BMP-2 vs. BMP-4 expression and activity in glucocorticoid-arrested MC3T3-E1 osteoblasts: Smad signaling, not alkaline phosphatase activity, predicts rescue of mineralization

Bone morphogenetic protein 4 is involved in cadmium-associated bone damage

Cadmium (Cd) is a well-characterized bone toxic agent and can induce bone damage via inhibiting osteogenic differentiation. Bone morphogenetic protein (BMP)/SMAD signaling pathway can mediate osteogenic differentiation, but the association between Cd and BMP/SMAD signaling pathway is yet to be illuminated. To understand what elements of BMPs and SMADs are affected by Cd to influence osteogenic differentiation and if BMPs can be the biomarkers of which Cd-induced osteoporosis, human bone marrow mesenchymal stem cells (hBMSCs) were treated with cadmium chloride (CdCl2) in vitro to detect the expression of BMPs and SMADs, and 134 subjects were enrolled to explore if the BMPs can be potential biomarkers of Cd-associated bone damage. Our results showed that Cd exposure significantly promoted the adipogenic differentiation of hBMSCs and inhibited its osteogenic differentiation by inhibiting the expression of BMP-2/4, SMAD4, and p-SMAD1/5/9 complex. And mediation analyses yielded that BMP-4 mediated 39.32% (95% confidence interval 7.47, 85.00) of the total association between the Cd and the risk of Cd-associated bone damage. Moreover, during differentiation, BMP-4 had the potential to enhance mineralization compared with CdCl2 only group. These results reveal that BMP-4 can be a diagnostic biomarker and therapeutic target for Cd-associated bone damage.

Benzofuran pyran hybrid prevents glucocorticoid induced osteoporosis in mice via modulation of canonical Wnt/β-catenin signaling

Glucocorticoid induced osteoporosis (GIOP) is the second most leading cause of osteoporosis. We have identified a compound, a benzofuran pyran hybrid compound 4e that has osteogenic potential and we wanted to assess its efficacy in GIOP in male mice. We assessed the effect of dexamethasone and compound 4e on primary osteoblasts using various cell based and immunofluorescence assays. For in vivo studies we administered methylprednisolone and compound 4e as a prophylactic measure in male Balb/c mice for 28 days and then evaluated the effect on bone microarchitecture by microCT, bone formation by histology along with clinically relevant bone markers. Compound 4e preserved osteoblast differentiation as evident by higher ALP positive cells and mineralization in compound treated groups. Compound 4e also increased the expression of osteogenic genes. This compound guarded β-catenin expression both in vitro and in vivo as confirmed by western blot and immunofluorescence assays. This led to the preservation of bone microarchitecture and cortical thickness at 2.5 mg kg⁻¹ and 5 mg kg⁻¹ doses. Further compound 4e enhanced bone formation rate and regulated osteocyte death. The osteogenic potential of compound 4e was reflected by an increased level of serum marker osteocalcin and decreased levels of SOST and CTX-I. Overall, Compound 4e is able to overcome the catabolic effect of dexamethasone on bone by targeting the canonical WNT/β-catenin signaling as evidenced by both in vitro and in vivo studies.

Bad to the Bone: The Effects of Therapeutic Glucocorticoids on Osteoblasts and Osteocytes

Despite the continued development of specialized immunosuppressive therapies in the form of monoclonal antibodies, glucocorticoids remain a mainstay in the treatment of rheumatological and auto-inflammatory disorders. Therapeutic glucocorticoids are unmatched in the breadth of their immunosuppressive properties and deliver their anti-inflammatory effects at unparalleled speed. However, long-term exposure to therapeutic doses of glucocorticoids decreases bone mass and increases the risk of fractures - particularly in the spine - thus limiting their clinical use. Due to the abundant expression of glucocorticoid receptors across all skeletal cell populations and their respective progenitors, therapeutic glucocorticoids affect skeletal quality through a plethora of cellular targets and molecular mechanisms. However, recent evidence from rodent studies, supported by clinical data, highlights the considerable role of cells of the osteoblast lineage in the pathogenesis of glucocorticoid-induced osteoporosis: it is now appreciated that cells of the osteoblast lineage are key targets of therapeutic glucocorticoids and have an outsized role in mediating their undesirable skeletal effects. As part of this article, we review the molecular mechanisms underpinning the detrimental effects of supraphysiological levels of glucocorticoids on cells of the osteoblast lineage including osteocytes and highlight the clinical implications of recent discoveries in the field.

