Is ALS a systemic disorder? Evidence from muscle mitochondria

Heterozygous DHTKD1 Variants in Two European Cohorts of Amyotrophic Lateral Sclerosis Patients

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by progressive upper and lower motor neuron (LMN) loss. As ALS and other neurodegenerative diseases share genetic risk factors, we performed whole-exome sequencing in ALS patients focusing our analysis on genes implicated in neurodegeneration. Thus, variants in the DHTKD1 gene encoding dehydrogenase E1 and transketolase domain containing 1 previously linked to 2-aminoadipic and 2-oxoadipic aciduria, Charcot-Marie-Tooth (CMT) disease type 2, and spinal muscular atrophy (SMA) were identified. In two independent European ALS cohorts (n = 643 cases), 10 sporadic cases of 225 (4.4%) predominantly sporadic patients of cohort 1, and 12 familial ALS patients of 418 (2.9%) ALS families of cohort 2 harbored 14 different rare heterozygous DHTKD1 variants predicted to be deleterious. Four DHTKD1 variants were previously described pathogenic variants, seven were recurrent, and eight were located in the E1_dh dehydrogenase domain. Nonsense variants located in the E1_dh domain were significantly more prevalent in ALS patients versus controls. The phenotype of ALS patients carrying DHTKD1 variants partially overlapped with CMT and SMA by presence of sensory impairment and a higher frequency of LMN-predominant cases. Our results argue towards rare heterozygous DHTKD1 variants as potential contributors to ALS phenotype and, possibly, pathogenesis.

Prolonged NCX activation prevents SOD1 accumulation, reduces neuroinflammation, ameliorates motor behavior and prolongs survival in a ALS mouse model

Imbalance in cellular ionic homeostasis is a hallmark of several neurodegenerative diseases including Amyotrophic Lateral Sclerosis (ALS). Sodium-calcium exchanger (NCX) is a membrane antiporter that, operating in a bidirectional way, couples the exchange of Ca²⁺ and Na ⁺ ions in neurons and glial cells, thus controlling the intracellular homeostasis of these ions. Among the three NCX genes, NCX1 and NCX2 are widely expressed within the CNS, while NCX3 is present only in skeletal muscles and at lower levels of expression in selected brain regions. ALS mice showed a reduction in the expression and activity of NCX1 and NCX2 consistent with disease progression, therefore we aimed to investigate their role in ALS pathophysiology. Notably, we demonstrated that the pharmacological activation of NCX1 and NCX2 by the prolonged treatment of SOD1^G93A mice with the newly synthesized compound neurounina: (1) prevented the reduction in NCX activity observed in spinal cord; (2) preserved motor neurons survival in the ventral spinal horn of SOD1^G93A mice; (3) prevented the spinal cord accumulation of misfolded SOD1; (4) reduced astroglia and microglia activation and spared the resident microglia cells in the spinal cord; (5) improved the lifespan and mitigated motor symptoms of ALS mice. The present study highlights the significant role of NCX1 and NCX2 in the pathophysiology of this neurodegenerative disorder and paves the way for the design of a new pharmacological approach for ALS.

Plasma creatinine and oxidative stress biomarkers in amyotrophic lateral sclerosis

Objective: To determine the associations between plasma creatinine (PCr), plasma uric acid (PUA), and urinary oxidative stress (OS) biomarkers with the ALSFRS-R at baseline and survival in a large epidemiological cohort study (ALS COSMOS) with a well-phenotyped patient population (N = 355).Methods: Fasting plasma and first void urine samples were obtained. PCr, PUA, urinary 8-oxo-deoxy guanosine (8-oxodG), and 15-F_2t-isoprostane (IsoP) were analyzed at baseline, near the midpoint of follow-up, and at the final blood draw (before death or withdrawal from study). We estimated associations between these biomarkers and the ALSFRS-R at baseline and survival.Results: At baseline, PCr correlated with ALSFRS-R (Spearman r = 0.30), percent (%) FVC (r = 0.20), PUA (r = 0.37), and 8-oxodG (r = -0.13, all p < 0.05). Baseline PCr significantly predicted survival (adjusted hazard ratio 0.28, p < 0.001). Time to death from baseline was shortest for those in the lowest two PCr quartiles relative to the highest two quartiles. PCr and ALSFRS-R values were significantly correlated at all three time points (baseline: r = 0.29, midpoint: r = 0.23, final: r = 0.38, all p < 0.001). PCr and PUA significantly declined over time, whereas OS biomarkers significantly increased over time.Conclusions: To date, PCr predicted survival the best, compared to PUA, 8-oxodG, and IsoP. Although PCr represents the degree of muscle mass, it may also represent complex biochemical changes in ALS. Because the field has no reliable prognostic biomarkers, the importance of PCr warrants further investigation through clinical studies in ALS.

