RESUMO
Neurons subject to degeneration in Alzheimer's disease (AD) exhibit evidence of re-entry into a mitotic cell cycle even before the development of substantial AD brain pathology. In efforts to identify the initiating factors underlying these cell cycle events (CCEs), we have characterized the appearance of the neuronal CCEs in the genomic-based R1.40 transgenic mouse model of AD. Notably, R1.40 mice exhibit neuronal CCEs in a reproducible temporal and spatial pattern that recapitulates the neuronal vulnerability seen in human AD. Neuronal CCEs first appear at 6 months in the frontal cortex layers II/III. This is 6-8 months before detectable amyloid beta (Abeta) deposition, suggesting that specific amyloid precursor protein (APP) processing products are responsible for the induction of neuronal CCEs. Furthermore, a reduction in the levels of Abeta (achieved by shifting the genetic background from C57BL/6 to the DBA/2 mouse strain) dramatically delays the appearance of neuronal CCEs. More significantly, elimination of beta-secretase activity blocks the appearance of CCEs, providing direct genetic evidence that the amyloidogenic processing of APP is required for the induction of CCEs. Finally, in vitro preparations of oligomeric, but not monomeric, Abeta induce DNA synthesis in dissociated cortical neurons, and this response is blocked by antioligomer specific antibodies. Together, our data suggest that low molecular weight aggregates of Abeta induce neuronal cell cycle re-entry in mouse models of Alzheimer's disease.
Assuntos
Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/farmacologia , Ciclo Celular/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Fragmentos de Peptídeos/farmacologia , Fatores Etários , Doença de Alzheimer/genética , Secretases da Proteína Precursora do Amiloide/deficiência , Precursor de Proteína beta-Amiloide/genética , Animais , Ácido Aspártico Endopeptidases/deficiência , Bromodesoxiuridina/metabolismo , Proteínas de Ciclo Celular/metabolismo , Células Cultivadas , Córtex Cerebral/patologia , Modelos Animais de Doenças , Embrião de Mamíferos , Regulação da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica/genética , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Proteínas Associadas aos Microtúbulos/metabolismo , Mutação/genéticaRESUMO
The cells of Haloarcula vallismortis, an extreme halophilic archaebacterium, were permeabilized by various chemical, physical, and biological treatments. Biological permeabilization by lysozyme and papain showed effective results as observed by studying the in situ activity of halophilic glyceraldehyde-3-phosphate dehydrogenase (hGAPDH) as the model enzyme. Detergents N-cetyl-N, N, N-trimethyl ammonium bromide (CTAB) and digitonin also showed significant results. Other strains of halobacteria could also be permeabilized by lysozyme. The cell morphology did not show any significant change after permeabilization as observed by phase contrast microscopy. The enzyme characteristics of hGAPDH were studied in situ using permeabilized H. vallismortis cells. The properties, like optimum pH, Km for GAP and NAD(+), inhibition by heavy metals, sulphydryl reagents, and other compounds, showed remarkable similarity with those studied in vitro.