Physiological α-synuclein S129 phosphorylation mediates postsynaptic and nuclear interactions in the human brain

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Phosphorylation of alpha-synuclein (αsyn) at serine 129 (PS129) is a hallmark of synucleinopathies but also occurs physiologically.
• Technical challenges, such as postmortem dephosphorylation, have limited the study of physiological PS129 in human brains.
• Understanding physiological PS129 interactions is crucial for distinguishing normal αsyn function from disease pathology.

Purpose of the Study:

• To map the physiological PS129 and total αsyn interactomes in the human brain.
• To overcome technical barriers in studying postmortem brain tissue.
• To identify the specific cellular compartments and protein partners involved in physiological PS129 signaling.

Main Methods:

• Utilized biotinylation by antibody recognition (BAR) on surgically resected human temporal lobectomy tissues (no post-mortem interval).
• Mapped αsyn and PS129 interactomes, identifying specific, shared, and PS129-exclusive protein interactions.
• Confirmed findings in healthy cynomolgus macaques to validate physiological relevance.

Main Results:

• Identified 1,095 αsyn interactions, with 58 uniquely associated with PS129.
• PS129-specific interactions were enriched in postsynaptic density proteins (e.g., SHANK, DLGAP) and nuclear-associated proteins (e.g., HUWE1, HNRNPM).
• Physiological PS129 was localized near dendrites and within the nucleus, with significant overlap in non-human primates.

Conclusions:

• Physiological PS129 plays a critical, underappreciated role in postsynaptic neurons, extending from the active zone to the nucleus.
• The identified interactomes provide a benchmark for normal αsyn biology.
• This work illuminates the transition from normal αsyn function to synucleinopathy pathology.