A multi-faceted genotoxic network of alpha-synuclein in the nucleus and mitochondria of dopaminergic neurons in Parkinson's disease: Emerging concepts and challenges

Relationship among α‑synuclein, aging and inflammation in Parkinson's disease (Review)

Parkinson's disease (PD) is a common neurodegenerative pathology whose major clinical symptoms are movement disorders. The main pathological characteristics of PD are the selective death of dopaminergic (DA) neurons in the pars compacta of the substantia nigra and the presence of Lewy bodies containing α-synuclein (α-Syn) within these neurons. PD is associated with numerous risk factors, including environmental factors, genetic mutations and aging. In many cases, the complex interplay of numerous risk factors leads to the onset of PD. The mutated α-Syn gene, which expresses pathologicalα-Syn protein, can cause PD. Another important feature of PD is neuroinflammation, which is conducive to neuronal death. α-Syn is able to interact with certain cell types in the brain, including through phagocytosis and degradation of α-Syn by glial cells, activation of inflammatory pathways by α-Syn in glial cells, transmission of α-Syn between glial cells and neurons, and interactions between peripheral immune cells and α-Syn. In addition to the aforementioned risk factors, PD may also be associated with aging, as the prevalence of PD increases with advancing age. The aging process impairs the cellular clearance mechanism, which leads to chronic inflammation and the accumulation of intracellular α-Syn, which results in DA neuronal death. In the present review, the age-associated α-Syn pathogenicity and the interactions between α-Syn and certain types of cells within the brain are discussed to facilitate understanding of the mechanisms of PD pathogenesis, which may potentially provide insight for the future clinical treatment of PD.

Targeted protein degradation for the treatment of Parkinson's disease: Advances and future perspective

Parkinson's disease (PD) is a progressive disorder that belongs to a class of neurodegenerative disorders (NDs) called Synucleinopathies. It has characterized by the misfolding and aggregation of a-synuclein. Our understanding of PD continues to evolve, and so does our approach to treatment. including therapies aimed at delaying pathology, quitting neuronal loss, and shortening the course of the disease by selectively targeting essential proteins suspected to play a role in PD pathogenesis. One emerging approach that is generating significant interest is Targeted Protein Degradation (TPD). TPD is an innovative method that allows us to specifically break down certain proteins using specially designed molecules or peptides, like PROteolysis-TArgeting-Chimera (PROTACs). This approach holds great promise, particularly in the context of NDs. In this review, we will briefly explain PD and its pathogenesis, followed by discussing protein degradation systems and TPD strategy in PD by reviewing synthesized small molecules and peptides. Finally, future perspectives and challenges in the field are discussed.

α-synuclein promotes neuronal dysfunction and death by disrupting the binding of ankyrin to ß-spectrin

α-synuclein plays a key role in the pathogenesis of Parkinson's disease and related disorders, but critical interacting partners and molecular mechanisms mediating neurotoxicity are incompletely understood. We show that α-synuclein binds directly to ß-spectrin. Using males and females in a Drosophila model of α-synuclein-related disorders we demonstrate that ß-spectrin is critical for α-synuclein neurotoxicity. Further, the ankyrin binding domain of ß-spectrin is required for α-synuclein binding and neurotoxicity. A key plasma membrane target of ankyrin, Na+/K+ ATPase, is mislocalized when human α-synuclein is expressed in Drosophila. Accordingly, membrane potential is depolarized in α-synuclein transgenic fly brains. We examine the same pathway in human neurons and find that Parkinson's disease patient-derived neurons with a triplication of the α-synuclein locus show disruption of the spectrin cytoskeleton, mislocalization of ankyrin and Na+/K+ ATPase, and membrane potential depolarization. Our findings define a specific molecular mechanism by which elevated levels of α-synuclein in Parkinson's disease and related α-synucleinopathies leads to neuronal dysfunction and death.

