1
|
Lin L. Unconventional protein secretion: Exploring membrane proteins and beyond. Curr Opin Cell Biol 2025; 93:102469. [PMID: 39903992 DOI: 10.1016/j.ceb.2025.102469] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2024] [Revised: 01/16/2025] [Accepted: 01/16/2025] [Indexed: 02/06/2025]
Abstract
Protein secretion is essential for cellular communication and function, enabling the delivery of both soluble and integral membrane proteins to the extracellular space and the cell surface. While the classical endoplasmic reticulum (ER)-Golgi pathway has been extensively studied, emerging evidence highlights the existence of unconventional protein secretion (UcPS) pathways. Among these, the mechanisms that enable membrane proteins to bypass the Golgi apparatus remain poorly understood. In this review, I discuss recent advances that shed light on the processes governing Golgi-bypassing membrane secretion. These findings reveal that UcPS of membrane proteins is evolutionarily conserved, operates under both physiological and stress conditions, and involves diverse intermediate carriers and molecular players. Looking ahead, advances in technology and the development of more sophisticated functional assays, along with in vivo models, are expected to further unravel the molecular mechanisms and biological roles of these unconventional pathways.
Collapse
Affiliation(s)
- Long Lin
- Department of Biochemistry and Molecular Biology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, Hubei, China.
| |
Collapse
|
2
|
Benner O, Karr CH, Quintero-Gonzalez A, Tamkun MM, Chanda S. The Shab family potassium channels are highly enriched at the presynaptic terminals of human neurons. J Biol Chem 2025; 301:108235. [PMID: 39880095 PMCID: PMC11894309 DOI: 10.1016/j.jbc.2025.108235] [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: 11/12/2024] [Revised: 01/02/2025] [Accepted: 01/21/2025] [Indexed: 01/31/2025] Open
Abstract
The Shab family voltage-gated K+ channels (i.e., Kv2.1, Kv2.2) are widely expressed in mammalian brain and regulate neuronal action-potential firing. In addition to their canonical functions, the Kv2 proteins help establish direct attachments between plasma membrane and endoplasmic reticulum (ER), also known as ER-plasma membrane junctions. However, the biochemical properties and molecular organization of these ion channels have not yet been described in human neurons. Here, we have performed a systematic analysis of endogenous expression, post-translational modification, and subcellular distribution of the major components of Kv2 complex in neurons derived from human stem cells. We found that both Kv2.1, Kv2.2, and their auxiliary subunit AMIGO1 are significantly upregulated during early neurogenesis, localize at the cell surface, and already begin to assemble with each other. Human Kv2.1 and AMIGO1, but not Kv2.2, undergo substantial post-translational modification including phosphorylation and/or N-linked glycosylation. Acute pharmacological inhibition with Kv2 blockers also revealed their functional activation in human neurons. These proteins formed prominent clusters at cell bodies, dendritic branches, and axon initial segments. Interestingly, a large fraction of them also exhibited considerable accumulation at human presynaptic terminals, where they aggregated with the local ER network. This synaptic localization of Kv2 subunits was primarily restricted to presynaptic regions, as they demonstrated limited enrichment at postsynaptic densities. These results were highly reproducible in multiple stem cell lines used and alternative differentiation protocols tested, confirming that human presynaptic compartments can actively recruit the Shab family K+ ion channels.
Collapse
Affiliation(s)
- Orion Benner
- Biochemistry & Molecular Biology, Colorado State University, Fort Collins, Colorado, USA
| | - Charles H Karr
- Biochemistry & Molecular Biology, Colorado State University, Fort Collins, Colorado, USA
| | | | - Michael M Tamkun
- Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA; Molecular, Cellular & Integrated Neurosciences, Colorado State University, Fort Collins, Colorado, USA
| | - Soham Chanda
- Biochemistry & Molecular Biology, Colorado State University, Fort Collins, Colorado, USA; Molecular, Cellular & Integrated Neurosciences, Colorado State University, Fort Collins, Colorado, USA; Cell & Molecular Biology, Colorado State University, Fort Collins, Colorado, USA.
| |
Collapse
|
3
|
Eichel K. Endocytosis in the axon initial segment: Roles in neuronal polarity and plasticity. Curr Opin Neurobiol 2025; 90:102949. [PMID: 39689414 DOI: 10.1016/j.conb.2024.102949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2024] [Revised: 09/15/2024] [Accepted: 11/26/2024] [Indexed: 12/19/2024]
Abstract
The axon initial segment (AIS) is a specialized domain that maintains neuronal polarity and is the site of action potential generation, both of which underlie the neuron's ability to send and receive signals. Disruption of the AIS leads to a loss of neuronal polarity, altered neuronal signaling, and an array of neurological disorders. Therefore, understanding how the AIS forms and functions is a central question in cellular neuroscience that is essential to understanding neuronal physiology. Decades of study have identified many molecular components and mechanisms at the AIS. Recently, endocytosis at the AIS has been identified to function in both maintaining neuronal polarity and in mediating AIS plasticity through its ability to dynamically remodel the plasma membrane composition. This review discusses the emerging evidence for the roles of endocytosis in regulating AIS function and structural insights into how endocytosis can occur at the AIS.
Collapse
Affiliation(s)
- Kelsie Eichel
- Howard Hughes Medical Institute, University of Colorado Boulder, USA.
| |
Collapse
|
4
|
Tyagi S, Higerd-Rusli GP, Akin EJ, Baker CA, Liu S, Dib-Hajj FB, Waxman SG, Dib-Hajj SD. Real-time imaging of axonal membrane protein life cycles. Nat Protoc 2024; 19:2771-2802. [PMID: 38831222 PMCID: PMC11721981 DOI: 10.1038/s41596-024-00997-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Accepted: 02/12/2024] [Indexed: 06/05/2024]
Abstract
The construction of neuronal membranes is a dynamic process involving the biogenesis, vesicular packaging, transport, insertion and recycling of membrane proteins. Optical imaging is well suited for the study of protein spatial organization and transport. However, various shortcomings of existing imaging techniques have prevented the study of specific types of proteins and cellular processes. Here we describe strategies for protein tagging and labeling, cell culture and microscopy that enable the real-time imaging of axonal membrane protein trafficking and subcellular distribution as they progress through some stages of their life cycle. First, we describe a process for engineering membrane proteins with extracellular self-labeling tags (either HaloTag or SNAPTag), which can be labeled with fluorescent ligands of various colors and cell permeability, providing flexibility for investigating the trafficking and spatiotemporal regulation of multiple membrane proteins in neuronal compartments. Next, we detail the dissection, transfection and culture of dorsal root ganglion sensory neurons in microfluidic chambers, which physically compartmentalizes cell bodies and distal axons. Finally, we describe four labeling and imaging procedures that utilize these enzymatically tagged proteins, flexible fluorescent labels and compartmentalized neuronal cultures to study axonal membrane protein anterograde and retrograde transport, the cotransport of multiple proteins, protein subcellular localization, exocytosis and endocytosis. Additionally, we generated open-source software for analyzing the imaging data in a high throughput manner. The experimental and analysis workflows provide an approach for studying the dynamics of neuronal membrane protein homeostasis, addressing longstanding challenges in this area. The protocol requires 5-7 days and expertise in cell culture and microscopy.
Collapse
Affiliation(s)
- Sidharth Tyagi
- Medical Scientist Training Program, Yale School of Medicine, New Haven, CT, USA
- Center for Neuroscience and Regeneration Research, West Haven, CT, USA
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA
- Center for Restoration of Nervous System Function, VA Connecticut Healthcare System, West Haven, CT, USA
| | - Grant P Higerd-Rusli
- Medical Scientist Training Program, Yale School of Medicine, New Haven, CT, USA
- Center for Neuroscience and Regeneration Research, West Haven, CT, USA
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA
- Center for Restoration of Nervous System Function, VA Connecticut Healthcare System, West Haven, CT, USA
| | - Elizabeth J Akin
- Center for Neuroscience and Regeneration Research, West Haven, CT, USA
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA
- Center for Restoration of Nervous System Function, VA Connecticut Healthcare System, West Haven, CT, USA
- Department of Pharmacology, University of Nevada, Reno School of Medicine, Reno, NV, USA
| | - Christopher A Baker
- Center for Neuroscience and Regeneration Research, West Haven, CT, USA
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA
- Center for Restoration of Nervous System Function, VA Connecticut Healthcare System, West Haven, CT, USA
| | - Shujun Liu
- Center for Neuroscience and Regeneration Research, West Haven, CT, USA
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA
- Center for Restoration of Nervous System Function, VA Connecticut Healthcare System, West Haven, CT, USA
| | - Fadia B Dib-Hajj
- Center for Neuroscience and Regeneration Research, West Haven, CT, USA
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA
- Center for Restoration of Nervous System Function, VA Connecticut Healthcare System, West Haven, CT, USA
| | - Stephen G Waxman
- Center for Neuroscience and Regeneration Research, West Haven, CT, USA.
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA.
- Center for Restoration of Nervous System Function, VA Connecticut Healthcare System, West Haven, CT, USA.
| | - Sulayman D Dib-Hajj
- Center for Neuroscience and Regeneration Research, West Haven, CT, USA.
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA.
- Center for Restoration of Nervous System Function, VA Connecticut Healthcare System, West Haven, CT, USA.
| |
Collapse
|
5
|
Manville RW, Block SD, Illeck CL, Kottmeier J, Sidlow R, Abbott GW. A novel autism-associated KCNB1 mutation dramatically slows Kv2.1 potassium channel activation, deactivation and inactivation. Front Cell Neurosci 2024; 18:1438101. [PMID: 39135902 PMCID: PMC11317242 DOI: 10.3389/fncel.2024.1438101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2024] [Accepted: 07/15/2024] [Indexed: 08/15/2024] Open
Abstract
KCNB1, on human chromosome 20q13.3, encodes the alpha subunit of the Kv2.1 voltage gated potassium channel. Kv2.1 is ubiquitously expressed throughout the brain and is critical in controlling neuronal excitability, including in the hippocampus and pyramidal neurons. Human KCNB1 mutations are known to cause global development delay or plateauing, epilepsy, and behavioral disorders. Here, we report a sibling pair with developmental delay, absence seizures, autism spectrum disorder, hypotonia, and dysmorphic features. Whole exome sequencing revealed a heterozygous variant of uncertain significance (c. 342 C>A), p. (S114R) in KCNB1, encoding a serine to arginine substitution (S114R) in the N-terminal cytoplasmic region of Kv2.1. The siblings' father demonstrated autistic features and was determined to be an obligate KCNB1 c. 342 C>A carrier based on familial genetic testing results. Functional investigation of Kv2.1-S114R using cellular electrophysiology revealed slowing of channel activation, deactivation, and inactivation, resulting in increased net current after longer membrane depolarizations. To our knowledge, this is the first study of its kind that compares the presentation of siblings each with a KCNB1 disorder. Our study demonstrates that Kv2.1-S114R has profound cellular and phenotypic consequences. Understanding the mechanisms underlying KCNB1-linked disorders aids clinicians in diagnosis and treatment and provides potential therapeutic avenues to pursue.
