α-Synuclein Overexpression Increases Dopamine D2/3 Receptor Binding and Immune Activation in a Model of Early Parkinson’s Disease

2-Butoxytetrahydrofuran, Isolated from Holothuria scabra, Attenuates Aggregative and Oxidative Properties of α-Synuclein and Alleviates Its Toxicity in a Transgenic Caenorhabditis elegans Model of Parkinson's Disease

Aggregative α-synuclein and incurring oxidative stress are pivotal cascading events, leading to dopaminergic (DAergic) neuronal loss and contributing to clinical manifestations of Parkinson's disease (PD). Our previous study demonstrated that 2-butoxytetrahydrofuran (2-BTHF), isolated from Holothuria scabra (H. scabra), could inhibit amyloid-β aggregation and its ensuing toxicity, which leads to Alzheimer's disease. In the present study, we found that 2-BTHF also attenuated the aggregative and oxidative activities of α-synuclein and lessened its toxicity in a transgenic Caenorhabditis elegans (C. elegans) PD model. Such worms treated with 100 μM of 2-BTHF showed substantial reductions in α-synuclein accumulation and DAergic neurodegeneration. Mechanistically, 2-BTHF, at this concentration, significantly decreased aggregation of monomeric α-synuclein and restored locomotion and dopamine-dependent behaviors. Molecular docking exhibited potential bindings of 2-BTHF to HSF-1 and DAF-16 transcription factors. Additionally, 2-BTHF significantly increased the mRNA transcripts of genes encoding proteins involved in proteostasis, including the molecular chaperones hsp-16.2 and hsp-16.49, the ubiquitination/SUMOylation-related ubc-9 gene, and the autophagy-related genes atg-7 and lgg-1. Transcriptomic profiling revealed an additional mechanism of 2-BTHF in α-synuclein-expressing worms, which showed upregulation of PPAR signaling cascades that mediated fatty acid metabolism. 2-BTHF significantly restored lipid deposition, upregulated the fat-7 gene, and enhanced gcs-1-mediated glutathione synthesis in the C. elegans PD model. Taken together, this study demonstrated that 2-BTHF could abrogate aggregative and oxidative properties of α-synuclein and attenuate its toxicity, thus providing a possible therapeutic application for the treatment of α-synuclein-induced PD.

A single dose of cocaine raises SV2A density in hippocampus of adolescent rats

OBJECTIVE

Cocaine is a highly addictive psychostimulant that affects synaptic activity with structural and functional adaptations of neurons. The transmembrane synaptic vesicle glycoprotein 2A (SV2A) of pre-synaptic vesicles is commonly used to measure synaptic density, as a novel approach to the detection of synaptic changes. We do not know if a single dose of cocaine suffices to affect pre-synaptic SV2A density, especially during adolescence when synapses undergo intense maturation. Here, we explored potential changes of pre-synaptic SV2A density in target brain areas associated with the cocaine-induced boost of dopaminergic neurotransmission, specifically testing if the effects would last after the return of dopamine levels to baseline.

METHODS

We administered cocaine (20 mg/kg i.p.) or saline to rats in early adolescence, tested their activity levels and removed the brains 1 hour and 7 days after injection. To evaluate immediate and lasting effects, we did autoradiography with [3H]UCB-J, a specific tracer for SV2A, in medial prefrontal cortex, striatum, nucleus accumbens, amygdala, and dorsal and ventral areas of hippocampus. We also measured the striatal binding of [3H]GBR-12935 to test cocaine's occupancy of the dopamine transporter at both times of study.

RESULTS

We found a significant increase of [3H]UCB-J binding in the dorsal and ventral sections of hippocampus 7 days after the cocaine administration compared to saline-injected rats, but no differences 1 hour after the injection. The [3H]GBR-12935 binding remained unchanged at both times.

CONCLUSION

Cocaine provoked lasting changes of hippocampal synaptic SV2A density after a single exposure during adolescence.

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.

Selecting the Best Animal Model of Parkinson's Disease for Your Research Purpose: Insight from in vivo PET Imaging Studies

Parkinson's disease (PD) is a debilitating neurodegenerative multisystem disorder leading to motor and non-motor symptoms in millions of individuals. Despite intense research, there is still no cure, and early disease biomarkers are lacking. Animal models of PD have been inspired by basic elements of its pathogenesis, such as dopamine dysfunction, alpha-synuclein accumulation, neuroinflammation and disruption of protein degradation, and these have been crucial for a deeper understanding of the mechanisms of pathology, the identification of biomarkers, and evaluation of novel therapies. Imaging biomarkers are non-invasive tools to assess disease progression and response to therapies; their discovery and validation have been an active field of translational research. Here, we highlight different considerations of animal models of PD that can be applied to future research, in terms of their suitability to answer different research questions. We provide the reader with important considerations of the best choice of model to use based on the disease features of each model, including issues related to different species. In addition, positron emission tomography studies conducted in PD animal models in the last 5 years are presented. With a variety of different species, interventions and genetic information, the choice of the most appropriate model to answer research questions can be daunting, especially since no single model recapitulates all aspects of this complex disorder. Appropriate animal models in conjunction with in vivo molecular imaging tools, if selected properly, can be a powerful combination for the assessment of novel therapies and developing tools for early diagnosis.

Synaptic Vesicle Glycoprotein 2A: Features and Functions

In recent years, the field of neuroimaging dramatically moved forward by means of the expeditious development of specific radioligands of novel targets. Among these targets, the synaptic vesicle glycoprotein 2A (SV2A) is a transmembrane protein of synaptic vesicles, present in all synaptic terminals, irrespective of neurotransmitter content. It is involved in key functions of neurons, focused on the regulation of neurotransmitter release. The ubiquitous expression in gray matter regions of the brain is the basis of its candidacy as a marker of synaptic density. Following the development of molecules derived from the structure of the anti-epileptic drug levetiracetam, which selectively binds to SV2A, several radiolabeled markers have been synthetized to allow the study of SV2A distribution with positron emission tomography (PET). These radioligands permit the evaluation of in vivo changes of SV2A distribution held to be a potential measure of synaptic density in physiological and pathological conditions. The use of SV2A as a biomarker of synaptic density raises important questions. Despite numerous studies over the last decades, the biological function and the expressional properties of SV2A remain poorly understood. Some functions of SV2A were claimed, but have not been fully elucidated. While the expression of SV2A is ubiquitous, stronger associations between SV2A and Υ amino butyric acid (GABA)-ergic rather than glutamatergic synapses were observed in some brain structures. A further issue is the unclear interaction between SV2A and its tracers, which reflects a need to clarify what really is detected with neuroimaging tools. Here, we summarize the current knowledge of the SV2A protein and we discuss uncertain aspects of SV2A biology and physiology. As SV2A expression is ubiquitous, but likely more strongly related to a certain type of neurotransmission in particular circumstances, a more extensive knowledge of the protein would greatly facilitate the analysis and interpretation of neuroimaging results by allowing the evaluation not only of an increase or decrease of the protein level, but also of the type of neurotransmission involved.