Progranulin does not affect motor neuron degeneration in mutant SOD1 mice and rats

Motor neuron degeneration in amyotrophic lateral sclerosis (ALS) is familial in 10% of patients, with mutations in SOD1 and C9orf72 being the most frequent cause. There is convincing evidence for overlap between ALS and frontotemporal lobar degeneration at the genetic, pathological, and clinical level. Null mutations in progranulin (PGRN) are a frequent cause of familial frontotemporal lobar degeneration. PGRN exerts neurotrophic properties on motor neurons in vitro and in vivo. We therefore examined whether PGRN could affect disease progression in mutant SOD1 mice and rats, both established models for ALS. Overexpression of PGRN in mice and intracerebroventricular delivery of PGRN in rats did not affect onset or progression of motor neuron degeneration.     

Transgenics, toxicity and therapeutics in rodent models of mutant SOD1-mediated familial ALS

Gain-of-function mutations in the Cu,Zn-superoxide dismutase (SOD1) gene are implicated in progressive motor neuron death and paralysis in one form of inherited amyotrophic lateral sclerosis (ALS). At present, transgenic expression of 12 human SOD1 mutations driven by the endogenous promoter is disease-causative and uniformly lethal in mice and rats, despite tremendous biochemical and biophysical variation between the mutants tested. This contrasts with the subclinical motor neuron disease phenotypes of wild-type SOD1 transgenic and knockout mice. Molecular mechanisms such as glutamate-induced excitotoxicity, axonal transport blockade, mitochondrial dysfunction, neuroinflammation and apoptosis triggered by mutant SOD1 catalysed oxidative reactions and/or protein misfolding are proposed to drive ALS pathogenesis. Around 100 genetic cross-breeding experiments with transgenic mutant SOD1 mice have been performed to verify these mechanisms in vivo. Furthermore, mounting evidence from mice with cell restrictive, repressible or chimeric expression of mutant SOD1 transgenes and bone marrow transplants supports non-neuronal origins of neuroprotection in ALS. Transgenic mutant SOD1 rodents have also provided the benchmark preclinical tool for evaluation of over 150 potential therapeutic anti-oxidant, anti-aggregation, anti-glutamatergic, anti-inflammatory, anti-apoptotic and neurotrophic pharmacological agents. Recent promising findings from gene and antisense therapies, cell replacement and combinatorial drug approaches in transgenic mutant SOD1 rodents are also emerging, but await successful translation in patients. This review summarises the wealth of known genetic and therapeutic modifiers in rodent models with SOD1 mutations and discusses these in the wider context of ALS pathoetiology and treatment.     

Cellular and molecular approaches to motor neuron therapy in amyotrophic lateral sclerosis and spinal muscular atrophy

Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) are progressive fatal neurodegenerative diseases. They differ in their disease development but have in common a loss of motor neuron as they progress. Research is ongoing to further understand the origin of these diseases but this common thread of motor neuron loss has provided a target for the development of therapies for both ALS and SMA. It is the linked fields of gene and cell therapy that are providing some of the most interesting therapeutic possibilities.     

ALS-linked mutant SOD1 induces ER stress- and ASK1-dependent motor neuron death by targeting Derlin-1

Mutation in Cu/Zn-superoxide dismutase (SOD1) is a cause of familial amyotrophic lateral sclerosis (ALS). Mutant SOD1 protein (SOD1(mut)) induces motor neuron death, although the molecular mechanism of SOD1(mut)-induced cell death remains controversial. Here we show that SOD1(mut) specifically interacted with Derlin-1, a component of endoplasmic reticulum (ER)-associated degradation (ERAD) machinery and triggered ER stress through dysfunction of ERAD. SOD1(mut)-induced ER stress activated the apoptosis signal-regulating kinase 1 (ASK1)-dependent cell death pathway. Perturbation of binding between SOD1(mut) and Derlin-1 by Derlin-1-derived oligopeptide suppressed SOD1(mut)-induced ER stress, ASK1 activation, and motor neuron death. Moreover, deletion of ASK1 mitigated the motor neuron loss and extended the life span of SOD1(mut) transgenic mice. These findings demonstrate that ER stress-induced ASK1 activation, which is triggered by the specific interaction of Derlin-1 with SOD1(mut), is crucial for disease progression of familial ALS.     

