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质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，其构成磷脂的70- 80%。亲水性表面活性剂相关蛋白SP-A和SP-D被认为在肺的磷脂代谢和宿主防御机制中起重要作用。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)检测了SP-A对其生物活性（通过特异性受体对II型细胞的磷脂分泌的抑制作用）的结构要求。SP-A的C端抗胶原酶片段具有调节磷脂分泌和结合高亲和力受体的能力。抗人SP-A单克隆抗体阻断SP-A活性 ...更多信息 发现ty识别来自Glu-1的C-末端侧<202>，表明该区域参与与SP-A受体的结合。(2)与脂质形成复合物的天然SP-D抵消了SP-A对肺泡II型细胞磷脂分泌的抑制作用。(3)用β-<125>l标记的蛋白质作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)研究了SP-A介导的II型细胞对磷脂酰胆碱（PC）的摄取。当分析II型细胞摄取的放射性标记的二棕榈酰PC（DPPC）的亚细胞分布时，在SP-A存在下，在富含板状体的部分中回收了约52%的细胞相关放射性标记的DPPC，而在不存在SP-A的情况下，仅发现19%的细胞相关放射性标记的DPPC。结果表明，SP-A促进DPPC进入片层体.表面活性蛋白与糖脂的结合特异性研究了SP-A和SP-D与各种糖脂的直接结合。发现SP-A与半乳糖神经酰胺和脱唾液酸GM 2结合。SP-D与葡糖神经酰胺结合。由于细胞表面糖脂是多种微生物的受体，表面活性蛋白与糖脂的结合在肺防御系统中具有重要作用.特发性肺纤维化（IPF）和肺泡蛋白沉积症（PAP）患者血清中SP-A的出现。肺表面活性剂成分被认为在正常条件下仅存在于肺泡腔中而不存在于血流中。我们检测了肺疾病患者血清中是否存在SP-A。IPF患者（205*23 ng/ml，n=32）和PAP患者（285*23 ng/ml，n=6）的血清SP-A水平显著高于对照受试者（45*3 ng/ml，n=56）（平均值 *SEM，p&lt;0.01）。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