Expression of notch receptors, notch ligands, and fringe genes in hematopoiesis

Cis inhibition of NOTCH1 through JAGGED1 sustains embryonic hematopoietic stem cell fate

Hematopoietic stem cells (HSCs) develop from the hemogenic endothelium (HE) in the aorta- gonads-and mesonephros (AGM) region and reside within Intra-aortic hematopoietic clusters (IAHC) along with hematopoietic progenitors (HPC). The signalling mechanisms that distinguish HSCs from HPCs are unknown. Notch signaling is essential for arterial specification, IAHC formation and HSC activity, but current studies on how Notch segregates these different fates are inconsistent. We now demonstrate that Notch activity is highest in a subset of, GFI1 + , HSC-primed HE cells, and is gradually lost with HSC maturation. We uncover that the HSC phenotype is maintained due to increasing levels of NOTCH1 and JAG1 interactions on the surface of the same cell (cis) that renders the NOTCH1 receptor from being activated. Forced activation of the NOTCH1 receptor in IAHC activates a hematopoietic differentiation program. Our results indicate that NOTCH1-JAG1 cis-inhibition preserves the HSC phenotype in the hematopoietic clusters of the embryonic aorta.

Fringe family genes and their modulation of Notch signaling in cancer

Fringes are glycosyltransferases that transfer N-acetylglucosamine to the O-linked fucose of Notch receptors. They regulate the Notch signaling activity that drives tumor formation and progression, resulting in poor prognosis. However, the specific tumor-promoting role of Fringes differs depending on the type of cancer. Although a particular Fringe member could act as a tumor suppressor in one cancer type, it may act as an oncogene in another. This review discusses the tumorigenic role of the Fringe family (lunatic fringe, manic fringe, and radical fringe) in modulating Notch signaling in various cancers. Although the crucial functions of Fringes continue to emerge as more mechanistic studies are being pursued, further translational research is needed to explore their roles and therapeutic benefits in various malignancies.

Regulatory Crosstalk between Physiological Low O2 Concentration and Notch Pathway in Early Erythropoiesis

Physiological low oxygen (O2) concentration (<5%) favors erythroid development ex vivo. It is known that low O2 concentration, via the stabilization of hypoxia-induced transcription factors (HIFs), intervenes with Notch signaling in the control of cell fate. In addition, Notch activation is implicated in the regulation of erythroid differentiation. We test here if the favorable effects of a physiological O2 concentration (3%) on the amplification of erythroid progenitors implies a cooperation between HIFs and the Notch pathway. To this end, we utilized a model of early erythropoiesis ex vivo generated from cord blood CD34+ cells transduced with shHIF1α and shHIF2α at 3% O2 and 20% O2 in the presence or absence of the Notch pathway inhibitor. We observed that Notch signalization was activated by Notch2R−Jagged1 ligand interaction among progenitors. The inhibition of the Notch pathway provoked a modest reduction in erythroid cell expansion and promoted erythroid differentiation. ShHIF1α and particularly shHIF2α strongly impaired erythroid progenitors’ amplification and differentiation. Additionally, HIF/NOTCH signaling intersects at the level of multipotent progenitor erythroid commitment and amplification of BFU-E. In that, both HIFs contribute to the expression of Notch2R and Notch target gene HES1. Our study shows that HIF, particularly HIF2, has a determining role in the early erythroid development program, which includes Notch signaling.

The Role of Notch Signaling in Macrophages during Inflammation and Infection: Implication in Rheumatoid Arthritis?

Notch signaling coordinates numerous cellular processes and has been implicated in many pathological conditions, including rheumatoid arthritis (RA). Although the role of Notch signaling in development, maturation, differentiation, and activation of lymphocytes has been comprehensively reported, less is known about its role in myeloid cells. Certainly, limited data are available about the role of Notch signaling in macrophages during inflammation and infection. In this review, we discuss the recent advances pertaining to the role of Notch signaling in differentiation, activation, and metabolism of macrophages during inflammation and infection. We also highlight the reciprocal interplay between Notch signaling and other signaling pathways in macrophages under different inflammatory and infectious conditions including pathogenesis of RA. Finally, we discuss approaches that could consider Notch signaling as a potential therapeutic target against infection- and inflammation-driven diseases.

Pulmonary hemorrhage in children with Alagille syndrome undergoing cardiac catheterization

OBJECTIVES

To evaluate the incidence, severity, and outcomes of pulmonary hemorrhage in children with Alagille syndrome (AGS) undergoing cardiac catheterization, and to find variables associated with hemorrhage in this population.

BACKGROUND

Children with AGS have a high incidence of bleeding complications during invasive procedures. It has been our impression that catheterization-associated pulmonary hemorrhage is more common in children with AGS, but there are no published data on this topic.

METHODS

This was a retrospective single institution study of children with AGS undergoing catheterization from 2010 to 2018. Pulmonary hemorrhage was defined as angiographic or fluoroscopic evidence of extravasated blood in the lung parenchyma, or blood suctioned from the endotracheal tube with documentation of pulmonary hemorrhage by the anesthesiologist or intensivist. Univariate comparisons were made between catheterizations that did and did not have pulmonary hemorrhage.

RESULTS

Thirty children with AGS underwent 87 catheterizations, 32 (37%) with interventions on the branch pulmonary arteries (PA). There were 26 (30%) procedures with hemorrhage, the majority (65%) of which were self-limited or required less than 24 hr of mechanical ventilation. Moderate and severe hemorrhage occurred only in children with tetralogy of Fallot (TOF; 5 of 14, 36%). A higher right ventricle to aorta systolic pressure ratio (1.0 [0.85-1.1] vs. 0.88 [0.59-1.0], p = .029) and interventions on the branch PAs (14 of 26, 54% vs. 18 of 61, 30%, p = .032) were associated with hemorrhage.

CONCLUSIONS

Pulmonary hemorrhage was common in children with AGS undergoing both intervention and diagnostic cardiac catheterization, and was associated with TOF, higher RV to aorta pressure ratio, and interventions on the branch PAs.

