Ex-FABP: a fatty acid binding lipocalin developmentally regulated in chicken endochondral bone formation and myogenesis

Extracellular fatty acid binding protein (Ex-FABP) is a 21 kDa lipocalin sp ecifically binding fatty acids, expressed during chicken embryo development in hypertrophic cartilage, in muscle fibers and in blood granulocytes. In chondrocyte and myoblast cultures Ex-FABP expression is increased by inflam matory agents and repressed by anti-inflammatory agents. In adult cartilage Ex-FABP is expressed only in pathological conditions such as in dyschondro plastic and osteoarthritic chickens. The possible mammalian counterpart is the Neu-related lipocalin (NRL), a lipocalin overexpressed in rat mammary c ancer; NRL is homologous to the human neutrophil gelatinase associated lipo calin (NGAL) expressed in granulocytes and in epithelial cells in inflammat ion and malignancy and to the Sip24 (super-inducible protein 24), an acute phase lipocalin expressed in mouse after turpentine injection. Immunolocali zation and in situ hybridization showed that NRL/NGAL is expressed in hyper trophic cartilage, in forming skeletal muscle fibers and in developing hear t. In adult cartilage NRL/NGAL was expressed in articular cartilage from os teoarthritic patients and in chondrosarcoma. Moreover, NRL was induced in c hondrocyte and myoblast cultures by an inflammatory agent. We propose that these lipocalins (Ex-FABP, NRL/NGAL, Sip24) represent stress proteins physi ologically expressed in tissues where active remodeling is taking place dur ing development and also present in tissues characterized by an acute phase response due to pathological conditions. (C) 2000 Elsevier Science B.V. Al l rights reserved.