The induction of endochondral bone formation by transforming growth factor-beta(3): experimental studies in the non-human primate Papio ursinus

Mechanistic insights into the spontaneous induction of bone formation

The grand discovery of morphogens, or "form-generating substances", revealed that tissue morphogenesis is initiated by soluble molecular signals or morphogens primarily belonging to the transforming growth factor-β (TGF-β) supergene family. The regenerative potential of bone rests on its extracellular matrix, which is the repository of several morphogens that tightly control cellular differentiating pathways, cellular matrix deposition and remodeling. Alluringly, the matrix also contains specific factors transferred from the heterotopic implanted bone matrices initiating "Tissue Induction", as provocatively described in Nature in 1945. Later, it was found that selected genes and gene products of the TGF-β supergene family singly, synchronously, and synergistically mastermind the induction of bone formation. This review describes the phenomenon of the spontaneous and/or intrinsic osteoinductivity of calcium phosphate-based biomaterials and titanium' constructs without the applications of soluble osteogenetic molecular signals. The review shows the spontaneous induction of bone formation initiated by Ca++ activating stem cell differentiation and up-regulation of bone morphogenetic proteins genes. Expressed gene products are embedded into the concavities of the calcium phosphate-based substrata, initiating bone formation as a secondary response. Pure titanium's substrata do not initiate the spontaneous induction of bone formation. The induction of bone is solely dependent on acid, alkali and heat treatments to form apatite layers on the treated titanium surfaces. The induction of bone formation is achieved exclusively by apatite-based biomaterial surfaces. The hydroxyapatite, in its various forms and geometric configurations, finely tunes the induction of bone formation in heterotopic sites. Cellular differentiation by fine-tuning of the cellular molecular machinery is initiated by specific geometric modularity of the hydroxyapatite substrata that push cellular buttons that start the ripple-like cascade of "Tissue Induction", generating newly formed ossicles with bone marrow in heterotopic extraskeletal sites. The highlighted mechanistic insights into the spontaneous induction of bone formation are a research platform invocating selected molecular elements to construct the induction of bone formation.

Why Animal Experiments Are Still Indispensable in Bone Research: A Statement by the European Calcified Tissue Society

Major achievements in bone research have always relied on animal models and in vitro systems derived from patient and animal material. However, the use of animals in research has drawn intense ethical debate and the complete abolition of animal experimentation is demanded by fractions of the population. This phenomenon is enhanced by the reproducibility crisis in science and the advance of in vitro and in silico techniques. 3D culture, organ-on-a-chip, and computer models have improved enormously over the last few years. Nevertheless, the overall complexity of bone tissue cross-talk and the systemic and local regulation of bone physiology can often only be addressed in entire vertebrates. Powerful genetic methods such as conditional mutagenesis, lineage tracing, and modeling of the diseases enhanced the understanding of the entire skeletal system. In this review endorsed by the European Calcified Tissue Society (ECTS), a working group of investigators from Europe and the US provides an overview of the strengths and limitations of experimental animal models, including rodents, fish, and large animals, as well the potential and shortcomings of in vitro and in silico technologies in skeletal research. We propose that the proper combination of the right animal model for a specific hypothesis and state-of-the-art in vitro and/or in silico technology is essential to solving remaining important questions in bone research. This is crucial for executing most efficiently the 3R principles to reduce, refine, and replace animal experimentation, for enhancing our knowledge of skeletal biology, and for the treatment of bone diseases that affect a large part of society. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

In Vitro Osteoinductivity Assay of Hydroxylapatite Scaffolds, Obtained with Biomorphic Transformation Processes, Assessed Using Human Adipose Stem Cell Cultures

