Insights from late-onset familial parkinsonism on the pathogenesis of idiopathic Parkinson's disease

Roles of neuronal lysosomes in the etiology of Parkinson's disease

Therapeutic progress in neurodegenerative conditions such as Parkinson's disease has been hampered by a lack of detailed knowledge of its molecular etiology. The advancements in genetics and genomics have provided fundamental insights into specific protein players and the cellular processes involved in the onset of disease. In this respect, the autophagy-lysosome system has emerged in recent years as a strong point of convergence for genetics, genomics, and pathologic indications, spanning both familial and idiopathic Parkinson's disease. Most, if not all, genes linked to familial disease are involved, in a regulatory capacity, in lysosome function (e.g., LRRK2, alpha-synuclein, VPS35, Parkin, and PINK1). Moreover, the majority of genomic loci associated with increased risk of idiopathic Parkinson's cluster in lysosome biology and regulation (GBA as the prime example). Lastly, neuropathologic evidence showed alterations in lysosome markers in autoptic material that, coupled to the alpha-synuclein proteinopathy that defines the disease, strongly indicate an alteration in functionality. In this Brief Review article, I present a personal perspective on the molecular and cellular involvement of lysosome biology in Parkinson's pathogenesis, aiming at a larger vision on the events underlying the onset of the disease. The attempts at targeting autophagy for therapeutic purposes in Parkinson's have been mostly aimed at "indiscriminately" enhancing its activity to promote the degradation and elimination of aggregate protein accumulations, such as alpha-synuclein Lewy bodies. However, this approach is based on the assumption that protein pathology is the root cause of disease, while pre-pathology and pre-degeneration dysfunctions have been largely observed in clinical and pre-clinical settings. In addition, it has been reported that unspecific boosting of autophagy can be detrimental. Thus, it is important to understand the mechanisms of specific autophagy forms and, even more, the adjustment of specific lysosome functionalities. Indeed, lysosomes exert fine signaling capacities in addition to their catabolic roles and might participate in the regulation of neuronal and glial cell functions. Here, I discuss hypotheses on these possible mechanisms, their links with etiologic and risk factors for Parkinson's disease, and how they could be targeted for disease-modifying purposes.

Metabolic dysfunctions in the intranigral rotenone model of Parkinson's disease

Parkinson disease (PD) is a chronic neurodegenerative disorder characterized by a progressive loss of dopamine neurons in the substantia nigra pars compacta (SNpc). In the last years, a growing interest to study the relationship between metabolic dysfunction and neurodegenerative disease like PD has emerged. This study aimed to evaluate the occurrence of possible changes in metabolic homeostasis due to intranigral rotenone administration, a neurotoxin that damages dopaminergic neurons leading to motor impairments mimicking those that happen in PD. Male Wistar rats were distributed into two groups: sham (n = 10) or rotenone (n = 10). Sham group received, bilaterally, within the SNpc, 1 µL of vehicle dimethyl-sulfoxide (DMSO) and the experimental group was bilaterally injected with 1 µL of rotenone (12 µg/µL). Twenty-four hours after the stereotaxic surgeries, the animals underwent the open field test followed by subsequent peripheral blood and cerebrospinal fluid (CSF) samples collection for biochemical testing. The results showed that rotenone was able to replicate the typical motor behavior impairment seen in the disease, i.e., decrease in locomotion (P = 0.05) and increase in immobility (P = 0.01) with a strong correlation (r = - 0.85; P < 0.0001) between them. In addition, it was demonstrated that this model is able to decrease plasmatic total-cholesterol (P = 0.04) and HDL-cholesterol (P = 0.007) potentially impacting peripheral metabolism. Hence, it was revealed a potential ability to reproduce relevant metabolic dysfunctions like hyperglycemia which could be explained by acute and systemic mitochondrial rotenone toxicity and SNpc nigral toxicity. Such mechanisms may still be responsible for the potential occurrence of CSF-hyperglycemia (d = 0.7). Since intranigral rotenone is an early phase model of PD, the present results open a new road for studies aiming to investigate metabolic changes in PD.

Lysosomal Pathogenesis of Parkinson's Disease: Insights From LRRK2 and GBA1 Rodent Models

The discovery of mutations in LRRK2 and GBA1 that are linked to Parkinson's disease provided further evidence that autophagy and lysosome pathways are likely implicated in the pathogenic process. Their protein products are important regulators of lysosome function. LRRK2 has kinase-dependent effects on lysosome activity, autophagic efficacy and lysosomal Ca2+ signaling. Glucocerebrosidase (encoded by GBA1) is a hydrolytic enzyme contained in the lysosomes and contributes to the degradation of alpha-synuclein. PD-related mutations in LRRK2 and GBA1 slow the degradation of alpha-synuclein, thus directly implicating the dysfunction of the process in the neuropathology of Parkinson's disease. The development of genetic rodent models of LRRK2 and GBA1 provided hopes of obtaining reliable preclinical models in which to study pathogenic processes and perform drug validation studies. Here, I will review the extensive characterization of these models, their impact on understanding lysosome alterations in the course of Parkinson's disease and what novel insights have been obtained. In addition, I will discuss how these models fare with respect to the features of a "gold standard" animal models and what could be attempted in future studies to exploit LRRK2 and GBA1 rodent models in the fight against Parkinson's disease.

Druggable transcriptomic pathways revealed in Parkinson's patient-derived midbrain neurons

Complex genetic predispositions accelerate the chronic degeneration of midbrain substantia nigra neurons in Parkinson’s disease (PD). Deciphering the human molecular makeup of PD pathophysiology can guide the discovery of therapeutics to slow the disease progression. However, insights from human postmortem brain studies only portray the latter stages of PD, and there is a lack of data surrounding molecular events preceding the neuronal loss in patients. We address this gap by identifying the gene dysregulation of live midbrain neurons reprogrammed in vitro from the skin cells of 42 individuals, including sporadic and familial PD patients and matched healthy controls. To minimize bias resulting from neuronal reprogramming and RNA-seq methods, we developed an analysis pipeline integrating PD transcriptomes from different RNA-seq datasets (unsorted and sorted bulk vs. single-cell and Patch-seq) and reprogramming strategies (induced pluripotency vs. direct conversion). This PD cohort’s transcriptome is enriched for human genes associated with known clinical phenotypes of PD, regulation of locomotion, bradykinesia and rigidity. Dysregulated gene expression emerges strongest in pathways underlying synaptic transmission, metabolism, intracellular trafficking, neural morphogenesis and cellular stress/immune responses. We confirmed a synaptic impairment with patch-clamping and identified pesticides and endoplasmic reticulum stressors as the most significant gene-chemical interactions in PD. Subsequently, we associated the PD transcriptomic profile with candidate pharmaceuticals in a large database and a registry of current clinical trials. This study highlights human transcriptomic pathways that can be targeted therapeutically before the irreversible neuronal loss. Furthermore, it demonstrates the preclinical relevance of unbiased large transcriptomic assays of reprogrammed patient neurons.

