1
|
Bréhat J, Issop L, Morin D. History of Tspo deletion and induction in vivo: Phenotypic outcomes under physiological and pathological situations. Biochimie 2024; 224:80-90. [PMID: 38432291 DOI: 10.1016/j.biochi.2024.03.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 02/23/2024] [Accepted: 03/01/2024] [Indexed: 03/05/2024]
Abstract
The mitochondrial translocator protein (TSPO) is an outer mitochondrial protein membrane with high affinity for cholesterol. It is expressed in most tissues but is more particularly enriched in steroidogenic tissues. TSPO is involved in various biological mechanisms and TSPO regulation has been related to several diseases. However, despite a considerable number of published studies interested in TSPO over the past forty years, the precise function of the protein remains obscure. Most of the functions attributed to TSPO have been identified using pharmacological ligands of this protein, leading to much debate about the accuracy of these findings. In addition, research on the physiological role of TSPO has been hampered by the lack of in vivo deletion models. Studies to perform genetic deletion of Tspo in animal models have long been unsuccessful, which led to the conclusions that the deletion was deleterious and the gene essential to life. During the last decades, thanks to the significant technical advances allowing genome modification, several models of animal genetically modified for TSPO have been developed. These models have modified our view regarding TSPO and profoundly improved our fundamental knowledge on this protein. However, to date, they did not allow to elucidate the precise molecular function of TSPO and numerous questions persist concerning the physiological role of TSPO and its future as a therapeutic target. This article chronologically reviews the development of deletion and induction models of TSPO.
Collapse
Affiliation(s)
- Juliette Bréhat
- INSERM U955-IMRB, Team Ghaleh, UPEC, Ecole Nationale Vétérinaire d'Alfort, Créteil, France
| | - Leeyah Issop
- INSERM U955-IMRB, Team Ghaleh, UPEC, Ecole Nationale Vétérinaire d'Alfort, Créteil, France
| | - Didier Morin
- INSERM U955-IMRB, Team Ghaleh, UPEC, Ecole Nationale Vétérinaire d'Alfort, Créteil, France.
| |
Collapse
|
2
|
El Chemali L, Boutary S, Liu S, Liu GJ, Middleton RJ, Banati RB, Bahrenberg G, Rupprecht R, Schumacher M, Massaad-Massade L. GRT-X Stimulates Dorsal Root Ganglia Axonal Growth in Culture via TSPO and Kv7.2/3 Potassium Channel Activation. Int J Mol Sci 2024; 25:7327. [PMID: 39000434 PMCID: PMC11242890 DOI: 10.3390/ijms25137327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2024] [Revised: 06/27/2024] [Accepted: 06/30/2024] [Indexed: 07/16/2024] Open
Abstract
GRT-X, which targets both the mitochondrial translocator protein (TSPO) and the Kv7.2/3 (KCNQ2/3) potassium channels, has been shown to efficiently promote recovery from cervical spine injury. In the present work, we investigate the role of GRT-X and its two targets in the axonal growth of dorsal root ganglion (DRG) neurons. Neurite outgrowth was quantified in DRG explant cultures prepared from wild-type C57BL6/J and TSPO-KO mice. TSPO was pharmacologically targeted with the agonist XBD173 and the Kv7 channels with the activator ICA-27243 and the inhibitor XE991. GRT-X efficiently stimulated DRG axonal growth at 4 and 8 days after its single administration. XBD173 also promoted axonal elongation, but only after 8 days and its repeated administration. In contrast, both ICA27243 and XE991 tended to decrease axonal elongation. In dissociated DRG neuron/Schwann cell co-cultures, GRT-X upregulated the expression of genes associated with axonal growth and myelination. In the TSPO-KO DRG cultures, the stimulatory effect of GRT-X on axonal growth was completely lost. However, GRT-X and XBD173 activated neuronal and Schwann cell gene expression after TSPO knockout, indicating the presence of additional targets warranting further investigation. These findings uncover a key role of the dual mode of action of GRT-X in the axonal elongation of DRG neurons.
