Mutation screening of manganese superoxide dismutase in amyotrophic lateral sclerosis

Toolkit for cellular studies of mammalian mitochondrial inorganic polyphosphate

Introduction: Inorganic polyphosphate (polyP) is an ancient polymer which is extremely well-conserved throughout evolution, and found in every studied organism. PolyP is composed of orthophosphates linked together by high-energy bonds, similar to those found in ATP. The metabolism and the functions of polyP in prokaryotes and simple eukaryotes are well understood. However, little is known about its physiological roles in mammalian cells, mostly due to its unknown metabolism and lack of systematic methods and effective models for the study of polyP in these organisms. Methods: Here, we present a comprehensive set of genetically modified cellular models to study mammalian polyP. Specifically, we focus our studies on mitochondrial polyP, as previous studies have shown the potent regulatory role of mammalian polyP in the organelle, including bioenergetics, via mechanisms that are not yet fully understood. Results: Using SH-SY5Y cells, our results show that the enzymatic depletion of mitochondrial polyP affects the expression of genes involved in the maintenance of mitochondrial physiology, as well as the structure of the organelle. Furthermore, this depletion has deleterious effects on mitochondrial respiration, an effect that is dependent on the length of polyP. Our results also show that the depletion of mammalian polyP in other subcellular locations induces significant changes in gene expression and bioenergetics; as well as that SH-SY5Y cells are not viable when the amount and/or the length of polyP are increased in mitochondria. Discussion: Our findings expand on the crucial role of polyP in mammalian mitochondrial physiology and place our cell lines as a valid model to increase our knowledge of both mammalian polyP and mitochondrial physiology.

Insights into Manganese Superoxide Dismutase and Human Diseases

Redox equilibria and the modulation of redox signalling play crucial roles in physiological processes. Overproduction of reactive oxygen species (ROS) disrupts the body's antioxidant defence, compromising redox homeostasis and increasing oxidative stress, leading to the development of several diseases. Manganese superoxide dismutase (MnSOD) is a principal antioxidant enzyme that protects cells from oxidative damage by converting superoxide anion radicals to hydrogen peroxide and oxygen in mitochondria. Systematic studies have demonstrated that MnSOD plays an indispensable role in multiple diseases. This review focuses on preclinical evidence that describes the mechanisms of MnSOD in diseases accompanied with an imbalanced redox status, including fibrotic diseases, inflammation, diabetes, vascular diseases, neurodegenerative diseases, and cancer. The potential therapeutic effects of MnSOD activators and MnSOD mimetics are also discussed. Targeting this specific superoxide anion radical scavenger may be a clinically beneficial strategy, and understanding the therapeutic role of MnSOD may provide a positive insight into preventing and treating related diseases.

Genetic Variability of Inflammation and Oxidative Stress Genes Affects Onset, Progression of the Disease and Survival of Patients with Amyotrophic Lateral Sclerosis

Inflammation and oxidative stress are recognized as important contributors to amyotrophic lateral sclerosis (ALS) disease pathogenesis. Our aim was to evaluate the impact of selected single-nucleotide polymorphisms in genes involved in inflammation and oxidative stress on ALS susceptibility and modification. One-hundred-and-eighty-five ALS patients and 324 healthy controls were genotyped for nine polymorphisms in seven antioxidant and inflammatory genes using competitive allele-specific PCR. Logistic regression; nonparametric tests and survival analysis were used in the statistical analysis. Investigated polymorphisms were not associated with ALS susceptibility. Carriers of at least one polymorphic SOD2 rs4880 T or IL1B rs1071676 C allele more often had bulbar ALS onset (p = 0.036 and p = 0.039; respectively). IL1B rs1071676 was also associated with a higher rate of disease progression (p = 0.015). After adjustment for clinical parameters; carriers of two polymorphic IL1B rs1071676 C alleles had shorter survival (HR = 5.02; 95% CI = 1.92–13.16; p = 0.001); while carriers of at least one polymorphic CAT rs1001179 T allele had longer survival (HR = 0.68; 95% CI = 0.47–0.99; p = 0.046). Our data suggest that common genetic variants in the antioxidant and inflammatory pathways may modify ALS disease. Such genetic information could support the identification of patients that may be responsive to the immune or antioxidant system—based therapies.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

