ApoE4 Alters ABCA1 Membrane Trafficking in Astrocytes.

The APOE ε4 allele is the strongest genetic risk factor for late-onset Alzheimer's disease (AD). ApoE protein aggregation plays a central role in AD pathology, including the accumulation of ß-amyloid (Aß). Lipid-poor ApoE4 protein is prone to aggregate and lipidating ApoE4 protects it from aggregation. The mechanisms regulating ApoE4 aggregation in vivo are surprisingly not known. ApoE lipidation is controlled by the activity of the ATP binding cassette A1 (ABCA1). ABCA1 recycling and degradation is regulated by ADP-ribosylation factor 6 (ARF6). We found that ApoE4 promoted greater expression of ARF6 compared with ApoE3, trapping ABCA1 in late-endosomes and impairing its recycling to the cell membrane. This was associated with lower ABCA1-mediated cholesterol efflux activity, a greater percentage of lipid-free ApoE particles, and lower Aß degradation capacity. Human CSF from APOE ε4/ε4 carriers showed a lower ability to induce ABCA1-mediated cholesterol efflux activity and greater percentage of aggregated ApoE protein compared with CSF from APOE ε3/ε3 carriers. Enhancing ABCA1 activity rescued impaired Aß degradation in ApoE4-treated cells and reduced both ApoE and ABCA1 aggregation in the hippocampus of male ApoE4-targeted replacement mice. Together, our data demonstrate that aggregated and lipid-poor ApoE4 increases ABCA1 aggregation and decreases ABCA1 cell membrane recycling. Enhancing ABCA1 activity to reduce ApoE and ABCA1 aggregation is a potential therapeutic strategy for the prevention of ApoE4 aggregation-driven pathology.SIGNIFICANCE STATEMENT ApoE protein plays a key role in the formation of amyloid plaques, a hallmark of Alzheimer's disease (AD). ApoE4 is more aggregated and hypolipidated compared with ApoE3, but whether enhancing ApoE lipidation in vivo can reverse ApoE aggregation is not known. ApoE lipidation is controlled by the activity of the ATP binding cassette A1 (ABCA1). In this study, we demonstrated that the greater propensity of lipid-poor ApoE4 to aggregate decreased ABCA1 membrane recycling and its ability to lipidate ApoE. Importantly, enhancing ABCA1 activity to lipidate ApoE reduced ApoE and ABCA1 aggregation. This work provides critical insights into the interactions among ABCA1, ApoE lipidation and aggregation, and underscores the promise of stabilizing ABCA1 activity to prevent ApoE-driven aggregation pathology.

Central and Peripheral Mechanisms in ApoE4-Driven Diabetic Pathology.

Apolipoprotein E (APOE) ε4 gene allele and type 2 diabetes mellitus (T2DM) are prime risk factors for Alzheimer's disease (AD). Despite evidence linking T2DM and apoE4, the mechanism underlying their interaction is yet to be determined. In the present study, we employed a model of APOE-targeted replacement mice and high-fat diet (HFD)-induced insulin resistance to investigate diabetic mechanisms associated with apoE4 pathology and the extent to which they are driven by peripheral and central processes. Results obtained revealed an intriguing pattern, in which under basal conditions, apoE4 mice display impaired glucose and insulin tolerance and decreased insulin secretion, as well as cognitive and sensorimotor characteristics relative to apoE3 mice, while the HFD impairs apoE3 mice without significantly affecting apoE4 mice. Measurements of weight and fasting blood glucose levels increased in a time-dependent manner following the HFD, though no effect of genotype was observed. Interestingly, sciatic electrophysiological and skin intra-epidermal nerve fiber density (IENFD) peripheral measurements were not affected by the APOE genotype or HFD, suggesting that the observed sensorimotor and cognitive phenotypes are related to central nervous system processes. Indeed, measurements of hippocampal insulin receptor and glycogen synthase kinase-3ß (GSK-3ß) activation revealed a pattern similar to that obtained in the behavioral measurements while Akt activation presented a dominant effect of diet. HFD manipulation induced genotype-independent hyperlipidation of apoE, and reduced levels of brain apoE in apoE3 mice, rendering them similar to apoE4 mice, whose brain apoE levels were not affected by the diet. No such effect was observed in the peripheral plasma levels of apoE, suggesting that the pathological effects of apoE4 under the control diet and apoE3 under HFD conditions are related to the decreased levels of brain apoE. Taken together, our data suggests that diabetic mechanisms play an important role in mediating the pathological effects of apoE4 and that consequently, diabetic-related therapy may be useful in treating apoE4 pathology in AD.

