Adult cardiac Sca-1-positive cells differentiate into beating cardiomyocytes

Although somatic stem cells have been reported to exist in various adult organs, there have been few reports concerning stem cells in the heart. We here demonstrate that Sca-1-positive (Sca-1+) cells in adult hearts have some of the features of stem cells. Sca-1+ cells were isolated from adult murine hearts by a magnetic cell sorting system and cultured on gelatin-coated dishes. A fraction of Sca-1+ cells stuck to the culture dish and proliferated slowly. When treated with oxytocin, Sca-1+ cells expressed genes of cardiac transcription factors and contractile proteins and showed sarcomeric structure and spontaneous beating. Isoproterenol treatment increased the beating rate, which was accompanied by the intracellular Ca2+ transients. The cardiac Sca-1+ cells expressed oxytocin receptor mRNA, and the expression was up-regulated after oxytocin treatment. Some of the Sca-1+ cells expressed alkaline phosphatase after osteogenic induction and were stained with Oil-Red O after adipogenic induction. These results suggest that Sca-1+ cells in the adult murine heart have potential as stem cells and may contribute to the regeneration of injured hearts.