Fra-2/AP-1 controls bone formation by regulating osteoblast differentiation and collagen production

Progress in the Study of Fra-2 in Respiratory Diseases

Fos-related antigen-2 (Fra-2) is a member of the activating protein-1 (AP-1) family of transcription factors. It is involved in controlling cell growth and differentiation by regulating the production of the extracellular matrix (ECM) and coordinating the balance of signals within and outside the cell. Fra-2 is not only closely related to bone development, metabolism, and immune system and eye development but also in the progression of respiratory conditions like lung tumors, asthma, pulmonary fibrosis, and chronic obstructive pulmonary disease (COPD). The increased expression and activation of Fra-2 in various lung diseases has been shown in several studies. However, the specific molecular mechanisms through which Fra-2 affects the development of respiratory diseases are not yet understood. The purpose of this research is to summarize and delineate advancements in the study of the involvement of transcription factor Fra-2 in disorders related to the respiratory system.

Effect of dietary Eucommia ulmoides oliver polysaccharide on immune function and meat quality of Songliao Black Pigs

Eucommia ulmoides is a traditional Chinese herbal medicine, with pharmacological effects such as lowering blood pressure and enhancing immune function. The effects of dietary Eucommia ulmoides polysaccharide (EUP) on immune function and meat quality were studied in Songliao Black Pigs. Blood lymphocyte counts and percentage, concentrations of serum total protein and of albumin increased, whereas those of urea nitrogen and triglyceride decreased. White blood cell and lymphocyte counts, and serum IgA, IgE, IgG2 a and IFN-γ increased. Average daily weight gain, slaughter weight, lean meat rate and cooked meat rate increased, whereas pH24, feed-weight ratio, fat rate, yellowness (b#) and centrifugal dehydration rate decreased. Transcriptome sequencing of longissimus dorsi muscle detected 32 differentially expressed genes (DEGs), of which 26 were up-regulated and 6 down-regulated. A total of 19 genes were differentially expressed in the four groups, 18 of which were up-regulated. The DEGs included ADAMTS4, PER1, STAC, SERPINE1, FASN, THRSP, SP7 and KRT80 and the protein interaction network showed 20 up-regulated nodes, three down-regulated nodes and 14 DEGs. GO functional annotation and enrichment analysis showed that 34 items were significantly enriched, including transferase activity, actin binding, acetyl coenzyme A, acyl coenzyme A metabolism, adipose tissue development and acyl glycerol homeostasis. KEGG pathway analysis showed that the AMPK and PPAR signaling pathways were enriched. Dietary Eucommia polysaccharide enhanced immune function in Songliao Black Pigs, improved growth and carcass performance, increased the expression of genes related to meat quality traits and improved meat quality.

FasL impacts Tgfb signaling in osteoblastic cells

Fas ligand (FasL, CD178) belongs to classical apoptotic molecules, however, recent evidence expands the spectrum of FasL functions into non-apoptotic processes which also applies for the bone. Tgfb subfamily members (Tgfb1, Tgfb2, Tgfb3) represent major components in osteogenic pathways and extracellular matrix. Their possible association with FasL has not yet been investigated but can be postulated. To test such a hypothesis, FasL deficient (gld) calvaria-derived cells were examined with a focus on the expression of Tgfb receptor ligands. The qPCR analysis revealed significantly increased expression of Tgfb1, Tgfb2 and Tgfb3 in gld cells. To check the vice versa effect, the gld cells were stimulated by soluble FasL. As a consequence, a dramatic decrease in expression levels of all three ligands was observed. This phenomenon was also confirmed in IDG-SW3 (osteoblastic cells of endochondral origin). TFLink gateway identified Fosl2 as an exclusive candidate of FasL capable to impact expression of all three Tgfb ligands. However, Fosl2 siRNA did not cause any significant changes in expression of Tgfb ligands. Therefore, the upregulation of the three ligands is likely to occur separately. In this respect, we tested the only exclusive candidate transcription factor for Tgfb3, Prrx1. Additionally, an overlapping candidate for Tgfb1 and Tgfb2, Mef2c capable to modulate expression of sclerostin, was examined. Prrx1 as well as Mef2c were found upregulated in gld samples and their expression decreased after addition of FasL. The same effect of FasL treatment was observed in the IDG-SW3 model. Taken together, FasL deficiency causes an increase in the expression of Tgfb ligands and stimulation by FasL reduces Tgfb expression in osteoblastic cells. The candidates mediating the effect comprise Prrx1 for Tgfb3 and Mef2c for Tgfb1/2. These results indicate FasL as a novel cytokine interfering with Tgfb signaling and thus the complex osteogenic network. The emerging non-apoptotic functions of FasL in bone development and maintenance should also be considered in treatment strategies such as the anti-osteoporotic factor.

Xenopus tropicalis osteoblast-specific open chromatin regions reveal promoters and enhancers involved in human skeletal phenotypes and shed light on early vertebrate evolution

While understanding the genetic underpinnings of osteogenesis has far-reaching implications for skeletal diseases and evolution, a comprehensive characterization of the osteoblastic regulatory landscape in non-mammalian vertebrates is still lacking. Here, we compared the ATAC-Seq profile of Xenopus tropicalis (Xt) osteoblasts to a variety of non mineralizing control tissues, and identified osteoblast-specific nucleosome free regions (NFRs) at 527 promoters and 6747 distal regions. Sequence analyses, Gene Ontology, RNA-Seq and ChIP-Seq against four key histone marks confirmed that the distal regions correspond to bona fide osteogenic transcriptional enhancers exhibiting a shared regulatory logic with mammals. We report 425 regulatory regions conserved with human and globally associated to skeletogenic genes. Of these, 35 regions have been shown to impact human skeletal phenotypes by GWAS, including one trps1 enhancer and the runx2 promoter, two genes which are respectively involved in trichorhinophalangeal syndrome type I and cleidocranial dysplasia. Intriguingly, 60 osteoblastic NFRs also align to the genome of the elephant shark, a species lacking osteoblasts and bone tissue. To tackle this paradox, we chose to focus on dlx5 because its conserved promoter, known to integrate regulatory inputs during mammalian osteogenesis, harbours an osteoblast-specific NFR in both frog and human. Hence, we show that dlx5 is expressed in Xt and elephant shark odontoblasts, supporting a common cellular and genetic origin of bone and dentine. Taken together, our work (i) unravels the Xt osteogenic regulatory landscape, (ii) illustrates how cross-species comparisons harvest data relevant to human biology and (iii) reveals that a set of genes including bnc2, dlx5, ebf3, mir199a, nfia, runx2 and zfhx4 drove the development of a primitive form of mineralized skeletal tissue deep in the vertebrate lineage.

Redox signaling-mediated tumor extracellular matrix remodeling: pleiotropic regulatory mechanisms

BACKGROUND

The extracellular matrix (ECM), a fundamental constituent of all tissues and organs, is crucial for shaping the tumor microenvironment. Dysregulation of ECM remodeling has been closely linked to tumor initiation and progression, where specific signaling pathways, including redox signaling, play essential roles. Reactive oxygen species (ROS) are risk factors for carcinogenesis whose excess can facilitate the oxidative damage of biomacromolecules, such as DNA and proteins. Emerging evidence suggests that redox effects can aid the modification, stimulation, and degradation of ECM, thus affecting ECM remodeling. These alterations in both the density and components of the ECM subsequently act as critical drivers for tumorigenesis. In this review, we provide an overview of the functions and primary traits of the ECM, and it delves into our current understanding of how redox reactions participate in ECM remodeling during cancer progression. We also discuss the opportunities and challenges presented by clinical strategies targeting redox-controlled ECM remodeling to overcome cancer.

CONCLUSIONS

The redox-mediated ECM remodeling contributes importantly to tumor survival, progression, metastasis, and poor prognosis. A comprehensive investigation of the concrete mechanism of redox-mediated tumor ECM remodeling and the combination usage of redox-targeted drugs with existing treatment means may reveal new therapeutic strategy for future antitumor therapies.

Fosl2 Deficiency Predisposes Mice to Osteopetrosis, Leading to Bone Marrow Failure

Arthritis causes Fos-like 2 (Fosl2) inactivation, and various immune cells contribute to its pathogenesis. However, little is known about the role of Fosl2 in hematopoiesis and the possible pathological role of Fosl2 inactivation in the hematopoietic system in arthritis. In this study, we show that Fosl2 maintains hematopoietic stem cell (HSC) quiescence and differentiation while controlling the inflammatory response via macrophages. Fosl2-specific deletion in the hematopoietic system caused the expansion of HSCs and myeloid cell growth while affecting erythroid and B cell differentiation. Fosl2 inactivation enhanced macrophage M1 polarization and stimulated proinflammatory cytokines and myeloid growth factors, skewing HSCs toward myeloid cell differentiation, similar to hematopoietic alterations in arthritic mice. Loss of Fosl2 mediated by Vav-iCre also displays an unexpected deletion in embryonic erythro-myeloid progenitor-derived osteoclasts, leading to osteopetrosis and anemia. The reduced bone marrow cellularity in Vav-iCreFosl2f/f mice is a consequence of the reduced bone marrow space in osteopetrotic mice rather than a direct role of Fosl2 in hematopoiesis. Thus, Fosl2 is indispensable for erythro-myeloid progenitor-derived osteoclasts to maintain the medullary cavity to ensure normal hematopoiesis. These findings improve our understanding of the pathogenesis of bone-destructive diseases and provide important implications for developing therapeutic approaches for these diseases.

