The neuropathology of probable Alzheimer disease and mild cognitive impairment

Association of CSF α-Synuclein Seed Amplification Assay Positivity with Disease Progression and Cognitive Decline: A Longitudinal Alzheimer's Disease Neuroimaging Initiative Study

INTRODUCTION

CSF α-synuclein seed amplification assay (SAA) is a sensitive and specific tool for detecting Lewy body (LB) co-pathology in AD.

METHODS

1637 cross-sectional and 407 longitudinal CSF samples from ADNI were tested with SAA. We examined longitudinal dynamics of Aβ, α-synuclein seeds, and p-tau181, along with global and domain-specific cognition in stable SAA+, stable SAA-, and those who converted to SAA+ from SAA-.

RESULTS

SAA+ individuals had faster cognitive decline than SAA-, notably in MCI, and presented with earlier symptom onset. SAA+ conversion was associated with CSF Aβ42-positivity but did not impact progression of either Aβ42 or p-tau181 status. Aβ42, p-tau181, and α-syn SAA were all strong predictors of clinical progression, particularly Aβ42. In vitro α-syn SAA kinetic parameters were associated with participant demographics, clinical profiles, and cognitive decline.

DISCUSSION

These results highlight the interplay between Aβ and α-synuclein and their association with disease progression.

Obstructive Sleep Apnea Among Patients with Mild Cognitive Impairment

Background

Obstructive sleep apnea (OSA) is associated with cognitive disorders, but little is known about prevalence of co-occurring OSA and mild cognitive impairment (MCI) as well as about co-occurring OSA and Alzheimer's disease (AD). Pathophysiological models integrating OSA, cognitive deficits and neurodegeneration remain speculative. Findings in this area could contribute to the knowledge about pathophysiological processes in cognitive disorders and neurodegenerative processes, be helpful for the diagnosis of cognitive disorders and provide approaches for the treatment of cognitive disorders.

Objective

Examining the prevalence of OSA and patterns of cognitive deficits as well as AD biomarker profiles associated with OSA in a cohort of 104 MCI patients.

Methods

Assessments used include: respiratory polygraphy, The Consortium to Establish a Registry for Alzheimer's Disease Neuropsychological Battery (CERAD NB), Tau, phosphoTau181, amyloid-β-1-42/1-40, 18F-fluorodeoxyglucose positron emission tomography (F18-FDG-PET).

Results

Prevalence of OSA of any severity: 58,7% (Apnea Hypopnea Index (AHI)≥5/h), OSA in a moderate-to-severe extent (AHI≥15/h): 25%. Only 13.1% of MCI patients with OSA reported daytime sleepiness. MCI-OSA patients showed no specific neuropsychological pattern. Presence of OSA was not associated with specific AD biomarker profiles in the whole study group besides a positive association between AD positivity in an AD biomarker sub cohort.

Conclusions

OSA is highly prevalent in patients with MCI. It might often remain undiagnosed as only a small number of MCI-OSA patients report daytime sleepiness. OSA could contribute to MCI symptoms and even to AD pathology. Further research is needed to validate these findings and to investigate possible pathophysiological relationships between OSA and MCI as well as between OSA and AD.

Association of Egg Intake With Alzheimer's Dementia Risk in Older Adults: The Rush Memory and Aging Project

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder with increasing prevalence due to population aging. Eggs provide many nutrients important for brain health, including choline, omega-3 fatty acids, and lutein. Emerging evidence suggests that frequent egg consumption may improve cognitive performance on verbal tests, but whether consumption influences the risk of Alzheimer's dementia and AD is unknown.

OBJECTIVES

To examine the association of egg consumption with Alzheimer's dementia risk among the Rush Memory and Aging Project cohort.

METHODS

Dietary assessment was collected using a modified Harvard semiquantitative food frequency questionnaire. Participants' first food frequency questionnaire was used as the baseline measure of egg consumption. Multivariable adjusted Cox proportional hazards regression models were used to investigate the associations of baseline egg consumption amount with Alzheimer's dementia risk, adjusting for potential confounding factors. Subgroup analyses using Cox and logistic regression models were performed to investigate the associations with AD pathology in the brain. Mediation analysis was conducted to examine the mediation effect of dietary choline in the relationship between egg intake and incident Alzheimer's dementia.

RESULTS

This study included 1024 older adults {mean [±standard deviation (SD)] age = 81.38 ± 7.20 y}. Over a mean (±SD) follow-up of 6.7 ± 4.8 y, 280 participants (27.3%) were clinically diagnosed with Alzheimer's dementia. Weekly consumption of >1 egg/wk (hazard ratio [HR]: 0.53; 95% confidence interval [CI]: 0.34, 0.83) and ≥2 eggs/wk (HR: 0.53; 95% CI: 0.35, 0.81) was associated with a decreased risk of Alzheimer's dementia. Subgroup analysis of brain autopsies from 578 deceased participants showed that intakes of >1 egg/wk (HR: 0.51; 95% CI: 0.35, 0.76) and ≥2 eggs/wk (HR: 0.62; 95% CI: 0.44, 0.90) were associated with a lower risk of AD pathology in the brain. Mediation analysis showed that 39% of the total effect of egg intake on incident Alzheimer's dementia was mediated through dietary choline.

CONCLUSIONS

These findings suggest that frequent egg consumption is associated with a lower risk of Alzheimer's dementia and AD pathology, and the association with Alzheimer's dementia is partially mediated through dietary choline.

In vivo effect of LATE-NC on integrity of white matter connections to the hippocampus

INTRODUCTION

TAR DNA-binding protein 43 (TDP-43) is a highly prevalent proteinopathy that is involved in neurodegenerative processes, including axonal damage. To date, no ante mortem biomarkers exist for TDP-43, and few studies have directly assessed its impact on neuroimaging measures utilizing pathologic quantification.

METHODS

Ante mortem diffusion-weighted images were obtained from community-dwelling older adults. Regression models calculated the relationship between post mortem TDP-43 burden and ante mortem fractional anisotropy (FA) within each voxel in connection with the hippocampus, controlling for coexisting Alzheimer's disease and demographics.

RESULTS

Results revealed a significant negative relationship (false discovery rate [FDR] corrected p < .05) between post mortem TDP-43 and ante mortem FA in one cluster within the left medial temporal lobe connecting to the parahippocampal cortex, entorhinal cortex, and cingulate, aligning with the ventral subdivision of the cingulum. FA within this cluster was associated with cognition.

DISCUSSION

Greater TDP-43 burden is associated with lower FA within the limbic system, which may contribute to impairment in learning and memory.

HIGHLIGHTS

Post mortem TDP-43 pathological burden is associated with reduced ante mortem fractional anisotropy. Reduced FA located in the parahippocampal portion of the cingulum. FA in this area was associated with reduced episodic and semantic memory. FA in this area was associated with increased inward hippocampal surface deformation.

Brain Cell-based Genetic Subtyping and Drug Repositioning for Alzheimer Disease

Alzheimer's Disease (AD) is characterized by its complex and heterogeneous etiology and gradual progression, leading to high drug failure rates in late-stage clinical trials. In order to better stratify individuals at risk for AD and discern potential therapeutic targets we employed a novel procedure utilizing cell-based co-regulated gene networks and polygenic risk scores (cbPRSs). After defining genetic subtypes using extremes of cbPRS distributions, we evaluated correlations of the genetic subtypes with previously defined AD subtypes defined on the basis of domain-specific cognitive functioning and neuroimaging biomarkers. Employing a PageRank algorithm, we identified priority gene targets for the genetic subtypes. Pathway analysis of priority genes demonstrated associations with neurodegeneration and suggested candidate drugs currently utilized in diabetes, hypertension, and epilepsy for repositioning in AD. Experimental validation utilizing human induced pluripotent stem cell (hiPSC)-derived astrocytes demonstrated the modifying effects of estradiol, levetiracetam, and pioglitazone on expression of APOE and complement C4 genes, suggesting potential repositioning for AD.

Job-related exhaustion risk variant in UST is associated with dementia and DNA methylation

Previous genome-wide association and replication study for job-related exhaustion indicated a risk variant, rs13219957 in the UST gene. Epidemiological studies suggest connection of stress-related conditions and dementia risk. Therefore, we first studied association of rs13219957 and register-based incident dementia using survival models in the Finnish National FINRISK study surveys (N = 26,693). The AA genotype of rs13219957 was significantly associated with 40% increased risk of all-cause dementia. Then we analysed the UST locus association with brain pathology in the Vantaa 85+ cohort and found association with tau pathology (Braak stage) but not with amyloid pathology. Finally, in the functional analyses, rs13219957 showed a highly significant association with two DNA methylation sites of UST, and UST expression. Thus, the results suggest a common risk variant for a stress-related condition and dementia. Mechanisms to mediate the connection may include differential DNA methylation and transcriptional regulation of UST.

