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von Molitor E, Nürnberg E, Ertongur-Fauth T, Scholz P, Riedel K, Hafner M, Rudolf R, Cesetti T. Analysis of calcium signaling in live human Tongue cell 3D-Cultures upon tastant perfusion. Cell Calcium 2020; 87:102164. [PMID: 32014795 DOI: 10.1016/j.ceca.2020.102164] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 11/29/2019] [Accepted: 01/16/2020] [Indexed: 02/06/2023]
Abstract
Bridging the gap between two-dimensional cell cultures and complex in vivo tissues, three-dimensional cell culture models are of increasing interest in the fields of cell biology and pharmacology. However, present challenges hamper live cell imaging of three-dimensional cell cultures. These include (i) the stabilization of these structures under perfusion conditions, (ii) the recording of many z-planes at high spatio-temporal resolution, (iii) and the data analysis that ranges in complexity from whole specimens to single cells. Here, we addressed these issues for the time-lapse analysis of Ca2+ signaling in spheroids composed of human tongue-derived HTC-8 cells upon perfusion of gustatory substances. Live cell imaging setups for confocal and light sheet microscopy were developed that allow simple and robust spheroid stabilization and high-resolution microscopy with perfusion. Visualization of spheroids made of HTC-8 cells expressing the G-GECO fluorescent Ca2+ sensor revealed Ca2+ transients that showed similar kinetics but different amplitudes upon perfusion of bitter compounds Salicine and Saccharin. Dose-dependent responses to Saccharin required extracellular Ca2+. From the border towards the center of spheroids, compound-induced Ca2+ signals were progressively delayed and decreased in amplitude. Stimulation with ATP led to strong Ca2+ transients that were faster than those evoked by the bitter compounds and blockade of purinergic receptors with Suramin abutted the response to Saccharin, suggesting that ATP mediates a positive autocrine and paracrine feedback. Imaging of ATP-induced Ca2+ transients with light sheet microscopy allowed acquisition over a z-depth of 100 μm without losing spatial and temporal resolution. In summary, the presented approaches permit the study of fast cellular signaling in three-dimensional cultures upon compound perfusion.
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Affiliation(s)
- Elena von Molitor
- Institute of Molecular and Cell Biology, Hochschule Mannheim, 68163 Mannheim, Germany
| | - Elina Nürnberg
- Institute of Molecular and Cell Biology, Hochschule Mannheim, 68163 Mannheim, Germany
| | | | | | | | - Mathias Hafner
- Institute of Molecular and Cell Biology, Hochschule Mannheim, 68163 Mannheim, Germany.
| | - Rüdiger Rudolf
- Institute of Molecular and Cell Biology, Hochschule Mannheim, 68163 Mannheim, Germany; Interdisciplinary Center for Neurosciences, Heidelberg University, 69120 Heidelberg, Germany.
| | - Tiziana Cesetti
- Institute of Molecular and Cell Biology, Hochschule Mannheim, 68163 Mannheim, Germany
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2
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Perry JL, Ramachandran NK, Utama B, Hyser JM. Use of genetically-encoded calcium indicators for live cell calcium imaging and localization in virus-infected cells. Methods 2015; 90:28-38. [PMID: 26344758 PMCID: PMC4655165 DOI: 10.1016/j.ymeth.2015.09.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2015] [Revised: 08/31/2015] [Accepted: 09/01/2015] [Indexed: 01/09/2023] Open
Abstract
Calcium signaling is a ubiquitous and versatile process involved in nearly every cellular process, and exploitation of host calcium signals is a common strategy used by viruses to facilitate replication and cause disease. Small molecule fluorescent calcium dyes have been used by many to examine changes in host cell calcium signaling and calcium channel activation during virus infections, but disadvantages of these dyes, including poor loading and poor long-term retention, complicate analysis of calcium imaging in virus-infected cells due to changes in cell physiology and membrane integrity. The recent expansion of genetically-encoded calcium indicators (GECIs), including blue and red-shifted color variants and variants with calcium affinities appropriate for calcium storage organelles like the endoplasmic reticulum (ER), make the use of GECIs an attractive alternative for calcium imaging in the context of virus infections. Here we describe the development and testing of cell lines stably expressing both green cytoplasmic (GCaMP5G and GCaMP6s) and red ER-targeted (RCEPIAer) GECIs. Using three viruses (rotavirus, poliovirus and respiratory syncytial virus) previously shown to disrupt host calcium homeostasis, we show the GECI cell lines can be used to detect simultaneous cytoplasmic and ER calcium signals. Further, we demonstrate the GECI expression has sufficient stability to enable long-term confocal imaging of both cytoplasmic and ER calcium during the course of virus infections.
