Positive Progenitor Research Articles

Cytokine-immobilized microparticle-coated plates for culturing hematopoietic progenitor cells

The purpose of this study was to provide a culture method for an effective expansion of human CD 34 positive hematopoietic progenitor cells (CD 34 (+) HCs) utilizing low molecular weight heparin/protamine microparticles (LH/P MPs) which can be stably coated onto plastic surfaces and cytokines. CD 34 (+) HCs optimally proliferated on LH/P MP-coated plates in the presence of stem cell factor (SCF; 5 ng/ml), thrombopoietin (Tpo; 10 ng/ml), and Flt-3 ligand (Flt-3; 10 ng/ml) in hematopoietic progenitor growth medium (HPGM). After 6 days, the total cells expanded 16.5-fold. Those cytokines were shown to be partially immobilized on the LH/P MP-coated plates, and the immobilized cytokines were gradually released into the medium with half releasing time of 3-4 days. Since flow cytometry analyses revealed that 90% of initial cells and 44.5% of expanded cells were CD 34 positive, CD 34 (+) HCs were estimated to have increased 8.0-fold after 6 days, and to have increased to over 31.9-fold after 12 days. In contrast, cultured CD 34 (+) HCs on non-coated tissue culture plates increased only 2.9-fold in the identical medium after 6 days, and only 5.2-fold after 12 days.

Circulating Apoptotic Progenitor Cells in Patients with Congestive Heart Failure

BackgroundCirculating CD34+ endothelial progenitor cells (EPCs) are capable of differentiating into mature endothelial cells to assist in angiogenesis and vasculogenesis. We sought to quantify the numbers of apoptotic progenitors in patients with congestive heart failure.Methods and ResultsPeripheral blood mononuclear cells were isolated by Ficoll density-gradient from 58 patients with various degrees of heart failure and 23 matched controls. Apoptosis in progenitor CD34+ cells was assessed using the Annexin V-PE/PI detection kit, and FACS analysis was performed with triple staining for CD34, annexin-V and propidium iodide. The percentage of early and late apoptotic progenitor cells was determined in the subject groups and was correlated with clinical characteristics. While there was no significant difference in total CD34 positive cells or early apoptotic progenitors between control subjects and CHF patients (p = 0.42) or between severe and mild/moderate CHF groups (p = 0.544), there was an elevated number of late apoptotic progenitors in the severe CHF group compared with the mild/moderate CHF group (p = 0.03). Late apoptotic progenitors were significantly increased in CHF patients as compared to matched controls. There was also an inverse correlation between late apoptotic progenitors and ejection fraction (r = −0.252, p = 0.028) as well as a positive association with NYHA class (r = 0.223, p = 0.046).ConclusionSevere heart failure patients exhibited higher numbers of late apoptotic progenitors, and this was positively associated with NYHA class and negatively correlated with ejection fraction. This finding may shed light on the numerous factors governing the pathophysiology of CHF.

Fibroblast sheets co-cultured with endothelial progenitor cells improve cardiac function of infarcted hearts

We have already confirmed that cell sheet transplantation can improve damaged heart function via continuous cytokine secretion. In this study, we hypothesized that cytokine-secreting cell sheets co-cultured with an endothelial cell source may be more effective for repairing ischemic myocardium. Confluent rat fibroblasts cultured on temperature-responsive culture dishes were harvested as contiguous cell sheets by temperature reduction. Green fluorescent protein (GFP)-positive endothelial progenitor cells (EPCs) were seeded on fibroblast sheets to create co-cultured cell sheets, and sandwich-like constructs were engineered by stacking of the co-cultured cell sheets. These constructs were transplanted into rat myocardial infarction models. Cardiac function and histology were assessed in four groups: the sham operation (C) group, the isolated EPC injection (E) group, the transplantation of triple-layer fibroblast sheets (F) group, and the transplantation of triple-layer sandwich-like constructs (E + F) group. Echocardiography showed significant improvement of the fractional shortening in the E + F group in comparison with the C group (0.25 +/- 0.05 vs. 0.16 +/- 0.02). On histological examination, significantly less connective tissue formation was observed in the E, F, and E + F groups when compared to the C group (C, E, F, and E + F groups: 53 +/- 2%, 41 +/- 4%, 40 +/- 4%, and 32 +/- 7%, respectively). Additionally, increased blood vessel formation was detected in the E, F, and E + F groups compared with the C group (C, E, F, and E + F groups: 1.9% +/- 0.6%, 6.7% +/- 0.6%, 7.8% +/- 0.9%, and 10.2% +/- 2.4%, respectively). Furthermore, GFP-staining demonstrated that the newly formed blood vessels were composed of the co-cultured EPCs. Transplantation of cell sheets co-cultured with an endothelial cell source may be a new therapeutic strategy for myocardial tissue regeneration.

