Advances in Runx2 regulation and its isoforms

RUNX2 regulation in osteoblast differentiation: A possible therapeutic function of the lncRNA and miRNA-mediated network

Osteogenic differentiation is a crucial process in the formation of the skeleton and the remodeling of bones. It relies on a complex system of signaling pathways and transcription factors, including Runt-related transcription factor 2 (RUNX2). Non-coding RNAs (ncRNAs) control the bone-specific transcription factor RUNX2 through post-transcriptional mechanisms to regulate osteogenic differentiation. The most research has focused on microRNAs (miRNAs) and long ncRNAs (lncRNAs) in studying how they regulate RUNX2 for osteogenesis in both normal and pathological situations. This article provides a concise overview of the recent advancements in understanding the critical roles of lncRNA/miRNA/axes in controlling the expression of RUNX2 during bone formation. The possible application of miRNAs and lncRNAs as therapeutic agents for the treatment of disorders involving the bones and bones itself is also covered.

MiRNAs Expression Modulates Osteogenesis in Response to Exercise and Nutrition

In recent years, many articles have been published describing the impact of physical activity and diet on bone health. This review has aimed to figure out the possible epigenetic mechanisms that influence bone metabolism. Many studies highlighted the effects of macro and micronutrients combined with exercise on the regulation of gene expression through miRs. The present review will describe how physical activity and nutrition can prevent abnormal epigenetic regulation that otherwise could lead to bone-metabolism-related diseases, the most significant of which is osteoporosis. Nowadays, it is known that this effect can be carried out not only by endogenously produced miRs, but also through those intakes through the diet. Indeed, they have also been found in the transcriptome of animals and plants, and it is possible to hypothesise an interaction between miRNAs produced by different kingdoms and epigenetic influences on human gene expression. In particular, the key to the activation pathways triggered by diet and physical activity appears to be the activation of Runt-related transcription factor 2 (RUNX2), the expression of which is regulated by several miRs. Among the main miRs involved are exercise-induced miR21 and 21-5p, and food-induced miR 221-3p and 222-3p.

YBX1 Promotes the Inclusion of RUNX2 Alternative Exon 5 in Dental Pulp Stem Cells

Background and Objectives

RUNX2 plays an essential role during the odontoblast differentiation of dental pulp stem cells (DPSCs). RUNX2 Exon 5 is an alternative exon and essential for RUNX2 transcriptional activity. This study aimed to investigate the regulatory mechanisms of RUNX2 exon 5 alternative splicing in human DPSCs.

Methods and Results

The regulatory motifs of RUNX2 exon 5 were analyzed using the online SpliceAid program. The alternative splicing of RUNX2 exon 5 in DPSCs during mineralization-induced differentiation was analyzed by RT-PCR. To explore the effect of splicing factor YBX1 on exon 5 alternative splicing, gaining or losing function of YBX1 was performed by transfection of YBX1 overexpression plasmid or anti-YBX1 siRNA in DPSCs. Human RUNX2 exon 5 is evolutionarily conserved and alternatively spliced in DPSCs. There are three potential YBX1 binding motifs in RUNX2 exon 5. The inclusion of RUNX2 exon 5 and YBX1 expression level increased significantly during mineralization- induced differentiation in DPSCs. Overexpression of YBX1 significantly increased the inclusion of RUNX2 exon 5 in DPSCs. In contrast, silence of YBX1 significantly reduced the inclusion of exon 5 and the corresponding RUNX2 protein expression level. Knockdown of YBX1 reduced the expression of alkaline phosphatase (ALP) and osteocalcin (OC) and the mineralization ability of DPSCs, while overexpression of YBX1 increased the expression of ALP and OC and the mineralization ability of DPSCs.

Conclusions

Human RUNX2 exon 5 is conserved evolutionarily and alternatively spliced in DPSCs. Splicing factor YBX1 promotes the inclusion of RUNX2 exon 5 and improves the mineralization ability of DPSCs.

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.

Identification of a Novel Splice Site Mutation in RUNX2 Gene in a Family with Rare Autosomal Dominant Cleidocranial Dysplasia

Background:

Pathogenic variants of RUNX2, a gene that encodes an osteoblast-specific transcription factor, have been shown as the cause of CCD, which is a rare hereditary skeletal and dental disorder with dominant mode of inheritance and a broad range of clinical variability. Due to the relative lack of clinical complications resulting in CCD, the medical diagnosis of this disorder is challenging, which leaves it underdiagnosed.

Methods:

In this study, nine healthy and affected members of an Iranian family were investigated. PCR and sequencing of all exons and exon-intron boundaries of RUNX2 (NM_001024630) gene was performed on proband. Co-segregation analysis was conducted in the other family members for the identified variant. Additionally, a cohort of 100 Iranian ethnicity-matched healthy controls was screened by ARMS-PCR method.

Results:

The novel splice site variant (c.860-2A>G), which was identified in the intron 6 of RUNX2 gene, co-segregated with the disease in the family, and it was absent in healthy controls. Pathogenicity of this variant was determined by several software, including HSF, which predicts the formation or disruption of splice donor sites, splice acceptor sites, exonic splicing silencer sites, and exonic splicing enhancer sites. In silico analysis predicted this novel variant to be disease causing.

Conclusion:

The identified variant is predicted to have an effect on splicing, which leads to exon skipping and producing a truncated protein via introducing a premature stop codon.

Evolution and expansion of the RUNX2 QA repeat corresponds with the emergence of vertebrate complexity

Runt-related transcription factor 2 (RUNX2) is critical for the development of the vertebrate bony skeleton. Unlike other RUNX family members, RUNX2 possesses a variable poly-glutamine, poly-alanine (QA) repeat domain. Natural variation within this repeat is able to alter the transactivation potential of RUNX2, acting as an evolutionary 'tuning knob' suggested to influence mammalian skull shape. However, the broader role of the RUNX2 QA repeat throughout vertebrate evolution is unknown. In this perspective, we examine the role of the RUNX2 QA repeat during skeletal development and discuss how its emergence and expansion may have facilitated the evolution of morphological novelty in vertebrates.

