| Objective : pprI gene of Deinococcus radiodurans is a switch gene which plays a critical role in the radiation resistance of Deinococcus radiodurans. It can significantly and specifically induce the gene expression of recA and pprA which directly participate DNA damage repair in vivo. The protective effect of neutron radiation damage of this gene has been confirmed. However, the effect and mechanism of this gene on enhancing the radioresistance of mammalians exposed toγrays are not reported yet in the scientific literature.Materials and Methods: To explore the effect and mechanism of pprI on acute radiation injury of mice induced byγ-rays, the pCMV-HA-pprI plasmid was injected and transfected into the muscle of each mouse from the transgene group by the in vivo electroporation appearance. The mice of transfer pCMV-HA-pprI plasmid group, transfer pCMV-HA plasmid group and radiation group were exposed to 6Gyγ-ray radiation. Then the death rate, the blood cell count and lymphocyte rate,the pathological change of lung, testicle and kidney were observed;the apoptosis frequency of bone marrow cells, spleen cells and thymocyte cells were measured by flow cytometer;and the expression level of downstream Protein Rad51 and Rad52 which were homologisation analogues of recA gene in mammalian cells was identified by Western blotting.Results: The results showed that in the 30 days after radiation, the death rate of transfer pCMV-HA-pprI group was 1/10, obviously lower than 4/10 of radiation group and 2/10 of transfer pCMV-HA-pprI group. For the hemogram of mice, it was found that the leucocyte number of transfer pCMV-HA-pprI group was 0.42*109/L on the 7th days after radiation, significantly higher than the radiation group and transfer pCMV-HA group(P<0.05); the erythrocyte number of transfer pCMV-HA-pprI group was 6.38*1012/L on the 7th days after radiation, significantly higher than that of the radiation group and transfer pCMV-HA group(P<0.05); the platelet number of transfer pCMV-HA-pprI group was 202.00*109/L on the 7th days and 309.50*109/L on the 14th days after radiation, significantly higher than that of the radiation group and transfer pCMV-HA group(P<0.05); the lymphocyte ratio got right on the 35th days, obviously faster than the other groups. For the pathology of mice, it was that pprI gene expression can evidently repair the lung, testicle and kidney of mice which were exposed toγ-ray radiation, it can obviously reduce edema of lungs and pulmonary fibrosis, advanced the repair of testicle and the hyalinization and edema of kidney; For the cells apoptotic from mice, it was found that the apoptotic frequency of spleen cells of transfer pCMV-HA-pprI group was significantly lower than that of the radiation group and transfer pCMV-HA group on the 7th,14th, 28th days(P<0.05), and the apoptotic frequency of thymocytes was significantly lower than that of the radiation group and transfer pCMV-HA group on the 1st,7th,14th and 35th days(P<0.05); and the apoptotic frequency of bone marrow cells was significantly lower than that of the radiation group and transfer pCMV-HA group on the 1st,7th,14th and 28th days(P<0.05), and the apoptotic frequency of thymocytes and bone marrow cells were return to normal on the 28th days after radiation. For the detecting of the PprI protein,Rad51 protein and Rad52 protein in mice, it was demonstrated that pprI plasmid was successfully transferred to mice, Rad51 protein expressed higher, especially on the first day, however Rad52 protein was not change.Conclusion:1. In acute radiation injury induced byγrays, pprI gene electroporation in vivo could enhance theγrays radioresistance of mice, decrease the mice death rate obviously, alleviate the degree of white blood cell , red blood cells, and platelet, and advanced the recovery of the lymphocyte ratio on the 35 days after radiation, 2. In acute radiation injury induced byγrays, pprI gene electroporation in vivo could obviously alleviate the the pathology reaction of lung, testicle and kidney, speed up and advanced the repair of the organisms.3. In acute radiation injury induced byγrays, pprI gene electroporation in vivo could decrease the apoptosis rate of bone marrow cell , spleen and thymus lymphocyte obviously.4. The mechanism research of pprI gene electroporation in vivo showed that the prokaryotic gene pprI was successfully expressed in mammalian cells, it could increase the expression level of downstream Protein Rad51 which is homologisation analogues of recA gene in mammalian cells, and the pprI gene may react through Rad51 protein;5. pprI gene electroporation in vivo could be a new methond for treating acute severe radiation injury.
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