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The discovery of new pharmacological agents is needed to control the progression of osteoarthritis (OA), characterized by joint cartilage damage. Human OA chondrocyte (OAC) cultures were either applied to S-allylcysteine (SAC), a sulfur-containing amino acid derivative, or colchicine, an ancient anti-inflammatory therapeutic, for 24 h. SAC or colchicine did not change viability at 1 nM-10 [micro]M but inhibited p-JNK/pan-JNK. While SAC seems to be more effective, both agents inhibited reactive oxygen species (ROS), 3-nitrotyrosine (3-NT), lipid hydroperoxides (LPO), advanced lipoxidation end-products (ALEs as 4-hydroxy-2-nonenal, HNE), advanced glycation end-products (AGEs), and increased glutathione peroxidase (GPx) and type-II-collagen (COL2). IL-1[beta], IL-6, and osteopontin (OPN) were more strongly inhibited by SAC than by colchicine. In contrast, TNF-[alpha] was inhibited only by SAC, and COX2 was only inhibited by colchicine. Casp-1/ICE, GM-CSF, receptor for advanced glycation end-products (RAGE), and toll-like receptors (TLR4) were inhibited by both agents, but bone morphogenetic protein 7 (BMP7) was partially inhibited by SAC and induced by colchicine. Nuclear factor erythroid 2-related factor 2 (Nrf2) was induced by SAC; in contrast, it was inhibited by colchicine. Although they exert opposite effects on TNF-[alpha], COX2, BMP7, and Nrf2, SAC and colchicine exhibit anti-osteoarthritic properties in OAC by modulating redox-sensitive inflammatory signaling. Key words: osteoarthritis, chondrocytes, S-allylcysteine, colchicine, toll-like receptor-4, redox signaling, inflammation, nuclear factor erythroid 2-related factor 2, oxidative stress. La découverte de nouveaux agents pharmacologiques est nécessaire pour contrôler la progression de l'ostéoarthrite (OA) caractérisée par des dommages progressifs du cartilage articulaire. Des cultures de chondrocytes humains atteints d'OA (COA) ont été traitées à la S-allylcystéine (SAC), un dérivé d'acide aminé contenant du soufre, ou à la colchicine, un ancien traitement anti-inflammatoire, pendant 24 heures. La SAC ou la colchicine ne modifiaient pas la viabilité des cellules à des concentrations allant de 1 nM à 10 [micro]m, mais inhibaient p-JNK/pan-JNK. Bien que la SAC semble plus efficace, les deux agents inhibaient les dérivés réactifs de l'oxygène (DRO), la 3-nitrotyrosine (3-NT), les hydroperoxydes de lipides (LPO), les produits finaux de la lipoxydation avancée (ALE, comme le 4-hydroxy-2-nonenal, HNE) et les produits finaux de la glycation avancée (AGE), et augmentaient la glutathion-peroxydase (GPx) et le collagène de type-II (COL2). L'IL-1[beta], l'IL-6 et l'ostéopontine (OPN) étaient plus fortement inhibées par la SAC que par la colchicine. Cependant, le TNF-[alpha] était inhibé uniquement par la SAC, et la COX2, uniquement par la colchicine. La Casp-1/ICE, le GM-CSF, le récepteur pour les produits finaux de glycation avancée (RAGE) et les récepteurs << toll-like >> (TLR4) étaient inhibés par les deux agents, mais la protéine morphogénétique osseuse 7 (BMP7) était partiellement inhibée par la SAC alors qu'elle était induite par la colchicine. Le facteur nucléaire Nrf2 était induit par la SAC; en revanche, il était inhibé par la colchicine. Bien qu'exerçant des effets opposés sur le TNF-[alpha], la COX2, la BMP7 et le Nrf2, la SAC et la colchicine présentent des propriétés anti-ostéoarthrose chez les COA en modulant la signalisation inflammatoire sensible à l'état redox. [Traduit par la Rédaction] Mots-clés : ostéoarthrite, chondrocytes, S-allylcystéine, colchicine, récepteur de type péage-4, signalisation redox, inflammation, nucléaire facteur 2 lié au facteur érythroïde 2, stress oxydant., Introduction Osteoarthritis (OA) is the most common age-related progressive and disabling joint disease characterized by inflammation and erosion of articular cartilage (Kolasinski et al. 2020). Although OA is a leading [...]

