Early signs of motoneuron vulnerability in a disease model system: Characterization of transverse slice cultures of spinal cord isolated from embryonic ALS mice

Human post-mortem organotypic brain slice cultures: a tool to study pathomechanisms and test therapies

Human brain experimental models recapitulating age- and disease-related characteristics are lacking. There is urgent need for human-specific tools that model the complex molecular and cellular interplay between different cell types to assess underlying disease mechanisms and test therapies. Here we present an adapted ex vivo organotypic slice culture method using human post-mortem brain tissue cultured at an air-liquid interface to also study brain white matter. We assessed whether these human post-mortem brain slices recapitulate the in vivo neuropathology and if they are suitable for pathophysiological, experimental and pre-clinical treatment development purposes, specifically regarding leukodystrophies. Human post-mortem brain tissue and cerebrospinal fluid were obtained from control, psychiatric and leukodystrophy donors. Slices were cultured up to six weeks, in culture medium with or without human cerebrospinal fluid. Human post-mortem organotypic brain slice cultures remained viable for at least six weeks ex vivo and maintained tissue structure and diversity of (neural) cell types. Supplementation with cerebrospinal fluid could improve slice recovery. Patient-derived organotypic slice cultures recapitulated and maintained known in vivo neuropathology. The cultures also showed physiologic multicellular responses to lysolecithin-induced demyelination ex vivo, indicating their suitability to study intrinsic repair mechanisms upon injury. The slice cultures were applicable for various experimental studies, as multi-electrode neuronal recordings. Finally, the cultures showed successful cell-type dependent transduction with gene therapy vectors. These human post-mortem organotypic brain slice cultures represent an adapted ex vivo model suitable for multifaceted studies of brain disease mechanisms, boosting translation from human ex vivo to in vivo. This model also allows for assessing potential treatment options, including gene therapy applications. Human post-mortem brain slice cultures are thus a valuable tool in preclinical research to study the pathomechanisms of a wide variety of brain diseases in living human tissue.

Excitatory action of low frequency depolarizing GABA/glycine synaptic inputs is prevalent in prenatal spinal SOD1G93A motoneurons

Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset neurodegenerative disease characterized by progressive motor neuron degeneration and muscle paralysis. Recent evidence suggests the dysfunction of inhibitory signalling in ALS motor neurons. We have shown that embryonic day (E)17.5 spinal motoneurons (MNs) of the SOD1G93A mouse model of ALS exhibit an altered chloride homeostasis. At this prenatal stage, inhibition of spinal motoneurons (MNs) is mediated by depolarizing GABAergic/glycinergic postsynaptic potentials (dGPSPs). Here, using an ex vivo preparation and patch clamp recording from MNs with a chloride equilibrium set below spike threshold, we report that low input resistance (Rin ) E17.5 MNs from the SOD1G93A ALS mouse model do not correctly integrate dGPSPs evoked by electrical stimulations of GABA/glycine inputs at different frequencies. Indeed, firing activity of most wild-type (WT) MNs with low Rin was inhibited by incoming dGPSPs, whereas low Rin SOD1G93A MNs were excited or exhibited a dual response (excited by low frequency dGPSPs and inhibited by high frequency dGPSPs). Simulation highlighted the importance of the GABA/glycine input density and showed that pure excitation could be obtained in SOD-like MNs by moving GABA/glycine input away from the cell body to dendrites. This was in agreement with confocal imaging showing a lack of peri-somatic inhibitory terminals in SOD1G93A MNs compared to WT littermates. Putative fast ALS-vulnerable MNs with low Rin are therefore lacking functional inhibition at the near-term prenatal stage. KEY POINTS: We analysed the integration of GABAergic/glycinergic synaptic events by embryonic spinal motoneurons (MNs) in a mouse model of the amyotrophic lateral sclerosis (ALS) neurodegenerative disease. We found that GABAergic/glycinergic synaptic events do not properly inhibit ALS MNs with low input resistance, most probably corresponding to future vulnerable MNs. We used a neuron model to highlight the importance of the GABA/glycine terminal location and density in the integration of the GABAergic/glycinergic synaptic events. Confocal imaging showed a lack of GABA/glycine terminals on the cell body of ALS MNs. The present study suggests that putative ALS vulnerable MNs with low Rin lack functional inhibition at the near-term stage.

Artificial intelligence for neurodegenerative experimental models

INTRODUCTION

Experimental models are essential tools in neurodegenerative disease research. However, the translation of insights and drugs discovered in model systems has proven immensely challenging, marred by high failure rates in human clinical trials.

METHODS

Here we review the application of artificial intelligence (AI) and machine learning (ML) in experimental medicine for dementia research.

RESULTS

Considering the specific challenges of reproducibility and translation between other species or model systems and human biology in preclinical dementia research, we highlight best practices and resources that can be leveraged to quantify and evaluate translatability. We then evaluate how AI and ML approaches could be applied to enhance both cross-model reproducibility and translation to human biology, while sustaining biological interpretability.

DISCUSSION

AI and ML approaches in experimental medicine remain in their infancy. However, they have great potential to strengthen preclinical research and translation if based upon adequate, robust, and reproducible experimental data.

HIGHLIGHTS

There are increasing applications of AI in experimental medicine. We identified issues in reproducibility, cross-species translation, and data curation in the field. Our review highlights data resources and AI approaches as solutions. Multi-omics analysis with AI offers exciting future possibilities in drug discovery.

Synaptic expression of TAR-DNA-binding protein 43 in the mouse spinal cord determined using super-resolution microscopy

Amyotrophic Lateral Sclerosis (ALS) is characterised by a loss of motor neurons in the brain and spinal cord that is preceded by early-stage changes in synapses that may be associated with TAR-DNA-Binding Protein 43 (TDP-43) pathology. Cellular inclusions of hyperphosphorylated TDP-43 (pTDP-43) are a key hallmark of neurodegenerative diseases such ALS. However, there has been little characterisation of the synaptic expression of TDP-43 inside subpopulations of spinal cord synapses. This study utilises a range of high-resolution and super-resolution microscopy techniques with immunolabelling, as well as an aptamer-based TDP-43 labelling strategy visualised with single-molecule localisation microscopy, to characterise and quantify the presence of pTDP-43 in populations of excitatory synapses near where motor neurons reside in the lateral ventral horn of the mouse lumbar spinal cord. We observe that TDP-43 is expressed in approximately half of spinal cord synapses as nanoscale clusters. Synaptic TDP-43 clusters are found most abundantly at synapses associated with VGLUT1-positive presynaptic terminals, compared to VGLUT2-associated synapses. Our nanoscopy techniques showed no difference in the subsynaptic expression of pTDP-43 in the ALS mouse model, SOD1G93a, compared to healthy controls, despite prominent structural deficits in VGLUT1-associated synapses in SOD1G93a mice. This research characterises the basic synaptic expression of TDP-43 with nanoscale precision and provides a framework with which to investigate the potential relationship between TDP-43 pathology and synaptic pathology in neurodegenerative diseases.

An impaired splicing program underlies differentiation defects in hSOD1G93A neural progenitor cells

Amyotrophic lateral sclerosis (ALS) is an adult devastating neurodegenerative disease characterized by the loss of upper and lower motor neurons (MNs), resulting in progressive paralysis and death. Genetic animal models of ALS have highlighted dysregulation of synaptic structure and function as a pathogenic feature of ALS-onset and progression. Alternative pre-mRNA splicing (AS), which allows expansion of the coding power of genomes by generating multiple transcript isoforms from each gene, is widely associated with synapse formation and functional specification. Deciphering the link between aberrant splicing regulation and pathogenic features of ALS could pave the ground for novel therapeutic opportunities. Herein, we found that neural progenitor cells (NPCs) derived from the hSOD1G93A mouse model of ALS displayed increased proliferation and propensity to differentiate into neurons. In parallel, hSOD1G93A NPCs showed impaired splicing patterns in synaptic genes, which could contribute to the observed phenotype. Remarkably, master splicing regulators of the switch from stemness to neural differentiation are de-regulated in hSOD1G93A NPCs, thus impacting the differentiation program. Our data indicate that hSOD1G93A mutation impacts on neurogenesis by increasing the NPC pool in the developing mouse cortex and affecting their intrinsic properties, through the establishment of a specific splicing program.

