Identification of genes differentially expressed in osteoclast-like cells

Green tea polyphenol EGCg induces cell fusion via reactive oxygen species

Background

Osteoclasts are multinucleated cells formed by macrophage cell fusion that are responsible for bone resorption. Previously, we found that treating osteoclastic progenitor cells with (-)-epigallocatechin gallate (EGCg) increased cell fusion. In this study, we aimed to identify factors involved in the cell fusion induced by EGCg.

Methods

We hypothesized that EGCg-induced oxidative stress might be involved in cell fusion, and used macrophage cell line RAW264.7 cells. We evaluated cell fusion activity after adding the antioxidants N-acetyl-l-cysteine (NAC) or catalase in addition to EGCg. The mRNA expressions of genes related to cell fusion and bone resorption were quantified by real-time PCR. Finally, we added hydrogen peroxide and examined its effects on cell fusion and TRAP activity.

Results

EGCg-induced cell fusion was strongly inhibited by the addition of NAC in a dose-dependent manner (EGCg with 5 mM NAC; decreased to 1.5%; p < 0.05), while the inhibitory effect of catalase was limited (EGCg with 500 U/mL catalase; decreased to 27.7%; p < 0.05). DC-STAMP expression was significantly upregulated by EGCg compared with the untreated group, and the upregulation was significantly suppressed by 5 mM NAC. Conversely, Nfatc1 and TRAP expression were not upregulated by EGCg. These results suggest that EGCg induces DC-STAMP expression via reactive oxygen species production, which regulates cell fusion but does not affect the osteoclastic pathway. Although treatment with hydrogen peroxide promoted the formation of multinucleated cells, no increase in TRAP activity was observed, which was similar to EGCg treatment.

Conclusions

This study suggests that the increased cell fusion by EGCg may be induced by oxidative stress due to reactive oxygen species production.

Unkeito Suppresses RANKL-Mediated Osteoclastogenesis via the Blimp1-Bcl6 and NF-κB Signaling Pathways and Enhancing Osteoclast Apoptosis

Osteoporosis is a common bone disease, particularly in menopausal women. Herein, we screened four Kampo medicines (Unkeito (UKT), Kamishoyosan (KSS), Kamikihito (KKT), and Ninjinyoeito (NYT)), frequently used to treat menopausal syndromes, for their effects on receptor activator of nuclear factor-kappaB ligand (RANKL)-induced osteoclast differentiation in RAW 264 cells. Considering that UKT exhibited the most potent effect, we examined its effect on RANKL-induced osteoclastogenesis, the induction of osteoclast apoptosis, and the mechanisms underlying its effects. UKT inhibits RANKL-induced osteoclast differentiation in the early stage and decreases osteoclast-related genes, including tartrate-resistant acid phosphatase (Trap), dendritic cell-specific transmembrane protein (Dcstamp), matrix metalloproteinase-9 (Mmp9), and cathepsin K (Ctsk). Specifically, UKT inhibits the nuclear factor of activated T cells 1 (NFATc1), which is essential for osteoclastogenesis. UKT increases Bcl6, which antagonizes NFATc1 and Dc-stamp, thereby blocking the progression of osteoclasts to maturation. UKT also decreased nuclear translocation by downregulating the activity of p65/NF-κB. In addition, UKT enhances mononuclear osteoclast apoptosis via activation of caspase-3. Herein, we demonstrate that UKT suppresses RANKL-mediated osteoclastogenesis via the Blimp1–Bcl6 and NF-κB signaling pathways and enhances mononuclear osteoclast apoptosis. Furthermore, UKT prevents bone loss in OVX mice. Thus, UKT might be a potential therapeutic agent for postmenopausal osteoporosis.

