Obesity affects brain cortex gene expression in an APOE genotype and sex dependent manner.

OBJECTIVE: Obesity is the top modifiable risk factor for Alzheimer's disease. We hypothesized that high fat diet (HFD)-induced obesity alters brain transcriptomics in APOE-genotype and sex dependent manners. Here, we investigated interactions between HFD, APOE, and sex, using a knock-in mouse model of the human APOE3 and APOE4 alleles. METHODS: Six-month-old APOE3-TR and APOE4-TR mice were treated with either HFD or control chow. After 4 months, total RNA was extracted from the cerebral cortices and analyzed by poly-A enriched RNA sequencing on the Illumina platform. RESULTS: Female mice demonstrated profound HFD-induced transcriptomic changes while there was little to no effect in males. In females, APOE3 brains demonstrated about five times more HFD-induced transcriptomic changes (399 up-regulated and 107 down-regulated genes) compared to APOE4 brains (30 up-regulated and 60 down-regulated). Unsupervised clustering analysis revealed two gene sets that responded to HFD in APOE3 mice but not in APOE4 mice. Pathway analysis demonstrated that HFD in APOE3 mice affected cortical pathways related to feeding behavior, blood circulation, circadian rhythms, extracellular matrix, and cell adhesion. CONCLUSIONS: Female mice and APOE3 mice have the strongest cortical transcriptomic responses to HFD related to feeding behavior and extracellular matrix remodeling. The relative lack of response of the APOE4 brain to stress associated with obesity may leave it more susceptible to additional stresses that occur with aging and in AD.

CCR5 deficiency normalizes TIMP levels, working memory, and gamma oscillation power in APOE4 targeted replacement mice.

The APOE4 allele increases the risk for Alzheimer's disease (AD) in a dose-dependent manner and is also associated with cognitive decline in non-demented elderly controls. In mice with targeted gene replacement (TR) of murine APOE with human APOE3 or APOE4, the latter show reduced neuronal dendritic complexity and impaired learning. APOE4 TR mice also show reduced gamma oscillation power, a neuronal population activity which is important to learning and memory. Published work has shown that brain extracellular matrix (ECM) can reduce neuroplasticity as well as gamma power, while attenuation of ECM can instead enhance this endpoint. In the present study we examine human cerebrospinal fluid (CSF) samples from APOE3 and APOE4 individuals and brain lysates from APOE3 and APOE4 TR mice for levels of ECM effectors that can increase matrix deposition and restrict neuroplasticity. We find that CCL5, a molecule linked to ECM deposition in liver and kidney, is increased in CSF samples from APOE4 individuals. Levels of tissue inhibitor of metalloproteinases (TIMPs), which inhibit the activity of ECM-degrading enzymes, are also increased in APOE4 CSF as well as astrocyte supernatants brain lysates from APOE4 TR mice. Importantly, as compared to APOE4/wild-type heterozygotes, APOE4/CCR5 knockout heterozygotes show reduced TIMP levels and enhanced EEG gamma power. The latter also show improved learning and memory, suggesting that the CCR5/CCL5 axis could represent a therapeutic target for APOE4 individuals.

Chemotherapy promotes astrocytic response to Aß deposition, but not Aß levels, in a mouse model of amyloid and APOE.

Many cancer survivors experience cancer-related cognitive impairment (CRCI), which is characterized by problems of attention, working memory, and executive function following chemotherapy and/or hormonal treatment. APOE4, the strongest genetic risk factor for Alzheimer's Disease (AD), is also a risk factor for CRCI, especially among survivors exposed to chemotherapy. We explored whether the effects of APOE genotype to chemotherapy were associated with an increase in AD pathological processes, using a mouse model of amyloid (5XFAD) along with the E3 or E4 alleles of human APOE (E3FAD and E4FAD). Six-month-old female E3FAD mice (control n = 5, treated n = 5) and E4FAD (control n = 6, treated n = 6) were treated with two doses of doxorubicin (total 10 mg/kg) or DMSO vehicle. After six weeks, mice were euthanized and brains were analyzed by immunohistochemistry and biochemical assays. Doxorubicin-treated mice had the same level of Aß in the brain as control mice, as measured by 6E10 immunohistochemistry, Aß40 and Aß42 ELISAs, and plaque morphologies. Doxorubicin significantly increased the level of the astrocytic response to Aß deposits, which was independent of APOE genotype; no effects of doxorubicin were observed on the microglial responses. These data are consistent with a model in which the effects of doxorubicin on risk of CRCI are unrelated amyloid accumulation, but possibly related to glial responses to damage.

