Modify Alzheimer's Disease Risk Research Articles

Traumatic Brain Injury Alters the Trajectory of Age-Related Mitochondrial Change.

Some epidemiologic studies associate traumatic brain injury (TBI) with Alzheimer's disease (AD). To test whether a TBI-induced acceleration of age-related mitochondrial change could potentially mediate the reported TBI-AD association. We administered unilateral controlled cortical impact (CCI) or sham injuries to 5-month-old C57BL/6J and tau transgenic rTg4510 mice. In the non-transgenics, we assessed behavior (1-5 days, 1 month, and 15 months), lesion size (1 and 15 months), respiratory chain enzymes (1 and 15 months), and mitochondrial DNA copy number (mtDNAcn) (1 and 15 months) after CCI/sham. In the transgenics we quantified post-injury mtDNAcn and tangle burden. In the non-transgenics CCI caused acute behavioral deficits that improved or resolved by 1-month post-injury. Protein-normalized complex I and cytochrome oxidase activities were not significantly altered at 1 or 15 months, although complex I activity in the CCI ipsilesional cortex declined during that period. Hippocampal mtDNAcn was not altered by injury at 1 month, increased with age, and rose to the greatest extent in the CCI contralesional hippocampus. In the injured then aged transgenics, the ipsilesional hippocampus contained less mtDNA and fewer tangles than the contralesional hippocampus; mtDNAcn and tangle counts did not correlate. As mice age their brains increase mtDNAcn as part of a compensatory response that preserves mitochondrial function, and TBI enhances this response. TBI may, therefore, increase the amount of compensation required to preserve late-life mitochondrial function. If TBI does modify AD risk, altering the trajectory or biology of aging-related mitochondrial changes could mediate the effect.

Cell-autonomous effects of APOE4 in restricting microglial response in brain homeostasis and Alzheimer's disease.

Microglial involvement in Alzheimer's disease (AD) pathology has emerged as a risk-determining pathogenic event. While apolipoprotein E (APOE) is known to modify AD risk, it remains unclear how microglial apoE impacts brain cognition and AD pathology. Here, using conditional mouse models expressing apoE isoforms in microglia and central nervous system-associated macrophages (CAMs), we demonstrate a cell-autonomous effect of apoE3-mediated microglial activation and function, which are negated by apoE4. Expression of apoE3 in microglia/CAMs improves cognitive function, increases microglia surrounding amyloid plaque and reduces amyloid pathology and associated toxicity, whereas apoE4 expression either compromises or has no effects on these outcomes by impairing lipid metabolism. Single-cell transcriptomic profiling reveals increased antigen presentation and interferon pathways upon apoE3 expression. In contrast, apoE4 expression downregulates complement and lysosomal pathways, and promotes stress-related responses. Moreover, in the presence of mouse endogenous apoE, microglial apoE4 exacerbates amyloid pathology. Finally, we observed a reduction in Lgals3-positive responsive microglia surrounding amyloid plaque and an increased accumulation of lipid droplets in APOE4 human brains and induced pluripotent stem cell-derived microglia. Our findings establish critical isoform-dependent effects of microglia/CAM-expressed apoE in brain function and the development of amyloid pathology, providing new insight into how apoE4 vastly increases AD risk.

Relationship of fasting glucose and longitudinal Alzheimer's disease imaging markers.

IntroductionFasting glucose increases with age and is linked to modifiable Alzheimer's disease risk factors such as cardiovascular disease and Type 2 diabetes (T2D).MethodsWe leveraged available biospecimens and neuroimaging measures collected during the Alzheimer's Prevention Through Exercise (APEx) trial (n = 105) to examine the longitudinal relationship between change in blood glucose metabolism and change in regional cerebral amyloid deposition and gray and white matter (WM) neurodegeneration in older adults over 1 year of follow‐up.ResultsIndividuals with improving fasting glucose (n = 61) exhibited less atrophy and regional amyloid accumulation compared to those whose fasting glucose worsened over 1 year (n = 44). Specifically, while individuals with increasing fasting glucose did not yet show cognitive decline, they did have regional atrophy in the hippocampus and inferior parietal cortex, and increased amyloid accumulation in the precuneus cortex. Signs of early dementia pathology occurred in the absence of significant group differences in insulin or body composition, and was not modified by apolipoprotein E ε4 carrier status.DiscussionDysregulation of glucose in late life may signal preclinical brain change prior to clinically relevant cognitive decline. Additional work is needed to determine whether treatments specifically targeting fasting glucose levels may impact change in brain structure or cerebral amyloid in older adults.

