Electrophysiological analysis of a murine model of motoneuron disease

ICA-27243 improves neuromuscular function and preserves motoneurons in the transgenic SOD1G93A mice

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by the death of upper and lower motor neurons (MNs). Excessive neuronal excitability has been implicated in MN degeneration; thus, modulation of hyperexcitability appears as a promising therapeutic strategy. Potassium channels are attractive targets since they can be activated at subthreshold voltages and can regulate neuronal excitability. In this study, we assayed the effects of N-(6-Chloro-pyridin-3-yl)-3,4-difluorobenzamide compound, known as ICA-27243, as a potential treatment for ALS. ICA-27243 is a highly selective Kv7.2/7.3 opener used mainly in epilepsy models. In the in vitro model of spinal cord organotypic cultures (SCOCs) exposed to acute excitotoxicity, ICA-27243 prevented MN degeneration at a dose-of 10 ​μM. Administration of ICA-27243 to transgenic SOD1G93A ALS mice improved the decline of neuromuscular function, maintained locomotion and coordination in the rotarod, decreased spinal MN death and attenuated glial reactivity. In conclusion, we report here for the first time that ICA-27243 is an effective treatment for ALS, emphasizing the potential of targeting Kv channels to reduce neuronal hyperexcitability.

A mammalian-specific Alex3/Gαq protein complex regulates mitochondrial trafficking, dendritic complexity, and neuronal survival

Mitochondrial dynamics and trafficking are essential to provide the energy required for neurotransmission and neural activity. We investigated how G protein-coupled receptors (GPCRs) and G proteins control mitochondrial dynamics and trafficking. The activation of Gαq inhibited mitochondrial trafficking in neurons through a mechanism that was independent of the canonical downstream PLCβ pathway. Mitoproteome analysis revealed that Gαq interacted with the Eutherian-specific mitochondrial protein armadillo repeat-containing X-linked protein 3 (Alex3) and the Miro1/Trak2 complex, which acts as an adaptor for motor proteins involved in mitochondrial trafficking along dendrites and axons. By generating a CNS-specific Alex3 knockout mouse line, we demonstrated that Alex3 was required for the effects of Gαq on mitochondrial trafficking and dendritic growth in neurons. Alex3-deficient mice had altered amounts of ER stress response proteins, increased neuronal death, motor neuron loss, and severe motor deficits. These data revealed a mammalian-specific Alex3/Gαq mitochondrial complex, which enables control of mitochondrial trafficking and neuronal death by GPCRs.

Combining electromyography and Raman spectroscopy: optical EMG

INTRODUCTION/AIMS

Electromyography (EMG) remains a key component of the diagnostic work-up for suspected neuromuscular disease, but it does not provide insight into the molecular composition of muscle which can provide diagnostic information. Raman spectroscopy is an emerging neuromuscular biomarker capable of generating highly specific, molecular fingerprints of tissue. Here, we present "optical EMG," a combination of EMG and Raman spectroscopy, achieved using a single needle.

METHODS

An optical EMG needle was created to collect electrophysiological and Raman spectroscopic data during a single insertion. We tested functionality with in vivo recordings in the SOD1G93A mouse model of amyotrophic lateral sclerosis (ALS), using both transgenic (n = 10) and non-transgenic (NTg, n = 7) mice. Under anesthesia, compound muscle action potentials (CMAPs), spontaneous EMG activity and Raman spectra were recorded from both gastrocnemius muscles with the optical EMG needle. Standard concentric EMG needle recordings were also undertaken. Electrophysiological data were analyzed with standard univariate statistics, Raman data with both univariate and multivariate analyses.

RESULTS

A significant difference in CMAP amplitude was observed between SOD1G93A and NTg mice with optical EMG and standard concentric needles (p = .015 and p = .011, respectively). Spontaneous EMG activity (positive sharp waves) was detected in transgenic SOD1G93A mice only. Raman spectra demonstrated peaks associated with key muscle components. Significant differences in molecular composition between SOD1G93A and NTg muscle were identified through the Raman spectra.

DISCUSSION

Optical EMG can provide standard electrophysiological data and molecular Raman data during a single needle insertion and represents a potential biomarker for neuromuscular disease.

Potential Applications for Growth Hormone Secretagogues Treatment of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) arises from neuronal death due to complex interactions of genetic, molecular, and environmental factors. Currently, only two drugs, riluzole and edaravone, have been approved to slow the progression of this disease. However, ghrelin and other ligands of the GHS-R1a receptor have demonstrated interesting neuroprotective activities that could be exploited in this pathology. Ghrelin, a 28-amino acid hormone, primarily synthesized and secreted by oxyntic cells in the stomach wall, binds to the pituitary GHS-R1a and stimulates GH secretion; in addition, ghrelin is endowed with multiple extra endocrine bioactivities. Native ghrelin requires esterification with octanoic acid for binding to the GHS-R1a receptor; however, this esterified form is very labile and represents less than 10% of circulating ghrelin. A large number of synthetic compounds, the growth hormone secretagogues (GHS) encompassing short peptides, peptoids, and non-peptidic moieties, are capable of mimicking several biological activities of ghrelin, including stimulation of GH release, appetite, and elevation of blood IGF-I levels. GHS have demonstrated neuroprotective and anticonvulsant effects in experimental models of pathologies both in vitro and in vivo. To illustrate, some GHS, currently under evaluation by regulatory agencies for the treatment of human cachexia, have a good safety profile and are safe for human use. Collectively, evidence suggests that ghrelin and cognate GHS may constitute potential therapies for ALS.

Assessing the therapeutic impact of resveratrol in ALS SOD1-G93A mice with electrical impedance myography

To aid in the identification of new treatments for amyotrophic lateral sclerosis (ALS), convenient biomarkers are needed to effectively and uniformly measure drug efficacy. To this end, we assessed the effects of the nutraceutical resveratrol (RSV) on disease onset and overall survival in SOD1-G93A (ALS) mice and compared several standard biomarkers including body mass, motor score (MS), paw grip endurance (PGE), and compound motor action potential (CMAP) amplitude, with the technique of electrical impedance myography (EIM) to follow disease progression. Eighteen ALS mice (nine females, nine males) received RSV in the chow (dose: 120 mg/kg/day) starting at 8 weeks of age; 19 ALS mice (nine females, 10 males) received normal chow; 10 wild type (WT) littermates (five females, five males) fed standard chow served as controls. Biomarker assessments were performed weekly beginning at 8 weeks. No differences in either disease onset or overall survival were found between RSV-treated and untreated ALS mice of either sex; moreover, all biomarkers failed to identify any beneficial effect of RSV when administered at this dose. Therefore, for the comparative evaluation of the ability of the various biomarkers to detect the earliest symptoms of disease, data from all animals (i.e., RSV-treated and untreated ALS mice of both sexes) were combined. Of the biomarkers tested, EIM impedance values, i.e., surface EIM longitudinal phase at 50 kHz (LP 50 kHz), and CMAP amplitude showed the earliest significant changes from baseline. LP 50 kHz values showed a rate of decline equivalent to that of CMAP amplitude and correlated with both PGE and CMAP amplitude [Spearman rho = 0.806 (p = 0.004) and 0.627 (p = 0.044), respectively]. Consistent with previous work, these findings indicate that surface EIM can serve as an effective non-invasive biomarker for preclinical drug testing in rodent models of ALS.

Sensory Involvement in Amyotrophic Lateral Sclerosis

Although amyotrophic lateral sclerosis (ALS) is pre-eminently a motor disease, the existence of non-motor manifestations, including sensory involvement, has been described in the last few years. Although from a clinical perspective, sensory symptoms are overshadowed by their motor manifestations, this does not mean that their pathological significance is not relevant. In this review, we have made an extensive description of the involvement of sensory and autonomic systems described to date in ALS, from clinical, neurophysiological, neuroimaging, neuropathological, functional, and molecular perspectives.

