Facilitated maturation of Ca²⁺ handling properties of human embryonic stem cell-derived cardiomyocytes by calsequestrin expression

Abstract

Cardiomyocytes (CMs) are nonregenerative. Self-renewable pluripotent human embryonic stem cells (hESCs) can differentiate into CMs for cell-based therapies. We recently reported that Ca 2+ handling, crucial to excitation-contraction coupling of hESC-derived CMs (hESC-CMs), is functional but immature. Such immature properties as smaller cytosolic Ca 2+ transient amplitudes, slower kinetics, and reduced Ca 2+ content of sarcoplasmic reticulum (SR) can be attributed to the differential developmental expression profiles of specific Ca 2+ handling and regulatory proteins in hESC-CMs and their adult counterparts. In particular, calsequestrin (CSQ), the most abundant, high-capacity but low-affinity, Ca 2+ -binding protein in the SR that is anchored to the ryanodine receptor, is robustly expressed in adult CMs but completely absent in hESC-CMs. Here we hypothesized that gene transfer of CSQ in hESC-CMs suffices to induce functional improvement of SR. Transduction of hESC-CMs by the recombinant adenovirus Ad-CMV-CSQ-IRES-GFP (Ad-CSQ) significantly increased the transient amplitude, upstroke velocity, and transient decay compared with the control Ad-CMV-GFP (Ad-GFP) and Ad-CMV-CSQΔ-IRES-GFP (Ad-CSQΔ, which mediated the expression of a nonfunctional, truncated version of CSQ) groups. Ad-CSQ increased the SR Ca 2+ content but did not alter L-type Ca 2+ current. Pharmacologically, untransduced wild-type, Ad-GFP-, Ad-CSQΔ-, and Ad-CSQ-transduced hESC-CMs behaved similarly. Whereas ryanodine significantly reduced the Ca 2+ transient amplitude and slowed the upstroke, thapsigargin slowed the decay. Neither triadin nor junctin was affected. We conclude that CSQ expression in hESC-CMs facilitates Ca 2+ handling maturation. Our results shed insights into the suitability of hESC-CMs for therapies and as certain heart disease models for drug screening.