Synapse-associated astrocyte mitochondria stabilize motor circuits to prevent excitotoxicity

Early stages of the devastating neurodegenerative disease amyotrophic lateral sclerosis (ALS) are characterized by motor neuron hyperexcitability. During this phase, peri-synaptic astrocytes are neuroprotective. When reactive, loss of wild-type astrocyte functions results in excitotoxicity. How astrocytes stabilize motor circuit function in early-stage ALS is poorly understood. Here, we used Drosophila motor neurons to define the role of astrocyte-motor neuron metabolic coupling in a model of ALS: astrocyte knockdown of the ALS-causing gene tbph/TARDBP. In wild-type, astrocyte mitochondria were dynamically trafficked towards active motor dendrites/synapses to meet local metabolic demand. Knockdown of tbph in astrocytes resulted in motor neuron hyperexcitability, reminiscent of early-stage ALS, which was met with a compensatory accumulation of astrocyte mitochondria near motor dendrites/synapses. Finally, we blocked mitochondria-synapse association in tbph knockdown animals and observed locomotor deficits and synapse loss. Thus, synapse-associated astrocyte mitochondria stabilize motor circuits to prevent the transition from hyperexcitability to excitotoxicity.

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Groucho/TLE opposes axial to hypaxial motor neuron development

10.1101/2020.03.10.986323 ◽

2020 ◽

Author(s):

Adèle Salin-Cantegrel ◽

Rola Dali ◽

Jae Woong Wang ◽

Marielle Beaulieu ◽

Mira Deshmukh ◽

...

Keyword(s):

Spinal Cord ◽

Motor Neuron ◽

Motor Neurons ◽

Molecular Mechanisms ◽

List Type ◽

Neuron Development ◽

In Ovo ◽

Motor Circuits ◽

Axial Muscles ◽

Muscle Innervation

ABSTRACTSpinal cord motor neuron diversity and the ensuing variety of motor circuits allow for the processing of elaborate muscular behaviours such as body posture and breathing. Little is known, however, about the molecular mechanisms behind the specification of axial and hypaxial motor neurons controlling postural and respiratory functions respectively. Here we show that the Groucho/TLE (TLE) transcriptional corepressor is a multi-step regulator of axial and hypaxial motor neuron diversification in the developing spinal cord. TLE first promotes axial motor neuron specification at the expense of hypaxial identity by cooperating with non-canonical WNT5A signalling within the motor neuron progenitor domain. TLE further acts during post-mitotic motor neuron diversification to promote axial motor neuron topology and axonal connectivity whilst suppressing hypaxial traits. These findings provide evidence for essential and sequential roles of TLE in the spatial and temporal coordination of events regulating the development of motor neurons influencing posture and controlling respiration.HIGHLIGHTSGroucho/TLE mediates non-canonical WNT signalling in developing motor neuronsNon canonical WNT:TLE pathway regulates thoracic motor neuron diversificationTLE promotes axial while inhibiting hypaxial motor neuron developmentTLE influences developing motor neuron topology and muscle innervationIN BRIEFSalin-Cantegrel et al use in ovo engineered approaches to show that a non-canonical WNT:TLE pathway coordinates temporally and spatially separated elements of motor neuron diversification, repressing hypaxial motor neuron development to promote the axial fate.GRAPHICAL ABSTRACTTLE contribution to the development of thoracic somatic motor columnsProgenitor cells in the ventral pMN domain are exposed to higher concentrations of non-canonical WNTs and express more TLE. Cooperation of non-canonical WNTs and TLE renders ventral pMN progenitors refractory to a respiratory MN fate, thereby contributing to the separation of MMC and RMC MN lineages. Differentiating MNs that maintain high TLE expression also maintain LHX3 expression, adopt axial motor neuron topology and connect to axial muscles. TLE activity in differentiating MMC MNs prevents the acquisition of respiratory MN topology and innervation traits.

