Motor neuron degeneration in a mouse model of seipinopathy

Heterozygosity for missense mutations (N88S/S90L) in BSCL2 (Berardinelli–Seip congenital lipodystrophy type 2)/Seipin is associated with a broad spectrum of motoneuron diseases. To understand the underlying mechanisms how the mutations lead to motor neuropathy, we generated transgenic mice with neuron-specific expression of wild-type (tgWT) or N88S/S90L mutant (tgMT) human Seipin. Transgenes led to the broad expression of WT or mutant Seipin in the brain and spinal cord. TgMT, but not tgWT, mice exhibited late-onset altered locomotor activities and gait abnormalities that recapitulate symptoms of seipinopathy patients. We found loss of alpha motor neurons in tgMT spinal cord. Mild endoreticular stress was present in both tgMT and tgWT neurons; however, only tgMT mice exhibited protein aggregates and disrupted Golgi apparatus. Furthermore, autophagosomes were significantly increased, along with elevated light chain 3 (LC3)-II level in tgMT spinal cord, consistent with the activation of autophagy pathway in response to mutant Seipin expression and protein aggregation. These results suggest that induction of autophagy pathway is involved in the cellular response to mutant Seipin in seipinopathy and that motoneuron loss is a key pathogenic process underlying the development of locomotor abnormalities.     

Role of type-specific neuron properties in a spinal cord motor network

Recent recordings from spinal neurons in hatchling frog tadpoles allow their type-specific properties to be defined. Seven main types of neuron involved in the control of swimming have been characterized. To investigate the significance of type-specific properties, we build models of each neuron type and assemble them into a network using known connectivity between: sensory neurons, sensory pathway interneurons, central pattern generator (CPG) interneurons and motoneurons. A single stimulus to a sensory neuron initiates swimming where modelled neuronal and network activity parallels physiological activity. Substitution of firing properties between neuron types shows that those of excitatory CPG interneurons are critical for stable swimming. We suggest that type-specific neuronal properties can reflect the requirements for involvement in one particular network response (like swimming), but may also reflect the need to participate in more than one response (like swimming and slower struggling). Action Editor: Eberhard E. Fetz     

Pathways to motor neuron degeneration in transgenic mouse models

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurological disorder characterized by the selective loss of motor neurons. A pathological hallmark of both sporadic and familial ALS is the presence of abnormal accumulations of neurofilament and peripherin proteins in motor neurons. In the past decade, transgenic mouse approaches have been used to address the role of such cytoskeletal abnormalities in motor neuron disease and also to unravel the pathogenesis caused by mutations in the gene coding for superoxide dismutase 1 (SOD1) that account for ~20% of familial ALS cases. In mouse models, disparate effects could result from different types of intermediate filament (IF) aggregates. Perikaryal IF accumulations induced by the overexpression of any of the three wild-type neurofilament proteins were quite well tolerated by motor neurons. Indeed, perikaryal swellings provoked by NF-H overexpression can even confer protection against toxicity of mutant SOD1. Other types of IF aggregates seem neurotoxic, such as those found in transgenic mice overexpressing either peripherin or an assembly-disrupting NF-L mutant. Moreover, understanding the toxicity of SOD1 mutations has been surprisingly difficult. The analysis of transgenic mice expressing mutant SOD1 has yielded complex results, suggesting that multiple pathways may contribute to disease that include the involvement of non-neuronal cells.     

Neuroprotective effects of amiodarone in a mouse model of ischemic stroke

Background

Ion channels play a crucial role in the development of ischemic brain injury. Recent studies have reported that the blockade of various types of ion channels improves outcomes in experimental stroke models. Amiodarone, one of the most effective drugs for life-threatening arrhythmia, works as a multiple channel blocker and its characteristics cover all four Vaughan-Williams classes. Although it is known that amiodarone indirectly contributes to preventing ischemic stroke by maintaining sinus rhythm in patients with atrial fibrillation, the direct neuroprotective effect of amiodarone has not been clarified. The purpose of this study was to investigate the direct effect of amiodarone on ischemic stroke in mice.