Mesenchymal stem cell-mediated Notch2 activation overcomes radiation-induced injury of the hematopoietic system

Radiation exposure severely damages the hematopoietic system. Although several radio-protectors have been proposed to prevent radiation-induced damage, most agents have limited efficacy. In the present study, we investigated whether mesenchymal stem cells (MSCs) could contribute to the expansion of hematopoietic cells and mitigate radiation-induced hematopoietic injury in vitro and in vivo. We found that co-culture with MSCs promoted hematopoietic progenitor/stem cell (HPSCs) maintenance by providing a bone marrow-like microenvironment. In addition, we showed that MSCs prevented radiation-induced damage to HPSCs, as evidenced by the lack of DNA damage and apoptosis. Intravenously injected MSCs rapidly migrated to the bone marrow (BM) and prevented loss of BM cellularity, which reduced lethality and ameliorated pancytopenia in the BM of whole body-irradiated mice. We demonstrated that MSC-derived Jagged1 attenuated radiation-induced cytotoxicity of HPSCs, and that this was mediated by Notch signaling and expression of downstream proteins Bcl2 and p63 in HPSCs. In addition, Notch2 depletion significantly reduced the MSC-mediated radio-protective effect in human- and mouse-derived HPSCs. Collectively, our data show that activation of Notch and its associated downstream signaling pathways prevent radiation-induced hematopoietic injury. Therefore, enhancing Jagged1-Notch2 signaling could provide therapeutic benefit by protecting the hematopoietic system against damage after radiation.

A novel neuregulin - jagged1 paracrine loop in breast cancer transendothelial migration

Background

The interaction of breast cancer cells with other cells in the tumor microenvironment plays an important role in metastasis. Invasion and intravasation, two critical steps in the metastatic process, are influenced by these interactions. Macrophages are of particular interest when it comes to studying tumor cell invasiveness. Previous studies have shown that there is paracrine loop signaling between breast cancer cells and macrophages involving colony stimulating factor 1 (CSF-1) produced by tumor cells and epidermal growth factor (EGF) production by macrophages. In this paper, we identify a novel paracrine loop between tumor cells and macrophages involving neuregulin (NRG1) and notch signaling.

Methods

The aim of this study was to determine the role of NRG1, a ligand of the ErbB3 receptor, in macrophage stimulation of tumor cell transendothelial migration and intravasation. We used fluorescence-activated cell sorting (FACS) and western blot to determine ErbB3 and NRG1 expression, respectively. An in vitro transendothelial migration (iTEM) assay was used to examine the effects of short hairpin (sh)RNA targeting NRG1 in tumor cells and clustered regularly interspaced short palindromic repeats (CRISPR) knockout of jagged 1 (JAG1) in macrophages. Orthotopic xenograft injections in mice were used to confirm results in vivo.

Results

In our system, macrophages were the primary cells showing expression of ErbB3, and a blocking antibody against ErbB3 resulted in a significant decrease in macrophage-induced transendothelial migration of breast cancer cells. Stimulation of macrophages with NRG1 upregulated mRNA and protein expression of JAG1, a ligand of the Notch receptor, and JAG1 production by macrophages was important for transendothelial migration of tumor cells.

Conclusions

This study demonstrates that stimulation of macrophages by tumor cell NRG1 can enhance transendothelial migration and intravasation. We also demonstrate that this effect is due to induction of macrophage JAG1, an important ligand of the Notch signaling pathway.

The Regulatory Function of Eosinophils

Eosinophils are a minority circulating granulocyte classically viewed as being involved in host defense against parasites and promoting allergic reactions. However, a series of new regulatory functions for these cells have been identified in the past decade. During homeostasis, eosinophils develop in the bone marrow and migrate from the blood into target tissues following an eotaxin gradient, with interleukin-5 being a key cytokine for eosinophil proliferation, survival, and priming. In multiple target tissues, eosinophils actively regulate a variety of immune functions through their vast arsenal of granule products and cytokines, as well as direct cellular interaction with cells in proximity. The immunologic regulation of eosinophils extends from innate immunity to adaptive immunity and also involves non-immune cells. Herein, we summarize recent findings regarding novel roles of murine and human eosinophils, focusing on interactions with other hematopoietic cells. We also review new experimental tools available and remaining questions to uncover a greater understanding of this enigmatic cell.

Significance of Inactivated Genes in Leukemia: Pathogenesis and Prognosis

Epigenetic and genetic alterations are two mechanisms participating in leukemia, which can inactivate genes involved in leukemia pathogenesis or progression. The purpose of this review was to introduce various inactivated genes and evaluate their possible role in leukemia pathogenesis and prognosis. By searching the mesh words "Gene, Silencing AND Leukemia" in PubMed website, relevant English articles dealt with human subjects as of 2000 were included in this study. Gene inactivation in leukemia is largely mediated by promoter's hypermethylation of gene involving in cellular functions such as cell cycle, apoptosis, and gene transcription. Inactivated genes, such as ASPP1, TP53, IKZF1 and P15, may correlate with poor prognosis in acute lymphoid leukemia (ALL), chronic lymphoid leukemia (CLL), chronic myelogenous leukemia (CML) and acute myeloid leukemia (AML), respectively. Gene inactivation may play a considerable role in leukemia pathogenesis and prognosis, which can be considered as complementary diagnostic tests to differentiate different leukemia types, determine leukemia prognosis, and also detect response to therapy. In general, this review showed some genes inactivated only in leukemia (with differences between B-ALL, T-ALL, CLL, AML and CML). These differences could be of interest as an additional tool to better categorize leukemia types. Furthermore; based on inactivated genes, a diverse classification of Leukemias could represent a powerful method to address a targeted therapy of the patients, in order to minimize side effects of conventional therapies and to enhance new drug strategies.

Bortezomib and Arsenic Trioxide Activity on a Myelodysplastic Cell Line (P39): A Gene Expression Study

Objective:

We aimed to understand the molecular pathways affected by bortezomib and arsenic trioxide treatment on myelomonocytoid cell line P39.

Materials and Methods:

Oligonucleotide microarray platforms were used for gene expression and pathway analysis. Confirmation studies were performed using quantitative real time PCR.

Results:

Bortezomib treatment has shown upregulated DIABLO and NF-κBIB (a NF-κB inhibitor) and downregulated NF-κB1, NF-κB2, and BIRC1 gene expressions. Combination treatment of the two compounds showed gene expression deregulations in concordance by the results of single bortezomib treatment. Especially, P53 was a pathway more significantly modified and a gene network centralized around the beta estradiol gene. Beta estradiol, BRCA2, and FOXA1 genes were remarkable deregulations in our findings.

Conclusion:

Results support the suggestions about possible use of proteasome inhibitors in the treatment of high-risk myelodysplastic syndrome (MDS). NF-κB was observed as an important modulator in leukemic transformation of MDS.

