Antisense-induced reduction of presenilin 1 expression selectively increases the production of amyloid beta 42 in transfected cells

Autosomal dominant mutations in the presenilin 1 (PS1) gene are associated with familiar, early-onset Alzheimer's disease. Although the pathogenic mec hanism of these mutations is unclear, their common feature is that they lea d to an increased concentration of amyloid beta-peptide (A beta) 42 in the plasma of early-onset patients, in the conditioned media of transfected cel ls, and in the brains of transgenic mice that overexpress mutant PS1. To ad dress the mechanism(s) by which the pathogenic PS1 mutations increase A bet a 42, we constructed human cell lines expressing a doxycyclin (dox)-inducib le antisense PS1 RNA and measured its effects on the levels of PS1, amyloid precursor protein (APP), and A beta. In time course experiments, we observ ed a statistically significant (p = 0.0038) more than twofold elevation in secreted A beta 42 as early as 12 days after addition of dox. This correlat ed with an 80% decrease in the 46-kDa PS1 holoprotein and a 30% decrease in the 26-kDa N-terminal fragment (NTF). Furthermore, there was a significant fivefold (p = 0.002) increase in A beta 42 after 14-day dox treatment; thi s correlated with a >90% decrease in PS1 holoprotein and 60% decrease in NT F. At no time point did we observe significant changes in A beta 40, APP ho loprotein, presenilin 2, or tubulin. Ten days after the removal of dox, we observed a return to constitutive levels for A beta 42, PS1 holoprotein, an d NTF. These results suggest that in human cell lines, the reduction of nor mal PS1 activity results in the increased production of A beta 42. Furtherm ore, our results are consistent with a loss of function or dominant negativ e mechanism for the pathogenic PS1 mutations.