Collapse
Affiliation(s)
- Léa El Chemali
- Maladies et Hormones du Système Nerveux, Inserm, Université Paris-Saclay, 94276 Le Kremlin-Bicêtre, France
| | - Suzan Boutary
- Maladies et Hormones du Système Nerveux, Inserm, Université Paris-Saclay, 94276 Le Kremlin-Bicêtre, France
| | - Song Liu
- Maladies et Hormones du Système Nerveux, Inserm, Université Paris-Saclay, 94276 Le Kremlin-Bicêtre, France
| | - Guo-Jun Liu
- Australian Nuclear Science and Technology Organisation (ANSTO), Kirrawee, NSW 2232, Australia
- Faculty of Medicine and Health, University of Sydney, Camperdown, NSW 2006, Australia
| | - Ryan J Middleton
- Australian Nuclear Science and Technology Organisation (ANSTO), Kirrawee, NSW 2232, Australia
| | - Richard B Banati
- Faculty of Medicine and Health, University of Sydney, Camperdown, NSW 2006, Australia
| | - Gregor Bahrenberg
- Global Preclinical R&D, Grünenthal Innovation, Grünenthal GmbH, Zieglerstraße 6, D-52078 Aachen, Germany
| | - Rainer Rupprecht
- Department of Psychiatry and Psychotherapy, University of Regensburg, D-93053 Regensburg, Germany
| | - Michael Schumacher
- Maladies et Hormones du Système Nerveux, Inserm, Université Paris-Saclay, 94276 Le Kremlin-Bicêtre, France
| | - Liliane Massaad-Massade
- Maladies et Hormones du Système Nerveux, Inserm, Université Paris-Saclay, 94276 Le Kremlin-Bicêtre, France
| |
Collapse
|
3
|
Vicente-Rodríguez M, Mancuso R, Peris-Yague A, Simmons C, Gómez-Nicola D, Perry VH, Turkheimer F, Lovestone S, Parker CA, Cash D. Pharmacological modulation of TSPO in microglia/macrophages and neurons in a chronic neurodegenerative model of prion disease. J Neuroinflammation 2023; 20:92. [PMID: 37032328 PMCID: PMC10084680 DOI: 10.1186/s12974-023-02769-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Accepted: 03/20/2023] [Indexed: 04/11/2023] Open
Abstract
Neuroinflammation is an important component of many neurodegenerative diseases, whether as a primary cause or a secondary outcome. For that reason, either as diagnostic tools or to monitor progression and/or pharmacological interventions, there is a need for robust biomarkers of neuroinflammation in the brain. Mitochondrial TSPO (18 kDa Translocator protein) is one of few available biomarkers of neuroinflammation for which there are clinically available PET imaging agents. In this study, we further characterised neuroinflammation in a mouse model of prion-induced chronic neurodegeneration (ME7) including a pharmacological intervention via a CSF1R inhibitor. This was achieved by autoradiographic binding of the second-generation TSPO tracer, [3H]PBR28, along with a more comprehensive examination of the cellular contributors to the TSPO signal changes by immunohistochemistry. We observed regional increases of TSPO in the ME7 mouse brains, particularly in the hippocampus, cortex and thalamus. This increased TSPO signal was detected in the cells of microglia/macrophage lineage as well as in astrocytes, endothelial cells and neurons. Importantly, we show that the selective CSF1R inhibitor, JNJ-40346527 (JNJ527), attenuated the disease-dependent increase in TSPO signal, particularly in the dentate gyrus of the hippocampus, where JNJ527 attenuated the number of Iba1+ microglia and neurons, but not GFAP+ astrocytes or endothelial cells. These findings suggest that [3H]PBR28 quantitative autoradiography in combination with immunohistochemistry are important translational tools for detecting and quantifying neuroinflammation, and its treatments, in neurodegenerative disease. Furthermore, we demonstrate that although TSPO overexpression in the ME7 brains was driven by various cell types, the therapeutic effect of the CSF1R inhibitor was primarily to modulate TSPO expression in microglia and neurons, which identifies an important route of biological action of this particular CSF1R inhibitor and provides an example of a cell-specific effect of this type of therapeutic agent on the neuroinflammatory process.
Collapse
Affiliation(s)
- Marta Vicente-Rodríguez
- Department of Neuroimaging, BRAIN Centre (Biomarker Research and Imaging for Neuroscience), Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK.
- The Wellcome Trust Consortium for the Neuroimmunology of Mood Disorders and Alzheimer's Disease (NIMA), London, UK.
- Departamento de Ciencias Farmacéuticas y de la Salud, Facultad de Farmacia, Universidad San Pablo-CEU, CEU Universities, Madrid, Spain.
