Perinatal expression of genes that may participate in lipid metabolism by lipid-laden lung fibroblasts

Although a morphologically distinct population of lipid-laden interstitial cells (lipofibroblasts, LF), has been identified, the origins and functions of this population during lung development and disease remain undefined. Illumination of the developmental and functional characteristics of two other populations of lipid-laden mesenchymal cells, namely adipocytes and hepatic lipocytes, has fashioned tools that can be used to explore similar properties in pulmonary LFs. As the LF is transiently a very abundant cell in the perinatal lung, we elected to study the perinatal ontogeny of the expression of several genes that are involved in the acquisition of lipids by adipocytes, and may be involved in promoting the triglyceride accumulation that is the morphologic hallmark of the pulmonary LF. We found that the maximal expression of peroxisome proliferator-activated receptor-gamma (PPAR-gamma), at gestational day 21 in the LF, precedes the rise at birth, in the expression of genes that are involved in the hydrolysis of triglycerides at the plasma membrane (lipoprotein lipase, LPL), transport of fatty acids across the plasma membrane (fatty acid transporter, FAT) and in the cytoplasm (adipocyte lipid binding protein, ALBP). The steady-state levels of LPL, FAT, and ALBP mRNAs that were isolated from whole lung tissue showed a similar temporal pattern. The levels of the protein products of the LPL and ALBP genes changed in tandem with those of their precursor mRNAs in the LF, suggesting that these gene products are under pre-translational control. These findings indicate that characteristic adipocyte genes are also expressed in lipid-laden pulmonary fibroblasts and may participate in triglyceride accumulation and metabolism by these cells.