Adult-onset Neurodegenerative Disorder Research Articles

Advancements in the Study of Clinical Features and Molecular Functions in Heterogeneous TAF1-associated Clinical Phenotypes

Purpose of review: TATA-binding protein (TBP)-associated factor 1 (TAF1) encodes the largest component of the transcription factor IID (TFIID) complex, which binds to core promoters and serves as a scaffold for assembly of the RNA polymerase II transcription complex. Variants in TAF1 are associated with X-linked dystonia-parkinsonism (XDP) and X-linked syndromic mental retardation-33 (MRXS33). This review provides a concise summary of the genetic and clinicopathological features of TAF1 variants related to phenotype. Recent findings: XDP is an adult-onset X-linked progressive neurodegenerative disorder presenting dystonia and parkinsonism and caused by a SINE-VNTR-Alu (SVA)-type retrotransposon within TAF1. TAF1/MRXS33 intellectual disability syndrome is characterized by global developmental delay, intellectual disability, facial dysmorphia, generalized hypotonia, and neurological abnormalities due to the missense variants in TAF1. Various symptoms of TAF1 missense mutations may be related to mutations in different functional regions of the protein. The clinical manifestations of XDP and MRXS33, both caused by variants of TAF1, present prominent heterogeneity, which could be influenced by whether the TAF1 mutation is located in the coding region, the time when TAF1 expression decreases, and the effect on downstream gene expression. Summary: TAF1 is linked to many different phenotypes because of its variable regulation of coding and noncoding elements, which makes its mechanistic roles in disease challenging to interpret. However, it is important to note that strategies to correct TAF1 splicing could provide therapeutic benefits in different diseases.

Imaging Markers of Multiple System Atrophy and Their Association With Disease Severity: A Cross-Sectional Study.

Background Multiple system atrophy (MSA) is a rare, adult-onset neurodegenerative disorder marked by autonomic failure, parkinsonism, and cerebellar ataxia, with subtypes classified as parkinsonian (MSA-P), cerebellar (MSA-C), and autonomic (MSA-A). This study aims to identify MRI biomarkers for MSA and their correlation with disease severity. Methodology A total of 30 patients with probable MSA (20 MSA-C, 10 MSA-P) aged 45-65 years were studied. Motor and non-motor symptoms were assessed using the Unified Multiple System Atrophy Rating Scale (UMSARS), and all patients underwent 3T MRI brain imaging. Data analysis was performed using SPSS version 22 (IBM Corp., Armonk, NY, USA) with Spearman's correlation for clinical-imaging correlations. Results The mean age of the study population was 54.43 years, with a male predominance (56.7%). The most common symptoms included gait ataxia (43.3%) and urinary dysfunction (96.7%), with orthostatic symptoms in 33.3%. Moderate disease severity was observed, with mean UMSARS scores of 15.9 (Part 1) and 16 (Part 2), showing no significant subtype differences. MRI revealed abnormalities in all patients, predominantly cerebellar atrophy (90%). The "hot cross bun" (HCB) sign was seen in 75% of MSA-C patients, but none of MSA-P patients showed the same. The HCB sign was significantly correlated with severity in MSA-C (USMSARS-4). Putaminal signs were less frequent and slightly more prevalent in MSA-P, without significant clinical-imaging correlation. Conclusions This study reinforces the critical role of MRI biomarkers in the diagnosis of MSA patients. Notably, the HCB sign exhibited a significant association with clinical severity in MSA-C patients, while such correlation was absent in MSA-P cases.

Genetic profiles of multiple system atrophy revealed by exome sequencing, long-read sequencing and spinocerebellar ataxia repeat expansion analysis.

