Striatal tyrosine hydroxylase-positive neurons are associated with L-DOPA-induced dyskinesia in hemiparkinsonian mice

Dysfunction of synaptic endocytic trafficking in Parkinson's disease

Parkinson's disease is characterized by the selective degeneration of dopamine neurons in the nigrostriatal pathway and dopamine deficiency in the striatum. The precise reasons behind the specific degeneration of these dopamine neurons remain largely elusive. Genetic investigations have identified over 20 causative PARK genes and 90 genomic risk loci associated with both familial and sporadic Parkinson's disease. Notably, several of these genes are linked to the synaptic vesicle recycling process, particularly the clathrin-mediated endocytosis pathway. This suggests that impaired synaptic vesicle recycling might represent an early feature of Parkinson's disease, followed by axonal degeneration and the eventual loss of dopamine cell bodies in the midbrain via a "dying back" mechanism. Recently, several new animal and cellular models with Parkinson's disease-linked mutations affecting the endocytic pathway have been created and extensively characterized. These models faithfully recapitulate certain Parkinson's disease-like features at the animal, circuit, and cellular levels, and exhibit defects in synaptic membrane trafficking, further supporting the findings from human genetics and clinical studies. In this review, we will first summarize the cellular and molecular findings from the models of two Parkinson's disease-linked clathrin uncoating proteins: auxilin (DNAJC6/PARK19) and synaptojanin 1 (SYNJ1/PARK20). The mouse models carrying these two PARK gene mutations phenocopy each other with specific dopamine terminal pathology and display a potent synergistic effect. Subsequently, we will delve into the involvement of several clathrin-mediated endocytosis-related proteins (GAK, endophilin A1, SAC2/INPP5F, synaptotagmin-11), identified as Parkinson's disease risk factors through genome-wide association studies, in Parkinson's disease pathogenesis. We will also explore the direct or indirect roles of some common Parkinson's disease-linked proteins (alpha-synuclein (PARK1/4), Parkin (PARK2), and LRRK2 (PARK8)) in synaptic endocytic trafficking. Additionally, we will discuss the emerging novel functions of these endocytic proteins in downstream membrane traffic pathways, particularly autophagy. Given that synaptic dysfunction is considered as an early event in Parkinson's disease, a deeper understanding of the cellular mechanisms underlying synaptic vesicle endocytic trafficking may unveil novel targets for early diagnosis and the development of interventional therapies for Parkinson's disease. Future research should aim to elucidate why generalized synaptic endocytic dysfunction leads to the selective degeneration of nigrostriatal dopamine neurons in Parkinson's disease.

Long-Term Effects of Perinatal Exposure to a Glyphosate-Based Herbicide on Melatonin Levels and Oxidative Brain Damage in Adult Male Rats

Concerns have been raised regarding the potential adverse health effects of the ubiquitous herbicide glyphosate. Here, we investigated long-term effects of developmental exposure to a glyphosate-based herbicide (GBH) by analyzing serum melatonin levels and cellular changes in the striatum of adult male rats (90 days old). Pregnant and lactating rats were exposed to 3% GBH (0.36% glyphosate) through drinking water from gestational day 5 to postnatal day 15. The offspring showed reduced serum melatonin levels (43%) at the adult age compared with the control group. The perinatal exposure to GBH also induced long-term oxidative stress-related changes in the striatum demonstrated by increased lipid peroxidation (45%) and DNA/RNA oxidation (39%) together with increased protein levels of the antioxidant enzymes, superoxide dismutase (SOD1, 24%), glutamate-cysteine ligase (GCLC, 58%), and glutathione peroxidase 1 (GPx1, 31%). Moreover, perinatal GBH exposure significantly increased the total number of neurons (20%) and tyrosine hydroxylase (TH)-positive neurons (38%) in the adult striatum. Mechanistic in vitro studies with primary rat pinealocytes exposed to 50 µM glyphosate demonstrated a decreased melatonin secretion partially through activation of metabotropic glutamate receptor 3 (mGluR3), while higher glyphosate levels (100 or 500 µM) also reduced the pinealocyte viability. Since decreased levels of the important antioxidant and neuroprotector melatonin have been associated with an increased risk of developing neurodegenerative disorders, this demonstrates the need to consider the melatonin hormone system as a central endocrine-related target of glyphosate and other environmental contaminants.

