Mécanismes moléculaires de la sclérose latérale amyotrophique : apports récents de l’analyse de modèles animaux

Specific Physical Exercise Improves Energetic Metabolism in the Skeletal Muscle of Amyotrophic-Lateral- Sclerosis Mice

Amyotrophic Lateral Sclerosis is an adult-onset neurodegenerative disease characterized by the specific loss of motor neurons, leading to muscle paralysis and death. Although the cellular mechanisms underlying amyotrophic lateral sclerosis (ALS)-induced toxicity for motor neurons remain poorly understood, growing evidence suggest a defective energetic metabolism in skeletal muscles participating in ALS-induced motor neuron death ultimately destabilizing neuromuscular junctions. In the present study, we report that a specific exercise paradigm, based on a high intensity and amplitude swimming exercise, significantly improves glucose metabolism in ALS mice. Using physiological tests and a biophysics approach based on nuclear magnetic resonance (NMR), we unexpectedly found that SOD1(G93A) ALS mice suffered from severe glucose intolerance, which was counteracted by high intensity swimming but not moderate intensity running exercise. Furthermore, swimming exercise restored the highly ALS-sensitive tibialis muscle through an autophagy-linked mechanism involving the expression of key glucose transporters and metabolic enzymes, including GLUT4 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Importantly, GLUT4 and GAPDH expression defects were also found in muscles from ALS patients. Moreover, we report that swimming exercise induced a triglyceride accumulation in ALS tibialis, likely resulting from an increase in the expression levels of lipid transporters and biosynthesis enzymes, notably DGAT1 and related proteins. All these data provide the first molecular basis for the differential effects of specific exercise type and intensity in ALS, calling for the use of physical exercise as an appropriate intervention to alleviate symptoms in this debilitating disease.

Protein folding stress in neurodegenerative diseases: a glimpse into the ER

Several neurodegenerative diseases share common neuropathology, primarily featuring the presence in the brain of abnormal protein inclusions containing specific misfolded proteins. Recent evidence indicates that alteration in organelle function is a common pathological feature of protein misfolding disorders, highlighting perturbations in the homeostasis of the endoplasmic reticulum (ER). Signs of ER stress have been detected in most experimental models of neurological disorders and more recently in brain samples from human patients with neurodegenerative disease. To cope with ER stress, cells activate an integrated signaling response termed the unfolded protein response (UPR), which aims to reestablish homeostasis in part through regulation of genes involved in protein folding, quality control and degradation pathways. Here we discuss the particular mechanisms currently proposed to be involved in the generation of protein folding stress in different neurodegenerative conditions and speculate about possible therapeutic interventions.

Amyotrophic lateral sclerosis pathogenesis: a journey through the secretory pathway

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motoneuron degenerative disease characterized by the selective loss of motoneurons in the spinal ventral horn, most brainstem nuclei, and the cerebral cortex. Although approximately 90% of ALS cases are sporadic (sALS), analyses of familial ALS (fALS)-causative genes have generated relevant insight into molecular events involved in the pathology. Here we overview an emerging concept indicating the occurrence of secretory pathway stress in the disease process. These alterations include a failure in the protein folding machinery at the endoplasmic reticulum (ER), engagement of the unfolded protein response (UPR), modifications of the Golgi apparatus network, impaired vesicular trafficking, inhibition of protein quality control mechanisms, oxidative damage to ER proteins, and sustained activation of degradative pathways such as autophagy. A common feature predicted for most of these alterations is abnormal protein homeostasis associated with the accumulation of misfolded proteins at the ER, possibly leading to chronic ER stress and neuronal dysfunction. Signs of ER stress are observed even during presymptomatic stages in fALS mouse models, and pharmacological strategies to alleviate protein misfolding slow disease progression. Because the secretory pathway stress occurs in both sALS and several forms of fALS, it may offer a unique common target for possible therapeutic strategies to treat this devastating disease.

