Lineage-specific hematopoietic growth factors

Kostmann syndrome or infantile genetic agranulocytosis, part two: Understanding the underlying genetic defects in severe congenital neutropenia

Congenital neutropenia in man was first reported 50 years ago by the Swedish paediatrician Rolf Kostmann. He coined the term 'infantile genetic agranulocytosis' for this condition, which is now known as Kostmann syndrome. Recent studies have revealed mutations in ELA-2, encoding the neutrophil granule protease, neutrophil elastase, in autosomal dominant neutropenia, and mutations in HAX-1, encoding an anti-apoptotic protein, in autosomal recessive neutropenia.

CONCLUSION

Future studies should aim to clarify the mechanisms underlying the evolution of secondary malignancies in these patients.

Human hair follicles are an extrarenal source and a nonhematopoietic target of erythropoietin

Erythropoietin primarily serves as an essential growth factor for erythrocyte precursor cells. However, there is increasing evidence that erythropoietin (EPO)/EPO receptor (EPO-R) signaling operates as a potential tissue-protective system outside the bone marrow. Arguing that growing hair follicles (HF) are among the most rapidly proliferating tissues, we have here explored whether human HFs are sources of EPO and targets of EPO-R-mediated signaling. Human scalp skin and microdissected HFs were assessed for EPO and EPO-R expression, and the effects of EPO on organ-cultured HFs were assessed in the presence/absence of a classical apoptosis-inducing chemotherapeutic agent. Here, we show that human scalp HFs express EPO on the mRNA and protein level in situ, up-regulate EPO transcription under hypoxic conditions, and express transcripts for EPO-R and the EPO-stimulatory transcriptional cofactor hypoxia-inducible factor-1alpha. Although EPO does not significantly alter human hair growth in vitro, it significantly down-regulates chemotherapy-induced intrafollicular apoptosis and changes the gene expression program of the HFs. The current study points to intriguing targets of EPO beyond the erythropoietic system: human HFs are an extrarenal site of EPO production and an extrahematopoietic site of EPO-R expression. They may recruit EPO/EPO-R signaling e.g., for modulating HF apoptosis under conditions of hypoxia and chemotherapy-induced stress.

Thrombopoietin promotes β1-integrin–mediated adhesion in hematopoietic cells via the small GTPase Rap1

OBJECTIVE

The interactions between cells and extracellular matrices in the bone marrow microenvironment are critical for normal hematopoiesis, controlling cell survival, proliferation, differentiation, and motility. A number of hematopoietic growth factors and cytokines can mediate these interactions by changing expression and/or activity of specific integrins, or by changing cell shape. Thrombopoietin (TPO) has previously been shown to stimulate adhesion. in certain hematopoietic cell types, although the exact mechanisms by which adhesion is promoted remain elusive.

MATERIALS AND METHODS

The role of TPO in hematopoietic cell adhesion was determined with fibronectin adhesion and binding assays, flow cytometry, and immunocytochemistry using the hematopoietic cell line UT-7/TPO and bone marrow-derived primary mouse megakaryocytes. The role of Rapl in TPO-mediated adhesion was determined using a RaplGAP overexpressing UT-7/TPO cell line, in which Rapl could not be activated.

RESULTS

We found that TPO promoted hematopoietic cell adhesion by causing cytoskeletal reorganization and not by increasing integrin expression, localization, or affinity, as previously hypothesized. Through studies using the UT-7/TPO-RaplGAP cell line, we found that TPO-mediated cell shape change occurred via activation of Rapl.

CONCLUSIONS

These data demonstrate an important role for TPO in mediating interactions in the bone marrow microenvironment and make a significant contribution to our understanding of how TPO may affect hematopoiesis.

Role of thrombopoietin in mast cell differentiation

Mast cells are important elements of the body response to foreign antigens, being those represented either by small molecules (allergic response) or harbored by foreign microorganisms (response to parasite infection). These cells derive from hematopoietic stem/progenitor cells present in the marrow. However, in contrast with most of the other hematopoietic lineages, mast cells do not differentiate in the marrow but in highly vascularized extramedullary sites, such as the skin or the gut. Mast cell differentiation in the marrow is activated as part of the body response to parasites. We will review here the mast cell differentiation pathway and what is known of its major intrinsic and extrinsic control mechanisms. It will also be described that thrombopoietin, the ligand for the Mpl receptor, in addition to its pivotal rule in the control of thrombocytopoiesis and of hematopoietic stem/progenitor cell proliferation, exerts a regulatory function in mast cell differentiation. Some of the possible implications of this newly described biological activity of thrombopoietin will be discussed.

