Effects of translocator protein (18 kDa) ligands on microglial activation and neuronal death in the quinolinic-acid-injected rat striatum.
Ontology highlight
ABSTRACT:
SUBMITTER: Leaver KR
PROVIDER: S-EPMC3369788 | biostudies-other | 2012 Feb
REPOSITORIES: biostudies-other
Similar Datasets
Project description:UNLABELLED:11C-PBR28 PET can detect the 18-kDa translocator protein (TSPO) expressed within macrophages. However, quantitative evaluation of the signal in brain tissue from donors with multiple sclerosis (MS) shows that PBR28 binds the TSPO with high affinity (binding affinity [Ki], ?4 nM), low affinity (Ki, ?200 nM), or mixed affinity (2 sites with Ki, ?4 nM and ?300 nM). Our study tested whether similar binding behavior could be detected in brain tissue from donors with no history of neurologic disease, with TSPO-binding PET ligands other than 11C-PBR28, for TSPO present in peripheral blood, and with human brain PET data acquired in vivo with 11C-PBR28. METHODS:The affinity of TSPO ligands was measured in the human brain postmortem from donors with a history of MS (n=13), donors without any history of neurologic disease (n=20), and in platelets from healthy volunteers (n=13). Binding potential estimates from thirty-five 11C-PBR28 PET scans from an independent sample of healthy volunteers were analyzed using a gaussian mixture model. RESULTS:Three binding affinity patterns were found in brains from subjects without neurologic disease in similar proportions to those reported previously from studies of MS brains. TSPO ligands showed substantial differences in affinity between subjects classified as high-affinity binders (HABs) and low-affinity binders (LABs). Differences in affinity between HABs and LABs are approximately 50-fold with PBR28, approximately 17-fold with PBR06, and approximately 4-fold with DAA1106, DPA713, and PBR111. Where differences in affinity between HABs and LABs were low (?4-fold), distinct affinities were not resolvable in binding curves for mixed-affinity binders (MABs), which appeared to express 1 class of sites with an affinity approximately equal to the mean of those for HABs and LABs. Mixed-affinity binding was detected in platelets from an independent sample (HAB, 69%; MAB, 31%), although LABs were not detected. Analysis of 11C-PBR28 PET data was not inconsistent with the existence of distinct subpopulations of HABs, MABs, and LABs. CONCLUSION:With the exception of 11C-PK11195, all TSPO PET ligands in current clinical application recognize HABs, LABs, and MABs in brain tissue in vitro. Knowledge of subjects' binding patterns will be required to accurately quantify TSPO expression in vivo using PET.
| S-EPMC3161826 | biostudies-literature
Project description:TSPO is mainly expressed in the mitochondrial outer membrane of microglia in the central nervous system, and its expression is greatly increased when microglia are activated. However, the role and mechanism of this protein in microglial activation is not well characterized. In this study, we investigated the role of TSPO in microglial activation by isolating primary microglia from TSPO knockout mice and constructing TSPO-knockdown microglial cell line. We found that TSPO deficiency significantly inhibited microglial activation induced by LPS or IL-4. Mechanistically, TSPO deficiency greatly decreased the mitochondrial membrane potential and ATP production. Moreover, an analysis of cellular energy metabolism showed that TSPO deficiency suppressed mitochondrial oxidative phosphorylation (OXPHOS) and glycolysis, resulting in microglial overall metabolic deficits. Together, our results reveal a crucial role of TSPO in microglial activation through the regulation of mitochondrial metabolism, thus providing a potential therapeutic target for neuroinflammation-related diseases of the central nervous system.
| S-EPMC7339871 | biostudies-literature
Project description:Numerous studies have suggested that the phenotypic transformation of microglia plays a role in the pathogenesis of Parkinson's disease (PD). Translocator protein (TSPO) is an 18 kDa translocator membrane protein that acts as a marker of neuroinflammation and suppresses neuroinflammation; however, its underlying mechanism remains unclear. Although TSPO ligands were found to be protective in several neurodegenerative paradigms, few studies have evaluated their effects on microglial polarization, and underlying mechanisms need to be explored. In the present study, we examined the effects of TSPO and PK11195, a TSPO ligand, on lipopolysaccharide (LPS)+interferon (IFN)-γ-induced inflammatory factors and oxidative stress in microglia using enzyme-linked immunosorbent assay. The effect of TSPO and PK11195 on LPS+IFN-γ-induced microglial cell apoptosis was examined using immunofluorescence (IF), flow cytometry, and western blotting. The interaction between TSPO and P47 was investigated using IF and co-immunoprecipitation analysis. In vivo experiments confirmed the influence of TSPO and its ligand on motility, a-Syn, and dopaminergic neuronal damage. Our findings indicate that TSPO may regulate the microglial phenotype in PD via P47, suggesting a potential role in anti-PD therapy.
