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J. Biol. Chem., Vol. 282, Issue 49, 35722-35732, December 7, 2007

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Internalization of β-Amyloid Peptide by Primary Neurons in the Absence of Apolipoprotein E^*

Lucila Saavedra, Amany Mohamed, Victoria Ma, Satyabrata Kar^¶, and Elena Posse de Chaves¹

From the Departments of Pharmacology and ^¶Medicine and the Centre for Neuroscience, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada

Extracellular accumulation of β-amyloid peptide (Aβ) has been linked to the development of Alzheimer disease. The importance of intraneuronal Aβ has been recognized more recently. Although considerable evidence indicates that extracellular Aβ contributes to the intracellular pool of Aβ, the mechanisms involved in Aβ uptake by neurons are poorly understood. We examined the molecular mechanisms involved in Aβ-(1–42) internalization by primary neurons in the absence of apolipoprotein E. We demonstrated that Aβ-(1–42) is more efficiently internalized by axons than by cell bodies of sympathetic neurons, suggesting that Aβ-(1–42) uptake might be mediated by proteins enriched in the axons. Although the acetylcholine receptor 7nAChR, previously suggested to be involved in Aβ internalization, is enriched in axons, our results indicate that it does not mediate Aβ-(1–42) internalization. Moreover, receptors of the low density lipoprotein receptor family are not essential for Aβ-(1–42) uptake in the absence of apolipoprotein E because receptor-associated protein had no effect on Aβ uptake. By expressing the inactive dynamin mutant dynK44A and the clathrin hub we found that Aβ-(1–42) internalization is independent of clathrin but dependent on dynamin, which suggests an endocytic pathway involving caveolae/lipid rafts. Confocal microscopy studies showing that Aβ did not co-localize with the early endosome marker EEA1 further support a clathrin-independent mechanism. The lack of co-localization of Aβ with caveolin in intracellular vesicles and the normal uptake of Aβ by neurons that do not express caveolin indicate that Aβ does not require caveolin either. Instead partial co-localization of Aβ-(1–42) with cholera toxin subunit B and sensitivity to reduction of cellular cholesterol and sphingolipid levels suggest a caveolae-independent, raft-mediated mechanism. Understanding the molecular events involved in neuronal Aβ internalization might identify potential therapeutic targets for Alzheimer disease.

Received for publication, March 1, 2007 , and in revised form, September 11, 2007.

^* This work was supported by grants from the Canadian Institutes of Health and Research and a personal donation from William Sim. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. 1 and 2.

¹ To whom correspondence should be addressed: Dept. of Pharmacology, 9-28 Medical Science Bldg., Faculty of Medicine, University of Alberta, Edmonton, Alberta T6G 2H7, Canada. Tel.: 780-492-5966; Fax: 780-492-4325; E-mail: elena.chaves{at}ualberta.ca.

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