Multiple system atrophy (MSA) is a progressive, adult-onset neurodegenerative disorder clinically characterized by combinations of autonomic failure, parkinsonism, cerebellar ataxia and pyramidal signs. Although a few genetic factors have been reported to contribute to the disease, its mutational profiles have not been systemically studied. To address the genetic profiles of clinically diagnosed MSA patients, exome sequencing and triplet repeat detection was conducted in 205 MSA patients, including one familial case. The pathogenicity of variants was determined according to the American College of Medical Genetics and Genomics and the Association for Molecular Pathology guidelines. In the familial patient, a novel heterozygous COQ2 pathogenic variant (p.Ala351Thr) was identified in the MSA pedigree. In the sporadic patients, 29 pathogenic variants were revealed in 21 genes, and the PARK7 p.Ala104Thr variant was significantly associated with MSA (p = 0.0018). Moreover, burden tests demonstrated that the pathogenic variants were enriched in cerebellar ataxia-related genes in patients. Furthermore, repeat expansion analyses revealed that two patients carried the pathogenic CAG repeat expansion in the CACNA1A gene (SCA6), one patient carried the (ACAGG)exp/(ACAGG)exp expansion in RFC1 and one carried the GAA-pure expansion in FGF14 gene. In conclusion, a novel COQ2 pathogenic variant was identified in a familial MSA patient, and repeat expansions in CACNA1A, RFC1 and FGF14 gene were detected in four sporadic patients. Moreover, a PARK7 variant and the burden of pathogenic variants in cerebellar ataxia-related genes were associated with MSA.

Phase Separation of SARS-CoV-2 Nucleocapsid Protein with TDP-43 Is Dependent on C-Terminus Domains.

The SARS-CoV-2 nucleocapsid protein (N protein) is critical in viral replication by undergoing liquid-liquid phase separation to seed the formation of a ribonucleoprotein (RNP) complex to drive viral genomic RNA (gRNA) translation and in suppressing both stress granules and processing bodies, which is postulated to increase uncoated gRNA availability. The N protein can also form biomolecular condensates with a broad range of host endogenous proteins including RNA binding proteins (RBPs). Amongst these RBPs are proteins that are associated with pathological, neuronal, and glial cytoplasmic inclusions across several adult-onset neurodegenerative disorders, including TAR DNA binding protein 43 kDa (TDP-43) which forms pathological inclusions in over 95% of amyotrophic lateral sclerosis cases. In this study, we demonstrate that the N protein can form biomolecular condensates with TDP-43 and that this is dependent on the N protein C-terminus domain (N-CTD) and the intrinsically disordered C-terminus domain of TDP-43. This process is markedly accelerated in the presence of RNA. In silico modeling suggests that the biomolecular condensate that forms in the presence of RNA is composed of an N protein quadriplex in which the intrinsically disordered TDP-43 C terminus domain is incorporated.

Ultra-high-field 7-Tesla magnetic resonance imaging in fragile X tremor/ataxia syndrome (FXTAS).

Fragile X tremor/ataxia syndrome (FXTAS) is an adult-onset neurodegenerative disorder characterized by premutation expansion of fragile X mental retardation 1 (FMR1) gene. It is a common single-gene cause of tremor, ataxia, and cognitive decline in adults. FXTAS affects the central, peripheral and autonomic nervous systems, leading to a range of neurological symptoms from dementia to dysautonomia. A characteristic imaging feature of FXTAS is symmetric T2 hyperintensity in the deep white matter of the cerebellar hemispheres and middle cerebral peduncle. However, recent studies have reported additional findings on diffusion weighted images (DWI), such as a symmetric high-intensity band-like signal at the cerebral corticomedullary junction. These findings, along with the characteristic cerebellar signal alterations, overlap with imaging findings seen in adult-onset neuronal intranuclear inclusion disease (NIID). Importantly, recent pathology studies have shown that both FXTAS and NIID can manifest intranuclear inclusion bodies, posing a diagnostic challenge and potential for misdiagnosis. We describe a 58-year-old man with FXTAS who received an erroneous diagnosis based on imaging and histopathology results. We emphasize the potential pitfalls in distinguishing NIID from FXTAS and stress the importance of genetic analysis in all cases with suspected NIID and FXTAS for confirmation. Additionally, we present the 7T MRI brain findings of FXTAS.

Stability of Mosaic Divergent Repeat Interruptions in X-Linked Dystonia-Parkinsonism.

