Impaired synaptic function is linked to cognition in Parkinson's disease

Area of Science:

• Neuroscience
• Neurology
• Biochemistry

Background:

• Cognitive impairment is common in Parkinson's disease (PD), but its mechanisms are unclear.
• Reduced cortical metabolism and cerebrospinal fluid (CSF) amyloid-beta (Aβ) levels are observed in PD and linked to cognitive deficits.
• Aβ release may reflect synaptic activity, suggesting a role for synaptic dysfunction.

Purpose of the Study:

• To investigate the hypothesis that synapse dysfunction connects cortical hypometabolism, reduced CSF Aβ, and alpha-synuclein (α-synuclein) in PD.
• To examine correlations between hypometabolism, CSF Aβ, and synapse-related markers (CSF neurogranin, α-synuclein).

Main Methods:

• 30 mild-to-moderate PD patients and 26 controls underwent clinical assessment, lumbar puncture, MRI, 18F-fludeoxyglucose-PET, and neuropsychological testing.
• Cognitive tests were repeated in PD patients after 2 years.

Main Results:

• CSF Aβ levels were within the normal range for all subjects.
• In PD patients, significant correlations were found between cortical glucose metabolism, CSF Aβ, α-synuclein, and neurogranin.
• Cortical clusters identified by PET and CSF biomarkers strongly correlated with cognitive parameters.
• CSF neurogranin levels were lower in PD patients, correlating with Aβ, α-synuclein, and motor stage.
• Cognition showed little change over 2 years, but cognitive test performance remained associated with cortical metabolism.

Conclusions:

• CSF Aβ, α-synuclein, and neurogranin concentrations are linked to cortical metabolism and cognitive decline in PD.
• Synaptic dysfunction, potentially driven by Aβ and α-synuclein dysmetabolism, may be central to cognitive impairment development in Parkinson's disease.