The role of DC-STAMP in maintenance of immune tolerance through regulation of dendritic cell function

Immunohistochemical Characterization of M1, M2, and M4 Macrophages in Leprosy Skin Lesions

Mycobacterium leprae is the etiological agent of leprosy. Macrophages (Mφs) are key players involved in the pathogenesis of leprosy. In this study, immunohistochemical analysis was performed to examine the phenotype of Mφ subpopulations, namely M1, M2, and M4, in the skin lesions of patients diagnosed with leprosy. Based on the database of treatment-naïve patients treated between 2015 and 2019 at the Department of Dermatology of the University of the State of Pará, Belém, routine clinical screening samples were identified. The monolabeling protocol was used for M1 macrophages (iNOS, IL-6, TNF-α) and M2 macrophages (IL-10, IL-13, CD163, Arginase 1, TGF-β, FGFb), and the double-labeling protocol was used for M4 macrophages (IL-6, MMP7, MRP8, TNF-α e CD68). To confirm the M4 macrophage lineage, double labeling of the monoclonal antibodies CD68 and MRP8 was also performed. Our results demonstrated a statistically significant difference for the M1 phenotype among the Virchowian (VV) (4.5 ± 1.3, p < 0.0001), Borderline (1.6 ± 0.4, p < 0.0001), and tuberculoid (TT) (12.5 ± 1.8, p < 0.0001) clinical forms of leprosy. Additionally, the M2 phenotype showed a statistically significant difference among the VV (12.5 ± 2.3, p < 0.0001), Borderline (1.3 ± 0.2, p < 0.0001), and TT (3.2 ± 0.7, p < 0.0001) forms. For the M4 phenotype, a statistically significant difference was observed in the VV (9.8 ± 1.7, p < 0.0001), Borderline (1.2 ± 0.2, p < 0.0001), and TT (2.6 ± 0.7, p < 0.0001) forms. A significant correlation was observed between the VV M1 and M4 (r = 0.8712; p = 0.0000) and between the VV M2 × TT M1 (r = 0.834; p = 0.0002) phenotypes. The M1 Mφs constituted the predominant Mφ subpopulation in the TT and Borderline forms of leprosy, whereas the M2 Mφs showed increased immunoexpression and M4 was the predominant Mφ phenotype in VV leprosy. These results confirm the relationship of the Mφ profile with chronic pathological processes of the inflammatory response in leprosy.

Upregulation of dendrocyte-expressed seven transmembrane protein is associated with unfavorable outcomes in differentiated thyroid cancer

PURPOSE

Dendritic cell infiltrates are increased in thyroid cancer but may have a defective ability to provoke effective immune responses. In this study, we aimed to identify potential thyroid cancer biomarkers linked to dendritic cell development and evaluate their prognostic relevance.

METHODS

Through a bioinformatics search, we identified the dendrocyte-expressed seven transmembrane protein (DCSTAMP) as a prognostic gene involved in dendritic cell differentiation for thyroid cancer. Immunohistochemical analyses of DCSTAMP expression were performed and correlated with clinical outcomes.

RESULTS

DCSTAMP was overexpressed in a variety of types of thyroid cancers, while normal thyroid tissue or benign thyroid lesions exhibited low or undetectable DCSTAMP immunoreactivity. The results of automated quantification were consistent with subjective semiquantitative scoring. Among 144 patients with differentiated thyroid cancer, high DCSTAMP expression was associated with papillary tumor type (p < 0.001), extrathyroidal extension (p = 0.007), lymph node metastasis (p < 0.001), and BRAF V600E mutation (p = 0.029). Patients with tumors showing high DCSTAMP expression had shorter overall (p = 0.027) and recurrence-free (p = 0.042) survival.

CONCLUSION

This study provides the first evidence of DCSTAMP overexpression in thyroid cancer. Apart from the prognostic implications, studies are needed to explore its potential immunomodulatory role in thyroid cancer.

Dendritic cell-specific transmembrane protein is required for synovitis and bone resorption in inflammatory arthritis

Objective

Dendritic Cell-Specific Transmembrane Protein (DC-STAMP) is essential for the formation of fully functional multinucleated osteoclasts. DC-STAMP deficient mice, under physiological conditions, exhibit osteopetrosis and develop systemic autoimmunity with age. However, the function of DC-STAMP in inflammation is currently unknown. We examined whether genetic ablation of DC-STAMP attenuates synovitis and bone erosion in TNF transgenic (Tg) and K/BxN serum-induced murine rheumatoid arthritis.

Methods

We evaluated arthritis onset in Tg(hTNF) mice lacking DC-STAMP and 50:50 chimeric mice by visual examination, measurement of ankle width, micro-CT-scan analysis and quantitation of the area occupied by osteoclasts in bone sections. To further investigate the cellular and molecular events modulated by DC-STAMP, we measured serum cytokines, determined changes in cytokine mRNA expression by monocytes activated with IL4 or LPS/IFNγ and enumerated immune cells in inflamed mouse joints.

Results

Synovitis, bone loss and matrix destruction are markedly reduced in Dcstamp-/-;Tg(hTNF) mice. These mice had significantly lower CCL2 and murine TNF serum levels and exhibited impaired monocyte joint migration compared to Tg(hTNF) mice. The reduced arthritic severity in Dcstamp deficient mice was associated with compromised monocyte chemotaxis, cytokine production, and M2 polarization.

Conclusion

These results reveal that DC-STAMP modulates both bone resorption and inflammation and may serve as an activity biomarker and therapeutic target in inflammatory arthritis and metabolic bone disease.

