Targeting programmed cell death in neurodegenerative diseases

Dopamine and adult neurogenesis

Dopamine is an important neurotransmitter implicated in the regulation of mood, motivation and movement. We have reviewed here recent data suggesting that dopamine, in addition to being a neurotransmitter, also plays a role in the regulation of endogenous neurogenesis in the adult mammalian brain. In addition, we approach a highly controversial question: can the adult human brain use neurogenesis to replace the dopaminergic neurones in the substantia nigra that are lost in Parkinson's disease?

Dissecting the signaling pathway of nicotine-mediated neuroprotection in a mouse Alzheimer disease model

Nicotine has a therapeutic benefit in treating Alzheimer's disease (AD). In the present study we show that nicotine decreases accumulation of beta-amyloid (Abeta) in the cortex and hippocampus of APP (V717I) transgenic mice. Nicotine prevents activation of NF-kappaB and c-Myc by inhibiting the activation of MAP kinases (MAPKs). As a result, the activity of inducible NOS and the production of NO are down-regulated. RNA interference experiments show that the above nicotine-mediated process requires alpha7 nAChR. Nicotine decreases Abeta via the activation of alpha7nAChRs through MAPK, NF-kappaB, and c-myc pathways. Nicotine also inhibits apoptosis and cell cycle progression in this mouse line. The dissected signaling pathway of nicotine-mediated neuroprotection in the present study provides a mechanistic basis for the potential development of drug targets for treating AD.

Neuronal life-and-death signaling, apoptosis, and neurodegenerative disorders

When subjected to excessive oxidative stress, neurons may respond adaptively to overcome the stress, or they may activate a programmed cell death pathway called apoptosis. Apoptosis is characterized by alterations in mitochondria and the endoplasmic reticulum and activation of cysteine proteases called caspases. Increasing evidence suggests that apoptotic biochemical cascades are involved in the dysfunction and death of neurons in neurodegenerative disorders such as Alzheimer's, Parkinson, and Huntington's diseases. Studies of normal aging, of genetic mutations that cause disease, and of environmental factors that affect disease risk are revealing cellular and molecular alterations that may cause excessive oxidative stress and trigger neuronal apoptosis. Accumulation of self-aggregating proteins such as amyloid beta-peptide, tau, alpha-synuclein, and huntingtin may be involved in apoptosis both upstream and downstream of oxidative stress. Membrane-associated oxidative stress resulting in perturbed lipid metabolism and disruption of cellular calcium homeostasis may trigger apoptosis in several different neurodegenerative disorders. Counteracting neurodegenerative processes are an array of mechanisms including neurotrophic factor signaling, antioxidant enzymes, protein chaperones, antiapoptotic proteins, and ionostatic systems. Emerging findings suggest that the resistance of neurons to death during aging can be enhanced by modifications of diet and lifestyle.

Recent clinical failures in Parkinson's disease with apoptosis inhibitors underline the need for a paradigm shift in drug discovery for neurodegenerative diseases

Understanding the mechanisms of neuronal death in concert with the identification of drugable molecular targets key to this process has held great promise for the development of novel chemical entities (NCEs) to halt neurodegenerative disease progression. Two key targets involved in the apoptotic process identified over the past decade include the mixed lineage kinase (MLK) family and glyceraldehyde phosphate dehydrogenase (GAPDH). Two NCEs, CEP-1347 and TCH346, directed against these respective targets have progressed to the clinic. For each, robust neuroprotective activity was demonstrated in multiple in vitro and in vivo models of neuronal cell death, but neither NCE proved effective Parkinson's disease (PD) patients. These recent clinical failures require a reassessment of both the relevance of apoptosis to neurodegenerative disease etiology and the available animal models used to prioritize NCEs for advancement to the clinic in this area.

Neuroanatomical phenotyping in the mouse: the dopaminergic system

Voluntary movement in animals is modulated by a number of subcortical systems. One of these resides in the basal nuclei and their associated projections and utilizes dopamine as a neurotransmitter. Apart from regulating movement, the dopaminergic axis is also involved in the control of goal-oriented behavior, cognition, and mood. Disorders of this system result in common human neurologic disorders such as Parkinson's and Huntington's diseases, as well contributing to a host of behavioral conditions, such as schizophrenia, attention deficit hyperactivity disorder, and addiction. Many individual mouse models of human dopaminergic dysfunction have been described in varying degrees of detail. However, when evaluating this region of the brain, the veterinary pathologist is confronted by a paucity of information summarizing the comparative aspects of the anatomy, physiology, and pathology of the central dopaminergic system. In this review, a systematic approach to anatomic phenotyping of the central dopaminergic system in the mouse is described and illustrated using tyrosine hydroxylase immunohistochemistry. Differences between murine neuroanatomy and comparable regions of the nonhuman primate brain are highlighted. Although the mouse is the focus of this review, conditions in domestic animals characterized by lesions within the basal nuclei and its projections are also briefly described. Murine behavioral and motor tests that accompany abnormalities of specific anatomic regions of the dopaminergic axis are summarized. Finally, we review mouse models of Parkinson's and Huntington's diseases, as well as those genetically altered mice that elucidate aspects of dopamine metabolism and receptor function.

Pathways of neurodegeneration and experimental models of basal ganglia disorders: downstream effects of mitochondrial inhibition

The basal ganglia circuit plays a key role in the regulation of voluntary movements as well as in behavioural control and cognitive functions. The main pathogenic role of mitochondrial dysfunctions is now accepted in the neurodegenerative process and the mitochondria have been successfully used as subcellular targets to obtain relevant experimental models of basal ganglia neurodegenerative disorders. Mitochondrial toxins act through an inhibition of the respiratory chain complexes. These toxins, by uncoupling cellular respiration, shift the cell into a state of oxidative stress and trigger several bidirectional links with the excitotoxic process. Moreover, the in vitro inhibition of the respiratory chain complexes alters the electrophysiological properties of the neurons. The downstream effects triggered by mitochondrial complexes inhibition provide a model integrating genetic and environmental pathogenic factors to explain the selective neuronal vulnerability.

Soluble oligomers of amyloid-beta peptide induce neuronal apoptosis by activating a cPLA2-dependent sphingomyelinase-ceramide pathway

Recent data have revealed that soluble oligomeric amyloid-beta peptide (Abeta) may be the proximate effectors of neuronal injuries and death in Alzheimer's disease (AD) by unknown mechanisms. Consistently, we recently demonstrated the critical role of a redox-sensitive cytosolic calcium-dependent phospholipase A2 (cPLA2)-arachidonic acid (AA) pathway in Abeta oligomer-induced cell death. According to the involvement of oxidative stress and polyunsaturated fatty acids like AA in the regulation of sphingomyelinase (SMase) activity, the present study underlines the role of SMases in soluble Abeta-induced apoptosis. Soluble Abeta oligomers induced the activation of both neutral and acidic SMases, as demonstrated by the direct measurement of their enzymatic activities, by the inhibitory effects of both specific neutral and acidic SMase inhibitors, and by gene knockdown using antisense oligonucleotides. Furthermore, soluble Abeta-mediated activation of SMases and subsequent cell death were found to be inhibited by antioxidant molecules and a cPLA2-specific inhibitor or antisense oligonucleotide. We also demonstrate that sphingosine-1-phosphate is a potent neuroprotective factor against soluble Abeta oligomer-induced cell death and apoptosis by inhibiting soluble Abeta-induced activation of acidic sphingomyelinase. These results suggest that Abeta oligomers induce neuronal death by activating neutral and acidic SMases in a redox-sensitive cPLA2-AA pathway.

