Background

Cardiotoxicity represents a major complication of cancer therapy with anthracyclines, whose main known compound is doxorubicine (DOX). Besides DOX-induced acute side effects, cardiotoxicity can manifest during the course or after therapy, limiting the patient’s quality of life or even lead to therapy discontinuation eventually. Although mechanisms of DOX-induced toxic cardiomyopathy (DICM) are not entirely understood, CaMKIIδ-activity is known to be increased upon acute DOX exposure, contributing to impaired intracellular Calcium (Ca) handling. However, currently no studies have addressed the question, whether CaMKIIδ is involved in DOX-induced long-term cardiotoxicity.

Aim

We aimed to investigate cardiac function and intracellular Ca handling using an in-vivo DOX treated mouse model, examining whether CaMKIIδ is involved in DOX-induced long-term cardiotoxicity.

Material and Methods

Cardiac function and excitation-contraction coupling of CaMKIIδ^WT and CaMKIIδ^-/- (global CaMKIIδ knockout) mice were tested in an in-vivo DOX treated mouse model (cumulative dose 12 mg/kg, intraperitoneal injection). Cardiac function was determined by echocardiography after 12 weeks. Ca handling of freshly isolated cardiomyocytes was assessed by epifluorescence microscopy (Fura2-AM) and confocal microscopy (Fluo4-AM). Histological analyses regarding cardiac fibrosis and cell dimensions were examined.

Results

Long-term DOX exposure reduced left ventricular ejection fraction (EF) and markedly increased cardiac fibrosis in CaMKIIδ^WT mice. Moreover, CaMKIIδ^WT hearts displayed decreased myocytes volume indicating cellular atrophy following DOX treatment. Coinciding with the reduction in EF, CaMKIIδ^WT myocytes showed depressed Ca transient amplitudes as well as an increased Ca transient decay (indicating slowed relaxation). Spontaneous diastolic Ca leakage from the sarcoplasmic reticulum (SR) was dramatically increased. In contrast, CaMKIIδ^-/- mice showed an attenuated impairment of cardiac function following DOX exposure which was in line with largely maintained cardiac calcium handling as compared to their respective WT control.

Conclusion

Our study highlights for the first time that CaMKIIδ contributes to long-term DOX-induced cardiotoxicity. We found that chronic DOX treatment induced depressed cardiac function and myocardial fibrosis, associated with impaired intracellular calcium handling, which was greatly attenuated in our CaMKIIδ^-/- mouse model.