RESUMO
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.
Assuntos
Transportador 1 de Cassete de Ligação de ATP/metabolismo , Apolipoproteína E4/metabolismo , Astrócitos/metabolismo , Membrana Celular/metabolismo , Fator 6 de Ribosilação do ADP , Idoso , Idoso de 80 Anos ou mais , Animais , Apolipoproteína E4/farmacologia , Astrócitos/efeitos dos fármacos , Linhagem Celular Transformada , Membrana Celular/efeitos dos fármacos , Células Cultivadas , Cricetinae , Feminino , Células HeLa , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Pessoa de Meia-Idade , Ligação Proteica/efeitos dos fármacos , Ligação Proteica/fisiologia , Transporte Proteico/efeitos dos fármacos , Transporte Proteico/fisiologiaRESUMO
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.
Assuntos
Acetilcolina/metabolismo , Apolipoproteína E4/metabolismo , Hipocampo/metabolismo , Fatores Etários , Animais , Apolipoproteína E3/genética , Apolipoproteína E4/genética , Colina O-Acetiltransferase/metabolismo , Guanosina 5'-O-(3-Tiotrifosfato)/farmacologia , Hipocampo/efeitos dos fármacos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , N-Metilescopolamina/farmacologia , Receptores Muscarínicos/metabolismo , Trítio/metabolismo , Proteínas Vesiculares de Transporte de Acetilcolina/metabolismoRESUMO
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.
Assuntos
Apolipoproteína E4/genética , Retina/crescimento & desenvolvimento , Vasos Retinianos/crescimento & desenvolvimento , Animais , Animais Recém-Nascidos , Apolipoproteína E4/metabolismo , Western Blotting , Genótipo , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Microscopia Confocal , Modelos Animais , Retina/citologia , Retina/metabolismo , Vasos Retinianos/citologia , Vasos Retinianos/metabolismoRESUMO
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.
Assuntos
Doença de Alzheimer/genética , Apolipoproteína E4/genética , Transtornos Cognitivos/fisiopatologia , Modelos Animais de Doenças , Hipocampo/fisiopatologia , Envelhecimento , Doença de Alzheimer/fisiopatologia , Animais , Transtornos Cognitivos/genética , Humanos , Aprendizagem/fisiologia , Memória/fisiologia , Camundongos , Camundongos Endogâmicos C57BLRESUMO
BACKGROUND: Apolipoprotein E4 (APOE4) is the most prevalent genetic risk factor of Alzheimer's disease. Several studies suggest that APOE4 binding to its receptors is associated with their internalization and accumulation in intracellular compartments. Importantly, this phenomenon also occurs with other, non-ApoE receptors. Based on these observations, we hypothesized that APOE4 pathological effects are mediated by impairment in the life cycle of distinct receptors (APOER2, LRP1, IR, VEGFR). OBJECTIVE: To examine the effects of APOE genotype on receptors protein levels and compartmentalization. METHODS: Primary mouse neurons were prepared from APOE3 or APOE4 targeted replacement mice, or APOE-KO mice. Specific receptors protein levels were evaluated in these neurons, utilizing immunofluorescent staining. Additionally, surface membrane protein levels of those receptors were assessed by cell surface biotinylation assay and ELISA. Receptors' colocalization with intracellular compartments was assessed by double staining and confocal microscopy, followed by colocalization analysis. Finally, LRP1 or APOER2 were knocked-down with CRISPR/Cas9 system to examine their role in mediating APOE4 effects on the receptors. RESULTS: Our results revealed lower receptors' levels in APOE4, specifically on the membrane surface. Additionally, APOE4 affects the compartmentation of these receptors in two patterns: the first was observed with LRP1 and was associated with decreased receptor levels in numerous intracellular compartments. The second was obtained with the other receptors and was associated with their accumulation in early endosomes and their decrease in the late endosomes. CONCLUSIONS: These results provide a unifying mechanism, in which APOE4 drives the down regulation of various receptors, which plays important roles in distinct APOE4 related pathological processes.
