Natural history of mild cognitive impairment in older persons

Discovery of Proteoforms Associated with Alzheimer's Disease Through Quantitative Top-Down Proteomics

The complex nature of Alzheimer's disease (AD) and its heterogenous clinical presentation has prompted numerous large-scale -omic analyses aimed at providing a global understanding of the pathophysiological processes involved. AD involves isoforms, proteolytic products, and post-translationally modified proteins such as amyloid beta (Aβ) and microtuble-associated protein tau. Top-down proteomics (TDP) directly measures these species, and thus, offers a comprehensive view of pathologically relevant proteoforms that are difficult to analyze using traditional proteomic techniques. Here, we broadly explored associations between proteoforms and clinicopathological traits of AD by deploying a quantitative TDP approach across frontal cortex of 103 subjects selected from the ROS and MAP cohorts. The approach identified 1,213 proteins and 11,782 proteoforms, of which 154 proteoforms had at least one significant association with a clinicopathological phenotype. One important finding included identifying Aβ C-terminal truncation state as the key property for differential association between amyloid plaques and cerebral amyloid angiopathy (CAA). Furthermore, various N-terminally truncated forms of Aβ had noticeably stronger association with amyloid plaques and global cognitive function. Additionally, we discovered six VGF neuropeptides that were positively associated with cognitive function independent of pathological burden. The database of brain cortex proteoforms provides a valuable context for functional characterization of the proteins involved in Alzheimer's disease and other late-onset brain pathologies.

Unraveling sex differences in Alzheimer's disease and related endophenotypes with brain proteomes

INTRODUCTION

Sex differences exist in Alzheimer's disease (AD), but the underlying mechanisms remain unclear.

METHODS

We examined brain proteomes profiled from the dorsolateral prefrontal cortex of 770 donors (66.2% female).

RESULTS

Proteome-wide differential expression analysis in males and females jointly identified many significant proteins for AD dementia (n = 1228), amyloid beta (n = 1183), tangles (n = 1309), and global cognitive trajectory (n = 2325) at a false discovery rate of <0.05. Sex-stratified analyses also identified many proteins associated with AD or its endophenotypes. Finally, we found 10 proteins with significant sex-by-trait interactions, including one in AD clinical diagnosis (MARCKS), seven in cognitive trajectories (TOGARAM1, PLCD3, SLC22A5, MTFR1L, DCUN1D5, S100A12, and TRIM46), and two in cerebral pathologies (PANK4 and SOS1).

DISCUSSION

The 10 proteins with sex interaction in AD cover a range of functions likely relevant for AD pathogenesis, including estrogen response, inflammation, and mitochondrial biology, and their specific roles in AD ought to be studied. Future work should test their potential as sex-specific AD biomarkers.

HIGHLIGHTS

At the phenotypic level, we found sex differences in baseline cognitive performance, cognitive trajectories, and AD hallmark pathologies. Proteome-wide differential expression analyses identified many brain proteins associated with AD and its endophenotypes in either sex alone or when considered together. We found 10 brain proteins with significant sex interactions in AD and its endophenotypes, which could be investigated as potential sex-specific biomarkers of AD.

Assessing Cognitive Decline and Dementia Risk in Black and White Older Adults with Blood Biomarkers pTau217, GFAP, NfL, and Aβ ratio

Background

Alzheimer's disease blood-based biomarkers are a cost-effective early-detection method that, for precision medicine reasons, needs to be studied in both Blackand White. Few studies have a long follow-up of cognition. We studied a blood-biomarkers panel, cognitive decline, and dementia risk in a large number of Black and White participants.

Methods

Participants without dementia were followed annually up to 15 years, after plasma biomarker measurement (NfL, GFAP, amyloid-beta 42/40 ratio, pTau217). Data included demographics, medical history, blood tests (e.g., kidney function), MMSE, APOEε4, annual evaluations of cognition, and clinician-based dementia evaluation. The biomarkers' association with comorbidities, cognitive decline, and risk of dementia was examined within race. To examine racial differences, we repeated analyses using a subset Mahalanobis-balanced 1:1 on sex, age, education, Latino/Non-Latino, and clinical status (hypertension, diabetes, GFR, BMI, and heart disease).

Results

Biomarkers were measured in 431 Black and 583 White (respectively mean age of 77 and 80, 17% and 21% men), generating a balanced sample of 366:366. Biomarker's levels were similar between races. Within races, the associations of blood biomarkers with multiple comorbidities (especially kidney dysfunction and BMI) remained after controlling for demographics, APOE ε4, and dementia or death within 5 years. Men had lower GFAP levels than women (all p=<0.001). pTau217 was associated with decline in global cognition and all domains within races, and when comparing races, it was associated with a faster decline in global cognition and semantic memory in Black. The discrimination of dementia of pTau217 (AUC 3year, Black 0.81, CI=0.74, 0.89; AUC 3year, White 0.77, CI=0.71, 0.83) was good relative to age alone (AUC 3 year, Black 0.69, CI=0.58, 0.79; AUC 3 year, White 0.68, CI=0.62, 0.75), and MMSE (AUC 3 year, Black 0.81, CI=0.74, AUC 3 year, White 0.89; AUC 3 year, White 0.72, CI=0.65, 0.80). The discrimination of pTau217 did not improve by adding race or other biomarker information.

Discussion

pTau217 was highly associated with dementia risk and cognitive decline. The association of blood biomarkers with cognitive decline in Black and White participants was similar. Higher levels of pTau217 were, however, associated with semantic memory decline in Black adults. The combination of pTau217 with other biomarkers or MMSE did not improve dementia discrimination.

Evaluation of the efficacy of Tai Chi on the cognitive function of patients with mild cognitive dysfunction and research on its mechanism

Introduction

Studies have revealed that Tai Chi can enhance cognitive functions among patients with mild cognitive impairment (MCI). However, the precise mechanisms underlying this improvement remain elusive.

Methods

Consequently, we conducted a study involving 54 elderly inpatients with MCI residing in a combined medical and elderly care facility in Chengdu, who were randomly divided into three groups: a control group engaging in daily living activities, a Tai Chi group that performed Tai Chi exercises in addition to control group activities, and a walking group that undertook walking activities as a supplement to the control group regimen. The intervention period lasted for 24 weeks, comprising 12 weeks of exercise and an additional 12 weeks of follow-up. The Montreal Cognitive Assessment (MoCA), Trail Making Test-A (TMT-A), Auditory Verbal Learning Test (AVLT), and biochemical assessments (measuring brain-derived neurotrophic factor, BDNF, and platelet factor 4, PF4) were administered to investigate overall cognitive function, executive function, memory capacity, and changes in serum concentrations of BDNF and PF4 before, after, and during the follow-up period. Data were analyzed using IBM SPSS 26.0, with statistical methods encompassing descriptive analysis, ANOVA, rank-sum test, repeated measures ANOVA, and generalized estimating equations.

Results

Our findings indicated that after 24 weeks of intervention, the Tai Chi group exhibited improvements in cognitive function, executive function, and memory compared to the control group. This enhancement may be attributed to an increased expression of serum BDNF.

Discussion

In conclusion, our study underscores the potential of Tai Chi in ameliorating cognitive function among elderly patients with mild cognitive impairment, thereby offering significant implications for clinical prevention and treatment strategies targeting this condition.

Life-Space Mobility Is Related to Loneliness Among Living-Alone Older Adults: Longitudinal Analysis With Motion Sensor Data

BACKGROUND

Life-space mobility can be a behavioral indicator of loneliness. This study examined the association between life-space mobility measured with motion sensors and weekly vs. annually reported loneliness.

METHODS

Participants were older adults who lived alone. Passive infrared motion sensors were placed in the bathroom, bedroom, kitchen, and living room. Time spent in each room and out-of-home across the day was derived and used as the measure of life-space mobility. Participants reported via weekly questionnaires whether they felt lonely. In annual visits, the UCLA loneliness scale was administered to a subsample (n = 71), and the scores were categorized into high, moderate, and low groups. We used generalized estimating equations (GEE) to correlate life-space mobility with weekly and yearly loneliness. Repeated observations from each individual were bootstrapped for 1000 rounds to associate annual and weekly loneliness measures.

RESULTS

We analyzed 4995 weeks of data from 139 participants (age = 78.1 ± 8.6, 74% female, 23% African Americans, 14% with MCI diagnosis). An additional hour in the bedroom in the afternoon was associated with a 21.4% increased odds (OR = 1.214, p = 0.049) of experiencing loneliness in the week. An additional hour out-of-home in the morning and in the afternoon was associated with 18.2% (OR = 0.818, p = 0.040) and 15.3% (OR = 0.847, p = 0.018) fewer odds of experiencing weekly loneliness. In the subsample with annual loneliness assessments, an additional hour out-of-home was associated with 38.1% (OR = 0.619, p = 0.006) fewer odds of being in the high UCLA loneliness group. Compared with the low UCLA group, those with high UCLA scores were five times more likely to report loneliness weekly (OR = 5.260, p = 0.0004).

CONCLUSIONS

Frequent and objective measurements of mobility combined with self-reported social wellbeing information can offer new insights into the experience of loneliness and provide opportunities for timely interventions.

Evidence for cPLA2 activation in Alzheimer's Disease Synaptic Pathology

Background

Synapses are essential for learning and memory, and their loss predicts cognitive decline in Alzheimer's disease (AD). Synaptic loss is associated with excitotoxicity, neuroinflammation, amyloid-β, and tau pathology, but the molecular mechanisms remain unclear. There is an urgent need to identify new targets to modify the disease and slow synaptic loss and cognitive decline. This study examines if calcium-dependent phospholipase A2 (cPLA2) is implicated in AD synaptic loss. cPLA2 catalyzes membrane phospholipids to release arachidonic acid, which can be metabolized into inflammatory eicosanoids.

