scholarly journals APP interacts with LRP4 and agrin to coordinate the development of the neuromuscular junction in mice

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Hong Y Choi ◽  
Yun Liu ◽  
Christian Tennert ◽  
Yoshie Sugiura ◽  
Andromachi Karakatsani ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Molecular Mechanisms ◽  
Synapse Formation ◽  
Transmembrane Domain ◽  
Neuromuscular Synapse ◽  
Apoe Receptor ◽  
Cultured Myotubes ◽  
Perinatal Lethality ◽  
And Function ◽  
Achr Clustering

ApoE, ApoE receptors and APP cooperate in the pathogenesis of Alzheimer’s disease. Intriguingly, the ApoE receptor LRP4 and APP are also required for normal formation and function of the neuromuscular junction (NMJ). In this study, we show that APP interacts with LRP4, an obligate co-receptor for muscle-specific tyrosine kinase (MuSK). Agrin, a ligand for LRP4, also binds to APP and co-operatively enhances the interaction of APP with LRP4. In cultured myotubes, APP synergistically increases agrin-induced acetylcholine receptor (AChR) clustering. Deletion of the transmembrane domain of LRP4 (LRP4 ECD) results in growth retardation of the NMJ, and these defects are markedly enhanced in APP−/−;LRP4ECD/ECD mice. Double mutant NMJs are significantly reduced in size and number, resulting in perinatal lethality. Our findings reveal novel roles for APP in regulating neuromuscular synapse formation through hetero-oligomeric interaction with LRP4 and agrin and thereby provide new insights into the molecular mechanisms that govern NMJ formation and maintenance.

scholarly journals Neuregulin/ErbB regulate neuromuscular junction development by phosphorylation of α-dystrobrevin

2011 ◽  
Vol 195 (7) ◽  
pp. 1171-1184 ◽  
Author(s):  
Nadine Schmidt ◽  
Mohammed Akaaboune ◽  
Nadesan Gajendran ◽  
Isabel Martinez-Pena y Valenzuela ◽  
Sarah Wakefield ◽  
...  
Keyword(s):  
Nervous System ◽  
Synaptic Transmission ◽  
Acetylcholine Receptors ◽  
Synapse Formation ◽  
Neuromuscular Synapse ◽  
Muscle Membrane ◽  
Erbb Signaling ◽  
Cultured Myotubes ◽  
The Stability ◽  
And Function

Neuregulin (NRG)/ErbB signaling is involved in numerous developmental processes in the nervous system, including synapse formation and function in the central nervous system. Although intensively investigated, its role at the neuromuscular synapse has remained elusive. Here, we demonstrate that loss of neuromuscular NRG/ErbB signaling destabilized anchoring of acetylcholine receptors (AChRs) in the postsynaptic muscle membrane and that this effect was caused by dephosphorylation of α-dystrobrevin1, a component of the postsynaptic scaffold. Specifically, in mice in which NRG signaling to muscle was genetically or pharmacologically abolished, postsynaptic AChRs moved rapidly from the synaptic to the perisynaptic membrane, and the subsynaptic scaffold that anchors the AChRs was impaired. These defects combined compromised synaptic transmission. We further show that blockade of NRG/ErbB signaling abolished tyrosine phosphorylation of α-dystrobrevin1, which reduced the stability of receptors in agrin-induced AChR clusters in cultured myotubes. Our data indicate that NRG/ErbB signaling maintains high efficacy of synaptic transmission by stabilizing the postsynaptic apparatus via phosphorylation of α-dystrobrevin1.

Astrocyte-neuron crosstalk through Hedgehog signaling mediates cortical circuit assembly

2020 ◽  
Author(s):  
Yajun Xie ◽  
Aaron T. Kuan ◽  
Wengang Wang ◽  
Zachary T. Herbert ◽  
Olivia Mosto ◽  
...  
Keyword(s):  
Cortical Neurons ◽  
Molecular Mechanisms ◽  
Synapse Formation ◽  
Critical Role ◽  
Shh Signaling ◽  
Shh Pathway ◽  
Cortical Astrocytes ◽  
Functional Features ◽  
And Function ◽  
Circuit Assembly

