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Dissanayake KN, Redman RR, Mackenzie H, Eddleston M, Ribchester RR. "Calcium bombs" as harbingers of synaptic pathology and their mitigation by magnesium at murine neuromuscular junctions. Front Mol Neurosci 2022; 15:937974. [PMID: 35959105 PMCID: PMC9361872 DOI: 10.3389/fnmol.2022.937974] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Accepted: 07/04/2022] [Indexed: 12/24/2022] Open
Abstract
Excitotoxicity is thought to be an important factor in the onset and progression of amyotrophic lateral sclerosis (ALS). Evidence from human and animal studies also indicates that early signs of ALS include degeneration of motor nerve terminals at neuromuscular junctions (NMJs), before degeneration of motor neuron cell bodies. Here we used a model of excitotoxicity at NMJs in isolated mouse muscle, utilizing the organophosphorus (OP) compound omethoate, which inhibits acetylcholinesterase activity. Acute exposure to omethoate (100 μM) induced prolonged motor endplate contractures in response to brief tetanic nerve stimulation at 20-50 Hz. In some muscle fibers, Fluo-4 fluorescence showed association of these contractures with explosive increases in Ca2+ ("calcium bombs") localized to motor endplates. Calcium bombs were strongly and selectively mitigated by increasing Mg2+ concentration in the bathing medium from 1 to 5 mM. Overnight culture of nerve-muscle preparations from WldS mice in omethoate or other OP insecticide components and their metabolites (dimethoate, cyclohexanone, and cyclohexanol) induced degeneration of NMJs. This degeneration was also strongly mitigated by increasing [Mg2+] from 1 to 5 mM. Thus, equivalent increases in extracellular [Mg2+] mitigated both post-synaptic calcium bombs and degeneration of NMJs. The data support a link between Ca2+ and excitotoxicity at NMJs and suggest that elevating extracellular [Mg2+] could be an effective intervention in treatment of synaptic pathology induced by excitotoxic triggers.
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Affiliation(s)
- Kosala N. Dissanayake
- Euan MacDonald Centre for Motor Neurone Disease Research, The University of Edinburgh, Edinburgh, United Kingdom,Centre for Discovery Brain Sciences, The University of Edinburgh, Edinburgh, United Kingdom
| | - Robert R. Redman
- Euan MacDonald Centre for Motor Neurone Disease Research, The University of Edinburgh, Edinburgh, United Kingdom,Centre for Discovery Brain Sciences, The University of Edinburgh, Edinburgh, United Kingdom
| | - Harry Mackenzie
- Euan MacDonald Centre for Motor Neurone Disease Research, The University of Edinburgh, Edinburgh, United Kingdom,Centre for Discovery Brain Sciences, The University of Edinburgh, Edinburgh, United Kingdom
| | - Michael Eddleston
- Clinical Pharmacology, Toxicology and Therapeutics, Centre for Cardiovascular Science, Queen’s Medical Research Institute, The University of Edinburgh, Edinburgh, United Kingdom
| | - Richard R. Ribchester
- Euan MacDonald Centre for Motor Neurone Disease Research, The University of Edinburgh, Edinburgh, United Kingdom,Centre for Discovery Brain Sciences, The University of Edinburgh, Edinburgh, United Kingdom,*Correspondence: Richard R. Ribchester,
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Yang X, Yun Y, Wang P, Zhao J, Sun X. Upregulation of RCAN1.4 by HIF1α alleviates OGD-induced inflammatory response in astrocytes. Ann Clin Transl Neurol 2022; 9:1224-1240. [PMID: 35836352 PMCID: PMC9380140 DOI: 10.1002/acn3.51624] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2022] [Revised: 06/03/2022] [Accepted: 06/28/2022] [Indexed: 11/11/2022] Open
Abstract