Glucocorticoid signaling and exercise-induced downregulation of the mineralocorticoid receptor in the induction of adult mouse dentate neurogenesis by treadmill running

Physical exercise is known to promote adult neurogenesis, although the underlying mechanisms remain unclear. Glucocorticoid (corticosterone in rodents) is a factor that is known to affect neurogenesis. As physical exercise modulates corticosterone secretion, we hypothesized that corticosterone signaling is involved in exercise-induced adult neurogenesis. We chose treadmill running (TR) to accurately define the intensity and duration of exercise. Our results showed that 5 weeks of TR increased the doublecortin (DCX)-positive neuronal progenitor cells (NPCs) in adult hippocampus and transiently increased the serum corticosterone level at the end of the TR protocol. This protocol reduced the levels of hippocampal mineralocorticoid receptor (MR); however, glucocorticoid receptor levels were unaltered. We then investigated whether reducing corticosterone levels by bilateral adrenalectomy (ADX) attenuated the TR-enhanced adult neurogenesis. Our results showed that ADX not only blocked the TR-induced downregulation of MR, but also reduced the number of TR-enhanced NPCs. In order to examine the role of MR downregulation in TR-induced adult neurogenesis, animals were treated repeatedly with a selective MR antagonist, spironolactone, for 3 weeks. The results revealed that spironolactone increased the number of spontaneously occurring and TR-induced NPC in the dentate area. Further analysis revealed that spironolactone treatment did not alter precursor cell proliferation, but increased the number of DCX-positive NPCs, suggesting that blockage of MR signaling either facilitates the differentiation of progenitor cells towards neurons and/or enhances the survival of NPCs. Taken together, the data indicated that induction of NPCs in the dentate area of adult hippocampus by TR is partly due to the downregulation of glucocorticoid/MR signaling, which subsequently enhances differentiation along a neuronal lineage and/or NPC survival.

CC-Chemokine Ligand 20/Macrophage Inflammatory Protein-3α and CC-Chemokine Receptor 6 Are Overexpressed in Myeloma Microenvironment Related to Osteolytic Bone Lesions

The expression of the chemokine CC-chemokine ligand 20 (CCL20)/macrophage inflammatory protein (MIP)-3alpha and its receptor CC-chemokine receptor 6 (CCR6) by multiple myeloma (MM) and microenvironment cells and their potential relationship with osteoclast (OC) formation and osteolytic bone lesions in MM patients was investigated in this study. First, we found that MM cells rarely produce CCL20/MIP-3alpha but up-regulate its production by bone marrow (BM) osteoprogenitor cells and osteoblasts in coculture with the involvement of soluble factors as interleukin-1beta and tumor necrosis factor alpha. MM cells also stimulate both CCL20/MIP-3alpha and CCR6 expression by OCs in coculture. Thereafter, we showed that CCL20/MIP-3alpha significantly increases both the number of multinucleated tartrate-resistant acid phosphatase-positive OCs and receptor activator of nuclear factor-kappaB-positive OC progenitor cells similar to CCL3/MIP-1alpha. Finally, we found that blocking anti-CCL20/MIP-3alpha and anti-CCR6 antibodies significantly inhibits MM-induced OC formation. In vitro data were further expanded in vivo analyzing a total number of 64 MM patients. Significantly higher CCL20/MIP-3alpha levels were detected in MM patients versus monoclonal gammopathy of uncertain significance (MGUS) subjects and in MM osteolytic patients versus nonosteolytic ones. Moreover, a significant increase of CCL20/MIP-3alpha-positive osteoblasts in osteolytic MM patients compared with nonosteolytic ones was observed. Interestingly, no significant difference in BM CCL20/MIP-3alpha expression and level was observed between MGUS and nonosteolytic MM patients. Our data indicate that CCL20/MIP-3alpha and its receptor CCR6 are up-regulated in the bone microenvironment by MM cells and contribute to OC formation and osteolytic bone lesions in MM patients.

