Non-steady-state hematopoiesis regulated by the C/EBPβ transcription factor

Cebp1 and Cebpβ transcriptional axis controls eosinophilopoiesis in zebrafish

Eosinophils are a group of granulocytes well known for their capacity to protect the host from parasites and regulate immune function. Diverse biological roles for eosinophils have been increasingly identified, but the developmental pattern and regulation of the eosinophil lineage remain largely unknown. Herein, we utilize the zebrafish model to analyze eosinophilic cell differentiation, distribution, and regulation. By identifying eslec as an eosinophil lineage-specific marker, we establish a Tg(eslec:eGFP) reporter line, which specifically labeled cells of the eosinophil lineage from early life through adulthood. Spatial-temporal analysis of eslec+ cells demonstrates their organ distribution from larval stage to adulthood. By single-cell RNA-Seq analysis, we decipher the eosinophil lineage cells from lineage-committed progenitors to mature eosinophils. Through further genetic analysis, we demonstrate the role of Cebp1 in balancing neutrophil and eosinophil lineages, and a Cebp1-Cebpβ transcriptional axis that regulates the commitment and differentiation of the eosinophil lineage. Cross-species functional comparisons reveals that zebrafish Cebp1 is the functional orthologue of human C/EBPεP27 in suppressing eosinophilopoiesis. Our study characterizes eosinophil development in multiple dimensions including spatial-temporal patterns, expression profiles, and genetic regulators, providing for a better understanding of eosinophilopoiesis.

C/EBPβ-induced lymphoid-to-myeloid transdifferentiation emulates granulocyte-monocyte progenitor biology

CCAAT/enhancer-binding protein beta (C/EBPβ) induces primary v-Abl immortalized mouse B cells to transdifferentiate (BT, B cell transdifferentiation) into granulocyte-macrophage progenitor-like cells (GMPBTs). GMPBTs maintain cytokine-independent self-renewal, lineage choice, and multilineage differentiation. Single-cell transcriptomics demonstrated that GMPBTs comprise a continuum of myelomonopoietic differentiation states that seamlessly fit into state-to-fate maps of normal granulocyte-macrophage progenitors (GMPs). Inactivating v-Abl kinase revealed the dependence on activated CSF2-JAK2-STAT5 signaling. Deleting IRF8 diminished monopoiesis and enhanced granulopoiesis while removing C/EBPβ-abrogated self-renewal and granulopoiesis but permitted macrophage differentiation. The GMPBT culture system is easily scalable to explore the basics of GMP biology and lineage commitment and largely reduces ethically and legislatively debatable, labor-intensive, and costly animal experiments.

PU.1 is required to restrain myelopoiesis during chronic inflammatory stress

Chronic inflammation is a common feature of aging and numerous diseases such as diabetes, obesity, and autoimmune syndromes and has been linked to the development of hematological malignancy. Blood-forming hematopoietic stem cells (HSC) can contribute to these diseases via the production of tissue-damaging myeloid cells and/or the acquisition of mutations in epigenetic and transcriptional regulators that initiate evolution toward leukemogenesis. We previously showed that the myeloid "master regulator" transcription factor PU.1 is robustly induced in HSC by pro-inflammatory cytokines such as interleukin (IL)-1β and limits their proliferative activity. Here, we used a PU.1-deficient mouse model to investigate the broader role of PU.1 in regulating hematopoietic activity in response to chronic inflammatory challenges. We found that PU.1 is critical in restraining inflammatory myelopoiesis via suppression of cell cycle and self-renewal gene programs in myeloid-biased multipotent progenitor (MPP) cells. Our data show that while PU.1 functions as a key driver of myeloid differentiation, it plays an equally critical role in tailoring hematopoietic responses to inflammatory stimuli while limiting expansion and self-renewal gene expression in MPPs. These data identify PU.1 as a key regulator of "emergency" myelopoiesis relevant to inflammatory disease and leukemogenesis.

Neutrophil sub-types in maintaining immune homeostasis during steady state, infections and sterile inflammation

INTRODUCTION

Neutrophils are component of innate immune system and a) eliminate pathogens b) maintain immune homeostasis by regulating other immune cells and c) contribute to the resolution of inflammation. Neutrophil mediated inflammation has been described in pathogenesis of various diseases. This indicates neutrophils do not represent homogeneous population but perform multiple functions through confined subsets. Hence, in the present review we summarize various studies describing the heterogeneous nature of neutrophils and associated functions during steady state and pathological conditions.

METHODOLOGY

We performed extensive literature review with key words 'Neutrophil subpopulations' 'Neutrophil subsets', Neutrophil and infections', 'Neutrophil and metabolic disorders', 'Neutrophil heterogeneity' in PUBMED.

RESULTS

Neutrophil subtypes are characterized based on buoyancy, cell surface markers, localization and maturity. Recent advances in high throughput technologies indicate the existence of functionally diverse subsets of neutrophils in bone marrow, blood and tissues in both steady state and pathological conditions. Further, we found proportions of these subsets significantly vary in pathological conditions. Interestingly, stimulus specific activation of signalling pathways in neutrophils have been demonstrated.

CONCLUSION

Neutrophil sub-populations differ among diseases and hence, mechanisms regulating formation, sustenance, proportions and functions of these sub-types vary between physiological and pathological conditions. Hence, mechanistic insights of neutrophil subsets in disease specific manner may facilitate development of neutrophil-targeted therapies.

Novel Insights into the Role of Kras in Myeloid Differentiation: Engaging with Wnt/β-Catenin Signaling

Cells of the HL-60 myeloid leukemia cell line can be differentiated into neutrophil-like cells by treatment with dimethyl sulfoxide (DMSO). The molecular mechanisms involved in this differentiation process, however, remain unclear. This review focuses on the differentiation of HL-60 cells. Although the Ras proteins, a group of small GTP-binding proteins, are ubiquitously expressed and highly homologous, each has specific molecular functions. Kras was shown to be essential for normal mouse development, whereas Hras and Nras are not. Kras knockout mice develop profound hematopoietic defects, indicating that Kras is required for hematopoiesis in adults. The Wnt/β-catenin signaling pathway plays a crucial role in regulating the homeostasis of hematopoietic cells. The protein β-catenin is a key player in the Wnt/β-catenin signaling pathway. A great deal of evidence shows that the Wnt/β-catenin signaling pathway is deregulated in malignant tumors, including hematological malignancies. Wild-type Kras acts as a tumor suppressor during DMSO-induced differentiation of HL-60 cells. Upon DMSO treatment, Kras translocates to the plasma membrane, and its activity is enhanced. Inhibition of Kras attenuates CD11b expression. DMSO also elevates levels of GSK3β phosphorylation, resulting in the release of unphosphorylated β-catenin from the β-catenin destruction complex and its accumulation in the cytoplasm. The accumulated β-catenin subsequently translocates into the nucleus. Inhibition of Kras attenuates Lef/Tcf-sensitive transcription activity. Thus, upon treatment of HL-60 cells with DMSO, wild-type Kras reacts with the Wnt/β-catenin pathway, thereby regulating the granulocytic differentiation of HL-60 cells. Wild-type Kras and the Wnt/β-catenin signaling pathway are activated sequentially, increasing the levels of expression of C/EBPα, C/EBPε, and granulocyte colony-stimulating factor (G-CSF) receptor.

