Midbrain dopaminergic neuronal degeneration in a transgenic mouse model of familial amyotrophic lateral sclerosis

In-depth analysis of data from the RAS-ALS study reveals new insights in rasagiline treatment for amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE

In 2016, we concluded a randomized controlled trial testing 1 mg rasagiline per day add-on to standard therapy in 252 amyotrophic lateral sclerosis (ALS) patients. This article aims at better characterizing ALS patients who could possibly benefit from rasagiline by reporting new subgroup analysis and genetic data.

METHODS

We performed further exploratory in-depth analyses of the study population and investigated the relevance of single nucleotide polymorphisms (SNPs) related to the dopaminergic system.

RESULTS

Placebo-treated patients with very slow disease progression (loss of Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised [ALSFRS-R] per month before randomization of ≤0.328 points) showed a per se survival probability after 24 months of 0.85 (95% confidence interval = 0.65-0.94). The large group of intermediate to fast progressing ALS patients showed a prolonged survival in the rasagiline group compared to placebo after 6 and 12 months (p = 0.02, p = 0.04), and a reduced decline of ALSFRS-R after 18 months (p = 0.049). SNP genotypes in the MAOB gene and DRD2 gene did not show clear associations with rasagiline treatment effects.

CONCLUSIONS

These results underline the need to consider individual disease progression at baseline in future ALS studies. Very slow disease progressors compromise the statistical power of studies with treatment durations of 12-18 months using clinical endpoints. Analysis of MAOB and DRD2 SNPs revealed no clear relationship to any outcome parameter. More insights are expected from future studies elucidating whether patients with DRD2CC genotype (Rs2283265) show a pronounced benefit from treatment with rasagiline, pointing to the opportunities precision medicine could open up for ALS patients in the future.

Longitudinal course of neurofilament light chain levels in amyotrophic lateral sclerosis-insights from a completed randomized controlled trial with rasagiline

BACKGROUND AND PURPOSE

Rasagiline might be disease modifying in patients with amyotrophic lateral sclerosis (ALS). The aim was to evaluate the effect of rasagiline 2 mg/day on neurofilament light chain (NfL), a prognostic biomarker in ALS.

METHODS

In 65 patients with ALS randomized in a 3:1 ratio to rasagiline 2 mg/day (n = 48) or placebo (n = 17) in a completed randomized controlled multicentre trial, NfL levels in plasma were measured at baseline, month 6 and month 12. Longitudinal changes in NfL levels were evaluated regarding treatment and clinical parameters.

RESULTS

Baseline NfL levels did not differ between the study arms and correlated with disease progression rates both pre-baseline (r = 0.64, p < 0.001) and during the study (r = 0.61, p < 0.001). NfL measured at months 6 and 12 did not change significantly from baseline in both arms, with a median individual NfL change of +1.4 pg/mL (interquartile range [IQR] -5.6, 14.2) across all follow-up time points. However, a significant difference in NfL change at month 12 was observed between patients with high and low NfL baseline levels treated with rasagiline (high [n = 13], -6.9 pg/mL, IQR -20.4, 6.0; low [n = 18], +5.9 pg/mL, IQR -1.4, 19.7; p = 0.025). Additionally, generally higher longitudinal NfL variability was observed in patients with high baseline levels, whereas disease progression rates and disease duration at baseline had no impact on the longitudinal NfL course.

CONCLUSION

Post hoc NfL measurements in completed clinical trials are helpful in interpreting NfL data from ongoing and future interventional trials and could provide hypothesis-generating complementary insights. Further studies are warranted to ultimately differentiate NfL response to treatment from other factors.

Clinical studies in amyotrophic lateral sclerosis

PURPOSE OF REVIEW

The purpose of this review is to discuss the most important recent clinical studies in amyotrophic lateral sclerosis (ALS), including their impact on clinical practice, their methodology, and open questions to be addressed in the future.

RECENT FINDINGS

This article focuses on studies, which provided either a positive primary endpoint or positive post hoc analysis, including edaravone, sodium phenylbutyrate-taurursodiol, rasagiline, tofersen, and high-caloric, fat-rich nutrition. It also covers recent developments in the design of clinical ALS studies with regard to inclusion criteria, stratification factors, and outcome parameters.

SUMMARY

Recent clinical studies have indicated various substances to be considered for treatment of ALS. Edaravone has been approved by the US Food and Drug Association (FDA) but not by the European Medicines Agency (EMA), and further studies testing oral formulations are currently conducted. A follow-up study with sodium phenylbutyrate-taurursodiol is ongoing, while follow-up studies for rasagiline and high-caloric, fat-rich nutrition are planned. A phase III study with tofersen was negative but nevertheless yielded promising results. Important developments regarding the design of clinical ALS studies include the implementation of neurofilament light chain (NfL) levels as a standard outcome parameter and the consideration of progression rate for therapeutic response and stratification.

Cortical Hyperexcitability in the Driver’s Seat in ALS

Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by the degeneration of cortical and spinal motor neurons. With no effective treatment available to date, patients face progressive paralysis and eventually succumb to the disease due to respiratory failure within only a few years. Recent research has revealed the multifaceted nature of the mechanisms and cell types involved in motor neuron degeneration, thereby opening up new therapeutic avenues. Intriguingly, two key features present in both ALS patients and rodent models of the disease are cortical hyperexcitability and hyperconnectivity, the mechanisms of which are still not fully understood. We here recapitulate current findings arguing for cell autonomous and non-cell autonomous mechanisms causing cortical excitation and inhibition imbalance, which is involved in the degeneration of motor neurons in ALS. Moreover, we will highlight recent evidence that strongly indicates a cardinal role for the motor cortex as a main driver and source of the disease, thus arguing for a corticofugal trajectory of the pathology.

Cortical and Striatal Electroencephalograms and Apomorphine Effects in the FUS Mouse Model of Amyotrophic Lateral Sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of motor neurons resulting in muscle atrophy. In contrast to the lower motor neurons, the role of upper (cortical) neurons in ALS is yet unclear. Maturation of locomotor networks is supported by dopaminergic (DA) projections from substantia nigra to the spinal cord and striatum.

OBJECTIVE

To examine the contribution of DA mediation in the striatum-cortex networks in ALS progression.

METHODS

We studied electroencephalogram (EEG) from striatal putamen (Pt) and primary motor cortex (M1) in ΔFUS(1-359)-transgenic (Tg) mice, a model of ALS. EEG from M1 and Pt were recorded in freely moving young (2-month-old) and older (5-month-old) Tg and non-transgenic (nTg) mice. EEG spectra were analyzed for 30 min before and for 60 min after systemic injection of a DA mimetic, apomorphine (APO), and saline.

RESULTS

In young Tg versus nTg mice, baseline EEG spectra in M1 were comparable, whereas in Pt, beta activity in Tg mice was enhanced. In older Tg versus nTg mice, beta dominated in EEG from both M1 and Pt, whereas theta and delta 2 activities were reduced. In younger Tg versus nTg mice, APO increased theta and decreased beta 2 predominantly in M1. In older mice, APO effects in these frequency bands were inversed and accompanied by enhanced delta 2 and attenuated alpha in Tg versus nTg mice.

