Transcriptional regulation of the human Runx2/Cbfa1 gene promoter by bone morphogenetic protein-7

GDF10 is a negative regulator of vascular calcification

Cardiovascular mortality is particularly high and increasing in patients with chronic kidney disease, with vascular calcification (VC) as a major pathophysiologic feature. VC is a highly regulated biological process similar to bone formation involving osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs). We have previously demonstrated that loss of T-cell death-associated gene 51 (TDAG51) expression leads to an attenuation of medial VC. We now show a significant induction of circulating levels of growth differentiation factor 10 (GDF10) in TDAG51-/- mice, which was of interest due to its established role as an inhibitor of osteoblast differentiation. The objective of this study was to examine the role of GDF10 in the osteogenic transdifferentiation of VSMCs. Using primary mouse and human VSMCs, as well as ex vivo aortic ring cultures, we demonstrated that treatment with recombinant human (rh) GDF10 mitigated phosphate-mediated hydroxyapatite (HA) mineral deposition. Furthermore, ex vivo aortic rings from GDF10-/- mice exhibited increased HA deposition compared to C57BL/6J controls. To explain our observations, we identified that rhGDF10 treatment reduced protein expression of runt-related transcription factor 2, a key driver of osteogenic transdifferentiation of VSMCs and VC. In support of these findings, in vivo treatment with rhGDF10 attenuated VD3-induced VC. Furthermore, we demonstrated an increase in circulating GDF10 in patients with chronic kidney disease with clinically defined severe VC, as assessed by coronary artery calcium score. Thus, our studies identify GDF10 as a novel inhibitor of mineral deposition and as such, may represent a potential novel biomarker and therapeutic target for the detection and management of VC.

The Potential Influence of Uremic Toxins on the Homeostasis of Bones and Muscles in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) often experience a high accumulation of protein-bound uremic toxins (PBUTs), specifically indoxyl sulfate (IS) and p-cresyl sulfate (pCS). In the early stages of CKD, the buildup of PBUTs inhibits bone and muscle function. As CKD progresses, elevated PBUT levels further hinder bone turnover and exacerbate muscle wasting. In the late stage of CKD, hyperparathyroidism worsens PBUT-induced muscle damage but can improve low bone turnover. PBUTs play a significant role in reducing both the quantity and quality of bone by affecting osteoblast and osteoclast lineage. IS, in particular, interferes with osteoblastogenesis by activating aryl hydrocarbon receptor (AhR) signaling, which reduces the expression of Runx2 and impedes osteoblast differentiation. High PBUT levels can also reduce calcitriol production, increase the expression of Wnt antagonists (SOST, DKK1), and decrease klotho expression, all of which contribute to low bone turnover disorders. Furthermore, PBUT accumulation leads to continuous muscle protein breakdown through the excessive production of reactive oxygen species (ROS) and inflammatory cytokines. Interactions between muscles and bones, mediated by various factors released from individual tissues, play a crucial role in the mutual modulation of bone and muscle in CKD. Exercise and nutritional therapy have the potential to yield favorable outcomes. Understanding the underlying mechanisms of bone and muscle loss in CKD can aid in developing new therapies for musculoskeletal diseases, particularly those related to bone loss and muscle wasting.

Growth Factor Delivery Using a Collagen Membrane for Bone Tissue Regeneration

The use of biomaterials and bioactive agents has shown promise in bone defect repair, leading to the development of strategies for bone regeneration. Various artificial membranes, especially collagen membranes (CMs) that are widely used for periodontal therapy and provide an extracellular matrix-simulating environment, play a significant role in promoting bone regeneration. In addition, numerous growth factors (GFs) have been used as clinical applications in regenerative therapy. However, it has been established that the unregulated administration of these factors may not work to their full regenerative potential and could also trigger unfavorable side effects. The utilization of these factors in clinical settings is still restricted due to the lack of effective delivery systems and biomaterial carriers. Hence, considering the efficiency of bone regeneration, both spaces maintained using CMs and GFs can synergistically create successful outcomes in bone tissue engineering. Therefore, recent studies have demonstrated a significant interest in the potential of combining CMs and GFs to effectively promote bone repair. This approach holds great promise and has become a focal point in our research. The purpose of this review is to highlight the role of CMs containing GFs in the regeneration of bone tissue, and to discuss their use in preclinical animal models of regeneration. Additionally, the review addresses potential concerns and suggests future research directions for growth factor therapy in the field of regenerative science.

Crosstalk between protein kinase C α and transforming growth factor β signaling mediated by Runx2 in intestinal epithelial cells

Tight coordination of growth regulatory signaling is required for intestinal epithelial homeostasis. Protein kinase C α (PKCα) and transforming growth factor β (TGFβ) are negative regulators of proliferation with tumor suppressor properties in the intestine. Here, we identify novel crosstalk between PKCα and TGFβ signaling. RNA-Seq analysis of nontransformed intestinal crypt-like cells and colorectal cancer cells identified TGFβ receptor 1 (TGFβR1) as a target of PKCα signaling. RT-PCR and immunoblot analysis confirmed that PKCα positively regulates TGFβR1 mRNA and protein expression in these cells. Effects on TGFβR1 were dependent on Ras-extracellular signal-regulated kinase 1/2 (ERK) signaling. Nascent RNA and promoter-reporter analysis indicated that PKCα induces TGFβR1 transcription, and Runx2 was identified as an essential mediator of the effect. PKCα promoted ERK-mediated activating phosphorylation of Runx2, which preceded transcriptional activation of the TGFβR1 gene and induction of Runx2 expression. Thus, we have identified a novel PKCα→ERK→Runx2→TGFβR1 signaling axis. In further support of a link between PKCα and TGFβ signaling, PKCα knockdown reduced the ability of TGFβ to induce SMAD2 phosphorylation and cell cycle arrest, and inhibition of TGFβR1 decreased PKCα-induced upregulation of p21Cip1 and p27Kip1 in intestinal cells. The physiological relevance of these findings is also supported by The Cancer Genome Atlas data showing correlation between PKCα, Runx2, and TGFβR1 mRNA expression in human colorectal cancer. PKCα also regulated TGFβR1 in endometrial cancer cells, and PKCα, Runx2, and TGFβR1 expression correlates in uterine tumors, indicating that crosstalk between PKCα and TGFβ signaling may be a common mechanism in diverse epithelial tissues.

RUNX2 Regulates Osteoblast Differentiation via the BMP4 Signaling Pathway

RUNX2 is a master osteogenic transcription factor, and mutations in RUNX2 cause the inherited skeletal disorder cleidocranial dysplasia (CCD). Studies have revealed that RUNX2 is not only a downstream target of the bone morphogenetic protein (BMP) pathway but can also regulate the expression of BMPs. However, the underlying mechanism of the regulation of BMPs by RUNX2 remains unknown. In this project, we diagnosed a CCD patient with a 7.86-Mb heterozygous deletion on chromosome 6 containing all exons of RUNX2 by multiplex ligation-dependent probe amplification (MLPA) and whole-genome sequencing (WGS). Bone marrow mesenchymal stem cells (BMSCs) were further extracted from patient alveolar bone fragments (CCD-BMSCs), an excellent natural model to explore the possible mechanism. The osteogenic differentiation ability of CCD-BMSCs was severely affected by RUNX2 heterozygous deletion. Also, BMP4 decreased most in BMP ligands, and CHRDL1, a BMP antagonist, was abnormally elevated in CCD-BMSCs. Furthermore, BMP4 treatment essentially rescued the osteogenic capacity of CCD-BMSCs, and RUNX2 overexpression reversed the abnormal expression of BMP4 and CHRDL1. Notably, we constructed CRISPR/Cas9 Runx2^+/m MC3T3-E1 cells, which simulated a variant in CCD-BMSCs, to exclude the interference of other gene deletions and the heterogeneity of the genetic background of primary cells, and verified all findings from the CCD-BMSCs. Moreover, the luciferase reporter experiment showed that RUNX2 could inhibit the transcription of CHRDL1. Through immunofluorescence, the inhibitory effect of CHRDL1 on BMP4/Smad signaling was confirmed in MC3T3-E1 cells. These results revealed that RUNX2 regulated the BMP4 pathway by inhibiting CHRDL1 transcription. We collectively identified a novel RUNX2/CHRDL1/BMP4 axis to regulate osteogenic differentiation and noted that BMP4 might be a valuable therapeutic option for treating bone diseases.