Comprehensive In Vitro Testing of Calcium Phosphate-Based Bioceramics with Orthopedic and Dentistry Applications

Recently, a large spectrum of biomaterials emerged, with emphasis on various pure, blended, or doped calcium phosphates (CaPs). Although basic cytocompatibility testing protocols are referred by International Organization for Standardization (ISO) 10993 (parts 1-22), rigorous in vitro testing using cutting-edge technologies should be carried out in order to fully understand the behavior of various biomaterials (whether in bulk or low-dimensional object form) and to better gauge their outcome when implanted. In this review, current molecular techniques are assessed for the in-depth characterization of angiogenic potential, osteogenic capability, and the modulation of oxidative stress and inflammation properties of CaPs and their cation- and/or anion-substituted derivatives. Using such techniques, mechanisms of action of these compounds can be deciphered, highlighting the signaling pathway activation, cross-talk, and modulation by microRNA expression, which in turn can safely pave the road toward a better filtering of the truly functional, application-ready innovative therapeutic bioceramic-based solutions.

HDACs control RUNX2 expression in cancer cells through redundant and cell context-dependent mechanisms

Background

RUNX2 is a Runt-related transcription factor required during embryogenesis for skeletal development and morphogenesis of other organs including thyroid and breast gland. Consistent evidence indicates that RUNX2 expression is aberrantly reactivated in cancer and supports tumor progression. The mechanisms leading to RUNX2 expression in cancer has only recently began to emerge. Previously, we showed that suppressing the activity of the epigenetic regulators HDACs significantly represses RUNX2 expression highlighting a role for these enzymes in RUNX2 reactivation in cancer. However, the molecular mechanisms by which HDACs control RUNX2 are still largely unexplored. Here, to fill this gap, we investigated the role of different HDACs in RUNX2 expression regulation in breast and thyroid cancer, tumors that majorly rely on RUNX2 for their development and progression.

Methods

Proliferation assays and evaluation of RUNX2 mRNA levels by qRT-PCR were used to evaluate the effect of several HDACi and specific siRNAs on a panel of cancer cell lines. Moreover, ChIP and co-IP assays were performed to elucidate the molecular mechanism underneath the RUNX2 transcriptional regulation. Finally, RNA-sequencing unveiled a new subset of genes whose transcription is regulated by the complex RUNX2-HDAC6.

Results

In this study, we showed that Class I HDACs and in particular HDAC1 are required for RUNX2 efficient transcription in cancer. Furthermore, we found an additional and cell-specific function of HDAC6 in driving RUNX2 expression in thyroid cancer cells. In this model, HDAC6 likely stabilizes the assembly of the transcriptional complex, which includes HDAC1, on the RUNX2 P2 promoter potentiating its transcription. Since a functional interplay between RUNX2 and HDAC6 has been suggested, we used RNA-Seq profiling to consolidate this evidence in thyroid cancer and to extend the knowledge on this cooperation in a setting in which HDAC6 also controls RUNX2 expression.

Conclusions

Overall, our data provide new insights into the molecular mechanisms controlling RUNX2 in cancer and consolidate the rationale for the use of HDACi as potential pharmacological strategy to counteract the pro-oncogenic program controlled by RUNX2 in cancer cells.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1350-5) contains supplementary material, which is available to authorized users.

Regulation of Runx2 by MicroRNAs in osteoblast differentiation

Bone is one of the most dynamic organs in the body that continuously undergoes remodeling through bone formation and resorption. A cascade of molecules and pathways results in the osteoblast differentiation that is attributed to osteogenesis, or bone formation. The process of osteogenesis is achieved through participation of the Wnt pathway, FGFs, BMPs/TGF-β, and transcription factors such as Runx2 and Osx. The activity and function of the master transcription factor, Runx2, is of utmost significance as it can induce the function of osteoblast differentiation markers. A number of microRNAs [miRNAs] have been recently identified in the regulation of Runx2 expression/activity, thus affecting the process of osteogenesis. miRNAs that target Runx2 corepressors favor osteogenesis, while miRNAs that target Runx2 coactivators inhibit osteogenesis. In this review, we focus on the regulation of Runx2 by miRNAs in osteoblast differentiation and their potential for treating bone and bone-related diseases.

Role of RUNX2 transcription factor in epithelial mesenchymal transition in non-small cell lung cancer: Epigenetic control of the RUNX2 P1 promoter

Lung cancer has a high mortality rate in men and women worldwide. Approximately 15% of diagnosed patients with this type of cancer do not exceed the 5-year survival rate. Unfortunately, diagnosis is established in advanced stages, where other tissues or organs can be affected. In recent years, lineage-specific transcription factors have been associated with a variety of cancers. One such transcription factor possibly regulating cancer is RUNX2, the master gene of early and late osteogenesis. In thyroid and prostate cancer, it has been reported that RUNX2 regulates expression of genes important in tumor cell migration and invasion. In this study, we report on RUNX2/ p57 overexpression in 16 patients with primary non-small cell lung cancer and/or metastatic lung cancer associated with H3K27Ac at P1 gene promoter region. In some patients, H3K4Me3 enrichment was also detected, in addition to WDR5, MLL2, MLL4, and UTX enzyme recruitment, members of the COMPASS-LIKE complex. Moreover, transforming growth factor-β induced RUNX2/ p57 overexpression and specific RUNX2 knockdown supported a role for RUNX2 in epithelial mesenchymal transition, which was demonstrated through loss of function assays in adenocarcinoma A549 lung cancer cell line. Furthermore, RUNX2 increased expression of epithelial mesenchymal transition genes VIMENTIN, TWIST1, and SNAIL1, which reflected increased migratory capacity in lung adenocarcinoma cells.

Metabolomics profiling of cleidocranial dysplasia

OBJECTIVES

Cleidocranial dysplasia (CCD) is a rare autosomal-dominantly inherited skeletal dysplasia that is predominantly associated with heterozygous mutations of RUNX2. However, no information is available regarding metabolic changes associated with CCD at present.

MATERIALS AND METHODS

We analyzed members of a CCD family and checked for mutations in the RUNX2 coding sequence using the nucleotide BLAST program. The 3D protein structure of mutant RUNX2 was predicted by I-TASSER. Finally, we analyzed metabolites extracted from plasma using LC-MS/MS.

RESULTS

We identified a novel mutation (c.1061insT) that generates a premature termination in the RUNX2 coding region, which, based on protein structure prediction models, likely alters the protein's function. Interestingly, metabolomics profiling indicated that 30 metabolites belonging to 13 metabolic pathways were significantly changed in the CCD patients compared to normal controls.

CONCLUSIONS

The results highlight interesting correlations between a RUNX2 mutation, metabolic changes, and the clinical features in a family with CCD. The results also contribute to our understanding of the pathogenetic processes underlying this rare disorder.

