EGFR signaling in growth plate development

描述（由申请人提供）：生长板的发育对纵向骨生长至关重要。这个过程包括软骨细胞增殖、成熟和肥大、矿化、基质重塑和从软骨到骨的转变，是由循环的全身激素和局部产生的生长因子严格控制的。然而，调控机制尚未完全阐明。以往的研究注意到表皮生长因子受体（EGFR）活性的改变导致生长板结构异常，但其具体的分子机制尚未研究。我们最近发现，用egfr特异性抑制剂治疗的幼龄生长大鼠生长板软骨出现了严重缺陷，其特征是骺生长板增厚和大量肥大软骨细胞积聚。进一步研究表明，EGFR抑制剂抑制基质金属蛋白酶（MMP9和13）的表达，增加胶原原纤维的数量，降低生长板软骨ECM降解。与此一致，EGFR配体TGF¿强烈刺激原代软骨细胞中MMP9和13的表达。因此，我们假设EGFR信号通过促进生长板中MMP的表达来调节ECM降解和增生性软骨骨置换。我们提出以下目标来验证这一假设：1)确定软骨降解和生长板发育是否需要软骨生成的EGFR信号传导；2)研究EGFR信号传导刺激MMP9和13软骨生成表达的分子机制。特别是，我们将利用药理学大鼠模型、软骨细胞特异性EGFR敲除小鼠模型和原代软骨细胞培养来检查生长板表型并分析其潜在机制。我们的长期目标是研究EGFR信号在软骨功能中的作用。该项目的研究结果将表明，EGFR信号是调节软骨内成骨的新途径，也是治疗软骨退化异常的骨骼疾病（包括儿童生长板疾病和骨关节炎）的潜在药物靶点。此外，作为一名新的研究者，我将受益匪浅

DESCRIPTION (provided by applicant): Growth plate development is critical for longitudinal bone growth. This process, including chondrocyte proliferation, maturation and hypertrophy, mineralization, matrix remodeling and transition from cartilage to bone, is tightly controlled by circulating systemic hormones and locally produced growth factors. However, the regulatory mechanisms have not been fully elucidated. Previous studies noticed that altering epidermal growth factor receptor (EGFR) activity resulted in abnormal growth plate structures but the detailed molecular mechanisms have not been studied yet. We recently found that young growing rats treated with EGFR-specific inhibitors developed profound defects in growth plate cartilage characterized by epiphyseal growth plate thickening and massive accumulation of hypertrophic chondrocytes. Further studies demonstrate that EGFR inhibitors suppressed the expression of matrix metalloproteinases (MMP9 and 13), increased the amount of collagen fibrils, and decreased cartilage ECM degradation in the growth plate. Consistently, TGF¿, an EGFR ligand, strongly stimulated the expression of MMP9 and 13 in primary chondrocytes. Hence, we hypothesize that EGFR signaling regulates ECM degradation and replacement of hypertrophic cartilage with bone by promoting MMP expression in the growth plate. We propose the following aims to test this hypothesis: 1) determine whether chondrogenic EGFR signaling is required for cartilage degradation and growth plate development~ 2) investigate the molecular mechanisms by which EGFR signaling stimulates chondrogenic expression of MMP9 and 13. In particular, we will utilize a pharmacological rat model, a chondrocyte-specific EGFR knockout mouse model, and primary chondrocyte cultures to examine the growth plate phenotypes and analyze the underlying mechanisms. Our long-term goal is to study the role of EGFR signaling in cartilage function. Findings from this project will suggest EGFR signaling as a novel pathway regulating endochondral ossification and a potential pharmaceutical target for skeletal disorders that have abnormal cartilage degradation, including childhood growth plate disorders and osteoarthritis. In addition, as a new investigator, I will be greatly benefited from this award by generating preliminary data to be used for competing future research supports.