Early deficits in GABA inhibition parallels an increase in L-type Ca2+ currents in the jaw motor neurons of SOD1G93A mouse model for ALS

Amyotrophic Lateral Sclerosis (ALS) involves protracted pre-symptomatic periods of abnormal motor neuron (MN) excitability occurring in parallel with central and peripheral synaptic perturbations. Focusing on inhibitory control of MNs, we first compared longitudinal changes in pre-synaptic terminal proteins for GABA and glycine neurotransmitters around the soma of retrogradely identified trigeminal jaw closer (JC) MNs and ChAT-labeled midbrain extraocular (EO) MNs in the SOD1^G93A mouse model for ALS. Fluorescence immunocytochemistry and confocal imaging were used to quantify GAD67 and GlyT2 synaptic bouton density (SBD) around MN soma at pre-symptomatic ages ∼P12 (postnatal), ∼P50 (adult) and near disease end-stage (∼P135) in SOD1^G93A mice and age-matched wild-type (WT) controls. We noted reduced GAD67 innervation in the SOD1^G93A trigeminal jaw closer MNs around P12, relative to age-matched WT and no significant difference around P50 and P135. In contrast, both GAD67 and GlyT2 innervation were elevated in the SOD1^G93A EO MNs at the pre-symptomatic time points. Considering trigeminal MNs are vulnerable in ALS while EO MNs are spared, we suggest that upregulation of inhibition in the latter might be compensatory. Notable contrast also existed in the innate co-expression patterns of GAD67 and GlyT2 with higher mutual information (co-dependency) in EO MNs compared to JC in both SOD1^G93A and WT mice, especially at adult stages (P50 and P135). Around P12 when GAD67 terminals expression was low in the mutant, we further tested for persistent GABA inhibition in those MNs using in vitro patch-clamp electrophysiology. Our results show that SOD1^G93A JC MNs have reduced persistent GABA inhibition, relative to WT. Pharmacological blocking of an underlying tonically active GABA conductance using the GABA-α5 subunit inverse agonist, L-655-708, disinhibited WT JC MNs and lowered their recruitment threshold, suggesting its role in the control of intrinsic MN excitability. Quantitative RT-PCR in laser dissected JC MNs further supported a reduction in GABA-α5 subunit mRNA expression in the mutant. In light of our previous report that JC MNs forming putative fast motor units have lower input threshold in the SOD1^G93A mice, we suggest that our present result on reduced GABA-α5 tonic inhibition provides for a mechanism contributing to such imbalance. In parallel with reduced GABA inhibition, we noted an increase in voltage-gated L-type Ca²⁺ currents in the mutant JC MNs around P12. Together these results support that, early modifications in intrinsic properties of vulnerable MNs could be an adaptive response to counter synaptic deficits.

Inhibitory interneurons show early dysfunction in a SOD1 mouse model of amyotrophic lateral sclerosis

Few studies in amyotrophic lateral sclerosis (ALS) measure effects of the disease on inhibitory interneurons synapsing onto motoneurons (MNs). However, inhibitory interneurons could contribute to dysfunction, particularly if altered before MN neuropathology, and establish a long-term imbalance of inhibition/excitation. We directly assessed excitability and morphology of glycinergic (GlyT2 expressing) ventral lumbar interneurons from SOD1G93AGlyT2eGFP (SOD1) and wild-type GlyT2eGFP (WT) mice on postnatal days 6-10. Patch clamp revealed dampened excitability in SOD1 interneurons, including depolarized persistent inward currents (PICs), increased voltage and current threshold for firing action potentials, along with a marginal decrease in afterhyperpolarization duration. Primary neurites of ventral SOD1 inhibitory interneurons were larger in volume and surface area than WT. GlyT2 interneurons were then divided into three subgroups based on location: (1) interneurons within 100 μm of the ventral white matter, where Renshaw cells (RCs) are located, (2) interneurons interspersed with MNs in lamina IX, and (3) interneurons in the intermediate ventral area including laminae VII and VIII. Ventral interneurons in the RC area were the most profoundly affected, exhibiting more depolarized PICs and larger primary neurites. Interneurons in lamina IX had depolarized PIC onset. In lamina VII-VIII, interneurons were least affected. In summary, inhibitory interneurons show very early region-specific perturbations poised to impact excitatory/inhibitory balance of MNs, modify motor output and provide early biomarkers of ALS. Therapeutics like riluzole that universally reduce CNS excitability could exacerbate the inhibitory dysfunction described here. KEY POINTS: Spinal inhibitory interneurons could contribute to amyotrophic lateral sclerosis (ALS) pathology, but their excitability has never been directly measured. We studied the excitability and morphology of glycinergic interneurons in early postnatal transgenic mice (SOD1G93A GlyT2eGFP). Interneurons were less excitable and had marginally smaller somas but larger primary neurites in SOD1 mice. GlyT2 interneurons were analysed according to their localization within the ventral spinal cord. Interestingly, the greatest differences were observed in the most ventrally located interneurons. We conclude that inhibitory interneurons show presymptomatic changes that may contribute to excitatory/inhibitory imbalance in ALS.

A KO mouse model for the lncRNA Lhx1os produces motor neuron alterations and locomotor impairment

Here, we describe a conserved motor neuron-specific long non-coding RNA, Lhx1os, whose knockout in mice produces motor impairment and postnatal reduction of mature motor neurons (MNs). The ER stress-response pathway result specifically altered with the downregulation of factors involved in the unfolded protein response (UPR). Lhx1os was found to bind the ER-associated PDIA3 disulfide isomerase and to affect the expression of the same set of genes controlled by this protein, indicating that the two factors act in conjunction to modulate the UPR. Altogether, the observed phenotype and function of Lhx1os indicate its important role in the control of MN homeostasis and function.

Distributed interfacing by nanoscale photodiodes enables single-neuron light activation and sensory enhancement in 3D spinal explants

Among emerging technologies developed to interface neuronal signaling, engineering electrodes at the nanoscale would yield more precise biodevices opening to progress in neural circuit investigations and to new therapeutic potential. Despite remarkable progress in miniature electronics for less invasive neurostimulation, most nano-enabled, optically triggered interfaces are demonstrated in cultured cells, which precludes the studies of natural neural circuits. We exploit here free-standing silicon-based nanoscale photodiodes to optically modulate single, identified neurons in mammalian spinal cord explants. With near-infrared light stimulation, we show that activating single excitatory or inhibitory neurons differently affects sensory circuits processing in the dorsal horn. We successfully functionalize nano-photodiodes to target single molecules, such as glutamate AMPA receptor subunits, thus enabling light activation of specific synaptic pathways. We conclude that nano-enabled neural interfaces can modulate selected sensory networks with low invasiveness. The use of nanoscale photodiodes can thus provide original perspective in linking neural activity to specific behavioral outcome.

Mid1 is associated with androgen-dependent axonal vulnerability of motor neurons in spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is an adult-onset hereditary neurodegenerative disease caused by the expansions of CAG repeats in the androgen receptor (AR) gene. Androgen-dependent nuclear accumulation of pathogenic AR protein causes degeneration of lower motor neurons, leading to progressive muscle weakness and atrophy. While the successful induction of SBMA-like pathology has been achieved in mouse models, mechanisms underlying motor neuron vulnerability remain unclear. In the present study, we performed a transcriptome-based screening for genes expressed exclusively in motor neurons and dysregulated in the spinal cord of SBMA mice. We found upregulation of Mid1 encoding a microtubule-associated RNA binding protein which facilitates the translation of CAG-expanded mRNAs. Based on the finding that lower motor neurons begin expressing Mid1 during embryonic stages, we developed an organotypic slice culture system of the spinal cord obtained from SBMA mouse fetuses to study the pathogenic role of Mid1 in SBMA motor neurons. Impairment of axonal regeneration arose in the spinal cord culture in SBMA mice in an androgen-dependent manner, but not in mice with non-CAG-expanded AR, and was either exacerbated or ameliorated by Mid1 overexpression or knockdown, respectively. Hence, an early Mid1 expression confers vulnerability to motor neurons, at least by inducing axonogenesis defects, in SBMA.

