Global neuropathologic severity of Alzheimer's disease and locus coeruleus vulnerability influences plasma phosphorylated tau levels

BACKGROUND

Advances in ultrasensitive detection of phosphorylated tau (p-tau) in plasma has enabled the use of blood tests to measure Alzheimer's disease (AD) biomarker changes. Examination of postmortem brains of participants with antemortem plasma p-tau levels remains critical to understanding comorbid and AD-specific contribution to these biomarker changes.

METHODS

We analyzed 35 population-based Mayo Clinic Study of Aging participants with plasma p-tau at threonine 181 and threonine 217 (p-tau181, p-tau217) available within 3 years of death. Autopsied participants included cognitively unimpaired, mild cognitive impairment, AD dementia, and non-AD neurodegenerative disorders. Global neuropathologic scales of tau, amyloid-β, TDP-43, and cerebrovascular disease were examined. Regional digital pathology measures of tau (phosphorylated threonine 181 and 217 [pT181, pT217]) and amyloid-β (6F/3D) were quantified in hippocampus and parietal cortex. Neurotransmitter hubs reported to influence development of tangles (nucleus basalis of Meynert) and amyloid-β plaques (locus coeruleus) were evaluated.

RESULTS

The strongest regional associations were with parietal cortex for tau burden (p-tau181 R = 0.55, p = 0.003; p-tau217 R = 0.66, p < 0.001) and amyloid-β burden (p-tau181 R = 0.59, p < 0.001; p-tau217 R = 0.71, p < 0.001). Linear regression analysis of global neuropathologic scales explained 31% of variability in plasma p-tau181 (Adj. R2 = 0.31) and 59% in plasma p-tau217 (Adj. R2 = 0.59). Neither TDP-43 nor cerebrovascular disease global scales independently contributed to variability. Global scales of tau pathology (β-coefficient = 0.060, p = 0.016) and amyloid-β pathology (β-coefficient = 0.080, p < 0.001) independently predicted plasma p-tau217 when modeled together with co-pathologies, but only amyloid-β (β-coefficient = 0.33, p = 0.021) significantly predicted plasma p-tau181. While nucleus basalis of Meynert neuron count/mm2 was not associated with plasma p-tau levels, a lower locus coeruleus neuron count/mm2 was associated with higher plasma p-tau181 (R = -0.50, p = 0.007) and higher plasma p-tau217 (R = -0.55, p = 0.002). Cognitive scores (Adj. R2 = 0.25-0.32) were predicted by the global tau scale, but not by the global amyloid-β scale or plasma p-tau when modeled simultaneously.

CONCLUSIONS

Higher soluble plasma p-tau levels may be the result of an intersection between insoluble deposits of amyloid-β and tau accumulation in brain, and may be associated with locus coeruleus degeneration.

Mid- and Late-Life Physical Activity and Neuropsychiatric Symptoms in Dementia-Free Older Adults: Mayo Clinic Study of Aging

OBJECTIVE

This study examined associations between physical activity (PA) and neuropsychiatric symptoms (NPS) in older adults free of dementia.

METHODS

This cross-sectional study included 3,222 individuals ≥70 years of age (1,655 men; mean±SD age=79.2±5.6; cognitively unimpaired, N=2,723; mild cognitive impairment, N=499) from the population-based Mayo Clinic Study of Aging. PA (taken as a presumed predictor) in midlife (i.e., when participants were 50-65 years of age) and late life (i.e., the year prior to assessment) was assessed with a self-reported, validated questionnaire; PA intensity and frequency were used to calculate composite scores. NPS (taken as presumed outcomes) were assessed with the Neuropsychiatric Inventory Questionnaire, Beck Depression Inventory (BDI-II), and Beck Anxiety Inventory (BAI). Regression analyses included midlife and late-life PA in each model, which were adjusted for age, sex, education, apolipoprotein E ɛ4 status, and medical comorbidity.

RESULTS

Higher late-life PA was associated with lower odds of having apathy (OR=0.89, 95% CI=0.84-0.93), appetite changes (OR=0.92, 95% CI=0.87-0.98), nighttime disturbances (OR=0.95, 95% CI=0.91-0.99), depression (OR=0.94, 95% CI=0.90-0.97), irritability (OR=0.93, 95% CI=0.89-0.97), clinical depression (OR=0.92, 95% CI=0.88-0.97), and clinical anxiety (OR=0.90, 95% CI=0.86-0.94), as well as lower BDI-II (β estimate=-0.042, 95% CI=-0.051 to -0.033) and BAI (β estimate=-0.030, 95% CI=-0.040 to -0.021) scores. Higher midlife PA was associated only with higher BDI-II scores (β estimate=0.011, 95% CI=0.004 to 0.019). Sex modified the associations between PA and NPS.

