Lack of Schnurri-2 expression associates with reduced bone remodeling and osteopenia

An angiogenic approach to osteoanabolic therapy targeting the SHN3-SLIT3 pathway

Often, disorders of impaired bone formation involve not only a cell intrinsic defect in the ability of osteoblasts to form bone, but moreover a broader dysfunction of the skeletal microenvironment that limits osteoblast activity. Developing approaches to osteoanabolic therapy that not only augment osteoblast activity but moreover correct this microenvironmental dysfunction may enable both more effective osteoanabolic therapies and also addressing a broader set of indications where vasculopathy or other forms microenvironment dysfunction feature prominently. We here review evidence that SHN3 acts as a suppressor of not only the cell intrinsic bone formation activity of osteoblasts, but moreover of the creation of a local osteoanabolic microenvironment. Mice lacking Schnurri3 (SHN3, HIVEP3) display a very robust increase in bone formation, that is due to de-repression of ERK pathway signaling in osteoblasts. In addition to loss of SHN3 augmenting the differentiation and bone formation activity of osteoblasts, loss of SHN3 increases secretion of SLIT3 by osteoblasts, which in a skeletal context acts as an angiogenic factor. Through this angiogenic activity, SLIT3 creates an osteoanabolic microenvironment, and accordingly treatment with SLIT3 can increase bone formation and enhance fracture healing. These features both validate vascular endothelial cells as a therapeutic target for disorders of low bone mass alongside the traditionally targeted osteoblasts and osteoclasts and indicate that targeting the SHN3/SLIT3 pathway provides a new mechanism to induce therapeutic osteoanabolic responses.

miRNAs as potential game-changers in bone diseases: Future medicinal and clinical uses

MicroRNAs (miRNAs), short, highly conserved non-coding RNA, influence gene expression by sequential mechanisms such as mRNA breakdown or translational repression. Many biological processes depend on these regulating substances, thus changes in their expression have an impact on the maintenance of cellular homeostasis and result in the emergence of a variety of diseases. Relevant studies have shown in recent years that miRNAs are involved in many stages of bone development and growth. Additionally, abnormal production of miRNA in bone tissues has been closely associated with the development of numerous bone disorders, such as osteonecrosis, bone cancer, and bone metastases. Many pathological processes, including bone loss, metastasis, the proliferation of osteosarcoma cells, and differentiation of osteoblasts and osteoclasts, are under the control of miRNAs. By bringing together the most up-to-date information on the clinical relevance of miRNAs in such diseases, this study hopes to further the study of the biological features of miRNAs in bone disorders and explore their potential as a therapeutic target.

Control Release of Adenosine Potentiate Osteogenic Differentiation within a Bone Integrative EGCG-g-NOCC/Collagen Composite Scaffold toward Guided Bone Regeneration in a Critical-Sized Calvarial Defect

The regeneration of critical-sized bone defects with biomimetic scaffolds remains clinically challenging due to avascular necrosis, chronic inflammation, and altered osteogenic activity. Two confounding mechanisms, efficacy manipulation, and temporal regulation dictate the scaffold's bone regenerative ability. Equally critical is the priming of the mesenchymal stromal cells (MSCs) toward lineage-specific differentiation into bone-forming osteoblast, which particularly depends on varied mechanochemical and biological cues during bone tissue regeneration. This study sought to design and develop an optimized osteogenic scaffold, adenosine/epigallocatechin gallate-N,O-carboxymethyl chitosan/collagen type I (AD/EGCG-g-NOCC@clgn I), having osteoinductive components toward swift bone regeneration in a calvarial defect BALB/c mice model. The ex vivo findings distinctly establish the pro-osteogenic potential of adenosine and EGCG, stimulating MSCs toward osteoblast differentiation with significantly increased expression of alkaline phosphatase, calcium deposits, and enhanced osteocalcin expression. Moreover, the 3D matrix recapitulates extracellular matrix (ECM) properties, provides a favorable microenvironment, structural support against mechanical stress, and acts as a reservoir for sustained release of osteoinductive molecules for cell differentiation, proliferation, and migration during matrix osteointegration observed. Evidence from in vivo experiments, micro-CT analyses, histology, and histomorphometry signify accelerated osteogenesis both qualitatively and quantitatively: effectual bone union with enhanced bone formation and new ossified tissue in 4 mm sized defects. Our results suggest that the optimized scaffold serves as an adjuvant to guide bone tissue regeneration in critical-sized calvarial defects with promising therapeutic efficacy.

