Transforming growth factor-beta isoforms and the induction of bone formation: implications for reconstructive craniofacial surgery

Advanced platelet rich fibrin demonstrates improved osteogenic induction potential in human periodontal ligament cells, growth factor production and mechanical properties as compared to leukocyte and platelet fibrin and injectable platelet rich fibrin

OBJECTIVES

This cross-sectional invitro research aimed to compare and contrast the macroscopic and microscopic, mechanical and biochemical features of leukocyte-rich platelet-rich fibrin, advanced platelet-rich fibrin, and injectable platelet-rich fibrin.

MATERIALS AND METHODS

In all, 150 samples were taken from males aged 18 to 25 with good systemic health (n = 50 each for i-PRF, A-PRF, and L-PRF). The samples were assessed for clot length, clot width, membrane length and width. Microscopic parameters assessed were the distribution of cells and fibrin structure. Mechanical tests were performed for tensile strength using a universal testing machine and growth factor analysis was performed for platelet derived growth factor (PDGF), vascular endothelial growth factor (VEGF), and transforming growth factor (TGF)- β on Days 1, 3 and 7 using commercially available ELISA kits. The osteogenic potential was analyzed in a culture of human periodontal ligament cells for 21 days using cell viability assay, alkaline phosphatase formation and alizarin red staining for mineralization.

RESULTS

L-PRF demonstrates statistically superior clot length, width, weight, membrane length, width and weight in comparison to A-PRF (p < 0.05). L-PRF demonstrates a denser fibrin structure in comparison to A-PRF and i-PRF (p < 0.05). The cells in L-PRF are most commonly situated in the proximal of the clot where as they are distributed in the proximal and middle aspect for A-PRF(p < 0.05). A-PRF demonstrates the highest tensile strength followed by L-PRF (p < 0.05). When growth factor release was evaluated, A-PRF showed noticeably increased release of all growth factors, namely PDGF-BB, TGF-ß, and VEGF, in comparison to i-PRF and L-PRF (p < 0.05). On days 7 and 14, the cell viability of human periodontal ligament cells in co-culture with A-PRF was statistically substantially greater than that of L-PRF and i-PRF (p < 0.05). Alkaline phosphatase levels were statistically substantially higher in A-PRF, followed by i-PRF and L-PRF on days 14 and 21 (p < 0.05). After 21 days of culture, A-PRF treated cultures had much more Alizarin Red staining than L-PRF and i-PRF cultures did (p < 0.05).

CONCLUSION

It was determined that although L-PRF exhibits greater size and weight in comparison to A-PRF and i-PRF, A-PRF has superior mechanical properties, increased growth factor releases of TGF-b, PDGF-BB, and VEGF as well as superior cell viability, alkaline phosphatase production, and mineralization on human periodontal ligament cells.

CLINICAL RELEVANCE

Based on these findings, A-PRF can be recommended for improved delivery of growth factors and osteogenesis whereas L-PRF is better-suited for applications relying on the size of membrane.

The topography and proliferative activity of cells immunoreactive to various growth factors in rat femoral bone tissues after experimental fracture and implantation of titanium implants with bioactive biodegradable coatings

BACKGROUND

Biodegradable implant coatings promote proliferation and expression of BMP-2, VEGF, and TGF-β2 genes and enhance BMP-2, VEGF, and TGF-β2 regulatory effects at different stages of reparative osteogenesis.

OBJECTIVE

To study the topography and ratio of PCNA-, VEGF-, BMP-2-, and TGF-β2-immunoreactive cells in rat femoral bone after closed fracture and implantation of titanium implants with biodegradable calcium phosphate and hydroxyapatite coatings.

METHODS

Standard titanium implant screws and similar implants with bioactive coatings were used. A total of 18 rats were randomly divided into three groups, two experimental and a control one. The rats in the first experimental group were implanted with implants without specific coating, while those in the second group, with implants with specific coatings. The control rats were subjected to the same fracture as the experimental ones without subsequent implantation. On days 7, 14, and 30 of experiment, the rats were sampled for histological examination. Histological sections were prepared and processed for PCNA, BMP-2, VEGF, and TGF-β2 immunoreactivity.

RESULTS

In the regeneration zone, PCNA-immunoreactive cells substantially outnumbered other immunoreactive cell types. During the first two weeks after fracture, in the immediate vicinity of implant surface, the rate of VEGF production increased in osteoblast subpopulations and level of TGF-32 immunoreactivity decreased in chondroblasts. The level of TGF-32 was maximum on day 30 of experiment. BMP-2-immunoreactive osteocytes were found in the zone of external general plates. They accumulated at implants with calcium phosphate coating. Their number gradually increased by day 30 of experiment.

CONCLUSIONS

The present data suggest that biodegradable implant coatings promote proliferation and expression of BMP-2, VEGF, and TGF-β2 genes and enhance BMP-2, VEGF, and TGF-β2 regulatory effects at different stages of reparative osteogenesis.

Controlled JAGGED1 delivery induces human embryonic palate mesenchymal cells to form osteoblasts

Osteoblast commitment and differentiation are controlled by multiple growth factors including members of the Notch signaling pathway. JAGGED1 is a cell surface ligand of the Notch pathway that is necessary for murine bone formation. The delivery of JAGGED1 to induce bone formation is complicated by its need to be presented in a bound form to allow for proper Notch receptor signaling. In this study, we investigate whether the sustained release of JAGGED1 stimulates human mesenchymal cells to commit to osteoblast cell fate using polyethylene glycol malemeide (PEG-MAL) hydrogel delivery system. Our data demonstrated that PEG-MAL hydrogel constructs are stable in culture for at least three weeks and maintain human mesenchymal cell viability with little cytotoxicity in vitro. JAGGED1 loaded on PEG-MAL hydrogel (JAGGED1-PEG-MAL) showed continuous release from the gel for up to three weeks, with induction of Notch signaling using a CHO cell line with a Notch1 reporter construct, and qPCR gene expression analysis in vitro. Importantly, JAGGED1-PEG-MAL hydrogel induced mesenchymal cells towards osteogenic differentiation based on increased Alkaline phosphatase activity and osteoblast genes expression including RUNX2, ALP, COL1, and BSP. These results thus indicated that JAGGED1 delivery in vitro using PEG-MAL hydrogel induced osteoblast commitment, suggesting that this may be a viable in vivo approach to bone regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 552-560, 2018.

