ABSTRACT
Discovered in 1993, inositol pyrophosphates are evolutionarily conserved signaling metabolites whose versatile modes of action are being increasingly appreciated. These include their emerging roles as energy regulators, phosphodonors, steric/allosteric regulators, and G protein-coupled receptor messengers. Through studying enzymes that metabolize inositol pyrophosphates, progress has also been made in elucidating the various cellular and physiological functions of these pyrophosphate-containing, energetic molecules. The two main forms of inositol pyrophosphates, 5-IP7 and IP8, synthesized respectively by inositol-hexakisphosphate kinases (IP6Ks) and diphosphoinositol pentakisphosphate kinases (PPIP5Ks), regulate phosphate homeostasis, ATP synthesis, and several other metabolic processes ranging from insulin secretion to cellular energy utilization. Here, we review the current understanding of the catalytic and regulatory mechanisms of IP6Ks and PPIP5Ks, as well as their counteracting phosphatases. We also highlight the genetic and cellular evidence implicating inositol pyrophosphates as essential mediators of mammalian metabolic homeostasis.
Subject(s)
Inositol Phosphates , Phosphotransferases (Phosphate Group Acceptor) , Signal Transduction , Humans , Inositol Phosphates/metabolism , Animals , Phosphotransferases (Phosphate Group Acceptor)/metabolism , Phosphotransferases (Phosphate Group Acceptor)/genetics , Homeostasis , Energy Metabolism , Adenosine Triphosphate/metabolism , Phosphoric Monoester Hydrolases/metabolism , Phosphoric Monoester Hydrolases/geneticsABSTRACT
The inositol pyrophosphate IP7 (5-diphosphoinositolpentakisphosphate), formed by a family of three inositol hexakisphosphate kinases (IP6Ks), modulates diverse cellular activities. We now report that IP7 is a physiologic inhibitor of Akt, a serine/threonine kinase that regulates glucose homeostasis and protein translation, respectively, via the GSK3ß and mTOR pathways. Thus, Akt and mTOR signaling are dramatically augmented and GSK3ß signaling reduced in skeletal muscle, white adipose tissue, and liver of mice with targeted deletion of IP6K1. IP7 affects this pathway by potently inhibiting the PDK1 phosphorylation of Akt, preventing its activation and thereby affecting insulin signaling. IP6K1 knockout mice manifest insulin sensitivity and are resistant to obesity elicited by high-fat diet or aging. Inhibition of IP6K1 may afford a therapeutic approach to obesity and diabetes.
Subject(s)
Inositol Phosphates/metabolism , Proto-Oncogene Proteins c-akt/metabolism , Weight Gain , Adipogenesis , Aging/metabolism , Animals , Cell Culture Techniques , Diet , Diphosphates/metabolism , Inositol/metabolism , Insulin/metabolism , Insulin Resistance , Mice , Obesity/metabolism , Phosphorylation , Phosphotransferases (Phosphate Group Acceptor)/geneticsABSTRACT
Inositol pyrophosphates, such as 5-diphosphoinositol pentakisphosphate (IP7), are generated by a family of inositol hexakisphosphate kinases (IP6Ks), of which IP6K2 has been implicated in various cellular functions including neuroprotection. Absence of IP6K2 causes impairment of oxidative phosphorylation regulated by creatine kinase-B. In the present study, we show that IP6K2 is involved in attenuation of PINK1-mediated mitochondrial autophagy (mitophagy) in the brain. Up-regulation of dynamin-related protein (Drp-1), as well as increased expression of mitochondrial biogenesis markers (PGC1-α and NRF-1) in the cerebella of IP6K2-deleted mice (IP6K2-knockout), point to the involvement of IP6K2 in the regulation of mitochondrial fission. Knockdown of IP6K2 also leads to augmented glycolysis, potentially as a compensatory mechanism for decreased mitochondrial respiration. Overexpressing IP6K2 as well as IP6K2-kinase dead mutant in IP6K2-knockdown N2A cells reverses the expression of mitophagy markers, demonstrating that IP6K2-induced mitoprotection is catalytically/kinase independent. IP6K2 supplementation in K2-PINK1 double-knockdown N2A cells fails to reverse the expression of the mitophagic marker, LC3-II, indicating that the mitoprotective effect of IP6K2 is dependent on PINK1. Overall, our study reveals a key neuroprotective role of IP6K2 in the prevention of PINK1-mediated mitophagy in the brain.
