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Diurnal patterns of soluble amyloid precursor protein metabolites in the human central nervous system.

ABSTRACT: The amyloid-β (Aβ) protein is diurnally regulated in both the cerebrospinal fluid and blood in healthy adults; circadian amplitudes decrease with aging and the presence of cerebral Aβ deposits. The cause of the Aβ diurnal pattern is poorly understood. One hypothesis is that the Amyloid Precursor Protein (APP) is diurnally regulated, leading to APP product diurnal patterns. APP in the central nervous system is processed either via the β-pathway (amyloidogenic), generating soluble APP-β (sAPPβ) and Aβ, or the α-pathway (non-amyloidogenic), releasing soluble APP-α (sAPPα). To elucidate the potential contributions of APP to the Aβ diurnal pattern and the balance of the α- and β- pathways in APP processing, we measured APP proteolytic products over 36 hours in human cerebrospinal fluid from cognitively normal and Alzheimer's disease participants. We found diurnal patterns in sAPPα, sAPPβ, Aβ40, and Aβ42, which diminish with increased age, that support the hypothesis that APP is diurnally regulated in the human central nervous system and thus results in Aβ diurnal patterns. We also found that the four APP metabolites were positively correlated in all participants without cerebral Aβ deposits. This positive correlation suggests that the α- and β- APP pathways are non-competitive under normal physiologic conditions where APP availability may be the limiting factor that determines sAPPα and sAPPβ production. However, in participants with cerebral Aβ deposits, there was no correlation of Aβ to sAPP metabolites, suggesting that normal physiologic regulation of cerebrospinal fluid Aβ is impaired in the presence of amyloidosis. Lastly, we found that the ratio of sAPPβ to sAPPα was significantly higher in participants with cerebral Aβ deposits versus those without deposits. Therefore, the sAPPβ to sAPPα ratio may be a useful biomarker for cerebral amyloidosis.

SUBMITTER: Dobrowolska JA

PROVIDER: S-EPMC3960093 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Importance:Recent studies found that the concentration of amyloid-? (A?) fluctuates with the sleep-wake cycle. Although the amplitude of this day/night pattern attenuates with age and amyloid deposition, to our knowledge, the association of A? kinetics (ie, production, turnover, and clearance) with this oscillation has not been studied. Objective:To determine the association between A? kinetics, age, amyloid levels, and the A? day/night pattern in humans. Design, Setting, and Participants:We measured A? concentrations and kinetics in 77 adults aged 60 to 87 years with and without amyloid deposition by a novel precise mass spectrometry method at the Washington University School of Medicine in St Louis, Missouri. We compared findings of 2 orthogonal methods, enzyme-linked immunosorbent assay and mass spectrometry, to validate the day/night patterns and determine more precise estimates of the cosinor parameters. In vivo labeling of central nervous system proteins with stable isotopically labeled leucine was performed, and kinetics of A?40 and A?42 were measured. Interventions:Serial cerebrospinal fluid collection via indwelling lumbar catheter over 36 to 48 hours before, during, and after in vivo labeling, with a 9-hour primed constant infusion of 13C6-leucine. Main Outcomes and Measures:The amplitude, linear increase, and other cosinor measures of each participant's serial cerebrospinal fluid A? concentrations and A? turnover rates. Results:Of the 77 participants studied, 46 (59.7%) were men, and the mean (range) age was 72.6 (60.4-87.7) years. Day/night patterns in A? concentrations were more sharply defined by the precise mass spectrometry method than by enzyme-linked immunosorbent assay (mean difference of SD of residuals: A?40, -7.42 pM; P?<?.001; A?42, -3.72 pM; P?<?.001). Amyloid deposition diminished day/night amplitude and linear increase of A?42 but not of A?40. Increased age diminished day/night amplitude of both A?40 and A?42. After controlling for amyloid deposition, amplitude of A?40 was positively associated with production rates (r?=?0.42; P?<?.001), while the linear rise was associated with turnover rates (r?=?0.28; P?<?.05). The amplitude and linear rise of A?42 were both associated with turnover (r?=?-0.38; P?<?.001) and production (r?=?0.238; P?<?.05) rates. Conclusions and Relevance:Amyloid deposition is associated with premature loss of normal A?42 day/night patterns in older adults, suggesting the previously reported effects of age and amyloid on A?42 amplitude at least partially affect each other. Production and turnover rates suggest that day/night A? patterns are modulated by both production and clearance mechanisms active in sleep-wake cycles and that amyloid deposition may impair normal circadian patterns. These findings may be important for the designs of future secondary prevention trials for Alzheimer disease.

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Diurnal patterns of soluble amyloid precursor protein metabolites in the human central nervous system.

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