Role of the intestinal microvasculature in necrotizing enterocolitis

摘要 坏死性小肠结肠炎（NEC）是早产儿发病和死亡的主要原因。共同的长期 并发症是短肠综合征和神经发育迟缓，这显著影响了患者的生活质量。 这些病人。与其他新生儿疾病相比，目前没有具体的治疗干预措施来预防或治疗新生儿疾病。 治疗NEC。我们发现了新的证据，表明不发达的肠道微血管系统在以前未被认识到的 但在NEC扮演着重要角色事实上，我们表明，正常的肠道粘膜微血管系统经历了显着的 在围产期的发展，胎儿肠道表达高水平的血管内皮细胞， 血管生成的关键调节因子-生长因子-A（VEGF）及其受体VEGFR2。此外，有缺陷的VEGFR2 信号传导促进新生小鼠模型中的NEC。VEGFR2控制转录因子FoxM1的表达 调节细胞周期进程，在新生儿肠内皮细胞（EndCs），和小鼠过表达FoxM1， 保护NEC。我们的初步数据进一步表明，在新生儿肠道，血管生长和EndC 增殖是由胚胎巨噬细胞（eMf）通过胰岛素样生长因子-1（IGF-1）依赖性 机制，IGF-1诱导VEGF表达，从而通过促进肠上皮细胞增殖， 微血管扩张这些数据为我们的总体假设提供了基础，即在早产儿中， 氧介导的肠道促血管生成信号通路（如VEGF/VEGFR2）下调， 在肠道微血管系统充分发育之前分娩。围产期应激（如炎症） 通过肠eMf减少IGF-1分泌，从而减少EndC IGF-1介导的VEGF产生。所得 VEGFR2信号传导的减少损害FoxM1依赖性EndC增殖和随后的血管发育。 因此，不发达的肠微血管系统虽然足以用于"无菌"禁食的肠，但变得 不足以满足出生后应激如肠内喂养和细菌定植的代谢需求， 这导致肠缺血和坏死。在这个提议中，我们将检验一个假设，即在婴儿中， NEC风险较高，肠eMf产生IGF-1的缺乏降低了EndCs中的VEGFR2/FoxM1信号传导，因此 在围产期扰乱肠粘膜毛细血管的正常发育， 在围产期应激下易于发生NEC（例如，炎症、缺氧、配方喂养）。我们将解决以下问题 具体目的：1）确定缺陷性EndC VEGFR2信号传导如何促进NEC。为了实现这一目标，我们将利用新的 具有内皮细胞特异性VEGFR2缺陷或具有内皮细胞特异性FoxM1表达的小鼠; 2）定义 eMf促进新生儿肠EndCs和微血管中VEGFR2信号传导的细胞机制 防止NEC的发展。在这个目标中，我们将确定如何eMf衍生的IGF-1促进内皮细胞信号转导 保护NEC。这些研究将描述炎症和肠道微血管之间的相互作用 NEC发病机制的研究进展，并将为测试新的治疗策略提供坚实的基础 其可以保留局部VEGFR2信号以防止NEC。

ABSTRACT Necrotizing enterocolitis (NEC) is a major cause of morbidity and mortality for premature infants. Common long-term complications are short gut syndrome and neurodevelopmental delay, which significantly impact the quality of life of these patients. In contrast to other neonatal diseases, no specific therapeutic intervention currently exists to prevent or treat NEC. We found novel evidence that an underdeveloped gut microvasculature plays a previously unrecognized but crucial role in NEC. Indeed, we show that the normal gut mucosal microvasculature undergoes significant development during the perinatal period, and that the fetal intestine expresses high levels of both vascular endothelial growth factor-A (VEGF), a key regulator of angiogenesis, and its receptor VEGFR2. Furthermore, defective VEGFR2 signaling promotes NEC in a neonatal mouse model. VEGFR2 controls the expression of FoxM1, a transcription factor regulating cell cycle progression, in neonatal intestinal endothelial cells (EndCs), and mice overexpressing FoxM1 are protected against NEC. Our preliminary data further suggest that in the neonatal intestine, vascular growth and EndC proliferation are supported by embryonic macrophages (eMf) via an insulin-like growth factor-1 (IGF-1)-dependent mechanism, with IGF-1 inducing VEGF expression and thereby protecting against NEC by promoting intestinal microvascular expansion. These data provide the basis for our overarching premise that, in premature infants, the oxygen-mediated downregulation of intestinal pro-angiogenic signaling pathways (such as VEGF/VEGFR2) due to birth occurs before the intestinal microvasculature sufficiently develops. Perinatal stresses (such as inflammation) reduce IGF-1 secretion by intestinal eMf, thereby decreasing EndC IGF-1-mediated VEGF production. The resultant decrease in VEGFR2 signaling impairs FoxM1-dependent EndC proliferation and subsequent vascular development. Therefore, the underdeveloped intestinal microvasculature, while sufficient for a “sterile” fasted intestine, becomes inadequate to meet the metabolic demand of postnatal stresses such as enteral feeding and bacterial colonization, and this results in intestinal ischemia and necrosis. In this proposal, we will test the hypothesis that, in infants at high risk for NEC, lack of IGF-1 production by intestinal eMf decreases VEGFR2/FoxM1 signaling in EndCs, thus perturbing the normal development of intestinal mucosal capillaries during the perinatal period and making the intestine prone to NEC under perinatal stresses (e.g., inflammation, hypoxia, formula-feeding). We will address the following specific aims: 1) Determine how defective EndC VEGFR2 signaling promotes NEC. For this aim, we will utilize novel mice with endothelial cell-specific VEGFR2 deficiency or with endothelial cell-specific FoxM1 expression; 2) Define the cellular mechanisms by which eMf promote VEGFR2 signaling in neonatal intestinal EndCs and microvascular development to prevent NEC. In this aim, we will determine how eMf-derived IGF-1 promote endothelial cell signaling to protect against NEC. These studies will characterize the interaction between inflammation and gut microvasculature development in the pathogenesis of NEC and will provide a solid foundation for testing novel therapeutic strategies that can preserve local VEGFR2 signaling to prevent NEC.