Msx2 mediates the inhibitory action of TNF-alpha on osteoblast differentiation

Vascular calcification and cellular signaling pathways as potential therapeutic targets

Increased vascular calcification (VC) is observed in patients with cardiovascular diseases such as atherosclerosis, diabetes, and chronic kidney disease. VC is divided into three types according to its location: intimal, medial, and valvular. Various cellular signaling pathways are associated with VC, including the Wnt, mitogen-activated protein kinase, phosphatidylinositol-3 kinase/Akt, cyclic nucleotide-dependent protein kinase, protein kinase C, calcium/calmodulin-dependent kinase II, adenosine monophosphate-activated protein kinase/mammalian target of rapamycin, Ras homologous GTPase, apoptosis, Notch, and cytokine signaling pathways. In this review, we discuss the literature concerning the key cellular signaling pathways associated with VC and their role as potential therapeutic targets. Inhibitors to these pathways represent good candidates for use as potential therapeutic agents for the prevention and treatment of VC.

Nociceptor-Macrophage Interactions in Apical Periodontitis: How Biomolecules Link Inflammation with Pain

Periradicular tissues have a rich supply of peripheral afferent neurons, also known as nociceptive neurons, originating from the trigeminal nerve. While their primary function is to relay pain signals to the brain, these are known to be involved in modulating innate and adaptive immunity by initiating neurogenic inflammation (NI). Studies have investigated neuroanatomy and measured the levels of biomolecules such as cytokines and neuropeptides in human saliva, gingival crevicular fluid, or blood/serum samples in apical periodontitis (AP) to validate the possible role of trigeminal nociceptors in inflammation and tissue regeneration. However, the contributions of nociceptors and the mechanisms involved in the neuro-immune interactions in AP are not fully understood. This narrative review addresses the complex biomolecular interactions of trigeminal nociceptors with macrophages, the effector cells of the innate immune system, in the clinical manifestations of AP.

Liver-bone crosstalk in non-alcoholic fatty liver disease: Clinical implications and underlying pathophysiology

Osteoporosis is a common complication of many types of chronic liver diseases (CLDs), such as cholestatic liver disease, viral hepatitis, and alcoholic liver disease. Non-alcoholic fatty liver disease (NAFLD) is a highly prevalent metabolic liver disease, affecting almost one third of adults around the world, and is emerging as the dominant cause of CLDs. Liver serves as a hub for nutrient and energy metabolism in the body, and its crosstalk with other tissues, such as adipose tissue, heart, and brain, has been well recognized. However, much less is known about the crosstalk that occurs between the liver and bone. Moreover, the mechanisms by which CLDs increase the risk for osteoporosis remain unclear. This review summarizes the latest research on the liver-bone axis and discusses the relationship between NAFLD and osteoporosis. We cover key signaling molecules secreted by liver, such as insulin-like growth factor-1 (IGF-1), fibroblast growth factor 21 (FGF21), insulin-like growth factor binding protein 1 (IGFBP1), fetuin-A, tumor necrosis factor-alpha (TNF-α), and osteopontin (OPN), and their relevance to the homeostasis of bone metabolism. Finally, we consider the disordered liver metabolism that occurs in patients with NAFLD and how this disrupts signaling to the bone, thereby perturbing the balance between osteoclasts and osteoblasts and leading to osteoporosis or hepatic osteodystrophy (HOD).

Intercellular Communication Reveals Therapeutic Potential of Epithelial-Mesenchymal Transition in Triple-Negative Breast Cancer

(1) Background: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with high intra-tumoral heterogeneity. The epithelial-mesenchymal transition (EMT) is one of the inducers of cancer metastasis and migration. However, the description of the EMT process in TNBC using single-cell RNA sequencing (scRNA-seq) remains unclear. (2) Methods: In this study, we analyzed 8938 cellular gene expression profiles from five TNBC patients. We first scored each malignant cell based on functional pathways to determine its EMT characteristics. Then, a pseudo-time trajectory analysis was employed to characterize the cell trajectories. Furthermore, CellChat was used to identify the cellular communications. (3) Results: We identified 888 epithelium-like and 846 mesenchyme-like malignant cells, respectively. A further pseudo-time trajectory analysis indicated the transition trends from epithelium-like to mesenchyme-like in malignant cells. To characterize the potential regulators of the EMT process, we identified 10 dysregulated transcription factors (TFs) between epithelium-like and mesenchyme-like malignant cells, in which overexpressed forkhead box protein A1 (FOXA1) was recognized as a poor prognosis marker of TNBC. Furthermore, we dissected the cell-cell communications via ligand-receptor (L-R) interactions. We observed that tumor-associated macrophages (TAMs) may support the invasion of malignant epithelial cells, based on CXCL-CXCR2 signaling. The tumor necrosis factor (TNF) signaling pathway secreted by TAMs was identified as an outgoing communication pattern, mediating the communications between monocytes/TAMs and malignant epithelial cells. Alternatively, the TNF-related ligand-receptor (L-R) pairs showed promising clinical implications. Some immunotherapy and anti-neoplastic drugs could interact with the L-R pairs as a potential strategy for the treatment of TNBC. In summary, this study enhances the understanding of the EMT process in the TNBC microenvironment, and dissections of EMT-related cell communications also provided us with potential treatment targets.

Strontium based Astragalus polysaccharides promote osteoblasts differentiation and mineralization

Bone formation and repair represent a clinical challenge. In this work, we designed and synthesized strontium Astragalus polysaccharide (APS-Sr), a novel polysaccharide compound that should have therapeutic effects on both anti-inflammation and promoting bone formation. Using material characterization techniques, including SEM, FITR, XRD, etc., we verified the successful synthesis of this compound. Moreover, we examined the potential of this compound for promoting bone repair and inhibiting inflammatory response by cell proliferation assay, ALP and Alizarin Red staining experiments and RT-qPCR. The biological experiment results showed that APS-Sr can effectively inhibit inflammatory factors, promote osteogenic differentiation and up-regulate the bone growth factors. It is therefore believed that APS-Sr should be a promising polysaccharide compound in bone-related biomedical applications.

MiR-151b inhibits osteoblast differentiation via downregulating Msx2

PURPOSE

MicroRNA-151b (miR-151b) showed altered expression in ovariectomized rat model of osteoporosis. This study established an ovariectomy-induced osteoporotic rat model to investigate the role of miR-151b in osteoblasts.

METHODS

Eighteen female Sprague-Dawley (SD) rats were divided randomly into Sham and OVX group (n = 9). The transfections with different miRNAs and expression vectors were confirmed by RT-qPCR. The protein expression of Msx2 was detected by Western blots. The interaction between miR-151b and Msx2D was evaluated by RNA pull-down and dual luciferase reporter assay.

RESULTS

The expression of miR-151b was significantly increased in femoral tissues of ovariectomy-induced osteoporotic rats. The expression of osteogenesis marker genes including RUNX2, ALP, OCN, OSX, and Msx2 were all significantly increased in osteogenic medium (OM) incubated primary osteoblasts and MC3T3-E1 cells. The interaction between miR-151b and Msx2 was confirmed by luciferase reporter assay and RNA pull-down. Moreover, overexpression of miR-151b significantly inhibited Msx2 in both MC3T3-E1 cells and primary osteoblasts, while miR-151b inhibitor had the opposite effect on the expression of Msx2. In addition, in primary osteoblasts and MC3T3-E1 cells, miR-151b overexpression, or Msx2 silence significantly decreased the expression of OSX, ALP, RUNX2, and OCN.

CONCLUSION

MiR-151b could inhibit osteoblast proliferation, differentiation, and mineralization via downregulating Msx2 in both MC3T3-E1 cells and primary osteoblasts. MiR-151b might serve as a novel therapeutic target for osteoporosis.

