Excitotoxic lesion of rat brain with quinolinic acid induces expression of p53 messenger RNA and protein and p53-inducible genes Bax and Gadd-45 in brain areas showing DNA fragmentation

Aberrant generation of dentate gyrus granule cells is associated with epileptic susceptibility in p53 conditional knockout mice

Neuronal apoptosis is a mechanism used to clear the cells of oxidative stress or DNA damage and refine the final number of neurons for a functional neuronal circuit. The tumor suppressor protein p53 is a key regulator of the cell cycle and serves as a checkpoint for eliminating neurons with high DNA damage, hyperproliferative signals or cellular stress. During development, p53 is largely expressed in progenitor cells. In the adult brain, p53 expression is restricted to the neurogenic niches where it regulates cell proliferation and self-renewal. To investigate the functional consequences of p53 deletion in the cortex and hippocampus, we generated a conditional mutant mouse (p53-cKO) in which p53 is deleted from pallial progenitors and their derivatives. Surprisingly, we did not find any significant change in the number of neurons in the mutant cortex or CA region of the hippocampus compared with control mice. However, p53-cKO mice exhibit more proliferative cells in the subgranular zone of the dentate gyrus and more granule cells in the granular cell layer. Glutamatergic synapses in the CA3 region are more numerous in p53-cKO mice compared with control littermates, which correlates with overexcitability and higher epileptic susceptibility in the mutant mice.

GADD45A: With or without you

The growth arrest and DNA damage inducible (GADD)45 family includes three small and ubiquitously distributed proteins (GADD45A, GADD45B, and GADD45G) that regulate numerous cellular processes associated with stress signaling and injury response. Here, we provide a comprehensive review of the current literature investigating GADD45A, the first discovered member of the family. We first depict how its levels are regulated by a myriad of genotoxic and non-genotoxic stressors, and through the combined action of intricate transcriptional, posttranscriptional, and even, posttranslational mechanisms. GADD45A is a recognized tumor suppressor and, for this reason, we next summarize its role in cancer, as well as the different mechanisms by which it regulates cell cycle, DNA repair, and apoptosis. Beyond these most well-known actions, GADD45A may also influence catabolic and anabolic pathways in the liver, adipose tissue and skeletal muscle, among others. Not surprisingly, GADD45A may trigger AMP-activated protein kinase activity, a master regulator of metabolism, and is known to act as a transcriptional coregulator of numerous nuclear receptors. GADD45A has also been reported to display a cytoprotective role by regulating inflammation, fibrosis and oxidative stress in several organs and tissues, and is regarded an important contributor for the development of heart failure. Overall data point to that GADD45A may play an important role in metabolic, neurodegenerative and cardiovascular diseases, and also autoimmune-related disorders. Thus, the potential mechanisms by which dysregulation of GADD45A activity may contribute to the progression of these diseases are also reviewed below.

The dangerous "West Coast Swing" by hyperglycaemia and chronic stress in the mouse hippocampus: Role of kynurenine catabolism

Growing epidemiological studies highlight a bi-directional relationship between depressive symptoms and diabetes mellitus. However, the detrimental impact of their co-existence on mental health suggests the need to treat this comorbidity as a separate entity rather than the two different pathologies. Herein, we characterized the peculiar mechanisms activated in mouse hippocampus from the concurrent development of hyperglycaemia, characterizing the different diabetes subtypes, and chronic stress, recognized as a possible factor predisposing to major depression. Our work demonstrates that kynurenine overproduction, leading to apoptosis in the hippocampus, is triggered in a different way depending on hyperglycaemia or chronic stress. Indeed, in the former, kynurenine appears produced by infiltered macrophages whereas, in the latter, peripheral kynurenine preferentially promotes resident microglia activation. In this scenario, QA, derived from kynurenine catabolism, appears a key mediator causing glutamatergic synapse dysfunction and apoptosis, thus contributing to brain atrophy. We demonstrated that the coexistence of hyperglycaemia and chronic stress worsened hippocampal damage through alternative mechanisms, such as GLUT-4 and BDNF down-expression, denoting mitochondrial dysfunction and apoptosis on one hand and evoking the compromission of neurogenesis on the other. Overall, in the degeneration of neurovascular unit, hyperglycaemia and chronic stress interacted each other as the partners of a "West Coast Swing" in which the leading role can be assumed alternatively by each partner of the dance. The comprehension of these mechanisms can open novel perspectives in the management of diabetic/depressed patients, but also in the understanding the pathogenesis of other neurodegenerative disease characterized by the compromission of hippocampal function.

Gadd45 in Neuronal Development, Function, and Injury

The growth arrest and DNA damage-inducible (Gadd) 45 proteins have been associated with numerous cellular mechanisms including cell cycle control, DNA damage sensation and repair, genotoxic stress, neoplasia, and molecular epigenetics. The genes were originally identified in in vitro screens of irradiation- and interleukin-induced transcription and have since been implicated in a host of normal and aberrant central nervous system processes. These include early and postnatal development, injury, cancer, memory, aging, and neurodegenerative and psychiatric disease states. The proteins act through a variety of molecular signaling cascades including the MAPK cascade, cell cycle control mechanisms, histone regulation, and epigenetic DNA demethylation. In this review, we provide a comprehensive discussion of the literature implicating each of the three members of the Gadd45 family in these processes.

Effects of pyrethroids on brain development and behavior: Deltamethrin

Deltamethrin (DLM) is a Type II pyrethroid pesticide widely used in agriculture, homes, public spaces, and medicine. Epidemiological studies report that increased pyrethroid exposure during development is associated with neurobehavioral disorders. This raises concern about the safety of these chemicals for children. Few animal studies have explored the long-term effects of developmental exposure to DLM on the brain. Here we review the CNS effects of pyrethroids, with emphasis on DLM. Current data on behavioral and cognitive effects after developmental exposure are emphasized. Although, the acute mechanisms of action of DLM are known, how these translate to long-term effects is only beginning to be understood. But existing data clearly show there are lasting effects on locomotor activity, acoustic startle, learning and memory, apoptosis, and dopamine in mice and rats after early exposure. The most consistent neurochemical findings are reductions in the dopamine transporter and the dopamine D1 receptor. The data show that DLM is developmentally neurotoxic but more research on its mechanisms of long-term effects is needed.

Long-Term Intake of Uncaria rhynchophylla Reduces S100B and RAGE Protein Levels in Kainic Acid-Induced Epileptic Seizures Rats

Epileptic seizures are crucial clinical manifestations of recurrent neuronal discharges in the brain. An imbalance between the excitatory and inhibitory neuronal discharges causes brain damage and cell loss. Herbal medicines offer alternative treatment options for epilepsy because of their low cost and few side effects. We established a rat epilepsy model by injecting kainic acid (KA, 12 mg/kg, i.p.) and subsequently investigated the effect of Uncaria rhynchophylla (UR) and its underlying mechanisms. Electroencephalogram and epileptic behaviors revealed that the KA injection induced epileptic seizures. Following KA injection, S100B levels increased in the hippocampus. This phenomenon was attenuated by the oral administration of UR and valproic acid (VA, 250 mg/kg). Both drugs significantly reversed receptor potentiation for advanced glycation end product proteins. Rats with KA-induced epilepsy exhibited no increase in the expression of metabotropic glutamate receptor 3, monocyte chemoattractant protein 1, and chemokine receptor type 2, which play a role in inflammation. Our results provide novel and detailed mechanisms, explaining the role of UR in KA-induced epileptic seizures in hippocampal CA1 neurons.

