Characterization of hematopoietic stem cells in p53-deficient mice

与野生型对照相比，我们研究了P53基因缺陷小鼠[P53(-)]在造血方面的可能变化。外周血细胞和骨髓有核细胞数无差异，而P53(-)骨髓造血祖细胞的比例似乎有所增加。注射5FU后2天，P53(-)骨髓中HPP-CFCs数量明显增加。然后，我们检测了转化生长因子-β对造血祖细胞的影响，发现转化生长因子-β对巨核系祖细胞的增殖有明显的抑制作用，而对红系和粒-巨噬系祖细胞的抑制作用不明显。有趣的是，在P53(-)中，TGF-β对HPP-CFCs的抑制作用未被完全消除，这表明HPP-CFCs中存在一种对TGF-β不敏感的亚群。与HPP-CFCs相比，P53(-)中的CFU-Mk仍然受到转化生长因子-β的抑制。因此，HPP-cfc可能受转化生长因子-β通过与P53相关的信号通路调节。经不同剂量照射后，p5 3(-)细胞中的cFU-S和cFU-GM的存活曲线较平坦。根据脾集落末端标记，P53(-)显示较高的凋亡率，这不受辐射的调节。这些结果表明，造血干细胞中也存在P53基因缺失，从而逃脱了辐射诱导的细胞凋亡。体内动力学研究表明，在BrdUrd标记后，P53(-)中的CFU-GM迅速增殖，但CFU-GM的增长部分大小与对照组相同。综上所述，P53基因的破坏可能会改变干细胞的动力学，但外周血中分化细胞的数量可以通过未知的调节机制得到纠正。

We investigated possible changes in hematopoiesis in p53-deficient mice [p53(-)] in comparison with those in wild-type controls. There was no difference in the numbers of peripheral blood cells and marrow nucleated cells, while the frequency of hematopoietic progenitors in marrow of p53(-) seems to have increased. The number of HPP-CFC in p53(-) marrow, 2 days after injection of 5FU,markedly increased. Then, we examined the effect of TGF-beta on hematopoietic progenitors, and found that the proliferation of megakaryocyte-progenitors was markedly inhibited by TGF-beta, whereas erythroid and granulocyte-macrophage progenitors were not significantly inhibited. TGF-beta also completely inhibited the growth of HPP-CFC.It is interesting that in the p53(-), the inhibitory action of TGF-beta on the HPP-CFC was incompletely abolished, which suggests that there is a subpopulation of HPP-CFC less sensitive to the regulation by TGF-beta. In contrast to HPP-CFC,the CFU-Mk in the p53(-) remained inhibited by TGF-beta. Thus, HPP-CFC might be regulated by TGF-beta through their signal pathways which are linked to p53. CFU-S and CFU-GM in p53(-) after graded doses of irradiation showed a flatter survival curve. According to the end-labeling for spleen colonies, p53(-) showed rather high incidence of apoptosis, which was not modulated by irradiation. These results showed a possible mechanism escaped from the radiation-induced apoptosis due to lack of p53 gene also in hematopoietic stem cells. In vivo kinetics studies revealed that CFU-GM in p53(-) rapidly proliferated after the start of labeling by BrdUrd but the size of growing fraction of CFU-GM was same as that in the control mice. In conclusion, the stem cell kinetics should be altered by disruption of p53 gene, but the numbers of differentiated cells in peripheral blood are corrected by unknown regulating mechanisms.