Expanding insights of mitochondrial dysfunction in Parkinson's disease

The quest to disentangle the aetiopathogenesis of Parkinson's disease has been heavily influenced by the genes associated with the disease. The alpha-synuclein-centric theory of protein aggregation with the adjunct of parkin-driven proteasome deregulation has, in recent years, been complemented by the discovery and increasing knowledge of the functions of DJ1, PINK1 and OMI/HTRA2, which are all associated with the mitochondria and have been implicated in cellular protection against oxidative damage. We critically review how these genes fit into and enhance our understanding of the role of mitochondrial dysfunction in Parkinson's disease, and consider how oxidative stress might be a potential unifying factor in the aetiopathogenesis of the disease.

Targeted induction of apoptosis in cancer management: the emerging role of tumor necrosis factor-related apoptosis-inducing ligand receptor activating agents

Targeted induction of programmed cell death or apoptosis via the extrinsic apoptotic pathway represents an unexploited therapeutic strategy to destroy cancer cells. The activation of cell surface receptors by the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) results in direct stimulation of apoptotic signaling pathways (extrinsic stimulation). Molecules that directly activate these receptors, such as agonistic monoclonal antibodies to the TRAIL receptors and recombinant TRAIL, are being developed as monotherapies and as part of combination therapies with existing chemotherapeutic drugs and other therapeutic modalities. This article examines the TRAIL receptors as potential targets for activating the TRAIL-mediated apoptosis pathway and presents the current status of novel therapeutics that exploit this pathway, particularly focusing on agonistic monoclonal antibodies to the TRAIL receptors. The preclinical activity, the status of ongoing evaluations, and the potential clinical impact of these novel agents are reviewed.

Does levodopa slow or hasten the rate of progression of Parkinson's disease?

Levodopa therapy, as originally established by George Cotzias [2, 3], is the most powerful treatment for Parkinson's disease (PD). Levodopa's toxicity to neurons in vitro has raised concerns if it might hasten the progression of PD, although in vivo animal studies suggest it may be neuroprotective.

OBJECTIVE

To discuss the results of the ELLDOPA trial that was carried out to determine if levodopa therapy influences the rate of progression of Parkinson's disease (PD).

DESIGN

ELLDOPA was a multicenter, parallel-group, double-blind, dosage-ranging, randomized, controlled clinical trial.

SETTING

Academic movement disorders clinics at 38 sites in the United States and Canada.

PATIENTS

Three hundred and sixty-one patients with early PD of less than 2 years' duration who did not require symptomatic therapy.

INTERVENTIONS

Subjects were randomly assigned to one of four treatment groups: carbidopa/levodopa 12.5/50 mg t. i. d. (N=92), 25/100 mg t. i. d. (N=88), 50/200 mg t. i. d. (N=91), or matching placebo (N=90). The dosage was gradually escalated over 9 weeks and then maintained until Week 40, at which time active treatment was withdrawn over 3 days. After 2 weeks without active treatment (Week 42), a final assessment of PD severity was obtained.

OUTCOME MEASURES

The prespecified primary clinical outcome was the change in the total Unified Parkinson's Disease Rating Scale (UPDRS) between baseline and Week 42, comparing the four treatment groups. The primary neuroimaging component of the study in a subgroup of 142 subjects was the percent change in striatal (123)iodine 2-beta-carboxymethoxy-3-beta-(4-iodophe nyl)tropane (beta-CIT) uptake between baseline and Week 40 visits. The neuroimaging substudy utilized single photon emission computed tomography (SPECT) of the dopamine transporter.

RESULTS

All dosages of levodopa exerted clinical benefit compared to placebo on the UPDRS scores throughout the study, including 2 weeks after discontinuing levodopa. The UPDRS scores at Week 42 failed to reach the level encountered in the placebo group (change of 7.8+/-9.0, 1.9+/-6.0, 1.9+/-6.9, and -1.4+/-7.8, for placebo, 150 mg/day, 300 mg/ day, and 600 mg/day, respectively, p<0.0001). Nausea (p=0.001) and dyskinesias (p=0.0001) were more common in the levodopa groups, especially with the higher dosages. Freezing appeared around the same time, but was more common in the placebo (14 %) and 150 mg/day group (10 %). The percent decline of beta-CIT uptake in the striatum was significantly more pronounced in the levodopa groups than the placebo group (-7.2%, -4%, -6%, and -1.4% in 600 mg/day, 300 mg/day, 150 mg/day, and placebo, respectively; p=0.035).

CONCLUSIONS

The clinical outcomes not only indicate that levodopa is effective in a dose-dependent manner in overcoming the signs and symptoms of PD, they also support the concept that the drug does not hasten the disease progression, but rather may slow down the rate of the disease. The clinical study failed to demonstrate any evidence of levodopa worsening early PD. However, the beta-CIT SPECT substudy indicates the opposite effect, namely that levodopa causes a more rapid decline in the integrity of the dopamine transporter located in the nigrostriatal nerve terminals in the striatum. These contradictory findings warrant further investigation into the effect of levodopa on PD. OTHER OBSERVATIONS: The ELLDOPA study was the first levodopa dose-response study ever conducted. It showed that dose is a factor in the cause of producing motor complications of dyskinesias and wearing-off, and that these can develop as early as 5 to 6 months. On the other hand, freezing of gait could be delayed or its occurrence reduced by high dosage levodopa, compared to placebo or low-dose levodopa. Withdrawal of levodopa over a 3-day step-down can be safely carried out without inducing the neuroleptic-like syndrome. The UPDRS was shown to be a reliable linear marker for disease progression. The ELLDOPA study also called into question the interpretation of beta-CIT SPECT in the presence of dopaminergic agents. Neuroimaging in ELLDOPA also showed that some people diagnosed with early PD do not have a dopaminergic deficit, calling into question how difficult the correct diagnosis may be in people with early symptoms of PD.

