No abstract

Twenty percent of the familial form of amyotrophic lateral sclerosis (ALS) is caused by mutations in the Cu, Zn-superoxide dismutase gene (SOD1) through the gain of a toxic function. The nature of this toxic function of mutant SOD1 has remained largely unknown. Here we show that WT SOD1 not only hastens onset of the ALS phenotype but can also convert an unaffected phenotype to an ALS phenotype in mutant SOD1 transgenic mouse models. Further analyses of the single-and double-transgenic mice revealed that conversion of mutant SOD1 from a soluble form to an aggregated and detergent-insoluble form was associated with development of the ALS phenotype in transgenic mice. Conversion of WT SOD1 from a soluble form to an aggregated and insoluble form also correlates with exacerbation of the disease or conversion to a disease phenotype in double-transgenic mice. This conversion, observed in the mitochondrial fraction of the spinal cord, involved formation of insoluble SOD1 dimers and multimers that are crosslinked through intermolecular disulfide bonds via oxidation of cysteine residues in SOD1. Our data thus show a molecular mechanism by which SOD1, an important protein in cellular defense against free radicals, is converted to aggregated and apparently ALS-associated toxic dimers and multimers by redox processes. These findings provide evidence of direct links among oxidation, protein aggregation, mitochondrial damage, and SOD1-mediated ALS, with possible applications to the aging process and other late-onset neurodegenerative disorders. Importantly, rational therapy based on these observations can now be developed and tested.crosslinked ͉ disulfide bonds ͉ oxidation ͉ protein aggregation ͉ neurodegeneration A myotrophic lateral sclerosis (ALS) is a progressive paralytic disorder caused by degeneration of the motor neurons in brain and spinal cord (1). Most of the ALS cases are sporadic, with Ϸ5-10% being familial. The progressive paralysis in ALS usually affects respiratory function, leading to ventilatory failure and death; 50% of patients die within 3 years of onset of symptoms, and 90% die within 5 years. The juvenile form of ALS usually has a prolonged course of two to four decades. There is no known effective treatment for this fatal disease, although marginal delay in mortality has been noted with the drug riluzole (2).Familial ALS can be transmitted as either a dominant or a recessive trait. We and our collaborators have previously shown that mutations in the Cu, Zn-superoxide dismutase gene (SOD1) are associated with Ϸ20% of familial ALS cases (3, 4). The pathogenic mechanisms underlying this disease are still largely unknown. Most, but not all, transgenic mice overexpressing ALS-associated SOD1 mutants develop ALS-like disease (5), and transgenic mice overexpressing human WT SOD1 (hwtSOD1) or SOD1-deficient mice do not develop ALS-like disease (5, 6), suggesting that mutant SOD1 requires a threshold of expression to cause the disease through the gain of a toxic property.Thus far, Ͼ100 mutations, widely distrib...

gamma-Aminobutyric acid type-A (GABAA) receptors are the major sites of fast synaptic inhibition in the brain. They are presumed to be pentameric heteroligomers assembled from four classes of subunits with multiple members: alpha (1-6), beta (1-3), gamma (1-3) and delta (1). Here, GABAA receptors consisting of alpha 1, beta 1 and gamma 2L subunits, coexpressed in mammalian cells with the tyrosine kinase vSRC (the transforming gene product of the Rous sarcoma virus), were phosphorylated on tyrosine residues within the gamma 2L and beta 1 subunits. Tyrosine phosphorylation enhanced the whole-cell current induced by GABA. Site-specific mutagenesis of two tyrosine residues within the predicted intracellular domain of the gamma 2L subunit abolished tyrosine phosphorylation of this subunit and eliminated receptor modulation. A similar modulation of GABAA receptor function was observed in primary neuronal cultures. As GABAA receptors are critical in mediating fast synaptic inhibition, such a regulation by tyrosine kinases may therefore have profound effects on the control of neuronal excitation.

Progressive external ophthalmoplegia (PEO) is a canonical feature of mitochondrial disease, but in many patients its genetic basis is unknown. Using exome sequencing, Pfeffer et al. identify mutations in SPG7 as an important cause of PEO associated with spasticity and ataxia, and uncover evidence of disordered mtDNA maintenance in patients.