Serca1 Truncated Proteins Unable to Pump Calcium Reduce the Endoplasmic Reticulum Calcium Concentration and Induce Apoptosis

By pumping calcium from the cytosol to the ER, sarco/endoplasmic reticulum calcium ATPases (SERCAs) play a major role in the control of calcium signaling. We describe two SERCA1 splice variants (S1Ts) characterized by exon 4 and/or exon 11 splicing, encoding COOH terminally truncated proteins, having only one of the seven calcium-binding residues, and thus unable to pump calcium. As shown by semiquantitative RT-PCR, S1T transcripts are differentially expressed in several adult and fetal human tissues, but not in skeletal muscle and heart. S1T proteins expression was detected by Western blot in nontransfected cell lines. In transiently transfected cells, S1T homodimers were revealed by Western blot using mildly denaturing conditions. S1T proteins were shown, by confocal scanning microscopy, to colocalize with endogenous SERCA2b into the ER membrane. Using ER-targeted aequorin (erAEQ), we have found that S1T proteins reduce ER calcium and reverse elevation of ER calcium loading induced by SERCA1 and SERCA2b. Our results also show that SERCA1 variants increase ER calcium leakage and are consistent with the hypothesis of a cation channel formed by S1T homodimers. Finally, when overexpressed in liver-derived cells, S1T proteins significantly induce apoptosis. These data reveal a further mechanism modulating Ca2+ accumulation into the ER of nonmuscle cells and highlight the relevance of S1T proteins to the control of apoptosis

Transcription- and phosphorylation-dependent control of a functional interplay between XBP1s and PINK1 governs mitophagy and potentially impacts Parkinson disease pathophysiology

© 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.Parkinson disease (PD)-affected brains show consistent endoplasmic reticulum (ER) stress and mitophagic dysfunctions. The mechanisms underlying these perturbations and how they are directly linked remain a matter of questions. XBP1 is a transcription factor activated upon ER stress after unconventional splicing by the nuclease ERN1/IREα thereby yielding XBP1s, whereas PINK1 is a kinase considered as the sensor of mitochondrial physiology and a master gatekeeper of mitophagy process. We showed that XBP1s transactivates PINK1 in human cells, primary cultured neurons and mice brain, and triggered a pro-mitophagic phenotype that was fully dependent of endogenous PINK1. We also unraveled a PINK1-dependent phosphorylation of XBP1s that conditioned its nuclear localization and thereby, governed its transcriptional activity. PINK1-induced XBP1s phosphorylation occurred at residues reminiscent of, and correlated to, those phosphorylated in substantia nigra of sporadic PD-affected brains. Overall, our study delineated a functional loop between XBP1s and PINK1 governing mitophagy that was disrupted in PD condition.Abbreviations: 6OHDA: 6-hydroxydopamine; baf: bafilomycin A1; BECN1: beclin 1; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CASP3: caspase 3; CCCP: carbonyl cyanide chlorophenylhydrazone; COX8A: cytochrome c oxidase subunit 8A; DDIT3/CHOP: DNA damage inducible transcript 3; EGFP: enhanced green fluorescent protein; ER: endoplasmic reticulum; ERN1/IRE1α: endoplasmic reticulum to nucleus signaling 1; FACS: fluorescence-activated cell sorting; HSPD1/HSP60: heat shock protein family D (Hsp60) member 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MFN2: mitofusin 2; OPTN: optineurin; PD: Parkinson disease; PINK1: PTEN-induced kinase 1; PCR: polymerase chain reaction:; PRKN: parkin RBR E3 ubiquitin protein ligase; XBP1s [p-S61A]: XBP1s phosphorylated at serine 61; XBP1s [p-T48A]: XBP1s phosphorylated at threonine 48; shRNA: short hairpin RNA, SQSTM1/p62: sequestosome 1; TIMM23: translocase of inner mitochondrial membrane 23; TM: tunicamycin; TMRM: tetramethyl rhodamine methylester; TOMM20: translocase of outer mitochondrial membrane 20; Toy: toyocamycin; TP: thapsigargin; UB: ubiquitin; UB (S65): ubiquitin phosphorylated at serine 65; UPR: unfolded protein response, XBP1: X-box binding protein 1; XBP1s: spliced X-box binding protein 1.info:eu-repo/semantics/publishedVersio

Calcium Signalling in Alzheimer’s Disease: From Pathophysiological Regulation to Therapeutic Approaches

Alzheimer’s disease (AD) is a neurodegenerative pathology representing a socioeconomic challenge, however, the complex mechanism behind the disease is not yet fully understood [...

Alterations of the Endoplasmic Reticulum (ER) Calcium Signaling Molecular Components in Alzheimer’s Disease

Sustained imbalance in intracellular calcium (Ca2+) entry and clearance alters cellular integrity, ultimately leading to cellular homeostasis disequilibrium and cell death. Alzheimer’s disease (AD) is the most common cause of dementia. Beside the major pathological features associated with AD-linked toxic amyloid beta (Aβ) and hyperphosphorylated tau (p-tau), several studies suggested the contribution of altered Ca2+ handling in AD development. These studies documented physical or functional interactions of Aβ with several Ca2+ handling proteins located either at the plasma membrane or in intracellular organelles including the endoplasmic reticulum (ER), considered the major intracellular Ca2+ pool. In this review, we describe the cellular components of ER Ca2+ dysregulations likely responsible for AD. These include alterations of the inositol 1,4,5-trisphosphate receptors’ (IP3Rs) and ryanodine receptors’ (RyRs) expression and function, dysfunction of the sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) activity and upregulation of its truncated isoform (S1T), as well as presenilin (PS1, PS2)-mediated ER Ca2+ leak/ER Ca2+ release potentiation. Finally, we highlight the functional consequences of alterations of these ER Ca2+ components in AD pathology and unravel the potential benefit of targeting ER Ca2+ homeostasis as a tool to alleviate AD pathogenesis

