Smad signaling in skeletal development and regeneration

Shape-fitting collagen-PLA composite promotes osteogenic differentiation of porcine adipose stem cells

Craniomaxillofacial bone defects can occur as a result of congenital, post-oncologic, and high-energy impact conditions. The scale and irregularity of such defects motivate new biomaterials to promote regeneration of the damaged bone. We have recently described a mineralized collagen scaffold capable of instructing stem cell osteogenic differentiation and new bone infill in the absence of traditional osteogenic supplements. Herein, we report the integration of a millimeter-scale reinforcing poly (lactic acid) frame fabricated via 3D-printing into the mineralized collagen scaffold with micron-scale porosity to form a multi-scale mineralized collagen-PLA composite. We describe modifications to the PLA frame design to increase the compressive strength (Young's Modulus, ultimate stress and strain) of the composite. A critical challenge beyond increasing the compressive strength of the collagen scaffold is addressing challenges inherent with the irregularity of clinical defects. As a result, we examined the potential for modifying the frame architecture to render the composite with increased compressive strength in one axis or radial compressibility and shape-fitting capacity in an orthogonal axis. A library of mineralized collagen-PLA composites was mechanically characterized via compression testing and push-out test to describe mechanical performance and shape-fitting capacity. We also report in vitro comparison of the bioactivity of porcine adipose derived stem cells in the mineralized collagen-PLA composite versus the mineralized collagen scaffold via metabolic activity, gene expression, and functional matrix synthesis. The results suggest that incorporation of the PLA reinforcing frame does not negatively influence the osteoinductive nature of the mineralized collagen scaffold. Together, these findings suggest a strategy to address often competing bioactivity, mechanical strength, and shape-fitting design requirements for biomaterials for craniomaxillofacial bone regeneration.

Retinoic acid increases the effect of bone morphogenetic protein type 2 on osteogenic differentiation of human adipose-derived stem cells

BACKGROUND

Bone morphogenetic protein type 2 (BMP-2) and retinoic acid (RA) are osteoinductive factors that stimulate endogenous mechanisms of bone repair which can be applied on management of osseous defects in oral and maxillofacial fields.

OBJECTIVE

Considering the different results of RA on osteogenesis and its possible use to substitute/potency BMP-2 effects, this study evaluated the outcomes of BMP-2, RA, and BMP-2+RA treatments on in vitro osteogenic differentiation of human adipose-derived stem cells (ASCs) and the signaling pathway(s) involved.

MATERIAL AND METHODS

ASCs were treated every other day with basic osteogenic medium (OM) alone or supplemented with BMP-2, RA, or BMP-2+RA. Alkaline phosphatase (ALP) activity was determined using the r-nitrophenol method. Extracellular matrix mineralization was evaluated using von Kossa staining and calcium quantification. Expression of osteonectin and osteocalcin mRNA were determined using qPCR. Smad1, Smad4, phosphorylated Smad1/5/8, BMP-4, and BMP-7 proteins expressions were analyzed using western blotting. Signaling pathway was evaluated using the IPA® software.

RESULTS

RA promoted the highest ALP activity at days 7, 14, 21, and 28, in comparison to BMP-2 and BMP-2+RA. BMP-2+RA best stimulated phosphorylated Smad1/5/8 protein expression at day 7 and Smad4 expression at days 7, 14, 21, and 28. Osteocalcin and osteonectin mRNA expressions were best stimulated by BMP-2+RA at day 7. Matrix mineralization was most improved by BMP-2+RA at days 12 and 32. Additionally, BMP-2+RA promoted the highest BMP signaling pathway activation at days 7 and 14, and demonstrated more activation of differentiation of bone-forming cells than OM alone.

CONCLUSIONS

In summary, RA increased the effect of BMP-2 on osteogenic differentiation of human ASCs.

Graphene-Induced Osteogenic Differentiation Is Mediated by the Integrin/FAK Axis

Graphene is capable of promoting osteogenesis without chemical induction. Nevertheless, the underlying mechanism(s) remain largely unknown. The objectives here were: (i) to assess whether graphene scaffolds are capable of supporting osteogenesis in vivo and; (ii) to ascertain the participation of the integrin/FAK mechanotransduction axis during the osteogenic differentiation induced by graphene. MSC-impregnated graphene scaffolds (n = 6) were implanted into immunocompromised mice (28 days). Alternatively, MSCs were seeded onto PDMS substrates (modulus of elasticity = 130, 830 and 1300 kPa) coated with a single monomolecular layer of graphene and cultured in basal medium (10 days). The ensuing expressions of FAK-p397, integrin, ROCK1, F-actin, Smad p1/5, RUNX2, OCN and OPN were evaluated by Western blot (n = 3). As controls, MSCs were plated onto uncoated PDMS in the presence of mechanotransduction inhibitors (echistatin, Y27632 and DMH1). MSC-impregnated graphene scaffolds exhibited positive immunoexpression of bone-related markers (RUNX2 and OPN) without the assistance of osteogenic inducers. In vitro, regardless of the stiffness of the underlying PDMS substrate, MSCs seeded onto graphene-coated PDMS substrates demonstrated higher expressions of all tested osteogenic and integrin/FAK proteins tested compared to MSCs seeded onto PDMS alone. Hence, graphene promotes osteogenesis via the activation of the mechanosensitive integrin/FAK axis.

MiRNA-10b Reciprocally Stimulates Osteogenesis and Inhibits Adipogenesis Partly through the TGF-β/SMAD2 Signaling Pathway

As the population ages, the medical and socioeconomic impact of age-related bone disorders will further increase. An imbalance between osteogenesis and adipogenesis of mesenchymal stem cells (MSCs) can lead to various bone and metabolic diseases such as osteoporosis. Thus, understanding the molecular mechanisms underlying MSC osteogenic and adipogenic differentiation is important for the discovery of novel therapeutic paradigms for these diseases. miR-10b has been widely reported in tumorigenesis, cancer invasion and metastasis. However, the effects and potential mechanisms of miR-10b in the regulation of MSC adipogenic and osteogenic differentiation have not been explored. In this study, we found that the expression of miR-10b was positively correlated with bone formation marker genes ALP, RUNX2 and OPN, and negatively correlated with adipogenic markers CEBPα, PPARγ and AP2 in clinical osteoporosis samples. Overexpression of miR-10b enhanced osteogenic differentiation and inhibited adipogenic differentiation of human adipose-derived mesenchymal stem cells (hADSCs) in vitro, whereas downregulation of miR-10b reversed these effects. Furthermore, miR-10b promoted ectopic bone formation in vivo. Target prediction and dual luciferase reporter assays identified SMAD2 as a potential target of miR-10b. Silencing endogenous SMAD2 expression in hADSCs enhanced osteogenesis but repressed adipogenesis. Pathway analysis indicated that miR-10b promotes osteogenic differentiation and bone formation via the TGF-β signaling pathway, while suppressing adipogenic differentiation may be primarily mediated by other pathways. Taken together, our findings imply that miR-10b acts as a critical regulator for balancing osteogenic and adipogenic differentiation of hADSCs by repressing SMAD2 and partly through the TGF-β pathway. Our study suggests that miR-10b is a novel target for controlling bone and metabolic diseases.

Combined sustained release of BMP2 and MMP10 accelerates bone formation and mineralization of calvaria critical size defect in mice

The effect of dual delivery of bone morphogenetic protein-2 (BMP-2) and matrix metalloproteinase 10 (MMP10) on bone regeneration was investigated in a murine model of calvarial critical-size defect, hypothesizing that it would result in an enhanced bone formation. Critical-size calvarial defects (4 mm diameter) were created in mice and PLGA microspheres preloaded with either BMP-2, MMP10 or a microsphere combination of both were transplanted into defect sites at different doses. Empty microspheres were used as the negative control. Encapsulation efficiency was assessed and in vivo release kinetics of BMP-2 and MMP10 were examined over 14 days. Histological analyses were used to analyze bone formation after four and eight weeks. Combination with MMP10 (30 ng) significantly enhanced BMP-2 (600 ng)-mediated osteogenesis, as confirmed by the increase in percentage of bone fill (p < .05) at four weeks. Moreover, it also increased mineral apposition rate (p < .05), measured by double labeling with tetracycline and calceine. MMP10 accelerates bone repair by enhancing BMP-2-promoted bone healing and improving the mineralization rate. In conclusion combination of MMP10 and BMP-2 may become a promising strategy for repair and regeneration of bone defects.