Filgrastim en la enfermedad de Crohn refractaria con absceso intraabdominal

The application of recombinant human granulocyte colony-stimulating factor (filgrastim) seems to be a safe, well tolerated and potentially effective therapy for active Crohn's disease. We report the case of an adolescent boy with Crohn's disease and intra-abdominal abscess associated who had a significant response to treatment with recombinant human granulocyte colony-stimulating factor after all standard treatments had failed.

G-CSF enhances stem cell proliferation in rat hippocampus after transient middle cerebral artery occlusion

Granulocyte colony-stimulating factor (G-CSF) enhances the survival and stimulates the proliferation of neutrophil progenitors. Recently, the neurogenerative effect of G-CSF has been intensely investigated. In this study, we explored the possibility that G-CSF enhanced the cell proliferation in the rat dentate gyrus (DG) after focal cerebral ischemia, using a rat transient middle cerebral artery occlusion (tMCAO) model. At 7 days after tMCAO, the number of 5-bromodeoxyuridine (BrdU)-positive cells in the G-CSF-treated group was significantly increased compared with that in the vehicle-treated group in the ipsilateral SGZ (16.6+/-5.5/mm(2) in the vehicle-treated group versus 33.0+/-7.2/mm(2) in the G-CSF-treated group, **p<0.01) and in the ipsilateral GCL (14.2+/-2.8/mm(2) in the vehicle-treated group versus 21.0+/-3.8/mm(2) in the G-CSF-treated group, *p<0.05). This result showed the possibility of a neurogenerative role of G-CSF after tMCAO in rats.

Potentiation of neurogenesis and angiogenesis by G-CSF after focal cerebral ischemia in rats

Recently, granulocyte colony-stimulating factor (G-CSF) is expected to demonstrate beneficial effects on cerebral ischemia. Here, we showed the potential benefit of G-CSF administration after transient middle cerebral artery occlusion (tMCAO). Adult male Wistar rats received vehicle or G-CSF (50 microg/kg) subcutaneously after reperfusion, and were treated with 5-bromodeoxyuridine (BrdU, 50 mg/kg) once daily by the intraperitoneal route for 3 days after tMCAO. Nissl-stained sections at 7 days after tMCAO showed significant reduction of the infarction area (31%, P<0.01). At 7 days after tMCAO, BrdU plus NeuN double-positive cells increased by 43.3% in the G-CSF-treated group (P<0.05), and BrdU-positive endothelial cells were increased 2.29 times in the G-CSF-treated group, to a level as high as that in the vehicle-treated group (P<0.01), in the periischemic area. Our results indicate that G-CSF caused potentiation of neuroprotection and neurogenesis and is expected to have practical therapeutic potential in treating individuals after ischemic brain injury.

Acute myeloid leukemia or myelodysplastic syndrome following use of granulocyte colony-stimulating factors during breast cancer adjuvant chemotherapy

BACKGROUND

Recently, increasing numbers of women receiving adjuvant chemotherapy for breast cancer have also received granulocyte colony-stimulating factors (G-CSFs) or granulocyte-macrophage colony-stimulating factors (GM-CSFs). Although these growth factors support chemotherapy, their long-term safety has not been evaluated. We studied the association between G-CSF use and incidence of leukemia in a population-based sample of breast cancer patients.

METHODS

Among women aged 65 years or older in the Surveillance, Epidemiology, and End Results-Medicare database who were diagnosed with stages I-III breast cancer from January 1, 1991, to December 31, 1999, we identified those who received G-CSF or GM-CSF concurrently with chemotherapy. We used Cox proportional hazards models to estimate hazard ratios for the association of treatment with G-CSF or GM-CSF and subsequent (through December 31, 2003) diagnosis of acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS). All statistical tests were two-sided.

RESULTS

Of 5510 women treated with chemotherapy, 906 (16%) received G-CSF or GM-CSF therapy, and 64 (1.16%) were subsequently diagnosed with either MDS or AML before a cancer recurrence. Use of G-CSF and GM-CSF was associated with more recent diagnosis, younger age, urban residence, fewer comorbidities, receipt of radiation therapy, positive lymph nodes, and cyclophosphamide treatment. Of the 906 patients who were treated with G-CSF, 16 (1.77%) developed AML or MDS; of the 4604 patients not treated with G-CSF, 48 (1.04%) developed AML or MDS. The hazard rate ratio for AML or MDS among those treated with G-CSF or GM-CSF compared with those who were not was 2.14 (95% confidence interval [CI] = 1.12 to 4.08). AML or MDS developed within 48 months of breast cancer diagnosis in 1.8% of patients who received G-CSF or GM-CSF but only in 0.7% of patients who did not (hazard ratio = 2.59, 95% CI = 1.30 to 5.15).

