Expression of a dominant negative mutant of interleukin-1 beta converting enzyme in transgenic mice prevents neuronal cell death induced by trophic factor withdrawal and ischemic brain injury

Lipopolysaccharide-induced fever is dissociated from apoptotic cell death in the rat brain

Immune system activation induces increase in expression level and enzymatic activity of interleukin-1 beta converting enzyme (ICE) in rat brain. As ICE has been implicated in apoptotic cell death, a possible link may exist between immune system activation by bacterial endotoxic lipopolysaccharide (LPS) and apoptosis in rat brain. The aim of this study was to investigate possible effect of acute (5.5 h) or chronic (5 days) intraperitoneal (i.p.) administration and central injection of LPS on brain apoptotic cell death. Body temperature was continuously monitored for fever, a hallmark of immune activation. Detection of apoptotic cell death was carried out by using in situ labelling of DNA fragmentation in various brain structures. Despite the chronic or the acute pyrogenic effects of LPS, no evidence for apoptotic cell death was observed in any of the brain areas analysed, including hippocampus, hypothalamus, area postrema, subfornical organ, organum vasculosum of the lamina terminalis and nucleus tractus solitaris. Other well-known sites of apoptotic cell death, including brain of ischemic rat, mammary gland of post-lactating rat and rat intestine as well as Dnase-treated rat brain slices, were used as positive controls. These results suggest that ICE activation during fever development is dissociated from cell death by apoptosis in rat brain. Unlike peripheral targets of immunocompetent cytokines, a protective system, yet to be defined, may be present in the central nervous system and block the deleterious effects of infectious agents and cytokines.

Activation of caspase-1 in the nucleus requires nuclear translocation of pro-caspase-1 mediated by its prodomain

The interleukin-1beta-converting enzyme-like protease precursor, pro-caspase-1, has an N-terminal prodomain that is removed during cleavage activation of the protease. Here we show that tumor necrosis factor treatment of HeLa cells induced apoptosis without detectable proteolytic activation of caspase-1 in the cytosol. Instead, tumor necrosis factor induced the translocation of pro-caspase-1 to the nucleus where it was proteolytically activated, releasing the intact prodomain. We identified a nuclear localization signal in the prodomain, which was required for translocation of both pro-caspase-1 as well as its prodomain to the nucleus. Surprisingly, transfected MCF-7 carcinoma or embryonic kidney 293T cells expressing the prodomain alone underwent apoptosis. These results show that death signal-induced nuclear targeting is a novel activity of a caspase prodomain and indicate that caspase-1 and its prodomain may have hitherto unsuspected nuclear functions in apoptosis.

Rabies virus replication induces Bax-related, caspase dependent apoptosis in mouse neuroblastoma cells

Rabies virus has been shown to induce apoptosis in infected cells, but the intracellular pathway of cell killing is unknown. In this report, we show that rabies virus infected mouse neuroblastoma cells underwent chromatin condensation and DNA fragmentation within 48 h post-infection. An increased level of the apoptotic enhancer, Bax, was detected within 24 h after infection. In contrast to Bax, the production of the apoptotic antagonist, Bcl-2, remained unchanged. Shortly after detection of Bax, caspase 1 (ICE) was upregulated. Reduction of DNA fragmentation in rabies virus infected cultures pretreated with YVAD and DEVD suggested that more than one subfamily of caspase functioned in the death process. Significant degradation of the DNA repair enzyme, poly ADP-ribose polymerase (PARP), was revealed after caspase upregulation. This study showed that replication of rabies viruses in mouse neuroblastoma cells induced the Bax-related death program leading to destruction of the DNA repair system probably by caspase activity.