| | - Renzo Mancuso
- The Wellcome Trust Consortium for the Neuroimmunology of Mood Disorders and Alzheimer's Disease (NIMA), London, UK
- Microglia and Inflammation in Neurological Disorders (MIND) Lab, VIB Center for Molecular Neurology, VIB, Antwerp, Belgium
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
- Biological Sciences, Southampton General Hospital, University of Southampton, Southampton, UK
| | - Alba Peris-Yague
- Department of Neuroimaging, BRAIN Centre (Biomarker Research and Imaging for Neuroscience), Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK
| | - Camilla Simmons
- Department of Neuroimaging, BRAIN Centre (Biomarker Research and Imaging for Neuroscience), Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK
- The Wellcome Trust Consortium for the Neuroimmunology of Mood Disorders and Alzheimer's Disease (NIMA), London, UK
| | - Diego Gómez-Nicola
- The Wellcome Trust Consortium for the Neuroimmunology of Mood Disorders and Alzheimer's Disease (NIMA), London, UK
- Biological Sciences, Southampton General Hospital, University of Southampton, Southampton, UK
| | - V Hugh Perry
- The Wellcome Trust Consortium for the Neuroimmunology of Mood Disorders and Alzheimer's Disease (NIMA), London, UK
- Biological Sciences, Southampton General Hospital, University of Southampton, Southampton, UK
| | - Federico Turkheimer
- Department of Neuroimaging, BRAIN Centre (Biomarker Research and Imaging for Neuroscience), Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK
- The Wellcome Trust Consortium for the Neuroimmunology of Mood Disorders and Alzheimer's Disease (NIMA), London, UK
| | - Simon Lovestone
- The Wellcome Trust Consortium for the Neuroimmunology of Mood Disorders and Alzheimer's Disease (NIMA), London, UK
- Janssen Medical Ltd, High Wycombe, UK
| | - Christine A Parker
- Department of Neuroimaging, BRAIN Centre (Biomarker Research and Imaging for Neuroscience), Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK
- The Wellcome Trust Consortium for the Neuroimmunology of Mood Disorders and Alzheimer's Disease (NIMA), London, UK
- GlaxoSmithKline, Stevenage, London, UK
| | - Diana Cash
- Department of Neuroimaging, BRAIN Centre (Biomarker Research and Imaging for Neuroscience), Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, UK
- The Wellcome Trust Consortium for the Neuroimmunology of Mood Disorders and Alzheimer's Disease (NIMA), London, UK
| |
Collapse
|
4
|
Liu J, Hiser C, Li F, Hall R, Garavito RM, Ferguson-Miller S. New TSPO Crystal Structures of Mutant and Heme-Bound Forms with Altered Flexibility, Ligand Binding, and Porphyrin Degradation Activity. Biochemistry 2023; 62:1262-1273. [PMID: 36947867 PMCID: PMC10077581 DOI: 10.1021/acs.biochem.2c00612] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 03/09/2023] [Indexed: 03/24/2023]
Abstract
The ancient protein TSPO (translocator protein 18kD) is found in all kingdoms and was originally identified as a binding site of benzodiazepine drugs. Its physiological function remains unclear, although porphyrins are conserved ligands. Several crystal structures of bacterial TSPO and nuclear magnetic resonance structures of a mouse form have revealed monomer and dimer configurations, but there have been no reports of structures with a physiological ligand. Here, we present the first X-ray structures of Rhodobacter sphaeroides TSPO with a physiological ligand bound. Two different variants (substituting threonine for alanine at position 139 (A139T) and phenylalanine for alanine at position 138 (A138F)) yielded well-diffracting crystals giving structures of both apo- and heme-containing forms. Both variants have wild-type micromolar affinity for heme and protoporphyrin IX, but A139T has very low ability to accelerate the breakdown of porphyrin in the presence of light and oxygen. The binding of heme to one protomer of the dimer of either mutant induces a more rigid structure, both in the heme-binding protomer and the protomer without heme bound, demonstrating an allosteric response. Ensemble refinement of the X-ray data reveals distinct regions of altered flexibility in response to single heme binding to the dimer. The A139T variant shows a more rigid structure overall, which may relate to extra hydrogen bonding of waters captured in the heme crevice. As TSPO has been suggested to have a role in heme delivery from mitochondria to the cytoplasm, the new structures provide potential clues regarding the structural basis of such activity.
Collapse
Affiliation(s)
- Jian Liu
- Department
of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Carrie Hiser
- Department
of Biochemistry and Molecular Biology, Michigan
State University, East Lansing, Michigan 48824, United States
| | - Fei Li
- Amgen
Inc., San Francisco, California 94080, United States
| | - Robert Hall
- Pharmacology
and Chemical Biology, University of Pittsburgh
School of Medicine, Pittsburgh, Pennsylvania 15213, United States
| | - R. Michael Garavito
- Department
of Biochemistry and Molecular Biology, Michigan
State University, East Lansing, Michigan 48824, United States
| | - Shelagh Ferguson-Miller
- Department
of Biochemistry and Molecular Biology, Michigan
State University, East Lansing, Michigan 48824, United States
| |
Collapse
|
5
|
Liere P, Liu GJ, Pianos A, Middleton RJ, Banati RB, Akwa Y. The Comprehensive Steroidome in Complete TSPO/PBR Knockout Mice under Basal Conditions. Int J Mol Sci 2023; 24:ijms24032474. [PMID: 36768796 PMCID: PMC9916858 DOI: 10.3390/ijms24032474] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 01/23/2023] [Accepted: 01/25/2023] [Indexed: 01/31/2023] Open
Abstract
The 18 kDa translocator protein (TSPO/PBR) is a multifunctional evolutionary highly conserved outer mitochondrial membrane protein. Decades of research has reported an obligatory role of TSPO/PBR in both mitochondrial cholesterol transport and, thus, steroid production. However, the strict dependency of steroidogenesis on TSPO/PBR has remained controversial. The aim of this study was to provide insight into the steroid profile in complete C57BL/6-Tspotm1GuWu(GuwiyangWurra)-knockout male mice (TSPO-KO) under basal conditions. The steroidome in the brain, adrenal glands, testes and plasma was measured by gas chromatography coupled to tandem mass spectrometry (GC-MS/MS). We found that steroids present in wild-type (WT) mice were also detected in TSPO-KO mice, including pregnenolone (PREG), progestogens, mineralo-glucocorticosteroids and androgens. The concentrations of PREG and most metabolites were similar between genotypes, except a significant decrease in the levels of the 5α-reduced metabolites of progesterone (PROG) in adrenal glands and plasma and of the 5α-reduced metabolites of corticosterone (B) in plasma in TSPO-KO compared to WT animals, suggesting other regulatory functions for the TSPO/PBR. The expression levels of the voltage-dependent anion-selective channel (VDAC-1), CYP11A1 and 5α-reductase were not significantly different between both groups. Thus, the complete deletion of the tspo gene in male mice does not impair de novo steroidogenesis in vivo.