Behavioral Deficits Are Accompanied by Immunological and Neurochemical Changes in a Mouse Model for Neuropsychiatric Lupus (NP-SLE)

Neuropsychiatric symptoms of systemic lupus erythematosus (NP-SLE) have been understudied compared to end-organ failure and peripheral pathology. Neuropsychiatric symptoms, particularly affective and cognitive indications, may be among the earliest manifestations of SLE. Among the potential pathophysiological mechanisms responsible for NP-SLE are increased peripheral pro-inflammatory cytokines, subsequent induction of indoleamine-2,3-dioxygenase (IDO) and activation of the kynurenine pathway. In the MRL/MpJ-Faslpr (MRL/lpr) murine model of lupus, depression-like behavior and cognitive dysfunction is evident before significant levels of autoantibody titers and nephritis are present. We examined the behavioral profile of MRL/lpr mice and their congenic controls, a comprehensive plasma cytokine and chemokine profile, and brain levels of serotonin and kynurenine pathway metabolites. Consistent with previous studies, MRL/lpr mice had increased depression-like behavior and visuospatial memory impairment. Plasma levels of different inflammatory molecules (Haptoglobin, interleukin 10 (IL-10), interferon γ-inducible protein 10 (IP-10/CXCL10), lymphotactin, macrophage inhibitory protein 3β (MIP-3β/CCL19), monocyte chemotactic protein 1, 3 and 5 (MCP-1/CCL2, MCP-3/CCL7, MCP-5/CCL12), vascular cell adhesion molecule 1 (VCAM-1), lymphotactin and interferon γ (IFN-γ)) were increased in MRL/lpr mice. In cortex and hippocampus, MRL/lpr mice had increased levels of kynurenine pathway metabolites (kynurenine, 3-hydroxykynurenine, 3-hydroxynthranilic acid and quinolinic acid). Therefore, our study suggests that increased cytokine expression may be critical in the regulation subtle aspects of brain function in NP-SLE via induction of IDO and tryptophan/kynurenine metabolism.

p53 and mitochondrial function in neurons

The p53 tumor suppressor plays a central role in dictating cell survival and death as a cellular sensor for a myriad of stresses including DNA damage, oxidative and nutritional stress, ischemia and disruption of nucleolar function. Activation of p53-dependent apoptosis leads to mitochondrial apoptotic changes via the intrinsic and extrinsic pathways triggering cell death execution most notably by release of cytochrome c and activation of the caspase cascade. Although it was previously believed that p53 induces apoptotic mitochondrial changes exclusively through transcription-dependent mechanisms, recent studies suggest that p53 also regulates apoptosis via a transcription-independent action at the mitochondria. Recent evidence further suggests that p53 can regulate necrotic cell death and autophagic activity including mitophagy. An increasing number of cytosolic and mitochondrial proteins involved in mitochondrial metabolism and respiration are regulated by p53, which influences mitochondrial ROS production as well. Cellular redox homeostasis is also directly regulated by p53 through modified expression of pro- and anti-oxidant proteins. Proper regulation of mitochondrial size and shape through fission and fusion assures optimal mitochondrial bioenergetic function while enabling adequate mitochondrial transport to accommodate local energy demands unique to neuronal architecture. Abnormal regulation of mitochondrial dynamics has been increasingly implicated in neurodegeneration, where elevated levels of p53 may have a direct contribution as the expression of some fission/fusion proteins are directly regulated by p53. Thus, p53 may have a much wider influence on mitochondrial integrity and function than one would expect from its well-established ability to transcriptionally induce mitochondrial apoptosis. However, much of the evidence demonstrating that p53 can influence mitochondria through nuclear, cytosolic or intra-mitochondrial sites of action has yet to be confirmed in neurons. Nonetheless, as mitochondria are essential for supporting normal neuronal functions and in initiating/propagating cell death signaling, it appears certain that the mitochondria-related functions of p53 will have broader implications than previously thought in acute and progressive neurological conditions, providing new therapeutic targets for treatment.

Quinolinic acid: an endogenous neurotoxin with multiple targets

Quinolinic acid (QUIN), a neuroactive metabolite of the kynurenine pathway, is normally presented in nanomolar concentrations in human brain and cerebrospinal fluid (CSF) and is often implicated in the pathogenesis of a variety of human neurological diseases. QUIN is an agonist of N-methyl-D-aspartate (NMDA) receptor, and it has a high in vivo potency as an excitotoxin. In fact, although QUIN has an uptake system, its neuronal degradation enzyme is rapidly saturated, and the rest of extracellular QUIN can continue stimulating the NMDA receptor. However, its toxicity cannot be fully explained by its activation of NMDA receptors it is likely that additional mechanisms may also be involved. In this review we describe some of the most relevant targets of QUIN neurotoxicity which involves presynaptic receptors, energetic dysfunction, oxidative stress, transcription factors, cytoskeletal disruption, behavior alterations, and cell death.

Conformational altered p53 affects neuronal function: relevance for the response to toxic insult and growth-associated protein 43 expression

The role of p53 in neurodegenerative diseases is essentially associated with neuronal death. Recently an alternative point of view is emerging, as altered p53 conformation and impaired protein function have been found in fibroblasts and blood cells derived from Alzheimer's disease patients. Here, using stable transfected SH-SY5Y cells overexpressing APP751wt (SY5Y-APP) we demonstrated that the expression of an unfolded p53 conformation compromised neuronal functionality. In particular, these cells showed (i) augmented expression of amyloid precursor protein (APP) and its metabolites, including the C-terminal fragments C99 and C83 and β-amyloid peptide (ii) high levels of oxidative markers, such as 4-hydroxy-2-nonenal Michael-adducts and 3-nitro-tyrosine and (iii) altered p53 conformation, mainly due to nitration of its tyrosine residues. The consequences of high-unfolded p53 expression resulted in loss of p53 pro-apoptotic activity, and reduction of growth-associated protein 43 (GAP-43) mRNA and protein levels. The role of unfolded p53 in cell death resistance and lack of GAP-43 transcription was demonstrated by ZnCl₂ treatment. Zinc supplementation reverted p53 wild-type tertiary structure, increased cells sensitivity to acute cytotoxic injury and GAP-43 levels in SY5Y-APP clone.

Neuroprotection by mefenamic acid against D-serine: involvement of oxidative stress, inflammation and apoptosis

Mefenamic acid, a non-steroidal antiinflammatory drug (NSAID), directly and dose-dependently exhibits neuroprotective activity. In our study, we investigated the effects of mefenamic acid against d-serine on oxidative stress in the hippocampus, cortex and cerebellum of rats. Furthermore, the potential inflammatory and apoptotic effects of d-serine and potential protective effect of mefenamic acid were determined at mRNA and protein levels of TNF-α, IL-1β, Bcl-2 and Bax. We found that d-serine significantly increased oxidative stress, levels of inflammation- and apoptosis-related molecules in a region specific manner. Mefenamic acid treatment provided significant protection against the elevation of lipid peroxidation, protein oxidation, levels of TNF-α, IL-1β and Bax. As a conclusion, we suggest that d-serine, as a potential neurodegenerative agent, may have a pivotal role in the regulation of oxidative stress, inflammation and apoptosis; and NSAIDs, such as mefenamic acid, may assist other therapeutics in treating disorders where d-serine-induced neurotoxic mechanisms are involved in.

