Distinct nuclear and cytoplasmic localization of caspase cleavage products in two models of induced apoptotic death in dopamine neurons of the substantia nigra

Preferential rabbit antibody responses to C-termini of NOTCH3 peptide immunogens

Antibodies raised in peptide-immunized rabbits have been used in biological research for decades. Although there has been wide implementation of this approach, specific proteins are occasionally difficult to target for multiple reasons. One consideration that was noted in mice is that humoral responses may preferentially target the carboxyl terminus of the peptide sequence which is not present in the intact protein. To shed light on the frequency of preferential rabbit antibody responses to C-termini of peptide immunogens, we present our experience with generation of rabbit antibodies to human NOTCH3. A total of 23 antibodies were raised against 10 peptide sequences of human NOTCH3. Over 70% (16 of 23) of these polyclonal antibodies were determined to be C-terminal preferring: NOTCH3 peptide-reactive antibodies largely targeted the terminating free carboxyl group of the immunizing peptide. The antibodies that preferred C-terminal epitopes reacted weakly or not at all with recombinant target sequences with extension the C-terminus that eliminated the free carboxyl group of the immunogen structure; furthermore, each of these antisera revealed no antibody reactivity to proteins truncated before the C-terminus of the immunogen. In immunocytochemical applications of these anti-peptide antibodies, we similarly found reactivity to recombinant targets that best binding to cells expressing the free C-terminus of the immunizing sequence. In aggregate, our experience demonstrates a strong propensity for rabbits to mount antibody responses to C-terminal epitopes of NOTCH3-derived peptides which is predicted to limit their use against the native protein. We discuss some potential approaches to overcome this bias that could improve the efficiency of generation of antibodies in this commonly utilized experimental paradigm.

Non-Apoptotic Caspase-3 Activation Mediates Early Synaptic Dysfunction of Indirect Pathway Neurons in the Parkinsonian Striatum

Non-apoptotic caspase-3 activation is critically involved in dendritic spine loss and synaptic dysfunction in Alzheimer’s disease. It is, however, not known whether caspase-3 plays similar roles in other pathologies. Using a mouse model of clinically manifest Parkinson’s disease, we provide the first evidence that caspase-3 is transiently activated in the striatum shortly after the degeneration of nigrostriatal dopaminergic projections. This caspase-3 activation concurs with a rapid loss of dendritic spines and deficits in synaptic long-term depression (LTD) in striatal projection neurons forming the indirect pathway. Interestingly, systemic treatment with a caspase inhibitor prevents both the spine pruning and the deficit of indirect pathway LTD without interfering with the ongoing dopaminergic degeneration. Taken together, our data identify transient and non-apoptotic caspase activation as a critical event in the early plastic changes of indirect pathway neurons following dopamine denervation.

Leaf Extracts of Anchomanes difformis Ameliorated Kidney and Pancreatic Damage in Type 2 Diabetes

Kidney disease in diabetes is one of the common microvascular complications of diabetes mellitus implicated in end-stage renal failure. This study explored the ability of Anchomanes difformis to ameliorate kidney and pancreatic damage in type 2 diabetes mellitus using male Wistar rats. Two weeks of fructose (10%) administration followed by streptozotocin (40 mg/kg) were used to induce type 2 diabetes. Leaf extract (aqueous) of Anchomanes difformis (200 mg and 400 mg/kgBW) was administered orally for six weeks. Body weights were monitored, urea and creatinine were measured. Interleukins (IL)-1β, IL-6, IL-10, IL-18, and TNFα were measured in the kidney lysate. CAT, SOD, ORAC, FRAP, and MDA levels were also evaluated in the kidney. Transcription factors (Nrf2 and NF-ĸB/p65) and apoptotic markers (Bcl2 and caspase 3) were investigated in the kidney. Histological sections of the pancreas and kidney tissues were examined for any visible pathology. Supplementation with Anchomanesdifformis enhanced antioxidant status, modulated inflammatory response, and reduced apoptosis in the kidney. It also restored the kidney and pancreatic histoarchitecture of the treated diabetic rats. The pathophysiology associated with diabetic nephropathy and pancreatic damage showcase the importance of exploring the use of antidiabetic, nephroprotective agents such as Anchomanes difformis to kidney damage in type 2 diabetes.

Traumatic Brain Injury Preserves Firing Rates But Disrupts Laminar Oscillatory Coupling and Neuronal Entrainment in Hippocampal CA1

While hippocampal-dependent learning and memory are particularly vulnerable to traumatic brain injury (TBI), the functional status of individual hippocampal neurons and their interactions with oscillations are unknown following injury. Using the most common rodent TBI model and laminar recordings in CA1, we found a significant reduction in oscillatory input into the radiatum layer of CA1 after TBI. Surprisingly, CA1 neurons maintained normal firing rates despite attenuated input, but did not maintain appropriate synchronization with this oscillatory input or with local high-frequency oscillations. Normal synchronization between these coordinating oscillations was also impaired. Simultaneous recordings of medial septal neurons known to participate in theta oscillations revealed increased GABAergic/glutamatergic firing rates postinjury under anesthesia, potentially because of a loss of modulating feedback from the hippocampus. These results suggest that TBI leads to a profound disruption of connectivity and oscillatory interactions, potentially disrupting the timing of CA1 neuronal ensembles that underlie aspects of learning and memory.

