Cooperative effects in differentiation and proliferation between PDGF-BB and matrix derived synthetic peptides in human osteoblasts

Self-assembled peptide hydrogel loaded with functional peptide Dentonin accelerates vascularized bone tissue regeneration in critical-size bone defects

Regeneration of oral craniofacial bone defects is a complex process, and reconstruction of large bone defects without the use of exogenous cells or bioactive substances remains a major challenge. Hydrogels are highly hydrophilic polymer networks with the potential to promote bone tissue regeneration. In this study, functional peptide Dentonin was loaded onto self-assembled peptide hydrogels (RAD) to constitute functionally self-assembling peptide RAD/Dentonin hydrogel scaffolds with a view that RAD/Dentonin hydrogel could facilitate vascularized bone regeneration in critical-size calvarial defects. The functionalized peptide RAD/Dentonin forms highly ordered β-sheet supramolecular structures via non-covalent interactions like hydrogen bonding, ultimately assembling into nano-fiber network. RAD/Dentonin hydrogels exhibited desirable porosity and swelling properties, and appropriate biodegradability. RAD/Dentonin hydrogel supported the adhesion, proliferation and three-dimensional migration of bone marrow mesenchymal stem cells (BMSCs) and has the potential to induce differentiation of BMSCs towards osteogenesis through activation of the Wnt/β-catenin pathway. Moreover, RAD/Dentonin hydrogel modulated paracrine secretion of BMSCs and increased the migration, tube formation and angiogenic gene expression of human umbilical vein endothelial cells (HUVECs), which boosted the angiogenic capacity of HUVECs. In vivo, RAD/Dentonin hydrogel significantly strengthened vascularized bone formation in rat calvarial defect. Taken together, these results indicated that the functionalized self-assembling peptide RAD/Dentonin hydrogel effectively enhance osteogenic differentiation of BMSCs, indirectly induce angiogenic effects in HUVECs, and facilitate vascularized bone regeneration in vivo. Thus, it is a promising bioactive material for oral and maxillofacial regeneration.

The Osteogenic Peptide P-15 for Bone Regeneration: A Narrative Review of the Evidence for a Mechanism of Action

Bone regeneration is a complex multicellular process involving the recruitment and attachment of osteoprogenitors and their subsequent differentiation into osteoblasts that deposit extracellular matrixes. There is a growing demand for synthetic bone graft materials that can be used to augment these processes to enhance the healing of bone defects resulting from trauma, disease or surgery. P-15 is a small synthetic peptide that is identical in sequence to the cell-binding domain of type I collagen and has been extensively demonstrated in vitro and in vivo to enhance the adhesion, differentiation and proliferation of stem cells involved in bone formation. These events can be categorized into three phases: attachment, activation and amplification. This narrative review summarizes the large body of preclinical research on P-15 in terms of these phases to describe the mechanism of action by which P-15 improves bone formation. Knowledge of this mechanism of action will help to inform the use of P-15 in clinical practice as well as the development of methods of delivering P-15 that optimize clinical outcomes.

Peptide-Based Biomaterials for Bone and Cartilage Regeneration

The healing of osteochondral defects (OCDs) that result from injury, osteochondritis, or osteoarthritis and bear lesions in the cartilage and bone, pain, and loss of joint function in middle- and old-age individuals presents challenges to clinical practitioners because of non-regenerative cartilage and the limitations of current therapies. Bioactive peptide-based osteochondral (OC) tissue regeneration is becoming more popular because it does not have the immunogenicity, misfolding, or denaturation problems associated with original proteins. Periodically, reviews are published on the regeneration of bone and cartilage separately; however, none of them addressed the simultaneous healing of these tissues in the complicated heterogeneous environment of the osteochondral (OC) interface. As regulators of cell adhesion, proliferation, differentiation, angiogenesis, immunomodulation, and antibacterial activity, potential therapeutic strategies for OCDs utilizing bone and cartilage-specific peptides should be examined and investigated. The main goal of this review was to study how they contribute to the healing of OCDs, either alone or in conjunction with other peptides and biomaterials.

