The changing scene of amyotrophic lateral sclerosis

Motoneuronal and muscle-selective removal of ALS-related misfolded proteins

ALS (amyotrophic lateral sclerosis), a fatal motoneuron (motor neuron) disease, occurs in clinically indistinguishable sporadic (sALS) or familial (fALS) forms. Most fALS-related mutant proteins identified so far are prone to misfolding, and must be degraded in order to protect motoneurons from their toxicity. This process, mediated by molecular chaperones, requires proteasome or autophagic systems. Motoneurons are particularly sensitive to misfolded protein toxicity, but other cell types such as the muscle cells could also be affected. Muscle-restricted expression of the fALS protein mutSOD1 (mutant superoxide dismutase 1) induces muscle atrophy and motoneuron death. We found that several genes have an altered expression in muscles of transgenic ALS mice at different stages of disease. MyoD, myogenin, atrogin-1, TGFβ1 (transforming growth factor β1) and components of the cell response to proteotoxicity [HSPB8 (heat shock 22kDa protein 8), Bag3 (Bcl-2-associated athanogene 3) and p62] are all up-regulated by mutSOD1 in skeletal muscle. When we compared the potential mutSOD1 toxicity in motoneuron (NSC34) and muscle (C2C12) cells, we found that muscle ALS models possess much higher chymotryptic proteasome activity and autophagy power than motoneuron ALS models. As a result, mutSOD1 molecular behaviour was found to be very different. MutSOD1 clearance was found to be much higher in muscle than in motoneurons. MutSOD1 aggregated and impaired proteasomes only in motoneurons, which were particularly sensitive to superoxide-induced oxidative stress. Moreover, in muscle cells, mutSOD1 was found to be soluble even after proteasome inhibition. This effect could be associated with a higher mutSOD1 autophagic clearance. Therefore muscle cells seem to manage misfolded mutSOD1 more efficiently than motoneurons, thus mutSOD1 toxicity in muscle may not directly depend on aggregation.

Many roads lead to Rome? Multiple modes of Cu,Zn superoxide dismutase destabilization, misfolding and aggregation in amyotrophic lateral sclerosis

ALS (amyotrophic lateral sclerosis) is a fatal neurodegenerative syndrome characterized by progressive paralysis and motor neuron death. Although the pathological mechanisms that cause ALS remain unclear, accumulating evidence supports that ALS is a protein misfolding disorder. Mutations in Cu,Zn-SOD1 (copper/zinc superoxide dismutase 1) are a common cause of familial ALS. They have complex effects on different forms of SOD1, but generally destabilize the protein and enhance various modes of misfolding and aggregation. In addition, there is some evidence that destabilized covalently modified wild-type SOD1 may be involved in disease. Among the multitude of misfolded/aggregated species observed for SOD1, multiple species may impair various cellular components at different disease stages. Newly developed antibodies that recognize different structural features of SOD1 represent a powerful tool for further unravelling the roles of different SOD1 structures in disease. Evidence for similar cellular targets of misfolded/aggregated proteins, loss of cellular proteostasis and cell–cell transmission of aggregates point to common pathological mechanisms between ALS and other misfolding diseases, such as Alzheimer's, Parkinson's and prion diseases, as well as serpinopathies. The recent progress in understanding the molecular basis for these devastating diseases provides numerous avenues for developing urgently needed therapeutics.

A post hoc analysis of subgroup outcomes and creatinine in the phase III clinical trial (EMPOWER) of dexpramipexole in ALS

Our objective was to compare the phase II and phase III (EMPOWER) studies of dexpramipexole in ALS and evaluate potential EMPOWER responder subgroups and biomarkers based on significant inter-study population differences. In a post hoc analysis, we compared the baseline population characteristics of both dexpramipexole studies and analyzed EMPOWER efficacy outcomes and laboratory measures in subgroups defined by significant inter-study differences. Results showed that, compared with phase II, the proportion of El Escorial criteria (EEC) definite participants decreased (p = 0.005), riluzole use increased (p = 0.002), and mean symptom duration increased (p = 0.037) significantly in EMPOWER. Baseline creatinine (p < 0.001) and on-study creatinine change (p < 0.001) correlated significantly with ALSFRS-R in EMPOWER. In the EMPOWER subgroup defined by EEC-definite ALS, riluzole use, and < median symptom duration (15.3 months), dexpramipexole-treated participants had reduced ALSFRS-R slope decline (p = 0.015), decreased mortality (p = 0.011), and reduced creatinine loss (p = 0.003). In conclusion, significant differences existed between the phase II and EMPOWER study populations in ALS clinical trials of dexpramipexole. In a post hoc analysis of EMPOWER subgroups defined by these differences, potential clinical benefits of dexpramipexole were identified in the subgroup of riluzole-treated, short-symptom duration, EEC-definite ALS participants. Creatinine loss correlated with disease progression and was reduced in dexpramipexole-treated participants, suggesting it as a candidate biomarker.

ALS as a distal axonopathy: molecular mechanisms affecting neuromuscular junction stability in the presymptomatic stages of the disease

Amyotrophic Lateral Sclerosis (ALS) is being redefined as a distal axonopathy, in that many molecular changes influencing motor neuron degeneration occur at the neuromuscular junction (NMJ) at very early stages of the disease prior to symptom onset. A huge variety of genetic and environmental causes have been associated with ALS, and interestingly, although the cause of the disease can differ, both sporadic and familial forms of ALS show a remarkable similarity in terms of disease progression and clinical manifestation. The NMJ is a highly specialized synapse, allowing for controlled signaling between muscle and nerve necessary for skeletal muscle function. In this review we will evaluate the clinical, animal experimental and cellular/molecular evidence that supports the idea of ALS as a distal axonopathy. We will discuss the early molecular mechanisms that occur at the NMJ, which alter the functional abilities of the NMJ. Specifically, we focus on the role of axon guidance molecules on the stability of the cytoskeleton and how these molecules may directly influence the cells of the NMJ in a way that may initiate or facilitate the dismantling of the neuromuscular synapse in the presymptomatic stages of ALS.

Neuronal AChE splice variants and their non-hydrolytic functions: redefining a target of AChE inhibitors?

AChE enzymatic inhibition is a core focus of pharmacological intervention in Alzheimer's disease (AD). Yet, AChE has also been ascribed non-hydrolytic functions, which seem related to its appearance in various isoforms. Neuronal AChE presents as a tailed form (AChE-T) predominantly found on the neuronal synapse, and a facultatively expressed readthough form (AChE-R), which exerts short to medium-term protective effects. Notably, this latter form is also found in the periphery. While these non-hydrolytic functions of AChE are most controversially discussed, there is evidence for them being additional targets of AChE inhibitors. This review aims to provide clarification as to the role of these AChE splice variants and their interplay with other cholinergic parameters and their being targets of AChE inhibition: AChE-R is particularly involved in the mediation of (anti-)apoptotic events in cholinergic cells, involving adaptation of various cholinergic parameters and a time-dependent link to the expression of neuroprotective factors. The AChE-T C-terminus is central to AChE activity regulation, while isolated AChE-T C-terminal fragments mediate toxic effects via the α7 nicotinic acetylcholine receptor. There is direct evidence for roles of AChE-T and AChE-R in neurodegeneration and neuroprotection, with these roles involving AChE as a key modulator of the cholinergic system: in vivo data further encourages the use of AChE inhibitors in the treatment of neurodegenerative conditions such as AD since effects on both enzymatic activity and the enzyme's non-hydrolytic functions can be postulated. It also suggests that novel AChE inhibitors should enhance protective AChE-R, while avoiding the concomitant up-regulation of AChE-T.

