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Sancho M, Klug NR, Harraz OF, Hill-Eubanks D, Nelson MT. Distinct potassium channel types in brain capillary pericytes. Biophys J 2024:S0006-3495(24)00169-3. [PMID: 38444160 DOI: 10.1016/j.bpj.2024.03.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 01/25/2024] [Accepted: 03/01/2024] [Indexed: 03/07/2024] Open
Abstract
Capillaries, composed of electrically coupled endothelial cells and overlying pericytes, constitute the vast majority of blood vessels in the brain. The most arteriole-proximate three to four branches of the capillary bed are covered by α-actin-expressing, contractile pericytes. These mural cells have a distinctive morphology and express different markers compared with their smooth muscle cell (SMC) cousins but share similar excitation-coupling contraction machinery. Despite this similarity, pericytes are considerably more depolarized than SMCs at low intravascular pressures. We have recently shown that pericytes, such as SMCs, possess functional voltage-dependent Ca2+ channels and ATP-sensitive K+ channels. Here, we further investigate the complement of pericyte ion channels, focusing on members of the K+ channel superfamily. Using NG2-DsRed-transgenic mice and diverse configurations of the patch-clamp technique, we demonstrate that pericytes display robust inward-rectifier K+ currents that are primarily mediated by the Kir2 family, based on their unique biophysical characteristics and sensitivity to micromolar concentrations of Ba2+. Moreover, multiple lines of evidence, including characteristic kinetics, sensitivity to specific blockers, biophysical attributes, and distinctive single-channel properties, established the functional expression of two voltage-dependent K+ channels: KV1 and BKCa. Although these three types of channels are also present in SMCs, they exhibit distinctive current density and kinetics profiles in pericytes. Collectively, these findings underscore differences in the operation of shared molecular features between pericytes and SMCs and highlight the potential contribution of these three K+ ion channels in setting pericyte membrane potential, modulating capillary hemodynamics, and regulating cerebral blood flow.
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Affiliation(s)
- Maria Sancho
- Department of Pharmacology, University of Vermont, Burlington, Vermont; Department of Physiology, Faculty of Medicine, Complutense University of Madrid, Madrid, Spain.
| | - Nicholas R Klug
- Department of Pharmacology, University of Vermont, Burlington, Vermont
| | - Osama F Harraz
- Department of Pharmacology, University of Vermont, Burlington, Vermont; Vermont Center for Cardiovascular and Brain Health, Larner College of Medicine, University of Vermont, Burlington, Vermont
| | | | - Mark T Nelson
- Department of Pharmacology, University of Vermont, Burlington, Vermont; Vermont Center for Cardiovascular and Brain Health, Larner College of Medicine, University of Vermont, Burlington, Vermont; Division of Cardiovascular Sciences, University of Manchester, Manchester, United Kingdom.
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2
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Dupré N, Gueniot F, Domenga-Denier V, Dubosclard V, Nilles C, Hill-Eubanks D, Morgenthaler-Roth C, Nelson MT, Keime C, Danglot L, Joutel A. Protein aggregates containing wild-type and mutant NOTCH3 are major drivers of arterial pathology in CADASIL. J Clin Invest 2024; 134:e175789. [PMID: 38386425 PMCID: PMC11014667 DOI: 10.1172/jci175789] [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: 09/19/2023] [Accepted: 02/20/2024] [Indexed: 02/24/2024] Open
Abstract
Loss of arterial smooth muscle cells (SMCs) and abnormal accumulation of the extracellular domain of the NOTCH3 receptor (Notch3ECD) are the 2 core features of CADASIL, a common cerebral small vessel disease caused by highly stereotyped dominant mutations in NOTCH3. Yet the relationship between NOTCH3 receptor activity, Notch3ECD accumulation, and arterial SMC loss has remained elusive, hampering the development of disease-modifying therapies. Using dedicated histopathological and multiscale imaging modalities, we could detect and quantify previously undetectable CADASIL-driven arterial SMC loss in the CNS of mice expressing the archetypal Arg169Cys mutation. We found that arterial pathology was more severe and Notch3ECD accumulation greater in transgenic mice overexpressing the mutation on a wild-type Notch3 background (TgNotch3R169C) than in knockin Notch3R170C/R170C mice expressing this mutation without a wild-type Notch3 copy. Notably, expression of Notch3-regulated genes was essentially unchanged in TgNotch3R169C arteries. We further showed that wild-type Notch3ECD coaggregated with mutant Notch3ECD and that elimination of 1 copy of wild-type Notch3 in TgNotch3R169C was sufficient to attenuate Notch3ECD accumulation and arterial pathology. These findings suggest that Notch3ECD accumulation, involving mutant and wild-type NOTCH3, is a major driver of arterial SMC loss in CADASIL, paving the way for NOTCH3-lowering therapeutic strategies.
