Regulation of α-synuclein expression in cultured cortical neurons

Low serum Α-SYNUCLEIN and oligomer Α-SYNUCLEIN levels in multiple sclerosis patients

INTRODUCTION

Multiple sclerosis (MS) is an autoimmune, inflammatory, demyelinating neurodegenerative disease progressing with attacks. Alpha-synuclein (α-Syn), a neuronal protein, has been previously associated with the inflammation and development of neurodegenerative diseases. Although the cause of neurodegeneration in multiple sclerosis is mainly associated with inflammation, α-Syn may play a role in the pathogenesis of MS, as in other classical neurodegenerative diseases such as synucleinopathies. In multiple sclerosis, α-Syn has been directly studied in central nervous system lesions and cerebrospinal fluid (CSF). However, there are few studies approaching variations in peripheral α-Syn in MS. The aim of our study was to investigate the correlation between disease progression and other clinical parameters by measuring serum α-Syn and oligomer α-Syn levels in MS patients.

MATERIAL AND METHOD

The study included 60 MS patients aged 18 years or older who were admitted to the Department of Neurology between 01.02.2020-01.04.2020 and diagnosed with MS according to the 2010 MC Donald criteria, and 60 age- and sex-matched healthy controls. Those who were in the MS attack period and received cortisone treatment in the past three months were excluded from the study. The serum α-Syn and oligomer α-Syn levels of the individuals in both groups were measured. The correlation between the serum α-Syn, oligomer α-Syn, oligomer α-Syn/α-Syn ratio levels of the MS patients and their age, disease duration, number of attacks, annualized relapse rate (ARR), disease type, EDSS scores and immunomodulatory drug type used was investigated. Statistical analysis was performed using the SPSS 22.0 software.

RESULTS

In our study, 73.3% of the MS patients were female and the mean age of the patients was 36.18 ± 9.5 years. The most common MS disease type was RRMS with 83.3%. Serum α-Syn (79.52 ± 34.81) and oligomer α-Syn (18.79 ± 10.48) levels were significantly lower in the MS patients compared to the control group (p < 0.001). Serum oligomer α-Syn/α-Syn ratio was higher in the MS patients compared to the control group and in SPMS compared to RRMS, but was not statistically significant. There was no significant correlation between the serum α-Syn, oligomer α-Syn and oligomer α-Syn/α-Syn ratio ratio of the MS patients and their age, disease duration, disease type, EDDS, ARR and immunomodulatory treatments. There was a significant positive correlation between α-Syn and oligomer α-Syn in MS patients (r: 0.29, p: 0.02).

CONCLUSION

In our study, serum α-Syn and oligomer α-Syn levels were lower in the MS patients compared to the control group. Low levels of α-Syn in MS may play a role in the development of neuroinflammation and may be a result of the diffuse neuronal and synaptic loss. There is a need for further studies on this subject.

A novel tool for monitoring endogenous alpha-synuclein transcription by NanoLuciferase tag insertion at the 3'end using CRISPR-Cas9 genome editing technique

α-synuclein (α-SYN) is a major pathologic contributor to Parkinson's disease (PD). Multiplication of α-SYN encoding gene (SNCA) is correlated with early onset of the disease underlining the significance of its transcriptional regulation. Thus, monitoring endogenous transcription of SNCA is of utmost importance to understand PD pathology. We developed a stable cell line expressing α-SYN endogenously tagged with NanoLuc luciferase reporter using CRISPR/Cas9-mediated genome editing. This allows efficient measurement of transcriptional activity of α-SYN in its native epigenetic landscape which is not achievable using exogenous transfection-based luciferase reporter assays. The NanoLuc activity faithfully monitored the transcriptional regulation of SNCA following treatment with different drugs known to regulate α-SYN expression; while exogenous promoter-reporter assays failed to reproduce the similar outcomes. To our knowledge, this is the first report showing endogenous monitoring of α-SYN transcription, thus making it an efficient drug screening tool that can be used for therapeutic intervention in PD.

Knockdown of α-synuclein in cerebral cortex improves neural behavior associated with apoptotic inhibition and neurotrophin expression in spinal cord transected rats

