骨骼為一種堅固的構造用來支撐動物的體重，而且骨骼也是一個處於動態平衡的器官，不斷的進行重塑、維持形狀以及修復。骨骼重塑(bone remodeling)的過程由成骨細胞參與骨質新生(bone formation)，以及蝕骨細胞參與骨質吸收(bone resorption)來進行骨骼的替舊換新，以維持健康、堅硬的骨骼。蝕骨細胞新生(osteoclastogenesis)為骨骼代謝一個必要的過程，蝕骨細胞新生過程主要是巨噬細胞受巨噬細胞群落刺激因子(macrophage colony-stimulating factor, M-CSF)及細胞核因子 kappa-B配位體受器活化因子(receptor activator of nuclear factor kappa-B ligand, RANKL)調控。內皮唾液酸蛋白(endosialin)亦可稱為腫瘤內皮細胞標誌一(tumor endothelial marker 1, TEM1)或CD248，屬類C型凝集素膜外受器，為一個高度唾液酸醣化之穿膜醣蛋白。CD248表現於纖維母細胞、周細胞以及部分種類之腫瘤細胞。我們利用RAW 264.7巨噬細胞株來觀察蝕骨細胞新生的過程。經由抗酒石酸性磷酸酶染色(trap stain)方法測試結果發現rCD248 D1蛋白能抑制RAW 264.7巨噬細胞由M-CSF與RANKL誘發的蝕骨細胞形成，而即時聚合酶鏈鎖反應結果顯示rCD248 D1蛋白能抑制與分化過程或是分解骨質相關的蛋白表現。但在M-CSF與RANKL誘發的分化訊息傳遞上，未看到rCD248 D1蛋白對其有抑制作用；另外在卵巢摘除的母小鼠上，發現給予rCD248 D1蛋白能減緩骨質疏鬆的情況。綜合以上結果推測rCD248 D1蛋白對於蝕骨細胞形成有抑制作用，同時具潛力可以抑制骨質疏鬆。

SUMMARY
Bone is a rigid structure to support body mass in animals, and the bone is a dynamic organ that undergoes continuous remolding, shaping and repairing. The process of bone remodeling involves bone formation and bone resorption which are mediated by osteoblasts and osteoclasts, respectively. Osteoclastogenesis needs macrophage colony stimulating factor(M-CSF) and the receptor activator of nuclear factor kappa-light-chain-enhancer of activated B cell ligand(RANKL) to promote macrophages to proceed the process. Endosialin (CD248) is a member of the C-type lectin-like domain containing proteins. CD248 is an orphan receptor expressed by fibroblasts and several tumor cells. In this study, we use RAW 264.7 cells to study the process of osteoclastogenesis. By using tartrate-resistant acid phosphatase (TRAP) stain, we revealed that the osteoclastogenesis of RAW 264.7 cell induced by M-CSF and RANKL was inhibited by recombinant CD248 D1 protein. Moreover, the treatment of rCD248 D1 protein induced a decrease in mRNA level of pre-osteoclast markers and bone resorption protein. But there was no changes in M-CSF and RANKL-induced signal pathways. On the other hand, in the ovariectomized mouse(Ovx) model, treatment with rCD248 D1 protein group shows better bone status than the control group Collectively, our results suggest that recombinant CD248 D1 protein may inhibit the osteoclast formation.

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