Zebrafish: a convenient tool for myelopoiesis research

Myelopoiesis is the process in which the mature myeloid cells, including monocytes/macrophages and granulocytes, are developed. Irregular myelopoiesis may cause and deteriorate a variety of hematopoietic malignancies such as leukemia. Myeloid cells and their precursors are difficult to capture in circulation, let alone observe them in real time. For decades, researchers had to face these difficulties, particularly in in-vivo studies. As a unique animal model, zebrafish possesses numerous advantages like body transparency and convenient genetic manipulation, which is very suitable in myelopoiesis research. Here we review current knowledge on the origin and regulation of myeloid development and how zebrafish models were applied in these studies.

Systemic Listeria monocytogenes infection in aged mice induces long-term neuroinflammation: the role of miR-155

BACKGROUND

Understanding mechanisms of pathologic neuroinflammation is essential for improving outcomes after central nervous system infections. Brain tissue-resident memory T cells (bT_RM) are recruited during central nervous system infection and promote pathogen control as well as noxious inflammation. Our prior studies in young mice showed optimal recruitment of CD8⁺ bT_RM during neuroinvasive Listeria monocytogenes (Lm) infection required miR-155, and was significantly inhibited by anti-miR-155 oligonucleotides. Since Lm is an important pathogen in the elderly, we hypothesized anti-miR-155 would also inhibit accumulation of CD8⁺ bT_RM in aged mice infected with Lm.

METHODS

Young (2 mo) and aged (> 18 mo) male C57BL/6 mice were infected intra-peritoneally with wild-type Lm, or avirulent Lm mutants lacking the genes required for intracellular motility (ΔactA) or phagosomal escape (Δhly), then were given antibiotics. Brain leukocytes and their intracellular cytokine production were quantified by flow cytometry >28d post-infection (p.i.). The role of miR-155 was tested by injecting mice with anti-miR-155 or control oligonucleotides along with antibiotics.

RESULTS

Aged mice had significantly more homeostatic CD8⁺ bT_RM than did young mice, which did not increase after infection with wild-type Lm despite 50% mortality, whereas young mice suffered no mortality after a larger inoculum. For direct comparison of post-infectious neuroinflammation after the same inoculum, young and aged mice were infected with 10⁷ CFU ΔactA Lm. This mutant caused no mortality and significantly increased CD8⁺ bT_RM 28d p.i. in both groups, whereas bone marrow-derived myeloid cells, particularly neutrophils, increased only in aged mice. Notably, anti-miR-155 reduced accumulation of brain myeloid cells in aged mice after infection, whereas CD8⁺ bT_RM were unaffected.

CONCLUSIONS

Systemic infection with Lm ΔactA is a novel model for studying infection-induced brain inflammation in aged mice without excessive mortality. CD8⁺ bT_RM increase in both young and aged mice after infection, whereas only in aged mice bone marrow-derived myeloid cells increase long-term. In aged mice, anti-miR-155 inhibits brain accumulation of myeloid cells, but not CD8⁺ bT_RM. These results suggest young and aged mice differ in manifestations and mechanisms of infection-induced neuroinflammation and give insight for developing therapies to ameliorate brain inflammation following severe infection in the elderly.

C/EBPβ sustains the oncogenic program of AML cells by cooperating with MYB and co-activator p300 in a transcriptional module

Transcription factor MYB is a key regulator of gene expression in hematopoietic cells and has emerged as a novel drug target for acute myeloid leukemia (AML). Studies aiming to identify potential MYB inhibitors have shown that the natural compound helenalin acetate (HA) inhibits viability and induces cell death and differentiation of AML cells by disrupting the MYB-induced gene expression program. Interestingly, CCAAT-box/enhancer binding protein beta (C/EBPβ), a transcription factor known to cooperate with MYB and the co-activator p300 in myeloid cells, rather than MYB itself, was identified as the primary target of HA. This supports a model in which MYB, C/EBPβ and p300 form the core of a transcriptional module that is essential for the maintenance of proliferative potential of AML cells, highlighting a novel role of C/EBPβ as a pro-leukemogenic factor.

Regulation of emergency granulopoiesis during infection

During acute infectious and inflammatory conditions, a large number of neutrophils are in high demand as they are consumed in peripheral organs. The hematopoietic system rapidly responds to the demand by turning from steady state to emergency granulopoiesis to expedite neutrophil generation in the bone marrow (BM). How the hematopoietic system integrates pathogenic and inflammatory stress signals into the molecular cues of emergency granulopoiesis has been the subject of investigations. Recent studies in the field have highlighted emerging concepts, including the direct sensing of pathogens by BM resident or sentinel hematopoietic stem and progenitor cells (HSPCs), the crosstalk of HSPCs, endothelial cells, and stromal cells to convert signals to granulopoiesis, and the identification of novel inflammatory molecules, such as C/EBP-β, ROS, IL-27, IFN-γ, CXCL1 with direct effects on HSPCs. In this review, we will provide a detailed account of emerging concepts while reassessing well-established cellular and molecular players of emergency granulopoiesis. While providing our views on the discrepant results and theories, we will postulate an updated model of granulopoiesis in the context of health and disease.

