Transcription factors that regulate monocyte/macrophage differentiation

Activated mesenchymal stem/stromal cells promote myeloid cell differentiation via CCL2/CCR2 signaling

Myeloid cells, which originate from hematopoietic stem/progenitor cells (HSPCs), play a crucial role in mitigating infections. This study aimed to explore the impact of mesenchymal stem/stromal cells (MSCs) on the differentiation of HSPCs and progenitors through the C-C motif chemokine CCL2/CCR2 signaling pathway. Murine MSCs, identified as PDGFRα+Sca-1+ cells (PαS cells), were found to secrete CCL2, particularly in response to lipopolysaccharide stimulation. MSC-secreted CCL2 promoted the differentiation of granulocyte/macrophage progenitors into the myeloid lineage. MSC-derived CCL2 plays an important role in the early phase of myeloid cell differentiation in vivo. Single-cell RNA sequencing analysis confirmed that CCL2-mediated cell fate determination was also observed in human bone marrow cells. These findings provide valuable insights for investigating the in vivo effects of MSC transplantation.

Temporal Analysis Reveals the Transient Differential Expression of Transcription Factors That Underlie the Trans-Differentiation of Human Monocytes to Macrophages

The activation of monocytes and their trans-differentiation into macrophages are critical processes of the immune response. Prior work has characterized the differences in the expression between monocytes and macrophages, but the transitional process between these cells is poorly detailed. Here, we analyzed the temporal changes of the transcriptome during trans-differentiation of primary human monocytes into M0 macrophages. We find changes with many transcription factors throughout the process, the vast majority of which exhibit a maximally different expression at the intermediate stages. A few factors, including AP-1, were previously known to play a role in immunological transitions, but most were not. Thus, these findings indicate that this trans-differentiation requires the dynamic expression of many transcription factors not previously discussed in immunology, and provide a foundation for the delineation of the molecular mechanisms associated with healthy or pathological responses that involve this transition.

Altered recruitment of Sp isoforms to HIV-1 long terminal repeat between differentiated monoblastic cell lines and primary monocyte-derived macrophages

Human immunodeficiency virus type 1 (HIV-1) transcription in cells of the monocyte-macrophage lineage is regulated by interactions between the HIV-1 long terminal repeat (LTR) and a variety of host cell and viral proteins. Binding of the Sp family of transcription factors (TFs) to the G/C box array of the LTR governs both basal as well as activated LTR-directed transcriptional activity. The effect of monocytic differentiation on Sp factor binding and transactivation was examined with respect to the HIV-1 LTR. The binding of Sp1, full-length Sp3 and truncated Sp3 to a high affinity HIV-1 Sp element was specifically investigated and results showed that Sp1 binding increased relative to the binding of the sum of full-length and truncated Sp3 binding following chemically-induced monocytic differentiation in monoblastic (U-937, THP-1) and myelomonocytic (HL-60) cells. In addition, Sp binding ratios from PMA-induced cell lines were shown to more closely approximate those derived from primary monocyte-derived macrophages (MDMs) than did ratios derived from uninduced cell lines. The altered Sp binding phenotype associated with changes in the transcriptional activation mediated by the HIV-1 G/C box array. Additionally, analysis of post-translational modifications on Sp1 and Sp3 revealed a loss of phosphorylation on serine and threonine residues with chemically-induced differentiation indicating that the activity of Sp factors is additionally regulated at the level of post-translational modifications (PTMs).

Identification of mRNA Signature for Predicting Prognosis Risk of Rectal Adenocarcinoma

Background: The immune system plays a crucial role in rectal adenocarcinoma (READ). Immune-related genes may help predict READ prognoses. Methods: The Cancer Genome Atlas dataset and GSE56699 were used as the training and validation datasets, respectively, and differentially expressed genes (DEGs) were identified. The optimal DEG combination was determined, and the prognostic risk model was constructed. The correlation between optimal DEGs and immune infiltrating cells was evaluated. Results: Nine DEGs were selected for analysis. Moreover, ADAMDEC1 showed a positive correlation with six immune infiltrates, most notably with B cells and dendritic cells. F13A1 was also positively correlated with six immune infiltrates, particularly macrophage and dendritic cells, whereas LGALS9C was negatively correlated with all immune infiltrates except B cells. Additionally, the prognostic risk model was strongly correlated with the actual situation. We retained only three prognosis risk factors: age, pathologic stage, and prognostic risk model. The stratified analysis revealed that lower ages and pathologic stages have a better prognosis with READ. Age and mRNA prognostic factors were the most important factors in determining the possibility of 3- and 5-year survival. Conclusion: In summary, we identified a nine-gene prognosis risk model that is applicable to the treatment of READ. Altogether, characteristics such as the gene signature and age have a strong predictive value for prognosis risk.

Cholesterol in the Cell Membrane-An Emerging Player in Atherogenesis

Membrane cholesterol is essential for cell membrane properties, just as serum cholesterol is important for the transport of molecules between organs. This review focuses on cholesterol transport between lipoproteins and lipid rafts on the surface of macrophages. Recent studies exploring this mechanism and recognition of the central dogma-the key role of macrophages in cardiovascular disease-have led to the notion that this transport mechanism plays a major role in the pathogenesis of atherosclerosis. The exact molecular mechanism of this transport remains unclear. Future research will improve our understanding of the molecular and cellular bases of lipid raft-associated cholesterol transport.

Temporal Quantitative Phosphoproteomics Profiling of Interleukin-33 Signaling Network Reveals Unique Modulators of Monocyte Activation

Interleukin-33 (IL-33), a member of the IL-1 superfamily cytokines, is an endogenous danger signal and a nuclear-associated cytokine. It is one of the essential mediators of both innate and adaptive immune responses. Aberrant IL-33 signaling has been demonstrated to play a defensive role against various infectious and inflammatory diseases. Although the signaling responses mediated by IL-33 have been previously reported, the temporal signaling dynamics are yet to be explored. To this end, we applied quantitative temporal phosphoproteomics analysis to elucidate pathways and proteins induced by IL-33 in THP-1 monocytes. Employing a TMT labeling-based quantitation and titanium dioxide (TiO₂)-based phosphopeptide enrichment strategy followed by mass spectrometry analysis, we identified and quantified 9448 unique phosphopeptides corresponding to 3392 proteins that showed differential regulation. Of these, 171 protein kinases, 60 phosphatases and 178 transcription factors were regulated at different phases of IL-33 signaling. In addition to the confirmed activation of canonical signaling modules including MAPK, NFκB, PI3K/AKT modules, pathway analysis of the time-dependent phosphorylation dynamics revealed enrichment of several cellular processes, including leukocyte adhesion, response to reactive oxygen species, cell cycle checkpoints, DNA damage and repair pathways. The detailed quantitative phosphoproteomic map of IL-33 signaling will serve as a potentially useful resource to study its function in the context of inflammatory and pathological conditions.

Systematic identification of genomic elements that regulate FCGR2A expression and harbor variants linked with autoimmune disease

BACKGROUND

FCGR2A binds antibody-antigen complexes to regulate the abundance of circulating and deposited complexes along with downstream immune and autoimmune responses. Although the abundance of FCRG2A may be critical in immune-mediated diseases, little is known about whether its surface expression is regulated through cis genomic elements and non-coding variants. In the current study, we aimed to characterize the regulation of FCGR2A expression, the impact of genetic variation and its association with autoimmune disease.

