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O’Brien F, Feetham CH, Staunton CA, Hext K, Barrett-Jolley R. Temperature modulates PVN pre-sympathetic neurones via transient receptor potential ion channels. Front Pharmacol 2023; 14:1256924. [PMID: 37920211 PMCID: PMC10618372 DOI: 10.3389/fphar.2023.1256924] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Accepted: 10/03/2023] [Indexed: 11/04/2023] Open
Abstract
The paraventricular nucleus (PVN) of the hypothalamus plays a vital role in maintaining homeostasis and modulates cardiovascular function via autonomic pre-sympathetic neurones. We have previously shown that coupling between transient receptor potential cation channel subfamily V Member 4 (Trpv4) and small-conductance calcium-activated potassium channels (SK) in the PVN facilitate osmosensing, but since TRP channels are also thermosensitive, in this report we investigated the temperature sensitivity of these neurones. Methods: TRP channel mRNA was quantified from mouse PVN with RT-PCR and thermosensitivity of Trpv4-like PVN neuronal ion channels characterised with cell-attached patch-clamp electrophysiology. Following recovery of temperature-sensitive single-channel kinetic schema, we constructed a predictive stochastic mathematical model of these neurones and validated this with electrophysiological recordings of action current frequency. Results: 7 thermosensitive TRP channel genes were found in PVN punches. Trpv4 was the most abundant of these and was identified at the single channel level on PVN neurones. We investigated the thermosensitivity of these Trpv4-like channels; open probability (Po) markedly decreased when temperature was decreased, mediated by a decrease in mean open dwell times. Our neuronal model predicted that PVN spontaneous action current frequency (ACf) would increase as temperature is decreased and in our electrophysiological experiments, we found that ACf from PVN neurones was significantly higher at lower temperatures. The broad-spectrum channel blocker gadolinium (100 µM), was used to block the warm-activated, Ca2+-permeable Trpv4 channels. In the presence of gadolinium (100 µM), the temperature effect was largely retained. Using econazole (10 µM), a blocker of Trpm2, we found there were significant increases in overall ACf and the temperature effect was inhibited. Conclusion: Trpv4, the abundantly transcribed thermosensitive TRP channel gene in the PVN appears to contribute to intrinsic thermosensitive properties of PVN neurones. At physiological temperatures (37°C), we observed relatively low ACf primarily due to the activity of Trpm2 channels, whereas at room temperature, where most of the previous characterisation of PVN neuronal activity has been performed, ACf is much higher, and appears to be predominately due to reduced Trpv4 activity. This work gives insight into the fundamental mechanisms by which the body decodes temperature signals and maintains homeostasis.
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Affiliation(s)
| | | | | | | | - Richard Barrett-Jolley
- Department of Musculoskeletal Ageing Science, Faculty of Health and Life Sciences, University of Liverpool, Liverpool, United Kingdom
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2
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Talbot F, Feetham CH, Mokrosiński J, Lawler K, Keogh JM, Henning E, Mendes de Oliveira E, Ayinampudi V, Saeed S, Bonnefond A, Arslan M, Yeo GSH, Froguel P, Bechtold DA, Adamson A, Humphreys N, Barroso I, Luckman SM, Farooqi IS. A rare human variant that disrupts GPR10 signalling causes weight gain in mice. Nat Commun 2023; 14:1450. [PMID: 36922513 PMCID: PMC10017677 DOI: 10.1038/s41467-023-36966-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 02/23/2023] [Indexed: 03/17/2023] Open
Abstract
Disruption of brain-expressed G protein-coupled receptor-10 (GPR10) causes obesity in animals. Here, we identify multiple rare variants in GPR10 in people with severe obesity and in normal weight controls. These variants impair ligand binding and G protein-dependent signalling in cells. Transgenic mice harbouring a loss of function GPR10 variant found in an individual with obesity, gain excessive weight due to decreased energy expenditure rather than increased food intake. This evidence supports a role for GPR10 in human energy homeostasis. Therapeutic targeting of GPR10 may represent an effective weight-loss strategy.