运动神经元病与下运动神经元综合征患者肌肉复合动作电位波幅变化比较

目的:肌萎缩侧索硬化(ALS)中确诊级的预后最差,可疑级的患者由于没有上运动神经元的损害又可将其归为下运动神经元综合征(LMNS)之中。LMNS中包含一些可治的疾病,如多灶性运动神经病(MMN),慢性运动轴索性神经病(CMAN),如能尽早将其从LMNS中分出并予以相应治疗可改善预后。本文将从复合肌肉动作电位(CMAP)波幅改变的角度对典型患者与LMNS患者进行比较研究。方法:将112例ALS患者分为确诊43例,拟诊38例,可疑31例,其中确诊、拟诊的患者代表典型ALS患者,可疑组均为单纯下运动神经元综合征的患者。对此112例患者予常规肌电图和神经电图检查,评价典型的ALS患者和LMNS患者的CMAP波幅改变的异同。结果:典型ALS患者的CMAP 波幅下降的例数(35例,81．4％)较可疑患者(14例,45．2％)明显增多(X2=4．938,P<0．05),但二者波幅下降的程度差异无显著意义(t=0．815,P>0．05)。在确诊ALS的病例中,同一患者其波幅水平是逐渐下降的,但不同患者的波幅水平与病程无相关性。在可疑患者波幅下降与典型ALS有以下不司:①短期内波幅明显下降者,运动轴索受损的严重程度与肌力不成比例;②发病2年内波幅下降明显者,无广泛肌电图损害;③波幅下降缓慢或保持正常者,病程往往超过2年,肌电图损害广泛。其中①和②部分患者试用免疫抑制剂有效,提示为MMN或CMAN。结论:CMAP波幅在LMNS和典型ALS中有不同的发展趋势,可为二者在诊断、鉴别诊断和预后方面提供重要的电生理依据。     

Screening for inhibitors of the SOD1 gene promoter: Pyrimethamine does not reduce SOD1 levels in cell and animal models

Mutations in the Cu/Zn superoxide dismutase (SOD1) gene are detected in 20% of familial and 3% of sporadic amyotrophic lateral sclerosis (ALS) cases. Although mutant SOD1 is known to induce motor neuron death via multiple adverse acquired functions, its exact pathogenic mechanism is not well defined. SOD1 toxicity is dose dependent; levels of mutant SOD1 protein in transgenic mice determine disease susceptibility, onset and rate of progression. We therefore sought to identify small molecules that reduce SOD1 levels by inhibiting the SOD1 promoter. We tested pyrimethamine (previously reported to suppress SOD1 expression), several compounds currently in trials in human and murine ALS, and a set of 1040 FDA-approved compounds. In a PC12 cell-based assay, no compounds reduced SOD1 promoter activity without concomitant cytotoxicity. Additionally, pyrimethamine failed to repress levels of SOD1 protein in HeLa cells or homogenates of liver, spinal cord and brain of wild-type mice. Thirty-four compounds (including riluzole, ceftriaxone, minocyclin, PBA, lithium, acetylcysteine) in human and mouse ALS trials and an additional set of 1040 FDA-approved compounds also showed no effect on SOD1 promoter activity. This present study thus failed to identify small molecule inhibitors of SOD1 gene expression.     

Size-dependent dendritic maladaptations of hypoglossal motor neurons in SOD1G93A mice

The total motor neuron (MN) somato-dendritic surface area is correlated with motor unit type. MNs with smaller surface areas innervate slow (S) and fast fatigue-resistant (FR) motor units, while MNs with larger surface areas innervate fast fatigue-intermediate (FInt) and fast fatigable (FF) motor units. Differences in MN surface area (equivalent to membrane capacitance) underpin the intrinsic excitability of MNs and are consistent with the orderly recruitment of motor units (S > FR > FInt > FF) via the Size Principle. In amyotrophic lateral sclerosis (ALS), large MNs controlling FInt and FF motor units exhibit earlier denervation and death, compared to smaller and more resilient MNs of type S and FR motor units that are spared until late in ALS. Abnormal dendritic morphologies in MNs precede neuronal death in human ALS and in rodent models. We employed Golgi-Cox methods to investigate somal size-dependent changes in the dendritic morphology of hypoglossal MNs in wildtype and SOD1^G93A mice (a model of ALS), at postnatal (P) day ~30 (pre-symptomatic), ~P60 (onset), and ~P120 (mid-disease) stages. In wildtype hypoglossal MNs, increased MN somal size correlated with increased dendritic length and spines in a linear fashion. By contrast, in SOD1^G93A mice, significant deviations from this linear correlation were restricted to the larger vulnerable MNs at pre-symptomatic (maladaptive) and mid-disease (degenerative) stages. These findings are consistent with excitability changes observed in ALS patients and in rodent models. Our results suggest that intrinsic or synaptic increases in MN excitability are likely to contribute to ALS pathogenesis, not compensate for it.     

