Division of Cardiovascular Surgery, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA.
Cardiovasc Res. 2013 Jul 1;99(1):175-84. doi: 10.1093/cvr/cvt083. Epub 2013 Apr 3.
Myxomatous mitral valve disease (MMVD) is associated with leaflet thickening, fibrosis, matrix remodelling, and leaflet prolapse. Molecular mechanisms contributing to MMVD, however, remain poorly understood. We tested the hypothesis that increased transforming growth factor-β (TGF-β) signalling and reactive oxygen species (ROS) are major contributors to pro-fibrotic gene expression in human and mouse mitral valves.
Using qRT-PCR, we found that increased expression of TGF-β1 in mitral valves from humans with MMVD (n = 24) was associated with increased expression of connective tissue growth factor (CTGF) and matrix metalloproteinase 2 (MMP2). Increased levels of phospho-SMAD2/3 (western blotting) and expression of SMAD-specific E3 ubiquitin-protein ligases (SMURF) 1 and 2 (qRT-PCR) suggested that TGF-β1 signalling occurred through canonical signalling cascades. Oxidative stress (dihydroethidium staining) was increased in human MMVD tissue and associated with increases in NAD(P)H oxidase catalytic subunits (Nox) 2 and 4, occurring despite increases in superoxide dismutase 1 (SOD1). In mitral valves from SOD1-deficient mice, expression of CTGF, MMP2, Nox2, and Nox4 was significantly increased, suggesting that ROS can independently activate pro-fibrotic and matrix remodelling gene expression patterns. Furthermore, treatment of mouse mitral valve interstitial cells with cell permeable antioxidants attenuated TGF-β1-induced pro-fibrotic and matrix remodelling gene expression in vitro.
Activation of canonical TGF-β signalling is a major contributor to fibrosis and matrix remodelling in MMVD, and is amplified by increases in oxidative stress. Treatments aimed at reducing TGF-β activation and oxidative stress in early MMVD may slow progression of MMVD.
黏液样心肌二尖瓣病（MMVD）与瓣叶增厚、纤维化、基质重塑和瓣叶脱垂有关。然而，导致 MMVD 的分子机制仍知之甚少。我们检验了以下假设，即转化生长因子-β（TGF-β）信号和活性氧（ROS）的增加是导致人类和小鼠二尖瓣纤维化基因表达的主要因素。
使用 qRT-PCR，我们发现 MMVD 患者二尖瓣中 TGF-β1 的表达增加与结缔组织生长因子（CTGF）和基质金属蛋白酶 2（MMP2）的表达增加相关。磷酸化 SMAD2/3（western blot）水平升高和 SMAD 特异性 E3 泛素蛋白连接酶（SMURF）1 和 2（qRT-PCR）的表达表明 TGF-β1 信号通过经典信号级联发生。人类 MMVD 组织中的氧化应激（二氢乙啶染色）增加，并与 NAD（P）H 氧化酶催化亚基（Nox）2 和 4 的增加相关，尽管超氧化物歧化酶 1（SOD1）增加。在 SOD1 缺陷型小鼠的二尖瓣中，CTGF、MMP2、Nox2 和 Nox4 的表达显著增加，表明 ROS 可以独立激活致纤维化和基质重塑基因表达模式。此外，用细胞通透性抗氧化剂处理小鼠二尖瓣间质细胞可减弱 TGF-β1 诱导的体外致纤维化和基质重塑基因表达。
经典 TGF-β 信号的激活是 MMVD 纤维化和基质重塑的主要原因，并且通过氧化应激的增加而放大。在 MMVD 早期，旨在减少 TGF-β 激活和氧化应激的治疗方法可能会减缓 MMVD 的进展。