The MAPK Erk5 is necessary for proper skeletogenesis involving a Smurf-Smad-Sox9 molecular axis

Erk5 belongs to the mitogen-activated protein kinase (MAPK) family. Following its phosphorylation by Mek5, Erk5 modulates several signaling pathways in a number of cell types. In this study, we demonstrated that Erk5 inactivation in mesenchymal cells causes abnormalities in skeletal development by inducing Sox9, an important transcription factor of skeletogenesis. We further demonstrate that Erk5 directly phosphorylates and activates Smurf2 (a ubiquitin E3 ligase) at Thr²⁴⁹, which promotes the proteasomal degradation of Smad proteins and phosphorylates Smad1 at Ser²⁰⁶ in the linker region known to trigger its proteasomal degradation by Smurf1. Smads transcriptionally activated the expression of Sox9 in mesenchymal cells. Accordingly, removal of one Sox9 allele in mesenchymal cells from Erk5-deficient mice rescued some abnormalities of skeletogenesis. These findings highlight the importance of the Mek5-Erk5-Smurf-Smad-Sox9 axis in mammalian skeletogenesis.

Development of Normal and Cleft Palate: A Central Role for Connective Tissue Growth Factor (CTGF)/CCN2

Development of the palate is the result of an organized series of events that require exquisite spatial and temporal regulation at the cellular level. There are a myriad of growth factors, receptors and signaling pathways that have been shown to play an important role in growth, elevation and/or fusion of the palatal shelves. Altered expression or activation of a number of these factors, receptors and signaling pathways have been shown to cause cleft palate in humans or mice with varying degrees of penetrance. This review will focus on connective tissue growth factor (CTGF) or CCN2, which was recently shown to play an essential role in formation of the secondary palate. Specifically, the absence of CCN2 in KO mice results in defective cellular processes that contribute to failure of palatal shelf growth, elevation and/or fusion. CCN2 is unique in that it has been shown to interact with a number of other factors important for palate development, including bone morphogenetic proteins (BMPs), fibroblast growth factors (FGFs), epidermal growth factor (EGF), Wnt proteins and transforming growth factor-βs (TGF-βs), thereby influencing their ability to bind to their receptors and mediate intracellular signaling. The role that these factors play in palate development and their specific interactions with CCN2 will also be reviewed. Future studies to elucidate the precise mechanisms of action for CCN2 and its interactions with other regulatory proteins during palatogenesis are expected to provide novel information with the potential for development of new pharmacologic or genetic treatment strategies for clinical intervention of cleft palate during development.

Genetic Engineering of Mesenchymal Stem Cells for Differential Matrix Deposition on 3D Woven Scaffolds

Tissue engineering approaches for the repair of osteochondral defects using biomaterial scaffolds and stem cells have remained challenging due to the inherent complexities of inducing cartilage-like matrix and bone-like matrix within the same local environment. Members of the transforming growth factor β (TGFβ) family have been extensively utilized in the engineering of skeletal tissues, but have distinct effects on chondrogenic and osteogenic differentiation of progenitor cells. The goal of this study was to develop a method to direct human bone marrow-derived mesenchymal stem cells (MSCs) to deposit either mineralized matrix or a cartilaginous matrix rich in glycosaminoglycan and type II collagen within the same biochemical environment. This differential induction was performed by culturing cells on engineered three-dimensionally woven poly(ɛ-caprolactone) (PCL) scaffolds in a chondrogenic environment for cartilage-like matrix production while inhibiting TGFβ3 signaling through Mothers against DPP homolog 3 (SMAD3) knockdown, in combination with overexpressing RUNX2, to achieve mineralization. The highest levels of mineral deposition and alkaline phosphatase activity were observed on scaffolds with genetically engineered MSCs and exhibited a synergistic effect in response to SMAD3 knockdown and RUNX2 expression. Meanwhile, unmodified MSCs on PCL scaffolds exhibited accumulation of an extracellular matrix rich in glycosaminoglycan and type II collagen in the same biochemical environment. This ability to derive differential matrix deposition in a single culture condition opens new avenues for developing complex tissue replacements for chondral or osteochondral defects.

Role of TGFβ Signaling in Maternal Ethanol-Induced Fetal Articular Cartilage Dysplasia and Adult Onset of Osteoarthritis in Male Rats

Based on our previous findings that prenatal ethanol exposure in offspring increased susceptibility to adult osteoarthritis, this study aimed to further investigate the direct toxicity of ethanol on fetal articular cartilage development. Rat bone marrow-derived stroma cells were capsulated in alginate beads, incubated in a chondrogenic differentiation medium, and cultured for 4 weeks with ethanol treatment at concentrations of 0, 4, 20, and 100 mM. Pregnant rats were treated with ethanol (4 g/kg/day) from gestational days (GDs) 9 to 20. At GD20 and postnatal weeks 2, 6, and 12, 8 male offspring were sacrificed, and 8 male offspring rats of 8-weeks old in each group were treated with or without intraarticular injection of papain for 4 weeks to verify the susceptibility of adult osteoarthritis. Ethanol treatment resulted in poor differentiation of bone marrow-derived stroma cells to chondrocytes and suppressed the expression of the transforming growth factor-β (TGFβ)-smad2/3-Sox9 signaling pathway. In animal experiments, the shape of articular cartilage in the ethanol treatment group was more disordered than that of the control group, the matrix was not deep, and the cartilage was thin, which showed poor cartilage development. The TGFβ signaling pathway in the ethanol treatment group was persistently low at all time points. After intraarticular injection of papain, histological analyses, and the Mankin score revealed increased cartilage destruction in the ethanol treatment group. Ethanol caused articular cartilage dysplasia that was programmed in adulthood via a low-functional TGFβ signaling pathway, and the tolerance of this articular cartilage to external stimuli was significantly decreased.

Nonmineralized and Mineralized Collagen Scaffolds Induce Differential Osteogenic Signaling Pathways in Human Mesenchymal Stem Cells

The instructive capabilities of extracellular matrix components in progenitor cell differentiation have recently generated significant interest in the development of bioinspired materials for regenerative applications. Previously, a correlation was described between the osteogenic capabilities of nanoparticulate mineralized collagen glycosaminoglycan scaffolds (MC-GAG) and an autogenous activation of small mothers against decapentaplegic ( Smad1/5) in the canonical bone morphogenetic protein receptor (BMPR) pathway with a diminished extracellular signal regulated kinase 1/2 (ERK1/2) activation when compared to nonmineralized collagen glycosaminoglycan scaffolds (Col-GAG). This work utilizes a canonical BMPR inhibitor (dorsomorphin homologue 1, DMH1) and an inhibitor of the mitogen activated protein kinase/ERK kinase (MEK)/(ERK) cascade (PD98059) to characterize the necessity of each pathway for osteogenesis. While DMH1 inhibits runt-related transcription factor 2 (Runx2) and bone sialoprotein II (BSPII) gene expression of primary human mesenchymal stem cells (hMSCs) on MC-GAG, PD98059 inhibits BSPII expression on Col-GAG independent of Runx2 expression. DMH1 inhibits mineralization on both Col-GAG and MC-GAG, however, PD98059 only inhibits mineralization on Col-GAG. DMH1 inhibits both Smad1/5 phosphorylation and Runx2 protein expression, whereas PD98059 inhibits ERK1/2 and c-Jun amino-terminal kinase 1/2 (JNK1/2) phosphorylation without affecting Runx2. Thus, activation of the canonical BMPR signaling is necessary for osteogenic differentiation and mineralization of hMSCs on Col-GAG or MC-GAG. The MEK/ERK cascade, intimately tied to JNK activation, is necessary for Runx2-independent osteogenesis on Col-GAG, while completely dispensable in osteogenesis on MC-GAG.