Knockout of the longevity gene Klotho perturbs aging and Alzheimer's disease-linked brain microRNAs and tRNA fragments

Overexpression of the longevity gene Klotho prolongs lifespan, while its knockout shortens lifespan and impairs cognition via perturbation of myelination and synapse formation. However, comprehensive analysis of Klotho knockout effects on mammalian brain transcriptomics is lacking. Here, we report that Klotho knockout alters the levels of aging- and cognition related mRNAs, long non-coding RNAs, microRNAs and tRNA fragments. These include altered neuronal and glial regulators in murine models of aging and Alzheimer's disease and in human Alzheimer's disease post-mortem brains. We further demonstrate interaction of the knockout-elevated tRNA fragments with the spliceosome, possibly affecting RNA processing. Last, we present cell type-specific short RNA-seq datasets from FACS-sorted neurons and microglia of live human brain tissue demonstrating in-depth cell-type association of Klotho knockout-perturbed microRNAs. Together, our findings reveal multiple RNA transcripts in both neurons and glia from murine and human brain that are perturbed in Klotho deficiency and are aging- and neurodegeneration-related.

The pattern of cortical thickness associated with executive dysfunction in MCI and SCC: The MEMENTO cohort

BACKGROUND

The association between the pattern of cortical thickness (CT) and executive dysfunction (ED) in mild cognitive impairment (MCI) and subjective cognitive complaints (SCC) is still poorly understood. We aimed to investigate the association between CT and ED in a large French cohort (MEMENTO) of 2323 participants with MCI or SCC.

METHODS

All participants with available CT and executive function data (verbal fluency and Trail Making Test [TMT]) were selected (n=1924). Linear regressions were performed to determine relationships between executive performance and the brain parenchymal fraction (BPF) and CT using FreeSurfer.

RESULTS

The global executive function score was related to the BPF (sß: 0.091, P<0.001) and CT in the right supramarginal (sß: 0.060, P=0.041) and right isthmus cingulate (sß: 0.062, P=0.011) regions. Literal verbal fluency was related to the BPF (sß: 0.125, P<0.001) and CT in the left parsorbitalis region (sß: 0.045, P=0.045). Semantic verbal fluency was related to the BPF (sß: 0.101, P<0.001) and CT in the right supramarginal region (sß: 0.061, P=0.042). The time difference between the TMT parts B and A was related to the BPF (sß: 0.048, P=0.045) and CT in the right precuneus (sß: 0.073, P=0.019) and right isthmus cingulate region (sß: 0.054, P=0.032).

CONCLUSIONS

In a large clinically based cohort of participants presenting with either MCI or SCC (a potential early stage of Alzheimer's disease [AD]), ED was related to the BPF and CT in the left pars orbitalis, right precuneus, right supramarginal, and right isthmus cingulate regions. This pattern of lesions adds knowledge to the conventional anatomy of ED and could contribute to the early diagnosis of AD.

Cellular senescence induced by cholesterol accumulation is mediated by lysosomal ABCA1 in APOE4 and AD

Background

Cellular senescence is a hallmark of aging and has been implicated in Alzheimer's disease (AD) pathogenesis. Cholesterol accumulation drives cellular senescence; however, the underlying mechanisms are unclear. ATP-binding cassette transporter A1 (ABCA1) plays an important role in cholesterol homeostasis. ABCA1 expression and its trafficking is afiltered in APOE4 and AD cellular and mouse models. However, whether ABCA1 trafficking is involved in cellular senescence in APOE4 and AD remains unknown.

Methods

We examined the association between cellular senescence and ABCA1 expression in human postmortem brain samples using transcriptomic, histological, and biochemical analyses. An unbiased proteomic screening was performed to identify targets that mediate cellular ABCA1 trafficking. APOE4-TR mice, immortalized, primary and induced pluripotent stem cell (iPSC) models were used to examine the cholesterol-ABCA1-senescence pathways.

Results

Bulk and single nuclei transcriptomic profiling of the human dorsolateral prefrontal cortex from the Religious Order Study/Memory Aging Project (ROSMAP) revealed upregulation of cellular senescence transcriptome signatures in AD, which was strongly correlated with ABCA1 expression. Immunofluorescence and immunoblotting analyses confirmed increased ABCA1 expression in AD brain tissues, which was associated with lipofuscin-stained lipids and mTOR phosphorylation. Using discovery proteomics, caveolin-1, a sensor of cellular cholesterol accumulation, was identified to promote ABCA1 endolysosomal trafficking. Greater caveolin-1 expression was found in both APOE4-TR mouse models and AD human brains. Cholesterol induced mTORC1 activation was regulated by ABCA1 expression or its lysosomal trapping. Reducing cholesterol by cyclodextrin in APOE4-TR mice reduced ABCA1 lysosome trapping and increased ABCA1 recycling to efflux cholesterol to HDL particles, reducing mTORC1 activation and senescence-associated neuroinflammation. In human iPSC-derived astrocytes, the reduction of cholesterol by cyclodextrin attenuated inflammatory responses.

Conclusions

Cholesterol accumulation in APOE4 and AD induced caveolin-1 expression, which traps ABCA1 in lysosomes to activate mTORC1 pathways and induce cellular senescence. This study provided novel insights into how cholesterol accumulation in APOE4 and AD accelerates senescence.

Structural white matter properties and cognitive resilience to tau pathology

INTRODUCTION

We assessed whether macro- and/or micro-structural white matter properties are associated with cognitive resilience to Alzheimer's disease pathology years prior to clinical onset.

METHODS

We examined whether global efficiency, an indicator of communication efficiency in brain networks, and diffusion measurements within the limbic network and default mode network moderate the association between amyloid-β/tau pathology and cognitive decline. We also investigated whether demographic and health/risk factors are associated with white matter properties.

RESULTS

Higher global efficiency of the limbic network, as well as free-water corrected diffusion measures within the tracts of both networks, attenuated the impact of tau pathology on memory decline. Education, age, sex, white matter hyperintensities, and vascular risk factors were associated with white matter properties of both networks.

DISCUSSION

White matter can influence cognitive resilience against tau pathology, and promoting education and vascular health may enhance optimal white matter properties.

HIGHLIGHTS

Aβ and tau were associated with longitudinal memory change over ∼7.5 years. White matter properties attenuated the impact of tau pathology on memory change. Health/risk factors were associated with white matter properties.

2024 Alzheimer's disease facts and figures

This article describes the public health impact of Alzheimer's disease (AD), including prevalence and incidence, mortality and morbidity, use and costs of care and the ramifications of AD for family caregivers, the dementia workforce and society. The Special Report discusses the larger health care system for older adults with cognitive issues, focusing on the role of caregivers and non-physician health care professionals. An estimated 6.9 million Americans age 65 and older are living with Alzheimer's dementia today. This number could grow to 13.8 million by 2060, barring the development of medical breakthroughs to prevent or cure AD. Official AD death certificates recorded 119,399 deaths from AD in 2021. In 2020 and 2021, when COVID-19 entered the ranks of the top ten causes of death, Alzheimer's was the seventh-leading cause of death in the United States. Official counts for more recent years are still being compiled. Alzheimer's remains the fifth-leading cause of death among Americans age 65 and older. Between 2000 and 2021, deaths from stroke, heart disease and HIV decreased, whereas reported deaths from AD increased more than 140%. More than 11 million family members and other unpaid caregivers provided an estimated 18.4 billion hours of care to people with Alzheimer's or other dementias in 2023. These figures reflect a decline in the number of caregivers compared with a decade earlier, as well as an increase in the amount of care provided by each remaining caregiver. Unpaid dementia caregiving was valued at $346.6 billion in 2023. Its costs, however, extend to unpaid caregivers' increased risk for emotional distress and negative mental and physical health outcomes. Members of the paid health care and broader community-based workforce are involved in diagnosing, treating and caring for people with dementia. However, the United States faces growing shortages across different segments of the dementia care workforce due to a combination of factors, including the absolute increase in the number of people living with dementia. Therefore, targeted programs and care delivery models will be needed to attract, better train and effectively deploy health care and community-based workers to provide dementia care. Average per-person Medicare payments for services to beneficiaries age 65 and older with AD or other dementias are almost three times as great as payments for beneficiaries without these conditions, and Medicaid payments are more than 22 times as great. Total payments in 2024 for health care, long-term care and hospice services for people age 65 and older with dementia are estimated to be $360 billion. The Special Report investigates how caregivers of older adults with cognitive issues interact with the health care system and examines the role non-physician health care professionals play in facilitating clinical care and access to community-based services and supports. It includes surveys of caregivers and health care workers, focusing on their experiences, challenges, awareness and perceptions of dementia care navigation.

Profiles of Lifestyle Health Behaviors and Postmortem Dementia-Related Neuropathology

High engagement in lifestyle health behaviors appears to be protective against cognitive decline in aging. We investigated the association between patterns of modifiable lifestyle health behaviors and common brain neuropathologies of dementia as a possible mechanism. We examined 555 decedents from the Rush Memory and Aging Project, free of dementia at their initial concurrent report of lifestyle health behaviors of interest (physical, social, and cognitive activities, and healthy diet), and who underwent a postmortem neuropathology evaluation. First, we used latent profile analysis to group participants based on baseline behavior patterns. Second, we assessed the associations of profile membership with each neurodegenerative (global Alzheimer's disease [AD] pathology, amyloid-beta load, density of neurofibrillary tangles, and presence of cortical Lewy bodies and TAR DNA-binding protein 43 cytoplasmic inclusions) and neurovascular pathologies (presence of chronic gross or microscopic infarcts, arteriolosclerosis, atherosclerosis, and cerebral amyloid angiopathy), using separate linear or logistic regression models, adjusted for age at death, sex (core model), vascular disease risk factors, and vascular conditions (fully adjusted model). Participants had either consistently lower (N = 224) or consistently higher (N = 331) engagement across 4 lifestyle health behaviors. We generally found no differences in neuropathologies between higher and lower engagement groups in core or fully adjusted models; for example, higher engagement in lifestyle health behaviors was not associated with global AD pathology after core or full adjustment (both p > .8). In conclusion, we found no evidence of associations between patterns of lifestyle health behaviors and neuropathology. Other mechanisms may underlie protective effects of health behaviors against dementia.

