Homogeneous 2D and 3D alignment of cardiomyocyte in dilated cardiomyopathy revealed by intravital heart imaging

In contrast to hypertrophic cardiomyopathy, there has been reported no specific pattern of cardiomyocyte array in dilated cardiomyopathy (DCM), partially because lack of alignment assessment in a three-dimensional (3D) manner. Here we have established a novel method to evaluate cardiomyocyte alignment in 3D using intravital heart imaging and demonstrated homogeneous alignment in DCM mice. Whilst cardiomyocytes of control mice changed their alignment by every layer in 3D and position twistedly even in a single layer, termed myocyte twist, cardiomyocytes of DCM mice aligned homogeneously both in two-dimensional (2D) and in 3D and lost myocyte twist. Manipulation of cultured cardiomyocyte toward homogeneously aligned increased their contractility, suggesting that homogeneous alignment in DCM mice is due to a sort of alignment remodelling as a way to compensate cardiac dysfunction. Our findings provide the first intravital evidence of cardiomyocyte alignment and will bring new insights into understanding the mechanism of heart failure.

Abstract 13026: Homogeneous 2D and 3D Alignment of Cardiomyocytes in Dilated Cardiomyopathy Revealed by Intravital Heart Imaging

Background: In contrast to hypertrophic cardiomyopathy, there has been reported no specific pattern of cardiomyocyte array in dilated cardiomyopathy (DCM). This might be because it is assessed only on heart tissue sections two-dimensionally (2D). To address this, we sought to evaluate cardiomyocyte alignment in DCM three-dimensionally (3D) using intravital heart imaging techniques. Methods and Results: We observed cardiomyocytes of membrane fluorescent reporter mice up to 100μm depth by an intravital imaging system with two-photon microscopy. On each 2D images taken at 1μm interval, the angles of cardiomyocytes from a vertical line were measured and their distribution was plotted. Then the plots of all layers were merged so that layer-to-layer change of angle distribution can be visualized. In these merged plots, cardiomyocytes exhibited several peaks with a certain spread around each peak, suggesting that cardiomyocytes change their alignments by every layer in 3D and position twistedly even in a single layer (Figure). We next assessed cardiac mutant Troponin T knock-in mice as a DCM model. The angle distribution in these mice was less various within a single layer and between layers as well. These results indicate that cardiomyocytes of DCM model mice align homogeneously both in 2D and in 3D. To determine how homogeneous alignment contributes to cardiomyocyte contractility, we captured the motion of cultured cardiomyocytes and found that cardiomyocytes seeded on the top of linearly aligned fibers show greater motion than those seeded on randomly aligned fibers. Conclusion: Using intravital imaging, we have provided a first evidence of cardiomyocyte array in 3D and demonstrated that cardiomyocytes of DCM model mice align homogeneously both in 2D and in 3D. Homogeneous alignment of those mice might be the consequences of impaired cardiac function as a way to increase let ventricular contractility.