Recent advances on neuronal caspases in development and neurodegeneration

The concept of intrinsic versus extrinsic apoptosis

Regulated cell death is a vital and dynamic process in multicellular organisms that maintains tissue homeostasis and eliminates potentially dangerous cells. Apoptosis, one of the better-known forms of regulated cell death, is activated when cell-surface death receptors like Fas are engaged by their ligands (the extrinsic pathway) or when BCL-2-family pro-apoptotic proteins cause the permeabilization of the mitochondrial outer membrane (the intrinsic pathway). Both the intrinsic and extrinsic pathways of apoptosis lead to the activation of a family of proteases, the caspases, which are responsible for the final cell demise in the so-called execution phase of apoptosis. In this review, I will first discuss the most common types of regulated cell death on a morphological basis. I will then consider in detail the molecular pathways of intrinsic and extrinsic apoptosis, discussing how they are activated in response to specific stimuli and are sometimes overlapping. In-depth knowledge of the cellular mechanisms of apoptosis is becoming more and more important not only in the field of cellular and molecular biology but also for its translational potential in several pathologies, including neurodegeneration and cancer.

Fragile X Premutation rCGG Repeats Impair Synaptic Growth and Synaptic Transmission at Drosophila larval Neuromuscular Junction

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disease that develops in some premutation (PM) carriers of the FMR1 gene with alleles bearing 55-200 CGG repeats. The discovery of a broad spectrum of clinical and cell developmental abnormalities among PM carriers with or without FXTAS and in model systems suggests that neurodegeneration seen in FXTAS could be the inevitable end-result of pathophysiological processes set during early development. Hence, it is imperative to trace early PM-induced pathological abnormalities. Previous studies have shown that transgenic Drosophila carrying PM-length CGG repeats are sufficient to cause neurodegeneration. Here, we used the same transgenic model to understand the effect of CGG repeats on the structure and function of the developing nervous system. We show that presynaptic expression of CGG repeats restricts synaptic growth, reduces the number of synaptic boutons, leads to aberrant presynaptic varicosities, and impairs synaptic transmission at the larval neuromuscular junctions. The postsynaptic analysis shows that both glutamate receptors and subsynaptic reticulum proteins were normal. However, a high percentage of boutons show a reduced density of Bruchpilot protein, a key component of presynaptic active zones required for vesicle release. The electrophysiological analysis shows a significant reduction in quantal content, a measure of total synaptic vesicles released per excitation potential. Together, these findings suggest that synapse perturbation caused by rCGG repeats mediates presynaptically during larval NMJ development. We also suggest that the stress-activated c-Jun N-terminal kinase protein Basket and CIDE-N protein Drep-2 positively mediate Bruchpilot active zone defects caused by rCGG repeats.

Phage display and structural studies reveal plasticity in substrate specificity of caspase-3a from zebrafish

The regulation of caspase-3 enzyme activity is a vital process in cell fate decisions leading to cell differentiation and tissue development or to apoptosis. The zebrafish, Danio rerio, has become an increasingly popular animal model to study several human diseases because of their transparent embryos, short reproductive cycles, and ease of drug administration. While apoptosis is an evolutionarily conserved process in metazoans, little is known about caspases from zebrafish, particularly regarding substrate specificity and allosteric regulation compared to the human caspases. We cloned zebrafish caspase-3a (casp3a) and examined substrate specificity of the recombinant protein, Casp3a, compared to human caspase-3 (CASP3) by utilizing M13 bacteriophage substrate libraries that incorporated either random amino acids at P5-P1' or aspartate fixed at P1. The results show a preference for the tetrapeptide sequence DNLD for both enzymes, but the P4 position of zebrafish Casp3a also accommodates valine equally well. We determined the structure of zebrafish Casp3a to 2.28Å resolution by X-ray crystallography, and when combined with molecular dynamics simulations, the results suggest that a limited number of amino acid substitutions near the active site result in plasticity of the S4 sub-site by increasing flexibility of one active site loop and by affecting hydrogen-bonding with substrate. The data show that zebrafish Casp3a exhibits a broader substrate portfolio, suggesting overlap with the functions of caspase-6 in zebrafish development.

Protective effect of novel substituted nicotine hydrazide analogues against hypoxic brain injury in neonatal rats via inhibition of caspase

In hypoxic-ischemic injury of the brain of neonates, the level of caspase-3 was found to be aberrantly activated. Its overexpression leads to the alteration of cytoskeleton protein fodrin and loss of DNA repair enzyme which ultimately results in neurological impairment and disability. Concerning this, the present study was intended to develop novel nicotine hydrazide analogues as caspase inhibitors via efficient synthetic route. These compounds were subsequently tested for inhibitory activity against caspase-3 and -7 where they exhibit highly potent activity against caspase-3 revealing compound 5k as most potent inhibitor (IC50=19.4±2.5μM). In Western blot analysis, 5k considerably inhibits the overexpression of caspase-3. The aryl nicotinate of compound 5k, as indicated by molecular docking was found to engage His121 and critical enzyme thiols, i.e., Cys163 of caspase-3 for its potent activity. Moreover, histopathological examination of brain tissues and hippocampus neurons showed that compound 5k considerably improves the brain injury and exert neuroprotective effects in hypoxic-ischemic (HI). In brain homogenate, 5k significantly improves the activity of MDA, SOD, GSH-Px, CAT and T-AOC to exert its beneficial effect against oxidative stress induced by HI injury.

Nrf2 deficiency promotes apoptosis and impairs PAX7/MyoD expression in aging skeletal muscle cells

Skeletal muscle redox homeostasis is transcriptionally regulated by nuclear erythroid-2-p45-related factor-2 (Nrf2). We recently demonstrated that age-associated stress impairs Nrf2-ARE (antioxidant-response element) transcriptional signaling. Here, we hypothesize that age-dependent decline or genetic ablation of Nrf2 leads to accelerated apoptosis and skeletal muscle degeneration. Under basal-physiological conditions, disruption of Nrf2 significantly downregulates antioxidants and causes oxidative stress. Surprisingly, Nrf2-null mice had enhanced antioxidant capacity identical to wild-type (WT) upon acute endurance exercise stress (AEES), suggesting activation of Nrf2-independent mechanisms (i.e., PGC1α) against oxidative stress. Analysis of prosurvival pathways in the basal state reveals decreased AKT levels, whereas p-p53, a repressor of AKT, was increased in Nrf2-null vs WT mice. Upon AEES, AKT and p-AKT levels were significantly (p < 0.001) increased (>10-fold) along with profound downregulation of p-p53 (p < 0.01) in Nrf2-null vs WT skeletal muscle, indicating the onset of prosurvival mechanisms to compensate for the loss of Nrf2 signaling. However, we found a decreased stem cell population (PAX7) and MyoD expression (differentiation) along with profound activation of ubiquitin and apoptotic pathways in Nrf2-null vs WT mice upon AEES, suggesting that compensatory prosurvival mechanisms failed to overcome the programmed cell death and degeneration in skeletal muscle. Further, the impaired regeneration was sustained in Nrf2-null vs WT mice after 1 week of post-AEES recovery. In an age-associated oxidative stress condition, ablation of Nrf2 results in induction of apoptosis and impaired muscle regeneration.

