Chondrogenesis, joint formation, and articular cartilage regeneration

Stem-Cell-Driven Chondrogenesis: Perspectives on Amnion-Derived Cells

Regenerative medicine harnesses stem cells' capacity to restore damaged tissues and organs. In vitro methods employing specific bioactive molecules, such as growth factors, bio-inductive scaffolds, 3D cultures, co-cultures, and mechanical stimuli, steer stem cells toward the desired differentiation pathways, mimicking their natural development. Chondrogenesis presents a challenge for regenerative medicine. This intricate process involves precise modulation of chondro-related transcription factors and pathways, critical for generating cartilage. Cartilage damage disrupts this process, impeding proper tissue healing due to its unique mechanical and anatomical characteristics. Consequently, the resultant tissue often forms fibrocartilage, which lacks adequate mechanical properties, posing a significant hurdle for effective regeneration. This review comprehensively explores studies showcasing the potential of amniotic mesenchymal stem cells (AMSCs) and amniotic epithelial cells (AECs) in chondrogenic differentiation. These cells exhibit innate characteristics that position them as promising candidates for regenerative medicine. Their capacity to differentiate toward chondrocytes offers a pathway for developing effective regenerative protocols. Understanding and leveraging the innate properties of AMSCs and AECs hold promise in addressing the challenges associated with cartilage repair, potentially offering superior outcomes in tissue regeneration.

Ginsenoside Rg1/ADSCs supplemented with hyaluronic acid as the matrix improves rabbit temporomandibular joint osteoarthrosis

OBJECTIVE

To investigate whether and how ginsenoside Rg1/ADSCs supplemented with hyaluronic acid as the matrix can improve rabbit temporomandibular joint osteoarthrosis.

METHOD

Isolate and culture adipose stem cells, measure the activity of differentiated chondrocytes by MTT assay and expression of type II collagen in these cells by immunohistochemistry, in order to evaluate the effect of ginsenoside Rg1 on adipose stem cell proliferation and differentiation into chondrocytes.32 New Zealand white rabbits were randomly divided into four groups: blank group, model group, control group and experimental group, 8 in each group. Osteoarthritis model was established by intra-articular injection of papain. Two weeks after successful model building, medication was given for the rabbits in control group and experimental group. 0.6 mL ginsenoside Rg1/ ADSCs suspension was injected into superior joint space for the rabbits in control group, once a week; 0.6 mL ginsenoside Rg1/ ADSCs complex was injected for the rabbits in experimental group, once a week.

RESULTS

Ginsenoside Rg1 can promote ADSCs-derived chondrocytes' activity and expression of type II collagen. Scanning electron microscopy histology images showed cartilage lesions of the experimental group was significantly improved in comparison with control group.

CONCLUSION

Ginsenoside Rg1 can promote ADSCs differentiate into chondrocytes, and Ginsenoside Rg1/ADSCs supplemented with hyaluronic acid as the matrix can significantly improve rabbit temporomandibular joint osteoarthrosis.

Altered microRNAs in C3H10T1/2 cells induced by p.E95K mutant IHH signaling

Background

Indian Hedgehog (IHH), an important cell signaling protein, plays a key regulatory role in development of cartilage and chondrogenesis. Earlier studies have shown that heterozygous missense mutations in IHH gene may cause brachydactyly type A1 (BDA1), an autosomal dominant inheritance disease characterized by apparent shortness or absence of the middle phalanges of all digits. MicroRNAs (miRNAs) have been found to be significant post-transcriptional regulators of gene expression and significantly influence the process of bone-development. Therefore, it is possible that miRNAs are involved in the mechanism underlying the development of BDA1. However, the relationship between miRNAs and the pathogenesis of BDA1 remains unclear.

Methods

In this study, we used microarray-based miRNA profiling to investigate the role of miRNAs in BDA1 by characterization of differentially expressed miRNAs in C3H10T1/2 cell line induced by wild type (WT) and p.E95K mutant (MT) IHH signaling.

Results

Our results identified 6 differentially expressed miRNAs between WT and control (CT) group and 5 differentially expressed miRNAs between MT and CT groups. In particular, miR-135a-1-3p was found to be a significantly differentially expressed miRNA between WT and CT group. Results of dual-luciferase reporter gene experiment successfully discovered Hoxd10 was one of the target gene of miR-135a-1-3p. Additionally, our pathway analysis revealed that the targets of these miRNAs of interest were highly involved with Runx1/2, Notch and collagen-related pathways.

Conclusions

Taken together, our findings provided important clue for future study of the process of miRNA-regulation in IHH signaling and novel insights into the regulatory role of miRNA in pathogenesis of BDA1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41065-021-00207-8.

An ECHO of Cartilage: In Silico Prediction of Combinatorial Treatments to Switch Between Transient and Permanent Cartilage Phenotypes With Ex Vivo Validation

A fundamental question in cartilage biology is: what determines the switch between permanent cartilage found in the articular joints and transient hypertrophic cartilage that functions as a template for bone? This switch is observed both in a subset of OA patients that develop osteophytes, as well as in cell-based tissue engineering strategies for joint repair. A thorough understanding of the mechanisms regulating cell fate provides opportunities for treatment of cartilage disease and tissue engineering strategies. The objective of this study was to understand the mechanisms that regulate the switch between permanent and transient cartilage using a computational model of chondrocytes, ECHO. To investigate large signaling networks that regulate cell fate decisions, we developed the software tool ANIMO, Analysis of Networks with interactive Modeling. In ANIMO, we generated an activity network integrating 7 signal transduction pathways resulting in a network containing over 50 proteins with 200 interactions. We called this model ECHO, for executable chondrocyte. Previously, we showed that ECHO could be used to characterize mechanisms of cell fate decisions. ECHO was first developed based on a Boolean model of growth plate. Here, we show how the growth plate Boolean model was translated to ANIMO and how we adapted the topology and parameters to generate an articular cartilage model. In ANIMO, many combinations of overactivation/knockout were tested that result in a switch between permanent cartilage (SOX9+) and transient, hypertrophic cartilage (RUNX2+). We used model checking to prioritize combination treatments for wet-lab validation. Three combinatorial treatments were chosen and tested on metatarsals from 1-day old rat pups that were treated for 6 days. We found that a combination of IGF1 with inhibition of ERK1/2 had a positive effect on cartilage formation and growth, whereas activation of DLX5 combined with inhibition of PKA had a negative effect on cartilage formation and growth and resulted in increased cartilage hypertrophy. We show that our model describes cartilage formation, and that model checking can aid in choosing and prioritizing combinatorial treatments that interfere with normal cartilage development. Here we show that combinatorial treatments induce changes in the zonal distribution of cartilage, indication possible switches in cell fate. This indicates that simulations in ECHO aid in describing pathologies in which switches between cell fates are observed, such as OA.

