Beta-site APR cleaving enzyme (BACE1) is the rate-limiting enzyme in the production of amyloid (3 (Ap), the primary constituent of senile plaques in the brains of Alzheimer's disease (AD) patients. Evidence that BACE1 is up-regulated post-transcriptionally in response to energy inhibition, studies indicating that glucose metabolism is reduced in AD brains, and the observation that BACE1 protein levels are increased in post- mortem AD brains all support the hypothesis that post-transcriptional up-regulation of BACE1 in response to energy deprivation in the brain may, in part, be responsible for AP accumulation in sporadic Alzheimer's disease (SAD)- the predominant form of AD.
The aim of this study is to identify the specific post- transcriptional mechanism and signaling pathway(s) leading to BACE1 up-regulation in response to energy deprivation in vitro and in vivo. Preliminary studies in 293 cells indicate that BACE1 protein increases in response to energy deprivation are mediated by the BACE1 5'-untranslated region (UTR). First, we will determine whether a similar mechanism controls BACE1 protein levels in response to energy deprivation in cultured neurons. Then, luciferase reporter assays will be used to determine whether the BACE1 5'UTR is responsible for BACE1 protein increases under glucose-deficient conditions in both 293 cells and cultured neurons. Acute pharmacological induction of metabolic stress in a transgenic mouse line lacking the BACE1 5'UTR will be used to confirm this mechanism in vivo. Preliminary experiments indicate that phosphorylation of the alpha subunit of the eukaryotic translation initiation factor 2 (elF2alpha) may be mediating post-transcriptional increases in BACE1 protein under conditions of energy deprivation. We will use 293 cells and neurons deprived of glucose in vitro, as well as brains from mice subjected to acute and chronic energy deprivation to test for activation of kinases known to phosphorylate elF2alpha. We will then determine whether pharmacological induction of elF2alpha phosphorylation through treatment with thapsigargin leads to post-transcriptional increases in BACE1 protein in vitro. Finally, to establish this pathway as potential AD drug target, we will inhibit elF2alpha phosphorylation in vitro to determine whether BACE1 protein up-regulation can be blocked under glucose-deficient conditions. The predicted increase in AD occurrence and the current lack of effective treatment options have made the development of new and more effective drugs for AD treatment a public health priority. Completion of these aims will identify novel drug targets for the development of preventative AD therapies. ? ? ? ?
|O'Connor, Tracy; Sadleir, Katherine R; Maus, Erika et al. (2008) Phosphorylation of the translation initiation factor eIF2alpha increases BACE1 levels and promotes amyloidogenesis. Neuron 60:988-1009|