Mechanism of triptolide in treating ankylosing spondylitis through the anti‑ossification effect of the BMP/Smad signaling pathway

The present study aimed to examine the mechanism of triptolide in the treatment of ankylosing spondylitis (AS) through the anti‑ossification effect of bone morphogenetic protein (BMP)/small mothers against decapentaplegic (Smad) pathway. Male rats were randomly divided into five groups: Normal rat group; model group; triptolide low dose group (10 mg/kg); triptolide middle dose group (20 mg/kg); triptolide high dose group (40 mg/kg). The spinal joint capsules of each group of rats were collected to perform primary cell culture to determine the levels of cell proliferation. Western blot and reverse transcription‑polymerase chain reaction analyses, and ELISA were used to detect the mRNA and protein expression levels of core‑binding factor α1 (Cbfal), BMP receptor type II (BMPRII), Smad1, Smad4, Smad5 and Smad6, the protein expression of phosphorylation indicators, including phosphorylated (p)Smad1 and pSmad5, the mRNA expression of tumor necrosis factor‑α (TNF‑α), interleukin (IL)‑1β and IL‑6 in rat plasma, and the mRNA expression of BMP/Smads in fibroblasts induced by recombinant human (rh)BMP‑2. The effects on AS in the rats were also examined. The results revealed that, following intervention with triptolide, inflammation was suppressed, and the mRNA expression levels of TNF‑α, IL‑1β and IL‑6 were reduced. The expression levels of Cbfal, BMPRII, Smad1, Smad4 and Smad5 were also reduced, whereas the expression of Smad6 was increased. Following induction by rhBMP‑2, the effects of triptolide weakened, with the most marked effects observed at the highest concentration, suggesting that triptolide functions through the BMP/Smad signaling pathway. Taken together, the results suggested that triptolide may be used to treat AS, the mechanism of which may be through the BMP/Smad pathway.

The Effects of Cerium Valence States at Cerium Oxide Coatings on the Responses of Bone Mesenchymal Stem Cells and Macrophages

Ideal orthopedic coatings should trigger good osteogenic response and limited inflammatory response. The cerium valence states in ceria are associated with their anti-oxidative activity and anti-inflammatory property. In the study, we prepared two kinds of plasma sprayed CeO₂ coatings with different Ce⁴⁺ concentrations to investigate the effects of Ce valence states on the response of bone mesenchymal stem cells (BMSCs) and macrophage RAW264.7. Both the coatings (CeO₂-A and CeO₂-B) were characterized via XRD, SEM, and X-ray photoelectron spectroscopy. The CeO₂ coatings enhanced osteogenic behaviors of BMSCs in terms of cellular proliferation, alkaline phosphatase (ALP) activity and calcium deposition activity in comparison with the Ti substrate. In particular, the CeO₂-B coating (higher Ce⁴⁺ concentration) elicited greater effects than the CeO₂-A coating (higher Ce³⁺ concentration). RT-PCR and western blot results suggested that the CeO₂-B coating promoted BMSCs osteogenic differentiation through the SMAD-dependent BMP signaling pathway, which activated Runx2 expression and subsequently enhanced the expression of ALP and OCN. With respect to either CeO₂-A coating or Ti substrate, the CeO₂-B coating exerted greater effects on the macrophages, increasing the anti-inflammatory cytokines (IL-10 and IL-1ra) expression and suppressing the expression of the pro-inflammatory cytokines (TNF-α and IL-6) and ROS production. Furthermore, it also upregulated the expression of osteoinductive molecules (TGF-β1 and BMP2) in the macrophages. The regulation of cerium valence states at plasma sprayed ceria coatings can be a valuable strategy to improve osteogenic properties and alleviate inflammatory response.

Spatial and temporal expression of Smad signaling members during the development of mandibular condylar cartilage

The present study aimed to explore the underlying developmental mechanism of mothers against decapentaplegic homolog (Smad) signaling in the development of mandibular condylar cartilage. To achieve this, the expression levels of Smad2, 3, 4 and 7, and phosphorylated Smad2/3 were investigated at different time points in developing mandibular condylar cartilage. Mandibular condyles from C57BL/6J mice were dissected at the prenatal and postnatal stages. Serial sections were made and the distributions of Smad proteins were examined using immunohistochemical techniques intermittently between day 14.5 of gestation and postnatal day 7. All Smad proteins examined in the present study were expressed in the condylar blastema and during early chondrogenesis. At the postnatal stage, Smad2 and 4 were localized in proliferative and mineralized hypertrophic chondrocytes. Smad3 and 7 were expressed in proliferative and hypertrophic chondrocytes, including pre-hypertrophic and mineralized hypertrophic chondrocytes. Later, positive immunoreactivity of Smad3 reduced at postnatal day 7. A similar expression pattern to Smad3 was observed for p-Smad2/3, but p-Smad2/3 was located in the nuclei of proliferative chondrocytes. These results suggest that Smad signaling members are involved in the development of mandibular condylar cartilage. In addition, the spatial and temporal expression of these Smads indicate that Smad signaling is involved in regulating the differentiation of chondrocytes and endochondral ossification, in order to maintain normal chondrogenesis and morphogenesis of mandibular condylar cartilage.

Comprehensive transcriptome mining of the direct conversion of mesodermal cells

The direct reprogramming of somatic cells is a promising approach for regenerative medicine, especially in the production of mesoderm layer-derived cells. Meta-analysis studies provide precise insight into the undergoing processes and help increase the efficiency of reprogramming. Here, using 27 high-throughput expression data sets, we analyzed the direct reprogramming of mesodermal cells in humans and mice. Fibroblast-derived cells showed a common expression pattern of up- and down-regulated genes that were mainly involved in the suppression of the fibroblast-specific gene expression program, and may be used as markers of the initiation of reprogramming. Furthermore, we found a specific gene expression profile for each fibroblast-derived cell studied, and each gene set appeared to play specific functional roles in its cell type, suggesting their use as markers for their mature state. Furthermore, using data from protein-DNA interactions, we identified the main transcription factors (TFs) involved in the conversion process and ranked them based on their importance in their gene regulatory networks. In summary, our meta-analysis approach provides new insights on the direct conversion of mesodermal somatic cells, introduces a list of genes as markers for initiation and maturation, and identifies TFs for which manipulating their expression may increase the efficiency of direct conversion.

Reprogramming of Dermal Fibroblasts into Osteo-Chondrogenic Cells with Elevated Osteogenic Potency by Defined Transcription Factors

Recent studies using defined transcription factors to convert skin fibroblasts into chondrocytes have raised the question of whether osteo-chondroprogenitors expressing SOX9 and RUNX2 could also be generated during the course of the reprogramming process. Here, we demonstrated that doxycycline-inducible expression of reprogramming factors (KLF4 [K] and c-MYC [M]) for 6 days were sufficient to convert murine fibroblasts into SOX9+/RUNX2+ cellular aggregates and together with SOX9 (S) promoted the conversion efficiency when cultured in a defined stem cell medium, mTeSR. KMS-reprogrammed cells possess gene expression profiles akin to those of native osteo-chondroprogenitors with elevated osteogenic properties and can differentiate into osteoblasts and chondrocytes in vitro, but form bone tissue upon transplantation under the skin and in the fracture site of mouse tibia. Altogether, we provide a reprogramming strategy to enable efficient derivation of osteo-chondrogenic cells that may hold promise for cell replacement therapy not limited to cartilage but also for bone tissues.

Effects of the combined Herba Epimedii and Fructus Ligustri Lucidi on bone turnover and TGF-β1/Smads pathway in GIOP rats

ETHNOPHARMACOLOGICAL RELEVANCE

Kidney deficiency is the main pathogenesis of osteoporosis based on the theory of "kidney governing bones" in traditional Chinese medicine (TCM). Combined Herba Epimedii and Fructus Ligustri Lucidi, based on traditional Chinese formula Er-Zhi pills, were frequently used in TCM formulas that were prescribed for kidney tonifying and bone strengthening. However, it is unclear whether the combination of the two herbs may have a protective influence on glucocorticoid-induced osteoporosis (GIOP). The objective of this study was to evaluate the therapeutic effects and the underlying molecular mechanism of the decoction and the active fractions of the combined herbs in GIOP rats.

