THE ROLE OF PAF IN NEONATAL-NECROTIZING ENTEROCOLITIS

坏死性小肠结肠炎（NEC）是早产儿常见的胃肠道疾病，目前尚无明确的病因和治疗方法。目前的理论表明，缺氧、细菌定植、喂养和早产等许多因素都会导致疾病的发生，但将危险因素与肠道病理联系起来的最终共同途径仍不清楚。我们前期研究表明炎症介质血小板激活因子（PAF）可能参与肠坏死的发病机制。该提案的总体重点是研究 PAF 和 PAF 代谢改变在该疾病中的重要性，并描绘发病机制中涉及的具体机制。我们假设新生儿 NEC 中局部肠道 PAF 代谢发生改变，PAF 失调导致肠上皮细胞凋亡、紧密连接完整性破坏、粘膜通透性以及继发性炎症级联的激活，并且这种调节对于疾病的发展至关重要。因此，本提案的具体目标是：l) 阐明发育中和受损肠道中 PAF 代谢和生物活性改变的机制，2) 研究 PAF 诱导的粘膜损伤的机制，并描绘 PAF 诱导的粘膜损伤在 NEC 发病机制中的潜在作用。为了实现我们的目标，我们开发了一种模仿人类状况的 NEC 新生大鼠模型，并将研究 PAF 代谢改变对肠坏死发展以及肠损伤演变之前的病理生理事件的影响。此外，为了确定上皮细胞损伤的细胞和分子水平调节，我们将使用肠上皮的各种组织培养模型。为了阐明导致肠道微环境中 PAF 调节改变的具体机制，我们将评估局部 PAF 产生的激活、PAF 降解的减少或 PAF 受体表达和功能的改变是否是由典型的 NEC 危险因素（配方奶喂养和窒息）或发育成熟过程中的变化引起的。此外，我们将评估改变的PAF调节对细胞凋亡和粘膜通透性的影响，并阐明这些因素在NEC启动中的作用以及PAF受体激活后导致这些事件的信号转导机制。这些实验的结果应阐明将 NEC 危险因素与病理结果联系起来的关键机制，并可能为预防早产儿 NEC 提供新策略。

Necrotizing enterocolitis (NEC) is a common gastrointestinal disease of premature infants without clearly defined etiology or treatment. Current theory suggests that many factors including hypoxia, bacterial colonization, feeding, and prematurity contribute to the development of disease, but the final common pathway associating the risk factors with the intestinal pathology remains unclear. Our previous studies have shown that the inflammatory mediator platelet activating factor (PAF) may be involved in the pathogenesis of bowel necrosis. The overall emphasis of this proposal is to investigate the importance of PAF and altered PAF metabolism in this disease, and to delineate specific mechanisms involved in the pathogenesis. We hypothesize that local intestinal PAF metabolism is altered in neonatal NEC, that PAF dysregulation leads to apoptosis of intestinal epithelium, disruption of tight junctional integrity, mucosal permeability, and activation of the secondary inflammatory cascade, and that this modulation is critical for the development of the disease. Therefore the specific aims of this proposal are: l) To elucidate the mechanisms of altered PAF metabolism and biological activity in the developing and injured intestine, and 2) To investigate the mechanisms of PAF-induced mucosal damage, and to delineate the underlying role of PAF-induced mucosal damage in NEC pathogenesis. To accomplish our goals, we have developed a neonatal rat model of NEC that mimics the human condition, and will study the effects of altered PAF metabolism on the development of intestinal nectosis, and on pathophysiologic events preceding the evolution of bowel injury. in addition, to identify the cellular and molecular level regulation of epithelial cell damage, we will use various tissue culture models of the intestinal epithelium. To elucidate specific mechanisms resulting in altered PAF regulation in the intestinal microenvironment we will evaluate if activation of local PAF production, decreased PAF degradation, or altered PAF- receptor expression and function results from typical NEC risk factors (formula feeding and asphyxia) or change during developmental maturation. in addition, we will evaluate the effect of altered PAF regulation on apoptosis and mucosal penneability, and clarify the roles of these factors in the initiation of NEC and the signal transduction mechanisms that lead to these events following PAF receptor activation. Results from these experiments should clarify key mechanisms linking the risk factors of NEC with the pathologic outcome, and may provide new strategies for the prevention of NEC in premature newborns.