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The erythroid response to acute anemia relies on the rapid expansion in the spleen of a specialized population of erythroid progenitors termed stress BFU-E. This expansion requires BMP4/Madh5-dependent signaling in vivo; however, in vitro, BMP4 alone cannot recapitulate the expansion of stress BFU-E observed in vivo, which suggests that other signals are required. In this report we show that mutation of the Kit receptor results in a severe defect in the expansion of stress BFU-E, indicating a role for the Kit/SCF signaling pathway in stress erythropoiesis. In vitro analysis showed that BMP4 and SCF are necessary for the expansion of stress BFU-E, but only when spleen cells were cultured in BMP4 + SCF at low-oxygen concentrations did we recapitulate the expansion of stress BFU-E observed in vivo. Culturing spleen cells in BMP4, SCF under hypoxic conditions resulted in the preferential expansion of erythroid progenitors characterized by the expression of Kit, CD71, and TER119. This expression pattern is also seen in stress erythroid progenitors isolated from patients with sickle cell anemia and patients with beta-thalassemia. Taken together these data demonstrate that SCF and hypoxia synergize with BMP4 to promote the expansion and differentiation of stress BFU-E during the recovery from acute anemia.

Adaptive transcriptional responses to oxygen deprivation (hypoxia) are mediated by the hypoxia-inducible factors (HIFs), heterodimeric transcription factors composed of two basic helix-loop-helix-PAS family proteins. The transcriptional activity of HIF is determined by the hypoxic stabilization of the HIF-alpha proteins. HIF-1alpha and HIF-2alpha exhibit high sequence homology but have different mRNA expression patterns; HIF-1alpha is expressed ubiquitously whereas HIF-2alpha expression is more restricted to certain tissues, e.g., the endothelium, lung, brain, and neural crest derivatives. Germ-line deletion of either HIF subunit is embryonic lethal with unique features suggesting important roles for both HIF-alpha isoforms. Global deletion of Hif-2alpha results in distinct phenotypes depending on the mouse strain used for the mutation, clearly demonstrating an important role for HIF-2alpha in mouse development. The function of HIF-2alpha in adult life, however, remains incompletely understood. In this study, we describe the generation of a conditional murine Hif-2alpha allele and the effect of its acute postnatal ablation. Under very stringent conditions, we ablate Hif-2alpha after birth and compare the effect of acute global deletion of Hif-2alpha and Hif-1alpha. Our results demonstrate that HIF-2alpha plays a critical role in adult erythropoiesis, with acute deletion leading to anemia. Furthermore, although HIF-1alpha was first purified and cloned based on its affinity for the human erythropoietin (EPO) 3' enhancer hypoxia response element (HRE) and regulates Epo expression during mouse embryogenesis, HIF-2alpha is the critical alpha isoform regulating Epo under physiologic and stress conditions in adults.

MEK/ERK signaling plays a crucial role in a diverse set of cellular functions including cell proliferation, differentiation and survival, and recently has been reported to negatively regulate mouse embryonic stem cell (mESC) self-renewal by antagonizing STAT3 activity. However, its role in human ESCs (hESCs) remains unclear. Here we investigated the functions of MEK/ERK in controlling hESC activity. We demonstrated that MEK/ERK kinases were targets of fibroblast growth factor (FGF) pathway in hESCs. Surprisingly, we found that, in contrast to mESCs, high basal MEK/ERK activity was required for maintaining hESCs in an undifferentiated state. Inhibition of MEK/ERK activity by specific MEK inhibitors PD98059 and U0126, or by RNA interference, rapidly caused the loss of self-renewal capacity. We also showed that MEK/ERK signaling cooperated with phosphoinositide 3-kinase (PI3K)/AKT signaling in maintaining hESC pluripotency. However, MEK/ERK signaling had little or no effect on regulating hESC proliferation and survival, in contrast to PI3K/AKT signaling. Taken together, these findings reveal the unique and crucial role of MEK/ERK signaling in the determination of hESC cell fate and expand our understanding of the molecular mechanisms behind the FGF pathway maintenance of hESC pluripotency. Importantly, these data make evident the striking differences in the control of self-renewal between hESCs and mESCs.