Collapse
Affiliation(s)
- Rían W. Manville
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, CA, United States
| | - Samantha D. Block
- Faculty of Health Sciences, Ben-Gurion University of the Negev, Be’er Sheva, Israel
- Medical School for International Health, Ben-Gurion University of the Negev, Be’er Sheva, Israel
| | - Claire L. Illeck
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, CA, United States
| | - Jessica Kottmeier
- Department of Pediatric Genetics, Children’s Hospital, University of Missouri, Columbia, MO, United States
| | - Richard Sidlow
- Department of Pediatric Genetics, Children’s Hospital, University of Missouri, Columbia, MO, United States
| | - Geoffrey W. Abbott
- Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, CA, United States
| |
Collapse
|
6
|
Stewart RG, Camacena M, Copits BA, Sack JT. Distinct cellular expression and subcellular localization of Kv2 voltage-gated K + channel subtypes in dorsal root ganglion neurons conserved between mice and humans. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.01.530679. [PMID: 38187582 PMCID: PMC10769185 DOI: 10.1101/2023.03.01.530679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
The distinct organization of Kv2 voltage-gated potassium channels on and near the cell body of brain neurons enables their regulation of action potentials and specialized membrane contact sites. Somatosensory neurons have a pseudounipolar morphology and transmit action potentials from peripheral nerve endings through axons that bifurcate to the spinal cord and the cell body within ganglia including the dorsal root ganglia (DRG). Kv2 channels regulate action potentials in somatosensory neurons, yet little is known about where Kv2 channels are located. Here we define the cellular and subcellular localization of the Kv2 paralogs, Kv2.1 and Kv2.2, in DRG somatosensory neurons with a panel of antibodies, cell markers, and genetically modified mice. We find that relative to spinal cord neurons, DRG neurons have similar levels of detectable Kv2.1, and higher levels of Kv2.2. In older mice, detectable Kv2.2 remains similar while detectable Kv2.1 decreases. Both Kv2 subtypes adopt clustered subcellular patterns that are distinct from central neurons. Most DRG neurons co-express Kv2.1 and Kv2.2, although neuron subpopulations show preferential expression of Kv2.1 or Kv2.2. We find that Kv2 protein expression and subcellular localization is similar between mouse and human DRG neurons. We conclude that the organization of both Kv2 channels is consistent with physiological roles in the somata and stem axons of DRG neurons. The general prevalence of Kv2.2 in DRG as compared to central neurons and the enrichment of Kv2.2 relative to detectable Kv2.1, in older mice, proprioceptors, and axons suggest more widespread roles for Kv2.2 in DRG neurons.
Collapse
Affiliation(s)
- Robert G Stewart
- Department of Physiology and Membrane Biology, University of California Davis, Davis, CA 95616, USA
| | - Miriam Camacena
- Department of Physiology and Membrane Biology, University of California Davis, Davis, CA 95616, USA
| | - Bryan A Copits
- Washington University Pain Center, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Jon T Sack
- Department of Physiology and Membrane Biology, University of California Davis, Davis, CA 95616, USA
- Department of Anesthesiology and Pain Medicine, University of California Davis, Davis, CA 95616, USA
| |
Collapse
|
7
|
Delignat-Lavaud B, Kano J, Ducrot C, Massé I, Mukherjee S, Giguère N, Moquin L, Lévesque C, Burke S, Denis R, Bourque MJ, Tchung A, Rosa-Neto P, Lévesque D, De Beaumont L, Trudeau LÉ. Synaptotagmin-1-dependent phasic axonal dopamine release is dispensable for basic motor behaviors in mice. Nat Commun 2023; 14:4120. [PMID: 37433762 PMCID: PMC10336101 DOI: 10.1038/s41467-023-39805-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Accepted: 06/27/2023] [Indexed: 07/13/2023] Open
Abstract
In Parkinson's disease (PD), motor dysfunctions only become apparent after extensive loss of DA innervation. This resilience has been hypothesized to be due to the ability of many motor behaviors to be sustained through a diffuse basal tone of DA; but experimental evidence for this is limited. Here we show that conditional deletion of the calcium sensor synaptotagmin-1 (Syt1) in DA neurons (Syt1 cKODA mice) abrogates most activity-dependent axonal DA release in the striatum and mesencephalon, leaving somatodendritic (STD) DA release intact. Strikingly, Syt1 cKODA mice showed intact performance in multiple unconditioned DA-dependent motor tasks and even in a task evaluating conditioned motivation for food. Considering that basal extracellular DA levels in the striatum were unchanged, our findings suggest that activity-dependent DA release is dispensable for such tasks and that they can be sustained by a basal tone of extracellular DA. Taken together, our findings reveal the striking resilience of DA-dependent motor functions in the context of a near-abolition of phasic DA release, shedding new light on why extensive loss of DA innervation is required to reveal motor dysfunctions in PD.
Collapse
Affiliation(s)
- Benoît Delignat-Lavaud
- Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- Department of Neurosciences, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- SNC and CIRCA Research Groups, Université de Montréal, Montréal, QC, Canada
| | - Jana Kano
- Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- Department of Neurosciences, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- SNC and CIRCA Research Groups, Université de Montréal, Montréal, QC, Canada
| | - Charles Ducrot
- Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- Department of Neurosciences, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- SNC and CIRCA Research Groups, Université de Montréal, Montréal, QC, Canada
| | - Ian Massé
- Hôpital du Sacré-Cœur-de-Montréal, CIUSSS NIM, Université de Montréal, Montreal, QC, Canada
| | - Sriparna Mukherjee
- Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- Department of Neurosciences, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- SNC and CIRCA Research Groups, Université de Montréal, Montréal, QC, Canada
- Aligning Science Across Parkinson's (ASAP) Collaborative Research Network, Chevy Chase, MD, 20815, USA
| | - Nicolas Giguère
- Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- Department of Neurosciences, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- SNC and CIRCA Research Groups, Université de Montréal, Montréal, QC, Canada
| | - Luc Moquin
- Centre intégré universitaire de santé et de services sociaux (CIUSSS) de l'Ouest-de-l'Île-de-Montréal; Department of Neurology and Neurosurgery, Psychiatry and Pharmacology and Therapeutics, McGill University, Montreal, QC, Canada
| | | | - Samuel Burke
- Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- Department of Neurosciences, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- SNC and CIRCA Research Groups, Université de Montréal, Montréal, QC, Canada
| | - Raphaëlle Denis
- Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- Department of Neurosciences, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- SNC and CIRCA Research Groups, Université de Montréal, Montréal, QC, Canada
| | - Marie-Josée Bourque
- Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- Department of Neurosciences, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- SNC and CIRCA Research Groups, Université de Montréal, Montréal, QC, Canada
- Aligning Science Across Parkinson's (ASAP) Collaborative Research Network, Chevy Chase, MD, 20815, USA
| | - Alex Tchung
- Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- Department of Neurosciences, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada
- SNC and CIRCA Research Groups, Université de Montréal, Montréal, QC, Canada
| | - Pedro Rosa-Neto
- Centre intégré universitaire de santé et de services sociaux (CIUSSS) de l'Ouest-de-l'Île-de-Montréal; Department of Neurology and Neurosurgery, Psychiatry and Pharmacology and Therapeutics, McGill University, Montreal, QC, Canada
| | - Daniel Lévesque
- Faculty of Pharmacy, Université de Montréal, Montreal, QC, Canada
| | - Louis De Beaumont
- Hôpital du Sacré-Cœur-de-Montréal, CIUSSS NIM, Université de Montréal, Montreal, QC, Canada
| | - Louis-Éric Trudeau
- Department of Pharmacology and Physiology, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada.
- Department of Neurosciences, Faculty of Medicine, Université de Montréal, Montreal, QC, Canada.
- SNC and CIRCA Research Groups, Université de Montréal, Montréal, QC, Canada.
- Aligning Science Across Parkinson's (ASAP) Collaborative Research Network, Chevy Chase, MD, 20815, USA.
| |
Collapse
|
8
|
Abad-Rodríguez J, Brocca ME, Higuero AM. Glycans and Carbohydrate-Binding/Transforming Proteins in Axon Physiology. ADVANCES IN NEUROBIOLOGY 2023; 29:185-217. [PMID: 36255676 DOI: 10.1007/978-3-031-12390-0_7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
The mature nervous system relies on the polarized morphology of neurons for a directed flow of information. These highly polarized cells use their somatodendritic domain to receive and integrate input signals while the axon is responsible for the propagation and transmission of the output signal. However, the axon must perform different functions throughout development before being fully functional for the transmission of information in the form of electrical signals. During the development of the nervous system, axons perform environmental sensing functions, which allow them to navigate through other regions until a final target is reached. Some axons must also establish a regulated contact with other cells before reaching maturity, such as with myelinating glial cells in the case of myelinated axons. Mature axons must then acquire the structural and functional characteristics that allow them to perform their role as part of the information processing and transmitting unit that is the neuron. Finally, in the event of an injury to the nervous system, damaged axons must try to reacquire some of their immature characteristics in a regeneration attempt, which is mostly successful in the PNS but fails in the CNS. Throughout all these steps, glycans perform functions of the outermost importance. Glycans expressed by the axon, as well as by their surrounding environment and contacting cells, encode key information, which is fine-tuned by glycan modifying enzymes and decoded by glycan binding proteins so that the development, guidance, myelination, and electrical transmission functions can be reliably performed. In this chapter, we will provide illustrative examples of how glycans and their binding/transforming proteins code and decode instructive information necessary for fundamental processes in axon physiology.
Collapse
Affiliation(s)
- José Abad-Rodríguez
- Membrane Biology and Axonal Repair Laboratory, Hospital Nacional de Parapléjicos (SESCAM), Toledo, Spain.
| | - María Elvira Brocca
- Membrane Biology and Axonal Repair Laboratory, Hospital Nacional de Parapléjicos (SESCAM), Toledo, Spain
| | - Alonso Miguel Higuero
- Membrane Biology and Axonal Repair Laboratory, Hospital Nacional de Parapléjicos (SESCAM), Toledo, Spain
| |
Collapse
|
9
|
Characterising ion channel structure and dynamics using fluorescence spectroscopy techniques. Biochem Soc Trans 2022; 50:1427-1445. [DOI: 10.1042/bst20220605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2022] [Revised: 09/21/2022] [Accepted: 10/04/2022] [Indexed: 11/17/2022]
Abstract
Ion channels undergo major conformational changes that lead to channel opening and ion conductance. Deciphering these structure-function relationships is paramount to understanding channel physiology and pathophysiology. Cryo-electron microscopy, crystallography and computer modelling provide atomic-scale snapshots of channel conformations in non-cellular environments but lack dynamic information that can be linked to functional results. Biophysical techniques such as electrophysiology, on the other hand, provide functional data with no structural information of the processes involved. Fluorescence spectroscopy techniques help bridge this gap in simultaneously obtaining structure-function correlates. These include voltage-clamp fluorometry, Förster resonance energy transfer, ligand binding assays, single molecule fluorescence and their variations. These techniques can be employed to unearth several features of ion channel behaviour. For instance, they provide real time information on local and global rearrangements that are inherent to channel properties. They also lend insights in trafficking, expression, and assembly of ion channels on the membrane surface. These methods have the advantage that they can be carried out in either native or heterologous systems. In this review, we briefly explain the principles of fluorescence and how these have been translated to study ion channel function. We also report several recent advances in fluorescence spectroscopy that has helped address and improve our understanding of the biophysical behaviours of different ion channel families.
