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The role of the cardiac lymphatics and LYVE-1-dependent macrophages during neonatal mouse heart regeneration and transition to fibrotic repair

ABSTRACT: 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE301633 | GEO | 2025/08/05

REPOSITORIES: GEO

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Project description:Aims and introduction: Cardiac fibrosis is the hallmark of cardiac disease, particularly myocardial infarction (MI), and is one of the most prevalent causes of heart failure. MI is intricately linked to inflammation, extracellular matrix (ECM) remodelling, and cardiac fibrosis, however the mechanisms underpinning these events remain poorly understood. We recently identified that ECM1 has potential to play a key role in cardiac wound healing but the cellular origins in the heart and specific mechanisms of ECM1 in fibrosis remain elusive. Therefore, we investigated the spatiotemporal, cell specific, expression profile of ECM1 in the healthy and diseased mouse and human heart and investigate ECM1 dependent human cardiac fibroblast (HuCFb) cell signalling mechanisms. Methods and results: Western blotting, immunohistochemistry (IHC) and mRNA in-situ hybridisation revealed that ECM1 protein expression was significantly upregulated in human ischaemic and dilated heart failure patients, and predominantly localised interstitially to fibrotic, inflammatory, and peri-vascular areas. ECM1 specific analysis of the Litviňuková et al. (2020) single-cell and -nuclei RNA sequencing (sc/snRNAseq) dataset of healthy human hearts, and the Farbehi et al. (2019) scRNAseq dataset of mouse hearts post-MI demonstrated that ECM1 expression originates from fibroblasts, macrophages, and pericytes/vascular mural cells in the heart. Further, we identify that post-MI ECM1 is expressed in a temporal dynamic flux from unactivated fibroblasts in sham-operated mice, to M1 macrophages (M1MΦ) at day-3, and myofibroblasts and M2MΦ at day-7. Phosphoproteomics of ECM1 treated human cardiac fibroblast cells (HuCFb) alongside ECM1 to HuCFb cell surface protein binding pull-down and mass spectrometry, revealed that ECM1 signalling goes via proteins associated with Rho protein signal transduction, cell-cell adhesion, microtubule dynamics, and cell chemotaxis pathways, potentially initiated by ECM1 to CTNND1 binding on the cell surface. Further mechanistic analyses identified that ECM1 inhibits HuCFb cell migration and stimulates inflammatory (IL-6 and IL-1β mRNA expression), fibrotic (TGF-β1, TGF-β2 and Col1a2 mRNA expression), and non-canonical Wnt signalling pathways (Wnt5a mRNA expression and JNK1/2/3 and MYPT1 phosphorylation). Conclusions: This study demonstrates that ECM1 expression originates from macrophages and fibroblasts in the mouse and human heart. ECM1 has significant effects on HuCFb migration, inflammatory, fibrotic, Rho protein, and Wnt5a/non-canonical Wnt signalling pathways. Together, ECM1 plays an important role in cardiac wound healing and may represent a novel mechanism of inflammation-fibrosis crosstalk and progression post-MI.

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The role of the cardiac lymphatics and LYVE-1-dependent macrophages during neonatal mouse heart regeneration and transition to fibrotic repair

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