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Chen X, Bell NA, Coffman BL, Rabino AA, Garcia-Mata R, Kammermeier PJ, Yule DI, Axelrod D, Smrcka AV, Giovannucci DR, Anantharam A. A PACAP-activated network for secretion requires coordination of Ca 2+ influx and Ca 2+ mobilization. Mol Biol Cell 2024; 35:ar92. [PMID: 38758660 PMCID: PMC11244167 DOI: 10.1091/mbc.e24-02-0083] [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: 02/21/2024] [Revised: 04/26/2024] [Accepted: 05/07/2024] [Indexed: 05/19/2024] Open
Abstract
Chromaffin cells of the adrenal medulla transduce sympathetic nerve activity into stress hormone secretion. The two neurotransmitters principally responsible for coupling cell stimulation to secretion are acetylcholine and pituitary adenylate activating polypeptide (PACAP). In contrast to acetylcholine, PACAP evokes a persistent secretory response from chromaffin cells. However, the mechanisms by which PACAP acts are poorly understood. Here, it is shown that PACAP induces sustained increases in cytosolic Ca2+ which are disrupted when Ca2+ influx through L-type channels is blocked or internal Ca2+ stores are depleted. PACAP liberates stored Ca2+ via inositol trisphosphate receptors (IP3Rs) on the endoplasmic reticulum (ER), thereby functionally coupling Ca2+ mobilization to Ca2+ influx and supporting Ca2+-induced Ca2+-release. These Ca2+ influx and mobilization pathways are unified by an absolute dependence on phospholipase C epsilon (PLCε) activity. Thus, the persistent secretory response that is a defining feature of PACAP activity, in situ, is regulated by a signaling network that promotes sustained elevations in intracellular Ca2+ through multiple pathways.
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Affiliation(s)
- Xiaohuan Chen
- Department of Neurosciences, University of Toledo, Toledo, OH 43614
| | - Nicole A. Bell
- Department of Neurosciences, University of Toledo, Toledo, OH 43614
| | | | | | | | - Paul J. Kammermeier
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14627
| | - David I. Yule
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14627
| | | | - Alan V. Smrcka
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109
| | | | - Arun Anantharam
- Department of Neurosciences, University of Toledo, Toledo, OH 43614
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2
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Chen X, Bell NA, Coffman BL, Rabino AA, Garcia-Mata R, Kammermeier PJ, Yule DI, Axelrod D, Smrcka AV, Giovannucci DR, Anantharam A. A PACAP-activated network for secretion requires coordination of Ca 2+ influx and Ca 2+ mobilization. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.03.574069. [PMID: 38260572 PMCID: PMC10802325 DOI: 10.1101/2024.01.03.574069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
Chromaffin cells of the adrenal medulla transduce sympathetic nerve activity into stress hormone secretion. The two neurotransmitters principally responsible for coupling cell stimulation to secretion are acetylcholine and pituitary adenylate activating polypeptide (PACAP). In contrast to acetylcholine, PACAP evokes a persistent secretory response from chromaffin cells. However, the mechanisms by which PACAP acts are poorly understood. Here, it is shown that PACAP induces sustained increases in cytosolic Ca 2+ which are disrupted when Ca 2+ influx through L-type channels is blocked or internal Ca 2+ stores are depleted. PACAP liberates stored Ca 2+ via inositol trisphosphate receptors (IP3Rs) on the endoplasmic reticulum (ER), thereby functionally coupling Ca 2+ mobilization to Ca 2+ influx and supporting Ca 2+ -induced Ca 2+ -release. These Ca 2+ influx and mobilization pathways are unified by an absolute dependence on phospholipase C epsilon (PLCε) activity. Thus, the persistent secretory response that is a defining feature of PACAP activity, in situ , is regulated by a signaling network that promotes sustained elevations in intracellular Ca 2+ through multiple pathways.
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3
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Zalejski J, Sun J, Sharma A. Unravelling the Mystery inside Cells by Using Single-Molecule Fluorescence Imaging. J Imaging 2023; 9:192. [PMID: 37754956 PMCID: PMC10532472 DOI: 10.3390/jimaging9090192] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2023] [Revised: 09/01/2023] [Accepted: 09/14/2023] [Indexed: 09/28/2023] Open
Abstract
Live-cell imaging is a powerful technique to study the dynamics and mechanics of various biological molecules like proteins, organelles, DNA, and RNA. With the rapid evolution of optical microscopy, our understanding of how these molecules are implicated in the cells' most critical physiological roles deepens. In this review, we focus on how spatiotemporal nanoscale live-cell imaging at the single molecule level allows for profound contributions towards new discoveries in life science. This review will start by summarizing how single-molecule tracking has been used to analyze membrane dynamics, receptor-ligand interactions, protein-protein interactions, inner- and extra-cellular transport, gene expression/transcription, and whole organelle tracking. We then move on to how current authors are trying to improve single-molecule tracking and overcome current limitations by offering new ways of labeling proteins of interest, multi-channel/color detection, improvements in time-lapse imaging, and new methods and programs to analyze the colocalization and movement of targets. We later discuss how single-molecule tracking can be a beneficial tool used for medical diagnosis. Finally, we wrap up with the limitations and future perspectives of single-molecule tracking and total internal reflection microscopy.
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Affiliation(s)
| | | | - Ashutosh Sharma
- Department of Chemistry, University of Illinois Chicago, Chicago, IL 60607, USA; (J.Z.); (J.S.)
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4
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Sitarska E, Almeida SD, Beckwith MS, Stopp J, Czuchnowski J, Siggel M, Roessner R, Tschanz A, Ejsing C, Schwab Y, Kosinski J, Sixt M, Kreshuk A, Erzberger A, Diz-Muñoz A. Sensing their plasma membrane curvature allows migrating cells to circumvent obstacles. Nat Commun 2023; 14:5644. [PMID: 37704612 PMCID: PMC10499897 DOI: 10.1038/s41467-023-41173-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Accepted: 08/22/2023] [Indexed: 09/15/2023] Open
Abstract
To navigate through diverse tissues, migrating cells must balance persistent self-propelled motion with adaptive behaviors to circumvent obstacles. We identify a curvature-sensing mechanism underlying obstacle evasion in immune-like cells. Specifically, we propose that actin polymerization at the advancing edge of migrating cells is inhibited by the curvature-sensitive BAR domain protein Snx33 in regions with inward plasma membrane curvature. The genetic perturbation of this machinery reduces the cells' capacity to evade obstructions combined with faster and more persistent cell migration in obstacle-free environments. Our results show how cells can read out their surface topography and utilize actin and plasma membrane biophysics to interpret their environment, allowing them to adaptively decide if they should move ahead or turn away. On the basis of our findings, we propose that the natural diversity of BAR domain proteins may allow cells to tune their curvature sensing machinery to match the shape characteristics in their environment.
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Affiliation(s)
- Ewa Sitarska
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117, Heidelberg, Germany
- Collaboration for joint PhD degree between EMBL and Heidelberg University, Faculty of Biosciences, EMBL and Heidelberg University, Heidelberg, Germany
| | - Silvia Dias Almeida
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117, Heidelberg, Germany
- Division of Medical Image Computing, German Cancer Research Center (DKFZ), 69120, Heidelberg, Germany
| | | | - Julian Stopp
- Institute of Science and Technology Austria, 3400, Klosterneuburg, Austria
| | - Jakub Czuchnowski
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117, Heidelberg, Germany
| | - Marc Siggel
- EMBL Hamburg, European Molecular Biology Laboratory, 22607, Hamburg, Germany
- Centre for Structural Systems Biology, 22607, Hamburg, Germany
| | - Rita Roessner
- EMBL Hamburg, European Molecular Biology Laboratory, 22607, Hamburg, Germany
- Centre for Structural Systems Biology, 22607, Hamburg, Germany
| | - Aline Tschanz
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117, Heidelberg, Germany
- Collaboration for joint PhD degree between EMBL and Heidelberg University, Faculty of Biosciences, EMBL and Heidelberg University, Heidelberg, Germany
| | - Christer Ejsing
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117, Heidelberg, Germany
- Department of Biochemistry and Molecular Biology, Villum Center for Bioanalytical Sciences, University of Southern Denmark, Campusvej 55, 5230, Odense, Denmark
| | - Yannick Schwab
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117, Heidelberg, Germany
| | - Jan Kosinski
- EMBL Hamburg, European Molecular Biology Laboratory, 22607, Hamburg, Germany
- Centre for Structural Systems Biology, 22607, Hamburg, Germany
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, 69117, Heidelberg, Germany
| | - Michael Sixt
- Institute of Science and Technology Austria, 3400, Klosterneuburg, Austria
| | - Anna Kreshuk
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117, Heidelberg, Germany
| | - Anna Erzberger
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117, Heidelberg, Germany
| | - Alba Diz-Muñoz
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117, Heidelberg, Germany.
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5
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Nawara TJ, Mattheyses AL. Imaging nanoscale axial dynamics at the basal plasma membrane. Int J Biochem Cell Biol 2023; 156:106349. [PMID: 36566777 PMCID: PMC10634635 DOI: 10.1016/j.biocel.2022.106349] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Revised: 12/16/2022] [Accepted: 12/21/2022] [Indexed: 12/24/2022]
Abstract
Understanding of how energetically unfavorable plasma membrane shapes form, especially in the context of dynamic processes in living cells or tissues like clathrin-mediated endocytosis is in its infancy. Even though cutting-edge microscopy techniques that bridge this gap exist, they remain underused in biomedical sciences. Here, we demystify the perceived complexity of these advanced microscopy approaches and demonstrate their power in resolving nanometer axial dynamics in living cells. Total internal reflection fluorescence microscopy based approaches are the main focus of this review. We present clathrin-mediated endocytosis as a model system when describing the principles, data acquisition requirements, data interpretation strategies, and limitations of the described techniques. We hope this standardized description will bring the approaches for measuring nanoscale axial dynamics closer to the potential users and help in choosing the right approach to the right question.
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Affiliation(s)
- Tomasz J Nawara
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Alexa L Mattheyses
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA.
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6
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Babišová K, Mentelová L, Geisseová TK, Beňová-Liszeková D, Beňo M, Chase BA, Farkaš R. Apocrine secretion in the salivary glands of Drosophilidae and other dipterans is evolutionarily conserved. Front Cell Dev Biol 2023; 10:1088055. [PMID: 36712974 PMCID: PMC9880899 DOI: 10.3389/fcell.2022.1088055] [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: 11/03/2022] [Accepted: 12/15/2022] [Indexed: 01/15/2023] Open
Abstract
Apocrine secretion is a transport and secretory mechanism that remains only partially characterized, even though it is evolutionarily conserved among all metazoans, including humans. The excellent genetic model organism Drosophila melanogaster holds promise for elucidating the molecular mechanisms regulating this fundamental metazoan process. Two prerequisites for such investigations are to clearly define an experimental system to investigate apocrine secretion and to understand the evolutionarily and functional contexts in which apocrine secretion arose in that system. To this end, we recently demonstrated that, in D. melanogaster, the prepupal salivary glands utilize apocrine secretion prior to pupation to deliver innate immune and defense components to the exuvial fluid that lies between the metamorphosing pupae and its chitinous case. This finding provided a unique opportunity to appraise how this novel non-canonical and non-vesicular transport and secretory mechanism is employed in different developmental and evolutionary contexts. Here we demonstrate that this apocrine secretion, which is mechanistically and temporarily separated from the exocytotic mechanism used to produce the massive salivary glue secretion (Sgs), is shared across Drosophilidae and two unrelated dipteran species. Screening more than 30 species of Drosophila from divergent habitats across the globe revealed that apocrine secretion is a widespread and evolutionarily conserved cellular mechanism used to produce exuvial fluid. Species with longer larval and prepupal development than D. melanogaster activate apocrine secretion later, while smaller and more rapidly developing species activate it earlier. In some species, apocrine secretion occurs after the secretory material is first concentrated in cytoplasmic structures of unknown origin that we name "collectors." Strikingly, in contrast to the widespread use of apocrine secretion to provide exuvial fluid, not all species use exocytosis to produce the viscid salivary glue secretion that is seen in D. melanogaster. Thus, apocrine secretion is the conserved mechanism used to realize the major function of the salivary gland in fruitflies and related species: it produces the pupal exuvial fluid that provides an active defense against microbial invasion during pupal metamorphosis.
