Stem cell factor protects c-kit+ human primary erythroid cells from apoptosis

The role of CD71+ erythroid cells in the regulation of the immune response

Complex regulation of the immune response is necessary to support effective defense of an organism against hostile invaders and to maintain tolerance to harmless microorganisms and autoantigens. Recent studies revealed previously unappreciated roles of CD71⁺ erythroid cells (CECs) in regulation of the immune response. CECs physiologically reside in the bone marrow where erythropoiesis takes place. Under stress conditions, CECs are enriched in some organs outside of the bone marrow as a result of extramedullary erythropoiesis. However, the role of CECs goes well beyond the production of erythrocytes. In neonates, increased numbers of CECs contribute to their vulnerability to infectious diseases. On the other side, neonatal CECs suppress activation of immune cells in response to abrupt colonization with commensal microorganisms after delivery. CECs are also enriched in the peripheral blood of pregnant women as well as in the placenta and are responsible for the regulation of feto-maternal tolerance. In patients with cancer, anemia leads to increased frequency of CECs in the peripheral blood contributing to diminished antiviral and antibacterial immunity, as well as to accelerated cancer progression. Moreover, recent studies revealed the role of CECs in HIV and SARS-CoV-2 infections. CECs use a full arsenal of mechanisms to regulate immune response. These cells suppress proinflammatory responses of myeloid cells and T-cell proliferation by the depletion of ʟ-arginine by arginase. Moreover, CECs produce reactive oxygen species to decrease T-cell proliferation. CECs also secrete cytokines, including transforming growth factor β (TGF-β), which promotes T-cell differentiation into regulatory T-cells. Here, we comprehensively describe the role of CECs in orchestrating immune response and indicate some therapeutic approaches that might be used to regulate their effector functions in the treatment of human conditions.

Caspase-8: regulating life and death

Roles for cell death in development, homeostasis, and the control of infections and cancer have long been recognized. Although excessive cell damage results in passive necrosis, cells can be triggered to engage molecular programs that result in cell death. Such triggers include cellular stress, oncogenic signals that engage tumor suppressor mechanisms, pathogen insults, and immune mechanisms. The best-known forms of programmed cell death are apoptosis and a recently recognized regulated necrosis termed necroptosis. Of the two best understood pathways of apoptosis, the extrinsic and intrinsic (mitochondrial) pathways, the former is induced by the ligation of death receptors, a subset of the TNF receptor (TNFR) superfamily. Ligation of these death receptors can also induce necroptosis. The extrinsic apoptosis and necroptosis pathways regulate each other and their balance determines whether cells live. Integral in the regulation and initiation of death receptor-mediated activation of programmed cell death is the aspartate-specific cysteine protease (caspase)-8. This review describes the role of caspase-8 in the initiation of extrinsic apoptosis execution and the mechanism by which caspase-8 inhibits necroptosis. The importance of caspase-8 in the development and homeostasis and the way that dysfunctional caspase-8 may contribute to the development of malignancies in mice and humans are also explored.

Differentiation potential of o bombay human-induced pluripotent stem cells and human embryonic stem cells into fetal erythroid-like cells

Objective

There is constant difficulty in obtaining adequate supplies of blood components, as well as disappointing performance of "universal" red blood cells. Advances in somatic cell reprogramming of human-induced pluripotent stem cells (hiPSCs) have provided a valuable alternative source to differentiate into any desired cell type as a therapeutic promise to cure many human disease.

Materials and Methods

In this experimental study, we examined the erythroid differentiation potential of normal Bombay hiPSCs (B-hiPSCs) and compared results to human embryonic stem cell (hESC) lines. Because of lacking ABO blood group expression in B-hiPSCs, it has been highlighted as a valuable source to produce any cell type in vitro.

Results

Similar to hESC lines, hemangioblasts derived from B-hiPSCs expressed approximately 9% KDR⁺CD31⁺ and approximately 5% CD31⁺CD34⁺. In semisolid media, iPSC and hESC-derived hemangioblast formed mixed type of hematopoietic colony. In mixed colonies, erythroid progenitors were capable to express CD71⁺GPA⁺HbF⁺ and accompanied by endothelial cells differentiation.

