Expression of liver-type fatty acid-binding protein in murine lung and its release into serum upon challenge of lung with lipopolysaccharide

Fatty acid-binding proteins (FABP) in alveolar type II (TII) cells are required for surfactant synthesis and regulation. Beyond expression of heart-type (H-) and epidermal-type (E-) FABP in TII cells from mouse lung, we present the first evidence of the expression of liver-type (L-) FABP, by quantitative PCR and immunofluorescent confocal laser microscopy. Further, by making use of an acute mouse lung injury model, we examine whether these lipid-binding proteins are released into the bronchoalveolar fluid (BALF) and into the circulation upon challenge of the lung with lipopolysaccharide. Applying FABP-specific ELISAs, we found that neither H- nor E-FABP can be detected in BALF and serum above background levels, up to 24 h after insult. In contrast, L-FABP was detected in the BALF pellet, consisting of polymorphonuclear cells and alveolar macrophages, and in serum. A significant decrease in L-FABP levels in the BALF pellet was associated with a significant increase in serum levels 6 h post insult. As contributions of L-FABP from other organs were excluded, this protein could be used as a marker for acute lung injury.