MMP-2 functions as a negative regulator of chondrogenic cell condensation via down-regulation of the FAK-integrin beta1 interaction

Liquid plasma promotes angiogenesis through upregulation of endothelial nitric oxide synthase-induced extracellular matrix metabolism: potential applications of liquid plasma for vascular injuries

BACKGROUND

Applications of nonthermal plasma have expanded beyond the biomedical field to include antibacterial, anti-inflammatory, wound healing, and tissue regeneration. Plasma enhances epithelial cell repair; however, the potential damage to deep tissues and vascular structures remains under investigation.

RESULT

This study assessed whether liquid plasma (LP) increased nitric oxide (NO) production in human umbilical vein endothelial cells by modulating endothelial NO synthase (eNOS) phosphorylation and potential signaling pathways. First, we developed a liquid plasma product and confirmed the angiogenic effect of LP using the Matrigel plug assay. We found that the NO content increased in plasma-treated water. NO in plasma-treated water promoted cell migration and angiogenesis in scratch and tube formation assays via vascular endothelial growth factor mRNA expression. In addition to endothelial cell proliferation and migration, LP influenced extracellular matrix metabolism and matrix metalloproteinase activity. These effects were abolished by treatment with NG-L-monomethyl arginine, a specific inhibitor of NO synthase. Furthermore, we investigated the signaling pathways mediating the phosphorylation and activation of eNOS in LP-treated cells and the role of LKB1-adenosine monophosphate-activated protein kinase in signaling. Downregulation of adenosine monophosphate-activated protein kinase by siRNA partially inhibited LP-induced eNOS phosphorylation, angiogenesis, and migration.

CONCLUSION

The present study suggests that LP treatment may be a novel strategy for promoting angiogenesis in vascular damage. Video Abstract.

Focal adhesion kinase (FAK): its structure, characteristics, and signaling in skeletal system

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase and distributes important regulatory functions in skeletal system. Mesenchymal stem cell (MSC) possesses significant migration and differentiation capacity, is an important source of distinctive bone cells production and a prominent bone development pathway. MSC has a wide range of applications in tissue bioengineering and regenerative medicine, and is frequently employed for hematopoietic support, immunological regulation, and defect repair, although current research is insufficient. FAK has been identified to cross-link with many other keys signaling pathways in bone biology and is considered as a fundamental "crossroad" on the signal transduction pathway and a "node" in the signal network to mediate MSC lineage development in skeletal system. In this review, we summarized the structure, characteristics, cellular signaling, and the interactions of FAK with other signaling pathways in the skeletal system. The discovery of FAK and its mediated molecules will lead to a new knowledge of bone development and bone construction as well as considerable potential for therapeutic use in the treatment of bone-related disorders such as osteoporosis, osteoarthritis, and osteosarcoma.

The Role of Extracellular Matrix and Hydrogels in Mesenchymal Stem Cell Chondrogenesis and Cartilage Regeneration

Diseases associated with articular cartilage disintegration or loss are still therapeutically challenging. The traditional treatment approaches only alleviate the symptoms while potentially causing serious side effects. The limited self-renewal potential of articular cartilage provides opportunities for advanced therapies involving mesenchymal stem cells (MSCs) that are characterized by a remarkable regenerative capacity. The chondrogenic potential of MSCs is known to be regulated by the local environment, including soluble factors and the less discussed extracellular matrix (ECM) components. This review summarizes the process of chondrogenesis, and also the biological properties of the ECM mediated by mechanotransduction as well as canonical and non-canonical signaling. Our focus is also on the influence of the ECM's physical parameters, molecular composition, and chondrogenic factor affinity on the adhesion, survival, and chondrogenic differentiation of MSCs. These basic biological insights are crucial for a more precise fabrication of ECM-mimicking hydrogels to improve cartilage tissue reconstruction. Lastly, we provide an overview of hydrogel classification and characterization. We also include the results from preclinical models combining MSCs with hydrogels for the treatment of cartilage defects, to support clinical application of this construct. Overall, it is believed that the proper combination of MSCs, hydrogels, and chondrogenic factors can lead to complex cartilage regeneration.

Autophagy-related proteases accompany the transition of pre-chondrogenic cells into chondroblasts

BACKGROUND

Autophagy is classified as a form of programmed cell death. Nevertheless, besides the death-inducing function, autophagy enables removal of damaged organelles, energy savings, and thus cell survival. This applies in particular to cells with poor renewal capabilities, such as chondroblasts. Autophagy is regulated by a complex molecular network, including proteases and their substrates. In autopodium, autophagy-related proteases have been examined particularly within the context of the elimination of the interdigital tissue. However, the death-inducing effects of their expression/activation have not been specified yet. This work focuses on autophagy-associated proteases (cathepsins, matrix metalloproteinases, and caspases) involved in phalangeal cartilage of the mouse autopodium.

METHODS

PCR Array, Real Time PCR, and immunohistochemistry were used to follow the expression of autophagy-associated genesin vivo at two developmental stages prenatal/embryonic (E)12 vs. E14. Real Time PCR was then applied to investigate the influence of rapamycin (an inductor of autophagy) on the expression of autophagy-associated proteases in chondroblasts in vitro using micromass culture.

RESULTS

Several proteases showed increased expression levels during the transition of pre-chondrogenic cells into chondroblastsin vivo. The most significant increases were observed for Ctsb (fold regulation 2.22), Ctsd (fold regulation 2.37), Ctss (fold regulation 2.92), Mmp9 (up to 445%), and Casp8 (up to 250%). The transition was associated also with high expression of crucial autophagic inducers, such as Atgs. The in vitro treatment of chondroblasts by autophagy inductor rapamycin showed significantly decreased expression of cathepsins, a mild increase in expression of metalloproteinases, and no effect in caspase expression.

CONCLUSIONS

The present data provide a screening of autophagy-associated proteases accompanying the formation of cartilage in vivo and specify their expression under rapamycin treatment in vitro. Notably, the selected proteases are assigned to osteoarthritis, therefore their regulation might be used in clinically oriented studies.

