BMP2 induces osteoblast apoptosis in a maturation state and noggin-dependent manner

Emerging Role of Non-collagenous Bone Proteins as Osteokines in Extraosseous Tissues

Bone is a unique tissue, composed of various types of cells embedded in a calcified extracellular matrix (ECM), whose dynamic structure consists of organic and inorganic compounds produced by bone cells. The main inorganic component is represented by hydroxyapatite, whilst the organic ECM is primarily made up of type I collagen and non-collagenous proteins. These proteins play an important role in bone homeostasis, calcium regulation, and maintenance of the hematopoietic niche. Recent advances in bone biology have highlighted the importance of specific bone proteins, named "osteokines", possessing endocrine functions and exerting effects on nonosseous tissues. Accordingly, osteokines have been found to act as growth factors, cell receptors, and adhesion molecules, thus modifying the view of bone from a static tissue fulfilling mobility to an endocrine organ itself. Since bone is involved in a paracrine and endocrine cross-talk with other tissues, a better understanding of bone secretome and the systemic roles of osteokines is expected to provide benefits in multiple topics: such as identification of novel biomarkers and the development of new therapeutic strategies. The present review discusses in detail the known osseous and extraosseous effects of these proteins and the possible respective clinical and therapeutic significance.

Bone marrow stromal cells generate an osteoinductive microenvironment when cultured on titanium-aluminum-vanadium substrates with biomimetic multiscale surface roughness

Osseointegration of titanium-based implants possessing complex macroscale/microscale/mesoscale/nanoscale (multiscale) topographies support a direct and functional connection with native bone tissue by promoting recruitment, attachment and osteoblastic differentiation of bone marrow stromal cells (MSCs). Recent studies show that the MSCs on these surfaces produce factors, including bone morphogenetic protein 2 (BMP2) that can cause MSCs not on the surface to undergo osteoblast differentiation, suggesting they may produce an osteogenic environmentin vivo. This study examined if soluble factors produced by MSCs in contact with titanium-aluminum-vanadium (Ti6Al4V) implants possessing a complex multiscale biomimetic topography are able to induce osteogenesis ectopically. Ti6Al4V disks were grit-blasted and acid-etched to create surfaces possessing macroscale and microscale roughness (MM), micro/meso/nanoscale topography (MN), and macro/micro/meso/nanoscale topography (MMN^TM). Polyether-ether-ketone (PEEK) disks were also fabricated by machining to medical-grade specifications. Surface properties were assessed by scanning electron microscopy, contact angle, optical profilometry, and x-ray photoelectron spectroscopy. MSCs were cultured in growth media (GM). Proteins and local factors in their conditioned media (CM) were measured on days 4, 8, 10 and 14: osteocalcin, osteopontin, osteoprotegerin, BMP2, BMP4, and cytokines interleukins 6, 4 and 10 (IL6, IL4, and IL10). CM was collected from D14 MSCs on MMN^TMand tissue culture polystyrene (TCPS) and lyophilized. Gel capsules containing active demineralized bone matrix (DBM), heat-inactivated DBM (iDBM), and iDBM + MMN-GM were implanted bilaterally in the gastrocnemius of athymic nude mice (N= 8 capsules/group). Controls included iDBM + GM; iDBM + TCPS-CM from D5 to D10 MSCs; iDBM + MMN-CM from D5 to D10; and iDBM + rhBMP2 (R&D Systems) at a concentration similar to D5-D10 production of MSCs on MMN^TMsurfaces. Legs were harvested at 35D. Bone formation was assessed by micro computed tomography and histomorphometry (hematoxylin and eosin staining) with the histology scored according to ASTM 2529-13. DNA was greatest on PEEK at all time points; DNA was lowest on MN at early time points, but increased with time. Cells on PEEK exhibited small changes in differentiation with reduced production of BMP2. Osteoblast differentiation was greatest on the MN and MMN^TM, reflecting increased production of BMP2 and BMP4. Pro-regenerative cytokines IL4 and IL10 were increased on Ti-based surfaces; IL6 was reduced compared to PEEK. None of the media from TCPS cultures was osteoinductive. However, MMN-CM exhibited increased bone formation compared to iDBM and iDBM + rhBMP2. Furthermore, exogenous rhBMP2 alone, at the concentration found in MMN-CM collected from D5 to D10 cultures, failed to induce new bone, indicating that other factors in the CM play a critical role in that osteoinductive microenvironment. MSCs cultured on MMN^TMTi6Al4V surfaces differentiate and produce an increase in local factors, including BMP2, and the CM from these cultures can induce ectopic bone formation compared to control groups, indicating that the increased bone formation arises from the local response by MSCs to a biomimetic, multiscale surface topography.

BMP-2 and Noggin Immunoexpression in Ameloblastomas, Odontogenic Keratocysts, and Dentigerous Cysts

BMP-2 and Noggin are expressed in several tissues and participate in cell differentiation and proliferation during odontogenesis and tumor development. We evaluated the immunohistochemical expression of these proteins in ameloblastomas (AMs), odontogenic keratocysts (OKCs), and dentigerous cysts (DCs). The expression in AM (n.20), OKC (n.20), and DC (n.20) was evaluated by the percentage of positive cells and expression intensity, resulting in a total immunostaining score. Analysis of BMP-2 and Noggin revealed positivity in all cases. The Mann-Whitney test showed a statistically significant difference for Noggin between AM and DC and between OKC/DC. The mean DC scores were always higher than those of the other groups, regardless of the assessment method. Individual analysis of each lesion showed a positive and significant correlation between the percentage of cells positive for BMP-2 and Noggin in DC. We demonstrated the presence of BMP-2 and Noggin in AMs/OKCs/DCs. Marked expression of BMP-2 was observed in OKCs and AMs. There was also a positive correlation between BMP-2 and Noggin in DCs, suggesting a greater role of these markers in the bone formation and remodeling process since DCs are characterized by phases of bone quiescence and healing.

Attenuating effect of magnesium on pulmonary arterial calcification in rodent models of pulmonary hypertension

OBJECTIVE

Vascular calcification has been considered as a potential therapeutic target in pulmonary hypertension. Mg2+ has a protective role against calcification. This study aimed to investigate whether Mg2+ could alleviate pulmonary hypertension by reducing medial calcification of pulmonary arteries.

METHODS

Monocrotaline (MCT)-induced and chronic hypoxia-induced pulmonary hypertension rats were given an oral administration of 10% MgSO4 (10 ml/kg per day). Additionally, we administered Mg2+ in calcified pulmonary artery smooth muscle cells (PASMCs) after incubating with β-glycerophosphate (β-GP, 10 mmol/l).

RESULTS

In vivo, MCT-induced and chronic hypoxia-induced pulmonary hypertension indexes, including right ventricular systolic pressure, right ventricular mass index, and arterial wall thickness, as well as Alizarin Red S (ARS) staining-visualized calcium deposition, high calcium levels, and osteochondrogenic differentiation in pulmonary arteries, were mitigated by dietary Mg2+ intake. In vitro, β-GP-induced calcium-rich deposits stained by ARS, calcium content, as well as the detrimental effects of calcification to proliferation, migration, and resistance to apoptosis of PASMCs were alleviated by high Mg2+ but exacerbated by low Mg2+. Expression levels of mRNA and protein of β-GP-induced osteochondrogenic markers, RUNX Family Transcription Factor 2, and Msh Homeobox 2 were decreased by high Mg2+ but increased by low Mg2+; however, Mg2+ did not affect β-GP-induced expression of SRY-Box Transcription Factor 9. Moreover, mRNA expression and protein levels of β-GP-reduced calcification inhibitor, Matrix GLA protein was increased by high Mg2+ but decreased by low Mg2+.