Neutrophil Homeostasis and Emergency Granulopoiesis: The Example of Systemic Juvenile Idiopathic Arthritis

Neutrophils are key pathogen exterminators of the innate immune system endowed with oxidative and non-oxidative defense mechanisms. More recently, a more complex role for neutrophils as decision shaping cells that instruct other leukocytes to fine-tune innate and adaptive immune responses has come into view. Under homeostatic conditions, neutrophils are short-lived cells that are continuously released from the bone marrow. Their development starts with undifferentiated hematopoietic stem cells that pass through different immature subtypes to eventually become fully equipped, mature neutrophils capable of launching fast and robust immune responses. During severe (systemic) inflammation, there is an increased need for neutrophils. The hematopoietic system rapidly adapts to this increased demand by switching from steady-state blood cell production to emergency granulopoiesis. During emergency granulopoiesis, the de novo production of neutrophils by the bone marrow and at extramedullary sites is augmented, while additional mature neutrophils are rapidly released from the marginated pools. Although neutrophils are indispensable for host protection against microorganisms, excessive activation causes tissue damage in neutrophil-rich diseases. Therefore, tight regulation of neutrophil homeostasis is imperative. In this review, we discuss the kinetics of neutrophil ontogenesis in homeostatic conditions and during emergency myelopoiesis and provide an overview of the different molecular players involved in this regulation. We substantiate this review with the example of an autoinflammatory disease, i.e. systemic juvenile idiopathic arthritis.

UBQLN4 is activated by C/EBPβ and exerts oncogenic effects on colorectal cancer via the Wnt/β-catenin signaling pathway

Ubiquilin 4 (UBQLN4) is an important member of the ubiquitin-like protein family. An increasing number of studies have shown that UBQLN4 is an important regulator of tumorigenesis. Nevertheless, the biological function and detailed mechanisms of UBQLN4 in colorectal cancer (CRC) development and progression remain unclear. Here, we identified UBQLN4 upregulation in CRC tissues and it is positively associated with CRC size, TNM stage, and lymphatic metastasis. Patients with high UBQLN4 expression had a poor prognosis. Functionally, overexpression of UBQLN4 significantly promoted CRC cell proliferation, migration, and invasion, while UBQLN4 silencing elicited the opposite effect. This result was consistent with the conclusion that UBQLN4 expression correlated positively with the CRC size and lymphatic metastasis. In vivo, UBQLN4 silencing also inhibited tumor growth. Mechanistically, using gene set enrichment analysis (GSEA) and western blot experiments, we identified that UBQLN4 activated the Wnt/β-catenin signaling pathway to upregulate β-catenin and c-Myc expression, thereby promoting CRC proliferation, migration and invasion. A rescue experiment further verified this conclusion. Dual luciferase reporter, real-time quantitative PCR (RT-qPCR), western blot and chromatin immunoprecipitation (ChIP) assays indicated that the transcription factor CCAAT/enhancer-binding protein beta (C/EBPβ) directly bound to the UBQLN4 core promoter region and activated its transcription, upregulating β-catenin and c-Myc expression to promote CRC progression. Thus, our findings suggest that UBQLN4 is a key oncogene in CRC and may be a promising target for the diagnosis and treatment of patients with CRC.

C/EBPβ induces B-cell acute lymphoblastic leukemia and cooperates with BLNK mutations

BLNK (BASH/SLP‐65) encodes an adaptor protein that plays an important role in B‐cell receptor (BCR) signaling. Loss‐of‐function mutations in this gene are observed in human pre‐B acute lymphoblastic leukemia (ALL), and a subset of Blnk knock‐out (KO) mice develop pre‐B‐ALL. To understand the molecular mechanism of the Blnk mutation‐associated pre‐B‐ALL development, retroviral tagging was applied to KO mice using the Moloney murine leukemia virus (MoMLV). The Blnk mutation that significantly accelerated the onset of MoMLV‐induced leukemia and increased the incidence of pre‐B‐ALL Cebpb was identified as a frequent site of retroviral integration, suggesting that its upregulation cooperates with Blnk mutations. Transgenic expression of the liver‐enriched activator protein (LAP) isoform of Cebpb reduced the number of mature B‐lymphocytes in the bone marrow and inhibited differentiation at the pre‐BI stage. Furthermore, LAP expression significantly accelerated leukemogenesis in Blnk KO mice and alone acted as a B‐cell oncogene. Furthermore, an inverse relationship between BLNK and C/EBPβ expression was also noted in human pre‐B‐ALL cases, and the high level of CEBPB expression was associated with short survival periods in patients with BLNK‐downregulated pre‐B‐ALL. These results indicate the association between the C/EBPβ transcriptional network and BCR signaling in pre‐B‐ALL development and leukemogenesis. This study gives insight into ALL progression and suggests that the BCR/C/EBPβ pathway can be a therapeutic target.

Neutrophils at the crossroads of acute viral infections and severity

Neutrophils are versatile immune effector cells essential for mounting a first-line defense against invading pathogens. However, uncontrolled activation can lead to severe life-threatening complications. Neutrophils exist as a heterogeneous population, and their interaction with pathogens and other immune cells may shape the outcome of the host immune response. Diverse classes of viruses, including the recently identified novel SARS-CoV-2, have shown to alter the various aspects of neutrophil biology, offering possibilities for selective intervention. Here, we review heterogeneity within the neutrophil population, highlighting the functional consequences of circulating phenotypes and their critical involvement in exaggerating protective and pathological immune responses against the viruses. We discuss the recent findings of neutrophil extracellular traps (NETs) in COVID-19 pathology and cover other viruses, where neutrophil biology and NETs are crucial for developing disease severity. In the end, we have also pointed out the areas where neutrophil-mediated responses can be finely tuned to outline opportunities for therapeutic manipulation in controlling inflammation against viral infection.

C/EBPβ isoforms sequentially regulate regenerating mouse hematopoietic stem/progenitor cells

The transcription factor CCAAT enhancer-binding protein β (C/EBPβ) is required for stress-induced granulopoiesis at the level of hematopoietic stem/progenitor cells (HSPCs); however, its role and mechanisms of action in HSPCs are unknown. In this study, we assessed the regulation and functions of C/EBPβ in HSPCs, especially under stress conditions. After 5-fluorouracil treatment or bone marrow transplantation, Cebpb-/- HSPCs exhibited impaired cell-cycle activation and myeloid differentiation at the early and late phases of regeneration, respectively, whereas at steady state, Cebpb deficiency did not affect HSPCs. C/EBPβ was upregulated in response to hematopoietic stress, especially in CD150high long term-hematopoietic stem cells (LT-HSCs). Intracellular flow cytometric analysis that detected distinct domains of C/EBPβ revealed that, among the 3 isoforms of C/EBPβ, liver-enriched inhibitory protein (LIP) was upregulated in LT-HSCs prior to liver-enriched activating protein (LAP)/LAP* during regeneration. Early upregulation of LIP promoted cell-cycle entry of LT-HSCs by positively regulating Myc and expanded the HSPCs pool. Subsequent myeloid differentiation of amplified HSPCs was mediated by LAP/LAP*, which were upregulated at a later phase of regeneration. Collectively, our findings show that stress-induced sequential upregulation of C/EBPβ isoforms is critical for fine-tuning the proliferation and differentiation of regenerating HSPCs.