The molecular etiology and treatment of glucocorticoid-induced osteoporosis

Glucocorticoid-induced osteoporosis (GIOP) is the most common form of secondary osteoporosis, accounting for 20% of osteoporosis diagnoses. Using glucocorticoids for >6 months leads to osteoporosis in 50% of patients, resulting in an increased risk of fracture and death. Osteoblasts, osteocytes, and osteoclasts work together to maintain bone homeostasis. When bone formation and resorption are out of balance, abnormalities in bone structure or function may occur. Excess glucocorticoids disrupt the bone homeostasis by promoting osteoclast formation and prolonging osteoclasts' lifespan, leading to an increase in bone resorption. On the other hand, glucocorticoids inhibit osteoblasts' formation and facilitate apoptosis of osteoblasts and osteocytes, resulting in a reduction of bone formation. Several signaling pathways, signaling modulators, endocrines, and cytokines are involved in the molecular etiology of GIOP. Clinically, adults ≥40 years of age using glucocorticoids chronically with a high fracture risk are considered to have medical intervention. In addition to vitamin D and calcium tablet supplementations, the major therapeutic options approved for GIOP treatment include antiresorption drug bisphosphonates, parathyroid hormone N-terminal fragment teriparatide, and the monoclonal antibody denosumab. The selective estrogen receptor modulator can only be used under specific condition for postmenopausal women who have GIOP but fail to the regular GIOP treatment or have specific therapeutic contraindications. In this review, we focus on the molecular etiology of GIOP and the molecular pharmacology of the therapeutic drugs used for GIOP treatment.

Comprehensive circRNA expression profile and function network in osteoblast-like cells under simulated microgravity

BACKGROUND

Circular RNAs (circRNAs) are a new class of non-coding RNA with a stable structure formed by special loop splicing. Research increasingly suggests that circRNAs play a vital role in the pathogenesis and progression of various diseases. However, the roles of circRNAs in osteoblast differentiation under microgravity remain largely unknown. Here, we investigated the roles and mechanobiological response of circRNAs in osteoblasts under simulated microgravity.

METHODS

Differential circRNA and mRNA expression profiles of MC3T3-E1 cells during exposure to microgravity were screened by RNA transcriptome sequencing technology (RNA-seq). The selected RNAs were validated using quantitative real-time polymerase chain reaction (qRT-PCR). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were applied for gene function analyses.

RESULTS

A total of 427 circRNAs and 1912 mRNAs were differentially expressed along with osteogenic differentiation in the simulated microgravity group (SMG) compared to the control group (CON). Of these, 232 circRNAs and 991 mRNAs were upregulated, whereas 95 circRNAs and 921 mRNAs were downregulated (fold change ≥ 2, p < 0.05). The results showed that the parental genes of circRNAs and mRNAs were mainly enriched in anatomical structure morphogenesis, anchoring junction and protein binding. KEGG analysis results showed that the differentially expressed mRNAs were enriched in the regulation of the actin cytoskeleton, focal adhesion, and Ras signalling pathway. Subsequently, 9 core regulatory genes, including 6 mRNAs and 3 circRNAs, were identified based on their possible function in osteoblast differentiation. Based on this analysis, circ_014154 was selected as the target circRNA, which likely plays important roles in osteogenic differentiation processes under microgravity. The circRNA-miRNA-mRNA network showed that circRNAs might act as miRNA sponges to regulate osteoblast differentiation.

CONCLUSION

By presenting a better understanding of the molecular mechanisms of genes and circRNAs in simulated microgravity, the present study will provide a novel view of circRNAs in the regulation of osteogenic differentiation and bone formation.

Bone morphogenetic proteins in biomineralization of two endodontic restorative cements

To assess the effect of biodentine (BD) and MTA-angelus (MTA) on biocompatibility, BMP2, BMP4, and osteocalcin (OC) expression. Subcutaneously implanted tubes of four groups (MTA, BD, Control, and Sham) were kept over 15, 30, and 60 days; histological analyses were performed using H&E and Von Kossa; ELISA quantified IL-1β and IL-8 expression; and qRT-PCR verified gene expression of BMPs and OC. Sham showed slight changes in profile/intensity of inflammatory infiltrate in all periods. Control had an inflammatory score significantly higher than Sham at 15 days (p < .05). BD revealed a similar inflammatory response to Sham, without significant changes over periods. MTA group exhibited an increase in chronic inflammatory profile at 30 days, with significant reduction at 60 days, when compared to Sham (p < .05). At 30/60 days, experimental groups presented birefringent areas. At 30/60 days, BD and MTA significantly increase IL-1β compared to Control, whereas an increase in IL-8 was observed only in BD. At 30/60 days, BD produces an expression of BMP2 whereas MTA influenced BMP4 and OC. Materials tested are biocompatible and they have osteoinductive activity; the materials influenced the expression of the tested mediators differently, suggesting different affinities with the substrate and the dental substrates.

