Neonatal mouse cortical but not isogenic human astrocyte feeder layers enhance the functional maturation of induced pluripotent stem cell‐derived neurons in culture

Human induced pluripotent stem (iPS) cell‐derived neurons and astrocytes are attractive cellular tools for nervous system disease modeling and drug screening. Optimal utilization of these tools requires differentiation protocols that efficiently generate functional cell phenotypes in vitro. As nervous system function is dependent on networked neuronal activity involving both neuronal and astrocytic synaptic functions, we examined astrocyte effects on the functional maturation of neurons from human iPS cell‐derived neural stem cells (NSCs). We first demonstrate human iPS cell‐derived NSCs can be rapidly differentiated in culture to either neurons or astrocytes with characteristic cellular, molecular and physiological features. Although differentiated neurons were capable of firing multiple action potentials (APs), few cells developed spontaneous electrical activity in culture. We show spontaneous electrical activity was significantly increased by neuronal differentiation of human NSCs on feeder layers of neonatal mouse cortical astrocytes. In contrast, co‐culture on feeder layers of isogenic human iPS cell‐derived astrocytes had no positive effect on spontaneous neuronal activity. Spontaneous electrical activity was dependent on glutamate receptor‐channel function and occurred without changes in I_Na, I_K, V_m, and AP properties of iPS cell‐derived neurons. These data demonstrate co‐culture with neonatal mouse cortical astrocytes but not human isogenic iPS cell‐derived astrocytes stimulates glutamatergic synaptic transmission between iPS cell‐derived neurons in culture. We present RNA‐sequencing data for an immature, fetal‐like status of our human iPS cell‐derived astrocytes as one possible explanation for their failure to enhance synaptic activity in our co‐culture system.