CONCLUSION

We suggest that revealed EEG modifications in ΔFUS(1-359)-transgenic mice are associated with early alterations in the striatum-cortex interrelations and DA transmission followed by adaptive intracerebral transformations.

How Degeneration of Cells Surrounding Motoneurons Contributes to Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by the progressive degeneration of upper and lower motoneurons. Despite motoneuron death being recognized as the cardinal event of the disease, the loss of glial cells and interneurons in the brain and spinal cord accompanies and even precedes motoneuron elimination. In this review, we provide striking evidence that the degeneration of astrocytes and oligodendrocytes, in addition to inhibitory and modulatory interneurons, disrupt the functionally coherent environment of motoneurons. We discuss the extent to which the degeneration of glial cells and interneurons also contributes to the decline of the motor system. This pathogenic cellular network therefore represents a novel strategic field of therapeutic investigation.

Sesaminol prevents Parkinson's disease by activating the Nrf2-ARE signaling pathway

Parkinson's disease (PD) is a neurodegenerative disease caused by the degeneration of substantia nigra neurons due to oxidative stress. Sesaminol has strong antioxidant and anti-cancer effects. We investigated the preventive effect on PD as a new physiological action of sesaminol produced from sesaminol glycoside using in vitro and in vivo PD models. To prepare an in vitro PD model, 6-hydroxydopamine (6-OHDA) was added to human neuroblastoma (SH-SY5Y cells). The viability of SH-SY5Y cells decreased dose-dependently following 6-OHDA treatment, but the addition of sesaminol restored viability to the control level. 6-OHDA increased intracellular reactive oxygen species production, and the addition of sesaminol significantly suppressed this increase. No Nrf2 expression in the nucleus was observed in the control group, but a slight increase was observed in the 6-OHDA group. The sesaminol group showed strong expression of Nrf2 in the cytoplasm and nucleus. NAD(P)H: quinone oxidoreductase (NQO1) activity was enhanced in the 6-OHDA group and further enhanced in the sesaminol group. Furthermore, the neurotoxine rotenone was orally administrated to mice to prepare an in vivo PD model. The motor function of rotenone-treated mice was shorter than that of the control group, but a small amount of sesaminol restored it to the control level. The intestinal motility in the rotenone group was significantly lower than that in the control group, but it remained at the control level in the sesaminol group. The expression of α-synuclein in the substantia nigra increased in the rotenone group but decreased in the sesaminol group. The rotenone group exhibited shortening and damage to the colonic mucosa, but these abnormalities of the colonic mucosa were scarcely observed in the sesaminol group. These results suggest that sesaminol has a preventative effect on PD.

Cortical Circuit Dysfunction as a Potential Driver of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that affects selected cortical and spinal neuronal populations, leading to progressive paralysis and death. A growing body of evidences suggests that the disease may originate in the cerebral cortex and propagate in a corticofugal manner. In particular, transcranial magnetic stimulation studies revealed that ALS patients present with early cortical hyperexcitability arising from a combination of increased excitability and decreased inhibition. Here, we discuss the possibility that initial cortical circuit dysfunction might act as the main driver of ALS onset and progression, and review recent functional, imaging and transcriptomic studies conducted on ALS patients, along with electrophysiological, pathological and transcriptomic studies on animal and cellular models of the disease, in order to evaluate the potential cellular and molecular origins of cortical hyperexcitability in ALS.

Novel behavioural characteristics of the superoxide dismutase 1 G93A (SOD1G93A ) mouse model of amyotrophic lateral sclerosis include sex-dependent phenotypes

Amyotrophic lateral sclerosis (ALS) involves the rapid degeneration of upper and lower motor neurons leading to weakening and paralysis of voluntary movements. Mutations in copper-zinc superoxide dismutase 1 (SOD1) are a known genetic cause of ALS, and the SOD1 ^G93A mouse has been used extensively to investigate molecular mechanisms in ALS. In recent years, evidence suggests that ALS and frontotemporal dementia form a spectrum disorder ranging from motor to cognitive dysfunctions. Thus, we tested male and female SOD1 ^G93A mice for the first time before the onset of debilitating motor impairments in behavioural domains relevant to both ALS and frontotemporal dementia. SOD1 ^G93A males displayed reduced locomotion, exploration and increased anxiety-like behaviours compared with control males. Intermediate-term spatial memory was impaired in SOD1 ^G93A females, whereas long-term spatial memory deficits as well as lower acoustic startle response, and prepulse inhibition were identified in SOD1 ^G93A mice of both sexes compared with respective controls. Interestingly, SOD1 ^G93A males exhibited an increased conditioned cue freezing response. Nosing behaviours were also elevated in both male and female SOD1 ^G93A when assessed in social paradigms. In conclusion, SOD1 ^G93A mice exhibit a variety of sex-specific behavioural deficits beyond motor impairments supporting the notion of an ALS-frontotemporal spectrum disorder. Thus, SOD1 ^G93A mice may represent a useful model to test the efficacy of therapeutic interventions on clinical symptoms in addition to declining motor abilities.

[An early history of Japanese amyotrophic lateral sclerosis (ALS)-related diseases and the current development]

The present review focuses an early history of Japanese amyotrophic lateral sclerosis (ALS)-related diseases and the current development. In relation to foreign previous reports, five topics are introduced and discussed on ALS with dementia, ALS/Parkinsonism dementia complex (ALS/PDC), familial ALS (FALS), spinal bulbar muscular atrophy (SBMA), and multisystem involvement especially in cerebellar system of ALS including ALS/SCA (spinocerebellar ataxia) crossroad mutation Asidan. This review found the great contribution of Japanese reports on the above five topics, and confirmed the great development of ALS-related diseases over the past 120 years.

The concept and diagnostic criteria of primary lateral sclerosis

OBJECTIVES

Primary lateral sclerosis (PLS) is commonly considered as a motor neuron disease (MND) variant which almost exclusively affects upper motor neurons (UMN). There is still no consensus whether PLS should be regarded as an independent disease entity separate from amyotrophic lateral sclerosis (ALS) or as a comparatively slowly progressive variant of ALS. Given these different views, clinical diagnosis of PLS is a challenge. In this multicenter study, we analyzed clinical features of patients diagnosed with PLS in four specialized MND centers.

MATERIAL AND METHODS

We retrospectively analyzed clinical, laboratory, imaging, and electrophysiological data of 76 patients with PLS diagnosed in four specialized ALS centers. We analyzed the concept of the disease based on our findings and an extensive review of the literature.

RESULTS

We found that 79% of patients showed asymmetrical symptoms, 60% showed clinical or electrophysiological signs of lower motor neuron (LMN) involvement after a mean of 8.4 ± 5.0 years, and extrapyramidal and/or non-motoric symptoms were frequently observed. Interestingly, none of the patients diagnosed with PLS fulfilled the diagnostic criteria proposed by Pringle et al. in 1992.

