Supporting data for Matrix metalloproteinase 7 deficiency acts as a protective effect against vascular dysfunction during atherosclerosis

Atherosclerosis is a chronic inflammatory condition characterized by plaque buildup in the arterial lumen and is the underlying cause of cardiovascular disorders such as coronary artery disease (CAD) and stroke (Hurtutise, Jessica et al 2006). The pathogenesis of atherosclerosis involves the buildup of lipids, foam cells and necrotic debris in the intimal layer of the artery. The atherosclerotic plaque at the shoulder region is prone to rupture and when this occurs, blood clots are formed leading to myocardial infarction and death in patients (Lindstedt et al. 1999).There is a correlation between the induction of matrix metalloproteinase-7 (MMP-7), which is one of the zinc ion (Zn2+)-dependent endopeptidases capable of degrading or remodeling the extracellular matrix (ECM), and the occurrence and development of cardiovascular diseases, especially atherosclerosis (Tuomainen et al. 2014). An increased activity of MMP-7 appears to play an important role in the development of coronary artery disease (Alp et al. 2017), During the formation of atherosclerotic plaque, vascular smooth muscle cells secrete ECM proteins to form a fibrous cap , which helps to maintain plaque stability (Williams et al. 2010). Apoptosis of vascular smooth muscle cells leads to plaque instability in mice with atherosclerosis (von der Thüsen et al. 2002). MMP-7 promotes the cleavage of N-cadherin and the apoptosis of smooth muscle cells, thereby weakening the stability of the fibrous cap and increasing the risk of plaque rupture (Koutsouki et al. 2005; Williams et al. 2010). Additionally, MMP-7, while not being expressed in normal arteries (Halpert et al. 1996), is present in vascular cells and inflammatory macrophages in the atherosclerotic plaque (Burke 2004).Polymorphisms in the promoter region of the MMP-7 gene that contribute to its expression has been identified: the presence of MMP-7-181A/G allele in hypercholesterolemic patients appeared to be associated with a reduced coronary arterial luminal diameter (Jormsjö et al. 2001). People with MMP-7-181A/G (rs11568818) allele had higher plasma MMP-7 levels and a higher risk of developing atherosclerotic plaques in the femoral artery (Panayiotou et al. 2013; Lee et al. 2007). There was a strong association between high plasma MMP-7 levels and the risk of coronary artery events (Goncalves et al. 2015). Moreover, MMP-7 polymorphisms or increased plasma levels of MMP-7 are related to the reduction of reactive hyperemia index and lower microvascular response (Boumiza et al. 2017). Taken together, these findings suggest that an elevated MMP-7 level may contribute to vascular dysfunction in cardiovascular disease.<br>Based on these findings, it is hypothesized that up-regulation of MMP-7 expression may lead to endothelial dysfunction. In the present studies, we found that upregulation of MMP-7 in ApoE-deficient mice fed with high-fat diet is associated with the occurrence of endothelium-dependent contractions to acetylcholine, without affecting any endothelium-independent vascular responses in the aorta. Therefore, the protection by MMP-7-deficiency against vascular dysfunction in ApoE-deficient mice may be related to a direct action of MMP-7 on endothelial function. MMP-7 promotes the occurrence of endothelium-dependent contractions in ApoE-deficient mice fed with high-fat diet likely through enhancing the activity of cytosolic phospholipase A2 and upregulating cyclooxygenase-2 to increase endothelial production of prostanoids; this effect can be inhibited by MMP inhibitors.MMP-7-deficiency prevents the activation of NF-κB, a major transcription factor involved in inflammatory responses, and PI3K/AKT as well as MAPK/ERK in ApoE-deficient mice fed with high fat diet.These findings demonstrated that MMP-7 deficiency prevents the development of endothelial dysfunction and vascular inflammation during hyperlipidaemia, thereby inhibiting atherogenesis.

