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Gutorov R, Katz B, Peters M, Minke B. Membrane lipid modulations by methyl-β-cyclodextrin uncouple the Drosophila light-activated phospholipase C from TRP and TRPL channel gating. J Biol Chem 2024; 300:105484. [PMID: 37992804 PMCID: PMC10770611 DOI: 10.1016/j.jbc.2023.105484] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 11/05/2023] [Accepted: 11/14/2023] [Indexed: 11/24/2023] Open
Abstract
Sterols are hydrophobic molecules, known to cluster signaling membrane-proteins in lipid rafts, while methyl-β-cyclodextrin (MβCD) has been a major tool for modulating membrane-sterol content for studying its effect on membrane proteins, including the transient receptor potential (TRP) channels. The Drosophila light-sensitive TRP channels are activated downstream of a G-protein-coupled phospholipase Cβ (PLC) cascade. In phototransduction, PLC is an enzyme that hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) generating diacylglycerol, inositol-tris-phosphate, and protons, leading to TRP and TRP-like (TRPL) channel openings. Here, we studied the effects of MβCD on Drosophila phototransduction using electrophysiology while fluorescently monitoring PIP2 hydrolysis, aiming to examine the effects of sterol modulation on PIP2 hydrolysis and the ensuing light-response in the native system. Incubation of photoreceptor cells with MβCD dramatically reduced the amplitude and kinetics of the TRP/TRPL-mediated light response. MβCD also suppressed PLC-dependent TRP/TRPL constitutive channel activity in the dark induced by mitochondrial uncouplers, but PLC-independent activation of the channels by linoleic acid was not affected. Furthermore, MβCD suppressed a constitutively active TRP mutant-channel, trpP365, suggesting that TRP channel activity is a target of MβCD action. Importantly, whole-cell voltage-clamp measurements from photoreceptors and simultaneously monitored PIP2-hydrolysis by translocation of fluorescently tagged Tubby protein domain, from the plasma membrane to the cytosol, revealed that MβCD virtually abolished the light response when having little effect on the light-activated PLC. Together, MβCD uncoupled TRP/TRPL channel gating from light-activated PLC and PIP2-hydrolysis suggesting the involvement of distinct nanoscopic lipid domains such as lipid rafts and PIP2 clusters in TRP/TRPL channel gating.
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Affiliation(s)
- Rita Gutorov
- Faculty of Medicine, Institute for Medical Research Israel-Canada (IMRIC), Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University, Jerusalem, Israel
| | - Ben Katz
- Faculty of Medicine, Institute for Medical Research Israel-Canada (IMRIC), Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University, Jerusalem, Israel
| | - Maximilian Peters
- Faculty of Medicine, Institute for Medical Research Israel-Canada (IMRIC), Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University, Jerusalem, Israel
| | - Baruch Minke
- Faculty of Medicine, Institute for Medical Research Israel-Canada (IMRIC), Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University, Jerusalem, Israel.
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Rhodes-Mordov E, Brandwine-Shemmer T, Zaguri R, Gutorov R, Peters M, Minke B. Diacylglycerol Activates the Drosophila Light Sensitive Channel TRPL Expressed in HEK Cells. Int J Mol Sci 2023; 24:ijms24076289. [PMID: 37047261 PMCID: PMC10093889 DOI: 10.3390/ijms24076289] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 03/20/2023] [Accepted: 03/24/2023] [Indexed: 03/30/2023] Open
Abstract
Physiological activation by light of the Drosophila TRP and TRP-like (TRPL) channels requires the activation of phospholipase Cβ (PLC). The hydrolysis of phosphatidylinositol 4,5, bisphosphate (PIP2) by PLC is a crucial step in the still-unclear light activation, while the generation of Diacylglycerol (DAG) by PLC seems to be involved. In this study, we re-examined the ability of a DAG analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG) to activate the TRPL channels expressed in HEK cells. Unlike previous studies, we added OAG into the cytosol via a patch-clamp pipette and observed robust activation of the expressed TRPL channels. However, TRPL channel activation was much slower than the physiologically activated TRPL by light. Therefore, we used a picosecond-fast optically activated DAG analogue, OptoDArG. Inactive OptoDArG was added into the intracellular solution with the patch-clamp pipette, and it slowly accumulated on the surface membrane of the recorded HEK cell in the dark. A fast application of intense UV light to the recorded cell resulted in a robust and relatively fast TRPL-dependent current that was greatly accelerated by the constitutively active TRPLF557I pore-region mutation. However, this current of the mutant channel was still considerably slower than the native light-induced TRPL current, suggesting that DAG alone is not sufficient for TRPL channel activation under physiological conditions.
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Križaj D, Cordeiro S, Strauß O. Retinal TRP channels: Cell-type-specific regulators of retinal homeostasis and multimodal integration. Prog Retin Eye Res 2023; 92:101114. [PMID: 36163161 PMCID: PMC9897210 DOI: 10.1016/j.preteyeres.2022.101114] [Citation(s) in RCA: 17] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 08/03/2022] [Accepted: 08/08/2022] [Indexed: 02/05/2023]
Abstract
Transient receptor potential (TRP) channels are a widely expressed family of 28 evolutionarily conserved cationic ion channels that operate as primary detectors of chemical and physical stimuli and secondary effectors of metabotropic and ionotropic receptors. In vertebrates, the channels are grouped into six related families: TRPC, TRPV, TRPM, TRPA, TRPML, and TRPP. As sensory transducers, TRP channels are ubiquitously expressed across the body and the CNS, mediating critical functions in mechanosensation, nociception, chemosensing, thermosensing, and phototransduction. This article surveys current knowledge about the expression and function of the TRP family in vertebrate retinas, which, while dedicated to transduction and transmission of visual information, are highly susceptible to non-visual stimuli. Every retinal cell expresses multiple TRP subunits, with recent evidence establishing their critical roles in paradigmatic aspects of vertebrate vision that include TRPM1-dependent transduction of ON bipolar signaling, TRPC6/7-mediated ganglion cell phototransduction, TRP/TRPL phototransduction in Drosophila and TRPV4-dependent osmoregulation, mechanotransduction, and regulation of inner and outer blood-retina barriers. TRP channels tune light-dependent and independent functions of retinal circuits by modulating the intracellular concentration of the 2nd messenger calcium, with emerging evidence implicating specific subunits in the pathogenesis of debilitating diseases such as glaucoma, ocular trauma, diabetic retinopathy, and ischemia. Elucidation of TRP channel involvement in retinal biology will yield rewards in terms of fundamental understanding of vertebrate vision and therapeutic targeting to treat diseases caused by channel dysfunction or over-activation.
