Department of Vascular Physiology, National Cerebral and Cardiovascular Center Research Institute, Suita, Osaka, Japan.
Clin Chem. 2011 Oct;57(10):1398-405. doi: 10.1373/clinchem.2011.168625. Epub 2011 Aug 5.
C-reactive protein (CRP) is purported to be a risk factor that acts independently of LDL cholesterol in predicting all-cause mortality in patients with ischemic heart disease. Lectin-like oxidized LDL receptor 1 (LOX-1) impairs endothelial function and exacerbates myocardial injury. We recently demonstrated that CRP increased vascular permeability through direct binding to LOX-1. Here we examined, using a hypertensive rat model, whether LOX-1 is involved in CRP-induced complement activation.
In the cultured LOX-1-expressing cell line hLOX-1-CHO, CRP increased complement activation, but did not do so in native CHO cells. Depleting C1q from serum abolished CRP-induced complement activation. Incubation of CRP with serum on immobilized recombinant LOX-1 similarly showed that CRP activated C1q-requiring classical complement pathway in a LOX-1-dependent manner. Interestingly, the interaction between CRP and LOX-1 was dependent on Ca²⁺ ion and competed with phosphocholine, suggesting that LOX-1 bound to the B-face of CRP with a phosphocholine-binding domain. This was in contrast to Fcγ receptors, to which CRP bound in A-face with complement-binding domain. In vivo, intradermal injection of CRP to hypertensive SHRSP rats induced complement activation detected by C3d deposition and leukocyte infiltration around the injected area. Anti-LOX-1 antibody reduced the extent of complement activation and leukocyte infiltration.
LOX-1 appears to be involved in CRP-induced complement activation, and thus may serve to locate the site of CRP-induced complement activation and inflammation.
C 反应蛋白（CRP）被认为是一种独立于 LDL 胆固醇的风险因素，可预测缺血性心脏病患者的全因死亡率。凝集素样氧化型 LDL 受体 1（LOX-1）损害内皮功能并加重心肌损伤。我们最近证明，CRP 通过与 LOX-1 的直接结合增加血管通透性。在这里，我们使用高血压大鼠模型研究了 LOX-1 是否参与 CRP 诱导的补体激活。
在表达 LOX-1 的 hLOX-1-CHO 细胞系中，CRP 增加了补体激活，但在天然 CHO 细胞中没有。从血清中耗尽 C1q 可消除 CRP 诱导的补体激活。CRP 与固定化重组 LOX-1 孵育同样表明，CRP 以 LOX-1 依赖的方式激活 C1q 所需的经典补体途径。有趣的是，CRP 与 LOX-1 之间的相互作用依赖于 Ca²⁺离子，并与磷酸胆碱竞争，表明 LOX-1 与 CRP 的 B 面结合，具有磷酸胆碱结合域。这与 Fcγ 受体形成对比，CRP 通过补体结合域与 Fcγ 受体的 A 面结合。在体内，向高血压 SHRSP 大鼠皮内注射 CRP 可诱导 C3d 沉积和注射部位周围白细胞浸润，从而检测到补体激活。抗 LOX-1 抗体减少了补体激活和白细胞浸润的程度。
LOX-1 似乎参与了 CRP 诱导的补体激活，因此可能有助于定位 CRP 诱导的补体激活和炎症部位。
