Roles of SP-A, SP-B, and SP-C in modulation of lipid uptake by pulmonary epithelial cells in vitro.
The effects of the surfactant proteins (SP)-A, SP-B, and SP-C on binding and endocytosis of fluorescently labeled lipid vesicles were studied in rat type II epithelial cells and in MLE-12 cells, a pulmonary adenocarcinoma cell line with alveolar cell characteristics. Incorporation of SP-C in lipid vesicles markedly stimulated binding to the cell membrane at 4 degrees C and endocytosis of lipids at 37 degrees C. SP-C enhanced lipid uptake in MLE-12 cells, type II cells, and NIH 3T3 cells. SP-B stimulated lipid uptake in MLE-12 cells, but to a lesser degree. SP-B decreased the amount of lipid uptake stimulated by SP-C, SP-A did not increase endocytosis of lipids by MLE-12 cells or type II cells, but aggregates of lipid were observed associated with the cell surface in the presence of SP-A. Maintenance of active surfactant in the lung may be achieved through the selective uptake and degradation of surfactant subfractions depleted in SP-A and SP-B.
Horowitz
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AD
Division of Pulmonary Biology, Children's Hospital Research Foundation, Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA.
Moussavian
B
B
Whitsett
J A
JA
D000818:Animals; D002417:Cattle; D004705:Endocytosis; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D050356:Lipid Metabolism; D008055:Lipids / Q000493:pharmacokinetics*; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008856:Microscopy, Fluorescence; D011510:Proteolipids / Q000494:pharmacology*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013696:Temperature; D014407:Tumor Cells, Cultured
D008055:Lipids; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants