Followill D S, Travis E L
Department of Clinical Radiation Physics, University of Texas, M.D. Anderson Cancer Center, Houston 77030, USA.
Radiat Res. 1995 Dec;144(3):318-28.
These studies were undertaken to understand further the pathogenesis of consequential and primary fibrosis in mouse colon after irradiation. The distal 2.5 cm of colon of C3Hf/Kam mice was irradiated with either a single dose of 27 Gy or a split dose of 2 x 14.75 Gy separated by 10 days to induce a consequential or primary fibrotic lesion, respectively. The amount of total collagen in the two lesions was quantified by hydroxyproline, and tensile strength, an assay of tissue rigidity, was measured as a function of dose and time after irradiation. The relative distribution of collagen types I, III and IV in the colon was visualized by immunohistochemistry. Collagen types I, III and IV were quantified by immunoblot techniques, and in situ hybridization was used to identify and score the cells producing procollagen mRNA types I and III as a function of time after irradiation. The hydroxyproline and tensile strength measurements demonstrated that both lesions contained significantly increased amounts of collagen compared to controls. However, the ulcerated lesion of consequential fibrosis contained three times as much collagen and required a three- to fourfold increase in the peak force to rupture the colon as did the non-ulcerative lesion of primary fibrosis. The fibrosis accompanying the consequential lesion contained elevated levels of both collagen types I and III, but primary fibrosis contained only elevated levels of type I collagen compared to controls. The in situ hybridization studies showed cells producing increased amounts of procollagen mRNA 8 and 25 weeks before the elevated levels of collagen were detected for consequential and primary fibrosis, respectively. The cells producing the excess collagen mRNA were identified as fibroblasts. No distinction between the two lesions could be made based on the cell types producing the collagen. The distribution of labeled cells was localized to tissue areas showing specific immunofluorescence for the collagen types. These data show that the two histologically distinct lesions in irradiated colon, consequential and primary fibrosis, contain different collagen types and quantities of each type, suggesting that the underlying pathogenesis of these two lesions may be different.
开展这些研究是为了进一步了解小鼠结肠照射后继发性和原发性纤维化的发病机制。对C3Hf/Kam小鼠结肠远端2.5厘米分别给予单次27 Gy剂量照射或分两次、间隔10天给予2×14.75 Gy剂量照射，分别诱导继发性或原发性纤维化病变。通过羟脯氨酸对两种病变中的总胶原蛋白量进行定量，并测量拉伸强度（一种组织硬度测定方法）作为照射后剂量和时间的函数。通过免疫组织化学观察结肠中I、III和IV型胶原蛋白的相对分布。通过免疫印迹技术对I、III和IV型胶原蛋白进行定量，并使用原位杂交鉴定和评分产生I型和III型前胶原mRNA的细胞，作为照射后时间的函数。羟脯氨酸和拉伸强度测量结果表明，与对照组相比，两种病变中的胶原蛋白含量均显著增加。然而，继发性纤维化的溃疡性病变所含胶原蛋白量是原发性纤维化非溃疡性病变的三倍，且结肠破裂所需的峰值力增加了三到四倍。继发性病变伴随的纤维化中I型和III型胶原蛋白水平均升高，但与对照组相比，原发性纤维化仅I型胶原蛋白水平升高。原位杂交研究表明，在继发性和原发性纤维化中，分别在检测到胶原蛋白水平升高前8周和25周，产生前胶原mRNA的细胞数量增加。产生过量胶原蛋白mRNA的细胞被鉴定为成纤维细胞。基于产生胶原蛋白的细胞类型，无法区分这两种病变。标记细胞的分布定位于对各型胶原蛋白显示特异性免疫荧光的组织区域。这些数据表明，照射后结肠中两种组织学上不同的病变，继发性和原发性纤维化，含有不同类型的胶原蛋白以及每种类型的不同数量，这表明这两种病变的潜在发病机制可能不同。