ApoE4: an emerging therapeutic target for Alzheimer's disease.

BACKGROUND: The growing body of evidence indicating the heterogeneity of Alzheimer's disease (AD), coupled with disappointing clinical studies directed at a fit-for-all therapy, suggest that the development of a single magic cure suitable for all cases may not be possible. This calls for a shift in paradigm where targeted treatment is developed for specific AD subpopulations that share distinct genetic or pathological properties. Apolipoprotein E4 (apoE4), the most prevalent genetic risk factor of AD, is expressed in more than half of AD patients and is thus an important possible AD therapeutic target. REVIEW: This review focuses initially on the pathological effects of apoE4 in AD, as well as on the corresponding cellular and animal models and the suggested cellular and molecular mechanisms which mediate them. The second part of the review focuses on recent apoE4-targeted (from the APOE gene to the apoE protein and its interactors) therapeutic approaches that have been developed in animal models and are ready to be translated to human. Further, the issue of whether the pathological effects of apoE4 are due to loss of protective function or due to gain of toxic function is discussed herein. It is possible that both mechanisms coexist, with certain constituents of the apoE4 molecule and/or its downstream signaling mediating a toxic effect, while others are associated with a loss of protective function. CONCLUSION: ApoE4 is a promising AD therapeutic target that remains understudied. Recent studies are now paving the way for effective apoE4-directed AD treatment approaches.

Omega-3 fatty acids, lipids, and apoE lipidation in Alzheimer's disease: a rationale for multi-nutrient dementia prevention.

In the last decade, it has become obvious that Alzheimer's disease (AD) is closely linked to changes in lipids or lipid metabolism. One of the main pathological hallmarks of AD is amyloid-ß (Aß) deposition. Aß is derived from sequential proteolytic processing of the amyloid precursor protein (APP). Interestingly, both, the APP and all APP secretases are transmembrane proteins that cleave APP close to and in the lipid bilayer. Moreover, apoE4 has been identified as the most prevalent genetic risk factor for AD. ApoE is the main lipoprotein in the brain, which has an abundant role in the transport of lipids and brain lipid metabolism. Several lipidomic approaches revealed changes in the lipid levels of cerebrospinal fluid or in post mortem AD brains. Here, we review the impact of apoE and lipids in AD, focusing on the major brain lipid classes, sphingomyelin, plasmalogens, gangliosides, sulfatides, DHA, and EPA, as well as on lipid signaling molecules, like ceramide and sphingosine-1-phosphate. As nutritional approaches showed limited beneficial effects in clinical studies, the opportunities of combining different supplements in multi-nutritional approaches are discussed and summarized.

Apolipoprotein E4 reduces evoked hippocampal acetylcholine release in adult mice.

Apolipoprotein E4 (apoE4) is the most prevalent genetic risk factor for Alzheimer's disease. We utilized apoE4-targeted replacement mice (approved by the Tel Aviv University Animal Care Committee) to investigate whether cholinergic dysfunction, which increases during aging and is a hallmark of Alzheimer's disease, is accentuated by apoE4. This revealed that levels of the pre-synaptic cholinergic marker, vesicular acetylcholine transporter in the hippocampus and the corresponding electrically evoked release of acetylcholine, are similar in 4-month-old apoE4 and apolipoprotein E3 (apoE3) mice. Both parameters decrease with age. This decrease is, however, significantly more pronounced in the apoE4 mice. The levels of cholinacetyltransferase (ChAT), acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE) were similar in the hippocampus of young apoE4 and apoE3 mice and decreased during aging. For ChAT, this decrease was similar in the apoE4 and apoE3 mice, whereas it was more pronounced in the apoE4 mice, regarding their corresponding AChE and BuChE levels. The level of muscarinic receptors was higher in the apoE4 than in the apoE3 mice at 4 months and increased to similar levels with age. However, the relative representation of the M1 receptor subtype decreased during aging in apoE4 mice. These results demonstrate impairment of the evoked release of acetylcholine in hippocampus by apoE4 in 12-month-old mice but not in 4-month-old mice. The levels of ChAT and the extent of the M2 receptor-mediated autoregulation of ACh release were similar in the adult mice, suggesting that the apoE4-related inhibition of hippocampal ACh release in these mice is not driven by these parameters. Evoked ACh release from hippocampal and cortical slices is similar in 4-month-old apoE4 and apoE3 mice but is specifically and significantly reduced in hippocampus, but not cortex, of 12-month-old apoE4 mice. This effect is accompanied by decreased VAChT levels. These findings show that the hipocampal cholinergic nerve terminals are specifically affected by apoE4 and that this effect is age dependent.