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Locomotor deficits in ALS mice are paralleled by loss of V1-interneuron-connections onto fast motor neurons

10.1101/2020.06.23.166389 ◽

2020 ◽

Author(s):

Ilary Allodi ◽

Roser Montañana-Rosell ◽

Raghavendra Selvan ◽

Peter Löw ◽

Ole Kiehn

Keyword(s):

Motor Neuron ◽

Motor Neurons ◽

Inhibitory Synapses ◽

Neuron Death ◽

Spinal Interneurons ◽

Pathway Interaction ◽

Fast Twitch Muscle ◽

Motor Neuron Death ◽

Locomotor Deficits ◽

Induced Changes

AbstractALS is characterized by progressive inability to execute movements. Motor neurons innervating fast-twitch muscle fibers exhibit preferential degeneration. The reason for differential vulnerability of fast motor neurons, and its consequence on motor output is not known. Here, we show that fast motor neurons receive more inhibitory synaptic inputs than slow motor neurons, and loss of inhibitory synapses onto fast motor neurons precedes disease progression in the SOD1G93A mouse model of ALS. Loss of inhibitory synapses on fast motor neurons is accounted for by a loss of synapses from inhibitory V1 spinal interneurons. Deficits in V1-motor neuron connectivity appear prior to motor neuron death and are paralleled by development of specific SOD1G93A locomotor deficits. These distinct SOD1G93A locomotor deficits are phenocopied by silencing of inhibitory V1 spinal interneurons in wild-type mice. Silencing inhibitory V1 spinal interneurons does not exacerbate SOD1G93A locomotor deficits, suggesting phenotypic pathway interaction. Our study identifies a potential cell non-autonomous source of motor neuronal vulnerability in ALS, and links ALS-induced changes in locomotor phenotypes to inhibitory V1 interneurons.

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Integrins Have Cell-Type-Specific Roles in the Development of Motor Neuron Connectivity

Journal of Developmental Biology ◽

10.3390/jdb7030017 ◽

2019 ◽

Vol 7 (3) ◽

pp. 17 ◽

Cited By ~ 1

Author(s):

Devyn Oliver ◽

Emily Norman ◽

Heather Bates ◽

Rachel Avard ◽

Monika Rettler ◽

...

Keyword(s):

Nervous System ◽

Cell Adhesion ◽

Motor Neuron ◽

Motor Neurons ◽

Neuron Development ◽

Wild Type ◽

Cell Type ◽

C Elegans ◽

Cell Type Specific ◽

Two Phases

Formation of the nervous system requires a complex series of events including proper extension and guidance of neuronal axons and dendrites. Here we investigate the requirement for integrins, a class of transmembrane cell adhesion receptors, in regulating these processes across classes of C. elegans motor neurons. We show α integrin/ina-1 is expressed by both GABAergic and cholinergic motor neurons. Despite this, our analysis of hypomorphic ina-1(gm144) mutants indicates preferential involvement of α integrin/ina-1 in GABAergic commissural development, without obvious involvement in cholinergic commissural development. The defects in GABAergic commissures of ina-1(gm144) mutants included both premature termination and guidance errors and were reversed by expression of wild type ina-1 under control of the native ina-1 promoter. Our results also show that α integrin/ina-1 is important for proper outgrowth and guidance of commissures from both embryonic and post-embryonic born GABAergic motor neurons, indicating an ongoing requirement for integrin through two phases of GABAergic neuron development. Our findings provide insights into neuron-specific roles for integrin that would not be predicted based solely upon expression analysis.

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Control of hindbrain motor neuron differentiation by the homeobox gene Phox2b

Development ◽

10.1242/dev.127.7.1349 ◽

2000 ◽

Vol 127 (7) ◽

pp. 1349-1358 ◽

Cited By ~ 10

Author(s):

A. Pattyn ◽

M. Hirsch ◽

C. Goridis ◽

J.F. Brunet

Keyword(s):

Motor Neuron ◽

Motor Neurons ◽

Early Stage ◽

Control Point ◽

Homeobox Gene ◽

Homeodomain Protein ◽

Loss Of Function ◽

Dorsoventral Patterning ◽

Cns Neurons ◽

Mantle Layer

Motor neurons are a widely studied model of vertebrate neurogenesis. They can be subdivided in somatic, branchial and visceral motor neurons. Recent studies on the dorsoventral patterning of the rhombencephalon have implicated the homeobox genes Pax6 and Nkx2.2 in the early divergence of the transcriptional programme of hindbrain somatic and visceral motor neuronal differentiation. We provide genetic evidence that the paired-like homeodomain protein Phox2b is required for the formation of all branchial and visceral, but not somatic, motor neurons in the hindbrain. In mice lacking Phox2b, both the generic and subtype-specific programs of motoneuronal differentiation are disrupted at an early stage. Most motor neuron precursors die inside the neuroepithelium while those that emigrate to the mantle layer fail to switch on early postmitotic markers and to downregulate neuroepithelial markers. Thus, the loss of function of Phox2b in hindbrain motor neurons exemplifies a novel control point in the generation of CNS neurons.

