ABSTRACT
Recent studies have suggested that lymphatics help to restore heart function after cardiac injury1-6. Here we report that lymphatics promote cardiac growth, repair and cardioprotection in mice. We show that a lymphoangiocrine signal produced by lymphatic endothelial cells (LECs) controls the proliferation and survival of cardiomyocytes during heart development, improves neonatal cardiac regeneration and is cardioprotective after myocardial infarction. Embryos that lack LECs develop smaller hearts as a consequence of reduced cardiomyocyte proliferation and increased cardiomyocyte apoptosis. Culturing primary mouse cardiomyocytes in LEC-conditioned medium increases cardiomyocyte proliferation and survival, which indicates that LECs produce lymphoangiocrine signals that control cardiomyocyte homeostasis. Characterization of the LEC secretome identified the extracellular protein reelin (RELN) as a key component of this process. Moreover, we report that LEC-specific Reln-null mouse embryos develop smaller hearts, that RELN is required for efficient heart repair and function after neonatal myocardial infarction, and that cardiac delivery of RELN using collagen patches improves heart function in adult mice after myocardial infarction by a cardioprotective effect. These results highlight a lymphoangiocrine role of LECs during cardiac development and injury response, and identify RELN as an important mediator of this function.
Subject(s)
Heart/embryology , Lymphatic System/cytology , Lymphatic System/metabolism , Myocardium/cytology , Myocytes, Cardiac/cytology , Regeneration , Signal Transduction , Animals , Animals, Newborn , Apoptosis , Cell Adhesion Molecules, Neuronal/deficiency , Cell Adhesion Molecules, Neuronal/genetics , Cell Adhesion Molecules, Neuronal/metabolism , Cell Proliferation , Cell Survival , Cells, Cultured , Endothelial Cells/metabolism , Extracellular Matrix Proteins/deficiency , Extracellular Matrix Proteins/genetics , Extracellular Matrix Proteins/metabolism , Female , Humans , Integrin beta1/metabolism , Mice , Myocardial Infarction/metabolism , Myocardial Infarction/pathology , Myocytes, Cardiac/metabolism , Nerve Tissue Proteins/deficiency , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/metabolism , Organ Size , Organogenesis , Reelin Protein , Serine Endopeptidases/deficiency , Serine Endopeptidases/genetics , Serine Endopeptidases/metabolismABSTRACT
Recent findings indicate that mitochondrial respiration regulates blood endothelial cell proliferation; however, its role in differentiating lymphatic endothelial cells (LECs) is unknown. We hypothesized that mitochondria could work as a sensor of LECs' metabolic specific needs by determining their functional requirements according to their differentiation status and local tissue microenvironment. Accordingly, we conditionally deleted the QPC subunit of mitochondrial complex III in differentiating LECs of mouse embryos. Unexpectedly, mutant mice were devoid of a lymphatic vasculature by mid-gestation, a consequence of the specific down-regulation of main LEC fate regulators, particularly Vegfr3, leading to the loss of LEC fate. Mechanistically, this is a result of reduced H3K4me3 and H3K27ac in the genomic locus of key LEC fate controllers (e.g., Vegfr3 and Prox1). Our findings indicate that by sensing the LEC differentiation status and microenvironmental metabolic conditions, mitochondrial complex III regulates the critical Prox1-Vegfr3 feedback loop and, therefore, LEC fate specification and maintenance.