Histopathological changes of the spinal cord and motor neuron dynamics in SOD1 Tg mice

We analyzed the histopathological changes and the number of motor neurons (MNs) in the lumbar spinal cord of Cu/Zn superoxide dismutase transgenic (SOD1^G93ATg) mice, which are frequently used as a disease model of amyotrophic lateral sclerosis (ALS). In SOD1^G93ATg mice, hyaline inclusions and foamy vacuoles in the neuronal cell body were observed at 7 weeks of age before neurologic symptoms, and large vacuoles, spheroid formation, and nerve cell aggregation became prominent after 13 weeks of age. The number of healthy MNs was 28.7 to 37.1 cells/animal in wild-type mice and 9.3 to 13.6 cells/animal in transgenic (Tg) mice. Furthermore, the number of MNs, including degenerative neurons, in Tg mice was 27.3–36.1 cells/animal at 18 weeks of age and 17.8–19.6 cells/animal at 21 weeks of age. The present results provide useful information for the development of drugs in ALS treatment.

Thermosensitive chitosan-based hydrogels supporting motor neuron-like NSC-34 cell differentiation

Motor neuron diseases are neurodegenerative diseases that predominantly affect the neuromuscular system. To date, there are no valid therapeutic treatments for such diseases, and the classical experimental models fail in faithfully reproducing the pathological mechanisms behind them. In this regard, the use of three-dimensional (3D) culture systems, which more closely reproduce the native in vivo environment, can be a promising approach. Hydrogel-based systems are among the most used materials to reproduce the extracellular matrix, featuring an intrinsic similarity with its physiological characteristics. In this study, we developed a thermosensitive chitosan-based hydrogel combined with β-glycerophosphate (βGP) and sodium hydrogen carbonate (SHC), which give the system optimal mechanical properties and injectability, inducing the hydrogel sol-gel transition at 37 °C. An ad hoc protocol for the preparation of the hydrogel was established in order to obtain a highly homogeneous system, leading to reproducible physicochemical characteristics and easy cell encapsulation. All formulations supported the viability of a neuroblastoma/spinal cord hybrid cell line (NSC-34) beyond two weeks of culture and enabled cell differentiation towards a motor neuron-like morphology, characterized by the presence of extended neurites. Based on our results, these hydrogels represent excellent candidates for establishing 3D in vitro models of motor neuron diseases.

Estimating the effects of slicing on the electrophysiological properties of spinal motoneurons under normal and disease conditions

Although slice recordings from spinal motoneurons (MNs) are being widely used, the effects of slicing on the measured MN electrical properties under normal and disease conditions have not been assessed. Using high-fidelity cell models of neonatal wild-type (WT) and superoxide dismutase-1 (SOD) cells, we examined the effects of slice thickness, soma position within the slice, and slice orientation to estimate the error induced in measured MN electrical properties from spinal slices. Our results show that most MN electrical properties are not adversely affected by slicing, except for cell time constant, cell capacitance, and Ca²⁺ persistent inward current (PIC), which all exhibited large errors, regardless of the slice condition. Among the examined factors, soma position within the slice appears to be the strongest factor in influencing the magnitude of error in measured MN electrical properties. Transverse slices appear to have the least impact on measured MN electrical properties. Surprisingly, and despite their anatomical enlargement, we found that G85R-SOD MNs experience similar error in their measured electrical properties to those of WT MNs, but their errors are more sensitive to the soma position within the slice than WT MNs. Unless in thick and symmetrical slices, slicing appears to reduce motoneuron type differences. Accordingly, slice studies should attempt to record from MNs at the slice center to avoid large and inconsistent errors in measured cell properties and have valid cell measurements' comparisons. Our results, therefore, offer information that would enhance the rigor of MN electrophysiological data measured from the slice preparation under normal and disease conditions.NEW & NOTEWORTHY Although slice recordings from motoneurons are being widely used, the effects of slicing on the measured motoneuron electrical properties under normal and disease conditions have not been assessed. Using high-fidelity cell models of neonatal WT and SOD cells, we examined the effects of slice thickness, soma position within the slice, and slice orientation. Our results offer information that enhances the rigor of MN electrophysiological data measured from the slice preparation under normal and disease conditions.

Relaxation of synaptic inhibitory events as a compensatory mechanism in fetal SOD spinal motor networks

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease affecting motor neurons (MNs) during late adulthood. Here, with the aim of identifying early changes underpinning ALS neurodegeneration, we analyzed the GABAergic/glycinergic inputs to E17.5 fetal MNs from SOD1G93A (SOD) mice in parallel with chloride homeostasis. Our results show that IPSCs are less frequent in SOD animals in accordance with a reduction of synaptic VIAAT-positive terminals. SOD MNs exhibited an EGABAAR10 mV more depolarized than in WT MNs associated with a KCC2 reduction. Interestingly, SOD GABAergic/glycinergic IPSCs and evoked GABAAR-currents exhibited a slower decay correlated to elevated [Cl-]i. Computer simulations revealed that a slower relaxation of synaptic inhibitory events acts as compensatory mechanism to strengthen GABA/glycine inhibition when EGABAAR is more depolarized. How such mechanisms evolve during pathophysiological processes remain to be determined, but our data indicate that at least SOD1 familial ALS may be considered as a neurodevelopmental disease.

Organotypic brain slice cultures to model neurodegenerative proteinopathies

Organotypic slice cultures of brain or spinal cord have been a longstanding tool in neuroscience research but their utility for understanding Alzheimer's disease (AD) and other neurodegenerative proteinopathies has only recently begun to be evaluated. Organotypic brain slice cultures (BSCs) represent a physiologically relevant three-dimensional model of the brain. BSCs support all the central nervous system (CNS) cell types and can be produced from brain areas involved in neurodegenerative disease. BSCs can be used to better understand the induction and significance of proteinopathies underlying the development and progression of AD and other neurodegenerative disorders, and in the future may serve as bridging technologies between cell culture and in vivo experiments for the development and evaluation of novel therapeutic targets and strategies. We review the initial development and general use of BSCs in neuroscience research and highlight the advantages of these cultures as an ex vivo model. Subsequently we focus on i) BSC-based modeling of AD and other neurodegenerative proteinopathies ii) use of BSCs to understand mechanisms underlying these diseases and iii) how BSCs can serve as tools to screen for suitable therapeutics prior to in vivo investigations. Finally, we will examine i) open questions regarding the use of such cultures and ii) how emerging technologies such as recombinant adeno-associated viruses (rAAV) may be combined with these models to advance translational research relevant to neurodegenerative disorders.

Developmental Expression of Mutant PFN1 in Motor Neurons Impacts Neuronal Growth and Motor Performance of Young and Adult Mice

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease with limited treatment and no cure. Mutations in profilin 1 were identified as a cause of familial ALS (fALS) in 2012. We investigated the functional impact of mutant profilin 1 expression in spinal cords during mouse development. We developed a novel mouse model with the expression of profilin 1 C71G under the control of the Hb9 promoter, targeting expression to α-motor neurons in the spinal cord during development. Embryos of transgenic mice showed evidence of a significant reduction of brachial nerve diameter and a loss of Mendelian inheritance. Despite the lack of transgene expression, adult mice presented with significant motor deficits. Transgenic mice had a significant reduction in the number of motor neurons in the spinal cord. Further analysis of these motor neurons in aged transgenic mice revealed reduced levels of TDP-43 and ChAT expression. Although profilin 1 C71G was only expressed during development, adult mice presented with some ALS-associated pathology and motor symptoms. This study highlights the effect of profilin 1 during neurodevelopment and the impact that this may have in later ALS.