MATERIALS AND METHODS

Male Sprague-Dawley rats were divided into seven groups, including the normal control (NC), GIOP model (MO), active fractions low (100mg/kg, LAF), active fractions high (200mg/kg, HAF), decoction low (3.5g/kg, LD), decoction high (7g/kg, HD) and Calcium with Vitamin D3 (0.2773g/kg, CaD)-treated group. The GIOP model was established by intramuscular injection of dexamethasone (1mg/kg) twice a week for 8 weeks. Different kinds of indicators were measured, including bone mineral density (BMD), bone biomechanical properties, serum bone alkaline phosphatase (b-ALP), serum bone γ-carboxyglutamic acid-containing protein (BGP), serum bone morphogenetic protein-2 (BMP-2), serum tartrate-resistant acid phosphatase (TRACP) and serum carboxy terminal cross linked telopeptide of typeⅠcollagen (ICTP), bone mineral content (BMC) and bone structured histomorphometry. The protein and mRNA expression of TGF-β1, Smad2, Smad3, Smad4 and Smad7 were detected by Western blotting (WB) and quantitative real time polymerase chain reaction (qRT-PCR), respectively.

RESULTS

Administration of combined Herba Epimedii and Fructus Ligustri Lucidi decoction and combined active fractions could significantly prevent GC-induced bone loss by increasing the contents of serum b-ALP, BGP and BMP-2 as the markers of bone formation, reducing the serum TRACP and ICTP contents to inhibit bone resorption and enhancing BMC. They could also attenuate biomechanical properties and BMD reduction, deterioration of trabecular architecture in MO rats. The mRNA and protein expressions of TGF-β1, smad2, smad3 and smad4 were up-regulated, and the mRNA and protein expression of Smad7 was down-regulated following combined Herba Epimedii and Fructus Ligustri Lucidi treatment.

CONCLUSION

Combination of Herba Epimedii and Fructus Ligustri Lucidi exhibited protective effects on promoting bone formation and precluding bone resorption. The underlying mechanism may be attributed to its regulations on TGF-β1/Smads pathway. The substance bases of the combined herbs on anti-osteoporosis were total flavonoids of Herba Epimedii, total iridoids and flavonoids of Fructus Ligustri Lucidi.

Increased PLEKHO1 within osteoblasts suppresses Smad-dependent BMP signaling to inhibit bone formation during aging

Emerging evidence indicates that the dysregulation of protein ubiquitination plays a crucial role in aging‐associated diseases. Smad‐dependent canonical BMP signaling pathway is indispensable for osteoblastic bone formation, which could be disrupted by the ubiquitination and subsequent proteasomal degradation of Smad1/5, the key molecules for BMP signaling transduction. However, whether the dysregulation of Smad1/5 ubiquitination and disrupted BMP signaling pathway is responsible for the age‐related bone formation reduction is still underexplored. Pleckstrin homology domain‐containing family O member 1 (PLEKHO1) is a previously identified ubiquitination‐related molecule that could specifically target the linker region between the WW domains of Smurf1 to promote the ubiquitination of Smad1/5. Here, we found an age‐related increase in the expression of PLEKHO1 in bone specimens from either fractured patients or aging rodents, which was associated with the age‐related reduction in Smad‐dependent BMP signaling and bone formation. By genetic approach, we demonstrated that loss of Plekho1 in osteoblasts could promote the Smad‐dependent BMP signaling and alleviated the age‐related bone formation reduction. In addition, osteoblast‐specific Smad1 overexpression had beneficial effect on bone formation during aging, which could be counteracted after overexpressing Plekho1 within osteoblasts. By pharmacological approach, we showed that osteoblast‐targeted Plekho1 siRNA treatment could enhance Smad‐dependent BMP signaling and promote bone formation in aging rodents. Taken together, it suggests that the increased PLEKHO1 could suppress Smad‐dependent BMP signaling to inhibit bone formation during aging, indicating the translational potential of targeting PLEKHO1 in osteoblast as a novel bone anabolic strategy for reversing established osteoporosis during aging.

Pyrintegrin Induces Soft Tissue Formation by Transplanted or Endogenous Cells

Focal adipose deficiency, such as lipoatrophy, lumpectomy or facial trauma, is a formidable challenge in reconstructive medicine, and yet scarcely investigated in experimental studies. Here, we report that Pyrintegrin (Ptn), a 2,4-disubstituted pyrimidine known to promote embryonic stem cells survival, is robustly adipogenic and induces postnatal adipose tissue formation in vivo of transplanted adipose stem/progenitor cells (ASCs) and recruited endogenous cells. In vitro, Ptn stimulated human adipose tissue derived ASCs to differentiate into lipid-laden adipocytes by upregulating peroxisome proliferator-activated receptor (PPARγ) and CCAAT/enhancer-binding protein-α (C/EBPα), with differentiated cells increasingly secreting adiponectin, leptin, glycerol and total triglycerides. Ptn-primed human ASCs seeded in 3D-bioprinted biomaterial scaffolds yielded newly formed adipose tissue that expressed human PPARγ, when transplanted into the dorsum of athymic mice. Remarkably, Ptn-adsorbed 3D scaffolds implanted in the inguinal fat pad had enhanced adipose tissue formation, suggesting Ptn’s ability to induce in situ adipogenesis of endogenous cells. Ptn promoted adipogenesis by upregulating PPARγ and C/EBPα not only in adipogenesis induction medium, but also in chemically defined medium specifically for osteogenesis, and concurrently attenuated Runx2 and Osx via BMP-mediated SMAD1/5 phosphorylation. These findings suggest Ptn’s novel role as an adipogenesis inducer with a therapeutic potential in soft tissue reconstruction and augmentation.

Targeting osteoblastic casein kinase-2 interacting protein-1 to enhance Smad-dependent BMP signaling and reverse bone formation reduction in glucocorticoid-induced osteoporosis

The underlying mechanism of the reduced bone formation during the development of glucocorticoid-induced osteoporosis (GIO) remains unclear. Here, we found that the highly expressed CKIP-1 together with lowly expressed total and phosphorylated Smad1/5 in bone samples was accompanied by either the reduced serum bone formation markers in GIO patients or the decreased bone formation in GIO mice. In vitro studies showed that the highly expressed CKIP-1 could promote Smad1 ubiquitination to suppress the Smad-dependent BMP signaling and inhibit osteogenic differentiation and mineral deposition in MC3T3-E1 cells during glucocorticoid treatment. Further, the reduced bone formation in GIO mice could not only be prevented by osteoblasts-specific Ckip-1 ablation, but also be attenuated after osteoblasts-specific Smad1 overexpression. Moreover, osteoblasts-targeting CKIP-1 siRNA treatment also attenuated the bone formation reduction in GIO mice. These study suggest that the highly expressed CKIP-1 in osteoblasts could suppress the Smad-dependent BMP signaling and contribute to the bone formation reduction in GIO. Targeting osteoblastic CKIP-1 would be a novel bone anabolic strategy for GIO patients.

Expression of TGFβ-family signalling components in ageing cartilage: age-related loss of TGFβ and BMP receptors

OBJECTIVE

Ageing is the main risk factor for osteoarthritis (OA). We investigated if expression of transforming growth factor β (TGFβ)-family components, a family which is crucial for the maintenance of healthy articular cartilage, is altered during ageing in cartilage. Moreover, we investigated the functional significance of selected age-related changes.

DESIGN

Age-related changes in expression of TGFβ-family members were analysed by quantitative PCR in healthy articular cartilage obtained from 42 cows (age: ¾-10 years). To obtain functional insight of selected changes, cartilage explants were stimulated with TGFβ1 or bone morphogenetic protein (BMP) 9, and TGFβ1 and BMP response genes were measured.

RESULTS

Age-related cartilage thinning and loss of collagen type 2a1 expression (∼256-fold) was observed, validating our data set for studying ageing in cartilage. Expression of the TGFβ-family type I receptors; bAlk2, bAlk3, bAlk4 and bAlk5 dropped significantly with advancing age, whereas bAlk1 expression did not. Of the type II receptors, expression of bBmpr2 decreased significantly. Type III receptor expression was unaffected by ageing. Expression of the ligands bTgfb1 and bGdf5 also decreased with age. In explants, an age-related decrease in TGFβ1-response was observed for the pSmad3-dependent gene bSerpine1 (P = 0.016). In contrast, ageing did not affect BMP9 signalling, an Alk1 ligand, as measured by expression of the pSmad1/5 dependent gene bId1.

