Calcium Remodeling through Different Signaling Pathways in Heart Failure: Arrhythmogenesis Studies of Pyk2, Dystrophin, and Beta-adrenergic Receptor Signaling

Heart failure is a common clinical syndrome that ensues when the heart is no longer able to generate sufficient cardiac output to meet the demands of the body. It is one of the leading causes of death worldwide but with limited and non-ideal therapies at the moment. One reason behind this may be the complexity of significant alterations in multiple signaling pathways and concomitant structural and functional remodeling, especially Ca handling. Ca is critical in both the electrical and mechanical properties of cardiac myoctyes, and much is known about ionic currents and the normal excitation-contraction coupling process. In heart failure, distinct impaired signaling pathways induce significant alterations in how cardiac Ca handling is regulated. These alterations either directly cause certain arrhythmias or facilitate arrhythmias by association with electrical remodeling. The goal of this dissertation was to investigate the mechanisms of calcium remodeling through different signaling pathways in heart failure, and mechanisms on how the intricate and dynamic interactions between Ca handling and signaling pathways impairment facilitate arrhythmias in heart failure. To achieve this goal, a dual optical mapping system was designed to investigate electrical activity and Ca transient simultaneously. High spatio-temporal resolution mapping allows for quantifying conduction, repolarization and Ca cycling, especially on the interactions between action potential and Ca handling. In this dissertation, I investigated Ca remodeling in three different signaling pathways: stress activated signaling, cytoskeletal signaling and β adrenergic receptor signaling pathway. Proline-rich tyrosine kinase 2: Pyk2) is a non-receptor protein kinase regulated by intracellular Ca. It mediates a typical stress activated signaling pathways along with c-Src, P38 MAPK and regulates a broad range of key biological responses. By optically mapping the genetically engineered mouse model: Pyk2 knockout, I detected a protective role of Pyk2 with respect to ventricular tachyarrhythmia during parasympathetic stimulation by regulation of gene expression related to calcium handling. The mdx mouse model was introduced in the investigation of cytoskeletal signaling pathway. mdx mice is a common model for Duchenne muscular dystrophy, which is a clinical syndrome resulted from recessive of dystrophin and eventually develops into heart failure. The project suggested the association of mechanical stimulation and deficiency of dystrophin account for the cardiac mechanical defects and resulting Ca mishandling, but not either of the two above-mentioned entities alone. Ca mishandling leads to Ca cycling dispersion, which facilitates generation of arrhythmias. β Adrenergic receptor signaling pathway was investigated on explanted donor and failing human hearts. Distinct β adrenergic receptor subtypes were found to regulate remodeling differently. The association between remodeling of action potential and Ca transient provides crucial arrhythmic drivers and substrate in heart failure.