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Affiliation(s)
- Klaudia Babišová
- Laboratory of Developmental Genetics, Institute of Experimental Endocrinology, Biomedical Research Center v.v.i., Slovak Academy of Sciences, Bratislava, Slovakia
| | - Lucia Mentelová
- Laboratory of Developmental Genetics, Institute of Experimental Endocrinology, Biomedical Research Center v.v.i., Slovak Academy of Sciences, Bratislava, Slovakia,Department of Genetics, Comenius University, Bratislava, Slovakia
| | - Terézia Klaudia Geisseová
- Laboratory of Developmental Genetics, Institute of Experimental Endocrinology, Biomedical Research Center v.v.i., Slovak Academy of Sciences, Bratislava, Slovakia
| | - Denisa Beňová-Liszeková
- Laboratory of Developmental Genetics, Institute of Experimental Endocrinology, Biomedical Research Center v.v.i., Slovak Academy of Sciences, Bratislava, Slovakia
| | - Milan Beňo
- Laboratory of Developmental Genetics, Institute of Experimental Endocrinology, Biomedical Research Center v.v.i., Slovak Academy of Sciences, Bratislava, Slovakia
| | - Bruce A. Chase
- Department of Biology, University of Nebraska, Omaha, NE, United States
| | - Robert Farkaš
- Laboratory of Developmental Genetics, Institute of Experimental Endocrinology, Biomedical Research Center v.v.i., Slovak Academy of Sciences, Bratislava, Slovakia,*Correspondence: Robert Farkaš,
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7
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Ye H, Xu X, Wang J, Wang J, He Y, Mu Y, Shi G. Polarization effects on the fluorescence emission of zebrafish neurons using light-sheet microscopy. BIOMEDICAL OPTICS EXPRESS 2022; 13:6733-6744. [PMID: 36589590 PMCID: PMC9774877 DOI: 10.1364/boe.474588] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 11/21/2022] [Accepted: 11/22/2022] [Indexed: 06/17/2023]
Abstract
Light-sheet fluorescence microscopy (LSFM) makes use of a thin plane of light to optically section and image transparent tissues or organisms in vivo, which has the advantages of fast imaging speed and low phototoxicity. In this paper, we have employed light-sheet microscopy to investigate the polarization effects on fluorescence emission of zebrafish neurons via modifying the electric oscillation orientation of the excitation light. The intensity of the fluorescence emission from the excited zebrafish larvae follows a cosine square function with respect to the polarization state of the excitation light and reveals a 40% higher fluorescence emission when the polarization orientation is orthogonal to the illumination and detection axes. Through registration and subtraction of fluorescence images under different polarization states, we have demonstrated that most of the enhanced fluorescence signals are from the neuronal cells rather than the extracellular substance. This provides us a way to distinguish the cell boundaries and observe the organism structures with improved contrast and resolution.
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Affiliation(s)
- Hong Ye
- Jiangsu Key Laboratory of Medical Optics,
Suzhou Institute of Biomedical Engineering and Technology,
Chinese Academy of Sciences, Suzhou,
China
| | - Xin Xu
- Jiangsu Key Laboratory of Medical Optics,
Suzhou Institute of Biomedical Engineering and Technology,
Chinese Academy of Sciences, Suzhou,
China
- School of Biomedical Engineering (Suzhou),
Division of Life Sciences and Medicine, University of
Science and Technology of China, Hefei, China
| | - Jixiang Wang
- Jiangsu Key Laboratory of Medical Optics,
Suzhou Institute of Biomedical Engineering and Technology,
Chinese Academy of Sciences, Suzhou,
China
- School of Biomedical Engineering (Suzhou),
Division of Life Sciences and Medicine, University of
Science and Technology of China, Hefei, China
| | - Jing Wang
- Jiangsu Key Laboratory of Medical Optics,
Suzhou Institute of Biomedical Engineering and Technology,
Chinese Academy of Sciences, Suzhou,
China
- School of Biomedical Engineering (Suzhou),
Division of Life Sciences and Medicine, University of
Science and Technology of China, Hefei, China
| | - Yi He
- Jiangsu Key Laboratory of Medical Optics,
Suzhou Institute of Biomedical Engineering and Technology,
Chinese Academy of Sciences, Suzhou,
China
| | - Yu Mu
- Institute of Neuroscience, State Key
Laboratory of Neuroscience, Center for Excellence in Brain Science and
Intelligence Technology, Chinese Academy of
Sciences, Shanghai, China
| | - Guohua Shi
- Jiangsu Key Laboratory of Medical Optics,
Suzhou Institute of Biomedical Engineering and Technology,
Chinese Academy of Sciences, Suzhou,
China
- School of Biomedical Engineering (Suzhou),
Division of Life Sciences and Medicine, University of
Science and Technology of China, Hefei, China
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8
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Illuminating membrane structural dynamics of fusion and endocytosis with advanced light imaging techniques. Biochem Soc Trans 2022; 50:1157-1167. [PMID: 35960003 PMCID: PMC9444071 DOI: 10.1042/bst20210263] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 06/24/2022] [Accepted: 07/27/2022] [Indexed: 11/17/2022]
Abstract
Visualization of cellular dynamics using fluorescent light microscopy has become a reliable and indispensable source of experimental evidence for biological studies. Over the past two decades, the development of super-resolution microscopy platforms coupled with innovations in protein and molecule labeling led to significant biological findings that were previously unobservable due to the barrier of the diffraction limit. As a result, the ability to image the dynamics of cellular processes is vastly enhanced. These imaging tools are extremely useful in cellular physiology for the study of vesicle fusion and endocytosis. In this review, we will explore the power of stimulated emission depletion (STED) and confocal microscopy in combination with various labeling techniques in real-time observation of the membrane transformation of fusion and endocytosis, as well as their underlying mechanisms. We will review how STED and confocal imaging are used to reveal fusion and endocytic membrane transformation processes in live cells, including hemi-fusion; hemi-fission; hemi-to-full fusion; fusion pore opening, expansion, constriction and closure; shrinking or enlargement of the Ω-shape membrane structure after vesicle fusion; sequential compound fusion; and the sequential endocytic membrane transformation from flat- to O-shape via the intermediate Λ- and Ω-shape transition. We will also discuss how the recent development of imaging techniques would impact future studies in the field.
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9
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Rao TC, Nawara TJ, Mattheyses AL. Live-Cell Total Internal Reflection Fluorescence (TIRF) Microscopy to Investigate Protein Internalization Dynamics. Methods Mol Biol 2022; 2438:45-58. [PMID: 35147934 DOI: 10.1007/978-1-0716-2035-9_3] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The establishment of apicobasal or planar cell polarity involves many events that occur at or near the plasma membrane including focal adhesion dynamics, endocytosis, exocytosis, and cytoskeletal reorganization. It is desirable to visualize these events without interference from other regions deeper within the cell. Total internal reflection fluorescence (TIRF) microscopy utilizes an elegant optical sectioning approach to visualize fluorophores near the sample-coverslip interface. TIRF provides high-contrast fluorescence images with limited background and virtually no out-of-focus light, ideal for visualizing and tracking dynamics near the plasma membrane. In this chapter, we present a general experimental and analysis TIRF pipeline for studying cell surface receptor endocytosis. The approach presented can be easily applied to study other dynamic biological processes at or near the plasma membrane using TIRF microscopy.
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Affiliation(s)
- Tejeshwar C Rao
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Tomasz J Nawara
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Alexa L Mattheyses
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA.
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10
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Mahato J, Ray KK, Das S, Kadu P, Maji SK, Chowdhury A. Investigation of Structural Heterogeneity in Individual Amyloid Fibrils Using Polarization-Resolved Microscopy. J Phys Chem B 2021; 125:13406-13414. [PMID: 34861110 DOI: 10.1021/acs.jpcb.1c08604] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Amyloid fibrils are structurally heterogeneous protein aggregates that are implicated in a wide range of neurodegenerative and other proteopathic diseases. These fibrils exist in a variety of different tertiary and higher-level structures, and this exhibited polymorphism greatly complicates any structural study of amyloid fibrils. In this work, we demonstrate a method of using polarization-resolved microscopy to directly observe the structural heterogeneity of individual amyloid fibrils using amyloid-bound fluorophores. We formulate a mathematical quantity, helical anisotropy, which utilizes the polarized emission of amyloid-bound fluorophores to report on the local structure of individual fibrils. Using this method, we show how model amyloid fibrils generated from short peptides exhibit diverse structural properties both between different fibrils and within a single fibril, in a manner that is replicated for fibrils assembled from longer proteins. Our method represents an accessible and easily adaptable technique by which polymorphism in the structure of amyloid fibrils can be probed. Additionally, the methodology we describe here can be easily extended to the study of other fibrillar and otherwise ordered supramolecular structures.
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Affiliation(s)
- Jaladhar Mahato
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Korak Kumar Ray
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Subhadeep Das
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Pradeep Kadu
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Samir K Maji
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Arindam Chowdhury
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
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11
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Tanguy E, Wolf A, Wang Q, Chasserot-Golaz S, Ory S, Gasman S, Vitale N. Phospholipase D1-generated phosphatidic acid modulates secretory granule trafficking from biogenesis to compensatory endocytosis in neuroendocrine cells. Adv Biol Regul 2021; 83:100844. [PMID: 34876384 DOI: 10.1016/j.jbior.2021.100844] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 11/22/2021] [Accepted: 11/24/2021] [Indexed: 11/16/2022]
Abstract
Calcium-regulated exocytosis is a multi-step process that allows specialized secretory cells to release informative molecules such as neurotransmitters, neuropeptides, and hormones for intercellular communication. The biogenesis of secretory vesicles from the Golgi cisternae is followed by their transport towards the cell periphery and their docking and fusion to the exocytic sites of the plasma membrane allowing release of vesicular content. Subsequent compensatory endocytosis of the protein and lipidic constituents of the vesicles maintains cell homeostasis. Despite the fact that lipids represent the majority of membrane constituents, little is known about their contribution to these processes. Using a combination of electrochemical measurement of single chromaffin cell catecholamine secretion and electron microscopy of roof-top membrane sheets associated with genetic, silencing and pharmacological approaches, we recently reported that diverse phosphatidic acid (PA) species regulates catecholamine release efficiency by controlling granule docking and fusion kinetics. The enzyme phospholipase D1 (PLD1), producing PA from phosphatidylcholine, seems to be the major responsible of these effects in this model. Here, we extended this work using spinning disk confocal microscopy showing that inhibition of PLD activity also reduced the velocity of granules undergoing a directed motion. Furthermore, a dopamine β-hydroxylase (DβH) internalization assay revealed that PA produced by PLD is required for an optimal recovery of vesicular membrane content by compensatory endocytosis. Thus, among numerous roles that have been attributed to PA our work gives core to the key regulatory role in secretion that has been proposed in different cell models. Few leads to explain these multiple functions of PA along the secretory pathway are discussed.
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Affiliation(s)
- Emeline Tanguy
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, F-67000, Strasbourg, France
| | - Alexander Wolf
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, F-67000, Strasbourg, France
| | - Qili Wang
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, F-67000, Strasbourg, France
| | - Sylvette Chasserot-Golaz
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, F-67000, Strasbourg, France
| | - Stéphane Ory
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, F-67000, Strasbourg, France
| | - Stéphane Gasman
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, F-67000, Strasbourg, France
| | - Nicolas Vitale
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, F-67000, Strasbourg, France.
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12
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Anderson RH, Sochacki KA, Vuppula H, Scott BL, Bailey EM, Schultz MM, Kerkvliet JG, Taraska JW, Hoppe AD, Francis KR. Sterols lower energetic barriers of membrane bending and fission necessary for efficient clathrin-mediated endocytosis. Cell Rep 2021; 37:110008. [PMID: 34788623 PMCID: PMC8620193 DOI: 10.1016/j.celrep.2021.110008] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Revised: 08/03/2021] [Accepted: 10/26/2021] [Indexed: 01/16/2023] Open
Abstract
Clathrin-mediated endocytosis (CME) is critical for cellular signal transduction, receptor recycling, and membrane homeostasis in mammalian cells. Acute depletion of cholesterol disrupts CME, motivating analysis of CME dynamics in the context of human disorders of cholesterol metabolism. We report that inhibition of post-squalene cholesterol biosynthesis impairs CME. Imaging of membrane bending dynamics and the CME pit ultrastructure reveals prolonged clathrin pit lifetimes and shallow clathrin-coated structures, suggesting progressive impairment of curvature generation correlates with diminishing sterol abundance. Sterol structural requirements for efficient CME include 3′ polar head group and B-ring conformation, resembling the sterol structural prerequisites for tight lipid packing and polarity. Furthermore, Smith-Lemli-Opitz fibroblasts with low cholesterol abundance exhibit deficits in CME-mediated transferrin internalization. We conclude that sterols lower the energetic costs of membrane bending during pit formation and vesicular scission during CME and suggest that reduced CME activity may contribute to cellular phenotypes observed within disorders of cholesterol metabolism. Anderson et al. demonstrate that sterol abundance and identity play a dominant role in facilitating clathrin-mediated endocytosis. Detailed analyses of clathrin-coated pits under sterol depletion support a requirement for sterol-mediated membrane bending during multiple stages of endocytosis, implicating endocytic dysfunction within the pathogenesis of disorders of cholesterol metabolism.