CONCLUSIONS

The use of G-CSF was associated with a doubling in the risk of subsequent AML or MDS among the population that we studied, although the absolute risk remained low. Even if this association is confirmed, the benefits of G-CSF may still outweigh the risks. Meanwhile, however, G-CSF use should not be assumed to be risk free.

Tissue homeostasis and cancer

Epithelial cells are known to release an important amount of cytokines capable to modulate immune system functions. On the other hand, immune system cells can release cytokines, which play an important role in the control of the growth of epithelial cells. In this paper, we stand the hypothesis that a mutual (reciprocal) growth regulation exists between epithelial cells and immune system. We propose a model describing plausible cytokine circuits that may regulate (inhibit) both epithelial growth and epithelial inflammation. In addition, we describe how dysfunction of these circuits could lead to tumoral growth, excessive inflammation or both. A failure in the regulation of epithelial growth by the immune system could give rise to a neoplasm, and a failure in the regulation of the immune system by the epithelium could give rise to inflammatory or autoimmune diseases. This model may satisfactorily explain the link between inflammation and cancer.

Directing the differentiation of embryonic stem cells to neural stem cells

Embryonic stem cells (ESCs) are a potential source of neural derivatives that can be used in stem cell-based therapies designed to treat neurological disorders. The derivation of specific neuronal or glial cell types from ESCs invariably includes the production of neural stem cells (NSCs). We describe the basic mechanisms of neural induction during vertebrate embryogenesis and how this information helped formulate several protocols used to generate NSCs from ESCs. We highlight the advantages and disadvantages of each approach and review what has been learned about the intermediate stages in the transition from ESC to NSC. Recent data describing how specific growth factors and signaling molecules regulate production of NSCs are described and a model synthesizing this information is presented.

Granulocyte-colony stimulating factor (G-CSF) and G-CSF receptor expression in human ischemic stroke

Granulocyte-colony stimulating factor (G-CSF) receptor signaling counteracts detrimental pathways in ischemic stroke. In rodents, neuroprotection provided by the G-CSF system involves up-regulation of the G-CSF receptor and its ligand, G-CSF, during cerebral ischemia. The confirmation of a similar response in the human brain would be an important rationale for the use of G-CSF in clinical stroke trials. Therefore, the temporal and cellular profile of G-CSF and G-CSF receptor expression was examined in a series of human stroke brains. The median age of the 21 stroke patients was 67 years; median time from death to autopsy was 24 h (range: 10-67 h). In acute ischemic stroke, strong neuronal G-CSF receptor immunoreactivity was encountered in the infarct area and the peri-infarct rim as compared to the contralateral cortex. In subacute infarctions, microglial and macrophage G-CSF receptor immunoreactivity predominated, whereas chronic infarction was characterized by the presence of G-CSF receptor expressing reactive astrocytes. Neuronal G-CSF expression was encountered very early upon ischemic stroke. At later time-points, an up-regulation of vascular G-CSF expression in the peri-infarct area prevailed. In conclusion, the observed up-regulation of G-CSF receptors and G-CSF points towards a role in the pathophysiology of human ischemic stroke.

Beyond dimerization: a membrane-dependent activation model for interleukin-4 receptor-mediated signalling

Class I cytokine receptors efficiently transfer activation signals from the extracellular space to the cytoplasm and play a dominant role in growth control and differentiation of human tissues. Although a significant body of literature is devoted to this topic, a consistent mechanistic picture for receptor activation in the membrane environment is still missing. Using the interleukin-4 receptor (IL-4R) as an example, we propose that the membrane-proximal stem-loop of the extracellular domains contains pivotal elements of a rotational switch. Interfacial energies of amino acid side-chains contained in the highly conserved WSXWS at the surface of the lipid bilayer suggest a new functional role for this motif. A generic activation mechanism for this receptor class is presented, which may impact the design of a new generation of biophysical assay systems.

Signaling through Toll-like Receptor 7/8 Induces the Differentiation of Human Bone Marrow CD34+ Progenitor Cells along the Myeloid Lineage

Toll-like receptors (TLRs) play a key role in pathogen recognition and regulation of the innate and adaptive immune responses. Although TLR expression and signaling have been investigated in blood cells, it is currently unknown whether their bone marrow ancestors express TLRs and respond to their ligands. Here we found that TLRs (e.g. TLR4, TLR7 and TLR8) were expressed by freshly isolated human bone marrow (BM) hematopoietic CD34+ progenitor cells. Incubation of these primitive cells with TLR ligands such as immunostimulatory small interfering RNAs and R848, a specific ligand for TLR7/8, induced cytokine production (e.g. IL1-beta, IL6, IL8, TNF-alpha, GM-CSF). Moreover, TLR7/8 signaling induced the differentiation of BM CD34+ progenitors into cells with the morphology of macrophages and monocytic dendritic precursors characterized by the expression of CD13, CD14 and/or CD11c markers. By contrast, R848 ligand did not induce the expression of glycophorin A, an early marker for erythropoiesis. Collectively, the data indicate for the first time that human BM CD34+ progenitor cells constitutively express functional TLR7/TLR8, whose ligation can induce leukopoiesis without the addition of any exogenous cytokines. Thus, TLR signaling may regulate BM cell development in humans.