Role of Vascular Endothelial Growth Factor and Transforming Growth Factor-β2 in Rat Bone Tissue after Bone Fracture and Placement of Titanium Implants with Bioactive Bioresorbable Coatings

The study established enhanced expression of vascular endothelial growth factor (VEGF) in the subpopulation of osteoblasts located in the regeneration region of femoral bone fracture near the titanium implants with bioactive calcium phosphate and hydroxyapatite coatings and suppressed activity of transforming growth factor-β2 (TGF-β2) in chondroblasts during the two weeks after surgery. In the delayed posttraumatic period, the distribution of TGF-β2 inversely related to its maximal activity. The data revealed the up-regulating effect of bioresorbable coatings on expression of VEGF and TGF-β2 and their implication in the control over various stages of reparative osteogenesis.

Small Molecule Inhibition of Transforming Growth Factor Beta Signaling Enables the Endogenous Regenerative Potential of the Mammalian Calvarium

Current approaches for the treatment of skeletal defects are suboptimal, principally because the ability of bone to repair and regenerate is poor. Although the promise of effective cellular therapies for skeletal repair is encouraging, these approaches are limited by the risks of infection, cellular contamination, and tumorigenicity. Development of a pharmacological approach would therefore help avoid some of these potential risks. This study identifies transforming growth factor beta (TGFβ) signaling as a potential pathway for pharmacological modulation in vivo. We demonstrate that inhibition of TGFβ signaling by the small molecule SB431542 potentiates calvarial skeletal repair through activation of bone morphogenetic protein (BMP) signaling on osteoblasts and dura mater cells participating in healing of calvarial defects. Cells respond to inhibition of TGFβ signaling by producing higher levels of BMP2 that upregulates inhibitory Smad6 expression, thus providing a negative feedback loop to contain excessive BMP signaling. Importantly, study on human osteoblasts indicates that molecular mechanism(s) triggered by SB431542 are conserved. Collectively, these data provide insights into the use of small molecules to modulate key signaling pathways for repairing skeletal defects.

Redefining the induction of periodontal tissue regeneration in primates by the osteogenic proteins of the transforming growth factor-β supergene family

The molecular bases of periodontal tissue induction and regeneration are the osteogenic proteins of the transforming growth factor-β (TGF-β) supergene family. These morphogens act as soluble mediators for the induction of tissues morphogenesis sculpting the multicellular mineralized structures of the periodontal tissues with functionally oriented ligament fibers into newly formed cementum. Human TGF-β₃ (hTGF-β₃ ) in growth factor-reduced Matrigel^® matrix induces cementogenesis when implanted in class II mandibular furcation defects surgically prepared in the non-human primate Chacma baboon, Papio ursinus. The newly formed periodontal ligament space is characterized by running fibers tightly attached to the cementoid surface penetrating as mineralized constructs within the newly formed cementum assembling and initiating within the mineralized dentine. Angiogenesis heralds the newly formed periodontal ligament space, and newly sprouting capillaries are lined by cellular elements with condensed chromatin interpreted as angioblasts responsible for the rapid and sustained induction of angiogenesis. The inductive activity of hTGF-β₃ in Matrigel^® matrix is enhanced by the addition of autogenous morcellated fragments of the rectus abdominis muscle potentially providing myoblastic, pericytic/perivascular stem cells for continuous tissue induction and morphogenesis. The striated rectus abdominis muscle is endowed with stem cell niches in para/perivascular location, which can be dominant, thus imposing stem cell features or stemness to the surrounding cells. This capacity to impose stemness is morphologically shown by greater alveolar bone induction and cementogenesis when hTGF-β₃ in Matrigel^® matrix is combined with morcellated fragments of autogenous rectus abdominis muscle. The induction of periodontal tissue morphogenesis develops as a mosaic structure in which the osteogenic proteins of the TGF-β supergene family singly, synergistically and synchronously initiate and maintain tissue induction and morphogenesis. In primates, the presence of several homologous yet molecularly different isoforms with osteogenic activity highlights the biological significance of this apparent redundancy and indicates multiple interactions during embryonic development and bone regeneration in postnatal life. Molecular redundancy with associated different biological functionalities in primate tissues may simply represent the fine-tuning of speciation-related molecular evolution in anthropoid apes at the early Pliocene boundary, which resulted in finer tuning of the bone induction cascade.

Tissue segregation restores the induction of bone formation by the mammalian transforming growth factor-β(3) in calvarial defects of the non-human primate Papio ursinus

A diffusion molecular hypothesis from the dura and/or the leptomeninges below that would control the induction of calvarial membranous bone formation by the recombinant human transforming growth factor-β3 (hTGF-β3) was investigated. Coral-derived calcium carbonate-based macroporous constructs (25 mm diameter; 3.5/4 mm thickness) with limited hydrothermal conversion to hydroxyapatite (7% HA/CC) were inserted into forty calvarial defects created in 10 adult Chacma baboons Papio ursinus. In 20 defects, an impermeable nylon foil membrane (SupraFOIL(®)) was inserted between the cut endocranial bone and the underlying dura mater. Twenty of the macroporous constructs were preloaded with hTGF-β3 (125 μg in 1000 μl 20 mM sodium succinate, 4% mannitol pH4.0), 10 of which were implanted into defects segregated by the SupraFOIL(®) membrane, and 10 into non-segregated defects. Tissues were harvested on day 90, processed for decalcified and undecalcified histology and quantitative real-time polymerase chain reaction (qRT-PCR). Segregated untreated macroporous specimens showed a reduction of bone formation across the macroporous spaces compared to non-segregated constructs. qRT-PCR of segregated untreated specimens showed down regulation of osteogenic protein-1 (OP-1), osteocalcin (OC), bone morphogenetic protein-2 (BMP-2), RUNX-2 and inhibitor of DNA binding-2 and -3 (ID2,ID3) and up regulation of TGF-β3, a molecular signalling pathway inhibiting the induction of membranous bone formation. Non-segregated hTGF-β3/treated constructs also showed non-osteogenic expression profiles when compared to non-segregated untreated specimens. Segregated hTGF-β3/treated 7% HA/CC constructs showed significantly greater induction of bone formation across the macroporous spaces and, compared to non-segregated hTGF-β3/treated constructs, showed up regulation of OP-1, OC, BMP-2, RUNX-2, ID2 and ID3. Similar up-regulated expression profiles were seen for untreated non-segregated constructs. TGF-β signalling via ID genes creates permissive or refractory micro-environments that regulate the induction of calvarial bone formation which is controlled by the exogenous hTGF-β3 upon segregation of the calvarial defects. The dura is the common regulator of the induction of calvarial bone formation modulated by the presence or absence of the SupraFOIL(®) membrane with or without hTGF-β3.