Cerebral ischemia enhances polyamine oxidation: identification of enzymatically formed 3-aminopropanal as an endogenous mediator of neuronal and glial cell death

To elucidate endogenous mechanisms underlying cerebral damage during ischemia, brain polyamine oxidase activity was measured in rats subjected to permanent occlusion of the middle cerebral artery. Brain polyamine oxidase activity was increased significantly within 2 h after the onset of ischemia in brain homogenates (15.8 +/- 0.9 nmol/h/mg protein) as compared with homogenates prepared from the normally perfused contralateral side (7.4 +/- 0.5 nmol/h/mg protein) (P <0.05). The major catabolic products of polyamine oxidase are putrescine and 3-aminopropanal. Although 3-aminopropanal is a potent cytotoxin, essential information was previously lacking on whether 3-aminopropanal is produced during cerebral ischemia. We now report that 3-aminopropanal accumulates in the ischemic brain within 2 h after permanent forebrain ischemia in rats. Cytotoxic levels of 3-aminopropanal are achieved before the onset of significant cerebral cell damage, and increase in a time-dependent manner with spreading neuronal and glial cell death. Glial cell cultures exposed to 3-aminopropanal undergo apoptosis (LD50 = 160 microM), whereas neurons are killed by necrotic mechanisms (LD50 = 90 microM). The tetrapeptide caspase 1 inhibitor (Ac-YVAD-CMK) prevents 3-aminopropanal-mediated apoptosis in glial cells. Finally, treatment of rats with two structurally distinct inhibitors of polyamine oxidase (aminoguanidine and chloroquine) attenuates brain polyamine oxidase activity, prevents the production of 3-aminopropanal, and significantly protects against the development of ischemic brain damage in vivo. Considered together, these results indicate that polyamine oxidase-derived 3-aminopropanal is a mediator of the brain damaging sequelae of cerebral ischemia, which can be therapeutically modulated.

Roles of Bcl-2 and caspases in hypoxia-induced neuronal cell death: a possible neuroprotective mechanism of peptide growth factors

We examined whether apoptosis is involved in hypoxic cell death using primary cultures of rat cortical neurons and whether the cell death is associated with changes in Bcl-2 and Bax expressions and activities of caspases. Hypoxic insult accelerates apoptosis, as shown by apoptotic nuclei and by chromatin degradation of internucleosomal fragments. This apoptotic process is accompanied by a rapid and sustained down-regulation of Bcl-2, whereas levels of Bax are unchanged. Furthermore, hypoxic insult activates sequentially caspase-1-like and caspase-3-like proteases, following down-regulation of Bcl-2 expression. Peptide inhibitors of either caspase-1 or caspase-3 protect against neuronal death, although they do not prevent hypoxia-induced down-regulation of Bcl-2. Furthermore, treatment of cortical neurons with either insulin-like growth factor-1 (IGF-1) or basic fibroblast growth factor (bFGF), growth factors which are implicated to prevent neuronal loss in ischemic brain, partly prevented neuronal death accompanied by inhibition of alterations in Bcl-2 protein levels and caspase-3-like activities. These results suggest that hypoxia induces neuronal death by down-regulation of Bcl-2 protein levels followed by sequential activation of the caspases, and the protection from neuronal cell death of these growth factors under hypoxic conditions derives at least partly from their capability to prevent down-regulation of the anti-apoptotic protein levels.

Reduction of ischemic brain injury by topical application of glial cell line-derived neurotrophic factor after permanent middle cerebral artery occlusion in rats

BACKGROUND AND PURPOSE

Glial cell line-derived neurotrophic factor (GDNF) plays important roles in the survival and recovery of some mature neurons under pathological conditions. However, the effect of GDNF in ameliorating ischemic brain injury has not been well documented. Therefore, we investigated a possible effect of GDNF on the changes of infarct size, brain edema, DNA fragmentation, and immunoreactivities for caspases after permanent middle cerebral artery occlusion (MCAO) in rats.

METHODS

For the estimation of ischemic brain injury, we calculated the infarct size of MCA region and also measured the brain water content as edema formation at 24 hours after the MCAO. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick labeling (TUNEL) staining was performed for the detection of DNA fragmentation. Immunoreactivities for caspase-1 (ICE), caspase-2 (Nedd-2), and caspase-3 (CPP32) were stained.