Macro, Micro, and Molecular. Changes of the Osteochondral Interface in Osteoarthritis Development

Osteoarthritis (OA) is a long-term condition that causes joint pain and reduced movement. Notably, the same pathways governing cell growth, death, and differentiation during the growth and development of the body are also common drivers of OA. The osteochondral interface is a vital structure located between hyaline cartilage and subchondral bone. It plays a critical role in maintaining the physical and biological function, conveying joint mechanical stress, maintaining chondral microenvironment, as well as crosstalk and substance exchange through the osteochondral unit. In this review, we summarized the progress in research concerning the area of osteochondral junction, including its pathophysiological changes, molecular interactions, and signaling pathways that are related to the ultrastructure change. Multiple potential treatment options were also discussed in this review. A thorough understanding of these biological changes and molecular mechanisms in the pathologic process will advance our understanding of OA progression, and inform the development of effective therapeutics targeting OA.

Intersections Between Mitochondrial Metabolism and Redox Biology Mediate Posttraumatic Osteoarthritis

PURPOSE OF REVIEW

This review will cover foundational studies and recent findings that established key concepts for understanding the importance of redox biology to chondrocyte mitochondrial function and osteoarthritis pathophysiology after injury.

RECENT FINDINGS

Articular chondrocyte mitochondria can be protected with a wide variety of antioxidants that will be discussed within a framework suggested by classic studies. These agents not only underscore the importance of thiol metabolism and associated redox function for chondrocyte mitochondria but also suggest complex interactions with signal transduction pathways and other molecular features of osteoarthritis that require more thorough investigation. Emerging evidence also indicates that reductive stress could occur alongside oxidative stress. Recent studies have shed new light on historic paradoxes in chondrocyte redox and mitochondrial physiology, leading to the development of promising disease-modifying therapies for posttraumatic osteoarthritis.

Mechanical stress determines the configuration of TGFβ activation in articular cartilage

Our incomplete understanding of osteoarthritis (OA) pathogenesis has significantly hindered the development of disease-modifying therapy. The functional relationship between subchondral bone (SB) and articular cartilage (AC) is unclear. Here, we found that the changes of SB architecture altered the distribution of mechanical stress on AC. Importantly, the latter is well aligned with the pattern of transforming growth factor beta (TGFβ) activity in AC, which is essential in the regulation of AC homeostasis. Specifically, TGFβ activity is concentrated in the areas of AC with high mechanical stress. A high level of TGFβ disrupts the cartilage homeostasis and impairs the metabolic activity of chondrocytes. Mechanical stress stimulates talin-centered cytoskeletal reorganization and the consequent increase of cell contractile forces and cell stiffness of chondrocytes, which triggers αV integrin–mediated TGFβ activation. Knockout of αV integrin in chondrocytes reversed the alteration of TGFβ activation and subsequent metabolic abnormalities in AC and attenuated cartilage degeneration in an OA mouse model. Thus, SB structure determines the patterns of mechanical stress and the configuration of TGFβ activation in AC, which subsequently regulates chondrocyte metabolism and AC homeostasis.

The functional relationship between subchondral bone and articular cartilage is unclear. Here, the authors show that transforming growth factor-beta propagates the mechanical impact of subchondral bone on articular cartilage through αV integrin–talin mechanical transduction system in chondrocytes.

DNA hypomethylation during MSC chondrogenesis occurs predominantly at enhancer regions

Regulation of transcription occurs in a cell type specific manner orchestrated by epigenetic mechanisms including DNA methylation. Methylation changes may also play a key role in lineage specification during stem cell differentiation. To further our understanding of epigenetic regulation in chondrocytes we characterised the DNA methylation changes during chondrogenesis of mesenchymal stem cells (MSCs) by Infinium 450 K methylation array. Significant DNA hypomethylation was identified during chondrogenic differentiation including changes at many key cartilage gene loci. Integration with chondrogenesis gene expression data revealed an enrichment of significant CpGs in upregulated genes, while characterisation of significant CpG loci indicated their predominant localisation to enhancer regions. Comparison with methylation profiles of other tissues, including healthy and diseased adult cartilage, identified chondrocyte-specific regions of hypomethylation and the overlap with differentially methylated CpGs in osteoarthritis. Taken together we have associated DNA methylation levels with the chondrocyte phenotype. The consequences of which has potential to improve cartilage generation for tissue engineering purposes and also to provide context for observed methylation changes in cartilage diseases such as osteoarthritis.

Non-Coding RNAs in Cartilage Development: An Updated Review

In the development of the skeleton, the long bones are arising from the process of endochondral ossification (EO) in which cartilage is replaced by bone. This complex process is regulated by various factors including genetic, epigenetic, and environmental elements. It is recognized that DNA methylation, higher-order chromatin structure, and post-translational modifications of histones regulate the EO. With emerging understanding, non-coding RNAs (ncRNAs) have been identified as another mode of EO regulation, which is consist of microRNAs (miRNAs or miRs) and long non-coding RNAs (lncRNAs). There is expanding experimental evidence to unlock the role of ncRNAs in the differentiation of cartilage cells, as well as the pathogenesis of several skeletal disorders including osteoarthritis. Cutting-edge technologies such as epigenome-wide association studies have been employed to reveal disease-specific patterns regarding ncRNAs. This opens a new avenue of our understanding of skeletal cell biology, and may also identify potential epigenetic-based biomarkers. In this review, we provide an updated overview of recent advances in the role of ncRNAs especially focus on miRNA and lncRNA in the development of bone from cartilage, as well as their roles in skeletal pathophysiology.

PPAR-δ Agonist With Mesenchymal Stem Cells Induces Type II Collagen-Producing Chondrocytes in Human Arthritic Synovial Fluid

Osteoarthritis (OA) is an inflammatory joint disease characterized by degeneration of articular cartilage within synovial joints. An estimated 27 million Americans suffer from OA, and the population is expected to reach 67 million in the United States by 2030. Thus, it is urgent to find an effective treatment for OA. Traditional OA treatments have no disease-modifying effect, while regenerative OA therapies such as autologous chondrocyte implantation show some promise. Nonetheless, current regenerative therapies do not overcome synovial inflammation that suppresses the differentiation of mesenchymal stem cells (MSCs) to chondrocytes and the expression of type II collagen, the major constituent of functional cartilage. We discovered a synergistic combination that overcame synovial inflammation to form type II collagen-producing chondrocytes. The combination consists of peroxisome proliferator–activated receptor (PPAR) δ agonist, human bone marrow (hBM)-derived MSCs, and hyaluronic acid (HA) gel. Interestingly, those individual components showed their own strong enhancing effects on chondrogenesis. GW0742, a PPAR-δ agonist, greatly enhanced MSC chondrogenesis and the expression of type II collagen and glycosaminoglycan (GAG) in hBM-MSC-derived chondrocytes. GW0742 also increased the expression of transforming growth factor β that enhances chondrogenesis and suppresses cartilage fibrillation, ossification, and inflammation. HA gel also increased MSC chondrogenesis and GAG production. However, neither GW0742 nor HA gel could enhance the formation of type II collagen-producing chondrocytes from hBM-MSCs within human OA synovial fluid. Our data demonstrated that the combination of hBM-MSCs, PPAR-δ agonist, and HA gel significantly enhanced the formation of type II collagen-producing chondrocytes within OA synovial fluid from 3 different donors. In other words, the novel combination of PPAR-δ agonist, hBM-MSCs, and HA gel can overcome synovial inflammation to form type II collagen cartilage within human OA synovial fluid. This novel articularly injectable formula could improve OA treatment in the future clinical application.