SUMMARYNeuron-glia relationships play a critical role in the regulation of synapse formation and neuronal specification. The cellular and molecular mechanisms by which neurons and astrocytes communicate and coordinate are not well understood. Here we demonstrate that the canonical Sonic hedgehog (Shh) pathway is active in cortical astrocytes, where it acts to coordinate layer-specific synaptic connectivity and functional circuit development. We show that Ptch1 is a Shh receptor that is expressed by cortical astrocytes during development and that Shh signaling is necessary and sufficient to promote the expression of layer-specific astrocyte genes involved in regulating synapse formation and function. Loss of Shh in layer V neurons reduces astrocyte complexity and coverage by astrocytic processes in tripartite synapses, moreover, cell-autonomous activation of Shh signaling in astrocytes promotes cortical excitatory synapse formation. Together, these results suggest that Shh secreted from deep layer cortical neurons acts to specialize the molecular and functional features of astrocytes during development to shape circuit assembly and function.

scholarly journals Effect of salbutamol on neuromuscular junction function and structure in a mouse model of DOK7 congenital myasthenia

2020 ◽  
Vol 29 (14) ◽  
pp. 2325-2336 ◽  
Author(s):  
Richard G Webster ◽  
An E Vanhaesebrouck ◽  
Susan E Maxwell ◽  
Judith A Cossins ◽  
Weiwei Liu ◽  
...  
Keyword(s):  
Weight Gain ◽  
Neuromuscular Junction ◽  
Mouse Model ◽  
Structural Integrity ◽  
Ex Vivo ◽  
Adrenergic Agonists ◽  
Mice Model ◽  
Synaptic Structure ◽  
Perinatal Lethality ◽  
And Function

Abstract Congenital myasthenic syndromes (CMS) are characterized by fatigable muscle weakness resulting from impaired neuromuscular transmission. β2-adrenergic agonists are an effective treatment for DOK7-CMS. DOK7 is a component within the AGRN-LRP4-MUSK-DOK7 signalling pathway that is key for the formation and maintenance of the synaptic structure of the neuromuscular junction (NMJ). The precise mechanism of action of β2-adrenergic agonists at the NMJ is not fully understood. In this study, we investigated whether β2-adrenergic agonists improve both neurotransmission and structural integrity of the NMJ in a mouse model of DOK7-CMS. Ex-vivo electrophysiological techniques and microscopy of the NMJ were used to study the effect of salbutamol, a β2-adrenergic agonist, on synaptic structure and function. DOK7-CMS model mice displayed a severe phenotype with reduced weight gain and perinatal lethality. Salbutamol treatment improved weight gain and survival in DOK7 myasthenic mice. Model animals had fewer active NMJs, detectable by endplate recordings, compared with age-matched wild-type littermates. Salbutamol treatment increased the number of detectable NMJs during endplate recording. Correspondingly, model mice had fewer acetylcholine receptor-stained NMJs detected by fluorescent labelling, but following salbutamol treatment an increased number were detectable. The data demonstrate that salbutamol can prolong survival and increase NMJ number in a severe model of DOK7-CMS.

scholarly journals Neurexin–Neuroligin 1 regulates synaptic morphology and functions via the WAVE regulatory complex in Drosophila neuromuscular junction

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Guanglin Xing ◽  
Moyi Li ◽  
Yichen Sun ◽  
Menglong Rui ◽  
Yan Zhuang ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Molecular Mechanisms ◽  
Postsynaptic Membrane ◽  
Synaptic Function ◽  
Actin Assembly ◽  
Actin Reorganization ◽  
Synaptic Structure ◽  
Structural And Functional Properties ◽  
Regulatory Complex ◽  
And Function

Neuroligins are postsynaptic adhesion molecules that are essential for postsynaptic specialization and synaptic function. But the underlying molecular mechanisms of neuroligin functions remain unclear. We found that Drosophila Neuroligin 1 (DNlg1) regulates synaptic structure and function through WAVE regulatory complex (WRC)-mediated postsynaptic actin reorganization. The disruption of DNlg1, DNlg2, or their presynaptic partner neurexin (DNrx) led to a dramatic decrease in the amount of F-actin. Further study showed that DNlg1, but not DNlg2 or DNlg3, directly interacts with the WRC via its C-terminal interacting receptor sequence. That interaction is required to recruit WRC to the postsynaptic membrane to promote F-actin assembly. Furthermore, the interaction between DNlg1 and the WRC is essential for DNlg1 to rescue the morphological and electrophysiological defects in dnlg1 mutants. Our results reveal a novel mechanism by which the DNrx-DNlg1 trans-synaptic interaction coordinates structural and functional properties at the neuromuscular junction.

scholarly journals The Neuromuscular Junction in Health and Disease: Molecular Mechanisms Governing Synaptic Formation and Homeostasis

2020 ◽  
Vol 13 ◽  
Author(s):  
Pedro M. Rodríguez Cruz ◽  
Judith Cossins ◽  
David Beeson ◽  
Angela Vincent
Keyword(s):  
Neuromuscular Junction ◽  
Action Potential ◽  
Motor Neuron ◽  
Muscle Fiber ◽  
Neuromuscular Transmission ◽  
Molecular Mechanisms ◽  
Ex Vivo ◽  
Motor Nerve ◽  
And Function