Collapse
Affiliation(s)
- Philippe Liere
- Disease and Hormones of the Nervous System, U1195 Inserm-Université Paris Saclay, 80 rue du Général Leclerc, 94276 Kremlin-Bicêtre, France
| | - Guo-Jun Liu
- Australian Nuclear Science and Technology Organisation (ANSTO), Kirrawee, NSW 2232, Australia
- Faculty of Medicine and Health, Medical Imaging Sciences, Brain and Mind Centre, University of Sydney, Camperdown, NSW 2006, Australia
| | - Antoine Pianos
- Disease and Hormones of the Nervous System, U1195 Inserm-Université Paris Saclay, 80 rue du Général Leclerc, 94276 Kremlin-Bicêtre, France
| | - Ryan J. Middleton
- Australian Nuclear Science and Technology Organisation (ANSTO), Kirrawee, NSW 2232, Australia
| | - Richard B. Banati
- Australian Nuclear Science and Technology Organisation (ANSTO), Kirrawee, NSW 2232, Australia
- Faculty of Medicine and Health, Medical Imaging Sciences, Brain and Mind Centre, University of Sydney, Camperdown, NSW 2006, Australia
| | - Yvette Akwa
- Disease and Hormones of the Nervous System, U1195 Inserm-Université Paris Saclay, 80 rue du Général Leclerc, 94276 Kremlin-Bicêtre, France
- Correspondence: ; Tel.: +33-(0)1-49591878
| |
Collapse
|
6
|
Yue YY, Wang YC, Liao ZX, Hu FY, Liu QY, Dong J, Zhong M, Chen MH, Pan YM, Zhong H, Shang J. Peripheral benzodiazepine receptor TSPO needs to be reconsidered before using as a drug target for a pigmentary disorder. FASEB J 2022; 36:e22454. [PMID: 35839067 DOI: 10.1096/fj.202101746rr] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 06/19/2022] [Accepted: 07/06/2022] [Indexed: 11/11/2022]
Abstract
The peripheral benzodiazepine receptor (TSPO/PBR) is highly conserved among different species but with perplexing biochemical functions. Multiple ligands of TSPO show commendable regulatory activities in lots of biological functions, such as neuro-protection, cholesterol transport, and so on. These researches support that TSPO may be a potential target for disease treatment and drug development. Previous studies have shown that its ligands benzodiazepines show a satisfactory effect on melanogenic promotion. However, the potential application of TSPO in drug development for pigmentary disorder needs further investigation. In this study, we confirmed the melanogenesis induction of TSPO ligand, Ro5-4864 in mouse melanoma cell lines, human skin tissue, and zebrafish embryos by inducing melanin synthesis and melanosome transport. Molecular genetics and pharmacological studies showed that TSPO deficiency did not affect melanin production in B16F10 cells and zebrafish embryos, nor did it affect the melanin promotion effect of Ro5-4864. Whether or not TSPO exists, the expression of lots of melanogenesis-related proteins, such as TYR, TRP-1, DCT, Mlph, and Rab27 was upregulated with the Ro5-4864 administration. These results indicated that Ro5-4864 induces melanogenesis in a TSPO-independent manner, which is inconsistent with previous research. This research is a reminder that we need to be very careful during target validation in drug development.