Conclusion

Finally, iPS and ES cells have been directly induced to erythropoiesis without hemangioblast formation that produced CD71⁺HbF⁺ erythroid cells. Although we observed some variations in the efficiency of hematopoietic differentiation between iPSC and ES cells, the pattern of differentiation was similar among all three tested lines.

The Notch2-Jagged1 interaction mediates stem cell factor signaling in erythropoiesis

Stem cell factor (SCF), the ligand for the c-kit receptor, is essential for the production of red blood cells during development and stress erythropoiesis. SCF promotes erythroblast proliferation and survival, while delaying erythroid differentiation through mechanisms that are largely unknown. In cultures of primary human differentiating erythroblasts, we found that SCF induces an increase in the expression of Notch2, a member of the Notch family implicated in the control of cell growth and differentiation. Functional inhibition of either Notch or its ligand Jagged1 inhibited the effects of SCF on erythroid cell expansion. SCF also induced the expression of Hes-1 and GATA-2, which may contribute to transduce Notch2 signals in response to SCF. Transduction of primary erythroid precursors with a dominant-negative Notch2 mutant inhibited both basal and SCF-mediated erythroblast expansion, and counteracted the effects of SCF on erythroblast differentiation. These findings provide a clue to understand the effects of increased proliferation and delayed differentiation elicited by SCF on the erythroid compartment and indicate Notch2 as a new player in the regulation of red cell differentiation.

Effective erythropoiesis and HbF reactivation induced by kit ligand in beta-thalassemia

In human beta-thalassemia, the imbalance between alpha- and non-alpha-globin chains causes ineffective erythropoiesis, hemolysis, and anemia: this condition is effectively treated by an enhanced level of fetal hemoglobin (HbF). In spite of extensive studies on pharmacologic induction of HbF synthesis, clinical trials based on HbF reactivation in beta-thalassemia produced inconsistent results. Here, we investigated the in vitro response of beta-thalassemic erythroid progenitors to kit ligand (KL) in terms of HbF reactivation, stimulation of effective erythropoiesis, and inhibition of apoptosis. In unilineage erythroid cultures of 20 patients with intermedia or major beta-thalassemia, addition of KL, alone or combined with dexamethasone (Dex), remarkably stimulated cell proliferation (3-4 logs more than control cultures), while decreasing the percentage of apoptotic and dyserythropoietic cells (<5%). More important, in both thalassemic groups, addition of KL or KL plus Dex induced a marked increase of gamma-globin synthesis, thus reaching HbF levels 3-fold higher than in con-trol cultures (eg, from 27% to 75% or 81%, respectively, in beta-thalassemia major). These studies indicate that in beta-thalassemia, KL, alone or combined with Dex, induces an expansion of effective erythropoiesis and the reactivation of gamma-globin genes up to fetal levels and may hence be considered as a potential therapeutic agent for this disease.

Interstitial cells of Cajal in health and disease. Part II: ICC and gastrointestinal stromal tumours

Mesenchymal tumours in the gastrointestinal tract have long been problematic in terms of diagnosis, prognosis and therapy, but recent advances in immunohistochemistry and related therapies have allowed more specific diagnosis. In particular, the recognition that both the interstitial cells of Cajal (ICC) and many gastrointestinal stromal tumours (GISTs) are positive for c-kit and CD34 and have other features similar to those of ICC has led to the use of imatinib, a novel small molecule therapy that blocks the CD117/c-kit tyrosine kinase receptor, which shows remarkable efficacy in treatment of malignant and metastatic GISTs as well as other malignancies.

Evaluation of the Reactivity of Apoptosis Markers Before and After Cryopreservation in Cord Blood CD34+Cells

