Anthracyclines, such as doxorubicin, are effective chemotherapeutic agents for the treatment of cancer, but their clinical use is associated with severe and potentially life-threatening cardiotoxicity. Despite decades of research, treatment options remain limited. The mitochondria is commonly considered to be the main target of doxorubicin and mitochondrial dysfunction is the hallmark of doxorubicin-induced cardiotoxicity. Here, we review the pathogenic mechanisms of doxorubicin-induced cardiotoxicity and present an update on cardioprotective strategies for this disorder. Specifically, we focus on strategies that can protect the mitochondria and cover different therapeutic modalities encompassing small molecules, post-transcriptional regulators, and mitochondrial transfer. We also discuss the shortcomings of existing models of doxorubicin-induced cardiotoxicity and explore advances in the use of human pluripotent stem cell derived cardiomyocytes as a platform to facilitate the identification of novel treatments against this disorder.

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are the most promising source of cardiomyocytes (CMs) for experimental and clinical applications, but their use is largely limited by a structurally and functionally immature phenotype that most closely resembles embryonic or fetal heart cells. The application of physical stimuli to influence hPSC-CMs through mechanical and bioelectrical transduction offers a powerful strategy for promoting more developmentally mature CMs. Here we summarize the major events associated with in vivo heart maturation and structural development. We then review the developmental state of in vitro derived hPSC-CMs, while focusing on physical (electrical and mechanical) stimuli and contributory (metabolic and hypertrophic) factors that are actively involved in structural and functional adaptations of hPSC-CMs. Finally, we highlight areas for possible future investigation that should provide a better understanding of how physical stimuli may promote in vitro development and lead to mechanistic insights. Advances in the use of physical stimuli to promote developmental maturation will be required to overcome current limitations and significantly advance research of hPSC-CMs for cardiac disease modeling, in vitro drug screening, cardiotoxicity analysis and therapeutic applications.

We recently identified a novel protein called syncoilin, a putative intermediate filament protein that interacts with alpha-dystrobrevin, a member of the dystrophin-associated protein complex. Syncoilin is found at the neuromuscular junction, sarcolemma, and Z-lines and is thought to be important for muscle fiber integrity. Based on the similar protein structure and cellular localization of syncoilin and desmin, we proposed that these proteins interact in vivo. The data presented confirm an interaction between syncoilin and desmin and demonstrate their co-localization in skeletal muscle. Intriguingly, whereas these proteins interact, COS-7 cell expression studies show that desmin and syncoilin do not assemble into heterofilaments. Furthermore, fractionation assay and immunofluorescence study of H2K myoblasts and myotubes suggest that, unlike typical intermediate filament proteins, syncoilin does not participate in filament formation with any protein. However, it is possible that syncoilin is involved in the anchoring of the desmin intermediate filament network at the sarcolemma and the neuromuscular junction. This interaction is likely to be important for maintaining muscle fiber integrity and may also link the dystrophin-associated protein complex to the cytoskeleton. The dysfunction or absence of syncoilin may result in the disruption of the intermediate filament network leading to muscle necrosis. Syncoilin is therefore an ideal candidate gene for muscular dystrophies and desmin-related myopathies.

Background—: Differentiation of pluripotent human embryonic stem cells (hESCs) to the cardiac lineage represents a potentially unlimited source of ventricular cardiomyocytes (VCMs), but hESC-VCMs are developmentally immature. Previous attempts to profile hESC-VCMs primarily relied on transcriptomic approaches, but the global proteome has not been examined. Furthermore, most hESC-CM studies focus on pathways important for cardiac differentiation, rather than regulatory mechanisms for CM maturation. We hypothesized that gene products and pathways crucial for maturation can be identified by comparing the proteomes of hESCs, hESC-derived VCMs, human fetal and human adult ventricular and atrial CMs. Methods and Results—: Using two-dimensional–differential-in-gel electrophoresis, 121 differentially expressed (>1.5-fold; P <0.05) proteins were detected. The data set implicated a role of the peroxisome proliferator–activated receptor α signaling in cardiac maturation. Consistently, WY-14643, a peroxisome proliferator–activated receptor α agonist, increased fatty oxidative enzyme level, hyperpolarized mitochondrial membrane potential and induced a more organized morphology. Along this line, treatment with the thyroid hormone triiodothyronine increased the dynamic tension developed in engineered human ventricular cardiac microtissue by 3-fold, signifying their maturation. Conclusions—: We conclude that the peroxisome proliferator–activated receptor α and thyroid hormone pathways modulate the metabolism and maturation of hESC-VCMs and their engineered tissue constructs. These results may lead to mechanism-based methods for deriving mature chamber-specific CMs.

MicroRNAs (miRNAs) are crucial for the post-transcriptional control of protein-encoding genes and together with transcription factors (TFs) regulate gene expression; however, the regulatory activities of miRNAs during cardiac development are only partially understood. In this study, we tested the hypothesis that integrative computational approaches could identify miRNAs that experimentally could be shown to regulate cardiomyogenesis. We integrated expression profiles with bioinformatics analyses of miRNA and TF regulatory programs to identify candidate miRNAs involved with cardiac development. Expression profiling showed that miR-200c, which is not normally detected in adult heart, is progressively down-regulated both during cardiac development and in vitro differentiation of human embryonic stem cells (hESCs) to cardiomyocytes (CMs). We employed computational methodologies to predict target genes of both miR-200c and five key cardiac TFs to identify co-regulated gene networks. The inferred cardiac networks revealed that the cooperative action of miR-200c with these five key TFs, including three (GATA4, SRF and TBX5) targeted by miR-200c, should modulate key processes and pathways necessary for CM development and function. Experimentally, over-expression (OE) of miR-200c in hESC-CMs reduced the mRNA levels of GATA4, SRF and TBX5. Cardiac expression of Ca²⁺, K⁺ and Na⁺ ion channel genes (CACNA1C, KCNJ2 and SCN5A) were also significantly altered by knockdown or OE of miR-200c. Luciferase reporter assays validated miR-200c binding sites on the 3′ untranslated region of CACNA1C. In hESC-CMs, elevated miR-200c increased beating frequency, and repressed both Ca²⁺ influx, mediated by the L-type Ca²⁺ channel and Ca²⁺ transients. Our analyses demonstrate that miR-200c represses hESC-CM differentiation and maturation. The integrative computation and experimental approaches described here, when applied more broadly, will enhance our understanding of the interplays between miRNAs and TFs in controlling cardiac development and disease processes.