Skeletal Muscle Satellite Cells, Mitochondria, and MicroRNAs: Their Involvement in the Pathogenesis of ALS

Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND), is a fatal motor neuron disorder. It results in progressive degeneration and death of upper and lower motor neurons, protein aggregation, severe muscle atrophy and respiratory insufficiency. Median survival with ALS is between 2 and 5 years from the onset of symptoms. ALS manifests as either familial ALS (FALS) (~10% of cases) or sporadic ALS (SALS), (~90% of cases). Mutations in the copper/zinc (CuZn) superoxide dismutase (SOD1) gene account for ~20% of FALS cases and the mutant SOD1 mouse model has been used extensively to help understand the ALS pathology. As the precise mechanisms causing ALS are not well understood there is presently no cure. Recent evidence suggests that motor neuron degradation may involve a cell non-autonomous phenomenon involving numerous cell types within various tissues. Skeletal muscle is now considered as an important tissue involved in the pathogenesis of ALS by activating a retrograde signaling cascade that degrades motor neurons. Skeletal muscle heath and function are regulated by numerous factors including satellite cells, mitochondria and microRNAs. Studies demonstrate that in ALS these factors show various levels of dysregulation within the skeletal muscle. This review provides an overview of their dysregulation in various ALS models as well as how they may contribute individually and/or synergistically to the ALS pathogenesis.

Mitochondrial dysfunction in blood cells from amyotrophic lateral sclerosis patients

Mitochondrial dysfunction is implicated in amyotrophic lateral sclerosis, where the progressive degeneration of motor neurons results in muscle atrophy, paralysis and death. Abnormalities in both central nervous system and muscle mitochondria have previously been demonstrated in patient samples, indicating systemic disease. In this case-control study, venous blood samples were acquired from 24 amyotrophic lateral sclerosis patients and 21 age-matched controls. Platelets and peripheral blood mononuclear cells were isolated and mitochondrial oxygen consumption measured in intact and permeabilized cells with additions of mitochondrial substrates, inhibitors and titration of an uncoupler. Respiratory values were normalized to cell count and for two markers of cellular mitochondrial content, citrate synthase activity and mitochondrial DNA, respectively. Mitochondrial function was correlated with clinical staging of disease severity. Complex IV (cytochrome c-oxidase)-activity normalized to mitochondrial content was decreased in platelets from amyotrophic lateral sclerosis patients both when normalized to citrate synthase activity and mitochondrial DNA copy number. In mononuclear cells, complex IV-activity was decreased when normalized to citrate synthase activity. Mitochondrial content was increased in amyotrophic lateral sclerosis patient platelets. In mononuclear cells, complex I activity declined and mitochondrial content increased progressively with advancing disease stage. The findings are, however, based on small subsets of patients and need to be confirmed. We conclude that when normalized to mitochondria-specific content, complex IV-activity is reduced in blood cells from amyotrophic lateral sclerosis patients and that there is an apparent compensatory increase in cellular mitochondrial content. This supports systemic involvement in amyotrophic lateral sclerosis and suggests further study of mitochondrial function in blood cells as a future biomarker for the disease.

