Transforming growth factor-beta 1 (TGF-beta 1) up-regulation of collagen type II in primary cultures of rabbit articular chondrocytes (RAC) involves increased mRNA levels without affecting mRNA stability and procollagen processing

Cause and chondroprotective effects of prostaglandin E2 secretion during mesenchymal stromal cell chondrogenesis

Mesenchymal stromal cells (MSCs) that are promising for cartilage tissue engineering secrete high amounts of prostaglandin E2 (PGE2), an immunoactive mediator involved in endochondral bone development. This study aimed to identify drivers of PGE2 and its role in the inadvertent MSC misdifferentiation into hypertrophic chondrocytes. PGE2 release, which rose in the first three weeks of MSC chondrogenesis, was jointly stimulated by endogenous BMP, WNT, and hedgehog activity that supported the exogenous stimulation by TGF-β1 and insulin to overcome the PGE2 inhibition by dexamethasone. Experiments with PGE2 treatment or the inhibitor celecoxib or specific receptor antagonists demonstrated that PGE2, although driven by prohypertrophic signals, exerted broad autocrine antihypertrophic effects. This chondroprotective effect makes PGE2 not only a promising option for future combinatorial approaches to direct MSC tissue engineering approaches into chondral instead of endochondral development but could potentially have implications for the use of COX-2-selective inhibitors in osteoarthritis pain management.

The effects of losartan or angiotensin II receptor antagonists on cartilage: a systematic review

OBJECTIVE

The aim of this study is to analyze the latest evidence on the effects of losartan or Ang II receptor antagonists on cartilage repair, with a focus on their clinical relevance.

DESIGN

The PubMed, Embase, and Cochrane Library databases were searched up to November 12th 2021 to evaluate the effects of losartan or Ang II receptor antagonists on cartilage repair in in vitro studies and in vivo animal studies. Study design, sample characteristics, treatment type, duration, and outcomes were analyzed. The risk of bias and the quality of the eligible studies were assessed using the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) risk of bias assessment tool and Collaborative Approach to Meta-Analysis and Review of Animal Data from Experimental Studies (CAMARADES).

RESULTS

A total of 12 studies were included in this systematic review. Of the 12 eligible studies, two studies were in vitro human studies, three studies were in vitro animal studies, one study was an in vitro human and animal study, and six studies were in vivo animal studies. The risk bias and quality assessments were predominantly classified as moderate. Since meta-analysis was difficult due to differences in treatment type, dosage, route of administration, and method of outcome assessment among the eligible studies, qualitative evaluation was conducted for each study.

CONCLUSIONS

Both in vitro and in vivo studies provide evidence to demonstrate beneficial effects of Ang II receptor antagonists on osteoarthritis and cartilage defect models across animal species.

Multimodal fluorescence lifetime imaging and optical coherence tomography for longitudinal monitoring of tissue-engineered cartilage maturation in a preclinical implantation model

Significance

Cartilage tissue engineering is a promising strategy for effective curative therapies for treatment of osteoarthritis. However, tissue engineers depend predominantly on time-consuming, expensive, and destructive techniques as quality control to monitor the maturation of engineered cartilage. This practice can be impractical for large-scale biomanufacturing and prevents spatial and temporal monitoring of tissue growth, which is critical for the fabrication of clinically relevant-sized cartilage constructs. Nondestructive multimodal imaging techniques combining fluorescence lifetime imaging (FLIm) and optical coherence tomography (OCT) hold great potential to address this challenge.

Aim

The feasibility of using multimodal FLIm-OCT for nondestructive, spatial, and temporal monitoring of self-assembled cartilage tissue maturation in a preclinical mouse model is investigated.

Approach

Self-assembled cartilage constructs were developed for 4 weeks in vitro followed by 4 weeks of in vivo maturation in nude mice. Sterile and nondestructive in situ multispectral FLIm and OCT imaging were carried out at multiple time points ( t = 2 , 4, and 8 weeks) during tissue development. FLIm and 3D volumetric OCT images were reconstructed and used for the analysis of tissue biochemical homogeneity, morphology, and structural integrity. A biochemical homogeneity index was computed to characterize nonhomogeneous tissue growth at different time points. OCT images were validated against histology.

Results

FLIm detects heterogenous extracellular matrix (ECM) growth of tissue-engineered cartilage. The outer edge of the tissue construct exhibited longer fluorescence lifetime in 375 to 410 and 450 to 485 nm spectral channels, indicating increase in collagen content. Significant ( p < 0.05 ) decrease of construct homogeneity index was observed between t = 2 weeks and t = 4 weeks. Both FLIm and OCT images revealed defects (voids) at the center of the tissue construct during in vitro culture ( t = 2 and 4 weeks). Cyst formation during in vivo culture was detected by OCT and confirmed with histology.

Conclusions

The ability of multimodal FLIm-OCT to nondestructively monitor the heterogenous growth of engineered tissue constructs in situ is demonstrated. Spatial and temporal variation of construct ECM component was detected by FLIm. OCT reveals structural defects (voids and cysts). This multimodal approach has great potential to replace costly destructive tests in the manufacturing of tissue-engineered medical products, facilitating their clinical translation.

A Molecular Cascade Underlying Articular Cartilage Degeneration

Preserving of articular cartilage is an effective way to protect synovial joints from becoming osteoarthritic (OA) joints. Understanding of the molecular basis of articular cartilage degeneration will provide valuable information in the effort to develop cartilage preserving drugs. There are currently no disease-modifying OA drugs (DMOADs) available to prevent articular cartilage destruction during the development of OA. Current drug treatments for OA focus on the reduction of joint pain, swelling, and inflammation at advanced stages of the disease. However, based on discoveries from several independent research laboratories and our laboratory in the past 15 to 20 years, we believe that we have a functional molecular understanding of articular cartilage degeneration. In this review article, we present and discuss experimental evidence to demonstrate a sequential chain of the molecular events underlying articular cartilage degeneration, which consists of transforming growth factor beta 1, high-temperature requirement A1 (a serine protease), discoidin domain receptor 2 (a cell surface receptor tyrosine kinase for native fibrillar collagens), and matrix metalloproteinase 13 (an extracellularmatrix degrading enzyme). If, as we strongly suspect, this molecular pathway is responsible for the initiation and acceleration of articular cartilage degeneration, which eventually leads to progressive joint failure, then these molecules may be ideal therapeutic targets for the development of DMOADs.

TGFβ attenuates cartilage extracellular matrix degradation via enhancing FBXO6-mediated MMP14 ubiquitination

Objectives

FBXO6, a component of the ubiquitin E3 ligases, has been shown to bind high mannose N-linked glycoproteins and act as ubiquitin ligase subunits. Most proteins in the secretory pathway, such as matrix metalloproteinases, are modified with N-glycans and play important roles in the development of osteoarthritis (OA). However, whether FBXO6 exerts regulatory effects on the pathogenesis of OA remains undefined.

Methods

The expression of FBXO6 was examined in the cartilage of human and multiple mouse OA models. The role of FBXO6 in cartilage degeneration was analysed with global FBXO6^-/- mice, transgenic Col2a1-CreER^T2;FBXO6^f/f mice. The FBXO6 interacting partner MMP14 and its regulatory transcriptional factor SMAD2/3 were identified and validated in different pathological models as well as SMAD2^-/- mice.

Results

The expression of FBXO6 decreased in the cartilage from human OA samples, anterior cruciate ligament transaction (ACLT) -induced OA samples, spontaneous OA STR/ort samples and aged mice samples. Global knockout or conditional knockout of FBXO6 in cartilage promoted experimental OA process. The molecular mechanism study revealed that FBXO6 decreased MMP14 by ubiquitination and degradation, leading to inhibited proteolytic activation of MMP13. Interestingly, FBXO6 expression is regulated by transforming growth factor β (TGFβ)-SMAD2/3 signalling pathway. Therefore, the overexpression of FBXO6 protected mice from post-injury OA development.

Conclusions

TGFβ-SMAD2/3 signalling pathway suppressed MMP13 activation by upregulating of FBXO6 transcription and consequently promoting MMP14 proteasomal degradation. Inducement of FBXO6 expression in OA cartilage might provide a promising OA therapeutic strategy.

Complement component C1q is produced by isolated articular chondrocytes

OBJECTIVE

Inflammation and innate immune responses may contribute to development and progression of Osteoarthritis (OA). Chondrocytes are the sole cell type of the articular cartilage and produce extracellular-matrix molecules. How inflammatory mediators reach chondrocytes is incompletely understood. Previous studies have shown that chondrocytes express mRNA encoding complement proteins such as C1q, suggesting local protein production, which has not been demonstrated conclusively. The aim of this study is to explore C1q production at the protein level by chondrocytes.

DESIGN

We analysed protein expression of C1q in freshly isolated and cultured human articular chondrocytes using Western blot, ELISA and flow cytometry. We examined changes in mRNA expression of collagen, MMP-1 and various complement genes upon stimulation with pro-inflammatory cytokines or C1q. mRNA expression of C1 genes was determined in articular mouse chondrocytes.

