Phosphorylated α-synuclein in CSF and plasma does not reflect synucleinopathy

Area of Science:

• Neuroscience
• Biochemistry
• Biomarker Discovery

Background:

• Alpha-synuclein (α-syn) aggregation is implicated in neurodegenerative diseases.
• Phosphorylated α-synuclein at serine 129 (pS129 α-syn) is a key pathological hallmark.
• Developing sensitive assays for α-syn proteoforms is crucial for understanding disease mechanisms and identifying biomarkers.

Purpose of the Study:

• To develop and validate a sensitive single-molecule array (Simoa) assay for quantifying pS129 α-syn in human cerebrospinal fluid (CSF) and plasma.
• To evaluate the diagnostic utility of pS129 α-syn and other α-syn proteoforms in Parkinson's disease (PD) and Alzheimer's disease (AD).
• To investigate the relationship between soluble pS129 α-syn levels and synucleinopathy as determined by the α-synuclein seed amplification assay (synSAA).

Main Methods:

• Development of a novel Simoa Homebrew assay for pS129 α-syn quantification.
• Analysis of CSF and plasma samples from patients with PD, AD, and neurological controls.
• Measurement of pS129 α-syn alongside N-terminal and C-terminal α-syn proteoforms.
• Correlation analysis with synSAA outcomes.

Main Results:

• pS129 α-syn constitutes a minor fraction (1% in CSF, 0.001% in plasma) of total α-syn species.
• No correlation was found between CSF/plasma pS129 α-syn levels and synSAA results, suggesting it does not reflect active synucleinopathy.
• Significantly elevated levels of pS129 α-syn and other α-syn forms were observed in AD patients compared to PD patients and controls.

Conclusions:

• The developed Simoa assay provides sensitive detection of pS129 α-syn in biofluids.
• Soluble pS129 α-syn in CSF and plasma is not a reliable indicator of synucleinopathy.
• Elevated pS129 α-syn in AD suggests its potential role as a biomarker for synaptic degeneration in Alzheimer's disease.