METHODS

We applied CRISPR-based interference and editing to scrutinize 1.7 Mb of open chromatin surrounding the FCGR2A gene to identify regulatory elements. Relevant transcription factors (TFs) binding to these regions were defined through public databases. Genetic variants affecting regulation were identified using luciferase reporter assays and were verified in a cohort of 1996 genotyped healthy individuals using flow cytometry.

RESULTS

We identified a complex proximal region and five distal enhancers regulating FCGR2A. The proximal region split into subregions upstream and downstream of the transcription start site, was enriched in binding of inflammation-regulated TFs, and harbored a variant associated with FCGR2A expression in primary myeloid cells. One distal enhancer region was occupied by CCCTC-binding factor (CTCF) whose binding site was disrupted by a rare genetic variant, altering gene expression.

CONCLUSIONS

The FCGR2A gene is regulated by multiple proximal and distal genomic regions, with links to autoimmune disease. These findings may open up novel therapeutic avenues where fine-tuning of FCGR2A levels may constitute a part of treatment strategies for immune-mediated diseases.

TET2 mutations are associated with hypermethylation at key regulatory enhancers in normal and malignant hematopoiesis

Mutations in the epigenetic modifier TET2 are frequent in myeloid malignancies and clonal hematopoiesis of indeterminate potential (CHIP) and clonal cytopenia of undetermined significance (CCUS). Here, we investigate associations between TET2 mutations and DNA methylation in whole blood in 305 elderly twins, 15 patients with CCUS and 18 healthy controls. We find that TET2 mutations are associated with DNA hypermethylation at enhancer sites in whole blood in CHIP and in both granulocytes and mononuclear cells in CCUS. These hypermethylated sites are associated with leukocyte function and immune response and ETS-related and C/EBP-related transcription factor motifs. While the majority of TET2-associated hypermethylation sites are shared between CHIP and in AML, we find a set of AML-specific hypermethylated loci at active enhancer elements in hematopoietic stem cells. In summary, we show that TET2 mutations is associated with hypermethylated enhancers involved in myeloid differentiation in both CHIP, CCUS and AML patients.

Reduction of Cell Proliferation by Acute C2H6O Exposure

Simple Summary

Alcoholic beverages and acetaldehyde formed during their metabolism are carcinogenic to humans. Alcohol drinking may affect bone marrow stem cell niche, suppressing physiological hematopoiesis and ultimately reducing the organism’s capacity to fight against cancer, infections, and to promote tissue regeneration. To elucidate in vivo the cellular mechanisms associated with alcohol intake toxicity, we used a mouse model in which proliferating cells produce the firefly’s light-emitting protein. In this animal, alcohol exposure transiently “turns off the light”, indicating a negative effect on cell proliferation in the bone marrow and spleen. Pharmacological treatment with substances interfering with ethanol metabolism, reducing acetaldehyde production, partially restores the physiological cell proliferation rate. Over 560 million people worldwide have increased susceptibility to acetaldehyde toxicity and 4% of cancer deaths are attributable to alcohol. Our model might provide a suitable tool to further investigate in vivo the effects of alcohol metabolism and aldehydes production on carcinogenesis.

Abstract

Endogenous acetaldehyde production from the metabolism of ingested alcohol exposes hematopoietic progenitor cells to increased genotoxic risk. To develop possible therapeutic strategies to prevent or reverse alcohol abuse effects, it would be critical to determine the temporal progression of acute ethanol toxicity on progenitor cell numbers and proliferative status. We followed the variation of the cell proliferation rate in bone marrow and spleen in response to acute ethanol intoxication in the MITO-Luc mouse, in which NF-Y-dependent cell proliferation can be assessed in vivo by non-invasive bioluminescent imaging. One week after ethanol administration, bioluminescent signals in bone marrow and spleen decreased below the level corresponding to physiological proliferation, and they progressively resumed to pre-treatment values in approximately 4 weeks. Boosting acetaldehyde catabolism by administration of an aldehyde dehydrogenase activity activator or administration of polyphenols with antioxidant activity partially restored bone marrow cells’ physiological proliferation. These results indicate that in this mouse model, bioluminescent alteration reflects the reduction of the physiological proliferation rate of bone marrow progenitor cells due to the toxic effect of aldehydes generated by alcohol oxidation. In summary, this study presents a novel view of the impact of acute alcohol intake on bone marrow cell proliferation in vivo.

Single-cell transcriptome profiling of an adult human cell atlas of 15 major organs

BACKGROUND

As core units of organ tissues, cells of various types play their harmonious rhythms to maintain the homeostasis of the human body. It is essential to identify the characteristics of cells in human organs and their regulatory networks for understanding the biological mechanisms related to health and disease. However, a systematic and comprehensive single-cell transcriptional profile across multiple organs of a normal human adult is missing.

RESULTS

We perform single-cell transcriptomes of 84,363 cells derived from 15 tissue organs of one adult donor and generate an adult human cell atlas. The adult human cell atlas depicts 252 subtypes of cells, including major cell types such as T, B, myeloid, epithelial, and stromal cells, as well as novel COCH+ fibroblasts and FibSmo cells, each of which is distinguished by multiple marker genes and transcriptional profiles. These collectively contribute to the heterogeneity of major human organs. Moreover, T cell and B cell receptor repertoire comparisons and trajectory analyses reveal direct clonal sharing of T and B cells with various developmental states among different tissues. Furthermore, novel cell markers, transcription factors, and ligand-receptor pairs are identified with potential functional regulations in maintaining the homeostasis of human cells among tissues.

CONCLUSIONS

The adult human cell atlas reveals the inter- and intra-organ heterogeneity of cell characteristics and provides a useful resource in uncovering key events during the development of human diseases in the context of the heterogeneity of cells and organs.

Predicting transcription factor binding in single cells through deep learning

Characterizing genome-wide binding profiles of transcription factors (TFs) is essential for understanding biological processes. Although techniques have been developed to assess binding profiles within a population of cells, determining them at a single-cell level remains elusive. Here, we report scFAN (single-cell factor analysis network), a deep learning model that predicts genome-wide TF binding profiles in individual cells. scFAN is pretrained on genome-wide bulk assay for transposase-accessible chromatin sequencing (ATAC-seq), DNA sequence, and chromatin immunoprecipitation sequencing (ChIP-seq) data and uses single-cell ATAC-seq to predict TF binding in individual cells. We demonstrate the efficacy of scFAN by both studying sequence motifs enriched within predicted binding peaks and using predicted TFs for discovering cell types. We develop a new metric "TF activity score" to characterize each cell and show that activity scores can reliably capture cell identities. scFAN allows us to discover and study cellular identities and heterogeneity based on chromatin accessibility profiles.

