Dopamine transporter SLC6A3 genotype affects cortico-striatal activity of set-shifts in Parkinson's disease

Integrative analysis of plasma and substantia nigra in Parkinson's disease: unraveling biomarkers and insights from the lncRNA-miRNA-mRNA ceRNA network

Introduction

Parkinson's disease (PD) is a rapidly growing neurological disorder characterized by diverse movement symptoms. However, the underlying causes have not been clearly identified, and accurate diagnosis is challenging. This study aimed to identify potential biomarkers suitable for PD diagnosis and present an integrative perspective on the disease.

Methods

We screened the GSE7621, GSE8397-GPL96, GSE8397-GPL97, GSE20163, and GSE20164 datasets in the NCBI GEO database to identify differentially expressed (DE) mRNAs in the substantia nigra (SN). We also screened the GSE160299 dataset from the NCBI GEO database to identify DE lncRNAs and miRNAs in plasma. We then constructed 2 lncRNA-miRNA-mRNA competing endogenous RNA (ceRNA) regulatory networks based on the ceRNA hypothesis. To understand the biological function, we performed Kyoto Encyclopedia of Genes and Genomes pathway and Gene Ontology analyses for each ceRNA network. The receiver operating characteristic analyses (ROC) was used to assess ceRNA results.

Results

We identified 7 upregulated and 29 downregulated mRNAs as common DE mRNAs in the 5 SN datasets. In the blood dataset, we identified 31 DE miRNAs (9 upregulated and 22 downregulated) and 332 DE lncRNAs (69 upregulated and 263 downregulated). Based on the determined interactions, 5 genes (P2RX7, HSPA1, SLCO4A1, RAD52, and SIRT4) appeared to be upregulated as a result of 10 lncRNAs sponging 4 miRNAs (miR-411, miR-1193, miR-301b, and miR-514a-2/3). Competing with 9 genes (ANK1, CBLN1, RGS4, SLC6A3, SYNGR3, VSNL1, DDC, KCNJ6, and SV2C) for miR-671, a total of 26 lncRNAs seemed to function as ceRNAs, influencing genes to be downregulated.

Discussion

In this study, we successfully constructed 2 novel ceRNA regulatory networks in patients with PD, including 36 lncRNAs, 5 miRNAs, and 14 mRNAs. Our results suggest that these plasma lncRNAs are involved in the pathogenesis of PD by sponging miRNAs and regulating gene expression in the SN of the brain. We propose that the upregulated and downregulated lncRNA-mediated ceRNA networks represent mechanisms of neuroinflammation and dopamine neurotransmission, respectively. Our ceRNA network, which was associated with PD, suggests the potential use of DE miRNAs and lncRNAs as body fluid diagnostic biomarkers. These findings provide an integrated view of the mechanisms underlying gene regulation and interactions in PD.

Oligonol ameliorates liver function and brain function in the 5 × FAD mouse model: transcriptional and cellular analysis

Alzheimer's disease (AD) is a common neurodegenerative disease worldwide and is accompanied by memory deficits, personality changes, anxiety, depression, and social difficulties. For treatment of AD, many researchers have attempted to find medicinal resources with high effectiveness and without side effects. Oligonol is a low molecular weight polypeptide derived from lychee fruit extract. We investigated the effects of oligonol in 5 × FAD transgenic AD mice, which developed severe amyloid pathology, through behavioral tests (Barnes maze, marble burying, and nestle shredding) and molecular experiments. Oligonol treatment attenuated blood glucose levels and increased the antioxidant response in the livers of 5 × FAD mice. Moreover, the behavioral score data showed improvements in anxiety, depressive behavior, and cognitive impairment following a 2-month course of orally administered oligonol. Oligonol treatment not only altered the circulating levels of cytokines and adipokines in 5 × FAD mice, but also significantly enhanced the mRNA and protein levels of antioxidant enzymes and synaptic plasticity in the brain cortex and hippocampus. Therefore, we highlight the therapeutic potential of oligonol to attenuate neuropsychiatric problems and improve memory deficits in the early stage of AD.