FGF-2 targets sclerostin in bone and myostatin in skeletal muscle to mitigate the deleterious effects of glucocorticoid on musculoskeletal degradation

AIM

Myokines are associated with regulation of bone and muscle mass. However, limited information is available regarding the impact of myokines on glucocorticoid (GC) mediated adverse effects on the musculoskeletal system. This study investigates the role of myokine fibroblast growth factor-2 (FGF-2) in regulating GC-induced deleterious effects on bone and skeletal muscle.

METHODS

Primary osteoblast cells and C2C12 myoblast cell line were treated with FGF-2 and then exposed to dexamethasone (GC). FGF-2 mediated attenuation of the inhibitory effect of GC on osteoblast and myoblast differentiation and muscle atrophy was assessed through quantitative PCR and western blot analysis. Further, FGF-2 was administered subcutaneously to dexamethasone treated mice to collect bone and skeletal muscle tissue for in vivo analysis of bone microarchitecture, mechanical strength, histomorphometry and for histological alterations in treated tissue samples.

KEY FINDINGS

FGF-2 abrogated the dexamethasone induced inhibitory effect on osteoblast differentiation by modulating BMP-2 pathway and inhibiting Wnt antagonist sclerostin. Further, dexamethasone induced atrophy in C2C12 cells was mitigated by FGF-2 as evident from down regulation of atrogenes expression. FGF-2 prevented GC-induced impairment of mineral density, biomechanical strength, trabecular bone volume, cortical thickness and bone formation rate in mice. Additionally, skeletal muscle tissue from GC treated mice displayed weak myostatin immunostaining and reduced expression of atrogenes following FGF-2 treatment.

SIGNIFICANCE

FGF-2 mitigated GC induced effects through inhibition of sclerostin and myostatin expression in bone and muscle respectively. Taken together, this study exhibited the role of exogenous FGF-2 in sustaining osteoblastogenesis and inhibiting muscle atrophy in presence of glucocorticoid.

CKIP-1 suppresses odontoblastic differentiation of dental pulp stem cells via BMP2 pathway and can interact with NRP1

AIM

Casein kinase 2 interacting protein-1 (CKIP-1) is a recently discovered intracellular regulator of bone formation, muscle cell differentiation, and tumor cell proliferation. Our study aims to identify the inhibition of BMP2-Smad1/5 signaling by CKIP-1 in odontoblastic differentiation of human dental pulp stem cells (DPSCs).

MATERIALS AND METHODS

DPSCs infected CKIP-1 siRNA or transfected CKIP-1 full-length plasmid were cultured in odontoblastic differentiation medium or added noggin (200 ng/mL) for 21 days. We examined the effects of CKIP-1 on odontoblastic differentiation, mineralized nodules formation, and interaction by western blot, real-time polymerase chain reaction (RT-PCR), alkaline phosphatase (ALP) staining, alizarin red S staining, and immunoprecipitation.

RESULTS

Firstly, we have demonstrated that CKIP-1 expression markedly decreased time-dependently along with cell odontoblastic differentiation. Indeed, the silence of CKIP-1 upregulated odontoblastic differentiation via BMP2-Smad1/5 signaling, while CKIP-1 over-expression had a negative effect on odontoblastic differentiation of DPSCs. Furthermore, CKIP-1 could interact with Neuropilin-1 (NRP1).

CONCLUSIONS

This work provides data that advocates a novel perception on odontoblastic differentiation of DPSCs. Therefore, inhibiting the expression of CKIP-1 may be of great significance to the development of dental caries.

Identification of miR-200c-3p as a major regulator of SaoS2 cells activation induced by fluoride

The skeletal lesion of fluoride has become a major concern in many countries due to its damage to bone and joints and even leading to disability. Skeletal fluorosis is characterized by disturbance of bone metabolism, aberrant proliferation and activation of osteoblasts is critical for the pathogenesis. However, the mechanism underlying the osteotoxicity of fluoride has not been clearly illustrated and there is still limited information on the role of miRNAs in skeletal fluorosis. In this study, we found that NaF promoted SaoS2 proliferation and activation by activating BMP4/Smad pathway. NaF increased expression of miR-200c-3p and miR-200c-3p inhibitor reduced activation of SaoS2 induced by NaF via targeting Noggin to repress BMP4/Smad. These findings suggested an important regulatory role of miR-200c-3p on BMP4/Smad pathway during skeletal fluorosis. MiR-200c-3p might be a novel therapeutic target for skeletal fluorosis.

