Effects of transforming growth factor beta s and basic fibroblast growth factor on articular chondrocytes obtained from immobilised rabbit knees

Cell Cycle Synchronization of Primary Articular Chondrocytes Enhances Chondrogenesis

OBJECTIVE

Although tissue engineering is a promising option for articular cartilage repair, it has been challenging to generate functional cartilaginous tissue. While the synthetic response of chondrocytes can be influenced by various means, most approaches treat chondrocytes as a homogeneous population that would respond similarly. However, isolated cells heterogeneously progress through the cell cycle, which can affect macromolecular biosynthesis. As it is possible to synchronize cells within discrete cell cycle phases, the purpose of this study was to investigate the effects of cell cycle synchronization on the chondrogenic potential of primary articular chondrocytes.

DESIGN

Different methods of cell synchronization (serum starvation, thymidine, nocodazole, aphidicolin, and RO-3306) were tested for their ability to synchronize primary articular chondrocytes during the process of cell isolation. Cells (unsynchronized and synchronized) were then encapsulated in alginate gels, cultured for 4 weeks, and analyzed for their structural and biochemical properties.

RESULTS

The double-thymidine method yielded the highest level of cell purity, with cells synchronized in S phase. While the cells started to lose synchronization after 24 hours, tissue constructs developed from initially S phase synchronized cells had significantly higher glycosaminoglycan and collagen II amounts than those developed using unsynchronized cells.

CONCLUSIONS

Initial synchronization led to long-term changes in cartilaginous tissue formation. This effect was postulated to be due to the rapid auto-induction of TGF-βs by actively dividing S phase cells, thereby stimulating chondrogenesis. Cell synchronization methods may also be applied in conjunction with redifferentiation methods to improve the chondrogenic potential of dedifferentiated or diseased chondrocytes.

The role of TGF-β2 in cartilage development and diseases

Transforming growth factor-beta2 (TGF-β2) is recognized as a versatile cytokine that plays a vital role in regulation of joint development, homeostasis, and diseases, but its role as a biological mechanism is understood far less than that of its counterpart, TGF-β1. Cartilage as a load-resisting structure in vertebrates however displays a fragile performance when any tissue disturbance occurs, due to its lack of blood vessels, nerves, and lymphatics. Recent reports have indicated that TGF-β2 is involved in the physiological processes of chondrocytes such as proliferation, differentiation, migration, and apoptosis, and the pathological progress of cartilage such as osteoarthritis (OA) and rheumatoid arthritis (RA). TGF-β2 also shows its potent capacity in the repair of cartilage defects by recruiting autologous mesenchymal stem cells and promoting secretion of other growth factor clusters. In addition, some pioneering studies have already considered it as a potential target in the treatment of OA and RA. This article aims to summarize the current progress of TGF-β2 in cartilage development and diseases, which might provide new cues for remodelling of cartilage defect and intervention of cartilage diseases.

Enhancement of cartilage repair through the addition of growth plate chondrocytes in an immature skeleton animal model

Background

The treatment of articular cartilage damage is a major clinical problem. More often, this clinical issue affects children, which forces doctors to find the best treatment method.

Methods

The aim of this experimental study on 2-month-old Landrace pigs was to compare the results of two cartilage defect treatments: (1) filling the cartilage defect with a scaffold incubated with bone marrow aspirate supplemented with growth plate chondrocytes (the CELLS group) and (2) filling the cartilage defect with an empty scaffold implanted after drilling the subchondral bone (the CTRL group). The treatment outcomes were assessed macroscopically and microscopically.

Results

Based on the macroscopic evaluation, all animals showed a nearly normal morphology, with an average of 9.66/12 points (CTRL) and 10.44/12 points (CELLS). Based on the microscopic evaluation, 1 very good result and 8 good results were obtained in the CTRL group, with an average of 70.44%, while 5 very good results and 4 good results were obtained in the CELLS group, with an average of 79.61%.