The effects of the apoE4 genotype on the developing mouse retina.

Apolipoprotein E4 (apoE4), the most prevalent genetic risk factor for Alzheimer's disease (AD), is associated with neuronal and vascular impairments. The retina, which is as an extension of the central nervous system (CNS), is a particularly suitable model for studying developmental and functional aspects of the neuronal and vascular systems. This study investigates the apoE4-dependent developmental effects on the retinal vasculature and neuronal systems and on the levels of apoE and the vascular endothelial growth factor (VEGF) in the retina. This was performed utilizing retinas of 4, 7, 12, and of 120-day-old human-apoE4-targeted replacement mice and of corresponding mice that express the AD benign isoform, apoE3. The results obtained revealed retinal vascular pathology in the apoE4 mice, which started on the early post-natal days. This includes transient increase in vascular branching, and vascular buds which are round vascular elements representing sprouting or retracting vessels. These effects peaked and ended during the neonatal period. Examination of the synaptic system utilizing the pre-synaptic marker synaptophysin revealed a significant decrease of retinal synaptic density in the apoE4 mice, which was detectable by post-natal day 12 (P12). These morphological changes are associated with neonatal age-dependent elevation in the apoE levels in both apoE3 and apoE4 retinas which is more profound in the apoE4 mice and a corresponding increase in VEGF levels, which is less profound in the apoE4 mice. Additionally, we observed lower levels of retinal VEGF in the apoE4 mice compared to the apoE3 mice retinas on P12. These results show that apoE4 has a transient vascular effect during retinal development that ends in the neonatal period, which is accompanied by a synaptic effect that begins at the end of the neonatal period. These findings show that the apoE4 genotype can have distinct developmental effects on both the retinal vasculature and on neurons and suggest that the vascular effects of apoE4 may be related to reduced levels of VEGF.

Reversal of apoE4-driven brain pathology and behavioral deficits by bexarotene.

Apolipoprotein E4 (apoE4), the most prevalent genetic risk factor for Alzheimer's disease (AD), is less lipidated than its corresponding AD-benign form, apoE3, and it has been suggested that the pathological effects of apoE4 are mediated by lipid-related mechanisms. ATP-binding cassette transporters A1 and G1 (ABCA1 and ABCG1, respectively) are the most important apoE-lipidating proteins. The expression of these proteins, as well as that of apoE, is controlled by the transcription regulation retinoid X receptor (RXR)-liver X receptor (LXR) system. In the present study, we investigated the effects of the RXR agonist bexarotene on mRNA and protein levels of apoE, ABCA1, and ABCG1 in young, naive apoE3- and apoE4-targeted replacement mice and assessed the extent to which this reverses the apoE4-driven pathological phenotype. This investigation reveled that bexarotene increases the mRNA and protein levels of ABCA1 and ABCG1 in hippocampal neurons, but has no effect on the corresponding levels of apoE. These findings were associated with reversal of the lipidation deficiency of apoE4 and of the cognitive impairments of apoE4 mice in several tests. Furthermore, bexarotene reversed the apoE4-driven accumulation of Aß42 and hyperphosphorylated tau in hippocampal neurons, as well as the apoE4-induced reduction in the levels of the presynaptic marker vesicular glutamatergic transporter 1 (VGluT1). In conclusion, the results show that treatment of apoE4 mice with the RXR agonist bexarotene reverses the apoE4-induced cognitive and neuronal impairments in vivo and suggest that this is due to reversal of the lipidation deficiency of apoE4. This puts forward the possibility that RXR activation and increased levels of ABCA1 and ABCG1 could be useful in the treatment of human apoE4 carriers.

