Presynaptic proteins complexin-I and complexin-II differentially influence cognitive function in early and late stages of Alzheimer’s disease
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Progressive accumulation of Alzheimer’s disease-related pathology is associated with cognitive dysfunction. Differences in cognitive reserve may contribute to individual differences in cognitive function in the presence of comparable neuropathology. The protective effects of cognitive reserve could contribute differentially in early versus late stages of the disease. We investigated presynaptic proteins as measures of brain reserve (a subset of total cognitive reserve), and used Braak staging to estimate the progression of Alzheimer’s disease. Antemortem evaluations of cognitive function, postmortem assessments of pathologic indices, and presynaptic protein analyses, including the complexins I and II as respective measures of inhibitory and excitatory terminal function, were assayed in multiple key brain regions in 418 deceased participants from a community study. After covarying for demographic variables, pathologic indices, and overall synapse density, lower brain complexin-I and -II levels contributed to cognitive dysfunction (P < 0.01). Each complexin appeared to be dysregulated at a different Braak stage. Inhibitory complexin-I explained 14.4% of the variance in global cognition in Braak 0–II, while excitatory complexin-II explained 7.3% of the variance in Braak V–VI. Unlike other presynaptic proteins, complexins did not colocalize with pathologic tau within neuritic plaques, suggesting that these functional components of the synaptic machinery are cleared early from dystrophic neurites. Moreover, complexin levels showed distinct patterns of change related to memory challenges in a rat model, supporting the functional specificity of these proteins. The present results suggest that disruption of inhibitory synaptic terminals may trigger early cognitive impairment, while excitatory terminal disruption may contribute relatively more to later cognitive impairment.
KeywordsSynaptic pathology Inhibitory terminals Cognitive decline Dementia Braak staging Postmortem human brain Aging study
We thank Hong-Ying Li and Jenny Yang for their skillful technical assistance. The present work was financed with Grants from the Canadian Institutes of Health Research (MT-14037, MOP-81112). The Memory and Aging Project represents a collaborative, multidisciplinary and prospective research supported by the National Institute on Aging (Grants R01AG17917, R01AG42210). Dr. W.G. Honer was supported by the Jack Bell Chair in Schizophrenia.
Compliance with ethical standards
Conflict of interest
Dr. W.G. Honer has received consulting fees or sat on paid advisory boards for: In Silico, Lundbeck/Otsuka, Eli Lilly, and Roche. Dr. A.M. Barr is on the advisory board or received consulting fees from Roche Canada, and received educational grant support from BMS Canada. The Organizations cited above had no role in (and, therefore, did not influence) the design of this study, the interpretation of results, and/or preparation of the manuscript. All other authors have no financial interest on the reported data and declare that no competing interests exist.
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