Notch-1 (Notch) is a cell surface receptor that regulates cell-fate decisions in the developing nervous system, and it may also have roles in synaptic plasticity in the adult brain. Binding of its ligands results in the proteolytic cleavage of Notch by the ␥-secretase enzyme complex, thereby causing the release of a Notch intracellular domain (NICD) that translocates to the nucleus, in which it regulates transcription. Here we show that activation of Notch modulates ischemic neuronal cell death in vitro and in vivo. Specifically, our findings from the use of Notch-1 siRNA or the overexpression of NICD indicate that Notch activation contributes to cell death. Using modified NICD, we demonstrate an apoptosis-inducing function of NICD in both the nucleus and the cytosol. NICD transfectioninduced cell death was reduced by blockade of calcium signaling, caspase activation, and Janus kinase signaling. Inhibition of the Notch-activating enzyme, ␥-secretase, protected against ischemic neuronal cell death by targeting an apoptotic protease, cleaved caspase-3, nuclear factor-B (NF-B), and the pro-death BH3-only protein, Bcl-2-interacting mediator of cell death (Bim). Treatment of mice with a ␥-secretase inhibitor, compound E, reduced infarct size and improved functional outcome in a model of focal ischemic stroke. Furthermore, ␥-secretase inhibition reduced NICD, p-p65, and Bim levels in vivo. These findings suggest that Notch signaling endangers neurons after ischemic stroke by modulating the NF-B, pro-death protein Bim, and caspase pathways.

Abstractβ-secretase (BACE1), an enzyme responsible for the production of amyloid β-peptide (Aβ), is increased by oxidative stress and is elevated in the brains of patients with sporadic Alzheimer's disease (AD). Here we show that oxidative stress fails to induce BACE1 expression in presenilin-1 (γ-secretase)-deficient cells and in normal cells treated with γ-secretase inhibitors. Oxidative stress-induced β-secretase activity and sAPPβ levels were suppressed by γ-secretase inhibitors. Levels of γ-and β-secretase activities were greater in brain tissue samples from AD patients compared to non-demented control subjects, and the elevated BACE1 level in the brains of 3xTgAD mice was reduced by treatment with a γ-secretase inhibitor. Our findings suggest that γ-secretase mediates oxidative stress-induced expression of BACE1 resulting in excessive Aβ production in AD. The authors declare that they have no actual or potential conflicts of interest to disclose. Appropriate approval and procedures were used concerning human subjects and animals.

Earlier reports found that calsenilin is a transcriptional repressor or a subunit of plasma membrane channel, and indicated that calsenilin was present in the nucleus or plasma membrane. Immunohistochemical and subcellular fractionation analysis, however, revealed that calsenilin/DREAM/KChIP3 was distributed throughout the cytoplasm of SK-N-BE2(C), Jurkat, and HeLa cells. In addition, the expression of calsenilin suppressed the ATP-induced increase in intracellular Ca2+ concentrations. By increase in intracellular calcium concentration, calsenilin was translocated into the nucleus.

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