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Affiliation(s)
- Ruthellen H Anderson
- Sanford School of Medicine, University of South Dakota, Sioux Falls, SD 57105, USA; Cellular Therapies and Stem Cell Biology Group, Sanford Research, Sioux Falls, SD 57104, USA
| | - Kem A Sochacki
- Laboratory of Molecular Biophysics, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20814, USA
| | - Harika Vuppula
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, SD 57007, USA; BioSystems Networks and Translational Research Center, Brookings, SD 57007, USA
| | - Brandon L Scott
- Nanoscience and Nanoengineering, South Dakota School of Mines & Technology, Rapid City, SD 57701, USA
| | - Elizabeth M Bailey
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, SD 57007, USA; BioSystems Networks and Translational Research Center, Brookings, SD 57007, USA
| | - Maycie M Schultz
- Cellular Therapies and Stem Cell Biology Group, Sanford Research, Sioux Falls, SD 57104, USA
| | - Jason G Kerkvliet
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, SD 57007, USA; BioSystems Networks and Translational Research Center, Brookings, SD 57007, USA
| | - Justin W Taraska
- Laboratory of Molecular Biophysics, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20814, USA
| | - Adam D Hoppe
- Department of Chemistry and Biochemistry, South Dakota State University, Brookings, SD 57007, USA; BioSystems Networks and Translational Research Center, Brookings, SD 57007, USA.
| | - Kevin R Francis
- Cellular Therapies and Stem Cell Biology Group, Sanford Research, Sioux Falls, SD 57104, USA; Department of Pediatrics, Sanford School of Medicine, University of South Dakota, Sioux Falls, SD 57105, USA.
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13
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Nikolaus J, Hancock K, Tsemperouli M, Baddeley D, Karatekin E. Optimal Detection of Fusion Pore Dynamics Using Polarized Total Internal Reflection Fluorescence Microscopy. Front Mol Biosci 2021; 8:740408. [PMID: 34859048 PMCID: PMC8631473 DOI: 10.3389/fmolb.2021.740408] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Accepted: 10/06/2021] [Indexed: 11/13/2022] Open
Abstract
The fusion pore is the initial narrow connection that forms between fusing membranes. During vesicular release of hormones or neurotransmitters, the nanometer-sized fusion pore may open-close repeatedly (flicker) before resealing or dilating irreversibly, leading to kiss-and-run or full-fusion events, respectively. Pore dynamics govern vesicle cargo release and the mode of vesicle recycling, but the mechanisms are poorly understood. This is partly due to a lack of reconstituted assays that combine single-pore sensitivity and high time resolution. Total internal reflection fluorescence (TIRF) microscopy offers unique advantages for characterizing single membrane fusion events, but signals depend on effects that are difficult to disentangle, including the polarization of the excitation electric field, vesicle size, photobleaching, orientation of the excitation dipoles of the fluorophores with respect to the membrane, and the evanescent field depth. Commercial TIRF microscopes do not allow control of excitation polarization, further complicating analysis. To overcome these challenges, we built a polarization-controlled total internal reflection fluorescence (pTIRF) microscope and monitored fusion of proteoliposomes with planar lipid bilayers with single molecule sensitivity and ∼15 ms temporal resolution. Using pTIRF microscopy, we detected docking and fusion of fluorescently labeled small unilamellar vesicles, reconstituted with exocytotic/neuronal v-SNARE proteins (vSUVs), with a supported bilayer containing the cognate t-SNAREs (tSBL). By varying the excitation polarization angle, we were able to identify a dye-dependent optimal polarization at which the fluorescence increase upon fusion was maximal, facilitating event detection and analysis of lipid transfer kinetics. An improved algorithm allowed us to estimate the size of the fusing vSUV and the fusion pore openness (the fraction of time the pore is open) for every event. For most events, lipid transfer was much slower than expected for diffusion through an open pore, suggesting that fusion pore flickering limits lipid release. We find a weak correlation between fusion pore openness and vesicle area. The approach can be used to study mechanisms governing fusion pore dynamics in a wide range of membrane fusion processes.
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Affiliation(s)
- Joerg Nikolaus
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
| | - Kasey Hancock
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
- Integrated Physical and Engineering Biology Program, Yale University, New Haven, CT, United States
| | - Maria Tsemperouli
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
| | - David Baddeley
- Nanobiology Institute, Yale University, West Haven, CT, United States
- Cell Biology, Yale University, New Haven, CT, United States
| | - Erdem Karatekin
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
- Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
- Saints-Pères Paris Institute for the Neurosciences (SPPIN), Université de Paris, Centre National de la Recherche Scientifique (CNRS), Paris, France
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14
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Del Signore SJ, Kelley CF, Messelaar EM, Lemos T, Marchan MF, Ermanoska B, Mund M, Fai TG, Kaksonen M, Rodal AA. An autoinhibitory clamp of actin assembly constrains and directs synaptic endocytosis. eLife 2021; 10:69597. [PMID: 34324418 PMCID: PMC8321554 DOI: 10.7554/elife.69597] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Accepted: 06/21/2021] [Indexed: 01/05/2023] Open
Abstract
Synaptic membrane-remodeling events such as endocytosis require force-generating actin assembly. The endocytic machinery that regulates these actin and membrane dynamics localizes at high concentrations to large areas of the presynaptic membrane, but actin assembly and productive endocytosis are far more restricted in space and time. Here we describe a mechanism whereby autoinhibition clamps the presynaptic endocytic machinery to limit actin assembly to discrete functional events. We found that collective interactions between the Drosophila endocytic proteins Nwk/FCHSD2, Dap160/intersectin, and WASp relieve Nwk autoinhibition and promote robust membrane-coupled actin assembly in vitro. Using automated particle tracking to quantify synaptic actin dynamics in vivo, we discovered that Nwk-Dap160 interactions constrain spurious assembly of WASp-dependent actin structures. These interactions also promote synaptic endocytosis, suggesting that autoinhibition both clamps and primes the synaptic endocytic machinery, thereby constraining actin assembly to drive productive membrane remodeling in response to physiological cues. Neurons constantly talk to each other by sending chemical signals across the tiny gap, or ‘synapse’, that separates two cells. While inside the emitting cell, these molecules are safely packaged into small, membrane-bound vessels. Upon the right signal, the vesicles fuse with the external membrane of the neuron and spill their contents outside, for the receiving cell to take up and decode. The emitting cell must then replenish its vesicle supply at the synapse through a recycling mechanism known as endocytosis. To do so, it uses dynamically assembling rod-like ‘actin’ filaments, which work in concert with many other proteins to pull in patches of membrane as new vesicles. The proteins that control endocytosis and actin assembly abound at neuronal synapses, and, when mutated, are linked to many neurological diseases. Unlike other cell types, neurons appear to ‘pre-deploy’ these actin-assembly proteins to synaptic membranes, but to keep them inactive under normal conditions. How neurons control the way this machinery is recruited and activated remains unknown. To investigate this question, Del Signore et al. conducted two sets of studies. First, they exposed actin to several different purified proteins in initial ‘test tube’ experiments. This revealed that, depending on the conditions, a group of endocytosis proteins could prevent or promote actin assembly: assembly occurred only if the proteins were associated with membranes. Next, Del Signore et al. mutated these proteins in fruit fly larvae, and performed live cell microscopy to determine their impact on actin assembly and endocytosis. Consistent with the test tube findings, endocytosis mutants had more actin assembly overall, implying that the proteins were required to prevent random actin assembly. However, the same mutants had reduced levels of endocytosis, suggesting that the proteins were also necessary for productive actin assembly. Together, these experiments suggest that, much like a mousetrap holds itself poised ready to spring, some endocytic proteins play a dual role to restrain actin assembly when and where it is not needed, and to promote it at sites of endocytosis. These results shed new light on how neurons might build and maintain effective, working synapses. Del Signore et al. hope that this knowledge may help to better understand and combat neurological diseases, such as Alzheimer’s, which are linked to impaired membrane traffic and cell signalling.
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Affiliation(s)
| | | | | | - Tania Lemos
- Department of Biology, Brandeis University, Walltham, United States
| | | | | | - Markus Mund
- Department of Biochemistry and NCCR Chemical Biology, University of Geneva, Geneva, Switzerland
| | - Thomas G Fai
- Department of Mathematics, Brandeis University, Waltham, United States
| | - Marko Kaksonen
- Department of Biochemistry and NCCR Chemical Biology, University of Geneva, Geneva, Switzerland
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15
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Yang G, Li L, Liu Y, Liang K, Wei L, Chen L. Hyperglycemia-Induced Dysregulated Fusion Intermediates in Insulin-Secreting Cells Visualized by Super-Resolution Microscopy. Front Cell Dev Biol 2021; 9:650167. [PMID: 33937248 PMCID: PMC8083903 DOI: 10.3389/fcell.2021.650167] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 03/15/2021] [Indexed: 11/23/2022] Open
Abstract
Impaired insulin release is a hallmark of type 2 diabetes and is closely related to chronically elevated glucose concentrations, known as “glucotoxicity.” However, the molecular mechanisms by which glucotoxicity impairs insulin secretion remain poorly understood. In addition to known kiss-and-run and kiss-and-stay fusion events in INS-1 cells, ultrafast Hessian structured illumination microscopy (Hessian SIM) enables full fusion to be categorized according to the newly identified structures, such as ring fusion (those with enlarged pores) or dot fusion (those without apparent pores). In addition, we identified four fusion intermediates during insulin exocytosis: initial pore opening, vesicle collapse, enlarged pore formation, and final pore dilation. Long-term incubation in supraphysiological doses of glucose reduced exocytosis in general and increased the occurrence of kiss-and-run events at the expense of reduced full fusion. In addition, hyperglycemia delayed pore opening, vesicle collapse, and enlarged pore formation in full fusion events. It also reduced the size of apparently enlarged pores, all of which contributed to the compromised insulin secretion. These phenotypes were mostly due to the hyperglycemia-induced reduction in syntaxin-1A (Stx-1A) and SNAP-25 protein, since they could be recapitulated by the knockdown of endogenous Stx-1A and SNAP-25. These findings suggest essential roles for the vesicle fusion type and intermediates in regulating insulin secretion from pancreatic beta cells in normal and disease conditions.
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Affiliation(s)
- Guoyi Yang
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, School of Future Technology, Peking University, Beijing, China
| | - Liuju Li
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, School of Future Technology, Peking University, Beijing, China
| | - Yanmei Liu
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, School of Future Technology, Peking University, Beijing, China.,Institute for Brain Research and Rehabilitation, Key Laboratory of Brain, Cognition and Education Science, South China Normal University, Guangzhou, China
| | - Kuo Liang
- Department of General Surgery, Xuanwu Hospital, Capital Medical University, Beijing, China
| | - Lisi Wei
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, School of Future Technology, Peking University, Beijing, China
| | - Liangyi Chen
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, School of Future Technology, Peking University, Beijing, China.,PKU-IDG/McGovern Institute for Brain Research, Beijing, China.,Beijing Academy of Artificial Intelligence, Beijing, China.,Shenzhen Bay Laboratory, Shenzhen, China
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16
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de Vito G, Ricci P, Turrini L, Gavryusev V, Müllenbroich C, Tiso N, Vanzi F, Silvestri L, Pavone FS. Effects of excitation light polarization on fluorescence emission in two-photon light-sheet microscopy. BIOMEDICAL OPTICS EXPRESS 2020; 11:4651-4665. [PMID: 32923069 PMCID: PMC7449752 DOI: 10.1364/boe.396388] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 06/20/2020] [Accepted: 07/07/2020] [Indexed: 05/05/2023]
Abstract
Light-sheet microscopy (LSM) is a powerful imaging technique that uses a planar illumination oriented orthogonally to the detection axis. Two-photon (2P) LSM is a variant of LSM that exploits the 2P absorption effect for sample excitation. The light polarization state plays a significant, and often overlooked, role in 2P absorption processes. The scope of this work is to test whether using different polarization states for excitation light can affect the detected signal levels in 2P LSM imaging of typical biological samples with a spatially unordered dye population. Supported by a theoretical model, we compared the fluorescence signals obtained using different polarization states with various fluorophores (fluorescein, EGFP and GCaMP6s) and different samples (liquid solution and fixed or living zebrafish larvae). In all conditions, in agreement with our theoretical expectations, linear polarization oriented parallel to the detection plane provided the largest signal levels, while perpendicularly-oriented polarization gave low fluorescence signal with the biological samples, but a large signal for the fluorescein solution. Finally, circular polarization generally provided lower signal levels. These results highlight the importance of controlling the light polarization state in 2P LSM of biological samples. Furthermore, this characterization represents a useful guide to choose the best light polarization state when maximization of signal levels is needed, e.g. in high-speed 2P LSM.