Adenosine A2A receptors activation facilitates neuromuscular transmission in the pre-symptomatic phase of the SOD1(G93A) ALS mice, but not in the symptomatic phase

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease leading to motor neuron dysfunction resulting in impairment of neuromuscular transmission. A2A adenosine receptors have already been considered as a potential therapeutical target for ALS but their neuromodulatory role at the neuromuscular junction in ALS remains to be clarified. In the present work, we evaluated the effects of A2A receptors on neuromuscular transmission of an animal model of ALS: SOD1(G93A) mice either in the pre-symptomatic (4-6 weeks old) or in the symptomatic (12-14 weeks old) stage. Electrophysiological experiments were performed obtaining intracellular recordings in Mg2+ paralyzed phrenic nerve-hemidiaphragm preparations. Endplate potentials (EPPs), quantal content (q. c.) of EPPs, miniature endplate potentials (MEPPs) and giant miniature endplate potential (GMEPPs) were recorded. In the pre-symptomatic phase of the disease (4-6 weeks old mice), the selective A2A receptor agonist, CGS 21680, significantly enhanced (p<0.05 Unpaired t-test) the mean amplitude and q.c. of EPPs, and the frequency of MEPPs and GMEPPs at SOD1(G93A) neuromuscular junctions, the effect being of higher magnitude (p<0.05, Unpaired t-test) than age-matched control littermates. On the contrary, in symptomatic mice (12-14 weeks old), CGS 21680 was devoid of effect on both the amplitude and q.c. of EPPs and the frequency of MEPPs and GMEPPs (p<0.05 Paired t-test). The results herein reported clearly document that at the neuromuscular junction of SOD1(G93A) mice there is an exacerbation of A2A receptor-mediated excitatory effects at the pre-symptomatic phase, whereas in the symptomatic phase A2A receptor activation is absent. The results thus suggest that A2A receptors function changes with ALS progression.

Altered thiol chemistry in human amyotrophic lateral sclerosis-linked mutants of superoxide dismutase 1

Neurodegenerative diseases share a common characteristic, the presence of intracellular or extracellular deposits of protein aggregates in nervous tissues. Amyotrophic Lateral Sclerosis (ALS) is a severe and fatal neurodegenerative disorder, which affects preferentially motoneurons. Changes in the redox state of superoxide dismutase 1 (SOD1) are associated with the onset and development of familial forms of ALS. In human SOD1 (hSOD1), a conserved disulfide bond and two free cysteine residues can engage in anomalous thiol/disulfide exchange resulting in non-native disulfides, a hallmark of ALS that is related to protein misfolding and aggregation. Because of the many competing reaction pathways, traditional bulk techniques fall short at quantifying individual thiol/disulfide exchange reactions. Here, we adapt recently developed single-bond chemistry techniques to study individual disulfide isomerization reactions in hSOD1. Mechanical unfolding of hSOD1 leads to the formation of a polypeptide loop held by the disulfide. This loop behaves as a molecular jump rope that brings reactive Cys-111 close to the disulfide. Using force-clamp spectroscopy, we monitor nucleophilic attack of Cys-111 at either sulfur of the disulfide and determine the selectivity of the reaction. Disease-causing mutations G93A and A4V show greatly altered reactivity patterns, which may contribute to the progression of familial ALS.

Autophagy induction enhances TDP43 turnover and survival in neuronal ALS models

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) have distinct clinical features but a common pathology--cytoplasmic inclusions rich in transactive response element DNA-binding protein of 43 kDa (TDP43). Rare TDP43 mutations cause ALS or FTD, but abnormal TDP43 levels and localization may cause disease even if TDP43 lacks a mutation. Here we show that individual neurons vary in their ability to clear TDP43 and are exquisitely sensitive to TDP43 levels. To measure TDP43 clearance, we developed and validated a single-cell optical method that overcomes the confounding effects of aggregation and toxicity and discovered that pathogenic mutations shorten TDP43 half-life. New compounds that stimulate autophagy improved TDP43 clearance and localization and enhanced survival in primary murine neurons and in human stem cell-derived neurons and astrocytes harboring mutant TDP43. These findings indicate that the levels and localization of TDP43 critically determine neurotoxicity and show that autophagy induction mitigates neurodegeneration by acting directly on TDP43 clearance.

Potentiated Hsp104 variants suppress toxicity of diverse neurodegenerative disease-linked proteins

Protein misfolding is implicated in numerous lethal neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS) and Parkinson disease (PD). There are no therapies that reverse these protein-misfolding events. We aim to apply Hsp104, a hexameric AAA+ protein from yeast, to target misfolded conformers for reactivation. Hsp104 solubilizes disordered aggregates and amyloid, but has limited activity against human neurodegenerative disease proteins. Thus, we have previously engineered potentiated Hsp104 variants that suppress aggregation, proteotoxicity and restore proper protein localization of ALS and PD proteins in Saccharomyces cerevisiae, and mitigate neurodegeneration in an animal PD model. Here, we establish that potentiated Hsp104 variants possess broad substrate specificity and, in yeast, suppress toxicity and aggregation induced by wild-type TDP-43, FUS and α-synuclein, as well as missense mutant versions of these proteins that cause neurodegenerative disease. Potentiated Hsp104 variants also rescue toxicity and aggregation of TAF15 but not EWSR1, two RNA-binding proteins with a prion-like domain that are connected with the development of ALS and frontotemporal dementia. Thus, potentiated Hsp104 variants are not entirely non-specific. Indeed, they do not unfold just any natively folded protein. Rather, potentiated Hsp104 variants are finely tuned to unfold proteins bearing short unstructured tracts that are not recognized by wild-type Hsp104. Our studies establish the broad utility of potentiated Hsp104 variants.

Structural and functional hallmarks of amyotrophic lateral sclerosis progression in motor- and memory-related brain regions

Previous studies have shown that in amyotrophic lateral sclerosis (ALS) multiple motor and extra-motor regions display structural and functional alterations. However, their temporal dynamics during disease-progression are unknown. To address this question we employed a longitudinal design assessing motor- and novelty-related brain activity in two fMRI sessions separated by a 3-month interval. In each session, patients and controls executed a Go/NoGo-task, in which additional presentation of novel stimuli served to elicit hippocampal activity. We observed a decline in the patients' movement-related activity during the 3-month interval. Importantly, in comparison to controls, the patients' motor activations were higher during the initial measurement. Thus, the relative decrease seems to reflect a breakdown of compensatory mechanisms due to progressive neural loss within the motor-system. In contrast, the patients' novelty-evoked hippocampal activity increased across 3 months, most likely reflecting the build-up of compensatory processes typically observed at the beginning of lesions. Consistent with a stage-dependent emergence of hippocampal and motor-system lesions, we observed a positive correlation between the ALSFRS-R or MRC-Megascores and the decline in motor activity, but a negative one with the hippocampal activation-increase. Finally, to determine whether the observed functional changes co-occur with structural alterations, we performed voxel-based volumetric analyses on magnetization transfer images in a separate patient cohort studied cross-sectionally at another scanning site. Therein, we observed a close overlap between the structural changes in this cohort, and the functional alterations in the other. Thus, our results provide important insights into the temporal dynamics of functional alterations during disease-progression, and provide support for an anatomical relationship between functional and structural cerebral changes in ALS.

