Aberrant Hypertrophy in Smad3-Deficient Murine Chondrocytes Is Rescued by Restoring Transforming Growth Factor β-Activated Kinase 1/Activating Transcription Factor 2 Signaling

作者：Li, Tian-Fang; Gao, Lin; Sheu, Tzong-Jen; Sampson, Erik R.; Flick, Lisa M.; Konttinen, Yrjo T.; Chen, Di; Schwarz, Edward M.; Zuscik, Michael J.; Jonason, Jennifer H.; O'Keefe, Regis J.^*

来源：Arthritis and Rheumatism, 2010, 62(8): 2359-2369.

DOI：10.1002/art.27537

• P38 MAP KINASE
• TGF-BETA
• GENE-EXPRESSION
• MATRIX METALLOPROTEINASE-13
• OSTEOARTHRITIC CARTILAGE
• RHEUMATOID-ARTHRITIS
• ARTICULAR-CARTILAGE
• DIFFERENTIATION
• MICE
• SMAD

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 beta (TGF beta) signaling pathway, and the effects of ATF-2 overexpression and p38 activation in chondrocyte differentiation. @@@ Methods. Joint disease in Smad3-knockout (Smad3(-/-)) 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 DNA-binding 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(-/-) mice. @@@ Results. In Smad3(-/-) mice, an end-stage OA phenotype gradually developed. TGF beta-activated kinase 1 (TAK1)/ATF-2 signaling was disrupted in Smad3(-/-) mouse chondrocytes at the level of p38 MAP kinase (MAPK) activation, resulting in reduced ATF-2 phosphorylation and transcriptional activity. Reintroduction of Smad3 into Smad3(-/-) cells restored the normal p38 response to TGF beta. Phosphorylated p38 formed a complex with Smad3 by binding to a portion of Smad3 containing both the MAD homology 1 and linker domains. Additionally, Smad3 inhibited the dephosphorylation of p38 by MAPK phosphatase 1 (MKP-1). Both ATF-2 overexpression and p38 activation repressed type X collagen expression in wild-type and Smad3(-/-) chondrocytes. P38 was detected in articular cartilage and perichondrium; articular and sternal chondrocytes expressed p38 isoforms alpha, beta, and gamma, but not delta. @@@ Conclusion. Smad3 is involved in both the onset and progression of OA. Loss of Smad3 abrogates TAK1/ATF-2 signaling, most likely by disrupting the Smad3-phosphorylated p38 complex, thereby promoting p38 dephosphorylation and inactivation by MKP-1. ATF-2 and p38 activation inhibit chondrocyte hypertrophy. Modulation of p38 isoform activity may provide a new therapeutic approach for OA.

• 出版日期2010-8