Abstract
The effects of histamine and its receptor antagonists on mouse bone marrow cells (MBMC) and MC3T3-E1 cells were studied to elucidate the precise molecular mechanisms underlying histamine activities in the respective cell types. The studied parameters were osteoclast differentiation and expressions of receptor activator of nuclear factor κB ligand (RANKL), histamine receptors (HR), and osteoblast differentiation markers. The osteoclastogenesis was assessed by TRAP-dye method. Expressions of RANKL, HR and the osteoblast differentiation markers were evaluated by RT-PCR analysis. In MBMC, 1 μM histamine doubled the number of osteoclast-like cells in a dose-dependent manner. Expressions of RANKL peaked at histamine concentrations of 1 μM and 0.1 μM in MBMC and MC3T3-E1, respectively. H1R antagonist, but not H2R antagonist, inhibited RANKL expressions induced by histamine in MC3T3-E1. Histamine induced expressions of cell differentiation markers in MC3T3-E1, but not in MBMC, under the conditions that RANKL expressions were induced by histamine in both types of cells. These results indicate the following: (1) Histamine induction of osteoclastogenesis is mediated by RANKL expressed via H1R, but not via H2R in mouse osteoblast-like cells; (2) and the major target of histamine action is the RANKL-RANK signaling pathway in osteocytes. This observation is consistent with the traditionally recognized histamine action of bone resorption at the osteoclast site.