Subject(s)
Mitophagy , Phosphotransferases (Phosphate Group Acceptor) , Protein Kinases , Animals , Mice , Mice, Knockout , Phosphotransferases (Phosphate Group Acceptor)/genetics , Phosphotransferases (Phosphate Group Acceptor)/metabolism , Phosphotransferases (Phosphate Group Acceptor)/physiology , Protein Kinases/metabolism , Signal TransductionABSTRACT
Cocaine exerts its stimulant effect by inhibiting dopamine (DA) reuptake, leading to increased dopamine signaling. This action is thought to reflect the binding of cocaine to the dopamine transporter (DAT) to inhibit its function. However, cocaine is a relatively weak inhibitor of DAT, and many DAT inhibitors do not share cocaine's behavioral actions. Further, recent reports show more potent actions of the drug, implying the existence of a high-affinity receptor for cocaine. We now report high-affinity binding of cocaine associated with the brain acid soluble protein 1 (BASP1) with a dissociation constant (Kd) of 7 nM. Knocking down BASP1 in the striatum inhibits [3H]cocaine binding to striatal synaptosomes. Depleting BASP1 in the nucleus accumbens but not the dorsal striatum diminishes locomotor stimulation in mice. Our findings imply that BASP1 is a pharmacologically relevant receptor for cocaine.
Subject(s)
Calmodulin-Binding Proteins , Carrier Proteins , Cocaine , Cytoskeletal Proteins , Nerve Tissue Proteins , Receptors, Drug , Animals , Binding Sites , Calmodulin-Binding Proteins/genetics , Calmodulin-Binding Proteins/metabolism , Carrier Proteins/genetics , Carrier Proteins/metabolism , Cocaine/metabolism , Cocaine/pharmacology , Corpus Striatum/metabolism , Cytoskeletal Proteins/genetics , Cytoskeletal Proteins/metabolism , Dopamine/metabolism , Dopamine Plasma Membrane Transport Proteins/antagonists & inhibitors , Gene Knock-In Techniques , Humans , Mice , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/metabolism , Rats , Receptors, Drug/genetics , Receptors, Drug/metabolismABSTRACT
Hydrogen sulfide (H(2)S) has recently emerged as a mammalian gaseous messenger molecule, akin to nitric oxide and carbon monoxide. H(2)S is predominantly formed from Cys or its derivatives by the enzymes cystathionine ß-synthase and cystathionine γ-lyase. One of the mechanisms by which H(2)S signals is by sulfhydration of reactive Cys residues in target proteins. Although analogous to protein nitrosylation, sulfhydration is substantially more prevalent and usually increases the catalytic activity of targeted proteins. Physiological actions of sulfhydration include the regulation of inflammation and endoplasmic reticulum stress signalling as well as of vascular tension.
Subject(s)
Cystathionine beta-Synthase/metabolism , Cystathionine gamma-Lyase/metabolism , Cysteine , Hydrogen Sulfide/metabolism , Proteins , Animals , Cystathionine beta-Synthase/chemistry , Cystathionine gamma-Lyase/chemistry , Cysteine/chemistry , Cysteine/metabolism , Endoplasmic Reticulum Stress/physiology , Gases/chemistry , Gases/metabolism , Humans , Hydrogen Sulfide/chemistry , Inflammation/metabolism , Proteins/chemistry , Proteins/metabolism , Signal Transduction , Vasodilation/physiologyABSTRACT
My professional life over five decades meandered from a high school ambition to be a psychiatrist and understand the "mind" to biochemical studies of neurotransmitters and drugs. Hopefully, the tale of my quirky impatient curiosity about "too many" different areas will be useful for young scientists embarking on their own careers.