In vivo genome editing using novel AAV-PHP variants rescues motor function deficits and extends survival in a SOD1-ALS mouse model

CRISPR-based gene editing technology represents a promising approach to deliver therapies for inherited disorders, including amyotrophic lateral sclerosis (ALS). Toxic gain-of-function superoxide dismutase 1 (SOD1) mutations are responsible for ~20% of familial ALS cases. Thus, current clinical strategies to treat SOD1-ALS are designed to lower SOD1 levels. Here, we utilized AAV-PHP.B variants to deliver CRISPR-Cas9 guide RNAs designed to disrupt the human SOD1 (huSOD1) transgene in SOD1^G93A mice. A one-time intracerebroventricular injection of AAV.PHP.B-huSOD1-sgRNA into neonatal H11^Cas9 SOD1^G93A mice caused robust and sustained mutant huSOD1 protein reduction in the cortex and spinal cord, and restored motor function. Neonatal treatment also reduced spinal motor neuron loss, denervation at neuromuscular junction (NMJ) and muscle atrophy, diminished axonal damage and preserved compound muscle action potential throughout the lifespan of treated mice. SOD1^G93A treated mice achieved significant disease-free survival, extending lifespan by more than 110 days. Importantly, a one-time intrathecal or intravenous injection of AAV.PHP.eB-huSOD1-sgRNA in adult H11^Cas9 SOD1^G93A mice, immediately before symptom onset, also extended lifespan by at least 170 days. We observed substantial protection against disease progression, demonstrating the utility of our CRISPR editing preclinical approach for target evaluation. Our approach uncovered key parameters (e.g., AAV capsid, Cas9 expression) that resulted in improved efficacy compared to similar approaches and can also serve to accelerate drug target validation.

EST79232 and EST79376, Two Novel Sigma-1 Receptor Ligands, Exert Neuroprotection on Models of Motoneuron Degeneration

Motor neuron diseases (MNDs) include sporadic and hereditary neurological disorders characterized by progressive degeneration of motor neurons (MNs). Sigma-1 receptor (Sig-1R) is a protein enriched in MNs, and mutations on its gene lead to various types of MND. Previous studies have suggested that Sig-1R is a target to prevent MN degeneration. In this study, two novel synthesized Sig-1R ligands, coded EST79232 and EST79376, from the same chemical series, with the same scaffold and similar physicochemical properties but opposite functionality on Sig-1R, were evaluated as neuroprotective compounds to prevent MN degeneration. We used an in vitro model of spinal cord organotypic cultures under chronic excitotoxicity and two in vivo models, the spinal nerve injury and the superoxide dismutase 1 (SOD1)G93A mice, to characterize the effects of these Sig-1R ligands on MN survival and modulation of glial reactivity. The antagonist EST79376 preserved MNs in vitro and after spinal nerve injury but was not able to improve MN death in SOD1G93A mice. In contrast, the agonist EST79232 significantly increased MN survival in the three models of MN degeneration evaluated and had a mild beneficial effect on motor function in SOD1G93A mice. In vivo, Sig-1R ligand EST79232 had a more potent effect on preventing MN degeneration than EST79376. These data further support the interest in Sig-1R as a therapeutic target for neurodegeneration.

Characterization of somatosensory neuron involvement in the SOD1G93A mouse model

SOD1^G93A mice show loss of cutaneous small fibers, as in ALS patients. Our objective is to characterize the involvement of different somatosensory neuron populations and its temporal progression in the SOD1^G93A mice. We aim to further define peripheral sensory involvement, analyzing at the same time points the neuronal bodies located in the dorsal root ganglia (DRG) and the distal part of their axons in the skin, in order to shed light in the mechanisms of sensory involvement in ALS. We performed immunohistochemical analysis of peptidergic (CGRP), non-peptidergic (IB4) fibers in epidermis, as well as sympathetic sudomotor fibers (VIP) in the footpads of SOD1^G93A mice and wild type littermates at 4, 8, 12 and 16 weeks of age. We also immunolabeled and quantified neuronal bodies of IB4, CGRP and parvalbumin (PV) positive sensory neurons in lumbar DRG. We detected a reduction of intraepidermal nerve fiber density in the SOD1^G93A mice of both peptidergic and non-peptidergic axons, compared with the WT, being the non-peptidergic the fewest. Sweat gland innervation was similarly affected in the SOD1^G93A mouse at 12 weeks. Nonetheless, the number of DRG neurons from different sensory populations remained unchanged during all stages. Cutaneous sensory axons are affected in the SOD1^G93A mouse, with non-peptidergic being slightly more vulnerable than peptidergic axons. Loss or lack of growth of the distal portion of sensory axons with preservation of the corresponding neuronal bodies suggest a distal axonopathy.

Improving reproducibility of motor evoked potentials in mice

BACKGROUND

In preclinical research involving murine models of neurological diseases, Motor Evoked Potentials (MEPs) can detect pathological alterations in nerve conduction throughout the cortico-spinal tract. In mice, MEPs elicited by electrical stimulation of the motor cortex can be performed with epicranial or subdermal electrodes such as implanted screws or removable needles, which are associated with invasive surgery and variability in placement of the stimulating electrodes, respectively.

METHODS

We compared MEPs induced by epicranial or subcutaneous stimulation with a non-invasive surface cup electrode over five recording sessions, in healthy C57BL/6 mice. Additionally, using surface stimulation, we examined the recordings obtained with intramuscular needles or surface electrodes to understand if MEP reproducibility could be improved.

RESULTS

Resting motor threshold (RMT), MEP latency and amplitude were comparable among the different stimulation methods. Epicranial, subcutaneous and surface stimulation techniques presented good repeatability over time, with surface stimulation showing a significantly reduced inter-session variability. Compared with intramuscular needles, MEPs recorded with surface electrode showed reduced peak-to-peak amplitude at all timepoints. RMT and MEP latency were comparable with both recording methods. On the other hand, amplitudes recorded with the surface electrode presented a significantly lower inter-session variance, resulting in improved repeatability.

CONCLUSION

Overall, there is evidence for highly reproducible results using different stimulating methods, with indication for reduced inter-session variability for surface stimulation. Moreover, MEP recording with surface electrode provided a decrease in amplitude variability over time, indicating improved measurement stability when considering amplitude as functional outcome in longitudinal studies.

Sigma-1 Receptor is a Pharmacological Target to Promote Neuroprotection in the SOD1G93A ALS Mice

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disorder characterized by the death of motoneurons (MNs) with a poor prognosis. There is no available cure, thus, novel therapeutic targets are urgently needed. Sigma-1 receptor (Sig-1R) has been reported as a target to treat experimental models of degenerative diseases and, importantly, mutations in the Sig-1R gene cause several types of motoneuron disease (MND). In this study we compared the potential therapeutic effect of three Sig-1R ligands, the agonists PRE-084 and SA4503 and the antagonist BD1063, in the SOD1^G93A mouse model of ALS. Pharmacological administration was from 8 to 16 weeks of age, and the neuromuscular function and disease progression were evaluated using nerve conduction and rotarod tests. At the end of follow up (16 weeks), samples were harvested for histological and molecular analyses. The results showed that PRE-084, as well as BD1063 treatment was able to preserve neuromuscular function of the hindlimbs and increased the number of surviving MNs in the treated female SOD1^G93A mice. SA4503 tended to improve motor function and preserved neuromuscular junctions (NMJ), but did not improve MN survival. Western blot analyses revealed that the autophagic flux and the endoplasmic reticulum stress, two pathways implicated in the physiopathology of ALS, were not modified with Sig-1R treatments in SOD1^G93A mice. In conclusion, Sig-1R ligands are promising tools for ALS treatment, although more research is needed to ascertain their mechanisms of action.

