Cardiomyocyte survival and DNA reparation in myocardium of C57Bl/6 and mdx mice after dynamical stress

Abstract

Mdx mice cardiomyocytes are a perspective model to study survival of terminally differentiated cardiomyocytes and formation of cardiomyopathy under conditions of oxidative stress. It was previously observed that dynamical stress induced formation of low molecular DNA fragments. It is beyond question that DNA fragmentation develops because of formation of double strand DNA breaks (DNA DSB). To record appearance and disappearance of DNA DSB we used antibodies to phosphorylated histone H2Ax (histone gamma-H2Ax.). The presence of DNA DSB was estimated in 0.05% and 6.7% of cardiomyocytes in the myocardium form C57B1 and mdx mice without stress, respectively. The part of cardiomyocytes with DNA DSB increased in an hour after stress up to 1.0% and 41.7% in C57B1 and mdx mice, respectively. In 24 h after stress, the myocardium from mdx mice contained 5.2% of gamma-H2Ax-positive cardiomyocytes and no C57B1 myocardium was found with any amount of gamma-H2Ax-positive cells. The results presented show induction of DNA damage by dynamical stress and restoration of normal DNA structure in the cells of both strains in 24 h after stress. There was no mdx mice death after used dynamical stress. To estimate the real contribution of DNA repair to the survival of cardiomyocytes we have counted the cardiomyocyte loss. Morphometric analysis demonstrated that cell concentration in myocardium from mdx mice under normal conditions was less than that one in myocardium of C57B1/6. The cell loss varied between 20% for the base and 40% for the apex of mdx mice hearts. In 24 h after stress, the cell loss in the myocardium of mdx mice amounted to 2.5%. The difference between the number of cells with damaged DNA structure and the index of the real cell loss allows concluding that DNA repair makes a real contribution to the survival of mdx mice cardiomyocytes after dynamical stress.