X-Linked dystonia-parkinsonism (XDP) is an adult-onset neurodegenerative disorder characterized by rapidly progressive dystonia and parkinsonism. Mosaic Divergent Repeat Interruptions affecting motif Length and Sequence (mDRILS) were recently found within the TAF1 SVA repeat tract and were shown to associate with repeat stability and age at onset in XDP, specifically the AGGG [5'-SINE-VNTR-Alu(AGAGGG)2AGGG(AGAGGG)n] mDRILS. This study aimed to investigate the stability of mDRILS frequencies and stability of (AGAGGG)n repeat length during transmission in parent-offspring pairs. Fifty-six families (n = 130) were investigated for generational transmission of repeat length and mDRILS. The mDRILS stability of 16 individuals was assessed at two sampling points 1 year apart. DNA was sequenced with long-read technologies after long-range polymerase chain reaction amplification of the TAF1 SVA. Repeat number and mDRILS were detected with Noise-Cancelling Repeat Finder (NCRF). When comparing the repeat domain, 51 of 65 children had either contractions or expansions of the repeat length. The AGGG frequency remained stable across generations at 0.074 (IQR: 0.069-0.078) (z = -0.526; P = 0.599). However, the median AGGG frequency in children with an expansion (0.072 [IQR: 0.066-0.076]) was lower compared with children with retention or contraction (0.080 [IQR: 0.073-0.083]) (z = -0.007; P = 0.003). In a logistic regression model, the AGGG frequency predicted the outcome of either expansion or retention/contraction when including repeat number and sex as covariates (β = 80.7; z-score = 2.63; P = 0.0085). The AGGG frequency varied slightly over 1 year (0.070 [IQR: 0.063-0.080] to 0.073 [IQR: 0.069-0.078]). Our results show that a higher AGGG frequency may stabilize repeats across generations. This highlights the importance of further investigating mDRILS as a disease-modifying factor with generational differences. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Oligodendrocytes in amyotrophic lateral sclerosis and frontotemporal dementia: the new players on stage.

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are fatal adult-onset neurodegenerative disorders that share clinical, neuropathological and genetic features, which forms part of a multi-system disease spectrum. The pathological process leading to ALS and FTD is the result of the combination of multiple mechanisms that operate within specific populations of neurons and glial cells. The implication of oligodendrocytes has been the subject of a number of studies conducted on patients and related animal models. In this review we summarize our current knowledge on the alterations specific to myelin and the oligodendrocyte lineage occurring in ALS and FTD. We also consider different ways by which specific oligodendroglial alterations influence neurodegeneration and highlight the important role of oligodendrocytes in these two intrinsically associated neurodegenerative diseases.

Multiple system atrophy: an update and emerging directions of biomarkers and clinical trials.

Multiple system atrophy is a rare, debilitating, adult-onset neurodegenerative disorder that manifests clinically as a diverse combination of parkinsonism, cerebellar ataxia, and autonomic dysfunction. It is pathologically characterized by oligodendroglial cytoplasmic inclusions containing abnormally aggregated α-synuclein. According to the updated Movement Disorder Society diagnostic criteria for multiple system atrophy, the diagnosis of clinically established multiple system atrophy requires the manifestation of autonomic dysfunction in combination with poorly levo-dopa responsive parkinsonism and/or cerebellar syndrome. Although symptomatic management of multiple system atrophy can substantially improve quality of life, therapeutic benefits are often limited, ephemeral, and they fail to modify the disease progression and eradicate underlying causes. Consequently, effective breakthrough treatments that target the causes of disease are needed. Numerous preclinical and clinical studies are currently focusing on a set of hallmarks of neurodegenerative diseases to slow or halt the progression of multiple system atrophy: pathological protein aggregation, synaptic dysfunction, aberrant proteostasis, neuronal inflammation, and neuronal cell death. Meanwhile, specific biomarkers and measurements with higher specificity and sensitivity are being developed for the diagnosis of multiple system atrophy, particularly for early detection of the disease. More intriguingly, a growing number of new disease-modifying candidates, which can be used to design multi-targeted, personalized treatment in patients, are being investigated, notwithstanding the failure of most previous attempts.