Gene Therapy Overexpressing Neuregulin 1 Type I in Combination With Neuregulin 1 Type III Promotes Functional Improvement in the SOD1G93A ALS Mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting the neuromuscular system for which currently there is no effective therapy. Motoneuron (MN) degeneration involves several complex mechanisms, including surrounding glial cells and skeletal muscle contributions. Neuregulin 1 (NRG1) is a trophic factor present particularly in MNs and neuromuscular junctions. Our previous studies revealed that gene therapy overexpressing the isoform I (NRG1-I) in skeletal muscles as well as overexpressing the isoform III (NRG1-III) directly in the central nervous system are both effective in preserving MNs in the spinal cord of ALS mice, opening novel therapeutic approaches. In this study, we combined administration of both viral vectors overexpressing NRG1-I in skeletal muscles and NRG1-III in spinal cord of the SOD1G93A mice in order to obtain a synergistic effect. The results showed that the combinatorial gene therapy increased preservation of MNs and of innervated neuromuscular junctions and reduced glial reactivity in the spinal cord of the treated SOD1G93A mice. Moreover, NRG1 isoforms overexpression improved motor function of hindlimb muscles and delayed the onset of clinical disease. However, this combinatory gene therapy did not produce a synergic effect compared with single therapies, suggesting an overlap between NRG1-I and NRG1-III activated pathways and their beneficial effects.

Extensive phenotypic characterisation of a human TDP-43Q331K transgenic mouse model of amyotrophic lateral sclerosis (ALS)

The majority of preclinical studies in ALS have relied on transgenic models with overexpression of mutant human superoxide dismutase 1 (SOD1), widely regarded to have failed in terms of translation of therapeutic effects. However, there are still no widely accepted models of other genetic subtypes of ALS. The majority of patients show ubiquitinated cytoplasmic inclusions of TAR DNA binding protein of 43 kilodaltons (TDP-43) in spinal motor neurons at the end stage of disease and a small proportion have mutations in TARDBP, the gene encoding TDP-43. TDP-43 transgenic mouse models have been produced, but have not been widely adopted. Here, we characterised one of these models available from the Jackson Laboratory in detail. Compared to TDP-43^WT mice, TDP-43^Q331K mice had 43% less hindlimb muscle mass at 6 months and a 73% reduction in hindlimb compound muscle action potential at 8 months of age. Rotarod and gait analysis indicated motor system decline with elevated weight gain. At the molecular level, the lack of TDP-43 cellular pathology was confirmed with a surprising increase in nuclear TDP-43 in motor neurons. Power analysis indicated group sizes of 12–14 mice are needed to detect 10–20% changes in measured parameters with a power of 80%, providing valid readouts for preclinical testing. Overall, this model may represent a useful component of multi-model pre-clinical therapeutic studies for ALS.

Beneficial effects of dietary supplementation with green tea catechins and cocoa flavanols on aging-related regressive changes in the mouse neuromuscular system

Besides skeletal muscle wasting, sarcopenia entails morphological and molecular changes in distinct components of the neuromuscular system, including spinal cord motoneurons (MNs) and neuromuscular junctions (NMJs); moreover, noticeable microgliosis has also been observed around aged MNs. Here we examined the impact of two flavonoid-enriched diets containing either green tea extract (GTE) catechins or cocoa flavanols on age-associated regressive changes in the neuromuscular system of C57BL/6J mice. Compared to control mice, GTE- and cocoa-supplementation significantly improved the survival rate of mice, reduced the proportion of fibers with lipofuscin aggregates and central nuclei, and increased the density of satellite cells in skeletal muscles. Additionally, both supplements significantly augmented the number of innervated NMJs and their degree of maturity compared to controls. GTE, but not cocoa, prominently increased the density of VAChT and VGluT2 afferent synapses on MNs, which were lost in control aged spinal cords; conversely, cocoa, but not GTE, significantly augmented the proportion of VGluT1 afferent synapses on aged MNs. Moreover, GTE, but not cocoa, reduced aging-associated microgliosis and increased the proportion of neuroprotective microglial phenotypes. Our data indicate that certain plant flavonoids may be beneficial in the nutritional management of age-related deterioration of the neuromuscular system.

Neuroprotective Effects of Sigma 1 Receptor Ligands on Motoneuron Death after Spinal Root Injury in Mice

Loss of motor neurons (MNs) after spinal root injury is a drawback limiting the recovery after palliative surgery by nerve or muscle transfers. Research based on preventing MN death is a hallmark to improve the perspectives of recovery following severe nerve injuries. Sigma-1 receptor (Sig-1R) is a protein highly expressed in MNs, proposed as neuroprotective target for ameliorating MN degenerative conditions. Here, we used a model of L4-L5 rhizotomy in adult mice to induce MN degeneration and to evaluate the neuroprotective role of Sig-1R ligands (PRE-084, SA4503 and BD1063). Lumbar spinal cord was collected at 7, 14, 28 and 42 days post-injury (dpi) for immunohistochemistry, immunofluorescence and Western blot analyses. This proximal axotomy at the immediate postganglionic level resulted in significant death, up to 40% of spinal MNs at 42 days after injury and showed markedly increased glial reactivity. Sig-1R ligands PRE-084, SA4503 and BD1063 reduced MN loss by about 20%, associated to modulation of endoplasmic reticulum stress markers IRE1α and XBP1. These pathways are Sig-1R specific since they were not produced in Sig-1R knockout mice. These findings suggest that Sig-1R is a promising target for the treatment of MN cell death after neural injuries.

In Vivo Fiber Optic Raman Spectroscopy of Muscle in Preclinical Models of Amyotrophic Lateral Sclerosis and Duchenne Muscular Dystrophy

Neuromuscular diseases result in muscle weakness, disability, and, in many instances, death. Preclinical models form the bedrock of research into these disorders, and the development of in vivo and potentially translational biomarkers for the accurate identification of disease is crucial. Spontaneous Raman spectroscopy can provide a rapid, label-free, and highly specific molecular fingerprint of tissue, making it an attractive potential biomarker. In this study, we have developed and tested an in vivo intramuscular fiber optic Raman technique in two mouse models of devastating human neuromuscular diseases, amyotrophic lateral sclerosis, and Duchenne muscular dystrophy (SOD1G93A and mdx, respectively). The method identified diseased and healthy muscle with high classification accuracies (area under the receiver operating characteristic curves (AUROC): 0.76-0.92). In addition, changes in diseased muscle over time were also identified (AUROCs 0.89-0.97). Key spectral changes related to proteins and the loss of α-helix protein structure. Importantly, in vivo recording did not cause functional motor impairment and only a limited, resolving tissue injury was seen on high-resolution magnetic resonance imaging. Lastly, we demonstrate that ex vivo muscle from human patients with these conditions produced similar spectra to those observed in mice. We conclude that spontaneous Raman spectroscopy of muscle shows promise as a translational research tool.

Specific Expression of Glial-Derived Neurotrophic Factor in Muscles as Gene Therapy Strategy for Amyotrophic Lateral Sclerosis

Glial cell line-derived neurotrophic factor (GDNF) is a powerful neuroprotective growth factor. However, systemic or intrathecal administration of GDNF is associated with side effects. Here, we aimed to avoid this by restricting the transgene expression to the skeletal muscle by gene therapy. To specifically target most skeletal muscles in the mouse model of amyotrophic lateral sclerosis (ALS), SOD1G93A transgenic mice were intravenously injected with adeno-associated vectors coding for GDNF under the control of the desmin promoter. Treated and control SOD1G93A mice were evaluated by rotarod and nerve conduction tests from 8 to 20 weeks of age, and then histological and molecular analyses were performed. Muscle-specific GDNF expression delayed the progression of the disease in SOD1G93A female and male mice by preserving the neuromuscular function; increasing the number of innervated neuromuscular junctions, the survival of spinal motoneurons; and reducing glial reactivity in treated SOD1G93A mice. These beneficial actions are attributed to a paracrine protective mechanism from the muscle to the motoneurons by GDNF. Importantly, no adverse secondary effects were detected. These results highlight the potential of muscle GDNF-targeted expression for ALS therapy.

