Department of Medicine, Endocrinology and Diabetes, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
J Biol Chem. 2011 Feb 11;286(6):4912-21. doi: 10.1074/jbc.M110.199729. Epub 2010 Dec 7.
Endoplasmic reticulum (ER) stress is widely implicated in various pathological conditions such as diabetes. Previously, we reported that enhanced ER stress contributes to inflammation and vascular damage in diabetic and ischemia-induced retinopathy. However, the exact role of the signaling pathways activated by ER stress in vascular inflammation remains poorly understood. In the present study, we investigated the role of X-box binding protein 1 (XBP1) in retinal adhesion molecule expression, leukostasis, and vascular leakage. Exposure of human retinal endothelial cells to low dose ER stress inducers resulted in a robust activation of XBP1 but did not affect inflammatory gene expression. However, ER stress preconditioning almost completely abolished TNF-α-elicited NF-κB activation and adhesion molecule ICAM-1 and VCAM-1 expression. Pharmaceutical inhibition of XBP1 activation or knockdown of XBP1 by siRNA markedly attenuated the effects of preconditioning on inflammation. Moreover, loss of XBP1 led to an increase in ICAM-1 and VCAM-1 expression. Conversely, overexpression of spliced XBP1 attenuated TNF-α-induced phosphorylation of IKK, IκBα, and NF-κB p65, accompanied by decreased NF-κB activity and reduced adhesion molecule expression. Finally, in vivo studies show that activation of XBP1 by ER stress preconditioning prevents TNF-α-induced ICAM-1 and VCAM-1 expression, leukostasis, and vascular leakage in mouse retinas. These results collectively indicate a protective effect of ER stress preconditioning against retinal endothelial inflammation, which is likely through activation of XBP1-mediated unfolded protein response (UPR) and inhibition of NF-κB activation.
内质网（ER）应激广泛参与各种病理状况，如糖尿病。以前，我们报道过增强的 ER 应激有助于糖尿病和缺血诱导的视网膜病变中的炎症和血管损伤。然而，ER 应激激活的信号通路在血管炎症中的确切作用仍知之甚少。在本研究中，我们研究了 X 盒结合蛋白 1（XBP1）在视网膜粘附分子表达、白细胞滞流和血管渗漏中的作用。低剂量 ER 应激诱导剂暴露于人视网膜内皮细胞导致 XBP1 的强烈激活，但不影响炎症基因表达。然而，ER 应激预处理几乎完全消除了 TNF-α 诱导的 NF-κB 激活和粘附分子 ICAM-1 和 VCAM-1 的表达。XBP1 激活的药物抑制或 siRNA 敲低 XBP1 显著减弱了预处理对炎症的影响。此外，XBP1 的缺失导致 ICAM-1 和 VCAM-1 的表达增加。相反， spliced XBP1 的过表达减弱了 TNF-α 诱导的 IKK、IκBα 和 NF-κB p65 的磷酸化，伴随着 NF-κB 活性的降低和粘附分子表达的减少。最后，体内研究表明，ER 应激预处理通过激活 XBP1 防止 TNF-α 诱导的 ICAM-1 和 VCAM-1 表达、白细胞滞流和小鼠视网膜血管渗漏。这些结果共同表明 ER 应激预处理对视网膜内皮炎症具有保护作用，这可能是通过激活 XBP1 介导的未折叠蛋白反应（UPR）和抑制 NF-κB 激活。