Regulation of integrin and growth factor signaling in biomaterials for osteodifferentiation

Stem cells respond to the microenvironment (niche) they are located in. Under natural conditions, the extracellular matrix (ECM) is the essential component the in stem cell niche, in which both integrin ligands and growth factors are important regulators to directly or indirectly modulate the cell behavior. In this review, we summarize the current knowledge about the potential of integrin ligands and growth factors to induce osteogenic differentiation of stem cells, and discuss the signaling pathways that are initiated by both individual and cooperative parameters. The joint effect of integrin ligands and growth factors is highlighted as the multivalent interactions for bone therapy.

Effect of VEGF-A165 addition on the integration of a cortical allograft in a tibial segmental defect in rabbits

PURPOSE

Long-bone segmental defects caused by infection, fracture, or tumour are a challenge for orthopaedic surgeons. Structural allografts are sometimes used in their treatment but their poor biological characteristics are a liability. The objective of this study was to determine whether the addition of recombinant vascular endothelial growth factor-A (VEGF) to a structural allograft improved its integration into a rabbit tibial segmental defect in a non-union model.

METHODS

Tibial segmental defects were filled with heat sterilized allogenic tubular tibiae sections and then stabilized with a screw plate. In the VEGF treatment group (n = 6 tibiae), 2 μg of VEGF added to a 50 μl matrigel solution was inserted into the allograft cavity. In the control group (n = 6 tibiae), only matrigel was added. After 12 weeks, macroscopic and microscopic analysis, radiographs, and computerized micro-tomography (micro-CT) were performed. If allograft consolidation was present, a torsional resistance analysis was performed.

RESULTS

Addition of VEGF to the allograft decreased the rate of osteosynthesis failure compared with the control group (1/6 vs. 5/6, p = 0.08), increased trabecular continuity evaluated by micro-CT in the bone-allograft interphases (8/12 vs. 2/12, p = 0.036) and histological trabecular continuity (7/12 vs. 0/12, p = 0.0046). Full consolidation was observed in three tibiae of the VEGF group and one in the control group (differences not significant); however, torsional resistance showed no significant differences (n.s.).

CONCLUSION

Addition of VEGF to a structural allograph inserted into a rabbit tibial segmental defect increased allograft integration rate. Further research in this direction might help clinicians in dealing with large bone defects.

Transforming growth factor beta 1 augments calvarial defect healing and promotes suture regeneration

BACKGROUND

Repair of complex cranial defects is hindered by a paucity of appropriate donor tissue. Bone morphogenetic protein 2 (BMP2) and transforming growth factor beta 1 (TGFβ1) have been shown separately to induce bone formation through physiologically distinct mechanisms and potentially improve surgical outcome for cranial defect repair by obviating the need for donor tissue. We hypothesize that a combination of BMP2 and TGFβ1 would improve calvarial defect healing by augmenting physiologic osteogenic mechanisms.

METHODS/RESULTS

Coronal suturectomies (3×15 mm) were performed in 10-day-old New Zealand White rabbits. DermaMatrix™ (3×15mm) patterned with four treatments (vehicle, 350 ng BMP2, 200 ng TGFβ1, or 350 ng BMP2+200 ng TGFβ1) was placed in suturectomy sites and rabbits were euthanized at 6 weeks of age. Two-dimensional (2D) defect healing, bone volume, and bone density were quantified by computed tomography. Regenerated bone was qualitatively assessed histologically. One-way analysis of variance revealed significant group main effects for all bone quantity measures. Analysis revealed significant differences in 2D defect healing, bone volume, and bone density between the control group and all treatment groups, but no significant differences were detected among the three growth factor treatment groups. Qualitatively, TGFβ1 treatment produced bone with morphology most similar to native bone. TGFβ1-regenerated bone contained a suture-like tissue, growing from the lateral edge of the defect margin toward the midline. Unique to the BMP2 treatment group, regenerated bone contained lacunae with chondrocytes, demonstrating the presence of endochondral ossification.

CONCLUSIONS/SIGNIFICANCE

Total healing in BMP2 and TGFβ1 treatment groups is not significantly different. The combination of BMP2+TGFβ1 did not significantly increase bone healing compared with treatment with BMP2 or TGFβ1 alone postoperatively at 4 weeks. We highlight the potential use of TGFβ1 to regenerate calvarial bone and cranial sutures. TGFβ1 therapy significantly augmented bony defect healing at an earlier time point when compared with control, regenerated bone along the native intramembranous ossification pathway, and (unlike BMP2 alone or in combination with TGFβ1) permitted normal suture reformation. We propose a novel method of craniofacial bone regeneration using low-dose, spatially controlled growth factor therapies to minimize potentially harmful effects while maximizing local bioavailability and regenerating native tissues.

Multi-walled carbon nanotubes promote cementoblast differentiation and mineralization through the TGF-β/Smad signaling pathway

Excretion of cementum by cementoblasts on the root surface is a process indispensable for the formation of a functional periodontal ligament. This study investigated whether carboxyl group-functionalized multi-walled carbon nanotubes (MWCNT-COOH) could enhance differentiation and mineralization of mammalian cementoblasts (OCCM-30) and the possible signaling pathway involved in this process. Cementoblasts were incubated with various doses of MWCNT-COOH suspension. Cell viability was detected, and a scanning electron microscopy (SEM) observed both the nanomaterials and the growth of cells cultured with the materials. Alizarin red staining was used to investigate the formation of calcium deposits. Real-time PCR and western blot were used to detect cementoblast differentiation and the underlying mechanisms through the expression of the osteogenic genes and the downstream effectors of the TGF-β/Smad signaling. The results showed that 5 µg/mL MWCNT-COOH had the most obvious effects on promoting differentiation without significant toxicity. Alp, Ocn, Bsp, Opn, Col1 and Runx2 gene expression was up-regulated. Smad2 and Smad3 mRNA was up-regulated, while Smad7 was first down-regulated on Day 3 and later up-regulated on Day 7. The elevated levels of phospho-Smad2/3 were also confirmed by western blot. In sum, the MWCNT-COOH promoted cementoblast differentiation and mineralization, at least partially, through interactions with the TGF-β/Smad pathway.

