RESUMEN
The E693Q mutation in the amyloid beta precursor protein (APP) leads to cerebral amyloid angiopathy (CAA), with recurrent cerebral hemorrhagic strokes and dementia. In contrast to Alzheimer disease (AD), the brains of those affected by hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D) show few parenchymal amyloid plaques. We found that neuronal overexpression of human E693Q APP in mice (APPDutch mice) caused extensive CAA, smooth muscle cell degeneration, hemorrhages and neuroinflammation. In contrast, overexpression of human wild-type APP (APPwt mice) resulted in predominantly parenchymal amyloidosis, similar to that seen in AD. In APPDutch mice and HCHWA-D human brain, the ratio of the amyloid-beta40 peptide (Abeta40) to Abeta42 was significantly higher than that seen in APPwt mice or AD human brain. Genetically shifting the ratio of AbetaDutch40/AbetaDutch42 toward AbetaDutch42 by crossing APPDutch mice with transgenic mice producing mutated presenilin-1 redistributed the amyloid pathology from the vasculature to the parenchyma. The understanding that different Abeta species can drive amyloid pathology in different cerebral compartments has implications for current anti-amyloid therapeutic strategies. This HCHWA-D mouse model is the first to develop robust CAA in the absence of parenchymal amyloid, highlighting the key role of neuronally produced Abeta to vascular amyloid pathology and emphasizing the differing roles of Abeta40 and Abeta42 in vascular and parenchymal amyloid pathology.
Asunto(s)
Péptidos beta-Amiloides/metabolismo , Amiloidosis/metabolismo , Vasos Sanguíneos/metabolismo , Hemorragia Cerebral/metabolismo , Modelos Animales de Enfermedad , Factores de Edad , Anciano , Anciano de 80 o más Años , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Amiloidosis/complicaciones , Animales , Vasos Sanguíneos/patología , Vasos Sanguíneos/ultraestructura , Western Blotting/métodos , Encéfalo/metabolismo , Encéfalo/patología , Hemorragia Cerebral/complicaciones , Circulación Cerebrovascular , Encefalitis/etiología , Encefalitis/metabolismo , Encefalitis/patología , Ensayo de Inmunoadsorción Enzimática/métodos , Ácido Glutámico/genética , Glutamina/genética , Humanos , Inmunohistoquímica/métodos , Hibridación in Situ , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Microscopía Electrónica/métodos , Persona de Mediana Edad , Mutación/genética , Fragmentos de Péptidos/metabolismo , Piamadre/metabolismo , Cambios Post Mortem , Antígenos Thy-1/genéticaRESUMEN
APP23 transgenic mice overexpressing amyloid precursor protein (APP751) reproduce neuropathological changes associated with Alzheimer's disease such as high levels of amyloid plaques, cerebral amyloid angiopathy, and associated vascular pathologies. Functional magnetic resonance imaging (fMRI) was applied to characterize brain functionality in these mice through global pharmacological stimulation. The cerebral hemodynamic response to infusion of the GABA(A) antagonist bicuculline was significantly reduced in aged APP23 mice compared with age-matched wild-type littermates. This is in part attributable to a compromised cerebrovascular reactivity, as revealed by the reduced responsiveness to vasodilatory stimulation by acetazolamide. The study shows that fMRI is a sensitive tool to phenotype genetically engineered animals modeling neuropathologies.
Asunto(s)
Enfermedad de Alzheimer/fisiopatología , Precursor de Proteína beta-Amiloide/biosíntesis , Encéfalo/irrigación sanguínea , Encéfalo/fisiopatología , Hemodinámica , Acetazolamida/farmacología , Factores de Edad , Enfermedad de Alzheimer/genética , Precursor de Proteína beta-Amiloide/genética , Animales , Bicuculina/farmacología , Peso Corporal , Encéfalo/efectos de los fármacos , Inhibidores de Anhidrasa Carbónica/farmacología , Circulación Cerebrovascular/efectos de los fármacos , Circulación Cerebrovascular/genética , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Resistencia a Medicamentos/genética , Antagonistas del GABA/farmacología , Antagonistas de Receptores de GABA-A , Hemodinámica/efectos de los fármacos , Hemodinámica/genética , Humanos , Imagen por Resonancia Magnética , Ratones , Ratones Transgénicos , FenotipoRESUMEN
Alzheimer's Disease (AD) is a neurodegenerative disorder that is characterized by extracellular deposits of amyloid-beta peptide (Abeta) and a severe depletion of the cholinergic system, although the relationship between these two events is poorly understood. In the neocortex, there is a loss of cholinergic fibers and receptors and a decrease of both choline acetyltransferase (ChAT) and acetylcholinesterase enzyme activities. The nucleus basalis of Meynert (NBM), which provides the major cholinergic input to the neocortex, undergoes profound neuron loss in AD. In the present study, we have examined the cholinergic alterations in amyloid precursor protein transgenic mice (APP23), a mouse model of cerebral beta-amyloidosis. In aged APP23 mice, our results reveal modest decreases in cortical cholinergic enzyme activity compared with age-matched wild-type mice. Total cholinergic fiber length was more severely affected, with 29 and 35% decreases in the neocortex of aged APP23 mice compared with age-matched wild-type mice and young transgenic mice, respectively. However, there was no loss of cholinergic basal forebrain neurons in these aged APP23 mice, suggesting that the cortical cholinergic deficit in APP23 mice is locally induced by the deposition of amyloid and is not caused by a loss of cholinergic basal forebrain neurons. To study the impact of cholinergic basal forebrain degeneration on cortical amyloid deposition, we performed unilateral NBM lesions in adult APP23 mice. Three to 8 months after lesioning, a 38% reduction in ChAT activity and significant cholinergic fiber loss were observed in the ipsilateral frontal cortex. There was a 19% decrease in Abeta levels of the ipsilateral compared with contralateral frontal cortex with no change in the ratio of Abeta40 to Abeta42. We conclude that the severe cholinergic deficit in AD is caused by both the loss of cholinergic basal forebrain neurons and locally by cerebral amyloidosis in the neocortex. Moreover, our results suggest that disruption of the basal cholinergic forebrain system does not promote cerebral amyloidosis in APP23 transgenic mice.