Implication of the p53-Related miR-34c, -125b, and -203 in the Osteoblastic Differentiation and the Malignant Transformation of Bone Sarcomas

The formation of the skeleton occurs throughout the lives of vertebrates and is achieved through the balanced activities of two kinds of specialized bone cells: the bone-forming osteoblasts and the bone-resorbing osteoclasts. Impairment in the remodeling processes dramatically hampers the proper healing of fractures and can also result in malignant bone diseases such as osteosarcoma. MicroRNAs (miRNAs) are a class of small non-coding single-strand RNAs implicated in the control of various cellular activities such as proliferation, differentiation, and apoptosis. Their post-transcriptional regulatory role confers on them inhibitory functions toward specific target mRNAs. As miRNAs are involved in the differentiation program of precursor cells, it is now well established that this class of molecules also influences bone formation by affecting osteoblastic differentiation and the fate of osteoblasts. In response to various cell signals, the tumor-suppressor protein p53 activates a huge range of genes, whose miRNAs promote genomic-integrity maintenance, cell-cycle arrest, cell senescence, and apoptosis. Here, we review the role of three p53-related miRNAs, miR-34c, -125b, and -203, in the bone-remodeling context and, in particular, in osteoblastic differentiation. The second aim of this study is to deal with the potential implication of these miRNAs in osteosarcoma development and progression.

Genome-wide interaction study reveals age-dependent determinants of responsiveness to inhaled corticosteroids in individuals with asthma

While genome-wide association studies have identified genes involved in differential treatment responses to inhaled corticosteroids (ICS) in asthma, few studies have evaluated the potential effects of age in this context. A significant proportion of asthmatics experience exacerbations (hospitalizations and emergency department visits) during ICS treatment. We evaluated the interaction of genetic variation and age on ICS response (measured by the occurrence of exacerbations) through a genome-wide interaction study (GWIS) of 1,321 adult and child asthmatic patients of European ancestry. We identified 107 genome-wide suggestive (P<10-05) age-by-genotype interactions, two of which also met genome-wide significance (P<5x10-08) (rs34631960 [OR 2.3±1.6-3.3] in thrombospondin type 1 domain-containing protein 4 (THSD4) and rs2328386 [OR 0.5±0.3-0.7] in human immunodeficiency virus type I enhancer binding protein 2 (HIVEP2)) by joint analysis of GWIS results from discovery and replication populations. In addition to THSD4 and HIVEP2, age-by-genotype interactions also prioritized genes previously identified as asthma candidate genes, including DPP10, HDAC9, TBXAS1, FBXL7, and GSDMB/ORMDL3, as pharmacogenomic loci as well. This study is the first to link these genes to a pharmacogenetic trait for asthma.

Loss-of-function variants in HIVEP2 are a cause of intellectual disability

Intellectual disability (ID) affects 2-3% of the population. In the past, many genetic causes of ID remained unidentified due to its vast heterogeneity. Recently, whole exome sequencing (WES) studies have shown that de novo variants underlie a significant portion of sporadic cases of ID. Applying WES to patients with ID or global developmental delay at different centers, we identified three individuals with distinct de novo variants in HIVEP2 (human immunodeficiency virus type I enhancer binding protein), which belongs to a family of zinc-finger-containing transcriptional proteins involved in growth and development. Two of the variants were nonsense changes, and one was a 1 bp deletion resulting in a premature stop codon that was reported previously without clinical detail. In silico prediction programs suggest loss-of-function in the mutated allele leading to haploinsufficiency as a putative mechanism in all three individuals. All three patients presented with moderate-to-severe ID, minimal structural brain anomalies, hypotonia, and mild dysmorphic features. Growth parameters were in the normal range except for borderline microcephaly at birth in one patient. Two of the patients exhibited behavioral anomalies including hyperactivity and aggression. Published functional data suggest a neurodevelopmental role for HIVEP2, and several of the genes regulated by HIVEP2 are implicated in brain development, for example, SSTR-2, c-Myc, and genes of the NF-κB pathway. In addition, HIVEP2-knockout mice exhibit several working memory deficits, increased anxiety, and hyperactivity. On the basis of the genotype-phenotype correlation and existing functional data, we propose HIVEP2 as a causative ID gene.