SK-PC-B70M alleviates neurologic symptoms in G93A-SOD1 amyotrophic lateral sclerosis mice

SK-PC-B70M, an oleanolic-glycoside saponins fraction extracted from the root of Pulsatilla koreana, carries active ingredient(s) that protects the cytotoxicity induced by Aβ(1-42) in SK-N-SH cells. It was recently demonstrated that SK-PC-B70M improved scopolamine-induced deficits of memory consolidation and spatial working memory in rats, and reduced Aβ levels and plaque deposition in the brains of the Tg2576 mouse model of Alzheimer disease. In the present study, we investigated whether SK-PC-B70M produces helpful effects on the pathology of the G93A-SOD1 transgenic mouse model of amyotrophic lateral sclerosis (ALS). Administration of SK-PC-B70M (100 or 400 mg/kg/day) from 8 weeks to 16 weeks of age attenuated neurological deficits of G93A-SOD1 mice in several motor-function-related behavioral tests. SK-PC-B70M treatment significantly suppressed the accumulation of the by-products of lipid peroxidation, malonedialdehyde (MDA) and 4-hydroxy-2-nonenal (HNE), in the spinal cord of G93A-SOD1 mice. Moreover, histologic analysis stained with cresyl violet or anti-choline acetyltransferase (ChAT) revealed that SK-PC-B70M suppressed neuronal loss in the ventral horn of the spinal cords of G93A-SOD1 mice. These results suggest that SK-PC-B70M affords a beneficial effect on neurologic deficits of G93A-SOD1 ALS mice.

P-glycoprotein expression and function are increased in an animal model of amyotrophic lateral sclerosis

The efflux pumps located at the blood-brain barrier (BBB) prevent drugs entering the brain. As such, efflux pumps are a major obstacle to drug brain distribution. Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with little therapeutics available: riluzole is the only drug approved in its treatment. The lack of response to treatment in ALS may be, at least in part, due to increased activities of efflux pumps in relation to disease, leading to subtherapeutic brain concentrations of drugs. In the present study, we used a transgenic mouse model of ALS (G86R mSOD1 mice) to test this hypothesis. Expression and functionality of P-glycoprotein (ABCB1, P-gp) and Breast Cancer Resistance Protein (ABCG2, BCRP), two major efflux pumps, were studied. We observed an increased P-gp expression (1.5-fold) in presymptomatic mSOD1 mice compared to wild-type controls. Consistent with this, P-gp function was also increased by 1.5-fold and riluzole brain disposition was decreased by 1.7-fold in mSOD1 mice. Contrasting with this, BCRP expression and function were unaltered by the pathology. These results demonstrate that BBB transport proteins are modified in G86R mSOD1 mice ALS model. Such findings underline potential problems in extrapolating the results of animal studies to humans and developing clinical trials, especially for drugs transported by P-gp.

Microarray analysis of the cellular pathways involved in the adaptation to and progression of motor neuron injury in the SOD1 G93A mouse model of familial ALS

The cellular pathways of motor neuronal injury have been investigated in the SOD1 G93A murine model of familial amyotrophic lateral sclerosis (ALS) using laser-capture microdissection and microarray analysis. The advantages of this study include the following: analysis of changes specifically in motor neurons (MNs), while still detecting effects of interactions with neighboring cells; the ability to profile changes during disease progression, an approach not possible in human ALS; and the use of transgenic mice bred on a homogeneous genetic background, eliminating the confounding effects arising from a mixed genetic background. By using this rigorous approach, novel changes in key cellular pathways have been detected at both the presymptomatic and late stages, which have been validated by quantitative reverse transcription-PCR. At the presymptomatic stage (60 d), MNs extracted from SOD1 G93A mice show a significant increase in expression of genes subserving both transcriptional and translational functions, as well as lipid and carbohydrate metabolism, mitochondrial preprotein translocation, and respiratory chain function, suggesting activation of a strong cellular adaptive response. Mice 90 d old still show upregulation of genes involved in carbohydrate metabolism, whereas transcription and mRNA processing genes begin to show downregulation. Late in the disease course (120 d), important findings include the following: marked transcriptional repression, with downregulation of multiple transcripts involved in transcriptional and metabolic functions; upregulation of complement system components; and increased expression of key cyclins involved in cell-cycle regulation. The changes described in the motor neuron transcriptome evolving during the disease course highlight potential novel targets for neuroprotective therapeutic intervention.

