Synaptic loss is the strongest correlate of cognitive impairment in Alzheimer's disease. The density of synapses in the hippocampus and cortical regions correlates directly with memory performance, and post-mortem studies reveal dramatic synapse loss even in early disease stages.
Synaptic loss in AD results from multiple converging mechanisms:
Aβ oligomers directly target synapses[1]:
Receptor internalization:
Tau mislocalizes to dendrites in AD[2]:
| Marker | Change | Source |
|---|---|---|
| PSD-95 | Decreased | Post-synaptic |
| Synaptophysin | Decreased | Pre-synaptic |
| Synapsin | Decreased | Pre-synaptic |
| NSF | Decreased | Vesicle recycling |
Aβ and tau alter spine morphology[3]:
Receptor alterations:
Synaptic plasticity:
Microglia eliminate synapses via complement[4]:
Synapse loss correlates with:
| Marker | Method | Correlation |
|---|---|---|
| CSF neurogranin | ELISA | Synaptic loss |
| CSF SNAP-25 | ELISA | Presynaptic |
| FDG-PET | Imaging | Hypometabolism |
| rs-fMRI | Imaging | Functional connectivity |
Synaptic loss represents the proximate cause of cognitive impairment in AD. Understanding the mechanisms of synaptic vulnerability provides targets for therapeutic intervention. While current treatments provide modest symptomatic benefit, disease-modifying approaches targeting synaptic protection and repair offer hope for preserving cognitive function.
Synapses have enormous energy demands
Lacor PN. Synaptic targeting by Aβ oligomers. Journal of Neuroscience. 2007. ↩︎
Hoover BR. Tau mislocalization to dendritic spines. Neuron. 2010. ↩︎
Spires-Jones TL. Synaptic pathology in AD brain. Neurobiology of Aging. 2008. ↩︎
Stevens B. Complement mediates synaptic elimination. Neuron. 2007. ↩︎