Early ALS-type gait abnormalities in AMP-dependent protein kinase-deficient mice suggest a role for this metabolic sensor in early stages of the disease

Genetic influences on motor learning and performance and superperforming mutants revealed by random mutational survey of the mouse genome

Evolution depends upon genetic variations that influence physiology. As defined in a genetic screen, phenotypic performance may be enhanced or degraded by such mutations. We set out to detect mutations that influence motor function, including motor learning. Thus, we tested the motor effects of 36,444 non-synonymous coding/splicing mutations induced in the germline of C57BL/6J mice with N-ethyl-N-nitrosourea by measuring changes in the performance of repetitive rotarod trials while blinded to genotype. Automated meiotic mapping was used to implicate individual mutations in causation. In total, 32,726 mice bearing all the variant alleles were screened. This was complemented with the simultaneous testing of 1408 normal mice for reference. In total, 16.3% of autosomal genes were thus rendered detectably hypomorphic or nullified by mutations in homozygosity and motor tested in at least three mice. This approach allowed us to identify superperformance mutations in Rif1, Tk1, Fan1 and Mn1. These genes are primarily related, among other less well-characterized functions, to nucleic acid biology. We also associated distinct motor learning patterns with groups of functionally related genes. These functional sets included, preferentially, histone H3 methyltransferase activity for mice that learnt at an accelerated rate relative to the remaining mutant mice. The results allow for an estimation of the fraction of mutations that can modify a behaviour influential for evolution such as locomotion. They may also enable, once the loci are further validated and the mechanisms elucidated, the harnessing of the activity of the newly identified genes to enhance motor ability or to counterbalance disability or disease. KEY POINTS: We studied the effect of chemically induced random mutations on mouse motor performance. An array of mutations influenced the rate of motor learning. DNA regulation genes predominated among these mutant loci. Several mutations in unsuspected genes led to superperformance. Assuming little-biased mutagenicity, the results allow for an estimation of the probability for any spontaneous mutation to influence a behaviour such as motor learning and ultimate performance.

Coordination function index: A novel indicator for assessing hindlimb locomotor recovery in spinal cord injury rats based on catwalk gait parameters

In preclinical studies of spinal cord injury (SCI), behavioral assessments are crucial for evaluating treatment effectiveness. Commonly used methods include Basso, Beattie, Bresnahan (BBB) score and the Louisville swim scale (LSS), relying on subjective observations. The CatWalk automated gait analysis system is also widely used in SCI studies, providing extensive gait parameters from footprints. However, these parameters are often used independently or combined simply without utilizing the vast amount of data provided by CatWalk. Therefore, it is necessary to develop a novel approach encompassing multiple CatWalk parameters for a comprehensive and objective assessment of locomotor function. In this work, we screened 208 CatWalk XT gait parameters and identified 38 suitable for assessing hindlimb motor function recovery in a rat thoracic contusion SCI model. Exploratory factor analysis was used to reveal structural relationships among these parameters. Weighted scores for Coordination effectively differentiated hindlimb motor function levels, termed as the Coordinated Function Index (CFI). CFI showed high reliability, exhibiting high correlations with BBB scores, LSS, and T2WI lesion area. Finally, we simplified CFI based on factor loadings and correlation analysis, obtaining a streamlined version with reliable assessment efficacy. In conclusion, we developed a systematic assessment indicator utilizing multiple CatWalk parameters to objectively evaluate hindlimb motor function recovery in rats after thoracic contusion SCI.

Genetic influences on motor learning and superperformance mutants revealed by random mutational survey of mouse locomotion

Evolution depends upon genetic variations that influence physiology. As defined in a genetic screen, phenotypic performance may be enhanced or degraded by such mutations. We set out to detect mutations that influence motor function, including motor learning. Thus, we tested the motor effects of 36,444 non-synonymous coding/splicing mutations induced in the germline of C57BL/6J mice with N-ethyl-N-nitrosourea by measuring changes in the performance of repetitive rotarod trials while blinded to genotype. Automated meiotic mapping was used to implicate individual mutations in causation. 32,726 mice bearing all the variant alleles were screened. This was complemented with the simultaneous testing of 1,408 normal mice for reference. 16.3% of autosomal genes were thus rendered detectably hypomorphic or nullified by mutations in homozygosity and motor tested in at least 3 mice. This approach allowed us to identify superperformance mutations in Rif1, Tk1, Fan1 and Mn1. These genes are primarily related, among other less well characterized functions, to nucleic acid biology. We also associated distinct motor learning patterns with groups of functionally related genes. These functional sets included preferentially histone H3 methyltransferase activity for mice that learnt at an accelerated rate relative to the rest of mutant mice. The results allow for an estimation of the fraction of mutations that can modify a behavior influential for evolution such as locomotion. They may also enable, once the loci are further validated and the mechanisms elucidated, the harnessing of the activity of the newly identified genes to enhance motor ability or to counterbalance disability or disease.

