Cartilage morphogenetic proteins: role in joint development, homoeostasis, and regeneration

Effects of Simvastatin on Cartilage Homeostasis in Steroid-Induced Osteonecrosis of Femoral Head by Inhibiting Glucocorticoid Receptor

Steroid-induced osteonecrosis of femoral head (SONFH) is one of the most common bone disorders in humans. Statin treatment is beneficial in preventing the development of SONFH through anti-inflammation effects and inhibition of the glucocorticoid receptor (GR). However, potential mechanisms of statin action remain to be determined. In this study, pulse methylprednisolone (MP) treatment was used to induce SONFH in broilers, and then MP-treated birds were administrated with simvastatin simultaneously to investigate the changes in cartilage homeostasis. Meanwhile, chondrocytes were isolated, cultured, and treated with MP, simvastatin, or GR inhibitor in vitro. The changes in serum homeostasis factors, cell viability, and expression of GR were analyzed. The results showed that the morbidity of SONFH in the MP-treated group increased significantly compared with the simvastatin-treated and control group. Furthermore, MP treatment induced apoptosis and high-level catabolism and low-level anabolism in vitro and vivo, while simvastatin significantly decreased catabolism and slightly recovered anabolism via inhibiting GR and the hypoxia-inducible factor (HIF) pathway. The GR inhibitor or its siRNA mainly affected the catabolism of cartilage homeostasis in vitro. In conclusion, the occurrence of SONFH in broilers was related to the activation of GR and HIF pathway, and imbalance of cartilage homeostasis. Simvastatin and GR inhibitor maintained cartilage homeostasis via GR and the HIF pathway.

Material-Assisted Strategies for Osteochondral Defect Repair

The osteochondral (OC) unit plays a pivotal role in joint lubrication and in the transmission of constraints to bones during movement. The OC unit does not spontaneously heal; therefore, OC defects are considered to be one of the major risk factors for developing long-term degenerative joint diseases such as osteoarthritis. Yet, there is currently no curative treatment for OC defects, and OC regeneration remains an unmet medical challenge. In this context, a plethora of tissue engineering strategies have been envisioned over the last two decades, such as combining cells, biological molecules, and/or biomaterials, yet with little evidence of successful clinical transfer to date. This striking observation must be put into perspective with the difficulty in comparing studies to identify overall key elements for success. This systematic review aims to provide a deeper insight into the field of material-assisted strategies for OC regeneration, with particular considerations for the therapeutic potential of the different approaches (with or without cells or biological molecules), and current OC regeneration evaluation methods. After a brief description of the biological complexity of the OC unit, the recent literature is thoroughly analyzed, and the major pitfalls, emerging key elements, and new paths to success are identified and discussed.

Growth factor profile in calcified cartilage from the metaphysis of a calf costochondral junction, the site of initial bone formation

Endochondral bone formation is orchestrated by growth factors produced by chondrocytes and deposited in the cartilage matrix. Whilst some of these factors have been identified, the complete list and their relationship remains unknown. In the present study, the growth factors were isolated from non-calcified and calcified cartilage of costochondral junctions. Cartilage dissected from the ribs of 6-20-week-old calves was purchased from a local butcher within 24 h of the death of the animal. The isolation involved hyaluronidase digestion, guanidinium hydrochloride (GuHCl) extraction, HCl decalcification and GuHCl extraction of the decalcified matrix. Growth factors were purified by heparin chromatography and their quantities were estimated using ELISA. Decalcified cartilage was also used for protein sequence analysis (data are available via ProteomeXchange; ID, PXD021781). Bone morphogenetic protein-7 (BMP-7), growth/differentiation factor-5 (GDF-5) and NEL-like protein-1 (NELL-1), all known growth factors that stimulate bone formation, quantitatively accounted for the majority of the material obtained in all steps of isolation. Thus, cartilage serves as a store for growth factors. During initial bone formation septoclasts release osteoclastogenesis-stimulating factors deposited in non-calcified cartilage. Osteoclasts dissolve calcified cartilage and transport the released factors required for the stimulation of osteoprogenitor cells to deposit osteoid. High concentrations of BMP-7, GDF-5 and NELL-1 at the site of initial bone formation may suggest that their synergistic action favours osteogenesis.

Changes in DNA methylation accompany changes in gene expression during chondrocyte hypertrophic differentiation in vitro

During osteoarthritis (OA), articular chondrocytes undergo phenotypic changes that resemble developmental patterns characteristic of growth plate chondrocytes. These phenotypic alterations lead to a hypertrophy-like phenotype characterized by altered production of extracellular matrix constituents and increased collagenase activity, which, in turn, results in cartilage destruction in OA disease. Recent studies have shown that the phenotypic instability and dysregulated gene expression in OA are associated with changes in DNA methylation patterns. Subsequent efforts have aimed to identify changes in DNA methylation with functional impact in OA disease, to potentially uncover therapeutic targets. Here, we paired an in vitro 3D/pellet culture system that mimics chondrocyte hypertrophy with RNA sequencing (RNA-Seq) and enhanced reduced representation of bisulfite sequencing (ERRBS) to identify transcriptomic and epigenomic changes in murine primary articular chondrocytes undergoing hypertrophy-like differentiation. We identified hypertrophy-associated changes in DNA methylation patterns in vitro. Integration of RNA-Seq and ERRBS datasets identified associations between changes in methylation and gene expression. Our integrative analyses showed that hypertrophic differentiation of articular chondrocytes is accompanied by transcriptomic and epigenomic changes in vitro. We believe that our integrative approaches have the potential to uncover new targets for therapeutic intervention.

Prospects of circadian clock in joint cartilage development

Altering the food intake, exercise, and sleep patterns have a great influence on the homeostasis of the biological clock. This leads to accelerated aging of the articular cartilage, susceptibility to arthropathy and other aspects. Deficiency or overexpression of certain circadian clock-related genes accelerates the cartilage deterioration and leads to phenotypic variation in different joints. The process of joint cartilage development includes the formation of joint site, interzone, joint cavitation, epiphyseal ossification center, and cartilage maturation. The mechanism by which, biological clock regulates the cell-cycle, growth, metabolism, and other biological processes of chondrocytes is poorly understood. Here, we summarized the interaction between biological clock proteins and developmental pathways in chondrogenesis and provided the evidence from other tissues that further predicts the molecular patterns of these protein-protein networks in activation, proliferation, and differentiation. The purpose of this review is to gain deeper understanding of the evolution of cartilage and its irreversibility seen in damage and aging.