Collapse
|
10
|
Piccialli I, Sisalli MJ, de Rosa V, Boscia F, Tedeschi V, Secondo A, Pannaccione A. Increased K V2.1 Channel Clustering Underlies the Reduction of Delayed Rectifier K + Currents in Hippocampal Neurons of the Tg2576 Alzheimer's Disease Mouse. Cells 2022; 11:cells11182820. [PMID: 36139395 PMCID: PMC9497218 DOI: 10.3390/cells11182820] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2022] [Revised: 09/01/2022] [Accepted: 09/07/2022] [Indexed: 11/30/2022] Open
Abstract
Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the progressive deterioration of cognitive functions. Cortical and hippocampal hyperexcitability intervenes in the pathological derangement of brain activity leading to cognitive decline. As key regulators of neuronal excitability, the voltage-gated K+ channels (KV) might play a crucial role in the AD pathophysiology. Among them, the KV2.1 channel, the main α subunit mediating the delayed rectifier K+ currents (IDR) and controlling the intrinsic excitability of pyramidal neurons, has been poorly examined in AD. In the present study, we investigated the KV2.1 protein expression and activity in hippocampal neurons from the Tg2576 mouse, a widely used transgenic model of AD. To this aim we performed whole-cell patch-clamp recordings, Western blotting, and immunofluorescence analyses. Our Western blotting results reveal that KV2.1 was overexpressed in the hippocampus of 3-month-old Tg2576 mice and in primary hippocampal neurons from Tg2576 mouse embryos compared with the WT counterparts. Electrophysiological experiments unveiled that the whole IDR were reduced in the Tg2576 primary neurons compared with the WT neurons, and that this reduction was due to the loss of the KV2.1 current component. Moreover, we found that the reduction of the KV2.1-mediated currents was due to increased channel clustering, and that glutamate, a stimulus inducing KV2.1 declustering, was able to restore the IDR to levels comparable to those of the WT neurons. These findings add new information about the dysregulation of ionic homeostasis in the Tg2576 AD mouse model and identify KV2.1 as a possible player in the AD-related alterations of neuronal excitability.
Collapse
|
11
|
Higerd-Rusli GP, Alsaloum M, Tyagi S, Sarveswaran N, Estacion M, Akin EJ, Dib-Hajj FB, Liu S, Sosniak D, Zhao P, Dib-Hajj SD, Waxman SG. Depolarizing Na V and Hyperpolarizing K V Channels Are Co-Trafficked in Sensory Neurons. J Neurosci 2022; 42:4794-4811. [PMID: 35589395 PMCID: PMC9188389 DOI: 10.1523/jneurosci.0058-22.2022] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Revised: 05/04/2022] [Accepted: 05/05/2022] [Indexed: 11/21/2022] Open
Abstract
Neuronal excitability relies on coordinated action of functionally distinction channels. Voltage-gated sodium (NaV) and potassium (KV) channels have distinct but complementary roles in firing action potentials: NaV channels provide depolarizing current while KV channels provide hyperpolarizing current. Mutations and dysfunction of multiple NaV and KV channels underlie disorders of excitability, including pain and epilepsy. Modulating ion channel trafficking may offer a potential therapeutic strategy for these diseases. A fundamental question, however, is whether these channels with distinct functional roles are transported independently or packaged together in the same vesicles in sensory axons. We have used Optical Pulse-Chase Axonal Long-distance imaging to investigate trafficking of NaV and KV channels and other axonal proteins from distinct functional classes in live rodent sensory neurons (from male and female rats). We show that, similar to NaV1.7 channels, NaV1.8 and KV7.2 channels are transported in Rab6a-positive vesicles, and that each of the NaV channel isoforms expressed in healthy, mature sensory neurons (NaV1.6, NaV1.7, NaV1.8, and NaV1.9) is cotransported in the same vesicles. Further, we show that multiple axonal membrane proteins with different physiological functions (NaV1.7, KV7.2, and TNFR1) are cotransported in the same vesicles. However, vesicular packaging of axonal membrane proteins is not indiscriminate, since another axonal membrane protein (NCX2) is transported in separate vesicles. These results shed new light on the development and organization of sensory neuron membranes, revealing complex sorting of axonal proteins with diverse physiological functions into specific transport vesicles.SIGNIFICANCE STATEMENT Normal neuronal excitability is dependent on precise regulation of membrane proteins, including NaV and KV channels, and imbalance in the level of these channels at the plasma membrane could lead to excitability disorders. Ion channel trafficking could potentially be targeted therapeutically, which would require better understanding of the mechanisms underlying trafficking of functionally diverse channels. Optical Pulse-chase Axonal Long-distance imaging in live neurons permitted examination of the specificity of ion channel trafficking, revealing co-packaging of axonal proteins with opposing physiological functions into the same transport vesicles. This suggests that additional trafficking mechanisms are necessary to regulate levels of surface channels, and reveals an important consideration for therapeutic strategies that target ion channel trafficking for the treatment of excitability disorders.
Collapse
Affiliation(s)
- Grant P Higerd-Rusli
- MD/PhD Program
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Matthew Alsaloum
- MD/PhD Program
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Sidharth Tyagi
- MD/PhD Program
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Nivedita Sarveswaran
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Mark Estacion
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Elizabeth J Akin
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Fadia B Dib-Hajj
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Shujun Liu
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Daniel Sosniak
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Peng Zhao
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Sulayman D Dib-Hajj
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| | - Stephen G Waxman
- Center for Neuroscience and Regeneration Research and
- Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516
| |
Collapse
|
12
|
Kasatkina LA, Verkhusha VV. Transgenic mice encoding modern imaging probes: Properties and applications. Cell Rep 2022; 39:110845. [PMID: 35613592 PMCID: PMC9183799 DOI: 10.1016/j.celrep.2022.110845] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Revised: 03/31/2022] [Accepted: 04/28/2022] [Indexed: 12/04/2022] Open
Abstract
Modern biology is increasingly reliant on optical technologies, including visualization and longitudinal monitoring of cellular processes. The major limitation here is the availability of animal models to track the molecules and cells in their natural environment in vivo. Owing to the integrity of the studied tissue and the high stability of transgene expression throughout life, transgenic mice encoding fluorescent proteins and biosensors represent unique tools for in vivo studies in norm and pathology. We review the strategies for targeting probe expression in specific tissues, cell subtypes, or cellular compartments. We describe the application of transgenic mice expressing fluorescent proteins for tracking protein expression patterns, apoptotic events, tissue differentiation and regeneration, neurogenesis, tumorigenesis, and cell fate mapping. We overview the possibilities of functional imaging of secondary messengers, neurotransmitters, and ion fluxes. Finally, we provide the rationale and perspectives for the use of transgenic imaging probes in translational research and drug discovery.
Collapse
Affiliation(s)
- Ludmila A Kasatkina
- Department of Genetics and Gruss-Lipper Biophotonics Center, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Vladislav V Verkhusha
- Department of Genetics and Gruss-Lipper Biophotonics Center, Albert Einstein College of Medicine, Bronx, NY 10461, USA; Medicum, Faculty of Medicine, University of Helsinki, Helsinki 00290, Finland.
| |
Collapse
|
13
|
Eichel K, Shen K. The function of the axon initial segment in neuronal polarity. Dev Biol 2022; 489:47-54. [DOI: 10.1016/j.ydbio.2022.05.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 05/09/2022] [Accepted: 05/23/2022] [Indexed: 11/25/2022]
|
14
|
Dimou S, Dionysopoulou M, Sagia GM, Diallinas G. Golgi-Bypass Is a Major Unconventional Route for Translocation to the Plasma Membrane of Non-Apical Membrane Cargoes in Aspergillus nidulans. Front Cell Dev Biol 2022; 10:852028. [PMID: 35465316 PMCID: PMC9021693 DOI: 10.3389/fcell.2022.852028] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Accepted: 03/03/2022] [Indexed: 11/13/2022] Open
Abstract
Nutrient transporters have been shown to translocate to the plasma membrane (PM) of the filamentous fungus Aspergillus nidulans via an unconventional trafficking route that bypasses the Golgi. This finding strongly suggests the existence of distinct COPII vesicle subpopulations, one following Golgi-dependent conventional secretion and the other directed towards the PM. Here, we address whether Golgi-bypass concerns cargoes other than nutrient transporters and whether Golgi-bypass is related to cargo structure, size, abundance, physiological function, or polar vs. non-polar distribution in the PM. To address these questions, we followed the dynamic subcellular localization of two selected membrane cargoes differing in several of the aforementioned aspects. These are the proton-pump ATPase PmaA and the PalI pH signaling component. Our results show that neosynthesized PmaA and PalI are translocated to the PM via Golgi-bypass, similar to nutrient transporters. In addition, we showed that the COPII-dependent exit of PmaA from the ER requires the alternative COPII coat subunit LstA, rather than Sec24, whereas PalI requires the ER cargo adaptor Erv14. These findings strengthen the evidence of distinct cargo-specific COPII subpopulations and extend the concept of Golgi-independent biogenesis to essential transmembrane proteins, other than nutrient transporters. Overall, our findings point to the idea that Golgi-bypass might not constitute a fungal-specific peculiarity, but rather a novel major and cargo-specific sorting route in eukaryotic cells that has been largely ignored.
Collapse
Affiliation(s)
- Sofia Dimou
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, Greece
| | - Mariangela Dionysopoulou
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, Greece
| | - Georgia Maria Sagia
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, Greece
| | - George Diallinas
- Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, Athens, Greece
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology, Heraklion, Greece
- *Correspondence: George Diallinas,
| |
Collapse
|
15
|
Nabb AT, Bentley M. NgCAM and VAMP2 reveal that direct delivery and dendritic degradation maintain axonal polarity. Mol Biol Cell 2022; 33:ar3. [PMID: 34731031 PMCID: PMC8886818 DOI: 10.1091/mbc.e21-08-0425] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Neurons are polarized cells of extreme scale and compartmentalization. To fulfill their role in electrochemical signaling, axons must maintain a specific complement of membrane proteins. Despite being the subject of considerable attention, the trafficking pathway of axonal membrane proteins is not well understood. Two pathways, direct delivery and transcytosis, have been proposed. Previous studies reached contradictory conclusions about which of these mediates delivery of axonal membrane proteins to their destination, in part because they evaluated long-term distribution changes and not vesicle transport. We developed a novel strategy to selectively label vesicles in different trafficking pathways and determined the trafficking of two canonical axonal membrane proteins, neuron-glia cell adhesion molecule and vesicle-associated membrane protein-2. Results from detailed quantitative analyses of transporting vesicles differed substantially from previous studies and found that axonal membrane proteins overwhelmingly undergo direct delivery. Transcytosis plays only a minor role in axonal delivery of these proteins. In addition, we identified a novel pathway by which wayward axonal proteins that reach the dendritic plasma membrane are targeted to lysosomes. These results redefine how axonal proteins achieve their polarized distribution, a crucial requirement for elucidating the underlying molecular mechanisms.
Collapse
Affiliation(s)
- Alec T. Nabb
- Department of Biological Sciences and the Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY 12180
| | - Marvin Bentley
- Department of Biological Sciences and the Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY 12180,*Address correspondence to: Marvin Bentley ()
| |
Collapse
|
16
|
Petropavlovskiy A, Kogut J, Leekha A, Townsend C, Sanders S. A sticky situation: regulation and function of protein palmitoylation with a spotlight on the axon and axon initial segment. Neuronal Signal 2021; 5:NS20210005. [PMID: 34659801 PMCID: PMC8495546 DOI: 10.1042/ns20210005] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Revised: 09/19/2021] [Accepted: 09/21/2021] [Indexed: 11/17/2022] Open
Abstract
In neurons, the axon and axon initial segment (AIS) are critical structures for action potential initiation and propagation. Their formation and function rely on tight compartmentalisation, a process where specific proteins are trafficked to and retained at distinct subcellular locations. One mechanism which regulates protein trafficking and association with lipid membranes is the modification of protein cysteine residues with the 16-carbon palmitic acid, known as S-acylation or palmitoylation. Palmitoylation, akin to phosphorylation, is reversible, with palmitate cycling being mediated by substrate-specific enzymes. Palmitoylation is well-known to be highly prevalent among neuronal proteins and is well studied in the context of the synapse. Comparatively, how palmitoylation regulates trafficking and clustering of axonal and AIS proteins remains less understood. This review provides an overview of the current understanding of the biochemical regulation of palmitoylation, its involvement in various neurological diseases, and the most up-to-date perspective on axonal palmitoylation. Through a palmitoylation analysis of the AIS proteome, we also report that an overwhelming proportion of AIS proteins are likely palmitoylated. Overall, our review and analysis confirm a central role for palmitoylation in the formation and function of the axon and AIS and provide a resource for further exploration of palmitoylation-dependent protein targeting to and function at the AIS.