Conclusions

(1) Growth plate chondrocytes have high chondrogenic potential and thus offer new possibilities for cartilage cell therapy. (2) The implantation of a scaffold loaded with bone marrow-derived MSCs (mesenchymal stem cells) and growth plate chondrocytes into a cartilage defect is a good therapeutic method in immature patients. (3) Cartilage repair based on a scaffold with bone marrow aspirate-derived cells supplemented with autologous growth plate chondrocytes achieves better results than repair with marrow stimulation and a hyaluronic acid-based scaffold (overall microscopic rating). (4) Chondrocyte clustering is a manifestation of the cartilage repair process but requires further observation.

Electronic supplementary material

The online version of this article (10.1186/s13018-019-1302-y) contains supplementary material, which is available to authorized users.

Bioreactor-Controlled Physoxia Regulates TGF-β Signaling to Alter Extracellular Matrix Synthesis by Human Chondrocytes

Culturing articular chondrocytes under physiological oxygen tension exerts positive effects on their extracellular matrix synthesis. The underlying molecular mechanisms which enhance the chondrocytic phenotype are, however, still insufficiently elucidated. The TGF-β superfamily of growth factors, and the prototypic TGF-β isoforms in particular, are crucial in maintaining matrix homeostasis of these cells. We employed a feedback-controlled table-top bioreactor to investigate the role of TGF-β in microtissues of human chondrocytes over a wider range of physiological oxygen tensions (i.e., physoxia). We compared 1%, 2.5%, and 5% of partial oxygen pressure (pO₂) to the ‘normoxic’ 20%. We confirmed physoxic conditions through the induction of marker genes (PHD3, VEGF) and oxygen tension-dependent chondrocytic markers (SOX9, COL2A1). We identified 2.5% pO₂ as an oxygen tension optimally improving chondrocytic marker expression (ACAN, COL2A1), while suppressing de-differentiation markers (COL1A1,COL3A1). Expression of TGF-β isoform 2 (TGFB2) was, relatively, most responsive to 2.5% pO₂, while all three isoforms were induced by physoxia. We found TGF-β receptors ALK1 and ALK5 to be regulated by oxygen tension on the mRNA and protein level. In addition, expression of type III co-receptors betaglycan and endoglin appeared to be regulated by oxygen tension as well. R-Smad signaling confirmed that physoxia divergently regulated phosphorylation of Smad1/5/8 and Smad2/3. Pharmacological inhibition of canonical ALK5-mediated signaling abrogated physoxia-induced COL2A1 and PAI-1 expression. Physoxia altered expression of hypertrophy markers and that of matrix metalloproteases and their activity, as well as expression ratios of specific proteins (Sp)/Krüppel-like transcription factor family members SP1 and SP3, proving a molecular concept of ECM marker regulation. Keeping oxygen levels tightly balanced within a physiological range is important for optimal chondrocytic marker expression. Our study provides novel insights into transcriptional regulations in chondrocytes under physoxic in vitro conditions and may contribute to improving future cell-based articular cartilage repair strategies.

Effect of transforming growth factor-β2 on biological regulation of multilayer primary chondrocyte culture

Cytokines are extremely potent biomolecules that regulate cellular functions and play multiple roles in initiation and inhibition of disease. These highly specialised macromolecules are actively involved in control of cellular proliferation, apoptosis, cell migration and adhesion. This work, investigates the effect of transforming growth factor-beta2 (TGF-β2) on the biological regulation of chondrocyte and the repair of a created model wound on a multilayer culture system. Also the effect of this cytokine on cell length, proliferation, and cell adhesion has been investigated. Chondrocytes isolated from knee joint of rats and cultured at 4 layers. Each layer consisted of 2 × 10⁵ cells/ml with and without TGF-β2. The expression of mRNA and protein levels of TGF-β receptors and Smad1, 3, 4, and 7 have been analysed by RT-PCR and western blot analysis. The effect of different supplementations in chondrocyte cell proliferation, cell length, adhesion, and wound repair was statistically analysed by One-way ANOVA test. Our results showed that the TGFβ2 regulates mRNA levels of its own receptors, and of Smad3 and Smad7. Also the TGF-β2 caused an increase in chondrocyte cell length, but decreased its proliferation rate and the wound healing process. TGF-β2 also decreased cell adhesion ability to the surface of the culture flask. Since, TGF-β2 increased the cell size, but showed negative effect on cell proliferation and adhesion of CHC, the effect of manipulated TGF-β2 with other growth factors and/or proteins needs to be investigated to finalize the utilization of this growth factor and design of scaffolding in treatment of different types of arthritis.

