Netrin-1 Interrupts Amyloid-ß Amplification, Increases sAßPPα in vitro and in vivo, and Improves Cognition in a Mouse Model of Alzheimer's Disease.

ABSTRACT

Recent studies have shown that inoculation of susceptible mice with amyloid-ß (Aß) peptides accelerates Aß deposition in the brain, supporting the idea that Aß may be self-amplifying; however, the exact mechanism is not understood. Here we provide evidence that Aß may self-amplify, in part, by inhibiting α-secretase ADAM10 (a disintegrin and metalloprotease) cleavage of full-length Aß precursor protein (FL AßPP) and therefore allow greater ß-secretase processing, and that Aß itself is a substrate for ADAM10. Exposure of primary neuronal cultures from PDAßPP mice to exogenous rat Aß1- 40 resulted in increased de novo human Aß1-42 production and exposure of cells to Aß decreased production of ADAM10 cleavage product soluble AßPPα (sAßPPα). In a cell-free assay, Aß decreased ADAM10 cleavage of the chimeric substrate MBP-AßPPC125 and Aß itself was apparently cleaved by the enzyme. The axonal guidance and trophic factor netrin-1, however, reduced the Aß1- 40-induced Aß1-42 increase, increased sAßPPα, and reversed the Aß-induced sAßPPα decrease in vitro. In vivo, induction of netrin-1 expression in PDAßPPSwe/Ind transgenic mice resulted in reductions in both Aß1-42 and Aß1- 40, and ICV delivery of netrin-1 to PDAßPPSwe/Ind mice increased sAßPPα, decreased Aß, and improved working memory. Finally, to support further study of netrin-1's potential as a therapeutic for Alzheimer's disease, pilot gene therapy studies were performed and a netrin mimetic peptide synthesized and tested that, like netrin, can increase sAßPPα and decrease Aß1-42in vitro. Taken together, these data provide mechanistic insights into Aß self-amplification and the ability of netrin-1 to disrupt it.