Transcription Factors of the Alx Family: Evolutionarily Conserved Regulators of Deuterostome Skeletogenesis

Members of the alx gene family encode transcription factors that contain a highly conserved Paired-class, DNA-binding homeodomain, and a C-terminal OAR/Aristaless domain. Phylogenetic and comparative genomic studies have revealed complex patterns of alx gene duplications during deuterostome evolution. Remarkably, alx genes have been implicated in skeletogenesis in both echinoderms and vertebrates. In this review, we provide an overview of current knowledge concerning alx genes in deuterostomes. We highlight their evolutionarily conserved role in skeletogenesis and draw parallels and distinctions between the skeletogenic gene regulatory circuitries of diverse groups within the superphylum.

Human mesenchymal stem cells respond differentially to platelet preparations and synthesize hyaluronic acid in nucleus pulposus extracellular matrix

BACKGROUND CONTEXT

In recent years, autologous platelet-rich plasma (PRP) and bone marrow aspirate concentrate (BMAC) have been used as treatments for disc-related pain. A better understanding of the effects of leukocyte-rich (LR) versus leukocyte poor (LP-) PRP on bone marrow derived human mesenchymal stem/progenitor cells (hMSCs) is likely to improve future research studies, clinical practice and care for patients with chronic discogenic back pain.

PURPOSE

The primary aim of this study is to determine the effects of LR-PRP and LP-PRP on the proliferation and migration of hMSCs in pig nucleus pulposus (NP) extracellular matrix (ECM). The secondary aim is to characterize hMSC-dependent expression of the matrix remodeling enzymes metalloproteinases MMP-2, MMP-3, MMP-9 and tissue inhibitor of metalloproteinases TIMP-2, and to determine whether transplanted hMSCs can synthesize hyaluronic acid (HA).

STUDY DESIGN

Controlled laboratory study.

METHODS

Bone marrow-derived culture expanded hMSCs were seeded onto pig NP and cultured with LR-PRP, LP-PRP or serum/platelet releasate (PR). The same conditions without hMSCs were used as controls. hMSC proliferation, migration and dispersion was assessed via fluorescent microscopy, while HA synthesis, MMP-2, MMP-3, MMP-9, and TIMP-2 protein levels were assessed via enzyme linked immunosorbent assay. All funding was provided by a 501c(3) research foundation and does not have any commercial or sponsorship interests.

RESULTS

LP-PRP and PR cultures resulted in higher hMSC proliferation, migration, dispersion, and MMP-2 expression. LP-PRP cultures resulted in the highest HA production. LR-PRP cultures resulted in lower hMSC proliferation, negligible migration and dispersion, increased MMP-9 expression and lower HA production.

CONCLUSIONS

Human bone marrow-derived hMSCs seeded onto pig NP ECM are capable of synthesizing HA, indicating a transition towards a NP cell phenotype. This process was most enhanced by LP-PRP and marked by increased hMSC proliferation, MMP-2 production, HA synthesis and reduced MMP-9 levels.

CLINICAL SIGNIFICANCE

LP-PRP and PR, with or without hMSCs, may provide better outcomes than LR-PRP in lab investigations and clinical trials for discogenic pain. Bone marrow-derived hMSCs may hold promise as a treatment for disc degeneration.

Integrin α4 mediates ATDC5 cell adhesion to negatively charged synthetic polymer hydrogel leading to chondrogenic differentiation

Negatively charged synthetic hydrogels have been known to facilitate various cellular responses including cell adhesion, proliferation, and differentiation; however, the molecular mechanism of hydrogel-dependent control of cell behavior remains unclear. Recently, we reported that negatively charged poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) gel induces chondrogenic differentiation of ATDC5 cells via novel protein reservoir function. In this study, we identified the cell adhesion molecules binding to PAMPS gels that act as mechanoreceptors. First, we performed a pull-down assay by particle gels using cell membrane proteins of ATDC5, and found that multiple membrane proteins bound to the PAMPS gel, whereas the uncharged poly(N,N'-dimethylacrylamide) gel as control did not bind to any membrane proteins. Western blot analysis indicated differential binding of integrin (ITG) isoforms to the PAMPS gel, in which the α4 isoform, but not α5 and αv, efficiently bound to the PAMPS gel. ITG α4 knockdown decreased cell spreading of ATDC5 on PAMPS gels, whereas the enhanced expression increased the behavior. Furthermore, ITG α4 depletion suppressed PAMPS gel-induced expression of bone morphogenic protein (BMP) 4 contributing to chondrogenic differentiation, in concordance with the reduction of ERK activation. These results demonstrated that membrane protein binding to PAMPS gels occurred in a charge-dependent manner, and that ITG α4 plays a crucial role in cell spreading on PAMPS gels and acts as a mechanoreceptor triggering cellular signaling leads to chondrogenic differentiation.

Enhancement of the chondrogenic differentiation of mesenchymal stem cells and cartilage repair by ghrelin

Transforming growth factor beta (TGF-β) is commonly utilized in chondrogenic differentiation protocols, but this often results in incomplete maturation of the derived chondrocytes. Gene expression analysis, quantitation of sulfated glycosaminoglycan and collagen, and histological staining were performed to assess the effects of ghrelin. The signaling pathways involved were investigated with inhibitors or targeted by shRNAs. Joint cavity delivery of TGF-β with or without ghrelin, within a rat cartilage defect model was performed to evaluate the in vivo effects of ghrelin. Ghrelin dramatically enhanced gene expression levels of SOX9, ACAN, and COL II and resulted in increased synthesis of sulfated glycosaminoglycan (sGAG) and collagen in vitro. Combined treatment with TGF-β and ghrelin synergistically enhanced the phosphorylation of ERK1/2 and DMNT3A, which accounted for increased expression of chondrogenic genes. Delivery of ghrelin in combination with TGF-β after MSC implantation within a rat osteochondral defect model significantly enhanced de novo cartilage regeneration, as compared to delivery with TGF-β alone. In conclusion, ghrelin could significantly enhance MSC chondrogenic differentiation in vitro and can also enhance cartilage regeneration in vivo when used in combination with TGF-β. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1387-1397, 2019.