CONCLUSION

Mg2+ supplement is a powerful strategy to treat pulmonary hypertension by mitigating pulmonary arterial calcification as the calcification triggered physiological and pathological changes to PASMCs.

BMP-2 Long-Term Stimulation of Human Pre-Osteoblasts Induces Osteogenic Differentiation and Promotes Transdifferentiation and Bone Remodeling Processes

Bone morphogenic protein (BMP-) 2 plays an important role in the regeneration of bone defects by promoting osteogenic differentiation. However, several animal studies have reported adverse side effects of BMP-2, including osteoclast activation, induction of peroxisome proliferator- activated receptor gamma (PPARG)expression, and inflammation. High BMP-2 concentrations are thought to be responsible for these side effects. For this reason, primary pre-osteoblasts were exposed to lower BMP-2 concentrations (1 and 2 µg/mL). Long-term exposure (up to 28 days) was performed to investigate whether this stimulation protocol may promote osteogenic differentiation without causing the side effects mentioned above. The results showed that BMP-2 treatment for 14 or 28 days resulted in increased osteogenesis, through an increase in runt-related transcription factor 2, osterix, alkaline phosphatase, and integrin-binding sialoprotein expression. However, an increase in tumor necrosis factor alpha and receptor activator of nuclear factor kappa-Β ligand protein levels was observed after BMP-2 exposure, indicating also an increased potential for osteoclast activation by osteoblasts. Additionally, morphological changes like intracellular, filled vacuoles could be detected. Enhanced PPARG and perilipin 1 mRNA transcripts and lipid droplets indicated an induced adipogenic differentiation. Overall, the data demonstrate that long-term BMP-2 exposure promotes not only osteogenic differentiation but also adipogenesis and regulates mediators involved in osteoclast activation in vitro.

Dexamethasone Induces Apoptosis of Embryonic Palatal Mesenchymal Cells Through the GATA-6/Bone Morphogenetic Protein-2/p38 MAPK Pathway

ABSTRACT

Exposure to dexamethasone (DEX) causes cleft palate at high rates. Our previous studies proved that GATA binding protein 6 (GATA-6)/bone morphogenetic protein-2 (BMP-2) mediated apoptosis is related to DEX-induced cleft palate, but the specific mechanism is still unclear. The goal of this research was to understand the mechanism of apoptosis in cleft palate formation induced by DEX. Palatal mesenchymal cells from mouse embryos on embryonic day 13 were isolated as the experimental group, GATA-6 was silenced by GATA-6 small interfering Ribonucleic Acid (RNA). Cell Counting Kit-8, flow cytometry and Western Blot were applied to detect cell proliferation ability, cell cycle, the proportion of apoptotic cells, and the expression of apoptosis-related proteins of GATA-6 knockdown palatal mesenchymal cells. Further proteins on the BMP-2/Mitogen-activated protein kinase (MAPK) pathways were detected using Western Blot. T results showed that knockdown of GATA-6 by siRNA significantly decreased cell proliferation and increased the expression of apoptosis-related proteins. Bone morphogenetic protein-2/P38 mitogen Activated protein kinase (P38 MARK) pathway proteins decreased significantly among the GATA-6 knockdown group, DEX-cleft palate group and control +DEX groups. The results indicated that the GATA-6/BMP-2/P38 MAPK athway was involved in the apoptosis caused by GATA-6 silencing, which may be the possible mechanism of DEX inducing cleft palate.

SMAD4 contributes to chondrocyte and osteocyte development

Different cellular and molecular mechanisms contribute to chondrocyte and osteocyte development. Although vital roles of the mothers against decapentaplegic homolog 4 (also called 'SMAD4') have been discussed in different cancers and stem cell-related studies, there are a few reviews summarizing the roles of this protein in the skeletal development and bone homeostasis. In order to fill this gap, we discuss the critical roles of SMAD4 in the skeletal development. To this end, we review the different signalling pathways and also how SMAD4 defines stem cell features. We also elaborate how the epigenetic factors-ie DNA methylation, histone modifications and noncoding RNAs-make a contribution to the chondrocyte and osteocyte development. To better grasp the important roles of SMAD4 in the cartilage and bone development, we also review the genotype-phenotype correlation in animal models. This review helps us to understand the importance of the SMAD4 in the chondrocyte and bone development and the potential applications for therapeutic goals.

ASB2 is a novel E3 ligase of SMAD9 required for cardiogenesis

Cardiogenesis requires the orchestrated spatiotemporal tuning of BMP signalling upon the balance between induction and counter-acting suppression of the differentiation of the cardiac tissue. SMADs are key intracellular transducers and the selective degradation of SMADs by the ubiquitin-proteasome system is pivotal in the spatiotemporal tuning of BMP signalling. However, among three SMADs for BMP signalling, SMAD1/5/9, only the specific E3 ligase of SMAD9 remains poorly investigated. Here, we report for the first time that SMAD9, but not the other SMADs, is ubiquitylated by the E3 ligase ASB2 and targeted for proteasomal degradation. ASB2, as well as Smad9, is conserved among vertebrates. ASB2 expression was specific to the cardiac region from the very early stage of cardiac differentiation in embryogenesis of mouse. Knockdown of Asb2 in zebrafish resulted in a thinned ventricular wall and dilated ventricle, which were rescued by simultaneous knockdown of Smad9. Abundant Smad9 protein leads to dysregulated cardiac differentiation through a mechanism involving Tbx2, and the BMP signal conducted by Smad9 was downregulated under quantitative suppression of Smad9 by Asb2. Our findings demonstrate that ASB2 is the E3 ligase of SMAD9 and plays a pivotal role in cardiogenesis through regulating BMP signalling.

Quantitative proteomics reveals the effect of Yigu decoction (YGD) on protein expression in bone tissue

Background

Osteoporosis (OP) is a systemic bone disease characterized by decreased bone mass, destruction of the bone tissue microstructure, increased bone brittleness and an increased risk of fracture. OP has a high incidence rate and long disease course and is associated with serious complications. Yigu decoction (YGD) is a compound prescription in traditional Chinese medicine that is used to treat OP. However, its mechanism in OP is not clear. This study used a tandem mass tag (TMT)quantitative proteomics method to explore the potential bone-protective mechanism of YGD in an osteoporotic rat model.

Materials and methods

A rat model of OP was established by ovariectomy. Eighteen 12-week-old specific-pathogen-free female Wistar rats weighing 220 ± 10 g were selected. The eighteen rats were randomly divided into 3 groups (n = 6 in each group): the normal, model and YGD groups. The right femurs from each group were subjected to quantitative biological analysis. TMT quantitative proteomics was used to analyze the proteins extracted from the bone tissue of rats in the model and YGD groups, and the differentially expressed proteins after intervention with YGD were identified as biologically relevant proteins of interest. Functional annotation correlation analysis was also performed to explore the biological function and mechanism of YGD.

Result

Compared with the model group, the YGD group showed significant upregulation of 26 proteins (FC > 1.2, P < 0.05) and significant downregulation of 39 proteins (FC < 0.833, P < 0.05). Four important targets involved in OP and 5 important signaling pathways involved in bone metabolism were identified.

Conclusions

YGD can significantly increase the bone mineral density (BMD) of osteoporotic rats and may play a therapeutic role by regulating target proteins involved in multiple signaling pathways. Therefore, these results improve the understanding of the OP mechanism and provide an experimental basis for the clinical application of YGD in OP treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12014-021-09330-0.

