Abstract
Detecting the structural changes caused by volume and pressure overload is critical to comprehending the mechanisms of physiologic and pathologic hypertrophy. This study explores the structural changes at the crystallographic level in myosin filaments in volume- and pressure-overloaded myocardia through polarization-dependent second harmonic generation microscopy. Here, for the first time, we report that the ratio of nonlinear susceptibility tensor components d33/d15 increased significantly in volume- and pressure-overloaded myocardial tissues compared with the ratio in normal mouse myocardial tissues. Through cell stretch experiments, we demonstrated that mechanical tension plays an important role in the increase of d33/d15 in volume- and pressure-overloaded myocardial tissues.
Highlights
The crystallographic structure of cardiac myosin filaments is a major determinant of the strong binding of myosin heads to actin filaments and the accurate conformational changes in myosin heads mediating cardiac muscle-cell contraction
To explore the role of mechanical stretches that occur during volume overload and pressure overload in the changes in the ratio of the nonlinear susceptibility tensor components d33/d15, we studied the effect of simulated mechanical tension on the ratio of d33/d15
In the absence of stretch, the value of d31/d15 (0.99 ± 0.09) obtained from the cell culture was statistically the same as that obtained from normal myocardial tissues (Fig. 4(B)), while the value of d33/d15 was 0.49 ± 0.05, which was significantly smaller than the value retrieved from normal myocardial tissues
Summary
The crystallographic structure of cardiac myosin filaments is a major determinant of the strong binding of myosin heads to actin filaments and the accurate conformational changes in myosin heads mediating cardiac muscle-cell contraction. The structural changes in myosin filaments under pathological hypertrophy have been thought to contribute to a binding mismatch between myosin and actin filaments. The basic principle of this visualization is that the SHG signal is directly determined by the nonlinear susceptibility tensor, which is an optical property of the biomolecule (noncentrosymmetric biomolecules including, for example, myosin, collagen type I, and microtubule) associated with its crystal structure [3,4,5]. Polarization-dependent SHG microscopy is unique: It can retrieve the values of nonlinear susceptibility tensor components of a biomolecule and can be used to explore its crystallographic structure [3,6]. The values of nonlinear susceptibility tensor components of myosin filaments in different species are reportedly different [7], as are those values for the same myosin filaments in different physiological states (relaxed or contracted) [8,9]
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