Genetic Inhibition of Phosphorylation of the Translation Initiation Factor eIF2a Does Not Block Ab-Dependent Elevation of BACE1 and APP Levels or Reduce Amyloid Pathology in a Mouse Model of Alzheimer’s Disease

b-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) initiates the production of b-amyloid (Ab), the major constituent of amyloid plaques in Alzheimer’s disease (AD). BACE1 is elevated,2–3 fold in AD brain and is concentrated in dystrophic neurites near plaques, suggesting BACE1 elevation is Ab2dependent. Previously, we showed that phosphorylation of the translation initiation factor eIF2a de-represses translation of BACE1 mRNA following stress such as energy deprivation. We hypothesized that stress induced by Ab might increase BACE1 levels by the same translational mechanism involving eIF2a phosphorylation. To test this hypothesis, we used three different genetic strategies to determine the effects of reducing eIF2a phosphorylation on Ab-dependent BACE1 elevation in vitro and in vivo: 1) a two-vector adeno-associated virus (AAV) system to express constitutively active GADD34, the regulatory subunit of PP1c eIF2a phosphatase; 2) a non-phosphorylatable eIF2a S51A knockin mutation; 3) a BACE1-YFP transgene lacking the BACE1 mRNA 59 untranslated region (UTR) required for eIF2a translational regulation. The first two strategies were used in primary neurons and 5XFAD transgenic mice, while the third strategy was employed only in 5XFAD mice. Despite very effective reduction of eIF2a phosphorylation in both primary neurons and 5XFAD brains, or elimination of eIF2a-mediated regulation of BACE1-YFP mRNA translation in 5XFAD brains, Ab-dependent BACE1 elevation was not decreased. Additionally, robust inhibition of eIF2a phosphorylation did not block Ab-dependent APP elevation in primary neurons, nor did it reduc