RESULTS

Primary human articular chondrocytes express genes encoding C1q, C1QA, C1QB, C1QC, and secrete C1q to the extracellular medium. Stimulation of chondrocytes with pro-inflammatory cytokines upregulated C1QA, C1QB, C1QC mRNA expression, although this was not confirmed at the protein level. Extracellular C1q bound to the chondrocyte surface dose dependently. In a pilot study, binding of C1q to chondrocytes resulted in changes in the expression of collagens with a decrease in collagen type 2 and an increase in type 10. Mouse articular chondrocytes also expressed C1QA, C1QB, C1QC, C1R and C1S at the mRNA level.

CONCLUSIONS

C1q protein can be expressed and secreted by human articular chondrocytes and is able to bind to chondrocytes influencing the relative collagen expression.

Biologically Regulated Marrow Stimulation by Blocking TGF-β1 With Losartan Oral Administration Results in Hyaline-like Cartilage Repair: A Rabbit Osteochondral Defect Model

BACKGROUND

Microfracture or bone marrow stimulation (BMS) is often the first choice for clinical treatment of cartilage injuries; however, fibrocartilage, not pure hyaline cartilage, has been reported because of the development of fibrosis in the repair tissue. Transforming growth factor β1 (TGF-β1), which can promote fibrosis, can be inhibited by losartan and potentially be used to reduce fibrocartilage.

HYPOTHESIS

Blocking TGF-β1 would improve cartilage healing in a rabbit knee BMS model via decreasing the amount of fibrocartilage and increasing hyaline-like cartilage formation.

STUDY DESIGN

Controlled laboratory study.

METHODS

An osteochondral defect was made in the patellar groove of 48 New Zealand White rabbits. The rabbits were divided into 3 groups: a defect group (defect only), a BMS group (osteochondral defect + BMS), and a BMS + losartan group (osteochondral defect + BMS + losartan). For the rabbits in the BMS + losartan group, losartan was administrated orally from the day after surgery through the day of euthanasia. Rabbits were sacrificed 6 or 12 weeks postoperatively. Macroscopic appearance, microcomputed tomography, histological assessment, and TGF-β1 signaling pathway were evaluated at 6 and 12 weeks postoperatively.

RESULTS

The macroscopic assessment of the repair revealed that the BMS + losartan group was superior to the other groups tested. Microcomputed tomography showed superior healing of the bony defect in the BMS + losartan group in comparison with the other groups. Histologically, fibrosis in the repair tissue of the BMS + losartan group was significantly reduced when compared with the other groups. Results obtained with the modified O'Driscoll International Cartilage Repair Society grading system yielded significantly superior scores in the BMS + losartan group as compared with both the defect group and the BMS group (F value: 15.8, P < .001, P = .012, respectively). TGF-β1 signaling and TGF-β-activated kinase 1 of the BMS + losartan group were significantly suppressed in the synovial tissues.

CONCLUSION

By blocking TGF-β1 with losartan, the repair cartilage tissue after BMS was superior to the other groups and consisted primarily of hyaline cartilage. These results should be easily translated to the clinic because losartan is a Food and Drug Administration-approved drug and it can be combined with the BMS technique for optimal repair of chondral defects.

CLINICAL RELEVANCE

Biologically regulated marrow stimulation by blocking TGF-β1 (oral intake of losartan) provides superior repair via decreasing fibrocartilage formation and resulting in hyaline-like cartilage as compared with outcomes from BMS only.

TGFβ/BMP Signaling Pathway in Cartilage Homeostasis

Cartilage homeostasis is governed by articular chondrocytes via their ability to modulate extracellular matrix production and degradation. In turn, chondrocyte activity is regulated by growth factors such as those of the transforming growth factor β (TGFβ) family. Members of this family include the TGFβs, bone morphogenetic proteins (BMPs), and growth and differentiation factors (GDFs). Signaling by this protein family uniquely activates SMAD-dependent signaling and transcription but also activates SMAD-independent signaling via MAPKs such as ERK and TAK1. This review will address the pivotal role of the TGFβ family in cartilage biology by listing several TGFβ family members and describing their signaling and importance for cartilage maintenance. In addition, it is discussed how (pathological) processes such as aging, mechanical stress, and inflammation contribute to altered TGFβ family signaling, leading to disturbed cartilage metabolism and disease.

Tgfbr2 is required in Acan-expressing cells for maintenance of the intervertebral and sternocostal joints

BACKGROUND

Members of the transforming growth factor beta (TGF-β) family are secreted proteins that regulate skeletal development. TGF-β signaling is critical in embryonic development of the annulus fibrosus (AF) of the intervertebral disc (IVD). To address the question of the role of TGF-β signaling in postnatal development and maintenance of the skeleton, we generated mice in which Tgfbr2 was deleted at 2-weeks of age in Aggrecan (Acan)-expressing cells using inducible Cre/LoxP recombination.

METHODS

Localization of Cre recombination was visualized by crossing Acan^{tm1(cre/ERT2)Crm} mice to fluorescent mTmG reporter mice. Acan^{tm1(cre/ERT2)Crm} mice were mated to Tgfbr2 ^LoxP/LoxP mice and Cre recombinase was activated by tamoxifen injection at 2-weeks postnatally. Following tamoxifen injection, mice were aged to 3, 6, and 12-months and control mice were compared to the experimental (cKO) group. Mice were initially analyzed using X-ray and skeletal preparations. Sternocostal joints and IVD tissues were further analyzed histologically by hematoxylin and eosin (H&E), Safranin O, and Picrosirius Red staining as well as Col10 immunostaining.

RESULTS

Cre recombination was observed in the IVD and sternocostal joints. X-ray analysis revealed osteophyte formation within the disc space of 12-month-old cKO mice. Skeletal preparations confirmed calcification within the IVD and the sternocostal joints in cKO mice. H&E staining of cKO IVD revealed disorganized growth plates, delay in the formation of the bony endplate, and Col10 staining in the AF indicative of ectopic endochondral bone formation. Furthermore, proteoglycan loss was observed and collagen bundles within the inner AF were thinner and less organized. Alterations in the IVD were apparent beginning at 3 months and were progressively more visible at 6 and 12 months. Similarly, histological analysis of cKO sternocostal joints revealed joint calcification, proteoglycan loss, and disorganization of the collagen architecture at 12 months of age.

CONCLUSIONS

TGF-β signaling is important for postnatal development and maintenance of fibrocartilaginous IVD and sternocostal joints.

Electron microscopic observation of human auricular chondrocytes transplanted into peritoneal cavity of nude mice for cartilage regeneration

Restoration of damaged cartilage tissue has been deemed futile with current treatments. Although there have been many studies on cartilage regeneration thus far, there is no report that chondrocytes were completely re-differentiated in vitro. The clarification of cellular composition and matrix production during cartilage regeneration must be elucidated to fabricate viable mature cartilage in vitro. In order to achieve this aim, the chondrocytes cultured on coverslips were transplanted into the peritoneal cavities of mice. At different time points post-transplantation, the cartilage maturation progression and cells composing the regeneration were examined. Cartilage regeneration was confirmed by hematoxylin & eosin (HE) and toluidine blue staining. The maturation progression was carefully examined further by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At the first and second week time points, various cell shapes were observed using SEM. Chronologically, by the third week, the number of fibers increased, suggesting the progression of extracellular matrix (ECM) maturation. Observation through TEM revealed the chondrocytes located in close proximity to various cells including macrophage-like cells. On the second week, infiltration of lymphocytes and capillary vessels were observed, and after the third week, the chondrocytes had matured and were abundantly releasing extracellular matrix. Chronological observation of transplanted chondrocytes by electron microscopy revealed maturation of chondrocytes and accumulation of matrix during the re-differentiation process. Emerging patterns of host-derived cells such as macrophage-like cells and subsequent appearance of lymphocytes-like cells and angiogenesis were documented, providing crucial context for the identification of the cells responsible for in vivo cartilage regeneration.

Optimization of Methods for Articular Cartilage Surface Tissue Engineering: Cell Density and Transforming Growth Factor Beta Are Critical for Self-Assembly and Lubricin Secretion

OBJECTIVE

Lubricin/superficial zone protein (SZP)/proteoglycan4 (PRG4) plays an important role in boundary lubrication in articular cartilage. Lubricin is secreted by superficial zone chondrocytes and synoviocytes of the synovium. The specific objective of this investigation is to optimize the methods for tissue engineering of articular cartilage surface. The aim of this study is to investigate the effect of cell density on the self-assembly of superficial zone chondrocytes and lubricin secretion as a functional assessment.

DESIGN

Superficial zone chondrocytes were cultivated as a monolayer at low, medium, and high densities. Chondrocytes at the three different densities were treated with transforming growth factor beta (TGF-β)1 twice a week or daily, and the accumulated lubricin in the culture medium was analyzed by immunoblots and quantitated by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Cell numbers in low and medium densities were increased by TGF-β1; whereas cell numbers in high-density cell cultures were decreased by twice-a-week treatment of TGF-β1. On the other hand, the cell numbers were maintained by daily TGF-β treatment. Immunoblots and quantitation of lubricin by ELISA analysis indicated that TGF-β1 stimulated lubricin secretion by superficial zone chondrocytes at all densities with twice-a-week TGF-β treatment. It is noteworthy that the daily treatment of TGF-β1 increased lubricin much higher compared with twice-a-week treatment.