The Role of Growth Factors in Bioactive Coatings

With increasing obesity and an ageing population, health complications are also on the rise, such as the need to replace a joint with an artificial one. In both humans and animals, the integration of the implant is crucial, and bioactive coatings play an important role in bone tissue engineering. Since bone tissue engineering is about designing an implant that maximally mimics natural bone and is accepted by the tissue, the search for optimal materials and therapeutic agents and their concentrations is increasing. The incorporation of growth factors (GFs) in a bioactive coating represents a novel approach in bone tissue engineering, in which osteoinduction is enhanced in order to create the optimal conditions for the bone healing process, which crucially affects implant fixation. For the application of GFs in coatings and their implementation in clinical practice, factors such as the choice of one or more GFs, their concentration, the coating material, the method of incorporation, and the implant material must be considered to achieve the desired controlled release. Therefore, the avoidance of revision surgery also depends on the success of the design of the most appropriate bioactive coating. This overview considers the integration of the most common GFs that have been investigated in in vitro and in vivo studies, as well as in human clinical trials, with the aim of applying them in bioactive coatings. An overview of the main therapeutic agents that can stimulate cells to express the GFs necessary for bone tissue development is also provided. The main objective is to present the advantages and disadvantages of the GFs that have shown promise for inclusion in bioactive coatings according to the results of numerous studies.

Ad-Dressing Stem Cells: Hydrogels for Encapsulation

Regenerative medicine is a novel scientific field that employs the use of stem cells as cell-based therapy for the regeneration and functional restoration of damaged tissues and organs. Stem cells bear characteristics such as the capacity for self-renewal and differentiation towards specific lineages and, therefore, serve as a backup reservoir in case of tissue injuries. Therapeutically, they can be autologously or allogeneically transplanted for tissue regeneration; however, allogeneic stem cell transplantation can provoke host immune responses leading to a host-versus-transplant reaction. A probable solution to this problem is stem cell encapsulation, a technique that utilizes various biomaterials for the creation of a semi-permeable membrane that encases the stem cells. Stem cell encapsulation can be accomplished by employing a great variety of natural and/or synthetic hydrogels and offers many benefits in regenerative medicine, including protection from the host’s immune system and mechanical stress, improved cell viability, proliferation and differentiation, cryopreservation and controlled and continuous delivery of the stem-cell-secreted therapeutic agents. Here, in this review, we report and discuss almost all natural and synthetic hydrogels used in stem cell encapsulation, along with the benefits that these materials, alone or in combination, could offer to cell therapy through functional cell encapsulation.

Estrogen inhibits vascular calcification in rats via hypoxia-induced factor-1α signaling

OBJECTIVE

Calcification serves as a surrogate for atherosclerosis-associated vascular diseases, and coronary artery calcification is mediated by multiple pathogenic factors. Estrogen is a known factor that protects the arterial wall against atherosclerosis, but its role in the coronary artery calcification development remains largely unclear. This study tested the hypothesis that estrogen inhibits coronary artery calcification via the hypoxia-induced factor-1α pathway.

METHODS

Eight-week-old healthy female Sprague-Dawley rats were castrated, and vitamin D3 was administered orally to establish. Hypoxia-induced factor-1 inhibitor was administered to test its effect on vascular calcification and expression of bone morphogenetic protein 2 and runt-related transcription factor-2. Vascular smooth muscle cell calcification was induced with CaCl2 in rat aortic smooth muscle cells in the presence or absence of E2(17β-estradiol) and bone morphogenetic protein 2 siRNA intervention.

RESULTS

The estrogen levels in ovariectomized rats were significantly decreased, as determined by ELISA. Expression of hypoxia-induced factor-1α mRNA and protein was significantly increased in vascular cells with calcification as compared to those without calcification (p < 0.01). E2 treatment decreased the calcium concentration in vascular cell calcification and cell calcium nodules in vitro (p < 0.05). E2 also lowered the levels of hypoxia-induced factor-1α mRNA and protein (p < 0.01). Oral administration of the hypoxia-induced factor-1α inhibitor dimethyloxetane in castrated rats alleviated vascular calcification and expression of osteogenesis-related transcription factors, bone morphogenetic protein 2 and RUNX2 (p < 0.01). Finally, bone morphogenetic protein 2 siRNA treatment decreased the levels of p-Smad1/5/8 in A7r5 calcification cells (p < 0.01).

CONCLUSION

Estrogen deficiency enhances vascular calcification. Treatment with estrogen reduces the expression of hypoxia-induced factor-1α as well as vascular calcification in rats. The estrogen effects occur in a fashion dependent on hypoxia-induced factor-1α regulation of bone morphogenetic protein-2 and downstream Smad1/5/8.

Peroxisome Proliferator-Activated Receptor-γ Knockdown Impairs Bone Morphogenetic Protein-2-Induced Critical-Size Bone Defect Repair

The Food and Drug Administration-approved clinical dose (1.5 mg/mL) of bone morphogenetic protein-2 (BMP2) has been reported to induce significant adverse effects, including cyst-like adipose-infiltrated abnormal bone formation. These undesirable complications occur because of increased adipogenesis, at the expense of osteogenesis, through BMP2-mediated increases in the master regulatory gene for adipogenesis, peroxisome proliferator-activated receptor-γ (PPARγ). Inhibiting PPARγ during osteogenesis has been suggested to drive the differentiation of bone marrow stromal/stem cells toward an osteogenic, rather than an adipogenic, lineage. We demonstrate that knocking down PPARγ while concurrently administering BMP2 can reduce adipogenesis, but we found that it also impairs BMP2-induced osteogenesis and leads to bone nonunion in a mouse femoral segmental defect model. In addition, in vitro studies using the mouse bone marrow stromal cell line M2-10B4 and mouse primary bone marrow stromal cells confirmed that PPARγ knockdown inhibits BMP2-induced adipogenesis; attenuates BMP2-induced cell proliferation, migration, invasion, and osteogenesis; and escalates BMP2-induced cell apoptosis. More important, BMP receptor 2 and 1B expression was also significantly inhibited by the combined BMP2 and PPARγ knockdown treatment. These findings indicate that PPARγ is critical for BMP2-mediated osteogenesis during bone repair. Thus, uncoupling BMP2-mediated osteogenesis and adipogenesis using PPARγ inhibition to combat BMP2's adverse effects may not be feasible.

Advances in Porous Scaffold Design for Bone and Cartilage Tissue Engineering and Regeneration

IMPACT STATEMENT

Challenges in musculoskeletal tissue regeneration affect millions of patients globally. Scaffolds for tissue engineering bone and cartilage provide promising solutions that increase healing and decrease need for complicated surgical procedures. Porous scaffolds have emerged as an attractive alternative to traditional scaffolds. However, the success of advanced materials, use of biological factors, and manufacturing techniques can vary depending on use case. This review provides perspective on porous scaffold manufacturing, characterization and application, and can be used to inform future scaffold design.

The effect of surface topography and porosity on the tensile fatigue of 3D printed Ti-6Al-4V fabricated by selective laser melting

Additive manufacturing (3D printing) is emerging as a key manufacturing technique in medical devices. Selective laser melted (SLM) Ti-6Al-4V implants with interconnected porosity have become widespread in orthopedic applications where porous structures encourage bony ingrowth and the stiffness of the implant can be tuned to reduce stress shielding. The SLM technique allows high resolution control over design, including the ability to introduce porosity with spatial variations in pore size, shape, and connectivity. This study investigates the effect of construct design and surface treatment on tensile fatigue behavior of 3D printed Ti-6Al-4V. Samples were designed as solid, solid with an additional surface porous layer, or fully porous, while surface treatments included commercially available rotopolishing and SILC cleaning. All groups were evaluated for surface roughness and tested in tension to failure under monotonic and cyclic loading profiles. Surface treatments were shown to reduce surface roughness for all sample geometries. However, only fatigue behavior of solid samples was improved for treated as compared to non-treated surfaces Irrespective of surface treatment and resulting surface roughness, the fatigue strength of 3D printed samples containing bulk or surface porosity was approximately 10% of the ultimate tensile strength of identical 3D printed porous material. This study highlights the relative effect of surface treatment in solid and porous printed samples and the inherent decrease in fatigue properties of 3D printed porous samples designed for osseointegration.