Neuroprotective approaches to halt Parkinson's disease progression

One of the most significant threats in Parkinson's disease (PD) is neurodegeneration. Neurodegeneration at both nigral as well as non-nigral regions of the brain is considered responsible for disease progression in PD. The key factors that initiate neurodegeneration are oxidative stress, neuroinflammation, mitochondrial complex-1 inhibition, and abnormal α-synuclein (SNCA) protein aggregations. Nigral neurodegeneration results in motor symptoms (tremor, bradykinesia, rigidity, shuffling gait, and postural instability) whereas; non-nigral neurodegeneration is responsible for non-motor symptoms (depression, cognitive dysfunctions, sleep disorders, hallucination, and psychosis). The available therapies for PD aim at increasing dopamine levels. The medications such as Monoamine oxidase B (MAO-B) inhibitors, catechol o-methyltransferase (COMT) inhibitors, Dopamine precursor (Levodopa), dopamine agonists, and dopamine reuptake inhibitors drastically improve the motor symptoms and quality of life only in the early stages of the disease. However, dopa resistant motor symptoms (abnormality in posture, speech impediment, gait, and balance problems), dopa resistant non-motor signs (sleep problems, autonomic dysfunction, mood, and cognitive impairment, pain), and drug-related side effects (motor fluctuations, psychosis, and dyskinesias) are considered responsible for the failure of these therapies. Further, none of the treatments, alone or in combination, are capable of halting the disease progression in the long run. Therefore, there is a need to develop safe and efficient neuroprotective agents, which can slow or stop the disease progression for the better management of PD. In this review, an effort has been made to discuss the various mechanisms responsible for progressive neurodegeneration (disease progression) in PD and also multiple strategies available for halting disease progression.

LRRK2 along the Golgi and lysosome connection: a jamming situation

Parkinson's disease (PD) is an age-related neurodegenerative disorder, clinically characterized by bradykinesia, rigidity, and resting tremor. Leucine-Rich Repeat Kinase 2 (LRRK2) is a large, multidomain protein containing two enzymatic domains. Missense mutations in its coding sequence are amongst the most common causes of familial PD. The physiological and pathological impact of LRRK2 is still obscure, but accumulating evidence supports a role for LRRK2 in membrane and vesicle trafficking, mainly functioning in the endosome-recycling system, (synaptic) vesicle trafficking, autophagy, and lysosome biology. LRRK2 binds and phosphorylates key regulators of the endomembrane systems and is dynamically localized at the Golgi. The impact of LRRK2 on the Golgi may reverberate throughout the entire endomembrane system and occur in multiple intersecting pathways, including endocytosis, autophagy, and lysosomal function. This would lead to overall dysregulation of cellular homeostasis and protein catabolism, leading to neuronal dysfunction and accumulation of toxic protein species, thus underlying the possible neurotoxic effect of LRRK2 mutations causing PD.

Endosomal traffic and glutamate synapse activity are increased in VPS35 D620N mutant knock-in mouse neurons, and resistant to LRRK2 kinase inhibition

Vacuolar protein sorting 35 (VPS35) regulates neurotransmitter receptor recycling from endosomes. A missense mutation (D620N) in VPS35 leads to autosomal-dominant, late-onset Parkinson's disease. Here, we study the basic neurobiology of VPS35 and Parkinson's disease mutation effects in the D620N knock-in mouse and the effect of leucine-rich repeat kinase 2 (LRRK2) inhibition on synaptic phenotypes. The study was conducted using a VPS35 D620N knock-in mouse that expresses VPS35 at endogenous levels. Protein levels, phosphorylation states, and binding ratios in brain lysates from knock-in mice and wild-type littermates were assayed by co-immunoprecipitation and western blot. Dendritic protein co-localization, AMPA receptor surface expression, synapse density, and glutamatergic synapse activity in primary cortical cultures from knock-in and wild-type littermates were assayed using immunocytochemistry and whole-cell patch clamp electrophysiology. In brain tissue, we confirm VPS35 forms complexes with LRRK2 and AMPA-type glutamate receptor GluA1 subunits, in addition to NMDA-type glutamate receptor GluN1 subunits and D2-type dopamine receptors. Receptor and LRRK2 binding was unaltered in D620N knock-in mice, but we confirm the mutation results in reduced binding of VPS35 with WASH complex member FAM21, and increases phosphorylation of the LRRK2 kinase substrate Rab10, which is reversed by LRRK2 kinase inhibition in vivo. In cultured cortical neurons from knock-in mice, pRab10 is also increased, and reversed by LRRK2 inhibition. The mutation also results in increased endosomal recycling protein cluster density (VPS35-FAM21 co-clusters and Rab11 clusters), glutamate transmission, and GluA1 surface expression. LRRK2 kinase inhibition, which reversed Rab10 hyper-phosphorylation, did not rescue elevated glutamate release or surface GluA1 expression in knock-in neurons, but did alter AMPAR traffic in wild-type cells. The results improve our understanding of the cell biology of VPS35, and the consequences of the D620N mutation in developing neuronal networks. Together the data support a chronic synaptopathy model for latent neurodegeneration, providing phenotypes and candidate pathophysiological stresses that may drive eventual transition to late-stage parkinsonism in VPS35 PD. The study demonstrates the VPS35 mutation has effects that are independent of ongoing LRRK2 kinase activity, and that LRRK2 kinase inhibition alters basal physiology of glutamate synapses in vitro.

Understanding the Potential of Genome Editing in Parkinson's Disease

CRISPR is a simple and cost-efficient gene-editing technique that has become increasingly popular over the last decades. Various CRISPR/Cas-based applications have been developed to introduce changes in the genome and alter gene expression in diverse systems and tissues. These novel gene-editing techniques are particularly promising for investigating and treating neurodegenerative diseases, including Parkinson's disease, for which we currently lack efficient disease-modifying treatment options. Gene therapy could thus provide treatment alternatives, revolutionizing our ability to treat this disease. Here, we review our current knowledge on the genetic basis of Parkinson's disease to highlight the main biological pathways that become disrupted in Parkinson's disease and their potential as gene therapy targets. Next, we perform a comprehensive review of novel delivery vehicles available for gene-editing applications, critical for their successful application in both innovative research and potential therapies. Finally, we review the latest developments in CRISPR-based applications and gene therapies to understand and treat Parkinson's disease. We carefully examine their advantages and shortcomings for diverse gene-editing applications in the brain, highlighting promising avenues for future research.

Quantitative Profiling of Synuclein Species: Application to Transgenic Mouse Models of Parkinson's Disease

INTRODUCTION

Improved analytical tools for detailed characterization of synucleins in pre-clinical models of Parkinson's disease (PD) and related synucleinopathies are needed.

OBJECTIVE

Develop a multiple reaction monitoring (MRM) liquid chromatography tandem mass spectrometry (LC-MS/MS) assay to quantify species-specific sequences and structural heterogeneity in soluble α- and β-synucleins in brain tissue.

METHODS

Using a proteolytic digestion workflow, the MRM LC-MS/MS method assayed six proteotypic peptides from the α-synuclein sequence; three unique to mouse or human α-synuclein and three conserved in α- and β-synuclein. For quantification, we used labeled α-synuclein as the internal standard and an external calibration curve. As proof of concept, the synuclein LC-MS/MS method was applied to brain tissue specimens from M83 transgenic PD mice, which overexpresses human α-synuclein, relative to wild-type littermate controls.