Conventionally, mesenchymal stem cells (MSC) are generated by plating cells from bone marrow (BM) or other sources into culture flasks and selecting plastic-adherent cells with fibroblastoid morphology. These cells express CD9, CD10, CD13, CD73, CD105, CD166, and other markers but show only a weak or no expression of the embryonic markers stage-specific embryonic antigen-4 (SSEA-4), Oct-4 and nanog-3. Using a novel protocol we prepared MSC from BM and non-amniotic placenta (PL) by culture of Ficoll-selected cells in gelatin-coated flasks in the presence of a serum-free, basic fibroblast growth factor (b-FGF)-containing medium that was originally designed for the expansion of human embryonic stem cells (ESC). MSC generated in gelatin-coated flasks in the presence of ESC medium revealed a four-to fivefold higher proliferation rate than conventionally prepared MSC which were grown in uncoated flasks in serum-containing medium. In contrast, the colony forming unit fibroblast number was only 1.5- to twofold increased in PL-MSC and not affected in BM-MSC. PL-MSC grown in ESC medium showed an increased surface expression of SSEA-4 and frizzled-9 (FZD-9), an increased Oct-4 and nestin mRNA expression, and an induced expression of nanog-3. BM-MSC showed an induced expression of FZD-9, nanog-3, and Oct-4. In contrast to PL-MSC, only BM-MSC expressed the MSC-specific W8B2 antigen. When cultured under appropriate conditions, these MSC gave rise to functional adipocytes and osteoblast-like cells (mesoderm), glucagon and insulin expressing pancreatic-like cells (endoderm), as well as cells expressing the neuronal markers neuron-specific enolase, glutamic acid decarboxylase-67 (GAD), or class III beta-tubulin, and the astrocyte marker glial fibrillary acidic protein (ectoderm). In conclusion, using a novel protocol we demonstrate that adult BM-and neonatal PL-derived MSC can be induced to express high levels of FZD-9, Oct-4, nanog-3, and nestin and are able of multi-lineage differentiation.

Histone lysine methylation has important roles in the organization of chromatin domains and the regulation of gene expression. To analyze its function and modulate its activity, we screened for specific inhibitors against histone lysine methyltransferases (HMTases) using recombinant G9a as the target enzyme. From a chemical library comprising 125,000 preselected compounds, seven hits were identified. Of those, one inhibitor, BIX-01294 (diazepin-quinazolin-amine derivative), does not compete with the cofactor S-adenosyl-methionine, and selectively impairs the G9a HMTase and the generation of H3K9me2 in vitro. In cellular assays, transient incubation of several cell lines with BIX-01294 lowers bulk H3K9me2 levels that are restored upon removal of the inhibitor. Importantly, chromatin immunoprecipitation at several G9a target genes demonstrates reversible reduction of promoter-proximal H3K9me2 in inhibitor-treated mouse ES cells and fibroblasts. Our data identify a biologically active HMTase inhibitor that allows for the transient modulation of H3K9me2 marks in mammalian chromatin.

During development of the neural tube, inhibition of the Notch response as well as the activation of the Sonic Hedgehog (Shh) response results in the formation of neuronal cell types. To determine whether Shh and Notch act independently, we tested the effects of the Notch inhibitor DAPT (N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester) on neuralized, embryonic stem (ES) cell-derived embryoid bodies (EBs), while varying the levels of Shh pathway activation. Shh-resistant EBs were derived from Smo null ES cells, while EBs with constitutive high level of Shh pathway activation were derived from Ptc1 null ES cells. Intermediate levels of Shh pathway activation was achieved by the addition of ShhN to the EB culture medium. It was found that DAPT-mediated inhibition of the Notch response resulted in enhanced neuronal differentiation. In the absence of Shh, more interneurons were detected, while the main effect of DAPT on EBs with an activated Shh response was the precocious loss of ventral neuronal precursor-specific markers.

