ABSTRACT
Zebrafish exhibit robust regeneration following spinal cord injury, promoted by macrophages that control post-injury inflammation. However, the mechanistic basis of how macrophages regulate regeneration is poorly understood. To address this gap in understanding, we conducted a rapid in vivo phenotypic screen for macrophage-related genes that promote regeneration after spinal injury. We used acute injection of synthetic RNA Oligo CRISPR guide RNAs (sCrRNAs) that were pre-screened for high activity in vivo. Pre-screening of over 350 sCrRNAs allowed us to rapidly identify highly active sCrRNAs (up to half, abbreviated as haCRs) and to effectively target 30 potentially macrophage-related genes. Disruption of 10 of these genes impaired axonal regeneration following spinal cord injury. We selected 5 genes for further analysis and generated stable mutants using haCRs. Four of these mutants (tgfb1a, tgfb3, tnfa, sparc) retained the acute haCR phenotype, validating the approach. Mechanistically, tgfb1a haCR-injected and stable mutant zebrafish fail to resolve post-injury inflammation, indicated by prolonged presence of neutrophils and increased levels of il1b expression. Inhibition of Il-1ß rescues the impaired axon regeneration in the tgfb1a mutant. Hence, our rapid and scalable screening approach has identified functional regulators of spinal cord regeneration, but can be applied to any biological function of interest.
Subject(s)
RNA, Guide, Kinetoplastida/genetics , Regeneration/genetics , Spinal Cord Regeneration/genetics , Transforming Growth Factor beta1/genetics , Zebrafish Proteins/genetics , Animals , Axons/metabolism , Axons/physiology , Clustered Regularly Interspaced Short Palindromic Repeats/genetics , Disease Models, Animal , Macrophages/metabolism , Osteonectin/genetics , Recovery of Function/genetics , Spinal Cord/growth & development , Spinal Cord/pathology , Spinal Cord Injuries/genetics , Spinal Cord Injuries/pathology , Spinal Cord Injuries/therapy , Spinal Cord Regeneration/physiology , Transforming Growth Factor beta3/genetics , Zebrafish/genetics , Zebrafish/growth & developmentABSTRACT
Spinal cord injury leads to a massive response of innate immune cells in non-regenerating mammals, but also in successfully regenerating zebrafish. However, the role of the immune response in successful regeneration is poorly defined. Here we show that inhibiting inflammation reduces and promoting it accelerates axonal regeneration in spinal-lesioned zebrafish larvae. Mutant analyses show that peripheral macrophages, but not neutrophils or microglia, are necessary for repair. Macrophage-less irf8 mutants show prolonged inflammation with elevated levels of Tnf-α and Il-1ß. Inhibiting Tnf-α does not rescue axonal growth in irf8 mutants, but impairs it in wildtype animals, indicating a pro-regenerative role of Tnf-α. In contrast, decreasing Il-1ß levels or number of Il-1ß+ neutrophils rescue functional regeneration in irf8 mutants. However, during early regeneration, interference with Il-1ß function impairs regeneration in irf8 and wildtype animals. Hence, inflammation is dynamically controlled by macrophages to promote functional spinal cord regeneration in zebrafish.
