IRF2BP2-FOSL2 interaction regulates SOX9-mediated cartilage regeneration in osteoarthritis models
Hao Zhou, Tiantian Lu, Zhuoqun Gao, Can Cui, Zhiqiang Fang, Yu You, Jing Jiang, Jinjin Xu, Fang Wei, Jing Yu, Hu Zhou, Jinsong Li, Jian Luo, Lei Zhang, Yunyun Jin
Hao Zhou, Tiantian Lu, Zhuoqun Gao, Can Cui, Zhiqiang Fang, Yu You, Jing Jiang, Jinjin Xu, Fang Wei, Jing Yu, Hu Zhou, Jinsong Li, Jian Luo, Lei Zhang, Yunyun Jin
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Research Article Bone biology Cell biology

IRF2BP2-FOSL2 interaction regulates SOX9-mediated cartilage regeneration in osteoarthritis models

Abstract

Osteoarthritis (OA) is the most common degenerative joint disease. However, the molecular mechanisms underlying OA-induced cartilage degeneration remain elusive. Here, we identify IFN regulatory factor 2 binding protein 2 (IRF2BP2) as an important regulator of chondrocyte differentiation and articular cartilage regeneration. Irf2bp2 deficiency promoted chondrogenesis and inhibited chondrocyte terminal differentiation by transcriptionally upregulating the key chondrogenic marker SRY-box transcription factor 9 (SOX9), inducing its ectopic expression in the hypertrophic zone. Cartilage-specific KO of Irf2bp2 elevated SOX9 levels, attenuated OA progression in the destabilization of the medial meniscus (DMM) model, and enhanced cartilage regeneration and hyalinization in the microfracture model. Mechanistically, IRF2BP2 bound to and stabilized Fos-related antigen 2 (FOSL2), an activator protein 1 (AP-1) family member, thereby facilitating FOSL2/c-Jun complex formation and repressing SOX9 expression. Adeno-associated virus–mediated (AAV-mediated) FOSL2 overexpression reversed the protective phenotype observed in Irf2bp2-deficient mice. These findings establish the Hippo/IRF2BP2/FOSL2/SOX9 regulatory axis as critical for cartilage regeneration. Importantly, AAV-mediated IRF2BP2 knockdown, pharmacological targeting of the IRF2BP2/AP-1 axis using T-5224, and delivery of a peptide that disrupts IRF2BP2-FOSL2 binding via intra-articular injection all preserved cartilage integrity, offering potential therapeutic strategies for OA and cartilage regeneration.

Authors

Hao Zhou, Tiantian Lu, Zhuoqun Gao, Can Cui, Zhiqiang Fang, Yu You, Jing Jiang, Jinjin Xu, Fang Wei, Jing Yu, Hu Zhou, Jinsong Li, Jian Luo, Lei Zhang, Yunyun Jin

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Figure 1

Irf2bp2 deficiency leads to abnormal bone development and promotes SOX9 expression in cartilage.

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Irf2bp2 deficiency leads to abnormal bone development and promotes SOX9...
(A) Whole-mount skeletal staining with alizarin red and Alcian blue of WT and Irf2bp2–/– mice at P1. Scale bar: 5 mm. (B) Quantification of body length in A (n = 6). (C) Limb and sternum staining at P1. Scale bars: 1 mm and 2 mm. (D) SO staining of femurs at P1. Scale bar: 500 μm. (E) Quantification of the femur lengths in D (n = 8). (F) Alcian blue staining of primary articular chondrocytes from WT and Irf2bp2–/– newborn mice after 14 or 21 days of chondrogenic culturing. (G) Quantification of the Alcian blue staining in F (n = 9). (H) qRT-PCR analysis of Irf2bp2, Sox9, Col2a1, Mmp3, and Mmp13 mRNA levels in primary articular chondrocytes from WT and Irf2bp2–/– mice. (I) IF staining for HA in knee joints from WT and HA-Irf2bp2 mice at P1 and 12 weeks. Scale bars: 100 μm. (J) IF staining for SOX9 and Ki67 in WT and Irf2bp2–/– mice at P1. Scale bars: 100 μm. Original magnification, ×10. (K) Quantification of SOX9 and Ki67 in J (n = 4). (L) Representative view of 20-week-old Irf2bp2fl/fl and Irf2bp2Acan mice. (M) Quantification of body lengths in L (n = 8). (N) IF staining for SOX9 and Ki67 in Irf2bp2fl/fl and Irf2bp2Acan mice at 4 weeks. Scale bars: 100 μm. Original magnification, ×10. (O) Quantification of SOX9 and Ki67 in N (n = 4). In B, E, G, H, K, M, and O, data are shown as the mean ± SD. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001, by 2-tailed, unpaired Student’s t test (B, E, H, K, M, and O) and 1-way ANOVA, followed by Tukey’s multiple-comparison test (G). In I and J, dotted and curved lines indicate the surface of articular cartilage. Color bars denote skeletal zones: red indicates hypertrophic chondrocytes; blue indicates proliferative and prehypertrophic chondrocytes; and green indicates resting chondrocytes.