Lack of Evidence for Presenilins as Endoplasmic Reticulum Ca2+ Leak Channels

• DOI: 10.1074/jbc.m111.300491
• Publication Date: 2012-02-07T07:23:14Z
• Authors: Dustin Shilling; Don-On Daniel Mak; David E. Kang; J. Kevin Foskett
• Keywords: Neurons; Ionomycin; Ryanodine Receptor Calcium Release Channel; Fibroblasts; Endoplasmic Reticulum; Cell Line; Molecular Imaging; Kinetics; Mice; Alzheimer Disease; Gene Knockdown Techniques; Mutation; Presenilin-2; Presenilin-1; Animals; Inositol 1,4,5-Trisphosphate Receptors; Calcium; Calcium Channels; Calcium Signaling; Alleles

Familial Alzheimer disease (FAD) is linked to mutations in the presenilin (PS) homologs. FAD mutant PS expression has several cellular consequences, including exaggerated intracellular Ca(2+) ([Ca(2+)](i)) signaling due to enhanced agonist sensitivity and increased magnitude of [Ca(2+)](i) signals. The mechanisms underlying these phenomena remain controversial. It has been proposed that PSs are constitutively active, passive endoplasmic reticulum (ER) Ca(2+) leak channels and that FAD PS mutations disrupt this function resulting in ER store overfilling that increases the driving force for release upon ER Ca(2+) release channel opening. To investigate this hypothesis, we employed multiple Ca(2+) imaging protocols and indicators to directly measure ER Ca(2+) dynamics in several cell systems. However, we did not observe consistent evidence that PSs act as ER Ca(2+) 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 [Ca(2+)](i) versus time curve (AI) compared with cells expressing WT PS. However, an ER-targeted Ca(2+) 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 Ca(2+) leak channels and highlight the need to use ER-targeted Ca(2+) indicators when studying ER Ca(2+) dynamics.