Megakaryocyte development and platelet production

Megakaryocytopoiesis involves the commitment of haematopoietic stem cells, and the proliferation, maturation and terminal differentiation of the megakaryocytic progenitors. Circulating levels of thrombopoietin (TPO), the primary growth-factor for the megakaryocyte (MK) lineage, induce concentration-dependent proliferation and maturation of MK progenitors by binding to the c-Mpl receptor and signalling induction. Decreased platelet turnover rates results in increased concentration of free TPO, enabling the compensatory response of marrow MKs to increased platelet production. C-Mpl activity is orchestrated by a complex cascade of signalling molecules that induces the action of specific transcription factors to drive MK proliferation and maturation. Mature MKs form proplatelet projections that are fragmented into circulating particles. Newly developed thrombopoietic agents operating via c-Mpl receptor may prove useful in supporting platelet production in thrombocytopenic state. Herein, we review the regulation of megakaryocytopoiesis and platelet production in normal and disease state, and the new approaches to thrombopoietic therapy.

Growth factors and stroke

Current options for the treatment of stroke are extremely limited, partly because of the rapidity with which brain cells die when deprived of their blood supply. Several recent studies suggest that growth factors can produce improvement in animal models of stroke, even when administered at postischemic intervals of many hours to days, when conventional neuroprotective approaches are typically futile. Several growth factors can access the brain after systemic administration, making them more attractive as therapeutic agents. Finally, growth factors are key mediators of neurogenesis in the adult brain, which could have a role in brain repair and functional recovery following stroke.

Neutrophil elastase in cyclic and severe congenital neutropenia

Mutations in ELA2 encoding the neutrophil granule protease, neutrophil elastase (NE), are the major cause of the 2 main forms of hereditary neutropenia, cyclic neutropenia and severe congenital neutropenia (SCN). Genetic evaluation of other forms of neutropenia in humans and model organisms has helped to illuminate the role of NE. A canine form of cyclic neutropenia corresponds to human Hermansky-Pudlak syndrome type 2 (HPS2) and results from mutations in AP3B1 encoding a subunit of a complex involved in the subcellular trafficking of vesicular cargo proteins (among which NE appears to be one). Rare cases of SCN are attributable to mutations in the transcriptional repressor Gfi1 (among whose regulatory targets also include ELA2). The ultimate biochemical consequences of the mutations are not yet known, however. Gene targeting of ELA2 has thus far failed to recapitulate neutropenia in mice. The cycling phenomenon and origins of leukemic transformation in SCN remain puzzling. Nevertheless, mutations in all 3 genes are capable of causing the mislocalization of NE and may also induce the unfolded protein response, suggesting that there might a convergent pathogenic mechanism focusing on NE.

Granulocyte colony-stimulating factor and neutrophils—forgotten mediators of inflammatory disease

Recent studies have highlighted the functional capacity of neutrophils as powerful mediators of tissue inflammation. Granule-packaged proteases and reactive oxygen intermediates, which are important for intracellular digestion during phagocytosis, are released from neutrophils during inflammation. In the extracellular environment, neutrophil-derived proteases can cause local tissue damage, but also regulate the activity of cytokines, cytokine receptors and chemokines. Neutrophils can themselves produce an array of inflammatory mediators, including cytokines, chemokines and complement; these cells also express Fc receptors, which can bind and possibly transport immune complexes into the extravascular compartment, as well as activating neutrophils at opsonised surfaces. Blood-borne neutrophils interact with, and then exit through, the endothelium of blood vessels, after which these cells die and must be removed safely. The balance between neutrophil survival and clearance is crucial to the resolution of inflammation. A major regulator of neutrophil production and survival is the cytokine granulocyte colony-stimulating factor (G-CSF). Treatment with G-CSF can exacerbate underlying inflammatory diseases in humans and mice, and G-CSF deficiency is profoundly protective against collagen-induced arthritis in mice. These findings implicate G-CSF as an important proinflammatory cytokine. This article discusses the roles of neutrophils and G-CSF during chronic inflammatory diseases.