The TSPO-NOX1 axis controls phagocyte-triggered pathological angiogenesis in the eye

TSPO deficiency exacerbates acute lung injury via NLRP3 inflammasome-mediated pyroptosis

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a common cause of respiratory failure in many critically ill patients. Although inflammasome activation plays an important role in the induction of acute lung injury (ALI) and ARDS, the regulatory mechanism of this process is still unclear. When cells are stimulated by inflammation, the integrity and physiological function of mitochondria play a crucial part in pyroptosis. However, the underlying mechanisms and function of mitochondrial proteins in the process of pyroptosis are largely not yet known. Here, we identified the 18-kDa translocator protein (TSPO), a mitochondrial outer membrane protein, as an important mediator regulating nucleotide-binding domain, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) inflammasome activation in macrophages during ALI.

METHODS

TSPO gene knockout (KO) and lipopolysaccharide (LPS)-induced ALI/ARDS mouse models were employed to investigate the biological role of TSPO in the pathogenesis of ARDS. Murine macrophages were used to further characterize the effect of TSPO on the NLRP3 inflammasome pathway. Activation of NLRP3 inflammasome was preformed through LPS + adenosine triphosphate (ATP) co-stimulation, followed by detection of mitochondrial membrane potential, reactive oxygen species (ROS) production, and cell death to evaluate the potential biological function of TSPO. Comparisons between two groups were performed with a two-sided unpaired t -test.

RESULTS

TSPO- KO mice exhibited more severe pulmonary inflammation in response to LPS-induced ALI. TSPO deficiency resulted in enhanced activation of the NLRP3 inflammasome pathway, promoting more proinflammatory cytokine production of macrophages in LPS-injured lung tissue, including interleukin (IL)-1β, IL-18, and macrophage inflammatory protein (MIP)-2. Mitochondria in TSPO -KO macrophages tended to depolarize in response to cellular stress. The increased production of mitochondrial damage-associated molecular pattern led to enhanced mitochondrial membrane depolarization and pyroptosis in TSPO -KO cells.

CONCLUSION

TSPO may be the key regulator of cellular pyroptosis, and it plays a vital protective role in ARDS occurrence and development.

Redefining the ontogeny of hyalocytes as yolk sac-derived tissue-resident macrophages of the vitreous body

BACKGROUND

The eye is a highly specialized sensory organ which encompasses the retina as a part of the central nervous system, but also non-neural compartments such as the transparent vitreous body ensuring stability of the eye globe and a clear optical axis. Hyalocytes are the tissue-resident macrophages of the vitreous body and are considered to play pivotal roles in health and diseases of the vitreoretinal interface, such as proliferative vitreoretinopathy or diabetic retinopathy. However, in contrast to other ocular macrophages, their embryonic origin as well as the extent to which these myeloid cells might be replenished by circulating monocytes remains elusive.

RESULTS

In this study, we combine transgenic reporter mice, embryonic and adult fate mapping approaches as well as parabiosis experiments with multicolor immunofluorescence labeling and confocal laser-scanning microscopy to comprehensively characterize the murine hyalocyte population throughout development and in adulthood. We found that murine hyalocytes express numerous well-known myeloid cell markers, but concomitantly display a distinct immunophenotype that sets them apart from retinal microglia. Embryonic pulse labeling revealed a yolk sac-derived origin of murine hyalocytes, whose precursors seed the developing eye prenatally. Finally, postnatal labeling and parabiosis established the longevity of hyalocytes which rely on Colony Stimulating Factor 1 Receptor (CSF1R) signaling for their maintenance, independent of blood-derived monocytes.

CONCLUSION

Our study identifies hyalocytes as long-living progeny of the yolk sac hematopoiesis and highlights their role as integral members of the innate immune system of the eye. As a consequence of their longevity, immunosenescence processes may culminate in hyalocyte dysfunction, thereby contributing to the development of vitreoretinal diseases. Therefore, myeloid cell-targeted therapies that convey their effects through the modification of hyalocyte properties may represent an interesting approach to alleviate the burden imposed by diseases of the vitreoretinal interface.

Translocator protein (18 kDa) (Tspo) in the retina and implications for ocular diseases

Translocator protein (18 kDa) (Tspo), formerly known as peripheral benzodiazepine receptor is a highly conserved transmembrane protein primarily located in the outer mitochondrial membrane. In the central nervous system (CNS), especially in glia cells, Tspo is upregulated upon inflammation. Consequently, Tspo was used as a tool for diagnostic in vivo imaging of neuroinflammation in the brain and as a potential therapeutic target. Several synthetic Tspo ligands have been explored as immunomodulatory and neuroprotective therapy approaches. Although the function of Tspo and how its ligands exert these beneficial effects is not fully clear, it became a research topic of interest, especially in ocular diseases in the past few years. This review summarizes state-of-the-art knowledge of Tspo expression and its proposed functions in different cells of the retina including microglia, retinal pigment epithelium and Müller cells. Tspo is involved in cytokine signaling, oxidative stress and reactive oxygen species production, calcium signaling, neurosteroid synthesis, energy metabolism, and cholesterol efflux. We also highlight recent developments in preclinical models targeting Tspo and summarize the relevance of Tspo biology for ocular and retinal diseases. We conclude that glial upregulation of Tspo in different ocular pathologies and the use of Tspo ligands as promising therapeutic approaches in preclinical studies underline the importance of Tspo as a potential disease-modifying protein.

2-Desaza-annomontine (C81) impedes angiogenesis through reduced VEGFR2 expression derived from inhibition of CDC2-like kinases

Angiogenesis is a crucial process in the progression of various pathologies, like solid tumors, wet age-related macular degeneration, and chronic inflammation. Current anti-angiogenic treatments still have major drawbacks like limited efficacy in diseases that also rely on inflammation. Therefore, new anti-angiogenic approaches are sorely needed, and simultaneous inhibition of angiogenesis and inflammation is desirable. Here, we show that 2-desaza-annomontine (C81), a derivative of the plant alkaloid annomontine previously shown to inhibit endothelial inflammation, impedes angiogenesis by inhibiting CDC2-like kinases (CLKs) and WNT/β-catenin signaling. C81 reduced choroidal neovascularization in a laser-induced murine in vivo model, inhibited sprouting from vascular endothelial growth factor A (VEGF-A)-activated murine aortic rings ex vivo, and reduced angiogenesis-related activities of endothelial cells in multiple functional assays. This was largely phenocopied by CLK inhibitors and knockdowns, but not by inhibitors of the other known targets of C81. Mechanistically, CLK inhibition reduced VEGF receptor 2 (VEGFR2) mRNA and protein expression as well as downstream signaling. This was partly caused by a reduction of WNT/β-catenin pathway activity, as activating the pathway induced, while β-catenin knockdown impeded VEGFR2 expression. Surprisingly, alternative splicing of VEGFR2 was not detected. In summary, C81 and other CLK inhibitors could be promising compounds in the treatment of diseases that depend on angiogenesis and inflammation due to their impairment of both processes.

Enhanced angiogenesis in the thalamus induced by a novel TSPO ligand ameliorates cognitive deficits after focal cortical infarction

Neuronal loss in the ipsilateral thalamus after focal cortical infarction participates in post-stroke cognitive deficits, and enhanced angiogenesis in the thalamus is expected to reduce neuronal damage. We hypothesize that novel translocator protein (TSPO) ligand, 2-Cl-MGV-1, can promote angiogenesis, attenuate neuronal loss in the thalamus, and ameliorate post-stroke cognitive deficits. Cortical infarction was induced by distal middle cerebral artery occlusion (dMCAO) in stroke-prone renovascular hypertensive rats. 2-Cl-MGV-1 or dimethyl sulfoxide was administered 24 h after dMCAO and then for 6 or 13 days. Spatial learning and memory were assessed using the Morris water maze. Neuronal loss, TSPO expression, angiogenesis, and intrinsic pathway were determined by immunofluorescence and immunoblotting 7 and 14 days after dMCAO. Cortical infarction caused post-stroke cognitive deficits and secondary neuronal loss with gliosis in the ipsilateral thalamus within 14 days of dMCAO. Increased angiogenesis and elevated expression of vascular TSPO were detected in the ipsilateral thalamus, and treatment with 2-Cl-MGV-1 enhanced angiogenesis by stimulating the PI3K-AKT-mTOR pathway. The effects of 2-Cl-MGV-1 on angiogenesis coincided with reduced neuronal loss in the thalamus and contributed to improvements in post-stroke cognitive deficits. Our findings suggest that 2-Cl-MGV-1 stimulates angiogenesis, ameliorates neuronal loss in the thalamus, and improves post-stroke cognitive deficits.

