Bone-specific transcription factor Runx2 interacts with the 1alpha,25-dihydroxyvitamin D3 receptor to up-regulate rat osteocalcin gene expression in osteoblastic cells

MicroRNAs in fluorosis pathogenesis: impact on dental, skeletal, and soft tissues

Fluoride-induced toxicity (fluorosis) poses a significant health concern globally, affecting millions of individuals. Understanding the molecular mechanisms underlying fluorosis, particularly the role of microRNAs (miRNAs), is crucial for developing effective preventive and therapeutic strategies. This review explores the pivotal role of miRNAs in the pathogenesis of fluorosis, particularly examining its impact on both hard (skeletal and dental) and soft (brain, liver, kidney, heart, and reproductive organs) tissues. Skeletal fluorosis manifests as abnormal bone mineralization and structure, while dental fluorosis affects enamel formation. In vitro and in vivo studies suggest a significant involvement of miRNAs in the progression of these conditions. For skeletal fluorosis, miR-124, miR-155, and miR-200c-3p have been identified as key regulators, while miR-296-5p and miR-214-3p are implicated in dental fluorosis. Moreover, soft tissue fluorosis encompasses a spectrum of adverse effects on various organs, including the brain, liver, kidneys, heart, and reproductive system. In soft tissues, miRNAs, such as miR-124, miR-200c-3p, miR-132, and miR-34b-5p, have been linked to cellular damage and dysfunction. Notably, miRNAs exert their effects through the modulation of critical pathways involved in fluorosis pathology, including Wnt signaling, apoptosis, cell cycle, and autophagy. Understanding the regulatory roles of miRNAs in fluorosis pathogenesis holds promise for identifying biomarkers and therapeutic targets. However, further research is needed to elucidate the molecular mechanisms underlying miRNA-mediated responses to fluoride exposure. Integration of miRNA research into fluorosis studies could facilitate the development of diagnostic tools and therapeutic interventions, thus mitigating the detrimental effects of fluorosis on both hard and soft tissues.

Roles of osteocalcin in the central nervous system

BACKGROUND

Bone-derived protein osteocalcin, which has beneficial effects on brain function, may be a future research direction for neurological disorders. A growing body of evidence suggests a link between osteocalcin and neurological disorders, but the exact relationship is contradictory and unclear.

SCOPE OF REVIEW

The aim of this review is to summarize the current research on the interaction between osteocalcin and the central nervous system and to propose some speculative future research directions.

MAJOR CONCLUSIONS

In the normal central nervous system, osteocalcin is involved in neuronal structure, neuroprotection, and the regulation of cognition and anxiety. Studies on osteocalcin-related abnormalities in the central nervous system are divided into animal model studies and human studies, depending on the subject. In humans, the link between osteocalcin and brain function is inconsistent. These conflicting data may be due to methodological inconsistencies. By reviewing the related literature on osteocalcin, some comorbidities of the bone and nervous system and future research directions related to osteocalcin are proposed.

Epigenetic regulators controlling osteogenic lineage commitment and bone formation

Bone formation and homeostasis are controlled by environmental factors and endocrine regulatory cues that initiate intracellular signaling pathways capable of modulating gene expression in the nucleus. Bone-related gene expression is controlled by nucleosome-based chromatin architecture that limits the accessibility of lineage-specific gene regulatory DNA sequences and sequence-specific transcription factors. From a developmental perspective, bone-specific gene expression must be suppressed during the early stages of embryogenesis to prevent the premature mineralization of skeletal elements during fetal growth in utero. Hence, bone formation is initially inhibited by gene suppressive epigenetic regulators, while other epigenetic regulators actively support osteoblast differentiation. Prominent epigenetic regulators that stimulate or attenuate osteogenesis include lysine methyl transferases (e.g., EZH2, SMYD2, SUV420H2), lysine deacetylases (e.g., HDAC1, HDAC3, HDAC4, HDAC7, SIRT1, SIRT3), arginine methyl transferases (e.g., PRMT1, PRMT4/CARM1, PRMT5), dioxygenases (e.g., TET2), bromodomain proteins (e.g., BRD2, BRD4) and chromodomain proteins (e.g., CBX1, CBX2, CBX5). This narrative review provides a broad overview of the covalent modifications of DNA and histone proteins that involve hundreds of enzymes that add, read, or delete these epigenetic modifications that are relevant for self-renewal and differentiation of mesenchymal stem cells, skeletal stem cells and osteoblasts during osteogenesis.

Daytime administration of melatonin has better protective effects on bone loss in ovariectomized rats

OBJECTIVE

To explore the difference in the protective effects of intraperitoneal injection of exogenous melatonin of daytime or nighttime on bone loss in ovariectomized (OVX) rats.

METHODS

After bilateral ovariectomy and sham surgery, 40 rats were randomly divided into four groups: sham operation group (Sham), ovariectomy (OVX), and daytime melatonin injection group (OVX + DMLT, 9:00, 30 mg/kg/d) and nighttime injection of melatonin (OVX + NMLT, 22:00, 30 mg/kg/d). After 12 weeks of treatment, the rats were sacrificed. The distal femur, blood and femoral marrow cavity contents were saved. The rest of the samples were tested by Micro-CT, histology, biomechanics and molecular biology. Blood was used for bone metabolism marker measurements. CCK-8, ROS, and Cell apoptosis are performed using MC3E3-T1 cells.

RESULTS

Compared with treatment at night, the bone mass of the OVX rats was significantly increased after the daytime administration. All microscopic parameters of trabecular bone increased, only Tb.Sp decreased. Histologically, the bone microarchitecture of the OVX + DMLT was also more dense than the bone microarchitecture of the OVX + LMLT. In the biomechanical experiment, the femur samples of the day treatment group were able to withstand greater loads and deformation. In molecular biology experiments, bone formation-related molecules increased, while bone resorption-related molecules decreased. After treatment with melatonin administration at night, the expression of MT-1β was significantly decreased. In cell experiments, the MC3E3-T1 cells treated with low-dose MLT had higher cell viability and greater efficiency in inhibiting ROS production than the MC3E3-T1 cells treated with high-dose MLT, which in turn more effectively inhibited apoptosis.

CONCLUSION

Daytime administration of melatonin acquires better protective effects on bone loss than night in OVX rats.

Epigenetic regulation during 1,25-dihydroxyvitamin D3-dependent gene transcription

Multiple evidence accumulated over the years, demonstrates that vitamin D-dependent physiological control in vertebrates occurs primarily through the regulation of target gene transcription. In addition, there has been an increasing appreciation of the role of the chromatin organization of the genome on the ability of the active form of vitamin D, 1,25(OH)₂D₃, and its specific receptor VDR to regulate gene expression. Chromatin structure in eukaryotic cells is principally modulated through epigenetic mechanisms including, but not limited to, a wide number of post-translational modifications of histone proteins and ATP-dependent chromatin remodelers, which are operative in different tissues during response to physiological cues. Hence, there is necessity to understand in depth the epigenetic control mechanisms that operate during 1,25(OH)₂D₃-dependent gene regulation. This chapter provides a general overview about epigenetic mechanisms functioning in mammalian cells and discusses how some of these mechanisms represent important components during transcriptional regulation of the model gene system CYP24A1 in response to 1,25(OH)₂D₃.

Targeting Sirt1, AMPK, Nrf2, CK2, and Soluble Guanylate Cyclase with Nutraceuticals: A Practical Strategy for Preserving Bone Mass

There is a vast pre-clinical literature suggesting that certain nutraceuticals have the potential to aid the preservation of bone mass in the context of estrogen withdrawal, glucocorticoid treatment, chronic inflammation, or aging. In an effort to bring some logical clarity to these findings, the signaling pathways regulating osteoblast, osteocyte, and osteoclast induction, activity, and survival are briefly reviewed in the present study. The focus is placed on the following factors: the mechanisms that induce and activate the RUNX2 transcription factor, a key driver of osteoblast differentiation and function; the promotion of autophagy and prevention of apoptosis in osteoblasts/osteoclasts; and the induction and activation of NFATc1, which promotes the expression of many proteins required for osteoclast-mediated osteolysis. This analysis suggests that the activation of sirtuin 1 (Sirt1), AMP-activated protein kinase (AMPK), the Nrf2 transcription factor, and soluble guanylate cyclase (sGC) can be expected to aid the maintenance of bone mass, whereas the inhibition of the serine kinase CK2 should also be protective in this regard. Fortuitously, nutraceuticals are available to address each of these targets. Sirt1 activation can be promoted with ferulic acid, N1-methylnicotinamide, melatonin, nicotinamide riboside, glucosamine, and thymoquinone. Berberine, such as the drug metformin, is a clinically useful activator of AMPK. Many agents, including lipoic acid, melatonin, thymoquinone, astaxanthin, and crucifera-derived sulforaphane, can promote Nrf2 activity. Pharmacological doses of biotin can directly stimulate sGC. Additionally, certain flavonols, notably quercetin, can inhibit CK2 in high nanomolar concentrations that may be clinically relevant. Many, though not all, of these agents have shown favorable effects on bone density and structure in rodent models of bone loss. Complex nutraceutical regimens providing a selection of these nutraceuticals in clinically meaningful doses may have an important potential for preserving bone health. Concurrent supplementation with taurine, N-acetylcysteine, vitamins D and K2, and minerals, including magnesium, zinc, and manganese, plus a diet naturally high in potassium, may also be helpful in this regard.