Integrative multilevel exploration of the mechanism by which Er-Zhi-Wan alleviates the Parkinson's disease (PD)-like phenotype in the MPTP-induced PD mouse model

The neuroprotective effects of Er-Zhi-Wan (EZW), a well-known traditional Chinese formulation, in MPTP-induced Parkinson's disease (PD) models are poorly understood and require evaluation. A model of PD induced by MPTP was used to evaluate the neuroprotective effects of EZW in mice. The underlying pharmacological mechanisms of EZW for the prevention and treatment of PD were then explored using a combination of multilevel databases, network pharmacology, biological experiments, and LCMS/MS. In vivo data showed that pretreatment with EZW can be neuroprotective against MPTP-induced motor dysfunction and can effectively rescue dopaminergic neurons from MPTP-induced degeneration in mice. Furthermore, data from combined multilevel databases and network pharmacology analysis strategies suggested that the neuroprotective activity of EZW in the treatment of PD is mediated by a complicated multicomponent, multitarget network. Genes such as Grm2, Grm5, Drd2, and Grik2 were identified as important therapeutic targets. Subsequent experimental validation showed that EZW can broadly regulate the mRNA levels of these receptor genes as well as BDNF, and consequently increase the phosphorylation levels of CREB to stimulate CREB signaling. These targets and signaling systems may be responsible for the reversal of neuronal death by EZW after MPTP exposure. The LC-MS/MS results also identified a wide range of chemical components of EZW, including at least 53 precise compounds, further demonstrating the complexity of the network in which EZW exerts its neuroprotective activity. Our work provides evidence for the mechanism of EZW in MPTP-PD models and supports the neuroprotective function of EZW in neurodegenerative diseases.

Genetic Insights into the Molecular Pathophysiology of Depression in Parkinson's Disease

Background and Objectives: Parkinson's disease (PD) is a clinically heterogeneous disorder with poorly understood pathological contributing factors. Depression presents one of the most frequent non-motor PD manifestations, and several genetic polymorphisms have been suggested that could affect the depression risk in PD. Therefore, in this review we have collected recent studies addressing the role of genetic factors in the development of depression in PD, aiming to gain insights into its molecular pathobiology and enable the future development of targeted and effective treatment strategies. Materials and Methods: we have searched PubMed and Scopus databases for peer-reviewed research articles published in English (pre-clinical and clinical studies as well as relevant reviews and meta-analyses) investigating the genetic architecture and pathophysiology of PD depression. Results: in particular, polymorphisms in genes related to the serotoninergic pathway (sodium-dependent serotonin transporter gene, SLC6A4, tryptophan hydrolase-2 gene, TPH2), dopamine metabolism and neurotransmission (dopamine receptor D3 gene, DRD3, aldehyde dehydrogenase 2 gene, ALDH2), neurotrophic factors (brain-derived neurotrophic factor gene, BDNF), endocannabinoid system (cannabinoid receptor gene, CNR1), circadian rhythm (thyrotroph embryonic factor gene, TEF), the sodium-dependent neutral amino acid transporter B(0)AT2 gene, SLC6A15), and PARK16 genetic locus were detected as altering susceptibility to depression among PD patients. However, polymorphisms in the dopamine transporter gene (SLC6A3), monoamine oxidase A (MAOA) and B (MAOB) genes, catechol-O-methyltransferase gene (COMT), CRY1, and CRY2 have not been related to PD depression. Conclusions: the specific mechanisms underlying the potential role of genetic diversity in PD depression are still under investigation, however, there is evidence that they may involve neurotransmitter imbalance, mitochondrial impairment, oxidative stress, and neuroinflammation, as well as the dysregulation of neurotrophic factors and their downstream signaling pathways.

Associations between variants in levodopa metabolic pathway genes and levodopa-induced dyskinesia in Parkinson's disease

INTRODUCTION

Levodopa-induced dyskinesia (LID) is a common motor complication in Parkinson's disease (PD). Several genes in the levodopa metabolic pathway, such as COMT, DRDx and MAO-B, were reported associated with LID. However, there has been no systematic analyses between common variants in levodopa metabolic pathway genes and LID in a large sample of the Chinese population.

METHODS

Through the whole exome sequencing (WES) and target region sequencing, we aimed to explore the potential associations between common single nucleotide polymorphisms (SNPs) in the levodopa metabolic pathway and LID in Chinese PD individuals. Five hundred and two PD individuals were enrolled in our study, among them, 348 individuals underwent WES, and 154 individuals underwent target region sequencing. We acquired the genetic profile of 11 genes including COMT, DDC, DRD1-5, SLC6A3, TH and MAO-A/B. We established a stepwise strategy to filter SNPs, which finally included 34 SNPs in our analyses. And we used a two-stage study, with discovery (348 individuals with WES) and the replication (all 502 individuals) to confirm our findings.