Methods

Focal cerebral ischemia was induced via distal permanent middle cerebral artery occlusion (MCAO) in adult male mice. The amiodarone pre-treatment group received 50 mg/kg of amiodarone 1 h before MCAO; the amiodarone post-treatment groups received 50 mg/kg of amiodarone immediately after MCAO; the control group received vehicle only. In addition, the sodium channel opener veratrine and selective beta-adrenergic agonist isoprotelenol were used to elucidate the targeted pathway. Heart rate and blood pressure were monitored perioperatively. Infarct volume analysis was conducted 48 h after MCAO. The body asymmetry test and the corner test were used for neurological evaluation.

Results

Amiodarone pre-treatment and post-treatment reduced the heart rate but did not affect the blood pressure. No mice showed arrhythmia. Compared with the control group, the amiodarone pre-treatment group had smaller infarct volumes (8.9?±?2.1% hemisphere [mean?±?SD] vs. 11.2?±?1.4%; P?<?0.05) and improved functional outcomes: lower asymmetric body swing rates (52?±?17% vs. 65?±?18%; P?<?0.05) and fewer left turns (7.1?±?1.2 vs. 8.3?±?1.2; P?<?0.05). In contrast, amiodarone post-treatment did not improve the outcomes after MCAO. The neuroprotective effect of amiodarone pre-treatment was abolished by co-administration of veratrine but not by isoproterenol.

Conclusions

Amiodarone pre-treatment attenuated ischemic brain injury and improved functional outcomes without affecting heart rhythm and blood pressure. The present results showed that amiodarone pre-treatment has neuroprotective effects, at least in part, via blocking the sodium channels.

     

Neuromuscular degeneration (nmd): a mutation on mouse Chromosome 19 that causes motor neuron degeneration

Neuromuscular degeneration, nmd, is a spontaneous autosomal recessive mutation in the mouse producing progressive hindlimb impairment caused by spinal muscular atrophy. We used an intersubspecific intercross between B6.BKs-nmd ^2J/+ and Mus musculus castaneus (CAST/Ei) to map the nmd mutation to mouse Chromosome (Chr) 19 with the most likely gene order: nmd-(D19Se12, Pygm)-Cntf-Pomc2-D19Mit16-Cyp2c-Got1. nmd maps near muscle deficient, mdf, and has a very similar clinical phenotype, but allele tests and histological differences suggest that nmd is a distinct mutation at a different locus. Although closely linked, nmd recombined with the candidate genes muscle glycogen phosphorylase, Pygm, and ciliary neurotrophic factor, Cntf.     

Myelin formation in cultures of previously dissociated mouse spinal cord

Myelin formation in cultures of previously dissociated spinal cord from foetal mice is described. In addition to the expected pattern of myelination, in which axons are closely wrapped by myelin lamellae, redundant folds of myelin have been found, as have double sheaths surrounding a single axon. Hypotheses concerning the generation of these appearances are discussed. It is suggested that certain intracytoplasmic laminar bodies found in oligodendrocytes in vitro may be of mitochondrial origin.     

Rapamycin treatment augments motor neuron degeneration in SOD1G93A mouse model of amyotrophic lateral sclerosis

Aberrant protein misfolding may contribute to the pathogenesis of amyotrophic lateral sclerosis (ALS) but the detailed mechanisms are largely unknown. Our previous study has shown that autophagy is altered in the mouse model of ALS. In the present study, we systematically investigated the correlation of the autophagic alteration with the motor neurons (MNs) degeneration in the ALS mice. We have demonstrated that the autophagic protein marker LC3-II is markedly and specifically increased in the spinal cord MNs of the ALS mice. Electron microscopy and immunochemistry studies have shown that autophagic vacuoles are significantly accumulated in the dystrophic axons of spinal cord MNs of the ALS mice. All these changes in the ALS mice appear at the age of 90 d when the ALS mice display modest clinical symptoms; and they become prominent at the age of 120 d. The clinical symptoms are correlated with the progression of MNs degeneration. Moreover, we have found that p62/SQSTM1 is accumulated progressively in the spinal cord, indicating that the possibility of impaired autophagic flux in the SOD1^G93A mice. Furthermore, to our surprise, we have found that treatment with autophagy enhancer rapamycin accelerates the MNs degeneration, shortens the life span of the ALS mice, and has no obvious effects on the accumulation of SOD1 aggregates. In addition, we have demonstrated that rapamycin treatment in the ALS mice causes more severe mitochondrial impairment, higher Bax levels and greater caspase-3 activation. These findings suggest that selective degeneration of MNs is associated with the impairment of the autophagy pathway and that rapamycin treatment may exacerbate the pathological processing through apoptosis and other mechanisms in the ALS mice.     