Hippocampus-related cognitive impairments in young apoE4 targeted replacement mice.

We presently investigated the effects of apolipoprotein E4 (apoE4), the most prevalent genetic risk factor for Alzheimer's disease, on the cognitive performance of young targeted replacement apoE4 mice. We revealed that these mice were impaired in the object recognition and Morris water maze tests, both of which are associated with hippocampal learning and memory, relative to that of the apoE3 mice. These results are consistent with previous histological and biochemical findings that hippocampal neurons are specifically affected by apoE4. The suggestion that the behavioral impairments of the apoE4 mice are related to the hippocampal neuropathology of these mice is further supported by the fear conditioning test. This test revealed that the performance of the apoE4 mice in the contextual component, which is hippocampus related, was impaired, whereas their cued test response, which is amygdala driven, was not. The stress levels of the apoE4 and apoE3 mice, as unraveled by the light/dark anxiety test, were similar, suggesting that the observed cognitive impairments of the apoE4 mice are not related to differences in the basal anxiety levels of these mice. In conclusion, the present study shows that young apoE4 targeted replacement mice are impaired in numerous hippocampus-related learning and memory tasks.

APOE ε4: the most prevalent yet understudied risk factor for Alzheimer's disease.

Brain pathology of Alzheimer's diseases (AD) and the genetics of autosomal dominant familial AD have been the "lamp posts" under which the AD field has been looking for therapeutic targets. Although this approach still remains valid, none of the compounds tested to date have produced clinically meaningful results. This calls for developing complementary therapeutic approaches and AD targets. The allele ε4 of apolipoprotein E4 (APOE ε4), is the most prevalent genetic risk factor for sporadic AD, and is expressed in more than half of the AD patients. However, in spite of its genetic prominence, the allele APOE ε4 and its corresponding protein product apoE4 have been understudied. We presently briefly discuss the reasons underlying this situation and review newly developed AD therapeutic approaches that target apoE4 and which pave the way for future studies.

9-cis beta-carotene-enriched diet significantly improved cognition and decreased Alzheimer's disease neuropathology and neuroinflammation in Alzheimer's disease-like mouse models.

A significant progressive decline in beta-carotene (ßC) levels in the brain is associated with cognitive impairment and a higher prevalence of Alzheimer's disease (AD). In this study, we investigated whether the administration of 9-cis beta-carotene (9CBC)-rich powder of the alga Dunaliella bardawil, the best-known source of ßC in nature, inhibits the development of AD-like neuropathology and cognitive deficits. We demonstrated that in 3 AD mouse models, Tg2576, 5xFAD, and apoE4, 9CBC treatment improved long- and short-term memory, decreased neuroinflammation, and reduced the prevalence of ß-amyloid plaques and tau hyperphosphorylation. These findings suggest that 9CBC has the potential to be an effective preventive and symptomatic AD therapy.

The effects of apolipoproteins E3 and E4 on the transforming growth factor-ß system in targeted replacement mice.

BACKGROUND: This study examined the possibility that apolipoprotein E4 (apoE4), the most prevalent genetic risk factor of Alzheimer's disease, interacts isoform specifically with the transforming growth factor (TGF)-ß system. METHODS: This was pursued by measurements of the effects of apoE3 and apoE4 on the levels of TGF-ß ligands and on activation of the Smad system in brains of human apoE targeted replacement mice, utilizing Western blot. RESULTS: The study revealed that apoE4 reduces, isoform specifically, the levels of TGF-ß(1), TGF-ß(2) and TGF-ß(3) in the septum and of TGF-ß(3) in the hippocampus. In contrast, the levels and extent of phosphorylation of Smad1, 5 and 8 as well as of Smad2 and Smad3 in these brain areas were not affected by apoE4, suggesting that the apoE4-driven effects on the TGF-ß system may be mediated via the Smad-independent non-canonical pathway. CONCLUSION: The possible role of the TGF-ß system in mediating the pathological effects of apoE4 is discussed.

Anatomical localization of protease-activated receptor-1 and protease-mediated neuroglial crosstalk on peri-synaptic astrocytic endfeet.

