Transmissible long-term neuroprotective and pro-cognitive effects of 1-42 beta-amyloid with A2T icelandic mutation in an Alzheimer's disease mouse model.

ABSTRACT

The amyloid cascade hypothesis assumes that the development of Alzheimer's disease (AD) is driven by a self-perpetuating cycle, in which ß-amyloid (Aß) accumulation leads to Tau pathology and neuronal damages. A particular mutation (A673T) of the amyloid precursor protein (APP) was identified among Icelandic population. It provides a protective effect against Alzheimer- and age-related cognitive decline. This APP mutation leads to the reduced production of Aß with A2T (position in peptide sequence) change (Aßice). In addition, Aßice has the capacity to form protective heterodimers in association with wild-type Aß. Despite the emerging interest in Aßice during the last decade, the impact of Aßice on events associated with the amyloid cascade has never been reported. First, the effects of Aßice were evaluated in vitro by electrophysiology on hippocampal slices and by studying synapse morphology in cortical neurons. We showed that Aßice protects against endogenous Aß-mediated synaptotoxicity. Second, as several studies have outlined that a single intracerebral administration of Aß can worsen Aß deposition and cognitive functions several months after the inoculation, we evaluated in vivo the long-term effects of a single inoculation of Aßice or Aß-wild-type (Aßwt) in the hippocampus of transgenic mice (APPswe/PS1dE9) over-expressing Aß1-42 peptide. Interestingly, we found that the single intra-hippocampal inoculation of Aßice to mice rescued synaptic density and spatial memory losses four months post-inoculation, compared with Aßwt inoculation. Although Aß load was not modulated by Aßice infusion, the amount of Tau-positive neuritic plaques was significantly reduced. Finally, a lower phagocytosis by microglia of post-synaptic compounds was detected in Aßice-inoculated animals, which can partly explain the increased density of synapses in the Aßice animals. Thus, a single event as Aßice inoculation can improve the fate of AD-associated pathology and phenotype in mice several months after the event. These results open unexpected fields to develop innovative therapeutic strategies against AD.