The Cerebrospinal Fluid Free-Glycans Hex1 and HexNAc1Hex1Neu5Ac1 as Potential Biomarkers of Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder, affecting a growing number of elderly people. In order to improve the early and differential diagnosis of AD, better biomarkers are needed. Glycosylation is a protein post-translational modification that is modulated in the course of many diseases, including neurodegeneration. Aiming to improve AD diagnosis and differential diagnosis through glycan analytics methods, we report the glycoprotein glycome of cerebrospinal fluid (CSF) isolated from a total study cohort of 262 subjects. The study cohort consisted of patients with AD, healthy controls and patients suffering from other types of dementia. CSF free-glycans were also isolated and analyzed in this study, and the results reported for the first time the presence of 19 free glycans in this body fluid. The free-glycans consisted of complete or truncated N-/O-glycans as well as free monosaccharides. The free-glycans Hex1 and HexNAc1Hex1Neu5Ac1 were able to discriminate AD from controls and from patients suffering from other types of dementia. Regarding CSF N-glycosylation, high proportions of high-mannose, biantennary bisecting core-fucosylated N-glycans were found, whereby only about 20% of the N-glycans were sialylated. O-Glycans and free-glycan fragments were less sialylated in AD patients than in controls. To conclude, this comprehensive study revealed for the first time the biomarker potential of free glycans for the differential diagnosis of AD.

Neuropsychiatric symptoms and white matter hyperintensities in older adults without dementia

OBJECTIVE

We aimed to examine associations between neuropsychiatric symptoms (NPS) and white matter hyperintensities (WMH) status in older adults without dementia under the hypothesis that WMH increased the odds of having NPS.

DESIGN

Longitudinal analysis of data acquired from the National Alzheimer's Coordinating Center Uniform Data Set.

SETTINGS

Data were derived from 46 National Institute on Aging - funded Alzheimer's Disease Research Centers.

PARTICIPANTS

NACC participants aged ≥50 years with available data on WMH severity with a diagnosis of mild cognitive impairment (MCI) or who were cognitively unimpaired (CU) were studied. Among 4617 CU participants, 376 had moderate and 54 extensive WMH. Among 3170 participants with MCI, 471 had moderate and 88 had extensive WMH.

MEASUREMENTS

Using Cardiovascular Health Study (CHS) scores, WMH were coded as no to mild (CHS score: 0-4), moderate (score: 5-6) or extensive (score: 7-8). NPS were quantified on the Neuropsychiatric Inventory Questionnaire. Binary logistic regression models estimated the odds of reporting each of 12 NPS by WMH status separately for individuals with MCI or who were CU.

RESULTS

Compared to CU individuals with no to mild WMH, the odds of having elation [9.87, (2.63-37.10)], disinhibition [4.42, (1.28-15.32)], agitation [3.51, (1.29-9.54)] or anxiety [2.74, (1.28-5.88)] were higher for the extensive WMH group, whereas the odds of having disinhibition were higher for the moderate WMH group [1.94, (1.05-3.61)]. In the MCI group, he odds of NPS did not vary by WMH status.

CONCLUSIONS

Extensive WMH were associated with higher odds of NPS in CU older adults but not in those with MCI.

Biofluid biomarkers for Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease, with a complex pathogenesis and an irreversible course. Therefore, the early diagnosis of AD is particularly important for the intervention, prevention, and treatment of the disease. Based on the different pathophysiological mechanisms of AD, the research progress of biofluid biomarkers are classified and reviewed. In the end, the challenges and perspectives of future research are proposed.

The role of the Pin1-cis P-tau axis in the development and treatment of vascular contribution to cognitive impairment and dementia and preeclampsia

Tauopathies are neurodegenerative diseases characterized by deposits of abnormal Tau protein in the brain. Conventional tauopathies are often defined by a limited number of Tau epitopes, notably neurofibrillary tangles, but emerging evidence suggests structural heterogeneity among tauopathies. The prolyl isomerase Pin1 isomerizes cis P-tau to inhibit the development of oligomers, tangles and neurodegeneration in multiple neurodegenerative diseases such as Alzheimer's disease, traumatic brain injury, vascular contribution to cognitive impairment and dementia (VCID) and preeclampsia (PE). Thus, cis P-tau has emerged as an early etiological driver, blood marker and therapeutic target for multiple neurodegenerative diseases, with clinical trials ongoing. The discovery of cis P-tau and other tau pathologies in VCID and PE calls attention for simplistic classification of tauopathy in neurodegenerative diseases. These recent advances have revealed the exciting novel role of the Pin1-cis P-tau axis in the development and treatment of vascular contribution to cognitive impairment and dementia and preeclampsia.

Soluble Biomarkers of Cerebrovascular Pathologies

Vascular contributions to cognitive impairment and dementia (VCID) is an all-encompassing term that describes cognitive impairment due to cerebrovascular origins. With the advancement of imaging and pathological studies, we now understand that VCID is often comorbid with Alzheimer disease. While researchers in the Alzheimer disease field have been working for years to establish and test blood-based biomarkers for Alzheimer disease diagnosis, prognosis, clinical therapy discovery, and early detection, blood-based biomarkers for VCID are in their infancy and also face challenges. VCID is heterogeneous, comprising many different pathological entities (ischemic, or hemorrhagic), and spatial and temporal differences (acute or chronic). This review highlights pathways that are aiding the search for sensitive and specific blood-based cerebrovascular dysfunction markers, describes promising candidates, and explains ongoing initiatives to discover blood-based VCID biomarkers.

Biomarker-based staging of Alzheimer disease: rationale and clinical applications

Disease staging, whereby the spatial extent and load of brain pathology are used to estimate the severity of Alzheimer disease (AD), is pivotal to the gold-standard neuropathological diagnosis of AD. Current in vivo diagnostic frameworks for AD are based on abnormal concentrations of amyloid-β and tau in the cerebrospinal fluid or on PET scans, and breakthroughs in molecular imaging have opened up the possibility of in vivo staging of AD. Focusing on the key principles of disease staging shared across several areas of medicine, this Review highlights the potential for in vivo staging of AD to transform our understanding of preclinical AD, refine enrolment criteria for trials of disease-modifying therapies and aid clinical decision-making in the era of anti-amyloid therapeutics. We provide a state-of-the-art review of recent biomarker-based AD staging systems and highlight their contributions to the understanding of the natural history of AD. Furthermore, we outline hypothetical frameworks to stage AD severity using more accessible fluid biomarkers. In addition, by applying amyloid PET-based staging to recently published anti-amyloid therapeutic trials, we highlight how biomarker-based disease staging frameworks could illustrate the numerous pathological changes that have already taken place in individuals with mildly symptomatic AD. Finally, we discuss challenges related to the validation and standardization of disease staging and provide a forward-looking perspective on potential clinical applications.

Micro-RNA profiles of pathology and resilience in posterior cingulate cortex of cognitively intact elders

The posterior cingulate cortex (PCC) is a key hub of the default mode network underlying autobiographical memory retrieval, which falters early in the progression of Alzheimer's disease (AD). We recently performed RNA sequencing of post-mortem PCC tissue samples from 26 elderly Rush Religious Orders Study participants who came to autopsy with an ante-mortem diagnosis of no cognitive impairment but who collectively displayed a range of Braak I-IV neurofibrillary tangle stages. Notably, cognitively unimpaired subjects displaying high Braak stages may represent cognitive resilience to AD pathology. Transcriptomic data revealed elevated synaptic and ATP-related gene expression in Braak Stages III/IV compared with Stages I/II, suggesting these pathways may be related to PCC resilience. We also mined expression profiles for small non-coding micro-RNAs (miRNAs), which regulate mRNA stability and may represent an underexplored potential mechanism of resilience through the fine-tuning of gene expression within complex cellular networks. Twelve miRNAs were identified as differentially expressed between Braak Stages I/II and III/IV. However, the extent to which the levels of all identified miRNAs were associated with subject demographics, neuropsychological test performance and/or neuropathological diagnostic criteria within this cohort was not explored. Here, we report that a total of 667 miRNAs are significantly associated (rho > 0.38, P < 0.05) with subject variables. There were significant positive correlations between miRNA expression levels and age, perceptual orientation and perceptual speed. By contrast, higher miRNA levels correlated negatively with semantic and episodic memory. Higher expression of 15 miRNAs associated with lower Braak Stages I-II and 47 miRNAs were associated with higher Braak Stages III-IV, suggesting additional mechanistic influences of PCC miRNA expression with resilience. Pathway analysis showed enrichment for miRNAs operating in pathways related to lysine degradation and fatty acid synthesis and metabolism. Finally, we demonstrated that the 12 resilience-related miRNAs differentially expressed in Braak Stages I/II versus Braak Stages III/IV were predicted to regulate mRNAs related to amyloid processing, tau and inflammation. In summary, we demonstrate a dynamic state wherein differential PCC miRNA levels are associated with cognitive performance and post-mortem neuropathological AD diagnostic criteria in cognitively intact elders. We posit these relationships may inform miRNA transcriptional alterations within the PCC relevant to potential early protective (resilience) or pathogenic (pre-clinical or prodromal) responses to disease pathogenesis and thus may be therapeutic targets.