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Affiliation(s)
- David Križaj
- Departments of Ophthalmology, Neurobiology, and Bioengineering, University of Utah, Salt Lake City, USA
| | - Soenke Cordeiro
- Institute of Physiology, Faculty of Medicine, Christian-Albrechts-University Kiel, Germany
| | - Olaf Strauß
- Experimental Ophthalmology, Department of Ophthalmology, Charité - Universitätsmedizin Berlin, a Corporate Member of Freie Universität, Humboldt-University, The Berlin Institute of Health, Berlin, Germany.
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Sokabe T, Bradshaw HB, Tominaga M, Leishman E, Chandel A, Montell C. Endocannabinoids produced in photoreceptor cells in response to light activate Drosophila TRP channels. Sci Signal 2022; 15:eabl6179. [PMID: 36219683 PMCID: PMC9633101 DOI: 10.1126/scisignal.abl6179] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Drosophila phototransduction is a model for signaling cascades that culminate in the activation of transient receptor potential (TRP) cation channels. TRP and TRPL are the canonical TRP (TRPC) channels that are regulated by light stimulation of rhodopsin and engagement of Gαq and phospholipase Cβ (PLC). Lipid metabolite(s) generated downstream of PLC are essential for the activation of the TRPC channels in photoreceptor cells. We sought to identify the key lipids produced subsequent to PLC stimulation that contribute to channel activation. Here, using genetics, lipid analysis, and Ca2+ imaging, we found that light increased the amount of an abundant endocannabinoid, 2-linoleoyl glycerol (2-LG), in vivo. The increase in 2-LG amounts depended on the PLC and diacylglycerol lipase encoded by norpA and inaE, respectively. This endocannabinoid facilitated TRPC-dependent Ca2+ influx in a heterologous expression system and in dissociated ommatidia from compound eyes. Moreover, 2-LG and mechanical stimulation cooperatively activated TRPC channels in ommatidia. We propose that 2-LG is a physiologically relevant endocannabinoid that activates TRPC channels in photoreceptor cells.
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Affiliation(s)
- Takaaki Sokabe
- Department of Molecular, Cellular, and Developmental Biology and the Neuroscience Research Institute, University of California, Santa Barbara; California 93106, USA
- Division of Cell Signaling, National Institute for Physiological Sciences, and Thermal Biology Group, Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences; Okazaki, Aichi, 444-8787, Japan
- Department of Physiological Sciences, SOKENDAI; Okazaki, Aichi, 444-8787, Japan
| | - Heather B. Bradshaw
- Department of Psychological and Brain Sciences, Indiana University; Bloomington, Indiana, 47405, USA
| | - Makoto Tominaga
- Division of Cell Signaling, National Institute for Physiological Sciences, and Thermal Biology Group, Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences; Okazaki, Aichi, 444-8787, Japan
- Department of Physiological Sciences, SOKENDAI; Okazaki, Aichi, 444-8787, Japan
| | - Emma Leishman
- Department of Psychological and Brain Sciences, Indiana University; Bloomington, Indiana, 47405, USA
| | - Avinash Chandel
- Department of Molecular, Cellular, and Developmental Biology and the Neuroscience Research Institute, University of California, Santa Barbara; California 93106, USA
| | - Craig Montell
- Department of Molecular, Cellular, and Developmental Biology and the Neuroscience Research Institute, University of California, Santa Barbara; California 93106, USA
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Minke B, Pak WL. The light-activated TRP channel: the founding member of the TRP channel superfamily. J Neurogenet 2022; 36:55-64. [PMID: 36217603 DOI: 10.1080/01677063.2022.2121824] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The Drosophila light-activated Transient Receptor Potential (TRP) channel is the founding member of a large and diverse family of channel proteins. The Drosophila TRP (dTRP) channel, which generates the electrical response to light has been investigated in a great detail two decades before the first mammalian TRP channel was discovered. Thus, dTRP is unique among members of the TRP channel superfamily because its physiological role and the enzymatic cascade underlying its activation are established. In this article we outline the research leading to elucidation of dTRP as the light activated channel and focus on a major physiological property of the dTRP channel, which is indirect activation via a cascade of enzymatic reactions. These detailed pioneering studies, based on the genetic dissection approach, revealed that light activation of the Drosophila TRP channel is mediated by G-Protein-Coupled Receptor (GPCR)-dependent enzymatic cascade, in which phospholipase C β (PLC) is a crucial component. This physiological mechanism of Drosophila TRP channel activation was later found in mammalian TRPC channels. However, the initial studies on the mammalian TRPV1 channel indicated that it is activated directly by capsaicin, low pH and hot temperature (>42 °C). This mechanism of activation was apparently at odds with the activation mechanism of the TRPC channels in general and the Drosophila light activated TRP/TRPL channels in particular, which are target of a GPCR-activated PLC cascade. Subsequent studies have indicated that under physiological conditions TRPV1 is also target of a GPCR-activated PLC cascade in the generation of inflammatory pain. The Drosophila light-activated TRP channel is still a useful experimental paradigm because its physiological function as the light-activated channel is known, powerful genetic techniques can be applied to its further analysis, and signaling molecules involved in the activation of these channels are available.
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Affiliation(s)
- Baruch Minke
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada (IMRIC), Edmond and Lily Safra Center for Brain Sciences (ELSC), Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| | - William L Pak
- Department of Biological Sciences, Purdue University, West Lafayette, IN, USA
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The Role of Membrane Lipids in Light-Activation of Drosophila TRP Channels. Biomolecules 2022; 12:biom12030382. [PMID: 35327573 PMCID: PMC8945425 DOI: 10.3390/biom12030382] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 02/21/2022] [Accepted: 02/23/2022] [Indexed: 12/28/2022] Open
Abstract
Transient Receptor Potential (TRP) channels constitute a large superfamily of polymodal channel proteins with diverse roles in many physiological and sensory systems that function both as ionotropic and metabotropic receptors. From the early days of TRP channel discovery, membrane lipids were suggested to play a fundamental role in channel activation and regulation. A prominent example is the Drosophila TRP and TRP-like (TRPL) channels, which are predominantly expressed in the visual system of Drosophila. Light activation of the TRP and TRPL channels, the founding members of the TRP channel superfamily, requires activation of phospholipase Cβ (PLC), which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into Diacylglycerol (DAG) and Inositol 1, 4,5-trisphosphate (IP3). However, the events required for channel gating downstream of PLC activation are still under debate and led to several hypotheses regarding the mechanisms by which lipids gate the channels. Despite many efforts, compelling evidence of the involvement of DAG accumulation, PIP2 depletion or IP3-mediated Ca2+ release in light activation of the TRP/TRPL channels are still lacking. Exogeneous application of poly unsaturated fatty acids (PUFAs), a product of DAG hydrolysis was demonstrated as an efficient way to activate the Drosophila TRP/TRPL channels. However, compelling evidence for the involvement of PUFAs in physiological light-activation of the TRP/TRPL channels is still lacking. Light-induced mechanical force generation was measured in photoreceptor cells prior to channel opening. This mechanical force depends on PLC activity, suggesting that the enzymatic activity of PLC converting PIP2 into DAG generates membrane tension, leading to mechanical gating of the channels. In this review, we will present the roles of membrane lipids in light activation of Drosophila TRP channels and present the many advantages of this model system in the exploration of TRP channel activation under physiological conditions.