动脉粥样硬化（Atherosclerosis）是一种以动脉管腔内斑块形成为特征的慢性炎症性疾病，是冠状动脉粥样硬化性心脏病（CAD）、脑卒中等心血管疾病的根本病因（Hurtutise, Jessica等, 2006）。动脉粥样硬化的发病机制涉及动脉内膜层脂质、泡沫细胞及坏死碎片的沉积。斑块肩部的动脉粥样硬化斑块易于破裂，一旦发生破裂则会形成血栓，进而导致患者出现心肌梗死甚至死亡（Lindstedt等, 1999）。
基质金属蛋白酶-7（MMP-7）属于锌离子（Zn²+）依赖的内肽酶家族成员，能够降解或重塑细胞外基质（ECM）。已有研究表明，基质金属蛋白酶-7的表达上调与心血管疾病尤其是动脉粥样硬化的发生发展密切相关（Tuomainen等, 2014）。基质金属蛋白酶-7活性升高在冠状动脉粥样硬化性心脏病的发生发展中发挥重要作用（Alp等, 2017）。在动脉粥样硬化斑块形成过程中，血管平滑肌细胞会分泌细胞外基质蛋白以构成纤维帽，帮助维持斑块稳定性（Williams等, 2010）。血管平滑肌细胞凋亡会加剧动脉粥样硬化模型小鼠的斑块不稳定性（von der Thüsen等, 2002）。基质金属蛋白酶-7可介导N-钙粘蛋白的裂解并诱导平滑肌细胞凋亡，进而削弱纤维帽稳定性，升高斑块破裂风险（Koutsouki等, 2005; Williams等, 2010）。此外，正常动脉组织中不表达基质金属蛋白酶-7（Halpert等, 1996），但在动脉粥样硬化斑块的血管细胞及炎性巨噬细胞中可检测到其表达（Burke, 2004）。
研究已证实基质金属蛋白酶-7基因启动子区域的多态性可影响其表达：高胆固醇血症患者携带MMP-7-181A/G等位基因时，其冠状动脉管腔直径更小（Jormsjö等, 2001）。携带MMP-7-181A/G（rs11568818）等位基因的人群血浆基质金属蛋白酶-7水平更高，股动脉粥样硬化斑块的发病风险也随之升高（Panayiotou等, 2013; Lee等, 2007）。血浆基质金属蛋白酶-7水平升高与冠状动脉事件风险存在显著关联（Goncalves等, 2015）。此外，基质金属蛋白酶-7基因多态性或血浆基质金属蛋白酶-7水平升高还与反应性充血指数降低及微血管反应性下降相关（Boumiza等, 2017）。综合上述研究结果提示，血浆基质金属蛋白酶-7水平升高可能参与心血管疾病中的血管功能异常。
基于上述研究发现，本研究提出假说：基质金属蛋白酶-7表达上调可引发内皮功能障碍。在本研究中，我们发现高脂饮食喂养的载脂蛋白E缺陷（ApoE-deficient）小鼠中，基质金属蛋白酶-7的表达上调与主动脉内皮依赖性乙酰胆碱收缩反应的出现相关，且不会影响主动脉的内皮非依赖性血管反应。因此，基质金属蛋白酶-7缺失对载脂蛋白E缺陷小鼠血管功能异常的保护作用，可能与基质金属蛋白酶-7直接作用于内皮功能有关。高脂饮食喂养的载脂蛋白E缺陷小鼠中，基质金属蛋白酶-7可通过增强胞质磷脂酶A2（cytosolic phospholipase A2）活性、上调环氧合酶-2（cyclooxygenase-2）表达以增加内皮前列腺素类介质的生成，进而促进内皮依赖性收缩反应，该效应可被基质金属蛋白酶抑制剂阻断。基质金属蛋白酶-7缺失可抑制高脂饮食喂养的载脂蛋白E缺陷小鼠中核因子κB（NF-κB，核心炎症相关转录因子）、磷脂酰肌醇3-激酶/蛋白激酶B（PI3K/AKT）及丝裂原活化蛋白激酶/细胞外调节蛋白激酶（MAPK/ERK）通路的激活。上述研究结果证实，基质金属蛋白酶-7缺失可阻止高脂血症状态下内皮功能障碍及血管炎症的发生发展，从而抑制动脉粥样硬化的进程。