Lauzier Annie, Charbonneau Martine, Paquette Marilène, Harper Kelly, Dubois Claire M
Arthritis Res Ther. 2012 Jul 4;14(4):R159. doi: 10.1186/ar3899.
The microenvironment surrounding inflamed synovium leads to the activation of fibroblast-like synoviocytes (FLSs), which are important contributors to cartilage destruction in rheumatoid arthritic (RA) joints. Transglutaminase 2 (TG2), an enzyme involved in extracellular matrix (ECM) cross-linking and remodeling, is activated by inflammatory signals. This study was undertaken to assess the potential contribution of TG2 to FLS-induced cartilage degradation.
Transglutaminase (TGase) activity and collagen degradation were assessed with the immunohistochemistry of control, collagen-induced arthritic (CIA) or TG2 knockdown (shRNA)-treated joint tissues. TGase activity in control (C-FLS) and arthritic (A-FLS) rat FLSs was measured by in situ 5-(biotinamido)-pentylamine incorporation. Invadopodia formation and functions were measured in rat FLSs and cells from normal (control; C-FLS) and RA patients (RA-FLS) by in situ ECM degradation. Immunoblotting, enzyme-linked immunosorbent assay (ELISA), and p3TP-Lux reporter assays were used to assess transforming growth factor-β (TGF-β) production and activation.
TG2 and TGase activity were associated with cartilage degradation in CIA joints. In contrast, TGase activity and cartilage degradation were reduced in joints by TG2 knockdown. A-FLSs displayed higher TGase activity and TG2 expression in ECM than did C-FLSs. TG2 knockdown or TGase inhibition resulted in reduced invadopodia formation in rat and human arthritic FLSs. In contrast, increased invadopodia formation was noted in response to TGase activity induced by TGF-β, dithiothreitol (DTT), or TG2 overexpression. TG2-induced increases in invadopodia formation were blocked by TGF-β neutralization or inhibition of TGF-βR1.
TG2, through its TGase activity, is required for ECM degradation in arthritic FLS and CIA joints. Our findings provide a potential target to prevent cartilage degradation in RA.
炎症滑膜周围的微环境会导致成纤维样滑膜细胞（FLS）活化，而FLS是类风湿性关节炎（RA）关节软骨破坏的重要促成因素。转谷氨酰胺酶2（TG2）是一种参与细胞外基质（ECM）交联和重塑的酶，可被炎症信号激活。本研究旨在评估TG2对FLS诱导的软骨降解的潜在作用。
通过对对照、胶原诱导性关节炎（CIA）或TG2基因敲低（shRNA）处理的关节组织进行免疫组织化学，评估转谷氨酰胺酶（TGase）活性和胶原降解情况。通过原位5-（生物素酰胺基）-戊胺掺入法测定对照（C-FLS）和关节炎（A-FLS）大鼠FLS中的TGase活性。通过原位ECM降解法测定大鼠FLS以及来自正常（对照；C-FLS）和RA患者（RA-FLS）的细胞中的侵袭伪足形成和功能。采用免疫印迹法、酶联免疫吸附测定（ELISA）和p3TP-Lux报告基因测定法评估转化生长因子-β（TGF-β）的产生和活化情况。
TG2和TGase活性与CIA关节中的软骨降解相关。相比之下，TG2基因敲低可降低关节中的TGase活性和软骨降解。A-FLS在ECM中的TGase活性和TG2表达高于C-FLS。TG2基因敲低或TGase抑制可导致大鼠和人关节炎FLS中的侵袭伪足形成减少。相反，在TGF-β、二硫苏糖醇（DTT）或TG2过表达诱导的TGase活性作用下，侵袭伪足形成增加。TGF-β中和或TGF-βR1抑制可阻断TG2诱导的侵袭伪足形成增加。
TG2通过其TGase活性，是关节炎FLS和CIA关节中ECM降解所必需的。我们的研究结果为预防RA中的软骨降解提供了一个潜在靶点。