High Expression of DC-STAMP Gene Predicts Adverse Outcomes in AML

Acute myeloid leukemia (AML) is a genetically heterogeneous hematological malignancy with poor prognosis. We explored the RNA sequence data and clinical information of AML patients from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) database to search for the core molecule for prognosis. The DC-STAMP expression was significantly higher in AML patients, which was linked to old age, unfavorable cytogenetic risk, and death (all p < 0.05). Furthermore, it was revealed that high DC-STAMP expression was an independent unfavorable factor for overall survival (OS) by univariate analysis [hazard ratio (HR): 2.683; 95% confidence interval (CI): 1.723–4.178; p < 0.001] and multivariate analysis (HR: 1.733; 95% CI: 1.079–2.781; p = 0.023). The concordance index (C-index 0.734, 95% CI: 0.706–0.762), calibration curves, and decision curve analysis showed the certain predictive accuracy of a nomogram model based on multivariate analysis for OS. In addition, we found that the differentially expressed gene (DEG) enrichment pathways of high- and low-DC-STAMP expression group enrichment pathways were focused on channel activity and platelet alpha granule by the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG), while gene set enrichment analysis (GSEA) pathways were mainly involved in mTORC1 signaling and TNF-α signaling via the NF-kB pathway. Moreover, a protein–protein interaction (PPI) network demonstrated that DC-STAMP interacted with two hub genes (PPBP and PF4), which were highly regulated and associated with poor survival. Finally, high DC-STAMP expression showed a significantly positive correlation with four immune cell [NK CD56 (dim) cells, macrophages, cytotoxic cells, and CD8 (+) T cells] infiltration and high level of immune checkpoint genes (PDCD1, CD274, CTLA-4, and TIGIT). Therefore, our results suggest that high expression of DC-STAMP predicts adverse outcomes for AML patients.

Sperm membrane proteins DCST1 and DCST2 are required for sperm-egg interaction in mice and fish

The process of sperm-egg fusion is critical for successful fertilization, yet the underlying mechanisms that regulate these steps have remained unclear in vertebrates. Here, we show that both mouse and zebrafish DCST1 and DCST2 are necessary in sperm to fertilize the egg, similar to their orthologs SPE-42 and SPE-49 in C. elegans and Sneaky in D. melanogaster. Mouse Dcst1 and Dcst2 single knockout (KO) sperm are able to undergo the acrosome reaction and show normal relocalization of IZUMO1, an essential factor for sperm-egg fusion, to the equatorial segment. While both single KO sperm can bind to the oolemma, they show the fusion defect, resulting that Dcst1 KO males become almost sterile and Dcst2 KO males become sterile. Similar to mice, zebrafish dcst1 KO males are subfertile and dcst2 and dcst1/2 double KO males are sterile. Zebrafish dcst1/2 KO sperm are motile and can approach the egg, but are defective in binding to the oolemma. Furthermore, we find that DCST1 and DCST2 interact with each other and are interdependent. These data demonstrate that DCST1/2 are essential for male fertility in two vertebrate species, highlighting their crucial role as conserved factors in fertilization.

Evaluating Effects of Glatiramer Acetate Treatment on Amyloid Deposition and Tau Phosphorylation in the 3xTg Mouse Model of Alzheimer's Disease

Neuroinflammation driven by the accumulation of amyloid β (Aβ) can lead to neurofibrillary tangle formation in Alzheimer's Disease (AD). To test the hypothesis that an anti-inflammatory immunomodulatory agent might have beneficial effects on amyloid and tau pathology, as well as microglial phenotype, we evaluated glatiramer acetate (GA), a multiple sclerosis drug thought to bias type 2 helper T (T_h2) cell responses and alternatively activate myeloid cells. We administered weekly subcutaneous injections of GA or PBS to 15-month-old 3xTg AD mice, which develop both amyloid and tau pathology, for a period of 8 weeks. We found that subcutaneous administration of GA improved behavioral performance in novel object recognition and decreased Aβ plaque in the 3xTg AD mice. Changes in tau phosphorylation were mixed with specific changes in phosphoepitopes seen in immunohistochemistry but not observed in western blot. In addition, we found that there was a trend toward increased microglia complexity in 3xTg mice treated with GA, suggesting a shift toward homeostasis. These findings correlated with subtle changes in the microglial transcriptome, in which the most striking difference was the upregulation of Dcstamp. Lastly, we found no evidence of changes in proportions of major helper T cell (T_h) subtypes in the periphery. Overall, our study provides further evidence for the benefits of immunomodulatory therapies that alter the adaptive immune system with the goal of modifying microglia responses for the treatment of Alzheimer's Disease.

Integrative omics analyses uncover the mechanism underlying the immunotoxicity of perfluorooctanesulfonate in human lymphocytes

Perfluorooctanesulfonate (PFOS) is a man-made chemical widely used in industrial products. Due to its high persistence, PFOS has been detected in most animal species including the human population, wild animals, and aquatic organisms. Both cross-sectional studies and laboratory animal studies have shown hepatotoxicity, renal toxicity, and reproductive toxicity caused by PFOS exposure. Recently, a limited number of PFOS studies have raised concerns about its potential immune system effects. However, the molecular mechanism underlying the immunotoxicity of PFOS remains unknown. In this study, we used primary human lymphocytes as a model, together with integrative omics analyses, including the transcriptome and lipidome, and bioinformatics analysis, to resolve the immune toxicity effects of PFOS. Our results demonstrated that PFOS could alter the production of interleukins in human lymphocytes. Additionally, PFOS exposure could dysregulate clusters of genes and lipids that play important roles in immune functions, such as lymphocyte differentiation, inflammatory response, and immune response. The findings of this study offer novel insight into the molecular mechanisms underlying the immunotoxicity of PFOS, and open the potential of using the identified PFOS-responsive genes and lipids as biomarkers for risk assessment.

