Gene expression in the wildtype and top2b-deleted cardiomyocytes with or without doxorubicin treatment

To compare expression profiles in the cardiomyocytes with wild type top2b and those with top2b deletion after in vivo treatment of mice with doxorubicin or drug vehicle Doxorubicin is widely used in modern cancer treatments, despite the advent of targeted therapy. However, a dose-dependent cardiotoxicity often limits its clinical use. The prevailing theory hypothesizes that doxorubicin-induced cardiotoxicity is the result of reactive oxygen species (ROS) generation due to redox-cycling of doxorubicin. Here we showed that cardiomyocyte-specific deletion of Topoisomerase II beta (Top2b) markedly reduced DNA double-strand breaks, apoptosis, and functional damages in doxorubicin-treated hearts. To investigate transcriptomic changes after doxorubicin treatment in wild type mouse and mouse with cardiac specific deletion of Top2b, we examined the expression profiles in 4 groups of mice (3/group), ie. wildtype mice with or without doxorubicin treatment and mice with Top2b deletion in the cardiomyocytes with or without doxorubicin treatment. Mice were treated with doxorubicin (25mg/kg, i.p.) or PBS (drug vehicle) for 16 hr or 72 hr. The heart was removed and cardiomyocytes were isolated by using a Langendorff apparatus. After purification, total RNA was extracted from the cardiomyocytes, purified, and used for gene expression analysis. Compared with that in control cardiomyocytes or cardiomyocytes with Top2b deletion, doxorubicin caused a significant expression change in the genome of cardiomyocytes from the wildtype mice. Among the changes, multiple genes encoding mitochondrial structural protein and components of the respiratory chain complexes were down-regulated 72 hr after treatment while multiple genes in the p53 pathway were up-regulated 16 hr after treatment in the wildtype cardiomyocytes.