Transcriptomic Evidence Reveals the Molecular Basis for Functional Differentiation of Hemocytes in a Marine Invertebrate, Crassostrea gigas

Hemocytes play unequivocally central roles in host immune defense of bivalve mollusks, though the exact mechanisms underlying their functional differentiation are only partially understood. To this end, granulocytes and hyalinocytes were sorted via flow cytometry from hemocytes of the Pacific oyster Crassostrea gigas, and consequently quantitative transcriptomic analysis revealed a striking array of differentially expressed genes (DEGs), which were globally upregulated in granulocytes, dedicating to functional differentiation among oyster hemocytes. Our network of DEGs illustrated actively engaged signaling pathways, with Cdc42/Cdc42l being a core regulator of pathway network, which was validated by a dramatically reduced capacity for hemocyte phagocytosis in the presence of Cdc42 inhibitors. Additionally, a number of transcription factors were identified among DEGs, including ELK, HELT, and Fos, which were predominantly expressed in granulocytes. The AP-1 transcription factor Fos was confirmed to facilitate functional differentiation of hemocytes in an assay on binding to target genes by the AP-1 binding site, consistent with downstream phagocytosis and ROS production. Importantly, Cdc42/Cdc42l were also regulated by the expression of Fos, providing a possible regulatory mechanism-guided hemocyte functional differentiation. Findings in this study have bridged a knowledge gap on the mechanistic underpinnings of functional differentiation of hemocytes in a marine invertebrate C. gigas, which promise to facilitate research on the evolution of immune defense and functional differentiation of phagocyte in higher-order and more recent phyla.

Models for Monocytic Cells in the Tumor Microenvironment

Monocytes (Mos) are immune cells that critically regulate cancer, enabling tumor growth and modulating metastasis. Mos can give rise to tumor-associated macrophages (TAMs) and Mo-derived dendritic cells (moDCs), all of which shape the tumor microenvironment (TME). Thus, understanding their roles in the TME is key for improved immunotherapy. Concurrently, various biological and mechanical factors including changes in local cytokines, extracellular matrix production, and metabolic changes in the TME affect the roles of monocytic cells. As such, relevant TME models are critical to achieve meaningful insight on the precise functions, mechanisms, and effects of monocytic cells. Notably, murine models have yielded significant insight into human Mo biology. However, many of these results have yet to be confirmed in humans, reinforcing the need for improved in vitro human TME models for the development of cancer interventions. Thus, this chapter (1) summarizes current insight on the tumor biology of Mos, TAMs, and moDCs, (2) highlights key therapeutic applications relevant to these cells, and (3) discusses various TME models to study their TME-related activity. We conclude with a perspective on the future research trajectory of this topic.

Lung Macrophage Functional Properties in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is caused by the chronic exposure of the lungs to toxic particles and gases. These exposures initiate a persistent innate and adaptive immune inflammatory response in the airways and lung tissues. Lung macrophages (LMs) are key innate immune effector cells that identify, engulf, and destroy pathogens and process inhaled particles, including cigarette smoke and particulate matter (PM), the main environmental triggers for COPD. The number of LMs in lung tissues and airspaces is increased in COPD, suggesting a potential key role for LMs in initiating and perpetuating the chronic inflammatory response that underpins the progressive nature of COPD. The purpose of this brief review is to discuss the origins of LMs, their functional properties (chemotaxis, recruitment, mediator production, phagocytosis and apoptosis) and changes in these properties due to exposure to cigarette smoke, ambient particulate and pathogens, as well as their persistent altered functional properties in subjects with established COPD. We also explore the potential to therapeutically modulate and restore LMs functional properties, to improve impaired immune system, prevent the progression of lung tissue destruction, and improve both morbidity and mortality related to COPD.

Avertin affects murine colitis by regulating neutrophils and macrophages

Anesthetics are thought to be involved in immunomodulation. Avertin is one of the safest and most commonly used intravenous anesthetics in rodent experiments; it is also widely used in euthanasia of inflammatory bowel disease (IBD) models. This study aimed to define the role and mechanism of action of Avertin on murine colitis. We assessed the effects of a single Avertin injection on colitis using the disease activity index (DAI), pathology, enzyme-linked immunosorbent assay (ELISA), multiplex-ELISA, flow cytometry, and routine blood examination in wild-type (WT) and dextran sodium sulphate (DSS)-treated mice. Although Avertin caused acute cecitis in WT mice after 24 h and aggravated inflammation in the medium term, it alleviated inflammation in the late stage of DSS-induced colitis according to the DAI. Avertin upregulated MPO production and induced the accumulation of neutrophils and macrophages in intestinal mucosa of both WT and DSS-treated mice; the altered MPO might indicate a change in respiratory burst. However, it exhibited a more effective suppression of inflammatory factors secreted by macrophages as the colitis progressed. Avertin led to an increase in neutrophils and decrease in monocytes in both WT and DSS-treated mice blood. Our findings suggest that Avertin aggravates inflammation in the early and medium terms, but alleviates inflammation in the late stage of colitis by regulating neutrophils and macrophages.

Dysregulation of macrophage development and phenotype in diabetic human macrophages can be rescued by Hoxa3 protein transduction

Controlled inflammatory responses of myeloid cells recruited to wounds are essential for effective repair. In diabetes, the inflammatory response is prolonged and augmented over time, with increased myeloid cells present in the wound that fail to switch from a pro-inflammatory phenotype to a pro-healing phenotype. These defects lead to delayed angiogenesis and tissue repair and regeneration, and contribute to chronic wound formation. In mouse models of diabetes, this aberrant phenotype is partially mediated by stable intrinsic changes to the developing myeloid cells in the bone marrow, affecting their maturation and polarization potential. Previous studies have shown that freshly isolated peripheral blood mononuclear cells from diabetic patients are more inflammatory than non-diabetic counterparts. However, the phenotype of macrophages from human diabetic patients has not been well characterized. Here we show that diabetic-derived human macrophages cultured for 6 days in vitro maintain a pro-inflammatory priming and hyperpolarize to a pro-inflammatory phenotype when stimulated with LPS and INF-ɣ or TNF. In addition, diabetic-derived macrophages show maturation defects associated with reduced expression of the RUNX1 transcription factor that promotes myeloid cell development. Targeting intrinsic defects in myeloid cells by protein transduction of the Hoxa3 transcription factor can rescue some inflammation and maturation defects in human macrophages from diabetic patients via upregulation of Runx1. In addition, Hoxa3 can modulate the levels of p65/NF-κB and histone acetyltransferase and deacetylase activity, as well as inhibit acetylation of the TNF promoter. Altogether, these results show a link between myeloid cell maturation and inflammatory responses, and that diabetes induces intrinsic changes to human myeloid cells that are maintained over time, as well as potentially therapeutic Hoxa3-mediated mechanisms of controlling the inflammatory response in diabetes.

Revealing the Critical Regulators of Cell Identity in the Mouse Cell Atlas

Recent progress in single-cell technologies has enabled the identification of all major cell types in mouse. However, for most cell types, the regulatory mechanism underlying their identity remains poorly understood. By computational analysis of the recently published mouse cell atlas data, we have identified 202 regulons whose activities are highly variable across different cell types, and more importantly, predicted a small set of essential regulators for each major cell type in mouse. Systematic validation by automated literature and data mining provides strong additional support for our predictions. Thus, these predictions serve as a valuable resource that would be useful for the broad biological community. Finally, we have built a user-friendly, interactive web portal to enable users to navigate this mouse cell network atlas.

