The major components of amyloid in Alzheimer's disease (AD) brain are Abeta peptides that are derived by proteolytic cleavage of amyloid precursor protein (APP). Our preliminary data demonstrates that the X11alpha protein strongly influences APP metabolism in transfected HEK 293 cells. Specifically, X11alpha prolongs the half-life of cellular APP and retards recovery of its metabolic fragments, including the secreted amino-terminal fragments APPs, as well as Abeta40 and Abeta42 in conditioned medium. These effects are mediated by direct binding of the PTB-PI domain of Xllalpha to the YENPTY motif in the intracellular carboxy-terminus of APP. In addition, to a PTB-PI domain, X11alpha also contains two PDZ domains as well as an extended amino-terminus that may modulate Xllalpha effects on APP processing. We have recently found that Xllalpha exists as a heterotrimeric complex in mouse brain complexed with the mammalian homologues of the C. elegans Lin-2 and Lin-7 proteins. We propose to determine the potential modulatory influence of mammalian Lin-2 and Lin-7 on the inhibitory effects of X11alpha on cellular APP metabolism. We will study these effects by over-expression of wild type and dominant negative constructs of X11alpha, mLin-2 and mLin-7. Initial studies will be performed with transfected Hek 293 cells. Since APP metabolism is to some degree cell-type specific and Xllalpha is primarily a neuronal protein, we will also analyze the effects of Xllalpha, mLin-2 and mLin-7 on APP processing in neurons. We will perform these experiments in NT2 neurons infected with Semliki Forest Virus expressing the wild type and dominant negative constructs. We hypothesize that Xllalpha influences PP metabolism by altering its cellular trafficking. Thus, we will examine the cellular localization of PP, Xllalpha, mLin-2, and mLin-7 in wild type and infected cells. Finally, we hypothesize that the regional expression of APP, X11alpha, mLin-2, and mLin-7 in brain may inversely correlate with the regional neuropathology of AD, particular amyloid plaques. We will determine the regional expression and localization of these genes/proteins in normal and AD brain sections by immunohistochemistry and in situ hybridization. Collectively, this data will provide insights into the regulation of cellular APP trafficking and metabolism via these specific protein-protein interactions, and their potential roles in the development of AD. This information may lead to novel therapeutic strategies to delay the onset or slow the progression of amyloid deposition, dementia, and AD.
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