Identification of microRNA-regulated pathways using an integration of microRNA-mRNA microarray and bioinformatics analysis in CD34+ cells of myelodysplastic syndromes

The effect of microRNA (miRNA) and targeted mRNA on signal transduction is not fully understood in myelodysplastic syndromes (MDS). Here, we tried to identify the miRNAs-regulated pathways through a combination of miRNA and mRNA microarray in CD34+ cells from MDS patients. We identified 34 differentially expressed miRNAs and 1783 mRNAs in MDS. 25 dysregulated miRNAs and 394 targeted mRNAs were screened by a combination of Pearson’s correlation analysis and software prediction. Pathway analysis showed that several pathways such as Notch, PI3K/Akt might be regulated by those miRNA-mRNAs pairs. Through a combination of Pathway and miRNA-Gene or GO-Network analysis, miRNAs-regulated pathways, such as miR-195-5p/DLL1/Notch signaling pathway, were identified. Further qRT-PCR showed that miR-195-5p was up-regulated while DLL1 was down-regulated in patients with low-grade MDS compared with normal controls. Luciferase assay showed that DLL1 was a direct target of miR-195-5p. Overexpression of miR-195-5p led to increased cell apoptosis and reduced cell growth through inhibition of Notch signaling pathway. In conclusion, alteration expression of miRNAs and targeted mRNAs might have an important impact on cancer-related cellular pathways in MDS. Inhibition of Notch signaling pathway by miR-195-5p-DLL1 axis contributes to the excess apoptosis in low-grade MDS.

TNF-alpha and Notch signaling regulates the expression of HOXB4 and GATA3 during early T lymphopoiesis

During the early thymus colonization, Notch signaling activation on hematopoietic progenitor cells (HPCs) drives proliferation and T cell commitment. Although these processes are driven by transcription factors such as HOXB4 and GATA3, there is no evidence that Notch directly regulates their transcription. To evaluate the role of NOTCH and TNF signaling in this process, human CD34⁺ HPCs were cocultured with OP9-DL1 cells, in the presence or absence of TNF. The use of a Notch signaling inhibitor and a protein synthesis inhibitor allowed us to distinguish primary effects, mediated by direct signaling downstream Notch and TNF, from secondary effects, mediated by de novo synthesized proteins. A low and physiologically relevant concentration of TNF promoted T lymphopoiesis in OP9-DL1 cocultures. TNF positively modulated the expression of both transcripts in a Notch-dependent manner; however, GATA3 induction was mediated by a direct mechanism, while HOXB4 induction was indirect. Induction of both transcripts was repressed by a GSK3β inhibitor, indicating that activation of canonical Wnt signaling inhibits rather than induces their expression. Our study provides novel evidences of the mechanisms integrating Notch and TNF-alpha signaling in the transcriptional induction of GATA3 and HOXB4. This mechanism has direct implications in the control of self-renewal, proliferation, commitment, and T cell differentiation.

Endothelium-targeted human Delta-like 1 enhances the regeneration and homing of human cord blood stem and progenitor cells

Background

Umbilical cord blood (UCB) is becoming an alternative cell source for hematopoietic stem cell transplantation (HSCT). However, umbilical cord blood transplantation (UCBT) has been severely limited by low and finite numbers of hematopoietic stem cells and their delayed engraftment. New strategies are needed to improve ex vivo expansion efficiency and in vivo haematopoietic recovery.

Methods

We produced an endothelium-targeted soluble Notch ligand, the Delta-Serrate-Lag-2 (DSL) domain of human Delta-like 1 fused with a RGD motif (hD1R), and tested the effects of this protein on human umbilical cord blood hematopoietic stem and progenitor cell (UCB-HSPC) ex vivo and in vivo.

Results

hD1R-mediated ex vivo expansion system was able to significantly increase the absolute number of UCB-HSPCs. The hD1R-expanded cells had the enhanced homing and maintained long-term hematopoietic stem cell repopulation capacity in the bone marrow of immunodeficient nonobese diabetic-severe combined immunodeficient (NOD/SCID) mice. Moreover, systemic administration of hD1R promoted the in vivo regeneration of donor cells in recipient mice and accelerated hematopoietic recovery, particularly in settings wherein the HSPCs dose was limiting.

Conclusions

Our results indicated that hD1R might be applied in improving hematopoietic recovery and HSC engraftment in human UCBT.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0761-0) contains supplementary material, which is available to authorized users.

Jagged-1 signaling suppresses the IL-6 and TGF-β treatment-induced Th17 cell differentiation via the reduction of RORγt/IL-17A/IL-17F/IL-23a/IL-12rb1

Jagged-1 signaling has recently been reported to be involved in the Th17 cell differentiation. However, little is known about its mechanisms. Soluble Jagged-1 was used to activate the Jagged-1–Notch signaling to interfere with the IL-6 and TGF-β-induced Th17 cell skewing. Genes relevant to the autoimmunity or inflammation were screened for the first time in this system by qPCR array for the differential expressions. The 18 genes out of 84, including Clec7a, Il12b, Il12rb1, Il12rb2, Csf3, Il15, Il17a, Il17f, Il17rc, Il17rd, Il17re, Il23a, Myd88, Socs1, Stat4, Stat5a, Sykb and Tbx21, were downregulated, but only Cxcl2, Cxcl12 and Mmp3 were upregulated. The expressions of the genes, Rorγt, Il17a, Il17f, Il12rb1 and Il23a, induced by simultaneous IL-6 and TGF-β treatment were significantly suppressed by Jagged-1, followed by the reduction of RORγt, IL-17A, and IL-17F. Consistent with the attenuation of RORγt, and the reduced production and secretion of IL-17A and IL-17F in the cell supernatant and the in situ stained cells, the number of CD4⁺IL-17⁺ cells was also diminished. It is concluded that the Jagged-1–Notch signaling can suppress the IL-6 and TGF-β treatment-induced Th17 cell skewing through the attenuation of RORγt and, hence by, the down-regulation of IL-17A, IL-17F, IL-23a, and IL-12rb1.

The deposition of Notch1 in hepatitis B virus-associated nephropathy and its role in hepatitis B virus X protein-induced epithelial-mesenchymal transdifferentiation and immunity disorder in renal tubular epithelial cells

Notch1 plays an important role in the regulation of immune responses and epithelial-mesenchymal transdifferentiation (EMT). Previous studies have observed inflammatory cell infiltration and tubulointerstitial fibrosis in the renal biopsies from patients with HBV-associated glomerulonephritis (HBV-GN). We hypothesized that Notch1 may be involved in the progression of HBV-GN. In this study, we evaluated the distribution of Notch1 in patients with HBV-GN. Our results showed that Notch1 was mainly distributed in renal tubules and the interstitial area, and the expression levels of Notch1 had a positive correlation with the renal tubular pathology. In this respect, we used human proximal tubular epithelial cells (HK-2) as target cells, which were transiently transfected with the hepatitis B virus X (HBx) gene using a eukaryotic vector. HBx expression resulted in significantly increased detection of Notch1, alpha-smooth muscle actin (α-SMA), major histocompatibility complex-II (MHC-II), CD40 and interleukin-4 (IL-4). At the same time, E-cadherin and interferon-γ (IFN-γ) expression levels were significantly inhibited. These HBx-induced phenotypes were exacerbated by upregulation of Notch1. Knock-down of Notch1 by specific shRNA caused decreases of α-SMA, MHC-II, CD40 and IL-4, and increases of E-cadherin and IFN-γ. These findings suggest that Notch1 is significantly associated with renal tubular and interstitial lesions. Notch1 can mediate HBx-induced EMT of HK-2 cells, promote HBx-induced increases in immune molecule expression and exacerbation of cytokine disorders, which may contribute to the progression of HBV-GN. Inhibitors of Notch1 signalling may be useful as new therapeutics for the treatment of HBV-GN.

