Antibodies to Stem Cell Marker Antigens Reduce Engraftment of Hematopoietic Stem Cells

GPRASP proteins are critical negative regulators of hematopoietic stem cell transplantation

Hematopoietic stem cell (HSC) transplantation (HSCT) is often exploited to treat hematologic disease. Donor HSCs must survive, proliferate, and differentiate in the damaged environment of the reconstituting niche. Illuminating molecular mechanisms regulating the activity of transplanted HSCs will inform efforts to improve HSCT. Here, we report that G-protein-coupled receptor-associated sorting proteins (GPRASPs) function as negative regulators of HSCT. Silencing of Gprasp1 or Gprasp2 increased the survival, quiescence, migration, niche retention, and hematopoietic repopulating activity of hematopoietic stem and progenitor cells (HSPCs) posttransplant. We further show that GPRASP1 and GPRASP2 promote the degradation of CXCR4, a master regulator of HSC function during transplantation. CXCR4 accumulates in Gprasp-deficient HSPCs, boosting their function posttransplant. Thus, GPRASPs negatively regulate CXCR4 stability in HSCs. Our work reveals GPRASP proteins as negative regulators of HSCT and CXCR4 activity. Disruption of GPRASP/CXCR4 interactions could be exploited in the future to enhance the efficiency of HSCT.

Dynamic roles of angiopoietin-like proteins 1, 2, 3, 4, 6 and 7 in the survival and enhancement of ex vivo expansion of bone-marrow hematopoietic stem cells

Recent advances in hematopoietic stem cells (HSCs) expansion by growth factors including angiopoietin-like proteins (Angptls) have opened up the possibility to use HSCs in regenerative medicine. However, the unavailability of true in vitro HSCs expansion by these growth factors has limited the understanding of the cellular and molecular mechanism of HSCs expansion. Here, we report the functional role of mouse Angptls 1, 2, 3, 4, 6 and 7 and growth factors SCF, TPO, IGF-2 and FGF-1 on purified mouse bone-marrow (BM) Lineage(-)Sca-1(+)(Lin-Sca-1(+)) HSCs. The recombinant retroviral transduced-CHO-S cells that secrete Angptls in serum-free medium were used alone or in combination with growth factors (SCF, TPO, IGF-2 and FGF-1). None of the Angptls stimulated HSC proliferation, enhanced or inhibited HSCs colony formation, but they did support the survival of HSCs. By contrast, any of the six Angptls together with saturating levels of growth factors dramatically stimulated a 3- to 4.5-fold net expansion of HSCs compared to stimulation with a combination of those growth factors alone. These findings lead to an understanding of the basic function of Angptls on signaling pathways for the survival as well as expansion of HSCs in the bone marrow niche.

Homing and long-term engraftment of long- and short-term renewal hematopoietic stem cells

Long-term hematopoietic stem cells (LT-HSC) and short-term hematopoietic stem cells (ST-HSC) have been characterized as having markedly different in vivo repopulation, but similar in vitro growth in liquid culture. These differences could be due to differences in marrow homing. We evaluated this by comparing results when purified ST-HSC and LT-HSC were administered to irradiated mice by three different routes: intravenous, intraperitoneal, and directly into the femur. Purified stem cells derived from B6.SJL mice were competed with marrow cells from C57BL/6J mice into lethally irradiated C57BL/6J mice. Serial transplants into secondary recipients were also carried out. We found no advantage for ST-HSC engraftment when the cells were administered intraperitoneally or directly into femur. However, to our surprise, we found that the purified ST-HSC were not short-term in nature but rather gave long-term multilineage engraftment out to 387 days, albeit at a lower level than the LT-HSC. The ST-HSC also gave secondary engraftment. These observations challenge current models of the stem cell hierarchy and suggest that stem cells are in a continuum of change.

Efficient purification of neonatal porcine gonocytes with Nycodenz and differential plating

Gonocytes are the only type of germ cells present in the postnatal testis and give rise to spermatogonial stem cells. Purification of gonocytes has important implications for the study and manipulation of these cells and may provide insights for the ongoing investigation of the male germline stem cells. To obtain a pure population of gonocytes from piglet testis cells, a wide range of Nycodenz concentrations were investigated for density gradient centrifugation. We also examined differential plating of testis cells for various culture durations with different extracellular matrix (ECM) components (fibronectin, poly-d-lysine, poly-l-lysine, laminin and collagen Types I and IV). Gonocytes were highly enriched in pellets of testis cells after using 17% Nycodenz centrifugation to a purity of 81 ± 9%. After culturing testis cells on plates precoated with different ECM components for 120 min, the proportion of gonocytes increased among non-adherent cells (suspended in the medium), with fibronectin or poly-d-lysine resulting in the greatest (up to 85%) and laminin in the lowest (54%) gonocyte proportion. Combining the most promising ECM coatings (fibronectin and poly-d-lysine) and further extension of their culture duration to 240 min did not improve final gonocyte purity. However, centrifugation with 17% Nycodenz followed by differential plating with fibronectin and poly-d-lysine coating further purified gonocytes among the collected cells to >90%. These results provide a simple, quick and efficient approach for obtaining highly enriched populations of piglet gonocytes for use in the study and manipulation of these germline stem cells.

Neural stem cells: mechanisms of fate specification and nuclear reprogramming in regenerative medicine

Recently, intense interest in the potential use of neural stem cells (NSC) in the clinical therapy of brain disease and injury has resulted in rapid progress in research on the properties of NSC, their innate and directed differentiation potential and the induced reprogramming of differentiated somatic cells to revert to a pluripotent NSC-like state. The aim of this review is to give an overview of our current operational definitions of the NSC lineage, the growing understanding of extrinsic and intrinsic mechanisms, including heritable but reversible epigenetic chromatin modifications that regulate the maintenance and differentiation of NSC in vivo, and to emphasize ground-breaking efforts of cellular reprogramming with the view to generating patient-specific stem cells for cell replacement therapy. This is set against a summary of current practical procedures for the isolation, research and application of NSC, and of the state of the art in NSC-based regenerative medicine of the nervous system. Both provide the backdrop for the translation of recent findings into innovative clinical applications, with the hope of increasing the safety, efficiency and ethical acceptability of NSC-based therapies in the near future.