Osteoclast Multinucleation: Review of Current Literature

Multinucleation is a hallmark of osteoclast maturation. The unique and dynamic multinucleation process not only increases cell size but causes functional alterations through reconstruction of the cytoskeleton, creating the actin ring and ruffled border that enable bone resorption. Our understanding of the molecular mechanisms underlying osteoclast multinucleation has advanced considerably in this century, especially since the identification of DC-STAMP and OC-STAMP as “master fusogens”. Regarding the molecules and pathways surrounding these STAMPs, however, only limited progress has been made due to the absence of their ligands. Various molecules and mechanisms other than the STAMPs are involved in osteoclast multinucleation. In addition, several preclinical studies have explored chemicals that may be able to target osteoclast multinucleation, which could enable us to control pathogenic bone metabolism more precisely. In this review, we will focus on recent discoveries regarding the STAMPs and other molecules involved in osteoclast multinucleation.

Immune Complex-Driven Generation of Human Macrophages with Anti-Inflammatory and Growth-Promoting Activity

To maintain homeostasis, macrophages must be capable of assuming either an inflammatory or an anti-inflammatory phenotype. To better understand the latter, we stimulated human macrophages in vitro with TLR ligands in the presence of high-density immune complexes (IC). This combination of stimuli resulted in a broad suppression of inflammatory mediators and an upregulation of molecules involved in tissue remodeling and angiogenesis. Transcriptomic analysis of TLR stimulation in the presence of IC predicted the downstream activation of AKT and the inhibition of GSK3. Consequently, we pretreated LPS-stimulated human macrophages with small molecule inhibitors of GSK3 to partially phenocopy the regulatory effects of stimulation in the presence of IC. The upregulation of DC-STAMP and matrix metalloproteases was observed on these cells and may represent potential biomarkers for this regulatory activation state. To demonstrate the presence of these anti-inflammatory, growth-promoting macrophages in a human infectious disease, biopsies from patients with leprosy (Hanseniasis) were analyzed. The lepromatous form of this disease is characterized by hypergammaglobulinemia and defective cell-mediated immunity. Lesions in lepromatous leprosy contained macrophages with a regulatory phenotype expressing higher levels of DC-STAMP and lower levels of IL-12, relative to macrophages in tuberculoid leprosy lesions. Therefore, we propose that increased signaling by FcγR cross-linking on TLR-stimulated macrophages can paradoxically promote the resolution of inflammation and initiate processes critical to tissue growth and repair. It can also contribute to infectious disease progression.

Retinol Saturase Knock-Out Mice are Characterized by Impaired Clearance of Apoptotic Cells and Develop Mild Autoimmunity

Apoptosis and the proper clearance of apoptotic cells play a central role in maintaining tissue homeostasis. Previous work in our laboratory has shown that when a high number of cells enters apoptosis in a tissue, the macrophages that engulf them produce retinoids to enhance their own phagocytic capacity by upregulating several phagocytic genes. Our data indicated that these retinoids might be dihydroretinoids, which are products of the retinol saturase (RetSat) pathway. In the present study, the efferocytosis of RetSat-null mice was investigated. We show that among the retinoid-sensitive phagocytic genes, only transglutaminase 2 responded in macrophages and in differentiating monocytes to dihydroretinol. Administration of dihydroretinol did not affect the expression of the tested genes differently between differentiating wild type and RetSat-null monocytes, despite the fact that the expression of RetSat was induced. However, in the absence of RetSat, the expression of numerous differentiation-related genes was altered. Among these, impaired production of MFG-E8, a protein that bridges apoptotic cells to the α_vβ₃/β₅ integrin receptors of macrophages, resulted in impaired efferocytosis, very likely causing the development of mild autoimmunity in aged female mice. Our data indicate that RetSat affects monocyte/macrophage differentiation independently of its capability to produce dihydroretinol at this stage.

Highly diversified expansions shaped the evolution of membrane bound proteins in metazoans

The dramatic increase in membrane proteome complexity is arguably one of the most pivotal evolutionary events that underpins the origin of multicellular animals. However, the origin of a significant number of membrane families involved in metazoan development has not been clarified. In this study, we have manually curated the membrane proteomes of 22 metazoan and 2 unicellular holozoan species. We identify 123,014 membrane proteins in these 24 eukaryotic species and classify 86% of the dataset. We determine 604 functional clusters that are present from the last holozoan common ancestor (LHCA) through many metazoan species. Intriguingly, we show that more than 70% of the metazoan membrane protein families have a premetazoan origin. The data show that enzymes are more highly represented in the LHCA and expand less than threefold throughout metazoan species; in contrast to receptors that are relatively few in the LHCA but expand nearly eight fold within metazoans. Expansions related to cell adhesion, communication, immune defence, and developmental processes are shown in conjunction with emerging biological systems, such as neuronal development, cytoskeleton organization, and the adaptive immune response. This study defines the possible LHCA membrane proteome and describes the fundamental functional clusters that underlie metazoan diversity and innovation.