Role of microRNAs in progenitor cell commitment and osteogenic differentiation in health and disease (Review)

MicroRNAs (miRNAs) are considered 'micro- managers of gene expression' and awareness of their fundamental role in the control of biological functions is constantly increasing. Bone formation and homeostasis are complex processes involving the differentiation and interaction of various cell types. Several miRNAs have been shown to be involved in different pathways and stages in the regulation of normal and abnormal bone formation and turnover. This present review focuses on the involvement of miRNAs in terms of their effect on the commitment of bone marrow mesenchymal stem cells towards osteogenesis, adipogenesis and chondrogenesis, respectively. The miRNAs involved in regulating osteoblast, chondroblast and osteoclast activity, are also taken into consideration, as are their interactions. miRNA expression levels, which may differ significantly in healthy versus pathological conditions, can be readily monitored and represent useful biomarkers. Several studies have suggested that miRNAs offer potential as useful biomarkers of bone pathologies, including osteoporosis and osteosarcoma. The development of efficient methods of delivering miRNA mimics or miRNA inhibitors into specific cells remains a challenge for novel therapeutic applications in the field of personalized medicine.

The long non-coding RNA ROCR contributes to SOX9 expression and chondrogenic differentiation of human mesenchymal stem cells

Long non-coding RNAs (lncRNAs) are expressed in a highly tissue-specific manner and function in various aspects of cell biology, often as key regulators of gene expression. In this study, we established a role for lncRNAs in chondrocyte differentiation. Using RNA sequencing we identified a human articular chondrocyte repertoire of lncRNAs from normal hip cartilage donated by neck of femur fracture patients. Of particular interest are lncRNAs upstream of the master chondrocyte transcription factor SOX9 locus. SOX9 is an HMG-box transcription factor that plays an essential role in chondrocyte development by directing the expression of chondrocyte-specific genes. Two of these lncRNAs are upregulated during chondrogenic differentiation of mesenchymal stem cells (MSCs). Depletion of one of these lncRNAs, LOC102723505, which we termed ROCR (regulator of chondrogenesis RNA), by RNA interference disrupted MSC chondrogenesis, concomitant with reduced cartilage-specific gene expression and incomplete matrix component production, indicating an important role in chondrocyte biology. Specifically, SOX9 induction was significantly ablated in the absence of ROCR, and overexpression of SOX9 rescued the differentiation of MSCs into chondrocytes. Our work sheds further light on chondrocyte-specific SOX9 expression and highlights a novel method of chondrocyte gene regulation involving a lncRNA.

Summary: This study identified a chondrocyte repertoire of lncRNAs and discovered that ROCR (regulator of chondrogenesis RNA) is important for MSC chondrogenesis and cartilage gene expression by promoting the expression of SOX9.

Prospects of siRNA applications in regenerative medicine

Small interfering RNA (siRNA) has established its reputation in the field of tissue engineering owing to its ability to silence the proteins that inhibit tissue regeneration. siRNA is capable of regulating cellular behavior during tissue regeneration processes. The concept of using siRNA technology in regenerative medicine derived from its ability to inhibit the expression of target genes involved in defective tissues and the possibility to induce the expression of tissue-inductive factors that improve the tissue regeneration process. To date, siRNA has been used as a suppressive biomolecule in different tissues, such as nervous tissue, bone, cartilage, heart, kidney, and liver. Moreover, various delivery systems have been applied in order to deliver siRNA to the target tissues. This review will provide an in-depth discussion on the development of siRNA and their delivery systems and mechanisms of action in different tissues.

Osteoprotegerin deficiency leads to deformation of the articular cartilage in femoral head

Osteoarthritis (OA) was a degenerative joint disease characterized by articular cartilage degradation and extensive remodeling of the subchondral bone. Multiple lines of evidence indicated that Osteoprotegerin (OPG), a member of TNF receptor superfamily that was expressed in the chondrocytes of articular cartilage and adjacent locations in the physiological setting, was involved in maintaining integrity of articular cartilage. OPG could prevent subchondral bone from resorption, and also protect cartilage from degradation. In this study, we used Osteoprotegerin-knockout mice (Opg-KO mice) to find out the role of OPG in articular cartilage. We examined articular cartilage in the femoral head of Opg-KO mice began in early adulthood using modern molecular and imaging methods. We found cartilage changes starting from adulthood and progressively with age, reminiscent of pathological changes in OA. Deficiency of OPG caused thinned articular cartilage and extensive remodeling of the subchondral bone in femoral head in comparison with wild-type mice (WT mice). Also, the articular cartilage of femoral head expressed significantly less of Aggrecan, Col-II and Col-X, but more Col-I and Matrix Metalloproteinases-13 (Mmp-13) than WT mice both at gene and protein level. Moreover, increased chondrocyte apoptosis and decreased chondrocyte proliferation were observed in femoral head of Opg-KO mice compared to WT mice. These data suggested that OPG played an important role in maintaining the homeostasis of articular cartilage of femoral head.

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.

Genome-Wide MicroRNA and Gene Analysis of Mesenchymal Stem Cell Chondrogenesis Identifies an Essential Role and Multiple Targets for miR-140-5p

microRNAs (miRNAs) are abundantly expressed in development where they are critical determinants of cell differentiation and phenotype. Accordingly miRNAs are essential for normal skeletal development and chondrogenesis in particular. However, the question of which miRNAs are specific to the chondrocyte phenotype has not been fully addressed. Using microarray analysis of miRNA expression during mesenchymal stem cell chondrogenic differentiation and detailed examination of the role of essential differentiation factors, such as SOX9, TGF-β, and the cell condensation phase, we characterize the repertoire of specific miRNAs involved in chondrocyte development, highlighting in particular miR-140 and miR-455. Further with the use of mRNA microarray data we integrate miRNA expression and mRNA expression during chondrogenesis to underline the particular importance of miR-140, especially the -5p strand. We provide a detailed identification and validation of direct targets of miR-140-5p in both chondrogenesis and adult chondrocytes with the use of microarray and 3'UTR analysis. This emphasizes the diverse array of targets and pathways regulated by miR-140-5p. We are also able to confirm previous experimentally identified targets but, additionally, identify a novel positive regulation of the Wnt signaling pathway by miR-140-5p. Wnt signaling has a complex role in chondrogenesis and skeletal development and these findings illustrate a previously unidentified role for miR-140-5p in regulation of Wnt signaling in these processes. Together these developments further highlight the role of miRNAs during chondrogenesis to improve our understanding of chondrocyte development and guide cartilage tissue engineering.