NADPH-oxidases as potential pharmacological targets for thrombosis and depression comorbidity

There is a complex interrelationship between the nervous system and the cardiovascular system. Comorbidities of cardiovascular diseases (CVD) with mental disorders, and vice versa, are prevalent. Adults with mental disorders such as anxiety and depression have a higher risk of developing CVD, and people with CVD have an increased risk of being diagnosed with mental disorders. Oxidative stress is one of the many pathways associated with the pathophysiology of brain and cardiovascular disease. Nicotinamide adenine dinucleotide phosphate oxidase (NOX) is one of the major generators of reactive oxygen species (ROS) in mammalian cells, as it is the enzyme that specifically produces superoxide. This review summarizes recent findings on the consequences of NOX activation in thrombosis and depression. It also discusses the therapeutic effects and pharmacological strategies of NOX inhibitors in CVD and brain disorders. A better comprehension of these processes could facilitate the development of new therapeutic approaches for the prevention and treatment of the comorbidity of thrombosis and depression.

History of Tspo deletion and induction in vivo: Phenotypic outcomes under physiological and pathological situations

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.

TOM40 mediates the effect of TSPO on postpartum depression partially through regulating calcium homeostasis in microglia

AIMS

To assess the effect of the translocator protein 18 kDa (TSPO) on postpartum depression and explore its mechanism.

METHODS

Postpartum depression (PPD) mouse model was established, and flow cytometry, immunofluorescence, Western blot analysis, real-time quantitative PCR, adeno-associated virus (AAV), co-immunoprecipitation-mass spectrometry and immunofluorescence co-staining were used to detect the effect of TSPO ligand ZBD-2 on PPD mice.

RESULTS

ZBD-2 inhibits the overactivation of microglia in the hippocampus and amygdala of PPD model mice. ZBD-2 not only inhibited the inflammation but also repressed the burst of reactive oxygen species (ROS) and mitochondrial ROS (mtROS). Meanwhile, ZBD-2 protects mitochondria from LPS-induced damages through inhibiting the influx of calcium. ZBD-2 modulated the calcium influx by increasing the level of translocase of the outer mitochondrial membrane 40 (TOM40) and reducing the interaction of TSPO and TOM40. In addition, the effect of ZBD-2 was partially dependent on anti-oxidative process. Knockdown of TOM40 by adeno-associated virus (AAV) in the hippocampus or amygdala dramatically reduced the effect of ZBD-2 on PPD, indicating that TOM40 mediates the effect of ZBD-2 on PPD.

CONCLUSIONS

TOM40 is required for the effect of ZBD-2 on treating anxiety and depression in PPD mice. This study reveals the role of microglia TSPO in PPD development and provides the new therapeutic strategy for PPD.

Functional role of translocator protein and its ligands in ocular diseases (Review)

The 18 kDa translocator protein (TSPO) is an essential outer mitochondrial membrane protein that is responsible for mitochondrial transport, maintenance of mitochondrial homeostasis and normal physiological cell function. The role of TSPO in the pathogenesis of ocular diseases is a growing area of interest. More notably, TSPO exerts positive effects in regulating various pathophysiological processes, such as the inflammatory response, oxidative stress, steroid synthesis and modulation of microglial function, in combination with a variety of specific ligands such as 1‑(2‑chlorophenyl‑N‑methylpropyl)‑3‑isoquinolinecarboxamide, 4'‑chlorodiazepam and XBD173. In the present review, the expression of TSPO in ocular tissues and the functional role of TSPO and its ligands in diverse ocular diseases was discussed.

Microglia depletion/repopulation does not affect light-induced retinal degeneration in mice

Reactive microglia are a hallmark of age-related retinal degenerative diseases including age-related macular degeneration (AMD). These cells are capable of secreting neurotoxic substances that may aggravate inflammation that leads to loss of photoreceptors and impaired vision. Despite their role in driving detrimental inflammation, microglia also play supporting roles in the retina as they are a crucial cellular component of the regulatory innate immune system. In this study, we used the colony stimulating factor 1 receptor (CSF1R)-antagonist PLX3397 to investigate the effects of microglia depletion and repopulation in a mouse model of acute retinal degeneration that mimics some aspects of dry AMD. Our main goal was to investigate whether microglia depletion and repopulation affects the outcome of light-induced retinal degeneration. We found that microglia depletion effectively decreased the expression of several key pro-inflammatory factors but was unable to influence the extent of retinal degeneration as determined by optical coherence tomography (OCT) and histology. Interestingly, we found prominent cell debris accumulation in the outer retina under conditions of microglia depletion, presumably due to the lack of efficient phagocytosis that could not be compensated by the retinal pigment epithelium. Moreover, our in vivo experiments showed that renewal of retinal microglia by repopulation did also not prevent rapid microglia activation or preserve photoreceptor death under conditions of light damage. We conclude that microglia ablation strongly reduces the expression of pro-inflammatory factors but cannot prevent photoreceptor loss in the light-damage paradigm of retinal degeneration.

Setanaxib mitigates oxidative damage following retinal ischemia-reperfusion via NOX1 and NOX4 inhibition in retinal ganglion cells

Glaucoma, a prevalent cause of permanent visual impairment worldwide, is characterized by the progressive degeneration of retinal ganglion cells (RGCs). NADPH oxidase (NOX) 1 and NOX4 are pivotal nodes in various retinal diseases. Setanaxib, a potent and highly selective inhibitor of NOX1 and NOX4, can impede the progression of various diseases. This study investigated the efficacy of setanaxib in ameliorating retinal ischemia-reperfusion (I/R) injury and elucidated its underlying mechanisms. The model of retinal I/R induced by acute intraocular hypertension and the oxygen-glucose deprivation/reoxygenation (OGD/R) model of primary RGCs were established. By suppressing NOX1 and NOX4 expression in RGCs, setanaxib mitigated I/R-induced retinal neuronal loss, structural disruption, and dysfunction. Setanaxib reduced TUNEL-positive cells, upregulated Bcl-2, and inhibited Bax, Bad, and cleaved-caspase-3 overexpression after I/R injury in vitro and in vivo. Moreover, setanaxib also significantly reduced cellular senescence, as demonstrated by downregulating SA-β-gal-positive and p16-INK4a expression. Furthermore, setanaxib significantly suppressed ROS production, Hif-1α and FOXO1 upregulation, and NRF2 downregulation in damaged RGCs. These findings highlight that the setanaxib effectively inhibited NOX1 and NOX4, thereby regulating ROS production and redox signal activation. This inhibition further prevents the activation of apoptosis and senescence related factors in RGCs, ultimately protecting them against retinal I/R injury. Consequently, setanaxib exhibits promising potential as a therapeutic intervention for glaucoma.

FGIN-1-27 Mitigates Radiation-induced Mitochondrial Hyperfunction and Cellular Hyperactivation in Cultured Astrocytes

Radiation-induced brain injury (RBI) poses a significant challenge in the context of radiotherapy for intracranial tumors, necessitating a comprehensive understanding of the cellular and molecular mechanisms involved. While prior investigations have underscored the role of astrocyte activation and excessive vascular endothelial growth factor production in microvascular damage associated with RBI, there remains a scarcity of studies examining the impact of radiation on astrocytes, particularly regarding organelles such as mitochondria. Thus, our study aimed to elucidate alterations in astrocyte and mitochondrial functionality following radiation exposure, with a specific focus on evaluating the potential ameliorative effects of translocator protein 18 kDa(TSPO) ligands. In this study, cultured astrocytes were subjected to X-ray irradiation, and their cellular states and mitochondrial functions were examined and compared to control cells. Our findings revealed that radiation-induced astrocytic hyperactivation, transforming them into the neurotoxic A1-type, concomitant with reduced cell proliferation. Additionally, radiation triggered mitochondrial hyperfunction, heightened the mitochondrial membrane potential, and increased oxidative metabolite production. However, following treatment with FGIN-1-27, a TSPO ligand, we observed a restoration of mitochondrial function and a reduction in oxidative metabolite production. Moreover, this intervention mitigated astrocyte hyperactivity, decreased the number of A1-type astrocytes, and restored cell proliferative capacity. In conclusion, our study has unveiled additional manifestations of radiation-induced astrocyte dysfunction and validated that TSPO ligands may serve as a promising therapeutic strategy to mitigate this dysfunction. It has potential clinical implications for the treatment of RBI.