Cartilage cell clusters

The formation of new cell clusters is a histological hallmark of arthritic cartilage but the biology of clusters and their role in disease are poorly understood. This is the first comprehensive review of clinical and experimental conditions associated with cluster formation. Genes and proteins that are expressed in cluster cells, the cellular origin of the clusters, mechanisms that lead to cluster formation and the role of cluster cells in pathogenesis are discussed.

Regulation of VEGF mRNA expression and protein secretion by TGF-beta2 in human retinal pigment epithelial cells

VEGF secretion by the human retinal pigment epithelium (hRPE) plays an important role in retinal and choroidal neovascularization. In this study, transforming growth factor-beta2 (TGF-beta2)-induced vascular endothelial growth factor (VEGF) gene expression was investigated in hRPE cells. Treatment of hRPE cells with TGF-beta2 for 24 and 48h as compared to 8h resulted in markedly increased VEGF secretion by fivefold and nine-fold, respectively. Induced VEGF mRNA peaked within 3h of stimulation and remained above the basal at 36h. Stimulation of VEGF expression by TGF-beta2 was blocked by cycloheximide, suggesting that de novo protein synthesis is required. Induced VEGF production was strongly inhibited by anti-inflammatory agents, dexamethasone and cyclosporin A. Despite of the weak stimulation of VEGF expression by TNF-alpha or bFGF alone, co-administration of either of these two cytokines synergized the effect of TGF-beta2 on VEGF mRNA expression and protein production. Quantitative RT-PCR revealed that the synergy was predominantly at the level of VEGF transcription. Moreover, TGF-beta2-induced RPE VEGF secretion was significantly reduced by inhibitors of mitogen-activated protein (MAP) kinase (MEK) (U0126), p38 (SB202190), c-Jun NH2-terminal kinase (JNK), Sp600125, protein tyrosine kinase (PTK) (Genistein), and phosphatidylinositol 3-kinase (PI3K) (Ly294002). Induced VEGF expression was completely abrogated by inhibitors of protein kinase C (PKC) (Ro318220), nuclear factor-kappaB (NF-kappaB) [caffeic acid phenethyl ester (CAPE)], and reactive oxygen species (ROS) [N-acetyl-cysteine (Nac) and diphenyleneiodonium (DPI)]. These results suggest that MEK, p38, JNK, PI3K, and NF-kappaB as well as multiple essential signaling intermediates, including PKC, PTK and ROS, are involved in hRPE VEGF up regulation by TGF-beta2.

The effect of a passive muscle stretching protocol on the articular cartilage

OBJECTIVE

The aim of this study is to evaluate the articular cartilage alterations of rat ankles, after applying unilateral cyclic passive muscle stretching protocol in previously immobilized rats.

METHODS

Twenty-two male albino rats divided into four groups, I--immobilized; IS--immobilized and stretched; S--stretched and C--control, were used in this experiment. The I and IS groups were immobilized for 4 weeks. In the muscle stretching protocol the treated ankle joint (groups IS and S) was manually full dorsal flexed 10 times for 60s with a 30s interval between each 60s period, 7 days a week for 3 weeks, to stretch the ankle plantar flexors muscle group. The right hind limb was free to move. At the end of the experiment, the ankles were removed, processed in paraffin and stained with hematoxylin-eosin and Safranin-O. Two blinded observers evaluated cellularity, chondrocyte cloning and Safranin-O staining through light microscopy. And a morphometric study was carried out using a hand count of chondrocyte cells and cartilage thickness measurement.

RESULTS

No significant effect of solely muscle stretching concerning cellularity, chondrocyte cloning and Safranin-O staining parameters was detected. However, IS group presented a significantly higher reduction of proteoglycans content than the solely stretched and solely immobilized groups and the morphometric analysis showed significant cellularity increase without thickness alteration compared to control.

CONCLUSIONS

These findings suggest that the stretching protocol used was harmful to the previously immobilized articular cartilage. However, the same stretching protocol did not harm the cartilage of non-immobilized groups.