RESULTS

Among the 502 PD individuals, 104 (20.7%) were diagnosed with LID. In the discovery stage, we found that COMT rs6269, DRD2 rs6275 and DRD2 rs1076560 were associated with LID. In the replication stage, associations between the three above-mentioned SNPs and LID were still present in all 502 individuals.

CONCLUSION

We demonstrated that in the Chinese population, COMT rs6269, DRD2 rs6275 and rs1076560 were significantly associated with LID. And rs6275 was reported associated with LID for the first time.

Premorbid performances determine the deleterious effects of nigrostriatal degeneration and pramipexole on behavioural flexibility

Subtle cognitive impairment can occur early in the course of Parkinson's disease (PD) and may manifest under different forms of executive dysfunction such as impaired cognitive flexibility. The precise contribution of nigrostriatal dopaminergic neurodegeneration to these non-motor features of the disease is poorly known. Whether such cognitive impairment associated with the disease process may also predate and contribute to the development of neuropsychiatric side-effects following dopamine replacement therapy remains largely unknown. To address these issues, we investigated the respective contributions of nigrostriatal degeneration and chronic treatment with the dopamine D3-preferring agonist pramipexole on behavioral flexibility in a rat model of PD. Flexible, intermediate and inflexible rats were identified based on baseline assessment of behavioral flexibility using an operant set-shifting task. Nigrostriatal degeneration was induced by bilateral viral-mediated expression of A53T mutated human α-synuclein in the substantia nigra pars compacta and behavioral flexibility was assessed after induction of nigrostriatal degeneration, and during chronic pramipexole treatment. Nigrostriatal degeneration impaired behavioral flexibility in flexible but not in inflexible rats. Pramipexole induced a decrease of behavioral flexibility that was exacerbated in lesioned rats and in the most flexible individuals. Furthermore, the deficits induced by pramipexole in lesioned rats affected different components of the task between flexible and inflexible individuals. This study demonstrates that nigrostriatal degeneration and pramipexole unequally impair behavioral flexibility, suggesting that the susceptibility to develop non-motor impairments upon treatment initiation could primarily depend on premorbid differences in behavioral flexibility.

Bioinformatics analysis of gene expression profile and functional analysis in periodontitis and Parkinson’s disease

Periodontitis is a chronic inflammatory disease inextricably linked to both the innate and acquired immune systems of the body. Parkinson’s disease (PD) is a neurodegenerative disease caused by immune system dysfunction. Although recent studies suggest that a clinical relationship exists between PD and periodontitis, the pathogenesis of this relationship is unclear. Therefore, in the present study, we obtained datasets of periodontitis and PD from the Gene Expression Omnibus (GEO) database and extracted 785 differentially expressed genes (DEGs), including 15 common upregulated genes and four common downregulated genes. We performed enrichment analyses of these DEGs using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes analyses. We found that the genes were mainly enriched in keratinocyte differentiation, neuronal cell bodies, and structural constituents of epidermis terms, and pathways such as immune response and synaptic pathways. In addition, we screened matching hub genes by constructing a protein–protein interaction (PPI) network map and a Molecular Complex Detection (MCODE) map using the Cytoscape software. The hub genes were then subjected to GO enrichment analysis, which revealed that the dopamine biosynthetic process, dopaminergic synapse and dopamine-binding terms, and dopaminergic synapse and serotonergic synapse pathways were primarily where they were expressed. Finally, we selected four of these genes for validation in the periodontitis and PD datasets, and we confirmed that these hub genes were highly sensitive and specific for diagnosing and monitoring PD and periodontitis. In conclusion, the above experimental results indicate that periodontitis is a high-risk factor for PD, and the association between these two conditions is mainly manifested in immune and dopamine-related pathways. Hub genes, such as the CDSN, TH, DDC, and SLC6A3 genes, may serve as potential biomarkers for diagnosing or detecting PD.

Current concepts in treating mild cognitive impairment in Parkinson's disease

Impairment in various aspects of cognition is recognized as an important non-motor symptom of Parkinson's disease (PD). Mild cognitive impairment in PD (PD-MCI) is common in non-demented PD patients and is often associated with severity of motor symptoms, disease duration and increasing age. Further, PD-MCI can have a significant negative effect on performance of daily life activities and may be a harbinger of development of PD dementia. Thus, there is significant interest in developing therapeutic strategies to ameliorate cognitive deficits in PD and improve cognitive functioning of PD patients. However, due to significant questions that remain regarding the pathophysiology of cognitive dysfunction in PD, remediation of cognitive dysfunction in PD has proven difficult. In this paper, we will focus on PD-MCI and will review some of the current therapeutic approaches being taken to try to improve cognitive functioning in patients with PD-MCI.