RESULTS

The synuclein MRM assay was linear over a wide concentration range (at least one order of magnitude). The assay had several advantages over ligand binding analytical methods, such as western blotting and enzyme-linked immunosorbent assays. These advantages included the ability to: quantify 1) total α-synuclein, 2) combined α- and β-synucleins, 3) species-specific contributions to total α-synuclein (e.g., in mice expressing both mouse and human α-synuclein), and 4) identify peptide-specific profile differences that may reflect post-translational modifications, all within a single analysis.

CONCLUSION

With improved and expanded analytical characteristics coupled with a streamlined sample preparation workflow, the quantitative synuclein profiling LC-MS/MS assay provides a versatile and efficient platform to characterize synuclein biology in pre-clinical models and the potential for application to human tissues and fluids.

Posttranslational modifications & lithium's therapeutic effect-Potential biomarkers for clinical responses in psychiatric & neurodegenerative disorders

Several neurodegenerative diseases and neuropsychiatric disorders display aberrant posttranslational modifications (PTMs) of one, or many, proteins. Lithium treatment has been used for mood stabilization for many decades, and is highly effective for large subsets of patients with diverse neurological conditions. However, the differential effectiveness and mode of action are not fully understood. In recent years, studies have shown that lithium alters several protein PTMs, altering their function, and consequently neuronal physiology. The impetus for this review is to outline the links between lithium's therapeutic mode of action and PTM homeostasis. We first provide an overview of the principal PTMs affected by lithium. We then describe several neuropsychiatric disorders in which PTMs have been implicated as pathogenic. For each of these conditions, we discuss lithium's clinical use and explore the putative mechanism of how it restores PTM homeostasis, and thereby cellular physiology. Evidence suggests that determining specific PTM patterns could be a promising strategy to develop biomarkers for disease and lithium responsiveness.

TLR7/8 in the Pathogenesis of Parkinson's Disease

Neuroinflammation and autoimmune mechanisms have a key part in the pathogenesis of Parkinson’s disease (PD). Therefore, we evaluated the role of Toll-like receptors (TLRs) as a link between inflammation and autoimmunity in PD. An in vivo model of PD was performed by administration of 1-metil 4-fenil 1,2,3,6-tetraidro-piridina (MPTP) at the dose of 20 mg/kg every 2 h for a total administration of 80/kg, both in single Knock Out (KO) mice for TLR7, TLR 8, and TLR9 and in double KO mice for TLR 7/8^-/-. All animals were compared with WT animals used as a control group. All animals were sacrificed after 7 days form the first administration of MPTP. The genetic absence of TLR 7 and 8 modified the PD pathway, increasing the immunoreactivity for TH and DAT compared to PD groups and decreasing microglia and astrocytes activation. Moreover, the deletion of TLR7 and TLR8 significantly reduced T-cell infiltration in the substantia nigra and lymph nodes, suggesting a reduction of T-cell activation. Therefore, our result highlights a possibility that an immunotherapy approach, by using a dual antagonist of TLR 7 and 8, could be considered as a possible target to develop new therapies for Parkinson diseases.

A Critical LRRK at the Synapse? The Neurobiological Function and Pathophysiological Dysfunction of LRRK2

Since the discovery of LRRK2 mutations causal to Parkinson's disease (PD) in the early 2000s, the LRRK2 protein has been implicated in a plethora of cellular processes in which pathogenesis could occur, yet its physiological function remains elusive. The development of genetic models of LRRK2 PD has helped identify the etiological and pathophysiological underpinnings of the disease, and may identify early points of intervention. An important role for LRRK2 in synaptic function has emerged in recent years, which links LRRK2 to other genetic forms of PD, most notably those caused by mutations in the synaptic protein α-synuclein. This point of convergence may provide useful clues as to what drives dysfunction in the basal ganglia circuitry and eventual death of substantia nigra (SN) neurons. Here, we discuss the evolution and current state of the literature placing LRRK2 at the synapse, through the lens of knock-out, overexpression, and knock-in animal models. We hope that a deeper understanding of LRRK2 neurobiology, at the synapse and beyond, will aid the eventual development of neuroprotective interventions for PD, and the advancement of useful treatments in the interim.

Kinase inhibition of G2019S-LRRK2 enhances autolysosome formation and function to reduce endogenous alpha-synuclein intracellular inclusions

The Parkinson's disease (PD)-associated kinase Leucine-Rich Repeat Kinase 2 (LRRK2) is a crucial modulator of the autophagy-lysosome pathway, but unclarity exists on the precise mechanics of its role and the direction of this modulation. In particular, LRRK2 is involved in the degradation of pathological alpha-synuclein, with pathogenic mutations precipitating neuropathology in cellular and animal models of PD, and a significant proportion of LRRK2 patients presenting Lewy neuropathology. Defects in autophagic processing and lysosomal degradation of alpha-synuclein have been postulated to underlie its accumulation and onset of neuropathology. Thus, it is critical to obtain a comprehensive knowledge on LRRK2-associated pathology. Here, we investigated a G2019S-LRRK2 recombinant cell line exhibiting accumulation of endogenous, phosphorylated alpha-synuclein. We found that G2019S-LRRK2 leads to accumulation of LC3 and abnormalities in lysosome morphology and proteolytic activity in a kinase-dependent fashion, but independent from constitutively active Rab10. Notably, LRRK2 inhibition was ineffective upon upstream blockade of autophagosome-lysosome fusion events, highlighting this step as critical for alpha-synuclein clearance.

Alpha-Synuclein and LRRK2 in Synaptic Autophagy: Linking Early Dysfunction to Late-Stage Pathology in Parkinson's Disease

The lack of effective disease-modifying strategies is the major unmet clinical need in Parkinson’s disease. Several experimental approaches have attempted to validate cellular targets and processes. Of these, autophagy has received considerable attention in the last 20 years due to its involvement in the clearance of pathologic protein aggregates and maintenance of neuronal homeostasis. However, this strategy mainly addresses a very late stage of the disease, when neuropathology and neurodegeneration have likely “tipped over the edge” and disease modification is extremely difficult. Very recently, autophagy has been demonstrated to modulate synaptic activity, a process distinct from its catabolic function. Abnormalities in synaptic transmission are an early event in neurodegeneration with Leucine-Rich Repeat Kinase 2 (LRRK2) and alpha-synuclein strongly implicated. In this review, we analyzed these processes separately and then discussed the unification of these biomolecular fields with the aim of reconstructing a potential “molecular timeline” of disease onset and progression. We postulate that the elucidation of these pathogenic mechanisms will form a critical basis for the design of novel, effective disease-modifying therapies that could be applied early in the disease process.

