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Functional properties of cells obtained from human cord blood CD34⁺ stem cells and mouse cardiac myocytes in coculture

¹Laboratorio di Patologia Vascolare, Istituto Dermopatico dell’ Immacolata, Istituto di Ricovero e Cura a Carattere Scientifico, Rome; ²Laboratorio di Biologia Vascolare e Terapia Genica, Centro Cardiologico Monzino, Istituto di Ricovero e Cura a Carattere Scientifico, Milan; ³Dipartimento di Ginecologia e Ostreticia, Università Cattolica del Sacro Cuore, Rome; ⁴Istituto per la Ricerca sul Cancro, Istituto di Ricovero e Cura a Carattere Scientifico Candiolo, Candiolo; ⁵Dipartimento di Fisiologia Umana e Farmacologia, Università di Roma La Sapienza, Rome; and ⁶Neurophysiology Doctorate Program, Università di Roma La Sapienza, Rome, Italy

Submitted 2 November 2007 ; accepted in final form 24 January 2008

Prior in vitro studies suggested that different types of hematopoietic stem cells may differentiate into cardiomyocytes. The present work examined whether human CD34⁺ cells from the human umbilical cord blood (hUCB), cocultured with neonatal mouse cardiomyocytes, acquire the functional properties of myocardial cells and express human cardiac genes. hUCB CD34⁺ cells were cocultured onto cardiomyocytes following an infection with a lentivirus-encoding enhanced green fluorescent protein (EGFP). After 7 days, mononucleated EGFP⁺ cells were tested for their electrophysiological features by patch clamp and for cytosolic [Ca²⁺] ([Ca²⁺]_i) homeostasis by [Ca²⁺]_i imaging of X-rhod1-loaded cells. Human Nkx2.5 and GATA-4 expression was examined in cocultured cell populations by real-time RT-PCR. EGFP⁺ cells were connected to surrounding cells by gap junctions, acquired electrophysiological properties similar to those of cardiomyocytes, and showed action potential-associated [Ca²⁺]_i transients. These cells also exhibited spontaneous sarcoplasmic reticulum [Ca²⁺]_i oscillations and the associated membrane potential depolarization. However, RT-PCR of both cell populations showed no upregulation of human-specific cardiac genes. In conclusion, under our experimental conditions, hUCB CD34⁺ cells cocultured with murine cardiomyocytes formed cells that exhibited excitation-contraction coupling features similar to those of cardiomyocytes. However, the expression of human-specific cardiac genes was undetectable by RT-PCR.

functional differentiation

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