Bioimaging: An Useful Tool to Monitor Differentiation of Human Embryonic Stem Cells into Chondrocytes

To improve the recovery of damaged cartilage tissue, pluripotent stem cell-based therapies are being intensively explored. A number of techniques exist that enable monitoring of stem cell differentiation, including immunofluorescence staining. This simple and fast method enables changes to be observed during the differentiation process. Here, two protocols for the differentiation of human embryonic stem cells into chondrocytes were used (monolayer cell culture and embryoid body formation). Cells were labeled for markers expressed during the differentiation process at different time points (pluripotent: NANOG, SOX2, OCT3/4, E-cadherin; prochondrogenic: SOX6, SOX9, Collagen type II; extracellular matrix components: chondroitin sulfate, heparan sulfate; beta-catenin, CXCR4, and Brachyury). Comparison of the signal intensity of differentiated cells to control cell populations (articular cartilage chondrocytes and human embryonic stem cells) showed decreased signal intensities of pluripotent markers, E-cadherin and beta-catenin. Increased signal intensities of prochondrogenic markers and extracellular matrix components were observed. The changes during chondrogenic differentiation monitored by evaluation of pluripotent and chondrogenic markers signal intensity were described. The changes were similar to several studies over chondrogenesis. These results were confirmed by semi-quantitative analysis of IF signals. In this research we indicate a bioimaging as a useful tool to monitor and semi-quantify the IF pictures during the differentiation of hES into chondrocyte-like.

Suppression of Nkx3.2 by phosphatidylinositol-3-kinase signaling regulates cartilage development by modulating chondrocyte hypertrophy

Phosphatidylinositol-3-kinase (PI3K) is a key regulator of diverse biological processes including cell proliferation, migration, survival, and differentiation. While a role of PI3K in chondrocyte differentiation has been suggested, its precise mechanisms of action are poorly understood. Here we show that PI3K signaling can down-regulate Nkx3.2 at both mRNA and protein levels in various chondrocyte cultures in vitro. In addition, we have intriguingly found that p85β, not p85α, is specifically employed as a regulatory subunit for PI3K-mediated Nkx3.2 suppression. Furthermore, we found that regulation of Nkx3.2 by PI3K requires Rac1-PAK1, but not Akt, signaling downstream of PI3K. Finally, using embryonic limb bud cultures, ex vivo long bone cultures, and p85β knockout mice, we demonstrated that PI3K-mediated suppression of Nkx3.2 in chondrocytes plays a role in the control of cartilage hypertrophy during skeletal development in vertebrates.

DAPT inhibits the chondrogenesis of human umbilical cord mesenchymal stem cells

Notch signaling plays a key role in cell proliferation and differentiation, and is important in several biological processes, but its role in the chondrogenesis of human umbilical cord mesenchymal stem cells (UC-MSCs) is still unknown. N-[N-(3,5- difluorophenacetyl-L-alanyl)]-(S)-phenylglycinet-butyl ester (DAPT) is the inhibitor of Notch pathway. The aim of this study is to investgate the influence of DAPT on the chondrogenesis of UC-MSCs. In our study, UC-MSCs were isolated from human umbilical cord and their characteristics were identified. The UC-MSCs were induced to differentiate into chondrocytes in vitro and treated with 5 μM DAPT. Glycosaminoglycan (GAG) and collagen type II (COL-2A1) were analyzed qualitatively and quantitatively. The gene expression of Notch-1, Hes-1, GAG and COL-2A1 were analyzed by quantitative polymerase chain reaction (qPCR). The UC-MSCs separated from human umbilical cord, followed the characteristics of Mesenchymal Stem Cells (MSCs). The gene expression of Notch-1 and Hes-1 decreased after chondrogenic induction but the percentage in G1 period and the content of GAG and COL-2A1 increased. The expression of all tested Notch signaling and proliferation genes declined when 5 μM DAPT was added, also the content of GAG and COL-2A1 also decreased. Our study revealed that Notch signaling exists in UC-MSCs and it may remain the proliferative activity of UC-MSCs. Once the chondrogenesis begins, Notch signaling strength decline evidently. DAPT inhibits the chondrogenesis of UC-MSCs.

Influence of Exercise and Intra-articular Site on Canals in Articular Calcified Cartilage of Equine Third Carpal Bones

The third carpal bone (C3) responds to exercise by adaptive modeling of bone and articular calcified cartilage along the dorsal load path. Canals penetrating articular calcified cartilage, thought to contain vascular tissue, are reported in numerous species. Their significance remains unclear. Our objective was to determine if the number of canals was significantly different in strenuously exercised and control young horses and in a site of intermittent high loading compared to sites sustaining lower habitual loads. Volumetric bone mineral density in the radial facet of C3 of strenuously exercised and gently exercised (control) 19-month-old thoroughbred horses ( n = 6/group) was determined by peripheral quantitative computed tomography. The hyaline cartilage was corroded to expose the surface of articular calcified cartilage. The number of canals penetrating the articular calcified cartilage surface in en face scanning electron microscopy images was compared in 4 regions. Volumetric bone mineral density of C3 was significantly greater ( P = .004) in strenuously exercised horses. There were 2 morphologically distinct groups of canals and significantly fewer ( P = .006) large canals in the dorsal than in the palmar aspect of C3 in control but not in exercised horses. Roughly circular depressions in the articular calcified cartilage surface around apparently forming canals were visible in some samples and have not been previously described in the literature. The canals may be evidence of chondroclastic activity reaching the interface of hyaline and calcified cartilage. Further work is needed to elucidate the relationships between presence of canals and the responses to exercise and to joint disease.

Establishment of human cell type-specific iPS cells with enhanced chondrogenic potential

The propensity of induced pluripotent stem (iPS) cells to differentiate into specific lineages may be influenced by a number of factors, including the selection of the somatic cell type used for reprogramming. Herein we report the generation of new iPS cells, which we derived from human articular chondrocytes and from cord blood mononucleocytes via lentiviral-mediated delivery of Oct4, Klf4, Sox2, and cMyc. Molecular, cytochemical, and cytogenic analyses confirmed the acquisition of hallmark features of pluripotency, as well as the retention of normal karyotypes following reprogramming of both the human articular chondrocytes (AC) and the cord blood (CB) cells. In vitro and in vivo functional analyses formally established the pluripotent differentiation capacity of all cell lines. Chondrogenic differentiation assays comparing iPS cells derived from AC, CB, and a well established dermal fibroblast cell line (HDFa-Yk26) identified enhanced proteoglycan-rich matrix formation and cartilage-associated gene expression from AC-derived iPS cells. These findings suggest that the tissue of origin may impact the fate potential of iPS cells for differentiating into specialized cell types, such as chondrocytes. Thus, we generated new cellular tools for the identification of inherent features driving high chondrogenic potential of reprogrammed cells.