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Affiliation(s)
- Nicolas Dupré
- Université Paris Cité, Institute of Psychiatry and Neuroscience of Paris (IPNP), INSERM U1266, Paris, France
| | - Florian Gueniot
- Université Paris Cité, Institute of Psychiatry and Neuroscience of Paris (IPNP), INSERM U1266, Paris, France
| | - Valérie Domenga-Denier
- Université Paris Cité, Institute of Psychiatry and Neuroscience of Paris (IPNP), INSERM U1266, Paris, France
| | - Virginie Dubosclard
- Université Paris Cité, Institute of Psychiatry and Neuroscience of Paris (IPNP), INSERM U1266, Paris, France
| | - Christelle Nilles
- Université Paris Cité, Institute of Psychiatry and Neuroscience of Paris (IPNP), INSERM U1266, Paris, France
| | - David Hill-Eubanks
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, Vermont, USA
| | - Christelle Morgenthaler-Roth
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS UMR 7104, INSERM U1258, Université de Strasbourg, Illkirch, France
| | - Mark T. Nelson
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, Vermont, USA
- Division of Cardiovascular Sciences, University of Manchester, Manchester, United Kingdom
| | - Céline Keime
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS UMR 7104, INSERM U1258, Université de Strasbourg, Illkirch, France
| | - Lydia Danglot
- Université Paris Cité, Institute of Psychiatry and Neuroscience of Paris (IPNP), INSERM U1266, Paris, France
| | - Anne Joutel
- Université Paris Cité, Institute of Psychiatry and Neuroscience of Paris (IPNP), INSERM U1266, Paris, France
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, Vermont, USA
- GHU Paris Psychiatrie et Neurosciences, Hôpital Sainte Anne, Paris, France
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3
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Taylor JL, Walsh KR, Mosneag IE, Danby TGE, Luka N, Chanda B, Schiessl I, Dunne RA, Hill-Eubanks D, Hennig GW, Allan SM, Nelson MT, Greenstein AS, Pritchard HAT. Uncoupling of Ca 2+ sparks from BK channels in cerebral arteries underlies hypoperfusion in hypertension-induced vascular dementia. Proc Natl Acad Sci U S A 2023; 120:e2307513120. [PMID: 37549299 PMCID: PMC10433456 DOI: 10.1073/pnas.2307513120] [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: 05/04/2023] [Accepted: 07/14/2023] [Indexed: 08/09/2023] Open
Abstract
The deficit in cerebral blood flow (CBF) seen in patients with hypertension-induced vascular dementia is increasingly viewed as a therapeutic target for disease-modifying therapy. Progress is limited, however, due to uncertainty surrounding the mechanisms through which elevated blood pressure reduces CBF. To investigate this, we used the BPH/2 mouse, a polygenic model of hypertension. At 8 mo of age, hypertensive mice exhibited reduced CBF and cognitive impairment, mimicking the human presentation of vascular dementia. Small cerebral resistance arteries that run across the surface of the brain (pial arteries) showed enhanced pressure-induced constriction due to diminished activity of large-conductance Ca2+-activated K+ (BK) channels-key vasodilatory ion channels of cerebral vascular smooth muscle cells. Activation of BK channels by transient intracellular Ca2+ signals from the sarcoplasmic reticulum (SR), termed Ca2+ sparks, leads to hyperpolarization and vasodilation. Combining patch-clamp electrophysiology, high-speed confocal imaging, and proximity ligation assays, we demonstrated that this vasodilatory mechanism is uncoupled in hypertensive mice, an effect attributable to physical separation of the plasma membrane from the SR rather than altered properties of BK channels or Ca2+ sparks, which remained intact. This pathogenic mechanism is responsible for the observed increase in constriction and can now be targeted as a possible avenue for restoring healthy CBF in vascular dementia.