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Chen Z, Kerwin M, Keenan O, Montell C. Conserved Modules Required for Drosophila TRP Function in Vivo. J Neurosci 2021; 41:5822-5832. [PMID: 34099505 PMCID: PMC8265800 DOI: 10.1523/jneurosci.0200-21.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2021] [Revised: 05/21/2021] [Accepted: 05/25/2021] [Indexed: 11/21/2022] Open
Abstract
Transient receptor potential (TRP) channels are broadly required in animals for sensory physiology. To provide insights into regulatory mechanisms, the structures of many TRPs have been solved. This has led to new models, some of which have been tested in vitro Here, using the classical TRP required for Drosophila visual transduction, we uncovered structural requirements for channel function in photoreceptor cells. Using a combination of molecular genetics, field recordings, protein expression analysis, and molecular modeling, we interrogated roles for the S4-S5 linker and the TRP domain, and revealed mutations in the S4-S5 linker that impair channel opening or closing. We also uncovered differential requirements for the two highly conserved motifs in the TRP domain for activation and protein stability. By performing genetic complementation, we found an intrasubunit interaction between the S4-S5 linker and the S5 segment that contributes to activation. This analysis highlights key structural requirements for TRP channel opening, closing, folding, and for intrasubunit interactions in a native context-Drosophila photoreceptor cells.SIGNIFICANCE STATEMENT The importance of TRP channels for sensory biology and human health has motivated tremendous effort in trying to understand the roles of the structural motifs essential for their activation, inactivation, and protein folding. In the current work, we have exploited the unique advantages of the Drosophila visual system to reveal mechanistic insights into TRP channel function in a native system-photoreceptor cells. Using a combination of electrophysiology (field recordings), cell biology, and molecular modeling, we have revealed roles of key motifs for activation, inactivation and protein folding of TRP in vivo.
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Affiliation(s)
- Zijing Chen
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California 93106
- Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California 93106
| | - Maggie Kerwin
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California 93106
- Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California 93106
| | - Orlaith Keenan
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California 93106
- Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California 93106
| | - Craig Montell
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California 93106
- Neuroscience Research Institute, University of California, Santa Barbara, Santa Barbara, California 93106
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Shieh BH, Nuzum L, Kristaponyte I. Exploring Excitotoxicity and Regulation of a Constitutively Active TRP Ca 2+ Channel in Drosophila. Fly (Austin) 2020; 15:8-27. [PMID: 33200658 DOI: 10.1080/19336934.2020.1851586] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Unregulated Ca2+ influx affects intracellular Ca2+ homoeostasis, which may lead to neuronal death. In Drosophila, following the activation of rhodopsin the TRP Ca2+ channel is open to mediate the light-dependent depolarization. A constitutively active TRP channel triggers the degeneration of TrpP365 /+ photoreceptors. To explore retinal degeneration, we employed a multidisciplinary approach including live imaging using GFP tagged actin and arrestin 2. Importantly, we demonstrate that the major rhodopsin (Rh1) was greatly reduced before the onset of rhabdomere degeneration; a great reduction of Rh1 affects the maintenance of rhabdomere leading to degeneration of photoreceptors. TrpP365 /+ also led to the up-regulation of CaMKII, which is beneficial as suppression of CaMKII accelerated retinal degeneration. We explored the regulation of TRP by investigating the genetic interaction between TrpP365 /+ and mutants affecting the turnover of diacylglycerol (DAG). We show a loss of phospholipase C in norpAP24 exhibited a great reduction of the DAG content delayed degeneration of TrpP365 /+ photoreceptors. In contrast, knockdown or mutations in DAG lipase (InaE) that is accompanied by slightly reduced levels of most DAG but an increased level of DAG 34:1, exacerbated retinal degeneration of TrpP365 /+. Together, our findings support the notion that DAG plays a role in regulating TRP. Interestingly, DAG lipase is likely required during photoreceptor development as TrpP365 /+; inaEN125 double mutants contained severely degenerated rhabdomeres.
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Affiliation(s)
- Bih-Hwa Shieh
- Department of Pharmacology, Center for Molecular Neuroscience and Vanderbilt Vision Research Center, Vanderbilt University , Nashville, TN, USA
| | - Lucinda Nuzum
- Department of Pharmacology, Center for Molecular Neuroscience and Vanderbilt Vision Research Center, Vanderbilt University , Nashville, TN, USA
| | - Inga Kristaponyte
- Department of Pharmacology, Center for Molecular Neuroscience and Vanderbilt Vision Research Center, Vanderbilt University , Nashville, TN, USA
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Ogueta M, Hardie RC, Stanewsky R. Light Sampling via Throttled Visual Phototransduction Robustly Synchronizes the Drosophila Circadian Clock. Curr Biol 2020; 30:2551-2563.e3. [PMID: 32502413 DOI: 10.1016/j.cub.2020.04.067] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 04/07/2020] [Accepted: 04/24/2020] [Indexed: 01/19/2023]
Abstract
The daily changes of light and dark exemplify a prominent cue for the synchronization of circadian clocks with the environment. The match between external and internal time is crucial for the fitness of organisms, and desynchronization has been linked to numerous physical and mental health problems. Organisms therefore developed complex and not fully understood mechanisms to synchronize their circadian clock to light. In mammals and in Drosophila, both the visual system and non-image-forming photoreceptors contribute to circadian clock resetting. In Drosophila, light-dependent degradation of the clock protein TIMELESS by the blue light photoreceptor Cryptochrome is considered the main mechanism for clock synchronization, although the visual system also contributes. To better understand the visual system contribution, we generated a genetic variant exhibiting extremely slow phototransduction kinetics, yet normal sensitivity. In this variant, the visual system is able to contribute its full share to circadian clock entrainment, both with regard to behavioral and molecular light synchronization. This function depends on an alternative phospholipase C-β enzyme, encoded by PLC21C, presumably playing a dedicated role in clock resetting. We show that this pathway requires the ubiquitin ligase CULLIN-3, possibly mediating CRY-independent degradation of TIMELESS during light:dark cycles. Our results suggest that the PLC21C-mediated contribution to circadian clock entrainment operates on a drastically slower timescale compared with fast, norpA-dependent visual phototransduction. Our findings are therefore consistent with the general idea that the visual system samples light over prolonged periods of time (h) in order to reliably synchronize their internal clocks with the external time.