Insulin antagonises pigment epithelium-derived factor (PEDF)-induced modulation of lineage commitment of myocytes and heterotrophic ossification

Extensive bone defects arising as a result of trauma, infection and tumour resection and other bone pathologies necessitates the identification of effective strategies in the form of tissue engineering, gene therapy and osteoinductive agents to enhance the bone repair process. PEDF is a multifunctional glycoprotein which plays an important role in regulating osteoblastic differentiation and bone formation. PEDF treatment of mice and human skeletal myocytes at physiological concentration inhibited myogenic differentiation and activated Erk1/2 MAPK- dependent osteogenic transdifferentiation of myocytes. In mice, insulin, a promoter of bone regeneration, attenuated PEDF-induced expression of osteogenic markers such as osteocalcin, alkaline phosphatase and mineralisation for bone formation in the muscle and surrounding adipose tissue. These results provide new insights into the molecular aspects of the antagonising effect of insulin on PEDF-dependent modulation of the differentiation commitment of musculoskeletal environment into osteogenesis, and suggest that PEDF may be developed as an effective clinical therapy for bone regeneration as its heterotopic ossification can be controlled via co-administration of insulin.

Biomaterials for the Delivery of Growth Factors and Other Therapeutic Agents in Tissue Engineering Approaches to Bone Regeneration

Bone fracture followed by delayed or non-union typically requires bone graft intervention. Autologous bone grafts remain the clinical "gold standard". Recently, synthetic bone grafts such as Medtronic's Infuse Bone Graft have opened the possibility to pharmacological and tissue engineering strategies to bone repair following fracture. This clinically-available strategy uses an absorbable collagen sponge as a carrier material for recombinant human bone morphogenetic protein 2 (rhBMP-2) and a similar strategy has been employed by Stryker with BMP-7, also known as osteogenic protein-1 (OP-1). A key advantage to this approach is its "off-the-shelf" nature, but there are clear drawbacks to these products such as edema, inflammation, and ectopic bone growth. While there are clinical challenges associated with a lack of controlled release of rhBMP-2 and OP-1, these are among the first clinical examples to wed understanding of biological principles with biochemical production of proteins and pharmacological principles to promote tissue regeneration (known as regenerative pharmacology). After considering the clinical challenges with such synthetic bone grafts, this review considers the various biomaterial carriers under investigation to promote bone regeneration. This is followed by a survey of the literature where various pharmacological approaches and molecular targets are considered as future strategies to promote more rapid and mature bone regeneration. From the review, it should be clear that pharmacological understanding is a key aspect to developing these strategies.

Growth Factor Delivery Systems for Tissue Engineering and Regenerative Medicine

Growth factors (GFs) are often a key component in tissue engineering and regenerative medicine approaches. In order to fully exploit the therapeutic potential of GFs, GF delivery vehicles have to meet a number of key design criteria such as providing localized delivery and mimicking the dynamic native GF expression levels and patterns. The use of biomaterials as delivery systems is the most successful strategy for controlled delivery and has been translated into different commercially available systems. However, the risk of side effects remains an issue, which is mainly attributed to insufficient control over the release profile. This book chapter reviews the current strategies, chemistries, materials and delivery vehicles employed to overcome the current limitations associated with GF therapies.

* Roughness and Hydrophilicity as Osteogenic Biomimetic Surface Properties

Successful dental and orthopedic implant outcomes are determined by the degree of osseointegration. Over the last 60 years, endosseous implants have evolved to stimulate osteogenesis without the need for exogenous biologics such as bone morphogenetic proteins. An understanding of the interaction between cells and the physical characteristics of their environments has led to development of bioactive implants. Implant surfaces that mimic the inherent chemistry, topography, and wettability of native bone have shown to provide cells in the osteoblast lineage with the structural cues to promote tissue regeneration and net new bone formation. Studies show that attachment, proliferation, differentiation, and local factor production are sensitive to these implant surface characteristics. This review focuses on how surface properties, including chemistry, topography, and hydrophilicity, modulate protein adsorption, cell behavior, biological reactions, and signaling pathways in peri-implant bone tissue, allowing the development of true biomimetics that promote osseointegration by providing an environment suitable for osteogenesis.

Bone Morphogenetic Protein 2 Alters Osteogenesis and Anti-Inflammatory Profiles of Mesenchymal Stem Cells Induced by Microtextured Titanium In Vitro<sup/>

OBJECTIVES

Microtextured titanium (Ti) induces osteoblast differentiation of mesenchymal stem cells (MSCs) in the absence of exogenous osteogenic factors; and high-energy surface modifications speed healing of microrough Ti implants. Bone morphogenetic protein 2 (BMP2) is used clinically to improve peri-implant bone formation and osseointegration but can cause inflammation and bone-related complications. In this study, we determined whether BMP2 alters human MSC differentiation, apoptosis, and inflammatory factor production when grown on Ti implants with different surface properties.

MATERIALS AND METHODS

Human MSCs were cultured on Ti substrates (smooth [PT], sandblasted acid-etched [SLA], hydrophilic-SLA [modSLA]), or tissue culture polystyrene (TCPS). After 7 days, inflammatory mRNAs were measured by polymerase chain reaction array. In addition, 7-day cultures were treated with exogenous BMP2 and osteogenic differentiation and production of local factors, proinflammatory interleukins, and anti-inflammatory interleukins assessed. Finally, osteogenic markers and interleukins were measured in MSCs cultured for 48 h on BMP2 dip-coated SLA and modSLA surfaces.

RESULTS

Expression of interleukins, chemokines, cytokines, and growth factors was affected by surface properties, particularly on modSLA. MSCs on Ti produced fewer resorptive and more osteogenic/anti-inflammatory factors than cells on TCPS. Addition of 100 ng/mL BMP2 not only increased differentiation but also increased proinflammatory and decreased anti-inflammatory/antiresorptive factors. Two hundred nanograms per milliliter BMP2 abolished osteogenesis and dramatically increased pro-osteoclastogenic factors. MSCs cultured on BMP2-dip-coated disks produced similar proinflammatory profiles with inhibited osteogenic differentiation and had increased apoptotic markers at the highest doses.

CONCLUSIONS

MSCs underwent osteogenesis and regulated inflammatory cytokines on microtextured Ti. Exogenous BMP2 inhibited MSC differentiation and stimulated a dose-dependent proinflammatory and apoptotic response. Use of BMP2 with microtextured metal implants may increase inflammation and possibly delay bone formation dependent on dose, suggesting that application of BMP2 clinically during implant insertion may need to be reevaluated.

Effects of Recombinant Human Lactoferrin on Osteoblast Growth and Bone Status in Piglets

Lactoferrin (LF), an ~80 kDa iron-binding glycoprotein, modulates many biological effects, including antimicrobial and immunomodulatory activities. Recently, it was shown that LF also regulates bone cell activity, suggesting its therapeutic effect on postmenopausal bone loss. However, a minimal amount is known regarding the effects of recombinant human LF (rhLF) supplementation on bone status in young healthy infants. We found osteoblast cell differentiation was significantly promoted in vitro. Furthermore, treatment of human osteoblast cells with rhLF rapidly induced phosphorylation of p44/p42 mitogen-activated protein kinase (p44/p42 MAPK, ERK1/2). In order to investigate the effects of rhLF on bone status in vivo, we used a piglet model, which is a useful model for human infants. Piglets were supplemented with rhLF milk for 30 days. Bone formation markers, Serum calcium concentration, bone mineral density (BMD), bone mineral content (BMC), tibia bone strength, and the overall metabolite profile analysis showed that rhLF was advantageous to the bone growth in piglets. These findings suggest that rhLF supplementation benefits neonate bone health by modulating bone formation.

