Differential effects of transforming growth factor-beta on the synthesis of extracellular matrix proteins by normal fetal rat calvarial bone cell populations

Advances with Platelet-Rich Plasma for Bone Healing

Despite significant advances in the understanding and delivery of osteosynthesis, fracture non-union remains a challenging clinical problem in orthopaedic surgery. To bridge the gap, basic science characterization of fracture healing provides a platform to identify and target biological strategies to enhance fracture healing. Of immense interest, Platelet-rich plasma (PRP) is a point of care orthobiologic that has been extensively studied in bone and soft tissue healing given its relative ease of translation from the benchtop to the clinic. The aim of this narrative review is to describe and relate pre-clinical in-vitro and in-vivo findings to clinical observations investigating the efficacy of PRP to enhance bone healing for primary fracture management and non-union treatment. A particular emphasis is placed on the heterogeneity of PRP preparation techniques, composition, activation strategies, and delivery. In the context of existing data, the routine use of PRP to enhance primary fracture healing and non-union management cannot be supported. However, it is acknowledged that extensive heterogeneity of PRP treatments in clinical studies adds obscurity; ultimately, refinement (and consensus) of PRP treatments for specific clinical indications, including repetition studies are warranted.

A review of platelet-rich plasma for enteric fistula management

Enteric fistula (EF), a serious complication after abdominal surgery, refers to unnatural communication between the gastrointestinal tract and the skin or other hollow organs. It is associated with infection, massive fluid/electrolyte loss, and malnutrition, resulting in an unhealed course. Despite advances in surgical techniques, wound care, infection control, and nutritional support, EF remains associated with considerable morbidity and mortality. Autologous platelet-rich plasma (PRP) containing elevated platelet concentrations has been proposed to promote healing in many tissues. However, the mechanism of action of PRP in EF treatment remains unclear owing to its complicated clinical manifestations. In this review, we summarized the clinical approaches, outlined the principal cytokines involved in the healing effects, and discussed the advantages of PRP for EF therapy. In addition, we defined the mechanism of autologous PRP in EF management, which is essential for further developing EF therapies.

β-TCP/S53P4 Scaffolds Obtained by Gel Casting: Synthesis, Properties, and Biomedical Applications

The objective of this study was to investigate the osteogenic and antimicrobial effect of bioactive glass S53P4 incorporated into β-tricalcium phosphate (β-TCP) scaffolds in vitro and the bone neoformation in vivo. β-TCP and β-TCP/S53P4 scaffolds were prepared by the gel casting method. Samples were morphologically and physically characterized through X-ray diffraction (XRD) and scanning electron microscope (SEM). In vitro tests were performed using MG63 cells. American Type Culture Collection reference strains were used to determine the scaffold's antimicrobial potential. Defects were created in the tibia of New Zealand rabbits and filled with experimental scaffolds. The incorporation of S53P4 bioglass promotes significant changes in the crystalline phases formed and in the morphology of the surface of the scaffolds. The β-TCP/S53P4 scaffolds did not demonstrate an in vitro cytotoxic effect, presented similar alkaline phosphatase activity, and induced a significantly higher protein amount when compared to β-TCP. The expression of Itg β1 in the β-TCP scaffold was higher than in the β-TCP/S53P4, and there was higher expression of Col-1 in the β-TCP/S53P4 group. Higher bone formation and antimicrobial activity were observed in the β-TCP/S53P4 group. The results confirm the osteogenic capacity of β-TCP ceramics and suggest that, after bioactive glass S53P4 incorporation, it can prevent microbial infections, demonstrating to be an excellent biomaterial for application in bone tissue engineering.

TGF-β1 upregulates secreted protein acidic and rich in cysteine expression in human granulosa-lutein cells: a potential mechanism for the pathogenesis of ovarian hyperstimulation syndrome

BACKGROUND

Ovarian hyperstimulation syndrome (OHSS) is a serious complication during in vitro fertilization (IVF) treatment. The upregulation of ovarian transforming growth factor-beta 1 (TGF-β1) is involved in the development of OHSS. The secreted protein acidic and rich in cysteine (SPARC) is a secreted multifunctional matricellular glycoprotein. Although the regulatory effects of TGF-β1 on SPARC expression have been reported, whether TGF-β1 regulates SPARC expression in the human ovary remains unknown. In addition, the role of SPARC in the pathogenesis of OHSS is unclear.

METHODS

A steroidogenic human ovarian granulosa-like tumor cell line, KGN, and primary culture of human granulosa-lutein (hGL) cells obtained from patients undergoing IVF treatment were used as experimental models. OHSS was induced in rats, and ovaries were collected. Follicular fluid samples were collected from 39 OHSS and 35 non-OHSS patients during oocyte retrieval. The underlying molecular mechanisms mediating the effect of TGF-β1 on SPARC expression were explored by a series of in vitro experiments.

RESULTS

TGF-β1 upregulated SPARC expression in both KGN and hGL cells. The stimulatory effect of TGF-β1 on SPARC expression was mediated by SMAD3 but not SMAD2. The transcription factors, Snail and Slug, were induced in response to the TGF-β1 treatment. However, only Slug was required for the TGF-β1-induced SPARC expression. Conversely, we found that the knockdown of SPARC decreased Slug expression. Our results also revealed that SPARC was upregulated in the OHSS rat ovaries and in the follicular fluid of OHSS patients. Knockdown of SPARC attenuated the TGF-β1-stimulated expression of vascular endothelial growth factor (VEGF) and aromatase, two markers of OHSS. Moreover, the knockdown of SPARC reduced TGF-β1 signaling by downregulating SMAD4 expression.

CONCLUSIONS

By illustrating the potential physiological and pathological roles of TGF-β1 in the regulation of SPARC in hGL cells, our results may serve to improve current strategies used to treat clinical infertility and OHSS. Video Abstract.

