1
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Heden TD, Franklin MP, Dailey C, Mashek MT, Chen C, Mashek DG. ACOT1 deficiency attenuates high-fat diet-induced fat mass gain by increasing energy expenditure. JCI Insight 2023; 8:e160987. [PMID: 37561578 PMCID: PMC10561717 DOI: 10.1172/jci.insight.160987] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 08/08/2023] [Indexed: 08/12/2023] Open
Abstract
Acyl-CoA thioesterase 1 (ACOT1) catalyzes the hydrolysis of long-chain acyl-CoAs to free fatty acids and CoA and is typically upregulated in obesity. Whether targeting ACOT1 in the setting of high-fat diet-induced (HFD-induced) obesity would be metabolically beneficial is not known. Here we report that male and female ACOT1KO mice are partially protected from HFD-induced obesity, an effect associated with increased energy expenditure without alterations in physical activity or food intake. In males, ACOT1 deficiency increased mitochondrial uncoupling protein-2 (UCP2) protein abundance while reducing 4-hydroxynonenal, a marker of oxidative stress, in white adipose tissue and liver of HFD-fed mice. Moreover, concurrent knockdown (KD) of UCP2 with ACOT1 in hepatocytes prevented increases in oxygen consumption observed with ACOT1 KD during high lipid loading, suggesting that UCP2-induced uncoupling may increase energy expenditure to attenuate weight gain. Together, these data indicate that targeting ACOT1 may be effective for obesity prevention during caloric excess by increasing energy expenditure.
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Affiliation(s)
- Timothy D. Heden
- Pennington Biomedical Research Center, Baton Rouge, Louisiana, USA
| | | | - Christina Dailey
- Department of Biochemistry, Molecular Biology and Biophysics and
| | - Mara T. Mashek
- Department of Biochemistry, Molecular Biology and Biophysics and
| | - Chen Chen
- Department of Biochemistry, Molecular Biology and Biophysics and
| | - Douglas G. Mashek
- Department of Biochemistry, Molecular Biology and Biophysics and
- Department of Medicine, Division of Diabetes, Endocrinology and Metabolism, Medical School, University of Minnesota, Minneapolis, Minnesota, USA
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2
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Galluccio M, Console L, Pochini L, Scalise M, Giangregorio N, Indiveri C. Strategies for Successful Over-Expression of Human Membrane Transport Systems Using Bacterial Hosts: Future Perspectives. Int J Mol Sci 2022; 23:ijms23073823. [PMID: 35409183 PMCID: PMC8998559 DOI: 10.3390/ijms23073823] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 03/28/2022] [Accepted: 03/28/2022] [Indexed: 02/06/2023] Open
Abstract
Ten percent of human genes encode for membrane transport systems, which are key components in maintaining cell homeostasis. They are involved in the transport of nutrients, catabolites, vitamins, and ions, allowing the absorption and distribution of these compounds to the various body regions. In addition, roughly 60% of FDA-approved drugs interact with membrane proteins, among which are transporters, often responsible for pharmacokinetics and side effects. Defects of membrane transport systems can cause diseases; however, knowledge of the structure/function relationships of transporters is still limited. Among the expression of hosts that produce human membrane transport systems, E. coli is one of the most favorable for its low cultivation costs, fast growth, handiness, and extensive knowledge of its genetics and molecular mechanisms. However, the expression in E. coli of human membrane proteins is often toxic due to the hydrophobicity of these proteins and the diversity in structure with respect to their bacterial counterparts. Moreover, differences in codon usage between humans and bacteria hamper translation. This review summarizes the many strategies exploited to achieve the expression of human transport systems in bacteria, providing a guide to help people who want to deal with this topic.
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Affiliation(s)
- Michele Galluccio
- Unit of Biochemistry and Molecular Biotechnology, Department of Biology, Ecology and Earth Sciences (DiBEST), University of Calabria, Via P. Bucci 4c, Arcavacata di Rende, 87036 Cosenza, Italy; (M.G.); (L.C.); (L.P.); (M.S.)
| | - Lara Console
- Unit of Biochemistry and Molecular Biotechnology, Department of Biology, Ecology and Earth Sciences (DiBEST), University of Calabria, Via P. Bucci 4c, Arcavacata di Rende, 87036 Cosenza, Italy; (M.G.); (L.C.); (L.P.); (M.S.)
| | - Lorena Pochini
- Unit of Biochemistry and Molecular Biotechnology, Department of Biology, Ecology and Earth Sciences (DiBEST), University of Calabria, Via P. Bucci 4c, Arcavacata di Rende, 87036 Cosenza, Italy; (M.G.); (L.C.); (L.P.); (M.S.)
| | - Mariafrancesca Scalise
- Unit of Biochemistry and Molecular Biotechnology, Department of Biology, Ecology and Earth Sciences (DiBEST), University of Calabria, Via P. Bucci 4c, Arcavacata di Rende, 87036 Cosenza, Italy; (M.G.); (L.C.); (L.P.); (M.S.)
| | - Nicola Giangregorio
- Institute of Biomembranes, Bioenergetics and Molecular Biotechnology (IBIOM), National Research Council (CNR), Via Amendola 165/A, 70126 Bari, Italy;
| | - Cesare Indiveri
- Unit of Biochemistry and Molecular Biotechnology, Department of Biology, Ecology and Earth Sciences (DiBEST), University of Calabria, Via P. Bucci 4c, Arcavacata di Rende, 87036 Cosenza, Italy; (M.G.); (L.C.); (L.P.); (M.S.)
- Institute of Biomembranes, Bioenergetics and Molecular Biotechnology (IBIOM), National Research Council (CNR), Via Amendola 165/A, 70126 Bari, Italy;
- Correspondence:
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3
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Tang R, Sun W, Zhang JC, Mao L, Quanquin N, Wu D, Sun Y. Expression of Human Uncoupling Protein-1 in Escherichia coli Decreases its Survival Under Extremely Acidic Conditions. Curr Microbiol 2022; 79:77. [DOI: 10.1007/s00284-022-02762-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Accepted: 01/08/2022] [Indexed: 11/03/2022]
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4
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Pan R, Chen Y. Management of Oxidative Stress: Crosstalk Between Brown/Beige Adipose Tissues and Skeletal Muscles. Front Physiol 2021; 12:712372. [PMID: 34603076 PMCID: PMC8481590 DOI: 10.3389/fphys.2021.712372] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 08/19/2021] [Indexed: 12/23/2022] Open
Abstract
Exercise plays an important role in the physiology, often depending on its intensity, duration, and frequency. It increases the production of reactive oxygen species (ROS). Meanwhile, it also increases antioxidant enzymes involved in the oxidative damage defense. Prolonged, acute, or strenuous exercise often leads to an increased radical production and a subsequent oxidative stress in the skeletal muscles, while chronic regular or moderate exercise results in a decrease in oxidative stress. Notably, under pathological state, such as obesity, aging, etc., ROS levels could be elevated in humans, which could be attenuated by proper exercise. Significantly, exercise stimulates the development of beige adipose tissue and potentially influence the function of brown adipose tissue (BAT), which is known to be conducive to a metabolic balance through non-shivering thermogenesis (NST) and may protect from oxidative stress. Exercise-related balance of the ROS levels is associated with a healthy metabolism in humans. In this review, we summarize the integrated effects of exercise on oxidative metabolism, and especially focus on the role of brown and beige adipose tissues in this process, providing more evidence and knowledge for a better management of exercise-induced oxidative stress.