Motoneuron deafferentation and gliosis occur in association with neuromuscular regressive changes during ageing in mice

BACKGROUND

The cellular mechanisms underlying the age-associated loss of muscle mass and function (sarcopenia) are poorly understood, hampering the development of effective treatment strategies. Here, we performed a detailed characterization of age-related pathophysiological changes in the mouse neuromuscular system.

METHODS

Young, adult, middle-aged, and old (1, 4, 14, and 24-30 months old, respectively) C57BL/6J mice were used. Motor behavioural and electrophysiological tests and histological and immunocytochemical procedures were carried out to simultaneously analyse structural, molecular, and functional age-related changes in distinct cellular components of the neuromuscular system.

RESULTS

Ageing was not accompanied by a significant loss of spinal motoneurons (MNs), although a proportion (~15%) of them in old mice exhibited an abnormally dark appearance. Dark MNs were also observed in adult (~9%) and young (~4%) animals, suggesting that during ageing, some MNs undergo early deleterious changes, which may not lead to MN death. Old MNs were depleted of cholinergic and glutamatergic inputs (~40% and ~45%, respectively, P < 0.01), suggestive of age-associated alterations in MN excitability. Prominent microgliosis and astrogliosis [~93% (P < 0.001) and ~100% (P < 0.0001) increase vs. adults, respectively] were found in old spinal cords, with increased density of pro-inflammatory M1 microglia and A1 astroglia (25-fold and 4-fold increase, respectively, P < 0.0001). Ageing resulted in significant reductions in the nerve conduction velocity and the compound muscle action potential amplitude (~30%, P < 0.05, vs. adults) in old distal plantar muscles. Compared with adult muscles, old muscles exhibited significantly higher numbers of both denervated and polyinnervated neuromuscular junctions, changes in fibre type composition, higher proportion of fibres showing central nuclei and lipofuscin aggregates, depletion of satellite cells, and augmented expression of different molecules related to development, plasticity, and maintenance of neuromuscular junctions, including calcitonin gene-related peptide, growth associated protein 43, agrin, fibroblast growth factor binding protein 1, and transforming growth factor-β1. Overall, these alterations occurred at varying degrees in all the muscles analysed, with no correlation between the age-related changes observed and myofiber type composition or muscle topography.

CONCLUSIONS

Our data provide a global view of age-associated neuromuscular changes in a mouse model of ageing and help to advance understanding of contributing pathways leading to development of sarcopenia.

Sigma 1 receptor as a therapeutic target for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult disease causing a progressive loss of upper and lower motoneurons, muscle paralysis and early death. ALS has a poor prognosis of 3-5 years after diagnosis with no effective cure. The aetiopathogenic mechanisms involved include glutamate excitotoxicity, oxidative stress, protein misfolding, mitochondrial alterations, disrupted axonal transport and inflammation. Sigma non-opioid intracellular receptor 1 (sigma 1 receptor) is a protein expressed in motoneurons, mainly found in the endoplasmic reticulum (ER) on the mitochondria-associated ER membrane (MAM) or in close contact with cholinergic postsynaptic sites. MAMs are sites that allow the assembly of several complexes implicated in essential survival cell functions. The sigma 1 receptor modulates essential mechanisms for motoneuron survival including excitotoxicity, calcium homeostasis, ER stress and mitochondrial dysfunction. This review updates sigma 1 receptor mechanisms and its alterations in ALS, focusing on MAM modulation, which may constitute a novel target for therapeutic strategies. 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.

Therapeutic Role of Neuregulin 1 Type III in SOD1-Linked Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating motoneuron (Mn) disease without effective cure currently available. Death of MNs in ALS is preceded by failure of neuromuscular junctions and axonal retraction. Neuregulin 1 (NRG1) is a neurotrophic factor highly expressed in MNs and neuromuscular junctions that support axonal and neuromuscular development and maintenance. NRG1 and its ErbB receptors are involved in ALS. Reduced NRG1 expression has been found in ALS patients and in the ALS SOD1G93A mouse model; however, the expression of the isoforms of NRG1 and its receptors is still controversial. Due to the reduced levels of NRG1 type III (NRG1-III) in the spinal cord of ALS patients, we used gene therapy based on intrathecal administration of adeno-associated virus to overexpress NRG1-III in SOD1G93A mice. The mice were evaluated from 9 to 16 weeks of age by electrophysiology and rotarod tests. At 16 weeks, samples were harvested for histological and molecular analyses. Our results indicate that overexpression of NRG1-III is able to preserve neuromuscular function of the hindlimbs, improve locomotor performance, increase the number of surviving MNs, and reduce glial reactivity in the treated female SOD1G93A mice. Furthermore, the NRG1-III/ErbB4 axis appears to regulate MN excitability by modulating the chloride transporter KCC2 and reduces the expression of the MN vulnerability marker MMP-9. However, NRG1-III did not have a significant effect on male mice, indicating relevant sex differences. These findings indicate that increasing NRG1-III at the spinal cord is a promising approach for promoting MN protection and functional improvement in ALS.

Methods for in vivo studies in rodents of chemotherapy induced peripheral neuropathy

Peripheral neuropathy is one of the most common, dose limiting, and long-lasting disabling adverse events of chemotherapy treatment. Unfortunately, no treatment has proven efficacy to prevent this adverse effect in patients or improve the nerve regeneration, once it is established. Experimental models, particularly using rats and mice, are useful to investigate the mechanisms related to axonal or neuronal degeneration and target loss of function induced by neurotoxic drugs, as well as to test new strategies to prevent the development of neuropathy and to improve functional restitution. Therefore, objective and reliable methods should be applied for the assessment of function and innervation in adequately designed in vivo studies of CIPN, taking into account the impact of age, sex and species/strains features. This review gives an overview of the most useful methods to assess sensory, motor and autonomic functions, electrophysiological and morphological tests in rodent models of peripheral neuropathy, focused on CIPN. We include as well a proposal of protocols that may improve the quality and comparability of studies undertaken in different laboratories. It is recommended to apply more than one functional method for each type of function, and to perform parallel morphological studies in the same targets and models.

Combined intramuscular and intraspinal transplant of bone marrow cells improves neuromuscular function in the SOD1G93A mice

Background

The simultaneous contribution of several etiopathogenic disturbances makes amyotrophic lateral sclerosis (ALS) a fatal and challenging disease. Here, we studied two different cell therapy protocols to protect both central and peripheral nervous system in a murine model of ALS.

Methods

Since ALS begins with a distal axonopathy, in a first assay, we performed injection of bone marrow cells into two hindlimb muscles of transgenic SOD1^G93A mice. In a second study, we combined intramuscular and intraspinal injection of bone marrow cells. Fluorescence-activated cell sorting was used to assess the survival of the transplanted cells into the injected tissues. The mice were assessed from 8 to 16 weeks of age by means of locomotion and electrophysiological tests. After follow-up, the spinal cord was processed for analysis of motoneuron survival and glial cell reactivity.

Results

We found that, after intramuscular injection, bone marrow cells were able to engraft within the muscle. However, bone marrow cell intramuscular injection failed to promote a general therapeutic effect. In the second approach, we found that bone marrow cells had limited survival in the spinal cord, but this strategy significantly improved motor outcomes. Moreover, we also found that the dual cell therapy tended to preserve spinal motoneurons at late stages of the disease and to reduce microgliosis, although this did not prolong mice survival.

Conclusion

Overall, our findings suggest that targeting more than one affected area of the motor system at once with bone marrow cell therapy results in a valuable therapeutic intervention for ALS.

