S. M. Majka et al. from University of Colorado reported in the August 2nd online edition of PNAS isolating and characterizing a subset of white adipocytes which are bone marrow-derived progenitor (BMP) cells which are not of mesenchymal origin. The investigators postulated that since bone marrow-derived cells do not circulate in the blood, these subset of white adipocytes were derived from cells of hematopoietic origin (meyloid lineage). With Cd45+, Lin+ Lac-Z-expressing cells from male donors, the researchers were able to conduct lineage tracing assays to determine the origin of the white adipocytes in various fat tissue compartments in female mice. Global gene expression analysis showed that BMP-derived adipocytes differed from conventional white and brown fat cells with decreased biogenesis, lipid oxidation, and upregulating inflammatory genes. The investigators also noted gender and age differences in which BMP-derived adipocytes accumulate with age, higher numbers in visceral than subcutaneous fat, and in female versus male mice. The authors concluded that fat cells derived from the myeloid lineage "account in part for adipose depot heterogeneity and detrimental changes in adipose metabolism and inflammation with aging and adiposity."

In the June 24th online edition of Stem Cells, V. L. Battula et al. from the University of Texas M.D. Anderson Cancer Center, reported their study on induction of epithelial-to-mesenchymal transition (EMT) in breast epithelial cells. The investigator noted that EMT normally is an embryonic process which is latent in normal adult tissues and diagnostic for aggressive metastatic breast cancers. The researchers conducted experiments in which ectotopic expression of Twist, Snail or TGF-β in immortalized human mammary epithelial cells can induced EMT and endow the cells with mesenchymal stem cell (MSC) traits. Similar to MSCs, these EMT-derived cells were CD44+, CD24-, CD45-, and CD140b+ (PDGFR-β). In vitro differentiation revealed EMT-derived cells could differentiate into adipocytes, chrondrocytes, and osteoblasts. Additionally, the investigators showed that EMT-derived homed in vivo toward wound sites and in vitro the cells migrated toward breast cancer cells, similar to MSCs. The authors concluded from their study results that "EMT-derived cells are similar to MSCs in gene expression, multilineage differentiation, and ability to migrate towards tumor cells and wound sites."

In the June 4th issue of Cell Stem Cell, Y. A. Zeng & R. Nusse from Stanford University School of Medicine reported isolating a Wnt-responsive subpopulation of stem cells in adult mammary glands. In cell cultures, Wnt protein was shown to expand clonally mammary stem cells for many generations. Additionally, mutants for the negative-feedback regulator, Axin2, were sensitized to Wnt signals and found to have a competitive advantage in mammary gland reconstitution assays. Transplantation assays of clonally expanded cells exposed to Wnt proteins maintained their ability to generate functional mammary glands. The authors concluded that "Wnt proteins serve as rate-limiting self-renewal signals acting directly on mammary stem cells."

In the April 27th online edition of the Journal of Cellular and Molecular Medicine, A. C. Gittenberger-de Groot et al. from the Leiden University Medical Center (Netherlands) identified a subpopulation of pluripotent epicardium-derived stem cells following epithelial-mesenchymal transition (EMT) during development of the proepicardia. The investigators reported from their observations that the EPDCs had the potential to differentiate into interstitial fibroblasts, coronary smooth muscle cell and adventitial fibroblast. The researchers also speculated that EPDCs may have the potential to differentiate into cardiomyocytes and endothelial cells suggesting that they may also comprise the cardiac stem cell niche. When adult-derived EPDCs were transplanted into animals with myocardial ischemia, the experimental results revealed improved cardiac function, angiogenesis and decreased tissue necrosis following implantation. Additionally, it was reported that combining EPDCs and adult cardiomyocyte progenitor cells had a synergistic effect in animals with myocardial ischemia. The authors noted that "reactivation of the endogenous epicardium in ischemia with re-expression of developmental genes and renewed EMT marks the onset of a novel therapeutic focus."

In the April 28th online edition of Stem Cells, E. Bachelard-Cascales et al. from the Université de Lyon (France) reported their study results in identifying a regulatory role for CD10 as a key factor for maintaining the stem cell compartment in the mammary ductal tree. CD10 is a zinc-dependent metalloprotease which is known to regulate growth of the ductal tree during mammary gland development. With FACS analysis, the investigators found that sorting for CD10 and EpCAM resulted in an enriched population of progenitor and mammosphere-forming cells with a CD10^high EpCAM^low phenotype. Moreover, sorting for CD10 alone resulted in an enriched subpopulation of sphere-forming cells. In vitro assays also demonstrated that protease activity of CD10 concomitant with adhesion of β1-integrin are required to prevent differentiation of mammary progenitors. The authors concluded from their study that their data suggest that "integrin-mediated contact with the basement membrane and cleavage of signaling factors by CD10 are key elements in the (stem cell) niche that maintains the progenitor and stem cell pools in the mammary lineage."

