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.

Type II collagen is composed of ␣1(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 Sp1⅐Sp3. 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-6⅐sIL-6R induced an increase in Sp3 recruitment to the detriment of Sp1. Knockdown of Sp1⅐Sp3 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 Sp1⅐Sp3 complex is involved. Additionally, Sp1 was shown to interact with Sp3 and HDAC1. Indeed, overexpression of a fulllength 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 Sp1⅐Sp3 ratio and DNA-binding activities, thus inhibiting COL2A1 transcription. Extracellular matrix (ECM)6 of articular cartilage contains tissue-specific macromolecules including types II, IX, and XI collagens and the large aggregating proteoglycan (PG) aggrecan (1). Type II collagen is the major collagen synthesized by chondrocytes in mature articular cartilage. Each ␣1(II) procollagen chain of the triple helix is encoded by the COL2A1 gene, whose transcription is regulated by DNA elements within both the promoter and the first intron regions (2). Thus, several binding sites of the intronic enhancer were shown to interact with transcription factors such as Sox9, L-Sox5, and Sox6 (3, 4), required for cartilage-specific expression of type II collagen during chondrogenesis in vivo (5), as well as with zinc finger transcription factors Sp1, Sp3, and C-Krox (6, 7). The three latter proteins are also able to bind to several binding sites identified in a 266-bp promoter of the human COL2A1 gene (6 -8). Sp1 was shown to be a strong activator of COL2A1 gene expression via the promoter binding sites, whereas Sp3 was found to prevent the Sp1 up-regulation of the COL2A1 promoter activity by binding to the same cis-acting elements (7).In healthy cartilage, chondrocytes maintain steady-state expression of collagens and PGs and are sensitive to a number of growth factors and cytokines that either enhance or reduce type II collagen synthesis. In osteoarthritis and rheumatoid arthritis, structural...

In osteoarthritis (OA), interleukin-1 (IL-1) stimulates the expression of metalloproteinases and aggrecanases, which induce cartilage degradation. IL-1 is also capable of reducing the production of cartilage-specific macromolecules, including type II collagen, through modulation of the transcription factors Sp1 and Sp3. Conversely, Transforming growth factor-beta (TGF-beta) counteracts with most of the IL-1 deleterious effects and contributes to cartilage homeostasis. However, OA chondrocytes progressively loose the expression of TGF-beta type II receptor and become insensitive to the factor. This downregulation is also driven by IL-1. This review provides insights into the molecular mechanisms that underly the interplay between IL-1 and TGF-beta in OA cartilage metabolism and enlightens the central role of Sp1 and Sp3 transcription factors in the matrix pathological alterations.

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