Institute of Toxicology, University Medical Center, Mainz, Germany.
Laboratory of Experimental Immunology, Ku Leuven, Leuven, Belgium.
DNA Repair (Amst). 2021 Feb;98:103037. doi: 10.1016/j.dnarep.2020.103037. Epub 2020 Dec 30.
Previously we showed that human monocytes isolated from peripheral blood display downregulation of several DNA repair proteins, including XRCC1, ligase III, PARP-1 and DNA-PK resulting in a deficiency of DNA repair, while in macrophages derived from monocytes the repair protein expression and DNA repair is restored. To see whether this is a specific phenomenon of human monocytes and macrophages, we assessed the expression of these repair genes in mice. We also addressed the question at which differentiation step in bone marrow cells downregulation of DNA repair gene expression occurs. The study revealed that mouse monocytes, similar to human, lack the expression of XRCC1, ligase III, PARP-1 and DNA-PK. If mice were treated with total body irradiation, they showed significant apoptosis in bone marrow monocytes, but not in peritoneal macrophages. This was also observed after treatment with the methylating anticancer drug temozolomide, resulting in high death rate of monocytes, but not macrophages. Monocytes arise from hematopoietic stem cells. Even the early stem cell fraction (LT-HSC) expressed detectable amounts of XRCC1, which was transiently upregulated, achieving the highest expression level in CMP (common myeloid progenitor) and, during the subsequent differentiation process, downregulated up to a non-detectable level in monocytes. The immediate monocyte precursor GMP also expressed ligase III, PARP-1 and DNA-PK. All these repair genes lacking in monocytes were upregulated again in macrophages. The sensitivity of monocytes, macrophages and precursor cells roughly correlated with their XRCC1 expression level. Monocytes, but not macrophages, also displayed strong γH2AX focal staining, indicating the presence of non-repaired DNA double-strand breaks following total body irradiation. Overall, the data revealed that murine monocytes exhibit the same DNA repair-impaired phenotype and high sensitivity compared to macrophages as observed in human. Therefore, the repair deficiency previously described for human monocytes appears to be a general property of this cell type.
先前我们表明，从外周血中分离出来的人单核细胞会下调几种 DNA 修复蛋白，包括 XRCC1、连接酶 III、PARP-1 和 DNA-PK，从而导致 DNA 修复缺陷，而在单核细胞衍生的巨噬细胞中，修复蛋白的表达和 DNA 修复则得以恢复。为了观察这是否是人类单核细胞和巨噬细胞的特有现象，我们评估了这些修复基因在小鼠中的表达情况。我们还研究了在骨髓细胞分化过程中哪个阶段会导致 DNA 修复基因表达下调。研究表明，与人类相似，小鼠单核细胞也缺乏 XRCC1、连接酶 III、PARP-1 和 DNA-PK 的表达。如果对小鼠进行全身照射，它们的骨髓单核细胞会出现明显的凋亡，但腹腔巨噬细胞不会。在使用甲基化抗癌药物替莫唑胺进行处理后，也观察到了这种情况，导致单核细胞死亡率很高，但巨噬细胞不会。单核细胞来源于造血干细胞。即使是早期的干细胞亚群（LT-HSC）也表达可检测到量的 XRCC1，其表达量短暂上调，在 CMP（共同髓系祖细胞）中达到最高水平，在随后的分化过程中，下调至单核细胞中无法检测到的水平。直接的单核细胞前体 GMP 也表达连接酶 III、PARP-1 和 DNA-PK。所有这些在单核细胞中缺失的修复基因在巨噬细胞中又重新上调。单核细胞、巨噬细胞和前体细胞的敏感性与其 XRCC1 表达水平大致相关。只有单核细胞而非巨噬细胞在全身照射后会显示出强烈的 γH2AX 焦点染色，表明存在未修复的 DNA 双链断裂。总的来说，这些数据表明，与巨噬细胞相比，小鼠单核细胞表现出相同的 DNA 修复缺陷表型和高敏感性，这与在人类中观察到的情况一致。因此，先前描述的人类单核细胞的修复缺陷似乎是该细胞类型的普遍特性。
