Neutral lysophosphatidylcholine mediates α-synuclein-induced synaptic vesicle clustering

Synaptic vesicle-omics in mice captures signatures of aging and synucleinopathy

Neurotransmitter release occurs through exocytosis of synaptic vesicles. α-Synuclein's function and dysfunction in Parkinson's disease and other synucleinopathies is thought to be tightly linked to synaptic vesicle binding. Age is the biggest risk factor for synucleinopathy, and ~15% of synaptic vesicle proteins have been linked to central nervous system diseases. Yet, age- and disease-induced changes in synaptic vesicles remain unexplored. Via systematic analysis of synaptic vesicles at the ultrastructural, protein, and lipid levels, we reveal specific changes in synaptic vesicle populations, proteins, and lipids over age in wild-type mice and in α-synuclein knockout mice with and without expression of human α-synuclein. Strikingly, we find several previously undescribed synaptic changes in mice lacking α-synuclein, suggesting that loss of α-synuclein function contributes to synaptic dysfunction. These findings not only provide insights into synaptic vesicle biology and disease mechanisms in synucleinopathy, but also serve as a baseline for further mechanistic exploration of age- and disease-related alterations in synaptic vesicles.

Enhanced Microglial Engulfment of Dopaminergic Synapses Induces Parkinson's Disease-Related Executive Dysfunction in an Acute LPC Infusion Targeting the mPFC

The dysfunction of the dopaminergic projection from the ventral tegmental area (VTA) to the medial prefrontal cortex (mPFC) is believed to play a key role in the pathophysiology of Parkinson's disease (PD) accompanied by executive dysfunction (EDF). In this study, we identified an abnormal increase in lysophosphatidylcholine (LPC) levels in PD patients, which closely correlates with the severity of cognitive impairment. LPC disrupts the miR-2885/TDP-43 signaling pathway in microglia, driving dopaminergic presynaptic engulfment. In LPC-exposed mice, microglial activation via miR-2885/TDP-43/p65 signaling led to inflammatory cytokine and complement release, marking dopaminergic synapses for phagocytosis with a "PS/C1q" signal. Following the inhibition of LPC-induced microglial activation through chemogenetic methods, we observed a significant reduction in the phagocytosis of dopaminergic synapses, resulting in improved executive function. The miR-2885 disrupted LPC-induced dopaminergic phagocytosis and alleviated EDF. Furthermore, the accumulation of excessive TDP-43 due to the loss of miR-2885 promoted the engulfment of dopaminergic synapses by facilitating the entry of p65 into the nucleus. Inhibiting TDP-43 levels effectively mitigated LPC-induced EDF. Additionally, supplementing dopamine receptor agonists enhanced the excitability of regional glutamatergic neurons, leading to improved executive function. In summary, LPC exposure in the mPFC impairs microglial regulation, leading to dopaminergic synaptic loss and underactivity of glutamatergic neurons. These changes drive the development of executive dysfunction in PD.

Double-Negative CD4 CD8 Absolute Count Plays a Mediating Role in the Causal Relationship Between Plasma Lipids and Parkinson's Disease: A Mendel Randomized Study

According to certain research, there might be a connection between Parkinson's disease and plasma lipidome. However, the causal effects between plasma lipidome and Parkinson's disease and whether immune cells act as a mediator remain unclear. According to some research, plasma lipids are an important risk factor for Parkinson's disease, however, whether there is a causative connection between the two is unclear. In this study, Mendelian randomization (MR) was utilized to investigate the causal effect of plasma lipidomics on Parkinson's disease while conducting mediation analysis to determine whether immune cells served as mediators in this association. Plasma lipidome, immune cells, and Parkinson's disease were identified from large-scale genome-wide association studies (GWAS) summary data. We explored the causal connections between the plasma lipidome, Parkinson's disease, and the immune system using Mendelian randomization (MR). Inverse variance weighting (IVW) was used as the main statistical method. Furthermore, we investigated the potential that immune cells play a mediating role in the pathway leading from the plasma lipidome to Parkinson's disease. There were two positive and four negative causal effects between genetic liability in the plasma lipidome and Parkinson's disease. In addition, there were four positive and three negative causal relationships between immune cells and Parkinson's disease. The immune cells function as a mediator. Immune cells functioned as mediating components in the pathway from plasma lipidome to Parkinson's disease, and both plasma lipidome and immune cells were causally related to Parkinson's disease. It is expected that immune cells and plasma lipid intervention can be used as a preventive and therapeutic strategy for Parkinson's disease.

