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Andreasen M, Nedergaard S. Effects of carbonic anhydrase activity on the excitability of hippocampal axons during high-frequency firing. Brain Res 2023; 1821:148604. [PMID: 37748571 DOI: 10.1016/j.brainres.2023.148604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Revised: 08/24/2023] [Accepted: 09/22/2023] [Indexed: 09/27/2023]
Abstract
Epileptic activity is known to cause a lowering of intraneuronal pH, which has been suggested to serve as a feedback signal to terminate seizures. The mechanism of such signaling is unclear, but likely involves an altered function of several types of ligand- and voltage-gated channels in postsynaptic membranes caused by increasing cytosolic and extracellular [H+]. In addition, axonal conduction properties may be altered by endogenous pH signals, but this has not been investigated. In the present study, we have recorded the axonal compound action potential (fiber volley) in hippocampal slices in the presence of glutamatergic and GABAergic antagonists. During high-frequency stimulation (HFS) of the Schaffer collaterals, the fiber volley was depressed and its latency from stimulus to peak increased. In the CA1 stratum radiatum these changes were enhanced when the carbonic anhydrase inhibitor acetazolamide (1 mM) was co-perfused. The enhancing effect of acetazolamide was absent after lowering of [Ca2+] in the perfusion medium. Acetazolamide had no detectable effect on HFS-evoked fiber volleys recorded from a more proximal site along the Schaffer collaterals (at the CA2-CA3 border) or from axons in the alveus of CA1. Intracellular acidification imposed by washout of NH4Cl (5 mM) had qualitatively similar effects on fiber volleys evoked at low frequency as those observed with acetazolamide during HFS in CA1 stratum radiatum. The results suggest that carbonic anhydrase-dependent pH regulation counteracts activity-induced reduction of the excitability of Schaffer collateral axons in CA1. A possible influence from local synaptic terminals on this effect is discussed.
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Affiliation(s)
- Mogens Andreasen
- Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Steen Nedergaard
- Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark.
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2
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Justs KA, Sempertegui S, Riboul DV, Oliva CD, Durbin RJ, Crill S, Stawarski M, Su C, Renden RB, Fily Y, Macleod GT. Mitochondrial phosphagen kinases support the volatile power demands of motor nerve terminals. J Physiol 2023; 601:5705-5732. [PMID: 37942946 PMCID: PMC10841428 DOI: 10.1113/jp284872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Accepted: 10/17/2023] [Indexed: 11/10/2023] Open
Abstract
Motor neurons are the longest neurons in the body, with axon terminals separated from the soma by as much as a meter. These terminals are largely autonomous with regard to their bioenergetic metabolism and must burn energy at a high rate to sustain muscle contraction. Here, through computer simulation and drawing on previously published empirical data, we determined that motor neuron terminals in Drosophila larvae experience highly volatile power demands. It might not be surprising then, that we discovered the mitochondria in the motor neuron terminals of both Drosophila and mice to be heavily decorated with phosphagen kinases - a key element in an energy storage and buffering system well-characterized in fast-twitch muscle fibres. Knockdown of arginine kinase 1 (ArgK1) in Drosophila larval motor neurons led to several bioenergetic deficits, including mitochondrial matrix acidification and a faster decline in the cytosol ATP to ADP ratio during axon burst firing. KEY POINTS: Neurons commonly fire in bursts imposing highly volatile demands on the bioenergetic machinery that generates ATP. Using a computational approach, we built profiles of presynaptic power demand at the level of single action potentials, as well as the transition from rest to sustained activity. Phosphagen systems are known to buffer ATP levels in muscles and we demonstrate that phosphagen kinases, which support such phosphagen systems, also localize to mitochondria in motor nerve terminals of fruit flies and mice. By knocking down phosphagen kinases in fruit fly motor nerve terminals, and using fluorescent reporters of the ATP:ADP ratio, lactate, pH and Ca2+ , we demonstrate a role for phosphagen kinases in stabilizing presynaptic ATP levels. These data indicate that the maintenance of phosphagen systems in motor neurons, and not just muscle, could be a beneficial initiative in sustaining musculoskeletal health and performance.
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Affiliation(s)
- Karlis A. Justs
- Integrative Biology and Neuroscience Graduate Program, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Sergio Sempertegui
- Department of Physics, College of Science, Florida Atlantic University, Boca Raton, FL, 33431, USA
| | - Danielle V. Riboul
- Integrative Biology and Neuroscience Graduate Program, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Carlos D. Oliva
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Ryan J. Durbin
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557
| | - Sarah Crill
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Michal Stawarski
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Chenchen Su
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Robert B. Renden
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557
| | - Yaouen Fily
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
| | - Gregory T. Macleod
- Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA
- Institute for Human Health & Disease Intervention, Florida Atlantic University, Jupiter, FL 33458, USA
- Stiles-Nicholson Brain Institute, Florida Atlantic University, Jupiter, FL 33458, USA
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3
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Karagas NE, Gupta R, Rastegari E, Tan KL, Leung HH, Bellen HJ, Venkatachalam K, Wong CO. Loss of Activity-Induced Mitochondrial ATP Production Underlies the Synaptic Defects in a Drosophila Model of ALS. J Neurosci 2022; 42:8019-8037. [PMID: 36261266 PMCID: PMC9617612 DOI: 10.1523/jneurosci.2456-21.2022] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Revised: 08/23/2022] [Accepted: 08/27/2022] [Indexed: 11/21/2022] Open
Abstract
Mutations in the gene encoding vesicle-associated membrane protein B (VAPB) cause a familial form of amyotrophic lateral sclerosis (ALS). Expression of an ALS-related variant of vapb (vapbP58S ) in Drosophila motor neurons results in morphologic changes at the larval neuromuscular junction (NMJ) characterized by the appearance of fewer, but larger, presynaptic boutons. Although diminished microtubule stability is known to underlie these morphologic changes, a mechanism for the loss of presynaptic microtubules has been lacking. By studying flies of both sexes, we demonstrate the suppression of vapbP58S -induced changes in NMJ morphology by either a loss of endoplasmic reticulum (ER) Ca2+ release channels or the inhibition Ca2+/calmodulin (CaM)-activated kinase II (CaMKII). These data suggest that decreased stability of presynaptic microtubules at vapbP58S NMJs results from hyperactivation of CaMKII because of elevated cytosolic [Ca2+]. We attribute the Ca2+ dyshomeostasis to delayed extrusion of cytosolic Ca2+ Suggesting that this defect in Ca2+ extrusion arose from an insufficient response to the bioenergetic demand of neural activity, depolarization-induced mitochondrial ATP production was diminished in vapbP58S neurons. These findings point to bioenergetic dysfunction as a potential cause for the synaptic defects in vapbP58S -expressing motor neurons.SIGNIFICANCE STATEMENT Whether the synchrony between the rates of ATP production and demand is lost in degenerating neurons remains poorly understood. We report that expression of a gene equivalent to an amyotrophic lateral sclerosis (ALS)-causing variant of vesicle-associated membrane protein B (VAPB) in fly neurons decouples mitochondrial ATP production from neuronal activity. Consequently, levels of ATP in mutant neurons are unable to keep up with the bioenergetic burden of neuronal activity. Reduced rate of Ca2+ extrusion, which could result from insufficient energy to power Ca2+ ATPases, results in the accumulation of residual Ca2+ in mutant neurons and leads to alterations in synaptic vesicle (SV) release and synapse development. These findings suggest that synaptic defects in a model of ALS arise from the loss of activity-induced ATP production.