Mutations in FUS lead to synaptic dysregulation in ALS-iPSC derived neurons

Amyotrophic lateral sclerosis (ALS) is a fatal, adult-onset neurodegenerative disorder characterized by progressive muscular weakness due to the selective loss of motor neurons. Mutations in the gene Fused in Sarcoma (FUS) were identified as one cause of ALS. Here, we report that mutations in FUS lead to upregulation of synaptic proteins, increasing synaptic activity and abnormal release of vesicles at the synaptic cleft. Consequently, FUS-ALS neurons showed greater vulnerability to glutamate excitotoxicity, which raised neuronal swellings (varicose neurites) and led to neuronal death. Fragile X mental retardation protein (FMRP) is an RNA-binding protein known to regulate synaptic protein translation, and its expression is reduced in the FUS-ALS lines. Collectively, our data suggest that a reduction of FMRP levels alters the synaptic protein dynamics, leading to synaptic dysfunction and glutamate excitotoxicity. Here, we present a mechanistic hypothesis linking dysregulation of peripheral translation with synaptic vulnerability in the pathogenesis of FUS-ALS.

CD4 T-cell aging exacerbates neuroinflammation in a late-onset mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset progressive neurodegenerative disorder characterized by the loss of upper and lower motor neurons in the brain and spinal cord. Accumulating evidence suggests that ALS is not solely a neuronal cell- or brain tissue-autonomous disease and that neuroinflammation plays a key role in disease progression. Furthermore, whereas both CD4 and CD8 T cells were observed in spinal cords of ALS patients and in mouse models of the disease, their role in the neuroinflammatory process, especially considering their functional changes with age, is not fully explored. In this study, we revealed the structure of the CD4 T-cell compartment during disease progression of early-onset SOD1G93A and late-onset SOD1G37R mouse models of ALS. We show age-related changes in the CD4 T-cell subset organization between these mutant SOD1 mouse models towards increased frequency of effector T cells in spleens of SOD1G37R mice and robust infiltration of CD4 T cells expressing activation markers and the checkpoint molecule PD1 into the spinal cord. The frequency of infiltrating CD4 T cells correlated with the frequency of infiltrating CD8 T cells which displayed a more exhausted phenotype. Moreover, RNA-Seq and immunohistochemistry analyses of spinal cords from SOD1G37R mice with early clinical symptoms demonstrated immunological trajectories reminiscent of a neurotoxic inflammatory response which involved proinflammatory T cells and antigen presentation related pathways. Overall, our findings suggest that age-related changes of the CD4 T cell landscape is indicative of a chronic inflammatory response, which aggravates the disease process and can be therapeutically targeted.

Degeneration of olivospinal tract in the upper cervical spinal cord of multiple system atrophy patients: Reappraisal of Helweg's triangular tract.

Multiple system atrophy (MSA) is an adult-onset neurodegenerative disorder that presents with variable combinations of autonomic dysfunction, cerebellar ataxia, parkinsonism, and pyramidal signs. The inferior olivary nucleus is targeted in MSA, with a phenotype of olivopontocerebellar atrophy in particular, and involvement of the olivocerebellar tract is well known. However, degeneration of the olivospinal tract has not been studied in MSA. We examined 97 spinal cords from consecutively autopsied patients with MSA. Myelin staining revealed that 22 cords (22.7%) had small, bilateral, triangular-shaped tract degeneration in the boundary of the anterior and lateral funiculi, which appeared continuously from C1 to C5. The anatomical pathway of the degenerated tract was consistent with the description of the olivospinal tract provided by Helweg in 1888. The MSA patients showing degeneration of this tract were younger at disease onset (average: 56.4 ± 8.7 years, range: 42-74), and had longer disease duration (average: 10.1 ± 4.8 years, range: 2-25) and more severe olivopontocerebellar changes compared to other MSA patients. Quantitative analyses revealed that patients with olivospinal tract degeneration had a lower neuronal density in the inferior olivary nucleus compared to other patients. Microglial density in this tract was negatively correlated with the neuronal density in the inferior olivary nucleus. The densities of glial cytoplasmic inclusions in the inferior olivary nucleus and in the olivospinal tract were strongly correlated with each other. Neurologically healthy controls (n = 22) and disease controls with Lewy body disease (n = 30), amyotrophic lateral sclerosis (n = 30), and progressive supranuclear palsy (n = 30) did not present the olivospinal tract degeneration. Our results indicate an impairment of the neural connection between the inferior olivary nucleus and the spinal cord in MSA patients, which may develop in a descending manner.