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Affiliation(s)
- Giuseppe de Vito
- University of Florence, Department of Neuroscience, Psychology, Drug Research and Child Health, Viale Pieraccini 6, Florence, FI 50139, Italy
- European Laboratory for Non-Linear Spectroscopy, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
| | - Pietro Ricci
- European Laboratory for Non-Linear Spectroscopy, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
| | - Lapo Turrini
- European Laboratory for Non-Linear Spectroscopy, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
- University of Florence, Department of Physics and Astronomy, Via Sansone 1, Sesto Fiorentino, FI 50019, Italy
| | - Vladislav Gavryusev
- European Laboratory for Non-Linear Spectroscopy, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
- University of Florence, Department of Physics and Astronomy, Via Sansone 1, Sesto Fiorentino, FI 50019, Italy
| | - Caroline Müllenbroich
- European Laboratory for Non-Linear Spectroscopy, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
- School of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow, G12 8QQ, UK
- National Institute of Optics, National Research Council, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
| | - Natascia Tiso
- University of Padova, Department of Biology, Via Ugo Bassi 58/B, Padua, PD 35131, Italy
| | - Francesco Vanzi
- European Laboratory for Non-Linear Spectroscopy, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
- University of Florence, Department of Biology, Via Madonna del Piano 6, Sesto Fiorentino, FI 50019, Italy
| | - Ludovico Silvestri
- European Laboratory for Non-Linear Spectroscopy, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
- University of Florence, Department of Physics and Astronomy, Via Sansone 1, Sesto Fiorentino, FI 50019, Italy
- National Institute of Optics, National Research Council, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
| | - Francesco Saverio Pavone
- European Laboratory for Non-Linear Spectroscopy, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
- University of Florence, Department of Physics and Astronomy, Via Sansone 1, Sesto Fiorentino, FI 50019, Italy
- National Institute of Optics, National Research Council, Via Nello Carrara 1, Sesto Fiorentino, FI 50019, Italy
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17
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Bendahmane M, Morales A, Kreutzberger AJB, Schenk NA, Mohan R, Bakshi S, Philippe JM, Zhang S, Kiessling V, Tamm LK, Giovannucci DR, Jenkins PM, Anantharam A. Synaptotagmin-7 enhances calcium-sensing of chromaffin cell granules and slows discharge of granule cargos. J Neurochem 2020; 154:598-617. [PMID: 32058590 DOI: 10.1111/jnc.14986] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Revised: 02/04/2020] [Accepted: 02/07/2020] [Indexed: 12/30/2022]
Abstract
Synaptotagmin-7 (Syt-7) is one of two major calcium sensors for exocytosis in adrenal chromaffin cells, the other being synaptotagmin-1 (Syt-1). Despite a broad appreciation for the importance of Syt-7, questions remain as to its localization, function in mediating discharge of dense core granule cargos, and role in triggering release in response to physiological stimulation. These questions were addressed using two distinct experimental preparations-mouse chromaffin cells lacking endogenous Syt-7 (KO cells) and a reconstituted system employing cell-derived granules expressing either Syt-7 or Syt-1. First, using immunofluorescence imaging and subcellular fractionation, it is shown that Syt-7 is widely distributed in organelles, including dense core granules. Total internal reflection fluorescence (TIRF) imaging demonstrates that the kinetics and probability of granule fusion in Syt-7 KO cells stimulated by a native secretagogue, acetylcholine, are markedly lower than in WT cells. When fusion is observed, fluorescent cargo proteins are discharged more rapidly when only Syt-1 is available to facilitate release. To determine the extent to which the aforementioned results are attributable purely to Syt-7, granules expressing only Syt-7 or Syt-1 were triggered to fuse on planar supported bilayers bearing plasma membrane SNARE proteins. Here, as in cells, Syt-7 confers substantially greater calcium sensitivity to granule fusion than Syt-1 and slows the rate at which cargos are released. Overall, this study demonstrates that by virtue of its high affinity for calcium and effects on fusion pore expansion, Syt-7 plays a central role in regulating secretory output from adrenal chromaffin cells.
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Affiliation(s)
- Mounir Bendahmane
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | - Alina Morales
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | - Alex J B Kreutzberger
- Center for Membrane and Cell Physiology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Noah A Schenk
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | - Ramkumar Mohan
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | - Shreeya Bakshi
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | - Julie M Philippe
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | - Shuang Zhang
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | - Volker Kiessling
- Center for Membrane and Cell Physiology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Lukas K Tamm
- Center for Membrane and Cell Physiology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - David R Giovannucci
- Department of Neuroscience, University of Toledo Medical School, Toledo, OH, USA
| | - Paul M Jenkins
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | - Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
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18
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Smith KA, Prantzalos ER, Anantharam A. Integrating Optical and Electrochemical Approaches to Assess the Actions of Dynamin at the Fusion Pore. Methods Mol Biol 2020; 2159:163-178. [PMID: 32529370 DOI: 10.1007/978-1-0716-0676-6_12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Of the techniques currently available to monitor dense core granule exocytosis in adrenal chromaffin cells, two have proven particularly useful: carbon-fiber amperometry and total internal reflection fluorescence (TIRF) microscopy. Amperometry enables the detection of oxidizable catecholamines escaping a fusion pore with millisecond time resolution. TIRF microscopy, and its variant polarized-TIRF (pTIRF) microscopy, provides information on the characteristics of fusion pores at temporally later stages. Used in conjunction, amperometry and TIRF microscopy allow an investigator to follow the fate of a fusion pore from its formation to expansion or reclosure. The properties of fusion pores, including their structure and dynamics, have been shown by multiple groups to be modified by the dynamin GTPase (Dyn1). In this chapter, we describe how amperometry and TIRF microscopy enable insights into dynamin-dependent effects on exocytosis in primary cultures of bovine adrenal chromaffin cells.
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Affiliation(s)
- Katherine A Smith
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA
| | | | - Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, USA.
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19
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Hummer BH, Maslar D, Soltero-Gutierrez M, de Leeuw NF, Asensio CS. Differential sorting behavior for soluble and transmembrane cargoes at the trans-Golgi network in endocrine cells. Mol Biol Cell 2019; 31:157-166. [PMID: 31825717 PMCID: PMC7001476 DOI: 10.1091/mbc.e19-10-0561] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Regulated secretion of neuropeptides and peptide hormones by secretory granules (SGs) is central to physiology. Formation of SGs occurs at the trans-Golgi network (TGN) where their soluble cargo aggregates to form a dense core, but the mechanisms controlling the sorting of regulated secretory cargoes (soluble and transmembrane) away from constitutively secreted proteins remain unclear. Optimizing the use of the retention using selective hooks method in (neuro-)endocrine cells, we now quantify TGN budding kinetics of constitutive and regulated secretory cargoes. We further show that, by monitoring two cargoes simultaneously, it becomes possible to visualize sorting to the constitutive and regulated secretory pathways in real time. Further analysis of the localization of SG cargoes immediately after budding from the TGN revealed that, surprisingly, the bulk of two studied transmembrane SG cargoes (phogrin and VMAT2) does not sort directly onto SGs during budding, but rather exit the TGN into nonregulated vesicles to get incorporated to SGs at a later step. This differential behavior of soluble and transmembrane cargoes suggests a more complex model of SG biogenesis than anticipated.
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Affiliation(s)
| | | | | | - Noah F de Leeuw
- Department of Physics and Astronomy, University of Denver, Denver, CO 80210
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20
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Live cell imaging of signaling and metabolic activities. Pharmacol Ther 2019; 202:98-119. [DOI: 10.1016/j.pharmthera.2019.06.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Accepted: 05/31/2019] [Indexed: 12/15/2022]
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21
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Zhang F, Guan Y, Yang Y, Hunt A, Wang S, Chen HY, Tao N. Optical Tracking of Nanometer-Scale Cellular Membrane Deformation Associated with Single Vesicle Release. ACS Sens 2019; 4:2205-2212. [PMID: 31348853 DOI: 10.1021/acssensors.9b01201] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Exocytosis involves interactions between secretory vesicles and the plasma membrane. Studying the membrane response is thus critical to understand this important cellular process and to differentiate different mediator release patterns. Here we introduce a label-free optical imaging method to detect the vesicle-membrane-interaction-induced membrane deformation associated with single exocytosis in mast cells. We show that the plasma membrane expands by a few tens of nanometers accompanying each vesicle-release event, but the dynamics of the membrane deformation varies from cell to cell, which reflect different exocytosis processes. Combining the temporal and spatial information allows us to resolve complex vesicle-release processes, such as two vesicle-release events that occur closely in time and location. Simultaneous following a vesicle release with fluorescence and membrane deformation tracking further allows us to determine the propagation speed of the vesicle-release-induced membrane deformation along the cell surface, which has an average value of 5.2 ± 1.8 μm/s.
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Affiliation(s)
- Fenni Zhang
- Biodesign Center for Bioelectronics and Biosensors, Arizona State University, Tempe, Arizona 85287, United States
- School of Electrical Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, United States
| | - Yan Guan
- Biodesign Center for Bioelectronics and Biosensors, Arizona State University, Tempe, Arizona 85287, United States
- School of Electrical Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, United States
| | - Yunze Yang
- Biodesign Center for Bioelectronics and Biosensors, Arizona State University, Tempe, Arizona 85287, United States
- School of Electrical Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, United States
| | - Ashley Hunt
- Biodesign Center for Bioelectronics and Biosensors, Arizona State University, Tempe, Arizona 85287, United States
| | - Shaopeng Wang
- Biodesign Center for Bioelectronics and Biosensors, Arizona State University, Tempe, Arizona 85287, United States
| | - Hong-Yuan Chen
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
| | - Nongjian Tao
- Biodesign Center for Bioelectronics and Biosensors, Arizona State University, Tempe, Arizona 85287, United States
- School of Electrical Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, United States
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22
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Machado R, Bendesky J, Brown M, Spendier K, Hagen GM. Imaging Membrane Curvature inside a FcεRI-Centric Synapse in RBL-2H3 Cells Using TIRF Microscopy with Polarized Excitation. J Imaging 2019; 5:63. [PMID: 31360699 PMCID: PMC6663088 DOI: 10.3390/jimaging5070063] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Accepted: 06/28/2019] [Indexed: 01/06/2023] Open
Abstract
Total internal reflection fluorescence microscopy with polarized excitation (P-TIRF) can be used to image nanoscale curvature phenomena in live cells. We used P-TIRF to visualize rat basophilic leukemia cells (RBL-2H3 cells) primed with fluorescent anti-dinitrophenyl (anti-DNP) immunoglobulin E (IgE) coming into contact with a supported lipid bilayer containing mobile, monovalent DNP, modeling an immunological synapse. The spatial relationship of the IgE-bound high affinity IgE receptor (FcεRI) to the ratio image of P-polarized excitation and S-polarized excitation was analyzed. These studies help correlate the dynamics of cell surface molecules with the mechanical properties of the plasma membrane during synapse formation.