CONCLUSIONS

Our data show that PLS as a disease entity is still not well enough defined and that there are different concepts about its clinical presentation. We believe that further prospective longitudinal studies are needed in order to refine diagnostic criteria to reflect current clinical practice. Furthermore, neuropathological and neuroimaging approaches might help to arrange PLS in the MND spectrum and its classification.

Mutant PFN1 causes ALS phenotypes and progressive motor neuron degeneration in mice by a gain of toxicity

Mutations in the profilin 1 (PFN1) gene cause amyotrophic lateral sclerosis (ALS), a neurodegenerative disease caused by the loss of motor neurons leading to paralysis and eventually death. PFN1 is a small actin-binding protein that promotes formin-based actin polymerization and regulates numerous cellular functions, but how the mutations in PFN1 cause ALS is unclear. To investigate this problem, we have generated transgenic mice expressing either the ALS-associated mutant (C71G) or wild-type protein. Here, we report that mice expressing the mutant, but not the wild-type, protein had relentless progression of motor neuron loss with concomitant progressive muscle weakness ending in paralysis and death. Furthermore, mutant, but not wild-type, PFN1 forms insoluble aggregates, disrupts cytoskeletal structure, and elevates ubiquitin and p62/SQSTM levels in motor neurons. Unexpectedly, the acceleration of motor neuron degeneration precedes the accumulation of mutant PFN1 aggregates. These results suggest that although mutant PFN1 aggregation may contribute to neurodegeneration, it does not trigger its onset. Importantly, these experiments establish a progressive disease model that can contribute toward identifying the mechanisms of ALS pathogenesis and the development of therapeutic treatments.

Increased frequency of pathologic findings on transcranial B-mode parenchymal sonography in patients with sporadic amyotrophic lateral sclerosis

Although amyotrophic lateral sclerosis (ALS) is characterized by involvement of motor neurons in the motor cortex, brainstem and spinal cord, there is accumulating evidence that it is a multisystem degenerative disease, with dysfunction of the striatonigral dopaminergic system as well. Transcranial B-mode sonography of the parenchyma enables depiction of the differing tissue echogenicity of midbrain and basal ganglia structures in various movement disorders. Transcranial B-mode sonography was performed in the standard manner in 101 patients with sporadic newly diagnosed ALS and 60 age- and gender-matched controls. Increased frequencies of pathologic substantia nigra hyper-echogenicity (p = 0.027), interrupted brainstem raphe (p = 0.003) and increased third ventricle diameter (p < 0.0001) were detected in ALS patients as compared with healthy controls. Only four ALS patients exhibited some features of parkinsonism. Pathologic findings on transcranial B-mode sonography of parenchyma did not correlate with clinical presentation, functional status or disease subtype. Our study provides additional evidence of multisystem involvement in ALS patients, particularly in subcortical areas.

Therapeutic targets for amyotrophic lateral sclerosis: current treatments and prospects for more effective therapies

Although amyotrophic lateral sclerosis (ALS) was described more than 130 years ago, the cause(s) of most cases of this adult motor neuron disease remains a mystery. With the discovery of mutations in one gene (Cu/Zn superoxide dismutase) as a primary cause of some forms of ALS, model systems have been developed that have helped us begin to understand mechanisms involved in motor neuron death and enabled testing of potential new therapies. Several other genes have been implicated as risk factors in motor neuron diseases, including neurofilaments, cytoplasmic dynein and dynactin, vascular endothelial growth factor, and angiogenin. With advances in the basic research of the disease, many hypotheses accounting for motor neuron death are being explored, including loss of trophic support, protein mishandling, mitochondrial dysfunction, excitotoxicity, axonal abnormalities and inflammation. Many of these mechanisms are the focus of research in other neurodegenerative disorders, such as Parkinson's, Alzheimer's and Huntington's disease.

PICK1 expression in reactive astrocytes within the spinal cord of amyotrophic lateral sclerosis (ALS) rats

AIMS

The protein interacting with C kinase 1 (PICK1), a PDZ domain-containing protein mainly expressed in the central nervous system, interacts with the glutamate receptor subunit GluR2, with the glutamate transporter GLT-1b and with the enzyme serine racemase. These three proteins appear as key actors in the glutamate-mediated excitotoxicity associated with amyotrophic lateral sclerosis (ALS), in both patients and animal models of the disease. In this study, we examined the expression of PICK1 in the spinal cord of transgenic rats expressing a mutated form of the human superoxide dismutase 1 (hSOD1(G93A) ) during the progression of the disease.

METHODS

Expression of PICK1 was examined by real-time qPCR at presymptomatic and symptomatic stages as well as at end-stage. The expression of PICK1 in the different cell types of the spinal cord was examined by immunohistochemistry.

RESULTS

The overall expression of PICK1 is not modified in cervical and lumbar spinal cord of transgenic (hSOD1(G93A) ) rats during the progression of the disease. Nonetheless, immunohistochemical studies of lumbar ventral horns revealed a shift of PICK1 expression from motor neurones in healthy rats to activated astrocytes in end-stage hSOD1(G93A) animals.

CONCLUSIONS

Considering the documented influence of PICK1 expression on d-serine release and glutamate transport in astrocytes, these findings point to a potential implication of PICK1 in the progression of ALS.

NAP (davunetide) modifies disease progression in a mouse model of severe neurodegeneration: protection against impairments in axonal transport

NAP (davunetide) is a novel neuroprotective compound with mechanism of action that appears to involve microtubule (MT) stabilization and repair. To evaluate, for the first time, the impact of NAP on axonal transport in vivo and to translate it to neuroprotection in a severe neurodegeneration, the SOD1-G93A mouse model for amyotrophic lateral sclerosis (ALS) was used. Manganese-enhanced magnetic resonance imaging (MRI), estimating axonal transport rates, revealed a significant reduction of the anterograde axonal transport in the ALS mice compared to healthy control mice. Acute NAP treatment normalized axonal transport rates in these ALS mice. Tau hyperphosphorylation, associated with MT dysfunction and defective axonal transport, was discovered in the brains of the ALS mice and was significantly reduced by chronic NAP treatment. Furthermore, in healthy wild type (WT) mice, NAP reversed axonal transport disruption by colchicine, suggesting drug-dependent protection against axonal transport impairment through stabilization of the neuronal MT network. Histochemical analysis showed that chronic NAP treatment significantly protected spinal cord motor neurons against ALS-like pathology. Sequential MRI measurements, correlating brain structure with ALS disease progression, revealed a significant damage to the ventral tegmental area (VTA), indicative of impairments to the dopaminergic pathways relative to healthy controls. Chronic daily NAP treatment of the SOD1-G93A mice, initiated close to disease onset, delayed degeneration of the trigeminal, facial and hypoglossal motor nuclei as was significantly apparent at days 90-100 and further protected the VTA throughout life. Importantly, protection of the VTA was significantly correlated with longevity and overall, NAP treatment significantly prolonged life span in the ALS mice.

