USING PATIENT-DERIVED <EM >PSEN1</EM> MUTANT IPSCS TO MODEL EXCITATION/INHIBITION IMBALANCE IN ALZHEIMER'S DISEASE

Mutations in the Presenilin-1 (PSEN1) gene lead to early-onset Alzheimer's disease (AD) and are associated with changes in brain oscillations and increased epileptic activity. At the cellular level, these alterations are caused by excitation/inhibition (E/I) imbalance, but the precise contribution of excitatory and inhibitory neurons remains unclear. We recently developed induced pluripotent stem cell (iPSC) induction protocols allowing the generation of stable human neuronal networks in well-defined E/I ratios. Using the transcription factors NGN2 or ASCL1/DLX2 respectively, pure populations of excitatory and inhibitory neurons were generated and subsequently mixed in controlled ratios. Here, we aimed to establish proof of concept that this method can also be used for patient-derived iPSCs. We generated cultures with fixed E/I ratios derived from a PSEN1 mutant and a healthy control line and performed electrophysiological, immunocytochemical and molecular analyses. Multi-electrode array (MEA) measurements showed effects of both E/I ratio and genotype on the development of network activity over time, which was partly confirmed with calcium imaging experiments. Immunostainings and proteomics measurements indicated robust neuronal maturation for both PSEN1 mutant and control lines. Potential genotype-driven differences were observed in the maintenance of stable E/I ratios over time and in the expression of proteins linked to excitatory and inhibitory neuron function. Taken together, these results suggest that patient iPSC-derived neuronal cultures with fixed E/I ratios are a promising model to study the cellular and molecular basis of AD-related neuronal network dysfunction. We are currently applying this method to additional lines to increase power and reproducibility.