The Importance of Gene Duplication and Domain Repeat Expansion for the Function and Evolution of Fertilization Proteins

The process of gene duplication followed by gene loss or evolution of new functions has been studied extensively, yet the role gene duplication plays in the function and evolution of fertilization proteins is underappreciated. Gene duplication is observed in many fertilization protein families including Izumo, DCST, ZP, and the TFP superfamily. Molecules mediating fertilization are part of larger gene families expressed in a variety of tissues, but gene duplication followed by structural modifications has often facilitated their cooption into a fertilization function. Repeat expansions of functional domains within a gene also provide opportunities for the evolution of novel fertilization protein. ZP proteins with domain repeat expansions are linked to species-specificity in fertilization and TFP proteins that experienced domain duplications were coopted into a novel sperm function. This review outlines the importance of gene duplications and repeat domain expansions in the evolution of fertilization proteins.

Comprehensive Transcriptomic Profiling of Murine Osteoclast Differentiation Reveals Novel Differentially Expressed Genes and LncRNAs

Osteoclasts are the sole bone resorbing cells, which undertake opposing roles to osteoblasts to affect skeletal mass and structure. However, unraveling the comprehensive molecular mechanisms behind osteoclast differentiation is necessitated to overcome limitations and scarcity of available data, particularly in relation with the emerging roles of long non-coding RNAs (LncRNAs) in gene expression. In this study, we performed comprehensive and progressive analyses of the dynamic transcriptomes of murine osteoclasts, generated in vitro. We compared the total RNA-based transcriptomes of murine bone marrow derived cells with differentiated osteoclasts, while focusing on potentially novel genes and LncRNAs, to uncover critical genes and their associated pathways, which are differentially regulated during osteoclast differentiation. We found 4,214 differentially regulated genes during osteoclast differentiation, which included various types of LncRNAs. Among the upregulated protein coding genes not previously associated with osteoclast are Pheta1, Hagh, Gfpt1 and Nol4, while downregulated genes included Plau, Ltf, Sell and Zfp831. Notably, we report Nol4 as a novel gene related to osteoclast activity since Nol4 knockout mice Nol4^{em1(International Mouse Phenotyping Consortium)J} exhibit increased bone mineral density. Moreover, the differentially expressed LncRNAs included antisense and long intergenic non-coding RNAs, among others. Overall, immune-related and metabolism-related genes were downregulated, while anatomical morphogenesis and remodeling-related genes were upregulated in early-differentiated osteoclasts with sustained downregulation of immune-related genes in mature osteoclasts. The gene signatures and the comprehensive transcriptome of osteoclast differentiation provided herein can serve as an invaluable resource for deciphering gene dysregulation in osteoclast-related pathologic conditions.

Swiprosin-1: Its Expression and Diverse Biological Functions

Swiprosin-1/EFhd2 is a Ca²⁺ binding adapter protein involved in the various cellular functions. Swiprosin-1 is significantly upregulated in a number of pathological conditions of inflammation, neurodegeneration, and cancer. Swiprosin-1 associated with actin and its expression level amplifies the production of proinflammatory mediators and modulates the activation of transcription factor during immune cells activation. This review aims at providing an overview of the expression and function of swiprosin-1/EFhd2 in various pathophysiological conditions. We also discussed the key role of swiprosin-1 in immune cell activation, cell migration, apoptosis, humoral immunity, cancer invasion and metastasis, neuronal transport, and major signaling cascades. J. Cell. Biochem. 119: 150-156, 2018. © 2017 Wiley Periodicals, Inc.

Fraternal twins: Swiprosin-1/EFhd2 and Swiprosin-2/EFhd1, two homologous EF-hand containing calcium binding adaptor proteins with distinct functions

