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 并发症为短肠综合征和神经发育迟缓，严重影响患者的生活质量。 这些病人。与其他新生儿疾病不同的是，目前没有专门的治疗干预措施来预防或 治疗NEC。我们发现了新的证据，表明未发育的肠道微血管系统发挥着以前未被认识到的作用 但在NEC中扮演着至关重要的角色。事实上，我们发现正常的肠道粘膜微血管系统经历了显著的 围产期发育，胎儿肠道高水平表达血管内皮细胞 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 在新生小鼠模型中，信号促进NEC。VEGFR2调控转录因子FOXM1的表达 调节细胞周期进程，在新生儿肠内皮细胞(EndCs)和过表达FOXM1的小鼠中 保护不受NEC攻击。我们的初步数据进一步表明，在新生儿的肠道中，血管生长和EndC 胚胎巨噬细胞(EMF)通过依赖胰岛素样生长因子-1(IGF-1)支持增殖 IGF-1诱导血管内皮生长因子表达从而通过促进肠道保护NEC的机制 微血管扩张。这些数据为我们的首要前提提供了基础，即在早产儿中， 氧介导的肠道促血管生成信号通路(如血管内皮生长因子/血管内皮生长因子R2)的下调 分娩发生在肠道微血管充分发育之前。围产期应激(如炎症) 减少肠道电动势分泌IGF-1，从而减少EndC-IGF-1介导的血管内皮生长因子的产生。由此产生的 VEGFR2信号的减少会损害FOXM1依赖的EndC的增殖和随后的血管发育。 因此，不发达的肠道微血管系统，虽然足够“无菌”的空腹肠道，但 不能满足肠道喂养和细菌定植等出生后应激的代谢需求， 这会导致肠道缺血和坏死。在这项提议中，我们将检验假设，在婴儿中， NEC的高风险，缺乏肠道电动势产生的IGF-1减少了EndCs中的VEGFR2/FOXM1信号，因此 扰乱围产期肠道粘膜毛细血管的正常发育，使肠道 在围产期应激(例如，炎症、缺氧、配方奶喂养)下容易发生NEC。我们将解决以下问题 具体目标：1)确定有缺陷的EndC VEGFR2信号通路如何促进NEC。为了达到这个目的，我们将利用小说 具有内皮细胞特异性VEGFR2缺陷或内皮细胞特异性FOXM1表达的小鼠；2)定义 电磁场促进新生肠道内皮细胞和微血管VEGFR2信号转导的细胞机制 防止NEC的发展。在这个目标中，我们将确定电动势衍生的IGF-1如何促进内皮细胞信号转导 以防止NEC的入侵。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，将为测试新的治疗策略提供坚实的基础 这可以保护局部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.