EXPRESSION OF FATTY-ACID-BINDING PROTEINS IN CELLS INVOLVED IN LUNG-SPECIFIC LIPID-METABOLISM

Members of the fatty-acid-binding protein (FABP) family are thought to play an important role in fatty acid transport within the cytosol and thus to be involved in lipid metabolism. As previous data on the occu rrence of distinct FABP types in total lung are contradictory, we dete rmined the expression of FABP types in three isolated cell types of ra t lung, which are characterised by active lipid metabolism. Alveolar t ype-II cells synthesise, store and secrete pulmonary surfactant, a pho spholipid-rich surface-tension-lowering agent, whereas lung fibroblast s, localised adjacent to the alveolar type-II cells, are assumed to pr ovide neutral lipid substrate to alveolar type-II cells around birth, and alveolar macrophages are known to degrade complex lipids. Initial screening by reverse transcriptase PCR revealed the occurrence of hear t (H-). epidermal (E-) and liver FABP in rat lung, the latter bring no t detectable in the three cell types studied, Cells were analysed by n orthern and western blotting, then quantitatively by sandwich ELISA. f or which recombinant rat E-FABP was prepared. E-FABP mRNA was found in all three cell types, and E-FABP was detected in the following amount s: 240.9 +/- 19.0 ng/mg cytosolic protein in alveolar type-II cells: 1 72.3 +/- 0.7 ng/mg protein for lung fibroblasts: and 36.9 +/- 3.5 ng/m g protein for alveolar macrophages. This indicates a basic function of E-FABP in cellular lipid metabolism. In contrast, H-FABP probably is involved in the metabolism of neutral lipids because H-FABP mRNA was f ound only in lung fibroblasts with a corresponding protein level of 31 5.5 +/- 6.9 ng/mg. Small amounts of H-FABP protein were present in alv eolar type-II cells and alveolar macrophages.