Alzheimer's Disease Prevention Health Coaching.

BackgroundWidespread lifestyle risk reduction at the community level is considered effective in decreasing Alzheimer’s disease (AD). To address the limited use of risk deduction in AD, this study aimed to explore the feasibility of community-level implementation. Diverse older adults (60+) living in Richmond, VA, with incomes below $12,000/year and managing diabetic/cardiovascular symptoms were offered weekly lifestyle telephone-health coaching for 12-weeks in 2019–2020 (Phase 1). The health coaching sessions were framed to provide AD lifestyle risk reduction education, goal setting, and support: motivations and self-efficacy. The study sample (n=40, mean age 68 years (range: 60–76 years)) was 90% African American/Black (n=36), 100% Non-Hispanic, and 45% males (n=18). Twenty-five participants (60%) reported experiencing some/often memory problems in the last 12-months. Thirty-nine (95%) of subjects successfully participated in coaching sessions; on average, 11 (91.9%) sessions per subject were completed. Participants provided positive anecdotal feedback and stated the need for continued health coaching. Consequently, n=30 (75%) of the original sample consented to continued health coaching during the 2020–2021 COVID-19 pandemic (Phase 2). All study subjects were examined at baseline (Time 1), 3-month (Time 2), covid-baseline (Time 3), and 3-months postcovid-baseline (Time 4). Repeated Measures ANOVAs were done to examine Time and Time*Memory Status effects.ResultsThere was a total risk reduction at Phase 1 (F=9.26; p=.004; effect size=.19). At Phase 2, alcohol use decreased (p=.05), quadratic time effects were observed in physical activity (p=.01–.02), and cubic time effects were observed in depression (p=.02). Overall, total risk reduction in Phase 2 was observed at F=5.05; p=.03 effect size=.16. Pre/post-test analyses indicated improvement in Memory Problem Time Interaction (p=.007), AD knowledge (p=.01–.03), and Tired Days (p=.04) across Phase 1. There was also improvement in Social Isolation Time Interaction (p=.03); Tobacco Addiction (p=.001); Poor Mental Health Days (p=.05), and Worried Days Time Interaction (p=.02−.01) across Phase 2. Between subject Memory Status effects, indicating poorer baseline levels for individuals reporting memory problems had greater improvement seen in memory complaints (p=.001), poor mental health days (.02), and tired days (.003−.01).ConclusionsThis preliminary work creates the impetus for future large-scale lifestyle AD risk reduction investigations to mitigate and improve modifiable AD risk among low-income, diverse older adults, including individuals reporting memory problems. Our findings surrounding participant engagement and positive trends in AD risk reduction support the hypothesis that telephone-based health coaching is a practical and feasible AD risk reduction intervention.

Spreading of Alzheimer tau seeds is enhanced by aging and template matching with limited impact of amyloid-β

In Alzheimer's disease (AD), deposition of pathological tau and amyloid-β (Aβ) drive synaptic loss and cognitive decline. The injection of misfolded tau aggregates extracted from human AD brains drives templated spreading of tau pathology within WT mouse brain. Here, we assessed the impact of Aβ copathology, of deleting loci known to modify AD risk (Ptk2b, Grn, and Tmem106b) and of pharmacological intervention with an Fyn kinase inhibitor on tau spreading after injection of AD tau extracts. The density and spreading of tau inclusions triggered by human tau seed were unaltered in the hippocampus and cortex of APPswe/PSEN1ΔE9 transgenic and AppNL-F/NL-F knock-in mice. In mice with human tau sequence replacing mouse tau, template matching enhanced neuritic tau burden. Human AD brain tau-enriched preparations contained aggregated Aβ, and the Aβ coinjection caused a redistribution of Aβ aggregates in mutant AD model mice. The injection-induced Aβ phenotype was spatially distinct from tau accumulation and could be ameliorated by depleting Aβ from tau extracts. These data suggest that Aβ and tau pathologies propagate by largely independent mechanisms after their initial formation. Altering the activity of the Fyn and Pyk2 (Ptk2b) kinases involved in Aβ-oligomer–induced signaling, or deleting expression of the progranulin and TMEM106B lysosomal proteins, did not alter the somatic tau inclusion burden or spreading. However, mouse aging had a prominent effect to increase the accumulation of neuritic tau after injection of human AD tau seeds into WT mice. These studies refine our knowledge of factors capable of modulating tau spreading.

