[Release of mtDNA from mitochondria and activation of its replication in tissues of irradiated mice]

A nessessary condition for normal functioning of mitochondria is the maintenance of certain numbers of intact mtDNA molecules. In the present study, we investigasted changes in the number of mtDNA copies in brain and spleen cells of mice subjected to irradiation. For the first time, we observed the irradiation-induced output of mtDNA fragments into brain and spleen cell cytosol. In the cytosol of these cells, examined in mice 5 h after 5 Gy irradiation, 1841 h.p. mtDNA fragments were detected able to persist for at 3 weeks. In addition, larger fragments of mtDNA (10,090 b.p.) were detected in the cytosol of brain cells of irradiated mice. The occurrence of mtDNA fragments in the cytosol of brain cells is accompanied with an increase in the number of mtDNA copies in the mitochondrial matrix. The induction of mtDNA replication in brain cells of irradiated animals may be considered as a compensatory reaction in response to mtDNA damage. A sharp decrease in the amount of mtDNA copies in the mitochondrial matrix of spleen cells on the first day after irradiation may be considered as apoptosis development. However, the compensatory reaction in brain cells was also noticed but in later terms.