CLINICAL RELEVANCE

This study provides the first metabolomics profiling in CCD patients, expands our insights into the pathogenesis of the disorder, may help in diagnostics and its refinements, and may lead to novel therapeutic approaches to CCD.

RUNX2 expression in thyroid and breast cancer requires the cooperation of three non-redundant enhancers under the control of BRD4 and c-JUN

Aberrant reactivation of embryonic pathways is a common feature of cancer. RUNX2 is a transcription factor crucial during embryogenesis that is aberrantly reactivated in many tumors, including thyroid and breast cancer, where it promotes aggressiveness and metastatic spreading. Currently, the mechanisms driving RUNX2 expression in cancer are still largely unknown. Here we showed that RUNX2 transcription in thyroid and breast cancer requires the cooperation of three distantly located enhancers (ENHs) brought together by chromatin three-dimensional looping. We showed that BRD4 controls RUNX2 by binding to the newly identified ENHs and we demonstrated that the anti-proliferative effects of bromodomain inhibitors (BETi) is associated with RUNX2 transcriptional repression. We demonstrated that each RUNX2 ENH is potentially controlled by a distinct set of TFs and we identified c-JUN as the principal pivot of this regulatory platform. We also observed that accumulation of genetic mutations within these elements correlates with metastatic behavior in human thyroid tumors. Finally, we identified RAINs, a novel family of ENH-associated long non-coding RNAs, transcribed from the identified RUNX2 regulatory unit. Our data provide a new model to explain how RUNX2 expression is reactivated in thyroid and breast cancer and how cancer-driving signaling pathways converge on the regulation of this gene.

Facing the facts: The Runx2 gene is associated with variation in facial morphology in primates

The phylogenetic and adaptive factors that cause variation in primate facial form-including differences among the major primate clades and variation related to feeding and/or social behavior-are relatively well understood. However, comparatively little is known about the genetic mechanisms that underlie diversity in facial form in primates. Because it is essential for osteoblastic differentiation and skeletal development, the runt-related transcription factor 2 (Runx2) is one gene that may play a role in these genetic mechanisms. Specifically, polymorphisms in the QA ratio (determined by the ratio of the number of polyglutamines to polyalanines in one functional domain of Runx2) have been shown to be correlated with variation in facial length and orientation in other mammal groups. However, to date, the relationship between variation in this gene and variation in facial form in primates has not been explicitly tested. To test the hypothesis that the QA ratio is correlated with facial form in primates, the current study quantified the QA ratio, facial length, and facial angle in a sample of 33 primate species and tested for correlation using phylogenetic generalized least squares. The results indicate that the QA ratio of the Runx2 gene is positively correlated with variation in relative facial length in anthropoid primates. However, no correlation was found in strepsirrhines, and there was no correlation between facial angle and the QA ratio in any groups. These results suggest that, in primates, the QA ratio of the Runx2 gene may play a role in modulating facial size, but not facial orientation. This study therefore provides important clues about the genetic and developmental mechanisms that may underlie variation in facial form in primates.

Runx2-I is an Early Regulator of Epithelial-Mesenchymal Cell Transition in the Chick Embryo

BACKGROUND

Although normally linked to bone and cartilage development, the Runt-related transcription factor, RUNX2, was reported in the mouse heart during development of the valves. We examined RUNX2 expression and function in the developing avian heart as it related to the epithelial-mesenchymal transition (EMT) in the atrioventricular canal. EMT can be separated into an activation stage involving hypertrophy and cell separation and an invasion stage where cells invade the extracellular matrix. The localization and activity of RUNX2 was explored in relation to these steps in the heart. As RUNX2 was also reported in cancer tissues, we examined its expression in the progression of esophageal cancer in staged tissues.

RESULTS

A specific isoform, RUNX2-I, is present and required for EMT by endothelia of the atrioventricular canal. Knockdown of RUNX2-I inhibits the cell-cell separation that is characteristic of initial activation of EMT. Loss of RUNX2-I altered expression of EMT markers to a greater extent during activation than during subsequent cell invasion. Transforming growth factor beta 2 (TGFβ2) mediates activation during cardiac endothelial EMT. Consistent with a role in activation, RUNX2-I is regulated by TGFβ2 and its activity is independent of similarly expressed Snai2 in regulation of EMT. Examination of RUNX2 expression in esophageal cancer showed its upregulation concomitant with the development of dysplasia and continued expression in adenocarcinoma.

CONCLUSIONS

These data introduce the RUNX2-I isoform as a critical early transcription factor mediating EMT in the developing heart after induction by TGFβ2. Its expression in tumor tissue suggests a similar role for RUNX2 in the EMT of metastasis. Developmental Dynamics 247:542-554, 2018. © 2017 Wiley Periodicals, Inc.

Vitamin D Effects on Osteoblastic Differentiation of Mesenchymal Stem Cells from Dental Tissues

1α,25-Dihydroxyvitamin D₃ (1,25(OH)₂D₃), the active metabolite of vitamin D (Vit D), increases intestinal absorption of calcium and phosphate, maintaining a correct balance of bone remodeling. Vit D has an anabolic effect on the skeletal system and is key in promoting osteoblastic differentiation of human Mesenchymal Stem Cells (hMSCs) from bone marrow. MSCs can be also isolated from the immature form of the tooth, the dental bud: Dental Bud Stem Cells (DBSCs) are adult stem cells that can effectively undergo osteoblastic differentiation. In this work we investigated the effect of Vit D on DBSCs differentiation into osteoblasts. Our data demonstrate that DBSCs, cultured in an opportune osteogenic medium, differentiate into osteoblast-like cells; Vit D treatment stimulates their osteoblastic features, increasing the expression of typical markers of osteoblastogenesis like RUNX2 and Collagen I (Coll I) and, in a more important way, determining a higher production of mineralized matrix nodules.

Systematic Analysis of Known and Candidate Lysine Demethylases in the Regulation of Myoblast Differentiation

Histone methylation dynamics plays a critical role in cellular programming during development. For example, specific lysine methyltransferases (KMTs) and lysine demethylases (KDMs) have been implicated in the differentiation of mesenchymal stem cells into various cell lineages. However, a systematic and functional analysis for an entire family of KMT or KDM enzymes has not been performed. Here, we test the function of all the known and candidate KDMs in myoblast and osteoblast differentiation using the C2C12 cell differentiation model system. Our analysis identified that LSD1 is the only KDM required for myogenic differentiation and that KDM3B, KDM6A, and KDM8 are the candidate KDMs required for osteoblast differentiation. We find that LSD1, via H3K4me1 demethylation, represses the master regulator of osteoblast differentiation RUNX2 to promote myogenesis in the C2C12 model system. Finally, MLL4 is required for efficient osteoblast differentiation in part by countering LSD1 H3K4me1 demethylation at the RUNX2 enhancer. Together, our findings provide additional mechanisms by which lysine methylation signaling impacts on cell fate decisions.

