Hyper-expression of human apolipoprotein E4 in astroglia and neurons does not enhance amyloid deposition in transgenic mice

Recent studies in mice have clearly demonstrated that eliminating Apo E alt ers the rate, character and distribution of A beta deposits. In the present study, we asked whether elevating the levels of Apo E can, in a dominant f ashion, influence amyloid deposition. We expressed human (Hu) Apo E4 via th e mouse prion protein promoter, resulting in high expression in both astroc ytes and neurons; only astrocytes efficiently secreted Hu Apo E4 (at least 5-fold more than endogenous). Mice hyper-expressing Hu Apo E4 developed nor mally and lived normal lifespans. The co-expression of Hu Apo E4 with a mut ant amyloid precursor protein (APP) (Mo/Hu APPswe) or mutant APP and mutant presenilin (PS1dE9) did not lead to proportional changes in the age of app earance, relative burden, character or distribution of A beta deposits. We suggest that these data are best explained by proposing that the mechanisms by which Apo E influences A beta deposition involves an aspect of its norm al function that is not augmented by hyper-expression.