Oral Uncaria rhynchophylla (UR) reduces kainic acid-induced epileptic seizures and neuronal death accompanied by attenuating glial cell proliferation and S100B proteins in rats

AIM OF THE STUDY

Epilepsy is a common clinical syndrome with recurrent neuronal discharges in cerebral cortex and hippocampus. Here we aim to determine the protective role of Uncaria rhynchophylla (UR), an herbal drug belong to Traditional Chinese Medicine (TCM), on epileptic rats.

MATERIALS AND METHODS

To address this issue, we tested the effect of UR on kainic acid (KA)-induced epileptic seizures and further investigate the underlying mechanisms.

RESULTS

Oral UR successfully decreased neuronal death and discharges in hippocampal CA1 pyramidal neurons. The population spikes (PSs) were decreased from 4.1 ± 0.4 mV to 2.1 ± 0.3 mV in KA-induced epileptic seizures and UR-treated groups, respectively. Oral UR protected animals from neuronal death induced by KA treatment (from 34 ± 4.6 to 191.7 ± 48.6 neurons/field) through attenuating glial cell proliferation and S100B protein expression but not GABAA and TRPV1 receptors.

CONCLUSIONS

The above results provide detail mechanisms underlying the neuroprotective action of UR on KA-induced epileptic seizure in hippocampal CA1 neurons.

Involment of p53, Bax, and Bcl-2 pathway in microcystins-induced apoptosis in rat testis

It has been reported that microcystins (MCs) could accumulate in the gonads of mammals and MCs exposure exerts obvious toxic effects on male reproductive system of mammals. We have comfirmedthat MCs could accumulate and induce apoptosis in rat testis. The p53, Bax, and Bcl-2 protein play important roles in mitochondria-dependent apoptotic pathway, and this study aimed to investigate whether the p53, Bax, and Bcl-2 pathway is involved in microcystins-induced apoptosis in rat testis and discussed the possible mechanisms. Our results show that MCs led to persistent increase of transcriptional and protein level of P53 and Bax expression but led to decrease of Bcl-2 expression, resulting in an increased ratio of Bax to Bcl-2, which might contribute to apoptotic cell death of rat testis following MCs treatment. The increased ratio of expression of Bax to that of Bcl-2 induced by MCs suggests their important role in MCs-induced apoptosis in rat testis tissue.

GADD45A protects against cell death in dorsal root ganglion neurons following peripheral nerve injury

A significant loss of neurons in the dorsal root ganglia (DRG) has been reported in animal models of peripheral nerve injury. Neonatal sensory neurons are more susceptible than adult neurons to axotomy- or nerve growth factor (NGF) withdrawal-induced cell death. To develop therapies for preventing irreversible sensory cell loss, it is essential to understand the molecular mechanisms responsible for DRG cell death and survival. Here we describe how the expression of the growth arrest- and DNA damage-inducible gene 45α (GADD45A) is correlated with neuronal survival after axotomy in vivo and after NGF withdrawal in vitro. GADD45A expression is low at birth and does not change significantly after spinal nerve ligation (SNL). In contrast, GADD45A is robustly up-regulated in the adult rat DRG 24 hr after SNL, and this up-regulation persists as long as the injured fibers are prevented from regenerating. In vitro delivery of GADD45A protects neonatal rat DRG neurons from NGF withdrawal-induced cytochrome c release and cell death. In addition, in vivo knockdown of GADD45A expression in adult injured DRG by small hairpin RNA increased cell death. Our results indicate that GADD45A protects neuronal cells from SNL-induced cell death.

Molecular mechanism of preconditioning

During the last 20 years, since the appearance of the first publication on ischemic preconditioning (PC), our knowledge of this phenomenon has increased exponentially. PC is defined as an increased tolerance to ischemia and reperfusion induced by previous sublethal period ischemia. This is the most powerful mechanism known to date for limiting the infract size. This adaptation occurs in a biphasic pattern (i) early preconditioning (lasts for 2-3 h) and (ii) late preconditioning (starting at 24 h lasting until 72-96 h after initial ischemia). Early preconditioning is more potent than delayed preconditioning in reducing infract size. Late preconditioning attenuates myocardial stunning and requires genomic activation with de novo protein synthesis. Early preconditioning depends on adenosine, opioids and to a lesser degree, on bradykinin and prostaglandins, released during ischemia. These molecules activate G-protein-coupled receptor, initiate activation of K(ATP) channel and generate oxygen-free radicals, and stimulate a series of protein kinases, which include protein kinase C, tyrosine kinase, and members of MAP kinase family. Late preconditioning is triggered by a similar sequence of events, but in addition essentially depends on newly synthesized proteins, which comprise iNOS, COX-2, manganese superoxide dismutase, and possibly heat shock proteins. The final mechanism of PC is still not very clear. The present review focuses on the possible role signaling molecules that regulate cardiomyocyte life and death during ischemia and reperfusion.

Apoptotic actions of p53 require transcriptional activation of PUMA and do not involve a direct mitochondrial/cytoplasmic site of action in postnatal cortical neurons

Recent studies in non-neuronal cells have shown that the tumor suppressor p53 can promote cell death through a transcription-independent mechanism involving its direct action with a subset of Bcl-2 family member proteins in the cytosol and at the mitochondria. In cultured cortical neurons, however, we could not find evidence supporting a significant contribution of the cytosolic/mitochondrial p53 pathway, and available evidence instead corroborated the requirement for the transcriptional activity of p53. When directly targeted to the cytosol/mitochondria, wild-type p53 lost its apoptosis-inducing activity in neurons but not in non-neuronal cells. The N-terminal p53 fragment (transactivation and proline-rich domains), which induces apoptosis in non-neuronal cells via the cytosolic/mitochondrial pathway, displayed no apoptogenic activity in neurons. In neuronal apoptosis induced by camptothecin or an MDM2 (murine double minute 2) inhibitor, nutlin-3, endogenous p53 protein did not accumulate in the cytosol/mitochondria, and transcriptional inhibition after p53 induction effectively blocked cell death. In addition, overexpression of a dominant-negative form of p53 (R273H) completely suppressed induction of proapoptotic p53 target genes and cell death. PUMA (p53-upregulated modulator of apoptosis) was one such gene induced by camptothecin, and its overexpression was sufficient to induce Bax (Bcl-2-associated X protein)-dependent neuronal death, whereas Noxa was not apoptogenic. These results collectively demonstrate that, in contrast to non-neuronal cells, the apoptotic activity of p53 in postnatal cortical neurons does not rely on its direct action at the cytosol/mitochondria but is exclusively mediated through its transcription-dependent functions. The uniqueness of p53-mediated apoptotic signaling in postnatal cortical neurons was further illustrated by the dispensable function of the proline-rich domain of p53.

Proapoptotic multidomain Bcl-2/Bax-family proteins: mechanisms, physiological roles, and therapeutic opportunities

Bcl-2-family proteins are central regulators of cell life and death. At least three major classes of Bcl-2-family proteins have been delineated, including proapoptotic proteins that contain several conserved regions of sequence similarity (termed 'multidomain'). In mammals, the multidomain proteins (MDPs) of the Bcl-2 family include Bax, Bak, and Bok. The founding member of the MDP group of Bcl-2-family proteins was discovered by Stanley Korsmeyer and co-workers, initiating an exciting area of cell death research. The status of current knowledge about the mechanisms and functions of MDPs is reviewed here, and some areas for future research are outlined. Therapeutic opportunities emerging from a growing understanding of MDPs with respect to their three-dimensional structures, biochemical actions, and roles in disease raise hopes that the foundation of basic research laid by Korsmeyer and others will eventually be translated into clinical benefits, leaving a legacy that benefits the world for many decades.