Tissue-Specific Decellularization Methods: Rationale and Strategies to Achieve Regenerative Compounds

The extracellular matrix (ECM) is a complex network with multiple functions, including specific functions during tissue regeneration. Precisely, the properties of the ECM have been thoroughly used in tissue engineering and regenerative medicine research, aiming to restore the function of damaged or dysfunctional tissues. Tissue decellularization is gaining momentum as a technique to obtain potentially implantable decellularized extracellular matrix (dECM) with well-preserved key components. Interestingly, the tissue-specific dECM is becoming a feasible option to carry out regenerative medicine research, with multiple advantages compared to other approaches. This review provides an overview of the most common methods used to obtain the dECM and summarizes the strategies adopted to decellularize specific tissues, aiming to provide a helpful guide for future research development.

Cartilage Homeostasis Affects Femoral Head Necrosis Induced by Methylprednisolone in Broilers

(1) Background: Since the large-scale poultry industry has been established, femoral head necrosis (FHN) has always been a major leg disease in fast-growing broilers worldwide. Previous research suggested that cartilage homeostasis could be taken into consideration in the cause of FHN, but the evidence is insufficient. (2) Methods: One-day-old broiler chickens were randomly divided into three groups, 16 broilers per group. The birds in group L were injected intramuscularly with methylprednisolone (MP) twice a week for four weeks (12.5 mg·kg⁻¹). The birds in group H were injected intramuscularly with MP (20 mg·kg⁻¹·d⁻¹) for 7 d (impulse treatment). The birds in group C were treated with sterile saline as a control group. Broilers were sacrificed at 42 and 56 d. Blood samples were collected from the jugular vein for ELISA and biochemical analysis. Bone samples, including femur, tibia, and humerus, were collected for histopathological analysis, bone parameters detection, and real-time quantitative PCR detection. (3) Results: The FHN broilers in group L and H both showed lower body weight (BW) and reduced bone parameters. In addition, the MP treatment resulted in reduced extracellular matrix (ECM) anabolism and enhanced ECM catabolism. Meanwhile, the autophagy and apoptosis of chondrocytes were enhanced, which led to the destruction of cartilage homeostasis. Moreover, the impulse MP injection increased the portion of birds with severer FHN, whereas the MP injection over a long period caused a more evident change in serum cytokine concentrations and bone metabolism indicators. (4) Conclusions: The imbalance of cartilage homeostasis may play a critical role in the development of FHN in broilers. FHN broilers induced by MP showed a more pronounced production of catabolic factors and suppressed the anabolic factors, which might activate the genes of the WNT signal pathway and hypoxia-inducible factors (HIFs), and then upregulate the transcription expression of ECM to restore homeostasis.

Cell therapy stimulates bone neoformation in calvaria defects in rats subjected to local irradiation

BACKGROUND

The purpose of the study was to analyze the effect of cell therapy on the repair process in calvaria defects in rats subjected to irradiation.

METHODS

Bone marrow mesenchymal cells were characterized for osteoblastic phenotype. Calvariae of male Wistar rats were irradiated (20 Gy) and, after 4 weeks, osteoblastic cells were placed in surgically created defects in irradiated (IRC) and control animals (CC), paired with untreated irradiated (IR) and control (C) animals. After 30 days, histological and microtomographic evaluation was performed to establish significant (P < 0.05) differences among the groups.

RESULTS

Higher alkaline phosphatase detection and activity, along with an increase in mineralized nodules, in the IRC, C and CC groups compared to the IR group, confirmed an osteoblastic phenotype. Histology showed impaired bone neoformation following irradiation, affecting bone marrow composition. Cell therapy in the IRC group improved bone neoformation compared to the IR group. Microtomography revealed increased bone volume, bone surface and trabecular number in IRC group compared to the IR group.

CONCLUSION

Cell therapy may improve bone neoformation in defects created after irradiation.

Regulation of articular chondrocyte catabolic genes by growth factor interaction

Osteoarthritis is characterized by a loss of articular cartilage homeostasis in which degradation exceeds formation. Several growth factors have been shown to promote cartilage formation by augmenting articular chondrocyte anabolic activity. This study tests the hypothesis that such growth factors also play an anticatabolic role. We transferred individual or combinations of the genes encoding insulin-like growth factor-I, bone morphogenetic protein-2, bone morphogenetic protein-7, transforming growth factor-β1, and fibroblast growth factor-2, into adult bovine articular chondrocytes and measured the expression of catabolic marker genes encoding A disintegrin and metalloproteinase with thrombospondin motifs-4 and -5, matrix metalloproteinases-3 and -13, and interleukin-6. When delivered individually, or in combination, these growth factor transgenes differentially regulated the direction, magnitude, and time course of expression of the catabolic marker genes. In concert, the growth factor transgenes regulated the marker genes in an interactive fashion that ranged from synergistic inhibition to synergistic stimulation. Synergistic stimulation prevailed over synergistic inhibition, reaching maxima of 15.2- and 2.7-fold, respectively. Neither the magnitude nor the time course of the effect of the transgene combinations could be predicted on the basis of the individual transgene effects. With few exceptions, the data contradict our hypothesis. The results demonstrate that growth factors that are traditionally viewed as chondrogenic tend also to promote catabolic gene expression. The competing actions of these potential therapeutic agents add an additional level of complexity to the selection of regulatory factors for restoring articular cartilage homeostasis or promoting repair.

Comparative Effectiveness of Structural versus Regulatory Protein Gene Transfer on Articular Chondrocyte Matrix Gene Expression

OBJECTIVE

The production of extracellular matrix is a necessary component of articular cartilage repair. Gene transfer is a promising method to improve matrix biosynthesis by articular chondrocytes. Gene transfer may employ transgenes encoding regulatory factors that stimulate the production of matrix proteins, or may employ transgenes that encode the proteins themselves. The objective of this study was to determine which of these 2 approaches would be the better choice for further development. We compared these 2 approaches using the transgenes encoding the structural matrix proteins, aggrecan or type II collagen, and the transgene encoding the anabolic factor, insulin-like growth factor I (IGF-I).

