Presenilin 2 modulates endoplasmic reticulum (ER)–mitochondria interactions and Ca ²⁺ cross-talk

Abstract

Presenilin mutations are the main cause of familial Alzheimer's disease (FAD). Presenilins also play a key role in Ca 2+ homeostasis, and their FAD-linked mutants affect cellular Ca 2+ handling in several ways. We previously have demonstrated that FAD-linked presenilin 2 (PS2) mutants decrease the Ca 2+ content of the endoplasmic reticulum (ER) by inhibiting sarcoendoplasmic reticulum Ca 2+ -ATPase (SERCA) activity and increasing ER Ca 2+ leak. Here we focus on the effect of presenilins on mitochondrial Ca 2+ dynamics. By using genetically encoded Ca 2+ indicators specifically targeted to mitochondria (aequorin-and GFP-based probes) in SH-SY5Y cells and primary neuronal cultures, we show that overexpression or down-regulation of PS2, but not of presenilin 1 (PS1), modulates the Ca 2+ shuttling between ER and mitochondria, with its FAD mutants strongly favoring Ca 2+ transfer between the two organelles. This effect is not caused by a direct PS2 action on mitochondrial Ca 2+ -uptake machinery but rather by an increased physical interaction between ER and mitochondria that augments the frequency of Ca 2+ hot spots generated at the cytoplasmic surface of the outer mitochondrial membrane upon stimulation. This PS2 function adds further complexity to the multifaceted nature of presenilins and to their physiological role within the cell. We also discuss the importance of this additional effect of FAD-linked PS2 mutants for the understanding of FAD pathogenesis.fluorescent Ca 2+ probe | intracellular organelle tethering | fluorescence resonance energy transfer A lzheimer's disease (AD) is the most common form of dementia in developed countries. The pathogenesis of AD is still largely mysterious, and most basic research in the field is concentrated on rare genetic forms of familial AD (FAD). The majority of FAD cases are caused by point mutations in genes for two homologous proteins, presenilin 1 (PS1) and presenilin 2 (PS2), that are essential components of the γ-secretase complex responsible for the production of the amyloid β peptides (Aβ) (1).Evidence has accumulated suggesting that FAD is linked to an imbalance of cellular Ca 2+ homeostasis (see refs. 2 and 3 for recent reviews). In particular, presenilins appear to play a key role in the control of Ca 2+ concentration within the endoplasmic reticulum (ER), [Ca 2+ ] ER : (i) Several FAD-linked presenilin mutants altered the expression or sensitivity of ER Ca 2+ release channels [ryanodine receptor (RyR) and inositol 1,4,5-trisphosphate receptor (IP 3 R)] in cell lines, neurons, and brain microsomes (see ref. 4 for a recent review); (ii) the sarcoendoplasmic reticulum Ca 2+ ATPase (SERCA) has been proposed as a target of presenilins, although opposite regulatory effects have been reported (5, 6); and (iii) it has been suggested that WT presenilins, but not FAD-linked presenilin mutants, form low-conductance Ca 2+ leak channels in the ER membrane (7,8). This last finding supports the "Ca 2+ overload" hypothesis for FAD, which proposes that the reduced ER Ca 2+ leak c...

Mitochondria-Associated Endoplasmic Reticulum Membrane (MAM) Integrity Is Required for Insulin Signaling and Is Implicated in Hepatic Insulin Resistance

“…HGP, hepatic glucose production; IR, insulin receptor. (3,(31)(32)(33). Using this method to evaluate ER-mitochondria interactions, we found that MAM integrity is required for efficient insulin action in hepatocytes.…”

A γ-Secretase Independent Role for Presenilin in Calcium Homeostasis Impacts Mitochondrial Function and Morphology in Caenorhabditis elegans

“…Moreover, ER-mitochondrial contacts are increased and ER-mitochondrial crosstalk is enhanced in PSEN1 knockout cells, in cells overexpressing the FAD mutant PSEN2, and in fibroblasts from FAD and sporadic AD patients (Zampese et al 2011;Area-Gomez et al 2012;Kipanyula et al 2012). Thus, PSENs are critically positioned where ER and mitochondria communicate and share contents (e.g., calcium, lipids, ATP).…”

Mitofusin 2 ablation increases endoplasmic reticulum–mitochondria coupling

“…MEFs (WT, Mfn2 −/− ) were grown as previously described (18), as were SH-SY5Y and HeLa cells (22). All materials were from Sigma-Aldrich unless otherwise specified.…”

“…Aequorin measurements were carried out as described (22) and are summarized in SI Materials and Methods.…”

“…On the other hand, when the presenilin 2 (PS2) familial Alzheimer disease mutant PS2-T122R was expressed in HeLa cells [a treatment shown to increase ER-mitochondria physical and functional coupling without altering organelles' morphology ( Fig. S3A) (22)], both types of analysis showed an increase in the organelles' colocalization (Fig. S3B).…”