This review of the literature supports the concept that ROS are not only deleterious agents involved in cartilage degradation, but that they also act as integral factors of intracellular signaling mechanisms. Further investigation is required to support the concept of antioxidant therapy in the management of joint diseases.

Mesenchymal stromal cells (MSCs) seeded onto biocompatible scaffolds have been proposed for repairing bone defects. When transplanted in vivo, MSCs (expanded in vitro in 21% O(2)) undergo temporary oxygen deprivation due to the lack of pre-existing blood vessels within these scaffolds. In the present study, the effects of temporary (48 h) exposure to hypoxia (

Hyaluronan (HA) is involved in wound healing and its biological properties depend on its molecular size. The effects of native HA and HA-12 and HA-880 saccharide fragments on human fibroblast proliferation and expression of matrix-related genes were studied. The three HA forms promoted cell adhesion and proliferation. Matrix metalloproteinase-1 and -3 mRNA were increased by all HA forms, whereas only HA-12 stimulated the expression of the tissue inhibitor of metalloproteinase 1. HA-12 enhanced type I collagen and transforming growth factor-b (TGF-b) 1 expression. Interestingly, HA-12 and native HA stimulated type III collagen and TGF-b3. HA and its fragments activated Akt and extracellular-regulated kinases 1/2 and p38. Inhibition of these signaling pathways suggested their implication in most of the effects. Only native HA activated nuclear factor-kB and activating protein 1. Use of CD44 siRNA suggests that this HA receptor is partly implicated in the effects, although it does not rule out the involvement of other receptors. Depending on its size, HA may exert differential regulation on the wound-healing process. Furthermore, the HA up-regulation of type III collagen and TGF-b3 expression suggests that it may promote a fetal-like cell environment that favors scarless healing.

Signal transducers and activators of transcription (STAT) factors are cytoplasmic proteins that can be activated by Janus kinases (JAK) and that modulate gene expression in response to cytokine receptor stimulation. STAT proteins dimerize, translocate into the nucleus, and activate specific target genes. In the present study, we show for the first time that interleukin-6 (IL), in the presence of its soluble receptor (sIL-6R), induces activation of JAK1, JAK2, and STAT1/STAT3 proteins in bovine articular chondrocytes. Western blotting and mobility shift assays demonstrated that this effect is accompanied by the DNA binding of the STAT proteins. The mitogen-activated protein kinase pathway was also activated in response to IL-6/sIL-6R association, as reflected by phosphorylation of ERK1 and ERK2 proteins. In these conditions, the expression of cartilage-specific matrix genes, type II collagen, aggrecan core, and link proteins was found to be markedly down-regulated. This negative effect was abolished by addition of parthenolide, an inhibitor of the STAT activation, whereas blockade of the MAP kinases with PD098059 was without significant effect. Thus, activation of the STAT signaling pathways, but not ERK-dependent pathways, is essential for down-regulation of the major cartilage-specific matrix genes by IL-6. In addition, a parallel reduction of Sox9 expression, a key factor of chondrocyte phenotype, was found in these experimental conditions. These IL-6 effects might contribute to the phenotype loss of chondrocytes in joint diseases and the alteration of articular cartilage associated with this pathology.

Sp1 and Sp3 effects on the transcription of the human ␣1(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.Differentiation of mesenchymal cells into chondrocytes results in the synthesis and secretion of a series of proteins characteristic of the cartilage matrix, including type II, IX, XI, and X collagens, the proteoglycan aggrecan, link protein, and cartilage matrix protein (1, 2). Type II collagen is considered as a critical phenotypic marker gene for analysis of molecular events involved in chondrogenesis process as well as in chondrocyte phenotype maintenance. Alteration of type II collagen expression in cartilage may be due to a variety of genetic, inflammatory, or degenerative circumstances and may lead to a variety of chondrodysplasias and joint diseases such as osteoarthritis (3-8). In osteoarthritis, chondrocytes undergo dedifferentiation and synthesize types I and III collagens at the expense of type II (9 -11). Similarly, when chondrocytes are subcultured in vitro as monolayers, they progressively reduce their synthesis of type II collagen (12-14), mimicking the behavior of osteoarthritic chondrocytes. However, they can recover the chondrocytic phenotype by transfer to three-dimensional culture systems (14 -16). Therefore, in vitro analysis of the molecular mechanisms that regulate COL2A1 gene expression can be an approach to understand the process of phenotype alteration in chondrocytes, and its impact on joint diseases.A 48-bp 1 minimal DNA element has been identified as an enhancer that directs chondrocyte-specific expression of the COL2A1 gene in transgenic mice (17)(18)(19). Such an element was also found in the rat COL2A1 gene (20, 21). ...