Histopathological alterations in the brain (optic tectum) of the fresh water teleost Channa punctatus in response to acute and subchronic exposure to the pesticide Chlorpyrifos

In the present investigation an attempt was made to assess the toxicity of the organophosphate pesticide Chlorpyrifos (0,0-diethyl-0-3,5,6-trichloro-2-pyridyl phosphorothioate; CPF) on the brain (optic tectum) of the teleost Channa punctatus (Bloch). Fish were exposed to acute (1.5, 3.0, 4.5, 6.0 and 7.5 μl/l) for 24 h and sublethal concentrations of CPF 1.79 μl/l (1/3 of LC₅₀) and 0.538 μl/l (1/10 of LC₅₀) for 3 and 7 days respectively. Several endpoints related to the histoarchitectural profile in the optic tectum were evaluated. Histological examination showed detachment in the superficial zone of the Stratum opticum, Str. marginale due to degeneration of neuronal cells. Spongiosis, congestion, necrosis and appearance of clear areas around the nucleus of mononuclear cells in the lining of the Str. fibrosum grisium superficiale, Str. griseum centrale, Str. album centrale were seen. Granular cells found in the innermost layer of optic tectum, i.e. the Str. periventriculare, were severely degenerated and vacuolized and they migrated toward the Torus semicircularis. The histopathological changes were more pronounced with higher concentrations of CPF. The degree of neurodegeneration found in the deep layers of the optic tectum in higher concentration treatment (6.0 and 7.5 μl/l) was more pronounced. These alterations of the optic tectum affected the functioning of motor coordination of the fish body, because CPF inhibited acetylcholine in neuronal synapses. Due to apoptosis in the superficial zone of the optic tectum, normal visual response was affected. Fish showed microphthalmia (reduced size and eye shrinkage in the eye orbit) because of detachment, necrosis, degeneration and vacuolization in different regions after CPF treatment. This study shows that CPF is highly toxic to fish and affect their population survival in environment.

In vitro toxicity of colistin on primary chick cortex neurons and its potential mechanism

Colistin is increasingly used as the last-line therapy for infections caused by Gram-negative 'superbugs'. Although colistin neurotoxicity was reported in the literature, there has no data on its mechanism. In the present study, we examined the effect of colistin on primary chick neuron cells, which were treated with 0.83, 4.15 and 8.3μg/mL colistin for 6, 12 and 24h. Cell viability was evaluated with 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assays after exposure to colistin. Formation of reactive oxygen species (ROS), nuclear morphology, caspase-3 activity and internucleosomal DNA fragmentation were examined. The results showed that, compared with the control, no significant change was observed in cell viability, ROS formation and caspase-3 activity in cells treated for 6, 12 and 24h with 0.83μg/mL colistin. However, in the 4.15 and 8.3μg/mL colistin-treated groups, the viability of chick primary neurons significantly decreased at 12 and 24h, respectively; caspase-3 activities were significantly increased to 5.1 and 7.4 fold at 6h, more earlier than the changes of ROS, which was significant increased to 124.5% and 143.5% (P<0.01) of control at 12h, respectively. The apoptosis of neuron cells was revealed by both nuclear morphological observations and internucleosomal DNA fragmentation in the 4.15 and 8.3μg/mL colistin-treated groups at 6, 12 and 24h. Our data demonstrated that colistin can induce apoptosis in primary chick cortex neurons through caspase-3 activation, which may be contributed with ROS-dependent and independent mechanism.

WITHDRAWN: Survivin, Caspase-3 and Caspase-9-activated proteins kinases in apoptosis

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Caspase-3 activation as a bifurcation point between plasticity and cell death

Death-mediating proteases such as caspases and caspase-3 in particular, have been implicated in neurodegenerative processes, aging and Alzheimer's disease. However, emerging evidence suggests that in addition to their classical role in cell death, caspases play a key role in modulating synaptic function. It is remarkable that active caspases-3, which can trigger widespread damage and degeneration, aggregates in structures as delicate as synapses and persists in neurons without causing acute cell death. Here, we evaluate this dichotomy, and discuss the hypothesis that caspase-3 may be a bifurcation point in cellular signaling, able to orient the neuronal response to stress down either pathological/apoptotic pathways or towards physiological cellular remodeling. We propose that temporal, spatial and other regulators of caspase activity are key determinants of the ultimate effect of caspase-3 activation in neurons. This concept has implications for differential roles of caspase-3 activation across the lifespan. Specifically, we propose that limited caspase-3 activation is critical for synaptic function in the healthy adult brain while chronic activation is involved in degenerative processes in the aging brain.

Towards gene therapy for deafness

Many hearing disorders are associated with the damage or loss of sensory hair cells (HC) which can produce a profound and irreversible deafness. Apoptosis pathway is reported to play an important role leading to rapid expansion of the HC lesion after exposure to intense noise. Furthermore, progress made over the last year in understanding molecular mechanisms involved in the proliferative and regenerative capacity of sensory cells in the mammalian inner ear has raised the possibility that targeted therapies might prevent the loss of these cells and preserve the patient's hearing. A first step towards the successful therapeutic exploitation is a better understanding of the different pathways that control survival and proliferation of sensory cells. In this review, we provide an overview of recent findings concerning the possibility to prevent apoptosis in auditory cells. We also show the current knowledge on the molecular mechanisms involved in the potential regenerative behavior of these cells and the progress of gene therapy to prevent deafness noise-induced.

Caspase-8 and p38MAPK in DATS-induced apoptosis of human CNE2 cells

Nasopharyngeal carcinoma is a common malignancy in Southern China of uncertain etiologic origin. Diallyl trisulfide (DATS), one of the major components of garlic (Allium sativum), is highly bactericidal and fungicidal. In this study, we investigated the function of p38 mitogen-activated protein kinase (MAPK) and caspase-8 in DATS-induced apoptosis of human CNE2 cells using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide], flow cytometry assay, and Western blotting. After CNE2 cells were treated with DATS (50, 100, or 150 μM) for 24 h, cell viability rates were 75.9, 63.4 and 39.6%, and apoptosis rates were 24.5, 36.9, and 62.4%, respectively. The data showed that DATS induced CNE2 cell death in a dose-dependent manner. After human CNE2 cells were treated with 100 μM DATS and inhibitors (10 μM SB203580 and Z-LETD-FMK for p38MAPK and caspase-8, respectively), changes in cell viability and apoptosis and in p38MAPK and caspase-8 activity were detected. Cell viability rates were 66.5 and 68.1% and decreased 9.9 and 11.5% compared with inhibitor treatment alone. Apoptosis rates were 31.53 and 29.98% and increased 9.1 and 10% compared with inhibitor treatment alone. The results indicated that DATS activates p38MAPK and caspase-8, but both inhibitors have an effect on P38MAPK and caspase-8 activity. In conclusion, our data indicate that p38MAPK and caspase-8 are involved in the process of DATS-induced apoptosis in human CNE2 cells and interact with each other.