Neurotropism and neuropathological effects of selected rhabdoviruses on intranasally-infected newborn mice

Viral neurotropism is the ability of viruses to infect neuronal cells. This is well studied for herpesviruses, rabies-related viruses, and a few others, but it is poorly investigated among almost all arboviruses. In this study, we describe both the neurotropism and the neuropathological effects of Amazonian rhabdoviruses on the brains of experimentally infected-newborn mice. Suckling mice were intranasally infected with 10(-4) to 10(-8) LD50 of viruses. Animals were anaesthetized and perfused after they had become sick. Immunohistochemistry using specific anti-virus and anti-active caspase three antibodies was performed. All infected animals developed fatal encephalitis. Survival time ranged from 18 h to 15 days. Viruses presented distinct species-dependent neurotropism for CNS regions. Histopathological analysis revealed variable degrees of necrosis and apoptosis in different brain regions. These results showed that viruses belonging to the Rhabdoviridae family possess distinct tropism for CNS structures and induce different pattern of cell death depending on the CNS region.

Beneficial effects of melatonin in experimental models of Alzheimer disease

Alzheimer's disease (AD), a progressive degenerative disorder, is characterized by the presence of amyloid deposits, neurofibrillary tangles and neuron loss. Emerging evidence indicates that antioxidants could be useful either for the prevention or treatment of AD. It has been shown that melatonin is a potent antioxidant and free radical scavenger. Additionally, melatonin stimulates several antioxidative enzymes and improves mitochondrial energy metabolism. These findings led us to study amyloid precursor protein transgenic mice, ovariectomized rats, and pheochromocytoma and astroglioma cell lines, to observe whether melatonin had any effect on Alzheimer's symptoms or pathological changes. We found that melatonin had many beneficial effects in experimental models of AD, including improvement of cognitive function, anti-oxidative injury, anti-apoptosis, inhibition of beta-amyloid (Abeta) deposition and Abeta fiber formation. Several groups have shown that melatonin has an inhibitory effect on tau protein hyperphosphorylation. These actions may potentially slow down or stop the progression of dementia.

Compounds blocking mutant huntingtin toxicity identified using a Huntington's disease neuronal cell model

Neuronal cell death in HD is believed to be largely a dominant cell-autonomous effect of the mutant huntingtin protein. We previously developed an inducible PC12 cell model which expresses an N-terminal huntingtin fragment with an expanded poly Q repeat (N63-148Q) under the control of the tet-off system. In order to evaluate the ability of compounds to protect against mutant huntingtin toxicity in our model, we measured LDH released by dead cells into the medium. We have now screened the library of 1040 compounds from the NINDS Custom Collection as part of a National Institute of Neurological Disorders and Stroke (NINDS) collaborative project. Each positive compound was tested at 3-8 concentrations. Five compounds significantly attenuated mutant huntingtin (htt)-induced LDH release without affecting the expression level of huntingtin and independent of effect on aggregates. We also tested a broad spectrum caspase inhibitor Z-VAD-fmk and previously proposed candidate compounds. This cell model can provide a method to screen potential therapeutic compounds for treating Huntington's disease.

Early melatonin supplementation alleviates oxidative stress in a transgenic mouse model of Alzheimer's disease

Multiple lines of evidence demonstrated that increased brain oxidative stress is a key feature of Alzheimer's disease (AD). Melatonin is a potent endogenous antioxidant and free radical scavenger. A transgenic mouse model for AD mimics the accumulation of senile plaques, neuronal loss, and memory impairment. Four-month-old transgenic mice were administrated melatonin at 10 mg/kg for 4 months. We investigated the long-term influence of melatonin on these mice before amyloid plaques were deposited. We found an increase in the levels of brain thiobarbituric acid-reactive substances (TBARS) and a decrease in glutathione (GSH) content, as well as accelerated upregulation of the apoptotic-related factors, such as Bax, caspase-3, and prostate apoptosis response-4 (Par-4) in transgenic mice, but not in wild-type (WT) littermates. Significantly, the increase in TBARS levels, reduction in superoxide dismutase activity, and GSH content were reinstated by melatonin. In addition, transgenic mice administered melatonin (10 mg/kg) showed a significant reduction in upregulated expression of Bax, caspase-3 and Par-4, indicating inhibited triggering of neuronal apoptosis. These results supported the hypothesis that oxidative stress was an early event in AD pathogenesis and that antioxidant therapy may be beneficial only if given at this stage of the disease process. In sharp contrast to conventional antioxidants, melatonin crosses the blood-brain barrier, is relatively devoid of toxicity, and constitutes a potential therapeutic candidate in AD treatment.

Complex I deficiency primes Bax-dependent neuronal apoptosis through mitochondrial oxidative damage

Dysfunction of mitochondrial complex I is a feature of human neurodegenerative diseases such as Leber hereditary optic neuropathy and Parkinson's disease. This mitochondrial defect is associated with a recruitment of the mitochondrial-dependent apoptotic pathway in vivo. However, in isolated brain mitochondria, complex I dysfunction caused by either pharmacological or genetic means fails to directly activate this cell death pathway. Instead, deficits of complex I stimulate intramitochondrial oxidative stress, which, in turn, increase the releasable soluble pool of cytochrome c within the mitochondrial intermembrane space. Upon mitochondrial permeabilization by the cell death agonist Bax, more cytochrome c is released to the cytosol from brain mitochondria with impaired complex I activity. Given these results, we propose a model in which defects of complex I lower the threshold for activation of mitochondrial-dependent apoptosis by Bax, thereby rendering compromised neurons more prone to degenerate. This molecular scenario may have far-reaching implications for the development of effective neuroprotective therapies for these incurable illnesses.

The neuroprotective action of JNK3 inhibitors based on the 6,7-dihydro-5H-pyrrolo[1,2-a]imidazole scaffold

Imidazole-based structures of p38 inhibitors served as a starting point for the design of JNK3 inhibitors. Construction of a 6,7-dihydro-5H-pyrrolo[1,2-a]imidazole scaffold led to the synthesis of the (S)-enantiomers, which exhibited p38/JNK3 IC50 ratio of up to 10 and were up to 20 times more potent inhibitors of JNK3 than the relevant (R)-enantiomers. The JNK3 inhibitory potency correlated well with inhibition of c-Jun phosphorylation and neuroprotective properties of the compounds in low K+-induced cell death of rat cerebellar granule neurones.

