Neutrophil extracellular traps impair regeneration

Fibrosis is a major health burden across diseases and organs. To remedy this, we study wound induced hair follicle regeneration (WIHN) as a model of non-fibrotic healing that recapitulates embryogenesis for de novo hair follicle morphogenesis after wounding. We have previously demonstrated that TLR3 promotes WIHN through binding dsRNA, but the source of which is still unclear. Here, we demonstrate that multiple distinct contexts of high WIHN all show a strong neutrophil signature, and given the likelihood of nuclear dsRNA release during the production of neutrophil extracellular trap (NETs), we hypothesized that mature neutrophils and NETs might promote WIHN. Consistent with this, in addition to the presence of mature neutrophils shortly after wounding, neutrophils remain within the wound after the barrier is reestablished, where they produce extracellular traps (NETs) that likely release spliceosomal U1 dsRNA. Contrary to our hypothesis, genetic models of neutrophil depletion show enhanced WIHN. Pad4 null mice that are defective in NET production also augment WIHN. Finally, using single-cell RNA sequencing, we identified a dramatic increase in mature neutrophils in the wound beds of low regenerating Tlr3-/- mice. Taken together, these results demonstrate that although mature neutrophils are stimulated by a common pro-regenerative cue, their presence and NETs hinder WIHN.