An ALS-associated mutation in the FUS 3'-UTR disrupts a microRNA-FUS regulatory circuitry

While the physiologic functions of the RNA-binding protein FUS still await thorough characterization, the pathonegetic role of FUS mutations in amyotrophic lateral sclerosis (ALS) is clearly established. Here we find that a human FUS mutation that leads to increased protein expression, and was identified in two ALS patients with severe outcome, maps to the seed sequence recognized by miR-141 and miR-200a in the 3'-UTR of FUS. We demonstrate that FUS and these microRNAs are linked by a feed-forward regulatory loop where FUS upregulates miR-141/200a, which in turn impact FUS protein synthesis. We also show that Zeb1, a target of miR-141/200a and transcriptional repressor of these two microRNAs, is part of the circuitry and reinforces it. Our results reveal a possible correlation between deregulation of this regulatory circuit and ALS pathogenesis, and open interesting perspectives in the treatment of these mutations through ad hoc-modified microRNAs.

Core promoter factor TAF9B regulates neuronal gene expression

Emerging evidence points to an unexpected diversification of core promoter recognition complexes that serve as important regulators of cell-type specific gene transcription. Here, we report that the orphan TBP-associated factor TAF9B is selectively up-regulated upon in vitro motor neuron differentiation, and is required for the transcriptional induction of specific neuronal genes, while dispensable for global gene expression in murine ES cells. TAF9B binds to both promoters and distal enhancers of neuronal genes, partially co-localizing at binding sites of OLIG2, a key activator of motor neuron differentiation. Surprisingly, in this neuronal context TAF9B becomes preferentially associated with PCAF rather than the canonical TFIID complex. Analysis of dissected spinal column from Taf9b KO mice confirmed that TAF9B also regulates neuronal gene transcription in vivo. Our findings suggest that alternative core promoter complexes may provide a key mechanism to lock in and maintain specific transcriptional programs in terminally differentiated cell types.

DOI:http://dx.doi.org/10.7554/eLife.02559.001

Almost all the cells in an organism contain the same genetic information, but they develop into many different types of cells that perform a variety of specialized functions in the body. Brain cells, for example, have a very different shape and function from red blood cells. A small group of proteins act inside cells to switch on the expression of genes it needs to carry out the specific functions of a given cell-type, and switch off the genes that are only needed in other cell types.

Some of these regulatory proteins called ‘core promoter factors’ bind to the DNA near the start of genes. These core factors are known to work in combination with various other proteins to switch genes on or off in specific cell types. However, the specific core promoter factors and partner proteins that guide a cell into becoming a neuron have not been well characterized.

Now, Herrera et al. have identified a core promoter factor called TAF9B that is produced at higher levels when mouse stem cells are coaxed into becoming the motor neurons that carry nerve impulses to muscles. The TAF9B protein works together with an enzyme (called PCAF) to help to switch on the genes that control the development of these cells. Without this regulatory protein, mouse stem cells grown in the lab fail to properly switch on the genes that are necessary to become motor neurons. These mutant stem cells also fail to efficiently switch off genes that stop stem cells from becoming more specialized. High levels of TAF9B were also found in the spinal cord of newborn mice and when Herrera et al. engineered mice that lack TAF9B, these mice did not properly regulate the expression of neuronal genes in their spines.

These new findings might, in the future, improve our ability to guide stem cells into forming neurons, or to reprogram other types of specialized cells into becoming motor neurons. This new information could also prove useful for researchers interested in better understanding neuronal development and might aid in the design of therapies to treat neuronal injuries or diseases, such as motor neuron disease.

DOI:http://dx.doi.org/10.7554/eLife.02559.002

Diffusion tensor tractography analysis of the corpus callosum fibers in amyotrophic lateral sclerosis

BACKGROUND AND PURPOSE

Involvement of the corpus callosum (CC) is reported to be a consistent feature of amyotrophic lateral sclerosis (ALS). We examined the CC pathology using diffusion tensor tractography analysis to identify precisely which fiber bundles are involved in ALS.

METHODS

Diffusion tensor imaging was performed in 14 sporadic ALS patients and 16 age-matched healthy controls. Whole brain tractography was performed using the multiple-region of interest (ROI) approach, and CC fiber bundles were extracted in two ways based on functional and structural relevance: (i) cortical ROI selection based on Brodmann areas (BAs), and (ii) the sulcal-gyral pattern of cortical gray matter using FreeSurfer software, respectively.

RESULTS

The mean fractional anisotropy (FA) values of the CC fibers interconnecting the primary motor (BA4), supplementary motor (BA6), and dorsolateral prefrontal cortex (BA9/46) were significantly lower in ALS patients than in controls, whereas those of the primary sensory cortex (BA1, BA2, BA3), Broca's area (BA44/45), and the orbitofrontal cortex (BA11/47) did not differ significantly between the two groups. The FreeSurfer ROI approach revealed a very similar pattern of abnormalities. In addition, a significant correlation was found between the mean FA value of the CC fibers interconnecting the primary motor area and disease severity, as assessed using the revised Amyotrophic Lateral Sclerosis Functional Rating Scale, and the clinical extent of upper motor neuron signs.

CONCLUSIONS

Our findings suggest that there is some degree of selectivity or a gradient in the CC pathology in ALS. The CC fibers interconnecting the primary motor and dorsolateral prefrontal cortices may be preferentially involved in ALS.

Fishing for causes and cures of motor neuron disorders

Motor neuron disorders (MNDs) are a clinically heterogeneous group of neurological diseases characterized by progressive degeneration of motor neurons, and share some common pathological pathways. Despite remarkable advances in our understanding of these diseases, no curative treatment for MNDs exists. To better understand the pathogenesis of MNDs and to help develop new treatments, the establishment of animal models that can be studied efficiently and thoroughly is paramount. The zebrafish (Danio rerio) is increasingly becoming a valuable model for studying human diseases and in screening for potential therapeutics. In this Review, we highlight recent progress in using zebrafish to study the pathology of the most common MNDs: spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS) and hereditary spastic paraplegia (HSP). These studies indicate the power of zebrafish as a model to study the consequences of disease-related genes, because zebrafish homologues of human genes have conserved functions with respect to the aetiology of MNDs. Zebrafish also complement other animal models for the study of pathological mechanisms of MNDs and are particularly advantageous for the screening of compounds with therapeutic potential. We present an overview of their potential usefulness in MND drug discovery, which is just beginning and holds much promise for future therapeutic development.

Side of limb-onset predicts laterality of gray matter loss in amyotrophic lateral sclerosis

Conflicting findings have been reported regarding the lateralized brain abnormality in patients with amyotrophic lateral sclerosis (ALS). In this study, we aimed to investigate the probable lateralization of gray matter (GM) atrophy in ALS patients. We focused on the relationship between the asymmetry in decreased GM volume and the side of disease onset in patients with limb-onset. Structural imaging evaluation of normalized atrophy (SIENAX) and voxel-based morphometry (VBM) were used to assess differences in global and local brain regions in patients with heterogeneous body onset and subgroups with different side of limb-onset. We found global brain atrophy and GM losses in the frontal and parietal areas in each patient group as well as left predominant GM losses in the total cohort. The intriguing findings in subgroup analyses demonstrated that the motor cortex in the contralateral hemisphere of the initially involved limb was most affected. We also found that regional brain atrophy was related to disease progression rate. Our observations suggested that side of limb-onset can predict laterality of GM loss in ALS patients and disease progression correlates with the extent of cortical abnormality.