Phosphorylation of Tau and α-Synuclein Induced Neurodegeneration in MPTP Mouse Model of Parkinson's Disease

PURPOSE

Parkinson's disease (PD) is the second most common neurodegenerative disease. The α-Synuclein is a major component of Lewy bodies and Lewy neurites, the pathologic hallmark of PD. It is known that α-Synuclein is phosphorylated (p-α-Synuclein) in PD and tau-hyperphosphorylation (p-Tau) is also a pathologic feature of PD. However, the relationship between p-Synuclein and p-Tau in PD is not clear, in particular in the MPTP model of PD. The purpose of this study was to reveal their relationship in the mouse MPTP model.

METHODS

Firstly, the p-α-Synuclein, α-Synuclein, p-Tau and Tau protein levels were analyzed. Then, GSK3β activation was determined using immunoblot and immunohistochemical staining. Finally, the dopaminergic neurodegeneration was assessed using Tyrosine Hydroxylase (TH) staining and retrograde labeling and microglial marker were labeled. Microglial activation and nigrostriatal pathway degeneration were observed.

RESULTS

The results showed that p-α-Synuclein, α-Synuclein, p-Tau and Tau were upregulated in both hippocampus and substantia nigra of the PD mouse model. Furthermore, p-α-Synuclein and p-Tau were localized in the same regions of substantial nigra (SN) and dentate gyrus (DG) of hippocampus (Hippo). The activated form of GSK3β (phosphor GSK3β Y216) was increased in multiple brain areas. The GSK3β inhibitor AZD1080 injected in MPTP mice suppressed the expression of p-Tau and p-GSK3β and improved motor functions.

CONCLUSION

These findings revealed that p-α-Synuclein and p-Tau proteins are key pathological events leading to neurodegeneration and motor dysfunctions in the mouse MPTP model of PD. Our data suggest that the interference with the GSK3β activity may be an effective approach for the treatment of PD.

Neuropathological Characteristics of Brachial Plexus Avulsion Injury With and Without Concomitant Spinal Cord Injury

Neonatal brachial plexus avulsion injury (BPAI) commonly occurs as a consequence of birth trauma and can result in lifetime morbidity; however, little is known regarding the evolving neuropathological processes it induces. In particular, mechanical forces during BPAI can concomittantly damage the spinal cord and may contribute to outcome. Here, we describe the functional and neuropathological outcome following BPAI, with or without spinal cord injury, in a novel pediatric animal model. Twenty-eight-day-old piglets underwent unilateral C5–C7 BPAI with and without limited myelotomy. Following avulsion, all animals demonstrated right forelimb monoparesis. Injury extending into the spinal cord conferred greater motor deficit, including long tract signs. Consistent with clinical observations, avulsion with myelotomy resulted in more severe neuropathological changes with greater motor neuron death, progressive axonopathy, and persistent glial activation. These data demonstrate neuropathological features of BPAI associated with poor functional outcome. Interestingly, in contrast to adult small animal models of BPAI, a degree of motor neuron survival was observed, even following severe injury in this neonatal model. If this is also the case in human neonatal BPAI, repair may permit functional restoration. This model also provides a clinically relevant platform for exploring the complex postavulsion neuropathological responses that may inform therapeutic strategies.

The 6-hydroxydopamine model and parkinsonian pathophysiology: Novel findings in an older model

The neurotoxin 6-hydroxydopamine (6-OHDA) is widely used to induce models of Parkinson's disease (PD). We now know that the model induced by 6-OHDA does not include all PD symptoms, although it does reproduce the main cellular processes involved in PD, such as oxidative stress, neurodegeneration, neuroinflammation, and neuronal death by apoptosis. In this review we analyse the factors affecting the vulnerability of dopaminergic neurons as well as the close relationships between neuroinflammation, neurodegeneration, and apoptosis in the 6-OHDA model. Knowledge of the mechanisms involved in neurodegeneration and cell death in this model is the key to identifying potential therapeutic targets for PD.

Loss of angiotensin II receptor expression in dopamine neurons in Parkinson's disease correlates with pathological progression and is accompanied by increases in Nox4- and 8-OH guanosine-related nucleic acid oxidation and caspase-3 activation

Background

In rodent models of Parkinson’s disease (PD), dopamine neuron loss is accompanied by increased expression of angiotensin II (AngII), its type 1 receptor (AT1), and NADPH oxidase (Nox) in the nigral dopamine neurons and microglia. AT1 blockers (ARBs) stymie such oxidative damage and neuron loss. Whether changes in the AngII/AT1/Nox4 axis contribute to Parkinson neuropathogenesis is unknown. Here, we studied the distribution of AT1 and Nox4 in dopamine neurons in two nigral subregions: the less affected calbindin-rich matrix and the first-affected calbindin-poor nigrosome 1 of three patients, who were clinically asymptomatic, but had nigral dopamine cell loss and Braak stages consistent with a neuropathological diagnosis of PD (prePD). For comparison, five clinically- and neuropathologically-confirmed PD patients and seven age-matched control patients (AMC) were examined.