Epigenetic-Mediated Regulation of Gene Expression for Biological Control and Cancer: Cell and Tissue Structure, Function, and Phenotype

Epigenetic gene regulatory mechanisms play a central role in the biological control of cell and tissue structure, function, and phenotype. Identification of epigenetic dysregulation in cancer provides mechanistic into tumor initiation and progression and may prove valuable for a variety of clinical applications. We present an overview of epigenetically driven mechanisms that are obligatory for physiological regulation and parameters of epigenetic control that are modified in tumor cells. The interrelationship between nuclear structure and function is not mutually exclusive but synergistic. We explore concepts influencing the maintenance of chromatin structures, including phase separation, recognition signals, factors that mediate enhancer-promoter looping, and insulation and how these are altered during the cell cycle and in cancer. Understanding how these processes are altered in cancer provides a potential for advancing capabilities for the diagnosis and identification of novel therapeutic targets.

Effects of Extracellular Osteoanabolic Agents on the Endogenous Response of Osteoblastic Cells

The complex multidimensional skeletal organization can adapt its structure in accordance with external contexts, demonstrating excellent self-renewal capacity. Thus, optimal extracellular environmental properties are critical for bone regeneration and inextricably linked to the mechanical and biological states of bone. It is interesting to note that the microstructure of bone depends not only on genetic determinants (which control the bone remodeling loop through autocrine and paracrine signals) but also, more importantly, on the continuous response of cells to external mechanical cues. In particular, bone cells sense mechanical signals such as shear, tensile, loading and vibration, and once activated, they react by regulating bone anabolism. Although several specific surrounding conditions needed for osteoblast cells to specifically augment bone formation have been empirically discovered, most of the underlying biomechanical cellular processes underneath remain largely unknown. Nevertheless, exogenous stimuli of endogenous osteogenesis can be applied to promote the mineral apposition rate, bone formation, bone mass and bone strength, as well as expediting fracture repair and bone regeneration. The following review summarizes the latest studies related to the proliferation and differentiation of osteoblastic cells, enhanced by mechanical forces or supplemental signaling factors (such as trace metals, nutraceuticals, vitamins and exosomes), providing a thorough overview of the exogenous osteogenic agents which can be exploited to modulate and influence the mechanically induced anabolism of bone. Furthermore, this review aims to discuss the emerging role of extracellular stimuli in skeletal metabolism as well as their potential roles and provide new perspectives for the treatment of bone disorders.

Bio-Functionalized Chitosan for Bone Tissue Engineering

Hybrid biomaterials allow for the improvement of the biological properties of materials and have been successfully used for implantology in medical applications. The covalent and selective functionalization of materials with bioactive peptides provides favorable results in tissue engineering by supporting cell attachment to the biomaterial through biochemical cues and interaction with membrane receptors. Since the functionalization with bioactive peptides may alter the chemical and physical properties of the biomaterials, in this study we characterized the biological responses of differently functionalized chitosan analogs. Chitosan analogs were produced through the reaction of GRGDSPK (RGD) or FRHRNRKGY (HVP) sequences, both carrying an aldehyde-terminal group, to chitosan. The bio-functionalized polysaccharides, pure or "diluted" with chitosan, were chemically characterized in depth and evaluated for their antimicrobial activities and biocompatibility toward human primary osteoblast cells. The results obtained indicate that the bio-functionalization of chitosan increases human-osteoblast adhesion (p < 0.005) and proliferation (p < 0.005) as compared with chitosan. Overall, the 1:1 mixture of HVP functionalized-chitosan:chitosan is the best compromise between preserving the antibacterial properties of the material and supporting osteoblast differentiation and calcium deposition (p < 0.005 vs. RGD). In conclusion, our results reported that a selected concentration of HVP supported the biomimetic potential of functionalized chitosan better than RGD and preserved the antibacterial properties of chitosan.

Bone mineral density, bone microstructure, and bone turnover markers in females with temporomandibular joint osteoarthritis

OBJECTIVE

The pathogenesis of the temporomandibular joint osteoarthritis (TMJ OA) has not been clearly revealed. This study aimed to investigate the pathogenesis of TMJ OA based on bone metabolism.

METHODS

Fifty-nine young (mean age 23.4 ± 3.4 years) and 41 post-menopausal females (mean age 57.2 ± 4.6 years) were enrolled. Areal bone mineral density (aBMD) was measured via dual-energy X-ray absorptiometry of the lumbar spine, femoral neck, total hip, and ultradistal radius. Levels of four bone resorption markers, serum ionized calcium and C-telopeptide of type I collagen (CTx) and urinary N-telopeptide of type I collagen and deoxypyridinoline, two bone formation markers, serum bone alkaline phosphatase and osteocalcin, and serum 25-dihydroxyvitamin D were analyzed at baseline and after 12 months. Condylar bone quality was assessed by 3D reconstructed CT images.

RESULTS

Significant differences in condylar bone quality and aBMDs of the lumbar spine in accordance with TMJ OA stages were observed in young and post-menopausal females. The level of CTx was significantly associated with the development and progression of TMJ OA only in young females, whereas 25-dihydroxyvitamine D demonstrated significant associations in young and post-menopausal females. Progression of TMJ OA was accompanied by reduced condylar bone quality and concomitant with lower lumbar spine aBMDs in young and post-menopausal females.

CONCLUSION

Bone metabolism and condylar quality might be involved in the development and progression of TMJ OA.

CLINICAL RELEVANCE

CTx could be considered as a potential diagnostic and monitoring marker in young females, and vitamin D showed a therapeutic potential for TMJ OA.

Genetic response to low‑intensity ultrasound on mouse ST2 bone marrow stromal cells

Although low‑intensity ultrasound (LIUS) is a clinically established procedure, the early cellular effect of LIUS on a genetic level has not yet been studied. The current study investigated the early response genes elicited by LIUS in bone marrow stromal cells (BMSCs) using global‑scale microarrays and computational gene expression analysis tools. Mouse ST2 BMSCs were treated with LIUS [I_SATA, 25 mW/cm² for 20 min with a frequency of 1.11 MHz in a pulsed‑wave mode (0.2‑s burst sine waves repeated at 1 kHz)], then cultured for 0.5, 1 and 3 h at 37˚C. The time course of changes in gene expression was evaluated using GeneChip^® high‑density oligonucleotide microarrays and Ingenuity^® Pathway Analysis tools. The results were verified by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). A single exposure of LIUS did not affect cell morphology, cell growth or alkaline phosphatase activity. However, 61 upregulated and 103 downregulated genes were identified from 0.5 to 3 h after LIUS treatment. Two significant gene networks, labeled E and H, were identified from the upregulated genes, while a third network, labeled T, was identified from the downregulated genes. Gene network E or H containing the immediate‑early genes FBJ osteosarcoma oncogene and early growth response 1 or the heat shock proteins heat shock protein 1a/b was associated mainly with the biological functions of bone physiology and protein folding or apoptosis, respectively. Gene network T containing transcription factors fos‑like antigen 1 and serum response factor was also associated with the biological functions of the gene expression. RT‑qPCR indicated that the expression of several genes in the gene networks E and H were elevated in LIUS‑treated cells. LIUS was demonstrated to induce gene expression after short application in mouse ST2 BMSCs. The results of the present study provide a basis for the elucidation of the detailed molecular mechanisms underlying the cellular effects of LIUS.