The Effects of Chronic Exposure to Ambient Traffic-Related Air Pollution on Alzheimer's Disease Phenotypes in Wildtype and Genetically Predisposed Male and Female Rats.

Background:Epidemiological data link traffic-related air pollution (TRAP) to increased risk of Alzheimer’s disease (AD). Preclinical data corroborating this association are largely from studies of male animals exposed acutely or subchronically to high levels of isolated fractions of TRAP. What remains unclear is whether chronic exposure to ambient TRAP modifies AD risk and the influence of sex on this interaction.Objectives:This study sought to assess effects of chronic exposure to ambient TRAP on the time to onset and severity of AD phenotypes in a preclinical model and to determine whether sex or genetic susceptibility influences outcomes.Methods:Male and female TgF344-AD rats that express human AD risk genes and wildtype littermates were housed in a vivarium adjacent to a heavily trafficked tunnel in Northern California and exposed for up to 14 months to filtered air (FA) or TRAP drawn from the tunnel and delivered to animals unchanged in real time. Refractive particles in the brain and AD phenotypes were quantified in 3-, 6-, 10-, and 15-month-old animals using hyperspectral imaging, behavioral testing, and neuropathologic measures.Results:Particulate matter (PM) concentrations in TRAP exposure chambers fluctuated with traffic flow but remained below 24-h PM with aerodynamic diameter less than or equal to 2.5 micrometers () U.S. National Ambient Air Quality Standards limits. Ultrafine PM was a predominant component of TRAP. Nano-sized refractive particles were detected in the hippocampus of TRAP animals. TRAP-exposed animals had more amyloid plaque deposition, higher hyperphosphorylated tau levels, more neuronal cell loss, and greater cognitive deficits in an age-, genotype-, and sex-dependent manner. TRAP-exposed animals also had more microglial cell activation, but not astrogliosis.Discussion:These data demonstrate that chronic exposure to ambient TRAP promoted AD phenotypes in wildtype and genetically susceptible rats. TRAP effects varied according to age, sex, and genotype, suggesting that AD progression depends on complex interactions between environment and genetics. These findings suggest current regulations are insufficient to protect the aging brain. https://doi.org/10.1289/EHP8905

Hypoxia compromises the mitochondrial metabolism of Alzheimer's disease microglia via HIF1.

Genetic Alzheimer's disease (AD) risk factors associate with reduced defensive amyloid β plaque-associated microglia (AβAM), but the contribution of modifiable AD risk factors to microglial dysfunction is unknown. In AD mouse models, we observe concomitant activation of the hypoxia-inducible factor 1 (HIF1) pathway and transcription of mitochondrial-related genes in AβAM, and elongation of mitochondria, a cellular response to maintain aerobic respiration under low nutrient and oxygen conditions. Overactivation of HIF1 induces microglial quiescence in cellulo, with lower mitochondrial respiration and proliferation. In vivo, overstabilization of HIF1, either genetically or by exposure to systemic hypoxia, reduces AβAM clustering and proliferation and increases Aβ neuropathology. In the human AD hippocampus, upregulation of HIF1α and HIF1 target genes correlates with reduced Aβ plaque microglial coverage and an increase of Aβ plaque-associated neuropathology. Thus, hypoxia (a modifiable AD risk factor) hijacks microglial mitochondrial metabolism and converges with genetic susceptibility to cause AD microglial dysfunction.

HAPPCAP‐AD (Human‐Application Combined Approach for Prevention of Alzheimer's Disease): A novel feasibility study of a personalized midlife intervention to prevent AD