Identification of a Prg4-expressing articular cartilage progenitor cell population in mice

OBJECTIVE

To generate knockin mice that express a tamoxifen-inducible Cre recombinase from the Prg4 locus (Prg4(GFPCreERt2) mice) and to use these animals to fate-map the progeny of Prg4-positive articular cartilage cells at various ages.

METHODS

We crossed Prg4(GFPCreERt2) mice with Rosa26(floxlacZ) or Rosa26(mTmG) reporter strains, admin-istered tamoxifen to the double heterozygous offspring at different ages, and assayed Cre-mediated recom-bination by histochemistry and/or fluorescence microscopy.

RESULTS

In 1-month-old mice, the expression of the Prg4(GFPCreERt2) allele mirrored the expression of endogenous Prg4 and, when tamoxifen was admin-istered for 10 days, caused Cre-mediated recombination in ∼70% of the superficial-most chondrocytes. Prg4(GFPCreERt2)-expressing cells were mostly confined to the top 3 cell layers of the articular cartilage in 1-month-old mice, but descendants of these cells were located in deeper regions of the articular cartilage in aged mice. On embryonic day 17.5, Prg4(GFPCreERt2)-expressing cells were largely restricted to the superficial-most cell layer of the forming joint, yet at ∼1 year, the progeny of these cells spanned the depth of the articular cartilage.

CONCLUSION

Our results suggest that Prg4-expressing cells located at the joint surface in the embryo serve as a progenitor population for all deeper layers of the mature articular cartilage. Also, our findings indicate that Prg4(GFPCreERt2) is expressed by superficial chondrocytes in young mice, but expands into deeper regions of the articular cartilage as the animals age. The Prg4(GFPCreERt2) allele should be a useful tool for inducing efficient Cre-mediated recombination of loxP-flanked alleles at sites of Prg4 expression.

Time evolution of in vivo articular cartilage repair induced by bone marrow stimulation and scaffold implantation in rabbits

PURPOSE

Tissue engineering techniques were used to study cartilage repair over a 12-month period in a rabbit model.

METHODS

A full-depth chondral defect along with subchondral bone injury were originated in the knee joint, where a biostable porous scaffold was implanted, synthesized of poly(ethyl acrylate-co-hydroxyethyl acrylate) copolymer. Morphological evolution of cartilage repair was studied 1 and 2 weeks, and 1, 3, and 12 months after implantation by histological techniques. The 3-month group was chosen to compare cartilage repair to an additional group where scaffolds were preseeded with allogeneic chondrocytes before implantation, and also to controls, who underwent the same surgery procedure, with no scaffold implantation.

RESULTS

Neotissue growth was first observed in the deepest scaffold pores 1 week after implantation, which spread thereafter; 3 months later scaffold pores were filled mostly with cartilaginous tissue in superficial and middle zones, and with bone tissue adjacent to subchondral bone. Simultaneously, native chondrocytes at the edges of the defect started to proliferate 1 week after implantation; within a month those edges had grown centripetally and seemed to embed the scaffold, and after 3 months, hyaline-like cartilage was observed on the condylar surface. Preseeded scaffolds slightly improved tissue growth, although the quality of repair tissue was similar to non-preseeded scaffolds. Controls showed that fibrous cartilage was mainly filling the repair area 3 months after surgery. In the 12-month group, articular cartilage resembled the untreated surface.

CONCLUSIONS

Scaffolds guided cartilaginous tissue growth in vivo, suggesting their importance in stress transmission to the cells for cartilage repair.

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.

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.

Gene expression profiling reveals similarities between the spatial architectures of postnatal articular and growth plate cartilage

Articular and growth plate cartilage are discrete tissues but arise from a common cartilaginous condensation and have comparable spatial architectures consisting of distinct layers of chondrocytes. To investigate similarities and differences between articular and growth plate cartilage and to explore transcriptional changes that occur during the onset of their divergence, we performed manual microdissection of 10-day-old rat proximal tibias, microarray analysis, bioinformatics, and real-time PCR to compare gene expression profiles in individual cartilage layers. We found that many genes that were spatially upregulated in the intermediate/deep zone of articular cartilage were also spatially upregulated in the resting zone of growth plate cartilage (overlap greater than expected by chance, P<0.001). Interestingly, the superficial zone of articular cartilage showed an expression profile with similarities to both the proliferative and hypertrophic zones of growth plate cartilage (P<0.001 each). Additionally, significant numbers of known proliferative zone markers (3 out of 6) and hypertrophic zone markers (27 out of 126) were spatially upregulated in the superficial zone (more than expected by chance, P<0.001 each). In conclusion, we provide evidence that the intermediate/deep zone of articular cartilage has a gene expression profile more similar to that of the resting zone of growth plate cartilage, whereas the superficial zone has a gene expression profile more similar to those of the proliferative and hypertrophic zones. These findings suggest that the superficial zone chondrocytes of articular cartilage differentiate according to a program that is not completely different from but instead has distinct similarities to the hypertrophic differentiation program of growth plate chondrocytes. We also present functional signaling pathways implicated by differential gene expression between articular and growth plate cartilage during their initial separation by the secondary ossification center.

Targeting TGFβ signaling in subchondral bone and articular cartilage homeostasis

Osteoarthritis (OA) is the most common degenerative joint disease and no disease-modifying therapy for OA is currently available. Targeting articular cartilage alone may not be sufficient to halt this disease progression. Articular cartilage and subchondral bone act as a functional unit. Increasing evidence indicates that transforming growth factor β (TGFβ) plays a crucial role in maintaining homeostasis of both articular cartilage and subchondral bone. Activation of extracellular matrix (ECM) latent TGFβ at the appropriate time and location is a prerequisite for its function. Aberrant activation of TGFβ in the subchondral bone in response to an abnormal mechanical loading environment induces formation of osteroid islets at the onset of OA. As a result, alteration of subchondral bone structure changes the stress distribution on the articular cartilage and leads to its degeneration. Thus, inhibition of TGFβ activity in the subchondral bone may provide a new avenue of treatment for OA. In this review we will discuss the role of TGFβ in the homeostasis of articular cartilage and subchondral bone as a novel target for OA therapy.