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Affiliation(s)
- Nicholas E Karagas
- Department of Integrative Biology and Pharmacology, McGovern Medical School at the University of Texas Health Sciences Center, Houston, Texas 77030
- Graduate Program in Biochemistry and Cell Biology, MD Anderson Cancer Center and University of Texas Health Sciences Center Graduate School of Biomedical Sciences, Houston, TX, 77030
| | - Richa Gupta
- Department of Integrative Biology and Pharmacology, McGovern Medical School at the University of Texas Health Sciences Center, Houston, Texas 77030
| | - Elham Rastegari
- Department of Integrative Biology and Pharmacology, McGovern Medical School at the University of Texas Health Sciences Center, Houston, Texas 77030
| | - Kai Li Tan
- Departments of Molecular and Human Genetics and Neuroscience, Baylor College of Medicine, Houston, TX 77030
- Graduate Program in Developmental Biology, Baylor College of Medicine, Houston, Texas 77030
- Duncan Neurological Research Institute, Texas Children Hospital, Houston, Texas 77030
| | - Ho Hang Leung
- Department of Biological Sciences, Rutgers University, Newark, New Jersey 07102
| | - Hugo J Bellen
- Departments of Molecular and Human Genetics and Neuroscience, Baylor College of Medicine, Houston, TX 77030
- Graduate Program in Developmental Biology, Baylor College of Medicine, Houston, Texas 77030
- Duncan Neurological Research Institute, Texas Children Hospital, Houston, Texas 77030
| | - Kartik Venkatachalam
- Department of Integrative Biology and Pharmacology, McGovern Medical School at the University of Texas Health Sciences Center, Houston, Texas 77030
- Graduate Program in Biochemistry and Cell Biology, MD Anderson Cancer Center and University of Texas Health Sciences Center Graduate School of Biomedical Sciences, Houston, TX, 77030
- Graduate Program in Neuroscience, MD Anderson Cancer Center and University of Texas Health Sciences Center Graduate School of Biomedical Sciences, Houston, TX, 77030
| | - Ching-On Wong
- Department of Biological Sciences, Rutgers University, Newark, New Jersey 07102
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4
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Turaev AV, Isaakova EA, Severov VV, Bogomazova AN, Zatsepin TS, Sardushkin MV, Aralov AV, Lagarkova MA, Pozmogova GE, Varizhuk AM. Genomic DNA i-motifs as fast sensors responsive to near-physiological pH microchanges. Biosens Bioelectron 2020; 175:112864. [PMID: 33309217 DOI: 10.1016/j.bios.2020.112864] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2020] [Revised: 11/11/2020] [Accepted: 11/24/2020] [Indexed: 02/06/2023]
Abstract
We report the design of robust sensors for measuring intracellular pH, based on the native DNA i-motifs (iMs) found in neurodegeneration- or carcinogenesis-related genes. Those iMs appear to be genomic regulatory elements and might modulate transcription in response to pH stimuli. Given their intrinsic sensitivity to minor pH changes within the physiological range, such noncanonical DNA structures can be used as sensor core elements without additional modules other than fluorescent labels or quenchers. We focused on several iMs that exhibited fast folding/unfolding kinetics. Using stopped-flow techniques and FRET-melting/annealing assays, we confirmed that the rates of temperature-driven iM-ssDNA transitions correlate with the rates of the pH-driven transitions. Thus, we propose FRET-based hysteresis analysis as an express method for selecting sensors with desired kinetic characteristics. For the leading fast-response sensor, we optimized the labelling scheme and performed intracellular calibration. Unlike the commonly used small-molecule pH indicators, that sensor was transferred efficiently to cell nuclei. Considering its favourable kinetic characteristics, the sensor can be used for monitoring proton dynamics in the nucleus. These results argue that the 'genome-inspired' design is a productive approach to the development of biocompatible molecular tools.
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Affiliation(s)
- Anton V Turaev
- Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia
| | - Ekaterina A Isaakova
- Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia
| | - Vjacheslav V Severov
- Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia
| | - Alexandra N Bogomazova
- Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia; Center for Precision Genome Editing and Genetic Technologies for Biomedicine, Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia
| | - Timofei S Zatsepin
- Skolkovo Institute of Science and Technology, Moscow Oblast, 143026, Russia
| | - Makar V Sardushkin
- Mendeleev University of Chemical Technology of Russia, Moscow, 125047, Russia
| | - Andrey V Aralov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Moscow, 117997, Russia
| | - Maria A Lagarkova
- Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia; Center for Precision Genome Editing and Genetic Technologies for Biomedicine, Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia
| | - Galina E Pozmogova
- Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia
| | - Anna M Varizhuk
- Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia; Center for Precision Genome Editing and Genetic Technologies for Biomedicine, Federal Research and Clinical Center of Physical-Chemical Medicine of Federal Medical Biological Agency, Moscow, 119435, Russia; Engelhardt Institute of Molecular Biology, Moscow, 119991, Russia.
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5
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Abstract
Although students initially learn of ionic buffering in basic chemistry, buffering and acid-base transport in biology often is relegated to specialized classes, discussions, or situations. That said, for physiology, nephrology, pulmonology, and anesthesiology, these basic principles often are critically important for mechanistic understanding, medical treatments, and assessing therapy effectiveness. This short introductory perspective focuses on basic chemistry and transport of buffers and acid-base equivalents, provides an outline of basic science acid-base concepts, tools used to monitor intracellular pH, model cellular responses to pH buffer changes, and the more recent development and use of genetically encoded pH-indicators. Examples of newer genetically encoded pH-indicators (pHerry and pHire) are provided, and their use for in vitro, ex vivo, and in vivo experiments are described. The continued use and development of these basic tools provide increasing opportunities for both basic and potentially clinical investigations.