Toxic Effects of Indoxyl Sulfate on Osteoclastogenesis and Osteoblastogenesis

Uremic toxins, such as indoxyl sulfate (IS) and kynurenine, accumulate in the blood in the event of kidney failure and contribute to further bone damage. To maintain the homeostasis of the skeletal system, bone remodeling is a persistent process of bone formation and bone resorption that depends on a dynamic balance of osteoblasts and osteoclasts. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates the toxic effects of uremic toxins. IS is an endogenous AhR ligand and is metabolized from tryptophan. In osteoclastogenesis, IS affects the expression of the osteoclast precursor nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) through AhR signaling. It is possible to increase osteoclast differentiation with short-term and low-dose IS exposure and to decrease differentiation with long-term and/or high-dose IS exposure. Coincidentally, during osteoblastogenesis, through the AhR signaling pathway, IS inhibits the phosphorylation of ERK, and p38 reduces the expression of the transcription factor 2 (Runx2), disturbing osteoblastogenesis. The AhR antagonist resveratrol has a protective effect on the IS/AhR pathway. Therefore, it is necessary to understand the multifaceted role of AhR in CKD, as knowledge of these transcription signals could provide a safe and effective method to prevent and treat CKD mineral bone disease.

Resveratrol Rescue Indoxyl Sulfate-Induced Deterioration of Osteoblastogenesis via the Aryl Hydrocarbon Receptor /MAPK Pathway

Indoxyl sulfate (IS), a uremic toxin derived from dietary tryptophan metabolism by the gut microbiota, is an endogenous aryl hydrocarbon receptor (AhR) agonist and a key player in bone remodeling. Resveratrol (RSV), an AhR antagonist, plays a protective role in shielding against AhR ligands. Our study explored the impact of IS on osteoblast differentiation and examined the possible mechanism of IS in controlling the expression of osteoblastogenesis markers through an in-depth investigation of AhR signaling. In vivo, we found histological architectural disruption of the femoral bones in 5/6 nephrectomies of young adult IS exposed mice, including reduced Runx2 antigen expression. RSV improved the diaphysis architecture, Runx2 expression, and trabecular quality. In vitro data suggest that IS at 500 and 1000 μM disturbed osteoblastogenesis through suppression of the ERK and p38 mitogen-activated protein kinase (MAPK) pathways, which were found to be downstream of AhR. RSV proved to ameliorate the anti-osteoblastogenic effects of IS through the inhibition of AhR and downstream signaling. Taken together, we demonstrated that the IS/AhR/MAPK signaling pathway plays a crucial role in the inhibition of osteoblastogenesis, and RSV has a potential therapeutic role in reversing the IS-induced decline in osteoblast development and suppressing abnormal bone turnover in chronic kidney disease patients.

Gain-of-function variants and overexpression of RUNX2 in patients with nonsyndromic midline craniosynostosis

Craniosynostosis (CS), the premature fusion of one or more cranial sutures, is a relatively common congenital anomaly, occurring in 3-5 per 10,000 live births. Nonsyndromic CS (NCS) accounts for up to 80% of all CS cases, yet the genetic factors contributing to the disorder remain largely unknown. The RUNX2 gene, encoding a transcription factor critical for bone and skull development, is a well known CS candidate gene, as copy number variations of this gene locus have been found in patients with syndromic craniosynostosis. In the present study, we aimed to characterize RUNX2 to better understand its role in the genetic etiology and in the molecular mechanisms underlying midline suture ossification in NCS. We report four nonsynonymous variants, one intronic variant and one 18 bp in-frame deletion in RUNX2 not found in our study control population. Significant difference in allele frequency (AF) for the deletion variant RUNX2 p.Ala84-Ala89del (ClinVar 257,095; dbSNP rs11498192) was observed in our sagittal NCS cohort when compared to the general population (P = 1.28 × 10^-6), suggesting a possible role in the etiology of NCS. Dual-luciferase assays showed that three of four tested RUNX2 variants conferred a gain-of-function effect on RUNX2, further suggesting their putative pathogenicity in the tested NCS cases. Downregulation of RUNX2 expression was observed in prematurely ossified midline sutures. Metopic sites showed significant downregulation of promoter 1-specific isoforms compared to sagittal sites. Suture-derived mesenchymal stromal cells showed an increased expression of RUNX2 over matched unfused suture derived cells. This demonstrates that RUNX2, and particularly the distal promoter 1-isoform group, are overexpressed in the osteogenic precursors within the pathological suture sites.

The BMP Pathway and Its Inhibitors in the Skeleton

Bone morphogenetic proteins (BMPs) constitute the largest subdivision of the transforming growth factor-β family of ligands. BMPs exhibit widespread utility and pleiotropic, context-dependent effects, and the strength and duration of BMP pathway signaling is tightly regulated at numerous levels via mechanisms operating both inside and outside the cell. Defects in the BMP pathway or its regulation underlie multiple human diseases of different organ systems. Yet much remains to be discovered about the BMP pathway in its original context, i.e., the skeleton. In this review, we provide a comprehensive overview of the intricacies of the BMP pathway and its inhibitors in bone development, homeostasis, and disease. We frame the content of the review around major unanswered questions for which incomplete evidence is available. First, we consider the gene regulatory network downstream of BMP signaling in osteoblastogenesis. Next, we examine why some BMP ligands are more osteogenic than others and what factors limit BMP signaling during osteoblastogenesis. Then we consider whether specific BMP pathway components are required for normal skeletal development, and if the pathway exerts endogenous effects in the aging skeleton. Finally, we propose two major areas of need of future study by the field: greater resolution of the gene regulatory network downstream of BMP signaling in the skeleton, and an expanded repertoire of reagents to reliably and specifically inhibit individual BMP pathway components.

Signalling Alterations in Bones of Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) Gene Deficient Mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with diverse developmental roles, including differentiation of skeletal elements. It is a positive regulatory factor of chondrogenesis and osteogenic differentiation in vitro, but little is known about its in vivo role in bone formation. In our experiments, diaphyses of long bones from hind limbs of PACAP gene-deficient mice showed changes in thickness and increased staining intensity. Our main goal was to perform a detailed morphological and molecular biological analysis of femurs from PACAP knockout (KO) and wild type (WT) mice. Transverse diameter and anterior cortical bone thickness of KO femurs showed significant alterations with disturbed Ca²⁺ accumulation and collagen type I expression. Higher expression and activity of alkaline phosphatase were also observed, accompanied by increased fragility PACAP KO femurs. Increased expression of the elements of bone morphogenic protein (BMP) and hedgehog signalling was also observed, and are possibly responsible for the compensation mechanism accounting for the slight morphological changes. In summary, our results show that lack of PACAP influences molecular and biomechanical properties of bone matrix, activating various signalling cascade changes in a compensatory fashion. The increased fragility of PACAP KO femur further supports the role of endogenous PACAP in in vivo bone formation.

