Energy metabolism in ALS: an underappreciated opportunity?

Motor Neuron Susceptibility in ALS/FTD

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the death of both upper and lower motor neurons (MNs) in the brain, brainstem and spinal cord. The neurodegenerative mechanisms leading to MN loss in ALS are not fully understood. Importantly, the reasons why MNs are specifically targeted in this disorder are unclear, when the proteins associated genetically or pathologically with ALS are expressed ubiquitously. Furthermore, MNs themselves are not affected equally; specific MNs subpopulations are more susceptible than others in both animal models and human patients. Corticospinal MNs and lower somatic MNs, which innervate voluntary muscles, degenerate more readily than specific subgroups of lower MNs, which remain resistant to degeneration, reflecting the clinical manifestations of ALS. In this review, we discuss the possible factors intrinsic to MNs that render them uniquely susceptible to neurodegeneration in ALS. We also speculate why some MN subpopulations are more vulnerable than others, focusing on both their molecular and physiological properties. Finally, we review the anatomical network and neuronal microenvironment as determinants of MN subtype vulnerability and hence the progression of ALS.

Type II diabetes mellitus and the incidence of amyotrophic lateral sclerosis

OBJECTIVE

The aim of this study was to investigate the relationship between type II diabetes mellitus (T2DM) and ALS incidence using the National Health Insurance Research Database and Serious Disabling Disease database of Taiwan.

METHODS

This was a population-based cohort study. The index date was the date of the first T2DM diagnosis + 365 days. We included T2DM patients diagnosis between 2000 and 2013 (n = 2,135,427). These patients were matched by sex, age, urbanization, and insurance premium at a ratio of 1:1 to include patients without diabetes mellitus. Competing risk-adjusted Cox regression analysis was performed to investigate the association between T2DM and the incidence of ALS.

RESULTS

In the patients not stratified by age, T2DM was not associated with the incidence of ALS after controlling for confounding factors. The interaction test of age subgroup (< 55 and ≥ 55 years) and T2DM on ALS risk was significance (p < 0.001). Subgroup analysis showed that T2DM was negatively associated with ALS in patients whose age at the first T2DM diagnosis was ≥ 55 years. Among T2DM patients, T2DM combined with hypertension was negatively associated with ALS among patients whose age at the first T2DM diagnosis was ≥ 55 years. Among T2DM patients, T2DM combined with hyperlipidemia was positively associated with ALS among patients whose age at the first T2DM diagnosis was < 55 years.

CONCLUSIONS

The late-onset of T2DM may exert negative association with ALS, especially when combined with hypertension. The early-onset of T2DM may exert positive association with ALS, especially when combined with hyperlipidemia.

The dual face of glutamate: from a neurotoxin to a potential survival factor-metabolic implications in health and disease

Glutamate is the major excitatory neurotransmitter in the central nervous system. Beyond this function, glutamate also plays a key role in intermediary metabolism in all organs and tissues, linking carbohydrate and amino acid metabolism via the tricarboxylic acid cycle. Under both physiological and pathological conditions, we have recently found that the ability of glutamate to fuel cell metabolism selectively relies on the activity of two main transporters: the sodium-calcium exchanger (NCX) and the sodium-dependent excitatory amino-acid transporters (EAATs). In ischemic settings, when glutamate is administered at the onset of the reoxygenation phase, the coordinate activity of EAAT and NCX allows glutamate to improve cell viability by stimulating ATP production. So far, this phenomenon has been observed in both cardiac and neuronal models. In this review, we focus on the most recent findings exploring the unusual activity of glutamate as a potential survival factor in different settings.

