Regulatory roles of pulmonary surfactant apoprotein and its receptor in metabolism of lung diseases.

肺表面活性物质是由肺泡II型细胞合成和分泌的脂类和蛋白质的复杂混合物。磷脂是肺表面活性物质的主要成分。磷脂的主要类别是磷脂酰胆碱，占磷脂的70%-80%。亲水性表面活性物质相关蛋白SP-A和SP-D被认为在肺内磷脂代谢和宿主防御机制中发挥重要作用。本研究的目的是探讨SP-A和SP-D在正常肺和病变肺中的作用。表面活性蛋白对磷脂代谢的调节。(1)SP-A对其生物活性的结构要求(通过特定的受体抑制II型细胞的磷脂分泌)。SP-A的C端胶原酶抗性片段具有调节磷脂分泌和结合高亲和力受体的能力。阻断人SP-A激活…的人SP-A单抗(2)天然SP-D与脂质形成复合体可拮抗SP-A对肺泡II型细胞磷脂分泌的抑制作用。(3)以L标记的蛋白质为探针进行的配体结合研究表明，SP-A和SP-D分别与磷脂酰胆碱和磷脂酰肌醇结合。(4)SP-A介导的磷脂酰胆碱摄取。当分析II型细胞摄取的放射性标记双棕榈酰PC(DPPC)的亚细胞分布时，在有SP-A存在的情况下，大约52%的细胞标记DPPC被回收到富含板层的部分，而在没有SP-A的情况下，只有19%的DPPC被回收。结果表明，SP-A促进DPPC进入片状小体。表面活性蛋白与糖脂的结合特性研究了SP-A和SP-D与不同糖脂的直接结合。发现SP-A可与半乳糖神经酰胺和asialo GM2结合。SP-D与葡萄糖神经酰胺结合。表面活性蛋白与糖脂的结合特性在肺防御系统中显得尤为重要，因为细胞表面的糖脂是各种微生物的受体。特发性肺纤维化(IPF)和肺泡蛋白沉积症(PAP)患者血清中SP-A的检测肺表面活性物质成分被认为只存在于肺泡腔，而在正常情况下不存在于血流中。我们检测了肺部疾病患者的血清中是否存在SP-A。IPF组(205×23 ng/ml，n=32)和PAP组(285×23 ng/ml，n=6)血清SP-A水平显著高于对照组(45×3 ng/ml，n=56)(P<0.01)。较少

Pulmonary surfactant is a complex mixture of lipids and proteins synthesized and secreted by alveolar type II cells. Phospholipids are the major components of pulmonary surfactant. The major class of phospholipids is phosphatidylcholine, which constitutes 70-80 % of phospholipids. The hydrophilic surfactant-associated proteins, SP-A and SP-D, are believed to play important roles in phospholipid metabolism and host-defense mechanism in the lung. The purpose of the present study was to investigate the roles of SP-A and SP-D in normal and diseased lungs.1. Regulation of phospholipid metabolism by surfactant proteins.(1) Structural requirement of SP-A for its biological activity (the inhibitory effect on phospholipid secretion by type II cells via a specific receptor) was examined. The C-terminal collegenase-resistent fragment of SP-A possessed the ability to regulate phospholipid secretion and to bind a high affinity receptor. Monoclonal antibody to human SP-A that blocked the SP-A activi … More ty was found to recognize the C-terminal side from Glu^<202>, suggesting the involvement of this region with the binding to SP-A receptor.(2) Native SP-D that formed a comlex with lipid counteracted the inhibitory effect of SP-A on phospholipid secretion by alveolar type II cells.(3) The ligand binding studies using ^<125>l-labeled proteins as probes revealed that SP-A and SP-D bound to phosphatidylcholine and phosphatidylinostitol, respectively.(4) SP-A-mediated uptake of phosphatidylcholine (PC) by type II cells was investigated. When subcellular distribution of radiolabeled dipalmitoyl PC (DPPC) taken up by type II cells was analyzed, approximately 52 % of cell-associated radiolabeled DPPC was recovered in the lamellabody-rich fraction in the presence of SP-A, whereas only 19 % was found to this fraction in the absence of SP-A. The result indicates that SP-A facilitates the incorporation of DPPC into lamellar bodies.2. Binding specificities of surfactant proteins for glycolipids.The direct binding of SP-A and SP-D to various glycolipids was investigated. SP-A was found to bind to galactosylceramide and asialo GM2. SP-D bound to glucosylceramide. The binding property of surfactant proteins to glycolipids appeas important in pulmonary defense system since cell surface glycolipids serve as receptors for various microorganism.3. Appearance of SP-A in the sera from patients with idiopathic pulmonary fibrosis (IPF) and pulmonary alveolar proteinosis (PAP). Lung surfactant components are believed to be present exclusively in the alveolar spaces and not in the blood stream under normal conditions. We examined whether SP-A appears in the sera of patients with lung diseases. The serum SP-A levels in patients with IPF (205*23 ng/ml, n=32) and PAP (285*23 ng/ml, n=6) were significantly higher than those in control subjects (45*3 ng/ml, n=56) (mean*SEM, p<0.01). Less