Mbalaviele G, Chen H, Boyce B F, Mundy G R, Yoneda T
University of Texas Health Science Center at San Antonio, Department of Medicine 78284, USA.
J Clin Invest. 1995 Jun;95(6):2757-65. doi: 10.1172/JCI117979.
A critical step in bone resorption is the fusion of mononuclear osteoclast precursors to form multinucleated osteoclasts. However, little is known of the molecular mechanisms that are responsible for this important process. Since the expression of proteins in the cadherin family of homophilic calcium-dependent cell adhesion molecules is involved in the fusion process for certain other cells, we examined their role in osteoclast formation. Immunohistochemical examination of human and mouse bone using monoclonal antibodies to human and mouse E-cadherin clearly demonstrated positive staining in osteoclasts. N- and P-cadherin were not detected. In cultures of murine marrow mononuclear cells in which osteoclasts form by cell fusion, E-cadherin expression determined by Western blotting reached the highest levels as fusion was taking place. Expression of E-cadherin gene fragment was also detected in the marrow cultures by polymerase chain reaction. To study the functional role of E-cadherin expression in osteoclastic differentiation, neutralizing monoclonal antibodies were examined for their effects on osteoclast formation. The antibodies decreased the number of tartrate-resistant acid phosphatase (a marker of murine osteoclast)-positive multinucleated cell (TRAP-positive MNC) by inhibiting the fusion of mononuclear osteoclast precursors, but not proliferation of these cells or their attachment to plastic dish surfaces. This inhibitory effect was reversible. Furthermore, synthetic peptides containing the cell adhesion recognition sequence of cadherins also decreased TRAP-positive MNC formation. The antibodies and peptides inhibited not only osteoclast formation but also bone resorption. Antibodies to other types of cadherins and control rat IgG had no effects in these culture systems. Our findings suggest that E-cadherin expression may be involved in fusion (differentiation) of hemopoietic osteoclast precursors into mature multinucleated osteoclasts.
骨吸收的一个关键步骤是单核破骨细胞前体融合形成多核破骨细胞。然而，对于这一重要过程的分子机制却知之甚少。由于钙黏蛋白家族中同嗜性钙依赖性细胞黏附分子的蛋白质表达参与了某些其他细胞的融合过程，我们研究了它们在破骨细胞形成中的作用。使用抗人及小鼠E-钙黏蛋白的单克隆抗体对人和小鼠骨骼进行免疫组织化学检查，结果清楚地显示破骨细胞中有阳性染色。未检测到N-钙黏蛋白和P-钙黏蛋白。在通过细胞融合形成破骨细胞的小鼠骨髓单核细胞培养物中，通过蛋白质印迹法测定的E-钙黏蛋白表达在融合发生时达到最高水平。通过聚合酶链反应也在骨髓培养物中检测到了E-钙黏蛋白基因片段的表达。为了研究E-钙黏蛋白表达在破骨细胞分化中的功能作用，检测了中和性单克隆抗体对破骨细胞形成的影响。这些抗体通过抑制单核破骨细胞前体的融合，而不是这些细胞的增殖或它们与塑料培养皿表面的附着，减少了抗酒石酸酸性磷酸酶（小鼠破骨细胞的标志物）阳性多核细胞（抗酒石酸酸性磷酸酶阳性MNC）的数量。这种抑制作用是可逆的。此外，含有钙黏蛋白细胞黏附识别序列的合成肽也减少了抗酒石酸酸性磷酸酶阳性MNC的形成。这些抗体和肽不仅抑制破骨细胞形成，还抑制骨吸收。针对其他类型钙黏蛋白的抗体和对照大鼠IgG在这些培养系统中没有作用。我们的研究结果表明，E-钙黏蛋白表达可能参与造血破骨细胞前体融合为成熟多核破骨细胞的过程。
