Endothelial KIT Signalling After Myocardial Infarction

急性心肌梗死（MI）对冠状动脉微循环造成严重损伤，导致血管解体和毛细血管稀疏。几天内，梗死区形成新的血管丛，有助于限制疤痕和左心室重构的程度。旁分泌作用的生长因子在心肌梗死后血管生成的调控中发挥着核心作用。在之前的项目中，我们发现单核细胞和巨噬细胞来源的细胞因子meteorin-like （METRNL）是一种新的血管生成生长因子和内皮KIT受体的高亲和力配体。我们发现KIT（+）和KIT（-）内皮细胞（ECs）都有助于梗死区域的毛细血管化。在metrnl缺陷小鼠中，KIT(+) ECs在梗死区域的扩张被选择性地消除，动物发生严重的心力衰竭。我们的单细胞RNA测序（scRNA-seq）分析发现KIT(+) ECs是心肌梗死后高度活化的细胞群。我们得出结论，KIT标记的EC群对伤口愈合至关重要。我们假设KIT与一种推定的共受体（见下文）一起，诱导了这种EC群体的扩张和激活。这两种假设都将在我们的项目中进行调查。为了直接分析内皮KIT受体对心肌梗死后血管生成和伤口愈合的重要性，我们培育了Kitfl/fl小鼠，在心肌梗死前选择性地删除ECs中的KIT。我们计划在METRNL缺陷和EC选择性KIT缺陷小鼠中进行序列scRNA-seq分析，以表征METRNL和KIT对EC室组成的影响，并鉴定心肌梗死后METRNL和KIT激活的靶基因。我们对METRNL和KIT是否也通过血管分泌生长因子影响梗死愈合特别感兴趣。我们小组最近的观察表明，并非所有表达KIT的细胞类型都对METRNL有反应，并表明存在一种共同受体使KIT(+) ECs对METRNL有反应。事实上，在生物信息学分析中，我们已经发现KIT(+) ECs中的一种候选共受体，与KIT一起，似乎是metrnl介导的血管生成作用所必需的。我们希望在分子水平上了解METRNL和/或KIT与这种共受体的相互作用，并在功能丧失小鼠模型中研究这种共受体对心肌梗死后血管生成和伤口愈合的重要性。我们的研究将有助于更好地了解心脏EC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.