Primary cultures of mouse spinal cord express the neonatal isoform of the inhibitory glycine receptor

Expression of the inhibitory glycine receptor complex was investigated in primary cultures of fetal mouse spinal cord using sensitive immunomethods. In these cells, glycine receptor is predominantly of the neonatal isoform characterized by a low affinity for the antagonist strychnine. It contains a ligand binding subunit that differs from that of the adult receptor in antigenic epitopes and apparent molecular weight. Whereas in vivo the neonatal receptor isoform is completely replaced by the adult isoform within 3 weeks after birth, this exchange of subtypes is not seen in culture. The increased expression of the cytoplasmic glycine receptor-associated polypeptide of 93 kd occurring after birth is also seen under culture conditions. Purification of glycine receptor from cultures yielded polypeptides of 49 kd and 93 kd, suggesting that the membrane-spanning core of the neonatal receptor may be a homooligomer composed of 49 kd subunits. About half of the 49 kd subunit is cleaved by trypsinization of the cultures, indicating a predominant cell surface localization of the receptor. Pulse-labeling experiments revealed the 49 kd subunit to be a metabolically stable glycoprotein (half-life approximately 2 days). After its synthesis, a transition time of 30-45 min is required for acquisition of a strychnine binding conformation.     

Neuroprotective effects of N-acetyl-cysteine and acetyl-L-carnitine after spinal cord injury in adult rats

Following the initial acute stage of spinal cord injury, a cascade of cellular and inflammatory responses will lead to progressive secondary damage of the nerve tissue surrounding the primary injury site. The degeneration is manifested by loss of neurons and glial cells, demyelination and cyst formation. Injury to the mammalian spinal cord results in nearly complete failure of the severed axons to regenerate. We have previously demonstrated that the antioxidants N-acetyl-cysteine (NAC) and acetyl-L-carnitine (ALC) can attenuate retrograde neuronal degeneration after peripheral nerve and ventral root injury. The present study evaluates the effects of NAC and ALC on neuronal survival, axonal sprouting and glial cell reactions after spinal cord injury in adult rats. Tibial motoneurons in the spinal cord were pre-labeled with fluorescent tracer Fast Blue one week before lumbar L5 hemisection. Continuous intrathecal infusion of NAC (2.4 mg/day) or ALC (0.9 mg/day) was initiated immediately after spinal injury using Alzet 2002 osmotic minipumps. Neuroprotective effects of treatment were assessed by counting surviving motoneurons and by using quantitative immunohistochemistry and Western blotting for neuronal and glial cell markers 4 weeks after hemisection. Spinal cord injury induced significant loss of tibial motoneurons in L4-L6 segments. Neuronal degeneration was associated with decreased immunostaining for microtubular-associated protein-2 (MAP2) in dendritic branches, synaptophysin in presynaptic boutons and neurofilaments in nerve fibers. Immunostaining for the astroglial marker GFAP and microglial marker OX42 was increased. Treatment with NAC and ALC rescued approximately half of the motoneurons destined to die. In addition, antioxidants restored MAP2 and synaptophysin immunoreactivity. However, the perineuronal synaptophysin labeling was not recovered. Although both treatments promoted axonal sprouting, there was no effect on reactive astrocytes. In contrast, the microglial reaction was significantly attenuated. The results indicate a therapeutic potential for NAC and ALC in the early treatment of traumatic spinal cord injury.     

Retinoids run rampant: multiple roles during spinal cord and motor neuron development

Learning how the incredible diversity of neurons in the vertebrate central nervous system (CNS) is generated is a central focus of developmental neuroscience. Three studies in the September 25, 2003, issue of Neuron bring us closer to this goal by revealing how the interplay between Fibroblast Growth Factor (FGF), retinoic acid (RA), and Sonic hedgehog (Shh) signaling regulate progression of spinal cord progenitor cells through various phases of development and specify particular types of spinal motor neurons (MNs).     