Thyroid Hormone Receptor-β (TRβ) Mediates Runt-Related Transcription Factor 2 (Runx2) Expression in Thyroid Cancer Cells: A Novel Signaling Pathway in Thyroid Cancer

Dysregulation of the thyroid hormone receptor (TR)β is common in human cancers. Restoration of functional TRβ delays tumor progression in models of thyroid and breast cancers implicating TRβ as a tumor suppressor. Conversely, aberrant expression of the runt-related transcription factor 2 (Runx2) is established in the progression and metastasis of thyroid, breast, and other cancers. Silencing of Runx2 diminishes tumor invasive characteristics. With TRβ as a tumor suppressor and Runx2 as a tumor promoter, a compelling question is whether there is a functional relationship between these regulatory factors in thyroid tumorigenesis. Here, we demonstrated that these proteins are reciprocally expressed in normal and malignant thyroid cells; TRβ is high in normal cells, and Runx2 is high in malignant cells. T3 induced a time- and concentration-dependent decrease in Runx2 expression. Silencing of TRβ by small interfering RNA knockdown resulted in a corresponding increase in Runx2 and Runx2-regulated genes, indicating that TRβ levels directly impact Runx2 expression and associated epithelial to mesenchymal transition molecules. TRβ specifically bound to 3 putative thyroid hormone-response element motifs within the Runx2-P1 promoter ((-)105/(+)133) as detected by EMSA and chromatin immunoprecipitation. TRβ suppressed Runx2 transcriptional activities, thus confirming TRβ regulation of Runx2 at functional thyroid hormone-response elements. Significantly, these findings indicate that a ratio of the tumor-suppressor TRβ and tumor-promoting Runx2 may reflect tumor aggression and serve as biomarkers in biopsy tissues. The discovery of this TRβ-Runx2 signaling supports the emerging role of TRβ as a tumor suppressor and reveals a novel pathway for intervention.

Multiple copy number variants in a pediatric patient with Hb H disease and intellectual disability

Two distinct syndromes that link α-thalassemia and intellectual disability (ID) have been described: ATR-X, due to mutations in the ATRX gene, and ATR-16, a contiguous gene deletion syndrome in the telomeric region of the short arm of chromosome 16. A critical region where the candidate genes for the ID map has been established. In a pediatric patient with Hemoglobin H disease, dysmorphic features and ID, 4 novel and clinically relevant Copy Number Variants were identified. PCR-GAP, MLPA and FISH analyses established the cause of the α-thalassemia. SNP-array analysis revealed the presence of 4 altered loci: 3 deletions (arr[hg19]Chr16(16p13.3; 88,165-1,507,988) x1; arr[hg19]Chr6(6p21.1; 44,798,701-45,334,537) x1 and arr[hg19]Chr17(17q25.3; 80,544,855-81,057,996) x1) and a terminal duplication (arr[hg19]Chr7(7p22.3-p22.2; 4,935-4,139,785) x3). The -α(3.7) mutation and the ∼1.51 Mb in 16p13.3 are involved in the alpha-thalassemic phenotype. However, the critical region for ATR-16 cannot be narrowed down. The deletion affecting 6p21.1 removes the first 2 exons and part of intron 2 of the RUNX2 gene. Although heterozygous loss of function mutations affecting this gene have been associated with cleidocranial dysplasia, the patient does not exhibit pathognomonic signs of this syndrome, possibly due to the fact that the isoform d of the transcription factor remains unaffected. This work highlights the importance of searching for cryptic deletions in patients with ID and reiterates the need of the molecular analysis when it is associated to microcytic hypochromic anemia with normal iron status.

Histone Deacetylase Inhibitors Repress Tumoral Expression of the Proinvasive Factor RUNX2

Aberrant reactivation of embryonic pathways occurs commonly in cancer. The transcription factor RUNX2 plays a fundamental role during embryogenesis and is aberrantly reactivated during progression and metastasization of different types of human tumors. In this study, we attempted to dissect the molecular mechanisms governing RUNX2 expression and its aberrant reactivation. We identified a new regulatory enhancer element, located within the RUNX2 gene, which is responsible for the activation of the RUNX2 promoter and for the regulation of its expression in cancer cells. Furthermore, we have shown that treatment with the anticancer compounds histone deacetylase inhibitor (HDACi) results in a profound inhibition of RUNX2 expression, which is determined by the disruption of the transcription-activating complex on the identified enhancer. These data envisage a possible targeting strategy to counteract the oncongenic function of RUNX2 in cancer cells and provide evidence that the cytotoxic activity of HDACi in cancer is not only dependent on the reactivation of silenced oncosuppressors but also on the repression of oncogenic factors that are necessary for survival and progression.

Vascular calcification is coupled with phenotypic conversion of vascular smooth muscle cells through Klf5-mediated transactivation of the Runx2 promoter

Both Klf5 (Krüppel-like factor 5) and Runx2 are involved in phenotypic switching of VSMC (vascular smooth muscle cells). However, the potential link between Klf5 and Runx2 in mediating vascular calcification remains unclear. The aim of the present study was to elucidate the actual relationship between Klf5 and Runx2 in mediating VSMC calcification. We found that high Pi (phosphate) increased the expression of Klf5, which is accompanied by loss of SM α-actin and SM22α (smooth muscle 22 α), as well as gain of Runx2 expression. Overexpression of Klf5 increased, while knockdown of Klf5 decreased, Runx2 expression and calcification. Further study showed that Klf5 bound directly to the Runx2 promoter and activated its transcription. Klf5 was also induced markedly in the calcified aorta of adenine-induced uremic rats. In conclusion, we demonstrate a critical role for Klf5-mediated induction of Runx2 in high Pi -induced VSMC calcification.