Results

AT1 and Nox4 immunoreactivity was noted in dopamine neurons in both the matrix and the nigrosome 1. The total cellular levels of AT1 in surviving dopamine neurons in the matrix and nigrosome 1 declined from AMC>prePD>PD, suggesting that an AngII/AT1/Nox4 axis orders neurodegenerative progression. In this vein, the loss of dopamine neurons was paralleled by a decline in total AT1 per surviving dopamine neuron. Similarly, AT1 in the nuclei of surviving neurons in the nigral matrix declined with disease progression, i.e., AMC>prePD>PD. In contrast, in nigrosome 1, the expression of nuclear AT1 was unaffected and similar in all groups. The ratio of nuclear AT1 to total AT1 (nuclear + cytoplasmic + membrane) in dopamine neurons increased stepwise from AMC to prePD to PD. The proportional increase in nuclear AT1 in dopamine neurons in nigrosome 1 of prePD and PD patients was accompanied by elevated nuclear expression of Nox4, oxidative damage to DNA, and caspase-3-mediated cell loss.

Conclusions

Our observations are consistent with the idea that AngII/AT1/Nox4 axis-mediated oxidative stress gives rise to the dopamine neuron dysfunction and loss characteristic of the neuropathological and clinical manifestations of PD and suggest that the chance for a neuron to survive increases in association with lower total as well as nuclear AT1 expression. Our results support the need for further evaluation of ARBs as disease-modifying agents in PD.

Activation of GSK-3β and caspase-3 occurs in Nigral dopamine neurons during the development of apoptosis activated by a striatal injection of 6-hydroxydopamine

The 6-Hydroxydopamine (6-OHDA) rat model of Parkinson's disease is essential for a better understanding of the pathological processes underlying the human disease and for the evaluation of promising therapeutic interventions. This work evaluated whether a single striatal injection of 6-OHDA causes progressive apoptosis of dopamine (DA) neurons and activation of glycogen synthase kinase 3β (GSK-3β) and caspase-3 in the substantia nigra compacta (SNc). The loss of DA neurons was shown by three neuron markers; tyrosine hydroxylase (TH), NeuN, and β-III tubulin. Apoptosis activation was determined using Apostain and immunostaining against cleaved caspase-3 and GSK-3β pY216. We also explored the possibility that cleaved caspase-3 is produced by microglia and astrocytes. Our results showed that the 6-OHDA caused loss of nigral TH(+) cells, progressing mainly in rostrocaudal and lateromedial directions. In the neostriatum, a severe loss of TH(+) terminals occurred from day 3 after lesion. The disappearance of TH(+) cells was associated with a decrease in NeuN and β-III tubulin immunoreactivity and an increase in Apostain, cleaved caspase-3, and GSK-3β pY216 in the SNc. Apostain immunoreactivity was observed from days 3 to 21 postlesion. Increased levels of caspase-3 immunoreactivity in TH(+) cells were detected from days 1 to 15, and the levels then decreased to day 30 postlesion. The cleaved caspase-3 also collocated with microglia and astrocytes indicating its participation in glial activation. Our results suggest that caspase-3 and GSK-3β pY216 activation might participate in the DA cell death and that the active caspase-3 might also participate in the neuroinflammation caused by the striatal 6-OHDA injection.

Interleukin (IL)-1 and IL-6 regulation of neural progenitor cell proliferation with hippocampal injury: differential regulatory pathways in the subgranular zone (SGZ) of the adolescent and mature mouse brain

Current data suggests an association between elevations in interleukin 1 (IL-1)α, IL-1β, and IL-6 and the proliferation of neural progenitor cells (NPCs) following brain injury. A limited amount of work implicates changes in these pro-inflammatory responses with diminished NPC proliferation observed as a function of aging. In the current study, adolescent (21day-old) and 1year-old CD-1 male mice were injected with trimethyltin (TMT, 2.3mg/kg, i.p.) to produce acute apoptosis of hippocampal dentate granule cells. In this model, fewer 5-bromo-2'-deoxyuridine (BrdU)+ NPC were observed in both naive and injured adult hippocampus as compared to the corresponding number seen in adolescent mice. At 48h post-TMT, a similar level of neuronal death was observed across ages, yet activated ameboid microglia were observed in the adolescent and hypertrophic process-bearing microglia in the adult. IL-1α mRNA levels were elevated in the adolescent hippocampus; IL-6 mRNA levels were elevated in the adult. In subgranular zone (SGZ) isolated by laser-capture microdissection, IL-1β was detected but not elevated by TMT, IL-1a was elevated at both ages, while IL-6 was elevated only in the adult. Naïve NPCs isolated from the hippocampus expressed transcripts for IL-1R1, IL-6Rα, and gp130 with significantly higher levels of IL-6Rα mRNA in the adult. In vitro, IL-1α (150pg/ml) stimulated proliferation of adolescent NPCs; IL-6 (10ng/ml) inhibited proliferation of adolescent and adult NPCs. Microarray analysis of SGZ post-TMT indicated a prominence of IL-1a/IL-1R1 signaling in the adolescent and IL-6/gp130 signaling in the adult.