The effect of parathyroid hormone (1-84) treatment on serum bone morphogenetic protein 4 and vascular endothelial growth factor in postmenopausal women with established osteoporosis

PURPOSE

To investigate the effect of 18 months' parathyroid hormone 1-84 (PTH 1-84) treatment on serum levels of bone morphogenetic protein 4 (BMP4) and vascular endothelial growth factor (VEGF), in postmenopausal women with established osteoporosis.

METHODS

Thirty-seven postmenopausal women with osteoporosis (mean age 72.9 ± 8.1 years old) and 23 healthy controls (mean age 68.9 ± 9.9 years old) were enrolled. Patients were treated with daily subcutaneous injections of PTH (1-84) 100 mcg for 18 months, plus calcium 1 gr and vitamin D 800 IU per os daily. Blood samples were taken every 6 months during the study.

RESULTS

At baseline, there were no differences considering anthropometric parameters, co-morbidities, current medications used between patients and controls. Mean serum VEGF levels were significantly higher in osteoporotic patients compared to controls (436.7 ± 259.7 vs. 260.3 ± 184.3 pg/ml, p = 0.006), while there were no differences in mean serum values of BMP4 (5.3 ± 1.7 vs. 5.7 ± 1.6 pg/ml, p = 0.40). Serum VEGF levels increased by approximately 20% after 12 months of PTH (1-84) treatment compared to baseline (p = 0.03) and by 22% after 18 months (p = 0.01). A significant increase of 10% in mean serum BMP4 levels was observed after 18 months of PTH (1-84) treatment compared to baseline (p = 0.02). In the control group we found no differences after 18 months compared to baseline in BMP4 (5.7 ± 1.6 vs. 6.0 ± 1.5 pg/ml, p = 0.53) and VEGF (260.3 ± 184.3 vs. 257.4 ± 107.1 pg/ml, p = 0.94).

CONCLUSIONS

PTH (1-84) treatment increased serum levels of VEGF and BMP4 in postmenopausal women with severe osteoporosis.

Targeting osteoblastic casein kinase-2 interacting protein-1 to enhance Smad-dependent BMP signaling and reverse bone formation reduction in glucocorticoid-induced osteoporosis

The underlying mechanism of the reduced bone formation during the development of glucocorticoid-induced osteoporosis (GIO) remains unclear. Here, we found that the highly expressed CKIP-1 together with lowly expressed total and phosphorylated Smad1/5 in bone samples was accompanied by either the reduced serum bone formation markers in GIO patients or the decreased bone formation in GIO mice. In vitro studies showed that the highly expressed CKIP-1 could promote Smad1 ubiquitination to suppress the Smad-dependent BMP signaling and inhibit osteogenic differentiation and mineral deposition in MC3T3-E1 cells during glucocorticoid treatment. Further, the reduced bone formation in GIO mice could not only be prevented by osteoblasts-specific Ckip-1 ablation, but also be attenuated after osteoblasts-specific Smad1 overexpression. Moreover, osteoblasts-targeting CKIP-1 siRNA treatment also attenuated the bone formation reduction in GIO mice. These study suggest that the highly expressed CKIP-1 in osteoblasts could suppress the Smad-dependent BMP signaling and contribute to the bone formation reduction in GIO. Targeting osteoblastic CKIP-1 would be a novel bone anabolic strategy for GIO patients.

Establishment of Immortalized BMP2/4 Double Knock-Out Osteoblastic Cells Is Essential for Study of Osteoblast Growth, Differentiation, and Osteogenesis

Bone morphogenetic proteins 2 and 4 (BMP2/4) are essential for osteoblast differentiation and osteogenesis. Generation of a BMP2/4 dual knock‐out (^ko/ko) osteoblastic cell line is a valuable asset for studying effects of BMP2/4 on skeletal development. In this study, our goal was to create immortalized mouse deleted BMP2/4 osteoblasts by infecting adenoviruses with Cre recombinase and green fluorescent protein genes into immortalized murine floxed BMP2/4 osteoblasts. Transduced BMP2/4^ko/ko cells were verified by green immunofluorescence and PCR. BMP2/4^ko/ko osteoblasts exhibited small size, slow cell proliferation rate and cell growth was arrested in G1 and G2 phases. Expression of bone‐relate genes was reduced in the BMP2/4^ko/ko cells, resulting in delay of cell differentiation and mineralization. Importantly, extracellular matrix remodeling was impaired in the BMP2/4^ko/ko osteoblasts as reflected by decreased Mmp‐2 and Mmp‐9 expressions. Cell differentiation and mineralization were rescued by exogenous BMP2 and/or BMP4. Therefore, we for the first time described establishment of an immortalized deleted BMP2/4 osteoblast line useful for study of mechanisms in regulating osteoblast lineages. J. Cell. Physiol. 231: 1189–1198, 2016. © 2015 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Fluid shear stress stimulates osteogenic differentiation of human periodontal ligament cells via the extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase signaling pathways