Expression of transforming growth factor and basic fibroblast growth factor and core protein of proteoglycan in human vertebral cartilaginous endplate of adolescent idiopathic scoliosis

STUDY DESIGN

To compare the expression of cytokines and core protein of proteoglycan in the scoliotic concave and convex cartilaginous endplate using immunohistochemical staining.

OBJECTIVES

To define the possible role of transforming growth factor beta 1 (TGFbeta1), basic fibroblast growth factor (bFGF), and core protein of proteoglycan in the development of adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Changes in the endplate composition have been implicated as possible etiologic factors in the pathogenesis of adolescent idiopathic scoliosis. Cytokines have exclusive effects on cartilage. Thus comparing the expression of the cytokines and matrix on the convex and concave sides of scoliotic endplate tissues may help to understand the role of endplate tissues in the induction and/or progression of idiopathic scoliosis.

METHODS

The convex and concave half of cartilage endplate was collected at the apex and end vertebrae from 12 patients. The expression of TGFbeta1, bFGF, and core protein on both sides was examined with the immunohistochemistry method, and results were analyzed with the image analysis system.

RESULTS

TGFbeta1, bFGF, and core protein of proteoglycan were all expressed in the cytoplasm of chondrocytes in the cartilaginous endplate. The area density and quantity density of TGFbeta1 and bFGF on the concave side are expressed in an even significantly higher level than that on the convex side (P > or = 0.05). The expression of the core protein of proteoglycan on the convex side is higher than that on the concave side, the difference is not significant (P > 0.05).

CONCLUSION

There was a significantly higher expression of TGFbeta1 and bFGF, although a lower expression of the core protein on the concave side, which suggests a possible etiological factor or a secondary change in the development of adolescent idiopathic scoliosis.

Influence of species and anatomical location on chondrocyte expansion

BACKGROUND

Bovine articular cartilage is often used to study chondrocytes in vitro. It is difficult to correlate in vitro studies using bovine chondrocytes with in vivo studies using other species such as rabbits and sheep. The aim of this investigation was to study the effect of species, anatomical location and exogenous growth factors on chondrocyte proliferation in vitro.

METHODS

Equine (EQ), bovine (BO) and ovine (OV) articular chondrocytes from metacarpophalangeal (fetlock (F)), shoulder (S) and knee (K) joints were cultured in tissue culture flasks. Growth factors (rh-FGFb: 10 ng/ml; rh-TGFbeta: 5 ng/ml) were added to the cultures at days 2 and 4. On day 6, cells were counted and flow cytometry analysis was performed to determine cell size and granularity. A three factor ANOVA with paired Tukey's correction was used for statistical analysis.

RESULTS

After 6 days in culture, cell numbers had increased in control groups of EQ-F, OV-S, OV-F and BO-F chondrocytes. The addition of rh-FGFb led to the highest increase in cell numbers in the BO-F, followed by EQ-F and OV-S chondrocytes. The addition of rh-TGFbeta increased cell numbers in EQ-S and EQ-F chondrocytes, but showed nearly no effect on EQ-K, OV-K, OV-S, OV-F and BO-F chondrocytes. There was an overall difference with the addition of growth factors between the different species and joints.

CONCLUSION

Different proliferation profiles of chondrocytes from the various joints were found. Therefore, we recommend performing in vitro studies using the species and site where subsequent in vivo studies are planned.

Cartilage tissue engineering PLLA scaffold with surface immobilized collagen and basic fibroblast growth factor

A previously reported "grafting and coating" method (J. Biomed. Mater. Res. (Appl. Biomater.) 63 (2002) 838) was modified and used to introduce stable collagen layer and incorporate basic fibroblast growth factor (bFGF) on PLLA scaffold surface to prepare tissue engineering scaffold with improved biocompatibility. To make the modification of the 3-D porous PLLA scaffold possible, grafting of polymethacrylic acid (PMAA) onto the PLLA surface was initiated by the -OOH/Fe2+ system instead of the UV light used in the former method. Water soluble carbodimmide chemistry was applied to graft collagen onto the PLLA scaffold surface, followed by physical coating of the collagen solution with or without basic fibroblast growth factor (bFGF). Surface modification of 2-D PLLA membrane was also done for fundamental understanding of the modification. The -COOH density on/in the PMAA grafted PLLA membrane/scaffold was measured by colorimetric method and the collagen content on/in the collagen immobilized PLLA membrane/scaffold was measured by ninhydrin method. Chondrocyte culturing on the collagen immobilized PLLA surfaces showed significantly improved cell spreading and growth. Incorporation of fibroblast growth factors in the collagen layer further enhanced the cell growth. This convenient and effective method can be used to prepare bioactive scaffolds with extra cellular matrix (ECM)-mimic composition for tissue engineering.