Successful elimination of non-neural cells and unachievable elimination of glial cells by means of commonly used cell culture manipulations during differentiation of GFAP and SOX2 positive neural progenitors (NHA) to neuronal cells

BackgroundAlthough extensive research has been performed to control differentiation of neural stem cells – still, the response of those cells to diverse cell culture conditions often appears to be random and difficult to predict. To this end, we strived to obtain stabilized protocol of NHA cells differentiation – allowing for an increase in percentage yield of neuronal cells.ResultsUncommitted GFAP and SOX2 positive neural progenitors – so-called, Normal Human Astrocytes (NHA) were differentiated in different environmental conditions to: only neural cells consisted of neuronal [MAP2+, GFAP-] and glial [GFAP+, MAP2-] population, non-neural cells [CD44+, VIMENTIN+, FIBRONECTIN+, MAP2-, GFAP-, S100β-, SOX2-], or mixture of neural and non-neural cells.In spite of successfully increasing the percentage yield of glial and neuronal vs. non-neural cells by means of environmental changes, we were not able to increase significantly the percentage of neuronal (GABA-ergic and catecholaminergic) over glial cells under several different cell culture testing conditions. Supplementing serum-free medium with several growth factors (SHH, bFGF, GDNF) did not radically change the ratio between neuronal and glial cells – i.e., 1,1:1 in medium without growth factors and 1,4:1 in medium with GDNF, respectively.ConclusionWe suggest that biotechnologists attempting to enrich in vitro neural cell cultures in one type of cells – such as that required for transplantology purposes, should consider the strong limiting influence of intrinsic factors upon extracellular factors commonly tested in cell culture conditions.

Observations on the microvasculature of bone defects filled with biodegradable nanoparticulate hydroxyapatite

The microvascularization of metaphyseal bone defects filled with nanoparticulate, biodegradable hydroxyapatite biomaterial with and without platelet factors enrichment was investigated in a minipig model. Results from morphological analysis and PECAM-1 immunohistochemistry showed the formation of new blood vessels into the bone defects by sprouting and intussusception of pre-existing ones. However, no significant differences were observed in the microvascularization of the different biomaterials applied (pure versus platelet factors-enriched hydroxyapatite), concerning the number of vessels and their morphological structure at day 20 after operation. The appearance of VEGFR-2 positive endothelial progenitor cells in the connective tissue between hydroxyapatite particles was also found to be independent from platelet factors enrichment of the hydroxyapatite bone substitute. In both groups formation of lymphatic vessels was detected with a podoplanin antibody. No differences were noted between HA/PLF- and HA/PLF+ implants with respect to the podoplanin expression level, the staining pattern or number of lymphatic vessels. In conclusion, the present study demonstrates different mechanisms of blood and lymphatic vessel formation in hydroxyapatite implants in minipigs.

Cochlear stem/progenitor cells from a postnatal cochlea respond to Jagged1 and demonstrate that notch signaling promotes sphere formation and sensory potential

Hair cells and supporting cells of the mammalian cochlea terminally differentiate during development. Recent in vitro evidence suggests the presence of hair cell progenitors in the postnatal cochlea. Phenotypic properties of these cells and factors that promote their ability to generate spheres in aggregate cultures have not been reported. We define an in vitro system that allows stem/progenitor cells harvested from the early postnatal cochlea to develop into spheres. These spheres contain Abcg2, Jagged1 and Notch1 positive progenitor cells that can divide and generate new hair cell-like cells, i.e. immunopositive for specific hair cell markers, including Myosin VI, Myosin VIIa, Math1 and ability to uptake FM1-43. We demonstrate that reducing Notch signaling with a gamma secretase inhibitor decreases the number of spheres generated following treatment of the stem/progenitor cell cultures. Additionally, activation of Notch by an exogenous soluble form of a Notch ligand, i.e. Jagged1 protein, promotes sphere formation and the sensory potential of cochlear stem/progenitor cells. Our findings suggest that Notch1/Jagged1 signaling plays a role in maintaining a population of Abcg2 sensory stem/progenitor cells in the postnatal cochlea.

