EFFECT OF EMPTYING ENDOPLASMIC RETICULUM (ER) CALCIUM STORES ON NEURONAL METABOLISM

The endoplasmic reticulum (ER) is the reservoir for calcium in cells. Luminal calcium levels are determined by calcium-sensing proteins that trigger calcium dynamics in response to calcium fluctuations. Here we report that Selenoprotein N (SEPN1) is a type II transmembrane protein that senses ER calcium fluctuations by binding this ion through a luminal EF-hand domain. In vitro and in vivo experiments show that via this domain, SEPN1 responds to diminished luminal calcium levels, dynamically changing its oligomeric state and enhancing its redox-dependent interaction with cellular partners, including the ER calcium pump sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA). Importantly, single amino acid substitutions in the EF-hand domain of SEPN1 identified as clinical variations are shown to impair its calcium-binding and calcium-dependent structural changes, suggesting a key role of the EF-hand domain in SEPN1 function. In conclusion, SEPN1 is a ER calcium sensor that responds to luminal calcium depletion, changing its oligomeric state and acting as a reductase to refill ER calcium stores.

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Inositol 1,4,5 trisphosphate releases calcium from specialized sites within Limulus photoreceptors

The Journal of Cell Biology ◽

10.1083/jcb.104.4.933 ◽

1987 ◽

Vol 104 (4) ◽

pp. 933-937 ◽

Cited By ~ 69

Author(s):

R Payne ◽

A Fein

Keyword(s):

Endoplasmic Reticulum ◽

Injection Site ◽

Intracellular Calcium ◽

Subcellular Distribution ◽

Smooth Endoplasmic Reticulum ◽

Image Intensifier ◽

Photoreceptor Cells ◽

Calcium Stores ◽

Inositol 1,4,5 Trisphosphate ◽

Probable Site

We have investigated the subcellular distribution and identity of inositol trisphosphate (InsP3)-sensitive calcium stores in living Limulus ventral photoreceptor cells, where light and InsP3 are known to raise intracellular calcium. We injected ventral photoreceptor cells with the photoprotein aequorin and viewed its luminescence with an image intensifier. InsP3 only elicited detectable aequorin luminescence when injected into the light-sensitive rhabdomeral (R)-lobe where aequorin luminescence induced by light was also confined. Calcium stores released by light and InsP3 are therefore localized to the R-lobe. Within the R-lobe, InsP3-induced aequorin luminescence was further confined around the injection site, due to rapid dilution and/or degradation of injected InsP3. Prominent cisternae of smooth endoplasmic reticulum are uniquely localized within the cell beneath the microvillar surface of the R-lobe (Calman, B., and S. Chamberlain, 1982, J. Gen. Physiol., 80:839-862). These cisternae are the probable site of InsP3 action.

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Heterologous expression of polycystin-1 inhibits endoplasmic reticulum calcium leak in stably transfected MDCK cells

AJP Renal Physiology ◽

10.1152/ajprenal.00348.2007 ◽

2008 ◽

Vol 294 (6) ◽

pp. F1279-F1286 ◽

Cited By ~ 18

Author(s):

Kimberly H. Weber ◽

Eun Kyung Lee ◽

Uma Basavanna ◽

Sabina Lindley ◽

Roy C. Ziegelstein ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Calcium Release ◽