Author(s): Steve Stegen [sup.1] , Kjell Laperre [sup.1] , Guy Eelen [sup.2] [sup.3] , Gianmarco Rinaldi [sup.4] [sup.5] , Peter Fraisl [sup.2] [sup.3] , Sophie Torrekens [sup.1] , Riet Van [...], Endochondral ossification, an important process in vertebrate bone formation, is highly dependent on correct functioning of growth plate chondrocytes.sup.1. Proliferation of these cells determines longitudinal bone growth and the matrix deposited provides a scaffold for future bone formation. However, these two energy-dependent anabolic processes occur in an avascular environment.sup.1,2. In addition, the centre of the expanding growth plate becomes hypoxic, and local activation of the hypoxia-inducible transcription factor HIF-1[alpha] is necessary for chondrocyte survival by unidentified cell-intrinsic mechanisms.sup.3-6. It is unknown whether there is a requirement for restriction of HIF-1[alpha] signalling in the other regions of the growth plate and whether chondrocyte metabolism controls cell function. Here we show that prolonged HIF-1[alpha] signalling in chondrocytes leads to skeletal dysplasia by interfering with cellular bioenergetics and biosynthesis. Decreased glucose oxidation results in an energy deficit, which limits proliferation, activates the unfolded protein response and reduces collagen synthesis. However, enhanced glutamine flux increases [alpha]-ketoglutarate levels, which in turn increases proline and lysine hydroxylation on collagen. This metabolically regulated collagen modification renders the cartilaginous matrix more resistant to protease-mediated degradation and thereby increases bone mass. Thus, inappropriate HIF-1[alpha] signalling results in skeletal dysplasia caused by collagen overmodification, an effect that may also contribute to other diseases involving the extracellular matrix such as cancer and fibrosis.Increased glutamine metabolism caused by unregulated HIF-1[alpha] signalling in mouse chondrocytes results in increased post-translational modification of collagen and skeletal dysplasia, demonstrating that strict regulation of HIF-1[alpha] signalling in chondrocytes is essential for normal bone growth.

Introduction Articular cartilage plays a crucial role in joint motion and load transmission (1, 2). The most common disease of articular cartilage, osteoarthritis, affects millions of humans and is a [...], Joints that have degenerated as a result of aging or Injury contain dead chondrocytes and damaged cartilage. Some studies have suggested that chondrocyte death precedes cartilage damage, but how the loss of chondrocytes affects cartilage integrity is not clear. In this study, we examined whether chondrocyte death undermines cartilage integrity in aging and injury using a rapid 3D confocal cartilage imaging technique coupled with standard histology. We induced autonomous expression of diphtheria toxin to kill articular surface chondrocytes in mice and determined that chondrocyte death did not lead to cartilage damage. Moreover, cartilage damage after surgical destabilization of the medial meniscus of the knee was increased in mice with intact chondrocytes compared with animals whose chondrocytes had been killed, suggesting that chondrocyte death does not drive cartilage damage in response to injury. These data imply that chondrocyte catabolism, not death, contributes to articular cartilage damage following injury. Therefore, therapies targeted at reducing the catabolic phenotype may protect against degenerative joint disease.

The wide diversity of skeletal proportions in mammals is evident upon a survey of any natural history museum's collections and allows us to distinguish between species even when reduced to [...]