Methods

cPLA2 levels were examined in synaptosomes isolated from the postmortem frontal cortex of individuals with no cognitive impairment (NCI), mild cognitive impairment (MCI), and AD dementia from the Religious Orders Study (ROS). Eicosanoids in synaptosomes were analyzed using lipidomics. Immunofluorescent staining investigated cPLA2 interactions with synaptic markers. Human iPSCs-derived neurons were used to study cPLA2 overactivation after exposure to amyloid-β 42 oligomers (Aβ42O), its relationships with synaptic markers, and the effects of cPLA2 inhibitors.

Results

We observed elevated cPLA2 (cPLA2α and cPLA2β) in AD synaptosomes and positive correlations with postsynaptic density protein 95 (PSD-95) and cognitive dysfunction. Eicosanoids were increased in AD synaptosomes and correlated with cPLA2, indicating cPLA2 activity at synapses/synaptosomes. Phosphorylated cPLA2α (p-cPLA2α) colocalized with PSD-95 in synaptosomes, and with postsynaptic Ca 2+ /calmodulin-dependent protein kinase IIα (CaMKIIα) and dendritic microtubule-associated protein 2 (MAP2) in NCI and AD brains, where their levels were reduced in AD. P-cPLA2α colocalizes with MAP2 at the neuronal soma associated with neuritic plaques and neurodegeneration in AD. Aβ42O activates cPLA2α in human iPSCs-derived neurons, leading to p-cPLA2α relocation from the cytosol to synaptic and dendritic sites to colocalize with CaMKIIα and MAP2, resulting in their reduction. P-cPLA2α also colocalized with PSD-95 in Aβ42O-exposed neurons, accompanied with increased PSD-95 intensity at soma membrane. These processes were reversed by the cPLA2 inhibitor ASB14780.

Conclusions

cPLA2 overactivation at synapses, dendrites, and excitatory neuronal somas is associated with synaptic loss, neuritic plaques and neurodegeneration, potentially contributing to cognitive decline in AD. Future research needs to explore the role of cPLA2 as a disease-modifying target for AD.

A cerebrospinal fluid synaptic protein biomarker for prediction of cognitive resilience versus decline in Alzheimer's disease

Rates of cognitive decline in Alzheimer's disease (AD) are extremely heterogeneous. Although biomarkers for amyloid-beta (Aβ) and tau proteins, the hallmark AD pathologies, have improved pathology-based diagnosis, they explain only 20-40% of the variance in AD-related cognitive impairment (CI). To discover novel biomarkers of CI in AD, we performed cerebrospinal fluid (CSF) proteomics on 3,397 individuals from six major prospective AD case-control cohorts. Synapse proteins emerged as the strongest correlates of CI, independent of Aβ and tau. Using machine learning, we derived the CSF YWHAG:NPTX2 synapse protein ratio, which explained 27% of the variance in CI beyond CSF pTau181:Aβ42, 11% beyond tau positron emission tomography, and 28% beyond CSF neurofilament, growth-associated protein 43 and neurogranin in Aβ+ and phosphorylated tau+ (A+T1+) individuals. CSF YWHAG:NPTX2 also increased with normal aging and 20 years before estimated symptom onset in carriers of autosomal dominant AD mutations. Regarding cognitive prognosis, CSF YWHAG:NPTX2 predicted conversion from A+T1+ cognitively normal to mild cognitive impairment (standard deviation increase hazard ratio = 3.0, P = 7.0 × 10-4) and A+T1+ mild cognitive impairment to dementia (standard deviation increase hazard ratio = 2.2, P = 8.2 × 10-16) over a 15-year follow-up, adjusting for CSF pTau181:Aβ42, CSF neurofilament, CSF neurogranin, CSF growth-associated protein 43, age, APOE4 and sex. We also developed a plasma proteomic signature of CI, which we evaluated in 13,401 samples, which partly recapitulated CSF YWHAG:NPTX2. Overall, our findings underscore CSF YWHAG:NPTX2 as a robust prognostic biomarker for cognitive resilience versus AD onset and progression, highlight the potential of plasma proteomics in replacing CSF measurement and further implicate synapse dysfunction as a core driver of AD dementia.

Translating the Post-Mortem Brain Multi-Omics Molecular Taxonomy of Alzheimer's Dementia to Living Humans

Alzheimer's disease (AD) dementia is characterized by significant molecular and phenotypic heterogeneity, which confounds its mechanistic understanding, diagnosis, and effective treatment. In this study, we harness the most comprehensive dataset of paired ante-mortem blood omics, clinical, psychological, and post-mortem brain multi-omics data and neuroimaging to extensively characterize and translate the molecular taxonomy of AD dementia to living individuals. First, utilizing a comprehensive integration of eight complementary molecular layers from brain multi-omics data (N = 1,189), we identified three distinct molecular AD dementia subtypes exhibiting strong associations with cognitive decline, sex, psychological traits, brain morphology, and characterized by specific cellular and molecular drivers involving immune, vascular, and oligodendrocyte precursor cells. Next, in a significant translational effort, we developed predictive models to convert these advanced brain-derived molecular profiles (AD dementia pseudotimes and subtypes) into blood-, MRI- and psychological traits-based markers. The translation results underscore both the promise of these models and the opportunities for further enhancement. Our findings enhance the understanding of AD heterogeneity, underscore the value of multi-scale molecular approaches for elucidating causal mechanisms, and lay the groundwork for the development of novel therapies in living persons that target multi-level brain molecular subtypes of AD dementia.

Brain 5-hydroxymethylcytosine alterations are associated with Alzheimer's disease neuropathology

5-hydroxymethylcytosine, also known as the sixth DNA base of the genome, plays an important role in brain aging and neurological disorders such as Alzheimer's disease. However, little is known about its genome-wide distribution and its association with Alzheimer's disease pathology. Here, we report a genome-wide profiling of 5-hydroxymethylcytosine in 1079 autopsied brains (dorsolateral prefrontal cortex) of older individuals and assess its association with multiple measures of Alzheimer's disease pathologies, including pathological diagnosis of Alzheimer's disease, amyloid-β load, and PHFtau tangle density. Of 197,765 5-hydroxymethylcytosine regions detected, we identified 2821 differentially hydroxymethylated regions associated with Alzheimer's disease neuropathology after controlling for multiple testing and covariates. Many differentially hydroxymethylated regions are located within known Alzheimer's disease loci, such as RIN3, PLCG2, ITGA2B, and USP6NL. Integrative multi-omics analyses support a potential mechanistic role of 5-hydroxymethylcytosine alterations in Alzheimer's disease. Our study presents a large-scale genome-wide atlas of 5-hydroxymethylcytosine in Alzheimer's brain and offers insight into the mechanism underlying Alzheimer's disease pathogenesis.

The Association of Dementia and Mild Cognitive Impairment With Outpatient Ambulatory Care Utilization in the Community

BACKGROUND

Ambulatory care is critical in delivering interventions for dementia and mild cognitive impairment (MCI), from basic services to novel therapeutics. Yet, little is known regarding how community-dwelling persons with dementia/MCI interact with clinicians in outpatient ambulatory settings. We assessed associations of dementia/MCI with outpatient ambulatory evaluation and management (E&M) visits.

METHODS

We included 2116 community-dwelling participants in Rush Alzheimer's Disease Center cohorts, with linked fee-for-service Medicare claims. Annually from 2011 to 2019, cohort neuropsychologic evaluations classified participants as dementia, MCI, or no cognitive impairment (NCI). Across groups, we compared annual probability of visiting providers and number of E&M visits, using repeated measures logistic or generalized Poisson mixed effects models.

RESULTS

Across 8672 person-years (PY) of follow-up, the mean age was 82 (SD 7.6) years; 77% of PYs were among females and 24% among Black participants. Controlling for demographics and comorbidity, the annual predicted probability of primary care visits was high in all groups (86%-92%). Although there were few visits with dementia-related specialists, we found a higher probability of these visits among those with dementia (15%) and MCI (17%) than NCI (12%; p = 0.009, dementia vs. NCI; p < 0.001, MCI vs. NCI). There were striking differences in visits to other medical specialties: the mean number of annual visits was 40% lower for those with dementia (p < 0.001) and 10% lower for MCI (p < 0.001) than NCI. Overall, dementia and MCI were associated with 19% (p < 0.001) and 4% (p = 0.005) fewer E&M visits, respectively, compared to NCI.

CONCLUSIONS

Older adults with dementia and MCI interact with primary care providers regularly and are more likely to use dementia-related specialists than those with NCI. Yet, we found lower utilization of other medical specialties, without compensatory increases in primary care, leading to fewer overall E&M visits, even in MCI. Together, the findings may suggest lost opportunities to address the scope of health issues in vulnerable groups.

Loss of endothelial CD2AP causes sex-dependent cerebrovascular dysfunction

Polymorphisms in CD2-associated protein (CD2AP) predispose to Alzheimer's disease (AD), but the underlying mechanisms remain unknown. Here, we show that loss of CD2AP in cerebral blood vessels is associated with cognitive decline in AD subjects and that genetic downregulation of CD2AP in brain vascular endothelial cells impairs memory function in male mice. Animals with reduced brain endothelial CD2AP display altered blood flow regulation at rest and during neurovascular coupling, defects in mural cell activity, and an abnormal vascular sex-dependent response to Aβ. Antagonizing endothelin-1 receptor A signaling partly rescues the vascular impairments, but only in male mice. Treatment of CD2AP mutant mice with reelin glycoprotein that mitigates the effects of CD2AP loss function via ApoER2 increases resting cerebral blood flow and even protects male mice against the noxious effect of Aβ. Thus, endothelial CD2AP plays critical roles in cerebrovascular functions and represents a novel target for sex-specific treatment in AD.