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Neurofilament subunit NF-H modulates axonal diameter by selectively slowing neurofilament transport.

The Journal of Cell Biology ◽

10.1083/jcb.135.3.711 ◽

1996 ◽

Vol 135 (3) ◽

pp. 711-724 ◽

Cited By ~ 128

Author(s):

J R Marszalek ◽

T L Williamson ◽

M K Lee ◽

Z Xu ◽

P N Hoffman ◽

...

Keyword(s):

Motor Neuron ◽

Motor Neuron Disease ◽

Motor Neurons ◽

Normal Level ◽

Wild Type Mouse ◽

Wild Type ◽

Myelinated Axons ◽

Axonal Diameter ◽

Axonal Swellings ◽

Neurofilament Transport

To examine the mechanism through which neurofilaments regulate the caliber of myelinated axons and to test how aberrant accumulations of neurofilaments cause motor neuron disease, mice have been constructed that express wild-type mouse NF-H up to 4.5 times the normal level. Small increases in NF-H expression lead to increased total neurofilament content and larger myelinated axons, whereas larger increases in NF-H decrease total neurofilament content and strongly inhibit radial growth. Increasing NF-H expression selectively slow neurofilament transport into and along axons, resulting in severe perikaryal accumulation of neurofilaments and proximal axonal swellings in motor neurons. Unlike the situation in transgenic mice expressing modest levels of human NF-H (Cote, F., J.F. Collard, and J.P. Julien. 1993. Cell. 73:35-46), even 4.5 times the normal level of wild-type mouse NF-H does not result in any overt phenotype or enhanced motor neuron degeneration or loss. Rather, motor neurons are extraordinarily tolerant of wild-type murine NF-H, whereas wild-type human NF-H, which differs from the mouse homolog at > 160 residue positions, mediates motor neuron disease in mice by acting as an aberrant, mutant subunit.

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Cooperative Mechanisms Between Leg Joints of Carausius morosusI. Nonspiking Interneurons That Contribute to Interjoint Coordination

Journal of Neurophysiology ◽

10.1152/jn.1998.79.6.2964 ◽

1998 ◽

Vol 79 (6) ◽

pp. 2964-2976 ◽

Cited By ~ 7

Author(s):

Dennis E. Brunn

Keyword(s):

Membrane Potential ◽

Motor Neuron ◽

Motor Neurons ◽

Stick Insect ◽

Interjoint Coordination ◽

Antagonistic Muscle ◽

Nonspiking Interneurons ◽

Active Motor ◽

Thoracic Part ◽

Depressor Muscle

Brunn, Dennis E. Cooperative mechanisms between leg joints of Carausius morosus. I. Nonspiking interneurons that contribute to interjoint coordination. J. Neurophysiol. 79: 2964–2976, 1998. Three nonspiking interneurons are described in this paper that influence the activity of the motor neurons of three muscles of the proximal leg joints of the stick insect. Interneurons were recorded and stained intracellularly by glass microelectrodes; motor neurons were recorded extracellularly with oil-hook electrodes. The motor neurons innervate the two subcoxal muscles, the protractor and retractor coxae, and the thoracic part of the depressor trochanteris muscle. The latter spans the subcoxal joint before inserting the trochanter, thus coupling the two proximal joints mechanically. The three interneurons are briefly described here. First, interneuron NS 1 was known to become more excited during the swing phase of the rear and the stance phase of the middle leg. When depolarized it excited several motor neurons of the retractor coxae. This investigation revealed that it inhibits the activity of protractor and thoracic depressor motor neurons when depolarized as well. In a pilocarpine-activated animal, the membrane potential showed oscillations in phase with the activity of protractor motor neurons, suggesting that NS 1 might contribute to the transition from swing to stance movement. Second, interneuron NS 2 inhibits motor neurons of protractor and thoracic depressor when depolarized. In both a quiescent and a pilocarpine-activated animal, hyperpolarizing stimuli excite motor neurons of both muscles via disinhibition. In one active animal the disinhibiting stimuli were sufficient to generate swing-like movements of the leg. In pilocarpine-activated preparations the membrane potential oscillated in correlation with the motor neuronal activity of the protractor coxae and thoracic depressor muscle. Hyperpolarizing stimuli induced or reinforced the protractor and thoracic depressor bursts and inhibited the activity of the motor neurons of the retractor coxae muscle, the antagonistic muscle of the protractor. Therefore interneuron NS 2 can be regarded as an important premotor interneuron for the switching from stance to swing and from swing to stance. Finally, interneuron NS 3 inhibits the spontaneously active motor neurons of both motor neuron pools in the quiescent animal. During pilocarpine-induced protractor bursts, depolarizing stimuli applied to the interneuron excited several protractor motor neurons with large action potentials and one motor neuron of the thoracic depressor. No oscillations of the membrane potentials were observed. Therefore this interneuron might contribute to the generation of rapid leg movements. The results demonstrated that the two proximal joints are coupled not only mechanically but also neurally and that the thoracic part of the depressor appears to function as a part of the swing-generating system.