Targeted exon capture and sequencing in sporadic amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that results in progressive degeneration of motor neurons, ultimately leading to paralysis and death. Approximately 10% of ALS cases are familial, with the remaining 90% of cases being sporadic. Genetic studies in familial cases of ALS have been extremely informative in determining the causative mutations behind ALS, especially as the same mutations identified in familial ALS can also cause sporadic disease. However, the cause of ALS in approximately 30% of familial cases and in the majority of sporadic cases remains unknown. Sporadic ALS cases represent an underutilized resource for genetic information about ALS; therefore, we undertook a targeted sequencing approach of 169 known and candidate ALS disease genes in 242 sporadic ALS cases and 129 matched controls to try to identify novel variants linked to ALS. We found a significant enrichment in novel and rare variants in cases versus controls, indicating that we are likely identifying disease associated mutations. This study highlights the utility of next generation sequencing techniques combined with functional studies and rare variant analysis tools to provide insight into the genetic etiology of a heterogeneous sporadic disease.

Amyotrophic lateral sclerosis (ALS), also known as Charcot disease or Lou Gehrig's disease, is one of the most common neuromuscular diseases worldwide. This disease is characterized by a progressive degeneration of motor neurons, leading to patient death within a few years after onset. Despite the fact that most ALS cases are sporadic, most of the ALS genetic studies have focused on familial forms, leading to the genetic determination of cause for 70% of cases of familial ALS but for only 10% of sporadic ALS cases. This, coupled with the dearth of families available for study, suggests that researchers should begin tapping into the relatively untouched reservoir of available sporadic samples to identify novel genetic causes of sporadic ALS. Here we take advantage of high-throughput target sequencing techniques to test four different hypotheses about the genetic causes of ALS in sporadic ALS and uncover new candidate genes and pathways implicated in ALS.

An emerging role for misfolded wild-type SOD1 in sporadic ALS pathogenesis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that targets motor neurons, leading to paralysis and death within a few years of disease onset. While several genes have been linked to the inheritable, or familial, form of ALS, much less is known about the cause(s) of sporadic ALS, which accounts for ~90% of ALS cases. Due to the clinical similarities between familial and sporadic ALS, it is plausible that both forms of the disease converge on a common pathway and, therefore, involve common factors. Recent evidence suggests the Cu,Zn-superoxide dismutase (SOD1) protein to be one such factor that is common to both sporadic and familial ALS. In 1993, mutations were uncovered in SOD1 that represent the first known genetic cause of familial ALS. While the exact mechanism of mutant-SOD1 toxicity is still not known today, most evidence points to a gain of toxic function that stems, at least in part, from the propensity of this protein to misfold. In the wild-type SOD1 protein, non-genetic perturbations such as metal depletion, disruption of the quaternary structure, and oxidation, can also induce SOD1 to misfold. In fact, these aforementioned post-translational modifications cause wild-type SOD1 to adopt a “toxic conformation” that is similar to familial ALS-linked SOD1 variants. These observations, together with the detection of misfolded wild-type SOD1 within human post-mortem sporadic ALS samples, have been used to support the controversial hypothesis that misfolded forms of wild-type SOD1 contribute to sporadic ALS pathogenesis. In this review, we present data from the literature that both support and contradict this hypothesis. We also discuss SOD1 as a potential therapeutic target for both familial and sporadic ALS.

