Differential effects of spinal cord gray and white matter on process outgrowth from grafted human NTERA2 neurons (NT2N, hNT).

Abstract

To investigate host effects on grafts of pure, postmitotic, human neurons, we assessed the morphologic and molecular phenotype of purified NTera2N (NT2N, hNT) neurons implanted into the spinal cord of athymic nude mice. NT2N neurons were implanted into both spinal cord gray matter and white matter of neonatal, adolescent, and adult mice and were evaluated at postimplantation times up to 15 months. NT2N neurons remained at the implantation site and showed process integration into all host areas, and each graft exhibited similar phenotypic features regardless of location or host age at implantation. Evidence of host oligodendrocyte ensheathment of NT2N neuronal processes was seen, and grafted NT2N neurons acquired and maintained the morphologic and molecular phenotype of mature neurons. The microenvironments of host gray matter and white matter appear to exert differential effects on implanted neuronal processes, because consistent differences were noted in the morphologies of graft processes extending into white matter versus gray matter. NT2N processes extended for long distances (>2 cm) within white matter, whereas NT2N processes located within gray matter had shorter trajectories. This suggests that NT2N neurons integrate similarly into spinal cord gray matter and white matter, but they extend processes that respond differentially to gray matter and white matter cues. Further studies of the model system described here may identify the host molecular signals that support and direct integration of grafted human neurons as well as the outgrowth of their processes in the nervous system.