Molecular and Cellular Determinants of Human Iron Overload Cardiomyopathy.

Iron overload cardiomyopathy (IOC) is a serious heart condition that is caused by elevated levels of systemic iron. IOC is characterized by both systolic and diastolic dysfunction as well as arrhythmias. It has been challenging to isolate the cardiac-specific cellular and molecular mechanisms driving IOC because the disease affects multiple interconnected organ systems. Here, we leverage stem cell technologies, cardiac tissue engineering, and protein reconstitution assays to model key aspects of human IOC in vitro and to probe the cellular and molecular mechanisms driving cardiac dysfunction. We demonstrate that human engineered heart tissues consisting of both cardiomyocytes and cardiac fibroblasts faithfully recapitulate key aspects of the human disease, including reduced systolic function, impaired diastolic function, and increased prevalence of arrhythmogenic events. We demonstrate that while both cardiomyocytes and cardiac fibroblasts show increased intracellular iron levels, leading to reduced viability, cardiomyocytes show higher levels of iron accumulation and higher levels of reactive oxygen species production. Moreover, we show that in a tissue, iron overload has little effect on the action potential kinetics; however, it directly impacts the amplitude and kinetics of the calcium transient, potentially driving arrhythmogenesis. Finally, we demonstrate that iron overload decreases force production, in part, through oxidative damage of sarcomeric proteins and direct iron-based inhibition of myosin. In summary, our results reveal new insights into the cellular and molecular mechanisms of human IOC pathogenesis, and they establish new in vitro models that can be harnessed to faithfully recapitulate key aspects of the human disease phenotype.