Proteomic and Metabolomic Analysis of Smooth Muscle Cells Derived From the Arterial Media and Adventitial Progenitors of Apolipoprotein E–Deficient Mice

We have recently demonstrated that stem cell antigen 1-positive (Sca-1(+)) progenitors exist in the vascular adventitia of apolipoprotein E-deficient (apoE(-/-)) mice and contribute to smooth muscle cell (SMC) accumulation in vein graft atherosclerosis. Using a combined proteomic and metabolomic approach, we now characterize these local progenitors, which participate in the formation of native atherosclerotic lesions in chow-fed apoE(-/-) mice. Unlike Sca-1(+) progenitors from embryonic stem cells, the resident Sca-1(+) stem cell population from the vasculature acquired a mature aortic SMC phenotype after platelet-derived growth factor-BB stimulation. It shared proteomic and metabolomic characteristics of apoE(-/-) SMCs, which were clearly distinct from wild-type SMCs under normoxic and hypoxic conditions. Among the differentially expressed proteins were key enzymes in glucose metabolism, resulting in faster glucose consumption and a compensatory reduction in baseline interleukin-6 secretion. The latter was associated with a marked upregulation of insulin-like growth factor binding proteins (IGFBPs) 3 and 6. Notably, reconstitution of interleukin-6 to levels measured in the conditioned medium of wild-type SMCs attenuated the elevated IGFBP expression in apoE(-/-) SMCs and their vascular progenitors. This coregulation of apoE, interleukin-6, and IGFBPs was replicated in wild-type SMCs from hypercholesterolemic mice and confirmed by silencing apoE expression in SMCs from normocholesterolemic mice. In summary, we provide evidence that Sca-1(+) progenitors contribute to native atherosclerosis in apoE(-/-) mice, that apoE deficiency and hypercholesterolemia alter progenitor cell behavior, and that inflammatory cytokines such as interleukin-6 act as metabolic regulators in SMCs of hyperlipidemic mice.

Differential expression of the carcinoembryonic antigen-related cell adhesion molecules panCD66, CD66a, CD66c and of sialyl-Lewis x (CD15s) on blast cells of acute leukemias

Expression of CD66 has been reported to occur on blast cells from children with acute lymphoblastic leukemia (ALL), but little is known about the differential expression pattern of panCD66 and other members of the CD66 family on blast cells from patients with acute myeloid leukemia (AML). We have performed flow cytometry immunophenotyping on blast cells from 28 patients with acute myeloid leukemia (AML), 13 patients with B-cell precursor acute lymphoblastic leukemia (BCP-ALL) and 7 patients with T-ALL using monoclonal antibodies (mAbs) against panCD66 (clone D14HD11), CD66a (clone 4.3.17), CD66c (clone 9A6) and CD15s. Expression of the panCD66 mAb was found to be positive in 13 of 28 patients with AML (46%) and in 6 of 13 patients with BCP-ALL (46%) but negative for all the seven patients with T-ALL. In AML, panCD66, CD66a and CD66c were more frequently coexpressed with CD65, CD15 and CD64 than with CD13, CD33 or the two progenitor markers CD34 and CD117. In contrast to CD15, the expression of the sialylated Lewis X (CD15s) was associated with CD117 positivity in the majority of AML cases (64 vs. 85%, P = 0.043). Radioimmunotherapeutic strategies targeting CD66 antigens should consider the heterogeneous expression pattern of CD66 molecules in acute leukemias especially in AML where expression is correlated with mature granulomonocytic cells but not with CD34 and CD117 positive progenitor cells.

Rh antigen expression during erythropoeisis: Comparison of cord and adult derived CD34 + cells

Objectives:Concentrations of O2 and CO2 in the fetal circulation differ to that in maternal blood. Previous studies done in algae demonstrate the functional role of Rh antigen as CO2 transporter. As a preliminary study, it was the aim of this project to compare the expression of Rh polypeptides on cord and adult red blood cell progenitors during ex vivo proliferation and differentiation of CD34+ cells during erythropoeisis.Materials and Methods:CD34 positive hematopoeitic progenitor cells were isolated from umbilical cord blood and adult peripheral blood using an immunomagnetic system and cultured in serum free medium containing erythropoietin in order to compel them along the erythroid lineage. Cultured cells were analyzed for cell surface marker expression by flow cytometry, using monoclonal antibodies to RhAG, Glycophorin A, Rh polypeptides, CD47 and Band 3. Cytospin analysis was also done to study the morphology of cultured cells.Results:The appearance of cell surface markers analyzed on different days of culture varied slightly between samples. There was no evidence to suggest that RhAG, GPA, CD47 and Band 3 expression was any different between adult and cord derived cells. Nevertheless, the results of Rh antigenic expression suggest a reasonable difference between the two groups with adult sample derived cells showing higher and earlier expression than cord blood derived cells. These preliminary findings require further investigation.Conclusion:Comparing the expression of cell surface markers especially Rh polypeptides between adult and cord blood derived erythroid progenitors might assist in discerning their functions and could be valuable in the study of erythropoeisis.