Collapse
Affiliation(s)
- Yun-Yun Yue
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, China
| | - Yi-Chuan Wang
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, China
| | - Zi-Xian Liao
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, China
| | - Fang-Yuan Hu
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, China
| | - Qiu-Yan Liu
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, China
| | - Jing Dong
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, China
| | - Min Zhong
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, China
| | - Ming-Han Chen
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, China
| | - Yu-Min Pan
- School of Chemistry and Pharmacy, Guangxi Normal University, Guilin, China
| | - Hui Zhong
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, China
| | - Jing Shang
- School of Traditional Chinese Pharmacy, China Pharmaceutical University, Nanjing, China.,State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing, China.,Jiangsu Key Laboratory of TCM Evaluation and Translational Research, China Pharmaceutical University, Nanjing, China.,NMPA Key Laboratory for Research and Evaluation of Cosmetics, National Institutes for Food and Drug Control, Beijing, China
| |
Collapse
|
7
|
Resolving the cellular specificity of TSPO imaging in a rat model of peripherally-induced neuroinflammation. Brain Behav Immun 2021; 96:154-167. [PMID: 34052363 PMCID: PMC8323128 DOI: 10.1016/j.bbi.2021.05.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/25/2020] [Revised: 03/09/2021] [Accepted: 05/25/2021] [Indexed: 12/20/2022] Open
Abstract
The increased expression of 18 kDa Translocator protein (TSPO) is one of the few available biomarkers of neuroinflammation that can be assessed in humans in vivo by positron emission tomography (PET). TSPO PET imaging of the central nervous system (CNS) has been widely undertaken, but to date no clear consensus has been reached about its utility in brain disorders. One reason for this could be because the interpretation of TSPO PET signal remains challenging, given the cellular heterogeneity and ubiquity of TSPO in the brain. The aim of the current study was to ascertain if TSPO PET imaging can be used to detect neuroinflammation induced by a peripheral treatment with a low dose of the endotoxin, lipopolysaccharide (LPS), in a rat model (ip LPS), and investigate the origin of TSPO signal changes in terms of their cellular sources and regional distribution. An initial pilot study utilising both [18F]DPA-714 and [11C]PK11195 TSPO radiotracers demonstrated [18F]DPA-714 to exhibit a significantly higher lesion-related signal in the intracerebral LPS rat model (ic LPS) than [11C]PK11195. Subsequently, [18F]DPA-714 was selected for use in the ip LPS study. Twenty-four hours after ip LPS, there was an increased uptake of [18F]DPA-714 across the whole brain. Further analyses of regions of interest, using immunohistochemistry and RNAscope Multiplex fluorescence V2 in situ hybridization technology, showed TSPO expression in microglia, monocyte derived-macrophages, astrocytes, neurons and endothelial cells. The expression of TSPO was significantly increased after ip LPS in a region-dependent manner: with increased microglia, monocyte-derived macrophages and astrocytes in the substantia nigra, in contrast to the hippocampus where TSPO was mostly confined to microglia and astrocytes. In summary, our data demonstrate the robust detection of peripherally-induced neuroinflammation in the CNS utilising the TSPO PET radiotracer, [18F]DPA-714, and importantly, confirm that the resultant increase in TSPO signal increase arises mostly from a combination of microglia, astrocytes and monocyte-derived macrophages.
Collapse
|
8
|
Hiser C, Montgomery BL, Ferguson-Miller S. TSPO protein binding partners in bacteria, animals, and plants. J Bioenerg Biomembr 2021; 53:463-487. [PMID: 34191248 PMCID: PMC8243069 DOI: 10.1007/s10863-021-09905-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Accepted: 06/12/2021] [Indexed: 12/11/2022]
Abstract
The ancient membrane protein TSPO is phylogenetically widespread from archaea and bacteria to insects, vertebrates, plants, and fungi. TSPO’s primary amino acid sequence is only modestly conserved between diverse species, although its five transmembrane helical structure appears mainly conserved. Its cellular location and orientation in membranes have been reported to vary between species and tissues, with implications for potential diverse binding partners and function. Most TSPO functions relate to stress-induced changes in metabolism, but in many cases it is unclear how TSPO itself functions—whether as a receptor, a sensor, a transporter, or a translocator. Much evidence suggests that TSPO acts indirectly by association with various protein binding partners or with endogenous or exogenous ligands. In this review, we focus on proteins that have most commonly been invoked as TSPO binding partners. We suggest that TSPO was originally a bacterial receptor/stress sensor associated with porphyrin binding as its most ancestral function and that it later developed additional stress-related roles in eukaryotes as its ability to bind new partners evolved.
Collapse
Affiliation(s)
- Carrie Hiser
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA. .,Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI, 48824, USA.
| | - Beronda L Montgomery
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA.,Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI, 48824, USA.,Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, 48824, USA
| | - Shelagh Ferguson-Miller
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA
| |
Collapse
|
9
|
Betlazar C, Middleton RJ, Banati R, Liu GJ. The Translocator Protein (TSPO) in Mitochondrial Bioenergetics and Immune Processes. Cells 2020; 9:cells9020512. [PMID: 32102369 PMCID: PMC7072813 DOI: 10.3390/cells9020512] [Citation(s) in RCA: 66] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2020] [Revised: 02/19/2020] [Accepted: 02/19/2020] [Indexed: 12/11/2022] Open
Abstract
The translocator protein (TSPO) is an outer mitochondrial membrane protein that is widely used as a biomarker of neuroinflammation, being markedly upregulated in activated microglia in a range of brain pathologies. Despite its extensive use as a target in molecular imaging studies, the exact cellular functions of this protein remain in question. The long-held view that TSPO plays a fundamental role in the translocation of cholesterol through the mitochondrial membranes, and thus, steroidogenesis, has been disputed by several groups with the advent of TSPO knockout mouse models. Instead, much evidence is emerging that TSPO plays a fundamental role in cellular bioenergetics and associated mitochondrial functions, also part of a greater role in the innate immune processes of microglia. In this review, we examine the more direct experimental literature surrounding the immunomodulatory effects of TSPO. We also review studies which highlight a more central role for TSPO in mitochondrial processes, from energy metabolism, to the propagation of inflammatory responses through reactive oxygen species (ROS) modulation. In this way, we highlight a paradigm shift in approaches to TSPO functioning.
