Abstract-Cardiac myocytes have been traditionally regarded as terminally differentiated cells that adapt to increased work and compensate for disease exclusively through hypertrophy. However, in the past few years, compelling evidence has accumulated suggesting that the heart has regenerative potential. Recent studies have even surmised the existence of resident cardiac stem cells, endothelial cells generating cardiomyocytes by cell contact or extracardiac progenitors for cardiomyocytes, but these findings are still controversial. We describe the isolation of undifferentiated cells that grow as self-adherent clusters (that we have termed "cardiospheres") from subcultures of postnatal atrial or ventricular human biopsy specimens and from murine hearts. These cells are clonogenic, express stem and endothelial progenitor cell antigens/markers, and appear to have the properties of adult cardiac stem cells. They are capable of long-term self-renewal and can differentiate in vitro and after ectopic (dorsal subcutaneous connective tissue) or orthotopic (myocardial infarction) transplantation in SCID beige mouse to yield the major specialized cell types of the heart: myocytes (ie, Key Words: adult stem cell Ⅲ myocardial regeneration and angiogenesis C ardiac myocytes have been traditionally regarded as terminally differentiated cells that adapt to increased work and compensate for disease exclusively through hypertrophy. 1 In the past few years, compelling evidence has accumulated suggesting that the heart has regenerative potential. [2][3][4][5] The origin and significance of the subpopulation of replicating myocytes are unknown; these issues could be relevant to understand the for mechanisms coaxing endogenous cardiomyocytes to reenter the cell cycle and to the search for strategies to transplant cardiac progenitor cells. 6 In fact, although embryonic stem cells have an exceptional capacity for proliferation and differentiation, potential immunogenic, arrhythmogenic, and, particularly, ethical considerations limit their current use. Moreover, autologous transplantation of skeletal myoblasts has been considered because of their high proliferative potential, their commitment to a well-differentiated myogenic lineage, their resistance to ischemia, and their origin, which overcomes ethical, immunological, and availability problems. However, even if phase II clinical trials with autologous skeletal myoblasts are ongoing, several problems related to potentially life-threatening arrhythmia (perhaps reflecting cellular uncoupling with host cardiomyocytes 7 ) must be taken into account when this approach is considered. Furthermore, although cardiomyocytes can be formed, at least ex vivo, from different adult stem cells, the ability of these cells to cross lineage boundaries is currently causing heated debate in the scientific community, 8 with the majority of reports indicating neoangiogenesis as the predominant in vivo effect of bone marrow or endothelial progenitor cells. 9,10 This report describes the identification and...

Stem cells were obtained from deciduous dental pulp of healthy subjects, aged 6-10 years. This stem cell population was cultured, expanded, and specifically selected, detecting using a FACsorter, c-kit, CD34, and STRO-1 antigen expression. Then, c-kit+/CD34+/STRO-1+ cells were replaced in the culture medium added of 20% FBS, leading to osteoblast differentiation. In fact, these cells, after a week, showed a large positivity for CD44, osteocalcin, and RUNX-2 markers. To achieve an adipocytic differentiation, cells, after sorting, were challenged with dexamethason 10(-8) mM in the same culture medium. To obtain myotube fusion, sorted cells were co-cultured in ATCC medium with mouse myogenic C2C12 cells and, after a week, human stem cell nuclei were found to be able to fuse, forming myotubes. Differentiated osteoblasts, as assessed by a large positivity to several specific antibodies, after 30 days of culture and already in vitro, started to secrete an extracellular mineralized matrix, which, 2 weeks later, built a considerable number of 3D woven bone samples, which showed a strong positivity to alkaline phosphatase (ALP), alizarin red, calcein, other than to specific antibodies. These bone samples, after in vivo transplantation into immunosuppressed rats, were remodeled in a lamellar bone containing entrapped osteocytes. Therefore, this study provides strong evidence that human deciduous dental pulp is an approachable "niche" of stromal stem cells, and that it is an ideal source of osteoblasts, as well as of mineralized tissue, ready for bone regeneration, transplantation, and tissue-based clinical therapies.

Numerous stem cell niches are present in the different tissues and organs of the adult human body. Among these tissues, dental pulp, entrapped within the ‘sealed niche’ of the pulp chamber, is an extremely rich site for collecting stem cells. In this study, we demonstrate that the isolation of human dental pulp stem cells by the explants culture method (hD-DPSCs) allows the recovery of a population of dental mesenchymal stem cells that exhibit an elevated proliferation potential. Moreover, we highlight that hD-DPSCs are not only capable of differentiating into osteoblasts and chondrocytes but are also able to switch their genetic programme when co-cultured with murine myoblasts. High levels of MyoD expression were detected, indicating that muscle-specific genes in dental pulp cells can be turned on through myogenic fusion, confirming thus their multipotency. A perivascular niche may be the potential source of hD-DPSCs, as suggested by the consistent Ca2+ release from these cells in response to endothelin-1 (ET-1) treatment, which is also able to significantly increase cell proliferation. Moreover, response to ET-1 has been found to be superior in hD-DPSCs than in DPSCs, probably due to the isolation method that promotes release of stem/progenitor cells from perivascular structures. The ability to isolate, expand and direct the differentiation of hD-DPSCs into several lineages, mainly towards myogenesis, offers an opportunity for the study of events associated with cell commitment and differentiation. Therefore, hD-DPSCs display enhanced differentiation abilities when compared to DPSCs, and this might be of relevance for their use in therapy.