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Phosphate and Endothelial Function: How Sensing of Elevated Inorganic Phosphate Concentration Generates Signals in Endothelial Cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2022; 1362:85-98. [DOI: 10.1007/978-3-030-91623-7_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Abbasian N, Bevington A, Burton JO, Herbert KE, Goodall AH, Brunskill NJ. Inorganic Phosphate (Pi) Signaling in Endothelial Cells: A Molecular Basis for Generation of Endothelial Microvesicles in Uraemic Cardiovascular Disease. Int J Mol Sci 2020; 21:ijms21196993. [PMID: 32977471 PMCID: PMC7583816 DOI: 10.3390/ijms21196993] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Revised: 09/16/2020] [Accepted: 09/21/2020] [Indexed: 12/22/2022] Open
Abstract
Hyperphosphataemia increases cardiovascular mortality in patients with kidney disease. Direct effects of high inorganic phosphate (Pi) concentrations have previously been demonstrated on endothelial cells (ECs), including generation of procoagulant endothelial microvesicles (MVs). However, no mechanism directly sensing elevated intracellular Pi has ever been described in mammalian cells. Here, we investigated the hypothesis that direct inhibition by Pi of the phosphoprotein phosphatase PP2A fulfils this sensing role in ECs, culminating in cytoskeleton disruption and MV generation. ECs were treated with control (1 mM [Pi]) vs. high (2.5 mM [Pi]), a condition that drives actin stress fibre depletion and MV generation demonstrated by confocal microscopy of F-actin and NanoSight Nanoparticle tracking, respectively. Immuno-blotting demonstrated that high Pi increased p-Src, p-PP2A-C and p-DAPK-1 and decreased p-TPM-3. Pi at 100 μM directly inhibited PP2A catalytic activity. Inhibition of PP2A enhanced inhibitory phosphorylation of DAPK-1, leading to hypophosphorylation of Tropomyosin-3 at S284 and MV generation. p-Src is known to perform inhibitory phosphorylation on DAPK-1 but also on PP2A-C. However, PP2A-C can itself dephosphorylate (and therefore inhibit) p-Src. The direct inhibition of PP2A-C by Pi is, therefore, amplified by the feedback loop between PP2A-C and p-Src, resulting in further PP2A-C inhibition. These data demonstrated that PP2A/Src acts as a potent sensor and amplifier of Pi signals which can further signal through DAPK-1/Tropomyosin-3 to generate cytoskeleton disruption and generation of potentially pathological MVs.
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Affiliation(s)
- Nima Abbasian
- Department of Cardiovascular Sciences, University of Leicester, and Leicester NIHR Cardiovascular Biomedical Research Unit, Leicester LE3 9QP, UK; (J.O.B.); (K.E.H.); (A.H.G.); (N.J.B.)
- Correspondence: (N.A.); (A.B.); Tel.: +44-(0)116-246-0951 (A.B.)
| | - Alan Bevington
- Department of Cardiovascular Sciences, University of Leicester, and Leicester NIHR Cardiovascular Biomedical Research Unit, Leicester LE3 9QP, UK; (J.O.B.); (K.E.H.); (A.H.G.); (N.J.B.)
- Correspondence: (N.A.); (A.B.); Tel.: +44-(0)116-246-0951 (A.B.)
| | - James O. Burton
- Department of Cardiovascular Sciences, University of Leicester, and Leicester NIHR Cardiovascular Biomedical Research Unit, Leicester LE3 9QP, UK; (J.O.B.); (K.E.H.); (A.H.G.); (N.J.B.)
- Department of Nephrology, Leicester General Hospital, Leicester LE5 4PW, UK
| | - Karl E. Herbert
- Department of Cardiovascular Sciences, University of Leicester, and Leicester NIHR Cardiovascular Biomedical Research Unit, Leicester LE3 9QP, UK; (J.O.B.); (K.E.H.); (A.H.G.); (N.J.B.)
| | - Alison H. Goodall
- Department of Cardiovascular Sciences, University of Leicester, and Leicester NIHR Cardiovascular Biomedical Research Unit, Leicester LE3 9QP, UK; (J.O.B.); (K.E.H.); (A.H.G.); (N.J.B.)
| | - Nigel J. Brunskill
- Department of Cardiovascular Sciences, University of Leicester, and Leicester NIHR Cardiovascular Biomedical Research Unit, Leicester LE3 9QP, UK; (J.O.B.); (K.E.H.); (A.H.G.); (N.J.B.)