Characterizing mobility patterns and malaria risk factors in semi-nomadic populations of Northern Kenya

While many studies have characterized mobility patterns and disease dynamics of individuals from settled populations, few have focused on more mobile populations. Highly mobile groups are often at higher disease risk due to their regular movement that may increase the variability of their environments, reduce their access to health care, and limit the number of intervention strategies suitable for their lifestyles. Quantifying the movements and their associated disease risks will be key to developing intervention strategies more suitable for mobile populations. Here, we worked with four semi-nomadic communities in Central Turkana, Kenya to 1) characterize mobility patterns of travelers from semi-nomadic communities and 2) test the hypothesis that semi-nomadic individuals are at greater risk of exposure to malaria during seasonal migrations than when staying at their semi-permanent settlements. From March-October, 2021, we conducted a study in semi-nomadic households (n=250) where some members traveled with their herd while others remained at the semi-permanent settlement. Participants provided medical and travel histories, demographics, and a dried blood spot for malaria testing before and after the travel period. Further, a subset of travelers was given GPS loggers to document their routes. Four travel patterns emerged from the logger data, Long Term, Transient, Day trip, and Static, with only Long Term and Transient trips being associated with malaria cases detected in individuals who carried GPS devices. After completing their trips, travelers had a higher prevalence of malaria than those who remained at the household (9.2% vs 4.4%), regardless of gender, age group, and catchment area. These findings highlight the need to develop intervention strategies amenable to mobile lifestyles that can ultimately help prevent the transmission of malaria.

Translocator protein (TSPO) expression in neoplastic cells and tumor-associated macrophages in meningiomas

Meningiomas are the most common primary intracranial tumors and show extensive infiltration of macrophages. The mitochondrial membrane protein translocator protein (TSPO) has been used as an in vivo marker of microglia and macrophage activation to visualize neuroinflammation. However, it is unknown which cell types express TSPO in meningiomas. Immunohistochemistry of 38 WHO grade 1-3 meningiomas was subjected to segmentation and deep learning classification of TSPO expression to either Iba1-positive tumor-associated macrophages (TAMs) or all other (mainly neoplastic) cells. A possible association between clinical data and TSPO expression intensities was also investigated. TAMs accounted for 15.9%-26% of all cells in the meningioma tissue. Mean fluorescence intensity of TSPO was significantly higher in TAMs (p < 0.0001), but the mass of neoplastic cells in the tumors exceeded that of TAMs. Thus, the summed fluorescence intensity of TSPO in meningioma cells was 64.1% higher than in TAMs (p = 0.0003). We observed no correlation between TSPO expression intensity and WHO grade. These results indicate that both macrophage-lineage and neoplastic cells in meningiomas express TSPO and that the SPECT-TSPO signal in meningiomas mainly reflects the latter; TSPO is expressed equally in parenchymal activated and resting macrophage/microglia lineage cells.

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.

NAT10 regulates the LPS-induced inflammatory response via the NOX2-ROS-NF-κB pathway in macrophages

Periodontitis is a chronic osteolytic inflammatory disease resulting from complex dynamic interactions among bacterial pathogens and the host immune response. Macrophages play a vital role in the pathogenesis of periodontitis by triggering periodontal inflammation and inducing periodontium destruction. N-Acetyltransferase 10 (NAT10) is an acetyltransferase that has been shown to catalyse N4-acetylcytidine (ac4C) mRNA modification and is related to cellular pathophysiological processes, including the inflammatory immune response. Nevertheless, whether NAT10 regulates the inflammatory response of macrophages in periodontitis remains unclear. In this study, the expression of NAT10 in macrophages was found to decrease during LPS-induced inflammation. NAT10 knockdown significantly reduced the generation of inflammatory factors, while NAT10 overexpression had the opposite effect. RNA sequencing revealed that the differentially expressed genes were enriched in the NF-κB signalling pathway and oxidative stress. Both the NF-κB inhibitor Bay11-7082 and the ROS scavenger N-acetyl-L-cysteine (NAC) could reverse the upregulation of inflammatory factors. NAC inhibited the phosphorylation of NF-κB, but Bay11-7082 had no effect on the production of ROS in NAT10-overexpressing cells, suggesting that NAT10 activated the LPS-induced NF-κB signalling pathway by regulating ROS generation. Furthermore, the expression and stability of Nox2 was promoted after NAT10 overexpression, indicating that Nox2 may be a potential target of NAT10. In vivo, the NAT10 inhibitor Remodelin reduced macrophage infiltration and bone resorption in ligature-induced periodontitis mice. In summary, these results showed that NAT10 accelerated LPS-induced inflammation via the NOX2-ROS-NF-κB pathway in macrophages and that its inhibitor Remodelin might be of potential therapeutic significance in periodontitis treatment.

Microglia and Other Cellular Mediators of Immunological Dysfunction in Schizophrenia: A Narrative Synthesis of Clinical Findings

Schizophrenia is a complex psychiatric condition that may involve immune system dysregulation. Since most putative disease mechanisms in schizophrenia have been derived from genetic association studies and fluid-based molecular analyses, this review aims to summarize the emerging evidence on clinical correlates to immune system dysfunction in this psychiatric disorder. We conclude this review by attempting to develop a unifying hypothesis regarding the relative contributions of microglia and various immune cell populations to the development of schizophrenia. This may provide important translational insights that can become useful for addressing the multifaceted clinical presentation of schizophrenia.

PET imaging of retinal inflammation in mice exposed to blue light using [18F]-DPA-714

Purpose

Positron emission tomography (PET) is widely used in high-precision imaging, which may provide a simple and noninvasive method for the detection of pathology and therapeutic effects. [18F]-DPA-714 is a second-generation translocator protein (TSPO) positron emission tomography radiotracer that shows great promise in a model of neuroinflammation. In this study, [18F]-DPA-714 micro-PET imaging was used to evaluate retinal inflammation in mice exposed to blue light, a well-established model of age-related macular degeneration (AMD) for molecular mechanism research and drug screening.

Methods

C57BL/6J melanized mice were subjected to 10,000, 15,000, and 20,000 lux blue light for 5 days (8 h/day) to develop the retinal injury model, and the structure and function of the retina were assessed using hematoxylin-eosin (HE) staining, electroretinography (ERG), and terminal-deoxynucleotidyl transferase (TdT)-mediated nick-end labeling (TUNEL) immunostaining. Then, [18F]-DPA-714 was injected approximately 100 μCi through each tail vein, and static imaging was performed 1 h after injection. Finally, the mice eyeballs were collected for biodistribution and immune analysis.

Results

The blue light exposure significantly destroyed the structure and function of the retina, and the uptake of [18F]-DPA-714 in the retinas of the mice exposed to blue light were the most significantly upregulated, which was consistent with the biodistribution data. In addition, the immunohistochemical, western blot, and immunofluorescence data showed an increase in microglial TSPO expression.

Conclusions

[18F]-DPA-714 micro-PET imaging might be a good method for evaluating early inflammatory status during retinal pathology.

Mitochondria in endothelial cells angiogenesis and function: current understanding and future perspectives

Endothelial cells (ECs) angiogenesis is the process of sprouting new vessels from the existing ones, playing critical roles in physiological and pathological processes such as wound healing, placentation, ischemia/reperfusion, cardiovascular diseases and cancer metastasis. Although mitochondria are not the major sites of energy source in ECs, they function as important biosynthetic and signaling hubs to regulate ECs metabolism and adaptations to local environment, thus affecting ECs migration, proliferation and angiogenic process. The understanding of the importance and potential mechanisms of mitochondria in regulating ECs metabolism, function and the process of angiogenesis has developed in the past decades. Thus, in this review, we discuss the current understanding of mitochondrial proteins and signaling molecules in ECs metabolism, function and angiogeneic signaling, to provide new and therapeutic targets for treatment of diverse cardiovascular and angiogenesis-dependent diseases.