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Affiliation(s)
- Fleur Talbot
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK
| | - Claire H Feetham
- Division of Diabetes, Endocrinology and Gastroenterology, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Jacek Mokrosiński
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK
| | - Katherine Lawler
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK
| | - Julia M Keogh
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK
| | - Elana Henning
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK
| | - Edson Mendes de Oliveira
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK
| | - Vikram Ayinampudi
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK
| | - Sadia Saeed
- Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
- Inserm UMR1283, CNRS UMR8199, European Genomic Institute for Diabetes (EGID), Institut Pasteur de Lille, Lille University Hospital, Lille, 59000, France
- Université de Lille, Lille, 59000, France
| | - Amélie Bonnefond
- Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
- Inserm UMR1283, CNRS UMR8199, European Genomic Institute for Diabetes (EGID), Institut Pasteur de Lille, Lille University Hospital, Lille, 59000, France
- Université de Lille, Lille, 59000, France
| | - Mohammed Arslan
- School of Life Sciences, Forman Christian College, Lahore, Pakistan
| | - Giles S H Yeo
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK
- MRC Metabolic Diseases Unit, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK
| | - Philippe Froguel
- Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
- Inserm UMR1283, CNRS UMR8199, European Genomic Institute for Diabetes (EGID), Institut Pasteur de Lille, Lille University Hospital, Lille, 59000, France
- Université de Lille, Lille, 59000, France
| | - David A Bechtold
- Division of Diabetes, Endocrinology and Gastroenterology, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Antony Adamson
- Genome Editing Unit, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Neil Humphreys
- Genome Editing Unit, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Inês Barroso
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK
- MRC Epidemiology Unit, University of Cambridge, Cambridge, UK
- Exeter Centre of Excellence for Diabetes Research (ExCEED), University of Exeter Medical School, Exeter, UK
| | - Simon M Luckman
- Division of Diabetes, Endocrinology and Gastroenterology, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK.
| | - I Sadaf Farooqi
- University of Cambridge Metabolic Research Laboratories and NIHR Cambridge Biomedical Research Centre, Wellcome-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ, UK.
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Worth AA, Shoop R, Tye K, Feetham CH, D'Agostino G, Dodd GT, Reimann F, Gribble FM, Beebe EC, Dunbar JD, Alexander-Chacko JT, Sindelar DK, Coskun T, Emmerson PJ, Luckman SM. The cytokine GDF15 signals through a population of brainstem cholecystokinin neurons to mediate anorectic signalling. eLife 2020; 9:55164. [PMID: 32723474 PMCID: PMC7410488 DOI: 10.7554/elife.55164] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 07/26/2020] [Indexed: 02/02/2023] Open
Abstract
The cytokine, GDF15, is produced in pathological states which cause cellular stress, including cancer. When over expressed, it causes dramatic weight reduction, suggesting a role in disease-related anorexia. Here, we demonstrate that the GDF15 receptor, GFRAL, is located in a subset of cholecystokinin neurons which span the area postrema and the nucleus of the tractus solitarius of the mouse. GDF15 activates GFRALAP/NTS neurons and supports conditioned taste and place aversions, while the anorexia it causes can be blocked by a monoclonal antibody directed at GFRAL or by disrupting CCK neuronal signalling. The cancer-therapeutic drug, cisplatin, induces the release of GDF15 and activates GFRALAP/NTS neurons, as well as causing significant reductions in food intake and body weight in mice. These metabolic effects of cisplatin are abolished by pre-treatment with the GFRAL monoclonal antibody. Our results suggest that GFRAL neutralising antibodies or antagonists may provide a co-treatment opportunity for patients undergoing chemotherapy.