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Affiliation(s)
- Maite Ogueta
- Institute of Neuro and Behavioral Biology, Westfälische Wilhelms University, 48149 Münster, Germany
| | - Roger C Hardie
- Department of Physiology, Development, and Neuroscience, Cambridge University, Cambridge CB2 3EG, UK
| | - Ralf Stanewsky
- Institute of Neuro and Behavioral Biology, Westfälische Wilhelms University, 48149 Münster, Germany.
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Ca2+ Signaling in Drosophila Photoreceptor Cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1131:857-879. [DOI: 10.1007/978-3-030-12457-1_34] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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11
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Light-Induced Opening of the TRP Channel in Isolated Membrane Patches Excised from Photosensitive Microvilli from Drosophila Photoreceptors. Neuroscience 2018; 396:66-72. [PMID: 30458219 DOI: 10.1016/j.neuroscience.2018.11.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2018] [Revised: 11/12/2018] [Accepted: 11/12/2018] [Indexed: 11/20/2022]
Abstract
Drosophila phototransduction occurs in light-sensitive microvilli arranged in a longitudinal structure of the photoreceptor, termed the rhabdomere. Rhodopsin (Rh), isomerized by light, couples to G-protein, which activates phospholipase C (PLC), which in turn cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) generating diacylglycerol (DAG), inositol trisphosphate and H+. This pathway opens the light-dependent channels, transient receptor potential (TRP) and transient receptor potential like (TRPL). PLC and TRP are held together in a protein assembly by the scaffold protein INAD. We report that the channels can be photoactivated in on-cell rhabdomeric patches and in excised patches by DAG. In excised patches, addition of PLC-activator, m-3M3FBS, or G-protein-activator, GTP-γ-S, opened TRP. These reagents were ineffective in PLC-mutant norpA and in the presence of PLC inhibitor U17322. However, DAG activated TRP even when PLC was pharmacologically or mutationally suppressed. These observations indicate that PLC, G-protein, and TRP were retained functional in these patches. DAG also activated TRP in the protein kinase C (PKC) mutant, inaC, excluding the possibility that PKC could mediate DAG-dependent TRP activation. Labeling diacylglycerol kinase (DGK) by fusion of fluorescent mCherry (mCherry-DGK) indicates that DGK, which returns DAG to dark levels, is highly expressed in the microvilli. In excised patches, TRP channels could be light-activated in the presence of GTP, which is required for G-protein activation. The evidence indicates that the proteins necessary for phototransduction are retained functionally after excision and that DAG is necessary and sufficient for TRP opening. This work opens up unique possibilities for studying, in sub-microscopic native membrane patches, the ubiquitous phosphoinositide signaling pathway and its regulatory mechanisms in unprecedented detail.
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Katz B, Minke B. The Drosophila light-activated TRP and TRPL channels - Targets of the phosphoinositide signaling cascade. Prog Retin Eye Res 2018; 66:200-219. [DOI: 10.1016/j.preteyeres.2018.05.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 04/29/2018] [Accepted: 05/02/2018] [Indexed: 01/28/2023]
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Steinritz D, Stenger B, Dietrich A, Gudermann T, Popp T. TRPs in Tox: Involvement of Transient Receptor Potential-Channels in Chemical-Induced Organ Toxicity-A Structured Review. Cells 2018; 7:cells7080098. [PMID: 30087301 PMCID: PMC6115949 DOI: 10.3390/cells7080098] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Revised: 07/24/2018] [Accepted: 07/31/2018] [Indexed: 12/28/2022] Open
Abstract
Chemicals can exhibit significant toxic properties. While for most compounds, unspecific cell damaging processes are assumed, a plethora of chemicals exhibit characteristic odors, suggesting a more specific interaction with the human body. During the last few years, G-protein-coupled receptors and especially chemosensory ion channels of the transient receptor potential family (TRP channels) were identified as defined targets for several chemicals. In some cases, TRP channels were suggested as being causal for toxicity. Therefore, these channels have moved into the spotlight of toxicological research. In this review, we screened available literature in PubMed that deals with the role of chemical-sensing TRP channels in specific organ systems. TRPA1, TRPM and TRPV channels were identified as essential chemosensors in the nervous system, the upper and lower airways, colon, pancreas, bladder, skin, the cardiovascular system, and the eyes. Regarding TRP channel subtypes, A1, M8, and V1 were found most frequently associated with toxicity. They are followed by V4, while other TRP channels (C1, C4, M5) are only less abundantly expressed in this context. Moreover, TRPA1, M8, V1 are co-expressed in most organs. This review summarizes organ-specific toxicological roles of TRP channels.
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Affiliation(s)
- Dirk Steinritz
- Bundeswehr Institute of Pharmacology and Toxicology, 80937 Munich, Germany.
- Walther-Straub-Institute of Pharmacology and Toxicology, Ludwig-Maximilians-Universität Munich, 80336 Munich, Germany.
| | - Bernhard Stenger
- Bundeswehr Institute of Pharmacology and Toxicology, 80937 Munich, Germany.
| | - Alexander Dietrich
- Walther-Straub-Institute of Pharmacology and Toxicology, Ludwig-Maximilians-Universität Munich, 80336 Munich, Germany.
| | - Thomas Gudermann
- Walther-Straub-Institute of Pharmacology and Toxicology, Ludwig-Maximilians-Universität Munich, 80336 Munich, Germany.
| | - Tanja Popp
- Bundeswehr Institute of Pharmacology and Toxicology, 80937 Munich, Germany.
- Walther-Straub-Institute of Pharmacology and Toxicology, Ludwig-Maximilians-Universität Munich, 80336 Munich, Germany.
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Laíns I, Kelly RS, Miller JB, Silva R, Vavvas DG, Kim IK, Murta JN, Lasky-Su J, Miller JW, Husain D. Human Plasma Metabolomics Study across All Stages of Age-Related Macular Degeneration Identifies Potential Lipid Biomarkers. Ophthalmology 2018; 125:245-254. [PMID: 28916333 PMCID: PMC8077680 DOI: 10.1016/j.ophtha.2017.08.008] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 08/01/2017] [Accepted: 08/07/2017] [Indexed: 12/24/2022] Open
Abstract
PURPOSE To characterize the plasma metabolomic profile of patients with age-related macular degeneration (AMD) using mass spectrometry (MS). DESIGN Cross-sectional observational study. PARTICIPANTS We prospectively recruited participants with a diagnosis of AMD and a control group (>50 years of age) without any vitreoretinal disease. METHODS All participants underwent color fundus photography, used for AMD diagnosis and staging, according to the Age-Related Eye Disease Study classification scheme. Fasting blood samples were collected and plasma was analyzed by Metabolon, Inc. (Durham, NC), using ultrahigh-performance liquid chromatography (UPLC) and high-resolution MS. Metabolon's hardware and software were used to identify peaks and control quality. Principal component analysis and multivariate regression were performed to assess differences in the metabolomic profiles of AMD patients versus controls, while controlling for potential confounders. For biological interpretation, pathway enrichment analysis of significant metabolites was performed using MetaboAnalyst. MAIN OUTCOME MEASURES The primary outcome measures were levels of plasma metabolites in participants with AMD compared with controls and among different AMD severity stages. RESULTS We included 90 participants with AMD (30 with early AMD, 30 with intermediate AMD, and 30 with late AMD) and 30 controls. Using UPLC and MS, 878 biochemicals were identified. Multivariate logistic regression identified 87 metabolites with levels that differed significantly between AMD patients and controls. Most of these metabolites (82.8%; n = 72), including the most significant metabolites, belonged to the lipid pathways. Analysis of variance revealed that of the 87 metabolites, 48 (55.2%) also were significantly different across the different stages of AMD. A significant enrichment of the glycerophospholipids pathway was identified (P = 4.7 × 10-9) among these metabolites. CONCLUSIONS Participants with AMD have altered plasma metabolomic profiles compared with controls. Our data suggest that the most significant metabolites map to the glycerophospholipid pathway. These findings have the potential to improve our understanding of AMD pathogenesis, to support the development of plasma-based metabolomics biomarkers of AMD, and to identify novel targets for treatment of this blinding disease.
