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German Congress of Orthopaedics and Traumatology (DKOU 2022)

25. - 28.10.2022, Berlin

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Nrf2/ARE signaling modulates Sox9 expression during cartilage degeneration

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  • presenting/speaker Yusuke Kubo - Anatomy and Cell Biology, RWTH Aachen University, Aachen, Germany
  • Rainer Beckmann - Anatomy and Cell Biology, RWTH Aachen University, Aachen, Germany
  • Athanassios Fragoulis - Anatomy and Cell Biology, RWTH Aachen University, Aachen, Germany
  • Claudius Conrads - Anatomy and Cell Biology, RWTH Aachen University, Aachen, Germany
  • Prathyusha Pavanram - Anatomy and Cell Biology, RWTH Aachen University, Aachen, Germany
  • Sven Nebelung - Diagnostic and Interventional Radiology, RWTH Aachen, Aachen, Germany
  • Michael Wolf - Orthodontics, Uniklinik RWTH Aachen, Aachen, Germany
  • Christoph Jan Wruck - Anatomy and Cell Biology, RWTH Aachen University, Aachen, Germany
  • Holger Jahr - Anatomy and Cell Biology, RWTH Aachen University, Aachen, Germany; Orthopaedic Surgery, Maastricht University Medical Center+, Maastricht, The Netherlands
  • Thomas Pufe - Anatomy and Cell Biology, RWTH Aachen University, Aachen, Germany

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2022). Berlin, 25.-28.10.2022. Düsseldorf: German Medical Science GMS Publishing House; 2022. DocAB20-901

doi: 10.3205/22dkou086, urn:nbn:de:0183-22dkou0860

Published: October 25, 2022

© 2022 Kubo et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at http://creativecommons.org/licenses/by/4.0/.

Outline

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Objectives: Oxidative stress has been implicated in the pathogenesis of osteoarthritis, and the Nuclear factor erythroid 2-related factor 2 (Nrf2)/ antioxidant response element (ARE) pathway is key in maintaining redox homeostasis. We thus investigated whether Nrf2/ARE signaling controls SOX9, an important factor regulating chondrogenic differentiation and hyaline cartilage degeneration in osteoarthritis.

Methods: SOX9 expression in human C-28/I2 chondrocytes was measured by RT-qPCR after shRNA-mediated knockdown of Nrf2 or its antagonist the Kelch-like erythroid cell-derived protein with cap ''n'' collar homology-associated protein 1 (Keap1). Putative ARE-binding sites in the proximal SOX9 promoter region were inactivated, subsequently cloned into pGL3, and then co-transfected with phRL-TK for dual-luciferase assays to verify whether Nrf2 transcriptionally regulates SOX9. Then, SOX9 promoter activities without and with Nrf2-inducer methysticin were compared. Sox9 expression in articular chondrocytes was correlated to cartilage thickness and degeneration in wild-type (WT) and Nrf2-knockout mice. Data were analyzed by one-way ANOVA, a Student's t-test, or Wilcoxon rank-sum test, according to the normal distribution. Statistical significance was set to p < 0.05.

Results and conclusion: Nrf2-specific RNAi significantly decreased SOX9 expression, whereas Keap1-specific RNAi increased it. Putative ARE sites (ARE1, ARE2) were identified in the SOX9 promoter region. ARE2 mutagenesis significantly reduced SOX9 promoter activity, but ARE1 excision did not. Functional ARE2 site was essential for methysticin-mediated induction of SOX9 promoter activity. Young Nrf2-knockout mice revealed significantly fewer Sox9-positive chondrocytes, while old Nrf2-knockout animals showed thinner cartilage and more severe cartilage degeneration.

These results suggest that Nrf2 directly regulates SOX9 expression in articular cartilage and that pharmacological Nrf2 induction may hold potential to diminish age-dependent cartilage degeneration in the knee through improving protective SOX9 expression.