AbstractBackgroundDeveloping efficient Alzheimer's disease (AD) prevention strategies is imperative as AD has no cure. Physical inactivity, obesity, type 2 diabetes [T2D], hypertension, smoking, depression, and low educational attainment, are the seven major potentially modifiable risk factors showing consistent association with AD. We have launched a novel, "real‐life", feasibility study of personalized 18‐months intervention for prevention of cognitive decline in middle‐aged individuals at high AD risk due to a parental family history. Our study implements an innovative approach combining a smartphone application (app) with study team guidance through phone‐calls. Our aims are to investigate: 1) The feasibility of our novel intervention and factors associated with adherence to it; 2) Whether our intervention improves AD risk factors and whether greater adherence is associated with larger improvement; and 3) Whether our intervention improves cognition and cerebral blood flow.MethodWe will recruit one hundred 40‐65 years old AD patients' offspring, to two groups (67 at the intervention group and 33 at the passive control). All participants will have at least two risk factors of the seven major modifiable AD risk factors. The 18‐months intervention will include advice for risk factors improvement, interactive follow‐up using a smartphone app and dynamic feedback on risk factors management for its modification, through both the app and the study team.ResultRecruitment has recently begun, through publishing an online eligibility questionnaire. Thus far, 200 individuals have completed the questionnaire, with 113 fulfilling eligibility criteria‐ among them 86% with physical inactivity, 87% with obesity, 38% with T2D, 17% with hypertension, 13% smoking, and 32% with depression. Thus far 33 participants have been recruited‐ Among them, 10 participants have completed the baseline evaluation, and have been randomized to the study's arms (8 of them had started the active intervention, with an average app‐adherence of 83%). additional 23 participants have completed partial base‐line evaluation.ConclusionResults of this study will provide feasibility data on the adherence to the human‐app approach, characteristics of those who adhere, on whether the approach improves risk factors, and will provide initial data on intervention effects on cognition. At AAIC, interim results will be presented.

Sleep and its regulation: An emerging pathogenic and treatment frontier in Alzheimer's disease.

A majority of patients with Alzheimer's disease (AD) experience some form of sleep disruption, including nocturnal sleep fragmentation, increased daytime napping, decreased slow-wave sleep (SWS, stage N3), and decreased rapid-eye-movement sleep (REM). Clinical studies are investigating whether such sleep disturbances are a consequence of the underlying disease, and whether they also contribute to the clinical and pathological manifestations of AD. Emerging research has provided a direct link between several of these sleep disruptions and AD pathophysiology, suggesting that treating sleep disorders in this population may target basic mechanisms of the disease. Here, we provide a comprehensive review of sleep disturbances associated with the spectrum of AD, ranging from the preclinical stages through dementia. We discuss how sleep interacts with AD pathophysiology and, critically, whether sleep impairments can be targeted to modify the disease course in a subgroup of affected AD patients. Ultimately, larger studies that fully utilize new diagnostic and experimental tools will be required to better define the most relevant sleep disturbance to target in AD, the interventions that best modulate this target symptom, and whether successful early intervention can modify AD risk and prevent dementia.

Association of Cardiovascular Risk Factors with Cerebral Perfusion in Whites and African Americans.

Midlife cardiovascular risk factors increase risk for Alzheimer's disease (AD). Despite disproportionately high cardiovascular disease and dementia rates, African Americans are under-represented in studies of AD risk and research-based guidance on targeting vascular risk factors is lacking. This study investigated relationships between specific cardiovascular risk factors and cerebral perfusion in White and African American adults enriched for AD risk. Participants included 397 cognitively unimpaired White (n = 330) and African American (n = 67) adults enrolled in the Wisconsin Alzheimer's Disease Research Center who underwent pseudo-continuous arterial spin labeling MRI. Multiple linear regression models examined independent relationships between cardiovascular risk factors and mean cerebral perfusion. Subsequent interaction and stratified models assessed the role for APOE genotype and race. When risk factor p-values were FDR-adjusted, diastolic blood pressure was significantly associated with mean perfusion. Tobacco use, triglycerides, waist-to-hip ratio, and a composite risk score were not associated with perfusion. Without FDR adjustment, a relationship was also observed between perfusion and obesity, cholesterol, and fasting glucose. Neither APOE genotype nor race moderated relationships between risk factors and perfusion. Higher diastolic blood pressure predicted lower perfusion more strongly than other cardiovascular risk factors. This relationship did not vary by racial group or genetic risk for AD, although the African American sample had greater vascular risk burden and lower perfusion rates. Our findings highlight the need to prioritize inclusion of underrepresented groups in neuroimaging studies and to continue exploring the link between modifiable risk factors, cerebrovascular health, and AD risk in underrepresented populations.

Mitochondria-Targeted Therapeutics for Alzheimer's Disease: The Good, the Bad, the Potential.