Chitosan-based membranes are widely investigated as scaffolds for tissue engineering applications, due to the biochemical and structural similarities between chitosan and the components of extracellular matrix. The morphological characteristics of the scaffolds, which determine the cells viability, are highly dependent on their preparation technique. This research compares chondrocytes viability seeded on chitosan scaffolds obtained from two different fabrication techniques: leaching out a porogenic agent and freeze-gelation. Because these techniques are based on chitosan solutions, the critical overlap and entanglement concentrations are important parameters to be identified and thus the dilute and concentrated regimes were calculated from rheological data. Hence, scaffolds were prepared from chitosan solutions at two concentration regimes, leading us to conclude that chitosan concentration in solution affected the final morphology of the scaffold. The preparation techniques that were used yielded scaffolds with adequate porosity to permit cell adhesion as was observed by scanning electronic microscopy, as well as good mechanical strength to support them measured by dynamic mechanical analysis. The histochemical results obtained after the chondrocytes culture assay showed that scaffolds within a three dimensional structure promoted a higher cell adherence and growth. POLYM. ENG. SCI., 52:2269-2276, 2012. © 2012 Society of Plastics Engineers, INTRODUCTION Cartilages have a minimal regenerative capacity which hinders the effective treatment of their injuries. Therefore, tissue engineering has become an important practice for rebuilding a defective or damaged tissue, [...]

The transcription factor SOX9 regulates cartilage extracellular matrix gene expression and is essential for chondrocyte differentiation. We previously showed that activation of p38 MAPK by cycloheximide in human chondrocytes leads to stabilization of SOX9 mRNA (Tew SR and Hardingham TE. J Biol Chem 281: 39471-39479, 2006). In this study we investigated whether regulation of p38 MAPK caused by changes in osmotic pressure could control SOX9 mRNA levels expression by a similar mechanism. Primary human articular chondrocytes isolated from osteoarthritic cartilage at passage 2-4 showed significantly raised SOX9 mRNA levels when exposed to hyperosmotic conditions for 5 h. The effect was strongest and most reproducible when actin stress fibers were disrupted by the Rho effector kinase inhibitor Y27632, or by culturing the cells within alginate beads. Freshly isolated chondrocytes, used within 24-48 h of isolation, did not contain actin stress fibers and upregulated SOX9 mRNA in response to hyperosmolarity in the presence and absence of Y27632. In these freshly isolated chondrocytes, hyperosmolarity led to an increase in the half-life of SOX9 mRNA, which was sensitive to the p38 MAPK inhibitor SB202190. SOX9 protein levels were increased by hyperosmotic culture over 24 h, and, in passaged chondrocytes, the activity of a COL2A1 enhancer driven luciferase assay was upregulated. However, in freshly isolated chondrocytes, COL2A1 mRNA levels were reduced by hyperosmotic conditions and the half-life was decreased. The results showed that the osmotic environment regulated both SOX9 and COL2A1 mRNA posttranscriptionally, but in fresh cells resulted in increased SOX9, but decreased COL2A1. osmolarity; p38 mitogen-activated protein kinase; mRNA stability; actin; COL2A1 doi: 10.1152/ajpcell.00571.2008

