Kessel, F. | bioRxiv Science

bioRxiv2026

A reparative neutrophil subpopulation promotes spinal cord regeneration in zebrafish by controlling macrophage inflammation via Il-4

In mammals, a dysregulated immune response is detrimental to spinal cord repair. In zebrafish, which are capable of spinal cord regeneration, the immune response promotes regeneration. Neutrophils are the first immune cells to arrive at a spinal cord injury site, but their role in successful regeneration is not fully understood. Here we show that ablating neutrophils, including a subpopulation that expresses the cytokine il4, increases expression of il1b (coding for Il-1{beta}) in macrophages/microglia and impairs anatomical and functional recovery after a spinal cord injury in larval zebrafish. Regeneration is fully rescued by over-expression of il4 alone or experimentally reducing Il-1{beta} levels. Disruption of il4 mimics the detrimental effect of neutrophil ablation for axonal regeneration and is also rescued by reducing Il-1{beta} levels. Hence, after spinal cord injury, a pro-regenerative neutrophil subpopulation promotes spinal cord regeneration in larval zebrafish by controlling expression of il1b in macrophages/microglia. For this neutrophil action, il4 expression is necessary and sufficient. HIGHLIGHTS- Neutrophil ablation impairs spinal cord repair in zebrafish - The neutrophil response can be replaced by reducing Il-1{beta} levels - A pro-regenerative subpopulation of neutrophils expresses il4 - il4 overexpression fully rescues effects of neutrophil ablation

neuroscience↗

bioRxiv2024

Macrophage crosstalk with neural progenitors and fibroblasts controls regenerative neurogenesis via Sema4ab after spinal cord injury in zebrafish

Zebrafish, in contrast to mammals, regenerate neurons after spinal cord injury, but little is known about the control mechanisms of this process. Here we use scRNA-seq and in vivo experiments to show that sema4ab, mainly expressed by lesion-reactive microglia, attenuates regenerative neurogenesis by changing the complex lesion environment. After spinal injury, disruption of sema4ab doubles the number of newly generated progenitor cells and neurons but attenuates axon regrowth and recovery of swimming function. Disruption of the plxnb1a/b receptors, selectively expressed by neural progenitor cells, increases regenerative neurogenesis. In addition, disruption of sema4ab alters activation state and cytokine expression of microglia, such that fibroblasts increase expression of the cytokine tgfb3, which strongly promotes regenerative neurogenesis. Hence, sema4ab in microglia attenuates regenerative neurogenesis in multiple ways, likely directly through plxnb1a/b receptors and indirectly, by controlling the inflammatory milieu and tgfb3 levels. Targeting Sema4A-dependent signalling in non-regenerating vertebrates may be a future strategy to improve regenerative outcomes. HIGHLIGHTS- Microglia suppress pro-regenerative fibroblast signalling in a spinal injury site - Fibroblasts promote regenerative neurogenesis via Tgfb3 signalling - sema4ab promotes microglia activation state after spinal injury - scRNA-seq reveals full complement of sema4ab-dependent changes on different cell types during repair of a spinal lesion site

neuroscience↗