Mutations in Parkinsonism-linked endocytic proteins synaptojanin1 and auxilin have synergistic effects on dopaminergic axonal pathology

Parkinson's disease (PD) is a neurodegenerative disorder characterized by defective dopaminergic (DAergic) input to the striatum. Mutations in two genes encoding synaptically enriched clathrin-uncoating factors, synaptojanin 1 (SJ1) and auxilin, have been implicated in atypical Parkinsonism. SJ1 knock-in (SJ1-KIRQ) mice carrying a disease-linked mutation display neurological manifestations reminiscent of Parkinsonism. Here we report that auxilin knockout (Aux-KO) mice display dystrophic changes of a subset of nigrostriatal DAergic terminals similar to those of SJ1-KIRQ mice. Furthermore, Aux-KO/SJ1-KIRQ double mutant mice have shorter lifespan and more severe synaptic defects than single mutant mice. These include increase in dystrophic striatal nerve terminals positive for DAergic markers and for the PD risk protein SV2C, as well as adaptive changes in striatal interneurons. The synergistic effect of the two mutations demonstrates a special lability of DAergic neurons to defects in clathrin uncoating, with implications for PD pathogenesis in at least some forms of this condition.

Neuroprotective Role of Nutritional Supplementation in Athletes

BACKGROUND

Neurodegenerative disorders belong to different classes of progressive/chronic conditions that affect the peripheral/central nervous system. It has been shown through studies that athletes who play sports involving repeated head trauma and sub-concussive impacts are more likely to experience neurological impairments and neurodegenerative disorders in the long run.

AIMS

The aim of the current narrative review article is to provide a summary of various nutraceuticals that offer promise in the prevention or management of sports-related injuries, especially concussions and mild traumatic brain injuries.

METHODS

This article reviews the various potential nutraceutical agents and their possible mechanisms in providing a beneficial effect in the injury recovery process. A thorough survey of the literature was carried out in the relevant databases to identify studies published in recent years. In the present article, we have also highlighted the major neurological disorders along with the associated nutraceutical(s) therapy in the management of disorders.

RESULTS

The exact pathological mechanism behind neurodegenerative conditions is complex as well as idiopathic. However, mitochondrial dysfunction, oxidative stress as well as intracellular calcium overload are some common reasons responsible for the progression of these neurodegenerative disorders. Owing to the multifaceted effects of nutraceuticals (complementary medicine), these supplements have gained importance as neuroprotective. These diet-based approaches inhibit different pathways in a physiological manner without eliciting adverse effects. Food habits and lifestyle of an individual also affect neurodegeneration.

CONCLUSION

Studies have shown nutraceuticals (such as resveratrol, omega-3-fatty acids) to be efficacious in terms of their neuroprotection against several neurodegenerative disorders and to be used as supplements in the management of traumatic brain injuries. Protection prior to injuries is needed since concussions or sub-concussive impacts may trigger several pathophysiological responses or cascades that can lead to long-term complications associated with CNS. Thus, the use of nutraceuticals as prophylactic treatment for neurological interventions has been proposed.

Cerebral Microstructural Alterations in Patients With Early Parkinson's Disease Detected With Quantitative Magnetic Resonance Measurements

Objective: Parkinson’s disease (PD) is the second most common neurodegenerative disease in the elderly. In early stages of PD, patients typically display normal brain magnet resonance imaging (MRI) in routine screening. Advanced imaging approaches are necessary to discriminate early PD patients from healthy controls. In this study, microstructural changes in relevant brain regions of early PD patients were investigated by using quantitative MRI methods.

Methods: Cerebral MRI at 3T was performed on 20 PD patients in early stages and 20 age and sex matched healthy controls. Brain relative proton density, T1, T2, and T2′ relaxation times were measured in 14 regions of interest (ROIs) in each hemisphere and compared between patients and controls to estimate PD related alterations.

Results: In comparison to matched healthy controls, the PD patients revealed decreased relative proton density in contralateral prefrontal subcortical area, upper and lower pons, in ipsilateral globus pallidus, and bilaterally in splenium corporis callosi, caudate nucleus, putamen, thalamus, and mesencephalon. The T1 relaxation time was increased in contralateral prefrontal subcortical area and centrum semiovale, putamen, nucleus caudatus and mesencephalon, whereas T2 relaxation time was elevated in upper pons bilaterally and in centrum semiovale ipsilaterally. T2′ relaxation time did not show significant changes.

Conclusion: Early Parkinson’s disease is associated with a distinct profile of brain microstructural changes which may relate to clinical symptoms. The quantitative MR method used in this study may be useful in early diagnosis of Parkinson’s disease. Limitations of this study include a small sample size and manual selection of the ROIs. Atlas-based or statistical mapping methods would be an alternative for an objective evaluation. More studies are necessary to validate the measurement methods for clinical use in diagnostics of early Parkinson’s disease.