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Peripheral neuropathy linked mRNA export factor GANP reshapes gene regulation in human motor neurons

10.1101/2021.05.18.444636 ◽

2021 ◽

Author(s):

Rosa Woldegebriel ◽

Jouni Kvist ◽

Matthew White ◽

Matilda Sinkko ◽

Satu Hanninen ◽

...

Keyword(s):

Protein Synthesis ◽

Motor Neuron ◽

Motor Neurons ◽

Nuclear Export ◽

Large Scale ◽

Early Stage ◽

Mrna Export ◽

Nuclear Pore ◽

Long Distance ◽

Human Motor

Loss-of-function of the mRNA export protein GANP (MCM3AP gene) cause early-onset sensorimotor neuropathy, characterised by axonal degeneration in long peripheral nerves. GANP functions as a scaffold at nuclear pore complexes, contributing to selective nuclear export of mRNAs. Here, we aimed to identify motor neuron specific transcripts that are regulated by GANP and may be limiting for local protein synthesis in motor neuron axons. We compared motor neurons with a gene edited mutation in the Sac3 mRNA binding domain of GANP to isogenic controls. We also examined patient-derived motor neurons. RNA sequencing of motor neurons as well as nuclear and axonal subcompartments showed that mutant GANP had a profound effect on motor neuron transcriptomes, with alterations in nearly 40 percent of all expressed genes and broad changes in splicing. Expression changes in multiple genes critical for neuronal functions, combined with compensatory upregulation of protein synthesis and early-stage metabolic stress genes, indicated that RNA metabolism was abnormal in GANP-deficient motor neurons. Surprisingly, limited evidence was found for large-scale nuclear retention of mRNA. This first study of neuropathy-linked GANP defects in human motor neurons shows that GANP has a wide gene regulatory role in a disease-relevant cell type that requires long-distance mRNA transport.

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Mutant PFN1 causes ALS phenotypes and progressive motor neuron degeneration in mice by a gain of toxicity

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1605964113 ◽

2016 ◽

Vol 113 (41) ◽

pp. E6209-E6218 ◽

Cited By ~ 44

Author(s):

Chunxing Yang ◽

Eric W. Danielson ◽

Tao Qiao ◽

Jake Metterville ◽

Robert H. Brown ◽

...

Keyword(s):

Motor Neuron ◽

Motor Neurons ◽

Actin Polymerization ◽

Disease Model ◽

Actin Binding ◽

Wild Type ◽

Motor Neuron Degeneration ◽

Neuron Degeneration ◽

Type Protein ◽

Wild Type Protein

Mutations in the profilin 1 (PFN1) gene cause amyotrophic lateral sclerosis (ALS), a neurodegenerative disease caused by the loss of motor neurons leading to paralysis and eventually death. PFN1 is a small actin-binding protein that promotes formin-based actin polymerization and regulates numerous cellular functions, but how the mutations in PFN1 cause ALS is unclear. To investigate this problem, we have generated transgenic mice expressing either the ALS-associated mutant (C71G) or wild-type protein. Here, we report that mice expressing the mutant, but not the wild-type, protein had relentless progression of motor neuron loss with concomitant progressive muscle weakness ending in paralysis and death. Furthermore, mutant, but not wild-type, PFN1 forms insoluble aggregates, disrupts cytoskeletal structure, and elevates ubiquitin and p62/SQSTM levels in motor neurons. Unexpectedly, the acceleration of motor neuron degeneration precedes the accumulation of mutant PFN1 aggregates. These results suggest that although mutant PFN1 aggregation may contribute to neurodegeneration, it does not trigger its onset. Importantly, these experiments establish a progressive disease model that can contribute toward identifying the mechanisms of ALS pathogenesis and the development of therapeutic treatments.

