RESUMEN
UNLABELLED: Essentials Evidence suggests a comorbidity between hyperhomocysteinemia (HHC) and Alzheimer's disease (AD). Homocysteine (HC) could affect the ß-amyloid (Aß)-fibrinogen interaction in AD pathology. AD patients with concomitant HHC have increased fibrin and Aß deposits in their brains. HC contributes to AD pathology via the Aß-fibrinogen interaction. SUMMARY: Background Accumulating clinical evidence suggests that hyperhomocysteinemia (HHC) is correlated with Alzheimer's disease (AD) and vascular dementia. Objective This study was carried out to elucidate the specific role of elevated homocysteine (HC) levels in AD pathophysiology. Methods Immunohistochemistry was used to examine ß-amyloid (Aß) deposition along blood vessels, also known as cerebral amyloid angiopathy (CAA), fibrin(ogen) deposition, and their correlation to each other in the brains of AD patients with and without HHC. To study AD-HHC co-morbidity in detail, an AD mouse model was administered a high methionine diet for several months. Parenchymal Aß plaques, CAA-positive vessels and fibrin deposits were then assessed by immunohistochemistry at different stages of AD progression. Memory deficits were evaluated with contextual fear conditioning and the Barnes maze. Additionally, the effect of HC and its metabolite, homocysteine thiolactone (HCTL), on the Aß-fibrinogen interaction was analyzed by pull-down, ELISA and fibrin clot formation and fibrinolysis assays in vitro. Results We found increased fibrin(ogen) levels and Aß deposits in the blood vessels and brain parenchyma of AD patients with HHC. We demonstrate that HC and HCTL enhance the interaction between fibrinogen and Aß, promote the formation of tighter fibrin clots and delay clot fibrinolysis. Additionally, we show that diet-induced HHC in an AD mouse model leads to severe CAA and parenchymal Aß deposition, as well as significant impairments in learning and memory. Conclusions These findings suggest that elevated levels of plasma HC/HCTL contribute to AD pathology via the Aß-fibrin(ogen) interaction.
Asunto(s)
Enfermedad de Alzheimer/complicaciones , Péptidos beta-Amiloides/química , Fibrinógeno/química , Hiperhomocisteinemia/complicaciones , Enfermedad de Alzheimer/tratamiento farmacológico , Animales , Biotinilación , Encéfalo/patología , Angiopatía Amiloide Cerebral/patología , Demencia Vascular/complicaciones , Demencia Vascular/tratamiento farmacológico , Modelos Animales de Enfermedad , Progresión de la Enfermedad , Fibrina/química , Fibrinólisis , Humanos , Hiperhomocisteinemia/tratamiento farmacológico , Inmunohistoquímica , Aprendizaje por Laberinto , Memoria , Metionina/química , Ratones , Ratones Transgénicos , Placa Amiloide/patología , Unión ProteicaRESUMEN
BACKGROUND: Excess fibrin in blood vessels is cleared by plasmin, the key proteolytic enzyme in fibrinolysis. Neurological disorders and head trauma can result in the disruption of the neurovasculature and the entry of fibrin and other blood components into the brain, which may contribute to further neurological dysfunction. OBJECTIVES: While chronic fibrin deposition is often implicated in neurological disorders, the pathological contributions attributable specifically to fibrin have been difficult to ascertain. An animal model that spontaneously acquires fibrin deposits could allow researchers to better understand the impact of fibrin in neurological disorders. METHODS: Brains of plasminogen (plg)- and tissue plasminogen activator (tPA)-deficient mice were examined and characterized with regard to fibrin accumulation, vascular and neuronal health, and inflammation. Furthermore, the inflammatory response following intrahippocampal lipopolysaccharide (LPS) injection was compared between plg(-/-) and wild type (WT) mice. RESULTS AND CONCLUSIONS: Both plg(-/-) and tPA(-/-) mice exhibited brain parenchymal fibrin deposits that appear to result from reduced neurovascular integrity. Markers of neuronal health and inflammation were not significantly affected by proximity to the vascular lesions. A compromised neuroinflammatory response was also observed in plg(-/-) compared to WT mice following intrahippocampal LPS injection. These results demonstrate that fibrin does not affect neuronal health in the absence of inflammation and suggest that plasmin may be necessary for a normal neuroinflammatory response in the mouse CNS.