Local drug delivery for enhancing fracture healing in osteoporotic bone

Fragility fractures can cause significant morbidity and mortality in patients with osteoporosis and inflict a considerable medical and socioeconomic burden. Moreover, treatment of an osteoporotic fracture is challenging due to the decreased strength of the surrounding bone and suboptimal healing capacity, predisposing both to fixation failure and non-union. Whereas a systemic osteoporosis treatment acts slowly, local release of osteogenic agents in osteoporotic fracture would act rapidly to increase bone strength and quality, as well as to reduce the bone healing period and prevent development of a problematic non-union. The identification of agents with potential to stimulate bone formation and improve implant fixation strength in osteoporotic bone has raised hope for the fast augmentation of osteoporotic fractures. Stimulation of bone formation by local delivery of growth factors is an approach already in clinical use for the treatment of non-unions, and could be utilized for osteoporotic fractures as well. Small molecules have also gained ground as stable and inexpensive compounds to enhance bone formation and tackle osteoporosis. The aim of this paper is to present the state of the art on local drug delivery in osteoporotic fractures. Advantages, disadvantages and underlying molecular mechanisms of different active species for local bone healing in osteoporotic bone are discussed. This review also identifies promising new candidate molecules and innovative approaches for the local drug delivery in osteoporotic bone.

Akt activation is required for TGF-β1-induced osteoblast differentiation of MC3T3-E1 pre-osteoblasts

Background

We have previously reported that repeated treatment of human periodontal ligament cells and murine pre-osteoblast MC3T3-E1 cells with transforming growth factor-beta 1 (TGF-β1) inhibited their osteoblastic differentiation because of decreased insulin-like growth factor-1 (IGF-1) secretion. We also found that IGF-1/PI3K signaling plays an important role in osteoblast differentiation induced by TGF-β1 treatment; however, the downstream signaling controlling this remains unknown. The aim of this current study is to investigate whether Akt activation is required for osteoblast differentiation.

Methodology/Principal Findings

MC3T3-E1 cells were cultured in osteoblast differentiation medium (OBM) with or without 0.1 ng/mL TGF-β1. OBM containing TGF-β1 was changed every 12 h to provide repeated TGF-β1 administration. MC3T3-E1 cells were infected with retroviral vectors expressing constitutively active (CA) or dominant-negative (DN)-Akt. Alkaline phosphatase (ALP) activity and osteoblastic marker mRNA levels were substantially decreased by repeated TGF-β1 treatment compared with a single TGF-β1 treatment. However, expression of CA-Akt restored ALP activity following TGF-β1 treatment. Surprisingly, ALP activity increased following multiple TGF-β1 treatments as the number of administrations of TGF-β1 increased. Activation of Akt significantly enhanced expression of osteocalcin, but TGF-β1 treatment inhibited this. Mineralization of MC3T3-E1 cells was markedly enhanced by CA-Akt expression under all medium conditions. Exogenous IGF-1 restored the down-regulation of osteoblast-related gene expression by repeated TGF-β1 administration. However, in cells expressing DN-Akt, these levels remained inhibited regardless of IGF-1 treatment. These findings indicate that Akt activation is required for the early phase of osteoblast differentiation of MC3T3-E1 cells induced by TGF-β1. However, Akt activation is insufficient to reverse the inhibitory effects of TGF-β1 in the late stages of osteoblast differentiation.

Conclusions

TGF-β1 could be an inducer or an inhibitor of osteoblastic differentiation of MC3T3-E1 cells depending on the state of Akt phosphorylation. Our results indicate that Akt is the molecular switch for TGF-β1-induced osteoblastic differentiation of MC3T3-E1 cells.

Cellular and morphological aspects of fibrodysplasia ossificans progressiva. Lessons of formation, repair, and bone bioengineering

Fibrodysplasia ossificans progressiva (FOP) is a rare congenital disease that causes bone formation within the muscles, tendons, ligaments and connective tissues. There is no cure for this disorder and only treatment of the symptoms is available. The purpose of this study was to review the literature and describe the clinical, cellular and molecular aspects of FOP. The material used for the study was obtained by reviewing scientific articles published in various literature-indexed databases. In view of its rarity and of the lack of insightful information and the unpredictability of its course, FOP is a challenging disorder for professionals who are confronted by it. However, this rare disease raises a great deal of interest because understanding the mechanism of mature bone formation can encourage research lines related to bone regeneration and the prevention of heterotopic ossification.

Platelet-rich plasma encapsulation in hyaluronic acid/gelatin-BCP hydrogel for growth factor delivery in BCP sponge scaffold for bone regeneration

Microporous calcium phosphate based synthetic bone substitutes are used for bone defect healing. Different growth factor loading has been investigated for enhanced bone regeneration. The platelet is a cellular component of blood which naturally contains a pool of necessary growth factors that mediate initiation, continuation, and completion of cellular mechanism of healing. In this work, we have investigated the encapsulation and immobilization of platelet-rich plasma (PRP) with natural polymers like hyaluronic acid (HA) and gelatin (Gel) and loading them in a biphasic calcium phosphate (BCP) scaffold, for a synthetic-allologous hybrid scaffold. Effect of PRP addition in small doses was evaluated for osteogenic potential in vitro and in vivo. BCP (10%) mixed HA–Gel hydrogel with or without PRP, was loaded into a BCP sponge scaffold. We investigated the hydrogel-induced improvement in mechanical property and PRP-mediated enhancement in biocompatibility. In vitro studies for cytotoxicity, cell attachment, and proliferation were carried out using MC3T3-E1 pre-osteoblast cells. In in vitro studies, the cell count, cell proliferation, and cell survival were higher in the scaffold with PRP loading than without PRP. However, in the in vivo studies using a rat model, the PRP scaffold was not superior to the scaffold without PRP. This discrepancy was investigated in terms of the interaction of PRP in the in vivo environment.