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Affiliation(s)
- Amy A Worth
- Faculty of Biology, Medicine and Health, The University of ManchesterManchesterUnited Kingdom
| | - Rosemary Shoop
- Faculty of Biology, Medicine and Health, The University of ManchesterManchesterUnited Kingdom
| | - Katie Tye
- Faculty of Biology, Medicine and Health, The University of ManchesterManchesterUnited Kingdom
| | - Claire H Feetham
- Faculty of Biology, Medicine and Health, The University of ManchesterManchesterUnited Kingdom
| | - Giuseppe D'Agostino
- Faculty of Biology, Medicine and Health, The University of ManchesterManchesterUnited Kingdom,Rowett Institute, University of AberdeenAberdeenUnited Kingdom
| | - Garron T Dodd
- School of Biomedical Sciences, The University of MelbourneVictoriaAustralia
| | - Frank Reimann
- Institute of Metabolic Science, Addenbrooke’s HospitalCambridgeUnited Kingdom
| | - Fiona M Gribble
- Institute of Metabolic Science, Addenbrooke’s HospitalCambridgeUnited Kingdom
| | - Emily C Beebe
- Lilly Research Laboratories, Eli Lilly & CompanyIndianapolisUnited States
| | - James D Dunbar
- Lilly Research Laboratories, Eli Lilly & CompanyIndianapolisUnited States
| | | | - Dana K Sindelar
- Lilly Research Laboratories, Eli Lilly & CompanyIndianapolisUnited States
| | - Tamer Coskun
- Lilly Research Laboratories, Eli Lilly & CompanyIndianapolisUnited States
| | - Paul J Emmerson
- Lilly Research Laboratories, Eli Lilly & CompanyIndianapolisUnited States
| | - Simon M Luckman
- Faculty of Biology, Medicine and Health, The University of ManchesterManchesterUnited Kingdom
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Feetham CH, O'Brien F, Barrett-Jolley R. Ion Channels in the Paraventricular Hypothalamic Nucleus (PVN); Emerging Diversity and Functional Roles. Front Physiol 2018; 9:760. [PMID: 30034342 PMCID: PMC6043726 DOI: 10.3389/fphys.2018.00760] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2018] [Accepted: 05/30/2018] [Indexed: 12/11/2022] Open
Abstract
The paraventricular nucleus of the hypothalamus (PVN) is critical for the regulation of homeostatic function. Although also important for endocrine regulation, it has been referred to as the "autonomic master controller." The emerging consensus is that the PVN is a multifunctional nucleus, with autonomic roles including (but not limited to) coordination of cardiovascular, thermoregulatory, metabolic, circadian and stress responses. However, the cellular mechanisms underlying these multifunctional roles remain poorly understood. Neurones from the PVN project to and can alter the function of sympathetic control regions in the medulla and spinal cord. Dysfunction of sympathetic pre-autonomic neurones (typically hyperactivity) is linked to several diseases including hypertension and heart failure and targeting this region with specific pharmacological or biological agents is a promising area of medical research. However, to facilitate future medical exploitation of the PVN, more detailed models of its neuronal control are required; populated by a greater compliment of constituent ion channels. Whilst the cytoarchitecture, projections and neurotransmitters present in the PVN are reasonably well documented, there have been fewer studies on the expression and interplay of ion channels. In this review we bring together an up to date analysis of PVN ion channel studies and discuss how these channels may interact to control, in particular, the activity of the sympathetic system.
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Affiliation(s)
- Claire H Feetham
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom
| | - Fiona O'Brien
- Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, United Kingdom
| | - Richard Barrett-Jolley
- Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, United Kingdom
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Khodai T, Nunn N, Worth AA, Feetham CH, Belle MDC, Piggins HD, Luckman SM. PACAP Neurons in the Ventromedial Hypothalamic Nucleus Are Glucose Inhibited and Their Selective Activation Induces Hyperglycaemia. Front Endocrinol (Lausanne) 2018; 9:632. [PMID: 30425681 PMCID: PMC6218416 DOI: 10.3389/fendo.2018.00632] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Accepted: 10/05/2018] [Indexed: 01/22/2023] Open
Abstract
Background: Glucose-sensing neurons are located in several parts of the brain, but are concentrated in the ventromedial nucleus of the hypothalamus (VMH). The importance of these VMH neurons in glucose homeostasis is well-established, however, little is known about their individual identity. In the present study, we identified a distinct glucose-sensing population in the VMH and explored its place in the glucose-regulatory network. Methods: Using patch-clamp electrophysiology on Pacap-cre::EYFP cells, we explored the glucose-sensing ability of the pituitary adenylate cyclase-activating peptide (PACAP) neurons both inside and outside the VMH. We also mapped the efferent projections of these neurons using anterograde and retrograde tracing techniques. Finally, to test the functionality of PACAPVMH in vivo, we used DREADD technology and measured systemic responses. Results: We demonstrate that PACAP neurons inside (PACAPVMH), but not outside the VMH are intrinsically glucose inhibited (GI). Anatomical tracing techniques show that PACAPVMH neurons project to several areas that can influence autonomic output. In vivo, chemogenetic stimulation of these neurons inhibits insulin secretion leading to reduced glucose tolerance, implicating their role in systemic glucose regulation. Conclusion: These findings are important as they identify, for the first time, a specific VMH neuronal population involved in glucose homeostasis. Identifying the different glucose-sensing populations in the VMH will help piece together the different arms of glucose regulation providing vital information regarding central responses to glucose metabolic disorders including hypoglycaemia.