Magnesium phosphate ceramics incorporating a novel indene compound promote osteoblast differentiation in vitro and bone regeneration in vivo

Incorporating bioactive molecules into synthetic ceramic scaffolds is challenging. In this study, to enhance bone regeneration, a magnesium phosphate (MgP) ceramic scaffold was incorporated with a novel indene compound, KR-34893. KR-34893 induced the deposition of minerals and expression of osteoblast marker genes in primary human bone marrow mesenchymal stem cells (BMSCs) and a mouse osteoblastic MC3T3-E1 cell line. Analysis of the mode of action showed that KR-34893 induced the phosphorylation of MAPK/extracellular signal-regulated kinase and extracellular signal-regulated kinase, and subsequently the expression of bone morphogenetic protein 7, accompanied by SMAD1/5/8 phosphorylation. Accordingly, KR-34893 was incorporated into an MgP scaffold prepared by 3D printing at room temperature, followed by cement reaction. KR-34893-incorporated MgP (KR-MgP) induced the expression of osteoblast differentiation marker genes in vitro. In a rat calvaria defect model, KR-MgP scaffolds enhanced bone regeneration and increased bone volume compared with MgP scaffolds, as assessed by micro-computed tomography and histological analyses. In conclusion, we developed a method for producing osteoinductive MgP scaffolds incorporating a bioactive organic compound, without high temperature sintering. The KR-MgP scaffolds enhanced osteoblast activation in vitro and bone regeneration in vivo.

A collagen membrane containing osteogenic protein-1 facilitates bone regeneration in a rat mandibular bone defect

OBJECTIVES

Osteogenic protein-1 (OP-1) has shown osteoinductive activities and is useful for clinical treatments, including bone regeneration. Regenerative procedures using a bioabsorbable collagen membrane (BCM) are well established in periodontal and implant dentistry. We evaluated the subsequent effects of the BCM in combination with OP-1 on bone regeneration in a rat mandibular circular critical-sized bone defect in vivo.

DESIGN

We used 8 rats that received surgery in both sides of the mandible, and created the total 16 defects which were divided into 4 groups: Group 1; no treatment, as a control, Group 2; BCM alone, Group 3; BCM containing low dose 0.5μg of OP-1 (L-OP-1), and Group 4; BCM containing high dose 2.0μg of OP-1 (H-OP-1). Newly formed bone was evaluated by micro computed tomography (micro-CT) and histological analyses at 8 weeks postoperatively. In quantitative and qualitative micro-CT analyses of the volume of new bone formation, bone density, and percentage of new bone area was evaluated.

RESULTS

BCM with rhOP-1 significantly increased and accelerated bone volume, bone mineral density, and percentage of new bone area compared to control and BCM alone at 8 weeks after surgery; these enhancements in bone regeneration in the OP-1-treated groups were dose-dependent.

CONCLUSIONS

OP-1 delivered with a BCM may have effective osteoinductive potency and be a good combination for bone regeneration. The use of such a combination device for osteogenesis may result in safer and more predictable bone regenerative outcomes in the future.

Osteogenic differentiation of mesenchymal stem cells is impaired by bone morphogenetic protein 7

PURPOSE

Mesenchymal stem cells (MSCs) are multipotent adult stem cells and present in practically all tissues but originally identified within the bone marrow (BM). The differentiation potential of these cells is generally impaired when culturing in vitro for cell expansion. The aim of this study is to speedily increase the numbers of bone marrow derived mesenchymal stem cells (BM-MSCs) with substantially maintaining their differentiation potential in vitro and improving bone formation in vivo.

MATERIALS AND METHODS

BM-MSCs isolated from rats were sequentially cultured in α-MEM containing basic fibroblast growth factor (FGF2) and/or insulin to stimulate proliferation and osteogenic commitment, and in the medium with the addition of bone morphogenetic protein 2 (BMP2) and/or bone morphogenetic protein 7 (BMP7) to arouse differentiation. The expression of genes markedly associating the commitment and differentiation were investigated in vitro using real-time PCR technique and mineralization assay, while the capacity of inducing bone formation by the established conditions was determined in vivo using a rat model.

RESULTS

The BM-MSCs greatly proliferated with active transcription of runx2 and osterix genes when induced by FGF2 and insulin. The in vitro mineralization was enhanced by BMP2, but the extent was diminished when BMP2 was replaced or supplemented by BMP7. Formation of new small blood vessels was notably detected when the cells were respectively challenged by FGF2 plus insulin and BMP2.

CONCLUSION

These data are valuable in choosing growth factors for proper bone repair. However, optimization of the established system would be essential when the cells of human source are applied.

Bone morphogenetic protein-5, a key molecule that mediates differentiation in MC3T3E1 osteoblast cell line

Bone morphogenetic protein-5 (BMP-5) is a member of the TGF receptor-β family with osteoinductive property. However, its physiological role in osteoblast differentiation is not defined. This study highlights the importance of BMP-5 in MC3T3E1 osteoblast differentiation. Pre-osteoblasts exposed to osteogenic media (ascorbic acid, 50 µg/ml and β-glycerophosphate, 10 mM) showed high protein expression of BMP-5 in cell lysates and cell culture supernatants, which peaked during early time-points of differentiation and declined with onset of mineralization. Attenuation of endogenous BMP-5 protein expression by RNA interference downregulated the expression of type I collagen (COLIA1), an early osteoblast differentiation marker but not osteocalcin, a late osteoblast differentiation marker. Further experiments to analyze the cell signaling components revealed that BMP-5 modulates COLIA1 expression via p38-Runx2 axis involving Runx2 (Ser19) phosphorylation. These effects were also observed when recombinant BMP-5 was added to pre-osteoblast cultures reinforcing the fact that BMP-5 is a modulator of COLIA1 expression. We conclude that BMP-5 has stage-specific role to play during MC3T3E1 osteoblast differentiation in part by autocrine p38/Runx2/COLIA1 signaling. © 2017 BioFactors, 43(4):558-566, 2017.

NUPR1, a new target in liver cancer: implication in controlling cell growth, migration, invasion and sorafenib resistance

Sorafenib, an oral multikinase inhibitor, is the only approved agent for the treatment of advanced hepatocellular carcinoma (HCC). However, its benefits are modest, and as its mechanisms of action remain elusive, a better understanding of its anticancer effects is needed. Based on our previous study results, we investigated here the implication of the nuclear protein 1 (NUPR1) in HCC and its role in sorafenib treatment. NUPR1 is a stress-inducible protein that is overexpressed in various malignancies, but its role in HCC is not yet fully understood. We found that NUPR1 expression was significantly higher in primary human HCC samples than in the normal liver. Knockdown of NUPR1 significantly increased cell sensitivity to sorafenib and inhibited the cell growth, migration and invasion of HCC cells, both in vitro and in vivo. Moreover, NUPR1 silencing influenced the expression of RELB and IER3 genes. Unsurprisingly, RELB and IER3 knockdown also inhibited HCC cell viability, growth and migration. Using gene expression profiling of HCC cells following stable NUPR1 knockdown, we found that genes functionally involved in cell death and survival, cellular response to therapies, lipid metabolism, cell growth and proliferation, molecular transport and cellular movement were mostly suppressed. Network analysis of dynamic gene expression identified NF-κB and ERK as downregulated gene nodes, and several HCC-related oncogenes were also suppressed. We identified Runt-related transcription factor 2 (RUNX2) gene as a NUPR1-regulated gene and demonstrated that RUNX2 gene silencing inhibits HCC cell viability, growth, migration and increased cell sensitivity to sorafenib. We propose that the NUPR1/RELB/IER3/RUNX2 pathway has a pivotal role in hepatocarcinogenesis. The identification of the NUPR1/RELB/IER3/RUNX2 pathway as a potential therapeutic target may contribute to the development of new treatment strategies for HCC management.

