Improving Connectivity Between Host and Neural Stem Cell Grafts After SCI

About This Grant

Significance to VA: There are few treatment options for Veterans with spinal cord injuries (SCI). Recently the Tuszynski lab has developed an approach where neuronal stem cells are implanted into the injury site. These grafted cells differentiate into neurons which extend axons caudally to form synapses with the host; simultaneously, host axons enter the graft and form synapses with graft neurons. This system restores connectivity across the lesion site and improves functional recovery in rodent and primate models. However, recovery is incomplete, in part because of only partial growth of host axons into and within the graft. Innovation and Impact: This CDA-1 proposal will use a new path to enhance the graft by exploiting the existing biology of the graft to enhance its functionality. Specifically, it will explore the role of axonal guidance cues (secreted molecules that attract or repel growing axons) in the graft and manipulate these cues to increase host axon growth into the graft and improve connectivity across the injury site. The Tuszynski lab is currently beginning the process of clinical implementation of our graft system. Success in this project and follow-up work in a CDA-2 award will lead to approaches which can be used to improve the functionality of grafts to improve recovery for SCI patients including Veterans. Specific Aims: This proposal will test the hypothesis that a mismatch of secreted guidance cues may limit host axon regeneration into the graft. This proposal will target mechanisms associated with axon growth into stem cell grafts and test whether modifying guidance cues will increase host axon regeneration into the graft. Aim 1 will focus on reducing the inhibitory effects of the injury site. Injury sites express Wnts which inhibit the growth of corticospinal tract (CST) axons via binding to the Ryk receptor. This aim will test the hypothesis that neutralization of the inhibitory effect of Wnts will increase CST axon growth into the graft. Aim 2 will focus on increasing the attractive environment of the graft. Axons that enter the graft grow towards appropriate interneuronal targets, indicating that some attractive cue exists; however, the relatively short distance of growth within the graft (1-2 mm) suggests that the effects of this cue are limited. A viral labeling and sequencing approach will be used to identify and validate these attractive cues released by the graft. Methodology: Both Aims will be performed in mice using a C4 contusion model of spinal cord injury. Regeneration of host CST axons into the graft will be assessed with histology (N=12 per group). Functional recovery following SCI will be assessed with behavioral performance on a skilled reaching task (N=30 per group). Treated animals will be compared to our current grafting paradigm to determine if these treatments improve the efficacy of the graft in recovery following SCI. Path to Translation/Implementation: Treatments for spinal cord injury are currently limited, and success of this proposal may increase the effectiveness and therapeutic potential of stem cell grafts. While work in this proposal is limited to mouse grafts, future work in a CDA-2 award would test any treatments identified here in human cell grafts which could then be implemented as part of a clinical product to treat Veterans with SCI. The proposed project will provide excellent research training for the applicant including systems neuroscience, spinal cord injury, and human disease. Additionally, he will learn multiple techniques including rodent models of SCI, mouse behavioral assessment, and RNA sequencing. The research environment of the Tuszynski lab is highly collaborative so he will gain exposure to many techniques and subject areas beyond his own research, refine his scientific presentation skills, mentor younger scientists, and network with leaders in the field. Finally, he will directly engage with Veterans by shadowing doctors at the VA San Diego Medical Center while they treat Veterans recovering from SCI. Overall, this CDA-1 grant will provide new insight into novel therapeutic avenues for spinal cord repair and allow the applicant to transition into a career as an independent investigator at the VA.