Estradiol improves behavior in FAD transgenic mice that express APOE3 but not APOE4 after ovariectomy.

Increasing evidence suggests that female individuals have a higher Alzheimer's disease (AD) risk associated with post-menopausal loss of circulating estradiol (E2). However, clinical data are conflicting on whether E2 lowers AD risk. One potential contributing factor is APOE. The greatest genetic risk factor for AD is APOE4, a factor that is pronounced in female individuals post-menopause. Clinical data suggests that APOE impacts the response of AD patients to E2 replacement therapy. However, whether APOE4 prevents, is neutral, or promotes any positive effects of E2 is unclear. Therefore, our goal was to determine whether APOE modulates the impact of E2 on behavior and AD pathology in vivo. To that end, mice that express human APOE3 (E3FAD) or APOE4 (E4FAD) and overproduce Aß42 were ovariectomized at either 4 months (early) or 8 months (late) and treated with vehicle or E2 for 4 months. In E3FAD mice, we found that E2 mitigated the detrimental effect of ovariectomy on memory, with no effect on Aß in the early paradigm and only improved learning in the late paradigm. Although E2 lowered Aß in E4FAD mice in the early paradigm, there was no impact on learning or memory, possibly due to higher Aß pathology compared to E3FAD mice. In the late paradigm, there was no effect on learning/memory and Aß pathology in E4FAD mice. Collectively, these data support the idea that, in the presence of Aß pathology, APOE impacts the response to E2 supplementation post-menopause.

APOE2 Heterozygosity Reduces Hippocampal Soluble Amyloid-ß42 Levels in Non-Hyperlipidemic Mice.

APOE2 lowers Alzheimer's disease (AD) risk; unfortunately, the mechanism remains poorly understood and the use of mice models is problematic as APOE2 homozygosity is associated with hyperlipidemia. In this study, we developed mice that are heterozygous for APOE2 and APOE3 or APOE4 and overexpress amyloid-ß peptide (Aß) (EFAD) to evaluate the effect of APOE2 dosage on Aß pathology. We found that heterozygous mice do not exhibit hyperlipidemia. Hippocampal but not cortical levels of soluble Aß42 followed the order E2/2FAD > E2/3FAD≤E3/3FAD and E2/2FAD > E2/4FAD < E4/4FAD without an effect on insoluble Aß42. These findings offer initial insights on the impact of APOE2 on Aß pathology.

A novel apoE-mimetic increases brain apoE levels, reduces Aß pathology and improves memory when treated before onset of pathology in male mice that express APOE3.

BACKGROUND: Alzheimer's disease (AD) is characterized by cognitive dysfunction and amyloid plaques composed of the amyloid-beta peptide (Aß). APOE is the greatest genetic risk for AD with APOE4 increasing risk up to ~ 15-fold compared to APOE3. Evidence suggests that levels and lipidation of the apoE protein could regulate AD progression. In glia, apoE is lipidated via cholesterol efflux from intracellular pools, primarily by the ATP-binding cassette transporter A1 (ABCA1). Therefore, increasing ABCA1 activity is suggested to be a therapeutic approach for AD. CS-6253 (CS) is a novel apoE mimetic peptide that was developed to bind and stabilize ABCA1 and maintain its localization into the plasma membrane therefore promoting cholesterol efflux. The goal of this study was to determine whether CS could modulate apoE levels and lipidation, Aß pathology, and behavior in a model that expresses human APOE and overproduce Aß. METHODS: In vitro, APOE3-glia or APOE4-glia were treated with CS. In vivo, male and female, E3FAD (5xFAD+/-/APOE3+/+) and E4FAD (5xFAD+/-/APOE4+/+) mice were treated with CS via intraperitoneal injection at early (from 4 to 8 months of age) and late ages (from 8 to 10 months of age). ApoE levels, ABCA1 levels and, apoE lipidation were measured by western blot and ELISA. Aß and amyloid levels were assessed by histochemistry and ELISA. Learning and memory were tested by Morris Water Maze and synaptic proteins were measured by Western blot. RESULTS: CS treatment increased apoE levels and cholesterol efflux in primary glial cultures. In young male E3FAD mice, CS treatment increased soluble apoE and lipid-associated apoE, reduced soluble oAß and insoluble Aß levels as well as Aß and amyloid deposition, and improved memory and synaptic protein levels. CS treatment did not induce any therapeutic benefits in young female E3FAD and E4FAD mice or in any groups when treatment was started at later ages. CONCLUSIONS: CS treatment reduced Aß pathology and improved memory only in young male E3FAD, the cohort with the least AD pathology. Therefore, the degree of Aß pathology or Aß overproduction may impact the ability of targeting ABCA1 to be an effective AD therapeutic. This suggests that ABCA1-stabilizing treatment by CS-6253 works best in conditions of modest Aß levels.