Sargassum spp. Ethanolic Extract Elicits Toxic Responses and Malformations in Zebrafish (Danio rerio) Embryos

The amount of Sargassum spp. arriving in the Caribbean Sea has increased steadily in the last few years, producing a profound environmental impact on the ecological dynamics of the coasts of the Yucatan Peninsula. We characterized the toxicological effects of an ethanolic extract of Sargassum spp. on zebrafish (Danio rerio) embryos (ZFEs) in a 96-h static bioassay using T1 (0.01 mg/L), T2 (0.1 mg/L), T3 (1 mg/L), T4 (10 mg/L), T5 (25 mg/L), T6 (50 mg/L), T7 (75 mg/L), T8 (100 mg/L), T9 (200 mg/L), and T10 (400 mg/L). In this extract, we detected 74 compounds by gas chromatography-mass spectrometry (GC-MS), of which hexadecanoic acid methyl ester, and 2-pentanone 4-hydroxy-4-methyl, were the most abundant. In ZFEs, a median lethal concentration of 251 mg/L was estimated. Exposed embryos exhibited extensive morphological changes, including edema in the yolk sac, scoliosis, and loss of pigmentation, as well as malformations of the head, tail, and eyes. By integrating these abnormalities using the Integrated Biological Response (IBRv2) and General Morphological Score (GMS) indices, we were able to determine that ZFEs exposed to 200 mg/L (T9) exhibited the most pronounced biological response in comparison with the other groups. In the comparative transcriptomic analysis, 66 genes were upregulated, and 246 genes were downregulated in the group exposed to 200 mg/L compared with the control group. In the upregulated genes, we identified several gene ontology-enriched terms, such as response to xenobiotic stimuli, cellular response to chemical stimulus, transcriptional regulation, pigment metabolic process, erythrocyte differentiation and embryonic hemopoiesis, extracellular matrix organization, and chondrocyte differentiation involved in endochondral bone morphogenesis, among others. In the down-regulated genes, we found many genes associated with nervous system processes, sensory and visual perception, response to abiotic stimulus, and the nucleoside phosphate biosynthetic process. The probable connections among the morphological changes observed in the transcriptome are thoroughly discussed. Our findings suggest that Sargassum spp. exposure can induce a wide negative impact on zebrafish embryos. Environ Toxicol Chem 2024;00:1-15. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Role of Fra-2 in cancer

Fos-related antigen-2 (Fra-2) is the most recently discovered member of the Fos family and, by dimerizing with Jun proteins, forms the activator protein 1 (AP-1) transcription factor. By inducing or repressing the transcription of several target genes, Fra-2 is critically involved in the modulation of cell response to a variety of extracellular stimuli, stressors and intracellular changes. In physiological conditions, Fra-2 has been found to be ubiquitously expressed in human cells, regulating differentiation and homeostasis of bone, muscle, nervous, lymphoid and other tissues. While other AP-1 members, like Jun and Fos, are well characterized, studies of Fra-2 functions in cancer are still at an early stage. Due to the lack of a trans-activating domain, which is present in other Fos proteins, it has been suggested that Fra-2 might inhibit cell transformation, eventually exerting an anti-tumor effect. In human malignancies, however, Fra-2 activity is enhanced (or induced) by dysregulation of microRNAs, oncogenes and extracellular signaling, suggesting a multifaceted role. Therefore, Fra-2 can promote or prevent transformation, proliferation, migration, epithelial-mesenchymal transition, drug resistance and metastasis formation in a tumor- and context-dependent manner. Intriguingly, recent data reports that Fra-2 is also expressed in cancer associated cells, contributing to the intricate crosstalk between neoplastic and non-neoplastic cells, that leads to the evolution and remodeling of the tumor microenvironment. In this review we summarize three decades of research on Fra-2, focusing on its oncogenic and anti-oncogenic effects in tumor progression and dissemination.

Role and Regulation of Transcription Factors in Osteoclastogenesis

Bones serve mechanical and defensive functions, as well as regulating the balance of calcium ions and housing bone marrow.. The qualities of bones do not remain constant. Instead, they fluctuate throughout life, with functions increasing in some situations while deteriorating in others. The synchronization of osteoblast-mediated bone formation and osteoclast-mediated bone resorption is critical for maintaining bone mass and microstructure integrity in a steady state. This equilibrium, however, can be disrupted by a variety of bone pathologies. Excessive osteoclast differentiation can result in osteoporosis, Paget's disease, osteolytic bone metastases, and rheumatoid arthritis, all of which can adversely affect people's health. Osteoclast differentiation is regulated by transcription factors NFATc1, MITF, C/EBPα, PU.1, NF-κB, and c-Fos. The transcriptional activity of osteoclasts is largely influenced by developmental and environmental signals with the involvement of co-factors, RNAs, epigenetics, systemic factors, and the microenvironment. In this paper, we review these themes in regard to transcriptional regulation in osteoclastogenesis.

New kids on the block: FOS and FOSB gene

FOS and FOSB proto-oncogens are involved in a wide variety of tumourigenic processes. FOS and FOSB gene rearrangements are observed in epithelioid haemangioma, pseudomyogenic haemangioendothelioma, osteoid osteoma/osteoblastoma/cementoblastoma and proliferative myositis/fasciitis. In this review, we provide an overview of FOS and FOSB, including their functions and the differences between lesions with known FOS/FOSB gene rearrangements. Additionally, we discuss the use of FOS/FOSB immunohistochemistry as a diagnostic tool for these lesions.

Runt-related Transcription Factors and Gene Regulatory Mechanisms in Skeletal Development and Diseases

PURPOSE OF REVIEW

Runt-related transcription factors (RUNX) play critical roles in skeletal development, metabolism, and diseases. In mammals, three RUNX members, namely RUNX1, RUNX2, and RUNX3, play distinct and redundant roles, although RUNX2 is a dominant factor in skeletal development and several skeletal diseases. This review is to provide an overview of the current understanding of RUNX-mediated transcriptional regulation in different skeletal cell types.

RECENT FINDINGS

Advances in chromatin immunoprecipitation and next-generation sequencing (ChIP-seq) have revealed genome-wide RUNX-mediated gene regulatory mechanisms, including their association with cis-regulatory elements and putative target genes. Further studies with genome-wide analysis and biochemical assays have shed light on RUNX-mediated pioneering action and involvements of RUNX2 in lipid-lipid phase separation. Emerging multi-layered mechanisms of RUNX-mediated gene regulations help us better understanding of skeletal development and diseases, which also provides clues to think how genome-wide studies can help develop therapeutic strategies for skeletal diseases.

Metabolic rewiring controlled by c-Fos governs cartilage integrity in osteoarthritis

OBJECTIVES

The activator protein-1 (AP-1) transcription factor component c-Fos regulates chondrocyte proliferation and differentiation, but its involvement in osteoarthritis (OA) has not been functionally assessed.

METHODS

c-Fos expression was evaluated by immunohistochemistry on articular cartilage sections from patients with OA and mice subjected to the destabilisation of the medial meniscus (DMM) model of OA. Cartilage-specific c-Fos knockout (c-FosΔCh) mice were generated by crossing c-fosfl/fl to Col2a1-CreERT mice. Articular cartilage was evaluated by histology, immunohistochemistry, RNA sequencing (RNA-seq), quantitative reverse transcription PCR (qRT-PCR) and in situ metabolic enzyme assays. The effect of dichloroacetic acid (DCA), an inhibitor of pyruvate dehydrogenase kinase (Pdk), was assessed in c-FosΔCh mice subjected to DMM.

RESULTS

FOS-positive chondrocytes were increased in human and murine OA cartilage during disease progression. Compared with c-FosWT mice, c-FosΔCh mice exhibited exacerbated DMM-induced cartilage destruction. Chondrocytes lacking c-Fos proliferate less, have shorter collagen fibres and reduced cartilage matrix. Comparative RNA-seq revealed a prominent anaerobic glycolysis gene expression signature. Consistently decreased pyruvate dehydrogenase (Pdh) and elevated lactate dehydrogenase (Ldh) enzymatic activities were measured in situ, which are likely due to higher expression of hypoxia-inducible factor-1α, Ldha, and Pdk1 in chondrocytes. In vivo treatment of c-FosΔCh mice with DCA restored Pdh/Ldh activity, chondrocyte proliferation, collagen biosynthesis and decreased cartilage damage after DMM, thereby reverting the deleterious effects of c-Fos inactivation.