Mdck Cells ◽

Calcium Ionophore ◽

Calcium Flux ◽

Calcium Stores ◽

Endoplasmic Reticulum Calcium ◽

Calcium Indicator ◽

Luminal Calcium ◽

Er Membrane

We previously found that polycystin-1 accelerated the decay of ligand-activated cytoplasmic calcium transients through enhanced reuptake of calcium into the endoplasmic reticulum (ER; Hooper KM, Boletta A, Germino GG, Hu Q, Ziegelstein RC, Sutters M. Am J Physiol Renal Physiol 289: F521–F530, 2005). Calcium flux across the ER membrane is determined by the balance of active uptake and passive leak. In the present study, we show that polycystin-1 inhibited calcium leak across the ER membrane, an effect that would explain the capacity of this protein to accelerate clearance of calcium from the cytoplasm following a calcium release response. Calcium leak was detected by measurement of the accumulation of calcium in the cytoplasm following treatment with thapsigargin. Heterologous polycystin-1, stably expressed in Madin-Darby canine kidney cells, attenuated the thapsigargin-induced calcium peak with no effect on basal calcium stores, mitochondrial calcium uptake, or extrusion of calcium across the plasma membrane. The capacity of polycystin-1 to limit the rate of decay of ER luminal calcium following inhibition of the pump was shown indirectly using the calcium ionophore ionomycin, and directly by loading the ER with a low-affinity calcium indicator. We conclude that disruption of ER luminal calcium homeostasis may contribute to the cyst phenotype in autosomal dominant polycystic kidney disease.

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Redox-assisted regulation of Ca2+ homeostasis in the endoplasmic reticulum by disulfide reductase ERdj5

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1605818113 ◽

2016 ◽

Vol 113 (41) ◽

pp. E6055-E6063 ◽

Cited By ~ 41

Author(s):

Ryo Ushioda ◽

Akitoshi Miyamoto ◽

Michio Inoue ◽

Satoshi Watanabe ◽

Masaki Okumura ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Disulfide Bond ◽

Plasma Membranes ◽

Dependent Manner ◽

Cellular Functions ◽

Endoplasmic Reticulum Calcium ◽

Disulfide Reductase ◽

Intracellular Ca ◽

Activity Dependent ◽

Er Calcium

Calcium ion (Ca2+) is an important second messenger that regulates numerous cellular functions. Intracellular Ca2+ concentration ([Ca2+]i) is strictly controlled by Ca2+ channels and pumps on the endoplasmic reticulum (ER) and plasma membranes. The ER calcium pump, sarco/endoplasmic reticulum calcium ATPase (SERCA), imports Ca2+ from the cytosol into the ER in an ATPase activity-dependent manner. The activity of SERCA2b, the ubiquitous isoform of SERCA, is negatively regulated by disulfide bond formation between two luminal cysteines. Here, we show that ERdj5, a mammalian ER disulfide reductase, which we reported to be involved in the ER-associated degradation of misfolded proteins, activates the pump function of SERCA2b by reducing its luminal disulfide bond. Notably, ERdj5 activated SERCA2b at a lower ER luminal [Ca2+] ([Ca2+]ER), whereas a higher [Ca2+]ER induced ERdj5 to form oligomers that were no longer able to interact with the pump, suggesting [Ca2+]ER-dependent regulation. Binding Ig protein, an ER-resident molecular chaperone, exerted a regulatory role in the oligomerization by binding to the J domain of ERdj5. These results identify ERdj5 as one of the master regulators of ER calcium homeostasis and thus shed light on the importance of cross talk among redox, Ca2+, and protein homeostasis in the ER.

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

Cells ◽

10.3390/cells9122577 ◽

2020 ◽

Vol 9 (12) ◽

pp. 2577

Author(s):

Mounia Chami ◽

Frédéric Checler

Keyword(s):

Alzheimer’S Disease ◽

Alzheimer's Disease ◽

Endoplasmic Reticulum ◽

Ryanodine Receptors ◽

Functional Consequences ◽

Intracellular Organelles ◽

And Function ◽

Molecular Components ◽

Cellular Components ◽

Er Calcium

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.

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Signaling pathways between the plasma membrane and endoplasmic reticulum calcium stores

Cellular and Molecular Life Sciences ◽

10.1007/pl00000765 ◽

2000 ◽

Vol 57 (8) ◽

pp. 1272-1286 ◽

Cited By ~ 73

Author(s):

J. W. Putney Jr.* ◽

C. M. Pedrosa Ribeiro

Keyword(s):

Endoplasmic Reticulum ◽

Plasma Membrane ◽

Signaling Pathways ◽

Calcium Stores ◽

Endoplasmic Reticulum Calcium

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Presynaptic Endoplasmic Reticulum Contributes Crucially to Short-term Plasticity in Small Hippocampal Synapses

10.1101/431866 ◽

2018 ◽

Cited By ~ 1

Author(s):

Nishant Singh ◽

Thomas Bartol ◽

Herbert Levine ◽

Terrence Sejnowski ◽

Suhita Nadkarni

Keyword(s):