α-Synuclein condensation in synaptic vesicle function and synucleinopathies

Research into the crosstalk between α-synuclein (α-syn) and synaptic vesicles (SVs) has gained considerable attention. Notably, the recently discovered liquid-liquid phase separation of α-syn involving SVs is crucial for performing their physiological functions and mediating the transition to pathological aggregates. This review first examines the functional interactions between α-syn and SVs in the context of α-syn's condensation state. It then explores how these interactions become disrupted under pathological conditions, leading to α-syn aggregation and subsequent synaptic dysfunction. Finally, the review discusses the therapeutic potential of targeting α-syn-SV interactions to restore synaptic function in diseased states. By connecting α-syn's physiological roles with its pathological effects, the article aims to shed light on its dual role as both a regulator of SVs and a driver of neurodegeneration.

Molecular Dynamics Simulation for Membrane Fusion

The soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) protein complex drives membrane fusion, and this process is further aided by accessory proteins, including complexin and α-synuclein. To understand the molecular mechanism underlying membrane fusion, we introduce an all-atom molecular dynamics (MD) simulation method. This method is used to understand and predict the conformations of protein and lipids, membrane geometry, and their interaction at femtosecond precision, by describing complex chemical systems with atomic models. Simulation results reveal information on distinct membrane fusion stages, including docking, hemifusion, and kiss-and-run fusion. Here, we introduce the simulation workflow, consisting of pre-MD construction, pre-MD setup in GROMACS, MD in GROMACS, and analysis.

N-acetylation of α-synuclein enhances synaptic vesicle clustering mediated by α-synuclein and lysophosphatidylcholine

Previously, we reported that α-synuclein (α-syn) clusters synaptic vesicles (SV) Diao et al., 2013, and neutral phospholipid lysophosphatidylcholine (LPC) can mediate this clustering Lai et al., 2023. Meanwhile, post-translational modifications (PTMs) of α-syn such as acetylation and phosphorylation play important yet distinct roles in regulating α-syn conformation, membrane binding, and amyloid aggregation. However, how PTMs regulate α-syn function in presynaptic terminals remains unclear. Here, based on our previous findings, we further demonstrate that N-terminal acetylation, which occurs under physiological conditions and is irreversible in mammalian cells, significantly enhances the functional activity of α-syn in clustering SVs. Mechanistic studies reveal that this enhancement is caused by the N-acetylation-promoted insertion of α-syn's N-terminus and increased intermolecular interactions on the LPC-containing membrane. N-acetylation in our work is shown to fine-tune the interaction between α-syn and LPC, mediating α-syn's role in synaptic vesicle clustering.

Research Progress of Phospholipid Vesicles in Biological Field

Due to their high biocompatibility, biodegradability, and facile surface functionalization, phospholipid vesicles as carriers have garnered significant attention in the realm of disease diagnosis and treatment. On the one hand, phospholipid vesicles can function as probes for the detection of various diseases by encapsulating nanoparticles, thereby enabling the precise localization of pathological changes and the monitoring of disease progression. On the other hand, phospholipid vesicles possess the capability to selectively target and deliver therapeutic agents, including drug molecules, genes and immune modulators, to affected sites, thereby enhancing the sustained release of these agents and improving therapeutic efficacy. Recent advancements in nanotechnology have led to an increased focus on the application of phospholipid vesicles in drug delivery, biological detection, gene therapy, and cell mimics. This review aims to provide a concise overview of the structure, characteristics, and preparation techniques of phospholipid vesicles of varying sizes. Furthermore, we will summarize the latest research developments regarding their use as nanomedicines and gene carriers in disease treatment. Additionally, we will elucidate the potential of phospholipid vesicles in facilitating the internalization, controlled release, and targeted delivery of therapeutic substrates. Through this review, we aspire to enhance the understanding of the evolution of phospholipid vesicles within the biological field, outline prospective research, and address the forthcoming challenges associated with phospholipid vesicles in disease diagnosis and treatment.