In this study, the in vitro biocompatibility and osteoinductive ability of a recently developed biomorphic hydroxylapatite ceramic scaffold (B-HA) derived from transformation of wood structures were analyzed using human adipose stem cells (hASCs). Cell viability and metabolic activity were evaluated in hASCs, parental cells and in recombinant genetically engineered hASC-eGFP cells expressing the green fluorescence protein. B-HA osteoinductivity properties, such as differentially expressed genes (DEG) involved in the skeletal development pathway, osteocalcin (OCN) protein expression and mineral matrix deposition in hASCs, were evaluated. In vitro induction of osteoblastic genes, such as Alkaline phosphatase (ALPL), Bone gamma-carboxyglutamate (gla) protein (BGLAP), SMAD family member 3 (SMAD3), Sp7 transcription factor (SP7) and Transforming growth factor, beta 3 (TGFB3) and Tumor necrosis factor (ligand) superfamily, member 11 (TNFSF11)/Receptor activator of NF-κB (RANK) ligand (RANKL), involved in osteoclast differentiation, was undertaken in cells grown on B-HA. Chondrogenic transcription factor SRY (sex determining region Y)-box 9 (SOX9), tested up-regulated in hASCs grown on the B-HA scaffold. Gene expression enhancement in the skeletal development pathway was detected in hASCs using B-HA compared to sintered hydroxylapatite (S-HA). OCN protein expression and calcium deposition were increased in hASCs grown on B-HA in comparison with the control. This study demonstrates the biocompatibility of the novel biomorphic B-HA scaffold and its potential use in osteogenic differentiation for hASCs. Our data highlight the relevance of B-HA for bone regeneration purposes.

DNA Methylation Signatures of Bone Metabolism in Osteoporosis and Osteoarthritis Aging-Related Diseases: An Updated Review

DNA methylation is one of the most studied epigenetic mechanisms that play a pivotal role in regulating gene expression. The epigenetic component is strongly involved in aging-bone diseases, such as osteoporosis and osteoarthritis. Both are complex multi-factorial late-onset disorders that represent a globally widespread health problem, highlighting a crucial point of investigations in many scientific studies. In recent years, new findings on the role of DNA methylation in the pathogenesis of aging-bone diseases have emerged. The aim of this systematic review is to update knowledge in the field of DNA methylation associated with osteoporosis and osteoarthritis, focusing on the specific tissues involved in both pathological conditions.

Synergistic interaction of hTGF-β3 with hBMP-6 promotes articular cartilage formation in chitosan scaffolds with hADSCs: implications for regenerative medicine

Background

Human TGF-β₃ has been used in many studies to induce genes coding for typical cartilage matrix components and accelerate chondrogenic differentiation, making it the standard constituent in most cultivation media used for the assessment of chondrogenesis associated with various stem cell types on carrier matrices. However, in vivo data suggests that TGF-β₃ and its other isoforms also induce endochondral and intramembranous osteogenesis in non-primate species to other mammals. Based on previously demonstrated improved articular cartilage induction by a using hTGF-β₃ and hBMP-6 together on hADSC cultures and the interaction of TGF- β with matrix in vivo, the present study investigates the interaction of a chitosan scaffold as polyanionic polysaccharide with both growth factors. The study analyzes the difference between chondrogenic differentiation that leads to stable hyaline cartilage and the endochondral ossification route that ends in hypertrophy by extending the usual panel of investigated gene expression and stringent employment of quantitative PCR.

Results

By assessing the viability, proliferation, matrix formation and gene expression patterns it is shown that hTGF-β₃ + hBMP-6 promotes improved hyaline articular cartilage formation in a chitosan scaffold in which ACAN with Col2A1 and not Col1A1 nor Col10A1 where highly expressed both at a transcriptional and translational level. Inversely, hTGF-β₃ alone tended towards endochondral bone formation showing according protein and gene expression patterns.

Conclusion

These findings demonstrate that clinical therapies should consider using hTGF-β₃ + hBMP-6 in articular cartilage regeneration therapies as the synergistic interaction of these morphogens seems to ensure and maintain proper hyaline articular cartilage matrix formation counteracting degeneration to fibrous tissue or ossification. These effects are produced by interaction of the growth factors with the polysaccharide matrix.