RESULTS

Both infarct size and brain edema after permanent MCAO were significantly reduced by topical application of GDNF (48% and 30% decreases, P=0.01). TUNEL staining and immunoreactivities for caspases were markedly induced at 12 hours after permanent MCAO in the vehicle-treated animals. However, the spatial distribution of those immunohistochemically positive cells was dissociative in each caspase. Induction of TUNEL staining and immunoreactivities for caspases-1 and -3 was greatly reduced with GDNF treatment, whereas the reduction of caspase-2 staining was only minimum.

CONCLUSIONS

These data suggest that the reduction of infarct size and brain edema by GDNF was greatly associated with the reduction of DNA fragmentation and apoptotic signals predominantly through caspases-1 and -3 cascades.

Anti-apoptosis therapy: a way of treating neural degeneration?

Many degenerative diseases involve apoptotic cell death--can they be treated with apoptosis inhibitors, while protecting the normal physiological function of the rescued cells? Reason for optimism comes from a recent study of mutant flies with an analogue of the human degenerative disease retinitis pigmentosa.

Synergistic effects of caspase inhibitors and MK-801 in brain injury after transient focal cerebral ischaemia in mice

1. Excitotoxic and apoptotic mechanisms have been implicated in the pathophysiology of cerebral ischaemia. Both MK-801, an NMDA receptor antagonist, or peptide inhibitors of the caspase family (z-VAD.FMK and z-DEVD.FMK), protect mouse brain from ischaemic cell damage. In this study, we examined whether these drugs which act via distinct mechanisms, afford even greater neuroprotection when given in combination following 2 h MCA occlusion (filament model) and 18 h reperfusion. 2. Given alone as pretreatment, MK-801 (1, 3 and 5 mg kg(-1), but not 0.3 mg kg(-1), i.p.) decreased infarct size by 34-75%. When injected 1 h after occlusion and before reperfusion, 3 mg kg(-1) reduced injury but not when administered I h after reperfusion. 3. Pretreatment with a subthreshold dose of MK-801 (0.3 mg kg(-1)) plus a subthreshold dose of z-VAD.FMK (27 ng) or z-DEVD (80 ng) significantly decreased infarct size by 29 and 30%, respectively, and enhanced neurological function. 4. Administering a subthreshold dose of z-VAD.FMK (27 ng) or z-DEVD.FMK (80 ng) as pretreatment extended the time window for MK-801 (3 mg kg(-1)) by 2 h from 1 h before reperfusion to at least 1 h after reperfusion. 5. Pretreating with a subthreshold dose of MK-801 (0.3 mg kg(-1)) extended the time window for z-DEVD.FMK (480 ng) from 1 h after reperfusion to at least 3 h after reperfusion. 6. We conclude that caspase inhibitors which putatively block apoptotic cell death and inhibit cytokine production and the NMDA antagonist MK-801 act synergistically and prolong their respective therapeutic windows in cerebral ischaemia.

Activation and cleavage of caspase-3 in apoptosis induced by experimental cerebral ischemia

We examined the expression, activation, and cellular localization of caspase-3 (CPP32) using immunohistochemistry, immunoblots, and cleavage of the fluorogenic substrate N-benzyloxycarbonyl-Asp-Glu-Val-Asp-7-amino-4-trifluoromethyl coumarin (zDEVD-afc) in adult mouse brain after temporary (2 hr) middle cerebral artery occlusion produced by filament insertion into the carotid artery. Immunoreactive caspase-3p32 but not its cleavage product caspase-3p20 was constitutively expressed in neurons throughout brain and was most prominent in neuronal perikarya within piriform cortex. Caspase-like enzyme activity was elevated in brain homogenate 0-3 hr after reperfusion and reached a peak within 30 to 60 min. Caspase-3p20 immunoreactivity became prominent in neuronal perikarya within the middle cerebral artery territory at the time of reperfusion and on immunoblots 1-12 hr later. DNA laddering (agarose gels) and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL)-stained cells were detected 6-24 hr after reperfusion. At 12-24 hr, immunoreactive p20 was visualized in TUNEL-positive cells, a finding also observed in apoptotic mouse cerebellar granule cells on postnatal day 5. Together, these observations suggest the existence of a time-dependent evolution of ischemic injury characterized by the close correspondence between caspase-like enzyme activation and an associated increase in immunoreactive product (caspase-3p20) beginning at or before reperfusion and followed several hours later by morphological and biochemical features of apoptosis.