CONCLUSIONS

These data demonstrate that daily treatment is optimal for the TGF-β1 response in a higher density of monolayer cultures. These findings have implications for self-assembly of surface zone chondrocytes of articular cartilage for application in tissue engineering of articular cartilage surface.

Development of chondrocyte-seeded electrosprayed nanoparticles for repair of articular cartilage defects in rabbits

Due to limited self-healing capacity in cartilages, there is a rising demand for an innovative therapy that promotes chondrocyte proliferation while maintaining its biofunctionality for transplantation. Chondrocyte transplantation has received notable attention; however, the tendencies of cell de-differentiation and de-activation of biofunctionality have been major hurdles in its development, delaying this therapy from reaching the clinic. We believe it is due to the non-stimulative environment in the injured cartilage, which is unable to provide sustainable physical and biological supports to the newly grafted chondrocytes. Therefore, we evaluated whether providing an appropriate matrix to the transplanted chondrocytes could manipulate cell fate and recovery outcomes. Here, we proposed the development of electrosprayed nanoparticles composed of cartilage specific proteins, namely collagen type II and hyaluronic acid, for implantation with pre-seeded chondrocytes into articular cartilage defects. The fabricated nanoparticles were pre-cultured with chondrocytes before implantation into injured articular cartilage. The study revealed a significant potential for nanoparticles to support pre-seeded chondrocytes in cartilage repair, serving as a protein delivery system while improving the survival and biofunctionality of transplanted chondrocytes for prolonged period of time.

Halofuginone attenuates articular cartilage degeneration by inhibition of elevated TGF‑β1 signaling in articular cartilage in a rodent osteoarthritis model

Osteoarthritis (OA) is the most common degenerative condition of the weight‑bearing joints worldwide without effective medical therapy. In order to investigate whether administration of halofuginone (HF) may attenuate OA, the present study allocated 3‑month‑old male mice into Sham group, vehicle‑treated anterior cruciate ligament transection (ACLT) group and HF‑treated ACLT group. The present study determined that HF treatment reduced the expression of matrix metallopeptidase‑13 and collagen X in articular cartilage. Additionally, it lowered the Osteoarthritis Research Society International‑Modified Mankin score and prevented the loss of articular cartilage from Safranin O and Fast Green staining. HF reduced the progression of osteoarthritis by downregulating abnormally elevated TGF‑β1 activity in articular cartilage. Administration of HF may be a potential preventive therapy for OA.

Conditional removal of the canonical TGF-β1 signaling delays condylar cartilage degeneration induced by a partial discectomy in mice

Recent emerging data indicate that the increase in the expression and activity of the transforming growth factor beta 1 (Tgf-β1) signaling may have detrimental effect to mature articular cartilage of knee joints. However, there is no information about whether or not this is the case in condylar cartilages. The objective of this study is to investigate the protein expression and activity of Tgf-β1 signaling in degenerative condylar cartilages. We also investigate biological effects of the conditional deletion of transforming growth factor receptor type II (Tgfbr2) in condylar cartilage of adult mice after a partial discectomy. Two mouse models of osteoarthritis (OA) were used to examine protein expressions of Tgf-β1 and p-Smad2/3 in condylar cartilages at early degenerative stages. In addition, cartilage specific Tgfbr2-deficient adult mice were subjected to a partial discectomy. The morphological condition of condylar cartilages was evaluated in mice at 4 and 12 weeks after the surgery. We found that protein levels of Tgf-β1 and p-Smad2/3 were increased in the degenerative condylar cartilage of the mouse models. The conditional removal of Tgfbr2 in mature condylar cartilage significantly delayed the progressive progression of the cartilage degeneration induced by a partial discectomy. We conclude that the increase in the expression and activity of Tgf-β1 signaling may have detrimental effect to mature condylar cartilages. Therefore, inhibition of Tgf-β1 signaling may be able to protect condylar cartilages from being degraded in mature temporomandibular joints.

Heterogeneous engineered cartilage growth results from gradients of media-supplemented active TGF-β and is ameliorated by the alternative supplementation of latent TGF-β

Transforming growth factor beta (TGF-β) has become one of the most widely utilized mediators of engineered cartilage growth. It is typically exogenously supplemented in the culture medium in its active form, with the expectation that it will readily transport into tissue constructs through passive diffusion and influence cellular biosynthesis uniformly. The results of this investigation advance three novel concepts regarding the role of TGF-β in cartilage tissue engineering that have important implications for tissue development. First, through the experimental and computational analysis of TGF-β concentration distributions, we demonstrate that, contrary to conventional expectations, media-supplemented exogenous active TGF-β exhibits a pronounced concentration gradient in tissue constructs, resulting from a combination of high-affinity binding interactions and a high cellular internalization rate. These gradients are sustained throughout the entire culture duration, leading to highly heterogeneous tissue growth; biochemical and histological measurements support that while biochemical content is enhanced up to 4-fold at the construct periphery, enhancements are entirely absent beyond 1 mm from the construct surface. Second, construct-encapsulated chondrocytes continuously secrete large amounts of endogenous TGF-β in its latent form, a portion of which undergoes cell-mediated activation and enhances biosynthesis uniformly throughout the tissue. Finally, motivated by these prior insights, we demonstrate that the alternative supplementation of additional exogenous latent TGF-β enhances biosynthesis uniformly throughout tissue constructs, leading to enhanced but homogeneous tissue growth. This novel demonstration suggests that latent TGF-β supplementation may be utilized as an important tool for the translational engineering of large cartilage constructs that will be required to repair the large osteoarthritic defects observed clinically.

Attenuation of the progression of articular cartilage degeneration by inhibition of TGF-β1 signaling in a mouse model of osteoarthritis

Transforming growth factor beta 1 (TGF-β1) is implicated in osteoarthritis. We therefore studied the role of TGF-β1 signaling in the development of osteoarthritis in a developmental stage-dependent manner. Three different mouse models were investigated. First, the Tgf-β receptor II (Tgfbr2) was specifically removed from the mature cartilage of joints. Tgfbr2-deficient mice were grown to 12 months of age and were then euthanized for collection of knee and temporomandibular joints. Second, Tgfbr2-deficient mice were subjected to destabilization of the medial meniscus (DMM) surgery. Knee joints were then collected from the mice at 8 and 16 weeks after the surgery. Third, wild-type mice were subjected to DMM at the age of 8 weeks. Immediately after the surgery, these mice were treated with the Tgfbr2 inhibitor losartan for 8 weeks and then euthanized for collection of knee joints. All joints were characterized for evidences of articular cartilage degeneration. Initiation or acceleration of articular cartilage degeneration was not observed by the genetic inactivation of Tgfbr2 in the joints at the age of 12 months. In fact, the removal of Tgfbr2 and treatment with losartan both delayed the progression of articular cartilage degeneration induced by DMM compared with control littermates. Therefore, we conclude that inhibition of Tgf-β1 signaling protects adult knee joints in mice against the development of osteoarthritis.

Advances in understanding cartilage remodeling

Cartilage remodeling is currently among the most popular topics in osteoarthritis research. Remodeling includes removal of the existing cartilage and replacement by neo-cartilage. As a loss of balance between removal and replacement of articular cartilage develops (particularly, the rate of removal surpasses the rate of replacement), joints will begin to degrade. In the last few years, significant progress in molecular understanding of the cartilage remodeling process has been made. In this brief review, we focus on the discussion of some current "controversial" observations in articular cartilage degeneration: (1) the biological effect of transforming growth factor-beta 1 on developing and mature articular cartilages, (2) the question of whether aggrecanase 1 (ADAMTS4) and aggrecanase 2 (ADAMTS5) are key enzymes in articular cartilage destruction, and (3) chondrocytes versus chondron in the development of osteoarthritis. It is hoped that continued discussion and investigation will follow to better clarify these topics. Clarification will be critical for those in search of novel therapeutic targets for the treatment of osteoarthritis.

Regulation and Role of TGFβ Signaling Pathway in Aging and Osteoarthritis Joints

Transforming growth factor beta (TGFβ) is a major signalling pathway in joints. This superfamilly is involved in numerous cellular processes in cartilage. Usually, they are considered to favor chondrocyte differentiation and cartilage repair. However, other studies show also deleterious effects of TGFβ which may induce hypertrophy. This may be explained at least in part by alteration of TGFβ signaling pathways in aging chondrocytes. This review focuses on the functions of TGFβ in joints and the regulation of its signaling mediators (receptors, Smads) during aging and osteoarthritis.

A novel in vitro bovine cartilage punch model for assessing the regeneration of focal cartilage defects with biocompatible bacterial nanocellulose

Introduction

Current therapies for articular cartilage defects fail to achieve qualitatively sufficient tissue regeneration, possibly because of a mismatch between the speed of cartilage rebuilding and the resorption of degradable implant polymers. The present study focused on the self-healing capacity of resident cartilage cells in conjunction with cell-free and biocompatible (but non-resorbable) bacterial nanocellulose (BNC). This was tested in a novel in vitro bovine cartilage punch model.