3D Organotypic Spinal Cultures: Exploring Neuron and Neuroglia Responses Upon Prolonged Exposure to Graphene Oxide

Graphene-based nanomaterials are increasingly engineered as components of biosensors, interfaces or drug delivery platforms in neuro-repair strategies. In these developments, the mostly used derivative of graphene is graphene oxide (GO). To tailor the safe development of GO nanosheets, we need to model in vitro tissue responses, and in particular the reactivity of microglia, a sub-population of neuroglia that acts as the first active immune response, when challenged by GO. Here, we investigated central nervous system (CNS) tissue reactivity upon long-term exposure to GO nanosheets in 3D culture models. We used the mouse organotypic spinal cord cultures, ideally suited for studying long-term interference with cues delivered at controlled times and concentrations. In cultured spinal segments, the normal presence, distribution and maturation of anatomically distinct classes of neurons and resident neuroglial cells are preserved. Organotypic explants were developed for 2 weeks embedded in fibrin glue alone or presenting GO nanosheets at 10, 25 and 50 μg/mL. We addressed the impact of such treatments on premotor synaptic activity monitored by patch clamp recordings of ventral interneurons. We investigated by immunofluorescence and confocal microscopy the accompanying glial responses to GO exposure, focusing on resident microglia, tested in organotypic spinal slices and in isolated neuroglia cultures. Our results suggest that microglia reactivity to accumulation of GO flakes, maybe due to active phagocytosis, may trim down synaptic activity, although in the absence of an effective activation of inflammatory response and in the absence of neuronal cell death.

Effects of Class II-Selective Histone Deacetylase Inhibitor on Neuromuscular Function and Disease Progression in SOD1-ALS Mice

Emerging evidence indicates that transcriptome alterations due to epigenetic deregulation concur to ALS pathogenesis. Accordingly, pan-histone deacetylase (HDAC) inhibitors delay ALS development in mice, but these compounds failed when tested in ALS patients. Possibly, lack of selectivity toward specific classes of HDACs weakens the therapeutic effects of pan-HDAC inhibitors. Here, we tested the effects of the HDAC Class II selective inhibitor MC1568 on disease evolution, motor neuron survival as well as skeletal muscle function in SOD1G93A mice. We report that HDACs did not undergo expression changes during disease evolution in isolated motor neurons of adult mice. Conversely, increase in specific Class II HDACs (-4, -5 and -6) occurs in skeletal muscle of mice with severe neuromuscular impairment. Importantly, treatment with MC1568 causes early improvement of motor performances that vanishes at later stages of disease. Notably, motor improvement is not paralleled by reduced motor neuron degeneration but by increased skeletal muscle electrical potentials, reduced activation of mir206/FGFBP1-dependent muscle reinnervation signaling, and increased muscle expression of myogenic genes.

Effect of Class II HDAC inhibition on glutamate transporter expression and survival in SOD1-ALS mice

Transcriptional deregulation emerges as a key pathogenetic mechanism in ALS pathogenesis, and non-class-specific histone deacetylase (HDACs) inhibitors proved of therapeutic efficacy in preclinical models of ALS. When tested in patients, however, these drugs failed, probably because of a lack of selectivity toward pathogenetic HDACs. Here, we studied the effects of MC1568, an inhibitor of Class-II HDACs which have been reported to contribute to ALS pathogenesis. We focused on transcriptional regulation of glutamate transporter EAAT2, whose reduced expression may contribute to motor neuron degeneration in ALS. We report that MC1568 highly increased EAAT2 transcripts in primary cultures of mouse glia, but these increases did not correlate with increased glutamate uptake capacity. Accordingly, we found that MC1568 augmented protein expression of EAAT2 together with its sumoylation, a post-translational modification typically altering protein function and localization. When tested in SOD1G93A mice, however, MC1568 fully restored the reduced spinal cord expression of EAAT2 and glutamate uptake up to control levels. A prolonged treatment with MC1568 (from onset to end stage) was unable to prolong survival of mice. Data reveal a key role of Class-II HDACs in expression and function of glutamate transporter, further corroborating preclinical and clinical evidence that the sole restoration of glutamate uptake is not of therapeutic relevance to ALS therapy.

Altered development in GABA co-release shapes glycinergic synaptic currents in cultured spinal slices of the SOD1(G93A) mouse model of amyotrophic lateral sclerosis

KEY POINTS

Increased environmental risk factors in conjunction with genetic susceptibility have been proposed with respect to the remarkable variations in mortality in amyotrophic lateral sclerosis (ALS). In vitro models allow the investigation of the genetically modified counter-regulator of motoneuron toxicity and may help in addressing ALS therapy. Spinal organotypic slice cultures from a mutant form of human superoxide dismutase 1 (SOD1G93A) mouse model of ALS allow the detection of altered glycinergic inhibition in spinal microcircuits. This altered inhibition improved spinal cord excitability, affecting motor outputs in early SOD1(G93A) pathogenesis.

ABSTRACT

Amyotrophic lateral sclerosis (ALS) is a fatal, adult-onset neurological disease characterized by a progressive degeneration of motoneurons (MNs). In a previous study, we developed organotypic spinal cultures from an ALS mouse model expressing a mutant form of human superoxide dismutase 1 (SOD1(G93A) ). We reported the presence of a significant synaptic rearrangement expressed by these embryonic cultured networks, which may lead to the altered development of spinal synaptic signalling, which is potentially linked to the adult disease phenotype. Recent studies on the same ALS mouse model reported a selective loss of glycinergic innervation in cultured MNs, suggestive of a contribution of synaptic inhibition to MN dysfunction and degeneration. In the present study, we further exploit organotypic cultures from wild-type and SOD1(G93A) mice to investigate the development of glycine-receptor-mediated synaptic currents recorded from the interneurons of the premotor ventral circuits. We performed single cell electrophysiology, immunocytochemistry and confocal microscopy and suggest that GABA co-release may speed the decay of glycine responses altering both temporal precision and signal integration in SOD1(G93A) developing networks at the postsynaptic site. Our hypothesis is supported by the finding of an increased MN bursting activity in immature SOD1(G93A) spinal cords and by immunofluorescence microscopy detection of a longer persistence of GABA in SOD1(G93A) glycinergic terminals in cultured and ex vivo spinal slices.

ALS Patient Stem Cells for Unveiling Disease Signatures of Motoneuron Susceptibility: Perspectives on the Deadly Mitochondria, ER Stress and Calcium Triad

Amyotrophic lateral sclerosis (ALS) is a largely sporadic progressive neurodegenerative disease affecting upper and lower motoneurons (MNs) whose specific etiology is incompletely understood. Mutations in superoxide dismutase-1 (SOD1), TAR DNA-binding protein 43 (TARDBP/TDP-43) and C9orf72, have been identified in subsets of familial and sporadic patients. Key associated molecular and neuropathological features include ubiquitinated TDP-43 inclusions, stress granules, aggregated dipeptide proteins from mutant C9orf72 transcripts, altered mitochondrial ultrastructure, dysregulated calcium homeostasis, oxidative and endoplasmic reticulum (ER) stress, and an unfolded protein response (UPR). Such impairments have been documented in ALS animal models; however, whether these mechanisms are initiating factors or later consequential events leading to MN vulnerability in ALS patients is debatable. Human induced pluripotent stem cells (iPSCs) are a valuable tool that could resolve this “chicken or egg” causality dilemma. Relevant systems for probing pathophysiologically affected cells from large numbers of ALS patients and discovering phenotypic disease signatures of early MN susceptibility are described. Performing unbiased ‘OMICS and high-throughput screening in relevant neural cells from a cohort of ALS patient iPSCs, and rescuing mitochondrial and ER stress impairments, can identify targeted therapeutics for increasing MN longevity in ALS.