Structural variants linked to Alzheimer's disease and other common age-related clinical and neuropathologic traits

BACKGROUND

Alzheimer's disease (AD) is a complex neurodegenerative disorder with substantial genetic influence. While genome-wide association studies (GWAS) have identified numerous risk loci for late-onset AD (LOAD), the functional mechanisms underlying most of these associations remain unresolved. Large genomic rearrangements, known as structural variants (SVs), represent a promising avenue for elucidating such mechanisms within some of these loci.

METHODS

By leveraging data from two ongoing cohort studies of aging and dementia, the Religious Orders Study and Rush Memory and Aging Project (ROS/MAP), we performed genome-wide association analysis testing 20,205 common SVs from 1088 participants with whole genome sequencing (WGS) data. A range of Alzheimer's disease and other common age-related clinical and neuropathologic traits were examined.

RESULTS

First, we mapped SVs across 81 AD risk loci and discovered 22 SVs in linkage disequilibrium (LD) with GWAS lead variants and directly associated with the phenotypes tested. The strongest association was a deletion of an Alu element in the 3'UTR of the TMEM106B gene, in high LD with the respective AD GWAS locus and associated with multiple AD and AD-related disorders (ADRD) phenotypes, including tangles density, TDP-43, and cognitive resilience. The deletion of this element was also linked to lower TMEM106B protein abundance. We also found a 22-kb deletion associated with depression in ROS/MAP and bearing similar association patterns as GWAS SNPs at the IQCK locus. In addition, we leveraged our catalog of SV-GWAS to replicate and characterize independent findings in SV-based GWAS for AD and five other neurodegenerative diseases. Among these findings, we highlight the replication of genome-wide significant SVs for progressive supranuclear palsy (PSP), including markers for the 17q21.31 MAPT locus inversion and a 1483-bp deletion at the CYP2A13 locus, along with other suggestive associations, such as a 994-bp duplication in the LMNTD1 locus, suggestively linked to AD and a 3958-bp deletion at the DOCK5 locus linked to Lewy body disease (LBD) (P = 3.36 × 10-4).

CONCLUSIONS

While still limited in sample size, this study highlights the utility of including analysis of SVs for elucidating mechanisms underlying GWAS loci and provides a valuable resource for the characterization of the effects of SVs in neurodegenerative disease pathogenesis.

Scam susceptibility is associated with a markedly accelerated onset of Alzheimer's disease dementia

INTRODUCTION

The association of scam susceptibility with the timing of Alzheimer's disease (AD) dementia onset is unknown.

METHODS

One thousand ninety-two older adults without dementia underwent assessments of scam susceptibility and annual clinical evaluations to document incident AD dementia. Accelerated failure time models examined the relation of scam susceptibility with dementia onset.

RESULTS

During a mean of 5 years of follow-up (standard deviation = 3.1), 188 individuals (17%) were diagnosed with incident AD dementia. A higher level of scam susceptibility was associated with a considerably earlier dementia onset ( β $\beta $  = -0.039; 95% confidence interval: -0.061, -0.017); those with a high level of susceptibility developed AD dementia at a mean age of 90.9 years compared to 98.2 for those with a low level. Results persisted after controlling for global cognition, sex, and education.

DISCUSSION

Scam susceptibility is associated with a markedly earlier onset of AD dementia. Assessment of susceptibility may facilitate early identification of individuals at risk of developing dementia.

HIGHLIGHTS

We examined whether scam susceptibility among older adults is associated with an accelerated onset of Alzheimer's disease dementia. Participants came from a large ongoing cohort study of aging. Scam susceptibility was assessed using a validated measure. Scam susceptibility was associated with a marked acceleration in dementia onset. Assessment of susceptibility may facilitate early identification of dementia.

Sense of purpose in life and extending the cognitive healthspan: evidence from multistate survival modeling

Having a sense of purpose in life predicts better maintenance of cognitive function in older adulthood and reduced risk of mild cognitive impairment (MCI) and dementia. However, little research has examined its influence on the rate of cognitive decline and length of cognitive healthspan. This study evaluated the role of sense of purpose on the risk and timing of transitions between normal cognition, MCI, and dementia. Older adults from the Memory and Aging Project (MAP; n = 1821) and the Health and Retirement Study (HRS; n = 10,542) were followed annually for 19 years and biennially for 12 years, respectively. Multistate survival models assessed whether sense of purpose predicted transitions across normal cognition, MCI, dementia, and death. More purposeful older adults had lower risk of developing MCI (HR = 0.82 in MAP; HR = 0.93 in HRS), higher likelihood of cognitive improvement, and longer cognitively healthy life expectancies. Results suggest sense of purpose may extend the cognitive healthspan.

Multi-omic subtypes of Alzheimer's dementia are differentially associated with psychological traits

Importance

Psychological traits reflecting neuroticism, depressive symptoms, loneliness, and purpose in life are risk factors of AD dementia; however, the underlying biologic mechanisms of these associations remain largely unknown.

Objective

To examine whether one or more multi-omic brain molecular subtypes of AD is associated with neuroticism, depressive symptoms, loneliness, and/or purpose in life.

Design

Two cohort-based studies; Religious Orders Study (ROS) and Rush Memory and Aging Project (MAP), both ongoing longitudinal clinical pathological studies that began enrollment in 1994 and 1997.

Setting

Older priests, nuns, and brothers from across the U.S. (ROS) and older adults from across the greater Chicago metropolitan area (MAP).

Participants

822 decedents with multi-omic data from the dorsolateral prefrontal cortex.

Exposures

Pseudotime, representing molecular distance from no cognitive impairment (NCI) to AD dementia, and three multi-omic brain molecular subtypes of AD dementia representing 3 omic pathways from no cognitive impairment (NCI) to AD dementia that differ by their omic constituents.

Main outcomes and measures

We first ran four separate linear regressions with neuroticism, depressive symptoms, loneliness, purpose in life as the outcomes, and pseudotime as the predictor, adjusting for age, sex and education. We then ran four separate analyses of covariance (ANCOVAs) with Bonferroni-corrected post-hoc tests to test whether the three multi-omic AD subtypes are differentially associated with the four traits, adjusting for the same covariates.

Results

Pseudotime was positively associated (p<0.05) with neuroticism and loneliness. AD subtypes were differentially associated with the traits: AD subtypes 1 and 3 were associated with neuroticism; AD subtype 2 with depressive symptoms; AD subtype 3 with loneliness, and AD subtype 2 with purpose in life.

Conclusions and Relevance

Three multi-omic brain molecular subtypes of AD dementia differentially share omic features with four psychological risk factors of AD dementia. Our data provide novel insights into the biology underlying well-established associations between psychological traits and AD dementia.

Relationship between hearing thresholds and cognitive function in hearing aid non-users and long-term users post-midlife

The extent of hearing loss requiring hearing aid (HA) to prevent cognitive decline is unclear; we assessed this post-midlife along with the relationship between hearing thresholds and cognitive function in those who had never used HA (non-users) or used HAs for >3 years (long-term users). This study comprised 117 individuals ≥55 years with an average hearing threshold of ≥25 dB HL in their better ear and 55 of the non-users and 62 of the long-term users. The Mini-Mental State Examination, the Symbol Digit Modalities Test (SDMT), and pure-tone and sound-field audiometry were assessed. Mean ± SD hearing levels of the non-user and long-term user group were 40.83 ± 8.16 and 51.13 ± 14.80 dB HL. Non-users showed a significant association (P = 0.01) between the hearing thresholds and SDMT scores, with a cutoff value of above 38.75 dB HL identified as affecting cognitive function. There were no significant associations for long-term users.

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

BACKGROUND

Cellular senescence, a hallmark of aging, has been implicated in Alzheimer's disease (AD) pathogenesis. Cholesterol accumulation is known to drive cellular senescence; however, its underlying mechanisms are not fully understood. ATP-binding cassette transporter A1 (ABCA1) plays an important role in cholesterol homeostasis, and its expression and trafficking are altered in APOE4 and AD models. However, the role of ABCA1 trafficking in cellular senescence associated with APOE4 and AD remains unclear.

METHODS

We examined the association between cellular senescence and ABCA1 expression in human postmortem brain samples using transcriptomic, histological, and biochemical analyses. Unbiased proteomic screening was performed to identify the proteins that mediate cellular ABCA1 trafficking. We created ABCA1 knock out cell lines and mouse models to validate the role of ABCA1 in cholesterol-induced mTORC1 activation and senescence. Additionally, we used APOE4-TR mice and induced pluripotent stem cell (iPSC) models to explore cholesterol-ABCA1-senescence pathways.

RESULTS

Transcriptomic profiling of the human dorsolateral prefrontal cortex from the Religious Order Study/Memory Aging Project (ROSMAP) cohort revealed the upregulation of cellular senescence transcriptome signatures in AD, which correlated with ABCA1 expression and oxysterol levels. Immunofluorescence and immunoblotting analyses confirmed increased lipofuscin-stained lipids and ABCA1 expression in AD brains and an association with mTOR phosphorylation. Discovery proteomics identified caveolin-1, a sensor of cellular cholesterol accumulation, as a key promoter of ABCA1 endolysosomal trafficking. Greater caveolin-1 expression was observed in APOE4-TR mouse models and AD human brains. Oxysterol induced mTORC1 activation and senescence were regulated by ABCA1 lysosomal trapping. Treatment of APOE4-TR mice with cyclodextrin reduced brain oxysterol levels, ABCA1 lysosome trapping, mTORC1 activation, and attenuated senescence and neuroinflammation markers. In human iPSC-derived astrocytes, the reduction of cholesterol by cyclodextrin attenuated inflammatory responses.