PDGF-induced PI3K-mediated signaling enhances the TGF-β-induced osteogenic differentiation of human mesenchymal stem cells in a TGF-β-activated MEK-dependent manner

Transforming growth factor-β (TGF-β) is a critical regulator of osteogenic differentiation and the platelet-derived growth factor (PDGF) is a chemoattractant or mitogen of osteogenic mesenchymal cells. However, the combined effects of these regulators on the osteogenic differentiation of mesenchymal cells remains unknown. In this study, we investigated the effects of TGF-β and/or PDGF on the osteogenic differentiation of human mesenchymal stem cells (hMSCs). The TGF-β-induced osteogenic differentiation of UE7T-13 cells, a bone marrow-derived hMSC line, was markedly enhanced by PDGF, although PDGF alone did not induce differentiation. TGF-β induced extracellular signal-regulated kinase (ERK) phosphorylation and PDGF induced Akt phosphorylation. In addition, the mitogen-activated protein kinase (MAPK)/ERK kinase (MEK) inhibitor, U0126, suppressed the osteogenic differentiation induced by TGF-β alone. Moreover, U0126 completely suppressed the osteogenic differentiation synergistically induced by TGF-β and PDGF, whereas the phosphoinositide-3-kinase (PI3K) inhibitor, LY294002, only partially suppressed this effect. These results suggest that the enhancement of TGF-β-induced osteogenic differentiation by PDGF-induced PI3K/Akt-mediated signaling depends on TGF-β-induced MEK activity. Thus, PDGF positively modulates the TGF-β-induced osteogenic differentiation of hMSCs through synergistic crosstalk between MEK- and PI3K/Akt-mediated signaling.

Proteomic analysis of gingival tissue and alveolar bone during alveolar bone healing

Bone tissue regeneration is orchestrated by the surrounding supporting tissues and involves the build-up of osteogenic cells, which orchestrate remodeling/healing through the expression of numerous mediators and signaling molecules. Periodontal regeneration models have proven useful for studying the interaction and communication between alveolar bone and supporting soft tissue. We applied a quantitative proteomic approach to analyze and compare proteins with altered expression in gingival soft tissue and alveolar bone following tooth extraction. For target identification and validation, hard and soft tissue were extracted from mini-pigs at the indicated times after tooth extraction. From triplicate experiments, 56 proteins in soft tissue and 27 proteins in alveolar bone were found to be differentially expressed before and after tooth extraction. The expression of 21 of those proteins was altered in both soft tissue and bone. Comparison of the activated networks in soft tissue and alveolar bone highlighted their distinct responsibilities in bone and tissue healing. Moreover, we found that there is crosstalk between identified proteins in soft tissue and alveolar bone with respect to cellular assembly, organization, and communication. Among these proteins, we examined in detail the expression patterns and associated networks of ATP5B and fibronectin 1. ATP5B is involved in nucleic acid metabolism, small molecule biochemistry, and neurological disease, and fibronectin 1 is involved in cellular assembly, organization, and maintenance. Collectively, our findings indicate that bone regeneration is accompanied by a profound interaction among networks regulating cellular resources, and they provide novel insight into the molecular mechanisms involved in the healing of periodontal tissue after tooth extraction.

Periodontal fibroblasts modulate proliferation and osteogenic differentiation of embryonic stem cells through production of fibroblast growth factors

BACKGROUND

Periodontal ligament fibroblasts (PLFs) maintain homeostasis of periodontal ligaments by producing paracrine factors that affect various functions of stem-like cells. It is hypothesized that PLFs induce proliferation and differentiation of stem cells more effectively than gingival fibroblasts (GFs) and skin fibroblasts (SFs).

METHODS

PLFs and GFs were isolated from extracted teeth and cultured in the presence and absence of osteogenesis-inducing factors. Mouse embryonic stem (mES) cells and SFs were purchased commercially. mES cells were incubated with culture supernatants of these fibroblasts or cocultured directly with the cells. Proliferation and mineralization in mES cells were determined at various times of incubation. Immunostaining and polymerase chain reaction were performed. The activity of mitogen-activated protein kinase and alkaline phosphatase (ALP) was also measured.

RESULTS

In cocultures, PLFs stimulated proliferation of mES cells more effectively than GFs or SFs. Similarly, the addition of culture supernatant of PLFs induced the most prominent proliferation of mES cells, and this was significantly inhibited by treatment with antibody against fibroblast growth factor (FGF)4 or the c-Jun N-terminal kinase inhibitor SP600125 (anthra[1,9-cd]pyrazol-6(2H)-one). Supplementation with culture supernatant from the fibroblasts induced osteogenic differentiation of mES cells in the order PLFs > GFs > SFs. These activities of PLFs were related to their potential to produce osteogenic markers, such as ALP and runt-related transcription factor-2 (Runx2), and to secrete FGF7. Pretreatment of mES cells with the extracellular signal-regulated kinase inhibitor PD98059 [2-(2-amino-3-methyoxyphenyl)-4H-1-benzopyran-4-one] or SP600125 clearly attenuated mineralization induced by culture supernatant of PLF with attendant decreases in mRNA levels of Runx2, bone sialoprotein, osteocalcin, and osteopontin.

CONCLUSION

PLFs regulate the proliferation and osteogenic differentiation of mES cells more strongly than GFs and SFs via the secretion of FGF through a mechanism that involves mitogen-activated protein kinase-mediated signaling.

The role of small molecules in musculoskeletal regeneration

The uses of bone morphogenetic proteins and parathyroid hormone therapeutics are fraught with several fundamental problems, such as cost, protein stability, immunogenicity, contamination and supraphysiological dosage. These downsides may effectively limit their more universal use. Therefore, there is a clear need for alternative forms of biofactors to obviate the drawbacks of protein-based inductive factors for bone repair and regeneration. Our group has studied small molecules with the capacity to regulate osteoblast differentiation and mineralization because their inherent physical properties minimize limitations observed in protein growth factors. For instance, in general, small molecule inducers are usually more stable, highly soluble, nonimmunogenic, more affordable and require lower dosages. Small molecules with the ability to induce osteoblastic differentiation may represent the next generation of bone regenerative medicine. This review describes efforts to develop small molecule-based biofactors for induction, paying specific attention to their novel roles in bone regeneration.