Ameloblastin, an Extracellular Matrix Protein, Affects Long Bone Growth and Mineralization

Matrix molecules such as the enamel-related calcium-binding phosphoprotein ameloblastin (AMBN) are expressed in multiple tissues, including teeth, bones, and cartilage. Here we have asked whether AMBN is of functional importance for timely long bone development and, if so, how it exerts its function related to osteogenesis. Adolescent AMBN-deficient mice (AMBN(Δ5-6) ) suffered from a 33% to 38% reduction in femur length and an 8.4% shorter trunk spinal column when compared with WT controls, whereas there was no difference between adult animals. On a cellular level, AMBN truncation resulted in a shortened growth plate and a 41% to 49% reduction in the number of proliferating tibia chondrocytes and osteoblasts. Bone marrow stromal cells (BMSCs) isolated from AMBN mutant mice displayed defects in proliferation and differentiation potential as well as cytoskeleton organization. Osteogenesis-related growth factors, such as insulin-like growth factor 1 (IGF1) and BMP7, were also significantly (46% to 73%) reduced in AMBN-deficient BMSCs. Addition of exogenous AMBN restored cytoskeleton structures in AMBN mutant BMSCs and resulted in a dramatic 400% to 600% increase in BMP2, BMP7, and Col1A expression. Block of RhoA diminished the effect of AMBN on osteogenic growth factor and matrix protein gene expression. Addition of exogenous BMP7 and IGF1 rescued the proliferation and differentiation potential of AMBN-deficient BMSCs. Confirming the effects of AMBN on long bone growth, back-crossing of mutant mice with full-length AMBN overexpressors resulted in a complete rescue of AMBN(Δ5-6) bone defects. Together, these data indicate that AMBN affects extracellular matrix production and cell adhesion properties in the long bone growth plate, resulting in altered cytoskeletal dynamics, increased osteogenesis-related gene expression, as well as osteoblast and chondrocyte proliferation. We propose that AMBN facilitates rapid long bone growth and an important growth spurt during the skeletogenesis of adolescent tooth-bearing vertebrates. © 2016 American Society for Bone and Mineral Research.

Osteogenic Ability of Canine Adipose-Derived Mesenchymal Stromal Cell Sheets in Relation to Culture Time

Cell sheets could be used for bone regeneration without requiring a scaffold and can be easily produced from autologous mesenchymal stromal cells (MSCs). We compared the osteogenic potential of MSC-derived cell sheets in relation to culture time. Undifferentiated cell sheets (U-CS) and osteogenic differentiated cell sheets (O-CS) were generated using canine adipose-derived MSCs. Undifferentiated cells (UCs) were used as the control. Osteogenic differentiation was assessed by assaying alkaline phosphatase (ALP) activity. Expression of osteogenesis-related genes was evaluated by reverse transcription-polymerase chain reaction at 4, 7, 14, and 21 days after initiation of culture. The calcium content in cells was measured, and the cells were stained with Alizarin red S (ARS). The mRNA expression of transforming growth factor-β in U-CS and O-CS at day 4 was higher than that in UCs (p < 0.05). The level of bone morphogenetic protein 7 mRNA in O-CS increased significantly at day 4 and was significantly higher than that of U-CS at day 7. The mRNA level of runt-related transcription factor-2 in both sheet types increased significantly at 7 days of culture. The mRNA level of ALP in O-CS and U-CS increased significantly at day 7, and ALP activity was highest at days 7 and 14, respectively (p < 0.05). The mRNA level of osteocalcin in U-CS and O-CS increased significantly at day 21. O-CS and U-CS showed negative ARS staining but their calcium contents increased marginally at day 21. The O-CS cells started to aggregate at days 10-12, and only a partial sheet remained at day 21. The upregulation of expression of genes related to osteogenic differentiation, peak in ALP activity, and morphological changes in cell sheets suggest that the optimal time for application of O-CS and U-CS is between 7 and 10 days and after 14 days of culture, respectively.

The effect of carrier type on bone regeneration of demineralized bone matrix in vivo

Demineralized bone matrix (DBM) is a bone substitute biomaterial used as an excellent grafting material. Some factors such as carrier type might affect the healing potential of this material. The background data discuss the present status of the field: Albumin as a main protein in blood and carboxymethyl cellulose (CMC) were applied frequently in the DBM gels. We investigated the bone-repairing properties of 2 DBMs with different carriers. Bone regeneration in 3 groups of rat calvaria treated with DBM from the Iranian Tissue Bank Research and Preparation Center, DBM from Hans Biomed Corporation, and an empty cavity was studied. Albumin and CMC as carriers were used. The results of bone regeneration in the samples after 1, 4, and 8 weeks of implantation were compared. The block of the histologic samples was stained with hematoxylin and eosin, and the percentage area of bone formation was calculated using the histomorphometry method. The results of in vivo tests showed a significantly stronger new regenerated bone occupation in the DBM with albumin carrier compared with the one with CMC 8 weeks after the implantation. The 2 types of DBM had a significant difference in bone regeneration. This difference is attributed to the type of carriers. Albumin could improve mineralization and bioactivity compared with CMC.

MicroRNAs regulate bone development and regeneration

MicroRNAs (miRNAs) are endogenous small noncoding ~22-nt RNAs, which have been reported to play a crucial role in maintaining bone development and metabolism. Osteogenesis originates from mesenchymal stem cells (MSCs) differentiating into mature osteoblasts and each period of bone formation is inseparable from the delicate regulation of various miRNAs. Of note, apprehending the sophisticated circuit between miRNAs and osteogenic homeostasis is of great value for artificial skeletal regeneration for severe bone defects. In this review, we highlight how different miRNAs interact with diverse osteo-related genes and endeavor to sketch the contours of potential manipulations of miRNA-modulated bone repair.

Emerging therapeutic targets for osteoporosis treatment

INTRODUCTION

To date, osteoporosis still remains a major public health burden especially for the aging populations. Over the last few decades treatments for osteoporosis have largely focused on anti-resorptive agents represented by bisphosphonates and estrogen therapy that dominated the market. Unsatisfactory efficacy, non-specificity and long-term safety of current therapies necessitate the need for new targets effectively preventing and treating of osteoporosis.

AREAS COVERED

This review expatiates on the mechanism of osteoporosis occurrence and bone remodeling cycle in detail. New targets of antiresorptive and anabolic agents based on the functions of osteoblasts and osteoclasts as well as associated signaling pathways are outlined.

EXPERT OPINION

Advanced understanding in the fields of bone remodeling, functions of osteoblasts, osteoclasts and osteocytes associated with osteoporosis occurrence offers the emerging bone-resorptive or bone-formative targets. Currently, molecules involving RANK-RANKL-OPG system and Wnt/β-catenin signaling pathway act as the most promising targets.

Parathyroid hormone-related protein protects renal tubuloepithelial cells from apoptosis by activating transcription factor Runx2

Runx2 is a key transcription factor in bone development regulating several processes, including osteoblast apoptosis. The antiapoptotic effects of parathyroid hormone (PTH) in osteoblasts depend on Runx2-mediated transcription of prosurvival genes. In the kidney, PTH-related protein (PTHrP) promotes tubulointerstitial cell survival by activating the PTH/PTHrP type 1 receptor. We found that Runx2 is expressed in renal tubuloepithelial MCT and HK2 cell lines in vitro and in the mouse kidney tubuloepithelium in vivo. The 1-36 amino-acid fragment of PTHrP was found to increase the expression and nuclear translocation of Runx2 in both cell lines in a dose- and time-dependent manner. PTHrP(1-36) protected renal tubuloepithelial cells from folic acid toxicity and serum deprivation, an effect inhibited by a dominant-negative Runx2 construct or a Runx2 siRNA. Furthermore, PTHrP(1-36) upregulated the antiapoptotic proteins Bcl-2 and osteopontin, and these effects were abolished by Runx2 siRNA. Runx2, osteopontin, and Bcl-2 were increased in tubuloepithelial cells from transgenic mice with PTHrP overexpression and in wild-type mice with acute or chronic renal failure. Thus, PTHrP regulates renal tubuloepithelial cell survival via Runx2 in the mammalian kidney.