METHODS

We transfected adult bovine articular chondrocytes with constructs encoding type II collagen, aggrecan, or IGF-I, and measured the expression of type II collagen ( COL2A1) and aggrecan ( ACAN) from their native genes and from their transgenes.

RESULTS

IGF-I gene ( IGF1) transfer increased the expression of the native chondrocyte COL2A1 and ACAN genes 2.4 and 2.9 times control, respectively. COL2A1 gene transfer did not significantly increase COL2A1 transcripts, even when the transgene included the genomic COL2A1 regulatory sequences stimulated by chondrogenic growth factors. In contrast, ACAN gene transfer increased ACAN transcripts up to 3.4 times control levels. IGF1, but not ACAN, gene transfer increased aggrecan protein production.

CONCLUSION

Taken together, these results suggest that the type II collagen and aggrecan production required for articular cartilage repair will be more effectively achieved by genes that encode anabolic regulatory factors than by genes that encode the matrix molecules themselves.

Modulating cell response on cellulose surfaces; tunable attachment and scaffold mechanics

Combining surface chemical modification of cellulose to introduce positively charged trimethylammonium groups by reaction with glycidyltrimethylammonium chloride (GTMAC) allowed for direct attachment of mammalian MG-63 cells, without addition of protein modifiers, or ligands. Very small increases in the surface charge resulted in significant increases in cell attachment: at a degree of substitution (DS) of only 1.4%, MG-63 cell attachment was > 90% compared to tissue culture plastic, whereas minimal attachment occurred on unmodified cellulose. Cell attachment plateaued above DS of ca. 1.85% reflecting a similar trend in surface charge, as determined from ζ-potential measurements and capacitance coupling (electric force microscopy). Cellulose film stiffness was modulated by cross linking with glyoxal (0.3-2.6% degree of crosslinking) to produce a range of materials with surface shear moduli from 76 to 448 kPa (measured using atomic force microscopy). Cell morphology on these materials could be regulated by tuning the stiffness of the scaffolds. Thus, we report tailored functionalised biomaterials based on cationic cellulose that can be tuned through surface reaction and glyoxal crosslinkin+g, to influence the attachment and morphology of cells. These scaffolds are the first steps towards materials designed to support cells and to regulate cell morphology on implanted biomaterials using only scaffold and cells, i.e. without added adhesion promoters.

Structural analyses of von Willebrand factor C domains of collagen 2A and CCN3 reveal an alternative mode of binding to bone morphogenetic protein-2

Bone morphogenetic proteins (BMPs) are secreted growth factors that promote differentiation processes in embryogenesis and tissue development. Regulation of BMP signaling involves binding to a variety of extracellular proteins, among which are many von Willebrand factor C (vWC) domain-containing proteins. Although the crystal structure of the complex of crossveinless-2 (CV-2) vWC1 and BMP-2 previously revealed one mode of the vWC/BMP-binding mechanism, other vWC domains may bind to BMP differently. Here, using X-ray crystallography, we present for the first time structures of the vWC domains of two proteins thought to interact with BMP-2: collagen IIA and matricellular protein CCN3. We found that these two vWC domains share a similar N-terminal fold that differs greatly from that in CV-2 vWC, which comprises its BMP-2-binding site. We analyzed the ability of these vWC domains to directly bind to BMP-2 and detected an interaction only between the collagen IIa vWC and BMP-2. Guided by the collagen IIa vWC domain crystal structure and conservation of surface residues among orthologous domains, we mapped the BMP-binding epitope on the subdomain 1 of the vWC domain. This binding site is different from that previously observed in the complex between CV-2 vWC and BMP-2, revealing an alternative mode of interaction between vWC domains and BMPs.

Treatment of stage II medication-related osteonecrosis of the jaw with necrosectomy and autologous bone marrow mesenchymal stem cells

Treatment strategies for medication-related osteonecrosis of the jaw (MRONJ) remain controversial. Although the AAOMS suggests a conservative approach, a surgical management with necrosectomy is often required when conservative management has failed. Moreover, recent studies have shown promising results using an early stage surgical treatment. Over the past decade, cell-based bone regeneration utilizing bone marrow mesenchymal stem cells (MSCs) received increased attention. MSCs are known to promote wound healing and induce new bone formation in compromised tissue. Accordingly, the aim of this study was to assess the role of MSCs in the management of MRONJ. This study included 6 patients referred to our department with the diagnosis of MRONJ. Upon informed consent, the patients underwent surgical resection of necrotic bone followed by MSCs grafting. The MSCs were separated from bone marrow cells aspirated from the iliac crest using a bone marrow aspirate concentrate system. The MSCs were grafted into the defect with autologous thrombin and the defect was covered with a collagen membrane. In all cases, bony edges were rounded and the wound was closed using a three-layered technique. In the follow-up from 12 to 54 months, all patients including those who had impaired conditions, sepsis, or pathological fracture, showed satisfactory healing with no signs of wound infection. This pilot study indicated that surgical management in combination with MSCs transplantation seems to be a promising treatment modality in the therapy of MRONJ.

Growth factor transgenes interactively regulate articular chondrocytes

Adult articular chondrocytes lack an effective repair response to correct damage from injury or osteoarthritis. Polypeptide growth factors that stimulate articular chondrocyte proliferation and cartilage matrix synthesis may augment this response. Gene transfer is a promising approach to delivering such factors. Multiple growth factor genes regulate these cell functions, but multiple growth factor gene transfer remains unexplored. We tested the hypothesis that multiple growth factor gene transfer selectively modulates articular chondrocyte proliferation and matrix synthesis. We tested the hypothesis by delivering combinations of the transgenes encoding insulin-like growth factor I (IGF-I), fibroblast growth factor-2 (FGF-2), transforming growth factor beta1 (TGF-β1), bone morphogenetic protein-2 (BMP-2), and bone morphogenetic protien-7 (BMP-7) to articular chondrocytes and measured changes in the production of DNA, glycosaminoglycan, and collagen. The transgenes differentially regulated all these chondrocyte activities. In concert, the transgenes interacted to generate widely divergent responses from the cells. These interactions ranged from inhibitory to synergistic. The transgene pair encoding IGF-I and FGF-2 maximized cell proliferation. The three-transgene group encoding IGF-I, BMP-2, and BMP-7 maximized matrix production and also optimized the balance between cell proliferation and matrix production. These data demonstrate an approach to articular chondrocyte regulation that may be tailored to stimulate specific cell functions, and suggest that certain growth factor gene combinations have potential value for cell-based articular cartilage repair.