α-Synuclein Promotes Neuronal Dysfunction and Death by Disrupting the Binding of Ankyrin to β-Spectrin

α-Synuclein plays a key role in the pathogenesis of Parkinson's disease and related disorders, but critical interacting partners and molecular mechanisms mediating neurotoxicity are incompletely understood. We show that α-synuclein binds directly to β-spectrin. Using males and females in a Drosophila model of α-synuclein-related disorders, we demonstrate that β-spectrin is critical for α-synuclein neurotoxicity. Further, the ankyrin binding domain of β-spectrin is required for α-synuclein binding and neurotoxicity. A key plasma membrane target of ankyrin, Na+/K+ ATPase, is mislocalized when human α-synuclein is expressed in Drosophila Accordingly, membrane potential is depolarized in α-synuclein transgenic fly brains. We examine the same pathway in human neurons and find that Parkinson's disease patient-derived neurons with a triplication of the α-synuclein locus show disruption of the spectrin cytoskeleton, mislocalization of ankyrin and Na+/K+ ATPase, and membrane potential depolarization. Our findings define a specific molecular mechanism by which elevated levels of α-synuclein in Parkinson's disease and related α-synucleinopathies lead to neuronal dysfunction and death.SIGNIFICANCE STATEMENT The small synaptic vesicle associate protein α-synuclein plays a critical role in the pathogenesis of Parkinson's disease and related disorders, but the disease-relevant binding partners of α-synuclein and proximate pathways critical for neurotoxicity require further definition. We show that α-synuclein binds directly to β-spectrin, a key cytoskeletal protein required for localization of plasma membrane proteins and maintenance of neuronal viability. Binding of α-synuclein to β-spectrin alters the organization of the spectrin-ankyrin complex, which is critical for localization and function of integral membrane proteins, including Na+/K+ ATPase. These finding outline a previously undescribed mechanism of α-synuclein neurotoxicity and thus suggest potential new therapeutic approaches in Parkinson's disease and related disorders.

α-Synuclein and Mechanisms of Epigenetic Regulation

Synucleinopathies are a group of neurodegenerative diseases with common pathological lesions associated with the excessive accumulation and abnormal intracellular deposition of toxic species of α-synuclein. The shared clinical features are chronic progressive decline of motor, cognitive, and behavioral functions. These disorders include Parkinson's disease, dementia with Lewy body, and multiple system atrophy. Vigorous research in the mechanisms of pathology of these illnesses is currently under way to find disease-modifying treatment and molecular markers for early diagnosis. α-Synuclein is a prone-to-aggregate, small amyloidogenic protein with multiple roles in synaptic vesicle trafficking, neurotransmitter release, and intracellular signaling events. Its expression is controlled by several mechanisms, one of which is epigenetic regulation. When transmitted to the nucleus, α-synuclein binds to DNA and histones and participates in epigenetic regulatory functions controlling specific gene transcription. Here, we discuss the various aspects of α-synuclein involvement in epigenetic regulation in health and diseases.

Rosmarinic Acid Inhibits Mitochondrial Damage by Alleviating Unfolded Protein Response

Mitochondria are essential organelles that perform important roles in cell biologies such as ATP synthesis, metabolic regulation, immunomodulatory, and apoptosis. Parkinson’s disease (PD) is connected with mitochondrial neuronal damage related to mitochondrial unfolded protein response (mtUPR). Rosmarinic acid (RA) is a naturally occurring hydroxylated polyphenolic chemical found in the Boraginaceae and the Labiatae subfamily Nepetoideae. This study looked into RA’s protective effect against mitochondrial loss in the substantia nigra (SN) caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), the underlying mechanism associated with the mtUPR. Pretreatment with RA reduced motor impairments and dopaminergic neuronal degeneration in the SN of a mouse model injected with MPTP. Pretreatment of SH-SY5Y cells from cell viability loss, morphological damage, and oxidative stress. Furthermore, RA pre-injection suppressed MPTP-induced mtUPR, lowered the expression of HSPA9, HSPE1, CLPP, LONP1, and SIRT 4, and protected the MPTP-mice and SH-SY5Y cells from mitochondrial failure. These findings imply that RA can prevent Parkinson’s disease by preventing mitochondrial damage in dopaminergic neurons in Parkinson’s disease via alleviating mitochondrial unfolded protein response.

