The Role of Microenvironment in Preserving the Potency of Adult Porcine Pulmonary Valve Stem Cells In Vitro

BACKGROUND AND OBJECTIVE: The potency of tissue resident stem cells is regulated primarily by inputs from the local microenvironment. Isolation of stem cells through enzymatic digestion of tissue may affect epigenetic regulation of cell fate and performance. Here we employ a non-enzymatic method to harvest and investigate tissue resident stem cells from the adult porcine pulmonary valve. METHODS AND RESULTS: The presence of c-Kit(+) stem cells within the valve tissue was confirmed by immunohistochemistry. An in vitro culture of minced valve leaflets was developed under the standard conditions (37°C with 5% CO(2)). The viability of the cellular outgrowths was evaluated over the subsequent 12 weeks. Under this culture condition, we identified a population of non-adherent c-Kit(+) cells and multiple cellular structures mimicking the phenotype of embryonic stem cells at different stages of development. Formation of multinucleated cells through cell fusion provided an active niche area for homing and interaction of the non-adherent c-Kit(+) cells. Expression of pluripotency markers Oct-4 and Nanog was detected in the newly formed multinucleated cells but not in mature colonies. Partial cell fusion was shown by fluorescent live-cell tracking, which confirmed intercellular molecular exchange between donor and recipient cells, resulting in altered cytoplasmic protein expression by the recipient cell. CONCLUSIONS: These results suggest a role for the microenvironment in decrypting the potential of the valve somatic stem cells in vitro. In addition, our data provide evidence for cell fusion, which may play a critical role in reversing somatic cell fate and spontaneous cellular reprogramming.