Effects of extracellular matrix on the morphology and behaviour of rabbit auricular chondrocytes in culture

Isolated chondrocytes dedifferentiate to a fibroblast-like shape on plastic substrata and proliferate extensively, but rarely form nodules. However, when dissociation is not complete and some cartilage remnants are included in the culture, proliferation decreases and cells grow in a reticular pattern with numerous nodules, which occasionally form small cartilage-like fragments. In an attempt to reproduce this stable chondrogenic state, we added a cartilage protein extract, a sugar extract, and hyaluronan to the medium of previously dedifferentiated chondrocytes. When protein extract was added, many cartilaginous nodules appeared. Hyaluronan produced changes in cell phenotype and behaviour, but not nodule formation. Protein extract has positive effects on the differentiation of previously proliferated chondrocytes and permits nodule formation and the extensive production of type-II collagen. A comparison with incompletely dissociated chondrocyte cultures suggests that the presence of some living cells anchored to their natural extracellular matrix provides some important additional factors for the phenotypical stability of chondrocytes on plastic surfaces. In order to elucidate if it is possible that the incidence of apoptosis is related to the results, we also characterized the molecular traits of apoptosis.

TGF-beta signaling in chondrocytes

Transforming growth factor-beta (TGF-beta) regulates a large variety of cellular activities. Binding of TGF- beta to its cell surface receptor triggers several signaling cascades, among which the TGF- beta -Smad pathway is the most extensively studied. TGF- beta also activates protein kinases, including MAPK, PKA and PKC, and modulates gene expression via its delicate interaction with other signaling pathways. During endochondral bone formation, TGF- beta acts as a potent inhibitor of the terminal differentiation of epiphyseal growth plate chondrocytes. This effect appears to be primarily mediated by Smad molecules, although MAPK-ATF2 signaling is also involved. The rate of chondrocyte maturation is tightly regulated through the interactions of Smad-mediated signaling, the Wnt signaling pathway, and the transcription factor Runx2. Improving our understanding of the exact mechanisms underlying TGF- beta -mediated signaling pathways and their effects may greatly impact the diagnosis and treatment of many common orthopaedic diseases.

Effects of growth factors on temporomandibular joint disc cells

The effects of growth factors on cartilaginous tissues are well documented. An exception is the temporomandibular joint (TMJ) disc, where data for growth factor effects on proliferation and biosynthesis are very limited. The purpose of this study was to quantify proliferation of and synthesis by TMJ disc cells cultured in monolayer with either platelet derived growth factor-AB (PDGF), basic fibroblast growth factor (bFGF) or insulin-like growth factor-I (IGF), at either a low (10 ng/ml) or high (100 ng/ml) concentration. Proliferation was assessed with a DNA quantitation technique, collagen synthesis was measured via a hydroxyproline assay, and GAG synthesis was determined with a dimethylmethylene blue dye binding assay at 14 days. Overall, the most beneficial growth factor was bFGF, which was most potent in increasing proliferation and GAG synthesis, and also effective in promoting collagen synthesis. At the high concentration, bFGF resulted in 96% more cells than the control and 30 to 45% more cells than PDGF and IGF. PDGF and bFGF were the most potent upregulators of GAG synthesis, producing 2-3 times more GAG than the control. IGF had no significant effect on GAG production, although at its higher concentration it increased collagen production by 4.5 times over the control. Collagen synthesis was promoted by bFGF at its lower concentration, with levels 4.2 times higher than the control, whereas PDGF had no significant effect on collagen production. In general, higher concentrations increased proliferation, whereas lower concentrations favoured biosynthesis.