ABBREVIATIONS

miR-151b: microRNA-151b; miRNAs: microRNAs; Msx2: Msh homeobox 2; MAPK: mitogen-activated protein kinase; STAT: signal transducer and activator of transcription; SD: Sprague-Dawley; BMD: bone mineral density; qRT-PCR: quantitative reverse transcription PCR; MTT: methyl thiazolyl tetrazolium; OVX: ovariectomy; ALP: alkaline phosphatase.

Evaluating the Expression of Candidate Homeobox Genes and Their Role in Local-Site Inflammation in Mucosal Tissue Obtained from Children with Non-Syndromic Cleft Lip and Palate

Craniofacial development including palatogenesis is a complex process which requires an orchestrated and spatiotemporal expression of various genes and factors for proper embryogenesis and organogenesis. One such group of genes essential for craniofacial development is the homeobox genes, transcriptional factors that are commonly associated with congenital abnormalities. Amongst these genes, DLX4, HOXB3, and MSX2 have been recently shown to be involved in the etiology of non-syndromic cleft lip and palate. Hence, we investigated the gene and protein expression of these genes in normal and cleft affected mucosal tissue obtained from 22 children, along with analyzing their role in promoting local-site inflammation using NF-κB. Additionally, we investigated the role of PTX3, which plays a critical role in tissue remodeling and wound repair. We found a residual gene and protein expression of DLX4 in cleft mucosa, although no differences in gene expression levels of HOXB3 and MSX2 were noted. However, a significant increase in protein expression for these genes was noted in the cleft mucosa (p < 0.05), indicating increased cellular proliferation. This was coupled with a significant increase in NF-κB protein expression in cleft mucosa (p < 0.05), highlighting the role of these genes in promotion of pro-inflammatory environment. Finally, no differences in gene expression of PTX3 were noted.

Progranulin promotes osteogenic differentiation of periodontal membrane stem cells in both inflammatory and non-inflammatory conditions

Objective

The growth factor progranulin (PGRN) is widely expressed and plays important roles in anti-inflammatory signaling and bone regeneration. However, the anti-inflammatory and pro-osteogenic roles of PGRN in periodontitis are seldom studied. We used an in vitro model to investigate whether PGRN can promote osteogenic differentiation of periodontal ligament stem cells (PDLSCs).

Methods

PDLSCs were treated with PGRN (0 to 100 ng/mL) and the optimal concentrations required to induce proliferation and osteogenesis were identified. PDLSCs were cultured with 10 ng/mL tumor necrosis factor (TNF)-α, 25 ng/mL PGRN, or 10 ng/mL TNF-α + 25 ng/ml PGRN; untreated PDLSCs were used as controls. The effects of PGRN on PDLSC proliferation and osteogenic differentiation were assessed.

Results

PGRN (5, 25, and 50 ng/mL) promoted PDLSC proliferation and osteogenic differentiation, with the 25-ng/mL dose showing the largest effect. Furthermore, 25 ng/mL PGRN reversed inhibition of osteogenic differentiation by TNF-α.

Conclusion

PGRN promotes PDLSC proliferation, osteogenic differentiation, and mineralization in both inflammatory and non-inflammatory conditions. The 25-ng/mL PRGN dose was the most suitable for inducing proliferation and osteogenesis. Further studies using animal models will be required to obtain pre-clinical evidence to support using PGRN as a treatment for periodontitis.

Correlation Between 25 Hydroxyvitamin D Levels and Nonalcoholic Fatty Liver Disease in Chinese Patients with Type 2 Diabetes Mellitus: A Cross-Sectional Study

Purpose

We aimed to analyze the serum vitamin D level in Chinese patients with type 2 diabetes mellitus (T2DM) and discuss its correlation with nonalcoholic fatty liver disease (NAFLD).

Patients and Methods

A total of 300 patients with T2DM (92 patients without NAFLD and 208 patients with NAFLD) were enrolled, and 25-hydroxyvitamin D [25-(OH)D] levels were compared between the two groups. Second, the NAFLD fibrosis score (NFS) and fatty liver index (FLI) were used to group patients with T2DM complicated by NAFLD, and the differences in serum 25-(OH)D in patients with different degrees of liver fibrosis were compared. Third, multiple regression analysis was used to analyze the independent predictors of liver fibrosis in patients with T2DM complicated by NAFLD.

Results

The level of 25-(OH)D in patients with T2DM complicated by NAFLD was significantly lower than that in patients with T2DM alone. Based on the NFS and FLI, the 25-(OH)D level of the hepatic fibrosis subgroup was significantly lower than that of the subgroup without liver fibrosis. 25-(OH)D was found to be an independent predictor of liver fibrosis in patients with T2DM complicated by NAFLD.

Conclusion

The serum 25-(OH)D level in patients with T2DM complicated by NAFLD was significantly reduced, and the 25-(OH)D level showed a gradual downward trend with the degree of liver fibrosis. Low concentrations of 25-(OH)D may be indicative of the degree of liver fibrosis in diabetic patients.

Expression of VEGFA-mRNA in classical and MSX2-mRNA in non-classical monocytes in patients with spondyloarthritis is associated with peripheral arthritis

Spondyloarthritis (SpA) is characterized by chronic inflammation and structural damage involving spine and peripheral joints. Monocytes, as part of innate immune system, following migration into affected tissue, may play a role in the pathogenesis of SpA. Here, potential associations between osteogenesis-linked gene expression profile in particular monocyte subpopulations and clinical signs of SpA were investigated. The 20 patients with axial and 16 with peripheral SpA were enrolled in the study. Monocyte subpopulations (classical—CD14⁺⁺CD16⁻, intermediate—CD14⁺⁺CD16⁺ and non-classical—CD14⁺CD16⁺⁺) were isolated from blood using flow cytometry and gene expression analysis was performed using real-time PCR method and TaqMan Array, Human Osteogenesis, Fast 96-well plates. Next, the characteristic clinical features shared by axial and peripheral SpA were analyzed in the context of the expression of selected genes in the three subpopulations of monocytes. We demonstrated that expression of VEGFA in classical and MSX2 in non-classical monocytes were associated with the number of swollen and painful peripheral joints of SpA patients. We conclude that monocytes may contribute to the development of peripheral arthritis in SpA patients. This might be possible through subpopulation specific effects, linking number of inflamed joints with expression of VEGFA in classical monocytes and MSX2 in non-classical monocytes.

Experimental periodontitis in Msx2 mutant mice induces alveolar bone necrosis

BACKGROUND

Msx2 homeoprotein is a key transcription factor of dental and periodontal tissue formation and is involved in many molecular pathways controlling mineralized tissue homeostasis such as Wnt/sclerostin pathway. This study evaluated the effect of Msx2-null mutation during experimental periodontitis in mice.

METHODS

Experimental periodontitis was induced for 30 days in wild-type and Msx2 knock-in Swiss mice using Porphyromonas gingivalis infected ligatures. In knock-in mice, Msx2 gene was replaced by n-LacZ gene encoding β-galactosidase. Periodontal tissue response was assessed by histomorphometry, tartrate-resistant acid phosphatase histoenzymology, β-galactosidase, sclerostin immunochemistry, and terminal deoxynucleotidyl transferase-mediated dUTP nickend labeling assay. Expression of Msx2 gene expression was also evaluated in human gingival biopsies using RT-qPCR.

RESULTS

During experimental periodontitis, osteonecrosis area and osteoclast number were significantly elevated in knock-in mice compared with wild-type mice. Epithelial downgrowth and bone loss was similar. Sclerostin expression in osteocytes appeared to be reduced during periodontitis in knock-in mice. Msx2 expression was detected in healthy and inflamed human gingival tissues.

CONCLUSION

These data indicated that Msx2 pathway influenced periodontal tissue response to experimental periodontitis and appeared to be a protective factor against alveolar bone osteonecrosis. As shown in other inflammatory processes such as atherothrombosis, genes initially characterized in early development could also play an important role in human periodontal pathogenesis.