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Affiliation(s)
- Michael F Romero
- Physiology and Biomedical Engineering, Nephrology and Hypertension, Mayo Clinic College of Medicine and Science, Rochester, MN.
| | - Adam J Rossano
- Physiology and Biomedical Engineering, Nephrology and Hypertension, Mayo Clinic College of Medicine and Science, Rochester, MN
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6
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tpHusion: An efficient tool for clonal pH determination in Drosophila. PLoS One 2020; 15:e0228995. [PMID: 32059043 PMCID: PMC7021318 DOI: 10.1371/journal.pone.0228995] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Accepted: 01/27/2020] [Indexed: 02/04/2023] Open
Abstract
Genetically encoded pH indicators (GEpHI) have emerged as important tools for investigating intracellular pH (pHi) dynamics in Drosophila. However, most of the indicators are based on the Gal4/UAS binary expression system. Here, we report the generation of a ubiquitously-expressed GEpHI. The fusion protein of super ecliptic pHluorin and FusionRed was cloned under the tubulin promoter (tpHusion) to drive it independently of the Gal4/UAS system. The function of tpHusion was validated in various tissues from different developmental stages of Drosophila. Differences in pHi were also indicated correctly in fixed tissues. Finally, we describe the use of tpHusion for comparative analysis of pHi in manipulated clones and the surrounding cells in epithelial tissues. Our findings establish tpHusion as a robust tool for studying pHi in Drosophila.
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7
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Neuronal Glutamatergic Synaptic Clefts Alkalinize Rather Than Acidify during Neurotransmission. J Neurosci 2020; 40:1611-1624. [PMID: 31964719 DOI: 10.1523/jneurosci.1774-19.2020] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 01/14/2020] [Accepted: 01/15/2020] [Indexed: 12/11/2022] Open
Abstract
The dogma that the synaptic cleft acidifies during neurotransmission is based on the corelease of neurotransmitters and protons from synaptic vesicles, and is supported by direct data from sensory ribbon-type synapses. However, it is unclear whether acidification occurs at non-ribbon-type synapses. Here we used genetically encoded fluorescent pH indicators to examine cleft pH at conventional neuronal synapses. At the neuromuscular junction of female Drosophila larvae, we observed alkaline spikes of over 1 log unit during fictive locomotion in vivo. Ex vivo, single action potentials evoked alkalinizing pH transients of only ∼0.01 log unit, but these transients summated rapidly during burst firing. A chemical pH indicator targeted to the cleft corroborated these findings. Cleft pH transients were dependent on Ca2+ movement across the postsynaptic membrane, rather than neurotransmitter release per se, a result consistent with cleft alkalinization being driven by the Ca2+/H+ antiporting activity of the plasma membrane Ca2+-ATPase at the postsynaptic membrane. Targeting the pH indicators to the microenvironment of the presynaptic voltage gated Ca2+ channels revealed that alkalinization also occurred within the cleft proper at the active zone and not just within extrasynaptic regions. Application of the pH indicators at the mouse calyx of Held, a mammalian central synapse, similarly revealed cleft alkalinization during burst firing in both males and females. These findings, made at two quite different non-ribbon type synapses, suggest that cleft alkalinization during neurotransmission, rather than acidification, is a generalizable phenomenon across conventional neuronal synapses.SIGNIFICANCE STATEMENT Neurotransmission is highly sensitive to the pH of the extracellular milieu. This is readily evident in the neurological symptoms that accompany systemic acid/base imbalances. Imaging data from sensory ribbon-type synapses show that neurotransmission itself can acidify the synaptic cleft, likely due to the corelease of protons and glutamate. It is not clear whether the same phenomenon occurs at conventional neuronal synapses due to the difficulties in collecting such data. If it does occur, it would provide for an additional layer of activity-dependent modulation of neurotransmission. Our findings of alkalinization, rather than acidification, within the cleft of two different neuronal synapses encourages a reassessment of the scope of activity-dependent pH influences on neurotransmission and short-term synaptic plasticity.
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8
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Stawarski M, Justs KA, Hernandez RX, Macleod GT. The application of 'kisser' probes for resolving the distribution and microenvironment of membrane proteins in situ. J Neurogenet 2018; 32:236-245. [PMID: 30175639 DOI: 10.1080/01677063.2018.1503260] [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] [Indexed: 12/28/2022]
Abstract
Membrane proteins play a lead role in the formation and function of synapses, but, despite revolutions in immunology and molecular genetics, limitations persist in our ability to investigate membrane proteins in the context of an intact synapse. Here, we introduce a simple but novel approach to resolving the distribution of endogenous membrane proteins in either live or fixed tissues. The technique involves transgenic expression of a protein with an extracellular tag, a generic transmembrane domain, and an intracellular terminus that mimics the intracellular anchoring motifs of the endogenous protein of interest. We provide three examples where these kisser probes can be used to answer questions regarding the synaptic distribution of endogenous proteins and their microenvironment that would be difficult to resolve by other contemporary means: (i) the live distribution of untagged proteins at the neuromuscular junction (Cacophony and Shaker), (ii) the relative distribution of an untagged protein (PMCA) in pre- versus post-synaptic membranes separated by only 20 nm across the cleft of a fixed synapse, and (iii) the live targeting of functional probes (chemical and protein fluorescent pH reporters) to membrane protein-defined subcellular domains.
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Affiliation(s)
- Michal Stawarski
- a Department of Biomedicine , University of Basel , Basel , Switzerland
| | - Karlis Anthony Justs
- b Wilkes Honors College , Florida Atlantic University, John D MacArthur Campus , Jupiter , FL, USA
| | - Roberto Xander Hernandez
- b Wilkes Honors College , Florida Atlantic University, John D MacArthur Campus , Jupiter , FL, USA
| | - Gregory Talisker Macleod
- b Wilkes Honors College , Florida Atlantic University, John D MacArthur Campus , Jupiter , FL, USA
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9
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Rajendran M, Claywell B, Haynes EP, Scales U, Henning CK, Tantama M. Imaging pH Dynamics Simultaneously in Two Cellular Compartments Using a Ratiometric pH-Sensitive Mutant of mCherry. ACS OMEGA 2018; 3:9476-9486. [PMID: 30197999 PMCID: PMC6120727 DOI: 10.1021/acsomega.8b00655] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Accepted: 08/06/2018] [Indexed: 05/09/2023]
Abstract
The regulation of pH is essential for proper organelle function, and organelle-specific changes in pH often reflect the dynamics of physiological signaling and metabolism. For example, mitochondrial energy production depends on the proton gradient maintained between the alkaline mitochondrial matrix and neutral cytosol. However, we still lack a quantitative understanding of how pH dynamics are coupled between compartments and how pH gradients are regulated at organelle boundaries. Genetically encoded pH sensors are well suited to address this problem because they can be targeted to specific subcellular locations and they facilitate live, single-cell analysis. However, most of these pH sensors are derivatives of green and yellow fluorescent proteins that are not spectrally compatible for dual-compartment imaging. Therefore, there is a need for ratiometric red fluorescent protein pH sensors that enable quantitative multicolor imaging of spatially resolved pH dynamics. In this work, we demonstrate that the I158E/Q160A mutant of the red fluorescent protein mCherry is an effective ratiometric pH sensor. It has a pKa of 7.3 and a greater than 3-fold change in ratio signal. To demonstrate its utility in cells, we measured activity and metabolism-dependent pH dynamics in cultured primary neurons and neuroblastoma cells. Furthermore, we were able to image pH changes simultaneously in the cytosol and mitochondria by using the mCherryEA mutant together with the green fluorescent pH sensor, ratiometric-pHluorin. Our results demonstrate the feasibility of studying interorganelle pH dynamics in live cells over time and the broad applicability of these sensors in studying the role of pH regulation in metabolism and signaling.
