Neurons Generated from APP/APLP1/APLP2 Triple Knockout Embryonic Stem Cells Behave Normally in Vitro and in Vivo: Lack of Evidence for a Cell Autonomous Role of the Amyloid Precursor Protein in Neuronal Differentiation

Abstract

Alzheimer's disease amyloid precursor protein (APP) has been implicated in many neurobiologic processes, but supporting evidence remains indirect. Studies are confounded by the existence of two partially redundant APP homologues, APLP1 and APLP2. APP/APLP1/APLP2 triple knockout (APP tKO) mice display cobblestone lissencephaly and are perinatally lethal. To circumvent this problem, we generated APP triple knockout embryonic stem (ES) cells and differentiated these to APP triple knockout neurons in vitro and in vivo. In comparison with wild-type (WT) ES cell-derived neurons, APP tKO neurons formed equally pure neuronal cultures, had unaltered in vitro migratory capacities, had a similar acquisition of polarity, and were capable of extending long neurites and forming active excitatory synapses. These data were confirmed in vivo in chimeric mice with APP tKO neurons expressing the enhanced green fluorescent protein (eGFP) present in a WT background brain. The results suggest that the loss of the APP family of proteins has no major effect on these critical neuronal processes and that the apparent multitude of functions in which APP has been implicated might be characterized by molecular redundancy. Our stem cell culture provides an excellent tool to circumvent the problem of lack of viability of APP/APLP triple knockout mice and will help to explore the function of this intriguing protein further in vitro and in vivo.

Functions of the APP gene family in the nervous system: insights from mouse models

“…These findings are further supported by previous results from Taylor et al who showed a requirement for APPsa for in vivo LTP in rats employing infusion of a-secretase inhibitor or recombinant APPsa and demonstrated that exogenously applied APPsa facilitates evoked NMDAR currents at the postsynaptic site (Taylor et al 2008). The requirement of APP and APLP2 for normal CNS function contrasts, however, with the normal differentiation and electrophysiological properties of cultured neurons lacking all three APP family members (Bergmans et al 2010) and highlights the importance to study APP family functions in the living organism.…”

APLP2 regulates neuronal stem cell differentiation during cortical development

“…Previously, we analysed neurons generated in vitro from triple ko APP/APLP1/APLP2 embryonic stem cells (Bergmans et al, 2010) and did not find any obvious phenotype. This prompted us to further investigate the role of APP gene family in vivo.…”

The Amyloid Precursor Protein (APP) Family Members are Key Players in S-adenosylmethionine Formation by MAT2A and Modify BACE1 and PSEN1 Gene Expression-Relevance for Alzheimer's Disease

“…APP/APLP2 and APLP1/APLP2 double knockout mice demonstrate a reduced viability similar to the triple knockout model and the APP/ APLP2 knockout mice suffer from defective neuromuscular synapses (9). Surprisingly, triple knockout neurons derived from triple knockout embryonic stem cells did not show macroscopic abnormalities (10). At the molecular level, a decreased expression of the vesicular glutamate transporter 2 was detected in glutamatergic neurons differentiated from APP/APLP2 knockout embryonic stem cells (11).…”