Dysregulated homeostasis of target tissues or autoantigens - A novel principle in autoimmunity

Monogenic autoimmune disorders provide a powerful tool for our understanding of the principles of autoimmunity due to the obvious impact of a single gene on the disease. So far, approximately 100 single gene defects causing murine monogenic autoimmune disorders have been reported and the functional characterization of these genes will provide significant progress in understanding the nature of autoimmunity. According to their function, genes leading to monogenic autoimmune disorders can be categorized into two groups. An expectable first group contains genes involved in the homeostasis of the immune system, including homeostasis of immune organs and immune cells. Intriguingly, the second group consists of genes functionally involved in the homeostasis of target tissues or autoantigens. According to our novel hypothesis, we propose that autoimmunity represents a consequence of a dysregulated homeostasis of the immune system and/or its targets including autoantigens and target tissues. In this review we refer to both aspects of homeostasis in autoimmunity with a highlight on the role of the homeostasis of target tissues and autoantigens.

Granulocyte-macrophage colony-stimulating factor-dependent CD11c-positive cells differentiate into active osteoclasts

Levels of circulating cytokines are elevated in inflammatory diseases. Previously, it was shown that interleukin (IL-)17A, in synergism with 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] and tumor necrosis factor α (TNFα), induces the release of granulocyte-macrophage colony-stimulating factor (GM-CSF) by murine osteoblasts in vitro. In this study, we further analyzed the effects of GM-CSF on osteoclast development in vitro. The effects of IL-17A, TNFα, and 1,25(OH)₂D₃ on the regulation of osteoclast development were investigated in cocultures of bone marrow-derived osteoclast progenitor cells (OPC) and mouse calvarial osteoblasts. Additionally, OPC were grown for 3days in media containing macrophage colony-stimulating factor (M-CSF), GM-CSF, or M-CSF/GM-CSF. Subsequently, the osteoclastogenic potential and the capacity to dissolve amorphous calcium phosphate were assessed in each of the three populations of OPC. IL-17A, in synergism with TNFα and 1,25(OH)₂D₃, inhibited the development of osteoclasts in cocultures by stimulating the osteoblast lineage cells to release GM-CSF. GM-CSF-treated OPC expressed traits characteristic of dendritic cells. Upon removal of GM-CSF and supplementation of the culture media with M-CSF/RANKL, the cells lost their dendritic cell characteristics and differentiated into osteoclasts. OPC pretreated with GM-CSF and M-CSF/GM-CSF exhibited delayed development to osteoclasts and an extended proliferation phase. Elevated levels of GM-CSF in systemic inflammatory diseases may cause an expansion of the OPC pools in the bone, bone marrow, and blood. Upon homing to the bone, this may lead to an increase in the number of osteoclasts and in bone resorption.

DC-STAMP Is an Osteoclast Fusogen Engaged in Periodontal Bone Resorption

Dendritic cell-specific transmembrane protein (DC-STAMP) plays a key role in the induction of osteoclast (OC) cell fusion, as well as DC-mediated immune regulation. While DC-STAMP gene expression is upregulated in the gingival tissue with periodontitis, its pathophysiological roles in periodontitis remain unclear. To evaluate the effects of DC-STAMP in periodontitis, anti-DC-STAMP-monoclonal antibody (mAb) was tested in a mouse model of ligature-induced periodontitis ( n = 6-7/group) where Pasteurella pneumotropica ( Pp)-reactive immune response activated T cells to produce receptor activator of nuclear factor kappa-B ligand (RANKL), which, in turn, promotes the periodontal bone loss via upregulation of osteoclastogenesis. DC-STAMP was expressed on the cell surface of mature multinuclear OCs, as well as immature mononuclear OCs, in primary cultures of RANKL-stimulated bone marrow cells. Anti-DC-STAMP-mAb suppressed the emergence of large, but not small, multinuclear OCs, suggesting that DC-STAMP is engaged in the late stage of cell fusion. Anti-DC-STAMP-mAb also inhibited pit formation caused by RANKL-stimulated bone marrow cells. Attachment of ligature to a second maxillary molar induced DC-STAMP messenger RNA and protein, along with elevated tartrate-resistant acid phosphatase-positive (TRAP+) OCs and alveolar bone loss. As we expected, systemic administration of anti-DC-STAMP-mAb downregulated the ligature-induced alveolar bone loss. Importantly, local injection of anti-DC-STAMP-mAb also suppressed alveolar bone loss and reduced the total number of multinucleated TRAP+ cells in mice that received ligature attachment. Attachment of ligature induced significantly elevated tumor necrosis factor-α, interleukin-1β, and RANKL in the gingival tissue compared with the control site without ligature ( P < 0.05), which was unaffected by local injection with either anti-DC-STAMP-mAb or control-mAb. Neither in vivo anti- Pp IgG antibody nor in vitro anti- Pp T-cell response and resultant production of RANKL was affected by anti-DC-STAMP-mAb. This study illustrated the roles of DC-STAMP in promoting local OC cell fusion without affecting adaptive immune responses to oral bacteria. Therefore, it is plausible that a novel therapeutic regimen targeting DC-STAMP could suppress periodontal bone loss.

Metronomic cyclophosphamide activation of anti-tumor immunity: tumor model, mouse host, and drug schedule dependence of gene responses and their upstream regulators

Background

Cyclophosphamide (CPA) can activate immunogenic tumor cell death, which induces immune-based tumor ablation and long-term anti-tumor immunity in a syngeneic C57BL/6 (B6) mouse GL261 glioma model when CPA is given on a 6-day repeating metronomic schedule (CPA/6d). In contrast, we find that two other syngeneic B6 mouse tumors, LLC lung carcinoma and B16F10 melanoma, do not exhibit these drug-induced immune responses despite their intrinsic sensitivity to CPA cytotoxicity.