Collapse
Affiliation(s)
- Calina Betlazar
- Human Health, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia; (R.J.M.); (R.B.)
- Discipline of Medical Imaging & Radiation Sciences, Faculty of Medicine and Health, Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, NSW 2050, Australia
- Correspondence: (C.B.); (G-J.L.)
| | - Ryan J. Middleton
- Human Health, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia; (R.J.M.); (R.B.)
| | - Richard Banati
- Human Health, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia; (R.J.M.); (R.B.)
- Discipline of Medical Imaging & Radiation Sciences, Faculty of Medicine and Health, Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, NSW 2050, Australia
| | - Guo-Jun Liu
- Human Health, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia; (R.J.M.); (R.B.)
- Discipline of Medical Imaging & Radiation Sciences, Faculty of Medicine and Health, Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, NSW 2050, Australia
- Correspondence: (C.B.); (G-J.L.)
| |
Collapse
|
10
|
Regulation of Mitochondrial, Cellular, and Organismal Functions by TSPO. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2017; 82:103-136. [PMID: 29413517 DOI: 10.1016/bs.apha.2017.09.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
In 1999, the enigma of the 18kDa mitochondrial translocator protein (TSPO), also known as the peripheral-type benzodiazepine receptor, was the seeming disparity of the many functions attributed to TSPO, ranging from the potential of TSPO acting as a housekeeping gene at molecular biological levels to adaptations to stress, and even involvement in higher emotional and cognitive functioning, such as anxiety and depression. In the years since then, knowledge regarding the many functions modulated by TSPO has expanded, and understanding has deepened. In addition, new functions could be firmly associated with TSPO, such as regulation of programmed cell death and modulation of gene expression. Interestingly, control by the mitochondrial TSPO over both of these life and death functions appears to include Ca++ homeostasis, generation of reactive oxygen species (ROS), and ATP production. Other mitochondrial functions under TSPO control are considered to be steroidogenesis and tetrapyrrole metabolism. As TSPO effects on gene expression and on programmed cell death can be related to the wide range of functions that can be associated with TSPO, several of these five elements of Ca++, ROS, ATP, steroids, and tetrapyrroles may indeed form the basis of TSPO's capability to operate as a multifunctional housekeeping gene to maintain homeostasis of the cell and of the whole multicellular organism.
Collapse
|
11
|
Classical and Novel TSPO Ligands for the Mitochondrial TSPO Can Modulate Nuclear Gene Expression: Implications for Mitochondrial Retrograde Signaling. Int J Mol Sci 2017; 18:ijms18040786. [PMID: 28387723 PMCID: PMC5412370 DOI: 10.3390/ijms18040786] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2017] [Revised: 03/24/2017] [Accepted: 03/27/2017] [Indexed: 12/22/2022] Open
Abstract
It is known that knockdown of the mitochondrial 18 kDa translocator protein (TSPO) as well as TSPO ligands modulate various functions, including functions related to cancer. To study the ability of TSPO to regulate gene expression regarding such functions, we applied microarray analysis of gene expression to U118MG glioblastoma cells. Within 15 min, the classical TSPO ligand PK 11195 induced changes in expression of immediate early genes and transcription factors. These changes also included gene products that are part of the canonical pathway serving to modulate general gene expression. These changes are in accord with real-time, reverse transcriptase (RT) PCR. At the time points of 15, 30, 45, and 60 min, as well as 3 and 24 h of PK 11195 exposure, the functions associated with the changes in gene expression in these glioblastoma cells covered well known TSPO functions. These functions included cell viability, proliferation, differentiation, adhesion, migration, tumorigenesis, and angiogenesis. This was corroborated microscopically for cell migration, cell accumulation, adhesion, and neuronal differentiation. Changes in gene expression at 24 h of PK 11195 exposure were related to downregulation of tumorigenesis and upregulation of programmed cell death. In the vehicle treated as well as PK 11195 exposed cell cultures, our triple labeling showed intense TSPO labeling in the mitochondria but no TSPO signal in the cell nuclei. Thus, mitochondrial TSPO appears to be part of the mitochondria-to-nucleus signaling pathway for modulation of nuclear gene expression. The novel TSPO ligand 2-Cl-MGV-1 appeared to be very specific regarding modulation of gene expression of immediate early genes and transcription factors.
