated exposure to strong magnetic fields, such as during magnetic resonance imaging (MRI), could elicit changes in the developing rat brain. Embryonic day 15 (E15) and postnatal day 14 (P14) rats were exposed to MRI using a 7.05T MR system. The animals were anesthetized and exposed for 35min per day for 4 successive days. Control animals were anesthetized but no MRI was performed. Body temperature was maintained at 37°C. BrdU was injected after each session (50mg/kg). One month later, cell proliferation, neurogenesis and astrogenesis in the dentate gyrus were evaluated, revealing no effects of MRI, neither in the E15, nor in the P14 group. DNA damage in the dentate gyrus in the P14 group was evaluated on P18, 1day after the last session, using TUNEL staining. There was no difference in the number of TUNEL-positive cells after MRI compared with controls, neither in mature neurons, nor in newborn progenitors (BrdU/TUNEL double-labeled cells). Novel object recognition was performed to assess memory function 1month after MRI. There was no difference in the recognition index observed after MRI compared with the control rats, neither for the E15, nor for the P14 group. In conclusion, repeated exposure to MRI did not appear to affect neurogenesis, cell death or memory function in rats, neither in late gestation (E15–E18) nor in young postnatal (P14–P17) rats. [ABSTRACT FROM AUTHOR]

Abstract: To date, there are very few in vivo studies addressing the role of Bcl-2 phosphorylation. In a model of neonatal hypoxic–ischemic (HI) brain injury, we characterized the spatial and temporal phosphorylation of Bcl-2 at serine-24 (PS24-Bcl-2), using a site-specific antibody. Very few cells positive for PS24-Bcl-2 were found in control animals, but the number increased during reperfusion in all investigated brain areas in the ipsilateral hemisphere after HI, particularly in the border region between intact and damaged tissue. The highest numbers were encountered 24 h post-HI. Phosphorylation of Bcl-2 at serine-24 coincided with cytochrome c release after hypoxia–ischemia and preceded caspase-3 activation. Injured neurons displayed a predominantly nuclear, but also mitochondrial, localization of PS24-Bcl-2 immunoreactivity. In conclusion, phosphorylation of Bcl-2 at serine 24 was induced by hypoxia–ischemia, presumably resulting in loss of its anti-apoptotic function. [Copyright &y& Elsevier]