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Cuentas-Condori A, Chen S, Krout M, Gallik KL, Tipps J, Gailey C, Flautt L, Kim H, Mulcahy B, Zhen M, Richmond JE, Miller DM. The epithelial Na + channel UNC-8 promotes an endocytic mechanism that recycles presynaptic components to new boutons in remodeling neurons. Cell Rep 2023; 42:113327. [PMID: 37906594 PMCID: PMC10921563 DOI: 10.1016/j.celrep.2023.113327] [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: 08/18/2022] [Revised: 06/01/2023] [Accepted: 10/06/2023] [Indexed: 11/02/2023] Open
Abstract
Circuit refinement involves the formation of new presynaptic boutons as others are dismantled. Nascent presynaptic sites can incorporate material from recently eliminated synapses, but the recycling mechanisms remain elusive. In early-stage C. elegans larvae, the presynaptic boutons of GABAergic DD neurons are removed and new outputs established at alternative sites. Here, we show that developmentally regulated expression of the epithelial Na+ channel (ENaC) UNC-8 in remodeling DD neurons promotes a Ca2+ and actin-dependent mechanism, involving activity-dependent bulk endocytosis (ADBE), that recycles presynaptic material for reassembly at nascent DD synapses. ADBE normally functions in highly active neurons to accelerate local recycling of synaptic vesicles. In contrast, we find that an ADBE-like mechanism results in the distal recycling of synaptic material from old to new synapses. Thus, our findings suggest that a native mechanism (ADBE) can be repurposed to dismantle presynaptic terminals for reassembly at new, distant locations.
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Affiliation(s)
- Andrea Cuentas-Condori
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Siqi Chen
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Mia Krout
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Kristin L Gallik
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - John Tipps
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Casey Gailey
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Leah Flautt
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA
| | - Hongkyun Kim
- Department of Cell Biology and Anatomy, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, IL 60064, USA
| | - Ben Mulcahy
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada
| | - Mei Zhen
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada
| | - Janet E Richmond
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - David M Miller
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37240, USA; Neurosience Program, Vanderbilt University, Nashville, TN 37240, USA.
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2
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Kaulich E, McCubbin PTN, Schafer WR, Walker DS. Physiological insight into the conserved properties of Caenorhabditis elegans acid-sensing degenerin/epithelial sodium channels. J Physiol 2023; 601:1625-1653. [PMID: 36200489 PMCID: PMC10424705 DOI: 10.1113/jp283238] [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: 04/30/2022] [Accepted: 09/28/2022] [Indexed: 11/08/2022] Open
Abstract
Acid-sensing ion channels (ASICs) are members of the diverse family of degenerin/epithelial sodium channels (DEG/ENaCs). They perform a wide range of physiological roles in healthy organisms, including in gut function and synaptic transmission, but also play important roles in disease, as acidosis is a hallmark of painful inflammatory and ischaemic conditions. We performed a screen for acid sensitivity on all 30 subunits of the Caenorhabditis elegans DEG/ENaC family using two-electrode voltage clamp in Xenopus oocytes. We found two groups of acid-sensitive DEG/ENaCs characterised by being either inhibited or activated by increasing proton concentrations. Three of these acid-sensitive C. elegans DEG/ENaCs were activated by acidic pH, making them functionally similar to the vertebrate ASICs. We also identified three new members of the acid-inhibited DEG/ENaC group, giving a total of seven additional acid-sensitive channels. We observed sensitivity to the anti-hypertensive drug amiloride as well as modulation by the trace element zinc. Acid-sensitive DEG/ENaCs were found to be expressed in both neurons and non-neuronal tissue, highlighting the likely functional diversity of these channels. Our findings provide a framework to exploit the C. elegans channels as models to study the function of these acid-sensing channels in vivo, as well as to study them as potential targets for anti-helminthic drugs. KEY POINTS: Acidosis plays many roles in healthy physiology, including synaptic transmission and gut function, but is also a key feature of inflammatory pain, ischaemia and many other conditions. Cells monitor acidosis of their surroundings via pH-sensing channels, including the acid-sensing ion channels (ASICs). These are members of the degenerin/epithelial sodium channel (DEG/ENaC) family, along with, as the name suggests, vertebrate ENaCs and degenerins of the roundworm Caenorhabditis elegans. By screening all 30 C. elegans DEG/ENaCs for pH dependence, we describe, for the first time, three acid-activated members, as well as three additional acid-inhibited channels. We surveyed both groups for sensitivity to amiloride and zinc; like their mammalian counterparts, their currents can be blocked, enhanced or unaffected by these modulators. Likewise, they exhibit diverse ion selectivity. Our findings underline the diversity of acid-sensitive DEG/ENaCs across species and provide a comparative resource for better understanding the molecular basis of their function.