CONCLUSIONS

Oxysterol accumulation in APOE4 and AD induced ABCA1 and caveolin-1 expression, contributing to lysosomal dysfunction and increased cellular senescence markers. This study provides novel insights into how cholesterol metabolism accelerates features of brain cellular senescence pathway and identifies therapeutic targets to mitigate these processes.

Longitudinal relationships between depressive symptoms, functional impairment, and physical activity in later late life

The purpose of this study was to investigate relationships between depressive symptoms, functional disability, and physical activity over time in community-dwelling older adults. The Religious Order Study and Rush Memory and Aging Project are longitudinal cohort studies based in the United States which began recruitment in 1994 and 1997, respectively. This analysis included 1611 participants (27.4% male, 92.9% White, 74.7% cognitively normal) who were included at age 80 and followed until age 90. Depressive symptoms were assessed using the modified Center for Epidemiologic Studies Depression scale. Functional disability was assessed using the Instrumental Activities of Daily Living (IADL) scale. Physical activity was self-reported hours of weekly exercise. Reciprocal temporal relationships between these variables were investigated using a random intercept cross-lagged panel model, which decomposes observed variables into stable between-person ('trait') and variable within-person ('state') components to estimate the directional effects between variables over time. Traits for depressive symptoms, IADL disability, and physical activity were correlated. IADL disability showed autoregressive effects; disability starting at age 82 strongly predicted subsequent disability. Consistent autoregressive effects were not observed for depressive symptoms nor physical activity. Several small cross-lagged effects between states were observed for IADL disability and physical activity, as well as for IADL disability and depressive symptoms. There were no direct effects between depressive symptoms and physical activity, but several paths through IADL disability were observed between ages 82 and 88. Functional disability played an important role in octogenarians, highlighting the importance of maintaining functional independence later in life.

Changes in the Parietal Lobe Subregion Volume at Various Stages of Alzheimer's Disease and the Role in Cognitively Normal and Mild Cognitive Impairment Conversion

BACKGROUND

Volume alterations in the parietal subregion have received less attention in Alzheimer's disease (AD), and their role in predicting conversion of mild cognitive impairment (MCI) to AD and cognitively normal (CN) to MCI remains unclear. In this study, we aimed to assess the volumetric variation of the parietal subregion at different cognitive stages in AD and to determine the role of parietal subregions in CN and MCI conversion.

METHODS

We included 662 participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database, including 228 CN, 221 early MCI (EMCI), 112 late MCI (LMCI), and 101 AD participants. We measured the volume of the parietal subregion based on the Human Brainnetome Atlas (BNA-246) using voxel-based morphometry among individuals at various stages of AD and the progressive and stable individuals in CN and MCI. We then calculated the area under the curve (AUC) of the receiver operating characteristic (ROC) curve to test the ability of parietal subregions to discriminate between different cognitive groups. The Cox proportional hazard model was constructed to determine which specific parietal subregions, alone or in combination, could be used to predict progression from MCI to AD and CN to MCI. Finally, we examined the relationship between the cognitive scores and parietal subregion volume in the diagnostic groups.

RESULTS

The left inferior parietal lobule (IPL)_6_5 (rostroventral area 39) showed the best ability to discriminate between patients with AD and those with CN (AUC = 0.688). The model consisting of the left IPL_6_4 (caudal area 40) and bilateral IPL_6_5 showed the best combination for predicting the CN progression to MCI. The left IPL_6_1 (caudal area 39) showed the best predictive power in predicting the progression of MCI to AD. Certain subregions of the volume correlated with cognitive scales.

CONCLUSION

Subregions of the angular gyrus are essential in the early onset and subsequent development of AD, and early detection of the volume of these regions may be useful in identifying the tendency to develop the disease and its treatment.

Molecular hallmarks of excitatory and inhibitory neuronal resilience and resistance to Alzheimer's disease

Background

A significant proportion of individuals maintain healthy cognitive function despite having extensive Alzheimer's disease (AD) pathology, known as cognitive resilience. Understanding the molecular mechanisms that protect these individuals can identify therapeutic targets for AD dementia. This study aims to define molecular and cellular signatures of cognitive resilience, protection and resistance, by integrating genetics, bulk RNA, and single-nucleus RNA sequencing data across multiple brain regions from AD, resilient, and control individuals.

Methods

We analyzed data from the Religious Order Study and the Rush Memory and Aging Project (ROSMAP), including bulk (n=631) and multi-regional single nucleus (n=48) RNA sequencing. Subjects were categorized into AD, resilient, and control based on β-amyloid and tau pathology, and cognitive status. We identified and prioritized protected cell populations using whole genome sequencing-derived genetic variants, transcriptomic profiling, and cellular composition distribution.

Results

Transcriptomic results, supported by GWAS-derived polygenic risk scores, place cognitive resilience as an intermediate state in the AD continuum. Tissue-level analysis revealed 43 genes enriched in nucleic acid metabolism and signaling that were differentially expressed between AD and resilience. Only GFAP (upregulated) and KLF4 (downregulated) showed differential expression in resilience compared to controls. Cellular resilience involved reorganization of protein folding and degradation pathways, with downregulation of Hsp90 and selective upregulation of Hsp40, Hsp70, and Hsp110 families in excitatory neurons. Excitatory neuronal subpopulations in the entorhinal cortex (ATP8B1+ and MEF2Chigh) exhibited unique resilience signaling through neurotrophin (modulated by LINGO1) and angiopoietin (ANGPT2/TEK) pathways. We identified MEF2C, ATP8B1, and RELN as key markers of resilient excitatory neuronal populations, characterized by selective vulnerability in AD. Protective rare variant enrichment highlighted vulnerable populations, including somatostatin (SST) inhibitory interneurons, validated through immunofluorescence showing co-expression of rare variant associated RBFOX1 and KIF26B in SST+ neurons in the dorsolateral prefrontal cortex. The maintenance of excitatory-inhibitory balance emerges as a key characteristic of resilience.

Conclusions

We identified molecular and cellular hallmarks of cognitive resilience, an intermediate state in the AD continuum. Resilience mechanisms include preservation of neuronal function, maintenance of excitatory/inhibitory balance, and activation of protective signaling pathways. Specific excitatory neuronal populations appear to play a central role in mediating cognitive resilience, while a subset of vulnerable SST interneurons likely provide compensation against AD-associated dysregulation. This study offers a framework to leverage natural protective mechanisms to mitigate neurodegeneration and preserve cognition in AD.

Alzheimer's disease-associated CD83(+) microglia are linked with increased immunoglobulin G4 and human cytomegalovirus in the gut, vagal nerve, and brain

INTRODUCTION

While there may be microbial contributions to Alzheimer's disease (AD), findings have been inconclusive. We recently reported an AD-associated CD83(+) microglia subtype associated with increased immunoglobulin G4 (IgG4) in the transverse colon (TC).

METHODS

We used immunohistochemistry (IHC), IgG4 repertoire profiling, and brain organoid experiments to explore this association.

RESULTS

CD83(+) microglia in the superior frontal gyrus (SFG) are associated with elevated IgG4 and human cytomegalovirus (HCMV) in the TC, anti-HCMV IgG4 in cerebrospinal fluid, and both HCMV and IgG4 in the SFG and vagal nerve. This association was replicated in an independent AD cohort. HCMV-infected cerebral organoids showed accelerated AD pathophysiological features (Aβ42 and pTau-212) and neuronal death.

DISCUSSION

Findings indicate complex, cross-tissue interactions between HCMV and the adaptive immune response associated with CD83(+) microglia in persons with AD. This may indicate an opportunity for antiviral therapy in persons with AD and biomarker evidence of HCMV, IgG4, or CD83(+) microglia.

HIGHLIGHTS

Cross-tissue interaction between HCMV and the adaptive immune response in a subset of persons with AD. Presence of CD83(+) microglial associated with IgG4 and HCMV in the gut. CD83(+) microglia are also associated presence of HCMV and IgG4 in the cortex and vagal nerve. Replication of key association in an independent cohort of AD subjects. HCMV infection of cerebral organoids accelerates the production of AD neuropathological features.

