Mechanisms Of Motor Neuron Degeneration Research Articles

The usage and advantages of several common amyotrophic lateral sclerosis animal models.

Amyotrophic lateral sclerosis is a fatal, multigenic, multifactorial neurodegenerative disease characterized by upper and lower motor neuron loss. Animal models are essential for investigating pathogenesis and reflecting clinical manifestations, particularly in developing reasonable prevention and therapeutic methods for human diseases. Over the decades, researchers have established a host of different animal models in order to dissect amyotrophic lateral sclerosis (ALS), such as yeast, worms, flies, zebrafish, mice, rats, pigs, dogs, and more recently, non-human primates. Although these models show different peculiarities, they are all useful and complementary to dissect the pathological mechanisms of motor neuron degeneration in ALS, contributing to the development of new promising therapeutics. In this review, we describe several common animal models in ALS, classified by the naturally occurring and experimentally induced, pointing out their features in modeling, the onset and progression of the pathology, and their specific pathological hallmarks. Moreover, we highlight the pros and cons aimed at helping the researcher select the most appropriate among those common experimental animal models when designing a preclinical ALS study.

Mouse model of voluntary movement deficits induced by needlestick injuries to the primary motor cortex

BackgroundMotor handicap is prevalent in patients with traumatic brain injury, but currently. there is a challenging task to prevent the degeneration of motor neurons and to fully recover the. voluntary movement after injury. New methodFor the first time, we propose to apply needlestick injuries to the primary motor cortex to create mouse model of voluntary movement deficits. Rotarod test, cylinder test and forepaw grip strength test were used to assay motor coordination of both C57BL/6 J and the triple immunodeficient NCG mice. Immunofluorescence staining of PKC-gamma, UCHL1, GFAP, Iba1 and Fluoro-Jade C was performed to analyze the numbers of motor neurons, microglia, astrocytes and degenerating neurons. ResultsMice on either C57BL/6 J or immunodeficient background with the unilateral primary motor cortex injury exhibit motor neuron death, activation of glial cells and deficits in voluntary movement. ConclusionsThe main finding of this study was that the unilateral primary motor cortex injured by needlesticks leads to reactive gliosis, motor neuron death and voluntary movement deficits in mice. This needlestick injury model of primary motor cortex might be useful for future exploration of underlying mechanisms of motor neuron degeneration and of promising treatment modalities such as cell transplantation to improve locomotor deficiency following neurotrauma.

Taking Cellular Heterogeneity Into Consideration When Modeling Astrocyte Involvement in Amyotrophic Lateral Sclerosis Using Human Induced Pluripotent Stem Cells.

Astrocytes are a large group of glial cells that perform a variety of physiological functions in the nervous system. They provide trophic, as well as structural, support to neuronal cells. Astrocytes are also involved in neuroinflammatory processes contributing to neuronal dysfunction and death. Growing evidence suggests important roles for astrocytes in non-cell autonomous mechanisms of motor neuron degeneration in amyotrophic lateral sclerosis (ALS). Understanding these mechanisms necessitates the combined use of animal and human cell-based experimental model systems, at least in part because human astrocytes display a number of unique features that cannot be recapitulated in animal models. Human induced pluripotent stem cell (hiPSC)-based approaches provide the opportunity to generate disease-relevant human astrocytes to investigate the roles of these cells in ALS. These approaches are facing the growing recognition that there are heterogenous populations of astrocytes in the nervous system which are not functionally equivalent. This review will discuss the importance of taking astrocyte heterogeneity into consideration when designing hiPSC-based strategies aimed at generating the most informative preparations to study the contribution of astrocytes to ALS pathophysiology.

RNA as a source of biomarkers for amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease, leads to the loss of motor neurons. There are currently no effective therapies to treat this disease as the molecular mechanisms of motor neuron degeneration are largely unknown. The diagnosis of ALS, or motor neuron disease, is not a simple process that can be carried out with one doctor visit or a single simple test. This has created a major problem for patients with ALS and their physicians since they are often not diagnosed until about a year into the disease. In order to combat this issue, new techniques of detecting the clinical and pathological changes of the disease are critical. These techniques are currently being studied and developed which can revolutionize the diagnosis of ALS. Once this technology is established, it may have application to monitor the progression of the disease. RNA-Seq is a powerful tool that has potential to identify RNA as small molecules in patients' biological samples (Plasma, Cerebral Spinal Fluid) which can be used to inform the system changes in patients with ALS. In this review, we will explore and discuss our current work on RNA-Seq and its development of biomarkers to diagnose and assess the rate of progression in the disease.