Expression and secretion of apoE isoforms in astrocytes and microglia during inflammation.

Neuroinflammation is a common feature in neurodegenerative diseases, modulated by the Alzheimer's disease risk factor, apolipoprotein E (APOE). In the brain, apoE protein is synthesized by astrocytes and microglia. We examined primary cultures of astrocytes and microglia from human APOE (E2, E3, and E4) targeted-replacement mice. Astrocytes secreted two species of apoE, whereas cellular apoE consisted of only one. Both forms of secreted astrocytic apoE were bound during glycoprotein isolation, and enzymatic removal of glycans produced a convergence of the two forms of apoE to a single form; thus, the two species of astrocyte-secreted apoE are differentially glycosylated. Microglia released only a single species of apoE, while cellular apoE consisted of two forms; the secreted apoE and one of the two forms of cellular apoE were glycosylated. We treated the primary glia with either endogenous (TNFα) or exogenous (LPS) pro-inflammatory stimuli. While LPS had no effect on astrocytic apoE, APOE2, and APOE3 microglia increased release of apoE; APOE4 microglia showed no effect. APOE4 microglia showed higher baseline secretion of TNFα compared to APOE2 and APOE3 microglia. TNFα treatment reduced the secretion and cellular expression of apoE only in APOE4 astrocytes. The patterns of apoE species produced by astrocytes and microglia were not affected by inflammation. No changes in APOE mRNA were observed in astrocytes after both treatments. Together, our data demonstrate that astrocytes and microglia differentially express and secrete glycosylated forms of apoE and that APOE4 astrocytes and microglia are deficient in immunomodulation compared to APOE2 and APOE3.

High-fat diet increases gliosis and immediate early gene expression in APOE3 mice, but not APOE4 mice.

BACKGROUND: APOE4 is the strongest genetic risk factor for Alzheimer's disease (AD), and obesity is a strong environmental risk factor for AD. These factors result in multiple central nervous system (CNS) disturbances and significantly increase chances of AD. Since over 20% of the US population carry the APOE4 allele and over 40% are obese, it is important to understand how these risk factors interact to affect neurons and glia in the CNS. METHODS: We fed male and female APOE3 and APOE4 knock-in mice a high-fat diet (HFD-45% kcal fat) or a "control" diet (CD-10% kcal fat) for 12 weeks beginning at 6 months of age. At the end of the 12 weeks, brains were collected and analyzed for gliosis, neuroinflammatory genes, and neuronal integrity. RESULTS: APOE3 mice on HFD, but not APOE4 mice, experienced increases in gliosis as measured by GFAP and Iba1 immunostaining. APOE4 mice on HFD showed a stronger increase in the expression of Adora2a than APOE3 mice. Finally, APOE3 mice on HFD, but not APOE4 mice, also showed increased neuronal expression of immediate early genes cFos and Arc. CONCLUSIONS: These findings demonstrate that APOE genotype and obesity interact in their effects on important processes particularly related to inflammation and neuronal plasticity in the CNS. During the early stages of obesity, the APOE3 genotype modulates a response to HFD while the APOE4 genotype does not. This supports a model where early dysregulation of inflammation in APOE4 brains could predispose to CNS damages from various insults and later result in the increased CNS damage normally associated with the APOE4 genotype.

O-glycosylation on cerebrospinal fluid and plasma apolipoprotein E differs in the lipid-binding domain.