Neuron-autonomous susceptibility to induced synuclein aggregation is exacerbated by endogenous Lrrk2 mutations and ameliorated by Lrrk2 genetic knock-out

Neuronal aggregates containing α-synuclein are a pathological hallmark of several degenerative diseases; including Parkinson’s disease, Parkinson’s disease with dementia and dementia with Lewy bodies. Understanding the process of α-synuclein aggregation, and discovering means of preventing it, may help guide therapeutic strategy and drug design. Recent advances provide tools to induce α-synuclein aggregation in neuronal cultures. Application of exogenous pre-formed fibrillar α-synuclein induces pathological phosphorylation and accumulation of endogenous α-synuclein, typical of that seen in disease. Genomic variability and mutations in α-synuclein and leucine-rich repeat kinase 2 proteins are the major genetic risk factors for Parkinson’s disease. Reports demonstrate fibril-induced α-synuclein aggregation is increased in cells from leucine-rich repeat kinase 2 pathogenic mutant (G2019S) overexpressing mice, and variously decreased by leucine-rich repeat kinase 2 inhibitors. Elsewhere in vivo antisense knock-down of leucine-rich repeat kinase 2 protein has been shown to protect mice from fibril-induced α-synuclein aggregation, whereas kinase inhibition did not. To help bring clarity to this issue, we took a purely genetic approach in a standardized neuron-enriched culture, lacking glia. We compared fibril treatment of leucine-rich repeat kinase 2 germ-line knock-out, and G2019S germ-line knock-in, mouse cortical neuron cultures with those from littermates. We found leucine-rich repeat kinase 2 knock-out neurons are resistant to α-synuclein aggregation, which predominantly forms within axons, and may cause axonal fragmentation. Conversely, leucine-rich repeat kinase 2 knock-in neurons are more vulnerable to fibril-induced α-synuclein accumulation. Protection and resistance correlated with basal increases in a lysosome marker in knock-out, and an autophagy marker in knock-in cultures. The data add to a growing number of studies that argue leucine-rich repeat kinase 2 silencing, and potentially kinase inhibition, may be a useful therapeutic strategy against synucleinopathy.

Neuropathology and pathogenesis of extrapyramidal movement disorders: a critical update-I. Hypokinetic-rigid movement disorders

Extrapyramidal movement disorders include hypokinetic rigid and hyperkinetic or mixed forms, most of them originating from dysfunction of the basal ganglia (BG) and their information circuits. The functional anatomy of the BG, the cortico-BG-thalamocortical, and BG-cerebellar circuit connections are briefly reviewed. Pathophysiologic classification of extrapyramidal movement disorder mechanisms distinguish (1) parkinsonian syndromes, (2) chorea and related syndromes, (3) dystonias, (4) myoclonic syndromes, (5) ballism, (6) tics, and (7) tremor syndromes. Recent genetic and molecular-biologic classifications distinguish (1) synucleinopathies (Parkinson's disease, dementia with Lewy bodies, Parkinson's disease-dementia, and multiple system atrophy); (2) tauopathies (progressive supranuclear palsy, corticobasal degeneration, FTLD-17; Guamian Parkinson-dementia; Pick's disease, and others); (3) polyglutamine disorders (Huntington's disease and related disorders); (4) pantothenate kinase-associated neurodegeneration; (5) Wilson's disease; and (6) other hereditary neurodegenerations without hitherto detected genetic or specific markers. The diversity of phenotypes is related to the deposition of pathologic proteins in distinct cell populations, causing neurodegeneration due to genetic and environmental factors, but there is frequent overlap between various disorders. Their etiopathogenesis is still poorly understood, but is suggested to result from an interaction between genetic and environmental factors. Multiple etiologies and noxious factors (protein mishandling, mitochondrial dysfunction, oxidative stress, excitotoxicity, energy failure, and chronic neuroinflammation) are more likely than a single factor. Current clinical consensus criteria have increased the diagnostic accuracy of most neurodegenerative movement disorders, but for their definite diagnosis, histopathological confirmation is required. We present a timely overview of the neuropathology and pathogenesis of the major extrapyramidal movement disorders in two parts, the first one dedicated to hypokinetic-rigid forms and the second to hyperkinetic disorders.

In silico drug screening by using genome-wide association study data repurposed dabrafenib, an anti-melanoma drug, for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by dopaminergic neuron loss. At present, there are no drugs that stop the progression of PD. As with other multifactorial genetic disorders, genome-wide association studies (GWASs) found multiple risk loci for PD, although their clinical significance remains uncertain. Here, we report the identification of candidate drugs for PD by a method using GWAS data and in silico databases. We identified 57 Food and Drug Administration-approved drug families as candidate neuroprotective drugs for PD. Among them, dabrafenib, which is known as a B-Raf kinase inhibitor and is approved for the treatment of malignant melanoma, showed remarkable cytoprotective effects in neurotoxin-treated SH-SY5Y cells and mice. Dabrafenib was found to inhibit apoptosis, and to enhance the phosphorylation of extracellular signal-regulated kinase (ERK), and inhibit the phosphorylation of c-Jun NH2-terminal kinase. Dabrafenib targets B-Raf, and we confirmed a protein-protein interaction between B-Raf and Rit2, which is coded by RIT2, a PD risk gene in Asians and Caucasians. In RIT2-knockout cells, the phosphorylation of ERK was reduced, and dabrafenib treatment improved the ERK phosphorylation. These data indicated that dabrafenib exerts protective effects against neurotoxicity associated with PD. By using animal model, we confirmed the effectiveness of this in silico screening method. Furthermore, our results suggest that this in silico drug screening system is useful in not only neurodegenerative diseases but also other common diseases such as diabetes mellitus and hypertension.

DL-3-n-butylphthalide therapy for Parkinson's disease: A randomized controlled trial

Currently available treatments for Parkinson's disease (PD) do not delay or prevent disease development and progression. DL-3-n-butylphthalide (NBP), isolated from Apium graveolens seeds, alleviates oxidative damage and mitochondrial dysfunction. It has been revealed to reduce the loss of dopamine neurons in pre-clinical PD models, and has been approved for the treatment of ischemic stroke patients. The purpose of the present study was to examine whether NBP has the capacity provide a benefit for PD patients and to slow disease progression. A randomized, controlled trial was performed between September 2014 and December 2016. Pairs of patients matched by age, gender and off-medication Unified PD Rating Scale motor subscale (UPDRS-III) scores, were randomly assigned to an NBP treatment group and a control group. All patients continued their originally prescribed medication regimen and those in the NBP group were administered NBP at 200 mg three times daily for 24 weeks. Primary outcome measures were changes in UPDRS-III, including tremor score and non-tremor score, the Pittsburgh sleep quality index (PSQI) and the PD 39-items questionnaire (PDQ) scores. Assessments were completed by blinded evaluators at baseline and 12, 24 and 48 weeks after randomization. All patients were monitored for adverse events (AEs). A total of 103 patients were enrolled in the present study. The NBP group exhibited significantly greater improvements in the non-tremor, PSQI and PDQ-39 scores than the control group, which generally exhibited no improvement. NBP-associated AEs were uncommon and primarily consisted of mild gastrointestinal symptoms. In conclusion, over the 6-month treatment period, NBP was safe and effective for improving the symptoms and impairing the progression of patients with PD (Trial registry number, ChiCTR1800018892).

Are we listening to everything the PARK genes are telling us?