Osteoblast role in the pathogenesis of rheumatoid arthritis

In the pathogenesis of several rheumatic diseases, such as rheumatoid arthritis, spondyloarthritis, osteoarthritis, osteoporosis, alterations in osteoblast growth, differentiation and activity play a role. In particular, in rheumatoid arthritis bone homeostasis is perturbed: in addition to stimulating the pathologic bone resorption process performed by osteoclasts in course of rheumatoid arthritis, proinflammatory cytokines (such as Tumor Necrosis factor-α, Interleukin-1) can also inhibit osteoblast differentiation and function, resulting in net bone loss. Mouse models of rheumatoid arthritis showed that complete resolution of inflammation (with maximal reduction in the expression of pro-inflammatory factors) is crucial for bone healing, performed by osteoblasts activity. In fact, abnormal activity of factors and systems involved in osteoblast function in these patients has been described. A better understanding of the pathogenic mechanisms involved in osteoblast dysregulation could contribute to explain the generalized and focal articular bone loss found in rheumatoid arthritis. Nevertheless, these aspects have not been frequently and directly evaluated in studies. This review article is focused on analysis of the current knowledge about the role of osteoblast dysregulation occurring in rheumatoid arthritis: a better knowledge of these mechanisms could contribute to the realization of new therapeutic strategies.

The role of stromal cells in inflammatory bone loss

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation, local and systemic bone loss and a lack of compensatory bone repair. Fibroblast-like synoviocytes (FLS) are the most abundant cells of the stroma and a key population in autoimmune diseases such as RA. An increasing body of evidence suggests that these cells play not only an important role in chronic inflammation and synovial hyperplasia, but also impact bone remodelling. Under inflammatory conditions FLS release inflammatory cytokines, regulate bone destruction and formation and communicate with immune cells to control bone homeostasis. Other stromal cells, such as osteoblasts and terminally differentiated osteoblasts, termed osteocytes, are also involved in the regulation of bone homeostasis and are dysregulated during inflammation. This review highlights our current understanding of how stromal cells influence the balance between bone formation and bone destruction. Increasing our understanding of these processes is critical to enable the development of novel therapeutic strategies with which to treat bone loss in RA.

Is SPARC an Evolutionarily Conserved Collagen Chaperone?

The construction of collagen fiber scaffolds, which provide the structural integrity of the extracellular matrix of connective tissues and basement membranes, is initiated by a complex mechanism of protein-folding, whereby pro-collagen α-chains are assembled into triple-helical procollagen molecules. This unique assembly of the procollagen molecules is guided by several endoplasmic reticulum resident molecular chaperones, including HSP47, which dissociates from procollagen molecules prior to their transport from the endoplasmic reticulum into the cis-Golgi network. SPARC, an evolutionarily conserved collagen-binding glycoprotein, which is frequently co-expressed with collagen in rapidly remodeling tissues, binds to the triple-helical region of procollagen molecules. Analysis of data from genome projects indicates that specific amino acids and sequences in SPARC that are critical for collagen binding are evolutionarily conserved in organisms ranging from nematodes to mammals. Studies of invertebrates, which do not encode HSP47, indicate that SPARC expression is required for the deposition of collagen IV in basal lamina during embryonic development. In mammals, defects in collagen deposition have been observed in normal and wound-healing tissues in the absence of SPARC expression. Based on these and other observations, we propose that intracellular SPARC acts as a collagen molecular chaperone in the endoplasmic reticulum, and that in higher organisms, SPARC acts in concert with HSP47 to ensure that only correctly folded procollagen molecules exit the endoplasmic reticulum. In contrast to HSP47, SPARC is transported from the endoplasmic reticulum through the Golgi network and into secretory vesicles for exocytosis at the plasma membrane. Hence, SPARC may also play a role in regulating post-endoplasmic reticulum events that promote collagen fibrillogenesis.

AFAP1 Is a Novel Downstream Mediator of TGF-β1 for CCN2 Induction in Osteoblasts

Background

CCN2 acts as an anabolic growth factor to regulate osteoblast differentiation and function. CCN2 is induced by TGF-β1 and acts as a mediator of TGF-β1 induced matrix production in osteoblasts and Src is required for CCN2 induction by TGF-β1; however, the molecular mechanisms that control CCN2 induction in osteoblasts are poorly understood. AFAP1 binds activated forms of Src and can direct the activation of Src in certain cell types, however a role for AFAP1 downstream of TGF-β1 or in osteoblats is undefined. In this study, we investigated the role of AFAP1 for CCN2 induction by TGF-β1 in primary osteoblasts.

Results

We demonstrated that AFAP1 expression in osteoblasts occurs in a biphasic pattern with maximal expression levels occurring during osteoblast proliferation (~day 3), reduced expression during matrix production/maturation (~day 14–21), an a further increase in expression during mineralization (~day 21). AFAP1 expression is induced by TGF-β1 treatment in osteoblasts during days 7, 14 and 21. In osteoblasts, AFAP1 binds to Src and is required for Src activation by TGF-β1 and CCN2 promoter activity and protein induction by TGF-β1 treatment was impaired using AFAP1 siRNA, indicating the requirement of AFAP1 for CCN2 induction by TGF-β1. We also demonstrated that TGF-β1 induction of extracellular matrix protein collagen XIIa occurs in an AFAP1 dependent fashion.

Conclusions

This study demonstrates that AFAP1 is an essential downstream signaling component of TGF-β1 for Src activation, CCN2 induction and collagen XIIa in osteoblasts.

Cell density sensing alters TGF-β signaling in a cell-type-specific manner, independent from Hippo pathway activation

Cell-cell contacts inhibit cell growth and proliferation in part by activating the Hippo pathway that drives the phosphorylation and nuclear exclusion of the transcriptional coactivators YAP and TAZ. Cell density and Hippo signaling have also been reported to block transforming growth factor β (TGF-β) responses, based on the ability of phospho-YAP/TAZ to sequester TGF-β-activated SMAD complexes in the cytoplasm. Herein, we provide evidence that epithelial cell polarization interferes with TGF-β signaling well upstream and independent of cytoplasmic YAP/TAZ. Rather, polarized basolateral presentation of TGF-β receptors I and II deprives apically delivered TGF-β of access to its receptors. Basolateral ligand delivery nonetheless remains entirely effective to induce TGF-β responses. These data demonstrate that cell-type-specific inhibition of TGF-β signaling by cell density is restricted to polarized epithelial cells and reflects the polarized distribution of TGF-β receptors, which thus affects SMAD activation irrespective of Hippo pathway activation.