Activation and cleavage of caspase-3 in apoptosis induced by experimental cerebral ischemia

We examined the expression, activation, and cellular localization of caspase-3 (CPP32) using immunohistochemistry, immunoblots, and cleavage of the fluorogenic substrate N-benzyloxycarbonyl-Asp-Glu-Val-Asp-7-amino-4-trifluoromethyl coumarin (zDEVD-afc) in adult mouse brain after temporary (2 hr) middle cerebral artery occlusion produced by filament insertion into the carotid artery. Immunoreactive caspase-3p32 but not its cleavage product caspase-3p20 was constitutively expressed in neurons throughout brain and was most prominent in neuronal perikarya within piriform cortex. Caspase-like enzyme activity was elevated in brain homogenate 0-3 hr after reperfusion and reached a peak within 30 to 60 min. Caspase-3p20 immunoreactivity became prominent in neuronal perikarya within the middle cerebral artery territory at the time of reperfusion and on immunoblots 1-12 hr later. DNA laddering (agarose gels) and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL)-stained cells were detected 6-24 hr after reperfusion. At 12-24 hr, immunoreactive p20 was visualized in TUNEL-positive cells, a finding also observed in apoptotic mouse cerebellar granule cells on postnatal day 5. Together, these observations suggest the existence of a time-dependent evolution of ischemic injury characterized by the close correspondence between caspase-like enzyme activation and an associated increase in immunoreactive product (caspase-3p20) beginning at or before reperfusion and followed several hours later by morphological and biochemical features of apoptosis.

Defects in regulation of apoptosis in caspase-2-deficient mice

During embryonic development, a large number of cells die naturally to shape the new organism. Members of the caspase family of proteases are essential intracellular death effectors. Herein, we generated caspase-2-deficient mice to evaluate the requirement for this enzyme in various paradigms of apoptosis. Excess numbers of germ cells were endowed in ovaries of mutant mice and the oocytes were found to be resistant to cell death following exposure to chemotherapeutic drugs. Apoptosis mediated by granzyme B and perforin was defective in caspase-2-deficient B lymphoblasts. In contrast, cell death of motor neurons during development was accelerated in caspase-2-deficient mice. In addition, caspase-2-deficient sympathetic neurons underwent apoptosis more effectively than wild-type neurons when deprived of NGF. Thus, caspase-2 acts both as a positive and negative cell death effector, depending upon cell lineage and stage of development.

Attenuation of delayed neuronal death after mild focal ischemia in mice by inhibition of the caspase family

