Date of Award
Doctor of Philosophy (PhD)
Bruce Z Gao, Committee Chair
Thomas K Borg
As the most important structural and functional protein of cardiomyocyte, myosin is sensitive to mechanical and hormonal stimulus during cardiac hypertrophy. Accumulating evidence suggests that the changes in myosin during cardiac hypertrophy can eventually lead to heart failure. Therefore, the effective detection of the structural changes in myosin is critical to understanding the underlying mechanisms of cardiac hypertrophy and contributes to the early diagnose and treatment of cardiac hypertrophy.
Changes in myosin during the development of cardiac hypertrophy are not limited to tissue, cellular or sub-cellular levels such as series and parallel addition of sarcomere. Before cardiac hypertrophy develops obvious symptoms or causes irreversible damage, two phenomena have been confirmed to be prevalent in early cardiac hypertrophy: mechanical tension overload and myosin expression transition, accounting for the molecular-level structural changes in myosin. This dissertation aims to explore the molecular-level structural changes in myosin by using second harmonic generation imaging technology. Specifically, a custom-built polarization-resolved second harmonic generation confocal microscope is applied to study the value changes in nonlinear susceptibility tensor components of cardiac myosin from volume- and pressure-overload induced hypertrophy animal models, cell culture and direction controllable stretch models, myosin expression transition animal models, and myosin expression transition cell culture models.
In this dissertation, we report for the first time: 1) that the ratio of nonlinear susceptibility tensor components of cardiac myosin (d33/d15) increases significantly in volume- and pressure-overloaded myocardia compared with the values in normal mouse myocardia; 2) that, through cell stretch experiments, mechanical tension is demonstrated to play an important role in the increase of d33/d15 in volume- and pressure-overloaded mouse myocardia; 3) that the polarization spectrum of cardiac myosin transits from C6 to C3v line profile by hypothyroidism drug (propylthiouracil) inducing the transition of the cardiac myosin expression from alpha to beta phenotype in rat myocardia; and we further prove that the parts that cause the differences in polarization spectra between alpha- and beta-myosin are located in the region of myosin filaments that form a crossbridge. 4) that, in cell culture experiments, we observe, for the first time, that polarization spectra dynamically transfer from C6 to C3v line profile in single cardiomyocyte by the induction of adrenergic agent (norepinephrine).
Our research shows that the polarization-resolved second harmonic generation microscopy is an effective tool to analyze the dynamic changes in myosin structure, at the molecular level in living cells, during cardiac hypertrophy. Clinically, our findings contribute to the early diagnosis of cardiac hypertrophy.
Yuan, Cai, "Polarization-Resolved Second Harmonic Generation Microscopy Study of Cardiac Hypertrophy" (2019). All Dissertations. 2418.