Drosophila DJ-1 mutants show oxidative stress-sensitive locomotive dysfunction

DJ-1 is linked to an early-onset autosomal recessive Parkinson's disease (PD) characterized primarily by selective loss of dopaminergic (DA) neurons, which results in motor disturbances. However, our understanding on how mutations in DJ-1 are related to PD is unclear. Here, we isolated the DJ-1 orthologue, DJ-1beta, in Drosophila and characterized its expression and loss-of-function mutants. We observed its strongest expression in the adult stage of development and ubiquitous expression in the larval brain. Our homozygous mutants showed severe defects in locomotor ability without loss of DA neurons, consistent with the previous mice DJ-1 mutant studies ([Goldberg, M.S., Pisani, A., Haburcak, M., Vortherms, T.A., Kitada, T., Costa, C., Tong, Y., Martella, G., Tscherter, A., Martins, A., et al., 2005. Nigrostriatal dopaminergic deficits and hypokinesia caused by inactivation of the familial Parkinsonism-linked gene DJ-1. Neuron 45, 489-496.]; [Kim, R.H., Smith, P.D., Aleyasin, H., Hayley, S., Mount, M.P., Pownall, S., Wakeham, A., You-Ten, A.J., Kalia, S.K., Horne, P., Westaway, D., Lozano, A.M., Anisman, H., Park, D.S., Mak, T.W., 2005. Hypersensitivity of DJ-1-deficient mice to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and oxidative stress. Proc. Natl. Acad. Sci. USA 102, 5215-5220.]; [Chen, L., Cagniard, B., Mathews, T., Jones, S., Koh, H.C., Ding, Y., Carvey, P.M., Ling, Z., Kang, U.J., Zhuang, X., 2005. Age-dependent motor deficits and dopaminergic dysfunction in DJ-1 null mice. J. Biol. Chem. 280, 21418-21426.]). The locomotor activity of DJ-1beta mutants was further decreased by paraquat-induced oxidative stress. Moreover, we found that Drosophila DJ-1 is prominently localized in mitochondria, suggesting that DJ-1 functions as a protector against oxidative stress in mitochondria.

Inhibitory effect of ganglioside GD1b on K+ current in hippocampal neurons and its involvement in apoptosis suppression

Gangliosides are endogenous membrane components enriched in neuronal cells. They have been shown to play regulatory roles in many cellular processes. Here, we show for the first time that ganglioside GD1b plays an antiapoptotic role in cultured hippocampal neurons. GD1b inhibited the voltage-dependent outward delayed rectifier current (I(K)) but not the transient outward A-type current in a dose-dependent manner, with an IC50 value of 15.2 microM. This effect appears to be somehow specific, because GD1b, but not GM1, GM2, GM3, GD1a, GD3, or GT1b, was effective in inhibiting I(K). Intracellular application of staurosporine (STS; 0.1 microM) resulted in rapid activation of I(K), which was partially reversed upon addition of the K+ channel blocker tetraethylammonium (TEA; 5 mM) and GD1b (10 microM). Furthermore, GD1b (10 microM) attenuated STS-induced neuronal apoptosis by nearly the same amount as 5 mM TEA. In addition, GD1b suppressed the apoptosis-associated caspase 3 activation that was activated by STS. Collectively, these findings suggest that GD1b plays an antiapoptotic role in cultured hippocampal neurons through its inhibitory effect on the I(K) and caspase activity.

No widespread induction of cell death genes occurs in pure motoneurons in an amyotrophic lateral sclerosis mouse model

To identify candidate genes that may be involved in motoneuron degeneration, we combined laser capture microdissection with microarray technology. Gene expression in motoneurons was analyzed during the progression of the disease in transgenic SOD1(G93A) mice that develop motoneuron loss. Three major observations were made: first, there was only a small number of genes that were differentially expressed in motoneurons at a pre-symptomatic age (27 out of 34 000 transcripts). Secondly, there is an early specific up-regulation of the gene coding for the intermediate filament vimentin that is increased even further during disease progression. Using in situ hybridization and immunohistochemical analysis, we show that vimentin expression was not only elevated in motoneurons but that the protein formed inclusions in the motoneuron cytoplasm. Thirdly, a time-course analysis of the motoneurons at a symptomatic age (90 and 120 days) showed a modest de-regulation of only a few genes associated with cell death pathways; however, a massive up-regulation of genes involved in cell growth and/or maintenance was observed. This is the first description of the gene profile of SOD1(G93A) motoneurons during disease progression and unexpectedly, no widespread induction of cell death-associated genes was detected in motoneurons of SOD1(G93A) mice.

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.

Defective Fas expression exacerbates neurotoxicity in a model of Parkinson's disease

Fas (CD95), a member of the tumor necrosis factor-receptor superfamily, has been studied extensively as a death-inducing receptor in the immune system. However, Fas is also widely expressed in a number of other tissues, including in neurons. Here, we report that defects in the Fas/Fas ligand system unexpectedly render mice highly susceptible to neural degeneration in a model of Parkinson's disease. We found that Fas-deficient lymphoproliferative mice develop a dramatic phenotype resembling clinical Parkinson's disease, characterized by extensive nigrostriatal degeneration accompanied by tremor, hypokinesia, and loss of motor coordination, when treated with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at a dose that causes no neural degeneration or behavioral impairment in WT mice. Mice with generalized lymphoproliferative disease, which express a mutated Fas ligand, display an intermediate phenotype between that of lymphoproliferative and WT mice. Moreover, Fas engagement directly protects neuronal cells from MPTP/1-methyl-4-phenylpyridinium ion toxicity in vitro. Our data show that decreased Fas expression renders dopaminergic neurons highly susceptible to degeneration in response to a Parkinson-causing neurotoxin. These findings constitute the first evidence for a neuroprotective role for Fas in vivo.

Genetic dissection of neurodegeneration and CNS inflammation

Inflammation and neurodegeneration characterize multiple sclerosis, as well as many other diseases of the central nervous system (CNS). The understanding of the molecular pathways that regulate these processes is of fundamental importance for the development of new therapies. Nerve lesions paradigms in animals can serve as important tools to dissect central features of human CNS disease and by using these models certain key regulators have also been identified. However, our knowledge of how aspects of neurodegeneration and CNS inflammation are regulated on a genomic level is very limited. Such knowledge may help to unravel disease mechanisms. By using a standardized nerve trauma model, ventral root avulsion (VRA), in a series of inbred rat strains we here demonstrate a potent genetic regulation of the degree of neuron death and glial activation. Genome wide mapping of these phenotypes in experimental rat strain crosses identifies several quantitative trait loci (QTLs) controlling nerve lesion-induced nerve cell death, local T cell accumulation and expression of MHC class II on microglia. This approach may lead to the identification of evolutionary conserved genetic polymorphisms in key controlling genes, which can serve as prime candidates for association studies in several human CNS diseases.

Pathogenesis of nigral cell death in Parkinson's disease

Parkinson's disease (PD) is primarily a sporadic condition which results mainly from the death of dopaminergic neurons in the substantia nigra. Its etiology remains enigmatic while its pathogenesis begins to be understood as a multifactorial cascade of deleterious factors. As of yet, most insights into PD pathogenesis are derived from toxic models of PD and show that the earlier cellular perturbations arising in dopaminergic neurons include oxidative stress and energy crisis. These alterations, rather than killing neurons, trigger subsequent death-related molecular pathways including elements of apoptosis. The fate of dopaminergic neurons in PD may also be influenced by additional factors such as excitotoxicity, emanating from the increased glutamatergic input from the subthalamic nucleus to the substantia nigra, and the glial response that arises in the striatum and the substantia nigra. In rare instances, PD can be familial, and those genetic forms have also provided clues to the pathogenesis of nigrostriatal dopaminergic neuron death including abnormalities in the mechanisms of protein folding and degradation as well as mitochondrial function. Although more remains to be elucidated about the pathogenic cascade in PD, the compilation of all of the aforementioned alterations starts to shed light on why and how nigral dopaminergic neurons may degenerate in this prominent disease, that is PD.

