TSPO ligand Ro5-4864 modulates microglia/macrophages polarization after subarachnoid hemorrhage in mice

TSPO in pancreatic beta cells and its possible involvement in type 2 diabetes

Amyloidosis forms a large family of pathologies associated with amyloid deposit generated by the formation of amyloid fibrils or plaques. The amyloidogenic proteins and peptides involved in these processes are targeted against almost all organs. In brain they are associated with neurodegenerative disease, and the Translocator Protein (TSPO), overexpressed in these inflammatory conditions, is one of the target for the diagnostic. Moreover, TSPO ligands have been described as promising therapeutic drugs for neurodegenerative diseases. Type 2 diabetes, another amyloidosis, is due to a beta cell mass decrease that has been linked to hIAPP (human islet amyloid polypeptide) fibril formation, leading to the reduction of insulin production. In the present study, in a first approach, we link overexpression of TSPO and inflammation in potentially prediabetic patients. In a second approach, we observed that TSPO deficient rats have higher level of insulin secretion in basal conditions and more IAPP fibrils formation compared with wild type animals. In a third approach, we show that diabetogenic conditions also increase TSPO overexpression and IAPP fibril formation in rat beta pancreatic cell line (INS-1E). These data open the way for further studies in the field of type 2 diabetes treatment or prevention.

Regulation of astrocyte metabolism by mitochondrial translocator protein 18 kDa

The mitochondrial translocator protein 18 kDa (TSPO) has been linked to functions from steroidogenesis to regulation of cellular metabolism and is an attractive therapeutic target for chronic CNS inflammation. Studies in Leydig cells and microglia indicate that TSPO function may vary between cells depending on their specialized roles. Astrocytes are critical for providing trophic and metabolic support in the brain. Recent work has highlighted that TSPO expression increases in astrocytes under inflamed conditions and may drive astrocyte reactivity. Relatively little is known about the role TSPO plays in regulating astrocyte metabolism and whether this protein is involved in immunometabolic processes in these cells. Using TSPO-deficient (TSPO-/-) mouse primary astrocytes in vitro (MPAs) and a human astrocytoma cell line (U373 cells), we performed extracellular metabolic flux analyses. We found that TSPO deficiency reduced basal cellular respiration and attenuated the bioenergetic response to glucopenia. Fatty acid oxidation was increased, and lactate production was reduced in TSPO-/- MPAs and U373 cells. Co-immunoprecipitation studies revealed that TSPO forms a complex with carnitine palmitoyltransferase 1a in U373 and MPAs, presenting a mechanism wherein TSPO may regulate FAO in these cells. Compared to TSPO+/+ cells, in TSPO-/- MPAs we observed attenuated tumor necrosis factor release following 3 h lipopolysaccharide (LPS) stimulation, which was enhanced at 24 h post-LPS stimulation. Together these data suggest that while TSPO acts as a regulator of metabolic flexibility, TSPO deficiency does not appear to modulate the metabolic response of MPAs to inflammation, at least in response to the model used in this study.

Machine learning and deep learning to identifying subarachnoid haemorrhage macrophage-associated biomarkers by bulk and single-cell sequencing

We investigated subarachnoid haemorrhage (SAH) macrophage subpopulations and identified relevant key genes for improving diagnostic and therapeutic strategies. SAH rat models were established, and brain tissue samples underwent single-cell transcriptome sequencing and bulk RNA-seq. Using single-cell data, distinct macrophage subpopulations, including a unique SAH subset, were identified. The hdWGCNA method revealed 160 key macrophage-related genes. Univariate analysis and lasso regression selected 10 genes for constructing a diagnostic model. Machine learning algorithms facilitated model development. Cellular infiltration was assessed using the MCPcounter algorithm, and a heatmap integrated cell abundance and gene expression. A 3 × 3 convolutional neural network created an additional diagnostic model, while molecular docking identified potential drugs. The diagnostic model based on the 10 selected genes achieved excellent performance, with an AUC of 1 in both training and validation datasets. The heatmap, combining cell abundance and gene expression, provided insights into SAH cellular composition. The convolutional neural network model exhibited a sensitivity and specificity of 1 in both datasets. Additionally, CD14, GPNMB, SPP1 and PRDX5 were specifically expressed in SAH-associated macrophages, highlighting its potential as a therapeutic target. Network pharmacology analysis identified some targeting drugs for SAH treatment. Our study characterised SAH macrophage subpopulations and identified key associated genes. We developed a robust diagnostic model and recognised CD14, GPNMB, SPP1 and PRDX5 as potential therapeutic targets. Further experiments and clinical investigations are needed to validate these findings and explore the clinical implications of targets in SAH treatment.