AIM: The recently published REPAIR-AMI and ASTAMI trial showed differences in contractile recovery of left ventricular function after infusion of bone marrow-derived cells in acute myocardial infarction. Since the trials used different protocols for cell isolation and storage (REPAIR-AMI: Ficoll, storage in X-vivo 10 medium plus serum; ASTAMI: Lymphoprep, storage in NaCl plus plasma), we compared the functional activity of BMC isolated by the two different protocols. METHODS AND RESULTS: The recovery of total cell number, colony-forming units (CFU), and the number of mesenchymal stem cells were significantly reduced to 77 +/- 4%, 83 +/- 16%, and 65 +/- 15%, respectively, when using the ASTAMI protocol compared with the REPAIR protocol. The capacity of the isolated BMC to migrate in response to stromal cell-derived factor 1 (SDF-1) was profoundly reduced when using the ASTAMI cell isolation procedure (42 +/- 8% and 78 +/- 3% reduction in healthy and CAD-patient cells, respectively). Finally, infusion of BMC into a hindlimb ischaemia model demonstrated a significantly blunted blood-flow-recovery by BMC isolated with the ASTAMI protocol (54 +/- 6% of the effect obtained by REPAIR cells). Comparison of the individual steps identified the use of NaCl and plasma for cell storage as major factors for functional impairment of the BMC. CONCLUSION: Cell isolation protocols have a major impact on the functional activity of bone marrow-derived progenitor cells. The assessment of cell number and viability may not entirely reflect the functional capacity of cells in vivo. Additional functional testing appears to be mandatory to assure proper cell function before embarking on clinical cell therapy trials.

OBJECTIVE: To investigate the kinetics of myocardial engraftment of bone marrow-derived mononuclear cells (BMNCs) after intracoronary injection using 99mTc-d,l-hexamethylpropylene amine oxime (99mTc-HMPAO) nuclear imaging in patients with acute and chronic anterior myocardial infarction. DESIGN: Nuclear imaging-derived tracking of BMNCs at 2 and 20 h after injection in the left anterior descending (LAD) coronary artery. SETTING: Academical cardiocentre. PATIENTS: Five patients with acute (mean (SD) age 58 (11) years; ejection fraction range 33-45%) and five patients with chronic (mean (SD) age 50 (6) years; ejection fraction range 28-34%) anterior myocardial infarction. INTERVENTIONS: A total of 24.2 x 10(8)-57.0 x 10(8) BMNCs (20% labelled with 700-1000 MBq 99mTc-HMPAO) were injected in the LAD coronary artery. RESULTS: At 2 h after BMNC injection, myocardial activity was observed in all patients with acute (range 1.31-5.10%) and in all but one patient with chronic infarction (range 1.10-3.0%). At 20 h, myocardial engraftment was noted only in three patients with acute myocardial infarction, whereas no myocardial activity was noted in any patient with chronic infarction. CONCLUSIONS: Engraftment of BMNCs shows dynamic changes within the first 20 h after intracoronary injection. Persistent myocardial engraftment was noted only in a subset of patients with acute myocardial infarction.

Remarkably, apoptosis was induced by exposing peritoneal resident macrophages (PRM) of C3H mice, but not other strains of mice, to ionizing radiation. The molecular mechanism of this strain-specific apoptosis in PRM was studied. The apoptosis elicited in C3H mouse PRM 4 h after exposure was effectively blocked by proteasome inhibitors. Irradiation-induced disruption of mitochondrial transmembrane potential and the release of cytochrome c into the cytosol were also suppressed by a proteasome inhibitor but not by a caspase inhibitor. To determine whether the apoptosis occurred due to a depletion of antiapoptotic proteins, Bcl-2 family proteins were examined. Irradiation markedly decreased the level of Mcl-1, but not Bcl-2, Bcl-X(L), Bax, A1, or cIAP1. Mcl-1's depletion was suppressed by a proteasome inhibitor but not by a caspase inhibitor. The amount of Mcl-1 was well correlated with the rate of apoptosis in C3H mouse PRM exposed to irradiation and not affected by irradiation in radioresistant B6 mouse PRM. Irradiation increased rather than decreased the Mcl-1 mRNA expression in C3H mouse PRM. On the other hand, Mcl-1 protein synthesis was markedly suppressed by irradiation. Global protein synthesis was also suppressed by irradiation in C3H mouse PRM but not in B6 mouse PRM. The down-regulation of Mcl-1 expression with Mcl-1-specific small interfering RNA or antisense oligonucleotide significantly induced apoptosis in both C3H and B6 mouse PRM without irradiation. It was concluded that the apoptosis elicited in C3H mouse PRM by ionizing radiation was attributable to the depletion of Mcl-1 through radiation-induced arrest of global protein synthesis.