Regulation of neural cell survival by HIV-1 infection

Infection by the lentivirus, human immunodeficiency virus type 1 (HIV-1), results in a variety of syndromes involving both the central (CNS) and the peripheral (PNS) nervous systems. Productive HIV-1 infection of the CNS is chiefly detectable in perivascular macrophages and microglia. HIV-1 encoded transcripts and proteins have also been detected in the PNS; however, productive viral replication appears to be sparse and restricted to the macrophage cell population. Despite the absence of productive infection of neurons, HIV-1 infection has been associated with neuronal loss in distinct regions of the brain. Neuronal cell loss may occur through both necrosis and apoptosis, although neuronal apoptosis appears to be a feature of AIDS, as only rare apoptotic neurons have been demonstrated in a few pre-AIDS cases. Although there is no clear consensus as to the underlying mechanism of HIV-induced neuropathogenesis, two complementary concepts predominate. Firstly, HIV-1 encoded proteins injure neurons directly without requiring the intermediary functions of nonneuronal cells. Alternatively, neuronal apoptosis may result indirectly from the secretion of neurotoxic host molecules by resident brain macrophages or microglia in response to HIV-1 infection, stimulation by viral proteins or immune activation. Herein, we review the neurological disorders and their underlying mechanisms associated with HIV infection, focusing on HIV-associated dementia (HAD) and HIV sensory neuropathy (HIV-SN). The evidence that neuronal loss in HIV-1-infected individuals may be due to neuronal apoptosis is then discussed. This review also summarizes the current data supporting both the direct and indirect mechanisms by which neuronal death may occur during infection with HIV-1 or the closely related lentiviruses SIV and FIV. Lastly, strategies are examined for treating or preventing HAD by targeting specific neurotoxic mechanisms.

Susceptibility of striatal neurons to excitotoxic injury correlates with basal levels of Bcl-2 and the induction of P53 and c-Myc immunoreactivity

The present studies evaluated the potential contribution of Bcl-2, p53, and c-Myc to the differential vulnerability of striatal neurons to the excitotoxin quinolinic acid (QA). In normal rat striatum, Bcl-2 immunoreactivity (Bcl-2-i) was most intense in large aspiny interneurons including choline acetyltransferase positive (CAT+) and parvalbumin positive (PARV+) neurons, but low in a majority of medium-sized neurons. In human brain, intense Bcl-2-i was seen in large striatal neurons but not in medium-sized spiny projection neurons. QA produced degeneration of numerous medium-sized neurons, but not those enriched in Bcl-2-i. Many Bcl-2-i-enriched interneurons including those with CAT+ and PARV+ survived QA injection, while medium-sized neurons labeled for calbindin D-28K (CAL D-28+) did not. In addition, proapoptotic proteins p53-i and c-Myc-i were robustly induced in medium-sized neurons, but not in most large neurons. The selective vulnerability of striatal medium spiny neurons to degeneration in a rodent model of Huntington's disease appears to correlate with their low levels of Bcl-2-i and high levels of induced p53-i and c-Myc-i.

Relationship between the Arg72Pro Polymorphism of p53 and outcome for patients with traumatic brain injury

OBJECTIVE

To determine the relationship between the Arg72Pro polymorphism of p53 and the outcome after traumatic brain injury (TBI) in humans.

DESIGN AND SETTING

A prospective study was carried out in a ten-bed surgical intensive care unit (SICU) of a university hospital.

PATIENTS

The study included 90 caucasian patients who had experienced a severe TBI within the previous 24 h. The exclusion criterion was a previous deficit in the central nervous system.

MEASUREMENTS AND RESULTS

The main recorded outcomes were values on the Glasgow Outcome Scale (GOS) at discharge from the SICU (GOS-0) and 6 months later (GOS-6). A blood sample was taken from each patient and all samples were analyzed by an allele-specific polymerase chain reaction for detection of Arg72Pro polymorphism of p53. These polymorphisms were tested for their association with values of GOS-0 and GOS-6. A two-tailed value of p<0.05 was considered statistically significant. The frequency of the argine/argine (Arg/Arg) genotype was greater among the patients who had a bad outcome at GOS-0 (69 vs 31% in the bad-outcome group; p=0.029). A multiple logistic regression analysis showed that patients with the Arg/Arg variation had a 2.9-fold greater risk of having a bad outcome at discharge from the SICU (95% confidence interval, 1.05-8.31; p=0.039 ). There was no similar relationship with respect to GOS-6.

CONCLUSION

The Arg/Arg genotype of the Arg72Pro polymorphism in p53 is associated with increased likelihood of a bad outcome at discharge from the SICU.

Maintaining appearances--the role of p53 in adult neurogenesis

In the adult mammalian brain, neuronal turnover continues to replenish cells in existing neuronal circuits, such as those involved either in odor discrimination or in learning and memory, throughout life. With age, however, the capacity for neurogenesis diminishes and these functions become impaired. Neuronal turnover is a two-step process, which first generates excess neuronal progenitors and then eliminates all but the few that differentiate into fully functional neurons. This process requires a fine balance between cell proliferation and cell death. Altered activity of the tumor suppressor p53 can upset this balance by affecting the rate of cell proliferation, but not the rate of cell death, in neurogenic regions of the adult brain. Genetically engineered mice in which p53 activity is increased demonstrate that premature loss of neurogenic capacity is linked to accelerated organismal aging.

Glucocorticoid regulation of glial responses during hippocampal neurodegeneration and regeneration

Glucocorticoids can prevent or accelerate neurodegeneration in the adult rat hippocampus. To investigate these actions of glucocorticoids, we previously cloned genes from the hippocampus. Adrenalectomy specifically increased glial fibrillary acidic protein and transforming growth factor (TGF)-beta1 mRNAs in the dentate gyrus and these effects were dependent on induced apoptosis. Corticosterone treatment prevented apoptosis, and decreased glial activation and the influx of activated microglia. Since these effects are opposite to injury and neurodegeneration, we propose that they represent adaptive actions of glucocorticoids, preventing cellular defense mechanisms from overshooting. We used adrenalectomy as a model to investigate how adult granule neurons die in vivo and the effects of neurotrophic factors in protecting against apoptosis. Neurotrophin-4/5 and TGF-beta1 protected granule neurons against adrenalectomy-induced apoptosis. Since neurogenesis is also greatly increased in the dentate gyrus following adrenalectomy, we compared the time course of birth and death with glial responses. TGF-beta1 mRNA increased before the detection of dying cells in the dentate gyrus, which was coincident with increased proliferation in the neurogenic zone. Glucocorticoids also increased Ndrg2 mRNA in glia in the neurogenic zone; Ndrg2 is a member of a novel gene family involved in neural differentiation and synapse formation. Therefore, studying the effects of glucocorticoid manipulation on the dentate gyrus is increasing our understanding of how mature neurons die by apoptosis and the role of glia in induced apoptosis and neurogenesis. Discovering how endocrine and inflammatory responses regulate neuron birth and survival is important for developing successful neuron replacement strategies to treat neurodegenerative diseases.