nNOS induction and NOSIP interaction impact granulopoiesis and neutrophil differentiation by modulating nitric oxide generation

Nitric oxide (NO), a versatile free radical and a signalling molecule, plays an important role in the haematopoiesis, inflammation and infection. Impaired proliferation and differentiation of myeloid cells lead to malignancies and Hematopoietic deficiencies. This study was aimed to define the role of nNOS derived NO in neutrophil differentiation (in-vitro) and granulopoiesis (in-vivo) using multipronged approaches. The results obtained from nNOS over-expressing K562 cells revealed induction in C/EBPα derived neutrophil differentiation as evident by an increase in the expression of neutrophil specific cell surface markers, genes, transcription factors and functionality. nNOS mediated response also involved G-CSFR-STAT-3 axis during differentiation. Consistent increase in NO generation was observed during neutrophil differentiation of mice and human CD34⁺ HSPCs. Furthermore, granulopoiesis was abrogated in the nNOS inhibitor treated mice, depicting a decrease in the numbers of BM mature and progenitor neutrophils. Likewise, in vitro inhibition of nNOS in human CD34⁺ HSPCs indicated an indispensable role of nNOS in neutrophil differentiation. Expression of nNOS inhibitory protein, NOSIP was significantly and consistently decreased during the final stage of differentiation and was linked with the augmentation in NO release. Moreover, neutrophils from CML patients had more NOSIP and less NO generation as compared to the PMNs from healthy individuals. The present study thus indicates a critical role of nNOS, and its interaction with NOSIP during neutrophil differentiation. The study also highlights the importance of nNOS in the neutrophil progenitor proliferation and differentiation warranting investigations to assess its role in the haematopoiesis-related disorders.

A road map from single-cell transcriptome to patient classification for the immune response to trauma

Immune dysfunction is an important factor driving mortality and adverse outcomes after trauma but remains poorly understood, especially at the cellular level. To deconvolute the trauma-induced immune response, we applied single-cell RNA sequencing to circulating and bone marrow mononuclear cells in injured mice and circulating mononuclear cells in trauma patients. In mice, the greatest changes in gene expression were seen in monocytes across both compartments. After systemic injury, the gene expression pattern of monocytes markedly deviated from steady state with corresponding changes in critical transcription factors, which can be traced back to myeloid progenitors. These changes were largely recapitulated in the human single-cell analysis. We generalized the major changes in human CD14⁺ monocytes into 6 signatures, which further defined 2 trauma patient subtypes (SG1 vs. SG2) identified in the whole-blood leukocyte transcriptome in the initial 12 hours after injury. Compared with SG2, SG1 patients exhibited delayed recovery, more severe organ dysfunction, and a higher incidence of infection and noninfectious complications. The 2 patient subtypes were also recapitulated in burn and sepsis patients, revealing a shared pattern of immune response across critical illness. Our data will be broadly useful to further explore the immune response to inflammatory diseases and critical illness.

Myeloid-Derived Suppressor Cell Differentiation in Cancer: Transcriptional Regulators and Enhanceosome-Mediated Mechanisms

Myeloid-derived Suppressor Cells (MDSCs) are a sub-population of leukocytes that are important for carcinogenesis and cancer immunotherapy. During carcinogenesis or severe infections, inflammatory mediators induce MDSCs via aberrant differentiation of myeloid precursors. Although several transcription factors, including C/EBPβ, STAT3, c-Rel, STAT5, and IRF8, have been reported to regulate MDSC differentiation, none of them are specifically expressed in MDSCs. How these lineage-non-specific transcription factors specify MDSC differentiation in a lineage-specific manner is unclear. The recent discovery of the c-Rel−C/EBPβ enhanceosome in MDSCs may help explain these context-dependent roles. In this review, we examine several transcriptional regulators of MDSC differentiation, and discuss the concept of non-modular regulation of MDSC signature gene expression by transcription factors such as c-Rel and C/EBPß.

The functional interplay of transcription factors and cell adhesion molecules in experimental myelodysplasia including hematopoietic stem progenitor compartment

Myelodysplastic syndrome is a heterogenous group of disorder with clonal dysregulated hematopoiesis characterized by bone marrow failure, cytogenetic and molecular abnormalities and variable risk of progression to acute myeloid leukemia (AML). The bone marrow niche plays a major role in maintaining the homeostasis and is often injured by the chemotherapeutic drugs leading to catastrophic consequences like myelodysplastic syndrome. In the present study, we made an attempt to find out the osteoblastic niche related alterations in the myelodysplastic bone marrow through mainly flowcytometric and fluorescent microscopic studies. We have also checked the condition of the myelodysplastic bone through micro computed tomography. The results revealed that the affected osteoblasts of the myelodysplastic bone marrow compelled the hematopoietic stem cell to come out of quiescence and become actively proliferating, and in this scenario the decline in expression of cell adhesion molecules like N-Cadherin, Intercellular adhesion molecule 1 (ICAM) and upregulated focal adhesion kinase (FAK) played a major role. The hike in number of osteoclasts in myelodysplastic cases than control also shattered the balance between bone formation and resorption ratio. We have recorded a dysregulated expression of transcription factors GATA2 and CEBPα (CCAAT-enhancer-binding-protein) in the hematopoietic stem progenitor compartment of the myelodysplastic bone marrow, the main reason behind the presence of abnormal myeloblasts in myelodysplastic cases. Collectively, we can say the coordinated perturbations in the osteoblastic niche, cell adhesion molecules together with the transcription factors has resulted in the uncontrolled proliferation of hematopoietic stem cell, dysregulated myelopoiesis, early trafficking of hematopoietic progenitors to blood compartment and at the same time pancytopenic peripheral blood conditions during the progression of N-Ethyl N Nitroso Urea (ENU) induced myelodysplasia.