Metabo-lipidomics of Fibroblasts and Mitochondrial-Endoplasmic Reticulum Extracts from ALS Patients Shows Alterations in Purine, Pyrimidine, Energetic, and Phospholipid Metabolisms

Amyotrophic lateral sclerosis (ALS) is characterized by a wide metabolic remodeling, as shown by recent metabolomics and lipidomics studies performed in samples from patient cohorts and experimental animal models. Here, we explored the metabolome and lipidome of fibroblasts from sporadic ALS patients (n = 13) comparatively to age- and sex-matched controls (n = 11), and the subcellular fraction containing the mitochondria and endoplasmic reticulum (mito-ER), given that mitochondrial dysfunctions and ER stress are important features of ALS patho-mechanisms. We also assessed the mitochondrial oxidative respiration and the mitochondrial genomic (mtDNA) sequence, although without yielding significant differences. Compared to controls, ALS fibroblasts did not exhibit a mitochondrial respiration defect nor an increased proportion of mitochondrial DNA mutations. In addition, non-targeted metabolomics and lipidomics analyses identified 124 and 127 metabolites, and 328 and 220 lipids in whole cells and the mito-ER fractions, respectively, along with partial least-squares-discriminant analysis (PLS-DA) models being systematically highly predictive of the disease. The most discriminant metabolomic features were the alteration of purine, pyrimidine, and energetic metabolisms, suggestive of oxidative stress and of pro-inflammatory status. The most important lipidomic feature in the mito-ER fraction was the disturbance of phosphatidylcholine PC (36:4p) levels, which we had previously reported in the cerebrospinal fluid of ALS patients and in the brain from an ALS mouse model. Thus, our results reveal that fibroblasts from sporadic ALS patients share common metabolic remodeling, consistent with other metabolic studies performed in ALS, opening perspectives for further exploration in this cellular model in ALS.

The Role of Iron in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by the degeneration of motor neurons in the motor cortex, brainstem, and spinal cord. The etiology and pathogenesis of this devastating disease remain largely unknown. Increasing evidence suggests that iron accumulation is involved in the onset and progression of ALS. In this review, we discuss the regulation of iron homoeostasis in the brain, the misregulation of iron homeostasis in ALS, and its possible roles in the mechanism of the disease. Finally, we summarize the recent progress and problems with respect to iron chelator therapies on ALS, aiming to propose a new therapeutic strategy to ameliorate the progression of the disease.

A High-throughput and Pathophysiologically Relevant Astrocyte-motor Neuron Co-culture Assay for Amyotrophic Lateral Sclerosis Therapeutic Discovery

Amyotrophic lateral sclerosis (ALS) is an adult onset neurological disorder characterized by loss of motor neurons leading to progressive muscle wasting and eventually death. Astrocytes play a key role in disease pathogenesis. However, the ability to study astrocytic support towards motor neurons in ALS has been limited by a lack of sustainable high-throughput human cell models. Moreover, the ability to assess how astrocytic support of motor neurons is influenced by drug treatment or nutritional supplementation has been hampered by the lack of robust methodology. We have developed a high-throughput astrocyte motor neuron co-culture assay, which, by using Hb9-GFP+ motor neurons enables researchers to assess how ALS affects the ability of astrocytes to support motor neurons in 384-well plates. Moreover, astrocyte function can be manipulated by nutritional supplementation or drug treatment to identify possible therapeutic targets.

Fungal Neurotoxins and Sporadic Amyotrophic Lateral Sclerosis

We review several lines of evidence that point to a potential fungal origin of sporadic amyotrophic lateral sclerosis (ALS). ALS is the most common form of motor neuron disease (MND) in adults. It is a progressive and fatal disease. Approximately 90% cases of ALS are sporadic, and 5-10% are due to genetic mutations (familial). About 25 genes implicated in familial ALS have been identified so far, including SOD1 and TARDBP, the gene encoding 43 kDa transactive response (TAR) DNA-binding protein (TDP-43). Despite intensive research over many decades, the aetiology of sporadic ALS is still unknown. An environmental cause, including grass or soil-associated fungal infections, is suggested from a range of widely diverse lines of evidence. Clusters of ALS have been reported in soccer players, natives of Guam and farmers. Grass-associated fungi are known to produce a range of neurotoxins and, in symbiotic associations, high levels of fungal SOD1. Exposure of neurons to fungal neurotoxins elicits a significant increase in glutamate production. High levels of glutamate stimulate TDP-43 translocation and modification, providing a link between fungal infection and one of the molecular and histologic hallmarks of sporadic ALS. A recent study provided evidence of a variety of fungi in the cerebrospinal fluid and brain tissue of ALS patients. This review provides a rational explanation for this observation. If a fungal infection could be confirmed as a potential cause of ALS, this could provide a straightforward treatment strategy for this fatal and incurable disease.