Changes in the intracellular calcium concentration govern cytoskeletal rearrangement, mitosis, apoptosis, transcriptional regulation or synaptic transmission, thereby, regulating cellular effector and organ functions. Calcium binding proteins respond to changes in the intracellular calcium concentration with structural changes, triggering enzymatic activation and association with downstream proteins. One type of calcium binding proteins are EF-hand super family proteins. Here, we describe two recently discovered homologous EF-hand containing adaptor proteins, Swiprosin-1/EF-hand domain containing 2 (EFhd2) and Swiprosin-2/EF-hand domain containing 1 (EFhd1), which are related to allograft inflammatory factor-1 (AIF-1). For reasons of simplicity and concision we propose to name Swiprosin-1/EFhd2 and Swiprosin-2/EFhd1 from now on EFhd2 and EFhd1, according to their respective gene symbols. AIF-1 and Swiprosin-1/EFhd2 are already present in Bilateria, for instance in Drosophila melanogaster and Caenhorhabditis elegans. Swiprosin-2/EFhd1 arose later from gene duplication in the tetrapodal lineage. Secondary structure prediction of AIF-1 reveals disordered regions and one functional EF-hand. Swiprosin-1/EFhd2 and Swiprosin-2/EFhd1 exhibit a disordered region at the N-terminus, followed by two EF-hands and a coiled-coil domain. Whereas both proteins are similar in their predicted overall structure they differ in a non-homologous stretch of 60 amino acids just in front of the EF-hands. AIF-1 controls calcium-dependent cytoskeletal rearrangement in innate immune cells by means of its functional EF-hand. We propose that Swiprosin-1/EFhd2 as well is a cytoskeleton associated adaptor protein involved in immune and brain cell function. Pro-inflammatory conditions are likely to modulate expression and function of Swiprosin-1/EFhd2. Swiprosin-2/EFhd1, on the other hand, modulates apoptosis and differentiation of neuronal and muscle precursor cells, probably through an association with mitochondria. We suggest furthermore that Swiprosin-2/EFhd1 is part of a cellular response to oxidative stress, which could explain its pro-survival activity in neuronal, muscle and perhaps some malignant tissues.

Swiprosin-1/EFhd2 controls B cell receptor signaling through the assembly of the B cell receptor, Syk, and phospholipase C gamma2 in membrane rafts

Compartmentalization of the BCR in membrane rafts is important for its signaling capacity. Swiprosin-1/EFhd2 (Swip-1) is an EF-hand and coiled-coil-containing adaptor protein with predicted Src homology 3 (SH3) binding sites that we identified in membrane rafts. We showed previously that Swip-1 amplifies BCR-induced apoptosis; however, the mechanism of this amplification was unknown. To address this question, we overexpressed Swip-1 and found that Swip-1 amplified the BCR-induced calcium flux in WEHI231, B62.1, and Bal17 cells. Conversely, the BCR-elicited calcium flux was strongly attenuated in Swip-1-silenced WEHI231 cells, and this was due to a decreased calcium mobilization from intracellular stores. Complementation of Swip-1 expression in Swip-1-silenced WEHI231 cells restored the BCR-induced calcium flux and enhanced spleen tyrosine kinase (Syk) tyrosine phosphorylation and activity as well as SLP65/BLNK/BASH and phospholipase C gamma2 (PLCgamma2) tyrosine phosphorylation. Furthermore, Swip-1 induced the constitutive association of the BCR itself, Syk, and PLCgamma2 with membrane rafts. Concomitantly, Swip-1 stabilized the association of BCR with tyrosine-phosphorylated proteins, specifically Syk and PLCgamma2, and enhanced the constitutive interaction of Syk and PLCgamma2 with Lyn. Interestingly, Swip-1 bound to the rSH3 domains of the Src kinases Lyn and Fgr, as well as to that of PLCgamma. Deletion of the predicted SH3-binding region in Swip-1 diminished its association and that of Syk and PLCgamma2 with membrane rafts, reduced its interaction with the SH3 domain of PLCgamma, and diminished the BCR-induced calcium flux. Hence, Swip-1 provides a membrane scaffold that is required for the Syk-, SLP-65-, and PLCgamma2-dependent BCR-induced calcium flux.

Upregulation of monocyte/macrophage HGFIN (Gpnmb/Osteoactivin) expression in end-stage renal disease

BACKGROUND AND OBJECTIVES

Hematopoietic growth factor-inducible neurokinin 1 (HGFIN), also known as Gpnmb and osteoactivin, is a transmembrane glycoprotein that is expressed in numerous cells, including osteoclasts, macrophages, and dendritic cells. It serves as an osteoblast differentiation factor, participates in bone mineralization, and functions as a negative regulator of inflammation in macrophages. Although measurable at low levels in monocytes, monocyte-to-macrophage transformation causes substantial increase in HGFIN expression. HGFIN is involved in systemic inflammation, bone demineralization, and soft tissue vascular calcification.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We explored HGFIN expression in monocytes and monocyte-derived macrophages in 21 stable hemodialysis patients and 22 control subjects.

