Modeling the cellular fate of alpha-synuclein aggregates: A pathway to pathology

Rational selection of the monoclonal α-synuclein antibody amlenetug (Lu AF82422) for the treatment of α-synucleinopathies

Amlenetug (Lu AF82422) is a human monoclonal antibody targeting α-synuclein in clinical development for multiple system atrophy. We describe a series of studies that characterize its functional properties and supported its selection as a viable clinical candidate. Amlenetug inhibits seeding induced in mouse primary neurons by various α-synuclein fibrillar assemblies and by aggregates isolated from MSA brain homogenate. In vivo, both co-injection of amlenetug with α-synuclein assemblies in mouse brain and peripheral administration inhibit α-synuclein seeding. Amlenetug inhibits uptake of α-synuclein seeds as well as accumulation of C-terminal truncated α-synuclein seeds and demonstrates binding to monomeric, aggregated, and truncated forms of human α-synuclein. The epitope of amlenetug was mapped to amino acids 112-117 and further characterized by crystallographic structure analysis. Based on our data, we hypothesize that targeting α-synuclein will potentially slow further disease progression by inhibiting further pathology development but be without impact on established pathology and symptoms.

ZSCAN21 mediates the pathogenic transcriptional induction of α-synuclein in cellular and animal models of Parkinson's disease

The expression level of α-synuclein is thought to play a crucial role in the pathogenesis of Parkinson's disease. However, little is known about the molecular mechanisms regulating the transcription of its gene, SNCA, particularly in the context of the disease. The transcription factor ZSCAN21 has been shown to act on SNCA, but whether ZSCAN21 is actually involved in the induction of SNCA transcription in Parkinson's disease is unknown. To address this question, we used the MPTP mouse model and LUHMES-derived dopaminergic neuronal spheroids, subjected to Parkinson's disease-related neurotoxins and mutations. We show that MPP+-treated spheroids recapitulate the main features of α-synuclein pathology and that MPP+-triggered transcriptional induction of SNCA is associated with ZSCAN21 stabilisation. Importantly, knock-down of ZSCAN21 prevents both the MPP+-triggered increase in α-synuclein mRNA and pre-mRNA levels in LUHMES-derived spheroids and the death of dopaminergic neurons in the substantia nigra of MPTP-treated mice. These effects are recapitulated by knockdown of TRIM17, a ZSCAN21 stabiliser which prevents its ubiquitination and degradation mediated by TRIM41. Moreover, reducing the interaction between ZSCAN21 and TRIM41, either by inserting Parkinson's disease-associated mutations into the TRIM41 gene or by preventing SUMOylation of ZSCAN21, results in both stabilisation of ZSCAN21 and induction of SNCA. Taken together, our data strongly suggest that ZSCAN21 is a crucial transcription factor for pathogenic α-synuclein expression and neurodegeneration in Parkinson's disease, pointing to its regulators, TRIM17 and TRIM41, as original therapeutic targets for a neuroprotective treatment of Parkinson's disease.

Intermittent fasting reduces alpha-synuclein pathology and functional decline in a mouse model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by dopaminergic neuron degeneration and α-synuclein (aSyn) accumulation. Environmental factors play a significant role in PD progression, highlighting the potential of non-pharmacological interventions. This study investigates the therapeutic effects of intermittent fasting (IF) in an rAAV-aSyn mouse model of PD. IF, initiated four weeks post-induction of aSyn pathology, improved motor function and reduced dopaminergic neuron and axon terminal degeneration. Additionally, IF preserved dopamine levels and synaptic integrity in the striatum. Mechanistically, IF enhanced autophagic activity, promoting phosphorylated-aSyn clearance and reducing its accumulation in insoluble brain fractions. Transcriptome analysis revealed IF-induced modulation of inflammation-related genes and microglial activation. Validation in primary cultures confirmed that autophagy activation and inflammatory modulators (CCL17, IL-36RN) mitigate aSyn pathology. These findings suggest that IF exerts neuroprotective effects, supporting further exploration of IF and IF-mimicking therapies as potential PD treatments.

Synergistic Multi-Pronged Interactions Mediate the Effective Inhibition of Alpha-Synuclein Aggregation by the Chaperone HtrA1