Diffusion tensor imaging of basal ganglia and thalamus in amyotrophic lateral sclerosis

PURPOSE

To assess the involvement of basal ganglia and thalamus in patients with amyotrophic lateral sclerosis (ALS) using diffusion tensor imaging (DTI) method.

METHODS

Fourteen definite-ALS patients and 12 age-matched controls underwent whole brain DTI on a 3T scanner. Mean-diffusivity (MD) and fractional anisotropy (FA) were obtained bilaterally from the basal ganglia and thalamus in the regions-of-interest (ROIs).

RESULTS

The MD was significantly higher (P < .02) in basal ganglia and thalamus in patients with ALS compared with controls. Correspondingly, the FA was significantly lower (P < .02) in these structures, except in caudate (P = .04) and putamen (P = .06) in patients compared with controls. There were mild to strong correlations (r = .3-.7) between the DTI measures of basal ganglia and finger-tap, foot-tap, and lip-and-tongue movement rate.

CONCLUSIONS

The increased MD in basal ganglia and thalamus and decreased FA in globus pallidus and thalamus are indicative of neuronal loss or dysfunction in these structures.

1H MRS of basal ganglia and thalamus in amyotrophic lateral sclerosis

Previous studies have evaluated motor and extramotor cerebral cortical regions in patients with amyotrophic lateral sclerosis (ALS) using (1) H MRS, but none have evaluated the thalamus or basal ganglia. The objective of this exploratory study was to evaluate the subclinical involvement of the basal ganglia and thalamus in patients with ALS using (1) H MRS. Fourteen patients (52±7 years) with sporadic definite ALS and 17 age-matched controls were studied using volumetric MRSI on a 3-T scanner. The concentration of the metabolites N-acetylaspartate (NAA), choline (Cho) and their ratio (NAA/Cho) were obtained bilaterally from the basal ganglia (lentiform nucleus, caudate) and thalamus. The maximum rates of finger and foot tap and lip and tongue movements were obtained to assess extrapyramidal and pyramidal tract function. In patients with ALS, relative to controls, the NAA concentration was significantly lower (p<0.02) in the basal ganglia and thalamus, and the Cho concentration was higher (p<0.01) in these structures, except in the caudate (p=0.04). Correspondingly, the NAA/Cho ratio was significantly lower (p<0.01) in these structures, except in the caudate (p=0.03), in patients than in controls. There were mild to strong correlations (r=0.4-0.7) between the metabolites of the basal ganglia and finger tap, foot tap and lip and tongue movement rates. In conclusion, decreased NAA in the basal ganglia and thalamus and increased Cho and decreased NAA/Cho in the lentiform nucleus and thalamus are indicative of neuronal loss or dysfunction and alterations in choline-containing membranes in these structures.

Nigrostriatal dysfunction in patients with amyotrophic lateral sclerosis and parkinsonism

The pathomechanism of amyotrophic lateral sclerosis (ALS) with parkinsonism (ALS-P) has not been clarified. We report two patients with ALS-P who showed dysfunction of the nigrostriatal system. The first patient showed tremor dominant, asymmetric parkinsonism which was more severe on the right side, while the second patient exhibited predominant freezing of gait. Both patients showed reduced uptake of [¹⁸F] N-(3-fluoropropyl)-2ß-carbon ethoxy-3ß-(4-iodophenyl) nortropane (¹⁸F-FP-CIT) in the posterior parts of bilateral putamina on positron emission tomography (PET). Based on our PET findings, we suggest that presynaptic nigrostriatal dysfunction may be involved in the pathomechanism of parkinsonism combined with ALS.

Induction of parkinsonism-related proteins in the spinal motor neurons of transgenic mouse carrying a mutant SOD1 gene

Amyotrophic lateral sclerosis is a progressive and fatal disease caused by selective death of motor neurons, and a number of these patients carry mutations in the superoxide dismutase 1 (SOD1) gene involved in ameliorating oxidative stress. Recent studies indicate that oxidative stress and disruption of mitochondrial homeostasis is a common mechanism for motor neuron degeneration in amyotrophic lateral sclerosis and the loss of midbrain dopamine neurons in Parkinson's disease. Therefore, the present study investigated the presence and alterations of familial Parkinson's disease-related proteins, PINK1 and DJ-1, in spinal motor neurons of G93ASOD1 transgenic mouse model of amyotrophic lateral sclerosis. Following onset of disease, PINK1 and DJ-1 protein expression increased in the spinal motor neurons. The activated form of p53 also increased and translocated to the nuclei of spinal motor neurons, followed by increased expression of p53-activated gene 608 (PAG608). This is the first report demonstrating that increased expression of PAG608 correlates with activation of phosphorylated p53 in spinal motor neurons of an amyotrophic lateral sclerosis model. These results provide further evidence of the profound correlations between spinal motor neurons of amyotrophic lateral sclerosis and parkinsonism-related proteins.

Amyloid pathology is associated with progressive monoaminergic neurodegeneration in a transgenic mouse model of Alzheimer's disease

beta-Amyloid (Abeta) pathology is an essential pathogenic component in Alzheimer's disease (AD). However, the significance of Abeta pathology, including Abeta deposits/oligomers and glial reactions, to neurodegeneration is unclear. In particular, despite the Abeta neurotoxicity indicated by in vitro studies, mouse models with significant Abeta deposition lack robust and progressive loss of forebrain neurons. Such results have fueled the view that Abeta pathology is insufficient for neurodegeneration in vivo. In this study, because monoaminergic (MAergic) neurons show degenerative changes at early stages of AD, we examined whether the APPswe/PS1DeltaE9 mouse model recapitulates progressive MAergic neurodegeneration occurring in AD cases. We show that the progression forebrain Abeta deposition in the APPswe/PS1DeltaE9 model is associated with progressive losses of the forebrain MAergic afferents. Significantly, axonal degeneration is associated with significant atrophy of cell bodies and eventually leads to robust loss (approximately 50%) of subcortical MAergic neurons. Degeneration of these neurons occurs without obvious local Abeta or tau pathology at the subcortical sites and precedes the onset of anxiety-associated behavior in the mice. Our results show that a transgenic mouse model of Abeta pathology develops progressive MAergic neurodegeneration occurring in AD cases.

Soluble misfolded subfractions of mutant superoxide dismutase-1s are enriched in spinal cords throughout life in murine ALS models

Mutants of superoxide dismutase-1 (SOD1) cause ALS by an unidentified cytotoxic mechanism. We have previously shown that the stable SOD1 mutants D90A and G93A are abundant and show the highest levels in liver and kidney in transgenic murine ALS models, whereas the unstable G85R and G127X mutants are scarce but enriched in the CNS. These data indicated that minute amounts of misfolded SOD1 enriched in the motor areas might exert the ALS-causing cytotoxicity. A hydrophobic interaction chromatography (HIC) protocol was developed with the aim to determine the abundance of soluble misfolded SOD1 in tissues in vivo. Most G85R and G127X mutant SOD1s bound in the assay, but only minute subfractions of the D90A and G93A mutants. The absolute levels of HIC-binding SOD1 were, however, similar and broadly inversely related to lifespans in the models. They were generally enriched in the susceptible spinal cord. The HIC-binding SOD1 was composed of disulfide-reduced subunits lacking metal ions and also subunits that apparently carried nonnative intrasubunit disulfide bonds. The levels were high from birth until death and were comparable to the amounts of SOD1 that become sequestered in aggregates in the terminal stage. The HIC-binding SOD1 species ranged from monomeric to trimeric in size. These species form a least common denominator amongst SOD1 mutants with widely different molecular characteristics and might be involved in the cytotoxicity that causes ALS.