MicroRNAs and lncRNAs-A New Layer of Myeloid-Derived Suppressor Cells Regulation

Myeloid-derived suppressor cells (MDSCs) constitute an important component in regulating immune responses in several abnormal physiological conditions such as cancer. Recently, novel regulatory tumor MDSC biology modulating mechanisms, including differentiation, expansion and function, were defined. There is growing evidence that miRNAs and long non-coding RNAs (lncRNA) are involved in modulating transcriptional factors to become complex regulatory networks that regulate the MDSCs in the tumor microenvironment. It is possible that aberrant expression of miRNAs and lncRNA contributes to MDSC biological characteristics under pathophysiological conditions. This review provides an overview on miRNAs and lncRNAs epiregulation of MDSCs development and immunosuppressive functions in cancer.

MTL-CEBPA, a Small Activating RNA Therapeutic Upregulating C/EBP-α, in Patients with Advanced Liver Cancer: A First-in-Human, Multicenter, Open-Label, Phase I Trial

PURPOSE

Transcription factor C/EBP-α (CCAAT/enhancer-binding protein alpha) acts as a master regulator of hepatic and myeloid functions and multiple oncogenic processes. MTL-CEBPA is a first-in-class small activating RNA oligonucleotide drug that upregulates C/EBP-α.

PATIENTS AND METHODS

We conducted a phase I, open-label, dose-escalation trial of MTL-CEBPA in adults with advanced hepatocellular carcinoma (HCC) with cirrhosis, or resulting from nonalcoholic steatohepatitis or with liver metastases. Patients received intravenous MTL-CEBPA once a week for 3 weeks followed by a rest period of 1 week per treatment cycle in the dose-escalation phase (3+3 design).

RESULTS

Thirty-eight participants have been treated across six dose levels (28-160 mg/m2) and three dosing schedules. Thirty-four patients were evaluable for safety endpoints at 28 days. MTL-CEBPA treatment-related adverse events were not associated with dose, and no maximum dose was reached across the three schedules evaluated. Grade 3 treatment-related adverse events occurred in nine (24%) patients. In 24 patients with HCC evaluable for efficacy, an objective tumor response was achieved in one patient [4%; partial response (PR) for over 2 years] and stable disease (SD) in 12 (50%). After discontinuation of MTL-CEBPA, seven patients were treated with tyrosine kinase inhibitors (TKIs); three patients had a complete response with one further PR and two with SD.

CONCLUSIONS

MTL-CEBPA is the first saRNA in clinical trials and demonstrates an acceptable safety profile and potential synergistic efficacy with TKIs in HCC. These encouraging phase I data validate targeting of C/EBP-α and have prompted MTL-CEBPA + sorafenib combination studies in HCC.

Congenital neutropenia with variable clinical presentation in novel mutation of the SRP54 gene

BACKGROUND

The SRP54 (signal recognition protein 54) is a conserved component of the ribonucleoprotein complex that mediates cotranslational targeting and translocation of proteins to the endoplasmic reticulum. In 2017, mutations in the gene have been described as a cause of congenital neutropenia with or without pancreatic insufficiency, and since then, only limited cases were added to the literature.

METHODS

Two patients with neutropenia underwent hematological, immunological, and genetic work-up, including lymphocyte phenotyping, immunoglobulins, and complement levels, antineutrophil and antinuclear antibodies, bone marrow FISH panel for myelodysplastic syndrome, whole-exome sequencing, and in silico proteomic analysis.

RESULTS

Clinical findings in the two families revealed a wide spectrum of immunological and clinical manifestations, ranging from mild asymptomatic neutropenia during febrile illnesses to severe neutropenia and life-threatening infection requiring leg amputation. Immunological and hematological work-up showed isolated neutropenia with normal lymphocyte subpopulations, immunoglobulin and complement levels, and negative autoimmune tests. Bone marrow aspirations showed variability ranging from normal myelopoiesis to myeloid maturation arrest at the promyelocytic stage, with normal FISH panel for myelodysplastic syndrome. Genetic analysis identified a novel, de novo, in-frame deletion in the SRP54 gene, c.342-344delAAC, p.T115del. In silico proteomic analysis suggested impaired SRP54 protein function due to reduced GTP activity and stability.

CONCLUSIONS

We describe congenital neutropenia with variable clinical presentation in novel mutation of the SRP54 gene.

A Bayesian data fusion based approach for learning genome-wide transcriptional regulatory networks

BACKGROUND

Reverse engineering of transcriptional regulatory networks (TRN) from genomics data has always represented a computational challenge in System Biology. The major issue is modeling the complex crosstalk among transcription factors (TFs) and their target genes, with a method able to handle both the high number of interacting variables and the noise in the available heterogeneous experimental sources of information.

RESULTS

In this work, we propose a data fusion approach that exploits the integration of complementary omics-data as prior knowledge within a Bayesian framework, in order to learn and model large-scale transcriptional networks. We develop a hybrid structure-learning algorithm able to jointly combine TFs ChIP-Sequencing data and gene expression compendia to reconstruct TRNs in a genome-wide perspective. Applying our method to high-throughput data, we verified its ability to deal with the complexity of a genomic TRN, providing a snapshot of the synergistic TFs regulatory activity. Given the noisy nature of data-driven prior knowledge, which potentially contains incorrect information, we also tested the method's robustness to false priors on a benchmark dataset, comparing the proposed approach to other regulatory network reconstruction algorithms. We demonstrated the effectiveness of our framework by evaluating structural commonalities of our learned genomic network with other existing networks inferred by different DNA binding information-based methods.

CONCLUSIONS

This Bayesian omics-data fusion based methodology allows to gain a genome-wide picture of the transcriptional interplay, helping to unravel key hierarchical transcriptional interactions, which could be subsequently investigated, and it represents a promising learning approach suitable for multi-layered genomic data integration, given its robustness to noisy sources and its tailored framework for handling high dimensional data.

The complexity of neutrophils in health and disease: Focus on cancer

Neutrophils are essential soldiers of the immune response and their role have long been restricted to their activities in defence against microbial infections and during the acute phase of the inflammatory response. However, increasing number of investigations showed that neutrophils are endowed with plasticity and can participate in the orchestration of both innate and adaptive immune responses. Neutrophils have an impact on a broad range of disorders, including infections, chronic inflammations, and cancer. Neutrophils are present in the tumour microenvironment and have been reported to mediate both pro-tumour and anti-tumour responses. Neutrophils can contribute to genetic instability, tumour cell proliferation, angiogenesis and suppression of the anti-tumour immune response. In contrast, neutrophils are reported to mediate anti-tumour resistance by direct killing of tumour cells or by engaging cooperative interactions with other immune cells. Here we discuss the current understandings of neutrophils biology and functions in health and diseases, with a specific focus on their role in cancer biology and their prognostic significance in human cancer.