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Affiliation(s)
- Inês Laíns
- Retina Service, Massachusetts Eye and Ear, Harvard Ophthalmology AMD Center of Excellence, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts; Faculty of Medicine, University of Coimbra, Coimbra, Portugal; Association for Innovation and Biomedical Research on Light, Association for Innovation and Biomedical Research on Light and Image (AIBILI), Coimbra, Portugal; Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal
| | - Rachel S Kelly
- Systems Genetics and Genomics Unit, Channing Division of Network Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts
| | - John B Miller
- Retina Service, Massachusetts Eye and Ear, Harvard Ophthalmology AMD Center of Excellence, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts
| | - Rufino Silva
- Faculty of Medicine, University of Coimbra, Coimbra, Portugal; Association for Innovation and Biomedical Research on Light, Association for Innovation and Biomedical Research on Light and Image (AIBILI), Coimbra, Portugal; Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal
| | - Demetrios G Vavvas
- Retina Service, Massachusetts Eye and Ear, Harvard Ophthalmology AMD Center of Excellence, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts
| | - Ivana K Kim
- Retina Service, Massachusetts Eye and Ear, Harvard Ophthalmology AMD Center of Excellence, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts
| | - Joaquim N Murta
- Faculty of Medicine, University of Coimbra, Coimbra, Portugal; Association for Innovation and Biomedical Research on Light, Association for Innovation and Biomedical Research on Light and Image (AIBILI), Coimbra, Portugal; Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal
| | - Jessica Lasky-Su
- Systems Genetics and Genomics Unit, Channing Division of Network Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts
| | - Joan W Miller
- Retina Service, Massachusetts Eye and Ear, Harvard Ophthalmology AMD Center of Excellence, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts
| | - Deeba Husain
- Retina Service, Massachusetts Eye and Ear, Harvard Ophthalmology AMD Center of Excellence, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts.
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Phototransduction in Drosophila Is Compromised by Gal4 Expression but not by InsP 3 Receptor Knockdown or Mutation. eNeuro 2017; 4:eN-NWR-0143-17. [PMID: 28660247 PMCID: PMC5483600 DOI: 10.1523/eneuro.0143-17.2017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 05/15/2017] [Indexed: 01/18/2023] Open
Abstract
Drosophila phototransduction is mediated by phospholipase C, leading to activation of transient receptor potential (TRP) and TRP-like (TRPL) channels by mechanisms that are unresolved. A role for InsP3 receptors (IP3Rs) had been excluded because IP3R mutants (itpr) appeared to have normal light responses; however, this was recently challenged by Kohn et al. (“Functional cooperation between the IP3 receptor and phospholipase C secures the high sensitivity to light of Drosophila photoreceptors in vivo,” Journal of Neuroscience 35:2530), who reported defects in phototransduction after IP3R-RNAi knockdown. They concluded that InsP3-induced Ca2+ release plays a critical role in facilitating channel activation, and that previous failure to detect IP3R phenotypes resulted from trace Ca2+ in electrodes substituting for InsP3-induced Ca2+ release. In an attempt to confirm this, we performed electroretinograms, whole-cell recordings, and GCaMP6f Ca2+ imaging from both IP3R-RNAi flies and itpr-null mutants. Like Kohn et al., we used GMRGal4 to drive expression of UAS-IP3R-RNAi, but we also used controls expressing GMRGal4 alone. We describe several GMRGal4 phenotypes suggestive of compromised development, including reductions in sensitivity, dark noise, potassium currents, and cell size and capacitance, as well as extreme variations in sensitivity between cells. However, we found no effect of IP3R RNAi or mutation on photoreceptor responses or Ca2+ signals, indicating that the IP3R plays little or no role in Drosophila phototransduction.
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16
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Katz B, Gutorov R, Rhodes-Mordov E, Hardie RC, Minke B. Electrophysiological Method for Whole-cell Voltage Clamp Recordings from Drosophila Photoreceptors. J Vis Exp 2017. [PMID: 28654039 PMCID: PMC5608386 DOI: 10.3791/55627] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Whole-cell voltage clamp recordings from Drosophila melanogaster photoreceptors have revolutionized the field of invertebrate visual transduction, enabling the use of D. melanogaster molecular genetics to study inositol-lipid signaling and Transient Receptor Potential (TRP) channels at the single-molecule level. A handful of labs have mastered this powerful technique, which enables the analysis of the physiological responses to light under highly controlled conditions. This technique allows control over the intracellular and extracellular media; the membrane voltage; and the fast application of pharmacological compounds, such as a variety of ionic or pH indicators, to the intra- and extracellular media. With an exceptionally high signal-to-noise ratio, this method enables the measurement of dark spontaneous and light-induced unitary currents (i.e. spontaneous and quantum bumps) and macroscopic Light-induced Currents (LIC) from single D. melanogaster photoreceptors. This protocol outlines, in great detail, all the key steps necessary to perform this technique, which includes both electrophysiological and optical recordings. The fly retina dissection procedure for the attainment of intact and viable ex vivo isolated ommatidia in the bath chamber is described. The equipment needed to perform whole-cell and fluorescence imaging measurements are also detailed. Finally, the pitfalls in using this delicate preparation during extended experiments are explained.