Ezh2-dependent H3K27me3 modification dynamically regulates vitamin D3-dependent epigenetic control of CYP24A1 gene expression in osteoblastic cells

Epigenetic control is critical for the regulation of gene transcription in mammalian cells. Among the most important epigenetic mechanisms are those associated with posttranslational modifications of chromosomal histone proteins, which modulate chromatin structure and increased accessibility of promoter regulatory elements for competency to support transcription. A critical histone mark is trimethylation of histone H3 at lysine residue 27 (H3K27me3), which is mediated by Ezh2, the catalytic subunit of the polycomb group complex PRC2 to repress transcription. Treatment of cells with the active vitamin D metabolite 1,25(OH)₂ D₃ , results in transcriptional activation of the CYP24A1 gene, which encodes a 24-hydroxylase enzyme, that is, essential for physiological control of vitamin D3 levels. We report that the Ezh2-mediated deposition of H3K27me3 at the CYP24A1 gene promoter is a requisite regulatory component during transcriptional silencing of this gene in osteoblastic cells in the absence of 1,25(OH)₂ D₃ . 1,25(OH)₂ D₃ dependent transcriptional activation of the CYP24A1 gene is accompanied by a rapid release of Ezh2 from the promoter, together with the binding of the H3K27me3-specific demethylase Utx/Kdm6a and thereby subsequent erasing of the H3K27me3 mark. Importantly, we find that these changes in H3K27me3 enrichment at the CYP24A1 gene promoter are highly dynamic, as this modification is rapidly reacquired following the withdrawal of 1,25(OH)₂ D₃ .

Identification of a novel melatonin-binding nuclear receptor: Vitamin D receptor

Previous studies confirmed that melatonin regulates Runx2 expression but the mechanism is unclear. There is a direct interaction between Runx2 and the vitamin D receptor (VDR). Herein, we observed a direct interaction between melatonin and the VDR but not Runx2 using isothermal titration calorimetry. Furthermore, this direct binding was detected only in the C-terminal ligand binding domain (LBD) of the VDR but not in the N-terminal DNA-binding domain (DBD) or the hinge region. Spectrophotometry indicated that melatonin and vitamin D3 (VD3) had similar uptake rates, but melatonin's uptake was significantly inhibited by VD3 until the concentration of melatonin was obviously higher than that of VD3 in a preosteoblastic cell line MC3T3-E1. GST pull-down and yeast two-hybrid assay showed that the interactive smallest fragments were on the 319-379 position of Runx2 and the N-terminus 110-amino acid DBD of the VDR. Electrophoretic mobility shift assay (EMSA) demonstrated that Runx2 facilitated the affinity between the VDR and its specific DNA substrate, which was further documented by a fluorescent EMSA assay where Cy3 labeled Runx2 co-localized with the VDR-DNA complex. Another fluorescent EMSA assay confirmed that the binding of the VDR to Runx2 was significantly enhanced with an increasing concentrations of the VDR, especially in the presence of melatonin; it was further documented using a co-immunoprecipitation assay that this direct interaction was markedly enhanced by melatonin treatment in the MC3T3-E1 cells. Thus, the VDR is a novel melatonin-binding nuclear receptor, and melatonin indirectly regulates Runx2 when it directly binds to the LBD and the DBD of the VDR, respectively.

Switches in histone modifications epigenetically control vitamin D3-dependent transcriptional upregulation of the CYP24A1 gene in osteoblastic cells

In bone cells vitamin D dependent regulation of gene expression principally occurs through modulation of gene transcription. Binding of the active vitamin D metabolite, 1,25-dihydroxy vitamin D3 (1,25(OH)₂ D₃ ) to the vitamin D receptor (VDR) induces conformational changes in its C-terminal domain enabling competency for interaction with physiologically relevant coactivators, including SRC-1. Consequently, regulatory complexes can be assembled that support intrinsic enzymatic activities with competency to posttranslationally modify chromatin histones at target genomic sequences to epigenetically alter transcription. Here we examine specific transitions in representation and/or enrichment of epigenetic histone marks during 1,25(OH)₂ D₃ mediated upregulation of CYP24A1 gene expression in osteoblastic cells. This gene encodes the 24-hydroxylase enzyme, essential for biological control of vitamin D levels. We demonstrate that as the CYP24A1 gene promoter remains transcriptionally silent, there is enrichment of H4R3me2s together with its "writing" enzyme PRMT5 and decreased abundance of the istone H3 and H4 acetylation, H3R17me2a, and H4R3me2a marks as well as of their corresponding "writers." Exposure of osteoblastic cells to 1,25(OH)₂ D₃ stimulates the recruitment of a VDR/SRC-1 containing complex to the CYP24A1 promoter to mediate increased H3/H4 acetylation. VDR/SRC-1 binding occurs concomitant with the release of PRMT5 and the recruitment of the arginine methyltransferases CARM1 and PRMT1 to catalyze the deposition of the H3R17me2a and H4R3me2a marks, respectively. Our results indicate that these dynamic transitions of histone marks at the CYP24A1 promoter, provide a "chromatin context" that is transcriptionally competent for activation of the CYP24A1 gene in osteoblastic cells in response to 1,25(OH)₂ D₃ .

Dual usage of a stage-specific fluorescent reporter system based on a helper-dependent adenoviral vector to visualize osteogenic differentiation

We developed a reporter system that can be used in a dual manner in visualizing mature osteoblast formation. The system is based on a helper-dependent adenoviral vector (HDAdV), in which a fluorescent protein, Venus, is expressed under the control of the 19-kb human osteocalcin (OC) genomic locus. By infecting human and murine primary osteoblast (POB) cultures with this reporter vector, the cells forming bone-like nodules were specifically visualized by the reporter. In addition, the same vector was utilized to efficiently knock-in the reporter into the endogenous OC gene of human induced pluripotent stem cells (iPSCs), by homologous recombination. Neural crest-like cells (NCLCs) derived from the knock-in reporter iPSCs were differentiated into osteoblasts forming bone-like nodules and could be visualized by the expression of the fluorescent reporter. Living mature osteoblasts were then isolated from the murine mixed POB culture by fluorescence-activated cell sorting (FACS), and their mRNA expression profile was analyzed. Our study presents unique utility of reporter HDAdVs in stem cell biology and related applications.

Controlling hypoxia-inducible factor-2α is critical for maintaining bone homeostasis in mice

Pathological bone loss is caused by an imbalance between bone formation and resorption. The bone microenvironments are hypoxic, and hypoxia-inducible factor (HIF) is known to play notable roles in bone remodeling. However, the relevant functions of HIF-2α are not well understood. Here, we have shown that HIF-2α deficiency in mice enhances bone mass through its effects on the differentiation of osteoblasts and osteoclasts. In vitro analyses revealed that HIF-2α inhibits osteoblast differentiation by targeting Twist2 and stimulates RANKL-induced osteoclastogenesis via regulation of Traf6. In addition, HIF-2α appears to contribute to the crosstalk between osteoblasts and osteoclasts by directly targeting RANKL in osteoprogenitor cells. Experiments performed with osteoblast- and osteoclast-specific conditional knockout mice supported a role of HIF-2α in this crosstalk. HIF-2α deficiency alleviated ovariectomy-induced bone loss in mice, and specific inhibition of HIF-2α with ZINC04179524 significantly blocked RANKL-mediated osteoclastogenesis. Collectively, our results suggest that HIF-2α functions as a catabolic regulator in bone remodeling, which is critical for the maintenance of bone homeostasis.

1,25(OH)2D3 regulates the proangiogenic activity of pericyte through VDR-mediated modulation of VEGF production and signaling of VEGF and PDGF receptors

We have previously demonstrated that the active form of vitamin D (calcitriol; 1,25(OH)₂D₃) is a potent inhibitor of retinal neovascularization. However, the underlying molecular and cellular mechanisms involved remained poorly understood. Perivascular supporting cells including pericytes (PC) play important roles during angiogenesis, vascular maturation, and stabilization of blood vessels. How 1,25(OH)₂D₃ affects retinal PC proliferation and migration, and whether these effects are mediated through vitamin D receptor (VDR), are unknown. Here, we determined the impact of 1,25(OH)₂D₃ on retinal PC prepared from wild‐type (Vdr+/+) and VDR‐deficient (Vdr−/−) mice. Retinal PC expressed significantly higher VDR levels compared to retinal endothelial cells (EC). Unlike retinal EC, 1,25(OH)₂D₃ significantly decreased PC proliferation and migration and resulted in a G₀/G₁ cell cycle arrest. Although 1,25(OH)₂D₃ did not inhibit the proliferation of Vdr−/− PC, it did inhibit their migration. PC adhesion to various extracellular matrix (ECM) proteins and ECM production were also affected by incubation of PC with 1,25(OH)₂D₃. Vdr−/− PC were more adherent compared with Vdr+/+ cells. Mechanistically, incubation of Vdr+/+ PC with 1,25(OH)₂D₃ resulted in an increased expression of vascular endothelial growth factor (VEGF) and attenuation of signaling through VEGF‐R2 and platelet‐derived growth factor receptor‐beta. Incubation with soluble VEGF‐R1 (sFlt‐1) partially reversed the effect of VEGF on Vdr+/+ PC. In addition, incubation of Vdr+/+ PC with VEGF or inhibition of VEGF‐R2 increased VDR expression. Together, these results suggest an important role for retinal PC as a target for vitamin D and VDR action for attenuation of angiogenesis.

