Endothelial KIT Signalling After Myocardial Infarction

急性心肌梗死(MI)对冠脉微循环造成大量损伤，导致血管崩解和毛细血管稀疏。几天内，梗死区就会形成新的血管丛，有助于限制瘢痕形成和左心室重构的程度。旁分泌生长因子在心肌梗死后血管生成的调控中起着核心作用。在先前的项目中，我们鉴定了单核/巨噬细胞来源的细胞因子陨星样蛋白(Metrnl)是一种新的血管生成因子和内皮细胞KIT受体的高亲和力配体。我们发现KIT(+)和KIT(-)内皮细胞都有助于梗死区的毛细血管形成。在Metrnl基因缺陷的小鼠中，Kit(+)ECs在梗死区的扩张被选择性地取消，动物出现严重的心力衰竭。我们的单细胞RNA测序(scRNA-seq)分析确定KIT(+)内皮细胞是心肌梗塞后高度激活的细胞群。我们得出结论，KIT标记的EC群体对正确的伤口愈合至关重要。我们推测，KIT与一个假定的辅助受体(见下文)一起，诱导这一EC群体的扩张和激活。这两个假设都将在我们的项目中进行调查。为了直接分析内皮Kit受体在MI后血管生成和伤口愈合中的重要性，我们建立了在MI前选择性删除ECs中Kit的Kitfl/fl小鼠。此外，我们正在计划对Metrnl缺陷和EC选择性Kit缺陷小鼠进行序列scRNA-seq分析，以表征Metrn1和Kit对EC隔室组成的影响，并确定MI后Metrn1和Kit激活的靶基因。我们特别感兴趣的是Metrnl和KIT是否也通过血管分泌生长因子影响梗塞的愈合。我们小组最近的观察表明，并不是所有表达KIT的细胞类型都对Metrnl有反应，这表明存在辅受体呈现Kit(+)ECs对Metrnl有反应。事实上，在生物信息学分析中，我们发现了KIT(+)ECs中的一个共同受体候选者，它似乎与KIT一样，是Metrnl介导的血管生成效应所必需的。我们希望在分子水平上了解Metrnl和/或Kit与该辅助受体的可能相互作用，并在功能丧失的小鼠模型中研究该辅助受体在心肌梗死后血管生成和伤口愈合中的重要性。我们的研究将使我们能够更好地了解心脏内皮细胞的异质性及其对心肌梗死后血管修复的重要性。

Acute myocardial infarction (MI) inflicts massive injury to the coronary microcirculation leading to vascular disintegration and capillary rarefication. Within days, a new vascular plexus develops in the infarct region, helping to limit the extent of scarring and left ventricular remodelling. Paracrine-acting growth factors play a central role in the regulation of angiogenesis after MI. In the previous project, we identified the monocyte- and macrophage-derived cytokine meteorin-like (METRNL) as a new angiogenic growth factor and high-affinity ligand for the endothelial KIT receptor. We found that both KIT(+) and KIT(-) endothelial cells (ECs) contribute to the capillarisation of the infarct region. In Metrnl-deficient mice, the expansion of KIT(+) ECs in the infarct region was selectively abolished and the animals developed severe heart failure. Our single-cell RNA sequencing (scRNA-seq) analyses identify KIT(+) ECs as a highly activated cell population after MI. We conclude that KIT labels an EC population that is crucial for proper wound healing. We postulate that KIT, along with a putative co-receptor (see below), induces the expansion and activation of this EC population. Both hypotheses shall be investigated in our project. In order to directly analyse the importance of the endothelial KIT receptor for angiogenesis and wound healing after MI, we have generated Kitfl/fl mice to selectively delete Kit in ECs before MI. Furthermore, we are planning sequential scRNA-seq analyses in Metrnl-deficient and EC-selective Kit-deficient mice to characterise the influence of METRNL and KIT on the composition of the EC compartment and to identify METRNL and KIT-activated target genes after MI. We are particularly interested in whether METRNL and KIT also influence infarct healing via angiocrine growth factors. Recent observations from our group indicate that not all KIT-expressing cell types are responsive to METRNL and suggest that there is a co-receptor rendering KIT(+) ECs METRNL-responsive. Indeed, in a bioinformatic analysis, we have discovered a co-receptor candidate in KIT(+) ECs that appears to be required, alongside KIT, for METRNL-mediated angiogenetic effects. We want to understand the putative interaction of METRNL and/or KIT with this co-receptor at the molecular level and to investigate the co-receptor’s importance for angiogenesis and wound healing after MI in a loss-of-function mouse model. Our investigations will enable a better understanding of cardiac EC heterogeneity and its importance for vascular repair after MI.