CRISPR/Cas9-mediated ASXL1 mutations in U937 cells disrupt myeloid differentiation

Additional sex combs-like 1 (ASXL1) is a well‑known tumor suppressor gene and epigenetic modifier. ASXL1 mutations are frequent in myeloid malignances; these mutations are risk factors for the development of myelodysplasia and also appear as small clones during normal aging. ASXL1 appears to act as an epigenetic regulator of cell survival and myeloid differentiation; however, the molecular mechanisms underlying the malignant transformation of cells with ASXL1 mutations are not well defined. Using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein-9 nuclease (Cas9) genome editing, heterozygous and homozygous ASXL1 mutations were introduced into human U937 leukemic cells. Comparable cell growth and cell cycle progression were observed between wild-type (WT) and ASXL1-mutated U937 cells. Drug-induced cytotoxicity, as measured by growth inhibition and apoptosis in the presence of the cell-cycle active agent 5-fluorouracil, was variable among the mutated clones but was not significantly different from WT cells. In addition, ASXL1-mutated cells exhibited defects in monocyte/macrophage differentiation. Transcriptome analysis revealed that ASXL1 mutations altered differentiation of U937 cells by disturbing genes involved in myeloid differentiation, including cytochrome B-245 β chain and C-type lectin domain family 5, member A. Dysregulation of numerous gene sets associated with cell death and survival were also observed in ASXL1-mutated cells. These data provide evidence regarding the underlying molecular mechanisms induced by mutated ASXL1 in leukemogenesis.

Characteristics of functional enrichment and gene expression level of human putative transcriptional target genes

BACKGROUND

Transcriptional target genes show functional enrichment of genes. However, how many and how significantly transcriptional target genes include functional enrichments are still unclear. To address these issues, I predicted human transcriptional target genes using open chromatin regions, ChIP-seq data and DNA binding sequences of transcription factors in databases, and examined functional enrichment and gene expression level of putative transcriptional target genes.

RESULTS

Gene Ontology annotations showed four times larger numbers of functional enrichments in putative transcriptional target genes than gene expression information alone, independent of transcriptional target genes. To compare the number of functional enrichments of putative transcriptional target genes between cells or search conditions, I normalized the number of functional enrichment by calculating its ratios in the total number of transcriptional target genes. With this analysis, native putative transcriptional target genes showed the largest normalized number of functional enrichments, compared with target genes including 5-60% of randomly selected genes. The normalized number of functional enrichments was changed according to the criteria of enhancer-promoter interactions such as distance from transcriptional start sites and orientation of CTCF-binding sites. Forward-reverse orientation of CTCF-binding sites showed significantly higher normalized number of functional enrichments than the other orientations. Journal papers showed that the top five frequent functional enrichments were related to the cellular functions in the three cell types. The median expression level of transcriptional target genes changed according to the criteria of enhancer-promoter assignments (i.e. interactions) and was correlated with the changes of the normalized number of functional enrichments of transcriptional target genes.

CONCLUSIONS

Human putative transcriptional target genes showed significant functional enrichments. Functional enrichments were related to the cellular functions. The normalized number of functional enrichments of human putative transcriptional target genes changed according to the criteria of enhancer-promoter assignments and correlated with the median expression level of the target genes. These analyses and characters of human putative transcriptional target genes would be useful to examine the criteria of enhancer-promoter assignments and to predict the novel mechanisms and factors such as DNA binding proteins and DNA sequences of enhancer-promoter interactions.

Static and Dynamic DNA Loops form AP-1-Bound Activation Hubs during Macrophage Development

The three-dimensional arrangement of the human genome comprises a complex network of structural and regulatory chromatin loops important for coordinating changes in transcription during human development. To better understand the mechanisms underlying context-specific 3D chromatin structure and transcription during cellular differentiation, we generated comprehensive in situ Hi-C maps of DNA loops in human monocytes and differentiated macrophages. We demonstrate that dynamic looping events are regulatory rather than structural in nature and uncover widespread coordination of dynamic enhancer activity at preformed and acquired DNA loops. Enhancer-bound loop formation and enhancer activation of preformed loops together form multi-loop activation hubs at key macrophage genes. Activation hubs connect 3.4 enhancers per promoter and exhibit a strong enrichment for activator protein 1 (AP-1)-binding events, suggesting that multi-loop activation hubs involving cell-type-specific transcription factors represent an important class of regulatory chromatin structures for the spatiotemporal control of transcription.

Transcriptional mechanisms that control expression of the macrophage colony-stimulating factor receptor locus

The proliferation, differentiation, and survival of cells of the macrophage lineage depends upon signals from the macrophage colony-stimulating factor (CSF) receptor (CSF1R). CSF1R is expressed by embryonic macrophages and induced early in adult hematopoiesis, upon commitment of multipotent progenitors to the myeloid lineage. Transcriptional activation of CSF1R requires interaction between members of the E26 transformation-specific family of transcription factors (Ets) (notably PU.1), C/EBP, RUNX, AP-1/ATF, interferon regulatory factor (IRF), STAT, KLF, REL, FUS/TLS (fused in sarcoma/ranslocated in liposarcoma) families, and conserved regulatory elements within the mouse and human CSF1R locus. One element, the Fms-intronic regulatory element (FIRE), within intron 2, is conserved functionally across all the amniotes. Lineage commitment in multipotent progenitors also requires down-regulation of specific transcription factors such as MYB, FLI1, basic leucine zipper transcriptional factor ATF-like (BATF3), GATA-1, and PAX5 that contribute to differentiation of alternative lineages and repress CSF1R transcription. Many of these transcription factors regulate each other, interact at the protein level, and are themselves downstream targets of CSF1R signaling. Control of CSF1R transcription involves feed–forward and feedback signaling in which CSF1R is both a target and a participant; and dysregulation of CSF1R expression and/or function is associated with numerous pathological conditions. In this review, we describe the regulatory network behind CSF1R expression during differentiation and development of cells of the mononuclear phagocyte system.

Crude oil impairs immune function and increases susceptibility to pathogenic bacteria in southern flounder

Exposure to crude oil or its individual constituents can have detrimental impacts on fish species, including impairment of the immune response. Increased observations of skin lesions in northern Gulf of Mexico fish during the 2010 Deepwater Horizon oil spill indicated the possibility of oil-induced immunocompromisation resulting in bacterial or viral infection. This study used a full factorial design of oil exposure and bacterial challenge to examine how oil exposure impairs southern flounder (Paralichthys lethostigma) immune function and increases susceptibility to the bacteria Vibrio anguillarum, a causative agent of vibriosis. Fish exposed to oil prior to bacterial challenge exhibited 94.4% mortality within 48 hours of bacterial exposure. Flounder challenged with V. anguillarum without prior oil exposure had <10% mortality. Exposure resulted in taxonomically distinct gill and intestine bacterial communities. Mortality strongly correlated with V. anguillarum levels, where it comprised a significantly higher percentage of the microbiome in Oil/Pathogen challenged fish and was nearly non-existent in the No Oil/Pathogen challenged fish bacterial community. Elevated V. anguillarum levels were a direct result of oil exposure-induced immunosuppression. Oil-exposure reduced expression of immunoglobulin M, the major systemic fish antibody, and resulted in an overall downregulation in transcriptome response, particularly in genes related to immune function, response to stimulus and hemostasis. Ultimately, sediment-borne oil exposure impairs immune function, leading to increased incidences of bacterial infections. This type of sediment-borne exposure may result in long-term marine ecosystem effects, as oil-bound sediment in the northern Gulf of Mexico will likely remain a contamination source for years to come.

