Date of Award
Doctor of Philosophy (PhD)
In the last two decades, our understanding of cardiac arrhythmias has been accelerated immensely by the development of genetically engineered animals. Transgenic and knockout mice have been the “gold standard” platforms for delineating disease mechanisms. Much of our understanding of the pathogenesis of atrial and ventricular arrhythmias is gained from mouse models that alter the expression of specific ion channels or other proteins. However, cardiac arrhythmias such as atrial fibrillation are heterogeneous diseases with numerous distinct conditions that could not be explained exclusively by the disruption of ionic currents. Increasing evidence suggests disruption of signaling pathways in the pathogenesis of cardiac arrhythmias. Although crucial for studying disease mechanisms, animal models often fail to predict human response to treatments due to inter-species genetic and physiological differences. Cardiac slices obtained from human hearts have been demonstrated as an accurate model that more faithfully recapitulates human cardiac physiology. However, the use of the human cardiac slices for evaluating the transcriptional regulation of arrhythmia is hampered by tissue remodeling and dedifferentiation in long-term culture of the slices.
The first part of this dissertation aims to elucidate one of the potential mechanisms of sick sinus syndrome and atrial fibrillation induced by transient reactivation of Notch, a critical transcription factor during cardiac development and has been shown to be reactivated in the adult heart following cardiac injury. When Notch is transiently reactivated in the adult mice to mimic the injury response, the animals exhibits slowed heart rate, increased heart rate variability, frequent sinus pauses, and slowed atrial conduction. The electrical remodeling of the atrial myocardium results in increased susceptibility to atrial fibrillation. The transient reactivation of Notch also significantly altered the atrial gene expression profile, with many of the disrupted genes associated with cardiac arrhythmias by genome-wide association study.
The second part of this dissertation aims to address the lack the translation from animal research to human therapies by extending the human cardiac slice viability in culture. With the optimized culture parameters, human cardiac slices obtained from the left ventricular free wall remained electrically viable for up to 21 days in vitro and routinely maintained normal electrophysiology for up to 4 days. To genetically alter the human cardiac slices, a localized gene delivery technique was evaluated and optimized.
The third part of the dissertation aims to further improve long-term culture of human cardiac slices and to increase the availability of human tissue for research by developing a self-contained heart-on-a-chip system for automated culture of human cardiac slices. The system maintains optimal culture conditions and provides electrical stimulation and mechanical anchoring to minimize tissue dedifferentiation. The work allows for accelerated optimization of long-term culturing of human cardiac slice, which will enable study of arrhythmia mechanisms on human cardiac tissue via targeted control of transcription factors.
Igor R. Efimov, Stacey Rentschler
Nathaniel Huebsch, Colin Nichols, Jonathan Silva,