Y Gao1, I Morita, T Kubota, S Murota, T Aso. 1. Department of Obstetrics and Gynecology, Faculty of Medicine, Tokyo Medical and Dental University, Tokyo, Japan.
Abstract
OBJECTIVES: Estrogen deficiency caused by the menopause or ovariectomy leads to stimulation of osteoclastogenesis. The adhesion molecules, leukocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1), are necessary for osteoclast formation. In this study, the expression of LFA-1 and ICAM-1 on osteoclast precursors during osteoclast differentiation, and the involvement of ovariectomy in the expression, were investigated. METHODS: Spleen cells isolated from normal or ovariectomized (OVX) mice were co-cultured with TMS14, stromal cells derived from mouse bone marrow, in the absence or presence of 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) for 7 days. On days 3, 5 and 7 of culture, the expression of LFA-1 and ICAM-1 on osteoclast precursors was quantitated using indirect immunofluorescence and confocal laser cytometry, and, on day 7, the number of formed osteoclasts was measured by tartrate-resistant acid phosphatase (TRAP) stain. RESULTS: The level of ICAM-1 expression on osteoclast precursors gradually increased with osteoclast differentiation, whereas that of LFA-1 did not change. A high level of ICAM-1 was observed on the integrin beta 3-positive mononuclear cells. On the osteoclast precursors isolated from OVX mice, both the level of ICAM-1 expression per cell and the number of cells showing a high expression of ICAM-1 significantly increased, with an increase in the number of osteoclast-like cells. However, the level of LFA-1 did not change. CONCLUSIONS: These results indicate that the expression level of ICAM-1, but not that of LFA-1, is involved in osteoclast differentiation. Estrogen deficiency results in an increase in ICAM-1 expression on osteoclast precursors, which may be one of the mechanisms underlying bone loss following the menopause or ovariectomy.
OBJECTIVES: Estrogen deficiency caused by the menopause or ovariectomy leads to stimulation of osteoclastogenesis. The adhesion molecules, leukocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1), are necessary for osteoclast formation. In this study, the expression of LFA-1 and ICAM-1 on osteoclast precursors during osteoclast differentiation, and the involvement of ovariectomy in the expression, were investigated. METHODS: Spleen cells isolated from normal or ovariectomized (OVX) mice were co-cultured with TMS14, stromal cells derived from mouse bone marrow, in the absence or presence of 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) for 7 days. On days 3, 5 and 7 of culture, the expression of LFA-1 and ICAM-1 on osteoclast precursors was quantitated using indirect immunofluorescence and confocal laser cytometry, and, on day 7, the number of formed osteoclasts was measured by tartrate-resistant acid phosphatase (TRAP) stain. RESULTS: The level of ICAM-1 expression on osteoclast precursors gradually increased with osteoclast differentiation, whereas that of LFA-1 did not change. A high level of ICAM-1 was observed on the integrin beta 3-positive mononuclear cells. On the osteoclast precursors isolated from OVX mice, both the level of ICAM-1 expression per cell and the number of cells showing a high expression of ICAM-1 significantly increased, with an increase in the number of osteoclast-like cells. However, the level of LFA-1 did not change. CONCLUSIONS: These results indicate that the expression level of ICAM-1, but not that of LFA-1, is involved in osteoclast differentiation. Estrogen deficiency results in an increase in ICAM-1 expression on osteoclast precursors, which may be one of the mechanisms underlying bone loss following the menopause or ovariectomy.