Significance: Alzheimer's disease (AD) is the leading cause of dementia. Thus far, 99.6% of clinical trials, including those targeting energy metabolism, have failed to exert disease-modifying efficacy. Altered mitochondrial function and disruption to the brain bioenergetic system have long-been documented as early events during the pathological progression of AD. Recent Advances: While therapeutic approaches that directly promote mitochondrial bioenergetic machinery or eliminate reactive oxygen species have exhibited limited translatability, emerging strategies targeting nonenergetic aspects of mitochondria provide novel therapeutic targets with the potential to modify AD risk and progression. Growing evidence also reveals a critical link between mitochondrial phenotype and neuroinflammation via metabolic reprogramming of glial cells. Critical Issues: Herein, we summarize major classes of mitochondrion-centered AD therapeutic strategies. In addition, the discrepancy in their efficacy when translated from preclinical models to clinical trials is addressed. Key factors that differentiate the responsiveness to bioenergetic interventions, including sex, apolipoprotein E genotype, and cellular diversity in the brain, are discussed. Future Directions: We propose that the future development of mitochondria-targeted AD therapeutics should consider the interactions between bioenergetics and other disease mechanisms, which may require cell-type-specific targeting to distinguish neurons and non-neuronal cells. Moreover, a successful strategy will likely include stratification by metabolic phenotype, which varies by sex and genetic risk profile and dynamically changes throughout the course of disease. As the network of mitochondrial integration expands across intracellular and systems level biology, assessment of intended, the good, versus unintended consequences, the bad, will be required to reach the potential of mitochondrial therapeutics.

Association of Cardiovascular and Alzheimer's Disease Risk Factors with Intracranial Arterial Blood Flow in Whites and African Americans.

Alzheimer's disease (AD) has a higher prevalence among African Americans. Targeting cardiovascular and metabolic risk factors may be potential mechanisms to modify AD risk and address racial/ethnic disparities in AD dementia. This study investigated relationships among cardiovascular and metabolic risk factors, APOE genotype, AD biomarkers, and intracranial arterial blood flow in Whites and African Americans enriched for AD risk. 399 cognitively unimpaired adults from the Wisconsin Alzheimer's Disease Research Center completed physical and neuroimaging examinations. A 4D Flow MRI sequence (phase-contrast vastly under sampled isotropic projection imaging) measured intracranial arterial flow in the Circle of Willis. Linear mixed-effects regression models estimated relationships between risk factors and intracranial arterial flow and tested interactions with racial group, APOE genotype, and AD biomarkers, with separate models per risk factor. Higher fasting glucose was associated with lower intracranial arterial flow; no additional relationships between flow and risk factors were observed. Main effects of racial group were observed, without an interaction, indicating lower flow in African Americans compared to Whites. In race-stratified analyses, higher glucose and triglycerides were associated with lower flow for African Americans, but not for Whites. No main effects or interactions among risk factors, APOE, or AD biomarkers, and flow were observed. Elevated fasting glucose and triglycerides were associated with lower intracranial arterial flow; these relationships were more prominent in African Americans. Targeting metabolic risk factors may impact intracranial arterial health. Additional research is needed to determine if this will impact disparities in dementia prevalence.

Evidence-Based Prevention of Alzheimer's Disease: Systematic Review and Meta-Analysis of 243 Observational Prospective Studies and 153 Randomized Controlled Trials