Mutant human FUS Is ubiquitously mislocalized and generates persistent stress granules in primary cultured transgenic zebrafish cells

FUS mutations can occur in familial amyotrophic lateral sclerosis (fALS), a neurodegenerative disease with cytoplasmic FUS inclusion bodies in motor neurons. To investigate FUS pathology, we generated transgenic zebrafish expressing GFP-tagged wild-type or fALS (R521C) human FUS. Cell cultures were made from these zebrafish and the subcellular localization of human FUS and the generation of stress granule (SG) inclusions examined in different cell types, including differentiated motor neurons. We demonstrate that mutant FUS is mislocalized from the nucleus to the cytosol to a similar extent in motor neurons and all other cell types. Both wild-type and R521C FUS localized to SGs in zebrafish cells, demonstrating an intrinsic ability of human FUS to accumulate in SGs irrespective of the presence of disease-associated mutations or specific cell type. However, elevation in relative cytosolic to nuclear FUS by the R521C mutation led to a significant increase in SG assembly and persistence within a sub population of vulnerable cells, although these cells were not selectively motor neurons.

Pathogenesis/genetics of frontotemporal dementia and how it relates to ALS

One of the most interesting findings in the field of neurodegeneration in recent years is tfche discovery of a genetic mutation in the C9orf72 gene, the most common mutation found to be causative of sporadic and familial frontotemporal lobar degeneration (FTLD), amyotrophic lateral sclerosis (ALS) and concomitant FTD-ALS (DeJesus-Hernandez et al., 2011b; Renton et al., 2011). While clinical and molecular data, such as the identification of TDP-43 being a common pathological protein (Neumann et al., 2006) have hinted at such a link for years, the identification of what was formally known as “the chromosome 9 FTLD-ALS gene” has provided a foundation for better understanding of the relationship between the two. Indeed, it is now recognized that ALS and FTLD-TDP represent a disease spectrum. In this review, we will discuss the current genetic and pathological features of the FTLD-ALS spectrum.

Blood biomarkers for amyotrophic lateral sclerosis: myth or reality?

Amyotrophic lateral sclerosis (ALS) is a fatal condition primarily characterized by the selective loss of upper and lower motor neurons. At present, the diagnosis and monitoring of ALS is based on clinical examination, electrophysiological findings, medical history, and exclusion of confounding disorders. There is therefore an undeniable need for molecular biomarkers that could give reliable information on the onset and progression of ALS in clinical practice and therapeutic trials. From a practical point of view, blood offers a series of advantages, including easy handling and multiple testing at a low cost, that make it an ideal source of biomarkers. In this review, we revisited the findings of many studies that investigated the presence of systemic changes at the molecular and cellular level in patients with ALS. The results of these studies reflect the diversity in the pathological mechanisms contributing to disease (e.g., excitotoxicity, oxidative stress, neuroinflammation, metabolic dysfunction, and neurodegeneration, among others) and provide relatively successful evidence of the usefulness of a wide-ranging panel of molecules as potential biomarkers. More studies, hopefully internationally coordinated, would be needed, however, to translate the application of these biomarkers into benefit for patients.

Stem cell transplantation in neurological diseases: improving effectiveness in animal models

Neurological diseases afflict a growing proportion of the human population. There are two reasons for this: first, the average age of the population (especially in the industrialized world) is increasing, and second, the diagnostic tools to detect these pathologies are now more sophisticated and can be used on a higher percentage of the population. In many cases, neurological disease has a pharmacological treatment which, as in the case of Alzheimer's disease, Parkinson's disease, Epilepsy, and Multiple Sclerosis can reduce the symptoms and slow down the course of the disease but cannot reverse its effects or heal the patient. In the last two decades the transplantation approach, by means of stem cells of different origin, has been suggested for the treatment of neurological diseases. The choice of slightly different animal models and the differences in methods of stem cell preparation make it difficult to compare the results of transplantation experiments. Moreover, the translation of these results into clinical trials with human subjects is difficult and has so far met with little success. This review seeks to discuss the reasons for these difficulties by considering the differences between human and animal cells (including isolation, handling and transplantation) and between the human disease model and the animal disease model.

Pathogenic role of BECN1/Beclin 1 in the development of amyotrophic lateral sclerosis

Pharmacological activation of autophagy is becoming an attractive strategy to induce the selective degradation of aggregate-prone proteins. Recent evidence also suggests that autophagy impairment may underlie the pathogenesis of several neurodegenerative diseases. Mutations in the gene encoding SOD1 (superoxide disumutase 1) trigger familial amyotrophic lateral sclerosis (ALS), inducing its misfolding and aggregation and the progressive loss of motoneurons. It is still under debate whether autophagy has a protective or detrimental role in ALS. Here we evaluate the impact of BECN1/Beclin 1, an essential autophagy regulator, in ALS. BECN1 levels were upregulated in both cells and animals expressing mutant SOD1. To evaluate the impact of BECN1 to the pathogenesis of ALS in vivo, we generated mutant SOD1 transgenic mice heterozygous for Becn1. We observed an unexpected increase in life span of mutant SOD1 transgenic mice haploinsufficient for Becn1 compared with littermate control animals. These effects were accompanied by enhanced accumulation of SQSTM1/p62 and reduced levels of LC3-II, and an altered equilibrium between monomeric and oligomeric mutant SOD1 species in the spinal cord. At the molecular level, we detected an abnormal interaction of mutant SOD1 with the BECN1-BCL2L1 complex that may impact autophagy stimulation. Our data support a dual role of BECN1 in ALS and depict a complex scenario in terms of predicting the effects of manipulating autophagy in a disease context.

Erythropoietin modulates the immune-inflammatory response of a SOD1(G93A) transgenic mouse model of amyotrophic lateral sclerosis (ALS)

Temporal patterns of inflammatory cytokine levels reflect the immune-inflammatory role in pathogenic mechanisms of SOD1 animal model of Amyotrophic Lateral Sclerosis (ALS) and these cytokines have important roles in both toxic and protective functions depending on the stage of disease progression in ALS patients. Erythropoietin (EPO) has various neuroprotective effects, including the reduction of inflammation, the enhancement of survival signals, and the prevention of neuronal cell death. This study was undertaken to evaluate the temporal pattern of inflammatory cytokine levels induced by EPO treatment in the SOD1(G93A) mice model of ALS. We treated mice with 5 IU of EPO per gram of animal weight once every other week after the mice were 60 days old, and pro/anti-inflammatory cytokines were analyzed at 30, 60, 90, and 120 days of age. In untreated controls, pro-inflammatory cytokines (IFN-γ, TNF-α, IL-1β, CCL2 (MCP-1), CCL5 (RANTES), CXCL10 (IP-10), and IL-17A) were gradually increased with aging. In contrast, increment of anti-inflammatory cytokines (IL-4, IL-10, and TGF-β) showed the highest level at 90 days of age and their levels were remarkably faded until 120 days of age. EPO treatment, however, showed significantly decreased level of pro-inflammatory cytokines. And, up-regulated levels of anti-inflammatory cytokines with EPO were highly maintained until 120 days. In addition, the treatment of EPO delayed symptom onset, prolonged time of rotarod failure, and showed more preserved number of motoneurons. These findings suggest that EPO may be a potential therapeutic candidate having ability to modulate immune-inflammation in ALS.