Subject(s)
Molecular Biology/history , Neurophysiology/history , Neurotransmitter Agents/physiology , History, 20th Century , Humans , Substance-Related Disorders/physiopathologyABSTRACT
D-amino acids are being recognized as functionally important molecules in mammals. We recently identified endogenous D-cysteine in mammalian brain. D-cysteine is present in neonatal brain in substantial amounts (mM) and decreases with postnatal development. D-cysteine binds to MARCKS and a host of proteins implicated in cell division and neurodevelopmental disorders. D-cysteine decreases phosphorylation of MARCKS in neural progenitor cells (NPCs) affecting its translocation. D-cysteine controls NPC proliferation by inhibiting AKT signaling. Exogenous D-cysteine inhibits AKT phosphorylation at Thr 308 and Ser 473 in NPCs. D-cysteine treatment of NPCs led to 50% reduction in phosphorylation of Foxo1 at Ser 256 and Foxo3a at Ser 253. We hypothesize that in the developing brain endogenous D-cysteine is as a physiologic regulator of NPC proliferation by inhibiting AKT signaling mediated by Foxo1 and Foxo3a. Endogenous D-cysteine may regulate mammalian neurodevelopment with roles in schizophrenia and Alzheimer's disease (AD).
Subject(s)
Cysteine , Intracellular Signaling Peptides and Proteins , Animals , Cell Proliferation , Cysteine/metabolism , Intracellular Signaling Peptides and Proteins/metabolism , Mammals/metabolism , Membrane Proteins/metabolism , Phosphorylation , Proto-Oncogene Proteins c-akt/metabolism , StereoisomerismABSTRACT
Although most patients recover from acute COVID-19, some experience postacute sequelae of severe acute respiratory syndrome coronavirus 2 infection (PASC). One subgroup of PASC is a syndrome called "long COVID-19," reminiscent of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). ME/CFS is a debilitating condition, often triggered by viral and bacterial infections, leading to years-long debilitating symptoms including profound fatigue, postexertional malaise, unrefreshing sleep, cognitive deficits, and orthostatic intolerance. Some are skeptical that either ME/CFS or long COVID-19 involves underlying biological abnormalities. However, in this review, we summarize the evidence that people with acute COVID-19 and with ME/CFS have biological abnormalities including redox imbalance, systemic inflammation and neuroinflammation, an impaired ability to generate adenosine triphosphate, and a general hypometabolic state. These phenomena have not yet been well studied in people with long COVID-19, and each of them has been reported in other diseases as well, particularly neurological diseases. We also examine the bidirectional relationship between redox imbalance, inflammation, energy metabolic deficits, and a hypometabolic state. We speculate as to what may be causing these abnormalities. Thus, understanding the molecular underpinnings of both PASC and ME/CFS may lead to the development of novel therapeutics.
Subject(s)
COVID-19/metabolism , Encephalomyelitis/metabolism , Fatigue Syndrome, Chronic/metabolism , Animals , COVID-19/complications , COVID-19/etiology , COVID-19/immunology , Encephalomyelitis/immunology , Fatigue Syndrome, Chronic/immunology , Humans , Oxidation-Reduction , Post-Acute COVID-19 SyndromeABSTRACT
Inositol hexakisphosphate kinases (IP6Ks) regulate various biological processes. IP6Ks convert IP6 to pyrophosphates such as diphosphoinositol pentakisphosphate (IP7) and bis-diphosphoinositol tetrakisphosphate (IP8). IP7 is produced in mammals by a family of inositol hexakisphosphate kinases, IP6K1, IP6K2, and IP6K3, which have distinct biological functions. The inositol hexakisphosphate kinase 2 (IP6K2) controls cellular apoptosis. To explore roles for IP6K2 in brain function, we elucidated its protein interactome in mouse brain revealing a robust association of IP6K2 with creatine kinase-B (CK-B), a key enzyme in energy homeostasis. Cerebella of IP6K2-deleted mice (IP6K2-knockout [KO]) produced less phosphocreatine and ATP and generated higher levels of reactive oxygen species and protein oxidative damage. In IP6K2-KO mice, mitochondrial dysfunction was associated with impaired expression of the cytochrome-c1 subunit of complex III of the electron transport chain. We reversed some of these effects by combined treatment with N-acetylcysteine and phosphocreatine. These findings establish a role for IP6K2-CK-B interaction in energy homeostasis associated with neuroprotection.
