Defining the Robustness of Zebrafish Spinal Cord Regeneration

Primary and secondary tissue damage from spinal cord injury permanently impairs sensory and motor functions, causing irreversible paralysis. Developing therapies to treat and reverse spinal cord injury is an urgent need in regenerative medicine and remains an enormous research challenge. The path to an effective cure is likely to require a combination of molecular, cellular, electrostimulatory, and engineering approaches, and must be guided by a deeper understanding of the inherent regenerative capacity of spinal cord tissue. Following spinal cord injury, nerve cell death and scar formation inhibit regeneration. To date, attempts to alleviate the negative effects of scarring and to support cell survival and nerve regrowth after injury have not overcome the challenges of mammalian spinal cord regeneration. By contrast with mammals, teleost zebrafish can form new neurons, regrow axons, and recover the ability to swim just 6 to 8 weeks after a paralyzing injury that completely severs the spinal cord. Importantly, these regenerative events proceed without massive scarring. Instead, following injury, specialized non-neural glia and other cells build a tissue bridge to connect the two severed ends, allowing axons to grow across the wound and reestablish crucial connections. Encouraging key mammalian cells to adopt this bridging behavior would shift the mammalian spinal cord injury response from scarring to regeneration, potentially to an extent sufficient to save tissue function and restore locomotor function. This highly desirable outcome requires an extensive understanding of the molecular signals that enable or inhibit innate spinal cord regeneration. In preliminary studies, we have generated and bioinformatically assessed datasets of cellular and transcriptome changes that occur in reproducible minority cohorts of zebrafish that retain paralysis after transection injury, with the idea that factors preferentially induced in a failure context could inform barriers to regeneration. We propose to: 1) elucidate cell state changes over time associated with regeneration versus failure after spinal cord injury; and 2) define and manipulate the implicated molecular machinery to reduce the incidence of spontaneous regenerative failure. Our work will provide a new view and understanding of regenerative capacity in the context of spinal cord injury.