Injury to dopaminergic neurons development via the Lmx1a/Wnt1 autoregulatory loop induced by simazine

Simazine is a kind of persistent organic pollutant that is detected in both ground and water and has several routes of exposure. Here, we explored the mechanisms underlying simazine-related effects on dopaminergic neurons via development-related factors using mouse embryos and embryonic mesencephalic hybrid cell line (MN9D cells). We treated pregnant mice with 50 μg/kg bw, 200 μg/kg bw simazine from the 0.5 day to the 10.5 day of embryonic phase and MN9D cells with 600 μM simazine for 24 h to research the mechanism of dopaminergic neurons acute respond to simazine through preliminary experiments. Protein expressions of LIM homeobox transcription factor 1-alpha (Lmx1a) and LIM homeobox transcription factor 1-beta (Lmx1b) displayed a dose- and time-dependent increase after the exposure to simazine. In the 200 μg/kg bw of embryos and the 24h-600 μM of MN9D cells, protein levels of dopaminergic developmental factors were significantly upregulated, and dopaminergic function was significantly damaged for the abnormal expression of Dyt5b. We demonstrated simazine induced the injury to dopaminergic neurons via the Lmx1a/wingless-related integration site 1 (Wnt1) and Lmx1b pathways. In the transfection experiments, we knocked down Lmx1a and Lmx1b of cells to verify the potential target of simazine-induced injury to dopaminergic neurons, respectively. We detected the protein and mRNA levels of development-related genes of dopaminergic neurons and intracellular dopamine levels in different treatment groups. Based on our experiments' results, we demonstrated an acute response to 24 h-600 μM simazine treatment, the simazine-induced injury to dopaminergic neuronal which leads to abnormal dopamine levels and dopaminergic impairment is via the activation of the Lmx1a/Wnt1 autoregulatory loop. Lmx1a is a promising target in the search for the mechanisms underlying simazine-induced dopaminergic injury.

Alexithymia Is Associated with Reduced Quality of Life and Increased Caregiver Burden in Parkinson's Disease

Parkinson's disease (PD) is the second most frequent neurodegenerative disease of people who are beyond 50 years of age. People with PD (PwP) suffer from a large variety of motor and non-motor symptoms resulting in reduced health-related quality of life (HR-QoL). In the last two decades, alexithymia was identified as an additional non-motor symptom in PD. Alexithymia is defined as a cognitive affective disturbance resulting in difficulty to identify and distinguish feelings from bodily sensations of emotional arousal. In PD, the frequency of patients suffering of alexithymia is increased compared to healthy controls. The aim of the present study was to determine the relationship of alexithymia to HR-QoL of the PwP and caregiver burden of the corresponding caregiver. This cross-sectional questionnaire-based study used disease specific questionnaires for HR-QoL and caregiver burden. In total 119 PwP and their corresponding caregivers were included in the study. HR-QoL of the PwP correlated significantly with alexithymia (p < 0.001), especially the sub-components "identifying feelings" (p < 0.001) and "difficulties describing feelings" (p = 0.001). Caregiver burden also correlated significantly with PwP alexithymia (p < 0.001). However, caregiver burden was associated with sub-components "identifying feelings" (p < 0.008) and "external oriented thinking" (p < 0.004). These data support the importance of alexithymia as a non-motor symptom in PD.

A review of possible therapies for Parkinson's disease

Parkinson's disease (PD) is a complex condition with a wide range of symptoms, like impaired movement, tremors, apathy and depression, and many other symptoms. The disease results from degeneration of dopaminergic neural cells. No cure at present but symptomatic some palliative treatments are available to slow down the disease progression. According to the Parkinson's Foundation every year in U.S., approximately 60,000 Americans diagnosed with PD. Nearly one million will be living with PD in the U.S. by 2020, which is more than the combined number of people diagnosed with multiple sclerosis, muscular dystrophy and Amyotrophic Lateral Sclerosis (ALS). There is no diagnostic test for PD, yet, but this article will review all kinds symptomatic and disease-modifying therapy.

Possible therapies of Parkinson's disease: A review

Parkinson's disease (PD) is a complex condition with a wide range of symptoms, like impaired movement, tremors, apathy and depression, and many other symptoms. The disease results from degeneration of dopaminergic neural cells. No cure at present but symptomatic some palliative treatments are available to slow down the disease progression. According to the Parkinson's Foundation every year in U.S., approximately 60,000 Americans diagnosed with PD. Nearly one million will be living with PD in the U.S. by 2020, which is more than the combined number of people diagnosed with multiple sclerosis, muscular dystrophy and Amyotrophic Lateral Sclerosis (ALS). There is no diagnostic test for PD, yet, but this article will review all kinds symptomatic and disease-modifying therapy.