Endoplasmic Reticulum ◽

Calcium Influx ◽

Critical Role ◽

Presynaptic Terminal ◽

Calcium Stores ◽

Pathological State ◽

Calcium Dynamics ◽

Short Term ◽

Short Term Plasticity ◽

Release Probability

Short-term plasticity (STP) of the presynaptic terminal maintains a brief history of activity experienced by the synapse that may otherwise remain unseen by the postsynaptic neuron. These synaptic changes are primarily regulated by calcium dynamics in the presynaptic terminal. A rapid increase in intracellular calcium is initiated by the opening of voltage-dependent calcium channels in response to depolarization, the main source of calcium required for vesicle fusion. Separately, electron-microscopic studies of hippocampal CA3-CA1 synapses reveal the strong presence of endoplasmic reticulum (ER) in all presynaptic terminals. However, the precise role of the ER in modifying STP at the presynaptic terminal remains unexplored. To investigate the contribution of ER in modulating calcium dynamics in small hippocampal boutons, we performed in silico experiments in a physiologically-realistic canonical synaptic geometry based on reconstructions of CA3-CA1 Schaffer collaterals in the rat hippocampus. The model predicts that presynaptic calcium stores are critical in generating the observed paired-pulse ratio (PPR) of normal CA3-CA1 synapses. In control synapses with intact ER, SERCA pumps act as additional calcium buffers, lowering the intrinsic release probability of vesicle release and increasing PPR. In addition, the presence of ER allows ongoing activity to trigger calcium influx from the presynaptic ER via ryanodine receptors (RyRs) and inositol trisphosphate receptors (IP3Rs). Intracellular stores and their associated machinery also allows a synapse with a low release probability to operate more reliably due to attenuation of calcium fluctuations. Finally, blocking ER activity in the presynaptic terminal mimics the pathological state of a low facilitating synapse characterized in animal models of Alzheimer’s disease, and underscores the critical role played by presynaptic stores in normal function.

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Pregnancy associated plasma protein-aa regulates endoplasmic reticulum-mitochondria associations

eLife ◽

10.7554/elife.59687 ◽

2021 ◽

Vol 10 ◽

Author(s):

Mroj Alassaf ◽

Mary C Halloran

Keyword(s):

Endoplasmic Reticulum ◽

Growth Factor ◽

Plasma Protein ◽

Lateral Line ◽

Hair Cells ◽

Mitochondrial Function ◽

Mitochondrial Morphology ◽

Sensory Hair Cells ◽

Downstream Processes ◽

Er Calcium

Endoplasmic reticulum (ER) and mitochondria form close physical associations to facilitate calcium transfer, thereby regulating mitochondrial function. Neurons with high metabolic demands, such as sensory hair cells, are especially dependent on precisely regulated ER-mitochondria associations. We previously showed that the secreted metalloprotease Pregnancy associated plasma protein-aa (Pappaa) regulates mitochondrial function in zebrafish lateral line hair cells (Alassaf et al., 2019). Here, we show that pappaa mutant hair cells exhibit excessive and abnormally close ER-mitochondria associations, suggesting increased ER-mitochondria calcium transfer. pappaa mutant hair cells are more vulnerable to pharmacological induction of ER-calcium transfer. Additionally, pappaa mutant hair cells display ER stress and dysfunctional downstream processes of the ER-mitochondria axis including altered mitochondrial morphology and reduced autophagy. We further show that Pappaa influences ER-calcium transfer and autophagy via its ability to stimulate insulin-like growth factor-1 bioavailability. Together our results identify Pappaa as a novel regulator of the ER-mitochondria axis.