Prolonged Voluntary Running Negatively Affects Survival and Disease Prognosis of Male SOD1G93A Low-Copy Transgenic Mice

Amyotrophic Lateral Sclerosis (ALS) is a disease in which physical activity plays a controversial role. Epidemiological studies indicate an association between intense exercise and risk of developing ALS. To study the impact of physical activity on ALS, mouse models rely mostly on forced exercise. In this study we hypothesized that voluntary wheel running could represent a better model of the influence of exercise in the pathogenesis of ALS. We used an automated home-cage running-wheel system that enables individual monitoring of performance. To verify the effect of voluntary running on disease progression, prognosis and survival as well as motor functions, we challenged SOD1G93A low-copy male and female mice on one (1 RW, at age 24 weeks) or multiple (3 RW) running sessions at age 13, 18, and 24 weeks. In parallel we measured performance on Rotarod and Grip strength tests at different ages. Several parameters were analyzed through Principal Component Analysis in order to detect what indices correlate and may be useful for deeper understanding of the relation between exercise and disease development. We found mutant male mice more negatively affected than females by prolonged and repeated exercise. SOD1G93A low-copy male mice showed shorter survival, increased body weight loss and poorer disease prognosis when exposed to multiple running sessions. These findings could encourage the investigation of the pathogenetic mechanisms underlying the supposedly increased risk to develop ALS in humans engaged in specific and intense exercise activities.

Amyotrophic lateral sclerosis: the complex path to precision medicine

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease of the corticomotorneuronal network responsible for voluntary movement. There are well-established clinical, genetic and pathological overlaps between ALS and frontotemporal dementia (FTD), which together constitute the 'TDP-43 proteinopathies'. An ever-expanding list of genes in which mutation leads to typical ALS have implicated abnormalities in RNA processing, protein homoeostasis and axonal transport. How these apparently distinct pathways converge to cause the characteristic clinical syndrome of ALS remains unclear. Although there are major gaps in our understanding of the essential nature of ALS pathophysiology, the identification of genetic causes in up to 15% of ALS patients, coupled with advances in biotechnology and biomarker research provide a foundation for approaches to treatment based on 'precision medicine', and even prevention of the disease in pre-symptomatic mutation carriers in the future. Currently, multidisciplinary care remains the bedrock of management and this is increasingly being put onto an evidence-based footing.

New insights into the pathophysiology of fasciculations in amyotrophic lateral sclerosis: An ultrasound study

OBJECTIVE

To describe the fasciculation pattern in ALS and to analyse its clinical and pathophysiological significance.

METHODS

Ultrasound of 19 muscles was performed in 44 patients with a recent diagnosis (<90 days) of ALS. The number of fasciculations was recorded in each muscle and the muscle thickness and strength were additionally measured in limb muscles. A subgroup of patients were electromyographically assessed.

RESULTS

US was performed in 835 muscles and EMG was available in 263 muscles. US detected fasciculations more frequently than EMG. Fasciculations were widespread, especially in upper limbs onset patients and in the cervical region. Fasciculations' number inversely associated with ALSFR-R and body mass index (BMI) and directly with BMI loss and upper motor neuron (UMN) impairment. Our statistical model suggest that fasciculations increase with the initial lower motor neuron (LMN) degeneration, reach their peak when the muscle became mildly to moderately weak, decreasing afterwards with increasing muscle weakness and atrophy.

CONCLUSIONS

Our study suggests that both UMN and LMN degeneration trigger fasciculations causing BMI loss. The degree of LMN impairment could account for differences in fasciculations' rates within and between muscles.

SIGNIFICANCE

In ALS, fasciculations could explain the link between hyperexcitability and BMI loss.