Umbilical cord blood (CB) CD34(+) cells, on the basis of flow cytometry analysis, are comprised of multiple populations. In in vitro assays, only CD34(regular) FSC(high) cells are functional and low percentages of nonfunctional CD34(regular) FSC(low) cells were determined to be present in liquid-stored CB. Liquid-stored CD34(regular) FSC(high) cells prior to cryopreservation were judged to be functional by the formation of erythroid and myeloid colonies and transmigration assays. We have further evaluated the occurrence of apoptosis in CB CD34(+) cells using various apoptotic markers to understand better the influence of storage conditions that could be utilized with transplantation of CB. Of the CD34(regular) FSC(low) cells shown in the present study, 20-45% were labeled with the apoptotic reagents annexin-V, fluorescent caspase peptide substrates, and the anti-mitochondrial antibody APO2.7, but these cells were minimally stained with 7-aminoactinomycin-D (7-AAD). These apoptotic reagents identify different cellular targets, indicating the initiation of the apoptotic cascade prior to cryopreservation/thawing. Following cryopreservation and thawing, the apoptotic markers SYTO-16, tetramethyl rhodamine ethyl ester (TMRE), and 7-AAD showed the presence of apoptotic cells. After cryopreservation/thawing, enumeration of CB CD34(+) cells was reduced 10-65% when excluding cells positive for apoptotic markers. We attempted to limit the progression of apoptosis observed after cryopreservation/thawing by the addition of anti-apoptotic reagents z-VAD-fmk (100 microM) and Q-VD-OPH (100 microM) (peptide inhibitors of caspases) without or with the inclusion of survival reagents for CD34(+) cells-stromal-derived factor-1 (SDF-1), stem cell factor (SCF), thrombopoietin, and diprotin A, an inhibitor of CD26 prior to cryopreservation. The expression of apoptosis markers was minimally affected even when using combinations of caspase inhibitors/ CD34(+) cell survival cytokines in an attempt to block apoptosis caused by cryopreservation/thawing. Decreases in apoptosis marker reactivity following cryopreservation were not observed except for a reduced expression of APO2.7 reactivity with z-VAD-fmk and Q-VD-OPH caspase inhibitors. The ability of the inhibitors of apoptosis of CD34(+) cells to generate CFU-GM, CFU-MK, or BFUE colonies was also unaffected except with z-VAD-fmk (100 microM) and Q-VD-OPH (100 microM). The occurrence of apoptosis, as measured by flow cytometry with selected apoptotic markers, suggests a reduction in the number of viable CD34(+) cells.

The Human Orthologue of a Novel Apoptosis Response Gene Induced During Rat Myelomonocytic Stem Cell Apoptosis Maps to 20q13.12

Stem cell factor (SCF) stimulation of the receptor tyrosine kinase c-kit has effects on the proliferation, differentiation, and apoptotic regulation of hematopoietic progenitor cell populations. Rat bone marrow myelomonocytic stem cells (MSC) isolated in vitro by wheat germ agglutinin culture exclusively undergo self-renewal divisions when stimulated by SCF but bipotentially differentiate in the presence of dexamethasone or 1alpha,25-dihydroxyvitamin D(3) to granulocytes and macrophages, respectively. We show here that withdrawal of SCF from MSC induces rapid apoptosis in all stages of the cell cycle accompanied by development of an ultrastructural apoptotic morphology. To investigate immediate-early gene induction during MSC apoptosis, a differential display polymerase chain reaction (DD-PCR) screen coupled with rapid amplification of cDNA ends (RACE) PCR was performed. An immediate-early apoptosis response gene was isolated from growth factor-deprived MSC that was not expressed during self-renewal or differentiation induction cultures containing SCF. The protein contains a PEST region enriched in proline, glutamic acid, serine, and threonine residues common to proteins with a high turnover and has a cytoplasmic, vesicular localization in apoptotic MSC shown by immunohistochemistry. The human orthologous gene, isolated by RACE PCR, shows 86% homology to the rat protein and high similarity with a human uncharacterized hypothalamus predicted protein (HSMNP1) localized to the long arm of chromosome 20. Because deletions in this region are a common occurrence in a wide range of myeloproliferative disorders characterized by treatment resistance to apoptosis, HSMNP1 expression may play a role in normal and pathological myeloid development.

The anaemia of cancer: death by a thousand cuts

Cancer has a negative systemic impact on its host in addition to its local or metastatic effects, and no cancer complication is more ubiquitous than anaemia, a condition for which there is now a specific remedy, the recombinant growth factor erythropoietin. This is not a trivial therapeutic consideration, because cancer-associated anaemia has an adverse influence on survival regardless of tumour type. However, the pharmacological correction of anaemia with recombinant erythropoietin could promote tumour growth, whereas the use of tumour-necrosis factor-alpha (TNFalpha) and TNF-related apoptosis-inducing ligand as antitumour agents could exacerbate anaemia, thereby perpetuating tissue hypoxia and tumour progression.