Mll-COMPASS complexes mediate H3K4me3 enrichment and transcription of the osteoblast master gene Runx2/p57 in osteoblasts

Expression of Runx2/p57 is a hallmark of the osteoblast-lineage identity. Although several regulators that control the expression of Runx2/p57 during osteoblast-lineage commitment have been identified, the epigenetic mechanisms that sustain this expression in differentiated osteoblasts remain to be completely determined. Here, we assess epigenetic mechanisms associated with Runx2/p57 gene transcription in differentiating MC3T3 mouse osteoblasts. Our results show that an enrichment of activating histone marks at the Runx2/p57 P1 promoter is accompanied by the simultaneous interaction of Wdr5 and Utx proteins, both are components of COMPASS complexes. Knockdown of Wdr5 and Utx expression confirms the activating role of both proteins at the Runx2-P1 promoter. Other chromatin modifiers that were previously described to regulate Runx2/p57 transcription in mesenchymal precursor cells (Ezh2, Prmt5, and Jarid1b proteins) were not found to contribute to Runx2/p57 transcription in full-committed osteoblasts. We also determined the presence of additional components of COMPASS complexes at the Runx2/p57 promoter, evidencing that the Mll2/COMPASS- and Mll3/COMPASS-like complexes bind to the P1 promoter in osteoblastic cells expressing Runx2/p57 to modulate the H3K4me1 to H3K4me3 transition.

Effect of hydrogel elasticity and ephrinB2-immobilized manner on Runx2 expression of human mesenchymal stem cells

The objective of this study is to design the manner of ephrinB2 immobilized onto polyacrylamide (PAAm) hydrogels with varied elasticity and evaluate the effect of hydrogels elasticity and the immobilized manner of ephrinB2 on the Runx2 expression of human mesenchymal stem cells (hMSC). The PAAm hydrogels were prepared by the radical polymerization of acrylamide (AAm), and N,N'-methylenebisacrylamide (BIS). By changing the BIS concentration, the elasticity of PAAm hydrogels changed from 1 to 70kPa. For the bio-specific immobilization of ephrinB2, a chimeric protein of ephrinB2 and Fc domain was immobilized onto protein A-conjugated PAAm hydrogels by making use of the bio-specific interaction between the Fc domain and protein A. When hMSC were cultured on the ephrinB2-immobilized PAAm hydrogels with varied elasticity, the morphology of hMSC was of cuboidal shape on the PAAm hydrogels immobilized with ephrinB2 compared with non-conjugated ones, irrespective of the hydrogels elasticity. The bio-specific immobilization of ephrinB2 enhanced the level of Runx2 expression. The expression level was significantly high for the hydrogels of 3.6 and 5.9kPa elasticity with bio-specific immobilization of ephrinB2 compared with other hydrogels with the same elasticity. The hydrogels showed a significantly down-regulated RhoA activity. It is concluded that the Runx2 expression of hMSC is synergistically influenced by the hydrogels elasticity and their immobilized manner of ephrinB2 immobilized.

STATEMENT OF SIGNIFICANCE

Differentiation fate of mesenchymal stem cells (MSC) is modified by biochemical and biophysical factors, such as elasticity and signal proteins. However, there are few experiments about combinations of them. In this study, to evaluate the synergistic effect of them on cell properties of MSC, we established to design the manner of Eph signal ligand, ephrinB2, immobilized onto polyacrylamide hydrogels with varied elasticity. The gene expression level of an osteogenic maker, Runx2, was enhanced by the immobilized manner, and significantly enhanced for the hydrogels of around 4kPa elasticity with bio-specific immobilization of ephrinB2. This is the novel report describing to demonstrate that the Runx2 expression of MSC is synergistically influenced by the hydrogels elasticity and their manner of ephrinB2 immobilized.

Activated p300 acetyltransferase activity modulates aortic valvular calcification with osteogenic transdifferentiation and downregulation of Klotho

BACKGROUND

The calcific aortic valve (AV) disease is a common disease with the unclear mechanism, and optimal pharmacological treatment remains unavailable. Epigenetic modulation by histone acetyltransferase (HAT) plays a critical role in osteogenic transdifferentiation and atherosclerosis. The purposes of this study were to investigate whether HAT contributes to the pathophysiology of AV calcification and assess the therapeutic potential of HAT inhibition.

METHODS

Porcine valvular interstitial cells (VICs) were treated with osteogenic medium (10ng/mL of tumor necrosis factor-α and 4mmol/L of high phosphate) for 7days. We analyzed the RNA and protein expression of myofibroblastic (α-SMA, vimentin, collagen 1A1, collagen 3, Egr-1, MMP2, MMP9) and osteoblastic markers (osteocalcin and alkaline phosphatase) in VICs, and studied the effects of a p300 inhibitor (C646, 10μmol/L) on calcification (Alizarin Red S staining), osteogenesis, HAT activity, the mitogen-activated protein kinase (MAPK) and Akt pathway, and Klotho expression on VICs.

RESULTS

Osteogenic medium treated VICs had higher expressions of osteocalcin, alkaline phosphatase and acetylated lysine-9 of histone H3 (ac-H3K9) than control cells. C646 attenuated osteogenesis of VICs with simultaneous inhibition of the HAT activity of p300. There was neither significant increase of p300 protein nor p300 transcript during the osteogenesis process. Additionally, osteogenic medium treated VICs decreased the expression of Klotho, which is attenuated by C646.

CONCLUSIONS

Activated HAT activity of p300 modulates AV calcification through osteogenic transdifferentiation of VICs with Klotho modulation. P300 inhibition is a potential therapeutic target for AV calcification.

Gene-Activated Titanium Surfaces Promote In Vitro Osteogenesis

PURPOSE

Commercially pure titanium (CpTi) and its alloys possess favorable mechanical and biologic properties for use as implants in orthopedics and dentistry. However, failures in osseointegration still exist and are common in select individuals with risk factors such as smoking. Therefore, in this study, a proposal was made to enhance the potential for osseointegration of CpTi discs by coating their surfaces with nanoplexes comprising polyethylenimine (PEI) and plasmid DNA (pDNA) encoding bone morphogenetic protein-2 (pBMP-2).

MATERIALS AND METHODS

The nanoplexes were characterized for size and surface charge with a range of N/P ratios (the molar ratio of amine groups of PEI to phosphate groups in pDNA backbone). CpTi discs were surface characterized for morphology and composition before and after nanoplex coating using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD). The cytotoxicity and transfection ability of CpTi discs coated with nanoplexes of varying N/P ratios in human bone marrow-derived mesenchymal stem cells (BMSCs) was measured via MTS assays and flow cytometry, respectively.

RESULTS

The CpTi discs coated with nanoplexes prepared at an N/P ratio of 10 (N/P-10) were considered optimal, resulting in 75% cell viability and 14% transfection efficiency. Enzyme-linked immunosorbent assay results demonstrated a significant enhancement in BMP-2 protein secretion by BMSCs 7 days posttreatment with PEI/pBMP-2 nanoplexes (N/P-10) compared to the controls, and real-time PCR data demonstrated that the BMSCs treated with PEI/pBMP-2 nanoplex-coated CpTi discs resulted in an enhancement of Runx-2, alkaline phosphatase, and osteocalcin gene expressions on day 7 posttreatment. In addition, these BMSCs demonstrated enhanced calcium deposition on day 30 posttreatment as determined by qualitative (alizarin red staining) and quantitative (atomic absorption spectroscopy) assays.

CONCLUSION

It can be concluded that PEI/pBMP-2 nanoplex (N/P-10)-coated CpTi discs have the potential to induce osteogenesis and enhance osseointegration.

Regulation of the CCN genes by vitamin D: A possible adjuvant therapy in the treatment of cancer and fibrosis

The CCN family is composed of six cysteine-rich, modular, and conserved proteins whose functions span a variety of tissues and include cell proliferation, adhesion, angiogenesis, and wound healing. Roles for the CCN proteins throughout the entire body including the skin, kidney, brain, blood vessels, hematopoietic compartment and others, are continuously being elucidated. Likewise, an understanding of the regulation of this important gene family is constantly becoming clearer, through identification of transcription factors that directly activate, repress, or respond to upstream cell signaling pathways, as well as other forms of gene expression control. Vitamin D (1,25-dihydroxyvitamin D3 or calcitriol), a vitamin essential for numerous biological processes, acts as a potent gene expression modulator. The regulation of the CCN gene family members by calcitriol has been described in many contexts. Here, we provide a concise and thorough overview of what is known about calcitriol and its regulation of the CCN genes, and argue that its regulation is of physiological importance in a wide breadth of tissues in which CCN genes function. In addition, we highlight the effects of vitamin D on CCN gene expression in the setting of two common pathologic conditions, fibrosis and cancer, and propose that the therapeutic effects of vitamin D3 described in these disease states may in part be attributable to CCN gene modulation. As vitamin D is perfectly safe in a wide range of doses and already showing promise as an adjuvant therapeutic agent, a deeper understanding of its control of CCN gene expression may have profound implications in clinical management of disease.