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Affiliation(s)
- Jade L. Taylor
- Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, ManchesterM13 9PL, United Kingdom
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
| | - Katy R. Walsh
- Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, ManchesterM13 9PL, United Kingdom
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
- Division of Neuroscience, School of Biological Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, ManchesterM13 9PL, United Kingdom
| | - Ioana-Emilia Mosneag
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
- Division of Neuroscience, School of Biological Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, ManchesterM13 9PL, United Kingdom
| | - Thea G. E. Danby
- Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, ManchesterM13 9PL, United Kingdom
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
| | - Nadim Luka
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
- Division of Neuroscience, School of Biological Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, ManchesterM13 9PL, United Kingdom
| | - Bishal Chanda
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
- Division of Neuroscience, School of Biological Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, ManchesterM13 9PL, United Kingdom
| | - Ingo Schiessl
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
- Division of Neuroscience, School of Biological Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, ManchesterM13 9PL, United Kingdom
| | - Ross A. Dunne
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
| | - David Hill-Eubanks
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT05405
| | - Grant W. Hennig
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT05405
| | - Stuart M. Allan
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
- Division of Neuroscience, School of Biological Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, ManchesterM13 9PL, United Kingdom
| | - Mark T. Nelson
- Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, ManchesterM13 9PL, United Kingdom
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT05405
| | - Adam S. Greenstein
- Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, ManchesterM13 9PL, United Kingdom
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
- Manchester University Teaching Hospitals National Health Service Foundation Trust, ManchesterM13 9PL, United Kingdom
| | - Harry A. T. Pritchard
- Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, ManchesterM13 9PL, United Kingdom
- Geoffrey Jefferson Brain Research Centre, The Manchester Academic Health Science Centre, Northern Care Alliance National Health Service Foundation Trust, University of Manchester, ManchesterM13 9PL, United Kingdom
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4
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Mughal A, Nelson MT, Hill-Eubanks D. The post-arteriole transitional zone: a specialized capillary region that regulates blood flow within the CNS microvasculature. J Physiol 2023; 601:889-901. [PMID: 36751860 PMCID: PMC9992301 DOI: 10.1113/jp282246] [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: 08/19/2022] [Accepted: 01/13/2023] [Indexed: 02/09/2023] Open
Abstract
The brain is an energy hog, consuming available energy supplies at a rate out of all proportion to its relatively small size. This outsized demand, largely reflecting the unique computational activity of the brain, is met by an ensemble of neurovascular coupling mechanisms that link neuronal activity with local increases in blood delivery. This just-in-time replenishment strategy, made necessary by the limited energy-storage capacity of neurons, complicates the nutrient-delivery task of the cerebral vasculature, layering on a temporo-spatial requirement that invites - and challenges - mechanistic interpretation. The centre of gravity of research efforts to disentangle these mechanisms has shifted from an initial emphasis on astrocyte-arteriole-level processes to mechanisms that operate on the capillary level, a shift that has brought into sharp focus questions regarding the fine control of blood distribution to active neurons. As these investigations have drilled down into finer reaches of the microvasculature, they have revealed an arteriole-proximate subregion of CNS capillary networks that serves a regulatory function in directing blood flow into and within downstream capillaries. They have also illuminated differences in researchers' perspectives on the vascular structures and identity of mural cells in this region that impart the vasomodulatory effects that control blood distribution. In this review, we highlight the regulatory role of a variably named region of the microvasculature, referred to here as the post-arteriole transition zone, in channeling blood flow within CNS capillary networks, and underscore the contribution of dynamically contractile perivascular mural cell - generally, but not universally, recognized as pericytes - to this function.
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Affiliation(s)
- Amreen Mughal
- Department of Pharmacology, University of Vermont, Burlington, VT, USA
| | - Mark T. Nelson
- Department of Pharmacology, University of Vermont, Burlington, VT, USA
- Division of Cardiovascular Sciences, University of Manchester, Manchester, UK
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5
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Klug NR, Sancho M, Gonzales AL, Heppner TJ, O’Brien RIC, Hill-Eubanks D, Nelson MT. Intraluminal pressure elevates intracellular calcium and contracts CNS pericytes: Role of voltage-dependent calcium channels. Proc Natl Acad Sci U S A 2023; 120:e2216421120. [PMID: 36802432 PMCID: PMC9992766 DOI: 10.1073/pnas.2216421120] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [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: 09/27/2022] [Accepted: 01/24/2023] [Indexed: 02/23/2023] Open
Abstract
Arteriolar smooth muscle cells (SMCs) and capillary pericytes dynamically regulate blood flow in the central nervous system in the face of fluctuating perfusion pressures. Pressure-induced depolarization and Ca2+ elevation provide a mechanism for regulation of SMC contraction, but whether pericytes participate in pressure-induced changes in blood flow remains unknown. Here, utilizing a pressurized whole-retina preparation, we found that increases in intraluminal pressure in the physiological range induce contraction of both dynamically contractile pericytes in the arteriole-proximate transition zone and distal pericytes of the capillary bed. We found that the contractile response to pressure elevation was slower in distal pericytes than in transition zone pericytes and arteriolar SMCs. Pressure-evoked elevation of cytosolic Ca2+ and contractile responses in SMCs were dependent on voltage-dependent Ca2+ channel (VDCC) activity. In contrast, Ca2+ elevation and contractile responses were partially dependent on VDCC activity in transition zone pericytes and independent of VDCC activity in distal pericytes. In both transition zone and distal pericytes, membrane potential at low inlet pressure (20 mmHg) was approximately -40 mV and was depolarized to approximately -30 mV by an increase in pressure to 80 mmHg. The magnitude of whole-cell VDCC currents in freshly isolated pericytes was approximately half that measured in isolated SMCs. Collectively, these results indicate a loss of VDCC involvement in pressure-induced constriction along the arteriole-capillary continuum. They further suggest that alternative mechanisms and kinetics of Ca2+ elevation, contractility, and blood flow regulation exist in central nervous system capillary networks, distinguishing them from neighboring arterioles.
