?-synuclein interacts with SOD1 and promotes its oligomerization.
ABSTRACT: Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS) are both neurodegenerative diseases leading to impaired execution of movement. ?-Synuclein plays a central role in the pathogenesis of PD whereas Cu, Zn superoxide dismutase (SOD1) is a key player in a subset of familial ALS cases. Under pathological conditions both ?-synuclein and SOD1 form oligomers and fibrils. In this study we investigated the possible molecular interaction of ?-synuclein and SOD1 and its functional and pathological relevance.Using a protein-fragment complementation approach and co-IP, we found that ?-synuclein and SOD1 physically interact in living cells, human erythrocytes and mouse brain tissue. Additionally, our data show that disease related mutations in ?-synuclein (A30P, A53T) and SOD1 (G85R, G93A) modify the binding of ?-synuclein to SOD1. Notably, ?-synuclein accelerates SOD1 oligomerization independent of SOD1 activity.This study provides evidence for a novel interaction of ?-synuclein and SOD1 that might be relevant for neurodegenerative diseases.
Project description:In the neurodegenerative disease multiple system atrophy (MSA), ?-synuclein misfolds into a self-templating conformation to become a prion. To compare the biological activity of ?-synuclein prions in MSA and Parkinson's disease (PD), we developed nine ?-synuclein-YFP cell lines expressing point mutations responsible for inherited PD. MSA prions robustly infected wild-type, A30P, and A53T ?-synuclein-YFP cells, but they were unable to replicate in cells expressing the E46K mutation. Coexpression of the A53T and E46K mutations was unable to rescue MSA prion infection in vitro, establishing that MSA ?-synuclein prions are conformationally distinct from the misfolded ?-synuclein in PD patients. This observation may have profound implications for developing treatments for neurodegenerative diseases.
Project description:Parkinson disease (PD) is a neurodegenerative disease with motor as well as non-motor signs in the gastrointestinal tract that include dysphagia, gastroparesis, prolonged gastrointestinal transit time, constipation and difficulty with defecation. The gastrointestinal dysfunction commonly precedes the motor symptoms by decades. Most PD is sporadic and of unknown etiology, but a fraction is familial. Among familial forms of PD, a small fraction is caused by missense (A53T, A30P and E46K) and copy number mutations in SNCA which encodes alpha-synuclein, a primary protein constituent of Lewy bodies, the pathognomonic protein aggregates found in neurons in PD. We set out to develop transgenic mice expressing mutant alpha-synuclein (either A53T or A30P) from insertions of an entire human SNCA gene as models for the familial disease. Both the A53T and A30P lines show robust abnormalities in enteric nervous system (ENS) function and synuclein-immunoreactive aggregates in ENS ganglia by 3 months of age. The A53T line also has abnormal motor behavior but neither demonstrates cardiac autonomic abnormalities, olfactory dysfunction, dopaminergic neurotransmitter deficits, Lewy body inclusions or neurodegeneration. These animals recapitulate the early gastrointestinal abnormalities seen in human PD. The animals also serve as an in vivo system in which to investigate therapies for reversing the neurological dysfunction that target alpha-synuclein toxicity at its earliest stages.
Project description:Mutations in alpha-synuclein (alpha-Syn) cause Parkinson's disease (PD) in a small number of pedigrees with familial PD. Moreover, alpha-Syn accumulates as a major component of Lewy bodies and Lewy neurites, intraneuronal inclusions that are neuropathological hallmarks of PD. To better understand the pathogenic relationship between alterations in the biology of alpha-Syn and PD-associated neurodegeneration, we generated multiple lines of transgenic mice expressing high levels of either wild-type or familial PD-linked Ala-30 --> Pro (A30P) or Ala-53 --> Thr (A53T) human alpha-Syns. The mice expressing the A53T human alpha-Syn, but not wild-type or the A30P variants, develop adult-onset neurodegenerative disease with a progressive motoric dysfunction leading to death. Pathologically, affected mice exhibit neuronal abnormalities (in perikarya and neurites) including pathological accumulations of alpha-Syn and ubiquitin. Consistent with abnormal neuronal accumulation of alpha-Syn, brain regions with pathology exhibit increases in detergent-insoluble alpha-Syn and alpha-Syn aggregates. Our results demonstrate that the A53T mutant alpha-Syn causes significantly greater in vivo neurotoxicity as compared with other alpha-Syn variants. Further, alpha-Syn-dependent neurodegeneration is associated with abnormal accumulation of detergent-insoluble alpha-Syn.