Dual-specificity phosphatase 1 regulates cell cycle progression and apoptosis in cumulus cells by affecting mitochondrial function, oxidative stress, and autophagy

Dual-specificity phosphatase 1 ( DUSP1) is differentially expressed in cumulus cells of different physiological states, but its specific function and mechanism of action remain unclear. In this study, we explored the effects of DUSP1 expression inhibition on cell cycle progression, proliferation, apoptosis, and lactate and cholesterol levels in cumulus cells and examined reactive oxygen species levels, mitochondrial function, autophagy, and the expression of key cytokine genes. The results showed that inhibition of DUSP1 in cumulus cells caused abnormal cell cycle progression, increased cell proliferation, decreased apoptosis rates, increased cholesterol synthesis and lactic acid content, and increased cell expansion. The main reason for these effects was that inhibition of DUSP1 reduced ROS accumulation, increased glutathione level and mitochondrial membrane potential, and reduced autophagy levels in cells. These results indicate that DUSP1 limits the biological function of bovine cumulus cells under normal physiological conditions and will greatly contribute to further explorations of the physiological functions of cumulus cells and the interactions of the cumulus-oocyte complex.

The CCAAT/Enhancer-Binding Protein Family: Its Roles in MDSC Expansion and Function

Immunosuppressive cells have been highlighted in research due to their roles in tumor progression and treatment failure. Myeloid-derived suppressor cells (MDSCs) are among the major immunosuppressive cell populations in the tumor microenvironment, and transcription factors (TFs) are likely involved in MDSC expansion and activation. As key regulatory TFs, members of the CCAAT/enhancer-binding protein (C/EBP) family possibly modulate many biological processes, including cell growth, differentiation, metabolism, and death. Current evidence suggests that C/EBPs maintain critical regulation of MDSCs and are involved in the differentiation and function of MDSCs within the tumor microenvironment. To better understand the MDSC-associated transcriptional network and identify new therapy targets, we herein review recent findings about the C/EBP family regarding their participation in the expansion and function of MDSCs.

Long Non-coding RNAs: Regulators of the Activity of Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous cell population with potent immunosuppressive functions. They play major roles in cancer and many of the pathologic conditions associated with inflammation. Long non-coding RNAs (lncRNAs) are untranslated functional RNA molecules. The lncRNAs are involved in the control of a wide variety of cellular processes and are dysregulated in different diseases. They can participate in the modulation of immune function and activity of inflammatory cells, including MDSCs. This mini review focuses on the emerging role of lncRNAs in MDSC activity. We summarize how lncRNAs modulate the generation, recruitment, and immunosuppressive functions of MDSCs and the underlying mechanisms.

Kras promotes myeloid differentiation through Wnt/β-catenin signaling

Wild-type Kras, a small GTPase, inactivates Ras growth-promoting signaling. However, the role of Kras in differentiation of myeloid cells remains unclear. This study showed the involvement of Kras in a novel regulatory mechanism underlying the dimethyl sulfoxide (DMSO)-induced differentiation of human acute myeloid leukemia HL-60 cells. Kras was found to positively regulate DMSO-induced differentiation, with the activity of Kras increasing upon DMSO. Inhibition of Kras attenuated CD11b expression in differentiated HL-60 cells. GSK3β, an important component of Wnt signaling, was found to be a downstream signal of Kras. Phosphorylation of GSK3β was markedly enhanced by DMSO treatment. Moreover, inhibition of GSK3β enhanced CD11b expression and triggered the accumulation in the nucleus of β-catenin and Tcf in response to DMSO. Inhibitors of β-catenin-mediated pathways blocked CD11b expression, further indicating that β-catenin is involved in the differentiation of HL-60 cells. Elevated expression of C/EBPα and C/EBPɛ accompanied by the expression of granulocyte colony-stimulating factor (G-CSF) receptor was observed during differentiation. Taken together, these findings suggest that Kras engages in cross talk with the Wnt/β-catenin pathway upon DMSO treatment of HL-60 cells, thereby regulating the granulocytic differentiation of HL-60 cells. These results indicate that Kras acts as a tumor suppressor during the differentiation of myeloid cells.

Myelopoiesis, metabolism and therapy: a crucial crossroads in cancer progression

Cancers promote immunological stresses that induce alterations of the myelopoietic output, defined as emergency myelopoiesis, which lead to the generation of different myeloid populations endowed with tumor-promoting activities. New evidence indicates that acquisition of this tumor-promoting phenotype by myeloid cells is the result of a multistep process, encompassing initial events originating into the bone marrow and later steps operating in the tumor microenvironment. The careful characterization of these sequential mechanisms is likely to offer new potential therapeutic opportunities. Here, we describe relevant mechanisms of myeloid cells reprogramming that instate immune dysfunctions and limit effective responses to anticancer therapy and discuss the influence that metabolic events, as well as chemotherapy, elicit on such events.

Myelopoiesis, metabolism and therapy: a crucial crossroads in cancer progression

Cancers promote immunological stresses that induce alterations of the myelopoietic output, defined as emergency myelopoiesis, which lead to the generation of different myeloid populations endowed with tumor-promoting activities. New evidence indicates that acquisition of this tumor-promoting phenotype by myeloid cells is the result of a multistep process, encompassing initial events originating into the bone marrow and later steps operating in the tumor microenvironment. The careful characterization of these sequential mechanisms is likely to offer new potential therapeutic opportunities. Here, we describe relevant mechanisms of myeloid cells reprogramming that instate immune dysfunctions and limit effective responses to anticancer therapy and discuss the influence that metabolic events, as well as chemotherapy, elicit on such events.

Copper nanoparticle-induced uterine injury in female rats

Copper nanoparticles (Cu-NPs) have been used increasingly in various products and applications. Although recent studies have reported that exposure to Cu-NPs leads to organ accumulation and obvious toxicity, it remains unclear whether Cu-NPs can be translocated to and cause damage in the uterus. In this study, we investigated the potential for uterine injury and gene expression patterns in female rats exposed to 3.12, 6.25, or 12.5 mg/kg/d Cu-NPs via intraperitoneal injection for 14 consecutive days. The results indicated that exposure to Cu-NPs led to significant decreases in the relative uterine weight coefficients and increases in inflammatory cell infiltration, mitochondrial swelling and vacuolization, shortened and reduced endometrial epithelial cell microvilli, and apoptosis. Furthermore, exposure to Cu-NPs increased malondialdehyde (MDA) accumulation and decreased superoxide dismutase (SOD) levels. Signal transduction mechanism studies indicated that exposure to Cu-NPs activated caspases 3, 8, and 9 and BH3 interacting domain death agonist (tBid), reduced B cell leukemia/lymphoma 2 (Bcl-2) expression, and increased the expression of apoptotic peptidase activating factor 1 (Apaf-1), BCL2-associated X, apoptosis regulator (Bax), and cytochrome c. A microarray analysis revealed significant alterations in the expression of 963 genes; of these, 622 were upregulated and 341 were downregulated. The results of further evaluations of some altered genes, including matrix metallopeptidase 12 (Mmp12), using quantitative RT-PCR agreed with the microarray findings. These results provide strong evidence that Cu-NPs can trigger both intrinsic and extrinsic apoptotic pathways to mediate uterine injury, resulting in oxidative stress-related changes in gene expression.