Caspase-1 inhibitor Ac-YVAD-CHO attenuates quinolinic acid-induced increases in p53 and apoptosis in rat striatum

AIM

To study the effects of the caspase-1 inhibitor Ac-YVAD-CHO on quinolinic acid (QA)-induced apoptosis.

METHODS

Rats were pre-treated with intrastriatal infusion of Ac-YVAD-CHO (2-8 microg) before intrastriatal injection of QA (60 nmol). Striatal total proteins, genomic DNA, and nuclear proteins were isolated. The effects of Ac-YVAD-CHO on QA-induced caspase-1 activity, internucleosomal DNA fragmentation, IkappaB-alpha degradation, NF-kappaB, and AP-1 activation, and increases in p53 protein levels were measured with enzyme assays, agarose gel electrophoresis, electrophoresis mobility shift assays, and Western blot analysis.

RESULTS

Pre-treatment with Ac-YVAD-CHO inhibited QA-induced internucleosomal DNA fragmentation. Ac-YVAD-CHO inhibited QA-induced increases in caspase-1 activity and p53 protein levels, but had no effect on QA-induced IkappaB-alpha degradation, NF-kappaB or AP-1 activation.

CONCLUSION

Caspase-1 is involved in QA-induced p53 upregulation but not IkappaB-alpha degradation. Inhibition of caspase-1 attenuates QA-induced apoptosis in rat striatum.

The induction of cell cycle regulatory and DNA repair proteins in cisplatin-induced acute renal failure

The purpose of this study was to evaluate the expressions and the roles of proteins involved in cell cycle regulation and DNA repair in cis-diamminedichloroplatinum (II) (cisplatin or CDDP)-induced acute renal failure (ARF). Treatment with CDDP (6 mg/kg, iv) induced tubular damage and increased serum creatinine (Scr) and the number of TUNEL-positive cells in the outer stripe of the outer medulla in rats, which reached peak levels at 5 days after CDDP. The expressions of cyclin-dependent kinase inhibitors (p21 and p27), cyclin B1, cyclin D1, PCNA, GADD 45, and GADD 153 were significantly increased in the outer medulla, reaching peak levels at 3 days after CDDP. Increments of p27 and PCNA were observed in the same nuclei. Sodium arsenite (SA), a heavy metal, attenuated tubular damage and increased Scr- and TUNEL-positive cells at 5 days after CDDP. SA augmented CDDP-induced increment of p27 but suppressed the increased expression of cyclin B1 and cyclin D1 at 3 days after CDDP. SA-induced attenuation of nephrotoxicity was associated with enhanced expression of proliferating cell nuclear antigen (PCNA) and growth-arrest and DNA damage (GADD) 153 in damaged tubular cells. Our findings indicated that (1) proteins related to cell cycle regulation and DNA repair are induced in CDDP nephrotoxicity, (2) the SA-induced attenuation of CDDP nephrotoxicity is associated with increased expression of p27 and decreased expression of cyclin B1 and cyclin D1, they all induce cell cycle arrest at G1/S and G2/M, and (3) enhanced expression of DNA repair-related proteins is also associated with attenuation of CDDP-nephrotoxicity.

Expression, interaction, and proteolysis of death-associated protein kinase and p53 within vulnerable and resistant hippocampal subfields following seizures

Death-associated protein (DAP) kinase is a novel regulator of cell death whose in vivo target(s) and role in neuronal cell death remain uncertain. Since DAP kinase has been implicated in p53-mediated apoptosis, a pathway activated following epileptic brain injury, we examined the relationship between DAP kinase and p53 following seizures. Rats underwent brief (40-min) seizures evoked by intraamygdala kainic acid, which caused the death of ipsilateral CA3 neurons while preserving the contralateral CA3 subfield. Seizures caused a small decline in levels of the approximately 160-kD DAP kinase within injured ipsilateral hippocampus, commensurate with the appearance of an approximately 60-kD fragment, and proteolysis of the p53 inhibitor, murine double minute gene 2 (MDM2). Expression of p53 increased within the ipsilateral hippocampus, and DAP kinase was detected within p53 immunoprecipitates. In contrast, DAP kinase and MDM2 were not proteolyzed within the seizure damage-resistant contralateral hippocampus. Furthermore, DAP kinase and p53 did not interact within the contralateral hippocampus, and p53 cellular localization redistributed from the nucleus to cytoplasm commensurate with p53 proteolysis. These data suggest that DAP kinase may be involved in the p53 pathway during seizure-induced neuronal death.

HIV associated neurodegeneration requires p53 in neurons and microglia

HIV infection of the central nervous system leads to HIV-associated dementia (HAD) in a substantial subset of infected individuals. The pathogenesis of neuronal dysfunction in HAD is not well understood, but previous studies have demonstrated evidence for activation of apoptotic pathways. The tumor suppressor transcription factor p53 is an apical mediator of neuronal apoptosis following a variety of injurious stimuli. To determine whether p53 participates in HAD, we exposed cerebrocortical cultures from wild-type and p53 deficient mice to the neurotoxic HIV envelope protein gp120. Using neuron/microglia co-culture of mixed p53 genotype, we observed that both neurons and microglia require p53 for gp120 induced neuronal apoptosis. Additionally, accumulation of p53 protein in neurons was recently reported in post-mortem cortical tissue from a small group of HAD patients. Using a much larger cohort of HAD cases, we extend this finding and report that p53 protein also increases in non-neuronal cells, including microglia. Taken together these findings demonstrate a novel role for p53 in the microglial response to gp120. Additionally, these findings, in conjunction with a recent report that monocytes expressing HIV-Tat also secrete neurotoxins that promote p53 activation, suggest that distinct HIV proteins may converge on the p53 pathway to promote neurotoxicity.

Preconditioning potentiates redox signaling and converts death signal into survival signal

Reactive oxygen species (ROS) play a crucial role in the pathophysiology of ischemic heart disease by causing cardiac dysfunction and cell death. Several redox-sensitive anti- and pro-apoptotic transcription factors including NFkappaB and AP-1 progressively and steadily increase in the heart as a function of the duration of ischemia and reperfusion. When the heart is preconditioned to ischemic stress by repeated short-term ischemia and reperfusion, NFkappaB remains high while AP-1 is lowered to almost baseline value. The anti-apoptotic gene Bcl-2 is downregulated in the ischemic/reperfused heart, while it is upregulated in the adapted myocardium. Cardioprotective abilities of the preconditioning are abolished when heart is pre-perfused with N-acetyl cysteine, a scavenger for ROS, suggesting the role of ROS in redox signaling. Mammalian heart is protected by several defense systems which include among others, redox-regulated protein, thioredoxin. Reperfusion of ischemic myocardium results in the downregulation of thioredoxin 1 (Trx 1) expression, which was upregulated in the preconditioned myocardium. The increased expression of Trx 1 is completely blocked with an inhibitor of Trx 1, CDDP, which also abolished cardioprotection afforded by ischemic adaptation. The cardioprotective role of Trx 1 is confirmed further with transgenic mouse hearts overexpressing Trx 1. The Trx 1 mouse hearts displayed significantly improved post-ischemic ventricular recovery and reduced myocardial infarct size and apoptosis as compared to the corresponding wild-type mouse hearts. Taken together, preconditioning appears to potentiate redox signaling, which converts the "death signal" into "survival signal."