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Depletion of Calcium Stores in Injured Sensory Neurons

Anesthesiology ◽

10.1097/aln.0b013e3181ae63b0 ◽

2009 ◽

Vol 111 (2) ◽

pp. 393-405 ◽

Cited By ~ 16

Author(s):

Geza Gemes ◽

Marcel Rigaud ◽

Paul D. Weyker ◽

Stephen E. Abram ◽

Dorothee Weihrauch ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Sensory Neurons ◽

Dorsal Root Ganglia ◽

Dorsal Root ◽

Spinal Nerve ◽

Calcium Stores ◽

Functional Importance ◽

Electrophysiological Recordings ◽

Intracellular Ca ◽

Functional Consequences

Background Painful nerve injury leads to disrupted Ca signaling in primary sensory neurons, including decreased endoplasmic reticulum (ER) Ca storage. This study examines potential causes and functional consequences of Ca store limitation after injury. Methods Neurons were dissociated from axotomized fifth lumbar (L5) and the adjacent L4 dorsal root ganglia after L5 spinal nerve ligation that produced hyperalgesia, and they were compared to neurons from control animals. Intracellular Ca levels were measured with Fura-2 microfluorometry, and ER was labeled with probes or antibodies. Ultrastructural morphology was analyzed by electron microscopy of nondissociated dorsal root ganglia, and intracellular electrophysiological recordings were obtained from intact ganglia. Results Live neuron staining with BODIPY FL-X thapsigargin (Invitrogen, Carlsbad, CA) revealed a 40% decrease in sarco-endoplasmic reticulum Ca-ATPase binding in axotomized L5 neurons and a 34% decrease in L4 neurons. Immunocytochemical labeling for the ER Ca-binding protein calreticulin was unaffected by injury. Total length of ER profiles in electron micrographs was reduced by 53% in small axotomized L5 neurons, but it was increased in L4 neurons. Cisternal stacks of ER and aggregation of ribosomes occurred less frequently in axotomized neurons. Ca-induced Ca release, examined by microfluorometry with dantrolene, was eliminated in axotomized neurons. Pharmacologic blockade of Ca-induced Ca release with dantrolene produced hyperexcitability in control neurons, confirming its functional importance. Conclusions After axotomy, ER Ca stores are reduced by anatomic loss and possibly diminished sarco-endoplasmic reticulum Ca-ATPase. The resulting disruption of Ca-induced Ca release and protein synthesis may contribute to the generation of neuropathic pain.

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Functional visualization of the separate but interacting calcium stores sensitive to NAADP and cyclic ADP-ribose

Journal of Cell Science ◽

10.1242/jcs.113.24.4413 ◽

2000 ◽

Vol 113 (24) ◽

pp. 4413-4420 ◽

Cited By ~ 1

Author(s):

H.C. Lee ◽

R. Aarhus

Keyword(s):

Endoplasmic Reticulum ◽

Sea Urchin ◽

The Other ◽

Calcium Stores ◽

Cellular Functions ◽

Large Size ◽

Opposite Pole ◽

Visual Evidence ◽

Sea Urchin Egg ◽

Cyclic Adp Ribose

Cells possess multiple Ca(2+) stores and their selective mobilization provides the spatial-temporal Ca(2+) signals crucial in regulating diverse cellular functions. Except for the inositol trisphosphate (IP(3))-sensitive Ca(2+) stores, the identities and the mechanisms of how these internal stores are mobilized are largely unknown. In this study, we describe two Ca(2+) stores, one of which is regulated by cyclic ADP-ribose (cADPR) and the other by nicotinic acid adenine dinucleotide phosphate (NAADP). We took advantage of the large size of the sea urchin egg and stratified its organelles by centrifugation. Using photolysis to produce either uniform or localized increases of cADPR and NAADP from their respective caged analogs, the two separate stores could be visually identified by Ca(2+) imaging and shown to be segregated to the opposite poles of the eggs. The cADPR-pole also contained the IP(3)-sensitive Ca(2+) stores, the egg nucleus and the endoplasmic reticulum (ER); the latter was visualized using Bodipy-thapsigargin. On the other hand, the mitochondria, as visualized by rhodamine 123, were segregated to the opposite pole together with the NAADP-sensitive calcium stores. Fertilization of the stratified eggs elicited a Ca(2+) wave starting at the cADPR-pole and propagating toward the NAADP-pole. These results provide the first direct and visual evidence that the NAADP-sensitive Ca(2+) stores are novel and distinct from the ER. During fertilization, communicating signals appear to be transmitted from the ER to NAADP-sensitive Ca(2+) stores, leading to their activation.

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