Review of Associations of Diabetes and Insulin Resistance With Brain Health in Three Harmonised Cohort Studies of Ageing and Dementia

Diabetes increases the risk of dementia, and insulin resistance (IR) has emerged as a potential unifying feature. Here, we review published findings over the past 2 decades on the relation of diabetes and IR to brain health, including those related to cognition and neuropathology, in the Religious Orders Study, the Rush Memory and Aging Project, and the Minority Aging Research Study (ROS/MAP/MARS), three harmonised cohort studies of ageing and dementia at the Rush Alzheimer's Disease Center (RADC). A wide range of participant data, including information on medical conditions such as diabetes and neuropsychological tests, as well as other clinical and laboratory-based data collected annually. Neuropathology data are collected in participants who agree to autopsy at death. Recent studies have measured additional peripheral and brain IR data, including multi-omics. This review summarises findings from the RADC cohort studies that investigate the relation of diabetes and IR in older adults to cognition, neuropathology, omics in dementia, and other brain health measures. Examining the risk of clinically diagnosed dementia in older adults, our study found a 65% increased risk of Alzheimer's disease (AD) dementia in individuals with diabetes compared with those without. Regarding cognitive function, we have consistently observed associations of diabetes, as well as both peripheral and brain IR, with worse and declining performance in global cognition and specific cognitive domains, particularly semantic memory and perceptual speed. Studies utilising neuropathological data showed associations of diabetes and peripheral IR with brain infarcts, while brain IR measures, notably alpha serine/threonine-protein kinase1 (AKT1), were associated with both brain infarcts and AD pathology. Multi-omics studies suggested shared causal genes and pathways between diabetes and dementia. Recent epigenetic studies have revealed associations between IR and AD risk, along with distinct 5-hydroxymethylcytosine signatures in diabetes-associated AD. Furthermore, our studies have utilised other available data to investigate the impact of diabetes on neurological outcomes other than cognition and reported worsening of parkinsonian-like signs in diabetes. Recent studies have also explored risk factors for diabetes and have reported associations between lower literacy and decision-making abilities with elevated haemoglobin A1C levels, a peripheral IR measure. Overall, our findings, as summarised in this review, illustrate a range of mechanistic and other insights into the complex relationship of diabetes and IR with brain health. These findings may have important implications for future research on the ageing brain, including the prevention of cognitive decline and dementia in persons at risk for or with diabetes.

Transcranial Direct Current Stimulation for Global Cognition in Mild Cognitive Impairment

Mild cognitive impairment (MCI) is a condition characterized by noticeable deficits in memory retrieval or other cognitive domains than the individuals with the same age but do not significantly interfere with daily functioning. It represents an intermediate stage between normal aging and dementia, and a crucial opportunity for intervention prior to extensive cognitive decline. Transcranial direct current stimulation (tDCS), a non-invasive neuromodulation technique, has shown promise in enhancing global cognition in MCI. Current evidence suggests that tDCS provides short-term cognitive benefits, particularly in memory and attention, with moderate effects observed in processing speed. However, its impact on executive function and language remains inconsistent, highlighting variability in individual responses and study methodologies. While long-term efficacy remains uncertain due to limited longitudinal research and short follow-up periods, safety concerns, especially with self-administered tDCS such as in home-based tDCS, underscore the need for proper training and device innovation. Despite this, tDCS is a promising, portable tool for cognitive enhancement in MCI, with potential to delay progression to dementia. Addressing challenges such as optimizing stimulation protocols, accounting for individual neuroanatomical variability, and establishing long-term effectiveness will be essential for its broader clinical adoption. Future research should focus on standardizing methodologies, incorporating biomarkers to predict treatment response, and conducting large-scale, longitudinal studies to refine its therapeutic application.

Late-life social activity and subsequent risk of dementia and mild cognitive impairment

INTRODUCTION

Social activity is associated with better cognitive health in old age. To better translate epidemiological research for public health communication, we estimated relations of levels of social activity to average age at dementia onset.

METHODS

In the Rush Memory and Aging Project (MAP), we followed 1923 dementia-free older adults and conducted annual clinical evaluations of dementia/mild cognitive impairment (MCI).

RESULTS

During a mean follow-up of 6.7 (SD = 4.7) years, 545 participants developed dementia, and 695 developed MCI. Using Accelerated Failure Time models adjusted for age, sex, education, race/ethnicity, and marital status, we found predicted mean age of dementia onset for the least socially active was 87.7 years, approximately 5 years earlier than the most socially active (mean age = 92.2, p < .01); we found a similar 5-year difference in age at MCI onset by social activity.

DISCUSSION

Our findings highlight the value of social activity as a possible community-level intervention for reducing dementia.

HIGHLIGHTS

Accelerated failure time models estimated age at dementia onset by social activity level to aid interpretation. Higher social activity was associated with a 5-year older age at dementia onset. Economic research shows a 5-year delay translates to US$500,000 of healthcare savings per capita. Our findings help understand the public health significance of social activity.

Temporal Sequence of Incident Mild Cognitive Impairment, Incident Parkinsonism, and Risk of Death in Unimpaired Community-Dwelling Older Adults

BACKGROUND

Mild cognitive impairment (MCI) and parkinsonism affect many older adults. The objective of this study was to determine the sequence of their occurrence and associated risk of death.

METHODS

A total of 1255 community-dwelling unimpaired participants from 2 epidemiological cohorts were examined annually. MCI was based on neuropsychological testing and parkinsonism was based on the motor portion of the modified Unified Parkinson's Disease Rating Scale. A multistate Cox proportional hazards model simultaneously examined incidences of MCI, parkinsonism, and death.

RESULTS

The average age at baseline was 76.5 years (standard deviation [SD] = 7.2) and 73% were female. Incident MCI occurred almost as commonly as incident parkinsonism, yet compared with no impairment, the risk of death was higher for MCI (hazard ratio [HR] = 1.82, 95% confidence interval [CI] = 1.34, 2.47), but it was not different for parkinsonism (HR = 1.29; 95% CI =0.95, 1.75). The risk of death for participants with incident MCI who progressed to parkinsonism (40%) was not significantly different from those with MCI alone (HR = 1.25, 95% CI = 0.93, 1.69). However, the risk of death for participants with incident parkinsonism who progressed to MCI (51%) was significantly higher than those who did not progress (HR = 1.67, 95% CI = 1.27, 2.18), indicating that the risk of death is highest with the incidence of MCI.

CONCLUSIONS

The varied patterns of sequential occurrence of cognitive and motor impairment and associated risk of death suggest much greater heterogeneity than previously recognized. Further work is needed to determine the biology underlying the temporal evolution of these phenotypes, and if identification of the various subtypes improves risk stratification.

Plasticity of Human Microglia and Brain Perivascular Macrophages in Aging and Alzheimer's Disease

The complex roles of myeloid cells, including microglia and perivascular macrophages, are central to the neurobiology of Alzheimer's disease (AD), yet they remain incompletely understood. Here, we profiled 832,505 human myeloid cells from the prefrontal cortex of 1,607 unique donors covering the human lifespan and varying degrees of AD neuropathology. We delineated 13 transcriptionally distinct myeloid subtypes organized into 6 subclasses and identified AD-associated adaptive changes in myeloid cells over aging and disease progression. The GPNMB subtype, linked to phagocytosis, increased significantly with AD burden and correlated with polygenic AD risk scores. By organizing AD-risk genes into a regulatory hierarchy, we identified and validated MITF as an upstream transcriptional activator of GPNMB, critical for maintaining phagocytosis. Through cell-to-cell interaction networks, we prioritized APOE-SORL1 and APOE-TREM2 ligand-receptor pairs, associated with AD progression. In both human and mouse models, TREM2 deficiency disrupted GPNMB expansion and reduced phagocytic function, suggesting that GPNMB's role in neuroprotection was TREM2-dependent. Our findings clarify myeloid subtypes implicated in aging and AD, advancing the mechanistic understanding of their role in AD and aiding therapeutic discovery.

Epistatic effects of IGHG and FCGRIIB genes on the development of Alzheimer's disease in African Americans

Genome-wide association studies (GWAS) of Alzheimer's disease (AD) have identified a large number of susceptibility genes, but most of AD heritability remains unexplained, implying the existence of additional genes. Furthermore, the majority of the GWAS have been conducted in people of European descent, and the genes important for AD susceptibility in people of African descent have been underexplored. In this hypothesis-generating prospective cohort study, we genotyped 191 African Americans (AAs) from three longitudinal cohorts on aging for the IgG3 allotype GM6, which is expressed exclusively in people of African descent, and assessed its interaction with IGHG, FCGRIIB, and HLA-DRB1 genes. Cox proportional hazards modeling showed that GM6 by itself was not significantly associated with AD development. However, there was evidence of epistatic interaction: The risk of developing AD associated with GM6 positivity was significantly different (p = 0.0098) in non-GM17/GM17 participants compared with GM 17/GM17 participants. Specifically, in non-GM17/GM17 participants, the risk of AD was over fourfold higher in GM6-positive participants compared with GM 6-negative participants (HR = 4.63). Similarly, risk of developing AD associated with GM6 positivity was marginally different in non-FCGRIIB TT participants compared with FCGRIIB TT participants. In non-FCGRIIB TT participants, the risk of developing AD was over twofold higher in GM6-positive participants compared with GM6-negative participants (HR = 2.44). This is the first report suggesting that immunoglobulin GM allotypes might play a role in AD etiology among AAs; however, since this was largely a hypothesis-generating study, replication in larger cohorts would be required to confirm this finding.

Mild Cognitive Impairment: Quantifying a Qualitative Disorder

Mild cognitive impairment (MCI) has been described as a transitional state between normal aging and dementia, which can be both identified and tracked over time from qualitative and/or quantitative perspectives. Each definition of MCI involves some subjective cognitive complaint, some level of objective cognitive impairment, and generally intact daily functioning. Progression to dementia is common on follow-up in MCI, but stability and reversion to normal cognition can also occur. Quantitative methods might allow health care providers to evaluate and follow the subtle declines in MCI, as well as examine possible benefits of interventions with this at-risk condition.

