Elamaa Harri, Sormunen Raija, Rehn Marko, Soininen Raija, Pihlajaniemi Taina
Department of Medical Biochemistry and Molecular Biology, Biocenter Oulu, University of Oulu, Aapistie 7, FI 90220, Oulu, Finland.
Am J Pathol. 2005 Jan;166(1):221-9. doi: 10.1016/S0002-9440(10)62246-8.
Endostatin, a proteolytic fragment of type XVIII collagen, has been shown to inhibit angiogenesis, tumor growth, and endothelial cell proliferation and migration. We analyzed its functions in vivo by generating transgenic mice in which it was overexpressed in the skin and lens capsule under the keratin K14 promoter. Opacity of the lens occurred at 4 months of age in the mouse line J4, with the highest level of endostatin expression. The lens epithelial cells appeared to lose contact with the capsule and began to vacuolize. In 1-year-old mice the lens epithelial cell layer had entirely degenerated, and instead, large plaques of spindle-shaped cells had formed in the anterior region of the lens. Moreover, a widening of the epidermal basement membrane (BM) zone of the skin was observed in electron microscopy. The epidermal BM was conspicuously altered in the J4 mice with high transgene expression, including clear broadening and occurrence of pearl-like protrusions in some areas, whereas the BM was more even in appearance but consistently broadened in the mouse line G20 with moderate transgene expression. In both lines the BM was continuous. Measurements indicated that the lamina densa was 78.54 +/- 53.10 nm in line J4, the large variation reflecting the protrusions of the lamina densa, and 44.24 +/- 11.52 nm in line G20, compared with 33.74 +/- 9.96 nm in wild-type adult mice. Immunoelectron microscopy of wild-type mouse skin type XVIII collagen showed a polarized orientation in the BMs, with the C-terminal endostatin region localized in the lamina densa and the N terminus in average approximately 40 nm more on the dermal side. Type XVIII collagen was dispersed in the transgenic skin, suggesting that the transgene-derived endostatin fragment displaces the full-length collagen XVIII. This may impair the anchoring of the lamina densa to the dermis and thereby lead to loosening of the BMs, resembling the previously observed situation in collagen XVIII-null mice.
内皮抑素是 XVIII 型胶原蛋白的蛋白水解片段，已被证明可抑制血管生成、肿瘤生长以及内皮细胞的增殖和迁移。我们通过构建转基因小鼠来分析其体内功能，在角蛋白 K14 启动子的驱动下，内皮抑素在这些小鼠的皮肤和晶状体囊中过表达。在小鼠品系 J4 中，4 个月大时晶状体出现混浊，该品系内皮抑素表达水平最高。晶状体上皮细胞似乎与晶状体囊失去接触并开始空泡化。在 1 岁的小鼠中，晶状体上皮细胞层完全退化，取而代之的是在晶状体前部区域形成了大片梭形细胞。此外，在电子显微镜下观察到皮肤的表皮基底膜（BM）区变宽。在转基因表达水平高的 J4 小鼠中，表皮 BM 明显改变，包括明显变宽以及在某些区域出现珍珠样突起，而在转基因表达水平中等的 G20 小鼠品系中，BM 外观更均匀，但持续变宽。在这两个品系中，BM 都是连续的。测量表明，J4 品系的致密层为 78.54±53.10 nm，该较大差异反映了致密层的突起，G20 品系为 44.24±11.52 nm，而野生型成年小鼠为 33.74±9.96 nm。野生型小鼠皮肤 XVIII 型胶原蛋白的免疫电子显微镜检查显示，在 BM 中呈极化取向，C 端内皮抑素区域位于致密层，N 端平均在真皮侧约 40 nm 处。 XVIII 型胶原蛋白在转基因皮肤中分散，这表明转基因衍生的内皮抑素片段取代了全长 XVIII 型胶原蛋白。这可能会损害致密层与真皮的锚定，从而导致 BM 松弛，类似于之前在 XVIII 型胶原蛋白基因敲除小鼠中观察到的情况。
