Phosphorylation of the aggregate-forming protein alpha-synuclein on serine-129 inhibits its DNA-bending properties

Physiological roles of α-synuclein serine-129 phosphorylation - not an oxymoron

α-Synuclein (αS) is an abundant presynaptic protein that regulates neurotransmission. It is also a key protein implicated in a broad class of neurodegenerative disorders termed synucleinopathies, including Parkinson's disease (PD) and Lewy body dementia (LBD). Pathological αS deposits in these diseases, Lewy bodies (LBs)/neurites (LNs), contain about 90% of αS in its phospho-serine129 (pS129) form. Therefore, pS129 is widely used as a surrogate marker of pathology. However, recent findings demonstrate that pS129 is also physiologically triggered by neuronal activity to positively regulate synaptic transmission. In this opinion article, we contrast the literature on pathological and physiological pS129, with a special focus on the latter. We emphasize that pS129 is ambiguous and knowledge about the context is necessary to correctly interpret changes in pS129.

Introducing the Role of Genotoxicity in Neurodegenerative Diseases and Neuropsychiatric Disorders

Decades of research have identified genetic and environmental factors involved in age-related neurodegenerative diseases and, to a lesser extent, neuropsychiatric disorders. Genomic instability, i.e., the loss of genome integrity, is a common feature among both neurodegenerative (mayo-trophic lateral sclerosis, Parkinson's disease, Alzheimer's disease) and psychiatric (schizophrenia, autism, bipolar depression) disorders. Genomic instability is associated with the accumulation of persistent DNA damage and the activation of DNA damage response (DDR) pathways, as well as pathologic neuronal cell loss or senescence. Typically, DDR signaling ensures that genomic and proteomic homeostasis are maintained in both dividing cells, including neural progenitors, and post-mitotic neurons. However, dysregulation of these protective responses, in part due to aging or environmental insults, contributes to the progressive development of neurodegenerative and/or psychiatric disorders. In this Special Issue, we introduce and highlight the overlap between neurodegenerative diseases and neuropsychiatric disorders, as well as the emerging clinical, genomic, and molecular evidence for the contributions of DNA damage and aberrant DNA repair. Our goal is to illuminate the importance of this subject to uncover possible treatment and prevention strategies for relevant devastating brain diseases.

Positron Emission Tomography with [18F]ROStrace Reveals Progressive Elevations in Oxidative Stress in a Mouse Model of Alpha-Synucleinopathy

The synucleinopathies are a diverse group of neurodegenerative disorders characterized by the accumulation of aggregated alpha-synuclein (aSyn) in vulnerable populations of brain cells. Oxidative stress is both a cause and a consequence of aSyn aggregation in the synucleinopathies; however, noninvasive methods for detecting oxidative stress in living animals have proven elusive. In this study, we used the reactive oxygen species (ROS)-sensitive positron emission tomography (PET) radiotracer [18F]ROStrace to detect increases in oxidative stress in the widely-used A53T mouse model of synucleinopathy. A53T-specific elevations in [18F]ROStrace signal emerged at a relatively early age (6-8 months) and became more widespread within the brain over time, a pattern which paralleled the progressive development of aSyn pathology and oxidative damage in A53T brain tissue. Systemic administration of lipopolysaccharide (LPS) also caused rapid and long-lasting elevations in [18F]ROStrace signal in A53T mice, suggesting that chronic, aSyn-associated oxidative stress may render these animals more vulnerable to further inflammatory insult. Collectively, these results provide novel evidence that oxidative stress is an early and chronic process during the development of synucleinopathy and suggest that PET imaging with [18F]ROStrace holds promise as a means of detecting aSyn-associated oxidative stress noninvasively.