Loss of the APP regulator RHBDL4 preserves memory in an Alzheimer's disease mouse model

Characteristic cerebral pathological changes of Alzheimer's disease (AD) such as glucose hypometabolism or the accumulation of cleavage products of the amyloid precursor protein (APP), known as Aβ peptides, lead to sustained endoplasmic reticulum (ER) stress and neurodegeneration. To preserve ER homeostasis, cells activate their unfolded protein response (UPR). The rhomboid-like-protease 4 (RHBDL4) is an enzyme that participates in the UPR by targeting proteins for proteasomal degradation. We demonstrated previously that RHBLD4 cleaves APP in HEK293T cells, leading to decreased total APP and Aβ. More recently, we showed that RHBDL4 processes APP in mouse primary mixed cortical cultures as well. Here, we aim to examine the physiological relevance of RHBDL4 in the brain. We first found that brain samples from AD patients and an AD mouse model (APPtg) showed increased RHBDL4 mRNA and protein expression. To determine the effects of RHBDL4's absence on APP physiology in vivo, we crossed APPtg mice to a RHBDL4 knockout (R4 KO) model. RHBDL4 deficiency in APPtg mice led to increased total cerebral APP and Aβ levels when compared to APPtg controls. Contrary to expectations, as assessed by cognitive tests, RHBDL4 absence rescued cognition in 5-month-old female APPtg mice. Informed by unbiased RNAseq data, we demonstrated in vitro and in vivo that RHBDL4 absence leads to greater levels of active β-catenin due to decreased proteasomal clearance. Decreased β-catenin activity is known to underlie cognitive defects in APPtg mice and AD. Our work suggests that RHBDL4's increased expression in AD, in addition to regulating APP levels, leads to aberrant degradation of β-catenin, contributing to cognitive impairment.

Revealing the binding mechanism of BACE1 inhibitors through molecular dynamics simulations

Alzheimer's disease is a debilitating neurodegenerative disorder, and the Beta-Site Amyloid Precursor Protein Cleaving Enzyme 1 (BACE1) is a key therapeutic target in its treatment. This study employs molecular dynamics simulations and binding energy analysis to investigate the binding interactions between BACE1 and four selected small molecules: CNP520, D9W, NB641, and NB360. The binding model analysis indicates that the binding of BACE1 with four molecules are stable, except the loop regions show significant fluctuation. The binding free energy analyses reveal that NB360 exhibits the highest binding affinity with BACE1, surpassing other molecules (CNP520, D9W, and NB641). Detailed energy component assessments highlight the critical roles of electrostatic interactions and van der Waals forces in the binding process. Furthermore, residue contribution analysis identifies key amino acids influencing the binding process across all systems. Hydrogen bond analysis reveals a limited number of bonds between BACE1 and each small molecule, highlighting the importance of structural modifications to enable more stable hydrogen bonds. This research provides valuable insights into the molecular mechanisms of potential Alzheimer's disease therapeutics, guiding the way for improved drug design and the development of effective treatments targeting BACE1.Communicated by Ramaswamy H. Sarma.

Atherosclerosis and Hippocampal Volumes in Older Adults: The Role of Age and Blood Pressure

BACKGROUND

Lower hippocampal volume is associated with late-life cognitive decline and is an important, but nonspecific marker for clinical Alzheimer's dementia. Cerebrovascular disease may also be associated with hippocampal volume. Here we study the role of intracranial large vessel disease (atherosclerosis) in association with hippocampal volume and the potential role of age, average late-life blood pressure across all visits, and other factors (sex, apolipoprotein ε4 [APOE ε4], and diabetes).

METHODS AND RESULTS

Data came from 765 community-based older people (91 years old on average at death; 72% women), from 2 ongoing clinical-pathologic cohort studies. Participants completed baseline assessment, annual standardized blood pressure measurements, vascular risk assessment for diabetes, and blood draws to determine APOE genotype, and at death, brains were removed and underwent ex vivo magnetic resonance imaging and neuropathologic evaluation for atherosclerosis pathology and other cerebrovascular and neurodegenerative pathologies. Linear regression models examined the association of atherosclerosis and hippocampal to hemisphere volume ratio and whether age at death, blood pressure, and other factors modified associations. In linear regression models adjusted for demographics and neurodegenerative and other cerebrovascular pathologies, atherosclerosis severity was associated with a lower hippocampal to hemisphere volume ratio. In separate models, we found the effect of atherosclerosis on the ratio of hippocampal to hemisphere volume was attenuated among advanced age at death or having higher systolic blood pressure (interaction terms P≤0.03). We did not find confounding or interactions with sex, diabetes, or APOE ε4.

CONCLUSIONS

Atherosclerosis severity is associated with lower hippocampal volume, independent of neurodegenerative and other cerebrovascular pathologies. Higher systolic blood pressures and advanced age attenuate associations.

The role of exosomes in adult neurogenesis: implications for neurodegenerative diseases

Exosomes are cup-shaped extracellular vesicles with a lipid bilayer that is approximately 30 to 200 nm in thickness. Exosomes are widely distributed in a range of body fluids, including urine, blood, milk, and saliva. Exosomes exert biological function by transporting factors between different cells and by regulating biological pathways in recipient cells. As an important form of intercellular communication, exosomes are increasingly being investigated due to their ability to transfer bioactive molecules such as lipids, proteins, mRNAs, and microRNAs between cells, and because they can regulate physiological and pathological processes in the central nervous system. Adult neurogenesis is a multistage process by which new neurons are generated and migrate to be integrated into existing neuronal circuits. In the adult brain, neurogenesis is mainly localized in two specialized niches: the subventricular zone adjacent to the lateral ventricles and the subgranular zone of the dentate gyrus. An increasing body of evidence indicates that adult neurogenesis is tightly controlled by environmental conditions with the niches. In recent studies, exosomes released from different sources of cells were shown to play an active role in regulating neurogenesis both in vitro and in vivo, thereby participating in the progression of neurodegenerative disorders in patients and in various disease models. Here, we provide a state-of-the-art synopsis of existing research that aimed to identify the diverse components of exosome cargoes and elucidate the therapeutic potential of exosomal contents in the regulation of neurogenesis in several neurodegenerative diseases. We emphasize that exosomal cargoes could serve as a potential biomarker to monitor functional neurogenesis in adults. In addition, exosomes can also be considered as a novel therapeutic approach to treat various neurodegenerative disorders by improving endogenous neurogenesis to mitigate neuronal loss in the central nervous system.

Relative Contributions of Mixed Pathologies to Cognitive and Functional Symptoms in Brain Donors Exposed to Repetitive Head Impacts

OBJECTIVE

Exposure to repetitive head impacts (RHI) is associated with later-life cognitive symptoms and neuropathologies, including chronic traumatic encephalopathy (CTE). Cognitive decline in community cohorts is often due to multiple pathologies; however, the frequency and contributions of these pathologies to cognitive impairment in people exposed to RHI are unknown. Here, we examined the relative contributions of 13 neuropathologies to cognitive symptoms and dementia in RHI-exposed brain donors.

METHODS

Neuropathologists examined brain tissue from 571 RHI-exposed donors and assessed for the presence of 13 neuropathologies, including CTE, Alzheimer disease (AD), Lewy body disease (LBD), and transactive response DNA-binding protein 43 (TDP-43) inclusions. Cognitive status was assessed by presence of dementia, Functional Activities Questionnaire, and Cognitive Difficulties Scale. Spearman rho was calculated to assess intercorrelation of pathologies. Additionally, frequencies of pathological co-occurrence were compared to a simulated distribution assuming no intercorrelation. Logistic and linear regressions tested associations between neuropathologies and dementia status and cognitive scale scores.

RESULTS

The sample age range was 18-97 years (median = 65.0, interquartile range = 46.0-76.0). Of the donors, 77.2% had at least one moderate-severe neurodegenerative or cerebrovascular pathology. Stage III-IV CTE was the most common neurodegenerative disease (43.1%), followed by TDP-43 pathology, AD, and hippocampal sclerosis. Neuropathologies were intercorrelated, and there were fewer unique combinations than expected if pathologies were independent (p < 0.001). The greatest contributors to dementia were AD, neocortical LBD, hippocampal sclerosis, cerebral amyloid angiopathy, and CTE.

INTERPRETATION

In this sample of RHI-exposed brain donors with wide-ranging ages, multiple neuropathologies were common and correlated. Mixed neuropathologies, including CTE, underlie cognitive impairment in contact sport athletes. ANN NEUROL 2024;95:314-324.

