| Spinal cord injuries result in destruction of descending motor and ascending sensory tracts along with cellular loss, leading to permanent dysfunction with limited prospects for repair. The aim of current therapeutic strategies is to neutralize factors in the injured environment that inhibit axonal regeneration and to overcome the neurons' inherent inability to regenerate. In addition, cellular transplants can provide a permissive environment for regeneration and repair and introduce cells that may replace those lost to injury. The sequential restriction in developmental potential from multipotent neural stem cells through lineage-restricted precursors leads to the acquisition of mature cell types during CNS development. In the fetal spinal cord, immunoselection techniques allow for the purification of neuronal-restricted precursor (NRP) cells and glial-restricted precursor (GRP) cells. Multipotent neural stem cells and lineage-restricted precursor cells have emerged as promising candidates for cellular replacement as they are able to self-renew in vitro and have the potential to produce neurons, astrocytes, and/or oligodendrocytes. However, transplantation studies show that the adult spinal cord environment may not adequately permit the differentiation of multipotent neural stem cells, particularly their commitment into a neuronal phenotype. We therefore hypothesized that transplantation of lineage-restricted precursor cells may allow for cellular replacement and the control of differentiated cell types in the spinal cord environment. However, detecting transplanted cells in vivo have been difficult. In Chapter 2, cells derived from transgenic rats expressing the reporter gene human-placental alkaline phosphatase (AP) were assessed for their utility for transplant studies. In Chapter 3, survival and differentiation of NRP cells transplanted into the intact adult spinal cord are examined. In Chapter 4, GRP cells transplanted into the intact and injured spinal cord are assessed for their ability to survive, migrate, and differentiate. We show that cells isolated from AP transgenic rats ubiquitously express the reporter gene AP in precursor cells types and expression does not downregulate for at least 6 week in vivo. NRP and GRP cells survive after transplantation into the adult spinal cord and differentiate into mature cell types. Specifically, NRP cells differentiate into mature neurons that integrate with the host spinal cord, an environment that normally is non-neurogenic. Conversely, GRP cells transplanted into the intact and injured spinal cord survives and differentiates into astrocytes and oligodendrocytes. Moreover, GRP cells migrate extensively along white matter tracts. These results suggest that NRP and GRP cells may be useful cellular substrates for cellular replacement strategies following spinal cord injury. |
