Lewy body-associated proteins: victims, instigators, or innocent bystanders? The case of AIMP2 and alpha-synuclein

Methamphetamine Increases Tubulo-Vesicular Areas While Dissipating Proteins from Vesicles Involved in Cell Clearance

Cytopathology induced by methamphetamine (METH) is reminiscent of degenerative disorders such as Parkinson's disease, and it is characterized by membrane organelles arranged in tubulo-vesicular structures. These areas, appearing as clusters of vesicles, have never been defined concerning the presence of specific organelles. Therefore, the present study aimed to identify the relative and absolute area of specific membrane-bound organelles following a moderate dose (100 µM) of METH administered to catecholamine-containing PC12 cells. Organelles and antigens were detected by immunofluorescence, and they were further quantified by plain electron microscopy and in situ stoichiometry. This analysis indicated an increase in autophagosomes and damaged mitochondria along with a decrease in lysosomes and healthy mitochondria. Following METH, a severe dissipation of hallmark proteins from their own vesicles was measured. In fact, the amounts of LC3 and p62 were reduced within autophagy vacuoles compared with the whole cytosol. Similarly, LAMP1 and Cathepsin-D within lysosomes were reduced. These findings suggest a loss of compartmentalization and confirm a decrease in the competence of cell clearing organelles during catecholamine degeneration. Such cell entropy is consistent with a loss of energy stores, which routinely govern appropriate subcellular compartmentalization.

In situ stoichiometry amounts of p62 and poly-ubiquitin exceed the increase of alpha-synuclein during degeneration of catecholamine cells induced by autophagy inhibition in vitro

Neurodegenerative disorders are typically featured by the occurrence of neuronal inclusions. In the case of Parkinson's disease (PD) these correspond to Lewy bodies (LBs), which are routinely defined as proteinaceous inclusions composed of alpha-synuclein (alpha-syn). In turn, alpha-syn is considered to be the key protein in producing PD and fostering its progression. Recent studies challenged such a concept and emphasized the occurrence of other proteins such as p62 and poly-ubiquitin (Poly-ub) in the composition of LBs, which are also composed of large amounts of tubulo-vesicular structures. All these components, which accumulate within the cytosol of affected neurons in PD, may be the consequence of a dysfunction of major clearing pathways. In fact, autophagy-related systems are constantly impaired in inherited PD and genetic models of PD. The present study was designed to validate whether a pharmacological inhibition of autophagy within catecholamine cells produces cell damage and accumulation of specific proteins and tubulo-vesicular structures. The stoichiometry counts of single proteins, which accumulate within catecholamine neurons was carried out along with the area of tubulo-vesicular structures. In these experimental conditions p62 and Poly-ub accumulation exceeded at large the amounts of alpha-syn. In those areas where Poly-ub and p62 were highly expressed, tubulo-vesicular structures were highly represented compared with surrounding cytosol. The present study confirms new vistas about LBs composition and lends substance to the scenario that autophagy inhibition rather than a single protein dysfunction as key determinant of PD.

Is There a Place for Lewy Bodies before and beyond Alpha-Synuclein Accumulation? Provocative Issues in Need of Solid Explanations

In the last two decades, alpha-synuclein (alpha-syn) assumed a prominent role as a major component and seeding structure of Lewy bodies (LBs). This concept is driving ongoing research on the pathophysiology of Parkinson's disease (PD). In line with this, alpha-syn is considered to be the guilty protein in the disease process, and it may be targeted through precision medicine to modify disease progression. Therefore, designing specific tools to block the aggregation and spreading of alpha-syn represents a major effort in the development of disease-modifying therapies in PD. The present article analyzes concrete evidence about the significance of alpha-syn within LBs. In this effort, some dogmas are challenged. This concerns the question of whether alpha-syn is more abundant compared with other proteins within LBs. Again, the occurrence of alpha-syn compared with non-protein constituents is scrutinized. Finally, the prominent role of alpha-syn in seeding LBs as the guilty structure causing PD is questioned. These revisited concepts may be helpful in the process of validating which proteins, organelles, and pathways are likely to be involved in the damage to meso-striatal dopamine neurons and other brain regions involved in PD.