Genomic occupancy of HLH, AP1 and Runx2 motifs within a nuclease sensitive site of the Runx2 gene

Epigenetic mechanisms mediating expression of the Runt-related transcription factor Runx2 are critical for controlling its osteogenic activity during skeletal development. Here, we characterized bona fide regulatory elements within 120 kbp of the endogenous bone-related Runx2 promoter (P1) in osteoblasts by genomic DNase I footprinting and chromatin immuno-precipitations (ChIPs). We identified a ~10 kbp genomic domain spanning the P1 promoter that interacts with acetylated histones H3 and H4 reflecting an open chromatin conformation in MC3T3 osteoblasts. This large chromatin domain contains a single major DNaseI hypersensitive (DHS) region that defines a 0.4 kbp "basal core" promoter. This region encompasses two endogenous genomic protein/DNA interaction sites (i.e., footprints at Activating Protein 1 [AP1], E-box and Runx motifs). Helix-Loop-Helix (HLH)/E-box occupancy and presence of the DHS region persists in several mesenchymal cell types, but AP1 site occupancy occurs only during S phase when Runx2 expression is minimal. Point-mutation of the HLH/E box dramatically reduces basal promoter activity. Our results indicate that the Runx2 P1 promoter utilizes two stable principal protein/DNA interaction domains associated with AP1 and HLH factors. These sites function together with dynamic and developmentally responsive sites in a major DHS region to support epigenetic control of bone-specific transcription when osteoblasts transition into a quiescent or differentiated state.

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.

Interactions between extracellular signal-regulated kinase 1/2 and p38 MAP kinase pathways in the control of RUNX2 phosphorylation and transcriptional activity

RUNX2, a key transcription factor for osteoblast differentiation, is regulated by ERK1/2 and p38 MAP kinase-mediated phosphorylation. However, the specific contribution of each kinase to RUNX2-dependent transcription is not known. Here we investigate ERK and p38 regulation of RUNX2 using a unique P-RUNX2-specific antibody. Both MAP kinases stimulated RUNX2 Ser319 phosphorylation and transcriptional activity. However, a clear preference for ERK1 versus p38α/β was found when the ability of these MAPKs to phosphorylate and activate RUNX2 was compared. Similarly, ERK1 preferentially bound to a consensus MAPK binding site on RUNX2 that was essential for the activity of either kinase. To assess the relative contribution of ERK1/2 and p38 to osteoblast gene expression, MC3T3-E1 preosteoblast cells were grown in control or ascorbic acid (AA)-containing medium ± BMP2/7. AA-induced gene expression, which requires collagen matrix synthesis, was associated with parallel increases in P-ERK and RUNX2-S319-P in the absence of any changes in P-p38. This response was blocked by ERK, but not p38, inhibition. Significantly, in the presence of AA, BMP2/7 synergistically stimulated RUNX2 S319 phosphorylation and transcriptional activity without affecting total RUNX2 and this response was totally dependent on ERK/MAPK activity. In contrast, although p38 inhibition partially blocked BMP-dependent transcription, it did not affect RUNX2 S319 phosphorylation, suggesting the involvement of other phosphorylation sites and/or transcription factors in this response. Based on this work, we conclude that extracellular matrix and BMP regulation of RUNX2 phosphorylation and transcriptional activity in osteoblasts is predominantly mediated by ERK rather than p38 MAPKs.

The optimal dose of recombinant human osteogenic protein-1 enhances differentiation of mouse osteoblast-like cells: an in vitro study

OBJECTIVE

There is no certain conclusion on the effect of recombinant human Osteogenic Protein-1 (OP-1, BMP-7) on the proliferation of the osteoblast-like cell line, MC3T3-E1. Furthermore, the optimal dose of rhOP-1 on cell differentiation still needs to be elucidated. This investigation aims to delineate the biofunctional characteristics of rhOP-1 in inducing osteoblastogenesis of MC3T3-E1 through in vitro time-course and dose-response studies.

DESIGN

MC3T3-E1 cells were cultured for 1, 4, 7 days with the addition of different rhOP-1 concentrations (0, 10, 20, 50, 100, 200, 400 ng/ml), and cell proliferation and cell differentiation were examined.

RESULTS

MC3T3-E1 cell proliferation was stimulated by rhOP-1 in a dose-dependent manner (0-400 ng/ml) on day 1, whereas on day 4 and 7, it was still stimulated at low concentrations (10, 20, 50 ng/ml) but inhibited at high ones (200, 400 ng/ml). The alkaline phosphatase (ALP) activity, osteocalcin (OC) production, collagen deposition and extracellular matrix mineralization were dramatically elevated by rhOP-1 treatment, as a function of culture time and rhOP-1 concentration, and all of them reached a plateau at the concentration of 200 ng/ml. Real-time quantitative RT-PCR results showed Runx2, AKP-2, OC and Nog mRNA expressions increased in a dose- and time-dependent manner, and their expressions were significantly higher at high rhOP-1 concentrations than that of low ones. No significant differences were found between the effects of 200 ng/ml rhOP-1 and 400 ng/ml rhOP-1 on the differentiation of MC3T3-E1 cells, except the expression of Nog mRNA, whose expression level was much higher at 400 ng/ml than that at 200 ng/ml.

CONCLUSIONS

These results suggest that cell proliferation of MC3T3-E1 is depended on culture time and rhOP-1 concentration, rhOP-1 could stimulate the differentiation of MC3T3-E1 cells and the optimal concentration could be 200 ng/ml.

Resveratrol promotes osteogenesis of human mesenchymal stem cells by upregulating RUNX2 gene expression via the SIRT1/FOXO3A axis

Reports of the bone-protective effects of resveratrol, a naturally occurring phytoestrogen and agonist for the longevity gene SIRT1, have highlighted this compound as a candidate for therapy of osteoporosis. Moreover, SIRT1 antagonism enhances adipogenesis. There has been speculation that resveratrol can promote osteogenesis through SIRT1, but the mechanism remains unclear. In this study we investigated the molecular mechanism of how resveratrol can modulate the lineage commitment of human mesenchymal stem cells to osteogenesis other than adipogenesis. We found that resveratrol promoted spontaneous osteogenesis but prevented adipogenesis in human embryonic stem cell-derived mesenchymal progenitors. Resveratrol upregulated the expression of osteo-lineage genes RUNX2 and osteocalcin while suppressing adipo-lineage genes PPARγ2 and LEPTIN in adipogenic medium. Furthermore, we found that the osteogenic effect of resveratrol was mediated mainly through SIRT1/FOXO3A with a smaller contribution from the estrogenic pathway. Resveratrol activated SIRT1 activity and enhanced FOXO3A protein expression, a known target of SIRT1, in an independent manner. As a result, resveratrol increased the amount of the SIRT1-FOXO3A complex and enhanced FOXO3A-dependent transcriptional activity. Ectopic overexpression or silencing of SIRT1/FOXO3A expression regulated RUNX2 promoter activity, suggesting an important role for SIRT1-FOXO3A complex in regulating resveratrol-induced RUNX2 gene transcription. Further mutational RUNX2 promoter analysis and chromatin immunoprecipitation assay revealed that resveratrol-induced SIRT1-FOXO3A complex bound to a distal FOXO response element (-1269/-1263), an action that transactivated RUNX2 promoter activity in vivo. Taken together, our results describe a novel mechanism of resveratrol in promoting osteogenesis of human mesenchymal stem cells by upregulating RUNX2 gene expression via the SIRT1/FOXO3A axis.

Spata4 promotes osteoblast differentiation through Erk-activated Runx2 pathway

The spermatogenesis associated 4 gene (Spata4, previously named TSARG2) was demonstrated to participate in spermatogenesis. Here we report that Spata4 is expressed in osteoblasts and that overexpression of Spata4 accelerates osteoblast differentiation and mineralization in MC3T3-E1 cells. We found that Spata4 interacts with p-Erk1/2 in the cytoplasm and that overexpression of Spata4 enhances the phosphorylation of Erk1/2. Intriguingly, we observed that Spata4 increases the transcriptional activity of Runx2, a critical transcription factor regulating osteoblast differentiation. We showed that Spata4-activated Runx2 is through the activation of Erk1/2. Consistent with this observation, we found that overexpression of Spata4 increases the expression of osteoblastic marker genes, including osteocalcin (Ocn), Bmp2, osteopontin (Opn), type 1 collagen, osterix (Osx), and Runx2. We concluded that Spata4 promotes osteoblast differentiation and mineralization through the Erk-activated Runx2 pathway. Our findings provided new evidence that Spata4 plays a role in regulation of osteoblast differentiation.