Methods

Standardized bovine cartilage discs with a central defect filled with BNC were cultured for up to eight weeks with/without stimulation with transforming growth factor-β1 (TGF-β1. Cartilage formation and integrity were analyzed by histology, immunohistochemistry and electron microscopy. Content, release and neosynthesis of the matrix molecules proteoglycan/aggrecan, collagen II and collagen I were also quantified. Finally, gene expression of these molecules was profiled in resident chondrocytes and chondrocytes migrated onto the cartilage surface or the implant material.

Results

Non-stimulated and especially TGF-β1-stimulated cartilage discs displayed a preserved structural and functional integrity of the chondrocytes and surrounding matrix, remained vital in long-term culture (eight weeks) without signs of degeneration and showed substantial synthesis of cartilage-specific molecules at the protein and mRNA level. Whereas mobilization of chondrocytes from the matrix onto the surface of cartilage and implant was pivotal for successful seeding of cell-free BNC, chondrocytes did not immigrate into the central BNC area, possibly due to the relatively small diameter of its pores (2 to 5 μm). Chondrocytes on the BNC surface showed signs of successful redifferentiation over time, including increase of aggrecan/collagen type II mRNA, decrease of collagen type I mRNA and initial deposition of proteoglycan and collagen type II in long-term high-density pellet cultures. Although TGF-β1 stimulation showed protective effects on matrix integrity, effects on other parameters were limited.

Conclusions

The present bovine cartilage punch model represents a robust, reproducible and highly suitable tool for the long-term culture of cartilage, maintaining matrix integrity and homoeostasis. As an alternative to animal studies, this model may closely reflect early stages of cartilage regeneration, allowing the evaluation of promising biomaterials with/without chondrogenic factors.

Extracellular matrix production in vitro in cartilage tissue engineering

Cartilage tissue engineering is arising as a technique for the repair of cartilage lesions in clinical applications. However, fibrocartilage formation weakened the mechanical functions of the articular, which compromises the clinical outcomes. Due to the low proliferation ability, dedifferentiation property and low production of cartilage-specific extracellular matrix (ECM) of the chondrocytes, the cartilage synthesis in vitro has been one of the major limitations for obtaining high-quality engineered cartilage constructs. This review discusses cells, biomaterial scaffolds and stimulating factors that can facilitate the cartilage-specific ECM production and accumulation in the in vitro culture system. Special emphasis has been put on the factors that affect the production of ECM macromolecules such as collagen type II and proteoglycans in the review, aiming at providing new strategies to improve the quality of tissue-engineered cartilage.

Cartilage tissue engineering: molecular control of chondrocyte differentiation for proper cartilage matrix reconstruction

BACKGROUND

Articular cartilage defects are a veritable therapeutic problem because therapeutic options are very scarce. Due to the poor self-regeneration capacity of cartilage, minor cartilage defects often lead to osteoarthritis. Several surgical strategies have been developed to repair damaged cartilage. Autologous chondrocyte implantation (ACI) gives encouraging results, but this cell-based therapy involves a step of chondrocyte expansion in a monolayer, which results in the loss in the differentiated phenotype. Thus, despite improvement in the quality of life for patients, reconstructed cartilage is in fact fibrocartilage. Successful ACI, according to the particular physiology of chondrocytes in vitro, requires active and phenotypically stabilized chondrocytes.

SCOPE OF REVIEW

This review describes the unique physiology of cartilage, with the factors involved in its formation, stabilization and degradation. Then, we focus on some of the most recent advances in cell therapy and tissue engineering that open up interesting perspectives for maintaining or obtaining the chondrogenic character of cells in order to treat cartilage lesions.

MAJOR CONCLUSIONS

Current research involves the use of chondrocytes or progenitor stem cells, associated with "smart" biomaterials and growth factors. Other influential factors, such as cell sources, oxygen pressure and mechanical strain are considered, as are recent developments in gene therapy to control the chondrocyte differentiation/dedifferentiation process.

GENERAL SIGNIFICANCE

This review provides new information on the mechanisms regulating the state of differentiation of chondrocytes and the chondrogenesis of mesenchymal stem cells that will lead to the development of new restorative cell therapy approaches in humans. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Shearing of synovial fluid activates latent TGF-β

OBJECTIVE

TGF-β is synthesized in an inactive latent complex that is unable to bind to membrane receptors, thus unable to induce a cellular biological response until it has been activated. In addition to activation by chemical mediators, recent studies have demonstrated that mechanical forces may activate latent TGF-βvia integrin-mediated cellular contractions, or mechanical shearing of blood serum. Since TGF-β is present in synovial fluid in latent form, and since normal diarthrodial joint function produces fluid shear, this study tested the hypothesis that the native latent TGF-β1 of synovial fluid can be activated by shearing.

DESIGN

Synovial fluid from 26 bovine joints and three adult human joints was sheared at mean shear rates up to 4000 s(-1) for up to 15 h.

RESULTS

Unsheared synovial fluid was found to contain high levels of latent TGF-β1 (4.35 ± 2.02 ng/mL bovine, 1.84 ± 0.89 ng/mL human; mean ± radius of 95% confidence interval) and low amounts (<0.05 ng/mL) of the active peptide. Synovial fluid concentrations of active TGF-β1 increased monotonically with shear rate and shearing duration, reaching levels of 2.64 ± 1.22 ng/mL for bovine and 0.60 ± 0.39 ng/mL for human synovial fluid. Following termination of shearing, there was no statistical change in these active levels over the next 8 h for either species, demonstrating long-term stability of the activated peptide. The unsheared control group continued to exhibit negligible levels of active TGF-β1 at all times.

CONCLUSIONS

Results confirmed the hypothesis of this study and suggest that shearing of synovial fluid might contribute an additional biosynthetic effect of mechanical loading of diarthrodial joints.

An update on transforming growth factor-β (TGF-β): sources, types, functions and clinical applicability for cartilage/bone healing

Transforming growth factor-β (TGF-β) has been reviewed for its sources, types of isoforms, biochemical effects on cartilage formation/repair, and its possible clinical applications. Purification of three isoforms (TGF-β-1, β-2 and β-3) and their biochemical characterization revealed mainly their homo-dimer nature, with heterodimers in traces, each monomer comprised of 112 amino acids and MW. of 12 500 Da. While histo-chemical staining by a variety of dyes has revealed precise localization of TGF-β in tissues, immune-blot technique has thrown light on their expression as a function of age (neonatal vs. adult), as also on its quantum in an active and latent state. X-ray crystallographic studies and nuclear magnetic resonance (NMR) analysis have unraveled mysteries of their three-dimensional structures, essential for understanding their functions. Their similarities have led to interchangeability in assays, while differences have led to their specialized clinical applicability. For this purpose, their latent (inactive) form is changed to an active form through enzymatic processes of phosphorylation/glycosylation/transamination/proteolytic degradation. Their functions encompass differentiation and de-differentiation of chondrocytes, synthesis of collagen and proteoglycans (PGs) and thereby maintain homeostasis of cartilage in several degenerative diseases and repair through cell cycle signaling and physiological control. While several factors affecting their performance are already identified, their interplay and chronology of sequences of functions is yet to be understood. For its success in clinical applications, challenges in judicious dealing with the factors and their interplay need to be understood.

TGFbeta affects collagen cross-linking independent of chondrocyte phenotype but strongly depending on physical environment

Transforming growth factor beta (TGFbeta) is often used in cartilage tissue engineering to increase matrix formation by cells with various phenotypes. However, adverse effects of TGFbeta, such as extensive crosslinking in cultured fibroblasts, have also been reported. Our goal was to study effects of TGFbeta on collagen cross-linking and evaluating the role of cellular phenotype and physical environment. We therefore used four different cell populations in two very different physical environments: primary and expanded chondrocytes and fibroblasts embedded in alginate gel and attached to tissue culture plastic. Matrix production, collagen cross-linking, and alpha-smooth muscle actin (alphaSMA) were analyzed during 4 weeks with or without 2.5 ng/ mL TGFbeta2. TGFbeta2 did not affect collagen deposition by primary cells. In expanded cells, TGFbeta2 increased collagen deposition. Chondrocytes and fibroblasts in monolayer produced more collagen cross-links with TGFbeta2. In alginate, primary and expanded cells displayed an unexpected decrease in collagen cross-linking with TGFbeta2. alphaSMA was not present in alginate cultures and barely upregulated by TGFbeta2. Organized alphaSMA fibers were present in all monolayer cultures and became more pronounced with TGFbeta2. This study demonstrates that the physical environment determined by the substrate used co-determines the response of cells to TGFbeta. The presence of mechanical stress, determined with alphaSMA-staining, is probably responsible for the increase in collagen cross-linking upon addition of TGFbeta.