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Affiliation(s)
- Rosa Machado
- UCCS Center for the Biofrontiers Institute, University of Colorado at Colorado Springs, Colorado Springs, CO 80918, USA
| | - Justin Bendesky
- UCCS Center for the Biofrontiers Institute, University of Colorado at Colorado Springs, Colorado Springs, CO 80918, USA
| | - Madison Brown
- UCCS Center for the Biofrontiers Institute, University of Colorado at Colorado Springs, Colorado Springs, CO 80918, USA
- Department of Physics and Energy Science, University of Colorado at Colorado Springs, Colorado Springs, CO 80918, USA
| | - Kathrin Spendier
- UCCS Center for the Biofrontiers Institute, University of Colorado at Colorado Springs, Colorado Springs, CO 80918, USA
- Department of Physics and Energy Science, University of Colorado at Colorado Springs, Colorado Springs, CO 80918, USA
| | - Guy M. Hagen
- UCCS Center for the Biofrontiers Institute, University of Colorado at Colorado Springs, Colorado Springs, CO 80918, USA
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23
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Taraska JW. A primer on resolving the nanoscale structure of the plasma membrane with light and electron microscopy. J Gen Physiol 2019; 151:974-985. [PMID: 31253697 PMCID: PMC6683668 DOI: 10.1085/jgp.201812227] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Accepted: 06/10/2019] [Indexed: 12/20/2022] Open
Abstract
Taraska reviews the imaging methods that are being used to understand the structure of the plasma membrane at the molecular level. The plasma membrane separates a cell from its external environment. All materials and signals that enter or leave the cell must cross this hydrophobic barrier. Understanding the architecture and dynamics of the plasma membrane has been a central focus of general cellular physiology. Both light and electron microscopy have been fundamental in this endeavor and have been used to reveal the dense, complex, and dynamic nanoscale landscape of the plasma membrane. Here, I review classic and recent developments in the methods used to image and study the structure of the plasma membrane, particularly light, electron, and correlative microscopies. I will discuss their history and use for mapping the plasma membrane and focus on how these tools have provided a structural framework for understanding the membrane at the scale of molecules. Finally, I will describe how these studies provide a roadmap for determining the nanoscale architecture of other organelles and entire cells in order to bridge the gap between cellular form and function.
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Affiliation(s)
- Justin W Taraska
- Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD
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24
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Guček A, Gandasi NR, Omar-Hmeadi M, Bakke M, Døskeland SO, Tengholm A, Barg S. Fusion pore regulation by cAMP/Epac2 controls cargo release during insulin exocytosis. eLife 2019; 8:41711. [PMID: 31099751 PMCID: PMC6557626 DOI: 10.7554/elife.41711] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Accepted: 04/28/2019] [Indexed: 12/20/2022] Open
Abstract
Regulated exocytosis establishes a narrow fusion pore as initial aqueous connection to the extracellular space, through which small transmitter molecules such as ATP can exit. Co-release of polypeptides and hormones like insulin requires further expansion of the pore. There is evidence that pore expansion is regulated and can fail in diabetes and neurodegenerative disease. Here, we report that the cAMP-sensor Epac2 (Rap-GEF4) controls fusion pore behavior by acutely recruiting two pore-restricting proteins, amisyn and dynamin-1, to the exocytosis site in insulin-secreting beta-cells. cAMP elevation restricts and slows fusion pore expansion and peptide release, but not when Epac2 is inactivated pharmacologically or in Epac2-/- (Rapgef4-/-) mice. Consistently, overexpression of Epac2 impedes pore expansion. Widely used antidiabetic drugs (GLP-1 receptor agonists and sulfonylureas) activate this pathway and thereby paradoxically restrict hormone release. We conclude that Epac2/cAMP controls fusion pore expansion and thus the balance of hormone and transmitter release during insulin granule exocytosis. Insulin is the hormone that signals to the body to take up sugar from the blood. Specialized cells in the pancreas – known as β-cells – release insulin after a meal. Before that, insulin molecules are stored in tiny granules inside the β-cells; these granules must fuse with the cells’ surface membranes to release their contents. The first step in this process creates a narrow pore that allows small molecules, but not the larger insulin molecules, to seep out. The pore then widens to release the insulin. Since the small molecules are known to act locally in the pancreas, it is possible that this “molecular sieve” is biologically important. Yet it is not clear how the pore widens. One of the problems for people with type 2 diabetes is that they release less insulin into the bloodstream. Two kinds of drugs used to treat these patients work by stimulating β-cells to release their insulin. One way to achieve this is by raising the levels of a small molecule called cAMP, which is well known to help prepare insulin granules for release. The cAMP molecule also seems to slow the widening of the pore, and Gucek et al. have now investigated how this happens at a molecular level. By observing individual granules of human β-cells using a special microscope, Gucek et al. could watch how different drugs affect pore widening and content release. They also saw that cAMP activated a protein called Epac2, which then recruited two other proteins – amisyn and dynamin – to the small pores. These two proteins together then closed the pore, rather than expanding it to let insulin out. Type 2 diabetes patients sometimes have high levels of amisyn in their β-cells, which could explain why they do not release enough insulin. The microscopy experiments also revealed that two common anti-diabetic drugs activate Epac2 and prevent the pores from widening, thereby counteracting their positive effect on insulin release. The combined effect is likely a shift in the balance between insulin and the locally acting small molecules. These findings suggest that two common anti-diabetic drugs activate a common mechanism that may lead to unexpected outcomes, possibly even reducing how much insulin the β-cells can release. Future studies in mice and humans will have to investigate these effects in whole organisms.
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Affiliation(s)
- Alenka Guček
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
| | - Nikhil R Gandasi
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
| | | | - Marit Bakke
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | | | - Anders Tengholm
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
| | - Sebastian Barg
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
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25
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Abbineni PS, Bohannon KP, Bittner MA, Axelrod D, Holz RW. Identification of β-synuclein on secretory granules in chromaffin cells and the effects of α- and β-synuclein on post-fusion BDNF discharge and fusion pore expansion. Neurosci Lett 2019; 699:134-139. [PMID: 30711526 DOI: 10.1016/j.neulet.2019.01.056] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 01/11/2019] [Accepted: 01/30/2019] [Indexed: 11/24/2022]
Abstract
α-Synuclein is strongly implicated in the pathogenesis of Parkinson's disease as well as in other neurodegenerative diseases. However, its normal function in cells is not understood. The N-termini of α-, β-, and γ-synuclein contains six to seven 11-amino acid repeats that are predicted to form amphipathic helices. Membrane-binding and membrane-curving abilities of synuclein raise the possibility that synuclein could alter cellular processes that involve highly curved structures. In the present study we examined the localization of endogenous synuclein in bovine chromaffin cells by immunocytochemistry and its possible function to control protein discharge upon fusion of the granule with the plasma membrane by regulating the fusion pore. We found with quantitative immunocytochemistry that endogenous β-synuclein associates with secretory granules. Endogenous α-synuclein only rarely co-localizes with secretory granules. Overexpression of α-synuclein but not β-synuclein quickened the post- fusion discharge of BDNF-pHluorin by approxinately 30%. However, neither α- nor β-synuclein significantly altered curvature dynamics associated with fusion pore expansion that were measured by the combination of polarization and total internal reflection fluorescence microscopy (pTIRFM). Whatever the mechanism, the physiological significance of the small increased rate of post-fusion protein discharge caused by α-synuclein remains to be demonstrated, especially since endogenous β-, but not α-synuclein is the predominant synuclein isoform associated with chromaffin granules.
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Affiliation(s)
- Prabhodh S Abbineni
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, United States
| | - Kevin P Bohannon
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, United States
| | - Mary A Bittner
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, United States
| | - Daniel Axelrod
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, United States; Departments of Physics and LSA Biophysics, University of Michigan, Ann Arbor, MI, United States
| | - Ronald W Holz
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, United States.
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26
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Isoflurane Inhibits Dopaminergic Synaptic Vesicle Exocytosis Coupled to Ca V2.1 and Ca V2.2 in Rat Midbrain Neurons. eNeuro 2019; 6:eN-NWR-0278-18. [PMID: 30680310 PMCID: PMC6345200 DOI: 10.1523/eneuro.0278-18.2018] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Revised: 12/18/2018] [Accepted: 12/21/2018] [Indexed: 11/21/2022] Open
Abstract
Volatile anesthetics affect neuronal signaling by poorly understood mechanisms. Activation of central dopaminergic pathways has been implicated in emergence from general anesthesia. The volatile anesthetic isoflurane differentially inhibits glutamatergic and GABAergic synaptic vesicle (SV) exocytosis by reducing presynaptic Ca2+ influx without affecting the Ca2+-exocytosis relationship, but its effects on dopaminergic exocytosis are unclear. We tested the hypothesis that isoflurane inhibits exocytosis in dopaminergic neurons. We used electrical stimulation or depolarization by elevated extracellular KCl to evoke exocytosis measured by quantitative live-cell fluorescence imaging in cultured rat ventral tegmental area neurons. Using trains of electrically evoked action potentials (APs), isoflurane inhibited exocytosis in dopaminergic neurons to a greater extent (30 ± 4% inhibition; p < 0.0001) than in non-dopaminergic neurons (15 ± 5% inhibition; p = 0.014). Isoflurane also inhibited exocytosis evoked by elevated KCl in dopaminergic neurons (35 ± 6% inhibition; p = 0.0007), but not in non-dopaminergic neurons (2 ± 4% inhibition). Pharmacological isolation of presynaptic Ca2+ channel subtypes showed that isoflurane inhibited KCl-evoked exocytosis mediated exclusively by either CaV2.1 (P/Q-type Ca2+ channels; 30 ± 5% inhibition; p = 0.0002) or by CaV2.2 (N-type Ca2+ channels; 35 ± 11% inhibition; p = 0.015). Additionally, isoflurane inhibited single AP-evoked Ca2+ influx by 41 ± 3% and single AP-evoked exocytosis by 34 ± 6%. Comparable reductions in exocytosis and Ca2+ influx were produced by lowering extracellular [Ca2+]. Thus, isoflurane inhibits exocytosis from dopaminergic neurons by a mechanism distinct from that in non-dopaminergic neurons involving reduced Ca2+ entry through CaV2.1 and/or CaV2.2.
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27
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Abbineni PS, Bittner MA, Axelrod D, Holz RW. Chromogranin A, the major lumenal protein in chromaffin granules, controls fusion pore expansion. J Gen Physiol 2018; 151:118-130. [PMID: 30504267 PMCID: PMC6363410 DOI: 10.1085/jgp.201812182] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Accepted: 11/07/2018] [Indexed: 01/03/2023] Open
Abstract
Upon fusion of the secretory granule with the plasma membrane, small molecules are discharged through the immediately formed narrow fusion pore, but protein discharge awaits pore expansion. Recently, fusion pore expansion was found to be regulated by tissue plasminogen activator (tPA), a protein present within the lumen of chromaffin granules in a subpopulation of chromaffin cells. Here, we further examined the influence of other lumenal proteins on fusion pore expansion, especially chromogranin A (CgA), the major and ubiquitous lumenal protein in chromaffin granules. Polarized TIRF microscopy demonstrated that the fusion pore curvature of granules containing CgA-EGFP was long lived, with curvature lifetimes comparable to those of tPA-EGFP-containing granules. This was surprising because fusion pore curvature durations of granules containing exogenous neuropeptide Y-EGFP (NPY-EGFP) are significantly shorter (80% lasting <1 s) than those containing CgA-EGFP, despite the anticipated expression of endogenous CgA. However, quantitative immunocytochemistry revealed that transiently expressed lumenal proteins, including NPY-EGFP, caused a down-regulation of endogenously expressed proteins, including CgA. Fusion pore curvature durations in nontransfected cells were significantly longer than those of granules containing overexpressed NPY but shorter than those associated with granules containing overexpressed tPA, CgA, or chromogranin B. Introduction of CgA to NPY-EGFP granules by coexpression converted the fusion pore from being transient to being longer lived, comparable to that found in nontransfected cells. These findings demonstrate that several endogenous chromaffin granule lumenal proteins are regulators of fusion pore expansion and that alteration of chromaffin granule contents affects fusion pore lifetimes. Importantly, the results indicate a new role for CgA. In addition to functioning as a prohormone, CgA plays an important role in controlling fusion pore expansion.
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Affiliation(s)
| | - Mary A Bittner
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Daniel Axelrod
- Department of Pharmacology, University of Michigan, Ann Arbor, MI.,Department of Physics, LSA Biophysics, University of Michigan, Ann Arbor, MI
| | - Ronald W Holz
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
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28
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Vadakkan KI. A potential mechanism for first-person internal sensation of memory provides evidence for the relationship between learning and LTP induction. Behav Brain Res 2018; 360:16-35. [PMID: 30502355 DOI: 10.1016/j.bbr.2018.11.038] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2018] [Revised: 11/26/2018] [Accepted: 11/26/2018] [Indexed: 12/21/2022]
Abstract
Studies conducted to verify learning-induced changes anticipated from Hebb's postulate led to the finding of long-term potentiation (LTP). Even though several correlations have been found between behavioural markers of memory retrieval and LTP, it is not known how memories are retrieved using learning-induced changes. In this context, the following non-correlated findings between learning and LTP induction provide constraints for discovering the mechanism: 1) Requirement of high stimulus intensity for LTP induction in contrast to what is expected for a learning mechanism, 2) Delay of at least 20 to 30 s from stimulation to LTP induction, in contrast to mere milliseconds for associative learning, and 3) A sudden drop in peak-potentiated effect (short-term potentiation) that matches with short-lasting changes expected during working memory and occurs only at the time of delayed LTP induction. When memories are viewed as first-person internal sensations, a newly uncovered mechanism provides explanation for the relationship between memory and LTP. This work interconnects large number of findings from the fields of neuroscience and psychology and provides a further verifiable mechanism of learning.