Fluorescent false neurotransmitters visualize dopamine release from individual presynaptic terminals

The nervous system transmits signals between neurons via neurotransmitter release during synaptic vesicle fusion. In order to observe neurotransmitter uptake and release from individual presynaptic terminals directly, we designed fluorescent false neurotransmitters as substrates for the synaptic vesicle monoamine transporter. Using these probes to image dopamine release in the striatum, we made several observations pertinent to synaptic plasticity. We found that the fraction of synaptic vesicles releasing neurotransmitter per stimulus was dependent on the stimulus frequency. A kinetically distinct "reserve" synaptic vesicle population was not observed under these experimental conditions. A frequency-dependent heterogeneity of presynaptic terminals was revealed that was dependent in part on D2 dopamine receptors, indicating a mechanism for frequency-dependent coding of presynaptic selection.

JNK2 and JNK3 combined are essential for apoptosis in dopamine neurons of the substantia nigra, but are not required for axon degeneration

Activation of c-jun N-terminal kinase (JNK) by the mitogen-activated protein kinase cascade has been shown to play an important role in the death of dopamine neurons of the substantia nigra, one of the principal neuronal populations affected in Parkinson's disease. However, it has remained unknown whether the JNK2 and JNK3 isoforms, either singly or in combination, are essential for apoptotic death, and, if so, the mechanisms involved. In addition, it has been unclear whether they play a role in axonal degeneration of these neurons in disease models. To address these issues we have examined the effect of single and double jnk2 and jnk3 null mutations on apoptosis in a highly destructive neurotoxin model, that induced by intrastriatal 6-hydroxydopamine. We find that homozygous jnk2/3 double null mutations result in a complete abrogation of apoptosis and a prolonged survival of the entire population of dopamine neurons. In spite of this complete protection at the cell soma level, there was no protection of axons. These studies provide a striking demonstration of the distinctiveness of the mechanisms that mediate cell soma and axon degeneration, and they illustrate the need to identify and target pathways of axon degeneration in the development of neuroprotective therapeutics.

Neuronal apoptosis and autophagy cross talk in aging PS/APP mice, a model of Alzheimer's disease

Mechanisms of neuronal loss in Alzheimer's disease (AD) are poorly understood. Here we show that apoptosis is a major form of neuronal cell death in PS/APP mice modeling AD-like neurodegeneration. Pyknotic neurons in adult PS/APP mice exhibited apoptotic changes, including DNA fragmentation, caspase-3 activation, and caspase-cleaved alpha-spectrin generation, identical to developmental neuronal apoptosis in wild-type mice. Ultrastructural examination using immunogold cytochemistry confirmed that activated caspase-3-positive neurons also exhibited chromatin margination and condensation, chromatin balls, and nuclear membrane fragmentation. Numbers of apoptotic profiles in both cortex and hippocampus of PS/APP mice compared with age-matched controls were twofold to threefold higher at 6 months of age and eightfold higher at 21 to 26 months of age. Additional neurons undergoing dark cell degeneration exhibited none of these apoptotic features. Activated caspase-3 and caspase-3-cleaved spectrin were abundant in autophagic vacuoles, accumulating in dystrophic neurites of PS/APP mice similar to AD brains. Administration of the cysteine protease inhibitor, leupeptin, promoted accumulation of autophagic vacuoles containing activated caspase-3 in axons of PS/APP mice and, to a lesser extent, in those of wild-type mice, implying that this pro-apoptotic factor is degraded by autophagy. Leupeptin-induced autophagic impairment increased the number of apoptotic neurons in PS/APP mice. Our findings establish apoptosis as a mode of neuronal cell death in aging PS/APP mice and identify the cross talk between autophagy and apoptosis, which influences neuronal survival in AD-related neurodegeneration.

Histochemical methods for the detection of apoptosis in the nervous system

Neuroscientists often need to detect neuron death at the light microscope level in tissue sections derived from animal models of neurological disease. In many instances there is a need to detect apoptosis, the most common morphology of programmed cell death. This unit provides two protocols for the detection of apoptosis by immunostaining for either activated forms of caspases or their cleavage products. When used in conjunction with nuclear dyes, these protocols permit visualization not only of caspase activation, but also the nuclear chromatin clumps characteristic of apoptosis. The first protocol utilizes peroxidase-mediated chromogen deposition to visualize antibodies by brightfield microscopy. The second protocol utilizes fluorophores to visualize antibodies by epifluorescence. Double immunofluorescence labeling can be performed to identify the phenotype of cells in which caspases are activated. Not all cell death is apoptotic. Therefore, a third protocol is presented for suppressed silver staining, a useful method to screen for all morphologic forms of cell death.

Expression of FasL and its interaction with Fas are mediated by c-Jun N-terminal kinase (JNK) pathway in 6-OHDA-induced rat model of Parkinson disease

Our previous studies and those of others have strongly suggested that c-Jun N-terminal kinase (JNK) signaling pathway plays a critical role in 6-hydroxydopamine (6-OHDA)-induced dopaminergic neuron injury in the substantia nigra. However, the downstream mechanism that accounts for the proapoptotic actions of JNK in 6-OHDA lesion remains to be investigated in detail. Fas, a member of the tumor necrosis factor receptor family with proapoptotic functions, was reported to be elevated within the striatum and substantia nigra pars compacta (SNc) of Parkinson's disease (PD) patients. In the present study, we examined the changes in the protein level of Fas ligand (FasL) and its interaction with Fas in a rat model of PD. We demonstrate that the expression of FasL and not Fas was increased after 6-OHDA lesion; additionally, the interaction of FasL and Fas was increased due to 6-OHDA lesion. This indicates that the 6-OHDA-induced activation of Fas signaling pathway is mediated by JNK and that FasL may be a promising target in the therapeutic approach for PD patients.