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Affiliation(s)
- Eva Kaulich
- Neurobiology DivisionMRC Laboratory of Molecular BiologyCambridgeUK
| | | | - William R. Schafer
- Neurobiology DivisionMRC Laboratory of Molecular BiologyCambridgeUK
- Department of BiologyKU LeuvenLeuvenBelgium
| | - Denise S. Walker
- Neurobiology DivisionMRC Laboratory of Molecular BiologyCambridgeUK
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3
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Kaulich E, Grundy LJ, Schafer WR, Walker DS. The diverse functions of the DEG/ENaC family: linking genetic and physiological insights. J Physiol 2022; 601:1521-1542. [PMID: 36314992 PMCID: PMC10148893 DOI: 10.1113/jp283335] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Accepted: 10/25/2022] [Indexed: 11/06/2022] Open
Abstract
The DEG/ENaC family of ion channels was defined based on the sequence similarity between degenerins (DEG) from the nematode Caenorhabditis elegans and subunits of the mammalian epithelial sodium channel (ENaC), and also includes a diverse array of non-voltage-gated cation channels from across animal phyla, including the mammalian acid-sensing ion channels (ASICs) and Drosophila pickpockets. ENaCs and ASICs have wide ranging medical importance; for example, ENaCs play an important role in respiratory and renal function, and ASICs in ischaemia and inflammatory pain, as well as being implicated in memory and learning. Electrophysiological approaches, both in vitro and in vivo, have played an essential role in establishing the physiological properties of this diverse family, identifying an array of modulators and implicating them in an extensive range of cellular functions, including mechanosensation, acid sensation and synaptic modulation. Likewise, genetic studies in both invertebrates and vertebrates have played an important role in linking our understanding of channel properties to function at the cellular and whole animal/behavioural level. Drawing together genetic and physiological evidence is essential to furthering our understanding of the precise cellular roles of DEG/ENaC channels, with the diversity among family members allowing comparative physiological studies to dissect the molecular basis of these diverse functions.
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Affiliation(s)
- Eva Kaulich
- Neurobiology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, UK
| | - Laura J Grundy
- Neurobiology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, UK
| | - William R Schafer
- Neurobiology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, UK.,Department of Biology, KU Leuven, Leuven, Belgium
| | - Denise S Walker
- Neurobiology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge, UK
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4
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Tao L, Coakley S, Shi R, Shen K. Dendrites use mechanosensitive channels to proofread ligand-mediated neurite extension during morphogenesis. Dev Cell 2022; 57:1615-1629.e3. [PMID: 35709764 DOI: 10.1016/j.devcel.2022.05.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 04/18/2022] [Accepted: 05/23/2022] [Indexed: 11/03/2022]
Abstract
Ligand-receptor interactions guide axon navigation and dendrite arborization. Mechanical forces also influence guidance choices. However, the nature of such mechanical stimulations, the mechanosensor identity, and how they interact with guidance receptors are unknown. Here, we demonstrate that mechanosensitive DEG/ENaC channels are required for dendritic arbor morphogenesis in Caenorhabditis elegans. Inhibition of DEG/ENaC channels causes reduced dendritic outgrowth and branching in vivo, a phenotype that is alleviated by overexpression of the mechanosensitive channels PEZO-1/Piezo or YVC1/TrpY1. DEG/ENaCs trigger local Ca2+ transients in growing dendritic filopodia via activation of L-type voltage-gated Ca2+ channels. Anchoring of filopodia by dendrite ligand-receptor complexes is required for the mechanical activation of DEG/ENaC channels. Therefore, mechanosensitive channels serve as a checkpoint for appropriate chemoaffinity by activating Ca2+ transients required for neurite growth.
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Affiliation(s)
- Li Tao
- Howard Hughes Medical Institute, Department of Biology, Stanford University, Stanford, CA, USA
| | - Sean Coakley
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Rebecca Shi
- Howard Hughes Medical Institute, Department of Biology, Stanford University, Stanford, CA, USA; Neurosciences IDP, Stanford University, Stanford, CA 94305, USA
| | - Kang Shen
- Howard Hughes Medical Institute, Department of Biology, Stanford University, Stanford, CA, USA.