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Affiliation(s)
- Ruping Pan
- Department of Nuclear Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Yong Chen
- Department of Endocrinology, Internal Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.,Branch of National Clinical Research Center for Metabolic Diseases, Wuhan, China
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5
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Zhao RZ, Jiang S, Zhang L, Yu ZB. Mitochondrial electron transport chain, ROS generation and uncoupling (Review). Int J Mol Med 2019; 44:3-15. [PMID: 31115493 PMCID: PMC6559295 DOI: 10.3892/ijmm.2019.4188] [Citation(s) in RCA: 451] [Impact Index Per Article: 90.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2019] [Accepted: 04/19/2019] [Indexed: 12/18/2022] Open
Abstract
The mammalian mitochondrial electron transport chain (ETC) includes complexes I-IV, as well as the electron transporters ubiquinone and cytochrome c. There are two electron transport pathways in the ETC: Complex I/III/IV, with NADH as the substrate and complex II/III/IV, with succinic acid as the substrate. The electron flow is coupled with the generation of a proton gradient across the inner membrane and the energy accumulated in the proton gradient is used by complex V (ATP synthase) to produce ATP. The first part of this review briefly introduces the structure and function of complexes I-IV and ATP synthase, including the specific electron transfer process in each complex. Some electrons are directly transferred to O2 to generate reactive oxygen species (ROS) in the ETC. The second part of this review discusses the sites of ROS generation in each ETC complex, including sites IF and IQ in complex I, site IIF in complex II and site IIIQo in complex III, and the physiological and pathological regulation of ROS. As signaling molecules, ROS play an important role in cell proliferation, hypoxia adaptation and cell fate determination, but excessive ROS can cause irreversible cell damage and even cell death. The occurrence and development of a number of diseases are closely related to ROS overproduction. Finally, proton leak and uncoupling proteins (UCPS) are discussed. Proton leak consists of basal proton leak and induced proton leak. Induced proton leak is precisely regulated and induced by UCPs. A total of five UCPs (UCP1-5) have been identified in mammalian cells. UCP1 mainly plays a role in the maintenance of body temperature in a cold environment through non-shivering thermogenesis. The core role of UCP2-5 is to reduce oxidative stress under certain conditions, therefore exerting cytoprotective effects. All diseases involving oxidative stress are associated with UCPs.
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Affiliation(s)
- Ru-Zhou Zhao
- Department of Aerospace Physiology, Fourth Military Medical University, Xi'an, Shaanxi 710032, P.R. China
| | - Shuai Jiang
- Department of Aerospace Physiology, Fourth Military Medical University, Xi'an, Shaanxi 710032, P.R. China
| | - Lin Zhang
- Department of Aerospace Physiology, Fourth Military Medical University, Xi'an, Shaanxi 710032, P.R. China
| | - Zhi-Bin Yu
- Department of Aerospace Physiology, Fourth Military Medical University, Xi'an, Shaanxi 710032, P.R. China
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6
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Pohl EE, Rupprecht A, Macher G, Hilse KE. Important Trends in UCP3 Investigation. Front Physiol 2019; 10:470. [PMID: 31133866 PMCID: PMC6524716 DOI: 10.3389/fphys.2019.00470] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2018] [Accepted: 04/04/2019] [Indexed: 11/13/2022] Open
Abstract
Membrane uncoupling protein 3 (UCP3), a member of the mitochondrial uncoupling protein family, was discovered in 1997. UCP3's properties, such as its high homology to other mitochondrial carriers, especially to UCP2, its short lifetime and low specificity of UCP3 antibodies, have hindered progress in understanding its biological function and transport mechanism over decades. The abundance of UCP3 is highest in murine brown adipose tissue (BAT, 15.0 pmol/mg protein), compared to heart (2.7 pmol/mg protein) and the gastrocnemius muscle (1.7 pmol/mg protein), but it is still 400-fold lower than the abundance of UCP1, a biomarker for BAT. Investigation of UCP3 reconstituted in planar bilayer membranes revealed that it transports protons only when activated by fatty acids (FA). Although purine nucleotides (PN) inhibit UCP3-mediated transport, the molecular mechanism differs from that of UCP1. It remains a conundrum that two homologous proton-transporting proteins exist within the same tissue. Recently, we proposed that UCP3 abundance directly correlates with the degree of FA β-oxidation in cell metabolism. Further development in this field implies that UCP3 may have dual function in transporting substrates, which have yet to be identified, alongside protons. Evaluation of the literature with respect to UCP3 is a complex task because (i) UCP3 features are often extrapolated from its "twin" UCP2 without additional proof, and (ii) the specificity of antibodies against UCP3 used in studies is rarely evaluated. In this review, we primarily focus on recent findings obtained for UCP3 in biological and biomimetic systems.
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Affiliation(s)
- Elena E. Pohl
- Institute of Physiology, Pathophysiology and Biophysics, University of Veterinary Medicine, Vienna, Austria
| | - Anne Rupprecht
- Institute of Physiology, Pathophysiology and Biophysics, University of Veterinary Medicine, Vienna, Austria
- Institute of Pharmacology and Toxicology, Rostock University Medical Center, Rostock, Germany
| | - Gabriel Macher
- Institute of Physiology, Pathophysiology and Biophysics, University of Veterinary Medicine, Vienna, Austria
| | - Karolina E. Hilse
- Institute of Physiology, Pathophysiology and Biophysics, University of Veterinary Medicine, Vienna, Austria
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7
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Macher G, Koehler M, Rupprecht A, Kreiter J, Hinterdorfer P, Pohl EE. Inhibition of mitochondrial UCP1 and UCP3 by purine nucleotides and phosphate. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2018; 1860:664-672. [PMID: 29212043 PMCID: PMC6118327 DOI: 10.1016/j.bbamem.2017.12.001] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2017] [Revised: 11/04/2017] [Accepted: 12/01/2017] [Indexed: 11/26/2022]
Abstract
Mitochondrial membrane uncoupling protein 3 (UCP3) is not only expressed in skeletal muscle and heart, but also in brown adipose tissue (BAT) alongside UCP1, which facilitates a proton leak to support non-shivering thermogenesis. In contrast to UCP1, the transport function and molecular mechanism of UCP3 regulation are poorly investigated, although it is generally agreed upon that UCP3, analogous to UCP1, transports protons, is activated by free fatty acids (FFAs) and is inhibited by purine nucleotides (PNs). Because the presence of two similar uncoupling proteins in BAT is surprising, we hypothesized that UCP1 and UCP3 are differently regulated, which may lead to differences in their functions. By combining atomic force microscopy and electrophysiological measurements of recombinant proteins reconstituted in planar bilayer membranes, we compared the level of protein activity with the bond lifetimes between UCPs and PNs. Our data revealed that, in contrast to UCP1, UCP3 can be fully inhibited by all PNs and IC50 increases with a decrease in PN-phosphorylation. Experiments with mutant proteins demonstrated that the conserved arginines in the PN-binding pocket are involved in the inhibition of UCP1 and UCP3 to different extents. Fatty acids compete with all PNs bound to UCP1, but only with ATP bound to UCP3. We identified phosphate as a novel inhibitor of UCP3 and UCP1, which acts independently of PNs. The differences in molecular mechanisms of the inhibition between the highly homologous transporters UCP1 and UCP3 indicate that UCP3 has adapted to fulfill a different role and possibly another transport function in BAT.