Subject(s)
Creatine Kinase/genetics , Energy Metabolism/genetics , Phosphotransferases (Phosphate Group Acceptor)/genetics , Acetylcysteine/metabolism , Adenosine Triphosphate/biosynthesis , Animals , Apoptosis/genetics , Cytochromes c1/genetics , Electron Transport Complex III/genetics , Humans , Mice , Mice, Knockout , Mitochondria/genetics , Mitochondria/pathology , Phosphocreatine/biosynthesisABSTRACT
d-amino acids are increasingly recognized as important signaling molecules in the mammalian central nervous system. However, the d-stereoisomer of the amino acid with the fastest spontaneous racemization ratein vitro in vitro, cysteine, has not been examined in mammals. Using chiral high-performance liquid chromatography and a stereospecific luciferase assay, we identify endogenous d-cysteine in the mammalian brain. We identify serine racemase (SR), which generates the N-methyl-d-aspartate (NMDA) glutamate receptor coagonist d-serine, as a candidate biosynthetic enzyme for d-cysteine. d-cysteine is enriched more than 20-fold in the embryonic mouse brain compared with the adult brain. d-cysteine reduces the proliferation of cultured mouse embryonic neural progenitor cells (NPCs) by â¼50%, effects not shared with d-serine or l-cysteine. The antiproliferative effect of d-cysteine is mediated by the transcription factors FoxO1 and FoxO3a. The selective influence of d-cysteine on NPC proliferation is reflected in overgrowth and aberrant lamination of the cerebral cortex in neonatal SR knockout mice. Finally, we perform an unbiased screen for d-cysteine-binding proteins in NPCs by immunoprecipitation with a d-cysteine-specific antibody followed by mass spectrometry. This approach identifies myristoylated alanine-rich C-kinase substrate (MARCKS) as a putative d-cysteine-binding protein. Together, these results establish endogenous mammalian d-cysteine and implicate it as a physiologic regulator of NPC homeostasis in the developing brain.
Subject(s)
Brain/physiology , Neural Stem Cells/physiology , Racemases and Epimerases/physiology , Serine/metabolism , Animals , Animals, Newborn , Brain/cytology , Mice , Mice, Inbred C57BL , Mice, Knockout , Neural Stem Cells/cytology , Receptors, N-Methyl-D-Aspartate/metabolism , Serine/chemistryABSTRACT
Alzheimer's disease (AD), the most common cause of dementia and neurodegeneration in the elderly, is characterized by deterioration of memory and executive and motor functions. Neuropathologic hallmarks of AD include neurofibrillary tangles (NFTs), paired helical filaments, and amyloid plaques. Mutations in the microtubule-associated protein Tau, a major component of the NFTs, cause its hyperphosphorylation in AD. We have shown that signaling by the gaseous molecule hydrogen sulfide (H2S) is dysregulated during aging. H2S signals via a posttranslational modification termed sulfhydration/persulfidation, which participates in diverse cellular processes. Here we show that cystathionine γ-lyase (CSE), the biosynthetic enzyme for H2S, binds wild type Tau, which enhances its catalytic activity. By contrast, CSE fails to bind Tau P301L, a mutant that is present in the 3xTg-AD mouse model of AD. We further show that CSE is depleted in 3xTg-AD mice as well as in human AD brains, and that H2S prevents hyperphosphorylation of Tau by sulfhydrating its kinase, glycogen synthase kinase 3ß (GSK3ß). Finally, we demonstrate that sulfhydration is diminished in AD, while administering the H2S donor sodium GYY4137 (NaGYY) to 3xTg-AD mice ameliorates motor and cognitive deficits in AD.