Gene therapy for overexpressing Neuregulin 1 type I in skeletal muscles promotes functional improvement in the SOD1G93A ALS mice

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder affecting motoneurons (MNs), with no effective treatment currently available. The molecular mechanisms that are involved in MN death are complex and not fully understood, with partial contributions of surrounding glial cells and skeletal muscle to the disease. Neuregulin 1 (NRG1) is a trophic factor highly expressed in MNs and neuromuscular junctions. Recent studies have suggested a crucial role of the isoform I (NRG1-I) in the collateral reinnervation process in skeletal muscle, and NRG1-III in the preservation of MNs in the spinal cord, opening a window for developing novel therapies for neuromuscular diseases like ALS. In this study, we overexpressed NRG1-I widely in the skeletal muscles of the SOD1^G93A transgenic mouse. The results show that NRG1 gene therapy activated the survival pathways in muscle and spinal cord, increasing the number of surviving MNs and neuromuscular junctions and reducing the astroglial reactivity in the spinal cord of the treated SOD1^G93A mice. Furthermore, NRG1-I overexpression preserved motor function and delayed the onset of clinical disease. In summary, our data indicates that NRG1 plays an important role on MN survival and muscle innervation in ALS, and that viral-mediated overexpression of NRG1 isoforms may be considered as a promising approach for ALS treatment.

CSF1R inhibitor JNJ-40346527 attenuates microglial proliferation and neurodegeneration in P301S mice

Neuroinflammation and microglial activation are significant processes in Alzheimer's disease pathology. Recent genome-wide association studies have highlighted multiple immune-related genes in association with Alzheimer's disease, and experimental data have demonstrated microglial proliferation as a significant component of the neuropathology. In this study, we tested the efficacy of the selective CSF1R inhibitor JNJ-40346527 (JNJ-527) in the P301S mouse tauopathy model. We first demonstrated the anti-proliferative effects of JNJ-527 on microglia in the ME7 prion model, and its impact on the inflammatory profile, and provided potential CNS biomarkers for clinical investigation with the compound, including pharmacokinetic/pharmacodynamics and efficacy assessment by TSPO autoradiography and CSF proteomics. Then, we showed for the first time that blockade of microglial proliferation and modification of microglial phenotype leads to an attenuation of tau-induced neurodegeneration and results in functional improvement in P301S mice. Overall, this work strongly supports the potential for inhibition of CSF1R as a target for the treatment of Alzheimer's disease and other tau-mediated neurodegenerative diseases.

Neuroprotective Effects of Genistein in a SOD1-G93A Transgenic Mouse Model of Amyotrophic Lateral Sclerosis

Oxidant toxicity has been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS), an insidiously progressive neurodegenerative disorder involving upper and lower motor neurons. Here, we investigated the cellular and molecular mechanisms underlying the neuroprotective effects of an anti-oxidant genistein in SOD1-G93A transgenic mouse model of ALS. Rotarod test, hanging wire test and hindlimb clasping test were used to determined disease onset and assess motor performance. Immunostaining together with neuronal size measurement were used to count viable motor neurons. In addition, immunostaining procedure and ELISA kit were used to assess the inflammatory response in the spinal cord. Our results showed that Genistein administration suppressed the production of pro-inflammatory cytokines and alleviated gliosis in the spinal cord of SOD1-G93A mice. In addition, genistein administration induced autophagic processes and enhanced the viability of spinal motor neurons. As a result, genistein alleviated ALS-related symptoms and slightly prolonged the lifespan of SOD1-G93A mice. Taken together, our results indicate that genistein is neuroprotective in SOD1-G93A mice, suggesting genistein could be a promising treatment for human ALS. Graphical Abstract Genistein protects impariments in SOD1-G93A transgenic mouse model.

Muscle contractility dysfunction precedes loss of motor unit connectivity in SOD1(G93A) mice

INTRODUCTION

Electrophysiological measurements are used in longitudinal clinical studies to provide insight into the progression of amyotrophic lateral sclerosis (ALS) and the relationship between muscle weakness and motor unit (MU) degeneration. Here, we used a similar longitudinal approach in the Cu/Zn superoxide dismutase (SOD1[G93A]) mouse model of ALS.

METHODS

In vivo muscle contractility and MU connectivity assays were assessed longitudinally in SOD1(G93A) and wild type mice from postnatal days 35 to 119.

RESULTS

In SOD1(G93A) males, muscle contractility was reduced by day 35 and preceded MU loss. Muscle contractility and motor unit reduction were delayed in SOD1(G93A) females compared with males, but, just as with males, muscle contractility reduction preceded MU loss.

DISCUSSION

The longitudinal contractility and connectivity paradigm employed here provides additional insight into the SOD1(G93A) mouse model and suggests that loss of muscle contractility is an early finding that may precede loss of MUs and motor neuron death. Muscle Nerve 59:254-262, 2019.

Muscle specific kinase (MuSK) activation preserves neuromuscular junctions in the diaphragm but is not sufficient to provide a functional benefit in the SOD1G93A mouse model of ALS

Amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting motor neurons, is characterized by rapid decline of motor function and ultimately respiratory failure. As motor neuron death occurs late in the disease, therapeutics that prevent the initial disassembly of the neuromuscular junction may offer optimal functional benefit and delay disease progression. To test this hypothesis, we treated the SOD1^G93A mouse model of ALS with an agonist antibody to muscle specific kinase (MuSK), a receptor tyrosine kinase required for the formation and maintenance of the neuromuscular junction. Chronic MuSK antibody treatment fully preserved innervation of the neuromuscular junction when compared with control-treated mice; however, no preservation of diaphragm function, motor neurons, or survival benefit was detected. These data show that anatomical preservation of neuromuscular junctions in the diaphragm via MuSK activation does not correlate with functional benefit in SOD1^G93A mice, suggesting caution in employing MuSK activation as a therapeutic strategy for ALS patients.

Antisense oligonucleotides extend survival and reverse decrement in muscle response in ALS models

Mutations in superoxide dismutase 1 (SOD1) are responsible for 20% of familial ALS. Given the gain of toxic function in this dominantly inherited disease, lowering SOD1 mRNA and protein is predicted to provide therapeutic benefit. An early generation antisense oligonucleotide (ASO) targeting SOD1 was identified and tested in a phase I human clinical trial, based on modest protection in animal models of SOD1 ALS. Although the clinical trial provided encouraging safety data, the drug was not advanced because there was progress in designing other, more potent ASOs for CNS application. We have developed next-generation SOD1 ASOs that more potently reduce SOD1 mRNA and protein and extend survival by more than 50 days in SOD1G93A rats and by almost 40 days in SOD1G93A mice. We demonstrated that the initial loss of compound muscle action potential in SOD1G93A mice is reversed after a single dose of SOD1 ASO. Furthermore, increases in serum phospho-neurofilament heavy chain levels, a promising biomarker for ALS, are stopped by SOD1 ASO therapy. These results define a highly potent, new SOD1 ASO ready for human clinical trial and suggest that at least some components of muscle response can be reversed by therapy.

Nintedanib decreases muscle fibrosis and improves muscle function in a murine model of dystrophinopathy

Duchenne muscle dystrophy (DMD) is a genetic disorder characterized by progressive skeletal muscle weakness. Dystrophin deficiency induces instability of the sarcolemma during muscle contraction that leads to muscle necrosis and replacement of muscle by fibro-adipose tissue. Several therapies have been developed to counteract the fibrotic process. We report the effects of nintedanib, a tyrosine kinase inhibitor, in the mdx murine model of DMD. Nintedanib reduced proliferation and migration of human fibroblasts in vitro and decreased the expression of fibrotic genes such as COL1A1, COL3A1, FN1, TGFB1, and PDGFA. We treated seven mdx mice with 60 mg/kg/day nintedanib for 1 month. Electrophysiological studies showed an increase in the amplitude of the motor action potentials and an improvement of the morphology of motor unit potentials in the animals treated. Histological studies demonstrated a significant reduction of the fibrotic areas present in the skeletal muscles. Analysis of mRNA expression from muscles of treated mice showed a reduction in Col1a1, Col3a1, Tgfb1, and Pdgfa. Western blot showed a reduction in the expression of collagen I in skeletal muscles. In conclusion, nintedanib reduced the fibrotic process in a murine model of dystrophinopathy after 1 month of treatment, suggesting its potential use as a therapeutic drug in DMD patients.

