Human cardiac stem cells are involved in pathological processes

It has been proposed the use of resident stem cells (SCs) for the repair of cardiac injuries. However, several in vivo studies suggested a possible involvement of human cardiac SCs in ageing and disease states, such as heart failure. Therefore, the purpose of our study was to verify whether the population of pluripotent mesenchymal stem cells(PMSC), that we have recently identified as resident in the human heart, changes its properties in pathological states. Methods and Results Small cells (<30mcm) were isolated from left atria of explanted human hearts affected by ischemic cardiomyopathy (Recipient Heart, RH, n=8), and from fragments of donor derived atrial tissue (Donor Heart, DH, n=7). Cells were grown in a medium selective for multipotent cells. Cell lines were obtained from every isolated adult human atrium, but the cloning efficiency was significantly higher in DH with respect to RH (p<0.001). RH and DH cells shared a similar mesenchymal immunophenotype (CD45-/CD34-/CD38-/CD117-/CD133-/HLA-DR-/CD29lo/KDRlo/CD90hi/CD13hi/CD49ahi/CD49bhi) (n=15), and expressed, at protein level, the pluripotent state-specific transcription factors OCT-4 and Nanog. As evaluated by FACS and RT-PCR, only a small fraction of PMSCs (<10%) continue to express the cardiac-specific transcription factors GATA-4, Nkx2.5 and Myocardin. Moreover, when exposed to appropriate differentiation inducing conditions RH and DH PMSCs (n=5), were able to differentiate along an adipogenic, osteogenic, endothelial, myogenic, epithelial and neurogenic fate, as confirmed by immunofluorescence and RT-PCR analyses. Importantly, when cloned at a single cell level, cardiac derived cells retained all these characteristics. Although RH- and DH- derived cell lines possessed telomerase activity (n=15), the average telomeric length, as evaluated by FLOW-FISH, was significantly higher in DH. In conclusion: Cells with a wide differentiation potential can be isolated and grown from atria of DHs and RHs. Although these cells share many important SC features (immunophenotype, pluripotency, clonogenicity, telomerase activity), they differ in terms of telomeric length and growth kinetics, suggesting that pathological processes can impair the resident cardiac SC reservoir.