Immune off-target effects of Brentuximab Vedotin in relapsed/refractory Hodgkin Lymphoma

Hodgkin Lymphoma (HL) is associated with deep microenvironment re-shaping and myeloid dysfunction. Given that only limited data are available regarding the role of Brentuximab Vedotin (BV) as single agent in transplant-naive relapsed/refractory (R/R) patients and its off-target effects on immune system, we evaluated the amount of regulatory T-cells (T-regs), myeloid-derived suppressor cells (MDSC) subpopulations, and their functional marker, serum arginase-1 (s-Arg-1), in peripheral blood of 15 consecutive R/R HL patients. After a median of four BV cycles, the overall response rate (complete response + partial response) was 47%, with 4 (27%) complete metabolic remissions. BV reduced the absolute number of three MDSC subtypes and s-Arg-1 levels. Patients with baseline s-Arg-1 ≥200 ng/ml had inferior progression-free survival at 36 months compared to those with low s-Arg-1. T-regs dysfunction was recovered by BV: absolute T-regs count was increased after treatment with BV, independently of metabolic response achieved, with a significant reduction of CD30⁺ T-regs. Our data disclose off-target effects of BV in the microenvironment that could explain its deep and durable clinical efficacy.

The Ontogeny of a Neutrophil: Mechanisms of Granulopoiesis and Homeostasis

Comprising the majority of leukocytes in humans, neutrophils are the first immune cells to respond to inflammatory or infectious etiologies and are crucial participants in the proper functioning of both innate and adaptive immune responses. From their initial appearance in the liver, thymus, and spleen at around the eighth week of human gestation to their generation in large numbers in the bone marrow at the end of term gestation, the differentiation of the pluripotent hematopoietic stem cell into a mature, segmented neutrophil is a highly controlled process where the transcriptional regulators C/EBP-α and C/EBP-ε play a vital role. Recent advances in neutrophil biology have clarified the life cycle of these cells and revealed striking differences between neonatal and adult neutrophils based on fetal maturation and environmental factors. Here we detail neutrophil ontogeny, granulopoiesis, and neutrophil homeostasis and highlight important differences between neonatal and adult neutrophil populations.

C/EBPβ contributes to transcriptional activation of long non-coding RNA NEAT1 during APL cell differentiation

Emerging evidences have shown that long non-coding RNAs (lncRNAs) play critical roles in cancer development and cancer therapy. LncRNA Nuclear Enriched Abundant Transcript 1 (NEAT1) is indispensable during acute promyelocytic leukemia (APL) cell differentiation induced by all-trans retinoic acid (ATRA). However, the precise mechanism of NEAT1 upregulation has not been fully understood. In this study, we performed chromatin immunoprecipitation and luciferase reporter assays to demonstrate that C/EBP family transcription factor C/EBPβ bind to and transactivate the promoter of lncRNA NEAT1 through the C/EBPβ binding sites both around -54 bp and -1453 bp upstream of the transcription start site. Moreover, the expression of C/EBPβ was increased after ATRA treatment, and the binding of C/EBPβ in the NEAT1 promoter was also dramatically increased. Finally, knockdown of C/EBPβ significantly reduced the ATRA-induced upregulation of NEAT1. In conclusion, C/EBPβ directly activates the expression of NEAT1 through binding to the promoter of NEAT1. Knockdown of C/EBPβ impairs ATRA-induced transcriptional activation of NEAT1. Our data indicate that C/EBPβ contributes to ATRA-induced activation of NEAT1 during APL cell differentiation. Our results enrich our knowledge on the regulation of lncRNAs and the regulatory role of C/EBPβ in APL cell differentiation.

Copper nanoparticle-induced ovarian injury, follicular atresia, apoptosis, and gene expression alterations in female rats

Numerous studies have reported the accumulation of copper nanoparticles (Cu NPs) in organs and the corresponding damage, although whether Cu NPs can be translocated to the ovaries and their ovarian toxicity are still unknown. In this study, three groups of female rats were injected with 3.12, 6.25, or 12.5 mg/kg Cu NPs for 14 consecutive days. The pathological changes, hormone levels, apoptosis and apoptotic proteins, oxidative stress, and gene expression characteristics in the ovaries were then investigated. The results demonstrated that the Cu NPs exhibited obvious accumulation in the rat ovaries, leading to ovarian injury, an imbalance of sex hormones, and ovarian cell apoptosis. Cu NP exposure activated caspase 3, caspase 8, caspase 9, and tBid, decreased the protein levels of Bcl-2, increased the expression levels of the proteins Bax and cytochrome c, and promoted malondialdehyde (MDA) accumulation and superoxide dismutase (SOD) reduction. Furthermore, gene microarray analysis showed that Cu NPs (12.5 mg/kg/d) caused 321 differentially expressed genes. Of these, 180 and 141 genes were upregulated and downregulated, respectively. Hsd17b1, Hsd3b1, Hsd3b6, and Hsd3b were involved in steroid and hormone metabolism, whereas Mt3 and Cebpb were associated with apoptosis. Overall, these findings provide strong evidence that Cu NPs trigger both intrinsic and extrinsic apoptotic pathways and regulate key ovarian genes in oxidative stress-mediated ovarian dysfunction.

