Acute phase lipocalin Ex-FABP is involved in heart development and cell survival

Ex-FABP is an extracellular fatty acid binding protein, expressed during chicken embryo development in cartilage, muscle fibers, and blood granulocytes. Transfection of chondrocytes and myoblasts with anti-sense Ex-FABP cDNA results in inhibition of cell proliferation and apoptosis induction. Ex-FABP expression is dramatically enhanced by inflammatory stimuli and in pathological conditions. In this paper, by in situ whole mount and immunohistochemistry analysis we show that, at early developmental stage, Ex-FABP is diffuse in all tissues of chick embryos. Particularly high level of transcript and protein are expressed in the heart. During acute phase response (APR) induced by endotoxin LPS injection, a marked increase of Ex-FABP mRNA was observed in embryos, highest Ex-FABP expression being in heart and liver. To investigate in vivo the biological role of Ex-FABP, we have directly microinjected chicken embryos with antibody against Ex-FABP. Almost 70% of chicken embryos died and the target tissue was the heart. We detected in heart of the treated embryos a significant increase of apoptotic cells and high level of fatty acids. We propose that the accumulation of fatty acid, specific ligand of Ex-FABP, in the cell microenvironment is responsible of heart cell death, and we suggest that Ex-FABP may act as a survival protein by playing a role as scavenger for fatty acids.