Effects of brain microRNAs in cognitive trajectory and Alzheimer's disease

microRNAs (miRNAs) have a broad influence on gene expression; however, we have limited insights into their contribution to rate of cognitive decline over time or Alzheimer's disease (AD). Given this, we tested associations of 528 miRNAs with cognitive trajectory, AD hallmark pathologies, and AD clinical diagnosis using small RNA sequencing from the dorsolateral prefrontal cortex of 641 community-based donors. We found 311 miRNAs differentially expressed in AD or its endophenotypes after adjusting for technical and sociodemographic variables. Among these, 137 miRNAs remained differentially expressed after additionally adjusting for several co-occurring age-related cerebral pathologies, suggesting that some miRNAs are associated with the traits through co-occurring pathologies while others through mechanisms independent from pathologies. Pathway enrichment analysis of downstream targets of these differentially expressed miRNAs found enrichment in transcription, postsynaptic signalling, cellular senescence, and lipoproteins. In sex-stratified analyses, five miRNAs showed sex-biased differential expression for one or more AD endophenotypes, highlighting the role that sex has in AD. Lastly, we used Mendelian randomization to test whether the identified differentially expressed miRNAs contribute to the cause or are the consequence of the traits. Remarkably, 15 differentially expressed miRNAs had evidence consistent with a causal role, laying the groundwork for future mechanistic studies of miRNAs in AD and its endophenotypes.

The YTHDF Proteins Shape the Brain Gene Signatures of Alzheimer's Disease

The gene signatures of Alzheimer's Disease (AD) brains reflect an output of a complex interplay of genetic, epigenetic, epi-transcriptomic, and post-transcriptional regulations. To identify the most significant factor that shapes the AD brain signature, we developed a machine learning model (DEcode-tree) to integrate cellular and molecular factors explaining differential gene expression in AD. Our model indicates that YTHDF proteins, the canonical readers of N6-methyladenosine RNA modification (m6A), are the most influential predictors of the AD brain signature. We then show that protein modules containing YTHDFs are downregulated in human AD brains, and knocking out YTHDFs in iPSC-derived neural cells recapitulates the AD brain gene signature in vitro . Furthermore, eCLIP-seq analysis revealed that YTHDF proteins influence AD signatures through both m6A-dependent and independent pathways. These results indicate the central role of YTHDF proteins in shaping the gene signature of AD brains.

Development and Validation of the Communities Geriatric Mild Cognitive Impairment Risk Calculator (CGMCI-Risk)

Objectives: The aim was to develop and validate the Communities Geriatric Mild Cognitive Impairment Risk Calculator (CGMCI-Risk), aiding community healthcare workers in the early identification of individuals at high risk of mild cognitive impairment (MCI). Methods: Based on nationally representative community survey data, backward stepwise regression was employed to screen the variables, and logistic regression was utilized to construct the CGMCI-Risk. Internal validation was conducted using bootstrap resampling, while external validation was performed using temporal validation. The area under the receiver operating characteristic curve (AUROC), calibration curve, and decision curve analysis (DCA) were employed to evaluate the CGMCI-Risk in terms of discrimination, calibration, and net benefit, respectively. Results: The CGMCI-Risk model included variables such as age, educational level, sex, exercise, garden work, TV watching or radio listening, Instrumental Activity of Daily Living (IADL), hearing, and masticatory function. The AUROC was 0.781 (95% CI = 0.766 to 0.796). The calibration curve showed strong agreement, and the DCA suggested substantial clinical utility. In external validation, the CGMCI-Risk model maintained a similar performance with an AUROC of 0.782 (95% CI = 0.763 to 0.801). Conclusions: CGMCI-Risk is an effective tool for assessing cognitive function risk within the community. It uses readily predictor variables, allowing community healthcare workers to identify the risk of MCI in older adults over a three-year span.

CD33 and SHP-1/PTPN6 Interaction in Alzheimer's Disease

Large-scale genetic studies have identified numerous genetic risk factors that suggest a central role for innate immune cells in susceptibility to Alzheimer's disease (AD). CD33, an immunomodulatory transmembrane sialic acid binding protein expressed on myeloid cells, was identified as one such genetic risk factor associated with Alzheimer's disease. Several studies explored the molecular outcomes of genetic variation at the CD33 locus. It has been determined that the risk variant associated with AD increases the expression of the large isoform of CD33 (CD33M) in innate immune cells and alters its biological functions. CD33 is thought to signal via the interaction of its ITIM motif and the protein tyrosine phosphatase, SHP-1. Here, we utilize different molecular and computational approaches to investigate how AD-associated genetic variation in CD33 affects its interaction with SHP-1 in human microglia and microglia-like cells. Our findings demonstrate a genotype-dependent interaction between CD33 and SHP-1, which may functionally contribute to the AD risk associated with this CD33 variant. We also found that CD33-PTPN6 (SHP-1) gene-gene interactions impact AD-related traits, while CD33-PTPN11 (SHP-2) interactions do not.

Mitigation of synaptic and memory impairments via F-actin stabilization in Alzheimer's disease

BACKGROUND

Synaptic dysfunction, characterized by synapse loss and structural alterations, emerges as a prominent correlate of cognitive decline in Alzheimer's disease (AD). Actin cytoskeleton, which serves as the structural backbone of synaptic architecture, is observed to be lost from synapses in AD. Actin cytoskeleton loss compromises synaptic integrity, affecting glutamatergic receptor levels, neurotransmission, and synaptic strength. Understanding these molecular changes is crucial for developing interventions targeting synaptic dysfunction, potentially mitigating cognitive decline in AD.

METHODS

In this study, we investigated the synaptic actin interactome using mass spectrometry in a mouse model of AD, APP/PS1. Our objective was to explore how alterations in synaptic actin dynamics, particularly the interaction between PSD-95 and actin, contribute to synaptic and cognitive impairment in AD. To assess the impact of restoring F-actin levels on synaptic and cognitive functions in APP/PS1 mice, we administered F-actin stabilizing agent, jasplakinolide. Behavioral deficits in the mice were evaluated using the contextual fear conditioning paradigm. We utilized primary neuronal cultures to study the synaptic levels of AMPA and NMDA receptors and the dynamics of PSD-95 actin association. Furthermore, we analyzed postmortem brain tissue samples from subjects with no cognitive impairment (NCI), mild cognitive impairment (MCI), and Alzheimer's dementia (AD) to determine the association between PSD-95 and actin.

RESULTS

We found a significant reduction in PSD-95-actin association in synaptosomes from middle-aged APP/PS1 mice compared to wild-type (WT) mice. Treatment with jasplakinolide, an actin stabilizer, reversed deficits in memory recall, restored PSD-95-actin association, and increased synaptic F-actin levels in APP/PS1 mice. Additionally, actin stabilization led to elevated synaptic levels of AMPA and NMDA receptors, enhanced dendritic spine density, suggesting improved neurotransmission and synaptic strength in primary cortical neurons from APP/PS1 mice. Furthermore, analysis of postmortem human tissue with NCI, MCI and AD subjects revealed disrupted PSD-95-actin interactions, underscoring the clinical relevance of our preclinical studies.

CONCLUSION

Our study elucidates disrupted PSD-95 actin interactions across different models, highlighting potential therapeutic targets for AD. Stabilizing F-actin restores synaptic integrity and ameliorates cognitive deficits in APP/PS1 mice, suggesting that targeting synaptic actin regulation could be a promising therapeutic strategy to mitigate cognitive decline in AD.

Multi-omics analyses highlight molecular differences between clinical and neuropathological diagnoses in Alzheimer's disease

Both clinical diagnosis and neuropathological diagnosis are commonly used in literature to categorize individuals as Alzheimer's disease (AD) or non-AD in omics analyses. Whether these diagnostic strategies result in distinct profiles of molecular abnormalities is poorly understood. Here, we analysed one of the most commonly used AD omics datasets in the literature from the Religious Orders Study and Memory and Aging Project (ROSMAP) cohort and compared the two diagnosis strategies using brain transcriptome and metabolome by grouping individuals as non-AD and AD according to clinical or neuropathological diagnosis separately. Differentially expressed genes, associated pathways related with AD hallmarks and AD-related genes showed that the categorization based on neuropathological diagnosis more accurately reflects the disease state at the molecular level than the categorization based on clinical diagnosis. We further identified consensus biomarker candidates between the two diagnosis strategies such as 5-hydroxylysine, sphingomyelin and 1-myristoyl-2-palmitoyl-GPC as metabolite biomarkers and sphingolipid metabolism as a pathway biomarker, which could be robust AD biomarkers since they are independent of diagnosis strategies. We also used consensus AD and consensus non-AD individuals between the two diagnostic strategies to train a machine-learning based model, which we used to classify the individuals who were cognitively normal but diagnosed as AD based on neuropathological diagnosis (asymptomatic AD individuals). The majority of these individuals were classified as consensus AD patients for both omics data types. Our study provides a detailed characterization of both diagnostic strategies in terms of the association of the corresponding multi-omics profiles with AD.

Alzheimer disease-related biomarkers and cancer-related cognitive decline: the Thinking and Living with Cancer study

PURPOSE

We evaluated whether plasma Alzheimer disease (AD)-related biomarkers were associated with cancer-related cognitive decline among older breast cancer survivors.

METHODS

We included survivors aged 60-90 years with primary stage 0-III breast cancers (n = 236) and frequency-matched noncancer control paricipant (n = 154) who passed a cognitive screen and had banked plasma specimens. Participants were assessed at baseline (presystemic therapy) and annually for up to 60 months. Cognition was measured using tests of attention, processing speed, and executive function and learning and memory; perceived cognition was measured by the Functional Assessment of Cancer Therapy-Cognitive Function v3 Perceived Cognitive Impairments. Baseline plasma neurofilament light, glial fibrillary acidic protein, β-amyloid 42 and 40 and phosphorylated tau 181 were assayed using single molecule arrays. Mixed models tested associations between cognition and baseline AD biomarkers, time, group (survivor vs control participant), and their 2- and 3-way interactions, controlling for age, race, Wide Range 4 Achievement Test Word Reading score, comorbidity, and body mass index; 2-sided P values of .05 were considered statistically significant.

