SUMMARY Mushroom dendritic spine structures are essential for memory storage and the loss of mushroom spines may explain memory defects in Alzheimer's disease (AD). Here we show a significant reduction in the fraction of mushroom spines in hippocampal neurons from the presenilin-1 M146V knockin (KI) mouse model of familial AD (FAD). The stabilization of mushroom spines depends on STIM2-mediated neuronal store operated calcium influx (nSOC) and continuous activity of Ca2+-calmodulin-dependent protein kinase II (CaMKII). We demonstrate that STIM2-nSOC-CaMKII pathway is compromised in KI neurons, in aging neurons and in sporadic AD brains due to downregulation of STIM2 protein. We further establish that overexpression of STIM2 rescues synaptic nSOC, CaMKII activity and mushroom spine loss in KI neurons. Our results identify STIM2-nSOC-CaMKII synaptic pathway as a novel potential therapeutic target for treatment of AD and age-related memory decline.

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder. Familial AD (FAD) mutations in presenilins have) and from triple-transgenic AD mice (KI-PS1 M146V , Thy1-APP KM670/671NL , Thy1-tau P301L ). Obtained results provided additional support to the hypothesis that presenilins function as ER Ca 2ϩ leak channels in neurons. Interestingly, we discovered that presenilins play a major role in ER Ca 2ϩ leak function in hippocampal but not in striatal neurons. We further discovered that, in hippocampal neurons, loss of presenilin-mediated ER Ca 2ϩ leak function was compensated by an increase in expression and function of ryanodine receptors (RyanRs). Long-term feeding of the RyanR inhibitor dantrolene to amyloid precursor protein-presenilin-1 mice (Thy1-APP KM670/671NL , Thy1-PS1 L166P ) resulted in an increased amyloid load, loss of synaptic markers, and neuronal atrophy in hippocampal and cortical regions. These results indicate that disruption of ER Ca 2ϩ leak function of presenilins may play an important role in AD pathogenesis. IntroductionAlzheimer's disease (AD) is the most common form of agerelated dementia in human beings over the age of 60 years. Most cases of AD are idiopathic, but the small fractions of AD cases are familial and characterized by an earlier onset and genetic inheritance. Mutations in presenilin-1 (PS1) and presenilin-2 (PS2) account for ϳ40% of all known familial AD (FAD) cases in which a genetic cause has been identified (Tandon and Fraser, 2002). Presenilins are 50 kDa proteins that contain nine transmembrane domains (Laudon et al., 2005;Spasic et al., 2006) and reside in the endoplasmic reticulum (ER) membrane . Presenilins undergo endoproteolytic cleavage to N-terminal (NTF) and C-terminal (CTF) fragments. The complex of cleaved presenilins with nicastrin, aph-1, and pen-2 subunits moves from ER to plasma membrane, in which it functions as a ␥-secretase, which cleaves the amyloid precursor protein (APP) and releases the amyloid ␤-peptide (A␤), the principal constituent of the amyloid plaques in the brains of AD patients. Consistent with the role of presenilins as catalytic subunits of a ␥-secretase (De Strooper et al., 1998;Wolfe et al., 1999), FAD mutations in presenilins affect APP processing.In addition to changes in APP processing, many FAD mutations in presenilins result in deranged Ca 2ϩ signaling, and growing evidence indicate that neuronal Ca 2ϩ signaling disruptions may play an early and important role in AD pathogenesis (Bezprozvanny and Mattson, 2008). The connection between presenilins and Ca 2ϩ signaling was initially uncovered when it was reported that fibroblasts from FAD patients release supranormal amounts of Ca 2ϩ in response to inositol-1,4,5-trisphosphate (InsP 3 ) (Ito et al., 1994). Similar results were obtained in experiments with cells expressing FAD mutant presenilins (Leissring et al., 1999a,b) and in cortical and hippocampal neurons from presenilin FAD mutant knock-in mice (Guo et al., 1999;Chan et al., 2000;Schneider et al., 200...

Mushroom dendritic spine structures are essential for memory storage and the loss of mushroom spines may explain memory defects in aging and Alzheimer's disease (AD). The stability of mushroom spines depends on stromal interaction molecule 2 (STIM2)-mediated neuronal-store-operated Ca 2ϩ influx (nSOC) pathway, which is compromised in AD mouse models, in aging neurons, and in sporadic AD patients. Here, we demonstrate that the Transient Receptor Potential Canonical 6 (TRPC6) and Orai2 channels form a STIM2-regulated nSOC Ca 2ϩ channel complex in hippocampal mushroom spines. We further demonstrate that a known TRPC6 activator, hyperforin, and a novel nSOC positive modulator, NSN21778 (NSN), can stimulate activity of nSOC pathway in the spines and rescue mushroom spine loss in both presenilin and APP knock-in mouse models of AD. We further show that NSN rescues hippocampal long-term potentiation impairment in APP knock-in mouse model. We conclude that the STIM2-regulated TRPC6/Orai2 nSOC channel complex in dendritic mushroom spines is a new therapeutic target for the treatment of memory loss in aging and AD and that NSN is a potential candidate molecule for therapeutic intervention in brain aging and AD.