Growth factor delivery: how surface interactions modulate release in vitro and in vivo

Biomaterial scaffolds have been extensively used to deliver growth factors to induce new bone formation. The pharmacokinetics of growth factor delivery has been a critical regulator of their clinical success. This review will focus on the surface interactions that control the non-covalent incorporation of growth factors into scaffolds and the mechanisms that control growth factor release from clinically relevant biomaterials. We will focus on the delivery of recombinant human bone morphogenetic protein-2 from materials currently used in the clinical practice, but also suggest how general mechanisms that control growth factor incorporation and release delineated with this growth factor could extend to other systems. A better understanding of the changing mechanisms that control growth factor release during the different stages of preclinical development could instruct the development of future scaffolds for currently untreatable injuries and diseases.

Platelet rich plasma. A new treatment tool for the rheumatologist?

Platelet Rich Plasma (PRP) is a novel therapeutic tool that has revolutionized the world of sports medicine and trauma due to therapeutic success shown in the media. Subject to ongoing debate, the PRP is outlined along a spectrum of musculoskeletal therapies with many qualities that make it ideal for use in the rheumatology: effectiveness, safety, easy handling and low cost. Is PRP a product of marketing? Or, conversely, is an interesting tool to consider in the armamentarium of the rheumatologist. In the following review we will analyze in detail its principles, preparation, and management regimes. We will reflect on potential adverse effects and, finally, there will be a critical analysis of the scientific evidence that supports its potential use in the rheumatology clinic.

A Macroporous Bioreactor Super Activated by the Recombinant Human Transforming Growth Factor-β(3)

Macroporous single phase hydroxyapatite (HA) and biphasic HA/β-tricalcium phosphate with 33% post-sinter hydroxyapatite (HA/β-TCP) were combined with 25 or 125 μg recombinant human transforming growth factor-β3 (hTGF-β₃) to engineer a super activated bioreactor implanted in orthotopic calvarial and heterotopic rectus abdominis muscle sites and harvested on day 30 and 90. Coral-derived calcium carbonate fully converted (100%) and partially converted to 5 and 13% hydroxyapatite/calcium carbonate (5 and 13% HA/CC) pre-loaded with 125 and 250 μg hTGF-β₃, and 1:5 and 5:1 binary applications of hTGF-β₃: hOP-1 by weight, were implanted in the rectus abdominis and harvested on day 20 and 30, respectively, to monitor spatial/temporal morphogenesis by high doses of hTGF-β₃. Bone formation was assessed on decalcified paraffin-embedded sections by measuring the fractional volume of newly formed bone. On day 30 and 90, single phase HA implants showed greater amounts of bone when compared to biphasic specimens; 5 and 13% HA/CC pre-loaded with 125 and 250 μg hTGF-β₃ showed substantial induction of bone formation; 250 μg hTGF-β₃ induced as yet unreported massive induction of bone formation as early as 20 days prominently outside the profile of the macroporous constructs. The induction of bone formation is controlled by the implanted ratio of the recombinant morphogens, i.e., the 1:5 hTGF-β₃:hOP-1 ratio by weight was greater than the inverse ratio. The unprecedented tissue induction by single doses of 250 μg hTGF-β₃ resulting in rapid bone morphogenesis of vast mineralized ossicles with multiple trabeculations surfaced by contiguous secreting osteoblasts is the novel molecular and morphological frontier for the induction of bone formation in clinical contexts.

Inhibition of insulin-like growth factor-1 (IGF-1) expression by prolonged transforming growth factor-β1 (TGF-β1) administration suppresses osteoblast differentiation

TGF-β1 can regulate osteoblast differentiation not only positively but also negatively. However, the mechanisms of negative regulation are not well understood. We previously established the reproducible model for studying the suppression of osteoblast differentiation by repeated or high dose treatment with TGF-β1, although single low dose TGF-β1 strongly induced osteoblast differentiation. The mRNA expression and protein level of insulin-like growth factor-1 (IGF-1) were remarkably decreased by repeated TGF-β1 administration in human periodontal ligament cells, human mesenchymal stem cells, and murine preosteoblast MC3T3-E1 cells. Repeated TGF-β1 administration subsequently decreased alkaline phosphatase (ALP) activity and mRNA expression of osteoblast differentiation marker genes, such as RUNX2, ALP, and bone sialoprotein (BSP). Additionally, repeated administration significantly reduced the downstream signaling pathway of IGF-1, such as Akt phosphorylation in these cells. Surprisingly, exogenous and overexpressed IGF-1 recovered ALP activity and mRNA expression of osteoblast differentiation marker genes even with repeated TGF-β1 administration. These facts indicate that the key mechanism of inhibition of osteoblast differentiation induced by repeated TGF-β1 treatment is simply due to the down-regulation of IGF-1 expression. Inhibition of IGF-1 signaling using small interfering RNA (siRNA) against insulin receptor substrate-1 (IRS-1) suppressed mRNA expression of RUNX2, ALP, BSP, and IGF-1 even with single TGF-β1 administration. This study showed that persistence of TGF-β1 inhibited osteoblast differentiation via suppression of IGF-1 expression and subsequent down-regulation of the PI3K/Akt pathway. We think this fact could open the way to use IGF-1 as a treatment tool for bone regeneration in prolonged inflammatory disease.