The clip-segment of the von Willebrand domain 1 of the BMP modulator protein Crossveinless 2 is preformed

Bone Morphogenetic Proteins (BMPs) are secreted protein hormones that act as morphogens and exert essential roles during embryonic development of tissues and organs. Signaling by BMPs occurs via hetero-oligomerization of two types of serine/threonine kinase transmembrane receptors. Due to the small number of available receptors for a large number of BMP ligands ligand-receptor promiscuity presents an evident problem requiring additional regulatory mechanisms for ligand-specific signaling. Such additional regulation is achieved through a plethora of extracellular antagonists, among them members of the Chordin superfamily, that modulate BMP signaling activity by binding. The key-element in Chordin-related antagonists for interacting with BMPs is the von Willebrand type C (VWC) module, which is a small domain of about 50 to 60 residues occurring in many different proteins. Although a structure of the VWC domain of the Chordin-member Crossveinless 2 (CV2) bound to BMP-2 has been determined by X-ray crystallography, the molecular mechanism by which the VWC domain binds BMPs has remained unclear. Here we present the NMR structure of the Danio rerio CV2 VWC1 domain in its unbound state showing that the key features for high affinity binding to BMP-2 is a pre-oriented peptide loop.

BMP-2 shows characteristic extracellular patterns in osteoarthritic cartilage: a preliminary report

To determine bone morphogenetic protein (BMP)-2 protein and Aggrecan in osteoarthritic and healthy cartilage with special regard to localization and degree of cartilage damage 95 samples representing osteoarthritic cartilage and 17 samples out of normal cartilage were graded histological by Mankin Score and were studied by immunohistochemistry for the expression of BMP-2 and Aggrecan. BMP-2 protein was detected intracellular in normal and in osteoarthritic cartilage. Extracellular BMP-2 was detected exclusively in osteoarthritic cartilage and exhibits characteristic extracellular patterns: samples with BMP-2 in the extracellular matrix show BMP-2 negative coronae around BMP-2 positive cells. There is a statistically significant increase in the prevalence of extracellular BMP-2 with increasing ICRS grade/Mankin grade. Aggrecan was detected in the extracellular matrix und exhibited coronas throughout all layers. A decline of extracellular Aggrecan with increasing ICRS grade could be observed. Normal cartilage shows no intracellular Aggrecan whereas an increase in the prevalence of intracellular Aggrecan could be detected in osteoarthritic cartilage. The appearance of intracellular Aggrecan is often associated with extracellular BMP-2. The detection of BMP-2 protein in normal as well as in osteoarthritic cartilage highlights the importance of BMP-2 in tissue homeostasis and point to a putative role for maintaining tissue integrity during the development of osteoarthritis. The co-appearance of extracellular BMP-2 and intracellular Aggrecan indicates a functional relationship. The most interesting result is the characteristic distribution of extracellular BMP-2. These coronas seem to have an impact during progression of osteoarthritis and need to be further investigated.

Growth factor regulation of growth factor production by multiple gene transfer to chondrocytes

Of the many classes of molecules regulated by growth factors, growth factors themselves are not well investigated. We tested the hypothesis that combinations of endogenous growth factors interactively regulate the production of other growth factors. Growth factors have therapeutic potential for articular cartilage repair, and gene transfer is a promising approach to growth factor delivery. We tested the hypothesis using adult bovine articular chondrocytes treated with combinations of cDNAs encoding insulin-like growth factor I, bone morphogenetic protein-2 and protein-7, transforming growth factor β1, and fibroblast growth factor 2. We found that these growth factor transgenes regulated each other's growth factor production. This regulation ranged from stimulation to inhibition. Regulation by multiple transgenes was not predictable from the regulatory actions of the individual transgenes. Such interactions may be important for the selection of growth factor genes for cell-based therapies, including articular cartilage repair.

Glucuronoxylomannan facilitates generation of chondrocytes from bone marrow-derived mononuclear cells

Chondrocyte generation is an important process in cartilage and bone repair. Factors facilitating the induction of chondrocyte need to be further investigated. The present study aims to investigate the role of glucuronoxylomannan (Gxm) in the generation of chondrocytes. Human bone marrow cells were prepared using to generate the chondrocytes in the presence of Gxm. The results showed that Gxm has the capacity to facilitate the generation of chondrocytes in which transforming growth factor (TGF)-β played a critical role. The Bmmc-derived CD14+ cells were the major source of TGF-β in the culture. The present study indicates that Gxm is a potential drug candidate to be used in the generation of chondrocyte.

Regulation of articular chondrocyte aggrecan and collagen gene expression by multiple growth factor gene transfer

Gene transfer is a promising approach to the delivery of chondrotrophic growth factors to promote cartilage repair. It is unlikely that a single growth factor transgene will optimally regulate these cells. The aim of this study was to identify those growth factor transgene combinations that optimally regulate aggrecan, collagen type II and collagen type I gene expression by articular chondrocytes. We delivered combinations of the transgenes encoding fibroblast growth factor-2, insulin-like growth factor I, transforming growth factor beta1, bone morphogenetic protein-2, and/or bone morphogenetic protein-7 and assessed chondrocyte responses by measuring changes in the expression of aggrecan, type II collagen and type I collagen genes. These growth factor transgenes differentially regulated the magnitude and time course of all three-matrix protein genes. In concert, the transgenes regulated matrix gene expression in an interactive fashion that ranged from synergistic to inhibitory. Maximum stimulation of aggrecan (16-fold) and type II collagen (35-fold) expression was with the combination of IGF-I, BMP-2, and BMP-7 transgenes. The results indicate that the optimal choice of growth factor genes for cell-based cartilage repair cannot be predicted from observations of individual transgenes. Rather, such gene therapy will require an empirically based selection of growth factor gene combinations.