The generation of dopaminergic neurons by human neural stem cells is enhanced by Bcl-XL, both in vitro and in vivo

Progress in stem cell biology research is enhancing our ability to generate specific neuron types for basic and applied studies and to design new treatments for neurodegenerative diseases. In the case of Parkinson's disease (PD), alternative human dopaminergic (DAergic) neurons other than primary fetal tissue do not yet exist. One possible source could be human neural stem cells (hNSCs), although the yield in DAergic neurons and their survival are very limited. [see figure]. In this study, we found that Bcl-X(L) enhances (one-to-two orders of magnitude) the capacity for spontaneous dopaminergic differentiation of hNSCs, which then exceeds that of cultured human ventral mesencephalic tissue. Bcl-X(L) also enhanced total neuron generation by hNSCs, but to a lower extent. Neuronal phenotypes other than DA were not affected by Bcl-X(L), indicating an exquisitely specific effect on DAergic neurons. In vivo, grafts of Bcl-X(L)-overexpressing hNSCs do generate surviving human TH+ neurons in the adult rat 6-OH-dopamine lesioned striatum, something never seen when naive hNSCs were transplanted. Most of the data obtained here in terms of the effects of Bcl-X(L) are consistent with an enhanced survival type of mechanism and not supportive of induction, specification, or proliferation of DAergic precursors. From this in vitro and in vivo evidence, we conclude that enhancing Bcl-X(L) expression is important to obtain human DAergic neurons from hNSCs. These findings may facilitate the development of drug-screening and cell-replacement activities to discover new therapeutic strategies for PD.

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.

Application of a systems biology approach to developmental neurotoxicology

Systems biology can be applied to enhance the understanding of complex biological processes such as apoptosis in the developing brain. Systems biology, as applied to toxicology, provides a structure to arrange information in the form of a biological model. The approach allows for the subsequent and iterative perturbation of the initial model with the use of toxicants, and the comparison of the resulting data against the proposed biological model. It is postulated that the exposure of the developing rat to NMDA antagonists, e.g., ketamine or phencyclidine (PCP), causes a compensatory up-regulation of NMDA receptors, thereby making cells bearing these receptors more vulnerable to excitotoxic effects of endogenous glutamate. Although comprehensive gene expression/proteomic studies and mathematical modeling remain to be accomplished, a biological model has been established and perturbed in an iterative manner to allow confirmation of the biological pathway for NMDA antagonist-induced brain cell death in the developing rat.

Glycogen synthase kinase-3beta phosphorylates Bax and promotes its mitochondrial localization during neuronal apoptosis

Glycogen synthase kinase-3beta (GSK-3beta) is a critical activator of neuronal apoptosis induced by a diverse array of neurotoxic insults. However, the downstream substrates of GSK-3beta that ultimately induce neuronal death are unknown. Here, we show that GSK-3beta phosphorylates and regulates the activity of Bax, a pro-apoptotic Bcl-2 family member that stimulates the intrinsic (mitochondrial) death pathway by eliciting cytochrome c release from mitochondria. In cerebellar granule neurons undergoing apoptosis, inhibition of GSK-3beta suppressed both the mitochondrial translocation of an expressed green fluorescent protein (GFP)-Bax(alpha) fusion protein and the conformational activation of endogenous Bax. GSK-3beta directly phosphorylated Bax(alpha) on Ser163, a residue found within a species-conserved, putative GSK-3beta phosphorylation motif. Coexpression of GFP-Bax(alpha) with a constitutively active mutant of GSK-3beta, GSK-3beta(Ser9Ala), enhanced the in vivo phosphorylation of wild-type Bax(alpha), but not a Ser163Ala mutant of Bax(alpha), in transfected human embryonic kidney 293 (HEK293) cells. Moreover, cotransfection with constitutively active GSK-3beta promoted the localization of Bax(alpha) to mitochondria and induced apoptosis in both transfected HEK293 cells and cerebellar granule neurons. In contrast, neither a Ser163Ala point mutant of Bax(alpha) nor a naturally occurring splice variant that lacks 13 amino acids encompassing Ser163 (Bax(sigma)) were driven to mitochondria in HEK293 cells coexpressing constitutively active GSK-3beta. In a similar manner, either mutation or deletion of the identified GSK-3beta phosphorylation motif prevented the localization of Bax to mitochondria in cerebellar granule neurons undergoing apoptosis. Our results indicate that GSK-3beta exerts some of its pro-apoptotic effects in neurons by regulating the mitochondrial localization of Bax, a key component of the intrinsic apoptotic cascade.

Mitochondrial localization of the Parkinson's disease related protein DJ-1: implications for pathogenesis

Both homozygous (L166P, M26I, deletion) and heterozygous mutations (D149A, A104T) in the DJ-1 gene have been identified in Parkinson's disease (PD) patients. The biochemical function and subcellular localization of DJ-1 protein have not been clarified. To date the localization of DJ-1 protein has largely been described in studies over-expressing tagged DJ-1 protein in vitro. It is not known whether the subcellular localization of over-expressed DJ-1 protein is identical to that of endogenously expressed DJ-1 protein both in vitro and in vivo. To clarify the subcellular localization and function of DJ-1, we generated three highly specific antibodies to DJ-1 protein and investigated the subcellular localization of endogenous DJ-1 protein in both mouse brain tissues and human neuroblastoma cells. We have found that DJ-1 is widely distributed and is highly expressed in the brain. By cell fractionation and immunogold electron microscopy, we have identified an endogenous pool of DJ-1 in mitochondrial matrix and inter-membrane space. To further investigate whether pathogenic mutations might prevent the distribution of DJ-1 to mitochondria, we generated human neuroblastoma cells stably transfected with wild-type (WT) or mutant (M26I, L166P, A104T, D149A) DJ-1 and performed mitochondrial fractionation and confocal co-localization imaging studies. When compared with WT and other mutants, L166P mutant exhibits largely reduced protein level. However, the pathogenic mutations do not alter the distribution of DJ-1 to mitochondria. Thus, DJ-1 is an integral mitochondrial protein that may have important functions in regulating mitochondrial physiology. Our findings of DJ-1's mitochondrial localization may have important implications for understanding the pathogenesis of PD.