Age-related changes in the response of human articular cartilage to IL-1alpha and transforming growth factor-beta (TGF-beta): chondrocytes exhibit a diminished sensitivity to TGF-beta

Cartilage glycosaminoglycan (GAG) synthesis and composition, upon which its structural integrity depends, varies with age, is modified by anabolic and catabolic stimuli, and is regulated by UDP-glucuronate availability. However, how such stimuli, prototypically represented by transforming growth factor-beta1 (TGF-beta1) and IL-1alpha, modify GAG synthesis during aging of normal human articular cartilage is not known. Using explants, we show that chondroitin sulfate (CS):total GAG ratios decrease, whereas C6S:C4S ratios increase with cartilage maturation, and that chondrocytes in the cartilage mid-zone, but not the superficial or deep zones, exhibit uridine 5'-diphosphoglucose dehydrogenase (UDPGD) activity, which is also increased in mature cartilage. We also show that IL-1alpha treatment reduces both total GAG and CS synthesis, decreases C6S:C4S ratios (less C6S), but fails to modify chondrocyte UDPGD activity at all ages. On the other hand, TGF-beta1 increases total GAG synthesis in immature, but not mature, cartilage (stimulates CS but not non-CS), age-independently decreases C6S:C4S (more C4S), and increases chondrocyte UDPGD activity in a manner inversely correlated with age. Our findings show that TGF-beta1, but not IL-1alpha, modifies matrix synthesis such that its composition more closely resembles "less mature" articular cartilage. These effects of TGF-beta1, which appear to be restricted to periods of skeletal immaturity, are closely associated although not necessarily mechanistically linked with increases in chondrocyte UDPGD activity. The antianabolic effects of IL-1alpha are, on the other hand, likely to be independent of any direct modification in UDPGD activity and manifest equally in human cartilage of all ages.

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.

From genotype to phenotype: the differential expression of FGF, FGFR, and TGFbeta genes characterizes human cranioskeletal development and reflects clinical presentation in FGFR syndromes

Mutations in the fibroblast growth factor receptor (FGFR) genes 1, 2, and 3 are causal in a number of craniofacial dysostosis syndromes featuring craniosynostosis with basicranial and midfacial deformity. Great clinical variability is displayed in the pathologic phenotypes encountered. To investigate the influence of developmental genetics on clinical diversity in these syndromes, the expression of several genes implicated in their pathology was studied at sequential stages of normal human embryo-fetal cranial base and facial ossification (n = 6). At 8 weeks of gestation, FGFR1, FGFR2, and FGFR3 are equally expressed throughout the predifferentiated mesenchyme of the cranium, the endochondral skull base, and midfacial mesenchyme. Both clinically significant isoforms of FGFR2, IgIIIa/c and IgIIIa/b, are coexpressed in maxillary and basicranial ossification. By 10 to 13 weeks, FGFR1 and FGFR2 are broadly expressed in epithelia, osteogenic, and chondrogenic cell lineages. FGFR3, however, is maximally expressed in dental epithelia and proliferating chondrocytes of the skull base, but poorly expressed in the osteogenic tissues of the midface. FGF2 and FGF4, but not FGF7, and TGFbeta1 and TGFbeta3 are expressed throughout both osteogenic and chondrogenic tissues in early human craniofacial skeletogenesis. Maximal FGFR expression in the skull base proposes a pivotal role for syndromic growth dysplasia at this site. Paucity of FGFR3 expression in human midfacial development correlates with the relatively benign human mutant FGFR3 midfacial phenotypes. The regulation of FGFR expression in human craniofacial skeletogenesis against background excess ligand and selected cofactors may therefore play a profound role in the pathologic craniofacial development of children bearing FGFR mutations.

