Abstract
Alzheimer’s disease (AD) pathology is characterized by an early and prolonged decrease in the amyloid peptide (Aβ) levels concomitant with a later increase in phospho-tau concentrations in cerebrospinal fluid (CSF). We propose that changes in lipid metabolism can contribute to the abnormal processing of Aβ42 in AD. Our aim was to determine if polyunsaturated fatty acid (PUFA) metabolism can differentiate pre-symptomatic AD from normal aging and symptomatic AD. Using neuropsychology measures and Aβ42/T-tau in cerebrospinal fluid (CSF), we classify three groups of elderly study participants: cognitively healthy with normal Aβ42/T-tau (CH-NAT), cognitively healthy with pathological Aβ42/T-tau (CH-PAT), and AD individuals. We determined the size distribution and the concentration of CSF particles using light scattering and quantified PUFA composition in the nanoparticulate (NP) fraction, supernatant fluid (SF), and unesterified PUFA levels using gas chromatography combined with mass spectrometry. Four PUFAs (C20:2n-6, C20:3n-3, C22:4n-6, C22:5n-3) were enriched in NP of AD compared with CH-NAT. C20:3n-3 levels were higher in the NP fraction from AD compared with CH-PAT. When normalized to the number of NPs in CSF, PUFA levels were significantly higher in CH-NAT and CH-PAT compared with AD. In the SF fractions, only the levels of docosahexaenoic acid (DHA, C22:6n-3) differentiated all three clinical groups. Unesterified DHA was also higher in CH-NAT compared with the other clinical groups. Our studies also show that NP PUFAs in CH participants negatively correlate with CSF Aβ42 while C20:4n-6, DHA, and n-3 PUFAs in the SF fraction positively correlate with T-tau. The profile of PUFAs in different CSF fractions that correlate with Aβ42 or with T-tau are different for CH-NAT compared with CH-PAT. These studies show that PUFA metabolism is associated with amyloid and tau processing. Importantly, higher PUFA levels in the cognitively healthy study participants with abnormal Aβ42/T-tau suggest that PUFA enhances the cognitive resilience of the pre-symptomatic AD population. We propose that interventions that prevent PUFA depletion in the brain may prevent AD pathology by stabilizing Aβ42 and tau metabolism. Further studies to determine changes in PUFA composition during the progression from pre-symptomatic to AD should reveal novel biomarkers and potential preventive approaches.
Highlights
A hallmark of AD pathology is the formation of neurotoxic amyloid plaques and increased phosphorylation of total tau (Ttau) (Skoog et al, 2015)
We show that PUFA metabolism distinguishes pre-symptomatic AD from symptomatic AD, suggesting that PUFAs may contribute to the cognitive resilience of the pre-symptomatic population
The rank order of CSF Aβ42 was cognitively healthy (CH)-NAT>CH study participants with pathological Aβ42/T-tau (CH-PAT)>AD while this was reversed for T-tau
Summary
A hallmark of AD pathology is the formation of neurotoxic amyloid plaques and increased phosphorylation of total tau (Ttau) (Skoog et al, 2015). Lower levels of Aβ42 and higher levels of T-tau are found in cerebrospinal fluid of AD subjects leading to a lower Aβ42/T-tau ratio in AD compared with cognitively healthy (CH) study participants (Blennow et al, 2001; Harrington et al, 2013). These changes in Aβ42/T-tau have been recognized as a sensitive biomarker of AD (Skoog et al, 2015). What accounts for the cognitive resilience (Negash et al, 2013; Boros et al, 2017; Aiello Bowles et al, 2019) or reserve (Cummings et al, 1998; Persson et al, 2017; Menardi et al, 2018) in some elderly persons who have abnormal Aβ42? Since amyloid precursor protein (APP) is a membrane-bound protein influenced by membrane biophysics and trafficking (Askarova et al, 2011; Tan and Gleeson, 2019), we propose that changes in the lipid environment in postmitotic neurons may influence the processing and formation of amyloidogenic or non-amyloidogenic peptides
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