HIV and Bone Disease: A Perspective of the Role of microRNAs in Bone Biology upon HIV Infection

Increased life expectancy and the need for long-term antiretroviral therapy have brought new challenges to the clinical management of HIV-infected individuals. The prevalence of osteoporosis and fractures is increased in HIV-infected patients; thus optimal strategies for risk management and treatment in this group of patients need to be defined. Prevention of bone loss is an important component of HIV care as the HIV population grows older. Understanding the mechanisms by which HIV infection affects bone biology leading to osteoporosis is crucial to delineate potential adjuvant treatments. This review focuses on HIV-induced osteoporosis within the context of microRNAs (miRNAs) by reviewing first basic concepts of bone biology as well as current knowledge of the role of miRNAs in bone development. Evidence that HIV-associated osteoporosis is in part independent of therapies employed to treat HIV (HAART) is supported by cross-sectional and longitudinal studies and is the focus of this review.

Runx-2 gene expression is associated with age-related changes of bone mineral density in the healthy young-adult population

Bone mineral density (BMD) and peak bone mass (PBM) are important determinants of skeletal resistance. The development of bone densitometry improved the possibility of studying BMD and the influence of genetic and environmental factors on bone. Heredity factors are important for BMD, and Runx-2 is accepted as a regulator of osteoblasts and bone formation. The aim of our study was to evaluate the behavior of Runx-2 during skeletal maturity in the healthy young-adult population. We analyzed spine and hip BMD in 153 volunteers, 98 women and 55 men, using dual-energy X-ray absorptiometry. In a subgroup of these volunteers, a sample of peripheral blood was taken to perform gene expression analysis of Runx-2 both in peripheral mesenchymal stem cells (MSCs; 28 subjects) and in peripheral mononuclear cells (PBMCs; 140 subjects). In our work BMD was comparable in both genders after puberty, then became higher in men than women during the third and fourth decades. PBM was achieved in the third decade in women and in the fourth in men. More interestingly, Runx-2 gene expression highly correlated with BMD in both genders. MSCs and PBMCs showed the same gene expression profile of Runx-2. In conclusion, PBM is reached earlier in females, BMD becomes higher in males later in life, and BMD and PBM are strictly associated with Runx-2. In addition, PBMC should be considered an important source for gene expression analysis in bone diseases.

Runx2 isoform I controls a panel of proinvasive genes driving aggressiveness of papillary thyroid carcinomas

CONTEXT

The ability of tumor cells to invade adjacent tissues is governed by a complicated network of molecular signals, most of which have not yet been identified. In a recent work, we reported that the transcriptional regulator Id1 contributes to thyroid cancer progression by powering the invasion capacity of tumor cells.

OBJECTIVE

The intent of this work was to further investigate the biology of invasive thyroid tumors, through the analysis of the molecular interactions existing between Id1 and some of its target genes and through the characterization of the function of these factors in the progression of thyroid tumors.

RESULTS

We showed that Id1 controls the expression of the Runx2 isoform I and that this transcription factor plays a central role in mediating the Id1 proinvasive function in thyroid tumor cells. We demonstrated that Runx2 regulates proliferation, migration, and invasiveness by activating a panel of genes involved in matrix degradation and cellular invasion, which we previously identified as Id1 target genes in thyroid tumor cells. Finally, we show that Runx2 is strongly expressed in metastatic human thyroid tumors both at the primary site and in metastases.

CONCLUSION

Overall, our experiments demonstrate the existence of a previously unknown molecular axis that controls thyroid tumor invasiveness by altering the ability of tumor cells to interact with the surrounding microenvironment. These factors could prove to be valuable markers that permit early diagnosis of aggressive thyroid tumors.

Transforming growth factor beta signaling in adult cardiovascular diseases and repair

The majority of children with congenital heart disease now live into adulthood due to the remarkable surgical and medical advances that have taken place over the past half century. Because of this, adults now represent the largest age group with adult cardiovascular diseases. It includes patients with heart diseases that were not detected or not treated during childhood, those whose defects were surgically corrected but now need revision due to maladaptive responses to the procedure, those with exercise problems and those with age-related degenerative diseases. Because adult cardiovascular diseases in this population are relatively new, they are not well understood. It is therefore necessary to understand the molecular and physiological pathways involved if we are to improve treatments. Since there is a developmental basis to adult cardiovascular disease, transforming growth factor beta (TGFβ) signaling pathways that are essential for proper cardiovascular development may also play critical roles in the homeostatic, repair and stress response processes involved in adult cardiovascular diseases. Consequently, we have chosen to summarize the current information on a subset of TGFβ ligand and receptor genes and related effector genes that, when dysregulated, are known to lead to cardiovascular diseases and adult cardiovascular deficiencies and/or pathologies. A better understanding of the TGFβ signaling network in cardiovascular disease and repair will impact genetic and physiologic investigations of cardiovascular diseases in elderly patients and lead to an improvement in clinical interventions.

Molecular genetics of supernumerary tooth formation

Despite advances in the knowledge of tooth morphogenesis and differentiation, relatively little is known about the aetiology and molecular mechanisms underlying supernumerary tooth formation. A small number of supernumerary teeth may be a common developmental dental anomaly, while multiple supernumerary teeth usually have a genetic component and they are sometimes thought to represent a partial third dentition in humans. Mice, which are commonly used for studying tooth development, only exhibit one dentition, with very few mouse models exhibiting supernumerary teeth similar to those in humans. Inactivation of Apc or forced activation of Wnt/β(catenin signalling results in multiple supernumerary tooth formation in both humans and in mice, but the key genes in these pathways are not very clear. Analysis of other model systems with continuous tooth replacement or secondary tooth formation, such as fish, snake, lizard, and ferret, is providing insights into the molecular and cellular mechanisms underlying succesional tooth development, and will assist in the studies on supernumerary tooth formation in humans. This information, together with the advances in stem cell biology and tissue engineering, will pave ways for the tooth regeneration and tooth bioengineering.

The significance of RUNX2 in postnatal development of the mandibular condyle

OBJECTIVE

RUNX2, in the Runt gene family, is one of the most important transcription factors in the development of the skeletal system. Research in recent decades has shown that this factor plays a major role in the development, growth and maturation of bone and cartilage. It is also important in tooth development, mechanotransduction and angiogenesis, and plays a significant role in various pathological processes, i.e. tumor metastasization. Mutations in the RUNX2 gene correlate with the cleidocranial dysplasia (CCD) syndrome, important to dentistry, particularly orthodontics because of its dental and orofacial symptoms. Current research on experimentally-induced mouse mutants enables us to study the etiology and pathogenesis of these malformations at the cellular and molecular biological level. This study's aim is to provide an overview of the RUNX2 gene's function especially in skeletal development, and to summarize our research efforts to date, which has focused on investigating the influence of RUNX2 on mandibular growth, which is slightly or not at all altered in many CCD patients.