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Fictive Swimming Motor Patterns in Wild Type and Mutant Larval Zebrafish

Journal of Neurophysiology ◽

10.1152/jn.01248.2004 ◽

2005 ◽

Vol 93 (6) ◽

pp. 3177-3188 ◽

Cited By ~ 95

Author(s):

Mark A. Masino ◽

Joseph R. Fetcho

Keyword(s):

Motor Neurons ◽

Motor Pattern ◽

The Body ◽

Wild Type ◽

Burst Frequency ◽

Motor Patterns ◽

Larval Zebrafish ◽

Lateral Undulation ◽

Glycinergic Inhibition ◽

Circuit Function

Larval zebrafish provide a unique model for investigating the mechanisms involved in generating rhythmic patterns of behavior, such as swimming, due to the array of techniques available including genetics, optical imaging, and conventional electrophysiology. Because electrophysiological and imaging studies of rhythmic motor behaviors in paralyzed preparations depend on the ability to monitor the central motor pattern, we developed a fictive preparation in which the activity of axial motor neurons was monitored using extracellular recordings from peripheral nerves. We examined spontaneous and light induced fictive motor patterns in wild type and mutant larval zebrafish (4–6 days post-fertilization) paralyzed with curare. All spontaneous and light-induced preparations produced alternation of motor activity from side-to-side (mean contralateral phase = 50.7 ± 7.0%; mean burst frequency = 35.6 ± 4.7 Hz) and a progression of activity from head-to-tail (mean ipsilateral rostrocaudal delay = 0.8 ± 0.5 ms per segment), consistent with lateral undulation and forward propulsion during swimming, respectively. The basic properties of the motor pattern were similar in spontaneous and light-induced swimming. This fictive preparation can be used in combination with conventional electrophysiological and imaging methods to investigate normal circuit function as well as to elucidate functional deficits in mutant lines. Toward this end, we show that two accordion class mutants, accordion and bandoneon, have alternating activity on opposite sides of the body, contradicting the hypothesis that their deficit results from the absence of the reciprocal glycinergic inhibition that is typically found in the spinal cord of swimming vertebrates.

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Circuit dysfunction in SOD1-ALS model first detected in sensory feedback prior to motor neuron degeneration is alleviated by BMP signaling

10.1101/484337 ◽

2018 ◽

Author(s):

Aaron Held ◽

Paxton Major ◽

Asli Sahin ◽

Robert Reenan ◽

Diane Lipscombe ◽

...

Keyword(s):

Motor Neuron ◽

Motor Function ◽

Motor Neurons ◽

Sensory Feedback ◽

Early Stage ◽

Bmp Signaling ◽

Motor Deficits ◽

Motor Neuron Degeneration ◽

Neuron Degeneration ◽

Motor Circuit

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease whose origin and underlying cellular defects are still not fully understood. While motor neuron degeneration is the signature feature of ALS, it is not yet clear if motor neurons, or other cells of the motor circuit, are the site of disease initiation. To better understand the contribution of multiple cell types in ALS, we made use of a Drosophila Sod1G85R knock-in model, in which all cells harbor the disease allele. End-stage dSod1G85R animals exhibit severe motor deficits with clear degeneration of motor neurons. Interestingly, earlier in dSod1G85R larvae motor function is also compromised, but their motor neurons exhibit only subtle morphological and electrophysiological changes, that are unlikely to cause the observed decrease in locomotion. We analyzed the intact motor circuit and identified a defect in sensory feedback that likely accounts for the altered motor activity of dSod1G85R. Furthermore, we found that the cell-autonomous activation of BMP signaling in proprioceptor sensory neurons that relay the contractile status of muscles back to the central nerve cord, is able to completely rescue early stage motor defects and partially rescue late stage motor function to extend lifespan. Identifying a defect in sensory feedback as a potential initiating event in ALS motor dysfunction, coupled with the ability of modified proprioceptors to alleviate such motor deficits, underscores the critical role that non-motor neurons play in disease progression and highlights their potential as a site to identify early-stage ALS biomarkers and for therapeutic intervention.

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