Regulation of Notch 1 signaling in THP-1 cells enhances M2 macrophage differentiation

Macrophage polarization is emerging as an important area of research for the development of novel therapeutics to treat inflammatory diseases. Within the current study, the role of Notch1R in macrophage differentiation was investigated as well as downstream effects in THP-1 monocytes cultured in "inflammation mimicry" media. Interference of Notch signaling was achieved using either the pharmaceutical inhibitor DAPT or Notch1R small interfering RNA (siRNA), and Notch1R expression, macrophage phenotypes, and anti- and proinflammatory cytokine expression were evaluated. Data presented show that Notch1R expression on M1 macrophages as well as M1 macrophage differentiation is significantly elevated during cellular stress (P < 0.05). However, under identical culture conditions, interference to Notch signaling via Notch1R inhibition mitigated these results as well as promoted M2 macrophage differentiation. Moreover, when subjected to cellular stress, macrophage secretion of proinflammatory cytokines was significantly heightened (P < 0.05). Importantly, Notch1R inhibition not only diminished proinflammatory cytokine secretion but also enhanced anti-inflammatory protein release (P < 0.05). Our data suggest that Notch1R plays a pivotal role in M1 macrophage differentiation and heightened inflammatory responses. Therefore, we conclude that inhibition of Notch1R and subsequent downstream signaling enhances monocyte to M2 polarized macrophage outcomes and promotes anti-inflammatory mediation during cellular stress.

Pleiotropic roles of Notch signaling in normal, malignant, and developmental hematopoiesis in the human

The Notch signaling pathway is evolutionarily conserved across species and plays an important role in regulating cell differentiation, proliferation, and survival. It has been implicated in several different hematopoietic processes including early hematopoietic development as well as adult hematological malignancies in humans. This review focuses on recent developments in understanding the role of Notch signaling in the human hematopoietic system with an emphasis on hematopoietic initiation from human pluripotent stem cells and regulation within the bone marrow. Based on recent insights, we summarize potential strategies for treatment of human hematological malignancies toward the concept of targeting Notch signaling for fate regulation.

Notch1 regulates progenitor cell proliferation and differentiation during mouse yolk sac hematopoiesis

Loss-of-function studies have demonstrated the essential role of Notch in definitive embryonic mouse hematopoiesis. We report here the consequences of Notch gain-of-function in mouse embryo hematopoiesis, achieved by constitutive expression of Notch1 intracellular domain (N1ICD) in angiopoietin receptor tyrosine kinase receptor-2 (Tie2)-derived enhanced green fluorescence protein (EGFP(+)) hematovascular progenitors. At E9.5, N1ICD expression led to the absence of the dorsal aorta hematopoietic clusters and of definitive hematopoiesis. The EGFP(+) transient multipotent progenitors, purified from E9.5 to 10.5 Tie2-Cre;N1ICD yolk sac (YS) cells, had strongly reduced hematopoietic potential, whereas they had increased numbers of hemogenic endothelial cells. Late erythroid cell differentiation stages and mature myeloid cells (Gr1(+), MPO(+)) were also strongly decreased. In contrast, EGFP(+) erythro-myeloid progenitors, immature and intermediate differentiation stages of YS erythroid and myeloid cell lineages, were expanded. Tie2-Cre;N1ICD YS had reduced numbers of CD41(++) megakaryocytes, and these produced reduced below-normal numbers of immature colonies in vitro and their terminal differentiation was blocked. Cells from Tie2-Cre;N1ICD YS had a higher proliferation rate and lower apoptosis than wild-type (WT) YS cells. Quantitative gene expression analysis of FACS-purified EGFP(+) YS progenitors revealed upregulation of Notch1-related genes and alterations in genes involved in hematopoietic differentiation. These results represent the first in vivo evidence of a role for Notch signaling in YS transient definitive hematopoiesis. Our results show that constitutive Notch1 activation in Tie2(+) cells hampers YS hematopoiesis of E9.5 embryos and demonstrate that Notch signaling regulates this process by balancing the proliferation and differentiation dynamics of lineage-restricted intermediate progenitors.

Understanding the role of Notch in osteosarcoma

The Notch pathway has been described as an oncogene in osteosarcoma, but the myriad functions of all the members of this complex signaling pathway, both in malignant cells and nonmalignant components of tumors, make it more difficult to define Notch as simply an oncogene or a tumor suppressor. The cell-autonomous behaviors caused by Notch pathway manipulation may vary between cell lines but can include changes in proliferation, migration, invasiveness, oxidative stress resistance, and expression of markers associated with stemness or tumor-initiating cells. Beyond these roles, Notch signaling also plays a vital role in regulating tumor angiogenesis and vasculogenesis, which are vital aspects of osteosarcoma growth and behavior in vivo. Further, osteosarcoma cells themselves express relatively low levels of Notch ligand, making it likely that nonmalignant cells, especially endothelial cells and pericytes, are the major source of Notch activation in osteosarcoma tumors in vivo and in patients. As a result, Notch pathway expression is not expected to be uniform across a tumor but likely to be highest in those areas immediately adjacent to blood vessels. Therapeutic targeting of the Notch pathway is likewise expected to be complicated. Most pharmacologic approaches thus far have focused on inhibition of gamma secretase, a protease of the presenilin complex. This enzyme, however, has numerous other target proteins that would be expected to affect osteosarcoma behavior, including CD44, the WNT/β-catenin pathway, and Her-4. In addition, Notch plays a vital role in tissue and organ homeostasis in numerous systems, and toxicities, especially GI intolerance, have limited the effectiveness of gamma secretase inhibitors. New approaches are in development, and the downstream targets of Notch pathway signaling also may turn out to be good targets for therapy. In summary, a full understanding of the complex functions of Notch in osteosarcoma is only now unfolding, and this deeper knowledge will help position the field to better utilize novel therapies as they are developed.