MATERIALS AND METHODS

Immunohistochemical analyses were conducted to reveal RUNX2 in the condylar cartilage of normal mice and of heterozygous RUNX2 knockout mice in early and late growth phases; we also performed radiographic and cephalometric analyses.

RESULTS

We observed that RUNX2 is involved in normal condylar growth in the mouse and probably plays a significant role in osteogenesis and angiogenesis. The RUNX2 also has a biomechanical correlation in relation to cartilage compartmentalization. At the protein level, we noted no differences in the occurrence and distribution of RUNX2 in the condyle, except for a short phase during the 4th and 6th postnatal weeks, so that one allele might suffice for largely normal growth; other biological factors may have compensatory effects. However, we did observe small changes in a few cephalometric parameters concerning the mandibles of heterozygous knockout animals. We discuss potential correlations to our findings by relating them to the most current knowledge about the RUNX2 biology.

Multifunctional enhancers regulate mouse and human vitamin D receptor gene transcription

The vitamin D receptor (VDR) mediates the endocrine actions of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] and autoregulates the expression of its own gene in target cells. In studies herein, we used chromatin immunoprecipitation-chip analyses to examine further the activities of 1,25(OH)(2)D(3) and to assess the consequences of VDR/retinoid X receptor heterodimer binding at the VDR gene locus. We also explored mechanisms underlying the ability of retinoic acid, dexamethasone, and the protein kinase A activator forskolin to induce VDR up-regulation as well. We confirmed two previously identified intronic 1,25(OH)(2)D(3)-inducible enhancers and discovered two additional regions, one located 6 kb upstream of the VDR transcription start site. Although RNA polymerase II was present at the transcription start site in the absence of 1,25(OH)(2)D(3), it was strikingly up-regulated at both this site and at individual enhancers in its presence. 1,25(OH)(2)D(3) also increased basal levels of H4 acetylation at these enhancers as well. Surprisingly, many of these enhancers were targets for CCAAT enhancer-binding protein-beta and runt-related transcription factor 2; a subset also bound cAMP response element binding protein, retinoic acid receptor, and glucocorticoid receptor. Unexpectedly, many of these factors were resident at the Vdr gene locus in the absence of inducer, suggesting that they might contribute to basal Vdr gene expression. Indeed, small interfering RNA down-regulation of CCAAT enhancer-binding protein-beta suppressed basal VDR expression. These regulatory activities of 1,25(OH)(2)D(3), forskolin, and dexamethasone were recapitulated in MC3T3-E1 cells stably transfected with a full-length VDR bacterial artificial chromosome (BAC) clone-luciferase reporter gene. Finally, 1,25(OH)(2)D(3) also induced accumulation of VDR and up-regulated H4 acetylation at conserved regions in the human VDR gene. These data provide important new insights into VDR gene regulation in bone cells.

Post-translational Regulation of Runx2 in Bone and Cartilage

The Runx2 gene product is essential for mammalian bone development. In humans, Runx2 haploinsufficiency results in cleidocranial dysplasia, a skeletal disorder characterized by bone and dental abnormalities. At the molecular level, Runx2 acts as a transcription factor for genes expressed in hypertrophic chondrocytes and osteoblasts. Runx2 gene expression and protein function are regulated on multiple levels, including transcription, translation, and post-translational modification. Furthermore, Runx2 is involved in numerous protein-protein interactions, most of which either activate or repress transcription of target genes. In this review, we discuss expression of Runx2 during development as well as the post-translational regulation of Runx2 through modification by phosphorylation, ubiquitination, and acetylation.

RUNX2 mutations in cleidocranial dysplasia patients

OBJECTIVE

Mutations in the RUNX2 gene, a master regulator of bone formation, have been identified in cleidocranial dysplasia (CCD) patients. CCD is a rare autosomal-dominant disease characterized by the delayed closure of cranial sutures, defects in clavicle formation, and supernumerary teeth. The purposes of this study were to identify genetic causes of two CCD nuclear families and to report their clinical phenotypes.

MATERIALS AND METHODS

We identified two CCD nuclear families and performed mutational analyses to clarify the underlying molecular genetic etiology.

RESULTS

Mutational analysis revealed a novel nonsense mutation (c.273T>A, p.L93X) in family 1 and a de novo missense one (c.673C>T, p.R225W) in family 2. Individuals with a nonsense mutation showed maxillary hypoplasia, delayed eruption, multiple supernumerary teeth, and normal stature. In contrast, an individual with a de novo missense mutation in the Runt domain showed only one supernumerary tooth and short stature.

CONCLUSIONS

Mutational and phenotypic analyses showed that the severity of mutations on the skeletal system may not necessarily correlate with that of the disruption of tooth development.

Upregulation of MMP-13 via Runx2 in the stromal cell of Giant Cell Tumor of bone

Giant Cell Tumor of bone (GCT) is an aggressively osteolytic and cytokine-rich bone tumor. Previous work in our lab has shown that matrix metalloproteinase-13 (MMP-13) is the principal proteinase expressed by the mesenchymal stromal cells of GCT. The Runx2 transcription factor is known to have a binding site in the MMP-13 promoter region, and we have previously found this transcription factor to be constitutively expressed in GCT stromal cells. The purpose of this study was to determine the role of Runx2 in MMP-13 regulation in GCT stromal cells. Following in vitro stimulation of GCT stromal cells with incremental concentrations of cytokine IL-1beta or TNF-alpha, the level of MMP-13 mRNA expression increased dramatically over 100-fold with a concomitant increase in MMP-13 protein expression. Inhibition of the ERK and JNK signaling pathways inhibited the upregulation of MMP-13 in these cells. Runx2 siRNA knockdown resulted in MMP-13 knockdown, and this effect was amplified following cytokine stimulation. Our study provides the first evidence that Runx2 may play a crucial role in cytokine-mediated MMP-13 expression in GCT stromal cells.

RUNX2 mutations in Chinese patients with cleidocranial dysplasia

Cleidocranial dysplasia (CCD) is an autosomal dominant bone disease in humans caused by haploinsufficiency of the RUNX2 gene. The RUNX2 has two major isoforms derived from P1 and P2 promoters. Over 90 mutations of RUNX2 have been reported associated with CCD. In our study, DNA samples of nine individuals from three unrelated CCD families were collected and screened for all exons of RUNX2 and 2 kb of P1 and P2 promoters. We identified two point mutations in the RUNX2 gene in Case 1, including a nonsense mutation (c.577C>T) that has been reported previously and a silent substitution (c.240G>A). In vitro studies demonstrated that c.577C>T mutation led to truncated RUNX2 protein production and diminished stimulating effects on mouse osteocalcin promoter activity when compared with full-length Runx2-II and Runx2-I isoforms. These results confirm that loss of function RUNX2 mutation (c.577C>T) in Case 1 family is responsible for its CCD phenotype.