EpCAM expression in normal, non-pathological tissues

Epithelial Cell Adhesion Molecule (EpCAM) is a transmembrane glycoprotein that is associated with various cancers. Most normal, non-pathological epithelial tissue is EpCAM positive with the exception of epidermal keratinocytes, gastric parietal cells, myoepithelial cells, thymic cortical epithelial, and hepatocytes. However, during early liver development EpCAM expression is also observed. In our studies, we have demonstrated that EpCAM is expressed in non-pathological human livers on hepatic progenitors in livers of all donor ages, from 16 weeks gestation fetal livers to adult. Hepatic progenitors of the liver consist of the stem cells and their descendants, the hepatoblasts, that give rise to the hepatocytic and biliary lineages. Both hepatic stem cells and most hepatoblasts express EpCAM, but only hepatoblasts are alpha-fetoprotein positive. The percentage of EpCAM positive progenitors in human livers varies with donor age and is about 2.5% in the adult and 12.1% in fetuses. In vivo, hepatic stem cells have been found associated with the canals of Hering. Xeno-transplantation experiments with EpCAM positive human liver cells have revealed their potential for proliferation and differentiation to mature liver parenchymal cells.

Islet1 cardiovascular progenitors: a single source for heart lineages?

The creation of regenerative stem cell therapies for heart disease requires that we understand the molecular mechanisms that govern the fates and differentiation of the diverse muscle and non-muscle cell lineages of the heart. Recently, different cardiac cell types have been reported to arise from a common, multipotent Islet1 (Isl1)-positive progenitor, suggesting that a clonal model of heart lineage diversification might occur that is analogous to hematopoiesis. The ability to isolate, renew and differentiate Isl1(+) precursors from postnatal and embryonic hearts and from embryonic stem cells provides a powerful cell-based system for characterizing the signaling pathways that control cardiovascular progenitor formation, renewal, lineage specification and conversion to specific differentiated progeny.

Olfactory bulb hypoplasia in Prokr2 null mice stems from defective neuronal progenitor migration and differentiation

New neurons are added on a daily basis to the olfactory bulb (OB) of a mammal, and this phenomenon exists throughout its lifetime. These new cells are born in the subventricular zone and migrate to the OB via the rostral migratory stream (RMS). To examine the role of the prokineticin receptor 2 (Prokr2) in neurogenesis, we created a Prokr2 null mouse, and report a decrease in the volume of its OB and also a decrease in the number of bromodeoxyuridine (BrdU)-positive cells. There is disrupted architecture of the OB, with the glomerular layer containing terminal dUTP nick-end labeling (TUNEL) -positive nuclei and also a decrease in tyrosine hydroxylase-positive neurons in this layer. In addition, there are increased numbers of doublecortin-positive neuroblasts in the RMS and increased PSA-NCAM (polysialylated form of the neural cell adhesion molecule) -positive neuronal progenitors around the olfactory ventricle, indicating their detachment from homotypic chains is compromised. Finally, in support of this, Prokr2-deficient cells expanded in vitro as neurospheres are incapable of migrating towards a source of recombinant human prokineticin 2 (PROK2). Together, these findings suggest an important role for Prokr2 in OB neurogenesis.

Oncogenic Transformation of NIH 3T3 Fibroblasts by BCR-ABL Oncoprotein Requires the IL-3 Receptor.