The cardinal motor symptoms that define Parkinson's disease (PD) clinically have been recognized for over 200 years. That these symptoms arise following the loss of dopamine neurons in the substantia nigra has been known for the last 50. These long-established facts have fueled a broadly held expectation that degenerating dopaminergic neurons alone hold the key to understanding and curing PD. This prevalent expectation is at odds with the observation that many nonmotor symptoms, including depression and cognitive inflexibility among others, can appear years earlier than the overt dopaminergic neuron degeneration that drives motor abnormalities and are not improved by levodopa treatment. Thus, preserving or rescuing dopamine neuron health and function is of paramount importance, but this alone fails to capture the underlying neurobiology of earlier-appearing nonmotor symptoms. Insight into the complete landscape of disease-related abnormalities and the context in which they arise can be gleaned from a more comprehensive consideration of the PARK genes that are known to cause PD. Here, we make the case that a full incorporation of research showing when and where PARK genes are expressed as well as the impact of gene mutation on function throughout life, in tandem with research studying how dopaminergic neuron degeneration begins, is essential for a full understanding of the multi-dimensional etiology of PD. A broad view may also reveal something about long-term adjustments cells and systems make in response to gene mutation and help to identify mechanisms conferring the resilience or susceptibility of some cells and systems over others.

Altered dopamine release and monoamine transporters in Vps35 p.D620N knock-in mice

Vacuolar protein sorting 35 (VPS35) is a core component of the retromer trimer required for endosomal membrane-associated protein trafficking. The discovery of a missense mutation, Vps35 p.D620N implicates retromer dysfunction in the pathogenesis of Parkinson's disease (PD). We have characterized a knock-in mouse with a Vps35 p.D620N substitution (hereafter referred to as VKI) at 3 months of age. Standardized behavioral testing did not observe overt movement disorder. Tyrosine hydroxylase (TH)-positive nigral neuron counts and terminal expression in striata were comparable across genotypes. Fast scan cyclic voltammetry revealed increased dopamine release in VKI striatal slices. While extracellular dopamine collected via striatal microdialysis of freely moving animals was comparable across genotypes, the ratio of dopamine metabolites to dopamine suggests increased dopamine turnover in VKI homozygous mice. Western blot of striatal proteins revealed a genotype-dependent decrease in dopamine transporter (DAT) along with an increase in vesicular monoamine transporter 2 (VMAT2), albeit independent of changes in other synaptic markers. The reduction in DAT was further supported by immunohistochemical analysis. The data show that the dopaminergic system of VKI mice is profoundly altered relative to wild-type littermates. We conclude early synaptic dysfunction contributes to age-related pathophysiology in the nigrostriatal system that may lead to parkinsonism in man.

The role of T cells in the pathogenesis of Parkinson's disease

Recent evidence has shown that neuroinflammation plays a key role in the pathogenesis of Parkinson's disease (PD). However, different components of the brain's immune system may exert diverse effects on neuroinflammatory events in PD. The adaptive immune response, especially the T cell response, can trigger type 1 pro-inflammatory activities and suppress type 2 anti-inflammatory activities, eventually resulting in deregulated neuroinflammation and subsequent dopaminergic neurodegeneration. Additionally, studies have increasingly shown that therapies targeting T cells can alleviate neurodegeneration and motor behavior impairment in animal models of PD. Therefore, we conclude that abnormal T cell-mediated immunity is a fundamental pathological process that may be a promising translational therapeutic target for Parkinson's disease.

A new hypothesis for Parkinson's disease pathogenesis: GTPase-p38 MAPK signaling and autophagy as convergence points of etiology and genomics

The combination of genetics and genomics in Parkinson´s disease has recently begun to unveil molecular mechanisms possibly underlying disease onset and progression. In particular, catabolic processes such as autophagy have been increasingly gaining relevance as post-mortem evidence and experimental models suggested a participation in neurodegeneration and alpha-synuclein Lewy body pathology. In addition, familial Parkinson´s disease linked to LRRK2 and alpha-synuclein provided stronger correlation between etiology and alterations in autophagy. More detailed cellular pathways are proposed and genetic risk factors that associate with idiopathic Parkinson´s disease provide further clues in dissecting contributions of single players. Nevertheless, the fine-tuning of these processes remains elusive, as the initial stages of the pathways are not yet clarified.In this review, we collect literature evidence pointing to autophagy as the common, downstream target of Parkinsonian dysfunctions and augment current knowledge on the factors that direct the subsequent steps. Cell and molecular biology evidence indicate that p38 signaling underlies neurodegeneration and autoptic observations suggest a participation in neuropathology. Moreover, alpha-synuclein and LRRK2 also appear involved in the p38 pathway with additional roles in the regulation of GTPase signaling. Small GTPases are critical modulators of p38 activation and thus, their functional interaction with aSyn and LRRK2 could explain much of the detailed mechanics of autophagy in Parkinson´s disease.We propose a novel hypothesis for a more comprehensive working model where autophagy is controlled by upstream pathways, such as GTPase-p38, that have been so far underexplored in this context. In addition, etiological factors (LRRK2, alpha-synuclein) and risk loci might also combine in this common mechanism, providing a powerful experimental setting to dissect the cause of both familial and idiopathic disease.

Microglia Gone Rogue: Impacts on Psychiatric Disorders across the Lifespan

Microglia are the predominant immune response cells and professional phagocytes of the central nervous system (CNS) that have been shown to be important for brain development and homeostasis. These cells present a broad spectrum of phenotypes across stages of the lifespan and especially in CNS diseases. Their prevalence in all neurological pathologies makes it pertinent to reexamine their distinct roles during steady-state and disease conditions. A major question in the field is determining whether the clustering and phenotypical transformation of microglial cells are leading causes of pathogenesis, or potentially neuroprotective responses to the onset of disease. The recent explosive growth in our understanding of the origin and homeostasis of microglia, uncovering their roles in shaping of the neural circuitry and synaptic plasticity, allows us to discuss their emerging functions in the contexts of cognitive control and psychiatric disorders. The distinct mesodermal origin and genetic signature of microglia in contrast to other neuroglial cells also make them an interesting target for the development of therapeutics. Here, we review the physiological roles of microglia, their contribution to the effects of environmental risk factors (e.g., maternal infection, early-life stress, dietary imbalance), and their impact on psychiatric disorders initiated during development (e.g., Nasu-Hakola disease (NHD), hereditary diffuse leukoencephaly with spheroids, Rett syndrome, autism spectrum disorders (ASDs), and obsessive-compulsive disorder (OCD)) or adulthood (e.g., alcohol and drug abuse, major depressive disorder (MDD), bipolar disorder (BD), schizophrenia, eating disorders and sleep disorders). Furthermore, we discuss the changes in microglial functions in the context of cognitive aging, and review their implication in neurodegenerative diseases of the aged adult (e.g., Alzheimer’s and Parkinson’s). Taking into account the recent identification of microglia-specific markers, and the availability of compounds that target these cells selectively in vivo, we consider the prospect of disease intervention via the microglial route.

Identification of Ser465 as a novel PINK1 autophosphorylation site

Background

PINK1 (PTEN-induced putative kinase 1) gene is the causal gene for recessive familial type 6 of Parkinson’s disease (PARK6), which is an early-onset autosomal recessive inherited neurodegenerative disease. PINK1 has been reported to exert both autophosphorylation and phosphorylation activity, affecting cell damage under stress and other physiological responses. However, there has been no report on the identification of PINK1 autophosphorylation sites and their physiological functions.

