Electrophysiological Profile of Differentiating Human Central Canal Ependymal Stem-Progenitor Cells

Abstract

Following spinal cord injury (SCI), current treatments look to halt the spread of tissue damage to minimize pain, with limited effectiveness. Unfortunately, there is no widely used approach for promoting re-growth across the lesion site, a necessity for functional recovery. To that end, stem cell transplant and niche manipulation therapies are a promising tool for repairing damage from SCI and other neurodegenerative conditions. As most stem cell studies are based exclusively on animal models, we aimed to address several gaps in understanding that are fundamental for potential translation to humans. Since immunocytochemistry alone cannot adequately determine whether stem cells have differentiated into mature neurons, we used patchclamp electrophysiology to assess the passive and active electrical properties of stem cells from the central canal of the spinal cord throughout the in vitro differentiation process. Rat ependymal-stem progenitor cells (epSPCs) differentiate towards a majority astrocytic fate under intrinsic differentiation conditions in vitro. Human epSPCs, on the other hand, differentiate towards a majority neuronal fate. Electrophysiological recordings of these cells in intrinsic FBScontaining differentiation media and under BDNF-, GDNF-and RA-guided differentiation show no action potential firing from two to ten weeks in vitro. Passive membrane properties fail to reach that of typical mature neurons within this time frame. Surprisingly, the vast majority of cells showed voltage-dependent spontaneous synaptic currents with reversal near 0 mV, outward rectification, and decay kinetics that are consistent with excitatory glutamatergic responses. Further studies investigating the necessary timeline and the most effective differentiation media required for development of active membrane properties are needed, as is identification of the receptor subtypes responsible for the observed synaptic currents. This will help inform future transplant and stem cell niche manipulation strategies for the treatment of human neurological disorders.iii