Autologous Platelet Gel

Leg ulcers represent a particularly disabling complication in patients with sickle cell disease (SCD). Platelet gel (PG) is a novel therapeutic strategy used for accelerating wound healing of a wide range of tissues through the continuous release of platelet growth factors. Here, we describe the use of PG preparation according to Anitua’s PRGF (preparations rich in growth factors) protocol for treating chronic nonhealing ulcers in patients with SCD. A positive response occurred in 3 patients with an area reduction of 85.7% to 100%, which occurred within 7 to 10 weeks, and a 35.2% and 20.5% of area reduction in 2 other patients, who however, had large ulcers. After calcium chloride addition, the platelet-rich plasmas demonstrated enhanced platelet-derived growth factors–BB ( P < .001), transforming growth factor-β1 ( P = .015), vascular endothelial growth factors ( P = .03), and hepatocyte growth factors (nonsignificant) secretion. Furthermore, calcium chloride addition induced a significant decrease in platelet number ( P = .0134) and there was no leukocyte detection in the PG product. These results demonstrate that PG treatment might impact the healing of leg ulcers in sickle cell disease, especially in patients with small ulcers.

Exogenous activation of BMP-2 signaling overcomes TGFβ-mediated inhibition of osteogenesis in Marfan embryonic stem cells and Marfan patient-specific induced pluripotent stem cells

Marfan syndrome (MFS) is a hereditary disease caused by mutations in the gene encoding Fibrillin-1 (FBN1) and characterized by a number of skeletal abnormalities, aortic root dilatation, and sometimes ectopia lentis. Although the molecular pathogenesis of MFS was attributed initially to a structural weakness of the fibrillin-rich microfibrils within the extracellular matrix, more recent results have documented that many of the pathogenic abnormalities in MFS are the result of alterations in TGFβ signaling. Mutations in FBN1 are therefore associated with increased activity and bioavailability of TGF-β1, which is suspected to be the basis for phenotypical similarities of FBN1 mutations in MFS and mutations in the receptors for TGFβ in Marfan syndrome-related diseases. We have previously demonstrated that unique skeletal phenotypes observed in human embryonic stem cells carrying the monogenic FBN1 mutation (MFS cells) are faithfully phenocopied by cells differentiated from induced pluripotent-stem cells (MFSiPS) derived independently from MFS patient fibroblasts. In this study, we aimed to determine further the biochemical features of transducing signaling(s) in MFS stem cells and MFSiPS cells highlighting a crosstalk between TGFβ and BMP signaling. Our results revealed that enhanced activation of TGFβ signaling observed in MFS cells decreased their endogenous BMP signaling. Moreover, exogenous BMP antagonized the enhanced TGFβ signaling in both MFS stem cells and MFSiPS cells therefore, rescuing their ability to undergo osteogenic differentiation. This study advances our understanding of molecular mechanisms underlying the pathogenesis of bone loss/abnormal skeletogenesis in human diseases caused by mutations in FBN1.

Research progress in the mechanism of effect of PRP in bone deficiency healing

Platelet-rich plasma (PRP) therapy is a recently developed technique that uses a concentrated portion of autologous blood to try to improve and accelerate the healing of various tissues. There is a considerable interest in using these PRP products for the treatment used in bone deficiency healing. Because PRP products are safe and easy to prepare and administer, there has been increased attention toward using PRP in numerous clinical settings. The benefits of PRP therapy appear to be promising, and many investigators are exploring the ways in which this therapy can be used in the clinical setting. At present, the molecular mechanisms of bone defect repair studies have focused on three aspects of the inflammatory cytokines, growth factors and angiogenic factors. The role of PRP works mainly through these three aspects of bone repair. The purpose of this paper is to review the current evidence on the mechanism of the effect of PRP in bone deficiency healing.

Integration of multiple signaling pathways determines differences in the osteogenic potential and tissue regeneration of neural crest-derived and mesoderm-derived calvarial bones

The mammalian skull vault, a product of a unique and tightly regulated evolutionary process, in which components of disparate embryonic origin are integrated, is an elegant model with which to study osteoblast biology. Our laboratory has demonstrated that this distinct embryonic origin of frontal and parietal bones confer differences in embryonic and postnatal osteogenic potential and skeletal regenerative capacity, with frontal neural crest derived osteoblasts benefitting from greater osteogenic potential. We outline how this model has been used to elucidate some of the molecular mechanisms which underlie these differences and place these findings into the context of our current understanding of the key, highly conserved, pathways which govern the osteoblast lineage including FGF, BMP, Wnt and TGFβ signaling. Furthermore, we explore recent studies which have provided a tantalizing insight into way these pathways interact, with evidence accumulating for certain transcription factors, such as Runx2, acting as a nexus for cross-talk.

Prospective potency of TGF-β1 on maintenance and regeneration of periodontal tissue

Periodontal ligament (PDL) tissue, central in the periodontium, plays crucial roles in sustaining tooth in the bone socket. Irreparable damages of this tissue provoke tooth loss, causing a decreased quality of life. The question arises as to how PDL tissue is maintained or how the lost PDL tissue can be regenerated. Stem cells included in PDL tissue (PDLSCs) are widely accepted to have the potential to maintain or regenerate the periodontium, but PDLSCs are very few in number. In recent studies, undifferentiated clonal human PDL cell lines were developed to elucidate the applicable potentials of PDLSCs for the periodontal regenerative medicine based on cell-based tissue engineering. In addition, it has been suggested that transforming growth factor-beta 1 is an eligible factor for the maintenance and regeneration of PDL tissue.

Matricellular proteins in cardiac adaptation and disease

The term matricellular proteins describes a family of structurally unrelated extracellular macromolecules that, unlike structural matrix proteins, do not play a primary role in tissue architecture, but are induced following injury and modulate cell-cell and cell-matrix interactions. When released to the matrix, matricellular proteins associate with growth factors, cytokines, and other bioactive effectors and bind to cell surface receptors transducing signaling cascades. Matricellular proteins are upregulated in the injured and remodeling heart and play an important role in regulation of inflammatory, reparative, fibrotic and angiogenic pathways. Thrombospondin (TSP)-1, -2, and -4 as well as tenascin-C and -X secreted protein acidic and rich in cysteine (SPARC), osteopontin, periostin, and members of the CCN family (including CCN1 and CCN2/connective tissue growth factor) are involved in a variety of cardiac pathophysiological conditions, including myocardial infarction, cardiac hypertrophy and fibrosis, aging-associated myocardial remodeling, myocarditis, diabetic cardiomyopathy, and valvular disease. This review discusses the properties and characteristics of the matricellular proteins and presents our current knowledge on their role in cardiac adaptation and disease. Understanding the role of matricellular proteins in myocardial pathophysiology and identification of the functional domains responsible for their actions may lead to design of peptides with therapeutic potential for patients with heart disease.