Patient-Specific Cells for Modeling and Decoding Amyotrophic Lateral Sclerosis: Advances and Challenges.

Motor neuron loss or degeneration is the typical characteristic of amyotrophic lateral sclerosis (ALS), which often leads to weakness, paralysis, or even death. The underlying mechanisms of motor neuron degeneration and ALS progression remain elusive, and there is no effective treatment for ALS. The advances of stem cells and reprogramming techniques has made it possible to generate patient-specific motor neurons as cell models for studying disease mechanisms and drug discovery. This review comprehensively discusses recent approaches to generate motor neurons from stem cells and somatic cells and highlights the application of induced motor neurons to modeling ALS diseases, dissecting the pathogenesis, and screening new drugs. New perspectives are also discussed on generating patient-specific motor neuron subtypes that are affected by ALS or creating 3D spinal cord organoid models for better recapitulating and understanding ALS.

RNA-Seq Analysis of Spinal Cord Tissues from hPFN1G118V Transgenic Mouse Model of ALS at Pre-symptomatic and End-Stages of Disease

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that leads to the loss of motor neurons. The molecular mechanisms of motor neuron degeneration are largely unknown and there are currently no effective therapies to treat this disease. In this work, we report whole transcriptome profiling of spinal cords of mutant transgenic hPFN1G118V mice and their wildtype transgenic hPFN1WT controls at a pre-symptomatic stage and at the end-stage of disease. Analyses revealed that end-stage hPFN1G118V mice had 890 differentially expressed genes (747 up-regulated, 143 down-regulated) when compared to pre-symptomatic hPFN1G118V mice, and they had 836 differentially expressed genes (742 up-regulated, 94 down-regulated) when compared to age-matched hPFN1WT controls. Pre-symptomatic hPFN1G118V mice were not significantly different from age-matched hPFN1WT controls. Ingenuity Pathway Analysis identified inflammatory pathways significantly activated in end-stage hPFN1G118V samples, suggesting an excess of glial activation at end-stage disease, possibly due to an increase in glial composition within the spinal cord during disease progression. In conclusion, our RNA-Seq data identified molecules and pathways involved in the mechanisms of neurodegeneration that could potentially serve as therapeutic targets for ALS.

MiR126-5p Downregulation Facilitates Axon Degeneration and NMJ Disruption via a Non-Cell-Autonomous Mechanism in ALS.

Axon degeneration and disruption of neuromuscular junctions (NMJs) are key events in amyotrophic lateral sclerosis (ALS) pathology. Although the disease's etiology is not fully understood, it is thought to involve a non–cell-autonomous mechanism and alterations in RNA metabolism. Here, we identified reduced levels of miR126-5p in presymptomatic ALS male mice models, and an increase in its targets: axon destabilizing Type 3 Semaphorins and their coreceptor Neuropilins. Using compartmentalized in vitro cocultures, we demonstrated that myocytes expressing diverse ALS-causing mutations promote axon degeneration and NMJ dysfunction, which were inhibited by applying Neuropilin1 blocking antibody. Finally, overexpressing miR126-5p is sufficient to transiently rescue axon degeneration and NMJ disruption both in vitro and in vivo. Thus, we demonstrate a novel mechanism underlying ALS pathology, in which alterations in miR126-5p facilitate a non–cell-autonomous mechanism of motor neuron degeneration in ALS.SIGNIFICANCE STATEMENT Despite some progress, currently no effective treatment is available for amyotrophic lateral sclerosis (ALS). We suggest a novel regulatory role for miR126-5p in ALS and demonstrate, for the first time, a mechanism by which alterations in miR126-5p contribute to axon degeneration and NMJ disruption observed in ALS. We show that miR126-5p is altered in ALS models and that it can modulate Sema3 and NRP protein expression. Furthermore, NRP1 elevations in motor neurons and muscle secretion of Sema3A contribute to axon degeneration and NMJ disruption in ALS. Finally, overexpressing miR126-5p is sufficient to transiently rescue NMJ disruption and axon degeneration both in vitro and in vivo.