Structural and functional properties of bone are compromised in amyotrophic lateral sclerosis mice

In addition to muscle weakness, amyotrophic lateral sclerosis (ALS) is associated with an increased incidence of skeletal fractures. The SOD1^G93A mouse model recapitulates many features of human ALS. These mice also exhibit decreased bone mass. However, the functional, or biomechanical, behavior of the skeleton in SOD1^G93A mice has not been investigated. To do so, we examined skeletal phenotypes in end-stage (16-week-old) SOD1^G93A female mice and healthy littermate female controls (N = 9-10/group). Outcomes included trabecular and cortical bone microarchitecture by microcomputed tomography; stiffness and strength via three-point bending; resistance to crack growth by fracture toughness testing; and cortical bone matrix properties via cyclic reference point indentation. SOD1^G93A mice had similar bone size, but significantly lower trabecular bone mass (-54%), thinner trabeculae (-41%) and decreased cortical bone thickness (-17%) and cortical area (-18%) compared to control mice (all p < 0.01). In line with these bone mass and microstructure deficits, SOD1^G93A mice had significantly lower femoral bending stiffness (-27%) and failure moment (-41%), along with decreased fracture toughness (-18%) (all p < 0.001). This is the first study to demonstrate functional deficits in the skeleton of end-stage ALS mice, and imply multiple mechanisms for increased skeletal fragility and fracture risk in patients in ALS. Importantly, our results provide strong rationale for interventions to reduce fracture risk in ALS patients with advanced disease.

Quantitative analysis of motor evoked potentials in the neonatal lamb

Evoking motor potentials are an objective assessment method for neuromotor function, yet this was to our knowledge never done in neonatal lambs. There is neither a method for standardized quantification of motor evoked potentials (MEPs). We first aimed to evaluate the feasibility of MEP recording in neonatal lambs and test its validity. Second we aimed to develop an algorithm for its quantification and test its reliability since manual input is required. We recorded myogenic MEPs after transcranial motor cortex stimulation in 6 lambs aged 1–2 days. MEPs were also measured in one lamb undergoing Neuro-Muscular Blockade (NMB) and another undergoing lumbar spinal cord (SC) transection, both serving as controls. We computed 5 parameters using a custom-made algorithm: motor threshold, latency, area-under-the-curve, peak-to-peak amplitude and duration. Intra- and inter-observer reliability was analyzed. MEPs could be easily recorded, disappearing after NMB and SC transection. The algorithm allowed for analysis, hence physiologic readings of the parameters in all 4 limbs of all lambs were obtained. Our method was shown to have high intra- and inter-observer ( ≥70%) reliability for latency, area-under-the-curve and peak-to-peak amplitude. These results suggest that standardized MEP recording and analysis in neonatal lambs is feasible, and can reliably assess neuromotor function.

Granulocyte Colony-Stimulating Factor Ameliorates Skeletal Muscle Dysfunction in Amyotrophic Lateral Sclerosis Mice and Improves Proliferation of SOD1-G93A Myoblasts in vitro

<b><i>Background:</i></b> Amyotrophic lateral sclerosis (ALS) causes loss of upper and lower motor neurons as well as skeletal muscle (SKM) dysfunction and atrophy. SKM is one of the tissues involved in the development of ALS pathology, and studies in a SOD1-G93A mouse model of ALS have demonstrated alterations in SKM degeneration/regeneration marker expression in vivo and defective mutant myoblast proliferation in vitro. Granulocyte colony-stimulating factor (G-CSF) has been shown to alleviate SOD1-G93A pathology. However, it is unknown whether G-CSF may have a direct effect on SKM or derived myoblasts. <b><i>Objective:</i></b> To investigate effects of G-CSF and its analog pegfilgrastim (PEGF) on SOD1-G93A- associated SKM markers in vivo and those of G-CSF on myoblast proliferation in vitro. <b><i>Methods:</i></b> The effect of PEGF treatment on hematopoietic stem cell mobilization, survival, and motor function was determined. RNA expression of SKM markers associated with mutant SOD1 expression was quantified in response to PEGF treatment in vivo, and the effect of G-CSF on the proliferation of myoblasts derived from mutant and control muscles was determined in vitro. <b><i>Results:</i></b> Positive effects of PEGF on hematopoietic stem cell mobilization, survival, and functional assays in SOD1-G93A animals were confirmed. In vivo PEGF treatment augmented the expression of its receptor Csf3r and alleviated typical markers for mutant SOD1 muscle. Additionally, G-CSF was found to directly increase the proliferation of SOD1-G93A, but not wild-type primary myoblasts in vitro. <b><i>Conclusion:</i></b> Our results support the beneficial role of the G-CSF analog PEGF in a SOD1-G93A model of ALS. Thus, G-CSF and<b> </b>its analogs may be directly beneficial in diseases where the SKM function is compromised.

Sigma-1 Receptor in Motoneuron Disease

Amyotrophic Lateral Sclerosis (ALS ) is a neurodegenerative disease affecting spinal cord and brain motoneurons , leading to paralysis and early death. Multiple etiopathogenic mechanisms appear to contribute in the development of ALS , including glutamate excitotoxicity, oxidative stress , protein misfolding, mitochondrial defects, impaired axonal transport, inflammation and glial cell alterations. The Sigma-1 receptor is highly expressed in motoneurons of the spinal cord, particularly enriched in the endoplasmic reticulum (ER) at postsynaptic cisternae of cholinergic C-terminals. Several evidences point to participation of Sigma-1R alterations in motoneuron degeneration. Thus, mutations of the transmembrane domain of the Sigma-1R have been described in familial ALS cases. Interestingly, Sigma-1R KO mice display muscle weakness and motoneuron loss. On the other hand, Sigma-1R agonists promote neuroprotection and neurite elongation through activation of protein kinase C on motoneurons in vitro and in vivo after ventral root avulsion. Remarkably, treatment of SOD1 mice, the most usual animal model of ALS , with Sigma-1R agonists resulted in significantly enhanced motoneuron function and preservation, and increased animal survival. Sigma-1R activation also reduced microglial reactivity and increased the glial expression of neurotrophic factors. Two main interconnected mechanisms seem to underlie the effects of Sigma-1R manipulation on motoneurons: modulation of neuronal excitability and regulation of calcium homeostasis. In addition, Sigma-1R also contributes to regulating protein degradation, and reducing oxidative stress. Therefore, the multi-functional nature of the Sigma-1R represents an attractive target for treating aspects of ALS and other motoneuron diseases .

Neuregulin-1 promotes functional improvement by enhancing collateral sprouting in SOD1(G93A) ALS mice and after partial muscle denervation

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive degeneration of motoneurons, which is preceded by loss of neuromuscular connections in a "dying back" process. Neuregulin-1 (Nrg1) is a neurotrophic factor essential for the development and maintenance of neuromuscular junctions, and Nrg1 receptor ErbB4 loss-of-function mutations have been reported as causative for ALS. Our main goal was to investigate the role of Nrg1 type I (Nrg1-I) in SOD1(G93A) mice muscles. We overexpressed Nrg1-I by means of an adeno-associated viral (AAV) vector, and investigated its effect by means of neurophysiological techniques assessing neuromuscular function, as well as molecular approaches (RT-PCR, western blot, immunohistochemistry, ELISA) to determine the mechanisms underlying Nrg1-I action. AAV-Nrg1-I intramuscular administration promoted motor axon collateral sprouting by acting on terminal Schwann cells, preventing denervation of the injected muscles through Akt and ERK1/2 pathways. We further used a model of muscle partial denervation by transecting the L4 spinal nerve. AAV-Nrg1-I intramuscular injection enhanced muscle reinnervation by collateral sprouting, whereas administration of lapatinib (ErbB receptor inhibitor) completely blocked it. We demonstrated that Nrg1-I plays a crucial role in the collateral reinnervation process, opening a new window for developing novel ALS therapies for functional recovery rather than preservation.