Assuntos
Doença de Alzheimer , Camundongos , Animais , Doença de Alzheimer/patologia , Apolipoproteína E4/genética , Apolipoproteína E4/metabolismo , Camundongos Transgênicos , Apolipoproteínas E , Apolipoproteína E3/genética , Apolipoproteína E3/metabolismoRESUMO
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.
Assuntos
Doença de Alzheimer , Doenças Neuroinflamatórias , Animais , Camundongos , beta Caroteno/farmacologia , beta Caroteno/uso terapêutico , Doença de Alzheimer/tratamento farmacológico , Dieta , Cognição , Modelos Animais de Doenças , Placa AmiloideRESUMO
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.
Assuntos
Apolipoproteína E3/metabolismo , Apolipoproteína E4/metabolismo , Regulação da Expressão Gênica/genética , Transdução de Sinais/genética , Fator de Crescimento Transformador beta/metabolismo , Animais , Apolipoproteína E3/genética , Apolipoproteína E4/genética , Hipocampo/metabolismo , Humanos , Camundongos , Camundongos Transgênicos , Fosforilação/genética , Septo do Cérebro/metabolismo , Proteínas Smad/metabolismoRESUMO
The É4 allele of apolipoprotein E (apoE4) is the most prevalent genetic risk factor for Alzheimer's disease. ApoE4 is also associated with poor recovery and functional outcome following traumatic brain injury. This study examined the effects of the apoE genotype on brain pathology following acute injury, induced by penetration of a needle through the cortex and hippocampus, at 3 and 14 days following the injury in female apoE3 and apoE4 α-synuclein-deficient targeted replacement (TR) mice. The results obtained revealed a marked inflammatory, synaptic and vascular response following the needle penetration injury (NPI). These results were found to be affected by the apoE genotype such that the inflammatory response, as measured utilizing the astrocytic marker GFAP and the microglial marker iba1, was faster and more prolonged in the apoE4 than in the apoE3 mice. The synaptic changes following the injury included a transient increase in synaptophysin levels in the apoE3 and not in the apoE4 mice, which was associated with a subsequent decrease in glutamatergic synapses, as measured utilizing VGluT1, in apoE4 and not in the apoE3 mice. Unlike these effects, measurements of the vasculature utilizing collagen IV as a marker revealed a significant increase which was similar in both apoE3 and apoE4 mice. Taken together, these results show that following acute brain injury, there is an apoE4-specific inflammatory and neuronal response to the injury. The NPI model provides a useful tool for studying the mechanism underlying the effects of apoE4 following acute brain injury and for the development of a corresponding anti-apoE4-targeted treatment.