We studied the localization, activation and function of protease-activated receptor 1 (PAR-1) at the CNS synapse utilizing rat brain synaptosomes and slices. Confocal immunofluoresence and transmission electron microscopy in brain slices with pre-embedding diaminobenzidine (DAB) immunostaining found PAR-1 predominantly localized to the peri-synaptic astrocytic endfeet. Structural confocal immunofluorescence microscopy studies of isolated synaptosomes revealed spherical structures stained with anti-PAR-1 antibody which co-stained mainly for glial-filament acidic protein compared with the neuronal markers synaptophysin and PSD-95. Immunoblot studies of synaptosomes demonstrated an appropriate major band corresponding to PAR-1 and activation of the receptor by a specific agonist peptide (SFLLRN) significantly modulated phosphorylated extracellular signal-regulated kinase. A significant membrane potential depolarization was produced by thrombin (1 U/mL) and the PAR-1 agonist (100 µM) and depolarization by high K(+) elevated extracellular thrombin-like activity in the synaptosomes preparation. The results indicate PAR-1 localized to the peri-synaptic astrocytic endfeet is most likely activated by synaptic proteases and induces cellular signaling and modulation of synaptic electrophysiology. A protease mediated neuron-glia pathway may be important in both physiological and pathological regulation of the synapse.

Possible role of tau in mediating pathological effects of apoE4 in vivo prior to and following activation of the amyloid cascade.

Injection of the neprilysin inhibitor thiorphan into the brain induces the accumulation of Abeta in hippocampal CA1 neurons and septal neurons in apoE4 knock-in mice but not in mice that express the corresponding Alzheimer's disease benign isoform apoE3. We investigated the possible role of tau phosphorylation in mediating this synergistic pathological cross talk between apoE4 and the amyloid cascade. This revealed that in both apoE4 and apoE3 mice, activating the amyloid cascade by inhibiting neprilysin triggers the accumulation of AT100 phosphorylated tau in the perikarya of CA1 neurons. In contrast, in the septum this treatment elevated the level of phosphorylation of the tau AT100 epitope only in the apoE4 mice. This suggests that tau-related processes by themselves do not mediate the synergistic pathological effects of apoE4 and Abeta in CA1 neurons. However, tau and cytoskeletal-related mechanisms may mediate the synergistic pathological effects of apoE4 and Abeta in the septum. The basal levels of tau phosphorylation are also affected by the apoE genotype. This effect, which is associated with hyperphosphorylation of the tau AT8 epitope, is most prominent in hippocampal CA3 neurons. This suggests that the apoE4 mice are already stressed under nonstimulated conditions and that AT8 tau phosphorylation may contribute to their increased susceptibility to brain insults.

Activation of the amyloid cascade in apolipoprotein E4 transgenic mice induces lysosomal activation and neurodegeneration resulting in marked cognitive deficits.

The allele E4 of apolipoprotein E (apoE4), the most prevalent genetic risk factor for Alzheimer's disease, is associated histopathologically with elevated levels of brain amyloid. This led to the suggestion that the pathological effects of apoE4 are mediated by cross-talk interactions with amyloid beta peptide (Abeta), which accentuate the pathological effects of the amyloid cascade. The mechanisms underlying the Abeta-mediated pathological effects of apoE4 are unknown. We have shown recently that inhibition of the Abeta-degrading enzyme neprilysin in brains of wild-type apoE3 and apoE4 mice results in rapid and similar elevations in their total brain Abeta levels. However, the nucleation and aggregation of Abeta in these mice were markedly affected by the apoE genotype and were specifically enhanced in the apoE4 mice. We presently used the neprilysin inhibition paradigm to analyze the neuropathological and cognitive effects that are induced by apoE4 after activation of the amyloid cascade. This revealed that apoE4 stimulates isoform specifically the degeneration of hippocampal CA1 neurons and of entorhinal and septal neurons, which is accompanied by the accumulation of intracellular Abeta and apoE and with lysosomal activation. Furthermore, these neuropathological effects are associated isoform specifically with the occurrence of pronounced cognitive deficits in the ApoE4 mice. These findings provide the first in vivo evidence regarding the cellular mechanisms underlying the pathological cross talk between apoE4 and Abeta, as well as a novel model system of neurodegeneration in vivo that is uniquely suitable for studying the early stages of the amyloid cascade and the effects thereon of apoE4.