Proteomic analysis of muscle affected by motor neuron degeneration: the wobbler mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is the most common form of motor neuron disease in adult patients and characterized by progressive paralysis. The wobbler mouse (phenotype WR, genotype wr/wr) is an established animal model of human motor neuron disease and is characterized by a large variety of cellular abnormalities including muscular atrophy. In analogy to recent proteomic studies of cerebrospinal fluid and spinal cord, we have used here fluorescence difference in-gel electrophoresis to analyze global changes in the skeletal muscle proteome from WR versus normal mice. Relative concentrations of 21 proteins were found to be increased and 3 proteins were decreased. Mass spectrometric analysis identified these proteins to be associated with key metabolic pathways, the contractile apparatus, intermediate filaments and the cellular stress response. Drastically increased levels of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase were confirmed by immunoblotting and this finding agrees with the idea of an oxidative-to-glycolytic shift in disease-related muscular atrophy. The establishment of novel disease-specific biomarkers of motor neuron disease might be helpful in the design of improved diagnostic tools and the identification of novel therapeutic targets.     

Developmental expression of EphA4-tyrosine kinase receptor in the mouse brain and spinal cord

Eph receptor tyrosine kinases and their ephrin ligands are involved in some of the most important steps during the development of the central nervous system, including cell migration, axon guidance, topographic mapping and synapse formation. Moreover, in the adult, they have been implicated in plasticity and regulation of neural stem cell function. One member of the Eph family, EphA4, can bind to both classes of ephrins and may have multiple functions in nervous system development. In order to look for potential sites of EphA4 action during central nervous system development, we conducted a spatio-temporal analysis of EphA4 protein expression. We used immunohistochemistry in preference to in situ hybridization because of the high likelihood that EphA4 protein is expressed on axon tracts, long distances from EphA4 mRNA. In the telencephalon, EphA4 was expressed in the developing cortex from embryonic day 11 (E11) and, later, on major cortical tracts including the corpus callosum and cortico-spinal tract. Robust EphA4 expression was also found in the hippocampus and fornix, and cells and tracts in the striatum. In the diencephalon, the thalamus, the hypothalamus and thalamo-cortical projection were strongly positive. In the mesencephalon, a number of different nuclei were weakly positive, most prominently the red nucleus. In the rhombencephalon, many nuclei were strongly positive including the cerebellum and one of its afferent paths, the inferior cerebellar peduncle, as well as the olivary region. In the spinal cord, there was a dynamic pattern of expression through development, with persistent expression in the dorsal funiculus and ventral grey matter.     

ALS-IgG-induced selective motor neurone apoptosis in rat mixed primary spinal cord cultures

There is evidence that in sporadic amyotrophic lateral sclerosis (ALS) immunological mechanisms may be involved in the pathophysiology of the disease. We tested whether purified IgG from ALS patients induce cell death in rat mixed primary spinal cord cultures and compared this with the effect of IgG purified from patients with Guillain-Barré syndrome (GBS) or from healthy donors. Treatment with ALS-IgG increases caspase-3 apoptosis when compared with control IgG or with GBS-IgG, but does not induce death by necrosis. Because ALS is characterized by the selective loss of motor neurones, we next assessed the differential effect of ALS-IgG on motor neurones or astrocytes. We showed, semiquantitatively, that motor neurones are more susceptible to apoptosis when cultures were treated with ALS-IgG compared with control-IgG. In conclusion, we have demonstrated in primary spinal cord cultures that IgG from patients with ALS induces apoptosis selectively in motor neurones, and that the caspase-3 pathway is involved. This suggests that immunological mechanisms may contribute to the selective loss of motor neurones in ALS.     

Mapping of the motor neuron degeneration (Mnd) gene, a mouse model of amyotrophic lateral sclerosis (ALS).

The motor neuron degeneration mutation (Mnd) causes a late-onset, progressive degeneration of upper and lower motor neurons in mice. After establishing genetic and environmental conditions that distinguish the phenotypes of Mnd/Mnd from +/Mnd mice, Mnd was mapped to proximal Chr 8, using endogenous retroviruses as markers. The map location was confirmed with additional linked polymorphic markers. The outcross/intercross matings to the strain AKR/J, which were used to follow the segregation of the retroviral markers with respect to Mnd, also revealed the existence of a timing effect. Approximately one-fourth of the affected Mnd/Mnd F2 progeny showed accelerated disease. The Mnd mouse model should allow study of mechanisms affecting onset and progression of specific neuronal degeneration in both animal and human neurological disease.     

