HUMAN NEURONS DERIVED FROM A TERATOCARCINOMA CELL-LINE EXPRESS SOLELY THE 695-AMINO ACID AMYLOID PRECURSOR PROTEIN AND PRODUCE INTRACELLULAR BETA-AMYLOID OR A4 PEPTIDES

The beta-amyloid or beta/A4 peptides that accumulate as filamentous aggregates in the extracellular space of Alzheimer disease (AD) brains are derived from one or more alternatively spliced amyloid precursor proteins (APPs). The more abundant APPs in the central nervous system are the 695- (APP695), 751- (APP751), and 770- (APP770) amino acid isoforms, and each could be the source of beta/A4 peptide that accumulates in the AD brain. It is plausible that altered metabolism of these APPs by central nervous system neurons could lead to the release and deposition of beta/A4 peptide in brain parenchyma. Thus, we examined the expression and processing of the three major brain APPs in nearly pure human neurons (NT2N cells) derived from a teratocarcinoma cell line (NTera2/c1.D1 or NT2 cells) after retinoic acid treatment. NT2N neurons expressed almost exclusively APP695, whereas NT2 cells expressed predominantly APP751/770. Furthermore, the processing of the APPs in NT2N cells was distinct from NT2 and nonneuronal cells. Most significantly, the NT2N neurons but not the NT2 cells constitutively generated intracellular beta/A4 peptide and released it into the culture medium. This work demonstrates the intracellular production of beta/A4 peptide and suggests that cultured NT2N cells may provide a unique model system for understanding the contribution of neurons and APP695 to amyloidogenesis in the AD brain.