Zinc Supplementation Induced Transcriptional Changes in Primary Human Retinal Pigment Epithelium: A Single-Cell RNA Sequencing Study to Understand Age-Related Macular Degeneration

Zinc supplementation has been shown to be beneficial to slow the progression of age-related macular degeneration (AMD). However, the molecular mechanism underpinning this benefit is not well understood. This study used single-cell RNA sequencing to identify transcriptomic changes induced by zinc supplementation. Human primary retinal pigment epithelial (RPE) cells could mature for up to 19 weeks. After 1 or 18 weeks in culture, we supplemented the culture medium with 125 µM added zinc for one week. RPE cells developed high transepithelial electrical resistance, extensive, but variable pigmentation, and deposited sub-RPE material similar to the hallmark lesions of AMD. Unsupervised cluster analysis of the combined transcriptome of the cells isolated after 2, 9, and 19 weeks in culture showed considerable heterogeneity. Clustering based on 234 pre-selected RPE-specific genes divided the cells into two distinct clusters, we defined as more and less differentiated cells. The proportion of more differentiated cells increased with time in culture, but appreciable numbers of cells remained less differentiated even at 19 weeks. Pseudotemporal ordering identified 537 genes that could be implicated in the dynamics of RPE cell differentiation (FDR < 0.05). Zinc treatment resulted in the differential expression of 281 of these genes (FDR < 0.05). These genes were associated with several biological pathways with modulation of ID1/ID3 transcriptional regulation. Overall, zinc had a multitude of effects on the RPE transcriptome, including several genes involved in pigmentation, complement regulation, mineralization, and cholesterol metabolism processes associated with AMD.

More than meets the eye: The role of microglia in healthy and diseased retina

Microglia are the main resident immune cells of the nervous system and as such they are involved in multiple roles ranging from tissue homeostasis to response to insults and circuit refinement. While most knowledge about microglia comes from brain studies, some mechanisms have been confirmed for microglia cells in the retina, the light-sensing compartment of the eye responsible for initial processing of visual information. However, several key pieces of this puzzle are still unaccounted for, as the characterization of retinal microglia has long been hindered by the reduced population size within the retina as well as the previous lack of technologies enabling single-cell analyses. Accumulating evidence indicates that the same cell type may harbor a high degree of transcriptional, morphological and functional differences depending on its location within the central nervous system. Thus, studying the roles and signatures adopted specifically by microglia in the retina has become increasingly important. Here, we review the current understanding of retinal microglia cells in physiology and in disease, with particular emphasis on newly discovered mechanisms and future research directions.

Targeting TSPO Reduces Inflammation and Apoptosis in an In Vitro Photoreceptor-Like Model of Retinal Degeneration

The 18 kDa translocator protein (TSPO) is predominantly located in the mitochondrial outer membrane, playing an important role in steroidogenesis, inflammation, survival, and cell proliferation. Its expression in the CNS, and mainly in glial cells, is upregulated in neuropathologies and brain injury. In this study, the potential of targeting TSPO for the therapeutic treatment of inflammatory-based retinal neurodegeneration was evaluated by means of an in vitro model of lipopolysaccharide (LPS)-induced degeneration in 661 W cells, a photoreceptor-like cell line. After the assessment of the expression of TSPO in 661W cells, which, to the best of our knowledge, was never investigated so far, the anti-inflammatory and cytoprotective effects of a number of known TSPO ligands, belonging to the class of N,N-dialkyl-2-arylindol-3-ylglyoxylamides (PIGAs), were evaluated, using the classic TSPO ligand PK11195 as the reference standard. All tested PIGAs showed the ability to modulate the inflammatory and apoptotic processes in 661 W photoreceptor-like cells and to reduce LPS-driven cellular cytotoxicity. The protective effect of PIGAs was, in all cases, reduced by cotreatment with the pregnenolone synthesis inhibitor SU-10603, suggesting the involvement of neurosteroids in the protective mechanism. As inflammatory processes play a crucial role in the retinal neurodegenerative disease progression toward photoreceptors' death and complete blindness, targeting TSPO might represent a successful strategy to slow down this degenerative process that may lead to the inexorable loss of vision.

The efficient generation of knockout microglia cells using a dual-sgRNA strategy by CRISPR/Cas9

Gene deletion in microglia has become an important and exciting approach for studying neuroinflammation, especially after the development of the CRISPR/Cas9 system for genome editing during the last decade. In this study, we described a protocol for the highly efficient generation of knockout microglia cells using a dual-short guide RNA (sgRNA) strategy by CRISPR/Cas9. Leucine-rich repeat kinase 2 (LRRK2), a pathogenic gene of Parkinson's disease (PD), has played versatile roles during the disease development. Despite many key insights into LRRK2 studies, the normal and disease-related functions of LRRK2 in microglia and neuroinflammation remain to be fully investigated. Given the importance of LRRK2 in PD pathogenesis, we designed and applied the protocol to target LRRK2. Specifically, we designed two sgRNAs targeting the N terminus of LRRK2, spanning the 5' untranslated region (UTR) and exon 1, and screened knockout cells by single-cell expansion. In practice, the dual-sgRNA system can facilitate in obtaining knockout cells in a more convenient, rapid, and accurate way. Candidate knockout cells can be easily distinguished by genomic PCR and running on agarose gels, based on the different band sizes. Successful knockouts were further verified by Sanger sequencing and Western blot. Using this protocol, we obtained an LRRK2-deficient microglia cell line, which was characterized by longer cellular processes, enhanced adhesion, and weakened migration capacity. The knockout microglia may further serve as an important cellular tool to reveal conserved and novel aspects of LRRK2 functions in the development and progression of PD. Our protocol using dual-sgRNA targeting guarantees > 60% targeting efficiency and could also be applied to targeting other genes/loci, especially non-coding RNAs and regulatory elements.

Role of the TSPO–NOX4 axis in angiogenesis in glioblastoma

Objective: Angiogenesis is a pathological feature of glioblastoma. Nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4) is a vital source of reactive oxygen species (ROS) related to angiogenesis. However, signaling pathways correlated with the isoform oxidase are unknown. The aim of this study was to elucidate the detailed mechanism of the role of NOX4 in angiogenesis in glioblastoma.

Methods: Public datasets were searched for studies on immunohistochemistry and western blotting to evaluate NOX4 expression in glioma. The location of NOX4 expression was detected by immunofluorescence. We conducted conditional deletion of the translocator protein (TSPO) targeting the protein with the synthetic ligand XBD173 in the glioblastoma mouse model. NOX4 downregulation was conducted with the NOX4 inhibitor GLX351322, and ROS production and angiogenesis were detected in glioma tissues.

Results: Clinical samples and public datasets showed that NOX4 was upregulated and associated with the prognosis. NOX4 is mainly expressed in endothelial cells of glioblastoma. Both TSPO and NOX4 promoted angiogenesis in an ROS-dependent manner, suggesting that TSPO triggered ROS production in glioblastoma via NOX4.

Conclusion: These results showed that TSPO is an upstream target of NOX4-derived mitochondrial ROS, which is indispensable for NOX4-derived mitochondrial ROS-induced angiogenesis in glioblastoma. TSPO–NOX4 signaling could serve as a molecular target for therapeutic strategies for glioblastoma.

Genetic targeting or pharmacological inhibition of galectin-3 dampens microglia reactivity and delays retinal degeneration

Background

Dysfunctional humoral and cellular innate immunity are key components in the development and progression of age-related macular degeneration (AMD). Specifically, chronically activated microglia and their disturbed regulatory system contribute to retinal degeneration. Galectin-3, a β-galactose binding protein, is a potent driver of macrophage and microglia activation and has been implicated in neuroinflammation, including neurodegenerative diseases of the brain. Here, we hypothesized that genetic deficiency of galectin-3 or its modulation via TD139 dampens mononuclear phagocyte reactivity and delays retinal degeneration.