Organotypic Spinal Cord Culture: a Proper Platform for the Functional Screening

Recent improvements in organotypic slice culturing and its accompanying technological innovations have made this biological preparation increasingly useful ex vivo experimental model. Among organotypic slice cultures obtained from various central nervous regions, spinal cord slice culture is an absorbing model that represents several unique advantages over other current in vitro and in vivo models. The culture of developing spinal cord slices, as allows real-time observation of embryonic cells behaviors, is an instrumental platform for developmental investigation. Importantly, due to the ability of ex vivo models to recapitulate different aspects of corresponding in vivo conditions, these models have been subject of various manipulations to derive disease-relevant slice models. Moreover spinal cord slice cultures represent a potential platform for screening of different pharmacological agents and evaluation of cell transplantation and neuroregenerative materials. In this review, we will focus on studies carried out using the ex vivo model of spinal cord slice cultures and main advantages linked to practicality of these slices in both normal and neuropathological diseases and summarize them in different categories based on application.

Effect of the human SOD1-G93A gene on the Nrf2/ARE signaling pathway in NSC-34 cells

Dominant mutations in superoxide dismutase 1 (SOD1) are a frequent cause of the lethal neurodegenerative disease amyotrophic lateral sclerosis (ALS). The nuclear factor erythroid 2‑related factor 2 (Nrf2)/antioxidant response element (ARE) signaling pathway is the major cellular defense mechanism against oxidative stress, however, its role in ALS remains to be fully elucidated. Therefore, the present study aimed to investigate whether the human SOD1-G93A gene affected the Nrf2/ARE signaling pathway in an ALS cell model. The soma became round and the number of neurites decreased in the NSC-34 cells transfected with the hSOD1-G93A gene, and the neurites were shorter and oxidative stress was increased compared with the normal NSC-34 cells. Furthermore, the mRNA and protein expression of Nrf2, heme oxygenase-1 and

NAD(P)H

quinone oxidoreductase 1 was significantly decreased in the NSC-34 cells transfected with the human SOD1-G93A gene. The present study indicated that human SOD1-G93A damaged the Nrf2/ARE signaling pathway in the ALS cell model and reduced the ability of cells to protect against oxidative injury.

PTEN regulates AMPA receptor-mediated cell viability in iPS-derived motor neurons

Excitatory transmission in the brain is commonly mediated by the α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors. In amyotrophic lateral sclerosis (ALS), AMPA receptors allow cytotoxic levels of calcium into neurons, contributing to motor neuron injury. We have previously shown that oculomotor neurons resistant to the disease process in ALS show reduced AMPA-mediated inward calcium currents compared with vulnerable spinal motor neurons. We have also shown that PTEN (phosphatase and tensin homolog deleted on chromosome 10) knockdown via siRNA promotes motor neuron survival in models of spinal muscular atrophy (SMA) and ALS. It has been reported that inhibition of PTEN attenuates the death of hippocampal neurons post injury by decreasing the effective translocation of the GluR2 subunit into the membrane. In addition, leptin can regulate AMPA receptor trafficking via PTEN inhibition. Thus, we speculate that manipulation of AMPA receptors by PTEN may represent a potential therapeutic strategy for neuroprotective intervention in ALS and other neurodegenerative disorders. To this end, the first step is to establish a fibroblast-iPS-motor neuron in vitro cell model to study AMPA receptor manipulation. Here we report that iPS-derived motor neurons from human fibroblasts express AMPA receptors. PTEN depletion decreases AMPA receptor expression and AMPA-mediated whole-cell currents, resulting in inhibition of AMPA-induced neuronal death in primary cultured and iPS-derived motor neurons. Taken together, our results imply that PTEN depletion may protect motor neurons by inhibition of excitatory transmission that represents a therapeutic strategy of potential benefit for the amelioration of excitotoxicity in ALS and other neurodegenerative disorders.

Long-term measurement of muscle denervation and locomotor behavior in individual wild-type and ALS model mice

The increasing number of mouse models of human degenerative and injury-related diseases that affect motor behavior raises the importance of in vivo methodologies allowing measurement of physiological and behavioral changes over an extended period of time in individual animals. A method that provides long-term measurements of muscle denervation and its behavioral consequences in individual mice for several months is presented in this article. The method is applied to mSod1G93A mice, which model human amyotrophic lateral sclerosis (ALS). The denervation process of gastrocnemius and soleus muscles in mSod1G93A mice is demonstrated for up to 3 mo. The data suggest that as muscle denervation progresses, massive behavioral compensation occurs within the spinal cord that allows animals to walk almost normally until late ages. Only around the age of 84 days is the first sign of abnormal movement during walking behavior detected as an abnormal tibialis anterior activity profile that is manifested in subtle but abnormal swing movement during walking. Additionally, this method can be used with other mouse models of human diseases, such as spinal cord injury, intracerebral hemorrhage, Parkinson's diseases, and spinal muscular atrophy.

Microelectrode arrays in combination with in vitro models of spinal cord injury as tools to investigate pathological changes in network activity: facts and promises

Microelectrode arrays (MEAs) represent an important tool to study the basic characteristics of spinal networks that control locomotion in physiological conditions. Fundamental properties of this neuronal rhythmicity like burst origin, propagation, coordination, and resilience can, thus, be investigated at multiple sites within a certain spinal topography and neighboring circuits. A novel challenge will be to apply this technology to unveil the mechanisms underlying pathological processes evoked by spinal cord injury (SCI). To achieve this goal, it is necessary to fully identify spinal networks that make up the locomotor central pattern generator (CPG) and to understand their operational rules. In this review, the use of isolated spinal cord preparations from rodents, or organotypic spinal slice cultures is discussed to study rhythmic activity. In particular, this review surveys our recently developed in vitro models of SCI by evoking excitotoxic (or even hypoxic/dysmetabolic) damage to spinal networks and assessing the impact on rhythmic activity and cell survival. These pathological processes which evolve via different cell death mechanisms are discussed as a paradigm to apply MEA recording for detailed mapping of the functional damage and its time-dependent evolution.

Postnatal developmental profile of neurons and glia in motor nuclei of the brainstem and spinal cord, and its comparison with organotypic slice cultures

In vitro preparations of the neonatal rat spinal cord or brainstem are useful to investigate the organization of motor networks and their dysfunction in neurological disease models. Long-term spinal cord organotypic cultures can extend our understanding of such pathophysiological processes over longer times. It is, however, surprising that detailed descriptions of the type (and number) of neurons and glia in such preparations are currently unavailable to evaluate cell-selectivity of experimental damage. The focus of the present immunohistochemical study is the novel characterization of the cell population in the lumbar locomotor region of the rat spinal cord and in the brainstem motor nucleus hypoglossus at 0-4 postnatal days, and its comparison with spinal organotypic cultures at 2-22 days in vitro. In the nucleus hypoglossus, neurons were 40% of all cells and 80% of these were motoneurons. Astrocytes (35% of total cells) were the main glial cells, while microglia was <10%. In the spinal gray matter, the highest neuronal density was in the dorsal horn (>80%) and the lowest in the ventral horn (≤57%) with inverse astroglia numbers and few microglia. The number of neurons (including motoneurons) and astrocytes was stable after birth. Like in the spinal cord, motoneurons in organotypic spinal culture were <10% of ventral horn cells, with neurons <40%, and the rest made up by glia. The present report indicates a comparable degree of neuronal and glial maturation in brainstem and spinal motor nuclei, and that this condition is also observed in 3-week-old organotypic cultures.

