The urokinase plasminogen activator receptor-associated Protein/Endo180 iscoexpressed with its interaction partners urokinase plasminogen activator receptor and matrix metalloprotease-13 during osteogenesis

The urokinase plasminogen activator receptor-associated protein/Endo180 (uP ARAP/Endo180) is a newly discovered member of the macrophage mannose recept or family that was reported to interact with ligand-bound urokinase plasmin ogen activator receptor (uPAR), matrix metalloprotease-13 (MMP-13), and col lagen V on the cell surface. We have determined the sites of expression of this novel receptor during murine postimplantation development. uPARAP/Endo 180 was expressed in all tissues undergoing primary ossification, including the developing bones of the viscerocranium and calvarium that ossify intra membranously, and developing long bones undergoing endochondral ossificatio n. uPARAP/Endo180 mRNA was expressed by both immature osteoblasts and by ma ture osteocalcin-producing osteoblasts-osteocytes, and was coexpressed with MMP-13. Interestingly, osteoblasts also expressed uPAR. Besides bone-formi ng tissues, uPARAP/Endo180 expression was detected only in a mesenchymal co ndensation of the midbrain and in the developing lungs. The data suggest a function of this novel protease receptor in bone development, possibly medi ated through its interactions with uPAR, MMP-13, or collagen V.