Lipidomics of cellular and secreted phospholipids from differentiated human fetal type II alveolar epithelial cells

Maturation of fetal alveolar type II epithelial cells in utero is characterized by specific changes to lung surfactant phospholipids. Here we quantified the effects of hormonal differentiation in vitro on the molecular specificity of cellular and secreted phospholipids from human fetal type II epithelial cells, using electrospray ionization mass spectrometry. Differentiation, assessed by morphology and changes in gene expression, was accompanied by restricted and specific modifications to cell phospholipids, principally enrichments of shorter chain species of phosphatidylcholine (PC) and phosphatidylinositol (PI) that were not observe in fetal lung fibroblasts. Treatment of differentiated epithelial cells with secretagogues stimulated secretion of functional surfactant containing surfactant proteins B and C. Secreted material was further enriched in this same set of phospholipid species, but was characterized by increased contents of short chain monounsaturated and disaturated species other than dipalmitoyl PC (PC16:0/16:0), principally palmitoylmyristoyl PC (PC16:0/14:0) and palmitoylpalmitoleoyl PC (PC16:0/16:1). Mixtures of these PC molecular species, phosphatidylglycerol and SP-B/C were functionally active and rapidly generated low surface tension on compression in a pulsating bubble surfactometer. These results suggest that hormonally differentiated human fetal Type II cells do not select the molecular composition of surfactant phospholipid on the basis of saturation but, more probably, on acyl chain length.