Human immunodeficiency virus type 1 enhancer-binding protein 3 is essential for the expression of asparagine-linked glycosylation 2 in the regulation of osteoblast and chondrocyte differentiation

Human immunodeficiency virus type 1 enhancer-binding protein 3 (Hivep3) suppresses osteoblast differentiation by inducing proteasomal degradation of the osteogenesis master regulator Runx2. In this study, we tested the possibility of cooperation of Hivep1, Hivep2, and Hivep3 in osteoblast and/or chondrocyte differentiation. Microarray analyses with ST-2 bone stroma cells demonstrated that expression of any known osteochondrogenesis-related genes was not commonly affected by the three Hivep siRNAs. Only Hivep3 siRNA promoted osteoblast differentiation in ST-2 cells, whereas all three siRNAs cooperatively suppressed differentiation in ATDC5 chondrocytes. We further used microarray analysis to identify genes commonly down-regulated in both MC3T3-E1 osteoblasts and ST-2 cells upon knockdown of Hivep3 and identified asparagine-linked glycosylation 2 (Alg2), which encodes a mannosyltransferase residing on the endoplasmic reticulum. The Hivep3 siRNA-mediated promotion of osteoblast differentiation was negated by forced Alg2 expression. Alg2 suppressed osteoblast differentiation and bone formation in cultured calvarial bone. Alg2 was immunoprecipitated with Runx2, whereas the combined transfection of Runx2 and Alg2 interfered with Runx2 nuclear localization, which resulted in suppression of Runx2 activity. Chondrocyte differentiation was promoted by Hivep3 overexpression, in concert with increased expression of Creb3l2, whose gene product is the endoplasmic reticulum stress transducer crucial for chondrogenesis. Alg2 silencing suppressed Creb3l2 expression and chondrogenesis of ATDC5 cells, whereas infection of Alg2-expressing virus promoted chondrocyte maturation in cultured cartilage rudiments. Thus, Alg2, as a downstream mediator of Hivep3, suppresses osteogenesis, whereas it promotes chondrogenesis. To our knowledge, this study is the first to link a mannosyltransferase gene to osteochondrogenesis.

Immune-related functions of the Hivep gene family in East African cichlid fishes

Immune-related genes are often characterized by adaptive protein evolution. Selection on immune genes can be particularly strong when hosts encounter novel parasites, for instance, after the colonization of a new habitat or upon the exploitation of vacant ecological niches in an adaptive radiation. We examined a set of new candidate immune genes in East African cichlid fishes. More specifically, we studied the signatures of selection in five paralogs of the human immunodeficiency virus type I enhancer-binding protein (Hivep) gene family, tested their involvement in the immune defense, and related our results to explosive speciation and adaptive radiation events in cichlids. We found signatures of long-term positive selection in four Hivep paralogs and lineage-specific positive selection in Hivep3b in two radiating cichlid lineages. Exposure of the cichlid Astatotilapia burtoni to a vaccination with Vibrio anguillarum bacteria resulted in a positive correlation between immune response parameters and expression levels of three Hivep loci. This work provides the first evidence for a role of Hivep paralogs in teleost immune defense and links the signatures of positive selection to host-pathogen interactions within an adaptive radiation.

Emerging roles of zinc finger proteins in regulating adipogenesis

Proteins containing the zinc finger domain(s) are named zinc finger proteins (ZFPs), one of the largest classes of transcription factors in eukaryotic genomes. A large number of ZFPs have been studied and many of them were found to be involved in regulating normal growth and development of cells and tissues through diverse signal transduction pathways. Recent studies revealed that a small but increasing number of ZFPs could function as key transcriptional regulators involved in adipogenesis. Due to the prevalence of obesity and metabolic disorders, the investigation of molecular regulatory mechanisms of adipocyte development must be more completely understood in order to develop novel and long-term impact strategies for ameliorating obesity. In this review, we discuss recent work that has documented that ZFPs are important functional contributors to the regulation of adipogenesis. Taken together, these data lead to the conclusion that ZFPs may become promising targets to combat human obesity.