Stemness gene expression profile analysis in human umbilical cord mesenchymal stem cells

Umbilical cord mesenchymal stem cells (UC-MSCs) have several advantages for clinical therapy: the material is easily obtainable, the donation procedure is painless and there is low risk of viral contamination. UC-MSCs play important roles in tissue regeneration, tissue damage repair, autoimmune disease and graft-versus-host disease. In this study, we investigated the normal mRNA expression profile of UC-MSCs, and analyzed the candidate proteins responsible for the signaling pathway that may affect the differentiation characteristics of UC-MSCs. UC-MSCs were isolated by mincing UC samples into fragments and placing them in growth medium in a six-well plate. The immunophenotype characteristics and multilineage differentiation potential of the UC-MSCs were measured by flow cytometry and immunohistochemical assays. In addition, the pathway-focused gene expression profile of UC-MSCs was compared with those of normal or tumorous cells by realtime quantitative polymerase chain reaction. We successfully isolated and cultured UC-MSCs and analyzed the appropriate surface markers and their capacity for osteogenic, adipogenic and neural differentiation. In total, 168 genes focusing on signal pathways were examined. We found that the expression levels of some genes were much higher or lower than those of control cells, either normal or tumorous. UC-MSCs exhibit a unique mRNA expression profile of pathway-focused genes, especially some stemness genes, which warrants further investigation.

Stem cell- and growth factor-based regenerative therapies for avascular necrosis of the femoral head

Avascular necrosis (AVN) of the femoral head is a debilitating disease of multifactorial genesis, predominately affects young patients, and often leads to the development of secondary osteoarthritis. The evolving field of regenerative medicine offers promising treatment strategies using cells, biomaterial scaffolds, and bioactive factors, which might improve clinical outcome. Early stages of AVN with preserved structural integrity of the subchondral plate are accessible to retrograde surgical procedures, such as core decompression to reduce the intraosseous pressure and to induce bone remodeling. The additive application of concentrated bone marrow aspirates, ex vivo expanded mesenchymal stem cells, and osteogenic or angiogenic growth factors (or both) holds great potential to improve bone regeneration. In contrast, advanced stages of AVN with collapsed subchondral bone require an osteochondral reconstruction to preserve the physiological joint function. Analogously to strategies for osteochondral reconstruction in the knee, anterograde surgical techniques, such as osteochondral transplantation (mosaicplasty), matrix-based autologous chondrocyte implantation, or the use of acellular scaffolds alone, might preserve joint function and reduce the need for hip replacement. This review summarizes recent experimental accomplishments and initial clinical findings in the field of regenerative medicine which apply cells, growth factors, and matrices to address the clinical problem of AVN.

Growth differentiation factor-5 regulation of extracellular matrix gene expression in murine tendon fibroblasts

The synthesis and organization of extracellular matrix (ECM) of tendon, in resting and states of repair, are governed by fibroblasts. Growth differentiation factor-5 (GDF-5) may enhance the cellular response to tendon injury, thus improving the structural outcome of the regenerative tissue. This study was an attempt to identify potential mechanisms controlling the response of fibroblasts to injury and GDF-5, in the pursuit of improved tissue regeneration. There were two sets of experiments. Isolated mice Achilles tendon fibroblasts were treated with different concentrations of rGDF-5 (0-100 ng/ml) for 0-12 days in cell culture. The temporal effect of rGDF-5 on ECM gene expression was analysed for type I collagen and aggrecan expression. Microarray and gene expression analysis were performed on cells treated with 100 ng/ml for 4 days. Forty-five mice underwent bilateral mid-substance Achilles tendon tenotomy and suture repair. Repair sites were injected with 10 µg rGDF-5 or saline. Tendons were assessed histologically at 2, 4 and 6 weeks. Expression of ECM genes procollagen IX, aggrecan, matrix metalloproteinase 9 and fibromodulin were upregulated. Proinflammatory reaction genes were downregulated. rGDF-5 led to an increase in total DNA, glycosaminoglycan (GAG) and hydroxyproline (OHP). The OHP:DNA ratio of fibroblast cultures was increased over all time points, with increased GAG:DNA at day 12. rGDF-5 treatment showed improved collagen organization over controls. The results delineate the mode of action of rGDF-5 at the cellular and gene level. rGDF-5 could play a role in tendon repair and be used for future therapies that promote tendon healing.

Extracellular sulfatases support cartilage homeostasis by regulating BMP and FGF signaling pathways

The balance between anabolic and catabolic signaling pathways is critical in maintaining cartilage homeostasis and its disturbance contributes to joint diseases such as osteoarthritis (OA). A unique mechanism that modulates the activity of cell signaling pathways is controlled by extracellular heparan endosulfatases Sulf-1 and Sulf-2 (Sulfs) that are overexpressed in OA cartilage. This study addressed the role of Sulfs in cartilage homeostasis and in regulating bone morphogenetic protein (BMP)/Smad and fibroblast growth factor (FGF)/Erk signaling in articular cartilage. Spontaneous cartilage degeneration and surgically induced OA were significantly more severe in Sulf-1(-/-) and Sulf-2(-/-) mice compared with wild-type mice. MMP-13, ADAMTS-5, and the BMP antagonist noggin were elevated whereas col2a1 and aggrecan were reduced in cartilage and chondrocytes from Sulf(-/-) mice. Articular cartilage and cultured chondrocytes from Sulf(-/-) mice showed reduced Smad1 protein expression and Smad1/5 phosphorylation, whereas Erk1/2 phosphorylation was increased. In human chondrocytes, Sulfs siRNA reduced Smad phosphorylation but enhanced FGF-2-induced Erk1/2 signaling. These findings suggest that Sulfs simultaneously enhance BMP but inhibit FGF signaling in chondrocytes and maintain cartilage homeostasis. Approaches to correct abnormal Sulf expression have the potential to protect against cartilage degradation and promote cartilage repair in OA.