The roles of p38MAPK and caspase-3 in DADS-induced apoptosis in human HepG2 cells

Objectives

To explore the function of p38MAPK and caspase-3 in DADS-induced apoptosis in human HepG2 cells, and discuss the signal transduetion mechanism of HepG2 cells in the apoptosis process induced by DADS by using the inhibitors of p38MAPK (SB203580) and caspase-3 (Z-DEVD-FMK).

Methods

After the human HepG2 cells had been treated with the DADS and inhibitors for 24 h, cell viability was determined by the MTT method, apoptosis was evaluated by flow cytometry (FCM) and the expressions of p38MAPK and caspase-3 were measured by western-blot.

Results

Our results indicated that DADS activities the p38MAPK and caspase-3, but the inhibitors, SB203580 and Z-DEVD-FMK (for p38MAPKand for caspase-3, respectively), both have the effect of inhibitory activity on P38MAPK and caspase-3. Furthermore, a combination treatment with both DADS and inhibitor (SB203580 or Z-DEVD-FMK) decreases the inhibitory and apoptotic activity of HepG2 cells increased compared with DADS-treated.

Conclusions

Our data indicate that p38MAPK and caspase-3 are involved in the process of DADS-induced apoptosis in human HepG2 cells and interact with each other.

Unilateral blood flow decrease induces bilateral and symmetric responses in the immature brain

The effects of hemodynamic changes in the developing brain have yet to be fully understood. The aim of this study was to explore the relationship between perturbations of the cerebral blood flow in the developing brain via unilateral hypoperfusion in P7 rats. As expected, nuclear caspase-3 (casp3) cleavage and DNA fragmentation were detected at 48 hours after stroke in the injured cortex. Surprisingly, casp3 was also cleaved in the contralateral cortex, although without cell death markers. Delayed (48 hours) casp3 cleavage without DNA fragmentation was also identified after unilateral common carotid artery occlusion, both in the hypoperfused cortex and the unaffected cortex, producing mirror images. Upstream calpain activation, caspase-2 cleavage, and mitochondrial cytochrome c release initiated casp3 cleavage, but did not produce preconditioning. The neuronal marker NeuN co-localized with cleaved casp3 in cortical layers II-III and VI and with gaba-amino butyric acid in layer III. Indeed, collateral supply was provided from the opposite side during carotid artery occlusion but not after reperfusion, and the number of cleaved casp3-positive cells significantly negatively correlated with the common carotid artery immediate reperfusion percentage. In summary, unilateral hypoperfusion, while insufficient to induce cell death, may active bilateral and symmetric casp3 in the P7 rat brain. Additionally, the opposite healthy hemisphere is altered due to the injury and thus should not be used as an internal control.

Single-cell imaging of retinal ganglion cell apoptosis with a cell-penetrating, activatable peptide probe in an in vivo glaucoma model

Molecular imaging probes have potential for in vivo identification of apoptosis and other intracellular processes. TcapQ, a cell-penetrating, near-infrared fluorescent peptide probe designed to be optically silent through intramolecular fluorescence quenching and activated by effector caspases, has been previously described and validated in vitro. Herein, using NMDA-induced apoptosis of retinal ganglion cells (RGCs), representing an in vivo rat model of glaucoma, we assessed the ability of TcapQ to image single-cell apoptosis through effector caspase activity. Following intravitreal injection, intracellular TcapQ activation occurred specifically in RGCs, identified individual apoptotic cells, showed a clear dose-response relationship with NMDA, and colocalized with TUNEL labeling in the retina. There was a significant diminution of probe activation following pretreatment with a specific inhibitor of caspase-3. Stereospecificity was also exhibited by the lack of intracellular fluorescence upon administration of the noncleavable isomer, dTcapQ. TcapQ has potential utility in detecting and monitoring single-cell apoptosis in glaucoma in vivo.

Tributyltin exposure causes brain damage in Sebastiscus marmoratus

Tributyltin (TBT) is a ubiquitous marine environmental contaminant characterized primarily by its reproductive toxicity. However, the neurotoxic effect of TBT has not been extensively described, especially in fishes which have a high number of species in the marine environment. This study was conducted to investigate the neurotoxic effects of TBT at environmental levels (1, 10, and 100ngl(-1)) on female Sebastiscus marmoratus. The results showed that TBT exposure induced apoptosis in brain cells of three regions including the pallial areas of the telencephalon, the granular layer of the optic tectum, and the cerebellum. In addition, the increase of reactive oxygen species and nitric oxide levels, and the decrease of Na+/K+-ATPase activity were found in the brain. The results strongly indicated neurotoxicity of TBT to fishes. According to the regions in which apoptosis was found in the brain, TBT exposure might influence the schooling, sensory and motorial functions of fishes.

Distinct spatial and temporal activation of caspase pathways in neurons and glial cells after excitotoxic damage to the immature rat brain

Although cleaved caspase-3 is known to be involved in apoptotic cell death mechanisms in neurons, it can also be involved in a nonapoptotic role in astrocytes after postnatal excitotoxic injury. Here we evaluate participation of upstream pathways activating caspase-3 in neurons and glial cells, by studying the intrinsic pathway via caspase-9, the extrinsic pathway via caspase-8, and activation of the p53-dependent pathway. N-methyl-D-aspartate (NMDA) was injected intracortically in 9-day-old postnatal rats, which were sacrificed at several survival times between 4 hr postlesion (pl) and 7 days pl. We analyzed temporal and spatial expression of caspase-8, caspase-9, and p53 and correlation with neuronal and glial markers and caspase-3 activation. Caspase-9 was significantly activated at 10 hpl, strongly correlating with caspase-3. It was present mainly in damaged cortical and hippocampal neurons but was also seen in astrocytes and oligodendrocytes in layer VI and corpus callosum (cc). Caspase-8 showed a diminished correlation with caspase-3. It was present in cortical neurons at 10-72 hpl, showing layer specificity, and also in astroglial and microglial nuclei, mainly in layer VI and cc. p53 Expression increased at 10-72 hpl but did not correlate with caspase-3. p53 Was seen in neurons of the degenerating cortex and in some astrocytes and microglial cells of layer VI and cc. In conclusion, after neonatal excitotoxicity, mainly the mitochondrial intrinsic pathway mediates neuronal caspase-3 and cell death. In astrocytes, caspase-3 is not widely correlated with caspase-8, caspase-9, or p53, except in layer VI-cc astrocytes, where activation of upstream cascades occurs.