Disease-Associated Mutation A554V Disrupts Normal Autoinhibition of DNMT1.

DNA methyltransferase 1 (DNMT1) is the enzyme primarily responsible for propagation of the methylation pattern in cells. Mutations in DNMT1 have been linked to the development of adult-onset neurodegenerative disorders; these disease-associated mutations occur in the regulatory replication foci-targeting sequence (RFTS) domain of the protein. The RFTS domain is an endogenous inhibitor of DNMT1 activity that binds to the active site and prevents DNA binding. Here, we examine the impact of the disease-associated mutation A554V on normal RFTS-mediated inhibition of DNMT1. Wild-type and mutant proteins were expressed and purified to homogeneity for biochemical characterization. The mutation increased DNA binding affinity ~8-fold. In addition, the mutant enzyme exhibited increased DNA methylation activity. Circular dichroism (CD) spectroscopy revealed that the mutation does not significantly impact the secondary structure or relative thermal stability of the isolated RFTS domain. However, the mutation resulted in changes in the CD spectrum in the context of the larger protein; a decrease in relative thermal stability was also observed. Collectively, this evidence suggests that A554V disrupts normal RFTS-mediated autoinhibition of DNMT1, resulting in a hyperactive mutant enzyme. While the disease-associated mutation does not significantly impact the isolated RFTS domain, the mutation results in a weakening of the interdomain stabilizing interactions generating a more open, active conformation of DNMT1. Hyperactive mutant DNMT1 could be responsible for the increased DNA methylation observed in affected individuals.

Synchrotron-Based Fourier-Transform Infrared Micro-Spectroscopy of Cerebrospinal Fluid from Amyotrophic Lateral Sclerosis Patients Reveals a Unique Biomolecular Profile.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, with the most common adult-onset neurodegenerative disorder affecting motoneurons. Although disruptions in macromolecular conformation and homeostasis have been described in association with ALS, the underlying pathological mechanisms are still not completely understood, and unambiguous biomarkers are lacking. Fourier Transform Infrared Spectroscopy (FTIR) of cerebrospinal fluid (CSF) is appealing to extensive interest due to its potential to resolve biomolecular conformation and content, as this approach offers a non-invasive, label-free identification of specific biologically relevant molecules in a few microliters of CSF sample. Here, we analyzed the CSF of 33 ALS patients compared to 32 matched controls using FTIR spectroscopy and multivariate analysis and demonstrated major differences in the molecular contents. A significant change in the conformation and concentration of RNA is demonstrated. Moreover, significantly increased glutamate and carbohydrates are found in ALS. Moreover, key markers of lipid metabolism are strongly altered; specifically, we find a decrease in unsaturated lipids and an increase in peroxidation of lipids in ALS, whereas the total amount of lipids compared to proteins is reduced. Our study demonstrates that FTIR characterization of CSF could represent a powerful tool for ALS diagnosis and reveals central features of ALS pathophysiology.

Novel therapeutic strategies targeting mitochondria as a gateway in neurodegeneration.

In recent years, multiple disciplines have focused on mitochondrial biology and contributed to understanding its relevance towards adult-onset neurodegenerative disorders. These are complex dynamic organelles that have a variety of functions in ensuring cellular health and homeostasis. The plethora of mitochondrial functionalities confers them an intrinsic susceptibility to internal and external stressors (such as mutation accumulation or environmental toxins), particularly so in long-lived postmitotic cells such as neurons. Thus, it is reasonable to postulate an involvement of mitochondria in aging-associated neurological disorders, notably neurodegenerative pathologies including Alzheimer's disease and Parkinson's disease. On the other hand, biological effects resulting from neurodegeneration can in turn affect mitochondrial health and function, promoting a feedback loop further contributing to the progression of neuronal dysfunction and cellular death. This review examines state-of-the-art knowledge, focus on current research exploring mitochondrial health as a contributing factor to neuroregeneration, and the development of therapeutic approaches aimed at restoring mitochondrial homeostasis in a pathological setting.