Hypokalemic tubular disorders may lead to growth retardation which is resistant to growth hormone (GH) treatment. The mechanism of these alterations is unknown. Weaning female rats were grouped (n = 10) in control, potassium-depleted (KD), KD treated with intraperitoneal GH at 3.3 mg x [kg.sup.-1] x [day.sup.-1] during the last week (KDGH), and control pair-fed with KD (CPF). After 2 wk, KD rats were growth retarded compared with CPF rats, the osseous front advance ([+ or -] SD) being 67.07 [+ or -] 10.44 and 81.56 [+ or -] 12.70 [micro]m/day, respectively. GH treatment did not accelerate growth rate. The tibial growth plate of KD rats had marked morphological alterations: lower heights of growth cartilage (228.26 [+ or -] 23.58 [micro]m), hypertrophic zone (123.68 [+ or -] 13.49 [micro]m), and terminal chondrocytes (20.8 [+ or -] 2.39 [micro]m) than normokalemic CPF (264.21 [+ or -] 21.77, 153.18 [+ or -] 15.80, and 24.21 [+ or -] 5.86 [micro]m). GH administration normalized these changes except for the distal chondrocyte height. Quantitative PCR of insulin-like growth factor I (IGF-I), IGF-I receptor, and GH receptor genes in KD growth plates showed downregulation of IGF-I and upregulation of IGF-I receptor mRNAs, without changes in their distribution as analyzed by immunohistochemistry and in situ hybridization. GH did not further modify IGF-I mRNA expression. KD rats had normal hepatic IGF-I mRNA levels and low serum IGF-I values. GH increased liver IGF-I mRNA, but circulating IGF-I levels remained reduced. This study discloses the structural and molecular alterations induced by potassium depletion on the growth plate and shows that the lack of response to GH administration is associated with persistence of the disturbed process of chondrocyte hypertrophy and depressed mRNA expression of local IGF-I in the growth plate. tubulopathies; chondrocyte; cartilage

Linear growth in children is sensitive to nutritional status. Amino acids, in particular leucine, have been shown to regulate cell growth, proliferation, and differentiation through the mammalian target of rapamycin (mTOR), a nutrient-sensing protein kinase. Having recently demonstrated a role for mTOR in chondrogenesis, we hypothesized that leucine restriction, acting through mTOR, would inhibit growth plate chondrocyte proliferation and differentiation. The effect of leucine restriction was compared with that of the specific mTOR inhibitor, rapamycin. Leucine restriction produced a dose-dependent inhibition of fetal rat metatarsal explant growth. This was accounted by reduced cell proliferation and hypertrophy but not apoptosis, mTOR activity, as reflected by ribosomal protein $6 phosphorylation, was only partially inhibited by leucine restriction, whereas rapamycin abolished S6 phosphorylation. In chondrogenic ATDC5 cells, leucine restriction inhibited cell number, proteoglycan accumulation, and collagen X expression despite minimal inhibition of mTOR. Microarray analysis demonstrated that the effect of leucine restriction on ATDC5 cell gene expression differed from that of rapamycin. Out of 1,571 genes affected by leucine restriction and 535 genes affected by rapamycin, only 176 genes were affected by both. These findings indicate that the decreased chondrocyte growth and differentiation associated with leucine restriction is only partly attributable to inhibition of mTOR signaling. Thus nutrient restriction appears to directly modulate bone growth through unidentified mTOR-independent mechanisms in addition to the well-characterized mTOR nutrient-sensing pathway. mammalian target of rapamycin; rapamycin; gene expression

Decreased bone density and stature can occur in pediatric patients with inflammatory bowel disease (IBD). Little is known about how IBD broadly impacts the skeleton. To evaluate the influence of an acute episode of IBD on growing bone, 4-wk-old mice were administered 5% dextran sodium sulfate (DSS) for 5 days to induce colitis and their recovery was monitored. During active disease and early recovery, trabecular bone mineral density, bone volume, and thickness were decreased. Cortical bone thickness, outer perimeter, and density were also decreased, whereas inner perimeter and marrow area were increased. These changes appear to maintain bone strength since measures of moments of inertia were similar between DSS-treated and control mice. Histological (static and dynamic), serum, and RNA analyses indicate that a decrease in osteoblast maturation and function account for changes in bone density. Unlike some conditions of bone loss, marrow adiposity did not increase. Similar to reports in humans, bone length decreased and correlated with decreases in growth plate thickness and chondrocyte marker expression. During disease recovery, mice experienced a growth spurt that led to their achieving final body weights and bone length, density, and gene expression similar to healthy controls. Increased TNF-[alpha] and decreased IGF-I serum levels were observed with active disease and returned to normal with recovery. Changes in serum TNF-[alpha] (increased) and IGF-I (decreased) paralleled changes in bone parameters and returned to normal values with recovery, suggesting a potential role in the skeletal response. growth plate; cartilage; adipocyte; ulcerative colitis