Cell number in mesenchymal stem cell aggregates dictates cell stiffness and chondrogenesis

Background

Although mesenchymal stem/stromal cell (MSC) chondrogenic differentiation has been thoroughly investigated, the rudiments for enhancing chondrogenesis have remained largely dependent on external cues. Focus to date has been on extrinsic variables such as soluble signals, culture conditions (bioreactors), and mechanical stimulation. However, the role of intrinsic mechanisms of MSC programming-based mechanobiology remains to be explored. Since aggregation of MSCs, a prerequisite for chondrogenesis, generates tension within the cell agglomerate, we inquired if the initial number of cells forming the aggregate (aggregate cell number (ACN)) can impact chondrogenesis.

Methods

Aggregates of varying ACN were formed using well-established centrifugation approach. Progression of chondrogenic differentiation in the aggregates was assessed over 3 weeks in presence and absence of transforming growth factor-beta 1 (TGF-β1). Mechanical properties of the cells were characterized using high-throughput real-time deformability cytometry (RT-DC), and gene expression was analyzed using Affymetrix gene array. Expression of molecular markers linked to chondrogenesis was assessed using western blot and immunofluorescence.

Results

Reducing ACN from 500 k to 70 k lead to activation and acceleration of the chondrogenic differentiation, independent of soluble chondro-inductive factors, which involves changes to β-catenin-dependent TCF/LEF transcriptional activity and expression of anti-apoptotic protein survivin. RT-DC analysis revealed that stiffness and size of cells within aggregates are modulated by ACN. A direct correlation between progression of chondrogenesis and emergence of stiffer cell phenotype was found. Affymetrix gene array analysis revealed a downregulation of genes associated with lipid synthesis and regulation, which could account for observed changes in cell stiffness. Immunofluorescence and western blot analysis revealed that increasing ACN upregulates the expression of lipid raft protein caveolin-1, a β-catenin binding partner, and downregulates the expression of N-cadherin. As a demonstration of the relevance of these findings in MSC-based strategies for skeletal repair, it is shown that implanting aggregates within collagenous matrix not only decreases the necessity for high cell numbers but also leads to marked improvement in the quality of the deposited tissue.

Conclusions

This study presents a simple and donor-independent strategy to enhance the efficiency of MSC chondrogenic differentiation and identifies changes in cell mechanics coincident with MSC chondrogenesis with potential translational applications.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1103-y) contains supplementary material, which is available to authorized users.

Interplay between stiffness and degradation of architectured gelatin hydrogels leads to differential modulation of chondrogenesis in vitro and in vivo

The limited capacity of cartilage to heal large lesions through endogenous mechanisms has led to extensive effort to develop materials to facilitate chondrogenesis. Although physical-chemical properties of biomaterials have been shown to impact in vitro chondrogenesis, whether these findings are translatable in vivo is subject of debate. Herein, architectured 3D hydrogel scaffolds (ArcGel) (produced by crosslinking gelatin with ethyl lysine diisocyanate (LDI)) were used as a model system to investigate the interplay between scaffold mechanical properties and degradation on matrix deposition by human articular chondrocytes (HAC) from healthy donors in vitro and in vivo. Using ArcGel scaffolds of different tensile and shear modulus, and degradation behavior; in this study, we compared the fate of ex vivo engineered ArcGels-chondrocytes constructs, i.e. the traditional tissue engineering approach, with thede novoformation of cartilaginous tissue in HAC laden ArcGels in an ectopic nude mouse model. While the softer and fast degrading ArcGel (LNCO3) was more efficient at promoting chondrogenic differentiation in vitro, upon ectopic implantation, the stiffer and slow degrading ArcGel (LNCO8) was superior in maintaining chondrogenic phenotype in HAC and retention of cartilaginous matrix. Furthermore, surprisingly the de novo formation of cartilage tissue was promoted only in LNCO8. Since HAC cultured for only three days in the LNCO8 environment showed upregulation of hypoxia-associated genes, this suggests a potential role for hypoxia in the observed in vivo outcomes. In summary, this study sheds light on how immediate environment (in vivo versus in vitro) can significantly impact the outcomes of cell-laden biomaterials.

STATEMENT OF SIGNIFICANCE

In this study, 3D architectured hydrogels (ArcGels) with different mechanical and biodegradation properties were investigated for their potential to promote formation of cartilaginous matrix by human articular chondrocytes in vitro and in vivo. Two paradigms were explored (i) ex vivo engineering followed by in vivo implantation in ectopic site of nude mice and (ii) short in vitro culture (3 days) followed by implantation to induce de novo cartilage formation. Softer and fast degrading ArcGel were better at promoting chondrogenesis in vitro, while stiffer and slow degrading ArcGel were strikingly superior in both maintaining chondrogenesis in vivo and inducing de novo formation of cartilage. Our findings highlight the importance of the interplay between scaffold mechanics and degradation in chondrogenesis.

Extracellular matrix dynamics during mesenchymal stem cells differentiation

Mesenchymal stem cells (MSCs) are stromal cells that display self-renewal and multipotent differentiation capacity. The repertoire of mature cells generated ranges but is not restricted to: fat, bone and cartilage. Their potential importance for both cell therapy and maintenance of in vivo homeostasis is indisputable. Nonetheless, both their in vivo identity and use in cell therapy remain elusive. A drawback generated by this fact is that little is known about the MSC niche and how it impacts differentiation and homeostasis maintenance. Hence, the roles played by the extracellular matrix (ECM) and its main regulators namely: the Matrix Metalloproteinases (MMPs) and their counteracting inhibitors (TIMPs and RECK) upon stem cells differentiation are only now beginning to be unveiled. Here, we will focus on mesenchymal stem cells and review the main mechanisms involved in adipo, chondro and osteogenesis, discussing how the extracellular matrix can impact not only lineage commitment, but, also, their survival and potentiality. This review critically analyzes recent work in the field in an effort towards a better understanding of the roles of Matrix Metalloproteinases and their inhibitors in the above-cited events.