Folding of N-terminally acetylated α-synuclein upon interaction with lipid membranes

α-Synuclein (α-syn) is an abundant presynaptic neuronal protein whose aggregation is strongly associated with Parkinson's disease. It has been proposed that lipid membranes significantly affect α-syn's aggregation process. Extensive studies have been conducted to understand the interactions between α-syn and lipid membranes and have demonstrated that the N-terminus plays a critical role. However, the dynamics of the interactions and the conformational transitions of the N-terminus of α-syn at the atomistic scale details are still highly desired. In this study, we performed extensive enhanced sampling molecular dynamics simulations to quantify the folding and interactions of wild-type and N-terminally acetylated α-syn when interacting with lipid structures. We found that N-terminal acetylation significantly increases the helicity of the first few residues in solution or when interacting with lipid membranes. The observations in simulations showed that the binding of α-syn with lipid membranes mainly follows the induced-fit model, where the disordered α-syn binds with the lipid membrane through the electrostatic interactions and hydrophobic contacts with the packing defects; after stable insertion, N-terminal acetylation promotes the helical folding of the N-terminus to enhance the anchoring, thus increasing the binding affinity. We have shown the critical role of the first N-terminal residue methionine for recognition and anchoring to the negatively charged membrane. Although N-terminal acetylation neutralizes the positive charge of Met1 that may affect the electrostatic interactions of α-syn with membranes, the increase in helicity of the N-terminus should compensate for the binding affinity. This study provides detailed insight into the folding dynamics of α-syn's N-terminus with or without acetylation in solution and upon interaction with lipids, which clarifies how the N-terminal acetylation regulates the affinity of α-syn binding to lipid membranes. It also shows how packing defects and electrostatic effects coregulate the N-terminus of α-syn folding and its interaction with membranes.

Self-limiting multimerization of α-synuclein on membrane and its implication in Parkinson's diseases

α-Synuclein (α-syn), a crucial molecule in Parkinson's disease (PD), is known for its interaction with lipid membranes, which facilitates vesicle trafficking and modulates its pathological aggregation. Deciphering the complexity of the membrane-binding behavior of α-syn is crucial to understand its functions and the pathology of PD. Here, we used single-molecule imaging to show that α-syn forms multimers on lipid membranes with huge intermultimer distances. The multimers are characterized by self-limiting growth, manifesting in concentration-dependent exchanges of monomers, which are fast at micromolar concentrations and almost stop at nanomolar concentrations. We further uncovered movement patterns of α-syn's occasional trapping on membranes, which may be attributed to sparse lipid packing defects. Mutations such as E46K and E35K may disrupt the limit on the growth, resulting in larger multimers and accelerated amyloid fibril formation. This work emphasizes sophisticated regulation of α-syn multimerization on membranes as a critical underlying factor in the PD pathology.

N-acetylation of α-synuclein enhances synaptic vesicle clustering mediated by α-synuclein and lysophosphatidylcholine

Post-translational modifications (PTMs) of α-synuclein (α-syn) such as acetylation and phosphorylation play important yet distinct roles in regulating α-syn conformation, membrane binding, and amyloid aggregation. However, how PTMs regulate α-syn function in presynaptic terminals remains unclear. Previously, we reported that α-syn clusters synaptic vesicles (SV)1, and neutral phospholipid lysophosphatidylcholine (LPC) can mediate this clustering2. Here, based on our previous findings, we further demonstrate that N-terminal acetylation, which occurs under physiological conditions and is irreversible in mammalian cells, significantly enhances the functional activity of α-syn in clustering SVs. Mechanistic studies reveal that this enhancement is caused by the N-acetylation-promoted insertion of α-syn's N-terminus and increased intermolecular interactions on the LPC-containing membrane. Our work demonstrates that N-acetylation fine-tunes α-syn-LPC interaction for mediating α-syn's function in SV clustering.

Lysophosphatidylcholine binds α-synuclein and prevents its pathological aggregation

Accumulation of aggregated α-synuclein (α-syn) in Lewy bodies is the pathological hallmark of Parkinson's disease (PD). Genetic mutations in lipid metabolism are causative for a subset of patients with Parkinsonism. The role of α-syn's lipid interactions in its function and aggregation is recognized, yet the specific lipids involved and how lipid metabolism issues trigger α-syn aggregation and neurodegeneration remain unclear. Here, we found that α-syn shows a preference for binding to lysophospholipids (LPLs), particularly targeting lysophosphatidylcholine (LPC) without relying on electrostatic interactions. LPC is capable of maintaining α-syn in a compact conformation, significantly reducing its propensity to aggregate both in vitro and within cellular environments. Conversely, a reduction in the production of cellular LPLs is associated with an increase in α-syn accumulation. Our work underscores the critical role of LPLs in preserving the natural conformation of α-syn to inhibit improper aggregation, and establishes a potential connection between lipid metabolic dysfunction and α-syn aggregation in PD.