Association between SNCA rs356220 polymorphism and Parkinson's disease: A meta-analysis

Finemap-MiXeR: A variational Bayesian approach for genetic finemapping

Genome-wide association studies (GWAS) implicate broad genomic loci containing clusters of highly correlated genetic variants. Finemapping techniques can select and prioritize variants within each GWAS locus which are more likely to have a functional influence on the trait. Here, we present a novel method, Finemap-MiXeR, for finemapping causal variants from GWAS summary statistics, controlling for correlation among variants due to linkage disequilibrium. Our method is based on a variational Bayesian approach and direct optimization of the Evidence Lower Bound (ELBO) of the likelihood function derived from the MiXeR model. After obtaining the analytical expression for ELBO's gradient, we apply Adaptive Moment Estimation (ADAM) algorithm for optimization, allowing us to obtain the posterior causal probability of each variant. Using these posterior causal probabilities, we validated Finemap-MiXeR across a wide range of scenarios using both synthetic data, and real data on height from the UK Biobank. Comparison of Finemap-MiXeR with two existing methods, FINEMAP and SuSiE RSS, demonstrated similar or improved accuracy. Furthermore, our method is computationally efficient in several aspects. For example, unlike many other methods in the literature, its computational complexity does not increase with the number of true causal variants in a locus and it does not require any matrix inversion operation. The mathematical framework of Finemap-MiXeR is flexible and may also be applied to other problems including cross-trait and cross-ancestry finemapping.

Therapeutic Prospect of New Probiotics in Neurodegenerative Diseases

Increasing clinical and preclinical evidence implicates gut microbiome (GM) dysbiosis as a key susceptibility factor for neurodegenerative disorders, including Alzheimer's disease (AD) and Parkinson's disease (PD). In recent years, neurodegenerative diseases have been viewed as being driven not solely by defects in the brain, and the role of GM in modulating central nervous system function via the gut-brain axis has attracted considerable interest. Encouraged by current GM research, the development of new probiotics may lead to tangible impacts on the treatment of neurodegenerative disorders. This review summarizes current understandings of GM composition and characteristics associated with neurodegenerative diseases and research demonstrations of key molecules from the GM that affect neurodegeneration. Furthermore, applications of new probiotics, such as Clostridium butyricum, Akkermansia muciniphila, Faecalibacterium prausnitzii, and Bacteroides fragilis, for the remediation of neurodegenerative diseases are discussed.

Modeling neurodegenerative disorders in zebrafish

Neurodegeneration is a major cause of Alzheimer's, Parkinson's, Huntington's, multiple and amyotrophic lateral sclerosis, pontocerebellar hypoplasia, dementia and other related brain disorders. Their complex pathogenesis commonly includes genetic and neurochemical deficits, misfolded protein toxicity, demyelination, apoptosis and mitochondrial dysfunctions. Albeit differing in specific underlying mechanisms, neurodegenerative disorders typically display evolutionarily conserved mechanisms across taxa. Here, we review the role of zebrafish models in recapitulating major human and rodent neurodegenerative conditions, demonstrating this species as a highly relevant experimental model for research on neurodegenerative diseases, and discussing how these fish models can further clarify the underlying genetic, neurochemical, neuroanatomical and behavioral pathogenic mechanisms.

Bilirubin: A Promising Therapy for Parkinson's Disease

Following the increase in life expectancy, the prevalence of Parkinson's disease (PD) as the most common movement disorder is expected to rise. Despite the incredibly huge efforts in research to find the definitive biomarker, to date, the diagnosis of PD still relies mainly upon clinical symptoms. A wide range of treatments is available for PD, mainly alleviating the clinical symptoms. However, none of these current therapies can stop or even slow down the disease evolution. Hence, disease-modifying treatment is still a paramount unmet medical need. On the other side, bilirubin and its enzymatic machinery and precursors have offered potential benefits by targeting multiple mechanisms in chronic diseases, including PD. Nevertheless, only limited discussions are available in the context of neurological conditions, particularly in PD. Therefore, in this review, we profoundly discuss this topic to understand bilirubin's therapeutical potential in PD.

