LPCAT1 is essential for perinatal lung function and survival

描述（由申请人提供）：肺内的气液界面是一个高表面张力的区域，如果不加以修改，会导致肺泡塌陷和呼吸衰竭。在正常情况下，由肺泡II型细胞合成和分泌的由饱和磷脂组成的表面活性剂膜降低了这种高表面张力。肺表面活性剂还含有一系列蛋白，SP-A、SP-B、SP-C和SP-D，它们对表面活性剂膜的形成、表面活性剂稳态和宿主防御有不同的贡献。毫无疑问，肺表面活性物质缺乏或改变与新生儿呼吸窘迫综合征（RDS）有关，并导致成熟肺急性呼吸窘迫综合征（ARDS）中的肺功能障碍。磷脂约占肺表面活性剂质量的85%。最丰富的单一磷脂是饱和磷脂酰胆碱（SatPC），特别是双棕榈酰磷脂酰胆碱（DPPC）。SatPC既可以从头合成，也可以通过单饱和PC的去酰化然后再酰化的机制合成，通常与棕榈酸酯一起合成。体外表面活性剂合成的研究表明，后一种途径占II型细胞产生的DPPC的55- 75%。尽管30多年前在II型细胞中证实了用于再酰化的lysoPC酰基转移酶的活性，但相应的基因迄今尚未确定。该应用程序所附带的数据表明，我们已经鉴定并分离出了在II型细胞中高度富集的lysoPC酰基转移酶（LPCAT1）的小鼠cDNA。利用半胚转基因小鼠，我们也证明了LPCAT1表达的降低降低了发育中的肺中SatPC的水平，并与存活直接相关。我们将在三个具体目标中扩展这些研究。在第一个特异性目标中，我们将完全灭活胎儿的LPCAT1基因，并确定这如何影响存活、磷脂合成和肺部整体基因表达。在Specific Aim 2中，我们将产生LPCAT1的条件敲除，这将使我们能够定义成年动物中SatPC池大小与肺功能之间的关系。在具体目标3中，我们将利用LPCAT1在SatPC合成中的作用来确定其在SatPC转运到片层体的起始过程中的作用。这些研究的完成将填补我们在表面活性剂磷脂合成方面的重要空白，并可能对RDS和其他由肺表面活性剂不足引起的肺部疾病的治疗策略产生重大影响。

DESCRIPTION (provided by applicant): The air-liquid interface in the lung is a region of high surface tension that, if unmodified, causes alveolar collapse and respiratory failure. Under normal conditions, a surfactant film consisting of saturated phospholipids that is synthesized and secreted by alveolar type II cells reduces this high surface tension. Pulmonary surfactant also contains a family of proteins, SP-A, SP-B, SP-C, and SP-D, which variously contribute to formation of the surfactant film, surfactant homeostasis, and host defense. Pulmonary surfactant deficiency or alteration has been incontrovertibly linked to respiratory distress syndrome (RDS) in neonates and contributes to the lung dysfunction seen in acute respiratory distress syndrome (ARDS) in the mature lung. Phospholipids constitute approximately 85% of the mass of pulmonary surfactant. The single most abundant phospholipid, is saturated phosphatidylcholine (SatPC), particularly dipalmitoylphosphatidylcholine (DPPC). SatPC can be synthesized either de novo or by a mechanism involving the deacylation of monosaturated PC followed by reacylation, usually with palmitate. Studies on surfactant synthesis in vitro have shown that the latter pathway accounts for 55- 75% of the DPPC made by type II cells. Although activity of a lysoPC acyltransferase utilized in reacylation was demonstrated in type II cells over 30 years ago, the corresponding gene has not been heretofore identified. Data accompanying this application demonstrate that we have identified and isolated the mouse cDNA for a lysoPC acyltransferase (LPCAT1) that is highly enriched in type II cells. Using a hypomorphic transgenic mouse, we also demonstrated that decreased LPCAT1 expression reduces SatPC levels in the developing lung and directly correlates with survival. We will extend these studies in three Specific Aims. In the first Specific Aim we will completely inactivate the LPCAT1 gene in the fetus and determine how this affects survival, phospholipid synthesis, and overall gene expression in the lung. In Specific Aim 2 we will generate a conditional knockout of LPCAT1 that will allow us to define the relationship between SatPC pool size and lung function in the adult animal. In Specific Aim 3 we will exploit the role of LPCAT1 in SatPC synthesis to determine its role in the initiation of SatPC transport to lamellar bodies. The completion of these studies will fill important gaps in our knowledge regarding surfactant phospholipid synthesis, and may significantly impact strategies for the treatment of RDS and other lung diseases resulting from an insufficiency in pulmonary surfactant.