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Affiliation(s)
- Tansi Khodai
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom
| | - Nicolas Nunn
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom
| | - Amy A. Worth
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom
| | - Claire H. Feetham
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom
| | | | - Hugh D. Piggins
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom
| | - Simon M. Luckman
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom
- *Correspondence: Simon M. Luckman
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Wibberley A, Staunton CA, Feetham CH, Vereninov AA, Barrett-Jolley R. An in vitro model of skeletal muscle volume regulation. PLoS One 2015; 10:e0127889. [PMID: 26029913 PMCID: PMC4452315 DOI: 10.1371/journal.pone.0127889] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Accepted: 04/20/2015] [Indexed: 11/18/2022] Open
Abstract
INTRODUCTION Hypertonic media causes cells to shrink due to water loss through aquaporin channels. After acute shrinkage, cells either regulate their volume or, alternatively, undergo a number of metabolic changes which ultimately lead to cell death. In many cell types, hypertonic shrinkage is followed by apoptosis. Due to the complex 3D morphology of skeletal muscle and the difficulty in obtaining isolated human tissue, we have begun skeletal muscle volume regulation studies using the human skeletal muscle cell line TE671RD. In this study we investigated whether hypertonic challenge of the human skeletal muscle cell line TE671RD triggered cell death or evoked a cell volume recovery response. METHODS The cellular volume of TE671RD cells was calculated from the 2D surface area. Cell death was assessed by both the trypan blue live/dead assay and the TUNEL assay. RESULTS Medium osmolality was increased by addition of up to 200 mM sucrose. Addition of 200 mM sucrose resulted in mean cell shrinkage of 44±1% after 30 mins. At later time points (2 and 4 hrs) two separate cell subpopulations with differing mean cell volume became apparent. The first subpopulation (15±2% of the total cell number) continued to shrink whereas the second subpopulation had an increased cell volume. Cell death was observed in a small proportion of cells (approximately 6-8%). CONCLUSION We have established that a substantial proportion of TE671RD cells respond to hypertonic challenge with RVI, but that these cells are resistant to hypertonicity triggered cell death.
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Affiliation(s)
- Anna Wibberley
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, United Kingdom
| | - Caroline A. Staunton
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, United Kingdom
| | - Claire H. Feetham
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, United Kingdom
| | - Alexey A. Vereninov
- Laboratory of Cell Physiology, Institute of Cytology, Russian Academy of Sciences, St-Petersburg, Russia
| | - Richard Barrett-Jolley
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, United Kingdom
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Feetham CH, Nunn N, Barrett-Jolley R. The depressor response to intracerebroventricular hypotonic saline is sensitive to TRPV4 antagonist RN1734. Front Pharmacol 2015; 6:83. [PMID: 25954200 PMCID: PMC4407506 DOI: 10.3389/fphar.2015.00083] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Accepted: 04/02/2015] [Indexed: 11/18/2022] Open
Abstract
Several reports have shown that the periventricular region of the brain, including the paraventricular nucleus (PVN), is critical to sensing and responding to changes in plasma osmolality. Further studies also implicate the transient receptor potential ion channel, type V4 (TRPV4) channel in this homeostatic behavior. In previous work we have shown that TRPV4 ion channels couple to calcium-activated potassium channels in the PVN to decrease action potential firing frequency in response to hypotonicity. In the present study we investigated whether, similarly, intracerebroventricular (ICV) application of hypotonic solutions modulated cardiovascular parameters, and if so whether this was sensitive to a TRPV4 channel inhibitor. We found that ICV injection of 270 mOsmol artificial cerebrospinal fluid (ACSF) decreased mean blood pressure, but not heart rate, compared to naïve mice or mice injected with 300 mOsmol ACSF. This effect was abolished by treatment with the TRPV4 inhibitor RN1734. These data suggest that periventricular targets within the brain are capable of generating depressor action in response to TRPV4 ion channel activation. Potentially, in the future, the TRPV4 channel, or the TRPV4–KCa coupling mechanism, may serve as a therapeutic target for treatment of cardiovascular disease.