New pyrazolo[3,4-d]pyrimidines endowed with A431 antiproliferative activity and inhibitory properties of Src phosphorylation

New 4-aminopyrazolo[3,4-d]pyrimidines bearing various substituents at the position 1 and 6, were synthesized. The new compounds showed antiproliferative activity toward A431 cells, were found to be inhibitors of Src phosphorylation, and induced apoptotic cell death. In particular, 2h was a better inhibitor of Src phosphorylation than the reference compound PP2.

Detection of tryptase-, chymase+ cells in human CD34+ bone marrow progenitors

BACKGROUND

Mast cells (MCs) arise from haematopoietic stem cells. We have recently reported that CD34(+) progenitors derived from human bone marrow (BM) develop into tryptase+, chymase+ MCs when cultured in the presence of recombinant human stem cell factor (rhSCF) and recombinant human IL-6 (rhIL-6). In an experiment for the expression of chymase during differentiation, chymase+ cells were detected in human BM, but tryptase+ cells were not found.

OBJECTIVE

The purpose of this study was to show the appearance of chymase+ cells in CD34(+) cells with an origin different from MC differentiation.

METHODS

CD34(+) cells from human BM were sorted with anti-CD117 monoclonal antibody (mAb), and cytospins of CD34(+), CD34(+)CD117(+), or CD34(+)CD117(-) were prepared. These cells were cultured with rhSCF+rhIL-6 for 12 weeks. Some of the cells were subjected to either histological stain with Wright-Giemsa or immunocytochemistry with anti-chymase mAb. Real-time RT-PCR was also performed to compare the transcriptional level of chymase from each cell preparation.

RESULTS

Chymase was expressed in CD34(+) cells as well as human MCs by immunocytochemistry. Substantial CD34(+)CD117(-) cells, but not CD34(+)CD117(+) cells, were stained immunocytochemically with anti-chymase mAb. For 1 week culture with rhSCF+rhIL-6, no cells expressed chymase in any preparation. Real-time RT-PCR revealed positivity for chymase mRNA in CD34(+) cells, but it reduced at 1 week of culture, and increased as cells developed into MCs. Chymase mRNA in CD34(+)CD117(+) cells was negligible compared with that in CD34(+)CD117(-). Tryptase mRNA was below the detectable level in CD34(+) cells, and increased along with MC differentiation. After 12 weeks of culture, CD34(+)CD117(+) developed predominantly into MCs, whereas CD34(+)CD117(-) developed into monocytes/macrophages.

CONCLUSION

Our findings suggested that chymase is present not only in MCs but also in CD34(+)CD117(-) BM progenitors, but that its origin is different from the MC lineage.

Pyrazolo[3,4-d]pyrimidines Endowed with Antiproliferative Activity on Ductal Infiltrating Carcinoma Cells

Novel 1,4,6-trisubstituted pyrazolo[3,4-d]pyrimidines are reported with preliminary in vitro activity data indicating that several of them are potent inhibitors (better than the reference compound) of Src phosphorylation of the breast cancer cells 8701-BC, known to overexpress Src. The ability of such compounds to significantly reduce 8701-BC cell proliferation suggests that this scaffold could be a promising lead for the development of antitumoral agents able to block Src phosphorylation of breast cancer cells.

Stem cell factor protects erythroid precursor cells from chemotherapeutic agents via up-regulation of BCL-2 family proteins

Suppression of red blood cell production is a common complication of chemotherapy, causing anemia in a significant number of cancer patients. We have evaluated the sensitivity of human hematopoietic progenitors and erythroid precursor cells to chemotherapeutic drugs and found that probasophilic erythroblasts represent the stage of erythroid differentiation more vulnerable to the cytotoxic effects of myelosuppressive agents. Stem cell factor (SCF) supports proliferation and survival of early hematopoietic cells by binding to the c-kit receptor. In unilineage erythropoietic culture of CD34+ progenitors, short-term pretreatment of immature erythroid precursors with SCF results in protection from apoptosis induced by chemotherapeutic agents and restores normal proliferation and differentiation after removal of the cytotoxic stimulus. The levels of drug-induced caspase processing are significantly reduced in erythroblasts treated with SCF, indicating that activation of the c-kit receptor generates antiapoptotic signals acting before amplification of the caspase cascade. Accordingly, we found that SCF up-regulates Bcl-2 and Bcl-X L in erythroid precursors and that exogenous expression of these proteins protects erythroblasts from caspase activation and death induced by chemotherapeutic agents. These results suggest a possible mechanism for SCF-mediated protection of erythroid precursor cells from apoptosis and may contribute to devise new strategies for prevention and treatment of chemotherapy-induced anemia.