Thrombospondin-1 prevents excessive ossification in cartilage repair tissue induced by osteogenic protein-1

This study investigated the effect of thrombospondin-1 (TSP-1) on the formation of cartilage repair tissue in combination with stimulation by osteogenic protein-1 (OP-1). In miniature pigs, articular cartilage lesions in the femoral trochlea were treated by the microfracture technique and either received no further treatment (MFX), or were treated by additional application of recombinant osteogenic protein-1 (MFX+OP-1), recombinant TSP-1 (MFX+TSP-1), or a combination of both proteins (MFX+TSP-1+OP-1). Six and 26 weeks after surgery, the repair tissue and the degree of endochondral ossification were assessed by histochemical and immunohistochemical methods detecting collagen types I, II, X, TSP-1, and CD31. Microfracture treatment merely induced the formation of inferior fibrocartilaginous repair tissue. OP-1 stimulated chondrogenesis, but also induced chondrocyte hypertrophy, characterized by synthesis of collagen type X, and excessive bone formation. Application of TSP-1 inhibited inadvertant endochondral ossification, but failed to induce chondrogenesis. In contrast, the simultaneous application of both TSP-1 and OP-1 induced and maintained a permanent, nonhypertrophic chondrocyte-like phenotype within cartilage repair tissue. The data of this study demonstrate that OP-1 and TSP-1 complement each other in a functional manner. While OP-1 induces chondrogenesis of the ingrowing cells, TSP-1 prevents their further hypertrophic differentiation and prevents excessive endochondral ossification within the lesions.

Nell-1 enhances bone regeneration in a rat critical-sized femoral segmental defect model

BACKGROUND

Effective regeneration of bone is critical for fracture repair and incorporation and healing of bone grafts used during orthopedic, dental, and craniofacial reconstructions. Nel-like molecule-1 (Nell-1) is a secreted protein identified from prematurely fused cranial sutures of craniosynostosis patients that has been found to specifically stimulate osteogenic cell differentiation and bone formation. To test the in vivo osteoinductive capacity of Nell-1, a critical-sized femoral segmental defect model in athymic rats was used.

METHODS

A 6-mm defect, which predictably leads to nonunion if left untreated, was created in the left femur of each rat. Three treatment groups (n = 8 each) were created consisting of rats treated with (1) 1.5 mg/ml Nell-1, (2) 0.6 mg/ml Nell-1, and (3) phosphate-buffered saline only as a Nell-free control. Phosphate-buffered saline or Nell-1 was mixed with demineralized bone matrix as a carrier before implantation. All animals were euthanized 12 weeks after surgery, and bone regeneration was evaluated using radiographic, three-dimensional micro-computed tomographic, and histologic analysis.

RESULTS

Both Nell-1-treated groups had significantly greater bone formation compared with the Nell-free group, with bone volume increasing with increasing Nell-1 concentration.

CONCLUSIONS

Nell-1 in a demineralized bone matrix carrier can significantly improve bone regeneration in a critical-sized femoral segmental defect in a dose-dependent manner. The results of this study demonstrate that Nell-1 is a potent osteospecific growth factor that warrants further investigation. Results also support the potential application of Nell-1 as a bone graft substitute in multiple clinical scenarios involving repair of critical bone loss when autograft bone is limited or unavailable.

Nell-1 protein promotes bone formation in a sheep spinal fusion model

Bone morphogenetic proteins (BMPs) are widely used as bone graft substitutes in spinal fusion, but are associated with numerous adverse effects. The growth factor Nel-like molecule-1 (Nell-1) is mechanistically distinct from BMPs and can minimize complications associated with BMP therapies. This study evaluates the efficacy of Nell-1 combined with demineralized bone matrix (DBM) as a novel bone graft material for interbody spine fusion using sheep, a phylogenetically advanced animal with biomechanical similarities to human spine. Nell-1+sheep DBM or Nell-1+heat-inactivated DBM (inDBM) (to determine the osteogenic effect of residual growth factors in DBM) were implanted in surgical sites as follows: (1) DBM only (control) (n=8); (2) DBM+0.3 mg/mL Nell-1 (n=8); (3) DBM+0.6 mg/mL Nell-1 (n=8); (4) inDBM only (control) (n=4); (5) inDBM+0.3 mg/mL Nell-1 (n=4); (6) inDBM+0.6 mg/mL Nell-1 (n=4). Fusion was assessed by computed tomography, microcomputed tomography, and histology. One hundred percent fusion was achieved by 3 months in the DBM+0.6 mg/mL Nell-1 group and by 4 months in the inDBM+0.6 mg/mL Nell-1 group; bone volume and mineral density were increased by 58% and 47%, respectively. These fusion rates are comparable to published reports on BMP-2 or autograft bone efficacy in sheep. Nell-1 is an independently potent osteogenic molecule that is efficacious and easily applied when combined with DBM.

Osteogenic differentiation of human umbilical cord mesenchymal stromal cells in polyglycolic acid scaffolds

Although human umbilical cord mesenchymal stromal cells (hUCMSCs) have been shown to differentiate along an osteogenic lineage in monolayer culture, the potential of these cells has seldom before been investigated in three-dimensional scaffolds for bone tissue engineering applications. In this 6-week study, we observed osteogenic differentiation of hUCMSCs on polyglycolic acid (PGA) nonwoven mesh scaffolds, and compared seeding densities for potential use in bone tissue engineering. Cells were seeded into PGA meshes with densities of 5, 25, or 50 x 10(6) cells/mL scaffold and then cultured in osteogenic medium. Cell proliferation, osteogenic differentiation, and matrix formation were evaluated at weeks 0, 3, and 6. Osteogenic differentiation was observed based on positive alkaline phosphatase activity and an increase of collagen production and calcium incorporation into the extracellular matrix, which increased with higher cell density. During differentiation, runt-related transcription factor (RUNX2), type I collagen (CI), and osteocalcin (OCN) gene expression levels were also increased. In conclusion, exposed to osteogenic signals, hUCMSCs differentiated along an osteogenic lineage as determined by expression of osteogenic markers and matrix formation, and increasing the density of hUCMSCs seeded onto three-dimensional PGA scaffolds led to better osteogenic differentiation.

The role of NELL-1, a growth factor associated with craniosynostosis, in promoting bone regeneration

Efforts to enhance bone regeneration in orthopedic and dental cases have grown steadily for the past decade, in line with increasingly sophisticated regenerative medicine. To meet the unprecedented demand for novel osteospecific growth factors with fewer adverse effects compared with those of existing adjuncts such as BMPs, our group has identified a craniosynostosis-associated secreted molecule, NELL-1, which is a potent growth factor that is highly specific to the osteochondral lineage, and has demonstrated robust induction of bone in multiple in vivo models from rodents to pre-clinical large animals. NELL-1 is preferentially expressed in osteoblasts under direct transcriptional control of Runx2, and is well-regulated during skeletal development. NELL-1/Nell-1 can promote orthotopic bone regeneration via either intramembranous or endochondral ossification, both within and outside of the craniofacial complex. Unlike BMP-2, Nell-1 cannot initiate ectopic bone formation in muscle, but can induce bone marrow stromal cells (BMSCs) to form bone in a mouse muscle pouch model, exhibiting specificity that BMPs lack. In addition, synergistic osteogenic effects of Nell-1 and BMP combotherapy have been observed, and are likely due to distinct differences in their signaling pathways. NELL-1's unique role as a novel osteoinductive growth factor makes it an attractive alternative with promise for future clinical applications. [Note: NELL-1 and NELL-1 indicate the human gene and protein, respectively; Nell-1 and Nell-1 indicate the mouse gene and protein, respectively.]