Schnurri-3 regulates ERK downstream of WNT signaling in osteoblasts

Mice deficient in Schnurri-3 (SHN3; also known as HIVEP3) display increased bone formation, but harnessing this observation for therapeutic benefit requires an improved understanding of how SHN3 functions in osteoblasts. Here we identified SHN3 as a dampener of ERK activity that functions in part downstream of WNT signaling in osteoblasts. A D-domain motif within SHN3 mediated the interaction with and inhibition of ERK activity and osteoblast differentiation, and knockin of a mutation in Shn3 that abolishes this interaction resulted in aberrant ERK activation and consequent osteoblast hyperactivity in vivo. Additionally, in vivo genetic interaction studies demonstrated that crossing to Lrp5(-/-) mice partially rescued the osteosclerotic phenotype of Shn3(-/-) mice; mechanistically, this corresponded to the ability of SHN3 to inhibit ERK-mediated suppression of GSK3β. Inducible knockdown of Shn3 in adult mice resulted in a high-bone mass phenotype, providing evidence that transient blockade of these pathways in adults holds promise as a therapy for osteoporosis.

Effect of lyso-phosphatidylcholine and Schnurri-3 on osteogenic transdifferentiation of vascular smooth muscle cells to calcifying vascular cells in 3D culture

BACKGROUND

In vitro cell culture is a widely used technique for investigating a range of processes such as stem cell behavior, regenerative medicine, tissue engineering, and drug discovery. Conventional cell culture is performed in Petri dishes or flasks where cells typically attach to a flat glass or plastic surface as a cell monolayer. However, 2D cell monolayers do not provide a satisfactory representation of in vivo conditions. A 3D culture could be a much better system for representing the conditions that prevail in vivo.

METHODS AND RESULTS

To simulate 3D conditions, vascular smooth muscle cells (VSMCs) were loaded with gold-polyvmer-iron oxide hydrogel, enabling levitation of the cells by using spatially varying magnetic fields. These magnetically levitated 3D cultures appeared as freely suspended, clustered cells which proliferated 3-4 times faster than cells in conventional 2D cultures. When the levitated cells were treated with 10nM lysophosphatidylcholine (LPC), for 3days, cell clusters exhibited translucent extensions/rods 60-80μm wide and 200-250μm long. When 0.5μg/μl Schnurri-3 was added to the culture containing LPC, these extensions were smaller or absent. When excited with 590-650nm light, these extensions emitted intrinsic fluorescence at >667nm. When the 3D cultures were treated with a fluorescent probe specific for calcium hydroxyapatite (FITC-HABP-19), the cell extensions/rods emitted intensely at 518nm, the λmax for FITC emission. Pellets of cells treated with LPC were more enriched in calcium, phosphate, and glycosaminoglycans than cells treated with LPC and Schnurri-3.

CONCLUSIONS

In 3D cultures, VSMCs grow more rapidly and form larger calcification clusters than cells in 2D cultures. Transdifferentiation of VSMC into calcifying vascular cells is enhanced by LPC and attenuated by Schnurri-3.

GENERAL SIGNIFICANCE

The formation of calcified structures in 3D VSMC cultures suggests that similar structures may be formed in vivo.

Dentin phosphophoryn activates Smad protein signaling through Ca2+-calmodulin-dependent protein kinase II in undifferentiated mesenchymal cells

Dentin phosphophoryn (DPP) is a major noncollagenous protein in the dentin matrix. In this study, we demonstrate that pluripotent stem cells such as C3H10T1/2 and human bone marrow cells can be committed to the osteogenic lineage by DPP. Treatment with DPP can stimulate the release of intracellular Ca(2+). This calcium flux triggered the activation of Ca(2+)-calmodulin-dependent protein kinase II (CaMKII). Activated CaMKII induced the phosphorylation of Smad1 and promoted nuclear translocation of p-Smad1. Inhibition of store Ca(2+) depletion by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) or down-regulation of CaMKII by KN-62, a selective cell-permeable pharmacological inhibitor or a dominant negative plasmid of CaMKII, blocked DPP-mediated Smad1 phosphorylation. Activation of Smad1 resulted in the expression of osteogenic markers such as Runx2, Osterix, DMP1, Bone sialoprotein, Osteocalcin, NFATc1, and Schnurri-2, which have been implicated in osteoblast differentiation. These findings suggest that DPP is capable of triggering commitment of pluripotent stem cells to the osteogenic lineage.