Background: Evidence on preventing Alzheimer's disease (AD) is challenging to interpret due to varying study designs with heterogeneous endpoints and credibility. We completed a systematic review and meta-analysis of current evidence with prospective designs to propose clinical recommendations on AD prevention. Methods: Electronic databases and relevant websites were searched from inception to March 1, 2019. Both observational prospective studies (OPSs) and randomized controlled trials (RCTs) were included. The multivariable-adjusted effect estimates were pooled by random-effects models, with credibility assessment according to its risk of bias, inconsistency, and imprecision. Levels of evidence and classes of recommendations were summarized. Findings: A total of 44,676 reports were identified, and 243 OPSs and 153 RCTs were eligible for analysis after exclusion based on pre-decided criteria, among which 104 modifiable factors and 11 interventions were included for the meta-analyses. In the OPSs, 26 risk factors and 8 protective factors were found to significantly modify AD risk by an effect size of over 25%, amongst which eight factors were rated at a moderate-to-high level of evidence. Among the interventions tested in RCTs, physical exercise and the homocysteine lowering treatment were the most promising interventions to reduce AD risk. Finally, 21 recommendations are proposed based on the consolidated evidence, with 'Class I' recommendations targeting 19 factors: ten are with 'Level A' strong evidence (cognitive activity, hyperhomocysteinemia, high BMI in late-life, depression, stress, diabetes, head trauma, hypertension in midlife, orthostatic hypotension, and education) and nine with 'Level B' weaker evidence (obesity in midlife, weight loss in late-life, physical exercise, smoking, sleep, CVD, frailty, atrial fibrillation, and Vitamin C). In contrast, two interventions are not recommended: estrogen replacement therapy (Level A2) and acetylcholinesterase inhibitors (Level B). Interpretation: Our study mapped the current evidence profile and assessed the findings in order to guide future research directions for AD prevention. Evidence-based recommendations are proposed, offering clinicians and stakeholders current guidance for the prevention of AD. Funding Statement: The authors stated: There was no direct funding source for this study. Declaration of Interest: JTY serves as an associate editor-in-chief for Annals of Translational Medicine, is senior editor for Journal of Alzheimer's Disease. SA has received grants from Europe, Ipsen, and France Alzheimer, served as a consultant for Ipsen, Pierre Fabre, Lilly, Nestle, Sanof, and Servier, and received non-financial support from Biogen, Nutrition Sante, Pfzer, and Icon, and other support from the AMPA Association. SG has received clinical trial support from Lilly and Roche in DIAN-TU, TauRx Therapeutics (TauRx), and Lundbeck; has been a data safety monitoring board (DSMB) member of ADCS, ATRI, API, and Eisai; and has been a scientific adviser to Affiris, BoehringerIngelheim, Lilly, Roche, Servier, Sanofi, Schwabe, Takeda, and TauRx. PSA has received grants from the US Alzheimer’s Association, Janssen, Lilly, the US National Institute on Aging, and Toyama; and consulting fees from Abbott, Abbvie, Amgen, Anavex, AstraZeneca, Biogen Idec, Biotie, Bristol-Myers Squibb, Cardeus, Cohbar, Eisai, Elan, Eli Lilly, Genentech, Ichor, iPerian, Janssen, Lundbeck, Medivation, Merck, NeuroPhage, Novartis, Pfizer, Probiodrug, Roche, Somaxon, and Toyama, outside the submitted work. BV reports grants from Pierre Fabre, Avid, Exonhit, AbbVie, Lilly, Lundbeck, MSD, Otsuka, Regenron, Sanof, Roche, AstraZeneca, LPG Systems, Nestle, and Alzheon, and personal fees from Lilly, Lundbeck, MSD, Otsuka, Roche, Sanof, Biogen, Nestle, Transition Therapeutics, and Takeda. All other authors declare no competing interests. Ethics Approval Statement: The authors followed the recommendations by the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) 2009 guidelines.

APOE genotype affects metabolic and Alzheimer-related outcomes induced by Western diet in female EFAD mice.

Development of Alzheimer's disease (AD) is regulated by interactive effects of genetic and environmental risk factors. The most significant genetic risk factor for AD is the ε4 allele of apolipoprotein E ( APOE4), which has been shown to exert greater AD risk in women. An important modifiable AD risk factor is obesity and its associated metabolic dysfunctions. Whether APOE genotype might interact with obesity in females to regulate AD pathogenesis is unclear. To investigate this issue, we studied the effects of Western diet (WD) on female EFAD mice, a transgenic mouse model of AD that includes human APOE alleles ε3 (E3FAD) and ε4 (E4FAD). EFAD mice were fed either control (10% fat, 7% sugar) or WD (45% fat, 17% sugar), and both metabolic and neuropathologic outcomes were determined. Although E4FAD mice generally exhibited poorer metabolic status at baseline, E3FAD mice showed greater diet-induced metabolic impairments. Similarly, E4FAD mice exhibited higher levels of AD-related pathology overall, but only E3FAD showed significant increases on select measures of β-amyloid pathology after exposure to WD. These data demonstrate a gene-environment interaction between APOE and obesogenic diets in females. Understanding how AD-promoting effects of obesity are modulated by genetic factors will foster the identification of at-risk populations and development of preventive interventions.-Christensen, A., Pike, C. J. APOE genotype affects metabolic and Alzheimer-related outcomes induced by Western diet in female EFAD mice.