Mutant FUS causes DNA ligation defects to inhibit oxidative damage repair in Amyotrophic Lateral Sclerosis

Genome damage and defective repair are etiologically linked to neurodegeneration. However, the specific mechanisms involved remain enigmatic. Here, we identify defects in DNA nick ligation and oxidative damage repair in a subset of amyotrophic lateral sclerosis (ALS) patients. These defects are caused by mutations in the RNA/DNA-binding protein FUS. In healthy neurons, FUS protects the genome by facilitating PARP1-dependent recruitment of XRCC1/DNA Ligase IIIα (LigIII) to oxidized genome sites and activating LigIII via direct interaction. We discover that loss of nuclear FUS caused DNA nick ligation defects in motor neurons due to reduced recruitment of XRCC1/LigIII to DNA strand breaks. Moreover, DNA ligation defects in ALS patient-derived iPSC lines carrying FUS mutations and in motor neurons generated therefrom are rescued by CRISPR/Cas9-mediated correction of mutation. Our findings uncovered a pathway of defective DNA ligation in FUS-linked ALS and suggest that LigIII-targeted therapies may prevent or slow down disease progression.

Localization of RNAi Machinery to Axonal Branch Points and Growth Cones Is Facilitated by Mitochondria and Is Disrupted in ALS

Local protein synthesis in neuronal axons plays an important role in essential spatiotemporal signaling processes; however, the molecular basis for the post-transcriptional regulation controlling this process in axons is still not fully understood. Here we studied the axonal mechanisms underlying the transport and localization of microRNA (miRNA) and the RNAi machinery along the axon. We first identified miRNAs, Dicer, and Argonaute-2 (Ago2) in motor neuron (MN) axons. We then studied the localization of RNAi machinery and demonstrated that mitochondria associate with miR-124 and RNAi proteins in axons. Importantly, this co-localization occurs primarily at axonal branch points and growth cones. Moreover, using live cell imaging of a functional Cy3-tagged miR-124, we revealed that this miRNA is actively transported with acidic compartments in axons, and associates with stalled mitochondria at growth cones and axonal branch points. Finally, we observed enhanced retrograde transport of miR-124-Cy3, and a reduction in its localization to static mitochondria in MNs expressing the ALS causative gene hSOD1^G93A. Taken together, our data suggest that mitochondria participate in the axonal localization and transport of RNAi machinery, and further imply that alterations in this mechanism may be associated with neurodegeneration in ALS.

Bojungikgi-tang Improves Muscle and Spinal Cord Function in an Amyotrophic Lateral Sclerosis Model

Amyotrophic lateral sclerosis (ALS) is a motor neuron disease characterized by progressive motor function impairment, dysphagia, and respiratory failure. Owing to the complexity of its pathogenic mechanisms, an effective therapy for ALS is lacking. Herbal medicines with multiple targets have good efficacy and low adverse reactions for the treatment of neurodegenerative diseases. In this study, the effects of Bojungikgi-tang (BJIGT), an herbal medicine with eight component herbs, on muscle and spinal cord function were evaluated in an ALS animal model. Animals were randomly divided into three groups: a non-transgenic group (nTg, n = 24), a hSOD1^G93A transgenic group (Tg, n = 24), and a hSOD1^G93A transgenic group in which 8-week-old mice were orally administered BJIGT (1 mg/g) once daily for 6 weeks (Tg+BJIGT, n = 24). The effects of BJIGT were evaluated using a rotarod test, foot-printing, and survival analyses based on Kaplan-Meier survival curves. To determine the biological mechanism underlying the effects of BJIGT in hSOD1^G93A mice, western blotting, transmission electron microscopy, and Bungarotoxin staining were used. BJIGT improved motor function and extended the survival duration of hSOD1^G93A mice. In addition, BJIGT had protective effects, including anti-oxidative and anti-inflammatory effects, in both the spinal cord and muscle of hSOD1^G93A mice. Our results demonstrated that BJIGT causes muscle atrophy and the denervation of neuromuscular junctions in the gastrocnemius of hSOD1^G93A mice. The components of BJIGT may alleviate the symptoms of ALS via different mechanisms, and accordingly, BJIGT treatment may be an effective therapeutic approach.