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.

TRH Analog, Taltirelin Improves Motor Function of Hemi-PD Rats Without Inducing Dyskinesia via Sustained Dopamine Stimulating Effect

Thyrotropin-releasing hormone (TRH) and its analogs are able to stimulate the release of the endogenic dopamine (DA) in the central nervous system. However, this effect has not been tested in the Parkinson’s disease (PD), which is characterized by the DA deficiency due to the dopaminergic neurons loss in the substantia nigra. Here, we investigated the therapeutic effect of Taltirelin, a long-acting TRH analog on 6-hydroxydopamine-lesioned hemi-Parkinsonian rat model. 1–10 mg/kg Taltirelin i.p. administration significantly improved the locomotor function and halted the electrophysiological abnormities of PD animals without inducing dyskinesia even with high-dose for 7 days treatment. Microdialysis showed that Taltirelin gently and persistently promoted DA release in the cortex and striatum, while L-DOPA induced a sharp rise of DA especially in the cortex. The DA-releasing effect of Taltirelin was alleviated by reserpine, vanoxerine (GBR12909) or AMPT, indicating a mechanism involving vesicular monoamine transporter-2 (VMAT-2), dopamine transporter (DAT) and tyrosine hydroxylase (TH). The in vivo and in vitro experiments further supported that Taltirelin affected the regulation of TH expression in striatal neurons, which was mediated by p-ERK1/2. Together, this study demonstrated that Taltirelin improved motor function of hemi-PD rats without inducing dyskinesia, thus supporting a further exploration of Taltirelin for PD treatment.

CaMKII inhibition ameliorated levodopa-induced dyskinesia by downregulating tyrosine hydroxylase activity in an experimental model of Parkinson's disease

Levodopa (L-dopa) remains the best treatment for Parkinson's disease (PD). However, long-term L-dopa treatment induces dyskinesia. The mechanism of L-dopa-induced dyskinesia (LID) is not fully understood. Enhanced activity of protein kinase A (PKA) and pulsatile dopamine (DA) stimulation plays an important role in LID. Tyrosine hydroxylase (TH) is the rate-limiting enzyme for DA synthesis. Decreased TH activity causes reduced pulsatile DA stimulation, which in turn reduces LID. Moreover, TH is a substrate of CaMKII. However, it is unknown whether inhibition of CaMKII reduces LID by downregulating the activity of TH. In this study, we found that CaMKII antagonist KN-93 reduced DA released in PC12 cells; in the meantime, KN-93 reduced phosphorylated levels of CaMKIIα and TH at Ser 40. Intrastriatal administration of KN-93 reduced LID without affecting the antiparkinsonian effect of L-dopa in PD mice. Mechanistically, KN-93 treatmentreduced phosphorylated CaMKIIα levels and subsequently downregulated phosphorylated TH at Ser 40 expression. Consequently, extracellular DA efflux was reduced andthe activation threshold of the PKA pathway was lowered. Moreover, KN-93 treatment reduced the expression of Arc and Penk, two immediate early genes, induced by chronic L-dopa. These data indicate that inhibition of CaMKIIα decreases LID at least partially by suppressing TH activity and subsequently reducing extracellular DA efflux and the activity of the PKA pathway, suggesting that CaMKIIα may be an alternative target for the treatment of LID.

Dopaminergic Dysfunction in Mammalian Dopamine Neurons Induced by Simazine Neurotoxicity

Many studies have shown that the pollutant simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine), which has been overused, inhibits the proliferation of mammalian dopaminergic cells, and affects the developmental differentiation of mammalian dopaminergic neurons. However, few studies have shown the effects of simazine on dopaminergic metabolism in these cells. Therefore, we aim to examine the metabolic effects of simazine exposure in mouse dopaminergic progenitor neurons (MN9D) at different exposure times. The cells were treated with simazine at 0, 150, 300 and 600 µM for 12, 24 and 48 h, respectively. The content of dopamine in these cells was then examined using the enzyme-linked immunosorbent assay (ELISA) kit. Real-time quantitative polymerase chain reaction (PCR) and western blotting were performed to analyze the mRNA and protein expression of aromatic amino acid decarboxylase (AADC), tyrosine hydroxylase (DYT5b), dopamine transporter (DAT), monoamine vesicular transporter 2 (VMAT2), monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT). The results showed that simazine influenced the metabolism of dopamine and led to a decrease in dopamine level in these cells which may eventually lead to neurological disorders of the dopaminergic system.