Alpha-synuclein regulates the repair of genomic DNA double-strand breaks in a DNA-PKcs-dependent manner

α-synuclein (αSyn) is a presynaptic and nuclear protein that aggregates in important neurodegenerative diseases such as Parkinson's Disease (PD), Parkinson's Disease Dementia (PDD) and Lewy Body Dementia (LBD). Our past work suggests that nuclear αSyn may regulate forms of DNA double-strand break (DSB) repair in HAP1 cells after DNA damage induction with the chemotherapeutic agent bleomycin1. Here, we report that genetic deletion of αSyn specifically impairs the non-homologous end-joining (NHEJ) pathway of DSB repair using an extrachromosomal plasmid-based repair assay in HAP1 cells. Importantly, induction of a single DSB at a precise genomic location using a CRISPR/Cas9 lentiviral approach also showed the importance of αSyn in regulating NHEJ in HAP1 cells and primary mouse cortical neuron cultures. This modulation of DSB repair is dependent on the activity of the DNA damage response signaling kinase DNA-PKcs, since the effect of αSyn loss-of-function is reversed by DNA-PKcs inhibition. Using in vivo multiphoton imaging in mouse cortex after induction of αSyn pathology, we find an increase in longitudinal cell survival of inclusion-bearing neurons after Polo-like kinase (PLK) inhibition, which is associated with an increase in the amount of aggregated αSyn within inclusions. Together, these findings suggest that αSyn plays an important physiologic role in regulating DSB repair in both a transformed cell line and in primary cortical neurons. Loss of this nuclear function may contribute to the neuronal genomic instability detected in PD, PDD and DLB and points to DNA-PKcs and PLK as potential therapeutic targets.

Identification of histone acetylation modification sites in the striatum of subchronically manganese-exposed rats

Aim: To explore the specific histone acetylation sites and oxidative stress-related genes that are associated with the pathogenesis of manganese toxicity. Methods: We employed liquid chromatography-tandem mass spectrometry and bioinformatics analysis to identify acetylated proteins in the striatum of subchronic manganese-intoxicated rats. Results: We identified a total of 12 differentially modified histone acetylation sites: H3K9ac, H3K14ac, H3K18ac, H3K56ac and H3K79ac were upregulated and H3K27ac, H3K36ac, H4K91ac, H4K79ac, H4K31ac, H2BK16ac and H2BK20ac were downregulated. Additionally, we found that CAT, SOD1 and SOD2 might be epigenetically regulated and involved in the pathogenesis of manganism. Conclusion: This study identified histone acetylation sites and oxidative stress-related genes associated with the pathogenesis of manganese toxicity, and these findings are useful in the search for potential epigenetic targets for manganese toxicity.

Unraveling the Complex Interplay between Alpha-Synuclein and Epigenetic Modification

Alpha-synuclein (αS) is a small, presynaptic neuronal protein encoded by the SNCA gene. Point mutations and gene multiplication of SNCA cause rare familial forms of Parkinson’s disease (PD). Misfolded αS is cytotoxic and is a component of Lewy bodies, which are a pathological hallmark of PD. Because SNCA multiplication is sufficient to cause full-blown PD, gene dosage likely has a strong impact on pathogenesis. In sporadic PD, increased SNCA expression resulting from a minor genetic background and various environmental factors may contribute to pathogenesis in a complementary manner. With respect to genetic background, several risk loci neighboring the SNCA gene have been identified, and epigenetic alterations, such as CpG methylation and regulatory histone marks, are considered important factors. These alterations synergistically upregulate αS expression and some post-translational modifications of αS facilitate its translocation to the nucleus. Nuclear αS interacts with DNA, histones, and their modifiers to alter epigenetic status; thereby, influencing the stability of neuronal function. Epigenetic changes do not affect the gene itself but can provide an appropriate transcriptional response for neuronal survival through DNA methylation or histone modifications. As a new approach, publicly available RNA sequencing datasets from human midbrain-like organoids may be used to compare transcriptional responses through epigenetic alterations. This informatic approach combined with the vast amount of transcriptomics data will lead to the discovery of novel pathways for the development of disease-modifying therapies for PD.

Targeting α-synuclein post-translational modifications in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the progressive loss of dopaminergic neurons in the nigrostriatal pathway. Although the exact mechanisms underlying PD are still not completely understood, it is well accepted that α-synuclein plays key pathophysiological roles as the main constituent of the cytoplasmic inclusions known as Lewy bodies. Several post-translational modifications (PTMs), such as the best-known phosphorylation, target α-synuclein and are thus implicated in its physiological and pathological functions. In this review, we present (1) an overview of the pathophysiological roles of α-synuclein, (2) a descriptive analysis of α-synuclein PTMs, including phosphorylation, ubiquitination, SUMOylation, acetylation, glycation, truncation, and O-GlcNAcylation, as well as (3) a brief summary on α-synuclein PTMs as potential biomarkers for PD. A better understanding of α-synuclein PTMs is of paramount importance for elucidating the mechanisms underlying PD and can thus be expected to improve early detection and monitoring disease progression, as well as identify promising new therapeutic targets.