Increased number and differentiation of neural precursor cells in the brainstem of superoxide dismutase 1(G93A) (G1H) transgenic mouse model of amyotrophic lateral sclerosis

The superoxide dismutase 1(G93A G1H) (SOD1(G93A G1H)) transgenic mouse is a model of familial human amyotrophic lateral sclerosis (ALS) that has progressive neurodegeneration within the spinal cord and brainstem. In this study, we investigated the number and differentiation of neural precursor cells (NPCs). Nestin-positive NPCs were rarely seen in the nervous system of wild type controls or pre-disease mice at post-natal days 30 and 60. With disease onset on post-natal day 90, nestin labeled NPCs proliferated preferentially in the brainstem with maximal number and density at post-natal day 120. NPCs did not double-label with CNPase or O(4) markers of oligodendrocytes. The majority of the NPCs co-labeled with the astrocyte maker glial fibrillary acidic protein (GFAP) and a small number with the neuronal marker NeuN. At disease onset, 73 and 10% of NPCs co-expressed GFAP and NeuN respectively while at severe disease stage, 80 and 8% of the NPCs co-expressed GFAP and NeuN. Proliferating cell nuclear antigen (PCNA) was used to confirm that at least some of these cells undergo mitosis. Future studies could be directed at controlling the differentiation of these endogenous NPCs into neurons and astrocytes in order to ameliorate the degeneration within the brainstem of the ALS mouse.

The parkinsonian neurotoxin rotenone activates calpain and caspase-3 leading to motoneuron degeneration in spinal cord of Lewis rats

Exposure to environmental toxins increases the risk of neurodegenerative diseases including Parkinson's disease (PD). Rotenone is a neurotoxin that has been used to induce experimental Parkinsonism in rats. We used the rotenone model of experimental Parkinsonism to explore a novel aspect of extra-nigral degeneration, the neurodegeneration of spinal cord (SC), in PD. Rotenone administration to male Lewis rats caused significant neuronal cell death in cervical and lumbar SC as compared with control animals. Dying neurons were motoneurons as identified by double immunofluorescent labeling for terminal deoxynucleotidyl transferase, recombinant-mediated dUTP nick-end labeling-positive (TUNEL(+)) cells and choline acetyltransferase (ChAT)-immunoreactivity. Neuronal death was accompanied by abundant astrogliosis and microgliosis as evidenced from glial fibrillary acidic protein (GFAP)-immunoreactivity and OX-42-immunoreactivity, respectively, implicating an inflammatory component during neurodegeneration in SC. However, the integrity of the white matter in SC was not affected by rotenone administration as evidenced from the non co-localization of any TUNEL(+) cells with GFAP-immunoreactivity and myelin basic protein (MBP)-immunoreactivity, the selective markers for astrocytes and oligodendrocytes, respectively. Increased activities of 76 kD active m-calpain and 17/19 kD active caspase-3 further demonstrated involvement of these enzymes in cell death in SC. The finding of ChAT(+) cell death also suggested degeneration of SC motoneurons in rotenone-induced experimental Parkinsonism. Thus, this is the first report of its kind in which the selective vulnerability of a putative parkinsonian target outside of nigrostriatal system has been tested using an environmental toxin to understand the pathophysiology of PD. Moreover, rotenone-induced degeneration of SC motoneuron in this model of experimental Parkinsonism progressed with upregulation of calpain and caspase-3.

Heat-shock protein 105 interacts with and suppresses aggregation of mutant Cu/Zn superoxide dismutase: clues to a possible strategy for treating ALS

A dominant mutation in the gene for copper-zinc superoxide dismutase (SOD1) is the most frequent cause of the inherited form of amyotrophic lateral sclerosis. Mutant SOD1 provokes progressive degeneration of motor neurons by an unidentified acquired toxicity. Exploiting both affinity purification and mass spectrometry, we identified a novel interaction between heat-shock protein 105 (Hsp105) and mutant SOD1. We detected this interaction both in spinal cord extracts of mutant SOD1(G93A) transgenic mice and in cultured neuroblastoma cells. Expression of Hsp105, which is found in mouse motor neurons, was depressed in the spinal cords of SOD1(G93A) mice as disease progressed, while levels of expression of two other heat-shock proteins, Hsp70 and Hsp27, were elevated. Moreover, Hsp105 suppressed the formation of mutant SOD1-containing aggregates in cultured cells. These results suggest that techniques that raise levels of Hsp105 might be promising tools for alleviation of the mutant SOD1 toxicity.

Informatics-assisted Protein Profiling in a Transgenic Mouse Model of Amyotrophic Lateral Sclerosis

One of the causes of amyotrophic lateral sclerosis (ALS) is due to mutations in Cu,Zn-superoxide dismutase (SOD1). The mutant protein exhibits a toxic gain of function that adversely affects the function of neurons in the spinal cord, brain stem, and motor cortex. A proteomic analysis of protein expression in a widely used mouse model of ALS was undertaken to identify differences in protein expression in the spinal cords of mice expressing a mutant protein with the G93A mutation found in human ALS. Protein profiling was done on soluble and particulate fractions of spinal cord extracts using high throughput two-dimensional liquid chromatography coupled to tandem mass spectrometry. An integrated proteomics-informatics platform was used to identify relevant differences in protein expression based upon the abundance of peptides identified by database searching of mass spectrometry data. Changes in the expression of proteins associated with mitochondria were particularly prevalent in spinal cord proteins from both mutant G93A-SOD1 and wild-type SOD1 transgenic mice. G93A-SOD1 mouse spinal cord also exhibited differences in proteins associated with metabolism, protein kinase regulation, antioxidant activity, and lysosomes. Using gene ontology analysis, we found an overlap of changes in mRNA expression in presymptomatic mice (from microarray analysis) in three different gene categories. These included selected protein kinase signaling systems, ATP-driven ion transport, and neurotransmission. Therefore, alterations in selected cellular processes are detectable before symptomatic onset in ALS mouse models. However, in late stage disease, mRNA expression analysis did not reveal significant changes in mitochondrial gene expression but did reveal concordant changes in lipid metabolism, lysosomes, and the regulation of neurotransmission. Thus, concordance of proteomic and mRNA expression data within multiple categories validates the use of gene ontology analysis to compare different types of "omic" data.