Glucocorticoids Hijack Runx2 to Stimulate Wif1 for Suppression of Osteoblast Growth and Differentiation

Inhibition of Runx2 is one of many mechanisms that suppress bone formation in glucocorticoid (GC)-induced osteoporosis (GIO). We profiled mRNA expression in ST2/Rx2(dox) cells after treatment with doxycycline (dox; to induce Runx2) and/or the synthetic GC dexamethasone (dex). As expected, dex typically antagonized Runx2-driven transcription. Select genes, however, were synergistic stimulated and this was confirmed by RT-qPCR. Among the genes synergistically stimulated by GCs and Runx2 was Wnt inhibitory Factor 1 (Wif1), and Wif1 protein was readily detectable in medium conditioned by cultures co-treated with dox and dex, but neither alone. Cooperation between Runx2 and GCs in stimulating Wif1 was also observed in primary preosteoblast cultures. GCs strongly inhibited dox-driven alkaline phosphatase (ALP) activity in control ST2/Rx2(dox) cells, but not in cells in which Wif1 was silenced. Unlike its anti-mitogenic activity in committed osteoblasts, induction of Runx2 transiently increased the percentage of cells in S-phase and accelerated proliferation in the ST2 mesenchymal pluripotent cell culture model. Furthermore, like the inhibition of Runx2-driven ALP activity, dex antagonized the transient mitogenic effect of Runx2 in ST2/Rx2(dox) cultures, and this inhibition eased upon Wif1 silencing. Plausibly, homeostatic feedback loops that rely on Runx2 activation to compensate for bone loss in GIO are thwarted, exacerbating disease progression through stimulation of Wif1. J. Cell. Physiol. 232: 145-153, 2017. © 2016 Wiley Periodicals, Inc.

Fabrication of hydrogels with elasticity changed by alkaline phosphatase for stem cell culture

The objective of this study is to design hydrogels whose elasticity can be changed by alkaline phosphatase (ALP) in cell culture and evaluate the effect of hydrogel elasticity on an osteogenic gene expression of cells. Hydrogels were prepared by the radical polymerization of acrylamide (AAm), N,N'-methylenebisacrylamide (BIS), and Phosmer™M containing phosphate groups (PE-PAAm hydrogels). The storage modulus of PE-PAAm hydrogels prepared was changed by the preparation conditions. When human mesenchymal stem cells (hMSC) were cultured on the ALP-responsive PE-PAAm hydrogels in the presence or absence of ALP, the morphology of hMSC was observed and one of the osteogenic differentiation markers, Runx2, was evaluated. By ALP addition into the culture medium, the morphology of hMSC was changed into an elongated shape without cell damage. ALP addition modified the level of Runx2 gene expression, which was influenced by the modulus of PE-PAAm hydrogels. It is concluded that the elasticity change of hydrogel substrates in cell culture had an influence on the Runx2 gene expression of hMSC.

STATEMENT OF SIGNIFICANCE

Stem cells sense the surface elasticity of culture substrates, and their differentiation fate is biologically modified by substrate properties. Most of experiments have been performed in static conditions during cell culture, while the in vivo microenvironment is dynamically changed. In this study, we established to design an enzyme-responsive hydrogel whose elasticity can be changed by alkaline phosphatase (ALP) in cell culture to mimic in vivo conditions. As a result, the cells were deformed and the gene expression level of an osteogenic maker, Runx2, was modified by ALP treatment. This is the novel report describing to demonstrate that the dynamic alteration of hydrogel substrate elasticity could modulate the osteoblastic gene expression of human MSC in vitro.

Melatonin, bone regulation and the ubiquitin-proteasome connection: A review

Recently, investigators have shown that ubiquitin-proteasome-mediated protein degradation is critical in regulating the balance between bone formation and bone resorption. The major signal transduction pathways regulating bone formation are the RANK/NF-κB pathway and the Wnt/β-catenin pathway. These signal transduction pathways regulate the activity of mature osteoblasts and osteoclasts. In addition, the Wnt/β-catenin pathway is one of the major signaling pathways in the differentiation of osteoblasts. The ubiquitin ligases that are reported to be of major significance in regulating these pathways are the ubiquitin SCF(B-TrCP) ligase (which regulates activation of NF-κB via degradation of IkBα in osteoclasts, and regulates bone transcription factors via degradation of β-catenin), the Keap-Cul3-Rbx1 ligase (which regulates degradation of IkB kinase, Nrf2, and the antiapoptotic factor Bcl-2), and Smurf1. Also of significance in regulating osteoclastogenesis is the deubiquitinase, CYLD (cylindramatosis protein), which facilitates the separation of NF-κB from IkBα. The degradation of CYLD is also under the regulation of SCF(B-TrCP). Proteasome inhibitors influence the activity of mature osteoblasts and osteoclasts, but also modulate the differentiation of precursor cells into osteoblasts. Preclinical studies show that melatonin also influences bone metabolism by stimulating bone growth and inhibiting osteoclast activity. These actions of melatonin could be interpreted as being mediated by the ubiquitin ligases SCF(B-TrCP) and Keap-Cul3-Rbx, or as an inhibitory effect on proteasomes. Clinical trials of the use of melatonin in the treatment of bone disease, including multiple myeloma, using both continuous and intermittent modes of administration, are warranted.

Glucocorticoid-Induced Osteoporosis

Osteoporosis is among the most devastating side effects of glucocorticoid (GC) therapy for the management of inflammatory and auto-immune diseases. Evidence from both humans and mice indicate deleterious skeletal effects within weeks of pharmacological GC administration, both related and unrelated to a decrease in bone mineral density (BMD). Osteoclast numbers and bone resorption are also rapidly increased, and together with osteoblast inactivation and decreased bone formation, these changes lead the fastest loss in BMD during the initial disease phase. Bone resorption then decreases to sub-physiological levels, but persistent and severe inhibition of bone formation leads to further bone loss and progressively increased fracture risk, up to an order of magnitude higher than that observed in untreated individuals. Bone forming osteoblasts are thus considered the main culprits in GC-induced osteoporosis (GIO). Accordingly, we focus this review primarily on deleterious effects on osteoblasts: inhibition of cell replication and function and acceleration of apoptosis. Mediating these adverse effects, GCs target pivotal regulatory mechanisms that govern osteoblast growth, differentiation and survival. Specifically, GCs inhibit growth factor pathways, including Insulin Growth Factors, Growth Hormone, Hepatocyte Growth/Scatter Factor and IL6-type cytokines. They also inhibit downstream kinases, including PI3-kinase and the MAP kinase ERK, the latter attributable in part to direct transcriptional stimulation of MAP kinase phosphatase 1. Most importantly, however, GCs inhibit the Wnt signaling pathway, which plays a pivotal role in osteoblast replication, function and survival. They transcriptionally stimulate expression of Wnt inhibitors of both the Dkk and Sfrp families, and they induce reactive oxygen species (ROS), which result in loss of ß-catenin to ROS-activated FoxO transcription factors. Identification of dissociated GCs, which would suppress the immune system without causing osteoporosis, is proving more challenging than initially thought, and GIO is currently managed by co-treatment with bisphosphonates or PTH. These drugs, however, are not ideally suited for GIO. Future therapeutic approaches may aim at GC targets such as those mentioned above, or newly identified targets including the Notch pathway, the AP-1/Il11 axis and the osteoblast master regulator RUNX2.