In the April issue of Stem Cells and Development, C. V. Borlongan et al. from the Univ. of South Florida College of Medicine reported their study results in which they demonstrated the presence of pluripotent stem cells in human menstrual blood. Immunohistochemical assays of cultured menstrual blood revealed that the cells expressed the pluripotent stem cell markers Oct4, SSEA, and Nanog. In conditioned media, the cultured cells expressed the neuronal markers Nestin and MAP2. In co-culture experiments, the investigators found that media from menstrual blood-derived cultures exposed to primary rat neurons from oxygen glucose-deprived animals contained trophic factors such as VEGF, BDNF and NT-3, which were upregulated. Transplantation of the menstrual stem cells intracerebrally or intravenously into rats with induced experimental stroke resulted in reduced behavioral impairment as a reduction in tissue damage compared to vehicle controls. The authors concluded that "menstrual blood-derived cells exemplify a source of 'individually tailored' donor cells that completely match the transplant recipient, at least in women."

In April 7th online edition of Stem Cells, K. Marynka-Kalmani et al. from the Faculty of Medicine in Tel Aviv reported the identification of a novel population of robust stem cells isolated from the lamina propia of the oral muscosa (OMLP cells). These cells expressed the pluripotency transcription factors Oct4 and Sox2 as well as p75. The investigators reported they could isolate trillions of cells from a 4x2x1 mm biospy, irrespective of the donor's age. The freshly isolated cells were also found to differentiate in vitro into all three germ layer lineages. The researchers further noted that, surprisingly, the stem cells from the oral mucosa (OMSCs) formed tumors consisting of two germ layers-derived tissues when treated with dexamethasone and subsequently implanted into SCID mice. These tumors consisted of tissues (cartilage, bone, fat, striated muscle and neural tissue) normally produced by neural crest cells during embryogenesis. The authors concluded from their observations that "OMLP harbors a primitive stem cell population with distinct primitive neural crest-like phenotype and identifies the in vivo localization of putative ancestors for this population."

In the February issue of Nature Cell Biology, A. W. B. Joe et al. from the University of British Columbia reported their experimental results describing a new subpopulation of fibro/adipogenic progenitors (FAPs) in adult skeletal muscle. The investigators found that the FAPs differentiated into adipocytes and generated ecotopic white fat when administered subcutaneously or intramuscularly in a mouse model having fatty infiltration of the muscle. However, when the FAPs are transplanted into healthy muscle they are quiescent and proliferate only in response to tissue damage. In vitro co-cultivation data revealed that proliferating FAPs enhance the rate of differentiation of myogenic progenitors. The authors concluded from their observation that FAPs as "transient source of pro-differentiation signals" for activated and proliferating myogenic progenitors as part of the wound-healing response in muscle.

French scientists, K. J. Mitchell et al., from the Université Pierre et Marie Curie Paris VI published in the January 31st online edition of Nature Cell Biology identifying a subpopulation of myogenic progenitor cells which contribute to muscle generation. The investigators found these myogenic progenitors reside in the interstitium and expressed the stress mediator PW1. However, these interstitial cells (PICs) did not express Pax7. In vitro studies demonstrated that Pax7 mutant satellite cells demonstrated robust myogenic potential. Additionally, in vivo studies revealed that the PICs generated satellite cells while Pax7 mutant PICs were not myogenic and accumulated in the muscle tissues during postnatal development. The authors concluded from their observations that they identified a PW1+/Pax7- subpopulation of muscle progenitors while defining "a key role for Pax7 in a non-satellite cell population during postnatal muscle growth."

In the January 22nd online edition of Stem Cells, P-T Lee et al. from the National Yang-Ming Univ. School of Medicine (Taiwan) reported their study results on isolating adult mouse kidney progenitors (MKPC) and characterizin their physical and functional characteristics in vitro and in vivo. The investigators reported that the isolated spindle-shaped MKPCs were able to undergo 100 passages without cell senescence and expressed the markers Oct4, Wnt4, WT-1, vimentin, alpha-smooth actin, CD29, S100A4 (but not SSEA-1), and c-kit. The cells were harvested from the interstitium of the medulla and papulla. They had the potential to differentiate into endothelial cells and osteoblasts in vitro. MKPC were able to rescue inschemic renal damage via intra-renal injection. Seven days post-administration the researchers reported MKPCs forming blood vessels as well as contributing to the regeneration of renal tubules. Additionally, it was demonstrated that MKPC treatment reduces mortality in mice following renal ischemic injury. The authors concluded that the isolated MKPCs "represent a multipotent adult stem cell population, which may contribute to the renal repair and prolong survival after ischemic injury."