Defective lysosomal proteolysis and axonal transport are early pathogenic events that worsen with age leading to increased APP metabolism and synaptic Abeta in transgenic APP/PS1 hippocampus

Background: Axonal pathology might constitute one of the earliest manifestations of Alzheimer disease. Axonal dystrophies were observed in Alzheimer’s patients and transgenic models at early ages. These axonal dystrophies could reflect the disruption of axonal transport and the accumulation of multiple vesicles at local points. It has been also proposed that dystrophies might interfere with normal intracellular proteolysis. In this work, we have investigated the progression of the hippocampal pathology and the possible implication in Abeta production in young (6 months) and aged (18 months) PS1(M146L)/APP(751sl) transgenic mice. Results: Our data demonstrated the existence of a progressive, age-dependent, formation of axonal dystrophies, mainly located in contact with congophilic Abeta deposition, which exhibited tau and neurofilament hyperphosphorylation. This progressive pathology was paralleled with decreased expression of the motor proteins kinesin and dynein. Furthermore, we also observed an early decrease in the activity of cathepsins B and D, progressing to a deep inhibition of these lysosomal proteases at late ages. This lysosomal impairment could be responsible for the accumulation of LC3-II and ubiquitinated proteins within axonal dystrophies. We have also investigated the repercussion of these deficiencies on the APP metabolism. Our data demonstrated the existence of an increase in the amyloidogenic pathway, which was reflected by the accumulation of hAPPfl, C99 fragment, intracellular Abeta in parallel with an increase in BACE and gamma-secretase activities. In vitro experiments, using APPswe transfected N2a cells, demonstrated that any imbalance on the proteolytic systems reproduced the in vivo alterations in APP metabolism. Finally, our data also demonstrated that Abeta peptides were preferentially accumulated in isolated synaptosomes. Conclusion: A progressive age-dependent cytoskeletal pathology along with a reduction of lysosomal and, in minor extent, proteasomal activity could be directly implicated in the progressive accumulation of APP derived fragments (and Abeta peptides) in parallel with the increase of BACE-1 and gamma-secretase activities. This retard in the APP metabolism seemed to be directly implicated in the synaptic Abeta accumulation and, in consequence, in the pathology progression between synaptically connected regions

Abnormal accumulation of autophagic vesicles correlates with axonal and synaptic pathology in young Alzheimer’s mice hippocampus

Dystrophic neurites associated with amyloid plaques precede neuronal death and manifest early in Alzheimer’s disease (AD). In this work we have characterized the plaque-associated neuritic pathology in the hippocampus of young (4- to 6-month-old) PS1M146L/ APP751SL mice model, as the initial degenerative process underlying functional disturbance prior to neuronal loss. Neuritic plaques accounted for almost all fibrillar deposits and an axonal origin of the dystrophies was demonstrated. The early induction of autophagy pathology was evidenced by increased protein levels of the autophagosome marker LC3 that was localized in the axonal dystrophies, and by electron microscopic identification of numerous autophagic vesicles filling and causing the axonal swellings. Early neuritic cytoskeletal defects determined by the presence of phosphorylated tau (AT8-positive) and actin–cofilin rods along with decreased levels of kinesin-1 and dynein motor proteins could be responsible for this extensive vesicle accumulation within dystrophic neurites. Although microsomal Ab oligomers were identified, the presence of A11-immunopositive Ab plaques also suggested a direct role of plaque-associated Ab oligomers in defective axonal transport and disease progression. Most importantly, presynaptic terminals morphologically disrupted by abnormal autophagic vesicle buildup were identified ultrastructurally and further supported by synaptosome isolation. Finally, these early abnormalities in axonal and presynaptic structures might represent the morphological substrate of hippocampal dysfunction preceding synaptic and neuronal loss and could significantly contribute to AD pathology in the preclinical stages.Fondo de Investigación Sanitaria (FIS). Instituto de Salud Carlos III, España. PS09/00099, PS09/00151, PS09/00848 y PS09/00376Junta de Andalucía. SAS P09/496 y CTS-479

Factores implicados en la neurodegeneración y el aumento de aβ oligomérico soluble durante el proceso de envejecimiento en un modelo ps1m146lxappsl de la enfermedad de alzheimer

Los Objetivos del Trabajo son: 1. Identificación de la presencia de péptido β-amiloide soluble en el medio extracelular y caracterización de las posibles form as oligoméricas presentes en un modelo murino PS1M146LxAPP751-SL de la enfermedad de Alzheimer durante el proceso de envejecimiento del animal. 2. Determinación de la capacidad de las formas oligoméricas de Aβ para interrumpir las vías de señalización mediadas por neurotrofinas. 2.1 Estudio de la implicación del péptido APPα soluble en la fosforilación de GSK-3β a través de los receptores de insulina e IGF-1 y de la vía PI3KAKT- GSK-3β. 2.2 Estudio del efecto de las formas oligoméricas de Aβ en la inhibición de la fosforilación de fosforilación de GSK-3β a través de los receptores de insulina e IGF-1 y de la vía PI3K-AKT-GSK-3β. 3. Estudio de los mecanismos moleculares y celulares posiblemente implicados en un incremento de la concentración de formas oligoméricas de Aβ durante el proceso de envejecimiento en los animales PS1xAPP. 3.1 Estudio del procesamiento de la proteína APP y de las enzimas implicadas en la ruta de producción del β-amiloide. 3.2 Estudio de la implicación de los dominios de membrana del tipo Raft lipídicos en el procesamiento de APP. 3.3 Identificación de las evidencias celulares y bioquímicas asociadas a la alteración en los sistemas de transporte vesicular a nivel axonal. 3.4 Estudio de la acumulación de los precursores del β-amiloide en vesículas autofágicas y de las deficiencias en la degradación de las proteínas acumuladas por vía lisosomal. 3.5 Estudio de la acumulación del péptido β-amiloide en sinaptosomas como posible origen de los oligómeros solubles de Aβ. 3.6 Estudio de las formas oligoméricas de Aβ presentes en las placas, como posible fuente de oligómeros solubles de Aβ. Ver meno