Subject(s)
Alzheimer Disease/drug therapy , Cystathionine gamma-Lyase/genetics , Glycogen Synthase Kinase 3 beta/genetics , Hydrogen Sulfide/pharmacology , Morpholines/pharmacology , Neuroprotective Agents/pharmacology , Organothiophosphorus Compounds/pharmacology , tau Proteins/genetics , Alzheimer Disease/genetics , Alzheimer Disease/metabolism , Alzheimer Disease/pathology , Animals , Cystathionine gamma-Lyase/metabolism , Disease Models, Animal , Glycogen Synthase Kinase 3 beta/metabolism , HEK293 Cells , Hippocampus/drug effects , Hippocampus/metabolism , Hippocampus/pathology , Humans , Mice , Mice, Transgenic , Mutation , Neurofibrillary Tangles/drug effects , Neurofibrillary Tangles/metabolism , Neurofibrillary Tangles/pathology , Phosphorylation , Plaque, Amyloid/genetics , Plaque, Amyloid/metabolism , Plaque, Amyloid/pathology , Plaque, Amyloid/prevention & control , Protein Binding , Protein Processing, Post-Translational , Sulfates/metabolism , tau Proteins/metabolismABSTRACT
Inositol phosphates are widely produced throughout animal and plant tissues. Diphosphoinositol pentakisphosphate (InsP7) contains an energetic pyrophosphate bond. Here we demonstrate that disruption of inositol hexakisphosphate kinase 1 (InsP6K1), one of the three mammalian inositol hexakisphosphate kinases (InsP6Ks) that convert inositol hexakisphosphate (InsP6) to InsP7, conferred enhanced phosphatidylinositol-(3,4,5)-trisphosphate (PtdIns(3,4,5)P3)-mediated membrane translocation of the pleckstrin homology domain of the kinase Akt and thus augmented downstream PtdIns(3,4,5)P3 signaling in mouse neutrophils. Consequently, these neutrophils had greater phagocytic and bactericidal ability and amplified NADPH oxidase-mediated production of superoxide. These phenotypes were replicated in human primary neutrophils with pharmacologically inhibited InsP6Ks. In contrast, an increase in intracellular InsP7 blocked chemoattractant-elicited translocation of the pleckstrin homology domain to the membrane and substantially suppressed PtdIns(3,4,5)P3-mediated cellular events in neutrophils. Our findings establish a role for InsP7 in signal transduction and provide a mechanism for modulating PtdIns(3,4,5)P3 signaling in neutrophils.
Subject(s)
Inositol Phosphates/immunology , Neutrophils/immunology , Phosphatidylinositol Phosphates/immunology , Phosphotransferases (Phosphate Group Acceptor)/antagonists & inhibitors , Animals , Dimethyl Sulfoxide/pharmacology , HL-60 Cells , Humans , Immunity, Innate/immunology , Isoenzymes , Mice , Mice, Knockout , N-Formylmethionine Leucyl-Phenylalanine/pharmacology , Phagocytosis/immunology , Phosphotransferases (Phosphate Group Acceptor)/genetics , Phosphotransferases (Phosphate Group Acceptor)/immunology , Proto-Oncogene Proteins c-akt/immunology , RNA/chemistry , RNA/genetics , Reverse Transcriptase Polymerase Chain Reaction , Signal TransductionABSTRACT
Cocaine exerts its stimulant effect by inhibiting dopamine reuptake leading to increased dopamine signaling. This action is thought to reflect binding of cocaine to the dopamine transporter (DAT) to inhibit its function. However, cocaine is a relatively weak inhibitor of DAT, and many DAT inhibitors do not share the behavioral actions of cocaine. We previously showed that toxic levels of cocaine induce autophagic neuronal cell death. Here, we show that subnanomolar concentrations of cocaine elicit neural autophagy in vitro and in vivo. Autophagy inhibitors reduce the locomotor stimulant effect of cocaine in mice. Cocaine-induced autophagy degrades transporters for dopamine but not serotonin in the nucleus accumbens. Autophagy inhibition impairs cocaine conditioned place preference in mice. Our findings indicate that autophagic degradation of DAT modulates behavioral actions of cocaine.