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5
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Miller-Fleming TW, Cuentas-Condori A, Manning L, Palumbos S, Richmond JE, Miller DM. Transcriptional Control of Parallel-Acting Pathways That Remove Specific Presynaptic Proteins in Remodeling Neurons. J Neurosci 2021; 41:5849-5866. [PMID: 34045310 PMCID: PMC8265810 DOI: 10.1523/jneurosci.0893-20.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 04/29/2021] [Accepted: 05/20/2021] [Indexed: 11/21/2022] Open
Abstract
Synapses are actively dismantled to mediate circuit refinement, but the developmental pathways that regulate synaptic disassembly are largely unknown. We have previously shown that the epithelial sodium channel ENaC/UNC-8 triggers an activity-dependent mechanism that drives the removal of presynaptic proteins liprin-α/SYD-2, Synaptobrevin/SNB-1, RAB-3, and Endophilin/UNC-57 in remodeling GABAergic neurons in Caenorhabditis elegans (Miller-Fleming et al., 2016). Here, we report that the conserved transcription factor Iroquois/IRX-1 regulates UNC-8 expression as well as an additional pathway, independent of UNC-8, that functions in parallel to dismantle functional presynaptic terminals. We show that the additional IRX-1-regulated pathway is selectively required for the removal of the presynaptic proteins, Munc13/UNC-13 and ELKS, which normally mediate synaptic vesicle (SV) fusion and neurotransmitter release. Our findings are notable because they highlight the key role of transcriptional regulation in synapse elimination during development and reveal parallel-acting pathways that coordinate synaptic disassembly by removing specific active zone proteins.SIGNIFICANCE STATEMENT Synaptic pruning is a conserved feature of developing neural circuits but the mechanisms that dismantle the presynaptic apparatus are largely unknown. We have determined that synaptic disassembly is orchestrated by parallel-acting mechanisms that target distinct components of the active zone. Thus, our finding suggests that synaptic disassembly is not accomplished by en masse destruction but depends on mechanisms that dismantle the structure in an organized process.
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Affiliation(s)
| | - Andrea Cuentas-Condori
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee 37212
| | - Laura Manning
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois 60607
| | - Sierra Palumbos
- Neuroscience Program, Vanderbilt University, Nashville, Tennessee 37212
| | - Janet E Richmond
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois 60607
| | - David M Miller
- Neuroscience Program, Vanderbilt University, Nashville, Tennessee 37212
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee 37212
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6
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Johnson CK, Miller DD, Bianchi L. Effect of the protease plasmin on C. elegans hyperactive DEG/ENaC channels MEC-4(d) and UNC-8(d). MICROPUBLICATION BIOLOGY 2021; 2021. [PMID: 34189421 PMCID: PMC8223032 DOI: 10.17912/micropub.biology.000412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
C. elegans MEC-4 and UNC-8 belong to the DEG/ENaC family of voltage-independent Na+ channels and have been implicated in mechanosensation and synaptic remodeling. MEC-4 and UNC-8 hyperactive mutants, designated (d) mutants, conduct enhanced currents and cause cell death due to uncontrolled influx of cations. We show here that MEC-4(d) but not UNC-8(d) currents are further potentiated by treatment with the protease plasmin and that this effect is dependent upon co-expression with the chaperon protein MEC-6. Mammalian DEG/ENaC channels are cleaved by plasmin in the channel finger domain and both MEC-4 and UNC-8 have a predicted plasmin cleavage site in this domain. We previously showed that MEC-4(d), but not UNC-8(d), currents are increased by co-expression with MEC-6, which interacts with the channel via the finger domain. We suggest that interaction of the channel subunit with MEC-6 may render the plasmin cleavage site more accessible. Given that C. elegans expresses a homolog of plasmin, these effects might be relevant in vivo.