Age-dependent neurodegeneration and organelle transport deficiencies in mutant TDP43 patient-derived neurons are independent of TDP43 aggregation

TAR DNA-binding protein 43 (TDP43) plays a significant role in familiar and sporadic amyotrophic lateral sclerosis (ALS). The diverse postulated mechanisms by which TDP43 mutations cause the disease are not fully understood. Human wildtype and TDP43 S393L and G294V mutant spinal motor neuron cultures were differentiated from patient-derived iPSCs. Mutant hTDP43 and wildtype motor neuron cultures did not differ in neuron differentiation capacity during early maturation stage. During aging we detected a dramatic neurodegeneration including neuron loss and pathological neurofilament abnormalities only in TDP43 mutant cultures. Additionally mitochondria and lysosomes of aging spinal motor neurons revealed robust TDP43 mutation dependent abnormal phenotypes in size, shape, speed and motility which all appeared without TDP43 mislocalization or aggregation formation. Furthermore, D-sorbitol – known to induce stress granules and cytoplasmic mislocalization of TDP43 – rescued axonal trafficking phenotypes without signs of TDP43 mislocalization or aggregation formation. Our data indicate TDP43 mutation-dependent but cytosolic aggregation-independent mechanisms of motor neuron degeneration in TDP43 ALS.

Spinal cord-specific deletion of the glutamate transporter GLT1 causes motor neuron death in mice

Amyotrophic lateral sclerosis (ALS) is a chronic neurodegenerative disorder characterized by the selective loss of motor neurons. The precise mechanisms that cause the selective death of motor neurons remain unclear, but a growing body of evidence suggests that glutamate-mediated excitotoxicity has been considered to play an important role in the mechanisms of motor neuron degeneration in ALS. Reductions in glutamate transporter GLT1 have been reported in animal models of ALS and the motor cortex and spinal cord of ALS patients. However, it remains unknown whether the reduction in GLT1 has a primary role in the induction of motor neuron degeneration in ALS. Here, we generated conditional knockout mice that lacked GLT1 specifically in the spinal cord by crossing floxed-GLT1 mice and Hoxb8-Cre mice. Hoxb8-Cre/GLT1flox/flox mice showed motor deficits and motor neuron loss. Thus, loss of the glial glutamate transporter GLT1 is sufficient to cause motor neuron death in mice.

Excitatory and Inhibitory Neuronal Circuits in the Spinal Cord and Their Role in the Control of Motor Neuron Function and Degeneration.

The complex neuronal networks of the spinal cord coordinate a wide variety of motor functions, including walking, running, and voluntary and involuntary movements. This is accomplished by different groups of neurons, called center pattern generators, which control left-right alternation and flexor-extensor patterns. These spinal circuits, located in the ventral horns, are formed by several neuronal types, and the specific function of most of them has been identified by means of studies in vivo and in the isolated spinal cord of mice harboring genetically induced ablation of specific neuronal populations. These studies have shown that the coordinated activity of several interneuron types, mainly GABAergic and glycinergic inhibitory neurons, have a crucial role in the modulation of motor neurons activity that finally excites the corresponding muscles. A pharmacological experimental approach by administering in the spinal cord agonists and antagonists of glutamate, GABA, glycine, and acetylcholine receptors to alter their synaptic action has also produced important results, linking the deficits in the synaptic function with the resulting motor alterations. These results have also increased the knowledge of the mechanisms of motor neuron degeneration, which is characteristic of diseases such as amyotrophic lateral sclerosis, and therefore open the possibility of designing new strategies for the prevention and treatment of these diseases.

Inherited Paediatric Motor Neuron Disorders: Beyond Spinal Muscular Atrophy.

Paediatric motor neuron diseases encompass a group of neurodegenerative diseases characterised by the onset of muscle weakness and atrophy before the age of 18 years, attributable to motor neuron loss across various neuronal networks in the brain and spinal cord. While the genetic underpinnings are diverse, advances in next generation sequencing have transformed diagnostic paradigms. This has reinforced the clinical phenotyping and molecular genetic expertise required to navigate the complexities of such diagnoses. In turn, improved genetic technology and subsequent gene identification have enabled further insights into the mechanisms of motor neuron degeneration and how these diseases form part of a neurodegenerative disorder spectrum. Common pathophysiologies include abnormalities in axonal architecture and function, RNA processing, and protein quality control. This review incorporates an overview of the clinical manifestations, genetics, and pathophysiology of inherited paediatric motor neuron disorders beyond classic SMN1-related spinal muscular atrophy and describes recent advances in next generation sequencing and its clinical application. Specific disease-modifying treatment is becoming a clinical reality in some disorders of the motor neuron highlighting the importance of a timely and specific diagnosis.

