Wang J, Richter K K, Sung C C, Hauer-Jensen M
Department of Surgery, University of Arkansas for Medical Sciences, Little Rock 72205, USA.
Radiother Oncol. 1999 Feb;50(2):205-13. doi: 10.1016/s0167-8140(98)00113-3.
Transforming growth factor beta1 (TGF-beta1) appears to play an important role in the pathogenesis of chronic radiation-induced fibrosis in the intestine and several other organs. TGF-beta1 is secreted as a non-biologically active complex and its function depends on activation. In vitro data suggest that the mannose 6-phosphate/insulin-like growth factor-beta (M6P/IGF-II) receptor is involved in the mechanism of TGF-beta1 activation. Thus, we used a rat model of radiation enteropathy to examine the potential role of the M6P/IGF-II receptor in the in vivo regulation of TGF-beta1 activity and localization.
A scrotal hernia containing a loop of small intestine was created in male rats. The intestine in the scrotum was exposed to 0, 12, or 21 Gy single dose X-radiation. Groups of rats were euthanized 1 day and 2, 6 and 26 weeks after irradiation. Histopathologic injury was assessed with a radiation injury score (RIS). Computerized image analysis was used to identify M6P/IGF-II receptor-positive cells and to quantify extracellular matrix-associated TGF-beta1 immunoreactivity. Changes in urokinase plasminogen activator (uPA), tissue-like plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) immunoreactivity were also assessed.
In normal (sham-irradiated) intestine, M6P/IGF-II immunoreactivity was confined to relatively weak, but specific epithelial staining. Irradiated intestine exhibited a highly significant time- and dose-dependent increase in the number of M6P/IGF-II receptor-positive cells (P < 0.001). There was a striking spatial shift of M6P/IGF-II receptor immunoreactivity from epithelium during the early post-radiation phase to stromal cells, most notably fibroblasts during the later stages of injury. Irradiated intestine exhibited distinct co-localization of M6P/ IGF-II receptor-positive cells and extracellular matrix-associated TGF-beta1 in areas of histopathologic injury. There were highly significant associations between the number of M6P/IGF-II receptor-positive stromal cells and TGF-beta1 immunoreactivity (P < 0.001), radiation-induced fibrosis (P < 0.001) and RIS (P < 0.001). Endothelial tPA immunoreactivity decreased significantly after irradiation (P < 0.001), whereas uPA and PAI-1 immunoreactivity levels appeared to be unchanged.
M6P/IGF-II receptor upregulation may be a key factor in the in vivo control of TGF-beta1 activity and responsible for the tissue specificity of TGF-beta1 action after irradiation.
转化生长因子β1（TGF-β1）似乎在肠道及其他多个器官的慢性辐射诱导纤维化发病机制中发挥重要作用。TGF-β1以无生物活性的复合物形式分泌，其功能依赖于激活。体外数据表明，甘露糖6-磷酸/胰岛素样生长因子Ⅱ（M6P/IGF-II）受体参与TGF-β1的激活机制。因此，我们使用放射性肠病大鼠模型来研究M6P/IGF-II受体在体内对TGF-β1活性和定位调节中的潜在作用。
在雄性大鼠中制造一个包含一段小肠的阴囊疝。将阴囊内的小肠暴露于0、12或21 Gy的单次剂量X射线辐射。在照射后1天以及2、6和26周对几组大鼠实施安乐死。用辐射损伤评分（RIS）评估组织病理学损伤。使用计算机图像分析来识别M6P/IGF-II受体阳性细胞，并对细胞外基质相关的TGF-β1免疫反应性进行定量。还评估了尿激酶型纤溶酶原激活剂（uPA）、组织型纤溶酶原激活剂（tPA）和纤溶酶原激活剂抑制剂-1（PAI-1）免疫反应性的变化。
在正常（假照射）肠道中，M6P/IGF-II免疫反应性局限于相对较弱但特异的上皮染色。照射后的肠道中，M6P/IGF-II受体阳性细胞数量呈现出高度显著的时间和剂量依赖性增加（P < 0.001）。M6P/IGF-II受体免疫反应性在辐射后早期从上皮细胞向基质细胞发生了显著的空间转移，在损伤后期最明显的是成纤维细胞。照射后的肠道在组织病理学损伤区域呈现出M6P/IGF-II受体阳性细胞与细胞外基质相关的TGF-β1明显的共定位。M6P/IGF-II受体阳性基质细胞数量与TGF-β1免疫反应性（P < 0.001）、辐射诱导的纤维化（P < 0.001）和RIS（P < 0.001）之间存在高度显著的关联。照射后内皮细胞tPA免疫反应性显著降低（P < 0.001），而uPA和PAI-1免疫反应性水平似乎未发生变化。
M6P/IGF-II受体上调可能是体内控制TGF-β1活性的关键因素，并负责照射后TGF-β1作用的组织特异性。
