PARIS undergoes liquid-liquid phase separation and poly(ADP-ribose)-mediated solidification.

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons.
• Parkin-interacting substrate (PARIS) is implicated in PD pathogenesis.
• Protein aggregation and altered phase separation are key mechanisms in neurodegeneration.

Purpose of the Study:

• To investigate the pathophysiological properties of PARIS, specifically its phase separation behavior.
• To elucidate the role of poly(ADP-ribose) (PAR) in PARIS aggregation.
• To explore PARIS phase separation in cellular and animal models of Parkinson's disease.

Main Methods:

• In vitro studies of liquid-liquid phase separation (LLPS) and solid formation using PARIS domains.
• Biochemical assays to assess PARIS binding to poly(ADP-ribose) (PAR).
• Experiments using human iPSC-derived dopaminergic neurons and mouse models of PD (α-synuclein PFF injection, parkin KO mice).

Main Results:

• PARIS undergoes both liquid-liquid phase separation (LLPS) and amorphous solid formation.
• The N-terminal LCD1 domain is essential for LLPS, while the C-terminal PrLD drives solidification.
• PAR binding accelerates PARIS LLPS and solidification.
• PAR-mediated PARIS oligomerization occurs in dopaminergic neurons and is inhibited by a PARP inhibitor.
• PARIS solidification is observed in aged mice overexpressing PARIS and in mouse models of PD.

Conclusions:

• PARIS undergoes pathological liquid-liquid phase separation and solidification.
• PARylation significantly promotes PARIS solidification, linking PAR metabolism to protein aggregation in PD.
• These findings highlight PARIS phase separation and PARylation as critical events in Parkinson's disease pathogenesis.