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Affiliation(s)
- Megha Rajendran
- Department
of Chemistry, Institute for Integrative Neuroscience, and Institute of Inflammation, Immunology,
and Infectious Disease, Purdue University, 560 Oval Drive,
P.O. Box 68, West Lafayette, Indiana 47907, United States
| | - Benjamin Claywell
- Department
of Chemistry, Institute for Integrative Neuroscience, and Institute of Inflammation, Immunology,
and Infectious Disease, Purdue University, 560 Oval Drive,
P.O. Box 68, West Lafayette, Indiana 47907, United States
| | - Emily P. Haynes
- Department
of Chemistry, Institute for Integrative Neuroscience, and Institute of Inflammation, Immunology,
and Infectious Disease, Purdue University, 560 Oval Drive,
P.O. Box 68, West Lafayette, Indiana 47907, United States
| | - Umi Scales
- Department
of Chemistry, Institute for Integrative Neuroscience, and Institute of Inflammation, Immunology,
and Infectious Disease, Purdue University, 560 Oval Drive,
P.O. Box 68, West Lafayette, Indiana 47907, United States
| | - Chace K. Henning
- Department
of Chemistry, Institute for Integrative Neuroscience, and Institute of Inflammation, Immunology,
and Infectious Disease, Purdue University, 560 Oval Drive,
P.O. Box 68, West Lafayette, Indiana 47907, United States
| | - Mathew Tantama
- Department
of Chemistry, Institute for Integrative Neuroscience, and Institute of Inflammation, Immunology,
and Infectious Disease, Purdue University, 560 Oval Drive,
P.O. Box 68, West Lafayette, Indiana 47907, United States
- E-mail: . Phone: 765-494-5312
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10
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Reifenrath M, Boles E. A superfolder variant of pH-sensitive pHluorin for in vivo pH measurements in the endoplasmic reticulum. Sci Rep 2018; 8:11985. [PMID: 30097598 PMCID: PMC6086885 DOI: 10.1038/s41598-018-30367-z] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 07/27/2018] [Indexed: 11/09/2022] Open
Abstract
Many cellular processes are regulated via pH, and maintaining the pH of different organelles is crucial for cell survival. A pH-sensitive GFP variant, the so-called pHluorin, has proven to be a valuable tool to study the pH of the cytosol, mitochondria and other organelles in vivo. We found that the fluorescence intensity of Endoplasmic Reticulum (ER)-targeted pHluorin in the yeast Saccharomyces cerevisiae was very low and barely showed pH sensitivity, probably due to misfolding in the oxidative environment of the ER. We therefore developed a superfolder variant of pHluorin which enabled us to monitor pH changes in the ER and the cytosol of S. cerevisiae in vivo. The superfolder pHluorin variant is likely to be functional in cells of different organisms as well as in additional compartments that originate from the secretory pathway like the Golgi apparatus and pre-vacuolar compartments, and therefore has a broad range of possible future applications.
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Affiliation(s)
- Mara Reifenrath
- Institute of Molecular Biosciences, Faculty of Biological Sciences, Goethe University Frankfurt, Max-von-Laue Straße 9, 60438, Frankfurt am Main, Germany
| | - Eckhard Boles
- Institute of Molecular Biosciences, Faculty of Biological Sciences, Goethe University Frankfurt, Max-von-Laue Straße 9, 60438, Frankfurt am Main, Germany.
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11
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Boffi JC, Knabbe J, Kaiser M, Kuner T. KCC2-dependent Steady-state Intracellular Chloride Concentration and pH in Cortical Layer 2/3 Neurons of Anesthetized and Awake Mice. Front Cell Neurosci 2018; 12:7. [PMID: 29422838 PMCID: PMC5788967 DOI: 10.3389/fncel.2018.00007] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Accepted: 01/05/2018] [Indexed: 12/31/2022] Open
Abstract
Neuronal intracellular Cl− concentration ([Cl−]i) influences a wide range of processes such as neuronal inhibition, membrane potential dynamics, intracellular pH (pHi) or cell volume. Up to date, neuronal [Cl−]i has predominantly been studied in model systems of reduced complexity. Here, we implemented the genetically encoded ratiometric Cl− indicator Superclomeleon (SCLM) to estimate the steady-state [Cl−]i in cortical neurons from anesthetized and awake mice using 2-photon microscopy. Additionally, we implemented superecliptic pHluorin (SE-pHluorin) as a ratiometric sensor to estimate the intracellular steady-state pH (pHi) of mouse cortical neurons in vivo. We estimated an average resting [Cl−]i of 6 ± 2 mM with no evidence of subcellular gradients in the proximal somato-dendritic domain and an average somatic pHi of 7.1 ± 0.2. Neither [Cl−]i nor pHi were affected by isoflurane anesthesia. We deleted the cation-Cl− co-transporter KCC2 in single identified neurons of adult mice and found an increase of [Cl−]i to approximately 26 ± 8 mM, demonstrating that under in vivo conditions KCC2 produces low [Cl−]i in adult mouse neurons. In summary, neurons of the brain of awake adult mice exhibit a low and evenly distributed [Cl−]i in the proximal somato-dendritic compartment that is independent of anesthesia and requires KCC2 expression for its maintenance.