Abstract Bcr-Abl is a leukemia-inducing protein, which causes oncogenic transformation of myeloid progenitors in Philadelphia chromosome (Ph)-positive chronic myeloid leukemia (CML) and lymphoid progenitors in Ph+ acute lymphoid leukemia (ALL). Oncogenic transformation of hematopoietic cells by the Bcr-Abl oncoprotein directly involves the activation Jak2 tyrosine kinase and the Stat5 transcription factor. Both proteins are normally linked to the IL-3/GM-CSF receptors for growth and survival. Since fibroblastic cells are not targets of BCR-ABL induced oncogenesis, we determined whether forced expression of the IL-3 receptor would allow oncogenic transformation of NIH 3T3 fibroblasts known to be resistant to transformation by BCR-ABL. NIH 3T3 cells transduced with the human IL-3 receptor a and b chains were highly susceptible to oncogenic transformation by expression of BCR-ABL. Forced expression of both receptor chains but not either one alone allowed efficient foci formation of NIH 3T3 cells expressing BCR-ABL, and these cells formed colonies in soft agar whereas BCR-ABL positive NIH 3T3 cells lacking IL-3 receptor expression did not. The Bcr-Abl kinase inhibitor imatinib mesylate (1 mM) and the Jak kinase inhibitor AG490 (10 mM) strongly inhibited agar colony formation. A small molecule inhibitor of Jak2 kinase, 1,2,3,4,5,6-hexabromocyclohexane reported to be specific for Jak2 (Sandberg et al. J. Med. Chem, 2005)-significantly reduced the phosphorylation of Gab2 at the YxxM motif, which is needed for activation of the PI-3 kinase and Akt, two proteins that are part of the Bcr-Abl/Jak2 Network (Samanta et al. Cancer Res, 2006). These findings indicate that Bcr-Abl oncoprotein requires the IL-3 receptor/Jak2/Stat5 pathways for oncogenic transformation of NIH 3T3 fibroblasts, and may explain partially why Bcr-Abl oncogenesis is restricted to hematopoietic malignancies. Furthermore, this cell system in fibroblastic and other cell lineages will provide a model to probe the detailed steps that require IL-3 receptor and Jak2 for Bcr-Abl induced leukemia.

Excessive Isolated Erythrocytosis Linked to Induction of SCL/Tal1 and Erythropoietin Receptor Expression.

Abstract The JAK2 V617F mutation has been detected in more than 90% polycythemia vera patients and is associated with increased erythropoietin (EPO) sensitivity or EPO independence of erythroid progenitor cells during early erythropoiesis. To determine if other molecular lesions give rise to increased erythrocytosis and realizing that the JAK2 V617F mutation may not be the initiating event in polycythemia vera, we identified an individual with isolated, excessive erythrocytosis who showed erythroid precursor hypersensitivity to EPO; no mutations on sequencing genes for erythropoietin receptor (EPO-R), VHL, or HIF-1 IRE; normal serum EPO level; normal hemoglobin function and p50; normal cardiac, hepatic and pulmonary function; no JAK2 V617F mutation and no EPO independent BFU-E. While it was not certain that this individual’s erythrocytosis was lifelong, other relatives had increased hemoglobin levels. The cause of this individual’s increased erythropoiesis was investigated using EPO-stimulated cultures of hematopoietic progenitor cells isolated from peripheral blood. As with normal controls, cell numbers were not increased after 12 days of incubation with low levels of EPO (<0.1 U/ml). With 1U/ml of EPO, cell proliferation was similar to control early in erythropoiesis but increased markedly after 8 days so that by day 12 cell numbers were 3-fold greater than in control cultures with 95% benzidine positive cells compared with 76% for control and 82–87% for JAK2 V617F positive erythroid progenitor cells. Analyses of transcription factor expression revealed that induction of GATA-1 and down regulation of GATA-2 were similar to control. However, SCL/Tal1 and EKLF markedly increased beginning at day 8 to 10 and continued to rise during late erythropoiesis in contrast to control and JAK2 V617F positive cultures in which SCL/Tal1 and EKLF peaked at day 10 and decreased with late erythroid differentiation. Since increased beta-globin expression is concomitant with induction of EKLF, the rise in EKLF may account for the marked increase in benzidine positive cells from our subject. Moreover, expression of EPO-R followed the continuing rise in SCL/Tal1, increasing by 3.5 fold at day 12 compared with control cultures. This high EPO-R expression is consistent with the dramatic increase in cell proliferation during late erythropoiesis. Using forced expression of SCL/Tal1, reporter gene assay and gel mobility shift analysis in erythroid cells, we determined that SCL/Tal1 is able to bind to E-boxes located 3′ of the EPO-R proximal promoter and to activate transcription. Although EPO stimulation of erythroid progenitor cells activates EPO-R, we found that forced expression of EPO-R in primary erythroid progenitor cells in the presence of EPO increases expression of GATA-1 as well as SCL/Tal1 and EKLF, providing further evidence that specific increase in SCL/Tal1 but not GATA-1 must precede induction of EPO-R in this case of excessive erythrocytosis. These data demonstrate a link between high level induction of SCL/Tal1 expression and increased erythrocytosis and suggest a mechanism that contributes to increased erythropoietin sensitivity during late erythropoiesis.

Reversible Transplantable Chronic Phase CML-Like Disease in SCLtTA/BCR-ABL Transgenic Mice.

