Hadzic Ermina, To Bethia, Pest Michael A, Qin Ling, Beier Frank
Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, Western University, ON, Canada.
Department of Physiology and Pharmacology, Collaborative Specialization in Musculoskeletal Health Research, Western University, ON, Canada.
Osteoarthr Cartil Open. 2023 Jul 26;5(3):100387. doi: 10.1016/j.ocarto.2023.100387. eCollection 2023 Sep.
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- (TGF) 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 TGF production in cartilage-specific Mig6 deficient mice, to test whether this would prevent the formation of CONs.
We generated double knockout mice by crossing cartilage-specific and whole-body 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.
Mig-6 deficient mice display cartilage thickening and CONs at 12 weeks in both the elbow and knee joints, which is independent of TGF 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.
The articular cartilage displays increased thickness/cell density and CON formation independent of the presence of TGF, suggesting the anabolic phenotype in the Mig6-deficient mice is independent of TGF/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.
背景/目的：骨关节炎（OA）是一种全关节疾病，目前尚无改善病情的治疗方法。表皮生长因子受体（EGFR）信号通路在软骨/骨发育中起重要作用，其配体转化生长因子-（TGF）在OA中上调。相反，丝裂原诱导基因6（Mig6）是EGFR的负调节因子，软骨特异性Mig-6缺失会对软骨产生合成代谢作用并形成软骨骨结节（CON）。我们旨在通过抑制软骨特异性Mig6缺陷小鼠中TGF的产生来减弱EGFR信号传导，以测试这是否能阻止CON的形成。
我们通过将软骨特异性和全身小鼠杂交来生成双敲除小鼠，以产生实验性和对照野生型小鼠。使用膝关节和肘关节切片来检查关节软骨厚度、细胞密度和破骨细胞的存在情况。此外，完成免疫组织化学以分析磷酸化EGFR和SOX9。
Mig-6缺陷小鼠在12周时在肘关节和膝关节均表现出软骨增厚和CON，这与TGF配体的存在无关。同样，Mig6-cKO/Tgfa-KO和Mig6-cKO小鼠的关节软骨细胞密度增加，但Tgfa-KO小鼠没有，并且显示出SOX9和磷酸化EGFR染色增加。
关节软骨显示出厚度/细胞密度增加和CON形成，与TGF的存在无关，这表明Mig6缺陷小鼠中的合成代谢表型与TGF/EGFR结合无关。合成代谢表型可能是由于替代的EGFR配体激活或其他非EGFR特异性机制。需要更多的研究来阐明负责合成代谢作用的确切途径。
