22nd Annual NASA Space Radiation Investigators' Workshop (2011)
7108.pdf
Full body 0.15 Gy Iron Irradiation Affects Survival and Proliferation of BM-derived
EPCs
S. Sasi1, D. Park1, J. Wage1, *David A Goukassian1,2
(1)Center for Cardiovascular Research and Center of Cancer Systems Biology, Steward St
Elizabeth’s Medical Center, (2) Tufts University School of Medicine, Boston, MA, USA
Rradiation-induced chromosomal instability was demonstrated in the bone marrow (BM) for up
to 24 months after full body irradiation with either X-rays or neutrons, indicating that
chromosomal instability can be initiated and maintained in vivo. However, there is a significant
gap in studies to date assessing full body radiation-induced survival and function of BM-derived
endothelial progenitor cells (EPCs). It was shown for myeloid and lymphoid BM-derived stem
and progenitor cells that after space flights the numbers of these cells are reduced to just onehalf of their normal levels, suggesting that EPCs may be similarly reduced in the normal EPC
population. Neither data on BM-derived EPCs survival and proliferation during and after space
flights, nor DNA damage responses of EPCs to space radiation, are currently available. A
growing body of evidence indicates that heart and other organ-tissues vascular homeostasis
does not exclusively rely on proliferation of local endothelial cells (ECs) but also involves BM–
derived EPCs. Consequently, if EPCs are critical to endothelial maintenance and repair,
decrease in the total number of BM-derived EPC or their dysfunction could contribute to the
pathogenesis of ischemic and/or peripheral vascular diseases, as well as for maintenance of
normal vascular homeostasis in the heart. Astronauts will be exposed to radiation composed of a
spectrum of low-fluence protons and HZE nuclei (i.e., 56Fe). To assess the effect of low-dose
radiation on BM-derived EPCs we evaluated the effect of a full-body single dose (0.15 Gy, 1
Gev/n) Iron irradiation on the survival and proliferation of BM-derived EPCs over 28 postirradiation. We isolated and maintained BM-derived EPCs in corresponding selective EBM2
medium (supplemented with growth factors) ex-vivo for 48 and 72 hours (a minimum time
required to select EPC from total BM ex-vivo in the culture). Our results revealed that 2, 5, and
24 hrs after full-body irradiation there was 2-6-fold increase in EPC apoptosis ex-vivo (FACS
analysis, subGo/G1 fraction of the cells after PI staining), with the peak 6-fold increased
apoptosis at 5hrs (p<0.001). The EPC apoptosis was gradually decreased below control nonirradiated EPC levels by day 14. However, by day 28 there was a second significant 4-fold
increase (p<0.03) in EPC apoptosis. This data indicates that there is a bimodal (early 5 hrs and
delayed 28 days) increase in BM-derived EPC apoptosis after a single 0.15 Gy Iron radiation.
We also evaluated ex-vivo proliferation of BM-derived EPCs after Iron irradiation using
CyQUAT cell proliferation assay kit. We found that there was no significant proliferation up to
7 days post-irradiation. However there was ~45 (p<0.005) increase in the rate of EPC
proliferation on day 14, but the rate of EPC proliferation had dropped significantly (to 55% of 14
days, p<0.001) on day 28. Taken together these data suggest that early increase in BM-derived
EPC apoptosis may be a direct effect of radiation, whereas later increase in apoptosis and
decrease in proliferation could be a result of non-targeted effects. We conclude single low dose of
Iron irradiation may have long-lasting effect on survival and proliferation of BM-derived EPCs
and may induce delayed non-targeted effects.