Project description:Parkinson's disease (PD) is the second most common neurodegenerative disease. A key pathological feature of PD is Lewy bodies, of which the major protein component is ?-synuclein (?-syn). Human genetic studies have shown that mutations (A53T, A30P, E46K) and multiplication of the ?-syn gene are linked to familial PD. Mice overexpressing the human A53T mutant ?-syn gene develop severe movement disorders. However, the molecular mechanisms of ?-syn toxicity are not well understood. Recently, mitochondrial dysfunction has been linked with multiple neurodegenerative diseases including Parkinson's disease. Here we investigated whether mitochondrial motility, dynamics and respiratory function are affected in primary neurons from a mouse model expressing the human A53T mutation. We found that mitochondrial motility was selectively inhibited in A53T neurons while transport of other organelles was not affected. In addition, A53T expressing neurons showed impairment in mitochondrial membrane potential and mitochondrial respiratory function. Furthermore, we found that rapamycin, an autophagy inducer, rescued the decreased mitochondrial mobility. Taken together, these data demonstrate that A53T ?-syn impairs mitochondrial function and dynamics and the deficit of mitochondrial transport is reversible, providing further understanding of the disease pathogenesis and a potential therapeutic strategy for PD.
Project description:Background: Mutations in glucocerebrosidase (GBA), a lysosomal enzyme are the most common genetic risk factor for developing Parkinson's disease (PD). We studied how reduced GCase activity affects ?-synuclein (?-syn) and its mutants (A30P and A53T) aggregation, neurodegeneration, sleep and locomotor behavior in a fly model of PD. Methods: We developed drosophila with GBA gene knockdown (RNAi) (with reduced GCase activity) that simultaneously expresses either wildtype (WT) or mutants such as A30P or A53T ?-syn. Western blot and confocal microscopy were performed to study the ?-syn aggregation and neurodegeneration in these flies. We also studied the sleep and locomotor activity of those flies using Drosophila activity monitor (DAM) system. Results: Western blot analysis showed that GBA RNAi A53T ?-syn flies (30 days old) had an increased level of Triton insoluble synuclein (that corresponds to ?-syn aggregates) compared to corresponding A53T flies without GBA RNAi (control), while mRNA expression of ?-syn remained unchanged. Confocal imaging of whole brain staining of 30 days old drosophila showed a statistically significant decrease in neuron numbers in PPL1 cluster in flies expressing ?-syn WT, A30P and A53T in the presence GBA RNAi compared to corresponding control. Staining with conformation specific antibody for ?-syn aggregates showed an increased number of neurons staining for ?-syn aggregates in A53T fly brain with GBA RNAi compared to control A53T flies, thus confirming our protein analysis finding that under decreased GBA enzyme activity, mutant A53T aggregates more than the control A53T without GBA silencing. Sleep analysis revealed decreased total activity in GBA silenced flies expressing mutant A53T compared to both A53T control flies and GBA RNAi flies without synuclein expression. Conclusion: In A53T flies with reduced GCase activity, there is increased ?-syn aggregation and dopamine (DA) neuronal loss. This study demonstrates that reduced GCase activity both in the context of heterozygous GBA1 mutation associated with PD and in old age, contribute to increased aggregation of mutant ?-syn A53T and exacerbates the phenotype in a fly model of PD.
Project description:Altered synaptic function is thought to play a role in many neurodegenerative diseases, but little is known about the underlying mechanisms for synaptic dysfunction. The squid giant synapse (SGS) is a classical model for studying synaptic electrophysiology and ultrastructure, as well as molecular mechanisms of neurotransmission. Here, we conduct a multidisciplinary study of synaptic actions of misfolded human G85R-SOD1 causing familial amyotrophic lateral sclerosis (ALS). G85R-SOD1, but not WT-SOD1, inhibited synaptic transmission, altered presynaptic ultrastructure, and reduced both the size of the readily releasable pool (RRP) of synaptic vesicles and mobility from the reserved pool (RP) to the RRP. Unexpectedly, intermittent high-frequency stimulation (iHFS) blocked inhibitory effects of G85R-SOD1 on synaptic transmission, suggesting aberrant Ca2+ signaling may underlie G85R-SOD1 toxicity. Ratiometric Ca2+ imaging showed significantly increased presynaptic Ca2+ induced by G85R-SOD1 that preceded synaptic dysfunction. Chelating Ca2+ using EGTA prevented synaptic inhibition by G85R-SOD1, confirming the role of aberrant Ca2+ in mediating G85R-SOD1 toxicity. These results extended earlier findings in mammalian motor neurons and advanced our understanding by providing possible molecular mechanisms and therapeutic targets for synaptic dysfunctions in ALS as well as a unique model for further studies.
