Doxorubicin‐Induced Chronic Upregulation of Transforming Growth Factor‐beta

As a result of their treatment, childhood cancer survivors face an increased risk of acute and chronic heart failure. Epidemiological studies have shown the anticancer drug doxorubicin, while effective, to be cardiotoxic. Patients suffering from chronic doxorubicin cardiotoxicity exhibit interstitial fibrosis, one component of heart failure. This project aims to elucidate the mechanism of fibrosis in doxorubicin‐induced heart failure by examining changes in the transforming growth factor‐beta (TGF‐β) signaling pathway after exposure to doxorubicin. Our novel model involves treating 2 week old C57BL/6J mice with five weekly intraperitoneal injections of 3 mg/kg of doxorubicin. Cardiac tissue was collected one week after the final injection and at 80 weeks of age to assess early and long‐term recovery points. Data previously gathered by our lab show increased interstitial fibrosis in doxorubicin‐treated animals, even after exposure ceases. In vitro studies show a direct effect of doxorubicin on cardiac fibroblasts, inducing collagen production at the transcriptional level. Left ventricular TGF‐β levels increased in an age‐dependent and treatment‐dependent manner, as shown by immunohistochemistry. Cells positively‐stained for TGF‐β were more abundant in doxorubicin‐treated animals at the 7 week and 80 week time points compared to control mice (p=0.03 and p<0.001, respectively). Additionally, positively stained cells were located in the interstitium, indicating that the positive cells were cardiac fibroblasts. Preliminary data indicates an increase in matrix metalloproteinase‐2 (MMP‐2) in the 7 week doxorubicin‐treated mice. As a mediator of collagen degradation, MMP‐2 is an indicator of cardiac remodeling. Doxorubicin treatment causes sustained molecular changes evidenced by the short‐term and long‐term increases in the signaling cytokine TGF‐β in the murine left ventricle. Early changes in collagen and MMP‐2 indicate a cardiac remodeling phenotype in our model. This project shows that doxorubicin initiates changes to components of fibrosis, possibly driven by activation of the TGF‐β signaling pathway.