Menin promotes the Wnt signaling pathway in pancreatic endocrine cells

Menin is a tumor suppressor protein mutated in patients with multiple endocrine neoplasia type 1. We show that menin is essential for canonical Wnt/beta-catenin signaling in cultured rodent islet tumor cells. In these cells, overexpression of menin significantly enhances TCF gene assay reporter activity in response to beta-catenin activation. Contrastingly, inhibition of menin expression with Men1 siRNA decreases TCF reporter gene activity. Likewise, multiple endocrine neoplasia type 1 disease associated missense mutations of menin abrogate the ability to increase TCF reporter gene activity. We show that menin physically interacts with proteins involved in the canonical Wnt signaling pathway, including beta-catenin, TCF3 (TCFL1), and weakly with TCF4 (TCFL2). Menin overexpression increases expression of the Wnt/beta-catenin downstream target gene Axin2, which is associated with increased H3K4 trimethylation of the Axin2 gene promoter. Moreover, inhibition of menin expression by siRNA abrogates H3K4 trimethylation and Axin2 gene expression. Based on these studies, we hypothesized that Wnt signaling could inhibit islet cell proliferation because loss of menin function is thought to increase endocrine tumor cell proliferation. TGP61 rodent islet tumor cells treated with a glycogen synthase kinase 3beta inhibitor that increases Wnt pathway signaling had decreased cell proliferation compared with vehicle-treated cells. Collectively, these data suggest that menin has an essential role in Wnt/beta-catenin signaling through a mechanism that eventually affects histone trimethylation of the downstream target gene Axin2, and activation of Wnt/beta-catenin signaling inhibits islet tumor cell proliferation.

The muscle transcription factor MyoD promotes osteoblast differentiation by stimulation of the Osterix promoter

Transcription factors regulate tissue-specific differentiation of pluripotent mesenchyme to osteoblast (OB), myoblast (MB), and other lineages. Osterix (Osx) is an essential transcription factor for bone development because knockout results in lack of a mineralized skeleton. The proximal Osx promoter contains numerous binding sequences for MyoD and 14 repeats of a binding sequence for Myf5. These basic helix-loop-helix (bHLH) transcription factors have a critical role in MB differentiation and muscle development. We tested the hypothesis that bHLH transcription factors also support OB differentiation through regulation of Osx. Transfection of a MyoD expression vector into two primitive mesenchymal cell lines, C3H/10T1/2 and C2C12, stimulated a 1.2-kb Osx promoter-luciferase reporter 70-fold. Myf5 stimulated the Osx promoter 6-fold. Deletion analysis of the promoter revealed that one of three proximal bHLH sites is essential for MyoD activity. The Myf5 repeat conferred 60% of Myf5 activity with additional upstream sequence required for full activity. MyoD bound the active bHLH sequence and its 3'-flanking region, as shown by EMSA and chromatin immunoprecipitation assays. Real-time PCR revealed that primitive C2C12 and C3H/10T1/2 cells, pre-osteoblastic MC3T3 cells, and undifferentiated primary marrow stromal cells express the muscle transcription factors. C2C12 cells, which differentiate to MB spontaneously and form myotubules, were treated with bone morphogenetic protein 2 (BMP-2) to induce OB differentiation. BMP-2 stimulated expression of Osx and the differentiation marker alkaline phosphatase and blocked myotubule development. BMP-2 suppressed the muscle transcription factor myogenin, but expression of MyoD and Myf5 persisted. Silencing of MyoD inhibited BMP-2 stimulation of Osx and blocked the later appearance of bone alkaline phosphatase. MyoD support of Osx transcription contributes to early OB differentiation.

Family-based association study of polymorphisms in the RUNX2 locus with hand bone length and hand BMD

Osteoporosis is characterized by reduced bone strength. Bone size and bone mineral density (BMD) are major bone strength determinants. Identification of genes affecting the variability of these traits should improve prognosis and management of osteoporosis. This research was aimed to test the hypothesis of association of radiographic hand bone length (BL) and BMD with polymorphisms in the RUNX2 locus. Four SNPs linked to the two RUNX2 promoters were genotyped in 212 nuclear Caucasian families. These SNPs and four pairwise haplotypes were tested for association with eight BL and BMD traits, adjusted for covariates. We observed significant associations between polymorphisms linked to the RUNX2 P1 promoter and BL mean values for three studied bone groups: all 18 bones, proximal and medial bones (p = 0.0118, 0.0085, and 0.0056, respectively). Mean BMD values for all 18 bones, proximal and medial bones were associated with polymorphisms linked to the RUNX2 P2 promoter (p = 0.0032, 0.0077, 0.0007, respectively). Associations with BL and BMD mean values for medial and proximal bones remained significant even after correction for multiple testing. This study provides evidence of the association between polymorphisms linked to the two RUNX2 promoters and variability of hand BL and BMD. The results suggest independent roles for the two RUNX2 promoters in the determination of the traits studied.

Analysis of the Runx2 promoter in osseous and non-osseous cells and identification of HIF2A as a potent transcription activator

Little is known about the upstream regulator of Runx2, a master regulator of osteoblast differentiation in bone tissues. To elucidate the molecular mechanism of Runx2 gene expression, we analyzed Runx2 promoter activity in osseous (MC3T3-E1, KS483, Kusa) and non-osseous (NIH3T3, C3H10T1/2, mouse embryonic fibroblasts) cells and also identified Runx2 upstream regulator using a Runx2 promoter-derived luciferase reporter system. After cloning 15 serial deletion constructs from -6832 bp/+390 bp to -37 bp/+390 bp of the Runx2-P1 promoter, we performed a transient transfection assay in osseous and non-osseous cells. A reduction in Runx2 promoter activity was observed in two regions; one was between -3 kb and -1 kb, and the other was between -155 bp and -75 bp. The step-down pattern in promoter activity between -3 kb and -1 kb was observed only in osseous cells. Interestingly, the step-down pattern between -155 bp and -75 bp was revealed in both cell types. Consistently, beta-galactosidase staining in axial skeleton of -3 kb-Runx2-P1-LacZ transgenic mice was positive, but that of all skeletal tissues of -1 kb-Runx2-P1-LacZ transgenic mice was negative. To identify upstream regulators of the Runx2-P1 promoter, we screened 100 transcription factors using Runx2-P1-luciferase reporter constructs in NIH3T3 fibroblasts and HeLa cells. Among them, HIF2A was identified as the strongest activator of Runx2-P1 promoter activity. A HIF2A-responsive site on the Runx2 promoter was identified between -106 bp and -104 bp by mutation analysis. An electrophoretic mobility shift assay and chromatin immunoprecipitation assay confirmed the binding of HIF2A to the Runx2-P1 promoter in vitro and in vivo, respectively. Knock-down using siRNA against HIF2A confirmed that HIF2A is an important regulator of Runx2 gene expression. Collectively, these results suggest that the region between -3 kb and -1 kb is required for the minimal skeletal tissue-specific expression of Runx2, and that the region between -155 bp and -75 bp is important for its basal transcription, which may be in part mediated by HIF2A in bone tissues.