The misfolding, aggregation, and the seeded spread of alpha synuclein (α-Syn) aggregates are linked to the pathogenesis of various neurodegenerative diseases, including Parkinson's disease (PD). Understanding the mechanisms by which chaperone proteins prevent the production and seeding of α-Syn aggregates is crucial for developing effective therapeutic leads for tackling neurodegenerative diseases. We show that a catalytically inactive variant of the chaperone HtrA1 (HtrA1*) effectively inhibits both α-Syn monomer aggregation and templated fibril seeding, and demonstrate that this inhibition is mediated by synergistic interactions between its PDZ and Protease domains and α-Syn. Using biomolecular NMR, AFM and Rosetta-based computational analyses, we propose that the PDZ domain interacts with the C-terminal end of the monomer and the intrinsically disordered C-terminal domain of the α-Syn fibril. Furthermore, in agreement with sequence specificity calculations, the Protease domain cleaves in the aggregation-prone NAC domain at site T92/A93 in the monomer. Thus, through multi-pronged interactions and multi-site recognition of α-Syn, HtrA1* can effectively intervene at different stages along the α-Syn aggregation pathway, making it a robust inhibitor of α-Syn aggregation and templated seeding. Our studies illustrate, at high resolution, the crucial role of HtrA1 interactions with both the intrinsically disordered α-Syn monomers and with the dynamic flanking regions around the fibril core for inhibition of aggregation. This inhibition mechanism of the HtrA1 chaperone may provide a natural mechanistic blueprint for highly effective therapeutic agents against protein aggregation.

Significance Statement

PD and other synucleinopathies are marked by misfolding and aggregation of α-Syn, forming higher-order species that propagate aggregation in a prion-like manner. Understanding how chaperone proteins inhibit α-Syn aggregation and spread is essential for therapeutic development against neurodegeneration. Through an integrative approach of solution-based NMR, AFM, aggregation kinetics, and computational analysis, we reveal how a catalytically inactive variant of the chaperone HtrA1 effectively disrupts aggregation pathways. We find that the inactive Protease and PDZ domains of HtrA1 synergistically bind to key intrinsically disordered sites on both α-Syn monomers and fibrils, thereby effectively inhibiting both aggregation and templated seeding. Our work provides a natural and unique blueprint for designing inhibitors to prevent the formation and seeding of aggregates in neurodegenerative diseases.

Decoding the Cellular Trafficking of Prion-like Proteins in Neurodegenerative Diseases

The accumulation and spread of prion-like proteins is a key feature of neurodegenerative diseases (NDs) such as Alzheimer's disease, Parkinson's disease, or Amyotrophic Lateral Sclerosis. In a process known as 'seeding', prion-like proteins such as amyloid beta, microtubule-associated protein tau, α-synuclein, silence superoxide dismutase 1, or transactive response DNA-binding protein 43 kDa, propagate their misfolded conformations by transforming their respective soluble monomers into fibrils. Cellular and molecular evidence of prion-like propagation in NDs, the clinical relevance of their 'seeding' capacities, and their levels of contribution towards disease progression have been intensively studied over recent years. This review unpacks the cyclic prion-like propagation in cells including factors of aggregate internalization, endo-lysosomal leaking, aggregate degradation, and secretion. Debates on the importance of the role of prion-like protein aggregates in NDs, whether causal or consequent, are also discussed. Applications lead to a greater understanding of ND pathogenesis and increased potential for therapeutic strategies.

Multifaceted interactions mediated by intrinsically disordered regions play key roles in alpha synuclein aggregation

The aggregation of Alpha Synuclein (α-Syn) into fibrils is associated with the pathology of several neurodegenerative diseases. Pathologic aggregates of α-Syn adopt multiple fibril topologies and are known to be transferred between cells via templated seeding. Monomeric α-Syn is an intrinsically disordered protein (IDP) with amphiphilic N-terminal, hydrophobic-central, and negatively charged C-terminal domains. Here, we review recent work elucidating the mechanism of α-Syn aggregation and identify the key and multifaceted roles played by the N- and C-terminal domains in the initiation and growth of aggregates as well as in the templated seeding involved in cell-to-cell propagation. The charge content of the C-terminal domain, which is sensitive to environmental conditions like organelle pH, is a key regulator of intermolecular interactions involved in fibril growth and templated propagation. An appreciation of the complex and multifaceted roles played by the intrinsically disordered terminal domains suggests novel opportunities for the development of potent inhibitors against synucleinopathies.

Characterisation of Amyloid Aggregation and Inhibition by Diffusion-Based Single-Molecule Fluorescence Techniques

Protein amyloid aggregation has been associated with more than 50 human disorders, including the most common neurodegenerative disorders Alzheimer’s and Parkinson’s disease. Interfering with this process is considered as a promising therapeutic strategy for these diseases. Our understanding of the process of amyloid aggregation and its role in disease has typically been limited by the use of ensemble-based biochemical and biophysical techniques, owing to the intrinsic heterogeneity and complexity of the process. Single-molecule techniques, and particularly diffusion-based single-molecule fluorescence approaches, have been instrumental to obtain meaningful information on the dynamic nature of the fibril-forming process, as well as the characterisation of the heterogeneity of the amyloid aggregates and the understanding of the molecular basis of inhibition of a number of molecules with therapeutic interest. In this article, we reviewed some recent contributions on the characterisation of the amyloid aggregation process, the identification of distinct structural groups of aggregates in homotypic or heterotypic aggregation, as well as on the study of the interaction of amyloid aggregates with other molecules, allowing the estimation of the binding sites, affinities, and avidities as examples of the type of relevant information we can obtain about these processes using these techniques.