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Affiliation(s)
- Claire H Feetham
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool Liverpool, UK
| | - Nicolas Nunn
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool Liverpool, UK
| | - Richard Barrett-Jolley
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool Liverpool, UK
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Feetham CH, Nunn N, Lewis R, Dart C, Barrett-Jolley R. TRPV4 and K(Ca) ion channels functionally couple as osmosensors in the paraventricular nucleus. Br J Pharmacol 2015; 172:1753-68. [PMID: 25421636 PMCID: PMC4376454 DOI: 10.1111/bph.13023] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Revised: 11/13/2014] [Accepted: 11/16/2014] [Indexed: 12/04/2022] Open
Abstract
BACKGROUND AND PURPOSE Transient receptor potential vanilloid type 4 (TRPV4) and calcium-activated potassium channels (KCa ) mediate osmosensing in many tissues. Both TRPV4 and KCa channels are found in the paraventricular nucleus (PVN) of the hypothalamus, an area critical for sympathetic control of cardiovascular and renal function. Here, we have investigated whether TRPV4 channels functionally couple to KCa channels to mediate osmosensing in PVN parvocellular neurones and have characterized, pharmacologically, the subtype of KCa channel involved. EXPERIMENTAL APPROACH We investigated osmosensing roles for TRPV4 and KCa channels in parvocellular PVN neurones using cell-attached and whole-cell electrophysiology in mouse brain slices and rat isolated PVN neurons. Intracellular Ca(2+) was recorded using Fura-2AM. The system was modelled in the NEURON simulation environment. KEY RESULTS Hypotonic saline reduced action current frequency in hypothalamic slices; a response mimicked by TRPV4 channel agonists 4αPDD (1 μM) and GSK1016790A (100 nM), and blocked by inhibitors of either TRPV4 channels (RN1734 (5 μM) and HC067047 (300 nM) or the low-conductance calcium-activated potassium (SK) channel (UCL-1684 30 nM); iberiotoxin and TRAM-34 had no effect. Our model was compatible with coupling between TRPV4 and KCa channels, predicting the presence of positive and negative feedback loops. These predictions were verified using isolated PVN neurons. Both hypotonic challenge and 4αPDD increased intracellular Ca(2+) and UCL-1684 reduced the action of hypotonic challenge. CONCLUSIONS AND IMPLICATIONS There was functional coupling between TRPV4 and SK channels in parvocellular neurones. This mechanism contributes to osmosensing in the PVN and may provide a novel pharmacological target for the cardiovascular or renal systems.
