Human induced pluripotent stem cell-derived cardiomyocytes: insights into molecular, cellular, and functional phenotypes

Abstract

Disease models are essential for understanding cardiovascular disease pathogenesis and developing new therapeutics. The human induced pluripotent stem cell (iPSC) technology has generated significant enthusiasm for its potential application in basic and translational cardiac research. Patient-specific iPSC-derived cardiomyocytes offer an attractive experimental platform to model cardiovascular diseases, study the earliest stages of human development, accelerate predictive drug toxicology tests, and advance potential regenerative therapies. Harnessing the power of iPSC-derived cardiomyocytes could eliminate confounding species-specific and interpersonal variations and ultimately pave the way for the development of personalized medicine for cardiovascular diseases. However, the predictive power of iPSC-derived cardiomyocytes as a valuable model is contingent on comprehensive and rigorous molecular and functional characterization.

Keywords: cardiovascular disease modeling; cardiovascular diseases; induced pluripotent stem cells; myocytes, cardiac; precision medicine.

Figure 1. Current applications of patient-specific iPSC-CM technology

iPSC-CMs have been used for disease modeling of inherited cardiomyopathies and channelopathies, regenerative therapies, drug discovery and cardiotoxicity testing, as well as for studying metabolic abnormalities and cardiac development.

Figure 2. Expression of key structural and functional genes in iPSC-CMs

A) Schematic of the major structural and functional features of iPSC-CMs. In adult CMs, upon membrane depolarization a small amount of Ca²⁺ influx induced by activation of voltage-dependent L-type Ca2+ channels (CACNAC1) triggers the release of Ca²⁺ through the ryanodine receptors (RYR2) SR, termed Ca²⁺-induced Ca²⁺-release (CICR) mechanism. The released Ca²⁺ ions diffuse through the cytosolic space and bind to troponin C (TNNC1), resulting in the release of inhibition induced by troponin I (TNNI1), which activates the sliding of thin and thick filaments, and lead to cardiac contraction. Recovery occurs as Ca²⁺ is extruded by the Na²⁺/Ca²⁺ exchanger (NCX1) and returned to the SR by the sarco(endo)plasmic Ca²⁺-ATPase (ATP2A2) pumps on the nonjunctional region of the SR that are regulated by phospholamban (PLN). This process is conserved in iPSC-CMs, but major differences exist, such as a nascent SR, the presence of an Inositol 1,4,5-trisphosphate (IP₃)-releasable Ca²⁺ pool, and the complete absence of T-tubules. The genes encoding the major transmembrane ion channels involved in the generation of action potential are also shown. B) Immunofluorescence staining of cardiac troponin T and a-sarcomeric actinin in iPSC-CMs. C) Line-scan images and spontaneous Ca²⁺ transients in iPSC-CMs. KCNIP2: Potassium channel-interacting protein 2; KCNH2: Potassium voltage-gated channel, subfamily H (eag-related), member 2; KCNQ1: Potassium voltage-gated channel, KQT-like subfamily, member 1; NCX1: Na⁺/Ca²⁺ exchanger; KCNJ2: Potassium inwardly-rectifying channel, subfamily J, member 2; RYR2: Ryanodine receptor 2; SERCA2: ATPase, Ca²⁺ transporting, cardiac muscle, slow twitch 2; PLN: Phospholamban; CACNA1C; Calcium channel, voltage-dependent, L type, alpha 1C subunit; SCN5A: Sodium channel, voltage-gated, type V, alpha subunit; TNNT2: Troponin T type 2; MYL2: Myosin, light chain 2; MYL3: Myosin, light chain 3; TNNI3: Troponin I type 3; TNNC: Troponin C type 1; TTN: Titin; MYH6: Myosin, heavy chain 6, alpha; MYH7: Myosin, heavy chain 7, beta; MYBPC3: Myosin binding protein C; TPM1: Tropomyosin 1 (alpha); ACTC1: Actin, alpha, cardiac muscle 1.

Figure 3. Comparison of action potentials of ventricular-like iPSC-CMs and adult ventricular cardiomyocytes

Schematic of ventricular action potentials. Phases 0–4 are the rapid upstroke, early repolarization, plateau, late repolarization, and diastole, respectively. The ionic currents and the genes that generate the currents with schematics of the current trajectories are shown above and below the action potentials. For individual ion channel currents, the voltage dependence of channel-gating properties of ventricular-like iPSC-CMs is remarkably analogous to adult ventricular cardiomyocytes, but significant differences also exist, such as reduced or absence of inward rectifier K⁺ currents (I_K1) and the presence of prominent pacemaker currents that contribute to their automaticity.