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Vishnu N, Hamilton A, Bagge A, Wernersson A, Cowan E, Barnard H, Sancak Y, Kamer KJ, Spégel P, Fex M, Tengholm A, Mootha VK, Nicholls DG, Mulder H. Mitochondrial clearance of calcium facilitated by MICU2 controls insulin secretion. Mol Metab 2021; 51:101239. [PMID: 33932586 PMCID: PMC8163986 DOI: 10.1016/j.molmet.2021.101239] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 04/20/2021] [Accepted: 04/21/2021] [Indexed: 01/20/2023] Open
Abstract
OBJECTIVE Transport of Ca2+ into pancreatic β cell mitochondria facilitates nutrient-mediated insulin secretion. However, the underlying mechanism is unclear. Recent establishment of the molecular identity of the mitochondrial Ca2+ uniporter (MCU) and associated proteins allows modification of mitochondrial Ca2+ transport in intact cells. We examined the consequences of deficiency of the accessory protein MICU2 in rat and human insulin-secreting cells and mouse islets. METHODS siRNA silencing of Micu2 in the INS-1 832/13 and EndoC-βH1 cell lines was performed; Micu2-/- mice were also studied. Insulin secretion and mechanistic analyses utilizing live confocal imaging to assess mitochondrial function and intracellular Ca2+ dynamics were performed. RESULTS Silencing of Micu2 abrogated GSIS in the INS-1 832/13 and EndoC-βH1 cells. The Micu2-/- mice also displayed attenuated GSIS. Mitochondrial Ca2+ uptake declined in MICU2-deficient INS-1 832/13 and EndoC-βH1 cells in response to high glucose and high K+. MICU2 silencing in INS-1 832/13 cells, presumably through its effects on mitochondrial Ca2+ uptake, perturbed mitochondrial function illustrated by absent mitochondrial membrane hyperpolarization and lowering of the ATP/ADP ratio in response to elevated glucose. Despite the loss of mitochondrial Ca2+ uptake, cytosolic Ca2+ was lower in siMICU2-treated INS-1 832/13 cells in response to high K+. It was hypothesized that Ca2+ accumulated in the submembrane compartment in MICU2-deficient cells, resulting in desensitization of voltage-dependent Ca2+ channels, lowering total cytosolic Ca2+. Upon high K+ stimulation, MICU2-silenced cells showed higher and prolonged increases in submembrane Ca2+ levels. CONCLUSIONS MICU2 plays a critical role in β cell mitochondrial Ca2+ uptake. β cell mitochondria sequestered Ca2+ from the submembrane compartment, preventing desensitization of voltage-dependent Ca2+ channels and facilitating GSIS.
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Affiliation(s)
- N Vishnu
- Unit of Molecular Metabolism, Lund University Diabetes Center, Lund University, Malmö SE-205 02, Sweden
| | - A Hamilton
- Unit of Molecular Metabolism, Lund University Diabetes Center, Lund University, Malmö SE-205 02, Sweden
| | - A Bagge
- Unit of Molecular Metabolism, Lund University Diabetes Center, Lund University, Malmö SE-205 02, Sweden
| | - A Wernersson
- Unit of Molecular Metabolism, Lund University Diabetes Center, Lund University, Malmö SE-205 02, Sweden
| | - E Cowan
- Unit of Molecular Metabolism, Lund University Diabetes Center, Lund University, Malmö SE-205 02, Sweden
| | - H Barnard
- Unit of Molecular Metabolism, Lund University Diabetes Center, Lund University, Malmö SE-205 02, Sweden
| | - Y Sancak
- Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA
| | - K J Kamer
- Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA
| | - P Spégel
- Unit of Molecular Metabolism, Lund University Diabetes Center, Lund University, Malmö SE-205 02, Sweden
| | - M Fex
- Unit of Molecular Metabolism, Lund University Diabetes Center, Lund University, Malmö SE-205 02, Sweden
| | - A Tengholm
- Department of Medical Cell Biology, Uppsala University, Uppsala SE-751 23, Sweden
| | - V K Mootha
- Broad Institute of Harvard and MIT, Cambridge, MA 02142, USA
| | - D G Nicholls
- Unit of Molecular Metabolism, Lund University Diabetes Center, Lund University, Malmö SE-205 02, Sweden; Buck Institute for Research on Aging, Novato, CA 94945, USA
| | - H Mulder
- Unit of Molecular Metabolism, Lund University Diabetes Center, Lund University, Malmö SE-205 02, Sweden.