APOE genotype and sex modulate Alzheimer's disease pathology in aged EFAD transgenic mice.

Increasing evidence supports that age, APOE and sex interact to modulate Alzheimer's disease (AD) risk, however the underlying pathways are unclear. One way that AD risk factors may modulate cognition is by impacting amyloid beta (Aß) accumulation as plaques, and/or neuroinflammation Therefore, the goal of the present study was to evaluate the extent to which age, APOE and sex modulate Aß pathology, neuroinflammation and behavior in vivo. To achieve this goal, we utilized the EFAD mice, which express human APOE3 or APOE4 and have five familial AD mutations (FAD) that result in Aß42 overproduction. We assessed Aß levels, reactive glia and Morris water maze performance in 6-, 10-, 14-, and 18-month-old EFAD mice. Female APOE4 mice had the highest Aß deposition, fibrillar amyloid deposits and neuroinflammation as well as earlier behavior deficits. Interestingly, we found that female APOE3 mice and male APOE4 mice had similar levels of pathology. Collectively our data support that the combination of APOE4 and female sex is the most detrimental combination for AD, and that at older ages, female sex may be equivalent to APOE4 genotype.

A small-molecule TLR4 antagonist reduced neuroinflammation in female E4FAD mice.

BACKGROUND: APOE genotype is the greatest genetic risk factor for sporadic Alzheimer's disease (AD). APOE4 increases AD risk up to 12-fold compared to APOE3, an effect that is greater in females. Evidence suggests that one-way APOE could modulate AD risk and progression through neuroinflammation. Indeed, APOE4 is associated with higher glial activation and cytokine levels in AD patients and mice. Therefore, identifying pathways that contribute to APOE4-associated neuroinflammation is an important approach for understanding and treating AD. Human and in vivo evidence suggests that TLR4, one of the key receptors involved in the innate immune system, could be involved in APOE-modulated neuroinflammation. Consistent with that idea, we previously demonstrated that the TLR4 antagonist IAXO-101 can reduce LPS- and Aß-induced cytokine secretion in APOE4 glial cultures. Therefore, the goal of this study was to advance these findings and determine whether IAXO-101 can modulate neuroinflammation, Aß pathology, and behavior in mice that express APOE4. METHODS: We used mice that express five familial AD mutations and human APOE3 (E3FAD) or APOE4 (E4FAD). Female and male E4FAD mice and female E3FAD mice were treated with vehicle or IAXO-101 in two treatment paradigms: prevention from 4 to 6 months of age or reversal from 6 to 7 months of age. Learning and memory were assessed by modified Morris water maze. Aß deposition, fibrillar amyloid deposition, astrogliosis, and microgliosis were assessed by immunohistochemistry. Soluble levels of Aß and apoE, insoluble levels of apoE and Aß, and IL-1ß were measured by ELISA. RESULTS: IAXO-101 treatment resulted in lower Iba-1 coverage, lower number of reactive microglia, and improved memory in female E4FAD mice in both prevention and reversal paradigms. IAXO-101-treated male E4FAD mice also had lower Iba-1 coverage and reactivity in the RVS paradigm, but there was no effect on behavior. There was also no effect of IAXO-101 treatment on neuroinflammation and behavior in female E3FAD mice. CONCLUSION: Our data supports that TLR4 is a potential mechanistic therapeutic target for modulating neuroinflammation and cognition in APOE4 females.

Inhibition of ACAT as a Therapeutic Target for Alzheimer's Disease Is Independent of ApoE4 Lipidation.