Linking the Transcriptional Landscape of Bone Induction to Biomaterial Design Parameters

New engineering possibilities allow biomaterials to serve as active orchestrators of the molecular and cellular events of tissue regeneration. Here, the molecular control of tissue regeneration for calcium phosphate (CaP)-based materials is established by defining the parameters critical for tissue induction and those are linked to the molecular circuitry controlling cell physiology. The material properties (microporosity, ion composition, protein adsorption) of a set of synthesized osteoinductive and noninductive CaP ceramics are parameterized and these properties are correlated to a transcriptomics profile of osteogenic cells grown on the materials in vitro. Using these data, a genetic network controlling biomaterial-induced bone formation is built. By isolating the complex material properties into single-parameter test conditions, it is verified that a subset of these genes is indeed controlled by surface topography and ions released from the ceramics, respectively. The gene network points to a decisive role for extracellular matrix deposition in osteoinduction by genes such as tenascin C and hyaluronic acid synthase 2, which are controlled by calcium and phosphate ions as well as surface topography. This work provides insight into the biomaterial composition and material engineering aspects of bone void filling and can be used as a strategy to explore the interface between biomaterials and tissue regeneration.

Bone Morphogenetic Protein-2 Promotes Human Mesenchymal Stem Cell Survival and Resultant Bone Formation When Entrapped in Photocrosslinked Alginate Hydrogels

There is a substantial need to prolong cell persistence and enhance functionality in situ to enhance cell-based tissue repair. Bone morphogenetic protein-2 (BMP-2) is often used at high concentrations for osteogenic differentiation of mesenchymal stem cells (MSCs) but can induce apoptosis. Biomaterials facilitate the delivery of lower doses of BMP-2, reducing side effects and localizing materials at target sites. Photocrosslinked alginate hydrogels (PAHs) can deliver osteogenic materials to irregular-sized bone defects, providing improved control over material degradation compared to ionically cross-linked hydrogels. It is hypothesized that the delivery of MSCs and BMP-2 from a PAH increases cell persistence by reducing apoptosis, while promoting osteogenic differentiation and enhancing bone formation compared to MSCs in PAHs without BMP-2. BMP-2 significantly decreases apoptosis and enhances survival of photoencapsulated MSCs, while simultaneously promoting osteogenic differentiation in vitro. Bioluminescence imaging reveals increased MSC survival when implanted in BMP-2 PAHs. Bone defects treated with MSCs in BMP-2 PAHs demonstrate 100% union as early as 8 weeks and significantly higher bone volumes at 12 weeks, while defects with MSC-entrapped PAHs alone do not fully bridge. This study demonstrates that transplantation of MSCs with BMP-2 in PAHs achieves robust bone healing, providing a promising platform for bone repair.

Smad4 controls bone homeostasis through regulation of osteoblast/osteocyte viability

Regulation of osteoblast and osteocyte viability is essential for bone homeostasis. Smad4, a major transducer of bone morphogenetic protein and transforming growth factor-β signaling pathways, regulates apoptosis in various cell types through a mitochondrial pathway. However, it remains poorly understood whether Smad4 is necessary for the regulation of osteoblast and osteocyte viability. In this study, we analyzed Smad4Δ(Os) mice, in which Smad4 was subjected to tissue-specific disruption under the control of the 2.3-kb Col1a1 promoter, to understand the functional significance of Smad4 in regulating osteoblast/osteocyte viability during bone formation and remodeling. Smad4Δ(Os) mice showed a significant increase in osteoblast number and osteocyte density in the trabecular and cortical regions of the femur, whereas osteoclast activity was significantly decreased. The proliferation of osteoblasts/osteocytes did not alter, as shown by measuring 5'-bromo-2'deoxyuridine incorporation. By contrast, the percentage of TUNEL-positive cells decreased, together with a decrease in the Bax/Bcl-2 ratio and in the proteolytic cleavage of caspase 3, in Smad4Δ(Os) mice. Apoptosis in isolated calvaria cells from Smad4Δ(Os) mice decreased after differentiation, which was consistent with the results of the TUNEL assay and western blotting in Smad4Δ(Os) mice. Conversely, osteoblast cells overexpressing Smad4 showed increased apoptosis. In an apoptosis induction model of Smad4Δ(Os) mice, osteoblasts/osteocytes were more resistant to apoptosis than were control cells, and, consequently, bone remodeling was attenuated. These findings indicate that Smad4 has a significant role in regulating osteoblast/osteocyte viability and therefore controls bone homeostasis.

Sustained release of rhBMP-2 from microporous tricalciumphosphate using hydrogels as a carrier

Background

Tissue engineering and bone substitutes are subjects of intensive ongoing research. If the healing of bone fractures is delayed, osteoinductive materials that induce mesenchymal stem cells (MSCs) to form bone are necessary. The use of Bone Morphogenetic Protein - 2 is a common means to enhance effectiveness and accelerate the healing process. A delivery system that maintains and releases BMP biological activity in controlled fashion at the surgical site while preventing systemic diffusion (and thereby the risk of undesirable effects by controlling the amount of protein implanted) is essential.

In this study, we aimed to test a cylindrical TCP-scaffold (porosity ~ 40 %, mean pore size 5 μm, high interconnectivity) in comparison to BMP-2. Recombinant human BMP-2 was dissolved in different hydrogels as a carrier, namely gelatin and alginate cross-linked with CaCl₂-solution, or a solution of GDL and CaCO₃. FITC-labeled Protein A was used as a model substance for rhBMP-2 in the pre-trials. For loading, the samples were put in a flow chamber and sealed with silicone rings. Using a directional vacuum, the samples were loaded with the alginate-BMP-2-mixture and the loading success monitored by observing changes in a fluorescent dye (FITC labeled Protein A) under a fluorescence microscope. A fluorescence reader and ELISA were employed to measure the release. Efficacy was determined in cell culture experiments (MG63 cells) via Live-Dead-Assay, FACS, WST-1-Assay, pNPP alkaline phosphatase assay and confocal microscopy. For statistical analysis, we calculated the mean and standard deviation and carried out an analysis of variance.

Results

Directional vacuum makes it possible to load nearly 100 % of the interconnected micropores with alginate mixed with rhBMP-2. Using alginate hardened with CaCl₂ as a carrier, BMP-2's release can be decelerated significantly longer than with other hydrogels - eg, for over 28 days. The effects on osteoblast-like cells were an increase of the growth rate and expression of alkaline phosphatase while triggering no toxic effect.

Conclusion

The rhBMP-2-loaded microporous TCP scaffolds possess proliferative and osteoinductive potential. Alginate helps to lower the local growth factor dose below the cytotoxic limit, and allows the release period to be lengthened by at least 28 days.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-016-0275-8) contains supplementary material, which is available to authorized users.

GREM1 Is a Key Regulator of Synoviocyte Hyperplasia and Invasiveness

OBJECTIVE

To investigate the expression of Gremlin 1 (GREM1), an antagonist of bone morphogenetic protein, in rheumatoid arthritis (RA) synovia and its involvement in the hyperplasia and invasiveness of fibroblast-like synoviocytes of RA (RA-FLS).

METHODS

Computational analysis was introduced to identify FLS-predominant regulators. GREM1 expression was examined by immunohistochemistry, real-time PCR, and ELISA. FLS proliferation and apoptosis were determined using tetrazolium-based colorimetric assay and APOPercentage assay, respectively. FLS migration and invasion were evaluated by wound migration and Matrigel invasion assay, respectively. Expressions of Bax, Bcl2, pErk1/2, and pAkt were detected by Western blot analysis.