Assuntos
Apolipoproteína E4/genética , Lesões Encefálicas Traumáticas/metabolismo , Hipocampo/metabolismo , Alelos , Animais , Apolipoproteína E4/metabolismo , Lesões Encefálicas Traumáticas/genética , Lesões Encefálicas Traumáticas/patologia , Proteínas de Ligação ao Cálcio/genética , Proteínas de Ligação ao Cálcio/metabolismo , Feminino , Proteína Glial Fibrilar Ácida/genética , Proteína Glial Fibrilar Ácida/metabolismo , Hipocampo/patologia , Camundongos , Camundongos Endogâmicos C57BL , Proteínas dos Microfilamentos/genética , Proteínas dos Microfilamentos/metabolismo , Microglia/metabolismo , Neurônios/metabolismo , Sinaptofisina/genética , Sinaptofisina/metabolismoRESUMO
ApolipoproteinE4 (apoE4) is the most prevalent genetic risk factor for Alzheimer's disease (AD) and as such is a promising therapeutic target. This study examined the extent to which the pathological effects of apoE4 can be counteracted in vivo utilizing an immunological approach in which anti-apoE4 antibodies are applied peripherally by i.p. injections into apoE4-targeted replacement mice. Prerequisites for the successful pursuit of this objective are the availability of antibodies that specifically bind brain apoE4 and not apoE3, and demonstrating that direct application of these antibodies into the brain can counteract the effects of apoE4. Accordingly, it was shown that the antiapoE4 monoclonal antibody (mAb) 9D11 binds specifically to brain apoE4 and not apoE3. Direct i.c.v. application of mAb 9D11 prevented the apoE4-driven accumulation of Aß in hippocampal neurons following activation of the amyloid cascade by inhibiting the Aß-degrading enzyme neprilysin. These findings provide a proof-of-concept that anti-apoE4 mAb 9D11, when introduced into the brain, can counteract the apoE4 effects in vivo. Subsequent experiments, utilizing repeated i.p. injections of mAb 9D11, resulted in the formation of apoE/IgG complexes specifically in apoE4 mice. This was associated with reversal of the cognitive impairments of apoE4 in the Morris water maze and the novel object recognition test as well as with reversal of key apoE4-driven pathologies including the hyperphosphorylated tau and the reduced levels of the apoER2 receptor. These results indicate that anti-apoE4 immunotherapy counteracts the cognitive and brain pathological effects of apoE4, and suggest that such an approach could also benefit human apoE4 carriers.
Assuntos
Doença de Alzheimer/terapia , Anticorpos Monoclonais/administração & dosagem , Apolipoproteína E4/imunologia , Encéfalo/efeitos dos fármacos , Fatores Imunológicos/administração & dosagem , Doença de Alzheimer/metabolismo , Doença de Alzheimer/patologia , Animais , Apolipoproteína E3/imunologia , Encéfalo/metabolismo , Encéfalo/patologia , Modelos Animais de Doenças , Humanos , Imunização Passiva , Imunoglobulina G/metabolismo , Proteínas Relacionadas a Receptor de LDL/metabolismo , Masculino , Aprendizagem em Labirinto/efeitos dos fármacos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Neprilisina/antagonistas & inibidores , Neprilisina/metabolismo , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Neurônios/patologia , Nootrópicos/administração & dosagem , Fosforilação/efeitos dos fármacos , Reconhecimento Psicológico/efeitos dos fármacos , Proteínas tau/metabolismoRESUMO
The allele É4 of apolipoprotein E (apoE4) is the most prevalent genetic risk factor for Alzheimer's disease (AD) and is therefore a promising therapeutic target. Human and animal model studies suggest that apoE4 is hypolipidated; accordingly, we have previously shown that the retinoid X receptor (RXR) agonist bexarotene upregulates ABCA1, the main apoE-lipidating protein, resulting in increased lipidation of apoE4, and the subsequent reversal of the pathological effects of apoE4, namely: accumulation of Aß42 and hyperphosphorylated tau, as well as reduction in the levels of synaptic markers and cognitive deficits. Since the RXR system has numerous other targets, it is important to devise the means of activating ABCA1 selectively. We presently utilized CS-6253, a peptide shown to directly activate ABCA1 in vitro, and examined the extent to which it can affect the degree of lipidation of apoE4 in vivo and counteract the associated brain and behavioral pathologies. This revealed that treatment of young apoE4-targeted replacement mice with CS-6253 increases the lipidation of apoE4. This was associated with a reversal of the apoE4-driven Aß42 accumulation and tau hyperphosphorylation in hippocampal neurons, as well as of the synaptic impairments and cognitive deficits. These findings suggest that the pathological effects of apoE4 in vivo are associated with decreased activation of ABCA1 and impaired lipidation of apoE4 and that the downstream brain-related pathology and cognitive deficits can be counteracted by treatment with the ABCA1 agonist CS-6253. These findings have important clinical ramifications and put forward ABCA1 as a promising target for apoE4-related treatment of AD.