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Affiliation(s)
- Juan C Boffi
- Department of Functional Neuroanatomy, Institute for Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
| | - Johannes Knabbe
- Department of Functional Neuroanatomy, Institute for Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
| | - Michaela Kaiser
- Department of Functional Neuroanatomy, Institute for Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
| | - Thomas Kuner
- Department of Functional Neuroanatomy, Institute for Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
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12
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Ventimiglia D, Bargmann CI. Diverse modes of synaptic signaling, regulation, and plasticity distinguish two classes of C. elegans glutamatergic neurons. eLife 2017; 6:e31234. [PMID: 29160768 PMCID: PMC5705214 DOI: 10.7554/elife.31234] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 11/20/2017] [Indexed: 11/13/2022] Open
Abstract
Synaptic vesicle release properties vary between neuronal cell types, but in most cases the molecular basis of this heterogeneity is unknown. Here, we compare in vivo synaptic properties of two neuronal classes in the C. elegans central nervous system, using VGLUT-pHluorin to monitor synaptic vesicle exocytosis and retrieval in intact animals. We show that the glutamatergic sensory neurons AWCON and ASH have distinct synaptic dynamics associated with tonic and phasic synaptic properties, respectively. Exocytosis in ASH and AWCON is differentially affected by SNARE-complex regulators that are present in both neurons: phasic ASH release is strongly dependent on UNC-13, whereas tonic AWCON release relies upon UNC-18 and on the protein kinase C homolog PKC-1. Strong stimuli that elicit high calcium levels increase exocytosis and retrieval rates in AWCON, generating distinct tonic and evoked synaptic modes. These results highlight the differential deployment of shared presynaptic proteins in neuronal cell type-specific functions.
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Affiliation(s)
- Donovan Ventimiglia
- Lulu and Anthony Wang Laboratory of Neural Circuits and BehaviorThe Rockefeller UniversityNew YorkUnited States
| | - Cornelia I Bargmann
- Lulu and Anthony Wang Laboratory of Neural Circuits and BehaviorThe Rockefeller UniversityNew YorkUnited States
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13
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Tatapudy S, Benitez M, Nystul T. Methods for Imaging Intracellular pH of the Follicle Stem Cell Lineage in Live Drosophila Ovarian Tissue. J Vis Exp 2017. [PMID: 28994781 DOI: 10.3791/56316] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Changes in intracellular pH (pHi) play important roles in the regulation of many cellular functions, including metabolism, proliferation, and differentiation. Typically, pHi dynamics are determined in cultured cells, which are amenable to measuring and experimentally manipulating pHi. However, the recent development of new tools and methodologies has made it possible to study pHi dynamics within intact, live tissue. For Drosophila research, one important development was the generation of a transgenic line carrying a pHi biosensor, mCherry::pHluorin. Here, we describe a protocol that we routinely use for imaging live Drosophila ovarioles to measure pHi in the epithelial follicle stem cell (FSC) lineage in mCherry::pHluorin transgenic wild type lines; however, the methods described here can be easily adapted for other tissues, including the wing discs and eye epithelium. We describe techniques for expressing mCherry::pHluorin in the FSC lineage, maintaining ovarian tissue during live imaging, and acquiring and analyzing images to obtain pHi values.
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Affiliation(s)
- Sumitra Tatapudy
- Departments of Anatomy and OB/GYN-RS, University of California, San Francisco
| | - Marimar Benitez
- Departments of Anatomy and OB/GYN-RS, University of California, San Francisco
| | - Todd Nystul
- Departments of Anatomy and OB/GYN-RS, University of California, San Francisco;
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14
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Rossano AJ, Romero MF. Optical Quantification of Intracellular pH in Drosophila melanogaster Malpighian Tubule Epithelia with a Fluorescent Genetically-encoded pH Indicator. J Vis Exp 2017. [PMID: 28829430 DOI: 10.3791/55698] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Epithelial ion transport is vital to systemic ion homeostasis as well as maintenance of essential cellular electrochemical gradients. Intracellular pH (pHi) is influenced by many ion transporters and thus monitoring pHi is a useful tool for assessing transporter activity. Modern Genetically Encoded pH-Indicators (GEpHIs) provide optical quantification of pHi in intact cells on a cellular and subcellular scale. This protocol describes real-time quantification of cellular pHi regulation in Malpighian Tubules (MTs) of Drosophila melanogaster through ex vivo live-imaging of pHerry, a pseudo-ratiometric GEpHI with a pKa well-suited to track pH changes in the cytosol. Extracted adult fly MTs are composed of morphologically and functionally distinct sections of single-cell layer epithelia, and can serve as an accessible and genetically tractable model for investigation of epithelial transport. GEpHIs offer several advantages over conventional pH-sensitive fluorescent dyes and ion-selective electrodes. GEpHIs can label distinct cell populations provided appropriate promoter elements are available. This labeling is particularly useful in ex vivo, in vivo, and in situ preparations, which are inherently heterogeneous. GEpHIs also permit quantification of pHi in intact tissues over time without need for repeated dye treatment or tissue externalization. The primary drawback of current GEpHIs is the tendency to aggregate in cytosolic inclusions in response to tissue damage and construct over-expression. These shortcomings, their solutions, and the inherent advantages of GEpHIs are demonstrated in this protocol through assessment of basolateral proton (H+) transport in functionally distinct principal and stellate cells of extracted fly MTs. The techniques and analysis described are readily adaptable to a wide variety of vertebrate and invertebrate preparations, and the sophistication of the assay can be scaled from teaching labs to intricate determination of ion flux via specific transporters.
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Affiliation(s)
- Adam J Rossano
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine;
| | - Michael F Romero
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine; Department of Nephrology and Hypertension, Mayo Clinic College of Medicine;
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15
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Ulmschneider B, Grillo-Hill BK, Benitez M, Azimova DR, Barber DL, Nystul TG. Increased intracellular pH is necessary for adult epithelial and embryonic stem cell differentiation. J Cell Biol 2017; 215:345-355. [PMID: 27821494 PMCID: PMC5100294 DOI: 10.1083/jcb.201606042] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Revised: 08/18/2016] [Accepted: 10/05/2016] [Indexed: 12/19/2022] Open
Abstract
Despite extensive knowledge about the transcriptional regulation of stem cell differentiation, less is known about the role of dynamic cytosolic cues. We report that an increase in intracellular pH (pHi) is necessary for the efficient differentiation of Drosophila adult follicle stem cells (FSCs) and mouse embryonic stem cells (mESCs). We show that pHi increases with differentiation from FSCs to prefollicle cells (pFCs) and follicle cells. Loss of the Drosophila Na+-H+ exchanger DNhe2 lowers pHi in differentiating cells, impairs pFC differentiation, disrupts germarium morphology, and decreases fecundity. In contrast, increasing pHi promotes excess pFC cell differentiation toward a polar/stalk cell fate through suppressing Hedgehog pathway activity. Increased pHi also occurs with mESC differentiation and, when prevented, attenuates spontaneous differentiation of naive cells, as determined by expression of microRNA clusters and stage-specific markers. Our findings reveal a previously unrecognized role of pHi dynamics for the differentiation of two distinct types of stem cell lineages, which opens new directions for understanding conserved regulatory mechanisms.
