The chemotherapeutic Doxorubicin (DOX) has significantly increased survival rates of pediatric and adult cancer patients. However, 10 % of pediatric cancer survivors will 10-20 years later develop severe Dilated Cardiomyopathy (DCM) and the exact molecular mechanisms of disease progression after this long latency time remain puzzling. We here revisit the hypothesis that elevated apoptosis signaling or its increased likelihood after DOX exposure can lead to an impairment of cardiac function and cause a cardiac dilation. Based on recent literature evidences, we first argue why even little detectable apoptosis may be sufficient to cause a dilated phenotype. We then review findings suggesting that mature cardiomyocytes are protected against DOX-induced apoptosis downstream, but not upstream to Mitochondrial Outer Membrane Permeabilisation (MOMP). This lack of prevention of MOMP-induction then is proposed to alter the metabolic phenotype, induce hypertrophic remodeling and lead to functional cardiac impairment even in absence of cardiomyocyte apoptosis. We further discuss findings that DOX exposure can lead to increased sensitivity to further cardiomyocyte apoptosis, which may cause a gradual loss in cardiomyocytes over time and a compensatory hypertrophic remodeling after treatment, potentially explaining the long lag time in disease onset. We finally note similarities between DOX-exposed cardiomyocytes and apoptosisprimed cancer cells and propose computational systems biology as tool to predict patient individual DOX doses. In conclusion, combining recent findings in rodent hearts and cardiomyocytes exposed to DOX with insights from apoptosis signal transduction allowed us to obtain a molecularly deeper insight in this delayed and still enigmatic pathology of DCM. Key messages1. Differentiated cardiomyocyte are protected to post but not pre-MOMP apoptosis 2. MOMP-induction can lead to cardiac hypertrophy and metabolic remodeling after DOX 3. DOX-exposed cardiomyocytes may be more sensitive to apoptosis over life time 4. DOX-exposed cardiomyocytes show similarities to apoptosis-primed cancer cells

The rat cardiomyoblast cell line H9C2 has emerged as a valuable tool for studying cardiac development, mechanisms of disease and toxicology. We present here a rigorous proteomic analysis that monitored the changes in protein expression during differentiation of H9C2 cells into cardiomyocyte-like cells over time. Quantitative mass spectrometry followed by gene ontology (GO) enrichment analysis revealed that early changes in H9C2 differentiation are related to protein pathways of cardiac muscle morphogenesis and sphingolipid synthesis. These changes in the proteome were followed later in the differentiation time-course by alterations in the expression of proteins involved in cation transport and beta-oxidation.