Insights into the inhibitory mechanism of skullcapflavone II against α-synuclein aggregation and its mediated cytotoxicity

The dangerous self-assembled and infectious seeds of α-synuclein (αSN) play primary roles in Parkinson's disease. Accordingly, the inhibition of αSN fibrillation and elimination of toxic aggregates are the main therapeutic strategies. Skullcapflavone II (S.FII), a compound isolated from S. pinnatifida, has shown multiple neuroprotective features. Herein, we demonstrated that S.FII inhibited αSN aggregation with IC50 of 7.2 μM. It increased nucleation time and decreased fibril elongation rate and the species formed in the presence of S.FII were unable to act as seeds. Additionally, S.FII inhibited both secondary nucleation and seeding of αSN and disaggregated the mature preformed fibrils as well. The species formed in the presence of S.FII showed less toxicity. It also preserved neurite length and dopamine content of SH-SY5Y cells and attenuated the inflammatory responses in mixed glial cells. The Localized Surface Plasmon Resonance (LSPR) analysis indicated that S.FII interacts with αSN. Docking simulation studies on αSN fibrils revealed that S.FII could interact with the key residues of the salt bridges and glutamine ladder, which might lead to the destruction of fibril's structures. We also showed that S.FII passes through the blood-brain barrier in vitro and in vivo. Overall, these findings elucidate the neuroprotective roles of S.FII in reducing αSN pathogenicity.

α-Synuclein in Parkinson's disease and advances in detection

Parkinson's disease (PD) is a threatening neurodegenerative disorder that seriously affects patients' life quality. Substantial evidence links the overexpression and abnormal aggregation of alpha-synuclein (α-Syn) to PD. α-Syn has been identified as a characteristic biomarker of PD, which indicates its great value of diagnosis and designing effective therapeutic strategy. This article systematically summarizes the pathogenic process of α-Syn based on recent researches, outlines and compares commonly used analysis and detection technologies of α-Syn. Specifically, the detection of α-Syn by new electrochemical, photochemical, and crystal biosensors is mainly examined. Furthermore, the speculation of future study orientation is discussed, which provides reference for the further research and application of α-Syn as biomarker.

Roflupram attenuates α-synuclein-induced cytotoxicity and promotes the mitochondrial translocation of Parkin in SH-SY5Y cells overexpressing A53T mutant α-synuclein

We have previously shown that inhibition of cAMP-specific 3',5'-cyclic phosphodiesterase 4 (PDE4) protects against cellular toxicity in neuronal cells. Since α-synuclein (α-syn) toxicity contributes to the neurodegeneration of Parkinson's disease (PD). The aim of this study was to explore the effects and mechanisms of PDE4 on α-syn-induced neuronal toxicity. Using mutant human A53T α-syn overexpressed SH-SY5Y cells, we found that PDE4B knockdown reduced cellular apoptosis. Roflupram (ROF, 20 μM), a selective PDE4 inhibitor, produced similar protective effects and restored the morphological alterations of mitochondria. Mechanistic studies identified that α-syn enhanced the phosphorylation of Parkin at Ser131, followed by the decreased mitochondrial translocation of Parkin. Whereas both PDE4B knockdown and PDE4 inhibition by ROF blocked the effects of α-syn on Parkin phosphorylation and mitochondrial translocation. Moreover, PDE4 inhibition reversed the increase in the phosphorylation of p38 mitogen-activated protein kinase (MAPK) induced by α-syn. ROF treatment also reduced the binding of p38 MAPK to Parkin. Consistently, overexpression of PDE4B blocked the roles of ROF on p38 MAPK phosphorylation, Parkin phosphorylation, and the subsequent mitochondrial translocation of parkin. Furthermore, PDE4B overexpression attenuated the protective role of ROF, as evidenced by reduced mitochondria membrane potential and increased cellular apoptosis. Interestingly, ROF failed to suppress α-syn-induced cytotoxicity in the presence of a protein kinase A (PKA) inhibitor H-89. Our findings indicate that PDE4 facilitates α-syn-induced cytotoxicity via the PKA/p38 MAPK/Parkin pathway in SH-SY5Y cells overexpressing A53T mutant α-synuclein. PDE4 inhibition by ROF is a promising strategy for the prevention and treatment of α-syn-induced neurodegeneration.