Substantial thalamostriatal dopaminergic defect in Unverricht-Lundborg disease

PURPOSE

Unverricht-Lundborg disease (ULD) is currently classified as progressive myoclonus epilepsy. Myoclonus, the characteristic symptom in ULD, suggests that dopamine neurotransmission may be involved in the pathophysiology of ULD. Our purpose was to examine brain dopaminergic function in ULD patients.

METHODS

Four genetically and clinically diagnosed ULD patients and eight healthy controls were scanned with [(11)C]raclopride-PET. PET images were coregistered to individual 1.5 T MR images and region-of-interest analysis was performed for the striatum and thalamus. Standardized uptake values and individual voxel-wise binding potential maps of the patients and controls were also analyzed.

RESULTS

ULD patients had markedly higher (31-54%) dopamine D2-like receptor availabilities than healthy controls in both the striatum and the thalamus. The proportionally highest binding potentials were detected in the thalamus. There were no significant differences in the cerebellar uptake of [(11)C]raclopride in ULD patients versus healthy controls. Voxel-based results were in accordance with the region-of-interest analysis.

CONCLUSIONS

These results suggest that dopaminergic modulation at the level of the striatum and thalamus could be a crucial factor contributing to the symptoms of ULD. In the light of our data, we propose that ULD with dopamine dysfunction and dyskinetic symptoms shares certain pathophysiological mechanisms with classical movement disorders. Future studies are therefore warranted to study the effect of dopaminergic pharmacotherapy in ULD.

Apoptosis in the rat basal forebrain during development and following lesions of connections

Evidence suggests that neurotrophins are essential for the survival and phenotypic maintenance of cholinergic basal forebrain (BF) neurons. We evaluated the pattern of programmed cell death in the BF of the rat during development and after ablations of the cerebral cortex, a major target area and source of neurotrophins for BF neurons. We identified dying cells using the TUNEL (terminal deoxynucleotidyl-transferase-mediated dUTP-biotin nick end labelling) method and confirmed their apoptotic morphology with electron microscopy. Moreover, we demonstrated the expression of the apoptotic marker active caspase-3 in cells with features of apoptosis. TUNEL(+) cells were present in the developing BF during the first two postnatal weeks. Their frequency peaked at postnatal day (P)1 and at P5. TUNEL used in conjunction with immunofluorescence for neuronal nuclear protein (NeuN) showed that, at both peak stages, the majority of apoptotic cells were neurons. Extensive lesions of the cerebral cortex at different ages (P0, P7 and P14) did not induce significant changes in the frequency of apoptotic BF neurons. However, they resulted in alterations in the morphological phenotype of choline acetyltransferase (ChAT)-immunoreactive neurons in the BF, and a reduction in their number which was inversely proportional to the age at which the lesions were performed. We suggest that: (i) apoptosis is temporally coordinated with the morphological and neurochemical differentiation of BF neurons and the establishment of connections with their target areas; and (ii) cortical ablations do not affect the survival of BF neurons, but they influence the phenotype of cholinergic BF neurons.

Partial dopamine loss enhances activated caspase-3 activity: differential outcomes in striatal projection systems

Parkinson's disease (PD) is a basal ganglia disorder. Motor symptoms develop insidiously following substantial neurodegeneration of the dopamine (DA) neurons in the nigrostriatal system and produce slowed, infrequent movements, postural instability, and gait changes. A thorough understanding of neurochemical compensations occurring in the striatum during early stages of PD is crucial in identifying components that are altered initially as the DA is depleted. Producing an incomplete lesion of the nigrostriatal DA system in rats would mimic the principal early neurochemical features of human PD. We infused 6-hydroxydopamine unilaterally into the substantia nigra to reach a target of approximately 50% depletion in striatal DA at 4 weeks. This was evaluated by HPLC analysis of tissue DA content and monitored behaviorally by forepaw use reflecting asymmetries in striatal DA levels. DA loss was assessed by using tyrosine hydroxylase immunohistochemical staining, and the data were conjoined with the behavioral assessments. We found that activated caspase-3, its actin cleavage product fractin, and components of the apoptosome were increased significantly in DA-depleted striatum. Thus mobilization of the intrinsic programmed cell death pathway occurred, without cell loss. Elevations in apoptogenic proteins were pronounced in enkephalinergic striatopallidal neurons compared with the substance P-containing striatonigral neurons. Our findings suggest that cellular homeostatic imbalances that accompany even mild striatal DA depletion take time to develop, differentially affect the striatal output pathways, and may be an important feature of early-stage PD. These observations could be capitalized upon to develop therapeutic interventions in the preclinical phases of the disorder.

