APOE4 is the strongest genetic risk factor for late-onset Alzheimer’s disease (AD). ApoE4 increases brain amyloid-β (Aβ) pathology relative to other ApoE isoforms1. However, whether APOE independently influences tau pathology, the other major proteinopathy of AD and other tauopathies, or tau-mediated neurodegeneration, is not clear. By generating P301S tau transgenic mice on either a human ApoE knockin (KI) or ApoE knockout (KO) background, we show that P301S/E4 mice have significantly higher tau levels in the brain and a greater extent of somatodendritic tau redistribution by 3 months of age compared to P301S/E2, P301S/E3 and P301S/EKO mice. By 9 months of age, P301S mice with different ApoE genotypes display distinct p-tau staining patterns. P301S/E4 mice develop markedly more brain atrophy and neuroinflammation than P301S/E2 and P301S/E3 mice, whereas P301S/EKO mice are largely protected from these changes. In vitro, E4-expressing microglia exhibit higher innate immune reactivity following LPS treatment. Co-culturing P301S tau-expressing neurons with E4-expressing mixed glia results in a significantly higher level of TNFα secretion and markedly reduced neuronal viability compared to neuron/E2 and neuron/E3 co-cultures. Neurons co-cultured with EKO glia showed the greatest viability with the lowest level of secreted TNFα. Treatment of P301S neurons with recombinant ApoE (E2, E3, E4) also leads to some neuronal damage and death compared to the absence of ApoE, with ApoE4 exacerbating the effect. In individuals with a sporadic primary tauopathy, the presence of an ε4 allele is associated with more severe regional neurodegeneration. In Aβ-pathology positive individuals with symptomatic AD who usually have tau pathology, ε4-carriers demonstrate greater rates of disease progression. Our results demonstrate that ApoE affects tau pathogenesis, neuroinflammation, and tau-mediated neurodegeneration independent of Aβ pathology. ApoE4 exerts a “toxic” gain of function whereas the absence of ApoE is protective.

IMPORTANCE Racial differences in molecular biomarkers for Alzheimer disease may suggest race-dependent biological mechanisms.OBJECTIVE To ascertain whether there are racial disparities in molecular biomarkers for Alzheimer disease.

In Alzheimer’s disease (AD), deposition of insoluble amyloid-β (Aβ) is followed by intracellular aggregation of tau in the neocortex and subsequent neuronal cell loss, synaptic loss, brain atrophy, and cognitive impairment. By the time even the earliest clinical symptoms are detectable, Aβ accumulation is close to reaching its peak and neocortical tau pathology is frequently already present. The period in which AD pathology is accumulating in the absence of cognitive symptoms and represents a clinically relevant time window for therapeutic intervention. Sleep is increasingly recognized as a potential marker for AD pathology and future risk of cognitive impairment. Previous studies in animal models and humans have associated decreased non-rapid eye movement (NREM) sleep slow wave activity (SWA) with Aβ deposition. In this study, we analyzed cognitive performance, brain imaging, and cerebrospinal fluid (CSF) AD biomarkers in participants enrolled in longitudinal studies of aging. In addition, we monitored their sleep using a single-channel electroencephalography (EEG) device worn on the forehead. After adjusting for multiple covariates such as age and sex, we found that NREM SWA showed an inverse relationship with AD pathology, particularly tauopathy, and that this association was most evident at the lowest frequencies of NREM SWA. Given that our study participants were predominantly cognitively normal, this suggested that changes in NREM SWA, especially at 1–2 Hz, might be able to discriminate tau pathology and cognitive impairment either before or at the earliest stages of symptomatic AD.

Knowledge of within-person biomarker change will impact interpretation of biomarker outcomes in clinical trials that are dependent on disease stage.

Objective Deposition of Aβ-containing plaques as evidenced by amyloid imaging and CSF Aβ42 is an early indicator of preclinical Alzheimer disease (AD). To better understand their relationship during the earliest preclinical stages, we investigated baseline CSF markers in cognitively normal individuals at different stages of amyloid deposition defined by longitudinal amyloid imaging with Pittsburgh Compound B (PIB): 1) PIB-negative at baseline and follow-up (PIB−, normal); 2) PIB− at baseline but PIB-positive at follow-up (PIB converters, early preclinical AD); and 3) PIB-positive at baseline and follow-up (PIB+, preclinical AD). Methods Cognitively normal individuals (n=164) who had undergone baseline PIB scan and CSF collection within one year of each other and at least one additional PIB follow-up were included. Amyloid status was defined dichotomously using an a priori mean cortical cut-off. Results PIB converters (n=20) at baseline exhibited significantly lower CSF Aβ42 compared to those who remained PIB− (n=123), but higher compared to PIB+ group (n=21). A robust negative correlation (r=−0.879, p=0.0001) between CSF Aβ42 and absolute (but sub-threshold) PIB binding was observed during this early preclinical stage. The negative correlation was not as strong once individuals were PIB+ (r=−0.456, p=0.038), and there was no correlation in the stable PIB− group (p=0.905) or in the group (n=10) with early symptomatic AD (p=0.537). Interpretation CSF Ab42 levels are tightly coupled with cortical amyloid load in the earliest stages of preclinical AD, and began to decrease dramatically prior to the point when an abnormal threshold of cortical accumulation is detected with amyloid imaging.