Collapse
|
12
|
Liu GJ, Middleton RJ, Kam WWY, Chin DY, Hatty CR, Chan RHY, Banati RB. Functional gains in energy and cell metabolism after TSPO gene insertion. Cell Cycle 2017; 16:436-447. [PMID: 28103132 PMCID: PMC5351937 DOI: 10.1080/15384101.2017.1281477] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Recent loss-of-function studies in tissue-specific as well as global Tspo (Translocator Protein 18 kDa) knockout mice have not confirmed its long assumed indispensability for the translocation of cholesterol across the mitochondrial inter-membrane space, a rate-limiting step in steroid biosynthesis. Instead, recent studies in global Tspo knockout mice indicate that TSPO may play a more fundamental role in cellular bioenergetics, which may include the indirect down-stream regulation of transport or metabolic functions. To examine whether overexpression of the TSPO protein alters the cellular bioenergetic profile, Jurkat cells with low to absent endogenous expression were transfected with a TSPO construct to create a stable cell line with de novo expression of exogenous TSPO protein. Expression of TSPO was confirmed by RT-qPCR, radioligand binding with [3H]PK11195 and immunocytochemistry with a TSPO antibody. We demonstrate that TSPO gene insertion causes increased transcription of genes involved in the mitochondrial electron transport chain. Furthermore, TSPO insertion increased mitochondrial ATP production as well as cell excitability, reflected in a decrease in patch clamp recorded rectified K channel currents. These functional changes were accompanied by an increase in cell proliferation and motility, which were inhibited by PK11195, a selective ligand for TSPO. We suggest that TSPO may serve a range of functions that can be viewed as downstream regulatory effects of its primary, evolutionary conserved role in cell metabolism and energy production.
Collapse
Affiliation(s)
- Guo-Jun Liu
- a Australian Nuclear Science and Technology Organisation , Lucas Heights , NSW , Australia.,b Faculty of Health Science and Brain and Mind Centre, University of Sydney , NSW , Australia
| | - Ryan J Middleton
- a Australian Nuclear Science and Technology Organisation , Lucas Heights , NSW , Australia
| | - Winnie Wai-Ying Kam
- a Australian Nuclear Science and Technology Organisation , Lucas Heights , NSW , Australia.,c Department of Health Technology and Informatics , Hong Kong Polytechnic University , Hung Hom, Hong Kong , China
| | - David Y Chin
- d NCRIS Biologics Facility, Australian Institute for Bioengineering and Nanotechnology, University of Queensland , QLD , Australia
| | - Claire R Hatty
- a Australian Nuclear Science and Technology Organisation , Lucas Heights , NSW , Australia.,b Faculty of Health Science and Brain and Mind Centre, University of Sydney , NSW , Australia
| | - Ronald H Y Chan
- a Australian Nuclear Science and Technology Organisation , Lucas Heights , NSW , Australia.,b Faculty of Health Science and Brain and Mind Centre, University of Sydney , NSW , Australia
| | - Richard B Banati
- a Australian Nuclear Science and Technology Organisation , Lucas Heights , NSW , Australia.,b Faculty of Health Science and Brain and Mind Centre, University of Sydney , NSW , Australia
| |
Collapse
|
13
|
Wang H, Zhai K, Xue Y, Yang J, Yang Q, Fu Y, Hu Y, Liu F, Wang W, Cui L, Chen H, Zhang J, He W. Global Deletion of TSPO Does Not Affect the Viability and Gene Expression Profile. PLoS One 2016; 11:e0167307. [PMID: 27907096 PMCID: PMC5131929 DOI: 10.1371/journal.pone.0167307] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Accepted: 11/12/2016] [Indexed: 01/30/2023] Open
Abstract
Translocator Protein (18kDa, TSPO) is a mitochondrial outer membrane transmembrane protein. Its expression is elevated during inflammation and injury. However, the function of TSPO in vivo is still controversial. Here, we constructed a TSPO global knockout (KO) mouse with a Cre-LoxP system that abolished TSPO protein expression in all tissues and showed normal phenotypes in the physiological condition. The birth rates of TSPO heterozygote (Het) x Het or KO x KO breeding were consistent with Mendel’s Law, suggesting a normal viability of TSPO KO mice at birth. RNA-seq analysis showed no significant difference in the gene expression profile of lung tissues from TSPO KO mice compared with wild type mice, including the genes associated with bronchial alveoli immune homeostasis. The alveolar macrophage population was not affected by TSPO deletion in the physiological condition. Our findings contradict the results of Papadopoulos, but confirmed Selvaraj’s findings. This study confirms TSPO deficiency does not affect viability and bronchial alveolar immune homeostasis.