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Affiliation(s)
- Ben Katz
- Department of Medical Neurobiology, Faculty of Medicine and the Edmond and Lily Safra Center for Brain Sciences (ELSC), Hebrew University
| | - Rita Gutorov
- Department of Medical Neurobiology, Faculty of Medicine and the Edmond and Lily Safra Center for Brain Sciences (ELSC), Hebrew University
| | - Elisheva Rhodes-Mordov
- Department of Medical Neurobiology, Faculty of Medicine and the Edmond and Lily Safra Center for Brain Sciences (ELSC), Hebrew University
| | - Roger C Hardie
- Department of Physiology, Development and Neuroscience, University of Cambridge;
| | - Baruch Minke
- Department of Medical Neurobiology, Faculty of Medicine and the Edmond and Lily Safra Center for Brain Sciences (ELSC), Hebrew University;
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17
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Salem M, Bernach M, Bajdzienko K, Giavalisco P. A Simple Fractionated Extraction Method for the Comprehensive Analysis of Metabolites, Lipids, and Proteins from a Single Sample. J Vis Exp 2017. [PMID: 28605387 PMCID: PMC5608179 DOI: 10.3791/55802] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Understanding of complex biological systems requires the measurement, analysis and integration of multiple compound classes of the living cell, usually determined by transcriptomic, proteomic, metabolomics and lipidomic measurements. In this protocol, we introduce a simple method for the reproducible extraction of metabolites, lipids and proteins from biological tissues using a single aliquot per sample. The extraction method is based on a methyl tert-butyl ether: methanol: water system for liquid: liquid partitioning of hydrophobic and polar metabolites into two immiscible phases along with the precipitation of proteins and other macromolecules as a solid pellet. This method, therefore, provides three different fractions of specific molecular composition, which are fully compatible with common high throughput 'omics' technologies such as liquid chromatography (LC) or gas chromatography (GC) coupled to mass spectrometers. Even though the method was initially developed for the analysis of different plant tissue samples, it has proved to be fully compatible for the extraction and analysis of biological samples from systems as diverse as algae, insects, and mammalian tissues and cell cultures.
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Affiliation(s)
- Mohamed Salem
- Max Planck Institute of Molecular Plant Physiology, Golm, Germany; Department of Pharmacognosy, Faculty of Pharmacy, Cairo University
| | - Michal Bernach
- Max Planck Institute of Molecular Plant Physiology, Golm, Germany
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18
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Svobodova B, Groschner K. Reprint of "Mechanisms of lipid regulation and lipid gating in TRPC channels". Cell Calcium 2016; 60:133-41. [PMID: 27431463 DOI: 10.1016/j.ceca.2016.06.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Revised: 03/24/2016] [Accepted: 03/25/2016] [Indexed: 01/04/2023]
Abstract
TRPC proteins form cation channels that integrate and relay cellular signals by mechanisms involving lipid recognition and lipid-dependent gating. The lipohilic/amphiphilic molecules that function as cellular activators or modulators of TRPC proteins span a wide range of chemical structures. In this context, cellular redox balance is likely linked to the lipid recognition/gating features of TRPC channels. Both classical ligand-protein interactions as well as indirect and promiscuous sensory mechanisms have been proposed. Some of the recognition processes are suggested to involve ancillary lipid-binding scaffolds or regulators as well as dynamic protein-protein interactions determined by bilayer architecture. A complex interplay of protein-protein and protein-lipid interactions is likely to govern the gating and/or plasma membrane recruitment of TRPC channels, thereby providing a distinguished platform for signal integration and coincident signal detection. Both the primary molecular event(s) of lipid recognition by TRPC channels as well as the transformation of these events into distinct gating movements is poorly understood at the molecular level, and it remains elusive whether lipid sensing in TRPCs is conferred to a distinct sensor domain. Recent structural information on the molecular action of lipophilic activators in distantly related members of the TRP superfamily encourages speculations on TRPC gating mechanisms involved in lipid recognition/gating. This review aims to provide an update on the current understanding of the lipid-dependent control of TRPC channels with focus on the TRPC lipid sensing, signal-integration hub and a short discussion of potential links to redox signaling.
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Affiliation(s)
- Barbora Svobodova
- Institute of Biophysics, Medical University of Graz, A-8010 Graz, Austria
| | - Klaus Groschner
- Institute of Biophysics, Medical University of Graz, A-8010 Graz, Austria.
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19
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Mechanisms of lipid regulation and lipid gating in TRPC channels. Cell Calcium 2016; 59:271-9. [PMID: 27125985 DOI: 10.1016/j.ceca.2016.03.012] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Revised: 03/24/2016] [Accepted: 03/25/2016] [Indexed: 12/15/2022]
Abstract
TRPC proteins form cation channels that integrate and relay cellular signals by mechanisms involving lipid recognition and lipid-dependent gating. The lipohilic/amphiphilic molecules that function as cellular activators or modulators of TRPC proteins span a wide range of chemical structures. In this context, cellular redox balance is likely linked to the lipid recognition/gating features of TRPC channels. Both classical ligand-protein interactions as well as indirect and promiscuous sensory mechanisms have been proposed. Some of the recognition processes are suggested to involve ancillary lipid-binding scaffolds or regulators as well as dynamic protein-protein interactions determined by bilayer architecture. A complex interplay of protein-protein and protein-lipid interactions is likely to govern the gating and/or plasma membrane recruitment of TRPC channels, thereby providing a distinguished platform for signal integration and coincident signal detection. Both the primary molecular event(s) of lipid recognition by TRPC channels as well as the transformation of these events into distinct gating movements is poorly understood at the molecular level, and it remains elusive whether lipid sensing in TRPCs is conferred to a distinct sensor domain. Recent structural information on the molecular action of lipophilic activators in distantly related members of the TRP superfamily encourages speculations on TRPC gating mechanisms involved in lipid recognition/gating. This review aims to provide an update on the current understanding of the lipid-dependent control of TRPC channels with focus on the TRPC lipid sensing, signal-integration hub and a short discussion of potential links to redox signaling.