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Affiliation(s)
- Jacob L Perry
- Department of Molecular Virology and Microbiology and Alkek Center for Metagenomic and Microbiome Research, Baylor College of Medicine, Houston, TX 77030, United States
| | - Nina K Ramachandran
- Department of Molecular Virology and Microbiology and Alkek Center for Metagenomic and Microbiome Research, Baylor College of Medicine, Houston, TX 77030, United States
| | - Budi Utama
- Shared Equipment Authority, Rice University, Houston, TX 77030, United States
| | - Joseph M Hyser
- Department of Molecular Virology and Microbiology and Alkek Center for Metagenomic and Microbiome Research, Baylor College of Medicine, Houston, TX 77030, United States.
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Albrecht T, Zhao Y, Nguyen TH, Campbell RE, Johnson JD. Fluorescent biosensors illuminate calcium levels within defined beta-cell endosome subpopulations. Cell Calcium 2015; 57:263-74. [PMID: 25682167 DOI: 10.1016/j.ceca.2015.01.008] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Revised: 12/26/2014] [Accepted: 01/19/2015] [Indexed: 11/18/2022]
Abstract
Live cell imaging has revealed that calcium ions (Ca(2+)) pass in and out of many cellular organelles. However, technical hurdles have limited measurements of Ca(2+) in acidic organelles, such as endosomes. Although evidence hints that endosomes play a role in Ca(2+) signaling, direct measurements within endosomal lumina represent one of the final frontiers in organelle imaging. To measure Ca(2+) in a TiVAMP-positive endosome sub-population, the pH-resistant ratiometric Ca(2+) biosensor GEM-GECO1 and the ratiometric pH biosensor mKeima were used. A positive correlation between acidic endosomal pH and higher Ca(2+) was observed within these Rab5a- and Rab7-positive compartments. Ca(2+) concentration in most endosomes was estimated to be below 2μM, lower than Ca(2+) levels in several other intracellular stores, indicating that endosomes may take up Ca(2+) during physiological stimulation. Indeed, endosomes accumulated Ca(2+) during glucose-stimulation, a condition where endosomal pH did not change. Our biosensors permitted the first measurements revealing a role for endosomes in cellular Ca(2+) homeostasis during physiological stimulation.
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Affiliation(s)
- Tobias Albrecht
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Yongxin Zhao
- Department of Chemistry, University of Alberta, Edmonton, AB, Canada
| | - Trang Hai Nguyen
- Department of Chemistry, University of Alberta, Edmonton, AB, Canada
| | - Robert E Campbell
- Department of Chemistry, University of Alberta, Edmonton, AB, Canada
| | - James D Johnson
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada.