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.

α-synucleinopathy exerts sex-dimorphic effects on the multipurpose DNA repair/redox protein APE1 in mice and humans

Lewy body disorders are characterized by oxidative damage to DNA and inclusions rich in aggregated forms of α-synuclein. Among other roles, apurinic/apyrimidinic endonuclease 1 (APE1) repairs oxidative DNA damage, and APE1 polymorphisms have been linked to cases of Lewy body disorders. However, the link between APE1 and α-synuclein is unexplored. We report that knockdown or inhibition of APE1 amplified inclusion formation in primary hippocampal cultures challenged with preformed α-synuclein fibrils. Fibril infusions into the mouse olfactory bulb/anterior olfactory nucleus (OB/AON) elicited a modest decrease in APE1 expression in the brains of male mice but an increase in females. Similarly, men with Lewy body disorders displayed lower APE1 expression in the OB and amygdala compared to women. Preformed fibril infusions of the mouse OB/AON induced more robust base excision repair of DNA lesions in females than males. No fibril-mediated loss of APE1 expression was observed in male mice when the antioxidant N-acetylcysteine was added to their diet. These findings reveal a potential sex-biased link between α-synucleinopathy and APE1 in mice and humans. Further studies are warranted to determine how this multifunctional protein modifies α-synuclein inclusions and, conversely, how α-synucleinopathy and biological sex interact to modify APE1.

An Adaptive Role for DNA Double-Strand Breaks in Hippocampus-Dependent Learning and Memory

DNA double-strand breaks (DSBs), classified as the most harmful type of DNA damage based on the complexity of repair, lead to apoptosis or tumorigenesis. In aging, DNA damage increases and DNA repair decreases. This is exacerbated in disease, as post-mortem tissue from patients diagnosed with mild cognitive impairment (MCI) or Alzheimer's disease (AD) show increased DSBs. A novel role for DSBs in immediate early gene (IEG) expression, learning, and memory has been suggested. Inducing neuronal activity leads to increases in DSBs and upregulation of IEGs, while increasing DSBs and inhibiting DSB repair impairs long-term memory and alters IEG expression. Consistent with this pattern, mice carrying dominant AD mutations have increased baseline DSBs, and impaired DSB repair is observed. These data suggest an adaptive role for DSBs in the central nervous system and dysregulation of DSBs and/or repair might drive age-related cognitive decline (ACD), MCI, and AD. In this review, we discuss the adaptive role of DSBs in hippocampus-dependent learning, memory, and IEG expression. We summarize IEGs, the history of DSBs, and DSBs in synaptic plasticity, aging, and AD. DSBs likely have adaptive functions in the brain, and even subtle alterations in their formation and repair could alter IEGs, learning, and memory.

ATP13A2 Declines Zinc-Induced Accumulation of α-Synuclein in a Parkinson’s Disease Model

Parkinson’s disease (PD) is characterized by the presence of Lewy bodies caused by α-synuclein. The imbalance of zinc homeostasis is a major cause of PD, promoting α-synuclein accumulation. ATP13A2, a transporter found in acidic vesicles, plays an important role in Zn²⁺ homeostasis and is highly expressed in Lewy bodies in PD-surviving neurons. ATP13A2 is involved in the transport of zinc ions in lysosomes and exosomes and inhibits the aggregation of α-synuclein. However, the potential mechanism underlying the regulation of zinc homeostasis and α-synuclein accumulation by ATP13A2 remains unexplored. We used α-synuclein-GFP transgenic mice and HEK293 α-synuclein-DsRed cell line as models. The spatial exploration behavior of mice was significantly reduced, and phosphorylation levels of α-synuclein increased upon high Zn²⁺ treatment. High Zn²⁺ also inhibited the autophagy pathway by reducing LAMP2a levels and changing the expression of LC3 and P62, by reducing mitochondrial membrane potential and increasing the expression of cytochrom C, and by activating the ERK/P38 apoptosis signaling pathway, ultimately leading to increased caspase 3 levels. These protein changes were reversed after ATP13A2 overexpression, whereas ATP13A2 knockout exacerbated α-synuclein phosphorylation levels. These results suggest that ATP13A2 may have a protective effect on Zn²⁺-induced abnormal aggregation of α-synuclein, lysosomal dysfunction, and apoptosis.