Differences in clinical outcome of simian immunodeficiency virus (SIV) infection in disease-resistant African sooty mangabeys (SM) and disease-susceptible Asian rhesus macaques (RM) prompted us to examine the role of regulatory T cells (Tregs) in these two animal models. Results from a cross-sectional study revealed maintenance of the frequency and absolute number of peripheral Tregs in chronically SIV-infected SM while a significant loss occurred in chronically SIV-infected RM compared to uninfected animals. A longitudinal study of experimentally SIV-infected animals revealed a transient increase in the frequency of Tregs from baseline values following acute infection in RM, but no change in the frequency of Tregs occurred in SM during this period. Further examination revealed a strong correlation between plasma viral load (VL) and the level of Tregs in SIV-infected RM but not SM. A correlation was also noted in SIV-infected RM that control VL spontaneously or in response to antiretroviral chemotherapy. In addition, immunofluorescent cell count assays showed that while Treg-depleted peripheral blood mononuclear cells from RM led to a significant enhancement of CD4+ and CD8+ T-cell responses to select pools of SIV peptides, there was no detectable T-cell response to the same pool of SIV peptides in Treg-depleted cells from SIV-infected SM. Our data collectively suggest that while Tregs do appear to play a role in the control of viremia and the magnitude of the SIV-specific immune response in RM, their role in disease resistance in SM remains unclear.

Lysophosphatidic acid (LPA) is a naturally occurring phospholipid with growth-factor-like activities [van Corven, Groenink, Jalink, Eichholtz & Moolenaar (1989) Cell 45, 45-54]. We have examined various structural analogues of LPA for their ability to stimulate DNA synthesis in quiescent fibroblasts. When the acyl-chain length is varied, the rank order of mitogenic potency is: 1-oleoyl LPA congruent to 1-palmitoyl LPA greater than 1-myristoyl LPA greater than 1-lauroyl LPA greater than 1-decanoyl LPA; the last compound shows almost no activity over the concentration range tested (1-100 microM). An ether-linked LPA (1-O-hexadecylglycerol 3-phosphate) has much decreased mitogenic activity as compared with the ester-linked analogue at concentrations less than 25 microM, and becomes cytotoxic at higher concentrations. Hexadecylphosphate, which lacks a glycerol backbone, has negligible activity. On a molar basis, diacyl phosphatidic acid (PA) is about equally potent as the corresponding LPA analogue, showing similar acyl-chain-length dependence; the data argue against the possibility that the mitogenic action of PA is due to contaminating traces of LPA. Although the short-chain analogues of LPA and PA fail to antagonize the action of long-chain (L)PAs, the polyanionic drug suramin inhibits LPA- and PA-induced, DNA synthesis in a reversible and dose-dependent manner, at concentrations [IC50 (concn. giving 50% inhibition) approximately 70 microM] that do not affect epidermal-growth-factor-induced DNA synthesis. Suramin appears to act in the early G0/G1 phase of the cell cycle, blocking immediate responses to LPA such as phosphoinositide hydrolysis. We conclude that both LPA and PA can function as growth-promoting phospholipids, with the fatty acid chain length being a major determinant of mitogenic potency.

Neutropenia and neutrophil dysfunction are common in many diseases, although their etiology is often unclear. Previous views held that there was a single ER enzyme, glucose-6-phosphatase-alpha (G6Pase-alpha), whose activity--limited to the liver, kidney, and intestine--was solely responsible for the final stages of gluconeogenesis and glycogenolysis, in which glucose-6-phosphate (G6P) is hydrolyzed to glucose for release to the blood. Recently, we characterized a second G6Pase activity, that of G6Pase-beta (also known as G6PC), which is also capable of hydrolyzing G6P to glucose but is ubiquitously expressed and not implicated in interprandial blood glucose homeostasis. We now report that the absence of G6Pase-beta led to neutropenia; defects in neutrophil respiratory burst, chemotaxis, and calcium flux; and increased susceptibility to bacterial infection. Consistent with this, G6Pase-beta-deficient (G6pc3-/-) mice with experimental peritonitis exhibited increased expression of the glucose-regulated proteins upregulated during ER stress in their neutrophils and bone marrow, and the G6pc3-/- neutrophils exhibited an enhanced rate of apoptosis. Our results define a molecular pathway to neutropenia and neutrophil dysfunction of previously unknown etiology, providing a potential model for the treatment of these conditions.