Weighted Gene Coexpression Network Analysis Uncovers Critical Genes and Pathways for Multiple Brain Regions in Parkinson's Disease

Objective

In this study, we aimed to identify critical genes and pathways for multiple brain regions in Parkinson's disease (PD) by weighted gene coexpression network analysis (WGCNA).

Methods

From the GEO database, differentially expressed genes (DEGs) were separately identified between the substantia nigra, putamen, prefrontal cortex area, and cingulate gyrus of PD and normal samples with the screening criteria of p value < 0.05 and ∣log₂fold change (FC) | >0.585. Then, a coexpression network was presented by the WGCNA package. Gene modules related to PD were constructed. Then, PD-related DEGs were used for construction of PPI networks. Hub genes were determined by the cytoHubba plug-in. Functional enrichment analysis was then performed.

Results

DEGs were identified for the substantia nigra (17 upregulated and 52 downregulated genes), putamen (317 upregulated and 317 downregulated genes), prefrontal cortex area (39 upregulated and 72 downregulated genes), and cingulate gyrus (116 upregulated and 292 downregulated genes) of PD compared to normal samples. Gene modules were separately built for the four brain regions of PD. PPI networks revealed hub genes for the substantia nigra (SLC6A3, SLC18A2, and TH), putamen (BMP4 and SNAP25), prefrontal cortex area (SNAP25), and cingulate gyrus (CTGF, CDH1, and COL5A1) of PD. These DEGs in multiple brain regions were involved in distinct biological functions and pathways. GSEA showed that these DEGs were all significantly enriched in electron transport chain, proteasome degradation, and synaptic vesicle pathway.

Conclusion

Our findings revealed critical genes and pathways for multiple brain regions in PD, which deepened the understanding of PD-related molecular mechanisms.

Functional Correlates and Impact of Dietary Lactoferrin Intervention and its Concentration-dependence on Neurodevelopment and Cognition in Neonatal Piglets

SCOPE

Lactoferrin (Lf), a sialylated milk glycoprotein, promotes early neurodevelopment and cognition. Functional concentrations of Lf, however, remain unknown. Our objective is to determine the concentration-dependency of Lf on genes associated with neurodevelopment and cognition in neonatal piglets.

METHODS AND RESULTS

Piglets are given milk replacer with Lf at concentrations of 155 (low) or 285 mg kg^-1 day^-1 (high) from postnatal days 3 to 38. Gene expression associated with neurodevelopment, cognition, and cognate proteins were quantitated. This study found 1) The rate of learning and long-term memory was higher with 155 mg kg^-1 day^-1 assessed in an eight-arm radial maze; 2) Global gene transcription profiling showed this lower concentration upregulated genes and functions correlated with neurodevelopment and cognition, while the higher concentration regulated cellular processes for neuroprotection; 3) Expression of BDNF genes and proteins were higher with both concentrations, while genes regulating BDNF signaling, including SLC6A3, IGF-1 responded more to the lower concentration; 4) The lower concentration modulated genes in the five highest networks associated with cellularity and neurocognition, while the prevention of neurodevelopmental and neurological pathologies was associated with the higher concentration.

CONCLUSION

The lower concentrations of Lf enhanced neurodevelopment and cognition, while higher concentrations are greater neuroprotective, findings of potential novel clinical relevance.

Investigating the relationship between the SNCA gene and cognitive abilities in idiopathic Parkinson's disease using machine learning

Cognitive impairments are prevalent in Parkinson's disease (PD), but the underlying mechanisms of their development are unknown. In this study, we aimed to predict global cognition (GC) in PD with machine learning (ML) using structural neuroimaging, genetics and clinical and demographic characteristics. As a post-hoc analysis, we aimed to explore the connection between novel selected features and GC more precisely and to investigate whether this relationship is specific to GC or is driven by specific cognitive domains. 101 idiopathic PD patients had a cognitive assessment, structural MRI and blood draw. ML was performed on 102 input features including demographics, cortical thickness and subcortical measures, and several genetic variants (APOE, MAPT, SNCA, etc.). Using the combination of RRELIEFF and Support Vector Regression, 11 features were found to be predictive of GC including sex, rs894280, Edinburgh Handedness Inventory, UPDRS-III, education, five cortical thickness measures (R-parahippocampal, L-entorhinal, R-rostral anterior cingulate, L-middle temporal, and R-transverse temporal), and R-caudate volume. The rs894280 of SNCA gene was selected as the most novel finding of ML. Post-hoc analysis revealed a robust association between rs894280 and GC, attention, and visuospatial abilities. This variant indicates a potential role for the SNCA gene in cognitive impairments of idiopathic PD.