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Affiliation(s)
- Nicholas R. Klug
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT05405
| | - Maria Sancho
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT05405
| | - Albert L. Gonzales
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT05405
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, NV89557
| | - Thomas J. Heppner
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT05405
| | | | - David Hill-Eubanks
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT05405
| | - Mark T. Nelson
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT05405
- Division of Cardiovascular Sciences, University of Manchester, ManchesterM13 9PL, UK
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6
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Sancho M, Klug NR, Mughal A, Koide M, Huerta de la Cruz S, Heppner TJ, Bonev AD, Hill-Eubanks D, Nelson MT. Adenosine signaling activates ATP-sensitive K + channels in endothelial cells and pericytes in CNS capillaries. Sci Signal 2022; 15:eabl5405. [PMID: 35349300 DOI: 10.1126/scisignal.abl5405] [Citation(s) in RCA: 29] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The dense network of capillaries composed of capillary endothelial cells (cECs) and pericytes lies in close proximity to all neurons, ideally positioning it to sense neuron- and glial-derived compounds that enhance regional and global cerebral perfusion. The membrane potential (VM) of vascular cells serves as the physiological bridge that translates brain activity into vascular function. In other beds, the ATP-sensitive K+ (KATP) channel regulates VM in vascular smooth muscle, which is absent in the capillary network. Here, with transgenic mice that expressed a dominant-negative mutant of the pore-forming Kir6.1 subunit specifically in brain cECs or pericytes, we demonstrated that KATP channels were present in both cell types and robustly controlled VM. We further showed that the signaling nucleotide adenosine acted through A2A receptors and the Gαs/cAMP/PKA pathway to activate capillary KATP channels. Moreover, KATP channel stimulation in vivo increased cerebral blood flow (CBF), an effect that was blunted by expression of the dominant-negative Kir6.1 mutant in either capillary cell type. These findings establish an important role for KATP channels in cECs and pericytes in the regulation of CBF.
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Affiliation(s)
- Maria Sancho
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - Nicholas R Klug
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - Amreen Mughal
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - Masayo Koide
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA.,Vermont Center for Cardiovascular and Brain Health, Larner College of Medicine, University of Vermont, Burlington, VT 05405-0068, USA
| | | | - Thomas J Heppner
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - Adrian D Bonev
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - David Hill-Eubanks
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA
| | - Mark T Nelson
- Department of Pharmacology, University of Vermont, Burlington, VT 05405-0068, USA.,Vermont Center for Cardiovascular and Brain Health, Larner College of Medicine, University of Vermont, Burlington, VT 05405-0068, USA.,Division of Cardiovascular Sciences, University of Manchester, Manchester M13 9PL, UK
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7
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Longden TA, Mughal A, Hennig GW, Harraz OF, Shui B, Lee FK, Lee JC, Reining S, Kotlikoff MI, König GM, Kostenis E, Hill-Eubanks D, Nelson MT. Local IP 3 receptor-mediated Ca 2+ signals compound to direct blood flow in brain capillaries. Sci Adv 2021; 7:eabh0101. [PMID: 34290098 PMCID: PMC8294755 DOI: 10.1126/sciadv.abh0101] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Accepted: 06/04/2021] [Indexed: 05/10/2023]
Abstract
Healthy brain function depends on the finely tuned spatial and temporal delivery of blood-borne nutrients to active neurons via the vast, dense capillary network. Here, using in vivo imaging in anesthetized mice, we reveal that brain capillary endothelial cells control blood flow through a hierarchy of IP3 receptor-mediated Ca2+ events, ranging from small, subsecond protoevents, reflecting Ca2+ release through a small number of channels, to high-amplitude, sustained (up to ~1 min) compound events mediated by large clusters of channels. These frequent (~5000 events/s per microliter of cortex) Ca2+ signals are driven by neuronal activity, which engages Gq protein-coupled receptor signaling, and are enhanced by Ca2+ entry through TRPV4 channels. The resulting Ca2+-dependent synthesis of nitric oxide increases local blood flow selectively through affected capillary branches, providing a mechanism for high-resolution control of blood flow to small clusters of neurons.
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Affiliation(s)
- Thomas A Longden
- Department of Pharmacology, University of Vermont, Burlington, VT, USA.
- Department of Physiology, School of Medicine, University of Maryland, Baltimore, MD, USA
| | - Amreen Mughal
- Department of Pharmacology, University of Vermont, Burlington, VT, USA
| | - Grant W Hennig
- Department of Pharmacology, University of Vermont, Burlington, VT, USA
- Vermont Center for Cardiovascular and Brain Health, University of Vermont, Burlington, VT, USA
| | - Osama F Harraz
- Department of Pharmacology, University of Vermont, Burlington, VT, USA
- Division of Cardiovascular Sciences, University of Manchester, Manchester, UK
| | - Bo Shui
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Frank K Lee
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Jane C Lee
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Shaun Reining
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Michael I Kotlikoff
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Gabriele M König
- Institute of Pharmaceutical Biology, University of Bonn, 53115 Bonn, Germany
| | - Evi Kostenis
- Molecular, Cellular, and Pharmacobiology Section, Institute of Pharmaceutical Biology, University of Bonn, 53115 Bonn, Germany
| | | | - Mark T Nelson
- Department of Pharmacology, University of Vermont, Burlington, VT, USA.