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Affiliation(s)
- Gabriel Macher
- Institute of Physiology, Pathophysiology and Biophysics, University of Veterinary Medicine, Vienna, Austria
| | - Melanie Koehler
- Institute of Biophysics, Johannes Kepler University, Linz, Austria
| | - Anne Rupprecht
- Institute of Physiology, Pathophysiology and Biophysics, University of Veterinary Medicine, Vienna, Austria
| | - Jürgen Kreiter
- Institute of Physiology, Pathophysiology and Biophysics, University of Veterinary Medicine, Vienna, Austria
| | | | - Elena E Pohl
- Institute of Physiology, Pathophysiology and Biophysics, University of Veterinary Medicine, Vienna, Austria.
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8
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Rebuffet E, Frick A, Järvå M, Törnroth-Horsefield S. Cell-free production and characterisation of human uncoupling protein 1-3. Biochem Biophys Rep 2017; 10:276-281. [PMID: 28955755 PMCID: PMC5614671 DOI: 10.1016/j.bbrep.2017.04.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Revised: 04/04/2017] [Accepted: 04/07/2017] [Indexed: 11/22/2022] Open
Abstract
The uncoupling proteins (UCPs) leak protons across the inner mitochondrial membrane, thus uncoupling the proton gradient from ATP synthesis. The main known physiological role for this is heat generation by UCP1 in brown adipose tissue. However, UCPs are also believed to be important for protection against reactive oxygen species, fine-tuning of metabolism and have been suggested to be involved in disease states such as obesity, diabetes and cancer. Structural studies of UCPs have long been hampered by difficulties in sample preparation with neither expression in yeast nor refolding from inclusion bodies in E. coli yielding sufficient amounts of pure and stable protein. In this study, we have developed a protocol for cell-free expression of human UCP1, 2 and 3, resulting in 1 mg pure protein per 20 mL of expression media. Lauric acid, a natural UCP ligand, significantly improved protein thermal stability and was therefore added during purification. Secondary structure characterisation using circular dichroism spectroscopy revealed the proteins to consist of mostly α-helices, as expected. All three UCPs were able to bind GDP, a well-known physiological inhibitor, as shown by the Fluorescence Resonance Energy Transfer (FRET) technique, suggesting that the proteins are in a natively folded state. A protocol for cell-free expression of human uncoupling protein 1–3 is described. Addition of native membrane components increased expression levels. Addition of lauric acid increased protein stability in solution. CD spectroscopy confirms alpha-helical secondary structure as expected. All proteins binds GDP as demonstrated by Fluorescence Resonance Energy Transfer.
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Affiliation(s)
- Etienne Rebuffet
- Department of Chemistry and Molecular Biology, University of Gothenburg, Box 462, SE-405 30 Gothenburg, Sweden
| | - Anna Frick
- Department of Chemistry and Molecular Biology, University of Gothenburg, Box 462, SE-405 30 Gothenburg, Sweden
| | - Michael Järvå
- Department of Chemistry and Molecular Biology, University of Gothenburg, Box 462, SE-405 30 Gothenburg, Sweden
| | - Susanna Törnroth-Horsefield
- Department of Chemistry and Molecular Biology, University of Gothenburg, Box 462, SE-405 30 Gothenburg, Sweden.,Department of Biochemistry and Structural Biology, Centre for Molecular Protein Science, Lund University, Box 124, 221 00 Lund, Sweden
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9
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Crichton PG, Lee Y, Kunji ERS. The molecular features of uncoupling protein 1 support a conventional mitochondrial carrier-like mechanism. Biochimie 2017; 134:35-50. [PMID: 28057583 PMCID: PMC5395090 DOI: 10.1016/j.biochi.2016.12.016] [Citation(s) in RCA: 84] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2016] [Accepted: 12/24/2016] [Indexed: 12/14/2022]
Abstract
Uncoupling protein 1 (UCP1) is an integral membrane protein found in the mitochondrial inner membrane of brown adipose tissue, and facilitates the process of non-shivering thermogenesis in mammals. Its activation by fatty acids, which overcomes its inhibition by purine nucleotides, leads to an increase in the proton conductance of the inner mitochondrial membrane, short-circuiting the mitochondrion to produce heat rather than ATP. Despite 40 years of intense research, the underlying molecular mechanism of UCP1 is still under debate. The protein belongs to the mitochondrial carrier family of transporters, which have recently been shown to utilise a domain-based alternating-access mechanism, cycling between a cytoplasmic and matrix state to transport metabolites across the inner membrane. Here, we review the protein properties of UCP1 and compare them to those of mitochondrial carriers. UCP1 has the same structural fold as other mitochondrial carriers and, in contrast to past claims, is a monomer, binding one purine nucleotide and three cardiolipin molecules tightly. The protein has a single substrate binding site, which is similar to those of the dicarboxylate and oxoglutarate carriers, but also contains a proton binding site and several hydrophobic residues. As found in other mitochondrial carriers, UCP1 has two conserved salt bridge networks on either side of the central cavity, which regulate access to the substrate binding site in an alternating way. The conserved domain structures and mobile inter-domain interfaces are consistent with an alternating access mechanism too. In conclusion, UCP1 has retained all of the key features of mitochondrial carriers, indicating that it operates by a conventional carrier-like mechanism.
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Affiliation(s)
- Paul G Crichton
- Biomedical Research Centre, Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
| | - Yang Lee
- Laboratory of Molecular Biology, Medical Research Council, Cambridge Biomedical Campus, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Edmund R S Kunji
- Mitochondrial Biology Unit, Medical Research Council, Cambridge Biomedical Campus, Wellcome Trust, MRC Building, Hills Road, Cambridge CB2 0XY, United Kingdom.