The neuromuscular junction (NMJ) is a highly specialized synapse between a motor neuron nerve terminal and its muscle fiber that are responsible for converting electrical impulses generated by the motor neuron into electrical activity in the muscle fibers. On arrival of the motor nerve action potential, calcium enters the presynaptic terminal, which leads to the release of the neurotransmitter acetylcholine (ACh). ACh crosses the synaptic gap and binds to ACh receptors (AChRs) tightly clustered on the surface of the muscle fiber; this leads to the endplate potential which initiates the muscle action potential that results in muscle contraction. This is a simplified version of the events in neuromuscular transmission that take place within milliseconds, and are dependent on a tiny but highly structured NMJ. Much of this review is devoted to describing in more detail the development, maturation, maintenance and regeneration of the NMJ, but first we describe briefly the most important molecules involved and the conditions that affect their numbers and function. Most important clinically worldwide, are myasthenia gravis (MG), the Lambert-Eaton myasthenic syndrome (LEMS) and congenital myasthenic syndromes (CMS), each of which causes specific molecular defects. In addition, we mention the neurotoxins from bacteria, snakes and many other species that interfere with neuromuscular transmission and cause potentially fatal diseases, but have also provided useful probes for investigating neuromuscular transmission. There are also changes in NMJ structure and function in motor neuron disease, spinal muscle atrophy and sarcopenia that are likely to be secondary but might provide treatment targets. The NMJ is one of the best studied and most disease-prone synapses in the nervous system and it is amenable to in vivo and ex vivo investigation and to systemic therapies that can help restore normal function.

scholarly journals Neuron–glia interactions: the roles of Schwann cells in neuromuscular synapse formation and function

2011 ◽  
Vol 31 (5) ◽  
pp. 295-302 ◽  
Author(s):  
Yoshie Sugiura ◽  
Weichun Lin
Keyword(s):  
Schwann Cells ◽  
Motor Neurons ◽  
Nerve Terminal ◽  
Synapse Formation ◽  
Neuromuscular Synapse ◽  
Synaptic Activity ◽  
Nerve Terminals ◽  
Presynaptic Nerve Terminal ◽  
Presynaptic Nerve Terminals ◽  
And Function

The NMJ (neuromuscular junction) serves as the ultimate output of the motor neurons. The NMJ is composed of a presynaptic nerve terminal, a postsynaptic muscle and perisynaptic glial cells. Emerging evidence has also demonstrated an existence of perisynaptic fibroblast-like cells at the NMJ. In this review, we discuss the importance of Schwann cells, the glial component of the NMJ, in the formation and function of the NMJ. During development, Schwann cells are closely associated with presynaptic nerve terminals and are required for the maintenance of the developing NMJ. After the establishment of the NMJ, Schwann cells actively modulate synaptic activity. Schwann cells also play critical roles in regeneration of the NMJ after nerve injury. Thus, Schwann cells are indispensable for formation and function of the NMJ. Further examination of the interplay among Schwann cells, the nerve and the muscle will provide insights into a better understanding of mechanisms underlying neuromuscular synapse formation and function.

scholarly journals The highly conserved synapsin domain E mediates synapsin dimerization and phospholipid vesicle clustering

2010 ◽  
Vol 426 (1) ◽  
pp. 55-64 ◽  
Author(s):  
Ilaria Monaldi ◽  
Massimo Vassalli ◽  
Angela Bachi ◽  
Silvia Giovedì ◽  
Enrico Millo ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Synapse Formation ◽  
Phospholipid Composition ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Phospholipid Vesicle ◽  
Synapsin I ◽  
Protein Partners ◽  
And Function ◽  
Necessary And Sufficient