Caspase-mediated cell death predominates following engraftment of neural progenitor cells into traumatically injured rat brain

Neural progenitor cells (NPCs) have been shown to be a promising therapy for cell replacement and gene transfer in neurological diseases including traumatic brain injury (TBI). However, NPCs often survive poorly after transplantation despite immunosuppression, and the mechanisms of graft cell death are unknown. In this study, we evaluated caspase- and calpain-mediated mechanisms of cell death of neonatal mouse C17.2 progenitor cells, transplanted at 24 h following lateral fluid percussion brain injury (FP) in rats. Adult Male Sprague-Dawley rats (n = 30) were subjected to lateral FP injury (n = 18) or sham surgery (n = 12). C17.2 cells labeled with green fluorescent dye (CMFDA) were engrafted in the perilesional deep cortex, and animals were sacrificed at 24 h, 72 h and 1 week post-transplantation. Pro-apoptotic caspase-mediated cleavage products (Ab246) and calpain-mediated cleavage products (Ab38) were detected in the engrafted cells using immunohistochemistry. Only 2 to 4.5% of grafted NPCs were found to survive at 24 h post-transplantation, regardless of injury status of the host brain, although brain-injured animals had significantly fewer graft cells than sham-injured animals. Limited caspase and calpain-mediated graft cell death was observed in both sham- and brain-injured animals, and caspase-mediated graft cell death was significantly greater than calpain-mediated graft cell death in all animals. Brain-injured animals had significantly increased caspase-mediated graft cell death compared to sham-injured animals. These results suggest that both the caspase and calpain family of proteases are involved in graft cell death, and that caspase-mediated apoptotic graft cell death predominates in the acute post-traumatic period following TBI.

Novel surrogate markers for acute brain damage: cerebrospinal fluid levels corrrelate with severity of ischemic neurodegeneration in the rat

Previously, we identified proteins released from degenerating cultured cortical neurons as novel cerebrospinal fluid (CSF) markers for acute brain injury in the rat. Here, we investigate relationships between CSF changes in these novel markers and the severity of acute ischemic brain injury. Rats underwent sham surgery or 3,6,8, or 10 mins of transient global forebrain ischemia. At 48 h after insult, CSF levels of 14-3-3beta, 14-3-3zeta, and calpain cleavage products of alpha-spectrin and tau were quantified. Regional acute neurodegeneration was assessed by Fluoro-Jade and silver impregnation staining, and confirmed by immunohistochemical detection of the activation of calpain and caspase, cysteine proteases involved in neurodegenerative signaling. Ischemic neurodegeneration and activation of at least one cysteine protease were observed in the hippocampal CA1 sector, dentate hilus, caudate nucleus, parietal cortex, thalamus, and inferior colliculus. As expected, the total number of degenerating cells increased as a function of ischemia duration. Cerebrospinal fluid levels of the four marker proteins increased markedly after ischemia, and rose in proportion with its duration. Irrespective of the length of ischemia, CSF levels of the neuron-enriched proteins 14-3-3beta and calpain-cleaved tau correlated significantly with the magnitude of acute ischemic neurodegeneration. Additionally, CSF levels of the two proteins correlated with one another. These results show that certain proteins released from degenerating neurons are CSF markers for brain injury in the rat whose levels reflect the severity of acute ischemic neurodegeneration. Measurement of 14-3-3beta and calpain-cleaved tau may be useful for the minimally invasive diagnosis, prognosis, and therapeutic evaluation of acute brain damage.

CHOP/GADD153 is a mediator of apoptotic death in substantia nigra dopamine neurons in an in vivo neurotoxin model of parkinsonism

There is increasing evidence that neuron death in neurodegenerative diseases, such as Parkinson's disease, is due to the activation of programmed cell death. However, the upstream mediators of cell death remain largely unknown. One approach to the identification of upstream mediators is to perform gene expression analysis in disease models. Such analyses, performed in tissue culture models induced by neurotoxins, have identified up-regulation of CHOP/GADD153, a transcription factor implicated in apoptosis due to endoplasmic reticulum stress or oxidative injury. To evaluate the disease-related significance of these findings, we have examined the expression of CHOP/GADD153 in neurotoxin models of parkinsonism in living animals. Nuclear expression of CHOP protein is observed in developmental and adult models of dopamine neuron death induced by intrastriatal injection of 6-hydroxydopamine (6OHDA) and in models induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). CHOP is a mediator of neuron death in the adult 60HDA model because a null mutation results in a reduction in apoptosis. In the chronic MPTP model, however, while CHOP is robustly expressed, the null mutation does not protect from the loss of neurons. We conclude that the role of CHOP depends on the nature of the toxic stimulus. For 6OHDA, an oxidative metabolite of dopamine, it is a mediator of apoptotic death.