Huntingtin Decreases Susceptibility to a Spontaneous Seizure Disorder in FVN/B Mice.

Huntington disease (HD) is an adult-onset neurodegenerative disorder that is caused by a trinucleotide CAG repeat expansion in the HTT gene that codes for the protein huntingtin (HTT in humans or Htt in mice). HTT is a multi-functional, ubiquitously expressed protein that is essential for embryonic survival, normal neurodevelopment, and adult brain function. The ability of wild-type HTT to protect neurons against various forms of death raises the possibility that loss of normal HTT function may worsen disease progression in HD. Huntingtin-lowering therapeutics are being evaluated in clinical trials for HD, but concerns have been raised that decreasing wild-type HTT levels may have adverse effects. Here we show that Htt levels modulate the occurrence of an idiopathic seizure disorder that spontaneously occurs in approximately 28% of FVB/N mice, which we have called FVB/N Seizure Disorder with SUDEP (FSDS). These abnormal FVB/N mice demonstrate the cardinal features of mouse models of epilepsy including spontaneous seizures, astrocytosis, neuronal hypertrophy, upregulation of brain-derived neurotrophic factor (BDNF), and sudden seizure-related death. Interestingly, mice heterozygous for the targeted inactivation of Htt (Htt+/- mice) exhibit an increased frequency of this disorder (71% FSDS phenotype), while over-expression of either full length wild-type HTT in YAC18 mice or full length mutant HTT in YAC128 mice completely prevents it (0% FSDS phenotype). Examination of the mechanism underlying huntingtin's ability to modulate the frequency of this seizure disorder indicated that over-expression of full length HTT can promote neuronal survival following seizures. Overall, our results demonstrate a protective role for huntingtin in this form of epilepsy and provide a plausible explanation for the observation of seizures in the juvenile form of HD, Lopes-Maciel-Rodan syndrome, and Wolf-Hirschhorn syndrome. Adverse effects caused by decreasing huntingtin levels have ramifications for huntingtin-lowering therapies that are being developed to treat HD.

Concurrent sodium channel myotonia and amyotrophic lateral sclerosis supports shared pathogenesis

Amyotrophic lateral sclerosis (ALS) is an invariably fatal adult-onset neurodegenerative disorder; 10% of ALS is autosomal dominant but even sporadic ALS exhibits significant heritability. Dysfunctional voltage- gated sodium channels (NaVs) have been implicated in both sporadic and familial forms of the disease, but it is unclear whether these are an upstream cause or a downstream consequence. Rare missense mutations in the SCN4A gene, encoding NaV1.4, disrupt membrane excitability and cause autosomal dominant muscle channelopathies such as myotonia and hypo/hyperkalaemic periodic paralysis. We report two patients with congenital SCN4A channelopathy due to p.S1159P and p.R672H mutations who developed ALS in later life. Based on our finding we hypothesised that ALS may be linked to genetic mutations in other voltage gated ion channels. Rare-variant burden testing using whole genome sequenc- ing data from 4,495 ALS patients and 1,925 controls within the superfamily of voltage-gated ion channels (Accession: ssf81324) identified one gene, SCN7A, which passed multiple testing correction (p=0.0002, Firth logistic regression) consistent with an enrichment of ALS-associated mutations. We propose that genetic mutations within NaVs leading to neuromuscular excitotoxicity are an upstream cause of ALS. Early identification of ALS patients carrying NaV mutations might lead to personalised therapy with a sodium channel-blocking agent such as riluzole.j.franklin@doctors.org.uk