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4
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Lindenburg L, Merkx M. Engineering genetically encoded FRET sensors. SENSORS 2014; 14:11691-713. [PMID: 24991940 PMCID: PMC4168480 DOI: 10.3390/s140711691] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Revised: 06/24/2014] [Accepted: 06/26/2014] [Indexed: 01/15/2023]
Abstract
Förster Resonance Energy Transfer (FRET) between two fluorescent proteins can be exploited to create fully genetically encoded and thus subcellularly targetable sensors. FRET sensors report changes in energy transfer between a donor and an acceptor fluorescent protein that occur when an attached sensor domain undergoes a change in conformation in response to ligand binding. The design of sensitive FRET sensors remains challenging as there are few generally applicable design rules and each sensor must be optimized anew. In this review we discuss various strategies that address this shortcoming, including rational design approaches that exploit self-associating fluorescent domains and the directed evolution of FRET sensors using high-throughput screening.
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Affiliation(s)
- Laurens Lindenburg
- Laboratory of Chemical Biology and Institute of Complex Molecular Systems (ICMS), Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven 5600MB, The Netherlands.
| | - Maarten Merkx
- Laboratory of Chemical Biology and Institute of Complex Molecular Systems (ICMS), Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven 5600MB, The Netherlands.
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5
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Lindenburg LH, Vinkenborg JL, Oortwijn J, Aper SJA, Merkx M. MagFRET: the first genetically encoded fluorescent Mg2+ sensor. PLoS One 2013; 8:e82009. [PMID: 24312622 PMCID: PMC3846734 DOI: 10.1371/journal.pone.0082009] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Accepted: 10/29/2013] [Indexed: 01/14/2023] Open
Abstract
Magnesium has important structural, catalytic and signaling roles in cells, yet few tools exist to image this metal ion in real time and at subcellular resolution. Here we report the first genetically encoded sensor for Mg2+, MagFRET-1. This sensor is based on the high-affinity Mg2+ binding domain of human centrin 3 (HsCen3), which undergoes a transition from a molten-globular apo form to a compactly-folded Mg2+-bound state. Fusion of Cerulean and Citrine fluorescent domains to the ends of HsCen3, yielded MagFRET-1, which combines a physiologically relevant Mg2+ affinity (Kd = 148 µM) with a 50% increase in emission ratio upon Mg2+ binding due to a change in FRET efficiency between Cerulean and Citrine. Mutations in the metal binding sites yielded MagFRET variants whose Mg2+ affinities were attenuated 2- to 100-fold relative to MagFRET-1, thus covering a broad range of Mg2+ concentrations. In situ experiments in HEK293 cells showed that MagFRET-1 can be targeted to the cytosol and the nucleus. Clear responses to changes in extracellular Mg2+ concentration were observed for MagFRET-1-expressing HEK293 cells when they were permeabilized with digitonin, whereas similar changes were not observed for intact cells. Although MagFRET-1 is also sensitive to Ca2+, this affinity is sufficiently attenuated (Kd of 10 µM) to make the sensor insensitive to known Ca2+ stimuli in HEK293 cells. While the potential and limitations of the MagFRET sensors for intracellular Mg2+ imaging need to be further established, we expect that these genetically encoded and ratiometric fluorescent Mg2+ sensors could prove very useful in understanding intracellular Mg2+ homeostasis and signaling.
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Affiliation(s)
- Laurens H. Lindenburg
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Jan L. Vinkenborg
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Jorn Oortwijn
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Stijn J. A. Aper
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| | - Maarten Merkx
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
- * E-mail:
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Mbatia HW, Burdette SC. Photochemical Tools for Studying Metal Ion Signaling and Homeostasis. Biochemistry 2012; 51:7212-24. [DOI: 10.1021/bi3001769] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Hannah W. Mbatia
- University of Connecticut, 55 North Eagleville
Road, Storrs, Connecticut 06269-3060, United
States
| | - Shawn C. Burdette
- Worcester Polytechnic Institute, 100 Institute Road, Worcester, Massachusetts
01609-2280, United States
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Liu B, Zeng F, Wu G, Wu S. Nanoparticles as scaffolds for FRET-based ratiometric detection of mercury ions in water with QDs as donors. Analyst 2012; 137:3717-24. [DOI: 10.1039/c2an35434a] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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