CONCLUSIONS

Ageing negatively affects both the TGFβ-ALK5 and BMP-BMPR signalling routes, and aged chondrocytes display a lowered pSmad3-dependent response to TGFβ1. Because pSmad3 signalling is essential for cartilage homeostasis, we propose that this change contributes to OA development.

Chondrogenesis of Embryonic Stem Cell-Derived Mesenchymal Stem Cells Induced by TGFβ1 and BMP7 Through Increased TGFβ Receptor Expression and Endogenous TGFβ1 Production

For decades stem cells have proven to be invaluable to the study of tissue development. More recently, mesenchymal stem cells (MSCs) derived from embryonic stem cells (ESCs) (ESC-MSCs) have emerged as a cell source with great potential for the future of biomedical research due to their enhanced proliferative capability compared to adult tissue-derived MSCs and effectiveness of musculoskeletal lineage-specific cell differentiation compared to ESCs. We have previously compared the properties and differentiation potential of ESC-MSCs to bone marrow-derived MSCs. In this study, we evaluated the potential of TGFβ1 and BMP7 to induce chondrogenic differentiation of ESC-MSCs compared to that of TGFβ1 alone and further investigated the cellular phenotype and intracellular signaling in response to these induction conditions. Our results showed that the expression of cartilage-associated markers in ESC-MSCs induced by the TGFβ1 and BMP7 combination was increased compared to induction with TGFβ1 alone. The TGFβ1 and BMP7 combination upregulated the expression of TGFβ receptor and the production of endogenous TGFβs compared to TGFβ1 induction. The growth factor combination also increasingly activated both of the TGF and BMP signaling pathways, and inhibition of the signaling pathways led to reduced chondrogenesis of ESC-MSCs. Our findings suggest that by adding BMP7 to TGFβ1-supplemented induction medium, ESC-MSC chondrogenesis is upregulated through increased production of endogenous TGFβ and activities of TGFβ and BMP signaling. J. Cell. Biochem. 118: 172-181, 2017. © 2016 Wiley Periodicals, Inc.

Substrate Modulus Regulates Osteogenic Differentiation of Rat Mesenchymal Stem Cells through Integrin β1 and BMP Receptor Type IA

Osteoblast differentiation of mesenchymal stem cells is regulated by both soluble factor (e.g., bone morphogenetic proteins (BMP)) and mechanically transduced signaling, but the mechanisms have only been partially elucidated. In this study, physical association of BMP Receptor I (BMPRI) with integrin β1 sub-unit (Iβ1) was hypothesized to mediate osteoblast differentiation of rat bone marrow-derived mesenchymal stem cells (MSCs) on bone-like substrates. The effects of substrate modulus on osteoblast differentiation of MSCs were investigated for 2D poly(ester urethane) films with moduli varying from 5 - 266 MPa, which spans the range from collagen fibrils to trabecular bone. SMAD1/5 and p44/42 MAPK signaling, expression of markers of osteoblast differentiation, and matrix mineralization increased with increasing substrate modulus. The effects of substrate modulus on osteoblast differentiation were mediated by Iβ1, which was also expressed at higher levels on increasingly rigid substrates. Förster resonance energy transfer (FRET) and immunoprecipitation (IP) experiments showed that physical association of Iβ1 and BMP Receptor I (BMRPRI) increased with substrate modulus, resulting in activation of the BMP signaling pathway. Thus, these studies showed that integrin and BMP signaling converge to regulate osteoblast differentiation of MSCs, which may potentially guide the design of scaffolds and rhBMP-2 delivery systems for bone regeneration.

Zoledronic acid suppresses transforming growth factor-β-induced fibrogenesis by human gingival fibroblasts

Bisphosphonates (BPs) are analogues of pyro-phosphate that are known to prevent bone resorption by inhibiting osteoclast activity. Nitrogen-containing BPs, such as zoledronic acid (ZA), are widely used in the treatment of osteoporosis and bone metastasis. However, despite having benefits, ZA has been reported to induce BP-related osteonecrosis of the jaw (BRONJ) in cancer patients. The molecular pathological mechanisms responsible for the development of BRONJ, including necrotic bone exposure after tooth extraction, remain to be elucidated. In this study, we examined the effects of ZA on the transforming growth factor-β (TGF-β)-induced myofibroblast (MF) differentiation of human gingival fibroblasts (hGFs) and the migratory activity of hGFs, which are important for wound closure by fibrous tissue formation. The ZA maximum concentration in serum (Cmax) was found to be approximately 1.47 µM, which clinically, is found after the intravenous administration of 4 mg ZA, and ZA at this dose is considered appropriate for the treatment of cancer bone metastasis or bone diseases, such as Erdheim-Chester disease. At Cmax, ZA significantly suppressed i) the TGF-β-induced promotion of cell viability, ii) the TGF-β-induced expression of MF markers such as α-smooth muscle actin (α-SMA) and type I collagen, iii) the TGF-β-induced migratory activity of hGFs and iv) the expression level of TGF-β type I receptor on the surfaces of hGFs, as well as the TGF-β-induced phosphorylation of Smad2/3. Thus, ZA suppresses TGF-β-induced fibrous tissue formation by hGFs, possibly through the inhibition of Smad-dependent signal transduction. Our findings partly elucidate the molecular mechanisms underlying BRONJ and may prove to be beneficial to the identification of drug targets for the treatment of this symptom at the molecular level.

Mesenchymal Stem Cells and Their Clinical Applications in Osteoarthritis

Osteoarthritis is a chronic degenerative joint disorder characterized by articular cartilage destruction and osteophyte formation. Chondrocytes in the matrix have a relatively slow turnover rate, and the tissue itself lacks a blood supply to support repair and remodeling. Researchers have evaluated the effectiveness of stem cell therapy and tissue engineering for treating osteoarthritis. All sources of stem cells, including embryonic, induced pluripotent, fetal, and adult stem cells, have potential use in stem cell therapy, which provides a permanent biological solution. Mesenchymal stem cells (MSCs) isolated from bone marrow, adipose tissue, and umbilical cord show considerable promise for use in cartilage repair. MSCs can be sourced from any or all joint tissues and can modulate the immune response. Additionally, MSCs can directly differentiate into chondrocytes under appropriate signal transduction. They also have immunosuppressive and anti-inflammatory paracrine effects. This article reviews the current clinical applications of MSCs and future directions of research in osteoarthritis.

An Improved Immunostaining and Imaging Methodology to Determine Cell and Protein Distributions within the Bone Environment

Bone is a dynamic tissue that undergoes multiple changes throughout its lifetime. Its maintenance requires a tight regulation between the cells embedded within the bone matrix, and an imbalance among these cells may lead to bone diseases such as osteoporosis. Identifying cell populations and their proteins within bone is necessary for understanding bone biology. Immunolabeling is one approach used to visualize proteins in tissues. Efficient immunolabeling of bone samples often requires decalcification, which may lead to changes in the structural morphology of the bone. Recently, methyl-methacrylate embedding of non-decalcified tissue followed by heat-induced antigen retrieval has been used to process bone sections for immunolabeling. However, this technique is applicable for bone slices below 50-µm thickness while fixed on slides. Additionally, enhancing epitope exposure for immunolabeling is still a challenge. Moreover, imaging bone cells within the bone environment using standard confocal microscopy is difficult. Here we demonstrate for the first time an improved methodology for immunolabeling non-decalcified bone using a testicular hyaluronidase enzyme-based antigen retrieval technique followed by two-photon fluorescence laser microscopy (TPLM) imaging. This procedure allowed us to image key intracellular proteins in bone cells while preserving the structural morphology of the cells and the bone.

SMAD3 Is Upregulated in Human Osteoarthritic Cartilage Independent of the Promoter DNA Methylation

Objective.