Subject(s)
Cocaine , Animals , Autophagy , Cocaine/pharmacology , Dopamine Plasma Membrane Transport Proteins/metabolism , Dopamine Uptake Inhibitors/pharmacology , Mice , Nucleus Accumbens/metabolismABSTRACT
The apoptotic actions of p53 require its phosphorylation by a family of phosphoinositide-3-kinase-related-kinases (PIKKs), which include DNA-PKcs and ATM. These kinases are stabilized by the TTT (Tel2, Tti1, Tti2) cochaperone family, whose actions are mediated by CK2 phosphorylation. The inositol pyrophosphates, such as 5-diphosphoinositol pentakisphosphate (IP7), are generated by a family of inositol hexakisphosphate kinases (IP6Ks), of which IP6K2 has been implicated in p53-associated cell death. In the present study we report an apoptotic signaling cascade linking CK2, TTT, the PIKKs, and p53. We demonstrate that IP7, formed by IP6K2, binds CK2 to enhance its phosphorylation of the TTT complex, thereby stabilizing DNA-PKcs and ATM. This process stimulates p53 phosphorylation at serine 15 to activate the cell death program in human cancer cells and in murine B cells.
Subject(s)
Apoptosis , Ataxia Telangiectasia Mutated Proteins/metabolism , Carrier Proteins/metabolism , Casein Kinase II/metabolism , DNA-Activated Protein Kinase/metabolism , DNA-Binding Proteins/metabolism , Inositol Phosphates/metabolism , Nuclear Proteins/metabolism , Proto-Oncogene Proteins c-ets/metabolism , Telomere-Binding Proteins/metabolism , Tumor Suppressor Protein p53/metabolism , Animals , Ataxia Telangiectasia Mutated Proteins/genetics , B-Lymphocytes/enzymology , B-Lymphocytes/pathology , Binding Sites , Carrier Proteins/genetics , Casein Kinase II/genetics , DNA-Activated Protein Kinase/genetics , DNA-Binding Proteins/genetics , Enzyme Stability , HCT116 Cells , HEK293 Cells , Humans , Intracellular Signaling Peptides and Proteins , Mice, Knockout , Neoplasms/enzymology , Neoplasms/genetics , Neoplasms/pathology , Nuclear Proteins/genetics , Phosphorylation , Phosphotransferases (Phosphate Group Acceptor)/deficiency , Phosphotransferases (Phosphate Group Acceptor)/genetics , Proto-Oncogene Proteins c-ets/genetics , RNA Interference , Serine , Signal Transduction , Telomere-Binding Proteins/genetics , Transfection , Tumor Suppressor Protein p53/geneticsABSTRACT
Patients suffering from cholestasis, the slowing or stoppage of bile flow, commonly report experiencing an intense, chronic itch. Numerous pruritogens are up-regulated in cholestatic patient sera, including bile acids (BAs). Acute injection of BAs results in itch in both mice and humans, and BA-modulating therapy is effective in controlling patient itch. Here, we present evidence that human sensory neuron-expressed Mas-related G protein-coupled receptor X4 (MRGPRX4), an orphan member of the Mrgpr family of GPCRs, is a BA receptor. Using Ca2+ imaging, we determined that pathophysiologically relevant levels of numerous BAs activated MRGPRX4. No mouse Mrgpr orthologs were activated by BAs. To assess the in vivo relevance of BA activation of MRGPRX4, we generated a humanized mouse with targeted expression of MRGPRX4 in itch-encoding sensory neurons. BAs activated MRGPRX4+ sensory neurons at higher levels compared with WT neurons. Compared with control animals, MRGPRX4+ mice scratched more upon acute injection of BAs and in a model of cholestatic itch. Overall, these data suggest that targeting MRGPRX4 is a promising strategy for alleviating cholestatic itch.
Subject(s)
Bile Acids and Salts/metabolism , Cholestasis/complications , Pruritus/etiology , Receptors, G-Protein-Coupled/metabolism , Sensory Receptor Cells/metabolism , Animals , Cholestasis/metabolism , Humans , Mice , Pruritus/metabolismABSTRACT
Phosphorylation of histone H2AX is a major contributor to efficient DNA repair. We recently reported neurobehavioral deficits in mice lacking H2AX. Here we establish that this neural failure stems from impairment of mitochondrial function and repression of the mitochondrial biogenesis gene PGC-1α. H2AX loss leads to reduced levels of the major subunits of the mitochondrial respiratory complexes in mouse embryonic fibroblasts and in the striatum, a brain region particularly vulnerable to mitochondrial damage. These defects are substantiated by disruption of the mitochondrial shape in H2AX mutant cells. Ectopic expression of PGC-1α restores mitochondrial oxidative phosphorylation complexes and mitigates cell death. H2AX knockout mice display increased neuronal death in the brain when challenged with 3-nitropronionic acid, which targets mitochondria. This study establishes a role for H2AX in mitochondrial homeostasis associated with neuroprotection.