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Kimura M, Mochizuki H, Satou R, Iwasaki M, Kokubu E, Kono K, Nomura S, Sakurai T, Kuroda H, Shibukawa Y. Plasma Membrane Ca 2+-ATPase in Rat and Human Odontoblasts Mediates Dentin Mineralization. Biomolecules 2021; 11:biom11071010. [PMID: 34356633 PMCID: PMC8301758 DOI: 10.3390/biom11071010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Revised: 06/28/2021] [Accepted: 07/05/2021] [Indexed: 11/17/2022] Open
Abstract
Intracellular Ca2+ signaling engendered by Ca2+ influx and mobilization in odontoblasts is critical for dentinogenesis induced by multiple stimuli at the dentin surface. Increased Ca2+ is exported by the Na+–Ca2+ exchanger (NCX) and plasma membrane Ca2+–ATPase (PMCA) to maintain Ca2+ homeostasis. We previously demonstrated a functional coupling between Ca2+ extrusion by NCX and its influx through transient receptor potential channels in odontoblasts. Although the presence of PMCA in odontoblasts has been previously described, steady-state levels of mRNA-encoding PMCA subtypes, pharmacological properties, and other cellular functions remain unclear. Thus, we investigated PMCA mRNA levels and their contribution to mineralization under physiological conditions. We also examined the role of PMCA in the Ca2+ extrusion pathway during hypotonic and alkaline stimulation-induced increases in intracellular free Ca2+ concentration ([Ca2+]i). We performed RT-PCR and mineralization assays in human odontoblasts. [Ca2+]i was measured using fura-2 fluorescence measurements in odontoblasts isolated from newborn Wistar rat incisor teeth and human odontoblasts. We detected mRNA encoding PMCA1–4 in human odontoblasts. The application of hypotonic or alkaline solutions transiently increased [Ca2+]i in odontoblasts in both rat and human odontoblasts. The Ca2+ extrusion efficiency during the hypotonic or alkaline solution-induced [Ca2+]i increase was decreased by PMCA inhibitors in both cell types. Alizarin red and von Kossa staining showed that PMCA inhibition suppressed mineralization. In addition, alkaline stimulation (not hypotonic stimulation) to human odontoblasts upregulated the mRNA levels of dentin matrix protein-1 (DMP-1) and dentin sialophosphoprotein (DSPP). The PMCA inhibitor did not affect DMP-1 or DSPP mRNA levels at pH 7.4–8.8 and under isotonic and hypotonic conditions, respectively. We also observed PMCA1 immunoreactivity using immunofluorescence analysis. These findings indicate that PMCA participates in maintaining [Ca2+]i homeostasis in odontoblasts by Ca2+ extrusion following [Ca2+]i elevation. In addition, PMCA participates in dentinogenesis by transporting Ca2+ to the mineralizing front (which is independent of non-collagenous dentin matrix protein secretion) under physiological and pathological conditions following mechanical stimulation by hydrodynamic force inside dentinal tubules, or direct alkaline stimulation by the application of high-pH dental materials.
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Affiliation(s)
- Maki Kimura
- Department of Physiology, Tokyo Dental College, 2-9-18, Kanda-Misaki-cho, Chiyoda-ku, Tokyo 101-0061, Japan; (M.K.); (H.M.); (K.K.); (S.N.); (T.S.); (H.K.)
| | - Hiroyuki Mochizuki
- Department of Physiology, Tokyo Dental College, 2-9-18, Kanda-Misaki-cho, Chiyoda-ku, Tokyo 101-0061, Japan; (M.K.); (H.M.); (K.K.); (S.N.); (T.S.); (H.K.)
