Background/Purpose: TGF-β signaling plays an important role in chondrocyte differentiation and osteoarthritis (OA) pathogenesis. However TGF-β downstream target genes and signaling mechanism in OA development remains poorly understood. In the present studies, we investigated TGF-β signaling in OA development.
Methods: Tgfbr2 conditional knockout (Tgfbr2Col2ER) mice were generated by breeding Tgfbr2flox/flox mice with Col2-CreER transgenic mice. Deletion of the Tgfbr2 gene was achieved by administration of tamoxifen into 2-week-old Tgfbr2Col2ER mice. Changes in histology, gene expression and pain-related behavior were analyzed. Tgfbr2/Mmp13 and Tgfbr2/Adamts5 double KO mice were generated by breeding Tgfbr2Col2ER mice with Mmp13flox/flox mice and Adamts5-/- mice.
Results: Deletion of the Tgfbr2 gene in articular chondrocytes resulted in up-regulation of Runx2, Atf4, Mmp13, Adamts5 and Col10 expression. Histological analysis showed articular cartilage degradation, increased chondrocyte hypertrophy in superficial zone, early osteophyte formation, and increased subchondral bone mass in 3-month-old Tgfbr2Col2ER mice. Loss of entire articular cartilage, formation of extensive osteophytes, and substantially increased subchondral bone mass were observed in 6-month-old Tgfbr2Col2ER mice. Histomorphometric analysis and evaluation with OARSI scoring system showed a significant decrease in articular cartilage area in Tgfbr2Col2ER mice. Significant reduction in spontaneous rearing activity and ambulation counts were also observed in 4-, 5-, 6-, 7-, and 8-month-old Tgfbr2Col2ER mice. To determine if up-regulation of Mmp13 and Adamts5 expression is responsible for Tgfbr2Col2ER-induced OA development, we generated Tgfbr2/Mmp13 and Tgfbr2/Adamts5 double KO mice. Deletion of the Mmp13 gene significantly alleviates OA-like pathological changes observed in 3- and 6-month-old Tgfbr2Col2ER mice. In contrast, deletion of the Adamts5 gene only reversed OA-like phenotype in 3-month-old Tgfbr2Col2ER mice. These changes were confirmed by histomorphometric analysis and by evaluation with OARSI scoring system. We also investigated the signaling mechanism and found that inhibition of TGF-β signaling prevented Runx2 degradation. Runx2 directly bound to its binding site located in the proximal region of the Mmp13 promoter and activated Mmp13 transcription. ATF4 interacted with Runx2 and enhanced Runx2-induced Mmp13 transcription.
Conclusion: In this study, we demonstrate that inhibition of TGF-β signaling in articular chondrocytes leads to a progressive OA-like phenotype in mice. Mmp13 and Adamts5 are critical downstream target genes of TGF-β signaling during OA development.
Disclosure:
J. Li,
None;
J. Shen,
None;
S. Li,
None;
J. Dickerson,
None;
J. Kroin,
None;
H. J. Im,
None;
D. Chen,
None.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/inhibition-of-tgf-beta-signaling-in-articular-chondrocytes-leads-to-oa-like-pathological-defects-and-pain-related-behavior-change-in-mice/