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Affiliation(s)
- C H Feetham
- Institute of Ageing and Chronic Disease, Faculty of Health & Life Sciences, University of LiverpoolLiverpool, L69 3GA, UK
| | - N Nunn
- Faculty of Life Sciences, University of ManchesterManchester, M13 9PT, UK
| | - R Lewis
- Institute of Ageing and Chronic Disease, Faculty of Health & Life Sciences, University of LiverpoolLiverpool, L69 3GA, UK
| | - C Dart
- Institute of Ageing and Chronic Disease, Faculty of Health & Life Sciences, University of LiverpoolLiverpool, L69 3GA, UK
| | - R Barrett-Jolley
- Institute of Ageing and Chronic Disease, Faculty of Health & Life Sciences, University of LiverpoolLiverpool, L69 3GA, UK
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Feetham CH, Barrett-Jolley R. NK1-receptor-expressing paraventricular nucleus neurones modulate daily variation in heart rate and stress-induced changes in heart rate variability. Physiol Rep 2014; 2:e12207. [PMID: 25472606 PMCID: PMC4332202 DOI: 10.14814/phy2.12207] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The paraventricular nucleus of the hypothalamus (PVN) is an established center of cardiovascular control, receiving projections from other nuclei of the hypothalamus such as the dorsomedial hypothalamus and the suprachiasmatic nucleus. The PVN contains a population of "pre-autonomic neurones" which project to the intermediolateralis of the spinal cord and increase sympathetic activity, blood pressure, and heart rate. These spinally projecting neurones express a number of membrane receptors including GABA and substance P NK1 receptors. Activation of NK1-expressing neurones increases heart rate, blood pressure, and sympathetic activity. However, their role in the pattern of overall cardiovascular control remains unknown. In this work, we use specific saporin lesion of NK1-expressing PVN rat neurones with SSP-SAP and telemetrically measure resting heart rate and heart rate variability (HRV) parameters in response to mild psychological stress. The HRV parameter "low frequency/high frequency ratio" is often used as an indicator of sympathetic activity and is significantly increased with psychological stress in control rats (0.84 ± 0.14 to 2.02 ± 0.15; P < 0.001; n = 3). We find the stress-induced increase in this parameter to be blunted in the SSP-SAP-lesioned rats (0.83 ± 0.09 to 0.93 ± 0.21; P > 0.05; n = 3). We also find a shift in daily variation of heart rate rhythm and conclude that NK1-expressing PVN neurones are involved with coupling of the cardiovascular system to daily heart rate variation and the sympathetic response to psychological stress.
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Affiliation(s)
- Claire H Feetham
- Institute of Ageing and Chronic Disease, Centre for Integrative Mammalian Biology, University of Liverpool, Liverpool, UK
| | - Richard Barrett-Jolley
- Institute of Ageing and Chronic Disease, Centre for Integrative Mammalian Biology, University of Liverpool, Liverpool, UK
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Nunn N, Feetham CH, Martin J, Barrett-Jolley R, Plagge A. Elevated blood pressure, heart rate and body temperature in mice lacking the XLαs protein of the Gnas locus is due to increased sympathetic tone. Exp Physiol 2013; 98:1432-45. [PMID: 23748904 PMCID: PMC4223506 DOI: 10.1113/expphysiol.2013.073064] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Imbalances of energy homeostasis are often associated with cardiovascular complications. Previous work has shown that Gnasxl-deficient mice have a lean and hypermetabolic phenotype, with increased sympathetic stimulation of adipose tissue. The Gnasxl transcript from the imprinted Gnas locus encodes the trimeric G-protein subunit XLαs, which is expressed in brain regions that regulate energy homeostasis and sympathetic nervous system (SNS) activity. To determine whether Gnasxl knock-out (KO) mice display additional SNS-related phenotypes, we have now investigated the cardiovascular system. The Gnasxl KO mice were ∼20 mmHg hypertensive in comparison to wild-type (WT) littermates (P ≤ 0.05) and hypersensitive to the sympatholytic drug reserpine. Using telemetry, we detected an increased waking heart rate in conscious KOs (630 ± 10 versus 584 ± 12 beats min(-1), KO versus WT, P ≤ 0.05). Body temperature was also elevated (38.1 ± 0.3 versus 36.9 ± 0.4°C, KO versus WT, P ≤ 0.05). To investigate autonomic nervous system influences, we used heart rate variability analyses. We empirically defined frequency power bands using atropine and reserpine and verified high-frequency (HF) power and low-frequency (LF) LF/HF power ratio to be indicators of parasympathetic and sympathetic activity, respectively. The LF/HF power ratio was greater in KOs and more sensitive to reserpine than in WTs, consistent with elevated SNS activity. In contrast, atropine and exendin-4, a centrally acting agonist of the glucagon-like peptide-1 receptor, which influences cardiovascular physiology and metabolism, reduced HF power equally in both genotypes. This was associated with a greater increase in heart rate in KOs. Mild stress had a blunted effect on the LF/HF ratio in KOs consistent with elevated basal sympathetic activity. We conclude that XLαs is required for the inhibition of sympathetic outflow towards cardiovascular and metabolically relevant tissues.