CONCLUSIONS

c-Fos modulates cellular bioenergetics in chondrocytes by balancing pyruvate flux between anaerobic glycolysis and the tricarboxylic acid cycle in response to OA signals. We identify a novel metabolic adaptation of chondrocytes controlled by c-Fos-containing AP-1 dimers that could be therapeutically relevant.

Genomic Profiling of the Craniofacial Ossifying Fibroma by Next-Generation Sequencing

BACKGROUND

Ossifying fibroma (OF) of the craniofacial skeleton is a fibro-osseous lesion characterized by various patterns of bone formation in a cellular fibroblastic stroma. The molecular landscape of OF remains mostly unknown. There are a few known pathogenic abnormalities in OF, including HRPT2 mutations in conventional OF and SATB2 translocations in juvenile psammomatoid OF. On the other hand, conflicting reports exist regarding MDM2 gene amplification and chromosomal copy number alterations (CNA) in OF.

METHODS

Surgically removed biopsies and curettage specimens from OF patients were obtained. Clinical, radiographic, and pathologic features of tumors were reviewed. Genomic DNA was extracted from formalin-fixed, paraffin-embedded blocks of tumor tissue. Capture-based DNA next-generation sequencing targeting the coding regions 529 cancer genes and select introns was performed.

RESULTS

We identified 17 OF cases from 8 male and 8 female patients with mean age of 22 years (range 1-58 years). Nine case occurred in the gnathic bones and 8 in the extragnathic craniofacial bones. These cases included 3 juvenile psammomatoid OF, 6 conventional OF and 8 juvenile trabecular OF. Large-scale CNAs were present in 6 of 17 cases. Seven cases (41%) had focal amplifications including FOSB (n = 2, 11%), FOS (n = 4, 23%), COL1A1 (n = 4, 23%) and TBX3 (n = 5, 29%). Three cases (17%) had pathogenic CDC73 mutations. No cases showed focal MDM2 amplification.

CONCLUSIONS

Here, we provided a comprehensive molecular characterization of OF that reveals a heterogeneous genetic profile with occasional large-scale CNAs (n = 6, 35%). FOS, FOSB, and TBX3 genes that regulate AP-1 transcriptional complex are frequently altered in OF (n = 7, 41%), chiefly in juvenile trabecular OF. These genes encode transcription factors that act as downstream effectors of the MAP kinase signaling pathway. MDM2 amplification is an exceedingly rare event in OF, if present at all, so identification of this event should continue to raise concern for low-grade gnathic osteosarcoma. In summary, our findings suggest that OF represents a heterogeneous group of tumors at the genetic level but dysregulation of the AP-1 pathway may play a role in pathogenesis of juvenile trabecular OF.

Convergent alteration of the mesenchymal stem cell heterogeneity in adipose tissue during aging

Adipose-derived stem cells (ASCs) from distinct age groups possess different characteristics; however, the age-associated changes in ASCs heterogenicity remain largely unknown. In this study, several publicly available single-cell RNA sequencing (RNA-seq) data cohorts of inguinal adipose tissues, including young (2 weeks), adult (8 weeks), and old (18 months) C57BL/6 mice, were analyzed. Transcriptomic clustering of integrated single-cell RNA-seq data from different age groups revealed the existence of five ASCs subtypes. Interestingly, ASCs showed a loss of heterogeneity with aging, and ASCs subtype 4 (ASC-4) was the dominant subpopulation accounting for more than 98% of aged ASCs converging to the terminal differentiation state. The multidirectional differentiation potentials of different ASCs subtypes were largely distinct while the adipogenic ability of ASC-4 increased with age persistently. Regulon analysis of ASC subtypes further identified Cebpb as the ASC-4-specific transcription factor, which was known as one of the major adipogenic regulators. Analysis of ligand-receptor pairs between ASCs and other cell types in adipose tissue identified age-associated upregulation of inflammatory responses-associated factors including CCL2 and CCL7. Treatment with 100 ng/mL CCL2 in vitro could significantly promote the adipogenesis of ASCs through enhanced phosphorylation of AKT and decreased expression of β-catenin. In addition, supplementation of 100 ng/mL CCL7 could significantly increase the expression of inflammatory genes and ASC-4-specific transcriptional factors in 2-week-old ASCs, potentially acting as a driver of ASCs convergence. Our findings help to delineate the complex biological processes of ASCs aging and shed light on better regenerative and therapeutic applications of ASCs.

Investigating the role of ASCC1 in the causation of bone fragility

Bi-allelic variants in ASCC1 cause the ultrarare bone fragility disorder "spinal muscular atrophy with congenital bone fractures-2" (SMABF2). However, the mechanism by which ASCC1 dysfunction leads to this musculoskeletal condition and the nature of the associated bone defect are poorly understood. By exome sequencing, we identified a novel homozygous deletion in ASCC1 in a female infant. She was born with severe muscular hypotonia, inability to breathe and swallow, and virtual absence of spontaneous movements; showed progressive brain atrophy, gracile long bones, very slender ribs, and a femur fracture; and died from respiratory failure aged 3 months. A transiliac bone sample taken postmortem revealed a distinct microstructural bone phenotype with low trabecular bone volume, low bone remodeling, disordered collagen organization, and an abnormally high bone marrow adiposity. Proteomics, RNA sequencing, and qPCR in patient-derived skin fibroblasts confirmed that ASCC1 was hardly expressed on protein and RNA levels compared with healthy controls. Furthermore, we demonstrate that mutated ASCC1 is associated with a downregulation of RUNX2, the master regulator of osteoblastogenesis, and SERPINF1, which is involved in osteoblast and adipocyte differentiation. It also exerts an inhibitory effect on TGF-β/SMAD signaling, which is important for bone development. Additionally, knockdown of ASCC1 in human mesenchymal stromal cells (hMSCs) suppressed their differentiation capacity into osteoblasts while increasing their differentiation into adipocytes. This resulted in reduced mineralization and elevated formation of lipid droplets. These findings shed light onto the pathophysiologic mechanisms underlying SMABF2 and assign a new biological role to ASCC1 acting as an important pro-osteoblastogenic and anti-adipogenic regulator.

ATRA ameliorates fibrosis by suppressing the pro-fibrotic molecule Fra2/AP-1 in systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune connective tissue disease that leads to irreversible fibrosis of the skin and the internal organs. The etiology of SSc is complex, its pathophysiology is poorly understood, and clinical therapeutic options are restricted. Thus, research into medications and targets for treating fibrosis is essential and urgent. Fos-related antigen 2 (Fra2) is a transcription factor that is a member of the activator protein-1 family. Fra2 transgenic mice were shown to have spontaneous fibrosis. All-trans retinoic acid (ATRA) is a vitamin A intermediate metabolite and ligand for the retinoic acid receptor (RAR), which possesses anti-inflammatory and anti-proliferative properties. Recent research has demonstrated that ATRA also has an anti-fibrotic effect. However, the exact mechanism is not fully understood. Interestingly, we identified potential binding sites for the transcription factor RARα to the promoter region of the FRA2 gene through JASPAR and PROMO databases. In this study, the pro-fibrotic effect of Fra2 in SSc is confirmed. SSc dermal fibroblasts and bleomycin-induced fibrotic tissues of SSc animals exhibit increased levels of Fra2. Inhibition of Fra2 expression in SSc dermal fibroblasts with Fra2 siRNA markedly decreased collagen I expression. ATRA reduced the expressions of Fra2, collagen I, and α-smooth muscle actin(α-SMA) in SSc dermal fibroblasts and bleomycin-induced fibrotic tissues of SSc mice. In addition, chromatin immunoprecipitation and dual-luciferase assays demonstrated that retinoic acid receptor RARα binds to the FRA2 promoter and modulates its transcriptional activity. ATRA decreases collagen I expression both in vivo and in vitro via the reduction of Fra2 expression. This work establishes the rationale for expanding the use of ATRA in the treatment of SSc and indicates that Fra2 can be used as an anti-fibrotic target.