Long-term actions of BDNF on inhibitory synaptic transmission in identified neurons of the rat substantia gelatinosa

Peripheral nerve injury promotes the release of brain-derived neurotrophic factor (BDNF) from spinal microglial cells and primary afferent terminals. This induces an increase in dorsal horn excitability that contributes to "central sensitization" and to the onset of neuropathic pain. Although it is accepted that impairment of GABAergic and/or glycinergic inhibition contributes to this process, certain lines of evidence suggest that GABA release in the dorsal horn may increase after nerve injury. To resolve these contradictory findings, we exposed rat spinal cord neurons in defined-medium organotypic culture to 200 ng/ml BDNF for 6 days to mimic the change in spinal BDNF levels that accompanies peripheral nerve injury. Morphological and electrophysiological criteria and glutamic acid decarboxylase (GAD) immunohistochemistry were used to distinguish putative inhibitory tonic-islet-central neurons from putative excitatory delay-radial neurons. Whole cell recording in the presence of 1 μM tetrodotoxin showed that BDNF increased the amplitude of GABAergic and glycinergic miniature inhibitory postsynaptic currents (mIPSCs) in both cell types. It also increased the amplitude and frequency of spontaneous, action potential-dependent IPSCs (sIPSCs) in putative excitatory neurons. By contrast, BDNF reduced sIPSC amplitude in inhibitory neurons but frequency was unchanged. This increase in inhibitory drive to excitatory neurons and decreased inhibitory drive to inhibitory neurons seems inconsistent with the observation that BDNF increases overall dorsal horn excitability. One of several explanations for this discrepancy is that the action of BDNF in the substantia gelatinosa is dominated by previously documented increases in excitatory synaptic transmission rather than by impediment of inhibitory transmission.

Spinal cord explants use carbon nanotube interfaces to enhance neurite outgrowth and to fortify synaptic inputs

New developments in nanotechnology are increasingly designed to modulate relevant interactions between nanomaterials and neurons, with the aim of exploiting the physical properties of synthetic materials to tune desired and specific biological processes. Carbon nanotubes have been applied in several areas of nerve tissue engineering to study cell behavior or to instruct the growth and organization of neural networks. Recent reports show that nanotubes can sustain and promote electrical activity in networks of cultured neurons. However, such results are usually limited to carbon nanotube/neuron hybrids formed on a monolayer of dissociated brain cells. In the present work, we used organotypic spinal slices to model multilayer tissue complexity, and we interfaced such spinal segments to carbon nanotube scaffolds for weeks. By immunofluorescence, scanning and transmission electronic microscopy, and atomic force microscopy, we investigated nerve fiber growth when neuronal processes exit the spinal explant and develop in direct contact to the substrate. By single-cell electrophysiology, we investigated the synaptic activity of visually identified ventral interneurons, within the ventral area of the explant, thus synaptically connected, but located remotely, to the substrate/network interface. Here we show that spinal cord explants interfaced for weeks to purified carbon nanotube scaffolds expand more neuronal fibers, characterized by different mechanical properties and displaying higher growth cones activity. On the other hand, exploring spontaneous and evoked synaptic activity unmasks an increase in synaptic efficacy in neurons located at as far as 5 cell layers from the cell-substrate interactions.

Inhibitory synaptic regulation of motoneurons: a new target of disease mechanisms in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the third most common adult-onset neurodegenerative disease. It causes the degeneration of motoneurons and is fatal due to paralysis, particularly of respiratory muscles. ALS can be inherited, and specific disease-causing genes have been identified, but the mechanisms causing motoneuron death in ALS are not understood. No effective treatments exist for ALS. One well-studied theory of ALS pathogenesis involves faulty RNA editing and abnormal activation of specific glutamate receptors as well as failure of glutamate transport resulting in glutamate excitotoxicity; however, the excitotoxicity theory is challenged by the inability of anti-glutamate drugs to have major disease-modifying effects clinically. Nevertheless, hyperexcitability of upper and lower motoneurons is a feature of human ALS and transgenic (tg) mouse models of ALS. Motoneuron excitability is strongly modulated by synaptic inhibition mediated by presynaptic glycinergic and GABAergic innervations and postsynaptic glycine receptors (GlyR) and GABA(A) receptors; yet, the integrity of inhibitory systems regulating motoneurons has been understudied in experimental models, despite findings in human ALS suggesting that they may be affected. We have found in tg mice expressing a mutant form of human superoxide dismutase-1 (hSOD1) with a Gly93 → Ala substitution (G93A-hSOD1), causing familial ALS, that subsets of spinal interneurons degenerate. Inhibitory glycinergic innervation of spinal motoneurons becomes deficient before motoneuron degeneration is evident in G93A-hSOD1 mice. Motoneurons in these ALS mice also have insufficient synaptic inhibition as reflected by smaller GlyR currents, smaller GlyR clusters on their plasma membrane, and lower expression of GlyR1α mRNA compared to wild-type motoneurons. In contrast, GABAergic innervation of ALS mouse motoneurons and GABA(A) receptor function appear normal. Abnormal synaptic inhibition resulting from dysfunction of interneurons and motoneuron GlyRs is a new direction for unveiling mechanisms of ALS pathogenesis that could be relevant to new therapies for ALS.

Glycine receptor channels in spinal motoneurons are abnormal in a transgenic mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly evolving and fatal adult-onset neurological disease characterized by progressive degeneration of motoneurons. Our previous study showed that glycinergic innervation of spinal motoneurons is deficient in an ALS mouse model expressing a mutant form of human superoxide dismutase-1 with a Gly93→Ala substitution (G93A-SOD1). In this study, we have examined, using whole-cell patch-clamp recordings, glycine receptor (GlyR)-mediated currents in spinal motoneurons from these transgenic mice. We developed a dissociated spinal cord culture model using embryonic transgenic mice expressing enhanced green fluorescent protein (eGFP) driven by the Hb9 promoter. Motoneurons were identified as Hb9-eGFP-expressing (Hb9-eGFP(+)) neurons with a characteristic morphology. To examine GlyRs in ALS motoneurons, we bred G93A-SOD1 mice to Hb9-eGFP mice and compared glycine-evoked currents in cultured Hb9-eGFP(+) motoneurons prepared from G93A-SOD1 embryos and from their nontransgenic littermates. Glycine-evoked current density was significantly smaller in the G93A-SOD1 motoneurons compared with control. Furthermore, the averaged current densities of spontaneous glycinergic miniature IPSCs (mIPSCs) were significantly smaller in the G93A-SOD1 motoneurons than in control motoneurons. No significant differences in GABA-induced currents and GABAergic mIPSCs were observed between G93A-SOD1 and control motoneurons. Quantitative single-cell reverse transcription-PCR found lower GlyRα1 subunit mRNA expression in G93A-SOD1 motoneurons, indicating that the reduction of GlyR current may result from the downregulation of GlyR mRNA expression in motoneurons. Immunocytochemistry demonstrated a decrease of surface postsynaptic GlyR on G93A-SOD1 motoneurons. Our study suggests that selective alterations in GlyR function contribute to inhibitory insufficiency in motoneurons early in the disease process of ALS.

Motoneuron afterhyperpolarisation duration in amyotrophic lateral sclerosis

Motor unit (MU) potentials were registered from 20 ALS patients and 13 age-matched control individuals during isometric constant force contractions of brachial biceps (BB). The registered signals were decomposed into single MU potential trains. The estimates of duration of the afterhyperpolarisation (AHP) in MNs, derived from the interspike interval variability, was compared between ALS patients (124 MNs) and control subjects (111 MNs) and no significant differences were encountered. However, the relationship between TI and age for patients appeared to be qualitatively different from that of the control group. The dependence of patients' AHPs on relative force deficit (RFD), which quantified muscle involvement, was more specific. For RFDs below 30%, the AHP estimate was significantly lower than control values and then increased thereafter with increasing RFDs. Moreover, firing rates of patients with the smallest RFDs were significantly higher while firing rates of patients with the greatest RFDs were significantly lower than control values. The AHP shortening in the early stages of muscle impairment is consistent with the decrease in firing threshold of ‘fast' MNs found in spinal cord slices from neonatal SOD1 mice. The later elongation of the AHP may be caused by the higher vulnerability of ‘fast' MNs to degeneration and by the influence of reinnervation. Our results are comparable to what has been observed in acute experiments in animal models, providing a bridge between animal and clinical research that may be relevant for identification of mechanism(s) underlying neurodegeneration in ALS.