Integrative multi-omics analysis reveals the critical role of the PBXIP1 gene in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder, and its strongest risk factor is aging. A few studies have explored the relationship between aging and AD, while the underlying mechanism remains unclear. We assembled data across multi-omics (i.e., epigenetics, transcriptomics, and proteomics, based on frozen tissues from the dorsolateral prefrontal cortex) and neuropathological and clinical traits from the Religious Orders Study and Rush Memory and Aging Project (ROSMAP). Aging was assessed using six DNA methylation clocks (including the Horvath clock, Hannum clock, Levine clock, HorvathSkin clock, Lin clock, and Cortical clock) that capture mortality risk in literature. After accounting for age, we first identified a gene module (including 263 genes) that was related to the integrated aging measure of six clocks, as well as three neuropathological traits of AD (i.e., β-amyloid, Tau tangles, and tangle density). Interestingly, among 20 key genes with top intramodular connectivity of the module, PBXIP1 was the only one that was significantly associated with all three neuropathological traits of AD at the protein level after Bonferroni correction. Furthermore, PBXIP1 was associated with the clinical diagnosis of AD in both ROSMAP and three independent datasets. Moreover, PBXIP1 may be related to AD through its role in astrocytes and hippocampal neurons, and the mTOR pathway. The results suggest the critical role of PBXIP1 in AD and support the potential and feasibility of using multi-omics data to investigate mechanisms of complex diseases. However, more validations in different populations and experiments in vitro and in vivo are required in the future.

Application of blood-based biomarkers of Alzheimer's disease in clinical practice: Recommendations from Taiwan Dementia Society

Blood-based biomarkers (BBM) are potentially powerful tools that assist in the biological diagnosis of Alzheimer's disease (AD) in vivo with minimal invasiveness, relatively low cost, and good accessibility. This review summarizes current evidence for using BBMs in AD, focusing on amyloid, tau, and biomarkers for neurodegeneration. Blood-based phosphorylated tau and the Aβ42/Aβ40 ratio showed consistent concordance with brain pathology measured by CSF or PET in the research setting. In addition, glial fibrillary acidic protein (GFAP) and neurofilament light chain (NfL) are neurodegenerative biomarkers that show the potential to assist in the differential diagnosis of AD. Other pathology-specific biomarkers, such as α-synuclein and TAR DNA-binding protein 43 (TDP-43), can potentially detect AD concurrent pathology. Based on current evidence, the working group from the Taiwan Dementia Society (TDS) achieved consensus recommendations on the appropriate use of BBMs for AD in clinical practice. BBMs may assist clinical diagnosis and prognosis in AD subjects with cognitive symptoms; however, the results should be interpreted by dementia specialists and combining biochemical, neuropsychological, and neuroimaging information. Further studies are needed to evaluate BBMs' real-world performance and potential impact on clinical decision-making.

Association Between β-Amyloid Accumulation and Incident Dementia in Individuals 80 Years or Older Without Dementia

BACKGROUND AND OBJECTIVES

While the highest prevalence of dementia occurs in individuals older than 80 years, most imaging studies focused on younger populations. The rates of β-amyloid (Aβ) accumulation and the effect of Alzheimer disease (AD) pathology on progression to dementia in this age group remain unexplored. In this study, we examined the relationship between changes in Aβ deposition over time and incident dementia in nondemented individuals followed during a period of 11 years.

METHODS

We examined 94 participants (age 85.9 + 2.8 years) who had up to 5 measurements of Pittsburgh compound-B (PiB)-PET and clinical evaluations from 2009 to 2020. All 94 participants had 2 PiB-PET scans, 76 participants had 3 PiB-PET scans, 18 participants had 4 PiB-PET scans, and 10 participants had 5 PiB-PET scans. The rates of Aβ deposition were compared with 120 nondemented individuals younger than 80 years (69.3 ± 5.4 years) from the Australian Imaging, Biomarker, and Lifestyle (AIBL) study who had 3 or more annual PiB-PET assessments.

RESULTS

By 2020, 49% of the participants developed dementia and 63% were deceased. There was a gradual increase in Aβ deposition in all participants whether they were considered Aβ positive or negative at baseline. In a Cox model controlled for age, sex, education level, APOE-4 allele, baseline Mini-Mental State Examination, and mortality, short-term change in Aβ deposition was not significantly associated with incident dementia (HR 2.19 (0.41-11.73). However, baseline Aβ burden, cortical thickness, and white matter lesions volume were the predictors of incident dementia. Aβ accumulation was faster (p = 0.01) in the older cohort (5.6%/year) when compared with AIBL (4.1%/year). In addition, baseline Aβ deposition was a predictor of short-term change (mean time 1.88 years).

DISCUSSION

There was an accelerated Aβ accumulation in cognitively normal individuals older than 80 years. Baseline Aβ deposition was a determinant of incident dementia and short-term change in Aβ deposition suggesting that an active Aβ pathologic process was present when these participants were cognitively normal. Consequently, age may not be a limiting factor for the use of the emergent anti-Aβ therapies.

Region-based analysis with functional annotation identifies genes associated with cognitive function in South Asians from India

The prevalence of dementia among South Asians across India is approximately 7.4% in those 60 years and older, yet little is known about genetic risk factors for dementia in this population. Most known risk loci for Alzheimer's disease (AD) have been identified from studies conducted in European Ancestry (EA) but are unknown in South Asians. Using whole-genome sequence data from 2680 participants from the Diagnostic Assessment of Dementia for the Longitudinal Aging Study of India (LASI-DAD), we performed a gene-based analysis of 84 genes previously associated with AD in EA. We investigated associations with the Hindi Mental State Examination (HMSE) score and factor scores for general cognitive function and five cognitive domains. For each gene, we examined missense/loss-of-function (LoF) variants and brain-specific promoter/enhancer variants, separately, both with and without incorporating additional annotation weights (e.g., deleteriousness, conservation scores) using the variant-Set Test for Association using Annotation infoRmation (STAAR). In the missense/LoF analysis without annotation weights and controlling for age, sex, state/territory, and genetic ancestry, three genes had an association with at least one measure of cognitive function (FDR q<0.1). APOE was associated with four measures of cognitive function, PICALM was associated with HMSE score, and TSPOAP1 was associated with executive function. The most strongly associated variants in each gene were rs429358 (APOE ε4), rs779406084 (PICALM), and rs9913145 (TSPOAP1). rs779406084 is a rare missense mutation that is more prevalent in LASI-DAD than in EA (minor allele frequency=0.075% vs. 0.0015%); the other two are common variants. No genes in the brain-specific promoter/enhancer analysis met criteria for significance. Results with and without annotation weights were similar. Missense/LoF variants in some genes previously associated with AD in EA are associated with measures of cognitive function in South Asians from India. Analyzing genome sequence data allows identification of potential novel causal variants enriched in South Asians.

From theory to practice: translating the concept of cognitive resilience to novel therapeutic targets that maintain cognition in aging adults

While the concept of cognitive resilience is well-established it has not been defined in a way that can be measured. This has been an impediment to studying its underlying biology and to developing instruments for its clinical assessment. This perspective highlights recent work that has quantified the expression of cortical proteins associated with cognitive resilience, thus facilitating studies of its complex underlying biology and the full range of its clinical effects in aging adults. These initial studies provide empirical support for the conceptualization of resilience as a continuum. Like other conventional risk factors, some individuals manifest higher-than-average cognitive resilience and other individuals manifest lower-than-average cognitive resilience. These novel approaches for advancing studies of cognitive resilience can be generalized to other aging phenotypes and can set the stage for the development of clinical tools that might have the potential to measure other mechanisms of resilience in aging adults. These advances also have the potential to catalyze a complementary therapeutic approach that focuses on augmenting resilience via lifestyle changes or therapies targeting its underlying molecular mechanisms to maintain cognition and brain health even in the presence of untreatable stressors like brain pathologies that accumulate in aging adults.

Proteome-wide Analyses Identified Cortical Proteins Associated With Resilience for Varied Cognitive Abilities

BACKGROUND AND OBJECTIVES

Prior work suggests that cognitive resilience may contribute to the heterogeneity of cognitive decline. This study examined whether distinct cortical proteins provide resilience for different cognitive abilities.

METHODS

Participants were from the Religious Orders Study or the Rush Memory and Aging Project who had undergone annual assessments of 5 cognitive abilities and postmortem assessment of 9 Alzheimer disease and related dementia (ADRD) pathologies. Proteome-wide examination of the dorsolateral prefrontal cortex using tandem mass tag and liquid chromatography-mass spectrometry yielded 8,425 high-abundance proteins. We applied linear mixed-effect models to quantify residual cognitive change (cognitive resilience) of 5 cognitive abilities by regressing out cognitive decline related to age, sex, education, and indices of ADRD pathologies. Then we added terms for each of the individual proteins to identify cognitive resilience proteins associated with the different cognitive abilities.

RESULTS

We included 604 decedents (69% female; mean age at death = 89 years) with proteomic data. A total of 47 cortical proteins that provide cognitive resilience were identified: 22 were associated with specific cognitive abilities, and 25 were common to at least 2 cognitive abilities. NRN1 was the only protein that was associated with more than 2 cognitive abilities (semantic memory: estimate = 0.020, SE = 0.004, p = 2.2 × 10-6; episodic memory: estimate = 0.029, SE = 0.004, p = 5.8 × 10-1; and working memory: estimate = 0.021, SE = 0.004, p = 1.2 × 10-7). Exploratory gene ontology analysis suggested that among top molecular pathways, mitochondrial translation was a molecular mechanism providing resilience in episodic memory, while nuclear-transcribed messenger RNA catabolic processes provided resilience in working memory.