Collapse
Affiliation(s)
- Andrey A. Petropavlovskiy
- Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Rd E, Guelph N1G 2W1, Ontario, Canada
| | - Jordan A. Kogut
- Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Rd E, Guelph N1G 2W1, Ontario, Canada
| | - Arshia Leekha
- Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Rd E, Guelph N1G 2W1, Ontario, Canada
| | - Charlotte A. Townsend
- Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Rd E, Guelph N1G 2W1, Ontario, Canada
| | - Shaun S. Sanders
- Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Rd E, Guelph N1G 2W1, Ontario, Canada
| |
Collapse
|
17
|
Maverick EE, Leek AN, Tamkun MM. Kv2 channel-AMIGO β-subunit assembly modulates both channel function and cell adhesion molecule surface trafficking. J Cell Sci 2021; 134:jcs256339. [PMID: 34137443 PMCID: PMC8255027 DOI: 10.1242/jcs.256339] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 05/17/2021] [Indexed: 11/20/2022] Open
Abstract
The Kv2 channels encode delayed rectifier currents that regulate membrane potential in many tissues. They also have a non-conducting function to form stable junctions between the endoplasmic reticulum and plasma membranes, creating membrane contact sites that mediate functions distinct from membrane excitability. Therefore, proteins that interact with Kv2.1 and Kv2.2 channels can alter conducting and/or non-conducting channel properties. One member of the AMIGO family of proteins is an auxiliary β-subunit for Kv2 channels and modulates Kv2.1 electrical activity. However, the AMIGO family has two additional members of ∼50% similarity that have not yet been characterized as Kv2 β-subunits. In this work, we show that the surface trafficking and localization of all three AMIGOs are controlled by their assembly with both Kv2 channels. Additionally, assembly of each AMIGO with either Kv2.1 or Kv2.2 hyperpolarizes the channel activation midpoint by -10 mV. However, only AMIGO2 significantly slows inactivation and deactivation, leading to a prolonged open state of Kv2 channels. The co-regulatory effects of Kv2s and AMIGOs likely fine-tune both the electrical and non-electrical properties of the cells in which they are expressed.
Collapse
Affiliation(s)
- Emily E. Maverick
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA
- Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, CO 80523, USA
| | - Ashley N. Leek
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA
- Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, CO 80523, USA
| | - Michael M. Tamkun
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA
- Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, CO 80523, USA
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523, USA
| |
Collapse
|
18
|
Deardorff AS, Romer SH, Fyffe RE. Location, location, location: the organization and roles of potassium channels in mammalian motoneurons. J Physiol 2021; 599:1391-1420. [DOI: 10.1113/jp278675] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Accepted: 01/08/2021] [Indexed: 11/08/2022] Open
Affiliation(s)
- Adam S. Deardorff
- Department of Neuroscience, Cell Biology and Physiology, Wright State University Boonshoft School of Medicine Dayton OH 45435 USA
- Department of Neurology and Internal Medicine, Wright State University Boonshoft School of Medicine Dayton OH 45435 USA
| | - Shannon H. Romer
- Odyssey Systems Environmental Health Effects Laboratory, Navy Medical Research Unit‐Dayton Wright‐Patterson Air Force Base OH 45433 USA
| | - Robert E.W. Fyffe
- Department of Neuroscience, Cell Biology and Physiology, Wright State University Boonshoft School of Medicine Dayton OH 45435 USA
| |
Collapse
|
19
|
Antispasmodic Drug Drofenine as an Inhibitor of Kv2.1 Channel Ameliorates Peripheral Neuropathy in Diabetic Mice. iScience 2020; 23:101617. [PMID: 33089105 PMCID: PMC7559245 DOI: 10.1016/j.isci.2020.101617] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2019] [Revised: 07/22/2020] [Accepted: 09/23/2020] [Indexed: 12/30/2022] Open
Abstract
Diabetic peripheral neuropathy (DPN) is a common diabetic complication and has yet no efficient medication. Here, we report that antispasmodic drug drofenine (Dfe) blocks Kv2.1 and ameliorates DPN-like pathology in diabetic mice. The underlying mechanisms are investigated against the DPN mice with in vivo Kv2.1 knockdown through adeno associated virus AAV9-Kv2.1-RNAi. Streptozotocin (STZ) induced type 1 or db/db type 2 diabetic mice with DPN exhibited a high level of Kv2.1 protein in dorsal root ganglion (DRG) tissue and a suppressed neurite outgrowth in DRG neuron. Dfe promoted neurite outgrowth by inhibiting Kv2.1 channel and/or Kv2.1 mRNA and protein expression level. Moreover, it suppressed inflammation by repressing IκBα/NF-κB signaling, inhibited apoptosis by regulating Kv2.1-mediated Bcl-2 family proteins and Caspase-3 and ameliorated mitochondrial dysfunction through Kv2.1/CaMKKβ/AMPK/PGC1α pathway. Our work supports that Kv2.1 inhibition is a promisingly therapeutic strategy for DPN and highlights the potential of Dfe in treating this disease. Antispasmodic drug drofenine (Dfe) ameliorates DPN-like pathology in diabetic mice Dfe inhibits Kv2.1 channel and/or Kv2.1 mRNA and protein expression level Dfe represses inflammation, apoptosis, and mitochondrial dysfunction in DPN mice Kv2.1 inhibition is a therapeutic tactic and Dfe shows therapeutic potential for DPN
Collapse
|
20
|
Braun N, Sheikh ZP, Pless SA. The current chemical biology tool box for studying ion channels. J Physiol 2020; 598:4455-4471. [DOI: 10.1113/jp276695] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2020] [Accepted: 07/06/2020] [Indexed: 12/13/2022] Open
Affiliation(s)
- N. Braun
- Department of Drug Design and Pharmacology University of Copenhagen Jagtvej 160 Copenhagen 2100 Denmark
| | - Z. P. Sheikh
- Department of Drug Design and Pharmacology University of Copenhagen Jagtvej 160 Copenhagen 2100 Denmark
| | - S. A. Pless
- Department of Drug Design and Pharmacology University of Copenhagen Jagtvej 160 Copenhagen 2100 Denmark
| |
Collapse
|
21
|
Dimou S, Diallinas G. Life and Death of Fungal Transporters under the Challenge of Polarity. Int J Mol Sci 2020; 21:ijms21155376. [PMID: 32751072 PMCID: PMC7432044 DOI: 10.3390/ijms21155376] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 07/24/2020] [Accepted: 07/27/2020] [Indexed: 12/14/2022] Open
Abstract
Eukaryotic plasma membrane (PM) transporters face critical challenges that are not widely present in prokaryotes. The two most important issues are proper subcellular traffic and targeting to the PM, and regulated endocytosis in response to physiological, developmental, or stress signals. Sorting of transporters from their site of synthesis, the endoplasmic reticulum (ER), to the PM has been long thought, but not formally shown, to occur via the conventional Golgi-dependent vesicular secretory pathway. Endocytosis of specific eukaryotic transporters has been studied more systematically and shown to involve ubiquitination, internalization, and sorting to early endosomes, followed by turnover in the multivesicular bodies (MVB)/lysosomes/vacuole system. In specific cases, internalized transporters have been shown to recycle back to the PM. However, the mechanisms of transporter forward trafficking and turnover have been overturned recently through systematic work in the model fungus Aspergillus nidulans. In this review, we present evidence that shows that transporter traffic to the PM takes place through Golgi bypass and transporter endocytosis operates via a mechanism that is distinct from that of recycling membrane cargoes essential for fungal growth. We discuss these findings in relation to adaptation to challenges imposed by cell polarity in fungi as well as in other eukaryotes and provide a rationale of why transporters and possibly other housekeeping membrane proteins ‘avoid’ routes of polar trafficking.
Collapse
|
22
|
Shemesh OA, Linghu C, Piatkevich KD, Goodwin D, Celiker OT, Gritton HJ, Romano MF, Gao R, Yu CCJ, Tseng HA, Bensussen S, Narayan S, Yang CT, Freifeld L, Siciliano CA, Gupta I, Wang J, Pak N, Yoon YG, Ullmann JFP, Guner-Ataman B, Noamany H, Sheinkopf ZR, Park WM, Asano S, Keating AE, Trimmer JS, Reimer J, Tolias AS, Bear MF, Tye KM, Han X, Ahrens MB, Boyden ES. Precision Calcium Imaging of Dense Neural Populations via a Cell-Body-Targeted Calcium Indicator. Neuron 2020; 107:470-486.e11. [PMID: 32592656 DOI: 10.1016/j.neuron.2020.05.029] [Citation(s) in RCA: 79] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Revised: 05/09/2019] [Accepted: 05/20/2020] [Indexed: 01/11/2023]
Abstract
Methods for one-photon fluorescent imaging of calcium dynamics can capture the activity of hundreds of neurons across large fields of view at a low equipment complexity and cost. In contrast to two-photon methods, however, one-photon methods suffer from higher levels of crosstalk from neuropil, resulting in a decreased signal-to-noise ratio and artifactual correlations of neural activity. We address this problem by engineering cell-body-targeted variants of the fluorescent calcium indicators GCaMP6f and GCaMP7f. We screened fusions of GCaMP to natural, as well as artificial, peptides and identified fusions that localized GCaMP to within 50 μm of the cell body of neurons in mice and larval zebrafish. One-photon imaging of soma-targeted GCaMP in dense neural circuits reported fewer artifactual spikes from neuropil, an increased signal-to-noise ratio, and decreased artifactual correlation across neurons. Thus, soma-targeting of fluorescent calcium indicators facilitates usage of simple, powerful, one-photon methods for imaging neural calcium dynamics.
