Impaired glymphatic function is associated with synaptic loss in cognitive impairment

Area of Science:

• Neuroscience
• Biomarkers
• Alzheimer's Disease Research

Background:

• The glymphatic system clears waste from the brain, and its impairment is implicated in neurodegenerative diseases.
• Synaptic loss is a key feature of Alzheimer's disease (AD), correlating with cognitive decline.
• The interplay between glymphatic function, synaptic integrity, and AD pathology requires further elucidation.

Purpose of the Study:

• To investigate the correlation between glymphatic impairment and synaptic loss.
• To determine if amyloid-β (Aβ) pathology or reactive astrocytes influence this relationship.
• To explore the impact on cognitive performance across the AD pathological spectrum.

Main Methods:

• Utilized diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) as a glymphatic system biomarker.
• Employed synaptic vesicle glycoprotein 2A (SV2A) PET/MRI for synaptic density assessment.
• Measured plasma Aβ42/40 ratios and glial fibrillary acidic protein (GFAP) levels, performing mediation analyses.

Main Results:

• Lower ALPS index (greater glymphatic impairment) correlated significantly with reduced synaptic density.
• The ALPS index positively associated with SV2A PET SUVr in participants with Aβ deposition or higher GFAP.
• Hippocampal synaptic density fully mediated the link between glymphatic function (ALPS index) and global cognition.

Conclusions:

• Glymphatic system impairment is significantly associated with synaptic density loss in individuals with AD pathology.
• Reactive astrocytes (GFAP) and cerebral Aβ plaques appear to strengthen this association.
• Findings highlight a potential mechanism linking glymphatic dysfunction to synaptic degeneration and cognitive impairment in AD.