APOE4, encoding apolipoprotein E4 (apoE4), is the greatest genetic risk factor for Alzheimer's disease (AD), compared to the common APOE3. While the mechanism(s) underlying APOE4-induced AD risk remains unclear, increasing the lipidation of apoE4 is an important therapeutic target as apoE4-lipoproteins are poorly lipidated compared to apoE3-lipoproteins. ACAT (acyl-CoA: cholesterol-acyltransferase) catalyzes the formation of intracellular cholesteryl-ester droplets, reducing the intracellular free cholesterol (FC) pool. Thus, inhibiting ACAT increases the FC pool and facilitates lipid secretion to extracellular apoE-containing lipoproteins. Previous studies using commercial ACAT inhibitors, including avasimibe (AVAS), as well as ACAT-knock out (KO) mice, exhibit reduced AD-like pathology and amyloid precursor protein (APP) processing in familial AD (FAD)-transgenic (Tg) mice. However, the effects of AVAS with human apoE4 remain unknown. In vitro, AVAS induced apoE efflux at concentrations of AVAS measured in the brains of treated mice. AVAS treatment of male E4FAD-Tg mice (5xFAD+/-APOE4+/+) at 6-8 months had no effect on plasma cholesterol levels or distribution, the original mechanism for AVAS treatment of CVD. In the CNS, AVAS reduced intracellular lipid droplets, indirectly demonstrating target engagement. Surrogate efficacy was demonstrated by an increase in Morris water maze measures of memory and postsynaptic protein levels. Amyloid-beta peptide (Aß) solubility/deposition and neuroinflammation were reduced, critical components of APOE4-modulated pathology. However, there was no increase in apoE4 levels or apoE4 lipidation, while amyloidogenic and non-amyloidogenic processing of APP were significantly reduced. This suggests that the AVAS-induced reduction in Aß via reduced APP processing was sufficient to reduce AD pathology, as apoE4-lipoproteins remained poorly lipidated.

The role of APOE in transgenic mouse models of AD.

Identified in 1993, APOE4 is the greatest genetic risk factor for Alzheimer's disease (AD), increasing risk up to 15-fold compared to the common variant APOE3. Since the mid 1990's, transgenic (Tg) mice have been developed to model AD pathology and progression, primarily via expression of the familial AD (FAD) mutations in the presence of mouse-APOE (m-APOE). APOE4, associated with enhanced amyloid-ß (Aß) accumulation, has rarely been the focus in designing FAD-Tg mouse models. Initially, FAD-Tg mice were crossed with human (h)-APOE driven by heterologous promoters to identify an APOE genotype-specific AD phenotype. These models were later supplemented with FAD-Tg mice crossed with APOE-knockouts (APOE-/- or APOE-KO) and h-APOE-targeted replacement (h-APOE-TR) mice, originally generated to study the role of APOE genotype in peripheral lipid metabolism and atherosclerotic lesion development. Herein, we compare the m- and h-APOE multi-gene clusters, and then critically review the relevant history and approaches to developing a Tg mouse model to characterize APOE-dependent AD pathology, in combination with genetic (sex, age) and modifiable (e.g., inflammation, obesity) risk factors. Finally, we present recent data from the EFAD mice, which express 5xFAD mutations with the expression of the human apoE isoforms (E2FAD, E3FAD and E4FAD). This includes a study of 6- and 18-month-old male and female E3FAD and E4FAD, a comparison that enables examination of the interaction among the main AD risk factors: age, APOE genotype and sex. While no single transgenic mouse can capture the effects of all modifiable and genetic risk factors, going forward, a conscious effort needs to be made to include the factors that most significantly modulate AD pathology.

EFAD transgenic mice as a human APOE relevant preclinical model of Alzheimer's disease.

Identified in 1993, APOE4 is the greatest genetic risk factor for sporadic Alzheimer's disease (AD), increasing risk up to 15-fold compared with APOE3, with APOE2 decreasing AD risk. However, the functional effects of APOE4 on AD pathology remain unclear and, in some cases, controversial. In vivo progress to understand how the human (h)-APOE genotypes affect AD pathology has been limited by the lack of a tractable familial AD-transgenic (FAD-Tg) mouse model expressing h-APOE rather than mouse (m)-APOE. The disparity between m- and h-apoE is relevant for virtually every AD-relevant pathway, including amyloid-ß (Aß) deposition and clearance, neuroinflammation, tau pathology, neural plasticity and cerebrovascular deficits. EFAD mice were designed as a temporally useful preclinical FAD-Tg-mouse model expressing the h-APOE genotypes for identifying mechanisms underlying APOE-modulated symptoms of AD pathology. From their first description in 2012, EFAD mice have enabled critical basic and therapeutic research. Here we review insights gleaned from the EFAD mice and summarize future directions.

Behavioral and physiological characterization of PKC-dependent phosphorylation in the Grin2a∆PKC mouse.