Wnt Signaling Alteration in the Spinal Cord of Amyotrophic Lateral Sclerosis Transgenic Mice: Special Focus on Frizzled-5 Cellular Expression Pattern

BACKGROUND

Amyotrophic lateral sclerosis is a chronic neurodegenerative disease characterized by progressive paralysis due to degeneration of motor neurons by unknown causes. Recent evidence shows that Wnt signaling is involved in neurodegenerative processes, including Amyotrophic Lateral Sclerosis. However, to date, little is known regarding the expression of Wnt signaling components in this fatal condition. In the present study we used transgenic SOD1G93A mice to evaluate the expression of several Wnt signaling components, with special focus on Frizzled-5 cellular expression alteration along disease progression.

FINDINGS

Based on previous studies demonstrating the expression of Wnts and their transcriptional regulation during Amyotrophic lateral sclerosis development, we have analyzed the mRNA expression of several Wnt signaling components in the spinal cord of SOD1G93A transgenic mice at different stages of the disease by using real time quantitative PCR analysis. Strikingly, one of the molecules that seemed not to be altered at mRNA level, Frizzled-5, showed a clear up-regulation at late stages in neurons, as evidenced by immunofluorescence assays. Moreover, increased Frizzled-5 appears to correlate with a decrease in NeuN signal in these cells, suggesting a correlation between neuronal affectation and the increased expression of this receptor.

CONCLUSIONS

Our data suggest the involvement of Wnt signaling pathways in the pathophysiology of Amyotrophic Lateral Sclerosis and, more specifically, the implication of Frizzled-5 receptor in the response of neuronal cells against neurodegeneration. Nevertheless, further experimental studies are needed to shed light on the specific role of Frizzled-5 and the emerging but increasing Wnt family of proteins research field as a potential target for this neuropathology.

CSF1R blockade slows the progression of amyotrophic lateral sclerosis by reducing microgliosis and invasion of macrophages into peripheral nerves

Inflammation is a common neuropathological feature in several neurological disorders, including amyotrophic lateral sclerosis (ALS). We have studied the contribution of CSF1R signalling to inflammation in ALS, as a pathway previously reported to control the expansion and activation of microglial cells. We found that microglial cell proliferation in the spinal cord of SOD1^G93A transgenic mice correlates with the expression of CSF1R and its ligand CSF1. Administration of GW2580, a selective CSF1R inhibitor, reduced microglial cell proliferation in SOD1^G93A mice, indicating the importance of CSF1-CSF1R signalling in microgliosis in ALS. Moreover, GW2580 treatment slowed disease progression, attenuated motoneuron cell death and extended survival of SOD1^G93A mice. Electrophysiological assessment revealed that GW2580 treatment protected skeletal muscle from denervation prior to its effects on microglial cells. We found that macrophages invaded the peripheral nerve of ALS mice before CSF1R-induced microgliosis occurred. Interestingly, treatment with GW2580 attenuated the influx of macrophages into the nerve, which was partly caused by the monocytopenia induced by CSF1R inhibition. Overall, our findings provide evidence that CSF1R signalling regulates inflammation in the central and peripheral nervous system in ALS, supporting therapeutic targeting of CSF1R in this disease.

The Potential Role of Motor Unit Number Estimation as an Additional Diagnostic and Prognostic Value in Canine Neurology

Motor unit number estimation (MUNE) is an electrophysiological technique to assess the number of motor units innervating a single muscle or muscle group of interest. It may quantify axonal loss in any disease involving injury or degeneration of ventral horn cells or motor axons. Since MUNE has rarely been used in veterinary medicine, our study aimed to evaluate its potential role as an additional diagnostic and prognostic parameter in canine neurology. Therefore, we examined five healthy dogs and seven dogs suffering from diseases that necessitated general anesthesia for further diagnostics and treatment and that were not expected to interfere with the results of electrodiagnostic testing. By using the incremental technique to study MUNE in the cranial tibial muscle, we determined the number of motor units, the size of the compound muscle action potential, and the mean size of individual motor unit potentials of each dog as well as the mean values for each group. Moreover, we studied the correlation between these parameters. Taking the results into consideration, we addressed the difficulties and limitations of this technique. We, furthermore, pointed out possible fields of application for MUNE in canine neurology, and emphasized several aspects that future studies should focus on when applying MUNE to canine patients.

Electrophysiological Motor Unit Number Estimation (MUNE) Measuring Compound Muscle Action Potential (CMAP) in Mouse Hindlimb Muscles

Compound muscle action potential (CMAP) and motor unit number estimation (MUNE) are electrophysiological techniques that can be used to monitor the functional status of a motor unit pool in vivo. These measures can provide insight into the normal development and degeneration of the neuromuscular system. These measures have clear translational potential because they are routinely applied in diagnostic and clinical human studies. We present electrophysiological techniques similar to those employed in humans to allow recordings of mouse sciatic nerve function. The CMAP response represents the electrophysiological output from a muscle or group of muscles following supramaximal stimulation of a peripheral nerve. MUNE is an electrophysiological technique that is based on modifications of the CMAP response. MUNE is a calculated value that represents the estimated number of motor neurons or axons (motor control input) supplying the muscle or group of muscles being tested. We present methods for recording CMAP responses from the proximal leg muscles using surface recording electrodes following the stimulation of the sciatic nerve in mice. An incremental MUNE technique is described using submaximal stimuli to determine the average single motor unit potential (SMUP) size. MUNE is calculated by dividing the CMAP amplitude (peak-to-peak) by the SMUP amplitude (peak-to-peak). These electrophysiological techniques allow repeated measures in both neonatal and adult mice in such a manner that facilitates rapid analysis and data collection while reducing the number of animals required for experimental testing. Furthermore, these measures are similar to those recorded in human studies allowing more direct comparisons.

Amyotrophic lateral sclerosis: Current perspectives from basic research to the clinic

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive degeneration of upper and lower motoneurons, leading to muscle weakness and paralysis, and finally death. Considerable recent advances have been made in basic research and preclinical therapeutic attempts using experimental models, leading to increasing clinical and translational research in the context of this disease. In this review we aim to summarize the most relevant findings from a variety of aspects about ALS, including evaluation methods, animal models, pathophysiology, and clinical findings, with particular emphasis in understanding the role of every contributing mechanism to the disease for elucidating the causes underlying degeneration of motoneurons and the development of new therapeutic strategies.

Measuring Neuromuscular Junction Functionality in the SOD1(G93A) Animal Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that leads to motor neuron degeneration, alteration in neuromuscular junctions (NMJs), muscle atrophy, and paralysis. To investigate the NMJ functionality in ALS we tested, in vitro, two innervated muscle types excised from SOD1^G93A transgenic mice at the end-stage of the disease: the Soleus, a postural muscle almost completely paralyzed at that stage, and the diaphragm, which, on the contrary, is functional until death. To this aim we employed an experimental protocol that combined two types of electrical stimulation: the direct stimulation and the stimulation through the nerve. The technique we applied allowed us to determine the relevance of NMJ functionality separately from muscle contractile properties in SOD1^G93A animal model. Functional measurements revealed that the muscle contractility of transgenic diaphragms is almost unaltered in comparison to control muscles, while transgenic Soleus muscles were severely compromised. In contrast, when stimulated via the nerve, both transgenic muscle types showed a strong decrease of the contraction force, a slowing down of the kinetic parameters, as well as alterations in the neurotransmission failure parameter. All together, these results confirm a severely impaired functionality in the SOD1^G93A neuromuscular junctions.

Presymptomatic electrophysiological tests predict clinical onset and survival in SOD1(G93A) ALS mice

INTRODUCTION

We assessed the predictive value of electrophysiological tests as a marker of clinical disease onset and survival in superoxide-dismutase 1 (SOD1)(G93A) mice.

METHODS

We evaluated the accuracy of electrophysiological tests in differentiating transgenic versus wild-type mice. We made a correlation analysis of electrophysiological parameters and the onset of symptoms, survival, and number of spinal motoneurons.