Objective Ischemic stroke is a leading cause of human mortality and long‐term disability worldwide. As one of the main forms of regulator of calcineurin 1 (RCAN1), the contribution of RCAN1.4 in diverse biological and pathological conditions has been implicated. But the role of RCAN1.4 in ischemic stroke progression remains elusive. This study is to explore the expression changes and roles of RCAN1.4 in ischemic stroke as well as the underlying mechanisms for these changes and effects of RCAN1.4 in ischemic stroke. Methods Middle cerebral artery occlusion model in C57BL/6J mice and oxygen–glucose deprivation (OGD) model in primary astrocytes were performed to induce the cerebral ischemic stroke. The expression pattern of RCAN1.4 was assessed using real‐time quantitative PCR and western blotting in vivo and in vitro. Mechanistically, the underlying mechanism for the elevation of RCAN1.4 in the upstream was investigated. Lentiviruses were administrated, and the effect of RCAN1.4 in postischemic inflammation was clearly clarified. Results Here we uncovered that RCAN1.4 was dramatically increased in mouse ischemic brains and OGD‐induced primary astrocytes. HIF1α, activated upon OGD, significantly upregulated RCAN1.4 gene expression through specifically binding to the RCAN1.4 promoter region and activating its promoter activity. The functional hypoxia‐responsive element (HRE) was located between −254 and −245 bp in the RCAN1.4 promoter region. Moreover, elevated RCAN1.4 alleviated the release of pro‐inflammatory cytokines TNFα, IL1β, IL6 and reduced expression of iNOS, COX2 in primary astrocytes upon OGD, whereas RCAN1.4 silencing has the opposite effect. Of note, RCAN1.4 overexpression inhibited OGD‐induced NF‐κB activation in primary astrocytes, leading to decreased degradation of IκBα and reduced nuclear translocation of NF‐κB/p65. Interpretation Our results reveal a novel mechanism underscoring the upregulation of RCAN1.4 by HIF1α and the protective effect of RCAN1.4 against postischemic inflammation, suggesting its significance as a promising therapeutic target for ischemic stroke treatment.
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Affiliation(s)
- Xiaxin Yang
- Department of Neurology, Qilu Hospital of Shandong University, Jinan, Shandong Province, China
| | - Yan Yun
- Department of Radiology, Qilu Hospital of Shandong University, Jinan, Shandong Province, China
| | - Pin Wang
- NHC Key Laboratory of Otorhinolaryngology, Qilu Hospital of Shandong University, Jinan, Shandong Province, China.,Department of Otorhinolaryngology, Qilu Hospital of Shandong University, Jinan, Shandong Province, China
| | - Juan Zhao
- NHC Key Laboratory of Otorhinolaryngology, Qilu Hospital of Shandong University, Jinan, Shandong Province, China.,Department of Otorhinolaryngology, Qilu Hospital of Shandong University, Jinan, Shandong Province, China
| | - Xiulian Sun
- NHC Key Laboratory of Otorhinolaryngology, Qilu Hospital of Shandong University, Jinan, Shandong Province, China.,Brain Research Institute, Qilu Hospital of Shandong University, Jinan, Shandong Province, China.,The Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education, Chinese National Health Commission, Qilu Hospital of Shandong University, Jinan, Shandong Province, China
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Samigullin DV, Khaziev EF, Zhilyakov NV, Bukharaeva EA, Nikolsky EE. Loading a Calcium Dye into Frog Nerve Endings Through the Nerve Stump: Calcium Transient Registration in the Frog Neuromuscular Junction. J Vis Exp 2017. [PMID: 28715368 PMCID: PMC5609652 DOI: 10.3791/55122] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
One of the most feasible methods of measuring presynaptic calcium levels in presynaptic nerve terminals is optical recording. It is based on using calcium-sensitive fluorescent dyes that change their emission intensity or wavelength depending on the concentration of free calcium in the cell. There are several methods used to stain cells with calcium dyes. Most common are the processes of loading the dyes through a micropipette or pre-incubating with the acetoxymethyl ester forms of the dyes. However, these methods are not quite applicable to neuromuscular junctions (NMJs) due to methodological issues that arise. In this article, we present a method for loading a calcium-sensitive dye through the frog nerve stump of the frog nerve into the nerve endings. Since entry of external calcium into nerve terminals and the subsequent binding to the calcium dye occur within the millisecond time-scale, it is necessary to use a fast imaging system to record these interactions. Here, we describe a protocol for recording the calcium transient with a fast CCD camera.