Malonate induces cell death via mitochondrial potential collapse and delayed swelling through an ROS-dependent pathway

1. Herein we study the effects of the mitochondrial complex II inhibitor malonate on its primary target, the mitochondrion. 2. Malonate induces mitochondrial potential collapse, mitochondrial swelling, cytochrome c (Cyt c) release and depletes glutathione (GSH) and nicotinamide adenine dinucleotide coenzyme (NAD(P)H) stores in brain-isolated mitochondria. 3. Although, mitochondrial potential collapse was almost immediate after malonate addition, mitochondrial swelling was not evident before 15 min of drug presence. This latter effect was blocked by cyclosporin A (CSA), Ruthenium Red (RR), magnesium, catalase, GSH and vitamin E. 4. Malonate added to SH-SY5Y cell cultures produced a marked loss of cell viability together with the release of Cyt c and depletion of GSH and NAD(P)H concentrations. All these effects were not apparent in SH-SY5Y cells overexpressing Bcl-xL. 5. When GSH concentrations were lowered with buthionine sulphoximine, cytoprotection afforded by Bcl-xL overexpression was not evident anymore. 6. Taken together, all these data suggest that malonate causes a rapid mitochondrial potential collapse and reactive oxygen species production that overwhelms mitochondrial antioxidant capacity and leads to mitochondrial swelling. Further permeability transition pore opening and the subsequent release of proapoptotic factors such as Cyt c could therefore be, at least in part, responsible for malonate-induced toxicity.

Heterogeneous cellular environments modulate one-hit neuronal death kinetics

We recently demonstrated that cell loss kinetics in diverse forms of neurodegeneration (ND) suggests a universal death switch mechanism in which each cell is at a constant risk to initiate apoptosis. We proposed that mutant and injured neurons exist in a viable state typified by an increased risk of initiating death processes [Clarke, Collins, Leavitt, Andrews, Hayden, Lumsden, McInnes, A one-hit model of cell death in inherited neuronal degenerations, Nature 406 (2000) 195-199]. To date, however, measurements of cell death risk have been available only as averages across the affected cell population. Here we develop and apply a method of death kinetic analysis in which the risk factors vary across the neuronal population, as for example due to regional heterogeneities in the cellular microenvironment. We find that most cases of ND for which cell loss data has been obtained are better explained by death risks that vary from cell to cell, compared to death risk that is constant across the neuronal population. Strikingly, a common form of the frequency distribution defining the death risk heterogeneity is shared across most of these cases. This first characterization of the kinetic heterogeneity in one-hit neuronal death, therefore, suggests that the wide variety of ND now known may share mechanisms through which regional differences in the cellular microenvironment modulate the kinetics of cell loss.

N-Propargylamine protects SH-SY5Y cells from apoptosis induced by an endogenous neurotoxin, N-methyl(R)salsolinol, through stabilization of mitochondrial membrane and induction of anti-apoptotic Bcl-2

Propargylamine derivatives, rasagiline and (-)deprenyl, are anti-Parkinson agents and protect neurons from cell death as shown by in vivo and in vitro experiments. The studies on the chemical structure-activity relationship proved that the propargyl moiety is essentially required for the neuroprotective function. In this paper, neuroprotective activity of free N-propargylamine was studied using SH-SY5Y cells expressing only type A monoamine oxidase (MAO) against apoptosis induced by an endogenous dopaminergic neurotoxin, N-methyl(R)salsolinol. N-Propargylamine prevented apoptosis, whereas N-methylpropargylamine and propiolaldehyde did not. N-Propargylamine stabilized mitochondrial membrane potential and induced anti-apoptotic Bcl-2 at 1 microM-10 nM. N-Propargylamine inhibited MAO-A in competition to substrate with the apparent K(i) value of 28 microM, which was significantly higher than the concentration required for neuroprotection. It indicates that MAO inhibition is not prerequisite for the protective function of N-propargylamine. The anti-apoptotic function of N-propargylamine is discussed in terms of neuroprotection by propargylamines in neurodegenerative diseases, including Parkinson's disease.

The Charcot-Marie-Tooth type 2A gene product, Mfn2, up-regulates fuel oxidation through expression of OXPHOS system

Mitofusin-2 (Mfn2) is a mitochondrial membrane protein that participates in mitochondrial fusion in mammalian cells and mutations in the Mfn2 gene cause Charcot-Marie-Tooth neuropathy type 2A. Here, we show that Mfn2 loss-of-function inhibits pyruvate, glucose and fatty acid oxidation and reduces mitochondrial membrane potential, whereas Mfn2 gain-of-function increases glucose oxidation and mitochondrial membrane potential. As to the mechanisms involved, we have found that Mfn2 loss-of-function represses nuclear-encoded subunits of OXPHOS complexes I, II, III and V, whereas Mfn2 overexpression induced the subunits of complexes I, IV and V. Obesity-induced Mfn2 deficiency in rat skeletal muscle was also associated with a decrease in the subunits of complexes I, II, III and V. In addition, the effect of Mfn2 overexpression on mitochondrial metabolism was mimicked by a truncated Mfn2 mutant that is inactive as a mitochondrial fusion protein. Our results indicate that Mfn2 triggers mitochondrial energization, at least in part, by regulating OXPHOS expression through signals that are independent of its role as a mitochondrial fusion protein.

Cobalamin (vitamin B12) in subacute combined degeneration and beyond: traditional interpretations and novel theories

Subacute combined degeneration (SCD) is a neuropathy due to cobalamin (Cbl) (vitamin B(12)) deficiency acquired in adult age. Hitherto, the theories advanced to explain the pathogenesis of SCD have postulated a causal relationship between SCD lesions and the impairment of either or both of two Cbl-dependent reactions. We have identified a new experimental model, the totally gastrectomized rat, to reproduce the key morphological features of the disease [spongy vacuolation, intramyelinic and interstitial edema of the white matter of the central nervous system (CNS), and astrogliosis], and found new mechanisms responsible for the pathogenesis of SCD: the neuropathological lesions in TGX rats are not only due to mere vitamin withdrawal but also to the overproduction of the myelinolytic tumor necrosis factor (TNF)-alpha and the reduced synthesis of the two neurotrophic agents, epidermal growth factor (EGF) and interleukin-6. This deregulation of the balance between TNF-alpha and EGF synthesis induced by Cbl deficiency has been verified in the sera of patients with pernicious anemia (but not in those with iron-deficient anemia), and in the cerebrospinal fluid (CSF) of SCD patients. These new functions are not linked to the coenzyme functions of the vitamin, but it is still unknown whether they involve genetic or epigenetic mechanisms. Low Cbl levels have also been repeatedly observed in the sera and/or CSF of patients with Alzheimer's disease or multiple sclerosis, but whether Cbl deficit plays a role in the pathogenesis of these diseases is still unclear.