Sulfated hyaluronan and chondroitin sulfate derivatives interact differently with human transforming growth factor-β1 (TGF-β1)

This study demonstrates that the modification of hyaluronan (hyaluronic acid; Hya) and chondroitin sulfate (CS) with sulfate groups leads to different binding affinities for recombinant human transforming growth factor-β1 (TGF-β1) for comparable average degrees of sulfation (DS). In general, Hya derivates showed higher binding strength than CS derivatives. In either case, a higher degree of sulfation leads to a stronger interaction. The high-sulfated hyaluronan sHya3 (average DS≈3) exhibited the tightest interaction with TGF-β1, as determined by surface plasmon resonance and enzyme-linked immunosorbent assay. The binding strength was significantly weakened by carboxymethylation. Unmodified Hya and low-sulfated, native CS showed weak or no binding affinity. The interaction characteristics of the different sulfated glycosaminoglycans are promising for incorporation into bioengineered coatings of biomaterials to modulate growth factor binding in medical applications.

A novel library screen identifies immunosuppressors that promote osteoblast differentiation

Bone homeostasis can be compromised by an increase in osteoclast-mediated resorption and/or a decrease in osteoblast-mediated bone deposition. While many efforts have focused on treating osteoclast resorption, there has been less emphasis on identifying strategies for promoting osteoblast function. Herein, we describe a high-throughput screening assay to select for small molecules that augment bone morphogenetic protein-2 (BMP-2)-mediated osteoblast lineage commitment. After an initial screen of 5405 compounds; consisting of FDA-approved drugs, known bioactives, and compounds with novel chemical makeup, we identified 45 small molecules that promoted osteoblast commitment. Of the 45 candidates, there was a broad array of classes that included nine retinoid analogs/derivatives and four immunosuppressants, notably rapamycin and FK-506, which were chosen for further study. Treatment of osteoblast precursor cells with rapamycin or FK-506, either alone, or synergistically with BMP-2, increased levels of phospho-Smad 1/5/8 protein and transcription of Runx-2, Osx and Smad-7, consistent with a role in promoting osteoblast differentiation. Only FK-506 was able to enhance osteocalcin transcripts and Alizarin Red staining, both late markers for differentiation. When osteoblast differentiation was suppressed with exogenous TGF-β1 treatment, rapamycin (but not FK-506) was able to rescue expression of differentiation markers, indicating distinct but overlapping activity of these compounds. Collectively, these data add to an understanding of pathways engaged in osteoblastogenesis, support a role for non-redundant immunosuppressant signaling, and provide a novel approach for the discovery of potentially therapeutic compounds that affect bone remodeling.

Low-level laser therapy induces the expressions of BMP-2, osteocalcin, and TGF-β1 in hypoxic-cultured human osteoblasts

The aim of this study was to examine the effect of low-level laser therapy (LLLT) on the cell viability and the expression of hypoxia-inducible factor-1s (HIF-1s), bone morphogenic protein-2 (BMP-2), osteocalcin, type I collagen, transforming growth factor-β1 (TGF-β1), and Akt in hypoxic-cultured human osteoblasts. Human fetal osteoblast cells (cell line 1.19) were cultured under 1 % oxygen tension for 72 h. Cell cultures were divided into two groups. At the experimental side, low-level laser (808 nm, GaAlAs diode) was applied at 0, 24, and 48 h. After irradiation, each cell culture was incubated 24 h more under hypoxia. Total energy was 1.2, 2.4, and 3.6 J/cm(2), respectively. Non-irradiated cultures served as controls. Comparisons between the two groups were analyzed by t test; a p value <0.05 was considered statistically significant. Hypoxia resulted in a decrease in the expression of type I collagen, osteocalcin, and TGF-β1 (p < 0.001, p < 0.001, and p < 0.01, respectively). Cell viability and BMP-2 expression were not decreased by hypoxic condition. On the other hand, LLLT on hypoxic-cultured osteoblast promoted the expression of BMP-2, osteocalcin, and TGF-β1 (p < 0.05, p < 0.01, and p < 0.001, respectively). Cell proliferation was also increased time-dependently. However, hypoxia decreased in type I collagen expression (p < 0.001), and LLLT did not affect type I collagen expression in hypoxic-cultured osteoblasts. Furthermore, LLLT inhibited HIF-1 and Akt expression in hypoxic conditioned osteoblasts. We concluded that LLLT induces the expression of BMP-2, osteocalcin, and TGF- β1 in 1 % hypoxic-cultured human osteoblasts.

Ets-1 is essential for connective tissue growth factor (CTGF/CCN2) induction by TGF-β1 in osteoblasts

Background

Ets-1 controls osteoblast differentiation and bone development; however, its downstream mechanism of action in osteoblasts remains largely undetermined. CCN2 acts as an anabolic growth factor to regulate osteoblast differentiation and function. CCN2 is induced by TGF-β1 and acts as a mediator of TGF-β1 induced matrix production in osteoblasts; however, the molecular mechanisms that control CCN2 induction are poorly understood. In this study, we investigated the role of Ets-1 for CCN2 induction by TGF-β1 in primary osteoblasts.

Results

We demonstrated that Ets-1 is expressed and induced by TGF-β1 treatment in osteoblasts, and that Ets-1 over-expression induces CCN2 protein expression and promoter activity at a level similar to TGF-β1 treatment alone. Additionally, we found that simultaneous Ets-1 over-expression and TGF-β1 treatment synergize to enhance CCN2 induction, and that CCN2 induction by TGF-β1 treatment was impaired using Ets-1 siRNA, demonstrating the requirement of Ets-1 for CCN2 induction by TGF-β1. Site-directed mutagenesis of eight putative Ets-1 motifs (EBE) in the CCN2 promoter demonstrated that specific EBE sites are required for CCN2 induction, and that mutation of EBE sites in closer proximity to TRE or SBE (two sites previously shown to regulate CCN2 induction by TGF-β1) had a greater effect on CCN2 induction, suggesting potential synergetic interaction among these sites for CCN2 induction. In addition, mutation of EBE sites prevented protein complex binding, and this protein complex formation was also inhibited by addition of Ets-1 antibody or Smad 3 antibody, demonstrating that protein binding to EBE motifs as a result of TGF-β1 treatment require synergy between Ets-1 and Smad 3.