The Cell Autonomous and Non-Cell Autonomous Aspects of Neuronal Vulnerability and Resilience in Amyotrophic Lateral Sclerosis

Simple Summary

Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by a progressive paralysis due to the loss of particular neurons in our nervous system called motor neurons, that exert voluntary control of all our skeletal muscles. It is not entirely understood why motor neurons are particularly vulnerable in ALS, neither is it completely clear why certain groups of motor neurons, including those that regulate eye movement, are rather resilient to this disease. However, both vulnerability and resilience to ALS likely reflect cell intrinsic properties of different motor neuron subpopulations as well as non-cell autonomous events regulated by surrounding cell types. In this review we dissect the particular properties of different motor neuron types and their responses to disease that may underlie their respective vulnerabilities and resilience. Disease progression in ALS involves multiple cell types that are closely connected to motor neurons and we here also discuss their contributions to the differential vulnerability of motor neurons.

Abstract

Amyotrophic lateral sclerosis (ALS) is defined by the loss of upper motor neurons (MNs) that project from the cerebral cortex to the brain stem and spinal cord and of lower MNs in the brain stem and spinal cord which innervate skeletal muscles, leading to spasticity, muscle atrophy, and paralysis. ALS involves several disease stages, and multiple cell types show dysfunction and play important roles during distinct phases of disease initiation and progression, subsequently leading to selective MN loss. Why MNs are particularly vulnerable in this lethal disease is still not entirely clear. Neither is it fully understood why certain MNs are more resilient to degeneration in ALS than others. Brain stem MNs of cranial nerves III, IV, and VI, which innervate our eye muscles, are highly resistant and persist until the end-stage of the disease, enabling paralyzed patients to communicate through ocular tracking devices. MNs of the Onuf’s nucleus in the sacral spinal cord, that innervate sphincter muscles and control urogenital functions, are also spared throughout the disease. There is also a differential vulnerability among MNs that are intermingled throughout the spinal cord, that directly relate to their physiological properties. Here, fast-twitch fatigable (FF) MNs, which innervate type IIb muscle fibers, are affected early, before onset of clinical symptoms, while slow-twitch (S) MNs, that innervate type I muscle fibers, remain longer throughout the disease progression. The resilience of particular MN subpopulations has been attributed to intrinsic determinants and multiple studies have demonstrated their unique gene regulation and protein content in health and in response to disease. Identified factors within resilient MNs have been utilized to protect more vulnerable cells. Selective vulnerability may also, in part, be driven by non-cell autonomous processes and the unique surroundings and constantly changing environment close to particular MN groups. In this article, we review in detail the cell intrinsic properties of resilient and vulnerable MN groups, as well as multiple additional cell types involved in disease initiation and progression and explain how these may contribute to the selective MN resilience and vulnerability in ALS.

Therapeutic Targets in Amyotrophic Lateral Sclerosis: Focus on Ion Channels and Skeletal Muscle

Amyotrophic Lateral Sclerosis is a neurodegenerative disease caused by progressive loss of motor neurons, which severely compromises skeletal muscle function. Evidence shows that muscle may act as a molecular powerhouse, whose final signals generate in patients a progressive loss of voluntary muscle function and weakness leading to paralysis. This pathology is the result of a complex cascade of events that involves a crosstalk among motor neurons, glia, and muscles, and evolves through the action of converging toxic mechanisms. In fact, mitochondrial dysfunction, which leads to oxidative stress, is one of the mechanisms causing cell death. It is a common denominator for the two existing forms of the disease: sporadic and familial. Other factors include excitotoxicity, inflammation, and protein aggregation. Currently, there are limited cures. The only approved drug for therapy is riluzole, that modestly prolongs survival, with edaravone now waiting for new clinical trial aimed to clarify its efficacy. Thus, there is a need of effective treatments to reverse the damage in this devastating pathology. Many drugs have been already tested in clinical trials and are currently under investigation. This review summarizes the already tested drugs aimed at restoring muscle-nerve cross-talk and on new treatment options targeting this tissue.