Mechanism of HIV protein induced modulation of mesenchymal stem cell osteogenic differentiation

Background

A high incidence of decreased bone mineral density (BMD) has been associated with HIV infection. Normal skeletal homeostasis is controlled, at least in part, by the maturation and activity of mature osteoblasts. Previous studies by our group have demonstrated the ability of HIV proteins to perturb osteoblast function, and the degree of osteogenesis in differentiating mesenchymal stem cells (MSCs). This study attempts to further dissect the dynamics of this effect.

Methods

MSCs were cultured under both osteogenic (cultured in commercially available differentiation media) and quiescent (cultured in basal medium) conditions. Both cell populations were exposed to HIV p55-gag and HIV rev (100 ng/ml). Time points were taken at 3, 6, 9, and 15 days for osteogenic conditions, while quiescent cells were treated for 1 week. Cell function (alkaline phosphatase [ALP] activity, calcium deposition, and lipid levels) and the activity of the key MSC transcription factors, RUNX-2 and PPARgamma were determined post-exposure. Also, in cells cultured in differentiating conditions, cellular levels of connective tissue growth factor (CTGF) were analysed using whole cell ELISA, while BMP-2 secretion was also examined.

Results

In differentiating MSCs, exposure to HIV proteins caused significant changes in both the timing and magnitude of key osteogenic events and signals. Treatment with REV increased the overall rate of mineralization, and induced earlier increases in CTGF levels, RUNX-2 activity and BMP-2 secretion, than those observed in the normal course of differntiation. In contrast, p55-gag reduced the overall level of osteogenesis, and reduced BMP-2 secretion, RUNX-2 activity, CTGF levels and ALP activity at many of the timepoints examined. Finally, in cells cultured in basal conditions, treatment with HIV proteins did not in and of itself induce a significant degree of differentiation over the time period examined.

Conclusion

These data demonstrate that the effect of HIV proteins on bone is dependent on the differentiation status of the cells that they are in contact with. The effect on bone cell signalling provides insights into the mechanism of HIV induced decreases in bone mineral density.

HIV proteins regulate bone marker secretion and transcription factor activity in cultured human osteoblasts with consequent potential implications for osteoblast function and development

A high incidence of decreased bone mineral density (BMD) has increasingly been associated with HIV infection. In this study mesenchymal stem cell (MSC) and human osteoblast (hOB) cell lines were treated with HIV tat, HIV rev, HIV p55-gag, HIV gp120 and HTLV env (100 ng/ml, 24 h). Cells were then analyzed for calcium deposition, alkaline phosphatase (ALP) activity, and lipid levels using established methods. Real-time PCR with gene-specific primers was used to quantify the mRNA levels of the transcription factors RUNX-2 and PPARgamma, transcription factors known to be pro-osteogenic and pro-adipogenic, respectively. The levels of secreted bone markers and transcription factor activity were determined using commercial assays. In OBs, HIV p55-gag and gp120 were seen to reduce calcium deposition, ALP activity, levels of secreted BMP-2, -7, and RANK-L, and the expression and activity of RUNX-2. The levels of osteocalcin were also significantly reduced by p55-gag treatment, while gp120 also increased PPARgamma activity. Lipid levels were also increased by gp120 treatment. The ability of MSCs to develop into functioning OBs was also affected by the presence of HIV proteins, with p55-gag inducing a decrease in osteogenesis, while rev induced an increase. HIV proteins can potentially modulate OB development and function in vitro via modulation of bone maker secretion and RUNX-2 and PPARgamma transcription factor activity.

Runx2: of bone and stretch

Runx2 is a key transcriptional modulator of osteoblast differentiation that plays a fundamental role in osteoblast maturation and homeostasis. Runx2-null mice despite normal skeletal patterning have no osteoblasts and consequently bone tissue. Mutations of the runx2 gene in humans cause cleidocranial dysplasia. As a member of the Runx family of transcription factors, Runx2 operates by binding to the osteoblast-specific cis-acting element 2 (OSE2), which is found in the regulatory region of all main osteoblast-related genes controlling their expression. Its expression and/or activity are dictated by a number of different external cues while multiple signalling pathways that affect osteoblast function merge to and are integrated by Runx2. Among the various stimuli that modulate Runx2 activity, mechanical loading (strain/stretching) has been revealed to be one of the most critical signals that connect Runx2 with osteoblast function and bone remodelling through mechanotransduction.

A possible role of LIM mineralization protein 1 in tertiary dentinogenesis of dental caries treatment

Dental caries is a slowly progressive infectious disease with high risks. In response to dental caries stimuli, the tertiary dentin might be formed, protecting the dental pulp. Tertiary dentinogenesis contributes greatly to the treatment of carious lesions as well as the preservation and restoration of entire tooth function. A number of studies have found that application of exogenous growth factors such as transforming growth factors and bone morphogenetic proteins on unexposed pulps are able to signal tertiary dentinogenesis. Since precise mechanism of tertiary dentinogenesis is still not clear, more potential signaling factors might contribute to this process. Dentinogenesis shares many similarities with osteogenesis. The factors involved in osteogenesis and bone repair such as bone morphogenetic proteins 2, 7 and core binding factor alpha1 play important roles in dentinogenesis. LIM mineralization protein 1 is a critical positive regulator of osteoblast differentiation, bone formation and repair. It is logical to postulate that LIM mineralization protein 1 might be involved in odontoblast differentiation and dentin formation both in normal and in pathological conditions. Application of LIM mineralization protein 1 might be a promising approach for inducing tertiary dentinogenesis in dental caries treatment.