Effect on the dopaminergic metabolism induced by oral exposure to simazine during the prepubertal period in rats

The herbicide simazine is widely used in agricultural and non-agricultural fields. Studies have shown that simazine inhibits the proliferation of dopaminergic cells and affects the developmental differentiation of dopamine neurons. However, little is known about the effects of simazine on dopaminergic metabolism. Therefore, the present study examined the effects of simazine on Sprague‑Dawley (SD) rats from weaning to puberty (40 days exposure). Simazine was administered orally to SD rats at doses of 0, 12.5, 50 and 200 mg/kg body weight. The contents of dopamine (DA), levodopa, dihydroxy-phenyl-acetic acid and homovanillic acid in the striatum were then examined by high-performance liquid chromatography with a fluorescence detector. Quantitative polymerase chain reaction and western blotting were used to analyze the mRNA and protein expression of aromatic amino acid decarboxylase (AADC), tyrosine hydroxylase, orphan nuclear hormone (Nurr1), dopamine transporter (DAT), vesicular monoamine transporter 2 (VMAT2), monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT). The results indicated that simazine influenced the synthesis, transport and metabolism of DA and led to a reduction of DA levels in the striatum. One potential underlying mechanism is decreased levels of Nurr1, DAT and VMAT2 impacting upon the transport of DA; another is the decreased level of AADC and increased levels of MAO and COMT impacting upon the synthesis and metabolism of DA. These factors may eventually lead to neurological disorders of the dopaminergic system.

Antidyskinetic Effects of MEK Inhibitor Are Associated with Multiple Neurochemical Alterations in the Striatum of Hemiparkinsonian Rats

L-DOPA-induced dyskinesia (LID) represents one of the major problems of the long-term therapy of patients with Parkinson's disease (PD). Although, the pathophysiologic mechanisms underlying LID are not completely understood, activation of the extracellular signal regulated kinase (ERK) is recognized to play a key role. ERK is phosphorylated by mitogen-activated protein kinase kinase (MEK), and thus MEK inhibitor can prevent ERK activation. Here the effect of the MEK inhibitor PD98059 on LID and the associated molecular changes were examined. Rats with unilateral 6-OHDA lesions of the nigrostriatal pathway received daily L-DOPA treatment for 3 weeks, and abnormal involuntary movements (AIMs) were assessed every other day. PD98059 was injected in the lateral ventricle daily for 12 days starting from day 10 of L-DOPA treatment. Striatal molecular markers of LID were analyzed together with gene regulation using microarray. The administration of PD98059 significantly reduced AIMs. In addition, ERK activation and other associated molecular changes including ΔFosB were reversed in rats treated with the MEK inhibitor. PD98059 induced significant up-regulation of 418 transcripts and down-regulation of 378 transcripts in the striatum. Tyrosine hydroxylase (Th) and aryl hydrocarbon receptor nuclear translocator (Arnt) genes were down-regulated in lesioned animals and up-regulated in L-DOPA-treated animals. Analysis of protein levels showed that PD98059 reduced the striatal TH. These results support the association of p-ERK1/2, ΔFosB, p-H3 to the regulation of TH and ARNT in the mechanisms of LID, and pinpoint other gene regulatory changes, thus providing clues for identifying new targets for LID therapy.

Nutraceuticals against Neurodegeneration: A Mechanistic Insight

The mechanisms underlying neurodegenerative disorders are complex and multifactorial; however, accumulating evidences suggest few common shared pathways. These common pathways include mitochondrial dysfunction, intracellular Ca²⁺ overload, oxidative stress and inflammation. Often multiple pathways co-exist, and therefore limit the benefits of therapeutic interventions. Nutraceuticals have recently gained importance owing to their multifaceted effects. These food-based approaches are believed to target multiple pathways in a slow but more physiological manner without causing severe adverse effects. Available information strongly supports the notion that apart from preventing the onset of neuronal damage, nutraceuticals can potentially attenuate the continued progression of neuronal destruction. In this article, we i) review the common pathways involved in the pathogenesis of the toxicants-induced neurotoxicity and neurodegenerative disorders with special emphasis on Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Multiple sclerosis (MS) and Amyotrophic lateral sclerosis (ALS), and ii) summarize current research advancements on the effects of nutraceuticals against these detrimental pathways.