Complex modulation of cytokine-induced α-synuclein aggregation by glypican-1-derived heparan sulfate in neural cells

In Parkinson’s disease (PD), there is accumulation of α-synuclein (SYN) aggregates in neurons, which is promoted by neuroinflammation. The cytokines TNF-α, IL-1β and IL-6 induce accumulation of degradation products of the amyloid precursor protein (APP) combined with heparan sulfate (HS) chains released from glypican-1 (Gpc-1) by NO-dependent cleavage. We have investigated the effects of the cytokines and HS on SYN aggregation and secretion in dividing human neuroblastoma (SH-SY5Y) and inducible neural progenitor cells (NPC) by using immunofluorescence microscopy, vesicle isolation and slot blotting with antibodies recognizing SYN monomers and aggregates, Gpc-1, the released HS, endosomes, and autophagosomes. In SH-SY5Y cells, the capacity to release HS was fully utilized, while NPC displayed dormant capacity. TNF-α induced increased formation of SYN aggregates and clustering of HS in SH-SY5Y cells. When the supply of NO was simultaneously increased, SYN and HS accumulation disappeared. When NO formation was inhibited, SYN and HS aggregation also disappeared, but there was now a 4-fold increase in SYN secretion. In NPC, IL-6 induced increased aggregation of SYN and stimulated HS release from Gpc-1. Both SYN and HS co-localized with autophagosome marker. When HS-deficient Gpc-1 was simultaneously generated, by using a cyanobacterial neurotoxin, accumulation diminished and there was massive secretion of SYN. We suggest that the cytokines increase APP processing, which initiates NO-dependent release of HS from Gpc-1. The APP degradation products also trigger SYN aggregation. As HS can inhibit APP processing, HS- or NO-deficiency may result in autophagosomal dysfunction and both APP degradation products and SYN are secreted.

Oral Administration of Silibinin Ameliorates Cognitive Deficits of Parkinson's Disease Mouse Model by Restoring Mitochondrial Disorders in Hippocampus

Besides motor disorder, cognitive dysfunction is also common in Parkinson's disease (PD). Essentially no causal therapy for cognitive dysfunction of PD exists at present. In this study, a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD was used to analyze the neuroprotective potential of orally administered silibinin, a proverbial hepatoprotective flavonoid derived from the herb milk thistle (Silybum marianum). Results demonstrated that silibinin administration significantly attenuated MPTP-induced cognitive impairment in behavioral tests. Nissl staining results showed that MPTP injection significantly increases the loss of neurons in the hippocampus. However, these mice were protected by oral administration of silibinin, accompanying reduction in the cell apoptosis in the hippocampus. The hippocampal aggregates of α-synuclein (α-syn) appeared in MPTP-injected mice, but were significantly decreased by silibinin treatment. MPTP injection induced oxidative stress, as evidenced by increased malondialdehyde (MDA) and decreased superoxide dismutase (SOD). The oxidative stress was alleviated by silibinin treatment. Mitochondrial disorder including the decline of mitochondrial membrane potential (MMP) was another signature in the hippocampus of MPTP-treated mice, accompanying increased mitochondrial fission and decreased fusion. Silibinin administration restored these mitochondrial disorders, as expected for the protection against MPTP injury. These findings suggest that silibinin has a potential to be further developed as a therapeutic candidate for cognitive dysfunction in PD.

