Dataset Information

Apolipoprotein E ε4 Mediates Myelin Breakdown by Targeting Oligodendrocytes in Sporadic Alzheimer Disease.

ABSTRACT: White matter degradation in the frontal lobe is one of the earliest detectable changes in aging and Alzheimer disease. The ε4 allele of apolipoprotein E (APOE4) is strongly associated with such myelin pathology but the underlying cellular mechanisms remain obscure. We hypothesized that, as a lipid transporter, APOE4 directly triggers pathology in the cholesterol-rich myelin sheath independent of AD pathology. To test this, we performed immunohistochemistry on brain tissues from healthy controls, sporadic, and familial Alzheimer disease subjects. While myelin basic protein expression was largely unchanged, in frontal cortex the number of oligodendrocytes (OLs) was significantly reduced in APOE4 brains independent of their Braak stage or NIA-RI criteria. This high vulnerability of OLs was confirmed in humanized APOE3 or APOE4 transgenic mice. A gradual decline of OL numbers was found in the aging brain without associated neuronal loss. Importantly, the application of lipidated human APOE4, but not APOE3, proteins significantly reduced the formation of myelinating OL in primary cell culture derived from Apoe-knockout mice, especially in cholesterol-depleted conditions. Our findings suggest that the disruption of myelination in APOE4 carriers may represent a direct OL pathology, rather than an indirect consequence of amyloid plaque formation or neuronal loss.

SUBMITTER: Cheng GW

PROVIDER: S-EPMC9393713 | biostudies-literature | 2022 Aug

REPOSITORIES: biostudies-literature

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Apolipoprotein E ε4 Mediates Myelin Breakdown by Targeting Oligodendrocytes in Sporadic Alzheimer Disease.

Cheng Gerald Wai-Yeung GW Mok Kingston King-Shi KK Yeung Sunny Hoi-Sang SH Kofler Julia J Herrup Karl K Tse Kai-Hei KH

Journal of neuropathology and experimental neurology 20220801 9

White matter degradation in the frontal lobe is one of the earliest detectable changes in aging and Alzheimer disease. The ε4 allele of apolipoprotein E (APOE4) is strongly associated with such myelin pathology but the underlying cellular mechanisms remain obscure. We hypothesized that, as a lipid transporter, APOE4 directly triggers pathology in the cholesterol-rich myelin sheath independent of AD pathology. To test this, we performed immunohistochemistry on brain tissues from healthy controls, ...[more]

PMID: 35779013

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Project description:Importance:Older age, high levels of β-amyloid (Aβ), and the presence of the apolipoprotein E (APOE) ε4 allele are risk factors for Alzheimer disease (AD). However, the extent to which increasing age, Aβ, and ε4 are associated with memory decline remains unclear, and the age at which memory decline begins for Aβ-positive ε4 carriers and noncarriers has not been determined. Objective:To determine the association of age, Aβ level, and APOE ε4 with memory decline in a large group of cognitively healthy older adults. Design, Setting, and Participants:This longitudinal observational study included cognitively healthy older adults (age >60 years) enrolled in the Australian Imaging, Biomarkers and Lifestyle (AIBL) study from March 31, 2006, through March 31, 2017; of 1583 individuals enrolled, 1136 refused or were excluded owing to other criteria (eg, having mild cognitive impairment or AD). Participants underwent Aβ imaging in research clinics in Perth and Melbourne and more than 72 months of follow-up (at 18-month intervals). The association of age with memory was fitted to a quadratic model. Age was treated as a continuous, time-dependent variable. Exposures:β-Amyloid imaging using positron emission tomography, genotyping for APOE ɛ4, and longitudinal neuropsychological assessments of episodic memory during the 72-month follow-up. Main Outcomes and Measures:Episodic memory composite score. Results:Of the 447 participants, 203 (45.4%) were men and 244 (54.6%) were women; mean (SD) age was 72.5 (6.6) years. Equal proportions of female participants were observed in each Aβ-ɛ4 group (24 of 51 Aβ-positive ε4 noncarriers [47.1%] ; 35 of 64 Aβ-negative ε4 carriers [54.7%]; 40 of 72 Aβ-positive ε4 carriers [55.6%]; and 145 of 260 Aβ-negative ε4 noncarriers [55.8%]). Adults with Aβ findings (mean [SD] age, 74.4 [6.8] years) were approximately 4 years older than those negative for Aβ (mean [SD] age, 69.8 [6.1] years). Memory decline diverged significantly from Aβ-negative ɛ4 noncarriers at an earlier age in Aβ-positive ɛ4 carriers (64.5 years) than in Aβ-positive ɛ4 noncarriers (76.5 years), such that by 85 years of age, Aβ-positive ε4 carriers performed approximately 1.5 SD units worse on the episodic memory composite than Aβ-negative ε4 noncarriers and approximately 0.8 SD units worse than Aβ-positive ε4 noncarriers. Memory performance of Aβ-negative ɛ4 carriers did not differ from that of the Aβ-negative ɛ4 noncarriers (estimate [SE], 0.001 [0.001]; t = 0.526; P = .77). Conclusions and Relevance:Prior work has shown that Aβ and ε4 combine to influence memory decline in nondemented older adults. Results of this study indicate that increasing age may further exacerbate these effects. The estimates provided may be used to determine the risk of memory decline associated with Aβ and ε4 at each age.