Beneficial effects of FeTSPP, a peroxynitrite decomposition catalyst, in a mouse model of spinal cord injury

The aim of the present study was to assess the contribution of peroxynitrite formation in the pathophysiology of spinal cord injury (SCI) in mice. To this purpose, we used a peroxynitrite decomposition catalyst, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron III chloride (FeTSPP). Spinal cord trauma was induced by the application of vascular clips (force of 24g) to the dura via a four-level T5-T8 laminectomy. SCI in mice resulted in severe trauma characterized by edema, neutrophil infiltration, production of inflammatory mediators, tissue damage, and apoptosis. FeTSPP treatment (10-100 mg/kg, i.p.) significantly reduced in dose-dependent manner 1 and 4 h after the SCI (1) the degree of spinal cord inflammation and tissue injury (histological score), (2) neutrophil infiltration (myeloperoxidase activity), (3) nitrotyrosine formation and poly-(ADP-ribose) polymerase activation, (4) proinflammmaory cytokines expression, (5) NF-kappaB activation, and (6) apoptosis (TUNEL staining, Bax and Bcl-2 expression). Moreover, FeTSPP significantly ameliorated the recovery of limb function (evaluated by motor recovery score) in a dose-dependent manner. Taken together, our results clearly demonstrate that FeTSPP treatment reduces the development of inflammation and tissue injury associated with spinal cord trauma similarly to dexamethasone, a well-known antiinflammatory agent which we have used as positive control.     

Rapamycin treatment augments motor neuron degeneration in SOD1(G93A) mouse model of amyotrophic lateral sclerosis

Aberrant protein misfolding may contribute to the pathogenesis of amyotrophic lateral sclerosis (ALS) but the detailed mechanisms are largely unknown. Our previous study has shown that autophagy is altered in the mouse model of ALS. In the present study, we systematically investigated the correlation of the autophagic alteration with the motor neurons (MNs) degeneration in the ALS mice. We have demonstrated that the autophagic protein marker LC3-II is markedly and specifically increased in the spinal cord MNs of the ALS mice. Electron microscopy and immunochemistry studies have shown that autophagic vacuoles are significantly accumulated in the dystrophic axons of spinal cord MNs of the ALS mice. All these changes in the ALS mice appear at the age of 90 d when the ALS mice display modest clinical symptoms; and they become prominent at the age of 120 d. The clinical symptoms are correlated with the progression of MNs degeneration. Moreover, we have found that p62/SQSTM1 is accumulated progressively in the spinal cord, indicating that the possibility of impaired autophagic flux in the SOD1(G93A) mice. Furthermore, to our surprise, we have found that treatment with autophagy enhancer rapamycin accelerates the MNs degeneration, shortens the life span of the ALS mice, and has no obvious effects on the accumulation of SOD1 aggregates. In addition, we have demonstrated that rapamycin treatment in the ALS mice causes more severe mitochondrial impairment, higher Bax levels and greater caspase-3 activation. These findings suggest that selective degeneration of MNs is associated with the impairment of the autophagy pathway and that rapamycin treatment may exacerbate the pathological processing through apoptosis and other mechanisms in the ALS mice.     

小鼠脊髓损伤模型的建立及其评价

通过对模型的制备模拟脊髓损伤,研究其病理和影像的变化及脊髓组织的病理分析,为后期的唔疗提供了实验信息。使用7～8周龄小鼠,咬除T9～T10棘突及相应椎板,用重物压迫脊髓,缝合皮肤,制成脊髓损伤模型。分不同的时间进行行为学评分及病理和影像学的检测。结果显示对照组在不同时间行为学评分较高,而实验组评分较低。脊髓损伤区出现明显的病理改变和影像学的改变。可见在实验组中小鼠脊髓损伤区无脊髓组织残留,且出现明显的组织和影像改变,在行为学上两组相比具有显著差异,适用于脊髓再生的研究,从而为进一步研究脊髓损伤提供了较为可靠的模型。