Mechanobiology of cardiomyocyte development

Abstract

Cardiac cells are under constant, self-generated mechanical stress which can affect the differentiation of stem cells into cardiac myocytes, the development of differentiated cells and the maturation of cells in neonatal mammals. In this article, the effects of direct stretch, electrically induced beating and substrate elasticity on the behavior and development of cardiomyocytes are reviewed, with particular emphasis on the effects of substrate stiffness on cardiomyocyte maturation. In order to relate these observations to in vivo mechanical conditions, we isolated the left ventricle of Black Swiss mice from embryonic day 13.5 through post-natal day 14 and measured the elastic modulus of the epicardium using atomic force microscope indentation. We found that the elastic modulus of the epicardium significantly changes at birth, from an embryonic value of 12+/-4kPa to a neonatal value of 39+/-7kPa. This change is in the range shown to significantly affect the development of neonatal cardiomyocytes.

Figure 1

The elastic modulus of the epicardial surface of sections of the LV from embryonic and neonatal Black Swiss mice as measured by AFM increased significantly between timepoints of E16.5 and P2, with birth at E19, from an average embryonic elastic modulus of 12 ± 4 kPa to a postnatal modulus of 39 ± 7 kPa per ANOVA followed by t-test comparison between embryonic and postnatal data (P<.01). Data points represent averages of 3 to 4 samples measured 7 times at 7 positions per sample, with the highest and lowest discarded. Error bars represent S.E.M.

Figure 2

Sample indentation and retraction curve of the epicardium of an embryonic day 13 Black Swiss mouse. In this case the sample was indented nearly 1.5 μm and no clear transition between material properties was apparent. Typical samples in this study were indented only 1.0 μm. The approximately 300 nm difference between indentation and retraction is typical for all specimens in this study.

Figure 3

The elastic modulus of the epicardial surface of a section of the LV from one C57 mouse at 30 days post myocardial infarction induced by ligation of the left anterior descending coronary artery as measured by AFM was significantly higher in the ischemic region (56 +/− 6 kPa) than in the non-ischemic region (21 +/− 2 kPa) per ANOVA followed by t-test comparison between ischemic and non-ischemic regions (P<0.05). Data points represent averages of 7 measurements per position, with the highest and lowest discarded. Error bars represent standard deviation.