Blood-Derived α-Synuclein Aggregated in the Substantia Nigra of Parabiotic Mice

As a pathological biomarker of Parkinson’s disease, α-synuclein is thought to be a prion-like protein, but evidence for the transmission of α-synuclein from blood to the brain is unclear. The goals of this study were to determine whether blood-derived α-synuclein could enter the brains of mice and whether α-synuclein in the brain could be cleared by parabiosis. Heterochronic parabiosis was performed on SNCA^A53T transgenic mice (A53T mice) and wildtype mice. The levels of human α-synuclein in the blood and substantia nigra of wildtype mice were significantly increased after 4-month parabiosis with A53T mice. Moreover, the expression of α-synuclein filament, but not of total α-synuclein, was significantly increased in the substantia nigra of wildtype mice that were paired with A53T mice. However, the levels of human α-synuclein displayed no significant change in the serum, blood, or substantia nigra of A53T mice. These results provide direct evidence that pathological α-synuclein can be transmitted from blood to the brain in the heterochronic parabiosis system; however, it appears to be difficult to clear it from the brain in a short period of time.

Fatal attraction - The role of hypoxia when alpha-synuclein gets intimate with mitochondria

Alpha-synuclein aggregation and mitochondrial dysfunction are main pathological hallmarks of Parkinson's disease (PD) and several other neurodegenerative diseases, collectively known as synucleinopathies. However, increasing evidence suggests that they may not be sufficient to cause PD. Here we propose the role of hypoxia as a missing link that connects the complex interplay between alpha-synuclein biochemistry and pathology, mitochondrial dysfunctions and neurodegeneration in PD. We review the partly conflicting literature on alpha-synuclein binding to membranes and mitochondria and its impact on mitochondrial functions. From there, we focus on adverse changes in cellular environments, revolving around hypoxic stress, that may trigger or facilitate PD progression. Inter-dependent structural re-arrangements of mitochondrial membranes, including increased cytoplasmic exposure of mitochondrial cardiolipins and changes in alpha-synuclein localization and conformation are discussed consequences of such conditions. Enhancing cellular resilience could be an integral part of future combination-based therapies of PD. This may be achieved by boosting the capacity of cellular and specifically mitochondrial processes to regulate and adapt to altered proteostasis, redox, and inflammatory conditions and by inducing protective molecular and tissue re-modelling.

Molecular insights into α-synuclein interaction with individual human core histones, linker histone, and dsDNA

α-Synuclein (αS) plays a key role in Parkinson's disease (PD). The αS nuclear role, its binding affinity and specificity to histones and dsDNA remains unknown. Here, we have measured the binding affinity ( K d ) between αS wild-type (wt) and PD-specific αS S129-phosphorylation mimicking (S129E) mutant with full-length and flexible tail truncated individual core histones (H2a, H2b, H3, and H4), linker histone (H1), and carried out αS-dsDNA interaction studies. This study revealed that αS(wt) interacts specifically with N-terminal flexible tails of histone H3, H4, and flexible tails of H1. The αS(S129E) mutant recognizes histones similar to αS(wt) but binds with higher affinity. Intriguingly, αS(S129E) showed a binding affinity for control proteins (bovine serum albumin and lysozyme), while no interaction was seen for αS(wt). Based on our above observation, we contemplate that the physio-chemical properties of αS with S129-phosphorylation has changed compared to αS(wt), resulting in interaction for other proteins, which is the basis for Lewy body formation. Besides, this study showed αS binding to dsDNA is weak and nonspecific. Overall, αS specificity for histone binding suggests that its nuclear role is possibly driven through histone interaction.

Role of Hydrazine-Related Chemicals in Cancer and Neurodegenerative Disease

Hydrazine-related chemicals (HRCs) with carcinogenic and neurotoxic potential are found in certain mushrooms and plants used for food and in products employed in various industries, including aerospace. Their propensity to induce DNA damage (mostly O⁶-, N⁷- and 8-oxo-guanine lesions) resulting in multiple downstream effects is linked with both cancer and neurological disease. For cycling cells, unrepaired DNA damage leads to mutation and uncontrolled mitosis. By contrast, postmitotic neurons attempt to re-enter the cell cycle but undergo apoptosis or nonapoptotic cell death. Biomarkers of exposure to HRCs can be used to explore whether these substances are risk factors for sporadic amyotrophic laterals sclerosis and other noninherited neurodegenerative diseases, which is the focus of this paper.