Endothelium-targeted Delta-like 1 promotes hematopoietic stem cell expansion ex vivo and engraftment in hematopoietic tissues in vivo

BACKGROUND

Notch ligands enhance ex vivo expansion of hematopoietic stem cells (HSCs). But to use Notch ligands in HSC therapies of human diseases, efforts are required to improve ex vivo expansion efficiency and in vivo transplant engraftment.

DESIGN AND METHODS

We designed and produced an endothelium-targeted soluble Notch ligand, the DSL domain of Delta-like 1 fused with a RGD motif (D1R), and examined the effects of this protein on HSCs ex vivo and in vivo.

RESULTS

D1R efficiently promoted ex vivo expansion of both mouse bone marrow (BM) and human umbilical cord blood HSCs. HSCs expanded with D1R up-regulated many of the stemness-related genes, and showed high BM engraftment efficacy with long-term repopulation capacity after transplantation. Moreover, in vivo administration of D1R increased the number of BM HSCs in mice, and facilitated BM recovery of mice after irradiation. Injection of D1R significantly improved HSC engraftment and myeloid recovery after BM transplantation in irradiated mice. D1R enhanced HSC engraftment not only in BM, but also in the liver and spleen after BM transplantation in mice. D1R induced the formation of compact cell clusters containing the transplanted HSCs in close contact with endothelial cells, reminiscent of HSC niches, in the liver and spleen.

CONCLUSIONS

D1R might be applied in improving both HSC expansion ex vivo and HSC engraftment in vivo in transplantation.

Epigenetic inactivation of Notch-Hes pathway in human B-cell acute lymphoblastic leukemia

The Notch pathway can have both oncogenic and tumor suppressor roles, depending on cell context. For example, Notch signaling promotes T cell differentiation and is leukemogenic in T cells, whereas it inhibits early B cell differentiation and acts as a tumor suppressor in B cell leukemia where it induces growth arrest and apoptosis. The regulatory mechanisms that contribute to these opposing roles are not understood. Aberrant promoter DNA methylation and histone modifications are associated with silencing of tumor suppressor genes and have been implicated in leukemogenesis. Using methylated CpG island amplification (MCA)/DNA promoter microarray, we identified Notch3 and Hes5 as hypermethylated in human B cell acute lymphoblastic leukemia (ALL). We investigated the methylation status of other Notch pathway genes by bisulfite pyrosequencing. Notch3, JAG1, Hes2, Hes4 and Hes5 were frequently hypermethylated in B leukemia cell lines and primary B-ALL, in contrast to T-ALL cell lines and patient samples. Aberrant methylation of Notch3 and Hes5 in B-ALL was associated with gene silencing and was accompanied by decrease of H3K4 trimethylation and H3K9 acetylation and gain of H3K9 trimethylation and H3K27 trimethylation. 5-aza-2′-deoxycytidine treatment restored Hes5 expression and decreased promoter hypermethylation in most leukemia cell lines and primary B-ALL samples. Restoration of Hes5 expression by lentiviral transduction resulted in growth arrest and apoptosis in Hes5 negative B-ALL cells but not in Hes5 expressing T-ALL cells. These data suggest that epigenetic modifications are implicated in silencing of tumor suppressor of Notch/Hes pathway in B-ALL.

Notch4 is required for tumor onset and perfusion

BACKGROUND

Notch4 is a member of the Notch family of receptors that is primarily expressed in the vascular endothelial cells. Genetic deletion of Notch4 does not result in an overt phenotype in mice, thus the function of Notch4 remains poorly understood.

METHODS

We examined the requirement for Notch4 in the development of breast cancer vasculature. Orthotopic transplantation of mouse mammary tumor cells wild type for Notch4 into Notch4 deficient hosts enabled us to delineate the contribution of host Notch4 independent of its function in the tumor cell compartment.

RESULTS

Here, we show that Notch4 expression is required for tumor onset and early tumor perfusion in a mouse model of breast cancer. We found that Notch4 expression is upregulated in mouse and human mammary tumor vasculature. Moreover, host Notch4 deficiency delayed the onset of MMTV-PyMT tumors, wild type for Notch4, after transplantation. Vessel perfusion was decreased in tumors established in Notch4-deficient hosts. Unlike in inhibition of Notch1 or Dll4, vessel density and branching in tumors developed in Notch4-deficient mice were unchanged. However, final tumor size was similar between tumors grown in wild type and Notch4 null hosts.

CONCLUSION

Our results suggest a novel role for Notch4 in the establishment of tumor colonies and vessel perfusion of transplanted mammary tumors.

Expression of Notch receptor and its target gene Hes-1 in bone marrow CD34+ cells from patients with psoriasis

Psoriasis is an autoimmune disease mediated mainly by dysfunctional peripheral blood T cells. Both CD4+/CD8+ T cells and CD4+CD25+ regulatory T cells derived from psoriatic CD34+ bone marrow cells in vitro have been found to be functionally similar to those psoriatic circulating and lesional T cells. Notch signaling participates in diverse cell fate decisions during T cell development and has been reported to influence the proliferation of hematopoietic stem cells and the differentiation of T cells. The purpose of this study was to investigate the expression levels of Notch receptor 1, 2 and its target gene Hes-1 in CD34+ cells from patients with psoriasis. The total RNA and protein of CD34+ cells were extracted, and the mRNA as well as protein expression of Notch1, Notch2 and Hes-1 were investigated using real-time PCR and Western blot assays. We found that the mRNA and protein expression levels of Notch1 and Hes-1 in psoriasis patients were higher compared to normal controls, while the Notch2 mRNA and protein expression levels in psoriasis patients were similar to those of normal controls. The elevated Notch1 and Hes-1 expression levels in psoriatic CD34+ cells might be one reason for the immune disorders which are mainly mediated by T cells.

Protein segregation between dividing hematopoietic progenitor cells in the determination of the symmetry/asymmetry of cell division

In the present study, we investigated how the symmetry/asymmetry of cell division in mitotic CD34(+) cells can be evaluated by determining the plane of cell division and the potential distribution of proteins between daughter cells. The orientation of the mitotic spindle is dependent upon the positioning of the centrosomes, which determine the plane of cell division and the sharing of proteins. If the functions of unequally shared proteins are relevant to the kinetics of cell division, they could determine whether the daughter cells undergo self-renewal or differentiation. The kinetic function of the proteins of interest was investigated using a colony-replating assay and carboxyfluorescein succinimidyl ester (CFSE) staining. We used Notch/Numb as a model system, since they have a role in balancing symmetric/asymmetric divisions. Mitotic cells were examined microscopically and centrosomal markers γ-tubulin/pericentrin were used with activated Notch-1 and Numb. We monitored the first crucial divisions by CFSE staining and found an inverse relationship between activated Notch and Numb expression, suggesting a reciprocal regulation. We suggest that the subpopulations expressing activated Notch or Numb have different cell fates. To determine the influence of Notch signaling on progenitor cell self-renewal, we used the γ-secretase inhibitor N-[N-(3,5-Difluorophenacetyl-L-alanyl)]-S-phenylglycine t-Butyl ester (DAPT). DAPT influences self-renewal/differentiation outcome by affecting the frequency of symmetric renewal divisions without affecting the rate of divisions. Overall, the purpose of this study was to establish a cellular system for predicting the symmetry/asymmetry of hematopoietic progenitor divisions at the level of centrosomes and protein distribution and to investigate the influence of these proteins on progenitor cell kinetics.