Dopamine-derived Dopaminochrome Promotes H2O2 Release at Mitochondrial Complex I

Inhibitors of Complex I of the mitochondrial respiratory chain, such as rotenone, promote Parkinson disease-like symptoms and signs of oxidative stress. Dopamine (DA) oxidation products may be implicated in such a process. We show here that the o-quinone dopaminochrome (DACHR), a relatively stable DA oxidation product, promotes concentration (0.1-0.2 mum)- and respiration-dependent generation of H(2)O(2) at Complex I in brain mitochondria, with further stimulation by low concentrations of rotenone (5-30 nm). The rotenone effect required that contaminating Ca(2+) (8-10 mum) was not removed. DACHR apparently extracts an electron from the constitutively autoxidizable site in Complex I, producing a semiquinone, which then transfers an electron to O(2), generating O(2)(.) and then H(2)O(2). Mitochondrial removal of H(2)O(2) monoamine, formed by either oxidase activity or DACHR, was performed largely by glutathione peroxidase and glutathione reductase, which were negatively regulated by low intramitochondrial Ca(2+) levels. Thus, the H(2)O(2) formed accumulated in the medium if contaminating Ca(2+) was present; in the absence of Ca(2+), H(2)O(2) was completely removed if it originated from monoamine oxidase, but was less completely removed if it originated from DACHR. We propose that the primary action of rotenone is to promote extracellular O(2)(.) release via activation of NADPH oxidase in the microglia. In turn, O(2)(.) oxidizes DA to DACHR extracellularly. (The reaction is favored by the lack of GSH, which would otherwise preferably produce GSH adducts of dopaminoquinone.) Once formed, DACHR (which is resistant to GSH) enters neurons to activate the rotenone-stimulated redox cycle described.

Lentiviral-mediated silencing of SOD1 through RNA interference retards disease onset and progression in a mouse model of ALS

Mutations in Cu/Zn superoxide dismutase (encoded by SOD1), one of the causes of familial amyotrophic lateral sclerosis (ALS), lead to progressive death of motoneurons through a gain-of-function mechanism. RNA interference (RNAi) mediated by viral vectors allows for long-term reduction in gene expression and represents an attractive therapeutic approach for genetic diseases characterized by acquired toxic properties. We report that in SOD1(G93A) transgenic mice, a model for familial ALS, intraspinal injection of a lentiviral vector that produces RNAi-mediated silencing of SOD1 substantially retards both the onset and the progression rate of the disease.

Inhibition of neuronal apoptosis by the cyclin‐dependent kinase inhibitor GW8510: Identification of 3′ substituted indolones as a scaffold for the development of neuroprotective drugs

Increasing evidence suggests that neuronal apoptosis is triggered by the inappropriate activation of cyclin-dependent kinases leading to an abortive re-entry of neurons into the cell cycle. Pharmacological inhibitors of cell-cycle progression may therefore have value in the treatment of neurodegenerative diseases in humans. GW8510 is a 3' substituted indolone that was developed recently as an inhibitor of cyclin-dependent kinase 2 (CDK2). We found that GW8510 inhibits the death of cerebellar granule neurons caused by switching them from high potassium (HK) medium to low potassium (LK) medium. Although GW8510 inhibits CDK2 and other CDKs when tested in in vitro biochemical assays, when used on cultured neurons it only inhibits CDK5, a cytoplasmic CDK that is not associated with cell-cycle progression. Treatment of cultured HEK293T cells with GW8510 does not inhibit cell-cycle progression, consistent with its inability to inhibit mitotic CDKs in intact cells. Neuroprotection by GW8510 is independent of Akt and MEK-ERK signaling. Furthermore, GW8510 does not block the LK-induced activation of Gsk3beta and, while inhibiting c-jun phosphorylation, does not inhibit the increase in c-jun expression observed in apoptotic neurons. We also examined the effectiveness of other 3' substituted indolone compounds to protect against neuronal apoptosis. We found that like GW8510, the VEGF Receptor 2 Kinase Inhibitors [3-(1H-pyrrol-2-ylmethylene)-1,3-dihydroindol-2-one], {(Z)-3-[2,4-Dimethyl-3-(ethoxycarbonyl)pyrrol-5-yl)methylidenyl]indol-2-one} and [(Z)-5-Bromo-3-(4,5,6,6-tetrahydro-1H-indol-2-ylmethylene)-1,3-dihydroindol-2-one], the Src family kinase inhibitor SU6656 and a commercially available inactive structural analog of an RNA-dependent protein kinase inhibitor 5-Chloro-3-(3,5-dichloro-4-hydroxybenzylidene)-1,3-dihydro-indol-2-one, are all neuroprotective when tested on LK-treated neurons. Along with our recent identification of the c-Raf inhibitor GW5074 (also a 3' substituted indolone) as a neuroprotective compound, our findings identify the 3' substituted indolone as a core structure for the designing of neuroprotective drugs that may be used to treat neurodegenerative diseases in humans.

Widespread γ-secretase activity in the cell, but do we need it at the mitochondria?

gamma-Secretase cleavage of the amyloid precursor protein already subjected to a prior beta-secretase cleavage generates beta-amyloid (Abeta) peptide fragments, which are major constituents of the amyloid plagues found in Alzheimer's disease brain tissues. gamma-Secretase activity and components of the gamma-secretase complex are found in the endoplasmic reticulum-Golgi intermediate compartment, the Golgi, the trans-Golgi network, the plasma membrane, the endosomal-lysosomal system and recently, the mitochondria. Abeta fragments have been shown to be neurotoxic, leading to mitochondrial dysfunction and enhanced apoptotic cell death. However, if Abeta fragments are indeed detrimental to neurons, the widespread presence of enzymatic activity that would result in their generation in the cell appears to make little sense. The presence of a gamma-secretase complex in the mitochondrion, an organelle that is particularly susceptible to Abeta toxicity, is even more puzzling. Emerging evidence suggests that both secreted and intracellular Abeta fragments have endogenous functions. Also, while the fibrillogenic Abeta1-42 is clearly neurotoxic, the more abundant and soluble Abeta1-40 is an antioxidant and could potentially be neuroprotective in several ways. A "physiological" amount of Abeta1-40 production by cellular gamma-secretase activity may be part of the neuron's natural counter against oxidative damage, in addition to endogenous roles in neuronal survival and modulation of synaptic transmission. In any case, whether Abeta is produced locally in the mitochondria and the function for mitochondrial Abeta, if produced, is yet unclear.

BAG5 inhibits parkin and enhances dopaminergic neuron degeneration

Loss-of-function mutations in the parkin gene, which encodes an E3 ubiquitin ligase, are the major cause of early-onset Parkinson's disease (PD). Decreases in parkin activity may also contribute to neurodegeneration in sporadic forms of PD. Here, we show that bcl-2-associated athanogene 5 (BAG5), a BAG family member, directly interacts with parkin and the chaperone Hsp70. Within this complex, BAG5 inhibits both parkin E3 ubiquitin ligase activity and Hsp70-mediated refolding of misfolded proteins. BAG5 enhances parkin sequestration within protein aggregates and mitigates parkin-dependent preservation of proteasome function. Finally, BAG5 enhances dopamine neuron death in an in vivo model of PD, whereas a mutant that inhibits BAG5 activity attenuates dopaminergic neurodegeneration. This contrasts with the antideath functions ascribed to BAG family members and suggests a potential role for BAG5 in promoting neurodegeneration in sporadic PD through its functional interactions with parkin and Hsp70.

