NERVE GROWTH FACTOR-INDEPENDENT REDUCTION IN CHOLINE-ACETYLTRANSFERASE ACTIVITY IN PC12 CELLS EXPRESSING MUTANT PRESENILIN-1

Mutations in the presenilin genes (PS-l and PS-2) are linked to early onset familial Alzheimer's disease (AD), but the mechanisms by which t hese mutations cause the cognitive impairment characteristic of AD are unknown. Basal forebrain cholinergic neurons are involved in learning and memory processes, and reductions in choline acetyl-transferase (C hAT) activity are a characteristic feature of AD brain. We therefore h ypothesized that presenilin mutations suppress expression of the choli nergic phenotype. In rat PC12 cells stably transfected with the human PS-I gene containing the Leu --> Val mutation at codon 286 (L286V), we observed a drastic reduction (>90%) in basal ChAT activity compared w ith cells transfected with vector alone. By immunocytochemistry, a sim ilar decrease in ChAT protein levels was found in the mutant transfect ants. In cells differentiated with nerve growth factor, ChAT activity was again markedly lower in L286V-expressing cells than in control cel ls. We also observed reductions in ChAT activity in PC12 cells express ing the wild-type human PS-I gene but to a lesser extent than in L286V -expressing cells. The viability of cells transfected with either the wild-type or the mutant PS-I gene was not compromised. Our results sug gest that PS-I mutations may contribute to the cognitive impairment in AD by causing a nontoxic suppression of the cholinergic phenotype.