BACKGROUND

Fluid shear stress (FSS) is a major type of mechanical stress that is loaded on human periodontal ligament cells (hPDLCs) during mastication and orthodontic tooth movement. This study aims to clarify the effect of FSS on the osteogenic differentiation of hPDLCs and to further verify the involvement of mitogen-activated protein kinase (MAPK) signaling in this process.

METHODS

After isolation and characterization, hPDLCs were subjected to 2-hour FSS at 12 dynes/cm(2), and cell viability, osteogenic gene mRNA expression, alkaline phosphatase (ALP) activity, secretion of Type I collagen (COL-I), and calcium deposition were assayed. The levels of phosphorylated p38 and phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) in response to FSS were detected by Western blot, and the involvement of ERK1/2 and p38 MAPK signaling pathways in hPDLC osteogenesis under FSS was investigated using the specific MAPK inhibitors U0126 (2Z,3Z)-2,3-bis[amino(2-aminophenylthio)methylene]succinonitrile,ethanol) and SB203580 (4-[4-(4-fluorophenyl)-2-(4-[methylsulfinyl]phenyl)-1H-imidazol-5-yl]pyridine).

RESULTS

The application of FSS on hPDLCs induced an early morphologic change and rearrangement of filamentous actin. ALP activity, messenger RNA (mRNA) levels of osteogenic genes, COL-I, and osteoid nodules were significantly increased by FSS. Moreover, ERK1/2 and p38 were activated in different ways after FSS exposure. U0126 and SB203580 completely blocked the FSS-induced increases in ALP activity and osteogenic gene mRNA expression and osteoid nodules formation.

CONCLUSIONS

FSS is an effective approach for stimulating osteogenic differentiation of hPDLCs. The ERK1/2 and p38 MAPK signaling pathways are involved in this cellular process.

Glucocorticoid-Induced Osteoporosis

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

TGF-β/BMP signaling and other molecular events: regulation of osteoblastogenesis and bone formation

Transforming growth factor-beta (TGF-β)/bone morphogenetic protein (BMP) plays a fundamental role in the regulation of bone organogenesis through the activation of receptor serine/threonine kinases. Perturbations of TGF-β/BMP activity are almost invariably linked to a wide variety of clinical outcomes, i.e., skeletal, extra skeletal anomalies, autoimmune, cancer, and cardiovascular diseases. Phosphorylation of TGF-β (I/II) or BMP receptors activates intracellular downstream Smads, the transducer of TGF-β/BMP signals. This signaling is modulated by various factors and pathways, including transcription factor Runx2. The signaling network in skeletal development and bone formation is overwhelmingly complex and highly time and space specific. Additive, positive, negative, or synergistic effects are observed when TGF-β/BMP interacts with the pathways of MAPK, Wnt, Hedgehog (Hh), Notch, Akt/mTOR, and miRNA to regulate the effects of BMP-induced signaling in bone dynamics. Accumulating evidence indicates that Runx2 is the key integrator, whereas Hh is a possible modulator, miRNAs are regulators, and β-catenin is a mediator/regulator within the extensive intracellular network. This review focuses on the activation of BMP signaling and interaction with other regulatory components and pathways highlighting the molecular mechanisms regarding TGF-β/BMP function and regulation that could allow understanding the complexity of bone tissue dynamics.

The effect of five proteins on stem cells used for osteoblast differentiation and proliferation: a current review of the literature

Bone-tissue engineering is a therapeutic target in the field of dental implant and orthopedic surgery. It is therefore essential to find a microenvironment that enhances the growth and differentiation of osteoblasts both from mesenchymal stem cells (MSCs) and those derived from dental pulp. The aim of this review is to determine the relationship among the proteins fibronectin (FN), osteopontin (OPN), tenascin (TN), bone sialoprotein (BSP), and bone morphogenetic protein (BMP2) and their ability to coat different types of biomaterials and surfaces to enhance osteoblast differentiation. Pre-treatment of biomaterials with FN during the initial phase of osteogenic differentiation on all types of surfaces, including slotted titanium and polymers, provides an ideal microenvironment that enhances adhesion, morphology, and proliferation of pluripotent and multipotent cells. Likewise, in the second stage of differentiation, surface coating with BMP2 decreases the diameter and the pore size of the scaffold, causing better adhesion and reduced proliferation of BMP-MSCs. Coating oligomerization surfaces with OPN and BSP promotes cell adhesion, but it is clear that the polymeric coating material BSP alone is insufficient to induce priming of MSCs and functional osteoblastic differentiation in vivo. Finally, TN is involved in mineralization and can accelerate new bone formation in a multicellular environment but has no effect on the initial stage of osteogenesis.