Neuroprotection of muscarinic receptor agonist pilocarpine against glutamate-induced apoptosis in retinal neurons

Neuroprotection offers potential as an alternative therapy for glaucoma. Pilocarpine, as a typical muscarinic receptor agonist, remains among the major intraocular pressure lowering drugs for the conventional treatment of glaucoma. However, whether pilocarpine also possesses neuroprotection against glutamate cytotoxicity in retinal neurons is still unknown. In rat primary retinal cultures, identification of neuron, cell viability, apoptosis, intracellular Ca(2+) concentration, mitochondrial membrane potential, gene expression were studied by immunofluorescence, MTT, High Content Scanning, confocal microscopy, reverse-transcription PCR, and western blot analysis, respectively. Pretreatment of pilocarpine could prevent glutamate-induced neuron death, which was blocked by the non-selective antagonist atropine and the M1-selective muscarinic receptor antagonist pirenzepine. The antiapoptotic effect of pilocarpine was associated with maintaining calcium homeostasis, recovering mitochondrial membrane potential, and regulating the expression of Bcl-2 and Caspase-3. These studies demonstrated that pilocarpine had effective protection against glutamate-induced neuronal apoptosis through M1 muscarinic receptor. The results may provide an insight into the new mechanism of glaucoma therapy that pilocarpine may potentially act as a retinal neuroprotectant.

Caspase activation in fetal rat brain following experimental intrauterine inflammation

Intrauterine inflammation has been implicated in developmental brain injuries, including the development of periventricular leukomalacia (PVL) and cerebral palsy (CP). Previous studies in our rat model of intrauterine inflammation demonstrated apoptotic cell death in fetal brains within the first 5 days after lipopolysaccharide (LPS) administration to mothers and eventual dysmyelination. Cysteine-containing, aspartate-specific proteases, or caspases, are proteins involved with apoptosis through both intracellular (intrinsic pathway) and extracellular (extrinsic pathway) mechanisms. We hypothesized that cell death in our model would occur mainly via activation of the extrinsic pathway. We further hypothesized that Fas, a member of the tumor necrosis factor receptor (TNFR) superfamily, would be increased and the death inducing signaling complex (DISC) would be detectable. Pregnant rats were injected intracervically with LPS at E15 and immunoblotting, immunohistochemical and immunoprecipitation analyses were performed. The presence of the activated form of the effector caspase (caspase-3) was observed 24 h after LPS administration. Caspase activity assays demonstrated rapid increases in (i) caspases-9 and -10 within 1 h, (ii) caspase-8 at 2 h and (iii) caspase-3 at 4 h. At 24 h after LPS, activated caspase-3(+)/Fas(+) cells were observed within the developing white matter. Lastly, the DISC complex (caspase-8, Fas and Fas-associated death domain (FADD)) was observed within 30 min by immunoprecipitation. Apoptosis in our model occurs via both extrinsic and intrinsic pathways, and activation of Fas may play a role. Understanding the mechanisms of cell death in models of intrauterine inflammation may affect development of future strategies to mitigate these injuries in children.

Neurosecretases provide strategies to treat sporadic and familial Alzheimer disorders

Recent discoveries on neurosecretases and their trafficking to release fibril-forming neuropeptides or other products, are of interest to pathology, cell signaling and drug discovery. Nomenclature arose from the use of amyloid precursor protein (APP) as a prototypic type-1 substrate leading to the isolation of beta-secretase (BACE), multimeric complexes (gamma-secretase, gamma-SC) for intramembranal cleavage, and attributing a new function to well-characterized metalloproteases of the ADAM family (alpha-secretase) for normal APP turnover. While purified alpha/beta-secretases facilitate drug discovery, gamma-SC presents greater challenges for characterization and mechanisms of catalysis. The review comments on links between mutation or polymorphisms in relation to enzyme mechanisms and disease. The association between lipoprotein receptor LRP11 variants and sporadic Alzheimer's disease (SAD) offers scope to integrate components of pre- and post-Golgi membranes, or brain clathrin-coated vesicles within pathways for trafficking as targets for intervention. The presence of APP and metabolites in brain clathrin-coated vesicles as significant cargo with lipoproteins and adaptors focuses attention as targets for therapeutic intervention. This overview emphasizes the importance to develop new therapies targeting neurosecretases to treat a major neurological disorder that has vast economic and social implications.

Serum amyloid P component induces TUNEL-positive nuclei in rat brain after intrahippocampal administration

Serum amyloid P component (SAP)-induced neuronal apoptosis has been demonstrated on the primary culture of embryonic rat cerebral cortex in vitro. Here we present pieces of evidence that cell death is also induced by serum amyloid P component in living rat brain similarly to that in cell culture. Intrahippocampally administered SAP diffuses from the site of injection to the cortical and subcortical area of the rat brain and enters the cells of brain tissue in 1 week. It induces elevation of the number of in situ TdT-mediated dUTP-X nick end-labeled nuclei in the hippocampus, cortex and subcortical structures of rat central nervous system. DNA fragmentation, which is detected by the end labeling reaction, is characteristic to apoptosis. It develops in 4 weeks following exposure. Apoptosis is an important form of cell death in different neurodegenerative diseases including Alzheimer's disease. Our present work reveals that apoptosis can be induced by SAP beyond other hitherto known apoptosis inducing components of neurodegeneration. Hereby SAP seems to be an important component of the process, which leads to expanded neuronal loss in the pathomechanism of neurodegenerative diseases.

Differential regulation of inhibitors of apoptosis proteins in Alzheimer's disease brains

Neuronal degeneration linked to apoptosis can be inhibited by a family of proteins known as inhibitors of apoptosis proteins (IAPs). We examined three members of the IAP family that are implicated in the regulation of neuronal death. We assessed NAIP, XIAP, and cIAP-2 protein levels in the entorhinal cortex of non-demented, cognitively impaired and Alzheimer's disease cases. Levels of paired helical filament-1 (PHF-1), a marker of neurofibrillary tangles, were assessed to determine their relationship to IAP levels. NAIP was decreased in AD cases compared to mildly impaired and unimpaired cases, and this decrease was associated with increased PHF-1 levels. Low NAIP levels were associated with higher Braak and Braak tangle stage and cognitive dysfunction. XIAP levels were higher in AD cases and cIAP-2 levels did not vary with clinical status. Our data suggest that decreased NAIP may place neurons at risk for the development of tangles and apoptosis.