KLF4 as a rheostat of osteolysis and osteogenesis in prostate tumors in the bone

We previously showed that KLF4, a gene highly expressed in murine prostate stem cells, blocks the progression of indolent intraepithelial prostatic lesions into aggressive and rapidly growing tumors. Here, we show that the anti-tumorigenic effect of KLF4 extends to PC3 human prostate cancer cells growing in the bone. We compared KLF4 null cells with cells transduced with a DOX-inducible KLF4 expression system, and find KLF4 function inhibits PC3 growth in monolayer and soft agar cultures. Furthermore, KLF4 null cells proliferate rapidly, forming large, invasive, and osteolytic tumors when injected into mouse femurs, whereas KLF4 re-expression immediately after their intra-femoral inoculation blocks tumor development and preserves a normal bone architecture. KLF4 re-expression in established KLF4 null bone tumors inhibits their osteolytic effects, preventing bone fractures and inducing an osteogenic response with new bone formation. In addition to these profound biological changes, KLF4 also induces a transcriptional shift from an osteolytic program in KLF4 null cells to an osteogenic program. Importantly, bioinformatic analysis shows that genes regulated by KLF4 overlap significantly with those expressed in metastatic prostate cancer patients and in three individual cohorts with bone metastases, strengthening the clinical relevance of the findings in our xenograft model.

The Combined Effect of Nonalcoholic Fatty Liver Disease and Metabolic Syndrome on Osteoporosis in Postmenopausal Females in Eastern China

The present study evaluated the potential combined effects of NAFLD and MetS on the development of osteoporosis. The relationship between NAFLD and MetS and osteoporosis was assessed in 938 postmenopausal female participants. Moderate and severe NAFLDs were combined as significant NAFLD (SNAFLD). All the subjects were divided into 4 subgroups based on the status of SNAFLD and MetS. Relative excess risk of interaction (RERI), attributable proportion (AP) of interaction, and synergy index (SI) were used to investigate the additive interaction of those two factors. NAFLD, SNAFLD, and MetS were independent factors for osteoporosis with the adjustment of age and other confounders. The incidence of osteoporosis in MetS (+) SNAFLD (+) group was significantly higher than that in other three groups. RERI was 2.556 (95% CI = 0.475-4.636), AP was 0.454 (95% CI = 0.201-0.706), and SI was 2.231 (95% CI = 1.124 to 4.428), indicating the significant combined interaction of SNAFLD and MetS on the development of osteoporosis. SNAFLD and MetS are independent risk factors for osteoporosis in postmenopausal females, respectively. Moreover, SNAFLD and MetS have an additive effect on the development of osteoporosis.

Genetic variations for egg quality of chickens at late laying period revealed by genome-wide association study

With the extension of the egg-laying cycle, the rapid decline in egg quality at late laying period has aroused great concern in the poultry industry. Herein, we performed a genome-wide association study (GWAS) to identify genomic variations associated with egg quality, employing chicken 600 K high-density SNP arrays in a population of 1078 hens at 72 and 80 weeks of age. The results indicated that a genomic region spanning from 8.95 to 9.31 Mb (~0.36 Mb) on GGA13 was significantly associated with the albumen height (AH) and the haugh unit (HU), and the two most significant SNPs accounted for 3.12 ~ 5.75% of the phenotypic variance. Two promising genes, MSX2 and DRD1, were mapped to the narrow significant region, which was involved in embryonic and ovary development and found to be related to egg production, respectively. Moreover, three interesting genes, RHOA, SDF4 and TNFRSF4, identified from three significant loci, were considered to be candidate genes for egg shell colour. Findings in our study could provide worthy theoretical basis and technological support to improve late-stage egg quality for breeders.

Inflammatory Bowel Disease: Effects on Bone and Mechanisms

Inflammatory bowel disease (IBD) is associated with decreased bone mass and alterations in bone geometry from the time of diagnosis, before anti-inflammatory therapy is instituted. Deficits in bone mass can persist despite absence of symptoms of active IBD. The effects of IBD on the skeleton are complex. Protein-calorie malnutrition, inactivity, hypogonadism, deficits in calcium intake and vitamin D consumption and synthesis, stunted growth in children, decreased skeletal muscle mass, and inflammation all likely play a role. Preliminary studies suggest that the dysbiotic intestinal microbial flora present in IBD may also affect bone at a distance. Several mechanisms are possible. T cells activated by the gut microbiota may serve as "inflammatory shuttles" between the intestine and bone. Microbe-associated molecular patterns leaked into the circulation in IBD may activate immune responses in the bone marrow by immune cells and by osteocytes, osteoblasts, and osteoclasts that lead to decreased bone formation and increased resorption. Finally, intestinal microbial metabolites such as H₂S may also affect bone cell function. Uncovering these mechanisms will enable the design of microbial cocktails to help restore bone mass in patients with IBD.

Curcumin induces osteoblast differentiation through mild-endoplasmic reticulum stress-mediated such as BMP2 on osteoblast cells

AIMS

Curcumin (diferuloylmethane or [1E,6E]-1,7-bis[4-hydroxy-3-methoxyphenyl]-1,6heptadiene-3,5-dione) is a phenolic natural product derived from the rhizomes of the turmeric plant, Curcuma longa. It is reported to have various biological actions such as anti-oxidative, anti-inflammatory, and anti-cancer effects. However, the molecular mechanism of osteoblast differentiation by curcumin has not yet been reported.

MAIN METHODS

The cytotoxicity of curcumin was identified using the 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Expression of osteogenic markers and endoplasmic reticulum (ER) stress markers in C3H1-T1/2 cells were measured using reverse-transcriptase polymerase chain reaction (RT-PCR) and Western blotting. Alkaline phosphatase (ALP) staining was performed to assess ALP activity in C3H10T1/2 cells. Transcriptional activity was detected using a luciferase reporter assay.

KEY FINDINGS

Curcumin increased the expression of genes such as distal-less homeobox 5 (Dlx5), runt-related transcription factor 2 (Runx2), ALP, and osteocalcin (OC), which subsequently induced osteoblast differentiation in C3H10T1/2 cells. In addition, ALP activity and mineralization was found to be increased by curcumin treatment. Curcumin also induced mild ER stress similar to bone morphogenetic protein 2 (BMP2) function in osteoblast cells. Next, we confirmed that curcumin increased mild ER stress and osteoblast differentiation similar to BMP2 in C3H10T1/2 mesenchymal stem cells. Transient transfection studies also showed that curcumin increased ATF6-Luc activity, while decreasing the activities of CREBH-Luc and SMILE-Luc. In addition, similar to BMP2, curcumin induced the phosphorylation of Smad 1/5/9.

SIGNIFICANCE

Overall, these results demonstrate that curcumin-induced mild ER stress increases osteoblast differentiation via ATF6 expression in C3H10T1/2 cells.

IL15RA is required for osteoblast function and bone mineralization

Interleukin-15 receptor alpha (IL15RA) is an important component of interleukin-15 (IL15) pro-inflammatory signaling. In addition, IL15 and IL15RA are present in the circulation and are detected in a variety of tissues where they influence physiological functions such as muscle contractility and overall metabolism. In the skeletal system, IL15RA was previously shown to be important for osteoclastogenesis. Little is known, however, about its role in osteoblast function and bone mineralization. In this study, we evaluated bone structural and mechanical properties of an Il15ra whole-body knockout mouse (Il15ra^-/-) and used in vitro and bioinformatic analyses to understand the role IL15/IL15RA signaling on osteoblast function. We show that lack of IL15RA decreased bone mineralization in vivo and in isolated primary osteogenic cultures, suggesting a cell-autonomous effect. Il15ra^-/- osteogenic cultures also had reduced Rankl/Opg mRNA ratio, indicating defective osteoblast/osteoclast coupling. We analyzed the transcriptome of primary pre-osteoblasts from normal and Il15ra^-/- mice and identified 1150 genes that were differentially expressed at a FDR of 5%. Of these, 844 transcripts were upregulated and 306 were downregulated in Il15ra^-/- cells. The largest functional clusters, highlighted using DAVID analysis, were related to metabolism, immune response, bone mineralization and morphogenesis. The transcriptome analysis was validated by qPCR of some of the most significant hits. Using bioinformatic approaches, we identified candidate genes, including Cd200 and Enpp1, that could contribute to the reduced mineralization. Silencing Il15ra using shRNA in the calvarial osteoblast MC3T3-E1 cell line decreased ENPP1 activity. Taken together, these data support that IL15RA plays a cell-autonomous role in osteoblast function and bone mineralization.

