Transplantation of bone marrow stromal cells enhances infiltration and survival of CNP and Schwann cells to promote axonal sprouting following complete transection of spinal cord in adult rats.

This study aimed to investigate the roles of bone marrow stromal cells (BMSCs) in promoting axonal regeneration after complete transection of spinal cord in adult rats. Transplantation was done 9 days after injury. Only a few BMSCs were detected at the injury site 8 weeks after transplantation, yet there was robust growth of axons. The scarcity of surviving BMSCs may attribute to the adverse conditions in their ambient environment. In this connection, the immediate accumulation of a large number of macrophages/reactive microglia following BMSCs transplantation and subsequent cavitation of tissues may be detrimental to their survival. An unexpected finding following BMSCs transplantation was the marked increase in the nestin, GFAP, NF200, olig 3 and CNP positive cells at the injury site. Immunoelectron microscopy showed CNP cells were oval or fibroblast-like and had multiple perineurial-like compartments with long extending filopodia. The spatial relationship between regenerating axons and CNP-positive cells was also confirmed by double immunofluorescence staining. Our results suggest that transplantation of BMSCs elicits the influx and survival of local cells including CNP positive cells and Schwann cells into injury site, which provide structural support for the axon regeneration and remyelination after spinal cord injury.