Genome-wide repression of NF-κB target genes by transcription factor MIBP1 and its modulation by O-linked β-N-acetylglucosamine (O-GlcNAc) transferase

The transcription factor c-MYC intron binding protein 1 (MIBP1) binds to various genomic regulatory regions, including intron 1 of c-MYC. This factor is highly expressed in postmitotic neurons in the fetal brain and may be involved in various biological steps, such as neurological and immunological processes. In this study, we globally characterized the transcriptional targets of MIBP1 and proteins that interact with MIBP1. Microarray hybridization followed by gene set enrichment analysis revealed that genes involved in the pathways downstream of MYC, NF-κB, and TGF-β were down-regulated when HEK293 cells stably overexpressed MIBP1. In silico transcription factor binding site analysis of the promoter regions of these down-regulated genes showed that the NF-κB binding site was the most overrepresented. The up-regulation of genes known to be in the NF-κB pathway after the knockdown of endogenous MIBP1 in HT1080 cells supports the view that MIBP1 is a down-regulator of the NF-κB pathway. We also confirmed the binding of the MIBP1 to the NF-κB site. By immunoprecipitation and mass spectrometry, we detected O-linked β-N-acetylglucosamine (O-GlcNAc) transferase as a prominent binding partner of MIBP1. Analyses using deletion mutants revealed that a 154-amino acid region of MIBP1 was necessary for its O-GlcNAc transferase binding and O-GlcNAcylation. A luciferase reporter assay showed that NF-κB-responsive expression was repressed by MIBP1, and stronger repression by MIBP1 lacking the 154-amino acid region was observed. Our results indicate that the primary effect of MIBP1 expression is the down-regulation of the NF-κB pathway and that this effect is attenuated by O-GlcNAc signaling.

CLIC4 and Schnurri-2: a dynamic duo in TGF-beta signaling with broader implications in cellular homeostasis and disease

CLIC4 is a highly conserved, multifunctional member of the chloride intracellular channel family of proteins. The protein is largely cytoplasmic but translocates to the nucleus upon a variety of stimuli including TGF-beta, TNF-alpha and etoposide. Nuclear resident CLIC4 causes growth arrest, terminal differentiation and apoptosis. Recently, it was discovered that TGF-beta causes CLIC4 to associate with Schnurri-2 and together they translocate to the nucleus and dissociate thereafter. The nuclear function of CLIC4 was further illuminated by the discovery that CLIC4 enhances TGF-beta signaling by associating with phospho-Smad2 and 3 and preventing their dephosphorylation. Enhanced TGF-beta dependent gene expression and growth inhibition are downstream consequences of this activity of CLIC4. In this article, we speculate on other consequences of the CLIC4 relation to TGF-beta signaling and the potential for CLIC4 to participate in other cellular functions related to normal homeostasis and disease.

The large zinc finger protein ZAS3 is a critical modulator of osteoclastogenesis

Background

Mice deficient in the large zinc finger protein, ZAS3, show postnatal increase in bone mass suggesting that ZAS3 is critical in the regulation of bone homeostasis. Although ZAS3 has been shown to inhibit osteoblast differentiation, its role on osteoclastogenesis has not been determined. In this report we demonstrated the role of ZAS3 in bone resorption by examining the signaling mechanisms involved in osteoclastogenesis.

Methodology/Principal Findings

Comparison of adult wild-type and ZAS3 knockout (ZAS3−/−) mice showed that ZAS3 deficiency led to thicker bones that are more resistant to mechanical fracture. Additionally, ZAS3−/− bones showed fewer osteoclasts and inefficient M-CSF/sRANKL-mediated osteoclastogenesis ex vivo. Utilizing RAW 264.7 pre-osteoclasts, we demonstrated that overexpression of ZAS3 promoted osteoclastogenesis and the expression of crucial osteoclastic molecules, including phospho-p38, c-Jun, NFATc1, TRAP and CTSK. Contrarily, ZAS3 silencing by siRNA inhibited osteoclastogenesis. Co-immunoprecipitation experiments demonstrated that ZAS3 associated with TRAF6, the major receptor associated molecule in RANK signaling. Furthermore, EMSA suggested that nuclear ZAS3 could regulate transcription by binding to gene regulatory elements.

