Chair for Biofunctionality, Research Center for Nutrition and Food Science (ZIEL), Center for Diet and Disease (CDD), Technische Universität München, Freising-Weihenstephan, Germany.
Department of Gastroenterology, Hospital Clínic i Provincial/IDIBAPS, CIBER EHD, Barcelona, Spain.
Gut. 2012 Sep;61(9):1269-1278. doi: 10.1136/gutjnl-2011-300767. Epub 2011 Oct 13.
Inflammatory bowel diseases (IBDs) feature multiple cellular stress responses, including endoplasmic reticulum (ER) unfolded protein responses (UPRs). UPRs represent autoregulatory pathways that adjust organelle capacity to cellular demand. A similar mechanism, mitochondrial UPR (mtUPR), has been described for mitochondria. ER UPR in intestinal epithelial cells (IECs) contributes to the development of intestinal inflammation, and since mitochondrial alterations and dysfunction are implicated in the pathogenesis of IBDs, the authors characterised mtUPR in the context of intestinal inflammation.
Truncated ornithine transcarbamylase was used to selectively induce mtUPR in a murine IEC line. Dextran sodium sulphate (DSS) was administered to PKR (double-stranded-RNA-activated protein kinase) knockout mice to induce IEC stress in vivo and to test for their susceptibility to DSS-induced colitis. Expression levels of the mitochondrial chaperone chaperonin 60 (CPN60) and PKR were quantified in IECs from patients with IBDs and from murine models of colitis using immunohistochemistry and Western blot analysis.
Selective mtUPR induction by truncated ornithine transcarbamylase transfection triggered the phosphorylation of eukaryotic translation initiation factor (eIF) 2α and cJun through the recruitment of PKR. Using pharmacological inhibitors and small inhibitory RNA, the authors identified mtUPR-induced eIF2α phosphorylation and transcription factor activation (cJun/AP1) as being dependent on the activities of the mitochondrial protease ClpP and the cytoplasmic kinase PKR. Pkr(-/-) mice failed to induce CPN60 in IECs upon DSS treatment at early time points and subsequently showed an almost complete resistance to DSS-induced colitis. Under inflammatory conditions, primary IECs from patients with IBDs and two murine models of colitis exhibited a strong induction of the mtUPR marker protein CPN60 associated with enhanced expression of PKR.
PKR integrates mtUPR into the disease-relevant ER UPR via eIF2α phosphorylation and AP1 activation. Induction of mtUPR and PKR was observed in IECs from murine models and patients with IBDs. The authors' results indicate that PKR might link mitochondrial stress to intestinal inflammation.
炎症性肠病（IBD）具有多种细胞应激反应，包括内质网（ER）未折叠蛋白反应（UPR）。UPR 代表调节细胞器与细胞需求相适应的自身调节途径。类似的机制，即线粒体 UPR（mtUPR），已在 线粒体中进行了描述。肠上皮细胞（IECs）中的 ER UPR 有助于肠道炎症的发展，并且由于线粒体改变和功能障碍与 IBD 的发病机制有关，作者在肠道炎症的背景下对 mtUPR 进行了表征。
使用截断的鸟氨酸转氨甲酰酶选择性诱导鼠 IEC 系中的 mtUPR。葡聚糖硫酸钠（DSS）用于 PKR（双链 RNA 激活的蛋白激酶）敲除小鼠体内诱导 IEC 应激，以测试其对 DSS 诱导的结肠炎的易感性。使用免疫组织化学和 Western blot 分析，从 IBD 患者和结肠炎的鼠模型中定量测定 IEC 中的线粒体伴侣 chaperonin 60（CPN60）和 PKR 的表达水平。
选择性 mtUPR 诱导通过截断的鸟氨酸转氨甲酰酶转染触发真核翻译起始因子（eIF）2α的磷酸化和 cJun 通过 PKR 的募集。作者使用药理学抑制剂和小干扰 RNA 发现，mtUPR 诱导的 eIF2α 磷酸化和转录因子激活（cJun/AP1）依赖于线粒体蛋白酶 ClpP 和细胞质激酶 PKR 的活性。DSS 处理时，早期 Pkr（-/-）小鼠未能诱导 IEC 中的 CPN60，随后对 DSS 诱导的结肠炎几乎完全耐药。在炎症条件下，来自 IBD 患者和两种结肠炎鼠模型的原代 IEC 表现出与 PKR 表达增强相关的强烈 mtUPR 标记蛋白 CPN60 的诱导。
PKR 通过 eIF2α 磷酸化和 AP1 激活将 mtUPR 整合到与疾病相关的 ER UPR 中。在鼠模型和 IBD 患者的 IEC 中观察到 mtUPR 和 PKR 的诱导。作者的结果表明，PKR 可能将线粒体应激与肠道炎症联系起来。