- Vermont Center for Cardiovascular and Brain Health, University of Vermont, Burlington, VT, USA
- Division of Cardiovascular Sciences, University of Manchester, Manchester, UK
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8
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Mughal A, Harraz OF, Gonzales AL, Hill-Eubanks D, Nelson MT. PIP 2 Improves Cerebral Blood Flow in a Mouse Model of Alzheimer's Disease. Function (Oxf) 2021; 2:zqab010. [PMID: 33763649 PMCID: PMC7955025 DOI: 10.1093/function/zqab010] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 02/16/2021] [Accepted: 02/16/2021] [Indexed: 02/05/2023]
Abstract
Alzheimer's disease (AD) is a leading cause of dementia and a substantial healthcare burden. Despite this, few treatment options are available for controlling AD symptoms. Notably, neuronal activity-dependent increases in cortical cerebral blood flow (CBF; functional hyperemia) are attenuated in AD patients, but the associated pathological mechanisms are not fully understood at the molecular level. A fundamental mechanism underlying functional hyperemia is activation of capillary endothelial inward-rectifying K+ (Kir2.1) channels by neuronally derived potassium (K+), which evokes a retrograde capillary-to-arteriole electrical signal that dilates upstream arterioles, increasing blood delivery to downstream active regions. Here, using a mouse model of familial AD (5xFAD), we tested whether this impairment in functional hyperemia is attributable to reduced activity of capillary Kir2.1 channels. In vivo CBF measurements revealed significant reductions in whisker stimulation (WS)-induced and K+-induced hyperemic responses in 5xFAD mice compared with age-matched controls. Notably, measurements of whole-cell currents in freshly isolated 5xFAD capillary endothelial cells showed that Kir2.1 current density was profoundly reduced, suggesting a defect in Kir2.1 function. Because Kir2.1 activity absolutely depends on binding of phosphatidylinositol 4,5-bisphosphate (PIP2) to the channel, we hypothesized that capillary Kir2.1 channel impairment could be corrected by exogenously supplying PIP2. As predicted, a PIP2 analog restored Kir2.1 current density to control levels. More importantly, systemic administration of PIP2 restored K+-induced CBF increases and WS-induced functional hyperemic responses in 5xFAD mice. Collectively, these data provide evidence that PIP2-mediated restoration of capillary endothelial Kir2.1 function improves neurovascular coupling and CBF in the setting of AD.
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Affiliation(s)
- Amreen Mughal
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT, USA
| | - Osama F Harraz
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT, USA,Vermont Center for Cardiovascular and Brain Health, University of Vermont, Burlington, VT, USA
| | - Albert L Gonzales
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT, USA,Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, NV, USA
| | - David Hill-Eubanks
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT, USA
| | - Mark T Nelson
- Department of Pharmacology, Larner College of Medicine, University of Vermont, Burlington, VT, USA,Vermont Center for Cardiovascular and Brain Health, University of Vermont, Burlington, VT, USA,Division of Cardiovascular Sciences, University of Manchester, Manchester, UK,Address correspondence to M.T.N. (e-mail: )
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9
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Harraz OF, Longden TA, Hill-Eubanks D, Nelson MT. PIP 2 depletion promotes TRPV4 channel activity in mouse brain capillary endothelial cells. eLife 2018; 7:38689. [PMID: 30084828 PMCID: PMC6117155 DOI: 10.7554/elife.38689] [Citation(s) in RCA: 95] [Impact Index Per Article: 15.8] [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: 05/26/2018] [Accepted: 08/06/2018] [Indexed: 01/08/2023] Open
Abstract
We recently reported that the inward-rectifier Kir2.1 channel in brain capillary endothelial cells (cECs) plays a major role in neurovascular coupling (NVC) by mediating a neuronal activity-dependent, propagating vasodilatory (hyperpolarizing) signal. We further demonstrated that Kir2.1 activity is suppressed by depletion of plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP2). Whether cECs express depolarizing channels that intersect with Kir2.1-mediated signaling remains unknown. Here, we report that Ca2+/Na+-permeable TRPV4 (transient receptor potential vanilloid 4) channels are expressed in cECs and are tonically inhibited by PIP2. We further demonstrate that depletion of PIP2 by agonists, including putative NVC mediators, that promote PIP2 hydrolysis by signaling through Gq-protein-coupled receptors (GqPCRs) caused simultaneous disinhibition of TRPV4 channels and suppression of Kir2.1 channels. These findings collectively support the concept that GqPCR activation functions as a molecular switch to favor capillary TRPV4 activity over Kir2.1 signaling, an observation with potentially profound significance for the control of cerebral blood flow. Capillaries form branching networks that surround all cells of the body. They allow oxygen and nutrient exchange between blood and tissue, but this is not their only role. Capillaries in the brain form a tight barrier that prevents components carried in the blood from easily reaching the brain compartment. They also detect the activity of neurons and trigger on-demand increases in blood flow to active regions of the brain. This role, revealed only recently, depends upon ion channels on the surface of the capillary cells. Active neurons release potassium ions, which open a type of ion channel called Kir2.1 that allows potassium inside the cell to flow out. This process is repeated in neighboring capillary cells until it reaches an upstream vessel, where it causes the vessel to relax and increase the blood flow. Kir2.1 channels sit astride the membranes of capillary cells, where they can interact with other membrane molecules. One such molecule, called PIP2, plays several roles in relaying signals from the outside to the inside of cells. It also physically interacts with channels in the membrane, including Kir2.1 channels. If PIP2 levels are low, Kir2.1 channel activity decreases. Here, Harraz et al. discovered that capillary cells