Developmental expression of wild-type and mutant presenilin-1 in hippocampal neurons from transgenic mice: Evidence for novel species-specific properties of human presenilin-1

Presenilins 1 (PS1) and 2 (PS2) are multispanning transmembrane proteins as sociated with familial Alzheimer disease (FAD). They are developmentally re gulated, being expressed at highest levels during neuronal differentiation and are sustained at a lower level throughout life. We investigated the dis tribution and metabolism of endogenous murine PS1 as well as human wild-typ e (wtPS1) and the familial AD Met146Leu (M146L) mutant presenilins in disso ciated cultures of hippocampal neurons derived from control and transgenic mice. We found that the PS1 endoproteolytic fragments and, to a lesser exte nt, the full-length protein, were expressed as early as day 3 post-plating. Both species increased until the cells were fully differentiated at day 12 . Confocal microscopy revealed that presenilin is present in the Golgi and endoplasmic reticulum and, as in punctate, vesicle-like structures within d eveloping neurites and growth cones. Using a human-specific PS1 antibody, w e were able to independently examine the distribution of the transgenic pro tein which, although similar to the endogenous, showed some unique qualitie s. These included (i) some heterogeneity in the proteolytic fragments of hu man PS1; (ii) significantly reduced levels of full-length human PS1, possib ly as a result of preferential processing; and (iii) a more discrete intrac ellular distribution of human PS1. Colocalization with organelle-specific p roteins revealed that PS1 was located in a diffuse staining pattern in the MAP2-positive dendrites and in a punctate manner in GAP43-positive axons. P S1 showed considerable overlap with GAP43, particularly at the growth cones . Similar patterns of PS1 distribution were detected in cultures derived fr om transgenic animals expressing human wild-type or mutant presenilins. The studies demonstrate that mutant presenilins are not grossly different in t heir processing or distribution within cultured neurons, which may represen t more physiological models as compared to transfection systems. Our data a lso suggest that the molecular pathology associated with Ps 1 mutations res ults from subtle alterations in presenilin function, which can be further i nvestigated using these transgenic neuronal cell culture models.