P4‐004: The presence of beta‐amyloid 1‐42 nicotinic acetylcholine receptors in an in vitro presynaptic model causes dysregulated calcium signaling, mitochondrial dysfunction and altered ERK signaling on sustained exposure to beta‐amyloid

Abstract

Background: Epidemiological studies have linked psychological stress to AD risk and a large body of research has shown connections between stress, stress hormones and Ab accumulation as well as tau pathology in preclinical models. An understanding of the molecular mechanisms by which stress hormones accelerate Ab production has been lacking. Our work has focused on the link between corticotropin releasing hormone (CRH) and increased production of Ab. CRH is a critical mediator of stress responses in the hypothalamic-pituitary-adrenal (HPA) axis; CRH signals through two G protein-coupled receptors (GPCRs), CRHR1 and 2. Methods: Ab production, presenilin levels, gamma-secretase activity and subcellular distribution were assessed following CRH, corticosterone and CRHR antagonist treatment of human neuroglioma, neuroblastoma cells, and primary neuronal cultures. In addition effects on Ab levels were assessed following CRHR1 receptor overexpression or RNAi mediated knockdown. Co-immunoprecipitation studies and trafficking of g -secretase and CRHR1 were also performed. Results: CRH treatment consistently increased Ab42 production and in some cell lines also increased Ab40, but to a lesser extent. Thus, CRH increased the ratio of Ab42:Ab40. The effect of CRH on Ab 42 was not blocked by CRHR antagonists, suggesting that the mechanism by which CRH increases Ab might be independent of CRHR intracellular signaling. CRHR1 internalization assays revealed that CRH and CRHR1 antagonist treatment induced the endocytosis of CRHR1 and promoted the internalization of g -secretase. In addition, CRHR1 and g -secretase were co-localized in lipid raft fractions and, upon CRH treatment, more g -secretase accumulated in lipid rafts. These results indicate that CRH modulates intracellular trafficking and activity of g -secretase. Co-immunoprecipitation showed that small fractions of g -secretase complex were associated with CRHR1 and CRHR1 knock down decreased both Ab 40 and Ab 42 production, suggesting that CRHR1 may constitutively regulate g -secretase. Conclusions: CRH increases Ab42 production through CRHR1 induced alterations in g -secretase localization and activity. These data provide the first mechanistic link between physiologic stress CRH and augmentation of AD pathology.