ApoE4-dependent Abeta-mediated neurodegeneration is associated with inflammatory activation in the hippocampus but not the septum.

Apolipoprotein E4 (ApoE4), the most prevalent genetic risk factor for Alzheimer's disease, is histopathologically associated with increased deposition of amyloid-beta and brain inflammation and with impaired neuronal plasticity and repair. We have recently shown that the activation of the amyloid cascade by inhibition of the Abeta-degrading enzyme, neprilysin, stimulates the isoform-specific degeneration of hippocampal CA1 neurons and septal neurons in apoE4 transgenic mice and that this effect is accompanied by the accumulation of intracellular Abeta in the affected neurons. We presently examined the extent to which this apoE4-dependent Abeta-mediated neurodegeneration is associated with brain area specific inflammatory activation. This revealed that the activation of the amyloid cascade in apoE transgenic mice results in the activation of microgliosis and astrogliosis in the hippocampus of apoE4, but not in apoE3 transgenic mice. The effect was most pronounced in the hippocampal CA1 subfield and its initial kinetics followed that of the accumulation of Abeta in CA1 neurons. In contrast, the corresponding apoE4-dependent Abeta degeneration of septal neurons was not associated with the activation of either gliosis or astrogliosis in this brain area. These animal model findings, that the association between brain inflammation and neurodegeneration is brain area specific, suggest that neuropathological inflammatory interactions in AD may also be brain area specific and that consequently the efficacy of putative anti-inflammatory intervention may also be brain area selective.

Extra-Hippocampal Learning Deficits in Young Apolipoprotein E4 Mice and Their Synaptic Underpinning.

The E4 allele of apolipoprotein (apoE4) is the primary genetic risk factor for late onset Alzheimer's disease (AD), yet the exact manner in which apoE4 leads to the development of AD is undetermined. Human and animal studies report that apoE4-related memory deficits appear earlier than the AD clinical manifestation, thus suggesting the existence of early, pre-pathological, apoE4 impairments that may later lead to AD onset. While current research regards the hippocampus as the initial and primary effected locus by apoE4, we presently investigate the possibility that apoE4 innately impairs any brain area that requires synaptic plasticity. To test this hypothesis, we trained young (3-4-month-old) target-replacement apoE3 and apoE4 mice in conditioned taste aversion (CTA) acquisition and extinction learnings- hippocampus-independent learnings that are easily performed at a young age. Synaptic vesicular markers analysis was conducted in the gustatory cortex (GC), basolateral amygdala (BLA), medial prefrontal cortex (mPFC), and hippocampal CA3 to reveal underlying apoE4-related impairments. We have found that young apoE4 mice are severely impaired in CTA acquisition and extinction learning. CTA acquisition impairments were correlated with reduced vGat and vGlut levels in the BLA and GC, but not in the CA3. CTA extinction was correlated with lower synaptophysin and vGlut levels in the mPFC, a central region in CTA extinction. Our results support apoE4-related early-life plasticity impairments that precede the AD clinical manifestations and affect any brain area that depends on extensive plasticity; early impairments that may promote the development of AD pathologies later in life.

The Effects of APOE4 on Mitochondrial Dynamics and Proteins in vivo.

This study examined the effects of apolipoprotein E4 (APOE4), the most prevalent genetic risk factor for Alzheimer's disease (AD), on proteins involved in mitochondrial dynamics and autophagy, in the hippocampus of targeted replacement mice. Immunohistochemical measurements revealed that the levels of the mitochondrial fusion-mediating protein, MFN1, were higher, whereas those of corresponding fission-regulating protein, DRP-1, were lower in the hippocampus of ApoE4 mice than in the corresponding ApoE3 mice, indicating that APOE4 is associated with increased mitochondrial fusion and decreased fission. A similar ApoE4-driven decrease in DRP-1 was also observed in AD brains. The levels of the mitochondrial proteins COX1 and Tom40, were higher in the ApoE4 mice, which is consistent with the increased fusion. Measurements of the levels of cleaved PINK1 and parkin, which mark and target mitochondria for mitophagic degradation, revealed lower levels of cleaved PINK1, suggesting reduced mitochondrial membrane potential, and higher levels of parkin in the hippocampus of ApoE4 compared with the ApoE3 mice, indicating altered mitophagy. The levels of the ubiquitin-binding scaffold protein, p62/SQSTM1, which directs selected cargo to the autophagosomes, were also higher in the ApoE4 mice. These findings suggest that APOE4 is associated with enhanced mitochondrial fusion and decreased fission. Additionally, the results indicate that mitophagy/autophagy is reduced in ApoE4 mice, resulting in higher levels of proteins such as parkin and p62, which are normally degraded during this process. Taken together, these results suggest a novel mechanism that may underlie the pathological effects of APOE4 and indicate that use of APOE4 genotyping could pave the way for identification of novel APOE4-related therapeutic targets.

