MiR ‐145‐5p Attenuates Doxorubicin‐Induced Heart Injury Through Targeting Cardiomyocyte Pyroptosis

Doxorubicin (DOX), a potent anthracycline chemotherapeutic, exhibits dose‐dependent cardiotoxicity that limits its clinical utility. Although miR‐145‐5p demonstrates cardioprotective properties in cardiovascular diseases, its role in DOX‐induced cardiomyopathy remains undefined. This study investigated the therapeutic potential of miR‐145‐5p against DOX‐induced cardiotoxicity and its underlying mechanism. Wistar rats received cumulative DOX dosing (15 mg/kg total) to establish cardiotoxicity, with miR‐145‐5p overexpression achieved via adeno‐associated virus serotype 9 (AAV9) delivery. Cardiac function was assessed by echocardiography and serum biomarkers, including creatine kinase‐MB isoenzyme (CK‐MB), cardiac troponin T (c‐TnT), C‐reactive protein (CRP), and N‐terminal pro‐B‐type natriuretic peptide (NT‐proBNP). Histopathology (Hematoxylin & Eosin/Masson's Trichrome staining), apoptosis (TUNEL), oxidative stress (dihydroethidium staining/malondialdehyde/glutathione), and NLRP3 inflammasome activation (ELISA/Western blot/immunohistochemistry) were evaluated. Clinical relevance was determined by quantifying serum miR‐145‐5p and SOX9 mRNA in healthy controls and breast cancer patients before and after DOX treatment. DOX significantly downregulated miR‐145‐5p and upregulated SOX9 in rat myocardium and H9C2 cells. DOX‐treated patients displayed reduced serum miR‐145‐5p and increased SOX9 mRNA compared with pre‐chemotherapy baselines. AAV9‐miR‐145‐5p attenuated DOX‐induced systolic dysfunction, reduced serum biomarkers, ameliorated histopathological injury and fibrosis, suppressed apoptosis and oxidative stress, and inhibited NLRP3 inflammasome activation (decreased NLRP3, ASC, caspase‐1, IL‐1β, and IL‐18). miR‐145‐5p directly targeted the SOX9 3′UTR, and SOX9 overexpression reversed miR‐145‐5p–mediated reductions in CK release, ROS production, apoptosis, and NLRP3 expression in H9C2 cells. These findings demonstrate that miR‐145‐5p protects against DOX cardiotoxicity by targeting SOX9 to inhibit NLRP3 inflammasome–mediated pyroptosis, offering a potential therapeutic strategy.