Collectively, these observations lend further credibility to our postulation of radiation-induced reprogramming of BM cells, at the molecular level. Implications of Radiation-Induced Changes in Bone Marrow Hematopoietic Progenitor Cells In our studies into the effects of low-dose low-LET 1H and high-LET 56Fe-IR on BM hematopoietic progenitor populations, the most striking results were the significant loss of cell numbers and the changes in pluripotent markers in the surviving cells. over a period of up to 10?months after exposure. Both 1H- and 56Fe-IR increased the expression of pluripotent stem cell markers in L-MPPs and 10?months post-IR exposure. We postulate that low doses of 1H- and 56Fe-IR may induce endogenous cellular reprogramming of BM hematopoietic progenitor cells to assume a (S)-3,5-DHPG more primitive pluripotent phenotype and that IR-induced oxidative DNA damage may lead to mutations in these BM progenitors. This could then be propagated to successive cell lineages. Persistent impairment of BM progenitor cell populations can disrupt hematopoietic homeostasis and lead to hematologic disorders, and these findings warrant further mechanistic studies into the effects of low-dose IR on the functional capacity of BM-derived hematopoietic cells including their self-renewal and pluripotency. that particle radiation, such as 1H and 56Fe, which induce profound changes in BM hematopoietic cells, including at the molecular level, may play a significant role in the development of hematological cancers, and thus merits further studies. Exposure to 1H and 56Fe Radiation has Long-Term Effects on Bone Marrow Hematopoietic Multipotent Progenitor Populations 1H and 56Fe Radiation Induced Significant Decrease in Bone Marrow Multipotent Progenitor Cell Numbers To extend our knowledge of the effects of particle radiation on BM hematopoietic populations, whole-body radiation was performed on mice with 0.5?Gy (1?GeV) 1H and 0.15?Gy (1?GeV/n) 56Fe particles. Fluorescence-activated cell sorting (FACS) was then used to isolate early and late multipotent progenitors (E- and L-MPPs) from BM cells (S)-3,5-DHPG over a time course of 40?weeks post-IR. E-MPPs were defined as Lin?/c-kit+/Sca1+/CD34+/AC133+ and L-MPPs were Lin-/c-kit+/Sca1+/CD34+/AC133? (43, 44). Compared to control mice, 1H-IR caused an initial transient spike in E-MPP and L-MPP cell numbers followed by significant downregulation of these populations at 8?weeks post-IR (Figures ?(Figures1A,B;1A,B; Table ?Table1).1). In contrast, 56Fe-IR caused significant loss of E-MPPs and L-MPPs immediately after IR, which was maintained up to 8?weeks post-IR (Figures ?(Figures1A,B;1A,B; Table ?Table1).1). By 40?weeks, the E-MPP and L-MPP populations had recovered and were comparable to control levels for both 1H and 56Fe radiation (Figures ?(Figures1A,B).1A,B). These findings are consistent with the study that showed -IR, even at the MAD-3 low dose of 0.4?Gy, was observed to rapidly induce apoptosis in human embryonic stem (ES) cells (45). Open in a separate window Figure 1 E-MPP and L-MPP cell numbers are downregulated by 56Fe- and 1H-IR but recover to control levels by 40?weeks post-IR. Effect of full-body single dose of proton (1H) at 0.5?Gy, 1?GeV and iron (56Fe) at 0.15?Gy, 1?GeV/nucleon of ionizing radiation (IR) on survival of multipotent progenitor cell populations was examined. The survival of (A) E-MPPs and (B) L-MPPs in the BM after particle IR in C57BL/6NT mice were determined at 1, 2, 4, 8, 12, 28, and 40?weeks post-IR. Total BM-derived (S)-3,5-DHPG mononuclear cells were triple-stained with FITC-labeled RAM34 antibody (that consists of CD34, c-kit, and Sca1 antibodies), PE-Cy7-AC133, and PE-hematopoietic lineage cocktail (CD3e, Ly-6G/Ly-6C, CD11b, CD45R/B220, TER-119), then sorted by FASC for (A) E-MPPs (CD34+/c-kit+/Sca-1+/AC133+/Lin?) and (B) L-MPPs (CD34+/c-kit+/Sca-1+/AC133?/Lin?). Percentage changes in cell numbers were calculated relative to control sham irradiated mice, which was set to 100% for each time point. Solid lines represent mean??SEM (was examined in the L-MPPs for a period of 40?weeks following irradiation with 1H or 56Fe particles. The qRT-PCR analysis revealed a significant increase in expression of these markers at 8 and 40?weeks after both 1H and 56Fe irradiation (Figures 2ACC). Of note, it has been shown that ES cells exposed to 3?Gy high-LET carbon ion radiation also maintain their pluripotent state and express.