DISCUSSION

This study identified cortical proteins associated with various cognitive abilities. Differential associations across abilities may reflect distinct underlying biological pathways. These data provide potential high-value targets for further mechanistic and drug discovery studies to develop targeted treatments to prevent loss of cognition.

Comparison of multiple linear regression and machine learning methods in predicting cognitive function in older Chinese type 2 diabetes patients

INTRODUCTION

The prevalence of type 2 diabetes (T2D) has increased dramatically in recent decades, and there are increasing indications that dementia is related to T2D. Previous attempts to analyze such relationships principally relied on traditional multiple linear regression (MLR). However, recently developed machine learning methods (Mach-L) outperform MLR in capturing non-linear relationships. The present study applied four different Mach-L methods to analyze the relationships between risk factors and cognitive function in older T2D patients, seeking to compare the accuracy between MLR and Mach-L in predicting cognitive function and to rank the importance of risks factors for impaired cognitive function in T2D.

METHODS

We recruited older T2D between 60-95 years old without other major comorbidities. Demographic factors and biochemistry data were used as independent variables and cognitive function assessment (CFA) was conducted using the Montreal Cognitive Assessment as an independent variable. In addition to traditional MLR, we applied random forest (RF), stochastic gradient boosting (SGB), Naïve Byer's classifier (NB) and eXtreme gradient boosting (XGBoost).

RESULTS

Totally, the test cohort consisted of 197 T2D (98 men and 99 women). Results showed that all ML methods outperformed MLR, with symmetric mean absolute percentage errors for MLR, RF, SGB, NB and XGBoost respectively of 0.61, 0.599, 0.606, 0.599 and 0.2139. Education level, age, frailty score, fasting plasma glucose and body mass index were identified as key factors in descending order of importance.

CONCLUSION

In conclusion, our study demonstrated that RF, SGB, NB and XGBoost are more accurate than MLR for predicting CFA score, and identify education level, age, frailty score, fasting plasma glucose, body fat and body mass index as important risk factors in an older Chinese T2D cohort.

Associations of cortical SPP1 and ITGAX with cognition and common neuropathologies in older adults

INTRODUCTION

The secreted phosphoprotein 1 (SPP1) gene expressed by CD11c+ cells is known to be associated with microglia activation and neuroinflammatory diseases. As most studies rely on mouse models, we investigated these genes and proteins in the cortical brain tissue of older adults and their role in Alzheimer's disease (AD) and related disorders.

METHODS

We leveraged protein measurements, single-nuclei, and RNASeq data from the Religious Orders Study and Rush Memory and Aging Project (ROSMAP) of over 1200 samples for association analysis.

RESULTS

Expression of SPP1 and its encoded protein osteopontin were associated with faster cognitive decline and greater odds of common neuropathologies. At single-cell resolution,  integrin subunit alpha X (ITGAX) was highly expressed in microglia, where specific subpopulations were associated with AD and cerebral amyloid angiopathy.

DISCUSSION

The study provides evidence of SPP1 and ITGAX association with cognitive decline and common neuropathologies identifying a microglial subset associated with disease.

Left Frontoparietal Control Network Connectivity Moderates the Effect of Amyloid on Cognitive Decline in Preclinical Alzheimer's Disease: The A4 Study

BACKGROUND

Stronger resting-state functional connectivity of the default mode and frontoparietal control networks has been associated with cognitive resilience to Alzheimer's disease related pathology and neurodegeneration in smaller cohort studies.

OBJECTIVES

We investigated whether these networks are associated with longitudinal CR to AD biomarkers of beta-amyloid (Aβ).

DESIGN

Longitudinal mixed.

SETTING

The Anti-Amyloid Treatment in Asymptomatic Alzheimer's Disease (A4) study and its natural history observation arm, the Longitudinal Evaluation of Amyloid Risk and Neurodegeneration (LEARN) study.

PARTICIPANTS

A sample of 1,021 cognitively unimpaired older adults (mean age = 71.2 years [SD = 4.7 years], 61% women, 42% APOEε4 carriers, 52% Aβ positive).

MEASUREMENTS

Global cognitive performance (Preclinical Alzheimer's Cognitive Composite) was assessed over an average 5.4 year follow-up period (SD = 2 years). Cortical Aβ and functional connectivity (left and right frontoparietal control and default mode networks) were estimated from fMRI and PET, respectively, at baseline. Covariates included baseline age, APOEε4 carrier status, years of education, adjusted gray matter volume, head motion, study group, cumulative treatment exposure, and cognitive test version.

RESULTS

Mixed effects models revealed that functional connectivity of the left frontoparietal control network moderated the negative effect of Aβ on cognitive change (p = .025) such that stronger connectivity was associated with reduced Aβ-related cognitive decline.

CONCLUSIONS

Our results demonstrate a potential protective effect of functional connectivity in preclinical AD, such that stronger connectivity in this network is associated with slower Aβ-related cognitive decline.

Identifying individuals with non-Alzheimer's disease co-pathologies: A precision medicine approach to clinical trials in sporadic Alzheimer's disease

INTRODUCTION

Biomarkers remain mostly unavailable for non-Alzheimer's disease neuropathological changes (non-ADNC) such as transactive response DNA-binding protein 43 (TDP-43) proteinopathy, Lewy body disease (LBD), and cerebral amyloid angiopathy (CAA).

METHODS

A multilabel non-ADNC classifier using magnetic resonance imaging (MRI) signatures was developed for TDP-43, LBD, and CAA in an autopsy-confirmed cohort (N = 214).

RESULTS

A model using demographic, genetic, clinical, MRI, and ADNC variables (amyloid positive [Aβ+] and tau+) in autopsy-confirmed participants showed accuracies of 84% for TDP-43, 81% for LBD, and 81% to 93% for CAA, outperforming reference models without MRI and ADNC biomarkers. In an ADNI cohort (296 cognitively unimpaired, 401 mild cognitive impairment, 188 dementia), Aβ and tau explained 33% to 43% of variance in cognitive decline; imputed non-ADNC explained an additional 16% to 26%. Accounting for non-ADNC decreased the required sample size to detect a 30% effect on cognitive decline by up to 28%.

DISCUSSION

Our results lead to a better understanding of the factors that influence cognitive decline and may lead to improvements in AD clinical trial design.

Visual Functions Are Associated with Biomarker Changes in Alzheimer's Disease

Background

While various biomarkers of Alzheimer's disease (AD) have been associated with general cognitive function, their association to visual-perceptive function across the AD spectrum warrant more attention due to its significant impact on quality of life. Thus, this study explores how AD biomarkers are associated with decline in this cognitive domain.

Objective

To explore associations between various fluid and imaging biomarkers and visual-based cognitive assessments in participants across the AD spectrum.

Methods

Data from participants (N = 1,460) in the Alzheimer's Disease Neuroimaging Initiative were analyzed, including fluid and imaging biomarkers. Along with the Mini-Mental State Examination (MMSE), three specific visual-based cognitive tests were investigated: Trail Making Test (TMT) A and TMT B, and the Boston Naming Test (BNT). Locally estimated scatterplot smoothing curves and Pearson correlation coefficients were used to examine associations.

Results

MMSE showed the strongest correlations with most biomarkers, followed by TMT-B. The p-tau181/Aβ1-42 ratio, along with the volume of the hippocampus and entorhinal cortex, had the strongest associations among the biomarkers.

Conclusions

Several biomarkers are associated with visual processing across the disease spectrum, emphasizing their potential in assessing disease severity and contributing to progression models of visual function and cognition.

Neuroimaging determinants of cognitive impairment in the memory clinic: how important is the vascular burden?

While neurodegenerative and vascular neurocognitive disorder (NCD) often co-occur, the contribution of vascular lesions, especially stroke lesions identified on MRI, to global cognition in a real-life memory clinic population remains unclear. The main objective of this retrospective study was to determine NCD neuroimaging correlates: the GM atrophy pattern and vascular lesions (especially stroke lesion localization by voxel-based lesion-symptom mapping, VLSM) in a memory clinic. We included 336 patients with mild or major NCD who underwent cerebral MRI and a neuropsychological assessment. The GM atrophy pattern (obtained by voxel-based morphometry, VBM) and the stroke lesion localization (obtained by VLSM) associated with G5 z-score (a global cognitive score), were included as independent variables with other neuroimaging and clinical indices in a stepwise linear regression model. The mean age was 70.3 years and the mean MMSE score 21.3. On MRI, 75 patients had at least one stroke lesion. The G 5 z-score was associated with GM density in the pattern selected by the VBM analysis (R2 variation = 0.166, p < 0.001) and the presence of a stroke lesion in the region selected by the VSLM analysis (mainly in the right frontal region; R2 variation = 0.018, p = 0.008). The interaction between the two factors was insignificant (p = 0.374). In conclusion, in this first study combining VBM and VLSM analysis in a memory clinic, global cognition was associated with a specific GM atrophy pattern and the presence of a stroke lesion mainly in the right frontal region.

