Background: Intracellular reactive oxygen species (ROS) have dual effects depending on their cellular level. ROS act as secondary messengers at a low concentration, although ROS exhaust the hematopoietic stem cell (HSC) compartment at a higher oxidized state. So, we investigated whether maintaining a low level of ROS could preserve the hematopoietic stem cell function according to the MnSOD over expression.
Methods: Human MnSOD cDNA was introduced into mouse HSCs and progenitor cells by using a MSCV-PGK-GFP retrovirus. The hematopoietic function of over-expressing MnSOD was evaluated in vitro on a colony-forming cell assay and in vivo in a competitive transplantation model. MnSOD-transduced, lineage negative, GFP+ B6.SJL (CD45.1+) mouse bone marrow cells were transplanted into lethally irradiated C57BL/6J (CD45.2+) mice in competition with CD45.1/45.2 double positive bone marrow mononuclear cells. We also measured the basal mRNA levels of antioxidants, including MnSOD, catalase and cellular glutathione peroxidase (GPx1), of C57BL/6J HSCs.
Results: On the colony-forming cell assay, a MnSOD over expression significantly preserved the CFU-M with irradiation as compared with the mice without irradiation. HSCs with an MnSOD over expression showed a tendency for higher engraftment ability on the competitive transplantation assay even after 200 cGy re-irradiation, and we observed a significantly higher myeloid differentiation potential after the second serial transplantation. The basal mRNA levels of MnSOD and catalase were less than 1∼2% and 2∼5%, respectively, in the long-term and short-term HSCs, respectively, and these cells didn't activate in spite of radiation stress.
Conclusion: These results show that only an over expression of MnSOD without downstream catalase activation can not augment the mouse hematopoietic stem cell repopulation activity. (Korean J Hematol 2009;44:82-91.)

Keywords: Superoxide dismutase, Hematopoietic stem cells, Transplantation