Synapsins are abundant SV (synaptic vesicle)-associated phosphoproteins that regulate synapse formation and function. The highly conserved C-terminal domain E was shown to contribute to several synapsin functions, ranging from formation of the SV reserve pool to regulation of the kinetics of exocytosis and SV cycling, although the molecular mechanisms underlying these effects are unknown. In the present study, we used a synthetic 25-mer peptide encompassing the most conserved region of domain E (Pep-E) to analyse the role of domain E in regulating the interactions between synapsin I and liposomes mimicking the phospholipid composition of SVs (SV–liposomes) and other pre-synaptic protein partners. In affinity-chromatography and cross-linking assays, Pep-E bound to endogenous and purified exogenous synapsin I and strongly inhibited synapsin dimerization, indicating a role in synapsin oligomerization. Consistently, Pep-E (but not its scrambled version) counteracted the ability of holo-synapsin I to bind and coat phospholipid membranes, as analysed by AFM (atomic force microscopy) topographical scanning, and significantly decreased the clustering of SV–liposomes induced by holo-synapsin I in FRET (Förster resonance energy transfer) assays, suggesting a causal relationship between synapsin oligomerization and vesicle clustering. Either Pep-E or a peptide derived from domain C was necessary and sufficient to inhibit both dimerization and vesicle clustering, indicating the participation of both domains in these activities of synapsin I. The results provide a molecular explanation for the effects of domain E in nerve terminal physiology and suggest that its effects on the size and integrity of SV pools are contributed by the regulation of synapsin dimerization and SV clustering.

scholarly journals Neurotrophin signaling among neurons and glia during formation of tripartite synapses

2004 ◽  
Vol 1 (4) ◽  
pp. 339-349 ◽  
Author(s):  
SARINA B. ELMARIAH ◽  
ETHAN G. HUGHES ◽  
EUN JOO OH ◽  
RITA J. BALICE-GORDON
Keyword(s):  
Gabaa Receptor ◽  
Molecular Mechanisms ◽  
Synapse Formation ◽  
Synaptic Modulators ◽  
Central Synapses ◽  
Receptor Clusters ◽  
And Function ◽  
Neurotrophin Signaling

Synapse formation in the CNS is a complex process that involves the dynamic interplay of numerous signals exchanged between pre- and postsynaptic neurons as well as perisynaptic glia. Members of the neurotrophin family, which are widely expressed in the developing and mature CNS and are well-known for their roles in promoting neuronal survival and differentiation, have emerged as key synaptic modulators. However, the mechanisms by which neurotrophins modulate synapse formation and function are poorly understood. Here, we summarize our work on the role of neurotrophins in synaptogenesis in the CNS, in particular the role of these signaling molecules and their receptors, the Trks, in the development of excitatory and inhibitory hippocampal synapses. We discuss our results that demonstrate that postsynaptic TrkB signaling plays an important role in modulating the formation and maintenance of NMDA and GABAA receptor clusters at central synapses, and suggest that neurotrophin signaling coordinately modulates these receptors as part of mechanism that promotes the balance between excitation and inhibition in developing circuits. We also discuss our results that demonstrate that astrocytes promote the formation of GABAergic synapses in vitro by differentially regulating the development of inhibitory presynaptic terminals and postsynaptic GABAA receptor clusters, and suggest that glial modulation of inhibitory synaptogenesis is mediated by neurotrophin-dependent and -independent signaling. Together, these findings extend our understanding of how neuron–glia communication modulates synapse formation, maintenance and function, and set the stage for defining the cellular and molecular mechanisms by which neurotrophins and other cell–cell signals direct synaptogenesis in the developing brain.

scholarly journals A novel pathway for MuSK to induce key genes in neuromuscular synapse formation

2003 ◽  
Vol 161 (4) ◽  
pp. 727-736 ◽  
Author(s):  
Eric Lacazette ◽  
Sophie Le Calvez ◽  
Nadesan Gajendran ◽  
Hans Rudolf Brenner
Keyword(s):  
Synapse Formation ◽  
Regulatory Element ◽  
Neuromuscular Synapse ◽  
Expression Vectors ◽  
The Novel ◽  
Reporter Construct ◽  
Specific Expression ◽  
Cultured Myotubes ◽  
Signaling Components

At the developing neuromuscular junction the Agrin receptor MuSK is the central organizer of subsynaptic differentiation induced by Agrin from the nerve. The expression of musk itself is also regulated by the nerve, but the mechanisms involved are not known. Here, we analyzed the activation of a musk promoter reporter construct in muscle fibers in vivo and in cultured myotubes, using transfection of multiple combinations of expression vectors for potential signaling components. We show that neuronal Agrin by activating MuSK regulates the expression of musk via two pathways: the Agrin-induced assembly of muscle-derived neuregulin (NRG)-1/ErbB, the pathway thought to regulate acetylcholine receptor (AChR) expression at the synapse, and via a direct shunt involving Agrin-induced activation of Rac. Both pathways converge onto the same regulatory element in the musk promoter that is also thought to confer synapse-specific expression to AChR subunit genes. In this way, a positive feedback signaling loop is established that maintains musk expression at the synapse when impulse transmission becomes functional. The same pathways are used to regulate synaptic expression of AChRε . We propose that the novel pathway stabilizes the synapse early in development, whereas the NRG/ErbB pathway supports maintenance of the mature synapse.

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