RESULTS

Through global transcriptome profiling, we identified a GREM1 gene predominantly expressed in RA-FLS. Indeed, the GREM1 expression was higher in synovia, synovial fluids, and FLS of patients with RA than in those of patients with osteoarthritis, and its levels correlated well with proinflammatory cytokine concentrations. Knockdown of GREM1 transcripts using short interfering RNA (siRNA) reduced the proliferation and survival of RA-FLS along with downregulation of pErk1/2, pAkt, and Bcl2 expressions, whereas it induced Bax expression. Conversely, the addition of recombinant GREM1 to RA-FLS showed the opposite results. Moreover, GREM1 siRNA decreased the migratory and invasive capacity of RA-FLS, whereas exogenous GREM1 increased it. The GREM1-induced FLS survival, migration, and invasion were completely blocked by neutralizing antibodies to ανβ3 integrin on RA-FLS, suggesting that ανβ3 integrin mediates the antiapoptotic and promigratory effects of GREM1.

CONCLUSION

GREM1 is highly expressed in RA joints, and functions as a regulator of survival, proliferation, migration, and invasion of RA-FLS.

Gene delivery of osteoinductive signals to a human fetal osteoblast cell line induces cell death in a dose-dependent manner

Gene delivery provides a powerful tool for regulating tissue regeneration by activating or inhibiting specific genes associated with targeted signaling pathways. Up-regulating bone morphogenetic protein-2 (BMP-2) or silencing GNAS and Noggin gene expression in stem cells has been shown to enhance osteogenic differentiation and bone tissue formation. However, few studies have examined how such gene delivery would influence other differentiated cell types residing in the bone. In this study, we examined the effects of DNA delivery of BMP-2 and siRNA delivery of GNAS or Noggin on a widely used human fetal osteoblast cell line (hFOB1.19) using biomaterials-mediated gene delivery. Our results showed that both GNAS and Noggin siRNA delivery increased cell death in hFOB1.19 in a dose-dependent manner. In particular, groups treated with the highest doses of BMP-2, siGNAS or siNoggin showed a more than 50% decline in cell proliferation and a 90% decline in cell viability compared to untransfected and sham DNA/siRNA-transfected controls. TUNEL staining showed that BMP-2, siGNAS or siNoggin induced cell apoptosis in hFOBs. In contrast, cells transfected using sham DNA or siRNA showed no noticeable cell death or apoptosis. These results elucidate the nuanced responses of progenitor and immortalized cell populations to the delivery of exogenous osteoinductive genes. In particular, they highlight the differences between immortalized and primary cell lines and underscore the importance of targeted gene delivery mechanisms in the regeneration of injured bone tissue.

Surface-mediated delivery of siRNA from fibrin hydrogels for knockdown of the BMP-2 binding antagonist noggin

Antagonists and inhibitory molecules responsible for maintaining tissue homeostasis can present a significant barrier to healing when tissue engineering/regenerative medicine strategies are employed. One example of this situation is the up-regulation of antagonists such as noggin in response to increasing concentrations of bone morphogenetic protein-2 (BMP-2) present from endogenous bone repair processes or delivered exogenously from biomaterials (synthetic bone grafts). While recombinant human (rh)BMP-2 delivered from synthetic bone grafts has been shown to be an effective alternative to autografts and allografts, the supraphysiological doses of rhBMP-2 have led to clinically-adverse side effects. The high rhBMP-2 dosage may be required, in part, to overcome the presence of antagonists such as noggin. Small interfering RNA (siRNA) is an appealing approach to overcome this problem because it can knock-down antagonists or inhibitory molecules in a temporary manner. Here, we conducted fundamental studies on the delivery of siRNA from material surfaces as a means to knock-down antagonists like noggin. Non-viral cationic lipid (Lipofectamine)-siRNA complexes were delivered from a fibrin hydrogel surface to MC3T3-E1 preosteoblasts that were treated with a supraphysiological dose of rhBMP-2 to achieve noggin mRNA expression levels higher than cells naïve to rhBMP-2. Confocal microscopy and flow cytometry showed intracellular uptake of siRNA in over 98% of MC3T3-E1 cells after 48 h. Doses of 0.5 and 1 μg noggin siRNA were able to significantly reduce noggin mRNA to levels equivalent to those in MC3T3-E1 cells not exposed to rhBMP-2 with no effects on cell viability.

STATEMENT OF SIGNIFICANCE

Small interfering RNA (siRNA) has been considered for treatment of diseases ranging from Alzheimer's to cancer. However, the ability to use siRNA in conjunction with biomaterials to direct tissue regeneration processes has received relatively little attention. Using the bone morphogenetic protein 2 antagonist, noggin, as a model, this research describes an approach to knock-down molecules that are inhibitory to desired regenerative pathways at the mRNA level via siRNA delivery from a hydrogel surface. Interactions between the material (fibrin) surface and polycation-siRNA complexes, release of the siRNA from the material surface, high levels of cellular uptake/internalization of siRNA, and significant knockdown of the targeting (noggin) mRNA are demonstrated. Broader future applications include those to nerve regeneration, cardiovascular tissue engineering, directing (stem) cell behavior, and mitigating inflammatory responses to materials.

Altered cytoskeletal organization characterized lethal but not surviving Brtl+/- mice: insight on phenotypic variability in osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable bone disease with dominant and recessive transmission. It is characterized by a wide spectrum of clinical outcomes ranging from very mild to lethal in the perinatal period. The intra- and inter-familiar OI phenotypic variability in the presence of an identical molecular defect is still puzzling to the research field. We used the OI murine model Brtl(+/-) to investigate the molecular basis of OI phenotypic variability. Brtl(+/-) resembles classical dominant OI and shows either a moderately severe or a lethal outcome associated with the same Gly349Cys substitution in the α1 chain of type I collagen. A systems biology approach was used. We took advantage of proteomic pathway analysis to functionally link proteins differentially expressed in bone and skin of Brtl(+/-) mice with different outcomes to define possible phenotype modulators. The skin/bone and bone/skin hybrid networks highlighted three focal proteins: vimentin, stathmin and cofilin-1, belonging to or involved in cytoskeletal organization. Abnormal cytoskeleton was indeed demonstrated by immunohistochemistry to occur only in tissues from Brtl(+/-) lethal mice. The aberrant cytoskeleton affected osteoblast proliferation, collagen deposition, integrin and TGF-β signaling with impairment of bone structural properties. Finally, aberrant cytoskeletal assembly was detected in fibroblasts obtained from lethal, but not from non-lethal, OI patients carrying an identical glycine substitution. Our data demonstrated that compromised cytoskeletal assembly impaired both cell signaling and cellular trafficking in mutant lethal mice, altering bone properties. These results point to the cytoskeleton as a phenotypic modulator and potential novel target for OI treatment.

Dysregulation of Mitochondrial Functions and Osteogenic Differentiation in Cisd2-Deficient Murine Induced Pluripotent Stem Cells

Wolfram syndrome 2 (WFS2) is a premature aging syndrome caused by an irreversible mitochondria-mediated disorder. Cisd2, which regulates mitochondrial electron transport, has been recently identified as the causative gene of WFS2. The mouse Cisd2 knockout (KO) (Cisd2(-/-)) recapitulates most of the clinical manifestations of WFS2, including growth retardation, osteopenia, and lordokyphosis. However, the precise mechanisms underlying osteopenia in WFS2 and Cisd2 KO mice remain unknown. In this study, we collected embryonic fibroblasts from Cisd2-deficient embryos and reprogrammed them into induced pluripotent stem cells (iPSCs) via retroviral transduction with Oct4/Sox2/Klf4/c-Myc. Cisd2-deficient mouse iPSCs (miPSCs) exhibited structural abnormalities in their mitochondria and an impaired proliferative capability. The global gene expression profiles of Cisd2(+/+), Cisd2(+/-), and Cisd2(-/-) miPSCs revealed that Cisd2 functions as a regulator of both mitochondrial electron transport and Wnt/β-catenin signaling, which is critical for cell proliferation and osteogenic differentiation. Notably, Cisd2(-/-) miPSCs exhibited impaired Wnt/β-catenin signaling, with the downregulation of downstream genes, such as Tcf1, Fosl1, and Jun and the osteogenic regulator Runx2. Several differentiation markers for tridermal lineages were globally impaired in Cisd2(-/-) miPSCs. Alizarin red S staining and flow cytometry analysis further revealed that Cisd2(-/-) miPSCs failed to undergo osteogenic differentiation. Taken together, our results, as determined using an miPSC-based platform, have demonstrated that Cisd2 regulates mitochondrial function, proliferation, intracellular Ca(2+) homeostasis, and Wnt pathway signaling. Cisd2 deficiency impairs the activation of Wnt/β-catenin signaling and thereby contributes to the pathogeneses of osteopenia and lordokyphosis in WFS2 patients.