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10
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The conserved regulation of mitochondrial uncoupling proteins: From unicellular eukaryotes to mammals. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1858:21-33. [PMID: 27751905 DOI: 10.1016/j.bbabio.2016.10.003] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Revised: 09/29/2016] [Accepted: 10/13/2016] [Indexed: 12/19/2022]
Abstract
Uncoupling proteins (UCPs) belong to the mitochondrial anion carrier protein family and mediate regulated proton leak across the inner mitochondrial membrane. Free fatty acids, aldehydes such as hydroxynonenal, and retinoids activate UCPs. However, there are some controversies about the effective action of retinoids and aldehydes alone; thus, only free fatty acids are commonly accepted positive effectors of UCPs. Purine nucleotides such as GTP inhibit UCP-mediated mitochondrial proton leak. In turn, membranous coenzyme Q may play a role as a redox state-dependent metabolic sensor that modulates the complete activation/inhibition of UCPs. Such regulation has been observed for UCPs in microorganisms, plant and animal UCP1 homologues, and UCP1 in mammalian brown adipose tissue. The origin of UCPs is still under debate, but UCP homologues have been identified in all systematic groups of eukaryotes. Despite the differing levels of amino acid/DNA sequence similarities, functional studies in unicellular and multicellular organisms, from amoebae to mammals, suggest that the mechanistic regulation of UCP activity is evolutionarily well conserved. This review focuses on the regulatory feedback loops of UCPs involving free fatty acids, aldehydes, retinoids, purine nucleotides, and coenzyme Q (particularly its reduction level), which may derive from the early stages of evolution as UCP first emerged.
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11
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Hoang T, Kuljanin M, Smith MD, Jelokhani-Niaraki M. A biophysical study on molecular physiology of the uncoupling proteins of the central nervous system. Biosci Rep 2015; 35:e00226. [PMID: 26182433 PMCID: PMC4613710 DOI: 10.1042/bsr20150130] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 06/04/2015] [Indexed: 01/16/2023] Open
Abstract
Mitochondrial inner membrane uncoupling proteins (UCPs) facilitate transmembrane (TM) proton flux and consequently reduce the membrane potential and ATP production. It has been proposed that the three neuronal human UCPs (UCP2, UCP4 and UCP5) in the central nervous system (CNS) play significant roles in reducing cellular oxidative stress. However, the structure and ion transport mechanism of these proteins remain relatively unexplored. Recently, we reported a novel expression system for obtaining functionally folded UCP1 in bacterial membranes and applied this system to obtain highly pure neuronal UCPs in high yields. In the present study, we report on the structure and function of the three neuronal UCP homologues. Reconstituted neuronal UCPs were dominantly helical in lipid membranes and transported protons in the presence of physiologically-relevant fatty acid (FA) activators. Under similar conditions, all neuronal UCPs also exhibited chloride transport activities that were partially inhibited by FAs. CD, fluorescence and MS measurements and semi-native gel electrophoresis collectively suggest that the reconstituted proteins self-associate in the lipid membranes. Based on SDS titration experiments and other evidence, a general molecular model for the monomeric, dimeric and tetrameric functional forms of UCPs in lipid membranes is proposed. In addition to their shared structural and ion transport features, neuronal UCPs differ in their conformations and proton transport activities (and possibly mechanism) in the presence of different FA activators. The differences in FA-activated UCP-mediated proton transport could serve as an essential factor in understanding and differentiating the physiological roles of UCP homologues in the CNS.
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Affiliation(s)
- Tuan Hoang
- Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5 Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario, Canada, N1G 2W1
| | - Miljan Kuljanin
- Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5
| | - Matthew D Smith
- Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5 Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario, Canada, N1G 2W1
| | - Masoud Jelokhani-Niaraki
- Department of Chemistry and Biochemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5 Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario, Canada, N1G 2W1
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12
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Hoang T, Matovic T, Parker J, Smith MD, Jelokhani-Niaraki M. Role of positively charged residues of the second transmembrane domain in the ion transport activity and conformation of human uncoupling protein-2. Biochemistry 2015; 54:2303-13. [PMID: 25789405 DOI: 10.1021/acs.biochem.5b00177] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Residing at the inner mitochondrial membrane, uncoupling protein-2 (UCP2) mediates proton transport from the intermembrane space (IMS) to the mitochondrial matrix and consequently reduces the rate of ATP synthesis in the mitochondria. The ubiquitous expression of UCP2 in humans can be attributed to the protein's multiple physiological roles in tissues, including its involvement in protective mechanisms against oxidative stress, as well as glucose and lipid metabolisms. Currently, the structural properties and ion transport mechanism of UCP2 and other UCP homologues remain poorly understood. UCP2-mediated proton transport is activated by fatty acids and inhibited by di- and triphosphate purine nucleotides. UCP2 also transports chloride and some other small anions. Identification of key amino acid residues of UCP2 in its ion transport pathway can shed light on the protein's ion transport function. On the basis of our previous studies, the second transmembrane helix segment (TM2) of UCP2 exhibited chloride channel activity. In addition, it was suggested that the positively charged residues on TM2 domains of UCPs 1 and 2 were important for their chloride transport activity. On this basis, to further understand the role of these positively charged residues on the ion transport activity of UCP2, we recombinantly expressed four TM2 mutants: R76Q, R88Q, R96Q, and K104Q. The wild type UCP2 and its mutants were purified and reconstituted into liposomes, and their conformation and ion (proton and chloride) transport activity were studied. TM2 Arg residues at the matrix interface of UCP2 proved to be crucial for the protein's anion transport function, and their absence resulted in highly diminished Cl(-) transport rates. On the other hand, the two other positively charged residues of TM2, located at the UCP2-IMS interface, could participate in the salt-bridge formation in the protein and promote the interhelical tight packing in the UCP2. Absence of these residues did not influence Cl(-) transport rates, but disturbed the dense packing in UCP2 and resulted in higher UCP2-mediated proton transport rates in the presence of long chain fatty acids. Overall, the outcome of this study provides a deeper and more detailed molecular image of UCP2's ion transport mechanism.