Collapse
Affiliation(s)
- Huaishan Wang
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
| | - Kangle Zhai
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
| | - Yingchao Xue
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
| | - Jia Yang
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
| | - Qi Yang
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
| | - Yi Fu
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
| | - Yu Hu
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
| | - Fang Liu
- Beijing Thorgene Medical Laboratory, Yizhuang Biomedical Park, Beijing, China
| | - Weiqing Wang
- Department of Otolaryngology, Peking Union Medical College Hospital, Chinese Academy of Medical Science and Peking Union Medical College, Beijing, China
| | - Lianxian Cui
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
| | - Hui Chen
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
| | - Jianmin Zhang
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
- * E-mail: (WH); (JZ)
| | - Wei He
- Department of Immunology, Research Center on Pediatric Development and Diseases, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and School of Basic Medicine, Peking Union Medical College, State Key Laboratory of Medical Molecular Biology, Beijing, China
- * E-mail: (WH); (JZ)
| |
Collapse
|
14
|
Selvaraj V, Tu LN. Current status and future perspectives: TSPO in steroid neuroendocrinology. J Endocrinol 2016; 231:R1-R30. [PMID: 27422254 DOI: 10.1530/joe-16-0241] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 07/15/2016] [Indexed: 12/21/2022]
Abstract
The mitochondrial translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), has received significant attention both as a diagnostic biomarker and as a therapeutic target for different neuronal disease pathologies. Recently, its functional basis believed to be mediating mitochondrial cholesterol import for steroid hormone production has been refuted by studies examining both in vivo and in vitro genetic Tspo-deficient models. As a result, there now exists a fundamental gap in the understanding of TSPO function in the nervous system, and its putative pharmacology in neurosteroid production. In this review, we discuss several recent findings in steroidogenic cells that are in direct contradiction to previous studies, and necessitate a re-examination of the purported role for TSPO in de novo neurosteroid biosynthesis. We critically examine the pharmacological effects of different TSPO-binding drugs with particular focus on studies that measure neurosteroid levels. We highlight the basis of key misconceptions regarding TSPO that continue to pervade the literature, and the need for interpretation with caution to avoid negative impacts. We also summarize the emerging perspectives that point to new directions that need to be investigated for understanding the molecular function of TSPO, only after which the true potential of this therapeutic target in medicine may be realized.
Collapse
Affiliation(s)
- Vimal Selvaraj
- Department of Animal ScienceCornell University, Ithaca, New York, USA
| | - Lan N Tu
- Department of Animal ScienceCornell University, Ithaca, New York, USA
| |
Collapse
|
15
|
Betlazar C, Middleton RJ, Banati RB, Liu GJ. The impact of high and low dose ionising radiation on the central nervous system. Redox Biol 2016; 9:144-156. [PMID: 27544883 PMCID: PMC4993858 DOI: 10.1016/j.redox.2016.08.002] [Citation(s) in RCA: 80] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 08/06/2016] [Accepted: 08/09/2016] [Indexed: 12/12/2022] Open
Abstract
Responses of the central nervous system (CNS) to stressors and injuries, such as ionising radiation, are modulated by the concomitant responses of the brains innate immune effector cells, microglia. Exposure to high doses of ionising radiation in brain tissue leads to the expression and release of biochemical mediators of ‘neuroinflammation’, such as pro-inflammatory cytokines and reactive oxygen species (ROS), leading to tissue destruction. Contrastingly, low dose ionising radiation may reduce vulnerability to subsequent exposure of ionising radiation, largely through the stimulation of adaptive responses, such as antioxidant defences. These disparate responses may be reflective of non-linear differential microglial activation at low and high doses, manifesting as an anti-inflammatory or pro-inflammatory functional state. Biomarkers of pathology in the brain, such as the mitochondrial Translocator Protein 18 kDa (TSPO), have facilitated in vivo characterisation of microglial activation and ‘neuroinflammation’ in many pathological states of the CNS, though the exact function of TSPO in these responses remains elusive. Based on the known responsiveness of TSPO expression to a wide range of noxious stimuli, we discuss TSPO as a potential biomarker of radiation-induced effects. Ionising radiation can modulate responses of microglial cells in the CNS. High doses can induce ROS formation, oxidative stress and neuroinflammation. Low doses can mitigate tissue damage via antioxidant defences. TSPO as a potential biomarker and modulator of radiation induced effects in the CNS. Non-linear differential microglial activation to high and low doses is proposed.
Collapse
Affiliation(s)
- Calina Betlazar
- Bioanalytics group, Life Sciences, Australian Nuclear Science and Technology Organisation (ANSTO), New Illawarra Road, Lucas Heights, NSW 2234, Australia; Discipline of Medical Imaging & Radiation Sciences, Faculty of Health Sciences, The University of Sydney, 75 East Street, Lidcombe, NSW 2141, Australia
| | - Ryan J Middleton
- Bioanalytics group, Life Sciences, Australian Nuclear Science and Technology Organisation (ANSTO), New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - Richard B Banati
- Bioanalytics group, Life Sciences, Australian Nuclear Science and Technology Organisation (ANSTO), New Illawarra Road, Lucas Heights, NSW 2234, Australia; Discipline of Medical Imaging & Radiation Sciences, Faculty of Health Sciences, The University of Sydney, 75 East Street, Lidcombe, NSW 2141, Australia.
| | - Guo-Jun Liu
- Bioanalytics group, Life Sciences, Australian Nuclear Science and Technology Organisation (ANSTO), New Illawarra Road, Lucas Heights, NSW 2234, Australia; Discipline of Medical Imaging & Radiation Sciences, Faculty of Health Sciences, The University of Sydney, 75 East Street, Lidcombe, NSW 2141, Australia.
| |
Collapse
|