MUSCARINIC REGULATION OF ALZHEIMERS-DISEASE AMYLOID PRECURSOR PROTEINSECRETION AND AMYLOID BETA-PROTEIN PRODUCTION IN HUMAN NEURONAL NT2N CELLS

The Alzheimer amyloid precursor protein (APP) undergoes complex proces sing resulting in the production of a 4-kDa amyloid peptide (A beta) w hich has been implicated in the pathogenesis of Alzheimer's disease, R ecent studies have shown that cells can secrete carboxyl ter minus tru ncated APP derivatives (APP-S) in response to physiological stimulus. We have used human central nervous system neurons (NT2N) derived from a teratocarcinoma cell line (NT2) to study the signal transduction pat hways involved in APP-S secretion and AP production. Muscarinic recept ors (m2 and m3) as well as the heterotrimeric GTP binding protein G(q) and the beta 1 isoform of phospholipase C were present in NT2N neuron s, Stimulation of the muscarinic receptor with carbachol resulted in p hospholipase C activation as shown by a transient increase in the seco nd messengers 1,2-diacyl-sn-glycerol and inositol 1,4,5-trisphosphate. Carbachol also caused an increase in intracellular Ca2+ levels measur ed in single NT2N neurons, Under these conditions, carbachol caused a time-dependent a-fold increase in APP-S secretion into the medium, In contrast, prolonged treatment with carbachol caused a decrease in A be ta production into the medium. These results suggest that APP-S secret ion and A beta production in NT2N neurons are regulated by the muscari nic/phospholipase C signal transduction pathway, Furthermore, activati on of this pathway results in dissociation of APP-S secretion and A be ta production.