Activation and dedifferentiation of chondrocytes: implications in cartilage injury and repair

Role of Cartilage Forming Cells in Regenerative Medicine for Cartilage Repair

Currently, cartilage repair remains a major challenge for researchers and physicians due to its limited healing capacity. Cartilage regeneration requires suitable cells; these must be easily obtained and expanded, able to produce hyaline matrix with proper mechanical properties, and demonstrate sustained integration with native tissue. At present, there is a wide variety of possible cell sources for cartilage regeneration; this review explores the diversity of sources for cartilage forming cells and the distinctive characteristics, advantages, limitations, and potential applications of each cell source. We place emphasis on cell sources used for in vitro and clinical studies.

Small hyaluronan oligosaccharides induce inflammation by engaging both toll-like-4 and CD44 receptors in human chondrocytes

Small degradation fragments of hyaluronan (HA) may stimulate an inflammatory response in a variety of tissues at the injury site. HA oligosaccharides are endogenous ligands for the cluster determinant 44 (CD44) receptor as well as for toll-like receptor 4 (TLR-4). Previous data have shown that HA fragments may induce pro-inflammatory cytokine expression by interacting with both the CD44 receptor and TLR-4. CD44 and TLR-4 stimulation activates different inflammatory pathways that culminate with the activation of the transcriptional nuclear factor kappaB (NF-kappaB) which is responsible for the expression of inflammation mediators such as tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-1 beta (IL-1beta). The aim of this study was to investigate the inflammatory effects of very small HA oligosaccharides on both TLR-4 and CD44 involvement in normal human articular chondrocytes. Adding HA fragments to chondrocyte cultures up-regulated CD44 and TLR-4 expression, activated NF-kappaB translocation and increased the pro-inflammatory cytokines TNF-alpha, IL-6 and IL-1beta. The addition of a specific CD44 blocking antibody reduced CD44 and all inflammatory cytokine expression as well as protein production. However, cytokine expression remained significantly higher than in untreated chondrocytes. TLR-4 expression was not affected. The treatment with TLR-4 blocking antibody decreased TLR-4 and inflammatory cytokine expression, although cytokine expression was significantly higher than in control cells. CD44 expression was unaffected. The addition of both CD44 and TLR-4 blocking antibodies significantly reduced CD44, TLR-4 and inflammatory cytokine expression.