Transforming growth factor-β1 primes proliferating adult neural progenitor cells to electrophysiological functionality.

The differentiation of adult neural progenitors (NPCs) into functional neurons is still a limiting factor in the neural stem cell field but mandatory for the potential use of NPCs in therapeutic approaches. Neuronal function requires the appropriate electrophysiological properties. Here, we demonstrate that priming of NPCs using transforming growth factor (TGF)-β1 under conditions that usually favor NPCs' proliferation induces electrophysiological neuronal properties in adult NPCs. Gene chip array analyses revealed upregulation of voltage-dependent ion channel subunits (Kcnd3, Scn1b, Cacng4, and Accn1), neurotransmitters, and synaptic proteins (Cadps, Snap25, Grik4, Gria3, Syngr3, and Gria4) as well as other neuronal proteins (doublecortin [DCX], Nrxn1, Sept8, and Als2cr3). Patch-clamp analysis demonstrated that control-treated cells expressed only voltage-dependent K(+) -channels of the delayed-rectifier type and the A-type channels. TGF-β1-treated cells possessed more negative resting potentials than nontreated cells owing to the presence of delayed-rectifier and inward-rectifier channels. Furthermore, TGF-β1-treated cells expressed voltage-dependent, TTX-sensitive Na(+) channels, which showed increasing current density with TGF-β1 treatment duration and voltage-dependent (+)BayK8644-sensitive L-Type Ca(2+) channels. In contrast to nontreated cells, TGF-β1-treated cells responded to current injections with action-potentials in the current-clamp mode. Furthermore, TGF-β1-treated cells responded to application of GABA with an increase in membrane conductance and showed spontaneous synaptic currents that were blocked by the GABA-receptor antagonist picrotoxine. Only NPCs, which were treated with TGF-β1, showed Na(+) channel currents, action potentials, and GABAergic currents. In summary, stimulation of NPCs by TGF-β1 fosters a functional neuronal phenotype, which will be of relevance for future cell replacement strategies in neurodegenerative diseases or acute CNS lesions.