Comparative epigenetic influence of autologous versus fetal bovine serum on mesenchymal stem cells through in vitro osteogenic and adipogenic differentiation

Mesenchymal stem cells (MSCs) derived from bone marrow (BM) represents a useful source of adult stem cells for cell therapy and tissue engineering. MSCs are present at a low frequency in the BM; therefore expansion is necessary before performing clinical studies. Fetal bovine serum (FBS) as a nutritional supplement for in vitro culture of MSCs is a suitable additive for human cell culture, but not regarding subsequent use of these cells for clinical treatment of human patients due to the risk of viral and prion transmission as well as xenogeneic immune responses after transplantation. Recently, autologous serum (AS) has been as a supplement to replace FBS in culture medium. We compared the effect of FBS versus AS on the histone modification pattern of MSCs through in vitro osteogenesis and adipogenesis. Differentiation of stem cells under various serum conditions to a committed state involves global changes in epigenetic patterns that are critically determined by chromatin modifications. Chromatin immunoprecipitation (ChIP) coupled with real-time PCR showed significant changes in the acetylation and methylation patterns in lysine 9 (Lys9) of histone H3 on the regulatory regions of stemness (Nanog, Sox2, Rex1), osteogenic (Runx2, Oc, Sp7) and adipogenic (Ppar-γ, Lpl, adiponectin) marker genes in undifferentiated MSCs, FBS and AS. All epigenetic changes occurred in a serum dependent manner which resulted in higher expression level of stemness genes in undifferentiated MSCs compared to differentiated MSCs and increased expression levels of osteogenic genes in AS compared to FBS. Adipogenic genes showed greater expression in FBS compared to AS. These findings have demonstrated the epigenetic influence of serum culture conditions on differentiation potential of MSCs, which suggest that AS is possibly more efficient serum for osteogenic differentiation of MSCs in cell therapy purposes.

Novel target genes of RUNX2 transcription factor and 1,25-dihydroxyvitamin D3

The RUNX2 transcription factor is indispensable for skeletal development and controls bone formation by acting as a signaling hub and transcriptional regulator to coordinate target gene expression. A signaling partner of RUNX2 is the nuclear vitamin D receptor (VDR) that becomes active when bound by its ligand 1,25-dihydroxyvitamin D3 (VD3). RUNX2 and VDR unite to cooperatively regulate the expression of numerous genes. In this study, we overexpressed RUNX2 in NIH3T3 fibroblasts concomitantly treated with VD3 and show that RUNX2 alone, or in combination with VD3, failed to promote an osteoblastic phenotype in NIH3T3 cells. However, the expression of numerous osteoblast-related genes was up-regulated by RUNX2 and large-scale gene expression profiling using microarrays identified over 800 transcripts that displayed a twofold of greater change in expression in response to RUNX2 overexpression or VD3 treatment. Functional analysis using gene ontology (GO) revealed GO terms for ossification, cellular motility, biological adhesion, and chromosome organization were enriched in the pool of genes regulated by RUNX2. For the set of genes whose expression was modulated by VD3, the GO terms response to hormone stimulus, chemotaxis, and metalloendopeptidase activity where overrepresented. Our study provides a functional insight into the consequences of RUNX2 overexpression and VD3 treatment in NIH3T3 cells in addition to identifying candidate genes whose expression is controlled by either factor individually or through their functional cooperation.

Epigenetic Control of the Bone-master Runx2 Gene during Osteoblast-lineage Commitment by the Histone Demethylase JARID1B/KDM5B

Transcription factor Runx2 controls bone development and osteoblast differentiation by regulating expression of a significant number of bone-related target genes. Here, we report that transcriptional activation and repression of the Runx2 gene via its osteoblast-specific P1 promoter (encoding mRNA for the Runx2/p57 isoform) is accompanied by selective deposition and elimination of histone marks during differentiation of mesenchymal cells to the osteogenic and myoblastic lineages. These epigenetic profiles are mediated by key components of the Trithorax/COMPASS-like and Polycomb group complexes together with histone arginine methylases like PRMT5 and lysine demethylases like JARID1B/KDM5B. Importantly, knockdown of the H3K4me2/3 demethylase JARID1B, but not of the demethylases UTX and NO66, prevents repression of the Runx2 P1 promoter during myogenic differentiation of mesenchymal cells. The epigenetically forced expression of Runx2/p57 and osteocalcin, a classical bone-related target gene, under myoblastic-differentiation is accompanied by enrichment of the H3K4me3 and H3K27ac marks at the Runx2 P1 promoter region. Our results identify JARID1B as a key component of a potent epigenetic switch that controls mesenchymal cell fate into myogenic and osteogenic lineages.

Noncoding RNAs: Possible Players in the Development of Fluorosis

Fluorosis is caused by excess of fluoride intake over a long period of time. Aberrant change in the Runt-related transcription factor 2 (RUNX2) mediated signaling cascade is one of the decisive steps during the pathogenesis of fluorosis. Up to date, role of fluoride on the epigenetic alterations is not studied. In the present study, global expression profiling of short noncoding RNAs, in particular miRNAs and snoRNAs, was carried out in sodium fluoride (NaF) treated human osteosarcoma (HOS) cells to understand their possible role in the development of fluorosis. qPCR and in silico hybridization revealed that miR-124 and miR-155 can be directly involved in the transcriptional regulation of Runt-related transcription factor 2 (RUNX2) and receptor activator of nuclear factor κ-B ligand (RANKL) genes. Compared to control, C/D box analysis revealed marked elevation in the number of UG dinucleotides and D-box sequences in NaF exposed HOS cells. Herein, we report miR-124 and miR-155 as the new possible players involved in the development of fluorosis. We show that the alterations in UG dinucleotides and D-box sequences of snoRNAs could be due to NaF exposure.

Possible functional links among brain- and skull-related genes selected in modern humans

The sequencing of the genomes from extinct hominins has revealed that changes in some brain-related genes have been selected after the split between anatomically-modern humans and Neanderthals/Denisovans. To date, no coherent view of these changes has been provided. Following a line of research we initiated in Boeckx and Benítez-Burraco (2014a), we hypothesize functional links among most of these genes and their products, based on the existing literature for each of the gene discussed. The genes we focus on are found mutated in different cognitive disorders affecting modern populations and their products are involved in skull and brain morphology, and neural connectivity. If our hypothesis turns out to be on the right track, it means that the changes affecting most of these proteins resulted in a more globular brain and ultimately brought about modern cognition, with its characteristic generativity and capacity to form and exploit cross-modular concepts, properties most clearly manifested in language.

UV-activated 7-dehydrocholesterol-coated titanium implants promote differentiation of human umbilical cord mesenchymal stem cells into osteoblasts

Vitamin D metabolites are essential for bone regeneration and mineral homeostasis. The vitamin D precursor 7-dehydrocholesterol can be used after UV irradiation to locally produce active vitamin D by osteoblastic cells. Furthermore, UV-irradiated 7-dehydrocholesterol is a biocompatible coating for titanium implants with positive effects on osteoblast differentiation. In this study, we examined the impact of titanium implants surfaces coated with UV-irradiated 7-dehydrocholesterol on the osteogenic differentiation of human umbilical cord mesenchymal stem cells. First, the synthesis of cholecalciferol (D3) was achieved through the incubation of the UV-activated 7-dehydrocholesterol coating for 48 h at 23℃. Further, we investigated in vitro the biocompatibility of this coating in human umbilical cord mesenchymal stem cells and its potential to enhance their differentiation towards the osteogenic lineage. Human umbilical cord mesenchymal stem cells cultured onto UV-irradiated 7-dehydrocholesterol-coated titanium implants surfaces, combined with osteogenic supplements, upregulated the gene expression of several osteogenic markers and showed higher alkaline phosphatase activity and calcein blue staining, suggesting increased mineralization. Thus, our results show that the use of UV irradiation on 7-dehydrocholesterol -treated titanium implants surfaces generates a bioactive coating that promotes the osteogenic differentiation of human umbilical cord mesenchymal stem cells, with regenerative potential for improving osseointegration in titanium-based bone anchored implants.

Selective Distal Enhancer Control of the Mmp13 Gene Identified through Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR) Genomic Deletions

Matrix metalloproteinase 13 (Mmp13, collagenase-3) plays an essential role in bone metabolism and mineral homeostasis. It is regulated by numerous factors, including BMP-2, parathyroid hormone, and 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3), through transcription factors such as Runt-related transcription factor 2 (RUNX2), CCAAT/enhancer-binding protein β (C/EBPβ), OSX, and vitamin D receptor (VDR). During osteoblast maturation, the basal expression of Mmp13 and its sensitivity to 1,25(OH)2D3 are strikingly increased. In this report, ChIP-sequencing analysis in mouse preosteoblasts revealed that the Mmp13 gene was probably regulated by three major enhancers located -10, -20, and -30 kb upstream of the gene promoter, occupied by activated VDR and prebound C/EBPβ and RUNX2, respectively. Initially, bacterial artificial chromosome clone recombineering and traditional mutagenesis defined binding sites for VDR and RUNX2. We then employed a CRISPR/Cas9 gene editing approach to delete the -10 and -30 kb Mmp13 enhancers, a region proximal to the promoter, and VDR or RUNX2. VDR-mediated up-regulation of Mmp13 transcription was completely abrogated upon removal of the -10 kb enhancer, resulting in a 1,25(OH)2D3-directed repression of Mmp13. Deletion of either the -30 kb enhancer or RUNX2 resulted in a complete loss of basal transcript activity and a ChIP-identified destabilization of the chromatin enhancer environment and factor binding. Whereas enhancer deletions only affected Mmp13 expression, the RUNX2 deletion led to changes in gene expression, a reduction in cellular proliferation, and an inability to differentiate. We conclude that the Mmp13 gene is regulated via at least three specific distal enhancers that display independent activities yet are able to integrate response from multiple signaling pathways in a model of activation and suppression.