Inhibitors of apoptosis and of excitotoxic cell death reduce brain damage after transient and permanent middle cerebral artery occlusion. We compared the neuroprotective effects of two caspase family inhibitors with the N-methyl-D-aspartate receptor antagonist (+)-MK-801 hydrogen maleate (MK-801) in a newly characterized cycloheximide-sensitive murine model of transient middle cerebral artery occlusion (30 minutes) in which apoptotic cell death is prominent. Ischemic infarction, undetected by 2,3,5-triphenyltetrazolium chloride staining at 24-hour reperfusion, featured prominently in the striatum at 72 hours and 7 days on hematoxylin-eosin-stained sections. Markers of apoptosis, such as oligonucleosomal DNA damage (laddering) and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL)-positive cells first appeared at 24 hours and increased significantly at 72 hours and 7 days after reperfusion. The TUNEL-labeled cells were mostly neurons and stained negative for glial (GFAP, glial fibrillary acid protein) and leukocyte specific markers (CD-45). The caspase inhibitors, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VAD.FMK; 120 ng intracerebroventricularly) or N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone (z-DEVD.FMK; 480 ng intracerebroventricularly) decreased infarct size and neurologic deficits when administered 6 hours after reperfusion. The extent of protection was greater than in models of more prolonged ischemia or after permanent occlusion, and the therapeutic window was extended from 0 to 1 hours after 2-hour middle cerebral artery occlusion to at least 6 hours after brief ischemia. Also, z-VAD.FMK and z-DEVD.FMK treatment decreased oligonucleosomal DNA damage (DNA laddering) as assessed by quantitative autoradiography after gel electrophoresis. By contrast, MK-801 protected brain tissue only when given before ischemia (3 mg/kg intraperitoneally), but not at 3 or 6 hours after reperfusion. Despite a decrease in infarct size after MK-801 pretreatment, the amount of DNA laddering did not decrease 72 hours after reperfusion, thereby suggesting a mechanism distinct from inhibition of apoptosis. Hence, 30 minutes of reversible ischemia augments apoptotic cell death, which can be attenuated by delayed z-VAD.FMK and z-DEVD.FMK administration with preservation of neurologic function. By contrast, the therapeutic window for MK-801 does not extend beyond the time of occlusion, probably because its primary mechanism of action does not block the development of apoptotic cell death.

Conditional genome alteration in mice

The recent ability to inactivate specific genes in mice has significantly accelerated our understanding of molecular, cellular, and even behavioral aspects of normal and disease processes. However, this ability has also demonstrated the extreme complexity of genetic determination in mammals, in particular, that genes in the same family or pathway can be functionally redundant and that a given gene often has multiple roles. Thus, inactivation of a gene often does not indicate its complete spectrum of functions. To circumvent this problem, many new tools and novel applications of classic techniques have been developed to place spatial and temporal restrictions on the genomic alterations. These approaches include chimera and mosaic studies, organ transplantation, complementation assays, dominant negative mutants, conditional gene knockouts, and lineage-specific gene rescue. Not only has this opened up more sophisticated ways to make genomic alterations, but it has provided the opportunity to create animal models for sporadic human genetic diseases.

Murine caspase-11, an ICE-interacting protease, is essential for the activation of ICE

We report here the inactivation of a member of the Ice/Ced-3 (caspase) family of cell death genes, casp-11, by gene targeting. Like Ice-deficient mice, casp-11 mutant mice are resistant to endotoxic shock induced by lipopolysaccharide. Production of both IL-1alpha and IL-1beta after lipopolysaccharide stimulation, a crucial event during septic shock and an indication of ICE activation, is blocked in casp-11 mutant mice. casp-11 mutant embryonic fibroblast cells are resistant to apoptosis induced by overexpression of ICE. Furthermore, we found that pro-caspase-11 physically interacts with pro-ICE in cells, and the expression of casp-11 is essential for activation of ICE. Our data suggest that caspase-11 is a component of ICE complex and is required for the activation of ICE.

Sealing one's fate: control of cell death in neurons

BCL-2 family members and caspases are essential components of the death machinery in neurons. Identification of Apaf-1 as the mammalian homologue of Caenorhabditis elegans ced-4 provided the final proof of the complete conservation of the C. elegans programmed cell death pathway in mammals. When neurons are deprived of trophic factors, a sequence of events is initiated, which includes a reduction in macromolecule synthesis, elevation of c-Jun and cyclin D1, and activation of BAX. The final episode of this sequence is the activation of caspases, which may mark the death commitment point at which neurons cannot be rescued by addition of trophic factors. In addition, recent evidence suggests that the components in the developmental programmed cell death pathway may play a critical role in neurodegenerative disorders.