Notch signaling in developmental and tumor angiogenesis

The discovery that Notch, a key regulator of cell fate determination, is functional in the vasculature has greatly improved our understanding of differentiation and specialization of vessels. Notch signaling has been proven to be critical for arterial specification, sprouting angiogenesis, and vessel maturation. In newly forming vascular sprouts, Notch promotes the distinction between the leading "tip" endothelial cell and the growing "stalk" cell, the endothelial cells that eventually form a new capillary. Notch signaling has also been implicated in vessel stability by regulating vascular mural cell function. More recently, macrophages carrying an activated Notch have been implicated in shaping the course of new sprout formation. Tumor vessels abide by similar principles and use Notch signaling in similar ways. An exciting discovery, made by several researchers, shows that blocking Notch function in tumor vasculature provides a means by which to suppress tumor growth. The authors discuss the developmental and physiological role of Notch in the vasculature and apply this knowledge to an overview of how Notch targeting in the tumor environment can affect tumor angiogenesis and growth.

Notch1 controls macrophage recruitment and Notch signaling is activated at sites of endothelial cell anastomosis during retinal angiogenesis in mice

Notch is a critical regulator of angiogenesis, vascular differentiation, and vascular integrity. We investigated whether Notch signaling affects macrophage function during retinal angiogenesis in mice. Retinal macrophage recruitment and localization in mice with myeloid-specific loss of Notch1 was altered, as these macrophages failed to localize at the leading edge of the vascular plexus and at vascular branchpoints. Furthermore, these retinas were characterized by elongated endothelial cell sprouts that failed to anastomose with neighboring sprouts. Using Notch reporter mice, we demonstrate that retinal macrophages localize between Dll4-positive tip cells and at vascular branchpoints, and that these macrophages had activated Notch signaling. Taken together, these data demonstrate that Notch signaling in macrophages is important for their localization and interaction with endothelial cells during sprouting angiogenesis.

Notch2 signaling is required for proper mast cell distribution and mucosal immunity in the intestine

Notch receptor-mediated signaling is involved in the developmental process and functional modulation of lymphocytes, as well as in mast cell differentiation. Here, we investigated whether Notch signaling is required for antipathogen host defense regulated by mast cells. Mast cells were rarely found in the small intestine of wild-type C57BL/6 mice but accumulated abnormally in the lamina propria of the small-intestinal mucosa of the Notch2-conditional knockout mice in naive status. When transplanted into mast cell–deficient Wsh/Wsh mice, Notch2-null bone marrow-derived mast cells were rarely found within the epithelial layer but abnormally localized to the lamina propria, whereas control bone marrow-derived mast cells were mainly found within the epithelial layer. After the infection of Notch2 knockout and control mice with L3 larvae of Strongyloides venezuelensis, the abundant number of mast cells was rapidly mobilized to the epithelial layer in the control mice. In contrast, mast cells were massively accumulated in the lamina propria of the small intestinal mucosa in Notch2-conditional knockout mice, accompanied by impaired eradication of Strongyloides venezuelensis. These findings indicate that cell-autonomous Notch2 signaling in mast cells is required for proper localization of intestinal mast cells and further imply a critical role of Notch signaling in the host-pathogen interface in the small intestine.

Activating Notch signaling post-SCI modulates angiogenesis in penumbral vascular beds but does not improve hindlimb locomotor recovery

Manipulation of Notch signaling has led to significant tumor shrinkage as well as recovery from several traumatic and ischemic injury models indicating its potential clinical application. We have tested both an agonist and antagonist of Notch signaling to study the effects of Notch-mediated angiogenesis on spinal cord vascular pathology following traumatic injury. Initial neonatal retinal vascularization assays showed their respective bioactivities in vivo. Mice were treated with either the antagonist Jagged1-Fc chimera (Jag1-Fc) or agonist Notch1 antibody (N1 Ab) immediately following a mid-thoracic contusive injury through an initial jugular bolus and tail vein injections for 3 days post-injury. After 14 days, activating Notch signaling decreased the overall vascular density within the penumbral gray matter compared to controls while maintaining the density of perfused vessels. Inhibiting Notch signaling did not change the density or perfusion of microvessels within the lesion penumbra. Furthermore, neither activation nor inhibition of Notch signaling significantly altered inflammation, hypoxia, and lesion volume in the epicenter and penumbra. Importantly, neither treatment changed locomotor function. In postnatal retinal vascular assays, administration of Jag1-Fc and N1 Ab increased and decreased both tip cell numbers and branch points in each treatment, respectively. However, these agents did not modulate primary CNS EC proliferation in vitro in spite of sufficient Notch ligand expression. We conclude that Notch signaling, while an important part of developmental angiogenesis, may play a lesser role in mediating vascular recovery following traumatic injury to the CNS.

Notch1 deficiency results in decreased inflammation during wound healing and regulates vascular endothelial growth factor receptor-1 and inflammatory cytokine expression in macrophages

We investigated whether Notch signaling plays a role in regulating macrophage responses to inflammation. In a wound healing assay, macrophage recruitment was decreased in Notch1(+/-) mice, and the wounds were characterized by decreased TNF-α expression. As wound healing progressed, Notch1(+/-) wounds had increased vascularization and collagen deposition compared with wild-type wounds. In mice with myeloid-specific Notch1 deletion, wounds had decreased macrophage recruitment as well as decreased TNF-α expression, indicating the specific role of Notch1 in the inflammatory response in these cells. In vitro, we found that vascular endothelial growth factor receptor-1 (VEGFR-1) was upregulated in macrophages in response to LPS/IFN-γ and that this upregulation depended on Notch signaling. Furthermore, macrophages from Notch1(+/-) mice had decreased expression of VEGFR-1 compared with macrophages from wild-type mice, whereas VEGFR-1 expression in Notch4(-/-) macrophages was normal. Inhibition of Notch signaling decreased induction of the inflammatory cytokines IL-6, IL-12, CXCL10, MCP-1, monokine induced by IFN-γ, and TNF-α in macrophages in response to LPS/IFN-γ. Additionally, macrophages from Notch1(+/-) mice demonstrated decreased induction of IL-6, IL-12, and TNF-α in response to stimulation compared with wild-type mice. Thus, both pharmacological inhibition of Notch and genetic analysis demonstrate that Notch1 regulates VEGFR-1 and cytokine expression in macrophages. We have also established that Notch1 is important for the inflammatory response during wound healing in mice.

