不同年龄小鼠造血系统辐射损伤与修复的比较观察

目的 观察辐射对不同年龄小鼠（幼年鼠、青年鼠、老年鼠）造血系统的损伤及恢复的影响，探讨幼年鼠、老年鼠受照后造血系统的变化及其与青年鼠的差异。 方法 不同年龄（幼年鼠：3周龄、青年鼠：8周龄、老年鼠：14月龄）雄性C57BL/6小鼠各60只，按照随机区组法分为对照组、2 Gy照射组、4 Gy照射组，每组各20只。其中，照射组小鼠用137Cs γ射线给予全身照射，对照组给予假照射。分别于照射后第3、7、14、28天取材，检测小鼠外周血计数、单侧股骨骨髓有核细胞计数、骨髓中造血干细胞（HSC）百分比、造血祖细胞（HPC）百分比及粒单系造血祖细胞集落形成单位（CFU-GM）绝对百分比。多组间比较采用单因素方差分析，两组间比较采用t检验。 结果 照射组小鼠白细胞计数、单侧股骨骨髓有核细胞计数、HSC百分比和HPC百分比在第3天降至最低值，其中，幼年鼠2 Gy、4 Gy照射组白细胞计数分别下降至同组对照组的34.8%（t=6.129，P<0.05）、19.6%（t=7.084，P<0.05），青年鼠2 Gy、4 Gy照射组白细胞计数分别下降至同组对照组的43.8%（t=3.043，P<0.05）、20.0%（t=7.084，P<0.05），老年鼠2 Gy、4 Gy照射组白细胞计数分别下降至同组对照组的19.0%（t=22.080，P<0.05）、8.4%（t=24.590，P<0.05）， 4 Gy照射组降低程度重于2 Gy照射组，且呈剂量依赖性。第28天时幼年鼠照射组单侧股骨骨髓有核细胞计数未恢复正常，4 Gy照射组HSC绝对百分比仍低于50%，HPC绝对百分比恢复至50%左右。青年鼠照射组CFU-GM在第28天恢复至正常水平，而幼年鼠照射组（2 Gy照射：t=2.067，P<0.05；4 Gy照射：t=3.358，P<0.05）和老年鼠照射组（2 Gy照射：t=2.586，P<0.05；4 Gy照射：t=4.772，P<0.05）在第28天时显著低于青年鼠照射组，仍未恢复至正常水平。 结论 照射组小鼠造血系统大多数指标在第3天出现急性抑制且呈剂量依赖性，3 d后为损伤恢复期，多数指标在第28天可恢复至正常水平。与青年鼠相比，幼年鼠的血小板和造血干细胞功能对辐射损伤更为敏感，老年鼠的骨髓细胞增殖功能恢复能力下降。

Comparison of radiation damage and recovery of hematopoietic system in mice of different ages

Objective To observe and compare the effects of radiation on the damage and recovery of hematopoietic system in mice of different ages (juvenile, adult, and aged mice). Methods Sixty male C57BL/6 mice of various ages were randomly divided into control, 2 Gy irradiation, and 4 Gy irradiation groups. The control group received sham irradiation, and the other two were administered with 137Cs γ total body irradiation. On the 3rd, 7th, 14th, and 28th days after irradiation, peripheral blood was collected, white blood cells, red blood cells and platelets were counted, unilateral femur bone marrow nucleated cell counts were determined, and percentages of hematopoietic stem cell (HSC), hematopoietic progenitor cell (HPC) and colony forming unit-granulocyte macrophage were calculated. One way ANOVA was used for comparison among groups, while t test was used for comparison between two groups. Results White blood cell count, unilateral femur bone marrow nucleated cell count, hematopoietic stem cell and progenitor cell count of irradiated mice were reduced to the lowest values on the 3rd day. Compared with the control group, the white blood cell count of juvenile mice decreased to 34.8% (2 Gy irradiation) (t=6.129, P<0.05) and 19.6% (4 Gy irradiation) (t=7.084, P<0.05), while adult mice decreased to 43.8% (2 Gy irradiation) (t=3.043, P<0.05) and 20.0% (4 Gy irradiation) (t=7.084, P<0.05), aged mice decreased to 19.0% (2 Gy irradiation) (t=22.080, P<0.05) and 8.4% (4 Gy irradiation) (t=24.590, P<0.05). The decrease in 4 Gy group was more serious than that in 2 Gy group in a dose-dependent manner. At 28th day after irradiation, unilateral femur bone marrow nucleated cell count in irradiated juvenile mice did not return to normal, the HSC percentage in the juvenile mice of 4 Gy group was still lower than 50%, and the HPC percentage of irradiated juvenile mice recovered to approximately 50% of that of the control group. At 28th day after irradiation, the percentage of colony forming unit-granulocyte macrophage returned to normal for the irradiated adult mice, however, the irradiated juvenile mice (2 Gy irradiation: t=2.067, P<0.05; 4 Gy irradiation: t=3.358, P<0.05) and aged mice (2 Gy irradiation: t=2.586, P<0.05; 4 Gy irradiation: t=4.772, P<0.05) were significantly lower than those of adult mice, which did not return to normal level. Conclusions After irradiation, majority of the hematopoietic system of the irradiated group showed acute, dose-dependent inhibition on the 3rd day. After the recovery period, most of the indicators returned to normal values on the 28th day. The results suggest that the hematopoietic stem cell functions in juvenile mice are more sensitive to radiation injury and poorly recover after radiation compared with those in adult mice. In addition, the recovery for bone marrow cell proliferation was decreased in aged mice.