The O-glycoprotein apolipoprotein E (APOE), the strongest genetic risk factor for Alzheimer's disease, associates with lipoproteins. Cerebrospinal fluid (CSF) APOE binds only high-density lipoproteins (HDLs), while plasma APOE attaches to lipoproteins of diverse sizes with binding fine-tuned by the C-terminal loop. To better understand the O-glycosylation on this critical molecule and differences across tissues, we analyzed the O-glycosylation on APOE isolated from the plasma and CSF of aged individuals. Detailed LC-MS/MS analyses allowed the identification of the glycosite and the attached glycan and site occupancy for all detectable glycosites on APOE and further three-dimensional modeling of physiological glycoforms of APOE. APOE is O-glycosylated at several sites: Thr8, Thr18, Thr194, Ser197, Thr289, Ser290 and Ser296. Plasma APOE held more abundant (20.5%) N-terminal (Thr8) sialylated core 1 (Neu5Acα2-3Galß1-3GalNAcα1-) glycosylation compared to CSF APOE (0.1%). APOE was hinge domain glycosylated (Thr194 and Ser197) in both CSF (27.3%) and plasma (10.3%). CSF APOE held almost 10-fold more abundant C-terminal (Thr289, Ser290 and Ser296) glycosylation (36.8% of CSF peptide283-299 was glycosylated, 3.8% of plasma peptide283-299), with sialylated and disialylated (Neu5Acα2-3Galß1-3(Neu5Acα2-6) GalNAcα1-) core 1 structures. Modeling suggested that C-terminal glycosylation, particularly the branched disialylated structure, could interact across domains including the receptor-binding domain. These data, although limited by sample size, suggest that there are tissue-specific APOE glycoforms. Sialylated glycans, previously shown to improve HDL binding, are more abundant on the lipid-binding domain of CSF APOE and reduced in plasma APOE. This indicates that APOE glycosylation may be implicated in lipoprotein-binding flexibility.

APOE in the normal brain.

The APOE4 protein affects the primary neuropathological markers of Alzheimer's disease (AD): amyloid plaques, neurofibrillary tangles, and gliosis. These interactions have been investigated to understand the strong effect of APOE genotype on risk of AD. However, APOE genotype has strong effects on processes in normal brains, in the absence of the hallmarks of AD. We propose that CNS APOE is involved in processes in the normal brains that in later years apply specifically to processes of AD pathogenesis. We review the differences of the APOE protein found in the CNS compared to the plasma, including post-translational modifications (glycosylation, lipidation, multimer formation), focusing on ways that the common APOE isoforms differ from each other. We also review structural and functional studies of young human brains and control APOE knock-in mouse brains. These approaches demonstrate the effects of APOE genotype on microscopic neuron structure, gross brain structure, and behavior, primarily related to the hippocampal areas. By focusing on the effects of APOE genotype on normal brain function, approaches can be pursued to identify biomarkers of APOE dysfunction, to promote normal functions of the APOE4 isoform, and to prevent the accumulation of the pathologic hallmarks of AD with aging.

ApoE Lipidation as a Therapeutic Target in Alzheimer's Disease.

Apolipoprotein E (APOE) is the major cholesterol carrier in the brain, affecting various normal cellular processes including neuronal growth, repair and remodeling of membranes, synaptogenesis, clearance and degradation of amyloid ß (Aß) and neuroinflammation. In humans, the APOE gene has three common allelic variants, termed E2, E3, and E4. APOE4 is considered the strongest genetic risk factor for Alzheimer's disease (AD), whereas APOE2 is neuroprotective. To perform its normal functions, apoE must be secreted and properly lipidated, a process influenced by the structural differences associated with apoE isoforms. Here we highlight the importance of lipidated apoE as well as the APOE-lipidation targeted therapeutic approaches that have the potential to correct or prevent neurodegeneration. Many of these approaches have been validated using diverse cellular and animal models. Overall, there is great potential to improve the lipidated state of apoE with the goal of ameliorating APOE-associated central nervous system impairments.

High-density lipoprotein mimetic peptide 4F mitigates amyloid-ß-induced inhibition of apolipoprotein E secretion and lipidation in primary astrocytes and microglia.

