Automated analysis of the morphological features and internal organization of sarcomeres in cardiomyocytes derived from human-induced pluripotent stem cells

Abstract

Morphological and structural features of sarcomeres from cardiomyocytes are relevant indicators of the maturity and efficiency of the contractile apparatus. Hence, it is crucial to develop robust characterization methods to quantify the morphology and organization of sarcomeres. Develop an interface of the SarcOmere Texture Analysis (SOTA) coded by Sutcliffe et al. (Scientific Reports, 2017) for routine analysis and determine the morphological and structural differences induced by the linear micropatterning of human induced pluripotent stem cell cardiomyocytes (iPSC-CMs). A Matlab interface was generated in order to measure morphological parameters of cardiomyocytes and sarcomeres. Cell shape was assessed by the elongation (ratio of major to minor axis length). The length and orientation of sarcomeres were measured. A sarcomere organization score (SarcOgScore), was calculated from the correlation between pixels in the different orientations of pictures, typically ranging from 0 to 2 (above 0.1 for cells with well-organized sarcomeres). This interface was applied on immunofluorescence images of alpha-actinin stained cardiomyocytes (128 unpatterned and 120 micropatterned iPSC-CM). Micropatterned iPSC-CMs were significantly more elongated (4.119 ± 1.423 vs. 1.414 ± 0.441, P < 0.0001), and with a higher sarcomere organization score (0.147 ± 0.093 vs. 0.082 ± 0.052, P < 0.0001). There was a lower difference between cell and sarcomere orientations in micropatterned iPSC-CMs (3.5 ± 4.4° vs. 27.6 ± 21.4°, P < 0.0001) indicating a better alignment of sarcomere structures. In cells with SarcOrgScore > 0.1, micropatterned iPSC-CMs exhibited higher sarcomeres length than unpatterned iPSC-CMs (1.783 ± 0.123 μm vs. 1.697 ± 0.232 μm, P < 0.05), overall suggesting an improved maturation of these cells. We established the usefulness of a method to quantify the global organization of myofilament and evaluate the level of sarcomere disarray in iPSC-CMs.