Regulation of astrocyte metabolism by mitochondrial translocator protein 18kDa

The mitochondrial translocator protein 18kDa (TSPO) has been linked to a variety of functions from steroidogenesis to regulation of cellular metabolism and is an attractive therapeutic target for chronic CNS inflammation. Studies in the periphery using Leydig cells and hepatocytes, as well as work in microglia, indicate that the function of TSPO may vary between cells depending on their specialised roles. Astrocytes are critical for providing trophic and metabolic support in the brain as part of their role in maintaining brain homeostasis. Recent work has highlighted that TSPO expression increases in astrocytes under inflamed conditions and may drive astrocyte reactivity. However, relatively little is known about the role TSPO plays in regulating astrocyte metabolism and whether this protein is involved in immunometabolic processes in these cells. Using TSPO-deficient (TSPO-/-) mouse primary astrocytes in vitro (MPAs) and a human astrocytoma cell line (U373 cells), we performed metabolic flux analyses. We found that loss of TSPO reduced basal astrocyte respiration and increased the bioenergetic response to glucose reintroduction following glucopenia, while increasing fatty acid oxidation (FAO). Lactate production was significantly reduced in TSPO-/- astrocytes. Co-immunoprecipitation studies in U373 cells revealed that TSPO forms a complex with carnitine palmitoyltransferase 1a, which presents a mechanism wherein TSPO may regulate FAO in astrocytes. Compared to TSPO+/+ cells, inflammation induced by 3h lipopolysaccharide (LPS) stimulation of TSPO-/- MPAs revealed attenuated tumour necrosis factor release, which was enhanced in TSPO-/- MPAs at 24h LPS stimulation. Together these data suggest that while TSPO acts as a regulator of metabolic flexibility in astrocytes, loss of TSPO does not appear to modulate the metabolic response of astrocytes to inflammation, at least in response to the stimulus/time course used in this study.

Translocator protein in the rise and fall of central nervous system neurons

Translocator protein (TSPO), a 18 kDa protein found in the outer mitochondrial membrane, has historically been associated with the transport of cholesterol in highly steroidogenic tissues though it is found in all cells throughout the mammalian body. TSPO has also been associated with molecular transport, oxidative stress, apoptosis, and energy metabolism. TSPO levels are typically low in the central nervous system (CNS), but a significant upregulation is observed in activated microglia during neuroinflammation. However, there are also a few specific regions that have been reported to have higher TSPO levels than the rest of the brain under normal conditions. These include the dentate gyrus of the hippocampus, the olfactory bulb, the subventricular zone, the choroid plexus, and the cerebellum. These areas are also all associated with adult neurogenesis, yet there is no explanation of TSPO's function in these cells. Current studies have investigated the role of TSPO in microglia during neuron degeneration, but TSPO's role in the rest of the neuron lifecycle remains to be elucidated. This review aims to discuss the known functions of TSPO and its potential role in the lifecycle of neurons within the CNS.

CNS-peripheral immune interactions in hemorrhagic stroke

Stroke is a sudden and rapidly progressing ischemic or hemorrhagic cerebrovascular disease. When stroke damages the brain, the immune system becomes hyperactive, leading to systemic inflammatory response and immunomodulatory disorders, which could significantly impact brain damage, recovery, and prognosis of stroke. Emerging researches suggest that ischemic stroke-induced spleen contraction could activate a peripheral immune response, which may further aggravate brain injury. This review focuses on hemorrhagic strokes including intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH) and discusses the central nervous system-peripheral immune interactions after hemorrhagic stroke induction. First, inflammatory progression after ICH and SAH is investigated. As a part of this review, we summarize the various kinds of inflammatory cell infiltration to aggravate brain injury after blood-brain barrier interruption induced by hemorrhagic stroke. Then, we explore hemorrhagic stroke-induced systemic inflammatory response syndrome (SIRS) and discuss the interactions of CNS and peripheral inflammatory response. In addition, potential targets related to inflammatory response for ICH and SAH are discussed in this review, which may lead to novel therapeutic strategies for hemorrhagic stroke.