Implication of endogenous beta-endorphin in the inhibition of the morphine-induced rewarding effect by the direct activation of spinal protein kinase C in mice

It has often been proposed that opioid addiction does not arise as a consequence of opioid treatment for pain. Recently, we demonstrated that activated protein kinase C (PKC) in the spinal cord associated with chronic pain-like hyperalgesia suppressed the morphine-induced rewarding effect in mice. In the present study, we investigated whether a gene deletion for an endogenous mu-opioid peptide beta-endorphin could affect pain-like behavior and the suppression of the morphine-induced rewarding effect by the direct activation of PKC in the spinal cord. We found that activation of spinal PKC by intrathecal (i.t.) treatment with phorbol 12,13-dibutyrate (PDBu), a specific PKC activator, caused thermal hyperalgesia, pain-like behaviors and suppression of the morphine-induced rewarding effect. This suppression of morphine reward was eliminated in mice that lacked beta-endorphin. In contrast, thermal hyperalgesia and pain-like behaviors were not affected in beta-endorphin knockout mice. These results suggest that the activation of PKC in the spinal cord may play an essential role in the suppression of the morphine-induced rewarding effect in mice with neuropathic pain through the constant release of beta-endorphin.     

Pyruvate slows disease progression in a G93A SOD1 mutant transgenic mouse model

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease caused by selective motor neuron death, and currently no effective treatment is available for ALS. In this study, we investigated the neuroprotective effects of pyruvate, which acts as an anti-oxidant and as an energy source. We treated G93A SOD1 transgenic mice with pyruvate (from 70 days of age, i.p., at 1000 mg/kg/week), and found that it prolonged average lifespan by 12.3 days (10.5%), slowed disease progression, and improved motor performance, but did not delay disease onset. Pyruvate treatment was also associated with reduced nitrotyrosine immunoreactivity, gliosis, and increased Bcl-2 expression in the spinal cords of G93A SOD1 transgenic mice. These results suggest that pyruvate treatment may be a potential therapeutic strategy in ALS.     

Dual transplantation of human neural stem cells into cervical and lumbar cord ameliorates motor neuron disease in SOD1 transgenic rats

Stem cells provide novel sources of cell therapies for motor neuron disease that have recently entered clinical trials. In the present study, we transplanted human neural stem cells (NSCs) into the ventral horn of both the lumbar (L4–L5) and cervical (C4–C5) protuberance of SOD1 G93A rats, in an effort to test the feasibility and general efficacy of a dual grafting paradigm addressing several muscle groups in the front limbs, hind limbs and the respiratory apparatus. Transplantation was done prior to the onset of motor neuron disease. Compared with animals that had received dead NSC grafts (serving as controls), rats with live NSCs grafted at the two spinal levels lived 17 days longer. Disease onset in dually grafted animals was delayed by 10 days compared to control animals. Disease duration in NSC-grafted animals was longer by 7 days compared to controls. Our results support the potential of NSC grafts at multiple levels of spinal cord as future cellular therapy for motor neuron disease.     

A morphological analysis of the motor neuron degeneration and microglial reaction in acute and chronic in vivo aluminum chloride neurotoxicity

The monthly intracisternal inoculation of aluminum chloride (AlCl₃) to young adult New Zealand white rabbits induces motor neuron degeneration marked by intraneuronal neurofilamentous aggregates similar to that observed in amyotrophic lateral sclerosis (ALS). However, in contrast to ALS, this process occurs in the experimental paradigm in the absence of a glial response. In addition, whereas ALS is a fatal disorder, the cessation of aluminum exposure leads to both clinical and neuropathological recovery. Because microglia can influence neuronal regeneration, we have examined the effect of both acute and chronic aluminum exposure on microglial activation in vivo. We have studied microglial morphology in young adult New Zealand white rabbits receiving either single (1000 μg) or repeated sublethal (100 μg monthly) intracisternal inoculums of AlCl₃. In addition, rabbits receiving 1000 μg AlCl₃ inoculums were studied following an unilateral sciatic axotomy 48 h prior to the AlCl₃ exposure. Our studies demonstrate that microglial activation in vivo is inhibited by AlCl₃ exposure, and that a correlation exists between the extent of microglia suppression and the potential for recovery. This suggests that microglial activation is an important determinant of neuronal injury.     

