血纖維蛋白溶酶原（plasminogen, Plg）是血纖維蛋白溶酶（plasmin, Plm）的前驅物，其具有纖維蛋白溶解功能（fibrinolysis），是血栓的溶解的主要酵素。當細胞表面上特異性的Plg受體與Plg結合後，Plg被尿激酶型血纖維蛋白溶解酶原活化因子（uPA）分解活化成Plm，其位於細胞表面使細胞具有水解活性。在發炎反應中Plm的蛋白水解活性，調控巨噬細胞移動具有重要的角色。本實驗室先前的研究發現內皮細胞上的凝血酶調節素（thrombomodulin, TM）是一種Plg受體。TM參與在uPA對Plg的活化，並調控內皮細胞周圍的蛋白水解活性。然而，在TM與Plg交互作用是否參與在Plg誘導的白血球移動仍不清楚。在本篇研究中，我們提出巨噬細胞上的TM能與Plg一起調控細胞的移動。實驗結果顯示Plg能隨著劑量增加，而增加其與THP-1細胞結合。當THP-1細胞的TM基因表現減量時，其結合Plg及活化Plg的能力，比TM基因正常表現的細胞較低。此外，THP-1的細胞移動能受到uPA刺激Plg活化所調控。在小鼠實驗中，我們利用thioglycollate刺激腹膜炎的模式，發現在TM的胺基端類凝集素功能區（domain 1, D1）缺失的小鼠（TMLeD/LeD），其巨噬細胞浸潤至腹腔的數目相較於正常基因型小鼠少。從TMLeD/LeD小鼠分離出的巨噬細胞對於與Plg結合、Plg活化、Plg誘發的細胞移動以及Plg調控基質金屬蛋白酶-9（matrix metalloproteinases-9, MMP-9）活化的能力都低於TM基因表現正常小鼠之巨噬細胞。然而，我們發現Plg活性測試以及巨噬細胞浸潤在野生型（TMf/f）與白血球細胞上特異性凝血酶調節素剔除（LysMCre/TMf/f）小鼠中沒有顯著性的差異。在共軛焦顯微鏡下觀察，發現TMLeD/LeD小鼠的巨噬細胞相較於正常基因型小鼠其Plg與TM共位的現象較少。綜合以上的結果，巨噬細胞的TM能透過D1去促進Plg所誘發的巨噬細胞移動。這項研究證明TM與Plg的結合在巨噬細胞具有促進細胞移行的功能。

Plasminogen (Plg), a precursor of the serine protease plasmin (Plm), functions as a major enzyme in fibrinolytic system, which mediates the dissolution of blood clot. After Plg binding to specific Plg receptors on cell-surface, urokinase-type Plg activator (uPA) can activate and convert Plg to Plm, which possesses cell-associated proteolytic activity. Plm-mediated proteolytic activity plays an important role in macrophage migration in inflammation. In the previous studies, we demonstrated that thrombomodulin (TM) is a novel Plg receptor and is involved in uPA-mediated activation of Plg in regulating pericellular proteolysis in endothelial cells. However, whether TM/Plg interaction is involved in Plg-mediated leukocyte migration is unknown. Here, we report that TM in association with Plg participates in macrophage migration. We demonstrated that Plg bound to THP-1 cells dose-dependently. The binding of Plg and the rate of Plg activation were decreased in THP-1 cells when TM was knocked down in comparison with TM-expressed cells. uPA-induced Plg activation was required in the migration of THP-1 cells. The number of macrophage infiltration to peritoneum in thioglycollate-induced peritonitis in lectin-like domain (domain 1, D1) of TM deletion mice (TMLeD/LeD) was significantly decreased than that in TMWT/WT mice. Furthermore, the macrophages isolated from TMLeD/LeD mice ascites exhibited reduced Plg-associated activities, including Plg binding and activation, Plg-triggered cell migration, and Plg-induced activation of matrix metalloproteinases-9 activity. However, the myeloid-specific TM-deficient mice (LysMcre/TMflox/flox mice) had no significant effects on Plg activation and macrophage infiltration into the peritoneal cavity as compared with TM wild-type (TMflox/flox) mice. Less colocalization of Plg and TM was observed in macrophages from TMLeD/LeD mice as compared with that from TMWT/WT mice as observed using confocal microseopy. In conclusion, we proposed that Plg interacts with TM in macrophage to promote plg-mediated macrophage migration and lectin-like domain of TM is involved in the process. The association of TM/Plg in the migration of macrophages is a new biological function of TM in inflammation.

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