Impact physiologique du transfert de calcium entre le réticulum endoplasmique (RE) et la mitochondrie (rôle de l'isoforme SERCAI tronquée (S1T) dans le stress du RE et la maladie d'Alzheimer )

PARIS5-BU Méd.Cochin (751142101) / SudocSudocFranceF

Impact de la signalisation calcique dans les maladies de la chaine respiratoire mitochondriale (étude du déficit du complexe II associé au syndrôme de Leigh)

Nonobstant les avancées des connaissances sur les bases génétiques de la phosphorylation oxydative (OXPHOS) liées aux maladies les facteurs déterminants à la moléculaire et / ou cellulaire, pour dysfonctionnement de tissus spécifiques ne sont pas complètement compris. Nous avons étudié les événements cellulaires associés, déficit du complexe II de respiratoire mitochondriale dans deux modèles: fïbroblastes humains issus d'un patient avec mutation SDHA (succinate dehydrogenase subunit A) et les fïbroblastes et les cellules neuronales dérivées des cellules chroniquement traitées avec des inhibiteurs du complexe II. La mutation ou l'inhibition du complexe II ont été présentés afin de déterminer une augmentation importante signaux Ca2+ basal et provoqué par des agonistes dans le cytosol et les mitochondries, en parallèle avec le dysfonctionnement mitochondrial (la perte du potentiel de membrane mitochondrial ( mit), réduction de la production de l'ATP mitochondrial ([ATP]mt) et des espèces réactives d'oxygène (ROS)). Le surcharge Ca2+ Cytosolique et mitochondrial a été associé à: i / une baisse l'expression de SERCA2b et PMCA; ii / augmentation de la fuite du Ca2+ RE; iii / diminution de la motilité mitochondriale; iv / augmentation des sites contacts RE-mitochondrie et v / augmentation de la capacité d'absorption du calcium mitochondrial. Fait intéressant, nous avons montré que les cellules déficientes en complexe II ont développé une production d'ATP glycolytique Ca2+ dépendant. En outre, l'augmentation de la charge Ça2 *mitochondriale a lieu avant la perte Aymit et a été montré pour être impliquée dans le développement de la pathologie mitochondriale. Ces résultats ont révélés l'importance de la signalisation Ca2+ dans le contrôle des bioénergétiques cellulaires liés au déficit complexe II de la chaîne respiratoire. Nos résultats peuvent contribuer à la compréhension de la pathologie liée à la carence en complexe II et des maladies de la chaîne respiratoire mitochondriale en général.Despite advanced knowledge on the genetic basis of oxidative phosphorylation (OXPHOS)-related diseases, the molecular and/or cellular detenninants for tissue specific dysfunction are not completely understood. We studied the cellular events associated with initochondrial respiratory complex II deficiency in two models: human fibroblasts derived from a patient harbouring SDHA (succinate dehydrogenase subunit A) mutation and fibroblasts and neuronal derived cells treated chronically with complex II inhibitors. Mutation or inhibition of complex II were shown to determine a large increase of basal and agonist-evoked Ca2+ signals in the cytosol and the mitochondria, in parallel with initochondrial dysfunction (membrane potential ( mit) loss, [ATP] reduction and Reactive Oxygen Species (ROS) production). Cytosolic and initochondrial Ca2+ overload was shown to be associated with: i/ down- expression of SERCA2b and PMCA; ii/ increased ER Ca2+ leakage; iii/ decreased initochondrial motility; iv/ increased ER-mitochondria contact sites; and v/ increased initochondrial calcium uptake capacity. Interestingly, we showed that complex II deficient cells developed a Ca2+ dependent glycolytic ATP production. Moreover, increased mitochondria! Ca2+ load occurred prior to Av|/nl), loss and was shown to be implicated in the development of initochondrial pathology. These results revealed the importance of Ca2+ signalling in the control of the cellular bioenergetics outcomes linked to respiratory chain complex II deficiency. Our findings may help in the understanding of the pathology linked to complex II deficiency and to mitochondrial respiratory chain diseases in generalPARIS5-BU Méd.Cochin (751142101) / SudocSudocFranceF

Mitophagy in Alzheimer's disease: Molecular defects and therapeutic approaches.

Mitochondrial dysfunctions are central players in Alzheimer's disease (AD). In addition, impairments in mitophagy, the process of selective mitochondrial degradation by autophagy leading to a gradual accumulation of defective mitochondria, have also been reported to occur in AD. We provide an updated overview of the recent discoveries and advancements on mitophagic molecular dysfunctions in AD-derived fluids and cells as well as in AD brains. We discuss studies using AD cellular and animal models that have unraveled the contribution of relevant AD-related proteins (Tau, Aβ, APP-derived fragments and APOE) in mitophagy failure. In accordance with the important role of impaired mitophagy in AD, we report on various therapeutic strategies aiming at stimulating mitophagy in AD and we summarize the benefits of these potential therapeutic strategies in human clinical trials