Consequences of noggin expression by neural stem, glial, and neuronal precursor cells engrafted into the injured spinal cord.

Bone morphogenetic proteins (BMPs) are a large class of secreted factors, which serve as modulators of development in multiple organ systems, including the CNS. Studies investigating the potential of stem cell transplantation for restoration of function and cellular replacement following traumatic spinal cord injury (SCI) have demonstrated that the injured adult spinal cord is not conducive to neurogenesis or oligodendrogenesis of engrafted CNS precursors. In light of recent findings that BMP expression is modulated by SCI, we hypothesized that they may play a role in lineage restriction of multipotent grafts. To test this hypothesis, neural stem or precursor cells were engineered to express noggin, an endogenous antagonist of BMP action, prior to transplantation or in vitro challenge with recombinant BMPs. Adult rats were subjected to both contusion and focal ischemic SCI. One week following injury, the animals were transplanted with either EGFP- or noggin-expressing neural stem or precursor cells. Results demonstrate that noggin expression does not antagonize terminal astroglial differentiation in the engrafted stem cells. Furthermore, neutralizing endogenous BMP in the injured spinal cord significantly increased both the lesion volume and the number of infiltrating macrophages in injured spinal cords receiving noggin-expressing stem cell grafts compared with EGFP controls. These data strongly suggest that endogenous factors in the injured spinal microenvironment other than the BMPs restrict the differentiation of engrafted pluripotent neural stem cells as well as suggest other roles for BMPs in tissue protection in the injured CNS.