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Affiliation(s)
- Bryne Ulmschneider
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94143.,Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, San Francisco, CA 94143
| | - Bree K Grillo-Hill
- Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143.,Department of Biological Sciences, San Jose State University, San Jose, CA 95192
| | - Marimar Benitez
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94143.,Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, San Francisco, CA 94143
| | - Dinara R Azimova
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94143.,Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, San Francisco, CA 94143
| | - Diane L Barber
- Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143
| | - Todd G Nystul
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94143 .,Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, San Francisco, CA 94143
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16
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Chiacchiaretta M, Latifi S, Bramini M, Fadda M, Fassio A, Benfenati F, Cesca F. Neuronal hyperactivity causes Na +/H + exchanger-induced extracellular acidification at active synapses. J Cell Sci 2017; 130:1435-1449. [PMID: 28254883 DOI: 10.1242/jcs.198564] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 02/28/2017] [Indexed: 12/12/2022] Open
Abstract
Extracellular pH impacts on neuronal activity, which is in turn an important determinant of extracellular H+ concentration. The aim of this study was to describe the spatio-temporal dynamics of extracellular pH at synaptic sites during neuronal hyperexcitability. To address this issue we created ex.E2GFP, a membrane-targeted extracellular ratiometric pH indicator that is exquisitely sensitive to acidic shifts. By monitoring ex.E2GFP fluorescence in real time in primary cortical neurons, we were able to quantify pH fluctuations during network hyperexcitability induced by convulsant drugs or high-frequency electrical stimulation. Sustained hyperactivity caused a pH decrease that was reversible upon silencing of neuronal activity and located at active synapses. This acidic shift was not attributable to the outflow of synaptic vesicle H+ into the cleft nor to the activity of membrane-exposed H+ V-ATPase, but rather to the activity of the Na+/H+-exchanger. Our data demonstrate that extracellular synaptic pH shifts take place during epileptic-like activity of neural cultures, emphasizing the strict links existing between synaptic activity and synaptic pH. This evidence may contribute to the understanding of the physio-pathological mechanisms associated with hyperexcitability in the epileptic brain.
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Affiliation(s)
- Martina Chiacchiaretta
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy
| | - Shahrzad Latifi
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy
| | - Mattia Bramini
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy
| | - Manuela Fadda
- Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy
| | - Anna Fassio
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy
| | - Fabio Benfenati
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy
| | - Fabrizia Cesca
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy
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17
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Rossano AJ, Kato A, Minard KI, Romero MF, Macleod GT. Na + /H + exchange via the Drosophila vesicular glutamate transporter mediates activity-induced acid efflux from presynaptic terminals. J Physiol 2016; 595:805-824. [PMID: 27641622 DOI: 10.1113/jp273105] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Accepted: 09/14/2016] [Indexed: 01/26/2023] Open
Abstract
KEY POINTS Intracellular pH regulation is vital to neurons as nerve activity produces large and rapid acid loads in presynaptic terminals. Rapid clearance of acid loads is necessary to maintain control of neurotransmission, but neuronal acid clearance mechanisms remain poorly understood. Glutamate is loaded into synaptic vesicles via the vesicular glutamate transporter (VGLUT), a mechanism conserved across phyla, and this study reports a previously unknown role for VGLUT as an acid-extruding protein when deposited in the plasmamembrane during exocytosis. The finding was made in Drosophila (fruit fly) larval motor neurons through a combined pharamacological and genetic dissection of presynaptic pH homeostatic mechanisms. A dual role for VGLUT serves to integrate neuronal activity and pH regulation in presynaptic nerve terminals. ABSTRACT Neuronal activity can result in transient acidification of presynaptic terminals, and such shifts in cytosolic pH (pHcyto ) probably influence mechanisms underlying forms of synaptic plasticity with a presynaptic locus. As neuronal activity drives acid loading in presynaptic terminals, we hypothesized that the same activity might drive acid efflux mechanisms to maintain pHcyto homeostasis. To better understand the integration of neuronal activity and pHcyto regulation we investigated the acid extrusion mechanisms at Drosophila glutamatergic motorneuron terminals. Expression of a fluorescent genetically encoded pH indicator, named 'pHerry', in the presynaptic cytosol revealed acid efflux following nerve activity to be greater than that predicted from measurements of the intrinsic rate of acid efflux. Analysis of activity-induced acid transients in terminals deficient in either endocytosis or exocytosis revealed an acid efflux mechanism reliant upon synaptic vesicle exocytosis. Pharmacological and genetic dissection in situ and in a heterologous expression system indicate that this acid efflux is mediated by conventional plasmamembrane acid transporters, and also by previously unrecognized intrinsic H+ /Na+ exchange via the Drosophila vesicular glutamate transporter (DVGLUT). DVGLUT functions not only as a vesicular glutamate transporter but also serves as an acid-extruding protein when deposited on the plasmamembrane.
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Affiliation(s)
- Adam J Rossano
- School of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX, 78229, USA
| | - Akira Kato
- Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8503, Japan.,Physiology & Biomedical Engineering and Nephrology & Hypertension, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
| | - Karyl I Minard
- Biological Sciences & Wilkes Honors College, Florida Atlantic University, Jupiter, FL, 33431, USA
| | - Michael F Romero
- Physiology & Biomedical Engineering and Nephrology & Hypertension, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
| | - Gregory T Macleod
- Biological Sciences & Wilkes Honors College, Florida Atlantic University, Jupiter, FL, 33431, USA
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18
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Expression of Carbonic Anhydrase I in Motor Neurons and Alterations in ALS. Int J Mol Sci 2016; 17:ijms17111820. [PMID: 27809276 PMCID: PMC5133821 DOI: 10.3390/ijms17111820] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 10/20/2016] [Accepted: 10/24/2016] [Indexed: 12/27/2022] Open
Abstract
Carbonic anhydrase I (CA1) is the cytosolic isoform of mammalian α-CA family members which are responsible for maintaining pH homeostasis in the physiology and pathology of organisms. A subset of CA isoforms are known to be expressed and function in the central nervous system (CNS). CA1 has not been extensively characterized in the CNS. In this study, we demonstrate that CA1 is expressed in the motor neurons in human spinal cord. Unexpectedly, a subpopulation of CA1 appears to be associated with endoplasmic reticulum (ER) membranes. In addition, the membrane-associated CA1s are preferentially upregulated in amyotrophic lateral sclerosis (ALS) and exhibit altered distribution in motor neurons. Furthermore, long-term expression of CA1 in mammalian cells activates apoptosis. Our results suggest a previously unknown role for CA1 function in the CNS and its potential involvement in motor neuron degeneration in ALS.