Spinal cord injury (SCI) often causes severe functional impairment with poor recovery. The treatment, however, is far from satisfaction, and the mechanisms remain unclear. By using proteomics and western blot, we found spinal cord transection (SCT) resulted in a significant down-regulation of α-synuclein (SNCA) in the motor cortex of SCT rats at 3 days post-operation. In order to detect the role of SNCA, we used SNCA-ORF/shRNA lentivirus to upregulate or knockdown SNCA expression. In vivo, SNCA-shRNA lentivirus injection into the cerebral cortex motor area not only inhibited SNCA expression, but also significantly enhanced neurons' survival, and attenuated neuronal apoptosis, as well as promoted motor and sensory function recovery in hind limbs. While, overexpression SNCA exhibited the opposite effects. In vitro, cortical neurons transfected with SNCA-shRNA lentivirus gave rise to an optimal neuronal survival and neurite outgrowth, while it was accompanied by reverse efficiency in SNCA-ORF group. In molecular level, SNCA silence induced the upregulation of Bcl-2 and the downregulation of Bax, and the expression of NGF, BDNF and NT3 was substantially upregulated in cortical neurons. Together, endogenous SNCA play a crucial role in motor and sensory function regulation, in which, the underlying mechanism may be linked to the regulation of apoptosis associated with apoptotic gene (Bax, Bcl2) and neurotrophic factors expression (NGF, BDNF and NT3). These finds provide novel insights to understand the role of SNCA in cerebral cortex after SCT, and it may be as a novel treatment target for SCI repair in future clinic trials.

Up-regulation of SNCA gene expression: implications to synucleinopathies

Synucleinopathies are a group of neurodegenerative diseases that share a common pathological lesion of intracellular protein inclusions largely composed by aggregates of alpha-synuclein protein. Accumulating evidence, including genome wide association studies, has implicated alpha-synuclein (SNCA) gene in the etiology of synucleinopathies. However, the precise variants within SNCA gene that contribute to the sporadic forms of Parkinson's disease (PD), dementia with Lewy bodies (DLB), multiple system atrophy (MSA), and other synucleinopathies and their molecular mechanisms of action remain elusive. It has been suggested that SNCA expression levels are critical for the development of these diseases. Here, we review several model systems that have been developed to advance the understanding of the role of SNCA expression levels in the etiology of synucleinopathies. We also describe different molecular mechanisms that regulate SNCA gene expression and discuss possible strategies for SNCA down-regulation as means for therapeutic approaches. Finally, we highlight some examples that underscore the relationships between the genetic association findings and the regulatory mechanisms of SNCA expression, which suggest that genetic variability in SNCA locus is directly responsible, at least in part, to the changes in gene expression and explain the reported associations of SNCA with synucleinopathies. Future studies utilizing induced pluripotent stem cells (iPSCs)-derived neuronal lines and genome editing by CRISPR/Cas9, will allow us to validate, characterize, and manipulate the effects of particular cis-genetic variants on SNCA expression. Moreover, this model system will enable us to compare different neuronal and glial lineages involved in synucleinopathies representing an attractive strategy to elucidate-common and specific-SNCA-genetic variants, regulatory mechanisms, and vulnerable expression levels underlying synucleinopathy spectrum disorders. This forthcoming knowledge will support the development of precision medicine for synucleinopathies.

Complex Effects of the ZSCAN21 Transcription Factor on Transcriptional Regulation of α-Synuclein in Primary Neuronal Cultures and in Vivo

α-Synuclein, a presynaptic neuronal protein encoded by the SNCA gene, is strongly implicated in Parkinson disease (PD). PD pathogenesis is linked to increased SNCA levels; however, the transcriptional elements that control SNCA expression are still elusive. Previous experiments in PC12 cells demonstrated that the transcription factor zinc finger and SCAN domain containing 21 (ZSCAN21) plays an important regulatory role in SNCA transcription. Currently, we characterized the role of ZSCAN21 in SNCA transcription in primary neuronal cultures and in vivo We found that ZSCAN21 is developmentally expressed in neurons in different rat brain regions. We confirmed its binding in the intron 1 region of SNCA in rat cortical cultures. Lentivirus-mediated silencing of ZSCAN21 increased significantly SNCA promoter activity, mRNA, and protein levels in such cultures. In contrast, ZSCAN21 silencing reduced SNCA in neurosphere cultures. Interestingly, ZSCAN21 overexpression in cortical neurons led to robust mRNA but negligible protein expression, suggesting that ZSCAN21 protein levels are tightly regulated post-transcriptionally and/or post-translationally in primary neurons. Efficient adeno-associated virus-mediated knockdown of ZSCAN21 in the postnatal and adult hippocampus, an area linked with non-motor PD symptoms, revealed no significant alterations in SNCA levels. Overall, our study demonstrates that ZSCAN21 is involved in the transcriptional regulation of SNCA in primary neuronal cultures, but the direction of the effect is variable, likely depending on neuronal maturation. However, the unaltered SNCA levels observed following ZSCAN21 down-regulation in the rat brain, possibly due to compensatory mechanisms, imply that ZSCAN21 is not a master regulator of SNCA in vivo.

Discovery of functional non-coding conserved regions in the α-synuclein gene locus

Several single nucleotide polymorphisms (SNPs) and the Rep-1 microsatellite marker of the α-synuclein ( SNCA) gene have consistently been shown to be associated with Parkinson’s disease, but the functional relevance is unclear. Based on these findings we hypothesized that conserved cis-regulatory elements in the SNCA genomic region regulate expression of SNCA, and that SNPs in these regions could be functionally modulating the expression of SNCA, thus contributing to neuronal demise and predisposing to Parkinson’s disease.