Adenoviral transduction of hTGF-beta1 enhances the chondrogenesis of bone marrow derived stromal cells

TGF-beta1 plays a necessary and important role in the induction of chondrogenic differentiation of bone marrow stromal cells (BMSCs). In this study, porcine BMSCs were infected with a replication-deficient adenovirus expression vector carrying the hTGF-beta1 gene. The transduced BMSCs were cultured as pelleted micromasses in vitro for 21 days, seeded onto disk-shaped PGA scaffolds for 3 days and subsequently implanted into the subcutaneous tissue of mice. BMSCs transduced with AdhTGF-beta1 expressed and secreted more hTGF-beta1 protein in vitro than those of the control group. Histological and immunohistological examination of the pellets revealed robust chondrogenic differentiation. Tissues made from cells transduced with AdhTGF-beta1 exhibited neocartilage formation after 3 weeks in vivo. The neocartilage occupied 42 +/- 5% of the total tissue volume which was significantly greater than that of the control group. Furthermore, there was extensive staining for sulfated proteoglycans and type II collagen in the AdhTGF-beta1 group compared to controls, and quantification of GAG content showed significantly greater amounts of GAG in experimental groups. The results demonstrate that transfer of hTGF-beta1 into BMSCs via adenoviral transduction can induce chondrogenic differentiation in vitro and enhance chondrogenesis in vivo.

Systematic assessment of growth factor treatment on biochemical and biomechanical properties of engineered articular cartilage constructs

OBJECTIVE

To determine the effects of bone morphogenetic protein-2 (BMP-2), insulin-like growth factor (IGF-I), and transforming growth factor-beta1 (TGF-beta1) on the biochemical and biomechanical properties of engineered articular cartilage constructs under serum-free conditions.

METHODS

A scaffoldless approach for tissue engineering, the self-assembly process, was employed. The study consisted of two phases. In the first phase, the effects of BMP-2, IGF-I, and TGF-beta1, at two concentrations and two dosage frequencies each were assessed on construct biochemical and biomechanical properties. In phase II, the effects of growth factor combination treatments were determined. Compressive and tensile mechanical properties, glycosaminoglycan (GAG) and collagen content, histology for GAG and collagen, and immunohistochemistry (IHC) for collagen types I and II were assessed.

RESULTS

In phase I, BMP-2 and IGF-I treatment resulted in significant, >1-fold increases in aggregate modulus, accompanied by increases in GAG production. Additionally, TGF-beta1 treatment resulted in significant, approximately 1-fold increases in both aggregate modulus and tensile modulus, with corresponding increases in GAG and collagen content. In phase II, combined treatment with BMP-2 and IGF-I increased aggregate modulus and GAG content further than either growth factor alone, while TGF-beta1 treatment alone remained the only treatment to also enhance tensile properties and collagen content.

DISCUSSION

This study determined systematically the effects of multiple growth factor treatments under serum-free conditions, and is the first to demonstrate significant increases in both compressive and tensile biomechanical properties as a result of growth factor treatment. These findings are exciting as coupling growth factor application with the self-assembly process resulted in tissue engineered constructs with functional properties approaching native cartilage values.

Interleukin-6 (IL-6) and/or soluble IL-6 receptor down-regulation of human type II collagen gene expression in articular chondrocytes requires a decrease of Sp1.Sp3 ratio and of the binding activity of both factors to the COL2A1 promoter

Type II collagen is composed of alpha1(II) chains encoded by the COL2A1 gene. Alteration of this cartilage marker is a common feature of osteoarthritis. Interleukin-6 (IL-6) is a pro-inflammatory cytokine that needs a soluble form of receptor called sIL-6R to exert its effects in some cellular models. In that case, sIL-6R exerts agonistic action. This mechanism can make up for the partial or total absence of membrane-anchored IL-6 receptors in some cell types, such as chondrocytes. Our study shows that IL-6, sIL-6R, or both inhibit type II collagen production by rabbit articular chondrocytes through a transcriptional control. The cytokine and/or sIL-6R repress COL2A1 transcription by a -63/-35 sequence that binds Sp1.Sp3. Indeed, IL-6 and/or sIL-6R inhibit Sp1 and Sp3 expression and their binding activity to the 63-bp promoter. In chromatin immunoprecipitation experiments, IL-6.sIL-6R induced an increase in Sp3 recruitment to the detriment of Sp1. Knockdown of Sp1.Sp3 by small interference RNA and decoy strategies were found to prevent the IL-6- and/or sIL-6R-induced inhibition of COL2A1 transcription, indicating that each of these Sp proteins is required for down-regulation of the target gene and that a heterotypic Sp1.Sp3 complex is involved. Additionally, Sp1 was shown to interact with Sp3 and HDAC1. Indeed, overexpression of a full-length Sp3 cDNA blocked the Sp1 up-regulation of the 63-bp COL2A1 promoter activity, and by itself, inhibits COL2A1 transcription. We can conclude that IL-6, sIL-6R, or both in combination decrease both the Sp1.Sp3 ratio and DNA-binding activities, thus inhibiting COL2A1 transcription.

The effects of TGF-beta1 and IGF-I on the biomechanics and cytoskeleton of single chondrocytes

OBJECTIVE

Ascertaining how mechanical forces and growth factors mediate normal and pathologic processes in single chondrocytes can aid in developing strategies for the repair and replacement of articular cartilage destroyed by injury or disease. This study examined effects of transforming growth factor-beta1 (TGF-beta1) and insulin-like growth factor-I (IGF-I) on the biomechanics and cytoskeleton of single zonal chondrocytes.

METHOD

Superficial and middle/deep bovine articular chondrocytes were seeded on tissue culture treated plastic for 3 and 18 h and treated with TGF-beta1 (5 ng/mL), IGF-I (100 ng/mL), or a combination of TGF-beta1 (5 ng/mL)+IGF-I (100ng/mL). Single chondrocytes from all treatments were individually studied using viscoelastic creep testing and stained with rhodamine phalloidin for the F-actin cytoskeleton. Lastly, real-time RT-PCR was performed for beta-actin.

RESULTS

Creep testing demonstrated that all growth factor treatments stiffened cells. Image analysis of rhodamine phalloidin stained chondrocytes showed that cells from all growth factor groups had significantly higher fluorescence than controls, mirroring creep testing results. Growth factors altered cell morphology, since chondrocytes exposed to growth factors remained more rounded, exhibited greater cell heights, and were less spread. Finally, real-time RT-PCR revealed no significant effect of growth factor exposure on beta-actin mRNA abundance. However, beta-actin expression varied zonally, suggesting that this gene would be unsuitable as a PCR housekeeping gene.

CONCLUSIONS

These results indicate that TGF-beta1 and IGF-I increase F-actin levels in single chondrocytes leading to stiffening of cells; however, there does not appear to be direct transcriptional regulation of unpolymerized beta-actin. This suggests that the observed response is most likely due to signaling cross-talk between growth factor receptors and integrin/focal adhesion complexes.

The phylogenetically conserved molluscan chitinase-like protein 1 (Cg-Clp1), homologue of human HC-gp39, stimulates proliferation and regulates synthesis of extracellular matrix components of mammalian chondrocytes

Members of chitinase-like proteins (CLPs) have attracted much attention because of their ability to promote cell proliferation in insects (imaginal disc growth factors) and mammals (YKL-40). To gain insights into the molecular processes underlying the physiological control of growth and development in Lophotrochozoa, we report here the cloning and biochemical characterization of the first Lophotrochozoan CLP from the oyster Crassostrea gigas (Cg-Clp1). Gene expression profiles monitored by real time quantitative reverse transcription-PCR in different adult tissues and during development support the involvement of this protein in the control of growth and development in C. gigas. Recombinant Cg-Clp1 demonstrates a strong affinity for chitin but no chitinolytic activity, as was described for the HC-gp39 mammalian homolog. Furthermore, transient expression of Cg-Clp1 in primary cultures of rabbit articular chondrocytes as well as the use of both purified recombinant protein and conditioned medium from Cg-Clp1-expressing rabbit articular chondrocytes established that Cg-Clp1 stimulates cell proliferation and regulates extracellular matrix component synthesis, showing for the first time a possible involvement of a CLP on type II collagen synthesis regulation. These observations together with the fact that Cg-Clp1 gene organization strongly resembles that of its mammalian homologues argue for an early evolutionary origin and a high conservation of this class of proteins at both the structural and functional levels.

TGF-beta1 immobilized tri-co-polymer for articular cartilage tissue engineering

Tri-co-polymer with composition of gelatin, hyaluronic acid and chondroitin-6-sulfate has been used to mimic the cartilage extracellular matrix as scaffold for cartilage tissue engineering. In this study, we try to immobilize TGF-beta1 onto the surface of the tri-co-polymer sponge to suppress the undesired differentiation during the cartilage growth in vitro. The scaffold was synthesized with a pore size in a range of 300-500 microm. TGF-beta1 was immobilized on the surface of the tri-co-polymer scaffold with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) as a crosslinking agent. Tri-co-polymer scaffolds with and without TGF-beta1 were seeded with porcine chondrocytes and cultured in a spinner flask for 2, 4, and 6 weeks. The chondrocytes were characterized by the methods of immunohistochemical staining with anti-type II collagen and anti-S-100 protein monoclonal antibody, and RT-PCR. After culturing for 4 weeks, chondrocytes showed positive in S-100 protein, Alcian blue, and type II collagen for the scaffold with TGF-beta1 immobilization. There is no observed type I and type X collagen expression in the scaffolds from the observation of RT-PCR. In addition, the scaffold without TGF-beta1 immobilization, type X collagen, can be detected after cultured for 2 weeks. Type I collagen was progressively expressed after 4 weeks. These results can conclude that TGF-beta1 immobilized scaffold can suppress chondrocytes toward prehypertrophic chondrocytes and osteolineage cells. The tri-co-polymer sponge with TGF-beta1 immobilization should have a great potential in cartilage tissue engineering in the future.