Methods

Galectin-3 expression in AMD patients was analyzed by immunohistochemical stainings. Galectin-3 knockout and BALB/cJ mice were exposed to white bright light with an intensity of 15,000 lux for 1 h and Cx3cr1^GFP/+ mice to focal blue light of 50,000 lux for 10 min. BALB/cJ and Cx3cr1^GFP/+ mice received intraperitoneal injections of 15 mg/kg TD139 or vehicle for five consecutive days, starting one day prior to light exposure. The effects of galectin-3 deficiency or inhibition on microglia were analyzed by immunohistochemical stainings and in situ hybridization of retinal sections and flat mounts. Pro-inflammatory cytokine levels in the retina and retinal pigment epithelium (RPE) were quantified by qRT-PCR and transcriptomic changes were analyzed by RNA-sequencing. Retinal thickness and structure were evaluated by optical coherence tomography.

Results

We found that galectin-3 expression was strongly upregulated in reactive retinal mononuclear phagocytes of AMD patients and in the two related mouse models of light-induced retinal degeneration. The experimental in vivo data further showed that specific targeting of galectin-3 by genetic knockout or administration of the small-molecule inhibitor TD139 reduced microglia reactivity and delayed retinal damage in both light damage conditions.

Conclusion

This study defines galectin-3 as a potent driver of retinal degeneration and highlights the protein as a drug target for ocular immunomodulatory therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02589-6.

Single cell RNA sequencing confirms retinal microglia activation associated with early onset retinal degeneration

Mutations in the Membrane-type frizzled related protein (Mfrp) gene results in an early-onset retinal degeneration associated with retinitis pigmentosa, microphthalmia, optic disc drusen and foveal schisis. In the current study, a previously characterized mouse model of human retinal degeneration carrying homozygous c.498_499insC mutations in Mfrp (Mfrp^KI/KI) was used. Patients carrying this mutation have retinal degeneration at an early age. The model demonstrates subretinal deposits and develops early-onset photoreceptor degeneration. We observed large subretinal deposits in Mfrp^KI/KI mice which were strongly CD68 positive and co-localized with autofluorescent spots. Single cell RNA sequencing of Mfrp^KI/KI mice retinal microglia showed a significantly higher number of pan-macrophage marker Iba-1 and F4/80 positive cells with increased expression of activation marker (CD68) and lowered microglial homeostatic markers (TMEM119, P2ry13, P2ry13, Siglech) compared with wild type mice confirming microglial activation as observed in retinal immunostaining showing microglia activation in subretinal region. Trajectory analysis identified a small cluster of microglial cells with activation transcriptomic signatures that could represent a subretinal microglia population in Mfrp^KI/KI mice expressing higher levels of APOE. We validated these findings using immunofluorescence staining of retinal cryosections and found a significantly higher number of subretinal Iba-1/ApoE positive microglia in Mfrp^KI/KI mice with some subretinal microglia also expressing lowered levels of microglial homeostatic marker TMEM119, confirming microglial origin. In summary, we confirm that Mfrp^KI/KI mice carrying the c.498_499insC mutation had a significantly higher population of activated microglia in their retina with distinct subsets of subretinal microglia. Further, studies are required to confirm whether the association of increased subretinal microglia in MfrpKI/KI mice are causal in degeneration.

The Role of Myrrh Metabolites in Cancer, Inflammation, and Wound Healing: Prospects for a Multi-Targeted Drug Therapy

Background: Myrrh extract is a well-known medicinal plant with significant therapeutic benefits attributed to the activity of its diverse metabolites. It has promising activity against cancer and inflammatory diseases, and could serve as a potential therapeutic alternative since most therapeutic agents have severe side effects that impair quality of life. Method: The current study identified the active metabolites from the myrrh resin methanolic extract. Then, the extracts were tested for in vitro anti-inflammatory and anti-cancer activity using cancer cell lines and Tamm-Horsfall Protein 1 (Thp-1)-like macrophage cell lines. Furthermore, using an in vivo rat model, the extracts’ anti-inflammatory and wound-healing activity was investigated. In addition, in silico predictions of the myrrh constituents highlighted the pharmacokinetic properties, molecular targets, and safety profile, including cytochrome P 450 (CYP) inhibition and organ toxicity. Results: Nine secondary metabolites were identified, and computational predictions suggested a good absorption profile, anticancer, anti-inflammatory, and wound-healing effects. The myrrh extract had moderate cytotoxic activity against both HL60 and K562 leukemia cell lines and the KAIMRC1 breast cancer cell line. Myrrh caused a dose-dependent effect on macrophages to increase the reactive oxygen species (ROS) levels, promote their polarization to classically activated macrophages (M1) and alternatively activated macrophages (M2) phenotypes, and consequently induce apoptosis, highlighting its ability to modulate macrophage function, which could potentially aid in several desired therapeutic processes, including the resolution of inflammation, and autophagy which is an important aspect to consider in cancer treatment. The topical application of myrrh improved wound healing, with no delayed inflammatory response, and promoted complete re-epithelization of the skin, similar to the positive control. In conclusion, we provide evidence for the methanolic extract of myrrh having cytotoxic activity against cancer cells and anti-inflammatory wound-healing properties, which may be attributed to its role in modulating macrophage function. Furthermore, we suggest the active constituents responsible for these properties, which warrants further studies focusing on the precise roles of the active metabolites.

Microglia as Therapeutic Target for Radiation-Induced Brain Injury

Radiation-induced brain injury (RIBI) after radiotherapy has become an increasingly important factor affecting the prognosis of patients with head and neck tumor. With the delivery of high doses of radiation to brain tissue, microglia rapidly transit to a pro-inflammatory phenotype, upregulate phagocytic machinery, and reduce the release of neurotrophic factors. Persistently activated microglia mediate the progression of chronic neuroinflammation, which may inhibit brain neurogenesis leading to the occurrence of neurocognitive disorders at the advanced stage of RIBI. Fully understanding the microglial pathophysiology and cellular and molecular mechanisms after irradiation may facilitate the development of novel therapy by targeting microglia to prevent RIBI and subsequent neurological and neuropsychiatric disorders.

The Effects of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) Oxidase and Erythropoietin, and Their Interactions in Angiogenesis: Implications in Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a leading cause of vision impairment and blindness in premature infants. Oxidative stress is implicated in its pathophysiology. NADPH oxidase (NOX), a major enzyme responsible for reactive oxygen species (ROS) generation in endothelial cells, has been studied for its involvement in physiologic and pathologic angiogenesis. Erythropoietin (EPO) has gained interest recently due to its tissue protective and angiogenic effects, and it has been shown to act as an antioxidant. In this review, we summarize studies performed over the last five years regarding the role of various NOXs in physiologic and pathologic angiogenesis. We also discuss the effect of EPO in tissue and vasoprotection, and the intersection of EPO and NOX-mediated oxidative stress in angiogenesis and the pathophysiology of ROP.

Nicotinic Acetylcholine Receptors and Microglia as Therapeutic and Imaging Targets in Alzheimer's Disease

Amyloid-β (Aβ) accumulation and tauopathy are considered the pathological hallmarks of Alzheimer’s disease (AD), but attenuation in choline signaling, including decreased nicotinic acetylcholine receptors (nAChRs), is evident in the early phase of AD. Currently, there are no drugs that can suppress the progression of AD due to a limited understanding of AD pathophysiology. For this, diagnostic methods that can assess disease progression non-invasively before the onset of AD symptoms are essential, and it would be valuable to incorporate the concept of neurotheranostics, which simultaneously enables diagnosis and treatment. The neuroprotective pathways activated by nAChRs are attractive targets as these receptors may regulate microglial-mediated neuroinflammation. Microglia exhibit both pro- and anti-inflammatory functions that could be modulated to mitigate AD pathogenesis. Currently, single-cell analysis is identifying microglial subpopulations that may have specific functions in different stages of AD pathologies. Thus, the ability to image nAChRs and microglia in AD according to the stage of the disease in the living brain may lead to the development of new diagnostic and therapeutic methods. In this review, we summarize and discuss the recent findings on the nAChRs and microglia, as well as their methods for live imaging in the context of diagnosis, prophylaxis, and therapy for AD.