Manganese in health and disease

Manganese is an important metal for human health, being absolutely necessary for development, metabolism, and the antioxidant system. Nevertheless, excessive exposure or intake may lead to a condition known as manganism, a neurodegenerative disorder that causes dopaminergic neuronal death and parkinsonian-like symptoms. Hence, Mn has a paradoxal effect in animals, a Janus-faced metal. Extensive work has been carried out to understand Mn-induced neurotoxicity and to find an effective treatment. This review focuses on the requirement for Mn in human health as well as the diseases associated with excessive exposure to this metal.

The SOD2 C47T polymorphism influences NAFLD fibrosis severity: evidence from case-control and intra-familial allele association studies

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is a complex disease trait where genetic variations and environment interact to determine disease progression. The association of PNPLA3 with advanced disease has been consistently demonstrated but many other modifier genes remain unidentified. In NAFLD, increased fatty acid oxidation produces high levels of reactive oxygen species. Manganese-dependent superoxide dismutase (MnSOD), encoded by the SOD2 gene, plays an important role in protecting cells from oxidative stress. A common non-synonymous polymorphism in SOD2 (C47T; rs4880) is associated with decreased MnSOD mitochondrial targeting and activity making it a good candidate modifier of NAFLD severity.

METHODS

The relevance of the SOD2 C47T polymorphism to fibrotic NAFLD was assessed by two complementary approaches: we sought preferential transmission of alleles from parents to affected children in 71 family trios and adopted a case-control approach to compare genotype frequencies in a cohort of 502 European NAFLD patients.

RESULTS

In the family study, 55 families were informative. The T allele was transmitted on 47/76 (62%) possible occasions whereas the C allele was transmitted on only 29/76 (38%) occasions, p=0.038. In the case control study, the presence of advanced fibrosis (stage>1) increased with the number of T alleles, p=0.008 for trend. Multivariate analysis showed susceptibility to advanced fibrotic disease was determined by SOD2 genotype (OR 1.56 (95% CI 1.09-2.25), p=0.014), PNPLA3 genotype (p=0.041), type 2 diabetes mellitus (p=0.009) and histological severity of NASH (p=2.0×10(-16)).

CONCLUSIONS

Carriage of the SOD2 C47T polymorphism is associated with more advanced fibrosis in NASH.

Effect of manganese-superoxide dismutase genetic polymorphisms IVS3-23T/G on noise susceptibility in Taiwan

PURPOSE

The aim of the study is to investigate the distribution of manganese-superoxide dismutase (SOD2) genetic polymorphisms IVS3-23T/G and their influence on noise susceptibility in Asians.

MATERIALS AND METHODS

Questionnaires about history of noise exposure were administered to factory workers, and audiometric data and blood specimens were obtained during their routine annual health examinations. The SOD2 typing was extended with polymerase chain reaction and screened with single-strand conformation polymorphism. The associations of genetic polymorphisms with noise-induced hearing loss (NIHL) were analyzed.

RESULTS

The allele frequencies of T and G in the population of this study were 0.868 and 0.132, respectively. In 200 screened participants, individuals with T/G genotype were significantly more vulnerable to noise (adjusted odds ratio, 6.222; 95% confidence interval, 1.498-25.855) than the wild type (ie, T/T) by logistic regressions.

CONCLUSIONS

The distributions of SOD2 genetic polymorphisms for Asians are different from those reported on Europeans. Individuals with T/G genotype were more vulnerable to noise. This single nucleotide polymorphism is worthy of more studies for the application to NIHL monitoring.

Genetic studies of amyotrophic lateral sclerosis: controversies and perspectives

The genetic causes of amyotrophic lateral sclerosis (ALS) are slowly being dissected out with the help of recent advances in genetic technology. Linkage studies and association studies examining candidate genes, candidate pathways, and genome-wide association have been used, based on direct sequencing and correlations between genetic variations. Copy number and microsatellite variants have also been examined, although the ideal methods for analysis are still being developed. In this review we examine the evidence for a genetic basis to ALS, discuss the challenges and difficulties faced and summarize the support for the reported genetic causes of ALS.