Asunto(s)
Precursor de Proteína beta-Amiloide/metabolismo , Amiloidosis/patología , Fibras Colinérgicas/patología , Acetilcolinesterasa/metabolismo , Envejecimiento/metabolismo , Enfermedad de Alzheimer/patología , Enfermedad de Alzheimer/fisiopatología , Amiloide/análisis , Precursor de Proteína beta-Amiloide/genética , Amiloidosis/fisiopatología , Animales , Núcleo Basal de Meynert/patología , Recuento de Células , Tamaño de la Célula , Colina O-Acetiltransferasa/metabolismo , Modelos Animales de Enfermedad , Progresión de la Enfermedad , Femenino , Lóbulo Frontal/enzimología , Lóbulo Frontal/patología , Inmunohistoquímica , Masculino , Ratones , Ratones Transgénicos , Neocórtex/química , Neocórtex/patología , Neuronas/enzimología , Neuronas/patología , Prosencéfalo/enzimología , Prosencéfalo/patologíaRESUMEN
beta-Site APP-cleaving enzyme (BACE) initiates the processing of the amyloid precursor protein (APP) leading to the generation of beta-amyloid, the main component of Alzheimer's disease senile plaques. BACE (Asp2, memapsin 2) is a type I transmembrane aspartyl protease and is responsible for the beta-secretase cleavage of APP producing different endoproteolytic fragments referred to as the carboxy-terminal C99, C89 and the soluble ectodomain sAPPbeta. Here we describe two transgenic mouse lines expressing human BACE in the brain. Overexpression of BACE augments the amyloidogenic processing of APP as demonstrated by decreased levels of full-length APP and increased levels of C99 and C89 in vivo. In mice expressing huBACE in addition to human APP wild-type or carrying the Swedish mutation, the induction of APP processing characterized by elevated C99, C89 and sAPPbeta, results in increased brain levels of beta-amyloid peptides Abeta40 and Abeta42 at steady-state.
Asunto(s)
Péptidos beta-Amiloides/metabolismo , Ácido Aspártico Endopeptidasas/metabolismo , Encéfalo/metabolismo , Secretasas de la Proteína Precursora del Amiloide , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Animales , Ácido Aspártico Endopeptidasas/genética , Western Blotting , Endopeptidasas , Expresión Génica , Humanos , Hibridación in Situ , Ratones , Ratones Transgénicos , Mutación , Neuronas/citología , Neuronas/metabolismo , Fragmentos de Péptidos/metabolismo , Procesamiento Proteico-Postraduccional , ARN Mensajero/análisis , ARN Mensajero/metabolismo , TransgenesRESUMEN
The Cu-binding beta-amyloid precursor protein (APP), and the amyloid Abeta peptide have been proposed to play a role in physiological metal regulation. There is accumulating evidence of an unbalanced Cu homeostasis with a causative or diagnostic link to Alzheimer's disease. Whereas elevated Cu levels are observed in APP knockout mice, APP overexpression results in reduced Cu in transgenic mouse brain. Moreover, Cu induces a decrease in Abeta levels in APP-transfected cells in vitro. To investigate the influence of bioavailable Cu, transgenic APP23 mice received an oral treatment with Cu-supplemented sucrose-sweetened drinking water (1). Chronic APP overexpression per se reduced superoxide dismutase 1 activity in transgenic mouse brain, which could be restored to normal levels after Cu treatment (2). A significant increase of brain Cu indicated its bioavailability on Cu treatment in APP23 mice, whereas Cu levels remained unaffected in littermate controls (3). Cu treatment lowered endogenous CNS Abeta before a detectable reduction of amyloid plaques. Thus, APP23 mice reveal APP-induced alterations linked to Cu homeostasis, which can be reversed by addition of dietary Cu.