Dopamine transporter immunoreactivity in peripheral blood mononuclear cells in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a chronic progressive neuromuscular disorder of unknown etiology, characterized by weakness, muscle wasting, fasciculations, and increased reflexes, with conserved intellect and higher functions. The neuropathology of ALS is mostly confined to damage of the motor neurons in the cerebral cortex, some motor nuclei of the brainstem, and anterior horns of the spinal cord. However, there is evidence for the involvement of other neuronal systems in the disease. In particular, damage of the dopamine neurons has been shown by neurochemical and imaging studies in the brain and spinal cord of ALS patients. Recent reports suggest that peripheral blood mononuclear cells (PBMC) may represent a useful in vivo model to study neurochemical alterations that occur in neurodegenerative disorders. Here we demonstrate the significant reduction of dopamine transporter immunoreactivity in PBMC of patients affected by ALS with respect to healthy subjects. These results extend our knowledge of damage of the dopamine system in ALS to peripheral cells. Thus, the original concept of ALS as an isolated degeneration of motor neurons seems to extend to a more widespread understanding of the disease with involvement of other neuronal systems in the central as well as peripheral nervous system.

Ascending neuropathology in the CNS of a mutant SOD1 mouse model of amyotrophic lateral sclerosis

Transgenic mice expressing a mutated human Cu/Zn superoxide dismutase (SOD1) gene develop a motor neuron disease similar to familial amyotrophic lateral sclerosis (FALS). While the histopathology and the inflammatory reactions in the spinal cord of these mice are well described, their spatiotemporal extension into brain areas and the relationship between degenerative and inflammatory events remain obscure. In the present study, we investigated the time course and extent of degenerative changes and inflammatory reactions in the CNS during progression of the disease in a transgenic FALS model, the SOD1-G93A mouse with histological and immunohistochemical methods. Compared to non-transgenic littermates, the SOD1-G93A transgenics developed widespread degeneration in both motor and extra-motor regions up to telencephalic regions, including the cerebral cortex but sparing distinct regions like the striatum and hippocampus. We provide evidence that these degenerative processes are accompanied by intense inflammatory reactions in the brain, which spatiotemporally correlate with degeneration and comprise besides strong astro- and microgliotic reactions also an influx of peripheral immune cells such as T-lymphocytes and dendritic cells. Both degeneration and inflammatory reactions spread caudocranially, starting at 2 months in the spinal cord and reaching the telencephalon at 5 months of age. Since the corticospinal tract lacked any signs of degeneration, we conclude that the upper and the lower motor neurons degenerate independently of each other.

Early abnormalities in transgenic mouse models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative and fatal human disorder characterized by progressive loss of motor neurons. Transgenic mouse models of ALS are very useful to study the initial mechanisms underlying this neurodegenerative disease. We will focus here on the earlier abnormalities observed in superoxide dismutase 1 (SOD1) mutant mice. Several hypotheses have been advanced to explain the selective loss of motor neurons such as apoptosis, neurofilament disorganisation, oxidative stress, mitochondrial dysfunction, astrogliosis and excitotoxicity. Although disease onset appears at adulthood, recent studies have detected abnormalities during embryonic and postnatal maturation in animal models of ALS. We reported that SOD1(G85R) mutant mice exhibit specific delays in acquiring sensory-motor skills during the first week after birth. In addition, physiological measurements on in vitro spinal cord preparations reveal defects in evoking rhythmic activity with N-methyl-DL-aspartate and serotonin at lumbar, but not sacral roots. This is potentially significant, as functions involving sacral roots are spared at late stages of the disease. Moreover, electrical properties of SOD1 lumbar motoneurons are altered as early as the second postnatal week when mice begin to walk. Alterations concern the input resistance and the gain of SOD1 motoneurons which are lower than in control motoneurons. Whether or not the early changes in discharge firing are responsible for the uncoupling between motor axon terminals and muscles is still an open question. A link between these early electrical abnormalities and the late degeneration of motoneurons is proposed in this short review. Our data suggest that ALS, as other neurodegenerative diseases, could be a consequence of an abnormal development of neurons and network properties. We hypothesize that the SOD1 mutation could induce early changes during the period of maturation of motor systems and that compensatory mechanisms-linked to developmental spinal plasticity-might explain the late onset of the disease.

Targeted Antioxidative and Neuroprotective Properties of the Dopamine Agonist Pramipexole and Its Nondopaminergic Enantiomer SND919CL2x [(+)2-Amino-4,5,6,7-tetrahydro-6-lpropylamino-benzathiazole Dihydrochloride]

Pramipexole has been shown to possess neuroprotective properties in vitro that are partly independent of its dopaminergic agonism. The site of neuroprotective action is still unknown. Using [(3)H]pramipexole, we show that the drug enters and accumulates in cells and mitochondria. Detoxification of reactive oxygen species (ROS) by pramipexole is shown in vitro and in vivo by evaluating mitochondrial ROS release and aconitase-2 activity, respectively. Pramipexole and its (+)-enantiomer SND919CL2X [low-affinity dopamine agonist; (+)2-amino-4,5,6,7-tetrahydro-6-l-propylamino-benzathiazole dihydrochloride] possess equipotent efficacy toward hydrogen peroxide and nitric oxide generated in vitro and inhibit cell death in glutathione-depleted neuroblastoma cells. IC(50) values ranged from 15 to 1000 microM, consistent with the reactivity of the respective radical and the compartmentalization of ROS generation and ROS detoxification. Finally, both compounds were tested in superoxide dismutase 1-G93A mice, a model of familial amyotrophic lateral sclerosis. SND919CL2X (100 mg/kg) prolongs survival time and preserves motor function in contrast to pramipexole (3 mg/kg), which shows an increase in running wheel activity before disease onset, presumably caused by the dopaminergic agonism. We conclude that both enantiomers, in addition to their dopaminergic activity, are able to confer neuroprotective effects by their ability to accumulate in brain, cells, and mitochondria where they detoxify ROS. However, a clinical use of pramipexole as a mitochondria-targeted antioxidant is unlikely, because the high doses needed for antioxidative action in vitro are not accessible in vivo due to dopaminergic side effects. In contrast, SND919CL2X may represent the prototype of a mitochondria-targeted neuroprotectant because it has the same antioxidative properties without causing adverse effects.

Magnetic resonance imaging reveals neuronal degeneration in the brainstem of the superoxide dismutase 1G93A G1H transgenic mouse model of amyotrophic lateral sclerosis

Magnetic resonance imaging (MRI) is becoming the preferred neuroimaging modality for the diagnosis of human amyotrophic lateral sclerosis (ALS). A useful animal model of ALS is the superoxide dismutase 1G93A G1H transgenic mouse, which shows many of the clinico-pathological features of the human condition. We have employed a 4.7-Tesla MRI instrument to determine whether a noninvasive imaging approach can reveal pathological changes in the nervous system of this animal model. Our T2-weighted MRI revealed consistent changes in brain and brainstem of these mice. Hyperintensities, indicative of neuropathology, were observed in several areas including the nucleus ambiguus, facial nucleus, trigeminal motor nucleus, rostroventrolateral reticular nucleus, lateral paragigantocellular nucleus and the substantia nigra. Histology analysis including neuronal counts of the imaged brains confirmed the T2-weighted MRI findings. Enlarged ventricles and hypointense striations, indicative of global atrophy, were also observed in the brain and cerebellum. This atrophy was confirmed by fresh brain weight data. The extensive global degeneration involving multiple structures suggests a multisystem disease that is similar to human ALS.