Emerging potential of gene silencing approaches targeting anti-chondrogenic factors for cell-based cartilage repair

The field of cartilage repair has exponentially been growing over the past decade. Here, we discuss the possibility to achieve satisfactory regeneration of articular cartilage by means of human mesenchymal stem cells (hMSCs) depleted of anti-chondrogenic factors and implanted in the site of injury. Different types of molecules including transcription factors, transcriptional co-regulators, secreted proteins, and microRNAs have recently been identified as negative modulators of chondroprogenitor differentiation and chondrocyte function. We review the current knowledge about these molecules as potential targets for gene knockdown strategies using RNA interference (RNAi) tools that allow the specific suppression of gene function. The critical issues regarding the optimization of the gene silencing approach as well as the delivery strategies are discussed. We anticipate that further development of these techniques will lead to the generation of implantable hMSCs with enhanced potential to regenerate articular cartilage damaged by injury, disease, or aging.

Effects of matrix metalloproteinases on the fate of mesenchymal stem cells

Mesenchymal stem cells (MSCs) have great potential as a source of cells for cell-based therapy because of their ability for self-renewal and differentiation into functional cells. Moreover, matrix metalloproteinases (MMPs) have a critical role in the differentiation of MSCs into different lineages. MSCs also interact with exogenous MMPs at their surface, and regulate the pericellular localization of MMP activities. The fate of MSCs is regulated by specific MMPs associated with a key cell lineage. Recent reports suggest the integration of MMPs in the differentiation, angiogenesis, proliferation, and migration of MSCs. These interactions are not fully understood and warrant further investigation, especially for their application as therapeutic tools to treat different diseases. Therefore, overexpression of a single MMP or tissue-specific inhibitor of metalloproteinase in MSCs may promote transdifferentiation into a specific cell lineage, which can be used for the treatment of some diseases. In this review, we critically discuss the identification of various MMPs and the signaling pathways that affect the differentiation, migration, angiogenesis, and proliferation of MSCs.

MicroRNA-9 regulates the development of knee osteoarthritis through the NF-kappaB1 pathway in chondrocytes

It has been suggested that microRNA-9 (miR-9) is associated with the development of knee osteoarthritis (OA). This study was aimed to investigate the association between the mechanism of miR-9 targeting nuclear factor kappa-B1 (NF-κB1) and the proliferation and apoptosis of knee OA chondrocytes.Cartilage samples were collected from 25 patients with knee OA and 10 traumatic amputees, and another 15 OA rat models, together with 15 rats without knee OA lesions were also established. MiR-9 expressions in both knee OA cartilage and normal cartilage samples were detected using quantitative real-time PCR. The expressions of related genes (NF-κB1, IL-6, and MMP-13) in the two groups were also detected. Dual luciferase reporter gene assay was employed to examine the effect of miR-9 on the luciferase activity of NF-κB1 3'UTR. Knee OA chondrocytes were transfected with miR-9 mimics, miR-9 inhibitor, and NF-κB1 siRNA, respectively, and changes in cellular proliferation and apoptosis were detected via MTT assay and flow cytometric analysis, respectively. Western blotting assay was used to detect the expressions of NF-κB1, interleukin-6 (IL-6), and matrix metalloproteinase-13 (MMP-13).According to results from human OA samples and rat OA models, miR-9 was significantly downregulated in knee OA cartilage tissues compared with normal cartilage tissues (P < 0.01). The expressions of NF-κB1, IL-6, and MMP-13 in knee OA cartilage tissues were significantly higher than those in normal cartilage tissues (P < 0.01). Dual luciferase reporter gene assay showed that miR-9 could bind to the 3'UTR of NF-κB1 and significantly inhibit the luciferase activity by 37% (P < 0.01). Upregulation of miR-9 or downregulation of NF-κB1 could promote cell proliferation and suppress cell apoptosis.Conclusively, downregulated miR-9 can facilitate proliferation and antiapoptosis of knee OA chondrocytes by directly binding to NF-kB1, implying that stimulating miR-9 expressions might assist in treatment of knee OA.

Enhancement of Matrix Metalloproteinase-2 (MMP-2) as a Potential Chondrogenic Marker during Chondrogenic Differentiation of Human Adipose-Derived Stem Cells

Human adipose-derived stem cells (hASCs) have a capacity to undergo adipogenic, chondrogenic, and osteogenic differentiation. Recently, hASCs were applied to various fields including cell therapy for tissue regeneration. However, it is hard to predict the direction of differentiation of hASCs in real-time. Matrix metalloproteinases (MMPs) are one family of proteolytic enzymes that plays a pivotal role in regulating the biology of stem cells. MMPs secreted by hASCs are expected to show different expression patterns depending on the differentiation state of hASCs because biological functions exhibit different patterns during the differentiation of stem cells. Here, we investigated proteolytic enzyme activity, especially MMP-2 activity, in hASCs during their differentiation. The activities of proteolytic enzymes and MMP-2 were higher during chondrogenic differentiation than during adipogenic and osteogenic differentiation. During chondrogenic differentiation, mRNA expression of MMP-2 and the level of the active form of MMP-2 were increased, which also correlated with Col II. It is concluded that proteolytic enzyme activity and the level of the active form of MMP-2 were increased during chondrogenic differentiation, which was accelerated in the presence of Col II protein. According to our findings, MMP-2 could be a candidate maker for real-time detection of chondrogenic differentiation of hASCs.

