Reactive fibrosis precedes doxorubicin‐induced heart failure through sterile inflammation

Abstract Aims Doxorubicin (DOX)‐induced heart failure has a poor prognosis, and effective treatments have not been established. Because DOX shows cumulative cardiotoxicity, we hypothesized that minimal cardiac remodelling occurred at the initial stage in activating cardiac fibroblasts. Our aim was to investigate the initial pathophysiology of DOX‐exposed cardiac fibroblasts and propose prophylaxis. Methods and results An animal study was performed using a lower dose of DOX (4 mg/kg/week for 3 weeks, i.p.) than a toxic cumulative dose. Histological analysis was performed with terminal deoxynucleotidyl transferase‐mediated dUTP nick‐end labelling assay, picrosirius red staining, and immunohistochemical staining. The mechanism was analysed in vitro with a low dose of DOX, which did not induce cell apoptosis. Microarray analysis was performed. Differentially expressed genes were confirmed by enrichment analysis. Mitochondrial damage was assessed by mitochondrial membrane potential. The production of inflammatory cytokines and fibrosis markers was assessed by western blot, quantitative polymerase chain reaction, and ELISA. A phosphokinase antibody array was performed to detect related signalling pathways. Low‐dose DOX did not induced cell death, and fibrosis was localized to the perivascular area in mice. Microarray analysis suggested that DOX induced genes associated with the innate immune system and inflammatory reactions, resulting in cardiac remodelling. DOX induced mitochondrial damage and increased the expression of interleukin‐1. DOX also promoted the expression of fibrotic markers, such as alpha smooth muscle actin and galectin‐3. These responses were induced through stress‐activated protein kinase/c‐Jun NH2‐terminal kinase signalling. A peroxisome proliferator‐activated receptor (PPARγ) agonist attenuated the expression of fibrotic markers through suppressing stress‐activated protein kinase/c‐Jun NH2‐terminal kinase. Furthermore, this molecule also suppressed DOX‐induced early fibrotic responses in vivo. Conclusions Low‐dose DOX provoked reactive fibrosis through sterile inflammation evoked by the damaged mitochondria