Defective mitochondrial dynamics is an early event in skeletal muscle of an amyotrophic lateral sclerosis mouse model

Mitochondria are dynamic organelles that constantly undergo fusion and fission to maintain their normal functionality. Impairment of mitochondrial dynamics is implicated in various neurodegenerative disorders. Amyotrophic lateral sclerosis (ALS) is an adult-onset neuromuscular degenerative disorder characterized by motor neuron death and muscle atrophy. ALS onset and progression clearly involve motor neuron degeneration but accumulating evidence suggests primary muscle pathology may also be involved. Here, we examined mitochondrial dynamics in live skeletal muscle of an ALS mouse model (G93A) harboring a superoxide dismutase mutation (SOD1^G93A). Using confocal microscopy combined with overexpression of mitochondria-targeted photoactivatable fluorescent proteins, we discovered abnormal mitochondrial dynamics in skeletal muscle of young G93A mice before disease onset. We further demonstrated that similar abnormalities in mitochondrial dynamics were induced by overexpression of mutant SOD1^G93A in skeletal muscle of normal mice, indicating the SOD1 mutation drives ALS-like muscle pathology in the absence of motor neuron degeneration. Mutant SOD1^G93A forms aggregates inside muscle mitochondria and leads to fragmentation of the mitochondrial network as well as mitochondrial depolarization. Partial depolarization of mitochondrial membrane potential in normal muscle by carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) caused abnormalities in mitochondrial dynamics similar to that in the SOD1^G93A model muscle. A specific mitochondrial fission inhibitor (Mdivi-1) reversed the SOD1^G93A action on mitochondrial dynamics, indicating SOD1^G93A likely promotes mitochondrial fission process. Our results suggest that accumulation of mutant SOD1^G93A inside mitochondria, depolarization of mitochondrial membrane potential and abnormal mitochondrial dynamics are causally linked and cause intrinsic muscle pathology, which occurs early in the course of ALS and may actively promote ALS progression.

Clinical perspective on oxidative stress in sporadic amyotrophic lateral sclerosis

Sporadic amyotrophic lateral sclerosis (ALS) is one of the most devastating neurological diseases; most patients die within 3 to 4 years after symptom onset. Oxidative stress is a disturbance in the pro-oxidative/antioxidative balance favoring the pro-oxidative state. Autopsy and laboratory studies in ALS indicate that oxidative stress plays a major role in motor neuron degeneration and astrocyte dysfunction. Oxidative stress biomarkers in cerebrospinal fluid, plasma, and urine are elevated, suggesting that abnormal oxidative stress is generated outside of the central nervous system. Our review indicates that agricultural chemicals, heavy metals, military service, professional sports, excessive physical exertion, chronic head trauma, and certain foods might be modestly associated with ALS risk, with a stronger association between risk and smoking. At the cellular level, these factors are all involved in generating oxidative stress. Experimental studies indicate that a combination of insults that induce modest oxidative stress can exert additive deleterious effects on motor neurons, suggesting that multiple exposures in real-world environments are important. As the disease progresses, nutritional deficiency, cachexia, psychological stress, and impending respiratory failure may further increase oxidative stress. Moreover, accumulating evidence suggests that ALS is possibly a systemic disease. Laboratory, pathologic, and epidemiologic evidence clearly supports the hypothesis that oxidative stress is central in the pathogenic process, particularly in genetically susceptive individuals. If we are to improve ALS treatment, well-designed biochemical and genetic epidemiological studies, combined with a multidisciplinary research approach, are needed and will provide knowledge crucial to our understanding of ALS etiology, pathophysiology, and prognosis.

Mutations that affect mitochondrial functions and their association with neurodegenerative diseases

Mitochondria are essential for mammalian and human cell function as they generate ATP via aerobic respiration. The proteins required in the electron transport chain are mainly encoded by the circular mitochondrial genome but other essential mitochondrial proteins such as DNA repair genes, are coded in the nuclear genome and require transport into the mitochondria. In this review we summarize current knowledge on the association of point mutations and deletions in the mitochondrial genome that are detrimental to mitochondrial function and are associated with accelerated ageing and neurological disorders including Alzheimer's, Parkinson's, Huntington's and Amyotrophic lateral sclerosis (ALS). Mutations in the nuclear encoded genes that disrupt mitochondrial functions are also discussed. It is evident that a greater understanding of the causes of mutations that adversely affect mitochondrial metabolism is required to develop preventive measures against accelerated ageing and neurological disorders caused by mitochondrial dysfunction.