Caspase-3 activation in astrocytes following postnatal excitotoxic damage correlates with cytoskeletal remodeling but not with cell death or proliferation

Caspase-3 has classically been defined as the main executioner of programmed cell death. However, recent data supports the participation of this protease in non-apoptotic cellular events including cell proliferation, cell cycle regulation, and cellular differentiation. In this study, astroglial cleavage of caspase-3 was analyzed following excitotoxic damage in postnatal rats to determine if its presence is associated with apoptotic cell death, cell proliferation, or cytoskeletal remodeling. A well-characterized in vivo model of excitotoxicity was studied, where damage was induced by intracortical injection of N-methyl-D-asparate (NMDA) in postnatal day 9 rats. Our results demonstrate that cleaved caspase-3 was mainly observed in the nucleus of activated astrocytes in the lesioned hemisphere as early as 4 h postlesion and persisted until the glial scar was formed at 7-14 days, and it was not associated with TUNEL labeling. Caspase-3 enzymatic activity was detected at 10 h and 1 day postlesion in astrocytes, and co-localized with caspase-cleaved fragments of glial fibrillary acidic protein (CCP-GFAP). However, at longer survival times, when astroglial hypertrophy was observed, astroglial caspase-3 did not generally correlate with GFAP cleavage, but instead was associated with de novo expression of vimentin. Moreover, astroglial caspase-3 cleavage was not associated with BrdU incorporation. These results provide further evidence for a nontraditional role of caspases in cellular function that is independent of cell death and suggest that caspase activation is important for astroglial cytoskeleton remodeling following cellular injury.

Changes of apoptosis-related proteins in hippocampus of SAM mouse in development and aging

Expression of Caspase and Bcl-2 proteins was examined in the hippocampus of senescence-accelerated mice (SAM, P8 and R1 strain) from E19 to 16 months of age. Immunoblotting analysis showed no upregulation of pro-apoptotic proteins (caspase-2L, -3, -6, -8, -9, and Bax) with age while all the anti-apoptotic proteins (caspase-2S, Bcl-2, and Bcl-XL) remained unchanged during aging. Terminal dUTP nick end labeling (TUNEL) and electron microscopy on the hippocampus of 3- and 16-month-old SAM revealed very few TUNEL positive cells in both groups. Morphometric study further showed neuronal loss in the hippocampus was not age-related. Our results suggest apoptosis and cell loss are minor events in the hippocampus of SAM mice and are unlikely to be the cause of functional decline during aging in SAM.

Transcriptional regulation of caspases in experimental pneumococcal meningitis

Apoptosis and necrosis in brain account for neurological sequelae in survivors of bacterial meningitis. In meningitis, several mechanisms may trigger death pathways leading to activation of transcription factors regulating caspases mRNA synthesis. Therefore, we used a multiprobe RNA protection assay (RPA) to examine the expression of 9 caspase-mRNA in the course of experimental Streptococcus pneumoniae meningitis in mouse brain. Caspase-6, -7 and -11 mRNA were elevated 6 hours after infection. 12 hours after infection caspases-1, -2, -8 and -12 mRNA rose. Caspase-14 mRNA was elevated 18 h and caspase-3 mRNA 24 h after infection. In situ hybridization detected caspases-3, -8, -11 and -12 mRNA in neurons of the hippocampal formation and neocortex. Development of sepsis was paralleled by increased transcription of caspases mRNA in the spleen. In TNFalpha-deficient mice all caspases examined were less upregulated, in TNF-receptor 1/2 knockout mice caspases-1, -2, -7, -11 and -14 mRNA were increased compared to infected control animals. In caspase-1 deficient mice, caspases-11, and -12 mRNA levels did not rise in meningitis indicating the necessity of caspase-1 activating these caspases. Hippocampal formations of newborn mice incubated with heat-inactivated S. pneumoniae R6 showed upregulation of caspase-1, -3, -11 and -12 mRNA. These observations suggest a tightly regulated caspases network at the transcriptional level in addition to the known cascade at the protein level.

Caspase-cleaved amyloid precursor protein in Alzheimer's disease

Caspase-3 mediated cleavage of the amyloid precursor protein (APP) has been proposed as a putative mechanism underlying amyloidosis and neuronal cell death in Alzheimer's disease (AD). We utilized an antibody that selectively recognizes the neo epitope generated by caspase-3 mediated cleavage of APP (alphadeltaC(csp)-APP) to determine if this proteolytic event occurs in senile plaques in the inferior frontal gyrus and superior temporal gyrus of autopsied AD and age-matched control brains. Consistent with a role for caspase-3 activation in AD pathology, alphadeltaC(csp)-APP immunoreactivity colocalized with a subset of TUNEL-positive pyramidal neurons in AD brains. AlphadeltaC(csp)-APP immunoreactivity was found in neurons and glial cells, as well as in small- and medium-size particulate elements, resembling dystrophic terminals and condensed nuclei, respectively, in AD and age-matched control brains. There were a larger number of alphadeltaC(csp)-APP immunoreactive elements in the inferior frontal gyrus and superior temporal gyrus of subjects with AD pathology than age-matched controls. AlphadeltaC(csp)-APP immunoreactivity in small and medium size particulate elements were the main component colocalized with 30% of senile plaques in the inferior frontal gyrus and superior temporal gyrus of AD brains. In some control brains, alphadeltaC(csp)-APP immunoreactivity appeared to be associated with a clinical history of metabolic encephalopathy. Our results suggest that apoptosis contributes to cell death resulting from amyloidosis and plaque deposition in AD.

Transthyretin inhibition of amyloid beta aggregation and toxicity

OBJECTIVES

The aim of this study was to investigate transthyretin (prealbumin) effects on Abeta25-35-induced cytotoxicity.

DESIGN AND METHODS

In view of the well-recognized literature data demonstrating that Abeta25-35 fibrillar aggregates cause in vitro cytotoxicity to human red blood cells and apoptotic changes to SK-N-BE neuroblastoma cells in cultures (ultrastructural evidence), we tested transthyretin effects on these two experimental models.

RESULTS

Incubation of Abeta25-35 with transthyretin (at transthyretin concentrations equal to CSF physiological levels) demonstrated both inhibition of red blood cells lysis and neutralization of SK-N-BE neuroblastoma cells ultrastructural apoptotic changes. Moreover, transthyretin was shown to be able to inhibit the formation of fibrillar macroaggregates of Abeta25-35.

CONCLUSIONS

The findings imply that experimental systems investigating Abeta-induced cytotoxicity consider the protective interaction of transthyretin with Abeta; an interaction to be considered also in vivo in view of the fact that transthyretin immunoreactivity has been previously demonstrated in amyloid plaques of brains from Alzheimer's disease patients.

