Different levels of the neuronal nitric oxide synthase isoform modulate the rate of osteoclastic differentiation of TIB‐71 and CRL‐2278 RAW 264.7 murine cell clones

It has been clearly established that osteoclasts, which play a crucial role in bone resorption, differentiate from hematopoietic cells belonging to the monocyte/macrophage lineage in the presence of macrophage‐colony stimulating factor (M‐CSF) and receptor activator of NF‐κB ligand (RANKL). We have here investigated the M‐CSF‐ and RANKL‐induced osteoclastic differentiation of two distinct clones of the murine monocytic/macrophagic RAW 264.7 cell line, known as TIB‐71 and CRL‐2278, the latter cell clone being defective for the expression of the inducible nitric oxide synthase isoform in response to interferon‐γ or lipopolysaccharide. CRL‐2278 cells demonstrated a more rapid osteoclastic differentiation than TIB‐71 cells, as documented by morphology, tartrate‐resistant acid phosphatase positivity, and bone resorption activity. The enhanced osteoclastic differentiation of CRL‐2278 was accompanied by a higher rate of cells in the S/G2‐M phases of cell cycle as compared to TIB‐71. The analysis of nitric oxide synthase (NOS) isoforms clearly demonstrated that only neuronal NOS was detectable at high levels in CRL‐2278 but not in TIB cells under all tested conditions. Moreover, the broad inhibitor of NOS activity L‐NAME significantly inhibited osteoclastic differentiation of CRL‐2278 cells. Altogether, these results demonstrate that a basal constitutive neuronal NOS activity positively affects the RANKL/M‐CSF‐related osteoclastic differentiation. © 2005 Wiley‐Liss, Inc.