| | - Ryouichi Satou
- Department of Epidemiology and Public Health, Tokyo Dental College, Chiyodaku, Tokyo 101-0061, Japan; (R.S.); (M.I.)
| | - Miyu Iwasaki
- Department of Epidemiology and Public Health, Tokyo Dental College, Chiyodaku, Tokyo 101-0061, Japan; (R.S.); (M.I.)
| | - Eitoyo Kokubu
- Department of Microbiology, Tokyo Dental College, Chiyodaku, Tokyo 101-0061, Japan;
| | - Kyosuke Kono
- Department of Physiology, Tokyo Dental College, 2-9-18, Kanda-Misaki-cho, Chiyoda-ku, Tokyo 101-0061, Japan; (M.K.); (H.M.); (K.K.); (S.N.); (T.S.); (H.K.)
| | - Sachie Nomura
- Department of Physiology, Tokyo Dental College, 2-9-18, Kanda-Misaki-cho, Chiyoda-ku, Tokyo 101-0061, Japan; (M.K.); (H.M.); (K.K.); (S.N.); (T.S.); (H.K.)
| | - Takeshi Sakurai
- Department of Physiology, Tokyo Dental College, 2-9-18, Kanda-Misaki-cho, Chiyoda-ku, Tokyo 101-0061, Japan; (M.K.); (H.M.); (K.K.); (S.N.); (T.S.); (H.K.)
| | - Hidetaka Kuroda
- Department of Physiology, Tokyo Dental College, 2-9-18, Kanda-Misaki-cho, Chiyoda-ku, Tokyo 101-0061, Japan; (M.K.); (H.M.); (K.K.); (S.N.); (T.S.); (H.K.)
- Department of Dental Anesthesiology, Kanagawa Dental University, 1-23, Ogawacho, Kanagawa, Yokosuka-shi 238-8570, Japan
| | - Yoshiyuki Shibukawa
- Department of Physiology, Tokyo Dental College, 2-9-18, Kanda-Misaki-cho, Chiyoda-ku, Tokyo 101-0061, Japan; (M.K.); (H.M.); (K.K.); (S.N.); (T.S.); (H.K.)
- Correspondence:
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Fang B, Zhao Q, Ling W, Zhang Y, Ou M. Hypoxia induces HT-22 neuronal cell death via Orai1/CDK5 pathway-mediated Tau hyperphosphorylation. Am J Transl Res 2019; 11:7591-7603. [PMID: 31934303 PMCID: PMC6943478] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Accepted: 12/07/2019] [Indexed: 06/10/2023]
Abstract
Hypoxia and apoptosis are involved in the pathogenesis of Alzheimer's disease (AD). Hypoxia induces the formation of amyloid precursor protein in neurons, leading to the abnormal deposition of β-amyloid protein and hyperphosphorylation of Tau. Such changes increase the risk of AD. In the present study, a cellular model of hypoxia-induced AD was established by exposing HT-22 mouse hippocampal neurons to the chemical hypoxia-mimicking agent cobalt chloride (CoCl2). It was found that hypoxia increased neuronal apoptosis. Hypoxia caused an abnormal increase in the expression of the intracellular calcium channel protein Orai1 and cyclin-dependent kinase 5 (CDK5), resulting in hyperphosphorylation of Tau. Treatment with small-interfering RNA against Orai1 (siOrai1) or an Orai1-overexpression plasmid effectively intervened the CDK5-mediated hyperphosphorylation of Tau. In summary, following hypoxic injury of neuron, the Orai1-induced expression of CDK5 leads to Tau hyperphosphorylation. Tau hyperphosphorylation is an important pathophysiological manifestation in AD patients. These results indicated that hypoxia induces HT-22 cell death by Orai1/CDK5 pathway mediated Tau hyperphosporylation. This study simulated the pathological process associated with AD and proposed that hypoxia of intravascular cells with normal blood oxygen saturation might be one of a pathogenic mechanisms of AD. Therefore, this work may provide a new theoretical basis for AD prevention and treatment.
