Physiological Control of Nitric Oxide in Neuronal BACE1 Translation by Heme-Regulated eIF2α Kinase HRI Induces Synaptogenesis

Hippocampus is the brain center for memory formation, a process that requires synaptogenesis. However, hippocampus is dramatically compromised in Alzheimer's disease due to the accumulation of amyloid β-peptide, whose production is initiated by β-site APP Cleaving Enzyme 1 (BACE1). It is known that pathological stressors activate BACE1 translation through the phosphorylation of the eukaryotic initiation factor-2α (eIF2α) by GCN2, PERK, or PKR kinases, leading to amyloidogenesis. However, BACE1 physiological regulation is still unclear. Since nitric oxide (NO) participates directly in hippocampal glutamatergic signaling, we investigated the neuronal role of the heme-regulated eukaryotic initiation factor eIF2α kinase (HRI), which can bind NO by a heme group, in BACE1 translation and its physiological consequences. We found that BACE1 is expressed on glutamate activation with NO being the downstream effector by triggering eIF2α phosphorylation, as it was obtained by Western blot and luciferase assay. It is due to the activation of HRI by NO as assayed by Western blot and immunofluorescence with an HRI inhibitor and HRI siRNA. BACE1 expression was early detected at synaptic spines, contributing to spine growth and consolidating the hippocampal memory as assayed with mice treated with HRI or neuronal NO synthase inhibitors. We provide the first description that HRI and eIF2α are working in physiological conditions in the brain under the control of nitric oxide and glutamate signaling, and also that BACE1 has a physiological role in hippocampal function. We conclude that BACE1 translation is controlled by NO through HRI in glutamatergic hippocampal synapses, where it plays physiological functions, allowing the spine growth and memory consolidation.