Developments in treatments for amyotrophic lateral sclerosis via intracerebroventricular or intrathecal delivery

INTRODUCTION

Amyotrophic lateral scleroses (ALS) are neurodegenerative disorders primarily affecting the motor system. These incurable disorders are relentlessly progressive and typically limit survival to 2 - 5 years after disease onset. An improved knowledge about disease-causing genes, disease proteins and pathways has revealed considerable heterogeneity in ALS. Novel targeted therapies are being developed, but getting these beyond the BBB remains a challenge.

AREAS COVERED

The authors review the intracerebroventricular and intrathecal delivery of drugs for the treatment of ALS in preclinical and clinical studies.

EXPERT OPINION

Lack of BBB permeability should not hold back the development of promising treatments for ALS, as the available evidence suggest that direct intrathecal or intracerebroventricular administration of drug is a feasible delivery route in patients with ALS.

Deciphering genetic interactions between ALS genes using C. elegans

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder causing selective death of motor neurons in which it is speculated that 10% of cases have a familial history. In the past 20 years, many genes causative for ALS have been discovered, but the link between them and their roles in neurodegeneration remain unknown. The identification of genes associated with both ALS and frontotemporal dementia (FTD), along with the observation of patients affected by both diseases, have suggested that they are part of the same neurodegenerative spectrum. Investigating possible genetic interactions among ALS/FTD genes could help understand the role of these genes in neurodegeneration. To pursue this goal, our group has developed several ALS models to study potential genetic interactions. More recently, we characterized the deletion mutant alfa-1, the ortholog of C9ORF72, to evaluate the potential genetic interactions between C9ORF72/alfa-1 and other ALS genes. Here, we discuss the genetic interactions identified in our models and how some of these proteins may also be linked to other neurodegenerative disorders.

Global CNS transduction of adult mice by intravenously delivered rAAVrh.8 and rAAVrh.10 and nonhuman primates by rAAVrh.10

Some recombinant adeno-associated viruses (rAAVs) can cross the neonatal blood-brain barrier (BBB) and efficiently transduce cells of the central nervous system (CNS). However, in the adult CNS, transduction levels by systemically delivered rAAVs are significantly reduced, limiting their potential for CNS gene therapy. Here, we characterized 12 different rAAVEGFPs in the adult mouse CNS following intravenous delivery. We show that the capability of crossing the adult BBB and achieving widespread CNS transduction is a common character of AAV serotypes tested. Of note, rAAVrh.8 is the leading vector for robust global transduction of glial and neuronal cell types in regions of clinical importance such as cortex, caudate-putamen, hippocampus, corpus callosum, and substantia nigra. It also displays reduced peripheral tissue tropism compared to other leading vectors. Additionally, we evaluated rAAVrh.10 with and without microRNA (miRNA)-regulated expressional detargeting from peripheral tissues for systemic gene delivery to the CNS in marmosets. Our results indicate that rAAVrh.8, along with rh.10 and 9, hold the best promise for developing novel therapeutic strategies to treat neurological diseases in the adult patient population. Additionally, systemically delivered rAAVrh.10 can transduce the CNS efficiently, and its transgene expression can be limited in the periphery by endogenous miRNAs in adult marmosets.

Roles of vascular endothelial growth factor in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal devastating neurodegenerative disorder, involving progressive degeneration of motor neurons in spinal cord, brainstem, and motor cortex. Riluzole is the only drug approved in ALS but it only confers a modest improvement in survival. In spite of a high number of clinical trials no other drug has proved effectiveness. Recent studies support that vascular endothelial growth factor (VEGF), originally described as a key angiogenic factor, also plays a key role in the nervous system, including neurogenesis, neuronal survival, neuronal migration, and axon guidance. VEGF has been used in exploratory clinical studies with promising results in ALS and other neurological disorders. Although VEGF is a very promising compound, translating the basic science breakthroughs into clinical practice is the major challenge ahead. VEGF-B, presenting a single safety profile, protects motor neurons from degeneration in ALS animal models and, therefore, it will be particularly interesting to test its effects in ALS patients. In the present paper the authors make a brief description of the molecular properties of VEGF and its receptors and review its different features and therapeutic potential in the nervous system/neurodegenerative disease, particularly in ALS.

Autophagy and its normal and pathogenic states in the brain

Autophagy is a conserved catabolic process that delivers the cytosol and cytosolic constituents to the lysosome. Its fundamental role is to maintain cellular homeostasis and to protect cells from varying insults, including misfolded proteins and damaged organelles. Beyond these roles, the highly specialized cells of the brain have further adapted autophagic pathways to suit their distinct needs. In this review, we briefly summarize our current understanding of the different forms of autophagy and then offer a closer look at how these pathways impact neuronal and glial functions. The emerging evidence indicates that not only are autophagy pathways essential for neural health, but they have a direct impact on developmental and neurodegenerative processes. Taken together, as we unravel the complex roles autophagy pathways play, we will gain the necessary insight to modify these pathways to protect the human brain and treat neurodegenerative diseases.

Worming forward: amyotrophic lateral sclerosis toxicity mechanisms and genetic interactions in Caenorhabditis elegans

Neurodegenerative diseases share pathogenic mechanisms at the cellular level including protein misfolding, excitotoxicity and altered RNA homeostasis among others. Recent advances have shown that the genetic causes underlying these pathologies overlap, hinting at the existence of a genetic network for neurodegeneration. This is perhaps best illustrated by the recent discoveries of causative mutations for amyotrophic lateral sclerosis (ALS) and frontotemporal degeneration (FTD). Once thought to be distinct entities, it is now recognized that these diseases exist along a genetic spectrum. With this wealth of discoveries comes the need to develop new genetic models of ALS and FTD to investigate not only pathogenic mechanisms linked to causative mutations, but to uncover potential genetic interactions that may point to new therapeutic targets. Given the conservation of many disease genes across evolution, Caenorhabditis elegans is an ideal system to investigate genetic interactions amongst these genes. Here we review the use of C. elegans to model ALS and investigate a putative genetic network for ALS/FTD that may extend to other neurological disorders.

Human induced pluripotent stem cells are a novel source of neural progenitor cells (iNPCs) that migrate and integrate in the rodent spinal cord

Transplantation of human neural progenitor cells (NPCs) into the brain or spinal cord to replace lost cells, modulate the injury environment, or create a permissive milieu to protect and regenerate host neurons is a promising therapeutic strategy for neurological diseases. Deriving NPCs from human fetal tissue is feasible, although problematic issues include limited sources and ethical concerns. Here we describe a new and abundant source of NPCs derived from human induced pluripotent stem cells (iPSCs). A novel chopping technique was used to transform adherent iPSCs into free-floating spheres that were easy to maintain and were expandable (EZ spheres) (Ebert et al. [2013] Stem Cell Res 10:417-427). These EZ spheres could be differentiated towards NPC spheres with a spinal cord phenotype using a combination of all-trans retinoic acid (RA) and epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2) mitogens. Suspension cultures of NPCs derived from human iPSCs or fetal tissue have similar characteristics, although they were not similar when grown as adherent cells. In addition, iPSC-derived NPCs (iNPCs) survived grafting into the spinal cord of athymic nude rats with no signs of overgrowth and with a very similar profile to human fetal-derived NPCs (fNPCs). These results suggest that human iNPCs behave like fNPCs and could thus be a valuable alternative for cellular regenerative therapies of neurological diseases.