Collapse
Affiliation(s)
- Or A Shemesh
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; Department of Biological Engineering, MIT, Cambridge, MA, USA; MIT Center for Neurobiological Engineering, MIT, Cambridge, MA, USA; Department of Brain and Cognitive Sciences, MIT, Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA; Department of Neurobiology and Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Changyang Linghu
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; MIT Center for Neurobiological Engineering, MIT, Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA; Department of Electrical Engineering and Computer Science, MIT, Cambridge, MA, USA
| | - Kiryl D Piatkevich
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; Department of Biological Engineering, MIT, Cambridge, MA, USA; MIT Center for Neurobiological Engineering, MIT, Cambridge, MA, USA; Department of Brain and Cognitive Sciences, MIT, Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA; School of Life Sciences, Westlake University, Hangzhou, Zhejiang Province, China
| | - Daniel Goodwin
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; MIT Center for Neurobiological Engineering, MIT, Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA
| | - Orhan Tunc Celiker
- MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA; Department of Electrical Engineering and Computer Science, MIT, Cambridge, MA, USA
| | - Howard J Gritton
- Boston University, Department of Biomedical Engineering, Boston, MA 02215, USA
| | - Michael F Romano
- Boston University, Department of Biomedical Engineering, Boston, MA 02215, USA
| | - Ruixuan Gao
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA
| | - Chih-Chieh Jay Yu
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; Department of Biological Engineering, MIT, Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA
| | - Hua-An Tseng
- Boston University, Department of Biomedical Engineering, Boston, MA 02215, USA
| | - Seth Bensussen
- Boston University, Department of Biomedical Engineering, Boston, MA 02215, USA
| | - Sujatha Narayan
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Chao-Tsung Yang
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Limor Freifeld
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; MIT Center for Neurobiological Engineering, MIT, Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA; Faculty of Biomedical Engineering, Technion, Haifa, Israel
| | - Cody A Siciliano
- Vanderbilt Center for Addiction Research, Department of Pharmacology, Vanderbilt University, Nashville, TN 37232, USA
| | - Ishan Gupta
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; Department of Biological Engineering, MIT, Cambridge, MA, USA; MIT Center for Neurobiological Engineering, MIT, Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA
| | - Joyce Wang
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, MIT, Cambridge, MA 02139, USA
| | - Nikita Pak
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; MIT Center for Neurobiological Engineering, MIT, Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA; Department of Mechanical Engineering, MIT, Cambridge, MA, USA
| | - Young-Gyu Yoon
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; MIT Center for Neurobiological Engineering, MIT, Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA; Department of Electrical Engineering and Computer Science, MIT, Cambridge, MA, USA; School of Electrical Engineering, KAIST Institute for Health Science and Technology, Daejeon, Republic of Korea
| | - Jeremy F P Ullmann
- Epilepsy Genetics Program, Department of Neurology, Boston Children's Hospital & Harvard Medical School, Boston, MA, USA
| | - Burcu Guner-Ataman
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA
| | - Habiba Noamany
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, MIT, Cambridge, MA 02139, USA
| | - Zoe R Sheinkopf
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; Department of Neurology, Brigham and Women's Hospital, Boston, MA, USA
| | | | - Shoh Asano
- Internal Medicine Research Unit, Pfizer, Cambridge, MA, USA
| | - Amy E Keating
- Department of Biological Engineering, MIT, Cambridge, MA, USA; Department of Biology, MIT, Cambridge, MA, USA; Koch Institute, MIT, Cambridge, MA 02139, USA
| | - James S Trimmer
- Department of Physiology and Membrane Biology, University of California, Davis School of Medicine, Davis, CA, USA
| | - Jacob Reimer
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA; Center for Neuroscience and AI, Baylor College of Medicine, Houston, TX, USA
| | - Andreas S Tolias
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA; Center for Neuroscience and AI, Baylor College of Medicine, Houston, TX, USA; Department of Electrical and Computer Engineering, Rice University, Houston, TX, USA
| | - Mark F Bear
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, MIT, Cambridge, MA 02139, USA
| | - Kay M Tye
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, MIT, Cambridge, MA 02139, USA; Salk Institute for Biological Studies, La Jolla, CA 92037, USA
| | - Xue Han
- Boston University, Department of Biomedical Engineering, Boston, MA 02215, USA
| | - Misha B Ahrens
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
| | - Edward S Boyden
- The MIT Media Laboratory, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; Department of Biological Engineering, MIT, Cambridge, MA, USA; MIT Center for Neurobiological Engineering, MIT, Cambridge, MA, USA; Department of Brain and Cognitive Sciences, MIT, Cambridge, MA, USA; MIT McGovern Institute for Brain Research, MIT, Cambridge, MA, USA; Koch Institute, MIT, Cambridge, MA 02139, USA.
| |
Collapse
|
23
|
Dimou S, Martzoukou O, Dionysopoulou M, Bouris V, Amillis S, Diallinas G. Translocation of nutrient transporters to cell membrane via Golgi bypass in Aspergillus nidulans. EMBO Rep 2020; 21:e49929. [PMID: 32452614 DOI: 10.15252/embr.201949929] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 04/15/2020] [Accepted: 04/24/2020] [Indexed: 02/06/2023] Open
Abstract
Nutrient transporters, being polytopic membrane proteins, are believed, but not formally shown, to traffic from their site of synthesis, the ER, to the plasma membrane through Golgi-dependent vesicular trafficking. Here, we develop a novel genetic system to investigate the trafficking of a neosynthesized model transporter, the well-studied UapA purine transporter of Aspergillus nidulans. We show that sorting of neosynthesized UapA to the plasma membrane (PM) bypasses the Golgi and does not necessitate key Rab GTPases, AP adaptors, microtubules or endosomes. UapA PM localization is found to be dependent on functional COPII vesicles, actin polymerization, clathrin heavy chain and the PM t-SNARE SsoA. Actin polymerization proved to primarily affect COPII vesicle formation, whereas the essential role of ClaH seems indirect and less clear. We provide evidence that other evolutionary and functionally distinct transporters of A. nidulans also follow the herein identified Golgi-independent trafficking route of UapA. Importantly, our findings suggest that specific membrane cargoes drive the formation of distinct COPII subpopulations that bypass the Golgi to be sorted non-polarly to the PM, and thus serving house-keeping cell functions.
Collapse
Affiliation(s)
- Sofia Dimou
- Department of Biology, National and Kapodistrian University of Athens, Athens, Greece
| | - Olga Martzoukou
- Department of Biology, National and Kapodistrian University of Athens, Athens, Greece
| | | | - Vangelis Bouris
- Department of Biology, National and Kapodistrian University of Athens, Athens, Greece
| | - Sotiris Amillis
- Department of Biology, National and Kapodistrian University of Athens, Athens, Greece
| | - George Diallinas
- Department of Biology, National and Kapodistrian University of Athens, Athens, Greece
| |
Collapse
|
24
|
Cornejo VH, González C, Campos M, Vargas-Saturno L, Juricic MDLÁ, Miserey-Lenkei S, Pertusa M, Madrid R, Couve A. Non-conventional Axonal Organelles Control TRPM8 Ion Channel Trafficking and Peripheral Cold Sensing. Cell Rep 2020; 30:4505-4517.e5. [DOI: 10.1016/j.celrep.2020.03.017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Revised: 10/07/2019] [Accepted: 03/05/2020] [Indexed: 12/31/2022] Open
|
25
|
Hefting LL, D'Este E, Arvedsen E, Benned-Jensen T, Rasmussen HB. Multiple Domains in the Kv7.3 C-Terminus Can Regulate Localization to the Axon Initial Segment. Front Cell Neurosci 2020; 14:10. [PMID: 32116557 PMCID: PMC7010958 DOI: 10.3389/fncel.2020.00010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Accepted: 01/14/2020] [Indexed: 11/13/2022] Open
Abstract
The voltage-gated Kv7.2/Kv7.3 potassium channel is a critical regulator of neuronal excitability. It is strategically positioned at the axon initial segment (AIS) of neurons, where it effectively inhibits repetitive action potential firing. While the selective accumulation of Kv7.2/Kv7.3 channels at the AIS requires binding to the adaptor protein ankyrin G, it is currently unknown if additional molecular mechanisms contribute to the localization and fine-tuning of channel numbers at the AIS. Here, we utilized a chimeric approach to pinpoint regions within the Kv7.3 C-terminal tail with an impact upon AIS localization. This strategy identified two domains with opposing effects upon the AIS localization of Kv7.3 chimeras expressed in cultured hippocampal neurons. While a membrane proximal domain reduced AIS localization of Kv7.3 chimeras, helix D increased and stabilized chimera AIS localization. None of the identified domains were required for AIS localization. However, the domains modulated the relative efficiency of the localization raising the possibility that the two domains contribute to the regulation of Kv7 channel numbers and nanoscale organization at the AIS.
Collapse
Affiliation(s)
- Louise Leth Hefting
- Membrane Trafficking Group, Department of Biomedical Sciences, The Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Elisa D'Este
- Optical Microscopy Facility, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Emil Arvedsen
- Membrane Trafficking Group, Department of Biomedical Sciences, The Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Tau Benned-Jensen
- Membrane Trafficking Group, Department of Biomedical Sciences, The Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Hanne Borger Rasmussen
- Membrane Trafficking Group, Department of Biomedical Sciences, The Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| |
Collapse
|
26
|
Nirenberg VA, Yifrach O. Bridging the Molecular-Cellular Gap in Understanding Ion Channel Clustering. Front Pharmacol 2020; 10:1644. [PMID: 32082156 PMCID: PMC7000920 DOI: 10.3389/fphar.2019.01644] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Accepted: 12/16/2019] [Indexed: 01/07/2023] Open
Abstract
The clustering of many voltage-dependent ion channel molecules at unique neuronal membrane sites such as axon initial segments, nodes of Ranvier, or the post-synaptic density, is an active process mediated by the interaction of ion channels with scaffold proteins and is of immense importance for electrical signaling. Growing evidence indicates that the density of ion channels at such membrane sites may affect action potential conduction properties and synaptic transmission. However, despite the emerging importance of ion channel density for electrical signaling, how ion channel-scaffold protein molecular interactions lead to cellular ion channel clustering, and how this process is regulated are largely unknown. In this review, we emphasize that voltage-dependent ion channel density at native clustering sites not only affects the density of ionic current fluxes but may also affect the conduction properties of the channel and/or the physical properties of the membrane at such locations, all changes that are expected to affect action potential conduction properties. Using the concrete example of the prototypical Shaker voltage-activated potassium channel (Kv) protein, we demonstrate how insight into the regulation of cellular ion channel clustering can be obtained when the molecular mechanism of ion channel-scaffold protein interaction is known. Our review emphasizes that such mechanistic knowledge is essential, and when combined with super-resolution imaging microscopy, can serve to bridge the molecular-cellular gap in understanding the regulation of ion channel clustering. Pressing questions, challenges and future directions in addressing ion channel clustering and its regulation are discussed.
Collapse
Affiliation(s)
| | - Ofer Yifrach
- Department of Life Sciences and the Zlotowski Center for Neurosciences, Ben-Gurion University of the Negev, Be’er Sheva, Israel
| |
Collapse
|
27
|
Bar C, Barcia G, Jennesson M, Le Guyader G, Schneider A, Mignot C, Lesca G, Breuillard D, Montomoli M, Keren B, Doummar D, Billette de Villemeur T, Afenjar A, Marey I, Gerard M, Isnard H, Poisson A, Dupont S, Berquin P, Meyer P, Genevieve D, De Saint Martin A, El Chehadeh S, Chelly J, Guët A, Scalais E, Dorison N, Myers CT, Mefford HC, Howell KB, Marini C, Freeman JL, Nica A, Terrone G, Sekhara T, Lebre AS, Odent S, Sadleir LG, Munnich A, Guerrini R, Scheffer IE, Kabashi E, Nabbout R. Expanding the genetic and phenotypic relevance of KCNB1 variants in developmental and epileptic encephalopathies: 27 new patients and overview of the literature. Hum Mutat 2020; 41:69-80. [PMID: 31513310 DOI: 10.1002/humu.23915] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 08/28/2019] [Accepted: 09/09/2019] [Indexed: 12/28/2022]
Abstract
Developmental and epileptic encephalopathies (DEE) refer to a heterogeneous group of devastating neurodevelopmental disorders. Variants in KCNB1 have been recently reported in patients with early-onset DEE. KCNB1 encodes the α subunit of the delayed rectifier voltage-dependent potassium channel Kv 2.1. We review the 37 previously reported patients carrying 29 distinct KCNB1 variants and significantly expand the mutational spectrum describing 18 novel variants from 27 unreported patients. Most variants occur de novo and mainly consist of missense variants located on the voltage sensor and the pore domain of Kv 2.1. We also report the first inherited variant (p.Arg583*). KCNB1-related encephalopathies encompass a wide spectrum of neurodevelopmental disorders with predominant language difficulties and behavioral impairment. Eighty-five percent of patients developed epilepsies with variable syndromes and prognosis. Truncating variants in the C-terminal domain are associated with a less-severe epileptic phenotype. Overall, this report provides an up-to-date review of the mutational and clinical spectrum of KCNB1, strengthening its place as a causal gene in DEEs and emphasizing the need for further functional studies to unravel the underlying mechanisms.