Project description:ImportanceThe apolipoprotein E (APOE [GenBank, 348; OMIM, 107741]) ε4 allele is a common and well-established genetic risk factor for Alzheimer disease (AD). Sleep consolidation is also associated with AD risk, and previous work suggests that APOE genotype and sleep may interact to influence cognitive function.ObjectiveTo determine whether better sleep consolidation attenuates the relationship of the APOE genotype to the risk of incident AD and the burden of AD pathology.Design, setting, and participantsA prospective longitudinal cohort study with up to 6 years of follow-up was conducted. Participants included 698 community-dwelling older adults without dementia (mean age, 81.7 years; 77% women) in the Rush Memory and Aging Project.ExposuresWe used up to 10 days of actigraphic recording to quantify the degree of sleep consolidation and ascertained APOE genotype.Main outcomes and measuresParticipants underwent annual evaluation for AD during a follow-up period of up to 6 years. Autopsies were performed on 201 participants who died, and β-amyloid (Aβ) and neurofibrillary tangles were identified by immunohistochemistry and quantified.ResultsDuring the follow-up period, 98 individuals developed AD. In a series of Cox proportional hazards regression models, better sleep consolidation attenuated the effect of the ε4 allele on the risk of incident AD (hazard ratio, 0.67; 95% CI, 0.46-0.97; P = .04 per allele per 1-SD increase in sleep consolidation). In a series of linear mixed-effect models, better sleep consolidation also attenuated the effect of the ε4 allele on the annual rate of cognitive decline. In individuals who died, better sleep consolidation attenuated the effect of the ε4 allele on neurofibrillary tangle density (interaction estimate, -0.42; SE = 0.17; P = .02), which accounted for the effect of sleep consolidation on the association between APOE genotype and cognition proximate to death.Conclusions and relevanceBetter sleep consolidation attenuates the effect of APOE genotype on incident AD and development of neurofibrillary tangle pathology. Assessment of sleep consolidation may identify APOE+ individuals at high risk for incident AD, and interventions to enhance sleep consolidation should be studied as potentially useful means to reduce the risk of AD and development of neurofibrillary tangles in APOE ε4+ individuals.

Project description:ImportanceThe accumulation of aggregated β-amyloid and tau proteins into plaques and tangles is a central feature of Alzheimer disease (AD). While plaque and tangle accumulation likely contributes to neuron and synapse loss, disease-related changes to oligodendrocytes and myelin are also suspected of playing a role in development of AD dementia. Still, to our knowledge, little is known about AD-related myelin changes, and even when present, they are often regarded as secondary to concomitant arteriosclerosis or related to aging.ObjectiveTo assess associations between hallmark AD pathology and novel quantitative neuroimaging markers while being sensitive to white matter myelin content.Design, setting, and participantsMagnetic resonance imaging was performed at an academic research neuroimaging center on a cohort of 71 cognitively asymptomatic adults enriched for AD risk. Lumbar punctures were performed and assayed for cerebrospinal fluid (CSF) biomarkers of AD pathology, including β-amyloid 42, total tau protein, phosphorylated tau 181, and soluble amyloid precursor protein. We measured whole-brain longitudinal and transverse relaxation rates as well as the myelin water fraction from each of these individuals.Main outcomes and measuresAutomated brain mapping algorithms and statistical models were used to evaluate the relationships between age, CSF biomarkers of AD pathology, and quantitative magnetic resonance imaging relaxometry measures, including the longitudinal and transverse relaxation rates and the myelin water fraction.ResultsThe mean (SD) age for the 19 male participants and 52 female participants in the study was 61.6 (6.4) years. Widespread age-related changes to myelin were observed across the brain, particularly in late myelinating brain regions such as frontal white matter and the genu of the corpus callosum. Quantitative relaxometry measures were negatively associated with levels of CSF biomarkers across brain white matter and in areas preferentially affected in AD. Furthermore, significant age-by-biomarker interactions were observed between myelin water fraction and phosphorylated tau 181/β-amyloid 42, suggesting that phosphorylated tau 181/β-amyloid 42 levels modulate age-related changes in myelin water fraction.Conclusions and relevanceThese findings suggest amyloid pathologies significantly influence white matter and that these abnormalities may signify an early feature of the disease process. We expect that clarifying the nature of myelin damage in preclinical AD may be informative on the disease's course and lead to new markers of efficacy for prevention and treatment trials.

Dataset Information

Apolipoprotein E ε4 Mediates Myelin Breakdown by Targeting Oligodendrocytes in Sporadic Alzheimer Disease.

Publications

Apolipoprotein E ε4 Mediates Myelin Breakdown by Targeting Oligodendrocytes in Sporadic Alzheimer Disease.

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