Extracellular Protease Inhibition Alters the Phenotype of Chondrogenically Differentiating Human Mesenchymal Stem Cells (MSCs) in 3D Collagen Microspheres

Matrix remodeling of cells is highly regulated by proteases and their inhibitors. Nevertheless, how would the chondrogenesis of mesenchymal stem cells (MSCs) be affected, when the balance of the matrix remodeling is disturbed by inhibiting matrix proteases, is incompletely known. Using a previously developed collagen microencapsulation platform, we investigated whether exposing chondrogenically differentiating MSCs to intracellular and extracellular protease inhibitors will affect the extracellular matrix remodeling and hence the outcomes of chondrogenesis. Results showed that inhibition of matrix proteases particularly the extracellular ones favors the phenotype of fibrocartilage rather than hyaline cartilage in chondrogenically differentiating hMSCs by upregulating type I collagen protein deposition and type II collagen gene expression without significantly altering the hypertrophic markers at gene level. This study suggests the potential of manipulating extracellular proteases to alter the outcomes of hMSC chondrogenesis, contributing to future development of differentiation protocols for fibrocartilage tissues for intervertebral disc and meniscus tissue engineering.

PDGF‑stimulated dispersal of cell clusters and disruption of fibronectin matrix on three-dimensional collagen matrices requires matrix metalloproteinase-2

Previous studies showed that morphogenic cell clustering depends on fibronectin fibrillar matrix assembly under procontractile conditions. The present study shows that disruption of fibronectin matrix necessary for dispersal of cell clusters under promigratory conditions requires matrix metalloproteinases, especially MMP-2.

Formation of cell clusters is a common morphogenic cell behavior observed during tissue and organ development and homeostasis, as well as during pathological disorders. Dynamic regulation of cell clustering depends on the balance between contraction of cells into clusters and migration of cells as dispersed individuals. Previously we reported that under procontractile culture conditions, fibronectin fibrillar matrix assembly by human fibroblasts functioned as a nucleation center for cell clustering on three-dimensional collagen matrices. Here we report that switching preformed cell clusters from procontractile to promigratory culture conditions results in cell dispersal out of clusters and disruption of FN matrix. Experiments using small interfering RNA silencing and pharmacological inhibition demonstrated that matrix metalloproteinase activity involving MMP-2 was necessary for fibronectin matrix disruption and dispersal of cell clusters.

Cross-talk between TGF-beta/SMAD and integrin signaling pathways in regulating hypertrophy of mesenchymal stem cell chondrogenesis under deferral dynamic compression

The molecular mechanisms of mechanotransduction in regulating mesenchymal stem cell (MSC) chondrogenesis are not fully understood and represent an area of growing investigation. In this study, human MSC was subjected to chondrogenic differentiation in chitosan-coated poly L-lactide-co-ɛ-caprolactone scaffolds under free swelling or deferral dynamic compression conditions. The effect of deferral dynamic compression to MSC chondrogenesis and late stage hypertrophy development was investigated, and the involvement of TGF-β/SMAD pathway and integrin β1 signaling was analyzed. Deferral dynamic compression enhanced cartilage formation and suppressed chondrocyte hypertrophy. Differential cell morphology and cytoskeletal organization were induced under dynamic compression, together with the activation of TGF-β/Activin/Nodal and suppression of the BMP/GDP signaling. This was accompanied by the repression of integrin/FAK/ERK signaling in the non-hypertrophic cells when compared to the free swelling samples. Inhibition studies blocking TGF-β/Activin/Nodal signaling heightened hypertrophy, activate BMP/SMAD1/5/8 and integrin signaling, while inhibition of integrin-ECM interaction suppressed hypertrophy and activate TGF-β/SMAD2/3 in the free-swelling samples. This study demonstrates the roles of TGF-β/SMAD and integrin signaling, and suggests cross-talk between these two signaling pathways, in regulating the compression-driven hypertrophy development.

Directed differentiation of induced pluripotent stem cells into chondrogenic lineages for articular cartilage treatment

In recent years, increases in the number of articular cartilage injuries caused by environmental factors or pathological conditions have led to a notable rise in the incidence of premature osteoarthritis. Osteoarthritis, considered a disease of civilization, is the leading cause of disability. At present, standard methods for treating damaged articular cartilage, including autologous chondrocyte implantation or microfracture, are short-term solutions with important side effects. Emerging treatments include the use of induced pluripotent stem cells, a technique that could provide a new tool for treatment of joint damage. However, research in this area is still early, and no optimal protocol for transforming induced pluripotent stem cells into chondrocytes has yet been established. Developments in our understanding of cartilage developmental biology, together with the use of modern technologies in the field of tissue engineering, provide an opportunity to create a complete functional model of articular cartilage.

Mechanotransduction pathways linking the extracellular matrix to the nucleus

Cells contain several mechanosensing components that transduce mechanical signals into biochemical cascades. During cell-ECM adhesion, a complex network of molecules mechanically couples the extracellular matrix (ECM), cytoskeleton, and nucleoskeleton. The network comprises transmembrane receptor proteins and focal adhesions, which link the ECM and cytoskeleton. Additionally, recently identified protein complexes extend this linkage to the nucleus by linking the cytoskeleton and the nucleoskeleton. Despite numerous studies in this field, due to the complexity of this network, our knowledge of the mechanisms of cell-ECM adhesion at the molecular level remains remarkably incomplete. Herein, we present a review of the structures of key molecules involved in cell-ECM adhesion, along with an evaluation of their predicted roles in mechanical sensing. Additionally, specific binding events prompted by force-induced conformational changes of each molecule are discussed. Finally, we propose a model for the biomechanical events prominent in cell-ECM adhesion.