The Underlying Mechanism of Paeonia lactiflora Pall. in Parkinson's Disease Based on a Network Pharmacology Approach

Background: Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide, yet as of currently, there is no disease-modifying therapy that could delay its progression. Paeonia lactiflora Pall. is the most frequently used herb in formulas for PD in Traditional Chinese Medicine and also a potential neuroprotective agent for neurodegenerative diseases, while its mechanisms remain poorly understood. In this study, we aim to explore the underlying mechanism of P. lactiflora in treating PD utilizing a network pharmacology approach. Methods: The protein targets of P. lactiflora ingredients and PD were first obtained from several databases. To clarify the key targets, a Protein-Protein-Interaction (PPI) network was constructed and analyzed on the String database, and then enrichment analysis was performed by the Metascape platform to determine the main Gene Ontology biological processes and Kyoto Encyclopedia of Genes and Genomes pathways. Finally, the Ingredient-Target-Pathway (I-T-P) network was constructed and analyzed by Cytoscape software. Results: Six active ingredients of P. lactiflora (kaempferol, ß-sitosterol, betulinic acid, palbinone, paeoniflorin and (+)-catechin) as well as six core targets strongly related to PD treatment [AKT1, interleukin-6, CAT, Tumor necrosis factor (TNF), CASP3, and PTGS2] were identified. The main pathways were shown to involve neuroactive ligand-receptor interaction, Calcium signaling pathway, PI3-Akt signaling pathway, TNF signaling pathway, and apoptosis signaling pathway. The main biological process included the regulation of neurotransmitter levels. Conclusion: P. lactiflora may retard neurodegeneration by reducing neuroinflammation, inhibiting intrinsic and extrinsic apoptosis, and may improve motor and non-motor symptoms by regulating the levels of neurotransmitters. Our study has revealed the mechanism of P. lactiflora in the treatment of PD and may contribute to novel drug development for PD.

The Role of the SLC Transporters Protein in the Neurodegenerative Disorders

The solute carrier (SLC) superfamily is one of the major sub-groups of membrane proteins in mammalian cells. The solute carrier proteins include more than 400 different membrane-spanning solute carriers organized with 65 families in the human. In solute carrier family neurons, neurotransmitter is considered to be a pharmacological target of neuropsychiatric drugs because of their important role in the recovery of neurotransmitters such as GABA, glutamate, serotonin, dopamine and noradrenaline and regulation of their concentration in synaptic regions. Therefore, solute carrier transporters play vital and different roles in neurodegenerative disorders. In this article, the role of solute carrier transporters in neurodegenerative disorders such as Alzheimer disease, amyotrophic lateral sclerosis, Huntington disease, Parkinson’s diseases, depression, post-traumatic stress disorder, dementia, schizophrenia, and Epilepsy reviewed and discussed to see how defects or absences in SLC transporter cause neurodegenerative disorders. In this review, we try to summarize what is known about solute carriers with respect to brain distribution and expression. The review summarizes current knowledge on the roles of solute carrier transporters in neurodegenerative disorders.

Bioinformatic analysis for the identification of key candidate genes and pathways in the substantia nigra in Parkinson's disease

Parkinson's disease is one of the most common diseases in the elderly population, and the substantia nigra is generally involved in the disease process; however, the signaling pathways and related genes underlying Parkinson's disease remain unclear. This study integrated three cohorts of profile datasets to elucidate the potential key candidate genes and pathways in Parkinson's disease. The expression profiles of GSE8397, GSE20186 and GSE49036 were included 55 available substantia nigra tissue samples from individuals diagnosed with Parkinson's disease and 33 substantia nigra tissue samples from healthy controls. These samples were integrated and thoroughly analyzed. Differentially expressed genes (DEGs) were sorted, and candidate genes and pathway enrichments were analyzed. A DEG-associated protein-protein interaction network analysis was performed. 27 shared downregulated DEGs were identified from the three GSE datasets. The DEGs were clustered based on function and signaling pathway with significant enrichment analysis. 52 edges were identified from the DEG protein-protein interaction network complex, which included dopamine metabolism, nerve conduction, reduced neuronal toxicity and proliferation pathways. Using integrated bioinformatic analysis, we identified candidate genes and pathways in Parkinson's disease that could improve our understanding of underlying molecular events, which could be potential therapeutic targets for Parkinson's disease.