The Role of Osteopontin in Microglia Biology: Current Concepts and Future Perspectives

The innate immune landscape of the central nervous system (CNS), including the brain and the retina, consists of different myeloid cell populations with distinct tasks to fulfill. Whereas the CNS borders harbor extraparenchymal CNS-associated macrophages whose main duty is to build up a defense against invading pathogens and other damaging factors from the periphery, the resident immune cells of the CNS parenchyma and the retina, microglia, are highly dynamic cells with a plethora of functions during homeostasis and disease. Therefore, microglia are constantly sensing their environment and closely interacting with surrounding cells, which is in part mediated by soluble factors. One of these factors is Osteopontin (OPN), a multifunctional protein that is produced by different cell types in the CNS, including microglia, and is upregulated in neurodegenerative and neuroinflammatory conditions. In this review, we discuss the current literature about the interaction between microglia and OPN in homeostasis and several disease entities, including multiple sclerosis (MS), Alzheimer’s and cerebrovascular diseases (AD, CVD), amyotrophic lateral sclerosis (ALS), age-related macular degeneration (AMD) and diabetic retinopathy (DR), in the context of the molecular pathways involved in OPN signaling shaping the function of microglia. As nearly all CNS diseases are characterized by pathological alterations in microglial cells, accompanied by the disturbance of the homeostatic microglia phenotype, the emergence of disease-associated microglia (DAM) states and their interplay with factors shaping the DAM-signature, such as OPN, is of great interest for therapeutical interventions in the future.

TSPO Ligands Protect against Neuronal Damage Mediated by LPS-Induced BV-2 Microglia Activation

Neuroinflammation is a critical pathological process of neurodegenerative diseases, and alleviating the inflammatory response caused by abnormally activated microglia might be valuable for treatment. The 18 kDa translocator protein (TSPO), a biomarker of neuroinflammation, is significantly elevated in activated microglia. However, the role of TSPO in microglia activation has not been well demonstrated. In this study, we evaluated the role of TSPO and its ligands PK11195 and Midazolam in LPS-activated BV-2 microglia cells involving mitophagy process and the nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome activation. In the microglia-neuron coculture system, the neurotoxicity induced by LPS-activated microglia and the neuroprotective effects of PK11195 and Midazolam were evaluated. Our results showed that after being stimulated by LPS, the expression of TSPO was increased, and the process of mitophagy was inhibited in BV-2 microglia cells. Inhibition of mitophagy was reversed by pretreatment with PK11195 and Midazolam. And the NLRP3 inflammasome was increased in LPS-activated BV-2 microglia cells in the microglia-neuron coculture system; pretreatment with PK11195 and Midazolam limited this undesirable situation. Lastly, PK11195 and Midazolam improved the cell viability and reduced apoptosis of neuronal cells in the microglia-neuron coculture system. Taken together, TSPO ligands PK11195 and Midazolam showed neuroprotective effects by reducing the inflammatory response of LPS-activated microglia, which may be related to the enhancement of mitophagy and the inhibition of NLRP3 inflammasome.

Serum Iba-1, GLUT5, and TSPO in Patients With Diabetic Retinopathy: New Biomarkers for Early Retinal Neurovascular Alterations? A Pilot Study

Purpose

This study explored the possibility of highlighting early retinal neurovascular alterations of diabetic retinopathy (DR) by monitoring in DR patients the serum levels of microglial biomarkers ionized calcium-binding adapter molecule 1 (Iba-1), glucose transporter 5 (GLUT5), and translocator protein (TSPO), along with serum changes of the endothelial dysfunction marker arginase-1.

Methods

Serum markers were determined by enzyme-linked immunosorbent assay in 50 patients: 12 non-diabetic subjects, 14 diabetic patients without DR, 13 patients with non-proliferative DR (NPDR), and 11 patients with proliferative DR (PDR). The results were correlated with hyperreflective retinal spots (HRS), observed with optical coherence tomography (OCT).

Results

Although HRS were absent in diabetic patients without DR, NPDR patients showed an average of 4 ± 1 HRS, whereas the highest presence was detected in PDR patients, with 8 ± 1 HRS (P < 0.01 vs. NPDR). HRS were positively correlated (P < 0.01) with serum levels of arginase-1 (r = 0.91), Iba-1 (r = 0.96), GLUT5 (r = 0.94), and TSPO (r = 0.88). Moreover, serum proinflammatory cytokines and chemokines showed a positive correlation (P < 0.01) with HRS number and the serum markers analyzed.

Conclusions

Serum markers of microglial activation positively correlate with retinal HRS in NPDR and PDR patients.

Translational Relevance

These data corroborate the possibility of highlighting early retinal neurovascular changes due to diabetes by monitoring circulating microglial markers.

Targeting Microglia to Treat Degenerative Eye Diseases

Microglia have been implicated in many degenerative eye disorders, including retinitis pigmentosa, age-related macular degeneration, glaucoma, diabetic retinopathy, uveitis, and retinal detachment. While the exact roles of microglia in these conditions are still being discovered, evidence from animal models suggests that they can modulate the course of disease. In this review, we highlight current strategies to target microglia in the eye and their potential as treatments for both rare and common ocular disorders. These approaches include depleting microglia with chemicals or radiation, reprogramming microglia using homeostatic signals or other small molecules, and inhibiting the downstream effects of microglia such as by blocking cytokine activity or phagocytosis. Finally, we describe areas of future research needed to fully exploit the therapeutic value of microglia in eye diseases.

PET imaging of retinal inflammation in mice exposed to blue light using [18F]-DPA-714

Purpose

Positron emission tomography (PET) is widely used in high-precision imaging, which may provide a simple and noninvasive method for the detection of pathology and therapeutic effects. [¹⁸F]-DPA-714 is a second-generation translocator protein (TSPO) positron emission tomography radiotracer that shows great promise in a model of neuroinflammation. In this study, [¹⁸F]-DPA-714 micro-PET imaging was used to evaluate retinal inflammation in mice exposed to blue light, a well-established model of age-related macular degeneration (AMD) for molecular mechanism research and drug screening.

Methods

C57BL/6J melanized mice were subjected to 10,000, 15,000, and 20,000 lux blue light for 5 days (8 h/day) to develop the retinal injury model, and the structure and function of the retina were assessed using hematoxylin-eosin (HE) staining, electroretinography (ERG), and terminal-deoxynucleotidyl transferase (TdT)-mediated nick-end labeling (TUNEL) immunostaining. Then, [¹⁸F]-DPA-714 was injected approximately 100 μCi through each tail vein, and static imaging was performed 1 h after injection. Finally, the mice eyeballs were collected for biodistribution and immune analysis.

Results

The blue light exposure significantly destroyed the structure and function of the retina, and the uptake of [¹⁸F]-DPA-714 in the retinas of the mice exposed to blue light were the most significantly upregulated, which was consistent with the biodistribution data. In addition, the immunohistochemical, western blot, and immunofluorescence data showed an increase in microglial TSPO expression.

Conclusions

[¹⁸F]-DPA-714 micro-PET imaging might be a good method for evaluating early inflammatory status during retinal pathology.

Inhibition of estrogen signaling in myeloid cells increases tumor immunity in melanoma

Immune checkpoint blockade (ICB) therapies have significantly prolonged patient survival across multiple tumor types, particularly in melanoma. Interestingly, sex-specific differences in response to ICB have been observed, with males receiving a greater benefit from ICB than females, although the mechanism or mechanisms underlying this difference are unknown. Mining published transcriptomic data sets, we determined that the response to ICBs is influenced by the functionality of intratumoral macrophages. This puts into context our observation that estrogens (E2) working through the estrogen receptor α (ERα) stimulated melanoma growth in murine models by skewing macrophage polarization toward an immune-suppressive state that promoted CD8+ T cell dysfunction and exhaustion and ICB resistance. This activity was not evident in mice harboring macrophage-specific depletion of ERα, confirming a direct role for estrogen signaling within myeloid cells in establishing an immunosuppressed state. Inhibition of ERα using fulvestrant, a selective estrogen receptor downregulator (SERD), decreased tumor growth, stimulated adaptive immunity, and increased the antitumor efficacy of ICBs. Further, a gene signature that determines ER activity in macrophages predicted survival in patients with melanoma treated with ICB. These results highlight the importance of E2/ER signaling as a regulator of intratumoral macrophage polarization, an activity that can be therapeutically targeted to reverse immune suppression and increase ICB efficacy.