Transforming Growth Factor-β3/Chitosan Sponge (TGF-β3/CS) Facilitates Osteogenic Differentiation of Human Periodontal Ligament Stem Cells

Periodontal disease is the main reason for tooth loss in adults. Tissue engineering and regenerative medicine are advanced technologies used to manage soft and hard tissue defects caused by periodontal disease. We developed a transforming growth factor-β3/chitosan sponge (TGF-β3/CS) to repair periodontal soft and hard tissue defects. We investigated the proliferation and osteogenic differentiation behaviors of primary human periodontal ligament stem cells (hPDLSCs) to determine the bioactivity and potential application of TGF-β3 in periodontal disease. We employed calcein-AM/propidium iodide (PI) double labeling or cell membranes (CM)-Dil labeling coupled with fluorescence microscopy to trace the survival and function of cells after implantation in vitro and in vivo. The mineralization of osteogenically differentiated hPDLSCs was confirmed by measuring alkaline phosphatase (ALP) activity and calcium content. The levels of COL I, ALP, TGF-βRI, TGF-βRII, and Pp38/t-p38 were assessed by western blotting to explore the mechanism of bone repair prompted by TGF-β3. When hPDLSCs were implanted with various concentrations of TGF-β3/CS (62.5-500 ng/mL), ALP activity was the highest in the TGF-β3 (250 ng/mL) group after 7 d (p < 0.05 vs. control). The calcium content in each group was increased significantly after 21 and 28 d (p < 0.001 vs. control). The optimal result was achieved by the TGF-β3 (500 ng/mL) group. These results showed that TGF-β3/CS promotes osteogenic differentiation of hPDLSCs, which may involve the p38 mitogen-activated protein kinase (MAPK) signaling pathway. TGF-β3/CS has the potential for application in the repair of incomplete alveolar bone defects.

Bone marrow mononuclear cells versus mesenchymal stem cells from adipose tissue on bone healing in an Old World primate: can this be extrapolated to humans?

ABSTRACT In veterinary medicine, the cell therapy is still unexplored and there are many unanswered questions that researchers tend to extrapolate to humans in an attempt to treat certain injuries. Investigating this subject in nonhuman primates turns out to be an unparalleled opportunity to better understand the dynamics of stem cells against some diseases. Thus, we aimed to compare the efficiency of bone marrow mononuclear cells (BMMCs) and mesenchymal stem cells (MSCs) from adipose tissue of Chlorocebus aethiops in induced bone injury. Ten animals were used, male adults subjected, to bone injury the iliac crests. The MSCs were isolated by and cultured. In an autologous manner, the BMMCs were infused in the right iliac crest, and MSCs from adipose tissue in the left iliac crest. After 4.8 months, the right iliac crests fully reconstructed, while left iliac crest continued to have obvious bone defects for up to 5.8 months after cell infusion. The best option for treatment of injuries with bone tissue loss in old world primates is to use autologous MSCs from adipose tissue, suggesting we can extrapolate the results to humans, since there is phylogenetic proximity between species.

The Induction of Bone Formation: The Translation Enigma

A paradigmatic shift in the way of thinking is what bone tissue engineering science requires to decrypt the translation conundrum from animal models into human. The deductive work of Urist (1965), who discerned the principle of bone induction from the pioneering works of Senn, Huggins, Lacroix, Levander, and other bone regenerative scientists, provided the basis that has assisted future bone tissue regenerative scientists to extend the bone tissue engineering field and its potential uses for bone regenerative medicine in humans. However, major challenges remain that are preventing the formation of bone by induction clinically. Growing experimental evidence is indicating that bone inductive studies are non-translatable from animal models into a clinical environment. This is preventing bone tissue engineering from reaching the next phase in development. Countless studies are trying to discern how the formation of bone by induction functions mechanistically, so as to try and solve this enigmatic problem. However, are the correct questions being asked? Why do bone inductive animal studies not translate into humans? Why do bone induction principles not yield the same extent of bone formation as an autogenous bone graft? What are bone tissue engineering scientists missing? By critically re-assessing the past and present discoveries of the bone induction field, this review article attempts to re-discover the field of bone formation by induction, identifying some key features that may have been missed. These include a detailed library of all proteins in bones and their arrangement in the 3D superstructure of the bone together with some other important criteria not considered by tissue engineering scientists. The review therefore not only re-iterates possible avenues of research that need to be re-explored but also seeks to guide present and future scientists in how they assess their own research in light of experimental design and results. By addressing these issues bone formation by induction without autografts might finally become clinically viable.

