Short Duration Electrical Stimulation to Enhance Neurite Outgrowth and Maturation of Adult Neural Stem Progenitor Cells

New therapies are desperately needed for human central nervous system (CNS) regeneration to circumvent the lack of innate regenerative ability following traumatic injuries. Previously attempted therapies have been stymied by barriers to CNS regeneration largely because of protective mechanisms such as the blood brain barrier, inhibitory molecules, and glial scar formation. The application of electric stimulation (ES) has shown promise for enhancing peripheral nervous system regeneration, but is in its infancy in CNS regeneration. The objective of this study is to better understand how short duration ES can be harnessed to direct adult neural stem progenitor cell (NSPC) neurogenesis, neurite extension, and maturation. Herein, NSPCs were exposed to physiological levels of electrical stimulation of 0.53 or 1.83 V/m (applied power supply setting of 1.2 and 2.5 V) of direct current (DC) for 10 min/days for 2 days with a total differentiation time of 3 days. Culturing conditions consisted of either mitogenic growth factors or the neuronal differentiation factor interferon-γ (IFN-γ). Stimulated NSPCs showed lengths that were over five times longer than unstimulated controls (112.0 ± 88.8 μm at 0.53 V/m vs. 21.3 ± 8.5 μm for 0 V/m with IFN-γ) with the longest neurites reaching up to 600 µm. Additionally, ES resulted in mature neuronal morphologies and signs of differentiation through positive βIII tubulin, neuronal nuclei (NeuN), and better organized filamentous-actin (f-actin) staining with growth cone formation. Additionally, the neurites and soma of stimulated NSPCs showed increases in intracellular Ca²⁺ during stimulation, signifying the presence of functional neurons capable of electrical conductance and communication with other cells. Our study demonstrates that short stimulation times (10 min/ day) result in significant neurite extension of stem cells in a quick time frame (3  days). This ES modality is potentially advantageous for promoting axon re-growth at an injury site using delivered adult stem cells; however, significant work still remains to understand both the delivery approach of cells as well as ES application in vivo.