Nitro-oleic acid regulates growth factor-induced differentiation of bone marrow-derived macrophages

Many diseases accompanied by chronic inflammation are connected with dysregulated activation of macrophage subpopulations. Recently, we reported that nitro-fatty acids (NO₂-FAs), products of metabolic and inflammatory reactions of nitric oxide and nitrite, modulate macrophage and other immune cell functions. Bone marrow cell suspensions were isolated from mice and supplemented with macrophage colony-stimulating factor (M-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF) in combination with NO₂-OA for different times. RAW 264.7 macrophages were used for short-term (1-5min) experiments. We discovered that NO₂-OA reduces cell numbers, cell colony formation, and proliferation of macrophages differentiated with colony-stimulating factors (CSFs), all in the absence of toxicity. In a case of GM-CSF-induced bone marrow-derived macrophages (BMMs), NO₂-OA acts via downregulation of signal transducer and activator of transcription 5 and extracellular signal-regulated kinase (ERK) activation. In the case of M-CSF-induced BMMs, NO₂-OA decreases activation of M-CSFR and activation of related PI3K and ERK. Additionally, NO₂-OA also attenuates activation of BMMs. In aggregate, we demonstrate that NO₂-OA regulates the process of macrophage differentiation and that NO₂-FAs represent a promising therapeutic tool in the treatment of inflammatory pathologies linked with increased accumulation of macrophages in inflamed tissues.

Monitoring the Response of Hyperbilirubinemia in the Mouse Brain by In Vivo Bioluminescence Imaging

Increased levels of unconjugated bilirubin are neurotoxic, but the mechanism leading to neurological damage has not been completely elucidated. Innovative strategies of investigation are needed to more precisely define this pathological process. By longitudinal in vivo bioluminescence imaging, we noninvasively visualized the brain response to hyperbilirubinemia in the MITO-Luc mouse, in which light emission is restricted to the regions of active cell proliferation. We assessed that acute hyperbilirubinemia promotes bioluminescence in the brain region, indicating an increment in the cell proliferation rate. Immunohistochemical detection in brain sections of cells positive for both luciferase and the microglial marker allograft inflammatory factor 1 suggests proliferation of microglial cells. In addition, we demonstrated that brain induction of bioluminescence was altered by pharmacological displacement of bilirubin from its albumin binding sites and by modulation of the blood-brain barrier permeability, all pivotal factors in the development of bilirubin-induced neurologic dysfunction. We also determined that treatment with minocycline, an antibiotic with anti-inflammatory and neuroprotective properties, or administration of bevacizumab, an anti-vascular endothelial growth factor antibody, blunts bilirubin-induced bioluminescence. Overall the study supports the use of the MITO-Luc mouse as a valuable tool for the rapid response monitoring of drugs aiming at preventing acute bilirubin-induced neurological dysfunction.

Identifying Cell Type-Specific Transcription Factors by Integrating ChIP-seq and eQTL Data-Application to Monocyte Gene Regulation

We describe a novel computational approach to identify transcription factors (TFs) that are candidate regulators in a human cell type of interest. Our approach involves integrating cell type-specific expression quantitative trait locus (eQTL) data and TF data from chromatin immunoprecipitation-to-tag-sequencing (ChIP-seq) experiments in cell lines. To test the method, we used eQTL data from human monocytes in order to screen for TFs. Using a list of known monocyte-regulating TFs, we tested the hypothesis that the binding sites of cell type-specific TF regulators would be concentrated in the vicinity of monocyte eQTLs. For each of 397 ChIP-seq data sets, we obtained an enrichment ratio for the number of ChIP-seq peaks that are located within monocyte eQTLs. We ranked ChIP-seq data sets according to their statistical significances for eQTL overlap, and from this ranking, we observed that monocyte-regulating TFs are more highly ranked than would be expected by chance. We identified 27 TFs that had significant monocyte enrichment scores and mapped them into a protein interaction network. Our analysis uncovered two novel candidate monocyte-regulating TFs, BCLAF1 and SIN3A. Our approach is an efficient method to identify candidate TFs that can be used for any cell/tissue type for which eQTL data are available.

Role of Monocytes and Intestinal Macrophages in Crohn's Disease and Ulcerative Colitis

Monocytes and macrophages are part of the body's first line of defence, eliminating pathogens by phagocytosis or by releasing a broad array of inflammatory mediators, such as cytokines, chemokines, and proteases. In humans, 3 subsets of monocytes are described in blood with seemingly different functions, the classical (CD14CD16) monocytes, the intermediate (CD14CD16) monocytes, and the nonclassical (CD14CD16) monocytes. In the intestine, macrophages can be divided into resident and inflammatory macrophages that are distinguished by low and high expression of CD14, respectively. However, the roles and function of the 3 monocyte subsets in health and disease are not fully understood. In this review, we describe what is known about the origin of human intestinal macrophages and their blood monocytic counterparts and many of their numerous distinct mechanisms influencing the intestinal immune system.

Characterization of a Rat Subcutaneous Malignant Fibrous Histiocytoma and Its Tumor Lines, with Reference to Histiocytic Features

Malignant fibrous histiocytoma (MFH) is regarded as soft tissue-derived undifferentiated pleomorphic sarcoma, of which the histogenesis remains to be proven. To investigate the cellular characteristics, a homotransplantable tumor line (KJ) was established from a spontaneous MFH that developed in the subcutis of an aged F344 rat. KJ tumors have been produced in syngeneic rats by serial subcutaneous implantation of tissue fragments. The original and KJ tumors consisted of oval and fusiform cells arranged in interlacing bundles with fibrous stroma. Occasional giant cells with bizarre nuclei were observed. Enzyme/immunohistochemically, neoplastic cells reacted to ED1 and ED2 (antibodies specific for rat histiocytes/macrophages), and showed a positive reaction to vimentin and lysosomal enzyme markers such as acid phosphatase (ACP) and nonspecific esterase (Non-SE). Electron microscopically, neoplastic cells possessed lysosomal granules in cytoplasm. A cloned cell line (KJ-A) was isolated from a KJ tumor. KJ-A cells showed positive reactions to ED1, ED2, ACP, and Non-SE, and had cytoplasmic lysosomal granules. Tumors induced by KJ-A cells exhibited histologic and enzyme/immunohistochemical findings similar to those of KJ tumors. Lipopolysaccharide (LPS) treatment increased the number of ED1-positive cells and the expression of tumor necrosis factor-α mRNA by reverse transcription-polymerase chain reaction. Collectively, it is likely that rat MFH cells originally possess histiocyte/macrophage-like features that may be enhanced by LPS. Because tumor lines are useful for in vivo and in vitro studies concerning different characteristics of the original neoplasms. KJ and KJ-A should prove useful for studies concerning the morphogenesis of MFH.

Identification of the microRNA networks contributing to macrophage differentiation and function

Limited evidence is available about the specific miRNA networks that regulate differentiation of specific immune cells. In this study, we characterized miRNA expression and associated alterations in expression with putative mRNA targets that are critical during differentiation of macrophages. In an effort to map the dynamic changes in the bone marrow (BM), we profiled whole BM cultures during differentiation into macrophages. We identified 112 miRNAs with expression patterns that were differentially regulated 5-fold or more during BMDM development. With TargetScan and MeSH databases, we identified 1267 transcripts involved in 30 canonical pathways linked to macrophage biology as potentially regulated by these specific 112 miRNAs. Furthermore, by employing miRanda and Ingenuity Pathways Analysis (IPA) analysis systems, we identified 18 miRNAs that are temporally linked to the expression of CSF1R, CD36, MSR1 and SCARB1; 7 miRNAs linked to the regulation of the transcription factors RUNX1 and PU.1, and 14 miRNAs target the nuclear receptor PPARα and PPARγ. This novel information provides an important reference resource for further study of the functional links between miRNAs and their target mRNAs for the regulation of differentiation and function of macrophages.