MicroRNA-9 regulates survival of chondroblasts and cartilage integrity by targeting protogenin

Background

Studies have shown the roles of miR-9 and its validated target, protogenin (PRTG) in the differentiation of chondroblasts to chondrocyte and in the pathogenesis of osteoarthritis (OA). We hypothesized that miR-9 plays a distinct role in endochondral ossification and OA pathogenesis and the present study was undertaken to identify this role. In the studies, chondroblasts were isolated from limb bud of chick and mouse embryos and articular chondrocytes were isolated from rabbit and human cartilage. Osteoarthritic chondrocytes were isolated from cartilage from patients undergoing total knee replacement. Using these cells, we analyzed the changes in the expression of genes and proteins, tested the expression level of miR-9, and applied a target validation system. We also performed functional study of miR-9 and PRTG.

Results

With the progression of chondrogenesis, decreased miR-9 level was observed at the time of numerous apoptotic cell deaths. And chondrocytes isolated from normal human articular cartilage expressed miR-9, and this expression was significantly reduced in OA chondrocytes, especially decreased its expression in parallel with the degree of cartilage degradation. Over-expression of PRTG induced the activation of caspase-3 signaling and increased apoptosis. However, the co-treatment with the miR-9 precursor or PRTG-specific siRNA blocked this apoptotic signaling.

Conclusion

This study shows that PRTG is regulated by miR-9, plays an inhibitory action on survival of chondroblasts and articular chondrocytes during chondrogenesis and OA pathogenesis.

MicroRNA-34a modulates cytoskeletal dynamics through regulating RhoA/Rac1 cross-talk in chondroblasts

MicroRNAs (miRNAs) have been implicated in various cellular processes, such as cell fate determination, cell death, and tumorigenesis. In the present study, we investigated the role of miRNA-34a (miR-34a) in the reorganization of the actin cytoskeleton, which is essential for chondrocyte differentiation. miRNA arrays to identify genes that appeared to be up-regulated or down-regulated during chondrogenesis were applied with chondrogenic progenitors treated with JNK inhibitor. PNA-based antisense oligonucleotides and miRNA precursor were used for investigation of the functional roles of miR-34a. We found that, in chick chondroprogenitors treated with JNK inhibitor, which suppresses chondrogenic differentiation, the expression levels of miR-34a and RhoA1 are up-regulated through modulation of Rac1 expression. Blockade of miR-34a via the use of PNA-based antisense oligonucleotides was associated with decreased protein expression of RhoA (a known modulator of stress fiber expression), down-regulation of stress fibers, up-regulation of Rac1, and recovery of protein level of type II collagen. miR-34a regulates RhoA/Rac1 cross-talk and negatively modulates reorganization of the actin cytoskeleton, which is one of the essential processes for establishing chondrocyte-specific morphology.

Biomimetic extracellular matrix-incorporated scaffold induces osteogenic gene expression in human marrow stromal cells

Engineering biomaterials mimicking the biofunctionality of the extracellular matrix (ECM) is important in instructing and eliciting cell response. The native ECM is highly dynamic and has been shown to support cellular attachment, migration, and differentiation. The advantage of synthesizing an ECM-based biomaterial is that it mimics the native cellular environment. However, the ECM has tissue-specific composition and patterned arrangement. In this study, we have employed biomimetic strategies to develop a novel collagen/chitosan template that is embedded with the native ECM of differentiating human marrow stromal cells (HMSCs) to facilitate osteoblast differentiation. The scaffold was characterized for substrate stiffness by magnetic resonance imaging and nanoindentation and by immunohistochemical analysis for the presence of key ECM proteins. Gene expression analysis showed that the ECM scaffold supported osteogenic differentiation of undifferentiated HMSCs as significant changes were observed in the expression levels of growth factors, transcription factors, proteases, receptors, and ECM proteins. Finally, we demonstrate that the scaffold had the ability to nucleate calcium phosphate polymorphs to form a mineralized matrix. The results from this study suggest that the three-dimensional native ECM scaffold directly controls cell behavior and supports the osteogenic differentiation of mesenchymal stem cells.

Defining the earliest transcriptional steps of chondrogenic progenitor specification during the formation of the digits in the embryonic limb

The characterization of genes involved in the formation of cartilage is of key importance to improve cell-based cartilage regenerative therapies. Here, we have developed a suitable experimental model to identify precocious chondrogenic events in vivo by inducing an ectopic digit in the developing embryo. In this model, only 12 hr after the implantation of a Tgfβ bead, in the absence of increased cell proliferation, cartilage forms in undifferentiated interdigital mesoderm and in the course of development, becomes a structurally and morphologically normal digit. Systematic quantitative PCR expression analysis, together with other experimental approaches allowed us to establish 3 successive periods preceding the formation of cartilage. The “pre-condensation stage”, occurring within the first 3 hr of treatment, is characterized by the activation of connective tissue identity transcriptional factors (such as Sox9 and Scleraxis) and secreted factors (such as Activin A and the matricellular proteins CCN-1 and CCN-2) and the downregulation of the galectin CG-8. Next, the “condensation stage” is characterized by intense activation of Smad 1/5/8 BMP-signaling and increased expression of extracellular matrix components. During this period, the CCN matricellular proteins promote the expression of extracellular matrix and cell adhesion components. The third period, designated the “pre-cartilage period”, precedes the formation of molecularly identifiable cartilage by 2–3 hr and is characterized by the intensification of Sox 9 gene expression, along with the stimulation of other pro-chondrogenic transcription factors, such as HifIa. In summary, this work establishes a temporal hierarchy in the regulation of pro-chondrogenic genes preceding cartilage differentiation and provides new insights into the relative roles of secreted factors and cytoskeletal regulators that direct the first steps of this process in vivo.