Stride-level analysis of mouse open field behavior using deep-learning-based pose estimation

Gait and posture are often perturbed in many neurological, neuromuscular, and neuropsychiatric conditions. Rodents provide a tractable model for elucidating disease mechanisms and interventions. Here, we develop a neural-network-based assay that adopts the commonly used open field apparatus for mouse gait and posture analysis. We quantitate both with high precision across 62 strains of mice. We characterize four mutants with known gait deficits and demonstrate that multiple autism spectrum disorder (ASD) models show gait and posture deficits, implying this is a general feature of ASD. Mouse gait and posture measures are highly heritable and fall into three distinct classes. We conduct a genome-wide association study to define the genetic architecture of stride-level mouse movement in the open field. We provide a method for gait and posture extraction from the open field and one of the largest laboratory mouse gait and posture data resources for the research community.

Sheppard et al. present a method for gait and posture analysis in the common open field apparatus using neural-network-based pose estimation. They apply this high-throughput method to dissect the genetic architecture of mouse movement.

Evidence that corticofugal propagation of ALS pathology is not mediated by prion-like mechanism

Amyotrophic lateral sclerosis (ALS) arises from the combined degeneration of motor neurons (MN) and corticospinal neurons (CSN). Recent clinical and pathological studies suggest that ALS might start in the motor cortex and spread along the corticofugal axonal projections (including the CSN), either via altered cortical excitability and activity or via prion-like propagation of misfolded proteins. Using mouse genetics, we recently provided the first experimental arguments in favour of the corticofugal hypothesis, but the mechanism of propagation remained an open question. To gain insight into this matter, we tested here the possibility that the toxicity of the corticofugal projection neurons (CFuPN) to their targets could be mediated by their cell autonomous-expression of an ALS causing transgene and possible diffusion of toxic misfolded proteins to their spinal targets. We generated a Crym-CreER^T2 mouse line to ablate the SOD1^G37R transgene selectively in CFuPN. This was sufficient to fully rescue the CSN and to limit spasticity, but had no effect on the burden of misfolded SOD1 protein in the spinal cord, MN survival, disease onset and progression. The data thus indicate that in ALS corticofugal propagation is likely not mediated by prion-like mechanisms, but could possibly rather rely on cortical hyperexcitability.

What skeletal muscle has to say in amyotrophic lateral sclerosis: Implications for therapy

Amyotrophic lateral sclerosis (ALS) is an adult onset disorder characterized by progressive neuromuscular junction (NMJ) dismantling and degeneration of motor neurons leading to atrophy and paralysis of voluntary muscles responsible for motion and breathing. Except for a minority of patients harbouring genetic mutations, the origin of most ALS cases remains elusive. Peripheral tissues, and particularly skeletal muscle, have lately demonstrated an active contribution to disease pathology attracting a growing interest for these tissues as therapeutic targets in ALS. In this sense, molecular mechanisms essential for cell and tissue homeostasis have been shown to be deregulated in the disease. These include muscle metabolism and mitochondrial activity, RNA processing, tissue-resident stem cell function responsible for muscle regeneration, and proteostasis that regulates muscle mass in adulthood. This review aims to compile scientific evidence that demonstrates the role of skeletal muscle in ALS pathology and serves as reference for development of novel therapeutic strategies targeting this tissue to delay disease onset and progression. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

Synergistic toxicity in an in vivo model of neurodegeneration through the co-expression of human TDP-43M337V and tauT175D protein

Although it has been suggested that the co-expression of multiple pathological proteins associated with neurodegeneration may act synergistically to induce more widespread neuropathology, experimental evidence of this is sparse. We have previously shown that the expression of Thr¹⁷⁵Asp-tau (tau^T175D) using somatic gene transfer with a stereotaxically-injected recombinant adeno-associated virus (rAAV9) vector induces tau pathology in rat hippocampus. In this study, we have examined whether the co-expression of human tau^T175D with mutant human TDP-43 (TDP-43^M337V) will act synergistically. Transgenic female Sprague-Dawley rats that inducibly express mutant human TDP-43^M337V using the choline acetyltransferase (ChAT) tetracycline response element (TRE) driver with activity modulating tetracycline-controlled transactivator (tTA) were utilized in these studies. Adult rats were injected with GFP-tagged tau protein constructs in a rAAV9 vector through bilateral stereotaxic injection into the hippocampus. Injected tau constructs were: wild-type GFP-tagged 2N4R human tau (tau^WT; n = 8), GFP-tagged tau^T175D 2N4R human tau (tau^T175D, pseudophosphorylated, toxic variant, n = 8), and GFP (control, n = 8). Six months post-injection, mutant TDP-43^M337V expression was induced for 30 days. Behaviour testing identified motor deficits within 3 weeks after TDP-43 expression irrespective of tau expression, though social behaviour and sensorimotor gating remained unchanged. Increased tau pathology was observed in the hippocampus of both tau^WT and tau^T175D expressing rats and tau^T175D pathology was increased in the presence of cholinergic neuronal expression of human TDP-43^M337V. These data indicate that co-expression of pathological TDP-43 and tau protein exacerbate the pathology associated with either individual protein.

