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，病因不明，治疗方法不清。目前的理论表明，许多因素，包括缺氧，细菌定植，喂养和早产有助于疾病的发展，但最终的共同途径与肠道病理的危险因素仍不清楚。我们前期的研究表明，炎症介质血小板活化因子（PAF）可能参与了肠坏死的发病机制。该建议的总体重点是研究PAF和PAF代谢改变在这种疾病中的重要性，并描述参与发病机制的具体机制。我们假设，局部肠PAF代谢改变新生儿NEC，PAF失调导致肠上皮细胞凋亡，破坏紧密连接的完整性，粘膜通透性，和激活继发性炎症级联反应，这种调制是至关重要的疾病的发展。因此，本研究的具体目的是：1）阐明PAF在发育和损伤肠道中代谢和生物活性改变的机制; 2）研究PAF诱导的粘膜损伤机制，并阐明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，我们已经开发了一种模拟人类条件的NEC新生大鼠模型，并将研究PAF代谢改变对肠坏死发展的影响，以及对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，我们将使用各种肠上皮的组织培养模型。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由典型的NEC风险因素（配方喂养和窒息）或发育成熟过程中的变化引起。此外，我们将评估PAF调节改变对细胞凋亡和粘膜通透性的影响，并阐明这些因子在NEC起始中的作用以及PAF受体激活后导致这些事件的信号转导机制。这些实验的结果应该澄清NEC的危险因素与病理结果的关键机制，并可能提供新的策略，为预防NEC的早产儿。

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.