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29
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Abbineni PS, Axelrod D, Holz RW. Visualization of expanding fusion pores in secretory cells. J Gen Physiol 2018; 150:1640-1646. [PMID: 30470717 PMCID: PMC6279363 DOI: 10.1085/jgp.201812186] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Accepted: 11/06/2018] [Indexed: 11/20/2022] Open
Abstract
Abbineni et al. examine recent imaging work on fusion pores and discuss the dynamics of PI-4,5-P2 accumulation on granule membranes.
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Affiliation(s)
- Prabhodh S Abbineni
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI
| | - Daniel Axelrod
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI .,Department of Physics and LSA Biophysics, University of Michigan Medical School, Ann Arbor, MI
| | - Ronald W Holz
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI
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30
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Karatekin E. Toward a unified picture of the exocytotic fusion pore. FEBS Lett 2018; 592:3563-3585. [PMID: 30317539 PMCID: PMC6353554 DOI: 10.1002/1873-3468.13270] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 09/30/2018] [Accepted: 10/10/2018] [Indexed: 11/07/2022]
Abstract
Neurotransmitter and hormone release involve calcium-triggered fusion of a cargo-loaded vesicle with the plasma membrane. The initial connection between the fusing membranes, called the fusion pore, can evolve in various ways, including rapid dilation to allow full cargo release, slow expansion, repeated opening-closing and resealing. Pore dynamics determine the kinetics of cargo release and the mode of vesicle recycling, but how these processes are controlled is poorly understood. Previous reconstitutions could not monitor single pores, limiting mechanistic insight they could provide. Recently developed nanodisc-based fusion assays allow reconstitution and monitoring of single pores with unprecedented detail and hold great promise for future discoveries. They recapitulate various aspects of exocytotic fusion pores, but comparison is difficult because different approaches suggested very different exocytotic fusion pore properties, even for the same cell type. In this Review, I discuss how most of the data can be reconciled, by recognizing how different methods probe different aspects of the same fusion process. The resulting picture is that fusion pores have broadly distributed properties arising from stochastic processes which can be modulated by physical constraints imposed by proteins, lipids and membranes.
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Affiliation(s)
- Erdem Karatekin
- Department of Cellular and Molecular Physiology, Yale University, New Haven, CT, USA
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale University, West Haven, CT, USA
- Centre National de la Recherche Scientifique (CNRS), Paris, France
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31
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Schenk NA, Dahl PJ, Hanna MG, Audhya A, Tall GG, Knight JD, Anantharam A. A simple supported tubulated bilayer system for evaluating protein-mediated membrane remodeling. Chem Phys Lipids 2018; 215:18-28. [PMID: 30012406 DOI: 10.1016/j.chemphyslip.2018.06.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Accepted: 06/29/2018] [Indexed: 01/31/2023]
Abstract
Fusion and fission of cellular membranes involve dramatic, protein-mediated changes in membrane curvature. Many of the experimental methods useful for investigating curvature sensing or generation require specialized equipment. We have developed a system based on supported lipid bilayers (SLBs) in which lipid tubules are simple to produce and several types of membrane remodeling events can be readily imaged using widely available instrumentation (e.g., tubule fission and/or membrane budding). Briefly, high ionic strength during lipid bilayer deposition results in incorporation of excess lipids in the SLB. After sequentially washing with water and physiological ionic strength buffer solutions, lipid tubules form spontaneously. We find that tubule formation results from solution-dependent spreading of the SLB; washing from water into physiological ionic strength buffer solution leads to expansion of the bilayer and formation of tubules. Conversely, washing from physiological buffer into water results in contraction of the membrane and loss of tubules. We demonstrate the utility of these supported tubulated bilayers, termed "STuBs," with an investigation of Sar1B, a small Ras family G-protein known to influence membrane curvature. The addition of Sar1B to STuBs results in dramatic changes in tubule topology and eventual tubule fission. Overall, STuBs are a simple experimental system, useful for monitoring protein-mediated effects on membrane topology in real time, under physiologically relevant conditions.
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Affiliation(s)
- Noah A Schenk
- Department of Pharmacology, University of Michigan, United States
| | - Peter J Dahl
- Department of Pharmacology, University of Michigan, United States
| | - Michael G Hanna
- Department of Biomolecular Chemistry, University of Wisconsin-Madison School of Medicine and Public Health, United States
| | - Anjon Audhya
- Department of Biomolecular Chemistry, University of Wisconsin-Madison School of Medicine and Public Health, United States
| | - Gregory G Tall
- Department of Pharmacology, University of Michigan, United States
| | | | - Arun Anantharam
- Department of Pharmacology, University of Michigan, United States.
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32
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Johnson DS, Bleck M, Simon SM. Timing of ESCRT-III protein recruitment and membrane scission during HIV-1 assembly. eLife 2018; 7:36221. [PMID: 29972351 PMCID: PMC6080951 DOI: 10.7554/elife.36221] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 07/02/2018] [Indexed: 12/20/2022] Open
Abstract
The Endosomal Sorting Complexes Required for Transport III (ESCRT-III) proteins are critical for cellular membrane scission processes with topologies inverted relative to clathrin-mediated endocytosis. Some viruses appropriate ESCRT-IIIs for their release. By imaging single assembling viral-like particles of HIV-1, we observed that ESCRT-IIIs and the ATPase VPS4 arrive after most of the virion membrane is bent, linger for tens of seconds, and depart ~20 s before scission. These observations suggest that ESCRT-IIIs are recruited by a combination of membrane curvature and the late domains of the HIV-1 Gag protein. ESCRT-IIIs may pull the neck into a narrower form but must leave to allow scission. If scission does not occur within minutes of ESCRT departure, ESCRT-IIIs and VPS4 are recruited again. This mechanistic insight is likely relevant for other ESCRT-dependent scission processes including cell division, endosome tubulation, multivesicular body and nuclear envelope formation, and secretion of exosomes and ectosomes.
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Affiliation(s)
- Daniel S Johnson
- Laboratory of Cellular Biophysics, The Rockefeller University, New York, United States.,Department of Physics and Astronomy, Hofstra University, Hempstead, United States
| | - Marina Bleck
- Laboratory of Cellular Biophysics, The Rockefeller University, New York, United States
| | - Sanford M Simon
- Laboratory of Cellular Biophysics, The Rockefeller University, New York, United States
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33
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Sharma S, Lindau M. The fusion pore, 60 years after the first cartoon. FEBS Lett 2018; 592:3542-3562. [PMID: 29904915 DOI: 10.1002/1873-3468.13160] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2018] [Revised: 06/07/2018] [Accepted: 06/12/2018] [Indexed: 11/10/2022]
Abstract
Neurotransmitter release occurs in the form of quantal events by fusion of secretory vesicles with the plasma membrane, and begins with the formation of a fusion pore that has a conductance similar to that of a large ion channel or gap junction. In this review, we propose mechanisms of fusion pore formation and discuss their implications for fusion pore structure and function. Accumulating evidence indicates a direct role of soluble N-ethylmaleimide-sensitive-factor attachment receptor proteins in the opening of fusion pores. Fusion pores are likely neither protein channels nor purely lipid, but are of proteolipidic composition. Future perspectives to gain better insight into the molecular structure of fusion pores are discussed.
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Affiliation(s)
- Satyan Sharma
- Laboratory for Nanoscale Cell Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Manfred Lindau
- Laboratory for Nanoscale Cell Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.,School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
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34
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Somasundaram A, Taraska JW. Local protein dynamics during microvesicle exocytosis in neuroendocrine cells. Mol Biol Cell 2018; 29:1891-1903. [PMID: 29874123 PMCID: PMC6085826 DOI: 10.1091/mbc.e17-12-0716] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Calcium-triggered exocytosis is key to many physiological processes, including neurotransmitter and hormone release by neurons and endocrine cells. Dozens of proteins regulate exocytosis, yet the temporal and spatial dynamics of these factors during vesicle fusion remain unclear. Here we use total internal reflection fluorescence microscopy to visualize local protein dynamics at single sites of exocytosis of small synaptic-like microvesicles in live cultured neuroendocrine PC12 cells. We employ two-color imaging to simultaneously observe membrane fusion (using vesicular acetylcholine ACh transporter tagged to pHluorin) and the dynamics of associated proteins at the moments surrounding exocytosis. Our experiments show that many proteins, including the SNAREs syntaxin1 and VAMP2, the SNARE modulator tomosyn, and Rab proteins, are preclustered at fusion sites and rapidly lost at fusion. The ATPase N-ethylmaleimide–sensitive factor is locally recruited at fusion. Interestingly, the endocytic Bin-Amphiphysin-Rvs domain–containing proteins amphiphysin1, syndapin2, and endophilins are dynamically recruited to fusion sites and slow the loss of vesicle membrane-bound cargo from fusion sites. A similar effect on vesicle membrane protein dynamics was seen with the overexpression of the GTPases dynamin1 and dynamin2. These results suggest that proteins involved in classical clathrin-mediated endocytosis can regulate exocytosis of synaptic-like microvesicles. Our findings provide insights into the dynamics, assembly, and mechanistic roles of many key factors of exocytosis and endocytosis at single sites of microvesicle fusion in live cells.
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Affiliation(s)
- Agila Somasundaram
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892
| | - Justin W Taraska
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892
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35
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MacDougall DD, Lin Z, Chon NL, Jackman SL, Lin H, Knight JD, Anantharam A. The high-affinity calcium sensor synaptotagmin-7 serves multiple roles in regulated exocytosis. J Gen Physiol 2018; 150:783-807. [PMID: 29794152 PMCID: PMC5987875 DOI: 10.1085/jgp.201711944] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 05/07/2018] [Indexed: 12/19/2022] Open
Abstract
MacDougall et al. review the structure and function of the calcium sensor synaptotagmin-7 in exocytosis. Synaptotagmin (Syt) proteins comprise a 17-member family, many of which trigger exocytosis in response to calcium. Historically, most studies have focused on the isoform Syt-1, which serves as the primary calcium sensor in synchronous neurotransmitter release. Recently, Syt-7 has become a topic of broad interest because of its extreme calcium sensitivity and diversity of roles in a wide range of cell types. Here, we review the known and emerging roles of Syt-7 in various contexts and stress the importance of its actions. Unique functions of Syt-7 are discussed in light of recent imaging, electrophysiological, and computational studies. Particular emphasis is placed on Syt-7–dependent regulation of synaptic transmission and neuroendocrine cell secretion. Finally, based on biochemical and structural data, we propose a mechanism to link Syt-7’s role in membrane fusion with its role in subsequent fusion pore expansion via strong calcium-dependent phospholipid binding.
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Affiliation(s)
| | - Zesen Lin
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Nara L Chon
- Department of Chemistry, University of Colorado, Denver, CO
| | - Skyler L Jackman
- Vollum Institute, Oregon Health & Science University, Portland, OR
| | - Hai Lin
- Department of Chemistry, University of Colorado, Denver, CO
| | | | - Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
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36
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MARQUES D, MIRANDA A, SILVA A, MUNRO P, DE BEULE P. On the influence of lipid-induced optical anisotropy for the bioimaging of exo- or endocytosis with interference microscopic imaging. J Microsc 2018; 270:150-155. [DOI: 10.1111/jmi.12668] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2017] [Accepted: 11/21/2017] [Indexed: 12/01/2022]
Affiliation(s)
- D. MARQUES
- Departamento de Física, Faculdade de Ciências e Tecnologia; Universidade Nova de Lisboa; Campus de Caparica Caparica Portugal
- Applied Nano-Optics Group, Department of Life Sciences; International Iberian Nanotechnology Laboratory; Braga Portugal
| | - A. MIRANDA
- Applied Nano-Optics Group, Department of Life Sciences; International Iberian Nanotechnology Laboratory; Braga Portugal
| | - A.G. SILVA
- Departamento de Física, Faculdade de Ciências e Tecnologia; Universidade Nova de Lisboa; Campus de Caparica Caparica Portugal
| | - P.R.T. MUNRO
- Department of Medical Physics and Biomedical Engineering; University College London; London U.K
| | - P.A.A. DE BEULE
- Applied Nano-Optics Group, Department of Life Sciences; International Iberian Nanotechnology Laboratory; Braga Portugal
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37
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Bendahmane M, Bohannon KP, Bradberry MM, Rao TC, Schmidtke MW, Abbineni PS, Chon NL, Tran S, Lin H, Chapman ER, Knight JD, Anantharam A. The synaptotagmin C2B domain calcium-binding loops modulate the rate of fusion pore expansion. Mol Biol Cell 2018; 29:834-845. [PMID: 29444959 PMCID: PMC5905296 DOI: 10.1091/mbc.e17-11-0623] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 01/22/2018] [Accepted: 02/07/2018] [Indexed: 01/19/2023] Open
Abstract
In chromaffin cells, the kinetics of fusion pore expansion vary depending on which synaptotagmin isoform (Syt-1 or Syt-7) drives release. Our recent studies have shown that fusion pores of granules harboring Syt-1 expand more rapidly than those harboring Syt-7. Here we sought to define the structural specificity of synaptotagmin action at the fusion pore by manipulating the Ca2+-binding C2B module. We generated a chimeric Syt-1 in which its C2B Ca2+-binding loops had been exchanged for those of Syt-7. Fusion pores of granules harboring a Syt-1 C2B chimera with all three Ca2+-binding loops of Syt-7 (Syt-1:7C2B123) exhibited slower rates of fusion pore expansion and neuropeptide cargo release relative to WT Syt-1. After fusion, this chimera also dispersed more slowly from fusion sites than WT protein. We speculate that the Syt-1:7 C2B123 and WT Syt-1 are likely to differ in their interactions with Ca2+ and membranes. Subsequent in vitro and in silico data demonstrated that the chimera exhibits a higher affinity for phospholipids than WT Syt-1. We conclude that the affinity of synaptotagmin for the plasma membrane, and the rate at which it releases the membrane, contribute in important ways to the rate of fusion pore expansion.