Conclusions

This study demonstrates that Ets-1 is an essential downstream signaling component for CCN2 induction by TGF-β1 in osteoblasts, and that specific EBE sites in the CCN2 promoter are required for CCN2 promoter transactivation in osteoblasts.

The regulatory function of SPARC in vascular biology

SPARC is a matricellular protein, able to modulate cell/ECM interactions and influence cell responses to growth factors, and therefore is particularly attuned to contribute to physiological processes involving changes in ECM and cell mobilization. Indeed, the list of biological processes affected by SPARC includes wound healing, tumor progression, bone formation, fibrosis, and angiogenesis. The process of angiogenesis is complex and involves a number of cellular processes such as endothelial cell proliferation, migration, ECM degradation, and synthesis, as well as pericyte recruitment to stabilize nascent vessels. In this review, we will summarize current results that explore the function of SPARC in the regulation of angiogenic events with a particular emphasis on the modulation of growth factor activity by SPARC in the context of blood vessel formation. The primary function of SPARC in angiogenesis remains unclear, as SPARC activity in some circumstances promotes angiogenesis and in others is more consistent with an anti-angiogenic activity. Undoubtedly, the mercurial nature of SPARC belies a redundancy of functional proteins in angiogenesis as well as cell-type-specific activities that alter signal transduction events in response to unique cellular milieus. Nonetheless, the investigation of cellular mechanisms that define functional activities of SPARC continue to contribute novel and exciting paradigms to vascular biology.

Effects of enamel matrix derivative and transforming growth factor-β1 on human osteoblastic cells

BACKGROUND

Extracellular matrix proteins are key factors that influence the regenerative capacity of tissues. The objective of the present study was to evaluate the effects of enamel matrix derivative (EMD), TGF-β1, and the combination of both factors (EMD+TGF-β1) on human osteoblastic cell cultures.

METHODS

Cells were obtained from alveolar bone of three adult patients using enzymatic digestion. Effects of EMD, TGF-β1, or a combination of both were analyzed on cell proliferation, bone sialoprotein (BSP), osteopontin (OPN) and alkaline phosphatase (ALP) immunodetection, total protein synthesis, ALP activity and bone-like nodule formation.

RESULTS

All treatments significantly increased cell proliferation compared to the control group at 24 h and 4 days. At day 7, EMD group showed higher cell proliferation compared to TGF-β1, EMD + TGF-β1 and the control group. OPN was detected in the majority of the cells for all groups, whereas fluorescence intensities for ALP labeling were greater in the control than in treated groups; BSP was not detected in all groups. All treatments decreased ALP levels at 7 and 14 days and bone-like nodule formation at 21 days compared to the control group.

CONCLUSIONS

The exposure of human osteoblastic cells to EMD, TGF-β1 and the combination of factors in vitro supports the development of a less differentiated phenotype, with enhanced proliferative activity and total cell number, and reduced ALP activity levels and matrix mineralization.

Biphasic effects of transforming growth factor β on bone morphogenetic protein-induced osteoblast differentiation

Bone morphogenetic proteins (BMPs) exert an important role in skeletal development, adult bone homeostasis, and fracture healing and have demonstrated clinical utility for bone regeneration. However, BMPs fall short as regenerative agents because high doses need to be used to obtain therapeutic effects. Determining the molecular mechanisms controlling BMP-induced bone formation may lead to the development of more effective BMP-based therapies. To identify kinases mediating BMP-induced osteoblast differentiation, we performed an siRNA screen to find kinases modulating BMP-6-induced alkaline phosphatase (ALP) activity. Surprisingly, although transforming growth factor β (TGF-β) generally is considered to antagonize BMP-induced osteoblast differentiation, C2C12  cells transfected with siRNAs targeting TGF-β receptors displayed reduced BMP-6-induced ALP activity. Furthermore, pharmacologic inhibitors blocking the TGF-β type I receptor impaired BMP-induced ALP activity in KS483 and C2C12 cells and mineralization of KS483 cells. Consistently, costimulation with BMPs and TGF-β further increased expression of osteoblast-specific genes, ALP activity, and mineralization of KS483 cells and primary mesenchymal stem cells compared with BMPs alone. The stimulatory and inhibitory effects of TGF-β were found to depend on timing and duration of the costimulation. TGF-β inhibited BMP-induced activation of a BMP-Smad-dependent luciferase reporter, suggesting that the stimulatory effect of TGF-β is not due to increased BMP-Smad activity. TGF-β also inhibited the BMP-induced expression of the BMP antagonist noggin and prolonged BMP activity. In conclusion, TGF-β, besides acting as an inhibitor, also can, by dampening the noggin-mediated negative-feedback loop, enhance BMP-induced osteoblast differentiation, which might be beneficial in fracture healing.

The use of autologous blood-derived growth factors in bone regeneration

Platelet-rich plasma (PRP) is defined as a portion of the plasma fraction of autologous blood having platelet concentrations above baseline. When activated the platelets release growth factors that play an essential role in bone healing such as Platelet-derived Growth Factor, Transforming Growth Factor-β, Vascular Endothelial Growth Factor and others.Multiple basic science and in vivo animal studies agree that PRP has a role in the stimulation of the healing cascade in ligament, tendon, muscle cartilage and in bone regeneration in the last years PRP had a widespread diffusion in the treatment of soft tissue and bone healing.The purpose of this review is to describe the biological properties of platelets and its factors, the methods used for producing PRP, to provide a background on the underlying basic science and an overview of evidence based medicine on clinical application of PRP in bone healing.

TGF-β1 as possible link between loss of bone mineral density and chronic inflammation

Background

The TGF family plays a key role in bone homeostasis. Systemic or topic application of proteins of this family apparently positively affects bone healing in vivo. However, patients with chronic inflammation, having increased TGF-β₁ serum-levels, often show reduced bone mineral content and disturbed bone healing. Therefore, we wanted to identify intracellular mechanisms induced by chronic presence of TGF-β₁ and their possible role in bone homeostasis in primary human osteoblasts.