Functionalized Surface Geometries Induce: "Bone: Formation by Autoinduction"

The induction of tissue formation, and the allied disciplines of tissue engineering and regenerative medicine, have flooded the twenty-first century tissue biology scenario and morphed into high expectations of a fulfilling regenerative dream of molecularly generated tissues and organs in assembling human tissue factories. The grand conceptualization of deploying soluble molecular signals, first defined by Turing as forms generating substances, or morphogens, stemmed from classic last century studies that hypothesized the presence of morphogens in several mineralized and non-mineralized mammalian matrices. The realization of morphogens within mammalian matrices devised dissociative extractions and chromatographic procedures to isolate, purify, and finally reconstitute the cloned morphogens, found to be members of the transforming growth factor-β (TGF-β) supergene family, with insoluble signals or substrata to induce de novo tissue induction and morphogenesis. Can we however construct macroporous bioreactors per se capable of inducing bone formation even without the exogenous applications of the osteogenic soluble molecular signals of the TGF-β supergene family? This review describes original research on coral-derived calcium phosphate-based macroporous constructs showing that the formation of bone is independent of the exogenous application of the osteogenic soluble signals of the TGF-β supergene family. Such signals are the molecular bases of the induction of bone formation. The aim of this review is to primarily describe today's hottest topic of biomaterials' science, i.e., to construct and define osteogenetic biomaterials' surfaces that per se, in its own right, do initiate the induction of bone formation. Biomaterials are often used to reconstruct osseous defects particularly in the craniofacial skeleton. Edentulism did spring titanium implants as tooth replacement strategies. No were else that titanium surfaces require functionalized geometric nanotopographic cues to set into motion osteogenesis independently of the exogenous application of the osteogenic soluble molecular signals. Inductive morphogenetic surfaces are the way ahead of biomaterials' science: the connubium of stem cells on primed functionalized surfaces precisely regulates gene expression and the induction of the osteogenic phenotype.

Genome-Wide DNA Methylation Study Identifies Significant Epigenomic Changes in Osteoarthritic Subchondral Bone and Similarity to Overlying Cartilage

OBJECTIVE

To perform a genome-wide DNA methylation study to identify differential DNA methylation patterns in subchondral bone underlying eroded and intact cartilage from patients with hip osteoarthritis (OA) and to compare these with DNA methylation patterns in overlying cartilage.

METHODS

Genome-wide DNA methylation profiling using Illumina HumanMethylation 450 arrays was performed on eroded and intact cartilage and subchondral bone from within the same joint of 12 patients undergoing hip arthroplasty. Genes with differentially methylated CpG sites were analyzed to identify shared pathways, upstream regulators, and overrepresented gene ontologies, and these patterns were compared with those of the overlying cartilage. Histopathology was graded by modified Mankin score and assessed for correlation with DNA methylation.

RESULTS

We identified 7,316 differentially methylated CpG sites in subchondral bone underlying eroded cartilage, most of which (∼75%) were hypomethylated, and 1,397 sites in overlying eroded cartilage, 126 of which were shared. Samples clustered into 3 groups with distinct histopathologic scores. We observed differential DNA methylation of genes including the RNA interference-processing gene AGO2, the growth factor TGFB3, the OA suppressor NFATC1, and the epigenetic effector HDAC4. Among known susceptibility genes in OA, 32 were differentially methylated in subchondral bone, 8 were differentially methylated in cartilage, and 5 were shared. Upstream regulator analysis using differentially methylated genes in OA subchondral bone showed a strong transforming growth factor β1 signature (P = 1 × 10(-40) ) and a tumor necrosis factor family signature (P = 3.2 × 10(-28) ), among others.

CONCLUSION

Our data suggest the presence of an epigenetic phenotype associated with eroded OA subchondral bone that is similar to that of overlying eroded OA cartilage.

The effect of quercetin delivery system on osteogenesis and angiogenesis under osteoporotic conditions

Bone regeneration under osteoporotic conditions with impaired angiogenesis, osteogenesis and remodeling represents a great challenge.