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Affiliation(s)
- Mounir Bendahmane
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109
| | - Kevin P. Bohannon
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109
| | - Mazdak M. Bradberry
- Department of Neuroscience, Howard Hughes Medical Institute. University of Wisconsin–Madison, Madison, WI 53705
| | - Tejeshwar C. Rao
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109
| | | | | | - Nara L. Chon
- Department of Chemistry, University of Colorado Denver, Denver, CO 80217
| | - Sherleen Tran
- Department of Chemistry, University of Colorado Denver, Denver, CO 80217
| | - Hai Lin
- Department of Chemistry, University of Colorado Denver, Denver, CO 80217
| | - Edwin R. Chapman
- Department of Neuroscience, Howard Hughes Medical Institute. University of Wisconsin–Madison, Madison, WI 53705
| | | | - Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109
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Talukder MA, Menyuk CR, Kostov Y. Distinguishing between whole cells and cell debris using surface plasmon coupled emission. BIOMEDICAL OPTICS EXPRESS 2018; 9:1977-1991. [PMID: 29675333 PMCID: PMC5905938 DOI: 10.1364/boe.9.001977] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Revised: 03/01/2018] [Accepted: 03/20/2018] [Indexed: 05/04/2023]
Abstract
Distinguishing between whole cells and cell debris is important in microscopy, e.g., in screening of pulmonary patients for infectious tuberculosis. We propose and theoretically demonstrate that whole cells and cell debris can be distinguished from the far-field pattern of surface plasmon coupled emission (SPCE) of a fluorescently-labeled sample placed on a thin metal layer. If fluorescently-labeled whole cells are placed on the metal film, SPCE takes place simultaneously at two or more different angles and creates two or more distinct rings in the far field. By contrast, if fluorescently-labeled cell debris are placed on the metal film, SPCE takes place at only one angle and creates one ring in the far-field. We find that the angular separation of the far-field rings is sufficiently distinct to use the presence of one or more rings to distinguish between whole cells and cell debris. The proposed technique has the potential for detection without the use of a microscope.
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Affiliation(s)
- Muhammad Anisuzzaman Talukder
- Department of Electrical and Electronic Engineering, Bangladesh University of Engineering and Technology, Dhaka 1205,
Bangladesh
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT,
United Kingdom
- Department of Computer Science and Electrical Engineering, University of Maryland, Baltimore County, MD 21250,
USA
| | - Curtis R. Menyuk
- Department of Computer Science and Electrical Engineering, University of Maryland, Baltimore County, MD 21250,
USA
| | - Yordan Kostov
- Center for Advanced Sensor Technology, University of Maryland, Baltimore County, MD 21227,
USA
- Department of Chemical, Biochemical and Environmental Engineering, University of Maryland, Baltimore County, MD 21250,
USA
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39
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Membrane bending occurs at all stages of clathrin-coat assembly and defines endocytic dynamics. Nat Commun 2018; 9:419. [PMID: 29379015 PMCID: PMC5789089 DOI: 10.1038/s41467-018-02818-8] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Accepted: 01/02/2018] [Indexed: 01/01/2023] Open
Abstract
Clathrin-mediated endocytosis (CME) internalizes plasma membrane by reshaping small regions of the cell surface into spherical vesicles. The key mechanistic question of how coat assembly produces membrane curvature has been studied with molecular and cellular structural biology approaches, without direct visualization of the process in living cells; resulting in two competing models for membrane bending. Here we use polarized total internal reflection fluorescence microscopy (pol-TIRF) combined with electron, atomic force, and super-resolution optical microscopy to measure membrane curvature during CME. Surprisingly, coat assembly accommodates membrane bending concurrent with or after the assembly of the clathrin lattice. Once curvature began, CME proceeded to scission with robust timing. Four color pol-TIRF showed that CALM accumulated at high levels during membrane bending, implicating its auxiliary role in curvature generation. We conclude that clathrin-coat assembly is versatile and that multiple membrane-bending trajectories likely reflect the energetics of coat assembly relative to competing forces. Two distinct and opposing models for clathrin-mediated endocytosis have been inferred from EM and structural biology data. Here the authors develop an optical method to directly visualize membrane-bending dynamics and show that coat assembly accommodates membrane bending during or after the assembly of the clathrin lattice, which is not predicted by either model.
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40
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Chandler T, Mehta S, Shroff H, Oldenbourg R, La Rivière PJ. Single-fluorophore orientation determination with multiview polarized illumination: modeling and microscope design. OPTICS EXPRESS 2017; 25:31309-31325. [PMID: 29245807 PMCID: PMC5941992 DOI: 10.1364/oe.25.031309] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Revised: 11/13/2017] [Accepted: 11/23/2017] [Indexed: 06/02/2023]
Abstract
We investigate the use of polarized illumination in multiview microscopes for determining the orientation of single-molecule fluorescence transition dipoles. First, we relate the orientation of single dipoles to measurable intensities in multiview microscopes and develop an information-theoretic metric-the solid-angle uncertainty-to compare the ability of multiview microscopes to estimate the orientation of single dipoles. Next, we compare a broad class of microscopes using this metric-single- and dual-view microscopes with varying illumination polarization, illumination numerical aperture (NA), detection NA, obliquity, asymmetry, and exposure. We find that multi-view microscopes can measure all dipole orientations, while the orientations measurable with single-view microscopes is halved because of symmetries in the detection process. We also find that choosing a small illumination NA and a large detection NA are good design choices, that multiview microscopes can benefit from oblique illumination and detection, and that asymmetric NA microscopes can benefit from exposure asymmetry.
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Affiliation(s)
- Talon Chandler
- University of Chicago, Department of Radiology, Chicago, Illinois 60637,
USA
| | - Shalin Mehta
- University of Chicago, Department of Radiology, Chicago, Illinois 60637,
USA
- Marine Biological Laboratory, Bell Center, Woods Hole, Massachusetts 02543,
USA
- (present address) Chan Zuckerberg Biohub, San Francisco, California 94158,
USA
| | - Hari Shroff
- Section on High Resolution Optical Imaging, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland 20892,
USA
- Marine Biological Laboratory, Whitman Center, Woods Hole, Massachusetts 02543,
USA
| | - Rudolf Oldenbourg
- Marine Biological Laboratory, Bell Center, Woods Hole, Massachusetts 02543,
USA
- Brown University, Department of Physics, Providence, Rhode Island 02912,
USA
| | - Patrick J. La Rivière
- University of Chicago, Department of Radiology, Chicago, Illinois 60637,
USA
- Marine Biological Laboratory, Whitman Center, Woods Hole, Massachusetts 02543,
USA
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41
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Uddin SZ, Talukder MA. Imaging of cell membrane topography using Tamm plasmon coupled emission. Biomed Phys Eng Express 2017. [DOI: 10.1088/2057-1976/aa881a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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42
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Kabbani AM, Kelly CV. The Detection of Nanoscale Membrane Bending with Polarized Localization Microscopy. Biophys J 2017; 113:1782-1794. [PMID: 29045872 PMCID: PMC5647545 DOI: 10.1016/j.bpj.2017.07.034] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 06/20/2017] [Accepted: 07/25/2017] [Indexed: 11/22/2022] Open
Abstract
The curvature of biological membranes at the nanometer scale is critically important for vesicle trafficking, organelle morphology, and disease propagation. The initiation of membrane bending occurs at a length scale that is irresolvable by most superresolution optical microscopy methods. Here, we report the development of polarized localization microscopy (PLM), a pointillist optical imaging technique for the detection of nanoscale membrane curvature in correlation with single-molecule dynamics and molecular sorting. PLM combines polarized total internal reflection fluorescence microscopy and single-molecule localization microscopy to reveal membrane orientation with subdiffraction-limited resolution without reducing localization precision by point spread function manipulation. Membrane curvature detection with PLM requires fewer localization events to detect curvature than three-dimensional single-molecule localization microscopy (e.g., photoactivated localization microscopy or stochastic optical reconstruction microscopy), which enables curvature detection 10× faster via PLM. With rotationally confined lipophilic fluorophores and the polarized incident fluorescence excitation, membrane-bending events are revealed with superresolution. Engineered hemispherical membrane curvature with a radius ≥24 nm was detected with PLM, and individual fluorophore localization precision was 13 ± 5 nm. Further, deciphering molecular mobility as a function of membrane topology was enabled. The diffusion coefficient of individual DiI molecules was 25 ± 5× higher in planar supported lipid bilayers than within nanoscale membrane curvature. Through the theoretical foundation and experimental demonstration provided here, PLM is poised to become a powerful technique for revealing the underlying biophysical mechanisms of membrane bending at physiological length scales.
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Affiliation(s)
- Abir M Kabbani
- Department of Physics and Astronomy, Wayne State University, Detroit, Michigan
| | - Christopher V Kelly
- Department of Physics and Astronomy, Wayne State University, Detroit, Michigan.
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43
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Bohannon KP, Bittner MA, Lawrence DA, Axelrod D, Holz RW. Slow fusion pore expansion creates a unique reaction chamber for co-packaged cargo. J Gen Physiol 2017; 149:921-934. [PMID: 28882880 PMCID: PMC5694939 DOI: 10.1085/jgp.201711842] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Accepted: 08/21/2017] [Indexed: 12/29/2022] Open
Abstract
A lumenal secretory granule protein can slow fusion pore dilation and thus its own discharge. Bohannon et al. demonstrate another outcome: the creation of a nanoscale chemical reaction chamber for granule contents in which the pH is suddenly neutralized upon fusion. A lumenal secretory granule protein, tissue plasminogen activator (tPA), greatly slows fusion pore dilation and thereby slows its own discharge. We investigated another outcome of the long-lived narrow fusion pore: the creation of a nanoscale chemical reaction chamber for granule contents in which the pH is suddenly neutralized upon fusion. Bovine adrenal chromaffin cells endogenously express both tPA and its primary protein inhibitor, plasminogen activator inhibitor 1 (PAI). We found by immunocytochemistry that tPA and PAI are co-packaged in the same secretory granule. It is known that PAI irreversibly and covalently inactivates tPA at neutral pH. We demonstrate with zymography that the acidic granule lumen protects tPA from inactivation by PAI. Immunocytochemistry, total internal reflection fluorescence (TIRF) microscopy, and polarized TIRF microscopy demonstrated that co-packaged PAI and tPA remain together in granules for many seconds in the nanoscale reaction chamber, more than enough time to inhibit tPA and create a new secreted protein species.