The apolipoprotein E (apoE) ε4 allele is the primary genetic risk factor for late-onset Alzheimer's disease (AD). ApoE in the brain is produced primarily by astrocytes; once secreted from these cells, apoE binds lipids and forms high-density lipoprotein (HDL)-like particles. Accumulation of amyloid-ß protein (Aß) in the brain is a key hallmark of AD, and is thought to initiate a pathogenic cascade leading to neurodegeneration and dementia. The level and lipidation state of apoE affect Aß aggregation and clearance pathways. Elevated levels of plasma HDL are associated with lower risk and severity of AD; the underlying mechanisms, however, have not been fully elucidated. This study was designed to investigate the impact of an HDL mimetic peptide, 4F, on the secretion and lipidation of apoE. We found that 4F significantly increases apoE secretion and lipidation in primary human astrocytes as well as in primary mouse astrocytes and microglia. Aggregated Aß inhibits glial apoE secretion and lipidation, causing accumulation of intracellular apoE, an effect that is counteracted by co-treatment with 4F. Pharmacological and gene editing approaches show that 4F mediates its effects partially through the secretory pathway from the endoplasmic reticulum to the Golgi apparatus and requires the lipid transporter ATP-binding cassette transporter A1. We conclude that the HDL mimetic peptide 4F promotes glial apoE secretion and lipidation and mitigates the detrimental effects of Aß on proper cellular trafficking and functionality of apoE. These findings suggest that treatment with such an HDL mimetic peptide may provide therapeutic benefit in AD. Read the Editorial Highlight for this article on page 580.

The Synergistic Effects of APOE Genotype and Obesity on Alzheimer's Disease Risk.

The APOE gene has three common alleles-E2, E3, and E4, with APOE4 being the strongest genetic risk factor for developing Alzheimer's Disease (AD). Obesity is a global epidemic and contributes to multiple metabolic problems. Obesity is also a risk factor for cognitive decline. Here, we review the effects of APOE4 and obesity on cognition and AD development, independently and together. We describe studies that have associated APOE4 with cognitive deficits and AD, as well as studies that have associated obesity to cognitive deficits and AD. We then describe studies that have examined the effects of obesity and APOE genotypes together, with a focus on APOE4 and high fat diets. Both human studies and rodent models have contributed to understanding the effects of obesity on the different APOE genotypes, and we outline possible underlying mechanisms associated with these effects. Data across approaches support a model in which APOE4 and obesity combine for greater detrimental effects on metabolism and cognition, in ways that are influenced by both age and sex.

The role of APOE on lipid homeostasis and inflammation in normal brains.

The role of APOE in the risk of Alzheimer's disease (AD) has largely focused on its effects on AD pathological processes. However, there are increasing data that APOE genotype affects processes in normal brains. Studies of young cognitively normal humans show effects of APOE genotype on brain structure and activity. Studies of normal APOE knock-in mice show effects of APOE genotype on brain structure, neuronal markers, and behavior. APOE interactions with molecules important for lipid efflux and lipid endocytosis underlie effects of APOE genotype on neuroinflammation and lipoprotein composition. These effects provide important targets for new therapies for reduction of the risk of AD before any signs of pathogenesis.

Very low density lipoprotein receptor regulates dendritic spine formation in a RasGRF1/CaMKII dependent manner.

Very Low Density Lipoprotein Receptor (VLDLR) is an apolipoprotein E receptor involved in synaptic plasticity, learning, and memory. However, it is unknown how VLDLR can regulate synaptic and cognitive function. In the present study, we found that VLDLR is present at the synapse both pre- and post-synaptically. Overexpression of VLDLR significantly increases, while knockdown of VLDLR decreases, dendritic spine number in primary hippocampal cultures. Additionally, knockdown of VLDLR significantly decreases synaptophysin puncta number while differentially regulating cell surface and total levels of glutamate receptor subunits. To identify the mechanism by which VLDLR induces these synaptic effects, we investigated whether VLDLR affects dendritic spine formation through the Ras signaling pathway, which is involved in spinogenesis and neurodegeneration. Interestingly, we found that VLDLR interacts with RasGRF1, a Ras effector, and knockdown of RasGRF1 blocks the effect of VLDLR on spinogenesis. Moreover, we found that VLDLR did not rescue the deficits induced by the absence of Ras signaling proteins CaMKIIα or CaMKIIß. Taken together, our results suggest that VLDLR requires RasGRF1/CaMKII to alter dendritic spine formation.

Ligand-induced homotypic and heterotypic clustering of apolipoprotein E receptor 2.