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Affiliation(s)
- Dmitry V Samigullin
- Laboratory of Biophysics of Synaptic Processes, Kazan Scientific Centre, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences; Open Laboratory of Neuropharmacology, Kazan Federal University; Department of Radiophotonics and Microwave Technologies, A.N. Tupolev Kazan National Research Technical University;
| | - Eduard F Khaziev
- Laboratory of Biophysics of Synaptic Processes, Kazan Scientific Centre, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences; Open Laboratory of Neuropharmacology, Kazan Federal University; Department of Radiophotonics and Microwave Technologies, A.N. Tupolev Kazan National Research Technical University
| | - Nikita V Zhilyakov
- Laboratory of Biophysics of Synaptic Processes, Kazan Scientific Centre, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences; Open Laboratory of Neuropharmacology, Kazan Federal University
| | - Ellya A Bukharaeva
- Laboratory of Biophysics of Synaptic Processes, Kazan Scientific Centre, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences; Open Laboratory of Neuropharmacology, Kazan Federal University
| | - Eugeny E Nikolsky
- Laboratory of Biophysics of Synaptic Processes, Kazan Scientific Centre, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences; Open Laboratory of Neuropharmacology, Kazan Federal University; Department of Medical and Biological Physics, Kazan State Medical University
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Zhang B, Yang Y, Tang J, Tao Y, Jiang B, Chen Z, Feng H, Yang L, Zhu G. Establishment of mouse neuron and microglial cell co-cultured models and its action mechanism. Oncotarget 2017; 8:43061-43067. [PMID: 28574841 PMCID: PMC5522127 DOI: 10.18632/oncotarget.17898] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2017] [Accepted: 04/15/2017] [Indexed: 01/02/2023] Open
Abstract
OBJECTIVE The objective of this study is to establish a co-culture model of mouse neurons and microglial cells, and to analyze the mechanism of action of oxygen glucose deprivation (OGD) and transient oxygen glucose deprivation (tOGD) preconditioning cell models. RESULTS Mouse primary neurons and BV2 microglial cells were successfully cultured, and the OGD and tOGD models were also established. In the co-culture of mouse primary neurons and microglial cells, the cell number of tOGD mouse neurons and microglial cells was larger than the OGD cell number, observed by a microscope. CCK-8 assay result showed that at 1h after treatment, the OD value in the control group is lower compared to all the other three groups (P < 0.05). The treatment group exhibited the highest OD value among the four groups. The results observed at 5h were consistent with the results at 1 h. Flow cytometry results showed that at 1h after treatment the apoptosis percentages is higher in the control group compared to other three groups (P < 0.05). MATERIALS AND METHODS Mouse brain tissues were collected and primary neurons cells were cultured. In the meantime mouse BV2 microglia cells were cultured. Two types of cells were co-cultured, and OGD and tOGD cell models were established. There were four groups in the experiment: control group (OGD), treatment group (tOGD+OGD), placebo group (tOGD+OGD+saline) and minocycline intervention group (tOGD+OGD+minocycline). CCK-8 kit was used to detect cell viability and flow cytometry was used to detect apoptosis. CONCLUSIONS In this study, mouse primary neurons and microglial cells were co-cultured. The OGD and tOGD models were established successfully. tOGD was able to effectively protect neurons and microglial cells from damage, and inhibit the apoptosis caused by oxygen glucose deprivation.