Lessons from models of SOD1-linked familial ALS

Ten years ago, the linkage between mutations in the gene coding for the antioxidant enzyme Cu,Zn superoxide dismutase (SOD1) and the neurodegenerative disease known as familial amyotrophic lateral sclerosis (FALS) was established. This finding has prompted a myriad of new studies in experimental models aimed at investigating the toxic function of the mutant enzymes. The cellular functions that are impaired in motoneurons as a consequence of molecular alterations induced by the expression of FALS SOD1 converge on pathways that might be activated in sporadic ALS by other toxic factors. Recent data demonstrate that, although motoneurons are lost in patients, other cell types are also affected and actively contribute to the pathogenesis of the disease.

Life span extension and reduced neuronal death after weekly intraventricular cyclosporin injections in the G93A transgenic mouse model of amyotrophic lateral sclerosis

Object. The authors investigated whether cyclosporin A (CsA), a cyclophilin ligand with mitochondrial permeability transition pore-blocking and calcineurin-inhibiting properties, affects motor function, neuronal death, and life span in the G93A transgenic mouse model of familial amyotrophic lateral sclerosis (FALS).

Methods. The G93A mice received weekly intracerebroventricular injections of CsA (20 µg/mouse/week) starting at the age of 65 days, and physical performance on an exercise wheel was monitored beginning at 84 days of age. Mice were allowed to survive for clinical observation of body weight, hindlimb weakness, and life span or until a defined end stage or were killed at 110 days of age for histological analysis.

Conclusions. Treatment with CsA significantly delayed the onset of hindlimb weakness and also extended the time from its onset to paralysis. The overall life span of CsA-treated G93A mice was significantly extended, by 12% compared with vehicle-treated transgenic littermates. The CsA also prolonged physical performance on the exercise wheel and delayed weight loss. Histologically, there was significant preservation of both cervical and lumbar spine motor neurons and also tyrosine hydroxylase—positive dopaminergic substantia nigra neurons in 110-day-old CsA-treated mice compared with their transgenic littermates. The local administration of CsA directly into the brain ventricles is an effective means of central nervous system drug delivery (because CsA does not readily cross the blood—brain barrier), which in this study ameliorated clinical and neuropathological features of FALS in G93A mice. The remarkably low intrathecal CsA dose required for neuroprotection reduces potential adverse effects of systemic immunosuppression or nephrotoxicity seen with chronic systemic delivery of the drug.

Additive neuroprotective effects of creatine and cyclooxygenase 2 inhibitors in a transgenic mouse model of amyotrophic lateral sclerosis

There is substantial evidence implicating both inflammation and mitochondrial dysfunction in amyotrophic lateral sclerosis (ALS) pathogenesis. We investigated the therapeutic effects of cyclooxygenase 2 (COX-2) inhibitors both alone and in combination with creatine in the G93A transgenic mouse model of ALS. Oral administration of either celecoxib or rofecoxib significantly improved motor performance, attenuated weight loss and extended survival. The administration of COX-2 inhibitors significantly reduced prostaglandin E2 levels at 110 days of age. The combination of creatine with COX-2 inhibitors produced additive neuroprotective effects and extended survival by approximately 30%. The COX-2 inhibitors significantly protected against depletion of anterior horn motor neurons and creatine with COX-2 inhibitors showed greater protection than COX-2 inhibitors alone. These results suggest that combinations of therapies targeting different disease mechanisms may be a useful strategy in the treatment of ALS.

Neuromuscular accumulation of mutant superoxide dismutase 1 aggregates in a transgenic mouse model of familial amyotrophic lateral sclerosis

Superoxide dismutase 1 (SOD1) aggregates are a histological and biochemical correlate of disease progression in neural tissues from mutant SOD1-linked forms of familial amyotrophic lateral sclerosis (FALS). In the present study, we assayed the monomeric and high molecular weight mutant SOD1 content of nervous, muscle and visceral tissues from transgenic SOD1(G93A) mice using immunoblotting and zymograms. A progressive age-dependent increase in mutant SOD1 level, aggregation and stabilisation by cross-species heterodimers was determined in lumbar spinal cord, sciatic nerve and gastrocnemius muscle. Such biochemical abnormalities were not present in cervical spinal cord, brainstem and diaphragm muscle, nor common to endogenous mouse SOD1. Mutant dismutase activity in general did not increase correspondingly with accumulating protein at later ages. These results suggest that peripheral targets such as hindlimb skeletal muscle and nerve accumulate mutant SOD1 aggregates and may therefore be susceptible to mutant SOD1-mediated toxicity, in addition to lower and upper motor neurons of the central nervous system in transgenic FALS mice.

Opposing effects of low and high-dose clozapine on survival of transgenic amyotrophic lateral sclerosis mice

Clozapine is a potent atypical neuroleptic or antipsychotic agent used to relieve symptoms of early-diagnosed schizophrenia. Aside from well-described dopamine and serotonin receptor blockade effects, clozapine may also be neuroprotective through its modulation of the p75 neurotrophin receptor (p75(NTR)) and superoxide dismutase 1 (SOD1) expression. The death-signalling activities of both p75(NTR) and mutant SOD1 are implicated in motor neuron degeneration in humans and transgenic mice with amyotrophic lateral sclerosis (ALS). We therefore investigated the effects of clozapine in cell culture and mouse models of ALS. Clozapine dose-dependently inhibited full-length and cleaved p75(NTR) but not SOD1 protein expression in the motor neuron-like (NSC-34) cell line. Furthermore, low concentrations of clozapine protected NSC-34 cells from paraquat-mediated superoxide toxicity, nerve growth factor (NGF)-induced death signalling, and serum deprivation, whereas high concentrations potentiated death. Systemic thrice-weekly administration of low and high-dose clozapine to mutant superoxide dismutase 1 (SOD1(G93A)) mice produced differential effects on disease onset and survival. Low-dose treatment was associated with delayed locomotor impairment and death, compared to high-dose clozapine, which accelerated paralysis and mortality (P < 0.05). Increased death was not attributable to toxicity, as clozapine-induced agranulocytosis was not detected from blood analysis. High-dose clozapine, however, produced extrapyramidal symptoms in mice manifest by hindlimb rigidity, despite reducing spinal cord p75(NTR) levels overall. These results suggest that although clozapine may exert p75(NTR)-mediated neuroprotective activity in vitro, its profound antagonistic effects on dopaminergic and serotonergic systems in vivo at high doses may exacerbate the phenotype of transgenic ALS mice.

