Connectivity of Neuronal Restricted Progenitors across a Model of Spinal Cord Injury.

摘要

Spinal cord injury (SCI) is a devastating condition characterized by disruption of axonal connections and permanent loss of function. Transplantation of neural progenitor cells (NPC), which reliably produce mature neurons and glia after transplantation in the injured spinal cord, is a promising therapeutic strategy for replacing neurons lost following SCI, but significant challenges remain regarding neuronal integration and functional connectivity. The overall goal of this thesis was to direct the functional integration of NPC derived neurons in a dorsal columns injury model of SCI. Specifically, this project tested the ability of NPC grafts to produce glutamatergic neurons that could reestablish connectivity by forming neuronal relays between injured dorsal column sensory axons and the denervated dorsal column nuclei (DCN).;Results presented in chapter 2 demonstrate that NPC grafts comprised of neuronal and glial restricted progenitors (NRP and GRP, respectively) produced glutamatergic and GABAergic neurons within the injury site. Additionally, results presented in chapter 2 demonstrated that injection of BDNF lentivirus in the DCN created a gradient of BDNF and that graft neurons responded by extending axons towards the source of BDNF. Results in chapter 3 demonstrate that NPC-derived neurons could extend axons into the DCN and make synapses with host neurons. Additionally, acute NRP/GRP grafts could support host axon regeneration into, but not beyond, the graft site. Host axons that entered the graft site made structural and functional synapses with graft neurons as shown with tracing, electron microscopy and induction of immediate early genes. Finally, the results in chapter 3 demonstrate that grafted axons relay physiological sensory signals from the hindlimb to the DCN. However, we did not detect robust responses from the post-synaptic host neurons in the DCN. These findings provide the first evidence for the ability of NPC to form a neuronal relay by extending active axons across the injured spinal cord to the intended target establishing a critical step for neural repair with stem cells.