Redundancy and Molecular Evolution: The Rapid Induction of Bone Formation by the Mammalian Transforming Growth Factor-β3 Isoform

The soluble osteogenic molecular signals of the transforming growth factor-β (TGF-β) supergene family are the molecular bases of the induction of bone formation and postnatal bone tissue morphogenesis with translation into clinical contexts. The mammalian TGF-β3 isoform, a pleiotropic member of the family, controls a vast array of biological processes including the induction of bone formation. Recombinant hTGF-β3 induces substantial bone formation when implanted with either collagenous bone matrices or coral-derived macroporous bioreactors in the rectus abdominis muscle of the non-human primate Papio ursinus. In marked contrast, the three mammalian TGF-βs do not initiate the induction of bone formation in rodents and lagomorphs. The induction of bone by hTGF-β3/preloaded bioreactors is orchestrated by inducing fibrin-fibronectin rings that structurally organize tissue patterning and morphogenesis within the macroporous spaces. Induced advancing extracellular matrix rings provide the structural anchorage for hyper chromatic cells, interpreted as differentiating osteoblasts re-programmed by hTGF-β3 from invading myoblastic and/or pericytic differentiated cells. Runx2 and Osteocalcin expression are significantly up-regulated correlating to multiple invading cells differentiating into the osteoblastic phenotype. Bioreactors pre-loaded with recombinant human Noggin (hNoggin), a BMPs antagonist, show down-regulation of BMP-2 and other profiled osteogenic proteins' genes resulting in minimal bone formation. Coral-derived macroporous constructs preloaded with binary applications of hTGF-β3 and hNoggin also show down-regulation of BMP-2 with the induction of limited bone formation. The induction of bone formation by hTGF-β3 is via the BMPs pathway and it is thus blocked by hNoggin. Our systematic studies in P. ursinus with translational hTGF-β3 in large cranio-mandibulo-facial defects in humans are now requesting the re-evaluation of "Bone: formation by autoinduction" in primate models including humans.

TGF-β Signaling Regulates Cementum Formation through Osterix Expression

TGF-β/BMPs have widely recognized roles in mammalian development, including in bone and tooth formation. To define the functional relevance of the autonomous requirement for TGF-β signaling in mouse tooth development, we analyzed osteocalcin-Cre mediated Tgfbr2 (OC(Cre)Tgfbr2(fl/fl)) conditional knockout mice, which lacks functional TGF-β receptor II (TβRII) in differentiating cementoblasts and cementocytes. Strikingly, OC(Cre)Tgfbr2(fl/fl) mutant mice exhibited a sharp reduction in cellular cementum mass with reduced matrix secretion and mineral apposition rates. To explore the molecular mechanisms underlying the roles of TGF-β signaling through TβRII in cementogenesis, we established a mouse cementoblast model with decreased TβRII expression using OCCM-30 cells. Interestingly, the expression of osterix (Osx), one of the major regulators of cellular cementum formation, was largely decreased in OCCM-30 cells lacking TβRII. Consequently, in those cells, functional ALP activity and the expression of genes associated with cementogenesis were reduced and the cells were partially rescued by Osx transduction. We also found that TGF-β signaling directly regulates Osx expression through a Smad-dependent pathway. These findings strongly suggest that TGF-β signaling plays a major role as one of the upstream regulators of Osx in cementoblast differentiation and cementum formation.

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.

Actions from head to toe: An update on Bone/Body Morphogenetic Proteins in health and disease

The pleiotropic actions of Bone Morphogenetic Proteins in many different tissues has led us to the conclusion that they may be viewed as Body Morphogenetic Proteins (BMPs). This is supported by a broad range of distinct BMP-related diseases. Here, we summarize highlights from the 10th international BMP conference, which took place from September 16th to 20th 2014 in Berlin. Attendees updated us on recently identified common and context-specific mechanisms of BMP signaling and function. This included for example new insights into BMP pro-domains, BMP receptors, role of BMPs in muscle and novel consequences of ACVRI mutations. Currently, new BMPs are entering clinical trials with the BMP pathway considered as a 'druggable' target. We conclude that various recent and ongoing approaches could indeed help patients in the near future.

