Anabolic phenotype in cartilage-specific mitogen-inducible gene-6 knockout mice is independent of transforming growth factor-α

Ermina Hadzic; Bethia To; Michael A Pest; Ling Qin; Frank Beier

doi:10.1016/j.ocarto.2023.100387

Anabolic phenotype in cartilage-specific mitogen-inducible gene-6 knockout mice is independent of transforming growth factor-α

Osteoarthr Cartil Open. 2023 Jul 26;5(3):100387. doi: 10.1016/j.ocarto.2023.100387. eCollection 2023 Sep.

Authors

Ermina Hadzic^{1

2

3}, Bethia To¹, Michael A Pest¹, Ling Qin⁴, Frank Beier^{1

3}

Affiliations

¹ Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, Western University, ON, Canada.
² Department of Physiology and Pharmacology, Collaborative Specialization in Musculoskeletal Health Research, Western University, ON, Canada.
³ Bone and Joint Institute, Western University, ON, Canada.
⁴ Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, PA, USA.

Abstract

Background/objective: Osteoarthritis (OA) is a whole joint disorder with no disease modifying treatment currently available. The Epidermal Growth Factor Receptor (EGFR) signaling pathway plays an important role in cartilage/bone development and its ligand transforming growth factor-α (TGFα) is upregulated in OA. In contrast, Mitogen-inducible gene 6 (Mig6) is a negative regulator of EGFR, and cartilage-specific Mig-6 deletion results in anabolic effects on cartilage and formation of chondro-osseus nodules (CON). We aimed to attenuate EGFR signaling by inhibiting TGFα production in cartilage-specific Mig6 deficient mice, to test whether this would prevent the formation of CONs.

Methods: We generated double knockout mice by crossing cartilage-specific Mig-6^fl/flCol2a1-Cre^+/- and whole-body Tgfa^± mice to generate experimental and control wild-type mice. Knee and elbow sections were used to examine articular cartilage thickness, cell density, and osteoclast presence. Additionally, immunohistochemistry was completed to analyze phospho-EGFR and SOX9.

Results: Mig-6 deficient mice display cartilage thickening and CONs at 12 weeks in both the elbow and knee joints, which is independent of TGFα ligand presence. Similarly, articular cartilage cell density is increased in Mig6-cKO/Tgfa-KO and Mig6-cKOmice, but not Tgfa-KO mice, and displays increased SOX9 and phospho-EGFR staining.

Conclusion: The articular cartilage displays increased thickness/cell density and CON formation independent of the presence of TGFα, suggesting the anabolic phenotype in the Mig6-deficient mice is independent of TGFα/EGFR binding. The anabolic phenotype may be due to an alternative EGFR ligand activation, or other non-EGFR specific mechanism. More research is required to elucidate the exact pathway responsible for the anabolic effects.

Keywords: Animal model; Chondrocyte; Epidermal growth factor receptor; Mitogen inducible gene 6; Transforming growth factor-alpha; Transgenic mice.

Abstract

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