contain another type of ion channel, called TRPV4, which is also regulated by PIP2. But unlike Kir2.1, its activity increases when PIP2 levels drop. Moreover, TRPV4 channels allow sodium and calcium ions to flow into the cell, which has an effect opposite to that of potassium flowing out of the cell. Capillary cells also have receptor proteins called GqPCRs that are activated by chemical signals released by active neurons in the brain. GqPCRs break down PIP2, so their activity turns Kir2.1 channels off and TRPV4 channels on. This resets the system so that it is ready to respond to new signals from active neurons. GqPCRs work as molecular switches to control the balance between Kir2.1 and TRPV4 channels and turn brain blood flow up and down. GqPCRs and ion channels that depend on PIP2 can also be found in other types of cells. These findings could reveal clues about how signals are switched on and off in different cells. Understanding the role of PIP2 in signaling could also unveil what happens when signaling go wrong.
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Affiliation(s)
- Osama F Harraz
- Department of Pharmacology, University of Vermont, Burlington, United States
| | - Thomas A Longden
- Department of Pharmacology, University of Vermont, Burlington, United States
| | - David Hill-Eubanks
- Department of Pharmacology, University of Vermont, Burlington, United States
| | - Mark T Nelson
- Department of Pharmacology, University of Vermont, Burlington, United States.,Institute of Cardiovascular Sciences, Manchester, United Kingdom
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Harraz OF, Longden TA, Dabertrand F, Hill-Eubanks D, Nelson MT. Endothelial GqPCR activity controls capillary electrical signaling and brain blood flow through PIP 2 depletion. Proc Natl Acad Sci U S A 2018; 115:E3569-E3577. [PMID: 29581272 PMCID: PMC5899484 DOI: 10.1073/pnas.1800201115] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [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] [Indexed: 12/30/2022] Open
Abstract
Brain capillaries play a critical role in sensing neural activity and translating it into dynamic changes in cerebral blood flow to serve the metabolic needs of the brain. The molecular cornerstone of this mechanism is the capillary endothelial cell inward rectifier K+ (Kir2.1) channel, which is activated by neuronal activity-dependent increases in external K+ concentration, producing a propagating hyperpolarizing electrical signal that dilates upstream arterioles. Here, we identify a key regulator of this process, demonstrating that phosphatidylinositol 4,5-bisphosphate (PIP2) is an intrinsic modulator of capillary Kir2.1-mediated signaling. We further show that PIP2 depletion through activation of Gq protein-coupled receptors (GqPCRs) cripples capillary-to-arteriole signal transduction in vitro and in vivo, highlighting the potential regulatory linkage between GqPCR-dependent and electrical neurovascular-coupling mechanisms. These results collectively show that PIP2 sets the gain of capillary-initiated electrical signaling by modulating Kir2.1 channels. Endothelial PIP2 levels would therefore shape the extent of retrograde signaling and modulate cerebral blood flow.
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Affiliation(s)
- Osama F Harraz
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, VT 05405
| | - Thomas A Longden
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, VT 05405
| | - Fabrice Dabertrand
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, VT 05405
| | - David Hill-Eubanks
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, VT 05405
| | - Mark T Nelson
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, VT 05405;
- Institute of Cardiovascular Sciences, University of Manchester, M13 9PL Manchester, United Kingdom
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Heppner TJ, Tykocki NR, Hill-Eubanks D, Nelson MT. Transient contractions of urinary bladder smooth muscle are drivers of afferent nerve activity during filling. ACTA ACUST UNITED AC 2016; 147:323-35. [PMID: 26976828 PMCID: PMC4810069 DOI: 10.1085/jgp.201511550] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [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] [Received: 11/30/2015] [Accepted: 02/12/2016] [Indexed: 01/23/2023]
Abstract
Activation of afferent nerves during urinary bladder (UB) filling conveys the sensation of UB fullness to the central nervous system (CNS). Although this sensory outflow is presumed to reflect graded increases in pressure associated with filling, UBs also exhibit nonvoiding, transient contractions (TCs) that cause small, rapid increases in intravesical pressure. Here, using an ex vivo mouse bladder preparation, we explored the relative contributions of filling pressure and TC-induced pressure transients to sensory nerve stimulation. Continuous UB filling caused an increase in afferent nerve activity composed of a graded increase in baseline activity and activity associated with increases in intravesical pressure produced by TCs. For each ∼4-mmHg pressure increase, filling pressure increased baseline afferent activity by ∼60 action potentials per second. In contrast, a similar pressure elevation induced by a TC evoked an ∼10-fold greater increase in afferent activity. Filling pressure did not affect TC frequency but did increase the TC rate of rise, reflecting a change in the length-tension relationship of detrusor smooth muscle. The frequency of afferent bursts depended on the TC rate of rise and peaked before maximum pressure. Inhibition of small- and large-conductance Ca(2+)-activated K(+) (SK and BK) channels increased TC amplitude and afferent nerve activity. After inhibiting detrusor muscle contractility, simulating the waveform of a TC by gently compressing the bladder evoked similar increases in afferent activity. Notably, afferent activity elicited by simulated TCs was augmented by SK channel inhibition. Our results show that afferent nerve activity evoked by TCs represents the majority of afferent outflow conveyed to the CNS during UB filling and suggest that the maximum TC rate of rise corresponds to an optimal length-tension relationship for efficient UB contraction. Furthermore, our findings implicate SK channels in controlling the gain of sensory outflow independent of UB contractility.
