Lack of Evidence for Presenilins as Endoplasmic Reticulum Ca2+ Leak Channels
Lack of Evidence for Presenilins as Endoplasmic Reticulum Ca2+ Leak Channels
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DOI：
10.1074/jbc.m111.300491
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发表时间：
2012-03-30
影响因子：
4.8
通讯作者：
Foskett, J. Kevin
中科院分区：
文献类型：
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作者：
Shilling, Dustin;Mak, Don-On Daniel;Foskett, J. Kevin
家族性阿尔茨海默病(FAD)与早老素(PS)同源物突变有关。FAD突变型PS的表达具有多种细胞后果，包括由于激动剂敏感性增强和[Ca~(2+)](I)信号幅度增加而导致的细胞内Ca~(2+)([Ca~(2+)](I))信号增强。这些现象背后的机制仍然存在争议。已经提出PSS是结构性的主动的、被动的内质网(ER)钙离子泄漏通道，FAD PS突变破坏了这一功能，导致ER储备库过度填充，从而增加了ER钙释放通道开放时释放的驱动力。为了验证这一假说，我们采用了多种钙离子成像方案和指示剂来直接测量几个细胞系统中的内质网钙动力学。然而，我们没有观察到PSS作为内质网钙离子泄漏通道的一致证据。然而，我们证实了以前提出这一假设的报告中使用的间接测量所做的观察。特别是，与表达WT PS的细胞相比，缺乏PS或表达FAD连锁PS突变的细胞在离子霉素诱导的[Ca~(2+)](I)-时间曲线(AI)下的面积增加。然而，一项针对内质网的钙指标显示，这并不反映内质网存储超载。莫能菌素预处理选择性地减弱缺乏PS或表达Fad PS等位基因的细胞的AI。这些发现与PSS形成内质网钙离子泄漏通道的假设相矛盾，并强调了在研究内质网钙离子动力学时需要使用内质网靶向钙离子指示剂。
Familial Alzheimer disease (FAD) is linked to mutations in the presenilin (PS) homologs. FAD mutant PS expression has several cellular consequences, including exaggerated intracellular Ca2+ ([Ca2+](i)) signaling due to enhanced agonist sensitivity and increased magnitude of [Ca2+](i) signals. The mechanisms underlying these phenomena remain controversial. It has been proposed that PSs are constitutively active, passive endoplasmic reticulum (ER) Ca2+ leak channels and that FAD PS mutations disrupt this function resulting in ER store overfilling that increases the driving force for release upon ER Ca2+ release channel opening. To investigate this hypothesis, we employed multiple Ca2+ imaging protocols and indicators to directly measure ER Ca2+ dynamics in several cell systems. However, we did not observe consistent evidence that PSs act as ER Ca2+ leak channels. Nevertheless, we confirmed observations made using indirect measurements employed in previous reports that proposed this hypothesis. Specifically, cells lacking PS or expressing a FAD-linked PS mutation displayed increased area under the ionomycin-induced [Ca2+](i) versus time curve (AI) compared with cells expressing WT PS. However, an ER-targeted Ca2+ indicator revealed that this did not reflect overloaded ER stores. Monensin pretreatment selectively attenuated the AI in cells lacking PS or expressing a FAD PS allele. These findings contradict the hypothesis that PSs form ER Ca2+ leak channels and highlight the need to use ER-targeted Ca2+ indicators when studying ER Ca2+ dynamics.