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19
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20
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Marland JRK, Hasel P, Bonnycastle K, Cousin MA. Mitochondrial Calcium Uptake Modulates Synaptic Vesicle Endocytosis in Central Nerve Terminals. J Biol Chem 2015; 291:2080-6. [PMID: 26644474 PMCID: PMC4732196 DOI: 10.1074/jbc.m115.686956] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Indexed: 12/15/2022] Open
Abstract
Presynaptic calcium influx triggers synaptic vesicle (SV) exocytosis and modulates subsequent SV endocytosis. A number of calcium clearance mechanisms are present in central nerve terminals that regulate intracellular free calcium levels both during and after stimulation. During action potential stimulation, mitochondria rapidly accumulate presynaptic calcium via the mitochondrial calcium uniporter (MCU). The role of mitochondrial calcium uptake in modulating SV recycling has been debated extensively, but a definitive conclusion has not been achieved. To directly address this question, we manipulated the expression of the MCU channel subunit in primary cultures of neurons expressing a genetically encoded reporter of SV turnover. Knockdown of MCU resulted in ablation of activity-dependent mitochondrial calcium uptake but had no effect on the rate or extent of SV exocytosis. In contrast, the rate of SV endocytosis was increased in the absence of mitochondrial calcium uptake and slowed when MCU was overexpressed. MCU knockdown did not perturb activity-dependent increases in presynaptic free calcium, suggesting that SV endocytosis may be controlled by calcium accumulation and efflux from mitochondria in their immediate vicinity.
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Affiliation(s)
- Jamie Roslin Keynes Marland
- From the Centre for Integrative Physiology, George Square, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Philip Hasel
- From the Centre for Integrative Physiology, George Square, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Katherine Bonnycastle
- From the Centre for Integrative Physiology, George Square, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Michael Alan Cousin
- From the Centre for Integrative Physiology, George Square, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom
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21
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Daniele F, Di Cairano ES, Moretti S, Piccoli G, Perego C. TIRFM and pH-sensitive GFP-probes to evaluate neurotransmitter vesicle dynamics in SH-SY5Y neuroblastoma cells: cell imaging and data analysis. J Vis Exp 2015. [PMID: 25741799 DOI: 10.3791/52267] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Synaptic vesicles release neurotransmitters at chemical synapses through a dynamic cycle of fusion and retrieval. Monitoring synaptic activity in real time and dissecting the different steps of exo-endocytosis at the single-vesicle level are crucial for understanding synaptic functions in health and disease. Genetically-encoded pH-sensitive probes directly targeted to synaptic vesicles and Total Internal Reflection Fluorescence Microscopy (TIRFM) provide the spatio-temporal resolution necessary to follow vesicle dynamics. The evanescent field generated by total internal reflection can only excite fluorophores placed in a thin layer (<150 nm) above the glass cover on which cells adhere, exactly where the processes of exo-endocytosis take place. The resulting high-contrast images are ideally suited for vesicles tracking and quantitative analysis of fusion events. In this protocol, SH-SY5Y human neuroblastoma cells are proposed as a valuable model for studying neurotransmitter release at the single-vesicle level by TIRFM, because of their flat surface and the presence of dispersed vesicles. The methods for growing SH-SY5Y as adherent cells and for transfecting them with synapto-pHluorin are provided, as well as the technique to perform TIRFM and imaging. Finally, a strategy aiming to select, count, and analyze fusion events at whole-cell and single-vesicle levels is presented. To validate the imaging procedure and data analysis approach, the dynamics of pHluorin-tagged vesicles are analyzed under resting and stimulated (depolarizing potassium concentrations) conditions. Membrane depolarization increases the frequency of fusion events and causes a parallel raise of the net fluorescence signal recorded in whole cell. Single-vesicle analysis reveals modifications of fusion-event behavior (increased peak height and width). These data suggest that potassium depolarization not only induces a massive neurotransmitter release but also modifies the mechanism of vesicle fusion and recycling. With the appropriate fluorescent probe, this technique can be employed in different cellular systems to dissect the mechanisms of constitutive and stimulated secretion.
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Affiliation(s)
- Federica Daniele
- Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano
| | - Eliana S Di Cairano
- Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano
| | - Stefania Moretti
- Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano
| | | | - Carla Perego
- Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano; CEND Center of Excellence in Neurodegenerative Diseases, Università degli Studi di Milano;
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22
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Proton-mediated block of Ca2+ channels during multivesicular release regulates short-term plasticity at an auditory hair cell synapse. J Neurosci 2015; 34:15877-87. [PMID: 25429130 DOI: 10.1523/jneurosci.2304-14.2014] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synaptic vesicles release both neurotransmitter and protons during exocytosis, which may result in a transient acidification of the synaptic cleft that can block Ca(2+) channels located close to the sites of exocytosis. Evidence for this effect has been reported for retinal ribbon-type synapses, but not for hair cell ribbon synapses. Here, we report evidence for proton release from bullfrog auditory hair cells when they are held at more physiological, in vivo-like holding potentials (Vh = -60 mV) that facilitate multivesicular release. During paired recordings of hair cells and afferent fibers, L-type voltage-gated Ca(2+) currents showed a transient block, which was highly correlated with the EPSC amplitude (or the amount of glutamate release). This effect was masked at Vh = -90 mV due to the presence of a T-type Ca(2+) current and blocked by strong pH buffering with HEPES or TABS. Increasing vesicular pH with internal methylamine in hair cells also abolished the transient block. High concentrations of intracellular Ca(2+) buffer (10 mm BAPTA) greatly reduced exocytosis and abolished the transient block of the Ca(2+) current. We estimate that this transient block is due to the rapid multivesicular release of ∼600-1300 H(+) ions per synaptic ribbon. Finally, during a train of depolarizing pulses, paired pulse plasticity was significantly changed by using 40 mm HEPES in addition to bicarbonate buffer. We propose that this transient block of Ca(2+) current leads to more efficient exocytosis per Ca(2+) ion influx and it may contribute to spike adaptation at the auditory nerve.
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23
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Abstract
To maintain communication, neurons must recycle their synaptic vesicles with high efficiency. This process places a huge burden on the clathrin-mediated endocytic machinery, but the consequences of this are poorly understood. We found that the amount of clathrin in a presynaptic terminal is not fixed. During stimulation, clathrin moves out of synapses as a function of stimulus strength and neurotransmitter release probability, which, together with membrane coat formation, transiently reduces the available pool of free clathrin triskelia. Correlative functional and morphological experiments in cholinergic autapses established by superior cervical ganglion neurons in culture show that presynaptic terminal function is compromised if clathrin levels fall by 20% after clathrin heavy chain knock down using RNAi. Synaptic transmission is depressed due to a reduction of cytoplasmic and readily releasable pools of vesicles. However, synaptic depression reverts after dialysis of exogenous clathrin, thus compensating RNAi-induced depletion. Lowering clathrin levels also reduces quantal size, which occurs concomitantly with a decrease in the size of synaptic vesicles. Large dense-core vesicles are unaffected by clathrin knock down. Together, our results show that clathrin levels are a dynamic property of presynaptic terminals that can influence short-term plasticity in a stimulus-dependent manner.