Characterization of Chromatin Accessibility in Fetal Bovine Chondrocytes

Despite significant advances of the bovine epigenome investigation, new evidence for the epigenetic basis of fetal cartilage development remains lacking. In this study, the chondrocytes were isolated from long bone tissues of bovine fetuses at 90 days. The Assay for Transposase-Accessible Chromatin with high throughput sequencing (ATAC-seq) and transcriptome sequencing (RNA-seq) were used to characterize gene expression and chromatin accessibility profile in bovine chondrocytes. A total of 9686 open chromatin regions in bovine fetal chondrocytes were identified and 45% of the peaks were enriched in the promoter regions. Then, all peaks were annotated to the nearest gene for Gene Ontology (GO) and Kyoto Encylopaedia of Genes and Genomes (KEGG) analysis. Growth and development-related processes such as amide biosynthesis process (GO: 0043604) and translation regulation (GO: 006417) were enriched in the GO analysis. The KEGG analysis enriched endoplasmic reticulum protein processing signal pathway, TGF-β signaling pathway and cell cycle pathway, which are closely related to protein synthesis and processing during cell proliferation. Active transcription factors (TFs) were enriched by ATAC-seq, and were fully verified with gene expression levels obtained by RNA-seq. Among the top50 TFs from footprint analysis, known or potential cartilage development-related transcription factors FOS, FOSL2 and NFY were found. Overall, our data provide a theoretical basis for further determining the regulatory mechanism of cartilage development in bovine.

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.

Histopathogenesis of bone- and soft-tissue tumor spectrum with USP6 gene rearrangement: multiple partners involved in the tissue repair process

Primary aneurysmal bone cyst, nodular fasciitis, myositis ossificans and related lesions as well as fibroma of tendon sheath are benign tumors that share common histological features and a chromosomal rearrangement involving the ubiquitin-specific peptidase 6 (USP6) gene. The tumorigenesis of this tumor spectrum has become complex with the identification of an increasing number of new partners involved in USP6 rearrangements. Because traumatic involvement has long been mentioned in the histogenesis of most lesions in the USP6 spectrum and they morphologically resemble granulation tissue or callus, we attempted to shed light on the function and role USP6 partners play in tissue remodelling and the repair process and, to a lesser extent, bone metabolism.

Regulon active landscape reveals cell development and functional state changes of human primary osteoblasts in vivo

BACKGROUND

While transcription factor (TF) regulation is known to play an important role in osteoblast development, differentiation, and bone metabolism, the molecular features of TFs in human osteoblasts at the single-cell resolution level have not yet been characterized. Here, we identified modules (regulons) of co-regulated genes by applying single-cell regulatory network inference and clustering to the single-cell RNA sequencing profiles of human osteoblasts. We also performed cell-specific network (CSN) analysis, reconstructed regulon activity-based osteoblast development trajectories, and validated the functions of important regulons both in vivo and in vitro.

RESULTS

We identified four cell clusters: preosteoblast-S1, preosteoblast-S2, intermediate osteoblasts, and mature osteoblasts. CSN analysis results and regulon activity-based osteoblast development trajectories revealed cell development and functional state changes of osteoblasts. CREM and FOSL2 regulons were mainly active in preosteoblast-S1, FOXC2 regulons were mainly active in intermediate osteoblast, and RUNX2 and CREB3L1 regulons were most active in mature osteoblasts.

CONCLUSIONS

This is the first study to describe the unique features of human osteoblasts in vivo based on cellular regulon active landscapes. Functional state changes of CREM, FOSL2, FOXC2, RUNX2, and CREB3L1 regulons regarding immunity, cell proliferation, and differentiation identified the important cell stages or subtypes that may be predominantly affected by bone metabolism disorders. These findings may lead to a deeper understanding of the mechanisms underlying bone metabolism and associated diseases.

Emerging RUNX2-Mediated Gene Regulatory Mechanisms Consisting of Multi-Layered Regulatory Networks in Skeletal Development

Skeletal development is tightly coordinated by chondrocytes and osteoblasts, which are derived from skeletal progenitors, and distinct cell-type gene regulatory programs underlie the specification and differentiation of cells. Runt-related transcription factor 2 (Runx2) is essential to chondrocyte hypertrophy and osteoblast differentiation. Genetic studies have revealed the biological functions of Runx2 and its involvement in skeletal genetic diseases. Meanwhile, molecular biology has provided a framework for our understanding of RUNX2-mediated transactivation at a limited number of cis-regulatory elements. Furthermore, studies using next-generation sequencing (NGS) have provided information on RUNX2-mediated gene regulation at the genome level and novel insights into the multiple layers of gene regulatory mechanisms, including the modes of action of RUNX2, chromatin accessibility, the concept of pioneer factors and phase separation, and three-dimensional chromatin organization. In this review, I summarize the emerging RUNX2-mediated regulatory mechanism from a multi-layer perspective and discuss future perspectives for applications in the treatment of skeletal diseases.

The Localized Ionic Microenvironment in Bone Modelling/Remodelling: A Potential Guide for the Design of Biomaterials for Bone Tissue Engineering

Bone is capable of adjusting size, shape, and quality to maintain its strength, toughness, and stiffness and to meet different needs of the body through continuous remodeling. The balance of bone homeostasis is orchestrated by interactions among different types of cells (mainly osteoblasts and osteoclasts), extracellular matrix, the surrounding biological milieus, and waste products from cell metabolisms. Inorganic ions liberated into the localized microenvironment during bone matrix degradation not only form apatite crystals as components or enter blood circulation to meet other bodily needs but also alter cellular activities as molecular modulators. The osteoinductive potential of inorganic motifs of bone has been gradually understood since the last century. Still, few have considered the naturally generated ionic microenvironment's biological roles in bone remodeling. It is believed that a better understanding of the naturally balanced ionic microenvironment during bone remodeling can facilitate future biomaterial design for bone tissue engineering in terms of the modulatory roles of the ionic environment in the regenerative process.

FOSL2 truncating variants in the last exon cause a neurodevelopmental disorder with scalp and enamel defects

PURPOSE

We aimed to investigate the molecular basis of a novel recognizable neurodevelopmental syndrome with scalp and enamel anomalies caused by truncating variants in the last exon of the gene FOSL2, encoding a subunit of the AP-1 complex.

METHODS

Exome sequencing was used to identify genetic variants in all cases, recruited through Matchmaker exchange. Gene expression in blood was analyzed using reverse transcription polymerase chain reaction. In vitro coimmunoprecipitation and proteasome inhibition assays in transfected HEK293 cells were performed to explore protein and AP-1 complex stability.

RESULTS

We identified 11 individuals from 10 families with mostly de novo truncating FOSL2 variants sharing a strikingly similar phenotype characterized by prenatal growth retardation, localized cutis scalp aplasia with or without skull defects, neurodevelopmental delay with autism spectrum disorder, enamel hypoplasia, and congenital cataracts. Mutant FOSL2 messenger RNAs escaped nonsense-mediated messenger RNA decay. Truncated FOSL2 interacts with c-JUN, thus mutated AP-1 complexes could be formed.

CONCLUSION

Truncating variants in the last exon of FOSL2 associate a distinct clinical phenotype by altering the regulatory degradation of the AP-1 complex. These findings reveal a new role for FOSL2 in human pathology.

Runx2 regulates chromatin accessibility to direct the osteoblast program at neonatal stages

The transcriptional regulator Runx2 (runt-related transcription factor 2) has essential but distinct roles in osteoblasts and chondrocytes in skeletal development. However, Runx2-mediated regulatory mechanisms underlying the distinctive programming of osteoblasts and chondrocytes are not well understood. Here, we perform an integrative analysis to investigate Runx2-DNA binding and chromatin accessibility ex vivo using neonatal osteoblasts and chondrocytes. We find that Runx2 engages with cell-type-distinct chromatin-accessible regions, potentially interacting with different combinations of transcriptional regulators, forming cell-type-specific hotspots, and potentiating chromatin accessibility. Genetic analysis and direct cellular reprogramming studies suggest that Runx2 is essential for establishment of chromatin accessibility in osteoblasts. Functional enhancer studies identify an Sp7 distal enhancer driven by Runx2-dependent binding and osteoblast-specific chromatin accessibility, contributing to normal osteoblast differentiation. Our findings provide a framework for understanding the regulatory landscape encompassing Runx2-mediated and cell-type-distinct enhancer networks that underlie the specification of osteoblasts.

Hojo et al. investigate the gene-regulatory landscape underlying specification of skeletal cell types in neonatal mice. Runx2, an osteoblast determinant, engages with cell-type-distinct chromatin-accessible regions and is essential for establishment of chromatin accessibility in osteoblasts. The study provides insights into enhancer networks in skeletal development.

Phylogenetic and Expression Analysis of Fos Transcription Factors in Zebrafish

Members of the FOS protein family regulate gene expression responses to a multitude of extracellular signals and are dysregulated in several pathological states. Whilst mouse genetic models have provided key insights into the tissue-specific functions of these proteins in vivo, little is known about their roles during early vertebrate embryonic development. This study examined the potential of using zebrafish as a model for such studies and, more broadly, for investigating the mechanisms regulating the functions of Fos proteins in vivo. Through phylogenetic and sequence analysis, we identified six zebrafish FOS orthologues, fosaa, fosab, fosb, fosl1a, fosl1b, and fosl2, which show high conservation in key regulatory domains and post-translational modification sites compared to their equivalent human proteins. During embryogenesis, zebrafish fos genes exhibit both overlapping and distinct spatiotemporal patterns of expression in specific cell types and tissues. Most fos genes are also expressed in a variety of adult zebrafish tissues. As in humans, we also found that expression of zebrafish FOS orthologs is induced by oncogenic BRAF-ERK signalling in zebrafish melanomas. These findings suggest that zebrafish represent an alternate model to mice for investigating the regulation and functions of Fos proteins in vertebrate embryonic and adult tissues, and cancer.