Koumine regulates macrophage M1/M2 polarization via TSPO, alleviating sepsis-associated liver injury in mice

BACKGROUND

Translocator protein (TSPO) is an 18-kDa transmembrane protein found primarily in the mitochondrial outer membrane, and it is implicated in inflammatory responses, such as cytokine release. Koumine (KM) is an indole alkaloid extracted from Gelsemium elegans Benth. It has been reported to be a high-affinity ligand of TSPO and to exert anti-inflammatory and immunomodulatory effects in our recent studies. However, the protective effect of KM on sepsis-associated liver injury (SALI) and its mechanisms are unknown.

PURPOSE

To explore the role of TSPO in SALI and then further explore the protective effect and mechanism of KM on SALI.

METHODS

The effect of KM on the survival rate of septic mice was confirmed in mouse models of caecal ligation and puncture (CLP)-induced and lipopolysaccharide (LPS)-induced sepsis. The protective effect of KM on CLP-induced SALI was comprehensively evaluated by observing the morphology of the mouse liver and measuring liver injury markers. The serum cytokine content was detected in mice by flow cytometry. Macrophage polarization in the liver was examined using western blotting. TSPO knockout mice were used to explore the role of TSPO in sepsis liver injury and verify the protective effect of KM on sepsis liver injury through TSPO.

RESULTS

KM significantly improved the survival rate of both LPS- and CLP-induced sepsis in mice. KM has a significant liver protective effect on CLP-induced sepsis in mice. KM treatment ameliorated liver ischaemia, improved liver pathological injuries, and decreased the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH) and proinflammatory cytokines in serum. Western blotting results showed that KM inhibited M1 polarization of macrophages and promoted M2 polarization. In TSPO knockout mice, we found that TSPO knockout can improve the survival rate of septic mice, ameliorate liver ischaemia, improve liver pathological injuries, and decrease the levels of ALT, AST, and LDH. In addition, TSPO knockout inhibits the M1 polarization of macrophages in the liver of septic mice and promotes M2 polarization and the serum levels of proinflammatory cytokines. Interestingly, in TSPO knockout septic mice, these protective effects of KM were no longer effective.

CONCLUSIONS

We report for the first time that TSPO plays a critical role in sepsis-associated liver injury by regulating the polarization of liver macrophages and reducing the inflammatory response. KM, a TSPO ligand, is a potentially desirable candidate for the treatment of SALI that may regulate macrophage M1/M2 polarization through TSPO in the liver.

Aquaporin 4 Depolarization-Enhanced Transferrin Infiltration Leads to Neuronal Ferroptosis after Subarachnoid Hemorrhage in Mice