Follistatin-like protein 1 regulates chondrocyte proliferation and chondrogenic differentiation of mesenchymal stem cells

OBJECTIVES

Chondrocytes, the only cells in the articular cartilage, play a pivotal role in osteoarthritis (OA) because they are responsible for maintenance of the extracellular matrix (ECM). Follistatin-like protein 1 (FSTL1) is a secreted protein found in mesenchymal stem cells (MSCs) and cartilage but whose function is unclear. FSTL1 has been shown to modify cell growth and survival. In this work, we sought to determine whether FSTL1 could regulate chondrogenesis and chondrogenic differentiation of MSCs.

METHODS

To study the role of FSTL1 in chondrogenesis, we used FSTL1 knockout (KO) mice generated in our laboratory. Proliferative capacity of MSCs, obtained from skulls of E18.5 embryos, was analysed by flow cytometry. Chondrogenic differentiation of MSCs was carried out in a pellet culture system. Gene expression differences were assessed by microarray analysis and real-time PCR. Phosphorylation of Smad3, p38 MAPK and Akt was analysed by western blotting.

RESULTS

The homozygous FSTL1 KO embryos showed extensive skeletal defects and decreased cellularity in the vertebral cartilage. Cell proliferation of FSTL1-deficient MSCs was reduced. Gene expression analysis in FSTL1 KO MSCs revealed dysregulation of multiple genes important for chondrogenesis. Production of ECM proteoglycans and collagen II expression were decreased in FSTL1-deficient MSCs differentiated into chondrocytes. Transforming growth factor β signalling in FSTL1 KO cells was significantly suppressed.

CONCLUSIONS

FSTL1 is a potent regulator of chondrocyte proliferation, differentiation and expression of ECM molecules. Our findings may lead to the development of novel strategies for cartilage repair and provide new disease-modifying treatments for OA.

Mechanical regulation of skeletal development

Development of the various components of a normal skeleton requires highly regulated signalling systems that co-ordinate spatial and temporal patterns of cell division, cell differentiation, and morphogenesis. Much work in recent decades has revealed cascades of molecular signalling, acting through key transcription factors to regulate, for example, organized chondrogenic and osteogenic differentiation. It is now clear that mechanical stimuli are also required for aspects of skeletogenesis but very little is known about how the mechanical signals are integrated with classic biochemical signalling. Spatially organized differentiation is vital to the production of functionally appropriate tissues contributing to precise, region specific morphologies, for example transient chondrogenesis of long bone skeletal rudiments, which prefigures osteogenic replacement of the cartilage template, compared with the production of permanent cartilage at the sites of articulation. Currently a lack of understanding of how these tissues are differentially regulated hampers efforts to specifically regenerate stable bone and cartilage. Here, we review current research revealing the influence of mechanical stimuli on specific aspects of skeletal development and refer to other developing systems to set the scene for current and future work to uncover the molecular mechanisms involved. We integrate this with a brief overview of the effects of mechanical stimulation on stem cells in culture bringing together developmental and tissue engineering aspects of mechanoregulation of cell behavior. A better understanding of the molecular mechanisms that link mechanical stimuli to transcriptional control guiding cell differentiation will lead to new ideas about how to effectively prime stem cells for tissue engineering and regenerative therapies.

Cartilage tissue engineering with controllable shape using a poly(lactic-co-glycolic acid)/collagen hybrid scaffold

It is of critical importance to prepare three-dimensional biodegradable porous scaffolds for cartilage tissue engineering. We developed a poly(lactic- co-glycolic acid)/collagen hybrid scaffold, which combined the advantages of natural type I collagen and synthetic polymer polylactin 910 knitted mesh (90:10 copolymer of glycolic acid and lactic acid), and a method using this poly(lactic- co-glycolic acid)/collagen scaffold to regenerate cartilage with controllable shape. The mechanically strong poly(lactic- co-glycolic acid) mesh served as a mechanical skeleton supporting the scaffold, and the collagen benefited cell seeding, distribution, and tissue formation. Bovine chondrocytes were cultured in the hybrid scaffold and transplanted into the subcutaneous sites of nude mice for 4 weeks. All the samples showed spatially uniform cell distribution, natural chondrocyte morphology, and deposition of abundant cartilaginous extracellular matrices such as type II collagen and aggrecan. Production of glycosaminoglycans per DNA reached 74.63% of the natural articular cartilage. The mechanical strength was 62.76% and 71.43% in Young’s modulus and stiffness, respectively, compared to the native articular cartilage. All the samples successfully maintained the original shapes. Our method provides a new strategy for regeneration of cartilage tissue with designed shapes.

Fibroblast growth factor 2 and transforming growth factor β1 induce precocious maturation of articular cartilage

OBJECTIVE

We have discovered that a combination of fibroblast growth factor 2 and transforming growth factor β1 induce profound morphologic changes in immature articular cartilage. The purpose of this study was to test the hypothesis that these changes represent accelerated postnatal maturation.

METHODS

Histochemical and biochemical assays were used to confirm the nature of the morphologic changes that accompany growth factor stimulation of immature bovine articular cartilage explants in serum-free culture medium. Growth factor-induced apoptosis, cellular proliferation, and changes in the collagen network were also quantitatively analyzed.

RESULTS

Growth factor stimulation resulted in rapid resorption from the basal aspect of immature cartilage explants that was simultaneously opposed by cellular proliferation from the apical aspect driven from a pool of chondroprogenitor cells we have previously described. Maturation-dependent changes in tissue stiffness, collagen crosslinking, and collagen fibril architecture as well as differentiation of the extracellular matrix into distinct pericellular, territorial, and interterritorial domains were all present in growth factor-stimulated cartilage samples and absent in control samples.

CONCLUSION

Our data demonstrate that it is possible to significantly enhance the maturation of cartilage tissue using specific growth factor stimulation. This may have applications in transplantation therapy or in the treatment of diseased cartilage, through phenotype modulation of osteoarthritic chondrocytes in order to stimulate growth and maturation of cartilage repair tissue.

New findings in osteoarthritis pathogenesis: therapeutic implications

This review focuses on the new perspectives which can provide insight into the crucial pathways that drive cartilage-bone physiopathology. In particular, we discuss the critical signaling and effector molecules that can activate cellular and molecular processes in both cartilage and bone cells and which may be relevant in cross talk among joint compartments: growth factors (bone morphogenetic proteins and transforming growth factor), hypoxia-related factors, cell-matrix interactions [discoidin domain receptor 2 (DDR2) and syndecan 4], signaling molecules [WNT, Hedgehog (Hh)]. With the continuous progression of our knowledge on the molecular pathways involved in cartilage and bone changes in osteoarthritis (OA), an increasing number of potentially effective candidates for OA therapy are already under scrutiny in clinical trials to ascertain their possible safe use in an attempt to identify molecules active in slowing or halting OA progression and reducing joint pain. We then review the principal molecules currently under clinical investigation.