Methodology/Principal Findings

Osteoblasts were isolated from femur heads of patients undergoing total hip replacement. Adenoviral reporter assays showed that in primary human osteoblasts TGF-β₁ mediates its signal via Smad2/3 and not Smad1/5/8. It induces proliferation as an intermediate response but decreases AP-activity and inorganic matrix production as a late response. In addition, expression levels of osteoblastic markers were strongly regulated (AP↓; Osteocalcin↓; Osteopontin↑; MGP↓; BMP 2↓; BSP2↓; OSF2↓; Osteoprotegerin↓; RANKL↑) towards an osteoclast recruiting phenotype. All effects were blocked by inhibition of Smad2/3 signaling with the Alk5-Inhibitor (SB431542). Interestingly, a rescue experiment showed that reduced AP-activities did not recover to base line levels, even 8 days after stopping the TGF-β₁ application.

Conclusions/Significance

In spite of the initial positive effects on cell proliferation, it is questionable if continuous Smad2/3 phosphorylation is beneficial for bone healing, because decreased AP-activity and BMP2 levels indicate a loss of function of the osteoblasts. Thus, inhibition of Smad2/3 phosphorylation might positively influence functional activity of osteoblasts in patients with chronically elevated TGF-β₁ levels and thus, could lead to an improved bone healing in vivo.

Growth factors and gene expression of stem cells: bone marrow compared with peripheral blood

PURPOSE

To evaluate and compare the presence of cytokines and growth factors in both bone marrow (BM) and peripheral blood.

MATERIAL

Samples of autogenous BM aspirate and peripheral blood (PB) from 7 patients ranging in age from 49 to 80 years were analyzed with real-time polymerase chain reaction technology to identify and compare selected gene expression for specific cytokines and growth factors. The genes selected for analysis included those involved in osteogenesis, hematogenesis, angiogenesis, extracellular matrix molecules, and cell-adhesion molecules. A maximum of 4 cc';s BM aspirate was taken from the anterior iliac crest and 0.5 mL of venous blood was drawn from each of 7 patients.

RESULTS

The results of the analysis indicate that both circulating blood and BM aspirate contain large quantities of a host of growth factors and cytokines. More platelet-derived growth factor is expressed in patient blood (PB) than in BM. Vascular endothelial growth factor alpha is expressed slightly greater in BM and vascular endothelial growth factor beta is slightly more prominent in PB. Transforming growth factors (TGFs) TGFA, TGFB1, and TGFB3 were equally expressed in BM and PB, and TGFB2 had a greater expression in PB. Bone morphogenetic proteins (BMPs) 1, 3, 7, 8B, R1A, and PR2 were almost equally expressed in BM and PB. BMPs 4 and 6 were expressed greater in PB. BMP2 was expressed more in BM. Extracellular matrix factors were equally expressed in PB and BM. Mesenchymal stem cell lineage markers varied in PB and BMA, and hematopoietic stem cell lineage markers were expressed more in PB than BM. Gene expression for angiogenic factors were equally expressed in PB and BM.

CONCLUSION

In this investigation, specific cytokines and growth factors in BM are compared with those in peripheral blood. Each has similar biologic effects and most expressed equally in BM and PB. However, BMP2 and vascular endothelial growth factor alpha had greater expression in BM.

Src is a major signaling component for CTGF induction by TGF-beta1 in osteoblasts

Connective tissue growth factor (CTGF/CCN2) is induced by transforming growth factor beta1 (TGF-beta1) where it acts as a downstream mediator of TGF-beta1 induced matrix production in osteoblasts. We have shown the requirement of Src, Erk, and Smad signaling for CTGF induction by TGF-beta1 in osteoblasts; however, the potential interaction among these signaling pathways remains undetermined. In this study we demonstrate that TGF-beta1 activates Src kinase in ROS17/2.8 cells and that treatment with the Src family kinase inhibitor PP2 prevents Src activation and CTGF induction by TGF-beta1. Additionally, inhibiting Src activation prevented Erk activation, Smads 2 and 3 activation and nuclear translocation by TGF-beta1, demonstrating that Src is an essential upstream signaling partner of both Erk and Smads in osteoblasts. MAPKs such as Erk can modulate the Smad pathway directly by mediating the phosphorylation of Smads or indirectly through activation/inactivation of required nuclear co-activators that mediate Smad DNA binding. When we treated cells with the Erk inhibitor, PD98059, it inhibited TGF-beta1-induced CTGF protein expression but had no effect on Src activation, Smad activation or Smad nuclear translocation. However PD98059 impaired transcriptional complex formation on the Smad binding element (SBE) of the CTGF promoter, demonstrating that Erk activation was required for SBE transactivation. These data demonstrate that Src is an essential upstream signaling transducer of Erk and Smad signaling with respect to TGF-beta1 in osteoblasts and that Smads and Erk function independently but are both essential for forming a transcriptionally active complex on the CTGF promoter in osteoblasts.

Significant type I and type III collagen production from human periodontal ligament fibroblasts in 3D peptide scaffolds without extra growth factors

We here report the development of two peptide scaffolds designed for periodontal ligament fibroblasts. The scaffolds consist of one of the pure self-assembling peptide scaffolds RADA16 through direct coupling to short biologically active motifs. The motifs are 2-unit RGD binding sequence PRG (PRGDSGYRGDS) and laminin cell adhesion motif PDS (PDSGR). RGD and laminin have been previously shown to promote specific biological activities including periodontal ligament fibroblasts adhesion, proliferation and protein production. Compared to the pure RADA16 peptide scaffold, we here show that these designer peptide scaffolds significantly promote human periodontal ligament fibroblasts to proliferate and migrate into the scaffolds (for approximately 300 microm/two weeks). Moreover these peptide scaffolds significantly stimulated periodontal ligament fibroblasts to produce extracellular matrix proteins without using extra additional growth factors. Immunofluorescent images clearly demonstrated that the peptide scaffolds were almost completely covered with type I and type III collagens which were main protein components of periodontal ligament. Our results suggest that these designer self-assembling peptide nanofiber scaffolds may be useful for promoting wound healing and especially periodontal ligament tissue regeneration.