C/EBPβ is required for survival of Ly6C- monocytes

The transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) is highly expressed in monocytes/macrophages. However, its roles in monopoiesis are largely unknown. Here, we investigated the roles of C/EBPβ in monopoiesis. Further subdivision of monocytes revealed that Cebpb messenger RNA was highly upregulated in Ly6C^- monocytes in bone marrow. Accordingly, the number of Ly6C^- monocytes was significantly reduced in Cebpb^-/- mice. Bone marrow chimera experiments and Mx1-Cre-mediated deletion of Cebpb revealed a cell-intrinsic and monocyte-specific requirement for C/EBPβ in monopoiesis. In Cebpb^-/- mice, turnover of Ly6C^- monocytes was highly accelerated and apoptosis of Ly6C^- monocytes was increased. Expression of Csf1r, which encodes a receptor for macrophage colony-stimulating factor, was significantly reduced in Ly6C^- monocytes of Cebpb^-/- mice. C/EBPβ bound to positive regulatory elements of Csf1r and promoted its transcription. Collectively, these results indicate that C/EBPβ is a critical factor for Ly6C^- monocyte survival, at least in part through upregulation of Csf1r.

CREB engages C/EBPδ to initiate leukemogenesis

cAMP response element binding protein (CREB) is frequently overexpressed in acute myeloid leukemia (AML) and acts as a proto-oncogene; however, it is still debated whether such overactivation alone is able to induce leukemia as its pathogenetic downstream signaling is still unclear. We generated a zebrafish model overexpressing CREB in the myeloid lineage, which showed an aberrant regulation of primitive hematopoiesis, and in 79% of adult CREB-zebrafish a block of myeloid differentiation, triggering to a monocytic leukemia akin the human counterpart. Gene expression analysis of CREB-zebrafish revealed a signature of 20 differentially expressed human homologous CREB targets in common with pediatric AML. Among them, we demonstrated that CREB overexpression increased CCAAT-enhancer-binding protein-δ (C/EBPδ) levels to cause myeloid differentiation arrest, and the silencing of CREB-C/EBPδ axis restored myeloid terminal differentiation. Then, C/EBPδ overexpression was found to identify a subset of pediatric AML affected by a block of myeloid differentiation at monocytic stage who presented a significant higher relapse risk and the enrichment of aggressive signatures. Finally, this study unveils the aberrant activation of CREB-C/EBPδ axis concurring to AML onset by disrupting the myeloid cell differentiation process. We provide a novel in vivo model to perform high-throughput drug screening for AML cure improvement.

Promotion of Expansion and Differentiation of Hematopoietic Stem Cells by Interleukin-27 into Myeloid Progenitors to Control Infection in Emergency Myelopoiesis

Emergency myelopoiesis is inflammation-induced hematopoiesis to replenish myeloid cells in the periphery, which is critical to control the infection with pathogens. Previously, pro-inflammatory cytokines such as interferon (IFN)-α and IFN-γ were demonstrated to play a critical role in the expansion of hematopoietic stem cells (HSCs) and myeloid progenitors, leading to production of mature myeloid cells, although their inhibitory effects on hematopoiesis were also reported. Therefore, the molecular mechanism of emergency myelopoiesis during infection remains incompletely understood. Here, we clarify that one of the interleukin (IL)-6/IL-12 family cytokines, IL-27, plays an important role in the emergency myelopoiesis. Among various types of hematopoietic cells in bone marrow, IL-27 predominantly and continuously promoted the expansion of only Lineage⁻Sca-1⁺c-Kit⁺ (LSK) cells, especially long-term repopulating HSCs and myeloid-restricted progenitor cells with long-term repopulating activity, and the differentiation into myeloid progenitors in synergy with stem cell factor. These progenitors expressed myeloid transcription factors such as Spi1, Gfi1, and Cebpa/b through activation of signal transducer and activator of transcription 1 and 3, and had enhanced potential to differentiate into migratory dendritic cells (DCs), neutrophils, and mast cells, and less so into macrophages, and basophils, but not into plasmacytoid DCs, conventional DCs, T cells, and B cells. Among various cytokines, IL-27 in synergy with the stem cell factor had the strongest ability to augment the expansion of LSK cells and their differentiation into myeloid progenitors retaining the LSK phenotype over a long period of time. The experiments using mice deficient for one of IL-27 receptor subunits, WSX-1, and IFN-γ revealed that the blood stage of malaria infection enhanced IL-27 expression through IFN-γ production, and the IL-27 then promoted the expansion of LSK cells, differentiating and mobilizing them into spleen, resulting in enhanced production of neutrophils to control the infection. Thus, IL-27 is one of the limited unique cytokines directly acting on HSCs to promote differentiation into myeloid progenitors during emergency myelopoiesis.

Emergency myelopoiesis is inflammation-induced hematopoiesis that is critical for controlling infection with pathogens, but the molecular mechanism remains incompletely understood. Here, we clarify that one of the interleukin (IL)-6/IL-12 family cytokines, IL-27, plays an important role in emergency myelopoiesis. Among various types of hematopoietic cells in bone marrow, IL-27 predominantly and continuously promoted expansion of only Lineage⁻Sca-1⁺c-Kit⁺ (LSK) cells, especially long-term repopulating hematopoietic stem cells, and differentiation into myeloid progenitors in synergy with stem cell factor. These progenitors expressed myeloid transcription factors such as Spi1, Gfi1, and Cebpa/b through activation of signal transducer and activator of transcription 1 and 3, and had enhanced potential to differentiate into neutrophils, but not into plasmacytoid dendritic cells. Among various cytokines, IL-27 in synergy with stem cell factor had the strongest ability to augment the expansion of LSK cells and their differentiation into myeloid progenitors. The blood stage of malaria infection was revealed to enhance IL-27 expression through interferon-γ production, and IL-27 then promoted the expansion of LSK cells, differentiating and mobilizing them into the spleen, resulting in enhanced production of neutrophils to control the infection. Thus, IL-27 is one of the limited unique cytokines directly acting on hematopoietic stem cells to promote differentiation into myeloid progenitors during emergency myelopoiesis.

Accelerated apoptosis of peripheral blood monocytes in Cebpb-deficient mice

The CCAAT/enhancer-binding protein β (C/EBPβ) transcription factor is required for granulopoiesis under stress conditions. However, little is known about its roles in steady state hematopoiesis. Here, we analyzed the peripheral blood and bone marrow of Cebpb(-/-) mice at steady state by flow cytometry and unexpectedly found that the number of peripheral blood monocytes was severely reduced, while the number of bone marrow monocytes was maintained. The ability of Cebpb(-/-) bone marrow cells to give rise to macrophages/monocytes in vitro was comparable to that of wild-type bone marrow cells. Apoptosis of monocytes was enhanced in the peripheral blood, but not in the bone marrow of Cebpb(-/-) mice. These results indicate that C/EBPβ is required for the survival of monocytes in peripheral blood.