Role of Superoxide Dismutase in Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS), or Lou Gehrig's disease, is an adult‐onset neurodegenerative disorder that has been linked to over 200 mutations from the SOD1 gene. The protein created from this gene is superoxide dismutase (SOD1), an enzyme responsible for breaking down toxic superoxide radicals by facilitating the binding to zinc and copper. Superoxide dismutase is a homodimer, composed of two identical subunits, and is located in the cytoplasm of the cell, Each subunit has 154 amino acid residues with a β‐barrel core, formed by 8 beta‐sheets, and three outer loops which are linked together by a disulfide bond, a hydrogen bond network, and a metal‐binding site for both zinc and copper. This metal‐binding site is responsible for the catalyzation of superoxide radicals to hydrogen peroxide and dioxygen. The redox reactions that SOD1 allows to occur are the oxidation of superoxide to dioxygen and the reduction of superoxide to hydrogen peroxide while alternating the oxidation states of Copper. The zinc molecule acts as a structural element for the reaction. The catalyzation of superoxide radicals to safer components occurs because the accumulation of superoxide radicals is toxic to the cell, and can lead to cell death. Another role of SOD1 is its responsibility in preventing oxidative stress. Oxidative stress is the result of the imbalance between reactive oxygen species such as superoxide, and the activity of superoxide dismutase to detoxify the affected areas. In cases of ALS, mutations cause this accumulation, which leads to motor neuron death. The most common mutation of SOD1 in the United States, as well as the one that causes the fastest onset for ALS to occur, is A5V, which is the replacement of the alanine residue with valine at position 5. This mutation can result in not only the accumulation of superoxide radicals but also the production of more neurotoxic radicals and fibrillar aggregates of misfolded SOD1, which can occur due to the absence of the disulfide bond or bound zinc ions. These effects lead to motor neuron death, which manifests as the symptoms of ALS. The symptoms of ALS are progressive muscle weakness, loss of voluntary muscle control, the decline of the ability to initiate movement, and paralysis. ALS, especially as a result of the A5V mutation, often leads to a shorter life expectancy. Amyotrophic Lateral Sclerosis currently has no cure, but there are many evolving therapies for the disease. Patients with ALS are encouraged to participate in gentle, low‐impact physical therapies and use special equipment to support communication, nutrition, and breathing. The drugs approved by the FDA to help treat ALS include Riluzole (Rilutek), which reduces damage to cells by blocking the release of glutamate, and Edaravone (Radicava) which removes free radicals. In addition, small‐molecule therapies are being developed to stabilize the native form of SOD1 in the absence of zinc or in the presence of protein mutations, which may reduce the effects of the manifestation of the disease. Further research is needed to determine specifically how mutations of SOD1 lead to motor neuron death, and the resulting symptoms of Amyotrophic Lateral Sclerosis.

Differential regulation of L84F SOD1 in motor neurons and skeletal muscles: an insight into ALS pathology

Amyotrophic lateral sclerosis (ALS) is an adult onset neurodegenerative disorder characterized by progressive deterioration of motor neurons leading to skeletal muscle denervation. Recent evidences have highlighted early involvement of neuromuscular junction (NMJ) in ALS pathogenesis. NMJ is a specialized tripartite chemical synapse which involves a well‐coordinated communication among the presynaptic motor neuron, postsynaptic skeletal muscle and terminal Schwann cells. Despite several evidences, series of events triggering NMJ disassembly in ALS are still obscure.The aim of our study is to investigate the cellular and molecular mechanisms of NMJ dysfunction in an in vitro Superoxide Dismutase 1 (SOD1) induced model of familial ALS. We have generated an ALS cell model based on a novel SOD1 mutation (L84F) identified previously in a family with a history of ALS. This mutation caused decrease in neurite outgrowth which led us to hypothesize that it may be involved in neuromuscular junction disassembly in ALS pathology.We have characterized cellular components of NMJ by differentiating hybrid spinal cord cell line (NSC‐34) into motor neurons and myoblast cell line (C2C12) into myotubes. Expression of mutant SOD1 led to decrease in mitochondrial footprints in axons and synaptic terminals and altered mitochondrial dynamics in motor neurons. However mitochondrial fission/fusion is not altered in muscles suggesting differential consequences of mutant protein. L84F SOD1 mutant readily formed detergent‐resistant aggregates in motor neurons but failed to accumulate in skeletal muscles. Skeletal muscles displayed increased levels of LC3‐II compared to motor neurons suggesting a robust proteasome machinery of muscles is responsible for clearance of mutant protein. Furthermore, motor neurons exhibited increased cell death compared to skeletal muscles when subjected to exogenous stress. Interestingly, we observed that condition media from skeletal muscles was able to rescue motor neurons from exogenous stress. We are currently identifying paracrine neuroprotective factors secreted by the muscles. It is noteworthy that mutant SOD1 led to altered expression of post synaptic acetylcholine receptor complex which might hamper neuromuscular transmission in ALS.To conclude, molecular cues from both neurons and muscles appear to play a role in compromising NMJ integrity in ALS.

