Transcriptional activation of ENPP2 by FoxO4 protects cardiomyocytes from doxorubicin-induced toxicity

It has been shown that ferroptosis is involved in doxorubicin (DOX)-induced cardiotoxicity and that ectonucleotide pyrophosphatase/phosphodiesterase 2 (ENPP2) can protect cardiomyocytes from ferroptosis. Thus, the present study aimed to investigate whether ENPP2 could protect cardiomyocytes from DOX-induced injury by inhibiting ferroptosis. H9c2 cardiomyocytes were exposed to various concentrations (0.625, 1.25, 2.5, 5 or 10 µM) of DOX for different time periods. Cell viability and ENPP2 expression were determined. ENPP2-overexpressing H9c2 cells were treated with DOX and subsequently cell viability, oxidative stress, autophagy and ferroptosis were measured using the corresponding assays (MTT assay, commercial kits and western blot analysis). Dual-luciferase reporter and chromatin immunoprecipitation assays, as well as bioinformatics analysis, were applied to detect the interaction between ENPP2 and FoxO4. Following FoxO4 overexpression in H9c2 cells, the aforementioned cellular processes were assessed. The results indicated that ENPP2 expression was downregulated following treatment of the cells with DOX. DOX also led to the decreased cell viability, reduced autophagy and elevated ferroptosis in H9c2 cells, which were notably reversed by ENPP2 overexpression. In addition, FoxO4 bound to the ENPP2 promoter, resulting in inhibition of its expression. Following FoxO4 overexpression in H9c2 cells, further experiments conducted using commercial kits and western blot analysis revealed that FoxO4 overexpression partially inhibited the effects of ENPP2 overexpression on DOX-induced oxidative stress, autophagy and ferroptosis in H9c2 cells. In conclusion, the data indicated that ENPP2 was transcriptionally regulated by FoxO4 to protect cardiomyocytes from DOX-induced toxicity by inhibiting ferroptosis. Therefore, specific treatment approaches targeting the FoxO4/ENPP2 axis and ferroptosis may provide potential therapies for alleviating DOX-induced cardiotoxicity.