Chondrogenesis and endochondral ossification are the cartilage differentiation processes that lead to skeletal formation and growth in the developing vertebrate as well as skeletal repair in the adult. The exquisite regulation of these processes, both in normal development and in pathologic situations, is impacted by a number of different types of stress. These include normal stressors such as mechanical loading and hypoxia as well pathologic stressors such as injury and/or inflammation and environmental toxins. This article provides an overview of the processes of chondrogenesis and endochondral ossification and their control at the molecular level. A summary of the influence of the most well-understood normal and pathologic stressors on the differentiation program is also presented., Introduction to cartilage Cartilage is a connective tissue that is comprised primarily of matrix (mainly collagens and proteoglycans) containing relatively sparse populations of chondrocytes, which perform matrix-generation and maintenance functions. [...]

The majority of the vertebrate skeleton develops through the process of endochondral ossification and involves successive steps of chondrogenesis, chondrocyte proliferation, and hypertrophic chondrocyte differentiation. Interruption of this program through gene mutations and hormonal or environmental factors contributes to numerous diseases, including growth disorders and chondrodysplasias. While a large number of growth factors and hormones have been implicated in the regulation of chondrocyte biology, relatively little is known about the intracellular signaling pathways involved. Recent data provide novel insights into the mechanisms governing acquisition of new phenotypes within the chondrogenic program and suggest multiple pivotal roles for members of the mitogen-activated protein kinase family and their downstream targets in cartilage development. These data are summarized and discussed here.

Chondrocyte proliferation and differentiation requires their attachment to the collagen type II-rich matrix of developing bone. This interaction is mediated by integrins and their cytoplasmic effectors, such as the integrin-linked kinase (ILK). To elucidate the molecular mechanisms whereby integrins control these processes, we have specifically inactivated the ILK gene in growth plate chondrocytes using the Cre-lox methodology. Mice carrying an ILK allele flanked by loxP sites (ILK-fl) were crossed to transgenic mice expressing the Cre recombinase under the control of the collagen type II promoter. Inactivation of both copies of the ILK-fl allele lead to a chondrodysplasia characterized by a disorganized growth plate and to dwarfism. Expression of chondrocyte differentiation markers such as collagen type II, collagen type X, Indian hedgehog and the PTH-PTHrP receptor was normal in ILK-deficient growth plates. In contrast, chondrocyte proliferation, assessed by BrdU or proliferating cell nuclear antigen labeling, was markedly reduced in the mutant growth plates. Cell-based assays showed that integrin-mediated adhesion of primary cultures of chondrocytes from mutant animals to collagen type II was impaired. ILK inactivation in chondrocytes resulted in reduced cyclin D1 expression, and this most likely explains the defect in chondrocyte proliferation observed when ILK is inactivated in growth plate cells.

[alpha] Melanocyte-stimulating hormone ([alpha]-MSH), a 13-amino acid peptide produced in the brain and pituitary gland, is a regulator of appetite and body weight, and its production is regulated by leptin, a factor that affects bone mass when administered centrally. [alpha]-MSH acts via melanocortin receptors. Humans deficient in melanocortin receptor 4 (MC4-R) have increased bone mass, and MC4-R has been identified in an osteoblast-like cell line. Thus [alpha]-MSH may act directly on the skeleton, a question addressed by the present studies. In primary cultures of osteoblasts and chondrocytes, [alpha]-MSH dose dependently ([greater than or equal to] [10.sup.-9] M) stimulated cell proliferation. In bone marrow cultures, [alpha]-MSH (>[10.sup.-9] M) stimulated osteoclastogenesis. Systemic administration of [alpha]-MSH to mice (20 injections of 4.5 [micro]g/day) decreased the trabecular bone volume in the proximal tibiae from 19.5 [+ or -] 1.8 to 15.2 [+ or -] 1.4% (P = 0.03) and reduced trabecular number (P = 0.001). Radiographic indexes of trabecular bone, assessed by phase-contrast X-ray imaging, confirmed the bone loss. It is concluded that [alpha]-MSH acts directly on bone, increasing bone turnover, and, when administered systemically, it decreases bone volume. The latter result may also be contributed to by [alpha]-MSH effects elsewhere, such as the adipocyte, pancreatic [beta]-cell, or central nervous system. osteoblast; osteoclast; chondrocyte; systemic administration