Project description:?-Synuclein (?S) is an intrinsically disordered protein that is associated with Parkinson's disease (PD) through its ability to self-assemble into oligomers and fibrils. Inhibition of this oligomerization cascade is an interesting approach to developing therapeutical strategies and ?-synuclein (?S) has been described as a natural negative regulator of this process. However, the biological background and molecular mechanisms by which this inhibition occurs is unclear. Herein, we focused on assessing the effect of ?S on the aggregation of five ?S pathological mutants linked to early-onset PD (A30P, E46K, H50Q, G51D and A53T). By coupling single molecule fluorescence spectroscopy to a cell-free protein expression system, we validated the ability of ?S to act as a chaperone of ?S, effectively inhibiting its aggregation. Interestingly, we found that ?S does so in a selective manner, i.e., is a more effective inhibitor for certain ?S pathological mutants-A30P and G51D-as compared to E46K, H50Q and A53T. Moreover, two-color coincidence experiments proved that this discrepancy is due to a preferential incorporation of ?S into smaller oligomers of ?S. This was validated by showing that the chaperoning effect was lost when proteins were mixed after being expressed individually. This study highlights the potential of fluorescence spectroscopy to deconstruct ?S aggregation cascade and its interplay with ?S.
Project description:?-Synuclein (AS) fibrils are the major component of Lewy bodies, the pathological hallmark of Parkinson's disease (PD). Here, we use results from an extensive investigation employing solid-state NMR to present a detailed structural characterization and conformational dynamics quantification of full-length AS fibrils. Our results show that the core extends with a repeated structural motif. This result disagrees with the previously proposed fold of AS fibrils obtained with limited solid-state NMR data. Additionally, our results demonstrate that the three single point mutations associated with early-onset PD-A30P, E46K and A53T-are located in structured regions. We find that E46K and A53T mutations, located in rigid ?-strands of the wild-type fibrils, are associated with major and minor structural perturbations, respectively.
Project description:Mutations in Cu/Zn superoxide dismutase 1 (SOD1) lead to Amyotrophic Lateral Sclerosis (ALS), a neurodegenerative disease that disproportionately affects glutamatergic and cholinergic motor neurons. Previous work with SOD1 overexpression models supports a role for SOD1 toxic gain of function in ALS pathogenesis. However, the impact of SOD1 loss of function in ALS cannot be directly examined in overexpression models. In addition, overexpression may obscure the contribution of SOD1 loss of function in the degeneration of different neuronal populations. Here, we report the first single-copy, ALS knock-in models in C. elegans generated by transposon- or CRISPR/Cas9- mediated genome editing of the endogenous sod-1 gene. Introduction of ALS patient amino acid changes A4V, H71Y, L84V, G85R or G93A into the C. elegans sod-1 gene yielded single-copy/knock-in ALS SOD1 models. These differ from previously reported overexpression models in multiple assays. In single-copy/knock-in models, we observed differential impact of sod-1 ALS alleles on glutamatergic and cholinergic neurodegeneration. A4V, H71Y, G85R, and G93A animals showed increased SOD1 protein accumulation and oxidative stress induced degeneration, consistent with a toxic gain of function in cholinergic motor neurons. By contrast, H71Y, L84V, and G85R lead to glutamatergic neuron degeneration due to sod-1 loss of function after oxidative stress. However, dopaminergic and serotonergic neuronal populations were spared in single-copy ALS models, suggesting a neuronal-subtype specificity previously not reported in invertebrate ALS SOD1 models. Combined, these results suggest that knock-in models may reproduce the neurotransmitter-type specificity of ALS and that both SOD1 loss and gain of toxic function differentially contribute to ALS pathogenesis in different neuronal populations.
Project description:Amyotrophic lateral sclerosis (ALS) generally is a late-onset neurodegenerative disease. Mutations in the Cu/Zn superoxide dismutase 1 (SOD1) gene account for approximately 20% of familial ALS and 2% of all ALS cases. Although a number of hypotheses have been proposed to explain mutant SOD1 toxicity, the molecular mechanisms of the disease remain unclear. SOD1-linked ALS is thought to function in a non-cell-autonomous manner such that motoneurons are critical for the onset, and glia contribute to progression of the disease. Recently, it has been shown in Drosophila melanogaster that expression of human SOD1 in a subset of neuronal cells causes synaptic transmission defects, modified motor function, and altered sensitivity to compounds that induce oxidative stress. Here we used the Gal4-UAS (Upstream Activation Sequence) system to further characterize flies expressing wild-type Drosophila SOD1 (dSOD1) and the mutant human SOD1G85R (G85R) allele in motoneurons and glia. Cell-specific expression of both dSOD1 and G85R was found to influence lifespan, affect sensitivity to hydrogen peroxide, and alter lipid peroxidation levels. To better understand the genetic consequences of G85R expression in motoneurons and glia, we conducted microarray analysis of both young flies (5 days old) and old flies (45 days old) expressing G85R selectively in motoneurons or glia and concurrently in motoneurons and glia. Results from this microarray experiment identified candidate genes for further investigation and may help elucidate the individual and combined contributions of motoneurons and glia in ALS.