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7
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Fechner S, D'Alessandro I, Wang L, Tower C, Tao L, Goodman MB. DEG/ENaC/ASIC channels vary in their sensitivity to anti-hypertensive and non-steroidal anti-inflammatory drugs. J Gen Physiol 2021; 153:211847. [PMID: 33656557 PMCID: PMC7933985 DOI: 10.1085/jgp.202012655] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Accepted: 01/12/2021] [Indexed: 12/19/2022] Open
Abstract
The degenerin channels, epithelial sodium channels, and acid-sensing ion channels (DEG/ENaC/ASICs) play important roles in sensing mechanical stimuli, regulating salt homeostasis, and responding to acidification in the nervous system. They have two transmembrane domains separated by a large extracellular domain and are believed to assemble as homomeric or heteromeric trimers. Based on studies of selected family members, these channels are assumed to form nonvoltage-gated and sodium-selective channels sensitive to the anti-hypertensive drug amiloride. They are also emerging as a target of nonsteroidal anti-inflammatory drugs (NSAIDs). Caenorhabditis elegans has more than two dozen genes encoding DEG/ENaC/ASIC subunits, providing an excellent opportunity to examine variations in drug sensitivity. Here, we analyze a subset of the C. elegans DEG/ENaC/ASIC proteins to test the hypothesis that individual family members vary not only in their ability to form homomeric channels but also in their drug sensitivity. We selected a panel of C. elegans DEG/ENaC/ASICs that are coexpressed in mechanosensory neurons and expressed gain-of-function or d mutants in Xenopus laevis oocytes. We found that only DEGT‑1d, UNC‑8d, and MEC‑4d formed homomeric channels and that, unlike MEC‑4d and UNC‑8d, DEGT‑1d channels were insensitive to amiloride and its analogues. As reported for rat ASIC1a, NSAIDs inhibit DEGT‑1d and UNC‑8d channels. Unexpectedly, MEC‑4d was strongly potentiated by NSAIDs, an effect that was decreased by mutations in the putative NSAID-binding site in the extracellular domain. Collectively, these findings reveal that not all DEG/ENaC/ASIC channels are amiloride-sensitive and that NSAIDs can both inhibit and potentiate these channels.
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Affiliation(s)
- Sylvia Fechner
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA
| | - Isabel D'Alessandro
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA
| | - Lingxin Wang
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA
| | - Calvin Tower
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA
| | - Li Tao
- Department of Biology, Stanford University, Stanford, CA
| | - Miriam B Goodman
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA
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8
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DEG/ENaC Ion Channels in the Function of the Nervous System: From Worm to Man. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1349:165-192. [DOI: 10.1007/978-981-16-4254-8_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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9
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Cuentas-Condori A, Miller Rd DM. Synaptic remodeling, lessons from C. elegans. J Neurogenet 2020; 34:307-322. [PMID: 32808848 PMCID: PMC7855814 DOI: 10.1080/01677063.2020.1802725] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2020] [Accepted: 07/07/2020] [Indexed: 02/08/2023]
Abstract
Sydney Brenner's choice of Caenorhabditis elegans as a model organism for understanding the nervous system has accelerated discoveries of gene function in neural circuit development and behavior. In this review, we discuss a striking example of synaptic remodeling in the C. elegans motor circuit in which DD class motor neurons effectively reverse polarity as presynaptic and postsynaptic domains at opposite ends of the DD neurite switch locations. Originally revealed by EM reconstruction conducted over 40 years ago, DD remodeling has since been investigated by live cell imaging methods that exploit the power of C. elegans genetics to reveal key effectors of synaptic plasticity. Although synapses are also extensively rewired in developing mammalian circuits, the underlying remodeling mechanisms are largely unknown. Here, we highlight the possibility that studies in C. elegans can reveal pathways that orchestrate synaptic remodeling in more complex organisms. Specifically, we describe (1) transcription factors that regulate DD remodeling, (2) the cellular and molecular cascades that drive synaptic remodeling and (3) examples of circuit modifications in vertebrate neurons that share some similarities with synaptic remodeling in C. elegans DD neurons.
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10
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Murray SM, Waddell BM, Wu CW. Neuron-specific toxicity of chronic acrylamide exposure in C. elegans. Neurotoxicol Teratol 2019; 77:106848. [PMID: 31756371 DOI: 10.1016/j.ntt.2019.106848] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 11/15/2019] [Accepted: 11/16/2019] [Indexed: 01/04/2023]
Abstract
Acrylamide is a food-borne chemical with well-known neurotoxic properties. To date, the toxicity mechanisms of chronic acrylamide exposure are not fully understood. Using the genetic model Caenorhabditis elegans, we found that chronic acrylamide exposure induces a locomotor defect that is characterized by severe uncoordination of muscle movement that is distinct from an overall reduction in activity. C. elegans exhibiting chronic acrylamide-induced locomotor defects show significant degeneration to the dopaminergic and cholinergic, but not GABAergic motor neurons. Degeneration of the dopaminergic and cholinergic neurons are found in 58% to 67% of C. elegans after chronic acrylamide exposure, with the varying degrees of severity ranging from neuronal blebbing to complete dendrite loss. The observed pattern of neurotoxicity does not have a heritable effect, as parental exposure to chronic acrylamide does not lead to neurodegeneration in the developed offspring. Overall, these finding illustrate that chronic acrylamide exposure cause locomotor defects by inducing degeneration of specific neuron types in C. elegans.