Reduction of mutant ATXN1 rescues premature death in a conditional SCA1 mouse model.

Spinocerebellar ataxia type 1 (SCA1) is an adult-onset neurodegenerative disorder. As disease progresses, motor neurons are affected, and their dysfunction contributes toward the inability to maintain proper respiratory function, a major driving force for premature death in SCA1. To investigate the isolated role of motor neurons in SCA1, we created a conditional SCA1 (cSCA1) mouse model. This model suppresses expression of the pathogenic SCA1 allele with a floxed stop cassette. cSCA1 mice crossed to a ubiquitous Cre line recapitulate all the major features of the original SCA1 mouse model; however, they took twice as long to develop. We found that the cSCA1 mice produced less than half of the pathogenic protein compared with the unmodified SCA1 mice at 3 weeks of age. In contrast, restricted expression of the pathogenic SCA1 allele in motor neurons only led to a decreased distance traveled of mice in the open field assay and did not affect body weight or survival. We conclude that a 50% or greater reduction of the mutant protein has a dramatic effect on disease onset and progression; furthermore, we conclude that expression of polyglutamine-expanded ATXN1 at this level specifically in motor neurons is not sufficient to cause premature lethality.

Tissue-specific and repeat length-dependent somatic instability of the X-linked dystonia parkinsonism-associated CCCTCT repeat

X-linked dystonia-parkinsonism (XDP) is a progressive adult-onset neurodegenerative disorder caused by insertion of a SINE-VNTR-Alu (SVA) retrotransposon in the TAF1 gene. The SVA retrotransposon contains a CCCTCT hexameric repeat tract of variable length, whose length is inversely correlated with age at onset. This places XDP in a broader class of repeat expansion diseases, characterized by the instability of their causative repeat mutations. Here, we observe similar inverse correlations between CCCTCT repeat length with age at onset and age at death and no obvious correlation with disease duration. To gain insight into repeat instability in XDP we performed comprehensive quantitative analyses of somatic instability of the XDP CCCTCT repeat in blood and in seventeen brain regions from affected males. Our findings reveal repeat length-dependent and expansion-based instability of the XDP CCCTCT repeat, with greater levels of expansion in brain than in blood. The brain exhibits regional-specific patterns of instability that are broadly similar across individuals, with cerebellum exhibiting low instability and cortical regions exhibiting relatively high instability. The spectrum of somatic instability in the brain includes a high proportion of moderate repeat length changes of up to 5 repeats, as well as expansions of ~ 20- > 100 repeats and contractions of ~ 20–40 repeats at lower frequencies. Comparison with HTT CAG repeat instability in postmortem Huntington’s disease brains reveals similar brain region-specific profiles, indicating common trans-acting factors that contribute to the instability of both repeats. Analyses in XDP brains of expansion of a different SVA-associated CCCTCT located in the LIPG gene, and not known to be disease-associated, reveals repeat length-dependent expansion at overall lower levels relative to the XDP CCCTCT repeat, suggesting that expansion propensity may be modified by local chromatin structure. Together, the data support a role for repeat length-dependent somatic expansion in the process(es) driving the onset of XDP and prompt further investigation into repeat dynamics and the relationship to disease.