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24
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Expression of multiple transgenes from a single construct using viral 2A peptides in Drosophila. PLoS One 2014; 9:e100637. [PMID: 24945148 PMCID: PMC4063965 DOI: 10.1371/journal.pone.0100637] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Accepted: 05/29/2014] [Indexed: 01/29/2023] Open
Abstract
Expression of multiple reporter or effector transgenes in the same cell from a single construct is increasingly necessary in various experimental paradigms. The discovery of short, virus-derived peptide sequences that mediate a ribosome-skipping event enables generation of multiple separate peptide products from one mRNA. Here we describe methods and vectors to facilitate easy production of polycistronic-like sequences utilizing these 2A peptides tailored for expression in Drosophila both in vitro and in vivo. We tested the separation efficiency of different viral 2A peptides in cultured Drosophila cells and in vivo and found that the 2A peptides from porcine teschovirus-1 (P2A) and Thosea asigna virus (T2A) worked best. To demonstrate the utility of this approach, we used the P2A peptide to co-express the red fluorescent protein tdTomato and the genetically-encoded calcium indicator GCaMP5G in larval motorneurons. This technique enabled ratiometric calcium imaging with motion correction allowing us to record synaptic activity at the neuromuscular junction in an intact larval preparation through the cuticle. The tools presented here should greatly facilitate the generation of 2A peptide-mediated expression of multiple transgenes in Drosophila.
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25
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Rangaraju V, Calloway N, Ryan TA. Activity-driven local ATP synthesis is required for synaptic function. Cell 2014; 156:825-35. [PMID: 24529383 DOI: 10.1016/j.cell.2013.12.042] [Citation(s) in RCA: 513] [Impact Index Per Article: 51.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Revised: 11/01/2013] [Accepted: 12/31/2013] [Indexed: 01/20/2023]
Abstract
Cognitive function is tightly related to metabolic state, but the locus of this control is not well understood. Synapses are thought to present large ATP demands; however, it is unclear how fuel availability and electrical activity impact synaptic ATP levels and how ATP availability controls synaptic function. We developed a quantitative genetically encoded optical reporter of presynaptic ATP, Syn-ATP, and find that electrical activity imposes large metabolic demands that are met via activity-driven control of both glycolysis and mitochondrial function. We discovered that the primary source of activity-driven metabolic demand is the synaptic vesicle cycle. In metabolically intact synapses, activity-driven ATP synthesis is well matched to the energetic needs of synaptic function, which, at steady state, results in ∼10(6) free ATPs per nerve terminal. Despite this large reservoir of ATP, we find that several key aspects of presynaptic function are severely impaired following even brief interruptions in activity-stimulated ATP synthesis.
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Affiliation(s)
- Vidhya Rangaraju
- Rockefeller/Sloan-Kettering/Weill Cornell Tri-Institutional Training Program in Chemical Biology, New York, NY 10065, USA; Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
| | - Nathaniel Calloway
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
| | - Timothy A Ryan
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA.
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26
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Abstract
Measurement of intracellular pH can be readily accomplished using tools and methods described in this chapter. We present a discussion of technical considerations of various ratiometric pH-sensitive probes including dyes and genetically encoded sensors. These probes can be used to measure pH across physical scales from macroscopic whole-mount tissues down to organelles and subcellular domains. We describe protocols for loading pH-sensitive probes into single cells or tissues and discuss ratiometric image acquisition and analysis.
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Affiliation(s)
- Bree K Grillo-Hill
- Department of Cell and Tissue Biology, University of California, San Francisco, California, USA
| | - Bradley A Webb
- Department of Cell and Tissue Biology, University of California, San Francisco, California, USA
| | - Diane L Barber
- Department of Cell and Tissue Biology, University of California, San Francisco, California, USA
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27
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Caldwell L, Harries P, Sydlik S, Schwiening CJ. Presynaptic pH and vesicle fusion in Drosophila larvae neurones. Synapse 2013; 67:729-40. [PMID: 23649934 PMCID: PMC4282566 DOI: 10.1002/syn.21678] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Accepted: 04/22/2013] [Indexed: 11/11/2022]
Abstract
Both intracellular pH (pHi) and synaptic cleft pH change during neuronal activity yet little is known about how these pH shifts might affect synaptic transmission by influencing vesicle fusion. To address this we imaged pH- and Ca2+-sensitive fluorescent indicators (HPTS, Oregon green) in boutons at neuromuscular junctions. Electrical stimulation of motor nerves evoked presynaptic Ca2+i rises and pHi falls (∼0.1 pH units) followed by recovery of both Ca2+i and pHi. The plasma-membrane calcium ATPase (PMCA) inhibitor, 5(6)-carboxyeosin diacetate, slowed both the calcium recovery and the acidification. To investigate a possible calcium-independent role for the pHi shifts in modulating vesicle fusion we recorded post-synaptic miniature end-plate potential (mEPP) and current (mEPC) frequency in Ca2+-free solution. Acidification by propionate superfusion, NH4+ withdrawal, or the inhibition of acid extrusion on the Na+/H+ exchanger (NHE) induced a rise in miniature frequency. Furthermore, the inhibition of acid extrusion enhanced the rise induced by propionate addition and NH4+ removal. In the presence of NH4+, 10 out of 23 cells showed, after a delay, one or more rises in miniature frequency. These findings suggest that Ca2+-dependent pHi shifts, caused by the PMCA and regulated by NHE, may stimulate vesicle release. Furthermore, in the presence of membrane permeant buffers, exocytosed acid or its equivalents may enhance release through positive feedback. This hitherto neglected pH signalling, and the potential feedback role of vesicular acid, could explain some important neuronal excitability changes associated with altered pH and its buffering. Synapse 67:729–740, 2013.
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Affiliation(s)
- Lesley Caldwell
- Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3EG, United Kingdom
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28
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Sinning A, Hübner CA. Minireview: pH and synaptic transmission. FEBS Lett 2013; 587:1923-8. [PMID: 23669358 DOI: 10.1016/j.febslet.2013.04.045] [Citation(s) in RCA: 122] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 04/26/2013] [Accepted: 04/26/2013] [Indexed: 11/30/2022]
Abstract
As a general rule a rise in pH increases neuronal activity, whereas it is dampened by a fall of pH. Neuronal activity per se also challenges pH homeostasis by the increase of metabolic acid equivalents. Moreover, the negative membrane potential of neurons promotes the intracellular accumulation of protons. Synaptic key players such as glutamate receptors or voltage-gated calcium channels show strong pH dependence and effects of pH gradients on synaptic processes are well known. However, the processes and mechanisms that allow controlling the pH in synaptic structures and how these mechanisms contribute to normal synaptic function are only beginning to be resolved.
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Affiliation(s)
- Anne Sinning
- Institute of Human Genetics, University Hospital Jena, Friedrich Schiller University Jena, Kollegiengasse 10, D-07743 Jena, Germany
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