Methods

To elucidate underlying mechanisms, we investigated gene expression and molecular pathway changes associated with the disparate immune responsiveness of these tumors to CPA/6d treatment.

Results

Global transcriptome analysis indicated substantial elevation of basal GL261 immune infiltration and strong CPA/6d activation of GL261 immune stimulatory pathways and their upstream regulators, but without preferential depletion of negative immune regulators compared to LLC and B16F10 tumors. In LLC tumors, where CPA/6d treatment is shown to be anti-angiogenic, CPA/6d suppressed VEGFA target genes and down regulated cell adhesion and leukocyte transendothelial migration genes. In GL261 tumors implanted in adaptive immune-deficient scid mice, where CPA/6d-induced GL261 regression is incomplete and late tumor growth rebound can occur, T cell receptor signaling and certain cytokine-cytokine receptor responses seen in B6 mice were deficient. Extending the CPA treatment interval from 6 to 9 days (CPA/9d) − which results in a strong but transient natural killer cell response followed by early tumor growth rebound − induced fewer cytokines and increased expression of drug metabolism genes.

Conclusions

These findings elucidate molecular response pathways activated by intermittent metronomic CPA treatment and identify deficiencies that characterize immune-unresponsive tumor models and drug schedules.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2597-2) contains supplementary material, which is available to authorized users.

Luman is involved in osteoclastogenesis through the regulation of DC-STAMP expression, stability and localization

Luman (also known as CREB3) is a type-II transmembrane transcription factor belonging to the OASIS family that localizes to the endoplasmic reticulum (ER) membrane under normal conditions. In response to ER stress, OASIS-family members are subjected to regulated intramembrane proteolysis (RIP), following which the cleaved N-terminal fragments translocate to the nucleus. In this study, we show that treatment of bone marrow macrophages (BMMs) with cytokines – macrophage colony-stimulating factor (M-CSF) and RANKL (also known as TNFSF11) – causes a time-dependent increase in Luman expression, and that Luman undergoes RIP and becomes activated during osteoclast differentiation. Small hairpin (sh)RNA-mediated knockdown of Luman in BMMs prevented the formation of multinucleated osteoclasts, concomitant with the suppression of DC-STAMP, a protein that is essential for cell–cell fusion in osteoclastogenesis. The N-terminus of Luman facilitates promoter activity of DC-STAMP, resulting in upregulation of DC-STAMP expression. Furthermore, Luman interacts with DC-STAMP, and controls its stability and localization. These results suggest that Luman regulates the multinucleation of osteoclasts by promoting cell fusion of mononuclear osteoclasts through DC-STAMP induction and intracellular distribution during osteoclastogenesis.

Highlighted Article: Luman, an ER-resident transcription factor, regulates the multinucleation of osteoclasts by promoting cell fusion of mononuclear osteoclasts through DC-STAMP induction and transportation during osteoclastogenesis.

DC-STAMP, the key fusion-mediating molecule in osteoclastogenesis

As a member of the mononuclear phagocyte system, osteoclasts (OC) absorb the bone matrix and participate in bone modeling by keeping a balance with osteoblasts (OB) and stromal cells. Mature OC derive from the fusion of mononuclear osteoclasts (mOC) and the fusion is considered as the indispensable process for the osteoclastogenesis and absorbing activity of OC. DC-STAMP (dendritic cell-specific transmembrane protein) has been validated playing a key role in the fusion of mOC. DC-STAMP is mainly expressed in OC, macrophages and dendritic cells (DC). While DC-STAMP was discovered in DC, more attentions have been paid to DC-STAMP in OC in this decade. This review will mainly focus on the function of DC-STAMP in OC. Studies on DC-STAMP in DC may also provide new sight for the study of DC-STAMP in OC. Since the function of DC-STAMP is still poorly understood and few studies have been implemented for illustration, many issues are still unknown and need to be revealed. We will also discuss these questions in this review.

Classic selective sweeps revealed by massive sequencing in cattle

Human driven selection during domestication and subsequent breed formation has likely left detectable signatures within the genome of modern cattle. The elucidation of these signatures of selection is of interest from the perspective of evolutionary biology, and for identifying domestication-related genes that ultimately may help to further genetically improve this economically important animal. To this end, we employed a panel of more than 15 million autosomal SNPs identified from re-sequencing of 43 Fleckvieh animals. We mainly applied two somewhat complementary statistics, the integrated Haplotype Homozygosity Score (iHS) reflecting primarily ongoing selection, and the Composite of Likelihood Ratio (CLR) having the most power to detect completed selection after fixation of the advantageous allele. We find 106 candidate selection regions, many of which are harboring genes related to phenotypes relevant in domestication, such as coat coloring pattern, neurobehavioral functioning and sensory perception including KIT, MITF, MC1R, NRG4, Erbb4, TMEM132D and TAS2R16, among others. To further investigate the relationship between genes with signatures of selection and genes identified in QTL mapping studies, we use a sample of 3062 animals to perform four genome-wide association analyses using appearance traits, body size and somatic cell count. We show that regions associated with coat coloring significantly (P<0.0001) overlap with the candidate selection regions, suggesting that the selection signals we identify are associated with traits known to be affected by selection during domestication. Results also provide further evidence regarding the complexity of the genetics underlying coat coloring in cattle. This study illustrates the potential of population genetic approaches for identifying genomic regions affecting domestication-related phenotypes and further helps to identify specific regions targeted by selection during speciation, domestication and breed formation of cattle. We also show that Linkage Disequilibrium (LD) decays in cattle at a much faster rate than previously thought.