Collapse
Affiliation(s)
- Claire Bar
- Department of Pediatric Neurology, Reference Centre for Rare Epilepsies, Hôpital Necker-Enfants Malades, Paris, France
- Imagine institute, laboratory of Translational Research for Neurological Disorders, INSERM UMR 1163, Imagine Institute, Paris, France
- Université Paris Descartes-Sorbonne Paris Cité, Paris, France
| | - Giulia Barcia
- Imagine institute, laboratory of Translational Research for Neurological Disorders, INSERM UMR 1163, Imagine Institute, Paris, France
- Université Paris Descartes-Sorbonne Paris Cité, Paris, France
- Department of genetics, Necker Enfants Malades hospital, Assistance Publique-Hôpitaux de Paris, Paris, France
| | | | - Gwenaël Le Guyader
- Department of genetics, University hospital Poitiers, Poitiers Cedex, France
- EA3808-NEUVACOD Unité Neurovasculaire et Troubles Cognitifs, Pôle Biologie Santé, Université de Poitiers, Poitiers, France
| | - Amy Schneider
- Department of Medicine, Epilepsy Research Centre, Austin Health, The University of Melbourne, Heidelberg, Victoria, Australia
| | - Cyril Mignot
- Institut du Cerveau et de la Moelle épinière, INSERM, U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Paris, France
- Département de Génétique et de Cytogénétique, Centre de Reference Déficience Intellectuelle de Causes Rares, APHP, Hôpital Pitié-Salpêtrière, GRC UPMC (Déficience Intellectuelle et Autisme), Paris, France
| | - Gaetan Lesca
- Department of genetics, Hospices Civils de Lyon, Lyon, France
- Neurosciences centre of Lyon, INSERM U1028, UMR CNRS 5292, Université Claude Bernard Lyon 1, Bron Cedex, France
| | - Delphine Breuillard
- Department of Pediatric Neurology, Reference Centre for Rare Epilepsies, Hôpital Necker-Enfants Malades, Paris, France
| | - Martino Montomoli
- Pediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, Department of Neuroscience, A Meyer Children's Hospital, University of Florence, Florence, Italy
| | - Boris Keren
- Département de Génétique et de Cytogénétique, Centre de Reference Déficience Intellectuelle de Causes Rares, APHP, Hôpital Pitié-Salpêtrière, GRC UPMC (Déficience Intellectuelle et Autisme), Paris, France
| | - Diane Doummar
- Department of Pediatric Neurology, Hôpital Armand Trousseau, AP-HP, Paris, France
| | | | - Alexandra Afenjar
- Département de Génétique et Embryologie Médicale, Pathologies Congénitales du Cervelet-LeucoDystrophies, Centre de Référence déficiences intellectuelles de causes rares, AP-HP, Hôpital Armand Trousseau, GRC n°19, Sorbonne Université, Paris, France
| | - Isabelle Marey
- Département de Génétique et de Cytogénétique, Centre de Reference Déficience Intellectuelle de Causes Rares, APHP, Hôpital Pitié-Salpêtrière, GRC UPMC (Déficience Intellectuelle et Autisme), Paris, France
| | - Marion Gerard
- Department of genetics, CHU Côte de Nacre, Caen, France
| | | | - Alice Poisson
- Reference Center for Diagnosis and Management of Genetic Psychiatric Disorders, Centre Hospitalier le Vinatier and EDR-Psy Team, Centre National de la Recherche Scientifique & Lyon 1 Claude Bernard University, Villeurbanne, France
| | - Sophie Dupont
- Institut du Cerveau et de la Moelle épinière, INSERM, U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Paris, France
- Epileptology and Rehabilitation department, GH Pitie-Salpêtrière-Charles Foix, AP-HP, Paris, France
| | - Patrick Berquin
- Department of pediatric neurology Amiens-Picardie university hospital, Université de Picardie Jules Verne, Amiens, France
| | - Pierre Meyer
- Department of pediatric neurology, Montpellier university hospital, Montpellier, France
- PhyMedExp, U1046 INSERM, UMR9214 CNRS, Montpellier, France
| | - David Genevieve
- Service de génétique clinique et du Département de Génétique Médicale, Maladies Rares et Médecine Personnalisée, Centre de référence maladies rares anomalies du développement, CHU Montpellier, Montpellier, France
| | - Anne De Saint Martin
- Department of Pediatric Neurology, Strasbourg University Hospital, Strasbourg, France
| | - Salima El Chehadeh
- Department of genetics, Hôpital de Hautepierre, Hôpitaux Universitaires de Strasbourg, Strasbourg, France
| | - Jamel Chelly
- Department of genetics, Hôpital de Hautepierre, Hôpitaux Universitaires de Strasbourg, Strasbourg, France
| | - Agnès Guët
- Department of Pediatric, Louis-Mourier Hospital, Colombes, France
| | - Emmanuel Scalais
- Department of Pediatric Neurology, Centre Hospitalier de Luxembourg, Luxembourg City, Luxembourg City, Luxembourg
| | - Nathalie Dorison
- Department of pediatric Neurosurgery, Rothschild Foundation Hospital, Paris, France
| | - Candace T Myers
- Department of Pediatrics, University of Washington, Seattle, Washington
| | - Heather C Mefford
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, Washington
| | - Katherine B Howell
- Departments of Neurology and Paediatrics, Royal Children's Hospital, University of Melbourne, Melbourne, Victoria, Australia
- Murdoch Children's Research Institute, Melbourne, Victoria, Australia
| | - Carla Marini
- Pediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, Department of Neuroscience, A Meyer Children's Hospital, University of Florence, Florence, Italy
| | - Jeremy L Freeman
- Departments of Neurology and Paediatrics, Royal Children's Hospital, University of Melbourne, Melbourne, Victoria, Australia
- Murdoch Children's Research Institute, Melbourne, Victoria, Australia
| | - Anca Nica
- Department of Neurology, Center for Clinical Research (CIC 1414), Rennes University Hospital, Rennes, France
| | - Gaetano Terrone
- Department of Translational Medical Sciences, Section of Pediatrics-Child Neurology Unit, Federico II University, Naples, Italy
| | - Tayeb Sekhara
- Department of Pediatric Neurology, C.H.I.R.E.C, Brussels, Belgium
| | - Anne-Sophie Lebre
- Department of genetics, Maison Blanche hospital, University hospital, Reims, Reims, France
| | - Sylvie Odent
- Reference Centre for Rare Developmental Abnormalities, CLAD-Ouest, CHU Rennes, Rennes, France
- Institute of genetics and development, CNRS UMR 6290, Rennes university, Rennes, France
| | - Lynette G Sadleir
- Department of Paediatrics and Child Health, University of Otago, Wellington, New Zealand
| | - Arnold Munnich
- Université Paris Descartes-Sorbonne Paris Cité, Paris, France
- Department of genetics, Necker Enfants Malades hospital, Assistance Publique-Hôpitaux de Paris, Paris, France
| | - Renzo Guerrini
- Pediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, Department of Neuroscience, A Meyer Children's Hospital, University of Florence, Florence, Italy
| | - Ingrid E Scheffer
- Department of Medicine, Epilepsy Research Centre, Austin Health, The University of Melbourne, Heidelberg, Victoria, Australia
- Departments of Neurology and Paediatrics, Royal Children's Hospital, University of Melbourne, Melbourne, Victoria, Australia
- The Florey Institute of Neurosciences and Mental Health, Heidelberg, Victoria, Australia
| | - Edor Kabashi
- Imagine institute, laboratory of Translational Research for Neurological Disorders, INSERM UMR 1163, Imagine Institute, Paris, France
- Université Paris Descartes-Sorbonne Paris Cité, Paris, France
| | - Rima Nabbout
- Department of Pediatric Neurology, Reference Centre for Rare Epilepsies, Hôpital Necker-Enfants Malades, Paris, France
- Imagine institute, laboratory of Translational Research for Neurological Disorders, INSERM UMR 1163, Imagine Institute, Paris, France
- Université Paris Descartes-Sorbonne Paris Cité, Paris, France
| |
Collapse
|
28
|
Vierra NC, Kirmiz M, van der List D, Santana LF, Trimmer JS. Kv2.1 mediates spatial and functional coupling of L-type calcium channels and ryanodine receptors in mammalian neurons. eLife 2019; 8:49953. [PMID: 31663850 PMCID: PMC6839919 DOI: 10.7554/elife.49953] [Citation(s) in RCA: 68] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Accepted: 10/29/2019] [Indexed: 12/16/2022] Open
Abstract
The voltage-gated K+ channel Kv2.1 serves a major structural role in the soma and proximal dendrites of mammalian brain neurons, tethering the plasma membrane (PM) to endoplasmic reticulum (ER). Although Kv2.1 clustering at neuronal ER-PM junctions (EPJs) is tightly regulated and highly conserved, its function remains unclear. By identifying and evaluating proteins in close spatial proximity to Kv2.1-containing EPJs, we discovered that a significant role of Kv2.1 at EPJs is to promote the clustering and functional coupling of PM L-type Ca2+ channels (LTCCs) to ryanodine receptor (RyR) ER Ca2+ release channels. Kv2.1 clustering also unexpectedly enhanced LTCC opening at polarized membrane potentials. This enabled Kv2.1-LTCC-RyR triads to generate localized Ca2+ release events (i.e., Ca2+ sparks) independently of action potentials. Together, these findings uncover a novel mode of LTCC regulation and establish a unique mechanism whereby Kv2.1-associated EPJs provide a molecular platform for localized somatodendritic Ca2+ signals in mammalian brain neurons.
Collapse
Affiliation(s)
- Nicholas C Vierra
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, Davis, United States.,Department of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, United States
| | - Michael Kirmiz
- Department of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, United States
| | - Deborah van der List
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, Davis, United States.,Department of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, United States
| | - L Fernando Santana
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, Davis, United States
| | - James S Trimmer
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, Davis, United States.,Department of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, United States
| |
Collapse
|
29
|
Jędrychowska J, Korzh V. Kv2.1 voltage-gated potassium channels in developmental perspective. Dev Dyn 2019; 248:1180-1194. [PMID: 31512327 DOI: 10.1002/dvdy.114] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 09/01/2019] [Accepted: 09/03/2019] [Indexed: 11/11/2022] Open
Abstract
Kv2.1 voltage-gated potassium channels consist of two types of α-subunits: (a) electrically-active Kcnb1 α-subunits and (b) silent or modulatory α-subunits plus β-subunits that, similar to silent α-subunits, also regulate electrically-active subunits. Voltage-gated potassium channels were traditionally viewed, mainly by electrophysiologists, as regulators of the electrical activity of the plasma membrane in excitable cells, a role that is performed by transmembrane protein domains of α-subunits that form the electric pore. Genetic studies revealed a role for this region of α-subunits of voltage-gated potassium channels in human neurodevelopmental disorders, such as epileptic encephalopathy. The N- and C-terminal domains of α-subunits interact to form the cytoplasmic subunit of heterotetrameric potassium channels that regulate electric pores. Subsequent animal studies revealed the developmental functions of Kcnb1-containing voltage-gated potassium channels and illustrated their role during brain development and reproduction. These functions of potassium channels are discussed in this review in the context of regulatory interactions between electrically-active and regulatory subunits.