Multipotential Role of Growth Factor Mimetic Peptides for Osteochondral Tissue Engineering

Articular cartilage is characterized by a poor self-healing capacity due to its aneural and avascular nature. Once injured, it undergoes a series of catabolic processes which lead to its progressive degeneration and the onset of a severe chronic disease called osteoarthritis (OA). In OA, important alterations of the morpho-functional organization occur in the cartilage extracellular matrix, involving all the nearby tissues, including the subchondral bone. Osteochondral engineering, based on a perfect combination of cells, biomaterials and biomolecules, is becoming increasingly successful for the regeneration of injured cartilage and underlying subchondral bone tissue. To this end, recently, several peptides have been explored as active molecules and enrichment motifs for the functionalization of biomaterials due to their ability to be easily chemically synthesized, as well as their tunable physico-chemical features, low immunogenicity issues and functional group modeling properties. In addition, they have shown a good aptitude to penetrate into the tissue due to their small size and stability at room temperature. In particular, growth-factor-derived peptides can play multiple functions in bone and cartilage repair, exhibiting chondrogenic/osteogenic differentiation properties. Among the most studied peptides, great attention has been paid to transforming growth factor-β and bone morphogenetic protein mimetic peptides, cell-penetrating peptides, cell-binding peptides, self-assembling peptides and extracellular matrix-derived peptides. Moreover, recently, phage display technology is emerging as a powerful selection technique for obtaining functional peptides on a large scale and at a low cost. In particular, these peptides have demonstrated advantages such as high biocompatibility; the ability to be immobilized directly on chondro- and osteoinductive nanomaterials; and improving the cell attachment, differentiation, development and regeneration of osteochondral tissue. In this context, the aim of the present review was to go through the recent literature underlining the importance of studying novel functional motifs related to growth factor mimetic peptides that could be a useful tool in osteochondral repair strategies. Moreover, the review summarizes the current knowledge of the use of phage display peptides in osteochondral tissue regeneration.

Recent advances in design and applications of biomimetic self-assembled peptide hydrogels for hard tissue regeneration

Abstract

The development of natural biomaterials applied for hard tissue repair and regeneration is of great importance, especially in societies with a large elderly population. Self-assembled peptide hydrogels are a new generation of biomaterials that provide excellent biocompatibility, tunable mechanical stability, injectability, trigger capability, lack of immunogenic reactions, and the ability to load cells and active pharmaceutical agents for tissue regeneration. Peptide-based hydrogels are ideal templates for the deposition of hydroxyapatite crystals, which can mimic the extracellular matrix. Thus, peptide-based hydrogels enhance hard tissue repair and regeneration compared to conventional methods. This review presents three major self-assembled peptide hydrogels with potential application for bone and dental tissue regeneration, including ionic self-complementary peptides, amphiphilic (surfactant-like) peptides, and triple-helix (collagen-like) peptides. Special attention is given to the main bioactive peptides, the role and importance of self-assembled peptide hydrogels, and a brief overview on molecular simulation of self-assembled peptide hydrogels applied for bone and dental tissue engineering and regeneration.

Graphic abstract

The Role of Growth Factors in Bioactive Coatings

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

Recombinant platelet-derived growth factor-BB alleviates osteoarthritis in a rat model by decreasing chondrocyte apoptosis in vitro and in vivo

Osteoarthritis (OA) is a common joint disease that mainly affects the diarthrodial joints. Treatments for OA include non‐pharmacological interventions, topical and oral therapies, intra‐articular therapies and joint surgery. However, all the treatments mentioned above mainly aim to control the symptoms instead of improving or reversing the joint condition. In this research, we observed the effect of recombinant platelet‐derived growth factor (PDGF)‐BB on OA in a monosodium iodoacetate (MIA)–induced rat model and revealed the possible mechanisms. In vitro, the level of inflammation in the chondrocytes was gradually alleviated, and the apoptosis rate was gradually decreased by PDGF‐BB at increasing concentrations. The levels of p‐p38, Bax and caspase‐3 decreased, and the level of p‐Erk increased with increasing PDGF‐BB concentration. In vivo, PDGF‐BB could significantly reverse chondrocyte and matrix loss. Furthermore, high concentrations of PDGF‐BB could alleviate cartilage hyperplasia to remodel the tissue. The level of collagen II was up‐regulated, and the levels of collagen X and apoptosis were down‐regulated by increasing concentrations of PDGF‐BB. In conclusion, recombinant PDGF‐BB alleviated OA by down‐regulating caspase‐3‐dependent apoptosis. The effects of PDGF‐BB on OA mainly include inhibiting chondrocyte loss, reducing cartilage hyperplasia and osteophyte formation, and regulating collagen anabolism.