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Affiliation(s)
- Tuan Hoang
- §Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | | | | | - Matthew D Smith
- §Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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13
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Crichton PG, Lee Y, Ruprecht JJ, Cerson E, Thangaratnarajah C, King MS, Kunji ERS. Trends in thermostability provide information on the nature of substrate, inhibitor, and lipid interactions with mitochondrial carriers. J Biol Chem 2015; 290:8206-17. [PMID: 25653283 PMCID: PMC4375477 DOI: 10.1074/jbc.m114.616607] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Mitochondrial carriers, including uncoupling proteins, are unstable in detergents, which hampers structural and mechanistic studies. To investigate carrier stability, we have purified ligand-free carriers and assessed their stability with a fluorescence-based thermostability assay that monitors protein unfolding with a thiol-reactive dye. We find that mitochondrial carriers from both mesophilic and thermophilic organisms exhibit poor stability in mild detergents, indicating that instability is inherent to the protein family. Trends in the thermostability of yeast ADP/ATP carrier AAC2 and ovine uncoupling protein UCP1 allow optimal conditions for stability in detergents to be established but also provide mechanistic insights into the interactions of lipids, substrates, and inhibitors with these proteins. Both proteins exhibit similar stability profiles across various detergents, where stability increases with the size of the associated detergent micelle. Detailed analysis shows that lipids stabilize carriers indirectly by increasing the associated detergent micelle size, but cardiolipin stabilizes by direct interactions as well. Cardiolipin reverses destabilizing effects of ADP and bongkrekic acid on AAC2 and enhances large stabilizing effects of carboxyatractyloside, revealing that this lipid interacts in the m-state and possibly other states of the transport cycle, despite being in a dynamic interface. Fatty acid activators destabilize UCP1 in a similar way, which can also be prevented by cardiolipin, indicating that they interact like transport substrates. Our controls show that carriers can be soluble but unfolded in some commonly used detergents, such as the zwitterionic Fos-choline-12, which emphasizes the need for simple validation assays like the one used here.
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Affiliation(s)
- Paul G Crichton
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Yang Lee
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Jonathan J Ruprecht
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Elizabeth Cerson
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Chancievan Thangaratnarajah
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Martin S King
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
| | - Edmund R S Kunji
- From the Mitochondrial Biology Unit, Medical Research Council, Hills Road, Cambridge CB2 0XY, United Kingdom
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14
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Alves-Bezerra M, Cosentino-Gomes D, Vieira LP, Rocco-Machado N, Gondim KC, Meyer-Fernandes JR. Identification of uncoupling protein 4 from the blood-sucking insect Rhodnius prolixus and its possible role on protection against oxidative stress. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2014; 50:24-33. [PMID: 24746771 DOI: 10.1016/j.ibmb.2014.03.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2013] [Revised: 03/14/2014] [Accepted: 03/24/2014] [Indexed: 06/03/2023]
Abstract
Uncoupling proteins (UCPs) play a critical role in the control of the mitochondrial membrane potential (ΔΨm) due to their ability to dissipate the proton gradient, which results in the uncoupling of mitochondrial respiration from ATP production. Most reactive oxygen species generation in mitochondria occurs in complex III, due to an increase of semiquinone (Q(-)) half-life. When active, UCPs can account as a potential antioxidant system by decreasing ΔΨm and increasing mitochondrial respiration, thus reducing Q(-) life time. The hematophagous insect Rhodnius prolixus, a vector of Chagas disease, is exposed to a huge increase in oxidative stress after a blood meal because of the hydrolysis of hemoglobin and the release of the cytotoxic heme molecule. Although some protective mechanisms were already described for this insect and other hematophagous arthropods, the putative role of UCP proteins as antioxidants in this context has not been explored. In this report, two genes encoding UCP proteins (RpUcp4 and RpUcp5) were identified in the R. prolixus genome. RpUcp4 is the predominant transcript in most analyzed organs, and both mRNA and protein expression are upregulated (13- and 3-fold increase, respectively) in enterocytes the first day after the blood feeding. The increase in UCP4 expression is coincident with the decrease in hydrogen peroxide (H2O2) generation by midgut cells. Furthermore, in mitochondria isolated from enterocytes, the modulation of UCP activity by palmitic acid and GDP resulted in altered ΔΨm, as well as modulation of H2O2 generation rates. These results indicate that R. prolixus UCP4 may function in an antioxidation mechanism to protect the midgut cells against oxidative damage caused by blood digestion.
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Affiliation(s)
- Michele Alves-Bezerra
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Daniela Cosentino-Gomes
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Lisvane P Vieira
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Nathália Rocco-Machado
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Katia C Gondim
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Brazil
| | - José R Meyer-Fernandes
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; Instituto Nacional de Ciência e Tecnologia de Biologia Estrutural e Bioimagem, Brazil.
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15
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Donadelli M, Dando I, Fiorini C, Palmieri M. UCP2, a mitochondrial protein regulated at multiple levels. Cell Mol Life Sci 2014; 71:1171-90. [PMID: 23807210 PMCID: PMC11114077 DOI: 10.1007/s00018-013-1407-0] [Citation(s) in RCA: 125] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Revised: 05/16/2013] [Accepted: 06/10/2013] [Indexed: 12/11/2022]
Abstract
An ever-increasing number of studies highlight the role of uncoupling protein 2 (UCP2) in a broad range of physiological and pathological processes. The knowledge of the molecular mechanisms of UCP2 regulation is becoming fundamental in both the comprehension of UCP2-related physiological events and the identification of novel therapeutic strategies based on UCP2 modulation. The study of UCP2 regulation is a fast-moving field. Recently, several research groups have made a great effort to thoroughly understand the various molecular mechanisms at the basis of UCP2 regulation. In this review, we describe novel findings concerning events that can occur in a concerted manner at various levels: Ucp2 gene mutation (single nucleotide polymorphisms), UCP2 mRNA and protein expression (transcriptional, translational, and protein turn-over regulation), UCP2 proton conductance (ligands and post-transcriptional modifications), and nutritional and pharmacological regulation of UCP2.
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Affiliation(s)
- Massimo Donadelli
- Section of Biochemistry, Deparment of Life and Reproduction Sciences, University of Verona, Strada Le Grazie 8, 37134, Verona, Italy,
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16
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Hoang T, Smith MD, Jelokhani-Niaraki M. Expression, folding, and proton transport activity of human uncoupling protein-1 (UCP1) in lipid membranes: evidence for associated functional forms. J Biol Chem 2013; 288:36244-58. [PMID: 24196960 DOI: 10.1074/jbc.m113.509935] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Uncoupling protein-1 (UCP1) is abundantly expressed in the mitochondrial inner membrane of brown adipose tissues and has an important role in heat generation, mediated by its proton transport function. The structure and function of UCP1 are not fully understood, partially due to the difficulty in obtaining native-like folded proteins in vitro. In this study, using the auto-induction method, we have successfully expressed UCP1 in Escherichia coli membranes in high yield. Overexpressed UCP1 in bacterial membranes was extracted using mild detergents and reconstituted into phospholipid bilayers for biochemical studies. UCP1 was folded in octyl glucoside, as indicated by its high helical content and binding to ATP, a known UCP1 proton transport inhibitor. Reconstituted UCP1 in phospholipid vesicles also exhibited highly helical structures and proton transport that is activated by fatty acids and inhibited by purine nucleotides. Self-associated functional forms of UCP1 in lipid membranes were observed for the first time. The self-assembly of UCP1 into tetramers was unambiguously characterized by circular dichroism and fluorescence spectroscopy, analytical ultracentrifugation, and semi-native gel electrophoresis. In addition, the mitochondrial lipid cardiolipin stabilized the structure of associated UCP1 and enhanced the proton transport activity of the protein. The existence of the functional oligomeric states of UCP1 in the lipid membranes has important implications for understanding the structure and proton transport mechanism of this protein in brown adipose tissues as well as structure-function relationships of other mammalian UCPs in other tissues.