In a pair-wise comparison of a 206kb genomic region encompassing the SNCA gene, we revealed 34 evolutionary conserved DNA sequences between human and mouse. All elements were cloned into reporter vectors and assessed for expression modulation in dual luciferase reporter assays.  We found that 12 out of 34 elements exhibited either an enhancement or reduction of the expression of the reporter gene. Three elements upstream of the SNCA gene displayed an approximately 1.5 fold (p<0.009) increase in expression. Of the intronic regions, three showed a 1.5 fold increase and two others indicated a 2 and 2.5 fold increase in expression (p<0.002). Three elements downstream of the SNCA gene showed 1.5 fold and 2.5 fold increase (p<0.0009). One element downstream of SNCA had a reduced expression of the reporter gene of 0.35 fold (p<0.0009) of normal activity.

Our results demonstrate that the SNCA gene contains cis-regulatory regions that might regulate the transcription and expression of SNCA. Further studies in disease-relevant tissue types will be important to understand the functional impact of regulatory regions and specific Parkinson’s disease-associated SNPs and its function in the disease process.

Augmentation of phenotype in a transgenic Parkinson mouse heterozygous for a Gaucher mutation

The involvement of the protein α-synuclein (SNCA) in the pathogenesis of Parkinson's disease is strongly supported by the facts that (i) missense and copy number mutations in the SNCA gene can cause inherited Parkinson's disease; and (ii) Lewy bodies in sporadic Parkinson's disease are largely composed of aggregated SNCA. Unaffected heterozygous carriers of Gaucher disease mutations have an increased risk for Parkinson's disease. As mutations in the GBA gene encoding glucocerebrosidase (GBA) are known to interfere with lysosomal protein degradation, GBA heterozygotes may demonstrate reduced lysosomal SNCA degradation, leading to increased steady-state SNCA levels and promoting its aggregation. We have created mouse models to investigate the interaction between GBA mutations and synucleinopathies. We investigated the rate of SNCA degradation in cultured primary cortical neurons from mice expressing wild-type mouse SNCA, wild-type human SNCA, or mutant A53T SNCA, in a background of either wild-type Gba or heterozygosity for the L444P GBA mutation associated with Gaucher disease. We also tested the effect of this Gaucher mutation on motor and enteric nervous system function in these transgenic animals. We found that human SNCA is stable, with a half-life of 61 h, and that the A53T mutation did not significantly affect its half-life. Heterozygosity for a naturally occurring Gaucher mutation, L444P, reduced GBA activity by 40%, reduced SNCA degradation and triggered accumulation of the protein in culture. This mutation also resulted in the exacerbation of motor and gastrointestinal deficits found in the A53T mouse model of Parkinson's disease. This study demonstrates that heterozygosity for a Gaucher disease-associated mutation in Gba interferes with SNCA degradation and contributes to its accumulation, and exacerbates the phenotype in a mouse model of Parkinson's disease.

NADPH oxidase 1 mediates α-synucleinopathy in Parkinson's disease

Accumulation of misfolded α-synuclein is the pathological hallmark of Parkinson's disease (PD). Nevertheless, little is known about the mechanism contributing to α-synuclein aggregation and its further toxicity to dopaminergic neurons. Since oxidative stress can increase the expression and aggregation levels of α-synuclein, NADPH oxidases (Noxs), which are responsible for reactive oxygen species generation, could be major players in α-synucleinopathy. Previously, we demonstrated that Nox1 is expressed in dopaminergic neurons of the PD animal models as well as postmortem brain tissue of PD patients, and is responsible for oxidative stress and subsequent neuronal degeneration. Here, using paraquat (PQ)-based in vitro and in vivo PD models, we show that Nox1 has a crucial role in modulating the behavior of α-synuclein expression and aggregation in dopaminergic neurons. We observed in differentiated human dopaminergic cells that Nox1 and α-synuclein expressions are increased under PQ exposure. Nox1 knockdown significantly reduced both α-synuclein expression and aggregation, supporting the role of Nox1 in this process. Furthermore, in rats exposed to PQ, the selective knockdown of Nox1 in the substantia nigra, using adeno-associated virus encoding Nox1-specific shRNA, largely attenuated the PQ-mediated increase of α-synuclein and ubiquitin expression levels as well as α-synuclein aggregates (proteinase K resistant) and A11 oligomers. Significant reductions in oxidative stress level and dopaminergic neuronal loss were also observed. Our data reveal a new mechanism by which α-synuclein becomes a neuropathologic protein through Nox1-mediated oxidative stress. This finding may be used to generate new therapeutic interventions that slower the rate of α-synuclein aggregation and the progression of PD pathogenesis.