Apolipoprotein L6, a Novel Proapoptotic Bcl-2 Homology 3–Only Protein, Induces Mitochondria-Mediated Apoptosis in Cancer Cells

Cancer cells frequently possess defects in the genetic and biochemical pathways of apoptosis. Members of the Bcl-2 family play pivotal roles in regulating apoptosis and possess at least one of four Bcl-2 homology (BH) domains, designated BH1 to BH4. The BH3 domain is the only one conserved in proapoptotic BH3-only proteins and plays an important role in protein-protein interactions in apoptosis by regulating homodimerization and heterodimerization of the Bcl-2 family members. To date, 10 BH3-only proapoptotic proteins have been identified and characterized in the human genome. The completion of the Human Genome Project and the availability of various public databases and sequence analysis algorithms allowed us to use the bioinformatic database-mining approach to identify one novel BH3-only protein, apolipoprotein L6 (ApoL6). The full-length cDNA of ApoL6 was identified, cloned, and functionally expressed in p53-null colorectal cancer cells (DLD-1). We found that overexpression of wild-type ApoL6 induced mitochondria-mediated apoptosis in DLD-1 cells characterized by release of cytochrome c and Smac/DIABLO from mitochondria and activation of caspase-9, whereas ApoL6 BH3 domain deletion allele did not. In addition, overexpression of ApoL6 also induced activation of caspase-8. Furthermore, we showed that adenovirus harboring the full-length cDNA of ApoL6 induced marked apoptosis in a variety of cancer cell types, and ApoL6 recruited and interacted with lipid/fatty acid components during the induction of apoptosis. To our knowledge, this is the first example that intracellular overproduction of an apolipoprotein induces marked apoptosis.

Molecular targets for neuroprotection

Amyotrophic lateral sclerosis (ALS) is a fatal paralytic neurodegenerative disorder. Experimental models of ALS such as the transgenic rodents expressing mutant superoxide dimutase-1 are playing a pivotal role in our understanding of ALS pathogenesis, and in our testing of new therapeutic interventions aimed at protecting against neurodegeneration. Apoptosis has emerged as a significant pathogenic factor in several neurodegenerative diseases, including ALS. Constructed of multiple interacting molecules, the apoptosis machinery offers a host of attractive targets for pharmacological and genetic interventions to be tested in experimental models of ALS. Information generated by these pre-clinical studies holds the promise to provide sound scientific basis for the development of effective neuroprotective therapies for ALS.

Increased tau phosphorylation on mitogen-activated protein kinase consensus sites and cognitive decline in transgenic models for Alzheimer's disease and FTDP-17: evidence for distinct molecular processes underlying tau abnormalities

Abnormal tau phosphorylation occurs in several neurodegenerative disorders, including Alzheimer's disease (AD) and frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17). Here, we compare mechanisms of tau phosphorylation in mouse models of FTDP-17 and AD. Mice expressing a mutated form of human tau associated with FTDP-17 (tau(V337M)) showed age-related increases in exogenous tau phosphorylation in the absence of increased activation status of a number of kinases known to phosphorylate tau in vitro. In a "combined" model, expressing both tau(V337M) and the familial amyloid precursor protein AD mutation APP(V717I) in a CT100 fragment, age-dependent tau phosphorylation occurred at the same sites and was significantly augmented compared to "single" tau(V337M) mice. These effects were concomitant with increased activation status of mitogen-activated protein kinase (MAPK) family members (extracellular regulated kinases 1 and 2, p38, and c-Jun NH(2)-terminal kinase) but not glycogen synthase kinase-3alphabeta or cyclin-dependent kinase 5. The increase in MAPK activation was a discrete effect of APP(V717I)-CT100 transgene expression as near identical changes were observed in single APP(V717I)-CT100 mice. Age-dependent deficits in memory were also associated with tau(V337M) and APP(V717I)-CT100 expression. The data reveal distinct routes to abnormal tau phosphorylation in models of AD and FTDP-17 and suggest that in AD, tau irregularities may be linked to processing of APP C-terminal fragments via specific effects on MAPK activation status.

Mixed lineage kinase-c-jun N-terminal kinase signaling pathway: A new therapeutic target in Parkinson's disease

There is growing evidence that the molecular pathways of programmed cell death play a role in neurodegenerative disease, including Parkinson's disease, so there has been increased interest in them as therapeutic targets for the development of neuroprotective strategies. One pathway of cell death that has attracted particular attention is the mixed lineage kinase (MLK) -c-jun N-terminal kinase (JNK) signaling cascade, which leads to the phosphorylation and activation of the transcription factor c-jun. There is much evidence, from in vitro and in vivo studies, that this cascade can mediate cell death. In addition, there is evidence that it is operative upstream in the death process. It is possible that abrogation of this pathway may forestall death before irreversible cellular injury. One class of compounds that has shown promise for their ability to block cell death by inhibiting this cascade are the inhibitors of the MLKs, which are upstream in the activation of c-jun. One of these compounds, CEP1347, is now in a Phase II/III clinical trial for neuroprotection in PD. Whether this trial is successful or not, this signaling cascade is likely to be a focus of future therapeutic development. This review, therefore, outlines the principles of signaling within this kinase pathway, and the evidence for its role in cell death. We review the evidence that inhibition of the MLKs can prevent dopamine neuron cell death and the degeneration of their axons. These studies suggest important future directions for the development of therapies that will target this important cell death pathway.

Metal-catalyzed oxidation of alpha-synuclein: helping to define the relationship between oligomers, protofibrils, and filaments

Oxidative stress is implicated in a number of neuro-degenerative diseases and is associated with the selective loss of dopaminergic neurons of the substantia nigra in Parkinson's disease. The role of alpha-synuclein as a potential target of intracellular oxidants has been demonstrated by the identification of posttranslational modifications of synuclein within intracellular aggregates that accumulate in Parkinson's disease brains, as well as the ability of a number of oxidative insults to induce synuclein oligomerization. The relationship between these relatively small soluble oligomers, potentially neurotoxic synuclein protofibrils, and synuclein filaments remains unclear. We have found that metal-catalyzed oxidation of alpha-synuclein inhibited formation of synuclein filaments with a concomitant accumulation of beta sheet-rich oligomers that may represent synuclein protofibrils. Similar results with a number of oxidative and enzymatic treatments suggest that the covalent association of synuclein into higher molecular mass oligomers/protofibrils represents an alternate pathway from filament formation and renders synuclein less prone to proteasomal degradation.

A common vaccine for fighting neurodegenerative disorders: recharging immunity for homeostasis

Neurodegenerative conditions share common primary risk factors and mediators of disease progression. Because many degenerative disorders are age related, deteriorating immunity in aging patients might impose additional risk. Adaptive (T-cell-mediated) immunity is a defense mechanism that instructs microglia to fight off and clear away self-derived enemies. Such adaptive immunity can be boosted, without risking the development of autoimmune disease, by injecting weak agonists of self-antigens or by weakening the suppressive CD4+CD25+ regulatory T cells. If widely cross-reactive, the agonist might effectively counteract a variety of neurodegenerative disorders. Boosting of relevant T cells by vaccination could thus "recharge" a deteriorating immune system that has to contend with an increasing number of risk factors.