RESULTS

There were no group differences in baseline AD-related biomarkers except survivors had higher baseline neurofilament light levels than control participants (P = .013). Survivors had lower adjusted longitudinal attention, processing speed, and executive function than control participants starting from baseline and continuing over time (P ≤ .002). However, baseline AD-related biomarker levels were not independently associated with adjusted cognition over time, except control participants had lower attention, processing speed, and executive function scores with higher glial fibrillary acidic protein levels (P = .008).

CONCLUSION

The results do not support a relationship between baseline AD-related biomarkers and cancer-related cognitive decline. Further investigation is warranted to confirm the findings, test effects of longitudinal changes in AD-related biomarkers, and examine other mechanisms and factors affecting cognition presystemic therapy.

The MIND diet, brain transcriptomic alterations, and dementia

INTRODUCTION

Dietary patterns are associated with dementia risk, but the underlying molecular mechanisms are largely unknown.

METHODS

We used RNA sequencing data from post mortem prefrontal cortex tissue and annual cognitive evaluations from 1204 participants in the Religious Orders Study and Memory and Aging Project. We identified a transcriptomic profile correlated with the MIND diet (Mediterranean-Dietary Approaches to Stop Hypertension Intervention for Neurodegenerative Delay) among 482 individuals who completed ante mortem food frequency questionnaires; and examined its associations with cognitive health in the remaining 722 participants.

RESULTS

We identified a transcriptomic profile, consisting of 50 genes, correlated with the MIND diet score (p = 0.001). Each standard deviation increase in the transcriptomic profile score was associated with a slower annual rate of decline in global cognition (β = 0.011, p = 0.003) and lower odds of dementia (odds ratio = 0.76, p = 0.0002). Expressions of several genes (including TCIM and IGSF5) appeared to mediate the association between MIND diet and dementia.

DISCUSSION

A brain transcriptomic profile for healthy diets revealed novel genes potentially associated with cognitive health.

HIGHLIGHTS

Why healthy dietary patterns are associated with lower dementia risk are unknown. We integrated dietary, brain transcriptomic, and cognitive data in older adults. Mediterranean-Dietary Approaches to Stop Hypertension Intervention for Neurodegenerative Delay (MIND) diet intake is correlated with a specific brain transcriptomic profile. This brain transcriptomic profile score is associated with better cognitive health. More data are needed to elucidate the causality and functionality of identified genes.

Identification of a specific APOE transcript and functional elements associated with Alzheimer's disease

BACKGROUND

The APOE gene is the strongest genetic risk factor for late-onset Alzheimer's Disease (LOAD). However, the gene regulatory mechanisms at this locus remain incompletely characterized.

METHODS

To identify novel AD-linked functional elements within the APOE locus, we integrated SNP variants with multi-omics data from human postmortem brains including 2,179 RNA-seq samples from 3 brain regions and two ancestries (European and African), 667 DNA methylation samples, and ChIP-seq samples. Additionally, we plotted the expression trajectory of APOE transcripts in human brains during development.

RESULTS

We identified an AD-linked APOE transcript (jxn1.2.2) particularly observed in the dorsolateral prefrontal cortex (DLPFC). The APOE jxn1.2.2 transcript is associated with brain neuropathological features, cognitive impairment, and the presence of the APOE4 allele in DLPFC. We prioritized two independent functional SNPs (rs157580 and rs439401) significantly associated with jxn1.2.2 transcript abundance and DNA methylation levels. These SNPs are located within active chromatin regions and affect brain-related transcription factor-binding affinities. The two SNPs shared effects on the jxn1.2.2 transcript between European and African ethnic groups.

CONCLUSION

The novel APOE functional elements provide potential therapeutic targets with mechanistic insight into the disease etiology.

Psychological well-being trajectories preceding incident mild cognitive impairment and dementia

BACKGROUND

Poorer psychological well-being has been related to an increased dementia risk, but changes in psychological well-being along the dementia course are unclear. We explored psychological well-being trajectories before and after the diagnosis of mild cognitive impairment (MCI) and dementia.

METHODS

Within the Rush Memory and Aging Project, 910 cognitively intact older adults were followed annually for up to 14 years to detect incident MCI and dementia. Psychological well-being and its six components (self-acceptance, autonomy, environmental mastery, purpose in life, positive relation with others, and personal growth) were annually measured based on Ryff's Scales of Psychological Well-Being. Data were analysed using mixed-effect models with a backward timescale.

RESULTS

Compared with participants who remained cognitively intact, those who developed incident MCI had a faster decline in psychological well-being (β -0.015, 95% CI -0.027 to -0.003), leading to lower well-being 2 years before MCI diagnosis (mean difference at year -2, -0.099, 95% CI -0.187 to -0.012). Considering different well-being components, those who developed MCI had lower levels of purpose in life and personal growth beginning 3 years (-0.126, 95% CI -0.251 to -0.001) and 6 years (-0.139, 95% CI -0.268 to -0.009) before MCI, respectively. The slope of psychological well-being decline was similar before and after MCI diagnosis for each component except for positive relation with others, which had an accelerated decline after MCI (β -0.042, 95% CI-0.075 to -0.009). Well-being trajectories remained similar for individuals with MCI regardless of whether they later developed dementia.

CONCLUSIONS

Psychological well-being (specifically purpose in life and personal growth) became significantly lower before MCI diagnosis.

Structural variants linked to Alzheimer's Disease and other common age-related clinical and neuropathologic traits

Advances have led to a greater understanding of the genetics of Alzheimer's Disease (AD). However, the gap between the predicted and observed genetic heritability estimates when using single nucleotide polymorphisms (SNPs) and small indel data remains. Large genomic rearrangements, known as structural variants (SVs), have the potential to account for this missing genetic heritability. By leveraging data from two ongoing cohort studies of aging and dementia, the Religious Orders Study and Rush Memory and Aging Project (ROS/MAP), we performed genome-wide association analysis testing around 20,000 common SVs from 1,088 participants with whole genome sequencing (WGS) data. A range of Alzheimer's Disease and Related Disorders (AD/ADRD) clinical and pathologic traits were examined. Given the limited sample size, no genome-wide significant association was found, but we mapped SVs across 81 AD risk loci and discovered 22 SVs in linkage disequilibrium (LD) with GWAS lead variants and directly associated with AD/ADRD phenotypes (nominal P < 0.05). The strongest association was a deletion of an Alu element in the 3'UTR of the TMEM106B gene. This SV was in high LD with the respective AD GWAS locus and was associated with multiple AD/ADRD phenotypes, including tangle density, TDP-43, and cognitive resilience. The deletion of this element was also linked to lower TMEM106B protein abundance. We also found a 22 kb deletion associated with depression in ROSMAP and bearing similar association patterns as AD GWAS SNPs at the IQCK locus. In addition, genome-wide scans allowed the identification of 7 SVs, with no LD with SNPs and nominally associated with AD/ADRD traits. This result suggests potentially new ADRD risk loci not discoverable using SNP data. Among these findings, we highlight a 5.6 kb duplication of coding regions of the gene C1orf186 at chromosome 1 associated with indices of cognitive impairment, decline, and resilience. While further replication in independent datasets is needed to validate these findings, our results support the potential roles of common structural variations in the pathogenesis of AD/ADRD.

Lower GLUT1 and unchanged MCT1 in Alzheimer's disease cerebrovasculature

The brain is a highly demanding organ, utilizing mainly glucose but also ketone bodies as sources of energy. Glucose transporter-1 (GLUT1) and monocarboxylates transporter-1 (MCT1) respectively transport glucose and ketone bodies across the blood-brain barrier. While reduced glucose uptake by the brain is one of the earliest signs of Alzheimer's disease (AD), no change in the uptake of ketone bodies has been evidenced yet. To probe for changes in GLUT1 and MCT1, we performed Western immunoblotting in microvessel extracts from the parietal cortex of 60 participants of the Religious Orders Study. Participants clinically diagnosed with AD had lower cerebrovascular levels of GLUT1, whereas MCT1 remained unchanged. GLUT1 reduction was associated with lower cognitive scores. No such association was found for MCT1. GLUT1 was inversely correlated with neuritic plaques and cerebrovascular β-secretase-derived fragment levels. No other significant associations were found between both transporters, markers of Aβ and tau pathologies, sex, age at death or apolipoprotein-ε4 genotype. These results suggest that, while a deficit of GLUT1 may underlie the reduced transport of glucose to the brain in AD, no such impairment occurs for MCT1. This study thus supports the exploration of ketone bodies as an alternative energy source for the aging brain.

Single-cell multiregion dissection of Alzheimer's disease

Alzheimer's disease is the leading cause of dementia worldwide, but the cellular pathways that underlie its pathological progression across brain regions remain poorly understood1-3. Here we report a single-cell transcriptomic atlas of six different brain regions in the aged human brain, covering 1.3 million cells from 283 post-mortem human brain samples across 48 individuals with and without Alzheimer's disease. We identify 76 cell types, including region-specific subtypes of astrocytes and excitatory neurons and an inhibitory interneuron population unique to the thalamus and distinct from canonical inhibitory subclasses. We identify vulnerable populations of excitatory and inhibitory neurons that are depleted in specific brain regions in Alzheimer's disease, and provide evidence that the Reelin signalling pathway is involved in modulating the vulnerability of these neurons. We develop a scalable method for discovering gene modules, which we use to identify cell-type-specific and region-specific modules that are altered in Alzheimer's disease and to annotate transcriptomic differences associated with diverse pathological variables. We identify an astrocyte program that is associated with cognitive resilience to Alzheimer's disease pathology, tying choline metabolism and polyamine biosynthesis in astrocytes to preserved cognitive function late in life. Together, our study develops a regional atlas of the ageing human brain and provides insights into cellular vulnerability, response and resilience to Alzheimer's disease pathology.

