Protein aggregation inhibitors induce divergent transcriptional responses in a cellular model of a-synuclein seeded aggregation

Technical Summary

Problem Statement
Parkinson's disease (PD), dementia with Lewy Bodies (DLB), and multiple system atrophy (MSA) are progressive neurodegenerative disorders characterized by the pathological aggregation of alpha-synuclein (αSyn). Despite extensive research, effective therapeutic interventions remain elusive. A primary barrier is the limited understanding of the specific cellular effects caused by αSyn aggregation and its propagation, which hinders the identification of viable drug targets.

Methodology
To address these challenges, the study developed a scalable cellular seeding assay designed for the high-throughput screening of small molecules targeting cellular αSyn seeded aggregation. The assay utilizes a fluorescent reporter of αSyn combined with phenotypic screening to evaluate potential inhibitors within a cellular environment that mimics disease pathology.

The researchers applied this platform to evaluate three specific αSyn aggregation inhibitors that have been tested in clinical trials for PD: Minzasolmin, Emrusolmin, and Epigallocatechin gallate (EGCG). To understand the distinct molecular mechanisms of these compounds, the study employed multiplexed single-cell RNA sequencing (scRNA-seq) to profile gene expression changes. This approach allowed for the examination of cellular pathways associated with both αSyn overexpression and seeded aggregation, distinguishing between the effects of the compounds on cells with aggregated Syn versus those without.

Key Results
The screening and sequencing efforts yielded several critical findings:

• Pathway Identification: Two cellular activities were prominently affected by the aggregation and subsequent inhibition: lipid metabolism and ribosomal RNA (rRNA) processing.
• Divergent Transcriptional Responses: The study observed distinct patterns of transcriptional change among the tested compounds. While the effects of EGCG were confined strictly to cells containing aggregated αSyn, Minzasolmin and Emrusolmin induced transcriptional changes in cells that did not contain aggregated αSyn.
• Partial Reversal of Pathology: Each of the three compounds induced a partial reversal of the transcriptional effects caused by αSyn seeded aggregation. Specifically, the researchers identified 391 genes that were differentially expressed in the presence of seeded aggregation but returned to non-significant levels upon the addition of the compounds.

Key Contributions
This work bridges the gap between phenotypic screening and molecular pathway analysis. By integrating a scalable seeding assay with high-resolution single-cell transcriptomics, the study provides a framework for:

1. Evaluating the efficacy of aggregation inhibitors in a disease-relevant cellular context.
2. Uncovering the specific molecular signatures and divergent transcriptional responses induced by different therapeutic candidates.
3. Identifying a set of genes and pathways (specifically lipid metabolism and rRNA processing) that are modulated by these inhibitors.

Significance
The paper claims that the identified molecular signatures serve as a resource for testing and benchmarking future drug discovery leads for synucleinopathies. By elucidating the distinct cellular pathways affected by different inhibitors, this platform offers insights into druggable pathways, potentially aiding in the development of more effective therapeutic interventions for PD, DLB, and MSA. The study emphasizes that understanding these specific cellular effects is a necessary step toward overcoming the current limitations in treating these neurodegenerative disorders.