- Department of Nephrology, Leicester General Hospital, Leicester LE5 4PW, UK
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Abbasian N, Burton JO, Herbert KE, Tregunna BE, Brown JR, Ghaderi-Najafabadi M, Brunskill NJ, Goodall AH, Bevington A. Hyperphosphatemia, Phosphoprotein Phosphatases, and Microparticle Release in Vascular Endothelial Cells. J Am Soc Nephrol 2015; 26:2152-62. [PMID: 25745026 DOI: 10.1681/asn.2014070642] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Accepted: 10/31/2014] [Indexed: 01/27/2023] Open
Abstract
Hyperphosphatemia in patients with advanced CKD is thought to be an important contributor to cardiovascular risk, in part because of endothelial cell (EC) dysfunction induced by inorganic phosphate (Pi). Such patients also have an elevated circulating concentration of procoagulant endothelial microparticles (MPs), leading to a prothrombotic state, which may contribute to acute occlusive events. We hypothesized that hyperphosphatemia leads to MP formation from ECs through an elevation of intracellular Pi concentration, which directly inhibits phosphoprotein phosphatases, triggering a global increase in phosphorylation and cytoskeletal changes. In cultured human ECs (EAhy926), incubation with elevated extracellular Pi (2.5 mM) led to a rise in intracellular Pi concentration within 90 minutes. This was mediated by PiT1/slc20a1 Pi transporters and led to global accumulation of tyrosine- and serine/threonine-phosphorylated proteins, a marked increase in cellular Tropomyosin-3, plasma membrane blebbing, and release of 0.1- to 1-μm-diameter MPs. The effect of Pi was independent of oxidative stress or apoptosis. Similarly, global inhibition of phosphoprotein phosphatases with orthovanadate or fluoride yielded a global protein phosphorylation response and rapid release of MPs. The Pi-induced MPs expressed VE-cadherin and superficial phosphatidylserine, and in a thrombin generation assay, they displayed significantly more procoagulant activity than particles derived from cells incubated in medium with a physiologic level of Pi (1 mM). These data show a mechanism of Pi-induced cellular stress and signaling, which may be widely applicable in mammalian cells, and in ECs, it provides a novel pathologic link between hyperphosphatemia, generation of MPs, and thrombotic risk.
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Affiliation(s)
- Nima Abbasian
- Departments of Infection, Immunity and Inflammation and
| | - James O Burton
- Departments of Infection, Immunity and Inflammation and John Walls Renal Unit, University Hospitals of Leicester, Leicester, United Kingdom; and
| | - Karl E Herbert
- Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom; Leicester National Institute for Health Research Cardiovascular Biomedical Research Unit Cardiovascular Sciences, University of Leicester, United Kingdom
| | | | - Jeremy R Brown
- Departments of Infection, Immunity and Inflammation and John Walls Renal Unit, University Hospitals of Leicester, Leicester, United Kingdom; and
| | - Maryam Ghaderi-Najafabadi
- Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom; Leicester National Institute for Health Research Cardiovascular Biomedical Research Unit Cardiovascular Sciences, University of Leicester, United Kingdom
| | - Nigel J Brunskill
- Departments of Infection, Immunity and Inflammation and John Walls Renal Unit, University Hospitals of Leicester, Leicester, United Kingdom; and
| | - Alison H Goodall
- Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom; Leicester National Institute for Health Research Cardiovascular Biomedical Research Unit Cardiovascular Sciences, University of Leicester, United Kingdom
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Kemp GJ, Khouja HI, Ahmado A, Graham R, Russell G, Bevington A. Regulation of the phosphate (Pi) concentration in UMR 106 osteoblast-like cells: effect of Pi, Na+ and K+. Cell Biochem Funct 1993; 11:13-23. [PMID: 8384093 DOI: 10.1002/cbf.290110103] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Osteoblast-like cells possess Na-dependent transporters which accumulate orthophosphate (Pi) from the extracellular medium. This may be important in bone formation. Here we describe parallel measurements of Pi uptake and cellular [Pi] in such cells from the rat (UMR 106-01 and UMR 106-06) and human (OB), and in non-osteoblastic human fibroblasts (Detroit 532 (DET)). In UMR 106-01, cellular [Pi] was weakly dependent on extracellular [Pi] and higher than expected from passive transport alone. [32Pi]-uptake was inhibited by Na deprivation, but paradoxically increased on K deprivation. With Na, 87 per cent of cellular 32P was found in organic phosphorus pools after only 5 min. Na deprivation also decreased cellular [Pi], in both UMR 106-01 and DET, but the decrease was smaller than that in [32Pi]-uptake. Ouabain decreased [32Pi]-uptake and cellular [Pi] in DET, but not in UMR 106-01. Regulation of cellular [Pi] is therefore at least partly dependent on Na/Pi co-transport, but this does not seem to be an exclusive property of osteoblasts.
