Kv7.2/7.3 Channels are Enhanced During Striatal Development and Promote Neuronal Functional Maturation of iPS Cell-Derived Neurons

Abstract

M-currents, encoded by Kv7.2/7.3 genes, are low-threshold, voltage-gated potassium channels which contribute to resting membrane potential (Vm) and regulate neuronal excitability. Here, we tested the hypothesis that the development of mouse striatal neurons is associated with enhanced expression and activity of M-currents and that determined whether forced expression of Kv7.2/7.3 accelerates the functional maturation of neurons differentiating from human induced pluripotent stem (iPS) cells. Neurons from the developing mouse striatum were isolated at E13, E15 and E17 and cultured in vitro for up to 14 days; functional profiles of the neurons were explored using whole-cell patch-clamp. In some experiments, subventricular and mantle zones were separated by laser microdissection and channel subunit ontogenies determined by gene chip array. Shortly after isolation (1 day in vitro), there was a clear in vivo development-dependent hyperpolarisation of Vm (E13=-24.8±2.3 mV (n=26), E15=-40.0±2.2 mV (n=12), E17=-47.2±2.4 mV (n=9)). Although Vm continued to hyperpolarise in vitro, by 7 days these differences has disappeared (e.g. E13=-52.1±2.8 mV (n=8), E17 =-54.7±1.9 (n=5)). Associated with these observations, were parallel and progressive increases in M-current activity during in vivo and in vitro development, as evidenced by more pronounced responses to retigabine and XE991. Further, both Kv7.2 and 7.3 genes were progressively enriched in the mantle zone during in vivo development. Importantly, human iPS cell-derived neurons nucleofected with a concatenated Kv7.2/7.3 cDNA plasmid demonstrated a significantly hyperpolarized Vm (from −39.9±2.2 mV (n=12) to −51.3±1.1 mV (n=11)) and a dramatic increase in the proportion of cells generating action potentials spontaneously. Taken together, these data indicate that development of striatal neurons is associated with increased M-current expression and that this might be causative as suggested by the effect of forced Kv7.2/7.3 expression in the iPS cell-derived neurons.