Somatic nuclear mitochondrial DNA insertions are prevalent in the human brain and accumulate over time in fibroblasts

The transfer of mitochondrial DNA into the nuclear genomes of eukaryotes (Numts) has been linked to lifespan in nonhuman species and recently demonstrated to occur in rare instances from one human generation to the next. Here, we investigated numtogenesis dynamics in humans in 2 ways. First, we quantified Numts in 1,187 postmortem brain and blood samples from different individuals. Compared to circulating immune cells (n = 389), postmitotic brain tissue (n = 798) contained more Numts, consistent with their potential somatic accumulation. Within brain samples, we observed a 5.5-fold enrichment of somatic Numt insertions in the dorsolateral prefrontal cortex (DLPFC) compared to cerebellum samples, suggesting that brain Numts arose spontaneously during development or across the lifespan. Moreover, an increase in the number of brain Numts was linked to earlier mortality. The brains of individuals with no cognitive impairment (NCI) who died at younger ages carried approximately 2 more Numts per decade of life lost than those who lived longer. Second, we tested the dynamic transfer of Numts using a repeated-measures whole-genome sequencing design in a human fibroblast model that recapitulates several molecular hallmarks of aging. These longitudinal experiments revealed a gradual accumulation of 1 Numt every ~13 days. Numtogenesis was independent of large-scale genomic instability and unlikely driven by cell clonality. Targeted pharmacological perturbations including chronic glucocorticoid signaling or impairing mitochondrial oxidative phosphorylation (OxPhos) only modestly increased the rate of numtogenesis, whereas patient-derived SURF1-mutant cells exhibiting mtDNA instability accumulated Numts 4.7-fold faster than healthy donors. Combined, our data document spontaneous numtogenesis in human cells and demonstrate an association between brain cortical somatic Numts and human lifespan. These findings open the possibility that mito-nuclear horizontal gene transfer among human postmitotic tissues produces functionally relevant human Numts over timescales shorter than previously assumed.

Limbic-predominant age-related TDP-43 encephalopathy neuropathological change (LATE-NC) is associated with abnormalities in white matter structural integrity and connectivity: An ex-vivo diffusion MRI and pathology investigation

Limbic predominant age-related TDP-43 encephalopathy neuropathological change (LATE-NC) is common in older adults and is associated with neurodegeneration, cognitive decline and dementia. In this MRI and pathology investigation we tested the hypothesis that LATE-NC is associated with abnormalities in white matter structural integrity and connectivity of a network of brain regions typically harboring TDP-43 inclusions in LATE, referred to here as the "LATE-NC network". Ex-vivo diffusion MRI and detailed neuropathological data were collected on 184 community-based older adults. Linear regression revealed an independent association of higher LATE-NC stage with lower diffusion anisotropy in a set of white matter connections forming a pattern of connectivity that is consistent with the stereotypical spread of this pathology in the brain. Graph theory analysis revealed an association of higher LATE-NC stage with weaker integration and segregation in the LATE-NC network. Abnormalities were significant in stage 3, suggesting that they are detectable in later stages of the disease. Finally, LATE-NC network abnormalities were associated with faster cognitive decline, specifically in episodic and semantic memory.

Quantitative assessment of enlarged perivascular spaces via deep-learning in community-based older adults reveals independent associations with vascular neuropathologies, vascular risk factors and cognition

Enlarged perivascular spaces (EPVS) are common in older adults, but their neuropathologic correlates are unclear mainly because most work to date has relied on visual rating scales and/or clinical cohorts. The present study first developed a deep-learning model for automatic segmentation, localization and quantification of EPVS in ex vivo brain MRI, and then used this model to investigate the neuropathologic, clinical and cognitive correlates of EPVS in 817 community-based older adults that underwent autopsy. The new method exhibited high sensitivity in detecting EPVS as small as 3 mm3, good segmentation accuracy and consistency. Most EPVS were located in the frontal lobe, but the highest density was observed in the basal ganglia. EPVS in the cerebrum and specifically in the frontal lobe were associated with infarcts independent of other neuropathologies, while temporal and occipital EPVS were associated with cerebral amyloid angiopathy. EPVS in most brain lobes were also associated with diabetes mellitus independently of neuropathologies, while basal ganglia EPVS were independently associated with hypertension, supporting the notion of independent pathways from diabetes and hypertension to EPVS. Finally, EPVS were associated with lower cognitive performance independently of neuropathologies and clinical variables, suggesting that EPVS represent additional abnormalities contributing to lower cognition.

Psychosocial experiences are associated with human brain mitochondrial biology

Psychosocial experiences affect brain health and aging trajectories, but the molecular pathways underlying these associations remain unclear. Normal brain function relies on energy transformation by mitochondria oxidative phosphorylation (OxPhos). Two main lines of evidence position mitochondria both as targets and drivers of psychosocial experiences. On the one hand, chronic stress exposure and mood states may alter multiple aspects of mitochondrial biology; on the other hand, functional variations in mitochondrial OxPhos capacity may alter social behavior, stress reactivity, and mood. But are psychosocial exposures and subjective experiences linked to mitochondrial biology in the human brain? By combining longitudinal antemortem assessments of psychosocial factors with postmortem brain (dorsolateral prefrontal cortex) proteomics in older adults, we find that higher well-being is linked to greater abundance of the mitochondrial OxPhos machinery, whereas higher negative mood is linked to lower OxPhos protein content. Combined, positive and negative psychosocial factors explained 18 to 25% of the variance in the abundance of OxPhos complex I, the primary biochemical entry point that energizes brain mitochondria. Moreover, interrogating mitochondrial psychobiological associations in specific neuronal and nonneuronal brain cells with single-nucleus RNA sequencing (RNA-seq) revealed strong cell-type-specific associations for positive psychosocial experiences and mitochondria in glia but opposite associations in neurons. As a result, these "mind-mitochondria" associations were masked in bulk RNA-seq, highlighting the likely underestimation of true psychobiological effect sizes in bulk brain tissues. Thus, self-reported psychosocial experiences are linked to human brain mitochondrial phenotypes.

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.

Social activity mediates locus coeruleus tangle-related cognition in older adults

The locus coeruleus-noradrenaline system regulates brain-wide neural activity involved in cognition and behavior. Integrity of this subcortical neuromodulatory system is proposed to be a substrate of cognitive reserve that may be strengthened by lifetime cognitive and social activity. Conversely, accumulation of tau tangles in the brainstem locus coeruleus nuclei is recently studied as a very early marker of Alzheimer's disease (AD) pathogenesis and cognitive vulnerability, even among older adults without cognitive impairment or significant cerebral AD pathologies. This clinical-pathologic study examined whether locus coeruleus tangle density was cross-sectionally associated with lower antemortem cognitive performance and social activity among 142 cognitively unimpaired and impaired older adults and whether social activity, a putative reserve factor, mediated the association of tangle density and cognition. We found that greater locus coeruleus tangle density was associated with lower social activity for the whole sample and in the cognitively unimpaired group alone and these associations were independent of age, sex, education, depressive symptoms, and burden of cerebral amyloid and tau. The association of locus coeruleus tangle density with lower cognitive performance was partially mediated by level of social activity. These findings implicate the locus coeruleus-noradrenaline system in late-life social function and support that locus coeruleus tangle pathology is associated with lower levels of social activity, independent of cerebral AD pathologies, and specifically among older adults who are cognitively unimpaired. Early brainstem pathology may impact social function, and level of social function, in turn, influences cognition, prior to canonical stages of AD.

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.

Brain and serum lipidomic profiles implicate Lands cycle acyl chain remodeling association with APOEε4 and mild cognitive impairment

Introduction

At least one-third of the identified risk alleles from Genome-Wide Association Studies (GWAS) of Alzheimer's disease (AD) are involved in lipid metabolism, lipid transport, or direct lipid binding. In fact, a common genetic variant (ε4) in a cholesterol and phospholipid transporter, Apolipoprotein E (APOEε4), is the primary genetic risk factor for late-onset AD. In addition to genetic variants, lipidomic studies have reported severe metabolic dysregulation in human autopsy brain tissue, cerebrospinal fluid, blood, and multiple mouse models of AD.

Methods

We aimed to identify an overarching metabolic pathway in lipid metabolism by integrating analyses of lipidomics and transcriptomics from the Religious Order Study and Rush Memory Aging Project (ROSMAP) using differential analysis and network correlation analysis.

Results

Coordinated differences in lipids were found to be dysregulated in association with both mild cognitive impairment (MCI) and APOEε4 carriers. Interestingly, these correlations were weakened when adjusting for education. Indeed, the cognitively non-impaired APOEε4 carriers have higher education levels in the ROSMAP cohort, suggesting that this lipid signature may be associated with a resilience phenotype. Network correlation analysis identified multiple differential lipids within a single module that are substrates and products in the Lands Cycle for acyl chain remodeling. In addition, our analyses identified multiple genes in the Lands Cycle acyl chain remodeling pathway, which were associated with cognitive decline independent of amyloid-β (Aβ) load and tau tangle pathologies.

Discussion

Our studies highlight the critical differences in acyl chain remodeling in brain tissue from APOEε4 carriers and individual non-carriers with MCI. A coordinated lipid profile shift in dorsolateral prefrontal cortex from both APOEε4 carriers and MCI suggests differences in lipid metabolism occur early in disease stage and highlights lipid homeostasis as a tractable target for early disease modifying intervention.

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.