Doxorubicin exposure leads to cardiac fibroblast dysregulation and worsens fibrotic remodeling in the pathological heart.

Advances in cancer treatments have enabled long-term patient survival at increasing rates, however these therapies often have chronic adverse side effects of which cardiovascular disease is a major cause for concern. Specifically, patients treated with the anthracycline, doxorubicin (DOX), face significantly higher rates of delayed-onset heart failure (HF), clinically referred to as chronic DOX-induced cardiotoxicity (DIC), typically years or even decades following treatment despite showing no observable signs of acute cardiotoxicity. In patients, even low-dose DOX is known to induce cardiac fibrosis which increases the risk for HF, thus, implicating the cardiac fibroblast (CFB) as having a prominent role in chronic DIC. To determine possible roles for CFB in DIC we developed in vitro and in vivo models that tested the immediate and delayed effects of DOX administered at concentrations that mimic those used clinically. While, at these levels, DOX had very little effect on CFB viability in vitro, it did increase markers of CFB activation and dramatically altered the CFB transcriptome. These effects persisted even when CFB were subsequently treated with the canonical differentiation stimulus, transforming growth factor-β (TGFβ), consistent with a cellular memory of prior DOX exposure. In our in vivo model in mice, clinically relevant doses of DOX had essentially no effect on cardiac structure and function, however, prior exposure to DOX exacerbated cardiac dysfunction and structural remodeling in response to a subsequent stressor in the form of chronic angiotensin II/phenylephrine (ANGII/PE) infusion mimicking the effects of a common ailment (i.e. hypertension) DIC patients often face later in life. At the molecular level, DOX increased markers of CFB activation and cardiac fibrosis in mouse hearts in response to ANGII/PE that was coordinate with the severity of cardiac dysfunction. In summary, our mouse model mimicked the delayed deleterious effects of DOX on cardiac structure and function, suggesting that despite exhibiting no effect on CFB viability, DOX promotes maladaptive cardiac remodeling through an exaggerated response to a delayed stimulus that ultimately results in an exacerbated progression into HF.