CONCLUSIONS

Late-life PA was associated with a lower likelihood of clinical depression or anxiety and subclinical NPS. These findings need to be confirmed in a cohort study.

Neuropathologic scales of cerebrovascular disease associated with diffusion changes on MRI

Summarizing the multiplicity and heterogeneity of cerebrovascular disease (CVD) features into a single measure has been difficult in both neuropathology and imaging studies. The objective of this work was to evaluate the association between neuroimaging surrogates of CVD and two available neuropathologic CVD scales in those with both antemortem imaging CVD measures and postmortem CVD evaluation. Individuals in the Mayo Clinic Study of Aging with MRI scans within 5 years of death (N = 51) were included. Antemortem CVD measures were computed from diffusion MRI (dMRI), FLAIR, and T2* GRE imaging modalities and compared with postmortem neuropathologic findings using Kalaria and Strozyk Scales. Of all the neuroimaging measures, both regional and global dMRI measures were associated with Kalaria and Strozyk Scales (p < 0.05) and modestly correlated with global cognitive performance. The major conclusions from this study were: (i) microstructural white matter injury measurements using dMRI may be meaningful surrogates of neuropathologic CVD scales, because they aid in capturing diffuse (and early) changes to white matter and secondary neurodegeneration due to lesions; (ii) vacuolation in the corpus callosum may be associated with white matter changes measured on antemortem dMRI imaging; (iii) Alzheimer's disease neuropathologic change did not associate with neuropathologic CVD scales; and (iv) future work should be focused on developing better quantitative measures utilizing dMRI to optimally assess CVD-related neuropathologic changes.

Screening and enrollment of underrepresented ethnocultural and educational populations in the Alzheimer's Disease Neuroimaging Initiative (ADNI)

INTRODUCTION

An analysis of the ethnocultural and socioeconomic composition of Alzheimer's Disease Neuroimaging Initiative (ADNI) participants is needed to assess the generalizability of ADNI data to diverse populations.

METHODS

ADNI data collected between October 2004 and November 2020 were used to determine ethnocultural and educational composition of the sample and differences in the following metrics: screening, screen fails, enrollment, biomarkers.

RESULTS

Of 3739 screened individuals, 11% identified as being from ethnoculturally underrepresented populations (e.g., Black, Latinx) and 16% had <12 years of education. Of 2286 enrolled participants, 11% identified as ethnoculturally underrepresented individuals and 15% had <12 years of education. This participation is considerably lower than US Census data for adults 60+ (ethnoculturally underrepresented populations: 25%; <12 years of education: 4%). Individuals with <12 years of education failed screening at a higher rate.

DISCUSSION

Our findings suggest that ADNI results may not be entirely generalizable to ethnoculturally diverse and low education populations.

Optimum Differentiation of Frontotemporal Lobar Degeneration from Alzheimer Disease Achieved with Cross-Sectional Tau Positron Emission Tomography

OBJECTIVE

This study was undertaken to assess cross-sectional and longitudinal [¹⁸ F]-flortaucipir positron emission tomography (PET) uptake in pathologically confirmed frontotemporal lobar degeneration (FTLD) and to compare FTLD to cases with high and low levels of Alzheimer disease (AD) neuropathologic changes (ADNC).

METHODS

One hundred forty-three participants who had completed at least one flortaucipir PET and had autopsy-confirmed FTLD (n = 52) or high (n = 58) or low ADNC (n = 33) based on Braak neurofibrillary tangle stages 0-IV versus V-VI were included. Flortaucipir standard uptake value ratios (SUVRs) were calculated for 9 regions of interest (ROIs): an FTLD meta-ROI, midbrain, globus pallidum, an AD meta-ROI, entorhinal, inferior temporal, orbitofrontal, precentral, and medial parietal. Linear mixed effects models were used to compare mean baseline SUVRs and annual rate of change in SUVR by group. Sensitivity and specificity to distinguish FTLD from high and low ADNC were calculated.

RESULTS

Baseline uptake in the FTLD meta-ROI, midbrain, and globus pallidus was greater in FTLD than high and low ADNC. No region showed a greater rate of flortaucipir accumulation in FTLD. Baseline uptake in the AD-related regions and orbitofrontal and precentral cortices was greater in high ADNC, and all showed greater rates of accumulation compared to FTLD. Baseline differences were superior to longitudinal rates in differentiating FTLD from high and low ADNC. A simple baseline metric of midbrain/inferior temporal ratio of flortaucipir uptake provided good to excellent differentiation between FTLD and high and low ADNC (sensitivities/specificities = 94%/95% and 71%/70%).

INTERPRETATION

There are cross-sectional and longitudinal differences in flortaucipir uptake between FTLD and high and low ADNC. However, optimum differentiation between FTLD and ADNC was achieved with baseline uptake rather than longitudinal rates. ANN NEUROL 2022;92:1016-1029.