Flow-cytometric phosphoprotein analysis reveals agonist and temporal differences in responses of murine hematopoietic stem/progenitor cells

Hematopoietic stem cells (HSCs) are probably the best-studied adult tissue-restricted stem cells. Although methods for flow cytometric detection of phosphoproteins in hematopoeitic progenitors and mature cells are available, analogous protocols for HSC are lacking. We present a robust method to study intracellular signaling in immunophenotypically-defined murine HSC/progenitor cell (HPC)-enriched populations. Using this method, we uncover differences in the response dynamics of several phosphoproteins representative of the Ras/MAP-Kinase(K), PI3K, mTOR and Jak/STAT pathways in HSC/HPCs stimulated by Scf, Thpo, as well as several other important HSC/HPC agonists.

Isolation and assessment of long-term reconstituting hematopoietic stem cells from adult mouse bone marrow

Suspensions of multipotent hematopoietic stem cells with long-term repopulating activity can now be routinely isolated from adult mouse bone marrow at purities of 30%. A robust method for obtaining these cells in a single step using multiparameter cell sorting to isolate the CD45(mid)lin(-)Rho(-)SP subset is described here, together with a detailed protocol for assessing their regenerative activity in mice transplanted with single cells. These procedures provide unprecedented power and precision for characterizing the molecular and biological properties of cells with hematopoietic stem cell activity at the single cell level.

Enrichment of putative human epidermal stem cells based on cell size and collagen type IV adhesiveness

The enrichment and identification of human epidermal stem cells (EpSCs) are of paramount importance for both basic research and clinical application. Although several approaches for the enrichment of EpSCs have been established, enriching a pure population of viable EpSCs is still a challenging task. An improved approach is worth developing to enhance the purity and viability of EpSCs. Here we report that cell size combined with collagen type IV adhesiveness can be used in an improved approach to enrich pure and viable human EpSCs. We separated the rapidly adherent keratinocytes into three populations that range in size from 5-7 microm (population A), to 7-9 microm (population B), to > or =9 microm (population C) in diameter, and found that human putative EpSCs could be further enriched in population A with the smallest size. Among the three populations, population A displayed the highest density of beta1-integrin receptor, contained the highest percentage of cells in G0/G1 phase, showed the highest nucleus to cytoplasm ratio, and possessed the highest colony formation efficiency (CFE). When injected into murine blastocysts, these cells participated in multi-tissue formation. More significantly, compared with a previous approach that sorted putative EpSCs according to beta1-integrin antibody staining, the viability of the EpSCs enriched by the improved approach was significantly enhanced. Our results provide a putative strategy for the enrichment of human EpSCs, and encourage further study into the role of cell size in stem cell biology.

Induction of chondrogenesis and superficial zone protein accumulation in synovial side population cells by BMP-7 and TGF-beta1

Synovial cells are known to contain a sub-population of cells with multipotent differentiating capacity including chondrocytes. However, the stem/progenitor cells in synovial cells have not been well characterized. Stem/progenitor cells can exclude Hoechst 33342 dye, and the cell fraction with this property is called "side population (SP)." SP cells are present in many adult tissues. The aim of this investigation was to identify, isolate, and characterize SP cells from bovine synovium. Hoechst dye efflux and fluorescence activated cell sorting showed that synovial cells contained 0.60% SP cells. In the presence of verapamil, an inhibitor of ABC transporters critical for the dye efflux property, the SP cell fraction was not observed, indicating the critical role of ABC transporters. Isoforms of ABC transporters (ABCG2 and ABCB1 mRNA) were highly expressed in SP cells derived from the synovial cells by real-time RT-PCR analysis. Bone morphogenetic protein-7 (BMP-7) induced type II collagen mRNA expression characteristic of chondrogenesis in articular cartilage with both SP and non-SP cells. In addition, expression of SZP mRNA, a marker of the surface layer of articular cartilage, was significantly up-regulated by BMP-7, and the protein accumulation of SZP was stimulated by both BMP-7 and TGF-beta1. Thus, synovial cells contain ABC transporter-dependent SP cells. These findings demonstrate that side population cells of synovium differentiate toward an articular chondrocyte phenotype of the surface layer and have direct implications for tissue engineering and regeneration of articular cartilage.

Exploitation of stem cell homing for gene delivery

Stem cells have been the focus of numerous investigations to treat diseases as far ranging as diabetes, chronic heart failure and multiple sclerosis over the past decade. The process of stem-cell-based repair of acute injury involves homing and engrafting of the stem cell of interest to the site of injury followed by either differentiation of the stem cell to indigenous end-organ cells or liberation of paracrine factors that lead to preservation and/or optimization of organ function. Recognition of the ability of stem cells to home to sites of acute injury suggests that, if appropriately defined and harnessed, stem cell homing could serve as a means of local drug delivery through the infusion of genetically engineering stem cells that secrete gene products of interest. The authors have recently demonstrated the use of this approach in preclinical studies of acute myocardial function. In addition, the use of engineered cells that home to appropriate niches have been used to correct genetic deficiency states (i.e., severe combined immunodeficiency, diabetes mellitus) in patients with otherwise chronic debilitating diseases. This review focuses on exploiting stem cell homing for gene transfer and on the state of the art and the challenges that face the field.