Hyaluronan promotes the chondrocyte response to BMP-7

OBJECTIVE

Chondrocytes exhibit specific responses to bone morphogenetic proteins (BMPs) and transforming growth factor-betas (TGF-betas). The bioactivity of these growth factors is regulated by numerous mediators. In our previous study, Smad1 was found to interact with the cytoplasmic domain of the hyaluronan receptor CD44. The purpose of this study was to determine the ability of hyaluronan in the pericellular matrix to modulate the chondrocyte responses to BMP-7 or TGF-beta1.

EXPERIMENTAL DESIGN

Nuclear translocation of Smad1, Smad2 and Smad4 was studied in bovine articular chondrocytes in response to BMP-7 and TGF-beta1. The effects of matrix disruption by hyaluronidase treatment and the initiation of matrix repair by the addition of hyaluronan on the nuclear translocation of Smad proteins, Smad1 phosphorylation and luciferase expression by a CD44 reporter construct in response to BMP-7 were also studied.

RESULTS

The disruption of the hyaluronan-dependent pericellular matrix of chondrocytes resulted in diminished nuclear translocation of endogenous Smad1 and Smad4 in response to BMP-7; however, the nuclear translocation of Smad2 and Smad4 in these matrix-depleted chondrocytes in response to TGF-beta1 was not diminished. Incubation of the matrix-depleted chondrocytes with exogenous hyaluronan restored Smad1 and Smad4 nuclear translocation and increased pCD44(499)-Luc luciferase expression in response to BMP-7. Both exogenous hyaluronan and matrix re-growth enhanced by hyaluronan synthase-2 (HAS2) transfection restored Smad1 phosphorylation.

CONCLUSIONS

Disruption of hyaluronan-CD44 interactions has little effect on the TGF-beta responses; however, re-establishing CD44-hyaluronan ligation promotes a robust cellular response to BMP-7 by articular chondrocytes. Thus, changes in cell-hyaluronan interactions may serve as a mechanism to modulate cellular responsiveness to BMP-7.

Regulation of the friction coefficient of articular cartilage by TGF-beta1 and IL-1beta

Articular cartilage functions to provide a low-friction surface for joint movement for many decades of life. Superficial zone protein (SZP) is a glycoprotein secreted by chondrocytes in the superficial layer of articular cartilage that contributes to effective boundary lubrication. In both cell and explant cultures, TGF-beta1 and IL-1beta have been demonstrated to, respectively, upregulate and downregulate SZP protein levels. It was hypothesized that the friction coefficient of articular cartilage could also be modulated by these cytokines through SZP regulation. The friction coefficient between cartilage explants (both untreated and treated with TGF-beta1 or IL-1beta) and a smooth glass surface due to sliding in the boundary lubrication regime was measured with a pin-on-disk tribometer. SZP was quantified using an enzyme-linked immunosorbant assay and localized by immunohistochemistry. Both TGF-beta1 and IL-1beta treatments resulted in the decrease of the friction coefficient of articular cartilage in a location- and time-dependent manner. Changes in the friction coefficient due to the TGF-beta1 treatment corresponded to increased depth of SZP staining within the superficial zone, while friction coefficient changes due to the IL-1beta treatment were independent of SZP depth of staining. However, the changes induced by the IL-1beta treatment corresponded to changes in surface roughness, determined from the analysis of surface images obtained with an atomic force microscope. These findings demonstrate that the low friction of articular cartilage can be modified by TGF-beta1 and IL-1beta treatment and that the friction coefficient depends on multiple factors, including SZP localization and surface roughness.

Bone morphogenetic proteins in tissue engineering: the road from the laboratory to the clinic, part I (basic concepts)

Discovered in 1965, bone morphogenetic proteins (BMPs) are a group of cytokines from the transforming growth factor-beta (TGFbeta) superfamily with significant roles in bone and cartilage formation. BMPs are used as powerful osteoinductive components of diverse tissue-engineering products for the healing of bone. Several BMPs with different physiological roles have been identified in humans. The purpose of this review is to cover the biological function of the main members of BMP family, the latest research on BMPs signalling pathways and advances in the production of recombinant BMPs for tissue engineering purposes.

Effects induced by BMPS in cultures of human articular chondrocytes: comparative studies

We compared anabolic and anti-catabolic activities of selected bone morphogenetic proteins (BMP-2, -4, -6, and -7) and cartilage-derived morphogenetic proteins (CDMP-1 and -2) in human normal adult articular chondrocytes. Ankle chondrocytes were cultured in alginate beads in the presence of 10% serum and treated with either growth factors only (each at 100 ng/ml) or the combination of interleukin-1 (IL-1 beta) (0.1 ng/ml) and BMPs. Chondrocyte metabolism was assessed by proteoglycan (PG) synthesis, content, DNA content, and cell survival. The results showed that BMP-2, -4, and -7 were more potent in stimulating PGs than other growth factors tested. The highest levels of PG synthesis were detected at day 9 in the presence of BMP-7. With regard to anti-catabolic properties, the effect depended upon treatment scheme (simultaneous or sequential). Under simultaneous cultures, BMP-2, -4, and -6 failed to counteract IL-1 beta induced inhibition of PG synthesis, while the CDMPs restored this parameter to serum control levels. Only BMP-7 showed consistent and pronounced anti-catabolic activity in either culture treatment scheme. None of the factors induced cell death or chondrocyte proliferation. In conclusion, the growth factors tested showed different levels of effects on human chondrocytes in culture, but only BMP-7 displayed both strong anabolic and anti-catabolic properties.

Chondrogenesis, bone morphogenetic protein-4 and mesenchymal stem cells

OBJECTIVE

As adult cartilage has very limited potential to regenerate, cartilage repair is challenging. Available treatments have several disadvantages, including formation of fibrocartilage instead of hyaline-like cartilage, as well as eventual ossification of the newly formed tissue. The focus of this review is the application of bone morphogenetic protein-4 (BMP-4) and mesenchymal stem cells (MSCs) in cartilage repair, a combination that could potentially lead to the formation of permanent hyaline-like cartilage in the defect.

METHODS

This review is based on recent literature in the orthopaedic and tissue engineering fields, and is focused on MCSs and bone morphogenetic proteins (BMPs).