The infiltration of blood components into the brain parenchyma through the lymphoid system is an important cause of subarachnoid hemorrhage injury. AQP4, a water channel protein located at the astrocyte foot, has been reported to regulate blood-brain barrier integrity, and its polarization is disrupted after SAH. Neuronal ferroptosis is involved in subarachnoid hemorrhage- (SAH-) induced brain injury, but the inducing factors are not completely clear. Transferrin is one of the inducing factors of ferroptosis. This study is aimed at researching the role and mechanism of AQP4 in brain injury after subarachnoid hemorrhage in mice. An experimental mouse SAH model was established by endovascular perforation. An AAV vector encoding AQP4 with a GFAP-specific promoter was administered to mice to achieve specific overexpression of AQP4 in astrocytes. PI staining, Fer-1 intervention, and transmission electron microscopy were used to detect neuronal ferroptosis, and dextran (40 kD) leakage was used to detect BBB integrity. Western blot analysis of perfused brain tissue protein samples was used to detect transferrin infiltration. First, neuronal ferroptosis 24 h after SAH was observed by PI staining and Fer-1 intervention. Second, a significant increase in transferrin infiltration was found in the brain parenchyma 24 h after SAH modeling, while transferrin content was positively correlated with neuronal ferroptosis. Then, we observed that AQP4 overexpression effectively improved AQP depolarization and BBB injury induced by SAH and significantly reduced transferrin infiltration and neuronal ferroptosis after SAH. Finally, we found that AQP4 overexpression could effectively improve the neurobehavioral ability of SAH mice, and the neurobehavioral ability was negatively correlated with transferrin brain content. Taken together, these data indicate that overexpression of AQP4 in the mouse brain can effectively improve post-SAH neuronal ferroptosis and brain injury, at least partly by inhibiting transferrin infiltration into the brain parenchyma in the glymphatic system.

The 18-kDa Translocator Protein PET Tracers as a Diagnostic Marker for Neuroinflammation: Development and Current Standing

Translocator protein (TSPO, 18 kDa) is an evolutionary, well-preserved, and tryptophan-rich 169-amino-acid protein which localizes on the contact sites between the outer and inner mitochondrial membranes of steroid-synthesizing cells. This mitochondrial protein is implicated in an extensive range of cellular activities, including steroid synthesis, cholesterol transport, apoptosis, mitochondrial respiration, and cell proliferation. The upregulation of TSPO is well documented in diverse disease conditions including neuroinflammation, cancer, brain injury, and inflammation in peripheral organs. On the basis of these outcomes, TSPO has been assumed to be a fascinating subcellular target for early stage imaging of the diseased state and for therapeutic purposes. The main outline of this Review is to give an update on dealing with the advances made in TSPO PET tracers for neuroinflammation, synchronously emphasizing the approaches applied for the design and advancement of new tracers with reference to their structure-activity relationship (SAR).

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

Activation of translocator protein alleviates mechanical allodynia and bladder dysfunction in cyclophosphamide-induced cystitis through repression of BDNF-mediated neuroinflammation

BACKGROUND

Bladder pain syndrome/interstitial cystitis (BPS/IC) is a refractory disease accompanied by bladder-related pain and hyperactivity. Studies have shown that the translocator protein (TSPO) modulates neuroinflammation and central sensitisation associated with pain. Moreover, we previously demonstrated that brain-derived neurotrophic factor (BDNF) regulates neuroinflammation and mechanical allodynia in cyclophosphamide (CYP)-induced cystitis through activation of glial cells. Here, we aimed to explore whether activation of TSPO attenuates mechanical allodynia and bladder dysfunction by regulating BDNF induced neuroinflammation in a CYP-induced cystitis model.

METHODS

Injection of CYP was performed to form a rat model of BPS/IC. The expression of TSPO was regulated by intrathecal injection of the TSPO agonist Ro5-4864. The von Frey filament test was applied to evaluate suprapubic allodynia. Bladder function was assessed using filling cystometry. Western blotting was used to detect the expression of TSPO, BDNF, GFAP, Iba-1, p-p38, p-JNK, TNF-α, and IL-1β, and double immunofluorescence was performed to localise TSPO in the L6-S1 spinal dorsal horn (SDH).

RESULTS

TSPO was activated in the SDH after CYP injection and was primarily colocalised with astrocytes. Ro5-4864 reversed mechanical allodynia and bladder dysfunction induced by CYP. Moreover, the upregulation of BDNF and activation of astrocytes and microglia was suppressed by Ro5-4864, resulting in downregulation of p-p38, p-JNK, TNF-α, and IL-1β.

CONCLUSIONS

Ro5-4864 alleviated mechanical allodynia and bladder dysfunction in the CYP model, possibly by inhibiting the elevation of BDNF and consequent activation of astrocytes and microglia induced neuroinflammation. TSPO may be a potential target for the treatment of BPS/IC.