Effects of a 4.7 T static magnetic field on fetal development in ICR mice

In order to determine the effects of a 4.7 T static magnetic field (SMF) on fetal development in mice, we evaluated fetal teratogenesis and endochondral ossification following exposure in utero. Pregnant ICR mice were exposed to a 4.7 T SMF from day 7.5 to 9.5 of gestation in a whole-body dose, and sacrificed on day 18.5 of gestation. We examined the incidence of prenatal death, external malformations and fetal skeletal malformations. There were no significant differences observed in the incidence of prenatal death and/or malformations between SMF-exposed mice and control mice. Further, we evaluated the immunoreactivity for the vascular endothelial growth factor (VEGF), which is implicated in angiogenesis and osteogenesis, in the sternum of fetal mice following magnetic exposure. Our studies also indicated that on day 16.5 of gestation following SMF exposure, the immunoreactivity for VEGF was increased compared to unexposed controls. However, it was decreased in the exposed group compared to the control group on day 18.5 of gestation. DNA and proteoglycan (PG) synthesis were also measured in rabbit costal growth plate chondrocytes in vitro. No significant differences were observed in DNA synthesis between the SMF exposed chondrocytes and the control chondrocytes; however, PG synthesis in SMF exposed chondrocytes increased compared to the controls. Based on these results, we suggest that while SMF exposure promoted the endochondral ossification of chondrocytes, it did not induce any harmful effects on fetal development in ICR mice.

Effects of hyaluronic acid on the morphology and proliferation of human chondrocytes in primary cell culture

Hyaline articular cartilage is a specialised connective tissue with weight bearing and adsorbing functions. Injury or loss of which often leads to impaired joint function and severe pain. Since the self-renewing abilities of hyaline articular cartilage are limited, there is major interest in the development of bioengineered cartilaginous implants. A cell-matrix-biocomposite composed of a collagen I/III scaffold seeded with autologous chondrocytes is currently being used in clinical trials; however, in order to optimise culture conditions, we cultured human condrocytes and seeded them on type I/III collagen membranes and on Thermanox plastic coverslips with media containing 0 to 500 microg/ml Hyaluronic Acid. After 4 days, the cells were either fixed or BrdU incorporation procedures begun. HE staining clearly demonstrated that cells grown in HA form three dimensional clusters and produce secretory vesicles as opposed to the monolayer control cells with noticeably fewer secretory vesicles. BrdU incorporation revealed a noticeable increase in cell proliferation in cells grown in 100 microg/ml; however, no comparable increase in 500 micorg/ml but rather a slight depression in proliferation. Immunohistochemistry for collagen II and aggrecan revealed an obvious increase in deposition of these two substances with increased HA administration as compared to the control; however, again, the higher concentration of HA, 500 microg/ml, did not result in a further increase in production. These results suggest that HA at 100 microg/ml not only influences chondrocytes to differentiate and produce more Collagen II and aggrecan, but also increases proliferation. We, therefore, propose that the addition of HA at low to middle dosages in condrocyte culturing might help improve condrocyte redifferentation and thus, the bioengineered cartilage.

The use of growth factors in cartilage repair

Articular cartilage, which enables smooth gliding of joints during skeletal motion, is vulnerable to injuries and degenerative diseases over time. Bone growth factors have a role in the preservation of the cartilage matrix. This article reviews the potential to treat cartilage damage for bone morphogenetic proteins, insulin-like growth factors, hepatocyte growth factor, basic fibroblast growth factor, and transforming growth factor beta.

Primary cultured chondrocytes of different origins respond differently to bFGF and TGF-beta

Responses of rib and ear chondrocytes to basic fibroblast growth factor (bFGF) and transforming growth factor-beta (TGF-beta) were investigated using high density primary culture isolated from the same rabbit. Degrees of tritiated thymidine, leucine, and proline incorporation were used as indicators of DNA, protein and collagen syntheses, respectively. 10 ng/ml bFGF increased thymidine, proline, and leucine incorporation into rib, but not ear, chondrocytes. 1 ng/ml TGF-beta enhanced thymidine incorporation into both chondrocytes but did not affect proline or leucine incorporation into the ear cells. When both growth factors were added simultaneously, both cells showed rises in syntheses of DNA, protein and collagen. Incorporation of [35S]sulfate, used as indicator of proteoglycan synthesis, was elevated by TGF-beta but was reduced by bFGF especially in the rib cells. This inhibitory effect of bFGF was not reversed by cotreatment with TGF-beta in both cell types. Thus, the origin and cellular differentiation states of chondrocytes seem to cause different responses to these growth factors.