Reduced ischemic brain injury in interleukin-1 beta converting enzyme-deficient mice

A variety of recent studies suggest a role for both inflammatory cytokines such as interleukin-1 beta (IL-1 beta), and apoptosis in ischemic brain injury. Because IL-1 beta converting enzyme (ICE) is required for the conversion of proIL-1 beta to its biologically active form, and has homology with proteins that regulate apoptosis in invertebrates, we studied the effect of cerebral ischemia on brain injury in mutant mice deficient in the ICE gene (ICE knockout [KO] mice). Focal cerebral ischemia, produced by occlusion of the middle cerebral artery, resulted in brain edema (increased water and sodium content) at 4 hours and a histologically defined brain lesion at 24 hours. Both of these markers of brain injury were significantly reduced in the ICE KO mice as compared to wild-type C57BL/6 mice. Regional cerebral blood flow, determined using the flow tracer, N-isopropyl [methyl 1,3-(14)C] p-iodoamphetamine (14C-IMP), was similar in the two strains of mice, indicating that the reduced brain injury in the KO mice was not a result of a lesser degree of ischemia. These data show that ICE contributes to the development of ischemic brain damage, and that it plays a role at an early time in the pathologic process. Although the mechanism of this effect is uncertain, our results suggest that pharmacologic inhibition of ICE may be a useful treatment for stroke.

Ischemic brain injury is mediated by the activation of poly(ADP-ribose)polymerase

Poly(ADP-ribose)polymerase (PARP, EC 2.4.2.30), an abundant nuclear protein activated by DNA nicks, mediates cell death in vitro by nicotinamide adenine dinucleotide (NAD) depletion after exposure to nitric oxide. The authors examined whether genetic deletion of PARP (PARP null mice) or its pharmacologic inhibition by 3-aminobenzamide (3-AB) attenuates tissue injury after transient cerebral ischemia. Twenty-two hours after reperfusion following 2 hours of filamentous middle cerebral artery occlusion, ischemic injury was decreased in PARP-/- and PARP+/- mice compared with PARP+/+ litter mates, and also was attenuated in 129/SV wild-type mice after 3-AB treatment compared with controls. Infarct sparing was accompanied by functional recovery in PARP-/- and 3-AB-treated mice. Increased poly(ADP-ribose) immunostaining observed in ischemic cell nuclei 5 minutes after reperfusion was reduced by 3-AB treatment. Levels of NAD--the substrate of PARP--were reduced 2 hours after reperfusion and were 35% of contralateral levels at 24 hours. The decreases were attenuated in PARP-/- mice and in 3-AB-treated animals. Poly(ADP-ribose)polymerase cleavage by caspase-3 (CPP-32) has been proposed as an important step in apoptotic cell death. Markers of apoptosis, such as oligonucleosomal DNA damage, total DNA fragmentation, and the density of terminal deoxynucleotidyl transferase dUTP nick-end-labelled (TUNEL +) cells, however, did not differ in ischemic brain tissue of PARP-/- mice or in 3-AB-treated animals versus controls, although there were differences in the number of TUNEL-stained cells reflecting the decrease in infarct size. Thus, ischemic brain injury activates PARP and contributes to cell death most likely by NAD depletion and energy failure, although the authors have not excluded a role for PARP in apoptotic cell death at earlier or later stages in ischemic cell death. Inhibitors of PARP activation could provide a potential therapy in acute stroke.

What does cell death have to do with aging?