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Affiliation(s)
- Binbin Fang
- Department of Clinical Laboratory, Wuxi Mental Health Center Affiliated with Nanjing Medical UniversityWuxi, Jiangsu, People’s Republic of China
| | - Qing Zhao
- Department of Pharmacy, Affiliated Hospital of Jiangnan UniversityWuxi, Jiangsu, People’s Republic of China
| | - Weiming Ling
- Department of Clinical Laboratory, Wuxi Mental Health Center Affiliated with Nanjing Medical UniversityWuxi, Jiangsu, People’s Republic of China
| | - Yuechun Zhang
- Department of Clinical Laboratory, Wuxi Mental Health Center Affiliated with Nanjing Medical UniversityWuxi, Jiangsu, People’s Republic of China
| | - Mengmeng Ou
- Department of Clinical Laboratory, Wuxi Mental Health Center Affiliated with Nanjing Medical UniversityWuxi, Jiangsu, People’s Republic of China
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Roles for the Endoplasmic Reticulum in Regulation of Neuronal Calcium Homeostasis. Cells 2019; 8:cells8101232. [PMID: 31658749 PMCID: PMC6829861 DOI: 10.3390/cells8101232] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Revised: 10/01/2019] [Accepted: 10/03/2019] [Indexed: 02/06/2023] Open
Abstract
By influencing Ca2+ homeostasis in spatially and architecturally distinct neuronal compartments, the endoplasmic reticulum (ER) illustrates the notion that form and function are intimately related. The contribution of ER to neuronal Ca2+ homeostasis is attributed to the organelle being the largest reservoir of intracellular Ca2+ and having a high density of Ca2+ channels and transporters. As such, ER Ca2+ has incontrovertible roles in the regulation of axodendritic growth and morphology, synaptic vesicle release, and neural activity dependent gene expression, synaptic plasticity, and mitochondrial bioenergetics. Not surprisingly, many neurological diseases arise from ER Ca2+ dyshomeostasis, either directly due to alterations in ER resident proteins, or indirectly via processes that are coupled to the regulators of ER Ca2+ dynamics. In this review, we describe the mechanisms involved in the establishment of ER Ca2+ homeostasis in neurons. We elaborate upon how changes in the spatiotemporal dynamics of Ca2+ exchange between the ER and other organelles sculpt neuronal function and provide examples that demonstrate the involvement of ER Ca2+ dyshomeostasis in a range of neurological and neurodegenerative diseases.
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A Closely Associated Phospholipase C Regulates Cation Channel Function through Phosphoinositide Hydrolysis. J Neurosci 2018; 38:7622-7634. [PMID: 30037836 DOI: 10.1523/jneurosci.0586-18.2018] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Revised: 06/28/2018] [Accepted: 07/17/2018] [Indexed: 11/21/2022] Open
Abstract
In the hemaphroditic sea snail, Aplysia californica, reproduction is initiated when the bag cell neurons secrete egg-laying hormone during a protracted afterdischarge. A source of depolarization for the afterdischarge is a voltage-gated, nonselective cation channel, similar to transient receptor potential (TRP) channels. Once the afterdischarge is triggered, phospholipase C (PLC) is activated to hydrolyze phosphatidylinositol-4,5-bisphosphate (PIP2) into diacylglycerol (DAG) and inositol trisphosphate (IP3). We previously reported that a DAG analog, 1-oleoyl-2-acetyl-sn-glycerol (OAG), activates a prominent, inward whole-cell cationic current that is enhanced by IP3 To examine the underlying mechanism, we investigated the effect of exogenous OAG and IP3, as well as PLC activation, on cation channel activity and voltage dependence in excised, inside-out patches from cultured bag cell neurons. OAG transiently elevated channel open probability (PO) when applied to excised patches; however, coapplication of IP3 prolonged the OAG-induced response. In patches exposed to OAG and IP3, channel voltage dependence was left-shifted; this was also observed with OAG, but not to the same extent. Introducing the PLC activator, m-3M3FBS, to patches increased channel PO, suggesting PLC may be physically linked to the channels. Accordingly, blocking PLC with U-73122 ablated the m-3M3FBS-induced elevation in PO Treatment with m-3M3FBS left-shifted cation channel voltage dependence to a greater extent than exogenous OAG and IP3 Finally, OAG and IP3 potentiated the stimulatory effect of PKC, which is also associated with the channel. Thus, the PLC-PKC signaling system is physically localized such that PIP2 breakdown products liberated during the afterdischarge modulate the cation channel and temporally influence neuronal activity.SIGNIFICANCE STATEMENT Using excised patches from Aplysia bag cell neurons, we present the first evidence of a nonselective cation channel physically associating with phospholipase C (PLC) at the single-channel level. PLC-mediated breakdown of phospholipids generates diacylglycerol and inositol trisphosphate, which activate the cation channel. This is mimicked by exogenous lipids; furthermore, these second messengers left-shift channel voltage dependence and enhance the response of the channel to protein kinase C. PLC-mediated lipid signaling controls single-channel currents to ensure depolarization is maintained for an extended period of firing, termed the afterdischarge, when the bag cell neurons secrete egg-laying hormone to trigger reproduction.