Slowly progressing lower motor neuron disease caused by a novel duplication mutation in exon 1 of the SOD1 gene

Familial amyotrophic lateral sclerosis accounts for about 5% of all cases of the neurodegenerative disorder amyotrophic lateral sclerosis. Genetic mutations in Cu/Zn superoxide dismutase (SOD1) have been associated with one kind of familial amyotrophic lateral sclerosis (ALS1). We identified a novel duplication mutation in exon 1 of the SOD1 gene in a Japanese family whose members had lower motor neuron diseases. The patients showed slow disease progression, with the onset of lower limb muscle weakness and exertional dyspnea. Some patients had mild motor and sensory neuropathy and/or bladder dysfunction, which is further evidence that SOD1 mutation results in a predominantly lower motor neuron phenotype.     

脊肌萎缩症研究进展

脊肌萎缩症是一组常见的引起婴幼儿死亡的遗传病, 因为缺乏治疗手段,该病研究曾不受重视。自1995年确定脊肌萎缩症致病基因是一种看家基因---运动神经元生存基因（SMN1）以来,围绕在这种疾病背后的谜团吸引了多国学者的兴趣,成为近年遗传病研究的一个热点,本文就脊肌萎缩症遗传基础,SMN蛋白生物功能,脊肌萎缩症携带者检测及治疗方面新策略等内容做一综述。     

Pre-symptomatic detection of chronic motor deficits and genotype prediction in congenic B6.SOD1 ALS mouse model

Amyotrophic lateral sclerosis (ALS) is an incurable progressive paralytic motor neuron disease with limited therapeutic options. Since their creation by Gurney et al. (1994) [Science 264:1772–1775], transgenic superoxide dismutase-1 with glycine to alanine switch at codon 93 (SOD1^G93A) mice have become the benchmark pre-clinical model for screening ALS therapies. Surprisingly, despite physiological, anatomical, ultrastructural and biochemical evidence of early motor system dysfunction, it has proven difficult to detect motor performance deficits in pre-symptomatic SOD1^G93A mice. As an alternative to conventional forced motor tests, we investigated the progression of motor performance deficits in freely behaving pre-symptomatic congenic B6.SOD1^G93A mice. We found that motor performance deficits began several weeks prior to the onset of overt clinical symptoms (postnatal day 45). More importantly, once motor performance deficits manifested, they persisted in parallel with disease progression. In addition, two physical measures of muscle girth revealed progressive hindlimb muscle atrophy that predicted genotype in individual pre-symptomatic mice with 80% accuracy. Together, these data suggest that muscle girth is a reliable and indirect measure of hindlimb muscle denervation and an early, objective marker for disease onset in congenic B6.SOD1^G93A ALS mice. Moreover, we present regression equations based on hindlimb muscle girth for predicting genotype in future studies using B6.SOD1^G93A mice. These findings support new objective criteria for clinical disease onset and provide objective measures that require little expertise. These studies demonstrate a cost-effective approach for more thorough evaluation of neuroprotective strategies that seek to disrupt disease mechanisms early in the disease process. To our knowledge, these findings are the first to report early chronic motor performance and physical deficits that are coincident with the earliest known motor dysfunction in any ALS mouse model.     

Bone loss in survival motor neuron (Smn−/− SMN2) genetic mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is characterized by degenerating lower motor neurons and an increased incidence of congenital bone fractures. Survival motor neuron (SMN) levels are significantly reduced due to deletions/mutations in the telomeric SMN1 gene in these patients. We utilized the Smn^?/? SMN2 mouse model of SMA to determine the functional role for SMN in bone remodelling. µCT analysis of lumber vertebrae, tibia and femur bones from SMA mice revealed an osteoporotic bone phenotype. Histological analysis demonstrated a thin porous cortex of cortical bone and thin trabeculae at the proximal end of the growth plate in the vertebrae of SMA mice compared to wild‐type mice. Histochemical staining of the vertebrae showed the presence of abundant activated osteoclasts on the sparse trabeculae and on the endosteal surface of the thin cortex in SMA mice. Histomorphometric analysis of vertebrae from SMA mice showed an increased number of osteoclasts. Serum TRAcP5b and urinary NTx levels were elevated, consistent with increased bone resorption in these mice. SMA mice showed a significant decrease in the levels of osteoblast differentiation markers, osteocalcin, osteopontin and osterix mRNA expression; however, there were no change in the levels of alkaline phosphatase expression compared to WT mice. SMA mouse bone marrow cultures revealed an increased rate of osteoclast formation (54%) and bone resorption capacity (46%) compared to WT mice. Pre‐osteoclast cells from SMA mice showed constitutive up‐regulation of RANK receptor signalling molecules critical for osteoclast differentiation. Our results implicate SMN function in bone remodelling and skeletal pathogenesis in SMA. Understanding basic mechanisms of SMN action in bone remodelling may uncover new therapeutic targets for preventing bone loss/fracture risk in SMA. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Histopathology of the late-onset motor neuron degeneration (Mnd) mutant in the mouse

