Insulin-Degrading Enzyme as a Downstream Target of Insulin Receptor Signaling Cascade: Implications for Alzheimer's Disease Intervention

Open Access
Publisher Website
Google Scholar
Abstract
Insulin-degrading enzyme (IDE) is one of the proteins that has been demonstrated to play a key role in degrading β-amyloid (Aβ) monomerin vitroandin vivo, raising the possibility of upregulating IDE as an approach to reduce Aβ. Little is known, however, about the cellular and molecular regulation of IDE protein. Because one of the main functions of IDE is to degrade insulin, we hypothesized that there is a negative feedback mechanism whereby stimulation of insulin receptor-mediated signaling upregulates IDE to prevent chronic activation of the pathway. We show that treatment of primary hippocampal neurons with insulin increased IDE protein levels by ∼25%. Insulin treatment also led to phosphatidylinositol-3 (PI3) kinase activation evidenced by Akt phosphorylation, which was blocked by PI3 kinase inhibitors, wortmannin and LY 294002. Inhibition of PI3 kinase abolished the IDE upregulation by insulin, indicating a cause-effect relationship between insulin signaling and IDE upregulation. Further support for this link was provided by the findings that deficient insulin signaling (decreased PI3 kinase subunit P85) was correlated with reduced IDE in Alzheimer's disease (AD) brains and in Tg2576 Swedish amyloid precursor protein transgenic mice fed a safflower oil-enriched (“Bad”) diet used to accelerate pathogenesis. Consistent with IDE function in the degradation of Aβ monomer, the IDE decrease in the Bad diet-fed Tg2576 mice was associated with increased Aβ monomer levels. Thesein vitroandin vivoanalyses validate the use of enhanced CNS insulin signaling as a potential strategy for AD intervention to correct the IDE defects occurring in AD.