Abstract Body: Background
Doxorubicin is an efficacious chemotherapy, yet its clinical use is limited by its cardiotoxic side effects, including cardiomyopathy and fibrosis. Dexrazoxane, the only FDA-approved cardioprotective agent, may compromise doxorubicin's anticancer effect. Thus, it is necessary to find alternative cardioprotective strategies. Doxorubicin-induced cardiomyopathy is often accompanied by cardiac fibrosis due to uncontrolled cardiac fibroblast activation. Our previous studies showed that doxorubicin induced cardiomyopathy through activation of cyclin-dependent kinase 7 (CDK7). This study aims to investigate the role of CDK7 in cardiac fibroblast activation and fibrosis.
Methods and Results
Direct doxorubicin (1μM) exposure inhibited the activation of neonatal rat cardiac fibroblasts (NRCFs). To examine whether doxorubicin induces indirect activation of cardiac fibroblasts, NRCFs were exposed to conditioned media from control- or doxorubicin-treated cardiomyocytes. Compared to control-conditioned media, doxorubicin-conditioned media significantly increased fibroblast activation via Erk and PI3K/Akt pathways. Doxorubicin-conditioned media-induced cardiac fibroblast activation was attenuated by siRNA-mediated CDK7 knockdown, or YKL-5-124-mediated CDK7 inhibition. Results were confirmed by western blot, immunofluorescence, and RT-qPCR. To evaluate CDK7’s role in fibrosis in vivo, tamoxifen-inducible fibroblast-specific CDK7 knockout male and female mice (Pdgfrα-CreERT2; Cdk7flox/flox) were generated. Echocardiography showed that cardiac-specific CDK7 knockout mice exhibited no cardiac dysfunction and, therefore, can be used for subsequent experiments. Statistical analysis: unpaired t-tests for two-group comparisons and two-way ANOVA for three or more group comparisons.
Conclusion
Our data suggest that doxorubicin activates cardiac fibroblasts indirectly via cardiomyocyte paracrine signaling and cell-to-cell communication. We have also shown that CDK7 is necessary for doxorubicin-induced fibroblast activation. Inhibiting CDK7 may be a novel therapeutic strategy to mitigate doxorubicin-induced cardiac fibrosis.