Stem cell factor increases the expression of FLIP that inhibits IFNgamma -induced apoptosis in human erythroid progenitor cells

Interferon gamma (IFNgamma) acts on human erythroid colony-forming cells (ECFCs) to up-regulate Fas, without a demonstrable change of Fas ligand (FasL) or Fas-associated DD-containing protein (FADD) expression and activates caspase-8 plus caspase-3, which produce apoptosis. Our previous data showed that stem cell factor (SCF) reduced the inhibitory effect of IFNgamma on human ECFCs when both factors were present in the cultures. However, the mechanism by which SCF prevents IFNgamma-induced apoptosis in ECFCs is unclear. In this study we used highly purified human ECFCs to investigate the mechanism of the effect of SCF on IFNgamma-induced apoptosis. Because the binding of FasL to Fas is the first step of the apoptosis cascade and IFNgamma strongly up-regulates Fas expression, we added FasL (50 ng/mL) to the cultures with IFNgamma to accentuate the IFNgamma-induced activation of caspase-8 and caspase-3 plus subsequent apoptosis. SCF (100 ng/mL) clearly inhibited the activation of caspase-8 and caspase-3 induced by IFNgamma and/or FasL, and it also reduced apoptosis as measured by the terminal dUTP nick-end labeling (TUNEL) assay. SCF did not decrease the surface expression of Fas on the ECFCs. FADD-like interleukin 1 beta (IL-1beta)-converting enzyme (FLICE)-inhibitory protein (FLIP) has been reported to interact with FADD and/or caspase-8 at the death-inducing signaling complex (DISC) level following Fas stimulation and acts as a dominant-negative caspase-8. SCF increased FLIP mRNA and protein expression, concomitant with reduced apoptosis, whereas IFNgamma and/or FasL did not change FLIP expression. Reduction of FLIP expression with antisense oligonucleotides decreased the capacity of SCF to inhibit IFNgamma-induced apoptosis, demonstrating a definite role for FLIP in the SCF-induced protection of ECFCs from IFNgamma-initiated apoptosis.

Hematopoietic stem cells and hematopoiesis

BACKGROUND

The highly orchestrated process of blood cell development and homeostasis is termed "hematopoiesis." Understanding the biology of hematopoietic stem cells as well as hematopoiesis is important to developing improved treatments for hematologic malignancies, congenital disorders, chemotherapy-related cytopenias, and blood and marrow transplants.

METHODS

The author reviews the current state of the art regarding hematopoietic stem cells and hematopoiesis.

RESULTS

Several new concepts, including stem cell plasticity, suggest the possibility that stem cells may have the ability to differentiate into other tissues in addition to blood cells.

CONCLUSIONS

While much is known about hematopoietic stem cells and hematopoiesis, much remains to be clarified about the environmental and genetic processes that govern the growth and development of the blood system. In addition, careful studies remain to be conducted to determine whether hematopoietic stem cells can differentiate into extra-hematopoietic tissues.

Stem cell factor: laboratory and clinical aspects

Stem cell factor is an essential haemopoietic progenitor cell growth factor with proliferative and anti-apoptotic functions. Molecular biologists have now dissected some of the various pathways through which this cytokine signals to the nucleus. At the same time, new molecules have become available which can inhibit SCF signalling. This provides an exciting prospect for the treatment of Kit+ malignancies such as acute myeloblastic leukaemia. The capacity of SCF to synergize with other cytokines has been exploited in the ex vivo expansion of haemopoietic progenitors and dendritic cells, which may also hold therapeutic promise. In this review the last 5 years' literature on these issues is reviewed and collated.