Abstract
Recent discovery of resident cardiac stem cells (CSCs), capable of cardiac lineage differentiation and paracrine mediated effects, suggest promise for cardiac tissue repair. The best site in the heart for obtaining CSCs remains to be determined. We therefore aim to investigate the differences between CSCs isolated from the right atrial appendage (RAA) and the left ventricle (LV) in patients undergoing on-pump cardiac surgery.
Isolated CSCs were characterized using flow cytometry for the CSC specific surface markers CD90 and CD105. Hematopoietic lineage cells were identified using the CD34 surface marker. To date, approximately 80% of isolated cells (n=10) have been confirmed to be CD34 negative and CD105 positive. To exclude fibroblast contamination, immunofluorescence was performed to detect the expression of β-MHC, confirming the ability of the CSCs to differentiate into a cardiomyocyte lineage.
Typically, administered CSCs undergo massive cell death in the first six weeks. Therefore, survival and paracrine factor production under conditions mimicking the microenvironment of the myocardial infarct territory were investigated. This involved measuring levels of apoptosis and production of important paracrine factors, SDF-1α and VEGF-A under conditions of hypoxia (1% O2) and serum starvation for 3 days. This was done via a luminescent caspase 3/7 assay and sandwich ELISA respectively. Results show (n = 3) lower relative caspase activity for RAA compared to LV at a ratio of 0.88 (95% CI 0.71 to 1.07, p = 0.107) and in the setting of serum starvation, hypoxia had a protective effect at a ratio of 0.79 and 0.87 for RAA and LV respectively (95% CI 0.56 to 1.11, p = 0.149 and 95% CI 0.79 to 0.95, p = 0.027). The relative expansion potential was also observed over the first 8 weeks (n=3). However, no statistically significant difference between RAA and LV expansion potential was shown. This is a preliminary study, establishing a foundation for a fair head-to-head comparison of RAA and LV. It is my hope that data collection will continue and with more statistical power, stronger statements will be made about either the equivalency, or the superiority of, one or the other cell types.¬