Domestication of cattle had a major impact on human civilization by providing protein and physical power for agrarian life style. Domestication followed by breed formation has likely left detectable signatures within the genome of modern cattle. Current cattle breeds, for instance, have a more uniform appearance and milder temper than their wild ancestors. The elucidation of these signatures of selection is of interest to identify domestication-related genes that help to genetically improve this economically important species. The development of novel sequencing technologies has enabled higher-resolution genomic analyses of past selection. In this paper, we exploited whole genome sequencing along with multiple statistical metrics to identify regions/genes putatively targeted by selection. We show strong signals of selection near to several candidate genes related to domesticated phenotypes such as coat coloring, neurobehavioral functioning and sensory perception, including KIT, MITF, MC1R, NRG4, Erbb4, TMEM132D and TAS2R16. By means of association mapping we additionally show that candidate selection regions for appearance traits overlap with major coat color QTLs. Our study demonstrates the utility of population based techniques for detecting past selection and is the first attempt to localize signatures of past selection in cattle based on massive re-sequencing of the entire genome.

Characterization of DC-STAMP+ Cells in Human Bone Marrow

Osteoclasts (OC), specialized cells derived from monocytes, maintain skeletal homeostasis under normal conditions but degrade bone in patients with rheumatoid (RA) and psoriatic arthritis (PsA). Monocytes initially develop in the bone marrow (BM), circulate in peripheral blood, and differentiate into distinct cell types with diverse functions. Imaging studies in (RA) patients and murine arthritis models demonstrate that bone marrow edema detected on MRI is the result of enhanced myelopoiesis which precedes the development of bone erosions detected on plain radiographs several years later. A major knowledge gap, however, is whether OC develop in the BM and circulate to the joint and if the differentiation to OC takes place in the joint space in response to differentiation signals such as RANKL and TNF. We have previously demonstrated that osteoclast precursors (OCP) are increased in the circulaton of patients with RA and PsA. We showed that DC-STAMP (Dendritic Cell-Specific Transmembrane protein), a 7-pass transmembrane protein expressed on the surface of monocytes, is essential for cell-to-cell fusion during OC differentiation and is a valid biomarker of OCP. Herein, we examined OCP in human bone marrow and identified one novel subset of DC-STAMP+CD45intermediate monocytes which was absent in the blood. We also found that OCPs reside in human BM with a higher frequency than in the peripheral blood. These findings support the notion that the BM is a major reservoir of circulating OCPs. In addition, we demonstrated that a higher frequency of DC-STAMP+ cells in the BM have detectable intracellular IFN-γ, IL-4 and IL-17A than DC-STAMP+ cells circulating in the peripheral blood. Finally, the frequency of DC-STAMP+ monocytes and T cells is signficantly higher in PsA BM compared to healthy controls, suggesting an enhanced myelopoiesis is a central event in inflammatory arthritis.

Dendritic cells: cellular mediators for immunological tolerance

In general, immunological tolerance is acquired upon treatment with non-specific immunosuppressive drugs. This indiscriminate immunosuppression of the patient often causes serious side-effects, such as opportunistic infectious diseases. Therefore, the need for antigen-specific modulation of pathogenic immune responses is of crucial importance in the treatment of inflammatory diseases. In this perspective, dendritic cells (DCs) can have an important immune-regulatory function, besides their notorious antigen-presenting capacity. DCs appear to be essential for both central and peripheral tolerance. In the thymus, DCs are involved in clonal deletion of autoreactive immature T cells by presenting self-antigens. Additionally, tolerance is achieved by their interactions with T cells in the periphery and subsequent induction of T cell anergy, T cell deletion, and induction of regulatory T cells (Treg). Various studies have described, modulation of DC characteristics with the purpose to induce antigen-specific tolerance in autoimmune diseases, graft-versus-host-disease (GVHD), and transplantations. Promising results in animal models have prompted researchers to initiate first-in-men clinical trials. The purpose of current review is to provide an overview of the role of DCs in the immunopathogenesis of autoimmunity, as well as recent concepts of dendritic cell-based therapeutic opportunities in autoimmune diseases.

An essential role for STAT6-STAT1 protein signaling in promoting macrophage cell-cell fusion

Macrophage lineage cells such as osteoclasts and foreign body giant cells (FBGCs) form multinuclear cells by cell-cell fusion of mononuclear cells. Recently, we reported that two seven-transmembrane molecules, osteoclast stimulatory transmembrane protein (OC-STAMP) and dendritic cell-specific transmembrane protein (DC-STAMP), were essential for osteoclast and FBGC cell-cell fusion in vivo and in vitro. However, signaling required to regulate FBGC fusion remained largely unknown. Here, we show that signal transducer and activator of transcription 1 (STAT1) deficiency in macrophages enhanced cell-cell fusion and elevated DC-STAMP expression in FBGCs. By contrast, lack of STAT6 increased STAT1 activation, significantly inhibiting cell-cell fusion and decreasing OC-STAMP and DC-STAMP expression in IL-4-induced FBGCs. Furthermore, either STAT1 loss or co-expression of OC-STAMP/DC-STAMP was sufficient to induce cell-cell fusion of FBGCs without IL-4. We conclude that the STAT6-STAT1 axis regulates OC-STAMP and DC-STAMP expression and governs fusogenic mechanisms in FBGCs.