RESULTS

Presymptomatic electrophysiological tests show great accuracy in differentiating transgenic versus wild-type mice, with the most sensitive parameter being the tibialis anterior compound muscle action potential (CMAP) amplitude. The CMAP amplitude at age 10 weeks correlated significantly with clinical disease onset and survival. Electrophysiological tests increased their survival prediction accuracy when evaluated at later stages of the disease and also predicted the amount of lumbar spinal motoneuron preservation.

CONCLUSIONS

Electrophysiological tests predict clinical disease onset, survival, and spinal motoneuron preservation in SOD1(G93A) mice. This is a methodological improvement for preclinical studies.

ALS as a distal axonopathy: molecular mechanisms affecting neuromuscular junction stability in the presymptomatic stages of the disease

Amyotrophic Lateral Sclerosis (ALS) is being redefined as a distal axonopathy, in that many molecular changes influencing motor neuron degeneration occur at the neuromuscular junction (NMJ) at very early stages of the disease prior to symptom onset. A huge variety of genetic and environmental causes have been associated with ALS, and interestingly, although the cause of the disease can differ, both sporadic and familial forms of ALS show a remarkable similarity in terms of disease progression and clinical manifestation. The NMJ is a highly specialized synapse, allowing for controlled signaling between muscle and nerve necessary for skeletal muscle function. In this review we will evaluate the clinical, animal experimental and cellular/molecular evidence that supports the idea of ALS as a distal axonopathy. We will discuss the early molecular mechanisms that occur at the NMJ, which alter the functional abilities of the NMJ. Specifically, we focus on the role of axon guidance molecules on the stability of the cytoskeleton and how these molecules may directly influence the cells of the NMJ in a way that may initiate or facilitate the dismantling of the neuromuscular synapse in the presymptomatic stages of ALS.

Changes in motor unit properties in SOD1 (G93A) rats

INTRODUCTION

In amyotrophic lateral sclerosis (ALS), progressive death of motor neurons results in denervation and reinnervation of muscles. It is not clear how ALS affects the properties of motor units (MUs).

METHODS

Properties of single MUs in the medial gastrocnemius (MG) muscle of rats bearing the human mutated superoxide dismutase gene type 1 (SOD1) were determined at 3 stages: asymptomatic (ALS I); early symptomatic (ALS II); and terminal (ALS III).

RESULTS

In ALS II, higher proportions of FF (fast fatigable) and S (slow) MUs were observed, whereas in ALS III higher percentages of S and lower percentages of FF MUs were noted compared with controls. S motor neurons reinnervated fast muscle fibers, and those MUs gained some properties of fast MUs, including lower fatigue resistance, greater force generation, and higher action potential amplitudes.

CONCLUSION

Changes in MU properties of SOD1 rats have progressive and multidirectional character and speed depending on the MU type.

Lack of synergistic effect of resveratrol and sigma-1 receptor agonist (PRE-084) in SOD1G⁹³A ALS mice: overlapping effects or limited therapeutic opportunity?

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is an adult onset neurodegenerative disease characterized by the loss of motoneurons (MNs) in the spinal cord, brainstem and motor cortex, causing progressive paralysis and death. Nowadays, there is no effective therapy and most patients die 2-5 years after diagnosis. Sigma-1R is a transmembrane protein highly expressed in the CNS and specially enriched in MNs. Mutations on the Sigma-1R leading to frontotemporal lobar degeneration-ALS were recently described in human patients. We previously reported the therapeutic role of the selective sigma-1R agonist 2-(4-morpholi-nethyl)1-phenylcyclohexanecarboxylate (PRE-084) in SOD1G93A ALS mice, that promoted spinal MN preservation and extended animal survival by controlling NMDA receptor calcium influx. Resveratrol (RSV, trans-3,4',5-trihydroxystilbene) is a natural polyphenol with promising neuroprotective effects. We recently found that RSV administration to SOD1G93A mice preserves spinal MN function and increases mice survival. These beneficial effects were associated to activation of Sirtuin 1 (Sirt1) and AMP-activated protein kinase (AMPK) pathways, leading to the modulation of autophagy and an increase of mitochondrial biogenesis. The main goal of this work was to assess the effect of combined RSV and PRE-084 administration in SOD1G93A ALS mice.

METHODS

We determined the locomotor performance of the animals by rotarod test and evaluated spinal motoneuron function using electrophysiological tests.

RESULTS

RSV plus PRE-084 treatment from 8 weeks of age significantly improved locomotor performance and spinal MN function, accompanied by a significant reduction of MN degeneration and an extension of mice lifespan. In agreement with our previous findings, there was an induction of PKC-specific phosphorylation of the NMDA-NR1 subunit and an increased expression and activation of Sirt1 and AMPK in the ventral spinal cord of treated SOD1G93A animals.

CONCLUSIONS

Although combined PRE and RSV treatment significantly ameliorated SOD1G93A mice, it did not show a synergistic effect compared to RSV-only and PRE-084-only treated groups.

Resveratrol improves motoneuron function and extends survival in SOD1(G93A) ALS mice

Amyotrophic lateral sclerosis (ALS) is an adult onset neurodegenerative disease that causes progressive paralysis and death due to degeneration of motoneurons in spinal cord, brainstem and motor cortex. Nowadays, there is no effective therapy and patients die 2-5 years after diagnosis. Resveratrol (trans-3,4',5-trihydroxystilbene) is a natural polyphenol found in grapes, with promising neuroprotective effects since it induces expression and activation of several neuroprotective pathways involving Sirtuin1 and AMPK. The objective of this work was to assess the effect of resveratrol administration on SOD1(G93A) ALS mice. We determined the onset of symptoms by rotarod test and evaluated upper and lower motoneuron function using electrophysiological tests. We assessed the survival of the animals and determined the number of spinal motoneurons. Finally, we further investigated resveratrol mechanism of action by means of western blot and immunohistochemical analysis. Resveratrol treatment from 8 weeks of age significantly delayed disease onset and preserved lower and upper motoneuron function in female and male animals. Moreover, resveratrol significantly extended SOD1(G93A) mice lifespan and promoted survival of spinal motoneurons. Delayed resveratrol administration from 12 weeks of age also improved spinal motoneuron function preservation and survival. Further experiments revealed that resveratrol protective effects were associated with increased expression and activation of Sirtuin 1 and AMPK in the ventral spinal cord. Both mediators promoted normalization of the autophagic flux and, more importantly, increased mitochondrial biogenesis in the SOD1(G93A) spinal cord. Taken together, our findings suggest that resveratrol may represent a promising therapy for ALS.

Differential effects on KCC2 expression and spasticity of ALS and traumatic injuries to motoneurons

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease manifested by progressive muscle atrophy and paralysis due to the loss of upper and lower motoneurons (MN). Spasticity appears in ALS patients leading to further disabling consequences. Loss of the inhibitory tone induced by downregulation of the potassium chloride cotransporter 2 (KCC2) in MN has been proposed to importantly contribute to the spastic behavior after spinal cord injury (SCI). The aim of the present study was to test whether the alterations in the expression of KCC2 are linked to the appearance of spasticity in the SOD^G93A ALS murine model. We compared SOD^G93A mice to wild type mice subjected to SCI to mimic the spinal MN disconnection from motor descending pathways, and to sciatic nerve lesion to mimic the loss of MN connectivity to muscle. Electrophysiological results show that loss of motor function is observed at presymptomatic stage (8 weeks) in SOD^G93A mice but hyperreflexia and spasticity do not appear until a late stage (16 weeks). However, KCC2 was not downregulated despite MN suffered disconnection both from muscles and upper MNs. Further experiments revealed decreased gephyrin expression, as a general marker of inhibitory systems, accompanied by a reduction in the number of Renshaw interneurons. Moreover, 5-HT fibers were increased in the ventral horn of the lumbar spinal cord at late stage of disease progression in SOD1^G93A mice. Taken together, the present results indicate that spasticity appears late in the ALS model, and may be mediated by a decrease in inhibitory interneurons and an increase of 5-HT transmission, while the absence of down-regulation of KCC2 could rather indicate an inability of MNs to respond to insults.