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17
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Smith MD, Jelokhani-Niaraki M. pH-induced changes in intrinsically disordered proteins. Methods Mol Biol 2012; 896:223-31. [PMID: 22821527 DOI: 10.1007/978-1-4614-3704-8_14] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
Intrinsically disordered proteins are typically enriched in amino acids that confer a relatively high net charge to the protein, which is an important factor leading to the lack of a compact structure. There are many different approaches that can be used to experimentally confirm whether a protein is intrinsically disordered. One such approach takes advantage of the distinctive amino acid composition to test whether a protein is a genuine IDP. In particular, the conformation of the protein can be monitored at different pHs; as opposed to globular or ordered proteins, IDPs will typically gain structure under highly acidic or basic conditions. Here, we describe circular dichroism and fluorescence spectroscopic experimental approaches in which the conformation of proteins is monitored as pH is altered as a way of testing whether the protein behaves as an intrinsically disordered protein.
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Affiliation(s)
- Matthew D Smith
- Department of Biology, Wilfrid Laurier University, Waterloo, ON, Canada.
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18
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Ho JWM, Ho PWL, Liu HF, So DHF, Chan KH, Tse ZHM, Kung MHW, Ramsden DB, Ho SL. UCP4 is a target effector of the NF-κB c-Rel prosurvival pathway against oxidative stress. Free Radic Biol Med 2012; 53:383-94. [PMID: 22580300 DOI: 10.1016/j.freeradbiomed.2012.05.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Revised: 04/08/2012] [Accepted: 05/01/2012] [Indexed: 01/11/2023]
Abstract
Mitochondrial uncoupling protein-4 (UCP4) enhances neuronal survival in 1-methyl-4-phenylpyridinium (MPP(+)) toxicity by suppressing oxidative stress and preserving intracellular ATP and mitochondrial membrane potential (MMP). NF-κB regulates neuronal viability via its complexes, p65 mediating cell death and c-Rel promoting cell survival. We reported previously that NF-κB mediates UCP4 neuroprotection against MPP(+) toxicity. Here, we investigated its link with the NF-κB c-Rel prosurvival pathway in alleviating mitochondrial dysfunction and oxidative stress. We overexpressed a c-Rel-encoding plasmid in SH-SY5Y cells and showed that c-Rel overexpression induced NF-κB activity without affecting p65 level. Overexpression of c-Rel increased UCP4 promoter activity and protein expression. Electrophoretic mobility shift assay showed that H(2)O(2) increased NF-κB binding to the UCP4 promoter and that NF-κB complexes were composed of p50/p50 and p50/c-Rel dimers. Under H(2)O(2)-induced oxidative stress, UCP4 knockdown significantly increased superoxide levels, decreased reduced glutathione (GSH) levels, and increased oxidized glutathione levels, compared to controls. UCP4 expression induced by c-Rel overexpression significantly decreased superoxide levels and preserved GSH levels and MMP under similar stress. These protective effects of c-Rel overexpression in H(2)O(2)-induced oxidative stress were significantly reduced after UCP4 knockdown, indicating that UCP4 is a target effector gene of the NF-κB c-Rel prosurvival pathway to mitigate the effects of oxidative stress.
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Affiliation(s)
- Jessica Wing-Man Ho
- Division of Neurology, University Department of Medicine, University of Hong Kong, Hong Kong, People's Republic of China
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19
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Ramsden DB, Ho PW, Ho JW, Liu H, So DH, Tse H, Chan K, Ho S. Human neuronal uncoupling proteins 4 and 5 (UCP4 and UCP5): structural properties, regulation, and physiological role in protection against oxidative stress and mitochondrial dysfunction. Brain Behav 2012; 2:468-78. [PMID: 22950050 PMCID: PMC3432969 DOI: 10.1002/brb3.55] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2011] [Revised: 03/07/2012] [Accepted: 03/09/2012] [Indexed: 01/07/2023] Open
Abstract
Uncoupling proteins (UCPs) belong to a large family of mitochondrial solute carriers 25 (SLC25s) localized at the inner mitochondrial membrane. UCPs transport protons directly from the intermembrane space to the matrix. Of five structural homologues (UCP1 to 5), UCP4 and 5 are principally expressed in the central nervous system (CNS). Neurons derived their energy in the form of ATP that is generated through oxidative phosphorylation carried out by five multiprotein complexes (Complexes I-V) embedded in the inner mitochondrial membrane. In oxidative phosphorylation, the flow of electrons generated by the oxidation of substrates through the electron transport chain to molecular oxygen at Complex IV leads to the transport of protons from the matrix to the intermembrane space by Complex I, III, and IV. This movement of protons to the intermembrane space generates a proton gradient (mitochondrial membrane potential; MMP) across the inner membrane. Complex V (ATP synthase) uses this MMP to drive the conversion of ADP to ATP. Some electrons escape to oxygen-forming harmful reactive oxygen species (ROS). Proton leakage back to the matrix which bypasses Complex V resulting in a major reduction in ROS formation while having a minimal effect on MMP and hence, ATP synthesis; a process termed "mild uncoupling." UCPs act to promote this proton leakage as means to prevent excessive build up of MMP and ROS formation. In this review, we discuss the structure and function of mitochondrial UCPs 4 and 5 and factors influencing their expression. Hypotheses concerning the evolution of the two proteins are examined. The protective mechanisms of the two proteins against neurotoxins and their possible role in regulating intracellular calcium movement, particularly with regard to the pathogenesis of Parkinson's disease are discussed.
