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

Abstract

Muscle damage elicits a sterile immune response that facilitates complete regeneration. Here, we utilized mass spectrometry-based lipidomics to map the mediator lipidome during the transition from inflammation to resolution and regeneration in skeletal muscle injury. We observed the temporal regulation of glycerophospholipids and the production of pro-inflammatory (e.g., leukotrienes, prostaglandins) and specialized pro-resolving (e.g., resolvins, lipoxins) lipid mediators, which 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-seq of macrophages stimulated with resolvin D2 (RvD2) showed similarities to transcriptional changes found during the temporal Ly6C hi to Ly6C lo macrophage transition. In vivo , RvD2 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.

The BACH1–HMOX1 Regulatory Axis Is Indispensable for Proper Macrophage Subtype Specification and Skeletal Muscle Regeneration

“…alternative markers, such as MHC class II, CD11b, and CCR2, and, thus, we acknowledge that profiling at the single-cell level would be needed to fully resolve this heterogeneity and understand the different function of each MF subset. Nonetheless, our results shown in this study and previously by our laboratory (11)(12)(13)57) support that Ly-6C high and Ly-6C low MFs in regenerating muscle display distinct inflammatory profiles and, thus, we believe that our CD45, Ly-6C, Ly-6G, and F4/80 gating strategy is sufficient to discriminate between inflammatory and repair type MFs. However, the epigenomic requirements and the main transcriptional drivers of the process are not known.…”

“…The phenotypic transition from inflammatory Ly-6C high to repair Ly-6C low cells is highly correlated with the tissue regeneration kinetics and is accompanied by a dynamic crosstalk between MFs and other muscle tissue components that lead to a hierarchical chromatin and transcriptional reprogramming process likely containing tissue-specific elements. This switch in MF phenotype has been documented extensively by multiple transcriptomic and lipidomic approaches by several laboratories, including ours (7,10,11,(18)(19)(20)57). Recently, muscle-infiltrating MFs were also gated based on their MHC class II expression (an indicator of Ag presentation) (58).…”

Age‐related decline of interferon‐gamma responses in macrophage impairs satellite cell proliferation and regeneration

“…It is known that Ly6C hi macrophages are recruited from circulation at 24 h after injury, 9 but the transcription profile is altered in Ly6C hi macrophages at various time points. 22,23 Therefore, we sorted CD45 + CD11b + F4/80 + Ly6C hi macrophages from young muscles at 1 and 3 days after injury and compared the expression of IFNRM signature genes in these cells. In addition to other IFNRM signature genes (Ifit3, Ifit1, Rsad2, Isg15, and Usp18), the expression of Cxcl10 was higher in macrophages at day 3 than in macrophages at day 1 ( Figure 4G).…”

Macrophages: The Potent Immunoregulatory Innate Immune Cells

“…The transition of monocytes into Ly6C hi (inflammatory) and Ly6C low (regenerative or repair) macrophages plays a crucial role in the process of muscle regeneration [161]. The Ly6C low macrophages in the skeletal muscle exhibit a distinct proresolving signature [specialized pro-resolving lipid mediators (SPMs), including resolvins (for example, RvD1, RvD2, RvE1)] that helps in the functional improvement in the process of muscle regeneration [162]. On the other hand Ly6C hi inflammatory monocytes further differentiate into skeletal tissue macrophages (both M1 and M2) and secrete pro-inflammatory cytokines (i.e.…”