Background
Doxorubicin (DOX) represents one of the most common chemotherapeutic agents, but its long-term efficacy is limited by side effects such as heart failure. Although mechanisms of Doxorubicin-induced toxic cardiomyopathy (DICM) are not entirely understood, reactive oxygen species (ROS) appear to be involved. DOX treatment results in elevated intracellular ROS and is known to increase CaMKIIδ activity which contributes to impaired Calcium handling.
Aim
Here, we tested whether redox-activated CaMKIIδ is involved in DOX-induced and CaMIIδ-mediated impairment of intracellular Calcium handling.
Methods
Ventricular myocytes were isolated from a redox-dead transgenic mouse model (CaMKIIδMM-VV), in which CaMKIIδ was made resistant to oxidative activation of CaMKIIδ by knock-in replacement of two oxidant-sensitive methionines with valines (Met281/282). In addition, cardiomyocytes were isolated from a global CaMKIIδ knockout model (CaMKIIδ-/-). Isolated cardiomyocytes were exposed to DOX (10 µM) and intracellular Calcium handling was assessed by epifluorescence microscopy (Fura 2-AM).
Results
Acute DOX exposure resulted in decreased calcium transient amplitudes and in a reduction of myocytes contractility in wild-type (WT) cardiomyocytes. In addition, DOX caused prolongation of relaxation time and led to a diminished SR Calcium content. Cardiomyocytes from redox-dead mice (CaMKIIδMM-VV) showed an attenuated impairment of these Calcium disturbances as compared to their respective WT control. Interestingly, cardiomyocytes from CaMKIIδ-/- mice with global CaMKIIδ deficiency were protected from DOX-induced impairment of cardiac Calcium handling.
Conclusion
Our data suggest that redox-activated CaMKIIδ is involved in acute DOX-induced cardiotoxicity in isolated cardiomyocytes. However, complete inhibition of CaMKIIδ activity appears to be needed to preserve cardiac Calcium handling upon acute DOX treatment.