Thrombospondin-2 and SPARC/osteonectin are critical regulators of bone remodeling

Thrombospondin-2 (TSP2) and osteonectin/BM-40/SPARC are matricellular proteins that are highly expressed by bone cells. Mice deficient in either of these proteins show phenotypic alterations in the skeleton, and these phenotypes are most pronounced under conditions of altered bone remodeling. For example, TSP2-null mice have higher cortical bone volume and are resistant to bone loss associated with ovariectomy, whereas SPARC-null mice have decreased trabecular bone volume and fail to demonstrate an increase in bone mineral density in response to a bone-anabolic parathyroid hormone treatment regimen. In vitro, marrow stromal cell (MSC) osteoprogenitors from TSP2-null mice have increased proliferation but delayed formation of mineralized matrix. Similarly, in cultures of SPARC-null MSCs, osteoblastic differentiation and mineralized matrix formation are decreased. Overall, both TSP2 and SPARC positively influence osteoblastic differentiation. Intriguingly, both of these matricellular proteins appear to impact MSC fate through mechanisms that could involve the Notch signaling system. This review provides an overview of the role of TSP2 and SPARC in regulating bone structure, function, and remodeling, as determined by both in vitro and in vivo studies.

The biology of platelet-rich plasma and its application in oral surgery: literature review

Platelet-rich plasma (PRP) is a new approach in tissue regeneration and a developing area for clinicians and researchers. It is used in various surgical fields, including oral and maxillofacial surgery. PRP is prepared from the patient's own blood and contains growth factors that influence wound healing. Of these growth factors, platelet-derived growth factor, transforming growth factor, insulin-like growth factor, and epidermal growth factor play a pivotal role in tissue repair mechanisms. Although the growth factors and mechanisms involved are still poorly understood, the easy application of PRP in the clinic and its possible beneficial outcome, including reduction of bleeding, rapid soft tissue healing, and bone regeneration, hold promise for new treatment approaches. However, animal studies and human trials demonstrate conflicting results regarding the application of PRP. Therefore the aim of this literature review is to evaluate the scientific evidence regarding the use of PRP in dentistry, to describe the different bioactive substances included in PRP and their participation in the healing process, to elucidate the different techniques and available technology for PRP preparation, to review animal and human studies, to clarify risks, and to provide guidance for future research.

The biology of platelet-rich plasma and its application in trauma and orthopaedic surgery: a review of the literature

Although mechanical stabilisation has been a hallmark of orthopaedic surgical management, orthobiologics are now playing an increasing role. Platelet-rich plasma (PRP) is a volume of plasma fraction of autologous blood having platelet concentrations above baseline. The platelet alpha granules are rich in growth factors that play an essential role in tissue healing, such as transforming growth factor-beta, vascular endothelial growth factor, and platelet-derived growth factor. PRP is used in various surgical fields to enhance bone and soft-tissue healing by placing supraphysiological concentrations of autologous platelets at the site of tissue damage. The easily obtainable PRP and its possible beneficial outcome hold promise for new regenerative treatment approaches. The aim of this literature review was to describe the bioactivities of PRP, to elucidate the different techniques for PRP preparation, to review animal and human studies, to evaluate the evidence regarding the use of PRP in trauma and orthopaedic surgery, to clarify risks, and to provide guidance for future research.

Cytokine Release from Osteoblasts in Response to Different Intensities of Pulsed Electromagnetic Field Stimulation

We use an in-vitro osteoblast cell culture model to investigate the effects of low-frequency (7.5 Hz) pulsed electromagnetic field (PEMF) stimulation on osteoblast population, cytokines (prostaglandin E(2) (PGE(2)), transforming growth factor beta1(TGFbeta1), and alkaline phosphatase (ALP) activity to find the optimal intensity of PEMF for osteoblast growth. The results demonstrate that PEMF can stimulate osteoblast growth, release of TGFbeta1, and, in addition, an increase of ALP activity. The synthesis and release of PGE(2) in the culture medium are reduced with increasing numbers of cells. Higher intensity does not necessarily mean increased osteoblast growth, and the most efficient intensity is about 2 mV/cm in this case. Although the lower intensities of the PEMF are yet to be determined, the results of this study can shed light on the mechanisms of PEMF stimulation on non union fracture therapy and osteoporosis prevention in the future.

Transforming growth factor-beta signaling in thoracic aortic aneurysm development: a paradox in pathogenesis

Thoracic aortic aneurysms (TAAs) are potentially devastating, and due to their asymptomatic behavior, pose a serious health risk characterized by the lack of medical treatment options and high rates of surgical morbidity and mortality. Independent of the inciting stimuli (biochemical/mechanical), TAA development proceeds by a multifactorial process influenced by both cellular and extracellular mechanisms, resulting in alterations of the structure and composition of the vascular extracellular matrix (ECM). While the role of enhanced ECM proteolysis in TAA formation remains undisputed, little attention has been focused on the upstream signaling events that drive the remodeling process. Recent evidence highlighting the dysregulation of transforming growth factor-beta (TGF-beta) signaling in ascending TAAs from Marfan syndrome patients has stimulated an interest in this intracellular signaling pathway. However, paradoxical discoveries have implicated both enhanced TGF-beta signaling and loss of function TGF-beta receptor mutations, in aneurysm formation; obfuscating a clear functional role for TGF-beta in aneurysm development. In an effort to elucidate this subject, TGF-beta signaling and its role in vascular remodeling and pathology will be reviewed, with the aim of identifying potential mechanisms of how TGF-beta signaling may contribute to the formation and progression of TAA.

Developmental expression of LC3alpha and beta: absence of fibronectin or autophagy phenotype in LC3beta knockout mice

Murine light chain 3 (LC3) exists as two isoforms, LC3alpha and beta: LC3beta is an RNA-binding protein that enhances fibronectin (FN) mRNA translation, and is also a marker of autophagy. We report embryonic expression patterns for LC3alpha and LC3beta, with some overlap but notable differences in the brain, and in tissues of non-neuronal origin. LC3beta knockout (-/-) mice develop normally without a compensatory increase in LC3alpha. LC3beta-/- embryonic fibroblasts (MEFs) exhibit reduced FN synthesis but maintain wild type (WT) levels of FN protein. No significant changes in proteins associated with FN turnover, i.e., caveolin-1, LRP-1, or matrix metalloproteinases were identified. Autophagosomes form in amino acid-starved LC3beta-/-MEFs, and Caesarean-delivered pups survive as long as WT pups without an increase in LC3-related proteins linked to autophagy. These results suggest novel compensatory mechanisms for loss of LC3beta, ensuring proper FN accumulation and autophagy during fetal and neonatal life.