The Landscape of Accessible Chromatin during Yak Adipocyte Differentiation

Although significant advancement has been made in the study of adipogenesis, knowledge about how chromatin accessibility regulates yak adipogenesis is lacking. We here described genome-wide dynamic chromatin accessibility in preadipocytes and adipocytes by using the assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq), and thus revealed the unique characteristics of open chromatin during yak adipocyte differentiation. The chromatin accessibility of preadipocytes and adipocytes exhibited a similar genomic distribution, displaying a preferential location within the intergenic region, intron, and promoter. The pathway enrichment analysis identified that genes with differential chromatin accessibility were involved in adipogenic metabolism regulation pathways, such as the peroxisome proliferator activated receptor-γ (PPAR) signaling pathway, wingless-type MMTV integration site (Wnt) signaling pathway, and extracellular matrix-receptor (ECM–receptor) interaction. Integration of ATAC-seq and mRNA-seq revealed that genes with a high expression were associated with high levels of chromatin accessibility, especially within 1 kb upstream and downstream of the transcription start site. In addition, we identified a series of transcription factors (TFs) related to adipogenesis and created the TF regulatory network, providing the possible interactions between TFs during yak adipogenesis. This study is crucial for advancing the understanding of transcriptional regulatory mechanisms of adipogenesis and provides valuable information for understanding the adaptation of plateau species to high-altitude environments by maintaining whole body homeostasis through fat metabolism.

Repression of enhancer RNA PHLDA1 promotes tumorigenesis and progression of Ewing sarcoma via decreasing infiltrating T‐lymphocytes: A bioinformatic analysis

Background: The molecular mechanisms of EWS-FLI-mediating target genes and downstream pathways may provide a new way in the targeted therapy of Ewing sarcoma. Meanwhile, enhancers transcript non-coding RNAs, known as enhancer RNAs (eRNAs), which may serve as potential diagnosis markers and therapeutic targets in Ewing sarcoma.

Materials and methods: Differentially expressed genes (DEGs) were identified between 85 Ewing sarcoma samples downloaded from the Treehouse database and 3 normal bone samples downloaded from the Sequence Read Archive database. Included in DEGs, differentially expressed eRNAs (DEeRNAs) and target genes corresponding to DEeRNAs (DETGs), as well as the differentially expressed TFs, were annotated. Then, cell type identification by estimating relative subsets of known RNA transcripts (CIBERSORT) was used to infer portions of infiltrating immune cells in Ewing sarcoma and normal bone samples. To evaluate the prognostic value of DEeRNAs and immune function, cross validation, independent prognosis analysis, and Kaplan–Meier survival analysis were implemented using sarcoma samples from the Cancer Genome Atlas database. Next, hallmarks of cancer by gene set variation analysis (GSVA) and immune gene sets by single-sample gene set enrichment analysis (ssGSEA) were identified to be significantly associated with Ewing sarcoma. After screening by co-expression analysis, most significant DEeRNAs, DETGs and DETFs, immune cells, immune gene sets, and hallmarks of cancer were merged to construct a co-expression regulatory network to eventually identify the key DEeRNAs in tumorigenesis of Ewing sarcoma. Moreover, Connectivity Map Analysis was utilized to identify small molecules targeting Ewing sarcoma. External validation based on multidimensional online databases and scRNA-seq analysis were used to verify our key findings.

Results: A six-different-dimension regulatory network was constructed based on 17 DEeRNAs, 29 DETFs, 9 DETGs, 5 immune cells, 24 immune gene sets, and 8 hallmarks of cancer. Four key DEeRNAs (CCR1, CD3D, PHLDA1, and RASD1) showed significant co-expression relationships in the network. Connectivity Map Analysis screened two candidate compounds, MS-275 and pyrvinium, that might target Ewing sarcoma. PHLDA1 (key DEeRNA) was extensively expressed in cancer stem cells of Ewing sarcoma, which might play a critical role in the tumorigenesis of Ewing sarcoma.

Conclusion: PHLDA1 is a key regulator in the tumorigenesis and progression of Ewing sarcoma. PHLDA1 is directly repressed by EWS/FLI1 protein and low expression of FOSL2, resulting in the deregulation of FOX proteins and CC chemokine receptors. The decrease of infiltrating T‐lymphocytes and TNFA signaling may promote tumorigenesis and progression of Ewing sarcoma.

Age-Dependent FOSB/ΔFOSB Response to Acute and Chronic Stress in the Extended Amygdala, Hypothalamic Paraventricular, Habenular, Centrally-Projecting Edinger-Westphal, and Dorsal Raphe Nuclei in Male Rats

FOS proteins are early-responding gene products that contribute to the formation of activator protein-1. Several acute and chronic stimuli lead to Fos gene expression, accompanied by an increase of nuclear FOS, which appears to decline with aging. FOSB is another marker to detect acute cellular response, while ΔFOSB mirrors long-lasting changes in neuronal activity upon chronic stress. The notion that the occurrence of stress-related mood disorders shows some age dependence suggests that the brain's stress sensitivity is also a function of age. To study age-dependent stress vulnerability at the immediate-early gene level, we aimed to describe how the course of aging affects the neural responses of FOSB/ΔFOSB in the acute restraint stress (ARS), and chronic variable mild stress (CVMS) in male rats. Fourteen brain areas [central, medial, basolateral (BLA) amygdala; dorsolateral- (BNSTdl), oval- (BNSTov), dorsomedial-, ventral- (BNSTv), and fusiform- (BNSTfu) divisions of the bed nucleus of the stria terminalis; medial and lateral habenula, hypothalamic paraventricular nucleus (PVN), centrally-projecting Edinger-Westphal nucleus, dorsal raphe nucleus, barrel field of somatosensory cortex (S1)] were examined in the course of aging. Eight age groups [1-month-old (M), 1.5 M, 2 M, 3 M, 6 M, 12 M, 18 M, and 24 M] of rats were exposed to a single ARS vs. controls. In addition, rats in six age groups (2, 3, 6, 12, 18, and 24 M) were subjected to CVMS. The FOSB/ΔFOSB immunoreactivity (IR) was a function of age in both controls, ARS- and CVMS-exposed rats. ARS increased the FOSB/ΔFOSB in all nuclei (except in BLA), but only BNSTfu, BNSTv, and PVN reacted throughout the examined lifespan. The CVMS did not increase the FOSB/ΔFOSB in BLA, BNSTov, BNSTdl, and S1. PVN showed a constantly maintained FOSB/ΔFOSB IR during the examined life period. The maximum stress-evoked FOSB/ΔFOSB signal was detected at 2-3 M periods in the ARS- and at 6 M, 18 M in CVMS- model. Corresponding to our previous observations on FOS, the FOSB/ΔFOSB response to stress decreased with age in most of the examined nuclei. Only the PVN exerted a sustained age-independent FOSB/ΔFOSB, which may reflect the long-lasting adaptation response and plasticity of neurons that maintain the hypothalamus-pituitary-adrenal axis response throughout the lifespan.

Osteogenic Commitment of Human Periodontal Ligament Cells Is Predetermined by Methylation, Chromatin Accessibility and Expression of Key Transcription Factors

Periodontal ligament stem cells (PDLCs) can be used as a valuable source in cell therapies to regenerate bone tissue. However, the potential therapeutic outcomes are unpredictable due to PDLCs’ heterogeneity regarding the capacity for osteoblast differentiation and mineral nodules production. Here, we identify epigenetic (DNA (hydroxy)methylation), chromatin (ATAC-seq) and transcriptional (RNA-seq) differences between PDLCs presenting with low (l) and high (h) osteogenic potential. The primary cell populations were investigated at basal state (cultured in DMEM) and after 10 days of osteogenic stimulation (OM). At a basal state, the expression of transcription factors (TFs) and the presence of gene regulatory regions related to osteogenesis were detected in h-PDLCs in contrast to neuronal differentiation prevalent in l-PDLCs. These differences were also observed under stimulated conditions, with genes and biological processes associated with osteoblast phenotype activated more in h-PDLCs. Importantly, even after the induction, l-PDLCs showed hypermethylation and low expression of genes related to bone development. Furthermore, the analysis of TFs motifs combined with TFs expression suggested the relevance of SP1, SP7 and DLX4 regulation in h-PDLCs, while motifs for SIX and OLIG2 TFs were uniquely enriched in l-PDLCs. Additional analysis including a second l-PDLC population indicated that the high expression of OCT4, SIX3 and PPARG TFs could be predictive of low osteogenic commitment. In summary, several biological processes related to osteoblast commitment were activated in h-PDLCs from the onset, while l-PDLCs showed delay in the activation of the osteoblastic program, restricted by the persistent methylation of gene related to bone development. These processes are pre-determined by distinguishable epigenetic and transcriptional patterns, the recognition of which could help in selection of PDLCs with pre-osteoblastic phenotype.