Methods

(1) We adopted mass spectrometry assay to identify the autophosphorylation site of PINK1, and autoradiography assay was further conducted to confirm this result. (2) Kinase activity assay was used to compare the kinase activity of both Ser465 mutant PINK1 and disease-causing mutant PINK1. (3) We use Pulse-chase analysis to measure whether Ser465 may affect PINK1 degradation. (4) Immunocytochemistry staining was used to study the PINK1 subcellular localization and Parkin transition in subcellular level.

Result

In our study, we identified the 465th serine residue (Ser465) as one of the autophosphorylation sites in PINK1 protein. The inactivation of Ser465 can decrease the kinase activity of PINK1. Either dissipated or excessive Ser465 site phosphorylation of PINK1 can slow down its degradation. PINK1 autophosphorylation contributes to the transit of Parkin to mitochondria, and has no effect on its subcellular localization. PARK6 causal mutations, T313 M and R492X, display the same characteristics as Ser465A mutation PINK1 protein, such as decreasing PINK1 kinase activity and affecting its interaction with Parkin.

Conclusion

Ser465 was identified as one of the autophosphorylation sites of PINK1, which affected PINK1 kinase activity. In addition, Ser465 is involved in the degradation of PINK1 and the transit of Parkin to mitochondria. T313 M and R492X, two novel PARK6 mutations on Thr313 and Arg492, were similar to Ser465 mutation, including decreasing PINK1 phosphorylation activity and Parkin subcellular localization.

Differential Alterations in Metabolism and Proteolysis-Related Proteins in Human Parkinson's Disease Substantia Nigra

Parkinson's disease is the most common neurodegenerative disorder after Alzheimer's disease, with the majority of cases being sporadic or "idiopathic". The aetiology of the sporadic form is still unknown, but there is a broad consensus that Parkinson's disease involves multiple pathways. In previous human post-mortem studies investigating substantia nigra of parkinsonian subjects, gene expression alterations in various metabolic pathways including protein folding, trafficking, aggregation, ubiquitination and oxidative stress were found. These studies revealed transcriptomic dysregulation of various genes, amongst others Skp1A and PSMC4 (part of ubiquitin-proteasome system), HSC70 (belonging to the chaperone family) and ALDH1A1 (an enzyme involved in the catabolism of dopamine). To investigate whether these alterations are manifested at the protein level, we performed immunohistochemical analysis in the substantia nigra of Parkinson's disease and compared them to Alzheimer's disease and non-neurological post-mortem controls. We were able to confirm cell-specific reductions in the protein content of ALHD1A1 and Skp1A in the dopaminergic neurons of the substantia nigra of Parkinsonian patients compared to Alzheimer's and control subjects. Furthermore, we observed particular distribution for HSC70 and PSMC4 in the cytoplasm and accumulation within Lewy body in the dopaminergic neurons of the substantia nigra in Parkinson patients. These findings, together with previous evidence, suggest a malfunction of the ubiquitin-proteasome and possible autophagy systems as major players in protein misfolding and aggregation in Parkinson's disease. Nevertheless, this needs further proof, possibly with trajectory time line.

[Epidemiology and causes of Parkinson's disease]

Parkinson's disease (PD) is the second most common neurodegenerative disease and has a growing socioeconomic impact due to demographic changes in the industrial nations. There are several forms of PD, a fraction of which (<5%) are monogenic, i. e. caused by mutations in single genes. At present, six genes have been established for the clinically classical form of parkinsonism including three autosomal dominantly (SNCA, LRRK2, VPS35) and three autosomal recessively inherited ones (Parkin, PINK1, DJ-1). In addition, there are a plethora of genes causing atypical forms of parkinsonism. In contrast, idiopathic PD is of a multifactorial nature. Genome-wide association studies have established a total of 26 genetic loci for this form of the disease; however, for most of these loci the underlying functional genetic variants have not yet been identified and the respective disease mechanisms remain unresolved. Furthermore, there are a number of environmental and life style factors that are associated with idiopathic PD. Exposure to pesticides and possibly a history of head trauma represent genuine risk factors. Other PD-associated factors, such as smoking and intake of coffee and alcohol may not represent risk factors per se and the cause-effect relationship has not yet been elucidated for most of these factors. A patient with a positive family history and/or an early age of disease onset should undergo counseling with respect to a possible monogenic form of the disease. Disease prediction based on genetic, environmental and life style factors is not yet possible for idiopathic PD and potential gene-specific therapies are currently in the development or early testing phase.

Port-to-port delivery: Mobilization of toxic sphingolipids via extracellular vesicles

The discovery that most cells produce extracellular vesicles (EVs) and release them in the extracellular milieu has spurred the idea that these membranous cargoes spread pathogenic mechanisms. In the brain, EVs may have multifold and important physiological functions, from deregulating synaptic activity to promoting demyelination to changes in microglial activity. The finding that small EVs (exosomes) contain α-synuclein and β-amyloid, among other pathogenic proteins, is an example of this notion, underscoring their potential role in the brains of patients with Parkinson's and Alzheimer's diseases. Given that they are membranous vesicles, we speculate that EVs also have an intrinsic capacity to incorporate sphingolipids. In conditions under which these lipids are elevated to toxic levels, such as in Krabbe's disease and metachromatic leukodystrophy, EVs may contribute to spread disease from sick to healthy cells. In this essay, we discuss a working hypothesis that brain cells in sphingolipidoses clear some of the accumulated lipid material to attempt restoring cell homeostasis via EV secretion. We hypothesize that secreted sphingolipid-loaded EVs shuttle pathogenic lipids to cells that are not intrinsically affected, contributing to establishing non-cell-autonomous defects. © 2016 Wiley Periodicals, Inc.

Identification of VPS35 p.D620N mutation-related Parkinson's disease in a Taiwanese family with successful bilateral subthalamic nucleus deep brain stimulation: a case report and literature review

Background

Vacuolar protein sorting 35 (VPS35) was recently reported to be a genetic cause for late-onset autosomal dominant Parkinson’s disease (PD). However, VPS35 mutations are rarely reported in Asian populations. Herein, we report the first Taiwanese family with the pathogenic VPS35 p.D620N mutation, including one patient treated successfully with subthalamic nucleus deep brain stimulation (STN-DBS).

Case presentation

A 61-year-old woman presented with progressive left hand resting tremor at the age of 42. Neurological examinations revealed mask face and akinetic-rigidity over left extremities. She showed a good response to levodopa treatment, and her unified Parkinson’s disease rating scale (UPDRS) motor scores improved from 42 to 15 under the levodopa equivalent dose of 1435 mg/day. She developed peak-dose dyskinesia and motor fluctuation seven years after the onset of symptoms, and received bilateral STN-DBS at the age of 55. Stimulation led to a marked improvement in her motor symptoms with a 37% improvement in the UPDRS motor score during the OFF period five years after surgery. The patient’s mother and three siblings were also diagnosed with PD in their forties, following an autosomal-dominant inheritance pattern. We performed genetic analysis of the proband using a targeted next generation sequencing (NGS) panel covering 17 known PD-causative genes. We identified a pathogenic missense mutation in VPS35 gene, c.1858G > A (p.D620N), in this patient.