Non‐neuronal Cells in ALS: Role of Glial, Immune cells and Blood‐CNS Barriers

Neurological dysfunction and motor neuron degeneration in amyotrophic lateral sclerosis (ALS) is strongly associated with neuroinflammation reflected by activated microglia and astrocytes in the CNS. In ALS endogenous triggers in the CNS such as aggregated protein and misfolded proteins activate a pathogenic response by innate immune cells. However, there is also strong evidence for a neuroprotective immune response in ALS. Emerging evidence also reveals changes in the peripheral adaptive immune responses as well as alterations in the blood brain barrier that may aid traffic of lymphocytes and antibodies into the CNS. Understanding the triggers of neuroinflammation is key to controlling neuronal loss. Here, we review the current knowledge regarding the roles of non-neuronal cells as well as the innate and adaptive immune responses in ALS. Existing ALS animal models, in particular genetic rodent models, are very useful to study the underlying pathogenic mechanisms of motor neuron degeneration. We also discuss the approaches used to target the pathogenic immune responses and boost the neuroprotective immune pathways as novel immunotherapies for ALS.

Large-scale screening in sporadic amyotrophic lateral sclerosis identifies genetic modifiers in C9orf72 repeat carriers

Sporadic amyotrophic lateral sclerosis (ALS) is considered to be a complex disease with multiple genetic risk factors contributing to the pathogenesis. Identification of genetic risk factors that co-occur frequently could provide relevant insight into underlying mechanisms of motor neuron degeneration. To dissect the genetic architecture of sporadic ALS, we undertook a large sequencing study in 755 apparently sporadic ALS cases and 959 controls, analyzing 10 ALS genes: SOD1, C9orf72, TARDBP, FUS, ANG, CHMP2B, ATXN2, NIPA1, SMN1, and UNC13A. We observed sporadic cases with multiple genetic risk variants in 4.1% compared with 1.3% in controls. The overall difference was not in excess of what is to be expected by chance (binomial test, p = 0.59). We did, however, observe a higher frequency than expected of C9orf72 repeat carriers with co-occurring susceptibility variants (ATXN2, NIPA1, and SMN1; p = 0.001), which is mainly because of the co-occurrence of NIPA1 repeats in 15% of C9orf72 repeat carriers (p = 0.006).

RNA-binding proteins associated molecular mechanisms of motor neuron degeneration pathogenesis.

Motor neuron diseases are neurodegenerative disorders that trigger motor neurons to degenerate and lead to paralysis. Our understanding on the mechanisms of motor neuron degeneration has been enhanced by recent cellular and molecular researches. In this review, I highlight advances in RNA-binding proteins associated molecular mechanisms of motor neuron degeneration pathogenesis including ribonucleoprotein-associated motor neuron degeneration which is focused on RNA-binding protein aggregation associated aberrant RNA metabolism and stress granules mediated translational repression, neurofilament associated aggregate formation, and prion protein associated accumulation of misfolded proteins. Progress overviewed above will be valuable to the development of more targeted diagnostic tests and therapies.

Oxidative Stress and Autophagic Alteration in Brainstem of SOD1-G93A Mouse Model of ALS

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease involving both upper and lower motor neurons. The mechanism of motor neuron degeneration is still unknown. Although many studies have been performed on spinal motor neurons, few have been reported on brainstem and its motor nuclei. The aim of this study was to investigate oxidative stress and autophagic changes in the brainstem and representative motor nuclei of superoxide dismutase 1 (SOD1)-G93A mouse model of ALS. The expression levels of cluster of differentiation molecule 11b (CD11b), glial fibrillary acidic protein, glutamate-cysteine ligase catalytic subunit, heme oxygenase-1, NAD(P)H: quinone oxidoreductase 1, voltage-dependent anion-selective channel protein 1, Sequestosome 1/p62 (p62), microtubule-associated protein 1 light chain 3B (LC3), and SOD1 proteins in brainstem were examined by Western blot analysis. Immunohistochemistry and immunofluorescence were performed to identify the cellular localization of SOD1, p62, and LC3B, respectively. The results showed that there were progressive asctrocytic proliferation and microglial activation, induction of antioxidant proteins, and increased p62 and LC3II expression in brainstem of SOD1-G93A mice. Additionally, SOD1 and p62 accumulated in hypoglossal, facial, and red nuclei, but not in oculomotor nucleus. Furthermore, electron microscope showed increased autophagic vacuoles in affected brainstem motor nuclei. Our results indicate that brainstem share similar gliosis, oxidative stress, and autophagic changes as the spinal cord in SOD1-G93A mice. Thus, SOD1 accumulation in astrocytes and neurons, oxidative stress, and altered autophagy are involved in motor neuron degeneration in the brainstem, similar to the motor neurons in spinal cord. Therefore, therapeutic trials in the SOD1G93A mice need to target the brainstem in addition to the spinal cord.