Expanding the role of proteasome homeostasis in Parkinson's disease: beyond protein breakdown

Proteasome is the principal hydrolytic machinery responsible for the great majority of protein degradation. The past three decades have testified prominent advances about proteasome involved in almost every aspect of biological processes. Nonetheless, inappropriate increase or decrease in proteasome function is regarded as a causative factor in several diseases. Proteasome abundance and proper assembly need to be precisely controlled. Indeed, various neurodegenerative diseases including Parkinson's disease (PD) share a common pathological feature, intracellular protein accumulation such as α-synuclein. Proteasome activation may effectively remove aggregates and prevent the neurodegeneration in PD, which provides a potential application for disease-modifying treatment. In this review, we build on the valuable discoveries related to different types of proteolysis by distinct forms of proteasome, and how its regulatory and catalytic particles promote protein elimination. Additionally, we summarize the emerging ideas on the proteasome homeostasis regulation by targeting transcriptional, translational, and post-translational levels. Given the imbalanced proteostasis in PD, the strategies for intensifying proteasomal degradation are advocated as a promising approach for PD clinical intervention.

Oligomeric α-Syn and SNARE complex proteins in peripheral extracellular vesicles of neural origin are biomarkers for Parkinson's disease

Blood-based biomarkers are needed to be used as easy, reproducible, and non-invasive tools for the diagnosis and prognosis of chronic neurodegenerative disorders including Parkinson's Disease (PD). In PD, aggregated toxic forms of α-Synuclein (α-Syn) accumulate within neurons in the brain and cause neurodegeneration; α-Syn interaction with SNARE proteins also results in synaptic disfunction. We isolated neural derived extravesicles (NDEs) from peripheral blood of 32 PD patients and 40 healthy controls (HC) and measured the concentrations of oligomeric α-Syn and of the presinaptic SNARE complex proteins: STX-1A, VAMP-2 and SNAP-25. Oligomeric α-Syn was significantly augmented whereas STX-1A and VAMP-2 were significantly reduced in NDEs of PD patients compared to HC (p < 0.001 in all cases). ROC curve analyses confirmed the discriminatory ability of NDEs oligomeric α-Syn, STX-1A and VAMP-2 levels to distinguish between PD patients and HC. Oligomeric α-Syn NDEs concentration also positively correlated with disease duration and severity of PD. These results are promising and confirm that NDEs cargoes likely reflect core pathogenic intracellular processes in their originating brain cells and could serve as novel easily accessible bio-markers. Further studies are needed to confirm results and eventually for testing rehabilitation programs and drug treatments effects.

α-Synuclein Regulates Iron Homeostasis via Preventing Parkin-Mediated DMT1 Ubiquitylation in Parkinson's Disease Models

Iron metabolism imbalance plays a key role in the neurodegeneration of Parkinson's disease (PD), thus iron homeostasis should be tightly controlled by iron transporters. α-Synuclein (α-Syn) serves as a ferrireductase and iron-binding protein, which is supposed to be linked with iron metabolism, but little is known about how α-Syn affects iron homeostasis in PD. Our previous findings that up-regulation of divalent metal transporter 1 (DMT1) accounted for the nigral iron accumulation in PD raised the question whether α-Syn disturbed iron homeostasis by modulating DMT1 expression. Using α-Syn overexpressed SH-SY5Y cells and mutant human A53T α-Syn transgenic mice, we found that α-Syn could up-regulate DMT1 protein levels, followed by enhanced ferrous iron influx and subsequent aggravated oxidative stress injury. Mechanistic studies identified that α-Syn-induced p38 mitogen-activated protein kinase (MAPK) activation phosphorylated parkin at Ser131, which inactivated parkin's E3 ubiquitin ligase activity and further reduced DMT1 ubiquitylation level. Our findings revealed that α-Syn affected brain iron homeostasis through modulating DMT1 protein stability and altering cellular iron uptake, which might provide direct evidence for the involvement of α-Syn in iron metabolism dysfunction and provide insight into PD-associated nigral iron deposition.