The vertebrate inner ear consists of a complex labyrinth of epithelial cells that is surrounded by a bony capsule. The molecular mechanisms coordinating the development of the membranous and bony labyrinths are largely unknown, Previously, using avian retrovirus encoding Noggin (RCAS-Noggin) or beads soaked with Noggin protein, we have shown that bone morphogenetic proteins (BMPs) are important for the development of the otic epithelium in the chicken inner ear. Here, using two additional recombinant avian retroviruses, dominant negative and constitutively active forms of BMP receptors IB (BMPRIB), we show that BMPs, possibly acting through BMPRIB, are important for otic capsule formation. We also show that Bmp2 is strongly expressed in the prospective semicircular canals starting from the canal outpouch stage, suggesting that BMP2 plays an important role in canal formation. In addition, by correlating expression patterns of Bmps, their receptors, and localization of phosphorylated R-Smad (phospho R-Smad) immunoreactivity, an indicator of BMP activation, we show that BMPs emanating from the otic epithelium influence chondrogenesis of the otic capsule including the cartilage surrounding the semicircular canals.

The Wnt antagonist Frzb-1 is expressed during limb skeletogenesis, but its roles in this complex multistep process are not fully understood. To address this issue, we determined Frzb-1 gene expression patterns during chick long bone development and carried out gain- and loss-of-function studies by misexpression of Frzb-1, Wnt-8 (a known Frzb-1 target), or different forms of the intracellular Wnt mediator LEF-1 in developing limbs and cultured chondrocytes. Frzb-1 expression was quite strong in mesenchymal prechondrogenic condensations and then characterized epiphyseal articular chondrocytes and prehypertrophic chondrocytes in growth plates. Virally driven Frzb-1 misexpression caused shortening of skeletal elements, joint fusion, and delayed chondrocyte maturation, with consequent inhibition of matrix mineralization, metalloprotease expression, and marrow/bone formation. In good agreement, misexpression of Frzb-1 or a dominant-negative form of LEF-1 in cultured chondrocytes maintained the cells at an immature stage. Instead, misexpression of Wnt-8 or a constitutively active LEF-1 strongly promoted chondrocyte maturation, hypertrophy, and calcification. Immunostaining revealed that the distribution of endogenous Wnt mediator [beta]-catenin changes dramatically in vivo and in vitro, from largely cytoplasmic in immature proliferating and prehypertrophic chondrocytes to nuclear in hypertrophic mineralizing chondrocytes. Misexpression of Frzb-1 prevented [beta]-catenin nuclear relocalization in chondrocytes in vivo or in vitro. The data demonstrate that Frzb-1 exerts a strong influence on limb skeletogenesis and is a powerful and direct modulator of chondrocyte maturation, phenotype, and function. Phases of skeletogenesis, such as terminal chondrocyte maturation and joint formation, appear to be particularly dependent on Wnt signaling and thus very sensitive to Frzb-1 antagonistic action. Key Words: Wnt signaling; Frzb-1; chondrocyte maturation; matrix mineralization; endochondral ossification; limb development.