Arthroscopic cartilage regeneration facilitating procedure for osteoarthritic knee

BACKGROUND

The effectiveness of arthroscopic treatment for osteoarthritic knee is a controversy. This study presents the technique of a novel concept of arthroscopic procedure and investigates its clinical outcome.

METHOD

An arthroscopic procedure targeted on elimination of focal abrasion phenomenon and regaining soft tissue balance around patello-femoral joint was applied to treat osteoarthritis knees. Five hundred and seventy-one knees of 367 patients with osteoarthritis received this procedure. There were 70 (19%) male and 297 (81%) female and the mean age was 60 years (SD 10). The Knee Society score (KSS) and the knee injury and osteoarthritis outcome score (KOOS) were used for subjective outcome study. The roentgenographic changes of femoral-tibial angle and joint space width were evaluated for objective outcomes. The mean follow-up period was 38 months (SD 3).

RESULTS

There were 505 knees in 326 patients available with more than 3 years follow-up and the mean follow-up period was 38 months (SD 3). The subjective satisfactory rate for the whole series was 85.5%. For 134 knees with comprehensive follow-up evaluation, the KSS and all subscales of the KOOS improved statistically. The femoral-tibial angle improved from 1.57 degrees (SD 3.92) to 1.93 degrees (SD 4.12) (mean difference: 0.35, SD 0.17). The joint space width increased from 2.02 millimeters (SD 1.24) to 2.17 millimeters (SD 1.17) (mean difference: 0.13, SD 0.05). The degeneration process of the medial compartment was found being reversed in 82.1% of these knees by radiographic evaluation.

CONCLUSIONS

Based on these observations arthroscopic cartilage regeneration facilitating procedure is an effective treatment for osteoarthritis of the knee joint and can be expected to satisfy the majority of patients and reverse the degenerative process of their knees.

Chondrogenesis, chondrocyte differentiation, and articular cartilage metabolism in health and osteoarthritis

Chondrogenesis occurs as a result of mesenchymal cell condensation and chondroprogenitor cell differentiation. Following chondrogenesis, the chondrocytes remain as resting cells to form the articular cartilage or undergo proliferation, terminal differentiation to chondrocyte hypertrophy, and apoptosis in a process termed endochondral ossification, whereby the hypertrophic cartilage is replaced by bone. Human adult articular cartilage is a complex tissue of matrix proteins that varies from superficial to deep layers and from loaded to unloaded zones. A major challenge to efforts to repair cartilage by stem cell-based and other tissue-engineering strategies is the inability of the resident chondrocytes to lay down a new matrix with the same properties as it had when it was formed during development. Thus, understanding and comparing the mechanisms of cartilage remodeling during development, osteoarthritis (OA), and aging may lead to more effective strategies for preventing cartilage damage and promoting repair. The pivotal proteinase that marks OA progression is matrix metalloproteinase 13 (MMP-13), the major type II collagen-degrading collagenase, which is regulated by both stress and inflammatory signals. We and other investigators have found that there are common mediators of these processes in human OA cartilage. We also observe temporal and spatial expression of these mediators in early through late stages of OA in mouse models and are analyzing the consequences of knockout or transgenic overexpression of critical genes. Since the chondrocytes in adult human cartilage are normally quiescent and maintain the matrix in a low turnover state, understanding how they undergo phenotypic modulation and promote matrix destruction and abnormal repair in OA may to lead to identification of critical targets for therapy to block cartilage damage and promote effective cartilage repair.

B2A peptide induces chondrogenic differentiation in vitro and enhances cartilage repair in rats

This study investigated whether the synthetic peptide B2A (B2A2-K-NS) could induce in vitro chondrogenic differentiation and enhance the in vivo repair of damaged cartilage in an osteoarthritis model. In vitro, micromass cultures of murine and human stem cells with and without B2A were used as models of chondrogenic differentiation. Micromasses were evaluated for gene expression using microarray analysis and quantitative PCR; and for extracellular matrix production by Alcian blue staining for sulfated glycosaminoglycan and immunochemical detection of collagen type II. In vivo, osteoarthritis was chemically induced in knees of adult rats by an injection of mono-iodoacetate (MIA) into the synovial space. Treatment was administered at 7- and 14 days after the MIA by injection into the synovial space of B2A or saline and terminated at 21 days, after which knee cartilage damage was determined and scored by histological analysis. In murine C3H10T1/2 micromass culture, B2A induced the expression of more than 11 genes associated with growth factors/receptors, transcription, and the extracellular matrix, including PDGF-AA. B2A also significantly increased the sulfated glycosaminoglycan and collagen of murine- and human micromass cultures. In the knee osteoarthritis model, B2A treatment enhanced cartilage repair compared to untreated knees as determined histologically by a decrease in damage indicators. These findings suggest that B2A induces stem cells chondrogenic differentiation in vitro and enhances cartilage repair in vivo. The results suggest that B2A might be useful to promote cartilage repair.

Reducing the number of laboratory animals used in tissue engineering research by restricting the variety of animal models. Articular cartilage tissue engineering as a case study

The use of laboratory animals in tissue engineering research is an important underexposed ethical issue. Several ethical questions may be raised about this use of animals. This article focuses on the possibilities of reducing the number of animals used. Given that there is considerable debate about the adequacy of the current animal models in tissue engineering research, we investigate whether it is possible to reduce the number of laboratory animals by selecting and using only those models that have greatest predictive value for future clinical application of the tissue engineered product. The field of articular cartilage tissue engineering is used as a case study. Based on a study of the scientific literature and interviews with leading experts in the field, an overview is provided of the animal models used and the advantages and disadvantages of each model, particularly in terms of extrapolation to the human situation. Starting from this overview, it is shown that, by skipping the small models and using only one large preclinical model, it is indeed possible to restrict the number of animal models, thereby reducing the number of laboratory animals used. Moreover, it is argued that the selection of animal models should become more evidence based and that researchers should seize more opportunities to choose or create characteristics in the animal models that increase their predictive value.

Human chondrogenic paraxial mesoderm, directed specification and prospective isolation from pluripotent stem cells

Directed specification and prospective isolation of chondrogenic paraxial mesoderm progeny from human pluripotent stem (PS) cells have not yet been achieved. Here we report the successful generation of KDR⁻PDGFRα⁺ progeny expressing paraxial mesoderm genes and the mesendoderm reporter MIXL1-GFP in a chemically defined medium containing the canonical WNT signaling activator, BMP-inhibitor, and the Nodal/Activin/TGFβ signaling controller. Isolated (GFP⁺)KDR⁻PDGFRα⁺ mesoderm cells were sensitive to sequential addition of the three chondrogenic factors PDGF, TGFβ and BMP. Under these conditions, the cells showed robust chondrogenic activity in micromass culture, and generated a hyaline-like translucent cartilage particle in serum-free medium. In contrast, both STRO1⁺ mesenchymal stem/stromal cells from adult human marrow and mesenchymal cells spontaneously arising from hPS cells showed a relatively weaker chondrogenic response in vitro, and formed more of the fibrotic cartilage particles. Thus, hPS cell-derived KDR⁻PDGFRα⁺ paraxial mesoderm-like cells have potential in engineered cartilage formation and cartilage repair.