Pilose antler peptide potentiates osteoblast differentiation and inhibits osteoclastogenesis via manipulating the NF-κB pathway

Bones are inflexible yet ever-changing metabolic organs, and bone homeostasis is maintained through two delicately regulated processes: bone construction and bone reabsorption. An imbalance in bone metabolism is linked to most orthopedic diseases, including osteoporosis and rheumatoid arthritis. Importantly, tumor necrosis factor-α (TNF-α) blocks osteoblast differentiation and stimulates osteoclast formation, resulting in delayed deposition of new bone and accelerated bone resorption, especially in rheumatoid arthritis patients with inflammatory conditions. Pilose antler peptide (PAP) isolated and purified from deer antlers has been shown to have beneficial effects on chronic inflammation. In the present study, we studied the impact of PAP on osteoblast differentiation and evaluated the regulatory mechanism, with particular emphasis on the effect of PAP on TNF-α-mediated NF-κB signaling. Mouse primary osteoblast cells were activated with bone morphogenetic protein-2 (BMP-2) for osteoblast differentiation. A significant stimulatory effect of PAP in osteoblastogenesis was observed using ALP activity and Alizarin Red S staining assays. Meanwhile, PAP significantly rescued TNF-α-induced impairment of osteoblast formation as well as mineralization. Furthermore, we found a similar trend upon analyzing osteoblast-specific gene expression. PAP significantly rescued TNF-α-mediated decrease in expression of osteoblast-specific genes. A molecular mechanism assay indicated that PAP significantly inhibited TNF-α-mediated stimulation of NF-κB signaling activity, as well as nuclear translocation of its subunit p65. Moreover, over-expression of p65 reversed the stimulatory effects of PAP on osteoblast differentiation. Furthermore, we also identified that PAP dose dependently inhibit osteoclastogenesis, and this effect might be achieved via suppressing NF-κB activity. In summary, this study shows that PAP promotes osteoblast differentiation and blocks TNF-α-mediated suppression of osteoblastogenesis in vitro via the NF-κB/p65 pathway, as well as inhibits osteoclastsogenesis in vitro. Therefore, PAP, a novel drug with both antiresorptive and osteoanabolic activity, shows therapeutic potential as an alternative treatment for osteolytic diseases, including rheumatoid arthritis and osteoporosis.

Strontium-Substituted Bioceramics Particles: A New Way to Modulate MCP-1 and Gro-α Production by Human Primary Osteoblastic Cells

Background: To avoid morbidity and limited availability associated with autografts, synthetic calcium phosphate (CaP) ceramics were extensively developed and used as bone filling materials. Controlling their induced-inflammatory response nevertheless remained a major concern. Strontium-containing CaP ceramics were recently demonstrated for impacting cytokines’ secretion pattern of human primary monocytes. The present study focuses on the ability of strontium-containing CaP to control the human primary bone cell production of two major inflammatory and pro-osteoclastogenic mediators, namely MCP-1 and Gro-α, in response to ceramics particles. Methods: This in vitro study was performed using human primary osteoblasts in which their response to ceramics was evaluated by PCR arrays, antibody arrays were used for screening and real-time PCR and ELISA for more focused analyses. Results: Study of mRNA and protein expression highlights that human primary bone cells are able to produce these inflammatory mediators and reveal that the adjunction of CaP in the culture medium leads to their enhanced production. Importantly, the current work determines the down-regulating effect of strontium-substituted CaP on MCP-1 and Gro-α production. Conclusion: Our findings point out a new capability of strontium to modulate human primary bone cells’ communication with the immune system.

Short-Term Effects of TNF Inhibitors on Bone Turnover Markers and Bone Mineral Density in Rheumatoid Arthritis

TNFα inhibitors (TNFαI) exert positive effects on disease activity in rheumatoid arthritis (RA). Bone involvement is a major determinant of functional impairment in this disease. Here we investigated the short-term effects of TNFαI therapy on bone metabolism and density. We studied 54 patients with RA starting a TNFαI biologic drug, in whom any factor known to interfere with bone metabolism was excluded or rigorously accounted for. We measured at baseline and after 6-month therapy bone turnover markers: N-propeptide of type I collagen (P1NP), and bone alkaline phosphates for bone formation and serum C-terminal telopeptide of type I collagen (CTX) for bone resorption. We also evaluated bone mineral density (BMD) at hip and lumbar by dual-energy X-ray absorptiometry. All bone markers rose significantly and these changes were not dependent on steroid dosage. A significant decrease in femoral neck BMD was also observed. These results indicate that TNFαI therapy in RA over 6 months is associated with an early increase in bone turnover and a decline in hip BMD.

Rocaglamide-A Potentiates Osteoblast Differentiation by Inhibiting NF-κB Signaling

Rheumatoid arthritis is a chronic inflammatory disease that leads to bone and cartilage erosion. The inhibition of osteoblast differentiation by the inflammatory factor TNF-α is critical for the pathogenesis of rheumatoid arthritis. To modulate TNF-α mediated inhibition of osteoblast differentiation is required to improve therapeutic efficacy of rheumatoid arthritis. Here, we explored the potential role of rocaglamide-A, a component of Aglaia plant, in osteoblast differentiation. Rocaglamide-A prevented TNF-α mediated inhibition of osteoblast differentiation, and promoted osteoblast differentiation directly, in both C2C12 and primary mesenchymal stromal cells. Mechanistically, Rocaglamide-A inhibited the phosphorylation of NF-κB component p65 protein and the accumulation of p65 in nucleus, which resulted in the diminished NF-κB responsible transcriptional activity. Oppositely, overexpression of p65 reversed rocaglamide-A's protective effects on osteoblast differentiation. Collectively, rocaglamide-A protected and stimulated osteoblast differentiation via blocking NF-κB pathway. It suggests that rocaglamide-A may be a good candidate to develop as therapeutic drug for rheumatoid arthritis associated bone loss diseases.

Is there an effect of obstructive sleep apnea syndrome on oxidative stress and inflammatory parameters in patients with craniofacial anomalies?

The aim of this study was to test the hypothesis that obstructive sleep apnea syndrome (OSAS) exhibits oxidative stress and inflammation in patients who have a congenital, craniofacial anomaly.This prospective, cross-sectional cohort study included ambulant sleep study data to asses OSAS in patients with syndromic craniosynostosis and Treacher Collins syndrome. Laboratory analyses were performed including malondialdehyde, tumor necrosis factor α (TNF-α), interleukin 6, and high-sensitivity C-reactive protein.Forty-eight patients were included; 11 were adults; 37 were children. The patients' body mass indexes were normal, with a median (SD) of 0.7 (-1.82 to 2.48) in children and 20.5 (15.2-29.4) in adults. Obstructive sleep apnea syndrome was diagnosed in 23 of 48 patients. It was mild (median obstructive apnea-hypopnea index [oAHI], 2.3; oxygenation-desaturation index [ODI], 0.9) in 16 patients and moderate/severe in 7 patients (median oAHI, 10.8; ODI, 5.0). Neither oxidative stress nor inflammation had a correlation with the oAHI and ODI. Only TNF-α was found significantly higher in both the OSAS and non-OSAS groups compared with the reference values (median, 15.1 pg/mL and 12.3 pg/mL versus 4.05 [0.0-8.1 pg/mL], P < 0.001 and P < 0.001, respectively).Based on our findings we conclude that (mainly mild) OSAS, oxidative stress, as well as high-sensitivity C-reactive protein and interleukin 6 levels are not abnormal in the day time in a population of nonobese patients with a craniofacial anomaly. The increased level of TNF-α cannot be explained by OSAS. Future research should focus on mapping chronobiologic changes for further interpretation of the results.