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Affiliation(s)
- G J Kemp
- Department of Human Metabolism and Clinical Biochemistry, Medical School, Sheffield, U.K
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Thompson CH, Kemp GJ, Radda GK. Changes in high-energy phosphates in rat skeletal muscle during acute respiratory acidosis. ACTA PHYSIOLOGICA SCANDINAVICA 1992; 146:15-9. [PMID: 1442123 DOI: 10.1111/j.1748-1716.1992.tb09388.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We used 31P magnetic resonance spectroscopy to study changes in phosphorus metabolite concentrations in rat skeletal muscle during respiratory acidosis (14 and 20% inspired CO2) and recovery. As intracellular pH fell (from 7.05 to 6.75 after 20 min of 20% CO2), intracellular [P(i)] increased by up to 50% while phosphocreatine concentration decreased by up to 8%. The sum of all intracellular phosphates remained constant. [ADP] decreased by up to 40% in accordance with the creatine kinase equilibrium but the phosphorylation potential [ATP]/([ADP][P(i)]) was preserved as a result of increased [P(i)]. This adjustment may be a mechanism for maintaining mitochondrial ATP synthesis despite low pH. Eventually this increase in cellular [P(i)] could lead to slow efflux of P(i) from the skeletal muscle cell contributing to the hyperphosphataemia of acute respiratory acidosis.
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Affiliation(s)
- C H Thompson
- M.R.C. Biochemical and Clinical Magnetic Resonance Unit, John Radcliffe Hospital, Oxford, UK
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Parkash M, Butterworth PJ. Efflux of inorganic phosphate from rat hepatocytes: lack of effect of insulin. Cell Biochem Funct 1991; 9:9-12. [PMID: 2065438 DOI: 10.1002/cbf.290090103] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Efflux of Pi from rat hepatocytes suspended in phosphate free-medium was studied by chemical assay of released Pi and by monitoring the loss in radioactivity of cells pre-labelled with [32P]-Pi. The release follows first-order kinetics fairly closely with a rate constant of 7 x 10(-3) min-1 approximately. Insulin at a concentration of 10(-8) M had no effect on the rate of Pi release and it is concluded therefore, that the insulin-stimulated accumulation of Pi described in the literature is the result of hormone action on Pi uptake by liver rather than on its release.
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Affiliation(s)
- M Parkash
- Department of Biochemistry, King's College London, UK
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Kemp GJ, Bevington A, Khodja D, Challa A, Russell RG. 32P-labelling anomalies in human erythrocytes. Is there more than one pool of cellular Pi? Biochem J 1989; 264:729-36. [PMID: 2695064 PMCID: PMC1133646 DOI: 10.1042/bj2640729] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
1. Human erythrocytes were incubated in autologous plasma containing [32P]Pi, and sampled by a method which avoids washing the cells. 2. In experiments of up to 3 h duration, the specific radioactivity of cellular Pi stabilized at a value below that of extracellular Pi. This can be explained on the basis of a single cellular Pi pool exchanging with a large unlabelled pool of cellular organic phosphates. 3. However, a rapid initial phase of labelling, occurring within 30 s, was inconsistent with the situation described in point 2. A possible explanation is that about 1/4 of cellular Pi occurs in a separate, fast-labelling pool. 4. When the extracellular Pi concentration was doubled, most of the corresponding increase in the steady-state cellular Pi concentration was accounted for by the apparent fast-labelling Pi pool, which also doubled. 5. The observed initial rate of labelling of cellular organic phosphates [which probably occurs through the reaction catalysed by glyceraldehyde-3-phosphate dehydrogenase (E.C. 1.2.1.12)] was considerably lower than that predicted from the flux through the Embden-Meyerhof pathway. This implies that the enzyme is exposed to Pi whose specific radioactivity is lower than the mean specific radioactivity of cellular Pi, and fails to support earlier suggestions that this enzyme uses extracellular Pi. 6. In 3 h incubations, the rate of organic phosphate labelling was roughly constant throughout, even though the specific radioactivity of cellular Pi had risen slowly to a plateau. Viewed in conjunction with point 5, this again suggests some inhomogeneity in cellular Pi. 7. Cellular Pi and extracellular Pi only reached isotopic steady state after 2 days. At this stage some organic phosphates were probably still incompletely labelled. 8. We conclude that, whatever their physical or technical reasons, such labelling inhomogeneities and slow attainment of isotopic steady state may cause serious misinterpretation of results if ignored during 32P-labelling of intact cells.
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Affiliation(s)
- G J Kemp
- Department of Human Metabolism and Clinical Biochemistry, University of Sheffield Medical School, U.K
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