Engineered Heart Tissue (EHT) from neonatal rat cardiomyocytes has been used successfully as in vitro model and in cardiac repair. Here, we hypothesized that human embryonic stem cells (hESC) can be used to generate EHT with properties of native myocardium.
Methods:
hESC (hES3-ENVY) were differentiated in embryoid bodies, enzymatically dispersed, and subjected to EHT-generation in circular casting molds (1.5x10
6
cells, 0.4 mg collagen, 10% Matrigel/EHT; inner/outer diameter - 2/4 mm). Contractile function was assessed 10 days after casting under isometric conditions (37°C, 1.5 Hz, Tyrode’s solution). Action potentials (AP) were recorded in spontaneously contracting EHTs with intracellular electrodes (37°C, Tyrode’s solution). Calcium gradients were assessed by confocal laser scanning microscopy (CLSM) after rhod-2 loading. EHT-morphology was examined by CLSM and electron microscopy (EM).
Results:
hESC-EHTs contracted synchronously and spontaneously at 1.1±0.1 Hz (n=3). Increasing concentrations of extracellular calcium (0.2–2.4 mM) enhanced force of contraction from 53±8 to 199±22 μN (n=8, p<0.05; EC
50
: 0.8±0.04 mM). Isoprenaline (1 μM) at 0.4 mM calcium increased twitch tension from 61±7 to 108±15 μN (n=8, p<0.05) and shortened relaxation time from 111±6 to 87±4 ms (n=3, p<0.05). Cardiomyocytes within EHTs formed a functional syncytium composed of predominantly oriented muscle strands with a high degree of sarcomere differentiation (CLSM, EM). Cell-cell contacts through adherens junctions were identified by EM. Synchronous calcium gradient spread in spontaneously contracting EHTs indicated electrical coupling of individual cells within the multicellular constructs. AP recordings identified pacemaker cells (spontaneous diastolic depolarization) and cells with a flat phase 4 of the AP (working myocardium-like cells). Pharmacological studies demonstrated the presence and functional relevance of I
Na
(10–30 μM flecainide), I
Ca
(1 μM nisoldipine), and I
Kr
(1–5 μM E4031).
Conclusion:
Human force-generating EHT with functional and morphological properties of native myocardium can be generated. Ultimately, hESC-EHTs may constitute a model system for substance screening and could further be utilized in cardiac repair.
Implantation of Spontaneously Beating Human iPS Cell-Derived ENGINEERED HEART TISSUE Does Not Provoke Ventricular Arrhythmias in a Guinea Pig Infarction Model