The Biological Function of MicroRNAs in Bone Tumors

Micro ribonucleic acids (miRNAs) are small endogenous noncoding RNAs molecules that regulate gene expression post-transcriptionally. A single miRNA is able to target hundreds of specific messenger RNA (mRNAs) by binding to the 3′-untranslated regions. miRNAs regulate different biological processes such as cell proliferation, differentiation and apoptosis. Altered miRNA expression is certainly related to the development of the most common human diseases, including tumors. Osteosarcoma (OS), Ewing’s Sarcoma (ES), and Chondrosarcoma (CS) are the most common primary bone tumors which affect mainly children and adolescents. A significant dysregulation of miRNA expression, in particular of mir-34, mir-21, mir-106, mir-143, and miR-100, has been revealed in OS, ES and CS. In this context, miRNAs can act as either tumor suppressor genes or oncogenes, contributing to the initiation and progression of bone tumors. The in-depth study of these small molecules can thus help to better understand their biological functions in bone tumors. Therefore, this review aims to examine the potential role of miRNAs in bone tumors, especially OS, ES and CS, and to suggest their possible use as potential therapeutic targets for the treatment of bone tumors and as biomarkers for early diagnosis.

Diversity of Vascular Niches in Bones and Joints During Homeostasis, Ageing, and Diseases

The bones and joints in the skeletal system are composed of diverse cell types, including vascular niches, bone cells, connective tissue cells and mineral deposits and regulate whole-body homeostasis. The capacity of maintaining strength and generation of blood lineages lies within the skeletal system. Bone harbours blood and immune cells and their progenitors, and vascular cells provide several immune cell type niches. Blood vessels in bone are phenotypically and functionally diverse, with distinct capillary subtypes exhibiting striking changes with age. The bone vasculature has a special impact on osteogenesis and haematopoiesis, and dysregulation of the vasculature is associated with diverse blood and bone diseases. Ageing is associated with perturbed haematopoiesis, loss of osteogenesis, increased adipogenesis and diminished immune response and immune cell production. Endothelial and perivascular cells impact immune cell production and play a crucial role during inflammation. Here, we discuss normal and maladapted vascular niches in bone during development, homeostasis, ageing and bone diseases such as rheumatoid arthritis and osteoarthritis. Further, we discuss the role of vascular niches during bone malignancy.

In Sickness and in Health: The Oxygen Reactive Species and the Bone

Oxidative stress plays a central role in physiological and pathological bone conditions. Its role in signalment and control of bone cell population differentiation, activity, and fate is increasingly recognized. The possibilities of its use and manipulation with therapeutic goals are virtually unending. However, how redox balance interplays with the response to mechanical stimuli is yet to be fully understood. The present work summarizes current knowledge on these aspects, in an integrative and broad introductory perspective.

The role of Ca2+ /Calcineurin/NFAT signalling pathway in osteoblastogenesis

The bone remodelling process is closely related to bone health. Osteoblasts and osteoclasts participate in the bone remodelling process under the regulation of various factors inside and outside. Excessive activation of osteoclasts or lack of function of osteoblasts will cause occurrence and development of multiple bone‐related diseases. Ca²⁺/Calcineurin/NFAT signalling pathway regulates the growth and development of many types of cells, such as cardiomyocyte differentiation, angiogenesis, chondrogenesis, myogenesis, bone development and regeneration, etc. Some evidences indicate that this signalling pathway plays an extremely important role in bone formation and bone pathophysiologic changes. This review discusses the role of Ca²⁺/Calcineurin/NFAT signalling pathway in the process of osteogenic differentiation, as well as the influence of regulating each component in this signalling pathway on the differentiation and function of osteoblasts, whereby the relationship between Ca²⁺/Calcineurin/NFAT signalling pathway and osteoblastogenesis could be deeper understood.

Mouse Models of Skin Fibrosis

Systemic sclerosis (SSc) is a rare systemic autoimmune disease associated with a high mortality. The first histopathological hallmarks are vasculopathy and inflammation, followed by fibrosis of the skin and internal organs. The molecular and cellular mechanisms are incompletely understood. Rodent models provide important insights into the pathogenesis of SSc and are a mainstay for the development of novel targeted therapies. Here we describe the mechanistic insights of inducible and genetic models, and also discuss in detail the limitations and pitfalls of the most frequently used SSc mouse models. We also describe protocols for running the established bleomycin-induced scleroderma skin fibrosis model.

FOSL2 Is Involved in the Regulation of Glycogen Content in Chicken Breast Muscle Tissue

The glycogen content in muscle of livestock and poultry animals affects the homeostasis of their body, growth performance, and meat quality after slaughter. FOS-like 2, AP-1 transcription factor subunit (FOSL2) was identified as a candidate gene related to muscle glycogen (MG) content in chicken in our previous study, but the role of FOSL2 in the regulation of MG content remains to be elucidated. Differential gene expression analysis and weighted gene coexpression network analysis (WGCNA) were performed on differentially expressed genes (DEGs) in breast muscle tissues from the high-MG-content (HMG) group and low-MG-content (LMG) group of Jingxing yellow chickens. Analysis of the 1,171 DEGs (LMG vs. HMG) identified, besides FOSL2, some additional genes related to MG metabolism pathway, namely PRKAG3, CEBPB, FOXO1, AMPK, and PIK3CB. Additionally, WGCNA revealed that FOSL2, CEBPB, MAP3K14, SLC2A14, PPP2CA, SLC38A2, PPP2R5E, and other genes related to the classical glycogen metabolism in the same coexpressed module are associated with MG content. Also, besides finding that FOSL2 expression is negatively correlated with MG content, a possible interaction between FOSL2 and CEBPB was predicted using the STRING (Search Tool for the Retrieval of Interacting Genes) database. Furthermore, we investigated the effects of lentiviral overexpression of FOSL2 on the regulation of the glycogen content in vitro, and the result indicated that FOSL2 decreases the glycogen content in DF1 cells. Collectively, our results confirm that FOSL2 has a key role in the regulation of the MG content in chicken. This finding is helpful to understand the mechanism of MG metabolism regulation in chicken and provides a new perspective for the production of high-quality broiler and the development of a comprehensive nutritional control strategy.

Inherited Defects of the ASC-1 Complex in Congenital Neuromuscular Diseases

Defects in transcriptional and cell cycle regulation have emerged as novel pathophysiological mechanisms in congenital neuromuscular disease with the recent identification of mutations in the TRIP4 and ASCC1 genes, encoding, respectively, ASC-1 and ASCC1, two subunits of the ASC-1 (Activating Signal Cointegrator-1) complex. This complex is a poorly known transcriptional coregulator involved in transcriptional, post-transcriptional or translational activities. Inherited defects in components of the ASC-1 complex have been associated with several autosomal recessive phenotypes, including severe and mild forms of striated muscle disease (congenital myopathy with or without myocardial involvement), but also cases diagnosed of motor neuron disease (spinal muscular atrophy). Additionally, antenatal bone fractures were present in the reported patients with ASCC1 mutations. Functional studies revealed that the ASC-1 subunit is a novel regulator of cell cycle, proliferation and growth in muscle and non-muscular cells. In this review, we summarize and discuss the available data on the clinical and histopathological phenotypes associated with inherited defects of the ASC-1 complex proteins, the known genotype–phenotype correlations, the ASC-1 pathophysiological role, the puzzling question of motoneuron versus primary muscle involvement and potential future research avenues, illustrating the study of rare monogenic disorders as an interesting model paradigm to understand major physiological processes.

Breast tumor stiffness instructs bone metastasis via maintenance of mechanical conditioning

While the immediate and transitory response of breast cancer cells to pathological stiffness in their native microenvironment has been well explored, it remains unclear how stiffness-induced phenotypes are maintained over time after cancer cell dissemination in vivo. Here, we show that fibrotic-like matrix stiffness promotes distinct metastatic phenotypes in cancer cells, which are preserved after transition to softer microenvironments, such as bone marrow. Using differential gene expression analysis of stiffness-responsive breast cancer cells, we establish a multigenic score of mechanical conditioning (MeCo) and find that it is associated with bone metastasis in patients with breast cancer. The maintenance of mechanical conditioning is regulated by RUNX2, an osteogenic transcription factor, established driver of bone metastasis, and mitotic bookmarker that preserves chromatin accessibility at target gene loci. Using genetic and functional approaches, we demonstrate that mechanical conditioning maintenance can be simulated, repressed, or extended, with corresponding changes in bone metastatic potential.

