Comparative transcriptome analysis of APPsα-DM and APLP2-KO brains

Despite its key role in Alzheimer pathogenesis, the physiological function(s) of the amyloid precursor protein (APP) and of its proteolytic fragments are still poorly understood. The secreted APPsα ectodomain has been shown to be involved in neuroprotection and synaptic plasticity. The γ-secretase generated APP intracellular domain, AICD, functions as a transcriptional regulator in heterologous reporter assays although its role for endogenous gene regulation has remained controversial. Previously, we have generated APPsα knockin (KI) mice expressing solely the secreted ectodomain APPsα. Here, we generated double mutants (APPsα-DM) by crossing APPsα-KI mice onto an APLP2-deficient background and show that APPsα rescues the postnatal lethality of the majority of APP/APLP2 double knockout mice. Despite normal CNS morphology and unaltered basal synaptic transmission, young APPsα-DM mice already showed pronounced hippocampal dysfunction, impaired spatial learning and a deficit in LTP. To gain further mechanistic insight into which domains/proteolytic fragments are crucial for hippocampal APP/APLP2 mediated functions, we performed a DNA microarray transcriptome profiling of prefrontal cortex and hippocampus of adult APLP2-KO (APLP2-/-) and APPsα-DM mice (APPα/αAPLP2-/- mice).Interestingly, this analysis failed to reveal major genotype-related transcriptional differences. Expression differences between cortex and hippocampus were, however, readily detectable. Prefrontal cortices and hippocampi of adult mice (38 - 40 weeks) of the following genotypes were analyzed: APLP2-KO (APLP2-/-) (n=3) and APPsα-DM (APPα/αAPLP2-/-) (n=3).