Metal-enhanced fluorescence biosensor integrated in capillary flow-driven microfluidic cartridge for highly sensitive immunoassays

Point-of-care testing (POCT) for low-concentration protein biomarkers remains challenging due to limitations in biosensor sensitivity and platform integration. This study addresses this gap by presenting a novel approach that integrates a metal-enhanced fluorescence (MEF) biosensor within a capillary flow-driven microfluidic cartridge (CFMC) for the ultrasensitive detection of the Parkinson's disease biomarker, aminoacyl-tRNA synthetase complex interacting multi-functional protein 2 (AIMP-2). Crucial point to this approach is the orientation-controlled immobilization of capture antibody on a nanodimple-structured MEF substrate within the CFMC. This strategy significantly enhances fluorescence signals without quenching, enabling accurate quantification of low-concentration AIMP-2 using a simple digital fluorescence microscope with a light-emitting diode excitation source and a digital camera. The resulting platform exhibits exceptional sensitivity, achieving a limit of detection in the pg/mL range for AIMP-2 in human serum. Additionally, the CFMC design incorporates a capillary-driven passive sample transport mechanism, eliminating the need for external pumps and further simplifying the detection process. Overall, this work demonstrates the successful integration of MEF biosensing with capillary microfluidics for point-of-care applications.

Protein-protein interactions regulating α-synuclein pathology

Parkinson's disease (PD) is a neurodegenerative disease characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the formation of Lewy bodies (LBs). The main proteinaceous component of LBs is aggregated α-synuclein (α-syn). However, the mechanisms underlying α-syn aggregation are not yet fully understood. Converging lines of evidence indicate that, under certain pathological conditions, various proteins can interact with α-syn and regulate its aggregation. Understanding these protein-protein interactions is crucial for unraveling the molecular mechanisms contributing to PD pathogenesis. In this review we provide an overview of the current knowledge on protein-protein interactions that regulate α-syn aggregation. Additionally, we briefly summarize the methods used to investigate the influence of protein-protein interactions on α-syn aggregation and propagation.

The Association of Lipids with Amyloid Fibrils

Amyloid formation continues to be a widely studied area because of its association with numerous diseases, such as Alzheimer’s and Parkinson’s diseases. Despite a large body of work on protein aggregation and fibril formation, there are still significant gaps in our understanding of the factors that differentiate toxic amyloid formation in vivo from alternative misfolding pathways. In addition to proteins, amyloid fibrils are often associated in their cellular context with several types of molecule, including carbohydrates, polyanions, and lipids. This review focuses in particular on evidence for the presence of lipids in amyloid fibrils and the routes by which those lipids may become incorporated. Chemical analyses of fibril composition, combined with studies to probe the lipid distribution around fibrils, provide evidence that in some cases, lipids have a strong association with fibrils. In addition, amyloid fibrils formed in the presence of lipids have distinct morphologies and material properties. It is argued that lipids are an integral part of many amyloid deposits in vivo, where their presence has the potential to influence the nucleation, morphology, and mechanical properties of fibrils. The role of lipids in these structures is therefore worthy of further study.

In situ proximity labeling identifies Lewy pathology molecular interactions in the human brain

The intracellular misfolding and accumulation of alpha-synuclein into structures collectively called Lewy pathology (LP) is a central phenomenon for the pathogenesis of synucleinopathies, including Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Understanding the molecular architecture of LP is crucial for understanding synucleinopathy disease origins and progression. Here we used a technique called biotinylation by antibody recognition (BAR) to label total (BAR-SYN1) and pathological alpha-synuclein (BAR-PSER129) in situ for subsequent mass spectrometry analysis. Results showed superior immunohistochemical detection of LP following the BAR-PSER129 protocol, particularly for fibers and punctate pathology within the striatum and cortex. Mass spectrometry analysis of BAR-PSER129-labeled LP identified 261 significantly enriched proteins in the synucleinopathy brain when compared to nonsynucleinopathy brains. In contrast, BAR-SYN1 did not differentiate between disease and nonsynucleinopathy brains. Pathway analysis of BAR-PSER129-enriched proteins revealed enrichment for 718 pathways; notably, the most significant KEGG pathway was PD, and Gene Ontology (GO) cellular compartments were the vesicle, extracellular vesicle, extracellular exosome, and extracellular organelle. Pathway clustering revealed several superpathways, including metabolism, mitochondria, lysosome, and intracellular vesicle transport. Validation of the BAR-PSER129-identified protein hemoglobin beta (HBB) by immunohistochemistry confirmed the interaction of HBB with PSER129 Lewy neurites and Lewy bodies. In summary, BAR can be used to enrich for LP from formalin-fixed human primary tissues, which allowed the determination of molecular signatures of LP. This technique has broad potential to help understand the phenomenon of LP in primary human tissue and animal models.