Perturbed neurogenesis in the adult hippocampus associated with presenilin-1 A246E mutation

in addition to its well-established role in gamma-secretase cleavage, presenilin (PS) also plays a role in regulating the stability of cytosolic beta-catenin, a protein involved in Wnt signaling. Several familial Alzheimer's disease-associated PSI mutations have been shown to increase the stability of the signaling pool of beta-catenin, correlating with enhanced cell, proliferation. Accordingly, we hypothesized that in the setting of PSI mutations, abnormal activation of Wnt/beta-catenin signaling leads to increased cell division. We tested this hypothesis by examining whether there is evidence of increased neurogenesis in the hippocampus of adult transgenic mice that overexpress the PSI A246E mutation. In PS1/PS2-deficient fibroblasts, expression of PS1 A246E Familial AD mutation failed to restore the rapid turnover of beta-catenin compared with wild-type PSI. We then examined whether the same mutation enhanced neurogenesis in vivo in adult hippocampus of PS1-deficient mice when restored by wild-type human PSI (PS1(-/-)WT) or A246E PSI mutation (PS1(-/-)AE). The PSI A246E mutation stimulated the proliferation of progenitor cells in the dentate gyrus of adult mice, as assessed by 5-bromo-2-deoxyuridine incorporation, but did not influence their survival or differentiation. These observations suggest that the PSI A246E mutation influences cell growth putatively via abnormal beta-catenin signaling in vivo.