RESULTS

Dialysis patients exhibited marked upregulation of colony-stimulating factor and IL-6 and significant downregulation of IL-10 in intact monocytes and transformed macrophages. HGFIN expression in intact monocytes was negligible in control subjects but conspicuously elevated (8.6-fold) in dialysis patients. As expected, in vitro monocyte-to-macrophage transformation resulted in marked upregulation of HGFIN in cells obtained from both groups but much more so in dialysis patients (17.5-fold higher). Upregulation of HGFIN and inflammatory cytokines in the uremic monocyte-derived macrophages occurred when grown in the presence of either normal or uremic serum, suggesting the enduring effect of the in vivo uremic milieu on monocyte/macrophage phenotype and function.

CONCLUSIONS

Uremic macrophages exhibit increased HGFIN gene and protein expression and heightened expression of proinflammatory and a suppressed expression of anti-inflammatory cytokines. Further studies are needed to determine the role of heightened monocyte/macrophage HGFIN expression in the pathogenesis of ESRD-induced inflammation and vascular and soft tissue calcification.

OS9 interacts with DC-STAMP and modulates its intracellular localization in response to TLR ligation

Dendritic cell-specific transmembrane protein (DC-STAMP) has been first identified as an EST in a cDNA library of human monocyte-derived dendritic cells (DC). DC-STAMP is a multimembrane spanning protein that has been implicated in skewing haematopoietic differentiation of bone marrow cells towards the myeloid lineage, and in cell fusion during osteoclastogenesis and giant cell formation. To gain molecular insight in how DC-STAMP exerts its function, DC-STAMP interacting proteins were identified in a yeast-2-hybrid analysis. Herein, we report that amplified in osteosarcoma 9 (OS9) physically interacts with DC-STAMP, and that both proteins colocalize in the endoplasmic reticulum in various cell lines, including immature DC. OS9 has previously been implicated in ER-to-Golgi transport and transcription factor turnover. Interestingly, we now demonstrate that toll-like receptor (TLR)-induced maturation of DC leads to the translocation of DC-STAMP from the ER to the Golgi while OS9 localization is unaffected. Applying TLR-expressing CHO cells we could confirm ER-to-Golgi translocation of DC-STAMP following TLR stimulation and demonstrated that the DC-STAMP/OS9 interaction is involved in this process. Collectively, the data indicate that OS9 is critically involved in the modulation of ER-to-Golgi transport of DC-STAMP in response to TLR triggering, suggesting a novel role for OS9 in myeloid differentiation and cell fusion.

Microphthalmia transcription factor regulates the expression of the novel osteoclast factor GPNMB

Microphthalmia transcription factor (MITF) regulates bone homeostasis by inducing expression of critical genes associated with osteoclast function. Gpnmb is a macrophage-enriched gene that has also been shown to be expressed in osteoblasts. Here, we have shown gpnmb to be highly induced in maturing murine osteoclasts. Microarray expression profile analysis identified gpnmb as a potential target of MITF in RAW264.7 cells, subclone C4 (RAW/C4), that overexpress this transcription factor. Electrophoretic mobility shift assays identified a MITF-binding site (M-box) in the gpnmb promoter that is conserved in different mammalian species. Anti-MITF antibody supershifted the DNA-MITF complex for the promoter site while MITF binding was abolished by mutation of this site. The gpnmb promoter was transactivated by co-expression of MITF in reporter gene assays while mutation of the gpnmb M-box prevented MITF transactivation. The induction of gpnmb expression during osteoclastogenesis was shown to exhibit similar kinetics to the known MITF targets, acp5 and clcn7. GPNMB expressed in RAW/C4 cells exhibited distinct subcellular distribution at different stages of osteoclast differentiation. At days 5 and 7, GPNMB protein co-localised with the osteoclast/macrophage lysosomal/endocytic marker MAC-3/LAMP-2, suggesting that GPNMB resides in the endocytic pathway of mature macrophages and is possibly targeted to the plasma membrane of bone-resorbing osteoclasts. The inclusion of gpnmb in the MITF regulon suggests a role for GPNMB in mature osteoclast function.