Conclusion/Significance

Collectively, the data suggested a novel role of ZAS3 as a positive regulator of osteoclast differentiation. ZAS3 deficiency caused increased bone mass, at least in part due to decreased osteoclast formation and bone resorption. These functions of ZAS3 were mediated via activation of multiple intracellular targets. In the cytoplasmic compartment, ZAS3 associated with TRAF6 to control NF-kB and MAP kinase signaling cascades. Nuclear ZAS3 acted as a transcriptional regulator for osteoclast-associated genes. Additionally, ZAS3 activated NFATc1 required for the integration of RANK signaling in the terminal differentiation of osteoclasts. Thus, ZAS3 was a crucial molecule in osteoclast differentiation, which might potentially serve as a target in the design of therapeutic interventions for the treatment of bone diseases related to increased osteoclast activity such as postmenopausal osteoporosis, Paget's disease, and rheumatoid arthritis.

Schnurri-2 deficiency counteracts against bone loss induced by ovariectomy

Schnurri (Shn)-2 is a transcriptional modulator of bone formation and bone resorption and its deficiency causes low turnover state with higher cancellous bone mass due to the defects in osteoclasts that exceeds the defects in osteoblasts in mice. We addressed whether such low turnover of bone remodeling in Shn2 deficiency may be modulated in the absence of estrogen that induces high turnover state in vivo. Ovariectomy reduced bone mass in wild type compared to sham operated control mice and such reduction in bone mass was also observed in Shn2 deficient mice. However, due to the high levels of basal bone mass in Shn2 deficient mice, the bone mass levels after ovariectomy were still comparable to sham operated wild-type mice. Analysis indicated that estrogen depletion increased bone resorption at similar levels in wild type and Shn2 deficient mice though the basal levels of osteoclast number was slightly lower in Shn2-deficient mice. In contrast, basal levels of bone marrow cell mineralization in cultures were low in Shn2-deficeint mice while estrogen depletion increased the mineralization levels to those that were comparable to sham wild type. This indicates that Shn2-deficient mice maintain bone mass at the levels comparable to wild-type sham mice even after ovariectomy-induced bone loss and this correlates with the high levels of mineralization activity in bone marrow cells after ovariectomy.

Progressive ankylosis protein (ANK) in osteoblasts and osteoclasts controls bone formation and bone remodeling

The progressive ankylosis gene (ank) encodes a transmembrane protein that transports intracellular inorganic pyrophosphate (PP(i)) to the extracellular milieu. ank/ank mice, which express a truncated nonfunctional ANK, showed a markedly reduced bone mass, bone-formation rate, and number of tartrate-resistant acid phosphatase-positive (TRAP(+)) multinucleated osteoclasts. ANK function deficiency suppressed osteoblastic differentiation of ank/ank bone marrow stromal cells, as indicated by the decrease in the expression of bone marker genes, including osterix, reduced alkaline phosphatase activity, and mineralization. Runx2 gene expression levels were not altered. Conversely, overexpression of ANK in the preosteoblastic cell line MC3T3-E1 resulted in increased expression of bone marker genes, including osterix. Whereas runx2 expression was not altered in ANK-overexpressing MC3T3-E1 cells, runx2 transcriptional activity was increased. Extracellular PP(i) or P(i) stimulated osteoblastogenic differentiation of MC3T3-E1 cells or partially rescued delayed osteoblastogenic differentiation of ank/ank bone marrow stromal cells. A loss of PP(i) transport function ANK mutation also stimulated osteoblastogenic differentiation of MC3T3-E1 cells. Furthermore, ANK function deficiency suppressed the formation of multinucleated osteoclasts from ank/ank bone marrow cells cultured in the presence of macrophage colony-stimulating factor and receptor activator of nuclear factor-kappaB ligand. In conclusion, ANK is a positive regulator of osteoblastic and osteoclastic differentiation events toward a mature osteoblastic and osteoclastic phenotype.