Ischemia-stimulated neurogenesis is regulated by proliferation, migration, differentiation and caspase activation of hippocampal precursor cells

A brief ischemic injury to the gerbil forebrain that caused selective damage in the CA1 region of the hippocampus also enhanced the production of new cells in the hippocampal neurogenic area. When evaluated 1 week after bromodeoxyuridine (BrdU) injection, approximately ten times more labeled cells were detected in the hippocampal dentate gyrus in ischemic animals than controls, indicating a stimulation of mitotic activity. To assess the temporal course of the survival and fate of these newborn cells, we monitored BrdU labeling and cell marker expression up to 60 days after ischemia (DAI). Loss of BrdU-positive cells was observed from both control and ischemic animals, but at 30 DAI and afterward, the ischemic group maintained more than 3 times as many BrdU-positive cells as the control group. In addition, ischemic injury also fostered the neuronal differentiation of these cells beyond the capacity observed in control animals and facilitated the migration of developing neurons to a neuronal cellular layer. The establishment of a temporal correlation between differentiation and migration provides evidence of the functional maturation of these cells. Surprisingly, we found that ischemic injury induced activation of caspase-3, not only in the CA1 region as expected, but also in the dentate subgranular zone (SGZ). Active caspase-3 immunoreactivity in the subgranular layer was co-localized with an early neuronal marker, suggesting that caspase-mediated apoptosis could mediate the loss of neurogenic cells in the SGZ. Inhibiting caspase-3 in the context of ischemia-induced neurogenesis might provide an opportunity for functional repair and a therapeutic outcome in the wake of ischemic injury.

Apoptosis in the mammalian CNS: Lessons from animal models

It is generally assumed that about half of the neurons produced during neurogenesis die before completion of maturation of the central nervous system (CNS). Neural cell death is also relevant in aging and several neurodegenerative diseases. Among the modalities by which neurons die, apoptosis has very much attracted the interest of investigators because in this type of cell death neurons are actively responsible for their own demise by switching on a number of genes and activating a series of specific intracellular pathways. This review focuses on the cellular and molecular mechanisms of apoptosis in normal and transgenic animal models related to naturally occurring neuronal death within the CNS. We will also consider some examples of apoptotic cell death in canine neuropathologies. A thorough analysis of naturally occurring neuronal death in vivo will offer a basis for parallel and future studies involving secondary neuronal loss such as those in neurodegenerative disorders, trauma or ischaemia.

Hox genes and their candidate downstream targets in the developing central nervous system

1. Homeobox (Hox) genes were originally discovered in the fruit fly Drosophila, where they function through a conserved homeodomain as transcriptional regulators to control embryonic morphogenesis. Since then over 1000 homeodomain proteins have been identified in several species. In vertebrates, 39 Hox genes have been identified as homologs of the original Drosophila complex, and like their Drosophila counterparts they are organized within chromosomal clusters. Vertebrate Hox genes have also been shown to play a critical role in embryonic development as transcriptional regulators. 2. Both the Drosophila and vertebrate Hox genes have been shown to interact with various cofactors, such as the TALE homeodomain proteins, in recognition of consensus sequences within regulatory elements of their target genes. These protein-protein interactions are believed to contribute to enhancing the specificity of target gene recognition in a cell-type or tissue- dependent manner. The regulatory activity of a particular Hox protein on a specific regulatory element is highly variable and dependent on its interacting partners within the transcriptional complex. 3. In vertebrates, Hox genes display spatially restricted patterns of expression within the developing CNS, both along the anterioposterior and dorsoventral axis of the embryo. Their restricted gene expression is suggestive of a regulatory role in patterning of the CNS, as well as in cell specification. Determining the precise function of individual Hox genes in CNS morphogenesis through classical mutational analyses is complicated due to functional redundancy between Hox genes. 4. Understanding the precise mechanisms through which Hox genes mediate embryonic morphogenesis requires the identification of their downstream target genes. Although Hox genes have been implicated in the regulation of several pathways, few target genes have been shown to be under their direct regulatory control. Development of methodologies used for the isolation of target genes and for the analysis of putative targets will be beneficial in establishing the genetic pathways controlled by Hox factors. 5. Within the developing CNS various cell adhesion molecules and signaling molecules have been identified as candidate downstream target genes of Hox proteins. These targets play a role in processes such as cell migration and differentiation, and are implicated in contributing to neuronal processes such as plasticity and/or specification. Hence, Hox genes not only play a role in patterning of the CNS during early development, but may also contribute to cell specification and identity.

Glycogen synthase kinase 3 beta induces caspase-cleaved tau aggregation in situ

Tau is a substrate of caspases, and caspase-cleaved tau has been detected in Alzheimer's disease brain but not in control brain. Furthermore, in vitro studies have revealed that caspase-cleaved tau is more fibrillogenic than full-length tau. Considering these previous findings, the purpose of this study was to determine how the caspase cleavage of tau affected tau function and aggregation in a cell model system. The effects of glycogen synthase kinase 3 beta (GSK3 beta), a well established tau kinase, on these processes also were examined. Tau or tau that had been truncated at Asp-421 to mimic caspase cleavage (Tau-D421) was transfected into cells with or without GSK3 beta, and phosphorylation, microtubule binding, and tau aggregation were examined. Tau-D421 was not as efficiently phosphorylated by GSK3 beta as full-length tau. Tau-D421 efficiently bound microtubules, and in contrast to the full-length tau, co-expression with GSK3 beta did not result in a reduction in the ability of Tau-D421 to bind microtubules. In the absence of GSK3 beta, neither Tau-D421 nor full-length tau formed Sarkosyl-insoluble inclusions. However, in the presence of GSK3 beta, Tau-D421, but not full-length tau, was present in the Sarkosyl-insoluble fraction and formed thioflavin-S-positive inclusions in the cell. Nonetheless, co-expression of GSK3 beta and Tau-D421 did not result in an enhancement of cell death. These data suggest that a combination of phosphorylation events and caspase activation contribute to the tau oligomerization process in Alzheimer's disease, with GSK3 beta-mediated tau phosphorylation preceding caspase cleavage.

Apoptosis in oligodendrocytes is associated with axonal degeneration in P301L tau mice

Transgenic mice overexpressing human tau with the P301L mutation develop neurofibrillary tangles, extensive gliosis, adult-onset motor abnormalities, and neuronal loss in affected brain regions. We investigated the mechanism of neuronal cell death in this model of tauopathy. There was no evidence of neuronal apoptosis at any age; however, a population of oligodendorocytes was immunopositive for TUNEL and activated caspase-3. EM confirmed that these oligodendrocytes were undergoing apoptosis. These data suggest that classical apoptosis is not a major mechanism of neuronal cell death associated with the tau dysfunction in this mouse model; however, prominent white matter pathology in the spinal cord suggests that axonal degeneration in dying neurons causes oligodendrocytes to undergo apoptosis. It is unknown if loss of oligodendrocytes either through apoptosis or through the formation of intracellular tau lesions further contributes to the neurodegeneration seen in these mice.

Intrauterine infection/inflammation during pregnancy and offspring brain damages: possible mechanisms involved

Intrauterine infection is considered as one of the major maternal insults during pregnancy. Intrauterine infection during pregnancy could lead to brain damage of the developmental fetus and offspring. Effects on the fetal, newborn, and adult central nervous system (CNS) may include signs of neurological problems, developmental abnormalities and delays, and intellectual deficits. However, the mechanisms or pathophysiology that leads to permanent brain damage during development are complex and not fully understood. This damage may affect morphogenic and behavioral phenotypes of the developed offspring, and that mice brain damage could be mediated through a final common pathway, which includes over-stimulation of excitatory amino acid receptor, over-production of vascularization/angiogenesis, pro-inflammatory cytokines, neurotrophic factors and apoptotic-inducing factors.