1,25-Dihydroxyvitamin D3 prevents bone loss of the secondary spongiosa in arthritic rats by an increase of bone formation and mineralization and inhibition of bone resorption

Background

Active vitamin D metabolites have been shown to have protective effects in experimental arthritis especially when used as preventive treatment. However, because the direct effects of 1,25-dihydroxyvitamin D3 (1,25(OH) ₂D₃) on bone formation and resorption are very complex, the net effect of 1,25(OH)₂D₃ on histomorphometric parameters of bone turnover and mineralisation should be investigated. Therefore, we examined the influence of 1,25(OH)₂D₃ therapy on arthritis-induced alterations of periarticular and axial bone as well as disease activity, inflammation and joint destruction in antigen-induced arthritis (AIA) of the rat.

Methods

AIA was induced in 20 eight-week-old female Wistar rats. 10 rats without arthritis were used as healthy controls. AIA rats received 1,25(OH)₂D₃ (0.2 μg/kg/day, i.p., n = 10) or vehicle (n = 10) at regular intervals for 28 consecutive days beginning 3 days before arthritis induction. Bone structure of the secondary spongiosa of the periarticular and axial bone was analyzed using histomorphometry. Parameters of mineralization were investigated using tetracycline labelling. Clinical disease activity, inflammation and joint destruction were measured by joint swelling and histological investigation, respectively.

Results

AIA led to significant periarticular bone loss. 1,25(OH)₂D₃ treatment resulted in a highly significant increase in trabecular bone volume and bone formation rate in comparison to both vehicle-treated AIA and healthy controls at periarticular (p < 0.01 and p < 0.001, respectively) and axial bone (p < 0.001 and p < 0.001, respectively). In addition, bone resorption was reduced by 1,25(OH)₂D₃ at the axial bone (p < 0.05 vs. vehicle-treated AIA). Joint swelling as well as histological signs of inflammation and joint destruction were not influenced by 1,25(OH)₂D₃.

Conclusions

The results of the study indicate a marked osteoanabolic effect of 1,25(OH)₂D₃ presumably due to a substantial increase in mineralization. Thus, 1,25(OH)₂D₃ may be an effective osteoanabolic treatment principle to antagonize the inflammation-associated suppression of bone formation in rheumatoid arthritis.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-345) contains supplementary material, which is available to authorized users.

Mitogen-activated protein kinase (MAPK)-regulated interactions between Osterix and Runx2 are critical for the transcriptional osteogenic program

The transcription factors Runx2 and Osx (Osterix) are required for osteoblast differentiation and bone formation. Runx2 expression occurs at early stages of osteochondroprogenitor determination, followed by Osx induction during osteoblast maturation. We demonstrate that coexpression of Osx and Runx2 leads to cooperative induction of expression of the osteogenic genes Col1a1, Fmod, and Ibsp. Functional interaction of Osx and Runx2 in the regulation of these promoters is mediated by enhancer regions with adjacent Sp1 and Runx2 DNA-binding sites. These enhancers allow formation of a cooperative transcriptional complex, mediated by the binding of Osx and Runx2 to their specific DNA promoter sequences and by the protein-protein interactions between them. We also identified the domains involved in the interaction between Osx and Runx2. These regions contain the amino acids in Osx and Runx2 known to be phosphorylated by p38 and ERK MAPKs. Inhibition of p38 and ERK kinase activities or mutation of their known phosphorylation sites in Osx or Runx2 strongly disrupts their physical interaction and cooperative transcriptional effects. Altogether, our results provide a molecular description of a mechanism for Osx and Runx2 transcriptional cooperation that is subject to further regulation by MAPK-activating signals during osteogenesis.

A functional N-terminal domain in C/EBPβ-LAP* is required for interacting with SWI/SNF and to repress Ric-8B gene transcription in osteoblasts

The chromatin remodeling complex SWI/SNF and the transcription factor C/EBPβ play critical roles in osteoblastic cells as they jointly control transcription of a number of bone-related target genes. The largest C/EBPβ isoform, LAP*, possesses a short additional N-terminal domain that has been proposed to mediate the interaction of this factor with SWI/SNF in myeloid cells. Here we examine the requirement of a functional N-terminus in C/EBPβ-LAP* for binding SWI/SNF and for recruiting this complex to the Ric-8B gene to mediate transcriptional repression. We find that both C/EBPβ-LAP* and SWI/SNF simultaneously bind to the Ric-8B promoter in differentiating osteoblasts that repress Ric-8B expression. This decreased expression of Ric-8B is not accompanied by significant changes in histone acetylation at the Ric-8B gene promoter sequence. A single aminoacid change at the C/EBPβ-LAP* N-terminus (R3L) that inhibits C/EBPβ-LAP*-SWI/SNF interaction, also prevents SWI/SNF recruitment to the Ric-8B promoter as well as C/EBPβ-LAP*-dependent repression of the Ric-8B gene. Inducible expression of the C/EBPβ-LAP*R3L protein in stably transfected osteoblastic cells demonstrates that this mutant protein binds to C/EBPβ-LAP*-target promoters and competes with the endogenous C/EBPβ factor. Together our results indicate that a functional N-terminus in C/EBPβ-LAP* is required for interacting with SWI/SNF and for Ric-8B gene repression in osteoblasts.

Glucocorticoids antagonize RUNX2 during osteoblast differentiation in cultures of ST2 pluripotent mesenchymal cells

The efficacy of glucocorticoids (GCs) in treating a wide range of autoimmune and inflammatory conditions is blemished by severe side effects, including osteoporosis. The chief mechanism leading to GC-induced osteoporosis is inhibition of bone formation, but the role of RUNX2, a master regulator of osteoblast differentiation and bone formation, has not been well studied. We assessed effects of the synthetic GC dexamethasone (dex) on transcription of RUNX2-stimulated genes during the differentiation of mesenchymal pluripotent cells into osteoblasts. Dex inhibited a RUNX2 reporter gene and attenuated locus-dependently RUNX2-driven expression of several endogenous target genes. The anti-RUNX2 activity of dex was not attributable to decreased RUNX2 expression, but rather to physical interaction between RUNX2 and the GC receptor (GR), demonstrated by co-immunoprecipitation assays and co-immunofluorescence imaging. Investigation of the RUNX2/GR interaction may lead to the development of bone-sparing GC treatment modalities for the management of autoimmune and inflammatory diseases.

Genomic occupancy of Runx2 with global expression profiling identifies a novel dimension to control of osteoblastogenesis

BACKGROUND

Osteogenesis is a highly regulated developmental process and continues during the turnover and repair of mature bone. Runx2, the master regulator of osteoblastogenesis, directs a transcriptional program essential for bone formation through genetic and epigenetic mechanisms. While individual Runx2 gene targets have been identified, further insights into the broad spectrum of Runx2 functions required for osteogenesis are needed.

RESULTS

By performing genome-wide characterization of Runx2 binding at the three major stages of osteoblast differentiation--proliferation, matrix deposition and mineralization--we identify Runx2-dependent regulatory networks driving bone formation. Using chromatin immunoprecipitation followed by high-throughput sequencing over the course of these stages, we identify approximately 80,000 significantly enriched regions of Runx2 binding throughout the mouse genome. These binding events exhibit distinct patterns during osteogenesis, and are associated with proximal promoters and also non-promoter regions: upstream, introns, exons, transcription termination site regions, and intergenic regions. These peaks were partitioned into clusters that are associated with genes in complex biological processes that support bone formation. Using Affymetrix expression profiling of differentiating osteoblasts depleted of Runx2, we identify novel Runx2 targets including Ezh2, a critical epigenetic regulator; Crabp2, a retinoic acid signaling component; Adamts4 and Tnfrsf19, two remodelers of the extracellular matrix. We demonstrate by luciferase assays that these novel biological targets are regulated by Runx2 occupancy at non-promoter regions.

CONCLUSIONS

Our data establish that Runx2 interactions with chromatin across the genome reveal novel genes, pathways and transcriptional mechanisms that contribute to the regulation of osteoblastogenesis.