Novel allele-dependent role for APOE in controlling the rate of synapse pruning by astrocytes

The strongest genetic risk factor influencing susceptibility to late-onset Alzheimer's disease (AD) is apolipoprotein E (APOE) genotype. APOE has three common isoforms in humans, E2, E3, and E4. The presence of two copies of the E4 allele increases risk by ∼12-fold whereas E2 allele is associated with an ∼twofold decreased risk for AD. These data put APOE central to AD pathophysiology, but it is not yet clear how APOE alleles modify AD risk. Recently we found that astrocytes, a major central nervous system cell type that produces APOE, are highly phagocytic and participate in normal synapse pruning and turnover. Here, we report a novel role for APOE in controlling the phagocytic capacity of astrocytes that is highly dependent on APOE isoform. APOE2 enhances the rate of phagocytosis of synapses by astrocytes, whereas APO4 decreases it. We also found that the amount of C1q protein accumulation in hippocampus, which may represent the accumulation of senescent synapses with enhanced vulnerability to complement-mediated degeneration, is highly dependent on APOE alleles: C1q accumulation was significantly reduced in APOE2 knock-in (KI) animals and was significantly increased in APOE4 KI animals compared with APOE3 KI animals. These studies reveal a novel allele-dependent role for APOE in regulating the rate of synapse pruning by astrocytes. They also suggest the hypothesis that AD susceptibility of APOE4 may originate in part from defective phagocytic capacity of astrocytes which accelerates the rate of accumulation of C1q-coated senescent synapses, enhancing synaptic vulnerability to classical-complement-cascade mediated neurodegeneration.

Partial loss of CALM function reduces Aβ42 production and amyloid deposition in vivo.

Aberrant production, clearance and deposition of amyloid-β protein (Aβ) in the human brain have been implicated in the aetiology of Alzheimer disease (AD). γ-Secretase is the enzyme responsible for generating various Aβ species, such as Aβ40 and toxic Aβ42. Recently, genome-wide association studies in late-onset AD patients have identified the endocytosis-related phosphatidylinositol-binding clathrin assembly protein (PICALM) gene as a genetic risk factor for AD. We previously found that the loss of expression of CALM protein encoded by PICALM affects the ratio of production of Aβ42, through the regulation of the clathrin-mediated endocytosis of γ-secretase. Here, we show that the binding capacity of the assembly protein 180 N-terminal homology (ANTH) domain of CALM to phosphatidylinositol-4,5-biphosphate, as well as to nicastrin, is critical to the modulation of the internalization of γ-secretase and to the Aβ42 production ratio. Moreover, reduction of CALM decreases Aβ deposition as well as brain levels of insoluble Aβ42 in vivo These results suggest that CALM expression modifies AD risk by regulating Aβ pathology.

Sex differences in metabolic aging of the brain: insights into female susceptibility to Alzheimer's disease

Despite recent advances in the understanding of clinical aspects of sex differences in Alzheimer's disease (AD), the underlying mechanisms, for instance, how sex modifies AD risk and why the female brain is more susceptible to AD, are not clear. The purpose of this study is to elucidate sex disparities in brain aging profiles focusing on 2 major areas—energy and amyloid metabolism—that are most significantly affected in preclinical development of AD. Total RNA isolated from hippocampal tissues of both female and male 129/C57BL/6 mice at ages of 6, 9, 12, or 15 months were comparatively analyzed by custom-designed Taqman low-density arrays for quantitative real-time polymerase chain reaction detection of a total of 182 genes involved in a broad spectrum of biological processes modulating energy production and amyloid homeostasis. Gene expression profiles revealed substantial differences in the trajectory of aging changes between female and male brains. In female brains, 44.2% of genes were significantly changed from 6 months to 9 months and two-thirds showed downregulation. In contrast, in male brains, only 5.4% of genes were significantly altered at this age transition. Subsequent changes in female brains were at a much smaller magnitude, including 10.9% from 9 months to 12 months and 6.1% from 12 months to 15 months. In male brains, most changes occurred from 12 months to 15 months and the majority were upregulated. Furthermore, gene network analysis revealed that clusterin appeared to serve as a link between the overall decreased bioenergetic metabolism and increased amyloid dyshomeostasis associated with the earliest transition in female brains. Together, results from this study indicate that: (1) female and male brains follow profoundly dissimilar trajectories as they age; (2) female brains undergo age-related changes much earlier than male brains; (3) early changes in female brains signal the onset of a hypometabolic phenotype at risk for AD. These findings provide a mechanistic rationale for female susceptibility to AD and suggest a potential window of opportunity for AD prevention and risk reduction in women.