The influence of SLC6A3 and DRD2 polymorphisms on levodopa-therapy in patients with sporadic Parkinson's disease

OBJECTIVES

The aim of this study was to evaluate a possible relationship between DRD2/ANKK1 (rs1800497) and SLC6A3/DAT1 (rs28363170) gene polymorphisms with the response to levodopa (L-DOPA)-therapy in patients with Parkinson's disease (PD).

METHODS

One hundred and ninety-five patients with idiopathic PD were investigated. Patients were genotyped for rs1800497 and rs28363170 polymorphisms using PCR-RFLP. Logistic regression was performed to assess the association of polymorphisms with the occurrence of the chronic complications of L-DOPA therapy.

KEY FINDINGS

Our results showed association between the occurrence of dyskinesia with an increased greater disease severity (P = 0.007), higher L-DOPA dose (P = 0.007) and use of dopamine agonist (P = 0.020). Moreover, there were significant protective effects for age (P = 0.004) and male subjects (P = 0.006).

CONCLUSIONS

Clinical and demographic characteristics of Brazilian PD patients and differences in DRD2 and DAT1 genes may to determine individual variations in the therapeutic response to L-DOPA in the Brazilian PD patients.

Functional MRI on executive functioning in aging and dementia: A scoping review of cognitive tasks

Cognitive decline with aging and dementia is especially poignant with regard to the executive functioning that is necessary for activities of daily independent living. The relationship between age-related neurodegeneration in the prefrontal cortex and executive functioning has been uniquely investigated using task-phase functional magnetic resonance imaging (fMRI) to detect brain activity in response to stimuli; however, a comprehensive list of task designs that have been implemented to task-phase fMRI is absent in the literature. The purpose of this review was to recognize what methods have been used to study executive functions with aging and dementia in fMRI tasks, and to describe and categorize them. The following cognitive subdomains were emphasized: cognitive flexibility, planning and decision-making, working memory, cognitive control/inhibition, semantic processing, attention and concentration, emotional functioning, and multitasking. Over 30 different task-phase fMRI designs were found to have been implemented in the literature, all adopted from standard neuropsychological assessments. Cognitive set-shifting and decision-making tasks were particularly well studied in regard to age-related neurodegeneration, while emotional functioning and multitasking designs were found to be the least utilized. Summarizing the information on which tasks have shown the greatest usability will assist in the future design and implementation of effective fMRI experiments targeting executive functioning.

SLC6A3 Polymorphism Predisposes to Dopamine Overdose in Parkinson's Disease

In Parkinson's disease (PD), cognitive functions mediated by brain regions innervated by ventral tegmental area (VTA) worsen with dopamine replacement therapy, whereas processes relying on regions innervated by the substantia nigra pars compacta (SNc) improve. The SLC6A3 gene encodes the dopamine transporter (DAT). The common 9R polymorphism produces higher DAT concentrations and consequently lower baseline dopamine than SLC6A3 wildtype. Whether SLC6A3 genotype modulates the effect of dopaminergic therapy on cognition in PD is not known. We investigated the effect of dopaminergic therapy and SLC6A3 genotype on encoding and recall of abstract images using the Aggie Figures Learning Test in PD patients. Encoding depends upon brain regions innervated by the VTA, whereas recall is mediated by widespread brain regions, a number innervated by the SNc. We found that dopaminergic therapy worsened encoding of abstract images in 9R carriers only. In contrast, dopaminergic therapy improved recall of abstract images in all PD patients, irrespective of SLC6A3 genotype. Our findings suggest that 9R-carrier PD patients are more predisposed to dopamine overdose and medication-induced impairment of cognitive functions mediated by VTA-innervated brain regions. Interestingly, PD patients without the 9R polymorphism did not show such an impairment. SLC6A3 genotype does not modulate the dopaminergic therapy-induced improvement of functions mediated by SNc-innervated regions in PD patients.

