THE ROLE OF PAF IN NEONATAL-NECROTIZING ENTEROCOLITIS

坏死性小肠结肠炎（NEC）是一种常见的早产儿胃肠道疾病，没有明确的病因和治疗方法。目前的理论认为，包括缺氧、细菌定植、喂养和早产在内的许多因素都有助于疾病的发展，但将危险因素与肠道病理联系起来的最终共同途径尚不清楚。我们之前的研究表明炎症介质血小板活化因子（PAF）可能参与肠坏死的发病机制。本提案的总体重点是研究PAF和改变的PAF代谢在该疾病中的重要性，并描述其发病机制的具体机制。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、粘膜通透性破坏和继发性炎症级联激活，这种调节对疾病的发展至关重要。因此，本研究的具体目的是：1)阐明PAF在发育和损伤的肠道中代谢和生物活性改变的机制；2)研究PAF诱导的粘膜损伤的机制，并阐明PAF诱导的粘膜损伤在NEC发病中的潜在作用。为了实现我们的目标，我们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，以及肠损伤演变前的病理生理事件。此外，为了确定上皮细胞损伤的细胞和分子水平调控，我们将使用肠上皮的各种组织培养模型。为了阐明肠道微环境中导致PAF调控改变的具体机制，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由典型的NEC危险因素（配方喂养和窒息）引起的，还是在发育成熟过程中发生的变化。此外，我们将评估PAF调节改变对细胞凋亡和粘膜渗透性的影响，并阐明这些因素在NEC启动中的作用，以及在PAF受体激活后导致这些事件的信号转导机制。这些实验结果将阐明NEC危险因素与病理结果之间的关键机制，并可能为早产儿NEC的预防提供新的策略。

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.