ApoE Receptor 2 (ApoER2) and the very low density lipoprotein receptor (VLDLR) are type I transmembrane proteins belonging to the LDLR family of receptors. They are neuronal proteins found in synaptic compartments that play an important role in neuronal migration during development. ApoER2 and VLDLR bind to extracellular glycoproteins, such as Reelin and F-spondin, which leads to phosphorylation of adaptor proteins and subsequent activation of downstream signaling pathways. It is thought that ApoER2 and VLDLR undergo clustering upon binding to their ligands, but no direct evidence of clustering has been shown. Here we show strong clustering of ApoER2 induced by the dimeric ligands Fc-RAP, F-spondin, and Reelin but relatively weak clustering with the ligand apoE in the absence of lipoproteins. This clustering involves numerous proteins besides ApoER2, including amyloid precursor protein and the synaptic adaptor protein PSD-95. Interestingly, we did not observe strong clustering of ApoER2 with VLDLR. Clustering was modulated by both extracellular and intracellular domains of ApoER2. Together, our data demonstrate that several multivalent ligands for ApoER2 induce clustering in transfected cells and primary neurons and that these complexes included other synaptic molecules, such as APP and PSD-95.

Human APOE4 increases microglia reactivity at Aß plaques in a mouse model of Aß deposition.

BACKGROUND: Having the apolipoprotein E4 (APOE-ϵ4) allele is the strongest genetic risk factor for the development of Alzheimer's disease (AD). Accumulation of amyloid beta (Aß) in the brain is influenced by APOE genotype. Transgenic mice co-expressing five familial AD mutations (5xFAD) in the presence of human APOE alleles (ϵ2, ϵ3 or ϵ4) exhibit APOE genotype-specific differences in early Aß accumulation, suggesting an interaction between APOE and AD pathology. Whether APOE genotype affects Aß-plaque-associated neuroinflammation remains unclear. In the current study, we address the role of APOE genotype on Aß-associated microglial reactivity in the EFAD transgenic mouse model. METHODS: We analyzed Aß-induced glial activation in the brains of 6-month-old EFAD transgenic mice (E2FAD, E3FAD and E4FAD). Region-specific morphological profiles of Aß plaques in EFAD brain sections were compared using immunofluorescence staining. We then determined the degree of glial activation in sites of Aß deposition while comparing levels of the inflammatory cytokine Interleukin-1ß (IL-1ß) by ELISA. Finally, we quantified parameters of Aß-associated microglial reactivity using double-stained EFAD brain sections. RESULTS: Characterization of Aß plaques revealed there were larger and more intensely stained plaques in E4FAD mice relative to E2FAD and E3FAD mice. E4FAD mice also had a greater percentage of compact plaques in the subiculum than E3FAD mice. Reactive microglia and dystrophic astrocytes were prominent in EFAD brains, and primarily localized to two sites of significant Aß deposition: the subiculum and deep layers of the cortex. Cortical levels of IL-1ß were nearly twofold greater in E4FAD mice relative to E3FAD mice. To control for differences in levels of Aß in the different EFAD mice, we analyzed the microglia within domains of specific Aß deposits. Morphometric analyses revealed increased measures of microglial reactivity in E4FAD mice, including greater dystrophy, increased fluorescence intensity and a higher density of reactive cells surrounding cortical plaques, than in E3FAD mice. CONCLUSIONS: In addition to altering morphological profiles of Aß deposition, APOE genotype influences Aß-induced glial activation in the adult EFAD cortex. These data support a role for APOE in modulating Aß-induced neuroinflammatory responses in AD progression, and support the use of EFAD mice as a suitable model for mechanistic studies of Aß-associated neuroinflammation.

Young APOE4 targeted replacement mice exhibit poor spatial learning and memory, with reduced dendritic spine density in the medial entorhinal cortex.

