L-FABP is exclusively expressed in alveolar macrophages within the myeloid lineage: evidence for a PPARalpha-independent expression

• Published in: The international journal of biochemistry & cell biology 2004-10, Vol.36 (10), p.2042-2053
• Main Authors: Schachtrup, Christian, Scholzen, Thomas E, Grau, Veronika, Luger, Thomas A, Sorg, Clemens, Spener, Friedrich, Kerkhoff, Claus
• Format: Article
• Language: English
• Subjects: Animals; Bone Marrow Cells - cytology; Bone Marrow Cells - metabolism; Carrier Proteins - biosynthesis; Carrier Proteins - metabolism; Cell Lineage; Dendritic Cells - cytology; Dendritic Cells - metabolism; Fatty Acid-Binding Proteins; Fluorescent Antibody Technique; Gene Expression; Gene Expression Regulation; Macrophages, Alveolar - cytology; Macrophages, Alveolar - metabolism; Mice; Mice, Inbred C57BL; Myeloid Cells - cytology; Myeloid Cells - metabolism; PPAR alpha - metabolism
• ISSN: 1357-2725

Peroxisome proliferator-activated receptors (PPARs) play a role in inflammation and, in particular, PPARgamma is involved in monocyte/macrophage differentiation. Members of the fatty acid-binding protein (FABP) family have been reported to function as transactivators for PPARs. Therefore, the expression of PPARs and FABPs in the myeloid lineage was investigated by real-time PCR and immunofluorescence analysis. We found adipocyte-, epidermal-, and heart-type FABP to be ubiquitously expressed within the myeloid lineage. In contrast, liver-type FABP was exclusively detected in murine alveolar macrophages (AM), confirmed on protein level by double fluorescence analysis. The PPAR subtypes also showed a temporally and spatially regulated expression pattern in myeloid cells: the beta-subtype was expressed in bone marrow, peritoneal, and alveolar macrophages, whereas it was not detected in dendritic cells (DCs). The gamma1-isoform was present in all cells, however, at different levels, whereas the gamma2-isoform was expressed in alveolar macrophages and dendritic cells. A low level PPARalpha mRNA could be detected in peritoneal macrophages and immature dendritic cells but not in mature dendritic cells and bone marrow macrophages. Interestingly, PPARalpha mRNA was also absent in the alveolar macrophages although liver-type FABP was expressed, indicating that gene expression of liver-type FABP was independent of PPARalpha. Since liver-type FABP is known as transactivator of PPARgamma the simultaneous expression of both proteins may have general implications for the activation of PPARgamma in alveolar macrophages.