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Encéfalo/metabolismo , Fibrina/metabolismo , Fibrinolisina/deficiencia , Plasminógeno/genética , Animales , Astrocitos/metabolismo , Encéfalo/patología , Femenino , Fibrinolisina/genética , Fibrinolisina/metabolismo , Fibrinólisis , Hipocampo/metabolismo , Inflamación , Lipopolisacáridos/química , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Neuronas/metabolismo , Activador de Tejido Plasminógeno/genéticaRESUMEN
Though the GluK4 kainate receptor subunit shows limited homology and a restricted expression pattern relative to other kainate receptor subunits, its ablation results in distinct behavioral and molecular phenotypes. GluK4 knockout mice demonstrated impairments in memory acquisition and recall in a Morris water maze test, suggesting a previously unreported role for kainate receptors in spatial memory. GluK4 knockout mice also showed marked hyperactivity and impaired pre-pulse inhibition, thereby mirroring two of the hallmark endophenotypes of patients with schizophrenia and bipolar disorder. Furthermore, we found that GluK4 is a key mediator of excitotoxic neurodegeneration: GluK4 knockout mice showed robust neuroprotection in the CA3 region of the hippocampus following intrahippocampal injection of kainate and widespread neuroprotection throughout the hippocampus following hypoxia-ischemia. Biochemical analysis of kainate- or sham-treated wild-type and GluK4 knockout hippocampal tissue suggests that GluK4 may act through the JNK pathway to regulate the molecular cascades that lead to excitotoxicity. Together, our findings suggest that GluK4 may be relevant to the understanding and treatment of human neuropsychiatric and neurodegenerative disorders.
Asunto(s)
Afecto/fisiología , Memoria/fisiología , Enfermedades Neurodegenerativas/inducido químicamente , Enfermedades Neurodegenerativas/genética , Receptores de Ácido Kaínico/fisiología , Animales , Western Blotting , Isquemia Encefálica/fisiopatología , Isquemia Encefálica/psicología , Región CA3 Hipocampal/fisiología , Muerte Celular/efectos de los fármacos , Potenciales Evocados Auditivos del Tronco Encefálico/efectos de los fármacos , Agonistas de Aminoácidos Excitadores/administración & dosificación , Agonistas de Aminoácidos Excitadores/toxicidad , Hipocampo , Hipoxia Encefálica/fisiopatología , Hipoxia Encefálica/psicología , Proteínas Quinasas JNK Activadas por Mitógenos/genética , Ácido Kaínico/administración & dosificación , Ácido Kaínico/toxicidad , Aprendizaje por Laberinto/efectos de los fármacos , Aprendizaje por Laberinto/fisiología , Ratones , Ratones Noqueados , Microinyecciones , Actividad Motora/efectos de los fármacos , Neuronas/efectos de los fármacos , Receptores de Ácido Kaínico/genética , Reflejo de Sobresalto/efectos de los fármacos , Técnicas Estereotáxicas , Accidente Cerebrovascular/genética , Accidente Cerebrovascular/patologíaRESUMEN
Brain lesions containing filamentous and aggregated alpha-synuclein are hallmarks of neurodegenerative synucleinopathies. Oxidative stress has been implicated in the formation of these lesions. Using HEK 293 cells stably transfected with wild-type and mutant alpha-synuclein, we demonstrated that intracellular generation of nitrating agents results in the formation of alpha-synuclein aggregates. Cells were exposed simultaneously to nitric oxide- and superoxide-generating compounds, and the intracellular formation of peroxynitrite was demonstrated by monitoring the oxidation of dihydrorhodamine 123 and the nitration of alpha-synuclein. Light microscopy using antibodies against alpha-synuclein and electron microscopy revealed the presence of perinuclear aggregates under conditions in which peroxynitrite was generated but not when cells were exposed to nitric oxide- or superoxide-generating compounds separately. alpha-Synuclein aggregates were observed in 20-30% of cells expressing wild-type or A53T mutant alpha-synuclein and in 5% of cells expressing A30P mutant alpha-synuclein. No evidence of synuclein aggregation was observed in untransfected cells or cells expressing beta-synuclein. In contrast, selective inhibition of the proteasome resulted in the formation of aggregates detected with antibodies to ubiquitin in the majority of the untransfected cells and cells expressing alpha-synuclein. However, alpha-synuclein did not colocalize with these aggregates, indicating that inhibition of the proteasome does not promote alpha-synuclein aggregation. In addition, proteasome inhibition did not alter the steady-state levels of alpha-synuclein, but addition of the lysosomotropic agent ammonium chloride significantly increased the amount of alpha-synuclein, indicating that lysosomes are involved in degradation of alpha-synuclein. Our data indicate that nitrative and oxidative insult may initiate pathogenesis of alpha-synuclein aggregates.