Nonalcoholic fatty liver disease and decreased bone mineral density: is there a link?

PURPOSE

Liver diseases are associated with decreased bone mineral density (BMD) and evidence suggests that nonalcoholic fatty liver disease (NAFLD) affects several extra-hepatic organs, interacting with the regulation of multiple endocrine and metabolic pathways. This review focuses on the rapidly expanding body of evidence that supports a strong association between NAFLD and the risk of decreased BMD, expression of low bone mass (osteoporosis), or reduced mineralization (osteomalacia).

METHODS

We identified studies by searching PubMed for original articles published in English through March 2015 using the keywords "nonalcoholic fatty liver disease" or "fatty liver" combined with "bone mineral density", "osteoporosis", or "osteomalacia".

RESULTS

Recent cross-sectional and case-control studies involving both adults and children have consistently shown that patients with NAFLD exhibit a greater prevalence of decreased BMD compared with age-, sex-, and body mass index-matched healthy controls. Accumulating clinical and experimental evidence suggests that NAFLD may contribute to the pathophysiology of low BMD, possibly through the direct contribution of NAFLD to whole-body and hepatic insulin resistance and/or the systemic release of multiple pro-inflammatory, pro-coagulant, and pro-fibrogenic mediators.

CONCLUSIONS

Although more research is needed before firm conclusions can be drawn, it appears that there is a non-chance, statistical association between NAFLD and low BMD. This finding argues for more careful monitoring and evaluation of BMD among patients with NAFLD. The potential contribution of NAFLD itself to the development and progression of decreased BMD warrants further study.

Cyclic AMP Response Element-binding Protein H (CREBH) Mediates the Inhibitory Actions of Tumor Necrosis Factor α in Osteoblast Differentiation by Stimulating Smad1 Degradation

Endoplasmic reticulum (ER) stress transducers, such as old astrocyte specifically induced substance (OASIS) and activating transcription factor 6 (ATF6), which are induced by bone morphogenetic protein 2 (BMP2), regulate bone formation and osteoblast differentiation. Here, we examined the role of cAMP response element-binding protein H (CREBH), a member of the same family of ER membrane-bound basic leucine zipper (bZIP) transcription factors as OASIS and ATF6, in osteoblast differentiation and bone formation. Proinflammatory cytokine TNFα increased CREBH expression by up-regulating the nuclear factor-κB (NF-κB) signaling pathway in osteoblasts, increased the level of N-terminal fragment of CREBH in the nucleus, and inhibited BMP2 induction of osteoblast specific gene expression. Overexpression of CREBH suppressed BMP2-induced up-regulation of the osteogenic markers runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), and osteocalcin (OC) in MC3T3-E1 cells and primary osteoblasts, as well as BMP2-induced ALP activity and OC protein production. In contrast, knockdown of CREBH attenuated the inhibitory effect of TNFα on BMP2-induced osteoblast differentiation. Mechanistic studies revealed that CREBH increased the expression of Smad ubiquitination regulatory factor 1 (Smurf1), leading to ubiquitin-dependent degradation of Smad1, whereas knockdown of CREBH inhibited TNFα-mediated degradation of Smad1 by Smurf1. Consistent with these in vitro findings, administration of Ad-CREBH inhibited BMP2-induced ectopic and orthotopic bone formation in vivo. Taken together, these results suggest that CREBH is a novel negative regulator of osteoblast differentiation and bone formation.

Msx1 role in craniofacial bone morphogenesis

The homeobox gene Msx1 encodes a transcription factor that is highly expressed during embryogenesis and postnatal development in bone. Mutations of the MSX1 gene in humans are associated with cleft palate and (or) tooth agenesis. A similar phenotype is observed in newborn mice invalidated for the Msx1 gene. However, little is known about Msx1 function in osteoblast differentiation and bone mineralization in vivo. In the present study, we aimed to explore the variations of individualized bone shape in a subtle way avoiding the often severe consequences associated with gene mutations. We established transgenic mice that specifically express Msx1 in mineral-matrix-secreting cells under the control of the mouse 2.3kb collagen 1 alpha 1 (Col1α1) promoter, which enabled us to investigate Msx1 function in bone in vivo. Adult transgenic mice (Msx1-Tg) presented altered skull shape and mineralization resulting from increased Msx1 expression during bone development. Serial section analysis of the mandibles showed a high amount of bone matrix in these mice. In addition, osteoblast number, cell proliferation and apoptosis were higher in Msx1-Tg mice than in controls with regional differences that could account for alterations of bone shape. However, Von Kossa staining and μCT analysis showed that bone mineralization was lower in Msx1-Tg mice than in controls due to alteration of osteoblastic differentiation. Msx1 appears to act as a modeling factor for membranous bone; it stimulates trabecular bone metabolism but limits cortical bone growth by promoting apoptosis, and concomitantly controls the collagen-based mineralization process.

[Effect of the peri-implantitis on the biological function of osteoblasts obtained from the mandibles]

OBJECTIVE

To study the effect of peri-implantitis inflammatory microenvironment on the biological function of jaw bone osteoblasts.

METHODS

Primary mandible osteoblasts from peri-implantitis and normal tissue were isolated and cultured. Third-generation purified osteoblasts were identified and detected. The proliferative activity of osteoblasts was evaluated through MTT assay. Osteocalcin (OCN), Runx2, and collagen I (Col I) mRNA levels were examined by real-time quantitative polymerase chain reaction. OCN protein levels were determined by Western blot.

RESULTS

: After 4 d of culture, the proliferative activity of osteoblasts from peri-implantitis became lower than that of normal tissue ( P <0.05). After 7 d of culture, OCN, Runx2, and Col I mRNA expression decreased ( P <0.05). The OCN protein levels also decreased ( P <0.05).

CONCLUSION

Peri-implantitis inflammatory microenvironment can decrease the proliferation and differentiation activity of mandible osteoblasts.

[Effect of the peri-implantitis on the biological function of osteoblasts obtained from the mandibles]

OBJECTIVE

To study the effect of peri-implantitis inflammatory microenvironment on the biological function of jaw bone osteoblasts.

METHODS

Primary mandible osteoblasts from peri-implantitis and normal tissue were isolated and cultured. Third-generation purified osteoblasts were identified and detected. The proliferative activity of osteoblasts was evaluated through MTT assay. Osteocalcin (OCN), Runx2, and collagen I (Col I) mRNA levels were examined by real-time quantitative polymerase chain reaction. OCN protein levels were determined by Western blot.

RESULTS

: After 4 d of culture, the proliferative activity of osteoblasts from peri-implantitis became lower than that of normal tissue ( P <0.05). After 7 d of culture, OCN, Runx2, and Col I mRNA expression decreased ( P <0.05). The OCN protein levels also decreased ( P <0.05).

CONCLUSION

Peri-implantitis inflammatory microenvironment can decrease the proliferation and differentiation activity of mandible osteoblasts.

