Single Cell Atlas of Injured Sciatic Nerve Tissue

Sciatic nerve crush (SNC) triggers sterile inflammation within the distal nerve and de-afferented dorsal root ganglia (DRGs). In the nerve, neutrophils and pro-inflammatory Ly6Chigh monocytes appear first and rapidly give way to Ly6Clow resolving macrophages. Transcriptional profiling of injured nerve tissue identifies six macrophage subpopulations, repair Schwann cells and mesenchymal cells as the main cell types. Macrophages at the nerve crush site are distinct from macrophages associated with degenerating nerve fibers. Monocytes and macrophages in the injured nerve “eat” apoptotic cell corpses of leukocytes and thereby contribute to an anti-inflammatory milieu. Studies with chimeric mice show that following SNC few blood-derived immune cells enter DRGs. Myeloid cells in the injured nerve, but not DRGs, express the receptor for the chemokine GM-CSF. In the absence of GM-CSF, conditioning-lesion induced regeneration of DRG neuron central projections is abrogated. Thus, a carefully orchestrated immune response in the nerve is required for conditioning-lesion induced neurorepair.