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20
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Salem MA, Jüppner J, Bajdzienko K, Giavalisco P. Protocol: a fast, comprehensive and reproducible one-step extraction method for the rapid preparation of polar and semi-polar metabolites, lipids, proteins, starch and cell wall polymers from a single sample. PLANT METHODS 2016; 12:45. [PMID: 27833650 PMCID: PMC5103428 DOI: 10.1186/s13007-016-0146-2] [Citation(s) in RCA: 117] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Accepted: 10/26/2016] [Indexed: 05/20/2023]
Abstract
BACKGROUND The elucidation of complex biological systems requires integration of multiple molecular parameters. Accordingly, high throughput methods like transcriptomics, proteomics, metabolomics and lipidomics have emerged to provide the tools for successful system-wide investigations. Unfortunately, optimized analysis of different compounds requires specific extraction procedures in combination with specific analytical instrumentation. However, the most efficient extraction protocols often only cover a restricted number of compounds due to the different physico-chemical properties of these biological compounds. Consequently, comprehensive analysis of several molecular components like polar primary metabolites next to lipids or proteins require multiple aliquots to enable the specific extraction procedures required to cover these diverse compound classes. This multi-parallel sample handling of different sample aliquots is therefore not only more sample intensive, it also requires more time and effort to obtain the required extracts. RESULTS To circumvent large sample amounts, distributed into several aliquots for the comprehensive extraction of most relevant biological compounds, we developed a simple, robust and reproducible two-phase liquid-liquid extraction protocol. This one-step extraction protocol allows for the analysis of polar-, semi-polar and hydrophobic metabolites, next to insoluble or precipitated compounds, including proteins, starch and plant cell wall components, from a single sample. The method is scalable regarding the used sample amounts but also the employed volumes and can be performed in microcentrifuge tubes, enabling high throughput analysis. The obtained fractions are fully compatible with common analytical methods, including spectroscopic, chromatographic and mass spectrometry-based techniques. To document the utility of the described protocol, we used 25 mg of Arabidopsis thaliana rosette leaves for the generation of multi-omics data sets, covering lipidomics, metabolomics and proteomics. The obtained data allowed us to measure and annotate more than 200 lipid compounds, 100 primary metabolites, 50 secondary metabolites and 2000 proteins. CONCLUSIONS The described extraction protocol provides a simple and straightforward method for the efficient extraction of lipids, metabolites and proteins from minute amounts of a single sample, enabling the targeted but also untargeted high-throughput analyses of diverse biological tissues and samples.
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Affiliation(s)
- Mohamed A. Salem
- Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
- Department of Pharmacognosy, Faculty of Pharmacy, Cairo University, Kasr El-Aini Street, Cairo, 11562 Egypt
| | - Jessica Jüppner
- Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
| | - Krzysztof Bajdzienko
- Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
| | - Patrick Giavalisco
- Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
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21
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Hardie RC, Juusola M. Phototransduction in Drosophila. Curr Opin Neurobiol 2015; 34:37-45. [DOI: 10.1016/j.conb.2015.01.008] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Accepted: 01/10/2015] [Indexed: 10/24/2022]
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22
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Ziegler AB, Ménagé C, Grégoire S, Garcia T, Ferveur JF, Bretillon L, Grosjean Y. Lack of Dietary Polyunsaturated Fatty Acids Causes Synapse Dysfunction in the Drosophila Visual System. PLoS One 2015; 10:e0135353. [PMID: 26308084 PMCID: PMC4550417 DOI: 10.1371/journal.pone.0135353] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 07/22/2015] [Indexed: 01/25/2023] Open
Abstract
Polyunsaturated fatty acids (PUFAs) are essential nutrients for animals and necessary for the normal functioning of the nervous system. A lack of PUFAs can result from the consumption of a deficient diet or genetic factors, which impact PUFA uptake and metabolism. Both can cause synaptic dysfunction, which is associated with numerous disorders. However, there is a knowledge gap linking these neuronal dysfunctions and their underlying molecular mechanisms. Because of its genetic manipulability and its easy, fast, and cheap breeding, Drosophila melanogaster has emerged as an excellent model organism for genetic screens, helping to identify the genetic bases of such events. As a first step towards the understanding of PUFA implications in Drosophila synaptic physiology we designed a breeding medium containing only very low amounts of PUFAs. We then used the fly’s visual system, a well-established model for studying signal transmission and neurological disorders, to measure the effects of a PUFA deficiency on synaptic function. Using both visual performance and eye electrophysiology, we found that PUFA deficiency strongly affected synaptic transmission in the fly’s visual system. These defects were rescued by diets containing omega-3 or omega-6 PUFAs alone or in combination. In summary, manipulating PUFA contents in the fly’s diet was powerful to investigate the role of these nutrients on the fly´s visual synaptic function. This study aims at showing how the first visual synapse of Drosophila can serve as a simple model to study the effects of PUFAs on synapse function. A similar approach could be further used to screen for genetic factors underlying the molecular mechanisms of synaptic dysfunctions associated with altered PUFA levels.
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Affiliation(s)
- Anna B. Ziegler
- CNRS, UMR6265 CSGA, 21000, Dijon, France
- INRA, UMR1324 CSGA, 21000, Dijon, France
- Université de Bourgogne-Franche-Comté, UMR CSGA, 21000, Dijon, France
- * E-mail: (ABZ); (YG)
| | - Cindy Ménagé
- CNRS, UMR6265 CSGA, 21000, Dijon, France
- INRA, UMR1324 CSGA, 21000, Dijon, France
- Université de Bourgogne-Franche-Comté, UMR CSGA, 21000, Dijon, France
| | - Stéphane Grégoire
- CNRS, UMR6265 CSGA, 21000, Dijon, France
- INRA, UMR1324 CSGA, 21000, Dijon, France
- Université de Bourgogne-Franche-Comté, UMR CSGA, 21000, Dijon, France
| | - Thibault Garcia
- CNRS, UMR6265 CSGA, 21000, Dijon, France
- INRA, UMR1324 CSGA, 21000, Dijon, France
- Université de Bourgogne-Franche-Comté, UMR CSGA, 21000, Dijon, France
| | - Jean-François Ferveur
- CNRS, UMR6265 CSGA, 21000, Dijon, France
- INRA, UMR1324 CSGA, 21000, Dijon, France
- Université de Bourgogne-Franche-Comté, UMR CSGA, 21000, Dijon, France
| | - Lionel Bretillon
- CNRS, UMR6265 CSGA, 21000, Dijon, France
- INRA, UMR1324 CSGA, 21000, Dijon, France
- Université de Bourgogne-Franche-Comté, UMR CSGA, 21000, Dijon, France
| | - Yael Grosjean
- CNRS, UMR6265 CSGA, 21000, Dijon, France
- INRA, UMR1324 CSGA, 21000, Dijon, France
- Université de Bourgogne-Franche-Comté, UMR CSGA, 21000, Dijon, France
- * E-mail: (ABZ); (YG)
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Calcium activates the light-dependent conductance in melanopsin-expressing photoreceptors of amphioxus. Proc Natl Acad Sci U S A 2015; 112:7845-50. [PMID: 26056310 DOI: 10.1073/pnas.1420265112] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Melanopsin, the photopigment of the "circadian" receptors that regulate the biological clock and the pupillary reflex in mammals, is homologous to invertebrate rhodopsins. Evidence supporting the involvement of phosphoinositides in light-signaling has been garnered, but the downstream effectors that control the light-dependent conductance remain unknown. Microvillar photoreceptors of the primitive chordate amphioxus also express melanopsin and transduce light via phospholipase-C, apparently not acting through diacylglycerol. We therefore examined the role of calcium in activating the photoconductance, using simultaneous, high time-resolution measurements of membrane current and Ca(2+) fluorescence. The light-induced calcium rise precedes the onset of the photocurrent, making it a candidate in the activation chain. Moreover, photolysis of caged Ca elicits an inward current of similar size, time course and pharmacology as the physiological photoresponse, but with a much shorter latency. Internally released calcium thus emerges as a key messenger to trigger the opening of light-dependent channels in melanopsin-expressing microvillar photoreceptors of early chordates.
