Applied Electric Fields promote human neural precursor migration in a substrate dependent manner

Ahmed, Umalkhair 1, 3 ; Iwasa, Stephanie 1, 3 ; Popovic, Milos 1, 3 ; Morshead, Cindi 1, 2

1 Institute of Biomaterials and Biomedical Engineering, University of Toronto; 2 Department of Surgery, University of Toronto; 3 Toronto Rehabilitation Institute, University Health Network

Adult neural precursor cells show great promise for the repair of central nervous system (CNS) tissue following injury or disease. While it is well established that CNS injury is able to stimlulate resident neural precursor cells (NPCs) in the periventricular region of the adult brain; inducing them to migrate to sites of injury and differentiate into mature neural phenotypes, it is also well known that the efficacy of this injury response is not sufficient to promote neural repair. One of the goals of regenerative medicine is to enhance this neural regenerative response of NPCs. Interestingly, NPCs are electrosensitive cells and we have demonstrated that the application of applied electric fields (EFs) are able to promote rapid and directed NPC migration, a process known as galvanotaxis. We have demonstrated cathodally directed galvanotaxis of murine NPCs and we are interested in whether human derived NPCs were equally responsive to EF application. We used human NPCs (hNPCs) and plated them on different substrates which are components of the extracellular matrix including Laminin, Fibronectin, MaxGel (a mimic of the human extracellular matrix) and Matrigel (derived from a mouse sarcoma cell line). With an EF application of 250mV/mm (optimized EF strength), the hNPCs underwent substrate dependent galvanotaxis. Time lapse imaging revealed hNPCs underwent cathodal migration on Fibronectin and Laminin, and strikingly migrated anodally on Matrigel. We hypothesized that the directness of migration could be mediated by substrate stiffness as matrix stiffness has been shown to modify cell behaviour such as proliferation kinetics and cell fate. The effects of substrate have not been examined in detail with regard to galvanotactic behaviour. To investigate the role of substrate stiffness we used atomic force microscopy (AFM) and revealed that Matrigel and Fibronectin had significantly different stiffness and topography. Moreover, a combination substrate containing equal amounts of fibronectin and matrigel resulted in an intermediate average directedness with the hNPCs migrating both anodally and cathodally. We are currently modifying the elastic moduli (stiffness) of the substrate and predict altered stiffness will correlate with changes in the directedness (anodal versus cathodal). These findings will direct future in vivo studies aimed at enhancing NPC migration to promote neural repair in vivo.