RESULTS

BMP-4, a stimulator of chondrogenesis, both in vitro and in vivo, is a potential therapeutic agent for cartilage regeneration. BMP-4 delivery can improve the healing process of an articular cartilage defect by stimulating the synthesis of the cartilage matrix constituents: type II collagen and aggrecan. BMP-4 has also been shown to suppress chondrogenic hypertrophy and maintain regenerated cartilage. Use of an appropriate carrier for BMP-4 is crucial for successful reconstruction of cartilage defects. Due to the relatively short half-life in vivo of BMP-4, there is a need to localize and maintain the delivery of BMP-4 to the injury site. Additionally, the delivery of MSCs to the wound site could improve cartilage regeneration; therefore, the carrier should function both as a cell and a protein delivery vehicle.

CONCLUSION

The role of BMP-4 in chondrogenesis is significant, and successful methods to deliver BMP-4, with or without MSCs, to the cartilage defect site are a promising therapy to treat cartilage defects.

Scaffold stiffness influences cell behavior: opportunities for skeletal tissue engineering

Skeletal defects resulting from trauma, tumors, or abnormal development frequently require surgical treatment to restore normal tissue function. To overcome the limitations associated with conventional surgical treatments, several tissue engineering approaches have been developed. In particular, the use of scaffolds enriched with stem cells appears to be a very promising strategy. A crucial issue in this approach is how to control stem cell behavior. In this respect, the effects of growth factors, scaffold surface characteristics, and external ‘active’ loading conditions on stem cell behavior have been investigated. Recently, it has become clear that the stiffness of a scaffold is a highly potent regulator of stem cell differentiation. In addition, the stiffness of a scaffold affects cell migration, which is important for the infiltration of host tissue cells. This review summarizes current knowledge on the role of the scaffold stiffness in the regulation of cell behavior. Furthermore, we discuss how this knowledge can be incorporated in scaffold design which may provide new opportunities in the context of orthopedic tissue engineering.

Differential regulation of lubricin/superficial zone protein by transforming growth factor beta/bone morphogenetic protein superfamily members in articular chondrocytes and synoviocytes

OBJECTIVE

To investigate the role of transforming growth factor beta (TGFbeta)/bone morphogenetic protein (BMP) superfamily members on accumulation of superficial zone protein (SZP) in articular chondrocytes and synoviocytes.

METHODS

Chondrocytes and synoviocytes were isolated from articular cartilage and synovium from calf stifle joints and cultured as monolayers in serum-free chemically defined medium. Articular chondrocytes were isolated from 3 distinct zones of the cartilage: superficial, middle, and deep. Accumulation of SZP in the culture medium in response to various members of the TGFbeta/BMP superfamily was demonstrated by immunoblotting and quantified by enzyme-linked immunosorbent assay.

RESULTS

TGFbeta stimulated SZP accumulation in both superficial zone chondrocytes and synoviocytes. The 3 isoforms of TGFbeta elicited a similar dose response. Inhibition of TGFbeta receptor type I kinase by the specific inhibitor SB431542 abolished the TGFbeta-stimulated accumulation of SZP. BMPs up-regulated SZP accumulation in the superficial zone; however, the magnitude of the effects was not as great as was observed with TGFbeta. There was an additive action between TGFbeta and BMP on SZP accumulation. The response of synoviocytes to BMP was stronger than that of superficial zone chondrocytes. Activin up-regulated SZP accumulation in synoviocytes, but not in chondrocytes.

CONCLUSION

TGFbeta is a critical regulator of SZP accumulation in both superficial zone articular chondrocytes and synoviocytes. TGFbeta and BMP have an additive effect. Synoviocytes are more sensitive to BMP family members and activins than are superficial zone articular chondrocytes. Thus, regulation of SZP accumulation by TGFbeta /BMP superfamily members is regulated differently in articular chondrocytes and synoviocytes.

Increased accumulation of superficial zone protein (SZP) in articular cartilage in response to bone morphogenetic protein-7 and growth factors

The purpose of this study was to investigate the role of bone morphogenetic proteins (BMPs), such as BMP-7, growth factors, and cytokines, in the accumulation of superficial zone protein (SZP) in bovine articular cartilage. Calf superficial articular cartilage discs and chondrocytes were obtained for explant and monolayer culture systems, respectively. Dose- and time-dependent actions of BMP-7 on SZP accumulation were investigated in both explant and monolayer culture systems. In addition, actions of various morphogens and growth factors [BMP-2, BMP-4, fibroblast growth factor 2 (FGF-2), insulin-like growth factor 1 (IGF-1), platelet-derived growth factor (PDGF), and transforming growth factor beta (TGF-beta1)], and cytokines [interleukin (IL)-1alpha, IL-1beta, and tumor necrosis factor (TNF-alpha)] alone, and in combination with BMP-7, on SZP accumulation were investigated in monolayer culture systems. SZP accumulation was quantified in both the cartilage and the medium using SDS-PAGE and subsequent immunoblotting. In both explant and monolayer cultures, BMP-7 increased SZP accumulation in a dose- and time-dependent fashion (p < 0.05). Furthermore, SZP accumulation was significantly increased in monolayer cultures by FGF-2, IGF-1, PDGF, and TGF-beta1 (p < 0.05). Both IL-1alpha and TNF-alpha significantly reduced SZP accumulation (p < 0.05). The inhibition of SZP accumulation by TNF-alpha was partially alleviated by concurrent treatment with BMP-7. The results of this investigation provide novel insights into the role of morphogens, especially BMP-7, growth factors, and cytokines in the accumulation of SZP in articular cartilage. This information has clinical implications because stimulation of SZP may ameliorate the pathology of joint function in arthritis. Furthermore, tissue engineering approaches to articular cartilage may depend on the optimal synthesis and assembly of SZP in the superficial zone to ensure functional tissue architecture.

Aging, osteoarthritis and transforming growth factor-beta signaling in cartilage

Osteoarthritis is a common malady of the musculoskeletal system affecting the articular cartilage. The increased frequency of osteoarthritis with aging indicates the complex etiology of this disease, which includes pathophysiology and joint stability including biomechanics. The balance between anabolic morphogens and growth factors and catabolic cytokines is at the crux of the problem of osteoarthritis. One such signal is transforming growth factor-beta (TGF-beta). The impaired TGF-beta signaling has been identified as a culprit in old mice in a recent article in this journal. This commentary places this discovery in the context of anabolic and catabolic signals and articular cartilage homeostasis in the joint.

