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 Building neuromuscular junctions in vitro

Development ◽  
2020 ◽  
Vol 147 (22) ◽  
pp. dev193920
Author(s):  
Susie Barbeau ◽  
Julie Tahraoui-Bories ◽  
Claire Legay ◽  
Cécile Martinat
Keyword(s):  
Human Disease ◽  
Molecular Mechanisms ◽  
Neuromuscular Junctions ◽  
Ex Vivo ◽  
Culture Methods ◽  
Recent Developments ◽  
Chemical Synapses ◽  
And Function

ABSTRACTThe neuromuscular junction (NMJ) has been the model of choice to understand the principles of communication at chemical synapses. Following groundbreaking experiments carried out over 60 years ago, many studies have focused on the molecular mechanisms underlying the development and physiology of these synapses. This Review summarizes the progress made to date towards obtaining faithful models of NMJs in vitro. We provide a historical approach discussing initial experiments investigating NMJ development and function from Xenopus to mice, the creation of chimeric co-cultures, in vivo approaches and co-culture methods from ex vivo and in vitro derived cells, as well as the most recent developments to generate human NMJs. We discuss the benefits of these techniques and the challenges to be addressed in the future for promoting our understanding of development and human disease.

Neuromuscular Junction Disorders

2021 ◽  
pp. 772-778
Author(s):  
Brent P. Goodman
Keyword(s):  
Neuromuscular Junction ◽  
Action Potential ◽  
Motor Unit ◽  
Safety Factor ◽  
Muscle Fiber ◽  
Nerve Terminal ◽  
Neuromuscular Transmission ◽  
Critical Component ◽  
End Plate ◽  
Unmyelinated Nerve

The neuromuscular junction (NMJ) is a critical component of the motor unit that is made up of the distal, unmyelinated nerve terminal, synaptic space, and end-plate region of the muscle fiber. Contraction of muscle fiber involves a coordinated series of steps that ultimately generates an action potential at the muscle end plate (also known as an end-plate potential). Normally the end-plate potential substantially exceeds the threshold necessary to trigger an action potential in the muscle fiber, and this difference is termed the safety factor of neuromuscular transmission. Disorders that affect the NMJ reduce this safety factor, a change that results in fatigable weakness.

scholarly journals Bioengineered model of the human motor unit with physiologically functional neuromuscular junctions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Rowan P. Rimington ◽  
Jacob W. Fleming ◽  
Andrew J. Capel ◽  
Patrick C. Wheeler ◽  
Mark P. Lewis
Keyword(s):  
Neuromuscular Junction ◽  
Motor Neuron ◽  
Motor Unit ◽  
Motor Nerve ◽  
Motor Units ◽  
Extracellular Matrices ◽  
Synaptic Membrane ◽  
Type I ◽  
Dependent Manner ◽  
Human Motor

AbstractInvestigations of the human neuromuscular junction (NMJ) have predominately utilised experimental animals, model organisms, or monolayer cell cultures that fail to represent the physiological complexity of the synapse. Consequently, there remains a paucity of data regarding the development of the human NMJ and a lack of systems that enable investigation of the motor unit. This work addresses this need, providing the methodologies to bioengineer 3D models of the human motor unit. Spheroid culture of iPSC derived motor neuron progenitors augmented the transcription of OLIG2, ISLET1 and SMI32 motor neuron mRNAs ~ 400, ~ 150 and ~ 200-fold respectively compared to monolayer equivalents. Axon projections of adhered spheroids exceeded 1000 μm in monolayer, with transcription of SMI32 and VACHT mRNAs further enhanced by addition to 3D extracellular matrices in a type I collagen concentration dependent manner. Bioengineered skeletal muscles produced functional tetanic and twitch profiles, demonstrated increased acetylcholine receptor (AChR) clustering and transcription of MUSK and LRP4 mRNAs, indicating enhanced organisation of the post-synaptic membrane. The number of motor neuron spheroids, or motor pool, required to functionally innervate 3D muscle tissues was then determined, generating functional human NMJs that evidence pre- and post-synaptic membrane and motor nerve axon co-localisation. Spontaneous firing was significantly elevated in 3D motor units, confirmed to be driven by the motor nerve via antagonistic inhibition of the AChR. Functional analysis outlined decreased time to peak twitch and half relaxation times, indicating enhanced physiology of excitation contraction coupling in innervated motor units. Our findings provide the methods to maximise the maturity of both iPSC motor neurons and primary human skeletal muscle, utilising cell type specific extracellular matrices and developmental timelines to bioengineer the human motor unit for the study of neuromuscular junction physiology.

scholarly journals Processing of ARIA and release from isolated nerve terminals

1999 ◽  
Vol 354 (1381) ◽  
pp. 411-416 ◽  
Author(s):  
Bomie Han ◽  
Gerald D. Fischbach
Keyword(s):  
Neuromuscular Junction ◽  
Action Potential ◽  
Acetylcholine Receptors ◽  
Molecular Layer ◽  
Postsynaptic Membrane ◽  
High Density ◽  
Small Contribution ◽  
Presynaptic Nerve Terminal ◽  
Voltage Gated

