Since cardiac transplantation is limited by the small availability of donor organs, regeneration of the diseased myocardium by cell transplantation is an attractive therapeutic modality. To determine the compatibility of human embryonic stem cellderived cardiomyocytes (hESC-CMs) (7 to 55 days old) with the myocardium, we investigated their functional properties regarding intracellular Ca ] i transient and contraction, indicating that at this developmental stage, contraction depends on transsarcolemmal Ca 2؉ influx rather than on sarcoplasmic reticulum Ca 2؉ release. Third, in agreement with the notion that a voltage-dependent Ca 2؉ current is present in hESC-CMs and contributes to the mechanical function, verapamil completely blocked contraction. Fourth, whereas hESC-CMs expressed SERCA2 and NCX at levels comparable to those of the adult porcine myocardium, calsequestrin and phospholamban were not expressed. Our study shows for the first time that functional properties related to intracellular Ca 2؉ handling of hESC-CMs differ markedly from the adult myocardium, probably due to immature sarcoplasmic reticulum capacity. STEM CELLS 2006;24:236 -245

Background-Pericytes represent a unique subtype of microvessel-residing perivascular cells with diverse angiogenic functions and multilineage developmental features of mesenchymal stem cells. Although various protocols for derivation of endothelial and/or smooth muscle cells from human pluripotent stem cells (hPSC, either embryonic or induced) have been described, the emergence of pericytes in the course of hPSC maturation has not yet been elucidated. Methods and Results-We found that during hPSC development, spontaneously differentiating embryoid bodies give rise to CD105 ϩ CD90 ϩ CD73 ϩ CD31 Ϫ multipotent clonogenic mesodermal precursors, which can be isolated and efficiently expanded. Isolated and propagated cells expressed characteristic pericytic markers, including CD146, NG2, and platelet-derived growth factor receptor ␤, but not the smooth muscle cell marker ␣-smooth muscle actin. Coimplantation of hPSC-derived endothelial cells with pericytes resulted in functional and rapid anastomosis to the murine vasculature. Administration of pericytes into immunodeficient mice with limb ischemia promoted significant vascular and muscle regeneration. At day 21 after transplantation, recruited hPSC pericytes were found incorporated into recovered muscle and vasculature. Conclusions-Derivation of vasculogenic and multipotent pericytes from hPSC can be used for the development of vasculogenic models using multiple vasculogenic cell types for basic research and drug screening and can contribute to angiogenic regenerative medicine. (Circulation. 2012;125:87-99.)Key Words: pluripotent stem cells Ⅲ ischemia Ⅲ mesenchymal stem cells Ⅲ pericytes Ⅲ vasculature I n adult tissues, the majority of blood vessels are composed of 3 layers including a luminal inner monolayer of endothelial cells (EC), tunica intimae, an intermediate muscular layer, tunica media, of smooth muscle cells (SMC) and an outer layer of fibroblast-like adventitial cells and connective tissue components, tunica adventitia. Microvessels, including capillaries, precapillary arterioles, postcapillary venues, and collecting venules are composed of internal endothelial layer surrounded by outer coverage of pericytes (also known as Rouget cells or mural cells). 1 Both perivascular SMC and pericytes have been shown to function as critical regulators of vascular development, stabilization, maturation, and remodeling mediated by transforming growth factor ␤ (TGF-␤), platelet-derived growth factor B, or angiopoietin-1. 2,3 Although related in function and anatomic localization, pericytes can be distinguished from SMC on the basis of their characteristic morphology and specific cell marker expression: Whereas SMC form a separate layer of the tunica media in blood vessels, pericytes are physically embedded within the endothelial basement membrane to promote mutual communication with the underlying endothelium. 4 In addition, SMC and the majority of pericytes in multiple human and murine tissue types express ␣-smooth muscle actin (␣-SMA), which is involved in regulatio...

Sudden cardiac death caused by ventricular arrhythmias is a disastrous event, especially when it occurs in young individuals. Among the five major arrhythmogenic disorders occurring in the absence of a structural heart disease is catecholaminergic polymorphic ventricular tachycardia (CPVT), which is a highly lethal form of inherited arrhythmias. Our study focuses on the autosomal recessive form of the disease caused by the missense mutation D307H in the cardiac calsequestrin gene, CASQ2. Because CASQ2 is a key player in excitation contraction coupling, the derangements in intracellular Ca2+ handling may cause delayed afterdepolarizations (DADs), which constitute the mechanism underlying CPVT. To investigate catecholamine-induced arrhythmias in the CASQ2 mutated cells, we generated for the first time CPVT-derived induced pluripotent stem cells (iPSCs) by reprogramming fibroblasts from skin biopsies of two patients, and demonstrated that the iPSCs carry the CASQ2 mutation. Next, iPSCs were differentiated to cardiomyocytes (iPSCs-CMs), which expressed the mutant CASQ2 protein. The major findings were that the β-adrenergic agonist isoproterenol caused in CPVT iPSCs-CMs (but not in the control cardiomyocytes) DADs, oscillatory arrhythmic prepotentials, after-contractions and diastolic [Ca2+]i rise. Electron microscopy analysis revealed that compared with control iPSCs-CMs, CPVT iPSCs-CMs displayed a more immature phenotype with less organized myofibrils, enlarged sarcoplasmic reticulum cisternae and reduced number of caveolae. In summary, our results demonstrate that the patient-specific mutated cardiomyocytes can be used to study the electrophysiological mechanisms underlying CPVT.