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.

Biomimetics for the induction of bone formation

The new strategy to initiate the induction of bone formation is to carve smart, self-inducing geometric cues assembled within biomimetic medical devices. These are endowed with the striking prerogative of differentiating myoblastic and/or pericytic stem cells into osteoblastic-like cells attached to the morphogenetic concavities; osteoblastic-like cells secrete osteogenic gene products of the TGF-beta supergene family, further differentiating invading stem cells into osteoblastic-like cells, and initiating bone formation by induction as a secondary response.

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.

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.

Smad signaling in skeletal development and regeneration

Smad proteins are intracellular molecules that mediate the canonical signaling cascade of TGFbeta superfamily growth factors. The TGFbeta superfamily comprises two groups of growth factors, BMPs and TGFbetas. Both groups can be further divided into several sub-groups based on sequence homologies and functional similarities. Ligands of the TGFbeta superfamily bind to cell surface receptors to activate Smad proteins in the cytoplasm; then the activated Smad proteins translocate into the nucleus to activate or repress specific target gene transcription. Both groups of growth factors play important roles in skeletal development and regeneration. However, whether these effects reflect signaling through canonical Smad pathways, or other non-canonical signaling pathways in vivo remains a mystery. Moreover, the mechanisms utilized by Smad proteins to initiate nuclear events and their interactions with cytoplasmic proteins are still under intensive investigation. This review will discuss the most recent progress understanding Smad signaling in the context of skeletal development and regeneration.

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

Craniofacial skeletal reconstruction remains a challenging problem despite major molecular and surgical developments in the understanding of bone formation by induction. The induction of bone formation has been a critical topic of research across the planet. The bone induction principle identified important cues for tissue engineering of bone, namely, osteogenic soluble molecular signals, the bone morphogenetic and osteogenic proteins, and insoluble signals or substrata including biomimetic bioactive matrices and responding stem cells. In primates, and in primates only, the osteogenic soluble molecular signals that initiate the induction of bone formation additionally include the 3 mammalian transforming growth factor-beta (TGF-beta) isoforms, members of the TGF-beta supergene family. The mammalian TGF-beta isoforms, when implanted in the rectus abdominis muscle of the nonhuman primate Papio ursinus, induce rapid and substantial endochondral bone formation resulting in large corticalized ossicles by day 30 after heterotopic implantation; in calvarial defects of the same nonhuman primates, identical or higher doses of the TGF-beta protein do not induce bone formation because of the overexpression of Smad-6 and Smad-7, gene product inhibitors of the TGF-beta signaling pathway. The addition of minced fragments of autogenous rectus abdominis muscle partially restores the osteoinductive activity of the human TGF-beta3 isoform resulting in the induction of bone formation in the treated calvarial defects. Recombinant human TGF-beta3 delivered by Matrigel matrix and implanted in class II and III furcation defects of mandibular molars of P. ursinus induce periodontal tissue regeneration. The addition of minced fragments of autogenous rectus abdominis muscle significantly enhances cementogenesis. This review highlights the induction of bone formation by the osteogenic proteins of the TGF-beta superfamily in the nonhuman primate P. ursinus and reviews combinatorial applications of myoblastic/myogenic stem cell-based therapeutics for bone induction and morphogenesis. The recruitment of myoendothelial cells is also discussed in the light of the intrinsic and spontaneous induction of bone formation by smart biomaterial matrices that induce bone differentiation in heterotopic extraskeletal sites of P. ursinus without the exogenous application of the osteogenic soluble molecular signals of the TGF-beta superfamily.

Regenerative frontiers in craniofacial reconstruction: grand challenges and opportunities for the mammalian transforming growth factor-β proteins

Science's fascination with bone and its repair processes span for thousands of years since the ancient Greek Hippocrates, the father of Medicine, made the key discovery that bone heals without scarring. Through the centuries, several lucid investigators perceived that the extracellular matrix of bone must be a reservoir of differentiating and morphogenetic factors ultimately responsible for its pronounced healing potential (reviewed in Urist, 1968, 1994; Reddi, 2000; Ripamonti et al., 2006).