Runx2 regulates survivin expression in prostate cancer cells

Previously we described that bone morphogenetic protein-7 (BMP7) could protect prostate cancer C4-2B cells from serum starvation-induced apoptosis via survivin induction. Here, for the first time, we identify Runx2 as a key regulator of survivin transcription. In C4-2B cells grown normally, suppression of Runx2 reduced survivin expression. Using ChIP assays, two regions of the survivin promoter, -1953 to -1812 (I) and -1485 to -1119 (II) encompassing consensus Runx-binding sites were examined. Runx2 was found to be associated with both regions, with a stronger affinity to region-I. In serum-starved cells neither region was occupied, but BMP7 restored association to region-II and not region-I. In reporter assays, transcription activity by BMP7 was significantly reduced when sequences including binding sites of region-II were deleted. Additionally, Runx2 expression was enhanced by BMP7 in these cells. Along with a strong survivin expression, a trend in increased Runx2 expression in human prostate cancer cells and tissues was noted. In the conditional Pten-knockout mouse, Runx2 level increased with growth of prostate tumor. The data define a novel role of Runx2 in regulating survivin expression in malignant epithelial cells and identify it as a critical factor in BMP signaling that protects cancer cells against apoptosis.

Osteopenia and osteoporosis in HIV: pathogenesis and treatment

PURPOSE OF REVIEW

Since the introduction of potent antiretroviral therapy, the emphasis in managing HIV patients has changed from treatment and prevention of opportunistic infections to dealing with toxicities of long-term antiretroviral therapy such as bone demineralization. To date, the pathogenic mechanisms underlying the initiation and progression of osteoporosis in HIV patients remain to be elucidated. This review focuses on recent advances in our understanding of the role of both HIV and antiretroviral therapy in driving bone disease and presents an update on current treatment options and new therapeutic agents targeting novel sites.

RECENT FINDINGS

Recent studies explored the role of HIV and individual antiretroviral therapy drugs in modifying the phenotype of bone cells. Studies have demonstrated effects on cell differentiation, maturation and function in response to both HIV and its treatment - effects mediated via direct alterations in both cell signaling and gene and protein expression.

SUMMARY

Evidence from clinical and cell biological investigations has demonstrated the importance of both HIV and antiretroviral therapy in the emergence of osteoporotic bone disease. Continued efforts aimed at deciphering the molecular basis of metabolic bone disease in HIV patients are necessary to ensure optimal treatment of current patients and to create novel therapeutic interventions.

Identification and functional characterization of ERK/MAPK phosphorylation sites in the Runx2 transcription factor

The Runx2 transcription factor is required for commitment of mesenchymal cells to bone lineages and is a major regulator of osteoblast-specific gene expression. Runx2 is subject to a number of post-transcriptional controls including selective proteolysis and phosphorylation. We previously reported that Runx2 is phosphorylated and activated by the ERK/MAPK pathway (Xiao, G., Jiang, D., Thomas, P., Benson, M. D., Guan, K., Karsenty, G., and Franceschi, R. T. (2000) J. Biol. Chem. 275, 4453-4459). In this study, we used a combination of in vitro and in vivo phosphorylation analysis, mass spectroscopy, and functional assays to identify two sites at Ser(301) and Ser(319) within the proline/serine/threonine domain of Runx2 that are required for this regulation. These sites are phosphorylated by activated ERK1 in vitro and in cell culture. In addition to confirming ERK-dependent phosphorylation at Ser(319), mass spectroscopy identified two other ERK-phosphorylated sites at Ser(43) and Ser(510). Furthermore, introduction of S301A,S319A mutations rendered Runx2 resistant to MAPK-dependent activation and reduced its ability to stimulate osteoblast-specific gene expression and differentiation after transfection into Runx2-null calvarial cells and mesenchymal cells. In contrast, S301E,S319E Runx2 mutants had enhanced transcriptional activity that was minimally dependent on MAPK signaling, consistent with the addition of a negative charge mimicking serine phosphorylation. These results emphasize the important role played by Runx2 phosphorylation in the control of osteoblast gene expression and provide a mechanism to explain how physiological signals acting on bone through the ERK/MAPK pathway can stimulate osteoblast-specific gene expression.

Signalling strategies for osteogenic differentiation of human umbilical cord mesenchymal stromal cells for 3D bone tissue engineering

Human umbilical cord mesenchymal stromal cells (hUCMSCs) have recently shown the capacity to differentiate into multiple cell lineages in all three embryonic germ layers. The osteogenic differentiation of hUCMSCs in monolayer culture has been reported, while the differentiation in three-dimensional biomaterials has not yet been reported for tissue-engineering applications. Thus, the aim of this study was to evaluate the feasibility of using hUCMSCs for bone tissue engineering. hUCMSCs were cultured in poly(L-lactic acid) (PLLA) scaffolds in osteogenic medium (OM) for 3 weeks, after which the scaffolds were exposed to several different media, including the OM, a mineralization medium (MM) and the MM with either 10 or 100 ng/ml insulin-like growth factor (IGF)-1. The osteogenic differentiation was confirmed by the up-regulation of Runx2 and OCN, calcium quantification and bone histology. Switching from the OM to the MM promoted collagen synthesis and calcium content per cell, while continuing in the OM retained more cells in the constructs and promoted higher osteogenic gene expression. The addition of IGF-1 into the MM had no effect on cell proliferation, differentiation and matrix synthesis. In conclusion, hUCMSCs show significant potential for bone tissue engineering and culturing in the OM throughout the entire period is beneficial for osteogenic differentiation of these cells.

Experimental assessment of calvarial bone defect re-ossification stimulation using low-intensity pulsed ultrasound

Ultrasound treatment has been proposed by several authors to enhance the repair of long bone injury. The present study investigated in a murine model the treatment by low-intensity pulsed ultrasound (LIPUS) of calvarial flat bone defect. The animals were operated to create bone defect and exposed to ultrasound for 5 min per day, 5 d per week, during two weeks. Two intensities of ultrasound (1 MHz, 100 Hz pulse repetition frequency and 20% duty cycle) were investigated: 100 and 300 mW/cm(2) spatial-averaged, time-averaged. Re-ossification surface and volume were determined after 30 and 60 days using computerized X-ray tomography in all animals of the control and treated groups. The results showed a significant increase of bone re-ossification in the group treated with the higher-intensity ultrasound (mean value of 18% volume reconstruction), whereas lower bone reconstruction was observed in the lower-intensity and control groups (respective mean values of 10 and 12% volume reconstruction).

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.

cis-Decoder discovers constellations of conserved DNA sequences shared among tissue-specific enhancers

: The use of cis-Decoder, a new tool for discovery of conserved sequence elements that are shared between similarly regulating enhancers, suggests that enhancers use overlapping repertoires of highly conserved core elements.

A systematic approach is described for analysis of evolutionarily conserved cis-regulatory DNA using cis-Decoder, a tool for discovery of conserved sequence elements that are shared between similarly regulated enhancers. Analysis of 2,086 conserved sequence blocks (CSBs), identified from 135 characterized enhancers, reveals most CSBs consist of shorter overlapping/adjacent elements that are either enhancer type-specific or common to enhancers with divergent regulatory behaviors. Our findings suggest that enhancers employ overlapping repertoires of highly conserved core elements.

Bone morphogenetic protein 7 expression associates with bone metastasis in breast carcinomas

BACKGROUND

We recently showed that bone morphogenetic protein 7 (BMP7) is overexpressed in primary breast tumors. Here we explored the clinical significance of BMP7 expression in breast cancer.

MATERIALS AND METHODS

This study included 483 breast cancer patients with complete clinicopathological information and up to 15 years of follow-up. Samples contained 241 lobular carcinomas, 242 ductal carcinomas, and 40 local recurrences. BMP7 protein expression was determined using immunohistochemistry.