PDGF‑BB promotes the differentiation and proliferation of MC3T3‑E1 cells through the Src/JAK2 signaling pathway

Platelet-derived growth factor-BB (PDGF-BB) serves a critical function in human osteoblast differentiation and proliferation. Src and Janus kinase 2 (JAK2) are involved in these processes. In our previous study, it was identified that Src could promote the phosphorylation of JAK2. However, it has yet to be determined whether the Src/JAK2 signaling pathway affects PDGF-BB-mediated osteoblast differentiation and proliferation. In the present study, western blotting, polymerase chain reaction, alizarin red staining, alkaline phosphatase and Cell Counting kit-8 were employed to explore these questions. Firstly, it was demonstrated that PDGF-BB activates the Src/JAK2 signaling pathway in MC3T3-E1 cells in a time-dependent manner. Furthermore, it was demonstrated that PDGF-BB expression promoted MC3T3-E1 cell differentiation and proliferation; this process was suppressed by AG1295, SU6656 and AG490, which are inhibitors of PDGFR-β, Src and JAK2, respectively. SU6656 downregulated the activity of Src and JAK2, while AG490 only downregulated JAK2 activity. Therefore, it was concluded that Src is upstream of JAK2. PDGF-BB also upregulated the expression of osteogenesis-associated genes, and the formation of mineral nodules. However, these effects were markedly inhibited by treatment with SU6656. This indicated that PDGF-BB promoted MC3T3-E1 cell differentiation and proliferation by activating the Src/JAK2 signaling pathway. These results suggested that PDGF-BB may have potential applications in the treatment of osteoporosis and bone fractures.

The use of bioactive peptides to modify materials for bone tissue repair

It has been well recognized that the modification of biomaterials with appropriate bioactive peptides could further enhance their functions. Especially, it has been shown that peptide-modified bone repair materials could promote new bone formation more efficiently compared with conventional ones. The purpose of this article is to give a general review of recent studies on bioactive peptide-modified materials for bone tissue repair. Firstly, the main peptides for inducing bone regeneration and commonly used methods to prepare peptide-modified bone repair materials are introduced. Then, current in vitro and in vivo research progress of peptide-modified composites used as potential bone repair materials are reviewed and discussed. Generally speaking, the recent related studies have fully suggested that the modification of bone repair materials with osteogenic-related peptides provide promising strategies for the development of bioactive materials and substrates for enhanced bone regeneration and the therapy of bone tissue diseases. Furthermore, we have proposed some research trends in the conclusion and perspectives part.

Incorporation of Human-Platelet-Derived Growth Factor-BB Encapsulated Poly(lactic-co-glycolic acid) Microspheres into 3D CORAGRAF Enhances Osteogenic Differentiation of Mesenchymal Stromal Cells

Tissue engineering aims to generate or facilitate regrowth or healing of damaged tissues by applying a combination of biomaterials, cells, and bioactive signaling molecules. In this regard, growth factors clearly play important roles in regulating cellular fate. However, uncontrolled release of growth factors has been demonstrated to produce severe side effects on the surrounding tissues. In this study, poly(lactic-co-glycolic acid) (PLGA) microspheres (MS) incorporated three-dimensional (3D) CORAGRAF scaffolds were engineered to achieve controlled release of platelet-derived growth factor-BB (PDGF-BB) for the differentiation of stem cells within the 3D polymer network. Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and microtomography were applied to characterize the fabricated scaffolds. In vitro study revealed that the CORAGRAF-PLGA-PDGF-BB scaffold system enhanced the release of PDGF-BB for the regulation of cell behavior. Stromal cell attachment, viability, release of osteogenic differentiation markers such as osteocalcin, and upregulation of osteogenic gene expression exhibited positive response. Overall, the developed scaffold system was noted to support rapid cell expansion and differentiation of stromal cells into osteogenic cells in vitro for bone tissue engineering applications.