The functional deficiency of bone marrow mesenchymal stromal cells in ALS patients is proportional to disease progression rate

Amyotrophic lateral sclerosis (ALS) is caused by motor neuron death. The relationship between the prognosis of ALS patients and the function of their bone marrow mesenchymal stromal cells (BM-MSCs) is unclear. We designed this study to assess the correlation between the progression rate of the ALS Functional Rating Scale-revised version (ΔFS), which is reported to predict prognosis, and the pluripotency and trophic factor secreting capacity of ALS patients' BM-MSCs. We evaluated ΔFS in 23 ALS patients and isolated BM-MSCs from those patients and five healthy people. Levels of Nanog, Oct-4, and Nestin mRNA were examined to evaluate pluripotency, and levels of BDNF, ECGF1, bFGF-2, HGF, IGF-1, PGF, TGF-1β, SDF-1α, GDNF, VEGF, and ANG mRNA were examined to assess trophic factor secreting capacity. In addition, we measured the protein levels of Nanog, Oct-4, Nestin, SDF-1α, ANG, bFGF-2, VEGF, IGF-1, GDNF, and BDNF. mRNA levels of Nanog, Oct-4, ECGF1, bFGF-2, HGF, IGF-1, PGF, TGF-1β, SDF-1α, GDNF, VEGF, and ANG were negatively correlations with ΔFS. However, those of Nestin and BDNF were not significantly correlated with ΔFS. Similarly, Nanog, Oct-4, SDF-1α, ANG, bFGF-2, VEGF, IGF-1, and GDNF protein levels had a significant negative correlation with ΔFS. Results indicate that the pluripotency and trophic factor secreting capacity of the BM-MSCs of ALS patients are reduced in proportion to a poorer prognosis. We therefore suggest that healthy allogeneic BM-MSCs might be a better option for cell therapy in ALS patients.

Investigation of MGF mRNA expression in patients with amyotrophic lateral sclerosis using parallel in vivo and in vitro approaches

In an animal model of ALS, intramuscular administration of MGF, the IGF-I Ec gene splice variant, improved muscle strength and increased both motor unit and motor neuron survival. Here we investigated whether there is a deficit in MGF production in the muscles of patients with ALS. We used complementary in vivo and in vitro techniques to study the IGF-I splice variant response of human muscle to exercise or mechanical stretch. We assessed the levels of MGF and IGF-IEa mRNA in muscle biopsy samples from healthy subjects and patients with ALS, before and after exercise. We used primary muscle cells to build three-dimensional collagen constructs and subjected them to a ramp stretch. Patients with ALS had similar baseline levels of MGF and IGF-IEa mRNA to healthy controls. No up-regulation was seen in either group within a short time of a single bout of low intensity exercise. Three-dimensional human muscle constructs also detected no response to a mechanical stretch from either control subjects or ALS. We conclude that the pathology of ALS does not include a deficit in baseline levels of MGF and IGF-IEa mRNA splice variants in muscle.

Hyperactive intracellular calcium signaling associated with localized mitochondrial defects in skeletal muscle of an animal model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disorder characterized by degeneration of motor neurons and atrophy of skeletal muscle. Mutations in the superoxide dismutase (SOD1) gene are linked to 20% cases of inherited ALS. Mitochondrial dysfunction has been implicated in the pathogenic process, but how it contributes to muscle degeneration of ALS is not known. Here we identify a specific deficit in the cellular physiology of skeletal muscle derived from an ALS mouse model (G93A) with transgenic overexpression of the human SOD1(G93A) mutant. The G93A skeletal muscle fibers display localized loss of mitochondrial inner membrane potential in fiber segments near the neuromuscular junction. These defects occur in young G93A mice prior to disease onset. Fiber segments with depolarized mitochondria show greater osmotic stress-induced Ca(2+) release activity, which can include propagating Ca(2+) waves. These Ca(2+) waves are confined to regions of depolarized mitochondria and stop propagating shortly upon entering the regions of normal, polarized mitochondria. Uncoupling of mitochondrial membrane potential with FCCP or inhibition of mitochondrial Ca(2+) uptake by Ru360 lead to cell-wide propagation of such Ca(2+) release events. Our data reveal that mitochondria regulate Ca(2+) signaling in skeletal muscle, and loss of this capacity may contribute to the progression of muscle atrophy in ALS.

