Amyloid b-peptide preconditioning reduces glutamate-induced neurotoxicity by promoting endocytosis of NMDA receptor Yasuaki Goto a , Tetsuhiro Niidome a , Akinori Akaike b , Takeshi Kihara a , Hachiro Sugimoto a, * a Department of Neuroscience for Drug Discovery, Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida-Shimodachi-cho, Sakyo-ku, Kyoto 606-8501, Japan b Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto 606-8501, Japan Received 20 September 2006 Available online 19 October 2006 Abstract Amyloid b-peptide (Ab) and glutamate are generally believed to be closely related to the pathogenesis of Alzheimer’s disease and cere- brovascular disease, respectively. Recent advances suggest that risk factors linked to cerebrovascular disease significantly increase the risk of developing Alzheimer’s disease. In this study, we examined the effects of pretreatment of cultured hippocampal neurons with Ab(1–42) (0.3, 0.5, and 1.0 lM) for 3 h (Ab preconditioning) on glutamate-induced neurotoxicity. Ab preconditioning significantly reduced both glutamate-induced neurotoxicity and the glutamate-induced increase in intracellular Ca 2+ concentration ([Ca 2+ ] i ). Ab pre- conditioning significantly reduced cell surface expression of N-methyl-D-aspartate (NMDA) glutamate receptor subunit protein NR1, although it exerted no significant effect on the total expression of NR1. These results suggest that Ab preconditioning reduced gluta- mate-induced neurotoxicity by promoting endocytosis of NMDA receptor, followed by inhibition of the increase in [Ca 2+ ] i . Our results support the notion of an association between Alzheimer’s disease and cerebrovascular disease, and suggest a new mechanism for neu- roprotection by promoting endocytosis of NMDA receptor. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Alzheimer’s disease; Amyloid b-peptide; Cell death; Glutamate; Hippocampus; NMDA receptor; Preconditioning Alzheimer’s disease is a neurodegenerative disorder characterized clinically by cognitive impairment and path- ologically by the appearance of senile plaques and neurofi- brillary tangles [1]. The major component of the senile plaques is amyloid b-peptide (Ab), which is a 39–43 amino acid peptide fragment derived from amyloid precursor pro- tein. Although the exact etiology of Alzheimer’s disease remains to be determined, it has been proposed that accu- mulation of Ab is closely related to the pathogenesis of Alzheimer’s disease. In addition to Ab, enhancement of excitotoxicity by glutamate has also been implicated in the pathogenesis of Alzheimer’s disease [2]. Several studies have demonstrated that Ab exacerbates glutamate-induced neuronal cell death [3,4], and inhibition of glutamate recep- tor reduces Ab-induced neuronal cell death [5,6]. These results suggest that the interaction between Ab- and gluta- mate-induced neuronal cell death is critical for the patho- genesis of Alzheimer’s disease. Ischemic preconditioning is an endogenous neuropro- tective mechanism by which sublethal ischemic events ren- der a tissue more tolerant to subsequent lethal ischemic events. In ischemic events, overactivation of NMDA gluta- mate receptor is widely believed to be the main signaling pathway to cell injury. Subtoxic preconditioning levels of NMDA protect neurons against excitotoxicity induced by toxic levels of glutamate [7–9]. A recent study demonstrat- ed that hypoxia causes an increase of the expression level of amyloid precursor protein, a decrease in a-secretase activity, and a decrease of the expression levels of two 0006-291X/$ - see front matter Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2006.10.030 * Corresponding author. Fax: +81 75 753 9269. E-mail address: hsugimot@pharm.kyoto-u.ac.jp (H. Sugimoto). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 351 (2006) 259–265 BBRC