A Potential Role for the Ketogenic Diet in Alzheimer's Disease Treatment: Exploring Pre-Clinical and Clinical Evidence

Given the remarkable progress in global health and overall quality of life, the significant rise in life expectancy has become intertwined with the surging occurrence of neurodegenerative disorders (NDs). This emerging trend is poised to pose a substantial challenge to the fields of medicine and public health in the years ahead. In this context, Alzheimer's disease (AD) is regarded as an ND that causes recent memory loss, motor impairment and cognitive deficits. AD is the most common cause of dementia in the elderly and its development is linked to multifactorial interactions between the environment, genetics, aging and lifestyle. The pathological hallmarks in AD are the accumulation of β-amyloid peptide (Aβ), the hyperphosphorylation of tau protein, neurotoxic events and impaired glucose metabolism. Due to pharmacological limitations and in view of the prevailing glycemic hypometabolism, the ketogenic diet (KD) emerges as a promising non-pharmacological possibility for managing AD, an approach that has already demonstrated efficacy in addressing other disorders, notably epilepsy. The KD consists of a food regimen in which carbohydrate intake is discouraged at the expense of increased lipid consumption, inducing metabolic ketosis whereby the main source of energy becomes ketone bodies instead of glucose. Thus, under these dietary conditions, neuronal death via lack of energy would be decreased, inasmuch as the metabolism of lipids is not impaired in AD. In this way, the clinical picture of patients with AD would potentially improve via the slowing down of symptoms and delaying of the progression of the disease. Hence, this review aims to explore the rationale behind utilizing the KD in AD treatment while emphasizing the metabolic interplay between the KD and the improvement of AD indicators, drawing insights from both preclinical and clinical investigations. Via a comprehensive examination of the studies detailed in this review, it is evident that the KD emerges as a promising alternative for managing AD. Moreover, its efficacy is notably enhanced when dietary composition is modified, thereby opening up innovative avenues for decreasing the progression of AD.

Multimodal lifestyle engagement patterns support cognitive stability beyond neuropathological burden

BACKGROUND

Modifiable lifestyle behaviors account for a large proportion of dementia risk. However, the combined contributions of multidomain lifestyle patterns to cognitive aging are poorly understood, as most studies have examined individual lifestyle behaviors in isolation and without neuropathological characterization. This study examined data-driven patterns of lifestyle behaviors across multiple domains among older adults and tested their associations with disease-specific neuropathological burden and cognitive decline.

METHODS

Participants included 2059 older adults enrolled in the longitudinal Memory and Aging Project (MAP) at the Rush Alzheimer's Disease Center; none of whom had dementia at baseline (73% no cognitive impairment (NCI), 27% mild cognitive impairment [MCI]). All participants completed cognitive testing annually. Lifestyle factors were measured during at least one visit and included (1) actigraphy-measured physical activity, as well as self-reported (2) sleep quality, (3) life space, (4) cognitive activities, (5) social activities, and (6) social network. A subset of participants (n = 791) had autopsy data for which burden of Alzheimer's disease (AD), cerebrovascular disease (CVD), Lewy body disease, and hippocampal sclerosis/TDP-43 was measured. Latent profile analysis across all 2059 participants identified distinct subgroups (i.e., classes) of lifestyle patterns. Linear mixed-effects models examined relationships between lifestyle classes and global cognitive trajectories, with and without covarying for all neuropathologies. Classes were also compared on rates of incident MCI/dementia.

RESULTS

Five classes were identified: Class 1Low Life Space (lowest lifestyle engagement), Class 2PA (high physical activity), Class 3Low Avg (low to average lifestyle engagement), Class 4Balanced (high average lifestyle engagement), and Class 5Social (large social network). Classes 4Balanced and 5Social had the lowest AD burden, and Class 2PA had the lowest CVD burden. Classes 2-5 had significantly less steep global cognitive decline compared to Class 1Low Life Space, with comparable effect sizes before and after covarying for neuropathological burden. Classes 4Balanced and 5Social exhibited the lowest rates of incident MCI/dementia.

CONCLUSIONS

Lifestyle behavior patterns among older adults account for differential rates of cognitive decline and clinical progression. Those with at least average engagement across all lifestyle domains exhibit greater cognitive stability after adjustment for neuropathology, highlighting the importance of engagement in multiple healthy lifestyle behaviors for later life cognitive health.

Ab initio and comparative 3D modeling of FAM222A-encoded protein and target-driven-based virtual screening for the identification of novel therapeutics against Alzheimer's disease

The complex nature of Alzheimer's disease (AD) makes it difficult to understand the exact molecular processes leading to neuron death. However, two molecular factors - the production of amyloid-beta plaques and tau tangles - are considered to be linked to AD. A genetic marker for brain atrophy, FAM222A, has been identified by the unique cross-phenotype meta-analysis of genetics imaging and the molecular features show an interaction between the protein aggregatin encoded by FAM222A and amyloid beta (Aβ)-peptide (1-42) via its N-terminal Aβ binding domain, thus increasing Aβ aggregation. Function of Aggregatin protein is unclear, and its 3D structure has not been investigated in experimental analysis, so far. Hence, in the present study, first time in literature, 3D models of FAM222A-encoded Aggregatin were systematically constructed by applying diverse homology modeling approaches and they were used as target structures at the virtual screening of FDA-approved drugs and drugs currently under research in clinical trials. Then, the identified hit molecules were chosen for further molecular dynamics (MD) simulations and post-MD analyses. Our integrated ligand-based and protein-driven-based virtual screening results show that Cefpiramide, Diniprofylline, Fostriecin, and Droperidol may target Aggregatin.

Trajectories of olfactory identification preceding incident mild cognitive impairment and dementia: a longitudinal study

BACKGROUND

The pattern of olfactory identification change in the early phases of dementing disorders is unclear. We aimed to assess olfactory identification trajectories preceding incident mild cognitive impairment (MCI) and dementia and explore the role of brain pathologies in these trajectories.

METHODS

Within the Rush Memory and Aging Project, 1318 dementia-free older adults were followed annually for up to 11 years. Olfactory identification was assessed using the Brief Smell Identification Test annually. Of 900 cognitively intact participants, incident MCI and dementia were diagnosed following standard criteria. Over follow-up, 518 participants died and underwent brain autopsies for neuropathological assessment. Data were analyzed using mixed-effect models with backward timescales.

FINDINGS

Compared to participants who remained cognitively intact, olfactory identification declined faster among those who developed MCI (β -0.09 [95% CI -0.13, -0.05]), leading to a significantly lower olfactory identification starting from five years preceding MCI diagnosis (mean difference at year -5: -0.39 [-0.71, -0.07]). Among participants with incident MCI, olfactory identification declined faster in those who developed dementia compared to those who did not (β -0.19 [-0.36, -0.01]), leading to a significantly lower olfactory identification starting from three years preceding dementia diagnosis (mean difference at year -3: -0.95 [-1.67, -0.23]). A faster decline in olfactory identification was associated with higher burdens of global Alzheimer's disease pathology, neurofibrillary tangles, and amyloid beta load.

INTERPRETATION

Olfactory identification declined faster preceding dementia disorders and Alzheimer's pathology may underlie these faster declines.

FUNDING

This study was funded by the National Institutes of Health (R01AG17917) and Swedish Research Council (2021-01647).

Brain Insulin Signaling is Associated with Late-Life Cognitive Decline

Type-2 diabetes is associated with an increased risk of dementia, and the underlying mechanism might involve abnormal insulin signaling in the brain. The objective of this study was to examine the association of postmortem brain insulin signaling with late-life cognitive decline. Among participants of Religious Orders Study, a community-based clinical-pathological cohort, 150 deceased and autopsied older individuals (75 with diabetes matched to 75 without by age at death, sex, and education) had postmortem brain insulin signaling measurements collected in the prefrontal cortex using ELISA and immunohistochemistry. By using adjusted linear mixed-effects models, we examined the association of postmortem brain insulin signaling with late-life cognitive function assessed longitudinally (mean follow-up duration = 9.4 years) using a battery of neuropsychological tests. We found that a higher level of serine/threonine-protein kinase (AKT) phosphorylation (pT308AKT1/total AKT1) was associated with a faster decline in global cognition (estimate = -0.023, p = 0.030), and three domains: episodic memory (estimate = -0.024, p = 0.032), working memory (estimate = -0.018, p = 0.012), and visuospatial abilities (estimate = -0.013, p = 0.027). The level of insulin receptor substrate-1 (IRS1) phosphorylation (pS307IRS1/total IRS1) was not associated with decline in global cognition or most cognitive domains, except for perceptual speed (estimate = 0.020, p = 0.020). The density of pS616IRS1-stained cells was not associated with decline in global cognition or any of the domains. In conclusion, these findings provide novel evidence for an association between brain insulin signaling and late-life cognitive decline. AKT phosphorylation is associated with a decline in global cognition and memory in particular, whereas IRS1 phosphorylation is associated with a decline in perceptual speed.