Roles for α-Synuclein in Gene Expression

α-Synuclein (α-Syn) is a small cytosolic protein associated with a range of cellular compartments, including synaptic vesicles, the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. In addition to its physiological role in regulating presynaptic function, the protein plays a central role in both sporadic and familial Parkinson’s disease (PD) via a gain-of-function mechanism. Because of this, several recent strategies propose to decrease α-Syn levels in PD patients. While these therapies may offer breakthroughs in PD management, the normal functions of α-Syn and potential side effects of its depletion require careful evaluation. Here, we review recent evidence on physiological and pathological roles of α-Syn in regulating activity-dependent signal transduction and gene expression pathways that play fundamental role in synaptic plasticity.

Silibinin attenuates motor dysfunction in a mouse model of Parkinson's disease by suppression of oxidative stress and neuroinflammation along with promotion of mitophagy

Silybum marianum (L.) Gaertn has been widely used to obtain a drug for the treatment of hepatic diseases. Silibinin (silybin), a flavonoid extracted and isolated from the fruit of S. marianumis investigated in our study to explore its motor protective potential on Parkinson's disease (PD) model mice induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). PD is a neurodegenerative disease that causes a debilitating movement disorder, characterized by a progressive loss of nigrostriatal (substantia nigra and striatum) dopaminergic neurons. Several studies have proven that neurodegeneration is aggravated by neuroinflammation, oxidative stress and/or the presence of α-synuclein (α-syn) aggregation. Essentially no causal therapy for PD exists at present. Our results demonstrate that silibinin significantly attenuates MPTP-induced movement disorder in behavioral tests. Immunohistochemical analysis shows that MPTP injection results in the loss of dopaminergic neurons in the substantia nigra, and the decrease of the striatal tyrosine hydroxylase. However, MPTP-injected mice were protected against dopaminergic neuronal loss by oral administration of silibinin (280 mg/kg) that increased expressions of PTEN-induced putative kinase 1 (PINK1) and Parkin, suggesting mitophagy activation. The neuroprotective mechanism of silibinin involves not only reduction of mitochondrial damage by repressing proinflammatory response and α-syn aggregation, but also enhancement of oxidative defense system. Namely, protection of dopaminergic nerves is due to promotion of mitophagy, leading to clearance of the toxic effects of damaged mitochondria. These findings suggest that silibinin has a potential to be further developed as a therapeutic candidate for PD.

α-Synuclein A53T Binds to Transcriptional Adapter 2-Alpha and Blocks Histone H3 Acetylation

α-Synuclein (α-syn) is a hallmark amyloidogenic protein component of Lewy bodies in dopaminergic neurons affected by Parkinson’s disease (PD). Despite the multi-faceted gene regulation of α-syn in the nucleus, the mechanism underlying α-syn crosstalk in chromatin remodeling in PD pathogenesis remains elusive. Here, we identified transcriptional adapter 2-alpha (TADA2a) as a novel binding partner of α-syn using the BioID system. TADA2a is a component of the p300/CBP-associated factor and is related to histone H3/H4 acetylation. We found that α-syn A53T was more preferentially localized in the nucleus than the α-syn wild-type (WT), leading to a stronger disturbance of TADA2a. Indeed, α-syn A53T significantly reduced the level of histone H3 acetylation in SH-SY5Y cells; its reduction was also evident in the striatum (STR) and substantia nigra (SN) of mice that were stereotaxically injected with α-syn preformed fibrils (PFFs). Interestingly, α-syn PFF injection resulted in a decrease in TADA2a in the STR and SN of α-syn PFF-injected mice. Furthermore, the levels of TADA2a and acetylated histone H3 were significantly decreased in the SN of patients with PD. Therefore, histone modification through α-syn A53T-TADA2a interaction may be associated with α-syn-mediated neurotoxicity in PD pathology.

