Lack of evidence for presenilins as endoplasmic reticulum Ca2+ leak channels.
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.
Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Dustin
D
Shilling
Don-On Daniel
DO
Mak
David E
DE
Kang
J Kevin
JK
Foskett
D000483:Alleles; D000544:Alzheimer Disease / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D055785:Gene Knockdown Techniques; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D057054:Molecular Imaging; D009154:Mutation; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D053764:Presenilin-1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D053766:Presenilin-2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D053764:Presenilin-1; D053766:Presenilin-2; D019837:Ryanodine Receptor Calcium Release Channel; D015759:Ionomycin; D002118:Calcium