To compare SMAD3 gene expression between human osteoarthritic and healthy cartilage and to examine whether expression is regulated by the promoter DNA methylation of the gene.

Methods.

Human cartilage samples were collected from patients undergoing total hip/knee joint replacement surgery due to primary osteoarthritis (OA), and from patients with hip fractures as controls. DNA/RNA was extracted from the cartilage tissues. Real-time quantitative PCR was performed to measure gene expression, and Sequenom EpiTyper was used to assay DNA methylation. Mann-Whitney test was used to compare the methylation and expression levels between OA cases and controls. Spearman rank correlation coefficient was calculated to examine the association between the methylation and gene expression.

Results.

A total of 58 patients with OA (36 women, 22 men; mean age 64 ± 9 yrs) and 55 controls (43 women, 12 men; mean age 79 ± 10 yrs) were studied. SMAD3 expression was on average 83% higher in OA cartilage than in controls (p = 0.0005). No difference was observed for DNA methylation levels in the SMAD3 promoter region between OA cases and controls. No correlation was found between SMAD3 expression and promoter DNA methylation.

Conclusion.

Our study demonstrates that SMAD3 is significantly overexpressed in OA. This overexpression cannot be explained by DNA methylation in the promoter region. The results suggest that the transforming growth factor-β/SMAD3 pathway may be overactivated in OA cartilage and has potential in developing targeted therapies for OA.

Fuyuan Decoction Enhances SOX9 and COL2A1 Expression and Smad2/3 Phosphorylation in IL-1β-Activated Chondrocytes

Fuyuan Decoction (FYD), a herbal formula in China, has been widely used for osteoarthritis (OA) treatment. Herein, we determined the effects of FYD on the expression of transcription factor SOX9 and its target gene collagen type II, alpha 1 (COL2A1) as well as the activation of Smad2/3 in interleukin- (IL-) 1β-stimulated SW1353 chondrosarcoma cells. Serum-derived FYD (FYD-CS) was prepared to treat SW1353 cells with or without SB431542, a TGF-β1 receptor inhibitor. Cell cycle progression was tested by flow cytometry. The expression of SOX9 and COL2A1 and the activation of Smad2/3 (p-Smad2/3) were analyzed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and/or western blot. The results showed that, after treatment, FYD-CS, while inducing S-phase cell cycle arrest, enhanced cell proliferation and protected the cells against IL-1β- and/or SB431542-induced cell growth inhibition. Furthermore, FYD-CS reversed the decreased expression of COL2A1 and SOX9 induced by IL-1β and SB431542 and blocked the decreased phosphorylation of Smad2/3 induced by IL-1β alone or in combination with SB431542. Our results suggest that FYD promotes COL2A1 and SOX9 expression as well as Smad2/3 activation in IL-1β-induced chondrocytes, thus benefiting cell survival.

Mesenchymal stem cells in regenerative medicine: Focus on articular cartilage and intervertebral disc regeneration

Musculoskeletal disorders represent a major cause of disability and morbidity globally and result in enormous costs for health and social care systems. Development of cell-based therapies is rapidly proliferating in a number of disease areas, including musculoskeletal disorders. Novel biological therapies that can effectively treat joint and spine degeneration are high priorities in regenerative medicine. Mesenchymal stem cells (MSCs) isolated from bone marrow (BM-MSCs), adipose tissue (AD-MSCs) and umbilical cord (UC-MSCs) show considerable promise for use in cartilage and intervertebral disc (IVD) repair. This review article focuses on stem cell-based therapeutics for cartilage and IVD repair in the context of the rising global burden of musculoskeletal disorders. We discuss the biology MSCs and chondroprogenitor cells and specifically focus on umbilical cord/Wharton's jelly derived MSCs and examine their potential for regenerative applications. We also summarize key components of the molecular machinery and signaling pathways responsible for the control of chondrogenesis and explore biomimetic scaffolds and biomaterials for articular cartilage and IVD regeneration. This review explores the exciting opportunities afforded by MSCs and discusses the challenges associated with cartilage and IVD repair and regeneration. There are still many technical challenges associated with isolating, expanding, differentiating, and pre-conditioning MSCs for subsequent implantation into degenerate joints and the spine. However, the prospect of combining biomaterials and cell-based therapies that incorporate chondrocytes, chondroprogenitors and MSCs leads to the optimistic view that interdisciplinary approaches will lead to significant breakthroughs in regenerating musculoskeletal tissues, such as the joint and the spine in the near future.

The role of microRNAs in bone remodeling

Bone remodeling is balanced by bone formation and bone resorption as well as by alterations in the quantities and functions of seed cells, leading to either the maintenance or deterioration of bone status. The existing evidence indicates that microRNAs (miRNAs), known as a family of short non-coding RNAs, are the key post-transcriptional repressors of gene expression, and growing numbers of novel miRNAs have been verified to play vital roles in the regulation of osteogenesis, osteoclastogenesis, and adipogenesis, revealing how they interact with signaling molecules to control these processes. This review summarizes the current knowledge of the roles of miRNAs in regulating bone remodeling as well as novel applications for miRNAs in biomaterials for therapeutic purposes.

Extracellular Ca2+ Promotes Odontoblastic Differentiation of Dental Pulp Stem Cells via BMP2-Mediated Smad1/5/8 and Erk1/2 Pathways

Ca(2+) is the main element of many pulp capping materials that are used to promote the regeneration of tertiary dentin, but the underlying molecular mechanism is not clear. In this study, we found that Ca(2+) increased the expression of the odontoblastic differentiation marker gene DSPP and promoted odontoblastic differentiation and mineralization of DPSCs, but inhibited ALP activity. Ca(2+) increases the expression of endogenous BMP2, which activates the Smad1/5/8 pathway and promotes the Smad1-Runx2 and Runx2-DSPP interaction in DPSCs. Inhibition of Smad1/5/8 with dorsomorphin partially blocked Runx2 activity; however, inhibition of the BMP2 receptor with Noggin nearly fully suppressed Runx2 activity. These results indicate that Ca(2+) promotes cell differentiation mainly via BMP2-mediated Smad-dependent and Smad-independent pathways. We then determined that the phosphorylation level of Erk1/2, but not JNK or p38, was significantly increased as a result of Ca(2+) stimulation. Blockage of Erk1/2 was found to inhibit Runx2 activity, indicating that Ca(2+) triggers the Erk1/2 pathway, which subsequently regulates Runx2 activity. In addition, inhibition of Erk1/2 differentially attenuated the phosphorylation levels of Smad1/5/8 and Smad2/3. Collectively, this study demonstrates that Ca(2+) activates the BMP2-mediated Smad1/5/8 and Erk1/2 pathways in DPSCs and that Smad1/5/8 and Erk1/2 signaling converge at Runx2 to control the odontoblastic differentiation of DPSCs.

The high affinity ALK1-ligand BMP9 induces a hypertrophy-like state in chondrocytes that is antagonized by TGFβ1

OBJECTIVE

In osteoarthritic cartilage, expression of the receptor ALK1 correlates with markers of deleterious chondrocyte hypertrophy. Recently, bone morphogenetic protein 9 (BMP9) was identified as a high affinity ligand for ALK1. Therefore, we studied if BMP9 signaling results in expression of hypertrophy markers in chondrocytes. Furthermore, because transforming growth factorß1 (TGFβ1) is a well known anti-hypertrophic factor, the interaction between BMP9 and TGFβ1 signaling was also studied.

DESIGN

Primary chondrocytes were isolated from bovine cartilage and stimulated with BMP9 and/or TGFβ1 to measure intracellular signaling via pSmads with the use of Western blot. Expression of Smad-responsive genes or hypertrophy-marker genes was measured using qPCR. To confirm observations on TGFβ/Smad3 responsive genes, a Smad3-dependent CAGA12-luc transcriptional reporter assay was performed in the chondrocyte G6 cell line.

