Aberrant hypertrophy in Smad3‐deficient murine chondrocytes is rescued by restoring transforming growth factor β–activated kinase 1/activating transcription factor 2 signaling: A potential clinical implication for osteoarthritis

Abstract

Objective. To investigate the biologic significance of Smad3 in the progression of osteoarthritis (OA), the crosstalk between Smad3 and activating transcription factor 2 (ATF-2) in the transforming growth factor ␤ (TGF␤) signaling pathway, and the effects of ATF-2 overexpression and p38 activation in chondrocyte differentiation.Methods. Joint disease in Smad3-knockout (Smad3 Ϫ/Ϫ ) mice was examined by microfocal computed tomography and histologic analysis. Numerous in vitro methods including immunostaining, real-time polymerase chain reaction, Western blotting, an ATF-2 DNAbinding assay, and a p38 kinase activity assay were used to study the various signaling responses and protein interactions underlying the altered chondrocyte phenotype in Smad3 Ϫ/Ϫ mice. Osteoarthritis (OA) is a chronic joint disease characterized by progressive degenerative changes in the composition, structure, and function of articular tissues. OA primarily affects articular cartilage, although pathologic changes are also observed in the synovial mem- Results. In Smad3

TGF-β regulates phosphorylation and stabilization of Sox9 protein in chondrocytes through p38 and Smad dependent mechanisms

“…Evidence of cross talk between Smads and p38 has been controversial, some studies previously demonstrated that loss of p38 activity decreased Smad2/3 nuclear localization in the presence of TGF-β50, and knockout of Smad3 showed decreased phosphorylation of p38 by TGF-β49. While other studies have shown that inhibition of p38 was not required to phosphorylate Smad251, and over-expression of dominant negative Smad3 did not inhibit TGF-β mediated activation of p3852.…”

“…4A,B) suggesting that, in addition to p38, Smads are also required for TGF-β to up-regulate Sox9 protein levels. Smad2/3 signaling plays an important role in cartilage development and homeostasis, and loss of Smad3 leads to loss of cartilage proteoglycans and an increase in hypertrophic differentiation of chondrocytes4849. Specifically how Smad2/3 functions to stabilize Sox9 protein is not known.…”

SnoN Suppresses Maturation of Chondrocytes by Mediating Signal Cross-talk between Transforming Growth Factor-β and Bone Morphogenetic Protein Pathways

“…Endogenous TGF-␤ Signaling Is Activated in Maturing Chondrocytes to Induce SnoN-Although the importance of TGF-␤ signaling in preventing hypertrophic conversion of chondrocytes has been demonstrated (23,24,47), the mode of TGF-␤ signaling during chondrocyte maturation and its direct target gene(s) responsible for inhibiting the differentiation remain largely unknown. While exogenously applied TGF-␤ has been reported to have a positive role in early chondrogenesis in vitro, SB431542 showed no effect on bone growth, whereas it dramatically enhanced the matrix calcification by the mature hypertrophic chondrocytes in a bone organ culture system (Fig.…”

The Transient Receptor Potential Channel, Vanilloid 5, Induces Chondrocyte Apoptosis via Ca2+ CaMKII–Dependent MAPK and Akt/ mTOR Pathways in a Rat Osteoarthritis Model

“…We speculate both p-JNK2 and p-JNK1 are critical to the phosphorylation of c-Jun. Four isoforms of p38 (-α, -β, -γ, and -δ) have been identified in chondrocytes in OA [35]. In this study, an antibody to phospho-p38 (Thr180/Tyr182; Cat.…”