In vitro models for evaluation of periodontal wound healing/regeneration

Periodontal wound healing and regeneration are highly complex processes, involving cells, matrices, molecules and genes that must be properly choreographed and orchestrated. As we attempt to understand and influence these clinical entities, we need experimental models to mimic the various aspects of human wound healing and regeneration. In vivo animal models that simulate clinical situations of humans can be costly and cumbersome. In vitro models have been devised to dissect wound healing/regeneration processes into discrete, analyzable steps. For soft tissue (e.g. gingival) healing, in vitro models range from simple culture of cells grown in monolayers and exposed to biological modulators or physical effectors and materials, to models in which cells are 'injured' by scraping and subsequently the 'wound' is filled with new or migrating cells, to three-dimensional models of epithelial-mesenchymal recombination or tissue explants. The cells employed are gingival keratinocytes, fibroblasts or endothelial cells, and their proliferation, migration, attachment, differentiation, survival, gene expression, matrix production or capillary formation are measured. Studies of periodontal regeneration also include periodontal ligament fibroblasts or progenitors, osteoblasts or osteoprogenitors, and cementoblasts. Regeneration models measure cellular proliferation, attachment and migration, as well as gene expression, transfer and differentiation into a mineralizing phenotype and biomineralization. Only by integrating data from models on all levels (i.e. a single cell to the whole organism) can various critical aspects of periodontal wound healing/regeneration be fully evaluated.

The role of peptides in bone healing and regeneration: a systematic review

BACKGROUND

Bone tissue engineering and the research surrounding peptides has expanded significantly over the last few decades. Several peptides have been shown to support and stimulate the bone healing response and have been proposed as therapeutic vehicles for clinical use. The aim of this comprehensive review is to present the clinical and experimental studies analysing the potential role of peptides for bone healing and bone regeneration.

METHODS

A systematic review according to PRISMA guidelines was conducted. Articles presenting peptides capable of exerting an upregulatory effect on osteoprogenitor cells and bone healing were included in the study.

RESULTS

Based on the available literature, a significant amount of experimental in vitro and in vivo evidence exists. Several peptides were found to upregulate the bone healing response in experimental models and could act as potential candidates for future clinical applications. However, from the available peptides that reached the level of clinical trials, the presented results are limited.

CONCLUSION

Further research is desirable to shed more light into the processes governing the osteoprogenitor cellular responses. With further advances in the field of biomimetic materials and scaffolds, new treatment modalities for bone repair will emerge.

Signaling between tumor cells and the host bone marrow microenvironment

Tumor cells with high skeletal homing affinity express numerous cell surface receptors that bind ligands produced in bone. Upon arrival, these cells survive in the host environment, encompassed in close proximity to bone marrow cells. Interactions between tumor cells and cells of the host microenvironment are essential to not only tumor cell survival but also their activation and proliferation into environment-modifying tumors. Through the production of RANKL, PTHrP, cytokines, and integrins, activated tumor cells stimulate osteoclastogenesis, enhance bone resorption, and subsequently release matrix-bound proteins that further promote tumor growth and bone resorption. In addition, alterations in the TGF-β/BMP and Wnt signaling pathways via tumor cell growth can either stimulate or suppress osteoblastic bone formation and function, leading to sclerotic or lytic bone disease, respectively. Hence, the presence of tumor cells in bone dysregulates bone remodeling, dramatically impairing skeletal integrity. Furthermore, through complex mechanisms, cells of the immune system interact with tumor cells to further impact bone remodeling. Lastly, with alterations in bone cell activity, the environment is permissive to promoting tumor growth further, suggesting an interdependence between tumor cells and bone cells in metastatic bone disease and multiple myeloma.

The chicken or the egg: PHEX, FGF23 and SIBLINGs unscrambled

The eggshell is an ancient innovation that helped the vertebrates' transition from the oceans and gain dominion over the land. Coincident with this conquest, several new eggshell and noncollagenous bone-matrix proteins (NCPs) emerged. The protein ovocleidin-116 is one of these proteins with an ancestry stretching back to the Triassic. Ovocleidin-116 is an avian homolog of Matrix Extracellular Phosphoglycoprotein (MEPE) and belongs to a group of proteins called Small Integrin-Binding Ligand Interacting Glycoproteins (SIBLINGs). The genes for these NCPs are all clustered on chromosome 5q in mice and chromosome 4q in humans. A unifying feature of the SIBLING proteins is an Acidic Serine Aspartate-Rich MEPE (ASARM)-associated motif. The ASARM motif and the released ASARM peptide play roles in mineralization, bone turnover, mechanotransduction, phosphate regulation and energy metabolism. ASARM peptides and motifs are physiological substrates for phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX), a Zn metalloendopeptidase. Defects in PHEX are responsible for X-linked hypophosphatemic rickets. PHEX interacts with another ASARM motif containing SIBLING protein, Dentin Matrix Protein-1 (DMP1). DMP1 mutations cause bone-renal defects that are identical with the defects caused by loss of PHEX function. This results in autosomal recessive hypophosphatemic rickets (ARHR). In both X-linked hypophosphatemic rickets and ARHR, increased fibroblast growth factor 23 (FGF23) expression occurs, and activating mutations in FGF23 cause autosomal dominant hypophosphatemic rickets (ADHR). ASARM peptide administration in vitro and in vivo also induces increased FGF23 expression. This review will discuss the evidence for a new integrative pathway involved in bone formation, bone-renal mineralization, renal phosphate homeostasis and energy metabolism in disease and health.