The neuromuscular junction is a specialized synapse in that every action potential in the presynaptic nerve terminal results in an action potential in the postsynaptic membrane, unlike most interneuronal synapses where a single presynaptic input makes only a small contribution to the population postsynaptic response. The postsynaptic membrane at the neuromuscular junction contains a high density of neurotransmitter (acetylcholine) receptors and a high density of voltage–gated Na + channels. Thus, the large acetylcholine activated current occurs at the same site where the threshold for action potential generation is low. Acetylcholine receptor inducing activity (ARIA), a 42 kD protein, that stimulates synthesis of acetylcholine receptors and voltage–gated Na + channels in cultured myotubes, probably plays the same roles at developing and mature motor endplates in vivo . ARIA is synthesized as part of a larger, transmembrane, precursor protein called proARIA. Delivery of ARIA from motor neuron cell bodies in the spinal cord to the target endplates involves several steps, including proteolytic cleavage of proARIA. ARIA is also expressed in the central nervous system and it is abundant in the molecular layer of the cerebellum. In this paper we describe our first experiments on the processing and release of ARIA from subcellular fractions containing synaptosomes from the chick cerebellum as a model system.

scholarly journals Fishing for Targets of Alien Metabolites: A Novel Peroxisome Proliferator-Activated Receptor (PPAR) Agonist from a Marine Pest

Marine Drugs ◽  
2018 ◽  
Vol 16 (11) ◽  
pp. 431 ◽  
Author(s):  
Rosa Vitale ◽  
Enrico D'Aniello ◽  
Stefania Gorbi ◽  
Andrea Martella ◽  
Cristoforo Silvestri ◽  
...  
Keyword(s):  
Native Species ◽  
Molecular Mechanisms ◽  
Ex Vivo ◽  
Invasion Biology ◽  
In Vitro Assays ◽  
Bioactive Metabolites ◽  
Peroxisome Proliferator ◽  
Invasive Pests

Although the chemical warfare between invasive and native species has become a central problem in invasion biology, the molecular mechanisms by which bioactive metabolites from invasive pests influence local communities remain poorly characterized. This study demonstrates that the alkaloid caulerpin (CAU)—a bioactive component of the green alga Caulerpa cylindracea that has invaded the entire Mediterranean basin—is an agonist of peroxisome proliferator-activated receptors (PPARs). Our interdisciplinary study started with the in silico prediction of the ligand-protein interaction, which was then validated by in vivo, ex vivo and in vitro assays. On the basis of these results, we candidate CAU as a causal factor of the metabolic and behavioural disorders observed in Diplodus sargus, a native edible fish of high ecological and commercial relevance, feeding on C. cylindracea. Moreover, given the considerable interest in PPAR activators for the treatment of relevant human diseases, our findings are also discussed in terms of a possible nutraceutical/pharmacological valorisation of the invasive algal biomasses, supporting an innovative strategy for conserving biodiversity as an alternative to unrealistic campaigns for the eradication of invasive pests.

scholarly journals hPSC-Derived Enteric Ganglioids Model Human ENS Development and Function

2022 ◽  
Author(s):  
Homa Majd ◽  
Ryan M Samuel ◽  
Jonathan T Ramirez ◽  
Ali Kalantari ◽  
Kevin Barber ◽  
...  
Keyword(s):  
Ex Vivo ◽  
Xenograft Model ◽  
Developmental Relationships ◽  
Drug Candidates ◽  
Effective Strategies ◽  
Wide Range ◽  
Functional Features ◽  
And Function

The enteric nervous system (ENS) plays a central role in gut physiology and mediating the crosstalk between the gastrointestinal (GI) tract and other organs. The human ENS has remained elusive, highlighting the need for an in vitro modeling and mapping blueprint. Here we map out the developmental and functional features of the human ENS, by establishing robust and scalable 2D ENS cultures and 3D enteric ganglioids from human pluripotent stem cells (hPSCs). These models recapitulate the remarkable neuronal and glial diversity found in primary tissue and enable comprehensive molecular analyses that uncover functional and developmental relationships within these lineages. As a salient example of the power of this system, we performed in-depth characterization of enteric nitrergic neurons (NO neurons) which are implicated in a wide range of GI motility disorders. We conducted an unbiased screen and identified drug candidates that modulate the activity of NO neurons and demonstrated their potential in promoting motility in mouse colonic tissue ex vivo. We established a high-throughput strategy to define the developmental programs involved in NO neuron specification and discovered that PDGFR inhibition boosts the induction of NO neurons in enteric ganglioids. Transplantation of these ganglioids in the colon of NO neuron-deficient mice results in extensive tissue engraftment, providing a xenograft model for the study of human ENS in vivo and the development of cell-based therapies for neurodegenerative GI disorders. These studies provide a framework for deciphering fundamental features of the human ENS and designing effective strategies to treat enteric neuropathies.  