Regulation of dendritic cell differentiation and function by Notch and Wnt pathways

The process of dendritic cell differentiation is governed by a tightly controlled signaling network regulated by cytokines and direct interaction between progenitor cells and bone marrow stroma. Notch signaling represents one of the major pathways activated during direct interaction between hematopoietic progenitor cells and bone marrow stroma. Wnt pathway is activated by soluble proteins produced by bone marrow stroma. Until recently, the role of Notch and Wnt signaling in the development of myeloid cells and dendritic cells in particular remained unclear. In this review, we discuss recent exciting findings that shed light on the critical role of Notch and Wnt pathways, their interaction in differentiation and function of dendritic cells, and their impact on immune responses.

Expression profile of Notch-1 in mechanically overloaded plantaris muscle of mice

AIM

We investigated the expression pattern of Notch-1 in normal and hypertrophied plantaris muscle of mice.

MAIN METHODS

We performed immunofluorescence of both Notch-1 and the Notch-1-linking molecules.

KEY FINDINGS

Immunofluorescence labeling revealed Notch-1 protein in Pax7-positive satellite cells during days 2-6. We observed clear co-localization between Notch-1 and myogenin (4.9+/-1.3%) in the hypertrophied muscle at 4days. Several mononuclei (possibly satellite cells) possessed both Notch-1 and Foxo1 in the plantaris muscle subjected to mechanical overloading (4.1+/-1.2%).

SIGNIFICANCE

Notch-1 may play an important role in the maintenance of quiescent satellite cells.

T-cell differentiation of multipotent hematopoietic cell line EML in the OP9-DL1 coculture system

OBJECTIVE

Multipotent hematopoietic cell line EML can differentiate into myeloid, erythroid, megakaryocytic, and B-lymphoid lineages, but it remained unknown whether EML cells have T-cell developmental potential as well. The goal of this study was to determine whether the coculture with OP9 stromal cells expressing Notch ligand Delta-like 1 (OP9-DL1) could induce differentiation of EML cells into T-cell lineage.

MATERIALS AND METHODS

EML cells were cocultured with control OP9 or OP9-DL1 stromal cells in the presence of cytokines (stem cell factor, interleukin-7, and Fms-like tyrosine kinase 3 ligand). Their T-cell lineage differentiation was assessed through flow cytometry and reverse transcription polymerase chain reaction expression analysis of cell surface markers and genes characterizing and associated with specific stages of T-cell development.

RESULTS

The phenotypic, molecular, and functional analysis has revealed that in EML/OP9-DL1 cocultures with cytokines, but not in control EML/OP9 cocultures, EML cell line undergoes T-cell lineage commitment and differentiation. In OP9-DL1 cocultures, EML cell line has differentiated into cells that 1) resembled double-negative, double-positive, and single-positive stages of T-cell development; 2) initiated expression of GATA-3, Pre-Talpha, RAG-1, and T-cell receptor-Vbeta genes; and 3) produced interferon-gamma in response to T-cell receptor stimulation.

CONCLUSIONS

These results support the notion that EML cell line has the capacity for T-cell differentiation. Remarkably, induction of T-lineage gene expression and differentiation of EML cells into distinct stages of T-cell development were very similar to previously described T-cell differentiation of adult hematopoietic stem cells and progenitors in OP9-DL1 cocultures. Thus, EML/OP9-DL1 coculture could be a useful experimental system to study the role of particular genes in T-cell lineage specification, commitment, and differentiation.

MFng is dispensable for mouse pancreas development and function

Notch signaling regulates pancreatic cell differentiation, and mutations of various Notch signaling components result in perturbed pancreas development. Members of the Fringe family of beta1,3-N-acetylglucosaminyltransferases, Manic Fringe (MFng), Lunatic Fringe (LFng), and Radical Fringe (RFng), modulate Notch signaling, and MFng has been suggested to regulate pancreatic endocrine cell differentiation. We have characterized the expression of the three mouse Fringe genes in the developing mouse pancreas between embryonic days 9 and 14 and show that the expression of MFng colocalized with the proendocrine transcription factor Ngn3. In contrast, the expression of LFng colocalized with the exocrine marker Ptf1a, whereas RFng was not expressed. Moreover, we show that expression of MFng is lost in Ngn3 mutant mice, providing evidence that MFng is genetically downstream of Ngn3. Gain- and loss-of-function analyses of MFng by the generation of mice that overexpress MFng in early pancreatic progenitor cells and mice with a targeted deletion of MFng provide, however, evidence that MFng is dispensable for pancreas development and function, since no pancreatic defects in these mice were observed.

Notch activation is associated with tetraploidy and enhanced chromosomal instability in meningiomas

The Notch signaling cascade is deregulated in diverse cancer types. Specific Notch function in cancer is dependent on the cellular context, the particular homologs expressed, and cross-talk with other signaling pathways. We have previously shown that components of the Notch signaling pathway are deregulated in meningiomas. However, the functional consequence of abnormal Notch signaling to meningiomas is unknown. Here, we report that exogenous expression of the Notch pathway effector, HES1, is associated with tetraploid cells in meningioma cell lines. Activated Notch1 and Notch2 receptors induced endogenous HES1 expression and were associated with tetraploidy in meningiomas. Tetraploid meningioma cells exhibited nuclear features of chromosomal instability and increased frequency of nuclear atypia, such as multipolar mitotic spindles and accumulation of cells with large nuclei. FACS-sorted tetraploid cells are viable but have higher rates of spontaneous apoptosis when compared with diploid cells. We have used spectral karyotyping to show that, in contrast to diploid cells, tetraploid cells develop a higher number of both numerical and structural chromosomal abnormalities. Our findings identify a novel function for the Notch signaling pathway in generating tetraploidy and contributing to chromosomal instability. We speculate that abnormal Notch signaling pathway is an initiating genetic mechanism for meningioma and potentially promotes tumor development.