Molecular determinants of glucocorticoid actions in inflammatory joint diseases

Since their discovery in 1948, glucocorticoids have been widely used clinically to treat inflammatory disorders like rheumatoid arthritis. However, their usefulness, especially in rheumatoid arthritis therapy, is hampered by severe side effects on bone leading to glucocorticoid-induced osteoporosis. The molecular and cellular mechanisms mediating the beneficial and adverse effects remain poorly understood. Nevertheless, advanced molecular biological analyses and in vivo approaches using conditional mutant mice have helped to unravel in part the underlying mechanisms of immunosuppression and side effects of glucocorticoid therapy in arthritis, thereby contributing to an improved understanding of these therapeutically important hormones.

Single bout short duration fluid shear stress induces osteogenic differentiation of MC3T3-E1 cells via integrin β1 and BMP2 signaling cross-talk

Fluid shear stress plays an important role in bone osteogenic differentiation. It is traditionally believed that pulsed and continuous stress load is more favorable for fracture recovery and bone homeostasis. However, according to our clinical practice, we notice that one single stress load is also sufficient to trigger osteogenic differentiation. In the present study, we subject osteoblast MC3T3-E1 cells to single bout short duration fluid shear stress by using a parallel plate flow system. The results show that 1 hour of fluid shear stress at 12 dyn/cm² promotes terminal osteogenic differentiation, including rearrangement of F-actin stress fiber, up-regulation of osteogenic genes expression, elevation of alkaline phosphatase activity, secretion of type I collagen and osteoid nodule formation. Moreover, collaboration of BMP2 and integrin β1 pathways plays a significant role in such differentiation processes. Our findings provide further experimental evidence to support the notion that single bout short duration fluid shear stress can promote osteogenic differentiation.

PGE2 and BMP-2 in bone and cartilage metabolism: 2 intertwining pathways

Osteoarthritis and lesions to cartilage tissue are diseases that frequently result in impaired joint function and patient disability. The treatment of osteoarthritis, along with local bone defects and systemic skeletal diseases, remains a significant clinical challenge for orthopaedic surgeons. Several bone morphogenetic proteins (BMPs) are known to have osteoinductive effects, whereof BMP-2 and BMP-7 are already approved for clinical applications. There is growing evidence that the metabolism of bone as well as the cartilage damage associated with the above disease processes are strongly inter-related with the interactions of the inflammation-related pathways (in particular prostaglandin E2 (PGE2)) and osteogenesis (in particular bone morphogenetic protein-2 (BMP-2)). There is strong evidence that the pathways of prostaglandins and bone morphogenetic proteins are intertwined, and they have recently come into focus in several experimental and clinical studies. This paper focuses on PGE2 and BMP-2 intertwining pathways in bone and cartilage metabolism, and summarizes the recent experimental and clinical data.

The multiple facets of glucocorticoid action in rheumatoid arthritis

Glucocorticoids have potent anti-inflammatory effects and have been used to treat patients with rheumatoid arthritis for more than 60 years. However, severe adverse effects of glucocorticoid treatment, including loss of bone mass and increased risk of fractures, are common. Data from studies of glucocorticoid-mediated gene regulation, which utilized conditional knockout mice in animal models of arthritis or glucocorticoid-induced osteoporosis, have substantially increased our understanding of the mechanisms by which glucocorticoids act via the glucocorticoid receptor. Following glucocorticoid binding, the receptor regulates gene expression either by interacting with DNA-bound transcription factors as a monomer or by binding directly to DNA as a dimer. In contrast to the old hypothesis that transrepression mechanisms involving monomeric glucocorticoid receptor actions were responsible for the anti-inflammatory effects of glucocorticoids, whereas dimeric glucocorticoid receptor binding resulted in adverse effects, data from animal models have shown that the anti-inflammatory and adverse effects of glucocorticoids are mediated by both monomeric and dimeric glucocorticoid receptor binding. This improved knowledge of the molecular mechanisms that underlie the beneficial and adverse effects of glucocorticoid therapy might lead to the development of rationales for novel glucocorticoid receptor ligands that could potentially have anti-inflammatory efficacy without adverse effects on bone.

