Abstract
Synaptic dysfunction, including excitatory-inhibitory imbalance, are early features of Alzheimer’s disease (AD; Tuapaemahara) preceding widespread degeneration and cognitive decline. Thus, approaches to enhance synaptic efficacy and restore excitatory-inhibitory balance may be promising therapeutic strategies. Mounting evidence suggests that endogenous neuromodulator, secreted amyloid precursor protein-alpha (sAPPα), and a bioactive derived peptide CTα16, rescue impaired learning in rodent AD models and alters the molecular organisation of synapses, moving AMPA-glutamate receptors to perisynaptic sites, enabling more efficacious synaptic activity. This positions sAPPα as a potential therapeutic for AD, although how sAPPα alters other glutamate receptors and its efficacy in human neurons remains unclear.
Using rodent neurons, we examined how sAPPα alters the synthesis and surface expression of receptors central to synaptic plasticity and memory, NMDA-glutamate receptors (NMDARs). To bridge the translational gap between rodent models and clinical application, we examined the ability of sAPPα and CTα16 to alter NMDAR surface expression in excitatory and inhibitory induced pluripotent stem cell-derived human neurons (iPSC-HNs).
Using Fluorescent Non-Canonical Amino Acid Tagging with Proximity Ligase Assay, we show sAPPα (1nM) biphasically increased expression of de novo GluN2B, a key plasticity-related NMDAR subunit, (30min: 1.6 ± 0.2, p = 0.007; 240 min: 1.8 ± 0.3, p = 0.011 vs. time-matched controls; n = 134–173 dendrites; one-sample t-test). In iPSC-HNs, using conventional immunochemistry, we found sAPPα increased GluN2B surface expression in a time- and cell type-specific manner (excitatory: 1.25 ± 0.1, 120 min, p<0.0001; inhibitory: 1.37 ± 0.1, 240 min, p<0.0001; n = 42–69 dendrites). CTα16 partially recapitulated sAPPα’s effect, significantly increasing GluN2B expression in excitatory neurons (1.3 ± 0.1, p = 0.0002; n = 41–65 dendrites).
These findings show that sAPPα regulates NMDARs, alongside AMPA-glutamate receptors to support sustained enhancement of synaptic efficacy. The novel finding of differential responses in excitatory versus inhibitory iPSC-HNs suggests sAPPα may target the excitatory-inhibitory imbalance implicated in early-AD. Demonstrating efficacy of sAPPα in human neuronal models represents a critical step toward translating sAPPα-based therapies.