Cell based advanced therapeutic medicinal products for bone repair: Keep it simple?

The development of cell based advanced therapeutic medicinal products (ATMPs) for bone repair has been expected to revolutionize the health care system for the clinical treatment of bone defects. Despite this great promise, the clinical outcomes of the few cell based ATMPs that have been translated into clinical treatments have been far from impressive. In part, the clinical outcomes have been hampered because of the simplicity of the first wave of products. In response the field has set-out and amassed a plethora of complexities to alleviate the simplicity induced limitations. Many of these potential second wave products have remained "stuck" in the development pipeline. This is due to a number of reasons including the lack of a regulatory framework that has been evolving in the last years and the shortage of enabling technologies for industrial manufacturing to deal with these novel complexities. In this review, we reflect on the current ATMPs and give special attention to novel approaches that are able to provide complexity to ATMPs in a straightforward manner. Moreover, we discuss the potential tools able to produce or predict 'goldilocks' ATMPs, which are neither too simple nor too complex.

Osteoblast maturation on microtextured titanium involves paracrine regulation of bone morphogenetic protein signaling

Osteoblasts are sensitive to surface microtopography and chemistry. Osteoblast differentiation and maturation are higher in vitro and bone formation and osseointegration enhanced in vivo on microstructured titanium (Ti) compared to smooth surfaces. Cells increased BMP2 expression on microtextured Ti alloy, suggesting a paracrine role in regulating osteoblast maturation. However, recent studies show that exogenous BMP2 inhibits osteoblast production of anti-inflammatory cytokines and osteocalcin, indicating that control of BMP-signaling may be involved. This study examined whether cells modulate BMP ligands, receptors, and inhibitors during osteoblast maturation on Ti, specifically focusing on the roles of BMP2 and Noggin (NOG). mRNA and protein for BMP2, BMP4, and BMP7 and receptors BMPR1A, BMPR1B, and BMPR2, and BMP inhibitors were upregulated on microtextured surfaces in comparison to smooth surfaces. Maturation on microstructured Ti was slightly enhanced with exogenous BMP2 while NOG addition inhibited osteoblast maturation. Cells with NOG knocked down significantly increased osteoblast maturation. These results demonstrate that BMP-related molecules are controlled during osteoblast maturation on microstructured Ti surfaces and that endogenous NOG is an important regulator of the process. Modifying paracrine BMP signaling may yield more robust bone formation than application of exogenous BMPs.

Superposition of nanostructures on microrough titanium-aluminum-vanadium alloy surfaces results in an altered integrin expression profile in osteoblasts

Recent studies of new surface modifications that superimpose well-defined nanostructures on microrough implants, thereby mimicking the hierarchical complexity of native bone, report synergistically enhanced osteoblast maturation and local factor production at the protein level compared to growth on surfaces that are smooth, nanorough, or microrough. Whether the complex micro/nanorough surfaces enhance the osteogenic response by triggering similar patterns of integrin receptors and their associated signaling pathways as with well-established microrough surfaces, is not well understood. Human osteoblasts (hOBs) were cultured until confluent for gene expression studies on tissue culture polystyrene (TCPS) or on titanium alloy (Ti6Al4V) disks with different surface topographies: smooth, nanorough, microrough, and micro/nanorough surfaces. mRNA expression of osteogenesis-related markers such as osteocalcin (BGLAP) and bone sialoprotein (BSP), bone morphogenetic protein 2 (BMP2), BMP4, noggin (NOG) and gremlin 1 (GREM1) were all higher on microrough and micro/nanorough surfaces, with few differences between them, compared to smooth and nanorough groups. Interestingly, expression of integrins α1 and α2, which interact primarily with collagens and laminin and have been commonly associated with osteoblast differentiation on microrough Ti and Ti6Al4V, were expressed at lower levels on micro/nanorough surfaces compared to microrough ones. Conversely, the αv subunit, which binds ligands such as vitronectin, osteopontin, and bone sialoprotein among others, had higher expression on micro/nanorough surfaces concomitantly with regulation of the β3 mRNA levels on nanomodified surfaces. These results suggest that the maturation of osteoblasts on micro/nanorough surfaces may be occurring through different integrin engagement than those established for microrough-only surfaces.

The effect of noggin interference in a rabbit posterolateral spinal fusion model

STUDY DESIGN

Noggin protein levels and spinal fusion rates were compared in a rabbit model after application of siRNA against BMP antagonist noggin in paraspinal muscle.

OBJECTIVE

To test whether endogenous BMPs are sufficient to form bone in the absence of their antagonists, using noggin siRNA to interrupt the negative feedback loop on endogenous BMP within the paraspinal muscles in rabbits. Unused Posterolateral lumbar fusion is a standard surgical treatment for many spinal disorders, yet even under ideal conditions the rate of non-fusion approaches 25 %. BMPs are effective in promoting bone formation, and are inhibited by antagonists such as noggin. We have previously shown that in this model, endogenous BMPs are present and endogenous BMP antagonist noggin is strongly increased during spinal fusion. Previous studies have found that noggin siRNA enhanced spinal fusion in combination with supra-physiological amounts of exogenous BMP; however, the effect of the siRNA alone remains unknown.

METHODS

A posterolateral intertransverse rabbit lumbar fusion was utilized, as established by Boden et al. SiRNA against noggin was electroporated into paraspinal muscle to determine its effect on fusion. Outcome measures included noggin protein expression, and assessment of spinal fusion at 6 weeks.

RESULTS

SiRNAs were effective in reducing overexpressed noggin in vitro. Noggin protein was successfully knocked down in vivo for the initial 7 days in our rabbit model and returned to detectable levels by 4 weeks and to normal levels by 6 weeks. The overall fusion rate was not significantly enhanced compared to established controls from our earlier work (Tang et al.).

CONCLUSIONS

Early noggin suppression does not appear to enhance the BMP activity sufficiently to significantly affect final fusion rates in our model.

Role of miR-17 family in the negative feedback loop of bone morphogenetic protein signaling in neuron

Bone morphogenetic protein (BMP) signaling is active in many tissues including the central nervous system, in which it regulates cell proliferation, differentiation and maturation. The modulation of BMP pathway is crucial since abnormality of BMP signaling may cause cellular malfunction such as apoptosis. There are evidences indicating that miR-17 family is involved in the BMP signaling. In the present study, we demonstrated that BMP2 stimulation directly increased the transcription of miR-17-92 and miR-106b-25 cluster via Smad activation, which leads to the up-regulation of mature miR-17/20a/93. In addition, we provided evidence that BMP2 activation repressed BMPRII expression through modulating miR-17 family in primary neurons. Furthermore, we proved that such negative regulation protected neurons from apoptosis induced by abnormal BMP signaling. Taken together, these results suggest a regulatory pathway of BMP-miR-17 family-BMPRII, which consist a negative feedback loop that balances BMP signaling and maintains cell homeostasis in neurons.