Chronic inflammation results in increased nitrogen monoxide (*NO) formation and the accumulation of nitrite (N[O.sup.-.sub.2]). Neutrophils stimulated by various inflammatory mediators release myeloperoxidase to produce the cytotoxic agent hypochlorous acid (HOCl). Exposure of chondrocytic SW1353 cells to HOCl resulted in a concentration- and time-dependent loss in viability, ATP, and glutathione levels. Treatment of cells with N[O.sup.-.sub.2] but not nitrate (N[O.sup.-.sub.3]) substantially decreased HOCl-dependent cellular toxicity even when N[O.sup.-.sub.2] was added at low ([micro]M) concentrations. In contrast, N[O.sup.-.sub.2] alone (even at 1 mM concentrations) did not affect cell viability or ATP and glutathione levels. These data suggest that N[O.sup.-.sub.2] accumulation at chronic inflammatory sites, where both HOCl and *NO are overproduced, may be cytoprotective against damage caused by HOCl. We propose that this is because HOCl is removed by reacting with N[O.sup.-.sub.2] to give nitryl chloride (N[O.sub.2]Cl), which is less damaging in our cell system. inflammation | cell toxicity | nitryl chloride | nitric oxide | arthritis

Regenerating or engineering new tissues and organs may one day allow routine replacement of lost or failing tissues and organs. However, these engineered tissues must not only grow to fill a defect and integrate with the host tissue, but often they must also grow in concert with the changing needs of the body over time. We hypothesized that tissues capable of growing with time could be engineered by supplying growth stimulus signals to cells from the biomaterial used for cell transplantation. In this study, chondrocytes and osteoblasts were cotransplanted on hydrogels modified with an RGD-containing peptide sequence to promote cell multiplication. New bone tissue was formed that grew in mass and cellularity by endochondral ossification in a manner similar to normal long-bone growth. Transplanted cells organized into structures that morphologically and functionally resembled growth plates. These engineered tissues could find utility in treating diseases and injuries of the growth plate, testing the effect of experimental drugs on growth-plate function and development, and investigating the biology of long-bone growth. Furthermore, this concept of promoting the growth of engineered tissues could find great utility in engineering numerous tissue types by way of the transplantation of a small number of precursor cells. bone | cartilage | alginate | adhesion ligands | endochondral ossification

Emerging medical technologies for effective and lasting repair of articular cartilage include delivery of cells or cell-seeded scaffolds to a defect site to initiate de novo tissue regeneration. Biocompatible scaffolds assist in providing a template for cell distribution and extracellular matrix (ECM) accumulation in a three-dimensional geometry. A major challenge in choosing an appropriate scaffold for cartilage repair is the identification of a material that can simultaneously stimulate high rates of cell division and high rates of cell synthesis of phenotypically specific ECM macromolecules until repair evolves into steady-state tissue maintenance. We have devised a self-assembling peptide hydrogel scaffold for cartilage repair and developed a method to encapsulate chondrocytes within the peptide hydrogel. During 4 weeks of culture in vitro, chondrocytes seeded within the peptide hydrogel retained their morphology and developed a cartilage-like ECM rich in proteoglycans and type II collagen, indicative of a stable chondrocyte phenotype. Time-dependent accumulation of this ECM was paralleled by increases in material stiffness, indicative of deposition of mechanically functional neo-tissue. Taken together, these results demonstrate the potential of a self-assembling peptide hydrogel as a scaffold for the synthesis and accumulation of a true cartilage-like ECM within a three-dimensional cell culture for cartilage tissue repair. three-dimensional cell culture | biological scaffold | regenerative medicine