Adseverin mediates RANKL-induced osteoclastogenesis by regulating NFATc1

Adseverin is a Ca2+-dependent actin filament-severing protein that has been reported to regulate exocytosis via rearrangements of the actin cytoskeleton in secretory cells. However, the role of adseverin in bone cells has not yet been well characterized. Here, we investigated the role of adseverin in osteoclastogenesis using primary osteoclast precursor cells. Adseverin expression was upregulated during RANKL (receptor activator of nuclear factor-κB ligand)-induced osteoclast differentiation. Moreover, genetic silencing of adseverin decreased the number of osteoclasts generated by RANKL. Adseverin knockdown also suppressed the RANKL-mediated induction of nuclear factor of activated T-cell c1 (NFATc1), which is a key transcription factor in osteoclastogenesis. In addition, adseverin knockdown impaired bone resorption and the secretion of bone-degrading enzymes from osteoclasts. These effects were accompanied by decreased NFATc1 expression and the activation of nuclear factor-κB. Collectively, our results indicate that adseverin has a crucial role in osteoclastogenesis by regulating NFATc1.

Selective phosphorylation during early macrophage differentiation

The differentiation of macrophages from monocytes is a tightly controlled and complex biological process. Although numerous studies have been conducted using biochemical approaches or global gene/protein profiling, the mechanisms of the early stages of differentiation remain unclear. Here we used SILAC-based quantitative proteomics approach to perform temporal phosphoproteome profiling of early macrophage differentiation. We identified a large set of phosphoproteins and grouped them as PMA-regulated and non-regulated phosphoproteins in the early stages of differentiation. Further analysis of the PMA-regulated phosphoproteins revealed that transcriptional suppression, cytoskeletal reorganization and cell adhesion were among the most significantly activated pathways. Some key involved regulators of these pathways are mTOR, MYB, STAT1 and CTNNB. Moreover, we were able to classify the roles and activities of several transcriptional factors during different differentiation stages and found that E2F is likely to be an important regulator during the relatively late stages of differentiation. This study provides the first comprehensive picture of the dynamic phosphoproteome during myeloid cells differentiation, and identifies potential molecular targets in leukemic cells.

Identification of transcription factor AML-1 binding site upstream of human cytomegalovirus UL111A gene

Human cytomegalovirus (HCMV) interleukin-10 (hcmvIL-10), encoded by HCMV UL111A gene, is a homolog of human IL-10. It exerts immunomodulatory effects that allow HCMV to evade host defense mechanisms. However, the exact mechanism underlying the regulation of hcmvIL-10 expression is not well understood. The transcription factor acute myeloid leukemia 1 (AML-1) plays an important role in the regulation of various genes involved in the differentiation of hematopoietic lineages. A putative AML-1 binding site is present within the upstream regulatory region (URR) of UL111A gene. To provide evidence that AML-1 is involved in regulating UL111A gene expression, we examined the interaction of AML-1 with the URR of UL111A in HCMV-infected human monocytic THP-1 cells using a chromatin immunoprecipitation assay. HcmvIL-10 transcription was detected in differentiated THP-1 cells, but not in undifferentiated ones. Furthermore, the URR of UL111A showed a higher intensity of AML-1 binding, a higher level of histone H3 acetyl-K9, but a lower level of histone H3 dimethyl-K9 in differentiated THP-1 cells than undifferentiated cells. Down-regulation of AML1 by RNA interference decreased the expression of the UL111A gene. Our results suggest that AML-1 may contribute to the epigenetic regulation of UL111A gene via histone modification in HCMV-infected differentiated THP-1 cells. This finding could be useful for the development of new anti-viral therapies.

Functional significance of mononuclear phagocyte populations generated through adult hematopoiesis

Tissue homeostasis requires a complete repertoire of functional macrophages in peripheral tissues. Recent evidence indicates that many resident tissue macrophages are seeded during embryonic development and persist through adulthood as a consequence of localized proliferation. Mononuclear phagocytes are also produced during adult hematopoiesis; these cells are then recruited to sites throughout the body, where they function in tissue repair and remodeling, resolution of inflammation, maintenance of homeostasis, and disease progression. The focus of this review is on mononuclear phagocytes that comprise the nonresident monocyte/macrophage populations in the body. Key features of monocyte differentiation are presented, focusing primarily on the developmental hierarchy that is established through this process, the markers used to identify discrete cell populations, and novel, functional attributes of these cells. These features are then explored in the context of the tumor microenvironment, where mononuclear phagocytes exhibit extensive plasticity in phenotype and function.

Glucocerebrosidase deficiency in zebrafish affects primary bone ossification through increased oxidative stress and reduced Wnt/β-catenin signaling

Loss of lysosomal glucocerebrosidase (GBA1) function is responsible for several organ defects, including skeletal abnormalities in type 1 Gaucher disease (GD). Enhanced bone resorption by infiltrating macrophages has been proposed to lead to major bone defects. However, while more recent evidences support the hypothesis that osteoblastic bone formation is impaired, a clear pathogenetic mechanism has not been depicted yet. Here, by combining different molecular approaches, we show that Gba1 loss of function in zebrafish is associated with defective canonical Wnt signaling, impaired osteoblast differentiation and reduced bone mineralization. We also provide evidence that increased reactive oxygen species production precedes the Wnt signaling impairment, which can be reversed upon human GBA1 overexpression. Type 1 GD patient fibroblasts similarly exhibit reduced Wnt signaling activity, as a consequence of increased β-catenin degradation. Our results support a novel model in which a primary defect in canonical Wnt signaling antecedes bone defects in type 1 GD.

Biology of infantile hemangioma

Infantile hemangioma (IH), the most common tumor of infancy, is characterized by an initial proliferation during infancy followed by spontaneous involution over the next 5-10 years, often leaving a fibro-fatty residuum. IH is traditionally considered a tumor of the microvasculature. However, recent data show the critical role of stem cells in the biology of IH with emerging evidence suggesting an embryonic developmental anomaly due to aberrant proliferation and differentiation of a hemogenic endothelium with a neural crest phenotype that possesses the capacity for endothelial, hematopoietic, mesenchymal, and neuronal differentiation. Current evidence suggests a putative placental chorionic mesenchymal core cell embolic origin of IH during the first trimester. This review outlines the emerging role of stem cells and their interplay with the cytokine niche that promotes a post-natal environment conducive for vasculogenesis involving VEGFR-2 and its ligand VEGF-A and the IGF-2 ligand in promoting cellular proliferation, and the TRAIL-OPG anti-apoptotic pathway in preventing cellular apoptosis in IH. The discovery of the role of the renin-angiotensin system in the biology of IH provides a plausible explanation for the programed biologic behavior and the β-blocker-induced accelerated involution of this enigmatic condition. This crucially involves the vasoactive peptide, angiotensin II, that promotes cellular proliferation in IH predominantly via its action on the ATIIR2 isoform. The role of the RAS in the biology of IH is further supported by the effect of captopril, an ACE inhibitor, in inducing accelerated involution of IH. The discovery of the critical role of RAS in IH represents a novel and fascinating paradigm shift in the understanding of human development, IH, and other tumors in general.