Conclusions

This is the first report of the VPS35 p.D620N mutation in a Taiwanese family. Additionally, our report contributes to the current understanding of genetically defined PD patients treated successfully with STN-DBS.

Initial elevations in glutamate and dopamine neurotransmission decline with age, as does exploratory behavior, in LRRK2 G2019S knock-in mice

LRRK2 mutations produce end-stage Parkinson’s disease (PD) with reduced nigrostriatal dopamine, whereas, asymptomatic carriers have increased dopamine turnover and altered brain connectivity. LRRK2 pathophysiology remains unclear, but reduced dopamine and mitochondrial abnormalities occur in aged G2019S mutant knock-in (GKI) mice. Conversely, cultured GKI neurons exhibit increased synaptic transmission. We assessed behavior and synaptic glutamate and dopamine function across a range of ages. Young GKI mice exhibit more vertical exploration, elevated glutamate and dopamine transmission, and aberrant D2-receptor responses. These phenomena decline with age, but are stable in littermates. In young GKI mice, dopamine transients are slower, independent of dopamine transporter (DAT), increasing the lifetime of extracellular dopamine. Slowing of dopamine transients is observed with age in littermates, suggesting premature ageing of dopamine synapses in GKI mice. Thus, GKI mice exhibit early, but declining, synaptic and behavioral phenotypes, making them amenable to investigation of early pathophysiological, and later parkinsonian-like, alterations. This model will prove valuable in efforts to develop neuroprotection for PD.

Habituation is altered in neuropsychiatric disorders-A comprehensive review with recommendations for experimental design and analysis

Abnormalities in the simplest form of learning, habituation, have been reported in a variety of neuropsychiatric disorders as etiologically diverse as Autism Spectrum Disorder, Fragile X syndrome, Schizophrenia, Parkinson's Disease, Huntington's Disease, Attention Deficit Hyperactivity Disorder, Tourette's Syndrome, and Migraine. Here we provide the first comprehensive review of what is known about alterations in this form of non-associative learning in each disorder. Across several disorders, abnormal habituation is predictive of symptom severity, highlighting the clinical significance of habituation and its importance to normal cognitive function. Abnormal habituation is discussed within the greater framework of learning theory and how it may relate to disease phenotype either as a cause, symptom, or therapy. Important considerations for the design and interpretation of habituation experiments are outlined with the hope that these will aid both clinicians and basic researchers investigating how this simple form of learning is altered in disease.

CpG and Non-CpG Methylation in Epigenetic Gene Regulation and Brain Function

DNA methylation is a major epigenetic mark with important roles in genetic regulation. Methylated cytosines are found primarily at CpG dinucleotides, but are also found at non-CpG sites (CpA, CpT, and CpC). The general functions of CpG and non-CpG methylation include gene silencing or activation depending on the methylated regions. CpG and non-CpG methylation are found throughout the whole genome, including repetitive sequences, enhancers, promoters, and gene bodies. Interestingly, however, non-CpG methylation is restricted to specific cell types, such as pluripotent stem cells, oocytes, neurons, and glial cells. Thus, accumulation of methylation at non-CpG sites and CpG sites in neurons seems to be involved in development and disease etiology. Here, we provide an overview of CpG and non-CpG methylation and their roles in neurological diseases.

A Human Neural Crest Stem Cell-Derived Dopaminergic Neuronal Model Recapitulates Biochemical Abnormalities in GBA1 Mutation Carriers

Numerically the most important risk factor for the development of Parkinson's disease (PD) is the presence of mutations in the glucocerebrosidase GBA1 gene. In vitro and in vivo studies show that GBA1 mutations reduce glucocerebrosidase (GCase) activity and are associated with increased α-synuclein levels, reflecting similar changes seen in idiopathic PD brain. We have developed a neural crest stem cell-derived dopaminergic neuronal model that recapitulates biochemical abnormalities in GBA1 mutation-associated PD. Cells showed reduced GCase protein and activity, impaired macroautophagy, and increased α-synuclein levels. Advantages of this approach include easy access to stem cells, no requirement to reprogram, and retention of the intact host genome. Treatment with a GCase chaperone increased GCase protein levels and activity, rescued the autophagic defects, and decreased α-synuclein levels. These results provide the basis for further investigation of GCase chaperones or similar drugs to slow the progression of PD.

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A neuronal model recapitulates biochemical abnormalities in GBA1 mutation PD

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Ambroxol rescued the autophagic defects in human GBA1 mutant neuronal cells

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Ambroxol decreased α-synuclein levels human GBA1 mutant neuronal cells

Genetic Determinants of Parkinson's Disease: Can They Help to Stratify the Patients Based on the Underlying Molecular Defect?

Parkinson's disease (PD) is a sporadic progressive neurodegenerative brain disorder with a relatively strong genetic background. We have reviewed the current literature about the genetic factors that could be indicative of pathophysiological pathways of PD and their applications in everyday clinical practice. Information on novel risk genes is coming from several genome-wide association studies (GWASs) and their meta-analyses. GWASs that have been performed so far enabled the identification of 24 loci as PD risk factors. These loci take part in numerous cellular processes that may contribute to PD pathology: protein aggregation, protein, and membrane trafficking, lysosomal autophagy, immune response, synaptic function, endocytosis, inflammation, and metabolic pathways are among the most important ones. The identified single nucleotide polymorphisms are usually located in the non-coding regions and their functionality remains to be determined, although they presumably influence gene expression. It is important to be aware of a very low contribution of a single genetic risk factor to PD development; therefore, novel prognostic indices need to account for the cumulative nature of genetic risk factors. A better understanding of PD pathophysiology and its genetic background will help to elucidate the underlying pathological processes. Such knowledge may help physicians to recognize subjects with the highest risk for the development of PD, and provide an opportunity for the identification of novel potential targets for neuroprotective treatment. Moreover, it may enable stratification of the PD patients according to their genetic fingerprint to properly personalize their treatment as well as supportive measures.

Systematic analysis of genetic variants in Han Chinese patients with sporadic Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative disorders. Accumulated evidence confirms that genetic factors play a considerable role in PD pathogenesis. To examine whether point variants or haplotypes are associated with PD development, genotyping of 35 variants in 22 PD-related genes was performed in a well-characterized cohort of 512 Han Chinese PD patients and 512 normal controls. Both Pearson's χ2 test and haplotype analysis were used to evaluate whether variants or their haplotypes were associated with PD in this cohort. The only statistically significant differences in genotypic and allelic frequencies between the patients and the controls were in the DnaJ heat shock protein family (Hsp40) member C10 gene (DNAJC10) variant rs13414223 (P = 0.004 and 0.002, respectively; odds ratio = 0.652, 95% confidence interval: 0.496-0.857). No other variants or haplotypes exhibited any significant differences between these two groups (all corrected P > 0.05). Our findings indicate that the variant rs13414223 in the DNAJC10 gene, a paralog of PD-related genes DNAJC6 and DNAJC13, may play a protective role in PD. This suggests it may be a PD-associated gene.