Microscale versus nanoscale scaffold architecture for mesenchymal stem cell chondrogenesis

Nanofiber scaffolds, produced by the electrospinning technique, have gained widespread attention in tissue engineering due to their morphological similarities to the native extracellular matrix. For cartilage repair, studies have examined their feasibility; however these studies have been limited, excluding the influence of other scaffold design features. This study evaluated the effect of scaffold design, specifically examining a range of nano to micron-sized fibers and resulting pore size and mechanical properties, on human mesenchymal stem cells (MSCs) derived from the adult bone marrow during chondrogenesis. MSC differentiation was examined on these scaffolds with an emphasis on temporal gene expression of chondrogenic markers and the pluripotent gene, Sox2, which has yet to be explored for MSCs during chondrogenesis and in combination with tissue engineering scaffolds. Chondrogenic markers of aggrecan, chondroadherin, sox9, and collagen type II were highest for cells on micron-sized fibers (5 and 9 μm) with pore sizes of 27 and 29 μm, respectively, in comparison to cells on nano-sized fibers (300 nm and 600 to 1400 nm) having pore sizes of 2 and 3 μm, respectively. Undifferentiated MSCs expressed high levels of the Sox2 gene but displayed negligible levels on all scaffolds with or without the presence of inductive factors, suggesting that the physical features of the scaffold play an important role in differentiation. Micron-sized fibers with large pore structures and mechanical properties comparable to the cartilage ECM enhanced chondrogenesis, demonstrating architectural features as well as mechanical properties of electrospun fibrous scaffolds enhance differentiation.

Ligand-independent activation of c-Met by fibronectin and α(5)β(1)-integrin regulates ovarian cancer invasion and metastasis

The role of the fibronectin receptor, α₅β₁-integrin, as an adhesion receptor and in angiogenesis, is well established. However, its role in cancer cell invasion and metastasis is less clear. We describe a novel mechanism by which fibronectin regulates ovarian cancer cell signaling and promotes metastasis. Fibronectin binding to α₅β₁-integrin led to a direct association of α₅-integrin with the receptor tyrosine kinase, c-Met, activating it in a hepatocyte growth factor/scatter factor (HGF/SF) independent manner. Subsequently, c-Met associated with Src and activated Src and focal adhesion kinase (FAK). Inhibition of α₅β₁-integrin decreased the phosphorylation of c-Met, FAK and Src, both in vitro and in vivo. Independent activation of c-Met by its native ligand, HGF/SF, or overexpression of a constitutively active FAK in HeyA8 cells could overcome the effect of α₅β₁-integrin inhibition on tumor cell invasion, indicating that α₅β₁-integrin is upstream of c-Met, Src and FAK. Inhibition of α₅β₁-integrin on cancer cells in two xenograft models of ovarian cancer metastasis resulted in a significant decrease of tumor burden, which was independent of the effect of α₅β₁-integrin on angiogenesis. These data suggest that fibronectin promotes ovarian cancer invasion and metastasis through an α₅β₁-integrin/c-Met/FAK/Src dependent signaling pathway, transducing signals through c-Met in a HGF/SF independent manner.

TGF-beta3 inhibits chondrogenesis by suppressing precartilage condensation through stimulation of N-cadherin shedding and reduction of cRREB-1 expression

Transforming growth factor-beta (TGF-beta) plays crucial roles in controlling cell differentiation and maintaining tissue integrity. Previously we reported that TGF-beta3 treatment decreased the mRNA expression of the gap junction protein, connexin 43 as well as cell number, which lead to the inhibition of chondrogenic condensation in cultured chick leg bud mesenchymal cells. The present study demonstrates that TGF-beta3 can induce cleavage in the ectodomain of neuronal cadherin (N-cadherin) at the initiation stage of chondrogenesis and reduce cell numbers, cellular adhesion and the expression level of connexin 43. Differential displayed PCR (DD-PCR) comparison of adherent- and non-adherent chick leg chondrogenic progenitor cells showed increased expression of the chick ras-responsive element binding transcription factor, cRREB-1, in adherent cells. In chick leg bud mesenchymal cells, cRREB-1 transcription was inhibited by TGF-beta3 at the early stage of chondrogenesis. Small interfering RNA (siRNA)-mediated knockdown of cRREB-1 reduced cell numbers, cellular adhesion, and the expression level of connexin 43 resulting in the inhibition of precartilage condensation. Taken together, these findings indicate that TGF-beta3 mediates the inhibitory signal necessary for precartilage condensation by stimulating N-cadherin shedding and reducing cRREB-1 expression levels.

Fibulin-3 negatively regulates chondrocyte differentiation

Fibulin-3 is a member of the fibulin family that has been newly recognized as extracellular matrix proteins. We assessed the effects of fibulin-3 overexpression on chondrocyte differentiation using the clonal murine cell line ATDC5. The ATDC5-FBLN3 stably expressing fibulin-3 protein was spindle-shaped cell compared to the ATDC5-mock with plump cell. The cell growth in the ATDC5-FBLN3 was accelerated in comparison to that in the ATDC5-mock. The ATDC5-FBLN3 was not stained by Alcian blue, nor was there any cartilage aggregate formed after the induction of chondrogenic differentiation. The expression of type II collagen, aggrecan, and type X collagen was completely suppressed in ATDC5-FBLN3 even after the induction of differentiation. The overexpression of fibulin-3 reduced the expression of Sox5 and Sox6, while it maintained the expression of Sox9. These findings suggest that fibulin-3 may play an important role as a negative regulator of chondrocyte differentiation.

Endothelial cells influence the osteogenic potential of bone marrow stromal cells

Background

Improved understanding of the interactions between bone cells and endothelial cells involved in osteogenesis should aid the development of new strategies for bone tissue engineering. The aim of the present study was to determine whether direct communication between bone marrow stromal cells (MSC) and human umbilical vein endothelial cells (EC) could influence the osteogenic potential of MSC in osteogenic factor-free medium.

Methods

After adding EC to MSC in a direct-contact system, cell viability and morphology were investigated with the WST assay and immnostaining. The effects on osteogenic differentiation of adding EC to MSC was systematically tested by the using Superarray assay and results were confirmed with real-time PCR.