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Affiliation(s)
- Sydney M Murray
- Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, 52 Campus Drive, University of Saskatchewan, SK S7N 5B4, Canada; Toxicology Centre, University of Saskatchewan, Saskatoon, SK S7N 5B3, Canada
| | - Brandon M Waddell
- Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, 52 Campus Drive, University of Saskatchewan, SK S7N 5B4, Canada
| | - Cheng-Wei Wu
- Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, 52 Campus Drive, University of Saskatchewan, SK S7N 5B4, Canada; Toxicology Centre, University of Saskatchewan, Saskatoon, SK S7N 5B3, Canada.
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11
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Tao L, Porto D, Li Z, Fechner S, Lee SA, Goodman MB, Xu XZS, Lu H, Shen K. Parallel Processing of Two Mechanosensory Modalities by a Single Neuron in C. elegans. Dev Cell 2019; 51:617-631.e3. [PMID: 31735664 DOI: 10.1016/j.devcel.2019.10.008] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2018] [Revised: 05/24/2019] [Accepted: 10/14/2019] [Indexed: 10/25/2022]
Abstract
Neurons convert synaptic or sensory inputs into cellular outputs. It is not well understood how a single neuron senses, processes multiple stimuli, and generates distinct neuronal outcomes. Here, we describe the mechanism by which the C. elegans PVD neurons sense two mechanical stimuli: external touch and proprioceptive body movement. These two stimuli are detected by distinct mechanosensitive DEG/ENaC/ASIC channels, which trigger distinct cellular outputs linked to mechanonociception and proprioception. Mechanonociception depends on DEGT-1 and activates PVD's downstream command interneurons through its axon, while proprioception depends on DEL-1, UNC-8, and MEC-10 to induce local dendritic Ca2+ increase and dendritic release of a neuropeptide NLP-12. NLP-12 directly modulates neuromuscular junction activity through the cholecystokinin receptor homolog on motor axons, setting muscle tone and movement vigor. Thus, the same neuron simultaneously uses both its axon and dendrites as output apparatus to drive distinct sensorimotor outcomes.
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Affiliation(s)
- Li Tao
- Howard Hughes Medical Institute, Department of Biology, Stanford University, Stanford, CA, USA
| | - Daniel Porto
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA
| | - Zhaoyu Li
- Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Sylvia Fechner
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA
| | - Sol Ah Lee
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA
| | - Miriam B Goodman
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA
| | - X Z Shawn Xu
- Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Hang Lu
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA
| | - Kang Shen
- Howard Hughes Medical Institute, Department of Biology, Stanford University, Stanford, CA, USA.
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12
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Matthewman C, Johnson CK, Miller DM, Bianchi L. Functional features of the "finger" domain of the DEG/ENaC channels MEC-4 and UNC-8. Am J Physiol Cell Physiol 2018; 315:C155-C163. [PMID: 29694233 DOI: 10.1152/ajpcell.00297.2017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
UNC-8 and MEC-4 are two members of the degenerin/epithelial Na+ channel (DEG/ENaC) family of voltage-independent Na+ channels that share a high degree of sequence homology and functional similarity. For example, both can be hyperactivated by genetic mutations [UNC-8(d) and MEC-4(d)] that induce neuronal death by necrosis. Both depend in vivo on chaperone protein MEC-6 for function, as demonstrated by the finding that neuronal death induced by hyperactive UNC-8 and MEC-4 channels is prevented by null mutations in mec-6. UNC-8 and MEC-4 differ functionally in three major ways: 1) MEC-4 is calcium permeable, whereas UNC-8 is not; 2) UNC-8, but not MEC-4, is blocked by extracellular calcium and magnesium in the micromolar range; and 3) MEC-6 increases the number of MEC-4 channels at the cell surface in oocytes but does not have this effect on UNC-8. We previously reported that Ca2+permeability of MEC-4 is conferred by the second transmembrane domain. We show here that the extracellular "finger" domain of UNC-8 is sufficient to mediate inhibition by divalent cations and that regulation by MEC-6 also depends on this region. Thus, our work confirms that the finger domain houses residues involved in gating of this channel class and shows for the first time that the finger domain also mediates regulation by chaperone protein MEC-6. Given that the finger domain is the most divergent region across the DEG/ENaC family, we speculate that it influences channel trafficking and function in a unique manner depending on the channel subunit.
