Blood STEM CELLS IN HEMATOLOGY

Hematopoietic origin of hepatic stellate cells in the adult liver

2008-02-08

Hepatic stellate cells are believed to play a key role in the development of liver fibrosis. Several studies have reported that bone marrow cells can give rise to hepatic stellate cells. We hypothesized that hepatic stellate cells are derived from hematopoietic stem cells. To test this hypothesis, we generated chimeric mice by transplantation of clonal populations of cells derived from single enhanced green fluorescent protein (EGFP)–marked Lin^–Sca-1⁺c-kit⁺CD34^– cells and examined the histology of liver tissues obtained from the chimeric mice with carbon tetrachloride (CCl₄)–induced injury. After 12 weeks of CCl₄ treatment, we detected EGFP⁺ cells in the liver, and some cells contained intracytoplasmic lipid droplets. Immunofluorescence analysis demonstrated that 50% to 60% of the EGFP⁺ cells were negative for CD45 and positive for vimentin, glial fibrillary acidic protein, ADAMTS13, and -smooth muscle actin. Moreover, EGFP⁺ cells isolated from the liver synthesized collagen I in culture. These phenotypes were consistent with those of hepatic stellate cells. The hematopoietic stem cell–derived hepatic stellate cells seen in male-to-male transplants revealed only one Y chromosome. Our findings suggest that hematopoietic stem cells contribute to the generation of hepatic stellate cells after liver injury and that the process does not involve cell fusion.

Identification of mesenchymal stem cells in aorta-gonad-mesonephros and yolk sac of human embryos

2008-02-08

Mesenchymal stem cells (MSCs) are multipotent stem cells that can generate various microenvironment components in bone marrow, ensuring a precise control over self-renewal and multilineage differentiation of hematopoietic stem cells. Nevertheless, their spatiotemporal correlation with embryonic hematopoiesis remains rudimentary, particularly in relation to the human being. Here, we reported that human aorta-gonad-mesonephros (AGM) resided with bona fide MSCs. They were highly proliferative as fibroblastoid population bearing uniform surface markers (CD45^–, CD34^–, CD105⁺, CD73⁺, CD29⁺, and CD44⁺), expressed pluripotential molecules Oct-4 and Nanog, and clonally demonstrated trilineage differentiation capacity (osteocytes, chondrocytes, and adipocytes). The frequency and absolute number of MSCs in aorta plus surrounding mesenchyme (E26-E27) were 0.3% and 164, respectively. Moreover, they were functionally equivalent to MSCs from adult bone marrow, that is, supporting long-term hematopoiesis and suppressing T-lymphocyte proliferation in vitro. In comparison, the matching yolk sac contained bipotent mesenchymal precursors that propagated more slowly and failed to generate chondrocytes in vitro. Together with previous knowledge, we propose that a proportion of MSCs initially develop in human AGM prior to their emergence in embryonic circulation and fetal liver.

CD150- side population cells represent a functionally distinct population of long-term hematopoietic stem cells

Weksberg, D. C., Chambers, S. M., Boles, N. C., Goodell, M. A. — 2008-02-08

Hematopoietic stem cells (HSCs) are a self-renewing population of bone marrow cells that replenish the cellular elements of blood throughout life. HSCs represent a paradigm for the study of stem-cell biology, because robust methods for prospective isolation of HSCs have facilitated rigorous characterization of these cells. Recently, a new isolation method was reported, using the SLAM family of cell-surface markers, including CD150 (SlamF1), to offer potential advantages over established protocols. We examined the overlap between SLAM family member expression with an established isolation scheme based on Hoechst dye efflux (side population; SP) in conjunction with canonical HSC cell-surface markers (Sca-1, c-Kit, and lineage markers). Importantly, we find that stringent gating of SLAM markers is essential to achieving purity in HSC isolation and that the inclusion of canonical HSC markers in the SLAM scheme can greatly augment HSC purity. Furthermore, we observe that both CD150⁺ and CD150^– cells can be found within the SP population and that both populations can contribute to long-term multilineage reconstitution. Thus, using SLAM family markers to isolate HSCs excludes a substantial fraction of the marrow HSC compartment. Interestingly, these 2 subpopulations are functionally distinct, with respect to lineage output as well as proliferative status.