Biomimetic matrices self-initiating the induction of bone formation

The new strategy of tissue engineering, and regenerative medicine at large, is to construct biomimetic matrices to mimic nature's hierarchical structural assemblages and mechanisms of simplicity and elegance that are conserved throughout genera and species. There is a direct spatial and temporal relationship of morphologic and molecular events that emphasize the biomimetism of the remodeling cycles of the osteonic corticocancellous bone versus the "geometric induction of bone formation," that is, the induction of bone by "smart" concavities assembled in biomimetic matrices of macroporous calcium phosphate-based constructs. The basic multicellular unit of the corticocancellous bone excavates a trench across the bone surface, leaving in its wake a hemiosteon rather than an osteon, that is, a trench with cross-sectional geometric cues of concavities after cyclic episodes of osteoclastogenesis, eventually leading to osteogenesis. The concavities per se are geometric regulators of growth-inducing angiogenesis and osteogenesis as in the remodeling processes of the corticocancellous bone. The concavities act as a powerful geometric attractant for myoblastic/myoendothelial and/or endothelial/pericytic stem cells, which differentiate into bone-forming cells. The lacunae, pits, and concavities cut by osteoclastogenesis within the biomimetic matrices are the driving morphogenetic cues that induce bone formation in a continuum of sequential phases of resorption/dissolution and formation. To induce the cascade of bone differentiation, the soluble osteogenic molecular signals of the transforming growth factor β supergene family must be reconstituted with an insoluble signal or substratum that triggers the bone differentiation cascade. By carving a series of repetitive concavities into solid and/or macroporous biomimetic matrices of highly crystalline hydroxyapatite or biphasic hydroxyapatite/β-tricalcium phosphate, we were able to embed smart biologic functions within intelligent scaffolds for tissue engineering of bone. The concavities assembled in the bioceramic constructs biomimetize the remodeling cycle of the corticocancellous bone and are endowed with multifunctional pleiotropic self-assembly capacities, initiating angiogenesis and bone formation by induction without the exogenous applications of the osteogenic-soluble molecular signals of the transforming growth factor β supergene family. The incorporation of specific biologic activities into biomimetic matrices by manipulating the geometry of the substratum, defined as geometric induction of bone formation, is now helping to engineer therapeutic osteogenesis in clinical contexts.

Effect of bone sialoprotein on proliferation and osteodifferentiation of human bone marrow-derived mesenchymal stem cells in vitro

We performed this study to investigate the effects of recombinant human bone sialoprotein (BSP) on the proliferation and osteodifferentiation of human BMSCs(hBMSCs). The hBMSC cultures were divided into 4 groups: control group, 10(-10) M BSP group (BSP group), osteogenic medium group (10 nM dexamethasone, 10 mM β-glycerophosphate, and 50 mg/L ascorbic acid, OM group) and BSP + OM group (OM plus10(-10) M BSP). Compared with the control group, cell growth of the other three groups slowed down, while fluorescence at the G(0)/G(1) phase increased. After 28 days, in the OM group and the BSP + OM group, the proportion of STRO-1-positive cells decreased by 22.7% and 38.4% and ALP activity increased by 50% and 71.43%, respectively. CD271 mRNA expression decreased while Cbfa1, osteocalcin and osterix mRNA levels increased in the OM and BSP + OM groups, and the mRNA level change was greater in the BSP + OM group. After 28 days, the number of nodules in the BSP + OM group was 112.5% more than that in the OM group, but nodules did not formed in the control or BSP group. We conclude that BSP is capable of inhibiting hBMSCs proliferation and enhancing their osteogenic differentiation and mineralization in the presence of OM.

The small molecule PKA-specific cyclic AMP analogue as an inducer of osteoblast-like cells differentiation and mineralization

Osteoblastic differentiation is an important landmark for bone formation, bone repair and regeneration; however, it is a very complex process controlled by different signalling mechanisms. Several groups have reported that the cyclic adenosine monophosphate (cAMP) signalling system is responsible for regulating osteoblast cell differentiation. Nonetheless, to date, the principle role of the cAMP molecules related to this process remains controversial. Moreover, the underlying cAMP-dependent signalling cascade governing the osteoblastic differentiation has not been clarified. In this study we investigated the roles of the cAMP-dependent protein kinase A (PKA) signalling in proliferation, differentiation and mineralization of osteoblast-like MC3T3-E1 cells, using the PKA-specific small molecule cAMP analogue, 6-Bnz-cAMP, at 100 µM. Alkaline phosphatase (ALP) activity, runt transcription factor 2 (Runx2), osteopontin (OPN) and osteocalcin (OCN) protein expressions were used as osteoblast-specific markers to demonstrate osteoblastic differentiation. Further, calcium measurement of the extracellular matrix was employed as the hallmark of matrix mineralization or calcification. We report here that activation of PKA by the small molecule 6-Bnz-cAMP induces osteoblastic differentiation and matrix mineralization of osteoblast-like MC3T3-E1 cells. Moreover, 6-Bnz-cAMP does not induce cytotoxicity to the cells, as revealed by our cell proliferation studies. Therefore, based on these findings, we propose that the PKA-specific small molecule 6-Bnz-cAMP may serve as a novel bone-inducing growth factor for repairing and regenerating bone tissues during bone-regenerative engineering.

Induction of bone formation by transforming growth factor-beta2 in the non-human primate Papio ursinus and its modulation by skeletal muscle responding stem cells

OBJECTIVES

Four adult non-human primates Papio ursinus were used to study induction of bone formation by recombinant human transforming growth factor-beta(2) (hTGF-beta(2)) together with muscle-derived stem cells.

MATERIALS AND METHODS

The hTGF-beta(2) was implanted in rectus abdominis muscles and in calvarial defects with and without addition of morcellized fragments of striated muscle, harvested from the rectus abdominis or temporalis muscles. Expression of osteogenic markers including osteogenic protein-1, bone morphogenetic protein-3 and type IV collagen mRNAs from generated specimens was examined by Northern blot analysis.

RESULTS

Heterotopic intramuscular implantation of 5 and 25 microg hTGF-beta(2) combined with 100 mg of insoluble collagenous bone matrix yielded large corticalized mineralized ossicles by day 30 with remodelling and induction of haematopoietic marrow by day 90. Addition of morcellized rectus abdominis muscle to calvarial implants enhanced induction of bone formation significantly by day 90.

CONCLUSIONS

In Papio ursinus, in marked contrast to rodents and lagomorphs, hTGF-beta(2) induced large corticalized and vascularized ossicles by day 30 after implantation into the rectus abdominis muscle. This striated muscle contains responding stem cells that enhance the bone induction cascade of hTGF-beta(2). Induction of bone formation by hTGF-beta(2) in the non-human primate Papio ursinus may occur as a result of expression of bone morphogenetic proteins on heterotopic implantation of hTGF-beta(2); the bone induction cascade initiated by mammalian TGF-beta proteins in Papio ursinus needs to be re-evaluated for novel molecular therapeutics for induction of bone formation in clinical contexts.