Uncoupling of growth plate maturation and bone formation in mice lacking both Schnurri-2 and Schnurri-3

Formation and remodeling of the skeleton relies on precise temporal and spatial regulation of genes expressed in cartilage and bone cells. Debilitating diseases of the skeletal system occur when mutations arise that disrupt these intricate genetic regulatory programs. Here, we report that mice bearing parallel null mutations in the adapter proteins Schnurri2 (Shn2) and Schnurri3 (Shn3) exhibit defects in patterning of the axial skeleton during embryogenesis. Postnatally, these compound mutant mice develop a unique osteochondrodysplasia. The deletion of Shn2 and Shn3 impairs growth plate maturation during endochondral ossification but simultaneously results in massively elevated trabecular bone formation. Hence, growth plate maturation and bone formation can be uncoupled under certain circumstances. These unexpected findings demonstrate that both unique and redundant functions reside in the Schnurri protein family that are required for proper skeletal patterning and remodeling.

Memory Th1/Th2 cell generation controlled by Schnurri-2

Schnurri (Shn) is a large zinc-finger containingprotein, which plays a critical role in cell growth, signal transduction and lymphocyte development. There are three orthologues (Shn-1, Shn-2 and Shn-3) in vertebrates. In Shn-2-deficient mice, the activation of NF-kappaB in CD4 T cells is upregulated and their ability to differentiate into Th2 cells is enhanced in part through the increased expression of GATA3. Shn-2 is found to compete with p50 NF-kappaB for binding to a consensus NF-kappaB motif and inhibit the NF-kappaB-driven promoter activity. In addition, Th2-driven allergic airway inflammation was enhanced in Shn-2-deficient mice. Therefore, Shn-2 appears to negatively control the differentiation of Th2 cells and Th2 responses through the repression of NF-kappaB function. Memory Th1/Th2 cells are not properly generated from Shn-2-deficient effector Th1/Th2 cells. The expression levels of CD69 and the number ofapoptotic cells are selectively increased in Shn-2-deficient Thl/Th2 cells when they are transferred into syngeneic host animals, in which memoryh Th1/Th2 cells are generated within a month. In addition, an increased susceptibility to apoptotic cell death is also observed in vitro accompanied with the increased expression of FasL, one of the NF-kappaB-dependent genes. Th2 effector cells overexpressing the p65 subunit of NF-kappaB demonstrate a decreased cell survival particularly in the lymph node. These results indicate that Shn-2-mediated repression of NF-kappaB is required for cell survival and the successful generation of memory Th1/Th2 cells. This may point to the possibility that after antigen clearance the recovery of the quiescent state in effector Th cells is required for the generation of memory Th cells. A repressor molecule Shn-2 plays an important role in this process.

Finding partners: how BMPs select their targets

The bone morphogenetic protein (BMP) signaling pathway is a conserved and evolutionarily ancient regulatory module affecting a large variety of cellular behaviors. The evolutionary flexibility in using BMP responses presumably arose by co-option of a canonical BMP signaling cascade to regulate the transcription of diverse batteries of target genes. This begs the question of how seemingly interchangeable BMP signaling components elicit widely different outputs in different cell types, an important issue in the context of understanding how BMP signaling integrates with gene regulatory networks to control development. Because a molecular understanding of how BMP signaling activates different batteries of target genes is an essential prerequisite to comprehending the roles of BMPs in regulating cellular responses, here we review the current knowledge of how BMP-regulated target genes are selected by the signal transduction machinery. We highlight recent studies suggesting the evolutionary conservation of BMP target gene regulation signaling by Schnurri family zinc finger proteins. Developmental Dynamics 238:1321-1331, 2009. (c) 2009 Wiley-Liss, Inc.

Oxytocin is an anabolic bone hormone

We report that oxytocin (OT), a primitive neurohypophyseal hormone, hitherto thought solely to modulate lactation and social bonding, is a direct regulator of bone mass. Deletion of OT or the OT receptor (Oxtr) in male or female mice causes osteoporosis resulting from reduced bone formation. Consistent with low bone formation, OT stimulates the differentiation of osteoblasts to a mineralizing phenotype by causing the up-regulation of BMP-2, which in turn controls Schnurri-2 and 3, Osterix, and ATF-4 expression. In contrast, OT has dual effects on the osteoclast. It stimulates osteoclast formation both directly, by activating NF-kappaB and MAP kinase signaling, and indirectly through the up-regulation of RANK-L. On the other hand, OT inhibits bone resorption by mature osteoclasts by triggering cytosolic Ca(2+) release and NO synthesis. Together, the complementary genetic and pharmacologic approaches reveal OT as a novel anabolic regulator of bone mass, with potential implications for osteoporosis therapy.

