Leptin is expressed in and secreted from primary cultures of human osteoblasts and promotes bone mineralization

The adipose hormone leptin and its receptor are important for regulation of food intake and energy metabolism. Leptin also is involved in the growth o f different tissues. In this study, we show the expression of leptin in pri mary cultures of normal human osteoblasts (hOBs) as evidenced by reverse tr anscriptase-polymerase chain reaction (RT-PCR) and immunocytochemistry. Rel ease of leptin into the medium also was found. Leptin was not detected in c ommercially available hOBs (NHOst) or in three different human monoclonal o steosarcoma cell lines. Leptin expression was observed in OBs in the minera lization and/or the osteocyte transition period but not during the matrix m aturation period. Furthermore, hOBs and osteosarcoma cell lines expressed t he long signal-transducing form of the leptin receptor (OB-Rb) as shown by RT-PCR. We observed no significant changes in leptin or OB-Rb genes in hOBs after incubation with recombinant leptin, indicating no autoregulation of the leptin expression. Incubation of both hOBs entering the mineralization phase and osteosarcoma cell lines with recombinant leptin markedly increase d the number of mineralized nodules as shown by alizarin S staining. These findings indicate that leptin may be of importance for osteoblastic cell gr owth and bone mineralization.