Our results challenge the dogma that the adult heart is a postmitotic organ and indicate that the regeneration of myocytes may be a critical component of the increase in muscle mass of the myocardium.

Our results show a high level of cardiac chimerism caused by the migration of primitive cells from the recipient to the grafted heart. Putative stem cells and progenitor cells were identified in control myocardium and in increased numbers in transplanted hearts.

No abstract

The aims of our study were to verify whether it was possible to generate in vitro, from different adult human tissues, a population of cells that behaved, in culture, as multipotent stem cells and if these latter shared common properties. To this purpose, we grew and cloned finite cell lines obtained from adult human liver, heart, and bone marrow and named them human multipotent adult stem cells (hMASCs). Cloned hMASCs, obtained from the 3 different tissues, expressed the pluripotent state-specific transcription factors Oct-4, NANOG, and REX1, displayed telomerase activity, and exhibited a wide range of differentiation potential, as shown both at a morphologic and functional level. hMASCs maintained a human diploid DNA content, and shared a common gene expression signature, compared with several somatic cell lines and irrespectively of the tissue of isolation. In particular, the pathways regulating stem cell self-renewal/maintenance, such as Wnt, Hedgehog, and Notch, were transcriptionally active. Our findings demonstrate that we have optimized an in vitro protocol to generate and expand cells from multiple organs that could be induced to acquire morphologic and func- IntroductionThe presently accumulated evidence indicates that adult bone marrow (BM) contains at least 2 populations of stem cells: hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs), responsible for the generation of the BM microenvironment. 1 Intriguingly, several reports have demonstrated the ability of MSCs to differentiate toward derivatives of germ layers other than mesoderm. [2][3][4][5][6] Although it is still unclear whether widely multipotent cells do exist in vivo and if they play a significant role in tissue repair and turnover, the ability to generate in vitro cells that, under defined culture conditions, display a very high developmental plasticity is nonetheless of important clinical relevance.Until now, the most convincing evidence, although debated, 7 of the possibility to grow in culture a population of widely multipotent cells in humans has been obtained only for BM, 8 while a similar feature has been just postulated for other adult human tissues. 9 We therefore planned to verify if human multipotent adult stem cells (hMASCs) could be produced from other adult human organs on top of BM, and we used this latter as a control/reference tissue.By systematically using a highly reproducible method, we were able to grow in culture cell lines from adult human liver, heart, and BM. These cell lines, once cloned at single-cell level, maintained the in vitro properties of parental lines, including the capability to differentiate into morphologically mature and functionally competent cells, even of tissues embryologically not related to the one of origin.Finally, we performed a comparative in vitro analysis on hMASCs originated from the 3 different sources with respect to immunophenotype, growth kinetics, specific transcriptional settings, telomerase activity, and global gene expression profile. Altogether the obtained result...