Reduction in the motoneuron inhibitory/excitatory synaptic ratio in an early-symptomatic mouse model of amyotrophic lateral sclerosis

Excitotoxicity is a widely studied mechanism underlying motoneuron degeneration in amyotrophic lateral sclerosis (ALS). Synaptic alterations that produce an imbalance in the ratio of inhibitory/excitatory synapses are expected to promote or protect against motoneuron excitotoxicity. In ALS patients, motoneurons suffer a reduction in their synaptic coverage, as in the transition from the presymptomatic (2-month-old) to early-symptomatic (3-month-old) stage of the hSOD1(G93A) mouse model of familial ALS. Net synapse loss resulted from inhibitory bouton loss and excitatory synapse gain. Furthermore, in 3-month-old transgenic mice, remaining inhibitory but not excitatory boutons attached to motoneurons showed reduction in the active zone length and in the spatial density of synaptic vesicles in the releasable pool near the active zone. Bouton degeneration/loss seems to be mediated by bouton vacuolization and by mechanical displacement due to swelling vacuolated dendrites. In addition, chronic treatment with a nitric oxide (NO) synthase inhibitor avoided inhibitory loss but not excitatory gain. These results indicate that NO mediates inhibitory loss occurring from the pre- to early-symptomatic stage of hSOD1(G93A) mice. This work contributes new insights on ALS pathogenesis, recognizing synaptic re-arrangement onto motoneurons as a mechanism favoring disease progression rather than as a protective homeostatic response against excitotoxic events.

Graft and host interactions following transplantation of neural stem cells to organotypic striatal cultures

AIMS

To investigate neural stem cell (NSC) interactions with striatal tissue following engraftment and the effects of growth factors.

MATERIALS & METHODS

Organotypic striatal slice cultures established from neonatal rats were used as an ex vivo model system. Survival, integration and differentiation of grafted NSCs from the previously generated C17.2 clone and host tissue response were investigated weekly for 28 days in vitro. To direct grafted cells towards a neuronal lineage, the role of growth factor supplementation and serum-free culturing conditions was studied using neural stem cells overexpressing neurotrophin-3 and Neurobasal/B27 culture medium.

RESULTS

Following engraftment, NSCs gradually integrated morphologically and formed a part of the host 3D cytoarchitecture. Compared with nongrafted cultures, NSC engraftment increased the overall survival of the organotypic cultures by 39%, and reduced the host cell necrosis by more than 80% (from 2.1 ± 0.5% to 0.3 ± 0.1%), the host cell apoptosis by more than 60% (from 1.4 ± 0.4% to 0.5 ± 0.1%) and the reactions to mechanical trauma by 30% (estimated by nestin and glial fibrillary acidic protein immunohistochemistry) 7 days after engraftment. Elevated neurotrophin-3 production in NSCs and serum-free culturing conditions directed grafted NSCs towards a neuronal lineage as indicated by increased Tuj1 and Map2ab expression. However, this did not alter the survival of organotypic cultures.

CONCLUSIONS

NSC engraftment was associated with rescue of imperiled host cells and reduction of host cell gliosis. These NSC effects were not related to the addition of growth factors, suggesting that other factors are involved in the supportive effects of the host following NSC engraftment.

NO orchestrates the loss of synaptic boutons from adult "sick" motoneurons: modeling a molecular mechanism

Synapse elimination is the main factor responsible for the cognitive decline accompanying many of the neuropathological conditions affecting humans. Synaptic stripping of motoneurons is also a common hallmark of several motor pathologies. Therefore, knowledge of the molecular basis underlying this plastic process is of central interest for the development of new therapeutic tools. Recent advances from our group highlight the role of nitric oxide (NO) as a key molecule triggering synapse loss in two models of motor pathologies. De novo expression of the neuronal isoform of NO synthase (nNOS) in motoneurons commonly occurs in response to the physical injury of a motor nerve and in the course of amyotrophic lateral sclerosis. In both conditions, this event precedes synaptic withdrawal from motoneurons. Strikingly, nNOS-synthesized NO is "necessary" and "sufficient" to induce synaptic detachment from motoneurons. The mechanism involves a paracrine/retrograde action of NO on pre-synaptic structures, initiating a downstream signaling cascade that includes sequential activation of (1) soluble guanylyl cyclase, (2) cyclic guanosine monophosphate-dependent protein kinase, and (3) RhoA/Rho kinase (ROCK) signaling. Finally, ROCK activation promotes phosphorylation of regulatory myosin light chain, which leads to myosin activation and actomyosin contraction. This latter event presumably contributes to the contractile force to produce ending axon retraction. Several findings support that this mechanism may operate in the most prevalent neurodegenerative diseases.

Intrinsic properties of lumbar motor neurones in the adult G127insTGGG superoxide dismutase-1 mutant mouse in vivo: evidence for increased persistent inward currents

AIM

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by a preferential loss of motor neurones. Previous publications using in vitro neonatal preparations suggest an increased excitability of motor neurones in various superoxide dismutase-1 (SOD1) mutant mice models of ALS which may contribute to excitotoxicity of the motor neurones.

METHODS

Using intracellular recording, we tested this hypothesis in vivo in the adult presymptomatic G127insTGGG (G127X) SOD1 mutant mouse model of ALS.

RESULTS

At resting membrane potentials the basic intrinsic properties of lumbar motor neurones in the adult presymptomatic G127X mutant are not significantly different from those of wild type. However, at more depolarized membrane potentials, motor neurones in the G127X SOD1 mutants can sustain higher frequency firing, showing less spike frequency adaption (SFA) and with persistent inward currents (PICs) being activated at lower firing frequencies and being more pronounced.

CONCLUSION

We demonstrated that, in vivo, at resting membrane potential, spinal motor neurones of the adult G127X mice do not show an increased excitability. However, when depolarized they show evidence of an increased PIC and less SFA which may contribute to excitotoxicity of these neurones as the disease progresses.

A transcription factor map as revealed by a genome-wide gene expression analysis of whole-blood mRNA transcriptome in multiple sclerosis

Background

Several lines of evidence suggest that transcription factors are involved in the pathogenesis of Multiple Sclerosis (MS) but complete mapping of the whole network has been elusive. One of the reasons is that there are several clinical subtypes of MS and transcription factors that may be involved in one subtype may not be in others. We investigate the possibility that this network could be mapped using microarray technologies and contemporary bioinformatics methods on a dataset derived from whole blood in 99 untreated MS patients (36 Relapse Remitting MS, 43 Primary Progressive MS, and 20 Secondary Progressive MS) and 45 age-matched healthy controls.

Methodology/Principal Findings

We have used two different analytical methodologies: a non-standard differential expression analysis and a differential co-expression analysis, which have converged on a significant number of regulatory motifs that are statistically overrepresented in genes that are either differentially expressed (or differentially co-expressed) in cases and controls (e.g., V$KROX_Q6, p-value <3.31E-6; V$CREBP1_Q2, p-value <9.93E-6, V$YY1_02, p-value <1.65E-5).

Conclusions/Significance

Our analysis uncovered a network of transcription factors that potentially dysregulate several genes in MS or one or more of its disease subtypes. The most significant transcription factor motifs were for the Early Growth Response EGR/KROX family, ATF2, YY1 (Yin and Yang 1), E2F-1/DP-1 and E2F-4/DP-2 heterodimers, SOX5, and CREB and ATF families. These transcription factors are involved in early T-lymphocyte specification and commitment as well as in oligodendrocyte dedifferentiation and development, both pathways that have significant biological plausibility in MS causation.

Postsynaptic alteration of NR2A subunit and defective autophosphorylation of alphaCaMKII at threonine-286 contribute to abnormal plasticity and morphology of upper motor neurons in presymptomatic SOD1G93A mice, a murine model for amyotrophic lateral sclerosis

Although amyotrophic lateral sclerosis (ALS) has long been considered as a lower motor neuron (MN) disease, degeneration of upper MNs arising from a combination of mechanisms including insufficient growth factor signaling and enhanced extracellular glutamate levels is now well documented. The observation that these mechanisms are altered in presymptomatic superoxide dismutase (SOD1) mice, an ALS mouse model, suggests that defective primary motor cortex (M1) synaptic activity might precede the onset of motor disturbances. To examine this point, we assessed the composition of AMPAR and NMDAR subunits and of the alphaCa²(+)/calmodulin-dependent kinase autophosphorylation at threonine-286 in the triton insoluble fraction from the M1 in postnatal P80-P85 SOD1(G93A) and wild-type mice. We show that presymptomatic SOD1(G93A) exhibit a selective decrease of NR2A subunit expression and of the alphaCa²(+)/calmodulin-dependent kinase autophosphorylation at threonine-286 in the triton insoluble fraction of upper MNs synapses. These molecular alterations are associated with synaptic plasticity defects, and a reduction in upper MN dendritic outgrowth revealing that abnormal neuronal connectivity in the M1 region precedes the onset of motor symptoms. We suggest that the progressive disruption of M1 corticocortical connections resulting from the SOD1(G93A) mutation might extend to adjacent regions and promote development of cognitive/dementia alterations frequently associated with ALS.

