Department of Medicine, Mass Spectrometry Resource, and Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Biol Chem. 2010 Feb 26;285(9):6693-705. doi: 10.1074/jbc.M109.084293. Epub 2009 Dec 23.
Our recent studies indicate that endoplasmic reticulum (ER) stress causes INS-1 cell apoptosis by a Ca(2+)-independent phospholipase A(2) (iPLA(2)beta)-mediated mechanism that promotes ceramide generation via sphingomyelin hydrolysis and subsequent activation of the intrinsic pathway. To elucidate the association between iPLA(2)beta and ER stress, we compared beta-cell lines generated from wild type (WT) and Akita mice. The Akita mouse is a spontaneous model of ER stress that develops hyperglycemia/diabetes due to ER stress-induced beta-cell apoptosis. Consistent with a predisposition to developing ER stress, basal phosphorylated PERK and activated caspase-3 are higher in the Akita cells than WT cells. Interestingly, basal iPLA(2)beta, mature SREBP-1 (mSREBP-1), phosphorylated Akt, and neutral sphingomyelinase (NSMase) are higher, relative abundances of sphingomyelins are lower, and mitochondrial membrane potential (DeltaPsi) is compromised in Akita cells, in comparison with WT cells. Exposure to thapsigargin accelerates DeltaPsi loss and apoptosis of Akita cells and is associated with increases in iPLA(2)beta, mSREBP-1, and NSMase in both WT and Akita cells. Transfection of Akita cells with iPLA(2)beta small interfering RNA, however, suppresses NSMase message, DeltaPsi loss, and apoptosis. The iPLA(2)beta gene contains a sterol-regulatory element, and transfection with a dominant negative SREBP-1 reduces basal mSREBP-1 and iPLA(2)beta in the Akita cells and suppresses increases in mSREBP-1 and iPLA(2)beta due to thapsigargin. These findings suggest that ER stress leads to generation of mSREBP-1, which can bind to the sterol-regulatory element in the iPLA(2)beta gene to promote its transcription. Consistent with this, SREBP-1, iPLA(2)beta, and NSMase messages in Akita mouse islets are higher than in WT islets.
我们最近的研究表明，内质网（ER）应激通过钙非依赖性磷脂酶 A2（iPLA2β）介导的机制引起 INS-1 细胞凋亡，该机制通过鞘磷脂水解促进神经酰胺生成，并随后激活内在途径。为了阐明 iPLA2β与 ER 应激之间的关联，我们比较了来自野生型（WT）和 Akita 小鼠的β细胞系。Akita 小鼠是一种自发的 ER 应激模型，由于 ER 应激诱导的β细胞凋亡而发展为高血糖/糖尿病。与发展 ER 应激的倾向一致，Akita 细胞中的基础磷酸化 PERK 和激活的 caspase-3 高于 WT 细胞。有趣的是，与 WT 细胞相比，Akita 细胞中的基础 iPLA2β、成熟 SREBP-1（mSREBP-1）、磷酸化 Akt 和中性鞘磷脂酶（NSMase）水平较高，鞘磷脂的相对丰度较低，线粒体膜电位（ΔPsi）受损。与 WT 细胞相比，阿霉素细胞暴露于 thapsigargin 会加速ΔPsi 丧失和 Akita 细胞凋亡，并与 WT 和 Akita 细胞中 iPLA2β、mSREBP-1 和 NSMase 的增加相关。然而，用 iPLA2β 小干扰 RNA 转染 Akita 细胞可抑制 NSMase 消息、ΔPsi 丧失和凋亡。iPLA2β 基因含有固醇调节元件，用显性负性 SREBP-1 转染可降低 Akita 细胞中的基础 mSREBP-1 和 iPLA2β，并抑制 thapsigargin 引起的 mSREBP-1 和 iPLA2β 的增加。这些发现表明 ER 应激导致 mSREBP-1 的产生，后者可以结合 iPLA2β 基因中的固醇调节元件以促进其转录。与此一致，Akita 小鼠胰岛中的 SREBP-1、iPLA2β 和 NSMase 消息高于 WT 胰岛。