Notch signaling in differentiation and function of dendritic cells

Hematopoietic stem cells give rise to multiple lineages of cells. This process is governed by a tightly controlled signaling network regulated by cytokines and a direct cell-cell contact. Notch signaling represents one of the major pathways activated during direct interaction between hematopoietic progenitor cells and bone marrow stroma. A critical role of Notch signaling in differentiation of T- and B-lymphocytes has now been established. Until recently, the role of Notch signaling in the development of myeloid cells and particular dendritic cells remained unclear. In this review, we discuss recent exciting findings that shed light on the critical role of Notch in differentiation and the function of dendritic cells and its impact on immune responses.

Human Th17 cell clones and natural immune responses

Immunomodulators such as lipopolysaccharides (LPS) and forskolin change the nature of dendritic cells (DCs) to induce Th1 and Th2 cells, respectively, thereby designated Th1 or Th2 adjuvants. Recent studies showed that Th17-inducing activity can be carried by certain polysaccharides such as beta-glucan derived from Candia albicans. Such activities can be scrutinized by using MLR, cAMP and possibly, differential expression of Notch ligand isoforms. In this review article, we also introduce an effective method to establish human Th17 cell clones and a transcriptome analysis using human Th subpopulations. In vivo relevance to human Th17 responses is discussed.

Coordinated regulation of transcription factors through Notch2 is an important mediator of mast cell fate

Mast cells are thought to participate in a wide variety of pathophysiological conditions. Mechanisms of regulation, however, of mast cell production and maturation are still to be elucidated. Mast cell developmental process is likely to be profoundly affected by cell-autonomous transcriptional regulators such as the GATA family and CCAAT/enhancer binding protein (C/EBP) family members. Extracellular regulators such as stem cell factor and IL-3 have essential roles in basal and inducible mast cell generation, respectively. The relationship, however, between the extracellular signaling and cellular transcriptional control is unclear, and the trigger of the mast cell development remains elusive. Notch signaling plays a fundamental role in the lymphopoietic compartment, but its role in myeloid differentiation is less clear. Here, we demonstrate that Notch signaling connects environmental cues and transcriptional control for mast cell fate decision. Delta1, an established Notch ligand, instructs bone marrow common myeloid progenitors and granulocyte-macrophage progenitors toward mast cell lineage at the expense of other granulocyte-macrophage lineages, depending on the function of the Notch2 gene. Notch2 signaling results in the up-regulation of Hes-1 and GATA3, whereas simultaneous overexpression of these transcription factors remarkably biases the progenitor fate toward the mast cell-containing colony-forming cells. C/EBPalpha mRNA was down-regulated in myeloid progenitors as a consequence of Hes-1 overexpression, in agreement with the recent proposal that the down-regulation of C/EBPalpha is necessary for mast cell fate determination. Taken together, signaling through Notch2 determines the fate of myeloid progenitors toward mast cell-producing progenitors, via coordinately up-regulating Hes-1 and GATA3.

Essential role of Notch signaling in effector memory CD8+ T cell-mediated airway hyperresponsiveness and inflammation

Adoptive transfer of in vivo-primed CD8(+) T cells or in vitro-generated effector memory CD8(+) T (T(EFF)) cells restores airway hyperresponsiveness (AHR) and airway inflammation in CD8-deficient (CD8(-/-)) mice. Examining transcription levels, there was a strong induction of Notch1 in T(EFF) cells compared with central memory CD8(+) T cells. Treatment of T(EFF) cells with a gamma-secretase inhibitor (GSI) strongly inhibited Notch signaling in these cells, and after adoptive transfer, GSI-treated T(EFF) cells failed to restore AHR and airway inflammation in sensitized and challenged recipient CD8(-/-) mice, or to enhance these responses in recipient wild-type (WT) mice. These effects of GSI were also associated with increased expression of the Notch ligand Delta1 in T(EFF) cells. Treatment of sensitized and challenged WT mice with Delta1-Fc resulted in decreased AHR and airway inflammation accompanied by higher levels of interferon gamma in bronchoalveolar lavage fluid. These results demonstrate a role for Notch in skewing the T cell response from a T helper (Th)2 to a Th1 phenotype as a consequence of the inhibition of Notch receptor activation and the up-regulation of the Notch ligand Delta1. These data are the first to show a functional role for Notch in the challenge phase of CD8(+) T cell-mediated development of AHR and airway inflammation, and identify Delta1 as an important regulator of allergic airway inflammation.

TPO-independent megakaryocytopoiesis

Megakaryocytopoiesis is a continuous developmental process of platelet production. In this process, a complex network of hemopoietic growth factors are involved, among which TPO (thrombopoietin) is the most thoroughly investigated regulator of MKs (megakaryocytes). In addition to TPO, other regulators also have non-negligible effects on megakaryocytopoiesis. The majority of their effects are independent of TPO signaling. To date, TPO-independent megakaryocytopoiesis forms a regulatory system that includes four signals and (an) unknown signaling pathway(s). These four pathways are the gp 130 (glycoprotein 130)-dependent signaling pathway, the Notch pathway, NMDA (N-methyl-d-aspartate) receptor-mediated signaling, and the SDF-1 (stromal cell-derived factor-1)/FGF-4 (fibroblast growth factor-4) paradigm. Understanding of the TPO-independent regulatory system is important because the system may offer additional opportunities to understand the developmental process and the mechanisms of disorders characterized by abnormal MK and platelet production, such as thrombocytopenia and thrombocythemia, and to advance the development of therapeutics.

JAGGED1 and delta1 differentially regulate the outcome of experimental autoimmune encephalomyelitis

Notch signaling plays an important role during T cell development in the thymus and in T cell activation but the role of Notch in autoimmunity is not clear. We investigated the role of Jagged1 and Delta1 in experimental autoimmune encephalomyelitis. During experimental autoimmune encephalomyelitis, Delta1 expression is up-regulated on dendritic cells and B cells after priming while Jagged1 is up-regulated only on dendritic cells. Administration of anti-Jagged1 Ab exacerbated clinical disease while that of anti-Delta1 Ab reduced the severity of the clinical disease. In contrast, administration of Jagged1-Fc protected from disease, that of Delta1-Fc exacerbated disease. Treatment with Jagged1-Fc was associated with increased IL-10-producing Ag-specific cells in the CNS, while anti-Jagged1 decreased the frequency of IL-10-producing cells. Treatment with Delta1-Fc increased Th1 cells in the CNS, while anti-Delta-1 decreased the frequency of Th1 cells. Manipulation of Delta1 or Jagged1 had no effect on the frequency of Th17 cells or FoxP3(+) cells. Moreover, Jagged1 may play a role in CNS homeostasis because murine astrocytes specifically express Jagged1 that is up-regulated by TGF-beta, whereas IFN-gamma, TNF-alpha, and IL-17 decrease Jagged1 expression. Our study provides novel data about differential roles of Notch ligands in regulating inflammation in the periphery as well as in the CNS.