Inflammation switches the differentiation program of Ly6Chi monocytes from antiinflammatory macrophages to inflammatory dendritic cells in the colon

Blood monocytes differentiate into distinct colonic macrophage or dendritic cell subsets depending on the presence or absence of inflammation

Dendritic cells (DCs) and macrophages (MPs) are important for immunological homeostasis in the colon. We found that F4/80^hiCX3CR1^hi (CD11b⁺CD103⁻) cells account for 80% of mouse colonic lamina propria MHC-II^hi cells. Both CD11c⁺ and CD11c⁻ cells within this population were identified as MPs based on multiple criteria, including an MP transcriptome revealed by microarray analysis. These MPs constitutively released high levels of IL-10 at least partially in response to the microbiota via an MyD88-independent mechanism. In contrast, cells expressing low to intermediate levels of F4/80 and CX3CR1 were identified as DCs based on phenotypic and functional analysis and comprise three separate CD11c^hi cell populations: CD103⁺CX3CR1⁻CD11b⁻ DCs, CD103⁺CX3CR1⁻CD11b⁺ DCs, and CD103⁻CX3CR1^intCD11b⁺ DCs. In noninflammatory conditions, Ly6C^hi monocytes (MOs) differentiated primarily into CD11c⁺ but not CD11c⁻ MPs. In contrast, during colitis, Ly6C^hi MOs massively invaded the colon and differentiated into proinflammatory CD103⁻CX3CR1^intCD11b⁺ DCs, which produced high levels of IL-12, IL-23, iNOS, and TNF. These findings demonstrate the dual capacity of Ly6C^hi blood MOs to differentiate into either regulatory MPs or inflammatory DCs in the colon and that the balance of these immunologically antagonistic cell types is dictated by microenvironmental conditions.

Regulation of human osteoclast development by dendritic cell-specific transmembrane protein (DC-STAMP)

Osteoclasts (OC) are bone-resorbing, multinucleated cells that are generated via fusion of OC precursors (OCP). The frequency of OCP is elevated in patients with erosive inflammatory arthritis and metabolic bone diseases. Although many cytokines and cell surface receptors are known to participate in osteoclastogenesis, the molecular mechanisms underlying the regulation of this cellular transformation are poorly understood. Herein, we focused our studies on the dendritic cell-specific transmembrane protein (DC-STAMP), a seven-pass transmembrane receptor-like protein known to be essential for cell-to-cell fusion during osteoclastogenesis. We identified an immunoreceptor tyrosine-based inhibitory motif (ITIM) in the cytoplasmic tail of DC-STAMP, and developed an anti-DC-STAMP monoclonal antibody 1A2 that detected DC-STAMP expression on human tumor giant cells, blocked OC formation in vitro, and distinguished four patterns of human PBMC with a positive correlation to OC potential. In freshly isolated monocytes, DC-STAMP(high) cells produced a higher number of OC in culture than DC-STAMP(low) cells and the surface expression of DC-STAMP gradually declined during osteoclastogenesis. Importantly, we showed that DC-STAMP is phosphorylated on its tyrosine residues and physically interacts with SHP-1 and CD16, an SH2-domain-containing tyrosine phosphatase and an ITAM-associated protein, respectively. Taken together, these data show that DC-STAMP is a potential OCP biomarker in inflammatory arthritis. Moreover, in addition to its effect on cell fusion, DC-STAMP dynamically regulates cell signaling during osteoclastogenesis.

DC-STAMP knock-down deregulates cytokine production and T-cell stimulatory capacity of LPS-matured dendritic cells

BACKGROUND

Dendritic cells (DCs) are the highly specialized antigen presenting cells of the immune system that play a key role in regulating immune responses. DCs can efficiently initiate immune responses or induce tolerance. Due to this dual function, DCs are studied in the context of immunotherapy for both cancer and autoimmune diseases. Characterization of DC-specific genes, leading to better understanding of DC immunobiology, will help to guide their use in clinical settings. We previously identified DC-STAMP, a multi-membrane spanning protein preferentially expressed by DCs. DC-STAMP resides in the endoplasmic reticulum (ER) of immature DCs and translocates towards the Golgi compartment upon maturation. In this study we knocked down DC-STAMP in mouse bone marrow-derived DCs (mBMDCs) to determine its function.

RESULTS

We demonstrate that DC-STAMP knock-down mBMDCs secrete less IL-6, IL-12, TNF-α and IL-10 while IL-1 production is enhanced. Moreover, LPS-matured DC-STAMP knock-down mBMDCs show impaired T cell activation potential and induction of Th1 responses in an alloreaction.

CONCLUSIONS

We show that DC-STAMP plays an important role in cytokine production by mBMDCs following LPS exposure. Our results reveal a novel function of DC-STAMP in regulating DC-initiated immune responses.