Increased sensitivity of myoblasts to oxidative stress in amyotrophic lateral sclerosis peripheral tissues

We compared mitochondrial respiratory chain function, mitochondrial DNA (mtDNA) integrity, and oxidative stress levels in muscle, myoblasts, fibroblasts and cybrids, from 12 amyotrophic lateral sclerosis (ALS) patients with 28 control samples. Mitochondrial respiratory chain enzyme activities were normal in muscle, myoblast and fibroblast cultures from ALS patients, as were levels of mtDNA in muscle. Rearranged muscle mtDNA species were not detected by Southern blot hybridization in any of the samples and no difference was found in the number of deleted mtDNA species detected by long-range PCR. Platelet-derived cybrid studies confirmed the absence of a systemic mtDNA abnormality. Aconitase activity measurements did not indicate increased oxidative damage in muscle tissue, or in myoblasts or fibroblasts from ALS patients cultured under basal conditions. We did, however, find an increased sensitivity to oxidative stress in myoblasts from ALS patients exposed to paraquat. This altered sensitivity appears to be due to a nuclear rather than a mtDNA abnormality. Motor neurons have a large relative size and metabolic activity, and would be expected to be exposed to a greater degree of oxidative stress than most tissues throughout life. In addition, neurons are postmitotic cells, with poor regenerative potential. We do not have a ready method to study this in neural tissue of living patients, but the oxidative stress identified in myoblasts would translate into oxidative damage more readily in motor neurons than in other tissues.

Interdisciplinary palliative care, including massage, in treatment of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive fatal neurological disease that affects approximately 20,000 Americans. Symptoms include muscle weakness, fatigue, twitching, atrophy, spasticity, pain, oropharyngeal dysfunction, pseudobulbar affect, weight loss, and respiratory impairment. Death occurs within 3-5 yr after onset of symptoms, with diagnosis taking from 11 to 17.5 months. The only FDA-approved drug for ALS is Riluzole, which only increases the life expectancy by a few months. All other treatments for ALS provide symptom management to improve the patient's quality of life. An interdisciplinary palliative care team for the ALS patient helps to reduce the stress that the illness places on families. Massage can be a useful adjunctive treatment for spasticity and pain when medication side effects are unwanted. A holistic interdisciplinary palliative care team supports both the patient and the family improving their quality of life.

Oxidative stress biomarkers in sporadic ALS

We aimed to investigate oxidative stress biomarkers in a cross-sectional pilot study of 50 participants with sporadic ALS (SALS) compared to 46 control subjects. We measured urinary 8-oxodeoxyguanosine (8-oxodG), urinary 15-F(2t)-isoprostane (IsoP), and plasma protein carbonyl by ELISA methods. We also determined if ELISA measurement of 8-oxodG could be validated against measures from high-pressure liquid chromatography coupled with electrochemical detection, the current standard method. We found that 8-oxodG and IsoP levels adjusted for creatinine were significantly elevated in SALS participants. These differences persisted after age and gender were controlled in regression analyses. These markers are highly and positively correlated with each other. 8-oxodG measured by the two techniques from the same urine sample were positively correlated (p<.0001). Protein carbonyl was not different between SALS participants and controls. In conclusion, using ELISA, we confirmed that certain oxidative stress biomarkers were elevated in SALS participants. ELISA may be reliable and thus useful in epidemiology studies requiring large numbers of samples to determine the significance of increased oxidative stress markers in SALS. Further studies are required.

Progression of cortical and spinal dysfunctions over time in amyotrophic lateral sclerosis

In view of the conflicting results about the links between lower and upper motor neuron (LMN, UMN) dysfunction in amyotrophic lateral sclerosis (ALS), we undertook this study to correlate their changes over time. Single motor units (MUs) were characterized by their macro-MU potentials, twitch amplitude, and excitatory responses to transcranial magnetic stimulation (TMS). Ten ALS patients were studied 2 to 4 times and their data were subdivided into epochs corresponding to mean disease duration of 12 (58 MUs), 20 (60 MUs), 32 (50 MUs), 43 (40 MUs), and 168 months (55 MUs). The MU size increased and the contractile effectiveness and the excitatory response rates decreased significantly with time. The contractile effectiveness of MUs producing normal excitatory responses decreased with time, whereas a gradual loss of excitatory responses was observed among MUs with normal electromechanical properties. Since no correlation was found between UMN and LMN dysfunction, we conclude that UMN and LMN probably degenerate independently in ALS.