Transcription of inflammatory genes: long noncoding RNA and beyond

The innate immune system must coordinate elaborate signaling pathways to turn on expression of hundreds of genes to provide protection against pathogens and resolve acute inflammation. Multiple genes within distinct functional categories are coordinately and temporally regulated by transcriptional on and off switches in response to distinct external stimuli. Three classes of transcription factors act together with transcriptional coregulators and chromatin-modifying complexes to control these programs. In addition, newer studies implicate long noncoding RNA (lncRNA) as additional regulators of these responses. LncRNAs promote, fine-tune, and restrain the inflammatory program. In this study, we provide an overview of gene regulation and the emerging importance of lncRNAs in the immune system.

Olive (Olea europaea) leaf extract induces apoptosis and monocyte/macrophage differentiation in human chronic myelogenous leukemia K562 cells: insight into the underlying mechanism

Differentiation therapy is an attractive approach aiming at reversing malignancy and reactivating endogenous differentiation programs in cancer cells. Olive leaf extract, known for its antioxidant activity, has been demonstrated to induce apoptosis in several cancer cells. However, its differentiation inducing properties and the mechanisms involved are still poorly understood. In this study, we investigated the effect of Chemlali Olive Leaf Extract (COLE) for its potential differentiation inducing effect on multipotent leukemia K562 cells. Results showed that COLE inhibits K562 cells proliferation and arrests the cell cycle at G0/G1, and then at G2/M phase over treatment time. Further analysis revealed that COLE induces apoptosis and differentiation of K562 cells toward the monocyte lineage. Microarray analysis was conducted to investigate the underlying mechanism of COLE differentiation inducing effect. The differentially expressed genes such as IFI16, EGR1, NFYA, FOXP1, CXCL2, CXCL3, and CXCL8 confirmed the commitment of K562 cells to the monocyte/macrophage lineage. Thus our results provide evidence that, in addition to apoptosis, induction of differentiation is one of the possible therapeutic effects of olive leaf in cancer cells.

Social stress up-regulates inflammatory gene expression in the leukocyte transcriptome via β-adrenergic induction of myelopoiesis

Across a variety of adverse life circumstances, such as social isolation and low socioeconomic status, mammalian immune cells have been found to show a conserved transcriptional response to adversity (CTRA) involving increased expression of proinflammatory genes. The present study examines whether such effects might stem in part from the selective up-regulation of a subpopulation of immature proinflammatory monocytes (Ly-6c(high) in mice, CD16(-) in humans) within the circulating leukocyte pool. Transcriptome representation analyses showed relative expansion of the immature proinflammatory monocyte transcriptome in peripheral blood mononuclear cells from people subject to chronic social stress (low socioeconomic status) and mice subject to repeated social defeat. Cellular dissection of the mouse peripheral blood mononuclear cell transcriptome confirmed these results, and promoter-based bioinformatic analyses indicated increased activity of transcription factors involved in early myeloid lineage differentiation and proinflammatory effector function (PU.1, NF-κB, EGR1, MZF1, NRF2). Analysis of bone marrow hematopoiesis confirmed increased myelopoietic output of Ly-6c(high) monocytes and Ly-6c(intermediate) granulocytes in mice subject to repeated social defeat, and these effects were blocked by pharmacologic antagonists of β-adrenoreceptors and the myelopoietic growth factor GM-CSF. These results suggest that sympathetic nervous system-induced up-regulation of myelopoiesis mediates the proinflammatory component of the leukocyte CTRA dynamic and may contribute to the increased risk of inflammation-related disease associated with adverse social conditions.

Induction of functional human macrophages from bone marrow promonocytes by M-CSF in humanized mice

Engraftment of human CD34⁺ hematopoietic stem/progenitor cells into immunodeficient mice leads to robust reconstitution of human T and B cells but not monocytes and macrophages. To identify the cause underlying the poor monocyte and macrophage reconstitution, we analyzed human myeloid cell development in humanized mice and found that it was blocked at the promonocyte stage in the bone marrow. Expression of human M-CSF or GM-CSF by hydrodynamic injection of cytokine-encoding plasmid completely abolished the accumulation of promonocytes in the bone marrow. M-CSF promoted the development of mature monocytes and tissue-resident macrophages whereas GM-CSF did not. Moreover, correlating with an increased human macrophages at the sites of infection, M-CSF-treated humanized mice exhibited an enhanced protection against influenza virus and Mycobacterium infection. Our study identifies the precise stage at which human monocyte/macrophage development is blocked in humanized mice and reveals overlapping and distinct functions of M-CSF and GM-CSF in human monocyte and macrophage development. The improved reconstitution and functionality of monocytes/macrophages in the humanized mice following M-CSF expression provide a superior in vivo system to investigate the role of macrophages in physiological and pathological processes.

Understanding macrophage differentiation during space flight: The importance of ground-based experiments before space flight

In preparation for a space flight on STS-126, two in vitro culture systems were used to investigate macrophage colony stimulating factor-dependent macrophage differentiation from mouse primary bone marrow cells. The patented Techshot Cell Cult Bioreactor and the BioServe Fluid Processing Apparatus (FPA) were operated in different orientations to determine their impact on macrophage growth and differentiation. Bone marrow cell parameters were determined after cells were grown in FPAs incubated at 37°C in vertical or horizontal orientations, and macrophage cell recovery was significantly higher from FPAs that were incubated in the horizontal orientation compared to "vertical" FPAs. Similarly, when bone marrow cells were grown in the Techshot bioreactor, there were significant differences in the numbers of macrophages recovered after 7 days, depending on movement and orientation of the bioreactor. Macrophage recovery was highest when the patented bioreactor was rotated in the horizontal, x-axis plane (merry-go-round fashion) compared to static and vertically, y-axis plane rotated (Ferris wheel fashion) bioreactors. In addition, the expression of F4/80 and other differentiation markers varied depending on whether macrophages differentiated in FPAs or in bioreactors. After 7 days, significant differences in size, granularity and molecule expression were seen even when the same primary bone marrow cells were used to seed the cultures. These data show that culture outcomes are highly dependent on the culture device and device orientation. Moreover, the impact of the culture system needs to be understood in order to interpret space flight data.

C/EBPα regulates osteoclast lineage commitment

Despite recent insights gained from the effects of targeted deletion of the Finkel-Biskis-Jinkins osteosarcoma oncogene (c-fos), Spleen focus-forming virus (SFFV) proviral integration 1 (PU.1), microphthalmia-associated transcription factor, NF-κB, and nuclear factor of activated cells cytoplasmic 1 (NFATc1) transcription factor genes, the mechanism underlying transcription factors specifying osteoclast (OC) lineage commitment from monocyte/macrophage remains unclear. To characterize the mechanism by which transcription factors regulate OC lineage commitment, we mapped the critical cis-regulatory element in the promoter of cathepsin K (Ctsk), which is expressed specifically in OCs, and found that CCAAT/enhancer binding protein α (C/EBPα) is the critical cis-regulatory element binding protein. Our results indicate that C/EBPα is highly expressed in pre- OCs and OCs. The combined presence of macrophage colony-stimulating factor and receptor activator of NF-κB ligand significantly induces high C/EBPα expression. Furthermore, C/EBPα(-/-) newborn mice exhibited impaired osteoclastogenesis, and a severe osteopetrotic phenotype, but unaffected monocyte/macrophage development. Impaired osteoclastogenesis of C/EBPα(-/-) mouse bone marrow cells can be rescued by c-fos overexpression. Ectopic expression of C/EBPα in mouse bone marrow cells and monocyte/macrophage cells, in the absence of receptor activator of NF-κB ligand, induces expression of receptor activator of NF-κB, c-fos, Nfatc1, and Ctsk, and it reprograms monocyte/macrophage cells to OC-like cells. Our results demonstrate that C/EBPα directly up-regulates c-fos expression. C/EBPα(+/-) mice exhibit an increase in bone density compared with C/EBPα(+/+) controls. These discoveries establish C/EBPα as the key transcriptional regulator of OC lineage commitment, providing a unique therapeutic target for diseases of excessive bone resorption, such as osteoporosis and arthritis.