The Role of MAPK's Signaling in Mediating ApoE4-Driven Pathology In Vivo.

BACKGROUND: Alzheimer's Disease (AD) is associated with impairments in key brain Mitogen- Activated Protein Kinase (MAPK) signaling cascades including the p38, c-Jun N-terminal kinase (JNK), ERK and Akt pathways. Apolipoprotein E4 (ApoE4) is the most prevalent genetic risk factor of AD. OBJECTIVES: To investigate the extent to which the MAPK signaling pathway plays a role in mediating the pathological effects of apoE4 and can be reversed by experimental manipulations. METHODS: Measurements of total level and activation of MAPK signaling pathway factors, obtained utilizing immunoblot assay of hippocampal tissues from naïve and viral-treated apoE3 and apoE4 targeted replacement mice. RESULTS: ApoE4 mice showed robust activation of the stress related p38 and JNK pathways and a corresponding decrease in Akt activity, which is coupled to activation of GSK3ß and tau hyperphosphorylation. There was no effect on the ERK pathway. We have previously shown that the apoE4- related pathology, namely; accumulation of Aß, hyper-phosphorylated tau, synaptic impairments and decreased VEGF levels can be reversed by up-regulation of VEGF level utilizing a VEGF-expressing adeno-associated virus. Utilizing this approach, we assessed the extent to which the AD-hallmark and synaptic pathologies of apoE4 are related to the corresponding MAPK signaling effects. This revealed that the reversal of the apoE4-driven pathology via VEGF treatment was associated with a reversal of the p38 and Akt related effects. CONCLUSION: Taken together, these results suggest that the p38 and Akt pathways play a role in mediating the AD-related pathological effects of apoE4 in the hippocampus.

Activation of the amyloid cascade by intracerebroventricular injection of the protease inhibitor phosphoramidon.

We presently investigated the pathological effects of prolonged inhibition of brain beta-amyloid (Abeta) degradation in vivo. The results obtained revealed that intracerebroventricular injection of the protease inhibitor phosphoramidon into wild-type mice for up to a month elevated the soluble and deposited brain Abeta levels and concomitantly induced the neurodegeneration of distinct hippocampal neurons as well as neuroinflammation. These findings reproduce pathological effects associated with the initial stages of the amyloid cascade and provide a novel model system for studying their underlying mechanisms.

The effects of apolipoprotein E genotype, α-synuclein deficiency, and sex on brain synaptic and Alzheimer's disease-related pathology.

INTRODUCTION: Alzheimer's disease (AD) and synucleinopathies share common pathological mechanisms. Apolipoprotein E4 (apoE4), the most prevalent genetic risk factor for AD, also increases the risk for dementia in pure synucleinopathies. We presently examined the effects of α-synuclein deficiency (α-syn-/-) and sex on apoE4-driven pathologies. METHODS: AD-related, synaptic, and vascular markers were analyzed in female and male α-syn-/- and α-syn+/+ apoE4, apoE3, and apoE3/E4 mice. RESULTS: ApoE4 was hypolipidated, and this effect was unchanged by α-syn-/- and sex. The levels of synaptic markers were lower, and the levels of AD-related parameters were higher in female α-syn-/- apoE4 mice compared with the corresponding apoE3 mice. By comparison, apoE4 had small effects on the AD parameters of male and female α-syn+/+ apoE4 mice. DISCUSSION: Although α-syn-/- does not affect the upstream lipidation impairment of apoE4, it acts as a "second hit" enhancer of the subsequent apoE4-driven pathologies.