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Affiliation(s)
- Bo Zhang
- Department of Neurosurgery, Southwest Hospital,Third Military Medical University, Chongqing, China
| | - Yunfeng Yang
- Department of Neurosurgery, Southwest Hospital,Third Military Medical University, Chongqing, China
| | - Jun Tang
- Department of Neurosurgery, Southwest Hospital,Third Military Medical University, Chongqing, China
| | - Yihao Tao
- Department of Neurosurgery, Southwest Hospital,Third Military Medical University, Chongqing, China
| | - Bing Jiang
- Department of Neurosurgery, Southwest Hospital,Third Military Medical University, Chongqing, China
| | - Zhi Chen
- Department of Neurosurgery, Southwest Hospital,Third Military Medical University, Chongqing, China
| | - Hua Feng
- Department of Neurosurgery, Southwest Hospital,Third Military Medical University, Chongqing, China
| | - Liming Yang
- Department of Neurosurgery, Southwest Hospital,Third Military Medical University, Chongqing, China
| | - Gang Zhu
- Department of Neurosurgery, Southwest Hospital,Third Military Medical University, Chongqing, China
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Applications of RISM data in digital libraries and digital musicology. INTERNATIONAL JOURNAL ON DIGITAL LIBRARIES 2017. [DOI: 10.1007/s00799-016-0205-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Preservation of neuromuscular function in symptomatic SOD1-G93A mice by peripheral infusion of methylene blue. Exp Neurol 2016; 285:96-107. [PMID: 27567739 DOI: 10.1016/j.expneurol.2016.08.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Revised: 07/31/2016] [Accepted: 08/23/2016] [Indexed: 12/14/2022]
Abstract
In mutant superoxide dismutase 1 (SOD1) mouse models of familial amyotrophic lateral sclerosis (fALS) some of the earliest signs of morphological and functional damage occur in the motor nerve terminals that innervate fast limb muscles. This study tested whether localized peripheral application of a protective drug could effectively preserve neuromuscular junctions in late-stage disease. Methylene blue (MB), which has mitochondria-protective properties, was infused via an osmotic pump into the anterior muscle compartment of one hind limb of late pre- symptomatic SOD1-G93A mice for ≥3weeks. When mice reached end-stage disease, peak twitch and tetanic contractions evoked by stimulation of the muscle nerve were measured in two anterior compartment muscles (tibialis anterior [TA] and extensor digitorum longus [EDL], both predominantly fast muscles). With 400μM MB in the infusion reservoir, muscles on the MB-infused side exhibited on average a ~100% increase in nerve-evoked contractile force compared to muscles on the contralateral non-infused side (p<0.01 for both twitch and tetanus in EDL and TA). Pairwise comparisons of endplate innervation also revealed a beneficial effect of MB infusion, with an average of 65% of endplates innervated in infused EDL, compared to only 35% on the non-infused side (p<0.01). Results suggested that MB's protective effects required an extracellular [MB] of ~1μM, were initiated peripherally (no evidence of retrograde transport into the spinal cord), and involved MB's reduced form. Thus peripherally-initiated actions of MB can help preserve neuromuscular structure and function in SOD1-G93A mice, even at late stages of disease.
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Brown R, Hynes-Allen A, Swan AJ, Dissanayake KN, Gillingwater TH, Ribchester RR. Activity-dependent degeneration of axotomized neuromuscular synapses in Wld S mice. Neuroscience 2015; 290:300-20. [PMID: 25617654 PMCID: PMC4362769 DOI: 10.1016/j.neuroscience.2015.01.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Revised: 01/10/2015] [Accepted: 01/12/2015] [Indexed: 12/12/2022]
Abstract
Use and disuse may influence synaptic maintenance but so far evidence for this has been indirect. We tested whether stimulation or disuse of neuromuscular junctions in adult WldS mice altered vulnerability to axotomy. Moderate activity optimized resistance to axotomy while disuse or stimulation increased the rate of synaptic degeneration.
