In the present study we report a fully human iPSC-derived cortical neuron/primary astrocyte co-culture system with sustained synchronized network activity. We found that differentiating hiPSC-derived neuronal cells in co-cultures progressively displayed more negative resting membrane potentials to a level sufficient to remove voltage-dependent inactivation of sodium channels and to fire repetitive action potentials. An increasing percentage of hiPSC-derived neurons fired action potentials over time, consistent with the extensive electrophysiological characterization of hiPSC-derived neurons that was published previously43. Besides the more negative resting membrane potential, a maturation-induced increase of the sodium channel density could contribute to the gradual increase in action potential firing capacity of the hiPSC-derived neurons. Moreover, simultaneously differentiated neurons in a human astrocyte co-culture system revealed increased activity, bursting frequency and calcium oscillation synchronization over time, representative of neuronal network activity. Human iPSC-derived neurons expressed cortical markers TBR1, CTIP2, and SATB2 indicative of both deep and upper layer cortical neurons and reached a purity of about 60% of the total cell population.