Evaluation and treatment approaches for neurological post-acute sequelae of COVID-19: A consensus statement and scoping review from the global COVID-19 neuro research coalition

Post-acute neurological sequelae of COVID-19 affect millions of people worldwide, yet little data is available to guide treatment strategies for the most common symptoms. We conducted a scoping review of PubMed/Medline from 1/1/2020-4/1/2023 to identify studies addressing diagnosis and treatment of the most common post-acute neurological sequelae of COVID-19 including: cognitive impairment, sleep disorders, headache, dizziness/lightheadedness, fatigue, weakness, numbness/pain, anxiety, depression and post-traumatic stress disorder. Utilizing the available literature and international disease-specific society guidelines, we constructed symptom-based differential diagnoses, evaluation and management paradigms. This pragmatic, evidence-based consensus document may serve as a guide for a holistic approach to post-COVID neurological care and will complement future clinical trials by outlining best practices in the evaluation and treatment of post-acute neurological signs/symptoms.

Dissecting the human leptomeninges at single-cell resolution

Emerging evidence shows that the meninges conduct essential immune surveillance and immune defense at the brain border, and the dysfunction of meningeal immunity contributes to aging and neurodegeneration. However, no study exists on the molecular properties of cell types within human leptomeninges. Here, we provide single nuclei profiling of dissected postmortem leptomeninges from aged individuals. We detect diverse cell types, including unique meningeal endothelial, mural, and fibroblast subtypes. For immune cells, we show that most T cells express CD8 and bear characteristics of tissue-resident memory T cells. We also identify distinct subtypes of border-associated macrophages (BAMs) that display differential gene expressions from microglia and express risk genes for Alzheimer's Disease (AD), as nominated by genome-wide association studies (GWAS). We discover cell-type-specific differentially expressed genes in individuals with Alzheimer's dementia, particularly in fibroblasts and BAMs. Indeed, when cultured, leptomeningeal cells display the signature of ex vivo AD fibroblasts upon amyloid-β treatment. We further explore ligand-receptor interactions within the leptomeningeal niche and computationally infer intercellular communications in AD. Thus, our study establishes a molecular map of human leptomeningeal cell types, providing significant insight into the border immune and fibrotic responses in AD.

Aquaporin-4 Deficiency is Associated with Cognitive Impairment and Alterations in astrocyte-neuron Lactate Shuttle

Cognitive impairment refers to notable declines in cognitive abilities including memory, language, and emotional stability leading to the inability to accomplish essential activities of daily living. Astrocytes play an important role in cognitive function, and homeostasis of the astrocyte-neuron lactate shuttle (ANLS) system is essential for maintaining cognitive functions. Aquaporin-4 (AQP-4) is a water channel expressed in astrocytes and has been shown to be associated with various brain disorders, but the direct relationship between learning, memory, and AQP-4 is unclear. We examined the relationship between AQP-4 and cognitive functions related to learning and memory. Mice with genetic deletion of AQP-4 showed significant behavioral and emotional changes including hyperactivity and instability, and impaired cognitive functions such as spatial learning and memory retention. 18 F-FDG PET imaging showed significant metabolic changes in the brains of AQP-4 knockout mice such as reductions in glucose absorption. Such metabolic changes in the brain seemed to be the direct results of changes in the expression of metabolite transporters, as the mRNA levels of multiple glucose and lactate transporters in astrocytes and neurons were significantly decreased in the cortex and hippocampus of AQP-4 knockout mice. Indeed, AQP-4 knockout mice showed significantly higher accumulation of both glucose and lactate in their brains compared with wild-type mice. Our results show that the deficiency of AQP-4 can cause problems in the metabolic function of astrocytes and lead to cognitive impairment, and that the deficiency of AQP4 in astrocyte endfeet can cause abnormalities in the ANLS system.

Phytochemical study of Lantana camara flowers, ecotoxicity, antioxidant, in vitro and in silico acetylcholinesterase: molecular docking, MD, and MM/GBSA calculations

Lantana camara L. (Verbenaceae), commonly called lead cambará, has often been used in folk medicine as antiseptic, antispasmodic, against hemorrhages, flu, colds, and diarrheic. This plant is considered a weed and an ornamental and medicinal plant and is an essential source of natural organic compounds, mainly flavonoids. This work aims to investigate the chemical composition and evaluate the biological properties such as antioxidant and acetylcholinesterase of the constituents from L. camara flowers. In addition, the computational simulation was carried out with the constituents identified. The results showed that methanolic extract of the flowers of L. camara presents toxicity, antioxidant activity with 97.8% inhibition percentage in the concentration of 0.25 mg mL-1 against the DPPH radical, and acetylcholinesterase activity. The phytochemical study of extract from L. camara flowers resulted in LC-MS identification of 18 polyphenolic compounds, such as phenolic acid derivatives, phenylethanoid glycosides, and flavonoids. In the in silico study, flavonoid isoverbascoside showed affinity energy of -9.9 kcal.mol-1 with the AChE enzyme. Their phytochemical content, mainly the presence of flavonoids and phenolic compounds in L. camara extracts, may be related to the antioxidant and anticholinesterase potential observed.

Selective serotonin reuptake inhibitor use, age-related neuropathology and cognition in late-life

The objective of this study was to evaluate an association of selective serotonin reuptake inhibitor (SSRI) use with late life cognitive decline and further investigate the association with brain pathology. Using the data are from two harmonized clinical-pathologic cohort studies with annual cognitive testing we found that SSRI use was associated with significantly faster global cognitive decline and this association was present in those with and without pre-existing cognitive impairment at the time of SSRI initiation. In separate analyses of persons who died during the study and underwent neuropathologic examination, SSRI use was related to higher level of paired helical filament tau tangles and faster rate of global cognitive decline. However, when SSRI use and tangles were included in the same model, the association of SSRI use with rate of global cognitive decline was reduced by more than 50% and no longer statistically significant. SSRI use was associated with higher postmortem level of tau tangles, possibly because SSRI are being used to treat neurobehavioral symptoms associated with dementia, and this relationship appears to partly account for the association of SSRI use with more rapid cognitive decline.

Knockout of the longevity gene Klotho perturbs aging- and Alzheimer's disease-linked brain microRNAs and tRNA fragments

Overexpression of the longevity gene Klotho prolongs, while its knockout shortens lifespan and impairs cognition via altered fibroblast growth factor signaling that perturbs myelination and synapse formation; however, comprehensive analysis of Klotho's knockout consequences on mammalian brain transcriptomics is lacking. Here, we report the altered levels under Klotho knockout of 1059 long RNAs, 27 microRNAs (miRs) and 6 tRNA fragments (tRFs), reflecting effects upon aging and cognition. Perturbed transcripts included key neuronal and glial pathway regulators that are notably changed in murine models of aging and Alzheimer's Disease (AD) and in corresponding human post-mortem brain tissue. To seek cell type distributions of the affected short RNAs, we isolated and FACS-sorted neurons and microglia from live human brain tissue, yielding detailed cell type-specific short RNA-seq datasets. Together, our findings revealed multiple Klotho deficiency-perturbed aging- and neurodegeneration-related long and short RNA transcripts in both neurons and glia from murine and human brain.

Single-Cell Sequencing in Neurodegenerative Disorders

Neurodegenerative disorders are typically characterized by late onset progressive damage to specific (sub)populations of cells of the nervous system that are essential for mobility, coordination, strength, sensation, and cognition. Addressing this selective cellular vulnerability has become feasible with the emergence of single-cell-omics technologies, which now represent the state-of-the-art approach to profile heterogeneity of complex tissues including human post-mortem brain at unprecedented resolution. In this review, we briefly recapitulate the experimental workflow of single-cell RNA sequencing and summarize the recent knowledge acquired with it in the most common neurodegenerative diseases: Parkinson's, Alzheimer's, Huntington's disease, and multiple sclerosis. We also discuss the possibility of applying single-cell approaches in the diagnostics and therapy of neurodegenerative disorders, as well as the limitations. While we are currently at the point of deeply exploring the transcriptomic changes in the affected cells, further technological developments hold a promise of manipulating the affected pathways once we understand them better.

Investigating predictors of progression from mild cognitive impairment to Alzheimer's disease based on different time intervals

BACKGROUND

Mild cognitive impairment (MCI) is the early stage of AD, and about 10-12% of MCI patients will progress to AD every year. At present, there are no effective markers for the early diagnosis of whether MCI patients will progress to AD. This study aimed to develop machine learning-based models for predicting the progression from MCI to AD within 3 years, to assist in screening and prevention of high-risk populations.

METHODS

Data were collected from the Alzheimer's Disease Neuroimaging Initiative, a representative sample of cognitive impairment population. Machine learning models were applied to predict the progression from MCI to AD, using demographic, neuropsychological test and MRI-related biomarkers. Data were divided into training (56%), validation (14%) and test sets (30%). AUC (area under ROC curve) was used as the main evaluation metric. Key predictors were ranked utilising their importance.

RESULTS

The AdaBoost model based on logistic regression achieved the best performance (AUC: 0.98) in 0-6 month prediction. Scores from the Functional Activities Questionnaire, Modified Preclinical Alzheimer Cognitive Composite with Trails test and ADAS11 (Unweighted sum of 11 items from The Alzheimer's Disease Assessment Scale-Cognitive Subscale) were key predictors.

CONCLUSION

Through machine learning, neuropsychological tests and MRI-related markers could accurately predict the progression from MCI to AD, especially in a short period time. This is of great significance for clinical staff to screen and diagnose AD, and to intervene and treat high-risk MCI patients early.