The apolipoprotein E4 (APOE-ε4) allele is the strongest genetic risk factor for developing late-onset Alzheimer's disease, and may predispose individuals to Alzheimer's-related cognitive decline by affecting normal brain function early in life. To investigate the impact of human APOE alleles on cognitive performance in mice, we trained 3-mo-old APOE targeted replacement mice (E2, E3, and E4) in the Barnes maze to locate and enter a target hole along the perimeter of the maze. Long-term spatial memory was probed 24 h and 72 h after training. We found that young E4 mice exhibited significantly impaired spatial learning and memory in the Barnes maze compared to E3 mice. Deficits in spatial cognition were also present in a second independent cohort of E4 mice tested at 18 mo of age. In contrast, cognitive performance in the hidden platform water maze was not as strongly affected by APOE genotype. We also examined the dendritic morphology of neurons in the medial entorhinal cortex of 3-mo-old TR mice, neurons important to spatial learning functions. We found significantly shorter dendrites and lower spine densities in basal shaft dendrites of E4 mice compared to E3 mice, consistent with spatial learning and memory deficits in E4 animals. These findings suggest that human APOE-ε4 may affect cognitive function and neuronal morphology early in life.

APOE4 genotype and aging impair injury-induced microglial behavior in brain slices, including toward Aß, through P2RY12.

Microglia are highly dynamic cells that play a critical role in tissue homeostasis through the surveillance of brain parenchyma and response to cues associated with damage. Aging and APOE4 genotype are the strongest risk factors for Alzheimer's disease (AD), but how they affect microglial dynamics remains unclear. Using ex vivo confocal microscopy, we analyzed microglial dynamic behaviors in the entorhinal cortex (EC) and hippocampus CA1 of 6-, 12-, and 21-month-old mice APOE3 or APOE4 knock-in mice expressing GFP under the CX3CR1 promoter. To study microglia surveillance, we imaged microglia baseline motility for 20 min and measured the extension and retraction of processes. We found that APOE4 microglia exhibited significantly less brain surveillance (27%) compared to APOE3 microglia in 6-month-old mice; aging exacerbated this deficit. To measure microglia response to damage, we imaged process motility in response to ATP, an injury-associated signal, for 30 min. We found APOE4 microglia extended their processes significantly slower (0.9 µm/min, p < 0.005) than APOE3 microglia (1.1 µm/min) in 6-month-old animals. APOE-associated alterations in microglia motility were observed in 12- and 21-month-old animals, and this effect was exacerbated with aging in APOE4 microglia. We measured protein and mRNA levels of P2RY12, a core microglial receptor required for process movement in response to damage. We found that APOE4 microglia express significantly less P2RY12 receptors compared to APOE3 microglia despite no changes in P2RY12 transcripts. To examine if the effect of APOE4 on the microglial response to ATP also applied to amyloid ß (Aß), we infused locally Hi-Lyte Fluor 555-labeled Aß in acute brain slices of 6-month-old mice and imaged microglia movement for 2 h. APOE4 microglia showed a significantly slower (p < 0.0001) process movement toward the Aß, and less Aß coverage at early time points after Aß injection. To test whether P2RY12 is involved in process movement in response to Aß, we treated acute brain slices with a P2RY12 antagonist before Aß injection; microglial processes no longer migrated towards Aß. These results provide mechanistic insights into the impact of APOE4 genotype and aging in dynamic microglial behaviors prior to gross Aß pathology and could help explain how APOE4 brains are more susceptible to AD pathogenesis.

The chemotherapeutic agent doxorubicin induces brain senescence, with modulation by APOE genotype.

Many cancer patients experience serious cognitive problems related to their treatment, which can greatly affect their quality of life. The molecular mechanisms of this cancer chemotherapy-induced cognitive impairment (CICI) are unknown, thus slowing the development of preventative approaches. We hypothesized that cancer chemotherapies could induce cellular senescence in the brain, creating a pro-inflammatory environment and damaging normal brain communication. We tested this hypothesis using the common chemotherapeutic agent doxorubicin in two independent mouse models. In the first model, we used mice that express tdTomato under the pdkn2a (p16) promoter; p16 is a regulator of cellular senescence, and its upregulation is denoted by the presence of fluorescently tagged cells. Two weeks after exposure to three doses of 5 mg/kg doxorubicin, the number of tdTomato positive cells were increased nearly three-fold in both the cerebral cortex and the hippocampus. tdTomato staining co-localized with neurons, microglia, oligodendrocyte precursor cells, and endothelial cells, but not astrocytes. In the second model, we used APOE knock-in mice, since the APOE4 allele is a risk factor for CICI in humans and mouse models. We isolated RNA from the cerebral cortex of APOE3 and APOE4 mice from one to 21 days after a single dose of 10 mg/kg doxorubicin. Using NanoString analysis of over 700 genes related to neuroinflammation and RT-qPCR analysis of cerebral cortex transcripts, we found two-fold induction of four senescence-related genes at three weeks in the APOE4 mice compared to the APOE3 control mice: p21(cdkn1a), p16, Gadd45a, and Egr1. We conclude that doxorubicin promotes cellular senescence pathways in the brain, supporting the hypothesis that drugs to eliminate senescent cells could be useful in preventing CICI.