Minute quantities of misfolded mutant superoxide dismutase-1 cause amyotrophic lateral sclerosis

Mutant forms of superoxide dismutase-1 (SOD1) cause amyotrophic lateral sclerosis (ALS) by an unknown noxious mechanism. Using an antibody against a novel epitope in the G127insTGGG mutation, mutant SOD1 was studied for the first time in spinal cord and brain of an ALS patient. The level was below 0.5% of the SOD1 level in controls. In corresponding transgenic mice the content of mutant SOD1 was also low, although it was enriched in spinal cord and brain compared with other tissues. In the mice the misfolded mutant SOD1 aggregated rapidly and 20% occurred in steady state as detergent-soluble protoaggregates. The misfolded SOD1 and the protoaggregates form, from birth until death, a potentially noxious burden that may induce the motor neuron injury. Detergent-resistant aggregates, as well as inclusions of mutant SOD1 in motor neurons and astrocytes, accumulated in spinal cord ventral horns of the patient and mice with terminal disease. The inclusions and aggregates may serve as terminal markers of long-term assault by misfolded SOD1 and protoaggregates.

Parkinson's disease: mechanisms and models

Parkinson's disease (PD) results primarily from the death of dopaminergic neurons in the substantia nigra. Current PD medications treat symptoms; none halt or retard dopaminergic neuron degeneration. The main obstacle to developing neuroprotective therapies is a limited understanding of the key molecular events that provoke neurodegeneration. The discovery of PD genes has led to the hypothesis that misfolding of proteins and dysfunction of the ubiquitin-proteasome pathway are pivotal to PD pathogenesis. Previously implicated culprits in PD neurodegeneration, mitochondrial dysfunction and oxidative stress, may also act in part by causing the accumulation of misfolded proteins, in addition to producing other deleterious events in dopaminergic neurons. Neurotoxin-based models (particularly MPTP) have been important in elucidating the molecular cascade of cell death in dopaminergic neurons. PD models based on the manipulation of PD genes should prove valuable in elucidating important aspects of the disease, such as selective vulnerability of substantia nigra dopaminergic neurons to the degenerative process.

Altered long-term corticostriatal synaptic plasticity in transgenic mice overexpressing human CU/ZN superoxide dismutase (GLY(93)-->ALA) mutation

Apart from the extensive loss of motor neurons, degeneration of midbrain dopaminergic cells has been described in both familial and sporadic forms of amyotrophic lateral sclerosis (ALS). Mice overexpressing the mutant human Cu/Zn superoxide dismutase (SOD1) show an ALS-like phenotype in that they show a progressive death of motor neurons accompanied by degeneration of dopaminergic cells. To describe the functional alterations specifically associated with this dopaminergic dysfunction, we have investigated the corticostriatal synaptic plasticity in mice overexpressing the human SOD1 (SOD1+) and the mutated (Gly(93)-->Ala) form (G93A+) of the same enzyme. We show that repetitive stimulation of the corticostriatal pathway generates long-term depression (LTD) in SOD1+ mice and in control (G93A-/SOD1-) animals, whereas in G93A+ mice the same stimulation generates an N-methyl-D-aspartic acid receptor-dependent long-term potentiation. No significant alterations were found in the intrinsic membrane properties of striatal medium spiny neurons and basal corticostriatal synaptic transmission of G93A+ mice. Bath perfusion of dopamine or the D(2) dopamine receptor agonist quinpirole restored LTD in G93A+ mice. Consistent with these in vitro results, habituation of locomotor activity and striatal-dependent active avoidance learning were impaired in G93A+ mice. Thus, degeneration of dopaminergic neurons in the substantia nigra of G93A+ mice causes substantial modifications in striatal synaptic plasticity and related behaviors, and may be a cellular substrate of the extrapyramidal motor and cognitive disorders observed in familial and sporadic ALS.

Degeneration of corticospinal and bulbospinal systems in the superoxide dismutase 1(G93A G1H) transgenic mouse model of familial amyotrophic lateral sclerosis

In the superoxide dismutase 1 (SOD1)(G93A G1H) transgenic mouse, the primary pathology and disease signs are associated with the degeneration of motor neurons in the lumbar spinal cord. It is unclear if the descending motor pathways from the cortex and brainstem are also compromised. The retrograde tracer Fluorogold was inserted into the T(12) segment of the spinal cord and the number of labelled neurons counted in the sensorimotor cortex and brainstem of 60, 90 and 110 day-old mice. A small loss of corticospinal and bulbospinal projections was detected at 60 days. By 110 days, 53% of corticospinal, 41% of bulbospinal and 43% of rubrospinal neurons were lost. The progressive loss of corticospinal axons was confirmed using the stereological fractionator method. These findings suggest that the expression of the SOD1(G93A G1H) mutant protein results in a disease that resembles the late stages of human motor neuron disease. This involves not only the destruction of lower motor neurons in the spinal cord, but also additional loss of descending cortical and bulbar neurons.

Resistance to striatal dopamine depletion induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice expressing human mutant Cu,Zn superoxide dismutase

Recent data indicate that overexpression of the enzyme Cu,Zn superoxide dismutase (SOD1) in mice confers neuroprotection against various dopamine neurotoxins like 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), methamphetamine, 6-hydroxydopamine and methylenedioxymethamphetamine. In the present study we investigated whether a mutant form of SOD1 (G93A), occurring in humans affected by amyotrophic lateral sclerosis, leads to a differential vulnerability of nigrostriatal dopaminergic neurons to the chronic dopamine depletion induced by the selective neurotoxin MPTP. Our results indicate that overexpression of both wild-type and human mutant SOD1 induces comparable neuroprotective effects against striatal dopaminergic depletion.

Engineered modeling and the secrets of Parkinson's disease

The development of new methods for manipulating the animal genome by transgenic and gene-targeting technologies provides a unique means of studying the most intimate aspects of countless human diseases, including Parkinson's disease (PD). In this review, the contribution of such engineered models to our current understanding of the pathophysiology, etiology and pathogenesis of PD will be discussed.

Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration

Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.

Transgenic ALS mice show increased vulnerability to the mitochondrial toxins MPTP and 3-nitropropionic acid

The pathogenesis of neurodegenerative diseases may involve a genetic predisposition acting in concert with environmental toxins. To test this hypothesis we examined whether transgenic mice with the G93A mutation in Cu,Zn superoxide dismutase show increased vulnerability to either 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 3-nitropropionic acid (3-NP). Compared to littermate controls G93A transgenic mice showed a greater loss of striatal dopamine, DOPAC, and HVA at 50, 70, and 120 days of age following administration of MPTP; however, cell loss in the substantia nigra was not greater. The G93A transgenic mice showed significantly increased vulnerability to striatal lesions produced by 3-NP compared with littermate controls at 120 days of age. The finding that G93A mice show increased vulnerability to mitochondrial toxins further implicates mitochondrial dysfunction in the pathogenesis of neuronal death in these mice. The findings support the hypothesis that a genetic defect can increase susceptibility to environmental toxins and that this may play a role in the pathogenesis of neurodegenerative diseases.