Purinergic Regulation of Neurogenesis Following Spinal Cord Injury in Danio Rerio

Abstract

In contrast to mammals, adult zebrafish undergo successful neural regeneration following spinal cord injury (SCI). Radial glia (RG) lining the zebrafish central canal undergo injury-induced proliferation and subsequent neuronal differentiation to replace damaged cells and restore motor function. However, the molecular mechanisms that underlie these processes remain elusive. Here, we demonstrate that signaling through the evolutionarily conserved purinergic P2X7 receptor is involved. Within the zebrafish spinal cord, P2X7 receptors have widespread distribution with specific localization to neurons and radial glia. At the protein level, the predominant P2X7 receptor isoforms in zebrafish did not include the full-length variant expressed throughout the murine central nervous system, but two truncated splice variants. In response to SCI, protein expression of the 50 kDa isoform became downregulated at 7 dpi and returned to basal levels of expression at 14 and 21 dpi when compared to naïve controls. Meanwhile, expression of the 37 kDa isoform did not change following injury. Pharmacological activation of P2X7 following SCI resulted in a greater number of proliferating cells around the central canal by 7 dpi, while P2X7 inhibition appeared to have no effect. At 14 dpi, these treatments did not have a significant effect on the number of neurons within the injured spinal cord. This data indicates that P2X7 receptor activation is sufficient to induce cellular proliferation, but not a necessary mediator of either proliferation or neurogenesis following SCI in adult zebrafish. Our findings suggest that unlike in humans, P2X7 signaling may not play a maladaptive role following SCI in adult zebrafish.