0018: Role of epac signalling in doxorubicin-induced cardiotoxicity

The canonical mechanisms underlying doxorubicin (Dox)-induced cardiotoxicity involve Reactive Oxygen Species production, DNA intercalation and topoisomerase II inhibition which trigger DNA damage, oxidative stress and alteration of calcium homeostasis leading to myocyte death and heart dysfunction. However, alternative mechanisms with prior or concomitant dox induced alteration of signalling pathways are emerging. β-adrenergic signalling and especially Epac (exchange protein directly activated by cAMP) could be worth investigating as Epac activate small G proteins Rac1 and Rho A known to be implicated in dox-induced cardiotoxicity. We investigated the time/dosedependent Dox effect in in vitro (neonatal rat cardiomyocytes) and in vivo on a mice models on 1/ the transcriptional activity of cardiac remodelling markers (ANF, SRE and SkM β-actin) 2/Epac's downstream effectors (small G proteins expression, MEF-2, NFAT) and 3/Epac's role in dox-induced DNA damage. In vitro, Dox treatment resulted in an alteration of Epac signalling through inhibition of stress and remodelling markers, a modulation of Epac's downstream effectors and a direct effect of Dox on Epac1 and Epac2 expression. Moreover, the protein level of DNA damage marker (H2AX pS139) was modulated by Epac1 and 2 inhibitors and by Epac2 inhibitor which suggest a new protective pathway through Epac1 specific inhibition. In vivo, echocardiography of Dox-treated mice (3 iv injections, 12 mg/kg total dose) showed a dilated cardiomyopathy from 15 weeks. At the molecular level, we observed a statistically significant Epac1, Epac2, Rho A and Rac1 expression modulation between 6 and 20 weeks suggesting a time-dependent regulation of Epac signalling in Dox-induced cardiotoxicity. Our results indicate for the first time an integrated time-course of Dox induced-alteration in Epac signalling, and a potential role of Epac in myocyte death induced by Dox.