Pulmonary surfactant is a complex of lipids and proteins produced and secreted by alveolar type II cells that provides the low surface tension at the air-liquid interface. The phospholipid most responsible for providing the low surface tension in the lung is dipalmitoylphosphatidylcholine. Dipalmitoylphosphatidylcholine is synthesized in large part by phosphatidylcholine (PC) remodeling, and a lysophosphatidylcholine (lysoPC) acyltransferase is thought to play a critical role in its synthesis. However, this acyltransferase has not yet been identified. We have cloned full-length rat and mouse cDNAs coding for a lysoPC acyltransferase (LPCAT). LPCAT encodes a 535-aa protein of Ϸ59 kDa that contains a transmembrane domain and a putative acyltransferase domain. When transfected into COS-7 cells and HEK293 cells, LPCAT significantly increased lysoPC acyltransferase activity. LPCAT preferred lysoPC as a substrate over lysoPA, lysoPI, lysoPS, lysoPE, or lysoPG and prefers palmitoyl-CoA to oleoyl-CoA as the acyl donor. This LPCAT was preferentially expressed in the lung, specifically within alveolar type II cells. Expression in the fetal lung and in rat type II cells correlated with the expression of the surfactant proteins. LPCAT expression in fetal lung explants was sensitive to dexamethasone and FGFs. KGF was a potent stimulator of LPCAT expression in cultured adult type II cells. We hypothesize that LPCAT plays a critical role in regulating surfactant phospholipid biosynthesis and suggest that understanding the regulation of LPCAT will offer important insight into surfactant phospholipid biosynthesis.biochemistry ͉ lung ͉ surfactant ͉ phosphatidylcholine

Keywords: type I cell; type II cell; surfactant; lipogenesisThe alveolar surface is covered by an epithelium composed of two main cell types (1, 2). Type I cells are large flat cells that cover ‫ف‬ 95% of the alveolar surface and through which gas exchange takes place, and their metabolic properties are just now being discovered (2). Type II cells have a distinct morphology with characteristic lamellar bodies, the intracellular storage form of pulmonary surfactant, and apical microvilli. Type II cells make and secrete pulmonary surfactant, and they proliferate to restore the epithelium after damage to the more sensitive type I cells. Type II cells also transport sodium and fluid from the apical to the basolateral surface and play an important role in innate immunity.Although methods for isolating and culturing adult rat and mouse type II cells and fetal human type II cells have been available for years, there has been limited success maintaining the differentiated functions of adult human alveolar epithelial cells in primary culture. In addition, there are no human cell lines that produce surfactant. H441 cells express surfactant protein (SP)-A and SP-B, whereas A549 cells do not express any of the surfactant proteins nor contain a higher percentage of surfactant phospholipids than fibroblasts (3). A variety of methods for

Bz-423 is a 1,4-benzodiazepine that suppresses disease in lupus-prone mice by selectively killing pathogenic lymphocytes, and it is less toxic compared to current lupus drugs. Cells exposed to Bz-423 rapidly generate O(2)(-) within mitochondria, and this reactive oxygen species is the signal initiating apoptosis. Phage display screening revealed that Bz-423 binds to the oligomycin sensitivity conferring protein (OSCP) component of the mitochondrial F(1)F(0)-ATPase. Bz-423 inhibited the F(1)F(0)-ATPase in vitro, and reconstitution experiments demonstrated that inhibition was mediated by the OSCP. This target was further validated by generating cells with reduced OSCP expression using RNA interference and studying the sensitivity of these cells to Bz-423. Our findings help explain the efficacy and selectivity of Bz-423 for autoimmune lymphocytes and highlight the OSCP as a target to guide the development of novel lupus therapeutics.

Respiratory distress syndrome (RDS), which is the leading cause of death in premature infants, is caused by surfactant deficiency. The most critical and abundant phospholipid in pulmonary surfactant is saturated phosphatidylcholine (SatPC), which is synthesized in alveolar type II cells de novo or by the deacylation-reacylation of existing phosphatidylcholine species. We recently cloned and partially characterized a mouse enzyme with characteristics of a lung lysophosphatidylcholine acyltransferase (LPCAT1) that we predicted would be involved in surfactant synthesis. Here, we describe our studies investigating whether LPCAT1 is required for pulmonary surfactant homeostasis. To address this issue, we generated mice bearing a hypomorphic allele of Lpcat1 (referred to herein as Lpcat1 GT/GT mice) using a genetrap strategy. Newborn Lpcat1 GT/GT mice showed varying perinatal mortality from respiratory failure, with affected animals demonstrating hallmarks of respiratory distress such as atelectasis and hyaline membranes. Lpcat1 mRNA levels were reduced in newborn Lpcat1 GT/GT mice and directly correlated with SatPC content, LPCAT1 activity, and survival. Surfactant isolated from dead Lpcat1 GT/GT mice failed to reduce minimum surface tension to wild-type levels. Collectively, these data demonstrate that full LPCAT1 activity is required to achieve the levels of SatPC essential for the transition to air breathing.