Global gene profiling reveals a downregulation of BMP gene expression in experimental atrophic nonunions compared to standard healing fractures

Nonunion is a challenging problem that may occur following certain bone fractures. However, there has been little investigation of the molecular basis of nonunions. Bone morphogenetic proteins (BMPs) play a significant role in osteogenesis. However, little is known about the expression patterns of BMPs in abnormal bone healing that results in nonunion formation. These facts prompted us to investigate and compare the gene expression patterns of BMPs and their antagonists in standard healing fractures and nonunions using rat experimental models. Standard closed healing fractures and experimental atrophic nonunions produced by periosteal cauterization at the fracture site were created in rat femurs. At postfracture days 3, 7, 10, 14, 21, and 28, total RNA was extracted from the callus of standard healing fracture and fibrous tissue of nonunion (n=4 per each time point and each group). Gene expression of BMPs, BMP antagonists, and other regulatory molecules were studied by methods including Genechip microarray and real-time quantitative RT-PCR. Gene expression of BMP-2, 3, 3B, 4, 6, 7, GDF-5, 7, and BMP antagonists noggin, drm, screlostin, and BAMBI were significantly lower in nonunions compared to standard healing fractures at several time points. Downregulation in expression of osteogenic BMPs may account for the nonunions of fracture. The balance between BMPs and their endogenous antagonists is critical for optimal fracture healing.

Noggin haploinsufficiency differentially affects tissue responses in destructive and remodeling arthritis

OBJECTIVE

The balance between destruction and homeostatic or reparative responses determines the outcome of arthritis. Increasing evidence suggests a role for signaling pathways, essential for development and growth, in the maintenance of tissue homeostasis and attempts at repair. Inappropriate activation of such pathways may also have a role in disease progression. We undertook this study to determine the effect of shifting the balance in bone morphogenetic protein (BMP) signaling in different mouse models of arthritis.

METHODS

Endogenous levels of noggin, a BMP antagonist, were reduced using heterozygous noggin(+/LacZ) mice in a model of inflammation-driven destruction (methylated bovine serum albumin [mBSA]-induced monarthritis), a model of systemic autoimmune arthritis (collagen-induced arthritis [CIA]), and a model of joint ankylosis (spontaneous arthritis in DBA/1 mice). In addition, we studied BMP inactivation by adenoviral noggin overexpression in destructive arthritis. Cartilage damage and activation of BMP signaling were studied by digital image analysis using Safranin O sulfated glycosaminoglycan staining and immunohistochemistry for phosphorylated Smads (Smads 1, 5, and 8), respectively.

RESULTS

Noggin haploinsufficiency provided protection for articular cartilage against destruction in mBSA-induced arthritis. Antagonist overexpression rendered cartilage more vulnerable in this model. Noggin gene transfer in knees affected by CIA also enhanced cartilage damage. Haploinsufficiency did not affect CIA, but noggin(+/LacZ) mice had an increased number of CD4-positive cells with normal immune responses. In noggin(+/LacZ) DBA/1 mice with spontaneous arthritis, we observed delayed progression from cartilage to bone formation.

CONCLUSION

Tight spatiotemporal control of BMP signaling appears to be critical in the response of joint tissues in models of arthritis.

Stem cell-based composite tissue constructs for regenerative medicine

A major task of contemporary medicine and dentistry is restoration of human tissues and organs lost to diseases and trauma. A decade-long intense effort in tissue engineering has provided the proof of concept for cell-based replacement of a number of individual tissues such as the skin, cartilage, and bone. Recent work in stem cell-based in vivo restoration of multiple tissue phenotypes by composite tissue constructs such as osteochondral and fibro-osseous grafts has demonstrated probable clues for bioengineered replacement of complex anatomical structures consisting of multiple cell lineages such as the synovial joint condyle, tendon-bone complex, bone-ligament junction, and the periodontium. Of greater significance is a tangible contribution by current attempts to restore the structure and function of multitissue structures using cell-based composite tissue constructs to the understanding of ultimate biological restoration of complex organs such as the kidney or liver. The present review focuses on recent advances in stem cell-based composite tissue constructs and attempts to outline challenges for the manipulation of stem cells in tailored biomaterials in alignment with approaches potentially utilizable in regenerative medicine of human tissues and organs.

Bone Morphogenetic Protein signaling in joint homeostasis and disease

Despite advances in therapies that target inflammation and tissue destruction in chronic arthritis, stimulation of tissue repair and restoration of joint function, the ultimate goal of treatment, is far from achieved. We introduce a new paradigm that may help to improve our understanding and management of chronic arthritis. The presence or absence of tissue responses distinguishes destructive arthritis, steady-state arthritis and remodeling arthritis. Increasing evidence suggests that reactivation of embryonic molecular pathways is an important mechanism to stimulate postnatal tissue repair. Bone Morphogenetic Proteins (BMPs) have critical roles in skeletal development and joint morphogenesis, but also in postnatal joint homeostasis and joint tissue remodeling. Therefore, modulation of BMP signaling may be an attractive therapeutic target in chronic arthritis to restore homeostasis and function of synovial joints.

Modulation of bone morphogenetic protein signaling inhibits the onset and progression of ankylosing enthesitis

Joint ankylosis is a major cause of disability in the human spondyloarthropathies. Here we report that this process partially recapitulates embryonic endochondral bone formation in a spontaneous model of arthritis in DBA/1 mice. Bone morphogenetic protein (BMP) signaling appears to be a key molecular pathway involved in this pathological cascade. Systemic gene transfer of noggin, a BMP antagonist, is effective both as a preventive and a therapeutic strategy in the mouse model, mechanistically interfering with enthesial progenitor cell proliferation in early stages of the disease process. Immunohistochemical staining for phosphorylated smad1/5 in enthesial biopsies of patients with spondyloarthropathy reveals active BMP signaling in similar target cells. Our data suggest that BMP signaling is an attractive therapeutic target for interfering with structural changes in spondyloarthropathy either as an alternative or complementary approach to current antiinflammatory treatments.