SYNDECANS IN MODELS OF BRONCHOPULMONARY DYSPLASIA

新生儿BPD发病机制的一个主要方面是对高FiO2下机械通气引起的损伤的炎症反应。换气的胎儿狒狒发展了BPD婴儿的病理生理、组织学和生化特征，并提供了一个机会来检验BPD发病机制的假说，并评估预防和治疗措施。我们研究了细胞表面的硫酸乙酰肝素蛋白多糖(HSPGs)，也就是众所周知的Syndecans。这些单膜跨膜蛋白含有胞外结构域，在N末端附近带有HS链，远离质膜。Syndecans位于每个贴壁细胞的表面，在那里它们充当各种生长因子、细胞因子、趋化因子和细胞黏附分子的共同受体，并在一定程度上协调对组织损伤的高度复杂的修复反应。具体地说，Syndecan-1和-4是在组织损伤时被诱导的，组织损伤期间产生的药物导致Syndecan胞外结构域从细胞表面完整地释放出来，产生可溶性的效应物，改变各种蛋白质的活性，并作为主要的负抑制物。含有syndecan-1基因靶向缺失的小鼠和在广泛作用的CMV启动子下转基因过表达syndecan-1的小鼠，在伤口修复方面显示出重大的缺陷：基因缺失的小鼠对损伤上皮细胞反应缓慢，高表达的小鼠分泌过量的可溶性syndecan-1外膜结构域，对损伤修复造成重大干扰。我们假设，高FiO2下机械通气对肺的持续性损伤导致了可溶性Syndecan胞外结构域的过度脱落，这些PG的生物活性延迟了修复反应，并促成了病理和临床上公认的BPD的变化，降低这些胞外结构域的水平将在一定程度上缓解向BPD的进展。具体地说，我们的目标是(I)将Syndecan的表达和脱落与呼吸机通气的早产儿肺的组织病理学变化相关联；(Ii)确定呼吸机肺中可溶性胞外结构域的生物活性；(Iii)建立狒狒肺培养，以研究Syndecan的诱导和脱落的机制，并产生Syndecan胞外结构域；(Iv)评估可溶性的胞外结构域是否与BPD模型中BPD的发生随意相关。

A major aspect of the pathogenesis of BPD in newborns is the inflammatory response to injury caused by mechanical ventilation at high FiO2. Ventilated fetal baboons develop the pathophysiological, histologic and biochemical features of the infant with BPD, and provide an opportunity to test hypothesis for the pathogenesis of BPD and to evaluate preventative and therapeutic measures. We study the cell surface heparan sulfate proteoglycans (HSPGs) known as the syndecans. These single membrane spanning protein contain extracellular domains (ectodomains) that bear HS chains near the N- termini, distant from the plasma membrane. Syndecans are on the surface of every adherent cell where they act as co-receptors for a variety of growth factors, cytokines, chemokines and cell adhesion molecules, as well as coordinate, in part, the highly complex reparative response to tissue injury. Specifically, syndecan-1 and -4 are induced in response to tissue injury, agents produced during tissue injury cause syndecan ectodomains to be released intact from cell surfaces, yielding soluble effectors that modify the activities of wide variety of proteins and act as dominant negative inhibitors. Mice containing a targeted deletion of the syndecan-1 gene and mice that transgenically over-express syndecan-1 under the broadly acting CMV promoter show major defects in wound repair: the null mice show slow epithelial response to injury and the over-expressing mice shed excessive amounts of the soluble syndecan-1 ectodomains, causing a major disturbance in repair of injury. We hypothesize that the persistent injury of the lung by mechanical ventilation at high FiO2 leads to excessive shedding of the soluble syndecan ectodomains, that the biological activities of these PGs delay the reparative response and contribute to the changes recognized pathologically and clinically as BPD, and reducing the level of these ectodomains will ameliorate, in part, the progression to BPD. Specifically, we aim to (i) to correlate syndecan expression and shedding with histopathological changes in ventilated pre-term baboon lungs; (ii) determine the biological activities of the soluble ectodomains from ventilated lungs; (iii) establish baboon lung cultures to investigate mechanisms of syndecan induction and shedding and to produce syndecan ectodomains; (iv) assess whether the soluble ectodomains are casually related to development of BPD in the baboon models.