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Affiliation(s)
- David B. Ramsden
- School of Medicine and School of Biosciences, University of Birmingham, United Kingdom
| | - Philip W.‐L. Ho
- Division of Neurology, Department of Medicine, University of Hong Kong, Hong Kong, PR China
- Research Centre of Heart, Brain, Hormone and Healthy Aging (HBHA), University of Hong Kong, Hong Kong, PR China
| | - Jessica W.‐M. Ho
- Division of Neurology, Department of Medicine, University of Hong Kong, Hong Kong, PR China
| | - Hui‐Fang Liu
- Division of Neurology, Department of Medicine, University of Hong Kong, Hong Kong, PR China
| | - Danny H.‐F. So
- Division of Neurology, Department of Medicine, University of Hong Kong, Hong Kong, PR China
| | - Ho‐Man Tse
- Division of Neurology, Department of Medicine, University of Hong Kong, Hong Kong, PR China
| | - Koon‐Ho Chan
- Division of Neurology, Department of Medicine, University of Hong Kong, Hong Kong, PR China
- Research Centre of Heart, Brain, Hormone and Healthy Aging (HBHA), University of Hong Kong, Hong Kong, PR China
| | - Shu‐Leong Ho
- Division of Neurology, Department of Medicine, University of Hong Kong, Hong Kong, PR China
- Research Centre of Heart, Brain, Hormone and Healthy Aging (HBHA), University of Hong Kong, Hong Kong, PR China
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20
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Hoang T, Smith MD, Jelokhani-Niaraki M. Toward understanding the mechanism of ion transport activity of neuronal uncoupling proteins UCP2, UCP4, and UCP5. Biochemistry 2012; 51:4004-14. [PMID: 22524567 DOI: 10.1021/bi3003378] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Neuronal uncoupling proteins (UCP2, UCP4, and UCP5) have crucial roles in the function and protection of the central nervous system (CNS). Extensive biochemical studies of UCP2 have provided ample evidence of its participation in proton and anion transport. To date, functional studies of UCP4 and UCP5 are scarce. In this study, we show for the first time that, despite a low level of amino acid sequence identity with the previously characterized UCPs (UCP1-UCP3), UCP4 and UCP5 share their functional properties. Recombinantly expressed in Escherichia coli, UCP2, UCP4, and UCP5 were isolated and reconstituted into liposome systems, where their conformations and ion (proton and chloride) transport properties were examined. All three neuronal UCPs are able to transport protons across lipid membranes with characteristics similar to those of the archetypal protein UCP1, which is activated by fatty acids and inhibited by purine nucleotides. Neuronal UCPs also exhibit transmembrane chloride transport activity. Circular dichroism spectroscopy shows that these three transporters exist in different conformations. In addition, their structures and functions are differentially modulated by the mitochondrial lipid cardiolipin. In total, this study supports the existence of general conformational and ion transport features in neuronal UCPs. On the other hand, it also emphasizes the subtle structural and functional differences between UCPs that could distinguish their physiological roles. Differentiation between structure-function relationships of neuronal UCPs is essential for understanding their physiological functions in the CNS.
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Affiliation(s)
- Tuan Hoang
- Department of Chemistry, Wilfrid Laurier University, Waterloo, ON, Canada
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21
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Ho PW, Ho JW, Liu HF, So DH, Tse ZH, Chan KH, Ramsden DB, Ho SL. Mitochondrial neuronal uncoupling proteins: a target for potential disease-modification in Parkinson's disease. Transl Neurodegener 2012; 1:3. [PMID: 23210978 PMCID: PMC3506996 DOI: 10.1186/2047-9158-1-3] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2011] [Accepted: 01/13/2012] [Indexed: 12/21/2022] Open
Abstract
This review gives a brief insight into the role of mitochondrial dysfunction and oxidative stress in the converging pathogenic processes involved in Parkinson's disease (PD). Mitochondria provide cellular energy in the form of ATP via oxidative phosphorylation, but as an integral part of this process, superoxides and other reactive oxygen species are also produced. Excessive free radical production contributes to oxidative stress. Cells have evolved to handle such stress via various endogenous anti-oxidant proteins. One such family of proteins is the mitochondrial uncoupling proteins (UCPs), which are anion carriers located in the mitochondrial inner membrane. There are five known homologues (UCP1 to 5), of which UCP4 and 5 are predominantly expressed in neural cells. In a series of previous publications, we have shown how these neuronal UCPs respond to 1-methyl-4-phenylpyridinium (MPP+; toxic metabolite of MPTP) and dopamine-induced toxicity to alleviate neuronal cell death by preserving ATP levels and mitochondrial membrane potential, and reducing oxidative stress. We also showed how their expression can be influenced by nuclear factor kappa-B (NF-κB) signaling pathway specifically in UCP4. Furthermore, we previously reported an interesting link between PD and metabolic processes through the protective effects of leptin (hormone produced by adipocytes) acting via UCP2 against MPP+-induced toxicity. There is increasing evidence that these endogenous neuronal UCPs can play a vital role to protect neurons against various pathogenic stresses including those associated with PD. Their expression, which can be induced, may well be a potential therapeutic target for various drugs to alleviate the harmful effects of pathogenic processes in PD and hence modify the progression of this disease.
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Affiliation(s)
- Philip Wl Ho
- Division of Neurology, Department of Medicine, University of Hong Kong, Pokfulam, Hong Kong SAR, China.
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22
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Pfeiffer M, Kayzer EB, Yang X, Abramson E, Kenaston MA, Lago CU, Lo HH, Sedensky MM, Lunceford A, Clarke CF, Wu SJ, McLeod C, Finkel T, Morgan PG, Mills EM. Caenorhabditis elegans UCP4 protein controls complex II-mediated oxidative phosphorylation through succinate transport. J Biol Chem 2011; 286:37712-20. [PMID: 21862587 DOI: 10.1074/jbc.m111.271452] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The novel uncoupling proteins (UCP2-5) are implicated in the mitochondrial control of oxidant production, insulin signaling, and aging. Attempts to understand their functions have been complicated by overlapping expression patterns in most organisms. Caenorhabditis elegans nematodes are unique because they express only one UCP ortholog, ceUCP4 (ucp4). Here, we performed detailed metabolic analyzes in genetically modified nematodes to define the function of the ceUCP4. The knock-out mutant ucp4 (ok195) exhibited sharply decreased mitochondrial succinate-driven (complex II) respiration. However, respiratory coupling and electron transport chain function were normal in ucp4 mitochondria. Surprisingly, isolated ucp4 mitochondria showed markedly decreased succinate uptake. Similarly, ceUCP4 inhibition blocked succinate respiration and import in wild type mitochondria. Genetic and pharmacologic inhibition of complex I function was selectively lethal to ucp4 worms, arguing that ceUCP4-regulated succinate transport is required for optimal complex II function in vivo. Additionally, ceUCP4 deficiency prolonged lifespan in the short-lived mev1 mutant that exhibits complex II-generated oxidant production. These results identify a novel function for ceUCP4 in the regulation of complex II-based metabolism through an unexpected mechanism involving succinate transport.