Alkaloid fraction of Uncaria rhynchophylla protects against N-methyl-D-aspartate-induced apoptosis in rat hippocampal slices

Uncaria rhynchophylla is a medicinal herb which has sedative and anticonvulsive effects and has been applied in the treatment of epilepsy in Oriental medicine. In this study, the effect of alkaloid fraction of U. rhynchophylla against N-methyl-D-aspartate (NMDA)-induced neuronal cell death was investigated. Pretreatment with an alkaloid fraction of U. rhynchophylla for 1 h decreased the degree of neuronal damage induced by NMDA exposure in cultured hippocampal slices and also inhibited NMDA-induced enhanced expressions of apoptosis-related genes such as c-jun, p53, and bax. In the present study, the alkaloid fraction of U. rhynchophylla was shown to have a protective property against NMDA-induced cytotoxicity by suppressing the NMDA-induced apoptosis in rat hippocampal slices.

Gene expression profiling of ciliary neurotrophic factor-overexpressing rat striatal progenitor cells (ST14A) indicates improved stress response during the early stage of differentiation

Neuronal progenitor cells delivering neurotrophic factors are a promising therapeutic tool for treatment of neurodegenerative diseases. Although several promising results have come from studies in different animal models, detailed knowledge of the action of neurotrophic factors in the CNS is still lacking. A clonally derived, immortalized rat striatal cell line (ST14A) expressing ciliary neurotrophic factor (CNTF) offers a stable and controlled background with which to analyze CNTF actions on the transcriptional level in CNS progenitor cells. To identify early transcriptional changes induced by CNTF expression, we transfected the CNTF gene into ST14A cells, which differentiate at the nonpermissive temperature of 39 degrees C via suppression of the immortalizing SV40 large T antigen. This shows a CNTF-dependent hypoxic/ischemic stress response during the earliest stage of differentiation, with expression of specific transcripts and evidence of translational repression leading to decreased protein synthesis in the transfected cells. This process is mediated by the Ras/MAP kinase pathway and is accompanied by impaired proliferation and metabolism as well as signs of neuronal differentiation. The stress-like response in the early stage of differentiation improves the ability of the transfected cells to respond to and cope with a stressful environment in vivo. The present data indicate higher viability, longer life, and greater differentiation capacity of CNTF-ST14A cells if they are used for transplantation. We conclude that the stress-like response during the early stage of differentiation improves the ability of the CNTF-ST14A cells to respond and adapt to a stressful environment, which renders them useful candidate cells for in vivo trials of treatment for neurodegenerative diseases in animal models, e.g., of Huntington's disease.

Deltamethrin induces apoptotic cell death in cultured cerebral cortical neurons

In this study we investigated the induction of apoptotic cell death and its potential mechanisms in cultured cortical neurons in response to deltamethrin exposure. The cultured cortical neurons were treated at 7 days with deltamethrin at concentrations of 10, 100, and 1000 nM, respectively. MTT assay showed that higher concentrations of deltamethrin (100 and 1000 nM) decreased neuronal viability in a time- and dose-dependent way. TUNEL staining revealed that numerous apoptotic cells appeared in the treated cultures compared to controls at 24, 48, and 72 h after treatment of 100 nM deltamethrin. Western blot analysis demonstrated that p53 and Bax expression were dramatically increased at the same time points, whereas Bcl-2 expression was significantly reduced at all time points after deltamethrin treatment. Further, we found that nitric oxide synthase inhibitor N(G)-nitro-L-arginine prevented deltamethrin-induced neuronal apoptosis and altered expression of p53, Bax, and Bcl-2. These results suggest that nitric oxide synthase might mediate deltamethrin-elicited neuronal apoptosis through modulating the expression of apoptosis-related genes.

p53-dependent cell death signaling in neurons

The p53 tumor suppressor gene is a sequence-specific transcription factor that activates the expression of genes engaged in promoting growth arrest or cell death in response to multiple forms of cellular stress. p53 expression is elevated in damaged neurons in acute models of injury such as ischemia and epilepsy and in brain tissue samples derived from animal models and patients with chronic neurodegenerative diseases. p53 deficiency or p53 inhibition protects neurons from a wide variety of acute toxic insults. Signal transduction pathways associated with p53-induced neuronal cell death are being characterized, suggesting that intervention may prove effective in maintaining neuronal viability and restoring function following neural injury and disease.

Methamphetamine-induced increase in striatal p53 DNA-binding activity is attenuated in Cu,Zn-superoxide dismutase transgenic mice

The striatal DNA-binding activities of p53 as a transcription factor were gradually increased at several days after a single methamphetamine (METH) injection, while they were more rapidly increased within several hours after repeated METH injections (x4 with a 2 h interval). The elevation of striatal p53 DNA-binding after repeated METH injections was markedly attenuated in Cu,Zn-superoxide dismutase transgenic mice, but not affected by treatments with N-methyl-D-aspartate or D1 receptor antagonists. The present results suggest that METH-induced production of reactive oxygen species activates striatal p53 DNA-binding activity; this, in turn, may activate other downstream pathways that are responsible for chronic neurotoxicity of METH.

Striatopallidal neurons are selectively protected by neurturin in an excitotoxic model of Huntington's disease

Excitotoxicity has been involved in the pathogenesis of several neurodegenerative disorders. Using intrastriatal quinolinic acid (QUIN) injection as an animal model of Huntington's disease, we attempt to identify the neurotransmitter phenotype of striatal projection neurons protected by neurturin (NRTN). Control or NRTN-secreting cell lines were grafted in the striatum before QUIN injection and striatal projection neurons were examined by retrograde Fluorogold labeling and in situ hybridization. Intrastriatal grafting of NRTN-secreting cell line selectively prevented the loss of striatopallidal neurons and also the decrease in the mRNA levels for their markers (glutamic acid decarboxylase 67 and preproenkephalin) induced by QUIN, without affecting striatonigral neurons. Thus, our findings show that NRTN is a selective neuroprotective factor for striatopallidal neurons, suggesting that it might be a candidate for the treatment of movement disorders in which this neuronal population is affected.

Involvement of c-Jun N-terminal kinase and caspase 3-like protease in DNA damage-induced, p53-mediated apoptosis of cultured mouse cerebellar granule neurons

In the previous studies, we have demonstrated that the tumor suppressor gene p53 is required for DNA strand break-induced neuronal apoptosis in organotypic slice cultures of cerebellum as well as in dissociated cerebellar neuron cultures. In this study, we further investigated the role of p53 in neuronal apoptosis, by examining whether caspases and c-Jun N-terminal kinase (JNK) are involved in the DNA strand break-induced apoptosis. The protein level of phospho-JNK increased in p53 wild-type mouse cerebellar granule neurons after exposure to bleomycin. On the other hand, the response was not observed in cerebellar granule neurons of p53-deficient mice. Caspase-3-like protease was activated and poly(ADP-ribose) polymerase (PARP) was cleaved in the bleomycin-induced apoptosis. Caspase-3-like protease inhibitor decreased the number of TUNEL-positive but not p53- or c-Jun-positive neurons in bleomycin-induced death. These results suggest that JNK and caspase-3-like protease are involved in the signaling cascade of DNA strand break-induced, p53-dependent apoptosis.

Redox regulation of cardiomyocyte survival and death

In this review, attempts were made to establish the role of reactive oxygen species as signaling molecules that regulate cardiomyocyte life and death during ischemia and reperfusion. Ischemia/reperfusion is a classical example because partial or mild ischemia can lead to simultaneous execution and repair of the cardiomyocytes, which is disrupted during severe ischemia leading to cell necrosis because of the lack of ATP. Apoptosis and repair processes are mediated by adaptive response in which oxygen free radicals function as typical signaling molecules through the activation of receptor tyrosine kinases, protein kinase C, and mitogen-activated protein kinases, as well as induction of redox-sensitive transcription factors and genes.