Abstract Chronic myeloid leukemia (CML) is a disorder arising from the transformation of hematopoietic stem cells (HSC). Treatment with kinase inhibitors eradicates BCR-ABL positive progenitors but spares quiescent leukemic HSC (Copland et al. Blood 2006, Hu et al. PNAS 2006). The exact mechanism of this discrepancy is unknown. To better characterize the biology of CML stem cells in vivo, we have previously generated an inducible transgenic mouse model in which stem-cell specific expression of BCR-ABL leads to chronic phase CML-like disease. Here, we followed these mice non-invasively using positron emission tomography (FDG-PET) and abdominal high-resolution ultrasound. Moreover, we performed bone marrow transplants to analyze whether the disease is cell-autonomous and whether the phenotype of the disease is affected by the scheduling of BCR-ABL induction or the donor cell type. Splenomegaly was detectable as early as day 7 in induced double-transgenic SCLtTA/BCR-ABL mice, with an increase of the percentage of Gr-1+/Mac-1+ myeloid cells in spleen and bone marrow. Splenomegaly and myeloid cell proliferation progressed, and there was a close correlation between in vivo ultrasound measurements of the spleen and splenic weights upon autopsy. FDG-PET analysis demonstrated enhanced glucose uptake in the bone marrow suggestive of hyperproliferation. In addition, both FDG-PET and ultrasound revealed abnormalities of the small intestine, characterized by increased FDG uptake and distension of the intestinal wall. Upon autopsy, the small intestine showed an increased infiltration by granulocytic cells. These phenotypic changes were also evident in mice transplanted with cells from the bone marrow of double-transgenic sibling mice and were reversible upon tetracycline re-administration, demonstrating that this abnormality arises from bone marrow cells and is not due to expression of the oncogene outside of the hematopoietic system. We analyzed whether pre-transplant induction of BCR-ABL affected the repopulation potential of HSC or the disease phenotype. When recipient mice receiving unfractionated bone marrow cells from 3-week induced donor mice were compared with non-induced donors, there was no difference in the development of neutrophilia, myeloproliferation, or splenomegaly. However, when FACS-sorted LinnegSca-1+c-kit+ HSC were used as donor cells, the disease latency increased from 8 to 11 weeks post-transplant, and the increase of Gr-1+Mac-1+ cells in the spleen was less pronounced than in mice receiving unfractionated bone marrow. In conclusion, this model reliably and efficiently demonstrates transplantable reversible chronic phase CML-like disease and may thus be valuable for the in vivo analysis of CML stem cell biology and susceptibility to stem-cell directed anti-leukemic therapies.

Abstract 421: Injection Of Self-assembled Nanopeptides With Clonal Cardiac Sca-1 Positive Cells Improve Cardiac Function After Myocardial Infarction

Biological scaffolds have been reported to offer microenvironment for the transplanted cells, support the cell survival and maintain the release of paracrine factors. However, it is still unknown what kinds of cell sources, scaffolds and their delivery methods are suitable for myocardial repair. Self-assembled nanopeptides, Puramatrix (PM), have been reported to be superior to the other scaffolds in terms of its animal free origin, biodegradability and non-immunogenic properties, which are prerequisite for the clinical application. To examine whether cell transplantation with PM can restore the cardiac function of C57BL/6 mouse myocardial infarction (MI) models, we injected the cell-PM complex into the peri-MI area and then overlay a thick hydrogel patch on the MI area. The mice were divided into following groups according to the transplanted cell types and matrices; bone marrow mononuclear cells with PM (BM/PM), clonal Sca-1 positive cardiac progenitors with PM (cSca-1/PM) and PM alone (PM). Non-treated MI models (Cont) were prepared as controls. Infarct area was examined by Masson trichrome staining and cardiac dimension and function were examined by echocardiography two weeks after transplantation. cSca-1/PM and PM attenuated ventricular enlargement in comparison with BM/PM and Cont (left ventricular diastolic dimension: cSca-1/PM 4.9 ± 0.6 mm, PM 5.3 ± 1.0 mm, BM/PM 6.6 ± 0.1 mm, Cont 6.1 ± 0.1 mm). Fractional shortening of cSca-1/PM and PM were higher than that of BM/PM and Cont (cSca-1/PM 14 ± 3.2%, PM 13 ± 2.3%, BM/PM 8.0 ± 2.5%, Cont 9.9 ± 3%). Infarct area of cSca-1/PM was smaller than that of BM/PM, PM and Cont (cSca-1/PM 36 ± 12%, BM/PM 50 ± 3.1%, PM 53 ± 18%, Cont 57 ± 4.0%). To elucidate the mechanisms of the beneficial effects of cSca-1/PM complex on the infarct area, the number of CD31 positive capillary was examined by immunohistochemical method. Capillary density in the infarct area of cSca-1/PM was higher than that of PM (cSca-1/PM 15%, PM 8%). In summary, transplantation of cSca-1 in combination with PM prevents cardiac remodeling, improves cardiac contraction and reduces infarct area partially through angiogenesis. Cell therapy with PM may enable us to circumvent the current problem in the efficiency of tissue engineering-based cell therapy.