The induction of bone formation by coral-derived calcium carbonate/hydroxyapatite constructs

The spontaneous induction of bone formation in heterotopic rectus abdominis and orthotopic calvarial sites by coral-derived biomimetic matrices of different chemical compositions was investigated in a long-term study in the non-human primate Papio ursinus. Coral-derived calcium carbonate constructs were converted to hydroxyapatite by hydrothermal exchange. Limited conversion produced hydroxyapatite/calcium carbonate (HA/CC) constructs of 5% and 13% hydroxyapatite. Rods of 20 mm in length and 7 mm in diameter were implanted in heterotopic rectus abdominis sites; discs 25 mm in diameter were implanted in orthotopic calvarial defects of six adult non-human primates P. ursinus. Heterotopic samples also included fully converted hydroxyapatite replicas sintered at 1100 degrees C. To further enhance spontaneous osteoinductive activity, fully converted hydroxyapatite replicas were coated with the synthetic peptide P15 known to increase the adhesion of fibroblasts to anorganic bovine mineral. Bone induction was assessed at 60, 90 and 365 days by histological examination, alkaline phosphatase and osteocalcin expression, as well as by the expression of BMP-7, GDF-10 and collagen type IV mRNAs. Induction of bone occurred in the concavities of the matrices at all time points. At 365 days, bone marrow was evident in the P15-coated and uncoated implants. Resorption of partially converted calcium carbonate/hydroxyapatite was apparent, as well as remodeling of the newly formed bone. Northern blot analyses of samples from heterotopic specimens showed high levels of expression of BMP-7 and collagen type IV mRNA in all specimen types at 60 days, correlating with the induction of the osteoblastic phenotype in invading fibrovascular cells. Orthotopic specimens showed prominent bone formation across the different implanted constructs. The concavities of the matrices biomimetize the remodeling cycle of the osteonic primate cortico-cancellous bone and promote the ripple-like cascade of the induction of bone formation. This study demonstrates for the first time that partially converted HA/CC constructs also induce spontaneous differentiation of bone, albeit only seen one year post-implantation.

Biomimetism, biomimetic matrices and the induction of bone formation

Bone formation by induction initiates by invocation of osteogenic soluble molecular signals of the transforming growth factor-β (TGF-β) superfamily; when combined with insoluble signals or substrata, the osteogenic soluble signals trigger the ripple-like cascade of cell differentiation into osteoblastic cell lines secreting bone matrix at site of surgical implantation. A most exciting and novel strategy to initiate bone formation by induction is to carve smart self-inducing geometric concavities assembled within biomimetic constructs. The assembly of a series of repetitive concavities within the biomimetic constructs is endowed with the striking prerogative of differentiating osteoblast-like cells attached to the biomimetic matrices initiating the induction of bone formation as a secondary response. Importantly, the induction of bone formation is initiated without the exogenous application of the osteogenic soluble molecular signals of the TGF-β superfamily. This manuscript reviews the available data on this fascinating phenomenon, i.e. biomimetic matrices that arouse and set into motion the mammalian natural ability to heal thus constructing biomimetic matrices that in their own right set into motion inductive regenerative phenomena initiating the cascade of bone differentiation by induction biomimetizing the remodelling cycle of the primate cortico-cancellous bone.

Induction of cementogenesis and periodontal ligament regeneration by recombinant human transforming growth factor-beta3 in Matrigel with rectus abdominis responding cells

BACKGROUND AND OBJECTIVE

In primates and in primates only, the transforming growth factor-b proteins induce endochondral bone formation. Transforming growth factor-b3 also induces periodontal tissue regeneration. Two regenerative treatments using human recombinant transforming growth factor-b3 were examined after implantation in mandibular furcation defects of the nonhuman primate, Papio ursinus.