TNF-α upregulates sclerostin expression in obese mice fed a high-fat diet

Sclerostin decreases bone mass by antagonizing the Wnt signaling pathway. We examined whether obesity-induced bone loss is associated with the expression of sclerostin. Five-week-old male mice were assigned to one of two groups (n = 10 each) and fed either a control diet (10% kcal from fat; CON) or a high-fat diet (60% kcal from fat; HF) for 12 weeks. Thex final body weight and whole body fat mass of the HF mice were higher than those of the CON mice. The distal femur cancellous bone mineral density and bone formation rate was lower in HF mice than in CON mice. The percent erosion surface was higher in the HF mice than the CON mice. The serum levels and femoral osteocytic protein expression levels of tumor necrosis factor-α (TNF-α) were significantly higher in HF mice than in CON mice. Sclerostin mRNA levels and osteocytic sclerostin protein levels in femoral cortex were also higher in HF mice than in CON mice. Sclerostin expression in MLO-Y4 osteocytes increased with TNF-α treatment, and TNF-α-induced sclerostin expression was blocked by the inhibition of NF-κB activation. Chromatin immunoprecipitation and a luciferase reporter assay demonstrated that NF-κB directly binds to the NF-κB binding elements on the mouse sost promoter and stimulates sclerostin expression. These results support a model in which, in the context of obesity or other inflammatory diseases that increase the production of TNF-α, TNF-α upregulates the expression of sclerostin through NF-κB signaling pathway, thus contributing to bone loss.

Classical and Paradoxical Effects of TNF-α on Bone Homeostasis

Tumor necrosis factor-α (TNF-α) plays an essential role in the regulation of bone homeostasis in several chronic immune and inflammatory joint diseases, where inhibition of TNF has led to significant clinical improvement. However, TNF-activated pathways and mechanisms involved in bone remodeling remain unclear. So far, TNF-α was known as an inhibitor of osteoblast differentiation and an activator of osteoclastogenesis. Recent contradictory findings indicated that TNF-α can also activate osteoblastogenesis. The paradoxical role of TNF-α in bone homeostasis seems to depend on the concentration and the differentiation state of the cell type used as well as on the exposure time. This review aims to summarize the recent contradictory findings on the regulation of bone homeostasis by TNF-α at the isolated cell, whole bone, and whole body levels. In addition, the involvement of TNF-α in the bone remodeling imbalance is observed in inflammatory joint diseases including rheumatoid arthritis and ankylosing spondylitis, which are associated with bone destruction and ectopic calcified matrix formation, respectively. Both diseases are associated with systemic/vertebral osteoporosis.

10(-7) m 17β-oestradiol enhances odonto/osteogenic potency of human dental pulp stem cells by activation of the NF-κB pathway

OBJECTIVES

Oestrogen has been proven to significantly enhance osteogenic potency, while oestrogen deficiency usually leads to impaired osteogenic differentiation of mesenchymal stem cells. However, little is known concerning direct effects of oestrogen on differentiation of human dental pulp stem cells (DPSCs).

MATERIALS AND METHODS

In this study, human DPSCs were isolated and treated with 10(-7)  m 17β-oestradiol (E2). Alkaline phosphatase (ALP) assay and alizarin red staining were performed.

RESULTS

Alkaline phosphatase and alizarin red showed that E2 treatment significantly enhanced ALP activity and mineralization ability of DPSCs, but had no effect on cell proliferation. Real-time RT-PCR and western blot assay demonstrated that odonto/osteogenic markers (ALP, RUNX2/RUNX2, OSX/OSX, OCN/OCN and DSPP/DSP) were significantly upregulated in the cells after E2 treatment. Moreover, phosphorylation of cytoplasmic IκBα/P65 and expression of nuclear P65 were enhanced in a time-dependent manner following E2 treatment, suggesting activation of NF-κB signaling. Conversely, inhibition of the NF-κB pathway suppressed E2-mediated upregulation of odonto/osteogenic markers, indicating that the NF-κB pathway was pivotal for E2-mediated differentiation.

CONCLUSION

These findings provide evidence that 10(-7)  m 17β-oestradiol promoted odonto/osteogenic differentiation of human DPSCs via activation of the NF-κB signaling pathway.

Persistent low level of osterix accelerates interleukin-6 production and impairs regeneration after tissue injury

Osterix (Osx) is an essential transcription factor for osteoblast differentiation and bone formation. Osx knockout show a complete absence of bone formation, whereas Osx conditional knockout in osteoblasts produce an osteopenic phenotype after birth. Here, we questioned whether Osx has a potential role in regulating physiological homeostasis. In Osx heterozygotes expressing low levels of Osx in bones, the expression levels of pro-inflammatory cytokines were significantly elevated, indicating that reduced Osx expression may reflect an inflammatory-prone state. In particular, the expression of interleukin-6, a key mediator of chronic inflammation, was increased in Osx heterozygotes and decreased in Osx overexpressing osteoblasts, and transcriptionally down-regulated by Osx. Although no significant differences were revealed in renal morphology and function between Osx heterozygotes and wild-type under normoxic conditions, recovery of kidneys after ischemic damage was remarkably delayed in Osx heterozygotes, as indicated by elevated blood urea nitrogen and creatinine levels, and by morphological alterations consistent with acute tubular necrosis. Eventually, protracted low Osx expression level caused an inflammatory-prone state in the body, resulting in the enhanced susceptibility to renal injury and the delayed renal repair after ischemia/reperfusion. This study suggests that the maintenance of Osx expression in bone is important in terms of preventing the onset of an inflammatory-prone state.

Interactions among bone, liver, and adipose tissue predisposing to diabesity and fatty liver

Growing epidemiological evidence connects obesity and its complications, including metabolic syndrome, diabetes, and nonalcoholic fatty liver disease (NAFLD) to reduced bone health and osteoporosis. Parallel to human studies, experimental data disclosed a complex network of interaction among adipose tissue, the liver, and the bone, which reciprocally modulate the function of each other. The main mediators of such crosstalk include hormonal/cytokine signals from the bone (osteopontin, osteocalcin, and osteoprotegerin), the liver (fetuin-A), and adipose tissue [leptin, tumor necrosis factor-α (TNF-α), and adiponectin]. Dysregulation of this network promotes the development of diabesity, NAFLD, and osteoporosis. We will review recent advances in understanding the mechanisms of bone-liver-adipose tissue interaction predisposing to obesity, diabetes, NAFLD, and osteoporosis and their potential clinical implications.

Tumor necrosis factor-α enhances the transcription of Smad ubiquitination regulatory factor 1 in an activating protein-1- and Runx2-dependent manner

Smad ubiquitination regulatory factor 1 (Smurf1) is an E3 ubiquitin ligase that negatively regulates osteoblast differentiation. Although tumor necrosis factor-α (TNF-α) has been shown to increase Smurf1 expression, the details of the regulatory mechanisms remain unclear. Here, we investigated the molecular mechanism by which TNF-α stimulates Smurf1 expression in C2C12 and primary cultured mouse calvarial cells. TNF-α treatment rapidly induced the activation of NF-κB and MAPKs. Smurf1 induction by TNF-α was blocked by the inhibition of JNK or ERK, while the inhibition of NF-κB and p38 MAPK had no effect on Smurf1 induction. TNF-α treatment or c-Jun overexpression enhanced the activity of a luciferase reporter that contained a 2.7 kb mouse Smurf1 promoter sequence. Site-directed mutagenesis of the Smurf1 reporter and chromatin immunoprecipitation analysis demonstrated that the activating protein-1 (AP-1) binding motif at -922 bp on the mouse Smurf1 promoter mediated TNF-α/JNK/AP-1-stimulated Smurf1 transcription. Interestingly, Smurf1 expression was not observed in Runx2-null mouse calvarial cells. When Runx2 was ectopically expressed in these cells, the basal and TNF-α-induced expression of Smurf1 was restored. Overexpression of Runx2 transactivated the Smurf1 promoter in a dose-dependent manner. Reporter and chromatin immunoprecipitation assays demonstrated that the Runx2-binding motif at -202 bp functioned in Runx2-mediated Smurf1 expression. ERK activation by TNF-α treatment or constitutively active MEK1 overexpression increased Smurf1 expression in a Runx2-dependent manner. These results suggest that the JNK/AP-1 and ERK/Runx2 signaling pathways mediate TNF-α-dependent Smurf1 transcription.