The patterns of spontaneous Ca2+ signals generated by ventral spinal neurons in vitro show time-dependent refinement

Embryonic spinal neurons maintained in organotypic slice culture are known to mimic certain maturation-dependent signalling changes. With such a model we investigated, in embryonic mouse spinal segments, the age-dependent spatio-temporal control of intracellular Ca(2+) signalling generated by neuronal populations in ventral circuits and its relation with electrical activity. We used Ca(2+) imaging to monitor areas located within the ventral spinal horn at 1 and 2 weeks of in vitro growth. Primitive patterns of spontaneous neuronal Ca(2+) transients (detected at 1 week) were typically synchronous. Remarkably, such transients originated from widespread propagating waves that became organized into large-scale rhythmic bursts. These activities were associated with the generation of synaptically mediated inward currents under whole-cell patch-clamp. Such patterns disappeared during longer culture of spinal segments: at 2 weeks in culture, only a subset of ventral neurons displayed spontaneous, asynchronous and repetitive Ca(2+) oscillations dissociated from background synaptic activity. We observed that the emergence of oscillations was a restricted phenomenon arising together with the transformation of ventral network electrophysiological bursting into asynchronous synaptic discharges. This change was accompanied by the appearance of discrete calbindin immunoreactivity against an unchanged background of calretinin-positive cells. It is attractive to assume that periodic oscillations of Ca(2+) confer a summative ability to these cells to shape the plasticity of local circuits through different changes (phasic or tonic) in intracellular Ca(2+).

Impairment of mitochondrial calcium handling in a mtSOD1 cell culture model of motoneuron disease

Background

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the selective loss of motor neurons (MN) in the brain stem and spinal cord. Intracellular disruptions of cytosolic and mitochondrial calcium have been associated with selective MN degeneration, but the underlying mechanisms are not well understood. The present evidence supports a hypothesis that mitochondria are a target of mutant SOD1-mediated toxicity in familial amyotrophic lateral sclerosis (fALS) and intracellular alterations of cytosolic and mitochondrial calcium might aggravate the course of this neurodegenerative disease. In this study, we used a fluorescence charged cool device (CCD) imaging system to separate and simultaneously monitor cytosolic and mitochondrial calcium concentrations in individual cells in an established cellular model of ALS.

Results

To gain insights into the molecular mechanisms of SOD1^G93A associated motor neuron disease, we simultaneously monitored cytosolic and mitochondrial calcium concentrations in individual cells. Voltage – dependent cytosolic Ca²⁺ elevations and mitochondria – controlled calcium release mechanisms were monitored after loading cells with fluorescent dyes fura-2 and rhod-2. Interestingly, comparable voltage-dependent cytosolic Ca²⁺ elevations in WT (SH-SY5Y^WT) and G93A (SH-SY5Y^G93A) expressing cells were observed. In contrast, mitochondrial intracellular Ca²⁺ release responses evoked by bath application of the mitochondrial toxin FCCP were significantly smaller in G93A expressing cells, suggesting impaired calcium stores. Pharmacological experiments further supported the concept that the presence of G93A severely disrupts mitochondrial Ca²⁺ regulation.

Conclusion

In this study, by fluorescence measurement of cytosolic calcium and using simultaneous [Ca²⁺]i and [Ca²⁺]_mito measurements, we are able to separate and simultaneously monitor cytosolic and mitochondrial calcium concentrations in individual cells an established cellular model of ALS. The primary goals of this paper are (1) method development, and (2) screening for deficits in mutant cells on the single cell level. On the technological level, our method promises to serve as a valuable tool to identify mitochondrial and Ca²⁺-related defects during G93A-mediated MN degeneration. In addition, our experiments support a model where a specialized interplay between cytosolic calcium profiles and mitochondrial mechanisms contribute to the selective degeneration of neurons in ALS.

Neuroprotective effects of erythropoietin posttreatment against kainate-induced excitotoxicity in mixed spinal cultures

Although the neuroprotective effects of erythropoietin (EPO) preconditioning are well known, the potential of postapplied EPO to protect neurons against excitotoxic injury has not been clearly established. Here we show that kainate (KA)-induced excitotoxicity, which plays a key role in secondary spinal cord injury, decreased neuron survival, inhibited neurite extension, and significantly reduced the expression of erythropoietin receptors (EpoR) in cultured spinal neurons. Posttreatment with EPO for 48 hr protected neurons against KA-induced injury, opposing KA-induced apoptosis and promoting regrowth of motoneuron neurites. These neuroprotective effects were paralleled by a restoration of EpoR expression. The importance of the EpoR signaling pathway was demonstrated using an EpoR blocking antibody, which neutralized the neuroprotective action of EPO posttreatment and prevented EPO-induced increases in EpoR expression. We also found that up-regulated EpoR stimulated the Janus kinase 2 (JAK2) pathway, which is known to facilitate neuronal growth and neurite regeneration. Although EPO posttreatment modestly attenuated KA-induced reactive gliosis in mixed neuron-glial cultures, blocking EpoR activity did not alter glial fibrillary acidic protein expression or astrocyte proliferation. In conclusion, 48 hr treatment with EPO following KA exposure induced EpoR-dependent protection against excitotoxic injury, demonstrating that preconditioning is not a prerequisite for neuroprotection by EPO. The neuroprotective effects of EPO posttreatment were mediated by an EpoR-dependent signaling pathway that possibly involves JAK2. The neuroprotective effect of EPO posttreatment against KA excitotoxicity appears to reflect direct effects on neurons and not indirect effects mediated by astrocytes.

Glycinergic innervation of motoneurons is deficient in amyotrophic lateral sclerosis mice: a quantitative confocal analysis

Altered motoneuron excitability is involved in amyotrophic lateral sclerosis pathobiology. To test the hypothesis that inhibitory interneuron innervation of spinal motoneurons is abnormal in an amyotrophic lateral sclerosis mouse model, we measured GABAergic, glycinergic, and cholinergic immunoreactive terminals on spinal motoneurons in mice expressing a mutant form of human superoxide dismutase-1 with a Gly93-->Ala substitution (G93A-SOD1) and in controls at different ages. Glutamic acid decarboxylase, glycine transporter-2, and choline acetyltransferase were used as markers for GABAergic, glycinergic, and cholinergic terminals, respectively. Triple immunofluorescent labeling of boutons contacting motoneurons was visualized by confocal microscopy and analyzed quantitatively. Glycine transporter-2-bouton density on lateral motoneurons was decreased significantly in G93A-SOD1 mice compared with controls. This reduction was absent at 6 weeks of age but present in asymptomatic 8-week-old mice and worsened with disease progression from 12 to 14 weeks of age. Motoneurons lost most glycinergic innervation by 16 weeks of age (end-stage) when there was a significant decrease in the numbers of motoneurons and choline acetyltransferase-positive boutons. No significant differences in glutamic acid decarboxylase-bouton densities were found in G93A-SOD1 mice. Reduction of glycinergic innervation preceded mitochondrial swelling and vacuolization. Calbindin-positive Renshaw cell number was decreased significantly at 12 weeks of age in G93A-SOD1 mice. Thus, either the selective loss of inhibitory glycinergic regulation of motoneuron function or glycinergic interneuron degeneration contributes to motoneuron degeneration in amyotrophic lateral sclerosis.