Assuntos
Transportador 1 de Cassete de Ligação de ATP/agonistas , Apolipoproteína E4/antagonistas & inibidores , Encéfalo/patologia , Transtornos Cognitivos/patologia , Peptídeos/farmacologia , Transportador 1 de Cassete de Ligação de ATP/metabolismo , Animais , Apolipoproteína E4/metabolismo , Encéfalo/efeitos dos fármacos , Transtornos Cognitivos/tratamento farmacológico , Transtornos Cognitivos/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Peptídeos/uso terapêuticoRESUMO
Apolipoprotein E4 (ApoE4), the most prevalent genetic risk factor for Alzheimer's disease (AD), is associated with increased neurodegeneration and vascular impairments. Vascular endothelial growth factor (VEGF), originally described as a key angiogenic factor, has recently been shown to play a crucial role in the nervous system. The objective of this research is to examine the role of VEGF in mediating the apoE4-driven pathologies. We show that hippocampal VEGF levels are lower in apoE4 targeted replacement mice compared to the corresponding apoE3 mice. This effect was accompanied by a specific decrease in both VEGF receptor-2 and HIF1-α. We next set to examine whether upregulation of VEGF can reverse apoE4-driven pathologies, namely the accumulation of hyperphosphorylated tau (AT8) and Aß42, and reduced levels of the pre-synaptic marker, VGluT1, and of the ApoE receptor, ApoER2. This was first performed utilizing intra-hippocampal injection of VEGF-expressing-lentivirus (LV-VEGF). This revealed that LV-VEGF treatment reversed the apoE4-driven cognitive deficits and synaptic pathologies. The levels of Aß42 and AT8, however, were increased in apoE3 mice, masking any potential effects of this treatment on the apoE4 mice. Follow-up experiments utilizing VEGF-expressing adeno-associated-virus (AAV-VEGF), which expresses VEGF specifically under the GFAP astrocytic promoter, prevented this effects on apoE3 mice, and reversed the apoE4-related increase in Aß42 and AT8. Taken together, these results suggest that apoE4-driven pathologies are mediated by a VEGF-dependent pathway, resulting in cognitive impairments and brain pathology. These animal model findings suggest that the VEGF system is a promising target for the treatment of apoE4 carriers in AD.
Assuntos
Apolipoproteína E4/metabolismo , Hipocampo/metabolismo , Hipocampo/patologia , Fator A de Crescimento do Endotélio Vascular/metabolismo , Peptídeos beta-Amiloides/metabolismo , Animais , Apolipoproteína E3/genética , Apolipoproteína E3/metabolismo , Apolipoproteína E4/genética , Dependovirus/genética , Modelos Animais de Doenças , Vetores Genéticos , Humanos , Subunidade alfa do Fator 1 Induzível por Hipóxia/metabolismo , Proteínas Relacionadas a Receptor de LDL/metabolismo , Lentivirus/genética , Masculino , Transtornos da Memória/metabolismo , Transtornos da Memória/patologia , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Fragmentos de Peptídeos/metabolismo , Sinapses/metabolismo , Sinapses/patologia , Fator A de Crescimento do Endotélio Vascular/genética , Receptor 2 de Fatores de Crescimento do Endotélio Vascular/metabolismo , Proteína Vesicular 1 de Transporte de Glutamato/metabolismo , Proteínas tau/metabolismoRESUMO
Apolipoprotein E4 (APOE ε4) is the most prevalent genetic risk factor for Alzheimer's disease (AD). Targeted replacement mice that express either APOE ε4 or its AD benign isoform, APOE ε3, are used extensively in behavioral, biochemical, and physiological studies directed at assessing the phenotypic effects of APOE ε4 and at unraveling the mechanisms underlying them. Such experiments often involve pursuing biochemical and behavioral measurements on the same cohort of mice. In view of the possible cross-talk interactions between brain parameters and cognitive performance, we presently investigated the extent to which the phenotypic expression of APOE ε4 and APOE ε4 in targeted replacement mice is affected by behavioral testing. This was performed using young, naïve APOE ε4 and APOE ε3 mice in which the levels of distinct brain parameters are affected by the APOE genotype (e.g., elevated levels of amyloid beta [Aß] and hyperphosphorylated tau and reduced levels of vesicular glutamate transporter (VGLUT) in hippocampal neurons of APOE ε4 mice). These mice were exposed to a fear-conditioning paradigm, and the resulting effects on the brain parameters were examined. The results obtained revealed that the levels of Aß, hyperphosphorylated tau, VGluT, and doublecortin of the APOE ε4 and APOE ε3 mice were markedly affected following the exposure of APOE ε4 and APOE ε3 mice to the fear-conditioning paradigm such that the isoform-specific effects of APOE ε4 on these parameters were greatly diminished. The finding that behavioral testing affects the APOE ε3 and APOE ε4 phenotypes and masks the differences between them has important theoretical and practical implications and suggests that the assessment of brain and behavioral parameters should be performed using different cohorts.
