Segment-specific fetal spinal cord-derived cells and SSEA-3 positive cells from human dermal fibroblasts : their fates analysis and therapeutic implication for spinal cord injury

Abstract

Cell-based therapies are promising to spinal cord injury (SCI) due to their potential to replace the lost cells. There are two concerns in selecting cell candidates for cell replacement therapy for SCI. One is their definitive neural fate, and the other is their clinical translation. Definitive neural fate is the fundamental requirement and depends on the intrinsic properties of cells as well as the extrinsic elements. Clinical translation requires cells to circumvent ethical controversy and immune rejection.

In the first part of the present study, we investigated whether consistent regional information between the graft and the host is required for the survival and cell fate determination of the grafted cells in the injured spinal cord. Neural progenitor cells (NPCs) and freshly isolated cells were generated from the cervical, thoracic and lumbar segments of rat E14 fetal spinal cord (FSC). Their intrinsic properties including regional information, cell compositions and differentiation capacity were assessed in vitro. Then, their survival and cell fates were investigated after they were grafted respectively in the same place in the injured spinal cord or the ligated musculocutaneous nerve. The results showed that segment-specific FSC NPCs and FSC cells maintained the regional information. The intrinsic features of segment-specific FSC NPCs in differentiation capacity and segment-specific FSC cells in cell compositions followed both temporal and spatial paradigms of FSC development. After transplantation, regardless of their regional information, all segment-specific FSC NPCs and FSC cells survived, with better survival rate in the case of FSC cells. Cell fates of the grafted cells in the injured spinal cord were consistent to the in vitro observations. MN-like cells were absent in the injured spinal cord but present in the lumbar FSC cells grafted in the ligated musculocutaneous nerve. Our results suggest that heterotopic transplantation of E14 FSC NPCs or FSC cells with different regional information from the host would not affect their survival and cell fates in the injured spinal cord. Their cell fates might be mainly determined by their intrinsic properties, while extrinsic elements (some permissive conditions in the peripheral nerve system) might effect how much they can fulfill their properties.

The second part of the present study focused on a small portion of SSEA-3 positive cells in human dermal fibroblasts, which has been suggested as a novel kind of multipotent cells and promising for the autologous transplantation for SCI. However, our data on analyzing the expression of pluripotent genes and the generation of clusters at the single cell level did not support the multipotency of the fibroblast-isolated SSEA-3 positive cells. In vitro neural induction condition and the injured spinal cord could induce the SSEA-3 positive cells expressing neural progenitor marker and immature neuronal marker, but were insufficient to push them further to acquire mature neural features. In addition, they had no locomotion improvement for the contusive SCI. Thus, our results suggest that SSEA-3 might be not a reliable marker for multipotent cells in human dermal fibroblasts and the positive cells might have little therapeutic potential for SCI.