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Functional cooperation between the IP3 receptor and phospholipase C secures the high sensitivity to light of Drosophila photoreceptors in vivo. J Neurosci 2015; 35:2530-46. [PMID: 25673847 DOI: 10.1523/jneurosci.3933-14.2015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Drosophila phototransduction is a model system for the ubiquitous phosphoinositide signaling. In complete darkness, spontaneous unitary current events (dark bumps) are produced by spontaneous single Gqα activation, while single-photon responses (quantum bumps) arise from synchronous activation of several Gqα molecules. We have recently shown that most of the spontaneous single Gqα activations do not produce dark bumps, because of a critical phospholipase Cβ (PLCβ) activity level required for bump generation. Surpassing the threshold of channel activation depends on both PLCβ activity and cellular [Ca(2+)], which participates in light excitation via a still unclear mechanism. We show here that in IP3 receptor (IP3R)-deficient photoreceptors, both light-activated Ca(2+) release from internal stores and light sensitivity were strongly attenuated. This was further verified by Ca(2+) store depletion, linking Ca(2+) release to light excitation. In IP3R-deficient photoreceptors, dark bumps were virtually absent and the quantum-bump rate was reduced, indicating that Ca(2+) release from internal stores is necessary to reach the critical level of PLCβ catalytic activity and the cellular [Ca(2+)] required for excitation. Combination of IP3R knockdown with reduced PLCβ catalytic activity resulted in highly suppressed light responses that were partially rescued by cellular Ca(2+) elevation, showing a functional cooperation between IP3R and PLCβ via released Ca(2+). These findings suggest that in contrast to the current dogma that Ca(2+) release via IP3R does not participate in light excitation, we show that released Ca(2+) plays a critical role in light excitation. The positive feedback between PLCβ and IP3R found here may represent a common feature of the inositol-lipid signaling.
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Speed and sensitivity of phototransduction in Drosophila depend on degree of saturation of membrane phospholipids. J Neurosci 2015; 35:2731-46. [PMID: 25673862 DOI: 10.1523/jneurosci.1150-14.2015] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Drosophila phototransduction is mediated via a G-protein-coupled PLC cascade. Recent evidence, including the demonstration that light evokes rapid contractions of the photoreceptors, suggested that the light-sensitive channels (TRP and TRPL) may be mechanically gated, together with protons released by PLC-mediated PIP2 hydrolysis. If mechanical gating is involved we predicted that the response to light should be influenced by altering the physical properties of the membrane. To achieve this, we used diet to manipulate the degree of saturation of membrane phospholipids. In flies reared on a yeast diet, lacking polyunsaturated fatty acids (PUFAs), mass spectrometry showed that the proportion of polyunsaturated phospholipids was sevenfold reduced (from 38 to ∼5%) but rescued by adding a single species of PUFA (linolenic or linoleic acid) to the diet. Photoreceptors from yeast-reared flies showed a 2- to 3-fold increase in latency and time to peak of the light response, without affecting quantum bump waveform. In the absence of Ca(2+) influx or in trp mutants expressing only TRPL channels, sensitivity to light was reduced up to ∼10-fold by the yeast diet, and essentially abolished in hypomorphic G-protein mutants (Gαq). PLC activity appeared little affected by the yeast diet; however, light-induced contractions measured by atomic force microscopy or the activation of ectopic mechanosensitive gramicidin channels were also slowed ∼2-fold. The results are consistent with mechanosensitive gating and provide a striking example of how dietary fatty acids can profoundly influence sensory performance in a classical G-protein-coupled signaling cascade.
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Molinari G. Is hydrogen ion (H(+)) the real second messenger in calcium signalling? Cell Signal 2015; 27:1392-7. [PMID: 25843778 DOI: 10.1016/j.cellsig.2015.03.023] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 03/10/2015] [Accepted: 03/23/2015] [Indexed: 11/28/2022]
Abstract
Most second messengers have the acknowledged ability to mobilize the segregated Ca(2+) from intracellular stores, although the mechanisms of mobilization are unclear. To study this problem, the fact that inositol 1,4,5-trisphosphate, and six other known endogenous Ca(2+) mobilizers are acids, or acid-generating compounds, is highlighted. In physiological conditions, a newly generated acid releases H(+). The transient rise of H(+) in the cytosol may induce the lowering of pH, mobilization of bound Ca(2+), protein conformational rearrangement, store depletion, and Ca(2+) influx. Accordingly, a new description of the basic mechanism for signal transduction in non-excitable cells and the related consequences is put forward.
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Affiliation(s)
- Giuliano Molinari
- Biochemical Specialist at Molinari Giuliano, Via Agrigento 56, 37138 Verona Italy.
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27
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Sato S, Kitamoto T, Sakai T. Modulation of innate and learned sexual behaviors by the TRP channel Painless expressed in the fruit fly brain: behavioral genetic analysis and its implications. Front Behav Neurosci 2014; 8:400. [PMID: 25520634 PMCID: PMC4251448 DOI: 10.3389/fnbeh.2014.00400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Accepted: 11/01/2014] [Indexed: 11/19/2022] Open
Abstract
Transient receptor potential (TRP) channels have attracted considerable attention because of their vital roles in primary sensory neurons, mediating responses to a wide variety of external environmental stimuli. However, much less is known about how TRP channels in the brain respond to intrinsic signals and are involved in neurophysiological processes that control complex behaviors. Painless (Pain) is the Drosophila TRP channel that was initially identified as a molecular sensor responsible for detecting noxious thermal and mechanical stimuli. Here, we review recent behavioral genetic studies demonstrating that Pain expressed in the brain plays a critical role in both innate and learned aspects of sexual behaviors. Several members of the TRP channel superfamily play evolutionarily conserved roles in sensory neurons as well as in other peripheral tissues. It is thus expected that brain TRP channels in vertebrates and invertebrates would have some common physiological functions. Studies of Pain in the Drosophila brain using a unique combination of genetics and physiological techniques should provide valuable insights into the fundamental principles concerning TRP channels expressed in the vertebrate and invertebrate brains.
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Affiliation(s)
- Shoma Sato
- Department of Biological Sciences, Tokyo Metropolitan University Hachiouji, Tokyo, Japan
| | - Toshihiro Kitamoto
- Department of Anesthesia and Pharmacology, University of Iowa Iowa City, Iowa, USA ; Interdisciplinary Graduate Programs in Genetics and Neuroscience, University of Iowa Iowa City, Iowa, USA
| | - Takaomi Sakai
- Department of Biological Sciences, Tokyo Metropolitan University Hachiouji, Tokyo, Japan
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