Mechanisms of Neurodegeneration in Various Forms of Parkinsonism-Similarities and Differences

Parkinson’s disease (PD), dementia with Lewy body (DLB), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and multiple system atrophy (MSA) belong to a group of neurodegenerative diseases called parkinsonian syndromes. They share several clinical, neuropathological and genetic features. Neurodegenerative diseases are characterized by the progressive dysfunction of specific populations of neurons, determining clinical presentation. Neuronal loss is associated with extra- and intracellular accumulation of misfolded proteins. The parkinsonian diseases affect distinct areas of the brain. PD and MSA belong to a group of synucleinopathies that are characterized by the presence of fibrillary aggregates of α-synuclein protein in the cytoplasm of selected populations of neurons and glial cells. PSP is a tauopathy associated with the pathological aggregation of the microtubule associated tau protein. Although PD is common in the world’s aging population and has been extensively studied, the exact mechanisms of the neurodegeneration are still not fully understood. Growing evidence indicates that parkinsonian disorders to some extent share a genetic background, with two key components identified so far: the microtubule associated tau protein gene (MAPT) and the α-synuclein gene (SNCA). The main pathways of parkinsonian neurodegeneration described in the literature are the protein and mitochondrial pathways. The factors that lead to neurodegeneration are primarily environmental toxins, inflammatory factors, oxidative stress and traumatic brain injury.

Dopamine, Alpha-Synuclein, and Mitochondrial Dysfunctions in Parkinsonian Eyes

Parkinson’s disease (PD) is characterized by motor dysfunctions including bradykinesia, tremor at rest and motor instability. These symptoms are associated with the progressive degeneration of dopaminergic neurons originating in the substantia nigra pars compacta and projecting to the corpus striatum, and by accumulation of cytoplasmic inclusions mainly consisting of aggregated alpha-synuclein, called Lewy bodies. PD is a complex, multifactorial disorder and its pathogenesis involves multiple pathways and mechanisms such as α-synuclein proteostasis, mitochondrial function, oxidative stress, calcium homeostasis, axonal transport, and neuroinflammation. Motor symptoms manifest when there is already an extensive dopamine denervation. There is therefore an urgent need for early biomarkers to apply disease-modifying therapeutic strategies. Visual defects and retinal abnormalities, including decreased visual acuity, abnormal spatial contrast sensitivity, color vision defects, or deficits in more complex visual tasks are present in the majority of PD patients. They are being considered for early diagnosis together with retinal imaging techniques are being considered as non-invasive biomarkers for PD. Dopaminergic cells can be found in the retina in a subpopulation of amacrine cells; however, the molecular mechanisms leading to visual deficits observed in PD patients are still largely unknown. This review provides a comprehensive analysis of the retinal abnormalities observed in PD patients and animal models and of the molecular mechanisms underlying neurodegeneration in parkinsonian eyes. We will review the role of α-synuclein aggregates in the retina pathology and/or in the onset of visual symptoms in PD suggesting that α-synuclein aggregates are harmful for the retina as well as for the brain. Moreover, we will summarize experimental evidence suggesting that the optic nerve pathology observed in PD resembles that seen in mitochondrial optic neuropathies highlighting the possible involvement of mitochondrial abnormalities in the development of PD visual defects. We finally propose that the eye may be considered as a complementary experimental model to identify possible novel disease’ pathways or to test novel therapeutic approaches for PD.

Ethionine Suppresses Mitochondria Autophagy and Induces Apoptosis via Activation of Reactive Oxygen Species in Neural Tube Defects

Abnormal development of central nervous system (CNS) caused by neural tube defects (NTDs) is not only remained the major contributor in the prevalence of stillbirths and neonatal deaths, but also represents a significant cause of lifelong physical disability in the surviving infants. Ethionine is a non-proteinogenic amino acid and antagonist of methionine. Methionine cycle is essential for the elimination of reactive oxygen species (ROS), while lysosomes are involved in the initiation of autophagy. However, its role in ethionine-induced cell death in neural tube defects, still need to be explored. In this study, we investigated the effect of ethionine on NTDs as well as the underlying mechanism involved in this process. Following the establishment of NTDs model using ethionine-induced C57BL/6 mice, ethionine was intraperitoneally injected at a dose of 500 mg/kg in E7.5. Our study revealed that ethionine has induced mitochondrial apoptosis in NTDs by reducing mitochondrial autophagy both in vivo and in vitro. These results provided a possible molecular mechanism for redox regulation of autophagic process.