Developmental status of neurons selectively vulnerable to rapidly triggered post-ischemic caspase activation

Caspase activation occurs within 1h of reperfusion in discrete cell populations of the adult rat brain following transient forebrain ischemia. Based on the proximity of these cells to regions of adult neurogenesis and the known susceptibility of developing neurons to apoptosis, we tested the hypothesis that rapidly triggered post-ischemic caspase activation occurs in immature neurons or neuroprogenitor cells. Adult male Long Evans rats were injected with BrdU to label mitotic cells 1, 7, or 28 days prior to being studied. Rats were then subjected to either sham surgery or 10-min transient forebrain ischemia. At 1h after reperfusion, rats underwent perfusion fixation and brains prepared for immunohistochemical analysis. Immunolabeling for caspase-substrate cleavage, using an antibody directed at the caspase derived fragment of alpha-spectrin, was observed in discrete cell populations of the rostral dentate gyrus, dorsal striatum, extreme paramedian CA1 hippocampus, indusium gresium, olfactory tubercle, and thalamus. No cells double-labeled for caspase-substrate cleavage and BrdU at any time point after BrdU injection. Furthermore, cells immunolabeled for caspase-substrate cleavage did not double-label for markers of immature neurons (doublecortin) or progenitor cells (nestin), but did double-label for the mature neuronal marker NeuN. These results indicate that the phenomenon of rapidly triggered caspase activation in the adult rat brain after transient forebrain ischemia is specific to mature neurons and does not occur in neuroprogenitor cells or immature neurons.

Ontogenic cell death in the nigrostriatal system

Like most neural systems, dopamine neurons of the substantia nigra undergo apoptotic natural cell death during development. In rodents, this occurs largely postnatally and is biphasic with an initial major peak just after birth and a second minor peak on postnatal day 14. As envisioned by classic neurotrophic theory, this event is regulated by interactions with the target of these neurons, the striatum, because a developmental target lesion results in an augmented natural cell death event with fewer nigral dopamine neurons surviving into adulthood. Until recently, the striatal target-derived neurotrophic factors providing developmental support of dopamine neurons were unknown, but there is now growing evidence that glial-cell-line-derived neurotrophic factor (GDNF) serves as a physiologic limiting neurotrophic factor for these neurons during the first phase of natural cell death. During this phase, intrastriatal injection of GDNF diminishes the natural cell death event and neutralizing antibodies augment it. Sustained overexpression of GDNF in the striatum throughout development in a unique double transgenic mouse model results in an increased number of dopamine neurons surviving the first phase of natural cell death. However, this increase does not persist into adulthood. Therefore, other factors or mechanisms must play important roles in the determination of the mature number of nigral dopamine neurons. Further elucidation of these mechanisms will be important in the development of neuroprotective and cell replacement therapies for Parkinson's disease.

Failure of neuronal protection by inhibition of glial activation in a rat model of striatonigral degeneration

Previous studies in rodent models of neurodegenerative disorders have demonstrated that minocycline exerts neuroprotective effects unrelated to its antimicrobial action. The purpose of the present study was to analyze whether minocycline exhibits neuroprotective activity in a rat model of striatonigral degeneration (SND), the core pathology underlying levodopa-unresponsive parkinsonism associated with multiple system atrophy (MSA). We observed no significant effect of minocycline on locomotor impairment in double-lesioned SND rats. Minocycline significantly suppressed astroglial and microglial activation (P < 0.01); however, 3'5'-monophosphate-regulated phosphoprotein (DARPP 32) immunohistochemistry revealed no significant differences in striatal lesion volume of minocycline-treated versus untreated control SND rats. Furthermore, there was no protection of nigral dopaminergic neurons in the double-lesion model. We conclude that despite its astrocytic and microglial suppression, minocycline failed to attenuate lesion-induced neuronal damage in the SND rat model.

CEP11004, a novel inhibitor of the mixed lineage kinases, suppresses apoptotic death in dopamine neurons of the substantia nigra induced by 6-hydroxydopamine

There is much evidence that the kinase cascade which leads to the phosphorylation of c-jun plays an important signaling role in the mediation of programmed cell death. We have previously shown that c-jun is phosphorylated in a model of induced apoptotic death in dopamine neurons of the substantia nigra in vivo. To determine the generality and functional significance of this response, we have examined c-jun phosphorylation and the effect on cell death of a novel mixed lineage kinase inhibitor, CEP11004, in the 6-hydroxydopamine model of induced apoptotic death in dopamine neurons. We found that expression of total c-jun and Ser73-phosphorylated c-jun is increased in this model and both colocalize with apoptotic morphology. CEP11004 suppresses apoptotic death to levels of 44 and 58% of control values at doses of 1.0 and 3.0 mg/kg, respectively. It also suppresses, to approximately equal levels, the number of profiles positive for the activated form of capase 9. CEP11004 markedly suppresses striatal dopaminergic fiber loss in these models, to only 22% of control levels. We conclude that c-jun phosphorylation is a general feature of apoptosis in living dopamine neurons and that the mixed lineage kinases play a functional role as up-stream mediators of cell death in these neurons.

Tissue microenvironments within functional cortical subdivisions adjacent to focal stroke

Stroke produces a region of complete cell death and areas of partial damage, injury, and gliosis. The spatial relationship of these regions of damage to the infarct core and within spared neuronal circuits has not been identified. A model of cortical stroke was developed within functional subsets of the somatosensory cortex. Infarct size, regions of apoptosis, oxidative DNA damage, heat shock protein induction, and subtypes of reactive gliosis were precisely mapped with the somatosensory body map, quantified, and interrelated. Three tissue microenvironments were recognized: zones of partial ischemic damage, heat shock protein induction, and distributed gliosis. These three zones involved progressively more distant cortical regions, each larger than the infarct core. The zone of partial ischemic damage represents an overlap region of apoptotic cell death, oxidative DNA damage, loss of synaptic connections, and local reactive gliosis. The zone of distributed gliosis occupies distinct functional areas of the somatosensory cortex. The tissue reorganization induced by stroke is much larger than the stroke site itself. Adjacent tissue microenvironments are sites of distinct reactive cellular signaling and may serve as a link between the processes of acute cell death and delayed neuronal plasticity after focal stroke.