Comparative promoter analysis in vivo: identification of a dendritic cell-specific promoter module

Dendritic cells (DCs) are important immune cells. This study focused on transcriptional networks active in murine DCs, but DCs are difficult to study using conventional molecular techniques. Therefore, comparative promoter analysis was used to identify evolutionarily conserved features between the murine CD11c and DC-STAMP promoters. A promoter framework consisting of 4 transcription factor binding sites was identified that included signal transducer and activator of transcription, homeodomain transcription factors, and 2 members of the Brn POU domain factors family. This promoter module was functionally verified by in vivo promoter analysis and site-directed mutagenesis. Hematopoietic stem cells were engineered by lentiviral vectors and expression of green fluorescent protein reporter was monitored in primary hematopoietic cell types that develop without further manipulation in irradiated recipient mice. The verified promoter module was then modeled and used in a bioinformatics-based search for other potential coregulated genes in murine DCs. A promoter database search identified 2 additional genes, Ppef2 and Pftk1, which have a similar promoter organization and are preferentially expressed in murine DCs. The results define a regulatory network linked to development of murine DCs.

The signalling from endoplasmic reticulum-resident bZIP transcription factors involved in diverse cellular physiology

Eukaryotic cells can adapt to endoplasmic reticulum (ER) dysfunction by producing diverse signals from the ER to the cytosol or nucleus. These signalling pathways are collectively known as the unfolded protein response (UPR). The canonical branches of the UPR are mediated by three ER membrane-bound proteins: PERK, IRE1 and ATF6. These ER stress transducers basically play important roles in cell survival after ER stress. Recently, novel types of ER stress transducers that share a region of high sequence similarity with ATF6 have been identified. They have a transmembrane domain, which allows them to associate with the ER, and possess a transcription-activation domain and a bZIP domain. These membrane-bound bZIP transcription factors include Luman, OASIS, BBF2H7, CREBH and CREB4. Despite their structural similarities with ATF6, differences in activating stimuli, tissue distribution and response element binding indicate specialized functions of each member on regulating the UPR in specific organs and tissues. Here, we summarize our current understanding of the biochemical characteristics and physiological functions of the ER-resident bZIP transcription factors.

DC-STAMP interacts with ER-resident transcription factor LUMAN which becomes activated during DC maturation

Dendritic cells (DCs) are the professional antigen-presenting cells (APC) which efficiently prime the immune response or induce tolerance. We recently identified Dendritic Cell Specific TrAnsMembrane Protein (DC-STAMP), a novel 470 amino acid protein preferentially expressed by dendritic cells. Previously we demonstrated that DC-STAMP re-localizes towards the Golgi upon DC maturation. To identify proteins that interact with DC-STAMP, a yeast-2-hybrid analysis was performed. Here, we report a physically interacting partner of DC-STAMP in the endoplasmic reticulum (ER), called LUMAN (also known as CREB3 or LZIP). LUMAN was previously described as an ER-resident transcription factor with unknown function. It is activated in a process called regulated intramembrane proteolysis (RIP), which involves translocation to the Golgi and subsequent proteolytic cleavage. The proteolytically activated form of the protein then translocates to the nucleus. Our data indicate that DC-STAMP plays an important role in the modulation of LUMAN activation. Moreover, we demonstrate that LUMAN is endogenously expressed by DC and becomes activated by RIP upon DC maturation induced by various different stimuli. These data define LUMAN/DC-STAMP as a novel regulatory circuit in DC.

The Blimp1-Bcl6 axis is critical to regulate osteoclast differentiation and bone homeostasis

Controlling osteoclastogenesis is critical to maintain physiological bone homeostasis and prevent skeletal disorders. Although signaling activating nuclear factor of activated T cells 1 (NFATc1), a transcription factor essential for osteoclastogenesis, has been intensively investigated, factors antagonistic to NFATc1 in osteoclasts have not been characterized. Here, we describe a novel pathway that maintains bone homeostasis via two transcriptional repressors, B cell lymphoma 6 (Bcl6) and B lymphocyte–induced maturation protein-1 (Blimp1). We show that Bcl6 directly targets ‘osteoclastic’ molecules such as NFATc1, cathepsin K, and dendritic cell-specific transmembrane protein (DC-STAMP), all of which are targets of NFATc1. Bcl6-overexpression inhibited osteoclastogenesis in vitro, whereas Bcl6-deficient mice showed accelerated osteoclast differentiation and severe osteoporosis. We report that Bcl6 is a direct target of Blimp1 and that mice lacking Blimp1 in osteoclasts exhibit osteopetrosis caused by impaired osteoclastogenesis resulting from Bcl6 up-regulation. Indeed, mice doubly mutant in Blimp1 and Bcl6 in osteoclasts exhibited decreased bone mass with increased osteoclastogenesis relative to osteoclast-specific Blimp1-deficient mice. These results reveal a Blimp1–Bcl6–osteoclastic molecule axis, which critically regulates bone homeostasis by controlling osteoclastogenesis and may provide a molecular basis for novel therapeutic strategies.

The emerging field of osteoimmunology

Recent studies have elucidated unanticipated connections between the immune and skeletal systems, and this relationship has led to the development of a new field known as osteoimmunology. The goal of research in this field is to: (1) further understand how the bone microenvironment influences immune cell ontogeny and subsequent effector functions, and (2) translate basic science findings in bone biology to clinical applications for autoimmune diseases that target the skeleton such as rheumatoid arthritis (RA). In this review, we will examine the recent findings of the interplay between the immune and skeletal systems. This discussion will focus on the cells and signaling pathways in osteoimmune interactions and how innate and adaptive immune effector cells as well as cytokines and chemokines play a role in the maintenance and dysregulation of skeletal-immune homeostasis. We will also discuss how immunomodulatory biologic drugs, which specifically target these cells and effector molecules, have transformed the treatment of autoimmune mediated inflammatory diseases (IMIDs) and metabolic bone diseases such as osteoporosis.