Expression of the copper-zinc superoxide dismutase gene in amyotrophic lateral sclerosis

Regulation of CuZnSOD and its redox signaling potential: implications for amyotrophic lateral sclerosis

SIGNIFICANCE

Molecular oxygen is a Janus-faced electron acceptor for biological systems, serving as a reductant for respiration, or as the genesis for oxygen-derived free radicals that damage macromolecules. Superoxide is well known to perturb nonheme iron proteins, including Fe/S proteins such as aconitase and succinate dehydrogenase, as well as other enzymes containing labile iron such as the prolyl hydroxylase domain-containing family of enzymes; whereas hydrogen peroxide is more specific for two-electron reactions with thiols on glutathione, glutaredoxin, thioredoxin, and the peroxiredoxins.

RECENT ADVANCES

Over the past two decades, familial cases of amyotrophic lateral sclerosis (ALS) have been shown to have an association with commonly altered superoxide dismutase 1 (SOD1) activity, expression, and protein structure. This has led to speculation that an altered redox balance may have a role in creating the ALS phenotype.

CRITICAL ISSUES

While SOD1 alterations in familial ALS are manifold, they generally create perturbations in the flux of electrons. The nexus of SOD1 between one- and two-electron signaling processes places it at a key signaling regulatory checkpoint for governing cellular responses to physiological and environmental cues.

FUTURE DIRECTIONS

The manner in which ALS-associated mutations adjust SOD1's role in controlling the flow of electrons between one- and two-electron signaling processes remains obscure. Here, we discuss the ways in which SOD1 mutations influence the form and function of copper zinc SOD, the consequences of these alterations on free radical biology, and how these alterations might influence cell signaling during the onset of ALS.

SOD1 Transcriptional and Posttranscriptional Regulation and Its Potential Implications in ALS

Copper-zinc superoxide dismutase (SOD1) is a detoxifying enzyme localized in the cytosol, nucleus, peroxisomes, and mitochondria. The discovery that mutations in SOD1 gene cause a subset of familial amyotrophic lateral sclerosis (FALS) has attracted great attention, and studies to date have been mainly focused on discovering mutations in the coding region and investigation at protein level. Considering that changes in SOD1 mRNA levels have been associated with sporadic ALS (SALS), a molecular understanding of the processes involved in the regulation of SOD1 gene expression could not only unravel novel regulatory pathways that may govern cellular phenotypes and changes in diseases but also might reveal therapeutic targets and treatments. This review seeks to provide an overview of SOD1 gene structure and of the processes through which SOD1 transcription is controlled. Furthermore, we emphasize the importance to focus future researches on investigating posttranscriptional mechanisms and their relevance to ALS.

Impaired post-translational folding of familial ALS-linked Cu, Zn superoxide dismutase mutants

Over 110 structurally diverse missense mutations in the superoxide dismutase (SOD1) gene have been linked to the pathogenesis of familial amyotrophic lateral sclerosis (FALS), yet the mechanism by which these lead to cytotoxicity still remains unknown. We have synthesized wild-type and mutant SOD1 in synchronized cell-free reticulocyte extracts replete with the full complement of molecular chaperones and folding facilitators that are normally required to fold this metalloenzyme. Here, we report that, despite being a small, single-domain protein, human SOD1 folds post-translationally to a hyperstable native-like conformation without a requirement for ATP-dependent molecular chaperones. SOD1 folding requires tight Zn but not Cu binding and proceeds through at least three kinetically and biochemically distinct states. We find that all 11 FALS-associated SOD1 mutants examined using this system delay the kinetics of folding, but do not necessarily preclude the formation of native-like states. These data suggest a model whereby impaired post-translational folding increases the population of on- and off-pathway folding intermediates that could provide an important source of proto-toxic protein, and suggest a unifying mechanism for SOD1-linked FALS pathogenesis.

Spinal cord molecular profiling provides a better understanding of amyotrophic lateral sclerosis pathogenesis

Research efforts in amyotrophic lateral sclerosis (ALS) have not yet provided a comprehensive explanation of the disease pathogenesis, which is emerging as a complex interaction between multiple factors. Gene expression studies traditionally based on single mRNA specie analysis have recently progressed to allow entire transcriptional profiles of affected tissues to be obtained through array-based methods. This experimental approach has significantly improved our understanding of the molecular changes occurring in ALS, although its limitations in the detection of low-abundance transcripts in tissues with a high level of complexity are becoming increasingly recognized. In this paper, experimental findings based on an expression study in post-mortem spinal cord from sporadic ALS individuals will be discussed in light of recently published data using array analysis in an animal model of the disease. Previous expression data obtained using conventional techniques are also compared. Through the analysis of the information arising from ALS post-mortem and animal model tissues studies, we have identified a pattern of molecular events in which factors implicated in the immune response, cytoprotection and growth-differentiation are differentially regulated in a time-dependent way from early to advanced stages of disease progression.

Localization of Nav1.5 sodium channel protein in the mouse brain

Na(v)1.5 or SCN5A is a member of the voltage-dependent family of sodium channels. The distribution of Na(v)1.5 protein was investigated in the mouse brain using immunohistochemistry. Immunostaining with a Na(v)1.5-specific antibody revealed that Na(v)1.5 protein was localized in certain distinct regions of brain including the cerebral cortex, thalamus, hypothalamus, basal ganglia, cerebellum and brain stem. Notably, we found that Na(v)1.5 protein co-localized with neurofilaments and clustered at a high density in the neuronal processes, mainly axons. These results suggest that Na(v)1.5 protein may play a role in the physiology of the central nervous system (generation and propagation of electrical signals by axons).