凝血酶調節素(TM)；是一個含有五個結構域的第一型穿膜蛋白。此蛋白質被發現
表現在許多不同種類的細胞中。例如:角質細胞、巨噬細胞、心肌細胞、內皮細
胞以及蝕骨細胞。在我們最近的研究中發現，凝血酶調節素在巨噬細胞分化成蝕
骨細胞的過程中扮演了負面調節者的角色，這意味著凝血酶調節素會抑制骨質的
吸收。人體的骨質密度的恆定主要就是由蝕骨細胞以及成骨細胞之間功能的互相
調控來達成。我們假設凝血酶調節素除了在蝕骨細胞裡扮演著抑制的角色外，很
可能在成骨細胞裡也有重要的功能。在過去的研究中雖然發現在成骨細胞內，凝
血酶調節素的基因可以被維他命 D3 刺激而大量表現，但針對凝血酶調節素在成
骨細胞的生理功能卻幾乎未被仔細研究過。
成骨細胞在骨生成中扮演著關鍵的角色，因為可以在骨損傷的癒合上看到成骨細
胞明顯的活化。同時，凝血酶調節素被發現可以促進表皮的傷口癒合。因此，我
們假設凝血酶調節素應該在骨癒合中扮演重要的角色。根據表皮傷口癒合的機制，
表皮細胞膜上的凝血酶調節素會因為傷口的刺激而表現量上升。同時會被膜上的
蛋白酶 rhomboid-like 2 (RDBDL2)從凝血酶調節素的第四個結構域-穿膜域進行
剪切，導致凝血酶調節素被釋放到培養液中；簡稱為可溶性的凝血酶調節素(sTM)。
並且 sTM 具有促進表皮傷口癒合的能力。首先，將人類的成骨細胞株(MG63)培
養在不含血清的培養液中，凝血酶調節素可以在培養液中被偵測到。再者，經由
模擬骨損傷的條件可以刺激 MG63 細胞表面的凝血酶調節素以及 RHBDL2 蛋白
酶表現量上升，並導致更多水溶性的凝血酶調節素被釋放到細胞外。我們發現這
些被釋放出來的凝血酶調節素可以影響成骨細胞的許多功能，例如:人類成骨細
胞(MG63)或是小鼠成骨細胞(MC3T3E1)經過損傷的刺激後得到的上層培養液，
都有刺激成骨細胞的爬行能力增加。反之；利用 shRNA 抑制凝血酶調節素的細
胞則抑制了其促進爬行的能力。而類凝血酶調節素生肽 168X (TM like peptide
168X) 也具有促進爬行效果，且與劑量呈正相關。此外，TM like peptide 168X 也
有刺激成骨細胞增生以及鈣鹽礦化的能力。進一步，我們利用人工引發第一型糖
尿病的小鼠進行顱骨穿孔的實驗，我們也觀察到 TM like peptide 168X 具有加速
骨癒合的效果。因此我們的結果顯示凝血酶調節素的確參與成骨細胞的生理功能，
而且凝血酶調節素對於治療骨損傷具有臨床的應用價值。

Thrombomodulin (TM), a type I transmembrane glycoprotein containing five functional
domains, is expressed in various cell types including endothelial cells, keratinocytes,
macrophages, and osteoblasts. Our recent report indicated that thrombomodulin domain
one (TMD1) functions as a negative regulator in osteoclastogenesis. However, the
physiological functions of TM in osteoblasts has not been studied yet. Osteoblasts which
are the major source of bone matrix are particularly active in bone healing. Our previous
studies showed that epithelial TM plays a critical role in promoting cutaneous wound
healing at least partially through the function of soluble TM (sTM) which is released from
the cell surface by a member of rhomboid serine protease family (rhomboid-like-2,
RHBDL2). We hypothesized that osteoblastic TM also has a role in mediating bone healing
through the production of sTM. First, we demonstrated that sTM can be detected in the
serum-free conditioned medium (CM) of human osteoblast cell line, MG-63 cells.
Furthermore, expression levels of full-length TM, RHBDL2 and sTM in MG-63 culture
were upregulated after scratch injury. The upregulation of sTM expression was inhibited
by treatment with RHBDL2 inhibitor-3, 4-dichloroisocoumarin (DCI). The CM of injury
cells but not the CM from TM-silenced cells could promote cell migration. In addition, the
TM like peptide 168X could promote cell migration, proliferation and calcium deposition
in MG63 cells. Furthermore, we demonstrated that TM like peptide 168X could enhance
calvarial bone healing in diabetic mice. In conclusion, we demonstrated the physiological
significance of osteoblastic TM in bone healing. sTM may have some application potential
for bone-related disorders.

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