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White SH, Sturgeon RM, Gu Y, Nensi A, Magoski NS. Tyrosine Phosphorylation Determines Afterdischarge Initiation by Regulating an Ionotropic Cholinergic Receptor. Neuroscience 2018; 372:273-288. [PMID: 29306054 DOI: 10.1016/j.neuroscience.2017.12.049] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Revised: 11/30/2017] [Accepted: 12/26/2017] [Indexed: 12/12/2022]
Abstract
Changes to neuronal activity often involve a rapid and precise transition from low to high excitability. In the marine snail, Aplysia, the bag cell neurons control reproduction by undergoing an afterdischarge, which begins with synaptic input releasing acetylcholine to open an ionotropic cholinergic receptor. Gating of this receptor causes depolarization and a shift from silence to continuous action potential firing, leading to the neuroendocrine secretion of egg-laying hormone and ovulation. At the onset of the afterdischarge, there is a rise in intracellular Ca2+, followed by both protein kinase C (PKC) activation and tyrosine dephosphorylation. To determine whether these signals influence the acetylcholine ionotropic receptor, we examined the bag cell neuron cholinergic response both in culture and isolated clusters using whole-cell and/or sharp-electrode electrophysiology. The acetylcholine-induced current was not altered by increasing intracellular Ca2+ via voltage-gated Ca2+ channels, clamping intracellular Ca2+ with exogenous Ca2+ buffers, or activating PKC with phorbol esters. However, lowering phosphotyrosine levels by inhibiting tyrosine kinases both reduced the cholinergic current and prevented acetylcholine from triggering action potentials or afterdischarge-like bursts. In other systems, acetylcholine receptors are often modulated by multiple signals, but bag cell neurons appear to be more restrictive in this regard. Prior work finds that, as the afterdischarge proceeds, tyrosine dephosphorylation leads to biophysical alterations that promote persistent firing. Because this firing is subsequent to the cholinergic input, inhibiting the acetylcholine receptor may represent a means of properly orchestrating synaptically induced changes in excitability.
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Affiliation(s)
- Sean H White
- Department of Biomedical and Molecular Sciences, Physiology and Neuroscience Graduate Programs, Centre for Neuroscience Studies, Queen's University, Kingston, ON K7L 3N6, Canada
| | - Raymond M Sturgeon
- Department of Biomedical and Molecular Sciences, Physiology and Neuroscience Graduate Programs, Centre for Neuroscience Studies, Queen's University, Kingston, ON K7L 3N6, Canada
| | - Yueling Gu
- Department of Biomedical and Molecular Sciences, Physiology and Neuroscience Graduate Programs, Centre for Neuroscience Studies, Queen's University, Kingston, ON K7L 3N6, Canada
| | - Alysha Nensi
- Department of Biomedical and Molecular Sciences, Physiology and Neuroscience Graduate Programs, Centre for Neuroscience Studies, Queen's University, Kingston, ON K7L 3N6, Canada
| | - Neil S Magoski
- Department of Biomedical and Molecular Sciences, Physiology and Neuroscience Graduate Programs, Centre for Neuroscience Studies, Queen's University, Kingston, ON K7L 3N6, Canada.
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