Expression of the Alzheimer's Disease Mutations AßPP695sw and PSEN1M146I in Double-Transgenic Göttingen Minipigs.

Mutations in the amyloid-ß protein precursor gene (AßPP), the presenilin 1 gene (PSEN1) or the presenilin 2 gene (PSEN2) that increase production of the AßPP-derived peptide Aß42 cause early-onset Alzheimer's disease. Rodent models of the disease show that further increase in Aß42 production and earlier brain pathology can be obtained by coexpressing AßPP and PSEN1 mutations. To generate such elevated Aß42 level in a large animal model, we produced Göttingen minipigs carrying in their genome one copy of a human PSEN1 cDNA with the Met146Ile (PSEN1M146I) mutation and three copies of a human AßPP695 cDNA with the Lys670Asn/Met671Leu (AßPPsw) double-mutation. Both transgenes were expressed in fibroblasts and in the brain, and their respective proteins were processed normally. Immunohistochemical staining with Aß42-specific antibodies detected intraneuronal accumulation of Aß42 in brains from a 10- and an 18-month-old pig. Such accumulation may represent an early event in the pathogenesis of Alzheimer's disease.

Localization and trafficking of endogenous anterior pharynx-defective 1, a component of Alzheimer's disease related gamma-secretase.

Anterior pharynx-defective 1 (Aph-1) is a multi-spanning membrane protein and an integral component of the high molecular weight gamma-secretase complex that also contains presenilin, nicastrin, and Pen-2. In order to clarify the existence of an endogenous fragment of Aph-1 and dissect the localization and processing of endogenous Aph-1 proteins, we examined cell lines and primary cell cultures with our own carboxyl terminal-specific antibodies for Aph-1aL. Fractionation and immunofluorescence studies indicated that the endogenous full-length Aph-1aL isoform localizes primarily to the endoplasmic reticulum as well as Golgi intermediate compartment, but small amount of it was detected at Golgi apparatus where most of its carboxyl terminal domain fragment existed. In primary neuronal and glial cultures, Aph-1aL was present in the neurites and glial cell processes. Endogenous Aph-1a and its proteolytic fragment have unique properties for cleavage control that may have implications for gamma-secretase regulation and intracellular distribution.

Mature glycosylation and trafficking of nicastrin modulate its binding to presenilins.

Nicastrin is an integral component of the high molecular weight presenilin complexes that control proteolytic processing of the amyloid precursor protein and Notch. We report here that nicastrin is most probably a type 1 transmembrane glycoprotein that is expressed at moderate levels in the brain and in cultured neurons. Immunofluorescence studies demonstrate that nicastrin is localized in the endoplasmic reticulum, Golgi, and a discrete population of vesicles. Glycosidase analyses reveal that endogenous nicastrin undergoes a conventional, trafficking-dependent maturation process. However, when highly expressed in transfected cells, there is a disproportionate accumulation of the endo-beta-N-acetylglucosaminidase H-sensitive, immature form, with no significant increase in the levels of the fully mature species. Immunoprecipitation revealed that presenilin-1 interacts preferentially with mature nicastrin, suggesting that correct trafficking and co-localization of the presenilin complex components are essential for activity. These findings demonstrate that trafficking and post-translational modifications of nicastrin are tightly regulated processes that accompany the assembly of the active presenilin complexes that execute gamma-secretase cleavage. These results also underscore the caveat that simple overexpression of nicastrin in transfected cells may result in the accumulation of large amounts of the immature protein, which is apparently unable to assemble into the active complexes capable of processing amyloid precursor protein and Notch.