| S-EPMC9208449 | biostudies-literature
Project description:The 18 kDa translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor, is expressed in the injured brain. It has become known as an imaging marker of "neuroinflammation" indicating active disease, and is best interpreted as a nondiagnostic biomarker and disease staging tool that refers to histopathology rather than disease etiology. The therapeutic potential of TSPO as a drug target is mostly based on the understanding that it is an outer mitochondrial membrane protein required for the translocation of cholesterol, which thus regulates the rate of steroid synthesis. This pivotal role together with the evolutionary conservation of TSPO has underpinned the belief that any loss or mutation of TSPO should be associated with significant physiological deficits or be outright incompatible with life. However, against prediction, full Tspo knockout mice are viable and across their lifespan do not show the phenotype expected if cholesterol transport and steroid synthesis were significantly impaired. Thus, the "translocation" function of TSPO remains to be better substantiated. Here, we discuss the literature before and after the introduction of the new nomenclature for TSPO and review some of the newer findings. In light of the controversy surrounding the function of TSPO, we emphasize the continued importance of identifying compounds with confirmed selectivity and suggest that TSPO expression is analyzed within specific disease contexts rather than merely equated with the reified concept of "neuroinflammation."
| S-EPMC8029074 | biostudies-literature
Project description:The translocator protein 18 kDa (TSPO) has been the focus of intense research by the biomedical community and the pharmaceutical industry because of its apparent involvement in many disease-related processes. These include steroidogenesis, apoptosis, inflammation, neurological disease and cancer, resulting in the use of TSPO as a biomarker and its potential as a drug target. Despite more than 30 years of study, the precise function of TSPO remains elusive. A recent breakthrough in determining the high-resolution crystal structures of bacterial homologs of mitochondrial TSPO provides new insight into the structural and functional properties at a molecular level and new opportunities for investigating the significance of this ancient and highly conserved protein family. The availability of atomic level structural information from different species also provides a platform for structure-based drug development. Here we briefly review current knowledge regarding TSPO and the implications of the new structures with respect to hypotheses and controversies in the field.
| S-EPMC4567528 | biostudies-literature
Project description:In the brain, translocator protein (18 kDa) (TSPO), previously called peripheral benzodiazepine receptor (PBR), is a glial protein that has been extensively used as a biomarker of brain injury and inflammation. However, the functional role of TSPO in glial cells is not well characterized. In this study, we show that the TSPO-specific ligands R-PK11195 (PK) and Ro5-4864 (Ro) increased microglia proliferation and phagocytosis with no effect on migration. Both ligands increased reactive oxygen species (ROS) production, and this effect may be mediated by NADPH-oxidase. PK and Ro also produced a small but detectable increase in IL-1? release. We also examined the effect of PK and Ro on the expression of proinflammatory genes and cytokine release in lipopolysaccharide (LPS) and adenosine triphosphate (ATP) activated microglia. PK or Ro had no effect on LPS-induced increase of pro-inflammatory genes, but they both decreased the ATP-induced increase of COX-2 gene expression. Ro, but not PK, enhanced the LPS-induced release of IL-1?. However, Ro decreased the ATP-induced release of IL-1? and TNF-?, and PK decreased the ATP-induced release of TNF-?. Exposure to Ro in the presence of LPS increased the number of apoptotic microglia, an effect that could be blocked by PK. These findings show that TSPO ligands modulate cellular functions consistent with microglia activation. Further, when microglia are activated, these ligands may have therapeutic potential by reducing the expression of pro-inflammatory genes and cytokine release. Finally, Ro-like ligands may be involved in the elimination of activated microglia via apoptosis.
| S-EPMC4425360 | biostudies-literature
Project description:It has been reported that neuroinflammation occurs in the central nervous system (CNS) in patients with neuropathic pain, Alzheimer's disease and autism spectrum disorder. The 18-kDa translocator protein TSPO is used as an imaging target in positron emission tomography to detect neuroinflammation, and its expression is correlated with microglial activation. However, the mechanism underlying the transcriptional regulation of Tspo induced by inflammation is not clear. Here, we revealed that lipopolysaccharide (LPS) -induced Tspo expression was activated by the AP-1 complex in a mouse microglial cell line, BV-2. Knockdown of c-Fos and c-Jun, the components of AP-1, reduced LPS-induced Tspo expression. Furthermore, the enrichment of Sp1 in the proximal promoter region of Tspo was increased in the presence of LPS. In addition, the binding of histone deacetylase 1 (HDAC1) to the enhancer region, which contains the AP-1 site, was decreased by LPS treatment, but there were no significant differences in HDAC1 binding to the proximal promoter region with or without LPS. These results indicated that HDAC1 is involved not in the proximal promoter region but in the enhancer region. Our study revealed that inflammatory signals induce the recruitment of AP-1 to the enhancer region and Sp1 to the proximal promoter region of the Tspo gene and that Sp1 may regulate the basal expression of Tspo.