The rise and fall of insulin signaling in Alzheimer's disease.

The prevalence of both diabetes and Alzheimer's disease (AD) are reaching epidemic proportions worldwide. Alarmingly, diabetes is also a risk factor for Alzheimer's disease. The AD brain is characterised by the accumulation of peptides called Aβ as plaques in the neuropil and hyperphosphorylated tau protein in the form of neurofibrillary tangles within neurons. How diabetes confers risk is unknown but a simple linear relationship has been proposed whereby the hyperinsulinemia associated with type 2 diabetes leads to decreased insulin signaling in the brain, with downregulation of the PI3K/AKT signalling pathway and its inhibition of the major tau kinase, glycogen synthase kinase 3β. The earliest studies of post mortem AD brain tissue largely confirmed this cascade of events but subsequent studies have generally found either an upregulation of AKT activity, or that the relationship between insulin signaling and AD is independent of glycogen synthase kinase 3β altogether. Given the lack of success of beta-amyloid-reducing therapies in clinical trials, there is intense interest in finding alternative or adjunctive therapeutic targets for AD. Insulin signaling is a neuroprotective pathway and represents an attractive therapeutic option. However, this incredibly complex signaling pathway is not fully understood in the human brain and particularly in the context of AD. Here, we review the ups and downs of the research efforts aimed at understanding how diabetes modifies AD risk.

THE IMPORTANCE OF RISK FACTOR MODIFICATION OVER THE LIFECOURSE

The pathophysiology of Alzheimer's Disease (AD) probably develops over decades, but the majority of epidemiological studies have focused on risk factor exposure from mid or later life. In addition, the timing and duration of effective AD prevention strategies remains unclear. A small but growing body of evidence suggests that risk factors earlier in the lifecourse may also contribute to an increased risk of cognitive aging. We present data from the Coronary Artery Risk Development in Young Adults Study (CARDIA), a biracial cohort of 3,499 adults (18-30 years old at enrollment). Risk factors including demographics, comorbidities, and lifestyle behaviors were evaluated over 25 years. At Year 25, cognitive function was assessed using the Digit Symbol Substitution Test (DSST), Stroop Interference Score, and Rey Auditory Verbal Learning Test (RAVLT). We also review findings from a study designed to determine the effect of midlife risk factor modification on projected prevalence of AD. Results from CARDIA suggest that early adult risk factors could contribute to midlife cognitive aging. Over 25 years, elevated levels of blood pressure, fasting blood glucose, and cholesterol were associated with worse cognitive performance on RAVLT, DSST, and Stroop in midlife (p<0.05 for all). Relationships were similar for other modifiable risk factors in early adulthood, including those defined by existing guidelines for healthy behaviors such as physical activity, nutrition and the American Heart Association's recommendations for ideal cardiovascular health. Epidemiological data also support a relationship between risk of AD and several potentially modifiable risk factors in mid and late life including diabetes, midlife hypertension, midlife obesity, smoking, depression, cognitive inactivity or low educational attainment, and physical inactivity. As a group, these risk factors could account for up to 50% of AD cases worldwide, and reduction of these risk factors could have a significant impact on AD prevalence. While there is robust evidence for modifiable risk factors and AD risk among older adults, recent findings also indicate that cognitive aging may begin even in midlife. Interventions that target risk factor exposure earlier in the lifecourse could play an important role in AD prevention.

Apolipoprotein E: Implications for AD neurobiology, epidemiology and risk assessment

Alzheimer disease (AD) is a common and devastating dementing illness for which there is no effective neuroprotective therapy or cure. The presence of the apolipoprotein E (apoE) ε4 allele is a well-established genetic modifier (risk factor) of sporadic AD. In this review, we provide an update on the implications of apoE for the neurobiology and epidemiology of AD. Moreover, recent evidence is adduced indicating that (i) many AD risk factors are potentially modifiable by adaptive lifestyle changes and pharmacotherapy and (ii) the potency of these modifiable AD determinants and responsiveness to intervention are often significantly impacted by the presence or absence of the ε4 allele. Delineation of the influences of the APOE genotype on modifiable AD risk factors and prevention may spur consideration of APOE testing for presymptomatic individuals seeking to define their personal risk.