Activity and disuse of synapses are thought to influence progression of several neurodegenerative diseases in which synaptic degeneration is an early sign. Here we tested whether stimulation or disuse renders neuromuscular synapses more or less vulnerable to degeneration, using axotomy as a robust trigger. We took advantage of the slow synaptic degeneration phenotype of axotomized neuromuscular junctions in flexor digitorum brevis (FDB) and deep lumbrical (DL) muscles of Wallerian degeneration-Slow (WldS) mutant mice. First, we maintained ex vivo FDB and DL nerve-muscle explants at 32 °C for up to 48 h. About 90% of fibers from WldS mice remained innervated, compared with about 36% in wild-type muscles at the 24-h checkpoint. Periodic high-frequency nerve stimulation (100 Hz: 1 s/100 s) reduced synaptic protection in WldS preparations by about 50%. This effect was abolished in reduced Ca2+ solutions. Next, we assayed FDB and DL innervation after 7 days of complete tetrodotoxin (TTX)-block of sciatic nerve conduction in vivo, followed by tibial nerve axotomy. Five days later, only about 9% of motor endplates remained innervated in the paralyzed muscles, compared with about 50% in 5 day-axotomized muscles from saline-control-treated WldS mice with no conditioning nerve block. Finally, we gave mice access to running wheels for up to 4 weeks prior to axotomy. Surprisingly, exercising WldS mice ad libitum for 4 weeks increased about twofold the amount of subsequent axotomy-induced synaptic degeneration. Together, the data suggest that vulnerability of mature neuromuscular synapses to axotomy, a potent neurodegenerative trigger, may be enhanced bimodally, either by disuse or by hyperactivity.
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Affiliation(s)
- R Brown
- Euan MacDonald Centre for Motor Neurone Disease Research, Hugh Robson Building, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
| | - A Hynes-Allen
- Euan MacDonald Centre for Motor Neurone Disease Research, Hugh Robson Building, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
| | - A J Swan
- Euan MacDonald Centre for Motor Neurone Disease Research, Hugh Robson Building, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
| | - K N Dissanayake
- Euan MacDonald Centre for Motor Neurone Disease Research, Hugh Robson Building, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
| | - T H Gillingwater
- Euan MacDonald Centre for Motor Neurone Disease Research, Hugh Robson Building, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
| | - R R Ribchester
- Euan MacDonald Centre for Motor Neurone Disease Research, Hugh Robson Building, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK.
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Ma M. Role of calpains in the injury-induced dysfunction and degeneration of the mammalian axon. Neurobiol Dis 2013; 60:61-79. [PMID: 23969238 PMCID: PMC3882011 DOI: 10.1016/j.nbd.2013.08.010] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Revised: 07/17/2013] [Accepted: 08/08/2013] [Indexed: 12/21/2022] Open
Abstract
Axonal injury and degeneration, whether primary or secondary, contribute to the morbidity and mortality seen in many acquired and inherited central nervous system (CNS) and peripheral nervous system (PNS) disorders, such as traumatic brain injury, spinal cord injury, cerebral ischemia, neurodegenerative diseases, and peripheral neuropathies. The calpain family of proteases has been mechanistically linked to the dysfunction and degeneration of axons. While the direct mechanisms by which transection, mechanical strain, ischemia, or complement activation trigger intra-axonal calpain activity are likely different, the downstream effects of unregulated calpain activity may be similar in seemingly disparate diseases. In this review, a brief examination of axonal structure is followed by a focused overview of the calpain family. Finally, the mechanisms by which calpains may disrupt the axonal cytoskeleton, transport, and specialized domains (axon initial segment, nodes, and terminals) are discussed.
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Affiliation(s)
- Marek Ma
- Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA, USA; Center for Resuscitation Science, University of Pennsylvania, Philadelphia, PA, USA.
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Ma M, Ferguson TA, Schoch KM, Li J, Qian Y, Shofer FS, Saatman KE, Neumar RW. Calpains mediate axonal cytoskeleton disintegration during Wallerian degeneration. Neurobiol Dis 2013; 56:34-46. [PMID: 23542511 PMCID: PMC3721029 DOI: 10.1016/j.nbd.2013.03.009] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Revised: 02/07/2013] [Accepted: 03/19/2013] [Indexed: 02/08/2023] Open
Abstract
In both the central nervous system (CNS) and peripheral nervous system (PNS), transected axons undergo Wallerian degeneration. Even though Augustus Waller first described this process after transection of axons in 1850, the molecular mechanisms may be shared, at least in part, by many human diseases. Early pathology includes failure of synaptic transmission, target denervation, and granular disintegration of the axonal cytoskeleton (GDC). The Ca(2+)-dependent protease calpains have been implicated in GDC but causality has not been established. To test the hypothesis that calpains play a causal role in axonal and synaptic degeneration in vivo, we studied transgenic mice that express human calpastatin (hCAST), the endogenous calpain inhibitor, in optic and sciatic nerve axons. Five days after optic nerve transection and 48 h after sciatic nerve transection, robust neurofilament proteolysis observed in wild-type controls was reduced in hCAST transgenic mice. Protection of the axonal cytoskeleton in sciatic nerves of hCAST mice was nearly complete 48 h post-transection. In addition, hCAST expression preserved the morphological integrity of neuromuscular junctions. However, compound muscle action potential amplitudes after nerve transection were similar in wild-type and hCAST mice. These results, in total, provide direct evidence that calpains are responsible for the morphological degeneration of the axon and synapse during Wallerian degeneration.