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Affiliation(s)
- Cristina Matthewman
- Department of Physiology and Biophysics, University of Miami, Miller School of Medicine , Miami, Florida.,Neuroscience Program, University of Miami, Miller School of Medicine , Miami, Florida
| | - Christina K Johnson
- Department of Physiology and Biophysics, University of Miami, Miller School of Medicine , Miami, Florida
| | - David M Miller
- Department of Cell and Developmental Biology and Neuroscience Program, Vanderbilt University , Nashville, Tennessee
| | - Laura Bianchi
- Department of Physiology and Biophysics, University of Miami, Miller School of Medicine , Miami, Florida.,Neuroscience Program, University of Miami, Miller School of Medicine , Miami, Florida
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13
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Gibson CL, Balbona JT, Niedzwiecki A, Rodriguez P, Nguyen KCQ, Hall DH, Blakely RD. Glial loss of the metallo β-lactamase domain containing protein, SWIP-10, induces age- and glutamate-signaling dependent, dopamine neuron degeneration. PLoS Genet 2018; 14:e1007269. [PMID: 29590100 PMCID: PMC5891035 DOI: 10.1371/journal.pgen.1007269] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Revised: 04/09/2018] [Accepted: 02/22/2018] [Indexed: 12/24/2022] Open
Abstract
Across phylogeny, glutamate (Glu) signaling plays a critical role in regulating neural excitability, thus supporting many complex behaviors. Perturbed synaptic and extrasynaptic Glu homeostasis in the human brain has been implicated in multiple neuropsychiatric and neurodegenerative disorders including Parkinson's disease, where theories suggest that excitotoxic insults may accelerate a naturally occurring process of dopamine (DA) neuron degeneration. In C. elegans, mutation of the glial expressed gene, swip-10, results in Glu-dependent DA neuron hyperexcitation that leads to elevated DA release, triggering DA signaling-dependent motor paralysis. Here, we demonstrate that swip-10 mutations induce premature and progressive DA neuron degeneration, with light and electron microscopy studies demonstrating the presence of dystrophic dendritic processes, as well as shrunken and/or missing cell soma. As with paralysis, DA neuron degeneration in swip-10 mutants is rescued by glial-specific, but not DA neuron-specific expression of wildtype swip-10, consistent with a cell non-autonomous mechanism. Genetic studies implicate the vesicular Glu transporter VGLU-3 and the cystine/Glu exchanger homolog AAT-1 as potential sources of Glu signaling supporting DA neuron degeneration. Degeneration can be significantly suppressed by mutations in the Ca2+ permeable Glu receptors, nmr-2 and glr-1, in genes that support intracellular Ca2+ signaling and Ca2+-dependent proteolysis, as well as genes involved in apoptotic cell death. Our studies suggest that Glu stimulation of nematode DA neurons in early larval stages, without the protective actions of SWIP-10, contributes to insults that ultimately drive DA neuron degeneration. The swip-10 model may provide an efficient platform for the identification of molecular mechanisms that enhance risk for Parkinson's disease and/or the identification of agents that can limit neurodegenerative disease progression.
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Affiliation(s)
- Chelsea L. Gibson
- Department of Pharmacology, Vanderbilt University, Nashville, TN, United States of America
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Boca Raton, FL, United States of America
| | - Joseph T. Balbona
- Department of Pharmacology, Vanderbilt University, Nashville, TN, United States of America
| | - Ashlin Niedzwiecki
- Department of Pharmacology, Vanderbilt University, Nashville, TN, United States of America
| | - Peter Rodriguez
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Boca Raton, FL, United States of America
| | - Ken C. Q. Nguyen
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, United States of America
| | - David H. Hall
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, United States of America
| | - Randy D. Blakely
- Department of Pharmacology, Vanderbilt University, Nashville, TN, United States of America
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Boca Raton, FL, United States of America
- Department of Psychiatry, Vanderbilt University, Nashville, TN, United States of America
- The Brain Institute, Florida Atlantic University, Jupiter, FL, United States of America
- * E-mail:
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14
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Matthewman C, Miller-Fleming TW, Miller DM, Bianchi L. Ca2+ permeability and Na+ conductance in cellular toxicity caused by hyperactive DEG/ENaC channels. Am J Physiol Cell Physiol 2016; 311:C920-C930. [PMID: 27760755 DOI: 10.1152/ajpcell.00247.2016] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Accepted: 10/12/2016] [Indexed: 12/22/2022]
Abstract
Hyperactivated DEG/ENaC channels cause neuronal death mediated by intracellular Ca2+ overload. Mammalian ASIC1a channels and MEC-4(d) neurotoxic channels in Caenorhabditis elegans both conduct Na+ and Ca2+, raising the possibility that direct Ca2+ influx through these channels contributes to intracellular Ca2+ overload. However, we showed that the homologous C. elegans DEG/ENaC channel UNC-8(d) is not Ca2+ permeable, yet it is neurotoxic, suggesting that Na+ influx is sufficient to induce cell death. Interestingly, UNC-8(d) shows small currents due to extracellular Ca2+ block in the Xenopus oocyte expression system. Thus, MEC-4(d) and UNC-8(d) differ both in current amplitude and Ca2+ permeability. Given that these two channels show a striking difference in toxicity, we wondered how Na+ conductance vs. Ca2+ permeability contributes to cell death. To address this question, we built an UNC-8/MEC-4 chimeric channel that retains the calcium permeability of MEC-4 and characterized its properties in Xenopus oocytes. Our data support the hypothesis that for Ca2+-permeable DEG/ENaC channels, both Ca2+ permeability and Na+ conductance contribute to toxicity. However, for Ca2+-impermeable DEG/ENaCs (e.g., UNC-8), our evidence shows that constitutive Na+ conductance is sufficient to induce toxicity, and that this effect is enhanced as current amplitude increases. Our work further refines the contribution of different channel properties to cellular toxicity induced by hyperactive DEG/ENaC channels.
