Internalized Amyloid-β (1-42) Peptide Inhibits the Store-Operated Calcium Entry in HT-22 Cells

Dysregulation in calcium signaling pathways plays a major role in the initiation of Alzheimer's disease (AD) pathogenesis. Accumulative experimental evidence obtained with cellular and animal models, as well as with AD brain samples, points out the high cytotoxicity of soluble small oligomeric forms of amyloid-beta peptides (A beta) in AD. In recent works, we have proposed that A beta-calmodulin (CaM) complexation may play a major role in neuronal Ca2+ signaling, mediated by CaM-binding proteins (CaMBPs). STIM1, a recognized CaMBP, plays a key role in store-operated calcium entry (SOCE), and it has been shown that the SOCE function is diminished in AD, resulting in the instability of dendric spines and enhanced amyloidogenesis. In this work, we show that 2 and 5 h of incubation with 2 mu M A beta(1-42) oligomers of the immortalized mouse hippocampal cell line HT-22 leads to the internalization of 62 +/- 11 nM and 135 +/- 15 nM of A beta(1-42), respectively. Internalized A beta(1-42) oligomers colocalize with the endoplasmic reticulum (ER) and co-immunoprecipitated with STIM1, unveiling that this protein is a novel target of A beta. Fluorescence resonance energy transfer measurements between STIM1 tagged with a green fluorescent protein (GFP) and A beta(1-42)-HiLyte (TM)-Fluor555 show that STIM1 can bind nanomolar concentrations of A beta(1-42) oligomers at a site located close to the CaM-binding site in STIM1. Internalized A beta(1-42) produced dysregulation of the SOCE in the HT-22 cells before a sustained alteration of cytosolic Ca2+ homeostasis can be detected, and is elicited by only 2 h of incubation with 2 mu M A beta(1-42) oligomers. We conclude that A beta(1-42)-induced SOCE dysregulation in HT-22 cells is caused by the inhibitory modulation of STIM1, and the partial activation of ER Ca2+-leak channels.

Automated summary

Dysregulation in calcium signaling pathways plays a major role in the initiation of Alzheimer's disease. This study reveals the complexation of Aβ with CaM-binding protein STIM1, leading to the dysregulation of Ca2+ signaling and enhanced amyloidogenesis.