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Affiliation(s)
- Marek Ma
- Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA, USA
- Center for Resuscitation Science, University of Pennsylvania, Philadelphia, PA, USA
| | - Toby A. Ferguson
- Shriners Pediatric Research Center, Temple University, Philadelphia, PA, USA
| | - Kathleen M. Schoch
- Spinal Cord and Brain Injury Research Center, Department of Physiology, University of Kentucky, Lexington, KY, USA
| | - Jian Li
- Department of Neurology, University of Pennsylvania, Philadelphia, PA, USA
| | - Yaping Qian
- Shriners Pediatric Research Center, Temple University, Philadelphia, PA, USA
| | - Frances S. Shofer
- Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Kathryn E. Saatman
- Spinal Cord and Brain Injury Research Center, Department of Physiology, University of Kentucky, Lexington, KY, USA
| | - Robert W. Neumar
- Department of Emergency Medicine, University of Pennsylvania, Philadelphia, PA, USA
- Center for Resuscitation Science, University of Pennsylvania, Philadelphia, PA, USA
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Nguyen KT, Zhang Z, Barrett EF, David G. Morphological and functional changes in innervation of a fast forelimb muscle in SOD1-G85R mice. Neurobiol Dis 2012; 48:399-408. [PMID: 22813866 DOI: 10.1016/j.nbd.2012.07.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Revised: 06/15/2012] [Accepted: 07/09/2012] [Indexed: 01/05/2023] Open
Abstract
Muscle endplates become denervated in mice that express mutations of human superoxide dismutase 1 (hSOD1), models of familial amyotrophic lateral sclerosis. This denervation is especially marked in fast limb muscles, and precedes death of motor neuron somata. This study used mice that expressed yellow fluorescent protein (YFP) in neurons to investigate changes in the morphology and function of axons and motor terminals innervating a fast forelimb muscle (epitrochleoanconeus, ETA) in presymptomatic and symptomatic hSOD1-G85R mice, compared to those in mice that express wild-type (wt) hSOD1. The percentage of endplates (identified using fluorescently-labeled α-bungarotoxin) innervated by motor terminals remained high in presymptomatic SOD1-G85R mice, but fell to ~50% in symptomatic mice. The number of large diameter (≥4 μm) axons in the ETA nerve also decreased as mice became symptomatic, and endplate innervation correlated best with the number of large diameter axons. Motor terminal function was assessed using changes in terminal YFP fluorescence evoked by trains of action potentials; different components of the pH-dependent YFP signals reflect stimulation-induced Ca2+ entry and vesicular exo/endocytosis. Most visible motor terminals (>90%) remained capable of responding to nerve stimulation in both pre- and symptomatic hSOD1-G85R mice, but with functional alterations. Responses in presymptomatic terminals suggested reduced acidification and increased vesicular release, whereas symptomatic terminals exhibited increased acidification and reduced vesicular release. The fact that most remaining terminals were able to respond to nerve stimulation suggests that motor terminal-protective therapies might contribute to preserving neuromuscular function in fALS mice.
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Affiliation(s)
- Khanh T Nguyen
- Department of Physiology and Biophysics, University of Miami Miller School of Medicine, P.O. Box 016430, Miami, FL 33101, USA
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