Imaging neuroinflammation with TSPO: A new perspective on the cellular sources and subcellular localization

Translocator Protein 18 kDa (TSPO), previously named Peripheral Benzodiazepine Receptor, is a well-validated and widely used biomarker of neuroinflammation to assess diverse central nervous system (CNS) pathologies in preclinical and clinical studies. Many studies have shown that in animal models of human neurological and neurodegenerative disease and in the human condition, TSPO levels increase in the brain neuropil, and this increase is driven by infiltration of peripheral inflammatory cells and activation of glial cells. Therefore, a clear understanding of the dynamics of the cellular sources of the TSPO response is critically important in the interpretation of Positron Emission Tomography (PET) studies and for understanding the pathophysiology of CNS diseases. Within the normal brain compartment, there are tissues and cells such as the choroid plexus, ependymal cells of the lining of the ventricles, and vascular endothelial cells that also express TSPO at even higher levels than in glial cells. However, there is a paucity of knowledge if these cell types respond and increase TSPO in the diseased brain. These cells do provide a background signal that needs to be accounted for in TSPO-PET imaging studies. More recently, there are reports that TSPO may be expressed in neurons of the adult brain and TSPO expression may be increased by neuronal activity. Therefore, it is essential to study this topic with a great deal of detail, methodological rigor, and rule out alternative interpretations and imaging artifacts. High levels of TSPO are present in the outer mitochondrial membrane. Recent studies have provided evidence of its localization in other cellular compartments including the plasma membrane and perinuclear regions which may define functions that are different from that in mitochondria. A greater understanding of the TSPO subcellular localization in glial cells and infiltrating peripheral immune cells and associated function(s) may provide an additional layer of information to the understanding of TSPO neurobiology. This review is an effort to outline recent advances in understanding the cellular sources and subcellular localization of TSPO in brain cells and to examine remaining questions that require rigorous investigation.

The AhR ligand 2, 2'-aminophenyl indole (2AI) regulates microglia homeostasis and reduces pro-inflammatory signaling

Retinal degeneration is a leading cause of visual impairment and blindness worldwide. Microglia reactivity is a hallmark of neurodegenerative diseases and a driving force for retinal cell death and disease progression. Thus, immunomodulation emerges as a potential therapeutic option. AhR deficiency is known to trigger inflammation and previous studies revealed important roles for AhR ligands in neuroprotection without focusing on microglia. Here, we investigate the anti-inflammatory and antioxidant effects of the synthetic aryl hydrocarbon receptor (AhR) ligand 2, 2'-aminophenyl indole (2AI) on microglia reactivity. We showed that 2AI potently reduced pro-inflammatory gene expression and induced antioxidant genes in activated human and murine microglia cells, in LPS-stimulated retinal explants as well as in stressed human ARPE-19 cells. 2AI also diminished LPS-induced nitric oxide (NO) release, their neurotoxic activity on photoreceptor cells, phagocytosis, and migration in murine BV-2 cells as important functional microglia parameters. siRNA-mediated knockdown of AhR partially prevented the previously observed gene regulatory effects in BV-2 cells. Our results show for the first time, that the synthetic AhR agonist 2AI regulates microglia homeostasis, highlighting AhR as a potential drug target for immunomodulatory and antioxidant therapies.

Maternally expressed gene 3 regulates retinal neovascularization in retinopathy of prematurity

The mouse model of oxygen induced retinopathy is suitable for the study of various retinal neovascularization diseases, including retinopathy of prematurity. The maternally expressed gene 3 (MEG3) has been demonstrated to have an inhibitory effect on diabetic retinopathy. In this study, we investigated the role of MEG3 overexpression in oxygen-induced retinopathy in mice. The results showed that MEG3 overexpression effectively inhibited the production of retinal neovascularization in oxygen-induced retinopathy mice. It acts by down-regulating the expression of phosphoinositide 3-kinase, serine/threonine kinase, and vascular endothelial growth factor and pro-inflammatory factors. MEG3 overexpression lentivirus has a future as a new method for the clinical treatment of retinopathy of prematurity. The animal experiments were approved by the Animal Ethics Committee of Shengjing Hospital of China Medical University, China (approval No. 2016PS074K) on February 25, 2016.

Reactive Oxygen Species in Macrophages: Sources and Targets

Reactive oxygen species (ROS) are fundamental for macrophages to eliminate invasive microorganisms. However, as observed in nonphagocytic cells, ROS play essential roles in processes that are different from pathogen killing, as signal transduction, differentiation, and gene expression. The different outcomes of these events are likely to depend on the specific subcellular site of ROS formation, as well as the duration and extent of ROS production. While excessive accumulation of ROS has long been appreciated for its detrimental effects, there is now a deeper understanding of their roles as signaling molecules. This could explain the failure of the “all or none” pharmacologic approach with global antioxidants to treat several diseases. NADPH oxidase is the first source of ROS that has been identified in macrophages. However, growing evidence highlights mitochondria as a crucial site of ROS formation in these cells, mainly due to electron leakage of the respiratory chain or to enzymes, such as monoamine oxidases. Their role in redox signaling, together with their exact site of formation is only partially elucidated. Hence, it is essential to identify the specific intracellular sources of ROS and how they influence cellular processes in both physiological and pathological conditions to develop therapies targeting oxidative signaling networks. In this review, we will focus on the different sites of ROS formation in macrophages and how they impact on metabolic processes and inflammatory signaling, highlighting the role of mitochondrial as compared to non-mitochondrial ROS sources.

Reactive Oxygen Species: Not Omnipresent but Important in Many Locations

Reactive oxygen species (ROS), such as the superoxide anion or hydrogen peroxide, have been established over decades of research as, on the one hand, important and versatile molecules involved in a plethora of homeostatic processes and, on the other hand, as inducers of damage, pathologies and diseases. Which effects ROS induce, strongly depends on the cell type and the source, amount, duration and location of ROS production. Similar to cellular pH and calcium levels, which are both strictly regulated and only altered by the cell when necessary, the redox balance of the cell is also tightly regulated, not only on the level of the whole cell but in every cellular compartment. However, a still widespread view present in the scientific community is that the location of ROS production is of no major importance and that ROS randomly diffuse from their cellular source of production throughout the whole cell and hit their redox-sensitive targets when passing by. Yet, evidence is growing that cells regulate ROS production and therefore their redox balance by strictly controlling ROS source activation as well as localization, amount and duration of ROS production. Hopefully, future studies in the field of redox biology will consider these factors and analyze cellular ROS more specifically in order to revise the view of ROS as freely flowing through the cell.

IL-17 signaling induces iNOS+ microglia activation in retinal vascular diseases

Activation of microglia and inflammation-mediated vascular damages are suggested to play a decisive role in the pathogenesis of various retinopathies. The inducible nitric oxide synthase (iNOS) was required for activated microglia-mediated injuries. However, the induction mechanism of microglia activation during retinal vascular diseases is still elusive. Here we showed that IL-17 induced microglia activation with high expression of iNOS and promoted the development of retinal vascular diseases. IL-17-dependent activation of the STAT3-iNOS pathway was essentially required for microglia activation, which promoted endothelial cell growth and accelerated vascular leakage and leukostasis via IL-6 in vitro and in vivo. Taken together, our data provide novel mechanistic insights on microglia activation-mediated retinopathy, unveil the specific role of IL-17 on microglia, and define novel therapeutic targets for treating retinal vascular diseases.

TSPO protein binding partners in bacteria, animals, and plants

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.

