Division of Plastic Surgery, Department of Surgery, McGill University, Montreal, Quebec, Canada.
Osteoarthritis Cartilage. 2010 Nov;18(11):1518-27. doi: 10.1016/j.joca.2010.09.002. Epub 2010 Sep 15.
Transforming growth factor-β (TGF-β) plays a critical role in cartilage homeostasis and deregulation of its signalling is implicated in osteoarthritis (OA). TGF-β isoforms signal through a pair of transmembrane serine/threonine kinases known as the type I and type II TGF-β receptors. Endoglin is a TGF-β co-receptor that binds TGF-β with high affinity in the presence of the type II TGF-β receptor. We have previously shown that endoglin is expressed in human chondrocytes and that it forms a complex with the TGF-β signalling receptors. However, the functional significance of endoglin expression in chondrocytes is unknown. Our objective was to determine whether endoglin regulates TGF-β/Smad signalling and extracellular matrix (ECM) production in human chondrocytes and whether its expression varies with chondrocyte differentiation state.
Endoglin function was determined by overexpression or antisense morpholino/siRNA knockdown of endoglin in human chondrocytes and measuring TGF-β-induced Smad phosphorylation, transcriptional activity and ECM production. Alterations in endoglin expression levels were determined during subculture-induced dedifferentiation of human chondrocytes and in normal vs OA cartilage samples.
Endoglin enhances TGF-β1-induced Smad1/5 phosphorylation and inhibits TGF-β1-induced Smad2 phosphorylation, Smad3-driven transcriptional activity and ECM production in human chondrocytes. In addition, the enhancing effect of endoglin siRNA knockdown on TGF-β1-induced Smad3-driven transcription is reversed by ALK1 overexpression. Furthermore, endoglin levels are increased in chondrocytes following subculture-induced dedifferentiation and in OA cartilage as compared to normal cartilage.
Together, our results suggest that endoglin regulates the balance between TGF-β/ALK1/Smad1/5 and ALK5/Smad2/3 signalling and ECM production in human chondrocytes and that endoglin may represent a marker for chondrocyte phenotype.
转化生长因子-β（TGF-β）在软骨稳态中起着关键作用，其信号转导失调与骨关节炎（OA）有关。TGF-β 同工型通过一对称为 I 型和 II 型 TGF-β 受体的跨膜丝氨酸/苏氨酸激酶信号转导。内皮糖蛋白是 TGF-β 的共受体，在 II 型 TGF-β 受体存在的情况下与 TGF-β 结合具有高亲和力。我们之前已经表明，内皮糖蛋白在人软骨细胞中表达，并且它与 TGF-β 信号转导受体形成复合物。然而，内皮糖蛋白在软骨细胞中的表达的功能意义尚不清楚。我们的目的是确定内皮糖蛋白是否调节人软骨细胞中的 TGF-β/Smad 信号转导和细胞外基质（ECM）的产生，以及其表达是否随软骨细胞分化状态而变化。
通过人软骨细胞中内皮糖蛋白的过表达或反义 morpholino/siRNA 敲低来确定内皮糖蛋白的功能，并测量 TGF-β 诱导的 Smad 磷酸化、转录活性和 ECM 产生。在人软骨细胞的亚培养诱导去分化过程中和在正常与 OA 软骨样本中，确定内皮糖蛋白表达水平的变化。
内皮糖蛋白增强 TGF-β1 诱导的 Smad1/5 磷酸化，并抑制 TGF-β1 诱导的 Smad2 磷酸化、Smad3 驱动的转录活性和 ECM 的产生。此外，内皮糖蛋白 siRNA 敲低对 TGF-β1 诱导的 Smad3 驱动的转录的增强作用可被 ALK1 的过表达逆转。此外，与正常软骨相比，在内皮糖蛋白在软骨细胞中在亚培养诱导去分化后和在 OA 软骨中增加。
总之，我们的结果表明，内皮糖蛋白调节人软骨细胞中 TGF-β/ALK1/Smad1/5 和 ALK5/Smad2/3 信号转导和 ECM 产生之间的平衡，并且内皮糖蛋白可能代表软骨细胞表型的标志物。