RESUMO
This study investigated the possible role of the ApoE receptors Lrp1 and Apoer2 in mediating the pathological effects of ApoE4 in ApoE-targeted-replacement mice expressing either the human ApoE3 or ApoE4 allele. In this study we show that activation of the amyloid cascade by inhibition of the Aß-degrading enzyme neprilysin results in upregulation of the ApoE receptor Lrp1 in the CA1 hippocampal neurons of 4-month-old ApoE4 mice, but not in the corresponding ApoE3 or ApoE-deficient (KO) mice. These results are in accordance with the previous findings that activation of the amyloid cascade induces Aß accumulation in the CA1 neurons of ApoE4 mice, but not in ApoE3 or ApoE-KO mice. This suggests that the apoE4-driven elevation of Lrp1 is mediated via a gain of function mechanism and may play a role in mediating the effects of ApoE4 on Aß. In contrast, no changes were observed in the levels of the corresponding Apoer2 receptor following the neprilysin inhibition. The ApoE receptors of naive ApoE4 mice were also affected differentially and isoform specifically by ApoE4. However, under these conditions, the effect was an ApoE4-driven reduction in the levels of Apoer2 in CA1 and CA3 pyramidal neurons, whereas the levels of Lrp1 were not affected. RT-PCR measurements revealed that the levels of Apoer2 and Lrp1 mRNA in the hippocampus of naïve and neprilysin-inhibited mice were not affected by ApoE4, suggesting that the observed effects of ApoE4 on the levels of these receptors is posttranscriptional. In conclusion, this study shows that the levels of hippocampal ApoE receptors Lrp1 and Apoer2 in vivo are affected isoform specifically by ApoE4 and that the type of receptor affected is context dependent.
