Tripartite Relationship Among Synaptic, Amyloid, and Tau Proteins An In Vivo and Postmortem Study

Objective To test the hypothesis that fundamental relationships along the amyloid, tau, and neurodegeneration (A/T/N) cascade depend on synaptic integrity in older adults in vivo and postmortem. Methods The 2 independent observational, cross-sectional cohorts included (1) in vivo community-dwelling, clinically normal adults from the University of California, San Francisco Memory and Aging Center who completed lumbar puncture and MRI (exclusion criteria, Clinical Dementia Rating score >0) and (2) postmortem decedents from the Rush Memory and Aging Project (exclusion criteria, inability to sign informed consent). In vivo measures included CSF synaptic proteins (synaptotagmin-1, synaptosome associated protein-25, neurogranin, and growth associated protein-43), beta-amyloid (A beta(42/40)), tau phosphorylated at amino acid 181 (ptau(181)), and MRI gray matter volume (GMV). Postmortem measures captured brain tissue levels of presynaptic proteins (complexin-I, complexin-II, vesicle associated membrane protein (VAMP), and SNARE complex) and neuritic plaque and neurofibrillary tangle (NFT) counts. Regression models tested statistical moderation of synaptic protein levels along the A/T/N cascade (synaptic proteins x amyloid on tau, and synaptic proteins x tau on GMV). Results Sixty-eight in vivo older adults (age 71 years, 43% female) and 633 decedents (age 90 years, 68% female, 34% clinically normal) were included. Each in vivo CSF synaptic protein moderated the relationship between A beta(42/40) and ptau(181) (-0.23 < beta < -0.12, p < 0.05) and the relationship between ptau(181) and GMV (-0.49 < -0.32, p < 0.05). Individuals with more abnormal CSF synaptic protein demonstrated expected relationships between A beta-ptau(181) and ptau(181)-brain volume, effects that were absent or reversed in those with more normal CSF synaptic protein. Postmortem analyses recapitulated CSF models. More normal brain tissue levels of complexin-I, VAMP, and SNARE moderated the adverse relationship between neuritic plaque and NFT counts (-0.10 < -0.08, p < 0.05). Conclusions Pathogenic relationships of A beta and tau may depend on synaptic state. Synaptic markers may help identify risk or resilience to AD proteinopathy.

Automated summary

The study suggests that the pathogenic relationships of Aβ and tau may depend on synaptic state, and synaptic markers may help identify risk or resilience to AD proteinopathy.