Activity-dependent plasticity in NMDA receptor-containing synapses can be regulated by phosphorylation of serines and tyrosines in the C-terminal domain of the receptor subunits by various kinases. We have previously identified S1291/S1312 as important sites for PKC phosphorylation; while Y1292/Y1312 are the sites indirectly phosphorylated by PKC via Src kinase. In the oocyte expression system, mutation of those Serine sites to Alanine (that cannot be phosphorylated) in the GluN2A subunit, resulted in a decreased PKC stimulated current enhancement through the receptors compared to wild-type NMDA receptors. To investigate the behavioral and physiological significance of those PKC-mediated phosphorylation sites in vivo, the Grin2a∆PKC mouse expressing GluN2A with four mutated amino acids: S1291A, S1312A, Y1292F and Y1387F was generated using homologous recombination. The Grin2a∆PKC mice exhibit reduced anxiety in the open field test, light dark emergence test, and elevated plus maze. The mutant mice show reduced alternation in a Y maze spontaneous alternation task and a in a non-reinforced T maze alternation task. Interestingly, when the mutant mice were exposed to novel environments, there was no increase in context-induced Fos levels in hippocampal CA1 and CA3 compared to home-cage Fos levels, while the Fos increased in the WT mice in CA1, CA3 and DG. When the SC-CA1 synapses in slices from mutant mice were stimulated using a theta-burst protocol, there was no impairment in LTP. Overall, these results suggest that at least one of those PKC-mediated phosphorylation sites regulates NMDAR-mediated signaling that modulates anxiety.

Foraging decisions in wild versus domestic Mus musculus: What does life in the lab select for?

What does domestication select for in terms of foraging and anti-predator behaviors? We applied principles of patch use and foraging theory to test foraging strategies and fear responses of three strains of Mus musculus: wild-caught, control laboratory, and genetically modified strains. Foraging choices were quantified using giving-up densities (GUDs) under three foraging scenarios: (1) patches varying in microhabitat (covered versus open), and initial resource density (low versus high); (2) daily variation in auditory cues (aerial predators and control calls); (3) patches with varying seed aggregations. Overall, both domestic strains harvested significantly more food than wild mice. Each strain revealed a significant preference for foraging under cover compared to the open, and predator calls had no detectable effects on foraging. Both domestic strains biased their harvest toward high quality patches; wild mice did not. In terms of exploiting favorable and avoiding unfavorable distributions of seeds within patches, the lab strain performed best, the wild strain worst, and the mutant strain in between. Our study provides support for hypothesis that domestic animals have more energy-efficient foraging strategies than their wild counterparts, but retain residual fear responses. Furthermore, patch-use studies can reveal the aptitudes and priorities of both domestic and wild animals.

Translocator protein 18 kDa negatively regulates inflammation in microglia.

Translocator protein 18 kDa (TSPO) is a mitochondrial outer membrane protein. Although TSPO expression is up-regulated during neuroinflammation, the role of TSPO and its signaling mechanisms in regulation of neuroinflammation remains to be elucidated at the molecular level. Here we demonstrate that TSPO is a negative regulator of neuroinflammation in microglia. Over-expression of TSPO decreased production of pro-inflammatory cytokines upon lipopolysaccharide treatment while TSPO knock-down had the opposite effect. Anti-inflammatory activity of TSPO is also supported by increased expression of alternatively activated M2 stage-related genes. These data suggest that up-regulation of TSPO level during neuroinflammation may be an adaptive response mechanism. We also provide the evidence that the repressive activity of TSPO is at least partially mediated by the attenuation of NF-κB activation. Neurodegenerative diseases are characterized by loss of specific subsets of neurons at the particular anatomical regions of the central nervous system. Cause of neuronal death is still largely unknown, but it is becoming clear that neuroinflammation plays a significant role in the pathophysiology of neurodegenerative diseases. Understanding the mechanisms underlying the inhibitory effects of TSPO on neuroinflammation can contribute to the therapeutic design for neurodegenerative diseases.

Brain region-specificity of palmitic acid-induced abnormalities associated with Alzheimer's disease.

BACKGROUND: Alzheimer's disease (AD) is a progressive, neurodegenerative disease mostly affecting the basal forebrain, cortex and hippocampus whereas the cerebellum is relatively spared. The reason behind this region-specific brain damage in AD is not well understood. Here, we report our data suggesting "differential free fatty acid metabolism in the different brain areas" as a potentially important factor in causing the region-specific damage observed in AD brain. FINDINGS: The astroglia from two different rat brain regions, cortex (region affected in AD) and cerebellum (unaffected region), were treated with 0.2 mM of palmitic acid. The conditioned media were then transferred to the cortical neurons to study the possible effects on the two main, AD-associated protein abnormalities, viz. BACE1 upregulation and hyperphosphorylation of tau. The conditioned media from palmitic-acid treated cortical astroglia, but not the cerebellar astroglia, significantly elevated levels of phosphorylated tau and BACE1 in cortical neurons as compared to controls (47 +/- 7% and 45 +/- 4%, respectively). CONCLUSION: The present data provide an experimental explanation for the region-specific damage observed in AD brain; higher fatty acid-metabolizing capacity of cortical astroglia as compared to cerebellar astroglia, may play a causal role in increasing vulnerability of cortex in AD, while sparing cerebellum.