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Affiliation(s)
- Kevin P Bohannon
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Mary A Bittner
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Daniel A Lawrence
- Department of Internal Medicine, University of Michigan, Ann Arbor, MI.,Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI
| | - Daniel Axelrod
- Department of Pharmacology, University of Michigan, Ann Arbor, MI.,Department of Physics, University of Michigan, Ann Arbor, MI.,LSA Biophysics, University of Michigan, Ann Arbor, MI
| | - Ronald W Holz
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
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44
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Kuhlmann JW, Junius M, Diederichsen U, Steinem C. SNARE-Mediated Single-Vesicle Fusion Events with Supported and Freestanding Lipid Membranes. Biophys J 2017; 112:2348-2356. [PMID: 28591607 DOI: 10.1016/j.bpj.2017.04.032] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Revised: 04/24/2017] [Accepted: 04/24/2017] [Indexed: 10/19/2022] Open
Abstract
In vitro single-vesicle fusion assays are important tools to analyze the details of SNARE-mediated fusion processes. In this study, we employed planar pore-spanning membranes (PSMs) prepared on porous silicon substrates with large pore diameters of 5 μm, allowing us to compare the process of vesicle docking and fusion on the supported parts of the PSMs (s-PSMs) with that on the freestanding membrane parts (f-PSM) under the exact same experimental conditions. The PSMs harbor the t-SNARE ΔN49-complex to investigate the dynamics and fusogenicity of single large unilamellar vesicles doped with the v-SNARE synaptobrevin 2 by means of spinning-disc confocal microscopy with a time resolution of 10 ms. Our results demonstrate that vesicles docked to the s-PSM were fully immobile, whereas those docked to the f-PSM were mobile with a mean diffusion coefficient of 0.42 μm2/s. Despite the different dynamics of the vesicles on the two membrane types, similar fusion kinetics were observed, giving rise to a common fusion mechanism. Further investigations of individual lipid mixing events on the s-PSMs revealed semi-stable post-fusion structures.
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Affiliation(s)
- Jan W Kuhlmann
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany
| | - Meike Junius
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany
| | - Ulf Diederichsen
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany
| | - Claudia Steinem
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany.
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45
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Stone MB, Shelby SA, Veatch SL. Super-Resolution Microscopy: Shedding Light on the Cellular Plasma Membrane. Chem Rev 2017; 117:7457-7477. [PMID: 28211677 PMCID: PMC5471115 DOI: 10.1021/acs.chemrev.6b00716] [Citation(s) in RCA: 104] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Lipids and the membranes they form are fundamental building blocks of cellular life, and their geometry and chemical properties distinguish membranes from other cellular environments. Collective processes occurring within membranes strongly impact cellular behavior and biochemistry, and understanding these processes presents unique challenges due to the often complex and myriad interactions between membrane components. Super-resolution microscopy offers a significant gain in resolution over traditional optical microscopy, enabling the localization of individual molecules even in densely labeled samples and in cellular and tissue environments. These microscopy techniques have been used to examine the organization and dynamics of plasma membrane components, providing insight into the fundamental interactions that determine membrane functions. Here, we broadly introduce the structure and organization of the mammalian plasma membrane and review recent applications of super-resolution microscopy to the study of membranes. We then highlight some inherent challenges faced when using super-resolution microscopy to study membranes, and we discuss recent technical advancements that promise further improvements to super-resolution microscopy and its application to the plasma membrane.
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Affiliation(s)
- Matthew B Stone
- Biophysics, University of Michigan, Chemistry 930 N University Ave, Ann Arbor 48109
| | - Sarah A Shelby
- Biophysics, University of Michigan, Chemistry 930 N University Ave, Ann Arbor 48109
| | - Sarah L Veatch
- Biophysics, University of Michigan, Chemistry 930 N University Ave, Ann Arbor 48109
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46
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Xie Z, Long J, Liu J, Chai Z, Kang X, Wang C. Molecular Mechanisms for the Coupling of Endocytosis to Exocytosis in Neurons. Front Mol Neurosci 2017; 10:47. [PMID: 28348516 PMCID: PMC5346583 DOI: 10.3389/fnmol.2017.00047] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2016] [Accepted: 02/10/2017] [Indexed: 11/13/2022] Open
Abstract
Neuronal communication and brain function mainly depend on the fundamental biological events of neurotransmission, including the exocytosis of presynaptic vesicles (SVs) for neurotransmitter release and the subsequent endocytosis for SV retrieval. Neurotransmitters are released through the Ca2+- and SNARE-dependent fusion of SVs with the presynaptic plasma membrane. Following exocytosis, endocytosis occurs immediately to retrieve SV membrane and fusion machinery for local recycling and thus maintain the homeostasis of synaptic structure and sustained neurotransmission. Apart from the general endocytic machinery, recent studies have also revealed the involvement of SNARE proteins (synaptobrevin, SNAP25 and syntaxin), synaptophysin, Ca2+/calmodulin, and members of the synaptotagmin protein family (Syt1, Syt4, Syt7 and Syt11) in the balance and tight coupling of exo-endocytosis in neurons. Here, we provide an overview of recent progress in understanding how these neuron-specific adaptors coordinate to ensure precise and efficient endocytosis during neurotransmission.
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Affiliation(s)
- Zhenli Xie
- Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong UniversityXi'an, China; Frontier Institute of Science and Technology, Xi'an Jiaotong UniversityXi'an, China; State Key Laboratory of Membrane Biology, Peking UniversityBeijing, China; Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China
| | - Jiangang Long
- Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong UniversityXi'an, China; Frontier Institute of Science and Technology, Xi'an Jiaotong UniversityXi'an, China
| | - Jiankang Liu
- Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong UniversityXi'an, China; Frontier Institute of Science and Technology, Xi'an Jiaotong UniversityXi'an, China
| | - Zuying Chai
- State Key Laboratory of Membrane Biology, Peking UniversityBeijing, China; Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China
| | - Xinjiang Kang
- State Key Laboratory of Membrane Biology, Peking UniversityBeijing, China; Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China; College of Life Sciences, Liaocheng UniversityLiaocheng, China; Key Laboratory of Medical Electrophysiology, Ministry of Education of China, Collaborative Innovation Center for Prevention and Treatment of Cardiovascular Disease, Institute of Cardiovascular Research, Southwest Medical UniversityLuzhou, China
| | - Changhe Wang
- Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong UniversityXi'an, China; Frontier Institute of Science and Technology, Xi'an Jiaotong UniversityXi'an, China; State Key Laboratory of Membrane Biology, Peking UniversityBeijing, China; Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China
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47
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Dissection of molecular assembly dynamics by tracking orientation and position of single molecules in live cells. Proc Natl Acad Sci U S A 2016; 113:E6352-E6361. [PMID: 27679846 DOI: 10.1073/pnas.1607674113] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Regulation of order, such as orientation and conformation, drives the function of most molecular assemblies in living cells but remains difficult to measure accurately through space and time. We built an instantaneous fluorescence polarization microscope, which simultaneously images position and orientation of fluorophores in living cells with single-molecule sensitivity and a time resolution of 100 ms. We developed image acquisition and analysis methods to track single particles that interact with higher-order assemblies of molecules. We tracked the fluctuations in position and orientation of molecules from the level of an ensemble of fluorophores down to single fluorophores. We tested our system in vitro using fluorescently labeled DNA and F-actin, in which the ensemble orientation of polarized fluorescence is known. We then tracked the orientation of sparsely labeled F-actin network at the leading edge of migrating human keratinocytes, revealing the anisotropic distribution of actin filaments relative to the local retrograde flow of the F-actin network. Additionally, we analyzed the position and orientation of septin-GFP molecules incorporated in septin bundles in growing hyphae of a filamentous fungus. Our data indicate that septin-GFP molecules undergo positional fluctuations within ∼350 nm of the binding site and angular fluctuations within ∼30° of the central orientation of the bundle. By reporting position and orientation of molecules while they form dynamic higher-order structures, our approach can provide insights into how micrometer-scale ordered assemblies emerge from nanoscale molecules in living cells.
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48
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Nikolaus J, Karatekin E. SNARE-mediated Fusion of Single Proteoliposomes with Tethered Supported Bilayers in a Microfluidic Flow Cell Monitored by Polarized TIRF Microscopy. J Vis Exp 2016. [PMID: 27585113 DOI: 10.3791/54349] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
In the ubiquitous process of membrane fusion the opening of a fusion pore establishes the first connection between two formerly separate compartments. During neurotransmitter or hormone release via exocytosis, the fusion pore can transiently open and close repeatedly, regulating cargo release kinetics. Pore dynamics also determine the mode of vesicle recycling; irreversible resealing results in transient, "kiss-and-run" fusion, whereas dilation leads to full fusion. To better understand what factors govern pore dynamics, we developed an assay to monitor membrane fusion using polarized total internal reflection fluorescence (TIRF) microscopy with single molecule sensitivity and ~15 msec time resolution in a biochemically well-defined in vitro system. Fusion of fluorescently labeled small unilamellar vesicles containing v-SNARE proteins (v-SUVs) with a planar bilayer bearing t-SNAREs, supported on a soft polymer cushion (t-SBL, t-supported bilayer), is monitored. The assay uses microfluidic flow channels that ensure minimal sample consumption while supplying a constant density of SUVs. Exploiting the rapid signal enhancement upon transfer of lipid labels from the SUV to the SBL during fusion, kinetics of lipid dye transfer is monitored. The sensitivity of TIRF microscopy allows tracking single fluorescent lipid labels, from which lipid diffusivity and SUV size can be deduced for every fusion event. Lipid dye release times can be much longer than expected for unimpeded passage through permanently open pores. Using a model that assumes retardation of lipid release is due to pore flickering, a pore "openness", the fraction of time the pore remains open during fusion, can be estimated. A soluble marker can be encapsulated in the SUVs for simultaneous monitoring of lipid and soluble cargo release. Such measurements indicate some pores may reseal after losing a fraction of the soluble cargo.
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Affiliation(s)
- Joerg Nikolaus
- Department of Cellular and Molecular Physiology, Yale University School of Medicine; Nanobiology Institute, Yale University
| | - Erdem Karatekin
- Department of Cellular and Molecular Physiology, Yale University School of Medicine; Nanobiology Institute, Yale University; Department of Molecular Biophysics and Biochemistry, Yale University; Laboratoire de Neurophotonique, Université Paris Descartes, Faculté des Sciences Fondamentales et Biomédicales, Centre National de la Recherche Scientifique (CNRS);
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49
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Finkenstaedt-Quinn SA, Qiu TA, Shin K, Haynes CL. Super-resolution imaging for monitoring cytoskeleton dynamics. Analyst 2016; 141:5674-5688. [PMID: 27549146 DOI: 10.1039/c6an00731g] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The cytoskeleton is a key cellular structure that is important in the control of cellular movement, structure, and sensing. To successfully image the individual cytoskeleton components, high resolution and super-resolution fluorescence imaging methods are needed. This review covers the three basic cytoskeletal elements and the relative benefits and drawbacks of fixed versus live cell imaging before moving on to recent studies using high resolution and super-resolution techniques. The techniques covered include the near-diffraction limited imaging methods of confocal microscopy and TIRF microscopy and the super-resolution fluorescence imaging methods of STORM, PALM, and STED.
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50
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Trexler AJ, Sochacki KA, Taraska JW. Imaging the recruitment and loss of proteins and lipids at single sites of calcium-triggered exocytosis. Mol Biol Cell 2016; 27:2423-34. [PMID: 27307587 PMCID: PMC4966983 DOI: 10.1091/mbc.e16-01-0057] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Accepted: 06/09/2016] [Indexed: 12/13/2022] Open
Abstract
Imaging of exocytic and endocytic proteins shows which are present at exocytic sites before, during, and after exocytosis in living cells. Rab proteins and SNARE modulators are lost, and dynamin, PIP2, and BAR-domain proteins are rapidly and transiently recruited, where they may modulate the nascent fusion pore. How and when the dozens of molecules that control exocytosis assemble in living cells to regulate the fusion of a vesicle with the plasma membrane is unknown. Here we image with two-color total internal reflection fluorescence microscopy the local changes of 27 proteins at single dense-core vesicles undergoing calcium-triggered fusion. We identify two broad dynamic behaviors of exocytic molecules. First, proteins enriched at exocytic sites are associated with DCVs long before exocytosis, and near the time of membrane fusion, they diffuse away. These proteins include Rab3 and Rab27, rabphilin3a, munc18a, tomosyn, and CAPS. Second, we observe a group of classical endocytic proteins and lipids, including dynamins, amphiphysin, syndapin, endophilin, and PIP2, which are rapidly and transiently recruited to the exocytic site near the time of membrane fusion. Dynamin mutants unable to bind amphiphysin were not recruited, indicating that amphiphysin is involved in localizing dynamin to the fusion site. Expression of mutant dynamins and knockdown of endogenous dynamin altered the rate of cargo release from single vesicles. Our data reveal the dynamics of many key proteins involved in exocytosis and identify a rapidly recruited dynamin/PIP2/BAR assembly that regulates the exocytic fusion pore of dense-core vesicles in cultured endocrine beta cells.
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Affiliation(s)
- Adam J Trexler
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892
| | - Kem A Sochacki
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892
| | - Justin W Taraska
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892
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