| S-EPMC6752844 | biostudies-literature
Project description:Background and purposeThe expression of the 18-kDA mitochondrial translocator protein (TSPO) in the brain is an attractive target to study neuroinflammation. However, the binding properties of TSPO ligands are reportedly dependent on genetic polymorphism of the TSPO gene (rs6971). The objective of this study is to investigate the rs6971 gene polymorphism in the Korean population.MethodsWe performed genetic testing on 109 subjects including patients with mild cognitive impairment, Alzheimer's disease (AD) dementia, non-AD dementia, and cognitively unimpaired participants. Magnetic resonance imaging scans and detailed neuropsychological tests were also performed, and 29 participants underwent 18F-DPA714 PET scans. Exon 4 of the TSPO gene containing the polymorphism rs6971 (Ala or Thr at position 147) was polymerase chain reaction amplified and sequenced using the Sanger method. The identified rs6971 genotype codes (C/C, C/T, or T/T) of the TSPO protein generated high-, mixed-, or low-affinity binding phenotypes (HABs, MABs, and LABs), respectively.ResultsWe found that 96.3% of the study subjects were HAB (105 out of 109 subjects), and 3.7% of the subjects were MAB (4 out of 109 subjects). 18F-DPA-714 PET scans showed nonspecific binding to the thalamus and brainstem, and increased tracer uptake throughout the cortex in cognitively impaired patients. The participant with the MAB polymorphism had a higher DPA714 signal throughout the cortex.ConclusionsThe majority of Koreans are HAB (aprox. 96%). Therefore, the polymorphism of the rs6971 gene would have a smaller impact on the availability of second-generation TSPO PET tracers.
| S-EPMC9085532 | biostudies-literature
Project description:Translocator protein 18 kDa (TSPO) was previously known as the peripheral benzodiazepine receptor (PBR) in eukaryotes, where it is mainly localized to the mitochondrial outer membrane. Considerable evidence indicates that it plays regulatory roles in steroidogenesis and apoptosis and is involved in various human diseases, such as metastatic cancer, Alzheimer's and Parkinson's disease, inflammation, and anxiety disorders. Ligands of TSPO are widely used as diagnostic tools and treatment options, despite there being no clear understanding of the function of TSPO. An ortholog in the photosynthetic bacterium Rhodobacter was independently discovered as the tryptophan-rich sensory protein (TspO) and found to play a role in the response to changes in oxygen and light conditions that regulate photosynthesis and respiration. As part of this highly conserved protein family found in all three kingdoms, the rat TSPO is able to rescue the knockout phenotype in Rhodobacter, indicating functional as well as structural conservation. Recently, a major breakthrough in the field was achieved: the determination of atomic-resolution structures of TSPO from different species by several independent groups. This now allows us to reexamine the function of TSPO with a molecular perspective. In this review, we focus on recently determined structures of TSPO and their implications for potential functions of this ubiquitous multifaceted protein. We suggest that TSPO is an ancient bacterial receptor/stress sensor that has developed additional interactions, partners, and roles in its mitochondrial outer membrane environment in eukaryotes.
| S-EPMC5125027 | biostudies-literature
Project description:An increase in astrocyte reactivity has been described in Alzheimer's disease and seems to be related to the presence of a pro-inflammatory environment. Reactive astrocytes show an increase in the density of the 18 kDa translocator protein (TSPO), but TSPO involvement in astrocyte functions remains poorly understood. The goal of this study was to better characterize the mechanisms leading to the increase in TSPO under inflammatory conditions and the associated consequences. For this purpose, the C6 astrocytic cell line was used in the presence of lipopolysaccharide (LPS) or TSPO overexpression mediated by the transfection of a plasmid encoding TSPO. The results show that nonlethal doses of LPS induced TSPO expression at mRNA and protein levels through a STAT3-dependent mechanism and increased the number of mitochondria per cell. LPS stimulated reactive oxygen species (ROS) production and decreased glucose consumption (quantified by the [18F]FDG uptake), and these effects were diminished by FEPPA, a TSPO antagonist. The transfection-mediated overexpression of TSPO induced ROS production, and this effect was blocked by FEPPA. In addition, a synergistic effect of overexpression of TSPO and LPS on ROS production was observed. These data show that the increase of TSPO in astrocytic cells is involved in the regulation of glucose metabolism and in the pro-inflammatory response. These data suggest that the overexpression of TSPO by astrocytes in Alzheimer's disease would have rather deleterious effects by promoting the pro-inflammatory response.
| S-EPMC10468775 | biostudies-literature