Abstract
Non-targeted effects (NTE) of ionizing radiation may initiate myeloid neoplasms (MN). Here, protein mediators (I) in irradiated human mesenchymal stromal cells (MSC) as the NTE source, (II) in MSC conditioned supernatant and (III) in human bone marrow CD34+ cells undergoing genotoxic NTE were investigated. Healthy sublethal irradiated MSC showed significantly increased levels of reactive oxygen species. These cells responded by increasing intracellular abundance of proteins involved in proteasomal degradation, protein translation, cytoskeleton dynamics, nucleocytoplasmic shuttling, and those with antioxidant activity. Among the increased proteins were THY1 and GNA11/14, which are signaling proteins with hitherto unknown functions in the radiation response and NTE. In the corresponding MSC conditioned medium, the three chaperones GRP78, CALR, and PDIA3 were increased. Together with GPI, these were the only four altered proteins, which were associated with the observed genotoxic NTE. Healthy CD34+ cells cultured in MSC conditioned medium suffered from more than a six-fold increase in γH2AX focal staining, indicative for DNA double-strand breaks, as well as numerical and structural chromosomal aberrations within three days. At this stage, five proteins were altered, among them IQGAP1, HMGB1, and PA2G4, which are involved in malign development. In summary, our data provide novel insights into three sequential steps of genotoxic signaling from irradiated MSC to CD34+ cells, implicating that induced NTE might initiate the development of MN.
Highlights
reactive oxygen species (ROS) were analyzed in 2 Gy-irradiated mesenchymal stromal cells (MSC) samples at 4 h after irradiation and in non-irradiated control MSC
ROS were analyzed in CD34+ cell samples expanded for 3 days in untreated medium followed by culture for 3 days in MSC conditioned medium or control medium, respectively
Furof 21 thermore, ROS were analyzed in CD34+ cell samples expanded for 3 days in untreated medium followed by culture for 3 days in MSC conditioned medium or control medium, respectively
Summary
Effects of IR, such as the development of secondary neoplasias, might be associated with the release of danger signals based on DNA damage and apoptosis gradients between irradiated and non-irradiated cells [2]. The response in irradiated cells might be initiated by the DNA damage response, apoptosis, and inflammation [2]. NTE might be initiated in HSPC by nearby or distant irradiated mesenchymal stromal cells (MSC) [7,8]. NTE may emerge as DNA damage (for example gene mutations, chromosomal aberrations, micronuclei, increased γH2AX foci), cell death (for example apoptosis, necrosis) and induction of cell survival mechanisms (for example adaptive response, increased DNA repair) [9,10,11,12]. While NTE have been demonstrated in mouse HSPC [7,8], they have so far not been detected in cultured human stem cells [13]
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