The role of transforming growth factor beta signaling in messenger RNA stability

Transforming growth factor beta (TGF-beta) is a biologically multipotent regulatory protein implicated in functions that include the regulation of cellular growth, differentiation, extracellular matrix formation, and wound healing. It also plays a role in the pathologies of Alzheimer's disease, cancer and autoimmune disorders. TGF-beta modulates gene expression by affecting transcriptional activation and mRNA turnover rate. Steady-state mRNA levels depend on both the transcriptional activity and mRNA half-life. The stability of mRNA can be modified by the binding of trans-acting factors to cis-elements on the message. These can protect the mRNA from cleavage by RNAses, or they may promote mRNA cleavage. Changes in mRNA stability can lead to changes in the proteome and subsequently in cellular metabolism. The SMAD family of proteins has been implicated in the transduction of the TGF-beta signal, where they regulate transcriptional activity. This review attempts to provide new insights into the role played by TGF-beta in the regulation of mRNA turnover.

Transforming growth factor (TGF)-beta-activated kinase 1 mimics and mediates TGF-beta-induced stimulation of type II collagen synthesis in chondrocytes independent of Col2a1 transcription and Smad3 signaling

Transforming growth factor (TGF)-beta, bone morphogenetic protein (BMP), and interleukin-1beta activate TGF-beta-activated kinase 1 (TAK1), which lies upstream of the p38 MAPK, JNK, and NF-kappaB pathways. Our knowledge remains incomplete of TAK1 target genes, requirement for cooperative signaling, and capacity for shared or segregated ligand-dependent responses. We show that adenoviral overexpression of TAK1a in articular chondrocytes stimulated type II collagen protein synthesis 3-6-fold and mimicked the response to TGF-beta1 and BMP2. Both factors activated endogenous TAK1 and its activating protein, TAB1, and the collagen response was inhibited by dominant-negative TAK1a. Isoform-specific antibodies to TGF-beta blocked the response to endogenous and exogenous TGF-beta but not the response to TAK1a. Expression of Smad3 did not stimulate type II collagen synthesis or enhance that caused by TGF-beta1 or TAK1a, in contrast to its effects on its endogenous targets, CTGF and plasminogen-activated inhibitor-1. TAK1a, overexpressed alone and immunoprecipitated, phosphorylated MKK6 and stimulated the plasminogen-activated inhibitor-1 promoter following transient transfection; both effects were enhanced by TAB1 coexpression, but type II collagen synthesis was not. Stimulation by TAK1a or TGF-beta did not require increased Col2a1 mRNA, and TAK1 actually reduced Col2a1 mRNA in parallel with the cartilage markers, SRY-type HMG box 9 (Sox9) and aggrecan. Thus, TAK1 increased target gene expression (Col2a1) by translational or posttranslational mechanisms as a Smad3-independent response shared by TGF-beta1 and BMP2.

Functional dichotomy: glutathione and vitamin E in homeostasis relevant to primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a complex chronic neurological disease that can result in blindness. The goal of understanding the aetiology of POAG is to be able to target effective treatment to individuals who will eventually go blind without it. Epidemiological studies of POAG have not specifically addressed the possibility that nutrition may play a role in the development of POAG. A handful of papers have considered that nutrition may have an impact on POAG patients. POAG is not believed to be a 'vitamin-deficiency disease'. The concept of 'vitamin-deficiency diseases' and the recommended daily allowances have not kept pace with the growing understanding of the cellular and molecular functions of vitamins and other micronutrients. The aetiology of POAG remains a mystery. Discoveries in cell physiology can be assimilated from the literature and applied to known homeostatic mechanisms of the eye. In this way the possible roles of nutritional components involved in the aetiology of POAG can be described. The mechanisms may be subject to many influences in ways that have yet to be defined. Two distinct changes in the trabecular meshwork can be identified: trabecular meshwork changes that cause intra-ocular pressure to increase and trabecular meshwork changes that are directly correlated to optic nerve atrophy. Compelling evidence suggests that collagen trabecular meshwork extracellular matrix (ECM) remodelling is correlated to increased intraocular pressure in POAG. Elastin trabecular meshwork ECM remodelling is correlated to POAG optic nerve atrophy. There appear to be two different pathways of ECM remodelling and apoptosis induction in POAG. The pathway for collagen remodelling and apoptosis induction seems to be exogenously influenced by water-soluble antioxidants, for example, glutathione. The pathway for elastin remodelling and apoptosis induction seems to be influenced by endogenous lipid-soluble antioxidants, for example, vitamin E. Roles can be defined for antioxidants in the two different pathways of ECM remodelling and apoptosis induction. This suggests that antioxidants are important in maintaining cellular homeostasis relevant to the aetiology of POAG.

Effects of transforming growth factor beta1 and dexamethasone on the growth and chondrogenic differentiation of adipose-derived stromal cells

The effects of soluble mediators and medium supplements commonly used to induce chondrogenic differentiation in different cell culture systems were investigated to define their dose-response profiles and potentially synergistic effects on the chondrogenic differentiation of adipose-derived adult stromal (ADAS) cells. Human ADAS cells were suspended within alginate beads and cultured in basal medium with insulin, transferrin, and selenious acid (ITS+) or fetal bovine serum (FBS) and treated with different doses and combinations of TGF-beta1 (0, 1, and 10 ng/mL) and dexamethasone (0, 10, and 100 nM). Cell growth and chondrogenic differentiation were assessed by measuring DNA content, protein and proteoglycan synthesis rates, and proteoglycan accumulation. The combination of ITS+ and TGF-beta1 significantly increased cell proliferation. Protein synthesis rates were increased by TGF-beta1 and dexamethasone in the presence of ITS+ or FBS. While TGF-beta1 significantly increased proteoglycan synthesis and accumulation by 1.5- to 2-fold in the presence of FBS, such effects were suppressed by dexamethasone. In summary, the combination of TGF-beta1 and ITS+ stimulated cell growth and synthesis of proteins and proteoglycans by human ADAS cells. The addition of dexamethasone appeared to amplify protein synthesis but had suppressive effects on proteoglycan synthesis and accumulation.

N-Butyryl Glucosamine Increases Matrix Gene Expression by Chondrocytes

Proteoglycan synthesis is dependent on N-acetyl glucosamine (GlcNAc) produced by the hexosamine biosynthetic pathway or obtained exogenously. Although used therapeutically to relieve symptoms of osteoarthritis, the actions of glucosamine and its analogs on cartilage are poorly understood. The purpose of this study was to determine the effects on chondrocytes of N-acylated-glucosamine analogs bearing alkyl chains of different lengths. Chondrocytes isolated from neonatal rat femoral condyles were cultured in the presence of glucosamine analogs. GlcNAc, N-proprionyl glucosamine (GlcNPro), or N-butyryl glucosamine (GlcNBu) did not alter cell number, lactate dehydrogenase release, or metabolic acid production, consistent with lack of cytotoxicity. Treatment of chondrocyte cultures with GlcNBu for 6 days significantly increased levels of type II collagen and aggrecan mRNA as determined by Northern blot analysis. In contrast, GlcNAc and GlcNPro had no significant effect. A significant increase in type II collagen mRNA was induced by GlcNBu within 3 days. GlcNBu did not alter stability of type II collagen mRNA, suggesting it acts on gene transcription. We have previously shown that tumor necrosis factor-alpha (TNFalpha) decreases levels of type II collagen mRNA. However, chondrocytes pretreated with GlcNBu maintained type II collagen mRNA at control levels in the presence of TNFalpha. These results establish that the N-butyrylated analog of glucosamine but not GlcNAc promotes matrix gene expression by chondrocytes. Thus, GlcNBu has the potential for use as a chondro-protective agent in osteoarthritis.

Immunohistochemical analysis of transforming growth factor beta isoforms and their receptors in human cartilage from normal and osteoarthritic femoral heads

OBJECTIVE

Osteoarthritis (OA) is characterized by erosion of cartilage and formation of osteophytes. Since transforming growth factor beta (TGF-beta) is known to be involved in chondrogenesis and osteogenesis, we studied by immunochemistry the expression of TGF-beta isoform types 1, 2, and 3 and their receptor types I and II in slightly and strongly altered areas of human OA cartilage and in osteophytes.

METHODS

Specimens were collected from femoral heads at the time of hip arthroplasty, selecting osteophytic regions and areas of slight or severe degradation according to the Mankin score. Cryostat sections were prepared and submitted to immunohistochemistry using appropriate antibodies to TGF-beta(1-3) and TGF-beta receptors I and II.

RESULTS

TGF-beta1 expression was shown to be depressed in strongly degraded cartilage, compared to normal and slightly altered areas. TGF-beta2 was barely detectable in all samples studied. In osteophytes, a marked overexpression of TGF-beta1 and -beta3 was observed. An important decrease in TGF-beta receptor II was found in fibrillated cartilage areas.