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Affiliation(s)
- Cristina Matthewman
- Department of Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, Florida.,Neuroscience Program, University of Miami, Miller School of Medicine, Miami, Florida
| | | | - David M Miller
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee; and.,Neuroscience Program, Vanderbilt University, Nashville, Tennessee
| | - Laura Bianchi
- Department of Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, Florida; .,Neuroscience Program, University of Miami, Miller School of Medicine, Miami, Florida
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15
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Miller-Fleming TW, Petersen SC, Manning L, Matthewman C, Gornet M, Beers A, Hori S, Mitani S, Bianchi L, Richmond J, Miller DM. The DEG/ENaC cation channel protein UNC-8 drives activity-dependent synapse removal in remodeling GABAergic neurons. eLife 2016; 5. [PMID: 27403890 PMCID: PMC4980115 DOI: 10.7554/elife.14599] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Accepted: 07/11/2016] [Indexed: 12/30/2022] Open
Abstract
Genetic programming and neural activity drive synaptic remodeling in developing neural circuits, but the molecular components that link these pathways are poorly understood. Here we show that the C. elegans Degenerin/Epithelial Sodium Channel (DEG/ENaC) protein, UNC-8, is transcriptionally controlled to function as a trigger in an activity-dependent mechanism that removes synapses in remodeling GABAergic neurons. UNC-8 cation channel activity promotes disassembly of presynaptic domains in DD type GABA neurons, but not in VD class GABA neurons where unc-8 expression is blocked by the COUP/TF transcription factor, UNC-55. We propose that the depolarizing effect of UNC-8-dependent sodium import elevates intracellular calcium in a positive feedback loop involving the voltage-gated calcium channel UNC-2 and the calcium-activated phosphatase TAX-6/calcineurin to initiate a caspase-dependent mechanism that disassembles the presynaptic apparatus. Thus, UNC-8 serves as a link between genetic and activity-dependent pathways that function together to promote the elimination of GABA synapses in remodeling neurons. DOI:http://dx.doi.org/10.7554/eLife.14599.001 The brain contains billions of nerve cells, or neurons, that communicate with one another through connections called synapses. As the brain develops, these circuits are extensively modified as new synapses are created and others are removed. Neurological disorders may emerge if these processes are not regulated correctly. Identifying the biological pathways that control the addition and removal of synapses could therefore provide new insights into how to treat human brain diseases. To communicate across a synapse, the signaling neuron releases chemicals called neurotransmitters that alter the activity of the receiving neuron. Some neurotransmitters, such as GABA, inhibit the activity of the receiving neuron. The activity of a neuron – and hence how often it releases neurotransmitters – depends on different ions moving into and out of the neuron through proteins called ion channels that are embedded in the cell membrane. For example, the movement of calcium ions into the neuron can trigger the release of neurotransmitters. The roundworm Caenorhabditis elegans is often used as a model organism to study how the brain develops. During development, the worm nervous system eliminates synapses that release GABA and reassembles them at new locations. However, the nervous system does not eliminate these synapses at random. Miller-Fleming, Petersen et al. now show that a C. elegans protein called UNC-8 is responsible for this effect. UNC-8 forms part of an ion channel that allows sodium ions to enter the neuron and is selectively produced in GABA neurons that are destined for remodeling. Miller-Fleming, Petersen et al. found that inside GABA-releasing neurons, calcium ions stimulate an enzyme called calcineurin that may in turn activate UNC-8. Sodium ions then enter the neuron through UNC-8 channels. This boosts the activity of the calcium ion channels, which further increases how many calcium ions enter the cell. Ultimately, the amount of calcium inside the neuron becomes high enough to activate an additional pathway that eliminates the synapse. This downstream pathway involves components of a cell-killing (or “apoptotic”) mechanism that is repurposed in this case to remove the GABA release apparatus at the synapse. Other proteins are likely to help UNC-8 sense the activity of neurons and destroy synapses in response. Further work is required to investigate these additional components and to determine how they work with UNC-8 to remove synapses in the nervous system during development. DOI:http://dx.doi.org/10.7554/eLife.14599.002