Subject(s)
Histones/metabolism , Mitochondria/metabolism , Neural Stem Cells/metabolism , Neurons/metabolism , Oxidative Phosphorylation , Animals , Cell Death , Electron Transport/physiology , Histones/genetics , Mice , Mice, Knockout , Mitochondria/genetics , Neural Stem Cells/cytology , Neurons/cytology , Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha/genetics , Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha/metabolism , PhosphorylationABSTRACT
Inositol polyphosphate multikinase (IPMK), the key enzyme for the biosynthesis of higher inositol polyphosphates and phosphatidylinositol 3,4,5-trisphosphate, also acts as a versatile signaling player in regulating tissue growth and metabolism. To elucidate neurobehavioral functions of IPMK, we generated mice in which IPMK was deleted from the excitatory neurons of the postnatal forebrain. These mice showed no deficits in either novel object recognition or spatial memory. IPMK conditional knockout mice formed cued fear memory normally but displayed enhanced fear extinction. Signaling analyses revealed dysregulated expression of neural genes accompanied by selective activation of the mechanistic target of rapamycin (mTOR) regulatory enzyme p85 S6 kinase 1 (S6K1) in the amygdala following fear extinction. The IPMK mutants also manifested facilitated hippocampal long-term potentiation. These findings establish a signaling action of IPMK that mediates fear extinction.
Subject(s)
Extinction, Psychological , Fear/psychology , Memory , Phosphotransferases (Alcohol Group Acceptor)/metabolism , Animals , Enzyme Activation , Gene Deletion , Mice , Mice, Knockout , Phosphotransferases (Alcohol Group Acceptor)/genetics , Prosencephalon/physiology , Signal Transduction , Up-RegulationABSTRACT
Glutamate is the most abundant excitatory neurotransmitter, present at the bulk of cortical synapses, and participating in many physiologic and pathologic processes ranging from learning and memory to stroke. The tripeptide, glutathione, is one-third glutamate and present at up to low millimolar intracellular concentrations in brain, mediating antioxidant defenses and drug detoxification. Because of the substantial amounts of brain glutathione and its rapid turnover under homeostatic control, we hypothesized that glutathione is a relevant reservoir of glutamate and could influence synaptic excitability. We find that drugs that inhibit generation of glutamate by the glutathione cycle elicit decreases in cytosolic glutamate and decreased miniature excitatory postsynaptic potential (mEPSC) frequency. In contrast, pharmacologically decreasing the biosynthesis of glutathione leads to increases in cytosolic glutamate and enhanced mEPSC frequency. The glutathione cycle can compensate for decreased excitatory neurotransmission when the glutamate-glutamine shuttle is inhibited. Glutathione may be a physiologic reservoir of glutamate neurotransmitter.
Subject(s)
Glutathione/metabolism , Synapses/metabolism , Animals , Cells, Cultured , Excitatory Postsynaptic Potentials/physiology , Glutamic Acid/metabolism , Homeostasis , Neurons/physiology , Rats, Sprague-Dawley , Synaptic Transmission/physiologyABSTRACT
Cells express a family of three inositol hexakisphosphate kinases (IP6Ks). Although sharing the same enzymatic activity, individual IP6Ks mediate different cellular processes. Here we report that IP6K3 is enriched at the leading edge of migrating cells where it associates with dynein intermediate chain 2 (DIC2). Using immunofluorescence microscopy and total internal reflection fluorescence microscopy, we found that DIC2 and IP6K3 are recruited interdependently to the leading edge of migrating cells, where they function coordinately to enhance the turnover of focal adhesions. Deletion of IP6K3 causes defects in cell motility and neuronal dendritic growth, eventually leading to brain malformations. Our results reveal a mechanism whereby IP6K3 functions in coordination with DIC2 in a confined intracellular microenvironment to promote focal adhesion turnover.