Collapse
Affiliation(s)
- Justyna Jędrychowska
- International Institute of Molecular and Cell Biology in Warsaw, Warsaw, Poland.,Postgraduate School of Molecular Medicine, Warsaw Medical University, Warsaw, Poland
| | - Vladimir Korzh
- International Institute of Molecular and Cell Biology in Warsaw, Warsaw, Poland
| |
Collapse
|
30
|
Iwata M, Watanabe S, Yamane A, Miyasaka T, Misonou H. Regulatory mechanisms for the axonal localization of tau protein in neurons. Mol Biol Cell 2019; 30:2441-2457. [PMID: 31364926 PMCID: PMC6743362 DOI: 10.1091/mbc.e19-03-0183] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Tau is a microtubule (MT)-associated protein that is thought to be localized to the axon. However, its precise localization in developing neurons and mechanisms for the axonal localization have not been fully addressed. In this study, we found that the axonal localization of tau in cultured rat hippocampal neurons mainly occur during early neuronal development. Interestingly, transient expression of human tau in very immature neurons, but not in mature neurons, mimicked the developmental localization of endogenous tau to the axon. We therefore were able to establish an experimental model, in which exogenously expressed tau can be properly localized to the axon. Using this model, we obtained a surprising finding that the axonal localization of tau did not require stable MT binding. Tau lacking the MT-binding domain (MTBD) exhibited high diffusivity but localized properly to the axon. In contrast, a dephosphorylation-mimetic mutant of the proline-rich region 2 showed reinforced MT binding and mislocalization. Our results suggest that tight binding to MTs prevents tau from entering the axon and results in mislocalization in the soma and dendrites when expressed in mature neurons. This study therefore provides a novel mechanism independent of MTBD for the axonal localization of tau.
Collapse
Affiliation(s)
- Minori Iwata
- Laboratory of Ion Channel Pathophysiology, Graduate School of Brain Science, Doshisha University, Kyotanabe-shi, Kyoto 610-0394, Japan
| | - Shoji Watanabe
- Laboratory of Ion Channel Pathophysiology, Graduate School of Brain Science, Doshisha University, Kyotanabe-shi, Kyoto 610-0394, Japan
| | - Ayaka Yamane
- Laboratory of Ion Channel Pathophysiology, Graduate School of Brain Science, Doshisha University, Kyotanabe-shi, Kyoto 610-0394, Japan
| | - Tomohiro Miyasaka
- Department of Neuropathology, Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe-shi, Kyoto 610-0394, Japan.,Center for Research in Neurodegenerative Diseases, Doshisha University, Kyotanabe-shi, Kyoto 610-0394, Japan
| | - Hiroaki Misonou
- Laboratory of Ion Channel Pathophysiology, Graduate School of Brain Science, Doshisha University, Kyotanabe-shi, Kyoto 610-0394, Japan.,Center for Research in Neurodegenerative Diseases, Doshisha University, Kyotanabe-shi, Kyoto 610-0394, Japan
| |
Collapse
|
31
|
Yeh CY, Ye Z, Moutal A, Gaur S, Henton AM, Kouvaros S, Saloman JL, Hartnett-Scott KA, Tzounopoulos T, Khanna R, Aizenman E, Camacho CJ. Defining the Kv2.1-syntaxin molecular interaction identifies a first-in-class small molecule neuroprotectant. Proc Natl Acad Sci U S A 2019; 116:15696-15705. [PMID: 31308225 PMCID: PMC6681760 DOI: 10.1073/pnas.1903401116] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The neuronal cell death-promoting loss of cytoplasmic K+ following injury is mediated by an increase in Kv2.1 potassium channels in the plasma membrane. This phenomenon relies on Kv2.1 binding to syntaxin 1A via 9 amino acids within the channel intrinsically disordered C terminus. Preventing this interaction with a cell and blood-brain barrier-permeant peptide is neuroprotective in an in vivo stroke model. Here a rational approach was applied to define the key molecular interactions between syntaxin and Kv2.1, some of which are shared with mammalian uncoordinated-18 (munc18). Armed with this information, we found a small molecule Kv2.1-syntaxin-binding inhibitor (cpd5) that improves cortical neuron survival by suppressing SNARE-dependent enhancement of Kv2.1-mediated currents following excitotoxic injury. We validated that cpd5 selectively displaces Kv2.1-syntaxin-binding peptides from syntaxin and, at higher concentrations, munc18, but without affecting either synaptic or neuronal intrinsic properties in brain tissue slices at neuroprotective concentrations. Collectively, our findings provide insight into the role of syntaxin in neuronal cell death and validate an important target for neuroprotection.
Collapse
Affiliation(s)
- Chung-Yang Yeh
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Zhaofeng Ye
- Department of Computational and Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
- School of Medicine, Tsinghua University, Beijing 100871, China
| | - Aubin Moutal
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson, AZ 85724
| | - Shivani Gaur
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Amanda M Henton
- Department of Otolaryngology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
- Pittsburgh Hearing Research Center, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Stylianos Kouvaros
- Department of Otolaryngology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
- Pittsburgh Hearing Research Center, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Jami L Saloman
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Karen A Hartnett-Scott
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Thanos Tzounopoulos
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
- Department of Otolaryngology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
- Pittsburgh Hearing Research Center, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Rajesh Khanna
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson, AZ 85724
| | - Elias Aizenman
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261;
- Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
- Pittsburgh Hearing Research Center, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Carlos J Camacho
- Department of Computational and Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261;
| |
Collapse
|
32
|
Jepson JEC, Praschberger R, Krishnakumar SS. Mechanisms of Neurological Dysfunction in GOSR2 Progressive Myoclonus Epilepsy, a Golgi SNAREopathy. Neuroscience 2019; 420:41-49. [PMID: 30954670 DOI: 10.1016/j.neuroscience.2019.03.057] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 03/22/2019] [Accepted: 03/26/2019] [Indexed: 10/27/2022]
Abstract
Successive fusion events between transport vesicles and their target membranes mediate trafficking of secreted, membrane- and organelle-localised proteins. During the initial steps of this process, termed the secretory pathway, COPII vesicles bud from the endoplasmic reticulum (ER) and fuse with the cis-Golgi membrane, thus depositing their cargo. This fusion step is driven by a quartet of SNARE proteins that includes the cis-Golgi t-SNARE Membrin, encoded by the GOSR2 gene. Mis-sense mutations in GOSR2 result in Progressive Myoclonus Epilepsy (PME), a severe neurological disorder characterised by ataxia, myoclonus and seizures in the absence of significant cognitive impairment. However, given the ubiquitous and essential function of ER-to-Golgi transport, why GOSR2 mutations cause neurological dysfunction and not lethality or a broader range of developmental defects has remained an enigma. Here we highlight new work that has shed light on this issue and incorporate insights into canonical and non-canonical secretory trafficking pathways in neurons to speculate as to the cellular and molecular mechanisms underlying GOSR2 PME. This article is part of a Special Issue entitled: SNARE proteins: a long journey of science in brain physiology and pathology: from molecular.
Collapse
Affiliation(s)
- James E C Jepson
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, UK.
| | - Roman Praschberger
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, UK
| | - Shyam S Krishnakumar
- Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, UK; Department of Cell Biology, Yale School of Medicine, New Haven, CT, USA
| |
Collapse
|
33
|
Lebowitz JJ, Pino JA, Mackie PM, Lin M, Hurst C, Divita K, Collins AT, Koutzoumis DN, Torres GE, Khoshbouei H. Clustered Kv2.1 decreases dopamine transporter activity and internalization. J Biol Chem 2019; 294:6957-6971. [PMID: 30824538 DOI: 10.1074/jbc.ra119.007441] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Revised: 02/26/2019] [Indexed: 01/16/2023] Open
Abstract
The dopamine transporter (DAT) regulates dopamine neurotransmission via reuptake of dopamine released into the extracellular space. Interactions with partner proteins alter DAT function and thereby dynamically shape dopaminergic tone important for normal brain function. However, the extent and nature of these interactions are incompletely understood. Here, we describe a novel physical and functional interaction between DAT and the voltage-gated K+ channel Kv2.1 (potassium voltage-gated channel subfamily B member 1 or KCNB1). To examine the functional consequences of this interaction, we employed a combination of immunohistochemistry, immunofluorescence live-cell microscopy, co-immunoprecipitation, and electrophysiological approaches. Consistent with previous reports, we found Kv2.1 is trafficked to membrane-bound clusters observed both in vivo and in vitro in rodent dopamine neurons. Our data provide evidence that clustered Kv2.1 channels decrease DAT's lateral mobility and inhibit its internalization, while also decreasing canonical transporter activity by altering DAT's conformational equilibrium. These results suggest that Kv2.1 clusters exert a spatially discrete homeostatic braking mechanism on DAT by inducing a relative increase in inward-facing transporters. Given recent reports of Kv2.1 dysregulation in neurological disorders, it is possible that alterations in the functional interaction between DAT and Kv2.1 affect dopamine neuron activity.
Collapse
Affiliation(s)
- Joseph J Lebowitz
- From the Departments of Neuroscience and.,T32 in Movement Disorders and Neurorestoration, Fixel Center for Neurological Diseases, UF Health, Gainesville, Florida 32610
| | - Jose A Pino
- Pharmacology and Experimental Therapeutics, College of Medicine, University of Florida, Gainesville, Florida 32610 and
| | | | - Min Lin
- From the Departments of Neuroscience and
| | | | | | | | - Dimitri N Koutzoumis
- Pharmacology and Experimental Therapeutics, College of Medicine, University of Florida, Gainesville, Florida 32610 and
| | - Gonzalo E Torres
- Pharmacology and Experimental Therapeutics, College of Medicine, University of Florida, Gainesville, Florida 32610 and
| | - Habibeh Khoshbouei
- From the Departments of Neuroscience and .,T32 in Movement Disorders and Neurorestoration, Fixel Center for Neurological Diseases, UF Health, Gainesville, Florida 32610
| |
Collapse
|
34
|
Alpizar SA, Cho IH, Hoppa MB. Subcellular control of membrane excitability in the axon. Curr Opin Neurobiol 2019; 57:117-125. [PMID: 30784979 DOI: 10.1016/j.conb.2019.01.020] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Accepted: 01/21/2019] [Indexed: 12/11/2022]
Abstract
Ion channels are microscopic pore proteins in the membrane that open and close in response to chemical and electrical stimuli. This simple concept underlies rapid electrical signaling in the brain as well as several important aspects of neural plasticity. Although the soma accounts for less than 1% of many neurons by membrane area, it has been the major site of measuring ion channel function. However, the axon is one of the longest processes found in cellular biology and hosts a multitude of critical signaling functions in the brain. Not only does the axon initiate and rapidly propagate action potentials (APs) across the brain but it also forms the presynaptic terminals that convert these electrical inputs into chemical outputs. Here, we review recent advances in the physiological role of ion channels within the diverse landscape of the axon and presynaptic terminals.
