Zholudeva, L. | Search bioRxiv

bioRxiv2026

Long-term Connectivity between Spinal Cord Tissue Transplants and the Injured Phrenic Motor Network

Restoring vital motor functions after spinal cord injury (SCI) remains a central challenge in neuroscience and regenerative medicine. Cervical SCI can cause life-threatening respiratory deficits by damaging the phrenic motor network that controls the diaphragm. Cellular transplantation offers a viable means to improve function by providing new neurons that can relay supraspinal drive to denervated spinal phrenic networks, yet the long-term stability of transplants is poorly defined. Here, we examine donor-host neuronal synaptic connectivity in a respiratory model of cervical SCI, 1-year post-transplantation in adult rats. Embryonically-derived spinal cord tissue was transplanted into the lesion cavity one-week post-SCI, and transplant integration and diaphragm function were assessed at 1-month and 1-year post-transplantation. At 1-month, transplant-recipients exhibited significantly greater diaphragm output than injured, vehicle control animals. The extent of recovery at 1-year, however, was significantly less, coinciding with anatomical changes in graft neuronal density and donor-host connectivity, revealed by transneuronal tracing (pseudorabies virus). These results demonstrate that embryonic spinal cord transplants can improve phrenic motor activity after cervical SCI, but that long-term efficacy may be limited by reduced donor-host connectivity. Significance StatementCell transplantation can repair injured spinal cord circuits, but whether donor-host connections persist long term remains unclear. Using a rat model of cervical spinal cord injury, we show that embryonic spinal cord transplants improve diaphragm activity and integrate with the injured phrenic motor network at early time points, but these benefits decline by 1 year after transplantation. This loss of functional recovery is accompanied by reduced transneuronal labeling of donor neurons and changes in graft tissue composition. These results provide important proof of principle that transplant-host connectivity can be evaluated over extended survival times and identify long-term stability of donor-host integration as a critical challenge for achieving durable respiratory repair after spinal cord injury.

neuroscience↗

bioRxiv2024

Human spinal interneurons repair the injured spinal cord through synaptic integration

Advances in cell therapy offer promise for some of the most devastating neural injuries, including spinal cord injury (SCI). Endogenous VSX2-expressing spinal V2a interneurons have been implicated as a key component in plasticity and therapeutically driven recovery post-SCI. While transplantation of generic V2a neurons may have therapeutic value, generation of human spinal V2a neurons with rostro-caudal specificity and assessment of their functional synaptic integration with the injured spinal cord has been elusive. Here, we efficiently differentiated optogenetically engineered cervical V2a spinal interneurons (SpINs) from human induced pluripotent stem cells and tested their capacity to form functional synapses with injured diaphragm motor networks in a clinically-relevant sub-acute model of cervical contusion injury. Neuroanatomical tracing and immunohistochemistry demonstrated transplant integration and synaptic connectivity with injured host tissue. Optogenetic activation of transplanted human V2a SpINs revealed functional synaptic connectivity to injured host circuits, culminating in improved diaphragm activity assessed by electromyography. Furthermore, optogenetic activation of host supraspinal pathways revealed functional innervation of transplanted cells by host neurons, which also led to enhanced diaphragm contraction indicative of a functional neuronal relay. Single cell analyses pre- and post-transplantation suggested the in vivo environment resulted in maturation of cervical SpINs that mediate the formation of neuronal relays, as well as differentiation of glial progenitors involved in repair of the damaged spinal cord. This study rigorously demonstrates feasibility of generating human cervical spinal V2a interneurons that develop functional host-transplant and transplant-host connectivity resulting in improved muscle activity post-SCI.

neuroscience↗