Synaptotagmin 4 supports spontaneous axon sprouting after spinal cord injury

Injuries to the central nervous system (CNS) can cause severe neurological deficits. Axonal regrowth is a fundamental process for the reconstruction of compensatory neuronal networks after injury; however, it is extremely limited in the adult mammalian CNS. In this study, we conducted a loss-of-function genetic screen in cortical neurons, combined with a web-resource-based phenotypic screen, and identified synaptotagmin 4 (Syt4) as a novel regulator of axon elongation. Silencing Syt4 in primary cultured cortical neurons inhibits neurite elongation, with changes in gene expression involved in signaling pathways related to neuronal development. In a spinal cord injury model, inhibition of Syt4 expression in cortical neurons prevented axonal sprouting of the corticospinal tract, as well as neurological recovery after injury. These results provide a novel therapeutic approach to CNS injury by modulating Syt4 function. Significance Statement Promoting axonal regrowth has been considered a promising therapeutic target for functional recovery after central nervous system injury. In the present study, we used a web-resource-based phenotypic screening followed by loss-of-functional screening for neurite elongation. We identified a novel role of synaptotagmin 4 (Syt4), a well-characterized regulator of synaptic function, in neurite elongation. In addition, Syt4 knockdown in corticospinal tract inhibited axonal regrowth and functional recovery after spinal cord injury. In this way, we provide a new screening method, which allows us to efficiently find new targets regulating CNS therapeutics.