Potentiated Hsp104 variants antagonize diverse proteotoxic misfolding events

There are no therapies that reverse the proteotoxic misfolding events that underpin fatal neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD). Hsp104, a conserved hexameric AAA+ protein from yeast, solubilizes disordered aggregates and amyloid but has no metazoan homolog and only limited activity against human neurodegenerative disease proteins. Here, we reprogram Hsp104 to rescue TDP-43, FUS, and α-synuclein proteotoxicity by mutating single residues in helix 1, 2, or 3 of the middle domain or the small domain of nucleotide-binding domain 1. Potentiated Hsp104 variants enhance aggregate dissolution, restore proper protein localization, suppress proteotoxicity, and in a C. elegans PD model attenuate dopaminergic neurodegeneration. Potentiating mutations reconfigure how Hsp104 subunits collaborate, desensitize Hsp104 to inhibition, obviate any requirement for Hsp70, and enhance ATPase, translocation, and unfoldase activity. Our work establishes that disease-associated aggregates and amyloid are tractable targets and that enhanced disaggregases can restore proteostasis and mitigate neurodegeneration.

Zebrafish models of human motor neuron diseases: advantages and limitations

Motor neuron diseases (MNDs) are an etiologically heterogeneous group of disorders of neurodegenerative origin, which result in degeneration of lower (LMNs) and/or upper motor neurons (UMNs). Neurodegenerative MNDs include pure hereditary spastic paraplegia (HSP), which involves specific degeneration of UMNs, leading to progressive spasticity of the lower limbs. In contrast, spinal muscular atrophy (SMA) involves the specific degeneration of LMNs, with symmetrical muscle weakness and atrophy. Amyotrophic lateral sclerosis (ALS), the most common adult-onset MND, is characterized by the degeneration of both UMNs and LMNs, leading to progressive muscle weakness, atrophy, and spasticity. A review of the comparative neuroanatomy of the human and zebrafish motor systems showed that, while the zebrafish was a homologous model for LMN disorders, such as SMA, it was only partially relevant in the case of UMN disorders, due to the absence of corticospinal and rubrospinal tracts in its central nervous system. Even considering the limitation of this model to fully reproduce the human UMN disorders, zebrafish offer an excellent alternative vertebrate model for the molecular and genetic dissection of MND mechanisms. Its advantages include the conservation of genome and physiological processes and applicable in vivo tools, including easy imaging, loss or gain of function methods, behavioral tests to examine changes in motor activity, and the ease of simultaneous chemical/drug testing on large numbers of animals. This facilitates the assessment of the environmental origin of MNDs, alone or in combination with genetic traits and putative modifier genes. Positive hits obtained by phenotype-based small-molecule screening using zebrafish may potentially be effective drugs for treatment of human MNDs.

[Epidemiology, clinical spectrum of ALS and differential diagnoses]

Amyotrophic Lateral Sclerosis (ALS) is the most common motor neuron disease in adults. Its incidence in France is estimated at 2.5 per 100,000 population and its prevalence between 5 and 8 per 100,000 inhabitants. Good prognostic factors are age of early onset, a longer time to diagnosis, initial damage to the spinal onset, early management of undernutrition and restrictive respiratory failure. The diagnosis of ALS is primarily clinical and is based on the evidence of involvement of the central motor neuron and peripheral neuron (NMP) in different territories or spinal or bulbar. The EMG confirms the achievement of NMP, shows the extension to clinically preserved areas and allows to exclude some differential diagnoses. The clinical spectrum of ALS is broad: conventional forms beginning brachial, lower limb or bulbar onsets, rarer forms to start breathing, pyramidal forms, forms with cognitive and behavioural impairment. In 5-10% of cases, ALS is familial. In 15% of cases, it is associated with frontotemporal degeneration rather than orbito-frontal type. The main differential diagnoses are guided by the clinic: combining pure motor neuropathy with or without conduction block, post-polio syndrome, cramp-fasciculation syndrome, myasthenia gravis, paraneoplastic syndromes, Sjögren syndrome, retroviral infections, some endocrine disorders, some metabolic diseases, genetic diseases (Kennedy and SMA) and inclusion body myositis.

Modeling ALS with iPSCs reveals that mutant SOD1 misregulates neurofilament balance in motor neurons

Amyotrophic lateral sclerosis (ALS) presents motoneuron (MN)-selective protein inclusions and axonal degeneration but the underlying mechanisms of such are unknown. Using induced pluripotent cells (iPSCs) from patients with mutation in the Cu/Zn superoxide dismutase (SOD1) gene, we show that spinal MNs, but rarely non-MNs, exhibited neurofilament (NF) aggregation followed by neurite degeneration when glia were not present. These changes were associated with decreased stability of NF-L mRNA and binding of its 3' UTR by mutant SOD1 and thus altered protein proportion of NF subunits. Such MN-selective changes were mimicked by expression of a single copy of the mutant SOD1 in human embryonic stem cells and were prevented by genetic correction of the SOD1 mutation in patient's iPSCs. Importantly, conditional expression of NF-L in the SOD1 iPSC-derived MNs corrected the NF subunit proportion, mitigating NF aggregation and neurite degeneration. Thus, NF misregulation underlies mutant SOD1-mediated NF aggregation and axonal degeneration in ALS MNs.

Pathways disrupted in human ALS motor neurons identified through genetic correction of mutant SOD1

Although many distinct mutations in a variety of genes are known to cause Amyotrophic Lateral Sclerosis (ALS), it remains poorly understood how they selectively impact motor neuron biology and whether they converge on common pathways to cause neuronal degeneration. Here, we have combined reprogramming and stem cell differentiation approaches with genome engineering and RNA sequencing to define the transcriptional and functional changes that are induced in human motor neurons by mutant SOD1. Mutant SOD1 protein induced a transcriptional signature indicative of increased oxidative stress, reduced mitochondrial function, altered subcellular transport, and activation of the ER stress and unfolded protein response pathways. Functional studies demonstrated that these pathways were perturbed in a manner dependent on the SOD1 mutation. Finally, interrogation of stem-cell-derived motor neurons produced from ALS patients harboring a repeat expansion in C9orf72 indicates that at least a subset of these changes are more broadly conserved in ALS.

Intrinsic membrane hyperexcitability of amyotrophic lateral sclerosis patient-derived motor neurons

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of the motor nervous system. We show using multielectrode array and patch-clamp recordings that hyperexcitability detected by clinical neurophysiological studies of ALS patients is recapitulated in induced pluripotent stem cell-derived motor neurons from ALS patients harboring superoxide dismutase 1 (SOD1), C9orf72, and fused-in-sarcoma mutations. Motor neurons produced from a genetically corrected but otherwise isogenic SOD1(+/+) stem cell line do not display the hyperexcitability phenotype. SOD1(A4V/+) ALS patient-derived motor neurons have reduced delayed-rectifier potassium current amplitudes relative to control-derived motor neurons, a deficit that may underlie their hyperexcitability. The Kv7 channel activator retigabine both blocks the hyperexcitability and improves motor neuron survival in vitro when tested in SOD1 mutant ALS cases. Therefore, electrophysiological characterization of human stem cell-derived neurons can reveal disease-related mechanisms and identify therapeutic candidates.

