Interleukin‐1β up‐regulation of Smad7 via NF‐κB activation in human chondrocytes

Abstract

Objective. We have previously shown that interleukin-1␤ (IL-1␤) impairs transforming growth factor ␤ (TGF␤) signaling through TGF␤ receptor type II (TGF␤RII) down-regulation and Smad7 upregulation. This mechanism could account for the reduced responsiveness of osteoarthritic chondrocytes to TGF␤ and the cartilage breakdown linked to this disease. The aim of this study was to investigate the molecular mechanism underlying the IL-1␤-induced stimulation of Smad7 in human articular chondrocytes.Methods. Human articular chondrocytes were treated with IL-1␤ in the presence of TGF␤1, pyrrolidine dithiocarbamate (a repressor of the NF-B pathway), or cycloheximide. Then, steady-state messenger RNA and protein levels were estimated by real-time reverse transcription-polymerase chain reaction and immunocytology. In addition, transient transfections of p65 expression vector or p65-targeted short hairpin RNA were performed to define the effect of NF-B on Smad7 expression.Results. TGF␤RII overexpression restored the TGF␤ response of human articular chondrocytes. However, this effect was transient, implying that a secondary mechanism was responsible for the alteration of the TGF␤ response with long-term exposure to IL-1␤. Moreover, IL-1␤ caused a late induction of the inhibitory Smad7. This effect was direct, since it did not require de novo synthesis. In addition, we established, by experiments with gain/loss of function, that the up-regulation of Smad7 by IL-1␤ is mediated through the NF-B pathway, especially the p65 subunit.Conclusion. These findings clarify the regulatory process of IL-1␤ on Smad7 expression. Understanding the molecular basis of IL-1␤ induction of Smad7 and the reduction of chondrocyte responsiveness to TGF␤ provides new insights into the molecular mechanisms of osteoarthritis and may facilitate the identification of novel approaches for its treatment.

Identification of microRNA-181a-5p and microRNA-4454 as mediators of facet cartilage degeneration

“…Furthermore, IL-1β-mediated elevation in the expression of ZNF440 was suppressed in the presence of miR-181a-5p or miR-4454 inhibitors, suggesting a crucial role of ZNF440 in miR-181a-5p or miR-4454 signaling in FJ OA chondrocytes. IL-1β has been previously shown to activate NF-κB in human OA chondrocytes (25,26). Previous studies have also reported links between miR-181 and miR-4454 and NF-κB signaling in other cells and tissues.…”

MicroRNA-182 targets SMAD7 to potentiate TGFβ-induced epithelial-mesenchymal transition and metastasis of cancer cells

“…While SMAD7 is known to be transcriptionally regulated by TGFβ and NFκB pathways294849, recent studies have reported that post-transcriptional regulation, such as protein acetylation and ubiquitination, plays key roles to control its protein level5051. Accumulating evidence has also shown the involvement of miRNAs, including miR-21, miR-106-25 and miR-216a/217, in the regulation of SMAD7 (refs 52, 53, 54).…”

Roles of inflammatory and anabolic cytokines in cartilage metabolism: signals and multiple effectors converge upon MMP-13 regulation in osteoarthritis

“…However, increased anabolic activity in OA cartilage has been observed and may be associated with cytokine-induced synthesis of prostaglandin E 2 (PGE 2 ), which feedback-regulates COL2A1 transcription in a positive manner (Goldring et al ., 1994; Miyamoto et al , 2003), or BMP-2 (Fukui et al , 2003; Sandell, 2007), which would, in turn, activate COL2A1 transcription and permit subsequent inhibition by cytokine-induced factors (Okazaki et al ., 2002; Tan et al , 2003). IL-1β differentially regulates inhibitory Smads, transcriptional mediators of TGF-β and BMP signaling, up-regulating Smad7 and down-regulating Smad6 in chondrocytes (Bauge et al , 2008). However, the cytoplasmic localization of these inhibitors in normal and OA cartilage does not correlate with down-regulation of anabolic genes (Kaiser et al , 2004).…”