Assuntos
Apolipoproteína E4/metabolismo , Hipocampo/metabolismo , Proteínas Relacionadas a Receptor de LDL/metabolismo , Células Piramidais/metabolismo , Receptores de LDL/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Peptídeos beta-Amiloides/metabolismo , Animais , Apolipoproteína E3/metabolismo , Hipocampo/efeitos dos fármacos , Humanos , Proteína-1 Relacionada a Receptor de Lipoproteína de Baixa Densidade , Lisossomos/metabolismo , Masculino , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Neprilisina/antagonistas & inibidores , Neprilisina/metabolismo , Inibidores de Proteases/farmacologia , Células Piramidais/efeitos dos fármacos , RNA Mensageiro/metabolismo , Transdução de Sinais/efeitos dos fármacos , Tiorfano/farmacologiaRESUMO
BACKGROUND: Recent findings suggest that the pathological effects of apoE4, the most prevalent genetic risk factor for Alzheimer's disease (AD), start many years before the onset of the disease and are already detectable at a young age. In the present study we investigated the extent to which such pathological and cognitive impairments also occur in young apoE4 mice. RESULTS: This study revealed that the levels of the presynaptic glutamatergic vesicular transporter, VGlut, in the CA3, CA1, and DG hippocampal subfields were lower in hippocampal neurons of young (4-month-old) apoE4-targeted replacement mice than in those of the apoE3 mice. In contrast, the corresponding inhibitory GABAergic nerve terminals and perikarya were not affected by apoE4.This synaptic effect was associated with hyperphosphorylation of tau in these neurons. In addition, apoE4 increased the accumulation of neuronal Aß42 and induced mitochondrial changes, both of which were specifically pronounced in CA3 neurons. Spatial navigation behavioral studies revealed that these hippocampal pathological effects of apoE4 are associated with corresponding behavioral impairments. Time-course studies revealed that the effects of apoE4 on tau hyperphosphorylation and the mitochondria were already apparent at the age of 1 month and that the apoE4-driven accumulation of neuronal Aß and reduced VGlut levels evolve later and are apparent at the age of 2-4 months. Furthermore, the levels of tau phosphorylation decrease in apoE3 mice and increase in apoE4 mice between 1 and 4 months, whereas the levels of Aß42 decrease in apoE3 mice and are not affected in apoE4 mice over the same time period. CONCLUSIONS: These findings show that apoE4 stimulates the accumulation of Aß42 and hyperphosphorylated tau and reduces the levels of VGlut in hippocampal neurons of young apoE4-targeted replacement mice and that these neurochemical effects are associated with cognitive impairments. This model is not associated with hypothesis-driven mechanistic manipulations and is thus most suitable for unbiased studies of the mechanisms underlying the pathological effects of apoE4.
Assuntos
Peptídeos beta-Amiloides/metabolismo , Apolipoproteína E4/genética , Hipocampo/patologia , Neurônios/patologia , Proteínas tau/metabolismo , Envelhecimento , Doença de Alzheimer/genética , Doença de Alzheimer/patologia , Animais , Comportamento Animal , Transtornos Cognitivos/genética , Transtornos Cognitivos/metabolismo , Transtornos Cognitivos/patologia , Ensaio de Imunoadsorção Enzimática , Imunofluorescência , Predisposição Genética para Doença , Hipocampo/metabolismo , Humanos , Immunoblotting , Imuno-Histoquímica , Camundongos , Camundongos Transgênicos , Microscopia Confocal , Neurônios/metabolismo , Fosforilação , Proteínas Vesiculares de Transporte de Glutamato/biossínteseRESUMO
Pyramidal neurons in the piriform cortex from olfactory-discrimination trained rats show enhanced intrinsic neuronal excitability that lasts for several days after learning. Such enhanced intrinsic excitability is mediated by long-term reduction in the post-burst after-hyperpolarization (AHP) which is generated by repetitive spike firing. AHP reduction is due to decreased conductance of a calcium-dependent potassium current, the sI(AHP). We have previously shown that learning-induced AHP reduction is maintained by persistent protein kinase C (PKC) and extracellular regulated kinase (ERK) activation. However, the molecular machinery underlying this long-lasting modulation of intrinsic excitability is yet to be fully described. Here we examine whether the CaMKII, which is known to be crucial in learning, memory and synaptic plasticity processes, is instrumental for the maintenance of learning-induced AHP reduction. KN93, that selectively blocks CaMKII autophosphorylation at Thr286, reduced the AHP in neurons from trained and control rat to the same extent. Consequently, the differences in AHP amplitude and neuronal adaptation between neurons from trained rats and controls remained. Accordingly, the level of activated CaMKII was similar in pirifrom cortex samples taken form trained and control rats. Our data show that although CaMKII modulates the amplitude of AHP of pyramidal neurons in the piriform cortex, its activation is not required for maintaining learning-induced enhancement of neuronal excitability.