Osteoinduction: a review of old concepts with new standards

Since the discovery of osteoinduction in the early 20th century, innovative biomaterials with osteoinductive potential have emerged. Over the last 50 years, however, our ability to describe biological phenomena accurately has been improved dramatically by advancements in cell and molecular biology. The aim of this review is to divide the osteoinduction phenomenon into 3 principles: (1) mesenchymal cell recruitment, (2) mesenchymal differentiation to bone-forming osteoblasts, and (3) ectopic bone formation in vivo. Furthermore, this review formulates guidelines for in vitro and in vivo experimental testing for accurately defining new biomaterials as osteoinductive. The use of growth factors with osteoinductive potential in periodontal and oral surgery is discussed. These concepts and guidelines aim to guide the future direction of emerging biomaterials in bone regeneration.

Regulation of bone-renal mineral and energy metabolism: the PHEX, FGF23, DMP1, MEPE ASARM pathway

More than 300 million years ago, vertebrates emerged from the vast oceans to conquer gravity and the dry land. With this transition, new adaptations occurred that included ingenious changes in reproduction, waste secretion, and bone physiology. One new innovation, the egg shell, contained an ancestral protein (ovocleidin-116) that likely first appeared with the dinosaurs and was preserved through the theropod lineage in modern birds and reptiles. Ovocleidin-116 is an avian homolog of matrix extracellular phosphoglycoprotein (MEPE) and belongs to a group of proteins called short integrin-binding ligand-interacting glycoproteins (SIBLINGs). These proteins are all localized to a defined region on chromosome 5q in mice and chromosome 4q in humans. A unifying feature of SIBLING proteins is an acidic serine aspartate-rich MEPE-associated motif (ASARM). Recent research has shown that the ASARM motif and the released ASARM peptide have regulatory roles in mineralization (bone and teeth), phosphate regulation, vascularization, soft-tissue calcification, osteoclastogenesis, mechanotransduction, and fat energy metabolism. The MEPE ASARM motif and peptide are physiological substrates for PHEX, a zinc metalloendopeptidase. Defects in PHEX are responsible for X-linked hypophosphatemic rickets (HYP). There is evidence that PHEX interacts with another ASARM motif containing SIBLING protein, dentin matrix protein-1 (DMP1). DMP1 mutations cause bone and renal defects that are identical with the defects caused by a loss of PHEX function. This results in autosomal recessive hypophosphatemic rickets (ARHR). In both HYP and ARHR, increased FGF23 expression plays a major role in the disease and in autosomal dominant hypophosphatemic rickets (ADHR), FGF23 half-life is increased by activating mutations. ASARM peptide administration in vitro and in vivo also induces increased FGF23 expression. FGF23 is a member of the fibroblast growth factor (FGF) family of cytokines, which surfaced 500 million years ago with the boney fish (i.e., teleosts) that do not contain SIBLING proteins. In terrestrial vertebrates, FGF23, like SIBLING proteins, is expressed in the osteocyte. The boney fish, however, are an-osteocytic, so a physiological bone-renal link with FGF23 and the SIBLINGs was cemented when life ventured from the oceans to the land during the Triassic period, approximately 300 million years ago. This link has been revealed by recent research that indicates a competitive displacement of a PHEX-DMP1 interaction by an ASARM peptide that leads to increased FGF23 expression. This review discusses the new discoveries that reveal a novel PHEX, DMP1, MEPE, ASARM peptide, and FGF23 bone-renal pathway. This pathway impacts not only bone formation, bone-renal mineralization, and renal phosphate homeostasis but also energy metabolism. The study of this new pathway is relevant for developing therapies for several diseases: bone-teeth mineral loss disorders, renal osteodystrophy, chronic kidney disease and bone mineralization disorders (CKD-MBD), end-stage renal diseases, ectopic arterial-calcification, cardiovascular disease renal calcification, diabetes, and obesity.