P4‐383: Notch signaling induces neuronal cell death via the NFkB‐Bim pathway in ischemic stroke

Abstract

Background:Notch-1 (Notch) is a cell surface receptor that regulates cell-fate decisions in thedevelopingnervous systemand itmayalsohave roles in synaptic plasticity in the adult brain.Bindingof its ligands results in the proteolytic cleavage ofNotch by theg-secretase enzyme complex, thereby causing the release of a Notch intracellular domain (NICD) that translocates to the nucleus, where it regulates transcription.Methods:Here we show that activation of Notch modulates ischemic neuronal cell death in vitro and in vivo. Specifically, we examined the effects of Notch-1 siRNA or the NICD mutants overexpression in neuronal cells. We investigated the effect of a g-secretase inhibitor against ischemic stroke of mice (MCAO: middle cerebral artery occlusion and reperfusion). Results: 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 transfection-induced cell death was reduced by blockade of calcium signaling, caspase activation and Janus kinase signaling. Inhibition of the Notch-activating enzyme, g-secretase, protected against ischemic neuronal cell death by targeting an apoptotic protease, cleaved caspase-3, nuclear factor kappa B (NFkB), and the prodeath BH3only protein, Bim (Bcl-2-interactingmediator of cell death). Treatment of mice with a g-secretase inhibitor, compound E, reduced infarct size and improved functional outcome in a model of focal ischemic stroke. Furthermore, g-secretase inhibition reduced NICD, p-P65 and Bim levels in vivo. Conclusions: These findings suggest that Notch signaling endangers neurons following ischemic stroke by modulating the NFkB, prodeath protein Bim, and caspase pathways.