Regulation of bone formation and immune cell development by Schnurri proteins

Although identified over a decade ago, the function and physiological significance of the mammalian Schnurri protein family remained largely unknown. However, the recent generation and characterization of mice bearing null mutations in the individual Schnurri genes has led to the discovery of unexpected yet central roles for these large zinc-finger proteins in several biological processes. Here, we review findings of these studies and discuss the importance of the Schnurri protein family in regulating both the immune and skeletal systems.

Synaptotagmin VII regulates bone remodeling by modulating osteoclast and osteoblast secretion

Maintenance of bone mass and integrity requires a tight balance between resorption by osteoclasts and formation by osteoblasts. Exocytosis of functional proteins is a prerequisite for the activity of both cells. In the present study, we show that synaptotagmin VII, a calcium sensor protein that regulates exocytosis, is associated with lysosomes in osteoclasts and bone matrix protein-containing vesicles in osteoblasts. Absence of synaptotagmin VII inhibits cathepsin K secretion and formation of the ruffled border in osteoclasts and bone matrix protein deposition in osteoblasts, without affecting the differentiation of either cell. Reflecting these in vitro findings, synaptotagmin VII-deficient mice are osteopenic due to impaired bone resorption and formation. Therefore, synaptotagmin VII plays an important role in bone remodeling and homeostasis by modulating secretory pathways functionally important in osteoclasts and osteoblasts.

Transcription factors controlling osteoblastogenesis

The recent development of molecular biology and mouse genetics and the analysis of the skeletal phenotype induced by genetic mutations in humans led to a better understanding of the role of transcription factors that govern bone formation. This review summarizes the role of transcription factors in osteoblastogenesis and provides an integrated perspective on how the activities of multiple classes of factors are coordinated for the complex process of developing the osteoblast phenotype. The roles of Runx2, the principal transcriptional regulator of osteoblast differentiation, Osterix, beta-Catenin and ATF which act downstream of Runx2, and other transcription factors that contribute to the control of osteoblastogenesis including the AP1, C/EBPs, PPARgamma and homeodomain, helix-loop-helix proteins are discussed. This review also updates the regulation of transcription factor expression by signaling factors and hormones that control osteoblastogenesis.

How the Smads regulate transcription

The primary signalling pathway downstream of ligands of the transforming growth factor beta (TGF-beta) superfamily is the Smad pathway. Activated receptors phosphorylate receptor-regulated Smads, which form homomeric complexes and heteromeric complexes with Smad4. These activated Smad complexes accumulate in the nucleus, where they are directly involved in the regulation of transcription of target genes. This apparently very simple pathway is subject to complex regulation, much of which is at the level of post-translational modifications of pathway components, in particular, the Smads. The enzymes responsible may be constitutively active, may be cell type-specific or may be regulated by other signalling pathways or by the cell cycle. In this way, signals from TGF-beta superfamily ligands are integrated with signals from other growth factors and cytokines, are regulated by the cell cycle and are dependent on cell type. This may go some way to explaining the pleiotropic nature of TGF-beta superfamily responses. In this review we focus on the mechanisms whereby the Smads are modified and regulated. We then go on to discuss how the activated Smad complexes regulate transcription.

Disruption of ZAS3 in mice alters NF-kappaB and AP-1 DNA binding and T-cell development

The large zinc finger proteins, ZAS, regulate the transcription of a variety of genes involved in cell growth, development, and metastasis. They also function in the signal transduction of the TGF-beta and TNF-alpha pathways. However, the endogenous protein of a representative member, ZAS3, is rapidly degraded in primary lymphocytes, which limits the determination of its physiological function in vitro. Therefore, we have generated mice with targeted disruption of ZAS3. Oligonucleotide-based microarray analyses revealed subtle but consistent differences in the expression of genes, many of which are associated with receptor or signal transduction activities between ZAS3+/+ and ZAS3-/- thymi. Gel mobility shift assays showed altered DNA binding activities of NF-kappaB and AP-1 proteins in ZAS3-deficient tissues, including the thymus. Lymphocyte analysis suggested a subtle but broad function of ZAS3 in regulating T-cell development and activation. In CD3+ ZAS3-/- thymocytes, the CD4/ CD8 ratio was decreased and CD69 expression was decreased. In peripheral CD4+ ZAS3-/- lymphocytes we observed an increased number of memory T cells.