Constitutive downregulation protein kinase C epsilon in hSOD1G93A astrocytes influences mGluR5 signaling and the regulation of glutamate uptake

Accumulating evidence indicates that motor neuron degeneration in amyotrophic lateral sclerosis (ALS) is a non-cell-autonomous process and that impaired glutamate clearance by astrocytes, leading to excitotoxicity, could participate in progression of the disease. In astrocytes derived from an animal model of ALS (hSOD1^G93A rats), activation of type 5 metabotropic glutamate receptor (mGluR5) fails to increase glutamate uptake, impeding a putative dynamic neuroprotective mechanism involving astrocytes. Using astrocyte cultures from hSOD1^G93A rats, we have demonstrated that the typical Ca²⁺ oscillations associated with mGluR5 activation were reduced, and that the majority of cells responded with a sustained elevation of intracellular Ca²⁺ concentration. Since the expression of protein kinase C epsilon isoform (PKCɛ) has been found to be considerably reduced in astrocytes from hSOD1^G93A rats, the consequences of manipulating its activity and expression on mGluR5 signaling and on the regulation of glutamate uptake have been examined. Increasing PKCɛ expression was found to restore Ca²⁺ oscillations induced by mGluR5 activation in hSOD1^G93A -expressing astrocytes. This was also associated with an increase in glutamate uptake capacity in response to mGluR5 activation. Conversely, reducing PKCɛ expression in astrocytes from wild-type animals with specific PKCɛ-shRNAs was found to alter the mGluR5 associated oscillatory signaling profile, and consistently reduced the regulation of the glutamate uptake-mediated by mGluR5 activation. These results suggest that PKCɛ is required to generate Ca²⁺ oscillations following mGluR5 activation, which support the regulation of astrocytic glutamate uptake. Reduced expression of astrocytic PKCɛ could impair this neuroprotective process and participate in the progression of ALS.

Modulating the catalytic activity of AMPK has neuroprotective effects against α-synuclein toxicity

Background

Metabolic perturbations and slower renewal of cellular components associated with aging increase the risk of Parkinson’s disease (PD). Declining activity of AMPK, a critical cellular energy sensor, may therefore contribute to neurodegeneration.

Methods

Here, we overexpress various genetic variants of the catalytic AMPKα subunit to determine how AMPK activity affects the survival and function of neurons overexpressing human α-synuclein in vivo.

Results

Both AMPKα1 and α2 subunits have neuroprotective effects against human α-synuclein toxicity in nigral dopaminergic neurons. Remarkably, a modified variant of AMPKα1 (T172Dα1) with constitutive low activity most effectively prevents the loss of dopamine neurons, as well as the motor impairments caused by α-synuclein accumulation. In the striatum, T172Dα1 decreases the formation of dystrophic axons, which contain aggregated α-synuclein. In primary cortical neurons, overexpression of human α-synuclein perturbs mitochondrial and lysosomal activities. Co-expressing AMPKα with α-synuclein induces compensatory changes, which limit the accumulation of lysosomal material and increase the mitochondrial mass.

Conclusions

Together, these results indicate that modulating AMPK activity can mitigate α-synuclein toxicity in nigral dopamine neurons, which may have implications for the development of neuroprotective treatments against PD.

Electronic supplementary material

The online version of this article (10.1186/s13024-017-0220-x) contains supplementary material, which is available to authorized users.

Measurement of mechanical withdrawal thresholds and gait analysis using the CatWalk method in a nucleus pulposus-applied rodent model

Background

There are some previous reports of gait analysis using a rodent pain model. Applying the CatWalk method, objective measurements of pain-related behavior could be evaluated, but this method has not been investigated using the nucleus pulposus (NP) applied model, which was developed as a model of lumber disc herniation. We aimed to measure mechanical withdrawal thresholds and analyze gait patterns using the CatWalk method for the evaluation of the pain-related behavior caused by NP application.