Rapid cell culture and pre-clinical screening of a transforming growth factor-beta (TGF-beta) inhibitor for orthopaedics

Background

Transforming growth factor-β (TGF-β) and bone morphogenetic proteins (BMPs) utilize parallel and related signaling pathways, however the interaction between these pathways in bone remains unclear. TGF-β inhibition has been previously reported to promote osteogenic differentiation in vitro, suggesting it may have a capacity to augment orthopaedic repair. We have explored this concept using an approach that represents a template for the testing of agents with prospective orthopaedic applications.

Methods

The effects of BMP-2, TGF-β1, and the TGF-β receptor (ALK-4/5/7) inhibitor SB431542 on osteogenic differentiation were tested in the MC3T3-E1 murine pre-osteoblast cell line. Outcome measures included alkaline phosphatase staining, matrix mineralization, osteogenic gene expression (Runx2, Alp, Ocn) and phosphorylation of SMAD transcription factors. Next we examined the effects of SB431542 in two orthopaedic animal models. The first was a marrow ablation model where reaming of the femur leads to new intramedullary bone formation. In a second model, 20 μg rhBMP-2 in a polymer carrier was surgically introduced to the hind limb musculature to produce ectopic bone nodules.

Results

BMP-2 and SB431542 increased the expression of osteogenic markers in vitro, while TGF-β1 decreased their expression. Both BMP-2 and SB431542 were found to stimulate pSMAD1 and we also observed a non-canonical repression of pSMAD2. In contrast, neither in vivo system was able to provide evidence of improved bone formation or repair with SB431542 treatment. In the marrow ablation model, systemic dosing with up to 10 mg/kg/day SB431542 did not significantly increase reaming-induced bone formation compared to vehicle only controls. In the ectopic bone model, local co-administration of 38 μg or 192 μg SB431542 did not increase bone formation.

Conclusions

ALK-4/5/7 inhibitors can promote osteogenic differentiation in vitro, but this may not readily translate to in vivo orthopaedic applications.

Soluble and insoluble signals sculpt osteogenesis in angiogenesis

The basic tissue engineering paradigm is tissue induction and morphogenesis by combinatorial molecular protocols whereby soluble molecular signals are combined with insoluble signals or substrata. The insoluble signal acts as a three-dimensional scaffold for the initiation of de novo tissue induction and morphogenesis. The osteogenic soluble molecular signals of the transforming growth factor-β (TGF-β) supergene family, the bone morphogenetic/osteogenic proteins (BMPs/OPs) and, uniquely in the non-human primate Papio ursinus (P. ursinus), the three mammalian TGF-β isoforms induce bone formation as a recapitulation of embryonic development. In this paper, I discuss the pleiotropic activity of the BMPs/OPs in the non-human primate P. ursinus, the induction of bone by transitional uroepithelium, and the apparent redundancy of molecular signals initiating bone formation by induction including the three mammalian TGF-β isoforms. Amongst all mammals tested so far, the three mammalian TGF-β isoforms induce endochondral bone formation in the non-human primate P. ursinus only. Bone tissue engineering starts by erecting scaffolds of biomimetic biomaterial matrices that mimic the supramolecular assembly of the extracellular matrix of bone. The molecular scaffolding lies at the hearth of all tissue engineering strategies including the induction of bone formation. The novel concept of tissue engineering is the generation of newly formed bone by the implantation of "smart" intelligent biomimetic matrices that per se initiate the ripple-like cascade of bone differentiation by induction without exogenously applied BMPs/OPs of the TGF-β supergene family. A comprehensive digital iconographic material presents the modified tissue engineering paradigm whereby the induction of bone formation is initiated by intelligent smart biomimetic matrices that per se initiate the induction of bone formation without the exogenous application of the soluble osteogenic molecular signals. The driving force of the intrinsic induction of bone formation by bioactive biomimetic matrices is the shape of the implanted substratum. The language of shape is the language of geometry; the language of geometry is the language of a sequence of repetitive concavities, which biomimetizes the remodelling cycle of the primate osteonic bone.

Synergistic induction of bone formation by hOP-1, hTGF-beta3 and inhibition by zoledronate in macroporous coral-derived hydroxyapatites

Thirty coral-derived calcium carbonate-based macroporous constructs with limited hydrothermal conversion to hydroxyapatite (7% HA/CC) were implanted in the rectus abdominis of three adult non-human primate Papio ursinus to investigate the intrinsic induction of bone formation. Macroporous constructs with 125 microg human recombinant osteogenic protein-1 (hOP-1) or 125 microg human recombinant transforming growth factor-beta(3) (hTGF-beta(3)) were also implanted. The potential synergistic interaction between morphogens was tested by implanting binary applications of hOP-1 and hTGF-beta(3) 5:1 by weight, respectively. To evaluate the role of osteoclastic activity on the implanted macroporous surfaces, coral-derived constructs were pre-loaded with 0.24 mg of bisphosphonate zoledronate (Zometa). To correlate the morphology of tissue induction with osteogenic gene expression and activation, harvested specimens on day 90 were analyzed for changes in OP-1 and TGF-beta(3) mRNA synthesis by quantitative real-time polymerase chain reaction (qRT-PCR). The induction of bone formation in 7% HA/CC solo correlated with OP-1 expression. Massive bone induction formed by binary applications of the recombinant morphogens. Single applications of hOP-1 and hTGF-beta(3) also resulted in substantial bone formation, not comparable however to synergistic binary applications. Zoledronate-treated macroporous constructs showed limited bone formation and in two specimens bone formation was altogether absent; qRT-PCR showed a prominent reduction of OP-1 gene expression whilst TGF-beta(3) expression was far greater than OP-1. The lack of bone formation by zoledronate-treated specimens indicates that osteoclastic activity on the implanted coral-derived constructs is critical for the spontaneous induction of bone formation. Indirectly, zoledronate-treated samples showing lack of OP-1 gene expression and absent or very limited bone formation by induction confirm that the spontaneous induction of bone formation by coral-derived macroporous constructs is initiated by secreted BMPs/OPs, in context the OP-1 isoform.

Osteoinduction: translating preclinical promise into clinical reality

This review, the second in a series of three editorials, focuses on the problems of translating basic scientific research on induction of bone into reliable clinical applications.