Differentiation of mesenchymal stem cells to osteoblasts and chondrocytes: a focus on adenosine receptors

Skeletogenesis, either during development, post-injury or for maintenance, is a carefully coordinated process reliant on the appropriate differentiation of mesenchymal stem cells. Some well described, as well as a new regulator of this process (adenosine receptors), are alike in that they signal via cyclic-AMP (cAMP). This review highlights the known contribution of cAMP signalling to mesenchymal stem cell differentiation to osteoblasts and to chondrocytes. Focus has been given to how these regulators influence the commitment of the osteochondroprogenitor to these separate lineages.

Effects of anti-tumor necrosis factor α agents on bone

PURPOSE OF REVIEW

Tumor necrosis factor (TNF) inhibitors are effective for achieving disease control in several inflammatory diseases. Although anti-TNF agents can inhibit bone loss in vitro, their role in the prevention of clinically relevant outcomes such as osteoporosis and fractures has not been clearly established.

RECENT FINDINGS

There are many studies of the effects of TNF inhibitors on markers of bone turnover; however, few have measured bone mineral density (BMD) or fractures. Most of these studies have small sample sizes and a minority had a placebo control group. Overall these studies suggest that the antiresorptive effects of anti-TNF therapy are related to control of disease activity.

SUMMARY

The antiresorptive effects of TNF inhibitors are likely related to their anti-inflammatory properties. Studies to date have not demonstrated any advantages of TNF inhibitors over traditional nonbiologic therapies in the prevention of bone loss and fractures.

Distal-less homeobox 5 inhibits adipogenic differentiation through the down-regulation of peroxisome proliferator-activated receptor γ expression

Distal-less homeobox 5 (Dlx5) is a positive regulator of osteoblast differentiation that contains a homeobox domain. Because there are possible reciprocal relationships between osteogenic and adipogenic differentiation of bone marrow mesenchymal stem cells (MSCs), we examined the regulatory role of Dlx5 in adipogenic differentiation in this study. Adipogenic stimuli suppressed the expression levels of Dlx5 mRNA in mouse bone marrow stromal cells. Over-expression of Dlx5 inhibited adipogenic differentiation in human bone marrow MSCs and 3T3-L1 preadipocytic cells whereas knockdown of Dlx5 enhanced adipogenic differentiation in 3T3-L1 cells. Over-expression of Dlx5 suppressed the expression of adipogenic marker genes, including CCAAT/enhancer-binding protein α (C/EBPα) and peroxisome proliferator-activated receptor γ (PPARγ). Dlx5-mediated suppression of adipogenic differentiation was overcome by over-expression of PPARγ but not by that of cAMP response element binding protein (CREB) or C/EBPα. Dlx5 decreased the transcriptional activity of CREB and C/EBPα in a dose-dependent manner. Dlx5 directly bound to CREB and C/EBPα and prevented them from binding to and subsequently transactivating the PPARγ promoter. These results suggest that Dlx5 plays an important regulatory role in fate determination of bone marrow MSCs toward the osteoblast lineage through the inhibition of adipocyte differentiation as well as the direct stimulation of osteoblast differentiation.

miR-155 modulates TNF-α-inhibited osteogenic differentiation by targeting SOCS1 expression

Bone morphogenetic proteins (BMPs) can induce ectopic bone formation, which is negatively regulated by inflammatory cytokines, such as tumor necrosis factor (TNF)-α. Recently, miR-155 has been reported to regulate the transforming growth factor (TGF)-β signaling pathway and inflammatory responses. However, whether and how miR-155 modulates TNF-α-regulated osteogenic differentiation have not been explored. In this study, we demonstrated that miR-155 was involved in TNF-α-mediated inhibition of osteogenic differentiation. Knockdown of miR-155 partially mitigated the inhibition of TNF-α on BMP-2-induced osteogenic differentiation. Bioinformatic analysis identified the candidate target site in the 3' untranslated region (3'UTR) of SOCS1. Knockdown of miR-155 increased SOCS1 protein expression during TNF-α stimulation in MC3T3-E1 cells. And transfection with miR-155 inhibited the wild-type, but not the mutant, 3'UTR of SOCS1-regulated luciferase activity, indicating that SOCS1 is a direct target of miR-155 in osteoblast cells. Furthermore, miR-155 expression could be induced by TNF-α through the JNK pathway. As the result of increased SOCS1 expression, knockdown of miR-155 significantly reduced the JNK/c-Jun activation. In addition, transfection of SOCS1 siRNA or overexpression of SOCS1 coding region could narrow the differences of alkaline phosphatase (ALP) and osteocalcin (OSC) expression between the control and miR-155 inhibitor transfected cells. These data indicated that miR-155 modulates TNF-α-regulated osteogenic differentiation by targeting SOCS1, at least partially through the SAPK/JNK pathway. These findings may provide new insights into understanding the regulatory role of miR-155 in the process of osteogenic differentiation in inflammatory condition.

Conditioned medium from bone marrow mesenchymal stem cells transiently retards osteoblast differentiation by downregulating runx2

Mesenchymal stem cells (MSCs) are attractive candidates for cell therapy and regenerative medicine because of their potential for proliferation and multilineage differentiation. MSCs secrete various cytokines, acting as trophic mediators to regulate neighboring cells. Osteoblasts are the cells directly responsible for forming new bone, and they are the final target of many osteogenic regulators. However, the induction effect of MSCs on osteoblasts is still unknown. In this study, we isolated osteoblasts from rat calvariae and investigated their proliferation and differentiation under induction of varied concentrations of MSC-conditioned medium (MSC-CM). Cells in the MSC-CM groups showed a reduction in cell proliferation at 3-6 days, and a decrease in the expression of osteocalcin and osteopontin at 3 days, with low levels of alkaline phosphatase activity. The expression of osteogenic markers went back to normal at 7 days. In order to evaluate the molecular mechanisms underlying this suppression, levels of two osteoblastic transcription factors, runt-related transcription factor 2 (Runx2) and osterix (Osx), were detected at both mRNA and protein levels. The results indicated that MSC-CM significantly inhibited Runx2 expression in a concentration-dependent manner. However, the effect was not due to the inhibition of Osx, for Osx was not significantly altered. This work demonstrates that MSCs may suppress osteoblast proliferation and transiently retard osteoblast differentiation by downregulating Runx2. These results highlight the need to take into account the paracrine effect of MSCs when using them in regenerative medicine for the repair of bone defects.

Glycogen synthase kinase-3 beta inhibitor suppresses Porphyromonas gingivalis lipopolysaccharide-induced CD40 expression by inhibiting nuclear factor-kappa B activation in mouse osteoblasts

Bone-forming osteoblasts have been recently reported capable of expressing the critical co-stimulatory molecule CD40 upon exposure to bacterial infection, which supports the unappreciated role of osteoblasts in modulating bone inflammation. Recent studies highlight the anti-inflammatory potential of glycogen synthase kinase-3β (GSK-3β) inhibitors; however, their effect on osteoblasts remains largely unclear. In the present study, we showed that treatment with SB216763, a highly specific GSK-3β inhibitor, resulted in a dose-dependent decrease in the mRNA and protein expression of CD40, as well as production of pro-inflammatory cytokines IL-6, TNF-α and IL-1β, in the Porphyromonas gingivalis-lipopolysaccharide (LPS)-stimulated murine osteoblastic-like MC3T3-E1 cells. Furthermore, inhibition of GSK-3β remarkably represses the LPS-induced activation of the nuclear factor kappa B (NF-κB) signaling pathway by suppressing IκBα phosphorylation, NF-κBp65 nuclear translocation, and NF-κBp65 DNA binding activity. Closer investigation by immunoprecipitation assay revealed that β-catenin can physically interact with NF-κBp65. The negative regulation effect of GSK-3β inhibitor on CD40 expression is mediated through β-catenin, for siRNA of β-catenin attenuated the GSK-3β inhibitor-induced repression of NF-κB activation and, consequently, the expression of CD40 and production of pro-inflammatory cytokines in LPS-stimulated MC3T3-E1 cells. Thus our results elucidate the molecular mechanisms whereby GSK-3β inhibitor prevents the LPS-induced CD40 expression on osteoblasts and provide supportive evidence of the potential role of GSK-3β inhibitors in suppressing the immune function of osteoblasts in inflammatory bone diseases.