Formation of high molecular weight caspase-3 complex in neonatal rat brain

Caspase-3 plays an essential role in normal brain development. Recently, a large protein complex known as apoptosome, which catalyzes the activation of caspase-3, has been reported. To investigate structural characteristics of caspase-3 in the developing brain, rat neonatal cortex extract was analysed by gel filtration chromatography. We show here the formation of high molecular complex including procaspase-3 in the extract. When the extract was activated by cytochrome c, caspase-3 recruitment to the apoptosome was not observed, although apoptotic protease activating factor-1 (Apaf-1), caspase-9, and X-linked inhibitor of apoptosis protein (XIAP) existed in the apoptosome. These results indicate that procaspase-3 exists as a high molecular weight complex during brain development.

PDNF, a human parasite-derived mimic of neurotrophic factors, prevents caspase activation, free radical formation, and death of dopaminergic cells exposed to the Parkinsonism-inducing neurotoxin MPP+

The neuraminidase/trans-sialidase of Trypanosoma cruzi, the agent of Chagas' disease, promotes differentiation and survival of growth factor-deprived neuronal and glial cells. To gain further insights into the possible neuroprotection of this parasite-derived counterpart of neurotrophic factors (PDNF), we sought to determine whether it mimics growth factors in a cellular model of neurodegenerative diseases. Ascertaining cell viability by morphology, vital dye exclusion, mitochondrial reducing function, and absence of DNA fragmentation, we show here that PDNF rescues from death two dopaminergic neuronal cell lines and one differentiated immortalized mesencephalic neurons exposed to the neurotoxin 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) and its toxic metabolite, 1-methyl-4-phenylpyridinium (MPP+), both widely used in models of Parkinson's disease. We further show that PDNF promoted survival at concentrations comparable to bona fide growth factors in a MAPK/Erk activation-dependent manner. PDNF also strongly suppresses the overproduction of MPTP-induced reactive oxygen species (ROS), and the activation of both initiator caspase-9 and effector caspase-3. This down-regulation of ROS and caspases explains, at least in part, the PDNF-induced salvaging of the dopaminergic cells from the Parkinsonism-promoting toxin, confirming the novel and striking functional mimicry by the trypanosome neuraminidase of host growth factors in a cellular model of neurodegeneration.

Pathways of survival induced by NGF and extracellular ATP after growth factor deprivation

In a previous work we demonstrated that extracellular adenosine-5'-triphosphate (ATP), acting on P2 receptors, exerts neuritogenic and trophic effects on the phaeochromocytoma PC12 cell line. These actions are comparable to those sustained by nerve growth factor (NGF) and involve several overlapping pathways. In this work, we describe some of the mechanisms recruited by ATP and NGF in maintaining PC12 cell survival after serum deprivation. We show that both ATP and NGF upregulate the expression of the stress-induced heat shock protein HSP70 and HSP90, whilst glucose-response protein GRP75 and GRP78 are not affected. In parallel with NGF, ATP prevents the cleavage and activation of caspase-2 and inhibits the release of cytochrome c from mitochondria into the cytoplasm. Finally, neither NGF, nor ATP directly modulate the expression of P2 receptors in the induction of cell survival. Our data contribute to dissect the biological mechanisms activated by extracellular purines exerting trophic actions and to establish that survival and neurite outgrowth lie on different mechanistic pathways.

Autonomic and motor neuron death is progressive and parallel in a lumbosacral ventral root avulsion model of cauda equina injury

Injuries to the cauda equina of the spinal cord result in autonomic and motor neuron dysfunction. We developed a rodent lumbosacral ventral root avulsion injury model of cauda equina injury to investigate the lesion effect in the spinal cord. We studied the retrograde effects of a unilateral L5-S2 ventral root avulsion on efferent preganglionic parasympathetic neurons (PPNs) and pelvic motoneurons in the L6 and S1 segments at 1, 2, 4, and 6 weeks postoperatively in the adult male rat. We used Fluoro-Gold-prelabeling techniques, immunohistochemistry, and quantitative stereologic analysis to show an injury-induced progressive and parallel death of PPNs and motoneurons. At 6 weeks after injury, only 22% of PPNs and 16% of motoneurons remained. Furthermore, of the neurons that survived at 6 weeks, the soma volume was reduced by 25% in PPNs and 50% in motoneurons. Choline acetyltransferase (ChAT) protein was expressed in only 30% of PPNs, but 80% of motoneurons remaining at 1 week postoperatively, suggesting early differential effects between these two neuronal types. However, all remaining PPNs and motoneurons were ChAT positive at 4 weeks postoperatively. Nuclear condensation and cleaved caspase-3 were detected in axotomized PPNs and motoneurons, suggesting apoptosis as a contributing mechanism of the neural death. We conclude that lumbosacral ventral root avulsions progressively deplete autonomic and motor neurons. The findings suggest that early neuroprotection will be an important consideration in future attempts of treating acute cauda equina injuries.

Tumour necrosis factor-alpha- vs. growth factor deprivation-promoted cell death: distinct converging pathways

Perturbations of neuronal physiological homeostasis are likely to underscore neuronal demise/impairments that are reportedly associated with aging of the central nervous system and age-related neurodegenerative diseases such as Alzheimer's disease (AD). A number of age- and/or disease-associated neurotoxic events has been described. These include abnormally modified proteins such as beta amyloid and hyper-phosphorylated Tau, cytokines such as tumour necrosis factor-alpha (TNFalpha), high levels of free radicals conducive to oxidative stress, and impaired/decreased neuronal trophic support by neurotrophic factors. Overall, it could be argued that toxic events in the aged brain are either active, such as those due to a direct action of cytokines, or passive, such as those due to lack of growth factor support. It is therefore conceivable that cellular responses to such diverse toxic stimuli are different, suggesting that interventions should be targeted accordingly. In order to begin answering this question, we determined in PC12 cells the time course of activity, in response to TNFalpha (active) or growth factor withdrawal (passive), of protein kinase c-zeta (PKCzeta), nuclear factor kappa B (NFkappaB), caspases 3 and 8, and poly (ADP-ribose) polymerase (PARP), key signal transduction elements associated with modulation of cell death/survival in PC12 cells. We found that the overall activity of PKCzeta, NFkappaB and caspase 8 was significantly different depending on the apoptotic initiator. The pattern of caspase 3 and PARP activity, however, was not statistically different between serum-free- and TNFalpha-induced cell death conditions. This suggests that two distinct cell responses are elicited that converge at caspase 3, which then induces downstream events involved in the execution of a common apoptotic programme. These results contribute to the aim of differentially targeting neuronal death in the aged brain (characterized by neurotrophic factor impairments) or in the diseased brain (e.g. AD, characterized by elevated levels of pro-inflammatory cytokines).