Differential effects of RUNX2 on the androgen receptor in prostate cancer: synergistic stimulation of a gene set exemplified by SNAI2 and subsequent invasiveness

Changes to androgen signaling during prostate carcinogenesis are associated with both inhibition of cellular differentiation and promotion of malignant phenotypes. The androgen receptor (AR)-binding transcription factor RUNX2 has been linked to prostate cancer progression but the underlying mechanisms have not been fully defined. In this study, we investigated the genome-wide influence of RUNX2 on androgen-induced gene expression and AR DNA binding in prostate cancer cells. RUNX2 inhibited the androgen response partly by promoting the dissociation of AR from its target genes such as the tumor suppressor NKX3-1. However, AR activity persists in the presence of RUNX2 at other AR target genes, some of which are cooperatively stimulated by androgen and RUNX2 signaling. These genes are associated with putative enhancers co-occupied by AR and RUNX2. One such gene, the invasion-promoting Snail family transcription factor SNAI2, was co-activated by AR and RUNX2. Indeed, these two transcription factors together, but neither alone stimulated prostate cancer cell invasiveness, which could be abolished by SNAI2 silencing. Furthermore, an immunohistochemical analysis of SNAI2 in archived primary prostate cancer specimens revealed a correlation with the RUNX2 histoscore, and simultaneous strong staining for SNAI2, RUNX2, and AR (but not any pair alone) was associated with disease recurrence. Overall, our findings suggest cooperation between AR and RUNX in the stimulation of oncogenes such as SNAI2, which might be targeted for individualized prostate cancer therapy.

Functional cooperation between vitamin D receptor and Runx2 in vitamin D-induced vascular calcification

The transdifferentiation of vascular smooth muscle cells (VSMCs) into osteoblast-like cells has been implicated in the context of vascular calcification. We investigated the roles of vitamin D receptor (Vdr) and runt-related transcription factor 2 (Runx2) in the osteoblastic differentiation of VSMCs in response to vitamin D₃ using in vitro VSMCs cultures and in vivo in Vdr knockout (Vdr^-/-) and Runx2 carboxy-terminus truncated heterozygous (Runx2^+/ΔC) mice. Treatment of VSMCs with active vitamin D₃ promoted matrix mineral deposition, and increased the expressions of Vdr, Runx2, and of osteoblastic genes but decreased the expression of smooth muscle myosin heavy chain in primary VSMCs cultures. Immunoprecipitation experiments suggested an interaction between Vdr and Runx2. Furthermore, silencing Vdr or Runx2 attenuated the procalcific effects of vitamin D₃. Functional cooperation between Vdr and Runx2 in vascular calcification was also confirmed in in vivo mouse models. Vascular calcification induced by high-dose vitamin D₃ was completely inhibited in Vdr^-/- or Runx2^+/ΔC mice, despite elevated levels of serum calcium or alkaline phosphatase. Collectively, these findings suggest that functional cooperation between Vdr and Runx2 is necessary for vascular calcification in response to vitamin D₃.

Enhanced CRAd activity using enhancer motifs driven by a nucleosome positioning sequence

Cancer development involves changes driven by the epigenetic machinery, including nucleosome positioning. Recently, the concept that adenoviral replication may be driven by tumor specific promoters (TSPs) gained support, and several conditionally replicative adenoviruses (CRAd) exhibited therapeutic efficacy in clinical trials. Here, we show for the first time that placing a nucleosome positioning sequence (NPS) upstream of a TSP combined with Wnt-responsive motifs (pART enhancer) enhanced the TSP transcriptional activity and increased the lytic activity of a CRAd. pART enhanced the transcriptional activity of the gastrointestinal cancer (GIC)-specific REG1A promoter (REG1A-pr); moreover, pART also increased the in vitro lytic activity of a CRAd whose replication was driven by REG1A-Pr. The pART enhancer effect in vitro and in vivo was strictly dependent on the presence of the NPS. Indeed, deletion of the NPS was strongly deleterious for the in vivo antitumor efficacy of the CRAd on orthotopically established pancreatic xenografts. pART also enhanced the specific activity of other heterologous promoters; moreover, the NPS was also able to enhance the responsiveness of hypoxia- and NFκB-response elements. We conclude that NPS could be useful for gene therapy approaches in cancer as well as other diseases.

Osteocalcin: skeletal and extra-skeletal effects

Osteocalcin (OC) is a non-collagenous, vitamin K-dependent protein secreted in the late stage of osteoblasts differentiation. The presence of the three residues of γ-carbossiglutamatic acid, specific of the active form of OC protein, allows the protein to bind calcium and consequently hydroxyapatite. The osteoblastic OC protein is encoded by the bone γ-carbossiglutamate gene whose transcription is principally regulated by the Runx2/Cbfa1 regulatory element and stimulated by vitamin D(3) through a steroid-responsive enhancer sequence. Even if data obtained in literature are controversial, the dual role of OC in bone can be presumed as follows: firstly, OC acts as a regulator of bone mineralization; secondly, OC regulates osteoblast and osteoclast activity. Recently the metabolic activity of OC, restricted to the un-carboxylated form has been demonstrated in osteoblast-specific knockout mice. This effect is mediated by the regulation of pancreatic β-cell proliferation and insulin secretion and adiponectin production by adipose tissue and leads to the regulation of glucose metabolism and fat mass. Nevertheless, clinical human studies only demonstrated the correlation between OC levels and factors related to energy metabolism. Thus further investigations in humans are required to demonstrate the role of OC in the regulation of human energy metabolism. Moreover, it is presumable that OC also acts on blood vessels by inducing angiogenesis and pathological mineralization. This review highlights the recent studies concerning skeletal and extra-skeletal effects of OC.

Nuclear receptors in bone physiology and diseases

During the last decade, our view on the skeleton as a mere solid physical support structure has been transformed, as bone emerged as a dynamic, constantly remodeling tissue with systemic regulatory functions including those of an endocrine organ. Reflecting this remarkable functional complexity, distinct classes of humoral and intracellular regulatory factors have been shown to control vital processes in the bone. Among these regulators, nuclear receptors (NRs) play fundamental roles in bone development, growth, and maintenance. NRs are DNA-binding transcription factors that act as intracellular transducers of the respective ligand signaling pathways through modulation of expression of specific sets of cognate target genes. Aberrant NR signaling caused by receptor or ligand deficiency may profoundly affect bone health and compromise skeletal functions. Ligand dependency of NR action underlies a major strategy of therapeutic intervention to correct aberrant NR signaling, and significant efforts have been made to design novel synthetic NR ligands with enhanced beneficial properties and reduced potential negative side effects. As an example, estrogen deficiency causes bone loss and leads to development of osteoporosis, the most prevalent skeletal disorder in postmenopausal women. Since administration of natural estrogens for the treatment of osteoporosis often associates with undesirable side effects, several synthetic estrogen receptor ligands have been developed with higher therapeutic efficacy and specificity. This review presents current progress in our understanding of the roles of various nuclear receptor-mediated signaling pathways in bone physiology and disease, and in development of advanced NR ligands for treatment of common skeletal disorders.

Discovery of novel vitamin D receptor interacting proteins that modulate 1,25-dihydroxyvitamin D3 signaling

The nuclear vitamin D receptor (VDR) modulates gene transcription in 1,25-dihydroxyvitamin D(3) (1,25D) target tissues such as kidney, intestine, and bone. VDR is also expressed in heart, and 1,25D deficiency may play a role in the acceleration of cardiovascular disease. Employing a yeast two-hybrid system and a human heart library, using both a 1,25D-independent and 1,25D-dependent screen, we discovered six candidate VDR interacting proteins (VIPs). These novel VIPs include CXXC5, FASTK, NR4A1, TPM2, MYL3 and XIRP1. Mammalian two-hybrid assays as well as GST pull-downs were used to confirm VIP-VDR interaction, and the combination of these two assays reveals that CXXC5, XIRP1, FASTK and NR4A1 interactions with VDR may be modulated by 1,25D. The functional effects of these VIPs on 1,25D-mediated gene expression were explored in transcriptional assays employing three separate and distinct 1,25D-responsive element (VDRE)-driven luciferase reporter genes in transfected Caco-2 and HEK-293 cells, and in a C2C12 myoblast line. FASTK and TPM2 activated expression in all cell line and promoter contexts, while CXXC5 and XIRP1 exhibited differing effects depending on the cell line and promoter employed, suggesting promoter and cell-specific effects of these unique VIPs on VDR signaling. Further evaluation of the interaction between CXXC5 and VDR revealed that CXXC5 acts in a dose-dependent manner to stimulate VDR-mediated transcription on select VDREs. Identification of novel heart VIPs and their influence on VDR activity may increase our understanding of how vitamin D impacts cardiac physiology and may facilitate development of VDR/VIP drug analogs to combat heart disease.