Alzheimer's disease-related biomarkers and cancer-related cognitive decline: the thinking and living with cancer study.

PURPOSE: We evaluated whether plasma Alzheimer's Disease (AD)-related biomarkers were associated with cancer-related cognitive decline (CRCD) among older breast cancer survivors. METHODS: We included survivors 60-90 years with primary stage 0-III breast cancers (n = 236) and frequency-matched non-cancer controls (n = 154) who passed a cognitive screen and had banked plasma specimens. Participants were assessed at baseline (pre-systemic therapy) and annually for up to 60-months. Cognition was measured using tests of attention, processing speed and executive function (APE) and learning and memory (LM); perceived cognition was measured by the FACT-Cog PCI. Baseline plasma neurofilament light (NfL), glial fibrillary acidic protein (GFAP), beta-amyloid 42/40 (Aß42/40) and phosphorylated tau (p-tau181) were assayed using single molecule arrays. Mixed models tested associations between cognition and baseline AD-biomarkers, time, group (survivor vs control) and their two- and three-way interactions, controlling for age, race, WRAT4 Word Reading score, comorbidity and BMI; two-sided 0.05 p-values were considered statistically significant. RESULTS: There were no group differences in baseline AD-related biomarkers except survivors had higher baseline NfL levels than controls (p = .013). Survivors had lower adjusted longitudinal APE than controls starting from baseline and continuing over time (p = <0.002). However, baseline AD-related biomarker levels were not independently associated with adjusted cognition over time, except controls had lower APE scores with higher GFAP levels (p = .008). CONCLUSION: The results do not support a relationship between baseline AD-related biomarkers and CRCD. 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 pre-systemic therapy.

APOE4-specific changes in Aß accumulation in a new transgenic mouse model of Alzheimer disease.

APOE4 is the greatest risk factor for Alzheimer disease (AD) and synergistic effects with amyloid-ß peptide (Aß) suggest interactions among apoE isoforms and different forms of Aß accumulation. However, it remains unclear how the APOE genotype affects plaque morphology, intraneuronal Aß, soluble Aß42, and oligomeric Aß (oAß), particularly in vivo. As the introduction of human APOE significantly delays amyloid deposition in transgenic mice expressing familial AD (FAD) mutations (FAD-Tg), 5xFAD-Tg mice, which exhibit amyloid deposition by age 2 months, were crossed with apoE-targeted replacement mice to produce the new EFAD-Tg mice. Compared with 5xFAD mice, Aß deposition was delayed by ∼4 months in the EFAD mice, allowing detection of early changes in Aß accumulation from 2-6 months. Although plaque deposition is generally greater in E4FAD mice, E2/E3FAD mice have significantly more diffuse and E4FAD more compact plaques. As a first report in FAD-Tg mice, the APOE genotypes had no effect on intraneuronal Aß accumulation in EFAD mice. In E4FAD mice, total apoE levels were lower and total Aß levels higher than in E2FAD and E3FAD mice. Profiles from sequential three-step extractions (TBS, detergent, and formic acid) demonstrated that the lower level of total apoE4 is reflected only in the detergent-soluble fraction, indicating that less apoE4 is lipoprotein-associated, and perhaps less lipidated, compared with apoE2 and apoE3. Soluble Aß42 and oAß levels were highest in E4FAD mice, although soluble apoE2, apoE3, and apoE4 levels were comparable, suggesting that the differences in soluble Aß42 and oAß result from functional differences among the apoE isoforms. Thus, APOE differentially regulates multiple aspects of Aß accumulation.