Neuroprotective action of flavopiridol, a cyclin-dependent kinase inhibitor, in colchicine-induced apoptosis

Flavopiridol was developed as a drug for cancer therapy due to its ability to inhibit cell cycle progression by targeting cyclin-dependent kinases (CDKs). In this study, we show that flavopiridol may also have a neuroprotective action. We show that at therapeutic dosage (or at micromolar range), flavopiridol almost completely prevents colchicine-induced apoptosis in cerebellar granule neurones. In agreement with this, flavopiridol inhibits both the release of cyt c and the activation of caspase-3 induced in response to colchicine treatment. We demonstrate that in this cellular model for neurotoxicity, neither re-entry in the cell cycle nor activation of stress-activated protein kinases, such as c-Jun N-terminal kinase (JNK) or p38 MAP kinase, is involved. In contrast, we show that colchicine-induced apoptosis correlates with a substantial increase in the expression of cdk5 and Par-4, which is efficiently prevented by flavopiridol. Accordingly, a cdk5 inhibitor such as roscovitine, but not a cdk4 inhibitor such as 3-ATA, was also able to protect neurons from apoptosis as well as prevent accumulation of cdk5 and Par-4 in response to colchicine. Our data suggest a potential therapeutic use of flavopiridol in disorders of the central nervous system in which cytoskeleton alteration mediated by cdk5 activation and Par-4 expression has been demonstrated, such as Alzheimer's disease.

Temporal assessment of caspase activation in experimental models of focal and global ischemia

Rodent models of focal and global ischemia were used to examine caspase activation. Several readouts were employed on identical tissue to provide correlative measurement of caspase induction, activation and enzymatic activity. In a rat focal ischemia model, caspase-3 enzymatic activity, as recorded by DEVD-AMC cleavage, peaked in penumbral cortex at 6-12 h following ischemia, correlating with increases in caspase 3-cleaved substrates of PARP and alpha-spectrin and subsequent disappearance of caspase-3 zymogen. Although induction of caspases 8 and 2 proteins was detectable as early as 6 h following ischemia, examination of the same tissues for caspase 8 or 2 enzymatic activities did not show significant modulation up to 12 h after ischemic insult. Caspase 9 induction was evident only after 24 h postischemia and did not correlate with elevated LDHD-AMC cleavage. Following global ischemia in gerbils, levels of caspase-3 enzyme activity peaked at 12 h in hippocampal tissue extracts. Cleaved caspase-3 signal was prominent in NeuN-positive layers in the CA1 region 6-12 h following ischemia. Interestingly, strong caspase-3 immunoreactivity was also detected in the subgranular zone of the dentate gyrus, a known region of ischemia-induced neurogenesis. Caspase-3 activation may be responsible for the loss of these cells, thereby hindering the endogenous recovery process.

Differential modulation of apoptosis-associated proteins by ethanol in rat cerebral cortex and cerebellum

Chronic ethanol treatment caused a differential modulation of apoptosis-associated proteins, cytochrome c release, concomitant with procaspase-9 and procaspase-3 activation leading to oligonucleosomal DNA fragmentation in rat cerebral cortex and cerebellum. Caspase-3 proform (32 kDa) showed decreased immunoreactivity in cortex and cerebellum, while the cleaved active fragment (17 kDa) increased significantly in cerebellum after ethanol treatment. Further, chronic ethanol treatment increased caspase-3 activity in cortex and to a higher extent in cerebellum, which was further confirmed by blocking experiments with caspase-3 specific inhibitor, N-acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO). We tested whether activated caspase-3 cleaves downstream substrates such as poly (ADP-ribose) polymerase-1 and protein kinase C-delta (PKC-delta). Western blots showed poly (ADP-ribose) polymerase-1 cleavage to its signature fragment of 85 kDa and decreased levels of PKC-delta in cerebral cortex and cerebellum after ethanol treatment, suggestive of caspase-3 activation. Elevated caspase-3 activity in cerebellum than cortex correlating with cytochrome c, caspase-9, active caspase-3 (p17), poly (ADP-ribose) polymerase-1 and PKC-delta data, suggests a mechanism by which ethanol might be exerting pro-apoptotic events in brain and how selective brain regions such as cerebellum are vulnerable to ethanol neurotoxicity in terms of cell death.

Ara-C induces apoptosis in monkey fibroblast cells

The effect of cytosine arabinoside (Ara-C) on cell viability has been studied in African green monkey kidney fibroblasts (CV1-P). It has been shown previously that Ara-C- induced cell death in neurons is mediated by apoptosis. We investigated whether Ara-C can induce apoptosis also in CV1-P cells, and if the apoptosis is p53-associated. For comparison, human neuroblastoma cells (SH-SY5Y) were studied as a model of human neuronal cells. SYTO13/propidium iodide staining revealed condensed and fragmented nuclei in both cell lines. Ara-C treatment for 48 h induced approximately 24% apoptosis in CV1-P cells whereas approximately 55% of SH-SY5Y cells were apoptotic. Ara-C increased the level of p53 in both CV1-P and SH-SY5Y cells compared to control. The maximum level of p53 in SH-SY5Y cells was reached at 12 h and this then rapidly faded whereas CV1-P cells p53 levels remained elevated after reaching their maximum. Caspase-3 activity was 5-fold higher in human neuroblastoma cells than in monkey fibroblasts, this reflected the decreased cell viability. Our results prove that Ara-C- induced apoptosis in CV1-P cells is associated with an increase of p53 and activation of caspase-3. Ara-C-induced toxicity in CV1-P cells is modest compared to that seen in neuronal cells.

In vivo cellular and molecular mechanisms of neuronal apoptosis in the mammalian CNS

Apoptosis has been recognized to be an essential process during neural development. It is generally assumed that about half of the neurons produced during neurogenesis die before completion of the central nervous system (CNS) maturation, and this process affects nearly all classes of neurons. In this review, we discuss the experimental data in vivo on naturally occurring neuronal death in normal, transgenic and mutant animals, with special attention to the cerebellum as a study model. The emerging picture is that of a dual wave of apoptotic cell death affecting central neurons at different stages of their life. The first wave consists of an early neuronal death of proliferating precursors and young postmitotic neuroblasts, and appears to be closely linked to cell cycle regulation. The second wave affects postmitotic neurons at later stages, and is much better understood in functional terms, mainly on the basis of the neurotrophic concept in its broader definition. The molecular machinery of late apoptotic death of postmitotic neurons more commonly follows the mitochondrial pathway of intracellular signal transduction, but the death receptor pathway may also be involved.Undoubtedly, analysis of naturally occurring neuronal death (NOND) in vivo will offer a basis for parallel and future studies aiming to elucidate the mechanisms of pathologic neuronal loss occurring as the result of conditions such as neurodegenerative disorders, trauma or ischemia.