Dynamic changes to lipid mediators support transitions among macrophage subtypes during muscle regeneration

Muscle damage elicits a sterile immune response that facilitates complete regeneration. Here, we used mass spectrometry-based lipidomics to map the mediator lipidome during the transition from inflammation to resolution and regeneration in skeletal muscle injury. We observed temporal regulation of glycerophospholipids and production of pro-inflammatory lipid mediators (for example, leukotrienes and prostaglandins) and specialized pro-resolving lipid mediators (for example, resolvins and lipoxins) that were modulated by ibuprofen. These time-dependent profiles were recapitulated in sorted neutrophils and Ly6C^hi and Ly6C^lo muscle-infiltrating macrophages, with a distinct pro-resolving signature observed in Ly6C^lo macrophages. RNA sequencing of macrophages stimulated with resolvin D2 showed similarities to transcriptional changes found during the temporal transition from Ly6C^hi macrophage to Ly6C^lo macrophage. In vivo, resolvin D2 increased Ly6C^lo macrophages and functional improvement of the regenerating muscle. These results reveal dynamic lipid mediator signatures of innate immune cells and provide a proof of concept for their exploitable effector roles in muscle regeneration.