Skwarchuk M W, Travis E L
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Int J Radiat Oncol Biol Phys. 1998 Aug 1;42(1):169-78. doi: 10.1016/s0360-3016(98)00201-6.
A strain difference in the development of radiation-induced fibrosis of the colorectum was recently observed. C57B1/6 mice developed colorectal obstruction with significantly higher incidence compared to C3Hf/Kam mice after partial volume irradiation with 30 Gy. Previous reports have demonstrated differences in cytokine mRNA levels in fibrosis-prone and -resistant mice after lung irradiation. The aims of this study are to determine if there are strain differences in: 1) the histology of the lesion, 2) mRNA levels for transforming growth factor beta (TGFbeta) isoforms and tumor necrosis factor alpha (TNFalpha), and 3) immunohistochemical staining patterns using antibodies against the TGFbeta isoforms and latency-associated peptide (LAP).
The colorectum of male C3Hf/Kam (C3H) and C57B1/6 (B6) mice were irradiated using a dose/length combination (30 Gy to 13.7 mm) that resulted in 10 or 100% incidence of obstruction by 6 months in each strain, respectively. Colorectal tissue was removed from 6 hours to 120 days after irradiation as well as from obstructed mice and prepared for histology, RNase protection assay, and immunofluorescence.
Distinct differences in the histological phenotype for the two strains were observed at times preceding obstruction. Samples from B6 mice showed increased hyperplastic crypts, colitis cystica profunda, and fibrosis within the lamina propria, compared to identically treated C3H mice. Fibrosis in the lamina propria of B6 mice appeared early, beginning at 75 days after irradiation, and was progressive, whereas fibrosis in C3H mice appeared simultaneous with obstruction and may have been a reaction to ulceration. No consistent strain difference in mRNA levels for TGFbeta1, 2, 3 or TNFalpha were observed, although mRNA levels of TGFbeta1 and TNFalpha were significantly elevated in both strains relative to nonirradiated controls. Immunofluorescent staining for TGFbeta1, 3 and LAP was observed in hyperplastic crypts and colitis cystica profunda adjacent to regions of fibrosis, histological changes that were present predominately in the B6 strain.
The response of the colorectum to irradiation involves changes in the expression of several different cytokines. However, the lack of a consistent strain difference in TGFbeta1, 2, 3 and TNFalpha mRNA levels, despite strain differences in both the incidence of colorectal obstruction and histological features preceding obstruction, suggests that mRNA changes in these fibrogenic cytokines are not the critical determinant of the strain difference and are not related to the process of radiation-induced colorectal fibrosis in these mouse strains. Strain-dependent differences were observed in the localization of active TGFbeta, but these differences were related to the histological changes specifically found in the irradiated colon of the B6 strain.
最近观察到结肠直肠放射性纤维化发展过程中存在品系差异。在用30 Gy进行部分容积照射后，C57B1/6小鼠发生结肠直肠梗阻的发生率显著高于C3Hf/Kam小鼠。先前的报告表明，肺照射后，易发生纤维化和抗纤维化小鼠的细胞因子mRNA水平存在差异。本研究的目的是确定在以下方面是否存在品系差异：1）病变的组织学；2）转化生长因子β（TGFβ）亚型和肿瘤坏死因子α（TNFα）的mRNA水平；3）使用抗TGFβ亚型和潜伏相关肽（LAP）抗体的免疫组织化学染色模式。
使用剂量/长度组合（30 Gy至13.7 mm）照射雄性C3Hf/Kam（C3H）和C57B1/6（B6）小鼠的结肠直肠，该组合分别导致每个品系在6个月时梗阻发生率为10%或100%。在照射后6小时至120天以及梗阻小鼠中取出结肠直肠组织，用于组织学、核糖核酸酶保护测定和免疫荧光检查。
在梗阻前的不同时间观察到两个品系在组织学表型上存在明显差异。与相同处理的C3H小鼠相比，B6小鼠的样本显示增生性隐窝增加、深部囊性结肠炎以及固有层内纤维化。B6小鼠固有层内的纤维化出现较早，在照射后75天开始，并呈进行性发展，而C3H小鼠的纤维化与梗阻同时出现，可能是对溃疡的一种反应。尽管相对于未照射的对照组，两个品系中TGFβ1、2、3或TNFα的mRNA水平均显著升高，但未观察到这些mRNA水平存在一致的品系差异。在纤维化区域附近的增生性隐窝和深部囊性结肠炎中观察到TGFβ1、3和LAP的免疫荧光染色，这些组织学变化主要出现在B6品系中。
结肠直肠对辐射反应涉及几种不同细胞因子表达的变化。然而，尽管结肠直肠梗阻发生率和梗阻前组织学特征存在品系差异，但TGFβ1、2、3和TNFα mRNA水平缺乏一致的品系差异，这表明这些促纤维化细胞因子的mRNA变化不是品系差异的关键决定因素，并且与这些小鼠品系中辐射诱导的结肠直肠纤维化过程无关。在活性TGFβ的定位上观察到品系依赖性差异，但这些差异与在B6品系照射结肠中特有的组织学变化有关。