When Lockshin and Zakeri discussed the relevance of apoptosis to aging 7 years ago, the common view was that apoptosis would have primarily a negative impact on aging by destroying essential and often irreplaceable cells. That view has now changed to one that acknowledges that there are two general ways in which apoptosis can play a role in aging: (1) elimination of damaged and presumably dysfunctional cells (e.g., fibroblasts, hepatocytes), which can then be replaced by cell proliferation, thereby maintaining homeostasis, and (2) elimination of essential post-mitotic cells (e.g., neurons, cardiac myocytes), which cannot be replaced, thereby leading to pathology. Evidence exists in two systems (fibroblasts and thymocytes/lymphocytes) that there are age-related decreases in the potential for apoptosis, although the molecular bases for the decreases in these two systems appear to differ. Upon becoming senescent, fibroblasts lose the ability to down-regulate expression of the bcl-2 gene in response to an apoptotic signal; thus, apoptosis is blocked even though an initiating signal has been received. In contrast, thymocytes/lymphocytes lack the ability to initiate the signal because of down-regulation of the cell surface receptor Fas. There is limited information available for other tissue types, and nothing is known about why and how age-related changes occur. An interesting observation is that the frequency of up-regulation of the bcl-2 gene as a result of chromosome translocation in otherwise normal B cells increases with age; the functional consequences of this phenomenon during aging are not known. The role of apoptosis in regulating cell number is also a promising area of research. The studies on liver damage and neoplastic lesions suggest an extremely important role for apoptosis in controlling cancer. This may be particularly important in the prostate where hypertrophy and/or cancer are a virtual certainty with ever-increasing age. It is not known whether the ability to undergo apoptosis declines in the prostate with increasing age, but it appears possible that it may, thus explaining the loss of control over cell number in this tissue. A particularly important area of research is whether apoptosis plays a role in the changing balance between bone formation and resorption observed during osteoporosis. Monica Driscoll has already pointed out that, "regulation and execution of cell death is an absolutely critical process that interfaces with nearly every aspect of life. Future investigation of the links of cell death to cellular aging and the aging of organisms should be an exciting enterprise." The results currently available do suggest that apoptosis is a process that may be important in aging, at least in some tissues, and the mechanism of its regulation, in particular, needs to be understood. Several tumor suppressor gene and oncogene products are involved in signal transduction associated with apoptosis, but it remains to be shown which of these, if any, are actually involved in "on-off" switches for apoptosis. Where great progress has been made is in understanding the events occurring after binding of either Fas ligand or tumor necrosis factor to their respective receptors. However, one area about which little is known is the identity of the signals that initiate this process in response to intracellular damage. Through continuing research on cell death mechanisms, funded by the NIA, we hope to provide answers to such fundamental questions as: 1. Are there age-related changes in apoptosis, and what role, if any, do these have in the aging process? 2. If age-related changes in apoptosis do occur, what molecular mechanisms are altered to produce these changes? 3. Can approaches be developed to improve the detection and elimination of damaged cells in vivo in tissues where cell replacement is possible? 4. Can death of damaged cells be attenuated or delayed in nonrenewable tissues, and, if so, is it advantageous to the org

Attenuation of transient focal cerebral ischemic injury in transgenic mice expressing a mutant ICE inhibitory protein

We used transgenic mice expressing a dominant negative mutation of interleukin-1 beta converting enzyme (ICE) (C285G) in a model of transient focal ischemia in order to investigate the role of ICE in ischemic brain damage. Transgenic mutant ICE mice (n = 11) and wild-type littermates (n = 9) were subjected to 3 h of middle cerebral artery occlusion followed by 24 h of reperfusion. Cerebral infarcts and brain swelling were reduced by 44% and 46%, respectively. Neurological deficits were also significantly reduced. Regional CBF, blood pressure, core temperature, and heart rate did not differ between groups when measured for up to 1 h after reperfusion. Increases in immunoreactive IL-1 beta levels, observed in ischemic wild-type brain at 30 min after reperfusion, were 77% lower in the mutant strain, indicating that proIL-1 beta cleavage is inhibited in the mutants. DNA fragmentation was reduced in the mutants 6 and 24 h after reperfusion. Hence, endogenous expression of an ICE inhibitor confers resistance to cerebral ischemia and brain swelling. Our results indicate that downregulation of ICE expression might provide a useful therapeutic target in cerebral ischemia.