Biology of umbilical cord blood progenitors in bone marrow niches

Within the bone marrow (BM), hematopoietic progenitor cells (HPCs) are localized in poorly oxygenated niches where they interact with the surrounding osteoblasts (OBs) through VLA4/VCAM-1 engagement, and are exposed to interleukin-6 (IL-6), stem cell factor (SCF), and chemokines such as CXCL12 (OB factors). Umbilical cord (UC) is more highly oxygenated that the BM microenvironment. When UC-HPCs are exposed to the 2% to 3% O(2) concentration found in the bone endosteum, their survival is significantly decreased. However, engagement of VLA-4 integrins on UCB-derived CD34(+) cells reduced cell death in 2% to 3% O(2) conditions, which was associated with an increase in phospho-Ser473 AKT and an increase in phospho-Ser9 GSK3b. Consistent with the role of GSK3b in destabilizing beta-catenin, there was more cytoplasmic beta-catenin in UC-HPCs exposed to 2% to 3% O(2) on fibronectin, compared with suspension culture. UC-HPCs cultured at 2% to 3% O(2) with OB factors showed an increase in nuclear beta-catenin and persistence of a small pool of CD34(+)38(-) HPCs. CFU assays followed by surface phenotyping of the plated colonies showed improved maintenance of mixed lineage colonies with both erythroid and megakaryocytic precursors. These studies provide a biologic perspective for how UC-derived HPCs adapt to the bone endosteum, which is low in oxygen and densely populated by osteoblasts.

Connective tissue growth factor (CTGF/CCN2) is a downstream mediator for TGF-beta1-induced extracellular matrix production in osteoblasts

Connective tissue growth factor (CTGF/CCN2) is a cysteine-rich, extracellular matrix (ECM) protein that acts as an anabolic growth factor to regulate osteoblast differentiation and function. Recent studies have identified CTGF as a downstream effector of transforming growth factor-beta1 (TGF-beta1) for certain functions in specific cell types. In this study, we examined the role of CTGF as a downstream mediator of TGF-beta1-induced ECM production and cell growth in osteoblasts. Using primary cultures, we demonstrated that TGF-beta1 is a potent inducer of CTGF expression in osteoblasts, and that this induction occurred at all stages of osteoblast differentiation from the proliferative through mineralization stages. TGF-beta1 treatment of osteoblasts increased the expression and synthesis of the ECM components, collagen and fibronectin. When CTGF-specific siRNA was used to prevent TGF-beta1 induction of CTGF expression, it also inhibited collagen and fibronectin production, thereby demonstrating the requirement of CTGF for their up-regulation. To examine the effects of TGF-beta1 on osteoblast cell growth, cultures were treated with TGF-beta1 during the proliferative stage. Cell number was significantly reduced and the cells exhibited a decrease in G1 cyclin expression, consistent with TGF-beta1-induced cell-cycle arrest. Cultures transfected with CTGF siRNA prior to TGF-beta1 treatment showed an even greater reduction in cell number, suggesting that TGF-beta1-induced growth arrest is independent of CTGF in osteoblasts. Collectively, these data demonstrate for the first time that CTGF is an essential downstream mediator for TGF-beta1-induced ECM production in osteoblasts, but these two growth factors function independently regarding their opposing effects on osteoblast proliferation.

Bioadjuvants for complex ankle and hindfoot reconstruction

Many reconstructive options exist for symptomatic hindfoot and ankle problems. Hindfoot and tibiotalar fusions are reliable procedures with consistent results. Unfortunately, many potential complications have been cited throughout the literature. Although the most important aspect in any fusion surgery is meticulous technique, advances in technology, including PRP, bone stimulators, and BMPs seem to be useful additions in the quest to achieve solid fusions with decreased complications.

TGFbeta3 expression in non-syndromic orofacial clefts

BACKGROUND

Genetic studies have demonstrated that non-syndromic cleft is composed of two separate entities - cleft palate only (CPO) and cleft of lip, alveolus with or without cleft palate (CL+/-P) -, both have a heterogeneous genetic background and environmental factors contribute to the onset of these malformations. Previous studies have shown that TGFbeta3 could be involved in these diseases, but no conclusive results have been reached.

PURPOSE

In order to detect if TGFbeta3 has a role in cleft diseases, a series of non-syndromic cleft patients and controls are analyzed for TGFbeta3 protein expression.

MATERIAL AND METHODS

Forty-three non-syndromic cleft patients and 21 unaffected subjects were involved in this study. Paraffin-embedded specimens were matched with the TGFbeta3 antibody and then scanned with a computerized image analyzer. TGFbeta3 was found to be absent (less than 10%), moderate (from 10% to 30%) and highly expressed (higher than 30%) in epithelium (EP), minor palatal salivary gland (GL) and fibres of elevator palati muscle (MU). Data was statistically analyzed with a Kruskal-Wallis test.

RESULTS

Only GL and EP have a statistically significant lower expression in non-syndromic cleft compared to unaffected subjects. A subsequent comparison between CL+/-P and CPO groups demonstrates a statistically significant difference only for GL, with a lower expression in GL of CPO patients.

CONCLUSIONS

TGFbeta3 is decreasingly expressed in GL of unaffected CL+/-P and CPO patients and thus further strength is given to a pathogenetic role of TGFbeta3 in the onset of clefts.

The role of platelet-rich plasma in foot and ankle surgery

Platelet-rich plasma (PRP), derived from autologous blood, is defined as a volume of plasma that has a platelet concentration that typically is five times greater (approximately 1,000,000/microl) than physiologic levels. PRP serves as a reservoir of critical growth factors, including platelet-derived growth factor, transforming growth factor-beta, and insulin-like growth factor-I. Although there is an abundance of literature pertaining to dental applications, this article highlights the use of PRP in orthopedic applications, ranging from PRP preparation to in vitro and in vivo studies to clinical research.

Transforming growth factor-beta1 to the bone

TGF-beta1 is a ubiquitous growth factor that is implicated in the control of proliferation, migration, differentiation, and survival of many different cell types. It influences such diverse processes as embryogenesis, angiogenesis, inflammation, and wound healing. In skeletal tissue, TGF-beta1 plays a major role in development and maintenance, affecting both cartilage and bone metabolism, the latter being the subject of this review. Because it affects both cells of the osteoblast and osteoclast lineage, TGF-beta1 is one of the most important factors in the bone environment, helping to retain the balance between the dynamic processes of bone resorption and bone formation. Many seemingly contradictory reports have been published on the exact functioning of TGF-beta1 in the bone milieu. This review provides an overall picture of the bone-specific actions of TGF-beta1 and reconciles experimental discrepancies that have been reported for this multifunctional cytokine.