MATERIAL AND METHODS

Class III furcation defects were surgically created bilaterally in the mandibular first and second molars of two adult Chacma baboons (P. ursinus). Different doses of recombinant transforming growth factor-beta3 reconstituted with Matrigel matrix were implanted in the rectus abdominis muscle to induce heterotopic ossicles for subsequent transplantation to selected furcation defects. Twenty days after heterotopic implantation, periodontal defects were re-exposed, further debrided and implanted with minced fragments of induced heterotopic ossicles. Contralateral class III furcation defects were implanted directly with recombinant transforming growth factor-beta3 in Matrigel matrix with the addition of minced fragments of autogenous rectus abdominis muscle. Treated quadrants were not subjected to oral hygiene procedures so as to study the effect of the direct application of the recombinant morphogen in Matrigel on periodontal healing. Histomorphometric analyses on undecalcified sections cut from specimen blocks harvested on day 60 measured the area of newly formed alveolar bone and the coronal extension of the newly formed cementum along the exposed root surfaces.

RESULTS

Morphometric analyses showed greater alveolar bone regeneration and cementogenesis in furcation defects implanted directly with 75 microg of transforming growth factor-beta3 in Matrigel matrix with the addition of minced muscle tissue.

CONCLUSION

Matrigel matrix is an optimal delivery system for the osteogenic proteins of the transforming growth factor-beta superfamily, including the mammalian transforming growth factor-beta3 isoform. The addition of minced fragments of rectus abdominis muscle provides responding stem cells for further tissue induction and morphogenesis by the transforming growth factor-beta3 protein.

Cementogenesis and the induction of periodontal tissue regeneration by the osteogenic proteins of the transforming growth factor-beta superfamily

The antiquity and severity of periodontal diseases are demonstrated by the hard evidence of alveolar bone loss in gnathic remains of the Pliocene/Pleistocene deposits of the Bloubank Valley at Sterkfontein, Swartkrans and Kromdrai in South Africa. Extant Homo has characterized and cloned a superfamily of proteins which include the bone morphogenetic proteins that regulate tooth morphogenesis at different stages of development as temporally and spatially connected events. The induction of cementogenesis, periodontal ligament and alveolar bone regeneration are regulated by the co-ordinated expression of bone morphogenetic proteins. Naturally derived and recombinant human bone morphogenetic proteins induce periodontal tissue regeneration in mammals. Morphological analyses on undecalcified sections cut at 3-6 mum on a series of mandibular molar Class II and III furcation defects induced in the non-human primate Papio ursinus show the induction of cementogenesis. Sharpey's fibers nucleate as a series of composite collagen bundles within the cementoid matrix in close relation to embedded cementocytes. Osteogenic protein-1 and bone morphogenetic protein-2 possess a structure-activity profile, as shown by the morphology of tissue regeneration, preferentially cementogenic and osteogenic, respectively. In Papio ursinus, transforming growth factor-beta(3) also induces cementogenesis, with Sharpey's fibers inserting into newly formed alveolar bone. Capillary sprouting and invasion determine the sequential insertion and alignment of individual collagenic bundles. The addition of responding stem cells prepared by finely mincing fragments of autogenous rectus abdominis muscle significantly enhances the induction of periodontal tissue regeneration when combined with transforming growth factor-beta(3) implanted in Class II and III furcation defects of Papio ursinus.

Simple application of fibronectin-mimetic coating enhances osseointegration of titanium implants

Integrin-mediated cell adhesion to biomolecules adsorbed onto biomedical devices regulates device integration and performance. Because of the central role of integrin-fibronectin (FN) interactions in osteoblastic function and bone formation, we evaluated the ability of FN-inspired biomolecular coatings to promote osteoblastic differentiation and implant osseointegration. Notably, these biomolecular coatings relied on physical adsorption of FN-based ligands onto biomedical-grade titanium as a simple, clinically translatable strategy to functionalize medical implants. Surfaces coated with a recombinant fragment of FN spanning the central cell binding domain enhanced osteoblastic differentiation and mineralization in bone marrow stromal cell cultures and increased implant osseointegration in a rat cortical bone model compared to passively adsorbed arginine-glycine-aspartic acid peptides, serum proteins and full-length FN. Differences in biological responses correlated with integrin binding specificity and signalling among surface coatings. This work validates a simple, clinically translatable, surface biofunctionalization strategy to enhance biomedical device integration.