Rheumatoid arthritis is one of the most critical diseases that impair the quality of life of patients, but its pathogenesis has not yet been fully understood. Osteopontin (OPN) is an extracellular matrix protein containing Arg-Gly-Asp (RGD) sequence, which interacts with [alpha]v[beta]3 integrins, promotes cell attachment, and cell migration and is expressed in both synovial cells and chondrocytes in rheumatoid arthritis; however, its functional relationship to arthritis has not been known. Therefore, we investigated the roles of OPN in the pathogenesis of inflammatory process in a rheumatoid arthritis model induced by a mixture of anti-type II collagen mAbs and lipopolysaccharide (mAbs/LPS). mAbs/LPS injection induced OPN expression in synovia as well as cartilage, and this expression was associated with joint swelling, destruction of the surface structures of the joint based on scanning electron microscopy, and loss of toluidine blue-positive proteoglycan content in the articular cartilage in wild-type mice. In contrast, OPN deficiency prevented the mice from such surface destruction, loss of proteoglycan in the articular joint cartilage, and swelling of the joints even when the mice were subjected to mAbs/LPS injection. Furthermore, mAbs/LPS injection in wild-type mice enhanced the levels of CD31-positive vessels in synovia and terminal deoxynucleotidyltransferase-mediated UTP end labeling-positive chondrocytes in the articular cartilage, whereas such angiogenesis as well as chondrocyte apoptosis was suppressed significantly in OPN-deficient mice. These results indicated that OPN plays a critical role in the destruction of joint cartilage in the rheumatoid arthritis model in mice via promotion of angiogenesis and induction of chondrocyte apoptosis.

Coordination of chondrogenesis and osteogenesis by fibroblast growth factor 18 (Fgf18) are discussed. It has been found that Fgf18 is expressed in the perichondrium and that mice homozygous for a targeted disruption of Fgf18 have a growth plate phenotype like that in mice that lack Fgfr3 and an ossification defect at sites that express Fgfr2. Gain of function mutations in fibroblast growth factor (FGF) receptors cause chondrodysplasia and craniosynostosis syndromes. Ligands interacting with FGF receptors (FGFRs) in developing bone and mechanisms by which FGF signaling regulates various things are are not well known.

Results indicate that hypoxic response and the oxygen sensitive hypoxia-inducible factor 1alpha (HIF1alpha) play a role in the development and cell survival in tissues affected by vascular flow. Data also show that expression of the vascular endothelial growth factor is regulated in a HIF1alpha- independent mannerin chondrocytes inducing ectopic angiogenesis.

The advances made in the areas of genetics and nutrition during this century have resulted in improved growth rates for livestock. However, one drawback has been the increased prevalence of long bone growth problems, such as rickets, avian tibial dyschondroplasia, and osteochondrosis. Growth plate cartilage, which regulates long bone development, must maintain a tightly controlled balance between cartilage synthesis and degradation as well as chondrocyte proliferation and apoptosis. This paper will briefly review the various nutritional factors, cell signals, and proteins that help regulate growth plate chondrocytes. Some of the growth plate diseases will be discussed with an emphasis on how a breakdown in growth plate metabolism is related to the observed problems. The author's intention is that readers will gain an appreciation for the complexity of this relatively small tissue and for why a better understanding of its physiology will be important in the years to come for the prevention of skeletal problems related to long bone growth. Key Words: Growth, Reviews, Osteochondritis, Dyschondroplasia, Growth Factors

A new pathway for mechanotransduction in human articular chondrocytes (HAC) is discussed. Chondrocytes are found in collagen-rich extracellular matrices in human cartilage. With adequate mechanical stimulation, chondrocyte function in HAC is enhanced. Scientific explanation for this remains elusive. However, integrins and integrin-associated signalling pathways have been found to affect the activation of plasma membrane apamin-sensitive CA2+-activated K+ channels that results in the hyperpolarization and enhancement of HAC.

The mechanism of glucose regulation of the insulin-like growth factor (IGF) response system in chondrocytes has been investigated. Primary rabbit chondrocytes were analyzed for changes in their IGF response system and in their ability to generate a synthetic response to IGF-I in media consisting of varying ambient glucose levels. Results show that IGF-I-resistance in chondrocytes treated with inappropriate glucose concentrations may play an important role as a pathogenic mechanism in degenerative cartilage disorders.