Amyloid-Beta Peptides Trigger Aggregation of Alpha-Synuclein In Vitro

Area of Science:

• Neuroscience
• Biochemistry
• Pathology

Background:

• Alzheimer's disease (AD), Parkinson's disease (PD), and dementia with Lewy bodies (DLB) are major causes of dementia.
• Many patients exhibit neuropathological hallmarks of both AD (amyloid plaques) and PD (Lewy bodies).
• The presence of alpha-synuclein (α-synuclein) in amyloid plaques suggests potential interactions between these proteins.

Purpose of the Study:

• To investigate the in vitro influence of amyloid-beta (Aβ) peptides, specifically Aβ(1-42) and pGlu-Aβ(3-42), on the aggregation of α-synuclein.
• To determine if these interactions affect the toxicity of α-synuclein.
• To confirm the co-occurrence of these proteins in vivo.

Main Methods:

• Thioflavin-T fluorescence assay to monitor α-synuclein aggregation.
• Transmission electron microscopy (TEM) with immunogold labeling to analyze fibril composition and interactions.
• Double immunofluorescence labeling in aged transgenic mouse brains to confirm in vivo co-occurrence.

Main Results:

• Low concentrations of Aβ(1-42) and pGlu-Aβ(3-42) significantly increased the aggregation propensity of α-synuclein in vitro.
• No significant effect on the toxicity of α-synuclein towards mouse primary neurons was observed.
• TEM analysis revealed direct interaction between α-synuclein and Aβ, accelerating fibril formation, likely due to enhanced nucleus formation.
• In vivo studies confirmed the co-localization of α-synuclein and Aβ species in the brains of aged transgenic mice.

Conclusions:

• Amyloid-beta peptides directly interact with and accelerate the aggregation of α-synuclein.
• This cross-talk between α-synuclein and Aβ species may be a key mechanism driving neurodegeneration in mixed dementia pathologies.
• The findings provide a molecular basis for the co-occurrence of Lewy bodies and amyloid plaques in common dementia cases.