scholarly journals Microbial enzymes induce colitis by reactivating triclosan in the mouse gastrointestinal tract

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Jianan Zhang ◽  
Morgan E. Walker ◽  
Katherine Z. Sanidad ◽  
Hongna Zhang ◽  
Yanshan Liang ◽  
...  
Keyword(s):  
Gut Microbiota ◽  
Molecular Mechanisms ◽  
Ex Vivo ◽  
Metabolic Activation ◽  
Consumer Products ◽  
Environmental Chemicals ◽  
Intestinal Microbes ◽  
Targeted Inhibition

AbstractEmerging research supports that triclosan (TCS), an antimicrobial agent found in thousands of consumer products, exacerbates colitis and colitis-associated colorectal tumorigenesis in animal models. While the intestinal toxicities of TCS require the presence of gut microbiota, the molecular mechanisms involved have not been defined. Here we show that intestinal commensal microbes mediate metabolic activation of TCS in the colon and drive its gut toxicology. Using a range of in vitro, ex vivo, and in vivo approaches, we identify specific microbial β-glucuronidase (GUS) enzymes involved and pinpoint molecular motifs required to metabolically activate TCS in the gut. Finally, we show that targeted inhibition of bacterial GUS enzymes abolishes the colitis-promoting effects of TCS, supporting an essential role of specific microbial proteins in TCS toxicity. Together, our results define a mechanism by which intestinal microbes contribute to the metabolic activation and gut toxicity of TCS, and highlight the importance of considering the contributions of the gut microbiota in evaluating the toxic potential of environmental chemicals.

scholarly journals Molecular Mechanisms of Aroma Persistence: From Noncovalent Interactions Between Aroma Compounds and Oral Mucosa to Metabolization of Aroma Compounds by Saliva and Oral Cells

2021 ◽  
Author(s):  
Carolina Muñoz-Gonzalez ◽  
Marine Brulé ◽  
Christophe Martin ◽  
Gilles Feron ◽  
Francis Canon
Keyword(s):  
Oral Mucosa ◽  
Molecular Mechanisms ◽  
Ex Vivo ◽  
Noncovalent Interactions ◽  
Aroma Compounds ◽  
Integral Approach ◽  
Exhaled Air ◽  
Oral Cells ◽  
Novel Model

<p>Aroma persistence plays a major role in the liking and wanting of orally consumed products (food, dental toiletries, tobacco, drugs, etc.). Here, we use an integral approach including <i>ex vivo</i> experiments using a novel model of oral mucosa and saliva in well controlled conditions as well as <i>in vivo</i> dynamic instrumental and sensory experiments. <i>Ex vivo</i> experiments show the ability of the mucosal pellicle, the thin layer of salivary proteins covering the oral mucosa, to interact with aroma compounds, as well as the ability of oral cells and saliva to metabolize carbonyl aroma compounds. <i>In vivo</i> evaluation of the exhaled air and perception of individuals after aroma sample consumption confirm <i>ex vivo</i> findings in a more real context. Thus, aroma compounds susceptible to be metabolized by saliva and oral cells show a lower aroma persistence than non metabolized compounds, for which other mechanisms such as the adsorption at the surface of the oral mucosa (mucosal pellicle) as a function of their hydrophobicity are involved. Thus, we argue that the physiological aspects occurring during the oral processing, and especially, metabolization of aroma compounds, have to be considered when studying the phenomenon of aroma persistence.</p>

scholarly journals Understanding the Effects of General Anesthetics on Cortical Network Activity Using Ex Vivo Preparations

2019 ◽  
Vol 130 (6) ◽  
pp. 1049-1063 ◽  
Author(s):  
Logan J. Voss ◽  
Paul S. García ◽  
Harald Hentschke ◽  
Matthew I. Banks
Keyword(s):  
Molecular Mechanisms ◽  
Ex Vivo ◽  
Brain Slices ◽  
Brain Regions ◽  
Cortical Network ◽  
Network Activity ◽  
Common Mechanism ◽  
General Anesthetics ◽  
Neural Basis

Abstract General anesthetics have been used to ablate consciousness during surgery for more than 150 yr. Despite significant advances in our understanding of their molecular-level pharmacologic effects, comparatively little is known about how anesthetics alter brain dynamics to cause unconsciousness. Consequently, while anesthesia practice is now routine and safe, there are many vagaries that remain unexplained. In this paper, the authors review the evidence that cortical network activity is particularly sensitive to general anesthetics, and suggest that disruption to communication in, and/or among, cortical brain regions is a common mechanism of anesthesia that ultimately produces loss of consciousness. The authors review data from acute brain slices and organotypic cultures showing that anesthetics with differing molecular mechanisms of action share in common the ability to impair neurophysiologic communication. While many questions remain, together, ex vivo and in vivo investigations suggest that a unified understanding of both clinical anesthesia and the neural basis of consciousness is attainable.

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