RESULTS

In primary chondrocytes, BMP9 potently induced phosphorylation of Smad1/5 and Smad2 to a lesser extent. BMP9-induced Smad1/5 phosphorylation was rapidly (2 h) reflected in gene expression, whereas Smad2 phosphorylation was not. Remarkably, BMP9 and TGFβ1 dose-dependently synergized on Smad2 phosphorylation, and showed an additive effect on expression of Smad3-dependent genes like bSerpine1 after 24 h. The activation of the TGFβ/Smad3 signaling cascade was confirmed using the CAGA12-luc transcriptional reporter. BMP9 selectively induced bAlpl and bColX expression, which are considered early markers of cellular hypertrophy, but this was potently antagonized by addition of a low dose of TGFβ1.

CONCLUSIONS

This study shows that in vitro in chondrocytes, BMP9 potently induces pSmad1/5 and a chondrocyte hypertrophy-like state, which is potently blocked by TGFβ1. This observation underlines the importance of TGFβ1 in maintenance of chondrocyte phenotype.

TGFβ signaling in cartilage development and maintenance

Members of the transforming growth factor beta (TGFβ) superfamily of secreted factors play essential roles in nearly every aspect of cartilage formation and maintenance. However, the mechanisms by which TGFβs transduce their effects in cartilage in vivo remain poorly understood. Mutations in several TGFβ family members, their receptors, extracellular modulators, and intracellular transducers have been described, and these usually impact the development of the cartilaginous skeleton. Furthermore, genome-wide association studies have linked components of the (TGFβ) superfamily to susceptibility to osteoarthritis. This review focuses on recent discoveries from genetic studies in the mouse regarding the regulation of TGFβ signaling in developing growth plate and articular cartilage, as well as the different modes of crosstalk between canonical and noncanonical TGFβ signaling. These new insights into TGFβ signaling in cartilage may open new prospects for therapies that maintain healthy articular cartilage.

Cartilage tissue engineering: recent advances and perspectives from gene regulation/therapy

Diseases in articular cartilages affect millions of people. Despite the relatively simple biochemical and cellular composition of articular cartilages, the self-repair ability of cartilage is limited. Successful cartilage tissue engineering requires intricately coordinated interactions between matrerials, cells, biological factors, and phycial/mechanical factors, and still faces a multitude of challenges. This article presents an overview of the cartilage biology, current treatments, recent advances in the materials, biological factors, and cells used in cartilage tissue engineering/regeneration, with strong emphasis on the perspectives of gene regulation (e.g., microRNA) and gene therapy.

Enhanced bioactivity of transform growth factor-β1 from sulfated chitosan microspheres for in vitro chondrogenesis of mesenchymal stem cells

Transform growth factor-β1 (TGF-β1) is an extremely powerful protein to induce the chondrogenesis of mesenchymal stem cells (MSCs) both in vitro and in vivo. However, due to the short-life of TGF-β1, the direct application of TGF-β1 may deteriorate its bioactivity and thereby the repair effect. In this study, uniform sulfated chitosan microspheres (SCMs) with a mean diameter of ∼ 2 μm were fabricated by membrane emulsification as a carrier for TGF-β1. The in vitro release study showed that TGF-β1 could be sustainedly released from the microspheres up to 16 days. Under the protection of SCMs, about 13 % TGF-β1 was preserved even after stored for 14 days. The microspheres cytotoxicity was evaluated by coculture of MSCs with different concentrations SCMs and no obvious deterioration of cell viability was observed when the concentration of SCMs is lower than 2 μg/1.0 × 104 cells. In comparison with the blank group, the addition of TGF-β1 either in free state or loaded in SCMs inhibited the proliferation trend of MSCs. Quantitative analysis of GAGs production and genes expression of COL II and aggrecan by qRT-PCR revealed that enhanced bioactivity of TGF-β1 was obtained in the group of TGF-β1/SCMs, indicating that SCMs could be functioned as a promising carrier of TGF-β1 for the in vitro chondrogenesis of MSCs.

GATA4 is essential for bone mineralization via ERα and TGFβ/BMP pathways

Osteoporosis is a disease characterized by low bone mass, leading to an increased risk of fragility fractures. GATA4 is a zinc-finger transcription factor that is important in several tissues, such as the heart and intestines, and has recently been shown to be a pioneer factor for estrogen receptor alpha (ERα) in osteoblast-like cells. Herein, we demonstrate that GATA4 is necessary for estrogen-mediated transcription and estrogen-independent mineralization in vitro. In vivo deletion of GATA4, driven by Cre-recombinase in osteoblasts, results in perinatal lethality, decreased trabecular bone properties, and abnormal bone development. Microarray analysis revealed GATA4 suppression of TGFβ signaling, necessary for osteoblast progenitor maintenance, and concomitant activation of BMP signaling, necessary for mineralization. Indeed, pSMAD1/5/8 signaling, downstream of BMP signaling, is decreased in the trabecular region of conditional knockout femurs, and pSMAD2/3, downstream of TGFβ signaling, is increased in the same region. Together, these experiments demonstrate the necessity of GATA4 in osteoblasts. Understanding the role of GATA4 to regulate the tissue specificity of estrogen-mediated osteoblast gene regulation and estrogen-independent bone differentiation may help to develop therapies for postmenopausal osteoporosis.

Mouse limb skeletal growth and synovial joint development are coordinately enhanced by Kartogenin

Limb development requires the coordinated growth of several tissues and structures including long bones, joints and tendons, but the underlying mechanisms are not wholly clear. Recently, we identified a small drug-like molecule - we named Kartogenin (KGN) - that greatly stimulates chondrogenesis in marrow-derived mesenchymal stem cells (MSCs) and enhances cartilage repair in mouse osteoarthritis (OA) models. To determine whether limb developmental processes are regulated by KGN, we tested its activity on committed preskeletal mesenchymal cells from mouse embryo limb buds and whole limb explants. KGN did stimulate cartilage nodule formation and more strikingly, boosted digit cartilaginous anlaga elongation, synovial joint formation and interzone compaction, tendon maturation as monitored by ScxGFP, and interdigit invagination. To identify mechanisms, we carried out gene expression analyses and found that several genes, including those encoding key signaling proteins, were up-regulated by KGN. Amongst highly up-regulated genes were those encoding hedgehog and TGFβ superfamily members, particularly TFGβ1. The former response was verified by increases in Gli1-LacZ activity and Gli1 mRNA expression. Exogenous TGFβ1 stimulated cartilage nodule formation to levels similar to KGN, and KGN and TGFβ1 both greatly enhanced expression of lubricin/Prg4 in articular superficial zone cells. KGN also strongly increased the cellular levels of phospho-Smads that mediate canonical TGFβ and BMP signaling. Thus, limb development is potently and harmoniously stimulated by KGN. The growth effects of KGN appear to result from its ability to boost several key signaling pathways and in particular TGFβ signaling, working in addition to and/or in concert with the filamin A/CBFβ/RUNX1 pathway we identified previously to orchestrate overall limb development. KGN may thus represent a very powerful tool not only for OA therapy, but also limb regeneration and tissue repair strategies.

Loss of jab1 in osteochondral progenitor cells severely impairs embryonic limb development in mice

The transcriptional cofactor Jab1 controls cell proliferation, apoptosis, and differentiation in diverse developmental processes by regulating the activity of various transcription factors. To determine the role of Jab1 during early limb development, we developed a novel Jab1(flox/flox) ; Prx1-Cre conditional Knockout (cKO) mutant mouse model in which Jab1 was deleted in the osteochondral progenitor cells of the limb buds. Jab1 cKO mutant mice displayed drastically shortened limbs at birth. The short-limb defect became apparent in Jab1 cKO mutants at E15.5 and increasingly worsened thereafter. By E18.5, Jab1 cKO mutant mice exhibited significantly shorter limbs with: very few hypertrophic chondrocytes, disorganized chondrocyte columns, much smaller primary ossification centers, and significantly increased apoptosis. Real-time RT-PCR analysis showed decreased expression of Sox9, Col2a1, Ihh, and Col10a1 in Jab1 cKO mutant long bones, indicating impaired chondrogenesis. Furthermore, in a micromass culture model of early limb mesenchyme cells, alcian blue staining showed a significant decrease in chondrogenesis in Jab1 cKO limb bud cells. The expression of Sox9 and its downstream targets Col2a1 and Aggrecan, as well as BMP signaling downstream targets, Noggin, Id1, and Ihh, were significantly decreased in Jab1 cKO micromass cultures. Moreover, over-expression of SOX9 in Jab1 cKO micromass cultures partially restored Col2a1and Aggrecan expression. Jab1-deficient micromass cultures also exhibited decreased BMP signaling response and reduced BMP-specific reporter activity ex vivo. In summary, our study demonstrates that Jab1 is an essential regulator of early embryonic limb development in vivo, likely in part by co-activating Sox9 and BMP signaling.