Mitochondria in amyotrophic lateral sclerosis: a trigger and a target

Strong evidence shows that mitochondrial dysfunction is involved in amyotrophic lateral sclerosis (ALS), but despite the fact that mitochondria play a central role in excitotoxicity, oxidative stress and apoptosis, the intimate underlying mechanism linking mitochondrial defects to motor neuron degeneration in ALS still remains elusive. Morphological and functional abnormalities occur in mitochondria in ALS patients and related animal models, although their exact nature and extent are controversial. Recent studies postulate that the mislocalization in mitochondria of mutant forms of copper-zinc superoxide dismutase (SOD1), the only well-documented cause of familial ALS, may account for the toxic gain of function of the enzyme, and hence induce motor neuron death. On the other hand, mitochondrial dysfunction in ALS does not seem to be restricted only to motor neurons as it is also present in other tissues, particularly the skeletal muscle. The presence of this 'systemic' defect in energy metabolism associated with the disease is supported in skeletal muscle tissue by impaired mitochondrial respiration and overexpression of uncoupling protein 3. In addition, the lifespan of transgenic mutant SOD1 mice is increased by a highly energetic diet compensating both the metabolic defect and the motorneuronal function. In this review, we will focus on the mitochondrial dysfunction linked to ALS and the cause-and-effect relationships between mitochondria and the pathological mechanisms thought to be involved in the disease.

Mutational analysis of the Cu/Zn superoxide dismutase gene in a Catalan ALS population: should all sporadic ALS cases also be screened for SOD1?

BACKGROUND

SOD1 gene mutations are the most common identified cause of ALS, accounting for approximately 20% of familial ALS cases and around 4% of sporadic ALS cases. However, the prevalence of SOD1 varies in different ethnic groups. No previous epidemiological studies have been carried out in Catalonia.

OBJECTIVE

To determine the prevalence of SOD1 gene mutations in a Catalan ALS population, and to analyze the genotype-phenotype relationship.

MATERIALS AND METHODS

30 different FALS pedigrees and 94 sporadic ALS patients were screened for SOD1 mutations using direct sequence analysis.

RESULTS

Five of the 30 FALS pedigrees (16.6%) carried a SOD1 mutant. The mutations identified in this group were G37R, D76V, S105L, I112M and N139H. Four SOD1 mutants (4.25%) were found in the sporadic ALS group (SALS). The overall frequency (FALS plus SALS) of SOD1 mutations in our series was 6.45%. In the SALS group, D90A was identified in a patient presenting the typical Scandinavian phenotype. A 53-year-old woman with no family history of ALS carried the N139H mutation. Two unrelated sporadic ALS cases carried the A140A SOD1 mutant.

CONCLUSIONS

The prevalence of the SOD1 mutation in FALS in Catalonia is similar to levels in other Mediterranean countries, but lower than those in reports studying the Belgian, Japanese, and Scottish populations. The prevalence of the SOD1 mutation was 4.25% in patients with no family history of ALS. These results may have significant repercussions on genetic counseling, and screening for the SOD1 mutation in sporadic ALS cases must therefore be considered.

Gene-based treatment of motor neuron diseases

Motor neuron diseases (MND), such as amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA), are progressive neurodegenerative diseases that share the common characteristic of upper and/or lower motor neuron degeneration. Therapeutic strategies for MND are designed to confer neuroprotection, using trophic factors, anti-apoptotic proteins, as well as antioxidants and anti-excitotoxicity agents. Although a large number of therapeutic clinical trials have been attempted, none has been shown satisfactory for MND at this time. A variety of strategies have emerged for motor neuron gene transfer. Application of these approaches has yielded therapeutic results in cell culture and animal models, including the SOD1 models of ALS. In this study we describe the gene-based treatment of MND in general, examining the potential viral vector candidates, gene delivery strategies, and main therapeutic approaches currently attempted. Finally, we discuss future directions and potential strategies for more effective motor neuron gene delivery and clinical translation.

The metabolic hypothesis in amyotrophic lateral sclerosis: insights from mutant Cu/Zn-superoxide dismutase mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by selective loss of motor neurons and progressive muscle atrophy. A subset of patients harbors point mutations in the gene encoding Cu/Zn-superoxide dismutase (SOD1), which allowed the generation of transgenic mice that express different SOD1 mutations and develop an ALS-like pathology. Recently, we reported in these mice the occurrence of a characteristic defect in energy homeostasis and the beneficial effect on the course of the disease of a high-energy fat-enriched diet. In this review, we discuss the implication of these findings in the light of classical clinical observations concerning metabolic alterations in human ALS.