Dimethylarginine dimethylaminohydrolase 2, a newly identified mitochondrial protein modulating nitric oxide synthesis in normal human chondrocytes

OBJECTIVE

The mitochondrion is known to be important to chondrocyte survival. This study was undertaken to analyze protein expression profiles in chondrocyte mitochondria that are affected by interleukin-1β (IL-1β).

METHODS

Normal human chondrocytes were isolated from knee cartilage obtained at autopsy from subjects with no history of joint disease. Cells were incubated for 48 hours with or without IL-1β (5 ng/ml). Proteins were separated by 2-dimensional electrophoresis and stained with Sypro Ruby, Coomassie brilliant blue, or silver. Qualitative and quantitative analyses were carried out using PDQuest software. Proteins were identified by mass spectrometry using matrix-assisted laser desorption ionization-time-of-flight/time-of-flight technology. The proteomic results were validated by real-time polymerase chain reaction, Western blotting, and microscopy. Nitric oxide (NO) was quantified using Griess reagent.

RESULTS

Comparative analysis revealed differential expression of signal transduction proteins that regulate cytoskeleton, transcription, metabolic, and stress-related pathways. In total extracts, dimethylarginine dimethylaminohydrolase 2 (DDAH-2) did not show any change in expression after stimulation with IL-1β. However, in mitochondrial extracts, DDAH-2 expression was significantly increased after exposure to IL-1β. Conventional immunofluorescence and confocal microscopy revealed the presence of DDAH-2 in the mitochondria of IL-1β-stimulated chondrocytes. These results were reproducible in cartilage explants treated with IL-1β. In addition, we demonstrated that inhibition of the expression of DDAH-2, as well as interruption of its translocation to the mitochondria, reduced the NO production induced by IL-1β. DDAH-2 protein expression was higher in osteoarthritic (OA) cartilage than in normal cartilage.

CONCLUSION

In the present study, the presence of DDAH-2 in normal human chondrocytes and cartilage was identified for the first time. DDAH-2 could play an important role in IL-1β-induced NO production and in OA pathogenesis.

Cartilage biology in osteoarthritis--lessons from developmental biology

The cellular and molecular mechanisms responsible for the initiation and progression of osteoarthritis (OA), and in particular cartilage degeneration in OA, are not completely understood. Increasing evidence implicates developmental processes in OA etiology and pathogenesis. Herein, we review this evidence. We first examine subtle changes in cartilage development and the specification and formation of joints, which predispose to OA development, and second, we review the switch from an articular to a hypertrophic chondrocyte phenotype that is thought to be part of the OA pathological process ultimately resulting in cartilage degeneration. The latest studies are summarized and we discuss the concepts emerging from these findings in cartilage biology, in the light of our understanding of the developmental processes involved.

Laser-induced regeneration of cartilage

Laser radiation provides a means to control the fields of temperature and thermo mechanical stress, mass transfer, and modification of fine structure of the cartilage matrix. The aim of this outlook paper is to review physical and biological aspects of laser-induced regeneration of cartilage and to discuss the possibilities and prospects of its clinical applications. The problems and the pathways of tissue regeneration, the types and features of cartilage will be introduced first. Then we will review various actual and prospective approaches for cartilage repair; consider possible mechanisms of laser-induced regeneration. Finally, we present the results in laser regeneration of joints and spine disks cartilages and discuss some future applications of lasers in regenerative medicine.

The role of hyaluronan produced by Has2 gene expression in development of the spine

STUDY DESIGN

Histologic analysis of spine development in cartilage-specific knockout mice.

OBJECTIVE

To evaluate the role hyaluronan produced by hyaluronan synthase-2 (Has2) in spine development.

SUMMARY OF BACKGROUND DATA

The Has2 gene is responsible for most hyaluronan production throughout the body, including the skeleton. However, it is not possible to study the involvement of hyaluronan in skeletal development using constitutive Has2 knockout mice, as the embryonic mice die early before skeletal development has occurred. This problem can be overcome by the use of cartilage-specific knockout mice.

METHODS

Mice possessing floxed Has2 genes were crossed with mice expressing Cre recombinase under control of the type II collagen promoter to generate cartilage-specific Has2 knockout mice. Spine development was studied by histology.

RESULTS

Knockout mice died near birth and displayed severe abnormality in skeletal development. The spine showed defects in vertebral body size and the formation of the intervertebral discs. There was no evidence for the formation of an organized primary center of ossification within the vertebrae, and the appearance and organization of the hypertrophic chondrocytes was abnormal. Although no organized endochondral ossification appeared to be taking place, there was excessive bone formation at the center of the vertebrae. There was also a generalized increased cellularity of the vertebral cartilage and a corresponding decrease in the abundance of extracellular matrix. The nucleus pulposus of the intervertebral discs were less flattened than in the control mice and possessed an increased amount of large vacuolated cells. Remnants of the notochord could also be seen between adjacent discs.

CONCLUSION

Hyaluronan production by Has2 is essential for normal vertebral and intervertebral disc development within the spine, and the absence of this synthase impairs the organization of both soft and hard tissue elements.

MicroRNA regulation associated chondrogenesis of mouse MSCs grown on polyhydroxyalkanoates

Microbial polyhydroxyalkanoates (PHA) including poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) were found to induce chondrogenesis of mesenchymal stem cells (MSCs) and preserve chondrocytic phenotype as well as support chondrocytes-specific extracellular matrix (ECM) secretion. In this study, mouse MSCs cultured on the PHBHHx films for 24 h showed up-regulated expression of chondrogenic marker genes including aggrecan, col2, sox9, col10 and pthrp. To further illustrate this phenomonon, chondrogenesis-related microRNA expression profiling was examined by quantitative real-time PCR (RT-PCR) based on results of microRNA array obtained from comparison between mouse MSCs and mature mouse chondrocytes. Among 44 microRNAs related to chondrogenesis on microrray studies, considering only broadly-conserved microRNAs, seven differentially-expressed microRNAs were selected to study their target genes related to chondrogenesis. Two microRNAs out of the seven, namely, miR-29a and miR-29b, were revealed to directly target 3' UTR of col2a1 encoding type II collagen by dual-luciferase assay, and their activity was under the regulation of Sox9, the SRY-related high mobility group-box gene 9. For the first time microRNAs were shown to regulate the stem cell differentiation processes mediated by cell-material interactions.