A polymorphism in SOD2 is associated with development of Alzheimer's disease

Genes involved in cellular mechanisms to repair oxidative damage are strong candidates as etiologic factors for Alzheimer's disease (AD). One important enzyme involved in this mechanism is superoxide dismutase 2 (SOD2). The gene for this enzyme lies within a single haplotype block at 6q25.3, a region showing evidence for linkage to AD in a genome scan. We genotyped four single nucleotide polymorphisms (SNPs) in SOD2 in families of the National Institute of Mental Health-AD Genetics Initiative (ADGI): rs2758346 in the 5' untranslated region (UTR), rs4880 in exon 2, rs2855116 in intron 3 and rs5746136 in the 3'UTR. Under a dominant model, family-based association tests showed significant evidence for association of AD with the first three loci in a candidate gene set of families with individuals having age of onset of at least 50 years and two affected and one unaffected sibling, and in a late-onset subset of families (families with all affected individuals having age of onset of at least 65 years) from the full ADGI sample. The alleles transmitted more frequently to cases than expected under the null hypothesis were T, C, G, and G. Global tests of the transmission of haplotypes indicate that the first two loci have the most consistent association with risk of AD. Because of the high linkage disequilibrium in this small (14 kb) gene, and the presence of 100 SNPs in this gene, 26 of which may have functional significance, additional genotyping and sequencing are needed to identify the functionally relevant SNP. We discuss the importance of our findings and the relevance of SOD2 to AD risk.

VEGF C2578A polymorphism does not contribute to amyotrophic lateral sclerosis susceptibility in sporadic Chinese patients

A linkage and association of the VEGF (vascular endothelial growth factor) C2578A polymorphism and amyotrophic lateral sclerosis (ALS) has been found in some studies. We analysed the C2578A polymorphism in sporadic ALS patients from a Chinese population. The polymorphism was analysed in 115 patients and 200 healthy individuals by amplifying across position 2705 to 2494 of the promoter region of the VEGF gene. It was found that the frequency of the allele A was 24% in ALS patients and 28% in healthy individuals (p = 0.264). Comparing the background of this polymorphism in healthy individuals between Chinese and Caucasians, significant decreases were found in the frequencies of the A/A genotype and allele A (p(s)<0.001). We concluded that VEGF C2578A polymorphism did not confer a susceptibility to sporadic Chinese ALS patients, which was in disagreement with that reported previously in Caucasian populations and might be ascribed to the different genetic background between Chinese and Caucasians.

Amyotrophic lateral sclerosis as a complex genetic disease

In complex diseases like ALS, there are multiple genetic and environmental factors all contributing to disease liability. The genetic factors causing susceptibility to developing ALS can be considered a spectrum from single genes with large effect sizes causing classical Mendelian ALS, to genes of smaller effect, producing apparently sporadic disease. We examine the statistical genetic principles that underpin this model and review what is known about ALS as a disease with complex genetics.

Association analysis of SOD2 variants with methamphetamine psychosis in Japanese and Taiwanese populations

SOD2 (superoxide dismutase 2) plays a crucial role in protecting the cells against damage caused by free radicals, by catalyzing their detoxification. On the other hand, cell damage caused by free radical generation following methamphetamine administration has been postulated as one of the possible pathophysiological mechanisms for methamphetamine psychosis. Hence, we investigated the association of SOD2 polymorphisms with the development of methamphetamine psychosis, in two independent populations of Japan and Taiwan. We recruited 116 patients with methamphetamine psychosis and 189 controls in Japan, and 135 patients with methamphetamine psychosis and 204 controls in Taiwan. The methamphetamine group was divided into two clinical subtypes: a transient type of psychosis (i.e., good prognosis) and a prolonged type of psychosis (i.e., poor prognosis), according to the course of the manifestation of psychosis. With reference to the genotypic and allelic frequencies of Ala/Val functional polymorphism in exon 2, we found significant differences between individuals with prolonged methamphetamine psychosis and control samples from Japan and Taiwan in the genotypic (P value 0.014 and 0.016, respectively) and in the allelic (P value 0.004 and 0.047, respectively) frequencies. Our results suggest that Ala/Val polymorphism of the SOD2 gene could be associated with the risk of developing methamphetamine psychosis.