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Affiliation(s)
| | - Sarah C Petersen
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, United States
| | - Laura Manning
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, United States
| | - Cristina Matthewman
- Department of Physiology and Biophysics, University of Miami, Miami, United States
| | - Megan Gornet
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, United States
| | - Allison Beers
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, United States
| | - Sayaka Hori
- Department of Physiology, Tokyo Women's Medical University, Tokyo, Japan
| | - Shohei Mitani
- Department of Physiology, Tokyo Women's Medical University, Tokyo, Japan
| | - Laura Bianchi
- Department of Physiology and Biophysics, University of Miami, Miami, United States
| | - Janet Richmond
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, United States
| | - David M Miller
- Neuroscience Program, Vanderbilt University, Nashville, United States.,Department of Cell and Developmental Biology, Vanderbilt University, Nashville, United States
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16
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Kamat S, Yeola S, Zhang W, Bianchi L, Driscoll M. NRA-2, a nicalin homolog, regulates neuronal death by controlling surface localization of toxic Caenorhabditis elegans DEG/ENaC channels. J Biol Chem 2014; 289:11916-11926. [PMID: 24567339 DOI: 10.1074/jbc.m113.533695] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hyperactivated DEG/ENaCs induce neuronal death through excessive cation influx and disruption of intracellular calcium homeostasis. Caenorhabditis elegans DEG/ENaC MEC-4 is hyperactivated by the (d) mutation and induces death of touch neurons. The analogous substitution in MEC-10 (MEC-10(d)) co-expressed in the same neurons is only mildly neurotoxic. We exploited the lower toxicity of MEC-10(d) to identify RNAi knockdowns that enhance neuronal death. We report here that knock-out of the C. elegans nicalin homolog NRA-2 enhances MEC-10(d)-induced neuronal death. Cell biological assays in C. elegans neurons show that NRA-2 controls the distribution of MEC-10(d) between the endoplasmic reticulum and the cell surface. Electrophysiological experiments in Xenopus oocytes support this notion and suggest that control of channel distribution by NRA-2 is dependent on the subunit composition. We propose that nicalin/NRA-2 functions in a quality control mechanism to retain mutant channels in the endoplasmic reticulum, influencing the extent of neuronal death. Mammalian nicalin may have a similar role in DEG/ENaC biology, therefore influencing pathological conditions like ischemia.
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Affiliation(s)
- Shaunak Kamat
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854
| | - Shrutika Yeola
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854
| | - Wenying Zhang
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854
| | - Laura Bianchi
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, Florida 33136.
| | - Monica Driscoll
- Department of Molecular Biology and Biochemistry, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854.
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17
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Abstract
The nematode Caenorhabditis elegans has served as a fruitful setting for cell death research for over three decades. A conserved pathway of four genes, egl-1/BH3-only, ced-9/Bcl-2, ced-4/Apaf-1, and ced-3/caspase, coordinates most developmental cell deaths in C. elegans. However, other cell death forms, programmed and pathological, have also been described in this animal. Some of these share morphological and/or molecular similarities with the canonical apoptotic pathway, while others do not. Indeed, recent studies suggest the existence of an entirely novel mode of programmed developmental cell destruction that may also be conserved beyond nematodes. Here, we review evidence for these noncanonical pathways. We propose that different cell death modalities can function as backup mechanisms for apoptosis, or as tailor-made programs that allow specific dying cells to be efficiently cleared from the animal.
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Affiliation(s)
- Maxime J Kinet
- Laboratory of Developmental Genetics, The Rockefeller University, New York, USA
| | - Shai Shaham
- Laboratory of Developmental Genetics, The Rockefeller University, New York, USA.
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