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Affiliation(s)
- Nicolas Nunn
- A. Plagge: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, UK. . R. Barrett-Jolley: Institute of Ageing and Chronic Disease, 4th floor UCD Building, University of Liverpool, Daulby Str., Liverpool, L69 3GA, UK.
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Lewis R, Feetham CH, Gentles L, Penny J, Tregilgas L, Tohami W, Mobasheri A, Barrett-Jolley R. Benzamil sensitive ion channels contribute to volume regulation in canine chondrocytes. Br J Pharmacol 2013; 168:1584-96. [PMID: 22928819 PMCID: PMC3605868 DOI: 10.1111/j.1476-5381.2012.02185.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2011] [Revised: 07/20/2012] [Accepted: 07/29/2012] [Indexed: 12/02/2022] Open
Abstract
BACKGROUND AND PURPOSE Chondrocytes exist within cartilage and serve to maintain the extracellular matrix. It has been postulated that osteoarthritic (OA) chondrocytes lose the ability to regulate their volume, affecting extracellular matrix production. In previous studies, we identified expression of epithelial sodium channels (ENaC) in human chondrocytes, but their function remained unknown. Although ENaC typically has Na(+) transport roles, it is also involved in the cell volume regulation of rat hepatocytes. ENaC is a member of the degenerin (Deg) family, and ENaC/Deg-like channels have a low conductance and high sensitivity to benzamil. In this study, we investigated whether canine chondrocytes express functional ENaC/Deg-like ion channels and, if so, what their function may be. EXPERIMENTAL APPROACH Canine chondrocytes were harvested from dogs killed for unassociated welfare reasons. We used immunohistochemistry and patch-clamp electrophysiology to investigate ENaC expression and video microscopy to analyse the effects of pharmacological inhibition of ENaC/Deg on cell volume regulation. KEY RESULTS Immunofluorescence showed that canine chondrocytes expressed ENaC protein. Single-channel recordings demonstrated expression of a benzamil-sensitive Na(+) conductance (9 pS), and whole-cell experiments show this to be approximately 1.5 nS per cell with high selectivity for Na(+) . Benzamil hyperpolarized chondrocytes by approximately 8 mV with a pD2 8.4. Chondrocyte regulatory volume decrease (RVI) was inhibited by benzamil (pD2 7.5) but persisted when extracellular Na(+) ions were replaced by Li(+) . CONCLUSION AND IMPLICATIONS Our data suggest that benzamil inhibits RVI by reducing the influx of Na(+) ions through ENaC/Deg-like ion channels and present ENaC/Deg as a possible target for pharmacological modulation of chondrocyte volume.
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Affiliation(s)
- R Lewis
- Musculoskeletal Biology, CIMA, Faculty of Health & Life Sciences, University of Liverpool, Liverpool, UK
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Abstract
Chondrocytes are the cells within cartilage which produce and maintain the extracellular matrix. Volume regulation in these cells is vital to their function and occurs in several different physiological and pathological contexts. Firstly, chondrocytes exist within an environment of changing osmolarity and compressive loads. Secondly, in osteoarthritic joint failure, cartilage water content changes and there is a notable increase in chondrocyte apoptosis. Thirdly, endochondral ossification requires chondrocyte swelling in association with hypertrophy. Regulatory volume decrease (RVD) and regulatory volume increase (RVI) have both been observed in articular chondrocytes and this review focuses on the mechanisms identified to account for these. There has been evidence so far to suggest TRPV4 is central to RVD; however other elements of the pathway have not yet been identified. Unlike RVD, RVI appears less robust in articular chondrocytes and there have been fewer mechanistic studies; the primary focus being on the Na(+)-K(+)-2Cl(-) co-transporter. The clinical significance of chondrocyte volume regulation remains unproven. Importantly however, transcript abundances of several ion channels implicated in volume control are changed in chondrocytes from osteoarthritic cartilage. A critical question is whether disturbances of volume regulation mechanisms lead to, result from or are simply coincidental to cartilage damage.
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Affiliation(s)
- Rebecca Lewis
- Department of Musculoskeletal Biology, Faculty of Health and Life Sciences, University of Liverpool, Liverpool, UK
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