Watson et al. demonstrate that mechanical conditioning by stiff microenvironments in breast tumors is maintained in cancer cells after dissemination to softer microenvironments, including bone marrow. They show that mechanical conditioning promotes invasion and osteolysis and establish a mechanical conditioning (MeCo) score, associated with bone metastasis in patients.

The Role of AP-1 Transcription Factors in Plasma Cell Biology and Multiple Myeloma Pathophysiology

Multiple myeloma (MM) is an incurable hematologic malignancy characterized by the clonal expansion of malignant plasma cells within the bone marrow. Activator Protein-1 (AP-1) transcription factors (TFs), comprised of the JUN, FOS, ATF and MAF multigene families, are implicated in a plethora of physiologic processes and tumorigenesis including plasma cell differentiation and MM pathogenesis. Depending on the genetic background, the tumor stage, and cues of the tumor microenvironment, specific dimeric AP-1 complexes are formed. For example, AP-1 complexes containing Fra-1, Fra-2 and B-ATF play central roles in the transcriptional control of B cell development and plasma cell differentiation, while dysregulation of AP-1 family members c-Maf, c-Jun, and JunB is associated with MM cell proliferation, survival, drug resistance, bone marrow angiogenesis, and bone disease. The present review article summarizes our up-to-date knowledge on the role of AP-1 family members in plasma cell differentiation and MM pathophysiology. Moreover, it discusses novel, rationally derived approaches to therapeutically target AP-1 TFs, including protein-protein and protein-DNA binding inhibitors, epigenetic modifiers and natural products.

FOS Rearrangement and Expression in Cementoblastoma

Cementoblastomas are rare odontogenic tumors developing in close proximity to the roots of teeth. Due to their striking morphologic resemblance to osteoblastomas of the peripheral skeleton, we set out to determine whether cementoblastomas harbor the same FOS rearrangements with overexpression of c-FOS as has recently been described for osteoblastomas. In total, 16 cementoblastomas were analyzed for FOS expression by immunohistochemistry and for FOS rearrangements by fluorescence in situ hybridization (FISH). We observed strong and diffuse staining of c-FOS in 71% of cementoblastomas and identified a FOS rearrangement in all cases (n=3) applicable for FISH. In the remaining cases, FISH failed due to decalcification. Cementoblastomas harbor similar FOS rearrangements and show overexpression of c-FOS like osteoblastomas, suggesting that both entities might represent parts of the spectrum of the same disease.

The AP1 Transcription Factor Fosl2 Promotes Systemic Autoimmunity and Inflammation by Repressing Treg Development

Regulatory T cells (Tregs) represent a major population in the control of immune homeostasis and autoimmunity. Here we show that Fos-like 2 (Fosl2), a TCR-induced AP1 transcription factor, represses Treg development and controls autoimmunity. Mice overexpressing Fosl2 (Fosl2^tg) indeed show a systemic inflammatory phenotype, with immune infiltrates in multiple organs. This phenotype is absent in Fosl2^tg × Rag2^-/- mice lacking T and B cells, and Fosl2 induces T cell-intrinsic reduction of Treg development that is responsible for the inflammatory phenotype. Fosl2^tg T cells can transfer inflammation, which is suppressed by the co-delivery of Tregs, while Fosl2 deficiency in T cells reduces the severity of autoimmunity in the EAE model. We find that Fosl2 could affect expression of FoxP3 and other Treg development genes. Our data highlight the importance of AP1 transcription factors, in particular Fosl2, during T cell development to determine Treg differentiation and control autoimmunity.

Regulation of Osteoblast Differentiation by Cytokine Networks

Osteoblasts, which are bone-forming cells, play pivotal roles in bone modeling and remodeling. Osteoblast differentiation, also known as osteoblastogenesis, is orchestrated by transcription factors, such as runt-related transcription factor 1/2, osterix, activating transcription factor 4, special AT-rich sequence-binding protein 2 and activator protein-1. Osteoblastogenesis is regulated by a network of cytokines under physiological and pathophysiological conditions. Osteoblastogenic cytokines, such as interleukin-10 (IL-10), IL-11, IL-18, interferon-γ (IFN-γ), cardiotrophin-1 and oncostatin M, promote osteoblastogenesis, whereas anti-osteoblastogenic cytokines, such as tumor necrosis factor-α (TNF-α), TNF-β, IL-1α, IL-4, IL-7, IL-12, IL-13, IL-23, IFN-α, IFN-β, leukemia inhibitory factor, cardiotrophin-like cytokine, and ciliary neurotrophic factor, downregulate osteoblastogenesis. Although there are gaps in the body of knowledge regarding the interplay of cytokine networks in osteoblastogenesis, cytokines appear to be potential therapeutic targets in bone-related diseases. Thus, in this study, we review and discuss our osteoblast, osteoblast differentiation, osteoblastogenesis, cytokines, signaling pathway of cytokine networks in osteoblastogenesis.

Integrated expression profiles of mRNA and miRNA in a gerbil model of fatty liver fibrosis treated with exenatide

BACKGROUND

The morbidity of nonalcoholic fatty liver disease (NAFLD) has increased consistently in recent years. Exenatide could reverse liver fibrosis and lower the occurrence of fatty liver. The aim of the study was to identify and characterize mRNA and miRNA expression to elucidate the mechanism of exenatide in the gerbil model.

METHODS

Gerbils were fed a high-fat diet for 8 weeks to induce a fibrosis model; then, the gerbil models were treated with exenatide for 4 weeks. The total RNA extracted from the liver tissue samples was used to prepare the library and sequence on a HiSeq 2000. Bioinformatic methods were employed to analyze the sequence data to identify the mRNAs and miRNAs and to acquire the miRNA-mRNA regulatory network.

RESULTS

By RNA-seq, 2344 differentially expressed genes (DEGs) and 72 miRNAs were found in the model group. Compared with the model group, 591 DEGs and 19 miRNAs were found in the quercetin group, whereas 876 DEGs and 18 miRNAs were found in the treatment group. The miRNA-mRNA regulatory network was constructed in a gerbil model. Immunohistochemistry and RNA sequencing confirmed that the therapeutic effect of exenatide may be derived from extrahepatic signal transduction. The key differential genes are CYP3A, CYP4A11, ACAA1, ACSM, PHX1, MAO, FMO, UGT, ACOX2, ABAT, PIK3C and PLCG1. The key miRNAs are miR-15a, miR-27b, miR-532-3P, miR-627, miR-3596, miR-142-3P, Let-7e-5p, miR-214-5, miR-101-3p, miR-378d. New miRNAs, such as novel_127, novel_143, novel_15, novel_204 are associated with liver fibrosis, while novel_127, novel_15, and novel_54 are associated with reverse treated with exenatide.

CONCLUSIONS

Our research represents the first description of mRNA/miRNA profiles in a gerbil model of fatty liver fibrosis treated with exenatide, which may provide insights into the pathogenesis or treatment of the metabolic syndrome.

Screening and verification of hub genes involved in osteoarthritis using bioinformatics

Osteoarthritis (OA) is one of the most common causes of disability and its development is associated with numerous factors. A major challenge in the treatment of OA is the lack of early diagnosis. In the present study, a bioinformatics method was employed to filter key genes that may be responsible for the pathogenesis of OA. From the Gene Expression Omnibus database, the datasets GSE55457, GSE12021 and GSE55325 were downloaded, which comprised 59 samples. Of these, 30 samples were from patients diagnosed with osteoarthritis and 29 were normal. Differentially expressed genes (DEGs) were obtained by downloading and analyzing the original data using bioinformatics. The Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathways were analyzed using the Database for Annotation, Visualization and Integrated Discovery online database. Protein-protein interaction network analysis was performed using the Search Tool for the Retrieval of Interacting Genes/proteins online database. BSCL2 lipid droplet biogenesis associated, seipin, FOS-like 2, activator protein-1 transcription factor subunit (FOSL2), cyclin-dependent kinase inhibitor 1A (CDKN1A) and kinectin 1 (KTN1) genes were identified as key genes by using Cytoscape software. Functional enrichment revealed that the DEGs were mainly accumulated in the ErbB, MAPK and PI3K-Akt pathways. Reverse transcription-quantitative PCR analysis confirmed a significant reduction in the expression levels of FOSL2, CDKN1A and KTN1 in OA samples. These genes have the potential to become novel diagnostic and therapeutic targets for OA.