Paraoxonase and superoxide dismutase gene polymorphisms and noise-induced hearing loss

BACKGROUND

Noise-induced cochlear epithelium damage can cause hearing loss in industrial workers. In experimental systems, noise induces the release of free radicals and may damage the cochlear sensorial epithelium. Therefore, genes involved in regulating the reactive oxygen species manganese-superoxide dismutase (SOD2) and the antioxidant paraoxonase (PON) could influence cochlea vulnerability to noise. We evaluated whether susceptibility to noise-induced hearing loss (NIHL) is associated with SOD2, PON1, and PON2 polymorphisms in workers exposed to prolonged loud noise.

METHODS

We enrolled 94 male workers from an aircraft factory in the study. The SOD2 gene was screened by denaturing reversed-phase HPLC, and the PON1 (Q192R and M55L) and PON2 (S311C) polymorphisms were analyzed by PCR amplification followed by digestion with restriction endonucleases.

RESULTS

Three known (A16V, IVS3-23T/G, and IVS3-60T/G) and two new SOD2 polymorphisms (IVS1+ 8A/G and IVS3+107T/A) were identified. Regression analysis showed that PON2 (SC+CC) [odds ratio (OR) = 5.01; 95% confidence interval (CI), 1.11-22.54], SOD2 IVS3-23T/G and IVS3-60T/G (OR = 5.09; 95% CI, 1.27-20.47), age (OR = 1.22; 95% CI, 1.09-1.36), and smoking (OR = 49.49; 95% CI, 5.09-480.66) were associated with NIHL. No association was detected for PON1 (QQ+RR) and PON1 (LL) genotypes.

CONCLUSIONS

Our data suggest that SOD2 and PON2 polymorphisms, by exerting variable local tissue antioxidant roles, could predispose to NIHL. However, caution should be exercised in interpreting these data given the small sample size and the difficulty in matching cases to controls regarding the overwhelming risk factor, i.e., smoking at least 10 cigarettes/day.

Superoxide dismutase multigene family: a comparison of the CuZn-SOD (SOD1), Mn-SOD (SOD2), and EC-SOD (SOD3) gene structures, evolution, and expression

Superoxide dismutases are an ubiquitous family of enzymes that function to efficiently catalyze the dismutation of superoxide anions. Three unique and highly compartmentalized mammalian superoxide dismutases have been biochemically and molecularly characterized to date. SOD1, or CuZn-SOD (EC 1.15.1.1), was the first enzyme to be characterized and is a copper and zinc-containing homodimer that is found almost exclusively in intracellular cytoplasmic spaces. SOD2, or Mn-SOD (EC 1.15.1.1), exists as a tetramer and is initially synthesized containing a leader peptide, which targets this manganese-containing enzyme exclusively to the mitochondrial spaces. SOD3, or EC-SOD (EC 1.15.1.1), is the most recently characterized SOD, exists as a copper and zinc-containing tetramer, and is synthesized containing a signal peptide that directs this enzyme exclusively to extracellular spaces. What role(s) these SODs play in both normal and disease states is only slowly beginning to be understood. A molecular understanding of each of these genes has proven useful toward the deciphering of their biological roles. For example, a variety of single amino acid mutations in SOD1 have been linked to familial amyotrophic lateral sclerosis. Knocking out the SOD2 gene in mice results in a lethal cardiomyopathy. A single amino acid mutation in human SOD3 is associated with 10 to 30-fold increases in serum SOD3 levels. As more information is obtained, further insights will be gained.