Results

Five days after the addition of EC to MSC in a ratio of 1:5 (EC/MSC) significant increases in cell proliferation and cellular bridges between the two cell types were detected, as well as increased mRNA expression of alkaline phosphatase (ALP). This effect was greater than that seen with addition of osteogenic factors such as dexamethasone, ascorbic acid and β-glycerophosphate to the culture medium. The expression of transcription factor Runx2 was enhanced in MSC incubated with osteogenic stimulatory medium, but was not influenced by induction with EC. The expression of Collagen type I was not influenced by EC but the cells grown in the osteogenic factor-free medium exhibited higher expression than those cultured with osteogenic stimulatory medium.

Conclusion

These results show that co-culturing of EC and MSC for 5 days influences osteogenic differentiation of MSC, an effect that might be independent of Runx2, and enhances the production of ALP by MSC.

Gene expression profile of multipotent mesenchymal stromal cells: Identification of pathways common to TGFbeta3/BMP2-induced chondrogenesis

Multipotent mesenchymal stromal cells (MSC) display a high potential for the development of novel treatment strategies for cartilage repair. However, the pathways involved in their differentiation to functional non hypertrophic chondrocytes remain largely unknown, despite the work on embryologic development and the identification of key growth factors including TGFbeta, Hh, Wnt and FGF. In this study, we asked if we could identify specific biological networks common to the growth factors used (TGFbeta3 or BMP-2). To address this question, we used DNA microarrays and performed large-scale expression profiling of MSC at different time points during their chondrogenic differentiation. By comparing these data with those obtained during the differentiation of MSC into osteoblasts and adipocytes, we identified 318 genes specific for chondrogenesis and developed a new algorithm to classify the genes according to their kinetic profile. We distributed the selected genes in five classes according to their kinetic of expression. We could reconstruct three phases characterized by functional pathways. The first phase corresponds to cell attachment and apoptosis induction; the second phase is characterized by a proliferation/differentiation step, and the third phase is characterized by a differentiation/hypertrophy pathway. Indeed, these data propose new pathways to understand the complexity of MSC differentiation to chondrocytes.

Morphogenetic and regulatory mechanisms during developmental chondrogenesis: new paradigms for cartilage tissue engineering

Cartilage is the first skeletal tissue to be formed during embryogenesis leading to the creation of all mature cartilages and bones, with the exception of the flat bones in the skull. Therefore, errors occurring during the process of chondrogenesis, the formation of cartilage, often lead to severe skeletal malformations such as dysplasias. There are hundreds of skeletal dysplasias, and the molecular genetic etiology of some remains more elusive than of others. Many efforts have aimed at understanding the morphogenetic event of chondrogenesis in normal individuals, of which the main morphogenetic and regulatory mechanisms will be reviewed here. For instance, many signaling molecules that guide chondrogenesis--for example, transforming growth factor-beta, bone morphogenetic proteins, fibroblast growth factors, and Wnts, as well as transcriptional regulators such as the Sox family--have already been identified. Moreover, extracellular matrix components also play an important role in this developmental event, as evidenced by the promotion of the chondrogenic potential of chondroprogenitor cells caused by collagen II and proteoglycans like versican. The growing evidence of the elements that control chondrogenesis and the increasing number of different sources of progenitor cells will, hopefully, help to create tissue engineering platforms that could overcome many developmental or degenerative diseases associated with cartilage defects.

Matrix metalloproteinases, T cell homing and beta-cell mass in type 1 diabetes

The pathogenesis of type 1 diabetes begins with the activation of autoimmune T killer cells and is followed by their homing into the pancreatic islets. After penetrating the pancreatic islets, T cells directly contact and destroy insulin-producing beta cells. This review provides an overview of the dynamic interactions which link T cell membrane type-1 matrix metalloproteinase (MT1-MMP) and the signaling adhesion CD44 receptor with T cell transendothelial migration and the subsequent homing of the transmigrated cells to the pancreatic islets. MT1-MMP regulates the functionality of CD44 in diabetogenic T cells. By regulating the functionality of T cell CD44, MT1-MMP mediates the transition of T cell adhesion to endothelial cells to the transendothelial migration of T cells, thus, controlling the rate at which T cells home into the pancreatic islets. As a result, the T cell MT1-MMP-CD44 axis controls the severity of the disease. Inhibition of MT1-MMP proteolysis of CD44 using highly specific and potent synthetic inhibitors, which have been clinically tested in cancer patients, reduces the rate of transendothelial migration and the homing of T cells. Result is a decrease in the net diabetogenic efficiency of T cells and a restoration of beta cell mass and insulin production in NOD mice. The latter is a reliable and widely used model of type I diabetes in humans. Overall, existing experimental evidence suggests that there is a sound mechanistic rationale for clinical trials of the inhibitors of T cell MT1-MMP in human type 1 diabetes patients.

Regulation of cartilage formation and maturation by mitogen-activated protein kinase signaling

The majority of bones comprising the adult vertebrate skeleton are generated from hyaline cartilage templates that form during embryonic development. A process known as endochondral ossification is responsible for the conversion of these transient cartilage anlagen into mature, calcified bone. Endochondral ossification is a highly regulated, multistep cell specification program involving the initial differentiation of prechondrogenic mesenchymal cells into hyaline chondrocytes, terminal differentiation of hyaline chondrocytes into hypertrophic chondrocytes, and finally, apoptosis of hypertrophic chondrocytes followed by bone matrix deposition. Recently, extensive research has been carried out describing roles for the three major mitogen-activated protein kinase (MAPK) signaling pathways, the extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and c-jun N-terminal kinase (JNK) pathways, in the successive stages of chondrogenic differentiation. In this review, we survey this research examining the involvement of ERK1/2, p38, and JNK pathway signaling in all aspects of the chondrogenic differentiation program from embryonic through postnatal stages of development. In addition, we summarize evidence from in vitro studies examining MAPK function in immortalized chondrogenic cell lines and adult mesenchymal stem cells. We also provide suggestions for future studies that may help ameliorate existing confusion concerning the specific roles of MAPK signaling at different stages of chondrogenesis.