Single-cell RNA landscape of intratumoral heterogeneity and immunosuppressive microenvironment in advanced osteosarcoma

Osteosarcoma is the most frequent primary bone tumor with poor prognosis. Through RNA-sequencing of 100,987 individual cells from 7 primary, 2 recurrent, and 2 lung metastatic osteosarcoma lesions, 11 major cell clusters are identified based on unbiased clustering of gene expression profiles and canonical markers. The transcriptomic properties, regulators and dynamics of osteosarcoma malignant cells together with their tumor microenvironment particularly stromal and immune cells are characterized. The transdifferentiation of malignant osteoblastic cells from malignant chondroblastic cells is revealed by analyses of inferred copy-number variation and trajectory. A proinflammatory FABP4+ macrophages infiltration is noticed in lung metastatic osteosarcoma lesions. Lower osteoclasts infiltration is observed in chondroblastic, recurrent and lung metastatic osteosarcoma lesions compared to primary osteoblastic osteosarcoma lesions. Importantly, TIGIT blockade enhances the cytotoxicity effects of the primary CD3+ T cells with high proportion of TIGIT+ cells against osteosarcoma. These results present a single-cell atlas, explore intratumor heterogeneity, and provide potential therapeutic targets for osteosarcoma.

The Multifaceted Output of c-Jun Biological Activity: Focus at the Junction of CD8 T Cell Activation and Exhaustion

c-Jun is a major component of the dimeric transcription factor activator protein-1 (AP-1), a paradigm for transcriptional response to extracellular signaling, whose components are basic-Leucine Zipper (bZIP) transcription factors of the Jun, Fos, activating transcription factor (ATF), ATF-like (BATF) and Jun dimerization protein 2 (JDP2) gene families. Extracellular signals regulate c-Jun/AP-1 activity at multiple levels, including transcriptional and posttranscriptional regulation of c-Jun expression and transactivity, in turn, establishing the magnitude and the duration of c-Jun/AP-1 activation. Another important level of c-Jun/AP-1 regulation is due to the capability of Jun family members to bind DNA as a heterodimer with every other member of the AP-1 family, and to interact with other classes of transcription factors, thereby acquiring the potential to integrate diverse extrinsic and intrinsic signals into combinatorial regulation of gene expression. Here, we review how these features of c-Jun/AP-1 regulation underlie the multifaceted output of c-Jun biological activity, eliciting quite distinct cellular responses, such as neoplastic transformation, differentiation and apoptosis, in different cell types. In particular, we focus on the current understanding of the role of c-Jun/AP-1 in the response of CD8 T cells to acute infection and cancer. We highlight the transcriptional and epigenetic regulatory mechanisms through which c-Jun/AP-1 participates in the productive immune response of CD8 T cells, and how its downregulation may contribute to the dysfunctional state of tumor infiltrating CD8 T cells. Additionally, we discuss recent insights pointing at c-Jun as a suitable target for immunotherapy-based combination approaches to reinvigorate anti-tumor immune functions.

FN1 promotes chondrocyte differentiation and collagen production via TGF-β/PI3K/Akt pathway in mice with femoral fracture

Fibronectin (FN) functions as a potent stimulator of osteogenic differentiation, and bone fracture healing. In FN family, FN1 acts as an interactive protein gene product to mediate chondrocyte adhesion. However, its effect on fracture healing remains elusive. Therefore, we aimed to investigate the involvement of FN1 in fracture healing. Hard callus formations were found at fracture site with thicker periosteum in lateral cortical bone area outside the fracture site in model mice. The decreased number of osteogenic cells in the middle of the callus region and increased extracellular matrix were suggestive of successful induction. Immunoblotting and RT-qPCR revealed that expression of FN1 was increased in tissues of fracture mice. As displayed by Safranin-fast green staining hematoxylin-eosin staining, the overexpression of FN1 at fracture site promoted osteoid formation and chondrocyte differentiation. The stimulating role of FN1 in collagen production was evidenced by increased levels of Col2, Col1, ColX, Osteonectin, and Osteocalcin and enhanced BMD, BV, BV/TV and Tb.Th values verified by immunoblotting and immunohistochemical staining. Additionally, the upregulation of FN1 contributed to promoted TGF-β, c-Caspase-9/t-Caspase-9 ratio and NF-κB p65 protein expression as well as lowered p-PI3K/PI3K and p-AKT/AKT ratios, implying the positive correlation between FN1 and the TGF-β/PI3K/Akt signaling pathway. The key findings of the present study provided evidence indicating that overexpression of FN1 contributes to fracture healing by activation of the TGF-β/PI3K/Akt signaling pathway.

Mechanisms of bone development and repair

Bone development occurs through a series of synchronous events that result in the formation of the body scaffold. The repair potential of bone and its surrounding microenvironment - including inflammatory, endothelial and Schwann cells - persists throughout adulthood, enabling restoration of tissue to its homeostatic functional state. The isolation of a single skeletal stem cell population through cell surface markers and the development of single-cell technologies are enabling precise elucidation of cellular activity and fate during bone repair by providing key insights into the mechanisms that maintain and regenerate bone during homeostasis and repair. Increased understanding of bone development, as well as normal and aberrant bone repair, has important therapeutic implications for the treatment of bone disease and ageing-related degeneration.

Dynamic regulation of histone modifications and long-range chromosomal interactions during postmitotic transcriptional reactivation

During mitosis, transcription of genomic DNA is dramatically reduced, before it is reactivated during nuclear reformation in anaphase/telophase. Many aspects of the underlying principles that mediate transcriptional memory and reactivation in the daughter cells remain unclear. Here, we used ChIP-seq on synchronized cells at different stages after mitosis to generate genome-wide maps of histone modifications. Combined with EU-RNA-seq and Hi-C analyses, we found that during prometaphase, promoters, enhancers, and insulators retain H3K4me3 and H3K4me1, while losing H3K27ac. Enhancers globally retaining mitotic H3K4me1 or locally retaining mitotic H3K27ac are associated with cell type-specific genes and their transcription factors for rapid transcriptional activation. As cells exit mitosis, promoters regain H3K27ac, which correlates with transcriptional reactivation. Insulators also gain H3K27ac and CCCTC-binding factor (CTCF) in anaphase/telophase. This increase of H3K27ac in anaphase/telophase is required for posttranscriptional activation and may play a role in the establishment of topologically associating domains (TADs). Together, our results suggest that the genome is reorganized in a sequential order, in which histone methylations occur first in prometaphase, histone acetylation, and CTCF in anaphase/telophase, transcription in cytokinesis, and long-range chromatin interactions in early G1. We thus provide insights into the histone modification landscape that allows faithful reestablishment of the transcriptional program and TADs during cell division.

Expansion of Bone Precursors through Jun as a Novel Treatment for Osteoporosis-Associated Fractures

Osteoporosis and osteoporotic fractures lead to decreased life quality and high healthcare costs. Current treatments prevent losses in bone mass and fractures to some extent but have side effects. Therefore, better therapies are needed. This study investigated whether the transcription factor Jun has a specific pro-osteogenic potency and whether modulating Jun could serve as a novel treatment for osteoporosis-associated fractures. We demonstrate that ectopically transplanted whole bones and distinct osteoprogenitors increase bone formation. Perinatal Jun induction disturbs growth plate architecture, causing a striking phenotype with shortened and thickened bones. Molecularly, Jun induces hedgehog signaling in skeletal stem cells. Therapeutically, Jun accelerates bone growth and healing in a drilling-defect model. Altogether, these results demonstrate that Jun drives bone formation by expanding osteoprogenitor populations and forcing them into the bone fate, providing a rationale for future clinical applications.

lncRNA UCA1 Promotes Gefitinib Resistance as a ceRNA to Target FOSL2 by Sponging miR-143 in Non-small Cell Lung Cancer

Exosomes could mediate cell-cell crosstalk in cancer progression by transferring long noncoding RNAs (lncRNAs). The aim of this study is to explore the roles of the exosomal lncRNA urothelial carcinoma-associated 1 (UCA1) on gefitinib resistance in non-small cell lung cancer (NSCLC). First, we detected the expression of UCA1 in gefitinib-resistant and gefitinib-sensitive NSCLC by quantitative real-time PCR; the expression occurred in tissues, cell lines, and exosomes. Cell phenotypes and animal experiments were performed to determine the effects of UCA1 and exosomal UCA1. Furthermore, bioinformatics online programs and luciferase reporter assay were used to validate the association of UCA1 and miR-143 in NSCLC cells. We observed that UCA1 was increased in both gefitinib-resistant NSCLC cells and their secreted exosomes. In vitro and in vivo experiments demonstrated that UCA1 knockdown impaired cell proliferation and promoted the gefitinib-induced cell apoptosis. Then we demonstrated that repressed UCA1 promoted the miR-143 expression, and miR-143 could bind to the predicted binding site of UCA1. We then dissected the effect of miR-143 on gefitinib resistance in NSCLC and proved the suppressive role of miR-143. Furthermore, we found that miR-143 displayed its role via modulating the FOSL2 expression. In summary, our findings indicate that exosomal UCA1 may serve as a promising therapeutic target for the treatment of epidermal growth factor receptor-positive (EGFR+) NSCLC patients.