Collapse
Affiliation(s)
- Scott A Alpizar
- Dartmouth College, Department of Biological Sciences, Hanover, NH, United States
| | - In Ha Cho
- Dartmouth College, Department of Biological Sciences, Hanover, NH, United States
| | - Michael B Hoppa
- Dartmouth College, Department of Biological Sciences, Hanover, NH, United States.
| |
Collapse
|
35
|
Kirmiz M, Palacio S, Thapa P, King AN, Sack JT, Trimmer JS. Remodeling neuronal ER-PM junctions is a conserved nonconducting function of Kv2 plasma membrane ion channels. Mol Biol Cell 2018; 29:2410-2432. [PMID: 30091655 PMCID: PMC6233057 DOI: 10.1091/mbc.e18-05-0337] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The endoplasmic reticulum (ER) and plasma membrane (PM) form junctions crucial to ion and lipid signaling and homeostasis. The Kv2.1 ion channel is localized at ER–PM junctions in brain neurons and is unique among PM proteins in its ability to remodel these specialized membrane contact sites. Here, we show that this function is conserved between Kv2.1 and Kv2.2, which differ in their biophysical properties, modulation, and cellular expression. Kv2.2 ER–PM junctions are present at sites deficient in the actin cytoskeleton, and disruption of the actin cytoskeleton affects their spatial organization. Kv2.2-containing ER–PM junctions overlap with those formed by canonical ER–PM tethers. The ability of Kv2 channels to remodel ER–PM junctions is unchanged by point mutations that eliminate their ion conduction but eliminated by point mutations within the Kv2-specific proximal restriction and clustering (PRC) domain that do not impact their ion channel function. The highly conserved PRC domain is sufficient to transfer the ER–PM junction–remodeling function to another PM protein. Last, brain neurons in Kv2 double-knockout mice have altered ER–PM junctions. Together, these findings demonstrate a conserved in vivo function for Kv2 family members in remodeling neuronal ER–PM junctions that is distinct from their canonical role as ion-conducting channels shaping neuronal excitability.
Collapse
Affiliation(s)
- Michael Kirmiz
- Department of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, CA 95616
| | - Stephanie Palacio
- Department of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, CA 95616
| | - Parashar Thapa
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616
| | - Anna N King
- Department of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, CA 95616
| | - Jon T Sack
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616.,Department of Anesthesiology and Pain Medicine, University of California, Davis, Davis, CA 95616
| | - James S Trimmer
- Department of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, CA 95616.,Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616
| |
Collapse
|
36
|
Affiliation(s)
- Elizabeth Wen Sun
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510
- Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT 06510
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510
| | - Pietro De Camilli
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510;
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510
- Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT 06510
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510
| |
Collapse
|
37
|
Identification of VAPA and VAPB as Kv2 Channel-Interacting Proteins Defining Endoplasmic Reticulum-Plasma Membrane Junctions in Mammalian Brain Neurons. J Neurosci 2018; 38:7562-7584. [PMID: 30012696 DOI: 10.1523/jneurosci.0893-18.2018] [Citation(s) in RCA: 97] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Revised: 06/01/2018] [Accepted: 07/07/2018] [Indexed: 11/21/2022] Open
Abstract
Membrane contacts between endoplasmic reticulum (ER) and plasma membrane (PM), or ER-PM junctions, are ubiquitous in eukaryotic cells and are platforms for lipid and calcium signaling and homeostasis. Recent studies have revealed proteins crucial to the formation and function of ER-PM junctions in non-neuronal cells, but little is known of the ER-PM junctions prominent in aspiny regions of mammalian brain neurons. The Kv2.1 voltage-gated potassium channel is abundantly clustered at ER-PM junctions in brain neurons and is the first PM protein that functions to organize ER-PM junctions. However, the molecular mechanism whereby Kv2.1 localizes to and remodels these junctions is unknown. We used affinity immunopurification and mass spectrometry-based proteomics on brain samples from male and female WT and Kv2.1 KO mice and identified the resident ER vesicle-associated membrane protein-associated proteins isoforms A and B (VAPA and VAPB) as prominent Kv2.1-associated proteins. Coexpression with Kv2.1 or its paralog Kv2.2 was sufficient to recruit VAPs to ER-PM junctions. Multiplex immunolabeling revealed colocalization of Kv2.1 and Kv2.2 with endogenous VAPs at ER-PM junctions in brain neurons from male and female mice in situ and in cultured rat hippocampal neurons, and KO of VAPA in mammalian cells reduces Kv2.1 clustering. The association of VAPA with Kv2.1 relies on a "two phenylalanines in an acidic tract" (FFAT) binding domain on VAPA and a noncanonical phosphorylation-dependent FFAT motif comprising the Kv2-specific clustering or PRC motif. These results suggest that Kv2.1 localizes to and organizes neuronal ER-PM junctions through an interaction with VAPs.SIGNIFICANCE STATEMENT Our study identified the endoplasmic reticulum (ER) proteins vesicle-associated membrane protein-associated proteins isoforms A and B (VAPA and VAPB) as proteins copurifying with the plasma membrane (PM) Kv2.1 ion channel. We found that expression of Kv2.1 recruits VAPs to ER-PM junctions, specialized membrane contact sites crucial to distinct aspects of cell function. We found endogenous VAPs at Kv2.1-mediated ER-PM junctions in brain neurons and other mammalian cells and that knocking out VAPA expression disrupts Kv2.1 clustering. We identified domains of VAPs and Kv2.1 necessary and sufficient for their association at ER-PM junctions. Our study suggests that Kv2.1 expression in the PM can affect ER-PM junctions via its phosphorylation-dependent association to ER-localized VAPA and VAPB.
Collapse
|
38
|
Kv2 potassium channels form endoplasmic reticulum/plasma membrane junctions via interaction with VAPA and VAPB. Proc Natl Acad Sci U S A 2018; 115:E7331-E7340. [PMID: 29941597 DOI: 10.1073/pnas.1805757115] [Citation(s) in RCA: 127] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Kv2.1 exhibits two distinct forms of localization patterns on the neuronal plasma membrane: One population is freely diffusive and regulates electrical activity via voltage-dependent K+ conductance while a second one localizes to micrometer-sized clusters that contain densely packed, but nonconducting, channels. We have previously established that these clusters represent endoplasmic reticulum/plasma membrane (ER/PM) junctions that function as membrane trafficking hubs and that Kv2.1 plays a structural role in forming these membrane contact sites in both primary neuronal cultures and transfected HEK cells. Clustering and the formation of ER/PM contacts are regulated by phosphorylation within the channel C terminus, offering cells fast, dynamic control over the physical relationship between the cortical ER and PM. The present study addresses the mechanisms by which Kv2.1 and the related Kv2.2 channel interact with the ER membrane. Using proximity-based biotinylation techniques in transfected HEK cells we identified ER VAMP-associated proteins (VAPs) as potential Kv2.1 interactors. Confirmation that Kv2.1 and -2.2 bind VAPA and VAPB employed colocalization/redistribution, siRNA knockdown, and Förster resonance energy transfer (FRET)-based assays. CD4 chimeras containing sequence from the Kv2.1 C terminus were used to identify a noncanonical VAP-binding motif. VAPs were first identified as proteins required for neurotransmitter release in Aplysia and are now known to be abundant scaffolding proteins involved in membrane contact site formation throughout the ER. The VAP interactome includes AKAPs, kinases, membrane trafficking machinery, and proteins regulating nonvesicular lipid transport from the ER to the PM. Therefore, the Kv2-induced VAP concentration at ER/PM contact sites is predicted to have wide-ranging effects on neuronal cell biology.
Collapse
|
39
|
Two Distinct Secretory Pathways for Differential Kv2.1 Localization in Neurons. J Neurosci 2018; 38:4261-4263. [PMID: 29720558 DOI: 10.1523/jneurosci.0236-18.2018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Revised: 03/24/2018] [Accepted: 03/29/2018] [Indexed: 11/21/2022] Open
|
40
|
Bourke AM, Bowen AB, Kennedy MJ. New approaches for solving old problems in neuronal protein trafficking. Mol Cell Neurosci 2018; 91:48-66. [PMID: 29649542 DOI: 10.1016/j.mcn.2018.04.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 04/05/2018] [Accepted: 04/06/2018] [Indexed: 11/16/2022] Open
Abstract
Fundamental cellular properties are determined by the repertoire and abundance of proteins displayed on the cell surface. As such, the trafficking mechanisms for establishing and maintaining the surface proteome must be tightly regulated for cells to respond appropriately to extracellular cues, yet plastic enough to adapt to ever-changing environments. Not only are the identity and abundance of surface proteins critical, but in many cases, their regulated spatial positioning within surface nanodomains can greatly impact their function. In the context of neuronal cell biology, surface levels and positioning of ion channels and neurotransmitter receptors play essential roles in establishing important properties, including cellular excitability and synaptic strength. Here we review our current understanding of the trafficking pathways that control the abundance and localization of proteins important for synaptic function and plasticity, as well as recent technological advances that are allowing the field to investigate protein trafficking with increasing spatiotemporal precision.
Collapse
Affiliation(s)
- Ashley M Bourke
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO, United States
| | - Aaron B Bowen
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO, United States
| | - Matthew J Kennedy
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO, United States.
| |
Collapse
|
41
|
González C, Cornejo VH, Couve A. Golgi bypass for local delivery of axonal proteins, fact or fiction? Curr Opin Cell Biol 2018; 53:9-14. [PMID: 29631154 DOI: 10.1016/j.ceb.2018.03.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Revised: 03/26/2018] [Accepted: 03/29/2018] [Indexed: 02/07/2023]
Abstract
Although translation of cytosolic proteins is well described in axons, much less is known about the synthesis, processing and trafficking of transmembrane and secreted proteins. A canonical rough endoplasmic reticulum or a stacked Golgi apparatus has not been detected in axons, generating doubts about the functionality of a local route. However, axons contain mRNAs for membrane and secreted proteins, translation factors, ribosomal components, smooth endoplasmic reticulum and post-endoplasmic reticulum elements that may contribute to local biosynthesis and plasma membrane delivery. Here we consider the evidence supporting a local secretory system in axons. We discuss exocytic elements and examples of autonomous axonal trafficking that impact development and maintenance. We also examine whether unconventional post-endoplasmic reticulum pathways may replace the canonical Golgi apparatus.
Collapse
Affiliation(s)
- Carolina González
- Department of Neuroscience, Facultad de Medicina, Universidad de Chile, Chile; Biomedical Neuroscience Institute (BNI), Facultad de Medicina, Universidad de Chile, Chile
| | - Víctor Hugo Cornejo
- Department of Neuroscience, Facultad de Medicina, Universidad de Chile, Chile; Biomedical Neuroscience Institute (BNI), Facultad de Medicina, Universidad de Chile, Chile
| | - Andrés Couve
- Department of Neuroscience, Facultad de Medicina, Universidad de Chile, Chile; Biomedical Neuroscience Institute (BNI), Facultad de Medicina, Universidad de Chile, Chile.
| |
Collapse
|
42
|
The Axon Initial Segment: An Updated Viewpoint. J Neurosci 2018; 38:2135-2145. [PMID: 29378864 DOI: 10.1523/jneurosci.1922-17.2018] [Citation(s) in RCA: 192] [Impact Index Per Article: 27.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2017] [Revised: 01/20/2018] [Accepted: 01/25/2018] [Indexed: 12/20/2022] Open
Abstract
At the base of axons sits a unique compartment called the axon initial segment (AIS). The AIS generates and shapes the action potential before it is propagated along the axon. Neuronal excitability thus depends crucially on the AIS composition and position, and these adapt to developmental and physiological conditions. The AIS also demarcates the boundary between the somatodendritic and axonal compartments. Recent studies have brought insights into the molecular architecture of the AIS and how it regulates protein trafficking. This Viewpoints article summarizes current knowledge about the AIS and highlights future challenges in understanding this key actor of neuronal physiology.
Collapse
|