CONCLUSIONS

The three major isoforms of TGF-beta are expressed in human OA cartilage, albeit the TGF-beta2 level is very low. Their expression patterns and the ratio of receptors I and II varies according to the degree of OA severity. The decrease in TGF-beta1 production and marked downregulation of receptor II in fibrillated cartilage may lead to reduced chondrocyte responsiveness to TGF-beta and contribute to the irreversibility of the disease. Overexpression of TGF-beta1 and -beta3 in osteophytes suggests that the two isoforms are involved in the formation of these structures.

Sp1 and Sp3 transcription factors mediate interleukin-1 beta down-regulation of human type II collagen gene expression in articular chondrocytes

Interleukin-1 beta (IL-1 beta) is a pleiotropic cytokine that was shown to inhibit the biosynthesis of articular cartilage components. Here we demonstrate that IL-1 beta inhibits the production of newly synthesized collagens in proliferating rabbit articular chondrocytes and that this effect is accompanied by a decrease in the steady-state levels of type II collagen mRNA. IL-1 beta down-regulates COL2A1 gene transcription through a -41/-33 bp sequence that binds a multimeric complex including Sp1 and Sp3 transcription factors. Specificity of IL-1 beta effects on COL2A1 promoter activity was demonstrated in experiments in which transfection of a wild type -50/+1 sequence of COL2A1 promoter as a decoy oligonucleotide abolished the IL-1 beta inhibition of a -63/+47 COL2A1-mediated transcription. By contrast, transfection of the related oligonucleotide harboring a targeted mutation in the -41/-33 sequence did not modify the negative effect the cytokine. Because we demonstrated previously that Sp1 was a strong activator of COL2A1 gene expression via the -63/+1 promoter region, whereas Sp3 overexpression blocked Sp1-induced promoter activity and inhibited COL2A1 gene transcription, we conclude that IL-1 beta down-regulation of that gene, as we found previously for transforming growth factor-beta 1, is mediated by an increase in the Sp3/Sp1 ratio. Moreover, IL-1 beta increased steady-state levels of Sp1 and Sp3 mRNAs, whereas it enhanced Sp3 protein expression and inhibited Sp1 protein biosynthesis. Nevertheless, IL-1 beta decreased the binding activity of both Sp1 and Sp3 to the 63-bp short COL2A1 promoter, suggesting that the cytokine exerts a post-transcriptional regulatory mechanism on Sp1 and Sp3 gene expressions. Altogether, these data indicate that modulation of Sp3/Sp1 ratio in cartilage could be a potential target to prevent or limit the tissue degradation.

Regulation of osteogenic proteins by chondrocytes

The purpose of this review is to summarize the current scientific knowledge of bone morphogenetic proteins (BMPs) in adult articular cartilage. We specifically focus on adult cartilage, since one of the major potential applications of the members of the BMP family may be a repair of adult tissue after trauma and/or disease. After reviewing cartilage physiology and BMPs, we analyze the data on the role of recombinant BMPs as anabolic agents in tissue formation and restoration in different in vitro and in vivo models following with the endogenous expression of BMPs and factors that regulate their expression. We also discuss recent transgenic modifications of BMP genes and subsequent effect on cartilage matrix synthesis. We found that the most studied BMPs in adult articular cartilage are BMP-7 and BMP-2 as well as transforming growth factor-beta (TGF-beta). There are a number of contradicting reports for some of these growth factors, since different models, animals, doses, time points, culture conditions and devices were used. However, regardless of the experimental conditions, only BMP-7 or osteogenic protein-1 (OP-1) exhibits the most convincing effects. It is the only BMP studied thus far in adult cartilage that demonstrates strong anabolic activity in vitro and in vivo with and without serum. OP-1 stimulates the synthesis of the majority of cartilage extracellular matrix proteins in adult articular chondrocytes derived from different species and of different age. OP-1 counteracts the degenerative effect of numerous catabolic mediators; it is also expressed in adult human, bovine, rabbit and goat articular cartilage. This review reveals the importance of the exploration of the BMPs in the cartilage field and highlights their significance for clinical applications in the treatment of cartilage-related diseases.

TNFα suppresses link protein and type II collagen expression in chondrocytes: Role of MEK1/2 and NF-κB signaling pathways

Tumor necrosis factor alpha (TNFalpha) inhibits matrix synthesis by chondrocytes in rheumatoid arthritis and osteoarthritis; however, the underlying signaling pathways are poorly characterized. This study investigated the TNFalpha-activated pathways regulating expression of two key components of the cartilage matrix-link protein and type II collagen. In rat articular chondrocytes, TNFalpha decreased link protein and type II collagen mRNA to undetectable levels within 48 h. Levels of link protein mRNA recovered more readily than type II collagen mRNA following removal of the cytokine. TNFalpha-mediated reduction in mRNA of both matrix molecules occurred at the level of transcription and, for link protein, mRNA stability. Turnover of type II collagen and link protein mRNA was dependent on new protein synthesis. In both prechondrocytes and articular chondrocytes, TNFalpha induced concentration-dependent activation of MEK1/2 and NF-kappaB, but not p38 or JNK. Sustained activation of NF-kappaB was observed for up to 72 h following continuous or transient exposure to TNFalpha. Using pharmacological and molecular approaches, the MEK1/2 and NF-kappaB pathways were found to mediate inhibition of type II collagen and link protein gene expression by TNFalpha. Both prechondrocytes and articular chondrocytes are targets of TNFalpha. This study identifies pathways through which TNFalpha perturbs the synthesis and organization of articular cartilage matrix during inflammation.

Down-regulation of human type II collagen gene expression by transforming growth factor-beta 1 (TGF-beta 1) in articular chondrocytes involves SP3/SP1 ratio

Although transforming growth factor beta1 (TGF-beta1) is generally considered as a stimulator of type I collagen production in smooth organs, we found that it can inhibit type II collagen biosynthesis in primary rabbit articular chondrocytes (RAC) at transcriptional levels. Constructs of promoter and first intron sequences associated with the luciferase reporter gene were used to delineate the gene sequences involved in TGF-beta1 control of human COL2A1 gene transcription. Cotransfection of these DNA fragments with a TbetaRII/I cDNA hybrid receptor, capable of inducing a TGF-beta1 dominant negative effect, showed that TGF-beta1 inhibits specifically COL2A1 gene transcription in RAC by a 63-bp proximal promoter. Footprint and gel retardation analyses revealed that the TGF-beta1-induced inhibition effect exerted through the 63-bp promoter sequence implies a multimeric complex that binds to the -41/-33 sequence and involves Sp1 and Sp3 transcription factors. Transfection of decoy Sp-binding oligonucleotides corroborated the implication of the proximal promoter in the TGF-beta1-induced inhibition of COL2A1 gene transcription. In addition, TGF-beta1 was found to increase the expression of Sp3 without significant changes to its binding level, but repressed both the biosynthesis and binding activity of Sp1. In functional assays, Sp3 inhibited the 63-bp promoter activity and prevented Sp1 induction of transcription. These findings suggest that TGF-beta1 inhibition of COL2A1 gene transcription in RAC is mediated by an increase of the Sp3/Sp1 ratio and by the repression of Sp1 transactivating effects on that gene.

Fluid-induced shear stress stimulates chondrocyte proliferation partially mediated via TGF-beta1

There is growing evidence that a hydrodynamic environment is beneficial for growing cartilage tissue-engineered constructs; however, the mechanisms by which fluid shear provides for a better construct are not well understood. In this study, we investigated one possible mechanism by which constructs grow faster under fluid shear: fluid shear upregulates chondrocyte proliferation. Further, we investigated if this effect is mediated by TGF-beta1, a known mediator of fluid shear effects in other cell types and a mitogen for chondrocytes. To test the hypotheses, primary bovine articular chondrocytes were cultured in monolayers (approximately 40,000 cells/cm(2)) to 80-85% confluency. After 24 h of growth arrest, cells were exposed to 3.5 Pa fluid shear stress for 96 h. Total DNA was compared between flow and static culture slides. Total TGF-beta1 was quantified in flow-conditioned media (CM) and static culture-CM. Mitogenic capacity of the CM, with or without anti-TGF-beta1 or anti-TbetaRII (TGF beta receptor type II) antibodies, was also assessed. Results show that fluid shear significantly up-regulates chondrocyte proliferation (p < 0.02). Further, total TGF-beta1 in the flow-CM was more than 3.5-fold higher (p < 0.03) and its mitogenicity significantly higher (p < 0.007) as compared to static culture-CM. Adding excess anti-TGF-beta1 or anti-TbetaRII antibodies partially, but significantly depressed mitogenicity (approximately 20% decrease) of the flow-CM. These results show that fluid shear stress upregulates chondrocyte proliferation and that this effect is partially mediated by TGF-beta1.