Vascular analysis as a proxy for mechanostransduction response in an isogenic, irradiated murine model of mandibular distraction osteogenesis

INTRODUCTION

Head and neck cancer is a debilitating and disfiguring disease. Although numerous treatment options exist, an array of debilitating side effects accompany them, causing physiological and social problems. Distraction osteogenesis (DO) can avoid many of the pathologies of current reconstructive strategies; however, due to the deleterious effects of radiation on bone vascularity, DO is generally ineffective. This makes investigating the effects of radiation on neovasculature during DO and creating quantifiable metrics to gauge the success of future therapies vital. The purpose of this study was to develop a novel isogenic rat model of impaired vasculogenesis of the regenerate mandible in order to determine quantifiable metrics of vascular injury and associated damage.

METHODS

Male Lewis rats were divided into two groups: DO only (n=5) AND Radiation Therapy (XRT)+DO (n=7). Afterwards, a distraction device was surgically implanted into the mandible. Finally, they were distracted a total of 5.1mm. Animals were perfused with a radiopaque casting agent concomitant with euthanasia, and subsequently demineralization, microcomputed tomography, and vascular analysis were performed.

RESULTS

Vessel volume fraction, vessel thickness, vessel number, and degree of anisotropy were diminished by radiation. Vessel separation was increased by radiation.

CONCLUSION

The DO group experienced vigorous vessel formation during distraction and neovascularization with a clear, directional progression, while the XRT/DO group saw weak vessel formation during distraction and neovascularization. Further studies are warranted to more deeply examine the impairments in osteogenic mechanotransductive pathways following radiation in the murine mandible. This isogenic model provides quantifiable metrics for future studies requiring a controlled approach to immunogenicity.

Cerium promotes bone marrow stromal cells migration and osteogenic differentiation via Smad1/5/8 signaling pathway

Cerium (Ce), one of the lanthanides (Ln), displays a variety of biochemical and physiological effects. However, the potential effect and mechanism of Ce on bone metabolism are not well understood. In this study, we investigated the putative role of Ce in regulating the migration and osteogenic differentiation of bone marrow stromal cells (BMSCs) and the underlying mechanism. The results indicated that Ce promoted BMSCs viability and ALP activity at lower concentrations (0.001 μM), and decreased the viability and ALP activity of BMSCs at higher concentrations (10 μM). Ce could also affect the expression of osteogenic transcription factors (Runx2, Satb2 and OCN) in BMSCs. Our results also showed that Ce promoted migration of BMSCs by increasing SDF-1 mRNA expression. As the Smad-dependent BMP signaling pathway plays an important role in migration and osteogenic differentiation of BMSCs, our results are in agreement with Ce promoting the phosphorylation of Smad1/5/8 and translocating to the nucleus by increase BMP2 expression. The activity of p-Smad1/5/8 increased SDF-1 and Runx2 expression level in BMSCs. In conclusion, our results support the notion that Ce promoted migration and osteogenic differentiation of BMSCs by Smad1/5/8 signaling pathway.

Angiogenic cytokine expression profiles in plasma and synovial fluid of primary knee osteoarthritis

PURPOSE

The aim of this study was to compare angiogenic cytokine levels in knee osteoarthritis (OA) patients and healthy controls and to investigate the relationships between angiogenic cytokines and the OA severity.

METHODS

Thirty-one knee OA patients and 15 healthy controls were recruited. Nine angiogenic cytokines (angiopoietin-2, follistatin, granulocyte-colony stimulating factor (G-CSF), hepatocyte growth factor (HGF), interleukin (IL)-8, leptin, platelet-derived growth factor-BB (PDGF-BB), platelet endothelial cell adhesion molecule (PECAM)-1, and vascular endothelial growth factor (VEGF)) in plasma and synovial fluid were measured using a multiplex immunoassay.

RESULTS

PECAM-1, HGF, VEGF, angiopoietin-2, follistatin, G-CSF, and IL-8 concentrations in plasma were significantly higher in OA patients than those in controls. Plasma angiopoietin-2 was significantly greater in advanced OA than in early OA. Synovial fluid VEGF was positively correlated with the severity (r = 0.367, P = 0.04). Plasma follistatin was significantly lower in advanced knee OA than in early OA and was negatively correlated with the severity (r = -0.374, P < 0.05).

CONCLUSIONS

Angiogenic cytokine concentrations in plasma can distinguish between controls and OA patients. Local and circulating levels of angiogenic cytokines could give an insight into the pathophysiology of OA. Follistatin, angiopoietin-2, and VEGF may have potential as biochemical markers for the assessment of OA severity.

Comparison of GDF5 and GDNF as neuroprotective factors for postnatal dopamine neurons in ventral mesencephalic cultures

Loss of dopamine neurons is associated with the motor deficits that occur in Parkinson's disease. Although many drugs have proven to be useful in the treatment of the symptoms of this disease, none has been shown to have a significant impact on the development of the disease. However, we believe that several neurotrophic factors have the potential to reduce its progression. Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor-β superfamily of neurotrophic factors, has been extensively studied in this regard. Less attention has been paid to growth/differentiation factor 5 (GDF5), another member of the same superfamily. This study compares GDNF and GDF5 in dissociated cultures prepared from ventral mesencephalon and in organotypic co-cultures containing substantia nigra, striatum, and neocortex. We report that both GDNF (10-500 ng/ml) and GDF5 (100-500 ng/ml) promoted the survival of dopamine neurons from the substantia nigra of postnatal rats, although GDNF was considerably more potent than GDF5. In contrast, neither factor had any significant effect on the survival of dopamine neurons from the rat ventral tegmental area. Using organotypic co-cultures, we also compared GDF5 with GDNF as chemoattractants for the innervation of the striatum and the neocortex by dopamine neurons from the substantia nigra. The addition of either GDF5 or GDNF (100-500 ng/ml) caused innervation by dopamine neurons into the cortex as well as the striatum, which did not occur in untreated cultures. Our results are consistent with similar findings suggesting that GDF5, like GDNF, deserves attention as a possible therapeutic intervention for Parkinson's disease.

MicroRNA-146a regulates human foetal femur derived skeletal stem cell differentiation by down-regulating SMAD2 and SMAD3

MicroRNAs (miRs) play a pivotal role in a variety of biological processes including stem cell differentiation and function. Human foetal femur derived skeletal stem cells (SSCs) display enhanced proliferation and multipotential capacity indicating excellent potential as candidates for tissue engineering applications. This study has examined the expression and role of miRs in human foetal femur derived SSC differentiation along chondrogenic and osteogenic lineages. Cells isolated from the epiphyseal region of the foetal femur expressed higher levels of genes associated with chondrogenesis while cells from the foetal femur diaphyseal region expressed higher levels of genes associated with osteogenic differentiation. In addition to the difference in osteogenic and chondrogenic gene expression, epiphyseal and diaphyseal cells displayed distinct miRs expression profiles. miR-146a was found to be expressed by human foetal femur diaphyseal cells at a significantly enhanced level compared to epiphyseal populations and was predicted to target various components of the TGF-β pathway. Examination of miR-146a function in foetal femur cells confirmed regulation of protein translation of SMAD2 and SMAD3, important TGF-β and activin ligands signal transducers following transient overexpression in epiphyseal cells. The down-regulation of SMAD2 and SMAD3 following overexpression of miR-146a resulted in an up-regulation of the osteogenesis related gene RUNX2 and down-regulation of the chondrogenesis related gene SOX9. The current findings indicate miR-146a plays an important role in skeletogenesis through attenuation of SMAD2 and SMAD3 function and provide further insight into the role of miRs in human skeletal stem cell differentiation modulation with implications therein for bone reparation.