Methods

Twenty-four nine-week-old female Sprague-Dawley rats were randomly divided into two experimental groups, the NP group (n = 12), in which autologous NP from the tail was applied to the left L5 dorsal root ganglion, and the sham-operated group (n = 12). Measurements of mechanical withdrawal thresholds were performed using von Frey filaments touching the left footpads, and gait analysis was performed using the CatWalk method. These experiments were conducted 1 day before surgery and 7, 14, 21, and 28 days after surgery. Data were statistically analyzed using the Wilcoxon rank-sum test.

Results

The NP group showed significantly lower withdrawal thresholds than the sham group at days 14 and 21. Stand (duration of contact of a paw with the glass plate) was significantly higher in the NP group at days 7 and 14, whereas step cycle (duration between two consecutive initial contacts of the same paw) and duty cycle (stand as a percentage of step cycle) were the same at day 7. Long initial dual stance (duration of ground contact for both hind paws simultaneously, but the first one in a step cycle of a target hind paw) of the right hind paw was measured at days 7 and 14. The left hind paw per right hind paw ratio of the stand index (speed at which the paw loses contact with the glass plate) and mean intensity (mean intensity of the complete paw) changed at day 7 or 14. Phase dispersion (parameter describing the temporal relationship between placement of two paws) of the hind paws decreased at day 7.

Conclusions

Rats with applied NP showed a decreased withdrawal threshold and abnormal gait. The differences in gait parameters between the NP and sham groups were observed at an earlier time point than the withdrawal thresholds. Gait analysis could be an effective method for understanding pain caused by applied NP.

AMPK in Neurodegenerative Diseases

Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis are neurodegenerative disorders that are characterized by a progressive degeneration of nerve cells eventually leading to dementia. While these diseases affect different neuronal populations and present distinct clinical features, they share in common several features and signaling pathways. In particular, energy metabolism defects, oxidative stress, and excitotoxicity are commonly described and might be correlated with AMP-activated protein kinase (AMPK) deregulation. AMPK is a master energy sensor which was reported to be overactivated in the brain of patients affected by these neurodegenerative disorders. While the exact role played by AMPK in these diseases remains to be clearly established, several studies reported the implication of AMPK in various signaling pathways that are involved in these diseases' progression. In this chapter, we review the current literature regarding the involvement of AMPK in the development of these diseases and discuss the common pathways involved.

The Role of Skeletal Muscle in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal adult‐onset disease primarily characterized by upper and lower motor neuron degeneration, muscle wasting and paralysis. It is increasingly accepted that the pathological process leading to ALS is the result of multiple disease mechanisms that operate within motor neurons and other cell types both inside and outside the central nervous system. The implication of skeletal muscle has been the subject of a number of studies conducted on patients and related animal models. In this review, we describe the features of ALS muscle pathology and discuss on the contribution of muscle to the pathological process. We also give an overview of the therapeutic strategies proposed to alleviate muscle pathology or to deliver curative agents to motor neurons. ALS muscle mainly suffers from oxidative stress, mitochondrial dysfunction and bioenergetic disturbances. However, the way by which the disease affects different types of myofibers depends on their contractile and metabolic features. Although the implication of muscle in nourishing the degenerative process is still debated, there is compelling evidence suggesting that it may play a critical role. Detailed understanding of the muscle pathology in ALS could, therefore, lead to the identification of new therapeutic targets.

AMPK Signalling and Defective Energy Metabolism in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is caused by selective loss of upper and lower motor neurons by complex mechanisms that are incompletely understood. Motor neurons are large, highly polarised and excitable cells with unusually high energetic demands to maintain resting membrane potential and propagate action potentials. This leads to higher ATP consumption and mitochondrial metabolism in motor neurons relative to other cells. Here, we review increasing evidence that defective energy metabolism and homeostasis contributes to selective vulnerability and degeneration of motor neurons in ALS. Firstly, we provide a brief overview of major energetic pathways in the CNS, including glycolysis, oxidative phosphorylation and the AMP-activated protein kinase (AMPK) signalling pathway, while highlighting critical metabolic interactions between neurons and astrocytes. Next, we review evidence from ALS patients and transgenic mutant SOD1 mice for weight loss, hypermetabolism, hyperlipidemia and mitochondrial dysfunction in disease onset and progression. Genetic and therapeutic modifiers of energy metabolism in mutant SOD1 mice will also be summarised. We also present evidence that additional ALS-linked proteins, TDP-43 and FUS, lead to energy disruption and mitochondrial defects in motor neurons. Lastly, we review emerging evidence including our own that dysregulation of the AMPK signalling cascade in motor neurons is an early and common event in ALS pathogenesis. We suggest that an imbalance in energy metabolism should be considered an important factor in both progression and potential treatment of ALS.