Recent advances in TGF-beta effects on chondrocyte metabolism. Potential therapeutic roles of TGF-beta in cartilage disorders

Novel approaches to treat osteoarthritis are required and progress in understanding the biology of cartilage disorders has led to the use of genes whose products stimulate cartilage repair or inhibit breakdown of the cartilaginous matrix. Among them, transforming growth factor-beta (TGF-beta) plays a significant role in promoting chondrocyte anabolism in vitro (enhancing matrix production, cell proliferation, osteochondrogenic differentiation) and in vivo (short-term intra-articular injections lead to increased bone formation and subsequent cartilage formation, beneficial effects on osteochondrogenesis). In vivo induction of the expression of TGF-beta and the use of gene transfer may provide a new approach for treatment of osteoarthritic lesions.

Sp3 represses the Sp1-mediated transactivation of the human COL2A1 gene in primary and de-differentiated chondrocytes

Sp1 and Sp3 effects on the transcription of the human alpha1(II) procollagen gene (COL2A1) were investigated in both differentiated and de-differentiated rabbit articular chondrocytes. Transient transfection with constructs of deleted COL2A1 promoter sequences driving the luciferase reporter gene revealed that the region spanning -266 to +121 base pairs showed Sp1-enhancing effects, whatever the differentiation state. In contrast, Sp3 did not influence COL2A1 gene transcription. Concomitant overexpression of the two Sp proteins demonstrated that Sp3 blocked the Sp1 induction of COL2A1 promoter activity. Moreover, inhibition of Sp1/Sp3 binding to their target DNA sequence decreased both COL2A1 gene transcription and Sp1-enhancing effects. DNase I footprinting and gel retardation assays revealed that Sp1 and Sp3 bind specifically to cis-sequences of the COL2A1 gene promoter whereby they exert their transcriptional effects. Sp1 and Sp3 levels were found to be reduced in de-differentiated chondrocytes, as revealed by DNA-binding and immunochemical study. Sp1 specifically activated collagen neosynthesis whatever the differentiation state of chondrocytes, suggesting that this factor exerts a major role in the expression of collagen type II. However, our data indicate that type II collagen-specific expression in chondrocytes depend on both the Sp1/Sp3 ratio and cooperation of Sp1 with other transcription factors, the amounts of which are also modulated by phenotype alteration.

The role of the extracellular matrix in articular chondrocyte regulation

The in vivo role of the extracellular matrix and the manner in which it interfaces with soluble regulators remains largely unknown. The current study reports the extracellular Type II collagen modulation of transforming growth factor-beta 1-stimulated proliferation, proteoglycan synthesis, messenger ribonucleic acid expression for transforming growth factor-beta 1, and integrin messenger ribonucleic acid expression in articular chondrocytes from adults. This study shows that this cytokine modulation occurs through a mechanism initiated by the attachment of Type II collagen to the beta1-integrin. Transforming growth factor-beta 1 stimulated deoxyribonucleic acid and proteoglycan synthesis in a bimodal fashion. Extracellular Type II collagen increased transforming growth factor-beta 1-stimulated deoxyribonucleic acid and proteoglycan synthesis, aggrecan gene expression as much as 400%, and alpha1(II) procollagen gene expression as much as 180% in a dose-dependent fashion. Heat inactivation of the Type II collagen abrogated the observed effects on deoxyribonucleic acid and proteoglycan synthesis. In contrast to Type II collagen, heat-denatured collagen and bovine serum albumin showed none of the observed effects. The presence of Type II collagen in the alginate bead cultures was found to diminish the messenger ribonucleic acid expression for alpha2 integrin and alter the cellular distribution pattern of the beta1 integrin receptors. Blocking of the beta1-integrin with cyclic-peptides containing the Arg-Gly-Asp sequences and antibodies reduced chondrocyte attachment to Type II collagen by 93%. The physiologic effects shown by the chondrocyte as a result of blocking this attachment to Type II collagen were a significant reduction in transforming growth factor-beta 1-stimulated deoxyribonucleic acid and proteoglycan synthesis. The conclusions elucidate the role played by the extracellular matrix in cytokine-specific regulation of the articular chondrocyte. The authors have shown that extracellular Type II collagen acts through a beta1-integrin mediated mechanism to modulate the chondrocyte response to transforming growth factor-beta 1.

Cytokine regulation of cartilage-derived retinoic acid-sensitive protein (CD-RAP) in primary articular chondrocytes: suppression by IL-1, bfGF, TGFbeta and stimulation by IGF-1

Cartilage-derived retinoic acid-sensitive protein (CD-RAP) is a secreted protein identified in our laboratory by RT-PCR and differential display [U.H. Dietz, L.J. Sandell. Cloning of a retinoic acid-sensitive mDNA expressed in cartilage and during chondrogenesis. J. Biol. Chem. 271 (1996) 3311-3316]. It is synthesized by chondrocytes throughout development and down-regulated by retinoic acid in coordination with type II collagen gene expression. To further explore the regulation CD-RAP in primary articular chondrocytes, we examined effects of selected cytokines on CD-RAP gene expression compared to their effects on type II collagen expression. Northern blot analysis showed that expression of CD-RAP mRNA was suppressed by bFGF, IL-1beta and retinoic acid in coordination with type II collagen mRNA. TGF-beta decreased CD-RAP expression while increasing type II collagen mRNA whereas both mRNAs were up-regulated by IGF-1. In chondrocytes dedifferentiated with retinoic acid, IGF-1 induced re-expression of both CD-RAP and type II collagen mRNAs. The mechanism of stimulation of CD-RAP by IGF-1 was further investigated. An mRNA stability assay revealed that IGF-1 had no effect on CD-RAP or type II collagen mRNA half life, suggesting that the enhancement by IGF-1 is due to increased gene transcription. To study the transcriptional mechanism, we used the 5'-flanking region of the CD-RAP gene fused to a promoter-less reporter plasmid encoding luciferase. Deletion analysis of the CD-RAP promoter indicated that an IGF-1-responsive element is present between nucleotides -475 and -458. These data indicate that CD-RAP expression can be regulated by cytokines known to influence chondrocyte metabolism and that IGF-1 up-regulates CD-RAP gene expression through a transcriptional mechanism.

Differential regulation of gelatinases by transforming growth factor beta-1 in normal equine chondrocytes

OBJECTIVE

Cartilage destruction in osteoarthritis (OA) is associated with increased levels of several matrix metalloproteinases (MMPs), including the gelatinases MMP-2 and MMP-9. While increases in some MMPs may be destructive, up-regulation of others may result from increases in normal tissue turnover. The production of MMP-2 and MMP-9 by the anabolic transforming growth factor beta-1 (TGF-beta1) in normal equine chondrocytes was investigated.

DESIGN

Equine chondrocytes from clinically normal femoropatellar joints were maintained in alginate beads. After serum deprivation, cells were exposed to TGF-beta1 at several concentrations for varying times. Activities of MMP-2 and MMP-9 were estimated by gelatin zymography, while mRNA for MMP-2, MMP-9 and collagen type II were detected using reverse transcription-polymerase chain reaction.

RESULTS

Stimulation with TGF-beta1 differentially regulated MMP-2 and MMP-9, with strong up-regulation of both MMP-9 mRNA and enzyme. Increases in MMP-9 enzyme were dose-dependent (0-49 h). There is some evidence suggesting a slight reduction in MMP-2 release following stimulation. Collagen type II mRNA was transiently increased following stimulation.

CONCLUSIONS

The different effects of TGF-beta1 on MMP-2 and MMP-9 production by normal chondrocytes suggests different roles for these enzymes. The increases in both MMP-9 and collagen type II mRNA following stimulation may suggest a role for MMP-9 in tissue maintenance. Therefore, increased MMP-9 may be secondary to, as distinct from a cause of, cartilage damage.

TGF-beta1 as a prognostic factor in the process of early osteoarthrosis in the rabbit knee

OBJECTIVE

To assess changes in knee joint fluid concentrations of transforming growth factor-beta1 (TGF-beta1) and proteoglycan (PG) fragments during the early course of post-traumatic osteoarthrosis (OA) after meniscectomy in the rabbit knee, and to ascertain whether the concentrations of these substances shortly after operation could be used as prognostic markers for the OA process.

DESIGN

In 15 rabbits with medial meniscectomy in one knee and a sham operation in the other knee, synovial lavage fluid samples were taken repeatedly, before operation, every third week post-operatively until 12 weeks, thereafter every sixth week, and at death. Five rabbits each were killed at 13, 25 and 40 weeks. Synovial lavage fluid samples from five non-operated rabbits served as controls. At death, two histological scores were formed that characterized the highest (MAX) and the overall (ALL) degree of OA changes in each joint.

RESULTS

TGF-beta1 and PG fragment concentrations in synovial lavage fluid correlated highly (R=0.81, P< 0.001). Both OA scores were higher in meniscectomized than controls (P< 0.05). The synovial lavage fluid concentration of TGF-beta1 at 3 weeks, but no other time point, correlated to the histological scores (ALL, R=0.58; MAX, R=0.52;P< 0.001).

CONCLUSION

Higher concentrations of TGF-beta1 in synovial lavage fluid early after surgery seemed indicative for the later development of more severe OA changes in contrast to lower concentrations. The association between TGF-beta1 and the changes found later in the cartilage was underlined by the high correlations between this substance and PG fragment concentrations in synovial lavage fluid at all time points.