LPS-stimulated inflammatory environment inhibits BMP-2-induced osteoblastic differentiation through crosstalk between TLR4/MyD88/NF-κB and BMP/Smad signaling

Bone morphogenetic protein-2 (BMP-2) is a novel differentiation factor that is capable of inducing osteoblast differentiation and bone formation, making it an attractive option in treatment of bone defects, fractures, and spine fusions. Inflammation, which was a common situation during bone healing, is recognized to inhibit osteogenic differentiation and bone formation. However, the effect of inflammation on BMP-2-induced osteoblastic differentiation remains ambiguous. In this study, we showed that an inflammatory environment triggered by lipopolysaccharide (LPS) in vitro would suppress BMP-2-induced osteogenic differentiation of bone marrow mesenchymal stem cells, which represented by decreased alkaline phosphatase (ALPase) activity and down-regulated osteogenic genes. In addition, LPS activated nuclear factor-κB (NF-κB) via a TLR4/MyD88-dependent manner and inhibited BMP-2-induced phosphorylation and nuclear translocation of Smad1/5/8. The blocking of NF-κB signaling by pretreatment with specific inhibitors such as BAY-11-7082, TPCK and PDTC, or by transfection with plasmids encoding p65 siRNA or IκBα siRNA could significantly reverse the inhibitory effect of LPS on BMP-2-induced BMP/Smad signaling and osteogenic differentiation. By contrast, even without stimulation of LPS, overexpression of p65 gene showed obvious inhibitory effects on BMP-2-induced BMP/Smad signaling and ALPase activity. These data indicate that the LPS-mediated inflammatory environment inhibits BMP-2-induced osteogenic differentiation, and that the crosstalk between TLR4/MyD88/NF-κB and BMP/Smad signaling negatively modulates the osteoinductive capacity of BMP-2.

Gene silencing of chordin improves BMP-2 effects on osteogenic differentiation of human adipose tissue-derived stromal cells

Although bone morphogenic protein (BMP)-2 is known to potently induce osteogenic differentiation of human mesenchymal stem cells, strong individual differences have been reported. In part, this is due to internal antagonists of BMP-2 for example, noggin and chordin, secreted by differentiating cells. This enabling study was performed to prove the hypothesis that osteogenic effects of BMP-2 can be improved by transient nonviral gene silencing of chordin. We investigated the effect of siRNA against chordin on osteogenic differentiation in human adipose tissue-derived stromal cells (hASC). Cells of two different donors were isolated after liposuction and proliferated for passage 4 or 5. On seeding, hASCs were transfected with siRNA using a commercial liposomal transfection reagent. Subsequently, cells were differentiated in the presence or absence of BMP-2 (100 ng/mL). Noncoding siRNA as well as siRNA against noggin served as a control. Osteogenic differentiation of hASC was determined by alkaline phosphase (ALP) activity and matrix mineralization. ALP activity of hASC treated with siRNA against chordin was increased for cells of both donors. In contrast, silencing of noggin had no effect in any of the donors. In combination with BMP-2, silencing of either chordin or noggin showed strongly improved ALP activity compared with the control group that was also supplemented with BMP-2. Mineralization was observed to start earlier in groups that received siRNA against chordin or noggin and showed increased amounts of incorporated calcium on day 15 compared with the control groups. Silencing chordin in hASCs was successful to increase BMP-2 effects on osteogenic differentiation in both donors, while effects of noggin silencing were reliably observed only in one of the two investigated donors. In contrast to noggin silencing, chordin silencing also increased osteogenic differentiation without supplemented BMP-2.

High-dose rhBMP-2 for adults: major and minor complications: a study of 502 spine cases

BACKGROUND

Use of recombinant human bone morphogenetic protein-2 (rhBMP-2) has increased considerably since its introduction in 2002. The complications associated with high-dose rhBMP-2 (≥ 40 mg) are unknown. The purpose of our study was to determine outcomes and medical and surgical complications associated with high-dose rhBMP-2 at short-term and long-term follow-up evaluations.

METHODS

Five hundred and two consecutive adult patients who had received high-dose rhBMP-2 as a part of spinal surgery from 2002 to 2009 at one institution were enrolled. Data were entered prospectively and studied and analyzed retrospectively. Surgical procedures in the thoracic and lumbar spine were included. Major and minor complications were documented intraoperatively, perioperatively, and at the latest follow-up examination. Complications potentially associated with rhBMP-2 use were evaluated for correlation with rhBMP-2 dose. Scoliosis Research Society (SRS) and Oswestry Disability Index (ODI) outcome measures were obtained before and after surgery.

RESULTS

On average, 115 mg (range, 40 to 351 mg) of rhBMP-2 was used. The average age of the patients (410 women and ninety-two men) at the time of the index procedure was 52.4 years (range, eighteen to eighty years). There were 265 primary and 237 revision procedures, and 261 patients had interbody fusion. An average of 11.5 vertebrae were instrumented. The average duration of follow-up was forty-two months (range, fourteen to ninety-two months). The diagnoses included idiopathic scoliosis (41%), degenerative scoliosis (31%), fixed sagittal imbalance (18%), and other diagnoses (10%). The rate of intraoperative complications was 8.2%. The rate of perioperative major surgical complications was 11.6%. The rate of perioperative major medical complications was 11.6%. Minor medical complications occurred in 18.9% of the cases, and minor surgical complications occurred in 2.6%. Logistic regression analysis and Pearson correlation did not identify a significant correlation between rhBMP-2 dosage and radiculopathy (r = -0.006), seroma (r = -0.003), or cancer (r = -0.05). Significant improvements in the ODI score (from a mean of 41 points to a mean of 26 points; p < 0.001) and the SRS total score (from a mean of 3.0 points to a mean of 3.7 points; p < 0.001) were noted at the latest follow-up evaluation.

CONCLUSIONS

This is the largest study of which we are aware that examines complications associated with high-dose rhBMP-2. Major surgical complications occurred in 11.6% of patients, and 11.6% experienced major medical complications. There was a cancer prevalence of 3.4%, but no correlation between increasing rhBMP-2 dosage and cancer, radiculopathy (seen in 1% of the patients), or seroma (seen in 0.6%) was found.

Microstructured titanium regulates interleukin production by osteoblasts, an effect modulated by exogenous BMP-2

Microtextured implant surfaces increase osteoblast differentiation in vitro and enhance bone-to-implant contact in vivo and clinically. These implants may be used in combination with recombinant human bone morphogenetic protein 2 (rhBMP-2) to enhance peri-implant bone formation. However, the effect of surface modifications alone or in combination with rhBMP-2 on the osteoblast-produced inflammatory microenvironment is unknown. MG63 cells were cultured on tissue culture polystyrene or titanium substrates: smooth pretreated (PT, Ra=0.2μm), sandblasted/acid-etched (SLA, Ra=3.2μm) or hydrophilic-SLA (modSLA). Expression and protein production of pro-inflammatory interleukins (IL1b, IL6, IL8, IL17) and anti-inflammatory interleukins (IL10) were measured in cells with or without rhBMP-2. To determine which BMP signaling pathways were involved, cultures were incubated with BMP pathway inhibitors to blockSmad (dorsomorphin), TAB/TAK1 ((5Z)-7-oxozeaenol) or PKA (H-8) signaling. Culture on rough SLA and modSLA surfaces decreased pro-inflammatory interleukins and increased anti-inflammatory IL10. This effect was negated in cells treated with rhBMP-2, which caused an increase in pro-inflammatory interleukins and a decrease in anti-inflammatory interleukins through TAB/TAK signaling. The results suggest that surface microtexture modulates the inflammatory process during osseointegration, an effect that may enhance healing. However, rhBMP-2 in combination with microtextured titanium implants can influence the effect of cells on these surfaces, and may adversely affect cells involved in osseointegration.