Systems level analysis of osteoclastogenesis reveals intrinsic and extrinsic regulatory interactions

Osteoclasts are bone-resorbing cells derived from the myeloid lineage that play a central role in bone remodeling and inflammatory bone erosion diseases. The receptor activator of NF-kappaB ligand (RANKL) produced by osteoblasts and activated immune cells initiates the development of osteoclasts in the bone marrow. Using time series gene expression data, the intrinsic processes and the extrinsic factors that control osteoclastogenesis were identified. The gene expression profiles display distinct commitment and differentiation phases. Analysis of the time course revealed several mechanistic details, including the complex role of cholesterol in osteoclast development. Epistatic interactions and the coordination between cellular processes that regulate development were inferred from the coexpression network. The coexpression network indicated that osteoclasts induce angiogenesis and recruit T-cells to the site of osteoclastogenesis early in the commitment phase. The resulting model provides an essential framework for a better understanding of the epigenetic program of osteoclastogenesis.

GpnmbIs Induced in Macrophages by IFN-γ and Lipopolysaccharide and Acts as a Feedback Regulator of Proinflammatory Responses

The process of inflammation requires the selective expression of a suite of genes in cells of the macrophage lineage. To identify candidate regulators of inflammation, we used cDNA microarrays to compare the transcriptome of inflammatory macrophages (thioglycolate-elicited peritoneal macrophages), bone marrow-derived macrophages, nonadherent spleen cells, and fibroblasts. We identified genes that were macrophage restricted and further elevated in inflammatory macrophages, and characterized the function of one such gene, gpnmb. Gpnmb mRNA expression was enriched in myelomonocytic cell lines and macrophage-related tissues and strongly up-regulated during macrophage differentiation. Epitope-tagged GPNMB expressed in RAW264.7 cells exhibited a perinuclear distribution and colocalized with the Golgi marker coat protein beta. Upon activation of macrophages with IFN-gamma and LPS, GPNMB translocated from the Golgi apparatus to vesicular compartments scattered toward the periphery. Gpnmb overexpression in RAW264.7 cells caused a 2-fold reduction in the production of the cytokines IL-6 and IL-12p40 and the inflammatory mediator NO in response to LPS. DBA mice, which have an inactivating point mutation in the gpnmb gene, exhibited reduced numbers of myeloid cells, elevated numbers of thioglycolate-elicited peritoneal macrophages, and higher levels of proinflammatory cytokines in response to LPS. Thus, GPNMB acts as a negative regulator of macrophage inflammatory responses.

Young, adult, and old rats have similar changes in mRNA expression of many skeletal genes after fracture despite delayed healing with age

Genes active in fracture healing are not well understood. Because age slows skeletal repair, the change in gene expression between animals of differing ages may illuminate novel pathways important to this healing response. To explore this, 6-, 26-, and 52-week-old female Sprague-Dawley rats were subjected to mid-diaphyseal femoral fracture with intramedullary fixation. The fracture callus was collected at 0, 0.4 (3 days), 1, 2, 4, or 6 weeks after fracture. RNA was extracted and pooled between two animals for each sample. Three samples were done for each time point for each age for a total of 54 Affymetrix U34A GeneChip microarrays. Of the 8700 genes on each array, 3300 were scored as present. Almost all of these genes were affected by femoral fracture with either upregulation or downregulation in the 6 weeks after fracture. Upregulated genes included markers for matrix genes for both cartilage and bone, osteoblasts, osteocytes, osteoclasts, fibroblasts, and mast cells. Downregulated genes included genes related to blood cell synthesis. Nearly all genes presently associated with bone metabolism showed the same response to fracture healing regardless of the age of the animal. In conclusion, skeletal fracture led to similar changes in RNA expression for most skeletal genes despite the delay in the formation of bone to bridge the fracture gap in old rats. Defects in the healing of skeletal trauma in older rats may lie in systems not normally studied by skeletal biologists.