Nuclear alpha-synuclein is present in the human brain and is modified in dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is pathologically defined by the cytoplasmic accumulation of alpha-synuclein (aSyn) within neurons in the brain. Predominately pre-synaptic, aSyn has been reported in various subcellular compartments in experimental models. Indeed, nuclear alpha-synuclein (aSyn^Nuc) is evident in many models, the dysregulation of which is associated with altered DNA integrity, transcription and nuclear homeostasis. However, the presence of aSyn^Nuc in human brain cells remains controversial, yet the determination of human brain aSyn^Nuc and its pathological modification is essential for understanding synucleinopathies. Here, using a multi-disciplinary approach employing immunohistochemistry, immunoblot, and mass-spectrometry (MS), we confirm aSyn^Nuc in post-mortem brain tissue obtained from DLB and control cases. Highly dependent on antigen retrieval methods, in optimal conditions, intra-nuclear pan and phospho-S129 positive aSyn puncta were observed in cortical neurons and non-neuronal cells in fixed brain sections and in isolated nuclear preparations in all cases examined. Furthermore, an increase in nuclear phospho-S129 positive aSyn immunoreactivity was apparent in DLB cases compared to controls, in both neuronal and non-neuronal cell types. Our initial histological investigations identified that aSyn^Nuc is affected by epitope unmasking methods but present under optimal conditions, and this presence was confirmed by isolation of nuclei and a combined approach of immunoblotting and mass spectrometry, where aSyn^Nuc was approximately tenfold less abundant in the nucleus than cytoplasm. Notably, direct comparison of DLB cases to aged controls identified increased pS129 and higher molecular weight species in the nuclei of DLB cases, suggesting putative pathogenic modifications to aSyn^Nuc in DLB. In summary, using multiple approaches we provide several lines of evidence supporting the presence of aSyn^Nuc in autoptic human brain tissue and, notably, that it is subject to putative pathogenic modifications in DLB that may contribute to the disease phenotype.

Characterization of a Novel Monoclonal Antibody for Serine-129 Phosphorylated α-Synuclein: A Potential Application for Clinical and Basic Research

The Lewy bodies (LBs) are the pathological hallmark of Parkinson's disease (PD). More than 90% of α-synuclein (α-syn) within LBs is phosphorylated at the serine-129 residue [pSer129 α-syn (p-α-syn)]. Although various studies have revealed that this abnormally elevated p-α-syn acts as a pathological biomarker and is involved in the pathogenic process of PD, the exact pathophysiological mechanisms of p-α-syn are still not fully understood. Therefore, the development of specific and reliable tools for p-α-syn detection is important. In this study, we generated a novel p-α-syn mouse monoclonal antibody (C140S) using hybridoma technology. To further identify the characteristics of C140S, we performed several in vitro assays using recombinant proteins, along with ex vivo assays utilizing the brains of Thy1-SNCA transgenic (Tg) mice, the preformed fibril (PFF)-treated neurons, and the brain sections of patients with PD. Our C140S specifically recognized human and mouse p-α-syn proteins both in vitro and ex vivo, and similar to commercial p-α-syn antibodies, the C140S detected higher levels of p-α-syn in the midbrain of the Tg mice. Using immunogold electron microscopy, these p-α-syn particles were partly deposited in the cytoplasm and colocalized with the outer mitochondrial membrane. In addition, the C140S recognized p-α-syn pathologies in the PFF-treated neurons and the amygdala of patients with PD. Overall, the C140S antibody was a specific and potential research tool in the detection and mechanistic studies of pathogenic p-α-syn in PD and related synucleinopathies.