Reversing deleterious protein aggregation with re-engineered protein disaggregases

Aberrant protein folding is severely problematic and manifests in numerous disorders, including amyotrophic lateral sclerosis (ALS), Parkinson disease (PD), Huntington disease (HD), and Alzheimer disease (AD). Patients with each of these disorders are characterized by the accumulation of mislocalized protein deposits. Treatments for these disorders remain palliative, and no available therapeutics eliminate the underlying toxic conformers. An intriguing approach to reverse deleterious protein misfolding is to upregulate chaperones to restore proteostasis. We recently reported our work to re-engineer a prion disaggregase from yeast, Hsp104, to reverse protein misfolding implicated in human disease. These potentiated Hsp104 variants suppress TDP-43, FUS, and α-synuclein toxicity in yeast, eliminate aggregates, reverse cellular mislocalization, and suppress dopaminergic neurodegeneration in an animal model of PD. Here, we discuss this work and its context, as well as approaches for further developing potentiated Hsp104 variants for application in reversing protein-misfolding disorders.

Mitochondrial dysfunction in amyotrophic lateral sclerosis - a valid pharmacological target?

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by the selective death of upper and lower motor neurons which ultimately leads to paralysis and ultimately death. Pathological changes in ALS are closely associated with pronounced and progressive changes in mitochondrial morphology, bioenergetics and calcium homeostasis. Converging evidence suggests that impaired mitochondrial function could be pivotal in the rapid neurodegeneration of this condition. In this review, we provide an update of recent advances in understanding mitochondrial biology in the pathogenesis of ALS and highlight the therapeutic value of pharmacologically targeting mitochondrial biology to slow disease progression.

Abnormal intracellular calcium signaling and SNARE-dependent exocytosis contributes to SOD1G93A astrocyte-mediated toxicity in amyotrophic lateral sclerosis

Motor neurons are progressively and predominantly degenerated in ALS, which is not only induced by multiple intrinsic pathways but also significantly influenced by the neighboring glial cells. In particular, astrocytes derived from the SOD1 mutant mouse model of ALS or from human familial or sporadic ALS patient brain tissue directly induce motor neuron death in culture; however, the mechanisms of pathological astroglial secretion remain unclear. Here we investigated abnormal calcium homeostasis and altered exocytosis in SOD1G93A astrocytes. We found that purinergic stimulation induces excess calcium release from the ER stores in SOD1G93A astrocytes, which results from the abnormal ER calcium accumulation and is independent of clearance mechanisms. Furthermore, pharmacological studies suggested that store-operated calcium entry (SOCE), a calcium refilling mechanism responsive to ER calcium depletion, is enhanced in SOD1G93A astrocytes. We found that oxidant-induced increased S-glutathionylation and calcium-independent puncta formation of the ER calcium sensor STIM1 underlies the abnormal SOCE response in SOD1G93A astrocytes. Enhanced SOCE contributes to ER calcium overload in SOD1G93A astrocytes and excess calcium release from the ER during ATP stimulation. In addition, ER calcium release induces elevated ATP release from SOD1G93A astrocytes, which can be inhibited by the overexpression of dominant-negative SNARE. Selective inhibition of exocytosis in SOD1G93A astrocytes significantly prevents astrocyte-mediated toxicity to motor neurons and delays disease onset in SOD1G93A mice. Our results characterize a novel mechanism responsible for calcium dysregulation in SOD1G93A astrocytes and provide the first in vivo evidence that astrocyte exocytosis contributes to the pathogenesis of ALS.

Resveratrol improves motoneuron function and extends survival in SOD1(G93A) ALS mice

Amyotrophic lateral sclerosis (ALS) is an adult onset neurodegenerative disease that causes progressive paralysis and death due to degeneration of motoneurons in spinal cord, brainstem and motor cortex. Nowadays, there is no effective therapy and patients die 2-5 years after diagnosis. Resveratrol (trans-3,4',5-trihydroxystilbene) is a natural polyphenol found in grapes, with promising neuroprotective effects since it induces expression and activation of several neuroprotective pathways involving Sirtuin1 and AMPK. The objective of this work was to assess the effect of resveratrol administration on SOD1(G93A) ALS mice. We determined the onset of symptoms by rotarod test and evaluated upper and lower motoneuron function using electrophysiological tests. We assessed the survival of the animals and determined the number of spinal motoneurons. Finally, we further investigated resveratrol mechanism of action by means of western blot and immunohistochemical analysis. Resveratrol treatment from 8 weeks of age significantly delayed disease onset and preserved lower and upper motoneuron function in female and male animals. Moreover, resveratrol significantly extended SOD1(G93A) mice lifespan and promoted survival of spinal motoneurons. Delayed resveratrol administration from 12 weeks of age also improved spinal motoneuron function preservation and survival. Further experiments revealed that resveratrol protective effects were associated with increased expression and activation of Sirtuin 1 and AMPK in the ventral spinal cord. Both mediators promoted normalization of the autophagic flux and, more importantly, increased mitochondrial biogenesis in the SOD1(G93A) spinal cord. Taken together, our findings suggest that resveratrol may represent a promising therapy for ALS.

Neuronal RNA-binding proteins in health and disease

In mammalian cells in general and in neurons in particular, mRNA maturation, translation, and degradation are highly complex and dynamic processes. RNA-binding proteins (RBPs) play crucial roles in all these events. First, they participate in the choice of pre-mRNA splice sites and in the selection of the polyadenylation sites, determining which of the possible isoforms is produced from a given precursor mRNA. Then, once in the cytoplasm, the protein composition of the RNP particles determines whether the mature mRNA is transported along the dendrites or the axon of a neuron to the synapses, how efficiently it is translated, and how stable it is. In agreement with their importance for neuronal function, mutations in genes that code for RBPs are associated with various neurological diseases. In this review, we illustrate how individual RBPs determine the fate of an mRNA, and we discuss how mutations in RBPs or perturbations of the mRNA metabolism can cause neurodegenerative disorders.

A seeded propagation of Cu, Zn-superoxide dismutase aggregates in amyotrophic lateral sclerosis

Abnormal accumulation of protein inclusions in motor neurons has been known as a major pathological change in amyotrophic lateral sclerosis (ALS). Increasing numbers of proteins including mutant Cu, Zn-superoxide dismutase (SOD1) have been identified as constituents of pathological inclusions in a form of insoluble fibrillar aggregates. Notably, protein fibrillar aggregates exhibit a self-perpetuating property, which can convert a soluble native protein into insoluble fibrillar aggregates. Such “seeding reaction” of protein fibrils can accelerate the aggregation significantly and would contribute to the spread of inclusion pathologies from an affected cell to its neighboring cells in neurodegenerative diseases. In ALS, a pathological change first occurs at the site of disease onset and then propagates throughout the affected tissues in a time-dependent manner; therefore, it can be assumed that seeded aggregation may be the key factor of disease progression in ALS. In this mini review, we will briefly summarize recent studies on possible roles of a seeded aggregation of SOD1 in pathomechanism of ALS.