A natural-like synthetic small molecule impairs bcr-abl signaling cascades and induces megakaryocyte differentiation in erythroleukemia cells

Over the past years, we synthesized a series of new molecules that are hybrids of spirocyclic ketones as complexity-bearing cores with bi- and ter-phenyls as privileged fragments. Some of these newly-shaped small molecules showed antiproliferative, pro-apoptotic and differentiating activity in leukemia cell lines. In the present study, to investigate more in depth the mechanisms of action of these molecules, the protein expression profiles of K562 cells treated with or without the compounds IND_S1, MEL_T1, IND_S7 and MEL_S3 were analyzed using two-dimensional gel electrophoresis coupled with mass spectrometry. Proteome comparisons revealed several differentially expressed proteins, mainly related to cellular metabolism, chaperone activity, cytoskeletal organization and RNA biogenesis. The major results were validated by Western blot and qPCR. To attempt integrating findings into a cellular signaling context, proteomic data were explored using MetaCore. Network analysis highlighted relevant relationships between the identified proteins and additional potential effectors. Notably, qPCR validation of central hubs showed that the compound MEL_S3 induced high mRNA levels of the transcriptional factors EGR1 and HNF4-alpha; the latter to our knowledge is reported here for the first time to be present in K562 cells. Consistently with the known EGR1 involvement in the regulation of differentiation along megakaryocyte lineage, MEL_S3-treated leukemia cells showed a marked expression of glycoprotein IIb/IIIa (CD41) and glycoprotein Ib (CD42), two important cell markers in megakaryocytic differentiation, together with morphological aspects of megakaryoblasts and megakaryocytes.

Monocytes and macrophages in cancer: development and functions

Monocytes and tumor-associated macrophages are part of the myeloid family, a group of hematopoietic derived cells. Monocytes are direct precursors of hematopoietic stem cell-derived macrophages. After their recruitment into the tumor tissue, they can differentiate into tumor-associated macrophages, a very heterogeneous cell population in terms of phenotype and pro-tumor function, supporting tumor initiation, local progression and distant metastasis. Therefore, targeting monocytes and macrophages is a promising immunotherapeutic approach. This review will focus on the development of monocytes as macrophage precursors, the functions of tumor-associated macrophages and the possibility of interfering with tumor development and progression by targeting these myeloid cells.

Inflammation and vascular injury: basic discovery to drug development

The invited special lecture at the 76(th) Annual Scientific Meeting of the Japanese Circulation Society focused on the central role of inflammation in vascular injury and repair. Early studies pioneered the concept that mechanical injury, such as balloon angioplasty and endovascular stent deployment, elicits an inflammatory response from the vessel wall. This hypothesis was developed and substantiated at a time when the prevailing dogma viewed restenosis following angioplasty as a primarily proliferative smooth muscle cell disease. Antibody targeting of Mac-1 reduced leukocyte accumulation and limited neointimal formation following balloon injury or stent implantation. Genetic absence of Mac-1 resulted in diminished leukocyte accumulation and neointimal thickening after carotid artery injury in mice. In the course of those studies, our laboratory made fundamental discoveries regarding the mechanism of leukocyte recruitment at sites of vascular injury and identified platelet glycoprotein (GP) Ibα, a component of the GPIb-IX-V complex, as the previously unknown platelet counter-receptor for Mac-1. Follow-on studies have focused extensively on the structure, function, and signaling of the leukocyte integrin Mac-1. The binding site for GPIbα in Mac-1 has been mapped and subsequently showed that leukocyte engagement of platelet GPIbα via Mac-1 is critical not only for the biological response to vascular injury, but also for thrombosis, vasculitis, glomerulonephritis, and multiple sclerosis, thereby advancing the hypothesis that virtually all inflammation is platelet-dependent. Furthermore, ligand engagement of Mac-1 initiates a novel gene program that promotes inflammation by activating NFκB and downregulating the expression of the forkhead transcription factor Foxp1 that controls monocyte differentiation. Small molecule inhibitors of Mac-1 function have been pursued, including targeting of Mac-1-GPIbα binding or the downstream tyrosine kinase spleen tyrosine kinase. Drs Teruo Inoue, Koichi Node, Tatsuya Fukotomi, Masashi Sakuma, Toshifumi Morooka, and Kohsuke Nakajima, valued Japanese collaborators and post-doctoral fellows, have contributed enormously to these discoveries.

Macrophage-related diseases of the gut: a pathologist's perspective

The resident macrophages of the gastrointestinal tract represent the largest population of macrophages in the human body and are usually located in the subepithelial lamina propria. This strategic location guarantees a first-line defense to the huge numbers of potentially harmful bacteria and antigenic stimuli that are present in the intestinal lumen. In non-inflamed mucosa, macrophages phagocytose and kill microbes in the absence of an inflammatory response. However, in the event of an epithelial breach and/or microbial invasion, new circulating monocytes and lymphocytes will be recruited to the damaged area of the gut, which will result in the secretion of proinflammatory mediators and engage a protective inflammatory response. Although macrophages are usually not conspicuous in normal mucosal samples of the gut, they can easily be detected when they accumulate exogenous particulate material or endogenous substances or when they become very numerous. These events will mostly occur in pathologic conditions, and this review presents an overview of the diseases which are either mediated by or affecting the resident macrophages of the gut.

Evaluation of in vitro macrophage differentiation during space flight

We differentiated mouse bone marrow cells in the presence of recombinant macrophage colony stimulating (rM-CSF) factor for 14 days during the flight of space shuttle Space Transportation System (STS)-126. We tested the hypothesis that the receptor expression for M-CSF, c-Fms was reduced. We used flow cytometry to assess molecules on cells that were preserved during flight to define the differentiation state of the developing bone marrow macrophages; including CD11b, CD31, CD44, Ly6C, Ly6G, F4/80, Mac2, c-Fos as well as c-Fms. In addition, RNA was preserved during the flight and was used to perform a gene microarray. We found that there were significant differences in the number of macrophages that developed in space compared to controls maintained on Earth. We found that there were significant changes in the distribution of cells that expressed CD11b, CD31, F4/80, Mac2, Ly6C and c-Fos. However, there were no changes in c-Fms expression and no consistent pattern of advanced or retarded differentiation during space flight. We also found a pattern of transcript levels that would be consistent with a relatively normal differentiation outcome but increased proliferation by the bone marrow macrophages that were assayed after 14 days of space flight. There also was a surprising pattern of space flight influence on genes of the coagulation pathway. These data confirm that a space flight can have an impact on the in vitro development of macrophages from mouse bone marrow cells.