Investigating the impact of cell maturity on transplantation success for CNS injury

Abstract

Globally, a total of 82 million people suffer from injuries to the central nervous system (CNS) and to date there is no cure. However, while humans and other mammals have a limited capacity for functional tissue repair, various other species exhibit near‐perfect CNS regeneration following injury. Understanding the factors that regulate the reparative response can therefore provide important insight into strategies for promoting regeneration in mammals. An emerging approach involves the localized delivery of exogenous neural stem cells (NSCs). Although preclinical studies have shown that NSCs can survive once transplanted, whether they differentiate into neurons and functionally integrate into the host tissue remains unclear. In addition, there are questions as to what stage of NSC maturity will provide the most therapeutic benefit. To address these questions, we investigated cell survival, differentiation, and long‐term sensorimotor recovery in a rat model of stroke following the delivery of human NSCs at three different stages of maturity: 1) undifferentiated NSCs (early stage), 2) neuronal progenitors (mid stage), and 3) mature neurons (late stage). To facilitate cell survival and integration into host tissue, cultured cells were encapsulated into a biocompatible, bioresorbable hyaluronan/methylcellulose hydrogel prior to delivery. Our results demonstrated that transplantation of early stage cells results in the greatest tissue and functional repair, relative to transplantation of more mature neurons. Surprisingly, we found that the transplantation process itself resulted in acute cell death in the late stage cells. This negatively impacted host tissue and negated any potential positive effects associated with cell maturity and the hydrogel vehicle, which itself showed some functional and tissue benefit. Whereas each transplant cell group (early, mid and late) started the experiment with a distinctive maturity profile that was maintained after 7 days post‐transplantation, by 50 days the pattern of neural marker expression between groups was nearly identical, highlighting the influence of the microenvironment on the terminal cell phenotype. Overall, we demonstrate that the phenotype of the cells before and after transplantation had an enormous impact on their survival and the consequent tissue and behavioral response, emphasizing the importance of characterizing injected cells in CNS regenerative strategies.Support or Funding InformationWe are grateful for funding from: the Canada First Research Excellence Fund to Medicine by Design at the University of Toronto (to MSS, CMM, AN), the Canadian Institutes of Health Research (Foundation grant to MSS, Operating grant to CMM) and the Natural Sciences and Engineering Research Council (CGS‐D to SLP).