The application of stem cell-derived cardiomyocytes in drug development and regenerative therapy carries huge potential for the advancement of disease treatment. However, these cells generally show an immature phenotype compared to their adult counterparts. Thriiodothyronine hormone (T3) is known to play an important role in cardiac development regulating various cardiac genes. In this study we examined the effect of T3 on gene expression and Ca2+-handling properties of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs).
HiPSC-CMs were commercially derived. QPCR analysis was used to compare gene expression levels of non-stimulated with T3-stimulated hiPSC-CMs (3 nM, 48 h) and with human adult and foetal heart tissue. The panel of analysed genes included contractile proteins, ion channels and T-tubules (TTs) and sarcoplasmic reticulum (SR) Ca2+-handling associated genes. Our analysis showed: 1) The expression levels of most genes analysed in non-stimulated iPSC-CMs were below adult controls and for some genes also notably below foetal cells (i.e. ryanodine receptor, RyR); 2) T3-treatment induced up-regulation of the SR Ca2+-ATPase SERCA (n=3, p < 0.05), Kv4.3 (Ito, n=3, p < 0.05), Kir2.1 (IK1) and α-MHC (α-myosin heavy chain) and down-regulation of NCX (Na+/Ca2+-exchanger) and Cav3.1 (T-type Ca2+ channel). In most cases gene expression was still different to adult heart control levels; 3) T3 did not increase the expression of β-MHC, other Ca2+-handling (RyR, phospholamban, calsequestrin) or TTs-related (Bin1, Tcap) genes.
Electrophysiological studies were performed on dispersed spontaneously beating hiPSC-CMs using a multielectrode array system. Both T3-stimulated and non-stimulated cells were sensitive to caffeine (empties SR Ca2+-stores) while treatment with thapsigargin (THG, inhibits SERCA-mediated Ca2+ reuptake) reduced the beating rate by about 30 % after 15 minutes at 1 μM (n=5; p < 0.05) with further reduction or complete cessation of contraction in 10 μM THG.
In summary, hiPSC-CMs showed dependence on intracellular Ca2+-stores for contraction. T3 treatment enhanced maturation of iPSC-CMs in some measure by shifting the expression of various genes, mainly ion channels, closer to the gene expression levels of adult controls but it did not alter the expression of others which are implicated in TTs-development or mature Ca2+-handling: most remained below adult levels.