A potential role for insulin resistance in experimental pulmonary hypertension

Patients with pulmonary arterial hypertension have increased prevalence of insulin resistance. We aimed to determine whether metabolic defects are associated with bone morphogenic protein receptor type 2 (Bmpr2) mutations in mice, and whether these may contribute to pulmonary vascular disease development. Metabolic phenotyping was performed on transgenic mice with inducible expression of Bmpr2 mutation, R899X. Phenotypic penetrance in Bmpr2(R899X) was assessed in a high-fat diet model of insulin resistance. Alterations in glucocorticoid responses were assessed in murine pulmonary microvascular endothelial cells and Bmpr2(R899X) mice treated with dexamethasone. Compared to controls, Bmpr2(R899X) mice showed increased weight gain and demonstrated insulin resistance as assessed by the homeostatic model assessment insulin resistance (1.0 ± 0.4 versus 2.2 ± 1.8) and by fat accumulation in skeletal muscle and decreased oxygen consumption. Bmpr2(R899X) mice fed a high-fat diet had strong increases in pulmonary hypertension penetrance (seven out of 11 versus three out of 11). In cell culture and in vivo experiments, Bmpr2 mutation resulted in a combination of constitutive glucocorticoid receptor activation and insensitivity. Insulin resistance is present as an early feature of Bmpr2 mutation in mice. Exacerbated insulin resistance through high-fat diet worsened pulmonary phenotype, implying a possible causal role in disease. Impaired glucocorticoid responses may contribute to metabolic defects.

Salvianolic acid B prevents bone loss in prednisone-treated rats through stimulation of osteogenesis and bone marrow angiogenesis

Glucocorticoid (GC) induced osteoporosis (GIO) is caused by the long-term use of GC for treatment of autoimmune and inflammatory diseases. The GC related disruption of bone marrow microcirculation and increased adipogenesis contribute to GIO development. However, neither currently available anti-osteoporosis agent is completely addressed to microcirculation and bone marrow adipogenesis. Salvianolic acid B (Sal B) is a polyphenolic compound from a Chinese herbal medicine, Salvia miltiorrhiza Bunge. The aim of this study was to determine the effects of Sal B on osteoblast bone formation, angiogenesis and adipogenesis-associated GIO by performing marrow adipogenesis and microcirculation dilation and bone histomorphometry analyses. (1) In vivo study: Bone loss in GC treated rats was confirmed by significantly decreased BMD, bone strength, cancellous bone mass and architecture, osteoblast distribution, bone formation, marrow microvessel density and diameter along with down-regulation of marrow BMPs expression and increased adipogenesis. Daily treatment with Sal B (40 mg/kg/d) for 12 weeks in GC male rats prevented GC-induced cancellous bone loss and increased adipogenesis while increasing cancellous bone formation rate with improved local microcirculation by capillary dilation. Treatment with Sal B at a higher dose (80 mg/kg/d) not only prevented GC-induced osteopenia, but also increased cancellous bone mass and thickness, associated with increase of marrow BMPs expression, inhibited adipogenesis and further increased microvessel diameters. (2) In vitro study: In concentration from 10⁻⁶ mol/L to 10⁻⁷ mol/L, Sal B stimulated bone marrow stromal cell (MSC) differentiation to osteoblast and increased osteoblast activities, decreased GC associated adipogenic differentiation by down-regulation of PPARγ mRNA expression, increased Runx2 mRNA expression without osteoblast inducement, and, furthermore, Sal B decreased Dickkopf-1 and increased β-catenin mRNA expression with or without adipocyte inducement in MSC. We conclude that Sal B prevented bone loss in GC-treated rats through stimulation of osteogenesis, bone marrow angiogenesis and inhibition of adipogenesis.

Stimulation of osteoblastic differentiation and mineralization in MC3T3-E1 cells by yeast hydrolysate

In a previous study, it was reported that yeast hydrolysate (YH) was effective in promoting bone growth in Sprague-Dawley (SD) rats. To further clarify the mechanism of YH, the effects of YH on proliferation, differentiation and gene expression in vitro were investigated using osteoblastic cell lines (MC3T3-E1). Cell proliferation increased significantly as much as 110% of the basal value when cells were treated with 100 µg/mL of YH. Alkaline phosphatase (ALP) activity increased significantly with a YH concentration of 25-100 µg/mL, and the activity increased 152% that of the control at 100 µg/mL. The calcium content increased as much as 129% at 100 µg/mL YH. The gene expression levels of ALP and collagen type II (COL II) significantly increased approximately 1.3-fold and 1.7-fold of control, respectively, at 100 µg/mL. YH increased significantly the mRNA level of bone sialoprotein (BSP) but not in a dose-dependent manner. The mRNA levels of bone morphogenetic proteins (BMP)-2, BMP-4, collagen type I (COL I) and osteonectin (ON) did not increase. In summary, YH increased the proliferation of osteoblasts and directly stimulated ALP and bone matrix proteins (e.g. BSP, COL II), and these increases trigger osteoblastic differentiation (e.g. mineralized nodule formation).