The motor neuron degeneration (Mnd) is characterized by a progressive deterioration of motor function (stiff-legged gait, abnormal limb placements and grasping, and finally paralysis; moving from rear to forelimbs). There is a dramatic degeneration of spinal cord motor neurons, more severe in the lumbosacral than in the other regions, as well as variable pathology in the lower cranial nerves. Upper motor neurons of the red nucleus, reticular formation of the pons and medulla, and restricted areas of the cerebral cortex are also affected. Degenerating motor neurons share many characteristics seen in the human disease amyotropic lateral sclerosis, including loss of Nissl substance, increases in lipofuscin and abnormal cytoplasmic inclusions. Additionally, Mnd, like ALS, is a disease of later life.     

Histopathology of the late-onset motor neuron degeneration (Mnd) mutant in the mouse

The motor neuron degeneration (Mnd) is characterized by a progressive deterioration of motor function (stiff-legged gait, abnormal limb placements and grasping, and finally paralysis; moving from rear to forelimbs). There is a dramatic degeneration of spinal cord motor neurons, more severe in the lumbosacral than in the other regions, as well as variable pathology in the lower cranial nerves. Upper motor neurons of the red nucleus, reticular formation of the pons and medulla, and restricted areas of the cerebral cortex are also affected. Degenerating motor neurons share many characteristics seen in the human disease amyotropic lateral sclerosis, including loss of Nissl substance, increases in lipofuscin and abnormal cytoplasmic inclusions. Additionally, Mnd, like ALS, is a disease of later life.     

应用基因组测序技术诊断缺失型脊肌萎缩症

目的 评价基因组测序技术在诊断缺失型脊肌萎缩症(spinal muscular atrophy,SMA)中的应用.方法 应用聚合酶链反应扩增100例SMA临床确诊患儿和110名对照样本的运动神经元存活基因(spinal muscular atrophy,SMN),基因组测序技术通过识别扩增片段中SMN1和SMN2的4个差异位点用来诊断SMN1的纯合缺失,并以多重连接探针扩增进行验证.结果 100例SMA样本中基因组测序显示差异位点仅有SMN2基因特有碱基峰,多重连接探针扩增检测示SMN1与SMN2拷贝数为0∶2或0∶3,表明SMN1基因纯合缺失.对照组中5例样本的差异位点仅为SMN1基因特有碱基峰,SMN1与SMN2拷贝数为2∶0,为SMN2纯合缺失.105例样本的差异位点均为杂合峰,SMN1与SMN2拷贝数为2∶2,未显示SMN1和SMN2的缺失.所有测序结果与MLPA检测结果一致.结论 基因组测序技术在进行缺失型脊肌萎缩症的分子诊断中具有特异、准确、实用的特点.     

X‐linked spinal muscular atrophy in mice caused by autonomous loss of ATP7A in the motor neuron

ATP7A is a copper‐transporting P‐type ATPase that is essential for cellular copper homeostasis. Loss‐of‐function mutations in the ATP7A gene result in Menkes disease, a fatal neurodegenerative disorder resulting in seizures, hypotonia and failure to thrive, due to systemic copper deficiency. Most recently, rare missense mutations in ATP7A that do not impact systemic copper homeostasis have been shown to cause X‐linked spinal muscular atrophy type 3 (SMAX3), a distal hereditary motor neuropathy. An understanding of the mechanistic and pathophysiological basis of SMAX3 is currently lacking, in part because the disease‐causing mutations have been shown to confer both loss‐ and gain‐of‐function properties to ATP7A, and because there is currently no animal model of the disease. In this study, the Atp7a gene was specifically deleted in the motor neurons of mice, resulting in a degenerative phenotype consistent with the clinical features in affected patients with SMAX3, including the progressive deterioration of gait, age‐dependent muscle atrophy, denervation of neuromuscular junctions and a loss of motor neuron cell bodies. Taken together, these data reveal autonomous requirements for ATP7A that reveal essential roles for copper in the maintenance and function of the motor neuron, and suggest that SMAX3 is caused by a loss of ATP7A function that specifically impacts the spinal motor neuron. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.