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Lineage tracing reveals the origins and dynamics of macrophages in lung injury and repair

ABSTRACT: Macrophages play a vital role in tissue repair and regeneration following injury. However, the cell fate, dynamic change, and functional roles of macrophages from different origins during lung injury and repair are not fully understood. Here we used genetic lineage tracing and scRNA-seq approaches to explore the temporal and spatial roles of tissue-resident and recruited macrophages during pulmonary fibrosis. We observed a sharp reduction in tissue-resident macrophages during the early inflammatory phase, with their number stabilizing during recovery. Monocytes contributed substantially to the macrophage population during the fibrotic phase, initially differentiating into interstitial macrophages and later transitioning into alveolar macrophages through a transient state. Genetic ablation of monocytes led to a reduction in recruited macrophages and alleviated pulmonary fibrosis. Mechanistically, Notch signaling was found to negatively correlate with Wnt/β-catenin signaling in regulating monocyte recruitment and pulmonary fibrosis. Our study revealed the dynamic contributions and functions of macrophages from various sources in lung injury and regeneration.

ORGANISM(S): Mus musculus

PROVIDER: GSE279529 | GEO | 2026/01/21

REPOSITORIES: GEO

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Project description:In adult mice, “heart attack” or myocardial infarction (MI) activates the cardiac lymphatics, which undergo sprouting angiogenesis (lymphangiogenesis) and function to drain interstitial fluid and traffic macrophages to mediastinal lymph nodes (MLNs). This prevents oedema and reduces inflammatory/fibrotic immune cell content to improve cardiac function. Given the importance of the adult cardiac lymphatics in macrophage clearance after injury, we investigated their role across the neonatal “regenerative window”. At post-natal day 1 (P1) neonatal mice fully regenerate their heart following MI, in a pro-regenerative macrophage-dependent manner, whereas equivalent injury at post-natal day 7 (P7) leads to scarring driven by pro-fibrotic macrophages. We hypothesised that lymphatics respond and function differently during this “window” to clear macrophage-specific subtypes, depending upon their requirement for regeneration versus fibrotic repair. Normal lymphatic growth and sprouting was evident in intact neonatal hearts until P16, with strain-dependent developmental differences. The response to injury revealed limited lymphangiogenesis (lymphatic vessel growth and sprouting) and minimal clearance of macrophages from P1 compared to P7 infarcted hearts, as determined by adoptive transfer, and monitoring of cleared macrophages to MLNs. This is coincident with maturation of lymphatic endothelial cell junctions across the neonatal period via transition from “zipper” (impermeable) to “button” (permeable) -type junctions and altered signalling between lymphatic endothelial cells and macrophages, including differential expression of the lymphangiocrine factor Reelin (RELN). Finally, in mice lacking the lymphatic endothelial receptor-1 (LYVE-1), that exhibit impaired transmigration of interstitial macrophages to lymphatic vessels, magnetic resonance imaging (MRI) revealed a surprising impaired functional outcome in P1 mice 28 days post-MI. Given our observations that pro-regenerative macrophages at P1 are not trafficked, this suggested a distinct role for LYVE-1 in tissue-resident macrophages, consistent with its expression pattern in developing and post-natal hearts. Macrophage-specific deletion of Lyve1 during neonatal heart injury revealed impaired heart regeneration, characterised by persistent fibrosis, a reduced neovascular response and reduced function. ScRNA-seq of Lyve1 deficient CD45+ cells revealed a loss of tissue-resident macrophages and an increase in recruited monocytes which is predicted to increase inflammation and fibrosis, worsening the outcome post-MI. Collectively, this study reveals that cardiac lymphatics are developmentally compromised for clearance in early neonates, which enables retention of pro-regenerative tissue-resident macrophages, and that LYVE-1 plays an essential role in maintaining this population to promote heart regeneration and prevent inflammation and fibrotic repair.

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Lineage tracing reveals the origins and dynamics of macrophages in lung injury and repair

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