Role of RUNX3 in bone morphogenetic protein signaling in colorectal cancer

Bone morphogenetic proteins (BMPs), members of the transforming growth factor-beta (TGF-beta) superfamily, are multifunctional cytokines regulating a broad spectrum of biological functions. Recent studies show the presence of BMP receptor 1a mutations in juvenile polyposis and frequent Smad4 mutations in colon cancer, suggesting that aberrations in BMP signaling play an important role in intestinal cancer pathogenesis. However, the exact molecular mechanisms remain poorly understood. The Runt domain transcription factor RUNX3 is an integral component of signaling pathways mediated by TGF-beta and BMPs. RUNX3 is a gastric and colon tumor suppressor, functioning downstream of TGF-beta. Recently, we showed the tumor-suppressive effects of RUNX3 by its ability to attenuate beta-catenin/T-cell factors (TCFs) transactivation in intestinal tumorigenesis. Here, we explore the molecular basis of the tumor-suppressive function of the BMP pathway through RUNX3 in colorectal carcinogenesis. BMP exerted a growth-suppressive effect in HT-29, a human colorectal cancer cell line. c-Myc oncogene was found to be downregulated by BMP and/or RUNX3. We show that upregulation of RUNX3 by BMP reduces c-Myc expression. Evidence is presented suggesting that RUNX3 downregulates c-Myc expression by two parallel pathways-directly at the transcriptional level and through attenuation of beta-catenin/TCFs, downstream of BMPs in colorectal cancer cells.

Starch-poly-epsilon-caprolactone microparticles reduce the needed amount of BMP-2

BMP-2 is currently administered clinically using collagen matrices often requiring large amounts of BMP-2 due to burst release over a short period of time. We developed and tested a novel injectable drug delivery system consisting of starch-poly-epsilon-caprolactone microparticles for inducing osteogenesis and requiring smaller amounts of BMP-2. We evaluated BMP-2 encapsulation efficiency and the in vitro release profile by enzyme-linked immunosorbent assay. BMP-2 was rapidly released during the first 12 hours, followed by sustained release for up to 10 days. We then evaluated the osteogenic potential of dexamethasone (standard osteogenic induction agent) and BMP-2 after incorporation and during release using an osteo/myoblast cell line (C2C12). Alkaline phosphatase activity was increased by released BMP-2. Mineralization occurred after stimulation with BMP-2-loaded microparticles. A luciferase assay for osteocalcin promoter activity showed high levels of activity upon treatment with BMP-2-loaded microparticles. In contrast, no osteogenesis occurred in C2C12 cells using dexamethasone-loaded microparticles. However, human adipose stem cells exposed to the microparticles produced high amounts of alkaline phosphatase. The data suggest starch-poly-epsilon-caprolactone microparticles are suitable carriers for the incorporation and controlled release of glucocorticoids and growth factors. Specifically, they reduce the amount of BMP-2 needed and allow more sustained osteogenic effects.

Immortalization and characterization of mouse floxed Bmp2/4 osteoblasts

Generation of a floxed Bmp2/4 osteoblast cell line is a valuable tool for studying the modulatory effects of Bmp2 and Bmp4 on osteoblast differentiation as well as relevant molecular events. In this study, primary floxed Bmp2/4 mouse osteoblasts were cultured and transfected with simian virus 40 large T-antigen. Transfection was verified by polymerase chain reaction (PCR) and immunohistochemistry. To examine the characteristics of the transfected cells, morphology, proliferation and mineralization were analyzed, expression of cell-specific genes including Runx2, ATF4, Dlx3, Osx, dentin matrix protein 1, bone sialoprotein, osteopontin, osteocalcin, osteonectin and collagen type I was detected. These results show that transfected floxed Bmp2/4 osteoblasts bypassed senescence with a higher proliferation rate, but retain the genotypic and phenotypic characteristics similar to the primary cells. Thus, we for the first time demonstrate the establishment of an immortalized mouse floxed Bmp2/4 osteoblast cell line.