The preventative effect of of Ro5-4864 (peripheral benzodiazepine receptor agonist) on spinal epidural fibrosis after laminectomy in a rat model

OBJECTIVE

To investigate the histopathological effects of a peripheral benzodiazepine receptor agonist (Ro5-4864) on epidural fibrosis (EF) in an experimental study model (post-laminectomy) in rats.

METHODS

A total of 32 albino Wistar rats were randomly divided into four equal groups (n = 8). In Group 1, no treatment was applied after laminectomy (control group). In Group 2, hemostasis was achieved after Laminectomy, and the surgical procedure was terminated by placing a 2-mm absorbable gelatin sponge dipped in saline into the epidural space. In Group 3, low-dose (4 mg/kg) Ro5-4864 was administered 30 minutes before the surgery. In Group 4, high-dose (8 mg/kg) Ro5-4864 was administered 30 minutes before the surgery. A histopathological examination was performed to evaluate arachnoidal invasion and EF.

RESULTS

Our data revealed the EF was significantly reduced in rats treated with high-dose Ro5-4864 (Group 4) compared to the control and saline-soaked Spongostan groups (p = 0.000 and p = 0.006, respectively). There was no significant difference between the groups treated with high- and low-dose Ro5-4864. Arachnoidal invasion was not seen in any of the rats in the high-dose R05-4864 group. However, the arachnoidal invasion results did not significantly differ between the study groups (p = 0.052 = 0.05).

CONCLUSIONS

Our study showed that Ro5-4864 could be effective in reducing EF in rats after.

Neuroprotective Strategies in Aneurysmal Subarachnoid Hemorrhage (aSAH)

Aneurysmal subarachnoid hemorrhage (aSAH) remains a disease with high mortality and morbidity. Since treating vasospasm has not inevitably led to an improvement in outcome, the actual emphasis is on finding neuroprotective therapies in the early phase following aSAH to prevent secondary brain injury in the later phase of disease. Within the early phase, neuroinflammation, thromboinflammation, disturbances in brain metabolism and early neuroprotective therapies directed against delayed cerebral ischemia (DCI) came into focus. Herein, the role of neuroinflammation, thromboinflammation and metabolism in aSAH is depicted. Potential neuroprotective strategies regarding neuroinflammation target microglia activation, metalloproteases, autophagy and the pathway via Toll-like receptor 4 (TLR4), high mobility group box 1 (HMGB1), NF-κB and finally the release of cytokines like TNFα or IL-1. Following the link to thromboinflammation, potential neuroprotective therapies try to target microthrombus formation, platelets and platelet receptors as well as clot clearance and immune cell infiltration. Potential neuroprotective strategies regarding metabolism try to re-balance the mismatch of energy need and supply following aSAH, for example, in restoring fuel to the TCA cycle or bypassing distinct energy pathways. Overall, this review addresses current neuroprotective strategies in aSAH, hopefully leading to future translational therapy options to prevent secondary brain injury.

Dopamine and Neuroinflammation in Schizophrenia - Interpreting the Findings from Translocator Protein (18kDa) PET Imaging

Schizophrenia is a complex disease whose pathophysiology is not yet fully understood. In addition to the long prevailing dopaminergic hypothesis, the evidence suggests that neuroinflammation plays a role in the pathophysiology of the disease. Recent studies using positron emission tomography (PET) that target a 18kDa translocator protein (TSPO) in activated microglial cells in an attempt to measure neuroinflammation in patients have shown a decrease or a lack of an increase in TSPO binding. Many biological and methodological considerations have been formulated to explain these findings. Although dopamine has been described as an immunomodulatory molecule, its potential role in neuroinflammation has not been explored in the aforementioned studies. In this review, we discuss the interactions between dopamine and neuroinflammation in psychotic states. Dopamine may inhibit neuroinflammation in activated microglia. Proinflammatory molecules released from microglia may decrease dopaminergic transmission. This could potentially explain why the levels of neuroinflammation in the brain of patients with schizophrenia seem to be unchanged or decreased compared to those in healthy subjects. However, most data are indirect and are derived from animal studies or from studies performed outside the field of schizophrenia. Further studies are needed to combine TSPO and dopamine imaging to study the association between microglial activation and dopamine system function.