Pleiotrophin (Osteoblast-Specific Factor-1, OSF-1) contains 136 AA residues. The sequence is very rich in cationic AA (24 % of the residues), lysine cluster sequences are found in the N-terminal and C-terminal ends of the structure. The OSF-1 gene was shown by Northern blotting analysis to be expressed in mouse calvarial osteoblast-enriched cells and in mouse brain tissues, but not in thymus, spleen, kidney, liver, lung, testis or heart. Pleiotrophin has the ability to promote adhesion, migration, expansion, and differentiation of human osteoprogenitor cells. In addition to certain types of cancer, the embryonic growth and differentiation factor pleiotrophin is found also in adults in inflammatory diseases. In osteoarthritis, pleiotrophin is especially expressed in early stages, and its concentrations in the synovial fluid could serve as a marker for the progress of the disease. Pleitrophin might be involved in cartilage repair in osteoarthritis, in particular, in earlier stages Synonyms: PTN, Heparin Affin Regulatory Protein, HARP, Heparin-binding growth factor-8, HBGF-8, Osteoblast-Specific Factor-1, OSF-1, Heparin-binding growth-associated molecule, HB-GAM, HBNF-1 Heparin-binding brain mitogen, Heparin-binding neurite outgrowth-promoting factor 1, HBBM, NEGF1