Dopaminergic neurons differentiating from LRRK2 G2019S induced pluripotent stem cells show early neuritic branching defects

Some mutations of the LRRK2 gene underlie autosomal dominant form of Parkinson’s disease (PD). The G2019S is a common mutation that accounts for about 2% of PD cases. To understand the pathophysiology of this mutation and its possible developmental implications, we developed an in vitro assay to model PD with human induced pluripotent stem cells (hiPSCs) reprogrammed from skin fibroblasts of PD patients suffering from the LRKK2 G2019S mutation. We differentiated the hiPSCs into neural stem cells (NSCs) and further into dopaminergic neurons. Here we show that NSCs bearing the mutation tend to differentiate less efficiently into dopaminergic neurons and that the latter exhibit significant branching defects as compared to their controls.

Network and Pathway-Based Analyses of Genes Associated with Parkinson's Disease

Parkinson's disease (PD) is a major neurodegenerative disease influenced by both genetic and environmental factors. Although previous studies have provided insights into the significant impacts of genetic factors on PD, the molecular mechanism underlying PD remains largely unclear. Under such situation, a comprehensive analysis focusing on biological function and interactions of PD-related genes will provide us valuable information to understand the pathogenesis of PD. In the current study, by reviewing the literatures deposited in PUBMED, we identified 242 genes genetically associated with PD, referred to as PD-related genes gene set (PDgset). Functional analysis revealed that biological processes and biochemical pathways related to neurodevelopment, metabolism, and immune system were enriched in PDgset. Then, pathway crosstalk analysis indicated that the enriched pathways could be grouped into two modules, with one module consisted of pathways mainly involved in neuronal signaling and another in immune response. Further, based on a global human interactome, we found that PDgset tended to have more moderate degree compared with cancer-related genes. Moreover, PD-specific molecular network was inferred using Steiner minimal tree algorithm and some potential related genes associated with PD were identified. In summary, by using network- and pathway-based methods to explore pathogenetic mechanism underlying PD, results from our work may have important implications for understanding the molecular mechanism underlying PD. Also, the framework proposed in our current work can be used to infer pathological molecular network and genes related to a specific disease.

Targeted methylation sequencing reveals dysregulated Wnt signaling in Parkinson disease

Parkinson disease (PD) is a progressive neurodegenerative movement disorder. Both environmental and genetic factors play important roles in PD etiology. A number of environmental toxins cause parkinsonism in human and animal models. Genetic studies of rare early onset familial PD cases resulted in identification of disease-linked mutations in multiple genes. Nevertheless, the potential interaction between environment and genetics in PD pathogenesis remains largely unknown. We hypothesized that environmental factors induce abnormal epigenetic regulation that is involved in the pathogenesis of both familial and sporadic PD. We determined the global methylation status of 80,000-110,000 CpG sites in each of the five sporadic PD patient brains and five age and postmodern interval matched control brains utilizing bisulfite padlock sequencing. Multiple genes involved in neurogenesis, particularly the ones in the Wnt signaling pathway, were hypermethylated in PD brains compared to their matched control brains. Consistent with the DNA methylation changes, marked reduction of protein expression was observed for four Wnt and neurogenesis related genes (FOXC1, NEURG2, SPRY1, and CTNNB1) in midbrain dopaminergic (DA) neurons of PD. The treatment of low concentration of 1-methyl-4-phenylpyridinium (MPP⁺) for cells resulted in downregulation of Wnt related genes. The study revealed an important link between the epigenetic disregulation of Wnt signaling and the pathogenesis and progression of PD.

Metformin Prevents Dopaminergic Neuron Death in MPTP/P-Induced Mouse Model of Parkinson's Disease via Autophagy and Mitochondrial ROS Clearance

BACKGROUND

Our previous study demonstrated that metabolic inflammation exacerbates dopaminergic neuronal degeneration in type 2 diabetes mice. Metformin, a typical oral hypoglycemic agent for diabetes, has been regarded as an activator of AMP-activated protein kinase and a regulator of systemic energy metabolism. Although metformin plays potential protective effects in many disorders, it is unclear whether metformin has a therapeutic role in dopaminergic neuron degeneration in Parkinson's disease.

METHODS

In the present study, a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid-induced mouse model of Parkinson's disease was established to explore the neuroprotective effect of metformin on dopaminergic neurons in substania nigra compacta. We next cultured SH-SY5Y cells to investigate the mechanisms for the neuroprotective effect of metformin.

RESULTS

We showed that treatment with metformin (5mg/mL in drinking water) for 5 weeks significantly ameliorated the degeneration of substania nigra compacta dopaminergic neurons, increased striatal dopaminergic levels, and improved motor impairment induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid. We further found that metformin inhibited microglia overactivation-induced neuroinflammation in substania nigra compacta of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid Parkinson's disease mice, which might contribute to the protective effect of metformin on neurodegeneration. Furthermore, metformin (2mM) activated AMP-activated protein kinase in SH-SY5Y cells, in turn inducing microtubule-associated protein 1 light chain 3-II-mediated autophagy and eliminating mitochondrial reactive oxygen species. Consequently, metformin alleviated MPP⁺-induced cytotoxicity and attenuated neuronal apoptosis.

CONCLUSIONS

Our findings demonstrate that metformin may be a pluripotent and promising drug for dopaminergic neuron degeneration, which will give us insight into the potential of metformin in terms of opening up novel therapeutic avenues for Parkinson's disease.

Associations of Matrix Metalloproteinase-9 and Tissue Inhibitory Factor-1 Polymorphisms With Parkinson Disease in Taiwan

Matrix metalloproteinases (MMPs) function in the degradation of extracellular matrix and are considered to play a role in the pathogenesis of neurodegenerative diseases including Parkinson disease (PD). MMPs activities are modulated by tissue inhibitors of metalloproteinases (TIMPs). This study examined whether the genetic polymorphisms of MMP-3, gelatinase (MMP-2 and MMP-9), TIMP-2, and TIMP-1 were associated with PD in Taiwan.A total of 359 PD patients and 332 controls were enrolled. The candidate genetic variants included MMP-2 rs2285053 (-735 C > T), MMP-3 rs3025058 (-1171 5A > 6A), MMP-9 rs3918241 (-1831 T > A), rs17576 (G > A, R279Q), and rs3787268 (G > A, intron), TIMP-1 rs4898 (T > C, F124F), and TIMP-2 rs7503607 (-269 G > T). Associations were tested by logistic regression, adjusted with gender and age at onset.Minor allele frequency of TIMP-1 rs4898 (36.0%) was significantly lower in the male PD patients than in the male controls (51.2%) (χ test, P = 0.004). When adjusted with gender and age at onset, MMP-9 rs17576 AA genotype was associated with PD susceptibility in a recessive fashion (odds ratios [OR] = 2.28, 95% confidence intervals [95% CI] = 1.12-4.62, P = 0.02). In males, TIMP-1 rs4898 C allele was associated with a protective effect on PD (OR = 0.75, 95% CI = 0.60-0.94, P = 0.014). We did not find association between the examined genetic variants of MMP-2, MMP-3, and TIMP-2 and PD susceptibility.This is the first study that demonstrated a protective effect of TIMP-1 rs4898 C allele on male PD and a modest association of MMP-9 rs17576 AA genotype with PD susceptibility in the Taiwan population. Further replication is needed for confirmation.