Activation of cell-cycle-associated proteins in neuronal death: a mandatory or dispensable path?

Cell-cycle-related proteins, such as cyclins or cyclin-dependent kinases, are re-expressed in neurons committed to death in response to a variety of insults, including excitotoxins, hypoxia and ischemia, loss of trophic support, or beta-amyloid peptide. In some of these conditions events that are typical of the mid-G1 phase, such as cyclin-dependent kinase 4/6 activation, are required for the induction of neuronal death. In other cases, the cycle must proceed further and recruit steps that are typical of the G1/S transition for death to occur. Finally, there are conditions in which cell-cycle proteins might be re-expressed, but do not contribute to neuronal death. We hypothesize that cell-cycle signaling becomes a mandatory component of neuronal demise when other mechanisms are not enough for neurons to reach the threshold for death. Under this scheme, the death threshold is set by the extent of DNA damage. Whenever the extent of DNA damage is below this threshold, a cell-cycle signaling becomes crucial for the induction of neuronal death through p53-dependent or -independent pathways.

Regulation of cardiomyocyte apoptosis by redox-sensitive transcription factors

Reperfusion of ischemic myocardium results in apoptotic cell death and DNA fragmentation. Several transcription factors are known to regulate the apoptotic cell death. This study sought to examine the regulation of cardiomyocyte apoptosis by these transcription factors. Isolated working rat hearts were divided into six groups: control, 15 min ischemia, 60 min ischemia, 15 min ischemia followed by 2 h reperfusion, ischemic stress adaptation by subjecting the hearts to four cyclic episodes to 5 min ischemia, each followed by 10 min of reperfusion, and adaptation followed by 15 min ischemia and 2 h reperfusion. Redox-regulated transcription factors, NF kappa B and AP-1 and the expression of two anti- and pro-apoptotic genes, Bcl-2 and p53 were determined. The results demonstrated NF kappa B and AP-1 progressively and steadily increased as a function of the duration of ischemia. In the adapted heart, NF kappa B binding remained high while AP-1 binding was lowered to almost baseline value. The anti-oxidant gene, Bcl-2 was downregulated in the ischemic/reperfused heart, but upregulated in the preconditioned myocardium. Significant induction of the expression of p53 occurred after ischemia and reperfusion. Apoptotic cells were barely detected in the adapted myocardium which was subjected to the same ischemia/reperfusion protocol. The results demonstrate for the first time differential regulation of cardiomyocyte apoptosis by pro- and anti-apoptotic transcription factors and genes as a function of different durations of ischemia and reperfusion.

Brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4/5 prevent the death of striatal projection neurons in a rodent model of Huntington's disease

Intrastriatal injection of quinolinate has been proven to be a very useful animal model to study the pathogenesis and treatment of Huntington's disease. To determine whether growth factors of the neurotrophin family are able to prevent the degeneration of striatal projection neurons, cell lines expressing brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or neurotrophin-4/5 (NT-4/5) were grafted in the adult rat striatum before quinolinate injection. Three days after lesioning, ongoing cell death was assessed by in situ detection of DNA fragmentation. In animals grafted with the control cell line, quinolinate injection induced a gradual cell loss that was differentially prevented by intrastriatal grafting of BDNF-, NT-3-, or NT-415-secreting cells. Seven days after lesioning, we characterized striatal projection neurons that were protected by neurotrophins. Quinolinate injection, alone or in combination with the control cell line, induced a selective loss of striatal projection neurons. Grafting of a BDNF-secreting cell line pre-vented the loss of all types of striatal projection neurons analyzed. Glutamic acid decarboxylase 67-, preproenkephalin-, and preprotachykinin A- but not prodynorphin-expressing neurons were protected by grafting of NT-3- or NT-4/5-secreting cells but with less efficiency than the BDNF-secreting cells. Our findings show that neurotrophins are able to promote the survival of striatal projection neurons in vivo and suggest that BDNF might be beneficial for the treatment of striatonigral degenerative disorders, including Huntington's disease.

Neuronal life and death: an essential role for the p53 family

Recent evidence indicates that the p53 tumor suppressor protein, and its related family member, p73, play an essential role in regulating neuronal apoptosis in both the developing and injured, mature nervous system. In the developing nervous system, they do so by regulating naturally-occurring cell death in neural progenitor cells and in postmitotic neurons, acting to ensure the apoptosis of cells that either do not appropriately undergo the progenitor to postmitotic neuron transition, or that fail to compete for sufficient quantities of trophic support. Somewhat surprisingly, in developing postmitotic neurons, p53 plays a proapoptotic role, while a naturally-occurring, truncated form of p73, DeltaNp73, antagonizes p53 and plays an anti-apoptotic role. In the mature nervous system, numerous studies indicate that p53 is essential for the neuronal death in response to a variety of insults, including DNA damage, ischemia and excitotoxicity. It is likely that all of these insults culminate in DNA damage, which may well be a common trigger for neuronal apoptosis. In this regard, the signaling pathways that are responsible for triggering p53-dependent neuronal apoptosis are starting to be elucidated, and involve cell cycle deregulation and activation of the JNK pathway. Finally, accumulating evidence indicates that p53 is perturbed in the CNS in a number of neurodegenerative disorders, leading to the hypothesis that longterm oxidative damage and/or excitotoxicity ultimately trigger p53-dependent apoptosis in the chronically degenerating nervous system.

Apoptosis after traumatic brain injury

Apoptosis of neurons and glia contribute to the overall pathology of traumatic brain injury (TBI) in both humans and animals. In both head-injured humans and following experimental brain injury, apoptotic cells have been observed alongside degenerating cells exhibiting classic necrotic morphology. Neurons undergoing apoptosis have been identified within contusions in the acute port-traumatic period, and in regions remote from the site of impact in the days and weeks after trauma. Apoptotic oligodendrocytes and astrocytes have been observed within injured white matter tracts. We review the regional and temporal patterns of apoptosis following TBI and the possible mechanisms underlying trauma-induced apoptosis. While excitatory amino acids, increases in intracellular calcium, and free radicals can all cause cells to undergo apoptosis, in vitro studies have determined that neural cells can undergo apoptosis via many other pathways. It is generally accepted that a shift in the balance between pro- and anti-apoptotic protein factors towards the expression of proteins that promote death may be one mechanism underlying apoptotic cell death. The effect of TBI on regional cellular patterns of expression of survival promoting-proteins such as Bcl-2, Bcl-xL, and extracellular signal regulated kinases, and death-inducing proteins such as Bax, c-Jun N-terminal kinase, tumor-suppressor gene, p53, and the caspase family of proteases are reviewed. Finally, in light of pharmacologic strategies that have been devised to reduce the extent of apoptotic cell death in animal models of TBI, our review also considers whether apoptosis may serve a protective role in the injured brain.

The role of p53 in neuronal cell death

The p53 tumor suppressor gene is a sequence-specific transcription factor that activates the expression of genes engaged in promoting growth arrest or cell death in response to genotoxic stress. A possible role for p53-related modulation of neuronal viability has been suggested by the finding that p53 expression is elevated in damaged neurons in acute models of injury such as ischemia and epilepsy and in brain tissue samples derived from patients with chronic neurodegenerative diseases. Moreover, the absence of p53 has been shown to protect neurons from a wide variety of acute toxic insults. Signal transduction pathways associated with p53-induced cell death are being unraveled and suggest that intervention may prove fruitful in maintaining neuronal viability and restoring function following cytopathic insults.