Protein kinase CK-1 inhibitors as new potential drugs for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease where motor neurons in cortex, brain stem, and spinal cord die progressively, resulting in muscle wasting, paralysis, and death. Currently, effective therapies for ALS are lacking; however, identification of pathological TAR DNA-binding protein 43 (TDP-43) as the hallmark lesion in sporadic ALS suggests new therapeutic targets for pharmacological intervention. Pathological TDP-43 phosphorylation appears to drive the onset and progression of ALS and may result from upregulation of the protein kinase CK-1 in affected neurons, resulting in postranslational TDP-43 modification. Consequently, brain penetrant specific CK-1 inhibitors may provide a new therapeutic strategy for treating ALS and other TDP-43 proteinopathies. Using a chemical genetic approach, we report the discovery and further optimization of a number of potent CK-1δ inhibitors. Moreover, these small heterocyclic molecules are able to prevent TDP-43 phosphorylation in cell cultures, to increase Drosophila lifespan by reduction of TDP-43 neurotoxicity, and are predicted to cross the blood-brain barrier. Thus, N-(benzothiazolyl)-2-phenyl-acetamides are valuable drug candidates for further studies and may be a new therapeutic approach for ALS and others pathologies in which TDP-43 is involved.

Role of energy metabolic deficits and oxidative stress in excitotoxic spinal motor neuron degeneration in vivo

MN (motor neuron) death in amyotrophic lateral sclerosis may be mediated by glutamatergic excitotoxicity. Previously, our group showed that the microdialysis perfusion of AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionate) in the rat lumbar spinal cord induced MN death and permanent paralysis within 12 h after the experiment. Here, we studied the involvement of energy metabolic deficiencies and of oxidative stress in this MN degeneration, by testing the neuroprotective effect of various energy metabolic substrates and antioxidants. Pyruvate, lactate, β-hydroxybutyrate, α-ketobutyrate and creatine reduced MN loss by 50–65%, preserved motor function and completely prevented the paralysis. Ascorbate, glutathione and glutathione ethyl ester weakly protected against motor deficits and reduced MN death by only 30–40%. Reactive oxygen species formation and 3-nitrotyrosine immunoreactivity were studied 1.5–2 h after AMPA perfusion, during the initial MN degenerating process, and no changes were observed. We conclude that mitochondrial energy deficiency plays a crucial role in this excitotoxic spinal MN degeneration, whereas oxidative stress seems a less relevant mechanism. Interestingly, we observed a clear correlation between the alterations of motor function and the number of damaged MNs, suggesting that there is a threshold of about 50% in the number of healthy MNs necessary to preserve motor function.

Mitochondrial energy substrates protect against in vivo excitotoxic spinal motor neuron degeneration and the consequent paralysis, whereas antioxidants are less efficient. These results allowed to establish a minimal threshold number of spinal motor neurons necessary to preserve motor function.

Partial loss of TDP-43 function causes phenotypes of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disease that causes motor neuron degeneration, progressive motor dysfunction, paralysis, and death. Although multiple causes have been identified for this disease, >95% of ALS cases show aggregation of transactive response DNA binding protein (TDP-43) accompanied by its nuclear depletion. Therefore, the TDP-43 pathology may be a converging point in the pathogenesis that originates from various initial triggers. The aggregation is thought to result from TDP-43 misfolding, which could generate cellular toxicity. However, the aggregation as well as the nuclear depletion could also lead to a partial loss of TDP-43 function or TDP-43 dysfunction. To investigate the impact of TDP-43 dysfunction, we generated a transgenic mouse model for a partial loss of TDP-43 function using transgenic RNAi. These mice show ubiquitous transgene expression and TDP-43 knockdown in both the periphery and the central nervous system (CNS). Strikingly, these mice develop progressive neurodegeneration prominently in cortical layer V and spinal ventral horn, motor dysfunction, paralysis, and death. Furthermore, examination of splicing patterns of TDP-43 target genes in human ALS revealed changes consistent with TDP-43 dysfunction. These results suggest that the CNS, particularly motor neurons, possess a heightened vulnerability to TDP-43 dysfunction. Additionally, because TDP-43 knockdown predominantly occur in astrocytes in the spinal cord of these mice, our results suggest that TDP-43 dysfunction in astrocytes is an important driver for motor neuron degeneration and clinical phenotypes of ALS.

Heterogeneous nuclear ribonucleoproteins in amyotrophic lateral sclerosis: what do we know?

ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset motor neuron disease that results from the progressive loss of motor neurons in the brainstem and spinal cord, and of upper motor neurons in the motor cortex. TDP-43 was the first protein identified in ALS. It is present in cytoplasmic inclusions in motor neurons of affected patient brains and spinal cords, a hallmark feature of this disease. Successive studies have identified missense mutations in TARDBP, and, to date, more than 40 mutations have been identified. Recent studies have indicated that altered RNA metabolism is a key feature of ALS. This article reviews an emerging role of heterogeneous nuclear ribonucleoproteins driving disease pathogenesis that include TDP-43, FUS, hnRNPA1, hnRNPA2/B1 and hnRNPA3. Determining the molecular pathways involved may provide a promising prospect for heterogeneous nuclear ribonucleoproteins being potential biomarkers in ALS in order to develop therapeutic strategies for mitigating this disease, for which there is currently no cure.

Modelling C9ORF72 hexanucleotide repeat expansion in amyotrophic lateral sclerosis and frontotemporal dementia

GGGGCC (G4C2) hexanucleotide repeat expansion in chromosome 9 open reading frame 72 (C9ORF72) has been identified as the most common genetic abnormality in both frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). To investigate the role of C9ORF72-related G4C2 repeat expansion in ALS and FTLD, several animal and cell culture models have been generated that reveal initial insights into the disease pathogenesis of C9 ALS/FTLD. These models include neurons differentiated from patient-derived pluripotent stem cells as well as genetically engineered cells and organisms that knock down C9ORF72 orthologues or express G4C2 repeats. Targeted reduction or knockdown of C9ORF72 homologues in zebrafish and mice so far produced conflicting results which neither rule out, nor confirm reduced expression of C9ORF72 as a pathogenic mechanism in C9 ALS/FTLD. In contrast, studies using patient-derived cells, as well as Drosophila and zebrafish models overexpressing disease-related hexanucleotide expansions, can cause repeat length-dependent formation of RNA foci, which directly and progressively correlate with cellular toxicity. RNA foci formation is accompanied by sequestration of specific RNA-binding proteins (RBPs), including Pur-alpha, hnRNPH and ADARB2, suggesting that G4C2-mediated sequestration and functional depletion of RBPs are cytotoxic and thus directly contribute to disease. Moreover, these studies provide experimental evidence that repeat-associated non-ATG translation of repeat-containing sense and antisense RNA leads to dipeptide-repeat proteins (DPRs) that can accumulate and aggregate, indicating that accumulation of DPRs may represent another pathogenic pathway underlying C9 ALS/FTLD. These studies in cell and animal models therefore identify RNA toxicity, RBP sequestration and accumulation of DPRs as emerging pathogenic pathways underlying C9 ALS/FTLD.

Pathological pain and the neuroimmune interface

Reciprocal signalling between immunocompetent cells in the central nervous system (CNS) has emerged as a key phenomenon underpinning pathological and chronic pain mechanisms. Neuronal excitability can be powerfully enhanced both by classical neurotransmitters derived from neurons, and by immune mediators released from CNS-resident microglia and astrocytes, and from infiltrating cells such as T cells. In this Review, we discuss the current understanding of the contribution of central immune mechanisms to pathological pain, and how the heterogeneous immune functions of different cells in the CNS could be harnessed to develop new therapeutics for pain control. Given the prevalence of chronic pain and the incomplete efficacy of current drugs--which focus on suppressing aberrant neuronal activity--new strategies to manipulate neuroimmune pain transmission hold considerable promise.