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Affiliation(s)
- Thomas J Heppner
- Department of Pharmacology, University of Vermont, Burlington, VT 05405
| | - Nathan R Tykocki
- Department of Pharmacology, University of Vermont, Burlington, VT 05405
| | | | - Mark T Nelson
- Department of Pharmacology, University of Vermont, Burlington, VT 05405 Institute of Cardiovascular Sciences, University of Manchester, Manchester M13 9NT, England, UK
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Ye W, Chang RB, Bushman JD, Tu YH, Mulhall E, Wilson CE, Cooper AJ, Chick WS, Hill-Eubanks D, Nelson MT, Kinnamon SC, Liman ER. Inhibition of KIR2.1 by Intracellular Acidification Contributes to Sour Taste Transduction. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.2294] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Heppner TJ, Herrera GM, Bonev AD, Hill-Eubanks D, Nelson MT. Ca2+ sparks and K(Ca) channels: novel mechanisms to relax urinary bladder smooth muscle. Adv Exp Med Biol 2004; 539:347-57. [PMID: 15088917 DOI: 10.1007/978-1-4419-8889-8_26] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/10/2023]
Abstract
Negative feedback pathways that relax and stabilize UBSM are critical to the proper functioning of the urinary bladder. The complex interactions between K(Ca) channels and RyRs are just beginning to be unraveled. The consequences of SK, BK, and RyR dysfunction would increase cell excitability and lead to urinary bladder instability. Although each of these channels is a potential target for the development of therapeutics to treat urinary incontinence, SK is of special interest, since this SK isoform does not appear to be present in vascular smooth muscle.
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Affiliation(s)
- Thomas J Heppner
- Department of Pharmacology, University of Vermont College of Medicine, Burlington, Vermont 05405, USA
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Hill-Eubanks D, Burstein ES, Spalding TA, Bräuner-Osborne H, Brann MR. Structure of a G-protein-coupling domain of a muscarinic receptor predicted by random saturation mutagenesis. J Biol Chem 1996; 271:3058-65. [PMID: 8621701 DOI: 10.1074/jbc.271.6.3058] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The third intracellular loop (i3) plays a critical role in the coupling of many receptors to G-proteins. In muscarinic receptor subtypes, the N- and C-terminal regions (Ni3 and Ci3) of this loop are sufficient to direct appropriate G-protein coupling. The relative functional contributions of all amino acids within Ni3 was evaluated by constructing libraries of m5 muscarinic receptors containing random mutations in Ni3 and screening them using high throughput assays based on ligand-dependent transformation of NIH 3T3 cells. In receptors that retained a wild type phenotype, the pattern of functionally tolerated substitutions is consistent with the presence of three turns of an alpha helix extending from the transmembrane domain. All of the amino acid positions that tolerate radical substitutions face away from a conserved hydrophobic face that ends with an arginine, and helix-disrupting proline substitutions were not observed. All of the mutant receptors with significantly compromised phenotypes had amino acid substitutions in residues predicted to form the hydrophobic face. Similar data from the Ci3 region (Burstein, E. S., Spalding, T. A., Hill-Eubanks, D., and Brann, M. R. (1995) J. Biol. Chem. 270, 3141-3146) are consistent with the presence of a single helical turn extending from the transmembrane domain, with an alanine that defines G-protein affinity. Functionally critical residues of Ni3 and Ci3 are predicted to be in close proximity where they form the G-protein-coupling domain.