Deletion of Mitochondrial Translocator Protein (TSPO) Gene Decreases Oxidative Retinal Pigment Epithelial Cell Death via Modulation of TRPM2 Channel

Simple Summary

18 kDa mitochondrial translocator protein (TSPO) is a mitochondria protein of the cellular outer membrane in the mitochondria of several cells, including ARPE19 is TSPO. Accumulating evince indicates that the presence of TSPO participated the modulations of Ca²⁺ homeostasis and mitochondrial free reactive oxygen species (fROS) generation. The deletion of TSPO gene provides to study the action of TSPO on the levels of apoptosis, ADP-ribose (ADPR), mitochondria-fROS (Mito-fROS), and apoptosis via the stimulation of Ca²⁺ permeable channels in the models of cell culture. The stimulations of oxidative stress and ADPR induce the activation of TRPM2 in the ARPE19. For clarifying the involvement of TSPO in retinal human diseases, we used the ARPE19 human cell culture model. The current results demonstrated that the deletion of TSPO induces the regulation of TRPM2 in the TSPO gene knockout ARPE19 (ARPE19-KO) In fact, the present results show that the presence of TSPO increased the upregulations of apoptosis and mitochondria oxidative cytotoxicity values via stimulation of TRPM2 in the ARPE19. Nevertheless, the blockages of PARP-1 (PJ34 and DPQ) and TRPM2 (2APB and ACA) downregulated the values of cell death and oxidative cytotoxicity in the ARPE19. In summary, present results clearly demonstrate that the deletion of TSPO decreases mitochondrial oxidative cytotoxicity-mediated cell death via the modulation of TRPM2 in the ARPE19.

Abstract

The current results indicated the possible protective actions of 18 kDa mitochondrial translocator protein (TSPO) deletion on TRPM2 stimulation, mitochondrial free ROS (Mito-fROS) and apoptotic harmful actions in the cells of adult retinal pigment epithelial19 (ARPE19). There was a direct relationship between TSPO and the disease of age-related macular degeneration. The nature of TSPO implicates upregulation of Mito-fROS and apoptosis via the activation of Ca²⁺ channels in ARPE19, although deletion of TSPO gene downregulates the activation. The decrease of oxidative cytotoxicity and apoptosis might induce in TSPO gene deleted cells by the inhibition of Mito-fROS and PARP-1 activation-induced TRPM2 cation channel activation. The ARPE19 cells were divided into two main groups as TSPO expressing (ARPE19) and non-expressing cells (ARPE19-KO). The levels of caspase -3 (Casp -3), caspase -9 (Casp -9), apoptosis, Mito-fROS, TRPM2 current and intracellular free Ca²⁺ were upregulated in the ARPE19 by the stimulations of H₂O₂ and ADP-ribose, although their levels were downregulated in the cells by the modulators of PARP-1 (DPQ and PJ34), TRPM2 (ACA and 2APB) and glutathione. However, the H₂O₂ and ADP-ribose-mediated increases were not observed in the ARPE19-KO. The expression levels of Bax, Casp -3, Casp -9 and PARP-1 were higher in the ARPE19 group as compared to the ARPE19-KO group. In summary, current results confirmed that TRPM2-mediated cell death and oxidative cytotoxicity in the ARPE19 cells were occurred by the presence of TSPO. The deletion of TSPO may be considered as a therapeutic way to TRPM2 activation-mediated retinal oxidative injury.

Emerging therapies and their delivery for treating age-related macular degeneration

Age-related macular degeneration (AMD) is the most common cause of blindness in the Western world and is characterised in its latter stages by retinal cell death and neovascularisation and earlier stages with the loss of parainflammatory homeostasis. Patients with neovascular AMD (nAMD) are treated with frequent intraocular injections of anti-vascular endothelial growth factor (VEGF) therapies, which are not only unpopular with patients but carry risks of sight-threatening complications. A minority of patients are unresponsive with no alternative treatment available, and some patients who respond initially eventually develop a tolerance to treatment. New therapeutics with improved delivery methods and sustainability of clinical effects are required, in particular for non-neovascular AMD (90% of cases and no current approved treatments). There are age-related and disease-related changes that occur which can affect ocular drug delivery. Here, we review the latest emerging therapies for AMD, their delivery routes and implications for translating to clinical practice.

Functions of ROS in Macrophages and Antimicrobial Immunity

Reactive oxygen species (ROS) are a chemically defined group of reactive molecules derived from molecular oxygen. ROS are involved in a plethora of processes in cells in all domains of life, ranging from bacteria, plants and animals, including humans. The importance of ROS for macrophage-mediated immunity is unquestioned. Their functions comprise direct antimicrobial activity against bacteria and parasites as well as redox-regulation of immune signaling and induction of inflammasome activation. However, only a few studies have performed in-depth ROS analyses and even fewer have identified the precise redox-regulated target molecules. In this review, we will give a brief introduction to ROS and their sources in macrophages, summarize the versatile roles of ROS in direct and indirect antimicrobial immune defense, and provide an overview of commonly used ROS probes, scavengers and inhibitors.

Secreted Phosphoprotein 1 Expression in Retinal Mononuclear Phagocytes Links Murine to Human Choroidal Neovascularization

Age-related macular degeneration (AMD) represents the most common cause of blindness in the elderly in the Western world. An impairment of the outer blood-retina barrier and a localized inflammatory microenvironment cause sprouting of choroidal neovascular membranes (CNV) in neovascular AMD that are in intimate contact with surrounding myeloid cells, such as retinal microglia, and ultimately lead to visual impairment. The discovery of novel target molecules to interfere with angiogenesis and inflammation is vital for future treatment approaches in AMD patients. To explore the transcriptional profile and the function of retinal microglia at sites of CNV, we performed a comprehensive RNA-seq analysis of retinal microglia in the mouse model of laser-induced choroidal neovascularization (mCNV). Here, we identified the angiogenic factor Osteopontin (Opn), also known as "secreted phosphoprotein 1" (Spp1), as one of the most highly expressed genes in retinal microglia in the course of CNV formation. We confirmed the presence of SPP1 at the lesion site in recruited retinal microglia in Cx3cr1 ^CreER:Rosa26-tdTomato reporter mice by confocal microscopy and in whole retinal tissue lysates by ELISA highlighting a massive local production of SPP1. Inhibition of SPP1 by intravitreal injection of an anti-SPP1 antibody significantly increased the lesion size compared to IgG-treated control eyes. In line with our results in rodents, we found an increased SPP1 mRNA expression in surgically extracted human choroidal neovascular (hCNV) membranes by the quantitative RNA-seq approach of massive analysis of cDNA ends (MACE). Numerous IBA1⁺SPP1⁺ myeloid cells were detected in human CNV membranes. Taken together, these results highlight the importance of SPP1 in the formation of CNV and potentially offer new opportunities for therapeutic intervention by modulating the SPP1 pathway.

Koumine Suppresses IL-1β Secretion and Attenuates Inflammation Associated With Blocking ROS/NF-κB/NLRP3 Axis in Macrophages

Koumine (KM), one of the primary constituents of Gelsemium elegans, has been used for the treatment of inflammatory diseases such as rheumatoid arthritis, but whether KM impacts the activation of the NOD-like receptor protein 3 (NLRP3) inflammasome remains unknown. This study aimed to explore the inhibitory effect of KM on NLRP3 inflammasome activation and the underlying mechanisms both in vitro using macrophages stimulated with LPS plus ATP, nigericin or monosodium urate (MSU) crystals and in vivo using an MSU-induced peritonitis model. We found that KM dose-dependently inhibited IL-1β secretion in macrophages after NLRP3 inflammasome activators stimulation. Furthermore, KM treatment efficiently attenuated the infiltration of neutrophils and suppressed IL-1β production in mice with MSU-induced peritonitis. These results indicated that KM inhibited NLRP3 inflammasome activation, and consistent with this finding, KM effectively inhibited caspase-1 activation, mature IL-1β secretion, NLRP3 formation and pro-IL-1β expression in LPS-primed macrophages treated with ATP, nigericin or MSU. The mechanistic study showed that, KM exerted a potent inhibitory effect on the NLRP3 priming step, which decreased the phosphorylation of IκBα and p65, the nuclear localization of p65, and the secretion of TNF-α and IL-6. Moreover, the assembly of NLRP3 was also interrupted by KM. KM blocked apoptosis-associated speck-like protein containing a CARD (ASC) speck formation and its oligomerization and hampered the NLRP3-ASC interaction. This suppression was attributed to the ability of KM to inhibit the production of reactive oxygen species (ROS). In support of this finding, the inhibitory effect of KM on ROS production was completely counteracted by H₂O₂, an ROS promoter. Our results provide the first indication that KM exerts an inhibitory effect on NLRP3 inflammasome activation associated with blocking the ROS/NF-κB/NLRP3 signal axis. KM might have potential clinical application in the treatment of NLRP3 inflammasome-related diseases.