Molecular mechanisms of selective dopaminergic neuronal death in Parkinson's disease

Parkinson's disease (PD) is a progressive neurological disease caused by selective degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc). Although PD has been heavily researched, the precise etiology of nigral cell loss is still unknown and, consequently, treatment is largely symptomatic rather than preventive. There are conflicting data regarding the mode of dopaminergic cell death in PD and, hence, this remains controversial. Several mutations in specific genes have recently been linked with hereditary forms of PD. Although none of these mutations are seen in idiopathic disease cases, the elucidation of these genetic defects sheds light on the nature of idiopathic PD. It is possible that dopaminergic neurogenesis also contributes to the etiology of idiopathic PD. In addition, intracellular as well as extracellular substances found in the SNc are believed to function as damaging pathogenetic factors. These factors, and the interactions among them, might hold the secret to the underlying causes of the selective death of dopaminergic neurons in PD.

Ectopic expression of cell cycle markers in models of induced programmed cell death in dopamine neurons of the rat substantia nigra pars compacta

There is increasing evidence that proteins normally involved in the cell cycle can regulate neuronal programmed cell death (PCD). However, it remains unknown whether cell cycle markers are expressed in normal, postmitotic, postmigratory neurons undergoing PCD in vivo. We have previously shown that natural cell death occurs postnatally in dopamine neurons of the substantia nigra pars compacta (SNpc). PCD can be induced postnatally in these neurons either by intrastriatal injection of the neurotoxin 6-hydroxydopamine (6-OHDA) or by medial forebrain bundle (MFB) axotomy. At the time of induction of death in these models, these neurons are long postmitotic and postmigratory. We have studied three cell cycle markers in these models: 5-bromo-2'-deoxyuridine (BrdU) incorporation (a marker of S phase), cdc2 protein expression (a marker of G2 phase), and expression of MPM2 (a marker of M phase), an epitope phosphorylated by cdc2. We report here that postmitotic dopaminergic neurons undergoing PCD in the SNpc following 6-OHDA and axotomy lesions incorporate BrdU and overexpress cdc2, but do not express MPM2. This is the first in vivo evidence that postmitotic dopamine neurons of the SNpc undergoing apoptosis express markers for S phase and G2 phase. These results raise the possibility that cell cycle regulatory proteins may play a role in the demise of dopaminergic neurons in Parkinson's disease, in which PCD has been postulated to play a role.

Comparison of calpain and caspase activities in the adult rat brain after transient forebrain ischemia

The role of calpain and caspase family proteases in postischemic neuronal death remains controversial. This study compared the timing, location, and relative activity of calpains and caspases in the adult rat brain following 10 min of transient forebrain ischemia. Western blots of cortical, striatal, and hippocampal homogenates demonstrated a alpha-spectrin cleavage pattern indicative of predominant calpain activity, which peaked between 24 and 48 h after reperfusion. However, immunohistochemical evidence of both caspase 3 activation and caspase-mediated substrate cleavage was detected as early as 1 h and as late as 7 days after reperfusion in circumscribed neuronal populations. Simultaneous or sequential caspase and calpain activation was also observed suggesting the potential for interaction of these protease systems. The complex spatiotemporal pattern of calpain and caspase activity observed in this study provides important insights for the development and evaluation of therapeutic strategies to reduce protease-mediated injury following global brain ischemia.

Medial forebrain bundle axotomy during development induces apoptosis in dopamine neurons of the substantia nigra and activation of caspases in their degenerating axons

There is growing evidence that programmed cell death may play a role in degenerative neurologic disease. The caspases are a family of cell death proteins that mediate proteolytic cascades in the death process. Although there is clear evidence that caspases play a role in the destruction of the components of the neuronal soma, it has been controversial whether they play a role in the degeneration of axons that accompanies the death of the cell body. It is important to define the molecular mechanisms of axonal degeneration, because terminal degeneration may occur early in neurodegenerative disease. We have therefore investigated whether caspases play a role in axonal degeneration in the dopaminergic nigrostriatal system following axotomy of the median forebrain bundle during development. We find that this lesion induces apoptosis in midbrain dopaminergic neurons at the level of the cell soma. Concomitantly with this induction of apoptosis, degeneration of dopaminergic axons occurs and is characterized by the formation of axonal swellings and spheroids. Immunohistochemical analysis reveals that the activated form of caspase-3 and a caspase cleavage product of beta-actin are abundantly expressed in these degenerating fibers. We conclude that caspases are activated in degenerating dopaminergic axons as the somata undergo programmed cell death in this model. These results raise the possibility that caspase activation may occur in other programmed cell death contexts for these neurons, and, if this is so, then their inhibition may be a useful therapeutic target.