Developmental regulation of BDNF and NT-3 expression by quinolinic acid in the striatum and its main connections

Interactions between neurotrophic factors and neurotransmitters participate in the formation and maintenance of appropriate connections, as well as in neurodegenerative processes. Here we have measured changes in the developmental expression pattern of BDNF and NT-3 in the striatum, cortex, and substantia nigra induced by intrastriatal injection of the N-methyl-d-aspartate glutamate receptor agonist quinolinic acid (QUIN). Animals were injected at different postnatal ages, and BDNF and NT-3 mRNA levels were determined 6 h after lesion using a ribonuclease protection assay. Our results show a biphasic increase in BDNF mRNA levels in striatum and in the ipsilateral cortex at postnatal day (P)5 and P21. In contrast, although NT-3 expression did not change in the striatum, it was down-regulated in the ipsilateral cortex at P5 and P30. Intrastriatal QUIN injection did not induce changes in either BDNF or NT-3 expression in the ipsilateral substantia nigra. These findings show that neurotrophin expression is developmentally regulated after excitotoxic injury, which suggests that this endogenous response may be involved in different neuronal maturation and vulnerability during development.

Role of p53 in DNA strand break-induced apoptosis in organotypic slice culture from the mouse cerebellum

Apoptosis occurs not only in mitotic cells but also in postmitotic neuronal cells. We previously suggested that the tumor suppressor gene p53 is required for DNA strand break-induced apoptosis in dissociated culture of cerebellar granule neurons. In this study, we examined the role of p53 in apoptosis using organotypic slice culture of cerebellum from p53 null and wild-type mice. Exposure to bleomycin significantly increased the numbers of TUNEL-, p53-, and c-Jun-positive neurons in the wild-type mouse cerebellar internal granular layer (IGL) and Purkinje cell layer (PL). However, in p53-deficient mice, these responses were not observed. These results are consistent with our previous observations in dissociated neuronal culture showing that the amount of c-Jun protein increases significantly after addition of bleomycin in p53 wild-type cerebellar granule cells. The results presented here also indicate that p53 is involved in DNA strand break-induced apoptosis of fully postmitotic central nervous system neurons and suggest that c-Jun expression occurs downstream of p53 expression.

Characterization of striatal lesions produced by glutamate uptake alteration: cell death, reactive gliosis, and changes in GLT1 and GADD45 mRNA expression

This study investigated the time course of the striatal lesions produced by continuous local injection of the glutamate uptake inhibitor, L-trans-pyrrolidine-2,4-dicarboxylate (PDC) at the rate of 25 nmol/h in rats. The extent of the neurodegeneration area (defined as the lesion area) did not significantly vary with the duration of the PDC treatment between 3 and 14 days, but was markedly reduced 3 months after cessation of the 14-day treatment, probably reflecting striatal atrophy. After the 3-day treatment, the lesion zone showed calcium precipitates and marked microglial reaction contrasting with the reduction of astroglial labeling and loss of the glutamate transporter GLT1 mRNA expression; however reactive astrocytes were observed around the lesion. After the 14-day treatment, the lesion zone presented reactive astrocytes and microglia without calcification, and a partial recovery of GLT1 mRNA expression. Interestingly, the growth arrest DNA damage-inducible GADD45 mRNA expression was induced around the lesion after 3 days but inside the lesion after 14 days of treatment. Three months after the 14-day treatment, the astroglial reactivity persisted within the lesion whereas most of the other markers examined tended to normalize. These data suggest that defective glutamate transport induces primary death of neurons and dysfunction of astrocytes. They strongly implicate reactive astrocytes with GLT1 and GADD45 transcripts in preventing secondary neuronal death.

Kainic acid-induced apoptosis in rat striatum is associated with nuclear factor-kappaB activation

The present study evaluated whether nuclear factor-kappaB (NF-kappaB) activation contributes to the apoptotic-like death of striatal neurons induced by kainic acid (KA) receptor stimulation. Intrastriatally infused KA (1.25-5.0 nmol) produced substantial neuronal loss as indicated by an 8-73% decrease in 67-kDa glutamic acid decarboxylase (p<0.05). KA (1.25-5.0 nmol) elicited internucleosomal DNA fragmentation that was inhibited by the AMPA/KA receptor antagonist NBQX (1,2,3,4-tetrahydro-6-nitro-2,3-dibenzo[f]quinoxaline-7-sulfonamide) but not by the NMDA receptor antagonist MK-801. A decrease in IkappaB-alpha protein levels, which was accompanied by an increase in NF-kappaB binding activity, was found from 6 to 72 h after KA (2.5 nmol) infusion. NF-kappaB was composed mainly of p65 and c-Rel as revealed by supershift assay. In addition, c-Myc and p53 increased from five- to sevenfold from 24 to 72 h after KA (2.5 nmol) administration. Immunohistochemistry revealed high levels of c-Myc and p53 immunoreactivity, mainly in medium-sized striatal neurons. Pretreatment with the cell-permeable recombinant peptide NF-kappaB SN50 (5-20 microg) blocked NF-kappaB nuclear translocation, but had no effect on AP-1 binding. NF-kappaB SN50 also inhibited the KA-induced up-regulation of c-Myc and p53, as well as internucleosomal DNA fragmentation. The apoptotic-like destruction of rat striatal neurons induced by KA receptor stimulation thus appears to involve biochemical mechanisms similar to those mediating the excitotoxic response to NMDA receptor stimulation. The present results provide additional support for the view that NF-kappaB activation contributes to c-Myc and p53 induction and subsequent apoptosis in an excitotoxic model of Huntington's disease.

Relationship between seizure-induced transcription of the DNA damage-inducible gene GADD45, DNA fragmentation, and neuronal death in focally evoked limbic epilepsy

We investigated the temporal and spatial profile of mRNA transcription for the growth arrest and DNA damage-inducible gene GADD45, DNA fragmentation, and neuronal death in rat brain following focally evoked limbic seizures. GADD45 mRNA was detected by in situ hybridization, whereas fragmented DNA was detected using in situ nick end-labeling by the large (Klenow) fragment of DNA polymerase I. Kainic acid (0.1 microg) was injected into the right amygdala of rats to induce seizures for 45 min, after which diazepam (30 mg/kg) was administered. GADD45 mRNA, DNA fragmentation, and cell death were quantified bilaterally within six limbic brain regions 0-96 h following seizure cessation. All animals underwent seizures of equivalent severity and duration as determined electrographically. In situ hybridization detected bilateral up-regulation of GADD45 mRNA throughout the CA1, CA3, and dentate gyrus of the hippocampus, the piriform and retrosplenial cortices, and the thalamus within 1 h of seizure termination. GADD45 mRNA levels remained elevated for up to 6 h, declining to baseline within all structures by 16 h. Klenow-positive cells were only found within the CA3 pyramidal layer of the ipsilateral hippocampus and appeared 16-72 h following seizure cessation. Morphologic cell death was also restricted to the CA3 subfield. These data demonstrate that focally evoked limbic seizures trigger early bihemispheric GADD45 mRNA transcription within connected limbic structures, whereas subsequent DNA fragmentation and cell death are restricted to selectively vulnerable brain regions.