Sirt1 overexpression protects murine osteoblasts against TNF-α-induced injury in vitro by suppressing the NF-κB signaling pathway

AIM

Sirtuin 1 (Sirt1) is the class III histone/protein deacetylase that interferes with the NF-κB signaling pathway, thereby has anti-inflammatory function. This study was undertaken to investigate whether Sirt1 could protect osteoblasts against TNF-α-induced injury in vitro.

METHODS

Murine osteoblastic cell line, MC3T3-E1, was used. Overexpress of Sirt1 protein in MC3T3-E1 cells was made by transfection the cells with Sirt1-overexpressing adenovirus. The levels of mRNAs and proteins were determined with qRT-PCR and Western blotting, respectively. The activity of NF-κB was examined using NF-κB luciferase assay. The NO concentration was measured using the Griess method.

RESULTS

Treatment of MC3T3-E1 cells with TNF-α (2.5-10 ng/mL) suppressed Sirt1 protein expression in a concentration-dependent manner. TNF-α (5 ng/mL) resulted in an increase in apoptosis and a reduction in ALP activity in the cells. Overexpression of Sirt1 in the cells significantly attenuated TNF-α-induced injury through suppressing apoptosis, increasing ALP activity, and increasing the expression of Runx2 and osteocalcin mRNAs. Furthermore, overexpression of Sirt1 in the cells significantly suppressed TNF-α-induced NF-κB activation, followed by reducing the expression of iNOS and NO formation. Sirt1 activator resveratrol (10 μmol/L) mimicked the protection of the cells by Sirt1 overexpression against TNF-α-induced injury, which was reversed by the Sirt1 inhibitor EX-527 (5 μmol/L).

CONCLUSION

Overexpression of Sirt1 protects MC3T3-E1 osteoblasts aganst TNF-α-induced cell injury in vitro, at least in part, via suppressing NF-κB signaling. Sirt1 may be a novel therapeutic target for treating rheumatoid arthritis-related bone loss.

Effects of combined mechanical stimulation on the proliferation and differentiation of pre-osteoblasts

We observed how combined mechanical stimuli affect the proliferation and differentiation of pre-osteoblasts. For this research, a bioreactor system was developed that can simultaneously stimulate cells with cyclic strain and ultrasound, each of which is known to effectively stimulate bone tissue regeneration. MC3T3-E1 pre-osteoblasts were chosen for bone tissue engineering due to their osteoblast-like characteristics. 3-D scaffolds were fabricated with polycaprolactone and poly-L-lactic acid using the salt leaching method. The cells were stimulated by the bioreactor with cyclic strain and ultrasound. The bioreactor was set at a frequency of 1.0 Hz and 10 % strain for cyclic strain and 1.0 MHz and 30 mW/cm(2) for ultrasound. Three experimental groups (ultrasound, cyclic strain, and combined stimulation) and a control group were examined. Each group was stimulated for 20 min/day. Mechanical stimuli did not affect MC3T3-E1 cell proliferation significantly up to 10 days when measured with the cell counting kit-8. However, gene expression analysis of collagen type-I, osteocalcin, RUNX2, and osterix revealed that the combined mechanical stimulation accelerated the matrix maturation of MC3T3-E1 cells. These results indicate that the combined mechanical stimulation can enhance the differentiation of pre-osteoblasts more efficiently than simple stimuli, in spite of no effect on cell proliferation.

Notch signaling pathway enhances bone morphogenetic protein 2 (BMP2) responsiveness of Msx2 gene to induce osteogenic differentiation and mineralization of vascular smooth muscle cells

Vascular calcification is regulated in a process similar to bone formation. BMP2 (bone morphogenetic protein 2) is essential for osteoblastic differentiation of mesenchymal progenitor cells and thus has been implicated in the development of vascular calcification. Here we examined whether Notch signaling interacts with BMP2 signaling to regulate osteogenic differentiation and mineralization of vascular smooth muscle cells (SMCs). BMP2 alone scarcely induced the expression of alkaline phosphatase (ALP), an ectoenzyme crucially required for active biomineralization, in human aortic SMCs (HASMCs), despite its strong induction in osteoblast precursor MC3T3-E1 cells. Notably, overexpression of the Notch1 intracellular domain (N1-ICD) markedly enhanced BMP2-mediated induction of ALP activity and mineralization of HASMCs. In HASMCs, expression of Msx2 gene, a well documented BMP2 target gene in osteoblasts, was barely induced by BMP2 alone, and N1-ICD clearly enhanced the BMP2-driven Msx2 gene expression. Deletion and site-directed mutation analysis of Msx2 gene promoter revealed that the RBPJk-binding site was necessary for BMP2 responsiveness. Using the RBPJk-deficient cells and siRNA for RBPJk, we showed that RBPJk was required for BMP2 induction of Msx2 gene expression and ALP activity. Moreover, we showed that Smad1, a transcription factor downstream of BMP2 signaling, interacted with N1-ICD to form a complex within the Msx2 promoter. Immunohistochemistry of human calcifying atherosclerotic plaques revealed colocalized expression of Notch1, BMP2, and Msx2. These results indicate that the Notch intracellular domain·RBPJk complex enhances the BMP2-induced Msx2 gene expression by cooperating with Smad1 and suggest that Notch signaling makes vascular SMC responsive to BMP2 and promotes vascular calcification.

Apelin attenuates the osteoblastic differentiation of vascular smooth muscle cells

Vascular calcification, which results from a process osteoblastic differentiation of vascular smooth muscle cells (VSMCs), is a major risk factor for cardiovascular morbidity and mortality. Apelin is a recently discovered peptide that is the endogenous ligand for the orphan G-protein-coupled receptor, APJ. Several studies have identified the protective effects of apelin on the cardiovascular system. However, the effects and mechanisms of apelin on the osteoblastic differentiation of VSMCs have not been elucidated. Using a culture of calcifying vascular smooth muscle cells (CVMSCs) as a model for the study of vascular calcification, the relationship between apelin and the osteoblastic differentiation of VSMCs and the signal pathway involved were investigated. Alkaline phosphatase (ALP) activity and osteocalcin secretion were examined in CVSMCs. The involved signal pathway was studied using the extracellular signal-regulated kinase (ERK) inhibitor, PD98059, the phosphatidylinositol 3-kinase (PI3-K) inhibitor, LY294002, and APJ siRNA. The results showed that apelin inhibited ALP activity, osteocalcin secretion, and the formation of mineralized nodules. APJ protein was detected in CVSMCs, and apelin activated ERK and AKT (a downstream effector of PI3-K). Suppression of APJ with siRNA abolished the apelin-induced activation of ERK and Akt. Furthermore, inhibition of APJ expression, and the activation of ERK or PI3-K, reversed the effects of apelin on ALP activity. These results showed that apelin inhibited the osteoblastic differentiation of CVSMCs through the APJ/ERK and APJ/PI3-K/AKT signaling pathway. Apelin appears to play a protective role against arterial calcification.