Identification of Critical Genes and miRNAs Associated with the Development of Parkinson's Disease

The purpose of this study was to explore the key mechanism involved in the pathogenesis of Parkinson's disease (PD) based on microarray analysis. The expression profile data of GSE7621, which contained 9 substantia nigra tissues isolated from normals and 16 substantia nigra tissues isolated from PD patients, was obtained from Gene Expression Omnibus. The differentially expressed genes (DEGs) were screened, followed by functional enrichment analysis and protein-protein interaction (PPI) network construction. After the miRNAs regulating the DEGs were predicted, the miRNA-DEG regulatory network was then constructed. Besides, the 6-hydroxydopamine rat model of PD was established and the expression of key DEGs and miRNA was detected. A total of 388 DEGs were identified, including 218 upregulated genes and 170 downregulated ones. Tyrosine hydroxylase (TH) and solute carrier family 6 member 3 (SLC6A3) were significantly related to the functional terms of catecholamine biosynthetic process and dopamine biosynthetic process. TH and SLC6A3 were hub nodes in the PPI network. EBF3 could be targeted by miR-218. Moreover, TH and SLC6A3 were found downregulated in the 6-OHDA rat model of PD, while miR-218 was markedly upregulated. Our results reveal that SLC6A3, TH, and EBF3 targeted by miR-218 could be involved in PD. These molecules might provide a new insight into the development of therapeutic strategies for PD.

Genetic Variation and Neuroplasticity: Role in Rehabilitation After Stroke

BACKGROUND AND PURPOSE

In many neurologic diagnoses, significant interindividual variability exists in the outcomes of rehabilitation. One factor that may impact response to rehabilitation interventions is genetic variation. Genetic variation refers to the presence of differences in the DNA sequence among individuals in a population. Genetic polymorphisms are variations that occur relatively commonly and, while not disease-causing, can impact the function of biological systems. The purpose of this article is to describe genetic polymorphisms that may impact neuroplasticity, motor learning, and recovery after stroke.

SUMMARY OF KEY POINTS

Genetic polymorphisms for brain-derived neurotrophic factor (BDNF), dopamine, and apolipoprotein E have been shown to impact neuroplasticity and motor learning. Rehabilitation interventions that rely on the molecular and cellular pathways of these factors may be impacted by the presence of the polymorphism. For example, it has been hypothesized that individuals with the BDNF polymorphism may show a decreased response to neuroplasticity-based interventions, decreased rate of learning, and overall less recovery after stroke. However, research to date has been limited and additional work is needed to fully understand the role of genetic variation in learning and recovery.

RECOMMENDATIONS FOR CLINICAL PRACTICE

Genetic polymorphisms should be considered as possible predictors or covariates in studies that investigate neuroplasticity, motor learning, or motor recovery after stroke. Future predictive models of stroke recovery will likely include a combination of genetic factors and other traditional factors (eg, age, lesion type, corticospinal tract integrity) to determine an individual's expected response to a specific rehabilitation intervention.

Meta-Analysis of Parkinson's Disease and Alzheimer's Disease Revealed Commonly Impaired Pathways and Dysregulation of NRF2-Dependent Genes

Many lines of evidence suggest that Parkinson's disease (PD) and Alzheimer's disease (AD) have common characteristics, such as mitochondrial dysfunction and oxidative stress. As the underlying molecular mechanisms are unclear, we perform a meta-analysis with 9 microarray datasets of PD studies and 7 of AD studies to explore it. Functional enrichment analysis revealed that PD and AD both showed dysfunction in the synaptic vesicle cycle, GABAergic synapses, phagosomes, oxidative phosphorylation, and TCA cycle pathways, and AD had more enriched genes. Comparing the differentially expressed genes between AD and PD, we identified 54 common genes shared by more than six tissues. Among them, 31 downregulated genes contained the antioxidant response element (ARE) consensus sequence bound by NRF2. NRF2 is a transcription factor, which protects cells against oxidative stress through coordinated upregulation of ARE-driven genes. To our surprise, although NRF2 was upregulated, its target genes were all downregulated. Further exploration found that MAFF was upregulated in all tissues and significantly negatively correlated with the 31 NRF2-dependent genes in diseased conditions. Previous studies have demonstrated over-expressed small MAFs can form homodimers and act as transcriptional repressors. Therefore, MAFF might play an important role in dysfunction of NRF2 regulatory network in PD and AD.

Methylation changes and pathways affected in preterm birth: a role for SLC6A3 in neurodevelopment

AIM

To analyze whether preterm newborns show differences in methylation patterns in comparison to full-term newborns in white blood cells.

PATIENTS & METHODS

Anthropometrical, biochemical features and methylation levels of preterm newborns (n = 24) and full-term newborns (n = 22) recruited in La Paz University Hospital (Spain) were assessed at 12 months of gestational age, whereas Bayley Scale of Infant Development was evaluated at 24/36 months.

