The Effect Of Granulocyte Colony-Stimulating Factor On Hematopoietic Stem Cell Injury After Ionizing Radiation Impact Of INOS On Radiosensitivity In Hematopoietic System

The possibility of nuclear accidents increasingly nowadays, which is a life threatening to the human beings; the hematopoietic system is exceedingly sensitive to ionizing radiation (IR). Acute radiation syndromes (ARSs) such as infection, bleeding, anemia and other clinical manifestations are mainly because of acute bone marrow (BM) suppression induced by IR. It could be successfully managed by the use of hematopoietic growth factors (HGFs), such as G-CSF. However, long-term bone marrow injury was easy to be overlooked in clinical because of its latency, which has comprised the patient’s life quality greatly. G-CSF can promote the proliferation and differentiation of the HSC and pre-granulocyte, and it is the only treatment recommended to be given to radiation victims soon after IR. However, clinical studies have shown that G-CSF impeded recovery from bone marrow damage caused by cytotoxic agents. It has been suggested that this adverse effect is caused by HSC and hematopoietic progenitor cell (HPC) proliferation and differentiation stimulated by G-CSF, which impairs HSC self-renewal and may exhaust the BM capacity to exacerbate IR-induced LT-BM injury. However, whether G-CSF accelerates HSC exhaustion after TBI and the associated mechanisms have yet to be elucidated and it is important for clinical medication rationally.Intracellular free radicals induced by IR are the important mechanism of hematopoietic system damage. The ROS and RNS in oxidative stress will damage the DNA and lipid, promote protein oxidation. Previous studies have shown that inhibitors of inducible NO synthase (iNOS) have a protective effect on radiation, and specific inhibitor of iNOS could alleviate the radiation induced vascular endothelial damage. However, it is still lack of research about the effect of iNOS on IR-induced hematopoietic system injury. The investigations in molecular mechanisms using knockout mouse will aid in the development of novel target-specific interventions to protect normal tissues from radiation injury.To investigate the effect of G-CSF on HSC and its mechanisms, C57BL/6 mice were exposed to 4 Gy,6Gy y-rays of total body irradiation (TBI) and euthanized one month after TBI for analysis. The results showed that G-CSF administration mitigated TBI-induced decreases in WBC and the suppression of HPC function (CFU-GM), whereas G-CSF exacerbated HSC injury after TBI; The increase in HSC damage was associated with increased ROS production, activation of p38MAPK and p16 in HSCs. Our findings suggest that although G-CSF administration can reduce ARS, it can also exacerbate TBI-induced LT-BM injury in part by promoting HSC senescence.inos-/-mice were used in the second part of our study to explore the impact of iNOS on the sensitivity and recovery of hematopoietic radiation damage. C57 mice were regarded as wide type (WT) mice. The results showed that 2Gy,4Gy IR induced bone marrow cells apoptosis and inhibit the proliferation of HPC of inos-/-in vitro,6Gy TBI decreased the WBC, RBC, HGB, PLT in peripheral blood and BMMNCs, and reduced the colony forming ability of HPC (CFU), damaged the function of HSC and promoted the HSC into cell cycling in inos-/-mice, but there was no significant difference between WT mice and inos-/-mice after IR exposure. The results suggested that inos deficiency didn’t affect the sensitivity and recovery of hematopoietic injury induced by IR. It suggested that the IR-induced cytotoxicity may be different from that induced by iNOS activated through inflammation. In addition, IR could increase oxidative stress so that induce the HSC apoptosis and senescence, the multiple signal transduction pathways damages caused by IR in hematopoietic system may conceal the cytotoxic effects of NO.Above all, our study showed that G-CSF will exacerbate IR-induced HSC injury partly by aggravating HSC senescence, providing the reference for clinical medication rationally, inos-/-mice were used in our study to elucidate that the impact of iNOS in IR-induced hematopoietic system injury, promoting the development of research in radiation injury mechanisms.