RESULTS

BMP7 was expressed in 47% of the primary tumor samples and 13% of the local recurrences. The primary tumors expressed BMP7 more often than the corresponding local recurrences (P = 0.004). BMP7 expression was dependent on the tumor subtype; 57% of the lobular carcinomas but only 37% of the ductal carcinomas were BMP7 positive (P = 0.0001). BMP7 expression was associated with accelerated bone metastasis formation (P = 0.040), especially in ductal carcinomas (P = 0.033), and multivariate analysis confirmed that BMP7 is an independent prognostic indicator for early bone metastasis development (P = 0.032).

CONCLUSION

BMP7 is clearly associated with bone metastasis formation and thus might have clinical utility in identification of patients with increased risk of bone metastasis. This is the first time that bone inducing factor BMP7 has been linked to the bone metastasis process in breast cancer.

Semi-quantitative RT-PCR analysis of LIM mineralization protein 1 and its associated molecules in cultured human dental pulp cells

OBJECTIVE

LIM mineralization protein 1 (LMP-1), an intracellular signaling molecule, regulates osteoblast differentiation and maturation, as well as bone formation. However, the role of LMP-1 in the differentiation of human dental pulp cells and formation of dentin has not been determined. The study was to investigate the expression of LMP-1, the related proteins, such as bone morphogenetic proteins 2, 6 and 7 (BMP-2, BMP-6 and BMP-7), and core binding factor alpha 1 (Cbfa1) during the differentiation of cultured human dental pulp cells and the formation of mineralized nodules.

DESIGN

Differentiation of human dental pulp cells was induced by dexamethasone, asorbic acid and beta-glycerophosphate. The formation of mineralized nodules, was determined by Von Kossa staining and immunocytochemistry detection of dentin sialoprotein. Expression of LMP-1, the related proteins and the differentiation marker alkaline phosphatase (ALP) was analysed by reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

The expression of LMP-1, BMP-2, BMP-6, BMP-7 and Cbfa1 was significantly increased in the process of dental pulp cells differentiation and the formation of mineralized nodules, while the pattern of the expression was distinct.

CONCLUSIONS

The elevated level of LMP-1, BMPs and Cbfa1 expression indicated they might play a role in the differentiation of human dental pulp cells and the formation of mineralized nodules.

Critical role of the extracellular signal-regulated kinase-MAPK pathway in osteoblast differentiation and skeletal development

The extracellular signal-regulated kinase (ERK)-mitogen-activated protein kinase (MAPK) pathway provides a major link between the cell surface and nucleus to control proliferation and differentiation. However, its in vivo role in skeletal development is unknown. A transgenic approach was used to establish a role for this pathway in bone. MAPK stimulation achieved by selective expression of constitutively active MAPK/ERK1 (MEK-SP) in osteoblasts accelerated in vitro differentiation of calvarial cells, as well as in vivo bone development, whereas dominant-negative MEK1 was inhibitory. The involvement of the RUNX2 transcription factor in this response was established in two ways: (a) RUNX2 phosphorylation and transcriptional activity were elevated in calvarial osteoblasts from TgMek-sp mice and reduced in cells from TgMek-dn mice, and (b) crossing TgMek-sp mice with Runx2+/- animals partially rescued the hypomorphic clavicles and undemineralized calvaria associated with Runx2 haploinsufficiency, whereas TgMek-dn; Runx2+/- mice had a more severe skeletal phenotype. This work establishes an important in vivo function for the ERK-MAPK pathway in bone that involves stimulation of RUNX2 phosphorylation and transcriptional activity.

Endoglin differentially modulates antagonistic transforming growth factor-beta1 and BMP-7 signaling

Transforming growth factor-beta1 (TGF-beta1) and BMP-7 (bone morphogenetic protein-7; OP-1) play central, antagonistic roles in kidney fibrosis, a setting in which the expression of endoglin (CD105), an accessory TGF-beta type III receptor, is increased. So far, endoglin is known as a negative regulator of TGF-beta/ALK-5 signaling. Here we analyzed the effect of BMP-7 on TGF-beta1 signaling and the role of endoglin for both pathways in endoglin-deficient L(6)E(9) cells. In this myoblastic cell line, TGF-beta1 and BMPs are opposing cytokines, interfering with myogenic differentiation. Both induce specific target genes of which Id1 (for BMPs) and collagen I (for TGF-beta1) are two examples. TGF-beta1 activated two distinct type I receptors, ALK-5 and ALK-1, in these cells. Although the ALK-5/Smad3 signaling pathway mediated collagen I expression, ALK-1/Smad1/Smad5 signaling mediated a transient Id1 up-regulation. In contrast, BMP-7 exclusively activated Smad1/Smad5 resulting in a more prolonged Id1 expression. Although BMP-7 had no impact on collagen I abundance, it antagonized TGF-beta1-induced collagen I expression and (CAGA)(12)-MLP-Luc activity, effects that are mediated by the ALK-5/Smad3 pathway. Finally, we found that the transient overexpression of endoglin, previously shown to inhibit TGF-beta1-induced ALK-5/Smad3 signaling, enhanced the BMP-7/Smad1/Smad5 pathway.

Cbfa-1 mediates nitric oxide regulation of MMP-13 in osteoblasts

During bone development, osteoblast differentiation requires remodeling of the extracellular matrix. Although underlying mechanisms have not been elucidated, evidence points to the participation of the nitric oxide (NO) and cyclic guanosine 3',5'-monophosphate (cGMP) system. Here, we detected increased matrix metalloproteinase (MMP)-13 mRNA, protein and activity, as well as increased inducible NO synthase (iNOS) and NO production during the differentiation of MC3T3-E1 osteoblasts. Transcriptional activity of the MMP-13 promoter was augmented by NO, 8-bromo-cGMP (8-Br-cGMP), and by a dominant-positive form of protein kinase G (PKG1-alpha). The stimulatory effect on the MMP-13 promoter was partially inhibited by mutation of the osteoblast-specific element 2 (OSE-2) binding site. Core binding factor-1 (Cbfa-1) expression peaked at 7 days of differentiation, and was phosphorylated by PKG in vitro. Cbfa-1 was localized to cell nuclei, and its translocation was inhibited by the iNOS inhibitor 1400W. Immunohistological examination revealed that MMP-13 and Cbfa-1 expression levels are both reduced in 17-day-old embryos of iNOS-deficient mice. Silencing of Cbfa-1 mRNA blocked MMP-13 expression without interfering with endogenous NO production, confirming its role in NO-induced MMP-13 expression by MC3T3-E1 cells. The results described here suggest a mechanism by which NO regulates osteogenesis.

BMP-7 and CBFA1 in allograft bone in vivo bone formation and the influence of gamma-irradiation

An initial study showed that morselized human bone grafts were osteoconductive and osteoinductive when implanted in nude rat tibial window defects, and 25 kGy of gamma-irradiation significantly reduced those properties. The mechanism of the osteoinductivity and the influence of gamma-irradiation required further investigation. In this study we assessed the paraffin sections of seven morselized human bone grafts implanted into rat tibial defects for 3 weeks after being treated with 0, 15, or 25 kGy gamma-radiation respectively. Osteoclast-like cell counting and protein expressions of bone morphogenetic protein-7 (BMP-7), core binding factor alpha1 (CBFA1), and proliferating cell nuclear antigen (PCNA) were investigated and the positive signals were quantitatively analyzed. More new bone formation was observed in the 0 and 15 kGy groups compared with 25 kGy groups. The newly formed bones were found mainly from the intact cortex into the defects bridged by the implanted grafts. A dense staining of BMP-7 and CBFA1 was noted in the osteoblast-like cells in those areas. The BMP-7 and CBFA1 staining was also seen in the cells surrounding the implanted grafts in the centre areas of the defects in distance from the intact cortex. Quantitative analysis of immunohistochemical staining of the centre areas of the defects showed that gamma-irradiation (15 and 25 kGy) significantly reduced the expression of CBFA1 and BMP-7. In conclusion, morselized human bone grafts may contain some factors, which induced osteoblast lineage differentiation and bone formation and gamma-irradiation damages those bone inducing factors.