Lack of Association between Nuclear Factor Erythroid-Derived 2-Like 2 Promoter Gene Polymorphisms and Oxidative Stress Biomarkers in Amyotrophic Lateral Sclerosis Patients

Oxidative stress involvement has been strongly hypothesized among the possible pathogenic mechanisms of motor neuron degeneration in amyotrophic lateral sclerosis (ALS). The intracellular redox balance is finely modulated by numerous complex mechanisms critical for cellular functions, among which the nuclear factor erythroid-derived 2-like 2 (NFE2L2/Nrf2) pathways. We genotyped, in a cohort of ALS patients (n = 145) and healthy controls (n = 168), three SNPs in Nrf2 gene promoter: −653 A/G, −651 G/A, and −617 C/A and evaluated, in a subset (n = 73) of patients, advanced oxidation protein products (AOPP), iron-reducing ability of plasma (FRAP), and plasma thiols (-SH) as oxidative damage peripheral biomarkers. Nrf2 polymorphisms were not different among patients and controls. Increased levels of AOPP (P < 0.05) and decreased levels of FRAP (P < 0.001) have been observed in ALS patients compared with controls, but no difference in -SH values was found. Furthermore, no association was found between biochemical markers of redox balance and Nrf2 polymorphisms. These data confirm an altered redox balance in ALS and indicate that, while being abnormally modified compared to controls, the oxidative stress biomarkers assessed in this study are independent from the −653 A/G, −651 G/A, and −617 C/A Nrf2 SNPs in ALS patients.

Calcium, mitochondria, and the pathogenesis of ALS: the good, the bad, and the ugly

Calcium, mitochondria, and the pathogenesis of ALS: the good, the bad, and the ugly

Amyotrophic Lateral Sclerosis and Novel Therapeutic Strategies

Research and key discoveries in the field of amyotrophic lateral sclerosis (ALS) have exponentially increased since the announcement in 1993 of the first ALS-causing mutations in the gene for the well-studied antioxidant enzyme Cu,Zn superoxide dismutase (SOD1). The etiology of sporadic ALS largely remains unknown and the mechanisms of motor neuron degeneration are still being investigated. The only FDA drug approved for the treatment of ALS is riluzole with only modest benefit to patients, but multiple drugs are currently in the development pipeline and in human ALS clinical trials. In this special issue, K. Venkova-Hristova et al. thoroughly reviewed studies of experimental therapeutics in animal models of ALS, including specific examples of those that proceeded into human clinical trials. Since none of the ALS human clinical trials succeeded despite positive results in animal models, the question of “why” has been on everyone's mind, with efforts to develop superior alternatives. This review discusses the potential reasons for the universal failure of preclinical successes to translate into positive clinical outcomes. It has become obvious that the lack of understanding of the precise mechanisms of motor neuron degeneration presents a major obstacle in the development of effective therapy for ALS. This review discusses the details of several major pathogenic pathways in ALS and the efforts of various groups to block one toxic pathway at a time, ranging from oxidative stress to protein aggregation. The authors discuss the pros and cons of ALS models and propose simultaneous targeting of multiple pathways as a more efficient strategy, due to the multifactorial nature of ALS pathology.

Molecular pathways of motor neuron injury in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a genetically diverse disease. At least 15 ALS-associated gene loci have so far been identified, and the causative gene is known in approximately 30% of familial ALS cases. Less is known about the factors underlying the sporadic form of the disease. The molecular mechanisms of motor neuron degeneration are best understood in the subtype of disease caused by mutations in superoxide dismutase 1, with a current consensus that motor neuron injury is caused by a complex interplay between multiple pathogenic processes. A key recent finding is that mutated TAR DNA-binding protein 43 is a major constituent of the ubiquitinated protein inclusions in ALS, providing a possible link between the genetic mutation and the cellular pathology. New insights have also indicated the importance of dysregulated glial cell-motor neuron crosstalk, and have highlighted the vulnerability of the distal axonal compartment early in the disease course. In addition, recent studies have suggested that disordered RNA processing is likely to represent a major contributing factor to motor neuron disease. Ongoing research on the cellular pathways highlighted in this Review is predicted to open the door to new therapeutic interventions to slow disease progression in ALS.

Strategies for clinical approach to neurodegeneration in Amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and ultimately fatal neurodegenerative disorder of unknown aetiology that involves the loss of upper and lower motor neurons in the cerebral cortex, brainstem and spinal cord. Significant progress in understanding the cellular mechanisms of motor neuron degeneration in ALS has not been matched with the development of therapeutic strategies to prevent disease progression, and riluzole remains the only available therapy, with only marginal effects on disease survival. More recently alterations of mRNA processing in genetically defined forms of ALS, as those related to TDP-43 and FUS-TLS gene mutations have provided important insights into the molecular networks implicated in the disease pathogenesis. Here we review some of the recent progress in promoting therapeutic strategies for neurodegeneration.