RESULTS

From all the statistically significant CpGs, methylation levels of cg00997378 (SLC6A3 gene) showed the highest differences (p < 0.0001), being associated with prematurity risk factors.

CONCLUSION

SLC6A3 methylation, previously related to attention-deficit/hyperactivity disorder, neuronal function and behavior, might be a potential epigenetic biomarker with value in the early diagnosis and management of neurodevelopmental diseases in newborns.

The dopaminergic system dynamic in the time perception: a review of the evidence

Dopaminergic system plays a key role in perception, which is an important executive function of the brain. Modulation in dopaminergic system forms an important biochemical underpinning of neural mechanisms of time perception in a very wide range, from milliseconds to seconds to longer daily rhythms. Distinct types of temporal experience are poorly understood, and the relationship between processing of different intervals by the brain has received little attention. A comprehensive understanding of interval timing functions should be sought within a wider context of temporal processing, involving genetic aspects, pharmacological models, cognitive aspects, motor control and the neurological diseases with impaired dopaminergic system. Particularly, an unexplored question is whether the role of dopamine in interval timing can be integrated with the role of dopamine in non-interval timing temporal components. In this review, we explore a wider perspective of dopaminergic system, involving genetic polymorphisms, pharmacological models, executive functions and neurological diseases on the time perception. We conclude that the dopaminergic system has great participation in impact on time perception and neurobiological basis of the executive functions and neurological diseases.

A systematic review and integrative approach to decode the common molecular link between levodopa response and Parkinson's disease

Background

PD is a progressive neurodegenerative disorder commonly treated by levodopa. The findings from genetic studies on adverse effects (ADRs) and levodopa efficacy are mostly inconclusive. Here, we aim to identify predictive genetic biomarkers for levodopa response (LR) and determine common molecular link with disease susceptibility. A systematic review for LR was conducted for ADR, and drug efficacy, independently. All included articles were assessed for methodological quality on 14 parameters. GWAS of PD were also reviewed. Protein-protein interaction (PPI) analysis using STRING and functional enrichment using WebGestalt was performed to explore the common link between LR and PD.

Results

From 37 candidate studies on levodopa toxicity, 18 genes were found associated, of which, CA_n STR 13, 14 (DRD2) was most significantly associated with dyskinesia, followed by rs1801133 (MTHFR) with hyper-homocysteinemia, and rs474559 (HOMER1) with hallucination. Similarly, 8 studies on efficacy resulted in 4 genes in which rs28363170, rs3836790 (SLC6A3) and rs4680 (COMT), were significant. To establish the molecular connection between LR with PD, we identified 35 genes significantly associated with PD. With 19 proteins associated with LR and 35 with PD, two independent PPI networks were constructed. Among the 67 nodes (263 edges) in LR, and 62 nodes (190 edges) in PD pathophysiology, UBC, SNCA, FYN, SRC, CAMK2A, and SLC6A3 were identified as common potential candidates.

Conclusion

Our study revealed the genetically significant polymorphism concerning the ADRs and levodopa efficacy. The six common genes may be used as predictive markers for therapy optimization and as putative drug target candidates.

Electronic supplementary material

The online version of this article (10.1186/s12920-017-0291-0) contains supplementary material, which is available to authorized users.

Markers of cognitive decline in PD: The case for heterogeneity

Cognitive impairment is highly prevalent and has a severe negative effect on health related and perceived quality of life in Parkinson's disease (PD). It is now established that 20-40% of persons with PD will develop cognitive deficits early in the disease. Moreover, the risk of developing dementia is six times higher in PD patients than in age-matched controls and it is estimated that 80% of patients will develop dementia after 20 years of the disease. In order to address these symptoms properly it is crucial to identify very early in the disease the patients who are most likely to develop dementia rapidly. Persons who meet criteria for mild cognitive impairment (MCI) exhibit measurable cognitive deficits but those deficits are not severe enough to interfere significantly with daily life. While the presence of MCI in PD increases the chance of developing dementia, various studies suggest that PD-MCI might consist of distinct subtypes with different pathophysiologies and prognoses. In this paper we comment on various biomarkers associated with cognitive decline in PD, specifically clinical, neuropathological, genetic and neuroimaging ones. We also discuss disrupted functional connectivity in PD-MCI and reveal preliminary results from our own group. We propose that the current studies looking at different types of biomarkers provide support for different causes being associated with cognitive decline in PD. Large-scale multi-disciplinary and multi-modal longitudinal studies are required to identify more specifically the different phenotypes associated with different cognitive profiles and evolution in PD.