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Affiliation(s)
- Matthew Pfeiffer
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Texas, Austin, Texas 78712, USA
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23
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Hirschberg V, Fromme T, Klingenspor M. Test systems to study the structure and function of uncoupling protein 1: a critical overview. Front Endocrinol (Lausanne) 2011; 2:63. [PMID: 22654819 PMCID: PMC3356129 DOI: 10.3389/fendo.2011.00063] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2011] [Accepted: 10/12/2011] [Indexed: 01/06/2023] Open
Abstract
The discovery of active brown adipose tissue (BAT) in healthy adult humans has renewed interest in the biology of this organ. BAT is capable of distributing nutrient energy in the form of heat allowing small mammals to efficiently defend their body temperature when acutely exposed to the cold. On the other hand BAT might be a target for the treatment of obesity and related diseases, as its pharmacological activation could allow release of excess energy stored in white adipose tissue depots. Energy dissipation in BAT depends on the activity of uncoupling protein 1 (UCP1), therefore a BAT-based obesity therapy requires a detailed understanding of structure and function of UCP1. Although UCP1 has been in the focus of research since its discovery, central questions concerning its mechanistic function and regulation are not yet resolved. They have been addressed in native mitochondria but also in several test systems, which are generally used to lower inter-experimental variability and to simplify analysis conditions. Different test systems have contributed to our current knowledge about UCP1 but of course all of them have certain limitations. We here provide an overview about research on UCP1 structure and function in test systems. So far, these have nearly exclusively been employed to study rodent and not human UCP1. Considering that the amino acid sequence of mouse and human UCP1 is only 79% identical, it will be essential to test whether the human version has a similarly high catalytic activity, allowing a relevant amount of energy dissipation in human BAT. Besides the issue of comparable mechanistic function a sufficiently high expression level of human UCP1 is a further prerequisite for anti-obesity therapeutic potential. Treatments which induce BAT hyperplasia and UCP1 expression in humans might therefore be equally important to discover as mere activators of the thermogenic process.
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Affiliation(s)
- Verena Hirschberg
- Molecular Nutritional Medicine, Else Kröner-Fresenius Zentrum, Technische Universität MünchenFreising, Germany
- *Correspondence: Verena Hirschberg, Molecular Nutritional Medicine, Else Kröner-Fresenius Zentrum, Technische Universität München, Gregor-Mendel-Str. 2, 85350 Freising-Weihenstephan, Germany e-mail:
| | - Tobias Fromme
- Molecular Nutritional Medicine, Else Kröner-Fresenius Zentrum, Technische Universität MünchenFreising, Germany
| | - Martin Klingenspor
- Molecular Nutritional Medicine, Else Kröner-Fresenius Zentrum, Technische Universität MünchenFreising, Germany
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24
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Bergman C, Kashiwaya Y, Veech RL. The effect of pH and free Mg2+ on ATP linked enzymes and the calculation of Gibbs free energy of ATP hydrolysis. J Phys Chem B 2010; 114:16137-46. [PMID: 20866109 DOI: 10.1021/jp105723r] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The apparent equilibrium constants, K′, of biochemical reactions containing substrates which bind [Mg2+] unequally can be significantly altered by changes in free intracellular [Mg2+]. Intracellular free [Mg2+] can be estimated by measurements of [citrate]/[isocitrate], a ratio known to vary with tissue free [Mg2+]. The combined equilibrium constant for glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and triose phosphate isomerase for the three reactions (K(GG-TPI)′) was corrected using new binding constants for dihydroxyacetone-phosphate and 3-phosphoglycerate. The result of this calculation is demonstrated in the calculation of the free energy of ATP hydrolysis. In addition, the dependence of the equilibrium constant for the glutamine synthetase reaction on pH and free [Mg2+] was demonstrated. Furthermore, a theory linking the ΔG′ value of mitochondrial complex I−II and the cytosolic ΔG′ value of ATP hydrolysis is discussed with evidence from previous publications.
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Affiliation(s)
- Christian Bergman
- Laboratory of Metabolic Control, NIAAA, NIH, DHHS, 5625 Fishers Lane, Bethesda, Maryland 20892, USA
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25
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Kashiwaya Y, Pawlosky R, Markis W, King MT, Bergman C, Srivastava S, Murray A, Clarke K, Veech RL. A ketone ester diet increases brain malonyl-CoA and Uncoupling proteins 4 and 5 while decreasing food intake in the normal Wistar Rat. J Biol Chem 2010; 285:25950-6. [PMID: 20529850 PMCID: PMC2923987 DOI: 10.1074/jbc.m110.138198] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Revised: 05/25/2010] [Indexed: 01/20/2023] Open
Abstract
Three groups of male Wistar rats were pair fed NIH-31 diets for 14 days to which were added 30% of calories as corn starch, palm oil, or R-3-hydroxybutyrate-R-1,3-butanediol monoester (3HB-BD ester). On the 14th day, animal brains were removed by freeze-blowing, and brain metabolites measured. Animals fed the ketone ester diet had elevated mean blood ketone bodies of 3.5 mm and lowered plasma glucose, insulin, and leptin. Despite the decreased plasma leptin, feeding the ketone ester diet ad lib decreased voluntary food intake 2-fold for 6 days while brain malonyl-CoA was increased by about 25% in ketone-fed group but not in the palm oil fed group. Unlike the acute effects of ketone body metabolism in the perfused working heart, there was no increased reduction in brain free mitochondrial [NAD(+)]/[NADH] ratio nor in the free energy of ATP hydrolysis, which was compatible with the observed 1.5-fold increase in brain uncoupling proteins 4 and 5. Feeding ketone ester or palm oil supplemented diets decreased brain L-glutamate by 15-20% and GABA by about 34% supporting the view that fatty acids as well as ketone bodies can be metabolized by the brain.
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Affiliation(s)
- Yoshihiro Kashiwaya
- From the Laboratory of Metabolic Control, NIAAA, National Institutes of Health, Rockville, Maryland 20852-9047
| | - Robert Pawlosky
- From the Laboratory of Metabolic Control, NIAAA, National Institutes of Health, Rockville, Maryland 20852-9047
| | - William Markis
- From the Laboratory of Metabolic Control, NIAAA, National Institutes of Health, Rockville, Maryland 20852-9047
| | - M. Todd King
- From the Laboratory of Metabolic Control, NIAAA, National Institutes of Health, Rockville, Maryland 20852-9047
| | - Christian Bergman
- From the Laboratory of Metabolic Control, NIAAA, National Institutes of Health, Rockville, Maryland 20852-9047
| | - Shireesh Srivastava
- From the Laboratory of Metabolic Control, NIAAA, National Institutes of Health, Rockville, Maryland 20852-9047
| | - Andrew Murray
- the Department of Physiology, Development & Neuroscience, University of Cambridge, Cambridge CB2 3EG, United Kingdom, and
| | - Kieran Clarke
- the Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford OX1 3PT, United Kingdom
| | - Richard L. Veech
- From the Laboratory of Metabolic Control, NIAAA, National Institutes of Health, Rockville, Maryland 20852-9047
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