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Affiliation(s)
- D Hill-Eubanks
- Molecular Neuropharmacology Section, Department of Psychiatry, University of Vermont, Burlington, Vermont 05405, USA
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Spalding TA, Burstein ES, Brauner-Osborne H, Hill-Eubanks D, Brann MR. Pharmacology of a constitutively active muscarinic receptor generated by random mutagenesis. J Pharmacol Exp Ther 1995; 275:1274-9. [PMID: 8531092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
We have isolated a mutant m5 muscarinic receptor that mediates robust functional responses in the absence of agonists. This constitutively active receptor was isolated from a library of receptors containing randomly introduced mutations in the sixth transmembrane domain and contains the substitutions serine 465 for tyrosine and threonine 486 for proline. Although these individual residues are not conserved in other G-protein-coupled receptors, they are predicted to be at the junction between the sixth transmembrane domain and the last extracellular loop. The mutant receptor (CAm5) was subjected to detailed pharmacological analysis. All of the antagonists tested (atropine, quinuclidinyl benzilate, N-methyl scopolamine, 4-diphenylacetoxy-N-methylpiperidine and pirenzepine) fully suppressed both the constitutive and agonist-induced activities of CAm5 revealing that these ligands are negative antagonists (inverse agonists). The potency of these ligands was similar at the mutant and wild-type receptors, suggesting that the antagonist binding site of this receptor is unchanged. The mutant had increased sensitivity to the agonists carbachol, arecoline, and McN-A-343 as measured both by functional response and by radioligand binding. These effects are explained and predicted by a model in which the primary effect of the mutations is to alter a spontaneous equilibrium existing between the active and inactive states of the receptor.
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Affiliation(s)
- T A Spalding
- Department of Psychiatry, University of Vermont, Burlington
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Burstein ES, Spalding TA, Hill-Eubanks D, Brann MR. Structure-function of muscarinic receptor coupling to G proteins. Random saturation mutagenesis identifies a critical determinant of receptor affinity for G proteins. J Biol Chem 1995; 270:3141-6. [PMID: 7852396 DOI: 10.1074/jbc.270.7.3141] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
To derive structure-function relationships for receptor-G protein coupling, libraries were created of human m5 muscarinic acetylcholine receptors (m5) randomly mutated in the C-terminal region of the third intracellular loop. Functional receptors were identified based on their ability to amplify NIH 3T3 cells in a ligand-dependent manner. These receptors either had wild-type phenotypes (Group 1) or were functionally impaired (Group 2). No "activated receptors" were identified. Tolerated substitutions in Group 2 receptors were randomly distributed and frequently included prolines and glycines. In contrast, tolerated substitutions in Group 1 receptors exhibited a periodicity proximal to transmembrane domain 6 were proline and glycine substitutions were not observed. These observations are consistent with a short alpha-helical extension of the C-terminal region of the third intracellular loop from transmembrane domain 6. Mutations at Ala-441 were most commonly associated with impaired function of Group 2 receptors. Twelve point mutations at Ala-441 were tested, and all caused marked increases in EC50 values with little effect on maximal response or agonist binding affinity. These results indicate that Ala-441 is a key determinant of m5 receptor affinity for G proteins and exists within the structural context of a short alpha-helix.
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Affiliation(s)
- E S Burstein
- Department of Psychiatry, University of Vermont, Burlington 05405
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Burstein E, Spalding T, Jørgensen H, Hill-Eubanks D, Brann M. Structure/function of muscarinic receptor coupling to G proteins: random-saturation mutagenesis identifies a critical determinant of receptor affinity for G proteins. Life Sci 1995. [DOI: 10.1016/0024-3205(95)93770-f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Brann MR, Jørgensen HB, Burstein ES, Spalding TA, Ellis J, Jones SV, Hill-Eubanks D. Studies of the pharmacology, localization, and structure of muscarinic acetylcholine receptors. Ann N Y Acad Sci 1993; 707:225-36. [PMID: 9137555 DOI: 10.1111/j.1749-6632.1993.tb38055.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- M R Brann
- Department of Psychiatry, University of Vermont, Burlington 05405, USA
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Brann MR, Ellis J, Jørgensen H, Hill-Eubanks D, Jones SV. Muscarinic acetylcholine receptor subtypes: localization and structure/function. Prog Brain Res 1993; 98:121-7. [PMID: 8248499 DOI: 10.1016/s0079-6123(08)62388-2] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Based on the sequence of the five cloned muscarinic receptor subtypes (m1-m5), subtype selective antibody and cDNA probes have been prepared. Use of these probes has demonstrated that each of the five subtypes has a markedly distinct distribution within the brain and among peripheral tissues. The distributions of these subtypes and their potential physiological roles are discussed. By use of molecular genetic manipulation of cloned muscarinic receptor cDNAs, the regions of muscarinic receptors that specify G-protein coupling and ligand binding have been defined in several recent studies. Overall, these studies have shown that amino acids within the third cytoplasmic loop of the receptors define their selectivities for different G-proteins and that multiple discontinuous epitopes contribute to their selectivities for different ligands. The residues that contribute to ligand binding and G-protein coupling are described, as well as the implied structures of these functional domains.
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Affiliation(s)
- M R Brann
- Department of Psychiatry, University of Vermont, Burlington 05405
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