Abstract 940: C-kit Positive Cardiac Progenitor Cells Contribute to the Embryonic Development of the Heart

Recently, a compartment of c-kit positive cardiac progenitor cells (CPCs) has been identified in the adult mouse heart. Whether CPCs are restricted to the adult myocardium or are present throughout ontogenesis and contribute to heart development is unknown. For this purpose, a transgenic mouse in which EGFP was driven by the c-kit promoter was employed. C-kit-EGFP positive cells were present in the heart at all stages of embryonic and fetal development, and their number increased with time reaching 400 cells at E17. Symmetric and asymmetric division of c-kit-positive cells was identified respectively by the uniform and non-uniform localization of the endocytic proteins, Numb and α-adaptin. The presence of symmetric and asymmetric division was consistent with the rapid expansion of the pool of c-kit positive cells and the simultaneous generation of a committed progeny. A fraction of c-kit-EGFP positive cells expressed the myocyte transcription factors Nkx2.5 and MEF2C or specific sarcomeric proteins, α-sarcomeric actin, β-cardiac actinin, β-myosin heavy chain and troponin T. These findings demonstrated a linear relationship between CPCs and myocyte formation. Importantly, observations by two-photon microscopy showed that c-kit-EGFP positive cells in the forming heart exhibited morphogenic movements. Conversely, c-kit-EGFP positive cells from extracardiac regions or from the yolk sac did not translocate to the developing heart. Importantly, cardiac c-kit positive cells were negative for markers of hematopoietic stem cells CD34 and CD45. When c-kit-EGFP-positive cells were isolated from the embryonic heart and plated in vitro at limiting dilution, they formed single-cell derived clones. Almost all cells in the clones continued to express c-kit and EGFP. However, few cells located at the periphery of the clones were no longer positive for c-kit and EGFP and began to express sarcoplasmic proteins. In conclusion, c-kit positive cells in the developing myocardium exhibit the properties of stem cells; they are clonogenic and self-renewing and participate in the growth of the embryonic and fetal heart.

The development of rat Leydig cell progenitors in vitro: how essential is luteinising hormone?

Luteinising hormone (LH) appears to be important for the establishment of the adult-type Leydig cell population. The role of LH in the initial steps of stem Leydig cell/precursor cell differentiation is less clear. The aim of the present study was to elucidate the role of LH in the differentiation of spindle-shaped mesenchymal-like cells into Leydig cell progenitors. Interstitial cells were isolated from rat testes at three different ages reflecting different phases in development, and cultured in the presence of increasing concentrations of LH (ranging from 0.01 to 10 ng/ml). Cells were isolated from 10-day-old rats when stem Leydig cells/precursor cells are abundant; 13-day-old rats when the first 3beta-hydroxysteroid dehydrogenase (3beta-HSD)-positive Leydig cell progenitors have developed in the strain of rats used in this study; and 18-day-old rats just prior to the wave of progenitor proliferation. Immunohistochemistry revealed that before stem Leydig cells differentiate into progenitor cells, they acquire functional LH receptors and become precursor cells. This was confirmed by an in vivo immunohistochemical double-labelling experiment. Addition of LH to the cultures increased the percentage of LH/3beta-HSD-labelled Leydig cell progenitors, while the percentage of cells solely expressing the LH receptor decreased. Cell proliferation was negligible, suggesting that the increase in 3beta-HSD-positive cells is the result of precursor cell differentiation. When interstitial cells were isolated from 13-day-old rats and to a lesser extent from 10-day-old rats, a small proportion of the precursors could develop into progenitor cells independent of the presence of LH. before Leydig stem cells differentiate into 3beta-HSD-positive progenitor cells, they acquire LH receptors and become precursor cells. LH appears to be essential, even at very low doses for the differentiation of these precursor cells into 3beta-HSD-positive progenitors, although a subpopulation of precursor cells can develop into progenitors independently of LH.