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EMBRYONIC STEM CELLS

Functional Sarcoplasmic Reticulum for Calcium Handling of Human Embryonic Stem Cell-Derived Cardiomyocytes: Insights for Driven Maturation

^aStem Cell Program and
^bDepartment of Cell Biology and Human Anatomy, University of California Davis, Davis, California, USA;
^cInstitute of Pediatric Regenerative Medicine, Shriners Hospital for Children of North America, Sacramento, California, USA

Key Words. Human embryonic stem cells • Cardiomyocytes • Maturation • Ca²⁺ handling • Sarcoplasmic reticulum

Correspondence: Ronald Li, Ph.D., University of California, Davis, Room 650, Shriners Hospital, 2425 Stockton Blvd., Sacramento, California 95817, USA. Telephone: (916) 453-2225; Fax: (916) 453-2238; e-mail: ronaldli{at}ucdavis.edu

Received July 10, 2007; accepted for publication August 29, 2007.
First published online in STEM CELLS EXPRESS   September 13, 2007.



Cardiomyocytes (CMs) are nonregenerative. Self-renewable pluripotent human embryonic stem cells (hESCs) can differentiate into CMs for cell-based therapies. In adult CMs, Ca²⁺-induced Ca²⁺ release from the sarcoplasmic reticulum (SR) via the ryanodine receptor (RyR) is key in excitation-contraction coupling. Therefore, proper Ca²⁺ handling properties of hESC-derived CMs are required for their successful functional integration with the recipient heart. Here, we performed a comprehensive analysis of CMs differentiated from the H1 (H1-CMs) and HES2 (HES2-CMs) hESC lines and human fetal (F) and adult (A) left ventricular (LV) CMs. Upon electrical stimulation, all of H1-, HES2-, and FLV-CMs generated similar Ca²⁺ transients. Caffeine induced Ca²⁺ release in 65% of FLV-CMs and 38% of H1- and HES2-CMs. Ryanodine significantly reduced the electrically evoked Ca²⁺ transient amplitudes of caffeine-responsive but not -insensitive HES2- and H1-CMs and slowed their upstroke; thapsigargin, which inhibits the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump, reduced the amplitude of only caffeine-responsive HES2- and H1-CMs and slowed the decay. SERCA2a expression was highest in ALV-CMs but comparable among H1-, HES2-, and FLV-CMs. The Na⁺-Ca²⁺ exchanger was substantially expressed in both HES2- and H1-CMs relative to FLV- and ALV-CMs. RyR was expressed in HES2-, H1-, and FLV-CMs, but the organized pattern for ALV-CMs was not observed. The regulatory proteins junctin, triadin, and calsequestrin were expressed in ALV-CMs but not HES2- and H1-CMs. We conclude that functional SRs are indeed expressed in hESC-CMs, albeit immaturely. Our results may lead to driven maturation of Ca²⁺ handling properties of hESC-CMs for enhanced contractile functions.

Disclosure of potential conflicts of interest is found at the end of this article.

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